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Re: [tree-ssa] New regressions as of 2003-11-04
- From: Richard Henderson <rth at redhat dot com>
- To: law at redhat dot com
- Cc: Andrew MacLeod <amacleod at redhat dot com>, Diego Novillo <dnovillo at redhat dot com>, Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>, Daniel Berlin <dberlin at dberlin dot org>, Jan Hubicka <jh at suse dot cz>, gcc mailing list <gcc at gcc dot gnu dot org>
- Date: Tue, 4 Nov 2003 16:27:00 -0800
- Subject: Re: [tree-ssa] New regressions as of 2003-11-04
- References: <20031104230929.GA24820@redhat.com> <200311050008.hA5089Du018421@speedy.slc.redhat.com>
On Tue, Nov 04, 2003 at 05:08:09PM -0700, law@redhat.com wrote:
> Another dom pass isn't going to improve this kind of code.
I mostly meant using domwalk and a custom widget to detect
what you want.
> Either the
> useless statement remover needs to be updated, or we need something to
> eliminate the PHI, or the out-of-ssa pass needs to get a lot smarter.
The best solution, of course, is to change
# bb 1
if (x.1 == -1) goto L2; else goto L3;
...
# bb 4
L4:
x.4 = PHI< -1(2), 0(3) >;
to
x.4 = PHI< x.1(1), 0(3) >;
Though likely after ccp, since we want the chance to prove constants
first.
r~