[Mesa-stable] [PATCH] configure.ac: fix test for SSE4.1 assembler support

[Emil Velikov]

On 9 December 2015 at 11:39, Oded Gabbay <oded.gabbay at gmail.com> wrote:
> On Wed, Dec 9, 2015 at 1:09 PM, Emil Velikov <emil.l.velikov at gmail.com> wrote:
>> On 9 December 2015 at 05:37, Jonathan Gray <jsg at jsg.id.au> wrote:
>>> Change the __m128i variables to be volatile so gcc 4.9 won't optimise
>>> all of them out with -O1 or greater.  The _mm_set1_epi32/pinsrd calls
>>> still get optimised out but now there is at least one SSE4.1 instruction
>>> generated via _mm_max_epu32/pmaxud.  When all of the sse4.1 instructions
>>> got optimised out the configure test would incorrectly pass when the
>>> compiler supported the intrinsics and the assembler didn't support the
>>> instructions.
>>>
>> Must admit that I was not expecting that one. Looks like pixman (the
>> inspiration for this check) is missing volatile as well. Does that one
>> build/run fine on OpenBSD ?
>>
>>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
>>> Signed-off-by: Jonathan Gray <jsg at jsg.id.au>
>>> Cc: "11.0 11.1" <mesa-stable at lists.freedesktop.org>
>> Reviewed-by: Emil Velikov <emil.velikov at collabora.com>
>>
>> I'll pick this in a couple of days (barring any objections).
>>
>> Thanks
>> Emil
>
> Adding pixman ML.
> I must admit ignorance on this one.
> I looked at configure.ac of pixman and I don't see any SSE4.1
> reference, and AFAIK, we don't use those instructions (only SSE2 and
> SSSE3).
> Is the above patch relevant for those as well ? because the tests in
> configure.ac does *not* contain volatile.
>
True, there is no SSE4.1 detection in pixman but the logic should
still holds. .Unless ... it is exclusive to SSE4.1, which I rather
doubt. Unfortunately there is no easy way to get older GCC on Arch
otherwise I would have tried it.

The full patch for reference http://patchwork.freedesktop.org/patch/67449/

-Emil