RISCWORLD 7/RISCWORLD_VOL7.iso/Software/Issue2/SDL.ARC/!gcc/docs/gcc

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 Permission is granted to copy, distribute and/or modify this document
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Software", the Front-Cover texts being (a) (see below), and with the
Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

 (a) The FSF's Front-Cover Text is:

 A GNU Manual

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 You have freedom to copy and modify this GNU Manual, like GNU
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funds for GNU development.

INFO-DIR-SECTION Programming
START-INFO-DIR-ENTRY
* gcc: (gcc).                  The GNU Compiler Collection.
END-INFO-DIR-ENTRY
 This file documents the use of the GNU compilers.

 Copyright (C) 1988, 1989, 1992, 1993, 1994, 1995, 1996, 1997, 1998,
1999, 2000, 2001, 2002, 2003, 2004 Free Software Foundation, Inc.

 Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU General Public License" and "Funding Free
Software", the Front-Cover texts being (a) (see below), and with the
Back-Cover Texts being (b) (see below).  A copy of the license is
included in the section entitled "GNU Free Documentation License".

 (a) The FSF's Front-Cover Text is:

 A GNU Manual

 (b) The FSF's Back-Cover Text is:

 You have freedom to copy and modify this GNU Manual, like GNU
software.  Copies published by the Free Software Foundation raise
funds for GNU development.



File: gcc,  Node: Top,  Next: G++ and GCC,  Up: (DIR)

Introduction
************

This manual documents how to use the GNU compilers, as well as their
features and incompatibilities, and how to report bugs.  It corresponds
to GCC version 3.4.1.  The internals of the GNU compilers, including
how to port them to new targets and some information about how to write
front ends for new languages, are documented in a separate manual.
*Note Introduction: (gccint)Top.

* Menu:

* G++ and GCC::     You can compile C or C++ programs.
* Standards::       Language standards supported by GCC.
* Invoking GCC::    Command options supported by `gcc'.
* C Implementation:: How GCC implements the ISO C specification.
* C Extensions::    GNU extensions to the C language family.
* C++ Extensions::  GNU extensions to the C++ language.
* Objective-C::     GNU Objective-C runtime features.
* Compatibility::   Binary Compatibility
* Gcov::            `gcov'---a test coverage program.
* Trouble::         If you have trouble using GCC.
* Bugs::            How, why and where to report bugs.
* Service::         How to find suppliers of support for GCC.
* Contributing::    How to contribute to testing and developing GCC.

* Funding::         How to help assure funding for free software.
* GNU Project::     The GNU Project and GNU/Linux.

* Copying::         GNU General Public License says
                     how you can copy and share GCC.
* GNU Free Documentation License:: How you can copy and share this manual.
* Contributors::    People who have contributed to GCC.

* Option Index::    Index to command line options.
* Keyword Index::    Index of concepts and symbol names.


File: gcc,  Node: G++ and GCC,  Next: Standards,  Prev: Top,  Up: Top

1 Programming Languages Supported by GCC
****************************************

GCC stands for "GNU Compiler Collection".  GCC is an integrated
distribution of compilers for several major programming languages.
These languages currently include C, C++, Objective-C, Java, Fortran,
and Ada.

 The abbreviation "GCC" has multiple meanings in common use.  The
current official meaning is "GNU Compiler Collection", which refers
generically to the complete suite of tools.  The name historically stood
for "GNU C Compiler", and this usage is still common when the emphasis
is on compiling C programs.  Finally, the name is also used when
speaking of the "language-independent" component of GCC: code shared
among the compilers for all supported languages.

 The language-independent component of GCC includes the majority of the
optimizers, as well as the "back ends" that generate machine code for
various processors.

 The part of a compiler that is specific to a particular language is
called the "front end".  In addition to the front ends that are
integrated components of GCC, there are several other front ends that
are maintained separately.  These support languages such as Pascal,
Mercury, and COBOL.  To use these, they must be built together with GCC
proper.

 Most of the compilers for languages other than C have their own names.
The C++ compiler is G++, the Ada compiler is GNAT, and so on.  When we
talk about compiling one of those languages, we might refer to that
compiler by its own name, or as GCC.  Either is correct.

 Historically, compilers for many languages, including C++ and Fortran,
have been implemented as "preprocessors" which emit another high level
language such as C.  None of the compilers included in GCC are
implemented this way; they all generate machine code directly.  This
sort of preprocessor should not be confused with the "C preprocessor",
which is an integral feature of the C, C++, and Objective-C languages.


File: gcc,  Node: Standards,  Next: Invoking GCC,  Prev: G++ and GCC,  Up: Top

2 Language Standards Supported by GCC
*************************************

For each language compiled by GCC for which there is a standard, GCC
attempts to follow one or more versions of that standard, possibly with
some exceptions, and possibly with some extensions.

 GCC supports three versions of the C standard, although support for
the most recent version is not yet complete.

 The original ANSI C standard (X3.159-1989) was ratified in 1989 and
published in 1990.  This standard was ratified as an ISO standard
(ISO/IEC 9899:1990) later in 1990.  There were no technical differences
between these publications, although the sections of the ANSI standard
were renumbered and became clauses in the ISO standard.  This standard,
in both its forms, is commonly known as "C89", or occasionally as
"C90", from the dates of ratification.  The ANSI standard, but not the
ISO standard, also came with a Rationale document.  To select this
standard in GCC, use one of the options `-ansi', `-std=c89' or
`-std=iso9899:1990'; to obtain all the diagnostics required by the
standard, you should also specify `-pedantic' (or `-pedantic-errors' if
you want them to be errors rather than warnings).  *Note Options
Controlling C Dialect: C Dialect Options.

 Errors in the 1990 ISO C standard were corrected in two Technical
Corrigenda published in 1994 and 1996.  GCC does not support the
uncorrected version.

 An amendment to the 1990 standard was published in 1995.  This
amendment added digraphs and `__STDC_VERSION__' to the language, but
otherwise concerned the library.  This amendment is commonly known as
"AMD1"; the amended standard is sometimes known as "C94" or "C95".  To
select this standard in GCC, use the option `-std=iso9899:199409'
(with, as for other standard versions, `-pedantic' to receive all
required diagnostics).

 A new edition of the ISO C standard was published in 1999 as ISO/IEC
9899:1999, and is commonly known as "C99".  GCC has incomplete support
for this standard version; see
`http://gcc.gnu.org/gcc-3.4/c99status.html' for details.  To select this
standard, use `-std=c99' or `-std=iso9899:1999'.  (While in
development, drafts of this standard version were referred to as "C9X".)

 Errors in the 1999 ISO C standard were corrected in a Technical
Corrigendum published in 2001.  GCC does not support the uncorrected
version.

 By default, GCC provides some extensions to the C language that on
rare occasions conflict with the C standard.  *Note Extensions to the C
Language Family: C Extensions.  Use of the `-std' options listed above
will disable these extensions where they conflict with the C standard
version selected.  You may also select an extended version of the C
language explicitly with `-std=gnu89' (for C89 with GNU extensions) or
`-std=gnu99' (for C99 with GNU extensions).  The default, if no C
language dialect options are given, is `-std=gnu89'; this will change to
`-std=gnu99' in some future release when the C99 support is complete.
Some features that are part of the C99 standard are accepted as
extensions in C89 mode.

 The ISO C standard defines (in clause 4) two classes of conforming
implementation.  A "conforming hosted implementation" supports the
whole standard including all the library facilities; a "conforming
freestanding implementation" is only required to provide certain
library facilities: those in `<float.h>', `<limits.h>', `<stdarg.h>',
and `<stddef.h>'; since AMD1, also those in `<iso646.h>'; and in C99,
also those in `<stdbool.h>' and `<stdint.h>'.  In addition, complex
types, added in C99, are not required for freestanding implementations.
The standard also defines two environments for programs, a
"freestanding environment", required of all implementations and which
may not have library facilities beyond those required of freestanding
implementations, where the handling of program startup and termination
are implementation-defined, and a "hosted environment", which is not
required, in which all the library facilities are provided and startup
is through a function `int main (void)' or `int main (int, char *[])'.
An OS kernel would be a freestanding environment; a program using the
facilities of an operating system would normally be in a hosted
implementation.

 GCC aims towards being usable as a conforming freestanding
implementation, or as the compiler for a conforming hosted
implementation.  By default, it will act as the compiler for a hosted
implementation, defining `__STDC_HOSTED__' as `1' and presuming that
when the names of ISO C functions are used, they have the semantics
defined in the standard.  To make it act as a conforming freestanding
implementation for a freestanding environment, use the option
`-ffreestanding'; it will then define `__STDC_HOSTED__' to `0' and not
make assumptions about the meanings of function names from the standard
library, with exceptions noted below.  To build an OS kernel, you may
well still need to make your own arrangements for linking and startup.
*Note Options Controlling C Dialect: C Dialect Options.

 GCC does not provide the library facilities required only of hosted
implementations, nor yet all the facilities required by C99 of
freestanding implementations; to use the facilities of a hosted
environment, you will need to find them elsewhere (for example, in the
GNU C library).  *Note Standard Libraries: Standard Libraries.

 Most of the compiler support routines used by GCC are present in
`libgcc', but there are a few exceptions.  GCC requires the
freestanding environment provide `memcpy', `memmove', `memset' and
`memcmp'.  Some older ports of GCC are configured to use the BSD
`bcopy', `bzero' and `bcmp' functions instead, but this is deprecated
for new ports.  Finally, if `__builtin_trap' is used, and the target
does not implement the `trap' pattern, then GCC will emit a call to
`abort'.

 For references to Technical Corrigenda, Rationale documents and
information concerning the history of C that is available online, see
`http://gcc.gnu.org/readings.html'

 There is no formal written standard for Objective-C.  The most
authoritative manual is "Object-Oriented Programming and the
Objective-C Language", available at a number of web sites

   * `http://developer.apple.com/techpubs/macosx/Cocoa/ObjectiveC/' is
     a recent version

   * `http://www.toodarkpark.org/computers/objc/' is an older example

   * `http://www.gnustep.org' has additional useful information

 There is no standard for treelang, which is a sample language front end
for GCC. Its only purpose is as a sample for people wishing to write a
new language for GCC. The language is documented in
`gcc/treelang/treelang.texi' which can be turned into info or HTML
format.

 *Note GNAT Reference Manual: (gnat_rm)Top, for information on standard
conformance and compatibility of the Ada compiler.

 *Note The GNU Fortran Language: (g77)Language, for details of the
Fortran language supported by GCC.

 *Note Compatibility with the Java Platform: (gcj)Compatibility, for
details of compatibility between `gcj' and the Java Platform.


File: gcc,  Node: Invoking GCC,  Next: C Implementation,  Prev: Standards,  Up: Top

3 GCC Command Options
*********************

When you invoke GCC, it normally does preprocessing, compilation,
assembly and linking.  The "overall options" allow you to stop this
process at an intermediate stage.  For example, the `-c' option says
not to run the linker.  Then the output consists of object files output
by the assembler.

 Other options are passed on to one stage of processing.  Some options
control the preprocessor and others the compiler itself.  Yet other
options control the assembler and linker; most of these are not
documented here, since you rarely need to use any of them.

 Most of the command line options that you can use with GCC are useful
for C programs; when an option is only useful with another language
(usually C++), the explanation says so explicitly.  If the description
for a particular option does not mention a source language, you can use
that option with all supported languages.

 *Note Compiling C++ Programs: Invoking G++, for a summary of special
options for compiling C++ programs.

 The `gcc' program accepts options and file names as operands.  Many
options have multi-letter names; therefore multiple single-letter
options may _not_ be grouped: `-dr' is very different from `-d -r'.

 You can mix options and other arguments.  For the most part, the order
you use doesn't matter.  Order does matter when you use several options
of the same kind; for example, if you specify `-L' more than once, the
directories are searched in the order specified.

 Many options have long names starting with `-f' or with `-W'--for
example, `-fforce-mem', `-fstrength-reduce', `-Wformat' and so on.
Most of these have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  This manual documents only one of
these two forms, whichever one is not the default.

 *Note Option Index::, for an index to GCC's options.

* Menu:

* Option Summary::    Brief list of all options, without explanations.
* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* Invoking G++::    Compiling C++ programs.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.
* Submodel Options::    Specifying minor hardware or convention variations,
                        such as 68010 vs 68020.
* Code Gen Options::    Specifying conventions for function calls, data layout
                        and register usage.
* Environment Variables:: Env vars that affect GCC.
* Precompiled Headers:: Compiling a header once, and using it many times.
* Running Protoize::    Automatically adding or removing function prototypes.


File: gcc,  Node: Option Summary,  Next: Overall Options,  Up: Invoking GCC

3.1 Option Summary
==================

Here is a summary of all the options, grouped by type.  Explanations are
in the following sections.

_Overall Options_
     *Note Options Controlling the Kind of Output: Overall Options.
          -c  -S  -E  -o FILE  -pipe  -pass-exit-codes
          -x LANGUAGE  -v  -###  --help  --target-help  --version

_C Language Options_
     *Note Options Controlling C Dialect: C Dialect Options.
          -ansi  -std=STANDARD  -aux-info FILENAME
          -fno-asm  -fno-builtin  -fno-builtin-FUNCTION
          -fhosted  -ffreestanding  -fms-extensions
          -trigraphs  -no-integrated-cpp  -traditional  -traditional-cpp
          -fallow-single-precision  -fcond-mismatch
          -fsigned-bitfields  -fsigned-char
          -funsigned-bitfields  -funsigned-char
          -fwritable-strings

_C++ Language Options_
     *Note Options Controlling C++ Dialect: C++ Dialect Options.
          -fabi-version=N  -fno-access-control  -fcheck-new
          -fconserve-space  -fno-const-strings
          -fno-elide-constructors
          -fno-enforce-eh-specs
          -ffor-scope  -fno-for-scope  -fno-gnu-keywords
          -fno-implicit-templates
          -fno-implicit-inline-templates
          -fno-implement-inlines  -fms-extensions
          -fno-nonansi-builtins  -fno-operator-names
          -fno-optional-diags  -fpermissive
          -frepo  -fno-rtti  -fstats  -ftemplate-depth-N
          -fuse-cxa-atexit  -fno-weak  -nostdinc++
          -fno-default-inline  -Wabi  -Wctor-dtor-privacy
          -Wnon-virtual-dtor  -Wreorder
          -Weffc++  -Wno-deprecated
          -Wno-non-template-friend  -Wold-style-cast
          -Woverloaded-virtual  -Wno-pmf-conversions
          -Wsign-promo  -Wsynth

_Objective-C Language Options_
     *Note Options Controlling Objective-C Dialect: Objective-C Dialect
     Options.
          -fconstant-string-class=CLASS-NAME
          -fgnu-runtime  -fnext-runtime
          -fno-nil-receivers
          -fobjc-exceptions
          -freplace-objc-classes
          -fzero-link
          -gen-decls
          -Wno-protocol  -Wselector -Wundeclared-selector

_Language Independent Options_
     *Note Options to Control Diagnostic Messages Formatting: Language
     Independent Options.
          -fmessage-length=N
          -fdiagnostics-show-location=[once|every-line]

_Warning Options_
     *Note Options to Request or Suppress Warnings: Warning Options.
          -fsyntax-only  -pedantic  -pedantic-errors
          -w  -Wextra  -Wall  -Waggregate-return
          -Wcast-align  -Wcast-qual  -Wchar-subscripts  -Wcomment
          -Wconversion  -Wno-deprecated-declarations
          -Wdisabled-optimization  -Wno-div-by-zero  -Wendif-labels
          -Werror  -Werror-implicit-function-declaration
          -Wfloat-equal  -Wformat  -Wformat=2
          -Wno-format-extra-args -Wformat-nonliteral
          -Wformat-security  -Wformat-y2k
          -Wimplicit  -Wimplicit-function-declaration  -Wimplicit-int
          -Wimport  -Wno-import  -Winit-self  -Winline
          -Wno-invalid-offsetof  -Winvalid-pch
          -Wlarger-than-LEN  -Wlong-long
          -Wmain  -Wmissing-braces
          -Wmissing-format-attribute  -Wmissing-noreturn
          -Wno-multichar  -Wnonnull  -Wpacked  -Wpadded
          -Wparentheses  -Wpointer-arith  -Wredundant-decls
          -Wreturn-type  -Wsequence-point  -Wshadow
          -Wsign-compare  -Wstrict-aliasing
          -Wswitch  -Wswitch-default  -Wswitch-enum
          -Wsystem-headers  -Wtrigraphs  -Wundef  -Wuninitialized
          -Wunknown-pragmas  -Wunreachable-code
          -Wunused  -Wunused-function  -Wunused-label  -Wunused-parameter
          -Wunused-value  -Wunused-variable  -Wwrite-strings

_C-only Warning Options_
          -Wbad-function-cast  -Wmissing-declarations
          -Wmissing-prototypes  -Wnested-externs  -Wold-style-definition
          -Wstrict-prototypes  -Wtraditional
          -Wdeclaration-after-statement

_Debugging Options_
     *Note Options for Debugging Your Program or GCC: Debugging Options.
          -dLETTERS  -dumpspecs  -dumpmachine  -dumpversion
          -fdump-unnumbered  -fdump-translation-unit[-N]
          -fdump-class-hierarchy[-N]
          -fdump-tree-original[-N]
          -fdump-tree-optimized[-N]
          -fdump-tree-inlined[-N]
          -feliminate-dwarf2-dups -feliminate-unused-debug-types
          -feliminate-unused-debug-symbols -fmem-report -fprofile-arcs
          -frandom-seed=STRING -fsched-verbose=N
          -ftest-coverage  -ftime-report
          -g  -gLEVEL  -gcoff -gdwarf-2
          -ggdb  -gstabs  -gstabs+  -gvms  -gxcoff  -gxcoff+
          -p  -pg  -print-file-name=LIBRARY  -print-libgcc-file-name
          -print-multi-directory  -print-multi-lib
          -print-prog-name=PROGRAM  -print-search-dirs  -Q
          -save-temps  -time

_Optimization Options_
     *Note Options that Control Optimization: Optimize Options.
          -falign-functions=N  -falign-jumps=N
          -falign-labels=N  -falign-loops=N
          -fbranch-probabilities -fprofile-values -fvpt -fbranch-target-load-optimize
          -fbranch-target-load-optimize2 -fcaller-saves  -fcprop-registers
          -fcse-follow-jumps  -fcse-skip-blocks  -fdata-sections
          -fdelayed-branch  -fdelete-null-pointer-checks
          -fexpensive-optimizations  -ffast-math  -ffloat-store
          -fforce-addr  -fforce-mem  -ffunction-sections
          -fgcse  -fgcse-lm  -fgcse-sm  -fgcse-las  -floop-optimize
          -fcrossjumping  -fif-conversion  -fif-conversion2
          -finline-functions  -finline-limit=N  -fkeep-inline-functions
          -fkeep-static-consts  -fmerge-constants  -fmerge-all-constants
          -fmove-all-movables  -fnew-ra  -fno-branch-count-reg
          -fno-default-inline  -fno-defer-pop
          -fno-function-cse  -fno-guess-branch-probability
          -fno-inline  -fno-math-errno  -fno-peephole  -fno-peephole2
          -funsafe-math-optimizations  -ffinite-math-only
          -fno-trapping-math  -fno-zero-initialized-in-bss
          -fomit-frame-pointer  -foptimize-register-move
          -foptimize-sibling-calls  -fprefetch-loop-arrays
          -fprofile-generate -fprofile-use
          -freduce-all-givs  -fregmove  -frename-registers
          -freorder-blocks  -freorder-functions
          -frerun-cse-after-loop  -frerun-loop-opt
          -frounding-math -fschedule-insns  -fschedule-insns2
          -fno-sched-interblock  -fno-sched-spec  -fsched-spec-load
          -fsched-spec-load-dangerous
          -fsched-stalled-insns=N -sched-stalled-insns-dep=N
          -fsched2-use-superblocks
          -fsched2-use-traces  -fsignaling-nans
          -fsingle-precision-constant
          -fstrength-reduce  -fstrict-aliasing  -ftracer  -fthread-jumps
          -funroll-all-loops  -funroll-loops  -fpeel-loops
          -funswitch-loops  -fold-unroll-loops  -fold-unroll-all-loops
          --param NAME=VALUE
          -O  -O0  -O1  -O2  -O3  -Os

_Preprocessor Options_
     *Note Options Controlling the Preprocessor: Preprocessor Options.
          -AQUESTION=ANSWER
          -A-QUESTION[=ANSWER]
          -C  -dD  -dI  -dM  -dN
          -DMACRO[=DEFN]  -E  -H
          -idirafter DIR
          -include FILE  -imacros FILE
          -iprefix FILE  -iwithprefix DIR
          -iwithprefixbefore DIR  -isystem DIR
          -M  -MM  -MF  -MG  -MP  -MQ  -MT  -nostdinc
          -P  -fworking-directory  -remap
          -trigraphs  -undef  -UMACRO  -Wp,OPTION
          -Xpreprocessor OPTION

_Assembler Option_
     *Note Passing Options to the Assembler: Assembler Options.
          -Wa,OPTION  -Xassembler OPTION

_Linker Options_
     *Note Options for Linking: Link Options.
          OBJECT-FILE-NAME  -lLIBRARY
          -nostartfiles  -nodefaultlibs  -nostdlib -pie
          -s  -static  -static-libgcc  -shared  -shared-libgcc  -symbolic
          -Wl,OPTION  -Xlinker OPTION
          -u SYMBOL

_Directory Options_
     *Note Options for Directory Search: Directory Options.
          -BPREFIX  -IDIR  -I-  -LDIR  -specs=FILE

_Target Options_
     *Note Target Options::.
          -V VERSION  -b MACHINE

_Machine Dependent Options_
     *Note Hardware Models and Configurations: Submodel Options.

     _M680x0 Options_
          -m68000  -m68020  -m68020-40  -m68020-60  -m68030  -m68040
          -m68060  -mcpu32  -m5200  -m68881  -mbitfield  -mc68000  -mc68020
          -mnobitfield  -mrtd  -mshort  -msoft-float  -mpcrel
          -malign-int  -mstrict-align  -msep-data  -mno-sep-data
          -mshared-library-id=n  -mid-shared-library  -mno-id-shared-library

     _M68hc1x Options_
          -m6811  -m6812  -m68hc11  -m68hc12   -m68hcs12
          -mauto-incdec  -minmax  -mlong-calls  -mshort
          -msoft-reg-count=COUNT

     _VAX Options_
          -mg  -mgnu  -munix

     _SPARC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mcmodel=CODE-MODEL
          -m32  -m64  -mapp-regs  -mno-app-regs
          -mfaster-structs  -mno-faster-structs
          -mflat  -mno-flat  -mfpu  -mno-fpu
          -mhard-float  -msoft-float
          -mhard-quad-float  -msoft-quad-float
          -mimpure-text  -mno-impure-text  -mlittle-endian
          -mstack-bias  -mno-stack-bias
          -munaligned-doubles  -mno-unaligned-doubles
          -mv8plus  -mno-v8plus  -mvis  -mno-vis
          -mcypress  -mf930  -mf934
          -msparclite  -msupersparc  -mv8

     _ARM Options_
          -mapcs-frame  -mno-apcs-frame
          -mapcs-26  -mapcs-32
          -mapcs-stack-check  -mno-apcs-stack-check
          -mapcs-float  -mno-apcs-float
          -mapcs-reentrant  -mno-apcs-reentrant
          -msched-prolog  -mno-sched-prolog
          -mlittle-endian  -mbig-endian  -mwords-little-endian
          -malignment-traps  -mno-alignment-traps
          -msoft-float  -mhard-float  -mfpe
          -mthumb-interwork  -mno-thumb-interwork
          -mcpu=NAME  -march=NAME  -mfpe=NAME
          -mstructure-size-boundary=N
          -mabort-on-noreturn
          -mlong-calls  -mno-long-calls
          -msingle-pic-base  -mno-single-pic-base
          -mpic-register=REG
          -mnop-fun-dllimport
          -mcirrus-fix-invalid-insns -mno-cirrus-fix-invalid-insns
          -mpoke-function-name
          -mthumb  -marm
          -mtpcs-frame  -mtpcs-leaf-frame
          -mcaller-super-interworking  -mcallee-super-interworking

     _MN10300 Options_
          -mmult-bug  -mno-mult-bug
          -mam33  -mno-am33
          -mam33-2  -mno-am33-2
          -mno-crt0  -mrelax

     _M32R/D Options_
          -m32r2 -m32rx -m32r
          -mdebug
          -malign-loops -mno-align-loops
          -missue-rate=NUMBER
          -mbranch-cost=NUMBER
          -mmodel=CODE-SIZE-MODEL-TYPE
          -msdata=SDATA-TYPE
          -mno-flush-func -mflush-func=NAME
          -mno-flush-trap -mflush-trap=NUMBER
          -G NUM

     _RS/6000 and PowerPC Options_
          -mcpu=CPU-TYPE
          -mtune=CPU-TYPE
          -mpower  -mno-power  -mpower2  -mno-power2
          -mpowerpc  -mpowerpc64  -mno-powerpc
          -maltivec  -mno-altivec
          -mpowerpc-gpopt  -mno-powerpc-gpopt
          -mpowerpc-gfxopt  -mno-powerpc-gfxopt
          -mnew-mnemonics  -mold-mnemonics
          -mfull-toc   -mminimal-toc  -mno-fp-in-toc  -mno-sum-in-toc
          -m64  -m32  -mxl-call  -mno-xl-call  -mpe
          -malign-power  -malign-natural
          -msoft-float  -mhard-float  -mmultiple  -mno-multiple
          -mstring  -mno-string  -mupdate  -mno-update
          -mfused-madd  -mno-fused-madd  -mbit-align  -mno-bit-align
          -mstrict-align  -mno-strict-align  -mrelocatable
          -mno-relocatable  -mrelocatable-lib  -mno-relocatable-lib
          -mtoc  -mno-toc  -mlittle  -mlittle-endian  -mbig  -mbig-endian
          -mdynamic-no-pic
          -mprioritize-restricted-insns=PRIORITY
          -msched-costly-dep=DEPENDENCE_TYPE
          -minsert-sched-nops=SCHEME
          -mcall-sysv  -mcall-netbsd
          -maix-struct-return  -msvr4-struct-return
          -mabi=altivec  -mabi=no-altivec
          -mabi=spe  -mabi=no-spe
          -misel=yes  -misel=no
          -mspe=yes  -mspe=no
          -mfloat-gprs=yes  -mfloat-gprs=no
          -mprototype  -mno-prototype
          -msim  -mmvme  -mads  -myellowknife  -memb  -msdata
          -msdata=OPT  -mvxworks  -mwindiss  -G NUM  -pthread

     _Darwin Options_
          -all_load  -allowable_client  -arch  -arch_errors_fatal
          -arch_only  -bind_at_load  -bundle  -bundle_loader
          -client_name  -compatibility_version  -current_version
          -dependency-file  -dylib_file  -dylinker_install_name
          -dynamic  -dynamiclib  -exported_symbols_list
          -filelist  -flat_namespace  -force_cpusubtype_ALL
          -force_flat_namespace  -headerpad_max_install_names
          -image_base  -init  -install_name  -keep_private_externs
          -multi_module  -multiply_defined  -multiply_defined_unused
          -noall_load  -nofixprebinding -nomultidefs  -noprebind  -noseglinkedit
          -pagezero_size  -prebind  -prebind_all_twolevel_modules
          -private_bundle  -read_only_relocs  -sectalign
          -sectobjectsymbols  -whyload  -seg1addr
          -sectcreate  -sectobjectsymbols  -sectorder
          -seg_addr_table  -seg_addr_table_filename  -seglinkedit
          -segprot  -segs_read_only_addr  -segs_read_write_addr
          -single_module  -static  -sub_library  -sub_umbrella
          -twolevel_namespace  -umbrella  -undefined
          -unexported_symbols_list  -weak_reference_mismatches
          -whatsloaded

     _MIPS Options_
          -EL  -EB  -march=ARCH  -mtune=ARCH
          -mips1  -mips2  -mips3  -mips4  -mips32  -mips32r2  -mips64
          -mips16  -mno-mips16  -mabi=ABI  -mabicalls  -mno-abicalls
          -mxgot  -mno-xgot  -membedded-pic  -mno-embedded-pic
          -mgp32  -mgp64  -mfp32  -mfp64  -mhard-float  -msoft-float
          -msingle-float  -mdouble-float  -mint64  -mlong64  -mlong32
          -GNUM  -membedded-data  -mno-embedded-data
          -muninit-const-in-rodata  -mno-uninit-const-in-rodata
          -msplit-addresses  -mno-split-addresses
          -mexplicit-relocs  -mno-explicit-relocs
          -mrnames  -mno-rnames
          -mcheck-zero-division  -mno-check-zero-division
          -mmemcpy  -mno-memcpy  -mlong-calls  -mno-long-calls
          -mmad  -mno-mad  -mfused-madd  -mno-fused-madd  -nocpp
          -mfix-sb1  -mno-fix-sb1  -mflush-func=FUNC
          -mno-flush-func  -mbranch-likely  -mno-branch-likely

     _i386 and x86-64 Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mfpmath=UNIT
          -masm=DIALECT  -mno-fancy-math-387
          -mno-fp-ret-in-387  -msoft-float  -msvr3-shlib
          -mno-wide-multiply  -mrtd  -malign-double
          -mpreferred-stack-boundary=NUM
          -mmmx  -msse  -msse2 -msse3 -m3dnow
          -mthreads  -mno-align-stringops  -minline-all-stringops
          -mpush-args  -maccumulate-outgoing-args  -m128bit-long-double
          -m96bit-long-double  -mregparm=NUM  -momit-leaf-frame-pointer
          -mno-red-zone -mno-tls-direct-seg-refs
          -mcmodel=CODE-MODEL
          -m32  -m64

     _HPPA Options_
          -march=ARCHITECTURE-TYPE
          -mbig-switch  -mdisable-fpregs  -mdisable-indexing
          -mfast-indirect-calls  -mgas  -mgnu-ld   -mhp-ld
          -mjump-in-delay -mlinker-opt -mlong-calls
          -mlong-load-store  -mno-big-switch  -mno-disable-fpregs
          -mno-disable-indexing  -mno-fast-indirect-calls  -mno-gas
          -mno-jump-in-delay  -mno-long-load-store
          -mno-portable-runtime  -mno-soft-float
          -mno-space-regs  -msoft-float  -mpa-risc-1-0
          -mpa-risc-1-1  -mpa-risc-2-0  -mportable-runtime
          -mschedule=CPU-TYPE  -mspace-regs  -msio  -mwsio
          -nolibdld  -static  -threads

     _Intel 960 Options_
          -mCPU-TYPE  -masm-compat  -mclean-linkage
          -mcode-align  -mcomplex-addr  -mleaf-procedures
          -mic-compat  -mic2.0-compat  -mic3.0-compat
          -mintel-asm  -mno-clean-linkage  -mno-code-align
          -mno-complex-addr  -mno-leaf-procedures
          -mno-old-align  -mno-strict-align  -mno-tail-call
          -mnumerics  -mold-align  -msoft-float  -mstrict-align
          -mtail-call

     _DEC Alpha Options_
          -mno-fp-regs  -msoft-float  -malpha-as  -mgas
          -mieee  -mieee-with-inexact  -mieee-conformant
          -mfp-trap-mode=MODE  -mfp-rounding-mode=MODE
          -mtrap-precision=MODE  -mbuild-constants
          -mcpu=CPU-TYPE  -mtune=CPU-TYPE
          -mbwx  -mmax  -mfix  -mcix
          -mfloat-vax  -mfloat-ieee
          -mexplicit-relocs  -msmall-data  -mlarge-data
          -msmall-text  -mlarge-text
          -mmemory-latency=TIME

     _DEC Alpha/VMS Options_
          -mvms-return-codes

     _H8/300 Options_
          -mrelax  -mh  -ms  -mn  -mint32  -malign-300

     _SH Options_
          -m1  -m2  -m2e  -m3  -m3e
          -m4-nofpu  -m4-single-only  -m4-single  -m4
          -m5-64media  -m5-64media-nofpu
          -m5-32media  -m5-32media-nofpu
          -m5-compact  -m5-compact-nofpu
          -mb  -ml  -mdalign  -mrelax
          -mbigtable  -mfmovd  -mhitachi  -mnomacsave
          -mieee  -misize  -mpadstruct  -mspace
          -mprefergot  -musermode

     _System V Options_
          -Qy  -Qn  -YP,PATHS  -Ym,DIR

     _ARC Options_
          -EB  -EL
          -mmangle-cpu  -mcpu=CPU  -mtext=TEXT-SECTION
          -mdata=DATA-SECTION  -mrodata=READONLY-DATA-SECTION

     _TMS320C3x/C4x Options_
          -mcpu=CPU  -mbig  -msmall  -mregparm  -mmemparm
          -mfast-fix  -mmpyi  -mbk  -mti  -mdp-isr-reload
          -mrpts=COUNT  -mrptb  -mdb  -mloop-unsigned
          -mparallel-insns  -mparallel-mpy  -mpreserve-float

     _V850 Options_
          -mlong-calls  -mno-long-calls  -mep  -mno-ep
          -mprolog-function  -mno-prolog-function  -mspace
          -mtda=N  -msda=N  -mzda=N
          -mapp-regs  -mno-app-regs
          -mdisable-callt  -mno-disable-callt
          -mv850e1
          -mv850e
          -mv850  -mbig-switch

     _NS32K Options_
          -m32032  -m32332  -m32532  -m32081  -m32381
          -mmult-add  -mnomult-add  -msoft-float  -mrtd  -mnortd
          -mregparam  -mnoregparam  -msb  -mnosb
          -mbitfield  -mnobitfield  -mhimem  -mnohimem

     _AVR Options_
          -mmcu=MCU  -msize  -minit-stack=N  -mno-interrupts
          -mcall-prologues  -mno-tablejump  -mtiny-stack

     _MCore Options_
          -mhardlit  -mno-hardlit  -mdiv  -mno-div  -mrelax-immediates
          -mno-relax-immediates  -mwide-bitfields  -mno-wide-bitfields
          -m4byte-functions  -mno-4byte-functions  -mcallgraph-data
          -mno-callgraph-data  -mslow-bytes  -mno-slow-bytes  -mno-lsim
          -mlittle-endian  -mbig-endian  -m210  -m340  -mstack-increment

     _MMIX Options_
          -mlibfuncs  -mno-libfuncs  -mepsilon  -mno-epsilon  -mabi=gnu
          -mabi=mmixware  -mzero-extend  -mknuthdiv  -mtoplevel-symbols
          -melf  -mbranch-predict  -mno-branch-predict  -mbase-addresses
          -mno-base-addresses  -msingle-exit  -mno-single-exit

     _IA-64 Options_
          -mbig-endian  -mlittle-endian  -mgnu-as  -mgnu-ld  -mno-pic
          -mvolatile-asm-stop  -mb-step  -mregister-names  -mno-sdata
          -mconstant-gp  -mauto-pic  -minline-float-divide-min-latency
          -minline-float-divide-max-throughput
          -minline-int-divide-min-latency
          -minline-int-divide-max-throughput  -mno-dwarf2-asm
          -mfixed-range=REGISTER-RANGE

     _D30V Options_
          -mextmem  -mextmemory  -monchip  -mno-asm-optimize
          -masm-optimize  -mbranch-cost=N  -mcond-exec=N

     _S/390 and zSeries Options_
          -mtune=CPU-TYPE  -march=CPU-TYPE
          -mhard-float  -msoft-float  -mbackchain  -mno-backchain
          -msmall-exec  -mno-small-exec  -mmvcle -mno-mvcle
          -m64  -m31  -mdebug  -mno-debug  -mesa  -mzarch  -mfused-madd  -mno-fused-madd

     _CRIS Options_
          -mcpu=CPU  -march=CPU  -mtune=CPU
          -mmax-stack-frame=N  -melinux-stacksize=N
          -metrax4  -metrax100  -mpdebug  -mcc-init  -mno-side-effects
          -mstack-align  -mdata-align  -mconst-align
          -m32-bit  -m16-bit  -m8-bit  -mno-prologue-epilogue  -mno-gotplt
          -melf  -maout  -melinux  -mlinux  -sim  -sim2
          -mmul-bug-workaround  -mno-mul-bug-workaround

     _PDP-11 Options_
          -mfpu  -msoft-float  -mac0  -mno-ac0  -m40  -m45  -m10
          -mbcopy  -mbcopy-builtin  -mint32  -mno-int16
          -mint16  -mno-int32  -mfloat32  -mno-float64
          -mfloat64  -mno-float32  -mabshi  -mno-abshi
          -mbranch-expensive  -mbranch-cheap
          -msplit  -mno-split  -munix-asm  -mdec-asm

     _Xstormy16 Options_
          -msim

     _Xtensa Options_
          -mconst16 -mno-const16
          -mfused-madd  -mno-fused-madd
          -mtext-section-literals  -mno-text-section-literals
          -mtarget-align  -mno-target-align
          -mlongcalls  -mno-longcalls

     _FRV Options_
          -mgpr-32  -mgpr-64  -mfpr-32  -mfpr-64
          -mhard-float  -msoft-float
          -malloc-cc  -mfixed-cc  -mdword  -mno-dword
          -mdouble  -mno-double
          -mmedia  -mno-media  -mmuladd  -mno-muladd
          -mlibrary-pic  -macc-4 -macc-8
          -mpack  -mno-pack  -mno-eflags  -mcond-move  -mno-cond-move
          -mscc  -mno-scc  -mcond-exec  -mno-cond-exec
          -mvliw-branch  -mno-vliw-branch
          -mmulti-cond-exec  -mno-multi-cond-exec  -mnested-cond-exec
          -mno-nested-cond-exec  -mtomcat-stats
          -mcpu=CPU

_Code Generation Options_
     *Note Options for Code Generation Conventions: Code Gen Options.
          -fcall-saved-REG  -fcall-used-REG
          -ffixed-REG  -fexceptions
          -fnon-call-exceptions  -funwind-tables
          -fasynchronous-unwind-tables
          -finhibit-size-directive  -finstrument-functions
          -fno-common  -fno-ident
          -fpcc-struct-return  -fpic  -fPIC -fpie -fPIE
          -freg-struct-return  -fshared-data  -fshort-enums
          -fshort-double  -fshort-wchar
          -fverbose-asm  -fpack-struct  -fstack-check
          -fstack-limit-register=REG  -fstack-limit-symbol=SYM
          -fargument-alias  -fargument-noalias
          -fargument-noalias-global  -fleading-underscore
          -ftls-model=MODEL
          -ftrapv  -fwrapv  -fbounds-check


* Menu:

* Overall Options::     Controlling the kind of output:
                        an executable, object files, assembler files,
                        or preprocessed source.
* C Dialect Options::   Controlling the variant of C language compiled.
* C++ Dialect Options:: Variations on C++.
* Objective-C Dialect Options:: Variations on Objective-C.
* Language Independent Options:: Controlling how diagnostics should be
                        formatted.
* Warning Options::     How picky should the compiler be?
* Debugging Options::   Symbol tables, measurements, and debugging dumps.
* Optimize Options::    How much optimization?
* Preprocessor Options:: Controlling header files and macro definitions.
                         Also, getting dependency information for Make.
* Assembler Options::   Passing options to the assembler.
* Link Options::        Specifying libraries and so on.
* Directory Options::   Where to find header files and libraries.
                        Where to find the compiler executable files.
* Spec Files::          How to pass switches to sub-processes.
* Target Options::      Running a cross-compiler, or an old version of GCC.


File: gcc,  Node: Overall Options,  Next: Invoking G++,  Prev: Option Summary,  Up: Invoking GCC

3.2 Options Controlling the Kind of Output
==========================================

Compilation can involve up to four stages: preprocessing, compilation
proper, assembly and linking, always in that order.  GCC is capable of
preprocessing and compiling several files either into several assembler
input files, or into one assembler input file; then each assembler
input file produces an object file, and linking combines all the object
files (those newly compiled, and those specified as input) into an
executable file.

 For any given input file, the file name suffix determines what kind of
compilation is done:

`FILE.c'
     C source code which must be preprocessed.

`FILE.i'
     C source code which should not be preprocessed.

`FILE.ii'
     C++ source code which should not be preprocessed.

`FILE.m'
     Objective-C source code.  Note that you must link with the library
     `libobjc.a' to make an Objective-C program work.

`FILE.mi'
     Objective-C source code which should not be preprocessed.

`FILE.h'
     C or C++ header file to be turned into a precompiled header.

`FILE.cc'
`FILE.cp'
`FILE.cxx'
`FILE.cpp'
`FILE.CPP'
`FILE.c++'
`FILE.C'
     C++ source code which must be preprocessed.  Note that in `.cxx',
     the last two letters must both be literally `x'.  Likewise, `.C'
     refers to a literal capital C.

`FILE.hh'
`FILE.H'
     C++ header file to be turned into a precompiled header.

`FILE.f'
`FILE.for'
`FILE.FOR'
     Fortran source code which should not be preprocessed.

`FILE.F'
`FILE.fpp'
`FILE.FPP'
     Fortran source code which must be preprocessed (with the
     traditional preprocessor).

`FILE.r'
     Fortran source code which must be preprocessed with a RATFOR
     preprocessor (not included with GCC).

     *Note Options Controlling the Kind of Output: (g77)Overall
     Options, for more details of the handling of Fortran input files.

`FILE.ads'
     Ada source code file which contains a library unit declaration (a
     declaration of a package, subprogram, or generic, or a generic
     instantiation), or a library unit renaming declaration (a package,
     generic, or subprogram renaming declaration).  Such files are also
     called "specs".

`FILE.adb'
     Ada source code file containing a library unit body (a subprogram
     or package body).  Such files are also called "bodies".

`FILE.s'
     Assembler code.

`FILE.S'
     Assembler code which must be preprocessed.

`OTHER'
     An object file to be fed straight into linking.  Any file name
     with no recognized suffix is treated this way.

 You can specify the input language explicitly with the `-x' option:

`-x LANGUAGE'
     Specify explicitly the LANGUAGE for the following input files
     (rather than letting the compiler choose a default based on the
     file name suffix).  This option applies to all following input
     files until the next `-x' option.  Possible values for LANGUAGE
     are:
          c  c-header  cpp-output
          c++  c++-header  c++-cpp-output
          objective-c  objective-c-header  objc-cpp-output
          assembler  assembler-with-cpp
          ada
          f77  f77-cpp-input  ratfor
          java
          treelang

`-x none'
     Turn off any specification of a language, so that subsequent files
     are handled according to their file name suffixes (as they are if
     `-x' has not been used at all).

`-pass-exit-codes'
     Normally the `gcc' program will exit with the code of 1 if any
     phase of the compiler returns a non-success return code.  If you
     specify `-pass-exit-codes', the `gcc' program will instead return
     with numerically highest error produced by any phase that returned
     an error indication.

 If you only want some of the stages of compilation, you can use `-x'
(or filename suffixes) to tell `gcc' where to start, and one of the
options `-c', `-S', or `-E' to say where `gcc' is to stop.  Note that
some combinations (for example, `-x cpp-output -E') instruct `gcc' to
do nothing at all.

`-c'
     Compile or assemble the source files, but do not link.  The linking
     stage simply is not done.  The ultimate output is in the form of an
     object file for each source file.

     By default, the object file name for a source file is made by
     replacing the suffix `.c', `.i', `.s', etc., with `.o'.

     Unrecognized input files, not requiring compilation or assembly,
     are ignored.

`-S'
     Stop after the stage of compilation proper; do not assemble.  The
     output is in the form of an assembler code file for each
     non-assembler input file specified.

     By default, the assembler file name for a source file is made by
     replacing the suffix `.c', `.i', etc., with `.s'.

     Input files that don't require compilation are ignored.

`-E'
     Stop after the preprocessing stage; do not run the compiler
     proper.  The output is in the form of preprocessed source code,
     which is sent to the standard output.

     Input files which don't require preprocessing are ignored.

`-o FILE'
     Place output in file FILE.  This applies regardless to whatever
     sort of output is being produced, whether it be an executable file,
     an object file, an assembler file or preprocessed C code.

     If you specify `-o' when compiling more than one input file, or
     you are producing an executable file as output, all the source
     files on the command line will be compiled at once.

     If `-o' is not specified, the default is to put an executable file
     in `a.out', the object file for `SOURCE.SUFFIX' in `SOURCE.o', its
     assembler file in `SOURCE.s', and all preprocessed C source on
     standard output.

`-v'
     Print (on standard error output) the commands executed to run the
     stages of compilation.  Also print the version number of the
     compiler driver program and of the preprocessor and the compiler
     proper.

`-###'
     Like `-v' except the commands are not executed and all command
     arguments are quoted.  This is useful for shell scripts to capture
     the driver-generated command lines.

`-pipe'
     Use pipes rather than temporary files for communication between the
     various stages of compilation.  This fails to work on some systems
     where the assembler is unable to read from a pipe; but the GNU
     assembler has no trouble.

`--help'
     Print (on the standard output) a description of the command line
     options understood by `gcc'.  If the `-v' option is also specified
     then `--help' will also be passed on to the various processes
     invoked by `gcc', so that they can display the command line options
     they accept.  If the `-Wextra' option is also specified then
     command line options which have no documentation associated with
     them will also be displayed.

`--target-help'
     Print (on the standard output) a description of target specific
     command line options for each tool.

`--version'
     Display the version number and copyrights of the invoked GCC.


File: gcc,  Node: Invoking G++,  Next: C Dialect Options,  Prev: Overall Options,  Up: Invoking GCC

3.3 Compiling C++ Programs
==========================

C++ source files conventionally use one of the suffixes `.C', `.cc',
`.cpp', `.CPP', `.c++', `.cp', or `.cxx'; C++ header files often use
`.hh' or `.H'; and preprocessed C++ files use the suffix `.ii'.  GCC
recognizes files with these names and compiles them as C++ programs
even if you call the compiler the same way as for compiling C programs
(usually with the name `gcc').

 However, C++ programs often require class libraries as well as a
compiler that understands the C++ language--and under some
circumstances, you might want to compile programs or header files from
standard input, or otherwise without a suffix that flags them as C++
programs.  You might also like to precompile a C header file with a
`.h' extension to be used in C++ compilations.  `g++' is a program that
calls GCC with the default language set to C++, and automatically
specifies linking against the C++ library.  On many systems, `g++' is
also installed with the name `c++'.

 When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.  *Note
Options Controlling C Dialect: C Dialect Options, for explanations of
options for languages related to C.  *Note Options Controlling C++
Dialect: C++ Dialect Options, for explanations of options that are
meaningful only for C++ programs.


File: gcc,  Node: C Dialect Options,  Next: C++ Dialect Options,  Prev: Invoking G++,  Up: Invoking GCC

3.4 Options Controlling C Dialect
=================================

The following options control the dialect of C (or languages derived
from C, such as C++ and Objective-C) that the compiler accepts:

`-ansi'
     In C mode, support all ISO C90 programs.  In C++ mode, remove GNU
     extensions that conflict with ISO C++.

     This turns off certain features of GCC that are incompatible with
     ISO C90 (when compiling C code), or of standard C++ (when
     compiling C++ code), such as the `asm' and `typeof' keywords, and
     predefined macros such as `unix' and `vax' that identify the type
     of system you are using.  It also enables the undesirable and
     rarely used ISO trigraph feature.  For the C compiler, it disables
     recognition of C++ style `//' comments as well as the `inline'
     keyword.

     The alternate keywords `__asm__', `__extension__', `__inline__'
     and `__typeof__' continue to work despite `-ansi'.  You would not
     want to use them in an ISO C program, of course, but it is useful
     to put them in header files that might be included in compilations
     done with `-ansi'.  Alternate predefined macros such as `__unix__'
     and `__vax__' are also available, with or without `-ansi'.

     The `-ansi' option does not cause non-ISO programs to be rejected
     gratuitously.  For that, `-pedantic' is required in addition to
     `-ansi'.  *Note Warning Options::.

     The macro `__STRICT_ANSI__' is predefined when the `-ansi' option
     is used.  Some header files may notice this macro and refrain from
     declaring certain functions or defining certain macros that the
     ISO standard doesn't call for; this is to avoid interfering with
     any programs that might use these names for other things.

     Functions which would normally be built in but do not have
     semantics defined by ISO C (such as `alloca' and `ffs') are not
     built-in functions with `-ansi' is used.  *Note Other built-in
     functions provided by GCC: Other Builtins, for details of the
     functions affected.

`-std='
     Determine the language standard.  This option is currently only
     supported when compiling C or C++.  A value for this option must be
     provided; possible values are

    `c89'
    `iso9899:1990'
          ISO C90 (same as `-ansi').

    `iso9899:199409'
          ISO C90 as modified in amendment 1.

    `c99'
    `c9x'
    `iso9899:1999'
    `iso9899:199x'
          ISO C99.  Note that this standard is not yet fully supported;
          see `http://gcc.gnu.org/gcc-3.4/c99status.html' for more
          information.  The names `c9x' and `iso9899:199x' are
          deprecated.

    `gnu89'
          Default, ISO C90 plus GNU extensions (including some C99
          features).

    `gnu99'
    `gnu9x'
          ISO C99 plus GNU extensions.  When ISO C99 is fully
          implemented in GCC, this will become the default.  The name
          `gnu9x' is deprecated.

    `c++98'
          The 1998 ISO C++ standard plus amendments.

    `gnu++98'
          The same as `-std=c++98' plus GNU extensions.  This is the
          default for C++ code.

     Even when this option is not specified, you can still use some of
     the features of newer standards in so far as they do not conflict
     with previous C standards.  For example, you may use
     `__restrict__' even when `-std=c99' is not specified.

     The `-std' options specifying some version of ISO C have the same
     effects as `-ansi', except that features that were not in ISO C90
     but are in the specified version (for example, `//' comments and
     the `inline' keyword in ISO C99) are not disabled.

     *Note Language Standards Supported by GCC: Standards, for details
     of these standard versions.

`-aux-info FILENAME'
     Output to the given filename prototyped declarations for all
     functions declared and/or defined in a translation unit, including
     those in header files.  This option is silently ignored in any
     language other than C.

     Besides declarations, the file indicates, in comments, the origin
     of each declaration (source file and line), whether the
     declaration was implicit, prototyped or unprototyped (`I', `N' for
     new or `O' for old, respectively, in the first character after the
     line number and the colon), and whether it came from a declaration
     or a definition (`C' or `F', respectively, in the following
     character).  In the case of function definitions, a K&R-style list
     of arguments followed by their declarations is also provided,
     inside comments, after the declaration.

`-fno-asm'
     Do not recognize `asm', `inline' or `typeof' as a keyword, so that
     code can use these words as identifiers.  You can use the keywords
     `__asm__', `__inline__' and `__typeof__' instead.  `-ansi' implies
     `-fno-asm'.

     In C++, this switch only affects the `typeof' keyword, since `asm'
     and `inline' are standard keywords.  You may want to use the
     `-fno-gnu-keywords' flag instead, which has the same effect.  In
     C99 mode (`-std=c99' or `-std=gnu99'), this switch only affects
     the `asm' and `typeof' keywords, since `inline' is a standard
     keyword in ISO C99.

`-fno-builtin'
`-fno-builtin-FUNCTION'
     Don't recognize built-in functions that do not begin with
     `__builtin_' as prefix.  *Note Other built-in functions provided
     by GCC: Other Builtins, for details of the functions affected,
     including those which are not built-in functions when `-ansi' or
     `-std' options for strict ISO C conformance are used because they
     do not have an ISO standard meaning.

     GCC normally generates special code to handle certain built-in
     functions more efficiently; for instance, calls to `alloca' may
     become single instructions that adjust the stack directly, and
     calls to `memcpy' may become inline copy loops.  The resulting
     code is often both smaller and faster, but since the function
     calls no longer appear as such, you cannot set a breakpoint on
     those calls, nor can you change the behavior of the functions by
     linking with a different library.

     With the `-fno-builtin-FUNCTION' option only the built-in function
     FUNCTION is disabled.  FUNCTION must not begin with `__builtin_'.
     If a function is named this is not built-in in this version of
     GCC, this option is ignored.  There is no corresponding
     `-fbuiltin-FUNCTION' option; if you wish to enable built-in
     functions selectively when using `-fno-builtin' or
     `-ffreestanding', you may define macros such as:

          #define abs(n)          __builtin_abs ((n))
          #define strcpy(d, s)    __builtin_strcpy ((d), (s))

`-fhosted'
     Assert that compilation takes place in a hosted environment.  This
     implies `-fbuiltin'.  A hosted environment is one in which the
     entire standard library is available, and in which `main' has a
     return type of `int'.  Examples are nearly everything except a
     kernel.  This is equivalent to `-fno-freestanding'.

`-ffreestanding'
     Assert that compilation takes place in a freestanding environment.
     This implies `-fno-builtin'.  A freestanding environment is one
     in which the standard library may not exist, and program startup
     may not necessarily be at `main'.  The most obvious example is an
     OS kernel.  This is equivalent to `-fno-hosted'.

     *Note Language Standards Supported by GCC: Standards, for details
     of freestanding and hosted environments.

`-fms-extensions'
     Accept some non-standard constructs used in Microsoft header files.

`-trigraphs'
     Support ISO C trigraphs.  The `-ansi' option (and `-std' options
     for strict ISO C conformance) implies `-trigraphs'.

`-no-integrated-cpp'
     Performs a compilation in two passes: preprocessing and compiling.
     This option allows a user supplied "cc1", "cc1plus", or "cc1obj"
     via the `-B' option. The user supplied compilation step can then
     add in an additional preprocessing step after normal preprocessing
     but before compiling. The default is to use the integrated cpp
     (internal cpp)

     The semantics of this option will change if "cc1", "cc1plus", and
     "cc1obj" are merged.

`-traditional'
`-traditional-cpp'
     Formerly, these options caused GCC to attempt to emulate a
     pre-standard C compiler.  They are now only supported with the
     `-E' switch.  The preprocessor continues to support a pre-standard
     mode.  See the GNU CPP manual for details.

`-fcond-mismatch'
     Allow conditional expressions with mismatched types in the second
     and third arguments.  The value of such an expression is void.
     This option is not supported for C++.

`-funsigned-char'
     Let the type `char' be unsigned, like `unsigned char'.

     Each kind of machine has a default for what `char' should be.  It
     is either like `unsigned char' by default or like `signed char' by
     default.

     Ideally, a portable program should always use `signed char' or
     `unsigned char' when it depends on the signedness of an object.
     But many programs have been written to use plain `char' and expect
     it to be signed, or expect it to be unsigned, depending on the
     machines they were written for.  This option, and its inverse, let
     you make such a program work with the opposite default.

     The type `char' is always a distinct type from each of `signed
     char' or `unsigned char', even though its behavior is always just
     like one of those two.

`-fsigned-char'
     Let the type `char' be signed, like `signed char'.

     Note that this is equivalent to `-fno-unsigned-char', which is the
     negative form of `-funsigned-char'.  Likewise, the option
     `-fno-signed-char' is equivalent to `-funsigned-char'.

`-fsigned-bitfields'
`-funsigned-bitfields'
`-fno-signed-bitfields'
`-fno-unsigned-bitfields'
     These options control whether a bit-field is signed or unsigned,
     when the declaration does not use either `signed' or `unsigned'.
     By default, such a bit-field is signed, because this is
     consistent: the basic integer types such as `int' are signed types.

`-fwritable-strings'
     Store string constants in the writable data segment and don't
     uniquize them.  This is for compatibility with old programs which
     assume they can write into string constants.

     Writing into string constants is a very bad idea; "constants"
     should be constant.

     This option is deprecated.


File: gcc,  Node: C++ Dialect Options,  Next: Objective-C Dialect Options,  Prev: C Dialect Options,  Up: Invoking GCC

3.5 Options Controlling C++ Dialect
===================================

This section describes the command-line options that are only meaningful
for C++ programs; but you can also use most of the GNU compiler options
regardless of what language your program is in.  For example, you might
compile a file `firstClass.C' like this:

     g++ -g -frepo -O -c firstClass.C

In this example, only `-frepo' is an option meant only for C++
programs; you can use the other options with any language supported by
GCC.

 Here is a list of options that are _only_ for compiling C++ programs:

`-fabi-version=N'
     Use version N of the C++ ABI.  Version 2 is the version of the C++
     ABI that first appeared in G++ 3.4.  Version 1 is the version of
     the C++ ABI that first appeared in G++ 3.2.  Version 0 will always
     be the version that conforms most closely to the C++ ABI
     specification.  Therefore, the ABI obtained using version 0 will
     change as ABI bugs are fixed.

     The default is version 2.

`-fno-access-control'
     Turn off all access checking.  This switch is mainly useful for
     working around bugs in the access control code.

`-fcheck-new'
     Check that the pointer returned by `operator new' is non-null
     before attempting to modify the storage allocated.  This check is
     normally unnecessary because the C++ standard specifies that
     `operator new' will only return `0' if it is declared `throw()',
     in which case the compiler will always check the return value even
     without this option.  In all other cases, when `operator new' has
     a non-empty exception specification, memory exhaustion is
     signalled by throwing `std::bad_alloc'.  See also `new (nothrow)'.

`-fconserve-space'
     Put uninitialized or runtime-initialized global variables into the
     common segment, as C does.  This saves space in the executable at
     the cost of not diagnosing duplicate definitions.  If you compile
     with this flag and your program mysteriously crashes after
     `main()' has completed, you may have an object that is being
     destroyed twice because two definitions were merged.

     This option is no longer useful on most targets, now that support
     has been added for putting variables into BSS without making them
     common.

`-fno-const-strings'
     Give string constants type `char *' instead of type `const char
     *'.  By default, G++ uses type `const char *' as required by the
     standard.  Even if you use `-fno-const-strings', you cannot
     actually modify the value of a string constant, unless you also use
     `-fwritable-strings'.

     This option might be removed in a future release of G++.  For
     maximum portability, you should structure your code so that it
     works with string constants that have type `const char *'.

`-fno-elide-constructors'
     The C++ standard allows an implementation to omit creating a
     temporary which is only used to initialize another object of the
     same type.  Specifying this option disables that optimization, and
     forces G++ to call the copy constructor in all cases.

`-fno-enforce-eh-specs'
     Don't check for violation of exception specifications at runtime.
     This option violates the C++ standard, but may be useful for
     reducing code size in production builds, much like defining
     `NDEBUG'.  The compiler will still optimize based on the exception
     specifications.

`-ffor-scope'
`-fno-for-scope'
     If `-ffor-scope' is specified, the scope of variables declared in
     a for-init-statement is limited to the `for' loop itself, as
     specified by the C++ standard.  If `-fno-for-scope' is specified,
     the scope of variables declared in a for-init-statement extends to
     the end of the enclosing scope, as was the case in old versions of
     G++, and other (traditional) implementations of C++.

     The default if neither flag is given to follow the standard, but
     to allow and give a warning for old-style code that would
     otherwise be invalid, or have different behavior.

`-fno-gnu-keywords'
     Do not recognize `typeof' as a keyword, so that code can use this
     word as an identifier.  You can use the keyword `__typeof__'
     instead.  `-ansi' implies `-fno-gnu-keywords'.

`-fno-implicit-templates'
     Never emit code for non-inline templates which are instantiated
     implicitly (i.e. by use); only emit code for explicit
     instantiations.  *Note Template Instantiation::, for more
     information.

`-fno-implicit-inline-templates'
     Don't emit code for implicit instantiations of inline templates,
     either.  The default is to handle inlines differently so that
     compiles with and without optimization will need the same set of
     explicit instantiations.

`-fno-implement-inlines'
     To save space, do not emit out-of-line copies of inline functions
     controlled by `#pragma implementation'.  This will cause linker
     errors if these functions are not inlined everywhere they are
     called.

`-fms-extensions'
     Disable pedantic warnings about constructs used in MFC, such as
     implicit int and getting a pointer to member function via
     non-standard syntax.

`-fno-nonansi-builtins'
     Disable built-in declarations of functions that are not mandated by
     ANSI/ISO C.  These include `ffs', `alloca', `_exit', `index',
     `bzero', `conjf', and other related functions.

`-fno-operator-names'
     Do not treat the operator name keywords `and', `bitand', `bitor',
     `compl', `not', `or' and `xor' as synonyms as keywords.

`-fno-optional-diags'
     Disable diagnostics that the standard says a compiler does not
     need to issue.  Currently, the only such diagnostic issued by G++
     is the one for a name having multiple meanings within a class.

`-fpermissive'
     Downgrade some diagnostics about nonconformant code from errors to
     warnings.  Thus, using `-fpermissive' will allow some
     nonconforming code to compile.

`-frepo'
     Enable automatic template instantiation at link time.  This option
     also implies `-fno-implicit-templates'.  *Note Template
     Instantiation::, for more information.

`-fno-rtti'
     Disable generation of information about every class with virtual
     functions for use by the C++ runtime type identification features
     (`dynamic_cast' and `typeid').  If you don't use those parts of
     the language, you can save some space by using this flag.  Note
     that exception handling uses the same information, but it will
     generate it as needed.

`-fstats'
     Emit statistics about front-end processing at the end of the
     compilation.  This information is generally only useful to the G++
     development team.

`-ftemplate-depth-N'
     Set the maximum instantiation depth for template classes to N.  A
     limit on the template instantiation depth is needed to detect
     endless recursions during template class instantiation.  ANSI/ISO
     C++ conforming programs must not rely on a maximum depth greater
     than 17.

`-fuse-cxa-atexit'
     Register destructors for objects with static storage duration with
     the `__cxa_atexit' function rather than the `atexit' function.
     This option is required for fully standards-compliant handling of
     static destructors, but will only work if your C library supports
     `__cxa_atexit'.

`-fno-weak'
     Do not use weak symbol support, even if it is provided by the
     linker.  By default, G++ will use weak symbols if they are
     available.  This option exists only for testing, and should not be
     used by end-users; it will result in inferior code and has no
     benefits.  This option may be removed in a future release of G++.

`-nostdinc++'
     Do not search for header files in the standard directories
     specific to C++, but do still search the other standard
     directories.  (This option is used when building the C++ library.)

 In addition, these optimization, warning, and code generation options
have meanings only for C++ programs:

`-fno-default-inline'
     Do not assume `inline' for functions defined inside a class scope.
     *Note Options That Control Optimization: Optimize Options.  Note
     that these functions will have linkage like inline functions; they
     just won't be inlined by default.

`-Wabi (C++ only)'
     Warn when G++ generates code that is probably not compatible with
     the vendor-neutral C++ ABI.  Although an effort has been made to
     warn about all such cases, there are probably some cases that are
     not warned about, even though G++ is generating incompatible code.
     There may also be cases where warnings are emitted even though
     the code that is generated will be compatible.

     You should rewrite your code to avoid these warnings if you are
     concerned about the fact that code generated by G++ may not be
     binary compatible with code generated by other compilers.

     The known incompatibilities at this point include:

        * Incorrect handling of tail-padding for bit-fields.  G++ may
          attempt to pack data into the same byte as a base class.  For
          example:

               struct A { virtual void f(); int f1 : 1; };
               struct B : public A { int f2 : 1; };

          In this case, G++ will place `B::f2' into the same byte
          as`A::f1'; other compilers will not.  You can avoid this
          problem by explicitly padding `A' so that its size is a
          multiple of the byte size on your platform; that will cause
          G++ and other compilers to layout `B' identically.

        * Incorrect handling of tail-padding for virtual bases.  G++
          does not use tail padding when laying out virtual bases.  For
          example:

               struct A { virtual void f(); char c1; };
               struct B { B(); char c2; };
               struct C : public A, public virtual B {};

          In this case, G++ will not place `B' into the tail-padding for
          `A'; other compilers will.  You can avoid this problem by
          explicitly padding `A' so that its size is a multiple of its
          alignment (ignoring virtual base classes); that will cause
          G++ and other compilers to layout `C' identically.

        * Incorrect handling of bit-fields with declared widths greater
          than that of their underlying types, when the bit-fields
          appear in a union.  For example:

               union U { int i : 4096; };

          Assuming that an `int' does not have 4096 bits, G++ will make
          the union too small by the number of bits in an `int'.

        * Empty classes can be placed at incorrect offsets.  For
          example:

               struct A {};

               struct B {
                 A a;
                 virtual void f ();
               };

               struct C : public B, public A {};

          G++ will place the `A' base class of `C' at a nonzero offset;
          it should be placed at offset zero.  G++ mistakenly believes
          that the `A' data member of `B' is already at offset zero.

        * Names of template functions whose types involve `typename' or
          template template parameters can be mangled incorrectly.

               template <typename Q>
               void f(typename Q::X) {}

               template <template <typename> class Q>
               void f(typename Q<int>::X) {}

          Instantiations of these templates may be mangled incorrectly.


`-Wctor-dtor-privacy (C++ only)'
     Warn when a class seems unusable because all the constructors or
     destructors in that class are private, and it has neither friends
     nor public static member functions.

`-Wnon-virtual-dtor (C++ only)'
     Warn when a class appears to be polymorphic, thereby requiring a
     virtual destructor, yet it declares a non-virtual one.  This
     warning is enabled by `-Wall'.

`-Wreorder (C++ only)'
     Warn when the order of member initializers given in the code does
     not match the order in which they must be executed.  For instance:

          struct A {
            int i;
            int j;
            A(): j (0), i (1) { }
          };

     The compiler will rearrange the member initializers for `i' and
     `j' to match the declaration order of the members, emitting a
     warning to that effect.  This warning is enabled by `-Wall'.

 The following `-W...' options are not affected by `-Wall'.

`-Weffc++ (C++ only)'
     Warn about violations of the following style guidelines from Scott
     Meyers' `Effective C++' book:

        * Item 11:  Define a copy constructor and an assignment
          operator for classes with dynamically allocated memory.

        * Item 12:  Prefer initialization to assignment in constructors.

        * Item 14:  Make destructors virtual in base classes.

        * Item 15:  Have `operator=' return a reference to `*this'.

        * Item 23:  Don't try to return a reference when you must
          return an object.


     Also warn about violations of the following style guidelines from
     Scott Meyers' `More Effective C++' book:

        * Item 6:  Distinguish between prefix and postfix forms of
          increment and decrement operators.

        * Item 7:  Never overload `&&', `||', or `,'.


     When selecting this option, be aware that the standard library
     headers do not obey all of these guidelines; use `grep -v' to
     filter out those warnings.

`-Wno-deprecated (C++ only)'
     Do not warn about usage of deprecated features.  *Note Deprecated
     Features::.

`-Wno-non-template-friend (C++ only)'
     Disable warnings when non-templatized friend functions are declared
     within a template.  Since the advent of explicit template
     specification support in G++, if the name of the friend is an
     unqualified-id (i.e., `friend foo(int)'), the C++ language
     specification demands that the friend declare or define an
     ordinary, nontemplate function.  (Section 14.5.3).  Before G++
     implemented explicit specification, unqualified-ids could be
     interpreted as a particular specialization of a templatized
     function.  Because this non-conforming behavior is no longer the
     default behavior for G++, `-Wnon-template-friend' allows the
     compiler to check existing code for potential trouble spots and is
     on by default.  This new compiler behavior can be turned off with
     `-Wno-non-template-friend' which keeps the conformant compiler code
     but disables the helpful warning.

`-Wold-style-cast (C++ only)'
     Warn if an old-style (C-style) cast to a non-void type is used
     within a C++ program.  The new-style casts (`static_cast',
     `reinterpret_cast', and `const_cast') are less vulnerable to
     unintended effects and much easier to search for.

`-Woverloaded-virtual (C++ only)'
     Warn when a function declaration hides virtual functions from a
     base class.  For example, in:

          struct A {
            virtual void f();
          };

          struct B: public A {
            void f(int);
          };

     the `A' class version of `f' is hidden in `B', and code like:

          B* b;
          b->f();

     will fail to compile.

`-Wno-pmf-conversions (C++ only)'
     Disable the diagnostic for converting a bound pointer to member
     function to a plain pointer.

`-Wsign-promo (C++ only)'
     Warn when overload resolution chooses a promotion from unsigned or
     enumeral type to a signed type, over a conversion to an unsigned
     type of the same size.  Previous versions of G++ would try to
     preserve unsignedness, but the standard mandates the current
     behavior.

`-Wsynth (C++ only)'
     Warn when G++'s synthesis behavior does not match that of cfront.
     For instance:

          struct A {
            operator int ();
            A& operator = (int);
          };

          main ()
          {
            A a,b;
            a = b;
          }

     In this example, G++ will synthesize a default `A& operator =
     (const A&);', while cfront will use the user-defined `operator ='.


File: gcc,  Node: Objective-C Dialect Options,  Next: Language Independent Options,  Prev: C++ Dialect Options,  Up: Invoking GCC

3.6 Options Controlling Objective-C Dialect
===========================================

(NOTE: This manual does not describe the Objective-C language itself.
See `http://gcc.gnu.org/readings.html' for references.)

 This section describes the command-line options that are only
meaningful for Objective-C programs, but you can also use most of the
GNU compiler options regardless of what language your program is in.
For example, you might compile a file `some_class.m' like this:

     gcc -g -fgnu-runtime -O -c some_class.m

In this example, `-fgnu-runtime' is an option meant only for
Objective-C programs; you can use the other options with any language
supported by GCC.

 Here is a list of options that are _only_ for compiling Objective-C
programs:

`-fconstant-string-class=CLASS-NAME'
     Use CLASS-NAME as the name of the class to instantiate for each
     literal string specified with the syntax `@"..."'.  The default
     class name is `NXConstantString' if the GNU runtime is being used,
     and `NSConstantString' if the NeXT runtime is being used (see
     below).  The `-fconstant-cfstrings' option, if also present, will
     override the `-fconstant-string-class' setting and cause `@"..."'
     literals to be laid out as constant CoreFoundation strings.

`-fgnu-runtime'
     Generate object code compatible with the standard GNU Objective-C
     runtime.  This is the default for most types of systems.

`-fnext-runtime'
     Generate output compatible with the NeXT runtime.  This is the
     default for NeXT-based systems, including Darwin and Mac OS X.
     The macro `__NEXT_RUNTIME__' is predefined if (and only if) this
     option is used.

`-fno-nil-receivers'
     Assume that all Objective-C message dispatches (e.g., `[receiver
     message:arg]') in this translation unit ensure that the receiver
     is not `nil'.  This allows for more efficient entry points in the
     runtime to be used.  Currently, this option is only available in
     conjunction with the NeXT runtime on Mac OS X 10.3 and later.

`-fobjc-exceptions'
     Enable syntactic support for structured exception handling in
     Objective-C, similar to what is offered by C++ and Java.
     Currently, this option is only available in conjunction with the
     NeXT runtime on Mac OS X 10.3 and later.

            @try {
              ...
                 @throw expr;
              ...
            }
            @catch (AnObjCClass *exc) {
              ...
                @throw expr;
              ...
                @throw;
              ...
            }
            @catch (AnotherClass *exc) {
              ...
            }
            @catch (id allOthers) {
              ...
            }
            @finally {
              ...
                @throw expr;
              ...
            }

     The `@throw' statement may appear anywhere in an Objective-C or
     Objective-C++ program; when used inside of a `@catch' block, the
     `@throw' may appear without an argument (as shown above), in which
     case the object caught by the `@catch' will be rethrown.

     Note that only (pointers to) Objective-C objects may be thrown and
     caught using this scheme.  When an object is thrown, it will be
     caught by the nearest `@catch' clause capable of handling objects
     of that type, analogously to how `catch' blocks work in C++ and
     Java.  A `@catch(id ...)' clause (as shown above) may also be
     provided to catch any and all Objective-C exceptions not caught by
     previous `@catch' clauses (if any).

     The `@finally' clause, if present, will be executed upon exit from
     the immediately preceding `@try ... @catch' section.  This will
     happen regardless of whether any exceptions are thrown, caught or
     rethrown inside the `@try ... @catch' section, analogously to the
     behavior of the `finally' clause in Java.

     There are several caveats to using the new exception mechanism:

        * Although currently designed to be binary compatible with
          `NS_HANDLER'-style idioms provided by the `NSException'
          class, the new exceptions can only be used on Mac OS X 10.3
          (Panther) and later systems, due to additional functionality
          needed in the (NeXT) Objective-C runtime.

        * As mentioned above, the new exceptions do not support handling
          types other than Objective-C objects.   Furthermore, when
          used from Objective-C++, the Objective-C exception model does
          not interoperate with C++ exceptions at this time.  This
          means you cannot `@throw' an exception from Objective-C and
          `catch' it in C++, or vice versa (i.e., `throw ... @catch').

     The `-fobjc-exceptions' switch also enables the use of
     synchronization blocks for thread-safe execution:

            @synchronized (ObjCClass *guard) {
              ...
            }

     Upon entering the `@synchronized' block, a thread of execution
     shall first check whether a lock has been placed on the
     corresponding `guard' object by another thread.  If it has, the
     current thread shall wait until the other thread relinquishes its
     lock.  Once `guard' becomes available, the current thread will
     place its own lock on it, execute the code contained in the
     `@synchronized' block, and finally relinquish the lock (thereby
     making `guard' available to other threads).

     Unlike Java, Objective-C does not allow for entire methods to be
     marked `@synchronized'.  Note that throwing exceptions out of
     `@synchronized' blocks is allowed, and will cause the guarding
     object to be unlocked properly.

`-freplace-objc-classes'
     Emit a special marker instructing `ld(1)' not to statically link in
     the resulting object file, and allow `dyld(1)' to load it in at
     run time instead.  This is used in conjunction with the
     Fix-and-Continue debugging mode, where the object file in question
     may be recompiled and dynamically reloaded in the course of
     program execution, without the need to restart the program itself.
     Currently, Fix-and-Continue functionality is only available in
     conjunction with the NeXT runtime on Mac OS X 10.3 and later.

`-fzero-link'
     When compiling for the NeXT runtime, the compiler ordinarily
     replaces calls to `objc_getClass("...")' (when the name of the
     class is known at compile time) with static class references that
     get initialized at load time, which improves run-time performance.
     Specifying the `-fzero-link' flag suppresses this behavior and
     causes calls to `objc_getClass("...")' to be retained.  This is
     useful in Zero-Link debugging mode, since it allows for individual
     class implementations to be modified during program execution.

`-gen-decls'
     Dump interface declarations for all classes seen in the source
     file to a file named `SOURCENAME.decl'.

`-Wno-protocol'
     If a class is declared to implement a protocol, a warning is
     issued for every method in the protocol that is not implemented by
     the class.  The default behavior is to issue a warning for every
     method not explicitly implemented in the class, even if a method
     implementation is inherited from the superclass.  If you use the
     `-Wno-protocol' option, then methods inherited from the superclass
     are considered to be implemented, and no warning is issued for
     them.

`-Wselector'
     Warn if multiple methods of different types for the same selector
     are found during compilation.  The check is performed on the list
     of methods in the final stage of compilation.  Additionally, a
     check is performed for each selector appearing in a
     `@selector(...)'  expression, and a corresponding method for that
     selector has been found during compilation.  Because these checks
     scan the method table only at the end of compilation, these
     warnings are not produced if the final stage of compilation is not
     reached, for example because an error is found during compilation,
     or because the `-fsyntax-only' option is being used.

`-Wundeclared-selector'
     Warn if a `@selector(...)' expression referring to an undeclared
     selector is found.  A selector is considered undeclared if no
     method with that name has been declared before the
     `@selector(...)' expression, either explicitly in an `@interface'
     or `@protocol' declaration, or implicitly in an `@implementation'
     section.  This option always performs its checks as soon as a
     `@selector(...)' expression is found, while `-Wselector' only
     performs its checks in the final stage of compilation.  This also
     enforces the coding style convention that methods and selectors
     must be declared before being used.

`-print-objc-runtime-info'
     Generate C header describing the largest structure that is passed
     by value, if any.



File: gcc,  Node: Language Independent Options,  Next: Warning Options,  Prev: Objective-C Dialect Options,  Up: Invoking GCC

3.7 Options to Control Diagnostic Messages Formatting
=====================================================

Traditionally, diagnostic messages have been formatted irrespective of
the output device's aspect (e.g. its width, ...).  The options described
below can be used to control the diagnostic messages formatting
algorithm, e.g. how many characters per line, how often source location
information should be reported.  Right now, only the C++ front end can
honor these options.  However it is expected, in the near future, that
the remaining front ends would be able to digest them correctly.

`-fmessage-length=N'
     Try to format error messages so that they fit on lines of about N
     characters.  The default is 72 characters for `g++' and 0 for the
     rest of the front ends supported by GCC.  If N is zero, then no
     line-wrapping will be done; each error message will appear on a
     single line.

`-fdiagnostics-show-location=once'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit _once_ source location information; that
     is, in case the message is too long to fit on a single physical
     line and has to be wrapped, the source location won't be emitted
     (as prefix) again, over and over, in subsequent continuation
     lines.  This is the default behavior.

`-fdiagnostics-show-location=every-line'
     Only meaningful in line-wrapping mode.  Instructs the diagnostic
     messages reporter to emit the same source location information (as
     prefix) for physical lines that result from the process of breaking
     a message which is too long to fit on a single line.



File: gcc,  Node: Warning Options,  Next: Debugging Options,  Prev: Language Independent Options,  Up: Invoking GCC

3.8 Options to Request or Suppress Warnings
===========================================

Warnings are diagnostic messages that report constructions which are
not inherently erroneous but which are risky or suggest there may have
been an error.

 You can request many specific warnings with options beginning `-W',
for example `-Wimplicit' to request warnings on implicit declarations.
Each of these specific warning options also has a negative form
beginning `-Wno-' to turn off warnings; for example, `-Wno-implicit'.
This manual lists only one of the two forms, whichever is not the
default.

 The following options control the amount and kinds of warnings produced
by GCC; for further, language-specific options also refer to *Note C++
Dialect Options:: and *Note Objective-C Dialect Options::.

`-fsyntax-only'
     Check the code for syntax errors, but don't do anything beyond
     that.

`-pedantic'
     Issue all the warnings demanded by strict ISO C and ISO C++;
     reject all programs that use forbidden extensions, and some other
     programs that do not follow ISO C and ISO C++.  For ISO C, follows
     the version of the ISO C standard specified by any `-std' option
     used.

     Valid ISO C and ISO C++ programs should compile properly with or
     without this option (though a rare few will require `-ansi' or a
     `-std' option specifying the required version of ISO C).  However,
     without this option, certain GNU extensions and traditional C and
     C++ features are supported as well.  With this option, they are
     rejected.

     `-pedantic' does not cause warning messages for use of the
     alternate keywords whose names begin and end with `__'.  Pedantic
     warnings are also disabled in the expression that follows
     `__extension__'.  However, only system header files should use
     these escape routes; application programs should avoid them.
     *Note Alternate Keywords::.

     Some users try to use `-pedantic' to check programs for strict ISO
     C conformance.  They soon find that it does not do quite what they
     want: it finds some non-ISO practices, but not all--only those for
     which ISO C _requires_ a diagnostic, and some others for which
     diagnostics have been added.

     A feature to report any failure to conform to ISO C might be
     useful in some instances, but would require considerable
     additional work and would be quite different from `-pedantic'.  We
     don't have plans to support such a feature in the near future.

     Where the standard specified with `-std' represents a GNU extended
     dialect of C, such as `gnu89' or `gnu99', there is a corresponding
     "base standard", the version of ISO C on which the GNU extended
     dialect is based.  Warnings from `-pedantic' are given where they
     are required by the base standard.  (It would not make sense for
     such warnings to be given only for features not in the specified
     GNU C dialect, since by definition the GNU dialects of C include
     all features the compiler supports with the given option, and
     there would be nothing to warn about.)

`-pedantic-errors'
     Like `-pedantic', except that errors are produced rather than
     warnings.

`-w'
     Inhibit all warning messages.

`-Wno-import'
     Inhibit warning messages about the use of `#import'.

`-Wchar-subscripts'
     Warn if an array subscript has type `char'.  This is a common cause
     of error, as programmers often forget that this type is signed on
     some machines.

`-Wcomment'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a Backslash-Newline appears in a `//' comment.

`-Wformat'
     Check calls to `printf' and `scanf', etc., to make sure that the
     arguments supplied have types appropriate to the format string
     specified, and that the conversions specified in the format string
     make sense.  This includes standard functions, and others
     specified by format attributes (*note Function Attributes::), in
     the `printf', `scanf', `strftime' and `strfmon' (an X/Open
     extension, not in the C standard) families.

     The formats are checked against the format features supported by
     GNU libc version 2.2.  These include all ISO C90 and C99 features,
     as well as features from the Single Unix Specification and some
     BSD and GNU extensions.  Other library implementations may not
     support all these features; GCC does not support warning about
     features that go beyond a particular library's limitations.
     However, if `-pedantic' is used with `-Wformat', warnings will be
     given about format features not in the selected standard version
     (but not for `strfmon' formats, since those are not in any version
     of the C standard).  *Note Options Controlling C Dialect: C
     Dialect Options.

     Since `-Wformat' also checks for null format arguments for several
     functions, `-Wformat' also implies `-Wnonnull'.

     `-Wformat' is included in `-Wall'.  For more control over some
     aspects of format checking, the options `-Wformat-y2k',
     `-Wno-format-extra-args', `-Wno-format-zero-length',
     `-Wformat-nonliteral', `-Wformat-security', and `-Wformat=2' are
     available, but are not included in `-Wall'.

`-Wformat-y2k'
     If `-Wformat' is specified, also warn about `strftime' formats
     which may yield only a two-digit year.

`-Wno-format-extra-args'
     If `-Wformat' is specified, do not warn about excess arguments to a
     `printf' or `scanf' format function.  The C standard specifies
     that such arguments are ignored.

     Where the unused arguments lie between used arguments that are
     specified with `$' operand number specifications, normally
     warnings are still given, since the implementation could not know
     what type to pass to `va_arg' to skip the unused arguments.
     However, in the case of `scanf' formats, this option will suppress
     the warning if the unused arguments are all pointers, since the
     Single Unix Specification says that such unused arguments are
     allowed.

`-Wno-format-zero-length'
     If `-Wformat' is specified, do not warn about zero-length formats.
     The C standard specifies that zero-length formats are allowed.

`-Wformat-nonliteral'
     If `-Wformat' is specified, also warn if the format string is not a
     string literal and so cannot be checked, unless the format function
     takes its format arguments as a `va_list'.

`-Wformat-security'
     If `-Wformat' is specified, also warn about uses of format
     functions that represent possible security problems.  At present,
     this warns about calls to `printf' and `scanf' functions where the
     format string is not a string literal and there are no format
     arguments, as in `printf (foo);'.  This may be a security hole if
     the format string came from untrusted input and contains `%n'.
     (This is currently a subset of what `-Wformat-nonliteral' warns
     about, but in future warnings may be added to `-Wformat-security'
     that are not included in `-Wformat-nonliteral'.)

`-Wformat=2'
     Enable `-Wformat' plus format checks not included in `-Wformat'.
     Currently equivalent to `-Wformat -Wformat-nonliteral
     -Wformat-security -Wformat-y2k'.

`-Wnonnull'
     Warn about passing a null pointer for arguments marked as
     requiring a non-null value by the `nonnull' function attribute.

     `-Wnonnull' is included in `-Wall' and `-Wformat'.  It can be
     disabled with the `-Wno-nonnull' option.

`-Winit-self (C, C++, and Objective-C only)'
     Warn about uninitialized variables which are initialized with
     themselves.  Note this option can only be used with the
     `-Wuninitialized' option, which in turn only works with `-O1' and
     above.

     For example, GCC will warn about `i' being uninitialized in the
     following snippet only when `-Winit-self' has been specified:
          int f()
          {
            int i = i;
            return i;
          }

`-Wimplicit-int'
     Warn when a declaration does not specify a type.

`-Wimplicit-function-declaration'
`-Werror-implicit-function-declaration'
     Give a warning (or error) whenever a function is used before being
     declared.

`-Wimplicit'
     Same as `-Wimplicit-int' and `-Wimplicit-function-declaration'.

`-Wmain'
     Warn if the type of `main' is suspicious.  `main' should be a
     function with external linkage, returning int, taking either zero
     arguments, two, or three arguments of appropriate types.

`-Wmissing-braces'
     Warn if an aggregate or union initializer is not fully bracketed.
     In the following example, the initializer for `a' is not fully
     bracketed, but that for `b' is fully bracketed.

          int a[2][2] = { 0, 1, 2, 3 };
          int b[2][2] = { { 0, 1 }, { 2, 3 } };

`-Wparentheses'
     Warn if parentheses are omitted in certain contexts, such as when
     there is an assignment in a context where a truth value is
     expected, or when operators are nested whose precedence people
     often get confused about.

     Also warn about constructions where there may be confusion to which
     `if' statement an `else' branch belongs.  Here is an example of
     such a case:

          {
            if (a)
              if (b)
                foo ();
            else
              bar ();
          }

     In C, every `else' branch belongs to the innermost possible `if'
     statement, which in this example is `if (b)'.  This is often not
     what the programmer expected, as illustrated in the above example
     by indentation the programmer chose.  When there is the potential
     for this confusion, GCC will issue a warning when this flag is
     specified.  To eliminate the warning, add explicit braces around
     the innermost `if' statement so there is no way the `else' could
     belong to the enclosing `if'.  The resulting code would look like
     this:

          {
            if (a)
              {
                if (b)
                  foo ();
                else
                  bar ();
              }
          }

`-Wsequence-point'
     Warn about code that may have undefined semantics because of
     violations of sequence point rules in the C standard.

     The C standard defines the order in which expressions in a C
     program are evaluated in terms of "sequence points", which
     represent a partial ordering between the execution of parts of the
     program: those executed before the sequence point, and those
     executed after it.  These occur after the evaluation of a full
     expression (one which is not part of a larger expression), after
     the evaluation of the first operand of a `&&', `||', `? :' or `,'
     (comma) operator, before a function is called (but after the
     evaluation of its arguments and the expression denoting the called
     function), and in certain other places.  Other than as expressed
     by the sequence point rules, the order of evaluation of
     subexpressions of an expression is not specified.  All these rules
     describe only a partial order rather than a total order, since,
     for example, if two functions are called within one expression
     with no sequence point between them, the order in which the
     functions are called is not specified.  However, the standards
     committee have ruled that function calls do not overlap.

     It is not specified when between sequence points modifications to
     the values of objects take effect.  Programs whose behavior
     depends on this have undefined behavior; the C standard specifies
     that "Between the previous and next sequence point an object shall
     have its stored value modified at most once by the evaluation of
     an expression.  Furthermore, the prior value shall be read only to
     determine the value to be stored.".  If a program breaks these
     rules, the results on any particular implementation are entirely
     unpredictable.

     Examples of code with undefined behavior are `a = a++;', `a[n] =
     b[n++]' and `a[i++] = i;'.  Some more complicated cases are not
     diagnosed by this option, and it may give an occasional false
     positive result, but in general it has been found fairly effective
     at detecting this sort of problem in programs.

     The present implementation of this option only works for C
     programs.  A future implementation may also work for C++ programs.

     The C standard is worded confusingly, therefore there is some
     debate over the precise meaning of the sequence point rules in
     subtle cases.  Links to discussions of the problem, including
     proposed formal definitions, may be found on our readings page, at
     `http://gcc.gnu.org/readings.html'.

`-Wreturn-type'
     Warn whenever a function is defined with a return-type that
     defaults to `int'.  Also warn about any `return' statement with no
     return-value in a function whose return-type is not `void'.

     For C++, a function without return type always produces a
     diagnostic message, even when `-Wno-return-type' is specified.
     The only exceptions are `main' and functions defined in system
     headers.

`-Wswitch'
     Warn whenever a `switch' statement has an index of enumeral type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  (The presence of a `default' label prevents this
     warning.)  `case' labels outside the enumeration range also
     provoke warnings when this option is used.

`-Wswitch-default'
     Warn whenever a `switch' statement does not have a `default' case.

`-Wswitch-enum'
     Warn whenever a `switch' statement has an index of enumeral type
     and lacks a `case' for one or more of the named codes of that
     enumeration.  `case' labels outside the enumeration range also
     provoke warnings when this option is used.

`-Wtrigraphs'
     Warn if any trigraphs are encountered that might change the
     meaning of the program (trigraphs within comments are not warned
     about).

`-Wunused-function'
     Warn whenever a static function is declared but not defined or a
     non\-inline static function is unused.

`-Wunused-label'
     Warn whenever a label is declared but not used.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-parameter'
     Warn whenever a function parameter is unused aside from its
     declaration.

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-variable'
     Warn whenever a local variable or non-constant static variable is
     unused aside from its declaration

     To suppress this warning use the `unused' attribute (*note
     Variable Attributes::).

`-Wunused-value'
     Warn whenever a statement computes a result that is explicitly not
     used.

     To suppress this warning cast the expression to `void'.

`-Wunused'
     All the above `-Wunused' options combined.

     In order to get a warning about an unused function parameter, you
     must either specify `-Wextra -Wunused' (note that `-Wall' implies
     `-Wunused'), or separately specify `-Wunused-parameter'.

`-Wuninitialized'
     Warn if an automatic variable is used without first being
     initialized or if a variable may be clobbered by a `setjmp' call.

     These warnings are possible only in optimizing compilation,
     because they require data flow information that is computed only
     when optimizing.  If you don't specify `-O', you simply won't get
     these warnings.

     If you want to warn about code which uses the uninitialized value
     of the variable in its own initializer, use the `-Winit-self'
     option.

     These warnings occur only for variables that are candidates for
     register allocation.  Therefore, they do not occur for a variable
     that is declared `volatile', or whose address is taken, or whose
     size is other than 1, 2, 4 or 8 bytes.  Also, they do not occur for
     structures, unions or arrays, even when they are in registers.

     Note that there may be no warning about a variable that is used
     only to compute a value that itself is never used, because such
     computations may be deleted by data flow analysis before the
     warnings are printed.

     These warnings are made optional because GCC is not smart enough
     to see all the reasons why the code might be correct despite
     appearing to have an error.  Here is one example of how this can
     happen:

          {
            int x;
            switch (y)
              {
              case 1: x = 1;
                break;
              case 2: x = 4;
                break;
              case 3: x = 5;
              }
            foo (x);
          }

     If the value of `y' is always 1, 2 or 3, then `x' is always
     initialized, but GCC doesn't know this.  Here is another common
     case:

          {
            int save_y;
            if (change_y) save_y = y, y = new_y;
            ...
            if (change_y) y = save_y;
          }

     This has no bug because `save_y' is used only if it is set.

     This option also warns when a non-volatile automatic variable
     might be changed by a call to `longjmp'.  These warnings as well
     are possible only in optimizing compilation.

     The compiler sees only the calls to `setjmp'.  It cannot know
     where `longjmp' will be called; in fact, a signal handler could
     call it at any point in the code.  As a result, you may get a
     warning even when there is in fact no problem because `longjmp'
     cannot in fact be called at the place which would cause a problem.

     Some spurious warnings can be avoided if you declare all the
     functions you use that never return as `noreturn'.  *Note Function
     Attributes::.

`-Wunknown-pragmas'
     Warn when a #pragma directive is encountered which is not
     understood by GCC.  If this command line option is used, warnings
     will even be issued for unknown pragmas in system header files.
     This is not the case if the warnings were only enabled by the
     `-Wall' command line option.

`-Wstrict-aliasing'
     This option is only active when `-fstrict-aliasing' is active.  It
     warns about code which might break the strict aliasing rules that
     the compiler is using for optimization. The warning does not catch
     all cases, but does attempt to catch the more common pitfalls. It
     is included in `-Wall'.

`-Wall'
     All of the above `-W' options combined.  This enables all the
     warnings about constructions that some users consider
     questionable, and that are easy to avoid (or modify to prevent the
     warning), even in conjunction with macros.  This also enables some
     language-specific warnings described in *Note C++ Dialect
     Options:: and *Note Objective-C Dialect Options::.

 The following `-W...' options are not implied by `-Wall'.  Some of
them warn about constructions that users generally do not consider
questionable, but which occasionally you might wish to check for;
others warn about constructions that are necessary or hard to avoid in
some cases, and there is no simple way to modify the code to suppress
the warning.

`-Wextra'
     (This option used to be called `-W'.  The older name is still
     supported, but the newer name is more descriptive.)  Print extra
     warning messages for these events:

        * A function can return either with or without a value.
          (Falling off the end of the function body is considered
          returning without a value.)  For example, this function would
          evoke such a warning:

               foo (a)
               {
                 if (a > 0)
                   return a;
               }

        * An expression-statement or the left-hand side of a comma
          expression contains no side effects.  To suppress the
          warning, cast the unused expression to void.  For example, an
          expression such as `x[i,j]' will cause a warning, but
          `x[(void)i,j]' will not.

        * An unsigned value is compared against zero with `<' or `>='.

        * A comparison like `x<=y<=z' appears; this is equivalent to
          `(x<=y ? 1 : 0) <= z', which is a different interpretation
          from that of ordinary mathematical notation.

        * Storage-class specifiers like `static' are not the first
          things in a declaration.  According to the C Standard, this
          usage is obsolescent.

        * The return type of a function has a type qualifier such as
          `const'.  Such a type qualifier has no effect, since the
          value returned by a function is not an lvalue.  (But don't
          warn about the GNU extension of `volatile void' return types.
          That extension will be warned about if `-pedantic' is
          specified.)

        * If `-Wall' or `-Wunused' is also specified, warn about unused
          arguments.

        * A comparison between signed and unsigned values could produce
          an incorrect result when the signed value is converted to
          unsigned.  (But don't warn if `-Wno-sign-compare' is also
          specified.)

        * An aggregate has an initializer which does not initialize all
          members.  For example, the following code would cause such a
          warning, because `x.h' would be implicitly initialized to
          zero:

               struct s { int f, g, h; };
               struct s x = { 3, 4 };

        * A function parameter is declared without a type specifier in
          K&R-style functions:

               void foo(bar) { }

        * An empty body occurs in an `if' or `else' statement.

        * A pointer is compared against integer zero with `<', `<=',
          `>', or `>='.

        * A variable might be changed by `longjmp' or `vfork'.

        * Any of several floating-point events that often indicate
          errors, such as overflow, underflow, loss of precision, etc.

        * (C++ only) An enumerator and a non-enumerator both appear in
          a conditional expression.

        * (C++ only) A non-static reference or non-static `const'
          member appears in a class without constructors.

        * (C++ only) Ambiguous virtual bases.

        * (C++ only) Subscripting an array which has been declared
          `register'.

        * (C++ only) Taking the address of a variable which has been
          declared `register'.

        * (C++ only) A base class is not initialized in a derived
          class' copy constructor.

`-Wno-div-by-zero'
     Do not warn about compile-time integer division by zero.  Floating
     point division by zero is not warned about, as it can be a
     legitimate way of obtaining infinities and NaNs.

`-Wsystem-headers'
     Print warning messages for constructs found in system header files.
     Warnings from system headers are normally suppressed, on the
     assumption that they usually do not indicate real problems and
     would only make the compiler output harder to read.  Using this
     command line option tells GCC to emit warnings from system headers
     as if they occurred in user code.  However, note that using
     `-Wall' in conjunction with this option will _not_ warn about
     unknown pragmas in system headers--for that, `-Wunknown-pragmas'
     must also be used.

`-Wfloat-equal'
     Warn if floating point values are used in equality comparisons.

     The idea behind this is that sometimes it is convenient (for the
     programmer) to consider floating-point values as approximations to
     infinitely precise real numbers.  If you are doing this, then you
     need to compute (by analyzing the code, or in some other way) the
     maximum or likely maximum error that the computation introduces,
     and allow for it when performing comparisons (and when producing
     output, but that's a different problem).  In particular, instead
     of testing for equality, you would check to see whether the two
     values have ranges that overlap; and this is done with the
     relational operators, so equality comparisons are probably
     mistaken.

`-Wtraditional (C only)'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and/or problematic constructs which
     should be avoided.

        * Macro parameters that appear within string literals in the
          macro body.  In traditional C macro replacement takes place
          within string literals, but does not in ISO C.

        * In traditional C, some preprocessor directives did not exist.
          Traditional preprocessors would only consider a line to be a
          directive if the `#' appeared in column 1 on the line.
          Therefore `-Wtraditional' warns about directives that
          traditional C understands but would ignore because the `#'
          does not appear as the first character on the line.  It also
          suggests you hide directives like `#pragma' not understood by
          traditional C by indenting them.  Some traditional
          implementations would not recognize `#elif', so it suggests
          avoiding it altogether.

        * A function-like macro that appears without arguments.

        * The unary plus operator.

        * The `U' integer constant suffix, or the `F' or `L' floating
          point constant suffixes.  (Traditional C does support the `L'
          suffix on integer constants.)  Note, these suffixes appear in
          macros defined in the system headers of most modern systems,
          e.g. the `_MIN'/`_MAX' macros in `<limits.h>'.  Use of these
          macros in user code might normally lead to spurious warnings,
          however GCC's integrated preprocessor has enough context to
          avoid warning in these cases.

        * A function declared external in one block and then used after
          the end of the block.

        * A `switch' statement has an operand of type `long'.

        * A non-`static' function declaration follows a `static' one.
          This construct is not accepted by some traditional C
          compilers.

        * The ISO type of an integer constant has a different width or
          signedness from its traditional type.  This warning is only
          issued if the base of the constant is ten.  I.e. hexadecimal
          or octal values, which typically represent bit patterns, are
          not warned about.

        * Usage of ISO string concatenation is detected.

        * Initialization of automatic aggregates.

        * Identifier conflicts with labels.  Traditional C lacks a
          separate namespace for labels.

        * Initialization of unions.  If the initializer is zero, the
          warning is omitted.  This is done under the assumption that
          the zero initializer in user code appears conditioned on e.g.
          `__STDC__' to avoid missing initializer warnings and relies
          on default initialization to zero in the traditional C case.

        * Conversions by prototypes between fixed/floating point values
          and vice versa.  The absence of these prototypes when
          compiling with traditional C would cause serious problems.
          This is a subset of the possible conversion warnings, for the
          full set use `-Wconversion'.

        * Use of ISO C style function definitions.  This warning
          intentionally is _not_ issued for prototype declarations or
          variadic functions because these ISO C features will appear
          in your code when using libiberty's traditional C
          compatibility macros, `PARAMS' and `VPARAMS'.  This warning
          is also bypassed for nested functions because that feature is
          already a GCC extension and thus not relevant to traditional
          C compatibility.

`-Wdeclaration-after-statement (C only)'
     Warn when a declaration is found after a statement in a block.
     This construct, known from C++, was introduced with ISO C99 and is
     by default allowed in GCC.  It is not supported by ISO C90 and was
     not supported by GCC versions before GCC 3.0.  *Note Mixed
     Declarations::.

`-Wundef'
     Warn if an undefined identifier is evaluated in an `#if' directive.

`-Wendif-labels'
     Warn whenever an `#else' or an `#endif' are followed by text.

`-Wshadow'
     Warn whenever a local variable shadows another local variable,
     parameter or global variable or whenever a built-in function is
     shadowed.

`-Wlarger-than-LEN'
     Warn whenever an object of larger than LEN bytes is defined.

`-Wpointer-arith'
     Warn about anything that depends on the "size of" a function type
     or of `void'.  GNU C assigns these types a size of 1, for
     convenience in calculations with `void *' pointers and pointers to
     functions.

`-Wbad-function-cast (C only)'
     Warn whenever a function call is cast to a non-matching type.  For
     example, warn if `int malloc()' is cast to `anything *'.

`-Wcast-qual'
     Warn whenever a pointer is cast so as to remove a type qualifier
     from the target type.  For example, warn if a `const char *' is
     cast to an ordinary `char *'.

`-Wcast-align'
     Warn whenever a pointer is cast such that the required alignment
     of the target is increased.  For example, warn if a `char *' is
     cast to an `int *' on machines where integers can only be accessed
     at two- or four-byte boundaries.

`-Wwrite-strings'
     When compiling C, give string constants the type `const
     char[LENGTH]' so that copying the address of one into a
     non-`const' `char *' pointer will get a warning; when compiling
     C++, warn about the deprecated conversion from string constants to
     `char *'.  These warnings will help you find at compile time code
     that can try to write into a string constant, but only if you have
     been very careful about using `const' in declarations and
     prototypes.  Otherwise, it will just be a nuisance; this is why we
     did not make `-Wall' request these warnings.

`-Wconversion'
     Warn if a prototype causes a type conversion that is different
     from what would happen to the same argument in the absence of a
     prototype.  This includes conversions of fixed point to floating
     and vice versa, and conversions changing the width or signedness
     of a fixed point argument except when the same as the default
     promotion.

     Also, warn if a negative integer constant expression is implicitly
     converted to an unsigned type.  For example, warn about the
     assignment `x = -1' if `x' is unsigned.  But do not warn about
     explicit casts like `(unsigned) -1'.

`-Wsign-compare'
     Warn when a comparison between signed and unsigned values could
     produce an incorrect result when the signed value is converted to
     unsigned.  This warning is also enabled by `-Wextra'; to get the
     other warnings of `-Wextra' without this warning, use `-Wextra
     -Wno-sign-compare'.

`-Waggregate-return'
     Warn if any functions that return structures or unions are defined
     or called.  (In languages where you can return an array, this also
     elicits a warning.)

`-Wstrict-prototypes (C only)'
     Warn if a function is declared or defined without specifying the
     argument types.  (An old-style function definition is permitted
     without a warning if preceded by a declaration which specifies the
     argument types.)

`-Wold-style-definition (C only)'
     Warn if an old-style function definition is used.  A warning is
     given even if there is a previous prototype.

`-Wmissing-prototypes (C only)'
     Warn if a global function is defined without a previous prototype
     declaration.  This warning is issued even if the definition itself
     provides a prototype.  The aim is to detect global functions that
     fail to be declared in header files.

`-Wmissing-declarations (C only)'
     Warn if a global function is defined without a previous
     declaration.  Do so even if the definition itself provides a
     prototype.  Use this option to detect global functions that are
     not declared in header files.

`-Wmissing-noreturn'
     Warn about functions which might be candidates for attribute
     `noreturn'.  Note these are only possible candidates, not absolute
     ones.  Care should be taken to manually verify functions actually
     do not ever return before adding the `noreturn' attribute,
     otherwise subtle code generation bugs could be introduced.  You
     will not get a warning for `main' in hosted C environments.

`-Wmissing-format-attribute'
     If `-Wformat' is enabled, also warn about functions which might be
     candidates for `format' attributes.  Note these are only possible
     candidates, not absolute ones.  GCC will guess that `format'
     attributes might be appropriate for any function that calls a
     function like `vprintf' or `vscanf', but this might not always be
     the case, and some functions for which `format' attributes are
     appropriate may not be detected.  This option has no effect unless
     `-Wformat' is enabled (possibly by `-Wall').

`-Wno-multichar'
     Do not warn if a multicharacter constant (`'FOOF'') is used.
     Usually they indicate a typo in the user's code, as they have
     implementation-defined values, and should not be used in portable
     code.

`-Wno-deprecated-declarations'
     Do not warn about uses of functions, variables, and types marked as
     deprecated by using the `deprecated' attribute.  (*note Function
     Attributes::, *note Variable Attributes::, *note Type
     Attributes::.)

`-Wpacked'
     Warn if a structure is given the packed attribute, but the packed
     attribute has no effect on the layout or size of the structure.
     Such structures may be mis-aligned for little benefit.  For
     instance, in this code, the variable `f.x' in `struct bar' will be
     misaligned even though `struct bar' does not itself have the
     packed attribute:

          struct foo {
            int x;
            char a, b, c, d;
          } __attribute__((packed));
          struct bar {
            char z;
            struct foo f;
          };

`-Wpadded'
     Warn if padding is included in a structure, either to align an
     element of the structure or to align the whole structure.
     Sometimes when this happens it is possible to rearrange the fields
     of the structure to reduce the padding and so make the structure
     smaller.

`-Wredundant-decls'
     Warn if anything is declared more than once in the same scope,
     even in cases where multiple declaration is valid and changes
     nothing.

`-Wnested-externs (C only)'
     Warn if an `extern' declaration is encountered within a function.

`-Wunreachable-code'
     Warn if the compiler detects that code will never be executed.

     This option is intended to warn when the compiler detects that at
     least a whole line of source code will never be executed, because
     some condition is never satisfied or because it is after a
     procedure that never returns.

     It is possible for this option to produce a warning even though
     there are circumstances under which part of the affected line can
     be executed, so care should be taken when removing
     apparently-unreachable code.

     For instance, when a function is inlined, a warning may mean that
     the line is unreachable in only one inlined copy of the function.

     This option is not made part of `-Wall' because in a debugging
     version of a program there is often substantial code which checks
     correct functioning of the program and is, hopefully, unreachable
     because the program does work.  Another common use of unreachable
     code is to provide behavior which is selectable at compile-time.

`-Winline'
     Warn if a function can not be inlined and it was declared as
     inline.  Even with this option, the compiler will not warn about
     failures to inline functions declared in system headers.

     The compiler uses a variety of heuristics to determine whether or
     not to inline a function.  For example, the compiler takes into
     account the size of the function being inlined and the the amount
     of inlining that has already been done in the current function.
     Therefore, seemingly insignificant changes in the source program
     can cause the warnings produced by `-Winline' to appear or
     disappear.

`-Wno-invalid-offsetof (C++ only)'
     Suppress warnings from applying the `offsetof' macro to a non-POD
     type.  According to the 1998 ISO C++ standard, applying `offsetof'
     to a non-POD type is undefined.  In existing C++ implementations,
     however, `offsetof' typically gives meaningful results even when
     applied to certain kinds of non-POD types. (Such as a simple
     `struct' that fails to be a POD type only by virtue of having a
     constructor.)  This flag is for users who are aware that they are
     writing nonportable code and who have deliberately chosen to
     ignore the warning about it.

     The restrictions on `offsetof' may be relaxed in a future version
     of the C++ standard.

`-Winvalid-pch'
     Warn if a precompiled header (*note Precompiled Headers::) is
     found in the search path but can't be used.

`-Wlong-long'
     Warn if `long long' type is used.  This is default.  To inhibit
     the warning messages, use `-Wno-long-long'.  Flags `-Wlong-long'
     and `-Wno-long-long' are taken into account only when `-pedantic'
     flag is used.

`-Wdisabled-optimization'
     Warn if a requested optimization pass is disabled.  This warning
     does not generally indicate that there is anything wrong with your
     code; it merely indicates that GCC's optimizers were unable to
     handle the code effectively.  Often, the problem is that your code
     is too big or too complex; GCC will refuse to optimize programs
     when the optimization itself is likely to take inordinate amounts
     of time.

`-Werror'
     Make all warnings into errors.


File: gcc,  Node: Debugging Options,  Next: Optimize Options,  Prev: Warning Options,  Up: Invoking GCC

3.9 Options for Debugging Your Program or GCC
=============================================

GCC has various special options that are used for debugging either your
program or GCC:

`-g'
     Produce debugging information in the operating system's native
     format (stabs, COFF, XCOFF, or DWARF).  GDB can work with this
     debugging information.

     On most systems that use stabs format, `-g' enables use of extra
     debugging information that only GDB can use; this extra information
     makes debugging work better in GDB but will probably make other
     debuggers crash or refuse to read the program.  If you want to
     control for certain whether to generate the extra information, use
     `-gstabs+', `-gstabs', `-gxcoff+', `-gxcoff', or `-gvms' (see
     below).

     Unlike most other C compilers, GCC allows you to use `-g' with
     `-O'.  The shortcuts taken by optimized code may occasionally
     produce surprising results: some variables you declared may not
     exist at all; flow of control may briefly move where you did not
     expect it; some statements may not be executed because they
     compute constant results or their values were already at hand;
     some statements may execute in different places because they were
     moved out of loops.

     Nevertheless it proves possible to debug optimized output.  This
     makes it reasonable to use the optimizer for programs that might
     have bugs.

     The following options are useful when GCC is generated with the
     capability for more than one debugging format.

`-ggdb'
     Produce debugging information for use by GDB.  This means to use
     the most expressive format available (DWARF 2, stabs, or the
     native format if neither of those are supported), including GDB
     extensions if at all possible.

`-gstabs'
     Produce debugging information in stabs format (if that is
     supported), without GDB extensions.  This is the format used by
     DBX on most BSD systems.  On MIPS, Alpha and System V Release 4
     systems this option produces stabs debugging output which is not
     understood by DBX or SDB.  On System V Release 4 systems this
     option requires the GNU assembler.

`-feliminate-unused-debug-symbols'
     Produce debugging information in stabs format (if that is
     supported), for only symbols that are actually used.

`-gstabs+'
     Produce debugging information in stabs format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program.

`-gcoff'
     Produce debugging information in COFF format (if that is
     supported).  This is the format used by SDB on most System V
     systems prior to System V Release 4.

`-gxcoff'
     Produce debugging information in XCOFF format (if that is
     supported).  This is the format used by the DBX debugger on IBM
     RS/6000 systems.

`-gxcoff+'
     Produce debugging information in XCOFF format (if that is
     supported), using GNU extensions understood only by the GNU
     debugger (GDB).  The use of these extensions is likely to make
     other debuggers crash or refuse to read the program, and may cause
     assemblers other than the GNU assembler (GAS) to fail with an
     error.

`-gdwarf-2'
     Produce debugging information in DWARF version 2 format (if that is
     supported).  This is the format used by DBX on IRIX 6.

`-gvms'
     Produce debugging information in VMS debug format (if that is
     supported).  This is the format used by DEBUG on VMS systems.

`-gLEVEL'
`-ggdbLEVEL'
`-gstabsLEVEL'
`-gcoffLEVEL'
`-gxcoffLEVEL'
`-gvmsLEVEL'
     Request debugging information and also use LEVEL to specify how
     much information.  The default level is 2.

     Level 1 produces minimal information, enough for making backtraces
     in parts of the program that you don't plan to debug.  This
     includes descriptions of functions and external variables, but no
     information about local variables and no line numbers.

     Level 3 includes extra information, such as all the macro
     definitions present in the program.  Some debuggers support macro
     expansion when you use `-g3'.

     Note that in order to avoid confusion between DWARF1 debug level 2,
     and DWARF2 `-gdwarf-2' does not accept a concatenated debug level.
     Instead use an additional `-gLEVEL' option to change the debug
     level for DWARF2.

`-feliminate-dwarf2-dups'
     Compress DWARF2 debugging information by eliminating duplicated
     information about each symbol.  This option only makes sense when
     generating DWARF2 debugging information with `-gdwarf-2'.

`-p'
     Generate extra code to write profile information suitable for the
     analysis program `prof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-pg'
     Generate extra code to write profile information suitable for the
     analysis program `gprof'.  You must use this option when compiling
     the source files you want data about, and you must also use it when
     linking.

`-Q'
     Makes the compiler print out each function name as it is compiled,
     and print some statistics about each pass when it finishes.

`-ftime-report'
     Makes the compiler print some statistics about the time consumed
     by each pass when it finishes.

`-fmem-report'
     Makes the compiler print some statistics about permanent memory
     allocation when it finishes.

`-fprofile-arcs'
     Add code so that program flow "arcs" are instrumented.  During
     execution the program records how many times each branch and call
     is executed and how many times it is taken or returns.  When the
     compiled program exits it saves this data to a file called
     `AUXNAME.gcda' for each source file. The data may be used for
     profile-directed optimizations (`-fbranch-probabilities'), or for
     test coverage analysis (`-ftest-coverage'). Each object file's
     AUXNAME is generated from the name of the output file, if
     explicitly specified and it is not the final executable, otherwise
     it is the basename of the source file. In both cases any suffix is
     removed (e.g.  `foo.gcda' for input file `dir/foo.c', or
     `dir/foo.gcda' for output file specified as `-o dir/foo.o').

        * Compile the source files with `-fprofile-arcs' plus
          optimization and code generation options. For test coverage
          analysis, use the additional `-ftest-coverage' option. You do
          not need to profile every source file in a program.

        * Link your object files with `-lgcov' or `-fprofile-arcs' (the
          latter implies the former).

        * Run the program on a representative workload to generate the
          arc profile information. This may be repeated any number of
          times. You can run concurrent instances of your program, and
          provided that the file system supports locking, the data
          files will be correctly updated. Also `fork' calls are
          detected and correctly handled (double counting will not
          happen).

        * For profile-directed optimizations, compile the source files
          again with the same optimization and code generation options
          plus `-fbranch-probabilities' (*note Options that Control
          Optimization: Optimize Options.).

        * For test coverage analysis, use `gcov' to produce human
          readable information from the `.gcno' and `.gcda' files.
          Refer to the `gcov' documentation for further information.


     With `-fprofile-arcs', for each function of your program GCC
     creates a program flow graph, then finds a spanning tree for the
     graph.  Only arcs that are not on the spanning tree have to be
     instrumented: the compiler adds code to count the number of times
     that these arcs are executed.  When an arc is the only exit or
     only entrance to a block, the instrumentation code can be added to
     the block; otherwise, a new basic block must be created to hold
     the instrumentation code.

`-ftest-coverage'
     Produce a notes file that the `gcov' code-coverage utility (*note
     `gcov'--a Test Coverage Program: Gcov.) can use to show program
     coverage. Each source file's note file is called `AUXNAME.gcno'.
     Refer to the `-fprofile-arcs' option above for a description of
     AUXNAME and instructions on how to generate test coverage data.
     Coverage data will match the source files more closely, if you do
     not optimize.

`-dLETTERS'
     Says to make debugging dumps during compilation at times specified
     by LETTERS.  This is used for debugging the compiler.  The file
     names for most of the dumps are made by appending a pass number
     and a word to the DUMPNAME. DUMPNAME is generated from the name of
     the output file, if explicitly specified and it is not an
     executable, otherwise it is the basename of the source file. In
     both cases any suffix is removed (e.g.  `foo.01.rtl' or
     `foo.02.sibling').  Here are the possible letters for use in
     LETTERS, and their meanings:

    `A'
          Annotate the assembler output with miscellaneous debugging
          information.

    `b'
          Dump after computing branch probabilities, to `FILE.12.bp'.

    `B'
          Dump after block reordering, to `FILE.31.bbro'.

    `c'
          Dump after instruction combination, to the file
          `FILE.20.combine'.

    `C'
          Dump after the first if conversion, to the file `FILE.14.ce1'.
          Also dump after the second if conversion, to the file
          `FILE.21.ce2'.

    `d'
          Dump after branch target load optimization, to to
          `FILE.32.btl'.  Also dump after delayed branch scheduling, to
          `FILE.36.dbr'.

    `D'
          Dump all macro definitions, at the end of preprocessing, in
          addition to normal output.

    `E'
          Dump after the third if conversion, to `FILE.30.ce3'.

    `f'
          Dump after control and data flow analysis, to `FILE.11.cfg'.
          Also dump after life analysis, to `FILE.19.life'.

    `F'
          Dump after purging `ADDRESSOF' codes, to `FILE.07.addressof'.

    `g'
          Dump after global register allocation, to `FILE.25.greg'.

    `G'
          Dump after GCSE, to `FILE.08.gcse'.  Also dump after jump
          bypassing and control flow optimizations, to `FILE.10.bypass'.

    `h'
          Dump after finalization of EH handling code, to `FILE.03.eh'.

    `i'
          Dump after sibling call optimizations, to `FILE.02.sibling'.

    `j'
          Dump after the first jump optimization, to `FILE.04.jump'.

    `k'
          Dump after conversion from registers to stack, to
          `FILE.34.stack'.

    `l'
          Dump after local register allocation, to `FILE.24.lreg'.

    `L'
          Dump after loop optimization passes, to `FILE.09.loop' and
          `FILE.16.loop2'.

    `M'
          Dump after performing the machine dependent reorganization
          pass, to `FILE.35.mach'.

    `n'
          Dump after register renumbering, to `FILE.29.rnreg'.

    `N'
          Dump after the register move pass, to `FILE.22.regmove'.

    `o'
          Dump after post-reload optimizations, to `FILE.26.postreload'.

    `r'
          Dump after RTL generation, to `FILE.01.rtl'.

    `R'
          Dump after the second scheduling pass, to `FILE.33.sched2'.

    `s'
          Dump after CSE (including the jump optimization that
          sometimes follows CSE), to `FILE.06.cse'.

    `S'
          Dump after the first scheduling pass, to `FILE.23.sched'.

    `t'
          Dump after the second CSE pass (including the jump
          optimization that sometimes follows CSE), to `FILE.18.cse2'.

    `T'
          Dump after running tracer, to `FILE.15.tracer'.

    `u'
          Dump after null pointer elimination pass to `FILE.05.null'.

    `U'
          Dump callgraph and unit-at-a-time optimization `FILE.00.unit'.

    `V'
          Dump after the value profile transformations, to
          `FILE.13.vpt'.

    `w'
          Dump after the second flow pass, to `FILE.27.flow2'.

    `z'
          Dump after the peephole pass, to `FILE.28.peephole2'.

    `Z'
          Dump after constructing the web, to `FILE.17.web'.

    `a'
          Produce all the dumps listed above.

    `H'
          Produce a core dump whenever an error occurs.

    `m'
          Print statistics on memory usage, at the end of the run, to
          standard error.

    `p'
          Annotate the assembler output with a comment indicating which
          pattern and alternative was used.  The length of each
          instruction is also printed.

    `P'
          Dump the RTL in the assembler output as a comment before each
          instruction.  Also turns on `-dp' annotation.

    `v'
          For each of the other indicated dump files (except for
          `FILE.01.rtl'), dump a representation of the control flow
          graph suitable for viewing with VCG to `FILE.PASS.vcg'.

    `x'
          Just generate RTL for a function instead of compiling it.
          Usually used with `r'.

    `y'
          Dump debugging information during parsing, to standard error.

`-fdump-unnumbered'
     When doing debugging dumps (see `-d' option above), suppress
     instruction numbers and line number note output.  This makes it
     more feasible to use diff on debugging dumps for compiler
     invocations with different options, in particular with and without
     `-g'.

`-fdump-translation-unit (C and C++ only)'
`-fdump-translation-unit-OPTIONS (C and C++ only)'
     Dump a representation of the tree structure for the entire
     translation unit to a file.  The file name is made by appending
     `.tu' to the source file name.  If the `-OPTIONS' form is used,
     OPTIONS controls the details of the dump as described for the
     `-fdump-tree' options.

`-fdump-class-hierarchy (C++ only)'
`-fdump-class-hierarchy-OPTIONS (C++ only)'
     Dump a representation of each class's hierarchy and virtual
     function table layout to a file.  The file name is made by
     appending `.class' to the source file name.  If the `-OPTIONS'
     form is used, OPTIONS controls the details of the dump as
     described for the `-fdump-tree' options.

`-fdump-tree-SWITCH (C++ only)'
`-fdump-tree-SWITCH-OPTIONS (C++ only)'
     Control the dumping at various stages of processing the
     intermediate language tree to a file.  The file name is generated
     by appending a switch specific suffix to the source file name.  If
     the `-OPTIONS' form is used, OPTIONS is a list of `-' separated
     options that control the details of the dump. Not all options are
     applicable to all dumps, those which are not meaningful will be
     ignored. The following options are available

    `address'
          Print the address of each node.  Usually this is not
          meaningful as it changes according to the environment and
          source file. Its primary use is for tying up a dump file with
          a debug environment.

    `slim'
          Inhibit dumping of members of a scope or body of a function
          merely because that scope has been reached. Only dump such
          items when they are directly reachable by some other path.

    `all'
          Turn on all options.

     The following tree dumps are possible:
    `original'
          Dump before any tree based optimization, to `FILE.original'.

    `optimized'
          Dump after all tree based optimization, to `FILE.optimized'.

    `inlined'
          Dump after function inlining, to `FILE.inlined'.

`-frandom-seed=STRING'
     This option provides a seed that GCC uses when it would otherwise
     use random numbers.  It is used to generate certain symbol names
     that have to be different in every compiled file. It is also used
     to place unique stamps in coverage data files and the object files
     that produce them. You can use the `-frandom-seed' option to
     produce reproducibly identical object files.

     The STRING should be different for every file you compile.

`-fsched-verbose=N'
     On targets that use instruction scheduling, this option controls
     the amount of debugging output the scheduler prints.  This
     information is written to standard error, unless `-dS' or `-dR' is
     specified, in which case it is output to the usual dump listing
     file, `.sched' or `.sched2' respectively.  However for N greater
     than nine, the output is always printed to standard error.

     For N greater than zero, `-fsched-verbose' outputs the same
     information as `-dRS'.  For N greater than one, it also output
     basic block probabilities, detailed ready list information and
     unit/insn info.  For N greater than two, it includes RTL at abort
     point, control-flow and regions info.  And for N over four,
     `-fsched-verbose' also includes dependence info.

`-save-temps'
     Store the usual "temporary" intermediate files permanently; place
     them in the current directory and name them based on the source
     file.  Thus, compiling `foo.c' with `-c -save-temps' would produce
     files `foo.i' and `foo.s', as well as `foo.o'.  This creates a
     preprocessed `foo.i' output file even though the compiler now
     normally uses an integrated preprocessor.

`-time'
     Report the CPU time taken by each subprocess in the compilation
     sequence.  For C source files, this is the compiler proper and
     assembler (plus the linker if linking is done).  The output looks
     like this:

          # cc1 0.12 0.01
          # as 0.00 0.01

     The first number on each line is the "user time," that is time
     spent executing the program itself.  The second number is "system
     time," time spent executing operating system routines on behalf of
     the program.  Both numbers are in seconds.

`-print-file-name=LIBRARY'
     Print the full absolute name of the library file LIBRARY that
     would be used when linking--and don't do anything else.  With this
     option, GCC does not compile or link anything; it just prints the
     file name.

`-print-multi-directory'
     Print the directory name corresponding to the multilib selected by
     any other switches present in the command line.  This directory is
     supposed to exist in `GCC_EXEC_PREFIX'.

`-print-multi-lib'
     Print the mapping from multilib directory names to compiler
     switches that enable them.  The directory name is separated from
     the switches by `;', and each switch starts with an `@' instead of
     the `-', without spaces between multiple switches.  This is
     supposed to ease shell-processing.

`-print-prog-name=PROGRAM'
     Like `-print-file-name', but searches for a program such as `cpp'.

`-print-libgcc-file-name'
     Same as `-print-file-name=libgcc.a'.

     This is useful when you use `-nostdlib' or `-nodefaultlibs' but
     you do want to link with `libgcc.a'.  You can do

          gcc -nostdlib FILES... `gcc -print-libgcc-file-name`

`-print-search-dirs'
     Print the name of the configured installation directory and a list
     of program and library directories `gcc' will search--and don't do
     anything else.

     This is useful when `gcc' prints the error message `installation
     problem, cannot exec cpp0: No such file or directory'.  To resolve
     this you either need to put `cpp0' and the other compiler
     components where `gcc' expects to find them, or you can set the
     environment variable `GCC_EXEC_PREFIX' to the directory where you
     installed them.  Don't forget the trailing '/'.  *Note Environment
     Variables::.

`-dumpmachine'
     Print the compiler's target machine (for example,
     `i686-pc-linux-gnu')--and don't do anything else.

`-dumpversion'
     Print the compiler version (for example, `3.0')--and don't do
     anything else.

`-dumpspecs'
     Print the compiler's built-in specs--and don't do anything else.
     (This is used when GCC itself is being built.)  *Note Spec Files::.

`-feliminate-unused-debug-types'
     Normally, when producing DWARF2 output, GCC will emit debugging
     information for all types declared in a compilation unit,
     regardless of whether or not they are actually used in that
     compilation unit.  Sometimes this is useful, such as if, in the
     debugger, you want to cast a value to a type that is not actually
     used in your program (but is declared).  More often, however, this
     results in a significant amount of wasted space.  With this
     option, GCC will avoid producing debug symbol output for types
     that are nowhere used in the source file being compiled.


File: gcc,  Node: Optimize Options,  Next: Preprocessor Options,  Prev: Debugging Options,  Up: Invoking GCC

3.10 Options That Control Optimization
======================================

These options control various sorts of optimizations.

 Without any optimization option, the compiler's goal is to reduce the
cost of compilation and to make debugging produce the expected results.
Statements are independent: if you stop the program with a breakpoint
between statements, you can then assign a new value to any variable or
change the program counter to any other statement in the function and
get exactly the results you would expect from the source code.

 Turning on optimization flags makes the compiler attempt to improve
the performance and/or code size at the expense of compilation time and
possibly the ability to debug the program.

 The compiler performs optimization based on the knowledge it has of
the program.  Using the `-funit-at-a-time' flag will allow the compiler
to consider information gained from later functions in the file when
compiling a function.  Compiling multiple files at once to a single
output file (and using `-funit-at-a-time') will allow the compiler to
use information gained from all of the files when compiling each of
them.

 Not all optimizations are controlled directly by a flag.  Only
optimizations that have a flag are listed.

`-O'
`-O1'
     Optimize.  Optimizing compilation takes somewhat more time, and a
     lot more memory for a large function.

     With `-O', the compiler tries to reduce code size and execution
     time, without performing any optimizations that take a great deal
     of compilation time.

     `-O' turns on the following optimization flags:
          -fdefer-pop
          -fmerge-constants
          -fthread-jumps
          -floop-optimize
          -fif-conversion
          -fif-conversion2
          -fdelayed-branch
          -fguess-branch-probability
          -fcprop-registers

     `-O' also turns on `-fomit-frame-pointer' on machines where doing
     so does not interfere with debugging.

`-O2'
     Optimize even more.  GCC performs nearly all supported
     optimizations that do not involve a space-speed tradeoff.  The
     compiler does not perform loop unrolling or function inlining when
     you specify `-O2'.  As compared to `-O', this option increases
     both compilation time and the performance of the generated code.

     `-O2' turns on all optimization flags specified by `-O'.  It also
     turns on the following optimization flags:
          -fforce-mem
          -foptimize-sibling-calls
          -fstrength-reduce
          -fcse-follow-jumps  -fcse-skip-blocks
          -frerun-cse-after-loop  -frerun-loop-opt
          -fgcse  -fgcse-lm  -fgcse-sm  -fgcse-las
          -fdelete-null-pointer-checks
          -fexpensive-optimizations
          -fregmove
          -fschedule-insns  -fschedule-insns2
          -fsched-interblock  -fsched-spec
          -fcaller-saves
          -fpeephole2
          -freorder-blocks  -freorder-functions
          -fstrict-aliasing
          -funit-at-a-time
          -falign-functions  -falign-jumps
          -falign-loops  -falign-labels
          -fcrossjumping

     Please note the warning under `-fgcse' about invoking `-O2' on
     programs that use computed gotos.

`-O3'
     Optimize yet more.  `-O3' turns on all optimizations specified by
     `-O2' and also turns on the `-finline-functions', `-fweb' and
     `-frename-registers' options.

`-O0'
     Do not optimize.  This is the default.

`-Os'
     Optimize for size.  `-Os' enables all `-O2' optimizations that do
     not typically increase code size.  It also performs further
     optimizations designed to reduce code size.

     `-Os' disables the following optimization flags:
          -falign-functions  -falign-jumps  -falign-loops
          -falign-labels  -freorder-blocks  -fprefetch-loop-arrays

     If you use multiple `-O' options, with or without level numbers,
     the last such option is the one that is effective.

 Options of the form `-fFLAG' specify machine-independent flags.  Most
flags have both positive and negative forms; the negative form of
`-ffoo' would be `-fno-foo'.  In the table below, only one of the forms
is listed--the one you typically will use.  You can figure out the
other form by either removing `no-' or adding it.

 The following options control specific optimizations.  They are either
activated by `-O' options or are related to ones that are.  You can use
the following flags in the rare cases when "fine-tuning" of
optimizations to be performed is desired.

`-fno-default-inline'
     Do not make member functions inline by default merely because they
     are defined inside the class scope (C++ only).  Otherwise, when
     you specify `-O', member functions defined inside class scope are
     compiled inline by default; i.e., you don't need to add `inline'
     in front of the member function name.

`-fno-defer-pop'
     Always pop the arguments to each function call as soon as that
     function returns.  For machines which must pop arguments after a
     function call, the compiler normally lets arguments accumulate on
     the stack for several function calls and pops them all at once.

     Disabled at levels `-O', `-O2', `-O3', `-Os'.

`-fforce-mem'
     Force memory operands to be copied into registers before doing
     arithmetic on them.  This produces better code by making all memory
     references potential common subexpressions.  When they are not
     common subexpressions, instruction combination should eliminate
     the separate register-load.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fforce-addr'
     Force memory address constants to be copied into registers before
     doing arithmetic on them.  This may produce better code just as
     `-fforce-mem' may.

`-fomit-frame-pointer'
     Don't keep the frame pointer in a register for functions that
     don't need one.  This avoids the instructions to save, set up and
     restore frame pointers; it also makes an extra register available
     in many functions.  *It also makes debugging impossible on some
     machines.*

     On some machines, such as the VAX, this flag has no effect, because
     the standard calling sequence automatically handles the frame
     pointer and nothing is saved by pretending it doesn't exist.  The
     machine-description macro `FRAME_POINTER_REQUIRED' controls
     whether a target machine supports this flag.  *Note Register
     Usage: (gccint)Registers.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-foptimize-sibling-calls'
     Optimize sibling and tail recursive calls.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fno-inline'
     Don't pay attention to the `inline' keyword.  Normally this option
     is used to keep the compiler from expanding any functions inline.
     Note that if you are not optimizing, no functions can be expanded
     inline.

`-finline-functions'
     Integrate all simple functions into their callers.  The compiler
     heuristically decides which functions are simple enough to be worth
     integrating in this way.

     If all calls to a given function are integrated, and the function
     is declared `static', then the function is normally not output as
     assembler code in its own right.

     Enabled at level `-O3'.

`-finline-limit=N'
     By default, GCC limits the size of functions that can be inlined.
     This flag allows the control of this limit for functions that are
     explicitly marked as inline (i.e., marked with the inline keyword
     or defined within the class definition in c++).  N is the size of
     functions that can be inlined in number of pseudo instructions
     (not counting parameter handling).  The default value of N is 600.
     Increasing this value can result in more inlined code at the cost
     of compilation time and memory consumption.  Decreasing usually
     makes the compilation faster and less code will be inlined (which
     presumably means slower programs).  This option is particularly
     useful for programs that use inlining heavily such as those based
     on recursive templates with C++.

     Inlining is actually controlled by a number of parameters, which
     may be specified individually by using `--param NAME=VALUE'.  The
     `-finline-limit=N' option sets some of these parameters as follows:

    `max-inline-insns-single'
          is set to N/2.

    `max-inline-insns-auto'
          is set to N/2.

    `min-inline-insns'
          is set to 130 or N/4, whichever is smaller.

    `max-inline-insns-rtl'
          is set to N.

     See below for a documentation of the individual parameters
     controlling inlining.

     _Note:_ pseudo instruction represents, in this particular context,
     an abstract measurement of function's size.  In no way, it
     represents a count of assembly instructions and as such its exact
     meaning might change from one release to an another.

`-fkeep-inline-functions'
     Even if all calls to a given function are integrated, and the
     function is declared `static', nevertheless output a separate
     run-time callable version of the function.  This switch does not
     affect `extern inline' functions.

`-fkeep-static-consts'
     Emit variables declared `static const' when optimization isn't
     turned on, even if the variables aren't referenced.

     GCC enables this option by default.  If you want to force the
     compiler to check if the variable was referenced, regardless of
     whether or not optimization is turned on, use the
     `-fno-keep-static-consts' option.

`-fmerge-constants'
     Attempt to merge identical constants (string constants and
     floating point constants) across compilation units.

     This option is the default for optimized compilation if the
     assembler and linker support it.  Use `-fno-merge-constants' to
     inhibit this behavior.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fmerge-all-constants'
     Attempt to merge identical constants and identical variables.

     This option implies `-fmerge-constants'.  In addition to
     `-fmerge-constants' this considers e.g. even constant initialized
     arrays or initialized constant variables with integral or floating
     point types.  Languages like C or C++ require each non-automatic
     variable to have distinct location, so using this option will
     result in non-conforming behavior.

`-fnew-ra'
     Use a graph coloring register allocator.  Currently this option is
     meant only for testing.  Users should not specify this option,
     since it is not yet ready for production use.

`-fno-branch-count-reg'
     Do not use "decrement and branch" instructions on a count register,
     but instead generate a sequence of instructions that decrement a
     register, compare it against zero, then branch based upon the
     result.  This option is only meaningful on architectures that
     support such instructions, which include x86, PowerPC, IA-64 and
     S/390.

     The default is `-fbranch-count-reg', enabled when
     `-fstrength-reduce' is enabled.

`-fno-function-cse'
     Do not put function addresses in registers; make each instruction
     that calls a constant function contain the function's address
     explicitly.

     This option results in less efficient code, but some strange hacks
     that alter the assembler output may be confused by the
     optimizations performed when this option is not used.

     The default is `-ffunction-cse'

`-fno-zero-initialized-in-bss'
     If the target supports a BSS section, GCC by default puts
     variables that are initialized to zero into BSS.  This can save
     space in the resulting code.

     This option turns off this behavior because some programs
     explicitly rely on variables going to the data section.  E.g., so
     that the resulting executable can find the beginning of that
     section and/or make assumptions based on that.

     The default is `-fzero-initialized-in-bss'.

`-fstrength-reduce'
     Perform the optimizations of loop strength reduction and
     elimination of iteration variables.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fthread-jumps'
     Perform optimizations where we check to see if a jump branches to a
     location where another comparison subsumed by the first is found.
     If so, the first branch is redirected to either the destination of
     the second branch or a point immediately following it, depending
     on whether the condition is known to be true or false.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fcse-follow-jumps'
     In common subexpression elimination, scan through jump instructions
     when the target of the jump is not reached by any other path.  For
     example, when CSE encounters an `if' statement with an `else'
     clause, CSE will follow the jump when the condition tested is
     false.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fcse-skip-blocks'
     This is similar to `-fcse-follow-jumps', but causes CSE to follow
     jumps which conditionally skip over blocks.  When CSE encounters a
     simple `if' statement with no else clause, `-fcse-skip-blocks'
     causes CSE to follow the jump around the body of the `if'.

     Enabled at levels `-O2', `-O3', `-Os'.

`-frerun-cse-after-loop'
     Re-run common subexpression elimination after loop optimizations
     has been performed.

     Enabled at levels `-O2', `-O3', `-Os'.

`-frerun-loop-opt'
     Run the loop optimizer twice.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fgcse'
     Perform a global common subexpression elimination pass.  This pass
     also performs global constant and copy propagation.

     _Note:_ When compiling a program using computed gotos, a GCC
     extension, you may get better runtime performance if you disable
     the global common subexpression elimination pass by adding
     `-fno-gcse' to the command line.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fgcse-lm'
     When `-fgcse-lm' is enabled, global common subexpression
     elimination will attempt to move loads which are only killed by
     stores into themselves.  This allows a loop containing a
     load/store sequence to be changed to a load outside the loop, and
     a copy/store within the loop.

     Enabled by default when gcse is enabled.

`-fgcse-sm'
     When `-fgcse-sm' is enabled, a store motion pass is run after
     global common subexpression elimination.  This pass will attempt
     to move stores out of loops.  When used in conjunction with
     `-fgcse-lm', loops containing a load/store sequence can be changed
     to a load before the loop and a store after the loop.

     Enabled by default when gcse is enabled.

`-fgcse-las'
     When `-fgcse-las' is enabled, the global common subexpression
     elimination pass eliminates redundant loads that come after stores
     to the same memory location (both partial and full redundancies).

     Enabled by default when gcse is enabled.

`-floop-optimize'
     Perform loop optimizations: move constant expressions out of
     loops, simplify exit test conditions and optionally do
     strength-reduction and loop unrolling as well.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fcrossjumping'
     Perform cross-jumping transformation. This transformation unifies
     equivalent code and save code size. The resulting code may or may
     not perform better than without cross-jumping.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fif-conversion'
     Attempt to transform conditional jumps into branch-less
     equivalents.  This include use of conditional moves, min, max, set
     flags and abs instructions, and some tricks doable by standard
     arithmetics.  The use of conditional execution on chips where it
     is available is controlled by `if-conversion2'.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fif-conversion2'
     Use conditional execution (where available) to transform
     conditional jumps into branch-less equivalents.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fdelete-null-pointer-checks'
     Use global dataflow analysis to identify and eliminate useless
     checks for null pointers.  The compiler assumes that dereferencing
     a null pointer would have halted the program.  If a pointer is
     checked after it has already been dereferenced, it cannot be null.

     In some environments, this assumption is not true, and programs can
     safely dereference null pointers.  Use
     `-fno-delete-null-pointer-checks' to disable this optimization for
     programs which depend on that behavior.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fexpensive-optimizations'
     Perform a number of minor optimizations that are relatively
     expensive.

     Enabled at levels `-O2', `-O3', `-Os'.

`-foptimize-register-move'
`-fregmove'
     Attempt to reassign register numbers in move instructions and as
     operands of other simple instructions in order to maximize the
     amount of register tying.  This is especially helpful on machines
     with two-operand instructions.

     Note `-fregmove' and `-foptimize-register-move' are the same
     optimization.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fdelayed-branch'
     If supported for the target machine, attempt to reorder
     instructions to exploit instruction slots available after delayed
     branch instructions.

     Enabled at levels `-O', `-O2', `-O3', `-Os'.

`-fschedule-insns'
     If supported for the target machine, attempt to reorder
     instructions to eliminate execution stalls due to required data
     being unavailable.  This helps machines that have slow floating
     point or memory load instructions by allowing other instructions
     to be issued until the result of the load or floating point
     instruction is required.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fschedule-insns2'
     Similar to `-fschedule-insns', but requests an additional pass of
     instruction scheduling after register allocation has been done.
     This is especially useful on machines with a relatively small
     number of registers and where memory load instructions take more
     than one cycle.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fno-sched-interblock'
     Don't schedule instructions across basic blocks.  This is normally
     enabled by default when scheduling before register allocation, i.e.
     with `-fschedule-insns' or at `-O2' or higher.

`-fno-sched-spec'
     Don't allow speculative motion of non-load instructions.  This is
     normally enabled by default when scheduling before register
     allocation, i.e.  with `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load'
     Allow speculative motion of some load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-fsched-spec-load-dangerous'
     Allow speculative motion of more load instructions.  This only
     makes sense when scheduling before register allocation, i.e. with
     `-fschedule-insns' or at `-O2' or higher.

`-fsched-stalled-insns=N'
     Define how many insns (if any) can be moved prematurely from the
     queue of stalled insns into the ready list, during the second
     scheduling pass.

`-fsched-stalled-insns-dep=N'
     Define how many insn groups (cycles) will be examined for a
     dependency on a stalled insn that is candidate for premature
     removal from the queue of stalled insns.  Has an effect only
     during the second scheduling pass, and only if
     `-fsched-stalled-insns' is used and its value is not zero.

`-fsched2-use-superblocks'
     When scheduling after register allocation, do use superblock
     scheduling algorithm.  Superblock scheduling allows motion across
     basic block boundaries resulting on faster schedules.  This option
     is experimental, as not all machine descriptions used by GCC model
     the CPU closely enough to avoid unreliable results from the
     algorithm.

     This only makes sense when scheduling after register allocation,
     i.e. with `-fschedule-insns2' or at `-O2' or higher.

`-fsched2-use-traces'
     Use `-fsched2-use-superblocks' algorithm when scheduling after
     register allocation and additionally perform code duplication in
     order to increase the size of superblocks using tracer pass.  See
     `-ftracer' for details on trace formation.

     This mode should produce faster but significantly longer programs.
     Also without `-fbranch-probabilities' the traces constructed may
     not match the reality and hurt the performance.  This only makes
     sense when scheduling after register allocation, i.e. with
     `-fschedule-insns2' or at `-O2' or higher.

`-fcaller-saves'
     Enable values to be allocated in registers that will be clobbered
     by function calls, by emitting extra instructions to save and
     restore the registers around such calls.  Such allocation is done
     only when it seems to result in better code than would otherwise
     be produced.

     This option is always enabled by default on certain machines,
     usually those which have no call-preserved registers to use
     instead.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fmove-all-movables'
     Forces all invariant computations in loops to be moved outside the
     loop.

`-freduce-all-givs'
     Forces all general-induction variables in loops to be
     strength-reduced.

     _Note:_ When compiling programs written in Fortran,
     `-fmove-all-movables' and `-freduce-all-givs' are enabled by
     default when you use the optimizer.

     These options may generate better or worse code; results are highly
     dependent on the structure of loops within the source code.

     These two options are intended to be removed someday, once they
     have helped determine the efficacy of various approaches to
     improving loop optimizations.

     Please let us (<[e-mail]> and <[e-mail]>) know how
     use of these options affects the performance of your production
     code.  We're very interested in code that runs _slower_ when these
     options are _enabled_.

`-fno-peephole'
`-fno-peephole2'
     Disable any machine-specific peephole optimizations.  The
     difference between `-fno-peephole' and `-fno-peephole2' is in how
     they are implemented in the compiler; some targets use one, some
     use the other, a few use both.

     `-fpeephole' is enabled by default.  `-fpeephole2' enabled at
     levels `-O2', `-O3', `-Os'.

`-fno-guess-branch-probability'
     Do not guess branch probabilities using a randomized model.

     Sometimes GCC will opt to use a randomized model to guess branch
     probabilities, when none are available from either profiling
     feedback (`-fprofile-arcs') or `__builtin_expect'.  This means that
     different runs of the compiler on the same program may produce
     different object code.

     In a hard real-time system, people don't want different runs of the
     compiler to produce code that has different behavior; minimizing
     non-determinism is of paramount import.  This switch allows users
     to reduce non-determinism, possibly at the expense of inferior
     optimization.

     The default is `-fguess-branch-probability' at levels `-O', `-O2',
     `-O3', `-Os'.

`-freorder-blocks'
     Reorder basic blocks in the compiled function in order to reduce
     number of taken branches and improve code locality.

     Enabled at levels `-O2', `-O3'.

`-freorder-functions'
     Reorder basic blocks in the compiled function in order to reduce
     number of taken branches and improve code locality. This is
     implemented by using special subsections `text.hot' for most
     frequently executed functions and `text.unlikely' for unlikely
     executed functions.  Reordering is done by the linker so object
     file format must support named sections and linker must place them
     in a reasonable way.

     Also profile feedback must be available in to make this option
     effective.  See `-fprofile-arcs' for details.

     Enabled at levels `-O2', `-O3', `-Os'.

`-fstrict-aliasing'
     Allows the compiler to assume the strictest aliasing rules
     applicable to the language being compiled.  For C (and C++), this
     activates optimizations based on the type of expressions.  In
     particular, an object of one type is assumed never to reside at
     the same address as an object of a different type, unless the
     types are almost the same.  For example, an `unsigned int' can
     alias an `int', but not a `void*' or a `double'.  A character type
     may alias any other type.

     Pay special attention to code like this:
          union a_union {
            int i;
            double d;
          };

          int f() {
            a_union t;
            t.d = 3.0;
            return t.i;
          }
     The practice of reading from a different union member than the one
     most recently written to (called "type-punning") is common.  Even
     with `-fstrict-aliasing', type-punning is allowed, provided the
     memory is accessed through the union type.  So, the code above
     will work as expected.  However, this code might not:
          int f() {
            a_union t;
            int* ip;
            t.d = 3.0;
            ip = &t.i;
            return *ip;
          }

     Every language that wishes to perform language-specific alias
     analysis should define a function that computes, given an `tree'
     node, an alias set for the node.  Nodes in different alias sets
     are not allowed to alias.  For an example, see the C front-end
     function `c_get_alias_set'.

     Enabled at levels `-O2', `-O3', `-Os'.

`-falign-functions'
`-falign-functions=N'
     Align the start of functions to the next power-of-two greater than
     N, skipping up to N bytes.  For instance, `-falign-functions=32'
     aligns functions to the next 32-byte boundary, but
     `-falign-functions=24' would align to the next 32-byte boundary
     only if this can be done by skipping 23 bytes or less.

     `-fno-align-functions' and `-falign-functions=1' are equivalent
     and mean that functions will not be aligned.

     Some assemblers only support this flag when N is a power of two;
     in that case, it is rounded up.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-falign-labels'
`-falign-labels=N'
     Align all branch targets to a power-of-two boundary, skipping up to
     N bytes like `-falign-functions'.  This option can easily make
     code slower, because it must insert dummy operations for when the
     branch target is reached in the usual flow of the code.

     `-fno-align-labels' and `-falign-labels=1' are equivalent and mean
     that labels will not be aligned.

     If `-falign-loops' or `-falign-jumps' are applicable and are
     greater than this value, then their values are used instead.

     If N is not specified or is zero, use a machine-dependent default
     which is very likely to be `1', meaning no alignment.

     Enabled at levels `-O2', `-O3'.

`-falign-loops'
`-falign-loops=N'
     Align loops to a power-of-two boundary, skipping up to N bytes
     like `-falign-functions'.  The hope is that the loop will be
     executed many times, which will make up for any execution of the
     dummy operations.

     `-fno-align-loops' and `-falign-loops=1' are equivalent and mean
     that loops will not be aligned.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-falign-jumps'
`-falign-jumps=N'
     Align branch targets to a power-of-two boundary, for branch targets
     where the targets can only be reached by jumping, skipping up to N
     bytes like `-falign-functions'.  In this case, no dummy operations
     need be executed.

     `-fno-align-jumps' and `-falign-jumps=1' are equivalent and mean
     that loops will not be aligned.

     If N is not specified or is zero, use a machine-dependent default.

     Enabled at levels `-O2', `-O3'.

`-frename-registers'
     Attempt to avoid false dependencies in scheduled code by making use
     of registers left over after register allocation.  This
     optimization will most benefit processors with lots of registers.
     It can, however, make debugging impossible, since variables will
     no longer stay in a "home register".

`-fweb'
     Constructs webs as commonly used for register allocation purposes
     and assign each web individual pseudo register.  This allows our
     register allocation pass to operate on pseudos directly, but also
     strengthens several other optimization passes, such as CSE, loop
     optimizer and trivial dead code remover.  It can, however, make
     debugging impossible, since variables will no longer stay in a
     "home register".

     Enabled at levels `-O3'.

`-fno-cprop-registers'
     After register allocation and post-register allocation instruction
     splitting, we perform a copy-propagation pass to try to reduce
     scheduling dependencies and occasionally eliminate the copy.

     Disabled at levels `-O', `-O2', `-O3', `-Os'.

`-fprofile-generate'
     Enable options usually used for instrumenting application to
     produce profile useful for later recompilation with profile
     feedback based optimization.  You must use `-fprofile-generate'
     both when compiling and when linking your program.

     The following options are enabled: `-fprofile-arcs',
     `-fprofile-values', `-fvpt'.

`-fprofile-use'
     Enable profile feedback directed optimizations, and optimizations
     generally profitable only with profile feedback available.

     The following options are enabled: `-fbranch-probabilities',
     `-fvpt', `-funroll-loops', `-fpeel-loops', `-ftracer'.


 The following options control compiler behavior regarding floating
point arithmetic.  These options trade off between speed and
correctness.  All must be specifically enabled.

`-ffloat-store'
     Do not store floating point variables in registers, and inhibit
     other options that might change whether a floating point value is
     taken from a register or memory.

     This option prevents undesirable excess precision on machines such
     as the 68000 where the floating registers (of the 68881) keep more
     precision than a `double' is supposed to have.  Similarly for the
     x86 architecture.  For most programs, the excess precision does
     only good, but a few programs rely on the precise definition of
     IEEE floating point.  Use `-ffloat-store' for such programs, after
     modifying them to store all pertinent intermediate computations
     into variables.

`-ffast-math'
     Sets `-fno-math-errno', `-funsafe-math-optimizations',
     `-fno-trapping-math', `-ffinite-math-only', `-fno-rounding-math'
     and `-fno-signaling-nans'.

     This option causes the preprocessor macro `__FAST_MATH__' to be
     defined.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

`-fno-math-errno'
     Do not set ERRNO after calling math functions that are executed
     with a single instruction, e.g., sqrt.  A program that relies on
     IEEE exceptions for math error handling may want to use this flag
     for speed while maintaining IEEE arithmetic compatibility.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

     The default is `-fmath-errno'.

`-funsafe-math-optimizations'
     Allow optimizations for floating-point arithmetic that (a) assume
     that arguments and results are valid and (b) may violate IEEE or
     ANSI standards.  When used at link-time, it may include libraries
     or startup files that change the default FPU control word or other
     similar optimizations.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

     The default is `-fno-unsafe-math-optimizations'.

`-ffinite-math-only'
     Allow optimizations for floating-point arithmetic that assume that
     arguments and results are not NaNs or +-Infs.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications.

     The default is `-fno-finite-math-only'.

`-fno-trapping-math'
     Compile code assuming that floating-point operations cannot
     generate user-visible traps.  These traps include division by
     zero, overflow, underflow, inexact result and invalid operation.
     This option implies `-fno-signaling-nans'.  Setting this option
     may allow faster code if one relies on "non-stop" IEEE arithmetic,
     for example.

     This option should never be turned on by any `-O' option since it
     can result in incorrect output for programs which depend on an
     exact implementation of IEEE or ISO rules/specifications for math
     functions.

     The default is `-ftrapping-math'.

`-frounding-math'
     Disable transformations and optimizations that assume default
     floating point rounding behavior.  This is round-to-zero for all
     floating point to integer conversions, and round-to-nearest for
     all other arithmetic truncations.  This option should be specified
     for programs that change the FP rounding mode dynamically, or that
     may be executed with a non-default rounding mode.  This option
     disables constant folding of floating point expressions at
     compile-time (which may be affected by rounding mode) and
     arithmetic transformations that are unsafe in the presence of
     sign-dependent rounding modes.

     The default is `-fno-rounding-math'.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that are affected by rounding mode.
     Future versions of GCC may provide finer control of this setting
     using C99's `FENV_ACCESS' pragma.  This command line option will
     be used to specify the default state for `FENV_ACCESS'.

`-fsignaling-nans'
     Compile code assuming that IEEE signaling NaNs may generate
     user-visible traps during floating-point operations.  Setting this
     option disables optimizations that may change the number of
     exceptions visible with signaling NaNs.  This option implies
     `-ftrapping-math'.

     This option causes the preprocessor macro `__SUPPORT_SNAN__' to be
     defined.

     The default is `-fno-signaling-nans'.

     This option is experimental and does not currently guarantee to
     disable all GCC optimizations that affect signaling NaN behavior.

`-fsingle-precision-constant'
     Treat floating point constant as single precision constant instead
     of implicitly converting it to double precision constant.


 The following options control optimizations that may improve
performance, but are not enabled by any `-O' options.  This section
includes experimental options that may produce broken code.

`-fbranch-probabilities'
     After running a program compiled with `-fprofile-arcs' (*note
     Options for Debugging Your Program or `gcc': Debugging Options.),
     you can compile it a second time using `-fbranch-probabilities',
     to improve optimizations based on the number of times each branch
     was taken.  When the program compiled with `-fprofile-arcs' exits
     it saves arc execution counts to a file called `SOURCENAME.gcda'
     for each source file  The information in this data file is very
     dependent on the structure of the generated code, so you must use
     the same source code and the same optimization options for both
     compilations.

     With `-fbranch-probabilities', GCC puts a `REG_BR_PROB' note on
     each `JUMP_INSN' and `CALL_INSN'.  These can be used to improve
     optimization.  Currently, they are only used in one place: in
     `reorg.c', instead of guessing which path a branch is mostly to
     take, the `REG_BR_PROB' values are used to exactly determine which
     path is taken more often.

`-fprofile-values'
     If combined with `-fprofile-arcs', it adds code so that some data
     about values of expressions in the program is gathered.

     With `-fbranch-probabilities', it reads back the data gathered
     from profiling values of expressions and adds `REG_VALUE_PROFILE'
     notes to instructions for their later usage in optimizations.

`-fvpt'
     If combined with `-fprofile-arcs', it instructs the compiler to add
     a code to gather information about values of expressions.

     With `-fbranch-probabilities', it reads back the data gathered and
     actually performs the optimizations based on them.  Currently the
     optimizations include specialization of division operation using
     the knowledge about the value of the denominator.

`-fnew-ra'
     Use a graph coloring register allocator.  Currently this option is
     meant for testing, so we are interested to hear about
     miscompilations with `-fnew-ra'.

`-ftracer'
     Perform tail duplication to enlarge superblock size. This
     transformation simplifies the control flow of the function
     allowing other optimizations to do better job.

`-funit-at-a-time'
     Parse the whole compilation unit before starting to produce code.
     This allows some extra optimizations to take place but consumes
     more memory.

`-funroll-loops'
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop.  `-funroll-loops' implies
     `-frerun-cse-after-loop'.  It also turns on complete loop peeling
     (i.e. complete removal of loops with small constant number of
     iterations).  This option makes code larger, and may or may not
     make it run faster.

`-funroll-all-loops'
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered.  This usually makes programs run more
     slowly.  `-funroll-all-loops' implies the same options as
     `-funroll-loops'.

`-fpeel-loops'
     Peels the loops for that there is enough information that they do
     not roll much (from profile feedback).  It also turns on complete
     loop peeling (i.e. complete removal of loops with small constant
     number of iterations).

`-funswitch-loops'
     Move branches with loop invariant conditions out of the loop, with
     duplicates of the loop on both branches (modified according to
     result of the condition).

`-fold-unroll-loops'
     Unroll loops whose number of iterations can be determined at
     compile time or upon entry to the loop, using the old loop
     unroller whose loop recognition is based on notes from frontend.
     `-fold-unroll-loops' implies both `-fstrength-reduce' and
     `-frerun-cse-after-loop'.  This option makes code larger, and may
     or may not make it run faster.

`-fold-unroll-all-loops'
     Unroll all loops, even if their number of iterations is uncertain
     when the loop is entered. This is done using the old loop unroller
     whose loop recognition is based on notes from frontend.  This
     usually makes programs run more slowly.  `-fold-unroll-all-loops'
     implies the same options as `-fold-unroll-loops'.

`-funswitch-loops'
     Move branches with loop invariant conditions out of the loop, with
     duplicates of the loop on both branches (modified according to
     result of the condition).

`-funswitch-loops'
     Move branches with loop invariant conditions out of the loop, with
     duplicates of the loop on both branches (modified according to
     result of the condition).

`-fprefetch-loop-arrays'
     If supported by the target machine, generate instructions to
     prefetch memory to improve the performance of loops that access
     large arrays.

     Disabled at level `-Os'.

`-ffunction-sections'
`-fdata-sections'
     Place each function or data item into its own section in the output
     file if the target supports arbitrary sections.  The name of the
     function or the name of the data item determines the section's name
     in the output file.

     Use these options on systems where the linker can perform
     optimizations to improve locality of reference in the instruction
     space.  Most systems using the ELF object format and SPARC
     processors running Solaris 2 have linkers with such optimizations.
     AIX may have these optimizations in the future.

     Only use these options when there are significant benefits from
     doing so.  When you specify these options, the assembler and
     linker will create larger object and executable files and will
     also be slower.  You will not be able to use `gprof' on all
     systems if you specify this option and you may have problems with
     debugging if you specify both this option and `-g'.

`-fbranch-target-load-optimize'
     Perform branch target register load optimization before prologue /
     epilogue threading.  The use of target registers can typically be
     exposed only during reload, thus hoisting loads out of loops and
     doing inter-block scheduling needs a separate optimization pass.

`-fbranch-target-load-optimize2'
     Perform branch target register load optimization after prologue /
     epilogue threading.

`--param NAME=VALUE'
     In some places, GCC uses various constants to control the amount of
     optimization that is done.  For example, GCC will not inline
     functions that contain more that a certain number of instructions.
     You can control some of these constants on the command-line using
     the `--param' option.

     The names of specific parameters, and the meaning of the values,
     are tied to the internals of the compiler, and are subject to
     change without notice in future releases.

     In each case, the VALUE is an integer.  The allowable choices for
     NAME are given in the following table:

    `max-crossjump-edges'
          The maximum number of incoming edges to consider for
          crossjumping.  The algorithm used by `-fcrossjumping' is
          O(N^2) in the number of edges incoming to each block.
          Increasing values mean more aggressive optimization, making
          the compile time increase with probably small improvement in
          executable size.

    `max-delay-slot-insn-search'
          The maximum number of instructions to consider when looking
          for an instruction to fill a delay slot.  If more than this
          arbitrary number of instructions is searched, the time
          savings from filling the delay slot will be minimal so stop
          searching.  Increasing values mean more aggressive
          optimization, making the compile time increase with probably
          small improvement in executable run time.

    `max-delay-slot-live-search'
          When trying to fill delay slots, the maximum number of
          instructions to consider when searching for a block with
          valid live register information.  Increasing this arbitrarily
          chosen value means more aggressive optimization, increasing
          the compile time.  This parameter should be removed when the
          delay slot code is rewritten to maintain the control-flow
          graph.

    `max-gcse-memory'
          The approximate maximum amount of memory that will be
          allocated in order to perform the global common subexpression
          elimination optimization.  If more memory than specified is
          required, the optimization will not be done.

    `max-gcse-passes'
          The maximum number of passes of GCSE to run.

    `max-pending-list-length'
          The maximum number of pending dependencies scheduling will
          allow before flushing the current state and starting over.
          Large functions with few branches or calls can create
          excessively large lists which needlessly consume memory and
          resources.

    `max-inline-insns-single'
          Several parameters control the tree inliner used in gcc.
          This number sets the maximum number of instructions (counted
          in GCC's internal representation) in a single function that
          the tree inliner will consider for inlining.  This only
          affects functions declared inline and methods implemented in
          a class declaration (C++).  The default value is 500.

    `max-inline-insns-auto'
          When you use `-finline-functions' (included in `-O3'), a lot
          of functions that would otherwise not be considered for
          inlining by the compiler will be investigated.  To those
          functions, a different (more restrictive) limit compared to
          functions declared inline can be applied.  The default value
          is 100.

    `large-function-insns'
          The limit specifying really large functions.  For functions
          greater than this limit inlining is constrained by `--param
          large-function-growth'.  This parameter is useful primarily
          to avoid extreme compilation time caused by non-linear
          algorithms used by the backend.  This parameter is ignored
          when `-funit-at-a-time' is not used.  The default value is
          3000.

    `large-function-growth'
          Specifies maximal growth of large function caused by inlining
          in percents.  This parameter is ignored when
          `-funit-at-a-time' is not used.  The default value is 200.

    `inline-unit-growth'
          Specifies maximal overall growth of the compilation unit
          caused by inlining.  This parameter is ignored when
          `-funit-at-a-time' is not used.  The default value is 150.

    `max-inline-insns-rtl'
          For languages that use the RTL inliner (this happens at a
          later stage than tree inlining), you can set the maximum
          allowable size (counted in RTL instructions) for the RTL
          inliner with this parameter.  The default value is 600.

    `max-unrolled-insns'
          The maximum number of instructions that a loop should have if
          that loop is unrolled, and if the loop is unrolled, it
          determines how many times the loop code is unrolled.

    `max-average-unrolled-insns'
          The maximum number of instructions biased by probabilities of
          their execution that a loop should have if that loop is
          unrolled, and if the loop is unrolled, it determines how many
          times the loop code is unrolled.

    `max-unroll-times'
          The maximum number of unrollings of a single loop.

    `max-peeled-insns'
          The maximum number of instructions that a loop should have if
          that loop is peeled, and if the loop is peeled, it determines
          how many times the loop code is peeled.

    `max-peel-times'
          The maximum number of peelings of a single loop.

    `max-completely-peeled-insns'
          The maximum number of insns of a completely peeled loop.

    `max-completely-peel-times'
          The maximum number of iterations of a loop to be suitable for
          complete peeling.

    `max-unswitch-insns'
          The maximum number of insns of an unswitched loop.

    `max-unswitch-level'
          The maximum number of branches unswitched in a single loop.

    `hot-bb-count-fraction'
          Select fraction of the maximal count of repetitions of basic
          block in program given basic block needs to have to be
          considered hot.

    `hot-bb-frequency-fraction'
          Select fraction of the maximal frequency of executions of
          basic block in function given basic block needs to have to be
          considered hot

    `tracer-dynamic-coverage'
    `tracer-dynamic-coverage-feedback'
          This value is used to limit superblock formation once the
          given percentage of executed instructions is covered.  This
          limits unnecessary code size expansion.

          The `tracer-dynamic-coverage-feedback' is used only when
          profile feedback is available.  The real profiles (as opposed
          to statically estimated ones) are much less balanced allowing
          the threshold to be larger value.

    `tracer-max-code-growth'
          Stop tail duplication once code growth has reached given
          percentage.  This is rather hokey argument, as most of the
          duplicates will be eliminated later in cross jumping, so it
          may be set to much higher values than is the desired code
          growth.

    `tracer-min-branch-ratio'
          Stop reverse growth when the reverse probability of best edge
          is less than this threshold (in percent).

    `tracer-min-branch-ratio'
    `tracer-min-branch-ratio-feedback'
          Stop forward growth if the best edge do have probability
          lower than this threshold.

          Similarly to `tracer-dynamic-coverage' two values are
          present, one for compilation for profile feedback and one for
          compilation without.  The value for compilation with profile
          feedback needs to be more conservative (higher) in order to
          make tracer effective.

    `max-cse-path-length'
          Maximum number of basic blocks on path that cse considers.

    `ggc-min-expand'
          GCC uses a garbage collector to manage its own memory
          allocation.  This parameter specifies the minimum percentage
          by which the garbage collector's heap should be allowed to
          expand between collections.  Tuning this may improve
          compilation speed; it has no effect on code generation.

          The default is 30% + 70% * (RAM/1GB) with an upper bound of
          100% when RAM >= 1GB.  If `getrlimit' is available, the
          notion of "RAM" is the smallest of actual RAM, RLIMIT_RSS,
          RLIMIT_DATA and RLIMIT_AS.  If GCC is not able to calculate
          RAM on a particular platform, the lower bound of 30% is used.
          Setting this parameter and `ggc-min-heapsize' to zero causes
          a full collection to occur at every opportunity.  This is
          extremely slow, but can be useful for debugging.

    `ggc-min-heapsize'
          Minimum size of the garbage collector's heap before it begins
          bothering to collect garbage.  The first collection occurs
          after the heap expands by `ggc-min-expand'% beyond
          `ggc-min-heapsize'.  Again, tuning this may improve
          compilation speed, and has no effect on code generation.

          The default is RAM/8, with a lower bound of 4096 (four
          megabytes) and an upper bound of 131072 (128 megabytes).  If
          `getrlimit' is available, the notion of "RAM" is the smallest
          of actual RAM, RLIMIT_RSS, RLIMIT_DATA and RLIMIT_AS.  If GCC
          is not able to calculate RAM on a particular platform, the
          lower bound is used.  Setting this parameter very large
          effectively disables garbage collection.  Setting this
          parameter and `ggc-min-expand' to zero causes a full
          collection to occur at every opportunity.

    `max-reload-search-insns'
          The maximum number of instruction reload should look backward
          for equivalent register.  Increasing values mean more
          aggressive optimization, making the compile time increase
          with probably slightly better performance.  The default value
          is 100.

    `max-cselib-memory-location'
          The maximum number of memory locations cselib should take
          into acount.  Increasing values mean more aggressive
          optimization, making the compile time increase with probably
          slightly better performance.  The default value is 500.

    `reorder-blocks-duplicate'
    `reorder-blocks-duplicate-feedback'
          Used by basic block reordering pass to decide whether to use
          unconditional branch or duplicate the code on its
          destination.  Code is duplicated when its estimated size is
          smaller than this value multiplied by the estimated size of
          unconditional jump in the hot spots of the program.

          The `reorder-block-duplicate-feedback' is used only when
          profile feedback is available and may be set to higher values
          than `reorder-block-duplicate' since information about the
          hot spots is more accurate.


File: gcc,  Node: Preprocessor Options,  Next: Assembler Options,  Prev: Optimize Options,  Up: Invoking GCC

3.11 Options Controlling the Preprocessor
=========================================

These options control the C preprocessor, which is run on each C source
file before actual compilation.

 If you use the `-E' option, nothing is done except preprocessing.
Some of these options make sense only together with `-E' because they
cause the preprocessor output to be unsuitable for actual compilation.

     You can use `-Wp,OPTION' to bypass the compiler driver and pass
     OPTION directly through to the preprocessor.  If OPTION contains
     commas, it is split into multiple options at the commas.  However,
     many options are modified, translated or interpreted by the
     compiler driver before being passed to the preprocessor, and `-Wp'
     forcibly bypasses this phase.  The preprocessor's direct interface
     is undocumented and subject to change, so whenever possible you
     should avoid using `-Wp' and let the driver handle the options
     instead.

`-Xpreprocessor OPTION'
     Pass OPTION as an option to the preprocessor.  You can use this to
     supply system-specific preprocessor options which GCC does not
     know how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xpreprocessor' twice, once for the option and once for the
     argument.

`-D NAME'
     Predefine NAME as a macro, with definition `1'.

`-D NAME=DEFINITION'
     Predefine NAME as a macro, with definition DEFINITION.  The
     contents of DEFINITION are tokenized and processed as if they
     appeared during translation phase three in a `#define' directive.
     In particular, the definition will be truncated by embedded
     newline characters.

     If you are invoking the preprocessor from a shell or shell-like
     program you may need to use the shell's quoting syntax to protect
     characters such as spaces that have a meaning in the shell syntax.

     If you wish to define a function-like macro on the command line,
     write its argument list with surrounding parentheses before the
     equals sign (if any).  Parentheses are meaningful to most shells,
     so you will need to quote the option.  With `sh' and `csh',
     `-D'NAME(ARGS...)=DEFINITION'' works.

     `-D' and `-U' options are processed in the order they are given on
     the command line.  All `-imacros FILE' and `-include FILE' options
     are processed after all `-D' and `-U' options.

`-U NAME'
     Cancel any previous definition of NAME, either built in or
     provided with a `-D' option.

`-undef'
     Do not predefine any system-specific or GCC-specific macros.  The
     standard predefined macros remain defined.

`-I DIR'
     Add the directory DIR to the list of directories to be searched
     for header files.  Directories named by `-I' are searched before
     the standard system include directories.  If the directory DIR is
     a standard system include directory, the option is ignored to
     ensure that the default search order for system directories and
     the special treatment of system headers are not defeated .

`-o FILE'
     Write output to FILE.  This is the same as specifying FILE as the
     second non-option argument to `cpp'.  `gcc' has a different
     interpretation of a second non-option argument, so you must use
     `-o' to specify the output file.

`-Wall'
     Turns on all optional warnings which are desirable for normal code.
     At present this is `-Wcomment', `-Wtrigraphs', `-Wmultichar' and a
     warning about integer promotion causing a change of sign in `#if'
     expressions.  Note that many of the preprocessor's warnings are on
     by default and have no options to control them.

`-Wcomment'
`-Wcomments'
     Warn whenever a comment-start sequence `/*' appears in a `/*'
     comment, or whenever a backslash-newline appears in a `//' comment.
     (Both forms have the same effect.)

`-Wtrigraphs'
     Most trigraphs in comments cannot affect the meaning of the
     program.  However, a trigraph that would form an escaped newline
     (`??/' at the end of a line) can, by changing where the comment
     begins or ends.  Therefore, only trigraphs that would form escaped
     newlines produce warnings inside a comment.

     This option is implied by `-Wall'.  If `-Wall' is not given, this
     option is still enabled unless trigraphs are enabled.  To get
     trigraph conversion without warnings, but get the other `-Wall'
     warnings, use `-trigraphs -Wall -Wno-trigraphs'.

`-Wtraditional'
     Warn about certain constructs that behave differently in
     traditional and ISO C.  Also warn about ISO C constructs that have
     no traditional C equivalent, and problematic constructs which
     should be avoided.

`-Wimport'
     Warn the first time `#import' is used.

`-Wundef'
     Warn whenever an identifier which is not a macro is encountered in
     an `#if' directive, outside of `defined'.  Such identifiers are
     replaced with zero.

`-Wunused-macros'
     Warn about macros defined in the main file that are unused.  A
     macro is "used" if it is expanded or tested for existence at least
     once.  The preprocessor will also warn if the macro has not been
     used at the time it is redefined or undefined.

     Built-in macros, macros defined on the command line, and macros
     defined in include files are not warned about.

     *Note:* If a macro is actually used, but only used in skipped
     conditional blocks, then CPP will report it as unused.  To avoid
     the warning in such a case, you might improve the scope of the
     macro's definition by, for example, moving it into the first
     skipped block.  Alternatively, you could provide a dummy use with
     something like:

          #if defined the_macro_causing_the_warning
          #endif

`-Wendif-labels'
     Warn whenever an `#else' or an `#endif' are followed by text.
     This usually happens in code of the form

          #if FOO
          ...
          #else FOO
          ...
          #endif FOO

     The second and third `FOO' should be in comments, but often are not
     in older programs.  This warning is on by default.

`-Werror'
     Make all warnings into hard errors.  Source code which triggers
     warnings will be rejected.

`-Wsystem-headers'
     Issue warnings for code in system headers.  These are normally
     unhelpful in finding bugs in your own code, therefore suppressed.
     If you are responsible for the system library, you may want to see
     them.

`-w'
     Suppress all warnings, including those which GNU CPP issues by
     default.

`-pedantic'
     Issue all the mandatory diagnostics listed in the C standard.
     Some of them are left out by default, since they trigger
     frequently on harmless code.

`-pedantic-errors'
     Issue all the mandatory diagnostics, and make all mandatory
     diagnostics into errors.  This includes mandatory diagnostics that
     GCC issues without `-pedantic' but treats as warnings.

`-M'
     Instead of outputting the result of preprocessing, output a rule
     suitable for `make' describing the dependencies of the main source
     file.  The preprocessor outputs one `make' rule containing the
     object file name for that source file, a colon, and the names of
     all the included files, including those coming from `-include' or
     `-imacros' command line options.

     Unless specified explicitly (with `-MT' or `-MQ'), the object file
     name consists of the basename of the source file with any suffix
     replaced with object file suffix.  If there are many included
     files then the rule is split into several lines using `\'-newline.
     The rule has no commands.

     This option does not suppress the preprocessor's debug output,
     such as `-dM'.  To avoid mixing such debug output with the
     dependency rules you should explicitly specify the dependency
     output file with `-MF', or use an environment variable like
     `DEPENDENCIES_OUTPUT' (*note Environment Variables::).  Debug
     output will still be sent to the regular output stream as normal.

     Passing `-M' to the driver implies `-E', and suppresses warnings
     with an implicit `-w'.

`-MM'
     Like `-M' but do not mention header files that are found in system
     header directories, nor header files that are included, directly
     or indirectly, from such a header.

     This implies that the choice of angle brackets or double quotes in
     an `#include' directive does not in itself determine whether that
     header will appear in `-MM' dependency output.  This is a slight
     change in semantics from GCC versions 3.0 and earlier.

`-MF FILE'
     When used with `-M' or `-MM', specifies a file to write the
     dependencies to.  If no `-MF' switch is given the preprocessor
     sends the rules to the same place it would have sent preprocessed
     output.

     When used with the driver options `-MD' or `-MMD', `-MF' overrides
     the default dependency output file.

`-MG'
     In conjunction with an option such as `-M' requesting dependency
     generation, `-MG' assumes missing header files are generated files
     and adds them to the dependency list without raising an error.
     The dependency filename is taken directly from the `#include'
     directive without prepending any path.  `-MG' also suppresses
     preprocessed output, as a missing header file renders this useless.

     This feature is used in automatic updating of makefiles.

`-MP'
     This option instructs CPP to add a phony target for each dependency
     other than the main file, causing each to depend on nothing.  These
     dummy rules work around errors `make' gives if you remove header
     files without updating the `Makefile' to match.

     This is typical output:

          test.o: test.c test.h

          test.h:

`-MT TARGET'
     Change the target of the rule emitted by dependency generation.  By
     default CPP takes the name of the main input file, including any
     path, deletes any file suffix such as `.c', and appends the
     platform's usual object suffix.  The result is the target.

     An `-MT' option will set the target to be exactly the string you
     specify.  If you want multiple targets, you can specify them as a
     single argument to `-MT', or use multiple `-MT' options.

     For example, `-MT '$(objpfx)foo.o'' might give

          $(objpfx)foo.o: foo.c

`-MQ TARGET'
     Same as `-MT', but it quotes any characters which are special to
     Make.  `-MQ '$(objpfx)foo.o'' gives

          $$(objpfx)foo.o: foo.c

     The default target is automatically quoted, as if it were given
     with `-MQ'.

`-MD'
     `-MD' is equivalent to `-M -MF FILE', except that `-E' is not
     implied.  The driver determines FILE based on whether an `-o'
     option is given.  If it is, the driver uses its argument but with
     a suffix of `.d', otherwise it take the basename of the input file
     and applies a `.d' suffix.

     If `-MD' is used in conjunction with `-E', any `-o' switch is
     understood to specify the dependency output file (but *note -MF:
     dashMF.), but if used without `-E', each `-o' is understood to
     specify a target object file.

     Since `-E' is not implied, `-MD' can be used to generate a
     dependency output file as a side-effect of the compilation process.

`-MMD'
     Like `-MD' except mention only user header files, not system
     -header files.

`-fpch-deps'
     When using precompiled headers (*note Precompiled Headers::), this
     flag will cause the dependency-output flags to also list the files
     from the precompiled header's dependencies.  If not specified only
     the precompiled header would be listed and not the files that were
     used to create it because those files are not consulted when a
     precompiled header is used.

`-x c'
`-x c++'
`-x objective-c'
`-x assembler-with-cpp'
     Specify the source language: C, C++, Objective-C, or assembly.
     This has nothing to do with standards conformance or extensions;
     it merely selects which base syntax to expect.  If you give none
     of these options, cpp will deduce the language from the extension
     of the source file: `.c', `.cc', `.m', or `.S'.  Some other common
     extensions for C++ and assembly are also recognized.  If cpp does
     not recognize the extension, it will treat the file as C; this is
     the most generic mode.

     *Note:* Previous versions of cpp accepted a `-lang' option which
     selected both the language and the standards conformance level.
     This option has been removed, because it conflicts with the `-l'
     option.

`-std=STANDARD'
`-ansi'
     Specify the standard to which the code should conform.  Currently
     CPP knows about C and C++ standards; others may be added in the
     future.

     STANDARD may be one of:
    `iso9899:1990'
    `c89'
          The ISO C standard from 1990.  `c89' is the customary
          shorthand for this version of the standard.

          The `-ansi' option is equivalent to `-std=c89'.

    `iso9899:199409'
          The 1990 C standard, as amended in 1994.

    `iso9899:1999'
    `c99'
    `iso9899:199x'
    `c9x'
          The revised ISO C standard, published in December 1999.
          Before publication, this was known as C9X.

    `gnu89'
          The 1990 C standard plus GNU extensions.  This is the default.

    `gnu99'
    `gnu9x'
          The 1999 C standard plus GNU extensions.

    `c++98'
          The 1998 ISO C++ standard plus amendments.

    `gnu++98'
          The same as `-std=c++98' plus GNU extensions.  This is the
          default for C++ code.

`-I-'
     Split the include path.  Any directories specified with `-I'
     options before `-I-' are searched only for headers requested with
     `#include "FILE"'; they are not searched for `#include <FILE>'.
     If additional directories are specified with `-I' options after
     the `-I-', those directories are searched for all `#include'
     directives.

     In addition, `-I-' inhibits the use of the directory of the current
     file directory as the first search directory for `#include "FILE"'.

`-nostdinc'
     Do not search the standard system directories for header files.
     Only the directories you have specified with `-I' options (and the
     directory of the current file, if appropriate) are searched.

`-nostdinc++'
     Do not search for header files in the C++-specific standard
     directories, but do still search the other standard directories.
     (This option is used when building the C++ library.)

`-include FILE'
     Process FILE as if `#include "file"' appeared as the first line of
     the primary source file.  However, the first directory searched
     for FILE is the preprocessor's working directory _instead of_ the
     directory containing the main source file.  If not found there, it
     is searched for in the remainder of the `#include "..."' search
     chain as normal.

     If multiple `-include' options are given, the files are included
     in the order they appear on the command line.

`-imacros FILE'
     Exactly like `-include', except that any output produced by
     scanning FILE is thrown away.  Macros it defines remain defined.
     This allows you to acquire all the macros from a header without
     also processing its declarations.

     All files specified by `-imacros' are processed before all files
     specified by `-include'.

`-idirafter DIR'
     Search DIR for header files, but do it _after_ all directories
     specified with `-I' and the standard system directories have been
     exhausted.  DIR is treated as a system include directory.

`-iprefix PREFIX'
     Specify PREFIX as the prefix for subsequent `-iwithprefix'
     options.  If the prefix represents a directory, you should include
     the final `/'.

`-iwithprefix DIR'
`-iwithprefixbefore DIR'
     Append DIR to the prefix specified previously with `-iprefix', and
     add the resulting directory to the include search path.
     `-iwithprefixbefore' puts it in the same place `-I' would;
     `-iwithprefix' puts it where `-idirafter' would.

`-isystem DIR'
     Search DIR for header files, after all directories specified by
     `-I' but before the standard system directories.  Mark it as a
     system directory, so that it gets the same special treatment as is
     applied to the standard system directories.

`-fdollars-in-identifiers'
     Accept `$' in identifiers.

`-fpreprocessed'
     Indicate to the preprocessor that the input file has already been
     preprocessed.  This suppresses things like macro expansion,
     trigraph conversion, escaped newline splicing, and processing of
     most directives.  The preprocessor still recognizes and removes
     comments, so that you can pass a file preprocessed with `-C' to
     the compiler without problems.  In this mode the integrated
     preprocessor is little more than a tokenizer for the front ends.

     `-fpreprocessed' is implicit if the input file has one of the
     extensions `.i', `.ii' or `.mi'.  These are the extensions that
     GCC uses for preprocessed files created by `-save-temps'.

`-ftabstop=WIDTH'
     Set the distance between tab stops.  This helps the preprocessor
     report correct column numbers in warnings or errors, even if tabs
     appear on the line.  If the value is less than 1 or greater than
     100, the option is ignored.  The default is 8.

`-fexec-charset=CHARSET'
     Set the execution character set, used for string and character
     constants.  The default is UTF-8.  CHARSET can be any encoding
     supported by the system's `iconv' library routine.

`-fwide-exec-charset=CHARSET'
     Set the wide execution character set, used for wide string and
     character constants.  The default is UTF-32 or UTF-16, whichever
     corresponds to the width of `wchar_t'.  As with
     `-ftarget-charset', CHARSET can be any encoding supported by the
     system's `iconv' library routine; however, you will have problems
     with encodings that do not fit exactly in `wchar_t'.

`-finput-charset=CHARSET'
     Set the input character set, used for translation from the
     character set of the input file to the source character set used
     by GCC. If the locale does not specify, or GCC cannot get this
     information from the locale, the default is UTF-8. This can be
     overridden by either the locale or this command line option.
     Currently the command line option takes precedence if there's a
     conflict. CHARSET can be any encoding supported by the system's
     `iconv' library routine.

`-fworking-directory'
     Enable generation of linemarkers in the preprocessor output that
     will let the compiler know the current working directory at the
     time of preprocessing.  When this option is enabled, the
     preprocessor will emit, after the initial linemarker, a second
     linemarker with the current working directory followed by two
     slashes.  GCC will use this directory, when it's present in the
     preprocessed input, as the directory emitted as the current
     working directory in some debugging information formats.  This
     option is implicitly enabled if debugging information is enabled,
     but this can be inhibited with the negated form
     `-fno-working-directory'.  If the `-P' flag is present in the
     command line, this option has no effect, since no `#line'
     directives are emitted whatsoever.

`-fno-show-column'
     Do not print column numbers in diagnostics.  This may be necessary
     if diagnostics are being scanned by a program that does not
     understand the column numbers, such as `dejagnu'.

`-A PREDICATE=ANSWER'
     Make an assertion with the predicate PREDICATE and answer ANSWER.
     This form is preferred to the older form `-A PREDICATE(ANSWER)',
     which is still supported, because it does not use shell special
     characters.

`-A -PREDICATE=ANSWER'
     Cancel an assertion with the predicate PREDICATE and answer ANSWER.

`-dCHARS'
     CHARS is a sequence of one or more of the following characters,
     and must not be preceded by a space.  Other characters are
     interpreted by the compiler proper, or reserved for future
     versions of GCC, and so are silently ignored.  If you specify
     characters whose behavior conflicts, the result is undefined.

    `M'
          Instead of the normal output, generate a list of `#define'
          directives for all the macros defined during the execution of
          the preprocessor, including predefined macros.  This gives
          you a way of finding out what is predefined in your version
          of the preprocessor.  Assuming you have no file `foo.h', the
          command

               touch foo.h; cpp -dM foo.h

          will show all the predefined macros.

    `D'
          Like `M' except in two respects: it does _not_ include the
          predefined macros, and it outputs _both_ the `#define'
          directives and the result of preprocessing.  Both kinds of
          output go to the standard output file.

    `N'
          Like `D', but emit only the macro names, not their expansions.

    `I'
          Output `#include' directives in addition to the result of
          preprocessing.

`-P'
     Inhibit generation of linemarkers in the output from the
     preprocessor.  This might be useful when running the preprocessor
     on something that is not C code, and will be sent to a program
     which might be confused by the linemarkers.

`-C'
     Do not discard comments.  All comments are passed through to the
     output file, except for comments in processed directives, which
     are deleted along with the directive.

     You should be prepared for side effects when using `-C'; it causes
     the preprocessor to treat comments as tokens in their own right.
     For example, comments appearing at the start of what would be a
     directive line have the effect of turning that line into an
     ordinary source line, since the first token on the line is no
     longer a `#'.

`-CC'
     Do not discard comments, including during macro expansion.  This is
     like `-C', except that comments contained within macros are also
     passed through to the output file where the macro is expanded.

     In addition to the side-effects of the `-C' option, the `-CC'
     option causes all C++-style comments inside a macro to be
     converted to C-style comments.  This is to prevent later use of
     that macro from inadvertently commenting out the remainder of the
     source line.

     The `-CC' option is generally used to support lint comments.

`-traditional-cpp'
     Try to imitate the behavior of old-fashioned C preprocessors, as
     opposed to ISO C preprocessors.

`-trigraphs'
     Process trigraph sequences.  These are three-character sequences,
     all starting with `??', that are defined by ISO C to stand for
     single characters.  For example, `??/' stands for `\', so `'??/n''
     is a character constant for a newline.  By default, GCC ignores
     trigraphs, but in standard-conforming modes it converts them.  See
     the `-std' and `-ansi' options.

     The nine trigraphs and their replacements are

          Trigraph:       ??(  ??)  ??<  ??>  ??=  ??/  ??'  ??!  ??-
          Replacement:      [    ]    {    }    #    \    ^    |    ~

`-remap'
     Enable special code to work around file systems which only permit
     very short file names, such as MS-DOS.

`--help'
`--target-help'
     Print text describing all the command line options instead of
     preprocessing anything.

`-v'
     Verbose mode.  Print out GNU CPP's version number at the beginning
     of execution, and report the final form of the include path.

`-H'
     Print the name of each header file used, in addition to other
     normal activities.  Each name is indented to show how deep in the
     `#include' stack it is.  Precompiled header files are also
     printed, even if they are found to be invalid; an invalid
     precompiled header file is printed with `...x' and a valid one
     with `...!' .

`-version'
`--version'
     Print out GNU CPP's version number.  With one dash, proceed to
     preprocess as normal.  With two dashes, exit immediately.


File: gcc,  Node: Assembler Options,  Next: Link Options,  Prev: Preprocessor Options,  Up: Invoking GCC

3.12 Passing Options to the Assembler
=====================================

You can pass options to the assembler.

`-Wa,OPTION'
     Pass OPTION as an option to the assembler.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-Xassembler OPTION'
     Pass OPTION as an option to the assembler.  You can use this to
     supply system-specific assembler options which GCC does not know
     how to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xassembler' twice, once for the option and once for the argument.



File: gcc,  Node: Link Options,  Next: Directory Options,  Prev: Assembler Options,  Up: Invoking GCC

3.13 Options for Linking
========================

These options come into play when the compiler links object files into
an executable output file.  They are meaningless if the compiler is not
doing a link step.

`OBJECT-FILE-NAME'
     A file name that does not end in a special recognized suffix is
     considered to name an object file or library.  (Object files are
     distinguished from libraries by the linker according to the file
     contents.)  If linking is done, these object files are used as
     input to the linker.

`-c'
`-S'
`-E'
     If any of these options is used, then the linker is not run, and
     object file names should not be used as arguments.  *Note Overall
     Options::.

`-lLIBRARY'
`-l LIBRARY'
     Search the library named LIBRARY when linking.  (The second
     alternative with the library as a separate argument is only for
     POSIX compliance and is not recommended.)

     It makes a difference where in the command you write this option;
     the linker searches and processes libraries and object files in
     the order they are specified.  Thus, `foo.o -lz bar.o' searches
     library `z' after file `foo.o' but before `bar.o'.  If `bar.o'
     refers to functions in `z', those functions may not be loaded.

     The linker searches a standard list of directories for the library,
     which is actually a file named `libLIBRARY.a'.  The linker then
     uses this file as if it had been specified precisely by name.

     The directories searched include several standard system
     directories plus any that you specify with `-L'.

     Normally the files found this way are library files--archive files
     whose members are object files.  The linker handles an archive
     file by scanning through it for members which define symbols that
     have so far been referenced but not defined.  But if the file that
     is found is an ordinary object file, it is linked in the usual
     fashion.  The only difference between using an `-l' option and
     specifying a file name is that `-l' surrounds LIBRARY with `lib'
     and `.a' and searches several directories.

`-lobjc'
     You need this special case of the `-l' option in order to link an
     Objective-C program.

`-nostartfiles'
     Do not use the standard system startup files when linking.  The
     standard system libraries are used normally, unless `-nostdlib' or
     `-nodefaultlibs' is used.

`-nodefaultlibs'
     Do not use the standard system libraries when linking.  Only the
     libraries you specify will be passed to the linker.  The standard
     startup files are used normally, unless `-nostartfiles' is used.
     The compiler may generate calls to memcmp, memset, and memcpy for
     System V (and ISO C) environments or to bcopy and bzero for BSD
     environments.  These entries are usually resolved by entries in
     libc.  These entry points should be supplied through some other
     mechanism when this option is specified.

`-nostdlib'
     Do not use the standard system startup files or libraries when
     linking.  No startup files and only the libraries you specify will
     be passed to the linker.  The compiler may generate calls to
     memcmp, memset, and memcpy for System V (and ISO C) environments
     or to bcopy and bzero for BSD environments.  These entries are
     usually resolved by entries in libc.  These entry points should be
     supplied through some other mechanism when this option is
     specified.

     One of the standard libraries bypassed by `-nostdlib' and
     `-nodefaultlibs' is `libgcc.a', a library of internal subroutines
     that GCC uses to overcome shortcomings of particular machines, or
     special needs for some languages.  (*Note Interfacing to GCC
     Output: (gccint)Interface, for more discussion of `libgcc.a'.)  In
     most cases, you need `libgcc.a' even when you want to avoid other
     standard libraries.  In other words, when you specify `-nostdlib'
     or `-nodefaultlibs' you should usually specify `-lgcc' as well.
     This ensures that you have no unresolved references to internal GCC
     library subroutines.  (For example, `__main', used to ensure C++
     constructors will be called; *note `collect2': (gccint)Collect2.)

`-pie'
     Produce a position independent executable on targets which support
     it.  For predictable results, you must also specify the same set
     of options that were used to generate code (`-fpie', `-fPIE', or
     model suboptions) when you specify this option.

`-s'
     Remove all symbol table and relocation information from the
     executable.

`-static'
     On systems that support dynamic linking, this prevents linking
     with the shared libraries.  On other systems, this option has no
     effect.

`-shared'
     Produce a shared object which can then be linked with other
     objects to form an executable.  Not all systems support this
     option.  For predictable results, you must also specify the same
     set of options that were used to generate code (`-fpic', `-fPIC',
     or model suboptions) when you specify this option.(1)

`-shared-libgcc'
`-static-libgcc'
     On systems that provide `libgcc' as a shared library, these options
     force the use of either the shared or static version respectively.
     If no shared version of `libgcc' was built when the compiler was
     configured, these options have no effect.

     There are several situations in which an application should use the
     shared `libgcc' instead of the static version.  The most common of
     these is when the application wishes to throw and catch exceptions
     across different shared libraries.  In that case, each of the
     libraries as well as the application itself should use the shared
     `libgcc'.

     Therefore, the G++ and GCJ drivers automatically add
     `-shared-libgcc' whenever you build a shared library or a main
     executable, because C++ and Java programs typically use
     exceptions, so this is the right thing to do.

     If, instead, you use the GCC driver to create shared libraries,
     you may find that they will not always be linked with the shared
     `libgcc'.  If GCC finds, at its configuration time, that you have
     a non-GNU linker or a GNU linker that does not support option
     `--eh-frame-hdr', it will link the shared version of `libgcc' into
     shared libraries by default.  Otherwise, it will take advantage of
     the linker and optimize away the linking with the shared version
     of `libgcc', linking with the static version of libgcc by default.
     This allows exceptions to propagate through such shared
     libraries, without incurring relocation costs at library load time.

     However, if a library or main executable is supposed to throw or
     catch exceptions, you must link it using the G++ or GCJ driver, as
     appropriate for the languages used in the program, or using the
     option `-shared-libgcc', such that it is linked with the shared
     `libgcc'.

`-symbolic'
     Bind references to global symbols when building a shared object.
     Warn about any unresolved references (unless overridden by the
     link editor option `-Xlinker -z -Xlinker defs').  Only a few
     systems support this option.

`-Xlinker OPTION'
     Pass OPTION as an option to the linker.  You can use this to
     supply system-specific linker options which GCC does not know how
     to recognize.

     If you want to pass an option that takes an argument, you must use
     `-Xlinker' twice, once for the option and once for the argument.
     For example, to pass `-assert definitions', you must write
     `-Xlinker -assert -Xlinker definitions'.  It does not work to write
     `-Xlinker "-assert definitions"', because this passes the entire
     string as a single argument, which is not what the linker expects.

`-Wl,OPTION'
     Pass OPTION as an option to the linker.  If OPTION contains
     commas, it is split into multiple options at the commas.

`-u SYMBOL'
     Pretend the symbol SYMBOL is undefined, to force linking of
     library modules to define it.  You can use `-u' multiple times with
     different symbols to force loading of additional library modules.

 ---------- Footnotes ----------

 (1) On some systems, `gcc -shared' needs to build supplementary stub
code for constructors to work.  On multi-libbed systems, `gcc -shared'
must select the correct support libraries to link against.  Failing to
supply the correct flags may lead to subtle defects.  Supplying them in
cases where they are not necessary is innocuous.


File: gcc,  Node: Directory Options,  Next: Spec Files,  Prev: Link Options,  Up: Invoking GCC

3.14 Options for Directory Search
=================================

These options specify directories to search for header files, for
libraries and for parts of the compiler:

`-IDIR'
     Add the directory DIR to the head of the list of directories to be
     searched for header files.  This can be used to override a system
     header file, substituting your own version, since these
     directories are searched before the system header file
     directories.  However, you should not use this option to add
     directories that contain vendor-supplied system header files (use
     `-isystem' for that).  If you use more than one `-I' option, the
     directories are scanned in left-to-right order; the standard
     system directories come after.

     If a standard system include directory, or a directory specified
     with `-isystem', is also specified with `-I', the `-I' option will
     be ignored.  The directory will still be searched but as a system
     directory at its normal position in the system include chain.
     This is to ensure that GCC's procedure to fix buggy system headers
     and the ordering for the include_next directive are not
     inadvertently changed.  If you really need to change the search
     order for system directories, use the `-nostdinc' and/or
     `-isystem' options.

`-I-'
     Any directories you specify with `-I' options before the `-I-'
     option are searched only for the case of `#include "FILE"'; they
     are not searched for `#include <FILE>'.

     If additional directories are specified with `-I' options after
     the `-I-', these directories are searched for all `#include'
     directives.  (Ordinarily _all_ `-I' directories are used this way.)

     In addition, the `-I-' option inhibits the use of the current
     directory (where the current input file came from) as the first
     search directory for `#include "FILE"'.  There is no way to
     override this effect of `-I-'.  With `-I.' you can specify
     searching the directory which was current when the compiler was
     invoked.  That is not exactly the same as what the preprocessor
     does by default, but it is often satisfactory.

     `-I-' does not inhibit the use of the standard system directories
     for header files.  Thus, `-I-' and `-nostdinc' are independent.

`-LDIR'
     Add directory DIR to the list of directories to be searched for
     `-l'.

`-BPREFIX'
     This option specifies where to find the executables, libraries,
     include files, and data files of the compiler itself.

     The compiler driver program runs one or more of the subprograms
     `cpp', `cc1', `as' and `ld'.  It tries PREFIX as a prefix for each
     program it tries to run, both with and without `MACHINE/VERSION/'
     (*note Target Options::).

     For each subprogram to be run, the compiler driver first tries the
     `-B' prefix, if any.  If that name is not found, or if `-B' was
     not specified, the driver tries two standard prefixes, which are
     `/usr/lib/gcc/' and `/usr/local/lib/gcc/'.  If neither of those
     results in a file name that is found, the unmodified program name
     is searched for using the directories specified in your `PATH'
     environment variable.

     The compiler will check to see if the path provided by the `-B'
     refers to a directory, and if necessary it will add a directory
     separator character at the end of the path.

     `-B' prefixes that effectively specify directory names also apply
     to libraries in the linker, because the compiler translates these
     options into `-L' options for the linker.  They also apply to
     includes files in the preprocessor, because the compiler
     translates these options into `-isystem' options for the
     preprocessor.  In this case, the compiler appends `include' to the
     prefix.

     The run-time support file `libgcc.a' can also be searched for using
     the `-B' prefix, if needed.  If it is not found there, the two
     standard prefixes above are tried, and that is all.  The file is
     left out of the link if it is not found by those means.

     Another way to specify a prefix much like the `-B' prefix is to use
     the environment variable `GCC_EXEC_PREFIX'.  *Note Environment
     Variables::.

     As a special kludge, if the path provided by `-B' is
     `[dir/]stageN/', where N is a number in the range 0 to 9, then it
     will be replaced by `[dir/]include'.  This is to help with
     boot-strapping the compiler.

`-specs=FILE'
     Process FILE after the compiler reads in the standard `specs'
     file, in order to override the defaults that the `gcc' driver
     program uses when determining what switches to pass to `cc1',
     `cc1plus', `as', `ld', etc.  More than one `-specs=FILE' can be
     specified on the command line, and they are processed in order,
     from left to right.


File: gcc,  Node: Spec Files,  Next: Target Options,  Prev: Directory Options,  Up: Invoking GCC

3.15 Specifying subprocesses and the switches to pass to them
=============================================================

`gcc' is a driver program.  It performs its job by invoking a sequence
of other programs to do the work of compiling, assembling and linking.
GCC interprets its command-line parameters and uses these to deduce
which programs it should invoke, and which command-line options it
ought to place on their command lines.  This behavior is controlled by
"spec strings".  In most cases there is one spec string for each
program that GCC can invoke, but a few programs have multiple spec
strings to control their behavior.  The spec strings built into GCC can
be overridden by using the `-specs=' command-line switch to specify a
spec file.

 "Spec files" are plaintext files that are used to construct spec
strings.  They consist of a sequence of directives separated by blank
lines.  The type of directive is determined by the first non-whitespace
character on the line and it can be one of the following:

`%COMMAND'
     Issues a COMMAND to the spec file processor.  The commands that can
     appear here are:

    `%include <FILE>'
          Search for FILE and insert its text at the current point in
          the specs file.

    `%include_noerr <FILE>'
          Just like `%include', but do not generate an error message if
          the include file cannot be found.

    `%rename OLD_NAME NEW_NAME'
          Rename the spec string OLD_NAME to NEW_NAME.


`*[SPEC_NAME]:'
     This tells the compiler to create, override or delete the named
     spec string.  All lines after this directive up to the next
     directive or blank line are considered to be the text for the spec
     string.  If this results in an empty string then the spec will be
     deleted.  (Or, if the spec did not exist, then nothing will
     happened.)  Otherwise, if the spec does not currently exist a new
     spec will be created.  If the spec does exist then its contents
     will be overridden by the text of this directive, unless the first
     character of that text is the `+' character, in which case the
     text will be appended to the spec.

`[SUFFIX]:'
     Creates a new `[SUFFIX] spec' pair.  All lines after this directive
     and up to the next directive or blank line are considered to make
     up the spec string for the indicated suffix.  When the compiler
     encounters an input file with the named suffix, it will processes
     the spec string in order to work out how to compile that file.
     For example:

          .ZZ:
          z-compile -input %i

     This says that any input file whose name ends in `.ZZ' should be
     passed to the program `z-compile', which should be invoked with the
     command-line switch `-input' and with the result of performing the
     `%i' substitution.  (See below.)

     As an alternative to providing a spec string, the text that
     follows a suffix directive can be one of the following:

    `@LANGUAGE'
          This says that the suffix is an alias for a known LANGUAGE.
          This is similar to using the `-x' command-line switch to GCC
          to specify a language explicitly.  For example:

               .ZZ:
               @c++

          Says that .ZZ files are, in fact, C++ source files.

    `#NAME'
          This causes an error messages saying:

               NAME compiler not installed on this system.

     GCC already has an extensive list of suffixes built into it.  This
     directive will add an entry to the end of the list of suffixes, but
     since the list is searched from the end backwards, it is
     effectively possible to override earlier entries using this
     technique.


 GCC has the following spec strings built into it.  Spec files can
override these strings or create their own.  Note that individual
targets can also add their own spec strings to this list.

     asm          Options to pass to the assembler
     asm_final    Options to pass to the assembler post-processor
     cpp          Options to pass to the C preprocessor
     cc1          Options to pass to the C compiler
     cc1plus      Options to pass to the C++ compiler
     endfile      Object files to include at the end of the link
     link         Options to pass to the linker
     lib          Libraries to include on the command line to the linker
     libgcc       Decides which GCC support library to pass to the linker
     linker       Sets the name of the linker
     predefines   Defines to be passed to the C preprocessor
     signed_char  Defines to pass to CPP to say whether `char' is signed
                  by default
     startfile    Object files to include at the start of the link

 Here is a small example of a spec file:

     %rename lib                 old_lib

     *lib:
     --start-group -lgcc -lc -leval1 --end-group %(old_lib)

 This example renames the spec called `lib' to `old_lib' and then
overrides the previous definition of `lib' with a new one.  The new
definition adds in some extra command-line options before including the
text of the old definition.

 "Spec strings" are a list of command-line options to be passed to their
corresponding program.  In addition, the spec strings can contain
`%'-prefixed sequences to substitute variable text or to conditionally
insert text into the command line.  Using these constructs it is
possible to generate quite complex command lines.

 Here is a table of all defined `%'-sequences for spec strings.  Note
that spaces are not generated automatically around the results of
expanding these sequences.  Therefore you can concatenate them together
or combine them with constant text in a single argument.

`%%'
     Substitute one `%' into the program name or argument.

`%i'
     Substitute the name of the input file being processed.

`%b'
     Substitute the basename of the input file being processed.  This
     is the substring up to (and not including) the last period and not
     including the directory.

`%B'
     This is the same as `%b', but include the file suffix (text after
     the last period).

`%d'
     Marks the argument containing or following the `%d' as a temporary
     file name, so that that file will be deleted if GCC exits
     successfully.  Unlike `%g', this contributes no text to the
     argument.

`%gSUFFIX'
     Substitute a file name that has suffix SUFFIX and is chosen once
     per compilation, and mark the argument in the same way as `%d'.
     To reduce exposure to denial-of-service attacks, the file name is
     now chosen in a way that is hard to predict even when previously
     chosen file names are known.  For example, `%g.s ... %g.o ... %g.s'
     might turn into `ccUVUUAU.s ccXYAXZ12.o ccUVUUAU.s'.  SUFFIX
     matches the regexp `[.A-Za-z]*' or the special string `%O', which
     is treated exactly as if `%O' had been preprocessed.  Previously,
     `%g' was simply substituted with a file name chosen once per
     compilation, without regard to any appended suffix (which was
     therefore treated just like ordinary text), making such attacks
     more likely to succeed.

`%uSUFFIX'
     Like `%g', but generates a new temporary file name even if
     `%uSUFFIX' was already seen.

`%USUFFIX'
     Substitutes the last file name generated with `%uSUFFIX',
     generating a new one if there is no such last file name.  In the
     absence of any `%uSUFFIX', this is just like `%gSUFFIX', except
     they don't share the same suffix _space_, so `%g.s ... %U.s ...
     %g.s ... %U.s' would involve the generation of two distinct file
     names, one for each `%g.s' and another for each `%U.s'.
     Previously, `%U' was simply substituted with a file name chosen
     for the previous `%u', without regard to any appended suffix.

`%jSUFFIX'
     Substitutes the name of the `HOST_BIT_BUCKET', if any, and if it is
     writable, and if save-temps is off; otherwise, substitute the name
     of a temporary file, just like `%u'.  This temporary file is not
     meant for communication between processes, but rather as a junk
     disposal mechanism.

`%|SUFFIX'
`%mSUFFIX'
     Like `%g', except if `-pipe' is in effect.  In that case `%|'
     substitutes a single dash and `%m' substitutes nothing at all.
     These are the two most common ways to instruct a program that it
     should read from standard input or write to standard output.  If
     you need something more elaborate you can use an `%{pipe:`X'}'
     construct: see for example `f/lang-specs.h'.

`%.SUFFIX'
     Substitutes .SUFFIX for the suffixes of a matched switch's args
     when it is subsequently output with `%*'.  SUFFIX is terminated by
     the next space or %.

`%w'
     Marks the argument containing or following the `%w' as the
     designated output file of this compilation.  This puts the argument
     into the sequence of arguments that `%o' will substitute later.

`%o'
     Substitutes the names of all the output files, with spaces
     automatically placed around them.  You should write spaces around
     the `%o' as well or the results are undefined.  `%o' is for use in
     the specs for running the linker.  Input files whose names have no
     recognized suffix are not compiled at all, but they are included
     among the output files, so they will be linked.

`%O'
     Substitutes the suffix for object files.  Note that this is
     handled specially when it immediately follows `%g, %u, or %U',
     because of the need for those to form complete file names.  The
     handling is such that `%O' is treated exactly as if it had already
     been substituted, except that `%g, %u, and %U' do not currently
     support additional SUFFIX characters following `%O' as they would
     following, for example, `.o'.

`%p'
     Substitutes the standard macro predefinitions for the current
     target machine.  Use this when running `cpp'.

`%P'
     Like `%p', but puts `__' before and after the name of each
     predefined macro, except for macros that start with `__' or with
     `_L', where L is an uppercase letter.  This is for ISO C.

`%I'
     Substitute any of `-iprefix' (made from `GCC_EXEC_PREFIX'),
     `-isysroot' (made from `TARGET_SYSTEM_ROOT'), and `-isystem' (made
     from `COMPILER_PATH' and `-B' options) as necessary.

`%s'
     Current argument is the name of a library or startup file of some
     sort.  Search for that file in a standard list of directories and
     substitute the full name found.

`%eSTR'
     Print STR as an error message.  STR is terminated by a newline.
     Use this when inconsistent options are detected.

`%(NAME)'
     Substitute the contents of spec string NAME at this point.

`%[NAME]'
     Like `%(...)' but put `__' around `-D' arguments.

`%x{OPTION}'
     Accumulate an option for `%X'.

`%X'
     Output the accumulated linker options specified by `-Wl' or a `%x'
     spec string.

`%Y'
     Output the accumulated assembler options specified by `-Wa'.

`%Z'
     Output the accumulated preprocessor options specified by `-Wp'.

`%a'
     Process the `asm' spec.  This is used to compute the switches to
     be passed to the assembler.

`%A'
     Process the `asm_final' spec.  This is a spec string for passing
     switches to an assembler post-processor, if such a program is
     needed.

`%l'
     Process the `link' spec.  This is the spec for computing the
     command line passed to the linker.  Typically it will make use of
     the `%L %G %S %D and %E' sequences.

`%D'
     Dump out a `-L' option for each directory that GCC believes might
     contain startup files.  If the target supports multilibs then the
     current multilib directory will be prepended to each of these
     paths.

`%M'
     Output the multilib directory with directory separators replaced
     with `_'.  If multilib directories are not set, or the multilib
     directory is `.' then this option emits nothing.

`%L'
     Process the `lib' spec.  This is a spec string for deciding which
     libraries should be included on the command line to the linker.

`%G'
     Process the `libgcc' spec.  This is a spec string for deciding
     which GCC support library should be included on the command line
     to the linker.

`%S'
     Process the `startfile' spec.  This is a spec for deciding which
     object files should be the first ones passed to the linker.
     Typically this might be a file named `crt0.o'.

`%E'
     Process the `endfile' spec.  This is a spec string that specifies
     the last object files that will be passed to the linker.

`%C'
     Process the `cpp' spec.  This is used to construct the arguments
     to be passed to the C preprocessor.

`%c'
     Process the `signed_char' spec.  This is intended to be used to
     tell cpp whether a char is signed.  It typically has the
     definition:
          %{funsigned-char:-D__CHAR_UNSIGNED__}

`%1'
     Process the `cc1' spec.  This is used to construct the options to
     be passed to the actual C compiler (`cc1').

`%2'
     Process the `cc1plus' spec.  This is used to construct the options
     to be passed to the actual C++ compiler (`cc1plus').

`%*'
     Substitute the variable part of a matched option.  See below.
     Note that each comma in the substituted string is replaced by a
     single space.

`%<`S''
     Remove all occurrences of `-S' from the command line.  Note--this
     command is position dependent.  `%' commands in the spec string
     before this one will see `-S', `%' commands in the spec string
     after this one will not.

`%:FUNCTION(ARGS)'
     Call the named function FUNCTION, passing it ARGS.  ARGS is first
     processed as a nested spec string, then split into an argument
     vector in the usual fashion.  The function returns a string which
     is processed as if it had appeared literally as part of the
     current spec.

     The following built-in spec functions are provided:

    ``if-exists''
          The `if-exists' spec function takes one argument, an absolute
          pathname to a file.  If the file exists, `if-exists' returns
          the pathname.  Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) crtbegin%O%s

    ``if-exists-else''
          The `if-exists-else' spec function is similar to the
          `if-exists' spec function, except that it takes two
          arguments.  The first argument is an absolute pathname to a
          file.  If the file exists, `if-exists-else' returns the
          pathname.  If it does not exist, it returns the second
          argument.  This way, `if-exists-else' can be used to select
          one file or another, based on the existence of the first.
          Here is a small example of its usage:

               *startfile:
               crt0%O%s %:if-exists(crti%O%s) \
               %:if-exists-else(crtbeginT%O%s crtbegin%O%s)

`%{`S'}'
     Substitutes the `-S' switch, if that switch was given to GCC.  If
     that switch was not specified, this substitutes nothing.  Note that
     the leading dash is omitted when specifying this option, and it is
     automatically inserted if the substitution is performed.  Thus the
     spec string `%{foo}' would match the command-line option `-foo'
     and would output the command line option `-foo'.

`%W{`S'}'
     Like %{`S'} but mark last argument supplied within as a file to be
     deleted on failure.

`%{`S'*}'
     Substitutes all the switches specified to GCC whose names start
     with `-S', but which also take an argument.  This is used for
     switches like `-o', `-D', `-I', etc.  GCC considers `-o foo' as
     being one switch whose names starts with `o'.  %{o*} would
     substitute this text, including the space.  Thus two arguments
     would be generated.

`%{`S'*&`T'*}'
     Like %{`S'*}, but preserve order of `S' and `T' options (the order
     of `S' and `T' in the spec is not significant).  There can be any
     number of ampersand-separated variables; for each the wild card is
     optional.  Useful for CPP as `%{D*&U*&A*}'.

`%{`S':`X'}'
     Substitutes `X', if the `-S' switch was given to GCC.

`%{!`S':`X'}'
     Substitutes `X', if the `-S' switch was _not_ given to GCC.

`%{`S'*:`X'}'
     Substitutes `X' if one or more switches whose names start with
     `-S' are specified to GCC.  Normally `X' is substituted only once,
     no matter how many such switches appeared.  However, if `%*'
     appears somewhere in `X', then `X' will be substituted once for
     each matching switch, with the `%*' replaced by the part of that
     switch that matched the `*'.

`%{.`S':`X'}'
     Substitutes `X', if processing a file with suffix `S'.

`%{!.`S':`X'}'
     Substitutes `X', if _not_ processing a file with suffix `S'.

`%{`S'|`P':`X'}'
     Substitutes `X' if either `-S' or `-P' was given to GCC.  This may
     be combined with `!', `.', and `*' sequences as well, although
     they have a stronger binding than the `|'.  If `%*' appears in
     `X', all of the alternatives must be starred, and only the first
     matching alternative is substituted.

     For example, a spec string like this:

          %{.c:-foo} %{!.c:-bar} %{.c|d:-baz} %{!.c|d:-boggle}

     will output the following command-line options from the following
     input command-line options:

          fred.c        -foo -baz
          jim.d         -bar -boggle
          -d fred.c     -foo -baz -boggle
          -d jim.d      -bar -baz -boggle

`%{S:X; T:Y; :D}'
     If `S' was given to GCC, substitutes `X'; else if `T' was given to
     GCC, substitutes `Y'; else substitutes `D'.  There can be as many
     clauses as you need.  This may be combined with `.', `!', `|', and
     `*' as needed.


 The conditional text `X' in a %{`S':`X'} or similar construct may
contain other nested `%' constructs or spaces, or even newlines.  They
are processed as usual, as described above.  Trailing white space in
`X' is ignored.  White space may also appear anywhere on the left side
of the colon in these constructs, except between `.' or `*' and the
corresponding word.

 The `-O', `-f', `-m', and `-W' switches are handled specifically in
these constructs.  If another value of `-O' or the negated form of a
`-f', `-m', or `-W' switch is found later in the command line, the
earlier switch value is ignored, except with {`S'*} where `S' is just
one letter, which passes all matching options.

 The character `|' at the beginning of the predicate text is used to
indicate that a command should be piped to the following command, but
only if `-pipe' is specified.

 It is built into GCC which switches take arguments and which do not.
(You might think it would be useful to generalize this to allow each
compiler's spec to say which switches take arguments.  But this cannot
be done in a consistent fashion.  GCC cannot even decide which input
files have been specified without knowing which switches take arguments,
and it must know which input files to compile in order to tell which
compilers to run).

 GCC also knows implicitly that arguments starting in `-l' are to be
treated as compiler output files, and passed to the linker in their
proper position among the other output files.


File: gcc,  Node: Target Options,  Next: Submodel Options,  Prev: Spec Files,  Up: Invoking GCC

3.16 Specifying Target Machine and Compiler Version
===================================================

The usual way to run GCC is to run the executable called `gcc', or
`<machine>-gcc' when cross-compiling, or `<machine>-gcc-<version>' to
run a version other than the one that was installed last.  Sometimes
this is inconvenient, so GCC provides options that will switch to
another cross-compiler or version.

`-b MACHINE'
     The argument MACHINE specifies the target machine for compilation.

     The value to use for MACHINE is the same as was specified as the
     machine type when configuring GCC as a cross-compiler.  For
     example, if a cross-compiler was configured with `configure
     i386v', meaning to compile for an 80386 running System V, then you
     would specify `-b i386v' to run that cross compiler.

`-V VERSION'
     The argument VERSION specifies which version of GCC to run.  This
     is useful when multiple versions are installed.  For example,
     VERSION might be `2.0', meaning to run GCC version 2.0.

 The `-V' and `-b' options work by running the
`<machine>-gcc-<version>' executable, so there's no real reason to use
them if you can just run that directly.


File: gcc,  Node: Submodel Options,  Next: Code Gen Options,  Prev: Target Options,  Up: Invoking GCC

3.17 Hardware Models and Configurations
=======================================

Earlier we discussed the standard option `-b' which chooses among
different installed compilers for completely different target machines,
such as VAX vs. 68000 vs. 80386.

 In addition, each of these target machine types can have its own
special options, starting with `-m', to choose among various hardware
models or configurations--for example, 68010 vs 68020, floating
coprocessor or none.  A single installed version of the compiler can
compile for any model or configuration, according to the options
specified.

 Some configurations of the compiler also support additional special
options, usually for compatibility with other compilers on the same
platform.

 These options are defined by the macro `TARGET_SWITCHES' in the
machine description.  The default for the options is also defined by
that macro, which enables you to change the defaults.

* Menu:

* M680x0 Options::
* M68hc1x Options::
* VAX Options::
* SPARC Options::
* ARM Options::
* MN10300 Options::
* M32R/D Options::
* RS/6000 and PowerPC Options::
* Darwin Options::
* MIPS Options::
* i386 and x86-64 Options::
* HPPA Options::
* Intel 960 Options::
* DEC Alpha Options::
* DEC Alpha/VMS Options::
* H8/300 Options::
* SH Options::
* System V Options::
* TMS320C3x/C4x Options::
* V850 Options::
* ARC Options::
* NS32K Options::
* AVR Options::
* MCore Options::
* IA-64 Options::
* D30V Options::
* S/390 and zSeries Options::
* CRIS Options::
* MMIX Options::
* PDP-11 Options::
* Xstormy16 Options::
* Xtensa Options::
* FRV Options::


File: gcc,  Node: M680x0 Options,  Next: M68hc1x Options,  Up: Submodel Options

3.17.1 M680x0 Options
---------------------

These are the `-m' options defined for the 68000 series.  The default
values for these options depends on which style of 68000 was selected
when the compiler was configured; the defaults for the most common
choices are given below.

`-m68000'
`-mc68000'
     Generate output for a 68000.  This is the default when the
     compiler is configured for 68000-based systems.

     Use this option for microcontrollers with a 68000 or EC000 core,
     including the 68008, 68302, 68306, 68307, 68322, 68328 and 68356.

`-m68020'
`-mc68020'
     Generate output for a 68020.  This is the default when the
     compiler is configured for 68020-based systems.

`-m68881'
     Generate output containing 68881 instructions for floating point.
     This is the default for most 68020 systems unless `--nfp' was
     specified when the compiler was configured.

`-m68030'
     Generate output for a 68030.  This is the default when the
     compiler is configured for 68030-based systems.

`-m68040'
     Generate output for a 68040.  This is the default when the
     compiler is configured for 68040-based systems.

     This option inhibits the use of 68881/68882 instructions that have
     to be emulated by software on the 68040.  Use this option if your
     68040 does not have code to emulate those instructions.

`-m68060'
     Generate output for a 68060.  This is the default when the
     compiler is configured for 68060-based systems.

     This option inhibits the use of 68020 and 68881/68882 instructions
     that have to be emulated by software on the 68060.  Use this
     option if your 68060 does not have code to emulate those
     instructions.

`-mcpu32'
     Generate output for a CPU32.  This is the default when the
     compiler is configured for CPU32-based systems.

     Use this option for microcontrollers with a CPU32 or CPU32+ core,
     including the 68330, 68331, 68332, 68333, 68334, 68336, 68340,
     68341, 68349 and 68360.

`-m5200'
     Generate output for a 520X "coldfire" family cpu.  This is the
     default when the compiler is configured for 520X-based systems.

     Use this option for microcontroller with a 5200 core, including
     the MCF5202, MCF5203, MCF5204 and MCF5202.

`-m68020-40'
     Generate output for a 68040, without using any of the new
     instructions.  This results in code which can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated
     on the 68040.

`-m68020-60'
     Generate output for a 68060, without using any of the new
     instructions.  This results in code which can run relatively
     efficiently on either a 68020/68881 or a 68030 or a 68040.  The
     generated code does use the 68881 instructions that are emulated
     on the 68060.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all m68k
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this can't be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.  The embedded
     targets `m68k-*-aout' and `m68k-*-coff' do provide software
     floating point support.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.

`-mnobitfield'
     Do not use the bit-field instructions.  The `-m68000', `-mcpu32'
     and `-m5200' options imply `-mnobitfield'.

`-mbitfield'
     Do use the bit-field instructions.  The `-m68020' option implies
     `-mbitfield'.  This is the default if you use a configuration
     designed for a 68020.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the `rtd'
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

     The `rtd' instruction is supported by the 68010, 68020, 68030,
     68040, 68060 and CPU32 processors, but not by the 68000 or 5200.

`-malign-int'
`-mno-align-int'
     Control whether GCC aligns `int', `long', `long long', `float',
     `double', and `long double' variables on a 32-bit boundary
     (`-malign-int') or a 16-bit boundary (`-mno-align-int').  Aligning
     variables on 32-bit boundaries produces code that runs somewhat
     faster on processors with 32-bit busses at the expense of more
     memory.

     *Warning:* if you use the `-malign-int' switch, GCC will align
     structures containing the above types  differently than most
     published application binary interface specifications for the m68k.

`-mpcrel'
     Use the pc-relative addressing mode of the 68000 directly, instead
     of using a global offset table.  At present, this option implies
     `-fpic', allowing at most a 16-bit offset for pc-relative
     addressing.  `-fPIC' is not presently supported with `-mpcrel',
     though this could be supported for 68020 and higher processors.

`-mno-strict-align'
`-mstrict-align'
     Do not (do) assume that unaligned memory references will be
     handled by the system.

`-msep-data'
     Generate code that allows the data segment to be located in a
     different area of memory from the text segment.  This allows for
     execute in place in an environment without virtual memory
     management.  This option implies -fPIC.

`-mno-sep-data'
     Generate code that assumes that the data segment follows the text
     segment.  This is the default.

`-mid-shared-library'
     Generate code that supports shared libraries via the library ID
     method.  This allows for execute in place and shared libraries in
     an environment without virtual memory management.  This option
     implies -fPIC.

`-mno-id-shared-library'
     Generate code that doesn't assume ID based shared libraries are
     being used.  This is the default.

`-mshared-library-id=n'
     Specified the identification number of the ID based shared library
     being compiled.  Specifying a value of 0 will generate more
     compact code, specifying other values will force the allocation of
     that number to the current library but is no more space or time
     efficient than omitting this option.



File: gcc,  Node: M68hc1x Options,  Next: VAX Options,  Prev: M680x0 Options,  Up: Submodel Options

3.17.2 M68hc1x Options
----------------------

These are the `-m' options defined for the 68hc11 and 68hc12
microcontrollers.  The default values for these options depends on
which style of microcontroller was selected when the compiler was
configured; the defaults for the most common choices are given below.

`-m6811'
`-m68hc11'
     Generate output for a 68HC11.  This is the default when the
     compiler is configured for 68HC11-based systems.

`-m6812'
`-m68hc12'
     Generate output for a 68HC12.  This is the default when the
     compiler is configured for 68HC12-based systems.

`-m68S12'
`-m68hcs12'
     Generate output for a 68HCS12.

`-mauto-incdec'
     Enable the use of 68HC12 pre and post auto-increment and
     auto-decrement addressing modes.

`-minmax'
`-nominmax'
     Enable the use of 68HC12 min and max instructions.

`-mlong-calls'
`-mno-long-calls'
     Treat all calls as being far away (near).  If calls are assumed to
     be far away, the compiler will use the `call' instruction to call
     a function and the `rtc' instruction for returning.

`-mshort'
     Consider type `int' to be 16 bits wide, like `short int'.

`-msoft-reg-count=COUNT'
     Specify the number of pseudo-soft registers which are used for the
     code generation.  The maximum number is 32.  Using more pseudo-soft
     register may or may not result in better code depending on the
     program.  The default is 4 for 68HC11 and 2 for 68HC12.



File: gcc,  Node: VAX Options,  Next: SPARC Options,  Prev: M68hc1x Options,  Up: Submodel Options

3.17.3 VAX Options
------------------

These `-m' options are defined for the VAX:

`-munix'
     Do not output certain jump instructions (`aobleq' and so on) that
     the Unix assembler for the VAX cannot handle across long ranges.

`-mgnu'
     Do output those jump instructions, on the assumption that you will
     assemble with the GNU assembler.

`-mg'
     Output code for g-format floating point numbers instead of
     d-format.


File: gcc,  Node: SPARC Options,  Next: ARM Options,  Prev: VAX Options,  Up: Submodel Options

3.17.4 SPARC Options
--------------------

These `-m' options are supported on the SPARC:

`-mno-app-regs'
`-mapp-regs'
     Specify `-mapp-regs' to generate output using the global registers
     2 through 4, which the SPARC SVR4 ABI reserves for applications.
     This is the default.

     To be fully SVR4 ABI compliant at the cost of some performance
     loss, specify `-mno-app-regs'.  You should compile libraries and
     system software with this option.

`-mfpu'
`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default.

`-mno-fpu'
`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all SPARC
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this cannot be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.  The embedded
     targets `sparc-*-aout' and `sparclite-*-*' do provide software
     floating point support.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GCC, with `-msoft-float' in order for this
     to work.

`-mhard-quad-float'
     Generate output containing quad-word (long double) floating point
     instructions.

`-msoft-quad-float'
     Generate output containing library calls for quad-word (long
     double) floating point instructions.  The functions called are
     those specified in the SPARC ABI.  This is the default.

     As of this writing, there are no SPARC implementations that have
     hardware support for the quad-word floating point instructions.
     They all invoke a trap handler for one of these instructions, and
     then the trap handler emulates the effect of the instruction.
     Because of the trap handler overhead, this is much slower than
     calling the ABI library routines.  Thus the `-msoft-quad-float'
     option is the default.

`-mno-flat'
`-mflat'
     With `-mflat', the compiler does not generate save/restore
     instructions and will use a "flat" or single register window
     calling convention.  This model uses %i7 as the frame pointer and
     is compatible with the normal register window model.  Code from
     either may be intermixed.  The local registers and the input
     registers (0-5) are still treated as "call saved" registers and
     will be saved on the stack as necessary.

     With `-mno-flat' (the default), the compiler emits save/restore
     instructions (except for leaf functions) and is the normal mode of
     operation.

     These options are deprecated and will be deleted in a future GCC
     release.

`-mno-unaligned-doubles'
`-munaligned-doubles'
     Assume that doubles have 8 byte alignment.  This is the default.

     With `-munaligned-doubles', GCC assumes that doubles have 8 byte
     alignment only if they are contained in another type, or if they
     have an absolute address.  Otherwise, it assumes they have 4 byte
     alignment.  Specifying this option avoids some rare compatibility
     problems with code generated by other compilers.  It is not the
     default because it results in a performance loss, especially for
     floating point code.

`-mno-faster-structs'
`-mfaster-structs'
     With `-mfaster-structs', the compiler assumes that structures
     should have 8 byte alignment.  This enables the use of pairs of
     `ldd' and `std' instructions for copies in structure assignment,
     in place of twice as many `ld' and `st' pairs.  However, the use
     of this changed alignment directly violates the SPARC ABI.  Thus,
     it's intended only for use on targets where the developer
     acknowledges that their resulting code will not be directly in
     line with the rules of the ABI.

`-mimpure-text'
     `-mimpure-text', used in addition to `-shared', tells the compiler
     to not pass `-z text' to the linker when linking a shared object.
     Using this option, you can link position-dependent code into a
     shared object.

     `-mimpure-text' suppresses the "relocations remain against
     allocatable but non-writable sections" linker error message.
     However, the necessary relocations will trigger copy-on-write, and
     the shared object is not actually shared across processes.
     Instead of using `-mimpure-text', you should compile all source
     code with `-fpic' or `-fPIC'.

     This option is only available on SunOS and Solaris.

`-mv8'
`-msparclite'
     These two options select variations on the SPARC architecture.
     These options are deprecated and will be deleted in a future GCC
     release.  They have been replaced with `-mcpu=xxx'.

`-mcypress'
`-msupersparc'
`-mf930'
`-mf934'
     These four options select the processor for which the code is
     optimized.  These options are deprecated and will be deleted in a
     future GCC release.  They have been replaced with `-mcpu=xxx'.

`-mcpu=CPU_TYPE'
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are `v7', `cypress', `v8', `supersparc', `sparclite',
     `f930', `f934', `hypersparc', `sparclite86x', `sparclet',
     `tsc701', `v9', `ultrasparc', and `ultrasparc3'.

     Default instruction scheduling parameters are used for values that
     select an architecture and not an implementation.  These are `v7',
     `v8', `sparclite', `sparclet', `v9'.

     Here is a list of each supported architecture and their supported
     implementations.

              v7:             cypress
              v8:             supersparc, hypersparc
              sparclite:      f930, f934, sparclite86x
              sparclet:       tsc701
              v9:             ultrasparc, ultrasparc3

     By default (unless configured otherwise), GCC generates code for
     the V7 variant of the SPARC architecture.  With `-mcpu=cypress',
     the compiler additionally optimizes it for the Cypress CY7C602
     chip, as used in the SPARCStation/SPARCServer 3xx series.  This is
     also appropriate for the older SPARCStation 1, 2, IPX etc.

     With `-mcpu=v8', GCC generates code for the V8 variant of the SPARC
     architecture.  The only difference from V7 code is that the
     compiler emits the integer multiply and integer divide
     instructions which exist in SPARC-V8 but not in SPARC-V7.  With
     `-mcpu=supersparc', the compiler additionally optimizes it for the
     SuperSPARC chip, as used in the SPARCStation 10, 1000 and 2000
     series.

     With `-mcpu=sparclite', GCC generates code for the SPARClite
     variant of the SPARC architecture.  This adds the integer
     multiply, integer divide step and scan (`ffs') instructions which
     exist in SPARClite but not in SPARC-V7.  With `-mcpu=f930', the
     compiler additionally optimizes it for the Fujitsu MB86930 chip,
     which is the original SPARClite, with no FPU.  With `-mcpu=f934',
     the compiler additionally optimizes it for the Fujitsu MB86934
     chip, which is the more recent SPARClite with FPU.

     With `-mcpu=sparclet', GCC generates code for the SPARClet variant
     of the SPARC architecture.  This adds the integer multiply,
     multiply/accumulate, integer divide step and scan (`ffs')
     instructions which exist in SPARClet but not in SPARC-V7.  With
     `-mcpu=tsc701', the compiler additionally optimizes it for the
     TEMIC SPARClet chip.

     With `-mcpu=v9', GCC generates code for the V9 variant of the SPARC
     architecture.  This adds 64-bit integer and floating-point move
     instructions, 3 additional floating-point condition code registers
     and conditional move instructions.  With `-mcpu=ultrasparc', the
     compiler additionally optimizes it for the Sun UltraSPARC I/II
     chips.  With `-mcpu=ultrasparc3', the compiler additionally
     optimizes it for the Sun UltraSPARC III chip.

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the instruction set or register set that
     the option `-mcpu=CPU_TYPE' would.

     The same values for `-mcpu=CPU_TYPE' can be used for
     `-mtune=CPU_TYPE', but the only useful values are those that
     select a particular cpu implementation.  Those are `cypress',
     `supersparc', `hypersparc', `f930', `f934', `sparclite86x',
     `tsc701', `ultrasparc', and `ultrasparc3'.

`-mv8plus'
`-mno-v8plus'
     With `-mv8plus', GCC generates code for the SPARC-V8+ ABI.  The
     difference from the V8 ABI is that the global and out registers are
     considered 64-bit wide.  This is enabled by default on Solaris in
     32-bit mode for all SPARC-V9 processors.

`-mvis'
`-mno-vis'
     With `-mvis', GCC generates code that takes advantage of the
     UltraSPARC Visual Instruction Set extensions.  The default is
     `-mno-vis'.

 These `-m' options are supported in addition to the above on SPARC-V9
processors in 64-bit environments:

`-mlittle-endian'
     Generate code for a processor running in little-endian mode. It is
     only available for a few configurations and most notably not on
     Solaris.

`-m32'
`-m64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits.  The 64-bit
     environment sets int to 32 bits and long and pointer to 64 bits.

`-mcmodel=medlow'
     Generate code for the Medium/Low code model: 64-bit addresses,
     programs must be linked in the low 32 bits of memory.  Programs
     can be statically or dynamically linked.

`-mcmodel=medmid'
     Generate code for the Medium/Middle code model: 64-bit addresses,
     programs must be linked in the low 44 bits of memory, the text and
     data segments must be less than 2GB in size and the data segment
     must be located within 2GB of the text segment.

`-mcmodel=medany'
     Generate code for the Medium/Anywhere code model: 64-bit
     addresses, programs may be linked anywhere in memory, the text and
     data segments must be less than 2GB in size and the data segment
     must be located within 2GB of the text segment.

`-mcmodel=embmedany'
     Generate code for the Medium/Anywhere code model for embedded
     systems: 64-bit addresses, the text and data segments must be less
     than 2GB in size, both starting anywhere in memory (determined at
     link time).  The global register %g4 points to the base of the
     data segment.  Programs are statically linked and PIC is not
     supported.

`-mstack-bias'
`-mno-stack-bias'
     With `-mstack-bias', GCC assumes that the stack pointer, and frame
     pointer if present, are offset by -2047 which must be added back
     when making stack frame references.  This is the default in 64-bit
     mode.  Otherwise, assume no such offset is present.


File: gcc,  Node: ARM Options,  Next: MN10300 Options,  Prev: SPARC Options,  Up: Submodel Options

3.17.5 ARM Options
------------------

These `-m' options are defined for Advanced RISC Machines (ARM)
architectures:

`-mapcs-frame'
     Generate a stack frame that is compliant with the ARM Procedure
     Call Standard for all functions, even if this is not strictly
     necessary for correct execution of the code.  Specifying
     `-fomit-frame-pointer' with this option will cause the stack
     frames not to be generated for leaf functions.  The default is
     `-mno-apcs-frame'.

`-mapcs'
     This is a synonym for `-mapcs-frame'.

`-mapcs-26'
     Generate code for a processor running with a 26-bit program
     counter, and conforming to the function calling standards for the
     APCS 26-bit option.

     This option is deprecated.  Future releases of the GCC will only
     support generating code that runs in apcs-32 mode.

`-mapcs-32'
     Generate code for a processor running with a 32-bit program
     counter, and conforming to the function calling standards for the
     APCS 32-bit option.

     This flag is deprecated.  Future releases of GCC will make this
     flag unconditional.

`-mthumb-interwork'
     Generate code which supports calling between the ARM and Thumb
     instruction sets.  Without this option the two instruction sets
     cannot be reliably used inside one program.  The default is
     `-mno-thumb-interwork', since slightly larger code is generated
     when `-mthumb-interwork' is specified.

`-mno-sched-prolog'
     Prevent the reordering of instructions in the function prolog, or
     the merging of those instruction with the instructions in the
     function's body.  This means that all functions will start with a
     recognizable set of instructions (or in fact one of a choice from
     a small set of different function prologues), and this information
     can be used to locate the start if functions inside an executable
     piece of code.  The default is `-msched-prolog'.

`-mhard-float'
     Generate output containing floating point instructions.  This is
     the default.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all ARM
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this cannot be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GCC, with `-msoft-float' in order for this
     to work.

`-mlittle-endian'
     Generate code for a processor running in little-endian mode.  This
     is the default for all standard configurations.

`-mbig-endian'
     Generate code for a processor running in big-endian mode; the
     default is to compile code for a little-endian processor.

`-mwords-little-endian'
     This option only applies when generating code for big-endian
     processors.  Generate code for a little-endian word order but a
     big-endian byte order.  That is, a byte order of the form
     `32107654'.  Note: this option should only be used if you require
     compatibility with code for big-endian ARM processors generated by
     versions of the compiler prior to 2.8.

`-malignment-traps'
     Generate code that will not trap if the MMU has alignment traps
     enabled.  On ARM architectures prior to ARMv4, there were no
     instructions to access half-word objects stored in memory.
     However, when reading from memory a feature of the ARM
     architecture allows a word load to be used, even if the address is
     unaligned, and the processor core will rotate the data as it is
     being loaded.  This option tells the compiler that such misaligned
     accesses will cause a MMU trap and that it should instead
     synthesize the access as a series of byte accesses.  The compiler
     can still use word accesses to load half-word data if it knows
     that the address is aligned to a word boundary.

     This option has no effect when compiling for ARM architecture 4 or
     later, since these processors have instructions to directly access
     half-word objects in memory.

`-mno-alignment-traps'
     Generate code that assumes that the MMU will not trap unaligned
     accesses.  This produces better code when the target instruction
     set does not have half-word memory operations (i.e.
     implementations prior to ARMv4).

     Note that you cannot use this option to access unaligned word
     objects, since the processor will only fetch one 32-bit aligned
     object from memory.

     The default setting is `-malignment-traps', since this produces
     code that will also run on processors implementing ARM architecture
     version 6 or later.

     This option is deprecated and will be removed in the next release
     of GCC.

`-mcpu=NAME'
     This specifies the name of the target ARM processor.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  Permissible names are: `arm2', `arm250',
     `arm3', `arm6', `arm60', `arm600', `arm610', `arm620', `arm7',
     `arm7m', `arm7d', `arm7dm', `arm7di', `arm7dmi', `arm70', `arm700',
     `arm700i', `arm710', `arm710c', `arm7100', `arm7500', `arm7500fe',
     `arm7tdmi', `arm8', `strongarm', `strongarm110', `strongarm1100',
     `arm8', `arm810', `arm9', `arm9e', `arm920', `arm920t',
     `arm926ejs', `arm940t', `arm9tdmi', `arm10tdmi', `arm1020t',
     `arm1026ejs', `arm1136js', `arm1136jfs' ,`xscale', `iwmmxt',
     `ep9312'.

`-mtune=NAME'
     This option is very similar to the `-mcpu=' option, except that
     instead of specifying the actual target processor type, and hence
     restricting which instructions can be used, it specifies that GCC
     should tune the performance of the code as if the target were of
     the type specified in this option, but still choosing the
     instructions that it will generate based on the cpu specified by a
     `-mcpu=' option.  For some ARM implementations better performance
     can be obtained by using this option.

`-march=NAME'
     This specifies the name of the target ARM architecture.  GCC uses
     this name to determine what kind of instructions it can emit when
     generating assembly code.  This option can be used in conjunction
     with or instead of the `-mcpu=' option.  Permissible names are:
     `armv2', `armv2a', `armv3', `armv3m', `armv4', `armv4t', `armv5',
     `armv5t', `armv5te', `armv6j', `iwmmxt', `ep9312'.

`-mfpe=NUMBER'
`-mfp=NUMBER'
     This specifies the version of the floating point emulation
     available on the target.  Permissible values are 2 and 3.  `-mfp='
     is a synonym for `-mfpe=', for compatibility with older versions
     of GCC.

`-mstructure-size-boundary=N'
     The size of all structures and unions will be rounded up to a
     multiple of the number of bits set by this option.  Permissible
     values are 8 and 32.  The default value varies for different
     toolchains.  For the COFF targeted toolchain the default value is
     8.  Specifying the larger number can produce faster, more
     efficient code, but can also increase the size of the program.
     The two values are potentially incompatible.  Code compiled with
     one value cannot necessarily expect to work with code or libraries
     compiled with the other value, if they exchange information using
     structures or unions.

`-mabort-on-noreturn'
     Generate a call to the function `abort' at the end of a `noreturn'
     function.  It will be executed if the function tries to return.

`-mlong-calls'
`-mno-long-calls'
     Tells the compiler to perform function calls by first loading the
     address of the function into a register and then performing a
     subroutine call on this register.  This switch is needed if the
     target function will lie outside of the 64 megabyte addressing
     range of the offset based version of subroutine call instruction.

     Even if this switch is enabled, not all function calls will be
     turned into long calls.  The heuristic is that static functions,
     functions which have the `short-call' attribute, functions that
     are inside the scope of a `#pragma no_long_calls' directive and
     functions whose definitions have already been compiled within the
     current compilation unit, will not be turned into long calls.  The
     exception to this rule is that weak function definitions,
     functions with the `long-call' attribute or the `section'
     attribute, and functions that are within the scope of a `#pragma
     long_calls' directive, will always be turned into long calls.

     This feature is not enabled by default.  Specifying
     `-mno-long-calls' will restore the default behavior, as will
     placing the function calls within the scope of a `#pragma
     long_calls_off' directive.  Note these switches have no effect on
     how the compiler generates code to handle function calls via
     function pointers.

`-mnop-fun-dllimport'
     Disable support for the `dllimport' attribute.

`-msingle-pic-base'
     Treat the register used for PIC addressing as read-only, rather
     than loading it in the prologue for each function.  The run-time
     system is responsible for initializing this register with an
     appropriate value before execution begins.

`-mpic-register=REG'
     Specify the register to be used for PIC addressing.  The default
     is R10 unless stack-checking is enabled, when R9 is used.

`-mcirrus-fix-invalid-insns'
     Insert NOPs into the instruction stream to in order to work around
     problems with invalid Maverick instruction combinations.  This
     option is only valid if the `-mcpu=ep9312' option has been used to
     enable generation of instructions for the Cirrus Maverick floating
     point co-processor.  This option is not enabled by default, since
     the problem is only present in older Maverick implementations.
     The default can be re-enabled by use of the
     `-mno-cirrus-fix-invalid-insns' switch.

`-mpoke-function-name'
     Write the name of each function into the text section, directly
     preceding the function prologue.  The generated code is similar to
     this:

               t0
                   .ascii "arm_poke_function_name", 0
                   .align
               t1
                   .word 0xff000000 + (t1 - t0)
               arm_poke_function_name
                   mov     ip, sp
                   stmfd   sp!, {fp, ip, lr, pc}
                   sub     fp, ip, #4

     When performing a stack backtrace, code can inspect the value of
     `pc' stored at `fp + 0'.  If the trace function then looks at
     location `pc - 12' and the top 8 bits are set, then we know that
     there is a function name embedded immediately preceding this
     location and has length `((pc[-3]) & 0xff000000)'.

`-mthumb'
     Generate code for the 16-bit Thumb instruction set.  The default
     is to use the 32-bit ARM instruction set.

`-mtpcs-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all non-leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-tpcs-frame'.

`-mtpcs-leaf-frame'
     Generate a stack frame that is compliant with the Thumb Procedure
     Call Standard for all leaf functions.  (A leaf function is one
     that does not call any other functions.)  The default is
     `-mno-apcs-leaf-frame'.

`-mcallee-super-interworking'
     Gives all externally visible functions in the file being compiled
     an ARM instruction set header which switches to Thumb mode before
     executing the rest of the function.  This allows these functions
     to be called from non-interworking code.

`-mcaller-super-interworking'
     Allows calls via function pointers (including virtual functions) to
     execute correctly regardless of whether the target code has been
     compiled for interworking or not.  There is a small overhead in
     the cost of executing a function pointer if this option is enabled.



File: gcc,  Node: MN10300 Options,  Next: M32R/D Options,  Prev: ARM Options,  Up: Submodel Options

3.17.6 MN10300 Options
----------------------

These `-m' options are defined for Matsushita MN10300 architectures:

`-mmult-bug'
     Generate code to avoid bugs in the multiply instructions for the
     MN10300 processors.  This is the default.

`-mno-mult-bug'
     Do not generate code to avoid bugs in the multiply instructions
     for the MN10300 processors.

`-mam33'
     Generate code which uses features specific to the AM33 processor.

`-mno-am33'
     Do not generate code which uses features specific to the AM33
     processor.  This is the default.

`-mno-crt0'
     Do not link in the C run-time initialization object file.

`-mrelax'
     Indicate to the linker that it should perform a relaxation
     optimization pass to shorten branches, calls and absolute memory
     addresses.  This option only has an effect when used on the
     command line for the final link step.

     This option makes symbolic debugging impossible.


File: gcc,  Node: M32R/D Options,  Next: RS/6000 and PowerPC Options,  Prev: MN10300 Options,  Up: Submodel Options

3.17.7 M32R/D Options
---------------------

These `-m' options are defined for Renesas M32R/D architectures:

`-m32r2'
     Generate code for the M32R/2.

`-m32rx'
     Generate code for the M32R/X.

`-m32r'
     Generate code for the M32R.  This is the default.

`-mmodel=small'
     Assume all objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction), and assume
     all subroutines are reachable with the `bl' instruction.  This is
     the default.

     The addressability of a particular object can be set with the
     `model' attribute.

`-mmodel=medium'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume all subroutines are reachable with the `bl'
     instruction.

`-mmodel=large'
     Assume objects may be anywhere in the 32-bit address space (the
     compiler will generate `seth/add3' instructions to load their
     addresses), and assume subroutines may not be reachable with the
     `bl' instruction (the compiler will generate the much slower
     `seth/add3/jl' instruction sequence).

`-msdata=none'
     Disable use of the small data area.  Variables will be put into
     one of `.data', `bss', or `.rodata' (unless the `section'
     attribute has been specified).  This is the default.

     The small data area consists of sections `.sdata' and `.sbss'.
     Objects may be explicitly put in the small data area with the
     `section' attribute using one of these sections.

`-msdata=sdata'
     Put small global and static data in the small data area, but do not
     generate special code to reference them.

`-msdata=use'
     Put small global and static data in the small data area, and
     generate special instructions to reference them.

`-G NUM'
     Put global and static objects less than or equal to NUM bytes into
     the small data or bss sections instead of the normal data or bss
     sections.  The default value of NUM is 8.  The `-msdata' option
     must be set to one of `sdata' or `use' for this option to have any
     effect.

     All modules should be compiled with the same `-G NUM' value.
     Compiling with different values of NUM may or may not work; if it
     doesn't the linker will give an error message--incorrect code will
     not be generated.

`-mdebug'
     Makes the M32R specific code in the compiler display some
     statistics that might help in debugging programs.

`-malign-loops'
     Align all loops to a 32-byte boundary.

`-mno-align-loops'
     Do not enforce a 32-byte alignment for loops.  This is the default.

`-missue-rate=NUMBER'
     Issue NUMBER instructions per cycle.  NUMBER can only be 1 or 2.

`-mbranch-cost=NUMBER'
     NUMBER can only be 1 or 2.  If it is 1 then branches will be
     preferred over conditional code, if it is 2, then the opposite will
     apply.

`-mflush-trap=NUMBER'
     Specifies the trap number to use to flush the cache.  The default
     is 12.  Valid numbers are between 0 and 15 inclusive.

`-mno-flush-trap'
     Specifies that the cache cannot be flushed by using a trap.

`-mflush-func=NAME'
     Specifies the name of the operating system function to call to
     flush the cache.  The default is __flush_cache_, but a function
     call will only be used if a trap is not available.

`-mno-flush-func'
     Indicates that there is no OS function for flushing the cache.



File: gcc,  Node: RS/6000 and PowerPC Options,  Next: Darwin Options,  Prev: M32R/D Options,  Up: Submodel Options

3.17.8 IBM RS/6000 and PowerPC Options
--------------------------------------

These `-m' options are defined for the IBM RS/6000 and PowerPC:
`-mpower'
`-mno-power'
`-mpower2'
`-mno-power2'
`-mpowerpc'
`-mno-powerpc'
`-mpowerpc-gpopt'
`-mno-powerpc-gpopt'
`-mpowerpc-gfxopt'
`-mno-powerpc-gfxopt'
`-mpowerpc64'
`-mno-powerpc64'
     GCC supports two related instruction set architectures for the
     RS/6000 and PowerPC.  The "POWER" instruction set are those
     instructions supported by the `rios' chip set used in the original
     RS/6000 systems and the "PowerPC" instruction set is the
     architecture of the Motorola MPC5xx, MPC6xx, MPC8xx
     microprocessors, and the IBM 4xx microprocessors.

     Neither architecture is a subset of the other.  However there is a
     large common subset of instructions supported by both.  An MQ
     register is included in processors supporting the POWER
     architecture.

     You use these options to specify which instructions are available
     on the processor you are using.  The default value of these
     options is determined when configuring GCC.  Specifying the
     `-mcpu=CPU_TYPE' overrides the specification of these options.  We
     recommend you use the `-mcpu=CPU_TYPE' option rather than the
     options listed above.

     The `-mpower' option allows GCC to generate instructions that are
     found only in the POWER architecture and to use the MQ register.
     Specifying `-mpower2' implies `-power' and also allows GCC to
     generate instructions that are present in the POWER2 architecture
     but not the original POWER architecture.

     The `-mpowerpc' option allows GCC to generate instructions that
     are found only in the 32-bit subset of the PowerPC architecture.
     Specifying `-mpowerpc-gpopt' implies `-mpowerpc' and also allows
     GCC to use the optional PowerPC architecture instructions in the
     General Purpose group, including floating-point square root.
     Specifying `-mpowerpc-gfxopt' implies `-mpowerpc' and also allows
     GCC to use the optional PowerPC architecture instructions in the
     Graphics group, including floating-point select.

     The `-mpowerpc64' option allows GCC to generate the additional
     64-bit instructions that are found in the full PowerPC64
     architecture and to treat GPRs as 64-bit, doubleword quantities.
     GCC defaults to `-mno-powerpc64'.

     If you specify both `-mno-power' and `-mno-powerpc', GCC will use
     only the instructions in the common subset of both architectures
     plus some special AIX common-mode calls, and will not use the MQ
     register.  Specifying both `-mpower' and `-mpowerpc' permits GCC
     to use any instruction from either architecture and to allow use
     of the MQ register; specify this for the Motorola MPC601.

`-mnew-mnemonics'
`-mold-mnemonics'
     Select which mnemonics to use in the generated assembler code.
     With `-mnew-mnemonics', GCC uses the assembler mnemonics defined
     for the PowerPC architecture.  With `-mold-mnemonics' it uses the
     assembler mnemonics defined for the POWER architecture.
     Instructions defined in only one architecture have only one
     mnemonic; GCC uses that mnemonic irrespective of which of these
     options is specified.

     GCC defaults to the mnemonics appropriate for the architecture in
     use.  Specifying `-mcpu=CPU_TYPE' sometimes overrides the value of
     these option.  Unless you are building a cross-compiler, you
     should normally not specify either `-mnew-mnemonics' or
     `-mold-mnemonics', but should instead accept the default.

`-mcpu=CPU_TYPE'
     Set architecture type, register usage, choice of mnemonics, and
     instruction scheduling parameters for machine type CPU_TYPE.
     Supported values for CPU_TYPE are `401', `403', `405', `405fp',
     `440', `440fp', `505', `601', `602', `603', `603e', `604', `604e',
     `620', `630', `740', `7400', `7450', `750', `801', `821', `823',
     `860', `970', `common', `ec603e', `G3', `G4', `G5', `power',
     `power2', `power3', `power4', `power5', `powerpc', `powerpc64',
     `rios', `rios1', `rios2', `rsc', and `rs64a'.

     `-mcpu=common' selects a completely generic processor.  Code
     generated under this option will run on any POWER or PowerPC
     processor.  GCC will use only the instructions in the common
     subset of both architectures, and will not use the MQ register.
     GCC assumes a generic processor model for scheduling purposes.

     `-mcpu=power', `-mcpu=power2', `-mcpu=powerpc', and
     `-mcpu=powerpc64' specify generic POWER, POWER2, pure 32-bit
     PowerPC (i.e., not MPC601), and 64-bit PowerPC architecture machine
     types, with an appropriate, generic processor model assumed for
     scheduling purposes.

     The other options specify a specific processor.  Code generated
     under those options will run best on that processor, and may not
     run at all on others.

     The `-mcpu' options automatically enable or disable the following
     options: `-maltivec', `-mhard-float', `-mmfcrf', `-mmultiple',
     `-mnew-mnemonics', `-mpower', `-mpower2', `-mpowerpc64',
     `-mpowerpc-gpopt', `-mpowerpc-gfxopt', `-mstring'.  The particular
     options set for any particular CPU will vary between compiler
     versions, depending on what setting seems to produce optimal code
     for that CPU; it doesn't necessarily reflect the actual hardware's
     capabilities.  If you wish to set an individual option to a
     particular value, you may specify it after the `-mcpu' option,
     like `-mcpu=970 -mno-altivec'.

     On AIX, the `-maltivec' and `-mpowerpc64' options are not enabled
     or disabled by the `-mcpu' option at present, since AIX does not
     have full support for these options.  You may still enable or
     disable them individually if you're sure it'll work in your
     environment.

`-mtune=CPU_TYPE'
     Set the instruction scheduling parameters for machine type
     CPU_TYPE, but do not set the architecture type, register usage, or
     choice of mnemonics, as `-mcpu=CPU_TYPE' would.  The same values
     for CPU_TYPE are used for `-mtune' as for `-mcpu'.  If both are
     specified, the code generated will use the architecture,
     registers, and mnemonics set by `-mcpu', but the scheduling
     parameters set by `-mtune'.

`-maltivec'
`-mno-altivec'
     These switches enable or disable the use of built-in functions that
     allow access to the AltiVec instruction set.  You may also need to
     set `-mabi=altivec' to adjust the current ABI with AltiVec ABI
     enhancements.

`-mabi=spe'
     Extend the current ABI with SPE ABI extensions.  This does not
     change the default ABI, instead it adds the SPE ABI extensions to
     the current ABI.

`-mabi=no-spe'
     Disable Booke SPE ABI extensions for the current ABI.

`-misel=YES/NO'
`-misel'
     This switch enables or disables the generation of ISEL
     instructions.

`-mspe=YES/NO'
`-mspe'
     This switch enables or disables the generation of SPE simd
     instructions.

`-mfloat-gprs=YES/NO'
`-mfloat-gprs'
     This switch enables or disables the generation of floating point
     operations on the general purpose registers for architectures that
     support it.  This option is currently only available on the
     MPC8540.

`-mfull-toc'
`-mno-fp-in-toc'
`-mno-sum-in-toc'
`-mminimal-toc'
     Modify generation of the TOC (Table Of Contents), which is created
     for every executable file.  The `-mfull-toc' option is selected by
     default.  In that case, GCC will allocate at least one TOC entry
     for each unique non-automatic variable reference in your program.
     GCC will also place floating-point constants in the TOC.  However,
     only 16,384 entries are available in the TOC.

     If you receive a linker error message that saying you have
     overflowed the available TOC space, you can reduce the amount of
     TOC space used with the `-mno-fp-in-toc' and `-mno-sum-in-toc'
     options.  `-mno-fp-in-toc' prevents GCC from putting floating-point
     constants in the TOC and `-mno-sum-in-toc' forces GCC to generate
     code to calculate the sum of an address and a constant at run-time
     instead of putting that sum into the TOC.  You may specify one or
     both of these options.  Each causes GCC to produce very slightly
     slower and larger code at the expense of conserving TOC space.

     If you still run out of space in the TOC even when you specify
     both of these options, specify `-mminimal-toc' instead.  This
     option causes GCC to make only one TOC entry for every file.  When
     you specify this option, GCC will produce code that is slower and
     larger but which uses extremely little TOC space.  You may wish to
     use this option only on files that contain less frequently
     executed code.

`-maix64'
`-maix32'
     Enable 64-bit AIX ABI and calling convention: 64-bit pointers,
     64-bit `long' type, and the infrastructure needed to support them.
     Specifying `-maix64' implies `-mpowerpc64' and `-mpowerpc', while
     `-maix32' disables the 64-bit ABI and implies `-mno-powerpc64'.
     GCC defaults to `-maix32'.

`-mxl-call'
`-mno-xl-call'
     On AIX, pass floating-point arguments to prototyped functions
     beyond the register save area (RSA) on the stack in addition to
     argument FPRs.  The AIX calling convention was extended but not
     initially documented to handle an obscure K&R C case of calling a
     function that takes the address of its arguments with fewer
     arguments than declared.  AIX XL compilers access floating point
     arguments which do not fit in the RSA from the stack when a
     subroutine is compiled without optimization.  Because always
     storing floating-point arguments on the stack is inefficient and
     rarely needed, this option is not enabled by default and only is
     necessary when calling subroutines compiled by AIX XL compilers
     without optimization.

`-mpe'
     Support "IBM RS/6000 SP" "Parallel Environment" (PE).  Link an
     application written to use message passing with special startup
     code to enable the application to run.  The system must have PE
     installed in the standard location (`/usr/lpp/ppe.poe/'), or the
     `specs' file must be overridden with the `-specs=' option to
     specify the appropriate directory location.  The Parallel
     Environment does not support threads, so the `-mpe' option and the
     `-pthread' option are incompatible.

`-malign-natural'
`-malign-power'
     On AIX, Darwin, and 64-bit PowerPC GNU/Linux, the option
     `-malign-natural' overrides the ABI-defined alignment of larger
     types, such as floating-point doubles, on their natural size-based
     boundary.  The option `-malign-power' instructs GCC to follow the
     ABI-specified alignment rules.  GCC defaults to the standard
     alignment defined in the ABI.

`-msoft-float'
`-mhard-float'
     Generate code that does not use (uses) the floating-point register
     set.  Software floating point emulation is provided if you use the
     `-msoft-float' option, and pass the option to GCC when linking.

`-mmultiple'
`-mno-multiple'
     Generate code that uses (does not use) the load multiple word
     instructions and the store multiple word instructions.  These
     instructions are generated by default on POWER systems, and not
     generated on PowerPC systems.  Do not use `-mmultiple' on little
     endian PowerPC systems, since those instructions do not work when
     the processor is in little endian mode.  The exceptions are PPC740
     and PPC750 which permit the instructions usage in little endian
     mode.

`-mstring'
`-mno-string'
     Generate code that uses (does not use) the load string instructions
     and the store string word instructions to save multiple registers
     and do small block moves.  These instructions are generated by
     default on POWER systems, and not generated on PowerPC systems.
     Do not use `-mstring' on little endian PowerPC systems, since those
     instructions do not work when the processor is in little endian
     mode.  The exceptions are PPC740 and PPC750 which permit the
     instructions usage in little endian mode.

`-mupdate'
`-mno-update'
     Generate code that uses (does not use) the load or store
     instructions that update the base register to the address of the
     calculated memory location.  These instructions are generated by
     default.  If you use `-mno-update', there is a small window
     between the time that the stack pointer is updated and the address
     of the previous frame is stored, which means code that walks the
     stack frame across interrupts or signals may get corrupted data.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating is used.

`-mno-bit-align'
`-mbit-align'
     On System V.4 and embedded PowerPC systems do not (do) force
     structures and unions that contain bit-fields to be aligned to the
     base type of the bit-field.

     For example, by default a structure containing nothing but 8
     `unsigned' bit-fields of length 1 would be aligned to a 4 byte
     boundary and have a size of 4 bytes.  By using `-mno-bit-align',
     the structure would be aligned to a 1 byte boundary and be one
     byte in size.

`-mno-strict-align'
`-mstrict-align'
     On System V.4 and embedded PowerPC systems do not (do) assume that
     unaligned memory references will be handled by the system.

`-mrelocatable'
`-mno-relocatable'
     On embedded PowerPC systems generate code that allows (does not
     allow) the program to be relocated to a different address at
     runtime.  If you use `-mrelocatable' on any module, all objects
     linked together must be compiled with `-mrelocatable' or
     `-mrelocatable-lib'.

`-mrelocatable-lib'
`-mno-relocatable-lib'
     On embedded PowerPC systems generate code that allows (does not
     allow) the program to be relocated to a different address at
     runtime.  Modules compiled with `-mrelocatable-lib' can be linked
     with either modules compiled without `-mrelocatable' and
     `-mrelocatable-lib' or with modules compiled with the
     `-mrelocatable' options.

`-mno-toc'
`-mtoc'
     On System V.4 and embedded PowerPC systems do not (do) assume that
     register 2 contains a pointer to a global area pointing to the
     addresses used in the program.

`-mlittle'
`-mlittle-endian'
     On System V.4 and embedded PowerPC systems compile code for the
     processor in little endian mode.  The `-mlittle-endian' option is
     the same as `-mlittle'.

`-mbig'
`-mbig-endian'
     On System V.4 and embedded PowerPC systems compile code for the
     processor in big endian mode.  The `-mbig-endian' option is the
     same as `-mbig'.

`-mdynamic-no-pic'
     On Darwin and Mac OS X systems, compile code so that it is not
     relocatable, but that its external references are relocatable.  The
     resulting code is suitable for applications, but not shared
     libraries.

`-mprioritize-restricted-insns=PRIORITY'
     This option controls the priority that is assigned to
     dispatch-slot restricted instructions during the second scheduling
     pass.  The argument PRIORITY takes the value 0/1/2 to assign
     NO/HIGHEST/SECOND-HIGHEST priority to dispatch slot restricted
     instructions.

`-msched-costly-dep=DEPENDENCE_TYPE'
     This option controls which dependences are considered costly by
     the target during instruction scheduling.  The argument
     DEPENDENCE_TYPE takes one of the following values: NO: no
     dependence is costly, ALL: all dependences are costly,
     TRUE_STORE_TO_LOAD: a true dependence from store to load is costly,
     STORE_TO_LOAD: any dependence from store to load is costly,
     NUMBER: any dependence which latency >= NUMBER is costly.

`-minsert-sched-nops=SCHEME'
     This option controls which nop insertion scheme will be used during
     the second scheduling pass. The argument SCHEME takes one of the
     following values: NO: Don't insert nops.  PAD: Pad with nops any
     dispatch group which has vacant issue slots, according to the
     scheduler's grouping.  REGROUP_EXACT: Insert nops to force costly
     dependent insns into separate groups.  Insert exactly as many nops
     as needed to force an insn to a new group, according to the
     estimated processor grouping.  NUMBER: Insert nops to force costly
     dependent insns into separate groups.  Insert NUMBER nops to force
     an insn to a new group.

`-mcall-sysv'
     On System V.4 and embedded PowerPC systems compile code using
     calling conventions that adheres to the March 1995 draft of the
     System V Application Binary Interface, PowerPC processor
     supplement.  This is the default unless you configured GCC using
     `powerpc-*-eabiaix'.

`-mcall-sysv-eabi'
     Specify both `-mcall-sysv' and `-meabi' options.

`-mcall-sysv-noeabi'
     Specify both `-mcall-sysv' and `-mno-eabi' options.

`-mcall-solaris'
     On System V.4 and embedded PowerPC systems compile code for the
     Solaris operating system.

`-mcall-linux'
     On System V.4 and embedded PowerPC systems compile code for the
     Linux-based GNU system.

`-mcall-gnu'
     On System V.4 and embedded PowerPC systems compile code for the
     Hurd-based GNU system.

`-mcall-netbsd'
     On System V.4 and embedded PowerPC systems compile code for the
     NetBSD operating system.

`-maix-struct-return'
     Return all structures in memory (as specified by the AIX ABI).

`-msvr4-struct-return'
     Return structures smaller than 8 bytes in registers (as specified
     by the SVR4 ABI).

`-mabi=altivec'
     Extend the current ABI with AltiVec ABI extensions.  This does not
     change the default ABI, instead it adds the AltiVec ABI extensions
     to the current ABI.

`-mabi=no-altivec'
     Disable AltiVec ABI extensions for the current ABI.

`-mprototype'
`-mno-prototype'
     On System V.4 and embedded PowerPC systems assume that all calls to
     variable argument functions are properly prototyped.  Otherwise,
     the compiler must insert an instruction before every non
     prototyped call to set or clear bit 6 of the condition code
     register (CR) to indicate whether floating point values were
     passed in the floating point registers in case the function takes
     a variable arguments.  With `-mprototype', only calls to
     prototyped variable argument functions will set or clear the bit.

`-msim'
     On embedded PowerPC systems, assume that the startup module is
     called `sim-crt0.o' and that the standard C libraries are
     `libsim.a' and `libc.a'.  This is the default for
     `powerpc-*-eabisim'.  configurations.

`-mmvme'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libmvme.a' and
     `libc.a'.

`-mads'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libads.a' and
     `libc.a'.

`-myellowknife'
     On embedded PowerPC systems, assume that the startup module is
     called `crt0.o' and the standard C libraries are `libyk.a' and
     `libc.a'.

`-mvxworks'
     On System V.4 and embedded PowerPC systems, specify that you are
     compiling for a VxWorks system.

`-mwindiss'
     Specify that you are compiling for the WindISS simulation
     environment.

`-memb'
     On embedded PowerPC systems, set the PPC_EMB bit in the ELF flags
     header to indicate that `eabi' extended relocations are used.

`-meabi'
`-mno-eabi'
     On System V.4 and embedded PowerPC systems do (do not) adhere to
     the Embedded Applications Binary Interface (eabi) which is a set of
     modifications to the System V.4 specifications.  Selecting `-meabi'
     means that the stack is aligned to an 8 byte boundary, a function
     `__eabi' is called to from `main' to set up the eabi environment,
     and the `-msdata' option can use both `r2' and `r13' to point to
     two separate small data areas.  Selecting `-mno-eabi' means that
     the stack is aligned to a 16 byte boundary, do not call an
     initialization function from `main', and the `-msdata' option will
     only use `r13' to point to a single small data area.  The `-meabi'
     option is on by default if you configured GCC using one of the
     `powerpc*-*-eabi*' options.

`-msdata=eabi'
     On System V.4 and embedded PowerPC systems, put small initialized
     `const' global and static data in the `.sdata2' section, which is
     pointed to by register `r2'.  Put small initialized non-`const'
     global and static data in the `.sdata' section, which is pointed
     to by register `r13'.  Put small uninitialized global and static
     data in the `.sbss' section, which is adjacent to the `.sdata'
     section.  The `-msdata=eabi' option is incompatible with the
     `-mrelocatable' option.  The `-msdata=eabi' option also sets the
     `-memb' option.

`-msdata=sysv'
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the `.sdata' section, which is pointed to by
     register `r13'.  Put small uninitialized global and static data in
     the `.sbss' section, which is adjacent to the `.sdata' section.
     The `-msdata=sysv' option is incompatible with the `-mrelocatable'
     option.

`-msdata=default'
`-msdata'
     On System V.4 and embedded PowerPC systems, if `-meabi' is used,
     compile code the same as `-msdata=eabi', otherwise compile code the
     same as `-msdata=sysv'.

`-msdata-data'
     On System V.4 and embedded PowerPC systems, put small global and
     static data in the `.sdata' section.  Put small uninitialized
     global and static data in the `.sbss' section.  Do not use
     register `r13' to address small data however.  This is the default
     behavior unless other `-msdata' options are used.

`-msdata=none'
`-mno-sdata'
     On embedded PowerPC systems, put all initialized global and static
     data in the `.data' section, and all uninitialized data in the
     `.bss' section.

`-G NUM'
     On embedded PowerPC systems, put global and static items less than
     or equal to NUM bytes into the small data or bss sections instead
     of the normal data or bss section.  By default, NUM is 8.  The `-G
     NUM' switch is also passed to the linker.  All modules should be
     compiled with the same `-G NUM' value.

`-mregnames'
`-mno-regnames'
     On System V.4 and embedded PowerPC systems do (do not) emit
     register names in the assembly language output using symbolic
     forms.

`-mlongcall'
`-mno-longcall'
     Default to making all function calls via pointers, so that
     functions which reside further than 64 megabytes (67,108,864
     bytes) from the current location can be called.  This setting can
     be overridden by the `shortcall' function attribute, or by
     `#pragma longcall(0)'.

     Some linkers are capable of detecting out-of-range calls and
     generating glue code on the fly.  On these systems, long calls are
     unnecessary and generate slower code.  As of this writing, the AIX
     linker can do this, as can the GNU linker for PowerPC/64.  It is
     planned to add this feature to the GNU linker for 32-bit PowerPC
     systems as well.

     On Mach-O (Darwin) systems, this option directs the compiler emit
     to the glue for every direct call, and the Darwin linker decides
     whether to use or discard it.

     In the future, we may cause GCC to ignore all longcall
     specifications when the linker is known to generate glue.

`-pthread'
     Adds support for multithreading with the "pthreads" library.  This
     option sets flags for both the preprocessor and linker.



File: gcc,  Node: Darwin Options,  Next: MIPS Options,  Prev: RS/6000 and PowerPC Options,  Up: Submodel Options

3.17.9 Darwin Options
---------------------

These options are defined for all architectures running the Darwin
operating system.  They are useful for compatibility with other Mac OS
compilers.

`-all_load'
     Loads all members of static archive libraries.  See man ld(1) for
     more information.

`-arch_errors_fatal'
     Cause the errors having to do with files that have the wrong
     architecture to be fatal.

`-bind_at_load'
     Causes the output file to be marked such that the dynamic linker
     will bind all undefined references when the file is loaded or
     launched.

`-bundle'
     Produce a Mach-o bundle format file.  See man ld(1) for more
     information.

`-bundle_loader EXECUTABLE'
     This specifies the EXECUTABLE that will be loading the build
     output file being linked. See man ld(1) for more information.

`-allowable_client  CLIENT_NAME'
`-arch_only'
`-client_name'
`-compatibility_version'
`-current_version'
`-dependency-file'
`-dylib_file'
`-dylinker_install_name'
`-dynamic'
`-dynamiclib'
`-exported_symbols_list'
`-filelist'
`-flat_namespace'
`-force_cpusubtype_ALL'
`-force_flat_namespace'
`-headerpad_max_install_names'
`-image_base'
`-init'
`-install_name'
`-keep_private_externs'
`-multi_module'
`-multiply_defined'
`-multiply_defined_unused'
`-noall_load'
`-nofixprebinding'
`-nomultidefs'
`-noprebind'
`-noseglinkedit'
`-pagezero_size'
`-prebind'
`-prebind_all_twolevel_modules'
`-private_bundle'
`-read_only_relocs'
`-sectalign'
`-sectobjectsymbols'
`-whyload'
`-seg1addr'
`-sectcreate'
`-sectobjectsymbols'
`-sectorder'
`-seg_addr_table'
`-seg_addr_table_filename'
`-seglinkedit'
`-segprot'
`-segs_read_only_addr'
`-segs_read_write_addr'
`-single_module'
`-static'
`-sub_library'
`-sub_umbrella'
`-twolevel_namespace'
`-umbrella'
`-undefined'
`-unexported_symbols_list'
`-weak_reference_mismatches'
`-whatsloaded'
     These options are available for Darwin linker. Darwin linker man
     page describes them in detail.


File: gcc,  Node: MIPS Options,  Next: i386 and x86-64 Options,  Prev: Darwin Options,  Up: Submodel Options

3.17.10 MIPS Options
--------------------

`-EB'
     Generate big-endian code.

`-EL'
     Generate little-endian code.  This is the default for `mips*el-*-*'
     configurations.

`-march=ARCH'
     Generate code that will run on ARCH, which can be the name of a
     generic MIPS ISA, or the name of a particular processor.  The ISA
     names are: `mips1', `mips2', `mips3', `mips4', `mips32',
     `mips32r2', and `mips64'.  The processor names are: `4kc', `4kp',
     `5kc', `20kc', `m4k', `r2000', `r3000', `r3900', `r4000', `r4400',
     `r4600', `r4650', `r6000', `r8000', `rm7000', `rm9000', `orion',
     `sb1', `vr4100', `vr4111', `vr4120', `vr4300', `vr5000', `vr5400'
     and `vr5500'.  The special value `from-abi' selects the most
     compatible architecture for the selected ABI (that is, `mips1' for
     32-bit ABIs and `mips3' for 64-bit ABIs).

     In processor names, a final `000' can be abbreviated as `k' (for
     example, `-march=r2k').  Prefixes are optional, and `vr' may be
     written `r'.

     GCC defines two macros based on the value of this option.  The
     first is `_MIPS_ARCH', which gives the name of target
     architecture, as a string.  The second has the form
     `_MIPS_ARCH_FOO', where FOO is the capitalized value of
     `_MIPS_ARCH'.  For example, `-march=r2000' will set `_MIPS_ARCH'
     to `"r2000"' and define the macro `_MIPS_ARCH_R2000'.

     Note that the `_MIPS_ARCH' macro uses the processor names given
     above.  In other words, it will have the full prefix and will not
     abbreviate `000' as `k'.  In the case of `from-abi', the macro
     names the resolved architecture (either `"mips1"' or `"mips3"').
     It names the default architecture when no `-march' option is given.

`-mtune=ARCH'
     Optimize for ARCH.  Among other things, this option controls the
     way instructions are scheduled, and the perceived cost of
     arithmetic operations.  The list of ARCH values is the same as for
     `-march'.

     When this option is not used, GCC will optimize for the processor
     specified by `-march'.  By using `-march' and `-mtune' together,
     it is possible to generate code that will run on a family of
     processors, but optimize the code for one particular member of
     that family.

     `-mtune' defines the macros `_MIPS_TUNE' and `_MIPS_TUNE_FOO',
     which work in the same way as the `-march' ones described above.

`-mips1'
     Equivalent to `-march=mips1'.

`-mips2'
     Equivalent to `-march=mips2'.

`-mips3'
     Equivalent to `-march=mips3'.

`-mips4'
     Equivalent to `-march=mips4'.

`-mips32'
     Equivalent to `-march=mips32'.

`-mips32r2'
     Equivalent to `-march=mips32r2'.

`-mips64'
     Equivalent to `-march=mips64'.

`-mips16'
`-mno-mips16'
     Use (do not use) the MIPS16 ISA.

`-mabi=32'
`-mabi=o64'
`-mabi=n32'
`-mabi=64'
`-mabi=eabi'
     Generate code for the given ABI.

     Note that the EABI has a 32-bit and a 64-bit variant.  GCC normally
     generates 64-bit code when you select a 64-bit architecture, but
     you can use `-mgp32' to get 32-bit code instead.

`-mabicalls'
`-mno-abicalls'
     Generate (do not generate) SVR4-style position-independent code.
     `-mabicalls' is the default for SVR4-based systems.

`-mxgot'
`-mno-xgot'
     Lift (do not lift) the usual restrictions on the size of the global
     offset table.

     GCC normally uses a single instruction to load values from the GOT.
     While this is relatively efficient, it will only work if the GOT
     is smaller than about 64k.  Anything larger will cause the linker
     to report an error such as:

          relocation truncated to fit: R_MIPS_GOT16 foobar

     If this happens, you should recompile your code with `-mxgot'.  It
     should then work with very large GOTs, although it will also be
     less efficient, since it will take three instructions to fetch the
     value of a global symbol.

     Note that some linkers can create multiple GOTs.  If you have such
     a linker, you should only need to use `-mxgot' when a single object
     file accesses more than 64k's worth of GOT entries.  Very few do.

     These options have no effect unless GCC is generating position
     independent code.

`-membedded-pic'
`-mno-embedded-pic'
     Generate (do not generate) position-independent code suitable for
     some embedded systems.  All calls are made using PC relative
     addresses, and all data is addressed using the $gp register.  No
     more than 65536 bytes of global data may be used.  This requires
     GNU as and GNU ld, which do most of the work.

`-mgp32'
     Assume that general-purpose registers are 32 bits wide.

`-mgp64'
     Assume that general-purpose registers are 64 bits wide.

`-mfp32'
     Assume that floating-point registers are 32 bits wide.

`-mfp64'
     Assume that floating-point registers are 64 bits wide.

`-mhard-float'
     Use floating-point coprocessor instructions.

`-msoft-float'
     Do not use floating-point coprocessor instructions.  Implement
     floating-point calculations using library calls instead.

`-msingle-float'
     Assume that the floating-point coprocessor only supports
     single-precision operations.

`-mdouble-float'
     Assume that the floating-point coprocessor supports
     double-precision operations.  This is the default.

`-mint64'
     Force `int' and `long' types to be 64 bits wide.  See `-mlong32'
     for an explanation of the default and the way that the pointer
     size is determined.

`-mlong64'
     Force `long' types to be 64 bits wide.  See `-mlong32' for an
     explanation of the default and the way that the pointer size is
     determined.

`-mlong32'
     Force `long', `int', and pointer types to be 32 bits wide.

     The default size of `int's, `long's and pointers depends on the
     ABI.  All the supported ABIs use 32-bit `int's.  The n64 ABI uses
     64-bit `long's, as does the 64-bit EABI; the others use 32-bit
     `long's.  Pointers are the same size as `long's, or the same size
     as integer registers, whichever is smaller.

`-G NUM'
     Put global and static items less than or equal to NUM bytes into
     the small data or bss section instead of the normal data or bss
     section.  This allows the data to be accessed using a single
     instruction.

     All modules should be compiled with the same `-G NUM' value.

`-membedded-data'
`-mno-embedded-data'
     Allocate variables to the read-only data section first if
     possible, then next in the small data section if possible,
     otherwise in data.  This gives slightly slower code than the
     default, but reduces the amount of RAM required when executing,
     and thus may be preferred for some embedded systems.

`-muninit-const-in-rodata'
`-mno-uninit-const-in-rodata'
     Put uninitialized `const' variables in the read-only data section.
     This option is only meaningful in conjunction with
     `-membedded-data'.

`-msplit-addresses'
`-mno-split-addresses'
     Enable (disable) use of the `%hi()' and `%lo()' assembler
     relocation operators.  This option has been superceded by
     `-mexplicit-relocs' but is retained for backwards compatibility.

`-mexplicit-relocs'
`-mno-explicit-relocs'
     Use (do not use) assembler relocation operators when dealing with
     symbolic addresses.  The alternative, selected by
     `-mno-explicit-relocs', is to use assembler macros instead.

     `-mexplicit-relocs' is usually the default if GCC was configured
     to use an assembler that supports relocation operators.  However,
     there are two exceptions:

        * GCC is not yet able to generate explicit relocations for the
          combination of `-mabi=64' and `-mno-abicalls'.  This will be
          addressed in a future release.

        * The combination of `-mabicalls' and `-fno-unit-at-a-time'
          implies `-mno-explicit-relocs' unless explicitly overridden.
          This is because, when generating abicalls, the choice of
          relocation depends on whether a symbol is local or global.
          In some rare cases, GCC will not be able to decide this until
          the whole compilation unit has been read.

`-mrnames'
`-mno-rnames'
     Generate (do not generate) code that refers to registers using
     their software names.  The default is `-mno-rnames', which tells
     GCC to use hardware names like `$4' instead of software names like
     `a0'.  The only assembler known to support `-rnames' is the
     Algorithmics assembler.

`-mcheck-zero-division'
`-mno-check-zero-division'
     Trap (do not trap) on integer division by zero.  The default is
     `-mcheck-zero-division'.

`-mmemcpy'
`-mno-memcpy'
     Force (do not force) the use of `memcpy()' for non-trivial block
     moves.  The default is `-mno-memcpy', which allows GCC to inline
     most constant-sized copies.

`-mlong-calls'
`-mno-long-calls'
     Disable (do not disable) use of the `jal' instruction.  Calling
     functions using `jal' is more efficient but requires the caller
     and callee to be in the same 256 megabyte segment.

     This option has no effect on abicalls code.  The default is
     `-mno-long-calls'.

`-mmad'
`-mno-mad'
     Enable (disable) use of the `mad', `madu' and `mul' instructions,
     as provided by the R4650 ISA.

`-mfused-madd'
`-mno-fused-madd'
     Enable (disable) use of the floating point multiply-accumulate
     instructions, when they are available.  The default is
     `-mfused-madd'.

     When multiply-accumulate instructions are used, the intermediate
     product is calculated to infinite precision and is not subject to
     the FCSR Flush to Zero bit.  This may be undesirable in some
     circumstances.

`-nocpp'
     Tell the MIPS assembler to not run its preprocessor over user
     assembler files (with a `.s' suffix) when assembling them.

`-mfix-sb1'
`-mno-fix-sb1'
     Work around certain SB-1 CPU core errata.  (This flag currently
     works around the SB-1 revision 2 "F1" and "F2" floating point
     errata.)

`-mflush-func=FUNC'
`-mno-flush-func'
     Specifies the function to call to flush the I and D caches, or to
     not call any such function.  If called, the function must take the
     same arguments as the common `_flush_func()', that is, the address
     of the memory range for which the cache is being flushed, the size
     of the memory range, and the number 3 (to flush both caches).  The
     default depends on the target GCC was configured for, but commonly
     is either `_flush_func' or `__cpu_flush'.

`-mbranch-likely'
`-mno-branch-likely'
     Enable or disable use of Branch Likely instructions, regardless of
     the default for the selected architecture.  By default, Branch
     Likely instructions may be generated if they are supported by the
     selected architecture.  An exception is for the MIPS32 and MIPS64
     architectures and processors which implement those architectures;
     for those, Branch Likely instructions will not be generated by
     default because the MIPS32 and MIPS64 architectures specifically
     deprecate their use.


File: gcc,  Node: i386 and x86-64 Options,  Next: HPPA Options,  Prev: MIPS Options,  Up: Submodel Options

3.17.11 Intel 386 and AMD x86-64 Options
----------------------------------------

These `-m' options are defined for the i386 and x86-64 family of
computers:

`-mtune=CPU-TYPE'
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  The
     choices for CPU-TYPE are:
    _i386_
          Original Intel's i386 CPU.

    _i486_
          Intel's i486 CPU.  (No scheduling is implemented for this
          chip.)

    _i586, pentium_
          Intel Pentium CPU with no MMX support.

    _pentium-mmx_
          Intel PentiumMMX CPU based on Pentium core with MMX
          instruction set support.

    _i686, pentiumpro_
          Intel PentiumPro CPU.

    _pentium2_
          Intel Pentium2 CPU based on PentiumPro core with MMX
          instruction set support.

    _pentium3, pentium3m_
          Intel Pentium3 CPU based on PentiumPro core with MMX and SSE
          instruction set support.

    _pentium-m_
          Low power version of Intel Pentium3 CPU with MMX, SSE and
          SSE2 instruction set support.  Used by Centrino notebooks.

    _pentium4, pentium4m_
          Intel Pentium4 CPU with MMX, SSE and SSE2 instruction set
          support.

    _prescott_
          Improved version of Intel Pentium4 CPU with MMX, SSE, SSE2
          and SSE3 instruction set support.

    _nocona_
          Improved version of Intel Pentium4 CPU with 64-bit
          extensions, MMX, SSE, SSE2 and SSE3 instruction set support.

    _k6_
          AMD K6 CPU with MMX instruction set support.

    _k6-2, k6-3_
          Improved versions of AMD K6 CPU with MMX and 3dNOW!
          instruction set support.

    _athlon, athlon-tbird_
          AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and SSE
          prefetch instructions support.

    _athlon-4, athlon-xp, athlon-mp_
          Improved AMD Athlon CPU with MMX, 3dNOW!, enhanced 3dNOW! and
          full SSE instruction set support.

    _k8, opteron, athlon64, athlon-fx_
          AMD K8 core based CPUs with x86-64 instruction set support.
          (This supersets MMX, SSE, SSE2, 3dNOW!, enhanced 3dNOW! and
          64-bit instruction set extensions.)

    _winchip-c6_
          IDT Winchip C6 CPU, dealt in same way as i486 with additional
          MMX instruction set support.

    _winchip2_
          IDT Winchip2 CPU, dealt in same way as i486 with additional
          MMX and 3dNOW!  instruction set support.

    _c3_
          Via C3 CPU with MMX and 3dNOW!  instruction set support.  (No
          scheduling is implemented for this chip.)

    _c3-2_
          Via C3-2 CPU with MMX and SSE instruction set support.  (No
          scheduling is implemented for this chip.)

     While picking a specific CPU-TYPE will schedule things
     appropriately for that particular chip, the compiler will not
     generate any code that does not run on the i386 without the
     `-march=CPU-TYPE' option being used.

`-march=CPU-TYPE'
     Generate instructions for the machine type CPU-TYPE.  The choices
     for CPU-TYPE are the same as for `-mtune'.  Moreover, specifying
     `-march=CPU-TYPE' implies `-mtune=CPU-TYPE'.

`-mcpu=CPU-TYPE'
     A deprecated synonym for `-mtune'.

`-m386'
`-m486'
`-mpentium'
`-mpentiumpro'
     These options are synonyms for `-mtune=i386', `-mtune=i486',
     `-mtune=pentium', and `-mtune=pentiumpro' respectively.  These
     synonyms are deprecated.

`-mfpmath=UNIT'
     Generate floating point arithmetics for selected unit UNIT.  The
     choices for UNIT are:

    `387'
          Use the standard 387 floating point coprocessor present
          majority of chips and emulated otherwise.  Code compiled with
          this option will run almost everywhere.  The temporary
          results are computed in 80bit precision instead of precision
          specified by the type resulting in slightly different results
          compared to most of other chips. See `-ffloat-store' for more
          detailed description.

          This is the default choice for i386 compiler.

    `sse'
          Use scalar floating point instructions present in the SSE
          instruction set.  This instruction set is supported by
          Pentium3 and newer chips, in the AMD line by Athlon-4,
          Athlon-xp and Athlon-mp chips.  The earlier version of SSE
          instruction set supports only single precision arithmetics,
          thus the double and extended precision arithmetics is still
          done using 387.  Later version, present only in Pentium4 and
          the future AMD x86-64 chips supports double precision
          arithmetics too.

          For i387 you need to use `-march=CPU-TYPE', `-msse' or
          `-msse2' switches to enable SSE extensions and make this
          option effective.  For x86-64 compiler, these extensions are
          enabled by default.

          The resulting code should be considerably faster in the
          majority of cases and avoid the numerical instability
          problems of 387 code, but may break some existing code that
          expects temporaries to be 80bit.

          This is the default choice for the x86-64 compiler.

    `sse,387'
          Attempt to utilize both instruction sets at once.  This
          effectively double the amount of available registers and on
          chips with separate execution units for 387 and SSE the
          execution resources too.  Use this option with care, as it is
          still experimental, because the GCC register allocator does
          not model separate functional units well resulting in
          instable performance.

`-masm=DIALECT'
     Output asm instructions using selected DIALECT. Supported choices
     are `intel' or `att' (the default one).

`-mieee-fp'
`-mno-ieee-fp'
     Control whether or not the compiler uses IEEE floating point
     comparisons.  These handle correctly the case where the result of a
     comparison is unordered.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not part of GCC.  Normally
     the facilities of the machine's usual C compiler are used, but
     this can't be done directly in cross-compilation.  You must make
     your own arrangements to provide suitable library functions for
     cross-compilation.

     On machines where a function returns floating point results in the
     80387 register stack, some floating point opcodes may be emitted
     even if `-msoft-float' is used.

`-mno-fp-ret-in-387'
     Do not use the FPU registers for return values of functions.

     The usual calling convention has functions return values of types
     `float' and `double' in an FPU register, even if there is no FPU.
     The idea is that the operating system should emulate an FPU.

     The option `-mno-fp-ret-in-387' causes such values to be returned
     in ordinary CPU registers instead.

`-mno-fancy-math-387'
     Some 387 emulators do not support the `sin', `cos' and `sqrt'
     instructions for the 387.  Specify this option to avoid generating
     those instructions.  This option is the default on FreeBSD,
     OpenBSD and NetBSD.  This option is overridden when `-march'
     indicates that the target cpu will always have an FPU and so the
     instruction will not need emulation.  As of revision 2.6.1, these
     instructions are not generated unless you also use the
     `-funsafe-math-optimizations' switch.

`-malign-double'
`-mno-align-double'
     Control whether GCC aligns `double', `long double', and `long
     long' variables on a two word boundary or a one word boundary.
     Aligning `double' variables on a two word boundary will produce
     code that runs somewhat faster on a `Pentium' at the expense of
     more memory.

     *Warning:* if you use the `-malign-double' switch, structures
     containing the above types will be aligned differently than the
     published application binary interface specifications for the 386
     and will not be binary compatible with structures in code compiled
     without that switch.

`-m96bit-long-double'
`-m128bit-long-double'
     These switches control the size of `long double' type. The i386
     application binary interface specifies the size to be 96 bits, so
     `-m96bit-long-double' is the default in 32 bit mode.

     Modern architectures (Pentium and newer) would prefer `long double'
     to be aligned to an 8 or 16 byte boundary.  In arrays or structures
     conforming to the ABI, this would not be possible.  So specifying a
     `-m128bit-long-double' will align `long double' to a 16 byte
     boundary by padding the `long double' with an additional 32 bit
     zero.

     In the x86-64 compiler, `-m128bit-long-double' is the default
     choice as its ABI specifies that `long double' is to be aligned on
     16 byte boundary.

     Notice that neither of these options enable any extra precision
     over the x87 standard of 80 bits for a `long double'.

     *Warning:* if you override the default value for your target ABI,
     the structures and arrays containing `long double' variables will
     change their size as well as function calling convention for
     function taking `long double' will be modified.  Hence they will
     not be binary compatible with arrays or structures in code
     compiled without that switch.

`-msvr3-shlib'
`-mno-svr3-shlib'
     Control whether GCC places uninitialized local variables into the
     `bss' or `data' segments.  `-msvr3-shlib' places them into `bss'.
     These options are meaningful only on System V Release 3.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return with the `ret' NUM
     instruction, which pops their arguments while returning.  This
     saves one instruction in the caller since there is no need to pop
     the arguments there.

     You can specify that an individual function is called with this
     calling sequence with the function attribute `stdcall'.  You can
     also override the `-mrtd' option by using the function attribute
     `cdecl'.  *Note Function Attributes::.

     *Warning:* this calling convention is incompatible with the one
     normally used on Unix, so you cannot use it if you need to call
     libraries compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

`-mregparm=NUM'
     Control how many registers are used to pass integer arguments.  By
     default, no registers are used to pass arguments, and at most 3
     registers can be used.  You can control this behavior for a
     specific function by using the function attribute `regparm'.
     *Note Function Attributes::.

     *Warning:* if you use this switch, and NUM is nonzero, then you
     must build all modules with the same value, including any
     libraries.  This includes the system libraries and startup modules.

`-mpreferred-stack-boundary=NUM'
     Attempt to keep the stack boundary aligned to a 2 raised to NUM
     byte boundary.  If `-mpreferred-stack-boundary' is not specified,
     the default is 4 (16 bytes or 128 bits), except when optimizing
     for code size (`-Os'), in which case the default is the minimum
     correct alignment (4 bytes for x86, and 8 bytes for x86-64).

     On Pentium and PentiumPro, `double' and `long double' values
     should be aligned to an 8 byte boundary (see `-malign-double') or
     suffer significant run time performance penalties.  On Pentium
     III, the Streaming SIMD Extension (SSE) data type `__m128' suffers
     similar penalties if it is not 16 byte aligned.

     To ensure proper alignment of this values on the stack, the stack
     boundary must be as aligned as that required by any value stored
     on the stack.  Further, every function must be generated such that
     it keeps the stack aligned.  Thus calling a function compiled with
     a higher preferred stack boundary from a function compiled with a
     lower preferred stack boundary will most likely misalign the
     stack.  It is recommended that libraries that use callbacks always
     use the default setting.

     This extra alignment does consume extra stack space, and generally
     increases code size.  Code that is sensitive to stack space usage,
     such as embedded systems and operating system kernels, may want to
     reduce the preferred alignment to `-mpreferred-stack-boundary=2'.

`-mmmx'
`-mno-mmx'

`-msse'
`-mno-sse'

`-msse2'
`-mno-sse2'

`-msse3'
`-mno-sse3'

`-m3dnow'
`-mno-3dnow'
     These switches enable or disable the use of built-in functions
     that allow direct access to the MMX, SSE, SSE2, SSE3 and 3Dnow
     extensions of the instruction set.

     *Note X86 Built-in Functions::, for details of the functions
     enabled and disabled by these switches.

     To have SSE/SSE2 instructions generated automatically from
     floating-point code, see `-mfpmath=sse'.

`-mpush-args'
`-mno-push-args'
     Use PUSH operations to store outgoing parameters.  This method is
     shorter and usually equally fast as method using SUB/MOV
     operations and is enabled by default.  In some cases disabling it
     may improve performance because of improved scheduling and reduced
     dependencies.

`-maccumulate-outgoing-args'
     If enabled, the maximum amount of space required for outgoing
     arguments will be computed in the function prologue.  This is
     faster on most modern CPUs because of reduced dependencies,
     improved scheduling and reduced stack usage when preferred stack
     boundary is not equal to 2.  The drawback is a notable increase in
     code size.  This switch implies `-mno-push-args'.

`-mthreads'
     Support thread-safe exception handling on `Mingw32'.  Code that
     relies on thread-safe exception handling must compile and link all
     code with the `-mthreads' option.  When compiling, `-mthreads'
     defines `-D_MT'; when linking, it links in a special thread helper
     library `-lmingwthrd' which cleans up per thread exception
     handling data.

`-mno-align-stringops'
     Do not align destination of inlined string operations.  This
     switch reduces code size and improves performance in case the
     destination is already aligned, but GCC doesn't know about it.

`-minline-all-stringops'
     By default GCC inlines string operations only when destination is
     known to be aligned at least to 4 byte boundary.  This enables
     more inlining, increase code size, but may improve performance of
     code that depends on fast memcpy, strlen and memset for short
     lengths.

`-momit-leaf-frame-pointer'
     Don't keep the frame pointer in a register for leaf functions.
     This avoids the instructions to save, set up and restore frame
     pointers and makes an extra register available in leaf functions.
     The option `-fomit-frame-pointer' removes the frame pointer for
     all functions which might make debugging harder.

`-mtls-direct-seg-refs'
`-mno-tls-direct-seg-refs'
     Controls whether TLS variables may be accessed with offsets from
     the TLS segment register (`%gs' for 32-bit, `%fs' for 64-bit), or
     whether the thread base pointer must be added.  Whether or not this
     is legal depends on the operating system, and whether it maps the
     segment to cover the entire TLS area.

     For systems that use GNU libc, the default is on.

 These `-m' switches are supported in addition to the above on AMD
x86-64 processors in 64-bit environments.

`-m32'
`-m64'
     Generate code for a 32-bit or 64-bit environment.  The 32-bit
     environment sets int, long and pointer to 32 bits and generates
     code that runs on any i386 system.  The 64-bit environment sets
     int to 32 bits and long and pointer to 64 bits and generates code
     for AMD's x86-64 architecture.

`-mno-red-zone'
     Do not use a so called red zone for x86-64 code.  The red zone is
     mandated by the x86-64 ABI, it is a 128-byte area beyond the
     location of the stack pointer that will not be modified by signal
     or interrupt handlers and therefore can be used for temporary data
     without adjusting the stack pointer.  The flag `-mno-red-zone'
     disables this red zone.

`-mcmodel=small'
     Generate code for the small code model: the program and its
     symbols must be linked in the lower 2 GB of the address space.
     Pointers are 64 bits.  Programs can be statically or dynamically
     linked.  This is the default code model.

`-mcmodel=kernel'
     Generate code for the kernel code model.  The kernel runs in the
     negative 2 GB of the address space.  This model has to be used for
     Linux kernel code.

`-mcmodel=medium'
     Generate code for the medium model: The program is linked in the
     lower 2 GB of the address space but symbols can be located
     anywhere in the address space.  Programs can be statically or
     dynamically linked, but building of shared libraries are not
     supported with the medium model.

`-mcmodel=large'
     Generate code for the large model: This model makes no assumptions
     about addresses and sizes of sections.  Currently GCC does not
     implement this model.


File: gcc,  Node: HPPA Options,  Next: Intel 960 Options,  Prev: i386 and x86-64 Options,  Up: Submodel Options

3.17.12 HPPA Options
--------------------

These `-m' options are defined for the HPPA family of computers:

`-march=ARCHITECTURE-TYPE'
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are `1.0' for PA 1.0, `1.1' for PA 1.1, and
     `2.0' for PA 2.0 processors.  Refer to `/usr/lib/sched.models' on
     an HP-UX system to determine the proper architecture option for
     your machine.  Code compiled for lower numbered architectures will
     run on higher numbered architectures, but not the other way around.

     PA 2.0 support currently requires gas snapshot 19990413 or later.
     The next release of binutils (current is 2.9.1) will probably
     contain PA 2.0 support.

`-mpa-risc-1-0'
`-mpa-risc-1-1'
`-mpa-risc-2-0'
     Synonyms for `-march=1.0', `-march=1.1', and `-march=2.0'
     respectively.

`-mbig-switch'
     Generate code suitable for big switch tables.  Use this option
     only if the assembler/linker complain about out of range branches
     within a switch table.

`-mjump-in-delay'
     Fill delay slots of function calls with unconditional jump
     instructions by modifying the return pointer for the function call
     to be the target of the conditional jump.

`-mdisable-fpregs'
     Prevent floating point registers from being used in any manner.
     This is necessary for compiling kernels which perform lazy context
     switching of floating point registers.  If you use this option and
     attempt to perform floating point operations, the compiler will
     abort.

`-mdisable-indexing'
     Prevent the compiler from using indexing address modes.  This
     avoids some rather obscure problems when compiling MIG generated
     code under MACH.

`-mno-space-regs'
     Generate code that assumes the target has no space registers.
     This allows GCC to generate faster indirect calls and use unscaled
     index address modes.

     Such code is suitable for level 0 PA systems and kernels.

`-mfast-indirect-calls'
     Generate code that assumes calls never cross space boundaries.
     This allows GCC to emit code which performs faster indirect calls.

     This option will not work in the presence of shared libraries or
     nested functions.

`-mlong-load-store'
     Generate 3-instruction load and store sequences as sometimes
     required by the HP-UX 10 linker.  This is equivalent to the `+k'
     option to the HP compilers.

`-mportable-runtime'
     Use the portable calling conventions proposed by HP for ELF
     systems.

`-mgas'
     Enable the use of assembler directives only GAS understands.

`-mschedule=CPU-TYPE'
     Schedule code according to the constraints for the machine type
     CPU-TYPE.  The choices for CPU-TYPE are `700' `7100', `7100LC',
     `7200', `7300' and `8000'.  Refer to `/usr/lib/sched.models' on an
     HP-UX system to determine the proper scheduling option for your
     machine.  The default scheduling is `8000'.

`-mlinker-opt'
     Enable the optimization pass in the HP-UX linker.  Note this makes
     symbolic debugging impossible.  It also triggers a bug in the
     HP-UX 8 and HP-UX 9 linkers in which they give bogus error
     messages when linking some programs.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries are not available for all HPPA
     targets.  Normally the facilities of the machine's usual C
     compiler are used, but this cannot be done directly in
     cross-compilation.  You must make your own arrangements to provide
     suitable library functions for cross-compilation.  The embedded
     target `hppa1.1-*-pro' does provide software floating point
     support.

     `-msoft-float' changes the calling convention in the output file;
     therefore, it is only useful if you compile _all_ of a program with
     this option.  In particular, you need to compile `libgcc.a', the
     library that comes with GCC, with `-msoft-float' in order for this
     to work.

`-msio'
     Generate the predefine, `_SIO', for server IO.  The default is
     `-mwsio'.  This generates the predefines, `__hp9000s700',
     `__hp9000s700__' and `_WSIO', for workstation IO.  These options
     are available under HP-UX and HI-UX.

`-mgnu-ld'
     Use GNU ld specific options.  This passes `-shared' to ld when
     building a shared library.  It is the default when GCC is
     configured, explicitly or implicitly, with the GNU linker.  This
     option does not have any affect on which ld is called, it only
     changes what parameters are passed to that ld.  The ld that is
     called is determined by the `--with-ld' configure option, GCC's
     program search path, and finally by the user's `PATH'.  The linker
     used by GCC can be printed using `which `gcc -print-prog-name=ld`'.

`-mhp-ld'
     Use HP ld specific options.  This passes `-b' to ld when building
     a shared library and passes `+Accept TypeMismatch' to ld on all
     links.  It is the default when GCC is configured, explicitly or
     implicitly, with the HP linker.  This option does not have any
     affect on which ld is called, it only changes what parameters are
     passed to that ld.  The ld that is called is determined by the
     `--with-ld' configure option, GCC's program search path, and
     finally by the user's `PATH'.  The linker used by GCC can be
     printed using `which `gcc -print-prog-name=ld`'.

`-mlong-calls'
     Generate code that uses long call sequences.  This ensures that a
     call is always able to reach linker generated stubs.  The default
     is to generate long calls only when the distance from the call
     site to the beginning of the function or translation unit, as the
     case may be, exceeds a predefined limit set by the branch type
     being used.  The limits for normal calls are 7,600,000 and 240,000
     bytes, respectively for the PA 2.0 and PA 1.X architectures.
     Sibcalls are always limited at 240,000 bytes.

     Distances are measured from the beginning of functions when using
     the `-ffunction-sections' option, or when using the `-mgas' and
     `-mno-portable-runtime' options together under HP-UX with the SOM
     linker.

     It is normally not desirable to use this option as it will degrade
     performance.  However, it may be useful in large applications,
     particularly when partial linking is used to build the application.

     The types of long calls used depends on the capabilities of the
     assembler and linker, and the type of code being generated.  The
     impact on systems that support long absolute calls, and long pic
     symbol-difference or pc-relative calls should be relatively small.
     However, an indirect call is used on 32-bit ELF systems in pic code
     and it is quite long.

`-nolibdld'
     Suppress the generation of link options to search libdld.sl when
     the `-static' option is specified on HP-UX 10 and later.

`-static'
     The HP-UX implementation of setlocale in libc has a dependency on
     libdld.sl.  There isn't an archive version of libdld.sl.  Thus,
     when the `-static' option is specified, special link options are
     needed to resolve this dependency.

     On HP-UX 10 and later, the GCC driver adds the necessary options to
     link with libdld.sl when the `-static' option is specified.  This
     causes the resulting binary to be dynamic.  On the 64-bit port,
     the linkers generate dynamic binaries by default in any case.  The
     `-nolibdld' option can be used to prevent the GCC driver from
     adding these link options.

`-threads'
     Add support for multithreading with the "dce thread" library under
     HP-UX.  This option sets flags for both the preprocessor and
     linker.


File: gcc,  Node: Intel 960 Options,  Next: DEC Alpha Options,  Prev: HPPA Options,  Up: Submodel Options

3.17.13 Intel 960 Options
-------------------------

These `-m' options are defined for the Intel 960 implementations:

`-mCPU-TYPE'
     Assume the defaults for the machine type CPU-TYPE for some of the
     other options, including instruction scheduling, floating point
     support, and addressing modes.  The choices for CPU-TYPE are `ka',
     `kb', `mc', `ca', `cf', `sa', and `sb'.  The default is `kb'.

`-mnumerics'
`-msoft-float'
     The `-mnumerics' option indicates that the processor does support
     floating-point instructions.  The `-msoft-float' option indicates
     that floating-point support should not be assumed.

`-mleaf-procedures'
`-mno-leaf-procedures'
     Do (or do not) attempt to alter leaf procedures to be callable
     with the `bal' instruction as well as `call'.  This will result in
     more efficient code for explicit calls when the `bal' instruction
     can be substituted by the assembler or linker, but less efficient
     code in other cases, such as calls via function pointers, or using
     a linker that doesn't support this optimization.

`-mtail-call'
`-mno-tail-call'
     Do (or do not) make additional attempts (beyond those of the
     machine-independent portions of the compiler) to optimize
     tail-recursive calls into branches.  You may not want to do this
     because the detection of cases where this is not valid is not
     totally complete.  The default is `-mno-tail-call'.

`-mcomplex-addr'
`-mno-complex-addr'
     Assume (or do not assume) that the use of a complex addressing
     mode is a win on this implementation of the i960.  Complex
     addressing modes may not be worthwhile on the K-series, but they
     definitely are on the C-series.  The default is currently
     `-mcomplex-addr' for all processors except the CB and CC.

`-mcode-align'
`-mno-code-align'
     Align code to 8-byte boundaries for faster fetching (or don't
     bother).  Currently turned on by default for C-series
     implementations only.

`-mic-compat'
`-mic2.0-compat'
`-mic3.0-compat'
     Enable compatibility with iC960 v2.0 or v3.0.

`-masm-compat'
`-mintel-asm'
     Enable compatibility with the iC960 assembler.

`-mstrict-align'
`-mno-strict-align'
     Do not permit (do permit) unaligned accesses.

`-mold-align'
     Enable structure-alignment compatibility with Intel's gcc release
     version 1.3 (based on gcc 1.37).  This option implies
     `-mstrict-align'.

`-mlong-double-64'
     Implement type `long double' as 64-bit floating point numbers.
     Without the option `long double' is implemented by 80-bit floating
     point numbers.  The only reason we have it because there is no
     128-bit `long double' support in `fp-bit.c' yet.  So it is only
     useful for people using soft-float targets.  Otherwise, we should
     recommend against use of it.



File: gcc,  Node: DEC Alpha Options,  Next: DEC Alpha/VMS Options,  Prev: Intel 960 Options,  Up: Submodel Options

3.17.14 DEC Alpha Options
-------------------------

These `-m' options are defined for the DEC Alpha implementations:

`-mno-soft-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions for
     floating-point operations.  When `-msoft-float' is specified,
     functions in `libgcc.a' will be used to perform floating-point
     operations.  Unless they are replaced by routines that emulate the
     floating-point operations, or compiled in such a way as to call
     such emulations routines, these routines will issue floating-point
     operations.   If you are compiling for an Alpha without
     floating-point operations, you must ensure that the library is
     built so as not to call them.

     Note that Alpha implementations without floating-point operations
     are required to have floating-point registers.

`-mfp-reg'
`-mno-fp-regs'
     Generate code that uses (does not use) the floating-point register
     set.  `-mno-fp-regs' implies `-msoft-float'.  If the floating-point
     register set is not used, floating point operands are passed in
     integer registers as if they were integers and floating-point
     results are passed in `$0' instead of `$f0'.  This is a
     non-standard calling sequence, so any function with a
     floating-point argument or return value called by code compiled
     with `-mno-fp-regs' must also be compiled with that option.

     A typical use of this option is building a kernel that does not
     use, and hence need not save and restore, any floating-point
     registers.

`-mieee'
     The Alpha architecture implements floating-point hardware
     optimized for maximum performance.  It is mostly compliant with
     the IEEE floating point standard.  However, for full compliance,
     software assistance is required.  This option generates code fully
     IEEE compliant code _except_ that the INEXACT-FLAG is not
     maintained (see below).  If this option is turned on, the
     preprocessor macro `_IEEE_FP' is defined during compilation.  The
     resulting code is less efficient but is able to correctly support
     denormalized numbers and exceptional IEEE values such as
     not-a-number and plus/minus infinity.  Other Alpha compilers call
     this option `-ieee_with_no_inexact'.

`-mieee-with-inexact'
     This is like `-mieee' except the generated code also maintains the
     IEEE INEXACT-FLAG.  Turning on this option causes the generated
     code to implement fully-compliant IEEE math.  In addition to
     `_IEEE_FP', `_IEEE_FP_EXACT' is defined as a preprocessor macro.
     On some Alpha implementations the resulting code may execute
     significantly slower than the code generated by default.  Since
     there is very little code that depends on the INEXACT-FLAG, you
     should normally not specify this option.  Other Alpha compilers
     call this option `-ieee_with_inexact'.

`-mfp-trap-mode=TRAP-MODE'
     This option controls what floating-point related traps are enabled.
     Other Alpha compilers call this option `-fptm TRAP-MODE'.  The
     trap mode can be set to one of four values:

    `n'
          This is the default (normal) setting.  The only traps that
          are enabled are the ones that cannot be disabled in software
          (e.g., division by zero trap).

    `u'
          In addition to the traps enabled by `n', underflow traps are
          enabled as well.

    `su'
          Like `su', but the instructions are marked to be safe for
          software completion (see Alpha architecture manual for
          details).

    `sui'
          Like `su', but inexact traps are enabled as well.

`-mfp-rounding-mode=ROUNDING-MODE'
     Selects the IEEE rounding mode.  Other Alpha compilers call this
     option `-fprm ROUNDING-MODE'.  The ROUNDING-MODE can be one of:

    `n'
          Normal IEEE rounding mode.  Floating point numbers are
          rounded towards the nearest machine number or towards the
          even machine number in case of a tie.

    `m'
          Round towards minus infinity.

    `c'
          Chopped rounding mode.  Floating point numbers are rounded
          towards zero.

    `d'
          Dynamic rounding mode.  A field in the floating point control
          register (FPCR, see Alpha architecture reference manual)
          controls the rounding mode in effect.  The C library
          initializes this register for rounding towards plus infinity.
          Thus, unless your program modifies the FPCR, `d' corresponds
          to round towards plus infinity.

`-mtrap-precision=TRAP-PRECISION'
     In the Alpha architecture, floating point traps are imprecise.
     This means without software assistance it is impossible to recover
     from a floating trap and program execution normally needs to be
     terminated.  GCC can generate code that can assist operating
     system trap handlers in determining the exact location that caused
     a floating point trap.  Depending on the requirements of an
     application, different levels of precisions can be selected:

    `p'
          Program precision.  This option is the default and means a
          trap handler can only identify which program caused a
          floating point exception.

    `f'
          Function precision.  The trap handler can determine the
          function that caused a floating point exception.

    `i'
          Instruction precision.  The trap handler can determine the
          exact instruction that caused a floating point exception.

     Other Alpha compilers provide the equivalent options called
     `-scope_safe' and `-resumption_safe'.

`-mieee-conformant'
     This option marks the generated code as IEEE conformant.  You must
     not use this option unless you also specify `-mtrap-precision=i'
     and either `-mfp-trap-mode=su' or `-mfp-trap-mode=sui'.  Its only
     effect is to emit the line `.eflag 48' in the function prologue of
     the generated assembly file.  Under DEC Unix, this has the effect
     that IEEE-conformant math library routines will be linked in.

`-mbuild-constants'
     Normally GCC examines a 32- or 64-bit integer constant to see if
     it can construct it from smaller constants in two or three
     instructions.  If it cannot, it will output the constant as a
     literal and generate code to load it from the data segment at
     runtime.

     Use this option to require GCC to construct _all_ integer constants
     using code, even if it takes more instructions (the maximum is
     six).

     You would typically use this option to build a shared library
     dynamic loader.  Itself a shared library, it must relocate itself
     in memory before it can find the variables and constants in its
     own data segment.

`-malpha-as'
`-mgas'
     Select whether to generate code to be assembled by the
     vendor-supplied assembler (`-malpha-as') or by the GNU assembler
     `-mgas'.

`-mbwx'
`-mno-bwx'
`-mcix'
`-mno-cix'
`-mfix'
`-mno-fix'
`-mmax'
`-mno-max'
     Indicate whether GCC should generate code to use the optional BWX,
     CIX, FIX and MAX instruction sets.  The default is to use the
     instruction sets supported by the CPU type specified via `-mcpu='
     option or that of the CPU on which GCC was built if none was
     specified.

`-mfloat-vax'
`-mfloat-ieee'
     Generate code that uses (does not use) VAX F and G floating point
     arithmetic instead of IEEE single and double precision.

`-mexplicit-relocs'
`-mno-explicit-relocs'
     Older Alpha assemblers provided no way to generate symbol
     relocations except via assembler macros.  Use of these macros does
     not allow optimal instruction scheduling.  GNU binutils as of
     version 2.12 supports a new syntax that allows the compiler to
     explicitly mark which relocations should apply to which
     instructions.  This option is mostly useful for debugging, as GCC
     detects the capabilities of the assembler when it is built and
     sets the default accordingly.

`-msmall-data'
`-mlarge-data'
     When `-mexplicit-relocs' is in effect, static data is accessed via
     "gp-relative" relocations.  When `-msmall-data' is used, objects 8
     bytes long or smaller are placed in a "small data area" (the
     `.sdata' and `.sbss' sections) and are accessed via 16-bit
     relocations off of the `$gp' register.  This limits the size of
     the small data area to 64KB, but allows the variables to be
     directly accessed via a single instruction.

     The default is `-mlarge-data'.  With this option the data area is
     limited to just below 2GB.  Programs that require more than 2GB of
     data must use `malloc' or `mmap' to allocate the data in the heap
     instead of in the program's data segment.

     When generating code for shared libraries, `-fpic' implies
     `-msmall-data' and `-fPIC' implies `-mlarge-data'.

`-msmall-text'
`-mlarge-text'
     When `-msmall-text' is used, the compiler assumes that the code of
     the entire program (or shared library) fits in 4MB, and is thus
     reachable with a branch instruction.  When `-msmall-data' is used,
     the compiler can assume that all local symbols share the same
     `$gp' value, and thus reduce the number of instructions required
     for a function call from 4 to 1.

     The default is `-mlarge-text'.

`-mcpu=CPU_TYPE'
     Set the instruction set and instruction scheduling parameters for
     machine type CPU_TYPE.  You can specify either the `EV' style name
     or the corresponding chip number.  GCC supports scheduling
     parameters for the EV4, EV5 and EV6 family of processors and will
     choose the default values for the instruction set from the
     processor you specify.  If you do not specify a processor type,
     GCC will default to the processor on which the compiler was built.

     Supported values for CPU_TYPE are

    `ev4'
    `ev45'
    `21064'
          Schedules as an EV4 and has no instruction set extensions.

    `ev5'
    `21164'
          Schedules as an EV5 and has no instruction set extensions.

    `ev56'
    `21164a'
          Schedules as an EV5 and supports the BWX extension.

    `pca56'
    `21164pc'
    `21164PC'
          Schedules as an EV5 and supports the BWX and MAX extensions.

    `ev6'
    `21264'
          Schedules as an EV6 and supports the BWX, FIX, and MAX
          extensions.

    `ev67'
    `21264a'
          Schedules as an EV6 and supports the BWX, CIX, FIX, and MAX
          extensions.

`-mtune=CPU_TYPE'
     Set only the instruction scheduling parameters for machine type
     CPU_TYPE.  The instruction set is not changed.

`-mmemory-latency=TIME'
     Sets the latency the scheduler should assume for typical memory
     references as seen by the application.  This number is highly
     dependent on the memory access patterns used by the application
     and the size of the external cache on the machine.

     Valid options for TIME are

    `NUMBER'
          A decimal number representing clock cycles.

    `L1'
    `L2'
    `L3'
    `main'
          The compiler contains estimates of the number of clock cycles
          for "typical" EV4 & EV5 hardware for the Level 1, 2 & 3 caches
          (also called Dcache, Scache, and Bcache), as well as to main
          memory.  Note that L3 is only valid for EV5.



File: gcc,  Node: DEC Alpha/VMS Options,  Next: H8/300 Options,  Prev: DEC Alpha Options,  Up: Submodel Options

3.17.15 DEC Alpha/VMS Options
-----------------------------

These `-m' options are defined for the DEC Alpha/VMS implementations:

`-mvms-return-codes'
     Return VMS condition codes from main.  The default is to return
     POSIX style condition (e.g. error) codes.


File: gcc,  Node: H8/300 Options,  Next: SH Options,  Prev: DEC Alpha/VMS Options,  Up: Submodel Options

3.17.16 H8/300 Options
----------------------

These `-m' options are defined for the H8/300 implementations:

`-mrelax'
     Shorten some address references at link time, when possible; uses
     the linker option `-relax'.  *Note `ld' and the H8/300:
     (ld)H8/300, for a fuller description.

`-mh'
     Generate code for the H8/300H.

`-ms'
     Generate code for the H8S.

`-mn'
     Generate code for the H8S and H8/300H in the normal mode.  This
     switch must be used either with -mh or -ms.

`-ms2600'
     Generate code for the H8S/2600.  This switch must be used with
     `-ms'.

`-mint32'
     Make `int' data 32 bits by default.

`-malign-300'
     On the H8/300H and H8S, use the same alignment rules as for the
     H8/300.  The default for the H8/300H and H8S is to align longs and
     floats on 4 byte boundaries.  `-malign-300' causes them to be
     aligned on 2 byte boundaries.  This option has no effect on the
     H8/300.


File: gcc,  Node: SH Options,  Next: System V Options,  Prev: H8/300 Options,  Up: Submodel Options

3.17.17 SH Options
------------------

These `-m' options are defined for the SH implementations:

`-m1'
     Generate code for the SH1.

`-m2'
     Generate code for the SH2.

`-m2e'
     Generate code for the SH2e.

`-m3'
     Generate code for the SH3.

`-m3e'
     Generate code for the SH3e.

`-m4-nofpu'
     Generate code for the SH4 without a floating-point unit.

`-m4-single-only'
     Generate code for the SH4 with a floating-point unit that only
     supports single-precision arithmetic.

`-m4-single'
     Generate code for the SH4 assuming the floating-point unit is in
     single-precision mode by default.

`-m4'
     Generate code for the SH4.

`-mb'
     Compile code for the processor in big endian mode.

`-ml'
     Compile code for the processor in little endian mode.

`-mdalign'
     Align doubles at 64-bit boundaries.  Note that this changes the
     calling conventions, and thus some functions from the standard C
     library will not work unless you recompile it first with
     `-mdalign'.

`-mrelax'
     Shorten some address references at link time, when possible; uses
     the linker option `-relax'.

`-mbigtable'
     Use 32-bit offsets in `switch' tables.  The default is to use
     16-bit offsets.

`-mfmovd'
     Enable the use of the instruction `fmovd'.

`-mhitachi'
     Comply with the calling conventions defined by Renesas.

`-mnomacsave'
     Mark the `MAC' register as call-clobbered, even if `-mhitachi' is
     given.

`-mieee'
     Increase IEEE-compliance of floating-point code.

`-misize'
     Dump instruction size and location in the assembly code.

`-mpadstruct'
     This option is deprecated.  It pads structures to multiple of 4
     bytes, which is incompatible with the SH ABI.

`-mspace'
     Optimize for space instead of speed.  Implied by `-Os'.

`-mprefergot'
     When generating position-independent code, emit function calls
     using the Global Offset Table instead of the Procedure Linkage
     Table.

`-musermode'
     Generate a library function call to invalidate instruction cache
     entries, after fixing up a trampoline.  This library function call
     doesn't assume it can write to the whole memory address space.
     This is the default when the target is `sh-*-linux*'.


File: gcc,  Node: System V Options,  Next: TMS320C3x/C4x Options,  Prev: SH Options,  Up: Submodel Options

3.17.18 Options for System V
----------------------------

These additional options are available on System V Release 4 for
compatibility with other compilers on those systems:

`-G'
     Create a shared object.  It is recommended that `-symbolic' or
     `-shared' be used instead.

`-Qy'
     Identify the versions of each tool used by the compiler, in a
     `.ident' assembler directive in the output.

`-Qn'
     Refrain from adding `.ident' directives to the output file (this is
     the default).

`-YP,DIRS'
     Search the directories DIRS, and no others, for libraries
     specified with `-l'.

`-Ym,DIR'
     Look in the directory DIR to find the M4 preprocessor.  The
     assembler uses this option.


File: gcc,  Node: TMS320C3x/C4x Options,  Next: V850 Options,  Prev: System V Options,  Up: Submodel Options

3.17.19 TMS320C3x/C4x Options
-----------------------------

These `-m' options are defined for TMS320C3x/C4x implementations:

`-mcpu=CPU_TYPE'
     Set the instruction set, register set, and instruction scheduling
     parameters for machine type CPU_TYPE.  Supported values for
     CPU_TYPE are `c30', `c31', `c32', `c40', and `c44'.  The default
     is `c40' to generate code for the TMS320C40.

`-mbig-memory'
`-mbig'
`-msmall-memory'
`-msmall'
     Generates code for the big or small memory model.  The small memory
     model assumed that all data fits into one 64K word page.  At
     run-time the data page (DP) register must be set to point to the
     64K page containing the .bss and .data program sections.  The big
     memory model is the default and requires reloading of the DP
     register for every direct memory access.

`-mbk'
`-mno-bk'
     Allow (disallow) allocation of general integer operands into the
     block count register BK.

`-mdb'
`-mno-db'
     Enable (disable) generation of code using decrement and branch,
     DBcond(D), instructions.  This is enabled by default for the C4x.
     To be on the safe side, this is disabled for the C3x, since the
     maximum iteration count on the C3x is 2^23 + 1 (but who iterates
     loops more than 2^23 times on the C3x?).  Note that GCC will try
     to reverse a loop so that it can utilize the decrement and branch
     instruction, but will give up if there is more than one memory
     reference in the loop.  Thus a loop where the loop counter is
     decremented can generate slightly more efficient code, in cases
     where the RPTB instruction cannot be utilized.

`-mdp-isr-reload'
`-mparanoid'
     Force the DP register to be saved on entry to an interrupt service
     routine (ISR), reloaded to point to the data section, and restored
     on exit from the ISR.  This should not be required unless someone
     has violated the small memory model by modifying the DP register,
     say within an object library.

`-mmpyi'
`-mno-mpyi'
     For the C3x use the 24-bit MPYI instruction for integer multiplies
     instead of a library call to guarantee 32-bit results.  Note that
     if one of the operands is a constant, then the multiplication will
     be performed using shifts and adds.  If the `-mmpyi' option is not
     specified for the C3x, then squaring operations are performed
     inline instead of a library call.

`-mfast-fix'
`-mno-fast-fix'
     The C3x/C4x FIX instruction to convert a floating point value to an
     integer value chooses the nearest integer less than or equal to the
     floating point value rather than to the nearest integer.  Thus if
     the floating point number is negative, the result will be
     incorrectly truncated an additional code is necessary to detect
     and correct this case.  This option can be used to disable
     generation of the additional code required to correct the result.

`-mrptb'
`-mno-rptb'
     Enable (disable) generation of repeat block sequences using the
     RPTB instruction for zero overhead looping.  The RPTB construct is
     only used for innermost loops that do not call functions or jump
     across the loop boundaries.  There is no advantage having nested
     RPTB loops due to the overhead required to save and restore the
     RC, RS, and RE registers.  This is enabled by default with `-O2'.

`-mrpts=COUNT'
`-mno-rpts'
     Enable (disable) the use of the single instruction repeat
     instruction RPTS.  If a repeat block contains a single
     instruction, and the loop count can be guaranteed to be less than
     the value COUNT, GCC will emit a RPTS instruction instead of a
     RPTB.  If no value is specified, then a RPTS will be emitted even
     if the loop count cannot be determined at compile time.  Note that
     the repeated instruction following RPTS does not have to be
     reloaded from memory each iteration, thus freeing up the CPU buses
     for operands.  However, since interrupts are blocked by this
     instruction, it is disabled by default.

`-mloop-unsigned'
`-mno-loop-unsigned'
     The maximum iteration count when using RPTS and RPTB (and DB on
     the C40) is 2^31 + 1 since these instructions test if the
     iteration count is negative to terminate the loop.  If the
     iteration count is unsigned there is a possibility than the 2^31 +
     1 maximum iteration count may be exceeded.  This switch allows an
     unsigned iteration count.

`-mti'
     Try to emit an assembler syntax that the TI assembler (asm30) is
     happy with.  This also enforces compatibility with the API
     employed by the TI C3x C compiler.  For example, long doubles are
     passed as structures rather than in floating point registers.

`-mregparm'
`-mmemparm'
     Generate code that uses registers (stack) for passing arguments to
     functions.  By default, arguments are passed in registers where
     possible rather than by pushing arguments on to the stack.

`-mparallel-insns'
`-mno-parallel-insns'
     Allow the generation of parallel instructions.  This is enabled by
     default with `-O2'.

`-mparallel-mpy'
`-mno-parallel-mpy'
     Allow the generation of MPY||ADD and MPY||SUB parallel
     instructions, provided `-mparallel-insns' is also specified.
     These instructions have tight register constraints which can
     pessimize the code generation of large functions.



File: gcc,  Node: V850 Options,  Next: ARC Options,  Prev: TMS320C3x/C4x Options,  Up: Submodel Options

3.17.20 V850 Options
--------------------

These `-m' options are defined for V850 implementations:

`-mlong-calls'
`-mno-long-calls'
     Treat all calls as being far away (near).  If calls are assumed to
     be far away, the compiler will always load the functions address
     up into a register, and call indirect through the pointer.

`-mno-ep'
`-mep'
     Do not optimize (do optimize) basic blocks that use the same index
     pointer 4 or more times to copy pointer into the `ep' register, and
     use the shorter `sld' and `sst' instructions.  The `-mep' option
     is on by default if you optimize.

`-mno-prolog-function'
`-mprolog-function'
     Do not use (do use) external functions to save and restore
     registers at the prologue and epilogue of a function.  The
     external functions are slower, but use less code space if more
     than one function saves the same number of registers.  The
     `-mprolog-function' option is on by default if you optimize.

`-mspace'
     Try to make the code as small as possible.  At present, this just
     turns on the `-mep' and `-mprolog-function' options.

`-mtda=N'
     Put static or global variables whose size is N bytes or less into
     the tiny data area that register `ep' points to.  The tiny data
     area can hold up to 256 bytes in total (128 bytes for byte
     references).

`-msda=N'
     Put static or global variables whose size is N bytes or less into
     the small data area that register `gp' points to.  The small data
     area can hold up to 64 kilobytes.

`-mzda=N'
     Put static or global variables whose size is N bytes or less into
     the first 32 kilobytes of memory.

`-mv850'
     Specify that the target processor is the V850.

`-mbig-switch'
     Generate code suitable for big switch tables.  Use this option
     only if the assembler/linker complain about out of range branches
     within a switch table.

`-mapp-regs'
     This option will cause r2 and r5 to be used in the code generated
     by the compiler.  This setting is the default.

`-mno-app-regs'
     This option will cause r2 and r5 to be treated as fixed registers.

`-mv850e1'
     Specify that the target processor is the V850E1.  The preprocessor
     constants `__v850e1__' and `__v850e__' will be defined if this
     option is used.

`-mv850e'
     Specify that the target processor is the V850E.  The preprocessor
     constant `__v850e__' will be defined if this option is used.

     If neither `-mv850' nor `-mv850e' nor `-mv850e1' are defined then
     a default target processor will be chosen and the relevant
     `__v850*__' preprocessor constant will be defined.

     The preprocessor constants `__v850' and `__v851__' are always
     defined, regardless of which processor variant is the target.

`-mdisable-callt'
     This option will suppress generation of the CALLT instruction for
     the v850e and v850e1 flavors of the v850 architecture.  The
     default is `-mno-disable-callt' which allows the CALLT instruction
     to be used.



File: gcc,  Node: ARC Options,  Next: NS32K Options,  Prev: V850 Options,  Up: Submodel Options

3.17.21 ARC Options
-------------------

These options are defined for ARC implementations:

`-EL'
     Compile code for little endian mode.  This is the default.

`-EB'
     Compile code for big endian mode.

`-mmangle-cpu'
     Prepend the name of the cpu to all public symbol names.  In
     multiple-processor systems, there are many ARC variants with
     different instruction and register set characteristics.  This flag
     prevents code compiled for one cpu to be linked with code compiled
     for another.  No facility exists for handling variants that are
     "almost identical".  This is an all or nothing option.

`-mcpu=CPU'
     Compile code for ARC variant CPU.  Which variants are supported
     depend on the configuration.  All variants support `-mcpu=base',
     this is the default.

`-mtext=TEXT-SECTION'
`-mdata=DATA-SECTION'
`-mrodata=READONLY-DATA-SECTION'
     Put functions, data, and readonly data in TEXT-SECTION,
     DATA-SECTION, and READONLY-DATA-SECTION respectively by default.
     This can be overridden with the `section' attribute.  *Note
     Variable Attributes::.



File: gcc,  Node: NS32K Options,  Next: AVR Options,  Prev: ARC Options,  Up: Submodel Options

3.17.22 NS32K Options
---------------------

These are the `-m' options defined for the 32000 series.  The default
values for these options depends on which style of 32000 was selected
when the compiler was configured; the defaults for the most common
choices are given below.

`-m32032'
`-m32032'
     Generate output for a 32032.  This is the default when the
     compiler is configured for 32032 and 32016 based systems.

`-m32332'
`-m32332'
     Generate output for a 32332.  This is the default when the
     compiler is configured for 32332-based systems.

`-m32532'
`-m32532'
     Generate output for a 32532.  This is the default when the
     compiler is configured for 32532-based systems.

`-m32081'
     Generate output containing 32081 instructions for floating point.
     This is the default for all systems.

`-m32381'
     Generate output containing 32381 instructions for floating point.
     This also implies `-m32081'.  The 32381 is only compatible with
     the 32332 and 32532 cpus.  This is the default for the
     pc532-netbsd configuration.

`-mmulti-add'
     Try and generate multiply-add floating point instructions `polyF'
     and `dotF'.  This option is only available if the `-m32381' option
     is in effect.  Using these instructions requires changes to
     register allocation which generally has a negative impact on
     performance.  This option should only be enabled when compiling
     code particularly likely to make heavy use of multiply-add
     instructions.

`-mnomulti-add'
     Do not try and generate multiply-add floating point instructions
     `polyF' and `dotF'.  This is the default on all platforms.

`-msoft-float'
     Generate output containing library calls for floating point.
     *Warning:* the requisite libraries may not be available.

`-mieee-compare'
`-mno-ieee-compare'
     Control whether or not the compiler uses IEEE floating point
     comparisons.  These handle correctly the case where the result of a
     comparison is unordered.  *Warning:* the requisite kernel support
     may not be available.

`-mnobitfield'
     Do not use the bit-field instructions.  On some machines it is
     faster to use shifting and masking operations.  This is the
     default for the pc532.

`-mbitfield'
     Do use the bit-field instructions.  This is the default for all
     platforms except the pc532.

`-mrtd'
     Use a different function-calling convention, in which functions
     that take a fixed number of arguments return pop their arguments
     on return with the `ret' instruction.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

     Also, you must provide function prototypes for all functions that
     take variable numbers of arguments (including `printf'); otherwise
     incorrect code will be generated for calls to those functions.

     In addition, seriously incorrect code will result if you call a
     function with too many arguments.  (Normally, extra arguments are
     harmlessly ignored.)

     This option takes its name from the 680x0 `rtd' instruction.

`-mregparam'
     Use a different function-calling convention where the first two
     arguments are passed in registers.

     This calling convention is incompatible with the one normally used
     on Unix, so you cannot use it if you need to call libraries
     compiled with the Unix compiler.

`-mnoregparam'
     Do not pass any arguments in registers.  This is the default for
     all targets.

`-msb'
     It is OK to use the sb as an index register which is always loaded
     with zero.  This is the default for the pc532-netbsd target.

`-mnosb'
     The sb register is not available for use or has not been
     initialized to zero by the run time system.  This is the default
     for all targets except the pc532-netbsd.  It is also implied
     whenever `-mhimem' or `-fpic' is set.

`-mhimem'
     Many ns32000 series addressing modes use displacements of up to
     512MB.  If an address is above 512MB then displacements from zero
     can not be used.  This option causes code to be generated which
     can be loaded above 512MB.  This may be useful for operating
     systems or ROM code.

`-mnohimem'
     Assume code will be loaded in the first 512MB of virtual address
     space.  This is the default for all platforms.



File: gcc,  Node: AVR Options,  Next: MCore Options,  Prev: NS32K Options,  Up: Submodel Options

3.17.23 AVR Options
-------------------

These options are defined for AVR implementations:

`-mmcu=MCU'
     Specify ATMEL AVR instruction set or MCU type.

     Instruction set avr1 is for the minimal AVR core, not supported by
     the C compiler, only for assembler programs (MCU types: at90s1200,
     attiny10, attiny11, attiny12, attiny15, attiny28).

     Instruction set avr2 (default) is for the classic AVR core with up
     to 8K program memory space (MCU types: at90s2313, at90s2323,
     attiny22, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434,
     at90s8515, at90c8534, at90s8535).

     Instruction set avr3 is for the classic AVR core with up to 128K
     program memory space (MCU types: atmega103, atmega603, at43usb320,
     at76c711).

     Instruction set avr4 is for the enhanced AVR core with up to 8K
     program memory space (MCU types: atmega8, atmega83, atmega85).

     Instruction set avr5 is for the enhanced AVR core with up to 128K
     program memory space (MCU types: atmega16, atmega161, atmega163,
     atmega32, atmega323, atmega64, atmega128, at43usb355, at94k).

`-msize'
     Output instruction sizes to the asm file.

`-minit-stack=N'
     Specify the initial stack address, which may be a symbol or
     numeric value, `__stack' is the default.

`-mno-interrupts'
     Generated code is not compatible with hardware interrupts.  Code
     size will be smaller.

`-mcall-prologues'
     Functions prologues/epilogues expanded as call to appropriate
     subroutines.  Code size will be smaller.

`-mno-tablejump'
     Do not generate tablejump insns which sometimes increase code size.

`-mtiny-stack'
     Change only the low 8 bits of the stack pointer.


File: gcc,  Node: MCore Options,  Next: IA-64 Options,  Prev: AVR Options,  Up: Submodel Options

3.17.24 MCore Options
---------------------

These are the `-m' options defined for the Motorola M*Core processors.

`-mhardlit'
`-mno-hardlit'
     Inline constants into the code stream if it can be done in two
     instructions or less.

`-mdiv'
`-mno-div'
     Use the divide instruction.  (Enabled by default).

`-mrelax-immediate'
`-mno-relax-immediate'
     Allow arbitrary sized immediates in bit operations.

`-mwide-bitfields'
`-mno-wide-bitfields'
     Always treat bit-fields as int-sized.

`-m4byte-functions'
`-mno-4byte-functions'
     Force all functions to be aligned to a four byte boundary.

`-mcallgraph-data'
`-mno-callgraph-data'
     Emit callgraph information.

`-mslow-bytes'
`-mno-slow-bytes'
     Prefer word access when reading byte quantities.

`-mlittle-endian'
`-mbig-endian'
     Generate code for a little endian target.

`-m210'
`-m340'
     Generate code for the 210 processor.


File: gcc,  Node: IA-64 Options,  Next: D30V Options,  Prev: MCore Options,  Up: Submodel Options

3.17.25 IA-64 Options
---------------------

These are the `-m' options defined for the Intel IA-64 architecture.

`-mbig-endian'
     Generate code for a big endian target.  This is the default for
     HP-UX.

`-mlittle-endian'
     Generate code for a little endian target.  This is the default for
     AIX5 and GNU/Linux.

`-mgnu-as'
`-mno-gnu-as'
     Generate (or don't) code for the GNU assembler.  This is the
     default.

`-mgnu-ld'
`-mno-gnu-ld'
     Generate (or don't) code for the GNU linker.  This is the default.

`-mno-pic'
     Generate code that does not use a global pointer register.  The
     result is not position independent code, and violates the IA-64
     ABI.

`-mvolatile-asm-stop'
`-mno-volatile-asm-stop'
     Generate (or don't) a stop bit immediately before and after
     volatile asm statements.

`-mb-step'
     Generate code that works around Itanium B step errata.

`-mregister-names'
`-mno-register-names'
     Generate (or don't) `in', `loc', and `out' register names for the
     stacked registers.  This may make assembler output more readable.

`-mno-sdata'
`-msdata'
     Disable (or enable) optimizations that use the small data section.
     This may be useful for working around optimizer bugs.

`-mconstant-gp'
     Generate code that uses a single constant global pointer value.
     This is useful when compiling kernel code.

`-mauto-pic'
     Generate code that is self-relocatable.  This implies
     `-mconstant-gp'.  This is useful when compiling firmware code.

`-minline-float-divide-min-latency'
     Generate code for inline divides of floating point values using
     the minimum latency algorithm.

`-minline-float-divide-max-throughput'
     Generate code for inline divides of floating point values using
     the maximum throughput algorithm.

`-minline-int-divide-min-latency'
     Generate code for inline divides of integer values using the
     minimum latency algorithm.

`-minline-int-divide-max-throughput'
     Generate code for inline divides of integer values using the
     maximum throughput algorithm.

`-mno-dwarf2-asm'
`-mdwarf2-asm'
     Don't (or do) generate assembler code for the DWARF2 line number
     debugging info.  This may be useful when not using the GNU
     assembler.

`-mfixed-range=REGISTER-RANGE'
     Generate code treating the given register range as fixed registers.
     A fixed register is one that the register allocator can not use.
     This is useful when compiling kernel code.  A register range is
     specified as two registers separated by a dash.  Multiple register
     ranges can be specified separated by a comma.

`-mearly-stop-bits'
`-mno-early-stop-bits'
     Allow stop bits to be placed earlier than immediately preceding the
     instruction that triggered the stop bit.  This can improve
     instruction scheduling, but does not always do so.


File: gcc,  Node: D30V Options,  Next: S/390 and zSeries Options,  Prev: IA-64 Options,  Up: Submodel Options

3.17.26 D30V Options
--------------------

These `-m' options are defined for D30V implementations:

`-mextmem'
     Link the `.text', `.data', `.bss', `.strings', `.rodata',
     `.rodata1', `.data1' sections into external memory, which starts
     at location `0x80000000'.

`-mextmemory'
     Same as the `-mextmem' switch.

`-monchip'
     Link the `.text' section into onchip text memory, which starts at
     location `0x0'.  Also link `.data', `.bss', `.strings', `.rodata',
     `.rodata1', `.data1' sections into onchip data memory, which
     starts at location `0x20000000'.

`-mno-asm-optimize'
`-masm-optimize'
     Disable (enable) passing `-O' to the assembler when optimizing.
     The assembler uses the `-O' option to automatically parallelize
     adjacent short instructions where possible.

`-mbranch-cost=N'
     Increase the internal costs of branches to N.  Higher costs means
     that the compiler will issue more instructions to avoid doing a
     branch.  The default is 2.

`-mcond-exec=N'
     Specify the maximum number of conditionally executed instructions
     that replace a branch.  The default is 4.


File: gcc,  Node: S/390 and zSeries Options,  Next: CRIS Options,  Prev: D30V Options,  Up: Submodel Options

3.17.27 S/390 and zSeries Options
---------------------------------

These are the `-m' options defined for the S/390 and zSeries
architecture.

`-mhard-float'
`-msoft-float'
     Use (do not use) the hardware floating-point instructions and
     registers for floating-point operations.  When `-msoft-float' is
     specified, functions in `libgcc.a' will be used to perform
     floating-point operations.  When `-mhard-float' is specified, the
     compiler generates IEEE floating-point instructions.  This is the
     default.

`-mbackchain'
`-mno-backchain'
     Generate (or do not generate) code which maintains an explicit
     backchain within the stack frame that points to the caller's frame.
     This may be needed to allow debugging using tools that do not
     understand DWARF-2 call frame information.  The default is not to
     generate the backchain.

`-msmall-exec'
`-mno-small-exec'
     Generate (or do not generate) code using the `bras' instruction to
     do subroutine calls.  This only works reliably if the total
     executable size does not exceed 64k.  The default is to use the
     `basr' instruction instead, which does not have this limitation.

`-m64'
`-m31'
     When `-m31' is specified, generate code compliant to the GNU/Linux
     for S/390 ABI.  When `-m64' is specified, generate code compliant
     to the GNU/Linux for zSeries ABI.  This allows GCC in particular
     to generate 64-bit instructions.  For the `s390' targets, the
     default is `-m31', while the `s390x' targets default to `-m64'.

`-mzarch'
`-mesa'
     When `-mzarch' is specified, generate code using the instructions
     available on z/Architecture.  When `-mesa' is specified, generate
     code using the instructions available on ESA/390. Note that
     `-mesa' is not possible with `-m64'.  When generating code
     compliant to the GNU/Linux for S/390 ABI, the default is `-mesa'.
     When generating code compliant to the GNU/Linux for zSeries ABI,
     the default is `-mzarch'.

`-mmvcle'
`-mno-mvcle'
     Generate (or do not generate) code using the `mvcle' instruction
     to perform block moves.  When `-mno-mvcle' is specified, use a
     `mvc' loop instead.  This is the default.

`-mdebug'
`-mno-debug'
     Print (or do not print) additional debug information when
     compiling.  The default is to not print debug information.

`-march=CPU-TYPE'
     Generate code that will run on CPU-TYPE, which is the name of a
     system representing a certain processor type. Possible values for
     CPU-TYPE are `g5', `g6', `z900', and `z990'.  When generating code
     using the instructions available on z/Architecture, the default is
     `-march=z900'.  Otherwise, the default is `-march=g5'.

`-mtune=CPU-TYPE'
     Tune to CPU-TYPE everything applicable about the generated code,
     except for the ABI and the set of available instructions.  The
     list of CPU-TYPE values is the same as for `-march'.  The default
     is the value used for `-march'.

`-mfused-madd'
`-mno-fused-madd'
     Generate code that uses (does not use) the floating point multiply
     and accumulate instructions.  These instructions are generated by
     default if hardware floating point is used.


File: gcc,  Node: CRIS Options,  Next: MMIX Options,  Prev: S/390 and zSeries Options,  Up: Submodel Options

3.17.28 CRIS Options
--------------------

These options are defined specifically for the CRIS ports.

`-march=ARCHITECTURE-TYPE'
`-mcpu=ARCHITECTURE-TYPE'
     Generate code for the specified architecture.  The choices for
     ARCHITECTURE-TYPE are `v3', `v8' and `v10' for respectively
     ETRAX 4, ETRAX 100, and ETRAX 100 LX.  Default is `v0' except for
     cris-axis-linux-gnu, where the default is `v10'.

`-mtune=ARCHITECTURE-TYPE'
     Tune to ARCHITECTURE-TYPE everything applicable about the generated
     code, except for the ABI and the set of available instructions.
     The choices for ARCHITECTURE-TYPE are the same as for
     `-march=ARCHITECTURE-TYPE'.

`-mmax-stack-frame=N'
     Warn when the stack frame of a function exceeds N bytes.

`-melinux-stacksize=N'
     Only available with the `cris-axis-aout' target.  Arranges for
     indications in the program to the kernel loader that the stack of
     the program should be set to N bytes.

`-metrax4'
`-metrax100'
     The options `-metrax4' and `-metrax100' are synonyms for
     `-march=v3' and `-march=v8' respectively.

`-mmul-bug-workaround'
`-mno-mul-bug-workaround'
     Work around a bug in the `muls' and `mulu' instructions for CPU
     models where it applies.  This option is active by default.

`-mpdebug'
     Enable CRIS-specific verbose debug-related information in the
     assembly code.  This option also has the effect to turn off the
     `#NO_APP' formatted-code indicator to the assembler at the
     beginning of the assembly file.

`-mcc-init'
     Do not use condition-code results from previous instruction;
     always emit compare and test instructions before use of condition
     codes.

`-mno-side-effects'
     Do not emit instructions with side-effects in addressing modes
     other than post-increment.

`-mstack-align'
`-mno-stack-align'
`-mdata-align'
`-mno-data-align'
`-mconst-align'
`-mno-const-align'
     These options (no-options) arranges (eliminate arrangements) for
     the stack-frame, individual data and constants to be aligned for
     the maximum single data access size for the chosen CPU model.  The
     default is to arrange for 32-bit alignment.  ABI details such as
     structure layout are not affected by these options.

`-m32-bit'
`-m16-bit'
`-m8-bit'
     Similar to the stack- data- and const-align options above, these
     options arrange for stack-frame, writable data and constants to
     all be 32-bit, 16-bit or 8-bit aligned.  The default is 32-bit
     alignment.

`-mno-prologue-epilogue'
`-mprologue-epilogue'
     With `-mno-prologue-epilogue', the normal function prologue and
     epilogue that sets up the stack-frame are omitted and no return
     instructions or return sequences are generated in the code.  Use
     this option only together with visual inspection of the compiled
     code: no warnings or errors are generated when call-saved
     registers must be saved, or storage for local variable needs to be
     allocated.

`-mno-gotplt'
`-mgotplt'
     With `-fpic' and `-fPIC', don't generate (do generate) instruction
     sequences that load addresses for functions from the PLT part of
     the GOT rather than (traditional on other architectures) calls to
     the PLT.  The default is `-mgotplt'.

`-maout'
     Legacy no-op option only recognized with the cris-axis-aout target.

`-melf'
     Legacy no-op option only recognized with the cris-axis-elf and
     cris-axis-linux-gnu targets.

`-melinux'
     Only recognized with the cris-axis-aout target, where it selects a
     GNU/linux-like multilib, include files and instruction set for
     `-march=v8'.

`-mlinux'
     Legacy no-op option only recognized with the cris-axis-linux-gnu
     target.

`-sim'
     This option, recognized for the cris-axis-aout and cris-axis-elf
     arranges to link with input-output functions from a simulator
     library.  Code, initialized data and zero-initialized data are
     allocated consecutively.

`-sim2'
     Like `-sim', but pass linker options to locate initialized data at
     0x40000000 and zero-initialized data at 0x80000000.


File: gcc,  Node: MMIX Options,  Next: PDP-11 Options,  Prev: CRIS Options,  Up: Submodel Options

3.17.29 MMIX Options
--------------------

These options are defined for the MMIX:

`-mlibfuncs'
`-mno-libfuncs'
     Specify that intrinsic library functions are being compiled,
     passing all values in registers, no matter the size.

`-mepsilon'
`-mno-epsilon'
     Generate floating-point comparison instructions that compare with
     respect to the `rE' epsilon register.

`-mabi=mmixware'
`-mabi=gnu'
     Generate code that passes function parameters and return values
     that (in the called function) are seen as registers `$0' and up,
     as opposed to the GNU ABI which uses global registers `$231' and
     up.

`-mzero-extend'
`-mno-zero-extend'
     When reading data from memory in sizes shorter than 64 bits, use
     (do not use) zero-extending load instructions by default, rather
     than sign-extending ones.

`-mknuthdiv'
`-mno-knuthdiv'
     Make the result of a division yielding a remainder have the same
     sign as the divisor.  With the default, `-mno-knuthdiv', the sign
     of the remainder follows the sign of the dividend.  Both methods
     are arithmetically valid, the latter being almost exclusively used.

`-mtoplevel-symbols'
`-mno-toplevel-symbols'
     Prepend (do not prepend) a `:' to all global symbols, so the
     assembly code can be used with the `PREFIX' assembly directive.

`-melf'
     Generate an executable in the ELF format, rather than the default
     `mmo' format used by the `mmix' simulator.

`-mbranch-predict'
`-mno-branch-predict'
     Use (do not use) the probable-branch instructions, when static
     branch prediction indicates a probable branch.

`-mbase-addresses'
`-mno-base-addresses'
     Generate (do not generate) code that uses _base addresses_.  Using
     a base address automatically generates a request (handled by the
     assembler and the linker) for a constant to be set up in a global
     register.  The register is used for one or more base address
     requests within the range 0 to 255 from the value held in the
     register.  The generally leads to short and fast code, but the
     number of different data items that can be addressed is limited.
     This means that a program that uses lots of static data may
     require `-mno-base-addresses'.

`-msingle-exit'
`-mno-single-exit'
     Force (do not force) generated code to have a single exit point in
     each function.


File: gcc,  Node: PDP-11 Options,  Next: Xstormy16 Options,  Prev: MMIX Options,  Up: Submodel Options

3.17.30 PDP-11 Options
----------------------

These options are defined for the PDP-11:

`-mfpu'
     Use hardware FPP floating point.  This is the default.  (FIS
     floating point on the PDP-11/40 is not supported.)

`-msoft-float'
     Do not use hardware floating point.

`-mac0'
     Return floating-point results in ac0 (fr0 in Unix assembler
     syntax).

`-mno-ac0'
     Return floating-point results in memory.  This is the default.

`-m40'
     Generate code for a PDP-11/40.

`-m45'
     Generate code for a PDP-11/45.  This is the default.

`-m10'
     Generate code for a PDP-11/10.

`-mbcopy-builtin'
     Use inline `movstrhi' patterns for copying memory.  This is the
     default.

`-mbcopy'
     Do not use inline `movstrhi' patterns for copying memory.

`-mint16'
`-mno-int32'
     Use 16-bit `int'.  This is the default.

`-mint32'
`-mno-int16'
     Use 32-bit `int'.

`-mfloat64'
`-mno-float32'
     Use 64-bit `float'.  This is the default.

`-mfloat32'
`-mno-float64'
     Use 32-bit `float'.

`-mabshi'
     Use `abshi2' pattern.  This is the default.

`-mno-abshi'
     Do not use `abshi2' pattern.

`-mbranch-expensive'
     Pretend that branches are expensive.  This is for experimenting
     with code generation only.

`-mbranch-cheap'
     Do not pretend that branches are expensive.  This is the default.

`-msplit'
     Generate code for a system with split I&D.

`-mno-split'
     Generate code for a system without split I&D.  This is the default.

`-munix-asm'
     Use Unix assembler syntax.  This is the default when configured for
     `pdp11-*-bsd'.

`-mdec-asm'
     Use DEC assembler syntax.  This is the default when configured for
     any PDP-11 target other than `pdp11-*-bsd'.


File: gcc,  Node: Xstormy16 Options,  Next: Xtensa Options,  Prev: PDP-11 Options,  Up: Submodel Options

3.17.31 Xstormy16 Options
-------------------------

These options are defined for Xstormy16:

`-msim'
     Choose startup files and linker script suitable for the simulator.


File: gcc,  Node: FRV Options,  Prev: Xtensa Options,  Up: Submodel Options

3.17.32 FRV Options
-------------------

`-mgpr-32'
     Only use the first 32 general purpose registers.

`-mgpr-64'
     Use all 64 general purpose registers.

`-mfpr-32'
     Use only the first 32 floating point registers.

`-mfpr-64'
     Use all 64 floating point registers

`-mhard-float'
     Use hardware instructions for floating point operations.

`-msoft-float'
     Use library routines for floating point operations.

`-malloc-cc'
     Dynamically allocate condition code registers.

`-mfixed-cc'
     Do not try to dynamically allocate condition code registers, only
     use `icc0' and `fcc0'.

`-mdword'
     Change ABI to use double word insns.

`-mno-dword'
     Do not use double word instructions.

`-mdouble'
     Use floating point double instructions.

`-mno-double'
     Do not use floating point double instructions.

`-mmedia'
     Use media instructions.

`-mno-media'
     Do not use media instructions.

`-mmuladd'
     Use multiply and add/subtract instructions.

`-mno-muladd'
     Do not use multiply and add/subtract instructions.

`-mlibrary-pic'
     Enable PIC support for building libraries

`-macc-4'
     Use only the first four media accumulator registers.

`-macc-8'
     Use all eight media accumulator registers.

`-mpack'
     Pack VLIW instructions.

`-mno-pack'
     Do not pack VLIW instructions.

`-mno-eflags'
     Do not mark ABI switches in e_flags.

`-mcond-move'
     Enable the use of conditional-move instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-cond-move'
     Disable the use of conditional-move instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mscc'
     Enable the use of conditional set instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-scc'
     Disable the use of conditional set instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mcond-exec'
     Enable the use of conditional execution (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-cond-exec'
     Disable the use of conditional execution.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mvliw-branch'
     Run a pass to pack branches into VLIW instructions (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-vliw-branch'
     Do not run a pass to pack branches into VLIW instructions.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mmulti-cond-exec'
     Enable optimization of `&&' and `||' in conditional execution
     (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-multi-cond-exec'
     Disable optimization of `&&' and `||' in conditional execution.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mnested-cond-exec'
     Enable nested conditional execution optimizations (default).

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mno-nested-cond-exec'
     Disable nested conditional execution optimizations.

     This switch is mainly for debugging the compiler and will likely
     be removed in a future version.

`-mtomcat-stats'
     Cause gas to print out tomcat statistics.

`-mcpu=CPU'
     Select the processor type for which to generate code.  Possible
     values are `simple', `tomcat', `fr500', `fr400', `fr300', `frv'.



File: gcc,  Node: Xtensa Options,  Next: FRV Options,  Prev: Xstormy16 Options,  Up: Submodel Options

3.17.33 Xtensa Options
----------------------

These options are supported for Xtensa targets:

`-mconst16'
`-mno-const16'
     Enable or disable use of `CONST16' instructions for loading
     constant values.  The `CONST16' instruction is currently not a
     standard option from Tensilica.  When enabled, `CONST16'
     instructions are always used in place of the standard `L32R'
     instructions.  The use of `CONST16' is enabled by default only if
     the `L32R' instruction is not available.

`-mfused-madd'
`-mno-fused-madd'
     Enable or disable use of fused multiply/add and multiply/subtract
     instructions in the floating-point option.  This has no effect if
     the floating-point option is not also enabled.  Disabling fused
     multiply/add and multiply/subtract instructions forces the
     compiler to use separate instructions for the multiply and
     add/subtract operations.  This may be desirable in some cases
     where strict IEEE 754-compliant results are required: the fused
     multiply add/subtract instructions do not round the intermediate
     result, thereby producing results with _more_ bits of precision
     than specified by the IEEE standard.  Disabling fused multiply
     add/subtract instructions also ensures that the program output is
     not sensitive to the compiler's ability to combine multiply and
     add/subtract operations.

`-mtext-section-literals'
`-mno-text-section-literals'
     Control the treatment of literal pools.  The default is
     `-mno-text-section-literals', which places literals in a separate
     section in the output file.  This allows the literal pool to be
     placed in a data RAM/ROM, and it also allows the linker to combine
     literal pools from separate object files to remove redundant
     literals and improve code size.  With `-mtext-section-literals',
     the literals are interspersed in the text section in order to keep
     them as close as possible to their references.  This may be
     necessary for large assembly files.

`-mtarget-align'
`-mno-target-align'
     When this option is enabled, GCC instructs the assembler to
     automatically align instructions to reduce branch penalties at the
     expense of some code density.  The assembler attempts to widen
     density instructions to align branch targets and the instructions
     following call instructions.  If there are not enough preceding
     safe density instructions to align a target, no widening will be
     performed.  The default is `-mtarget-align'.  These options do not
     affect the treatment of auto-aligned instructions like `LOOP',
     which the assembler will always align, either by widening density
     instructions or by inserting no-op instructions.

`-mlongcalls'
`-mno-longcalls'
     When this option is enabled, GCC instructs the assembler to
     translate direct calls to indirect calls unless it can determine
     that the target of a direct call is in the range allowed by the
     call instruction.  This translation typically occurs for calls to
     functions in other source files.  Specifically, the assembler
     translates a direct `CALL' instruction into an `L32R' followed by
     a `CALLX' instruction.  The default is `-mno-longcalls'.  This
     option should be used in programs where the call target can
     potentially be out of range.  This option is implemented in the
     assembler, not the compiler, so the assembly code generated by GCC
     will still show direct call instructions--look at the disassembled
     object code to see the actual instructions.  Note that the
     assembler will use an indirect call for every cross-file call, not
     just those that really will be out of range.


File: gcc,  Node: Code Gen Options,  Next: Environment Variables,  Prev: Submodel Options,  Up: Invoking GCC

3.18 Options for Code Generation Conventions
============================================

These machine-independent options control the interface conventions
used in code generation.

 Most of them have both positive and negative forms; the negative form
of `-ffoo' would be `-fno-foo'.  In the table below, only one of the
forms is listed--the one which is not the default.  You can figure out
the other form by either removing `no-' or adding it.

`-fbounds-check'
     For front-ends that support it, generate additional code to check
     that indices used to access arrays are within the declared range.
     This is currently only supported by the Java and Fortran 77
     front-ends, where this option defaults to true and false
     respectively.

`-ftrapv'
     This option generates traps for signed overflow on addition,
     subtraction, multiplication operations.

`-fwrapv'
     This option instructs the compiler to assume that signed arithmetic
     overflow of addition, subtraction and multiplication wraps around
     using twos-complement representation.  This flag enables some
     optimizations and disables other.  This option is enabled by
     default for the Java front-end, as required by the Java language
     specification.

`-fexceptions'
     Enable exception handling.  Generates extra code needed to
     propagate exceptions.  For some targets, this implies GCC will
     generate frame unwind information for all functions, which can
     produce significant data size overhead, although it does not
     affect execution.  If you do not specify this option, GCC will
     enable it by default for languages like C++ which normally require
     exception handling, and disable it for languages like C that do
     not normally require it.  However, you may need to enable this
     option when compiling C code that needs to interoperate properly
     with exception handlers written in C++.  You may also wish to
     disable this option if you are compiling older C++ programs that
     don't use exception handling.

`-fnon-call-exceptions'
     Generate code that allows trapping instructions to throw
     exceptions.  Note that this requires platform-specific runtime
     support that does not exist everywhere.  Moreover, it only allows
     _trapping_ instructions to throw exceptions, i.e. memory
     references or floating point instructions.  It does not allow
     exceptions to be thrown from arbitrary signal handlers such as
     `SIGALRM'.

`-funwind-tables'
     Similar to `-fexceptions', except that it will just generate any
     needed static data, but will not affect the generated code in any
     other way.  You will normally not enable this option; instead, a
     language processor that needs this handling would enable it on
     your behalf.

`-fasynchronous-unwind-tables'
     Generate unwind table in dwarf2 format, if supported by target
     machine.  The table is exact at each instruction boundary, so it
     can be used for stack unwinding from asynchronous events (such as
     debugger or garbage collector).

`-fpcc-struct-return'
     Return "short" `struct' and `union' values in memory like longer
     ones, rather than in registers.  This convention is less
     efficient, but it has the advantage of allowing intercallability
     between GCC-compiled files and files compiled with other
     compilers, particularly the Portable C Compiler (pcc).

     The precise convention for returning structures in memory depends
     on the target configuration macros.

     Short structures and unions are those whose size and alignment
     match that of some integer type.

     *Warning:* code compiled with the `-fpcc-struct-return' switch is
     not binary compatible with code compiled with the
     `-freg-struct-return' switch.  Use it to conform to a non-default
     application binary interface.

`-freg-struct-return'
     Return `struct' and `union' values in registers when possible.
     This is more efficient for small structures than
     `-fpcc-struct-return'.

     If you specify neither `-fpcc-struct-return' nor
     `-freg-struct-return', GCC defaults to whichever convention is
     standard for the target.  If there is no standard convention, GCC
     defaults to `-fpcc-struct-return', except on targets where GCC is
     the principal compiler.  In those cases, we can choose the
     standard, and we chose the more efficient register return
     alternative.

     *Warning:* code compiled with the `-freg-struct-return' switch is
     not binary compatible with code compiled with the
     `-fpcc-struct-return' switch.  Use it to conform to a non-default
     application binary interface.

`-fshort-enums'
     Allocate to an `enum' type only as many bytes as it needs for the
     declared range of possible values.  Specifically, the `enum' type
     will be equivalent to the smallest integer type which has enough
     room.

     *Warning:* the `-fshort-enums' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fshort-double'
     Use the same size for `double' as for `float'.

     *Warning:* the `-fshort-double' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fshort-wchar'
     Override the underlying type for `wchar_t' to be `short unsigned
     int' instead of the default for the target.  This option is useful
     for building programs to run under WINE.

     *Warning:* the `-fshort-wchar' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Use it to conform to a non-default application binary
     interface.

`-fshared-data'
     Requests that the data and non-`const' variables of this
     compilation be shared data rather than private data.  The
     distinction makes sense only on certain operating systems, where
     shared data is shared between processes running the same program,
     while private data exists in one copy per process.

`-fno-common'
     In C, allocate even uninitialized global variables in the data
     section of the object file, rather than generating them as common
     blocks.  This has the effect that if the same variable is declared
     (without `extern') in two different compilations, you will get an
     error when you link them.  The only reason this might be useful is
     if you wish to verify that the program will work on other systems
     which always work this way.

`-fno-ident'
     Ignore the `#ident' directive.

`-finhibit-size-directive'
     Don't output a `.size' assembler directive, or anything else that
     would cause trouble if the function is split in the middle, and the
     two halves are placed at locations far apart in memory.  This
     option is used when compiling `crtstuff.c'; you should not need to
     use it for anything else.

`-fverbose-asm'
     Put extra commentary information in the generated assembly code to
     make it more readable.  This option is generally only of use to
     those who actually need to read the generated assembly code
     (perhaps while debugging the compiler itself).

     `-fno-verbose-asm', the default, causes the extra information to
     be omitted and is useful when comparing two assembler files.

`-fpic'
     Generate position-independent code (PIC) suitable for use in a
     shared library, if supported for the target machine.  Such code
     accesses all constant addresses through a global offset table
     (GOT).  The dynamic loader resolves the GOT entries when the
     program starts (the dynamic loader is not part of GCC; it is part
     of the operating system).  If the GOT size for the linked
     executable exceeds a machine-specific maximum size, you get an
     error message from the linker indicating that `-fpic' does not
     work; in that case, recompile with `-fPIC' instead.  (These
     maximums are 8k on the SPARC and 32k on the m68k and RS/6000.  The
     386 has no such limit.)

     Position-independent code requires special support, and therefore
     works only on certain machines.  For the 386, GCC supports PIC for
     System V but not for the Sun 386i.  Code generated for the IBM
     RS/6000 is always position-independent.

`-fPIC'
     If supported for the target machine, emit position-independent
     code, suitable for dynamic linking and avoiding any limit on the
     size of the global offset table.  This option makes a difference
     on the m68k and the SPARC.

     Position-independent code requires special support, and therefore
     works only on certain machines.

`-fpie'
`-fPIE'
     These options are similar to `-fpic' and `-fPIC', but generated
     position independent code can be only linked into executables.
     Usually these options are used when `-pie' GCC option will be used
     during linking.

`-ffixed-REG'
     Treat the register named REG as a fixed register; generated code
     should never refer to it (except perhaps as a stack pointer, frame
     pointer or in some other fixed role).

     REG must be the name of a register.  The register names accepted
     are machine-specific and are defined in the `REGISTER_NAMES' macro
     in the machine description macro file.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-used-REG'
     Treat the register named REG as an allocable register that is
     clobbered by function calls.  It may be allocated for temporaries
     or variables that do not live across a call.  Functions compiled
     this way will not save and restore the register REG.

     It is an error to used this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model will produce
     disastrous results.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fcall-saved-REG'
     Treat the register named REG as an allocable register saved by
     functions.  It may be allocated even for temporaries or variables
     that live across a call.  Functions compiled this way will save
     and restore the register REG if they use it.

     It is an error to used this flag with the frame pointer or stack
     pointer.  Use of this flag for other registers that have fixed
     pervasive roles in the machine's execution model will produce
     disastrous results.

     A different sort of disaster will result from the use of this flag
     for a register in which function values may be returned.

     This flag does not have a negative form, because it specifies a
     three-way choice.

`-fpack-struct'
     Pack all structure members together without holes.

     *Warning:* the `-fpack-struct' switch causes GCC to generate code
     that is not binary compatible with code generated without that
     switch.  Additionally, it makes the code suboptimal.  Use it to
     conform to a non-default application binary interface.

`-finstrument-functions'
     Generate instrumentation calls for entry and exit to functions.
     Just after function entry and just before function exit, the
     following profiling functions will be called with the address of
     the current function and its call site.  (On some platforms,
     `__builtin_return_address' does not work beyond the current
     function, so the call site information may not be available to the
     profiling functions otherwise.)

          void __cyg_profile_func_enter (void *this_fn,
                                         void *call_site);
          void __cyg_profile_func_exit  (void *this_fn,
                                         void *call_site);

     The first argument is the address of the start of the current
     function, which may be looked up exactly in the symbol table.

     This currently disables function inlining.  This restriction is
     expected to be removed in future releases.

     A function may be given the attribute `no_instrument_function', in
     which case this instrumentation will not be done.  This can be
     used, for example, for the profiling functions listed above,
     high-priority interrupt routines, and any functions from which the
     profiling functions cannot safely be called (perhaps signal
     handlers, if the profiling routines generate output or allocate
     memory).

`-fstack-check'
     Generate code to verify that you do not go beyond the boundary of
     the stack.  You should specify this flag if you are running in an
     environment with multiple threads, but only rarely need to specify
     it in a single-threaded environment since stack overflow is
     automatically detected on nearly all systems if there is only one
     stack.

     Note that this switch does not actually cause checking to be done;
     the operating system must do that.  The switch causes generation
     of code to ensure that the operating system sees the stack being
     extended.

`-fstack-limit-register=REG'
`-fstack-limit-symbol=SYM'
`-fno-stack-limit'
     Generate code to ensure that the stack does not grow beyond a
     certain value, either the value of a register or the address of a
     symbol.  If the stack would grow beyond the value, a signal is
     raised.  For most targets, the signal is raised before the stack
     overruns the boundary, so it is possible to catch the signal
     without taking special precautions.

     For instance, if the stack starts at absolute address `0x80000000'
     and grows downwards, you can use the flags
     `-fstack-limit-symbol=__stack_limit' and
     `-Wl,--defsym,__stack_limit=0x7ffe0000' to enforce a stack limit
     of 128KB.  Note that this may only work with the GNU linker.

`-fargument-alias'
`-fargument-noalias'
`-fargument-noalias-global'
     Specify the possible relationships among parameters and between
     parameters and global data.

     `-fargument-alias' specifies that arguments (parameters) may alias
     each other and may alias global storage.
     `-fargument-noalias' specifies that arguments do not alias each
     other, but may alias global storage.
     `-fargument-noalias-global' specifies that arguments do not alias
     each other and do not alias global storage.

     Each language will automatically use whatever option is required by
     the language standard.  You should not need to use these options
     yourself.

`-fleading-underscore'
     This option and its counterpart, `-fno-leading-underscore',
     forcibly change the way C symbols are represented in the object
     file.  One use is to help link with legacy assembly code.

     *Warning:* the `-fleading-underscore' switch causes GCC to
     generate code that is not binary compatible with code generated
     without that switch.  Use it to conform to a non-default
     application binary interface.  Not all targets provide complete
     support for this switch.

`-ftls-model=MODEL'
     Alter the thread-local storage model to be used (*note
     Thread-Local::).  The MODEL argument should be one of
     `global-dynamic', `local-dynamic', `initial-exec' or `local-exec'.

     The default without `-fpic' is `initial-exec'; with `-fpic' the
     default is `global-dynamic'.


File: gcc,  Node: Environment Variables,  Next: Precompiled Headers,  Prev: Code Gen Options,  Up: Invoking GCC

3.19 Environment Variables Affecting GCC
========================================

This section describes several environment variables that affect how GCC
operates.  Some of them work by specifying directories or prefixes to
use when searching for various kinds of files.  Some are used to
specify other aspects of the compilation environment.

 Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (*note Directory Options::).  These take precedence
over places specified using environment variables, which in turn take
precedence over those specified by the configuration of GCC.  *Note
Controlling the Compilation Driver `gcc': (gccint)Driver.

`LANG'
`LC_CTYPE'
`LC_MESSAGES'
`LC_ALL'
     These environment variables control the way that GCC uses
     localization information that allow GCC to work with different
     national conventions.  GCC inspects the locale categories
     `LC_CTYPE' and `LC_MESSAGES' if it has been configured to do so.
     These locale categories can be set to any value supported by your
     installation.  A typical value is `en_UK' for English in the United
     Kingdom.

     The `LC_CTYPE' environment variable specifies character
     classification.  GCC uses it to determine the character boundaries
     in a string; this is needed for some multibyte encodings that
     contain quote and escape characters that would otherwise be
     interpreted as a string end or escape.

     The `LC_MESSAGES' environment variable specifies the language to
     use in diagnostic messages.

     If the `LC_ALL' environment variable is set, it overrides the value
     of `LC_CTYPE' and `LC_MESSAGES'; otherwise, `LC_CTYPE' and
     `LC_MESSAGES' default to the value of the `LANG' environment
     variable.  If none of these variables are set, GCC defaults to
     traditional C English behavior.

`TMPDIR'
     If `TMPDIR' is set, it specifies the directory to use for temporary
     files.  GCC uses temporary files to hold the output of one stage of
     compilation which is to be used as input to the next stage: for
     example, the output of the preprocessor, which is the input to the
     compiler proper.

`GCC_EXEC_PREFIX'
     If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
     names of the subprograms executed by the compiler.  No slash is
     added when this prefix is combined with the name of a subprogram,
     but you can specify a prefix that ends with a slash if you wish.

     If `GCC_EXEC_PREFIX' is not set, GCC will attempt to figure out an
     appropriate prefix to use based on the pathname it was invoked
     with.

     If GCC cannot find the subprogram using the specified prefix, it
     tries looking in the usual places for the subprogram.

     The default value of `GCC_EXEC_PREFIX' is `PREFIX/lib/gcc/' where
     PREFIX is the value of `prefix' when you ran the `configure'
     script.

     Other prefixes specified with `-B' take precedence over this
     prefix.

     This prefix is also used for finding files such as `crt0.o' that
     are used for linking.

     In addition, the prefix is used in an unusual way in finding the
     directories to search for header files.  For each of the standard
     directories whose name normally begins with `/usr/local/lib/gcc'
     (more precisely, with the value of `GCC_INCLUDE_DIR'), GCC tries
     replacing that beginning with the specified prefix to produce an
     alternate directory name.  Thus, with `-Bfoo/', GCC will search
     `foo/bar' where it would normally search `/usr/local/lib/bar'.
     These alternate directories are searched first; the standard
     directories come next.

`COMPILER_PATH'
     The value of `COMPILER_PATH' is a colon-separated list of
     directories, much like `PATH'.  GCC tries the directories thus
     specified when searching for subprograms, if it can't find the
     subprograms using `GCC_EXEC_PREFIX'.

`LIBRARY_PATH'
     The value of `LIBRARY_PATH' is a colon-separated list of
     directories, much like `PATH'.  When configured as a native
     compiler, GCC tries the directories thus specified when searching
     for special linker files, if it can't find them using
     `GCC_EXEC_PREFIX'.  Linking using GCC also uses these directories
     when searching for ordinary libraries for the `-l' option (but
     directories specified with `-L' come first).

`LANG'
     This variable is used to pass locale information to the compiler.
     One way in which this information is used is to determine the
     character set to be used when character literals, string literals
     and comments are parsed in C and C++.  When the compiler is
     configured to allow multibyte characters, the following values for
     `LANG' are recognized:

    `C-JIS'
          Recognize JIS characters.

    `C-SJIS'
          Recognize SJIS characters.

    `C-EUCJP'
          Recognize EUCJP characters.

     If `LANG' is not defined, or if it has some other value, then the
     compiler will use mblen and mbtowc as defined by the default
     locale to recognize and translate multibyte characters.

Some additional environments variables affect the behavior of the
preprocessor.

`CPATH'
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
     Each variable's value is a list of directories separated by a
     special character, much like `PATH', in which to look for header
     files.  The special character, `PATH_SEPARATOR', is
     target-dependent and determined at GCC build time.  For Microsoft
     Windows-based targets it is a semicolon, and for almost all other
     targets it is a colon.

     `CPATH' specifies a list of directories to be searched as if
     specified with `-I', but after any paths given with `-I' options
     on the command line.  This environment variable is used regardless
     of which language is being preprocessed.

     The remaining environment variables apply only when preprocessing
     the particular language indicated.  Each specifies a list of
     directories to be searched as if specified with `-isystem', but
     after any paths given with `-isystem' options on the command line.

     In all these variables, an empty element instructs the compiler to
     search its current working directory.  Empty elements can appear
     at the beginning or end of a path.  For instance, if the value of
     `CPATH' is `:/special/include', that has the same effect as
     `-I. -I/special/include'.

`DEPENDENCIES_OUTPUT'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the non-system header files
     processed by the compiler.  System header files are ignored in the
     dependency output.

     The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form `FILE TARGET', in which case the rules are written to file
     FILE using TARGET as the target name.

     In other words, this environment variable is equivalent to
     combining the options `-MM' and `-MF' (*note Preprocessor
     Options::), with an optional `-MT' switch too.

`SUNPRO_DEPENDENCIES'
     This variable is the same as `DEPENDENCIES_OUTPUT' (see above),
     except that system header files are not ignored, so it implies
     `-M' rather than `-MM'.  However, the dependence on the main input
     file is omitted.  *Note Preprocessor Options::.


File: gcc,  Node: Precompiled Headers,  Next: Running Protoize,  Prev: Environment Variables,  Up: Invoking GCC

3.20 Using Precompiled Headers
==============================

Often large projects have many header files that are included in every
source file.  The time the compiler takes to process these header files
over and over again can account for nearly all of the time required to
build the project.  To make builds faster, GCC allows users to
`precompile' a header file; then, if builds can use the precompiled
header file they will be much faster.

 *Caution:* There are a few known situations where GCC will crash when
trying to use a precompiled header.  If you have trouble with a
precompiled header, you should remove the precompiled header and
compile without it.  In addition, please use GCC's on-line
defect-tracking system to report any problems you encounter with
precompiled headers.  *Note Bugs::.

 To create a precompiled header file, simply compile it as you would any
other file, if necessary using the `-x' option to make the driver treat
it as a C or C++ header file.  You will probably want to use a tool
like `make' to keep the precompiled header up-to-date when the headers
it contains change.

 A precompiled header file will be searched for when `#include' is seen
in the compilation.  As it searches for the included file (*note Search
Path: (cpp)Search Path.) the compiler looks for a precompiled header in
each directory just before it looks for the include file in that
directory.  The name searched for is the name specified in the
`#include' with `.gch' appended.  If the precompiled header file can't
be used, it is ignored.

 For instance, if you have `#include "all.h"', and you have `all.h.gch'
in the same directory as `all.h', then the precompiled header file will
be used if possible, and the original header will be used otherwise.

 Alternatively, you might decide to put the precompiled header file in a
directory and use `-I' to ensure that directory is searched before (or
instead of) the directory containing the original header.  Then, if you
want to check that the precompiled header file is always used, you can
put a file of the same name as the original header in this directory
containing an `#error' command.

 This also works with `-include'.  So yet another way to use
precompiled headers, good for projects not designed with precompiled
header files in mind, is to simply take most of the header files used by
a project, include them from another header file, precompile that header
file, and `-include' the precompiled header.  If the header files have
guards against multiple inclusion, they will be skipped because they've
already been included (in the precompiled header).

 If you need to precompile the same header file for different
languages, targets, or compiler options, you can instead make a
_directory_ named like `all.h.gch', and put each precompiled header in
the directory.  (It doesn't matter what you call the files in the
directory, every precompiled header in the directory will be
considered.)  The first precompiled header encountered in the directory
that is valid for this compilation will be used; they're searched in no
particular order.

 There are many other possibilities, limited only by your imagination,
good sense, and the constraints of your build system.

 A precompiled header file can be used only when these conditions apply:

   * Only one precompiled header can be used in a particular
     compilation.

   * A precompiled header can't be used once the first C token is seen.
     You can have preprocessor directives before a precompiled header;
     you can even include a precompiled header from inside another
     header, so long as there are no C tokens before the `#include'.

   * The precompiled header file must be produced for the same language
     as the current compilation.  You can't use a C precompiled header
     for a C++ compilation.

   * The precompiled header file must be produced by the same compiler
     version and configuration as the current compilation is using.
     The easiest way to guarantee this is to use the same compiler
     binary for creating and using precompiled headers.

   * Any macros defined before the precompiled header (including with
     `-D') must either be defined in the same way as when the
     precompiled header was generated, or must not affect the
     precompiled header, which usually means that the they don't appear
     in the precompiled header at all.

   * Certain command-line options must be defined in the same way as
     when the precompiled header was generated.  At present, it's not
     clear which options are safe to change and which are not; the
     safest choice is to use exactly the same options when generating
     and using the precompiled header.

 For all of these but the last, the compiler will automatically ignore
the precompiled header if the conditions aren't met.  For the last item,
some option changes will cause the precompiled header to be rejected,
but not all incompatible option combinations have yet been found.  If
you find a new incompatible combination, please consider filing a bug
report, see *Note Bugs::.


File: gcc,  Node: Running Protoize,  Prev: Precompiled Headers,  Up: Invoking GCC

3.21 Running Protoize
=====================

The program `protoize' is an optional part of GCC.  You can use it to
add prototypes to a program, thus converting the program to ISO C in
one respect.  The companion program `unprotoize' does the reverse: it
removes argument types from any prototypes that are found.

 When you run these programs, you must specify a set of source files as
command line arguments.  The conversion programs start out by compiling
these files to see what functions they define.  The information gathered
about a file FOO is saved in a file named `FOO.X'.

 After scanning comes actual conversion.  The specified files are all
eligible to be converted; any files they include (whether sources or
just headers) are eligible as well.

 But not all the eligible files are converted.  By default, `protoize'
and `unprotoize' convert only source and header files in the current
directory.  You can specify additional directories whose files should
be converted with the `-d DIRECTORY' option.  You can also specify
particular files to exclude with the `-x FILE' option.  A file is
converted if it is eligible, its directory name matches one of the
specified directory names, and its name within the directory has not
been excluded.

 Basic conversion with `protoize' consists of rewriting most function
definitions and function declarations to specify the types of the
arguments.  The only ones not rewritten are those for varargs functions.

 `protoize' optionally inserts prototype declarations at the beginning
of the source file, to make them available for any calls that precede
the function's definition.  Or it can insert prototype declarations
with block scope in the blocks where undeclared functions are called.

 Basic conversion with `unprotoize' consists of rewriting most function
declarations to remove any argument types, and rewriting function
definitions to the old-style pre-ISO form.

 Both conversion programs print a warning for any function declaration
or definition that they can't convert.  You can suppress these warnings
with `-q'.

 The output from `protoize' or `unprotoize' replaces the original
source file.  The original file is renamed to a name ending with
`.save' (for DOS, the saved filename ends in `.sav' without the
original `.c' suffix).  If the `.save' (`.sav' for DOS) file already
exists, then the source file is simply discarded.

 `protoize' and `unprotoize' both depend on GCC itself to scan the
program and collect information about the functions it uses.  So
neither of these programs will work until GCC is installed.

 Here is a table of the options you can use with `protoize' and
`unprotoize'.  Each option works with both programs unless otherwise
stated.

`-B DIRECTORY'
     Look for the file `SYSCALLS.c.X' in DIRECTORY, instead of the
     usual directory (normally `/usr/local/lib').  This file contains
     prototype information about standard system functions.  This option
     applies only to `protoize'.

`-c COMPILATION-OPTIONS'
     Use COMPILATION-OPTIONS as the options when running `gcc' to
     produce the `.X' files.  The special option `-aux-info' is always
     passed in addition, to tell `gcc' to write a `.X' file.

     Note that the compilation options must be given as a single
     argument to `protoize' or `unprotoize'.  If you want to specify
     several `gcc' options, you must quote the entire set of
     compilation options to make them a single word in the shell.

     There are certain `gcc' arguments that you cannot use, because they
     would produce the wrong kind of output.  These include `-g', `-O',
     `-c', `-S', and `-o' If you include these in the
     COMPILATION-OPTIONS, they are ignored.

`-C'
     Rename files to end in `.C' (`.cc' for DOS-based file systems)
     instead of `.c'.  This is convenient if you are converting a C
     program to C++.  This option applies only to `protoize'.

`-g'
     Add explicit global declarations.  This means inserting explicit
     declarations at the beginning of each source file for each function
     that is called in the file and was not declared.  These
     declarations precede the first function definition that contains a
     call to an undeclared function.  This option applies only to
     `protoize'.

`-i STRING'
     Indent old-style parameter declarations with the string STRING.
     This option applies only to `protoize'.

     `unprotoize' converts prototyped function definitions to old-style
     function definitions, where the arguments are declared between the
     argument list and the initial `{'.  By default, `unprotoize' uses
     five spaces as the indentation.  If you want to indent with just
     one space instead, use `-i " "'.

`-k'
     Keep the `.X' files.  Normally, they are deleted after conversion
     is finished.

`-l'
     Add explicit local declarations.  `protoize' with `-l' inserts a
     prototype declaration for each function in each block which calls
     the function without any declaration.  This option applies only to
     `protoize'.

`-n'
     Make no real changes.  This mode just prints information about the
     conversions that would have been done without `-n'.

`-N'
     Make no `.save' files.  The original files are simply deleted.
     Use this option with caution.

`-p PROGRAM'
     Use the program PROGRAM as the compiler.  Normally, the name `gcc'
     is used.

`-q'
     Work quietly.  Most warnings are suppressed.

`-v'
     Print the version number, just like `-v' for `gcc'.

 If you need special compiler options to compile one of your program's
source files, then you should generate that file's `.X' file specially,
by running `gcc' on that source file with the appropriate options and
the option `-aux-info'.  Then run `protoize' on the entire set of
files.  `protoize' will use the existing `.X' file because it is newer
than the source file.  For example:

     gcc -Dfoo=bar file1.c -aux-info file1.X
     protoize *.c

You need to include the special files along with the rest in the
`protoize' command, even though their `.X' files already exist, because
otherwise they won't get converted.

 *Note Protoize Caveats::, for more information on how to use
`protoize' successfully.


File: gcc,  Node: C Implementation,  Next: C Extensions,  Prev: Invoking GCC,  Up: Top

4 C Implementation-defined behavior
***********************************

A conforming implementation of ISO C is required to document its choice
of behavior in each of the areas that are designated "implementation
defined."  The following lists all such areas, along with the section
number from the ISO/IEC 9899:1999 standard.

* Menu:

* Translation implementation::
* Environment implementation::
* Identifiers implementation::
* Characters implementation::
* Integers implementation::
* Floating point implementation::
* Arrays and pointers implementation::
* Hints implementation::
* Structures unions enumerations and bit-fields implementation::
* Qualifiers implementation::
* Preprocessing directives implementation::
* Library functions implementation::
* Architecture implementation::
* Locale-specific behavior implementation::


File: gcc,  Node: Translation implementation,  Next: Environment implementation,  Up: C Implementation

4.1 Translation
===============

   * `How a diagnostic is identified (3.10, 5.1.1.3).'

     Diagnostics consist of all the output sent to stderr by GCC.

   * `Whether each nonempty sequence of white-space characters other
     than new-line is retained or replaced by one space character in
     translation phase 3 (5.1.1.2).'


File: gcc,  Node: Environment implementation,  Next: Identifiers implementation,  Prev: Translation implementation,  Up: C Implementation

4.2 Environment
===============

The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.


File: gcc,  Node: Identifiers implementation,  Next: Characters implementation,  Prev: Environment implementation,  Up: C Implementation

4.3 Identifiers
===============

   * `Which additional multibyte characters may appear in identifiers
     and their correspondence to universal character names (6.4.2).'

   * `The number of significant initial characters in an identifier
     (5.2.4.1, 6.4.2).'

     For internal names, all characters are significant.  For external
     names, the number of significant characters are defined by the
     linker; for almost all targets, all characters are significant.



File: gcc,  Node: Characters implementation,  Next: Integers implementation,  Prev: Identifiers implementation,  Up: C Implementation

4.4 Characters
==============

   * `The number of bits in a byte (3.6).'

   * `The values of the members of the execution character set (5.2.1).'

   * `The unique value of the member of the execution character set
     produced for each of the standard alphabetic escape sequences
     (5.2.2).'

   * `The value of a `char' object into which has been stored any
     character other than a member of the basic execution character set
     (6.2.5).'

   * `Which of `signed char' or `unsigned char' has the same range,
     representation, and behavior as "plain" `char' (6.2.5, 6.3.1.1).'

   * `The mapping of members of the source character set (in character
     constants and string literals) to members of the execution
     character set (6.4.4.4, 5.1.1.2).'

   * `The value of an integer character constant containing more than
     one character or containing a character or escape sequence that
     does not map to a single-byte execution character (6.4.4.4).'

   * `The value of a wide character constant containing more than one
     multibyte character, or containing a multibyte character or escape
     sequence not represented in the extended execution character set
     (6.4.4.4).'

   * `The current locale used to convert a wide character constant
     consisting of a single multibyte character that maps to a member
     of the extended execution character set into a corresponding wide
     character code (6.4.4.4).'

   * `The current locale used to convert a wide string literal into
     corresponding wide character codes (6.4.5).'

   * `The value of a string literal containing a multibyte character or
     escape sequence not represented in the execution character set
     (6.4.5).'


File: gcc,  Node: Integers implementation,  Next: Floating point implementation,  Prev: Characters implementation,  Up: C Implementation

4.5 Integers
============

   * `Any extended integer types that exist in the implementation
     (6.2.5).'

   * `Whether signed integer types are represented using sign and
     magnitude, two's complement, or one's complement, and whether the
     extraordinary value is a trap representation or an ordinary value
     (6.2.6.2).'

     GCC supports only two's complement integer types, and all bit
     patterns are ordinary values.

   * `The rank of any extended integer type relative to another extended
     integer type with the same precision (6.3.1.1).'

   * `The result of, or the signal raised by, converting an integer to a
     signed integer type when the value cannot be represented in an
     object of that type (6.3.1.3).'

   * `The results of some bitwise operations on signed integers (6.5).'


File: gcc,  Node: Floating point implementation,  Next: Arrays and pointers implementation,  Prev: Integers implementation,  Up: C Implementation

4.6 Floating point
==================

   * `The accuracy of the floating-point operations and of the library
     functions in `<math.h>' and `<complex.h>' that return
     floating-point results (5.2.4.2.2).'

   * `The rounding behaviors characterized by non-standard values of
     `FLT_ROUNDS'  (5.2.4.2.2).'

   * `The evaluation methods characterized by non-standard negative
     values of `FLT_EVAL_METHOD' (5.2.4.2.2).'

   * `The direction of rounding when an integer is converted to a
     floating-point number that cannot exactly represent the original
     value (6.3.1.4).'

   * `The direction of rounding when a floating-point number is
     converted to a narrower floating-point number (6.3.1.5).'

   * `How the nearest representable value or the larger or smaller
     representable value immediately adjacent to the nearest
     representable value is chosen for certain floating constants
     (6.4.4.2).'

   * `Whether and how floating expressions are contracted when not
     disallowed by the `FP_CONTRACT' pragma (6.5).'

   * `The default state for the `FENV_ACCESS' pragma (7.6.1).'

   * `Additional floating-point exceptions, rounding modes,
     environments, and classifications, and their macro names (7.6,
     7.12).'

   * `The default state for the `FP_CONTRACT' pragma (7.12.2).'

   * `Whether the "inexact" floating-point exception can be raised when
     the rounded result actually does equal the mathematical result in
     an IEC 60559 conformant implementation (F.9).'

   * `Whether the "underflow" (and "inexact") floating-point exception
     can be raised when a result is tiny but not inexact in an IEC
     60559 conformant implementation (F.9).'



File: gcc,  Node: Arrays and pointers implementation,  Next: Hints implementation,  Prev: Floating point implementation,  Up: C Implementation

4.7 Arrays and pointers
=======================

   * `The result of converting a pointer to an integer or vice versa
     (6.3.2.3).'

     A cast from pointer to integer discards most-significant bits if
     the pointer representation is larger than the integer type,
     sign-extends(1) if the pointer representation is smaller than the
     integer type, otherwise the bits are unchanged.

     A cast from integer to pointer discards most-significant bits if
     the pointer representation is smaller than the integer type,
     extends according to the signedness of the integer type if the
     pointer representation is larger than the integer type, otherwise
     the bits are unchanged.

     When casting from pointer to integer and back again, the resulting
     pointer must reference the same object as the original pointer,
     otherwise the behavior is undefined.  That is, one may not use
     integer arithmetic to avoid the undefined behavior of pointer
     arithmetic as proscribed in 6.5.6/8.

   * `The size of the result of subtracting two pointers to elements of
     the same array (6.5.6).'


 ---------- Footnotes ----------

 (1) Future versions of GCC may zero-extend, or use a target-defined
`ptr_extend' pattern.  Do not rely on sign extension.


File: gcc,  Node: Hints implementation,  Next: Structures unions enumerations and bit-fields implementation,  Prev: Arrays and pointers implementation,  Up: C Implementation

4.8 Hints
=========

   * `The extent to which suggestions made by using the `register'
     storage-class specifier are effective (6.7.1).'

     The `register' specifier affects code generation only in these
     ways:

        * When used as part of the register variable extension, see
          *Note Explicit Reg Vars::.

        * When `-O0' is in use, the compiler allocates distinct stack
          memory for all variables that do not have the `register'
          storage-class specifier; if `register' is specified, the
          variable may have a shorter lifespan than the code would
          indicate and may never be placed in memory.

        * On some rare x86 targets, `setjmp' doesn't save the registers
          in all circumstances.  In those cases, GCC doesn't allocate
          any variables in registers unless they are marked `register'.


   * `The extent to which suggestions made by using the inline function
     specifier are effective (6.7.4).'

     GCC will not inline any functions if the `-fno-inline' option is
     used or if `-O0' is used.  Otherwise, GCC may still be unable to
     inline a function for many reasons; the `-Winline' option may be
     used to determine if a function has not been inlined and why not.



File: gcc,  Node: Structures unions enumerations and bit-fields implementation,  Next: Qualifiers implementation,  Prev: Hints implementation,  Up: C Implementation

4.9 Structures, unions, enumerations, and bit-fields
====================================================

   * `Whether a "plain" int bit-field is treated as a `signed int'
     bit-field or as an `unsigned int' bit-field (6.7.2, 6.7.2.1).'

   * `Allowable bit-field types other than `_Bool', `signed int', and
     `unsigned int' (6.7.2.1).'

   * `Whether a bit-field can straddle a storage-unit boundary
     (6.7.2.1).'

   * `The order of allocation of bit-fields within a unit (6.7.2.1).'

   * `The alignment of non-bit-field members of structures (6.7.2.1).'

   * `The integer type compatible with each enumerated type (6.7.2.2).'



File: gcc,  Node: Qualifiers implementation,  Next: Preprocessing directives implementation,  Prev: Structures unions enumerations and bit-fields implementation,  Up: C Implementation

4.10 Qualifiers
===============

   * `What constitutes an access to an object that has
     volatile-qualified type (6.7.3).'



File: gcc,  Node: Preprocessing directives implementation,  Next: Library functions implementation,  Prev: Qualifiers implementation,  Up: C Implementation

4.11 Preprocessing directives
=============================

   * `How sequences in both forms of header names are mapped to headers
     or external source file names (6.4.7).'

   * `Whether the value of a character constant in a constant expression
     that controls conditional inclusion matches the value of the same
     character constant in the execution character set (6.10.1).'

   * `Whether the value of a single-character character constant in a
     constant expression that controls conditional inclusion may have a
     negative value (6.10.1).'

   * `The places that are searched for an included `<>' delimited
     header, and how the places are specified or the header is
     identified (6.10.2).'

   * `How the named source file is searched for in an included `""'
     delimited header (6.10.2).'

   * `The method by which preprocessing tokens (possibly resulting from
     macro expansion) in a `#include' directive are combined into a
     header name (6.10.2).'

   * `The nesting limit for `#include' processing (6.10.2).'

     GCC imposes a limit of 200 nested `#include's.

   * `Whether the `#' operator inserts a `\' character before the `\'
     character that begins a universal character name in a character
     constant or string literal (6.10.3.2).'

   * `The behavior on each recognized non-`STDC #pragma' directive
     (6.10.6).'

   * `The definitions for `__DATE__' and `__TIME__' when respectively,
     the date and time of translation are not available (6.10.8).'

     If the date and time are not available, `__DATE__' expands to
     `"??? ?? ????"' and `__TIME__' expands to `"??:??:??"'.



File: gcc,  Node: Library functions implementation,  Next: Architecture implementation,  Prev: Preprocessing directives implementation,  Up: C Implementation

4.12 Library functions
======================

The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.


File: gcc,  Node: Architecture implementation,  Next: Locale-specific behavior implementation,  Prev: Library functions implementation,  Up: C Implementation

4.13 Architecture
=================

   * `The values or expressions assigned to the macros specified in the
     headers `<float.h>', `<limits.h>', and `<stdint.h>' (5.2.4.2,
     7.18.2, 7.18.3).'

   * `The number, order, and encoding of bytes in any object (when not
     explicitly specified in this International Standard) (6.2.6.1).'

   * `The value of the result of the sizeof operator (6.5.3.4).'



File: gcc,  Node: Locale-specific behavior implementation,  Prev: Architecture implementation,  Up: C Implementation

4.14 Locale-specific behavior
=============================

The behavior of these points are dependent on the implementation of the
C library, and are not defined by GCC itself.


File: gcc,  Node: C Extensions,  Next: C++ Extensions,  Prev: C Implementation,  Up: Top

5 Extensions to the C Language Family
*************************************

GNU C provides several language features not found in ISO standard C.
(The `-pedantic' option directs GCC to print a warning message if any
of these features is used.)  To test for the availability of these
features in conditional compilation, check for a predefined macro
`__GNUC__', which is always defined under GCC.

 These extensions are available in C and Objective-C.  Most of them are
also available in C++.  *Note Extensions to the C++ Language: C++
Extensions, for extensions that apply _only_ to C++.

 Some features that are in ISO C99 but not C89 or C++ are also, as
extensions, accepted by GCC in C89 mode and in C++.

* Menu:

* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a block.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls::    Dispatching a call to another function.
* Typeof::              `typeof': referring to the type of an expression.
* Lvalues::             Using `?:', `,' and casts in lvalues.
* Conditionals::        Omitting the middle operand of a `?:' expression.
* Long Long::        Double-word integers---`long long int'.
* Complex::             Data types for complex numbers.
* Hex Floats::          Hexadecimal floating-point constants.
* Zero Length::         Zero-length arrays.
* Variable Length::     Arrays whose length is computed at run time.
* Empty Structures::    Structures with no members.
* Variadic Macros::    Macros with a variable number of arguments.
* Escaped Newlines::    Slightly looser rules for escaped newlines.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on `void'-pointers and function pointers.
* Initializers::        Non-constant initializers.
* Compound Literals::   Compound literals give structures, unions
                         or arrays as values.
* Designated Inits::    Labeling elements of initializers.
* Cast to Union::       Casting to union type from any member of the union.
* Case Ranges::        `case 1 ... 9' and such.
* Mixed Declarations::    Mixing declarations and code.
* Function Attributes:: Declaring that functions have no side effects,
                         or that they can never return.
* Attribute Syntax::    Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments::        C++ comments are recognized.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   `\e' stands for the character <ESC>.
* Variable Attributes::    Specifying attributes of variables.
* Type Attributes::    Specifying attributes of types.
* Alignment::           Inquiring about the alignment of a type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Extended Asm::        Assembler instructions with C expressions as operands.
                         (With them you can define ``built-in'' functions.)
* Constraints::         Constraints for asm operands
* Asm Labels::          Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars::   Defining variables residing in specified registers.
* Alternate Keywords::  `__const__', `__asm__', etc., for header files.
* Incomplete Enums::    `enum foo;', with details to follow.
* Function Names::    Printable strings which are the name of the current
             function.
* Return Address::      Getting the return or frame address of a function.
* Vector Extensions::   Using vector instructions through built-in functions.
* Other Builtins::      Other built-in functions.
* Target Builtins::     Built-in functions specific to particular targets.
* Pragmas::             Pragmas accepted by GCC.
* Unnamed Fields::      Unnamed struct/union fields within structs/unions.
* Thread-Local::        Per-thread variables.


File: gcc,  Node: Statement Exprs,  Next: Local Labels,  Up: C Extensions

5.1 Statements and Declarations in Expressions
==============================================

A compound statement enclosed in parentheses may appear as an expression
in GNU C.  This allows you to use loops, switches, and local variables
within an expression.

 Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces.  For
example:

     ({ int y = foo (); int z;
        if (y > 0) z = y;
        else z = - y;
        z; })

is a valid (though slightly more complex than necessary) expression for
the absolute value of `foo ()'.

 The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type `void', and thus
effectively no value.)

 This feature is especially useful in making macro definitions "safe"
(so that they evaluate each operand exactly once).  For example, the
"maximum" function is commonly defined as a macro in standard C as
follows:

     #define max(a,b) ((a) > (b) ? (a) : (b))

But this definition computes either A or B twice, with bad results if
the operand has side effects.  In GNU C, if you know the type of the
operands (here let's assume `int'), you can define the macro safely as
follows:

     #define maxint(a,b) \
       ({int _a = (a), _b = (b); _a > _b ? _a : _b; })

 Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or the
initial value of a static variable.

 If you don't know the type of the operand, you can still do this, but
you must use `typeof' (*note Typeof::).

 In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression. For instance, if `A' is a class, then

             A a;

             ({a;}).Foo ()

will construct a temporary `A' object to hold the result of the
statement expression, and that will be used to invoke `Foo'.  Therefore
the `this' pointer observed by `Foo' will not be the address of `a'.

 Any temporaries created within a statement within a statement
expression will be destroyed at the statement's end.  This makes
statement expressions inside macros slightly different from function
calls.  In the latter case temporaries introduced during argument
evaluation will be destroyed at the end of the statement that includes
the function call.  In the statement expression case they will be
destroyed during the statement expression.  For instance,

     #define macro(a)  ({__typeof__(a) b = (a); b + 3; })
     template<typename T> T function(T a) { T b = a; return b + 3; }

     void foo ()
     {
       macro (X ());
       function (X ());
     }

will have different places where temporaries are destroyed.  For the
`macro' case, the temporary `X' will be destroyed just after the
initialization of `b'.  In the `function' case that temporary will be
destroyed when the function returns.

 These considerations mean that it is probably a bad idea to use
statement-expressions of this form in header files that are designed to
work with C++.  (Note that some versions of the GNU C Library contained
header files using statement-expression that lead to precisely this
bug.)


File: gcc,  Node: Local Labels,  Next: Labels as Values,  Prev: Statement Exprs,  Up: C Extensions

5.2 Locally Declared Labels
===========================

GCC allows you to declare "local labels" in any nested block scope. A
local label is just like an ordinary label, but you can only reference
it (with a `goto' statement, or by taking its address) within the block
in which it was declared.

 A local label declaration looks like this:

     __label__ LABEL;

or

     __label__ LABEL1, LABEL2, /* ... */;

 Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

 The label declaration defines the label _name_, but does not define
the label itself.  You must do this in the usual way, with `LABEL:',
within the statements of the statement expression.

 The local label feature is useful for complex macros.  If a macro
contains nested loops, a `goto' can be useful for breaking out of them.
However, an ordinary label whose scope is the whole function cannot be
used: if the macro can be expanded several times in one function, the
label will be multiply defined in that function.  A local label avoids
this problem.  For example:

     #define SEARCH(value, array, target)              \
     do {                                              \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { (value) = i; goto found; }              \
       (value) = -1;                                   \
      found:;                                          \
     } while (0)

 This could also be written using a statement-expression:

     #define SEARCH(array, target)                     \
     ({                                                \
       __label__ found;                                \
       typeof (target) _SEARCH_target = (target);      \
       typeof (*(array)) *_SEARCH_array = (array);     \
       int i, j;                                       \
       int value;                                      \
       for (i = 0; i < max; i++)                       \
         for (j = 0; j < max; j++)                     \
           if (_SEARCH_array[i][j] == _SEARCH_target)  \
             { value = i; goto found; }                \
       value = -1;                                     \
      found:                                           \
       value;                                          \
     })

 Local label declarations also make the labels they declare visible to
nested functions, if there are any.  *Note Nested Functions::, for
details.


File: gcc,  Node: Labels as Values,  Next: Nested Functions,  Prev: Local Labels,  Up: C Extensions

5.3 Labels as Values
====================

You can get the address of a label defined in the current function (or
a containing function) with the unary operator `&&'.  The value has
type `void *'.  This value is a constant and can be used wherever a
constant of that type is valid.  For example:

     void *ptr;
     /* ... */
     ptr = &&foo;

 To use these values, you need to be able to jump to one.  This is done
with the computed goto statement(1), `goto *EXP;'.  For example,

     goto *ptr;

Any expression of type `void *' is allowed.

 One way of using these constants is in initializing a static array that
will serve as a jump table:

     static void *array[] = { &&foo, &&bar, &&hack };

 Then you can select a label with indexing, like this:

     goto *array[i];

Note that this does not check whether the subscript is in bounds--array
indexing in C never does that.

 Such an array of label values serves a purpose much like that of the
`switch' statement.  The `switch' statement is cleaner, so use that
rather than an array unless the problem does not fit a `switch'
statement very well.

 Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.

 You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things will happen.  The best way
to avoid this is to store the label address only in automatic variables
and never pass it as an argument.

 An alternate way to write the above example is

     static const int array[] = { &&foo - &&foo, &&bar - &&foo,
                                  &&hack - &&foo };
     goto *(&&foo + array[i]);

This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.

 ---------- Footnotes ----------

 (1) The analogous feature in Fortran is called an assigned goto, but
that name seems inappropriate in C, where one can do more than simply
store label addresses in label variables.


File: gcc,  Node: Nested Functions,  Next: Constructing Calls,  Prev: Labels as Values,  Up: C Extensions

5.4 Nested Functions
====================

A "nested function" is a function defined inside another function.
(Nested functions are not supported for GNU C++.)  The nested function's
name is local to the block where it is defined.  For example, here we
define a nested function named `square', and call it twice:

     foo (double a, double b)
     {
       double square (double z) { return z * z; }

       return square (a) + square (b);
     }

 The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called "lexical scoping".  For example, here we show a nested function
which uses an inherited variable named `offset':

     bar (int *array, int offset, int size)
     {
       int access (int *array, int index)
         { return array[index + offset]; }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
     }

 Nested function definitions are permitted within functions in the
places where variable definitions are allowed; that is, in any block,
before the first statement in the block.

 It is possible to call the nested function from outside the scope of
its name by storing its address or passing the address to another
function:

     hack (int *array, int size)
     {
       void store (int index, int value)
         { array[index] = value; }

       intermediate (store, size);
     }

 Here, the function `intermediate' receives the address of `store' as
an argument.  If `intermediate' calls `store', the arguments given to
`store' are used to store into `array'.  But this technique works only
so long as the containing function (`hack', in this example) does not
exit.

 If you try to call the nested function through its address after the
containing function has exited, all hell will break loose.  If you try
to call it after a containing scope level has exited, and if it refers
to some of the variables that are no longer in scope, you may be lucky,
but it's not wise to take the risk.  If, however, the nested function
does not refer to anything that has gone out of scope, you should be
safe.

 GCC implements taking the address of a nested function using a
technique called "trampolines".  A paper describing them is available as

`http://people.debian.org/~aaronl/Usenix88-lexic.pdf'.

 A nested function can jump to a label inherited from a containing
function, provided the label was explicitly declared in the containing
function (*note Local Labels::).  Such a jump returns instantly to the
containing function, exiting the nested function which did the `goto'
and any intermediate functions as well.  Here is an example:

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       int i;
       /* ... */
       for (i = 0; i < size; i++)
         /* ... */ access (array, i) /* ... */
       /* ... */
       return 0;

      /* Control comes here from `access'
         if it detects an error.  */
      failure:
       return -1;
     }

 A nested function always has internal linkage.  Declaring one with
`extern' is erroneous.  If you need to declare the nested function
before its definition, use `auto' (which is otherwise meaningless for
function declarations).

     bar (int *array, int offset, int size)
     {
       __label__ failure;
       auto int access (int *, int);
       /* ... */
       int access (int *array, int index)
         {
           if (index > size)
             goto failure;
           return array[index + offset];
         }
       /* ... */
     }


File: gcc,  Node: Constructing Calls,  Next: Typeof,  Prev: Nested Functions,  Up: C Extensions

5.5 Constructing Function Calls
===============================

Using the built-in functions described below, you can record the
arguments a function received, and call another function with the same
arguments, without knowing the number or types of the arguments.

 You can also record the return value of that function call, and later
return that value, without knowing what data type the function tried to
return (as long as your caller expects that data type).

 However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language.  It is,
therefore, not recommended to use them outside very simple functions
acting as mere forwarders for their arguments.

 -- Built-in Function: void * __builtin_apply_args ()
     This built-in function returns a pointer to data describing how to
     perform a call with the same arguments as were passed to the
     current function.

     The function saves the arg pointer register, structure value
     address, and all registers that might be used to pass arguments to
     a function into a block of memory allocated on the stack.  Then it
     returns the address of that block.

 -- Built-in Function: void * __builtin_apply (void (*FUNCTION)(), void
          *ARGUMENTS, size_t SIZE)
     This built-in function invokes FUNCTION with a copy of the
     parameters described by ARGUMENTS and SIZE.

     The value of ARGUMENTS should be the value returned by
     `__builtin_apply_args'.  The argument SIZE specifies the size of
     the stack argument data, in bytes.

     This function returns a pointer to data describing how to return
     whatever value was returned by FUNCTION.  The data is saved in a
     block of memory allocated on the stack.

     It is not always simple to compute the proper value for SIZE.  The
     value is used by `__builtin_apply' to compute the amount of data
     that should be pushed on the stack and copied from the incoming
     argument area.

 -- Built-in Function: void __builtin_return (void *RESULT)
     This built-in function returns the value described by RESULT from
     the containing function.  You should specify, for RESULT, a value
     returned by `__builtin_apply'.


File: gcc,  Node: Typeof,  Next: Lvalues,  Prev: Constructing Calls,  Up: C Extensions

5.6 Referring to a Type with `typeof'
=====================================

Another way to refer to the type of an expression is with `typeof'.
The syntax of using of this keyword looks like `sizeof', but the
construct acts semantically like a type name defined with `typedef'.

 There are two ways of writing the argument to `typeof': with an
expression or with a type.  Here is an example with an expression:

     typeof (x[0](1))

This assumes that `x' is an array of pointers to functions; the type
described is that of the values of the functions.

 Here is an example with a typename as the argument:

     typeof (int *)

Here the type described is that of pointers to `int'.

 If you are writing a header file that must work when included in ISO C
programs, write `__typeof__' instead of `typeof'.  *Note Alternate
Keywords::.

 A `typeof'-construct can be used anywhere a typedef name could be
used.  For example, you can use it in a declaration, in a cast, or
inside of `sizeof' or `typeof'.

 `typeof' is often useful in conjunction with the
statements-within-expressions feature.  Here is how the two together can
be used to define a safe "maximum" macro that operates on any
arithmetic type and evaluates each of its arguments exactly once:

     #define max(a,b) \
       ({ typeof (a) _a = (a); \
           typeof (b) _b = (b); \
         _a > _b ? _a : _b; })

 The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within
the expressions that are substituted for `a' and `b'.  Eventually we
hope to design a new form of declaration syntax that allows you to
declare variables whose scopes start only after their initializers;
this will be a more reliable way to prevent such conflicts.

Some more examples of the use of `typeof':

   * This declares `y' with the type of what `x' points to.

          typeof (*x) y;

   * This declares `y' as an array of such values.

          typeof (*x) y[4];

   * This declares `y' as an array of pointers to characters:

          typeof (typeof (char *)[4]) y;

     It is equivalent to the following traditional C declaration:

          char *y[4];

     To see the meaning of the declaration using `typeof', and why it
     might be a useful way to write, let's rewrite it with these macros:

          #define pointer(T)  typeof(T *)
          #define array(T, N) typeof(T [N])

     Now the declaration can be rewritten this way:

          array (pointer (char), 4) y;

     Thus, `array (pointer (char), 4)' is the type of arrays of 4
     pointers to `char'.

 _Compatibility Note:_ In addition to `typeof', GCC 2 supported a more
limited extension which permitted one to write

     typedef T = EXPR;

with the effect of declaring T to have the type of the expression EXPR.
This extension does not work with GCC 3 (versions between 3.0 and 3.2
will crash; 3.2.1 and later give an error).  Code which relies on it
should be rewritten to use `typeof':

     typedef typeof(EXPR) T;

This will work with all versions of GCC.


File: gcc,  Node: Lvalues,  Next: Conditionals,  Prev: Typeof,  Up: C Extensions

5.7 Generalized Lvalues
=======================

Compound expressions, conditional expressions and casts are allowed as
lvalues provided their operands are lvalues.  This means that you can
take their addresses or store values into them.  All these extensions
are deprecated.

 Standard C++ allows compound expressions and conditional expressions
as lvalues, and permits casts to reference type, so use of this
extension is not supported for C++ code.

 For example, a compound expression can be assigned, provided the last
expression in the sequence is an lvalue.  These two expressions are
equivalent:

     (a, b) += 5
     a, (b += 5)

 Similarly, the address of the compound expression can be taken.  These
two expressions are equivalent:

     &(a, b)
     a, &b

 A conditional expression is a valid lvalue if its type is not void and
the true and false branches are both valid lvalues.  For example, these
two expressions are equivalent:

     (a ? b : c) = 5
     (a ? b = 5 : (c = 5))

 A cast is a valid lvalue if its operand is an lvalue.  This extension
is deprecated.  A simple assignment whose left-hand side is a cast
works by converting the right-hand side first to the specified type,
then to the type of the inner left-hand side expression.  After this is
stored, the value is converted back to the specified type to become the
value of the assignment.  Thus, if `a' has type `char *', the following
two expressions are equivalent:

     (int)a = 5
     (int)(a = (char *)(int)5)

 An assignment-with-arithmetic operation such as `+=' applied to a cast
performs the arithmetic using the type resulting from the cast, and then
continues as in the previous case.  Therefore, these two expressions are
equivalent:

     (int)a += 5
     (int)(a = (char *)(int) ((int)a + 5))

 You cannot take the address of an lvalue cast, because the use of its
address would not work out coherently.  Suppose that `&(int)f' were
permitted, where `f' has type `float'.  Then the following statement
would try to store an integer bit-pattern where a floating point number
belongs:

     *&(int)f = 1;

 This is quite different from what `(int)f = 1' would do--that would
convert 1 to floating point and store it.  Rather than cause this
inconsistency, we think it is better to prohibit use of `&' on a cast.

 If you really do want an `int *' pointer with the address of `f', you
can simply write `(int *)&f'.


File: gcc,  Node: Conditionals,  Next: Long Long,  Prev: Lvalues,  Up: C Extensions

5.8 Conditionals with Omitted Operands
======================================

The middle operand in a conditional expression may be omitted.  Then if
the first operand is nonzero, its value is the value of the conditional
expression.

 Therefore, the expression

     x ? : y

has the value of `x' if that is nonzero; otherwise, the value of `y'.

 This example is perfectly equivalent to

     x ? x : y

In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand
does, or may (if it is a macro argument), contain a side effect.  Then
repeating the operand in the middle would perform the side effect
twice.  Omitting the middle operand uses the value already computed
without the undesirable effects of recomputing it.


File: gcc,  Node: Long Long,  Next: Complex,  Prev: Conditionals,  Up: C Extensions

5.9 Double-Word Integers
========================

ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C89 mode and in C++.  Simply
write `long long int' for a signed integer, or `unsigned long long int'
for an unsigned integer.  To make an integer constant of type `long
long int', add the suffix `LL' to the integer.  To make an integer
constant of type `unsigned long long int', add the suffix `ULL' to the
integer.

 You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports fullword-to-doubleword a widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC.

 There may be pitfalls when you use `long long' types for function
arguments, unless you declare function prototypes.  If a function
expects type `int' for its argument, and you pass a value of type `long
long int', confusion will result because the caller and the subroutine
will disagree about the number of bytes for the argument.  Likewise, if
the function expects `long long int' and you pass `int'.  The best way
to avoid such problems is to use prototypes.


File: gcc,  Node: Complex,  Next: Hex Floats,  Prev: Long Long,  Up: C Extensions

5.10 Complex Numbers
====================

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C89 mode and in C++, and supports complex integer data
types which are not part of ISO C99.  You can declare complex types
using the keyword `_Complex'.  As an extension, the older GNU keyword
`__complex__' is also supported.

 For example, `_Complex double x;' declares `x' as a variable whose
real part and imaginary part are both of type `double'.  `_Complex
short int y;' declares `y' to have real and imaginary parts of type
`short int'; this is not likely to be useful, but it shows that the set
of complex types is complete.

 To write a constant with a complex data type, use the suffix `i' or
`j' (either one; they are equivalent).  For example, `2.5fi' has type
`_Complex float' and `3i' has type `_Complex int'.  Such a constant
always has a pure imaginary value, but you can form any complex value
you like by adding one to a real constant.  This is a GNU extension; if
you have an ISO C99 conforming C library (such as GNU libc), and want
to construct complex constants of floating type, you should include
`<complex.h>' and use the macros `I' or `_Complex_I' instead.

 To extract the real part of a complex-valued expression EXP, write
`__real__ EXP'.  Likewise, use `__imag__' to extract the imaginary
part.  This is a GNU extension; for values of floating type, you should
use the ISO C99 functions `crealf', `creal', `creall', `cimagf',
`cimag' and `cimagl', declared in `<complex.h>' and also provided as
built-in functions by GCC.

 The operator `~' performs complex conjugation when used on a value
with a complex type.  This is a GNU extension; for values of floating
type, you should use the ISO C99 functions `conjf', `conj' and `conjl',
declared in `<complex.h>' and also provided as built-in functions by
GCC.

 GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice-versa).  Only the DWARF2
debug info format can represent this, so use of DWARF2 is recommended.
If you are using the stabs debug info format, GCC describes a
noncontiguous complex variable as if it were two separate variables of
noncomplex type.  If the variable's actual name is `foo', the two
fictitious variables are named `foo$real' and `foo$imag'.  You can
examine and set these two fictitious variables with your debugger.


File: gcc,  Node: Hex Floats,  Next: Zero Length,  Prev: Complex,  Up: C Extensions

5.11 Hex Floats
===============

ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as `1.55e1', but also numbers such as `0x1.fp3'
written in hexadecimal format.  As a GNU extension, GCC supports this
in C89 mode (except in some cases when strictly conforming) and in C++.
In that format the `0x' hex introducer and the `p' or `P' exponent
field are mandatory.  The exponent is a decimal number that indicates
the power of 2 by which the significant part will be multiplied.  Thus
`0x1.f' is 1 15/16, `p3' multiplies it by 8, and the value of `0x1.fp3'
is the same as `1.55e1'.

 Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., `0x1.f'.  This
could mean `1.0f' or `1.9375' since `f' is also the extension for
floating-point constants of type `float'.


File: gcc,  Node: Zero Length,  Next: Variable Length,  Prev: Hex Floats,  Up: C Extensions

5.12 Arrays of Length Zero
==========================

Zero-length arrays are allowed in GNU C.  They are very useful as the
last element of a structure which is really a header for a
variable-length object:

     struct line {
       int length;
       char contents[0];
     };

     struct line *thisline = (struct line *)
       malloc (sizeof (struct line) + this_length);
     thisline->length = this_length;

 In ISO C90, you would have to give `contents' a length of 1, which
means either you waste space or complicate the argument to `malloc'.

 In ISO C99, you would use a "flexible array member", which is slightly
different in syntax and semantics:

   * Flexible array members are written as `contents[]' without the `0'.

   * Flexible array members have incomplete type, and so the `sizeof'
     operator may not be applied.  As a quirk of the original
     implementation of zero-length arrays, `sizeof' evaluates to zero.

   * Flexible array members may only appear as the last member of a
     `struct' that is otherwise non-empty.

   * A structure containing a flexible array member, or a union
     containing such a structure (possibly recursively), may not be a
     member of a structure or an element of an array.  (However, these
     uses are permitted by GCC as extensions.)

 GCC versions before 3.0 allowed zero-length arrays to be statically
initialized, as if they were flexible arrays.  In addition to those
cases that were useful, it also allowed initializations in situations
that would corrupt later data.  Non-empty initialization of zero-length
arrays is now treated like any case where there are more initializer
elements than the array holds, in that a suitable warning about "excess
elements in array" is given, and the excess elements (all of them, in
this case) are ignored.

 Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
I.e. in the following, `f1' is constructed as if it were declared like
`f2'.

     struct f1 {
       int x; int y[];
     } f1 = { 1, { 2, 3, 4 } };

     struct f2 {
       struct f1 f1; int data[3];
     } f2 = { { 1 }, { 2, 3, 4 } };

The convenience of this extension is that `f1' has the desired type,
eliminating the need to consistently refer to `f2.f1'.

 This has symmetry with normal static arrays, in that an array of
unknown size is also written with `[]'.

 Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting
data at subsequent offsets.  To avoid undue complication and confusion
with initialization of deeply nested arrays, we simply disallow any
non-empty initialization except when the structure is the top-level
object.  For example:

     struct foo { int x; int y[]; };
     struct bar { struct foo z; };

     struct foo a = { 1, { 2, 3, 4 } };        // Valid.
     struct bar b = { { 1, { 2, 3, 4 } } };    // Invalid.
     struct bar c = { { 1, { } } };            // Valid.
     struct foo d[1] = { { 1 { 2, 3, 4 } } };  // Invalid.


File: gcc,  Node: Empty Structures,  Next: Variadic Macros,  Prev: Variable Length,  Up: C Extensions

5.13 Structures With No Members
===============================

GCC permits a C structure to have no members:

     struct empty {
     };

 The structure will have size zero.  In C++, empty structures are part
of the language.  G++ treats empty structures as if they had a single
member of type `char'.


File: gcc,  Node: Variable Length,  Next: Empty Structures,  Prev: Zero Length,  Up: C Extensions

5.14 Arrays of Variable Length
==============================

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C89 mode and in C++.  (However, GCC's
implementation of variable-length arrays does not yet conform in detail
to the ISO C99 standard.)  These arrays are declared like any other
automatic arrays, but with a length that is not a constant expression.
The storage is allocated at the point of declaration and deallocated
when the brace-level is exited.  For example:

     FILE *
     concat_fopen (char *s1, char *s2, char *mode)
     {
       char str[strlen (s1) + strlen (s2) + 1];
       strcpy (str, s1);
       strcat (str, s2);
       return fopen (str, mode);
     }

 Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

 You can use the function `alloca' to get an effect much like
variable-length arrays.  The function `alloca' is available in many
other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

 There are other differences between these two methods.  Space allocated
with `alloca' exists until the containing _function_ returns.  The
space for a variable-length array is deallocated as soon as the array
name's scope ends.  (If you use both variable-length arrays and
`alloca' in the same function, deallocation of a variable-length array
will also deallocate anything more recently allocated with `alloca'.)

 You can also use variable-length arrays as arguments to functions:

     struct entry
     tester (int len, char data[len][len])
     {
       /* ... */
     }

 The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
`sizeof'.

 If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list--another GNU extension.

     struct entry
     tester (int len; char data[len][len], int len)
     {
       /* ... */
     }

 The `int len' before the semicolon is a "parameter forward
declaration", and it serves the purpose of making the name `len' known
when the declaration of `data' is parsed.

 You can write any number of such parameter forward declarations in the
parameter list.  They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the "real"
parameter declarations.  Each forward declaration must match a "real"
declaration in parameter name and data type.  ISO C99 does not support
parameter forward declarations.


File: gcc,  Node: Variadic Macros,  Next: Escaped Newlines,  Prev: Empty Structures,  Up: C Extensions

5.15 Macros with a Variable Number of Arguments.
================================================

In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can.  The syntax for
defining the macro is similar to that of a function.  Here is an
example:

     #define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)

 Here `...' is a "variable argument".  In the invocation of such a
macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas.  This set of
tokens replaces the identifier `__VA_ARGS__' in the macro body wherever
it appears.  See the CPP manual for more information.

 GCC has long supported variadic macros, and used a different syntax
that allowed you to give a name to the variable arguments just like any
other argument.  Here is an example:

     #define debug(format, args...) fprintf (stderr, format, args)

 This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.

 GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.

 In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument.  For example,
this invocation is invalid in ISO C, because there is no comma after
the string:

     debug ("A message")

 GNU CPP permits you to completely omit the variable arguments in this
way.  In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.

 To help solve this problem, CPP behaves specially for variable
arguments used with the token paste operator, `##'.  If instead you
write

     #define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)

 and if the variable arguments are omitted or empty, the `##' operator
causes the preprocessor to remove the comma before it.  If you do
provide some variable arguments in your macro invocation, GNU CPP does
not complain about the paste operation and instead places the variable
arguments after the comma.  Just like any other pasted macro argument,
these arguments are not macro expanded.


File: gcc,  Node: Escaped Newlines,  Next: Subscripting,  Prev: Variadic Macros,  Up: C Extensions

5.16 Slightly Looser Rules for Escaped Newlines
===============================================

Recently, the preprocessor has relaxed its treatment of escaped
newlines.  Previously, the newline had to immediately follow a
backslash.  The current implementation allows whitespace in the form of
spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline.  The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line.  This works within comments and
tokens, as well as between tokens.  Comments are _not_ treated as
whitespace for the purposes of this relaxation, since they have not yet
been replaced with spaces.


File: gcc,  Node: Subscripting,  Next: Pointer Arith,  Prev: Escaped Newlines,  Up: C Extensions

5.17 Non-Lvalue Arrays May Have Subscripts
==========================================

In ISO C99, arrays that are not lvalues still decay to pointers, and
may be subscripted, although they may not be modified or used after the
next sequence point and the unary `&' operator may not be applied to
them.  As an extension, GCC allows such arrays to be subscripted in C89
mode, though otherwise they do not decay to pointers outside C99 mode.
For example, this is valid in GNU C though not valid in C89:

     struct foo {int a[4];};

     struct foo f();

     bar (int index)
     {
       return f().a[index];
     }


File: gcc,  Node: Pointer Arith,  Next: Initializers,  Prev: Subscripting,  Up: C Extensions

5.18 Arithmetic on `void'- and Function-Pointers
================================================

In GNU C, addition and subtraction operations are supported on pointers
to `void' and on pointers to functions.  This is done by treating the
size of a `void' or of a function as 1.

 A consequence of this is that `sizeof' is also allowed on `void' and
on function types, and returns 1.

 The option `-Wpointer-arith' requests a warning if these extensions
are used.


File: gcc,  Node: Initializers,  Next: Compound Literals,  Prev: Pointer Arith,  Up: C Extensions

5.19 Non-Constant Initializers
==============================

As in standard C++ and ISO C99, the elements of an aggregate
initializer for an automatic variable are not required to be constant
expressions in GNU C.  Here is an example of an initializer with
run-time varying elements:

     foo (float f, float g)
     {
       float beat_freqs[2] = { f-g, f+g };
       /* ... */
     }


File: gcc,  Node: Compound Literals,  Next: Designated Inits,  Prev: Initializers,  Up: C Extensions

5.20 Compound Literals
======================

ISO C99 supports compound literals.  A compound literal looks like a
cast containing an initializer.  Its value is an object of the type
specified in the cast, containing the elements specified in the
initializer; it is an lvalue.  As an extension, GCC supports compound
literals in C89 mode and in C++.

 Usually, the specified type is a structure.  Assume that `struct foo'
and `structure' are declared as shown:

     struct foo {int a; char b[2];} structure;

Here is an example of constructing a `struct foo' with a compound
literal:

     structure = ((struct foo) {x + y, 'a', 0});

This is equivalent to writing the following:

     {
       struct foo temp = {x + y, 'a', 0};
       structure = temp;
     }

 You can also construct an array.  If all the elements of the compound
literal are (made up of) simple constant expressions, suitable for use
in initializers of objects of static storage duration, then the compound
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:

     char **foo = (char *[]) { "x", "y", "z" };

 Compound literals for scalar types and union types are is also
allowed, but then the compound literal is equivalent to a cast.

 As a GNU extension, GCC allows initialization of objects with static
storage duration by compound literals (which is not possible in ISO
C99, because the initializer is not a constant).  It is handled as if
the object was initialized only with the bracket enclosed list if
compound literal's and object types match.  The initializer list of the
compound literal must be constant.  If the object being initialized has
array type of unknown size, the size is determined by compound literal
size.

     static struct foo x = (struct foo) {1, 'a', 'b'};
     static int y[] = (int []) {1, 2, 3};
     static int z[] = (int [3]) {1};

The above lines are equivalent to the following:
     static struct foo x = {1, 'a', 'b'};
     static int y[] = {1, 2, 3};
     static int z[] = {1, 0, 0};


File: gcc,  Node: Designated Inits,  Next: Cast to Union,  Prev: Compound Literals,  Up: C Extensions

5.21 Designated Initializers
============================

Standard C89 requires the elements of an initializer to appear in a
fixed order, the same as the order of the elements in the array or
structure being initialized.

 In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C89 mode as well.  This extension is not implemented in
GNU C++.

 To specify an array index, write `[INDEX] =' before the element value.
For example,

     int a[6] = { [4] = 29, [2] = 15 };

is equivalent to

     int a[6] = { 0, 0, 15, 0, 29, 0 };

The index values must be constant expressions, even if the array being
initialized is automatic.

 An alternative syntax for this which has been obsolete since GCC 2.5
but GCC still accepts is to write `[INDEX]' before the element value,
with no `='.

 To initialize a range of elements to the same value, write `[FIRST ...
LAST] = VALUE'.  This is a GNU extension.  For example,

     int widths[] = { [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 };

If the value in it has side-effects, the side-effects will happen only
once, not for each initialized field by the range initializer.

Note that the length of the array is the highest value specified plus
one.

 In a structure initializer, specify the name of a field to initialize
with `.FIELDNAME =' before the element value.  For example, given the
following structure,

     struct point { int x, y; };

the following initialization

     struct point p = { .y = yvalue, .x = xvalue };

is equivalent to

     struct point p = { xvalue, yvalue };

 Another syntax which has the same meaning, obsolete since GCC 2.5, is
`FIELDNAME:', as shown here:

     struct point p = { y: yvalue, x: xvalue };

 The `[INDEX]' or `.FIELDNAME' is known as a "designator".  You can
also use a designator (or the obsolete colon syntax) when initializing
a union, to specify which element of the union should be used.  For
example,

     union foo { int i; double d; };

     union foo f = { .d = 4 };

will convert 4 to a `double' to store it in the union using the second
element.  By contrast, casting 4 to type `union foo' would store it
into the union as the integer `i', since it is an integer.  (*Note Cast
to Union::.)

 You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a designator applies to the next consecutive element of
the array or structure.  For example,

     int a[6] = { [1] = v1, v2, [4] = v4 };

is equivalent to

     int a[6] = { 0, v1, v2, 0, v4, 0 };

 Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an `enum' type.  For
example:

     int whitespace[256]
       = { [' '] = 1, ['\t'] = 1, ['\h'] = 1,
           ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 };

 You can also write a series of `.FIELDNAME' and `[INDEX]' designators
before an `=' to specify a nested subobject to initialize; the list is
taken relative to the subobject corresponding to the closest
surrounding brace pair.  For example, with the `struct point'
declaration above:

     struct point ptarray[10] = { [2].y = yv2, [2].x = xv2, [0].x = xv0 };

If the same field is initialized multiple times, it will have value from
the last initialization.  If any such overridden initialization has
side-effect, it is unspecified whether the side-effect happens or not.
Currently, GCC will discard them and issue a warning.


File: gcc,  Node: Case Ranges,  Next: Mixed Declarations,  Prev: Cast to Union,  Up: C Extensions

5.22 Case Ranges
================

You can specify a range of consecutive values in a single `case' label,
like this:

     case LOW ... HIGH:

This has the same effect as the proper number of individual `case'
labels, one for each integer value from LOW to HIGH, inclusive.

 This feature is especially useful for ranges of ASCII character codes:

     case 'A' ... 'Z':

 *Be careful:* Write spaces around the `...', for otherwise it may be
parsed wrong when you use it with integer values.  For example, write
this:

     case 1 ... 5:

rather than this:

     case 1...5:


File: gcc,  Node: Cast to Union,  Next: Case Ranges,  Prev: Designated Inits,  Up: C Extensions

5.23 Cast to a Union Type
=========================

A cast to union type is similar to other casts, except that the type
specified is a union type.  You can specify the type either with `union
TAG' or with a typedef name.  A cast to union is actually a constructor
though, not a cast, and hence does not yield an lvalue like normal
casts.  (*Note Compound Literals::.)

 The types that may be cast to the union type are those of the members
of the union.  Thus, given the following union and variables:

     union foo { int i; double d; };
     int x;
     double y;

both `x' and `y' can be cast to type `union foo'.

 Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:

     union foo u;
     /* ... */
     u = (union foo) x  ==  u.i = x
     u = (union foo) y  ==  u.d = y

 You can also use the union cast as a function argument:

     void hack (union foo);
     /* ... */
     hack ((union foo) x);


File: gcc,  Node: Mixed Declarations,  Next: Function Attributes,  Prev: Case Ranges,  Up: C Extensions

5.24 Mixed Declarations and Code
================================

ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements.  As an extension, GCC also allows this in
C89 mode.  For example, you could do:

     int i;
     /* ... */
     i++;
     int j = i + 2;

 Each identifier is visible from where it is declared until the end of
the enclosing block.


File: gcc,  Node: Function Attributes,  Next: Attribute Syntax,  Prev: Mixed Declarations,  Up: C Extensions

5.25 Declaring Attributes of Functions
======================================

In GNU C, you declare certain things about functions called in your
program which help the compiler optimize function calls and check your
code more carefully.

 The keyword `__attribute__' allows you to specify special attributes
when making a declaration.  This keyword is followed by an attribute
specification inside double parentheses.  The following attributes are
currently defined for functions on all targets: `noreturn', `noinline',
`always_inline', `pure', `const', `nothrow', `format', `format_arg',
`no_instrument_function', `section', `constructor', `destructor',
`used', `unused', `deprecated', `weak', `malloc', `alias',
`warn_unused_result' and `nonnull'.  Several other attributes are
defined for functions on particular target systems.  Other attributes,
including `section' are supported for variables declarations (*note
Variable Attributes::) and for types (*note Type Attributes::).

 You may also specify attributes with `__' preceding and following each
keyword.  This allows you to use them in header files without being
concerned about a possible macro of the same name.  For example, you
may use `__noreturn__' instead of `noreturn'.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`noreturn'
     A few standard library functions, such as `abort' and `exit',
     cannot return.  GCC knows this automatically.  Some programs define
     their own functions that never return.  You can declare them
     `noreturn' to tell the compiler this fact.  For example,

          void fatal () __attribute__ ((noreturn));

          void
          fatal (/* ... */)
          {
            /* ... */ /* Print error message. */ /* ... */
            exit (1);
          }

     The `noreturn' keyword tells the compiler to assume that `fatal'
     cannot return.  It can then optimize without regard to what would
     happen if `fatal' ever did return.  This makes slightly better
     code.  More importantly, it helps avoid spurious warnings of
     uninitialized variables.

     The `noreturn' keyword does not affect the exceptional path when
     that applies: a `noreturn'-marked function may still return to the
     caller by throwing an exception.

     Do not assume that registers saved by the calling function are
     restored before calling the `noreturn' function.

     It does not make sense for a `noreturn' function to have a return
     type other than `void'.

     The attribute `noreturn' is not implemented in GCC versions
     earlier than 2.5.  An alternative way to declare that a function
     does not return, which works in the current version and in some
     older versions, is as follows:

          typedef void voidfn ();

          volatile voidfn fatal;

`noinline'
     This function attribute prevents a function from being considered
     for inlining.

`always_inline'
     Generally, functions are not inlined unless optimization is
     specified.  For functions declared inline, this attribute inlines
     the function even if no optimization level was specified.

`pure'
     Many functions have no effects except the return value and their
     return value depends only on the parameters and/or global
     variables.  Such a function can be subject to common subexpression
     elimination and loop optimization just as an arithmetic operator
     would be.  These functions should be declared with the attribute
     `pure'.  For example,

          int square (int) __attribute__ ((pure));

     says that the hypothetical function `square' is safe to call fewer
     times than the program says.

     Some of common examples of pure functions are `strlen' or `memcmp'.
     Interesting non-pure functions are functions with infinite loops
     or those depending on volatile memory or other system resource,
     that may change between two consecutive calls (such as `feof' in a
     multithreading environment).

     The attribute `pure' is not implemented in GCC versions earlier
     than 2.96.

`const'
     Many functions do not examine any values except their arguments,
     and have no effects except the return value.  Basically this is
     just slightly more strict class than the `pure' attribute above,
     since function is not allowed to read global memory.

     Note that a function that has pointer arguments and examines the
     data pointed to must _not_ be declared `const'.  Likewise, a
     function that calls a non-`const' function usually must not be
     `const'.  It does not make sense for a `const' function to return
     `void'.

     The attribute `const' is not implemented in GCC versions earlier
     than 2.5.  An alternative way to declare that a function has no
     side effects, which works in the current version and in some older
     versions, is as follows:

          typedef int intfn ();

          extern const intfn square;

     This approach does not work in GNU C++ from 2.6.0 on, since the
     language specifies that the `const' must be attached to the return
     value.

`nothrow'
     The `nothrow' attribute is used to inform the compiler that a
     function cannot throw an exception.  For example, most functions in
     the standard C library can be guaranteed not to throw an exception
     with the notable exceptions of `qsort' and `bsearch' that take
     function pointer arguments.  The `nothrow' attribute is not
     implemented in GCC versions earlier than 3.2.

`format (ARCHETYPE, STRING-INDEX, FIRST-TO-CHECK)'
     The `format' attribute specifies that a function takes `printf',
     `scanf', `strftime' or `strfmon' style arguments which should be
     type-checked against a format string.  For example, the
     declaration:

          extern int
          my_printf (void *my_object, const char *my_format, ...)
                __attribute__ ((format (printf, 2, 3)));

     causes the compiler to check the arguments in calls to `my_printf'
     for consistency with the `printf' style format string argument
     `my_format'.

     The parameter ARCHETYPE determines how the format string is
     interpreted, and should be `printf', `scanf', `strftime' or
     `strfmon'.  (You can also use `__printf__', `__scanf__',
     `__strftime__' or `__strfmon__'.)  The parameter STRING-INDEX
     specifies which argument is the format string argument (starting
     from 1), while FIRST-TO-CHECK is the number of the first argument
     to check against the format string.  For functions where the
     arguments are not available to be checked (such as `vprintf'),
     specify the third parameter as zero.  In this case the compiler
     only checks the format string for consistency.  For `strftime'
     formats, the third parameter is required to be zero.  Since
     non-static C++ methods have an implicit `this' argument, the
     arguments of such methods should be counted from two, not one, when
     giving values for STRING-INDEX and FIRST-TO-CHECK.

     In the example above, the format string (`my_format') is the second
     argument of the function `my_print', and the arguments to check
     start with the third argument, so the correct parameters for the
     format attribute are 2 and 3.

     The `format' attribute allows you to identify your own functions
     which take format strings as arguments, so that GCC can check the
     calls to these functions for errors.  The compiler always (unless
     `-ffreestanding' is used) checks formats for the standard library
     functions `printf', `fprintf', `sprintf', `scanf', `fscanf',
     `sscanf', `strftime', `vprintf', `vfprintf' and `vsprintf'
     whenever such warnings are requested (using `-Wformat'), so there
     is no need to modify the header file `stdio.h'.  In C99 mode, the
     functions `snprintf', `vsnprintf', `vscanf', `vfscanf' and
     `vsscanf' are also checked.  Except in strictly conforming C
     standard modes, the X/Open function `strfmon' is also checked as
     are `printf_unlocked' and `fprintf_unlocked'.  *Note Options
     Controlling C Dialect: C Dialect Options.

`format_arg (STRING-INDEX)'
     The `format_arg' attribute specifies that a function takes a format
     string for a `printf', `scanf', `strftime' or `strfmon' style
     function and modifies it (for example, to translate it into
     another language), so the result can be passed to a `printf',
     `scanf', `strftime' or `strfmon' style function (with the
     remaining arguments to the format function the same as they would
     have been for the unmodified string).  For example, the
     declaration:

          extern char *
          my_dgettext (char *my_domain, const char *my_format)
                __attribute__ ((format_arg (2)));

     causes the compiler to check the arguments in calls to a `printf',
     `scanf', `strftime' or `strfmon' type function, whose format
     string argument is a call to the `my_dgettext' function, for
     consistency with the format string argument `my_format'.  If the
     `format_arg' attribute had not been specified, all the compiler
     could tell in such calls to format functions would be that the
     format string argument is not constant; this would generate a
     warning when `-Wformat-nonliteral' is used, but the calls could
     not be checked without the attribute.

     The parameter STRING-INDEX specifies which argument is the format
     string argument (starting from one).  Since non-static C++ methods
     have an implicit `this' argument, the arguments of such methods
     should be counted from two.

     The `format-arg' attribute allows you to identify your own
     functions which modify format strings, so that GCC can check the
     calls to `printf', `scanf', `strftime' or `strfmon' type function
     whose operands are a call to one of your own function.  The
     compiler always treats `gettext', `dgettext', and `dcgettext' in
     this manner except when strict ISO C support is requested by
     `-ansi' or an appropriate `-std' option, or `-ffreestanding' is
     used.  *Note Options Controlling C Dialect: C Dialect Options.

`nonnull (ARG-INDEX, ...)'
     The `nonnull' attribute specifies that some function parameters
     should be non-null pointers.  For instance, the declaration:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
              __attribute__((nonnull (1, 2)));

     causes the compiler to check that, in calls to `my_memcpy',
     arguments DEST and SRC are non-null.  If the compiler determines
     that a null pointer is passed in an argument slot marked as
     non-null, and the `-Wnonnull' option is enabled, a warning is
     issued.  The compiler may also choose to make optimizations based
     on the knowledge that certain function arguments will not be null.

     If no argument index list is given to the `nonnull' attribute, all
     pointer arguments are marked as non-null.  To illustrate, the
     following declaration is equivalent to the previous example:

          extern void *
          my_memcpy (void *dest, const void *src, size_t len)
              __attribute__((nonnull));

`no_instrument_function'
     If `-finstrument-functions' is given, profiling function calls will
     be generated at entry and exit of most user-compiled functions.
     Functions with this attribute will not be so instrumented.

`section ("SECTION-NAME")'
     Normally, the compiler places the code it generates in the `text'
     section.  Sometimes, however, you need additional sections, or you
     need certain particular functions to appear in special sections.
     The `section' attribute specifies that a function lives in a
     particular section.  For example, the declaration:

          extern void foobar (void) __attribute__ ((section ("bar")));

     puts the function `foobar' in the `bar' section.

     Some file formats do not support arbitrary sections so the
     `section' attribute is not available on all platforms.  If you
     need to map the entire contents of a module to a particular
     section, consider using the facilities of the linker instead.

`constructor'
`destructor'
     The `constructor' attribute causes the function to be called
     automatically before execution enters `main ()'.  Similarly, the
     `destructor' attribute causes the function to be called
     automatically after `main ()' has completed or `exit ()' has been
     called.  Functions with these attributes are useful for
     initializing data that will be used implicitly during the
     execution of the program.

     These attributes are not currently implemented for Objective-C.

`unused'
     This attribute, attached to a function, means that the function is
     meant to be possibly unused.  GCC will not produce a warning for
     this function.

`used'
     This attribute, attached to a function, means that code must be
     emitted for the function even if it appears that the function is
     not referenced.  This is useful, for example, when the function is
     referenced only in inline assembly.

`deprecated'
     The `deprecated' attribute results in a warning if the function is
     used anywhere in the source file.  This is useful when identifying
     functions that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated function, to enable users to easily find further
     information about why the function is deprecated, or what they
     should do instead.  Note that the warnings only occurs for uses:

          int old_fn () __attribute__ ((deprecated));
          int old_fn ();
          int (*fn_ptr)() = old_fn;

     results in a warning on line 3 but not line 2.

     The `deprecated' attribute can also be used for variables and
     types (*note Variable Attributes::, *note Type Attributes::.)

`warn_unused_result'
     The `warn_unused_result' attribute causes a warning to be emitted
     if a caller of the function with this attribute does not use its
     return value.  This is useful for functions where not checking the
     result is either a security problem or always a bug, such as
     `realloc'.

          int fn () __attribute__ ((warn_unused_result));
          int foo ()
          {
            if (fn () < 0) return -1;
            fn ();
            return 0;
          }

     results in warning on line 5.

`weak'
     The `weak' attribute causes the declaration to be emitted as a weak
     symbol rather than a global.  This is primarily useful in defining
     library functions which can be overridden in user code, though it
     can also be used with non-function declarations.  Weak symbols are
     supported for ELF targets, and also for a.out targets when using
     the GNU assembler and linker.

`malloc'
     The `malloc' attribute is used to tell the compiler that a function
     may be treated as if any non-`NULL' pointer it returns cannot
     alias any other pointer valid when the function returns.  This
     will often improve optimization.  Standard functions with this
     property include `malloc' and `calloc'.  `realloc'-like functions
     have this property as long as the old pointer is never referred to
     (including comparing it to the new pointer) after the function
     returns a non-`NULL' value.

`alias ("TARGET")'
     The `alias' attribute causes the declaration to be emitted as an
     alias for another symbol, which must be specified.  For instance,

          void __f () { /* Do something. */; }
          void f () __attribute__ ((weak, alias ("__f")));

     declares `f' to be a weak alias for `__f'.  In C++, the mangled
     name for the target must be used.

     Not all target machines support this attribute.

`visibility ("VISIBILITY_TYPE")'
     The `visibility' attribute on ELF targets causes the declaration
     to be emitted with default, hidden, protected or internal
     visibility.

          void __attribute__ ((visibility ("protected")))
          f () { /* Do something. */; }
          int i __attribute__ ((visibility ("hidden")));

     See the ELF gABI for complete details, but the short story is:

    "default"
          Default visibility is the normal case for ELF.  This value is
          available for the visibility attribute to override other
          options that may change the assumed visibility of symbols.

    "hidden"
          Hidden visibility indicates that the symbol will not be
          placed into the dynamic symbol table, so no other "module"
          (executable or shared library) can reference it directly.

    "protected"
          Protected visibility indicates that the symbol will be placed
          in the dynamic symbol table, but that references within the
          defining module will bind to the local symbol.  That is, the
          symbol cannot be overridden by another module.

    "internal"
          Internal visibility is like hidden visibility, but with
          additional processor specific semantics.  Unless otherwise
          specified by the psABI, GCC defines internal visibility to
          mean that the function is _never_ called from another module.
          Note that hidden symbols, while they cannot be referenced
          directly by other modules, can be referenced indirectly via
          function pointers.  By indicating that a symbol cannot be
          called from outside the module, GCC may for instance omit the
          load of a PIC register since it is known that the calling
          function loaded the correct value.

     Not all ELF targets support this attribute.

`regparm (NUMBER)'
     On the Intel 386, the `regparm' attribute causes the compiler to
     pass up to NUMBER integer arguments in registers EAX, EDX, and ECX
     instead of on the stack.  Functions that take a variable number of
     arguments will continue to be passed all of their arguments on the
     stack.

     Beware that on some ELF systems this attribute is unsuitable for
     global functions in shared libraries with lazy binding (which is
     the default).  Lazy binding will send the first call via resolving
     code in the loader, which might assume EAX, EDX and ECX can be
     clobbered, as per the standard calling conventions.  Solaris 8 is
     affected by this.  GNU systems with GLIBC 2.1 or higher, and
     FreeBSD, are believed to be safe since the loaders there save all
     registers.  (Lazy binding can be disabled with the linker or the
     loader if desired, to avoid the problem.)

`stdcall'
     On the Intel 386, the `stdcall' attribute causes the compiler to
     assume that the called function will pop off the stack space used
     to pass arguments, unless it takes a variable number of arguments.

`fastcall'
     On the Intel 386, the `fastcall' attribute causes the compiler to
     pass the first two arguments in the registers ECX and EDX.
     Subsequent arguments are passed on the stack. The called function
     will pop the arguments off the stack. If the number of arguments
     is variable all arguments are pushed on the stack.

`cdecl'
     On the Intel 386, the `cdecl' attribute causes the compiler to
     assume that the calling function will pop off the stack space used
     to pass arguments.  This is useful to override the effects of the
     `-mrtd' switch.

`longcall/shortcall'
     On the RS/6000 and PowerPC, the `longcall' attribute causes the
     compiler to always call this function via a pointer, just as it
     would if the `-mlongcall' option had been specified.  The
     `shortcall' attribute causes the compiler not to do this.  These
     attributes override both the `-mlongcall' switch and the `#pragma
     longcall' setting.

     *Note RS/6000 and PowerPC Options::, for more information on
     whether long calls are necessary.

`long_call/short_call'
     This attribute specifies how a particular function is called on
     ARM.  Both attributes override the `-mlong-calls' (*note ARM
     Options::) command line switch and `#pragma long_calls' settings.
     The `long_call' attribute causes the compiler to always call the
     function by first loading its address into a register and then
     using the contents of that register.   The `short_call' attribute
     always places the offset to the function from the call site into
     the `BL' instruction directly.

`function_vector'
     Use this attribute on the H8/300, H8/300H, and H8S to indicate
     that the specified function should be called through the function
     vector.  Calling a function through the function vector will
     reduce code size, however; the function vector has a limited size
     (maximum 128 entries on the H8/300 and 64 entries on the H8/300H
     and H8S) and shares space with the interrupt vector.

     You must use GAS and GLD from GNU binutils version 2.7 or later for
     this attribute to work correctly.

`interrupt'
     Use this attribute on the ARM, AVR, C4x, M32R/D and Xstormy16
     ports to indicate that the specified function is an interrupt
     handler.  The compiler will generate function entry and exit
     sequences suitable for use in an interrupt handler when this
     attribute is present.

     Note, interrupt handlers for the m68k, H8/300, H8/300H, H8S, and
     SH processors can be specified via the `interrupt_handler'
     attribute.

     Note, on the AVR, interrupts will be enabled inside the function.

     Note, for the ARM, you can specify the kind of interrupt to be
     handled by adding an optional parameter to the interrupt attribute
     like this:

          void f () __attribute__ ((interrupt ("IRQ")));

     Permissible values for this parameter are: IRQ, FIQ, SWI, ABORT
     and UNDEF.

`interrupt_handler'
     Use this attribute on the m68k, H8/300, H8/300H, H8S, and SH to
     indicate that the specified function is an interrupt handler.  The
     compiler will generate function entry and exit sequences suitable
     for use in an interrupt handler when this attribute is present.

`sp_switch'
     Use this attribute on the SH to indicate an `interrupt_handler'
     function should switch to an alternate stack.  It expects a string
     argument that names a global variable holding the address of the
     alternate stack.

          void *alt_stack;
          void f () __attribute__ ((interrupt_handler,
                                    sp_switch ("alt_stack")));

`trap_exit'
     Use this attribute on the SH for an `interrupt_handler' to return
     using `trapa' instead of `rte'.  This attribute expects an integer
     argument specifying the trap number to be used.

`eightbit_data'
     Use this attribute on the H8/300, H8/300H, and H8S to indicate
     that the specified variable should be placed into the eight bit
     data section.  The compiler will generate more efficient code for
     certain operations on data in the eight bit data area.  Note the
     eight bit data area is limited to 256 bytes of data.

     You must use GAS and GLD from GNU binutils version 2.7 or later for
     this attribute to work correctly.

`tiny_data'
     Use this attribute on the H8/300H and H8S to indicate that the
     specified variable should be placed into the tiny data section.
     The compiler will generate more efficient code for loads and stores
     on data in the tiny data section.  Note the tiny data area is
     limited to slightly under 32kbytes of data.

`saveall'
     Use this attribute on the H8/300, H8/300H, and H8S to indicate that
     all registers except the stack pointer should be saved in the
     prologue regardless of whether they are used or not.

`signal'
     Use this attribute on the AVR to indicate that the specified
     function is a signal handler.  The compiler will generate function
     entry and exit sequences suitable for use in a signal handler when
     this attribute is present.  Interrupts will be disabled inside the
     function.

`naked'
     Use this attribute on the ARM, AVR, C4x and IP2K ports to indicate
     that the specified function does not need prologue/epilogue
     sequences generated by the compiler.  It is up to the programmer
     to provide these sequences.

`model (MODEL-NAME)'
     On the M32R/D, use this attribute to set the addressability of an
     object, and of the code generated for a function.  The identifier
     MODEL-NAME is one of `small', `medium', or `large', representing
     each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction), and are
     callable with the `bl' instruction.

     Medium model objects may live anywhere in the 32-bit address space
     (the compiler will generate `seth/add3' instructions to load their
     addresses), and are callable with the `bl' instruction.

     Large model objects may live anywhere in the 32-bit address space
     (the compiler will generate `seth/add3' instructions to load their
     addresses), and may not be reachable with the `bl' instruction
     (the compiler will generate the much slower `seth/add3/jl'
     instruction sequence).

     On IA-64, use this attribute to set the addressability of an
     object.  At present, the only supported identifier for MODEL-NAME
     is `small', indicating addressability via "small" (22-bit)
     addresses (so that their addresses can be loaded with the `addl'
     instruction).  Caveat: such addressing is by definition not
     position independent and hence this attribute must not be used for
     objects defined by shared libraries.

`far'
     On 68HC11 and 68HC12 the `far' attribute causes the compiler to
     use a calling convention that takes care of switching memory banks
     when entering and leaving a function.  This calling convention is
     also the default when using the `-mlong-calls' option.

     On 68HC12 the compiler will use the `call' and `rtc' instructions
     to call and return from a function.

     On 68HC11 the compiler will generate a sequence of instructions to
     invoke a board-specific routine to switch the memory bank and call
     the real function. The board-specific routine simulates a `call'.
     At the end of a function, it will jump to a board-specific routine
     instead of using `rts'. The board-specific return routine simulates
     the `rtc'.

`near'
     On 68HC11 and 68HC12 the `near' attribute causes the compiler to
     use the normal calling convention based on `jsr' and `rts'.  This
     attribute can be used to cancel the effect of the `-mlong-calls'
     option.

`dllimport'
     On Microsoft Windows targets, the `dllimport' attribute causes the
     compiler to reference a function or variable via a global pointer
     to a pointer that is set up by the Microsoft Windows dll library.
     The pointer name is formed by combining `_imp__' and the function
     or variable name. The attribute implies `extern' storage.

     Currently, the attribute is ignored for inlined functions. If the
     attribute is applied to a symbol _definition_, an error is
     reported.  If a symbol previously declared `dllimport' is later
     defined, the attribute is ignored in subsequent references, and a
     warning is emitted.  The attribute is also overridden by a
     subsequent declaration as `dllexport'.

     When applied to C++ classes, the attribute marks non-inlined
     member functions and static data members as imports.  However, the
     attribute is ignored for virtual methods to allow creation of
     vtables using thunks.

     On cygwin, mingw and arm-pe targets, `__declspec(dllimport)' is
     recognized as a synonym for `__attribute__ ((dllimport))' for
     compatibility with other Microsoft Windows compilers.

     The use of the `dllimport' attribute on functions is not necessary,
     but provides a small performance benefit by eliminating a thunk in
     the dll. The use of the `dllimport' attribute on imported
     variables was required on older versions of GNU ld, but can now be
     avoided by passing the `--enable-auto-import' switch to ld. As
     with functions, using the attribute for a variable eliminates a
     thunk in the dll.

     One drawback to using this attribute is that a pointer to a
     function or variable marked as dllimport cannot be used as a
     constant address. The attribute can be disabled for functions by
     setting the `-mnop-fun-dllimport' flag.

`dllexport'
     On Microsoft Windows targets the `dllexport' attribute causes the
     compiler to provide a global pointer to a pointer in a dll, so
     that it can be referenced with the `dllimport' attribute. The
     pointer name is formed by combining `_imp__' and the function or
     variable name.

     Currently, the `dllexport'attribute is ignored for inlined
     functions, but export can be forced by using the
     `-fkeep-inline-functions' flag. The attribute is also ignored for
     undefined symbols.

     When applied to C++ classes. the attribute marks defined
     non-inlined member functions and static data members as exports.
     Static consts initialized in-class are not marked unless they are
     also defined out-of-class.

     On cygwin, mingw and arm-pe targets, `__declspec(dllexport)' is
     recognized as a synonym for `__attribute__ ((dllexport))' for
     compatibility with other Microsoft Windows compilers.

     Alternative methods for including the symbol in the dll's export
     table are to use a .def file with an `EXPORTS' section or, with
     GNU ld, using the `--export-all' linker flag.


 You can specify multiple attributes in a declaration by separating them
by commas within the double parentheses or by immediately following an
attribute declaration with another attribute declaration.

 Some people object to the `__attribute__' feature, suggesting that ISO
C's `#pragma' should be used instead.  At the time `__attribute__' was
designed, there were two reasons for not doing this.

  1. It is impossible to generate `#pragma' commands from a macro.

  2. There is no telling what the same `#pragma' might mean in another
     compiler.

 These two reasons applied to almost any application that might have
been proposed for `#pragma'.  It was basically a mistake to use
`#pragma' for _anything_.

 The ISO C99 standard includes `_Pragma', which now allows pragmas to
be generated from macros.  In addition, a `#pragma GCC' namespace is
now in use for GCC-specific pragmas.  However, it has been found
convenient to use `__attribute__' to achieve a natural attachment of
attributes to their corresponding declarations, whereas `#pragma GCC'
is of use for constructs that do not naturally form part of the
grammar.  *Note Miscellaneous Preprocessing Directives: (cpp)Other
Directives.


File: gcc,  Node: Attribute Syntax,  Next: Function Prototypes,  Prev: Function Attributes,  Up: C Extensions

5.26 Attribute Syntax
=====================

This section describes the syntax with which `__attribute__' may be
used, and the constructs to which attribute specifiers bind, for the C
language.  Some details may vary for C++ and Objective-C.  Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.

 There are some problems with the semantics of attributes in C++.  For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading.  Similarly, `typeid' does
not distinguish between types with different attributes.  Support for
attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.

 *Note Function Attributes::, for details of the semantics of attributes
applying to functions.  *Note Variable Attributes::, for details of the
semantics of attributes applying to variables.  *Note Type Attributes::,
for details of the semantics of attributes applying to structure, union
and enumerated types.

 An "attribute specifier" is of the form `__attribute__
((ATTRIBUTE-LIST))'.  An "attribute list" is a possibly empty
comma-separated sequence of "attributes", where each attribute is one
of the following:

   * Empty.  Empty attributes are ignored.

   * A word (which may be an identifier such as `unused', or a reserved
     word such as `const').

   * A word, followed by, in parentheses, parameters for the attribute.
     These parameters take one of the following forms:

        * An identifier.  For example, `mode' attributes use this form.

        * An identifier followed by a comma and a non-empty
          comma-separated list of expressions.  For example, `format'
          attributes use this form.

        * A possibly empty comma-separated list of expressions.  For
          example, `format_arg' attributes use this form with the list
          being a single integer constant expression, and `alias'
          attributes use this form with the list being a single string
          constant.

 An "attribute specifier list" is a sequence of one or more attribute
specifiers, not separated by any other tokens.

 In GNU C, an attribute specifier list may appear after the colon
following a label, other than a `case' or `default' label.  The only
attribute it makes sense to use after a label is `unused'.  This
feature is intended for code generated by programs which contains labels
that may be unused but which is compiled with `-Wall'.  It would not
normally be appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an `#ifdef' conditional. GNU C++ does not permit such
placement of attribute lists, as it is permissible for a declaration,
which could begin with an attribute list, to be labelled in C++.
Declarations cannot be labelled in C90 or C99, so the ambiguity does
not arise there.

 An attribute specifier list may appear as part of a `struct', `union'
or `enum' specifier.  It may go either immediately after the `struct',
`union' or `enum' keyword, or after the closing brace.  It is ignored
if the content of the structure, union or enumerated type is not
defined in the specifier in which the attribute specifier list is
used--that is, in usages such as `struct __attribute__((foo)) bar' with
no following opening brace.  Where attribute specifiers follow the
closing brace, they are considered to relate to the structure, union or
enumerated type defined, not to any enclosing declaration the type
specifier appears in, and the type defined is not complete until after
the attribute specifiers.

 Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular
declarator within a declaration.  Where an attribute specifier is
applied to a parameter declared as a function or an array, it should
apply to the function or array rather than the pointer to which the
parameter is implicitly converted, but this is not yet correctly
implemented.

 Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers.  (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
`section'.)  There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case).  In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler.  All attribute specifiers in this place relate to the
declaration as a whole.  In the obsolescent usage where a type of `int'
is implied by the absence of type specifiers, such a list of specifiers
and qualifiers may be an attribute specifier list with no other
specifiers or qualifiers.

 An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers.  Such attribute specifiers apply only to the
identifier before whose declarator they appear.  For example, in

     __attribute__((noreturn)) void d0 (void),
         __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
          d2 (void)

the `noreturn' attribute applies to all the functions declared; the
`format' attribute only applies to `d1'.

 An attribute specifier list may appear immediately before the comma,
`=' or semicolon terminating the declaration of an identifier other
than a function definition.  At present, such attribute specifiers apply
to the declared object or function, but in future they may attach to the
outermost adjacent declarator.  In simple cases there is no difference,
but, for example, in

     void (****f)(void) __attribute__((noreturn));

at present the `noreturn' attribute applies to `f', which causes a
warning since `f' is not a function, but in future it may apply to the
function `****f'.  The precise semantics of what attributes in such
cases will apply to are not yet specified.  Where an assembler name for
an object or function is specified (*note Asm Labels::), at present the
attribute must follow the `asm' specification; in future, attributes
before the `asm' specification may apply to the adjacent declarator,
and those after it to the declared object or function.

 An attribute specifier list may, in future, be permitted to appear
after the declarator in a function definition (before any old-style
parameter declarations or the function body).

 Attribute specifiers may be mixed with type qualifiers appearing inside
the `[]' of a parameter array declarator, in the C99 construct by which
such qualifiers are applied to the pointer to which the array is
implicitly converted.  Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.

 An attribute specifier list may appear at the start of a nested
declarator.  At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.  When
attribute specifiers follow the `*' of a pointer declarator, they may
be mixed with any type qualifiers present.  The following describes the
formal semantics of this syntax.  It will make the most sense if you
are familiar with the formal specification of declarators in the ISO C
standard.

 Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration `T D1',
where `T' contains declaration specifiers that specify a type TYPE
(such as `int') and `D1' is a declarator that contains an identifier
IDENT.  The type specified for IDENT for derived declarators whose type
does not include an attribute specifier is as in the ISO C standard.

 If `D1' has the form `( ATTRIBUTE-SPECIFIER-LIST D )', and the
declaration `T D' specifies the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE" for IDENT, then `T D1' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.

 If `D1' has the form `* TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST
D', and the declaration `T D' specifies the type
"DERIVED-DECLARATOR-TYPE-LIST TYPE" for IDENT, then `T D1' specifies
the type "DERIVED-DECLARATOR-TYPE-LIST
TYPE-QUALIFIER-AND-ATTRIBUTE-SPECIFIER-LIST TYPE" for IDENT.

 For example,

     void (__attribute__((noreturn)) ****f) (void);

specifies the type "pointer to pointer to pointer to pointer to
non-returning function returning `void'".  As another example,

     char *__attribute__((aligned(8))) *f;

specifies the type "pointer to 8-byte-aligned pointer to `char'".  Note
again that this does not work with most attributes; for example, the
usage of `aligned' and `noreturn' attributes given above is not yet
supported.

 For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes.  If an attribute that only applies
to types is applied to a declaration, it will be treated as applying to
the type of that declaration.  If an attribute that only applies to
declarations is applied to the type of a declaration, it will be treated
as applying to that declaration; and, for compatibility with code
placing the attributes immediately before the identifier declared, such
an attribute applied to a function return type will be treated as
applying to the function type, and such an attribute applied to an array
element type will be treated as applying to the array type.  If an
attribute that only applies to function types is applied to a
pointer-to-function type, it will be treated as applying to the pointer
target type; if such an attribute is applied to a function return type
that is not a pointer-to-function type, it will be treated as applying
to the function type.


File: gcc,  Node: Function Prototypes,  Next: C++ Comments,  Prev: Attribute Syntax,  Up: C Extensions

5.27 Prototypes and Old-Style Function Definitions
==================================================

GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition.  Consider the following example:

     /* Use prototypes unless the compiler is old-fashioned.  */
     #ifdef __STDC__
     #define P(x) x
     #else
     #define P(x) ()
     #endif

     /* Prototype function declaration.  */
     int isroot P((uid_t));

     /* Old-style function definition.  */
     int
     isroot (x)   /* ??? lossage here ??? */
          uid_t x;
     {
       return x == 0;
     }

 Suppose the type `uid_t' happens to be `short'.  ISO C does not allow
this example, because subword arguments in old-style non-prototype
definitions are promoted.  Therefore in this example the function
definition's argument is really an `int', which does not match the
prototype argument type of `short'.

 This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the `uid_t' type is `short', `int', or `long'.  Therefore, in
cases like these GNU C allows a prototype to override a later old-style
definition.  More precisely, in GNU C, a function prototype argument
type overrides the argument type specified by a later old-style
definition if the former type is the same as the latter type before
promotion.  Thus in GNU C the above example is equivalent to the
following:

     int isroot (uid_t);

     int
     isroot (uid_t x)
     {
       return x == 0;
     }

GNU C++ does not support old-style function definitions, so this
extension is irrelevant.


File: gcc,  Node: C++ Comments,  Next: Dollar Signs,  Prev: Function Prototypes,  Up: C Extensions

5.28 C++ Style Comments
=======================

In GNU C, you may use C++ style comments, which start with `//' and
continue until the end of the line.  Many other C implementations allow
such comments, and they are included in the 1999 C standard.  However,
C++ style comments are not recognized if you specify an `-std' option
specifying a version of ISO C before C99, or `-ansi' (equivalent to
`-std=c89').


File: gcc,  Node: Dollar Signs,  Next: Character Escapes,  Prev: C++ Comments,  Up: C Extensions

5.29 Dollar Signs in Identifier Names
=====================================

In GNU C, you may normally use dollar signs in identifier names.  This
is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.


File: gcc,  Node: Character Escapes,  Next: Variable Attributes,  Prev: Dollar Signs,  Up: C Extensions

5.30 The Character <ESC> in Constants
=====================================

You can use the sequence `\e' in a string or character constant to
stand for the ASCII character <ESC>.


File: gcc,  Node: Alignment,  Next: Inline,  Prev: Type Attributes,  Up: C Extensions

5.31 Inquiring on Alignment of Types or Variables
=================================================

The keyword `__alignof__' allows you to inquire about how an object is
aligned, or the minimum alignment usually required by a type.  Its
syntax is just like `sizeof'.

 For example, if the target machine requires a `double' value to be
aligned on an 8-byte boundary, then `__alignof__ (double)' is 8.  This
is true on many RISC machines.  On more traditional machine designs,
`__alignof__ (double)' is 4 or even 2.

 Some machines never actually require alignment; they allow reference
to any data type even at an odd address.  For these machines,
`__alignof__' reports the _recommended_ alignment of a type.

 If the operand of `__alignof__' is an lvalue rather than a type, its
value is the required alignment for its type, taking into account any
minimum alignment specified with GCC's `__attribute__' extension (*note
Variable Attributes::).  For example, after this declaration:

     struct foo { int x; char y; } foo1;

the value of `__alignof__ (foo1.y)' is 1, even though its actual
alignment is probably 2 or 4, the same as `__alignof__ (int)'.

 It is an error to ask for the alignment of an incomplete type.


File: gcc,  Node: Variable Attributes,  Next: Type Attributes,  Prev: Character Escapes,  Up: C Extensions

5.32 Specifying Attributes of Variables
=======================================

The keyword `__attribute__' allows you to specify special attributes of
variables or structure fields.  This keyword is followed by an
attribute specification inside double parentheses.  Some attributes are
currently defined generically for variables.  Other attributes are
defined for variables on particular target systems.  Other attributes
are available for functions (*note Function Attributes::) and for types
(*note Type Attributes::).  Other front ends might define more
attributes (*note Extensions to the C++ Language: C++ Extensions.).

 You may also specify attributes with `__' preceding and following each
keyword.  This allows you to use them in header files without being
concerned about a possible macro of the same name.  For example, you
may use `__aligned__' instead of `aligned'.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment for the variable or
     structure field, measured in bytes.  For example, the declaration:

          int x __attribute__ ((aligned (16))) = 0;

     causes the compiler to allocate the global variable `x' on a
     16-byte boundary.  On a 68040, this could be used in conjunction
     with an `asm' expression to access the `move16' instruction which
     requires 16-byte aligned operands.

     You can also specify the alignment of structure fields.  For
     example, to create a double-word aligned `int' pair, you could
     write:

          struct foo { int x[2] __attribute__ ((aligned (8))); };

     This is an alternative to creating a union with a `double' member
     that forces the union to be double-word aligned.

     As in the preceding examples, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     variable or structure field.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a variable or
     field to the maximum useful alignment for the target machine you
     are compiling for.  For example, you could write:

          short array[3] __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an `aligned'
     attribute specification, the compiler automatically sets the
     alignment for the declared variable or field to the largest
     alignment which is ever used for any data type on the target
     machine you are compiling for.  Doing this can often make copy
     operations more efficient, because the compiler can use whatever
     instructions copy the biggest chunks of memory when performing
     copies to or from the variables or fields that you have aligned
     this way.

     The `aligned' attribute can only increase the alignment; but you
     can decrease it by specifying `packed' as well.  See below.

     Note that the effectiveness of `aligned' attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for variables to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  If your linker is
     only able to align variables up to a maximum of 8 byte alignment,
     then specifying `aligned(16)' in an `__attribute__' will still
     only provide you with 8 byte alignment.  See your linker
     documentation for further information.

`cleanup (CLEANUP_FUNCTION)'
     The `cleanup' attribute runs a function when the variable goes out
     of scope.  This attribute can only be applied to auto function
     scope variables; it may not be applied to parameters or variables
     with static storage duration.  The function must take one
     parameter, a pointer to a type compatible with the variable.  The
     return value of the function (if any) is ignored.

     If `-fexceptions' is enabled, then CLEANUP_FUNCTION will be run
     during the stack unwinding that happens during the processing of
     the exception.  Note that the `cleanup' attribute does not allow
     the exception to be caught, only to perform an action.  It is
     undefined what happens if CLEANUP_FUNCTION does not return
     normally.

`common'
`nocommon'
     The `common' attribute requests GCC to place a variable in
     "common" storage.  The `nocommon' attribute requests the opposite
     - to allocate space for it directly.

     These attributes override the default chosen by the `-fno-common'
     and `-fcommon' flags respectively.

`deprecated'
     The `deprecated' attribute results in a warning if the variable is
     used anywhere in the source file.  This is useful when identifying
     variables that are expected to be removed in a future version of a
     program.  The warning also includes the location of the declaration
     of the deprecated variable, to enable users to easily find further
     information about why the variable is deprecated, or what they
     should do instead.  Note that the warning only occurs for uses:

          extern int old_var __attribute__ ((deprecated));
          extern int old_var;
          int new_fn () { return old_var; }

     results in a warning on line 3 but not line 2.

     The `deprecated' attribute can also be used for functions and
     types (*note Function Attributes::, *note Type Attributes::.)

`mode (MODE)'
     This attribute specifies the data type for the
     declaration--whichever type corresponds to the mode MODE.  This in
     effect lets you request an integer or floating point type
     according to its width.

     You may also specify a mode of `byte' or `__byte__' to indicate
     the mode corresponding to a one-byte integer, `word' or `__word__'
     for the mode of a one-word integer, and `pointer' or `__pointer__'
     for the mode used to represent pointers.

`packed'
     The `packed' attribute specifies that a variable or structure field
     should have the smallest possible alignment--one byte for a
     variable, and one bit for a field, unless you specify a larger
     value with the `aligned' attribute.

     Here is a structure in which the field `x' is packed, so that it
     immediately follows `a':

          struct foo
          {
            char a;
            int x[2] __attribute__ ((packed));
          };

`section ("SECTION-NAME")'
     Normally, the compiler places the objects it generates in sections
     like `data' and `bss'.  Sometimes, however, you need additional
     sections, or you need certain particular variables to appear in
     special sections, for example to map to special hardware.  The
     `section' attribute specifies that a variable (or function) lives
     in a particular section.  For example, this small program uses
     several specific section names:

          struct duart a __attribute__ ((section ("DUART_A"))) = { 0 };
          struct duart b __attribute__ ((section ("DUART_B"))) = { 0 };
          char stack[10000] __attribute__ ((section ("STACK"))) = { 0 };
          int init_data __attribute__ ((section ("INITDATA"))) = 0;

          main()
          {
            /* Initialize stack pointer */
            init_sp (stack + sizeof (stack));

            /* Initialize initialized data */
            memcpy (&init_data, &data, &edata - &data);

            /* Turn on the serial ports */
            init_duart (&a);
            init_duart (&b);
          }

     Use the `section' attribute with an _initialized_ definition of a
     _global_ variable, as shown in the example.  GCC issues a warning
     and otherwise ignores the `section' attribute in uninitialized
     variable declarations.

     You may only use the `section' attribute with a fully initialized
     global definition because of the way linkers work.  The linker
     requires each object be defined once, with the exception that
     uninitialized variables tentatively go in the `common' (or `bss')
     section and can be multiply "defined".  You can force a variable
     to be initialized with the `-fno-common' flag or the `nocommon'
     attribute.

     Some file formats do not support arbitrary sections so the
     `section' attribute is not available on all platforms.  If you
     need to map the entire contents of a module to a particular
     section, consider using the facilities of the linker instead.

`shared'
     On Microsoft Windows, in addition to putting variable definitions
     in a named section, the section can also be shared among all
     running copies of an executable or DLL.  For example, this small
     program defines shared data by putting it in a named section
     `shared' and marking the section shareable:

          int foo __attribute__((section ("shared"), shared)) = 0;

          int
          main()
          {
            /* Read and write foo.  All running
               copies see the same value.  */
            return 0;
          }

     You may only use the `shared' attribute along with `section'
     attribute with a fully initialized global definition because of
     the way linkers work.  See `section' attribute for more
     information.

     The `shared' attribute is only available on Microsoft Windows.

`tls_model ("TLS_MODEL")'
     The `tls_model' attribute sets thread-local storage model (*note
     Thread-Local::) of a particular `__thread' variable, overriding
     `-ftls-model=' command line switch on a per-variable basis.  The
     TLS_MODEL argument should be one of `global-dynamic',
     `local-dynamic', `initial-exec' or `local-exec'.

     Not all targets support this attribute.

`transparent_union'
     This attribute, attached to a function parameter which is a union,
     means that the corresponding argument may have the type of any
     union member, but the argument is passed as if its type were that
     of the first union member.  For more details see *Note Type
     Attributes::.  You can also use this attribute on a `typedef' for
     a union data type; then it applies to all function parameters with
     that type.

`unused'
     This attribute, attached to a variable, means that the variable is
     meant to be possibly unused.  GCC will not produce a warning for
     this variable.

`vector_size (BYTES)'
     This attribute specifies the vector size for the variable,
     measured in bytes.  For example, the declaration:

          int foo __attribute__ ((vector_size (16)));

     causes the compiler to set the mode for `foo', to be 16 bytes,
     divided into `int' sized units.  Assuming a 32-bit int (a vector of
     4 units of 4 bytes), the corresponding mode of `foo' will be V4SI.

     This attribute is only applicable to integral and float scalars,
     although arrays, pointers, and function return values are allowed
     in conjunction with this construct.

     Aggregates with this attribute are invalid, even if they are of
     the same size as a corresponding scalar.  For example, the
     declaration:

          struct S { int a; };
          struct S  __attribute__ ((vector_size (16))) foo;

     is invalid even if the size of the structure is the same as the
     size of the `int'.

`weak'
     The `weak' attribute is described in *Note Function Attributes::.

`dllimport'
     The `dllimport' attribute is described in *Note Function
     Attributes::.

`dlexport'
     The `dllexport' attribute is described in *Note Function
     Attributes::.


5.32.1 M32R/D Variable Attributes
---------------------------------

One attribute is currently defined for the M32R/D.

`model (MODEL-NAME)'
     Use this attribute on the M32R/D to set the addressability of an
     object.  The identifier MODEL-NAME is one of `small', `medium', or
     `large', representing each of the code models.

     Small model objects live in the lower 16MB of memory (so that their
     addresses can be loaded with the `ld24' instruction).

     Medium and large model objects may live anywhere in the 32-bit
     address space (the compiler will generate `seth/add3' instructions
     to load their addresses).

5.32.2 i386 Variable Attributes
-------------------------------

Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'

`ms_struct'
`gcc_struct'
     If `packed' is used on a structure, or if bit-fields are used it
     may be that the Microsoft ABI packs them differently than GCC
     would normally pack them.  Particularly when moving packed data
     between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may
     be necessary to access either format.

     Currently `-m[no-]ms-bitfields' is provided for the Microsoft
     Windows X86 compilers to match the native Microsoft compiler.


File: gcc,  Node: Type Attributes,  Next: Alignment,  Prev: Variable Attributes,  Up: C Extensions

5.33 Specifying Attributes of Types
===================================

The keyword `__attribute__' allows you to specify special attributes of
`struct' and `union' types when you define such types.  This keyword is
followed by an attribute specification inside double parentheses.  Six
attributes are currently defined for types: `aligned', `packed',
`transparent_union', `unused', `deprecated' and `may_alias'.  Other
attributes are defined for functions (*note Function Attributes::) and
for variables (*note Variable Attributes::).

 You may also specify any one of these attributes with `__' preceding
and following its keyword.  This allows you to use these attributes in
header files without being concerned about a possible macro of the same
name.  For example, you may use `__aligned__' instead of `aligned'.

 You may specify the `aligned' and `transparent_union' attributes
either in a `typedef' declaration or just past the closing curly brace
of a complete enum, struct or union type _definition_ and the `packed'
attribute only past the closing brace of a definition.

 You may also specify attributes between the enum, struct or union tag
and the name of the type rather than after the closing brace.

 *Note Attribute Syntax::, for details of the exact syntax for using
attributes.

`aligned (ALIGNMENT)'
     This attribute specifies a minimum alignment (in bytes) for
     variables of the specified type.  For example, the declarations:

          struct S { short f[3]; } __attribute__ ((aligned (8)));
          typedef int more_aligned_int __attribute__ ((aligned (8)));

     force the compiler to insure (as far as it can) that each variable
     whose type is `struct S' or `more_aligned_int' will be allocated
     and aligned _at least_ on a 8-byte boundary.  On a SPARC, having
     all variables of type `struct S' aligned to 8-byte boundaries
     allows the compiler to use the `ldd' and `std' (doubleword load and
     store) instructions when copying one variable of type `struct S' to
     another, thus improving run-time efficiency.

     Note that the alignment of any given `struct' or `union' type is
     required by the ISO C standard to be at least a perfect multiple of
     the lowest common multiple of the alignments of all of the members
     of the `struct' or `union' in question.  This means that you _can_
     effectively adjust the alignment of a `struct' or `union' type by
     attaching an `aligned' attribute to any one of the members of such
     a type, but the notation illustrated in the example above is a
     more obvious, intuitive, and readable way to request the compiler
     to adjust the alignment of an entire `struct' or `union' type.

     As in the preceding example, you can explicitly specify the
     alignment (in bytes) that you wish the compiler to use for a given
     `struct' or `union' type.  Alternatively, you can leave out the
     alignment factor and just ask the compiler to align a type to the
     maximum useful alignment for the target machine you are compiling
     for.  For example, you could write:

          struct S { short f[3]; } __attribute__ ((aligned));

     Whenever you leave out the alignment factor in an `aligned'
     attribute specification, the compiler automatically sets the
     alignment for the type to the largest alignment which is ever used
     for any data type on the target machine you are compiling for.
     Doing this can often make copy operations more efficient, because
     the compiler can use whatever instructions copy the biggest chunks
     of memory when performing copies to or from the variables which
     have types that you have aligned this way.

     In the example above, if the size of each `short' is 2 bytes, then
     the size of the entire `struct S' type is 6 bytes.  The smallest
     power of two which is greater than or equal to that is 8, so the
     compiler sets the alignment for the entire `struct S' type to 8
     bytes.

     Note that although you can ask the compiler to select a
     time-efficient alignment for a given type and then declare only
     individual stand-alone objects of that type, the compiler's
     ability to select a time-efficient alignment is primarily useful
     only when you plan to create arrays of variables having the
     relevant (efficiently aligned) type.  If you declare or use arrays
     of variables of an efficiently-aligned type, then it is likely
     that your program will also be doing pointer arithmetic (or
     subscripting, which amounts to the same thing) on pointers to the
     relevant type, and the code that the compiler generates for these
     pointer arithmetic operations will often be more efficient for
     efficiently-aligned types than for other types.

     The `aligned' attribute can only increase the alignment; but you
     can decrease it by specifying `packed' as well.  See below.

     Note that the effectiveness of `aligned' attributes may be limited
     by inherent limitations in your linker.  On many systems, the
     linker is only able to arrange for variables to be aligned up to a
     certain maximum alignment.  (For some linkers, the maximum
     supported alignment may be very very small.)  If your linker is
     only able to align variables up to a maximum of 8 byte alignment,
     then specifying `aligned(16)' in an `__attribute__' will still
     only provide you with 8 byte alignment.  See your linker
     documentation for further information.

`packed'
     This attribute, attached to `struct' or `union' type definition,
     specifies that each member of the structure or union is placed to
     minimize the memory required. When attached to an `enum'
     definition, it indicates that the smallest integral type should be
     used.

     Specifying this attribute for `struct' and `union' types is
     equivalent to specifying the `packed' attribute on each of the
     structure or union members.  Specifying the `-fshort-enums' flag
     on the line is equivalent to specifying the `packed' attribute on
     all `enum' definitions.

     In the following example `struct my_packed_struct''s members are
     packed closely together, but the internal layout of its `s' member
     is not packed - to do that, `struct my_unpacked_struct' would need
     to be packed too.

          struct my_unpacked_struct
           {
              char c;
              int i;
           };

          struct my_packed_struct __attribute__ ((__packed__))
            {
               char c;
               int  i;
               struct my_unpacked_struct s;
            };

     You may only specify this attribute on the definition of a `enum',
     `struct' or `union', not on a `typedef' which does not also define
     the enumerated type, structure or union.

`transparent_union'
     This attribute, attached to a `union' type definition, indicates
     that any function parameter having that union type causes calls to
     that function to be treated in a special way.

     First, the argument corresponding to a transparent union type can
     be of any type in the union; no cast is required.  Also, if the
     union contains a pointer type, the corresponding argument can be a
     null pointer constant or a void pointer expression; and if the
     union contains a void pointer type, the corresponding argument can
     be any pointer expression.  If the union member type is a pointer,
     qualifiers like `const' on the referenced type must be respected,
     just as with normal pointer conversions.

     Second, the argument is passed to the function using the calling
     conventions of the first member of the transparent union, not the
     calling conventions of the union itself.  All members of the union
     must have the same machine representation; this is necessary for
     this argument passing to work properly.

     Transparent unions are designed for library functions that have
     multiple interfaces for compatibility reasons.  For example,
     suppose the `wait' function must accept either a value of type
     `int *' to comply with Posix, or a value of type `union wait *' to
     comply with the 4.1BSD interface.  If `wait''s parameter were
     `void *', `wait' would accept both kinds of arguments, but it
     would also accept any other pointer type and this would make
     argument type checking less useful.  Instead, `<sys/wait.h>' might
     define the interface as follows:

          typedef union
            {
              int *__ip;
              union wait *__up;
            } wait_status_ptr_t __attribute__ ((__transparent_union__));

          pid_t wait (wait_status_ptr_t);

     This interface allows either `int *' or `union wait *' arguments
     to be passed, using the `int *' calling convention.  The program
     can call `wait' with arguments of either type:

          int w1 () { int w; return wait (&w); }
          int w2 () { union wait w; return wait (&w); }

     With this interface, `wait''s implementation might look like this:

          pid_t wait (wait_status_ptr_t p)
          {
            return waitpid (-1, p.__ip, 0);
          }

`unused'
     When attached to a type (including a `union' or a `struct'), this
     attribute means that variables of that type are meant to appear
     possibly unused.  GCC will not produce a warning for any variables
     of that type, even if the variable appears to do nothing.  This is
     often the case with lock or thread classes, which are usually
     defined and then not referenced, but contain constructors and
     destructors that have nontrivial bookkeeping functions.

`deprecated'
     The `deprecated' attribute results in a warning if the type is
     used anywhere in the source file.  This is useful when identifying
     types that are expected to be removed in a future version of a
     program.  If possible, the warning also includes the location of
     the declaration of the deprecated type, to enable users to easily
     find further information about why the type is deprecated, or what
     they should do instead.  Note that the warnings only occur for
     uses and then only if the type is being applied to an identifier
     that itself is not being declared as deprecated.

          typedef int T1 __attribute__ ((deprecated));
          T1 x;
          typedef T1 T2;
          T2 y;
          typedef T1 T3 __attribute__ ((deprecated));
          T3 z __attribute__ ((deprecated));

     results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No
     warning is issued for line 4 because T2 is not explicitly
     deprecated.  Line 5 has no warning because T3 is explicitly
     deprecated.  Similarly for line 6.

     The `deprecated' attribute can also be used for functions and
     variables (*note Function Attributes::, *note Variable
     Attributes::.)

`may_alias'
     Accesses to objects with types with this attribute are not
     subjected to type-based alias analysis, but are instead assumed to
     be able to alias any other type of objects, just like the `char'
     type.  See `-fstrict-aliasing' for more information on aliasing
     issues.

     Example of use:

          typedef short __attribute__((__may_alias__)) short_a;

          int
          main (void)
          {
            int a = 0x12345678;
            short_a *b = (short_a *) &a;

            b[1] = 0;

            if (a == 0x12345678)
              abort();

            exit(0);
          }

     If you replaced `short_a' with `short' in the variable
     declaration, the above program would abort when compiled with
     `-fstrict-aliasing', which is on by default at `-O2' or above in
     recent GCC versions.

5.33.1 i386 Type Attributes
---------------------------

     Two attributes are currently defined for i386 configurations:
`ms_struct' and `gcc_struct'

`ms_struct'
`gcc_struct'
     If `packed' is used on a structure, or if bit-fields are used it
     may be that the Microsoft ABI packs them differently than GCC
     would normally pack them.  Particularly when moving packed data
     between functions compiled with GCC and the native Microsoft
     compiler (either via function call or as data in a file), it may
     be necessary to access either format.

     Currently `-m[no-]ms-bitfields' is provided for the Microsoft
     Windows X86 compilers to match the native Microsoft compiler.

 To specify multiple attributes, separate them by commas within the
double parentheses: for example, `__attribute__ ((aligned (16),
packed))'.


File: gcc,  Node: Inline,  Next: Extended Asm,  Prev: Alignment,  Up: C Extensions

5.34 An Inline Function is As Fast As a Macro
=============================================

By declaring a function `inline', you can direct GCC to integrate that
function's code into the code for its callers.  This makes execution
faster by eliminating the function-call overhead; in addition, if any
of the actual argument values are constant, their known values may
permit simplifications at compile time so that not all of the inline
function's code needs to be included.  The effect on code size is less
predictable; object code may be larger or smaller with function
inlining, depending on the particular case.  Inlining of functions is an
optimization and it really "works" only in optimizing compilation.  If
you don't use `-O', no function is really inline.

 Inline functions are included in the ISO C99 standard, but there are
currently substantial differences between what GCC implements and what
the ISO C99 standard requires.

 To declare a function inline, use the `inline' keyword in its
declaration, like this:

     inline int
     inc (int *a)
     {
       (*a)++;
     }

 (If you are writing a header file to be included in ISO C programs,
write `__inline__' instead of `inline'.  *Note Alternate Keywords::.)
You can also make all "simple enough" functions inline with the option
`-finline-functions'.

 Note that certain usages in a function definition can make it
unsuitable for inline substitution.  Among these usages are: use of
varargs, use of alloca, use of variable sized data types (*note
Variable Length::), use of computed goto (*note Labels as Values::),
use of nonlocal goto, and nested functions (*note Nested Functions::).
Using `-Winline' will warn when a function marked `inline' could not be
substituted, and will give the reason for the failure.

 Note that in C and Objective-C, unlike C++, the `inline' keyword does
not affect the linkage of the function.

 GCC automatically inlines member functions defined within the class
body of C++ programs even if they are not explicitly declared `inline'.
(You can override this with `-fno-default-inline'; *note Options
Controlling C++ Dialect: C++ Dialect Options.)

 When a function is both inline and `static', if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option `-fkeep-inline-functions'.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition).  If there is a
nonintegrated call, then the function is compiled to assembler code as
usual.  The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.

 When an inline function is not `static', then the compiler must assume
that there may be calls from other source files; since a global symbol
can be defined only once in any program, the function must not be
defined in the other source files, so the calls therein cannot be
integrated.  Therefore, a non-`static' inline function is always
compiled on its own in the usual fashion.

 If you specify both `inline' and `extern' in the function definition,
then the definition is used only for inlining.  In no case is the
function compiled on its own, not even if you refer to its address
explicitly.  Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.

 This combination of `inline' and `extern' has almost the effect of a
macro.  The way to use it is to put a function definition in a header
file with these keywords, and put another copy of the definition
(lacking `inline' and `extern') in a library file.  The definition in
the header file will cause most calls to the function to be inlined.
If any uses of the function remain, they will refer to the single copy
in the library.

 Since GCC eventually will implement ISO C99 semantics for inline
functions, it is best to use `static inline' only to guarantee
compatibility.  (The existing semantics will remain available when
`-std=gnu89' is specified, but eventually the default will be
`-std=gnu99' and that will implement the C99 semantics, though it does
not do so yet.)

 GCC does not inline any functions when not optimizing unless you
specify the `always_inline' attribute for the function, like this:

     /* Prototype.  */
     inline void foo (const char) __attribute__((always_inline));


File: gcc,  Node: Extended Asm,  Next: Constraints,  Prev: Inline,  Up: C Extensions

5.35 Assembler Instructions with C Expression Operands
======================================================

In an assembler instruction using `asm', you can specify the operands
of the instruction using C expressions.  This means you need not guess
which registers or memory locations will contain the data you want to
use.

 You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.

 For example, here is how to use the 68881's `fsinx' instruction:

     asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));

Here `angle' is the C expression for the input operand while `result'
is that of the output operand.  Each has `"f"' as its operand
constraint, saying that a floating point register is required.  The `='
in `=f' indicates that the operand is an output; all output operands'
constraints must use `='.  The constraints use the same language used
in the machine description (*note Constraints::).

 Each operand is described by an operand-constraint string followed by
the C expression in parentheses.  A colon separates the assembler
template from the first output operand and another separates the last
output operand from the first input, if any.  Commas separate the
operands within each group.  The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
GCC.

 If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
operands would go.

 As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code.  These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using `%[NAME]' instead of a percentage sign followed by
the operand number.  Using named operands the above example could look
like:

     asm ("fsinx %[angle],%[output]"
          : [output] "=f" (result)
          : [angle] "f" (angle));

Note that the symbolic operand names have no relation whatsoever to
other C identifiers.  You may use any name you like, even those of
existing C symbols, but you must ensure that no two operands within the
same assembler construct use the same symbolic name.

 Output operand expressions must be lvalues; the compiler can check
this.  The input operands need not be lvalues.  The compiler cannot
check whether the operands have data types that are reasonable for the
instruction being executed.  It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input.  The extended `asm' feature is most often used for
machine instructions the compiler itself does not know exist.  If the
output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register.  In that case, GCC
will use the register as the output of the `asm', and then store that
register into the output.

 The ordinary output operands must be write-only; GCC will assume that
the values in these operands before the instruction are dead and need
not be generated.  Extended asm supports input-output or read-write
operands.  Use the constraint character `+' to indicate such an operand
and list it with the output operands.  You should only use read-write
operands when the constraints for the operand (or the operand in which
only some of the bits are to be changed) allow a register.

 You may, as an alternative, logically split its function into two
separate operands, one input operand and one write-only output operand.
The connection between them is expressed by constraints which say they
need to be in the same location when the instruction executes.  You can
use the same C expression for both operands, or different expressions.
For example, here we write the (fictitious) `combine' instruction with
`bar' as its read-only source operand and `foo' as its read-write
destination:

     asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));

The constraint `"0"' for operand 1 says that it must occupy the same
location as operand 0.  A number in constraint is allowed only in an
input operand and it must refer to an output operand.

 Only a number in the constraint can guarantee that one operand will be
in the same place as another.  The mere fact that `foo' is the value of
both operands is not enough to guarantee that they will be in the same
place in the generated assembler code.  The following would not work
reliably:

     asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));

 Various optimizations or reloading could cause operands 0 and 1 to be
in different registers; GCC knows no reason not to do so.  For example,
the compiler might find a copy of the value of `foo' in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to `foo''s own address).  Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.

 As of GCC version 3.1, one may write `[NAME]' instead of the operand
number for a matching constraint.  For example:

     asm ("cmoveq %1,%2,%[result]"
          : [result] "=r"(result)
          : "r" (test), "r"(new), "[result]"(old));

 Some instructions clobber specific hard registers.  To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings).  Here is a realistic
example for the VAX:

     asm volatile ("movc3 %0,%1,%2"
                   : /* no outputs */
                   : "g" (from), "g" (to), "g" (count)
                   : "r0", "r1", "r2", "r3", "r4", "r5");

 You may not write a clobber description in a way that overlaps with an
input or output operand.  For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list.  Variables declared to live in specific registers
(*note Explicit Reg Vars::), and used as asm input or output operands
must have no part mentioned in the clobber description.  There is no
way for you to specify that an input operand is modified without also
specifying it as an output operand.  Note that if all the output
operands you specify are for this purpose (and hence unused), you will
then also need to specify `volatile' for the `asm' construct, as
described below, to prevent GCC from deleting the `asm' statement as
unused.

 If you refer to a particular hardware register from the assembler code,
you will probably have to list the register after the third colon to
tell the compiler the register's value is modified.  In some assemblers,
the register names begin with `%'; to produce one `%' in the assembler
code, you must write `%%' in the input.

 If your assembler instruction can alter the condition code register,
add `cc' to the list of clobbered registers.  GCC on some machines
represents the condition codes as a specific hardware register; `cc'
serves to name this register.  On other machines, the condition code is
handled differently, and specifying `cc' has no effect.  But it is
valid no matter what the machine.

 If your assembler instructions access memory in an unpredictable
fashion, add `memory' to the list of clobbered registers.  This will
cause GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You will also want to add the `volatile' keyword if the memory affected
is not listed in the inputs or outputs of the `asm', as the `memory'
clobber does not count as a side-effect of the `asm'.  If you know how
large the accessed memory is, you can add it as input or output but if
this is not known, you should add `memory'.  As an example, if you
access ten bytes of a string, you can use a memory input like:

     {"m"( ({ struct { char x[10]; } *p = (void *)ptr ; *p; }) )}.

 Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to `x' away:
     int foo ()
     {
       int x = 42;
       int *y = &x;
       int result;
       asm ("magic stuff accessing an 'int' pointed to by '%1'"
             "=&d" (r) : "a" (y), "m" (*y));
       return result;
     }

 You can put multiple assembler instructions together in a single `asm'
template, separated by the characters normally used in assembly code
for the system.  A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as `\n\t').  Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character.  Note that
some assembler dialects use semicolons to start a comment.  The input
operands are guaranteed not to use any of the clobbered registers, and
neither will the output operands' addresses, so you can read and write
the clobbered registers as many times as you like.  Here is an example
of multiple instructions in a template; it assumes the subroutine
`_foo' accepts arguments in registers 9 and 10:

     asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
          : /* no outputs */
          : "g" (from), "g" (to)
          : "r9", "r10");

 Unless an output operand has the `&' constraint modifier, GCC may
allocate it in the same register as an unrelated input operand, on the
assumption the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction.  In such a case, use `&' for each output
operand that may not overlap an input.  *Note Modifiers::.

 If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the `asm'
construct, as follows:

     asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
          : "g" (result)
          : "g" (input));

This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.

 Speaking of labels, jumps from one `asm' to another are not supported.
The compiler's optimizers do not know about these jumps, and therefore
they cannot take account of them when deciding how to optimize.

 Usually the most convenient way to use these `asm' instructions is to
encapsulate them in macros that look like functions.  For example,

     #define sin(x)       \
     ({ double __value, __arg = (x);   \
        asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
        __value; })

Here the variable `__arg' is used to make sure that the instruction
operates on a proper `double' value, and to accept only those arguments
`x' which can convert automatically to a `double'.

 Another way to make sure the instruction operates on the correct data
type is to use a cast in the `asm'.  This is different from using a
variable `__arg' in that it converts more different types.  For
example, if the desired type were `int', casting the argument to `int'
would accept a pointer with no complaint, while assigning the argument
to an `int' variable named `__arg' would warn about using a pointer
unless the caller explicitly casts it.

 If an `asm' has output operands, GCC assumes for optimization purposes
the instruction has no side effects except to change the output
operands.  This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression.  Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.

 You can prevent an `asm' instruction from being deleted, moved
significantly, or combined, by writing the keyword `volatile' after the
`asm'.  For example:

     #define get_and_set_priority(new)              \
     ({ int __old;                                  \
        asm volatile ("get_and_set_priority %0, %1" \
                      : "=g" (__old) : "g" (new));  \
        __old; })

If you write an `asm' instruction with no outputs, GCC will know the
instruction has side-effects and will not delete the instruction or
move it outside of loops.

 The `volatile' keyword indicates that the instruction has important
side-effects.  GCC will not delete a volatile `asm' if it is reachable.
(The instruction can still be deleted if GCC can prove that
control-flow will never reach the location of the instruction.)  In
addition, GCC will not reschedule instructions across a volatile `asm'
instruction.  For example:

     *(volatile int *)addr = foo;
     asm volatile ("eieio" : : );

Assume `addr' contains the address of a memory mapped device register.
The PowerPC `eieio' instruction (Enforce In-order Execution of I/O)
tells the CPU to make sure that the store to that device register
happens before it issues any other I/O.

 Note that even a volatile `asm' instruction can be moved in ways that
appear insignificant to the compiler, such as across jump instructions.
You can't expect a sequence of volatile `asm' instructions to remain
perfectly consecutive.  If you want consecutive output, use a single
`asm'.  Also, GCC will perform some optimizations across a volatile
`asm' instruction; GCC does not "forget everything" when it encounters
a volatile `asm' instruction the way some other compilers do.

 An `asm' instruction without any operands or clobbers (an "old style"
`asm') will be treated identically to a volatile `asm' instruction.

 It is a natural idea to look for a way to give access to the condition
code left by the assembler instruction.  However, when we attempted to
implement this, we found no way to make it work reliably.  The problem
is that output operands might need reloading, which would result in
additional following "store" instructions.  On most machines, these
instructions would alter the condition code before there was time to
test it.  This problem doesn't arise for ordinary "test" and "compare"
instructions because they don't have any output operands.

 For reasons similar to those described above, it is not possible to
give an assembler instruction access to the condition code left by
previous instructions.

 If you are writing a header file that should be includable in ISO C
programs, write `__asm__' instead of `asm'.  *Note Alternate Keywords::.

5.35.1 Size of an `asm'
-----------------------

Some targets require that GCC track the size of each instruction used in
order to generate correct code.  Because the final length of an `asm'
is only known by the assembler, GCC must make an estimate as to how big
it will be.  The estimate is formed by counting the number of
statements in the pattern of the `asm' and multiplying that by the
length of the longest instruction on that processor.  Statements in the
`asm' are identified by newline characters and whatever statement
separator characters are supported by the assembler; on most processors
this is the ``;'' character.

 Normally, GCC's estimate is perfectly adequate to ensure that correct
code is generated, but it is possible to confuse the compiler if you use
pseudo instructions or assembler macros that expand into multiple real
instructions or if you use assembler directives that expand to more
space in the object file than would be needed for a single instruction.
If this happens then the assembler will produce a diagnostic saying that
a label is unreachable.

5.35.2 i386 floating point asm operands
---------------------------------------

There are several rules on the usage of stack-like regs in asm_operands
insns.  These rules apply only to the operands that are stack-like regs:

  1. Given a set of input regs that die in an asm_operands, it is
     necessary to know which are implicitly popped by the asm, and
     which must be explicitly popped by gcc.

     An input reg that is implicitly popped by the asm must be
     explicitly clobbered, unless it is constrained to match an output
     operand.

  2. For any input reg that is implicitly popped by an asm, it is
     necessary to know how to adjust the stack to compensate for the
     pop.  If any non-popped input is closer to the top of the
     reg-stack than the implicitly popped reg, it would not be possible
     to know what the stack looked like--it's not clear how the rest of
     the stack "slides up".

     All implicitly popped input regs must be closer to the top of the
     reg-stack than any input that is not implicitly popped.

     It is possible that if an input dies in an insn, reload might use
     the input reg for an output reload.  Consider this example:

          asm ("foo" : "=t" (a) : "f" (b));

     This asm says that input B is not popped by the asm, and that the
     asm pushes a result onto the reg-stack, i.e., the stack is one
     deeper after the asm than it was before.  But, it is possible that
     reload will think that it can use the same reg for both the input
     and the output, if input B dies in this insn.

     If any input operand uses the `f' constraint, all output reg
     constraints must use the `&' earlyclobber.

     The asm above would be written as

          asm ("foo" : "=&t" (a) : "f" (b));

  3. Some operands need to be in particular places on the stack.  All
     output operands fall in this category--there is no other way to
     know which regs the outputs appear in unless the user indicates
     this in the constraints.

     Output operands must specifically indicate which reg an output
     appears in after an asm.  `=f' is not allowed: the operand
     constraints must select a class with a single reg.

  4. Output operands may not be "inserted" between existing stack regs.
     Since no 387 opcode uses a read/write operand, all output operands
     are dead before the asm_operands, and are pushed by the
     asm_operands.  It makes no sense to push anywhere but the top of
     the reg-stack.

     Output operands must start at the top of the reg-stack: output
     operands may not "skip" a reg.

  5. Some asm statements may need extra stack space for internal
     calculations.  This can be guaranteed by clobbering stack registers
     unrelated to the inputs and outputs.


 Here are a couple of reasonable asms to want to write.  This asm takes
one input, which is internally popped, and produces two outputs.

     asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));

 This asm takes two inputs, which are popped by the `fyl2xp1' opcode,
and replaces them with one output.  The user must code the `st(1)'
clobber for reg-stack.c to know that `fyl2xp1' pops both inputs.

     asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");


File: gcc,  Node: Constraints,  Next: Asm Labels,  Prev: Extended Asm,  Up: C Extensions

5.36 Constraints for `asm' Operands
===================================

Here are specific details on what constraint letters you can use with
`asm' operands.  Constraints can say whether an operand may be in a
register, and which kinds of register; whether the operand can be a
memory reference, and which kinds of address; whether the operand may
be an immediate constant, and which possible values it may have.
Constraints can also require two operands to match.

* Menu:

* Simple Constraints::  Basic use of constraints.
* Multi-Alternative::   When an insn has two alternative constraint-patterns.
* Modifiers::           More precise control over effects of constraints.
* Machine Constraints:: Special constraints for some particular machines.


File: gcc,  Node: Simple Constraints,  Next: Multi-Alternative,  Up: Constraints

5.36.1 Simple Constraints
-------------------------

The simplest kind of constraint is a string full of letters, each of
which describes one kind of operand that is permitted.  Here are the
letters that are allowed:

whitespace
     Whitespace characters are ignored and can be inserted at any
     position except the first.  This enables each alternative for
     different operands to be visually aligned in the machine
     description even if they have different number of constraints and
     modifiers.

`m'
     A memory operand is allowed, with any kind of address that the
     machine supports in general.

`o'
     A memory operand is allowed, but only if the address is
     "offsettable".  This means that adding a small integer (actually,
     the width in bytes of the operand, as determined by its machine
     mode) may be added to the address and the result is also a valid
     memory address.

     For example, an address which is constant is offsettable; so is an
     address that is the sum of a register and a constant (as long as a
     slightly larger constant is also within the range of
     address-offsets supported by the machine); but an autoincrement or
     autodecrement address is not offsettable.  More complicated
     indirect/indexed addresses may or may not be offsettable depending
     on the other addressing modes that the machine supports.

     Note that in an output operand which can be matched by another
     operand, the constraint letter `o' is valid only when accompanied
     by both `<' (if the target machine has predecrement addressing)
     and `>' (if the target machine has preincrement addressing).

`V'
     A memory operand that is not offsettable.  In other words,
     anything that would fit the `m' constraint but not the `o'
     constraint.

`<'
     A memory operand with autodecrement addressing (either
     predecrement or postdecrement) is allowed.

`>'
     A memory operand with autoincrement addressing (either
     preincrement or postincrement) is allowed.

`r'
     A register operand is allowed provided that it is in a general
     register.

`i'
     An immediate integer operand (one with constant value) is allowed.
     This includes symbolic constants whose values will be known only at
     assembly time.

`n'
     An immediate integer operand with a known numeric value is allowed.
     Many systems cannot support assembly-time constants for operands
     less than a word wide.  Constraints for these operands should use
     `n' rather than `i'.

`I', `J', `K', ... `P'
     Other letters in the range `I' through `P' may be defined in a
     machine-dependent fashion to permit immediate integer operands with
     explicit integer values in specified ranges.  For example, on the
     68000, `I' is defined to stand for the range of values 1 to 8.
     This is the range permitted as a shift count in the shift
     instructions.

`E'
     An immediate floating operand (expression code `const_double') is
     allowed, but only if the target floating point format is the same
     as that of the host machine (on which the compiler is running).

`F'
     An immediate floating operand (expression code `const_double' or
     `const_vector') is allowed.

`G', `H'
     `G' and `H' may be defined in a machine-dependent fashion to
     permit immediate floating operands in particular ranges of values.

`s'
     An immediate integer operand whose value is not an explicit
     integer is allowed.

     This might appear strange; if an insn allows a constant operand
     with a value not known at compile time, it certainly must allow
     any known value.  So why use `s' instead of `i'?  Sometimes it
     allows better code to be generated.

     For example, on the 68000 in a fullword instruction it is possible
     to use an immediate operand; but if the immediate value is between
     -128 and 127, better code results from loading the value into a
     register and using the register.  This is because the load into
     the register can be done with a `moveq' instruction.  We arrange
     for this to happen by defining the letter `K' to mean "any integer
     outside the range -128 to 127", and then specifying `Ks' in the
     operand constraints.

`g'
     Any register, memory or immediate integer operand is allowed,
     except for registers that are not general registers.

`X'
     Any operand whatsoever is allowed.

`0', `1', `2', ... `9'
     An operand that matches the specified operand number is allowed.
     If a digit is used together with letters within the same
     alternative, the digit should come last.

     This number is allowed to be more than a single digit.  If multiple
     digits are encountered consecutively, they are interpreted as a
     single decimal integer.  There is scant chance for ambiguity,
     since to-date it has never been desirable that `10' be interpreted
     as matching either operand 1 _or_ operand 0.  Should this be
     desired, one can use multiple alternatives instead.

     This is called a "matching constraint" and what it really means is
     that the assembler has only a single operand that fills two roles
     which `asm' distinguishes.  For example, an add instruction uses
     two input operands and an output operand, but on most CISC
     machines an add instruction really has only two operands, one of
     them an input-output operand:

          addl #35,r12

     Matching constraints are used in these circumstances.  More
     precisely, the two operands that match must include one input-only
     operand and one output-only operand.  Moreover, the digit must be a
     smaller number than the number of the operand that uses it in the
     constraint.

`p'
     An operand that is a valid memory address is allowed.  This is for
     "load address" and "push address" instructions.

     `p' in the constraint must be accompanied by `address_operand' as
     the predicate in the `match_operand'.  This predicate interprets
     the mode specified in the `match_operand' as the mode of the memory
     reference for which the address would be valid.

OTHER-LETTERS
     Other letters can be defined in machine-dependent fashion to stand
     for particular classes of registers or other arbitrary operand
     types.  `d', `a' and `f' are defined on the 68000/68020 to stand
     for data, address and floating point registers.



File: gcc,  Node: Multi-Alternative,  Next: Modifiers,  Prev: Simple Constraints,  Up: Constraints

5.36.2 Multiple Alternative Constraints
---------------------------------------

Sometimes a single instruction has multiple alternative sets of possible
operands.  For example, on the 68000, a logical-or instruction can
combine register or an immediate value into memory, or it can combine
any kind of operand into a register; but it cannot combine one memory
location into another.

 These constraints are represented as multiple alternatives.  An
alternative can be described by a series of letters for each operand.
The overall constraint for an operand is made from the letters for this
operand from the first alternative, a comma, the letters for this
operand from the second alternative, a comma, and so on until the last
alternative.

 If all the operands fit any one alternative, the instruction is valid.
Otherwise, for each alternative, the compiler counts how many
instructions must be added to copy the operands so that that
alternative applies.  The alternative requiring the least copying is
chosen.  If two alternatives need the same amount of copying, the one
that comes first is chosen.  These choices can be altered with the `?'
and `!' characters:

`?'
     Disparage slightly the alternative that the `?' appears in, as a
     choice when no alternative applies exactly.  The compiler regards
     this alternative as one unit more costly for each `?' that appears
     in it.

`!'
     Disparage severely the alternative that the `!' appears in.  This
     alternative can still be used if it fits without reloading, but if
     reloading is needed, some other alternative will be used.


File: gcc,  Node: Modifiers,  Next: Machine Constraints,  Prev: Multi-Alternative,  Up: Constraints

5.36.3 Constraint Modifier Characters
-------------------------------------

Here are constraint modifier characters.

`='
     Means that this operand is write-only for this instruction: the
     previous value is discarded and replaced by output data.

`+'
     Means that this operand is both read and written by the
     instruction.

     When the compiler fixes up the operands to satisfy the constraints,
     it needs to know which operands are inputs to the instruction and
     which are outputs from it.  `=' identifies an output; `+'
     identifies an operand that is both input and output; all other
     operands are assumed to be input only.

     If you specify `=' or `+' in a constraint, you put it in the first
     character of the constraint string.

`&'
     Means (in a particular alternative) that this operand is an
     "earlyclobber" operand, which is modified before the instruction is
     finished using the input operands.  Therefore, this operand may
     not lie in a register that is used as an input operand or as part
     of any memory address.

     `&' applies only to the alternative in which it is written.  In
     constraints with multiple alternatives, sometimes one alternative
     requires `&' while others do not.  See, for example, the `movdf'
     insn of the 68000.

     An input operand can be tied to an earlyclobber operand if its only
     use as an input occurs before the early result is written.  Adding
     alternatives of this form often allows GCC to produce better code
     when only some of the inputs can be affected by the earlyclobber.
     See, for example, the `mulsi3' insn of the ARM.

     `&' does not obviate the need to write `='.

`%'
     Declares the instruction to be commutative for this operand and the
     following operand.  This means that the compiler may interchange
     the two operands if that is the cheapest way to make all operands
     fit the constraints.  GCC can only handle one commutative pair in
     an asm; if you use more, the compiler may fail.

`#'
     Says that all following characters, up to the next comma, are to be
     ignored as a constraint.  They are significant only for choosing
     register preferences.

`*'
     Says that the following character should be ignored when choosing
     register preferences.  `*' has no effect on the meaning of the
     constraint as a constraint, and no effect on reloading.



File: gcc,  Node: Machine Constraints,  Prev: Modifiers,  Up: Constraints

5.36.4 Constraints for Particular Machines
------------------------------------------

Whenever possible, you should use the general-purpose constraint letters
in `asm' arguments, since they will convey meaning more readily to
people reading your code.  Failing that, use the constraint letters
that usually have very similar meanings across architectures.  The most
commonly used constraints are `m' and `r' (for memory and
general-purpose registers respectively; *note Simple Constraints::), and
`I', usually the letter indicating the most common immediate-constant
format.

 For each machine architecture, the `config/MACHINE/MACHINE.h' file
defines additional constraints.  These constraints are used by the
compiler itself for instruction generation, as well as for `asm'
statements; therefore, some of the constraints are not particularly
interesting for `asm'.  The constraints are defined through these
macros:

`REG_CLASS_FROM_LETTER'
     Register class constraints (usually lowercase).

`CONST_OK_FOR_LETTER_P'
     Immediate constant constraints, for non-floating point constants of
     word size or smaller precision (usually uppercase).

`CONST_DOUBLE_OK_FOR_LETTER_P'
     Immediate constant constraints, for all floating point constants
     and for constants of greater than word size precision (usually
     uppercase).

`EXTRA_CONSTRAINT'
     Special cases of registers or memory.  This macro is not required,
     and is only defined for some machines.

 Inspecting these macro definitions in the compiler source for your
machine is the best way to be certain you have the right constraints.
However, here is a summary of the machine-dependent constraints
available on some particular machines.

_ARM family--`arm.h'_

    `f'
          Floating-point register

    `F'
          One of the floating-point constants 0.0, 0.5, 1.0, 2.0, 3.0,
          4.0, 5.0 or 10.0

    `G'
          Floating-point constant that would satisfy the constraint `F'
          if it were negated

    `I'
          Integer that is valid as an immediate operand in a data
          processing instruction.  That is, an integer in the range 0
          to 255 rotated by a multiple of 2

    `J'
          Integer in the range -4095 to 4095

    `K'
          Integer that satisfies constraint `I' when inverted (ones
          complement)

    `L'
          Integer that satisfies constraint `I' when negated (twos
          complement)

    `M'
          Integer in the range 0 to 32

    `Q'
          A memory reference where the exact address is in a single
          register (``m'' is preferable for `asm' statements)

    `R'
          An item in the constant pool

    `S'
          A symbol in the text segment of the current file

_AVR family--`avr.h'_

    `l'
          Registers from r0 to r15

    `a'
          Registers from r16 to r23

    `d'
          Registers from r16 to r31

    `w'
          Registers from r24 to r31.  These registers can be used in
          `adiw' command

    `e'
          Pointer register (r26-r31)

    `b'
          Base pointer register (r28-r31)

    `q'
          Stack pointer register (SPH:SPL)

    `t'
          Temporary register r0

    `x'
          Register pair X (r27:r26)

    `y'
          Register pair Y (r29:r28)

    `z'
          Register pair Z (r31:r30)

    `I'
          Constant greater than -1, less than 64

    `J'
          Constant greater than -64, less than 1

    `K'
          Constant integer 2

    `L'
          Constant integer 0

    `M'
          Constant that fits in 8 bits

    `N'
          Constant integer -1

    `O'
          Constant integer 8, 16, or 24

    `P'
          Constant integer 1

    `G'
          A floating point constant 0.0

_PowerPC and IBM RS6000--`rs6000.h'_

    `b'
          Address base register

    `f'
          Floating point register

    `v'
          Vector register

    `h'
          `MQ', `CTR', or `LINK' register

    `q'
          `MQ' register

    `c'
          `CTR' register

    `l'
          `LINK' register

    `x'
          `CR' register (condition register) number 0

    `y'
          `CR' register (condition register)

    `z'
          `FPMEM' stack memory for FPR-GPR transfers

    `I'
          Signed 16-bit constant

    `J'
          Unsigned 16-bit constant shifted left 16 bits (use `L'
          instead for `SImode' constants)

    `K'
          Unsigned 16-bit constant

    `L'
          Signed 16-bit constant shifted left 16 bits

    `M'
          Constant larger than 31

    `N'
          Exact power of 2

    `O'
          Zero

    `P'
          Constant whose negation is a signed 16-bit constant

    `G'
          Floating point constant that can be loaded into a register
          with one instruction per word

    `Q'
          Memory operand that is an offset from a register (`m' is
          preferable for `asm' statements)

    `R'
          AIX TOC entry

    `S'
          Constant suitable as a 64-bit mask operand

    `T'
          Constant suitable as a 32-bit mask operand

    `U'
          System V Release 4 small data area reference

_Intel 386--`i386.h'_

    `q'
          `a', `b', `c', or `d' register for the i386.  For x86-64 it
          is equivalent to `r' class. (for 8-bit instructions that do
          not use upper halves)

    `Q'
          `a', `b', `c', or `d' register. (for 8-bit instructions, that
          do use upper halves)

    `R'
          Legacy register--equivalent to `r' class in i386 mode.  (for
          non-8-bit registers used together with 8-bit upper halves in
          a single instruction)

    `A'
          Specifies the `a' or `d' registers.  This is primarily useful
          for 64-bit integer values (when in 32-bit mode) intended to
          be returned with the `d' register holding the most
          significant bits and the `a' register holding the least
          significant bits.

    `f'
          Floating point register

    `t'
          First (top of stack) floating point register

    `u'
          Second floating point register

    `a'
          `a' register

    `b'
          `b' register

    `c'
          `c' register

    `C'
          Specifies constant that can be easily constructed in SSE
          register without loading it from memory.

    `d'
          `d' register

    `D'
          `di' register

    `S'
          `si' register

    `x'
          `xmm' SSE register

    `y'
          MMX register

    `I'
          Constant in range 0 to 31 (for 32-bit shifts)

    `J'
          Constant in range 0 to 63 (for 64-bit shifts)

    `K'
          `0xff'

    `L'
          `0xffff'

    `M'
          0, 1, 2, or 3 (shifts for `lea' instruction)

    `N'
          Constant in range 0 to 255 (for `out' instruction)

    `Z'
          Constant in range 0 to `0xffffffff' or symbolic reference
          known to fit specified range.  (for using immediates in zero
          extending 32-bit to 64-bit x86-64 instructions)

    `e'
          Constant in range -2147483648 to 2147483647 or symbolic
          reference known to fit specified range.  (for using
          immediates in 64-bit x86-64 instructions)

    `G'
          Standard 80387 floating point constant

_Intel 960--`i960.h'_

    `f'
          Floating point register (`fp0' to `fp3')

    `l'
          Local register (`r0' to `r15')

    `b'
          Global register (`g0' to `g15')

    `d'
          Any local or global register

    `I'
          Integers from 0 to 31

    `J'
          0

    `K'
          Integers from -31 to 0

    `G'
          Floating point 0

    `H'
          Floating point 1

_Intel IA-64--`ia64.h'_

    `a'
          General register `r0' to `r3' for `addl' instruction

    `b'
          Branch register

    `c'
          Predicate register (`c' as in "conditional")

    `d'
          Application register residing in M-unit

    `e'
          Application register residing in I-unit

    `f'
          Floating-point register

    `m'
          Memory operand.  Remember that `m' allows postincrement and
          postdecrement which require printing with `%Pn' on IA-64.
          Use `S' to disallow postincrement and postdecrement.

    `G'
          Floating-point constant 0.0 or 1.0

    `I'
          14-bit signed integer constant

    `J'
          22-bit signed integer constant

    `K'
          8-bit signed integer constant for logical instructions

    `L'
          8-bit adjusted signed integer constant for compare pseudo-ops

    `M'
          6-bit unsigned integer constant for shift counts

    `N'
          9-bit signed integer constant for load and store
          postincrements

    `O'
          The constant zero

    `P'
          0 or -1 for `dep' instruction

    `Q'
          Non-volatile memory for floating-point loads and stores

    `R'
          Integer constant in the range 1 to 4 for `shladd' instruction

    `S'
          Memory operand except postincrement and postdecrement

_FRV--`frv.h'_

    `a'
          Register in the class `ACC_REGS' (`acc0' to `acc7').

    `b'
          Register in the class `EVEN_ACC_REGS' (`acc0' to `acc7').

    `c'
          Register in the class `CC_REGS' (`fcc0' to `fcc3' and `icc0'
          to `icc3').

    `d'
          Register in the class `GPR_REGS' (`gr0' to `gr63').

    `e'
          Register in the class `EVEN_REGS' (`gr0' to `gr63').  Odd
          registers are excluded not in the class but through the use
          of a machine mode larger than 4 bytes.

    `f'
          Register in the class `FPR_REGS' (`fr0' to `fr63').

    `h'
          Register in the class `FEVEN_REGS' (`fr0' to `fr63').  Odd
          registers are excluded not in the class but through the use
          of a machine mode larger than 4 bytes.

    `l'
          Register in the class `LR_REG' (the `lr' register).

    `q'
          Register in the class `QUAD_REGS' (`gr2' to `gr63').
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

    `t'
          Register in the class `ICC_REGS' (`icc0' to `icc3').

    `u'
          Register in the class `FCC_REGS' (`fcc0' to `fcc3').

    `v'
          Register in the class `ICR_REGS' (`cc4' to `cc7').

    `w'
          Register in the class `FCR_REGS' (`cc0' to `cc3').

    `x'
          Register in the class `QUAD_FPR_REGS' (`fr0' to `fr63').
          Register numbers not divisible by 4 are excluded not in the
          class but through the use of a machine mode larger than 8
          bytes.

    `z'
          Register in the class `SPR_REGS' (`lcr' and `lr').

    `A'
          Register in the class `QUAD_ACC_REGS' (`acc0' to `acc7').

    `B'
          Register in the class `ACCG_REGS' (`accg0' to `accg7').

    `C'
          Register in the class `CR_REGS' (`cc0' to `cc7').

    `G'
          Floating point constant zero

    `I'
          6-bit signed integer constant

    `J'
          10-bit signed integer constant

    `L'
          16-bit signed integer constant

    `M'
          16-bit unsigned integer constant

    `N'
          12-bit signed integer constant that is negative--i.e. in the
          range of -2048 to -1

    `O'
          Constant zero

    `P'
          12-bit signed integer constant that is greater than
          zero--i.e. in the range of 1 to 2047.


_IP2K--`ip2k.h'_

    `a'
          `DP' or `IP' registers (general address)

    `f'
          `IP' register

    `j'
          `IPL' register

    `k'
          `IPH' register

    `b'
          `DP' register

    `y'
          `DPH' register

    `z'
          `DPL' register

    `q'
          `SP' register

    `c'
          `DP' or `SP' registers (offsettable address)

    `d'
          Non-pointer registers (not `SP', `DP', `IP')

    `u'
          Non-SP registers (everything except `SP')

    `R'
          Indirect through `IP' - Avoid this except for `QImode', since
          we can't access extra bytes

    `S'
          Indirect through `SP' or `DP' with short displacement (0..127)

    `T'
          Data-section immediate value

    `I'
          Integers from -255 to -1

    `J'
          Integers from 0 to 7--valid bit number in a register

    `K'
          Integers from 0 to 127--valid displacement for addressing mode

    `L'
          Integers from 1 to 127

    `M'
          Integer -1

    `N'
          Integer 1

    `O'
          Zero

    `P'
          Integers from 0 to 255

_MIPS--`mips.h'_

    `d'
          General-purpose integer register

    `f'
          Floating-point register (if available)

    `h'
          `Hi' register

    `l'
          `Lo' register

    `x'
          `Hi' or `Lo' register

    `y'
          General-purpose integer register

    `z'
          Floating-point status register

    `I'
          Signed 16-bit constant (for arithmetic instructions)

    `J'
          Zero

    `K'
          Zero-extended 16-bit constant (for logic instructions)

    `L'
          Constant with low 16 bits zero (can be loaded with `lui')

    `M'
          32-bit constant which requires two instructions to load (a
          constant which is not `I', `K', or `L')

    `N'
          Negative 16-bit constant

    `O'
          Exact power of two

    `P'
          Positive 16-bit constant

    `G'
          Floating point zero

    `Q'
          Memory reference that can be loaded with more than one
          instruction (`m' is preferable for `asm' statements)

    `R'
          Memory reference that can be loaded with one instruction (`m'
          is preferable for `asm' statements)

    `S'
          Memory reference in external OSF/rose PIC format (`m' is
          preferable for `asm' statements)

_Motorola 680x0--`m68k.h'_

    `a'
          Address register

    `d'
          Data register

    `f'
          68881 floating-point register, if available

    `I'
          Integer in the range 1 to 8

    `J'
          16-bit signed number

    `K'
          Signed number whose magnitude is greater than 0x80

    `L'
          Integer in the range -8 to -1

    `M'
          Signed number whose magnitude is greater than 0x100

    `G'
          Floating point constant that is not a 68881 constant

_Motorola 68HC11 & 68HC12 families--`m68hc11.h'_

    `a'
          Register 'a'

    `b'
          Register 'b'

    `d'
          Register 'd'

    `q'
          An 8-bit register

    `t'
          Temporary soft register _.tmp

    `u'
          A soft register _.d1 to _.d31

    `w'
          Stack pointer register

    `x'
          Register 'x'

    `y'
          Register 'y'

    `z'
          Pseudo register 'z' (replaced by 'x' or 'y' at the end)

    `A'
          An address register: x, y or z

    `B'
          An address register: x or y

    `D'
          Register pair (x:d) to form a 32-bit value

    `L'
          Constants in the range -65536 to 65535

    `M'
          Constants whose 16-bit low part is zero

    `N'
          Constant integer 1 or -1

    `O'
          Constant integer 16

    `P'
          Constants in the range -8 to 2


_SPARC--`sparc.h'_

    `f'
          Floating-point register on the SPARC-V8 architecture and
          lower floating-point register on the SPARC-V9 architecture.

    `e'
          Floating-point register. It is equivalent to `f' on the
          SPARC-V8 architecture and contains both lower and upper
          floating-point registers on the SPARC-V9 architecture.

    `c'
          Floating-point condition code register.

    `d'
          Lower floating-point register. It is only valid on the
          SPARC-V9 architecture when the Visual Instruction Set is
          available.

    `b'
          Floating-point register. It is only valid on the SPARC-V9
          architecture when the Visual Instruction Set is available.

    `h'
          64-bit global or out register for the SPARC-V8+ architecture.

    `I'
          Signed 13-bit constant

    `J'
          Zero

    `K'
          32-bit constant with the low 12 bits clear (a constant that
          can be loaded with the `sethi' instruction)

    `L'
          A constant in the range supported by `movcc' instructions

    `M'
          A constant in the range supported by `movrcc' instructions

    `N'
          Same as `K', except that it verifies that bits that are not
          in the lower 32-bit range are all zero.  Must be used instead
          of `K' for modes wider than `SImode'

    `O'
          The constant 4096

    `G'
          Floating-point zero

    `H'
          Signed 13-bit constant, sign-extended to 32 or 64 bits

    `Q'
          Floating-point constant whose integral representation can be
          moved into an integer register using a single sethi
          instruction

    `R'
          Floating-point constant whose integral representation can be
          moved into an integer register using a single mov instruction

    `S'
          Floating-point constant whose integral representation can be
          moved into an integer register using a high/lo_sum
          instruction sequence

    `T'
          Memory address aligned to an 8-byte boundary

    `U'
          Even register

    `W'
          Memory address for `e' constraint registers.


_TMS320C3x/C4x--`c4x.h'_

    `a'
          Auxiliary (address) register (ar0-ar7)

    `b'
          Stack pointer register (sp)

    `c'
          Standard (32-bit) precision integer register

    `f'
          Extended (40-bit) precision register (r0-r11)

    `k'
          Block count register (bk)

    `q'
          Extended (40-bit) precision low register (r0-r7)

    `t'
          Extended (40-bit) precision register (r0-r1)

    `u'
          Extended (40-bit) precision register (r2-r3)

    `v'
          Repeat count register (rc)

    `x'
          Index register (ir0-ir1)

    `y'
          Status (condition code) register (st)

    `z'
          Data page register (dp)

    `G'
          Floating-point zero

    `H'
          Immediate 16-bit floating-point constant

    `I'
          Signed 16-bit constant

    `J'
          Signed 8-bit constant

    `K'
          Signed 5-bit constant

    `L'
          Unsigned 16-bit constant

    `M'
          Unsigned 8-bit constant

    `N'
          Ones complement of unsigned 16-bit constant

    `O'
          High 16-bit constant (32-bit constant with 16 LSBs zero)

    `Q'
          Indirect memory reference with signed 8-bit or index register
          displacement

    `R'
          Indirect memory reference with unsigned 5-bit displacement

    `S'
          Indirect memory reference with 1 bit or index register
          displacement

    `T'
          Direct memory reference

    `U'
          Symbolic address


_S/390 and zSeries--`s390.h'_

    `a'
          Address register (general purpose register except r0)

    `d'
          Data register (arbitrary general purpose register)

    `f'
          Floating-point register

    `I'
          Unsigned 8-bit constant (0-255)

    `J'
          Unsigned 12-bit constant (0-4095)

    `K'
          Signed 16-bit constant (-32768-32767)

    `L'
          Value appropriate as displacement.
         `(0..4095)'
               for short displacement

         `(-524288..524287)'
               for long displacement

    `M'
          Constant integer with a value of 0x7fffffff.

    `N'
          Multiple letter constraint followed by 4 parameter letters.
         `0..9:'
               number of the part counting from most to least
               significant

         `H,Q:'
               mode of the part

         `D,S,H:'
               mode of the containing operand

         `0,F:'
               value of the other parts (F - all bits set)
          The constraint matches if the specified part of a constant
          has a value different from it's other parts.

    `Q'
          Memory reference without index register and with short
          displacement.

    `R'
          Memory reference with index register and short displacement.

    `S'
          Memory reference without index register but with long
          displacement.

    `T'
          Memory reference with index register and long displacement.

    `U'
          Pointer with short displacement.

    `W'
          Pointer with long displacement.

    `Y'
          Shift count operand.


_Xstormy16--`stormy16.h'_

    `a'
          Register r0.

    `b'
          Register r1.

    `c'
          Register r2.

    `d'
          Register r8.

    `e'
          Registers r0 through r7.

    `t'
          Registers r0 and r1.

    `y'
          The carry register.

    `z'
          Registers r8 and r9.

    `I'
          A constant between 0 and 3 inclusive.

    `J'
          A constant that has exactly one bit set.

    `K'
          A constant that has exactly one bit clear.

    `L'
          A constant between 0 and 255 inclusive.

    `M'
          A constant between -255 and 0 inclusive.

    `N'
          A constant between -3 and 0 inclusive.

    `O'
          A constant between 1 and 4 inclusive.

    `P'
          A constant between -4 and -1 inclusive.

    `Q'
          A memory reference that is a stack push.

    `R'
          A memory reference that is a stack pop.

    `S'
          A memory reference that refers to a constant address of known
          value.

    `T'
          The register indicated by Rx (not implemented yet).

    `U'
          A constant that is not between 2 and 15 inclusive.

    `Z'
          The constant 0.


_Xtensa--`xtensa.h'_

    `a'
          General-purpose 32-bit register

    `b'
          One-bit boolean register

    `A'
          MAC16 40-bit accumulator register

    `I'
          Signed 12-bit integer constant, for use in MOVI instructions

    `J'
          Signed 8-bit integer constant, for use in ADDI instructions

    `K'
          Integer constant valid for BccI instructions

    `L'
          Unsigned constant valid for BccUI instructions




File: gcc,  Node: Asm Labels,  Next: Explicit Reg Vars,  Prev: Constraints,  Up: C Extensions

5.37 Controlling Names Used in Assembler Code
=============================================

You can specify the name to be used in the assembler code for a C
function or variable by writing the `asm' (or `__asm__') keyword after
the declarator as follows:

     int foo asm ("myfoo") = 2;

This specifies that the name to be used for the variable `foo' in the
assembler code should be `myfoo' rather than the usual `_foo'.

 On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.

 It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see *Note Explicit
Reg Vars::.  GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.

 You cannot use `asm' in this way in a function _definition_; but you
can get the same effect by writing a declaration for the function
before its definition and putting `asm' there, like this:

     extern func () asm ("FUNC");

     func (x, y)
          int x, y;
     /* ... */

 It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.
GCC does not as yet have the ability to store static variables in
registers.  Perhaps that will be added.


File: gcc,  Node: Explicit Reg Vars,  Next: Alternate Keywords,  Prev: Asm Labels,  Up: C Extensions

5.38 Variables in Specified Registers
=====================================

GNU C allows you to put a few global variables into specified hardware
registers.  You can also specify the register in which an ordinary
register variable should be allocated.

   * Global register variables reserve registers throughout the program.
     This may be useful in programs such as programming language
     interpreters which have a couple of global variables that are
     accessed very often.

   * Local register variables in specific registers do not reserve the
     registers.  The compiler's data flow analysis is capable of
     determining where the specified registers contain live values, and
     where they are available for other uses.  Stores into local
     register variables may be deleted when they appear to be dead
     according to dataflow analysis.  References to local register
     variables may be deleted or moved or simplified.

     These local variables are sometimes convenient for use with the
     extended `asm' feature (*note Extended Asm::), if you want to
     write one output of the assembler instruction directly into a
     particular register.  (This will work provided the register you
     specify fits the constraints specified for that operand in the
     `asm'.)

* Menu:

* Global Reg Vars::
* Local Reg Vars::


File: gcc,  Node: Global Reg Vars,  Next: Local Reg Vars,  Up: Explicit Reg Vars

5.38.1 Defining Global Register Variables
-----------------------------------------

You can define a global register variable in GNU C like this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Choose a
register which is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.

 Naturally the register name is cpu-dependent, so you would need to
conditionalize your program according to cpu type.  The register `a5'
would be a good choice on a 68000 for a variable of pointer type.  On
machines with register windows, be sure to choose a "global" register
that is not affected magically by the function call mechanism.

 In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

 Eventually there may be a way of asking the compiler to choose a
register automatically, but first we need to figure out how it should
choose and how to enable you to guide the choice.  No solution is
evident.

 Defining a global register variable in a certain register reserves that
register entirely for this use, at least within the current compilation.
The register will not be allocated for any other purpose in the
functions in the current compilation.  The register will not be saved
and restored by these functions.  Stores into this register are never
deleted even if they would appear to be dead, but references may be
deleted or moved or simplified.

 It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things
(unless you recompile them specially for the task at hand).

 It is not safe for one function that uses a global register variable to
call another such function `foo' by way of a third function `lose' that
was compiled without knowledge of this variable (i.e. in a different
source file in which the variable wasn't declared).  This is because
`lose' might save the register and put some other value there.  For
example, you can't expect a global register variable to be available in
the comparison-function that you pass to `qsort', since `qsort' might
have put something else in that register.  (If you are prepared to
recompile `qsort' with the same global register variable, you can solve
this problem.)

 If you want to recompile `qsort' or other source files which do not
actually use your global register variable, so that they will not use
that register for any other purpose, then it suffices to specify the
compiler option `-ffixed-REG'.  You need not actually add a global
register declaration to their source code.

 A function which can alter the value of a global register variable
cannot safely be called from a function compiled without this variable,
because it could clobber the value the caller expects to find there on
return.  Therefore, the function which is the entry point into the part
of the program that uses the global register variable must explicitly
save and restore the value which belongs to its caller.

 On most machines, `longjmp' will restore to each global register
variable the value it had at the time of the `setjmp'.  On some
machines, however, `longjmp' will not change the value of global
register variables.  To be portable, the function that called `setjmp'
should make other arrangements to save the values of the global register
variables, and to restore them in a `longjmp'.  This way, the same
thing will happen regardless of what `longjmp' does.

 All global register variable declarations must precede all function
definitions.  If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register
from being used for other purposes in the preceding functions.

 Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.

 On the SPARC, there are reports that g3 ... g7 are suitable registers,
but certain library functions, such as `getwd', as well as the
subroutines for division and remainder, modify g3 and g4.  g1 and g2
are local temporaries.

 On the 68000, a2 ... a5 should be suitable, as should d2 ... d7.  Of
course, it will not do to use more than a few of those.


File: gcc,  Node: Local Reg Vars,  Prev: Global Reg Vars,  Up: Explicit Reg Vars

5.38.2 Specifying Registers for Local Variables
-----------------------------------------------

You can define a local register variable with a specified register like
this:

     register int *foo asm ("a5");

Here `a5' is the name of the register which should be used.  Note that
this is the same syntax used for defining global register variables,
but for a local variable it would appear within a function.

 Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (*note Extended Asm::).  Both of these things
generally require that you conditionalize your program according to cpu
type.

 In addition, operating systems on one type of cpu may differ in how
they name the registers; then you would need additional conditionals.
For example, some 68000 operating systems call this register `%a5'.

 Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.  However, these registers are made
unavailable for use in the reload pass; excessive use of this feature
leaves the compiler too few available registers to compile certain
functions.

 This option does not guarantee that GCC will generate code that has
this variable in the register you specify at all times.  You may not
code an explicit reference to this register in an `asm' statement and
assume it will always refer to this variable.

 Stores into local register variables may be deleted when they appear
to be dead according to dataflow analysis.  References to local
register variables may be deleted or moved or simplified.


File: gcc,  Node: Alternate Keywords,  Next: Incomplete Enums,  Prev: Explicit Reg Vars,  Up: C Extensions

5.39 Alternate Keywords
=======================

`-ansi' and the various `-std' options disable certain keywords.  This
causes trouble when you want to use GNU C extensions, or a
general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords `asm', `typeof' and `inline'
are not available in programs compiled with `-ansi' or `-std' (although
`inline' can be used in a program compiled with `-std=c99').  The ISO
C99 keyword `restrict' is only available when `-std=gnu99' (which will
eventually be the default) or `-std=c99' (or the equivalent
`-std=iso9899:1999') is used.

 The way to solve these problems is to put `__' at the beginning and
end of each problematical keyword.  For example, use `__asm__' instead
of `asm', and `__inline__' instead of `inline'.

 Other C compilers won't accept these alternative keywords; if you want
to compile with another compiler, you can define the alternate keywords
as macros to replace them with the customary keywords.  It looks like
this:

     #ifndef __GNUC__
     #define __asm__ asm
     #endif

 `-pedantic' and other options cause warnings for many GNU C extensions.
You can prevent such warnings within one expression by writing
`__extension__' before the expression.  `__extension__' has no effect
aside from this.


File: gcc,  Node: Incomplete Enums,  Next: Function Names,  Prev: Alternate Keywords,  Up: C Extensions

5.40 Incomplete `enum' Types
============================

You can define an `enum' tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
`struct foo' without describing the elements.  A later declaration
which does specify the possible values completes the type.

 You can't allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

 This extension may not be very useful, but it makes the handling of
`enum' more consistent with the way `struct' and `union' are handled.

 This extension is not supported by GNU C++.


File: gcc,  Node: Function Names,  Next: Return Address,  Prev: Incomplete Enums,  Up: C Extensions

5.41 Function Names as Strings
==============================

GCC provides three magic variables which hold the name of the current
function, as a string.  The first of these is `__func__', which is part
of the C99 standard:

     The identifier `__func__' is implicitly declared by the translator
     as if, immediately following the opening brace of each function
     definition, the declaration
          static const char __func__[] = "function-name";

     appeared, where function-name is the name of the lexically-enclosing
     function.  This name is the unadorned name of the function.

 `__FUNCTION__' is another name for `__func__'.  Older versions of GCC
recognize only this name.  However, it is not standardized.  For
maximum portability, we recommend you use `__func__', but provide a
fallback definition with the preprocessor:

     #if __STDC_VERSION__ < 199901L
     # if __GNUC__ >= 2
     #  define __func__ __FUNCTION__
     # else
     #  define __func__ "<unknown>"
     # endif
     #endif

 In C, `__PRETTY_FUNCTION__' is yet another name for `__func__'.
However, in C++, `__PRETTY_FUNCTION__' contains the type signature of
the function as well as its bare name.  For example, this program:

     extern "C" {
     extern int printf (char *, ...);
     }

     class a {
      public:
       void sub (int i)
         {
           printf ("__FUNCTION__ = %s\n", __FUNCTION__);
           printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
         }
     };

     int
     main (void)
     {
       a ax;
       ax.sub (0);
       return 0;
     }

gives this output:

     __FUNCTION__ = sub
     __PRETTY_FUNCTION__ = void a::sub(int)

 These identifiers are not preprocessor macros.  In GCC 3.3 and
earlier, in C only, `__FUNCTION__' and `__PRETTY_FUNCTION__' were
treated as string literals; they could be used to initialize `char'
arrays, and they could be concatenated with other string literals.  GCC
3.4 and later treat them as variables, like `__func__'.  In C++,
`__FUNCTION__' and `__PRETTY_FUNCTION__' have always been variables.


File: gcc,  Node: Return Address,  Next: Vector Extensions,  Prev: Function Names,  Up: C Extensions

5.42 Getting the Return or Frame Address of a Function
======================================================

These functions may be used to get information about the callers of a
function.

 -- Built-in Function: void * __builtin_return_address (unsigned int
          LEVEL)
     This function returns the return address of the current function,
     or of one of its callers.  The LEVEL argument is number of frames
     to scan up the call stack.  A value of `0' yields the return
     address of the current function, a value of `1' yields the return
     address of the caller of the current function, and so forth. When
     inlining the expected behavior is that the function will return
     the address of the function that will be returned to.  To work
     around this behavior use the `noinline' function attribute.

     The LEVEL argument must be a constant integer.

     On some machines it may be impossible to determine the return
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function will
     return `0' or a random value. In addition,
     `__builtin_frame_address' may be used to determine if the top of
     the stack has been reached.

     This function should only be used with a nonzero argument for
     debugging purposes.

 -- Built-in Function: void * __builtin_frame_address (unsigned int
          LEVEL)
     This function is similar to `__builtin_return_address', but it
     returns the address of the function frame rather than the return
     address of the function.  Calling `__builtin_frame_address' with a
     value of `0' yields the frame address of the current function, a
     value of `1' yields the frame address of the caller of the current
     function, and so forth.

     The frame is the area on the stack which holds local variables and
     saved registers.  The frame address is normally the address of the
     first word pushed on to the stack by the function.  However, the
     exact definition depends upon the processor and the calling
     convention.  If the processor has a dedicated frame pointer
     register, and the function has a frame, then
     `__builtin_frame_address' will return the value of the frame
     pointer register.

     On some machines it may be impossible to determine the frame
     address of any function other than the current one; in such cases,
     or when the top of the stack has been reached, this function will
     return `0' if the first frame pointer is properly initialized by
     the startup code.

     This function should only be used with a nonzero argument for
     debugging purposes.


File: gcc,  Node: Vector Extensions,  Next: Other Builtins,  Prev: Return Address,  Up: C Extensions

5.43 Using vector instructions through built-in functions
=========================================================

On some targets, the instruction set contains SIMD vector instructions
that operate on multiple values contained in one large register at the
same time.  For example, on the i386 the MMX, 3Dnow! and SSE extensions
can be used this way.

 The first step in using these extensions is to provide the necessary
data types.  This should be done using an appropriate `typedef':

     typedef int v4si __attribute__ ((mode(V4SI)));

 The base type `int' is effectively ignored by the compiler, the actual
properties of the new type `v4si' are defined by the `__attribute__'.
It defines the machine mode to be used; for vector types these have the
form `VNB'; N should be the number of elements in the vector, and B
should be the base mode of the individual elements.  The following can
be used as base modes:

`QI'
     An integer that is as wide as the smallest addressable unit,
     usually 8 bits.

`HI'
     An integer, twice as wide as a QI mode integer, usually 16 bits.

`SI'
     An integer, four times as wide as a QI mode integer, usually 32
     bits.

`DI'
     An integer, eight times as wide as a QI mode integer, usually 64
     bits.

`SF'
     A floating point value, as wide as a SI mode integer, usually 32
     bits.

`DF'
     A floating point value, as wide as a DI mode integer, usually 64
     bits.

 Specifying a combination that is not valid for the current architecture
will cause GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type `V4SI' and your
architecture does not allow for this specific SIMD type, GCC will
produce code that uses 4 `SIs'.

 The types defined in this manner can be used with a subset of normal C
operations.  Currently, GCC will allow using the following operators on
these types: `+, -, *, /, unary minus, ^, |, &, ~'.

 The operations behave like C++ `valarrays'.  Addition is defined as
the addition of the corresponding elements of the operands.  For
example, in the code below, each of the 4 elements in A will be added
to the corresponding 4 elements in B and the resulting vector will be
stored in C.

     typedef int v4si __attribute__ ((mode(V4SI)));

     v4si a, b, c;

     c = a + b;

 Subtraction, multiplication, division, and the logical operations
operate in a similar manner.  Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.

 You can declare variables and use them in function calls and returns,
as well as in assignments and some casts.  You can specify a vector
type as a return type for a function.  Vector types can also be used as
function arguments.  It is possible to cast from one vector type to
another, provided they are of the same size (in fact, you can also cast
vectors to and from other datatypes of the same size).

 You cannot operate between vectors of different lengths or different
signedness without a cast.

 A port that supports hardware vector operations, usually provides a set
of built-in functions that can be used to operate on vectors.  For
example, a function to add two vectors and multiply the result by a
third could look like this:

     v4si f (v4si a, v4si b, v4si c)
     {
       v4si tmp = __builtin_addv4si (a, b);
       return __builtin_mulv4si (tmp, c);
     }


File: gcc,  Node: Other Builtins,  Next: Target Builtins,  Prev: Vector Extensions,  Up: C Extensions

5.44 Other built-in functions provided by GCC
=============================================

GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and will not be
documented here because they may change from time to time; we do not
recommend general use of these functions.

 The remaining functions are provided for optimization purposes.

 GCC includes built-in versions of many of the functions in the standard
C library.  The versions prefixed with `__builtin_' will always be
treated as having the same meaning as the C library function even if you
specify the `-fno-builtin' option. (*note C Dialect Options::) Many of
these functions are only optimized in certain cases; if they are not
optimized in a particular case, a call to the library function will be
emitted.

 Outside strict ISO C mode (`-ansi', `-std=c89' or `-std=c99'), the
functions `_exit', `alloca', `bcmp', `bzero', `dcgettext', `dgettext',
`dremf', `dreml', `drem', `exp10f', `exp10l', `exp10', `ffsll', `ffsl',
`ffs', `fprintf_unlocked', `fputs_unlocked', `gammaf', `gammal',
`gamma', `gettext', `index', `j0f', `j0l', `j0', `j1f', `j1l', `j1',
`jnf', `jnl', `jn', `mempcpy', `pow10f', `pow10l', `pow10',
`printf_unlocked', `rindex', `scalbf', `scalbl', `scalb',
`significandf', `significandl', `significand', `sincosf', `sincosl',
`sincos', `stpcpy', `strdup', `strfmon', `y0f', `y0l', `y0', `y1f',
`y1l', `y1', `ynf', `ynl' and `yn' may be handled as built-in functions.
All these functions have corresponding versions prefixed with
`__builtin_', which may be used even in strict C89 mode.

 The ISO C99 functions `_Exit', `acoshf', `acoshl', `acosh', `asinhf',
`asinhl', `asinh', `atanhf', `atanhl', `atanh', `cabsf', `cabsl',
`cabs', `cacosf', `cacoshf', `cacoshl', `cacosh', `cacosl', `cacos',
`cargf', `cargl', `carg', `casinf', `casinhf', `casinhl', `casinh',
`casinl', `casin', `catanf', `catanhf', `catanhl', `catanh', `catanl',
`catan', `cbrtf', `cbrtl', `cbrt', `ccosf', `ccoshf', `ccoshl',
`ccosh', `ccosl', `ccos', `cexpf', `cexpl', `cexp', `cimagf', `cimagl',
`cimag', `conjf', `conjl', `conj', `copysignf', `copysignl',
`copysign', `cpowf', `cpowl', `cpow', `cprojf', `cprojl', `cproj',
`crealf', `creall', `creal', `csinf', `csinhf', `csinhl', `csinh',
`csinl', `csin', `csqrtf', `csqrtl', `csqrt', `ctanf', `ctanhf',
`ctanhl', `ctanh', `ctanl', `ctan', `erfcf', `erfcl', `erfc', `erff',
`erfl', `erf', `exp2f', `exp2l', `exp2', `expm1f', `expm1l', `expm1',
`fdimf', `fdiml', `fdim', `fmaf', `fmal', `fmaxf', `fmaxl', `fmax',
`fma', `fminf', `fminl', `fmin', `hypotf', `hypotl', `hypot', `ilogbf',
`ilogbl', `ilogb', `imaxabs', `lgammaf', `lgammal', `lgamma', `llabs',
`llrintf', `llrintl', `llrint', `llroundf', `llroundl', `llround',
`log1pf', `log1pl', `log1p', `log2f', `log2l', `log2', `logbf', `logbl',
`logb', `lrintf', `lrintl', `lrint', `lroundf', `lroundl', `lround',
`nearbyintf', `nearbyintl', `nearbyint', `nextafterf', `nextafterl',
`nextafter', `nexttowardf', `nexttowardl', `nexttoward', `remainderf',
`remainderl', `remainder', `remquof', `remquol', `remquo', `rintf',
`rintl', `rint', `roundf', `roundl', `round', `scalblnf', `scalblnl',
`scalbln', `scalbnf', `scalbnl', `scalbn', `snprintf', `tgammaf',
`tgammal', `tgamma', `truncf', `truncl', `trunc', `vfscanf', `vscanf',
`vsnprintf' and `vsscanf' are handled as built-in functions except in
strict ISO C90 mode (`-ansi' or `-std=c89').

 There are also built-in versions of the ISO C99 functions `acosf',
`acosl', `asinf', `asinl', `atan2f', `atan2l', `atanf', `atanl',
`ceilf', `ceill', `cosf', `coshf', `coshl', `cosl', `expf', `expl',
`fabsf', `fabsl', `floorf', `floorl', `fmodf', `fmodl', `frexpf',
`frexpl', `ldexpf', `ldexpl', `log10f', `log10l', `logf', `logl',
`modfl', `modf', `powf', `powl', `sinf', `sinhf', `sinhl', `sinl',
`sqrtf', `sqrtl', `tanf', `tanhf', `tanhl' and `tanl' that are
recognized in any mode since ISO C90 reserves these names for the
purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with `__builtin_'.

 The ISO C90 functions `abort', `abs', `acos', `asin', `atan2', `atan',
`calloc', `ceil', `cosh', `cos', `exit', `exp', `fabs', `floor', `fmod',
`fprintf', `fputs', `frexp', `fscanf', `labs', `ldexp', `log10', `log',
`malloc', `memcmp', `memcpy', `memset', `modf', `pow', `printf',
`putchar', `puts', `scanf', `sinh', `sin', `snprintf', `sprintf',
`sqrt', `sscanf', `strcat', `strchr', `strcmp', `strcpy', `strcspn',
`strlen', `strncat', `strncmp', `strncpy', `strpbrk', `strrchr',
`strspn', `strstr', `tanh', `tan', `vfprintf', `vprintf' and `vsprintf'
are all recognized as built-in functions unless `-fno-builtin' is
specified (or `-fno-builtin-FUNCTION' is specified for an individual
function).  All of these functions have corresponding versions prefixed
with `__builtin_'.

 GCC provides built-in versions of the ISO C99 floating point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( `isgreater', `isgreaterequal',
`isless', `islessequal', `islessgreater', and `isunordered') , with
`__builtin_' prefixed.  We intend for a library implementor to be able
to simply `#define' each standard macro to its built-in equivalent.

 -- Built-in Function: int __builtin_types_compatible_p (TYPE1, TYPE2)
     You can use the built-in function `__builtin_types_compatible_p' to
     determine whether two types are the same.

     This built-in function returns 1 if the unqualified versions of the
     types TYPE1 and TYPE2 (which are types, not expressions) are
     compatible, 0 otherwise.  The result of this built-in function can
     be used in integer constant expressions.

     This built-in function ignores top level qualifiers (e.g., `const',
     `volatile').  For example, `int' is equivalent to `const int'.

     The type `int[]' and `int[5]' are compatible.  On the other hand,
     `int' and `char *' are not compatible, even if the size of their
     types, on the particular architecture are the same.  Also, the
     amount of pointer indirection is taken into account when
     determining similarity.  Consequently, `short *' is not similar to
     `short **'.  Furthermore, two types that are typedefed are
     considered compatible if their underlying types are compatible.

     An `enum' type is not considered to be compatible with another
     `enum' type even if both are compatible with the same integer
     type; this is what the C standard specifies.  For example, `enum
     {foo, bar}' is not similar to `enum {hot, dog}'.

     You would typically use this function in code whose execution
     varies depending on the arguments' types.  For example:

          #define foo(x)                                                  \
            ({                                                           \
              typeof (x) tmp;                                             \
              if (__builtin_types_compatible_p (typeof (x), long double)) \
                tmp = foo_long_double (tmp);                              \
              else if (__builtin_types_compatible_p (typeof (x), double)) \
                tmp = foo_double (tmp);                                   \
              else if (__builtin_types_compatible_p (typeof (x), float))  \
                tmp = foo_float (tmp);                                    \
              else                                                        \
                abort ();                                                 \
              tmp;                                                        \
            })

     _Note:_ This construct is only available for C.


 -- Built-in Function: TYPE __builtin_choose_expr (CONST_EXP, EXP1,
          EXP2)
     You can use the built-in function `__builtin_choose_expr' to
     evaluate code depending on the value of a constant expression.
     This built-in function returns EXP1 if CONST_EXP, which is a
     constant expression that must be able to be determined at compile
     time, is nonzero.  Otherwise it returns 0.

     This built-in function is analogous to the `? :' operator in C,
     except that the expression returned has its type unaltered by
     promotion rules.  Also, the built-in function does not evaluate
     the expression that was not chosen.  For example, if CONST_EXP
     evaluates to true, EXP2 is not evaluated even if it has
     side-effects.

     This built-in function can return an lvalue if the chosen argument
     is an lvalue.

     If EXP1 is returned, the return type is the same as EXP1's type.
     Similarly, if EXP2 is returned, its return type is the same as
     EXP2.

     Example:

          #define foo(x)                                                    \
            __builtin_choose_expr (                                         \
              __builtin_types_compatible_p (typeof (x), double),            \
              foo_double (x),                                               \
              __builtin_choose_expr (                                       \
                __builtin_types_compatible_p (typeof (x), float),           \
                foo_float (x),                                              \
                /* The void expression results in a compile-time error  \
                   when assigning the result to something.  */          \
                (void)0))

     _Note:_ This construct is only available for C.  Furthermore, the
     unused expression (EXP1 or EXP2 depending on the value of
     CONST_EXP) may still generate syntax errors.  This may change in
     future revisions.


 -- Built-in Function: int __builtin_constant_p (EXP)
     You can use the built-in function `__builtin_constant_p' to
     determine if a value is known to be constant at compile-time and
     hence that GCC can perform constant-folding on expressions
     involving that value.  The argument of the function is the value
     to test.  The function returns the integer 1 if the argument is
     known to be a compile-time constant and 0 if it is not known to be
     a compile-time constant.  A return of 0 does not indicate that the
     value is _not_ a constant, but merely that GCC cannot prove it is
     a constant with the specified value of the `-O' option.

     You would typically use this function in an embedded application
     where memory was a critical resource.  If you have some complex
     calculation, you may want it to be folded if it involves
     constants, but need to call a function if it does not.  For
     example:

          #define Scale_Value(X)      \
            (__builtin_constant_p (X) \
            ? ((X) * SCALE + OFFSET) : Scale (X))

     You may use this built-in function in either a macro or an inline
     function.  However, if you use it in an inlined function and pass
     an argument of the function as the argument to the built-in, GCC
     will never return 1 when you call the inline function with a
     string constant or compound literal (*note Compound Literals::)
     and will not return 1 when you pass a constant numeric value to
     the inline function unless you specify the `-O' option.

     You may also use `__builtin_constant_p' in initializers for static
     data.  For instance, you can write

          static const int table[] = {
             __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
             /* ... */
          };

     This is an acceptable initializer even if EXPRESSION is not a
     constant expression.  GCC must be more conservative about
     evaluating the built-in in this case, because it has no
     opportunity to perform optimization.

     Previous versions of GCC did not accept this built-in in data
     initializers.  The earliest version where it is completely safe is
     3.0.1.

 -- Built-in Function: long __builtin_expect (long EXP, long C)
     You may use `__builtin_expect' to provide the compiler with branch
     prediction information.  In general, you should prefer to use
     actual profile feedback for this (`-fprofile-arcs'), as
     programmers are notoriously bad at predicting how their programs
     actually perform.  However, there are applications in which this
     data is hard to collect.

     The return value is the value of EXP, which should be an integral
     expression.  The value of C must be a compile-time constant.  The
     semantics of the built-in are that it is expected that EXP == C.
     For example:

          if (__builtin_expect (x, 0))
            foo ();

     would indicate that we do not expect to call `foo', since we
     expect `x' to be zero.  Since you are limited to integral
     expressions for EXP, you should use constructions such as

          if (__builtin_expect (ptr != NULL, 1))
            error ();

     when testing pointer or floating-point values.

 -- Built-in Function: void __builtin_prefetch (const void *ADDR, ...)
     This function is used to minimize cache-miss latency by moving
     data into a cache before it is accessed.  You can insert calls to
     `__builtin_prefetch' into code for which you know addresses of
     data in memory that is likely to be accessed soon.  If the target
     supports them, data prefetch instructions will be generated.  If
     the prefetch is done early enough before the access then the data
     will be in the cache by the time it is accessed.

     The value of ADDR is the address of the memory to prefetch.  There
     are two optional arguments, RW and LOCALITY.  The value of RW is a
     compile-time constant one or zero; one means that the prefetch is
     preparing for a write to the memory address and zero, the default,
     means that the prefetch is preparing for a read.  The value
     LOCALITY must be a compile-time constant integer between zero and
     three.  A value of zero means that the data has no temporal
     locality, so it need not be left in the cache after the access.  A
     value of three means that the data has a high degree of temporal
     locality and should be left in all levels of cache possible.
     Values of one and two mean, respectively, a low or moderate degree
     of temporal locality.  The default is three.

          for (i = 0; i < n; i++)
            {
              a[i] = a[i] + b[i];
              __builtin_prefetch (&a[i+j], 1, 1);
              __builtin_prefetch (&b[i+j], 0, 1);
              /* ... */
            }

     Data prefetch does not generate faults if ADDR is invalid, but the
     address expression itself must be valid.  For example, a prefetch
     of `p->next' will not fault if `p->next' is not a valid address,
     but evaluation will fault if `p' is not a valid address.

     If the target does not support data prefetch, the address
     expression is evaluated if it includes side effects but no other
     code is generated and GCC does not issue a warning.

 -- Built-in Function: double __builtin_huge_val (void)
     Returns a positive infinity, if supported by the floating-point
     format, else `DBL_MAX'.  This function is suitable for
     implementing the ISO C macro `HUGE_VAL'.

 -- Built-in Function: float __builtin_huge_valf (void)
     Similar to `__builtin_huge_val', except the return type is `float'.

 -- Built-in Function: long double __builtin_huge_vall (void)
     Similar to `__builtin_huge_val', except the return type is `long
     double'.

 -- Built-in Function: double __builtin_inf (void)
     Similar to `__builtin_huge_val', except a warning is generated if
     the target floating-point format does not support infinities.
     This function is suitable for implementing the ISO C99 macro
     `INFINITY'.

 -- Built-in Function: float __builtin_inff (void)
     Similar to `__builtin_inf', except the return type is `float'.

 -- Built-in Function: long double __builtin_infl (void)
     Similar to `__builtin_inf', except the return type is `long
     double'.

 -- Built-in Function: double __builtin_nan (const char *str)
     This is an implementation of the ISO C99 function `nan'.

     Since ISO C99 defines this function in terms of `strtod', which we
     do not implement, a description of the parsing is in order.  The
     string is parsed as by `strtol'; that is, the base is recognized by
     leading `0' or `0x' prefixes.  The number parsed is placed in the
     significand such that the least significant bit of the number is
     at the least significant bit of the significand.  The number is
     truncated to fit the significand field provided.  The significand
     is forced to be a quiet NaN.

     This function, if given a string literal, is evaluated early enough
     that it is considered a compile-time constant.

 -- Built-in Function: float __builtin_nanf (const char *str)
     Similar to `__builtin_nan', except the return type is `float'.

 -- Built-in Function: long double __builtin_nanl (const char *str)
     Similar to `__builtin_nan', except the return type is `long
     double'.

 -- Built-in Function: double __builtin_nans (const char *str)
     Similar to `__builtin_nan', except the significand is forced to be
     a signaling NaN.  The `nans' function is proposed by WG14 N965.

 -- Built-in Function: float __builtin_nansf (const char *str)
     Similar to `__builtin_nans', except the return type is `float'.

 -- Built-in Function: long double __builtin_nansl (const char *str)
     Similar to `__builtin_nans', except the return type is `long
     double'.

 -- Built-in Function: int __builtin_ffs (unsigned int x)
     Returns one plus the index of the least significant 1-bit of X, or
     if X is zero, returns zero.

 -- Built-in Function: int __builtin_clz (unsigned int x)
     Returns the number of leading 0-bits in X, starting at the most
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_ctz (unsigned int x)
     Returns the number of trailing 0-bits in X, starting at the least
     significant bit position.  If X is 0, the result is undefined.

 -- Built-in Function: int __builtin_popcount (unsigned int x)
     Returns the number of 1-bits in X.

 -- Built-in Function: int __builtin_parity (unsigned int x)
     Returns the parity of X, i.e. the number of 1-bits in X modulo 2.

 -- Built-in Function: int __builtin_ffsl (unsigned long)
     Similar to `__builtin_ffs', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_clzl (unsigned long)
     Similar to `__builtin_clz', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_ctzl (unsigned long)
     Similar to `__builtin_ctz', except the argument type is `unsigned
     long'.

 -- Built-in Function: int __builtin_popcountl (unsigned long)
     Similar to `__builtin_popcount', except the argument type is
     `unsigned long'.

 -- Built-in Function: int __builtin_parityl (unsigned long)
     Similar to `__builtin_parity', except the argument type is
     `unsigned long'.

 -- Built-in Function: int __builtin_ffsll (unsigned long long)
     Similar to `__builtin_ffs', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_clzll (unsigned long long)
     Similar to `__builtin_clz', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_ctzll (unsigned long long)
     Similar to `__builtin_ctz', except the argument type is `unsigned
     long long'.

 -- Built-in Function: int __builtin_popcountll (unsigned long long)
     Similar to `__builtin_popcount', except the argument type is
     `unsigned long long'.

 -- Built-in Function: int __builtin_parityll (unsigned long long)
     Similar to `__builtin_parity', except the argument type is
     `unsigned long long'.


File: gcc,  Node: Target Builtins,  Next: Pragmas,  Prev: Other Builtins,  Up: C Extensions

5.45 Built-in Functions Specific to Particular Target Machines
==============================================================

On some target machines, GCC supports many built-in functions specific
to those machines.  Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.

* Menu:

* Alpha Built-in Functions::
* ARM Built-in Functions::
* X86 Built-in Functions::
* PowerPC AltiVec Built-in Functions::


File: gcc,  Node: Alpha Built-in Functions,  Next: ARM Built-in Functions,  Up: Target Builtins

5.45.1 Alpha Built-in Functions
-------------------------------

These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.

 The following built-in functions are always available.  They all
generate the machine instruction that is part of the name.

     long __builtin_alpha_implver (void)
     long __builtin_alpha_rpcc (void)
     long __builtin_alpha_amask (long)
     long __builtin_alpha_cmpbge (long, long)
     long __builtin_alpha_extbl (long, long)
     long __builtin_alpha_extwl (long, long)
     long __builtin_alpha_extll (long, long)
     long __builtin_alpha_extql (long, long)
     long __builtin_alpha_extwh (long, long)
     long __builtin_alpha_extlh (long, long)
     long __builtin_alpha_extqh (long, long)
     long __builtin_alpha_insbl (long, long)
     long __builtin_alpha_inswl (long, long)
     long __builtin_alpha_insll (long, long)
     long __builtin_alpha_insql (long, long)
     long __builtin_alpha_inswh (long, long)
     long __builtin_alpha_inslh (long, long)
     long __builtin_alpha_insqh (long, long)
     long __builtin_alpha_mskbl (long, long)
     long __builtin_alpha_mskwl (long, long)
     long __builtin_alpha_mskll (long, long)
     long __builtin_alpha_mskql (long, long)
     long __builtin_alpha_mskwh (long, long)
     long __builtin_alpha_msklh (long, long)
     long __builtin_alpha_mskqh (long, long)
     long __builtin_alpha_umulh (long, long)
     long __builtin_alpha_zap (long, long)
     long __builtin_alpha_zapnot (long, long)

 The following built-in functions are always with `-mmax' or
`-mcpu=CPU' where CPU is `pca56' or later.  They all generate the
machine instruction that is part of the name.

     long __builtin_alpha_pklb (long)
     long __builtin_alpha_pkwb (long)
     long __builtin_alpha_unpkbl (long)
     long __builtin_alpha_unpkbw (long)
     long __builtin_alpha_minub8 (long, long)
     long __builtin_alpha_minsb8 (long, long)
     long __builtin_alpha_minuw4 (long, long)
     long __builtin_alpha_minsw4 (long, long)
     long __builtin_alpha_maxub8 (long, long)
     long __builtin_alpha_maxsb8 (long, long)
     long __builtin_alpha_maxuw4 (long, long)
     long __builtin_alpha_maxsw4 (long, long)
     long __builtin_alpha_perr (long, long)

 The following built-in functions are always with `-mcix' or
`-mcpu=CPU' where CPU is `ev67' or later.  They all generate the
machine instruction that is part of the name.

     long __builtin_alpha_cttz (long)
     long __builtin_alpha_ctlz (long)
     long __builtin_alpha_ctpop (long)

 The following builtins are available on systems that use the OSF/1
PALcode.  Normally they invoke the `rduniq' and `wruniq' PAL calls, but
when invoked with `-mtls-kernel', they invoke `rdval' and `wrval'.

     void *__builtin_thread_pointer (void)
     void __builtin_set_thread_pointer (void *)


File: gcc,  Node: ARM Built-in Functions,  Next: X86 Built-in Functions,  Prev: Alpha Built-in Functions,  Up: Target Builtins

5.45.2 ARM Built-in Functions
-----------------------------

These built-in functions are available for the ARM family of
processors, when the `-mcpu=iwmmxt' switch is used:

     typedef int v2si __attribute__ ((vector_size (8)));
     typedef short v4hi __attribute__ ((vector_size (8)));
     typedef char v8qi __attribute__ ((vector_size (8)));

     int __builtin_arm_getwcx (int)
     void __builtin_arm_setwcx (int, int)
     int __builtin_arm_textrmsb (v8qi, int)
     int __builtin_arm_textrmsh (v4hi, int)
     int __builtin_arm_textrmsw (v2si, int)
     int __builtin_arm_textrmub (v8qi, int)
     int __builtin_arm_textrmuh (v4hi, int)
     int __builtin_arm_textrmuw (v2si, int)
     v8qi __builtin_arm_tinsrb (v8qi, int)
     v4hi __builtin_arm_tinsrh (v4hi, int)
     v2si __builtin_arm_tinsrw (v2si, int)
     long long __builtin_arm_tmia (long long, int, int)
     long long __builtin_arm_tmiabb (long long, int, int)
     long long __builtin_arm_tmiabt (long long, int, int)
     long long __builtin_arm_tmiaph (long long, int, int)
     long long __builtin_arm_tmiatb (long long, int, int)
     long long __builtin_arm_tmiatt (long long, int, int)
     int __builtin_arm_tmovmskb (v8qi)
     int __builtin_arm_tmovmskh (v4hi)
     int __builtin_arm_tmovmskw (v2si)
     long long __builtin_arm_waccb (v8qi)
     long long __builtin_arm_wacch (v4hi)
     long long __builtin_arm_waccw (v2si)
     v8qi __builtin_arm_waddb (v8qi, v8qi)
     v8qi __builtin_arm_waddbss (v8qi, v8qi)
     v8qi __builtin_arm_waddbus (v8qi, v8qi)
     v4hi __builtin_arm_waddh (v4hi, v4hi)
     v4hi __builtin_arm_waddhss (v4hi, v4hi)
     v4hi __builtin_arm_waddhus (v4hi, v4hi)
     v2si __builtin_arm_waddw (v2si, v2si)
     v2si __builtin_arm_waddwss (v2si, v2si)
     v2si __builtin_arm_waddwus (v2si, v2si)
     v8qi __builtin_arm_walign (v8qi, v8qi, int)
     long long __builtin_arm_wand(long long, long long)
     long long __builtin_arm_wandn (long long, long long)
     v8qi __builtin_arm_wavg2b (v8qi, v8qi)
     v8qi __builtin_arm_wavg2br (v8qi, v8qi)
     v4hi __builtin_arm_wavg2h (v4hi, v4hi)
     v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
     v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
     v2si __builtin_arm_wcmpeqw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtsw (v2si, v2si)
     v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
     v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
     v2si __builtin_arm_wcmpgtuw (v2si, v2si)
     long long __builtin_arm_wmacs (long long, v4hi, v4hi)
     long long __builtin_arm_wmacsz (v4hi, v4hi)
     long long __builtin_arm_wmacu (long long, v4hi, v4hi)
     long long __builtin_arm_wmacuz (v4hi, v4hi)
     v4hi __builtin_arm_wmadds (v4hi, v4hi)
     v4hi __builtin_arm_wmaddu (v4hi, v4hi)
     v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
     v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
     v2si __builtin_arm_wmaxsw (v2si, v2si)
     v8qi __builtin_arm_wmaxub (v8qi, v8qi)
     v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
     v2si __builtin_arm_wmaxuw (v2si, v2si)
     v8qi __builtin_arm_wminsb (v8qi, v8qi)
     v4hi __builtin_arm_wminsh (v4hi, v4hi)
     v2si __builtin_arm_wminsw (v2si, v2si)
     v8qi __builtin_arm_wminub (v8qi, v8qi)
     v4hi __builtin_arm_wminuh (v4hi, v4hi)
     v2si __builtin_arm_wminuw (v2si, v2si)
     v4hi __builtin_arm_wmulsm (v4hi, v4hi)
     v4hi __builtin_arm_wmulul (v4hi, v4hi)
     v4hi __builtin_arm_wmulum (v4hi, v4hi)
     long long __builtin_arm_wor (long long, long long)
     v2si __builtin_arm_wpackdss (long long, long long)
     v2si __builtin_arm_wpackdus (long long, long long)
     v8qi __builtin_arm_wpackhss (v4hi, v4hi)
     v8qi __builtin_arm_wpackhus (v4hi, v4hi)
     v4hi __builtin_arm_wpackwss (v2si, v2si)
     v4hi __builtin_arm_wpackwus (v2si, v2si)
     long long __builtin_arm_wrord (long long, long long)
     long long __builtin_arm_wrordi (long long, int)
     v4hi __builtin_arm_wrorh (v4hi, long long)
     v4hi __builtin_arm_wrorhi (v4hi, int)
     v2si __builtin_arm_wrorw (v2si, long long)
     v2si __builtin_arm_wrorwi (v2si, int)
     v2si __builtin_arm_wsadb (v8qi, v8qi)
     v2si __builtin_arm_wsadbz (v8qi, v8qi)
     v2si __builtin_arm_wsadh (v4hi, v4hi)
     v2si __builtin_arm_wsadhz (v4hi, v4hi)
     v4hi __builtin_arm_wshufh (v4hi, int)
     long long __builtin_arm_wslld (long long, long long)
     long long __builtin_arm_wslldi (long long, int)
     v4hi __builtin_arm_wsllh (v4hi, long long)
     v4hi __builtin_arm_wsllhi (v4hi, int)
     v2si __builtin_arm_wsllw (v2si, long long)
     v2si __builtin_arm_wsllwi (v2si, int)
     long long __builtin_arm_wsrad (long long, long long)
     long long __builtin_arm_wsradi (long long, int)
     v4hi __builtin_arm_wsrah (v4hi, long long)
     v4hi __builtin_arm_wsrahi (v4hi, int)
     v2si __builtin_arm_wsraw (v2si, long long)
     v2si __builtin_arm_wsrawi (v2si, int)
     long long __builtin_arm_wsrld (long long, long long)
     long long __builtin_arm_wsrldi (long long, int)
     v4hi __builtin_arm_wsrlh (v4hi, long long)
     v4hi __builtin_arm_wsrlhi (v4hi, int)
     v2si __builtin_arm_wsrlw (v2si, long long)
     v2si __builtin_arm_wsrlwi (v2si, int)
     v8qi __builtin_arm_wsubb (v8qi, v8qi)
     v8qi __builtin_arm_wsubbss (v8qi, v8qi)
     v8qi __builtin_arm_wsubbus (v8qi, v8qi)
     v4hi __builtin_arm_wsubh (v4hi, v4hi)
     v4hi __builtin_arm_wsubhss (v4hi, v4hi)
     v4hi __builtin_arm_wsubhus (v4hi, v4hi)
     v2si __builtin_arm_wsubw (v2si, v2si)
     v2si __builtin_arm_wsubwss (v2si, v2si)
     v2si __builtin_arm_wsubwus (v2si, v2si)
     v4hi __builtin_arm_wunpckehsb (v8qi)
     v2si __builtin_arm_wunpckehsh (v4hi)
     long long __builtin_arm_wunpckehsw (v2si)
     v4hi __builtin_arm_wunpckehub (v8qi)
     v2si __builtin_arm_wunpckehuh (v4hi)
     long long __builtin_arm_wunpckehuw (v2si)
     v4hi __builtin_arm_wunpckelsb (v8qi)
     v2si __builtin_arm_wunpckelsh (v4hi)
     long long __builtin_arm_wunpckelsw (v2si)
     v4hi __builtin_arm_wunpckelub (v8qi)
     v2si __builtin_arm_wunpckeluh (v4hi)
     long long __builtin_arm_wunpckeluw (v2si)
     v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
     v2si __builtin_arm_wunpckihw (v2si, v2si)
     v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
     v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
     v2si __builtin_arm_wunpckilw (v2si, v2si)
     long long __builtin_arm_wxor (long long, long long)
     long long __builtin_arm_wzero ()


File: gcc,  Node: X86 Built-in Functions,  Next: PowerPC AltiVec Built-in Functions,  Prev: ARM Built-in Functions,  Up: Target Builtins

5.45.3 X86 Built-in Functions
-----------------------------

These built-in functions are available for the i386 and x86-64 family
of computers, depending on the command-line switches used.

 The following machine modes are available for use with MMX built-in
functions (*note Vector Extensions::): `V2SI' for a vector of two
32-bit integers, `V4HI' for a vector of four 16-bit integers, and
`V8QI' for a vector of eight 8-bit integers.  Some of the built-in
functions operate on MMX registers as a whole 64-bit entity, these use
`DI' as their mode.

 If 3Dnow extensions are enabled, `V2SF' is used as a mode for a vector
of two 32-bit floating point values.

 If SSE extensions are enabled, `V4SF' is used for a vector of four
32-bit floating point values.  Some instructions use a vector of four
32-bit integers, these use `V4SI'.  Finally, some instructions operate
on an entire vector register, interpreting it as a 128-bit integer,
these use mode `TI'.

 The following built-in functions are made available by `-mmmx'.  All
of them generate the machine instruction that is part of the name.

     v8qi __builtin_ia32_paddb (v8qi, v8qi)
     v4hi __builtin_ia32_paddw (v4hi, v4hi)
     v2si __builtin_ia32_paddd (v2si, v2si)
     v8qi __builtin_ia32_psubb (v8qi, v8qi)
     v4hi __builtin_ia32_psubw (v4hi, v4hi)
     v2si __builtin_ia32_psubd (v2si, v2si)
     v8qi __builtin_ia32_paddsb (v8qi, v8qi)
     v4hi __builtin_ia32_paddsw (v4hi, v4hi)
     v8qi __builtin_ia32_psubsb (v8qi, v8qi)
     v4hi __builtin_ia32_psubsw (v4hi, v4hi)
     v8qi __builtin_ia32_paddusb (v8qi, v8qi)
     v4hi __builtin_ia32_paddusw (v4hi, v4hi)
     v8qi __builtin_ia32_psubusb (v8qi, v8qi)
     v4hi __builtin_ia32_psubusw (v4hi, v4hi)
     v4hi __builtin_ia32_pmullw (v4hi, v4hi)
     v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
     di __builtin_ia32_pand (di, di)
     di __builtin_ia32_pandn (di,di)
     di __builtin_ia32_por (di, di)
     di __builtin_ia32_pxor (di, di)
     v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpeqd (v2si, v2si)
     v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
     v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
     v2si __builtin_ia32_pcmpgtd (v2si, v2si)
     v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckhdq (v2si, v2si)
     v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
     v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
     v2si __builtin_ia32_punpckldq (v2si, v2si)
     v8qi __builtin_ia32_packsswb (v4hi, v4hi)
     v4hi __builtin_ia32_packssdw (v2si, v2si)
     v8qi __builtin_ia32_packuswb (v4hi, v4hi)

 The following built-in functions are made available either with
`-msse', or with a combination of `-m3dnow' and `-march=athlon'.  All
of them generate the machine instruction that is part of the name.

     v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
     v8qi __builtin_ia32_pavgb (v8qi, v8qi)
     v4hi __builtin_ia32_pavgw (v4hi, v4hi)
     v4hi __builtin_ia32_psadbw (v8qi, v8qi)
     v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
     v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
     v8qi __builtin_ia32_pminub (v8qi, v8qi)
     v4hi __builtin_ia32_pminsw (v4hi, v4hi)
     int __builtin_ia32_pextrw (v4hi, int)
     v4hi __builtin_ia32_pinsrw (v4hi, int, int)
     int __builtin_ia32_pmovmskb (v8qi)
     void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
     void __builtin_ia32_movntq (di *, di)
     void __builtin_ia32_sfence (void)

 The following built-in functions are available when `-msse' is used.
All of them generate the machine instruction that is part of the name.

     int __builtin_ia32_comieq (v4sf, v4sf)
     int __builtin_ia32_comineq (v4sf, v4sf)
     int __builtin_ia32_comilt (v4sf, v4sf)
     int __builtin_ia32_comile (v4sf, v4sf)
     int __builtin_ia32_comigt (v4sf, v4sf)
     int __builtin_ia32_comige (v4sf, v4sf)
     int __builtin_ia32_ucomieq (v4sf, v4sf)
     int __builtin_ia32_ucomineq (v4sf, v4sf)
     int __builtin_ia32_ucomilt (v4sf, v4sf)
     int __builtin_ia32_ucomile (v4sf, v4sf)
     int __builtin_ia32_ucomigt (v4sf, v4sf)
     int __builtin_ia32_ucomige (v4sf, v4sf)
     v4sf __builtin_ia32_addps (v4sf, v4sf)
     v4sf __builtin_ia32_subps (v4sf, v4sf)
     v4sf __builtin_ia32_mulps (v4sf, v4sf)
     v4sf __builtin_ia32_divps (v4sf, v4sf)
     v4sf __builtin_ia32_addss (v4sf, v4sf)
     v4sf __builtin_ia32_subss (v4sf, v4sf)
     v4sf __builtin_ia32_mulss (v4sf, v4sf)
     v4sf __builtin_ia32_divss (v4sf, v4sf)
     v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
     v4si __builtin_ia32_cmpltps (v4sf, v4sf)
     v4si __builtin_ia32_cmpleps (v4sf, v4sf)
     v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
     v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
     v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
     v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
     v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
     v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
     v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
     v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
     v4si __builtin_ia32_cmpordps (v4sf, v4sf)
     v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
     v4si __builtin_ia32_cmpltss (v4sf, v4sf)
     v4si __builtin_ia32_cmpless (v4sf, v4sf)
     v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
     v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
     v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
     v4si __builtin_ia32_cmpnless (v4sf, v4sf)
     v4si __builtin_ia32_cmpordss (v4sf, v4sf)
     v4sf __builtin_ia32_maxps (v4sf, v4sf)
     v4sf __builtin_ia32_maxss (v4sf, v4sf)
     v4sf __builtin_ia32_minps (v4sf, v4sf)
     v4sf __builtin_ia32_minss (v4sf, v4sf)
     v4sf __builtin_ia32_andps (v4sf, v4sf)
     v4sf __builtin_ia32_andnps (v4sf, v4sf)
     v4sf __builtin_ia32_orps (v4sf, v4sf)
     v4sf __builtin_ia32_xorps (v4sf, v4sf)
     v4sf __builtin_ia32_movss (v4sf, v4sf)
     v4sf __builtin_ia32_movhlps (v4sf, v4sf)
     v4sf __builtin_ia32_movlhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
     v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
     v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
     v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
     v2si __builtin_ia32_cvtps2pi (v4sf)
     int __builtin_ia32_cvtss2si (v4sf)
     v2si __builtin_ia32_cvttps2pi (v4sf)
     int __builtin_ia32_cvttss2si (v4sf)
     v4sf __builtin_ia32_rcpps (v4sf)
     v4sf __builtin_ia32_rsqrtps (v4sf)
     v4sf __builtin_ia32_sqrtps (v4sf)
     v4sf __builtin_ia32_rcpss (v4sf)
     v4sf __builtin_ia32_rsqrtss (v4sf)
     v4sf __builtin_ia32_sqrtss (v4sf)
     v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
     void __builtin_ia32_movntps (float *, v4sf)
     int __builtin_ia32_movmskps (v4sf)

 The following built-in functions are available when `-msse' is used.

`v4sf __builtin_ia32_loadaps (float *)'
     Generates the `movaps' machine instruction as a load from memory.

`void __builtin_ia32_storeaps (float *, v4sf)'
     Generates the `movaps' machine instruction as a store to memory.

`v4sf __builtin_ia32_loadups (float *)'
     Generates the `movups' machine instruction as a load from memory.

`void __builtin_ia32_storeups (float *, v4sf)'
     Generates the `movups' machine instruction as a store to memory.

`v4sf __builtin_ia32_loadsss (float *)'
     Generates the `movss' machine instruction as a load from memory.

`void __builtin_ia32_storess (float *, v4sf)'
     Generates the `movss' machine instruction as a store to memory.

`v4sf __builtin_ia32_loadhps (v4sf, v2si *)'
     Generates the `movhps' machine instruction as a load from memory.

`v4sf __builtin_ia32_loadlps (v4sf, v2si *)'
     Generates the `movlps' machine instruction as a load from memory

`void __builtin_ia32_storehps (v4sf, v2si *)'
     Generates the `movhps' machine instruction as a store to memory.

`void __builtin_ia32_storelps (v4sf, v2si *)'
     Generates the `movlps' machine instruction as a store to memory.

 The following built-in functions are available when `-msse3' is used.
All of them generate the machine instruction that is part of the name.

     v2df __builtin_ia32_addsubpd (v2df, v2df)
     v2df __builtin_ia32_addsubps (v2df, v2df)
     v2df __builtin_ia32_haddpd (v2df, v2df)
     v2df __builtin_ia32_haddps (v2df, v2df)
     v2df __builtin_ia32_hsubpd (v2df, v2df)
     v2df __builtin_ia32_hsubps (v2df, v2df)
     v16qi __builtin_ia32_lddqu (char const *)
     void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
     v2df __builtin_ia32_movddup (v2df)
     v4sf __builtin_ia32_movshdup (v4sf)
     v4sf __builtin_ia32_movsldup (v4sf)
     void __builtin_ia32_mwait (unsigned int, unsigned int)

 The following built-in functions are available when `-msse3' is used.

`v2df __builtin_ia32_loadddup (double const *)'
     Generates the `movddup' machine instruction as a load from memory.

 The following built-in functions are available when `-m3dnow' is used.
All of them generate the machine instruction that is part of the name.

     void __builtin_ia32_femms (void)
     v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
     v2si __builtin_ia32_pf2id (v2sf)
     v2sf __builtin_ia32_pfacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfadd (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
     v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
     v2sf __builtin_ia32_pfmax (v2sf, v2sf)
     v2sf __builtin_ia32_pfmin (v2sf, v2sf)
     v2sf __builtin_ia32_pfmul (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcp (v2sf)
     v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
     v2sf __builtin_ia32_pfrsqrt (v2sf)
     v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
     v2sf __builtin_ia32_pfsub (v2sf, v2sf)
     v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fd (v2si)
     v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)

 The following built-in functions are available when both `-m3dnow' and
`-march=athlon' are used.  All of them generate the machine instruction
that is part of the name.

     v2si __builtin_ia32_pf2iw (v2sf)
     v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
     v2sf __builtin_ia32_pi2fw (v2si)
     v2sf __builtin_ia32_pswapdsf (v2sf)
     v2si __builtin_ia32_pswapdsi (v2si)


File: gcc,  Node: PowerPC AltiVec Built-in Functions,  Prev: X86 Built-in Functions,  Up: Target Builtins

5.45.4 PowerPC AltiVec Built-in Functions
-----------------------------------------

These built-in functions are available for the PowerPC family of
computers, depending on the command-line switches used.

 The following machine modes are available for use with AltiVec built-in
functions (*note Vector Extensions::): `V4SI' for a vector of four
32-bit integers, `V4SF' for a vector of four 32-bit floating point
numbers, `V8HI' for a vector of eight 16-bit integers, and `V16QI' for
a vector of sixteen 8-bit integers.

 The following functions are made available by including `<altivec.h>'
and using `-maltivec' and `-mabi=altivec'.  The functions implement the
functionality described in Motorola's AltiVec Programming Interface
Manual.

 There are a few differences from Motorola's documentation and GCC's
implementation.  Vector constants are done with curly braces (not
parentheses).  Vector initializers require no casts if the vector
constant is of the same type as the variable it is initializing.  The
`vector bool' type is deprecated and will be discontinued in further
revisions.  Use `vector signed' instead.  If `signed' or `unsigned' is
omitted, the vector type will default to `signed'.  Lastly, all
overloaded functions are implemented with macros for the C
implementation.  So code the following example will not work:

       vec_add ((vector signed int){1, 2, 3, 4}, foo);

 Since vec_add is a macro, the vector constant in the above example will
be treated as four different arguments.  Wrap the entire argument in
parentheses for this to work.  The C++ implementation does not use
macros.

 _Note:_ Only the `<altivec.h>' interface is supported.  Internally,
GCC uses built-in functions to achieve the functionality in the
aforementioned header file, but they are not supported and are subject
to change without notice.

     vector signed char vec_abs (vector signed char, vector signed char);
     vector signed short vec_abs (vector signed short, vector signed short);
     vector signed int vec_abs (vector signed int, vector signed int);
     vector signed float vec_abs (vector signed float, vector signed float);

     vector signed char vec_abss (vector signed char, vector signed char);
     vector signed short vec_abss (vector signed short, vector signed short);

     vector signed char vec_add (vector signed char, vector signed char);
     vector unsigned char vec_add (vector signed char, vector unsigned char);

     vector unsigned char vec_add (vector unsigned char, vector signed char);

     vector unsigned char vec_add (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_add (vector signed short, vector signed short);
     vector unsigned short vec_add (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_add (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_add (vector signed int, vector signed int);
     vector unsigned int vec_add (vector signed int, vector unsigned int);
     vector unsigned int vec_add (vector unsigned int, vector signed int);
     vector unsigned int vec_add (vector unsigned int, vector unsigned int);
     vector float vec_add (vector float, vector float);

     vector unsigned int vec_addc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_adds (vector signed char,
                                    vector unsigned char);
     vector unsigned char vec_adds (vector unsigned char,
                                    vector signed char);
     vector unsigned char vec_adds (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_adds (vector signed char, vector signed char);
     vector unsigned short vec_adds (vector signed short,
                                     vector unsigned short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector signed short);
     vector unsigned short vec_adds (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_adds (vector signed short, vector signed short);

     vector unsigned int vec_adds (vector signed int, vector unsigned int);
     vector unsigned int vec_adds (vector unsigned int, vector signed int);
     vector unsigned int vec_adds (vector unsigned int, vector unsigned int);

     vector signed int vec_adds (vector signed int, vector signed int);

     vector float vec_and (vector float, vector float);
     vector float vec_and (vector float, vector signed int);
     vector float vec_and (vector signed int, vector float);
     vector signed int vec_and (vector signed int, vector signed int);
     vector unsigned int vec_and (vector signed int, vector unsigned int);
     vector unsigned int vec_and (vector unsigned int, vector signed int);
     vector unsigned int vec_and (vector unsigned int, vector unsigned int);
     vector signed short vec_and (vector signed short, vector signed short);
     vector unsigned short vec_and (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_and (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_and (vector signed char, vector signed char);
     vector unsigned char vec_and (vector signed char, vector unsigned char);

     vector unsigned char vec_and (vector unsigned char, vector signed char);

     vector unsigned char vec_and (vector unsigned char,
                                   vector unsigned char);

     vector float vec_andc (vector float, vector float);
     vector float vec_andc (vector float, vector signed int);
     vector float vec_andc (vector signed int, vector float);
     vector signed int vec_andc (vector signed int, vector signed int);
     vector unsigned int vec_andc (vector signed int, vector unsigned int);
     vector unsigned int vec_andc (vector unsigned int, vector signed int);
     vector unsigned int vec_andc (vector unsigned int, vector unsigned int);

     vector signed short vec_andc (vector signed short, vector signed short);

     vector unsigned short vec_andc (vector signed short,
                                     vector unsigned short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector signed short);
     vector unsigned short vec_andc (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_andc (vector signed char, vector signed char);
     vector unsigned char vec_andc (vector signed char,
                                    vector unsigned char);
     vector unsigned char vec_andc (vector unsigned char,
                                    vector signed char);
     vector unsigned char vec_andc (vector unsigned char,
                                    vector unsigned char);

     vector unsigned char vec_avg (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_avg (vector signed char, vector signed char);
     vector unsigned short vec_avg (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_avg (vector signed short, vector signed short);
     vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
     vector signed int vec_avg (vector signed int, vector signed int);

     vector float vec_ceil (vector float);

     vector signed int vec_cmpb (vector float, vector float);

     vector signed char vec_cmpeq (vector signed char, vector signed char);
     vector signed char vec_cmpeq (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_cmpeq (vector signed short,
                                    vector signed short);
     vector signed short vec_cmpeq (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_cmpeq (vector signed int, vector signed int);
     vector signed int vec_cmpeq (vector unsigned int, vector unsigned int);
     vector signed int vec_cmpeq (vector float, vector float);

     vector signed int vec_cmpge (vector float, vector float);

     vector signed char vec_cmpgt (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_cmpgt (vector signed char, vector signed char);
     vector signed short vec_cmpgt (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_cmpgt (vector signed short,
                                    vector signed short);
     vector signed int vec_cmpgt (vector unsigned int, vector unsigned int);
     vector signed int vec_cmpgt (vector signed int, vector signed int);
     vector signed int vec_cmpgt (vector float, vector float);

     vector signed int vec_cmple (vector float, vector float);

     vector signed char vec_cmplt (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_cmplt (vector signed char, vector signed char);
     vector signed short vec_cmplt (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_cmplt (vector signed short,
                                    vector signed short);
     vector signed int vec_cmplt (vector unsigned int, vector unsigned int);
     vector signed int vec_cmplt (vector signed int, vector signed int);
     vector signed int vec_cmplt (vector float, vector float);

     vector float vec_ctf (vector unsigned int, const char);
     vector float vec_ctf (vector signed int, const char);

     vector signed int vec_cts (vector float, const char);

     vector unsigned int vec_ctu (vector float, const char);

     void vec_dss (const char);

     void vec_dssall (void);

     void vec_dst (void *, int, const char);

     void vec_dstst (void *, int, const char);

     void vec_dststt (void *, int, const char);

     void vec_dstt (void *, int, const char);

     vector float vec_expte (vector float, vector float);

     vector float vec_floor (vector float, vector float);

     vector float vec_ld (int, vector float *);
     vector float vec_ld (int, float *):
     vector signed int vec_ld (int, int *);
     vector signed int vec_ld (int, vector signed int *);
     vector unsigned int vec_ld (int, vector unsigned int *);
     vector unsigned int vec_ld (int, unsigned int *);
     vector signed short vec_ld (int, short *, vector signed short *);
     vector unsigned short vec_ld (int, unsigned short *,
                                   vector unsigned short *);
     vector signed char vec_ld (int, signed char *);
     vector signed char vec_ld (int, vector signed char *);
     vector unsigned char vec_ld (int, unsigned char *);
     vector unsigned char vec_ld (int, vector unsigned char *);

     vector signed char vec_lde (int, signed char *);
     vector unsigned char vec_lde (int, unsigned char *);
     vector signed short vec_lde (int, short *);
     vector unsigned short vec_lde (int, unsigned short *);
     vector float vec_lde (int, float *);
     vector signed int vec_lde (int, int *);
     vector unsigned int vec_lde (int, unsigned int *);

     void float vec_ldl (int, float *);
     void float vec_ldl (int, vector float *);
     void signed int vec_ldl (int, vector signed int *);
     void signed int vec_ldl (int, int *);
     void unsigned int vec_ldl (int, unsigned int *);
     void unsigned int vec_ldl (int, vector unsigned int *);
     void signed short vec_ldl (int, vector signed short *);
     void signed short vec_ldl (int, short *);
     void unsigned short vec_ldl (int, vector unsigned short *);
     void unsigned short vec_ldl (int, unsigned short *);
     void signed char vec_ldl (int, vector signed char *);
     void signed char vec_ldl (int, signed char *);
     void unsigned char vec_ldl (int, vector unsigned char *);
     void unsigned char vec_ldl (int, unsigned char *);

     vector float vec_loge (vector float);

     vector unsigned char vec_lvsl (int, void *, int *);

     vector unsigned char vec_lvsr (int, void *, int *);

     vector float vec_madd (vector float, vector float, vector float);

     vector signed short vec_madds (vector signed short, vector signed short,
                                    vector signed short);

     vector unsigned char vec_max (vector signed char, vector unsigned char);

     vector unsigned char vec_max (vector unsigned char, vector signed char);

     vector unsigned char vec_max (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_max (vector signed char, vector signed char);
     vector unsigned short vec_max (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_max (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_max (vector signed short, vector signed short);
     vector unsigned int vec_max (vector signed int, vector unsigned int);
     vector unsigned int vec_max (vector unsigned int, vector signed int);
     vector unsigned int vec_max (vector unsigned int, vector unsigned int);
     vector signed int vec_max (vector signed int, vector signed int);
     vector float vec_max (vector float, vector float);

     vector signed char vec_mergeh (vector signed char, vector signed char);
     vector unsigned char vec_mergeh (vector unsigned char,
                                      vector unsigned char);
     vector signed short vec_mergeh (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergeh (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergeh (vector float, vector float);
     vector signed int vec_mergeh (vector signed int, vector signed int);
     vector unsigned int vec_mergeh (vector unsigned int,
                                     vector unsigned int);

     vector signed char vec_mergel (vector signed char, vector signed char);
     vector unsigned char vec_mergel (vector unsigned char,
                                      vector unsigned char);
     vector signed short vec_mergel (vector signed short,
                                     vector signed short);
     vector unsigned short vec_mergel (vector unsigned short,
                                       vector unsigned short);
     vector float vec_mergel (vector float, vector float);
     vector signed int vec_mergel (vector signed int, vector signed int);
     vector unsigned int vec_mergel (vector unsigned int,
                                     vector unsigned int);

     vector unsigned short vec_mfvscr (void);

     vector unsigned char vec_min (vector signed char, vector unsigned char);

     vector unsigned char vec_min (vector unsigned char, vector signed char);

     vector unsigned char vec_min (vector unsigned char,
                                   vector unsigned char);
     vector signed char vec_min (vector signed char, vector signed char);
     vector unsigned short vec_min (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_min (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_min (vector signed short, vector signed short);
     vector unsigned int vec_min (vector signed int, vector unsigned int);
     vector unsigned int vec_min (vector unsigned int, vector signed int);
     vector unsigned int vec_min (vector unsigned int, vector unsigned int);
     vector signed int vec_min (vector signed int, vector signed int);
     vector float vec_min (vector float, vector float);

     vector signed short vec_mladd (vector signed short, vector signed short,
                                    vector signed short);
     vector signed short vec_mladd (vector signed short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_mladd (vector unsigned short,
                                    vector signed short,
                                    vector signed short);
     vector unsigned short vec_mladd (vector unsigned short,
                                      vector unsigned short,
                                      vector unsigned short);

     vector signed short vec_mradds (vector signed short,
                                     vector signed short,
                                     vector signed short);

     vector unsigned int vec_msum (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed char, vector unsigned char,
                                 vector signed int);
     vector unsigned int vec_msum (vector unsigned short,
                                   vector unsigned short,
                                   vector unsigned int);
     vector signed int vec_msum (vector signed short, vector signed short,
                                 vector signed int);

     vector unsigned int vec_msums (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned int);
     vector signed int vec_msums (vector signed short, vector signed short,
                                  vector signed int);

     void vec_mtvscr (vector signed int);
     void vec_mtvscr (vector unsigned int);
     void vec_mtvscr (vector signed short);
     void vec_mtvscr (vector unsigned short);
     void vec_mtvscr (vector signed char);
     void vec_mtvscr (vector unsigned char);

     vector unsigned short vec_mule (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mule (vector signed char, vector signed char);
     vector unsigned int vec_mule (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mule (vector signed short, vector signed short);

     vector unsigned short vec_mulo (vector unsigned char,
                                     vector unsigned char);
     vector signed short vec_mulo (vector signed char, vector signed char);
     vector unsigned int vec_mulo (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_mulo (vector signed short, vector signed short);

     vector float vec_nmsub (vector float, vector float, vector float);

     vector float vec_nor (vector float, vector float);
     vector signed int vec_nor (vector signed int, vector signed int);
     vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
     vector signed short vec_nor (vector signed short, vector signed short);
     vector unsigned short vec_nor (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_nor (vector signed char, vector signed char);
     vector unsigned char vec_nor (vector unsigned char,
                                   vector unsigned char);

     vector float vec_or (vector float, vector float);
     vector float vec_or (vector float, vector signed int);
     vector float vec_or (vector signed int, vector float);
     vector signed int vec_or (vector signed int, vector signed int);
     vector unsigned int vec_or (vector signed int, vector unsigned int);
     vector unsigned int vec_or (vector unsigned int, vector signed int);
     vector unsigned int vec_or (vector unsigned int, vector unsigned int);
     vector signed short vec_or (vector signed short, vector signed short);
     vector unsigned short vec_or (vector signed short,
                                   vector unsigned short);
     vector unsigned short vec_or (vector unsigned short,
                                   vector signed short);
     vector unsigned short vec_or (vector unsigned short,
                                   vector unsigned short);
     vector signed char vec_or (vector signed char, vector signed char);
     vector unsigned char vec_or (vector signed char, vector unsigned char);
     vector unsigned char vec_or (vector unsigned char, vector signed char);
     vector unsigned char vec_or (vector unsigned char,
                                  vector unsigned char);

     vector signed char vec_pack (vector signed short, vector signed short);
     vector unsigned char vec_pack (vector unsigned short,
                                    vector unsigned short);
     vector signed short vec_pack (vector signed int, vector signed int);
     vector unsigned short vec_pack (vector unsigned int,
                                     vector unsigned int);

     vector signed short vec_packpx (vector unsigned int,
                                     vector unsigned int);

     vector unsigned char vec_packs (vector unsigned short,
                                     vector unsigned short);
     vector signed char vec_packs (vector signed short, vector signed short);

     vector unsigned short vec_packs (vector unsigned int,
                                      vector unsigned int);
     vector signed short vec_packs (vector signed int, vector signed int);

     vector unsigned char vec_packsu (vector unsigned short,
                                      vector unsigned short);
     vector unsigned char vec_packsu (vector signed short,
                                      vector signed short);
     vector unsigned short vec_packsu (vector unsigned int,
                                       vector unsigned int);
     vector unsigned short vec_packsu (vector signed int, vector signed int);

     vector float vec_perm (vector float, vector float,
                            vector unsigned char);
     vector signed int vec_perm (vector signed int, vector signed int,
                                 vector unsigned char);
     vector unsigned int vec_perm (vector unsigned int, vector unsigned int,
                                   vector unsigned char);
     vector signed short vec_perm (vector signed short, vector signed short,
                                   vector unsigned char);
     vector unsigned short vec_perm (vector unsigned short,
                                     vector unsigned short,
                                     vector unsigned char);
     vector signed char vec_perm (vector signed char, vector signed char,
                                  vector unsigned char);
     vector unsigned char vec_perm (vector unsigned char,
                                    vector unsigned char,
                                    vector unsigned char);

     vector float vec_re (vector float);

     vector signed char vec_rl (vector signed char, vector unsigned char);
     vector unsigned char vec_rl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_rl (vector signed short, vector unsigned short);

     vector unsigned short vec_rl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_rl (vector signed int, vector unsigned int);
     vector unsigned int vec_rl (vector unsigned int, vector unsigned int);

     vector float vec_round (vector float);

     vector float vec_rsqrte (vector float);

     vector float vec_sel (vector float, vector float, vector signed int);
     vector float vec_sel (vector float, vector float, vector unsigned int);
     vector signed int vec_sel (vector signed int, vector signed int,
                                vector signed int);
     vector signed int vec_sel (vector signed int, vector signed int,
                                vector unsigned int);
     vector unsigned int vec_sel (vector unsigned int, vector unsigned int,
                                  vector signed int);
     vector unsigned int vec_sel (vector unsigned int, vector unsigned int,
                                  vector unsigned int);
     vector signed short vec_sel (vector signed short, vector signed short,
                                  vector signed short);
     vector signed short vec_sel (vector signed short, vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_sel (vector unsigned short,
                                    vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_sel (vector signed char, vector signed char,
                                 vector signed char);
     vector signed char vec_sel (vector signed char, vector signed char,
                                 vector unsigned char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector signed char);
     vector unsigned char vec_sel (vector unsigned char,
                                   vector unsigned char,
                                   vector unsigned char);

     vector signed char vec_sl (vector signed char, vector unsigned char);
     vector unsigned char vec_sl (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sl (vector signed short, vector unsigned short);

     vector unsigned short vec_sl (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sl (vector signed int, vector unsigned int);
     vector unsigned int vec_sl (vector unsigned int, vector unsigned int);

     vector float vec_sld (vector float, vector float, const char);
     vector signed int vec_sld (vector signed int, vector signed int,
                                const char);
     vector unsigned int vec_sld (vector unsigned int, vector unsigned int,
                                  const char);
     vector signed short vec_sld (vector signed short, vector signed short,
                                  const char);
     vector unsigned short vec_sld (vector unsigned short,
                                    vector unsigned short, const char);
     vector signed char vec_sld (vector signed char, vector signed char,
                                 const char);
     vector unsigned char vec_sld (vector unsigned char,
                                   vector unsigned char,
                                   const char);

     vector signed int vec_sll (vector signed int, vector unsigned int);
     vector signed int vec_sll (vector signed int, vector unsigned short);
     vector signed int vec_sll (vector signed int, vector unsigned char);
     vector unsigned int vec_sll (vector unsigned int, vector unsigned int);
     vector unsigned int vec_sll (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_sll (vector unsigned int, vector unsigned char);

     vector signed short vec_sll (vector signed short, vector unsigned int);
     vector signed short vec_sll (vector signed short,
                                  vector unsigned short);
     vector signed short vec_sll (vector signed short, vector unsigned char);

     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_sll (vector unsigned short,
                                    vector unsigned char);
     vector signed char vec_sll (vector signed char, vector unsigned int);
     vector signed char vec_sll (vector signed char, vector unsigned short);
     vector signed char vec_sll (vector signed char, vector unsigned char);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_sll (vector unsigned char,
                                   vector unsigned char);

     vector float vec_slo (vector float, vector signed char);
     vector float vec_slo (vector float, vector unsigned char);
     vector signed int vec_slo (vector signed int, vector signed char);
     vector signed int vec_slo (vector signed int, vector unsigned char);
     vector unsigned int vec_slo (vector unsigned int, vector signed char);
     vector unsigned int vec_slo (vector unsigned int, vector unsigned char);

     vector signed short vec_slo (vector signed short, vector signed char);
     vector signed short vec_slo (vector signed short, vector unsigned char);

     vector unsigned short vec_slo (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_slo (vector unsigned short,
                                    vector unsigned char);
     vector signed char vec_slo (vector signed char, vector signed char);
     vector signed char vec_slo (vector signed char, vector unsigned char);
     vector unsigned char vec_slo (vector unsigned char, vector signed char);

     vector unsigned char vec_slo (vector unsigned char,
                                   vector unsigned char);

     vector signed char vec_splat (vector signed char, const char);
     vector unsigned char vec_splat (vector unsigned char, const char);
     vector signed short vec_splat (vector signed short, const char);
     vector unsigned short vec_splat (vector unsigned short, const char);
     vector float vec_splat (vector float, const char);
     vector signed int vec_splat (vector signed int, const char);
     vector unsigned int vec_splat (vector unsigned int, const char);

     vector signed char vec_splat_s8 (const char);

     vector signed short vec_splat_s16 (const char);

     vector signed int vec_splat_s32 (const char);

     vector unsigned char vec_splat_u8 (const char);

     vector unsigned short vec_splat_u16 (const char);

     vector unsigned int vec_splat_u32 (const char);

     vector signed char vec_sr (vector signed char, vector unsigned char);
     vector unsigned char vec_sr (vector unsigned char,
                                  vector unsigned char);
     vector signed short vec_sr (vector signed short, vector unsigned short);

     vector unsigned short vec_sr (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_sr (vector signed int, vector unsigned int);
     vector unsigned int vec_sr (vector unsigned int, vector unsigned int);

     vector signed char vec_sra (vector signed char, vector unsigned char);
     vector unsigned char vec_sra (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sra (vector signed short,
                                  vector unsigned short);
     vector unsigned short vec_sra (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sra (vector signed int, vector unsigned int);
     vector unsigned int vec_sra (vector unsigned int, vector unsigned int);

     vector signed int vec_srl (vector signed int, vector unsigned int);
     vector signed int vec_srl (vector signed int, vector unsigned short);
     vector signed int vec_srl (vector signed int, vector unsigned char);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
     vector unsigned int vec_srl (vector unsigned int,
                                  vector unsigned short);
     vector unsigned int vec_srl (vector unsigned int, vector unsigned char);

     vector signed short vec_srl (vector signed short, vector unsigned int);
     vector signed short vec_srl (vector signed short,
                                  vector unsigned short);
     vector signed short vec_srl (vector signed short, vector unsigned char);

     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned int);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned short);
     vector unsigned short vec_srl (vector unsigned short,
                                    vector unsigned char);
     vector signed char vec_srl (vector signed char, vector unsigned int);
     vector signed char vec_srl (vector signed char, vector unsigned short);
     vector signed char vec_srl (vector signed char, vector unsigned char);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned int);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned short);
     vector unsigned char vec_srl (vector unsigned char,
                                   vector unsigned char);

     vector float vec_sro (vector float, vector signed char);
     vector float vec_sro (vector float, vector unsigned char);
     vector signed int vec_sro (vector signed int, vector signed char);
     vector signed int vec_sro (vector signed int, vector unsigned char);
     vector unsigned int vec_sro (vector unsigned int, vector signed char);
     vector unsigned int vec_sro (vector unsigned int, vector unsigned char);

     vector signed short vec_sro (vector signed short, vector signed char);
     vector signed short vec_sro (vector signed short, vector unsigned char);

     vector unsigned short vec_sro (vector unsigned short,
                                    vector signed char);
     vector unsigned short vec_sro (vector unsigned short,
                                    vector unsigned char);
     vector signed char vec_sro (vector signed char, vector signed char);
     vector signed char vec_sro (vector signed char, vector unsigned char);
     vector unsigned char vec_sro (vector unsigned char, vector signed char);

     vector unsigned char vec_sro (vector unsigned char,
                                   vector unsigned char);

     void vec_st (vector float, int, float *);
     void vec_st (vector float, int, vector float *);
     void vec_st (vector signed int, int, int *);
     void vec_st (vector signed int, int, unsigned int *);
     void vec_st (vector unsigned int, int, unsigned int *);
     void vec_st (vector unsigned int, int, vector unsigned int *);
     void vec_st (vector signed short, int, short *);
     void vec_st (vector signed short, int, vector unsigned short *);
     void vec_st (vector signed short, int, vector signed short *);
     void vec_st (vector unsigned short, int, unsigned short *);
     void vec_st (vector unsigned short, int, vector unsigned short *);
     void vec_st (vector signed char, int, signed char *);
     void vec_st (vector signed char, int, unsigned char *);
     void vec_st (vector signed char, int, vector signed char *);
     void vec_st (vector unsigned char, int, unsigned char *);
     void vec_st (vector unsigned char, int, vector unsigned char *);

     void vec_ste (vector signed char, int, unsigned char *);
     void vec_ste (vector signed char, int, signed char *);
     void vec_ste (vector unsigned char, int, unsigned char *);
     void vec_ste (vector signed short, int, short *);
     void vec_ste (vector signed short, int, unsigned short *);
     void vec_ste (vector unsigned short, int, void *);
     void vec_ste (vector signed int, int, unsigned int *);
     void vec_ste (vector signed int, int, int *);
     void vec_ste (vector unsigned int, int, unsigned int *);
     void vec_ste (vector float, int, float *);

     void vec_stl (vector float, int, vector float *);
     void vec_stl (vector float, int, float *);
     void vec_stl (vector signed int, int, vector signed int *);
     void vec_stl (vector signed int, int, int *);
     void vec_stl (vector signed int, int, unsigned int *);
     void vec_stl (vector unsigned int, int, vector unsigned int *);
     void vec_stl (vector unsigned int, int, unsigned int *);
     void vec_stl (vector signed short, int, short *);
     void vec_stl (vector signed short, int, unsigned short *);
     void vec_stl (vector signed short, int, vector signed short *);
     void vec_stl (vector unsigned short, int, unsigned short *);
     void vec_stl (vector unsigned short, int, vector signed short *);
     void vec_stl (vector signed char, int, signed char *);
     void vec_stl (vector signed char, int, unsigned char *);
     void vec_stl (vector signed char, int, vector signed char *);
     void vec_stl (vector unsigned char, int, unsigned char *);
     void vec_stl (vector unsigned char, int, vector unsigned char *);

     vector signed char vec_sub (vector signed char, vector signed char);
     vector unsigned char vec_sub (vector signed char, vector unsigned char);

     vector unsigned char vec_sub (vector unsigned char, vector signed char);

     vector unsigned char vec_sub (vector unsigned char,
                                   vector unsigned char);
     vector signed short vec_sub (vector signed short, vector signed short);
     vector unsigned short vec_sub (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_sub (vector unsigned short,
                                    vector unsigned short);
     vector signed int vec_sub (vector signed int, vector signed int);
     vector unsigned int vec_sub (vector signed int, vector unsigned int);
     vector unsigned int vec_sub (vector unsigned int, vector signed int);
     vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
     vector float vec_sub (vector float, vector float);

     vector unsigned int vec_subc (vector unsigned int, vector unsigned int);

     vector unsigned char vec_subs (vector signed char,
                                    vector unsigned char);
     vector unsigned char vec_subs (vector unsigned char,
                                    vector signed char);
     vector unsigned char vec_subs (vector unsigned char,
                                    vector unsigned char);
     vector signed char vec_subs (vector signed char, vector signed char);
     vector unsigned short vec_subs (vector signed short,
                                     vector unsigned short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector signed short);
     vector unsigned short vec_subs (vector unsigned short,
                                     vector unsigned short);
     vector signed short vec_subs (vector signed short, vector signed short);

     vector unsigned int vec_subs (vector signed int, vector unsigned int);
     vector unsigned int vec_subs (vector unsigned int, vector signed int);
     vector unsigned int vec_subs (vector unsigned int, vector unsigned int);

     vector signed int vec_subs (vector signed int, vector signed int);

     vector unsigned int vec_sum4s (vector unsigned char,
                                    vector unsigned int);
     vector signed int vec_sum4s (vector signed char, vector signed int);
     vector signed int vec_sum4s (vector signed short, vector signed int);

     vector signed int vec_sum2s (vector signed int, vector signed int);

     vector signed int vec_sums (vector signed int, vector signed int);

     vector float vec_trunc (vector float);

     vector signed short vec_unpackh (vector signed char);
     vector unsigned int vec_unpackh (vector signed short);
     vector signed int vec_unpackh (vector signed short);

     vector signed short vec_unpackl (vector signed char);
     vector unsigned int vec_unpackl (vector signed short);
     vector signed int vec_unpackl (vector signed short);

     vector float vec_xor (vector float, vector float);
     vector float vec_xor (vector float, vector signed int);
     vector float vec_xor (vector signed int, vector float);
     vector signed int vec_xor (vector signed int, vector signed int);
     vector unsigned int vec_xor (vector signed int, vector unsigned int);
     vector unsigned int vec_xor (vector unsigned int, vector signed int);
     vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
     vector signed short vec_xor (vector signed short, vector signed short);
     vector unsigned short vec_xor (vector signed short,
                                    vector unsigned short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector signed short);
     vector unsigned short vec_xor (vector unsigned short,
                                    vector unsigned short);
     vector signed char vec_xor (vector signed char, vector signed char);
     vector unsigned char vec_xor (vector signed char, vector unsigned char);

     vector unsigned char vec_xor (vector unsigned char, vector signed char);

     vector unsigned char vec_xor (vector unsigned char,
                                   vector unsigned char);

     vector signed int vec_all_eq (vector signed char, vector unsigned char);

     vector signed int vec_all_eq (vector signed char, vector signed char);
     vector signed int vec_all_eq (vector unsigned char, vector signed char);

     vector signed int vec_all_eq (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_eq (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_eq (vector signed short, vector signed short);

     vector signed int vec_all_eq (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_eq (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_eq (vector signed int, vector unsigned int);
     vector signed int vec_all_eq (vector signed int, vector signed int);
     vector signed int vec_all_eq (vector unsigned int, vector signed int);
     vector signed int vec_all_eq (vector unsigned int, vector unsigned int);

     vector signed int vec_all_eq (vector float, vector float);

     vector signed int vec_all_ge (vector signed char, vector unsigned char);

     vector signed int vec_all_ge (vector unsigned char, vector signed char);

     vector signed int vec_all_ge (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_ge (vector signed char, vector signed char);
     vector signed int vec_all_ge (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_ge (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_ge (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_ge (vector signed short, vector signed short);

     vector signed int vec_all_ge (vector signed int, vector unsigned int);
     vector signed int vec_all_ge (vector unsigned int, vector signed int);
     vector signed int vec_all_ge (vector unsigned int, vector unsigned int);

     vector signed int vec_all_ge (vector signed int, vector signed int);
     vector signed int vec_all_ge (vector float, vector float);

     vector signed int vec_all_gt (vector signed char, vector unsigned char);

     vector signed int vec_all_gt (vector unsigned char, vector signed char);

     vector signed int vec_all_gt (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_gt (vector signed char, vector signed char);
     vector signed int vec_all_gt (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_gt (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_gt (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_gt (vector signed short, vector signed short);

     vector signed int vec_all_gt (vector signed int, vector unsigned int);
     vector signed int vec_all_gt (vector unsigned int, vector signed int);
     vector signed int vec_all_gt (vector unsigned int, vector unsigned int);

     vector signed int vec_all_gt (vector signed int, vector signed int);
     vector signed int vec_all_gt (vector float, vector float);

     vector signed int vec_all_in (vector float, vector float);

     vector signed int vec_all_le (vector signed char, vector unsigned char);

     vector signed int vec_all_le (vector unsigned char, vector signed char);

     vector signed int vec_all_le (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_le (vector signed char, vector signed char);
     vector signed int vec_all_le (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_le (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_le (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_le (vector signed short, vector signed short);

     vector signed int vec_all_le (vector signed int, vector unsigned int);
     vector signed int vec_all_le (vector unsigned int, vector signed int);
     vector signed int vec_all_le (vector unsigned int, vector unsigned int);

     vector signed int vec_all_le (vector signed int, vector signed int);
     vector signed int vec_all_le (vector float, vector float);

     vector signed int vec_all_lt (vector signed char, vector unsigned char);

     vector signed int vec_all_lt (vector unsigned char, vector signed char);

     vector signed int vec_all_lt (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_lt (vector signed char, vector signed char);
     vector signed int vec_all_lt (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_lt (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_lt (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_lt (vector signed short, vector signed short);

     vector signed int vec_all_lt (vector signed int, vector unsigned int);
     vector signed int vec_all_lt (vector unsigned int, vector signed int);
     vector signed int vec_all_lt (vector unsigned int, vector unsigned int);

     vector signed int vec_all_lt (vector signed int, vector signed int);
     vector signed int vec_all_lt (vector float, vector float);

     vector signed int vec_all_nan (vector float);

     vector signed int vec_all_ne (vector signed char, vector unsigned char);

     vector signed int vec_all_ne (vector signed char, vector signed char);
     vector signed int vec_all_ne (vector unsigned char, vector signed char);

     vector signed int vec_all_ne (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_all_ne (vector signed short,
                                   vector unsigned short);
     vector signed int vec_all_ne (vector signed short, vector signed short);

     vector signed int vec_all_ne (vector unsigned short,
                                   vector signed short);
     vector signed int vec_all_ne (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_all_ne (vector signed int, vector unsigned int);
     vector signed int vec_all_ne (vector signed int, vector signed int);
     vector signed int vec_all_ne (vector unsigned int, vector signed int);
     vector signed int vec_all_ne (vector unsigned int, vector unsigned int);

     vector signed int vec_all_ne (vector float, vector float);

     vector signed int vec_all_nge (vector float, vector float);

     vector signed int vec_all_ngt (vector float, vector float);

     vector signed int vec_all_nle (vector float, vector float);

     vector signed int vec_all_nlt (vector float, vector float);

     vector signed int vec_all_numeric (vector float);

     vector signed int vec_any_eq (vector signed char, vector unsigned char);

     vector signed int vec_any_eq (vector signed char, vector signed char);
     vector signed int vec_any_eq (vector unsigned char, vector signed char);

     vector signed int vec_any_eq (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_eq (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_eq (vector signed short, vector signed short);

     vector signed int vec_any_eq (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_eq (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_eq (vector signed int, vector unsigned int);
     vector signed int vec_any_eq (vector signed int, vector signed int);
     vector signed int vec_any_eq (vector unsigned int, vector signed int);
     vector signed int vec_any_eq (vector unsigned int, vector unsigned int);

     vector signed int vec_any_eq (vector float, vector float);

     vector signed int vec_any_ge (vector signed char, vector unsigned char);

     vector signed int vec_any_ge (vector unsigned char, vector signed char);

     vector signed int vec_any_ge (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_ge (vector signed char, vector signed char);
     vector signed int vec_any_ge (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_ge (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_ge (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_ge (vector signed short, vector signed short);

     vector signed int vec_any_ge (vector signed int, vector unsigned int);
     vector signed int vec_any_ge (vector unsigned int, vector signed int);
     vector signed int vec_any_ge (vector unsigned int, vector unsigned int);

     vector signed int vec_any_ge (vector signed int, vector signed int);
     vector signed int vec_any_ge (vector float, vector float);

     vector signed int vec_any_gt (vector signed char, vector unsigned char);

     vector signed int vec_any_gt (vector unsigned char, vector signed char);

     vector signed int vec_any_gt (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_gt (vector signed char, vector signed char);
     vector signed int vec_any_gt (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_gt (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_gt (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_gt (vector signed short, vector signed short);

     vector signed int vec_any_gt (vector signed int, vector unsigned int);
     vector signed int vec_any_gt (vector unsigned int, vector signed int);
     vector signed int vec_any_gt (vector unsigned int, vector unsigned int);

     vector signed int vec_any_gt (vector signed int, vector signed int);
     vector signed int vec_any_gt (vector float, vector float);

     vector signed int vec_any_le (vector signed char, vector unsigned char);

     vector signed int vec_any_le (vector unsigned char, vector signed char);

     vector signed int vec_any_le (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_le (vector signed char, vector signed char);
     vector signed int vec_any_le (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_le (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_le (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_le (vector signed short, vector signed short);

     vector signed int vec_any_le (vector signed int, vector unsigned int);
     vector signed int vec_any_le (vector unsigned int, vector signed int);
     vector signed int vec_any_le (vector unsigned int, vector unsigned int);

     vector signed int vec_any_le (vector signed int, vector signed int);
     vector signed int vec_any_le (vector float, vector float);

     vector signed int vec_any_lt (vector signed char, vector unsigned char);

     vector signed int vec_any_lt (vector unsigned char, vector signed char);

     vector signed int vec_any_lt (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_lt (vector signed char, vector signed char);
     vector signed int vec_any_lt (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_lt (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_lt (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_lt (vector signed short, vector signed short);

     vector signed int vec_any_lt (vector signed int, vector unsigned int);
     vector signed int vec_any_lt (vector unsigned int, vector signed int);
     vector signed int vec_any_lt (vector unsigned int, vector unsigned int);

     vector signed int vec_any_lt (vector signed int, vector signed int);
     vector signed int vec_any_lt (vector float, vector float);

     vector signed int vec_any_nan (vector float);

     vector signed int vec_any_ne (vector signed char, vector unsigned char);

     vector signed int vec_any_ne (vector signed char, vector signed char);
     vector signed int vec_any_ne (vector unsigned char, vector signed char);

     vector signed int vec_any_ne (vector unsigned char,
                                   vector unsigned char);
     vector signed int vec_any_ne (vector signed short,
                                   vector unsigned short);
     vector signed int vec_any_ne (vector signed short, vector signed short);

     vector signed int vec_any_ne (vector unsigned short,
                                   vector signed short);
     vector signed int vec_any_ne (vector unsigned short,
                                   vector unsigned short);
     vector signed int vec_any_ne (vector signed int, vector unsigned int);
     vector signed int vec_any_ne (vector signed int, vector signed int);
     vector signed int vec_any_ne (vector unsigned int, vector signed int);
     vector signed int vec_any_ne (vector unsigned int, vector unsigned int);

     vector signed int vec_any_ne (vector float, vector float);

     vector signed int vec_any_nge (vector float, vector float);

     vector signed int vec_any_ngt (vector float, vector float);

     vector signed int vec_any_nle (vector float, vector float);

     vector signed int vec_any_nlt (vector float, vector float);

     vector signed int vec_any_numeric (vector float);

     vector signed int vec_any_out (vector float, vector float);


File: gcc,  Node: Pragmas,  Next: Unnamed Fields,  Prev: Target Builtins,  Up: C Extensions

5.46 Pragmas Accepted by GCC
============================

GCC supports several types of pragmas, primarily in order to compile
code originally written for other compilers.  Note that in general we
do not recommend the use of pragmas; *Note Function Attributes::, for
further explanation.

* Menu:

* ARM Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Tru64 Pragmas::


File: gcc,  Node: ARM Pragmas,  Next: RS/6000 and PowerPC Pragmas,  Up: Pragmas

5.46.1 ARM Pragmas
------------------

The ARM target defines pragmas for controlling the default addition of
`long_call' and `short_call' attributes to functions.  *Note Function
Attributes::, for information about the effects of these attributes.

`long_calls'
     Set all subsequent functions to have the `long_call' attribute.

`no_long_calls'
     Set all subsequent functions to have the `short_call' attribute.

`long_calls_off'
     Do not affect the `long_call' or `short_call' attributes of
     subsequent functions.


File: gcc,  Node: RS/6000 and PowerPC Pragmas,  Next: Darwin Pragmas,  Prev: ARM Pragmas,  Up: Pragmas

5.46.2 RS/6000 and PowerPC Pragmas
----------------------------------

The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the `longcall' attribute is added to function
declarations by default.  This pragma overrides the `-mlongcall'
option, but not the `longcall' and `shortcall' attributes.  *Note
RS/6000 and PowerPC Options::, for more information about when long
calls are and are not necessary.

`longcall (1)'
     Apply the `longcall' attribute to all subsequent function
     declarations.

`longcall (0)'
     Do not apply the `longcall' attribute to subsequent function
     declarations.


File: gcc,  Node: Darwin Pragmas,  Next: Solaris Pragmas,  Prev: RS/6000 and PowerPC Pragmas,  Up: Pragmas

5.46.3 Darwin Pragmas
---------------------

The following pragmas are available for all architectures running the
Darwin operating system.  These are useful for compatibility with other
Mac OS compilers.

`mark TOKENS...'
     This pragma is accepted, but has no effect.

`options align=ALIGNMENT'
     This pragma sets the alignment of fields in structures.  The
     values of ALIGNMENT may be `mac68k', to emulate m68k alignment, or
     `power', to emulate PowerPC alignment.  Uses of this pragma nest
     properly; to restore the previous setting, use `reset' for the
     ALIGNMENT.

`segment TOKENS...'
     This pragma is accepted, but has no effect.

`unused (VAR [, VAR]...)'
     This pragma declares variables to be possibly unused.  GCC will not
     produce warnings for the listed variables.  The effect is similar
     to that of the `unused' attribute, except that this pragma may
     appear anywhere within the variables' scopes.


File: gcc,  Node: Solaris Pragmas,  Next: Tru64 Pragmas,  Prev: Darwin Pragmas,  Up: Pragmas

5.46.4 Solaris Pragmas
----------------------

For compatibility with the SunPRO compiler, the following pragma is
supported.

`redefine_extname OLDNAME NEWNAME'
     This pragma gives the C function OLDNAME the assembler label
     NEWNAME.  The pragma must appear before the function declaration.
     This pragma is equivalent to the asm labels extension (*note Asm
     Labels::).  The preprocessor defines `__PRAGMA_REDEFINE_EXTNAME'
     if the pragma is available.


File: gcc,  Node: Tru64 Pragmas,  Prev: Solaris Pragmas,  Up: Pragmas

5.46.5 Tru64 Pragmas
--------------------

For compatibility with the Compaq C compiler, the following pragma is
supported.

`extern_prefix STRING'
     This pragma renames all subsequent function and variable
     declarations such that STRING is prepended to the name.  This
     effect may be terminated by using another `extern_prefix' pragma
     with the empty string.

     This pragma is similar in intent to to the asm labels extension
     (*note Asm Labels::) in that the system programmer wants to change
     the assembly-level ABI without changing the source-level API.  The
     preprocessor defines `__PRAGMA_EXTERN_PREFIX' if the pragma is
     available.


File: gcc,  Node: Unnamed Fields,  Next: Thread-Local,  Prev: Pragmas,  Up: C Extensions

5.47 Unnamed struct/union fields within structs/unions.
=======================================================

For compatibility with other compilers, GCC allows you to define a
structure or union that contains, as fields, structures and unions
without names.  For example:

     struct {
       int a;
       union {
         int b;
         float c;
       };
       int d;
     } foo;

 In this example, the user would be able to access members of the
unnamed union with code like `foo.b'.  Note that only unnamed structs
and unions are allowed, you may not have, for example, an unnamed `int'.

 You must never create such structures that cause ambiguous field
definitions.  For example, this structure:

     struct {
       int a;
       struct {
         int a;
       };
     } foo;

 It is ambiguous which `a' is being referred to with `foo.a'.  Such
constructs are not supported and must be avoided.  In the future, such
constructs may be detected and treated as compilation errors.


File: gcc,  Node: Thread-Local,  Prev: Unnamed Fields,  Up: C Extensions

5.48 Thread-Local Storage
=========================

Thread-local storage (TLS) is a mechanism by which variables are
allocated such that there is one instance of the variable per extant
thread.  The run-time model GCC uses to implement this originates in
the IA-64 processor-specific ABI, but has since been migrated to other
processors as well.  It requires significant support from the linker
(`ld'), dynamic linker (`ld.so'), and system libraries (`libc.so' and
`libpthread.so'), so it is not available everywhere.

 At the user level, the extension is visible with a new storage class
keyword: `__thread'.  For example:

     __thread int i;
     extern __thread struct state s;
     static __thread char *p;

 The `__thread' specifier may be used alone, with the `extern' or
`static' specifiers, but with no other storage class specifier.  When
used with `extern' or `static', `__thread' must appear immediately
after the other storage class specifier.

 The `__thread' specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class.  It
may not be applied to block-scoped automatic or non-static data member.

 When the address-of operator is applied to a thread-local variable, it
is evaluated at run-time and returns the address of the current thread's
instance of that variable.  An address so obtained may be used by any
thread.  When a thread terminates, any pointers to thread-local
variables in that thread become invalid.

 No static initialization may refer to the address of a thread-local
variable.

 In C++, if an initializer is present for a thread-local variable, it
must be a CONSTANT-EXPRESSION, as defined in 5.19.2 of the ANSI/ISO C++
standard.

 See ELF Handling For Thread-Local Storage
(http://people.redhat.com/drepper/tls.pdf) for a detailed explanation of
the four thread-local storage addressing models, and how the run-time
is expected to function.

* Menu:

* C99 Thread-Local Edits::
* C++98 Thread-Local Edits::


File: gcc,  Node: C99 Thread-Local Edits,  Next: C++98 Thread-Local Edits,  Up: Thread-Local

5.48.1 ISO/IEC 9899:1999 Edits for Thread-Local Storage
-------------------------------------------------------

The following are a set of changes to ISO/IEC 9899:1999 (aka C99) that
document the exact semantics of the language extension.

   * `5.1.2  Execution environments'

     Add new text after paragraph 1

          Within either execution environment, a "thread" is a flow of
          control within a program.  It is implementation defined
          whether or not there may be more than one thread associated
          with a program.  It is implementation defined how threads
          beyond the first are created, the name and type of the
          function called at thread startup, and how threads may be
          terminated.  However, objects with thread storage duration
          shall be initialized before thread startup.

   * `6.2.4  Storage durations of objects'

     Add new text before paragraph 3

          An object whose identifier is declared with the storage-class
          specifier `__thread' has "thread storage duration".  Its
          lifetime is the entire execution of the thread, and its
          stored value is initialized only once, prior to thread
          startup.

   * `6.4.1  Keywords'

     Add `__thread'.

   * `6.7.1  Storage-class specifiers'

     Add `__thread' to the list of storage class specifiers in
     paragraph 1.

     Change paragraph 2 to

          With the exception of `__thread', at most one storage-class
          specifier may be given [...].  The `__thread' specifier may
          be used alone, or immediately following `extern' or `static'.

     Add new text after paragraph 6

          The declaration of an identifier for a variable that has
          block scope that specifies `__thread' shall also specify
          either `extern' or `static'.

          The `__thread' specifier shall be used only with variables.


File: gcc,  Node: C++98 Thread-Local Edits,  Prev: C99 Thread-Local Edits,  Up: Thread-Local

5.48.2 ISO/IEC 14882:1998 Edits for Thread-Local Storage
--------------------------------------------------------

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98)
that document the exact semantics of the language extension.

   * [intro.execution]

     New text after paragraph 4

          A "thread" is a flow of control within the abstract machine.
          It is implementation defined whether or not there may be more
          than one thread.

     New text after paragraph 7

          It is unspecified whether additional action must be taken to
          ensure when and whether side effects are visible to other
          threads.

   * [lex.key]

     Add `__thread'.

   * [basic.start.main]

     Add after paragraph 5

          The thread that begins execution at the `main' function is
          called the "main thread".  It is implementation defined how
          functions beginning threads other than the main thread are
          designated or typed.  A function so designated, as well as
          the `main' function, is called a "thread startup function".
          It is implementation defined what happens if a thread startup
          function returns.  It is implementation defined what happens
          to other threads when any thread calls `exit'.

   * [basic.start.init]

     Add after paragraph 4

          The storage for an object of thread storage duration shall be
          statically initialized before the first statement of the
          thread startup function.  An object of thread storage
          duration shall not require dynamic initialization.

   * [basic.start.term]

     Add after paragraph 3

          The type of an object with thread storage duration shall not
          have a non-trivial destructor, nor shall it be an array type
          whose elements (directly or indirectly) have non-trivial
          destructors.

   * [basic.stc]

     Add "thread storage duration" to the list in paragraph 1.

     Change paragraph 2

          Thread, static, and automatic storage durations are
          associated with objects introduced by declarations [...].

     Add `__thread' to the list of specifiers in paragraph 3.

   * [basic.stc.thread]

     New section before [basic.stc.static]

          The keyword `__thread' applied to a non-local object gives the
          object thread storage duration.

          A local variable or class data member declared both `static'
          and `__thread' gives the variable or member thread storage
          duration.

   * [basic.stc.static]

     Change paragraph 1

          All objects which have neither thread storage duration,
          dynamic storage duration nor are local [...].

   * [dcl.stc]

     Add `__thread' to the list in paragraph 1.

     Change paragraph 1

          With the exception of `__thread', at most one
          STORAGE-CLASS-SPECIFIER shall appear in a given
          DECL-SPECIFIER-SEQ.  The `__thread' specifier may be used
          alone, or immediately following the `extern' or `static'
          specifiers.  [...]

     Add after paragraph 5

          The `__thread' specifier can be applied only to the names of
          objects and to anonymous unions.

   * [class.mem]

     Add after paragraph 6

          Non-`static' members shall not be `__thread'.


File: gcc,  Node: C++ Extensions,  Next: Objective-C,  Prev: C Extensions,  Up: Top

6 Extensions to the C++ Language
********************************

The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs).
If you want to write code that checks whether these features are
available, you can test for the GNU compiler the same way as for C
programs: check for a predefined macro `__GNUC__'.  You can also use
`__GNUG__' to test specifically for GNU C++ (*note Predefined Macros:
(cpp)Common Predefined Macros.).

* Menu:

* Min and Max::        C++ Minimum and maximum operators.
* Volatiles::        What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage::       Where G++ puts inlines, vtables and such.
* C++ Interface::       You can use a single C++ header file for both
                        declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
                        each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
                        method denoted by a `->*' or `.*' expression.
* C++ Attributes::      Variable, function, and type attributes for C++ only.
* Strong Using::      Strong using-directives for namespace composition.
* Offsetof::            Special syntax for implementing `offsetof'.
* Java Exceptions::     Tweaking exception handling to work with Java.
* Deprecated Features:: Things will disappear from g++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.


File: gcc,  Node: Min and Max,  Next: Volatiles,  Up: C++ Extensions

6.1 Minimum and Maximum Operators in C++
========================================

It is very convenient to have operators which return the "minimum" or
the "maximum" of two arguments.  In GNU C++ (but not in GNU C),

`A <? B'
     is the "minimum", returning the smaller of the numeric values A
     and B;

`A >? B'
     is the "maximum", returning the larger of the numeric values A and
     B.

 These operations are not primitive in ordinary C++, since you can use
a macro to return the minimum of two things in C++, as in the following
example.

     #define MIN(X,Y) ((X) < (Y) ? : (X) : (Y))

You might then use `int min = MIN (i, j);' to set MIN to the minimum
value of variables I and J.

 However, side effects in `X' or `Y' may cause unintended behavior.
For example, `MIN (i++, j++)' will fail, incrementing the smaller
counter twice.  The GNU C `typeof' extension allows you to write safe
macros that avoid this kind of problem (*note Typeof::).  However,
writing `MIN' and `MAX' as macros also forces you to use function-call
notation for a fundamental arithmetic operation.  Using GNU C++
extensions, you can write `int min = i <? j;' instead.

 Since `<?' and `>?' are built into the compiler, they properly handle
expressions with side-effects;  `int min = i++ <? j++;' works correctly.


File: gcc,  Node: Volatiles,  Next: Restricted Pointers,  Prev: Min and Max,  Up: C++ Extensions

6.2 When is a Volatile Object Accessed?
=======================================

Both the C and C++ standard have the concept of volatile objects.  These
are normally accessed by pointers and used for accessing hardware.  The
standards encourage compilers to refrain from optimizations concerning
accesses to volatile objects that it might perform on non-volatile
objects.  The C standard leaves it implementation defined as to what
constitutes a volatile access.  The C++ standard omits to specify this,
except to say that C++ should behave in a similar manner to C with
respect to volatiles, where possible.  The minimum either standard
specifies is that at a sequence point all previous accesses to volatile
objects have stabilized and no subsequent accesses have occurred.  Thus
an implementation is free to reorder and combine volatile accesses
which occur between sequence points, but cannot do so for accesses
across a sequence point.  The use of volatiles does not allow you to
violate the restriction on updating objects multiple times within a
sequence point.

 In most expressions, it is intuitively obvious what is a read and what
is a write.  For instance

     volatile int *dst = SOMEVALUE;
     volatile int *src = SOMEOTHERVALUE;
     *dst = *src;

will cause a read of the volatile object pointed to by SRC and stores
the value into the volatile object pointed to by DST.  There is no
guarantee that these reads and writes are atomic, especially for objects
larger than `int'.

 Less obvious expressions are where something which looks like an access
is used in a void context.  An example would be,

     volatile int *src = SOMEVALUE;
     *src;

 With C, such expressions are rvalues, and as rvalues cause a read of
the object, GCC interprets this as a read of the volatile being pointed
to.  The C++ standard specifies that such expressions do not undergo
lvalue to rvalue conversion, and that the type of the dereferenced
object may be incomplete.  The C++ standard does not specify explicitly
that it is this lvalue to rvalue conversion which is responsible for
causing an access.  However, there is reason to believe that it is,
because otherwise certain simple expressions become undefined.  However,
because it would surprise most programmers, G++ treats dereferencing a
pointer to volatile object of complete type in a void context as a read
of the object.  When the object has incomplete type, G++ issues a
warning.

     struct S;
     struct T {int m;};
     volatile S *ptr1 = SOMEVALUE;
     volatile T *ptr2 = SOMEVALUE;
     *ptr1;
     *ptr2;

 In this example, a warning is issued for `*ptr1', and `*ptr2' causes a
read of the object pointed to.  If you wish to force an error on the
first case, you must force a conversion to rvalue with, for instance a
static cast, `static_cast<S>(*ptr1)'.

 When using a reference to volatile, G++ does not treat equivalent
expressions as accesses to volatiles, but instead issues a warning that
no volatile is accessed.  The rationale for this is that otherwise it
becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile
references.  Again, if you wish to force a read, cast the reference to
an rvalue.


File: gcc,  Node: Restricted Pointers,  Next: Vague Linkage,  Prev: Volatiles,  Up: C++ Extensions

6.3 Restricting Pointer Aliasing
================================

As with the C front end, G++ understands the C99 feature of restricted
pointers, specified with the `__restrict__', or `__restrict' type
qualifier.  Because you cannot compile C++ by specifying the `-std=c99'
language flag, `restrict' is not a keyword in C++.

 In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the
local context.

     void fn (int *__restrict__ rptr, int &__restrict__ rref)
     {
       /* ... */
     }

In the body of `fn', RPTR points to an unaliased integer and RREF
refers to a (different) unaliased integer.

 You may also specify whether a member function's THIS pointer is
unaliased by using `__restrict__' as a member function qualifier.

     void T::fn () __restrict__
     {
       /* ... */
     }

Within the body of `T::fn', THIS will have the effective definition `T
*__restrict__ const this'.  Notice that the interpretation of a
`__restrict__' member function qualifier is different to that of
`const' or `volatile' qualifier, in that it is applied to the pointer
rather than the object.  This is consistent with other compilers which
implement restricted pointers.

 As with all outermost parameter qualifiers, `__restrict__' is ignored
in function definition matching.  This means you only need to specify
`__restrict__' in a function definition, rather than in a function
prototype as well.


File: gcc,  Node: Vague Linkage,  Next: C++ Interface,  Prev: Restricted Pointers,  Up: C++ Extensions

6.4 Vague Linkage
=================

There are several constructs in C++ which require space in the object
file but are not clearly tied to a single translation unit.  We say that
these constructs have "vague linkage".  Typically such constructs are
emitted wherever they are needed, though sometimes we can be more
clever.

Inline Functions
     Inline functions are typically defined in a header file which can
     be included in many different compilations.  Hopefully they can
     usually be inlined, but sometimes an out-of-line copy is
     necessary, if the address of the function is taken or if inlining
     fails.  In general, we emit an out-of-line copy in all translation
     units where one is needed.  As an exception, we only emit inline
     virtual functions with the vtable, since it will always require a
     copy.

     Local static variables and string constants used in an inline
     function are also considered to have vague linkage, since they
     must be shared between all inlined and out-of-line instances of
     the function.

VTables
     C++ virtual functions are implemented in most compilers using a
     lookup table, known as a vtable.  The vtable contains pointers to
     the virtual functions provided by a class, and each object of the
     class contains a pointer to its vtable (or vtables, in some
     multiple-inheritance situations).  If the class declares any
     non-inline, non-pure virtual functions, the first one is chosen as
     the "key method" for the class, and the vtable is only emitted in
     the translation unit where the key method is defined.

     _Note:_ If the chosen key method is later defined as inline, the
     vtable will still be emitted in every translation unit which
     defines it.  Make sure that any inline virtuals are declared
     inline in the class body, even if they are not defined there.

type_info objects
     C++ requires information about types to be written out in order to
     implement `dynamic_cast', `typeid' and exception handling.  For
     polymorphic classes (classes with virtual functions), the type_info
     object is written out along with the vtable so that `dynamic_cast'
     can determine the dynamic type of a class object at runtime.  For
     all other types, we write out the type_info object when it is
     used: when applying `typeid' to an expression, throwing an object,
     or referring to a type in a catch clause or exception
     specification.

Template Instantiations
     Most everything in this section also applies to template
     instantiations, but there are other options as well.  *Note
     Where's the Template?: Template Instantiation.


 When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time.  This is known as
COMDAT support.

 On targets that don't support COMDAT, but do support weak symbols, GCC
will use them.  This way one copy will override all the others, but the
unused copies will still take up space in the executable.

 For targets which do not support either COMDAT or weak symbols, most
entities with vague linkage will be emitted as local symbols to avoid
duplicate definition errors from the linker.  This will not happen for
local statics in inlines, however, as having multiple copies will
almost certainly break things.

 *Note Declarations and Definitions in One Header: C++ Interface, for
another way to control placement of these constructs.


File: gcc,  Node: C++ Interface,  Next: Template Instantiation,  Prev: Vague Linkage,  Up: C++ Extensions

6.5 Declarations and Definitions in One Header
==============================================

C++ object definitions can be quite complex.  In principle, your source
code will need two kinds of things for each object that you use across
more than one source file.  First, you need an "interface"
specification, describing its structure with type declarations and
function prototypes.  Second, you need the "implementation" itself.  It
can be tedious to maintain a separate interface description in a header
file, in parallel to the actual implementation.  It is also dangerous,
since separate interface and implementation definitions may not remain
parallel.

 With GNU C++, you can use a single header file for both purposes.

     _Warning:_ The mechanism to specify this is in transition.  For the
     nonce, you must use one of two `#pragma' commands; in a future
     release of GNU C++, an alternative mechanism will make these
     `#pragma' commands unnecessary.

 The header file contains the full definitions, but is marked with
`#pragma interface' in the source code.  This allows the compiler to
use the header file only as an interface specification when ordinary
source files incorporate it with `#include'.  In the single source file
where the full implementation belongs, you can use either a naming
convention or `#pragma implementation' to indicate this alternate use
of the header file.

`#pragma interface'
`#pragma interface "SUBDIR/OBJECTS.h"'
     Use this directive in _header files_ that define object classes,
     to save space in most of the object files that use those classes.
     Normally, local copies of certain information (backup copies of
     inline member functions, debugging information, and the internal
     tables that implement virtual functions) must be kept in each
     object file that includes class definitions.  You can use this
     pragma to avoid such duplication.  When a header file containing
     `#pragma interface' is included in a compilation, this auxiliary
     information will not be generated (unless the main input source
     file itself uses `#pragma implementation').  Instead, the object
     files will contain references to be resolved at link time.

     The second form of this directive is useful for the case where you
     have multiple headers with the same name in different directories.
     If you use this form, you must specify the same string to `#pragma
     implementation'.

`#pragma implementation'
`#pragma implementation "OBJECTS.h"'
     Use this pragma in a _main input file_, when you want full output
     from included header files to be generated (and made globally
     visible).  The included header file, in turn, should use `#pragma
     interface'.  Backup copies of inline member functions, debugging
     information, and the internal tables used to implement virtual
     functions are all generated in implementation files.

     If you use `#pragma implementation' with no argument, it applies to
     an include file with the same basename(1) as your source file.
     For example, in `allclass.cc', giving just `#pragma implementation'
     by itself is equivalent to `#pragma implementation "allclass.h"'.

     In versions of GNU C++ prior to 2.6.0 `allclass.h' was treated as
     an implementation file whenever you would include it from
     `allclass.cc' even if you never specified `#pragma
     implementation'.  This was deemed to be more trouble than it was
     worth, however, and disabled.

     If you use an explicit `#pragma implementation', it must appear in
     your source file _before_ you include the affected header files.

     Use the string argument if you want a single implementation file to
     include code from multiple header files.  (You must also use
     `#include' to include the header file; `#pragma implementation'
     only specifies how to use the file--it doesn't actually include
     it.)

     There is no way to split up the contents of a single header file
     into multiple implementation files.

 `#pragma implementation' and `#pragma interface' also have an effect
on function inlining.

 If you define a class in a header file marked with `#pragma
interface', the effect on a function defined in that class is similar to
an explicit `extern' declaration--the compiler emits no code at all to
define an independent version of the function.  Its definition is used
only for inlining with its callers.

 Conversely, when you include the same header file in a main source file
that declares it as `#pragma implementation', the compiler emits code
for the function itself; this defines a version of the function that
can be found via pointers (or by callers compiled without inlining).
If all calls to the function can be inlined, you can avoid emitting the
function by compiling with `-fno-implement-inlines'.  If any calls were
not inlined, you will get linker errors.

 ---------- Footnotes ----------

 (1) A file's "basename" was the name stripped of all leading path
information and of trailing suffixes, such as `.h' or `.C' or `.cc'.


File: gcc,  Node: Template Instantiation,  Next: Bound member functions,  Prev: C++ Interface,  Up: C++ Extensions

6.6 Where's the Template?
=========================

C++ templates are the first language feature to require more
intelligence from the environment than one usually finds on a UNIX
system.  Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise.  There are two basic approaches to this
problem, which I will refer to as the Borland model and the Cfront
model.

Borland model
     Borland C++ solved the template instantiation problem by adding
     the code equivalent of common blocks to their linker; the compiler
     emits template instances in each translation unit that uses them,
     and the linker collapses them together.  The advantage of this
     model is that the linker only has to consider the object files
     themselves; there is no external complexity to worry about.  This
     disadvantage is that compilation time is increased because the
     template code is being compiled repeatedly.  Code written for this
     model tends to include definitions of all templates in the header
     file, since they must be seen to be instantiated.

Cfront model
     The AT&T C++ translator, Cfront, solved the template instantiation
     problem by creating the notion of a template repository, an
     automatically maintained place where template instances are
     stored.  A more modern version of the repository works as follows:
     As individual object files are built, the compiler places any
     template definitions and instantiations encountered in the
     repository.  At link time, the link wrapper adds in the objects in
     the repository and compiles any needed instances that were not
     previously emitted.  The advantages of this model are more optimal
     compilation speed and the ability to use the system linker; to
     implement the Borland model a compiler vendor also needs to
     replace the linker.  The disadvantages are vastly increased
     complexity, and thus potential for error; for some code this can be
     just as transparent, but in practice it can been very difficult to
     build multiple programs in one directory and one program in
     multiple directories.  Code written for this model tends to
     separate definitions of non-inline member templates into a
     separate file, which should be compiled separately.

 When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the
Borland model.  On other systems, G++ implements neither automatic
model.

 A future version of G++ will support a hybrid model whereby the
compiler will emit any instantiations for which the template definition
is included in the compile, and store template definitions and
instantiation context information into the object file for the rest.
The link wrapper will extract that information as necessary and invoke
the compiler to produce the remaining instantiations.  The linker will
then combine duplicate instantiations.

 In the mean time, you have the following options for dealing with
template instantiations:

  1. Compile your template-using code with `-frepo'.  The compiler will
     generate files with the extension `.rpo' listing all of the
     template instantiations used in the corresponding object files
     which could be instantiated there; the link wrapper, `collect2',
     will then update the `.rpo' files to tell the compiler where to
     place those instantiations and rebuild any affected object files.
     The link-time overhead is negligible after the first pass, as the
     compiler will continue to place the instantiations in the same
     files.

     This is your best option for application code written for the
     Borland model, as it will just work.  Code written for the Cfront
     model will need to be modified so that the template definitions
     are available at one or more points of instantiation; usually this
     is as simple as adding `#include <tmethods.cc>' to the end of each
     template header.

     For library code, if you want the library to provide all of the
     template instantiations it needs, just try to link all of its
     object files together; the link will fail, but cause the
     instantiations to be generated as a side effect.  Be warned,
     however, that this may cause conflicts if multiple libraries try
     to provide the same instantiations.  For greater control, use
     explicit instantiation as described in the next option.

  2. Compile your code with `-fno-implicit-templates' to disable the
     implicit generation of template instances, and explicitly
     instantiate all the ones you use.  This approach requires more
     knowledge of exactly which instances you need than do the others,
     but it's less mysterious and allows greater control.  You can
     scatter the explicit instantiations throughout your program,
     perhaps putting them in the translation units where the instances
     are used or the translation units that define the templates
     themselves; you can put all of the explicit instantiations you
     need into one big file; or you can create small files like

          #include "Foo.h"
          #include "Foo.cc"

          template class Foo<int>;
          template ostream& operator <<
                          (ostream&, const Foo<int>&);

     for each of the instances you need, and create a template
     instantiation library from those.

     If you are using Cfront-model code, you can probably get away with
     not using `-fno-implicit-templates' when compiling files that don't
     `#include' the member template definitions.

     If you use one big file to do the instantiations, you may want to
     compile it without `-fno-implicit-templates' so you get all of the
     instances required by your explicit instantiations (but not by any
     other files) without having to specify them as well.

     G++ has extended the template instantiation syntax given in the ISO
     standard to allow forward declaration of explicit instantiations
     (with `extern'), instantiation of the compiler support data for a
     template class (i.e. the vtable) without instantiating any of its
     members (with `inline'), and instantiation of only the static data
     members of a template class, without the support data or member
     functions (with (`static'):

          extern template int max (int, int);
          inline template class Foo<int>;
          static template class Foo<int>;

  3. Do nothing.  Pretend G++ does implement automatic instantiation
     management.  Code written for the Borland model will work fine, but
     each translation unit will contain instances of each of the
     templates it uses.  In a large program, this can lead to an
     unacceptable amount of code duplication.

     *Note Declarations and Definitions in One Header: C++ Interface,
     for more discussion of these pragmas.


File: gcc,  Node: Bound member functions,  Next: C++ Attributes,  Prev: Template Instantiation,  Up: C++ Extensions

6.7 Extracting the function pointer from a bound pointer to member function
===========================================================================

In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the `this' pointer, and
if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function.  If you are using
PMFs in an inner loop, you should really reconsider that decision.  If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.

 Note that you will still be paying the penalty for the call through a
function pointer; on most modern architectures, such a call defeats the
branch prediction features of the CPU.  This is also true of normal
virtual function calls.

 The syntax for this extension is

     extern A a;
     extern int (A::*fp)();
     typedef int (*fptr)(A *);

     fptr p = (fptr)(a.*fp);

 For PMF constants (i.e. expressions of the form `&Klasse::Member'), no
object is needed to obtain the address of the function.  They can be
converted to function pointers directly:

     fptr p1 = (fptr)(&A::foo);

 You must specify `-Wno-pmf-conversions' to use this extension.


File: gcc,  Node: C++ Attributes,  Next: Strong Using,  Prev: Bound member functions,  Up: C++ Extensions

6.8 C++-Specific Variable, Function, and Type Attributes
========================================================

Some attributes only make sense for C++ programs.

`init_priority (PRIORITY)'
     In Standard C++, objects defined at namespace scope are guaranteed
     to be initialized in an order in strict accordance with that of
     their definitions _in a given translation unit_.  No guarantee is
     made for initializations across translation units.  However, GNU
     C++ allows users to control the order of initialization of objects
     defined at namespace scope with the `init_priority' attribute by
     specifying a relative PRIORITY, a constant integral expression
     currently bounded between 101 and 65535 inclusive.  Lower numbers
     indicate a higher priority.

     In the following example, `A' would normally be created before
     `B', but the `init_priority' attribute has reversed that order:

          Some_Class  A  __attribute__ ((init_priority (2000)));
          Some_Class  B  __attribute__ ((init_priority (543)));

     Note that the particular values of PRIORITY do not matter; only
     their relative ordering.

`java_interface'
     This type attribute informs C++ that the class is a Java
     interface.  It may only be applied to classes declared within an
     `extern "Java"' block.  Calls to methods declared in this
     interface will be dispatched using GCJ's interface table
     mechanism, instead of regular virtual table dispatch.


 See also *Note Strong Using::.


File: gcc,  Node: Strong Using,  Next: Offsetof,  Prev: C++ Attributes,  Up: C++ Extensions

6.9 Strong Using
================

*Caution:* The semantics of this extension are not fully defined.
Users should refrain from using this extension as its semantics may
change subtly over time.  It is possible that this extension wil be
removed in future versions of G++.

 A using-directive with `__attribute ((strong))' is stronger than a
normal using-directive in two ways:

   * Templates from the used namespace can be specialized as though
     they were members of the using namespace.

   * The using namespace is considered an associated namespace of all
     templates in the used namespace for purposes of argument-dependent
     name lookup.

 This is useful for composing a namespace transparently from
implementation namespaces.  For example:

     namespace std {
       namespace debug {
         template <class T> struct A { };
       }
       using namespace debug __attribute ((__strong__));
       template <> struct A<int> { };   // ok to specialize

       template <class T> void f (A<T>);
     }

     int main()
     {
       f (std::A<float>());             // lookup finds std::f
       f (std::A<int>());
     }


File: gcc,  Node: Offsetof,  Next: Java Exceptions,  Prev: Strong Using,  Up: C++ Extensions

6.10 Offsetof
=============

G++ uses a syntactic extension to implement the `offsetof' macro.

 In particular:

       __offsetof__ (expression)

 is equivalent to the parenthesized expression, except that the
expression is considered an integral constant expression even if it
contains certain operators that are not normally permitted in an
integral constant expression.  Users should never use `__offsetof__'
directly; the only valid use of `__offsetof__' is to implement the
`offsetof' macro in `<stddef.h>'.


File: gcc,  Node: Java Exceptions,  Next: Deprecated Features,  Prev: Offsetof,  Up: C++ Extensions

6.11 Java Exceptions
====================

The Java language uses a slightly different exception handling model
from C++.  Normally, GNU C++ will automatically detect when you are
writing C++ code that uses Java exceptions, and handle them
appropriately.  However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC will guess incorrectly.
Sample problematic code is:

       struct S { ~S(); };
       extern void bar();    // is written in Java, and may throw exceptions
       void foo()
       {
         S s;
         bar();
       }

The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called `__gxx_personality_v0'.

 You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
`#pragma GCC java_exceptions' at the head of the file.  This `#pragma'
must appear before any functions that throw or catch exceptions, or run
destructors when exceptions are thrown through them.

 You cannot mix Java and C++ exceptions in the same translation unit.
It is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.


File: gcc,  Node: Deprecated Features,  Next: Backwards Compatibility,  Prev: Java Exceptions,  Up: C++ Extensions

6.12 Deprecated Features
========================

In the past, the GNU C++ compiler was extended to experiment with new
features, at a time when the C++ language was still evolving.  Now that
the C++ standard is complete, some of those features are superseded by
superior alternatives.  Using the old features might cause a warning in
some cases that the feature will be dropped in the future.  In other
cases, the feature might be gone already.

 While the list below is not exhaustive, it documents some of the
options that are now deprecated:

`-fexternal-templates'
`-falt-external-templates'
     These are two of the many ways for G++ to implement template
     instantiation.  *Note Template Instantiation::.  The C++ standard
     clearly defines how template definitions have to be organized
     across implementation units.  G++ has an implicit instantiation
     mechanism that should work just fine for standard-conforming code.

`-fstrict-prototype'
`-fno-strict-prototype'
     Previously it was possible to use an empty prototype parameter
     list to indicate an unspecified number of parameters (like C),
     rather than no parameters, as C++ demands.  This feature has been
     removed, except where it is required for backwards compatibility
     *Note Backwards Compatibility::.

 The named return value extension has been deprecated, and is now
removed from G++.

 The use of initializer lists with new expressions has been deprecated,
and is now removed from G++.

 Floating and complex non-type template parameters have been deprecated,
and are now removed from G++.

 The implicit typename extension has been deprecated and is now removed
from G++.

 The use of default arguments in function pointers, function typedefs
and and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.


File: gcc,  Node: Backwards Compatibility,  Prev: Deprecated Features,  Up: C++ Extensions

6.13 Backwards Compatibility
============================

Now that there is a definitive ISO standard C++, G++ has a specification
to adhere to.  The C++ language evolved over time, and features that
used to be acceptable in previous drafts of the standard, such as the
ARM [Annotated C++ Reference Manual], are no longer accepted.  In order
to allow compilation of C++ written to such drafts, G++ contains some
backwards compatibilities.  _All such backwards compatibility features
are liable to disappear in future versions of G++._ They should be
considered deprecated *Note Deprecated Features::.

`For scope'
     If a variable is declared at for scope, it used to remain in scope
     until the end of the scope which contained the for statement
     (rather than just within the for scope).  G++ retains this, but
     issues a warning, if such a variable is accessed outside the for
     scope.

`Implicit C language'
     Old C system header files did not contain an `extern "C" {...}'
     scope to set the language.  On such systems, all header files are
     implicitly scoped inside a C language scope.  Also, an empty
     prototype `()' will be treated as an unspecified number of
     arguments, rather than no arguments, as C++ demands.


File: gcc,  Node: Objective-C,  Next: Compatibility,  Prev: C++ Extensions,  Up: Top

7 GNU Objective-C runtime features
**********************************

This document is meant to describe some of the GNU Objective-C runtime
features.  It is not intended to teach you Objective-C, there are
several resources on the Internet that present the language.  Questions
and comments about this document to Ovidiu Predescu <[e-mail]>.

* Menu:

* Executing code before main::
* Type encoding::
* Garbage Collection::
* Constant string objects::
* compatibility_alias::


File: gcc,  Node: Executing code before main,  Next: Type encoding,  Prev: Objective-C,  Up: Objective-C

7.1 `+load': Executing code before main
=======================================

The GNU Objective-C runtime provides a way that allows you to execute
code before the execution of the program enters the `main' function.
The code is executed on a per-class and a per-category basis, through a
special class method `+load'.

 This facility is very useful if you want to initialize global variables
which can be accessed by the program directly, without sending a message
to the class first.  The usual way to initialize global variables, in
the `+initialize' method, might not be useful because `+initialize' is
only called when the first message is sent to a class object, which in
some cases could be too late.

 Suppose for example you have a `FileStream' class that declares
`Stdin', `Stdout' and `Stderr' as global variables, like below:


     FileStream *Stdin = nil;
     FileStream *Stdout = nil;
     FileStream *Stderr = nil;

     @implementation FileStream

     + (void)initialize
     {
         Stdin = [[FileStream new] initWithFd:0];
         Stdout = [[FileStream new] initWithFd:1];
         Stderr = [[FileStream new] initWithFd:2];
     }

     /* Other methods here */
     @end

 In this example, the initialization of `Stdin', `Stdout' and `Stderr'
in `+initialize' occurs too late.  The programmer can send a message to
one of these objects before the variables are actually initialized,
thus sending messages to the `nil' object.  The `+initialize' method
which actually initializes the global variables is not invoked until
the first message is sent to the class object.  The solution would
require these variables to be initialized just before entering `main'.

 The correct solution of the above problem is to use the `+load' method
instead of `+initialize':


     @implementation FileStream

     + (void)load
     {
         Stdin = [[FileStream new] initWithFd:0];
         Stdout = [[FileStream new] initWithFd:1];
         Stderr = [[FileStream new] initWithFd:2];
     }

     /* Other methods here */
     @end

 The `+load' is a method that is not overridden by categories.  If a
class and a category of it both implement `+load', both methods are
invoked.  This allows some additional initializations to be performed in
a category.

 This mechanism is not intended to be a replacement for `+initialize'.
You should be aware of its limitations when you decide to use it
instead of `+initialize'.

* Menu:

* What you can and what you cannot do in +load::


File: gcc,  Node: What you can and what you cannot do in +load,  Prev: Executing code before main,  Up: Executing code before main

7.1.1 What you can and what you cannot do in `+load'
----------------------------------------------------

The `+load' implementation in the GNU runtime guarantees you the
following things:

   * you can write whatever C code you like;

   * you can send messages to Objective-C constant strings (`@"this is a
     constant string"');

   * you can allocate and send messages to objects whose class is
     implemented in the same file;

   * the `+load' implementation of all super classes of a class are
     executed before the `+load' of that class is executed;

   * the `+load' implementation of a class is executed before the
     `+load' implementation of any category.


 In particular, the following things, even if they can work in a
particular case, are not guaranteed:

   * allocation of or sending messages to arbitrary objects;

   * allocation of or sending messages to objects whose classes have a
     category implemented in the same file;


 You should make no assumptions about receiving `+load' in sibling
classes when you write `+load' of a class.  The order in which sibling
classes receive `+load' is not guaranteed.

 The order in which `+load' and `+initialize' are called could be
problematic if this matters.  If you don't allocate objects inside
`+load', it is guaranteed that `+load' is called before `+initialize'.
If you create an object inside `+load' the `+initialize' method of
object's class is invoked even if `+load' was not invoked.  Note if you
explicitly call `+load' on a class, `+initialize' will be called first.
To avoid possible problems try to implement only one of these methods.

 The `+load' method is also invoked when a bundle is dynamically loaded
into your running program.  This happens automatically without any
intervening operation from you.  When you write bundles and you need to
write `+load' you can safely create and send messages to objects whose
classes already exist in the running program.  The same restrictions as
above apply to classes defined in bundle.


File: gcc,  Node: Type encoding,  Next: Garbage Collection,  Prev: Executing code before main,  Up: Objective-C

7.2 Type encoding
=================

The Objective-C compiler generates type encodings for all the types.
These type encodings are used at runtime to find out information about
selectors and methods and about objects and classes.

 The types are encoded in the following way:

`char'             `c'
`unsigned char'    `C'
`short'            `s'
`unsigned short'   `S'
`int'              `i'
`unsigned int'     `I'
`long'             `l'
`unsigned long'    `L'
`long long'        `q'
`unsigned long     `Q'
long'
`float'            `f'
`double'           `d'
`void'             `v'
`id'               `@'
`Class'            `#'
`SEL'              `:'
`char*'            `*'
unknown type       `?'
bit-fields         `b' followed by the starting position of the
                   bit-field, the type of the bit-field and the size of
                   the bit-field (the bit-fields encoding was changed
                   from the NeXT's compiler encoding, see below)

 The encoding of bit-fields has changed to allow bit-fields to be
properly handled by the runtime functions that compute sizes and
alignments of types that contain bit-fields.  The previous encoding
contained only the size of the bit-field.  Using only this information
it is not possible to reliably compute the size occupied by the
bit-field.  This is very important in the presence of the Boehm's
garbage collector because the objects are allocated using the typed
memory facility available in this collector.  The typed memory
allocation requires information about where the pointers are located
inside the object.

 The position in the bit-field is the position, counting in bits, of the
bit closest to the beginning of the structure.

 The non-atomic types are encoded as follows:

pointers       `^' followed by the pointed type.
arrays         `[' followed by the number of elements in the array
               followed by the type of the elements followed by `]'
structures     `{' followed by the name of the structure (or `?' if the
               structure is unnamed), the `=' sign, the type of the
               members and by `}'
unions         `(' followed by the name of the structure (or `?' if the
               union is unnamed), the `=' sign, the type of the members
               followed by `)'

 Here are some types and their encodings, as they are generated by the
compiler on an i386 machine:


Objective-C type   Compiler encoding
     int a[10];    `[10i]'
     struct {      `{?=i[3f]b128i3b131i2c}'
       int i;
       float f[3];
       int a:3;
       int b:2;
       char c;
     }


 In addition to the types the compiler also encodes the type
specifiers.  The table below describes the encoding of the current
Objective-C type specifiers:


Specifier          Encoding
`const'            `r'
`in'               `n'
`inout'            `N'
`out'              `o'
`bycopy'           `O'
`oneway'           `V'


 The type specifiers are encoded just before the type.  Unlike types
however, the type specifiers are only encoded when they appear in method
argument types.


File: gcc,  Node: Garbage Collection,  Next: Constant string objects,  Prev: Type encoding,  Up: Objective-C

7.3 Garbage Collection
======================

Support for a new memory management policy has been added by using a
powerful conservative garbage collector, known as the
Boehm-Demers-Weiser conservative garbage collector.  It is available
from `http://www.hpl.hp.com/personal/Hans_Boehm/gc/'.

 To enable the support for it you have to configure the compiler using
an additional argument, `--enable-objc-gc'.  You need to have garbage
collector installed before building the compiler.  This will build an
additional runtime library which has several enhancements to support
the garbage collector.  The new library has a new name, `libobjc_gc.a'
to not conflict with the non-garbage-collected library.

 When the garbage collector is used, the objects are allocated using the
so-called typed memory allocation mechanism available in the
Boehm-Demers-Weiser collector.  This mode requires precise information
on where pointers are located inside objects.  This information is
computed once per class, immediately after the class has been
initialized.

 There is a new runtime function `class_ivar_set_gcinvisible()' which
can be used to declare a so-called "weak pointer" reference.  Such a
pointer is basically hidden for the garbage collector; this can be
useful in certain situations, especially when you want to keep track of
the allocated objects, yet allow them to be collected.  This kind of
pointers can only be members of objects, you cannot declare a global
pointer as a weak reference.  Every type which is a pointer type can be
declared a weak pointer, including `id', `Class' and `SEL'.

 Here is an example of how to use this feature.  Suppose you want to
implement a class whose instances hold a weak pointer reference; the
following class does this:


     @interface WeakPointer : Object
     {
         const void* weakPointer;
     }

     - initWithPointer:(const void*)p;
     - (const void*)weakPointer;
     @end


     @implementation WeakPointer

     + (void)initialize
     {
       class_ivar_set_gcinvisible (self, "weakPointer", YES);
     }

     - initWithPointer:(const void*)p
     {
       weakPointer = p;
       return self;
     }

     - (const void*)weakPointer
     {
       return weakPointer;
     }

     @end

 Weak pointers are supported through a new type character specifier
represented by the `!' character.  The `class_ivar_set_gcinvisible()'
function adds or removes this specifier to the string type description
of the instance variable named as argument.


File: gcc,  Node: Constant string objects,  Next: compatibility_alias,  Prev: Garbage Collection,  Up: Objective-C

7.4 Constant string objects
===========================

GNU Objective-C provides constant string objects that are generated
directly by the compiler.  You declare a constant string object by
prefixing a C constant string with the character `@':

       id myString = @"this is a constant string object";

 The constant string objects are by default instances of the
`NXConstantString' class which is provided by the GNU Objective-C
runtime.  To get the definition of this class you must include the
`objc/NXConstStr.h' header file.

 User defined libraries may want to implement their own constant string
class.  To be able to support them, the GNU Objective-C compiler
provides a new command line options
`-fconstant-string-class=CLASS-NAME'.  The provided class should adhere
to a strict structure, the same as `NXConstantString''s structure:


     @interface MyConstantStringClass
     {
       Class isa;
       char *c_string;
       unsigned int len;
     }
     @end

 `NXConstantString' inherits from `Object'; user class libraries may
choose to inherit the customized constant string class from a different
class than `Object'.  There is no requirement in the methods the
constant string class has to implement, but the final ivar layout of
the class must be the compatible with the given structure.

 When the compiler creates the statically allocated constant string
object, the `c_string' field will be filled by the compiler with the
string; the `length' field will be filled by the compiler with the
string length; the `isa' pointer will be filled with `NULL' by the
compiler, and it will later be fixed up automatically at runtime by the
GNU Objective-C runtime library to point to the class which was set by
the `-fconstant-string-class' option when the object file is loaded (if
you wonder how it works behind the scenes, the name of the class to
use, and the list of static objects to fixup, are stored by the
compiler in the object file in a place where the GNU runtime library
will find them at runtime).

 As a result, when a file is compiled with the
`-fconstant-string-class' option, all the constant string objects will
be instances of the class specified as argument to this option.  It is
possible to have multiple compilation units referring to different
constant string classes, neither the compiler nor the linker impose any
restrictions in doing this.


File: gcc,  Node: compatibility_alias,  Prev: Constant string objects,  Up: Objective-C

7.5 compatibility_alias
=======================

This is a feature of the Objective-C compiler rather than of the
runtime, anyway since it is documented nowhere and its existence was
forgotten, we are documenting it here.

 The keyword `@compatibility_alias' allows you to define a class name
as equivalent to another class name.  For example:

     @compatibility_alias WOApplication GSWApplication;

 tells the compiler that each time it encounters `WOApplication' as a
class name, it should replace it with `GSWApplication' (that is,
`WOApplication' is just an alias for `GSWApplication').

 There are some constraints on how this can be used--

   * `WOApplication' (the alias) must not be an existing class;

   * `GSWApplication' (the real class) must be an existing class.



File: gcc,  Node: Compatibility,  Next: Gcov,  Prev: Objective-C,  Up: Top

8 Binary Compatibility
**********************

Binary compatibility encompasses several related concepts:

"application binary interface (ABI)"
     The set of runtime conventions followed by all of the tools that
     deal with binary representations of a program, including
     compilers, assemblers, linkers, and language runtime support.
     Some ABIs are formal with a written specification, possibly
     designed by multiple interested parties.  Others are simply the
     way things are actually done by a particular set of tools.

"ABI conformance"
     A compiler conforms to an ABI if it generates code that follows
     all of the specifications enumerated by that ABI.  A library
     conforms to an ABI if it is implemented according to that ABI.  An
     application conforms to an ABI if it is built using tools that
     conform to that ABI and does not contain source code that
     specifically changes behavior specified by the ABI.

"calling conventions"
     Calling conventions are a subset of an ABI that specify of how
     arguments are passed and function results are returned.

"interoperability"
     Different sets of tools are interoperable if they generate files
     that can be used in the same program.  The set of tools includes
     compilers, assemblers, linkers, libraries, header files, startup
     files, and debuggers.  Binaries produced by different sets of
     tools are not interoperable unless they implement the same ABI.
     This applies to different versions of the same tools as well as
     tools from different vendors.

"intercallability"
     Whether a function in a binary built by one set of tools can call a
     function in a binary built by a different set of tools is a subset
     of interoperability.

"implementation-defined features"
     Language standards include lists of implementation-defined
     features whose behavior can vary from one implementation to
     another.  Some of these features are normally covered by a
     platform's ABI and others are not.  The features that are not
     covered by an ABI generally affect how a program behaves, but not
     intercallability.

"compatibility"
     Conformance to the same ABI and the same behavior of
     implementation-defined features are both relevant for
     compatibility.

 The application binary interface implemented by a C or C++ compiler
affects code generation and runtime support for:

   * size and alignment of data types

   * layout of structured types

   * calling conventions

   * register usage conventions

   * interfaces for runtime arithmetic support

   * object file formats

 In addition, the application binary interface implemented by a C++
compiler affects code generation and runtime support for:
   * name mangling

   * exception handling

   * invoking constructors and destructors

   * layout, alignment, and padding of classes

   * layout and alignment of virtual tables

 Some GCC compilation options cause the compiler to generate code that
does not conform to the platform's default ABI.  Other options cause
different program behavior for implementation-defined features that are
not covered by an ABI.  These options are provided for consistency with
other compilers that do not follow the platform's default ABI or the
usual behavior of implementation-defined features for the platform.  Be
very careful about using such options.

 Most platforms have a well-defined ABI that covers C code, but ABIs
that cover C++ functionality are not yet common.

 Starting with GCC 3.2, GCC binary conventions for C++ are based on a
written, vendor-neutral C++ ABI that was designed to be specific to
64-bit Itanium but also includes generic specifications that apply to
any platform.  This C++ ABI is also implemented by other compiler
vendors on some platforms, notably GNU/Linux and BSD systems.  We have
tried hard to provide a stable ABI that will be compatible with future
GCC releases, but it is possible that we will encounter problems that
make this difficult.  Such problems could include different
interpretations of the C++ ABI by different vendors, bugs in the ABI, or
bugs in the implementation of the ABI in different compilers.  GCC's
`-Wabi' switch warns when G++ generates code that is probably not
compatible with the C++ ABI.

 The C++ library used with a C++ compiler includes the Standard C++
Library, with functionality defined in the C++ Standard, plus language
runtime support.  The runtime support is included in a C++ ABI, but
there is no formal ABI for the Standard C++ Library.  Two
implementations of that library are interoperable if one follows the
de-facto ABI of the other and if they are both built with the same
compiler, or with compilers that conform to the same ABI for C++
compiler and runtime support.

 When G++ and another C++ compiler conform to the same C++ ABI, but the
implementations of the Standard C++ Library that they normally use do
not follow the same ABI for the Standard C++ Library, object files
built with those compilers can be used in the same program only if they
use the same C++ library.  This requires specifying the location of the
C++ library header files when invoking the compiler whose usual library
is not being used.  The location of GCC's C++ header files depends on
how the GCC build was configured, but can be seen by using the G++ `-v'
option.  With default configuration options for G++ 3.3 the compile
line for a different C++ compiler needs to include

         -IGCC_INSTALL_DIRECTORY/include/c++/3.3

 Similarly, compiling code with G++ that must use a C++ library other
than the GNU C++ library requires specifying the location of the header
files for that other library.

 The most straightforward way to link a program to use a particular C++
library is to use a C++ driver that specifies that C++ library by
default.  The `g++' driver, for example, tells the linker where to find
GCC's C++ library (`libstdc++') plus the other libraries and startup
files it needs, in the proper order.

 If a program must use a different C++ library and it's not possible to
do the final link using a C++ driver that uses that library by default,
it is necessary to tell `g++' the location and name of that library.
It might also be necessary to specify different startup files and other
runtime support libraries, and to suppress the use of GCC's support
libraries with one or more of the options `-nostdlib', `-nostartfiles',
and `-nodefaultlibs'.


File: gcc,  Node: Gcov,  Next: Trouble,  Prev: Compatibility,  Up: Top

9 `gcov'--a Test Coverage Program
*********************************

`gcov' is a tool you can use in conjunction with GCC to test code
coverage in your programs.

* Menu:

* Gcov Intro::                     Introduction to gcov.
* Invoking Gcov::           How to use gcov.
* Gcov and Optimization::       Using gcov with GCC optimization.
* Gcov Data Files::             The files used by gcov.


File: gcc,  Node: Gcov Intro,  Next: Invoking Gcov,  Up: Gcov

9.1 Introduction to `gcov'
==========================

`gcov' is a test coverage program.  Use it in concert with GCC to
analyze your programs to help create more efficient, faster running
code and to discover untested parts of your program.  You can use
`gcov' as a profiling tool to help discover where your optimization
efforts will best affect your code.  You can also use `gcov' along with
the other profiling tool, `gprof', to assess which parts of your code
use the greatest amount of computing time.

 Profiling tools help you analyze your code's performance.  Using a
profiler such as `gcov' or `gprof', you can find out some basic
performance statistics, such as:

   * how often each line of code executes

   * what lines of code are actually executed

   * how much computing time each section of code uses

 Once you know these things about how your code works when compiled, you
can look at each module to see which modules should be optimized.
`gcov' helps you determine where to work on optimization.

 Software developers also use coverage testing in concert with
testsuites, to make sure software is actually good enough for a release.
Testsuites can verify that a program works as expected; a coverage
program tests to see how much of the program is exercised by the
testsuite.  Developers can then determine what kinds of test cases need
to be added to the testsuites to create both better testing and a better
final product.

 You should compile your code without optimization if you plan to use
`gcov' because the optimization, by combining some lines of code into
one function, may not give you as much information as you need to look
for `hot spots' where the code is using a great deal of computer time.
Likewise, because `gcov' accumulates statistics by line (at the lowest
resolution), it works best with a programming style that places only
one statement on each line.  If you use complicated macros that expand
to loops or to other control structures, the statistics are less
helpful--they only report on the line where the macro call appears.  If
your complex macros behave like functions, you can replace them with
inline functions to solve this problem.

 `gcov' creates a logfile called `SOURCEFILE.gcov' which indicates how
many times each line of a source file `SOURCEFILE.c' has executed.  You
can use these logfiles along with `gprof' to aid in fine-tuning the
performance of your programs.  `gprof' gives timing information you can
use along with the information you get from `gcov'.

 `gcov' works only on code compiled with GCC.  It is not compatible
with any other profiling or test coverage mechanism.


File: gcc,  Node: Invoking Gcov,  Next: Gcov and Optimization,  Prev: Gcov Intro,  Up: Gcov

9.2 Invoking gcov
=================

     gcov [OPTIONS] SOURCEFILE

 `gcov' accepts the following options:

`-h'
`--help'
     Display help about using `gcov' (on the standard output), and exit
     without doing any further processing.

`-v'
`--version'
     Display the `gcov' version number (on the standard output), and
     exit without doing any further processing.

`-a'
`--all-blocks'
     Write individual execution counts for every basic block. Normally
     gcov outputs execution counts only for the main blocks of a line.
     With this option you can determine if blocks within a single line
     are not being executed.

`-b'
`--branch-probabilities'
     Write branch frequencies to the output file, and write branch
     summary info to the standard output.  This option allows you to
     see how often each branch in your program was taken. Unconditional
     branches will not be shown, unless the `-u' option is given.

`-c'
`--branch-counts'
     Write branch frequencies as the number of branches taken, rather
     than the percentage of branches taken.

`-n'
`--no-output'
     Do not create the `gcov' output file.

`-l'
`--long-file-names'
     Create long file names for included source files.  For example, if
     the header file `x.h' contains code, and was included in the file
     `a.c', then running `gcov' on the file `a.c' will produce an
     output file called `a.c##x.h.gcov' instead of `x.h.gcov'.  This
     can be useful if `x.h' is included in multiple source files. If
     you uses the `-p' option, both the including and included file
     names will be complete path names.

`-p'
`--preserve-paths'
     Preserve complete path information in the names of generated
     `.gcov' files. Without this option, just the filename component is
     used. With this option, all directories are used, with '/'
     characters translated to '#' characters, '.' directory components
     removed and '..'  components renamed to '^'. This is useful if
     sourcefiles are in several different directories. It also affects
     the `-l' option.

`-f'
`--function-summaries'
     Output summaries for each function in addition to the file level
     summary.

`-o DIRECTORY|FILE'
`--object-directory DIRECTORY'
`--object-file FILE'
     Specify either the directory containing the gcov data files, or the
     object path name. The `.gcno', and `.gcda' data files are searched
     for using this option. If a directory is specified, the data files
     are in that directory and named after the source file name,
     without its extension. If a file is specified here, the data files
     are named after that file, without its extension. If this option
     is not supplied, it defaults to the current directory.

`-u'
`--unconditional-branches'
     When branch counts are given, include those of unconditional
     branches.  Unconditional branches are normally not interesting.


 `gcov' should be run with the current directory the same as that when
you invoked the compiler. Otherwise it will not be able to locate the
source files. `gcov' produces files called `MANGLEDNAME.gcov' in the
current directory. These contain the coverage information of the source
file they correspond to.  One `.gcov' file is produced for each source
file containing code, which was compiled to produce the data files. The
MANGLEDNAME part of the output file name is usually simply the source
file name, but can be something more complicated if the `-l' or `-p'
options are given. Refer to those options for details.

 The `.gcov' files contain the ':' separated fields along with program
source code. The format is

     EXECUTION_COUNT:LINE_NUMBER:SOURCE LINE TEXT

 Additional block information may succeed each line, when requested by
command line option. The EXECUTION_COUNT is `-' for lines containing no
code and `#####' for lines which were never executed. Some lines of
information at the start have LINE_NUMBER of zero.

 When printing percentages, 0% and 100% are only printed when the values
are _exactly_ 0% and 100% respectively. Other values which would
conventionally be rounded to 0% or 100% are instead printed as the
nearest non-boundary value.

 When using `gcov', you must first compile your program with two
special GCC options: `-fprofile-arcs -ftest-coverage'.  This tells the
compiler to generate additional information needed by gcov (basically a
flow graph of the program) and also includes additional code in the
object files for generating the extra profiling information needed by
gcov.  These additional files are placed in the directory where the
object file is located.

 Running the program will cause profile output to be generated.  For
each source file compiled with `-fprofile-arcs', an accompanying
`.gcda' file will be placed in the object file directory.

 Running `gcov' with your program's source file names as arguments will
now produce a listing of the code along with frequency of execution for
each line.  For example, if your program is called `tmp.c', this is
what you see when you use the basic `gcov' facility:

     $ gcc -fprofile-arcs -ftest-coverage tmp.c
     $ a.out
     $ gcov tmp.c
     90.00% of 10 source lines executed in file tmp.c
     Creating tmp.c.gcov.

 The file `tmp.c.gcov' contains output from `gcov'.  Here is a sample:

             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:int main (void)
     function main called 1 returned 1 blocks executed 75%
             1:    4:{
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i < 10; i++)
            10:   10:    total += i;
             -:   11:
             1:   12:  if (total != 45)
         #####:   13:    printf ("Failure\n");
             -:   14:  else
             1:   15:    printf ("Success\n");
             1:   16:  return 0;
             -:   17:}

 When you use the `-a' option, you will get individual block counts,
and the output looks like this:

             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:int main (void)
     function main called 1 returned 1 blocks executed 75%
             1:    4:{
             1:    4-block  0
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i < 10; i++)
            11:    9-block  0
            10:   10:    total += i;
            10:   10-block  0
             -:   11:
             1:   12:  if (total != 45)
             1:   12-block  0
         #####:   13:    printf ("Failure\n");
         $$$$$:   13-block  0
             -:   14:  else
             1:   15:    printf ("Success\n");
             1:   15-block  0
             1:   16:  return 0;
             1:   16-block  0
             -:   17:}

 In this mode, each basic block is only shown on one line - the last
line of the block. A multi-line block will only contribute to the
execution count of that last line, and other lines will not be shown to
contain code, unless previous blocks end on those lines.  The total
execution count of a line is shown and subsequent lines show the
execution counts for individual blocks that end on that line. After each
block, the branch and call counts of the block will be shown, if the
`-b' option is given.

 Because of the way GCC instruments calls, a call count can be shown
after a line with no individual blocks.  As you can see, line 13
contains a basic block that was not executed.

 When you use the `-b' option, your output looks like this:

     $ gcov -b tmp.c
     90.00% of 10 source lines executed in file tmp.c
     80.00% of 5 branches executed in file tmp.c
     80.00% of 5 branches taken at least once in file tmp.c
     50.00% of 2 calls executed in file tmp.c
     Creating tmp.c.gcov.

 Here is a sample of a resulting `tmp.c.gcov' file:

             -:    0:Source:tmp.c
             -:    0:Graph:tmp.gcno
             -:    0:Data:tmp.gcda
             -:    0:Runs:1
             -:    0:Programs:1
             -:    1:#include <stdio.h>
             -:    2:
             -:    3:int main (void)
     function main called 1 returned 1 blocks executed 75%
             1:    4:{
             1:    5:  int i, total;
             -:    6:
             1:    7:  total = 0;
             -:    8:
            11:    9:  for (i = 0; i < 10; i++)
     branch  0 taken 91% (fallthrough)
     branch  1 taken 9%
            10:   10:    total += i;
             -:   11:
             1:   12:  if (total != 45)
     branch  0 taken 0% (fallthrough)
     branch  1 taken 100%
         #####:   13:    printf ("Failure\n");
     call    0 never executed
             -:   14:  else
             1:   15:    printf ("Success\n");
     call    0 called 1 returned 100%
             1:   16:  return 0;
             -:   17:}

 For each basic block, a line is printed after the last line of the
basic block describing the branch or call that ends the basic block.
There can be multiple branches and calls listed for a single source
line if there are multiple basic blocks that end on that line.  In this
case, the branches and calls are each given a number.  There is no
simple way to map these branches and calls back to source constructs.
In general, though, the lowest numbered branch or call will correspond
to the leftmost construct on the source line.

 For a branch, if it was executed at least once, then a percentage
indicating the number of times the branch was taken divided by the
number of times the branch was executed will be printed.  Otherwise, the
message "never executed" is printed.

 For a call, if it was executed at least once, then a percentage
indicating the number of times the call returned divided by the number
of times the call was executed will be printed.  This will usually be
100%, but may be less for functions call `exit' or `longjmp', and thus
may not return every time they are called.

 The execution counts are cumulative.  If the example program were
executed again without removing the `.gcda' file, the count for the
number of times each line in the source was executed would be added to
the results of the previous run(s).  This is potentially useful in
several ways.  For example, it could be used to accumulate data over a
number of program runs as part of a test verification suite, or to
provide more accurate long-term information over a large number of
program runs.

 The data in the `.gcda' files is saved immediately before the program
exits.  For each source file compiled with `-fprofile-arcs', the
profiling code first attempts to read in an existing `.gcda' file; if
the file doesn't match the executable (differing number of basic block
counts) it will ignore the contents of the file.  It then adds in the
new execution counts and finally writes the data to the file.


File: gcc,  Node: Gcov and Optimization,  Next: Gcov Data Files,  Prev: Invoking Gcov,  Up: Gcov

9.3 Using `gcov' with GCC Optimization
======================================

If you plan to use `gcov' to help optimize your code, you must first
compile your program with two special GCC options: `-fprofile-arcs
-ftest-coverage'.  Aside from that, you can use any other GCC options;
but if you want to prove that every single line in your program was
executed, you should not compile with optimization at the same time.
On some machines the optimizer can eliminate some simple code lines by
combining them with other lines.  For example, code like this:

     if (a != b)
       c = 1;
     else
       c = 0;

can be compiled into one instruction on some machines.  In this case,
there is no way for `gcov' to calculate separate execution counts for
each line because there isn't separate code for each line.  Hence the
`gcov' output looks like this if you compiled the program with
optimization:

           100:   12:if (a != b)
           100:   13:  c = 1;
           100:   14:else
           100:   15:  c = 0;

 The output shows that this block of code, combined by optimization,
executed 100 times.  In one sense this result is correct, because there
was only one instruction representing all four of these lines.  However,
the output does not indicate how many times the result was 0 and how
many times the result was 1.

 Inlineable functions can create unexpected line counts.  Line counts
are shown for the source code of the inlineable function, but what is
shown depends on where the function is inlined, or if it is not inlined
at all.

 If the function is not inlined, the compiler must emit an out of line
copy of the function, in any object file that needs it.  If `fileA.o'
and `fileB.o' both contain out of line bodies of a particular
inlineable function, they will also both contain coverage counts for
that function.  When `fileA.o' and `fileB.o' are linked together, the
linker will, on many systems, select one of those out of line bodies
for all calls to that function, and remove or ignore the other.
Unfortunately, it will not remove the coverage counters for the unused
function body.  Hence when instrumented, all but one use of that
function will show zero counts.

 If the function is inlined in several places, the block structure in
each location might not be the same.  For instance, a condition might
now be calculable at compile time in some instances.  Because the
coverage of all the uses of the inline function will be shown for the
same source lines, the line counts themselves might seem inconsistent.


File: gcc,  Node: Gcov Data Files,  Prev: Gcov and Optimization,  Up: Gcov

9.4 Brief description of `gcov' data files
==========================================

`gcov' uses two files for profiling.  The names of these files are
derived from the original _object_ file by substituting the file suffix
with either `.gcno', or `.gcda'.  All of these files are placed in the
same directory as the object file, and contain data stored in a
platform-independent format.

 The `.gcno' file is generated when the source file is compiled with
the GCC `-ftest-coverage' option.  It contains information to
reconstruct the basic block graphs and assign source line numbers to
blocks.

 The `.gcda' file is generated when a program containing object files
built with the GCC `-fprofile-arcs' option is executed.  A separate
`.gcda' file is created for each object file compiled with this option.
It contains arc transition counts, and some summary information.

 The full details of the file format is specified in `gcov-io.h', and
functions provided in that header file should be used to access the
coverage files.


File: gcc,  Node: Trouble,  Next: Bugs,  Prev: Gcov,  Up: Top

10 Known Causes of Trouble with GCC
***********************************

This section describes known problems that affect users of GCC.  Most
of these are not GCC bugs per se--if they were, we would fix them.  But
the result for a user may be like the result of a bug.

 Some of these problems are due to bugs in other software, some are
missing features that are too much work to add, and some are places
where people's opinions differ as to what is best.

* Menu:

* Actual Bugs::              Bugs we will fix later.
* Cross-Compiler Problems::   Common problems of cross compiling with GCC.
* Interoperation::      Problems using GCC with other compilers,
               and with certain linkers, assemblers and debuggers.
* External Bugs::    Problems compiling certain programs.
* Incompatibilities::   GCC is incompatible with traditional C.
* Fixed Headers::       GCC uses corrected versions of system header files.
                           This is necessary, but doesn't always work smoothly.
* Standard Libraries::  GCC uses the system C library, which might not be
                           compliant with the ISO C standard.
* Disappointments::     Regrettable things we can't change, but not quite bugs.
* C++ Misunderstandings::     Common misunderstandings with GNU C++.
* Protoize Caveats::    Things to watch out for when using `protoize'.
* Non-bugs::        Things we think are right, but some others disagree.
* Warnings and Errors:: Which problems in your code get warnings,
                         and which get errors.


File: gcc,  Node: Actual Bugs,  Next: Cross-Compiler Problems,  Up: Trouble

10.1 Actual Bugs We Haven't Fixed Yet
=====================================

   * The `fixincludes' script interacts badly with automounters; if the
     directory of system header files is automounted, it tends to be
     unmounted while `fixincludes' is running.  This would seem to be a
     bug in the automounter.  We don't know any good way to work around
     it.

   * The `fixproto' script will sometimes add prototypes for the
     `sigsetjmp' and `siglongjmp' functions that reference the
     `jmp_buf' type before that type is defined.  To work around this,
     edit the offending file and place the typedef in front of the
     prototypes.

   * When `-pedantic-errors' is specified, GCC will incorrectly give an
     error message when a function name is specified in an expression
     involving the comma operator.


File: gcc,  Node: Cross-Compiler Problems,  Next: Interoperation,  Prev: Actual Bugs,  Up: Trouble

10.2 Cross-Compiler Problems
============================

You may run into problems with cross compilation on certain machines,
for several reasons.

   * Cross compilation can run into trouble for certain machines because
     some target machines' assemblers require floating point numbers to
     be written as _integer_ constants in certain contexts.

     The compiler writes these integer constants by examining the
     floating point value as an integer and printing that integer,
     because this is simple to write and independent of the details of
     the floating point representation.  But this does not work if the
     compiler is running on a different machine with an incompatible
     floating point format, or even a different byte-ordering.

     In addition, correct constant folding of floating point values
     requires representing them in the target machine's format.  (The C
     standard does not quite require this, but in practice it is the
     only way to win.)

     It is now possible to overcome these problems by defining macros
     such as `REAL_VALUE_TYPE'.  But doing so is a substantial amount of
     work for each target machine.  *Note Cross Compilation and
     Floating Point: (gccint)Cross-compilation.

   * At present, the program `mips-tfile' which adds debug support to
     object files on MIPS systems does not work in a cross compile
     environment.


File: gcc,  Node: Interoperation,  Next: External Bugs,  Prev: Cross-Compiler Problems,  Up: Trouble

10.3 Interoperation
===================

This section lists various difficulties encountered in using GCC
together with other compilers or with the assemblers, linkers,
libraries and debuggers on certain systems.

   * On many platforms, GCC supports a different ABI for C++ than do
     other compilers, so the object files compiled by GCC cannot be
     used with object files generated by another C++ compiler.

     An area where the difference is most apparent is name mangling.
     The use of different name mangling is intentional, to protect you
     from more subtle problems.  Compilers differ as to many internal
     details of C++ implementation, including: how class instances are
     laid out, how multiple inheritance is implemented, and how virtual
     function calls are handled.  If the name encoding were made the
     same, your programs would link against libraries provided from
     other compilers--but the programs would then crash when run.
     Incompatible libraries are then detected at link time, rather than
     at run time.

   * Older GDB versions sometimes fail to read the output of GCC version
     2.  If you have trouble, get GDB version 4.4 or later.

   * DBX rejects some files produced by GCC, though it accepts similar
     constructs in output from PCC.  Until someone can supply a coherent
     description of what is valid DBX input and what is not, there is
     nothing I can do about these problems.  You are on your own.

   * The GNU assembler (GAS) does not support PIC.  To generate PIC
     code, you must use some other assembler, such as `/bin/as'.

   * On some BSD systems, including some versions of Ultrix, use of
     profiling causes static variable destructors (currently used only
     in C++) not to be run.

   * On some SGI systems, when you use `-lgl_s' as an option, it gets
     translated magically to `-lgl_s -lX11_s -lc_s'.  Naturally, this
     does not happen when you use GCC.  You must specify all three
     options explicitly.

   * On a SPARC, GCC aligns all values of type `double' on an 8-byte
     boundary, and it expects every `double' to be so aligned.  The Sun
     compiler usually gives `double' values 8-byte alignment, with one
     exception: function arguments of type `double' may not be aligned.

     As a result, if a function compiled with Sun CC takes the address
     of an argument of type `double' and passes this pointer of type
     `double *' to a function compiled with GCC, dereferencing the
     pointer may cause a fatal signal.

     One way to solve this problem is to compile your entire program
     with GCC.  Another solution is to modify the function that is
     compiled with Sun CC to copy the argument into a local variable;
     local variables are always properly aligned.  A third solution is
     to modify the function that uses the pointer to dereference it via
     the following function `access_double' instead of directly with
     `*':

          inline double
          access_double (double *unaligned_ptr)
          {
            union d2i { double d; int i[2]; };

            union d2i *p = (union d2i *) unaligned_ptr;
            union d2i u;

            u.i[0] = p->i[0];
            u.i[1] = p->i[1];

            return u.d;
          }

     Storing into the pointer can be done likewise with the same union.

   * On Solaris, the `malloc' function in the `libmalloc.a' library may
     allocate memory that is only 4 byte aligned.  Since GCC on the
     SPARC assumes that doubles are 8 byte aligned, this may result in a
     fatal signal if doubles are stored in memory allocated by the
     `libmalloc.a' library.

     The solution is to not use the `libmalloc.a' library.  Use instead
     `malloc' and related functions from `libc.a'; they do not have
     this problem.

   * Sun forgot to include a static version of `libdl.a' with some
     versions of SunOS (mainly 4.1).  This results in undefined symbols
     when linking static binaries (that is, if you use `-static').  If
     you see undefined symbols `_dlclose', `_dlsym' or `_dlopen' when
     linking, compile and link against the file `mit/util/misc/dlsym.c'
     from the MIT version of X windows.

   * The 128-bit long double format that the SPARC port supports
     currently works by using the architecturally defined quad-word
     floating point instructions.  Since there is no hardware that
     supports these instructions they must be emulated by the operating
     system.  Long doubles do not work in Sun OS versions 4.0.3 and
     earlier, because the kernel emulator uses an obsolete and
     incompatible format.  Long doubles do not work in Sun OS version
     4.1.1 due to a problem in a Sun library.  Long doubles do work on
     Sun OS versions 4.1.2 and higher, but GCC does not enable them by
     default.  Long doubles appear to work in Sun OS 5.x (Solaris 2.x).

   * On HP-UX version 9.01 on the HP PA, the HP compiler `cc' does not
     compile GCC correctly.  We do not yet know why.  However, GCC
     compiled on earlier HP-UX versions works properly on HP-UX 9.01
     and can compile itself properly on 9.01.

   * On the HP PA machine, ADB sometimes fails to work on functions
     compiled with GCC.  Specifically, it fails to work on functions
     that use `alloca' or variable-size arrays.  This is because GCC
     doesn't generate HP-UX unwind descriptors for such functions.  It
     may even be impossible to generate them.

   * Debugging (`-g') is not supported on the HP PA machine, unless you
     use the preliminary GNU tools.

   * Taking the address of a label may generate errors from the HP-UX
     PA assembler.  GAS for the PA does not have this problem.

   * Using floating point parameters for indirect calls to static
     functions will not work when using the HP assembler.  There simply
     is no way for GCC to specify what registers hold arguments for
     static functions when using the HP assembler.  GAS for the PA does
     not have this problem.

   * In extremely rare cases involving some very large functions you may
     receive errors from the HP linker complaining about an out of
     bounds unconditional branch offset.  This used to occur more often
     in previous versions of GCC, but is now exceptionally rare.  If
     you should run into it, you can work around by making your
     function smaller.

   * GCC compiled code sometimes emits warnings from the HP-UX
     assembler of the form:

          (warning) Use of GR3 when
            frame >= 8192 may cause conflict.

     These warnings are harmless and can be safely ignored.

   * On the IBM RS/6000, compiling code of the form

          extern int foo;

          ... foo ...

          static int foo;

     will cause the linker to report an undefined symbol `foo'.
     Although this behavior differs from most other systems, it is not a
     bug because redefining an `extern' variable as `static' is
     undefined in ISO C.

   * In extremely rare cases involving some very large functions you may
     receive errors from the AIX Assembler complaining about a
     displacement that is too large.  If you should run into it, you
     can work around by making your function smaller.

   * The `libstdc++.a' library in GCC relies on the SVR4 dynamic linker
     semantics which merges global symbols between libraries and
     applications, especially necessary for C++ streams functionality.
     This is not the default behavior of AIX shared libraries and
     dynamic linking.  `libstdc++.a' is built on AIX with
     "runtime-linking" enabled so that symbol merging can occur.  To
     utilize this feature, the application linked with `libstdc++.a'
     must include the `-Wl,-brtl' flag on the link line.  G++ cannot
     impose this because this option may interfere with the semantics
     of the user program and users may not always use `g++' to link his
     or her application. Applications are not required to use the
     `-Wl,-brtl' flag on the link line--the rest of the `libstdc++.a'
     library which is not dependent on the symbol merging semantics
     will continue to function correctly.

   * An application can interpose its own definition of functions for
     functions invoked by `libstdc++.a' with "runtime-linking" enabled
     on AIX.  To accomplish this the application must be linked with
     "runtime-linking" option and the functions explicitly must be
     exported by the application (`-Wl,-brtl,-bE:exportfile').

   * AIX on the RS/6000 provides support (NLS) for environments outside
     of the United States.  Compilers and assemblers use NLS to support
     locale-specific representations of various objects including
     floating-point numbers (`.' vs `,' for separating decimal
     fractions). There have been problems reported where the library
     linked with GCC does not produce the same floating-point formats
     that the assembler accepts. If you have this problem, set the
     `LANG' environment variable to `C' or `En_US'.

   * Even if you specify `-fdollars-in-identifiers', you cannot
     successfully use `$' in identifiers on the RS/6000 due to a
     restriction in the IBM assembler.  GAS supports these identifiers.

   * On Ultrix, the Fortran compiler expects registers 2 through 5 to
     be saved by function calls.  However, the C compiler uses
     conventions compatible with BSD Unix: registers 2 through 5 may be
     clobbered by function calls.

     GCC uses the same convention as the Ultrix C compiler.  You can use
     these options to produce code compatible with the Fortran compiler:

          -fcall-saved-r2 -fcall-saved-r3 -fcall-saved-r4 -fcall-saved-r5

   * On the Alpha, you may get assembler errors about invalid syntax as
     a result of floating point constants.  This is due to a bug in the
     C library functions `ecvt', `fcvt' and `gcvt'.  Given valid
     floating point numbers, they sometimes print `NaN'.


File: gcc,  Node: External Bugs,  Next: Incompatibilities,  Prev: Interoperation,  Up: Trouble

10.4 Problems Compiling Certain Programs
========================================

Certain programs have problems compiling.

   * Parse errors may occur compiling X11 on a Decstation running
     Ultrix 4.2 because of problems in DEC's versions of the X11 header
     files `X11/Xlib.h' and `X11/Xutil.h'.  People recommend adding
     `-I/usr/include/mit' to use the MIT versions of the header files,
     or fixing the header files by adding this:

          #ifdef __STDC__
          #define NeedFunctionPrototypes 0
          #endif

   * On various 386 Unix systems derived from System V, including SCO,
     ISC, and ESIX, you may get error messages about running out of
     virtual memory while compiling certain programs.

     You can prevent this problem by linking GCC with the GNU malloc
     (which thus replaces the malloc that comes with the system).  GNU
     malloc is available as a separate package, and also in the file
     `src/gmalloc.c' in the GNU Emacs 19 distribution.

     If you have installed GNU malloc as a separate library package,
     use this option when you relink GCC:

          MALLOC=/usr/local/lib/libgmalloc.a

     Alternatively, if you have compiled `gmalloc.c' from Emacs 19, copy
     the object file to `gmalloc.o' and use this option when you relink
     GCC:

          MALLOC=gmalloc.o


File: gcc,  Node: Incompatibilities,  Next: Fixed Headers,  Prev: External Bugs,  Up: Trouble

10.5 Incompatibilities of GCC
=============================

There are several noteworthy incompatibilities between GNU C and K&R
(non-ISO) versions of C.

   * GCC normally makes string constants read-only.  If several
     identical-looking string constants are used, GCC stores only one
     copy of the string.

     One consequence is that you cannot call `mktemp' with a string
     constant argument.  The function `mktemp' always alters the string
     its argument points to.

     Another consequence is that `sscanf' does not work on some systems
     when passed a string constant as its format control string or
     input.  This is because `sscanf' incorrectly tries to write into
     the string constant.  Likewise `fscanf' and `scanf'.

     The best solution to these problems is to change the program to use
     `char'-array variables with initialization strings for these
     purposes instead of string constants.  But if this is not possible,
     you can use the `-fwritable-strings' flag, which directs GCC to
     handle string constants the same way most C compilers do.

   * `-2147483648' is positive.

     This is because 2147483648 cannot fit in the type `int', so
     (following the ISO C rules) its data type is `unsigned long int'.
     Negating this value yields 2147483648 again.

   * GCC does not substitute macro arguments when they appear inside of
     string constants.  For example, the following macro in GCC

          #define foo(a) "a"

     will produce output `"a"' regardless of what the argument A is.

   * When you use `setjmp' and `longjmp', the only automatic variables
     guaranteed to remain valid are those declared `volatile'.  This is
     a consequence of automatic register allocation.  Consider this
     function:

          jmp_buf j;

          foo ()
          {
            int a, b;

            a = fun1 ();
            if (setjmp (j))
              return a;

            a = fun2 ();
            /* `longjmp (j)' may occur in `fun3'. */
            return a + fun3 ();
          }

     Here `a' may or may not be restored to its first value when the
     `longjmp' occurs.  If `a' is allocated in a register, then its
     first value is restored; otherwise, it keeps the last value stored
     in it.

     If you use the `-W' option with the `-O' option, you will get a
     warning when GCC thinks such a problem might be possible.

   * Programs that use preprocessing directives in the middle of macro
     arguments do not work with GCC.  For example, a program like this
     will not work:

          foobar (
          #define luser
                  hack)

     ISO C does not permit such a construct.

   * K&R compilers allow comments to cross over an inclusion boundary
     (i.e. started in an include file and ended in the including file).
     I think this would be quite ugly and can't imagine it could be
     needed.

   * Declarations of external variables and functions within a block
     apply only to the block containing the declaration.  In other
     words, they have the same scope as any other declaration in the
     same place.

     In some other C compilers, a `extern' declaration affects all the
     rest of the file even if it happens within a block.

   * In traditional C, you can combine `long', etc., with a typedef
     name, as shown here:

          typedef int foo;
          typedef long foo bar;

     In ISO C, this is not allowed: `long' and other type modifiers
     require an explicit `int'.

   * PCC allows typedef names to be used as function parameters.

   * Traditional C allows the following erroneous pair of declarations
     to appear together in a given scope:

          typedef int foo;
          typedef foo foo;

   * GCC treats all characters of identifiers as significant.
     According to K&R-1 (2.2), "No more than the first eight characters
     are significant, although more may be used.".  Also according to
     K&R-1 (2.2), "An identifier is a sequence of letters and digits;
     the first character must be a letter.  The underscore _ counts as
     a letter.", but GCC also allows dollar signs in identifiers.

   * PCC allows whitespace in the middle of compound assignment
     operators such as `+='.  GCC, following the ISO standard, does not
     allow this.

   * GCC complains about unterminated character constants inside of
     preprocessing conditionals that fail.  Some programs have English
     comments enclosed in conditionals that are guaranteed to fail; if
     these comments contain apostrophes, GCC will probably report an
     error.  For example, this code would produce an error:

          #if 0
          You can't expect this to work.
          #endif

     The best solution to such a problem is to put the text into an
     actual C comment delimited by `/*...*/'.

   * Many user programs contain the declaration `long time ();'.  In the
     past, the system header files on many systems did not actually
     declare `time', so it did not matter what type your program
     declared it to return.  But in systems with ISO C headers, `time'
     is declared to return `time_t', and if that is not the same as
     `long', then `long time ();' is erroneous.

     The solution is to change your program to use appropriate system
     headers (`<time.h>' on systems with ISO C headers) and not to
     declare `time' if the system header files declare it, or failing
     that to use `time_t' as the return type of `time'.

   * When compiling functions that return `float', PCC converts it to a
     double.  GCC actually returns a `float'.  If you are concerned
     with PCC compatibility, you should declare your functions to return
     `double'; you might as well say what you mean.

   * When compiling functions that return structures or unions, GCC
     output code normally uses a method different from that used on most
     versions of Unix.  As a result, code compiled with GCC cannot call
     a structure-returning function compiled with PCC, and vice versa.

     The method used by GCC is as follows: a structure or union which is
     1, 2, 4 or 8 bytes long is returned like a scalar.  A structure or
     union with any other size is stored into an address supplied by
     the caller (usually in a special, fixed register, but on some
     machines it is passed on the stack).  The target hook
     `TARGET_STRUCT_VALUE_RTX' tells GCC where to pass this address.

     By contrast, PCC on most target machines returns structures and
     unions of any size by copying the data into an area of static
     storage, and then returning the address of that storage as if it
     were a pointer value.  The caller must copy the data from that
     memory area to the place where the value is wanted.  GCC does not
     use this method because it is slower and nonreentrant.

     On some newer machines, PCC uses a reentrant convention for all
     structure and union returning.  GCC on most of these machines uses
     a compatible convention when returning structures and unions in
     memory, but still returns small structures and unions in registers.

     You can tell GCC to use a compatible convention for all structure
     and union returning with the option `-fpcc-struct-return'.

   * GCC complains about program fragments such as `0x74ae-0x4000'
     which appear to be two hexadecimal constants separated by the minus
     operator.  Actually, this string is a single "preprocessing token".
     Each such token must correspond to one token in C.  Since this
     does not, GCC prints an error message.  Although it may appear
     obvious that what is meant is an operator and two values, the ISO
     C standard specifically requires that this be treated as erroneous.

     A "preprocessing token" is a "preprocessing number" if it begins
     with a digit and is followed by letters, underscores, digits,
     periods and `e+', `e-', `E+', `E-', `p+', `p-', `P+', or `P-'
     character sequences.  (In strict C89 mode, the sequences `p+',
     `p-', `P+' and `P-' cannot appear in preprocessing numbers.)

     To make the above program fragment valid, place whitespace in
     front of the minus sign.  This whitespace will end the
     preprocessing number.


File: gcc,  Node: Fixed Headers,  Next: Standard Libraries,  Prev: Incompatibilities,  Up: Trouble

10.6 Fixed Header Files
=======================

GCC needs to install corrected versions of some system header files.
This is because most target systems have some header files that won't
work with GCC unless they are changed.  Some have bugs, some are
incompatible with ISO C, and some depend on special features of other
compilers.

 Installing GCC automatically creates and installs the fixed header
files, by running a program called `fixincludes' (or for certain
targets an alternative such as `fixinc.svr4').  Normally, you don't
need to pay attention to this.  But there are cases where it doesn't do
the right thing automatically.

   * If you update the system's header files, such as by installing a
     new system version, the fixed header files of GCC are not
     automatically updated.  The easiest way to update them is to
     reinstall GCC.  (If you want to be clever, look in the makefile
     and you can find a shortcut.)

   * On some systems, in particular SunOS 4, header file directories
     contain machine-specific symbolic links in certain places.  This
     makes it possible to share most of the header files among hosts
     running the same version of SunOS 4 on different machine models.

     The programs that fix the header files do not understand this
     special way of using symbolic links; therefore, the directory of
     fixed header files is good only for the machine model used to
     build it.

     In SunOS 4, only programs that look inside the kernel will notice
     the difference between machine models.  Therefore, for most
     purposes, you need not be concerned about this.

     It is possible to make separate sets of fixed header files for the
     different machine models, and arrange a structure of symbolic
     links so as to use the proper set, but you'll have to do this by
     hand.

   * On Lynxos, GCC by default does not fix the header files.  This is
     because bugs in the shell cause the `fixincludes' script to fail.

     This means you will encounter problems due to bugs in the system
     header files.  It may be no comfort that they aren't GCC's fault,
     but it does mean that there's nothing for us to do about them.


File: gcc,  Node: Standard Libraries,  Next: Disappointments,  Prev: Fixed Headers,  Up: Trouble

10.7 Standard Libraries
=======================

GCC by itself attempts to be a conforming freestanding implementation.
*Note Language Standards Supported by GCC: Standards, for details of
what this means.  Beyond the library facilities required of such an
implementation, the rest of the C library is supplied by the vendor of
the operating system.  If that C library doesn't conform to the C
standards, then your programs might get warnings (especially when using
`-Wall') that you don't expect.

 For example, the `sprintf' function on SunOS 4.1.3 returns `char *'
while the C standard says that `sprintf' returns an `int'.  The
`fixincludes' program could make the prototype for this function match
the Standard, but that would be wrong, since the function will still
return `char *'.

 If you need a Standard compliant library, then you need to find one, as
GCC does not provide one.  The GNU C library (called `glibc') provides
ISO C, POSIX, BSD, SystemV and X/Open compatibility for GNU/Linux and
HURD-based GNU systems; no recent version of it supports other systems,
though some very old versions did.  Version 2.2 of the GNU C library
includes nearly complete C99 support.  You could also ask your
operating system vendor if newer libraries are available.


File: gcc,  Node: Disappointments,  Next: C++ Misunderstandings,  Prev: Standard Libraries,  Up: Trouble

10.8 Disappointments and Misunderstandings
==========================================

These problems are perhaps regrettable, but we don't know any practical
way around them.

   * Certain local variables aren't recognized by debuggers when you
     compile with optimization.

     This occurs because sometimes GCC optimizes the variable out of
     existence.  There is no way to tell the debugger how to compute the
     value such a variable "would have had", and it is not clear that
     would be desirable anyway.  So GCC simply does not mention the
     eliminated variable when it writes debugging information.

     You have to expect a certain amount of disagreement between the
     executable and your source code, when you use optimization.

   * Users often think it is a bug when GCC reports an error for code
     like this:

          int foo (struct mumble *);

          struct mumble { ... };

          int foo (struct mumble *x)
          { ... }

     This code really is erroneous, because the scope of `struct
     mumble' in the prototype is limited to the argument list
     containing it.  It does not refer to the `struct mumble' defined
     with file scope immediately below--they are two unrelated types
     with similar names in different scopes.

     But in the definition of `foo', the file-scope type is used
     because that is available to be inherited.  Thus, the definition
     and the prototype do not match, and you get an error.

     This behavior may seem silly, but it's what the ISO standard
     specifies.  It is easy enough for you to make your code work by
     moving the definition of `struct mumble' above the prototype.
     It's not worth being incompatible with ISO C just to avoid an
     error for the example shown above.

   * Accesses to bit-fields even in volatile objects works by accessing
     larger objects, such as a byte or a word.  You cannot rely on what
     size of object is accessed in order to read or write the
     bit-field; it may even vary for a given bit-field according to the
     precise usage.

     If you care about controlling the amount of memory that is
     accessed, use volatile but do not use bit-fields.

   * GCC comes with shell scripts to fix certain known problems in
     system header files.  They install corrected copies of various
     header files in a special directory where only GCC will normally
     look for them.  The scripts adapt to various systems by searching
     all the system header files for the problem cases that we know
     about.

     If new system header files are installed, nothing automatically
     arranges to update the corrected header files.  You will have to
     reinstall GCC to fix the new header files.  More specifically, go
     to the build directory and delete the files `stmp-fixinc' and
     `stmp-headers', and the subdirectory `include'; then do `make
     install' again.

   * On 68000 and x86 systems, for instance, you can get paradoxical
     results if you test the precise values of floating point numbers.
     For example, you can find that a floating point value which is not
     a NaN is not equal to itself.  This results from the fact that the
     floating point registers hold a few more bits of precision than
     fit in a `double' in memory.  Compiled code moves values between
     memory and floating point registers at its convenience, and moving
     them into memory truncates them.

     You can partially avoid this problem by using the `-ffloat-store'
     option (*note Optimize Options::).

   * On AIX and other platforms without weak symbol support, templates
     need to be instantiated explicitly and symbols for static members
     of templates will not be generated.

   * On AIX, GCC scans object files and library archives for static
     constructors and destructors when linking an application before the
     linker prunes unreferenced symbols.  This is necessary to prevent
     the AIX linker from mistakenly assuming that static constructor or
     destructor are unused and removing them before the scanning can
     occur.  All static constructors and destructors found will be
     referenced even though the modules in which they occur may not be
     used by the program.  This may lead to both increased executable
     size and unexpected symbol references.


File: gcc,  Node: C++ Misunderstandings,  Next: Protoize Caveats,  Prev: Disappointments,  Up: Trouble

10.9 Common Misunderstandings with GNU C++
==========================================

C++ is a complex language and an evolving one, and its standard
definition (the ISO C++ standard) was only recently completed.  As a
result, your C++ compiler may occasionally surprise you, even when its
behavior is correct.  This section discusses some areas that frequently
give rise to questions of this sort.

* Menu:

* Static Definitions::  Static member declarations are not definitions
* Name lookup::         Name lookup, templates, and accessing members of base classes
* Temporaries::         Temporaries may vanish before you expect
* Copy Assignment::     Copy Assignment operators copy virtual bases twice


File: gcc,  Node: Static Definitions,  Next: Name lookup,  Up: C++ Misunderstandings

10.9.1 Declare _and_ Define Static Members
------------------------------------------

When a class has static data members, it is not enough to _declare_ the
static member; you must also _define_ it.  For example:

     class Foo
     {
       ...
       void method();
       static int bar;
     };

 This declaration only establishes that the class `Foo' has an `int'
named `Foo::bar', and a member function named `Foo::method'.  But you
still need to define _both_ `method' and `bar' elsewhere.  According to
the ISO standard, you must supply an initializer in one (and only one)
source file, such as:

     int Foo::bar = 0;

 Other C++ compilers may not correctly implement the standard behavior.
As a result, when you switch to `g++' from one of these compilers, you
may discover that a program that appeared to work correctly in fact
does not conform to the standard: `g++' reports as undefined symbols
any static data members that lack definitions.


File: gcc,  Node: Name lookup,  Next: Temporaries,  Prev: Static Definitions,  Up: C++ Misunderstandings

10.9.2 Name lookup, templates, and accessing members of base classes
--------------------------------------------------------------------

The C++ standard prescribes that all names that are not dependent on
template parameters are bound to their present definitions when parsing
a template function or class.(1)  Only names that are dependent are
looked up at the point of instantiation.  For example, consider

       void foo(double);

       struct A {
         template <typename T>
         void f () {
           foo (1);        // 1
           int i = N;      // 2
           T t;
           t.bar();        // 3
           foo (t);        // 4
         }

         static const int N;
       };

 Here, the names `foo' and `N' appear in a context that does not depend
on the type of `T'.  The compiler will thus require that they are
defined in the context of use in the template, not only before the
point of instantiation, and will here use `::foo(double)' and `A::N',
respectively.  In particular, it will convert the integer value to a
`double' when passing it to `::foo(double)'.

 Conversely, `bar' and the call to `foo' in the fourth marked line are
used in contexts that do depend on the type of `T', so they are only
looked up at the point of instantiation, and you can provide
declarations for them after declaring the template, but before
instantiating it.  In particular, if you instantiate `A::f<int>', the
last line will call an overloaded `::foo(int)' if one was provided,
even if after the declaration of `struct A'.

 This distinction between lookup of dependent and non-dependent names is
called two-stage (or dependent) name lookup.  G++ implements it since
version 3.4.

 Two-stage name lookup sometimes leads to situations with behavior
different from non-template codes. The most common is probably this:

       template <typename T> struct Base {
         int i;
       };

       template <typename T> struct Derived : public Base<T> {
         int get_i() { return i; }
       };

 In `get_i()', `i' is not used in a dependent context, so the compiler
will look for a name declared at the enclosing namespace scope (which
is the global scope here).  It will not look into the base class, since
that is dependent and you may declare specializations of `Base' even
after declaring `Derived', so the compiler can't really know what `i'
would refer to.  If there is no global variable `i', then you will get
an error message.

 In order to make it clear that you want the member of the base class,
you need to defer lookup until instantiation time, at which the base
class is known.  For this, you need to access `i' in a dependent
context, by either using `this->i' (remember that `this' is of type
`Derived<T>*', so is obviously dependent), or using `Base<T>::i'.
Alternatively, `Base<T>::i' might be brought into scope by a
`using'-declaration.

 Another, similar example involves calling member functions of a base
class:

       template <typename T> struct Base {
           int f();
       };

       template <typename T> struct Derived : Base<T> {
           int g() { return f(); };
       };

 Again, the call to `f()' is not dependent on template arguments (there
are no arguments that depend on the type `T', and it is also not
otherwise specified that the call should be in a dependent context).
Thus a global declaration of such a function must be available, since
the one in the base class is not visible until instantiation time.  The
compiler will consequently produce the following error message:

       x.cc: In member function `int Derived<T>::g()':
       x.cc:6: error: there are no arguments to `f' that depend on a template
          parameter, so a declaration of `f' must be available
       x.cc:6: error: (if you use `-fpermissive', G++ will accept your code, but
          allowing the use of an undeclared name is deprecated)

 To make the code valid either use `this->f()', or `Base<T>::f()'.
Using the `-fpermissive' flag will also let the compiler accept the
code, by marking all function calls for which no declaration is visible
at the time of definition of the template for later lookup at
instantiation time, as if it were a dependent call.  We do not
recommend using `-fpermissive' to work around invalid code, and it will
also only catch cases where functions in base classes are called, not
where variables in base classes are used (as in the example above).

 Note that some compilers (including G++ versions prior to 3.4) get
these examples wrong and accept above code without an error.  Those
compilers do not implement two-stage name lookup correctly.

 ---------- Footnotes ----------

 (1) The C++ standard just uses the term "dependent" for names that
depend on the type or value of template parameters.  This shorter term
will also be used in the rest of this section.


File: gcc,  Node: Temporaries,  Next: Copy Assignment,  Prev: Name lookup,  Up: C++ Misunderstandings

10.9.3 Temporaries May Vanish Before You Expect
-----------------------------------------------

It is dangerous to use pointers or references to _portions_ of a
temporary object.  The compiler may very well delete the object before
you expect it to, leaving a pointer to garbage.  The most common place
where this problem crops up is in classes like string classes,
especially ones that define a conversion function to type `char *' or
`const char *'--which is one reason why the standard `string' class
requires you to call the `c_str' member function.  However, any class
that returns a pointer to some internal structure is potentially
subject to this problem.

 For example, a program may use a function `strfunc' that returns
`string' objects, and another function `charfunc' that operates on
pointers to `char':

     string strfunc ();
     void charfunc (const char *);

     void
     f ()
     {
       const char *p = strfunc().c_str();
       ...
       charfunc (p);
       ...
       charfunc (p);
     }

In this situation, it may seem reasonable to save a pointer to the C
string returned by the `c_str' member function and use that rather than
call `c_str' repeatedly.  However, the temporary string created by the
call to `strfunc' is destroyed after `p' is initialized, at which point
`p' is left pointing to freed memory.

 Code like this may run successfully under some other compilers,
particularly obsolete cfront-based compilers that delete temporaries
along with normal local variables.  However, the GNU C++ behavior is
standard-conforming, so if your program depends on late destruction of
temporaries it is not portable.

 The safe way to write such code is to give the temporary a name, which
forces it to remain until the end of the scope of the name.  For
example:

     string& tmp = strfunc ();
     charfunc (tmp.c_str ());


File: gcc,  Node: Copy Assignment,  Prev: Temporaries,  Up: C++ Misunderstandings

10.9.4 Implicit Copy-Assignment for Virtual Bases
-------------------------------------------------

When a base class is virtual, only one subobject of the base class
belongs to each full object.  Also, the constructors and destructors are
invoked only once, and called from the most-derived class.  However,
such objects behave unspecified when being assigned.  For example:

     struct Base{
       char *name;
       Base(char *n) : name(strdup(n)){}
       Base& operator= (const Base& other){
        free (name);
        name = strdup (other.name);
       }
     };

     struct A:virtual Base{
       int val;
       A():Base("A"){}
     };

     struct B:virtual Base{
       int bval;
       B():Base("B"){}
     };

     struct Derived:public A, public B{
       Derived():Base("Derived"){}
     };

     void func(Derived &d1, Derived &d2)
     {
       d1 = d2;
     }

 The C++ standard specifies that `Base::Base' is only called once when
constructing or copy-constructing a Derived object.  It is unspecified
whether `Base::operator=' is called more than once when the implicit
copy-assignment for Derived objects is invoked (as it is inside `func'
in the example).

 G++ implements the "intuitive" algorithm for copy-assignment: assign
all direct bases, then assign all members.  In that algorithm, the
virtual base subobject can be encountered more than once.  In the
example, copying proceeds in the following order: `val', `name' (via
`strdup'), `bval', and `name' again.

 If application code relies on copy-assignment, a user-defined
copy-assignment operator removes any uncertainties.  With such an
operator, the application can define whether and how the virtual base
subobject is assigned.


File: gcc,  Node: Protoize Caveats,  Next: Non-bugs,  Prev: C++ Misunderstandings,  Up: Trouble

10.10 Caveats of using `protoize'
=================================

The conversion programs `protoize' and `unprotoize' can sometimes
change a source file in a way that won't work unless you rearrange it.

   * `protoize' can insert references to a type name or type tag before
     the definition, or in a file where they are not defined.

     If this happens, compiler error messages should show you where the
     new references are, so fixing the file by hand is straightforward.

   * There are some C constructs which `protoize' cannot figure out.
     For example, it can't determine argument types for declaring a
     pointer-to-function variable; this you must do by hand.  `protoize'
     inserts a comment containing `???' each time it finds such a
     variable; so you can find all such variables by searching for this
     string.  ISO C does not require declaring the argument types of
     pointer-to-function types.

   * Using `unprotoize' can easily introduce bugs.  If the program
     relied on prototypes to bring about conversion of arguments, these
     conversions will not take place in the program without prototypes.
     One case in which you can be sure `unprotoize' is safe is when you
     are removing prototypes that were made with `protoize'; if the
     program worked before without any prototypes, it will work again
     without them.

     You can find all the places where this problem might occur by
     compiling the program with the `-Wconversion' option.  It prints a
     warning whenever an argument is converted.

   * Both conversion programs can be confused if there are macro calls
     in and around the text to be converted.  In other words, the
     standard syntax for a declaration or definition must not result
     from expanding a macro.  This problem is inherent in the design of
     C and cannot be fixed.  If only a few functions have confusing
     macro calls, you can easily convert them manually.

   * `protoize' cannot get the argument types for a function whose
     definition was not actually compiled due to preprocessing
     conditionals.  When this happens, `protoize' changes nothing in
     regard to such a function.  `protoize' tries to detect such
     instances and warn about them.

     You can generally work around this problem by using `protoize' step
     by step, each time specifying a different set of `-D' options for
     compilation, until all of the functions have been converted.
     There is no automatic way to verify that you have got them all,
     however.

   * Confusion may result if there is an occasion to convert a function
     declaration or definition in a region of source code where there
     is more than one formal parameter list present.  Thus, attempts to
     convert code containing multiple (conditionally compiled) versions
     of a single function header (in the same vicinity) may not produce
     the desired (or expected) results.

     If you plan on converting source files which contain such code, it
     is recommended that you first make sure that each conditionally
     compiled region of source code which contains an alternative
     function header also contains at least one additional follower
     token (past the final right parenthesis of the function header).
     This should circumvent the problem.

   * `unprotoize' can become confused when trying to convert a function
     definition or declaration which contains a declaration for a
     pointer-to-function formal argument which has the same name as the
     function being defined or declared.  We recommend you avoid such
     choices of formal parameter names.

   * You might also want to correct some of the indentation by hand and
     break long lines.  (The conversion programs don't write lines
     longer than eighty characters in any case.)


File: gcc,  Node: Non-bugs,  Next: Warnings and Errors,  Prev: Protoize Caveats,  Up: Trouble

10.11 Certain Changes We Don't Want to Make
===========================================

This section lists changes that people frequently request, but which we
do not make because we think GCC is better without them.

   * Checking the number and type of arguments to a function which has
     an old-fashioned definition and no prototype.

     Such a feature would work only occasionally--only for calls that
     appear in the same file as the called function, following the
     definition.  The only way to check all calls reliably is to add a
     prototype for the function.  But adding a prototype eliminates the
     motivation for this feature.  So the feature is not worthwhile.

   * Warning about using an expression whose type is signed as a shift
     count.

     Shift count operands are probably signed more often than unsigned.
     Warning about this would cause far more annoyance than good.

   * Warning about assigning a signed value to an unsigned variable.

     Such assignments must be very common; warning about them would
     cause more annoyance than good.

   * Warning when a non-void function value is ignored.

     Coming as I do from a Lisp background, I balk at the idea that
     there is something dangerous about discarding a value.  There are
     functions that return values which some callers may find useful;
     it makes no sense to clutter the program with a cast to `void'
     whenever the value isn't useful.

   * Making `-fshort-enums' the default.

     This would cause storage layout to be incompatible with most other
     C compilers.  And it doesn't seem very important, given that you
     can get the same result in other ways.  The case where it matters
     most is when the enumeration-valued object is inside a structure,
     and in that case you can specify a field width explicitly.

   * Making bit-fields unsigned by default on particular machines where
     "the ABI standard" says to do so.

     The ISO C standard leaves it up to the implementation whether a
     bit-field declared plain `int' is signed or not.  This in effect
     creates two alternative dialects of C.

     The GNU C compiler supports both dialects; you can specify the
     signed dialect with `-fsigned-bitfields' and the unsigned dialect
     with `-funsigned-bitfields'.  However, this leaves open the
     question of which dialect to use by default.

     Currently, the preferred dialect makes plain bit-fields signed,
     because this is simplest.  Since `int' is the same as `signed int'
     in every other context, it is cleanest for them to be the same in
     bit-fields as well.

     Some computer manufacturers have published Application Binary
     Interface standards which specify that plain bit-fields should be
     unsigned.  It is a mistake, however, to say anything about this
     issue in an ABI.  This is because the handling of plain bit-fields
     distinguishes two dialects of C.  Both dialects are meaningful on
     every type of machine.  Whether a particular object file was
     compiled using signed bit-fields or unsigned is of no concern to
     other object files, even if they access the same bit-fields in the
     same data structures.

     A given program is written in one or the other of these two
     dialects.  The program stands a chance to work on most any machine
     if it is compiled with the proper dialect.  It is unlikely to work
     at all if compiled with the wrong dialect.

     Many users appreciate the GNU C compiler because it provides an
     environment that is uniform across machines.  These users would be
     inconvenienced if the compiler treated plain bit-fields
     differently on certain machines.

     Occasionally users write programs intended only for a particular
     machine type.  On these occasions, the users would benefit if the
     GNU C compiler were to support by default the same dialect as the
     other compilers on that machine.  But such applications are rare.
     And users writing a program to run on more than one type of
     machine cannot possibly benefit from this kind of compatibility.

     This is why GCC does and will treat plain bit-fields in the same
     fashion on all types of machines (by default).

     There are some arguments for making bit-fields unsigned by default
     on all machines.  If, for example, this becomes a universal de
     facto standard, it would make sense for GCC to go along with it.
     This is something to be considered in the future.

     (Of course, users strongly concerned about portability should
     indicate explicitly in each bit-field whether it is signed or not.
     In this way, they write programs which have the same meaning in
     both C dialects.)

   * Undefining `__STDC__' when `-ansi' is not used.

     Currently, GCC defines `__STDC__' unconditionally.  This provides
     good results in practice.

     Programmers normally use conditionals on `__STDC__' to ask whether
     it is safe to use certain features of ISO C, such as function
     prototypes or ISO token concatenation.  Since plain `gcc' supports
     all the features of ISO C, the correct answer to these questions is
     "yes".

     Some users try to use `__STDC__' to check for the availability of
     certain library facilities.  This is actually incorrect usage in
     an ISO C program, because the ISO C standard says that a conforming
     freestanding implementation should define `__STDC__' even though it
     does not have the library facilities.  `gcc -ansi -pedantic' is a
     conforming freestanding implementation, and it is therefore
     required to define `__STDC__', even though it does not come with
     an ISO C library.

     Sometimes people say that defining `__STDC__' in a compiler that
     does not completely conform to the ISO C standard somehow violates
     the standard.  This is illogical.  The standard is a standard for
     compilers that claim to support ISO C, such as `gcc -ansi'--not
     for other compilers such as plain `gcc'.  Whatever the ISO C
     standard says is relevant to the design of plain `gcc' without
     `-ansi' only for pragmatic reasons, not as a requirement.

     GCC normally defines `__STDC__' to be 1, and in addition defines
     `__STRICT_ANSI__' if you specify the `-ansi' option, or a `-std'
     option for strict conformance to some version of ISO C.  On some
     hosts, system include files use a different convention, where
     `__STDC__' is normally 0, but is 1 if the user specifies strict
     conformance to the C Standard.  GCC follows the host convention
     when processing system include files, but when processing user
     files it follows the usual GNU C convention.

   * Undefining `__STDC__' in C++.

     Programs written to compile with C++-to-C translators get the
     value of `__STDC__' that goes with the C compiler that is
     subsequently used.  These programs must test `__STDC__' to
     determine what kind of C preprocessor that compiler uses: whether
     they should concatenate tokens in the ISO C fashion or in the
     traditional fashion.

     These programs work properly with GNU C++ if `__STDC__' is defined.
     They would not work otherwise.

     In addition, many header files are written to provide prototypes
     in ISO C but not in traditional C.  Many of these header files can
     work without change in C++ provided `__STDC__' is defined.  If
     `__STDC__' is not defined, they will all fail, and will all need
     to be changed to test explicitly for C++ as well.

   * Deleting "empty" loops.

     Historically, GCC has not deleted "empty" loops under the
     assumption that the most likely reason you would put one in a
     program is to have a delay, so deleting them will not make real
     programs run any faster.

     However, the rationale here is that optimization of a nonempty loop
     cannot produce an empty one, which holds for C but is not always
     the case for C++.

     Moreover, with `-funroll-loops' small "empty" loops are already
     removed, so the current behavior is both sub-optimal and
     inconsistent and will change in the future.

   * Making side effects happen in the same order as in some other
     compiler.

     It is never safe to depend on the order of evaluation of side
     effects.  For example, a function call like this may very well
     behave differently from one compiler to another:

          void func (int, int);

          int i = 2;
          func (i++, i++);

     There is no guarantee (in either the C or the C++ standard language
     definitions) that the increments will be evaluated in any
     particular order.  Either increment might happen first.  `func'
     might get the arguments `2, 3', or it might get `3, 2', or even
     `2, 2'.

   * Not allowing structures with volatile fields in registers.

     Strictly speaking, there is no prohibition in the ISO C standard
     against allowing structures with volatile fields in registers, but
     it does not seem to make any sense and is probably not what you
     wanted to do.  So the compiler will give an error message in this
     case.

   * Making certain warnings into errors by default.

     Some ISO C testsuites report failure when the compiler does not
     produce an error message for a certain program.

     ISO C requires a "diagnostic" message for certain kinds of invalid
     programs, but a warning is defined by GCC to count as a
     diagnostic.  If GCC produces a warning but not an error, that is
     correct ISO C support.  If test suites call this "failure", they
     should be run with the GCC option `-pedantic-errors', which will
     turn these warnings into errors.



File: gcc,  Node: Warnings and Errors,  Prev: Non-bugs,  Up: Trouble

10.12 Warning Messages and Error Messages
=========================================

The GNU compiler can produce two kinds of diagnostics: errors and
warnings.  Each kind has a different purpose:

     "Errors" report problems that make it impossible to compile your
     program.  GCC reports errors with the source file name and line
     number where the problem is apparent.

     "Warnings" report other unusual conditions in your code that _may_
     indicate a problem, although compilation can (and does) proceed.
     Warning messages also report the source file name and line number,
     but include the text `warning:' to distinguish them from error
     messages.

 Warnings may indicate danger points where you should check to make sure
that your program really does what you intend; or the use of obsolete
features; or the use of nonstandard features of GNU C or C++.  Many
warnings are issued only if you ask for them, with one of the `-W'
options (for instance, `-Wall' requests a variety of useful warnings).

 GCC always tries to compile your program if possible; it never
gratuitously rejects a program whose meaning is clear merely because
(for instance) it fails to conform to a standard.  In some cases,
however, the C and C++ standards specify that certain extensions are
forbidden, and a diagnostic _must_ be issued by a conforming compiler.
The `-pedantic' option tells GCC to issue warnings in such cases;
`-pedantic-errors' says to make them errors instead.  This does not
mean that _all_ non-ISO constructs get warnings or errors.

 *Note Options to Request or Suppress Warnings: Warning Options, for
more detail on these and related command-line options.


File: gcc,  Node: Bugs,  Next: Service,  Prev: Trouble,  Up: Top

11 Reporting Bugs
*****************

Your bug reports play an essential role in making GCC reliable.

 When you encounter a problem, the first thing to do is to see if it is
already known.  *Note Trouble::.  If it isn't known, then you should
report the problem.

* Menu:

* Criteria:  Bug Criteria.   Have you really found a bug?
* Reporting: Bug Reporting.  How to report a bug effectively.
* Known: Trouble.            Known problems.
* Help: Service.             Where to ask for help.


File: gcc,  Node: Bug Criteria,  Next: Bug Reporting,  Up: Bugs

11.1 Have You Found a Bug?
==========================

If you are not sure whether you have found a bug, here are some
guidelines:

   * If the compiler gets a fatal signal, for any input whatever, that
     is a compiler bug.  Reliable compilers never crash.

   * If the compiler produces invalid assembly code, for any input
     whatever (except an `asm' statement), that is a compiler bug,
     unless the compiler reports errors (not just warnings) which would
     ordinarily prevent the assembler from being run.

   * If the compiler produces valid assembly code that does not
     correctly execute the input source code, that is a compiler bug.

     However, you must double-check to make sure, because you may have a
     program whose behavior is undefined, which happened by chance to
     give the desired results with another C or C++ compiler.

     For example, in many nonoptimizing compilers, you can write `x;'
     at the end of a function instead of `return x;', with the same
     results.  But the value of the function is undefined if `return'
     is omitted; it is not a bug when GCC produces different results.

     Problems often result from expressions with two increment
     operators, as in `f (*p++, *p++)'.  Your previous compiler might
     have interpreted that expression the way you intended; GCC might
     interpret it another way.  Neither compiler is wrong.  The bug is
     in your code.

     After you have localized the error to a single source line, it
     should be easy to check for these things.  If your program is
     correct and well defined, you have found a compiler bug.

   * If the compiler produces an error message for valid input, that is
     a compiler bug.

   * If the compiler does not produce an error message for invalid
     input, that is a compiler bug.  However, you should note that your
     idea of "invalid input" might be my idea of "an extension" or
     "support for traditional practice".

   * If you are an experienced user of one of the languages GCC
     supports, your suggestions for improvement of GCC are welcome in
     any case.


File: gcc,  Node: Bug Reporting,  Prev: Bug Criteria,  Up: Bugs

11.2 How and where to Report Bugs
=================================

Bugs should be reported to our bug database.  Please refer to
`http://gcc.gnu.org/bugs.html' for up-to-date instructions how to
submit bug reports.  Copies of this file in HTML (`bugs.html') and
plain text (`BUGS') are also part of GCC releases.


File: gcc,  Node: Service,  Next: Contributing,  Prev: Bugs,  Up: Top

12 How To Get Help with GCC
***************************

If you need help installing, using or changing GCC, there are two ways
to find it:

   * Send a message to a suitable network mailing list.  First try
     <[e-mail]> (for help installing or using GCC), and if
     that brings no response, try <[e-mail]>.  For help changing
     GCC, ask <[e-mail]>.  If you think you have found a bug in
     GCC, please report it following the instructions at *note Bug
     Reporting::.

   * Look in the service directory for someone who might help you for a
     fee.  The service directory is found at
     `http://www.gnu.org/prep/service.html'.

 For further information, see `http://gcc.gnu.org/faq.html#support'.


File: gcc,  Node: Contributing,  Next: Funding,  Prev: Service,  Up: Top

13 Contributing to GCC Development
**********************************

If you would like to help pretest GCC releases to assure they work well,
our current development sources are available by CVS (see
`http://gcc.gnu.org/cvs.html').  Source and binary snapshots are also
available for FTP; see `http://gcc.gnu.org/snapshots.html'.

 If you would like to work on improvements to GCC, please read the
advice at these URLs:

     `http://gcc.gnu.org/contribute.html'
     `http://gcc.gnu.org/contributewhy.html'

for information on how to make useful contributions and avoid
duplication of effort.  Suggested projects are listed at
`http://gcc.gnu.org/projects/'.


File: gcc,  Node: Funding,  Next: GNU Project,  Prev: Contributing,  Up: Top

Funding Free Software
*********************

If you want to have more free software a few years from now, it makes
sense for you to help encourage people to contribute funds for its
development.  The most effective approach known is to encourage
commercial redistributors to donate.

 Users of free software systems can boost the pace of development by
encouraging for-a-fee distributors to donate part of their selling price
to free software developers--the Free Software Foundation, and others.

 The way to convince distributors to do this is to demand it and expect
it from them.  So when you compare distributors, judge them partly by
how much they give to free software development.  Show distributors
they must compete to be the one who gives the most.

 To make this approach work, you must insist on numbers that you can
compare, such as, "We will donate ten dollars to the Frobnitz project
for each disk sold."  Don't be satisfied with a vague promise, such as
"A portion of the profits are donated," since it doesn't give a basis
for comparison.

 Even a precise fraction "of the profits from this disk" is not very
meaningful, since creative accounting and unrelated business decisions
can greatly alter what fraction of the sales price counts as profit.
If the price you pay is $50, ten percent of the profit is probably less
than a dollar; it might be a few cents, or nothing at all.

 Some redistributors do development work themselves.  This is useful
too; but to keep everyone honest, you need to inquire how much they do,
and what kind.  Some kinds of development make much more long-term
difference than others.  For example, maintaining a separate version of
a program contributes very little; maintaining the standard version of a
program for the whole community contributes much.  Easy new ports
contribute little, since someone else would surely do them; difficult
ports such as adding a new CPU to the GNU Compiler Collection
contribute more; major new features or packages contribute the most.

 By establishing the idea that supporting further development is "the
proper thing to do" when distributing free software for a fee, we can
assure a steady flow of resources into making more free software.

     Copyright (C) 1994 Free Software Foundation, Inc.
     Verbatim copying and redistribution of this section is permitted
     without royalty; alteration is not permitted.


File: gcc,  Node: GNU Project,  Next: Copying,  Prev: Funding,  Up: Top

The GNU Project and GNU/Linux
*****************************

The GNU Project was launched in 1984 to develop a complete Unix-like
operating system which is free software: the GNU system.  (GNU is a
recursive acronym for "GNU's Not Unix"; it is pronounced "guh-NEW".)
Variants of the GNU operating system, which use the kernel Linux, are
now widely used; though these systems are often referred to as "Linux",
they are more accurately called GNU/Linux systems.

 For more information, see:
     `http://www.gnu.org/'
     `http://www.gnu.org/gnu/linux-and-gnu.html'


File: gcc,  Node: Copying,  Next: GNU Free Documentation License,  Prev: GNU Project,  Up: Top

GNU GENERAL PUBLIC LICENSE
**************************

                         Version 2, June 1991

     Copyright (C) 1989, 1991 Free Software Foundation, Inc.
     59 Temple Place - Suite 330, Boston, MA  02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

Preamble
========

The licenses for most software are designed to take away your freedom
to share and change it.  By contrast, the GNU General Public License is
intended to guarantee your freedom to share and change free
software--to make sure the software is free for all its users.  This
General Public License applies to most of the Free Software
Foundation's software and to any other program whose authors commit to
using it.  (Some other Free Software Foundation software is covered by
the GNU Library General Public License instead.)  You can apply it to
your programs, too.

 When we speak of free software, we are referring to freedom, not
price.  Our General Public Licenses are designed to make sure that you
have the freedom to distribute copies of free software (and charge for
this service if you wish), that you receive source code or can get it
if you want it, that you can change the software or use pieces of it in
new free programs; and that you know you can do these things.

 To protect your rights, we need to make restrictions that forbid
anyone to deny you these rights or to ask you to surrender the rights.
These restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

 For example, if you distribute copies of such a program, whether
gratis or for a fee, you must give the recipients all the rights that
you have.  You must make sure that they, too, receive or can get the
source code.  And you must show them these terms so they know their
rights.

 We protect your rights with two steps: (1) copyright the software, and
(2) offer you this license which gives you legal permission to copy,
distribute and/or modify the software.

 Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

 Finally, any free program is threatened constantly by software
patents.  We wish to avoid the danger that redistributors of a free
program will individually obtain patent licenses, in effect making the
program proprietary.  To prevent this, we have made it clear that any
patent must be licensed for everyone's free use or not licensed at all.

 The precise terms and conditions for copying, distribution and
modification follow.

    TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
  0. This License applies to any program or other work which contains a
     notice placed by the copyright holder saying it may be distributed
     under the terms of this General Public License.  The "Program",
     below, refers to any such program or work, and a "work based on
     the Program" means either the Program or any derivative work under
     copyright law: that is to say, a work containing the Program or a
     portion of it, either verbatim or with modifications and/or
     translated into another language.  (Hereinafter, translation is
     included without limitation in the term "modification".)  Each
     licensee is addressed as "you".

     Activities other than copying, distribution and modification are
     not covered by this License; they are outside its scope.  The act
     of running the Program is not restricted, and the output from the
     Program is covered only if its contents constitute a work based on
     the Program (independent of having been made by running the
     Program).  Whether that is true depends on what the Program does.

  1. You may copy and distribute verbatim copies of the Program's
     source code as you receive it, in any medium, provided that you
     conspicuously and appropriately publish on each copy an appropriate
     copyright notice and disclaimer of warranty; keep intact all the
     notices that refer to this License and to the absence of any
     warranty; and give any other recipients of the Program a copy of
     this License along with the Program.

     You may charge a fee for the physical act of transferring a copy,
     and you may at your option offer warranty protection in exchange
     for a fee.

  2. You may modify your copy or copies of the Program or any portion
     of it, thus forming a work based on the Program, and copy and
     distribute such modifications or work under the terms of Section 1
     above, provided that you also meet all of these conditions:

       a. You must cause the modified files to carry prominent notices
          stating that you changed the files and the date of any change.

       b. You must cause any work that you distribute or publish, that
          in whole or in part contains or is derived from the Program
          or any part thereof, to be licensed as a whole at no charge
          to all third parties under the terms of this License.

       c. If the modified program normally reads commands interactively
          when run, you must cause it, when started running for such
          interactive use in the most ordinary way, to print or display
          an announcement including an appropriate copyright notice and
          a notice that there is no warranty (or else, saying that you
          provide a warranty) and that users may redistribute the
          program under these conditions, and telling the user how to
          view a copy of this License.  (Exception: if the Program
          itself is interactive but does not normally print such an
          announcement, your work based on the Program is not required
          to print an announcement.)

     These requirements apply to the modified work as a whole.  If
     identifiable sections of that work are not derived from the
     Program, and can be reasonably considered independent and separate
     works in themselves, then this License, and its terms, do not
     apply to those sections when you distribute them as separate
     works.  But when you distribute the same sections as part of a
     whole which is a work based on the Program, the distribution of
     the whole must be on the terms of this License, whose permissions
     for other licensees extend to the entire whole, and thus to each
     and every part regardless of who wrote it.

     Thus, it is not the intent of this section to claim rights or
     contest your rights to work written entirely by you; rather, the
     intent is to exercise the right to control the distribution of
     derivative or collective works based on the Program.

     In addition, mere aggregation of another work not based on the
     Program with the Program (or with a work based on the Program) on
     a volume of a storage or distribution medium does not bring the
     other work under the scope of this License.

  3. You may copy and distribute the Program (or a work based on it,
     under Section 2) in object code or executable form under the terms
     of Sections 1 and 2 above provided that you also do one of the
     following:

       a. Accompany it with the complete corresponding machine-readable
          source code, which must be distributed under the terms of
          Sections 1 and 2 above on a medium customarily used for
          software interchange; or,

       b. Accompany it with a written offer, valid for at least three
          years, to give any third party, for a charge no more than your
          cost of physically performing source distribution, a complete
          machine-readable copy of the corresponding source code, to be
          distributed under the terms of Sections 1 and 2 above on a
          medium customarily used for software interchange; or,

       c. Accompany it with the information you received as to the offer
          to distribute corresponding source code.  (This alternative is
          allowed only for noncommercial distribution and only if you
          received the program in object code or executable form with
          such an offer, in accord with Subsection b above.)

     The source code for a work means the preferred form of the work for
     making modifications to it.  For an executable work, complete
     source code means all the source code for all modules it contains,
     plus any associated interface definition files, plus the scripts
     used to control compilation and installation of the executable.
     However, as a special exception, the source code distributed need
     not include anything that is normally distributed (in either
     source or binary form) with the major components (compiler,
     kernel, and so on) of the operating system on which the executable
     runs, unless that component itself accompanies the executable.

     If distribution of executable or object code is made by offering
     access to copy from a designated place, then offering equivalent
     access to copy the source code from the same place counts as
     distribution of the source code, even though third parties are not
     compelled to copy the source along with the object code.

  4. You may not copy, modify, sublicense, or distribute the Program
     except as expressly provided under this License.  Any attempt
     otherwise to copy, modify, sublicense or distribute the Program is
     void, and will automatically terminate your rights under this
     License.  However, parties who have received copies, or rights,
     from you under this License will not have their licenses
     terminated so long as such parties remain in full compliance.

  5. You are not required to accept this License, since you have not
     signed it.  However, nothing else grants you permission to modify
     or distribute the Program or its derivative works.  These actions
     are prohibited by law if you do not accept this License.
     Therefore, by modifying or distributing the Program (or any work
     based on the Program), you indicate your acceptance of this
     License to do so, and all its terms and conditions for copying,
     distributing or modifying the Program or works based on it.

  6. Each time you redistribute the Program (or any work based on the
     Program), the recipient automatically receives a license from the
     original licensor to copy, distribute or modify the Program
     subject to these terms and conditions.  You may not impose any
     further restrictions on the recipients' exercise of the rights
     granted herein.  You are not responsible for enforcing compliance
     by third parties to this License.

  7. If, as a consequence of a court judgment or allegation of patent
     infringement or for any other reason (not limited to patent
     issues), conditions are imposed on you (whether by court order,
     agreement or otherwise) that contradict the conditions of this
     License, they do not excuse you from the conditions of this
     License.  If you cannot distribute so as to satisfy simultaneously
     your obligations under this License and any other pertinent
     obligations, then as a consequence you may not distribute the
     Program at all.  For example, if a patent license would not permit
     royalty-free redistribution of the Program by all those who
     receive copies directly or indirectly through you, then the only
     way you could satisfy both it and this License would be to refrain
     entirely from distribution of the Program.

     If any portion of this section is held invalid or unenforceable
     under any particular circumstance, the balance of the section is
     intended to apply and the section as a whole is intended to apply
     in other circumstances.

     It is not the purpose of this section to induce you to infringe any
     patents or other property right claims or to contest validity of
     any such claims; this section has the sole purpose of protecting
     the integrity of the free software distribution system, which is
     implemented by public license practices.  Many people have made
     generous contributions to the wide range of software distributed
     through that system in reliance on consistent application of that
     system; it is up to the author/donor to decide if he or she is
     willing to distribute software through any other system and a
     licensee cannot impose that choice.

     This section is intended to make thoroughly clear what is believed
     to be a consequence of the rest of this License.

  8. If the distribution and/or use of the Program is restricted in
     certain countries either by patents or by copyrighted interfaces,
     the original copyright holder who places the Program under this
     License may add an explicit geographical distribution limitation
     excluding those countries, so that distribution is permitted only
     in or among countries not thus excluded.  In such case, this
     License incorporates the limitation as if written in the body of
     this License.

  9. The Free Software Foundation may publish revised and/or new
     versions of the General Public License from time to time.  Such
     new versions will be similar in spirit to the present version, but
     may differ in detail to address new problems or concerns.

     Each version is given a distinguishing version number.  If the
     Program specifies a version number of this License which applies
     to it and "any later version", you have the option of following
     the terms and conditions either of that version or of any later
     version published by the Free Software Foundation.  If the Program
     does not specify a version number of this License, you may choose
     any version ever published by the Free Software Foundation.

 10. If you wish to incorporate parts of the Program into other free
     programs whose distribution conditions are different, write to the
     author to ask for permission.  For software which is copyrighted
     by the Free Software Foundation, write to the Free Software
     Foundation; we sometimes make exceptions for this.  Our decision
     will be guided by the two goals of preserving the free status of
     all derivatives of our free software and of promoting the sharing
     and reuse of software generally.

                                NO WARRANTY
 11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO
     WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE
     LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
     HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT
     WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT
     NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
     FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS TO THE
     QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
     PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY
     SERVICING, REPAIR OR CORRECTION.

 12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN
     WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY
     MODIFY AND/OR REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE
     LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL,
     INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR
     INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
     DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU
     OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY
     OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN
     ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.

                      END OF TERMS AND CONDITIONS
How to Apply These Terms to Your New Programs
=============================================

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

 To do so, attach the following notices to the program.  It is safest
to attach them to the start of each source file to most effectively
convey the exclusion of warranty; and each file should have at least
the "copyright" line and a pointer to where the full notice is found.

     ONE LINE TO GIVE THE PROGRAM'S NAME AND A BRIEF IDEA OF WHAT IT DOES.
     Copyright (C) YEAR  NAME OF AUTHOR

     This program is free software; you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation; either version 2 of the License, or
     (at your option) any later version.

     This program is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.

     You should have received a copy of the GNU General Public License
     along with this program; if not, write to the Free Software Foundation,
     Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.

 Also add information on how to contact you by electronic and paper
mail.

 If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

     Gnomovision version 69, Copyright (C) YEAR NAME OF AUTHOR
     Gnomovision comes with ABSOLUTELY NO WARRANTY; for details
     type `show w'.
     This is free software, and you are welcome to redistribute it
     under certain conditions; type `show c' for details.

 The hypothetical commands `show w' and `show c' should show the
appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than `show w' and `show
c'; they could even be mouse-clicks or menu items--whatever suits your
program.

 You should also get your employer (if you work as a programmer) or your
school, if any, to sign a "copyright disclaimer" for the program, if
necessary.  Here is a sample; alter the names:

     Yoyodyne, Inc., hereby disclaims all copyright interest in the program
     `Gnomovision' (which makes passes at compilers) written by James Hacker.

     SIGNATURE OF TY COON, 1 April 1989
     Ty Coon, President of Vice

 This General Public License does not permit incorporating your program
into proprietary programs.  If your program is a subroutine library,
you may consider it more useful to permit linking proprietary
applications with the library.  If this is what you want to do, use the
GNU Library General Public License instead of this License.


File: gcc,  Node: GNU Free Documentation License,  Next: Contributors,  Prev: Copying,  Up: Top

GNU Free Documentation License
******************************

                      Version 1.2, November 2002

     Copyright (C) 2000,2001,2002 Free Software Foundation, Inc.
     59 Temple Place, Suite 330, Boston, MA  02111-1307, USA

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     The purpose of this License is to make a manual, textbook, or other
     functional and useful document "free" in the sense of freedom: to
     assure everyone the effective freedom to copy and redistribute it,
     with or without modifying it, either commercially or
     noncommercially.  Secondarily, this License preserves for the
     author and publisher a way to get credit for their work, while not
     being considered responsible for modifications made by others.

     This License is a kind of "copyleft", which means that derivative
     works of the document must themselves be free in the same sense.
     It complements the GNU General Public License, which is a copyleft
     license designed for free software.

     We have designed this License in order to use it for manuals for
     free software, because free software needs free documentation: a
     free program should come with manuals providing the same freedoms
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  1. APPLICABILITY AND DEFINITIONS

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 10. FUTURE REVISIONS OF THIS LICENSE

     The Free Software Foundation may publish new, revised versions of
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ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

       Copyright (C)  YEAR  YOUR NAME.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.2
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts.
       A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

 If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the "with...Texts." line with this:

         with the Invariant Sections being LIST THEIR TITLES, with
         the Front-Cover Texts being LIST, and with the Back-Cover Texts
         being LIST.

 If you have Invariant Sections without Cover Texts, or some other
combination of the three, merge those two alternatives to suit the
situation.

 If your document contains nontrivial examples of program code, we
recommend releasing these examples in parallel under your choice of
free software license, such as the GNU General Public License, to
permit their use in free software.


File: gcc,  Node: Contributors,  Next: Option Index,  Prev: GNU Free Documentation License,  Up: Top

Contributors to GCC
*******************

The GCC project would like to thank its many contributors.  Without
them the project would not have been nearly as successful as it has
been.  Any omissions in this list are accidental.  Feel free to contact
<[e-mail]> or <[e-mail]> if you have been left out or
some of your contributions are not listed.  Please keep this list in
alphabetical order.

   * Analog Devices helped implement the support for complex data types
     and iterators.

   * John David Anglin for threading-related fixes and improvements to
     libstdc++-v3, and the HP-UX port.

   * James van Artsdalen wrote the code that makes efficient use of the
     Intel 80387 register stack.

   * Abramo and Roberto Bagnara for the SysV68 Motorola 3300 Delta
     Series port.

   * Alasdair Baird for various bug fixes.

   * Giovanni Bajo for analyzing lots of complicated C++ problem
     reports.

   * Peter Barada for his work to improve code generation for new
     ColdFire cores.

   * Gerald Baumgartner added the signature extension to the C++ front
     end.

   * Godmar Back for his Java improvements and encouragement.

   * Scott Bambrough for help porting the Java compiler.

   * Wolfgang Bangerth for processing tons of bug reports.

   * Jon Beniston for his Microsoft Windows port of Java.

   * Daniel Berlin for better DWARF2 support, faster/better
     optimizations, improved alias analysis, plus migrating us to
     Bugzilla.

   * Geoff Berry for his Java object serialization work and various
     patches.

   * Eric Blake for helping to make GCJ and libgcj conform to the
     specifications.

   * Segher Boessenkool for various fixes.

   * Hans-J. Boehm for his garbage collector, IA-64 libffi port, and
     other Java work.

   * Neil Booth for work on cpplib, lang hooks, debug hooks and other
     miscellaneous clean-ups.

   * Eric Botcazou for fixing middle- and backend bugs left and right.

   * Per Bothner for his direction via the steering committee and
     various improvements to our infrastructure for supporting new
     languages.  Chill front end implementation.  Initial
     implementations of cpplib, fix-header, config.guess, libio, and
     past C++ library (libg++) maintainer.  Dreaming up, designing and
     implementing much of GCJ.

   * Devon Bowen helped port GCC to the Tahoe.

   * Don Bowman for mips-vxworks contributions.

   * Dave Brolley for work on cpplib and Chill.

   * Robert Brown implemented the support for Encore 32000 systems.

   * Christian Bruel for improvements to local store elimination.

   * Herman A.J. ten Brugge for various fixes.

   * Joerg Brunsmann for Java compiler hacking and help with the GCJ
     FAQ.

   * Joe Buck for his direction via the steering committee.

   * Craig Burley for leadership of the Fortran effort.

   * Stephan Buys for contributing Doxygen notes for libstdc++.

   * Paolo Carlini for libstdc++ work: lots of efficiency improvements
     to the C++ strings, streambufs and formatted I/O, hard detective
     work on the frustrating localization issues, and keeping up with
     the problem reports.

   * John Carr for his alias work, SPARC hacking, infrastructure
     improvements, previous contributions to the steering committee,
     loop optimizations, etc.

   * Stephane Carrez for 68HC11 and 68HC12 ports.

   * Steve Chamberlain for support for the Renesas SH and H8 processors
     and the PicoJava processor, and for GCJ config fixes.

   * Glenn Chambers for help with the GCJ FAQ.

   * John-Marc Chandonia for various libgcj patches.

   * Scott Christley for his Objective-C contributions.

   * Eric Christopher for his Java porting help and clean-ups.

   * Branko Cibej for more warning contributions.

   * The GNU Classpath project for all of their merged runtime code.

   * Nick Clifton for arm, mcore, fr30, v850, m32r work, `--help', and
     other random hacking.

   * Michael Cook for libstdc++ cleanup patches to reduce warnings.

   * R. Kelley Cook for making GCC buildable from a read-only directory
     as well as other miscellaneous build process and documentation
     clean-ups.

   * Ralf Corsepius for SH testing and minor bugfixing.

   * Stan Cox for care and feeding of the x86 port and lots of behind
     the scenes hacking.

   * Alex Crain provided changes for the 3b1.

   * Ian Dall for major improvements to the NS32k port.

   * Paul Dale for his work to add uClinux platform support to the m68k
     backend.

   * Dario Dariol contributed the four varieties of sample programs
     that print a copy of their source.

   * Russell Davidson for fstream and stringstream fixes in libstdc++.

   * Mo DeJong for GCJ and libgcj bug fixes.

   * DJ Delorie for the DJGPP port, build and libiberty maintenance, and
     various bug fixes.

   * Gabriel Dos Reis for contributions to G++, contributions and
     maintenance of GCC diagnostics infrastructure, libstdc++-v3,
     including valarray<>, complex<>, maintaining the numerics library
     (including that pesky <limits> :-) and keeping up-to-date anything
     to do with numbers.

   * Ulrich Drepper for his work on glibc, testing of GCC using glibc,
     ISO C99 support, CFG dumping support, etc., plus support of the
     C++ runtime libraries including for all kinds of C interface
     issues, contributing and maintaining complex<>, sanity checking
     and disbursement, configuration architecture, libio maintenance,
     and early math work.

   * Zdenek Dvorak for a new loop unroller and various fixes.

   * Richard Earnshaw for his ongoing work with the ARM.

   * David Edelsohn for his direction via the steering committee,
     ongoing work with the RS6000/PowerPC port, help cleaning up Haifa
     loop changes, doing the entire AIX port of libstdc++ with his bare
     hands, and for ensuring GCC properly keeps working on AIX.

   * Kevin Ediger for the floating point formatting of num_put::do_put
     in libstdc++.

   * Phil Edwards for libstdc++ work including configuration hackery,
     documentation maintainer, chief breaker of the web pages, the
     occasional iostream bug fix, and work on shared library symbol
     versioning.

   * Paul Eggert for random hacking all over GCC.

   * Mark Elbrecht for various DJGPP improvements, and for libstdc++
     configuration support for locales and fstream-related fixes.

   * Vadim Egorov for libstdc++ fixes in strings, streambufs, and
     iostreams.

   * Christian Ehrhardt for dealing with bug reports.

   * Ben Elliston for his work to move the Objective-C runtime into its
     own subdirectory and for his work on autoconf.

   * Marc Espie for OpenBSD support.

   * Doug Evans for much of the global optimization framework, arc,
     m32r, and SPARC work.

   * Christopher Faylor for his work on the Cygwin port and for caring
     and feeding the gcc.gnu.org box and saving its users tons of spam.

   * Fred Fish for BeOS support and Ada fixes.

   * Ivan Fontes Garcia for the Portugese translation of the GCJ FAQ.

   * Peter Gerwinski for various bug fixes and the Pascal front end.

   * Kaveh Ghazi for his direction via the steering committee, amazing
     work to make `-W -Wall' useful, and continuously testing GCC on a
     plethora of platforms.

   * John Gilmore for a donation to the FSF earmarked improving GNU
     Java.

   * Judy Goldberg for c++ contributions.

   * Torbjorn Granlund for various fixes and the c-torture testsuite,
     multiply- and divide-by-constant optimization, improved long long
     support, improved leaf function register allocation, and his
     direction via the steering committee.

   * Anthony Green for his `-Os' contributions and Java front end work.

   * Stu Grossman for gdb hacking, allowing GCJ developers to debug our
     code.

   * Michael K. Gschwind contributed the port to the PDP-11.

   * Ron Guilmette implemented the `protoize' and `unprotoize' tools,
     the support for Dwarf symbolic debugging information, and much of
     the support for System V Release 4.  He has also worked heavily on
     the Intel 386 and 860 support.

   * Bruno Haible for improvements in the runtime overhead for EH, new
     warnings and assorted bug fixes.

   * Andrew Haley for his amazing Java compiler and library efforts.

   * Chris Hanson assisted in making GCC work on HP-UX for the 9000
     series 300.

   * Michael Hayes for various thankless work he's done trying to get
     the c30/c40 ports functional.  Lots of loop and unroll
     improvements and fixes.

   * Dara Hazeghi for wading through myriads of target-specific bug
     reports.

   * Kate Hedstrom for staking the G77 folks with an initial testsuite.

   * Richard Henderson for his ongoing SPARC, alpha, ia32, and ia64
     work, loop opts, and generally fixing lots of old problems we've
     ignored for years, flow rewrite and lots of further stuff,
     including reviewing tons of patches.

   * Aldy Hernandez for working on the PowerPC port, SIMD support, and
     various fixes.

   * Nobuyuki Hikichi of Software Research Associates, Tokyo,
     contributed the support for the Sony NEWS machine.

   * Kazu Hirata for caring and feeding the Renesas H8/300 port and
     various fixes.

   * Manfred Hollstein for his ongoing work to keep the m88k alive, lots
     of testing and bug fixing, particularly of our configury code.

   * Steve Holmgren for MachTen patches.

   * Jan Hubicka for his x86 port improvements.

   * Falk Hueffner for working on C and optimization bug reports.

   * Bernardo Innocenti for his m68k work, including merging of
     ColdFire improvements and uClinux support.

   * Christian Iseli for various bug fixes.

   * Kamil Iskra for general m68k hacking.

   * Lee Iverson for random fixes and MIPS testing.

   * Andreas Jaeger for testing and benchmarking of GCC and various bug
     fixes.

   * Jakub Jelinek for his SPARC work and sibling call optimizations as
     well as lots of bug fixes and test cases, and for improving the
     Java build system.

   * Janis Johnson for ia64 testing and fixes, her quality improvement
     sidetracks, and web page maintenance.

   * Kean Johnston for SCO OpenServer support and various fixes.

   * Tim Josling for the sample language treelang based originally on
     Richard Kenner's ""toy" language".

   * Nicolai Josuttis for additional libstdc++ documentation.

   * Klaus Kaempf for his ongoing work to make alpha-vms a viable
     target.

   * David Kashtan of SRI adapted GCC to VMS.

   * Ryszard Kabatek for many, many libstdc++ bug fixes and
     optimizations of strings, especially member functions, and for
     auto_ptr fixes.

   * Geoffrey Keating for his ongoing work to make the PPC work for
     GNU/Linux and his automatic regression tester.

   * Brendan Kehoe for his ongoing work with G++ and for a lot of early
     work in just about every part of libstdc++.

   * Oliver M. Kellogg of Deutsche Aerospace contributed the port to the
     MIL-STD-1750A.

   * Richard Kenner of the New York University Ultracomputer Research
     Laboratory wrote the machine descriptions for the AMD 29000, the
     DEC Alpha, the IBM RT PC, and the IBM RS/6000 as well as the
     support for instruction attributes.  He also made changes to
     better support RISC processors including changes to common
     subexpression elimination, strength reduction, function calling
     sequence handling, and condition code support, in addition to
     generalizing the code for frame pointer elimination and delay slot
     scheduling.  Richard Kenner was also the head maintainer of GCC
     for several years.

   * Mumit Khan for various contributions to the Cygwin and Mingw32
     ports and maintaining binary releases for Microsoft Windows hosts,
     and for massive libstdc++ porting work to Cygwin/Mingw32.

   * Robin Kirkham for cpu32 support.

   * Mark Klein for PA improvements.

   * Thomas Koenig for various bug fixes.

   * Bruce Korb for the new and improved fixincludes code.

   * Benjamin Kosnik for his G++ work and for leading the libstdc++-v3
     effort.

   * Charles LaBrec contributed the support for the Integrated Solutions
     68020 system.

   * Jeff Law for his direction via the steering committee,
     coordinating the entire egcs project and GCC 2.95, rolling out
     snapshots and releases, handling merges from GCC2, reviewing tons
     of patches that might have fallen through the cracks else, and
     random but extensive hacking.

   * Marc Lehmann for his direction via the steering committee and
     helping with analysis and improvements of x86 performance.

   * Ted Lemon wrote parts of the RTL reader and printer.

   * Kriang Lerdsuwanakij for C++ improvements including template as
     template parameter support, and many C++ fixes.

   * Warren Levy for tremendous work on libgcj (Java Runtime Library)
     and random work on the Java front end.

   * Alain Lichnewsky ported GCC to the MIPS CPU.

   * Oskar Liljeblad for hacking on AWT and his many Java bug reports
     and patches.

   * Robert Lipe for OpenServer support, new testsuites, testing, etc.

   * Weiwen Liu for testing and various bug fixes.

   * Dave Love for his ongoing work with the Fortran front end and
     runtime libraries.

   * Martin von Lo"wis for internal consistency checking infrastructure,
     various C++ improvements including namespace support, and tons of
     assistance with libstdc++/compiler merges.

   * H.J. Lu for his previous contributions to the steering committee,
     many x86 bug reports, prototype patches, and keeping the GNU/Linux
     ports working.

   * Greg McGary for random fixes and (someday) bounded pointers.

   * Andrew MacLeod for his ongoing work in building a real EH system,
     various code generation improvements, work on the global
     optimizer, etc.

   * Vladimir Makarov for hacking some ugly i960 problems, PowerPC
     hacking improvements to compile-time performance, overall
     knowledge and direction in the area of instruction scheduling, and
     design and implementation of the automaton based instruction
     scheduler.

   * Bob Manson for his behind the scenes work on dejagnu.

   * Philip Martin for lots of libstdc++ string and vector iterator
     fixes and improvements, and string clean up and testsuites.

   * All of the Mauve project contributors, for Java test code.

   * Bryce McKinlay for numerous GCJ and libgcj fixes and improvements.

   * Adam Megacz for his work on the Microsoft Windows port of GCJ.

   * Michael Meissner for LRS framework, ia32, m32r, v850, m88k, MIPS,
     powerpc, haifa, ECOFF debug support, and other assorted hacking.

   * Jason Merrill for his direction via the steering committee and
     leading the G++ effort.

   * David Miller for his direction via the steering committee, lots of
     SPARC work, improvements in jump.c and interfacing with the Linux
     kernel developers.

   * Gary Miller ported GCC to Charles River Data Systems machines.

   * Alfred Minarik for libstdc++ string and ios bug fixes, and turning
     the entire libstdc++ testsuite namespace-compatible.

   * Mark Mitchell for his direction via the steering committee,
     mountains of C++ work, load/store hoisting out of loops, alias
     analysis improvements, ISO C `restrict' support, and serving as
     release manager for GCC 3.x.

   * Alan Modra for various GNU/Linux bits and testing.

   * Toon Moene for his direction via the steering committee, Fortran
     maintenance, and his ongoing work to make us make Fortran run fast.

   * Jason Molenda for major help in the care and feeding of all the
     services on the gcc.gnu.org (formerly egcs.cygnus.com)
     machine--mail, web services, ftp services, etc etc.  Doing all
     this work on scrap paper and the backs of envelopes would have
     been... difficult.

   * Catherine Moore for fixing various ugly problems we have sent her
     way, including the haifa bug which was killing the Alpha & PowerPC
     Linux kernels.

   * Mike Moreton for his various Java patches.

   * David Mosberger-Tang for various Alpha improvements, and for the
     initial IA-64 port.

   * Stephen Moshier contributed the floating point emulator that
     assists in cross-compilation and permits support for floating
     point numbers wider than 64 bits and for ISO C99 support.

   * Bill Moyer for his behind the scenes work on various issues.

   * Philippe De Muyter for his work on the m68k port.

   * Joseph S. Myers for his work on the PDP-11 port, format checking
     and ISO C99 support, and continuous emphasis on (and contributions
     to) documentation.

   * Nathan Myers for his work on libstdc++-v3: architecture and
     authorship through the first three snapshots, including
     implementation of locale infrastructure, string, shadow C headers,
     and the initial project documentation (DESIGN, CHECKLIST, and so
     forth).  Later, more work on MT-safe string and shadow headers.

   * Felix Natter for documentation on porting libstdc++.

   * Nathanael Nerode for cleaning up the configuration/build process.

   * NeXT, Inc. donated the front end that supports the Objective-C
     language.

   * Hans-Peter Nilsson for the CRIS and MMIX ports, improvements to
     the search engine setup, various documentation fixes and other
     small fixes.

   * Geoff Noer for this work on getting cygwin native builds working.

   * Diego Novillo for his SPEC performance tracking web pages and
     assorted fixes in the middle end and various back ends.

   * David O'Brien for the FreeBSD/alpha, FreeBSD/AMD x86-64,
     FreeBSD/ARM, FreeBSD/PowerPC, and FreeBSD/SPARC64 ports and
     related infrastructure improvements.

   * Alexandre Oliva for various build infrastructure improvements,
     scripts and amazing testing work, including keeping libtool issues
     sane and happy.

   * Melissa O'Neill for various NeXT fixes.

   * Rainer Orth for random MIPS work, including improvements to our o32
     ABI support, improvements to dejagnu's MIPS support, Java
     configuration clean-ups and porting work, etc.

   * Hartmut Penner for work on the s390 port.

   * Paul Petersen wrote the machine description for the Alliant FX/8.

   * Alexandre Petit-Bianco for implementing much of the Java compiler
     and continued Java maintainership.

   * Matthias Pfaller for major improvements to the NS32k port.

   * Gerald Pfeifer for his direction via the steering committee,
     pointing out lots of problems we need to solve, maintenance of the
     web pages, and taking care of documentation maintenance in general.

   * Andrew Pinski for processing bug reports by the dozen.

   * Ovidiu Predescu for his work on the Objective-C front end and
     runtime libraries.

   * Jerry Quinn for major performance improvements in C++ formatted
     I/O.

   * Ken Raeburn for various improvements to checker, MIPS ports and
     various cleanups in the compiler.

   * Rolf W. Rasmussen for hacking on AWT.

   * David Reese of Sun Microsystems contributed to the Solaris on
     PowerPC port.

   * Volker Reichelt for keeping up with the problem reports.

   * Joern Rennecke for maintaining the sh port, loop, regmove & reload
     hacking.

   * Loren J. Rittle for improvements to libstdc++-v3 including the
     FreeBSD port, threading fixes, thread-related configury changes,
     critical threading documentation, and solutions to really tricky
     I/O problems, as well as keeping GCC properly working on FreeBSD
     and continuous testing.

   * Craig Rodrigues for processing tons of bug reports.

   * Gavin Romig-Koch for lots of behind the scenes MIPS work.

   * Ken Rose for fixes to our delay slot filling code.

   * Paul Rubin wrote most of the preprocessor.

   * Pe'tur Runo'lfsson for major performance improvements in C++
     formatted I/O and large file support in C++ filebuf.

   * Chip Salzenberg for libstdc++ patches and improvements to locales,
     traits, Makefiles, libio, libtool hackery, and "long long" support.

   * Juha Sarlin for improvements to the H8 code generator.

   * Greg Satz assisted in making GCC work on HP-UX for the 9000 series
     300.

   * Roger Sayle for improvements to constant folding and GCC's RTL
     optimizers as well as for fixing numerous bugs.

   * Bradley Schatz for his work on the GCJ FAQ.

   * Peter Schauer wrote the code to allow debugging to work on the
     Alpha.

   * William Schelter did most of the work on the Intel 80386 support.

   * Bernd Schmidt for various code generation improvements and major
     work in the reload pass as well a serving as release manager for
     GCC 2.95.3.

   * Peter Schmid for constant testing of libstdc++ - especially
     application testing, going above and beyond what was requested for
     the release criteria - and libstdc++ header file tweaks.

   * Jason Schroeder for jcf-dump patches.

   * Andreas Schwab for his work on the m68k port.

   * Joel Sherrill for his direction via the steering committee, RTEMS
     contributions and RTEMS testing.

   * Nathan Sidwell for many C++ fixes/improvements.

   * Jeffrey Siegal for helping RMS with the original design of GCC,
     some code which handles the parse tree and RTL data structures,
     constant folding and help with the original VAX & m68k ports.

   * Kenny Simpson for prompting libstdc++ fixes due to defect reports
     from the LWG (thereby keeping us in line with updates from the
     ISO).

   * Franz Sirl for his ongoing work with making the PPC port stable
     for GNU/Linux.

   * Andrey Slepuhin for assorted AIX hacking.

   * Christopher Smith did the port for Convex machines.

   * Danny Smith for his major efforts on the Mingw (and Cygwin) ports.

   * Randy Smith finished the Sun FPA support.

   * Scott Snyder for queue, iterator, istream, and string fixes and
     libstdc++ testsuite entries.

   * Brad Spencer for contributions to the GLIBCPP_FORCE_NEW technique.

   * Richard Stallman, for writing the original GCC and launching the
     GNU project.

   * Jan Stein of the Chalmers Computer Society provided support for
     Genix, as well as part of the 32000 machine description.

   * Nigel Stephens for various mips16 related fixes/improvements.

   * Jonathan Stone wrote the machine description for the Pyramid
     computer.

   * Graham Stott for various infrastructure improvements.

   * John Stracke for his Java HTTP protocol fixes.

   * Mike Stump for his Elxsi port, G++ contributions over the years
     and more recently his vxworks contributions

   * Jeff Sturm for Java porting help, bug fixes, and encouragement.

   * Shigeya Suzuki for this fixes for the bsdi platforms.

   * Ian Lance Taylor for his mips16 work, general configury hacking,
     fixincludes, etc.

   * Holger Teutsch provided the support for the Clipper CPU.

   * Gary Thomas for his ongoing work to make the PPC work for
     GNU/Linux.

   * Philipp Thomas for random bug fixes throughout the compiler

   * Jason Thorpe for thread support in libstdc++ on NetBSD.

   * Kresten Krab Thorup wrote the run time support for the Objective-C
     language and the fantastic Java bytecode interpreter.

   * Michael Tiemann for random bug fixes, the first instruction
     scheduler, initial C++ support, function integration, NS32k, SPARC
     and M88k machine description work, delay slot scheduling.

   * Andreas Tobler for his work porting libgcj to Darwin.

   * Teemu Torma for thread safe exception handling support.

   * Leonard Tower wrote parts of the parser, RTL generator, and RTL
     definitions, and of the VAX machine description.

   * Tom Tromey for internationalization support and for his many Java
     contributions and libgcj maintainership.

   * Lassi Tuura for improvements to config.guess to determine HP
     processor types.

   * Petter Urkedal for libstdc++ CXXFLAGS, math, and algorithms fixes.

   * Brent Verner for work with the libstdc++ cshadow files and their
     associated configure steps.

   * Todd Vierling for contributions for NetBSD ports.

   * Jonathan Wakely for contributing libstdc++ Doxygen notes and XHTML
     guidance.

   * Dean Wakerley for converting the install documentation from HTML
     to texinfo in time for GCC 3.0.

   * Krister Walfridsson for random bug fixes.

   * Stephen M. Webb for time and effort on making libstdc++ shadow
     files work with the tricky Solaris 8+ headers, and for pushing the
     build-time header tree.

   * John Wehle for various improvements for the x86 code generator,
     related infrastructure improvements to help x86 code generation,
     value range propagation and other work, WE32k port.

   * Ulrich Weigand for work on the s390 port.

   * Zack Weinberg for major work on cpplib and various other bug fixes.

   * Matt Welsh for help with Linux Threads support in GCJ.

   * Urban Widmark for help fixing java.io.

   * Mark Wielaard for new Java library code and his work integrating
     with Classpath.

   * Dale Wiles helped port GCC to the Tahoe.

   * Bob Wilson from Tensilica, Inc. for the Xtensa port.

   * Jim Wilson for his direction via the steering committee, tackling
     hard problems in various places that nobody else wanted to work
     on, strength reduction and other loop optimizations.

   * Carlo Wood for various fixes.

   * Tom Wood for work on the m88k port.

   * Masanobu Yuhara of Fujitsu Laboratories implemented the machine
     description for the Tron architecture (specifically, the Gmicro).

   * Kevin Zachmann helped ported GCC to the Tahoe.

   * Gilles Zunino for help porting Java to Irix.


 In addition to the above, all of which also contributed time and
energy in testing GCC, we would like to thank the following for their
contributions to testing:

   * Michael Abd-El-Malek

   * Thomas Arend

   * Bonzo Armstrong

   * Steven Ashe

   * Chris Baldwin

   * David Billinghurst

   * Jim Blandy

   * Stephane Bortzmeyer

   * Horst von Brand

   * Frank Braun

   * Rodney Brown

   * Sidney Cadot

   * Bradford Castalia

   * Ralph Doncaster

   * Richard Emberson

   * Levente Farkas

   * Graham Fawcett

   * Robert A. French

   * Jo"rgen Freyh

   * Mark K. Gardner

   * Charles-Antoine Gauthier

   * Yung Shing Gene

   * David Gilbert

   * Simon Gornall

   * Fred Gray

   * John Griffin

   * Patrik Hagglund

   * Phil Hargett

   * Amancio Hasty

   * Bryan W. Headley

   * Kevin B. Hendricks

   * Joep Jansen

   * Christian Joensson

   * David Kidd

   * Tobias Kuipers

   * Anand Krishnaswamy

   * llewelly

   * Damon Love

   * Brad Lucier

   * Matthias Klose

   * Martin Knoblauch

   * Jesse Macnish

   * Stefan Morrell

   * Anon A. Mous

   * Matthias Mueller

   * Pekka Nikander

   * Jon Olson

   * Magnus Persson

   * Chris Pollard

   * Richard Polton

   * David Rees

   * Paul Reilly

   * Tom Reilly

   * Torsten Rueger

   * Danny Sadinoff

   * Marc Schifer

   * David Schuler

   * Vin Shelton

   * Tim Souder

   * Adam Sulmicki

   * George Talbot

   * Gregory Warnes

   * David E. Young

   * And many others

 And finally we'd like to thank everyone who uses the compiler, submits
bug reports and generally reminds us why we're doing this work in the
first place.


File: gcc,  Node: Option Index,  Next: Keyword Index,  Prev: Contributors,  Up: Top

Option Index
************

GCC's command line options are indexed here without any initial `-' or
`--'.  Where an option has both positive and negative forms (such as
`-fOPTION' and `-fno-OPTION'), relevant entries in the manual are
indexed under the most appropriate form; it may sometimes be useful to
look up both forms.

[index]
* Menu:

* ###:                                   Overall Options.    (line  174)
* -mf930:                                SPARC Options.      (line  122)
* -mf934:                                SPARC Options.      (line  122)
* A:                                     Preprocessor Options.
                                                             (line  474)
* all_load:                              Darwin Options.     (line   11)
* allowable_client:                      Darwin Options.     (line   87)
* ansi <1>:                              Non-bugs.           (line  102)
* ansi <2>:                              Other Builtins.     (line   22)
* ansi <3>:                              Preprocessor Options.
                                                             (line  308)
* ansi <4>:                              C Dialect Options.  (line   10)
* ansi:                                  Standards.          (line   13)
* arch_errors_fatal:                     Darwin Options.     (line   15)
* arch_only:                             Darwin Options.     (line   87)
* aux-info:                              C Dialect Options.  (line   97)
* b:                                     Target Options.     (line   13)
* B:                                     Directory Options.  (line   55)
* bcopy-builtin:                         PDP-11 Options.     (line   32)
* bind_at_load:                          Darwin Options.     (line   19)
* bundle:                                Darwin Options.     (line   24)
* bundle_loader:                         Darwin Options.     (line   28)
* c:                                     Link Options.       (line   20)
* C:                                     Preprocessor Options.
                                                             (line  521)
* c:                                     Overall Options.    (line  126)
* client_name:                           Darwin Options.     (line   87)
* compatibility_version:                 Darwin Options.     (line   87)
* crossjumping:                          Optimize Options.   (line  382)
* current_version:                       Darwin Options.     (line   87)
* D:                                     Preprocessor Options.
                                                             (line   33)
* d:                                     Debugging Options.  (line  199)
* da:                                    Debugging Options.  (line  327)
* dA:                                    Debugging Options.  (line  210)
* dB:                                    Debugging Options.  (line  217)
* db:                                    Debugging Options.  (line  214)
* dC:                                    Debugging Options.  (line  224)
* dc:                                    Debugging Options.  (line  220)
* dD <1>:                                Preprocessor Options.
                                                             (line  502)
* dD:                                    Debugging Options.  (line  234)
* dd:                                    Debugging Options.  (line  229)
* dE:                                    Debugging Options.  (line  238)
* dependency-file:                       Darwin Options.     (line   87)
* dF:                                    Debugging Options.  (line  245)
* df:                                    Debugging Options.  (line  241)
* dG:                                    Debugging Options.  (line  251)
* dg:                                    Debugging Options.  (line  248)
* dH:                                    Debugging Options.  (line  330)
* dh:                                    Debugging Options.  (line  255)
* dI:                                    Preprocessor Options.
                                                             (line  511)
* di:                                    Debugging Options.  (line  258)
* dj:                                    Debugging Options.  (line  261)
* dk:                                    Debugging Options.  (line  264)
* dL:                                    Debugging Options.  (line  271)
* dl:                                    Debugging Options.  (line  268)
* dM:                                    Preprocessor Options.
                                                             (line  490)
* dm:                                    Debugging Options.  (line  333)
* dM:                                    Debugging Options.  (line  275)
* dN <1>:                                Preprocessor Options.
                                                             (line  508)
* dN:                                    Debugging Options.  (line  282)
* dn:                                    Debugging Options.  (line  279)
* do:                                    Debugging Options.  (line  285)
* dP:                                    Debugging Options.  (line  342)
* dp:                                    Debugging Options.  (line  337)
* dR:                                    Debugging Options.  (line  291)
* dr:                                    Debugging Options.  (line  288)
* dS:                                    Debugging Options.  (line  298)
* ds:                                    Debugging Options.  (line  294)
* dT:                                    Debugging Options.  (line  305)
* dt:                                    Debugging Options.  (line  301)
* dU:                                    Debugging Options.  (line  311)
* du:                                    Debugging Options.  (line  308)
* dumpmachine:                           Debugging Options.  (line  504)
* dumpspecs:                             Debugging Options.  (line  512)
* dumpversion:                           Debugging Options.  (line  508)
* dv:                                    Debugging Options.  (line  346)
* dV:                                    Debugging Options.  (line  314)
* dw:                                    Debugging Options.  (line  318)
* dx:                                    Debugging Options.  (line  351)
* dy:                                    Debugging Options.  (line  355)
* dylib_file:                            Darwin Options.     (line   87)
* dylinker_install_name:                 Darwin Options.     (line   87)
* dynamic:                               Darwin Options.     (line   87)
* dynamiclib:                            Darwin Options.     (line   87)
* dZ:                                    Debugging Options.  (line  324)
* dz:                                    Debugging Options.  (line  321)
* E <1>:                                 Link Options.       (line   20)
* E:                                     Overall Options.    (line  147)
* EB <1>:                                ARC Options.        (line   12)
* EB:                                    MIPS Options.       (line    7)
* EL <1>:                                ARC Options.        (line    9)
* EL:                                    MIPS Options.       (line   10)
* exported_symbols_list:                 Darwin Options.     (line   87)
* fabi-version:                          C++ Dialect Options.
                                                             (line   20)
* falign-functions:                      Optimize Options.   (line  644)
* falign-jumps:                          Optimize Options.   (line  694)
* falign-labels:                         Optimize Options.   (line  662)
* falign-loops:                          Optimize Options.   (line  680)
* fargument-alias:                       Code Gen Options.   (line  314)
* fargument-noalias:                     Code Gen Options.   (line  314)
* fargument-noalias-global:              Code Gen Options.   (line  314)
* fbounds-check:                         Code Gen Options.   (line   15)
* fbranch-probabilities:                 Optimize Options.   (line  876)
* fbranch-target-load-optimize:          Optimize Options.   (line 1004)
* fbranch-target-load-optimize2:         Optimize Options.   (line 1010)
* fcall-saved <1>:                       Interoperation.     (line  197)
* fcall-saved:                           Code Gen Options.   (line  230)
* fcall-used:                            Code Gen Options.   (line  216)
* fcaller-saves:                         Optimize Options.   (line  516)
* fcheck-new:                            C++ Dialect Options.
                                                             (line   34)
* fcommon:                               Variable Attributes.
                                                             (line   92)
* fcond-mismatch:                        C Dialect Options.  (line  197)
* fconserve-space:                       C++ Dialect Options.
                                                             (line   44)
* fconstant-string-class:                Objective-C Dialect Options.
                                                             (line   24)
* fcse-follow-jumps:                     Optimize Options.   (line  311)
* fcse-skip-blocks:                      Optimize Options.   (line  320)
* fdata-sections:                        Optimize Options.   (line  985)
* fdelayed-branch:                       Optimize Options.   (line  435)
* fdelete-null-pointer-checks:           Optimize Options.   (line  404)
* fdiagnostics-show-location:            Language Independent Options.
                                                             (line   21)
* fdollars-in-identifiers <1>:           Interoperation.     (line  193)
* fdollars-in-identifiers:               Preprocessor Options.
                                                             (line  409)
* fdump-class-hierarchy:                 Debugging Options.  (line  374)
* fdump-translation-unit:                Debugging Options.  (line  366)
* fdump-tree:                            Debugging Options.  (line  382)
* fdump-unnumbered:                      Debugging Options.  (line  358)
* feliminate-dwarf2-dups:                Debugging Options.  (line  112)
* feliminate-unused-debug-symbols:       Debugging Options.  (line   53)
* feliminate-unused-debug-types:         Debugging Options.  (line  516)
* fexceptions:                           Code Gen Options.   (line   34)
* fexec-charset:                         Preprocessor Options.
                                                             (line  431)
* fexpensive-optimizations:              Optimize Options.   (line  417)
* ffast-math:                            Optimize Options.   (line  767)
* ffinite-math-only:                     Optimize Options.   (line  807)
* ffixed:                                Code Gen Options.   (line  204)
* ffloat-store <1>:                      Disappointments.    (line   79)
* ffloat-store:                          Optimize Options.   (line  753)
* ffor-scope:                            C++ Dialect Options.
                                                             (line   81)
* fforce-addr:                           Optimize Options.   (line  141)
* fforce-mem:                            Optimize Options.   (line  132)
* ffreestanding <1>:                     Function Attributes.
                                                             (line  168)
* ffreestanding <2>:                     C Dialect Options.  (line  162)
* ffreestanding:                         Standards.          (line   81)
* ffunction-sections:                    Optimize Options.   (line  985)
* fgcse:                                 Optimize Options.   (line  339)
* fgcse-las:                             Optimize Options.   (line  368)
* fgcse-lm:                              Optimize Options.   (line  350)
* fgcse-sm:                              Optimize Options.   (line  359)
* fgnu-runtime:                          Objective-C Dialect Options.
                                                             (line   33)
* fhosted:                               C Dialect Options.  (line  155)
* filelist:                              Darwin Options.     (line   87)
* finhibit-size-directive:               Code Gen Options.   (line  154)
* finline-functions:                     Optimize Options.   (line  173)
* finline-limit:                         Optimize Options.   (line  184)
* finput-charset:                        Preprocessor Options.
                                                             (line  444)
* finstrument-functions <1>:             Function Attributes.
                                                             (line  244)
* finstrument-functions:                 Code Gen Options.   (line  255)
* fkeep-inline-functions <1>:            Inline.             (line   51)
* fkeep-inline-functions:                Optimize Options.   (line  222)
* fkeep-static-consts:                   Optimize Options.   (line  228)
* flat_namespace:                        Darwin Options.     (line   87)
* fleading-underscore:                   Code Gen Options.   (line  329)
* floop-optimize:                        Optimize Options.   (line  375)
* fmem-report:                           Debugging Options.  (line  137)
* fmessage-length:                       Language Independent Options.
                                                             (line   15)
* fmove-all-movables:                    Optimize Options.   (line  529)
* fms-extensions <1>:                    C++ Dialect Options.
                                                             (line  116)
* fms-extensions:                        C Dialect Options.  (line  172)
* fnew-ra:                               Optimize Options.   (line  257)
* fnext-runtime:                         Objective-C Dialect Options.
                                                             (line   37)
* fno-access-control:                    C++ Dialect Options.
                                                             (line   30)
* fno-asm:                               C Dialect Options.  (line  113)
* fno-branch-count-reg:                  Optimize Options.   (line  262)
* fno-builtin <1>:                       Other Builtins.     (line   14)
* fno-builtin:                           C Dialect Options.  (line  127)
* fno-common <1>:                        Variable Attributes.
                                                             (line   92)
* fno-common:                            Code Gen Options.   (line  142)
* fno-const-strings:                     C++ Dialect Options.
                                                             (line   56)
* fno-cprop-registers:                   Optimize Options.   (line  725)
* fno-default-inline <1>:                Inline.             (line   46)
* fno-default-inline <2>:                Optimize Options.   (line  117)
* fno-default-inline:                    C++ Dialect Options.
                                                             (line  187)
* fno-defer-pop:                         Optimize Options.   (line  124)
* fno-elide-constructors:                C++ Dialect Options.
                                                             (line   67)
* fno-enforce-eh-specs:                  C++ Dialect Options.
                                                             (line   73)
* fno-for-scope:                         C++ Dialect Options.
                                                             (line   81)
* fno-function-cse:                      Optimize Options.   (line  273)
* fno-gnu-keywords:                      C++ Dialect Options.
                                                             (line   93)
* fno-guess-branch-probability:          Optimize Options.   (line  563)
* fno-ident:                             Code Gen Options.   (line  151)
* fno-implement-inlines <1>:             C++ Interface.      (line   91)
* fno-implement-inlines:                 C++ Dialect Options.
                                                             (line  110)
* fno-implicit-inline-templates:         C++ Dialect Options.
                                                             (line  104)
* fno-implicit-templates <1>:            Template Instantiation.
                                                             (line   87)
* fno-implicit-templates:                C++ Dialect Options.
                                                             (line   98)
* fno-inline:                            Optimize Options.   (line  167)
* fno-math-errno:                        Optimize Options.   (line  780)
* fno-nil-receivers:                     Objective-C Dialect Options.
                                                             (line   43)
* fno-nonansi-builtins:                  C++ Dialect Options.
                                                             (line  121)
* fno-operator-names:                    C++ Dialect Options.
                                                             (line  126)
* fno-optional-diags:                    C++ Dialect Options.
                                                             (line  130)
* fno-peephole:                          Optimize Options.   (line  554)
* fno-peephole2:                         Optimize Options.   (line  554)
* fno-rtti:                              C++ Dialect Options.
                                                             (line  145)
* fno-sched-interblock:                  Optimize Options.   (line  461)
* fno-sched-spec:                        Optimize Options.   (line  466)
* fno-show-column:                       Preprocessor Options.
                                                             (line  469)
* fno-signed-bitfields:                  C Dialect Options.  (line  230)
* fno-stack-limit:                       Code Gen Options.   (line  298)
* fno-trapping-math:                     Optimize Options.   (line  817)
* fno-unsigned-bitfields:                C Dialect Options.  (line  230)
* fno-weak:                              C++ Dialect Options.
                                                             (line  172)
* fno-working-directory:                 Preprocessor Options.
                                                             (line  454)
* fno-zero-initialized-in-bss:           Optimize Options.   (line  284)
* fnon-call-exceptions:                  Code Gen Options.   (line   48)
* fobjc-exceptions:                      Objective-C Dialect Options.
                                                             (line   50)
* fold-unroll-all-loops:                 Optimize Options.   (line  960)
* fold-unroll-loops:                     Optimize Options.   (line  952)
* fomit-frame-pointer:                   Optimize Options.   (line  146)
* foptimize-register-move:               Optimize Options.   (line  424)
* foptimize-sibling-calls:               Optimize Options.   (line  162)
* force_cpusubtype_ALL:                  Darwin Options.     (line   87)
* force_flat_namespace:                  Darwin Options.     (line   87)
* fpack-struct:                          Code Gen Options.   (line  247)
* fpcc-struct-return <1>:                Incompatibilities.  (line  174)
* fpcc-struct-return:                    Code Gen Options.   (line   70)
* fpch-deps:                             Preprocessor Options.
                                                             (line  281)
* fpeel-loops:                           Optimize Options.   (line  941)
* fpermissive:                           C++ Dialect Options.
                                                             (line  135)
* fPIC:                                  Code Gen Options.   (line  188)
* fpic:                                  Code Gen Options.   (line  170)
* fPIE:                                  Code Gen Options.   (line  198)
* fpie:                                  Code Gen Options.   (line  198)
* fprefetch-loop-arrays:                 Optimize Options.   (line  977)
* fpreprocessed:                         Preprocessor Options.
                                                             (line  412)
* fprofile-arcs <1>:                     Other Builtins.     (line  227)
* fprofile-arcs:                         Debugging Options.  (line  141)
* fprofile-generate:                     Optimize Options.   (line  732)
* fprofile-use:                          Optimize Options.   (line  741)
* fprofile-values:                       Optimize Options.   (line  895)
* frandom-string:                        Debugging Options.  (line  415)
* freduce-all-givs:                      Optimize Options.   (line  533)
* freg-struct-return:                    Code Gen Options.   (line   88)
* fregmove:                              Optimize Options.   (line  424)
* frename-registers:                     Optimize Options.   (line  707)
* freorder-blocks:                       Optimize Options.   (line  581)
* freorder-functions:                    Optimize Options.   (line  587)
* freplace-objc-classes:                 Objective-C Dialect Options.
                                                             (line  135)
* frepo <1>:                             Template Instantiation.
                                                             (line   62)
* frepo:                                 C++ Dialect Options.
                                                             (line  140)
* frerun-cse-after-loop:                 Optimize Options.   (line  328)
* frerun-loop-opt:                       Optimize Options.   (line  334)
* frounding-math:                        Optimize Options.   (line  832)
* fsched-spec-load:                      Optimize Options.   (line  471)
* fsched-spec-load-dangerous:            Optimize Options.   (line  476)
* fsched-stalled-insns:                  Optimize Options.   (line  481)
* fsched-stalled-insns-dep:              Optimize Options.   (line  486)
* fsched-verbose:                        Debugging Options.  (line  425)
* fsched2-use-superblocks:               Optimize Options.   (line  493)
* fsched2-use-traces:                    Optimize Options.   (line  504)
* fschedule-insns:                       Optimize Options.   (line  442)
* fschedule-insns2:                      Optimize Options.   (line  452)
* fshared-data:                          Code Gen Options.   (line  135)
* fshort-double:                         Code Gen Options.   (line  117)
* fshort-enums <1>:                      Non-bugs.           (line   37)
* fshort-enums <2>:                      Type Attributes.    (line  112)
* fshort-enums:                          Code Gen Options.   (line  106)
* fshort-wchar:                          Code Gen Options.   (line  125)
* fsignaling-nans:                       Optimize Options.   (line  852)
* fsigned-bitfields <1>:                 Non-bugs.           (line   52)
* fsigned-bitfields:                     C Dialect Options.  (line  230)
* fsigned-char:                          C Dialect Options.  (line  220)
* fsingle-precision-constant:            Optimize Options.   (line  867)
* fstack-check:                          Code Gen Options.   (line  283)
* fstack-limit-register:                 Code Gen Options.   (line  298)
* fstack-limit-symbol:                   Code Gen Options.   (line  298)
* fstats:                                C++ Dialect Options.
                                                             (line  153)
* fstrength-reduce:                      Optimize Options.   (line  296)
* fstrict-aliasing:                      Optimize Options.   (line  601)
* fsyntax-only:                          Warning Options.    (line   22)
* ftabstop:                              Preprocessor Options.
                                                             (line  425)
* ftemplate-depth:                       C++ Dialect Options.
                                                             (line  158)
* ftest-coverage:                        Debugging Options.  (line  190)
* fthread-jumps:                         Optimize Options.   (line  302)
* ftime-report:                          Debugging Options.  (line  133)
* ftracer:                               Optimize Options.   (line  917)
* ftrapv:                                Code Gen Options.   (line   22)
* funit-at-a-time:                       Optimize Options.   (line  922)
* funroll-all-loops:                     Optimize Options.   (line  935)
* funroll-loops <1>:                     Non-bugs.           (line  168)
* funroll-loops:                         Optimize Options.   (line  927)
* funsafe-math-optimizations:            Optimize Options.   (line  793)
* funsigned-bitfields <1>:               Non-bugs.           (line   52)
* funsigned-bitfields:                   C Dialect Options.  (line  230)
* funsigned-char:                        C Dialect Options.  (line  202)
* funswitch-loops:                       Optimize Options.   (line  947)
* funwind-tables:                        Code Gen Options.   (line   57)
* fuse-cxa-atexit:                       C++ Dialect Options.
                                                             (line  165)
* fverbose-asm:                          Code Gen Options.   (line  161)
* fvpt:                                  Optimize Options.   (line  903)
* fweb:                                  Optimize Options.   (line  714)
* fwide-exec-charset:                    Preprocessor Options.
                                                             (line  436)
* fworking-directory:                    Preprocessor Options.
                                                             (line  454)
* fwrapv:                                Code Gen Options.   (line   26)
* fwritable-strings <1>:                 Incompatibilities.  (line   22)
* fwritable-strings:                     C Dialect Options.  (line  236)
* fzero-link:                            Objective-C Dialect Options.
                                                             (line  145)
* G <1>:                                 System V Options.   (line   10)
* G <2>:                                 MIPS Options.       (line  177)
* G <3>:                                 RS/6000 and PowerPC Options.
                                                             (line  508)
* G:                                     M32R/D Options.     (line   57)
* g:                                     Debugging Options.  (line   10)
* gcoff:                                 Debugging Options.  (line   63)
* gdwarf-2:                              Debugging Options.  (line   81)
* gen-decls:                             Objective-C Dialect Options.
                                                             (line  155)
* ggdb:                                  Debugging Options.  (line   39)
* gnu-ld:                                HPPA Options.       (line  110)
* gstabs:                                Debugging Options.  (line   45)
* gstabs+:                               Debugging Options.  (line   57)
* gvms:                                  Debugging Options.  (line   85)
* gxcoff:                                Debugging Options.  (line   68)
* gxcoff+:                               Debugging Options.  (line   73)
* H:                                     Preprocessor Options.
                                                             (line  576)
* headerpad_max_install_names:           Darwin Options.     (line   87)
* help <1>:                              Preprocessor Options.
                                                             (line  568)
* help:                                  Overall Options.    (line  185)
* hp-ld:                                 HPPA Options.       (line  120)
* I <1>:                                 Directory Options.  (line   10)
* I:                                     Preprocessor Options.
                                                             (line   65)
* I- <1>:                                Directory Options.  (line   31)
* I-:                                    Preprocessor Options.
                                                             (line  345)
* idirafter:                             Preprocessor Options.
                                                             (line  386)
* if-conversion:                         Optimize Options.   (line  389)
* if-conversion2:                        Optimize Options.   (line  398)
* imacros:                               Preprocessor Options.
                                                             (line  377)
* image_base:                            Darwin Options.     (line   87)
* include:                               Preprocessor Options.
                                                             (line  366)
* init:                                  Darwin Options.     (line   87)
* install_name:                          Darwin Options.     (line   87)
* iprefix:                               Preprocessor Options.
                                                             (line  391)
* isystem:                               Preprocessor Options.
                                                             (line  403)
* iwithprefix:                           Preprocessor Options.
                                                             (line  397)
* iwithprefixbefore:                     Preprocessor Options.
                                                             (line  397)
* keep_private_externs:                  Darwin Options.     (line   87)
* L:                                     Directory Options.  (line   51)
* l:                                     Link Options.       (line   26)
* lobjc:                                 Link Options.       (line   53)
* M:                                     Preprocessor Options.
                                                             (line  174)
* m1:                                    SH Options.         (line    9)
* m10:                                   PDP-11 Options.     (line   29)
* m128bit-long-double:                   i386 and x86-64 Options.
                                                             (line  216)
* m16-bit:                               CRIS Options.       (line   69)
* m2:                                    SH Options.         (line   12)
* m210:                                  MCore Options.      (line   43)
* m3:                                    SH Options.         (line   18)
* m31:                                   S/390 and zSeries Options.
                                                             (line   35)
* m32 <1>:                               i386 and x86-64 Options.
                                                             (line  391)
* m32:                                   SPARC Options.      (line  218)
* m32-bit:                               CRIS Options.       (line   69)
* m32032:                                NS32K Options.      (line   13)
* m32081:                                NS32K Options.      (line   27)
* m32332:                                NS32K Options.      (line   18)
* m32381:                                NS32K Options.      (line   31)
* m32532:                                NS32K Options.      (line   23)
* m32r:                                  M32R/D Options.     (line   15)
* m32r2:                                 M32R/D Options.     (line    9)
* m32rx:                                 M32R/D Options.     (line   12)
* m340:                                  MCore Options.      (line   43)
* m386:                                  i386 and x86-64 Options.
                                                             (line  107)
* m3dnow:                                i386 and x86-64 Options.
                                                             (line  323)
* m3e:                                   SH Options.         (line   21)
* m4:                                    SH Options.         (line   35)
* m4-nofpu:                              SH Options.         (line   24)
* m4-single:                             SH Options.         (line   31)
* m4-single-only:                        SH Options.         (line   27)
* m40:                                   PDP-11 Options.     (line   23)
* m45:                                   PDP-11 Options.     (line   26)
* m486:                                  i386 and x86-64 Options.
                                                             (line  107)
* m4byte-functions:                      MCore Options.      (line   27)
* m5200:                                 M680x0 Options.     (line   59)
* m64 <1>:                               S/390 and zSeries Options.
                                                             (line   35)
* m64 <2>:                               i386 and x86-64 Options.
                                                             (line  391)
* m64:                                   SPARC Options.      (line  218)
* m68000:                                M680x0 Options.     (line   13)
* m68020:                                M680x0 Options.     (line   21)
* m68020-40:                             M680x0 Options.     (line   66)
* m68020-60:                             M680x0 Options.     (line   73)
* m68030:                                M680x0 Options.     (line   30)
* m68040:                                M680x0 Options.     (line   34)
* m68060:                                M680x0 Options.     (line   42)
* m6811:                                 M68hc1x Options.    (line   13)
* m6812:                                 M68hc1x Options.    (line   18)
* m68881:                                M680x0 Options.     (line   25)
* m68hc11:                               M68hc1x Options.    (line   13)
* m68hc12:                               M68hc1x Options.    (line   18)
* m68hcs12:                              M68hc1x Options.    (line   23)
* m68S12:                                M68hc1x Options.    (line   23)
* m8-bit:                                CRIS Options.       (line   69)
* m96bit-long-double:                    i386 and x86-64 Options.
                                                             (line  216)
* mabi-mmixware:                         MMIX Options.       (line   20)
* mabi=32:                               MIPS Options.       (line   87)
* mabi=64:                               MIPS Options.       (line   87)
* mabi=altivec:                          RS/6000 and PowerPC Options.
                                                             (line  403)
* mabi=eabi:                             MIPS Options.       (line   87)
* mabi=gnu:                              MMIX Options.       (line   20)
* mabi=n32:                              MIPS Options.       (line   87)
* mabi=no-altivec:                       RS/6000 and PowerPC Options.
                                                             (line  408)
* mabi=no-spe:                           RS/6000 and PowerPC Options.
                                                             (line  146)
* mabi=o64:                              MIPS Options.       (line   87)
* mabi=spe:                              RS/6000 and PowerPC Options.
                                                             (line  141)
* mabicalls:                             MIPS Options.       (line   95)
* mabort-on-noreturn:                    ARM Options.        (line  171)
* mabshi:                                PDP-11 Options.     (line   55)
* mac0:                                  PDP-11 Options.     (line   16)
* macc-4:                                FRV Options.        (line   59)
* macc-8:                                FRV Options.        (line   62)
* maccumulate-outgoing-args:             i386 and x86-64 Options.
                                                             (line  342)
* mads:                                  RS/6000 and PowerPC Options.
                                                             (line  433)
* maix-struct-return:                    RS/6000 and PowerPC Options.
                                                             (line  396)
* maix32:                                RS/6000 and PowerPC Options.
                                                             (line  196)
* maix64:                                RS/6000 and PowerPC Options.
                                                             (line  196)
* malign-300:                            H8/300 Options.     (line   31)
* malign-double:                         i386 and x86-64 Options.
                                                             (line  202)
* malign-int:                            M680x0 Options.     (line  125)
* malign-loops:                          M32R/D Options.     (line   73)
* malign-natural:                        RS/6000 and PowerPC Options.
                                                             (line  229)
* malign-power:                          RS/6000 and PowerPC Options.
                                                             (line  229)
* malignment-traps:                      ARM Options.        (line   87)
* malloc-cc:                             FRV Options.        (line   25)
* malpha-as:                             DEC Alpha Options.  (line  159)
* maltivec:                              RS/6000 and PowerPC Options.
                                                             (line  135)
* mam33:                                 MN10300 Options.    (line   17)
* maout:                                 CRIS Options.       (line   92)
* mapcs:                                 ARM Options.        (line   18)
* mapcs-26:                              ARM Options.        (line   21)
* mapcs-32:                              ARM Options.        (line   29)
* mapcs-frame:                           ARM Options.        (line   10)
* mapp-regs <1>:                         V850 Options.       (line   57)
* mapp-regs:                             SPARC Options.      (line   10)
* march <1>:                             CRIS Options.       (line   10)
* march <2>:                             S/390 and zSeries Options.
                                                             (line   63)
* march <3>:                             HPPA Options.       (line    9)
* march <4>:                             i386 and x86-64 Options.
                                                             (line   96)
* march <5>:                             MIPS Options.       (line   14)
* march:                                 ARM Options.        (line  144)
* masm-compat:                           Intel 960 Options.  (line   58)
* masm-optimize:                         D30V Options.       (line   24)
* masm=DIALECT:                          i386 and x86-64 Options.
                                                             (line  159)
* mauto-incdec:                          M68hc1x Options.    (line   26)
* mauto-pic:                             IA-64 Options.      (line   53)
* mb:                                    SH Options.         (line   38)
* mb-step:                               IA-64 Options.      (line   36)
* mbackchain:                            S/390 and zSeries Options.
                                                             (line   20)
* mbase-addresses:                       MMIX Options.       (line   54)
* mbcopy:                                PDP-11 Options.     (line   36)
* mbig <1>:                              TMS320C3x/C4x Options.
                                                             (line   18)
* mbig:                                  RS/6000 and PowerPC Options.
                                                             (line  328)
* mbig-endian <1>:                       IA-64 Options.      (line    9)
* mbig-endian <2>:                       MCore Options.      (line   39)
* mbig-endian <3>:                       RS/6000 and PowerPC Options.
                                                             (line  328)
* mbig-endian:                           ARM Options.        (line   75)
* mbig-memory:                           TMS320C3x/C4x Options.
                                                             (line   18)
* mbig-switch <1>:                       V850 Options.       (line   52)
* mbig-switch:                           HPPA Options.       (line   27)
* mbigtable:                             SH Options.         (line   54)
* mbit-align:                            RS/6000 and PowerPC Options.
                                                             (line  282)
* mbitfield <1>:                         NS32K Options.      (line   66)
* mbitfield:                             M680x0 Options.     (line   97)
* mbk:                                   TMS320C3x/C4x Options.
                                                             (line   27)
* mbranch-cheap:                         PDP-11 Options.     (line   65)
* mbranch-cost:                          D30V Options.       (line   29)
* mbranch-cost=NUMBER:                   M32R/D Options.     (line   82)
* mbranch-expensive:                     PDP-11 Options.     (line   61)
* mbranch-likely:                        MIPS Options.       (line  291)
* mbranch-predict:                       MMIX Options.       (line   49)
* mbuild-constants:                      DEC Alpha Options.  (line  142)
* mbwx:                                  DEC Alpha Options.  (line  171)
* mc68000:                               M680x0 Options.     (line   13)
* mc68020:                               M680x0 Options.     (line   21)
* mca:                                   Intel 960 Options.  (line    9)
* mcall-gnu:                             RS/6000 and PowerPC Options.
                                                             (line  388)
* mcall-linux:                           RS/6000 and PowerPC Options.
                                                             (line  384)
* mcall-netbsd:                          RS/6000 and PowerPC Options.
                                                             (line  392)
* mcall-prologues:                       AVR Options.        (line   43)
* mcall-solaris:                         RS/6000 and PowerPC Options.
                                                             (line  380)
* mcall-sysv:                            RS/6000 and PowerPC Options.
                                                             (line  367)
* mcall-sysv-eabi:                       RS/6000 and PowerPC Options.
                                                             (line  374)
* mcall-sysv-noeabi:                     RS/6000 and PowerPC Options.
                                                             (line  377)
* mcallee-super-interworking:            ARM Options.        (line  261)
* mcaller-super-interworking:            ARM Options.        (line  267)
* mcallgraph-data:                       MCore Options.      (line   31)
* mcc-init:                              CRIS Options.       (line   46)
* mcf:                                   Intel 960 Options.  (line    9)
* mcheck-zero-division:                  MIPS Options.       (line  235)
* mcirrus-fix-invalid-insns:             ARM Options.        (line  214)
* mcix:                                  DEC Alpha Options.  (line  171)
* mcmodel=embmedany:                     SPARC Options.      (line  240)
* mcmodel=kernel:                        i386 and x86-64 Options.
                                                             (line  412)
* mcmodel=large:                         i386 and x86-64 Options.
                                                             (line  424)
* mcmodel=medany:                        SPARC Options.      (line  234)
* mcmodel=medium:                        i386 and x86-64 Options.
                                                             (line  417)
* mcmodel=medlow:                        SPARC Options.      (line  223)
* mcmodel=medmid:                        SPARC Options.      (line  228)
* mcmodel=small:                         i386 and x86-64 Options.
                                                             (line  406)
* mcode-align:                           Intel 960 Options.  (line   47)
* mcomplex-addr:                         Intel 960 Options.  (line   39)
* mcond-exec <1>:                        FRV Options.        (line   98)
* mcond-exec:                            D30V Options.       (line   34)
* mcond-move:                            FRV Options.        (line   74)
* mconst-align:                          CRIS Options.       (line   60)
* mconst16:                              Xtensa Options.     (line   10)
* mconstant-gp:                          IA-64 Options.      (line   49)
* mcpu <1>:                              FRV Options.        (line  150)
* mcpu <2>:                              CRIS Options.       (line   10)
* mcpu <3>:                              ARC Options.        (line   23)
* mcpu <4>:                              TMS320C3x/C4x Options.
                                                             (line    9)
* mcpu <5>:                              DEC Alpha Options.  (line  223)
* mcpu <6>:                              i386 and x86-64 Options.
                                                             (line  101)
* mcpu <7>:                              RS/6000 and PowerPC Options.
                                                             (line   82)
* mcpu <8>:                              ARM Options.        (line  121)
* mcpu:                                  SPARC Options.      (line  127)
* mcpu32:                                M680x0 Options.     (line   51)
* mcypress:                              SPARC Options.      (line  122)
* MD:                                    Preprocessor Options.
                                                             (line  262)
* mdalign:                               SH Options.         (line   44)
* mdata:                                 ARC Options.        (line   30)
* mdata-align:                           CRIS Options.       (line   60)
* mdb:                                   TMS320C3x/C4x Options.
                                                             (line   32)
* mdebug <1>:                            S/390 and zSeries Options.
                                                             (line   59)
* mdebug:                                M32R/D Options.     (line   69)
* mdec-asm:                              PDP-11 Options.     (line   78)
* mdisable-callt:                        V850 Options.       (line   80)
* mdisable-fpregs:                       HPPA Options.       (line   37)
* mdisable-indexing:                     HPPA Options.       (line   44)
* mdiv:                                  MCore Options.      (line   15)
* mdouble:                               FRV Options.        (line   38)
* mdouble-float:                         MIPS Options.       (line  154)
* mdp-isr-reload:                        TMS320C3x/C4x Options.
                                                             (line   45)
* mdwarf2-asm:                           IA-64 Options.      (line   74)
* mdword:                                FRV Options.        (line   32)
* mdynamic-no-pic:                       RS/6000 and PowerPC Options.
                                                             (line  333)
* meabi:                                 RS/6000 and PowerPC Options.
                                                             (line  456)
* mearly-stop-bits:                      IA-64 Options.      (line   87)
* melf <1>:                              MMIX Options.       (line   44)
* melf:                                  CRIS Options.       (line   95)
* melinux:                               CRIS Options.       (line   99)
* melinux-stacksize:                     CRIS Options.       (line   25)
* memb:                                  RS/6000 and PowerPC Options.
                                                             (line  451)
* membedded-data:                        MIPS Options.       (line  186)
* membedded-pic:                         MIPS Options.       (line  124)
* mep:                                   V850 Options.       (line   16)
* mepsilon:                              MMIX Options.       (line   15)
* mesa:                                  S/390 and zSeries Options.
                                                             (line   43)
* metrax100:                             CRIS Options.       (line   31)
* metrax4:                               CRIS Options.       (line   31)
* mexplicit-relocs <1>:                  DEC Alpha Options.  (line  184)
* mexplicit-relocs:                      MIPS Options.       (line  206)
* mextmem:                               D30V Options.       (line    9)
* mextmemory:                            D30V Options.       (line   14)
* MF:                                    Preprocessor Options.
                                                             (line  208)
* mfast-fix:                             TMS320C3x/C4x Options.
                                                             (line   62)
* mfast-indirect-calls:                  HPPA Options.       (line   56)
* mfaster-structs:                       SPARC Options.      (line   88)
* mfix:                                  DEC Alpha Options.  (line  171)
* mfix-sb1:                              MIPS Options.       (line  275)
* mfixed-cc:                             FRV Options.        (line   28)
* mfixed-range:                          IA-64 Options.      (line   79)
* mflat:                                 SPARC Options.      (line   59)
* mfloat-gprs:                           RS/6000 and PowerPC Options.
                                                             (line  160)
* mfloat-ieee:                           DEC Alpha Options.  (line  179)
* mfloat-vax:                            DEC Alpha Options.  (line  179)
* mfloat32:                              PDP-11 Options.     (line   52)
* mfloat64:                              PDP-11 Options.     (line   48)
* mflush-func:                           MIPS Options.       (line  281)
* mflush-func=NAME:                      M32R/D Options.     (line   94)
* mflush-trap=NUMBER:                    M32R/D Options.     (line   87)
* mfmovd:                                SH Options.         (line   58)
* mfp:                                   ARM Options.        (line  153)
* mfp-reg:                               DEC Alpha Options.  (line   25)
* mfp-rounding-mode:                     DEC Alpha Options.  (line   85)
* mfp-trap-mode:                         DEC Alpha Options.  (line   63)
* mfp32:                                 MIPS Options.       (line  137)
* mfp64:                                 MIPS Options.       (line  140)
* mfpe:                                  ARM Options.        (line  153)
* mfpr-32:                               FRV Options.        (line   13)
* mfpr-64:                               FRV Options.        (line   16)
* mfpu <1>:                              PDP-11 Options.     (line    9)
* mfpu:                                  SPARC Options.      (line   20)
* mfull-toc:                             RS/6000 and PowerPC Options.
                                                             (line  169)
* mfused-madd <1>:                       Xtensa Options.     (line   19)
* mfused-madd <2>:                       S/390 and zSeries Options.
                                                             (line   77)
* mfused-madd <3>:                       MIPS Options.       (line  260)
* mfused-madd:                           RS/6000 and PowerPC Options.
                                                             (line  276)
* mg:                                    VAX Options.        (line   17)
* MG:                                    Preprocessor Options.
                                                             (line  217)
* mgas <1>:                              DEC Alpha Options.  (line  159)
* mgas:                                  HPPA Options.       (line   72)
* mgnu:                                  VAX Options.        (line   13)
* mgnu-as:                               IA-64 Options.      (line   18)
* mgnu-ld:                               IA-64 Options.      (line   23)
* mgotplt:                               CRIS Options.       (line   86)
* mgp32:                                 MIPS Options.       (line  131)
* mgp64:                                 MIPS Options.       (line  134)
* mgpr-32:                               FRV Options.        (line    7)
* mgpr-64:                               FRV Options.        (line   10)
* mh:                                    H8/300 Options.     (line   14)
* mhard-float <1>:                       FRV Options.        (line   19)
* mhard-float <2>:                       S/390 and zSeries Options.
                                                             (line   11)
* mhard-float <3>:                       MIPS Options.       (line  143)
* mhard-float <4>:                       RS/6000 and PowerPC Options.
                                                             (line  238)
* mhard-float <5>:                       ARM Options.        (line   53)
* mhard-float:                           SPARC Options.      (line   20)
* mhard-quad-float:                      SPARC Options.      (line   41)
* mhardlit:                              MCore Options.      (line   10)
* mhimem:                                NS32K Options.      (line  111)
* mhitachi:                              SH Options.         (line   61)
* mic-compat:                            Intel 960 Options.  (line   54)
* mic2.0-compat:                         Intel 960 Options.  (line   54)
* mic3.0-compat:                         Intel 960 Options.  (line   54)
* mieee <1>:                             SH Options.         (line   68)
* mieee:                                 DEC Alpha Options.  (line   39)
* mieee-compare:                         NS32K Options.      (line   55)
* mieee-conformant:                      DEC Alpha Options.  (line  134)
* mieee-fp:                              i386 and x86-64 Options.
                                                             (line  164)
* mieee-with-inexact:                    DEC Alpha Options.  (line   52)
* mimpure-text:                          SPARC Options.      (line   98)
* minit-stack:                           AVR Options.        (line   35)
* minline-all-stringops:                 i386 and x86-64 Options.
                                                             (line  363)
* minline-float-divide-max-throughput:   IA-64 Options.      (line   61)
* minline-float-divide-min-latency:      IA-64 Options.      (line   57)
* minline-int-divide-max-throughput:     IA-64 Options.      (line   69)
* minline-int-divide-min-latency:        IA-64 Options.      (line   65)
* minmax:                                M68hc1x Options.    (line   31)
* minsert-sched-nops:                    RS/6000 and PowerPC Options.
                                                             (line  355)
* mint16:                                PDP-11 Options.     (line   40)
* mint32 <1>:                            PDP-11 Options.     (line   44)
* mint32:                                H8/300 Options.     (line   28)
* mint64:                                MIPS Options.       (line  158)
* mintel-asm:                            Intel 960 Options.  (line   58)
* mips1:                                 MIPS Options.       (line   58)
* mips16:                                MIPS Options.       (line   80)
* mips2:                                 MIPS Options.       (line   61)
* mips3:                                 MIPS Options.       (line   64)
* mips32:                                MIPS Options.       (line   70)
* mips32r2:                              MIPS Options.       (line   73)
* mips4:                                 MIPS Options.       (line   67)
* mips64:                                MIPS Options.       (line   76)
* misel:                                 RS/6000 and PowerPC Options.
                                                             (line  150)
* misize:                                SH Options.         (line   71)
* missue-rate=NUMBER:                    M32R/D Options.     (line   79)
* mjump-in-delay:                        HPPA Options.       (line   32)
* mka:                                   Intel 960 Options.  (line    9)
* mkb:                                   Intel 960 Options.  (line    9)
* mknuthdiv:                             MMIX Options.       (line   33)
* ml:                                    SH Options.         (line   41)
* mlarge-data:                           DEC Alpha Options.  (line  195)
* mlarge-text:                           DEC Alpha Options.  (line  213)
* mleaf-procedures:                      Intel 960 Options.  (line   22)
* mlibfuncs:                             MMIX Options.       (line   10)
* mlibrary-pic:                          FRV Options.        (line   56)
* mlinker-opt:                           HPPA Options.       (line   82)
* mlinux:                                CRIS Options.       (line  104)
* mlittle:                               RS/6000 and PowerPC Options.
                                                             (line  322)
* mlittle-endian <1>:                    IA-64 Options.      (line   13)
* mlittle-endian <2>:                    MCore Options.      (line   39)
* mlittle-endian <3>:                    RS/6000 and PowerPC Options.
                                                             (line  322)
* mlittle-endian <4>:                    ARM Options.        (line   71)
* mlittle-endian:                        SPARC Options.      (line  212)
* mlong-calls <1>:                       V850 Options.       (line   10)
* mlong-calls <2>:                       MIPS Options.       (line  246)
* mlong-calls <3>:                       ARM Options.        (line  176)
* mlong-calls:                           M68hc1x Options.    (line   35)
* mlong-double-64:                       Intel 960 Options.  (line   70)
* mlong-load-store:                      HPPA Options.       (line   63)
* mlong32:                               MIPS Options.       (line  168)
* mlong64:                               MIPS Options.       (line  163)
* mlongcall:                             RS/6000 and PowerPC Options.
                                                             (line  522)
* mlongcalls:                            Xtensa Options.     (line   60)
* mloop-unsigned:                        TMS320C3x/C4x Options.
                                                             (line   94)
* MM:                                    Preprocessor Options.
                                                             (line  198)
* mmad:                                  MIPS Options.       (line  255)
* mmangle-cpu:                           ARC Options.        (line   15)
* mmax:                                  DEC Alpha Options.  (line  171)
* mmax-stack-frame:                      CRIS Options.       (line   22)
* mmc:                                   Intel 960 Options.  (line    9)
* mmcu:                                  AVR Options.        (line    9)
* MMD:                                   Preprocessor Options.
                                                             (line  277)
* mmedia: