Re: [PATCH 00/18] Support -mevex512 for AVX512

[Hongtao Liu <crazylht@gmail.com>]

On Thu, Sep 28, 2023 at 11:23 AM ZiNgA BuRgA <zingaburga@hotmail.com> wrote:
>
> That sounds about right.  The code I had in mind would perhaps look like:
>
>
> #if defined(__AVX512BW__) && defined(__AVX512VL__)
>      #if defined(__EVEX256__) && !defined(__EVEX512__)
>          // compiled code is AVX10.1/256 and AVX512 compatible
>      #else
>          // compiled code is only AVX512 compatible
>      #endif
>
>      // some code which only uses 256b instructions
>      __m256i...
> #endif
>
>
> The '__EVEX256__' define would avoid needing to check compiler versions.
Sounds reasonable, regarding how to set __EVEX256__, I think it should
be set/unset along with __AVX512VL__ and __EVEX512__ should not unset
__EVEX256__.

> Hopefully you can align it with whatever Clang does:
> https://discourse.llvm.org/t/rfc-design-for-avx10-feature-support/72661/18

>
> Thanks!
>
> On 28/09/2023 12:26 pm, Hu, Lin1 wrote:
> > Hi,
> >
> > Thanks for you reply.
> >
> > I'd like to verify that our understanding of your requirements is correct, and that __EVEX256__ can be considered a default macro to determine whether the compiler supports the __EVEX***__ series of switches.
> >
> > For example:
> >
> > I have a segment of code like:
> > #if defined(__EVEX512__):
> > __mm512.*__;
> > #else
> > __mm256.*__;
> > #endif
> >
> > But __EVEX512__ is undefined that doesn't mean I only need 256bit, maybe I use gcc-13, so I can still use 512bit.
> >
> > So the code should be:
> > #if defined(__EVEX512__):
> > __mm512.*__;
> > #elif defined(__EVEX256__):
> > __mm256.*__;
> > #else
> > __mm512.*__;
> > #endif
> >
> > If we understand correctly, we'll consider the request. But since we're about to have a vacation, follow-up replies may be a bit slower.
> >
> > BRs,
> > Lin
> >
> > -----Original Message-----
> > From: ZiNgA BuRgA <zingaburga@hotmail.com>
> > Sent: Thursday, September 28, 2023 8:32 AM
> > To: Hu, Lin1 <lin1.hu@intel.com>; gcc-patches@gcc.gnu.org
> > Subject: Re: [PATCH 00/18] Support -mevex512 for AVX512
> >
> > Thanks for the new patch!
> >
> > I see that there's a new __EVEX512__ define.  Will there be some __EVEX256__ (or maybe some max EVEX width) define, so that code can detect whether the compiler supports AVX10.1/256 without resorting to version checks?
> >
> >
>


-- 
BR,
Hongtao