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- From: greg@gmp.lonestar.org (G.R. Basile)
- Newsgroups: comp.dsp
- Subject: Re: compilers for DSP processors
- Keywords: compilers, dsp, assembly language, vliw, c
- Message-ID: <FFV7VB1w164w@gmp.lonestar.org>
- Date: 22 Dec 92 14:58:02 GMT
- References: <75774@apple.apple.COM>
- Organization: GMP Research Co., Dallas TX
- Lines: 41
-
- malcolm@Apple.COM (Malcolm Slaney) writes:
-
- > cmh@eng.cam.ac.uk (C.M. Hicks) writes:
- > >DSP chips are designed to be fast, and to slow them down with compiled code
- > >seems daft, particularly in real-time applications.
- >
- > On most reasonable processors, people have found that the compilers write
- > better code than humans do. Compilers can do a much better job of global
- > register allocation, scheduling, and all the other things that make for
- > good translations. This is especially true of today's RISC machines (DEC,
- > IBM, HP, Sun, Cray, MIPS). For a good exposition of the power of a compiler,
- > read John Ellis' book on the Bulldog compiler for VLIW machines.
- >
- well, since you drag in RISC chips,
-
- I did an application that decompressed G4 images and then scaled the images for
- a for a 300 page per minute printer . The C compiler was GNU and the risc was the
- Intel 80960CA. The code had beed optimized a lot in C and was still not fast
- enough.
-
-
- My usual experience with C compilers on DSP's that a 8 to 10 x increase
- in speed is possible in the c to asm port. After looking at the output
- of the GNU 80960 C compiler, I was impressed with the efficiency of the
- assembler output. I estimated that the increase in speed in the c to asm
- port would be a factor of 2 at best. I was able to attain a 3x speed increase
- on the G4 decompression code and A 8X IMPROVEMENT on the scaling code.
-
- This speed increase was due to 1) using a machine instruction the
- complier was clueless about, and 2) an optimization of the scaling algorithmn
- that would have been not obvious at the compiler level.
- >
- > Listen up DSP makers....compilers can write better assembly code than us
- > mere humans.....especially if you give the compiler a chance. Pay attention
- > to the lessons that the RISC people taught the CISC dinasours.
- >
- DSP makers... I would rather you use the extra microcode on the processors to
- give a fast, application specific instructions than to create instructions
- that would make a C compiler more efficient.
-
- Greg Basile
-