This is the mail archive of the
gcc@gcc.gnu.org
mailing list for the GCC project.
Re: GVN-PRE sucks -- well, for SPECCFP2000 mgrid anyway
- From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
- To: dberlin at dberlin dot org
- Cc: gcc at gcc dot gnu dot org
- Date: Sun, 15 Aug 04 22:28:21 EDT
- Subject: Re: GVN-PRE sucks -- well, for SPECCFP2000 mgrid anyway
> 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. It's not conceptually difficult to add some more things to
rematerialize. The problem, of course, is that reload is a mess and adding
*anything* to it will be non-trivial.
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.