[Pixman] [PATCH v2] configura.ac: fix test for SSE2 & SSSE3 assembler support

[Oded Gabbay]

This patch modifies the SSE2 & SSSE3 tests 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 SSE assembly
instructions (when using -O1 and higher), because then the configure test
might incorrectly pass even though the assembler doesn't support the
SSE instructions (the test will pass because the compiler does support
the intrinsics).

Signed-off-by: Oded Gabbay <oded.gabbay at gmail.com>
---
 configure.ac | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/configure.ac b/configure.ac
index 3a66909..ae4d3c6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -429,10 +429,11 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #include <mmintrin.h>
 #include <xmmintrin.h>
 #include <emmintrin.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_xor_si128 (a, b);
-    return 0;
+    return _mm_cvtsi128_si32(c);
 }]])], have_sse2_intrinsics=yes)
 CFLAGS=$xserver_save_CFLAGS
 
@@ -473,10 +474,11 @@ AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
 #include <xmmintrin.h>
 #include <emmintrin.h>
 #include <tmmintrin.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_maddubs_epi16 (a, b);
-    return 0;
+    return _mm_cvtsi128_si32(c);
 }]])], have_ssse3_intrinsics=yes)
 CFLAGS=$xserver_save_CFLAGS
 
-- 
2.5.0