Re: [PATCH 1/2] configure: avx2 and avx512f detection for clang

[Thomas Huth <thuth@redhat.com>]

On 23/07/2020 02.27, Shu-Chun Weng wrote:
> Since clang does not support "#pragma GCC", the instruction sets are
> always disabled. In this change, we
> 
>  1. wrap "#pragma GCC" inside "#ifndef __clang__",
>  2. only retain them around "#include <{e,i,s}mmintrin.h>" to work
>     around gcc bug,
>  3. and annotate each function with `__attribute__((target(*)))` which
>     is recognized by both gcc and clang.
> 
> Signed-off-by: Shu-Chun Weng <scw@google.com>
> ---
>  configure           | 16 ++++++++++++++--
>  util/bufferiszero.c | 33 +++++++++++++++++++++++----------
>  2 files changed, 37 insertions(+), 12 deletions(-)
> 
> diff --git a/configure b/configure
> index 4bd80ed507..d9ce3aa5db 100755
> --- a/configure
> +++ b/configure
> @@ -5808,10 +5808,16 @@ fi
>  
>  if test "$cpuid_h" = "yes" && test "$avx2_opt" != "no"; then
>    cat > $TMPC << EOF
> +#include <cpuid.h>
> +#ifndef __clang__
>  #pragma GCC push_options
>  #pragma GCC target("avx2")
> -#include <cpuid.h>
> +#endif
>  #include <immintrin.h>
> +#ifndef __clang__
> +#pragma GCC pop_options
> +#endif
> +__attribute__((target("avx2")))
>  static int bar(void *a) {
>      __m256i x = *(__m256i *)a;
>      return _mm256_testz_si256(x, x);

I wonder whether it would make more sense to pass "-mavx2" to the
compile_object call afterwards and simply remove the #pragmas here?
Did you try that already?

 Thomas