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Re: GVN-PRE sucks -- well, for SPECCFP2000 mgrid anyway
- From: Jeffrey A Law <law at redhat dot com>
- To: Richard Kenner <kenner at vlsi1 dot ultra dot nyu dot edu>
- Cc: dberlin at dberlin dot org, gcc at gcc dot gnu dot org
- Date: Mon, 16 Aug 2004 00:00:54 -0600
- Subject: Re: GVN-PRE sucks -- well, for SPECCFP2000 mgrid anyway
- Organization: Red Hat, Inc
- References: <10408160228.AA27440@vlsi1.ultra.nyu.edu>
- Reply-to: law at redhat dot com
On Sun, 2004-08-15 at 20:28, Richard Kenner wrote:
> > 1) let pre be pre and have the register allocator "rematerialize" the
> > guys that have been pulled out of the loop.
>
> I've always tried to argue this approach, but it never seems to get
> places with people, because it means the register allocator doing *a lot*.
>
> Not necessarly. After all, reload has "rematerialized" constants almost
> since day one and has also rematerialized some addition operations more
> recently.
True, but its ability to rematerialize is poor at best. And the
way it's structured, particularly for chains of insns producing an
ultimate value is, err, special.
> But I still agree with Kenny that it's the best approach: I don't think
> that complex interactions between passes to estimate register pressure
> will work well.
Likewise.
jeff