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Re: Optimal Optimizations: A Very Preliminary Report
- From: <tm_gccmail at mail dot kloo dot net>
- To: Nathanael Nerode <neroden at twcny dot rr dot com>
- Cc: gcc at gcc dot gnu dot org
- Date: Mon, 18 Aug 2003 11:35:47 -0700 (PDT)
- Subject: Re: Optimal Optimizations: A Very Preliminary Report
On Sun, 17 Aug 2003, Nathanael Nerode wrote:
> Michael Matz wrote:
> > Hi,
> >
> > On Tue, 12 Aug 2003, Nathanael Nerode wrote:
> >
> >
> >>(Incidentally, the evidence for that particular case indicates that
> >>-fschedule-insns should be abandoned entirely, while -fschedule-insns2
> >>should be standard.)
> >
> >
> > For this particular case! Scott is testing ooo architectures, which
> > generally do not benefit that greatly from scheduling anyway. The picture
> > is wholly different with in-order archs where pre-regalloc scheduling can
> > make a horribly high difference (if it's given that there is a reasonable
> > number of registers, so that scheduling does not interfere with regalloc
> > that much).
>
> Hmm. Which of our arches are out-of-order and which of them are
> in-order? I believe that -fschedule-insns has been reported to make
> things worse on sh, powerpc, x86, and ia64. :-/
As I've mentioned before, -fschedule-insns with throttling results
in up to a 20% gain on the SH architecture.
> Is there a way to set the default optimizations differently on a
> per-architecture basis? If there isn't, should there be? ;-)
We already do this. For the H8/300 we disable bbro.
Toshi