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[Bug rtl-optimization/50904] [4.7 regression] pessimization when -fno-protect-parens is enabled by -Ofast
- From: "rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Fri, 02 Dec 2011 16:32:52 +0000
- Subject: [Bug rtl-optimization/50904] [4.7 regression] pessimization when -fno-protect-parens is enabled by -Ofast
- Auto-submitted: auto-generated
- References: <bug-50904-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904
--- Comment #31 from rguenther at suse dot de <rguenther at suse dot de> 2011-12-02 16:32:52 UTC ---
On Fri, 2 Dec 2011, burnus at gcc dot gnu.org wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50904
>
> --- Comment #30 from Tobias Burnus <burnus at gcc dot gnu.org> 2011-12-02 16:29:46 UTC ---
> (In reply to comment #29)
> > And for the sake of completeness the evaluation of sub above and
> > x = (x + 2.d0**52) - 2.d0**52
> > should behave consistently if I read your Fortran standard
> > quotations correctly.
>
> Well, it kind of does, only when mixing (in GCC) -funsafe-math-optimizations
> with -fprotect-parens or (in ifort) "-assume protect_parens" with a non-strict
> -fp-model, you get a different results: 1.0 with the () version and 1.3 with
> the 'tmp' version.
Ok, which is, I suppose, a bug in both compilers.
Richard.