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[Bug optimization/11488] Scheduling severely worsens performance
- From: "neroden at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 11 Jul 2003 05:53:05 -0000
- Subject: [Bug optimization/11488] Scheduling severely worsens performance
- References: <20030710140519.11488.falk@debian.org>
- Reply-to: gcc-bugzilla 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.)