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[Bug tree-optimization/78386] Optimization -O2 and higher cause math inconsistency
- From: "joseph at codesourcery dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Wed, 16 Nov 2016 23:39:24 +0000
- Subject: [Bug tree-optimization/78386] Optimization -O2 and higher cause math inconsistency
- Auto-submitted: auto-generated
- References: <bug-78386-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78386
--- Comment #4 from joseph at codesourcery dot com <joseph at codesourcery dot com> ---
On Wed, 16 Nov 2016, pinskia at gcc dot gnu.org wrote:
> Most likely the use of fma.
Which applies with current x86_64 just as it does with powerpc. It should
be possible to reduce such an issue to a single function, with a specified
argument for which that function returns different results with different
optimization options. If it's an fma issue, using -ffp-contract=off
should eliminate the difference between optimization levels.