configura.ac: fix test for SSE4.1 assembler support

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 11.1" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

diff --git a/configure.ac b/configure.ac
index adc582b958153b2b4e5242ce2ea4ea8f4e63426d..7eb3d20741546ee3d2b55d5c3b8c514f260a39bc 100644 (file)
--- 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