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Re: Enabling -ftree-slp-vectorize on -O2/Os
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: gcc at gcc dot gnu dot org,Allan Sandfeld Jensen <linux at carewolf dot com>,Segher Boessenkool <segher at kernel dot crashing dot org>
- Date: Sun, 27 May 2018 07:37:06 +0200
- Subject: Re: Enabling -ftree-slp-vectorize on -O2/Os
- References: <2659301.XPQk3P0qmd@twilight> <20180526220532.GS17342@gate.crashing.org> <20109354.MqXXt4BNHg@twilight>
On May 27, 2018 1:25:25 AM GMT+02:00, Allan Sandfeld Jensen <linux@carewolf.com> wrote:
>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.
By default it combines integer ops where possible into word_mode registers. So yes, almost nothing.
Richard.
>'Allan