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[Bug target/71921] missed vectorization optimization
- From: "pinskia at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 27 Dec 2016 23:05:40 +0000
- Subject: [Bug target/71921] missed vectorization optimization
- Auto-submitted: auto-generated
- References: <bug-71921-4@http.gcc.gnu.org/bugzilla/>
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71921
--- Comment #18 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Arjan van de Ven from comment #17)
> (In reply to Andrew Pinski from comment #15)
> > Read https://gcc.gnu.org/ml/gcc-patches/2015-08/msg00693.html also. There
> > is much more to that thread than just in August IIRC. Some in September and
> > in October too.
>
> I understand the argument, but if that is true, wouldn't it be unsafe to use
> vmaxss as well, which gcc DOES generate?
Your argument is the opposite way around. MIN_EXPR/MAX_EXPR does not specify
the behavior with respect to NaNs so using vmaxss here is ok. But doing the
conversion without -ffast-math to MIN/MAX EXPR won't work in general. There
are some other passes which will use that the fact it is not specified and
optimizing in correctly. Or other targets which might emit MIN/MAX_EXPR
differently from x86. GCC is not just about x86.