Re: [PATCH] [x86] Avoid builtins for SSE/AVX2 immidiate logical shifts

[Jakub Jelinek <jakub@redhat.com>]

On Mon, Apr 24, 2017 at 09:33:09AM +0200, Allan Sandfeld Jensen wrote:
> --- a/gcc/config/i386/avx2intrin.h
> +++ b/gcc/config/i386/avx2intrin.h
> @@ -667,7 +667,7 @@ extern __inline __m256i
>  __attribute__ ((__gnu_inline__, __always_inline__, __artificial__))
>  _mm256_slli_epi16 (__m256i __A, int __B)
>  {
> -  return (__m256i)__builtin_ia32_psllwi256 ((__v16hi)__A, __B);
> +  return ((__B & 0xff) < 16) ? (__m256i)((__v16hi)__A << (__B & 0xff)) : _mm256_setzero_si256();
>  }

What is the advantage of doing that when you replace one operation with
several (&, <, ?:, <<)?
I'd say instead we should fold the builtins if in the gimple fold target
hook we see the shift count constant and can decide based on that.
Or we could use __builtin_constant_p (__B) to decide whether to use
the generic vector shifts or builtin, but that means larger IL.

	Jakub