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[Bug tree-optimization/42286] October 23rd change to tree-ssa-pre.c breaks calculix on powerpc with -ffast-math
- From: "segher at kernel dot crashing dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 5 Jan 2010 16:00:15 -0000
- Subject: [Bug tree-optimization/42286] October 23rd change to tree-ssa-pre.c breaks calculix on powerpc with -ffast-math
- References: <bug-42286-15150@http.gcc.gnu.org/bugzilla/>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Comment #8 from segher at kernel dot crashing dot org 2010-01-05 16:00 -------
(In reply to comment #6)
> IIRC the problem is that using fma causes the -0 argument for fsqrt (which
> behaves 100% correct). Thus a more sensible fix would be to do the 0+ on
> the fma result.
But a -0 result from fsqrt() is no problem /an sich/; problems
only show up when you pass a +/- 0 to a function with a discontinuity
there. Also, doing an extra addition on every fma is hugely expensive.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42286