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[Bug tree-optimization/42108] [4.6/4.7/4.8 Regression] 50% performance regression
- From: "rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Thu, 17 Jan 2013 14:42:11 +0000
- Subject: [Bug tree-optimization/42108] [4.6/4.7/4.8 Regression] 50% performance regression
- Auto-submitted: auto-generated
- References: <bug-42108-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42108
--- Comment #57 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-17 14:42:11 UTC ---
A proper fix these days (with tuples) is to add new tree codes that carry
the knowledge that
countm1.6_40 = _38 / _39;
may not trap. The frontend already knows this (step == _39 == 0 has undefined
behavior according to the language).
This is work in a similar area as no-undefined-overflow or the proposed
changes to make FP rounding modes explicit.