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Re: PTR-PLUS merge into the mainline
- From: Roman Zippel <zippel at linux-m68k dot org>
- To: Richard Guenther <rguenther at suse dot de>
- Cc: Andrew Pinski <pinskia at gmail dot com>, Andrew_Pinski at playstation dot sony dot com, gcc at gcc dot gnu dot org, gcc-patches at gcc dot gnu dot org
- Date: Thu, 5 Jul 2007 13:49:03 +0200 (CEST)
- Subject: Re: PTR-PLUS merge into the mainline
- References: <OFC6AC01DD.DCB69225-ON88257309.0010816F-88257309.0010FB88@playstation.sony.com> <Pine.LNX.firstname.lastname@example.org> <email@example.com> <Pine.LNX.firstname.lastname@example.org> <Pine.LNX.email@example.com>
On Thu, 5 Jul 2007, Richard Guenther wrote:
> > > The code to fold_binary was added by:
> > > r107218 | rguenth | 2005-11-19 03:29:10 -0800 (Sat, 19 Nov 2005) | 9 lines
> > >
> > > 2005-11-19 Richard Guenther <firstname.lastname@example.org>
> > >
> > > PR middle-end/23294
> > > * fold-const.c (fold_plusminus_mult_expr): New function.
> > > (fold_binary): Use to canonicalize PLUS_EXPR and MINUS_EXPR
> > > cases, remove now unnecessary code.
> > >
> > > * gcc.dg/tree-ssa/pr23294.c: New testcase.
> > >
> > > And it looks like it was doing this transformation this way on purpose.
> > > Now as I mentioned before the way this should be done is using PRE/FRE
> > > to catch the redudent multiplication.
> > I have to agree, IMHO it looks this optimization is done to early.
> > Richard, it would be great if you comment on this.
> > Thanks.
> No, the fold code just does canonicalization. If you remove that you
> just switch the cases that are not handled.
What makes "(i + 1) * 4" the canonical form of "(i * 4) + 4" compared to
other expressions like "(i * 4) + 8"?
> The real fix is in the
> value numberer that should value number both kinds the same.
Sorry, I have no idea what this means.