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Re: Optimal Optimizations: A Very Preliminary Report
- From: neroden at twcny dot rr dot com (Nathanael Nerode)
- To: gcc at gcc dot gnu dot org
- Date: Tue, 12 Aug 2003 16:40:16 -0400
- Subject: Re: Optimal Optimizations: A Very Preliminary Report
Toshi <tm_gccmail@mail.kloo.net> said:
>Please don't suggest abandoning -fschedule-insns unless you understand
>the full intricacies of the situation and have a viable alternative.
I'm not suggesting ripping it out of the code base.
However, it should *not* be activated by default at any optimization
level (until it is fixed), since it consistently makes things worse on
at least x86 and PowerPC. Currently it is activated by default at -O2,
which is stupid given that it's known to make things worse most of the
time.
>The current problem with sched1 isn't the concept of scheduling before
>register allocation; rather, it's allowing the scheduler unrestrained
>freedom to move instructions before register allocation which can
>raise register pressure unnecessarily. People are working on a solution
>for this already.
Yeah, but it doesn't look like the fix will be in for 3.4 or even 3.5.
It should be turned off.
--
Nathanael Nerode <neroden at gcc.gnu.org>
http://home.twcny.rr.com/nerode/neroden/fdl.html