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

[Oded Gabbay]

This patch modifies the SSE4.1 test in configure.ac to use a global
variable to initialize vector variables. In addition, we now return the
value of the computation instead of 0.

This is done so gcc 4.9 (and lower) won't optimize the SSE4.1 assembly
instructions (when using -O1 and higher), because then the configure test
might incorrectly pass even though the assembler doesn't support the
SSE4.1 instructions (the test will pass because the compiler does support the intrinsics).

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91806
Cc: "11.0" <mesa-stable at lists.freedesktop.org>
Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
---
 configure.ac | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/configure.ac b/configure.ac
index b6680d0..172ffae 100644
--- a/configure.ac
+++ b/configure.ac
@@ -383,10 +383,11 @@ save_CFLAGS="$CFLAGS"
 CFLAGS="$SSE41_CFLAGS $CFLAGS"
 AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #include <smmintrin.h>
+int param;
 int main () {
-    __m128i a = _mm_set1_epi32 (0), b = _mm_set1_epi32 (0), c;
+    __m128i a = _mm_set1_epi32 (param), b = _mm_set1_epi32 (param + 1), c;
     c = _mm_max_epu32(a, b);
-    return 0;
+    return _mm_cvtsi128_si32(c);
 }]])], SSE41_SUPPORTED=1)
 CFLAGS="$save_CFLAGS"
 if test "x$SSE41_SUPPORTED" = x1; then
-- 
2.5.0