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

[Jonathan Gray]

On Sat, Dec 12, 2015 at 06:41:56PM +0000, Emil Velikov wrote:
> On 10 December 2015 at 08:42, Oded Gabbay <oded.gabbay at gmail.com> wrote:
> > 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 ?
> >
> Precisely. If anyone wants to follow on Matt's suggestion we can pick
> that one as well. I'd like to get a patch for the next stable releases
> (next Friday for 11.0.x and just after new year for 11.1.1) so I'll
> take whatever's around :-)
> 
> -Emil

I avoided that as I wasn't sure if there was a case where autoconf
cared about the return code.  If someone wants to create a new diff
feel free, I have limited connectivity till the middle of next week.