[Bug optimization/11488] Scheduling severely worsens performance

[neroden at gcc dot gnu dot org]

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



------- Additional Comments From neroden at gcc dot gnu dot org  2003-07-11 05:53 -------
>The problem is that scheduling introduces false dependencies, which leads to
>excessive spilling.
This may be dumb, but why isn't scheduling run *after* the register allocator?  It seems altogether more logical to me, given the nature of the 
passes.  (Oh, right, that's an option, isn't it!  Do the numbers you're showing with -fno-schedule-insns reflect -fschedule-insns2 or 
-fno-schedule-insns2?  With post-regalloc scheduling, why is scheduling ever run before the register allocator?)

Failing that, I suppose we would have to preserve the pre-scheduling dependence information and feed it into the register allocator, which sounds 
quite difficult.

(Incidentally, I presume these problems are against the newest scheduler, the DFA one.  Target maintainers correct me if I'm confused.)