[Bug optimization/11488] Scheduling severely worsens performance

[pinskia at physics dot uc dot edu]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

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


pinskia at physics dot uc dot edu changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|                            |1
   Last reconfirmed|0000-00-00 00:00:00         |2003-07-11 05:28:41
               date|                            |


------- Additional Comments From pinskia at physics dot uc dot edu  2003-07-11 05:28 -------
I can confirm this behavior  on PowerPC. 
In fact it is even worse on PowerPC (TiBook G4 with Mac OS X 10.2.6):
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c 
[omni:~/src/gccPRs] pinskia% time ./a.out
6.600u 0.010s 0:06.83 96.7%     0+0k 0+1io 0pf+0w
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fno-schedule-insns
[omni:~/src/gccPRs] pinskia% time ./a.out
1.830u 0.000s 0:01.87 97.8%     0+0k 0+0io 0pf+0w
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fnew-ra
[omni:~/src/gccPRs] pinskia% time ./a.out
6.120u 0.020s 0:06.57 93.4%     0+0k 0+0io 0pf+0w
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fno-schedule-insns -fnew-ra
[omni:~/src/gccPRs] pinskia% time ./a.out
1.760u 0.000s 0:01.81 97.2%     0+0k 0+0io 0pf+0w

A factor of 3.6 slower is the code that gcc produces without -fno-schedule-insns.