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-funswitch-loops slowdown.is it possible to change settings in backend ?
- From: Bernd Roesch <nospamname at gmx dot de>
- To: gcc at gcc dot gnu dot org
- Cc: gcc at gcc dot gnu dot org
- Date: Tue, 23 Jun 2009 16:21:09 +0200
- Subject: -funswitch-loops slowdown.is it possible to change settings in backend ?
Hello
The -funswitch-loops Option seem work on gcc 4.3.0 and above not good for
speed.Test on m68k gcc.
It generate much larger code(wma123) and code is slower in many case (try
out ffmpeg H264 decode)i get report from a Athlon 2600+ with single channel
ram
running amiga 68k emulator.
But on my System use a AMD64 3000+ and Dual Channel ram running amiga
emulator
-funswitch-loops cause only large files but no slowdown.
but i guess on a real 68k/coldfire CPU without 2. level cache,
-funswitch-loops is more
not optimal.
gcc 3.4.0 have too this option set on -O3 or i am wrong ?
and here the speed is better and code is smaller
Is there a way to tweak some values on backend for specific CPU so
-funswitch-loops works 3.4.0(maybe unroll not so much loops ?
for now best solution for speed (H264 decode work on the system with single
Channel ram same ot little faster as 3.4.0 build.) is let disable
-funswitch-loops disable as far i get speedvalue reports.
here are some values that show too slowdown on compilers 4.2.4 and 4.3.0 but
on
X86
http://multimedia.cx/eggs/compiler-performance-profiling-with-ffmpeg/
Regards