[Bug rtl-optimization/11488] Pre-regalloc scheduling severely worsens performance

[mattst88 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=11488

Matt Turner <mattst88 at gmail dot com> changed:

           What    |Removed                     |Added
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                 CC|                            |mattst88 at gmail dot com

--- Comment #11 from Matt Turner <mattst88 at gmail dot com> ---
(In reply to Steven Bosscher from comment #10)
> Someone should try with -fsched-pressure...

On alpha with gcc-5.3.0:

% gcc -O2 -mbwx idct3.c && time ./a.out 
./a.out  1.72s user 0.00s system 99% cpu 1.721 total

% gcc -O2 -fno-schedule-insns -mbwx idct3.c && time ./a.out 
./a.out  0.96s user 0.01s system 99% cpu 0.970 total

% gcc -O2 -fsched-pressure -mbwx idct3.c && time ./a.out 
./a.out  1.01s user 0.00s system 99% cpu 1.016 total

(-mbwx is needed, otherwise -fsched-pressure/-fno-schedule-insns doesn't show
any benefit)

So it looks like -fsched-pressure helps significantly, but not quite as much as
-fno-schedule-insns.