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

[pinskia at physics dot uc dot edu]

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



------- Additional Comments From pinskia at physics dot uc dot edu  2003-07-11 05:59 -------
The Older Non-DFA one had the same problem on powerpc at least.
Here is the numbers with turning scheduling off:
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fno-schedule-insns -fnew-ra -fno-
schedule-insns2
[omni:~/src/gccPRs] pinskia% time ./a.out
1.920u 0.020s 0:02.45 79.1%     0+0k 7+1io 0pf+0w
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fno-schedule-insns -fno-schedule-insns2
[omni:~/src/gccPRs] pinskia% time ./a.out
2.070u 0.030s 0:02.41 87.1%     0+0k 0+0io 0pf+0w

Here is the numbers with just turning off the scheduling after the ra:
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c  -fno-schedule-insns2
[omni:~/src/gccPRs] pinskia% time ./a.out
9.820u 0.050s 0:11.10 88.9%     0+0k 0+1io 0pf+0w
[omni:~/src/gccPRs] pinskia% gcc -O3 idct3.c -fno-schedule-insns2 -fnew-ra
[omni:~/src/gccPRs] pinskia% time ./a.out
7.130u 0.030s 0:08.03 89.1%     0+0k 0+1io 0pf+0

You see that the scheduling before ra caused many problems and that the second 
schedular fixes some of those problems but it cannot fix all of them.