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[Bug tree-optimization/42108] [4.6/4.7/4.8 Regression] 50% performance regression


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.


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