Re: [PATCH 1/2] util/bufferiszero: Use __attribute__((target)) for avx2/avx512

[Daniel P . Berrangé]

On Sat, Dec 03, 2022 at 07:51:22PM -0600, Richard Henderson wrote:
> Use the attribute, which is supported by clang, instead of
> the #pragma, which is not supported and, for some reason,
> also not detected by the meson probe, so we fail by -Werror.
> 
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  meson.build         |  8 ++------
>  util/bufferiszero.c | 41 ++++++-----------------------------------
>  2 files changed, 8 insertions(+), 41 deletions(-)
> 


> diff --git a/util/bufferiszero.c b/util/bufferiszero.c
> index ec3cd4ca15..1790ded7d4 100644
> --- a/util/bufferiszero.c
> +++ b/util/bufferiszero.c
> @@ -64,18 +64,11 @@ buffer_zero_int(const void *buf, size_t len)
>  }
>  
>  #if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT) || 
> defined(__SSE2__)
> -/* Do not use push_options pragmas unnecessarily, because clang
> - * does not support them.
> - */
> -#if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
> -#pragma GCC push_options
> -#pragma GCC target("sse2")
> -#endif
> -#include <emmintrin.h>

So the old code included emmintrin.h, and possibly either
immintrin.h / simmintrin.h, but the new code only
includes immintrin.h.

I'm not saying that's wrong, I'm just wondering why it is
changing, as it feels possibly tangential to the pragma
-> attribute conversion. Could you mention this in the
commit message, or split it to a separate cleanup patch
if its a functionally unrelated change.

> +#include <immintrin.h>
>  
>  /* Note that each of these vectorized functions require len >= 64.  */
>  
> -static bool
> +static bool __attribute__((target("sse2")))
>  buffer_zero_sse2(const void *buf, size_t len)
>  {
>      __m128i t = _mm_loadu_si128(buf);
> @@ -104,20 +97,9 @@ buffer_zero_sse2(const void *buf, size_t len)
>  
>      return _mm_movemask_epi8(_mm_cmpeq_epi8(t, zero)) == 0xFFFF;
>  }
> -#if defined(CONFIG_AVX512F_OPT) || defined(CONFIG_AVX2_OPT)
> -#pragma GCC pop_options
> -#endif
>  
>  #ifdef CONFIG_AVX2_OPT
> -/* Note that due to restrictions/bugs wrt __builtin functions in gcc <= 4.8,
> - * the includes have to be within the corresponding push_options region, and
> - * therefore the regions themselves have to be ordered with increasing ISA.
> - */
> -#pragma GCC push_options
> -#pragma GCC target("sse4")
> -#include <smmintrin.h>
> -
> -static bool
> +static bool __attribute__((target("sse4")))
>  buffer_zero_sse4(const void *buf, size_t len)
>  {
>      __m128i t = _mm_loadu_si128(buf);
> @@ -145,12 +127,7 @@ buffer_zero_sse4(const void *buf, size_t len)
>      return _mm_testz_si128(t, t);
>  }
>  
> -#pragma GCC pop_options
> -#pragma GCC push_options
> -#pragma GCC target("avx2")
> -#include <immintrin.h>
> -
> -static bool
> +static bool __attribute__((target("avx2")))
>  buffer_zero_avx2(const void *buf, size_t len)
>  {
>      /* Begin with an unaligned head of 32 bytes.  */
> @@ -176,15 +153,10 @@ buffer_zero_avx2(const void *buf, size_t len)
>  
>      return _mm256_testz_si256(t, t);
>  }
> -#pragma GCC pop_options
>  #endif /* CONFIG_AVX2_OPT */
>  
>  #ifdef CONFIG_AVX512F_OPT
> -#pragma GCC push_options
> -#pragma GCC target("avx512f")
> -#include <immintrin.h>
> -
> -static bool
> +static bool __attribute__((target("avx512f")))
>  buffer_zero_avx512(const void *buf, size_t len)
>  {
>      /* Begin with an unaligned head of 64 bytes.  */
> @@ -210,8 +182,7 @@ buffer_zero_avx512(const void *buf, size_t len)
>      return !_mm512_test_epi64_mask(t, t);
>  
>  }
> -#pragma GCC pop_options
> -#endif
> +#endif /* CONFIG_AVX512F_OPT */
>  
>  
>  /* Note that for test_buffer_is_zero_next_accel, the most preferred
> -- 
> 2.34.1
> 

With regards,
Daniel
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