Make it harder for compiler to optimize away SIMD CMake tests

On at least one old version of Linux, a new compiler in
combination with an old assembler led to the compiler
understanding the SIMD code but optimizing it away, which made
the test pass even though the assembler could not handle it.
This changes the return value of the CMake tests to be based on
the SIMD operations, which should make them a lot more
difficult to optimize away.

Fixes #1493.

Change-Id: I3e021c3c718cf54afaadf131c5fa911b3933f61e

diff --git a/cmake/gmxTestSimd.cmake b/cmake/gmxTestSimd.cmake
index 1137db92ecdd9769ab158929b7e49459e82dfdd0..44bdd202cba78574cf1612802236fc556405a2ff 100644 (file)
--- a/cmake/gmxTestSimd.cmake
+++ b/cmake/gmxTestSimd.cmake
@@ -66,12 +66,12 @@ elseif(${GMX_SIMD} STREQUAL "SSE2")
 
     gmx_find_cflag_for_source(CFLAGS_SSE2 "C compiler SSE2 flag"
                               "#include<xmmintrin.h>
-                              int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_rsqrt_ps(x);return 0;}"
+                              int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_rsqrt_ps(x);return _mm_movemask_ps(x);}"
                               SIMD_C_FLAGS
                               "-msse2" "/arch:SSE2" "-hgnu")
     gmx_find_cxxflag_for_source(CXXFLAGS_SSE2 "C++ compiler SSE2 flag"
                                 "#include<xmmintrin.h>
-                                int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_rsqrt_ps(x);return 0;}"
+                                int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_rsqrt_ps(x);return _mm_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-msse2" "/arch:SSE2" "-hgnu")
 
@@ -87,12 +87,12 @@ elseif(${GMX_SIMD} STREQUAL "SSE4.1")
     # Note: MSVC enables SSE4.1 with the SSE2 flag, so we include that in testing.
     gmx_find_cflag_for_source(CFLAGS_SSE4_1 "C compiler SSE4.1 flag"
                               "#include<smmintrin.h>
-                              int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_dp_ps(x,x,0x77);return 0;}"
+                              int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_dp_ps(x,x,0x77);return _mm_movemask_ps(x);}"
                               SIMD_C_FLAGS
                               "-msse4.1" "/arch:SSE4.1" "/arch:SSE2" "-hgnu")
     gmx_find_cxxflag_for_source(CXXFLAGS_SSE4_1 "C++ compiler SSE4.1 flag"
                                 "#include<smmintrin.h>
-                                int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_dp_ps(x,x,0x77);return 0;}"
+                                int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_dp_ps(x,x,0x77);return _mm_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-msse4.1" "/arch:SSE4.1" "/arch:SSE2" "-hgnu")
 
@@ -144,14 +144,14 @@ elseif(${GMX_SIMD} STREQUAL "AVX_128_FMA")
 "#include<immintrin.h>
 ${INCLUDE_X86INTRIN_H}
 ${INCLUDE_INTRIN_H}
-int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_macc_ps(x,x,x);return 0;}"
+int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_macc_ps(x,x,x);return _mm_movemask_ps(x);}"
                               SIMD_C_FLAGS
                               "-mfma4" "-hgnu")
     gmx_find_cxxflag_for_source(CXXFLAGS_AVX_128_FMA "C++ compiler AVX (128 bit) FMA4 flag"
 "#include<immintrin.h>
 ${INCLUDE_X86INTRIN_H}
 ${INCLUDE_INTRIN_H}
-int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_macc_ps(x,x,x);return 0;}"
+int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_macc_ps(x,x,x);return _mm_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-mfma4" "-hgnu")
 
@@ -165,14 +165,14 @@ int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_macc_ps(x,x,x);return 0;}"
 "#include<immintrin.h>
 ${INCLUDE_X86INTRIN_H}
 ${INCLUDE_INTRIN_H}
-int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_frcz_ps(x);return 0;}"
+int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_frcz_ps(x);return _mm_movemask_ps(x);}"
                               SIMD_C_FLAGS
                               "-mxop")
     gmx_find_cxxflag_for_source(CXXFLAGS_AVX_128_XOP "C++ compiler AVX (128 bit) XOP flag"
 "#include<immintrin.h>
 ${INCLUDE_X86INTRIN_H}
 ${INCLUDE_INTRIN_H}
-int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_frcz_ps(x);return 0;}"
+int main(){__m128 x=_mm_set1_ps(0.5);x=_mm_frcz_ps(x);return _mm_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-mxop")
 
@@ -207,12 +207,12 @@ elseif(${GMX_SIMD} STREQUAL "AVX_256")
 
     gmx_find_cflag_for_source(CFLAGS_AVX "C compiler AVX (256 bit) flag"
                               "#include<immintrin.h>
-                              int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_add_ps(x,x);return 0;}"
+                              int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_add_ps(x,x);return _mm256_movemask_ps(x);}"
                               SIMD_C_FLAGS
                               "-mavx" "/arch:AVX" "-hgnu")
     gmx_find_cxxflag_for_source(CXXFLAGS_AVX "C++ compiler AVX (256 bit) flag"
                                 "#include<immintrin.h>
-                                int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_add_ps(x,x);return 0;}"
+                                int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_add_ps(x,x);return _mm256_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-mavx" "/arch:AVX" "-hgnu")
 
@@ -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 0;}"
+                              int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_fmadd_ps(x,x,x);return _mm256_movemask_ps(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 0;}"
+                                int main(){__m256 x=_mm256_set1_ps(0.5);x=_mm256_fmadd_ps(x,x,x);return _mm256_movemask_ps(x);}"
                                 SIMD_CXX_FLAGS
                                 "-march=core-avx2" "-mavx2" "/arch:AVX" "-hgnu") # no AVX2-specific flag for MSVC yet