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[Bug tree-optimization/31130] [4.3 Regression] VRP no longer derives range for division after negation
- From: "rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 13 Mar 2007 09:30:15 -0000
- Subject: [Bug tree-optimization/31130] [4.3 Regression] VRP no longer derives range for division after negation
- References: <bug-31130-10053@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #6 from rguenth at gcc dot gnu dot org 2007-03-13 09:30 -------
How tracking _two_ value ranges for signed quantities with undefined overflow.
One assuming it is undefined and one with wrapping semantics. Whenever you
fold
something using the value range you warn if the folding result would differ
if using either or the other variant, if they do not differ, don't warn. This
way you don't affect existing optimizations and strictly warn in the case the
transformation is done taking advantage of the undefined overflow.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31130