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

[Oded Gabbay]

On Wed, Dec 9, 2015 at 8:30 PM, Matt Turner <mattst88 at gmail.com> wrote:
> On Tue, Dec 8, 2015 at 9:37 PM, 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.
>>
>> 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>
>> ---
>>  configure.ac | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/configure.ac b/configure.ac
>> index 260934d..1d82e47 100644
>> --- a/configure.ac
>> +++ b/configure.ac
>> @@ -384,7 +384,7 @@ CFLAGS="$SSE41_CFLAGS $CFLAGS"
>>  AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>  #include <smmintrin.h>
>>  int main () {
>> -    __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>> +    volatile __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
>>      c = _mm_max_epu32(a, b);
>>      return 0;
>
> I would have extracted an int from the result of _mm_max_epu32 and
> returned that instead of 0.

Instead of the volatile I assume ?

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