When calling the _mm256_cvtps_ph instruction [1] using Clang [2] the following error manifests itself:
1>------ Build started: Project: CRoaringTest, Configuration: Debug x64 ------
1>main.c(19): error : ‘__builtin_ia32_vcvtps2ph256’ needs target feature f16c
1>C:\Program Files\LLVM\lib\clang\7.0.0\include\immintrin.h(100): note: expanded from macro ‘_mm256_cvtps_ph’
1>Done building project “CRoaringTest.vcxproj” – FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
I’m trying to call the following function:
__declspec ( noinline ) void float2half ( float * floats, short * halfs ) {
_mm_store_si128 ( ( __m128i* ) halfs, _mm256_cvtps_ph ( _mm256_load_ps ( floats ), 0 ) );
}
int main () {
float test [ 8 ] = { -0.0f, -1.0f, 2.0f, 3.0f, 4.0f, 5.0f, 6.0f, 7.0f };
short rest [ 8 ] = { 0 };
float2half ( test, rest );
for ( int32_t i = 0; i < 8; ++i ) {
printf ( "%i ", ( int ) rest [ i ] );
}
printf ( “\n” );
return 0;
}
I have a Broadwell CPU (i.e. it should work) and VS 15.6.6 compiles this just fine. In Debug the error is shown as per above, in Release, no error, but crashes.
degski
[1] https://software.intel.com/sites/landingpage/IntrinsicsGuide/#text=_mm256_cvtps_ph&expand=1711
[2] http://prereleases.llvm.org/win-snapshots/LLVM-7.0.0-r325576-win64.exe