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Re: Enabling -ftree-slp-vectorize on -O2/Os
- From: Allan Sandfeld Jensen <linux at carewolf dot com>
- To: Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: Sun, 27 May 2018 01:25:25 +0200
- Subject: Re: Enabling -ftree-slp-vectorize on -O2/Os
- References: <2659301.XPQk3P0qmd@twilight> <20180526220532.GS17342@gate.crashing.org>
On Sonntag, 27. Mai 2018 00:05:32 CEST Segher Boessenkool wrote:
> On Sat, May 26, 2018 at 11:32:29AM +0200, Allan Sandfeld Jensen wrote:
> > I brought this subject up earlier, and was told to suggest it again for
> > gcc 9, so I have attached the preliminary changes.
> >
> > My studies have show that with generic x86-64 optimization it reduces
> > binary size with around 0.5%, and when optimizing for x64 targets with
> > SSE4 or better, it reduces binary size by 2-3% on average. The
> > performance changes are negligible however*, and I haven't been able to
> > detect changes in compile time big enough to penetrate general noise on
> > my platform, but perhaps someone has a better setup for that?
> >
> > * I believe that is because it currently works best on non-optimized code,
> > it is better at big basic blocks doing all kinds of things than tightly
> > written inner loops.
> >
> > Anythhing else I should test or report?
>
> What does it do on other architectures?
>
>
I believe NEON would do the same as SSE4, but I can do a check. For
architectures without SIMD it essentially does nothing.
'Allan