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[Bug tree-optimization/31136] [4.2 Regression] FRE ignores bit-field truncation (C and C++ front-end don't produce bit-field truncation
- From: "pinskia at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 23 Mar 2007 08:01:32 -0000
- Subject: [Bug tree-optimization/31136] [4.2 Regression] FRE ignores bit-field truncation (C and C++ front-end don't produce bit-field truncation
- References: <bug-31136-12896@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #9 from pinskia at gmail dot com 2007-03-23 08:01 -------
Subject: Re: [4.2 Regression] FRE ignores bit-field truncation (C and C++
front-end don't produce bit-field truncation
On 3/23/07, Andrew Pinski <pinskia@gmail.com> wrote:
> On 23 Mar 2007 05:01:00 -0000, spark at gcc dot gnu dot org
> <gcc-bugzilla@gcc.gnu.org> wrote:
> > The problematic STRIP_SIGN_NOPS() call is from fold_unary()
> > which is called from try_combine_conversion() in tree-ssa-pre.c.
> >
> > STRIP_SIGN_NOPS() is called with the expression:
>
> No, STRIP_SIGN_NOPS is correct, just fold_unary is incorrect in its
> folding. It should have called fold_convert on the expression if the
> types are different and it is a constant.
Ok, the real issue is that we call fold with
NOP_EXPR<NOP_EXPR<INTEGER_CST>> instead of just NOP_EXPR<INTEGER_CST>
so you have to figure out where we should fold the first NOP_EXPR
instead of that patch.
-- Pinski
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31136