Make AVX2 check more robust

Apparently the GNU assembler version 2.20 supported some
parts of AVX2 (in particular the FMA floating-point ops),
which caused our cmake test to pass. This patch changes
it to test the integer addition instead, which isn't
supported in as-2.20 in my tests.

Change-Id: I79e516639fc78d1590d306f486eb027962388543

diff --git a/cmake/gmxTestSimd.cmake b/cmake/gmxTestSimd.cmake
index 44bdd202cba78574cf1612802236fc556405a2ff..f99a43f6de8303caa41c2f5da0f4b108cdceedc9 100644 (file)
--- a/cmake/gmxTestSimd.cmake
+++ b/cmake/gmxTestSimd.cmake
@@ -231,12 +231,12 @@ elseif(${GMX_SIMD} STREQUAL "AVX2_256")
 
     gmx_find_cflag_for_source(CFLAGS_AVX2 "C compiler AVX2 flag"
                               "#include<immintrin.h>
-                              int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_fmadd_ps(x,x,x);return _mm256_movemask_ps(x);}"
+                              int main(){__m256i x=_mm256_set1_epi32(5);x=_mm256_add_epi32(x,x);return _mm256_movemask_epi8(x);}"
                               SIMD_C_FLAGS
                               "-march=core-avx2" "-mavx2" "/arch:AVX" "-hgnu") # no AVX2-specific flag for MSVC yet
     gmx_find_cxxflag_for_source(CXXFLAGS_AVX2 "C++ compiler AVX2 flag"
                                 "#include<immintrin.h>
-                                int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_fmadd_ps(x,x,x);return _mm256_movemask_ps(x);}"
+                                int main(){__m256i x=_mm256_set1_epi32(5);x=_mm256_add_epi32(x,x);return _mm256_movemask_epi8(x);}"
                                 SIMD_CXX_FLAGS
                                 "-march=core-avx2" "-mavx2" "/arch:AVX" "-hgnu") # no AVX2-specific flag for MSVC yet