Re: [FFmpeg-devel] [FFmpeg-cvslog] x86/intreadwrite: use intrinsics instead of inline asm for AV_COPY128

["Martin Storsjö" <martin@martin.st>]

On Wed, 10 Jul 2024, James Almer wrote:

> ffmpeg | branch: master | James Almer <jamrial@gmail.com> | Wed Jul 10 13:00:20 2024 -0300| [bd1bcb07e0f29c135103a402d71b343a09ad1690] | committer: James Almer
>
> x86/intreadwrite: use intrinsics instead of inline asm for AV_COPY128
>
> This has the benefit of removing any SSE -> AVX penalty that may happen when
> the compiler emits VEX encoded instructions.
>
> Signed-off-by: James Almer <jamrial@gmail.com>
>
>> http://git.videolan.org/gitweb.cgi/ffmpeg.git/?a=commit;h=bd1bcb07e0f29c135103a402d71b343a09ad1690
> ---
>
> configure                    |  5 ++++-
> libavutil/x86/intreadwrite.h | 20 +++++++-------------
> 2 files changed, 11 insertions(+), 14 deletions(-)
>
> diff --git a/configure b/configure
> index f84fefeaab..7151ed1de3 100755
> --- a/configure
> +++ b/configure
> @@ -2314,6 +2314,7 @@ HEADERS_LIST="
>
> INTRINSICS_LIST="
>     intrinsics_neon
> +    intrinsics_sse
>     intrinsics_sse2
> "
>
> @@ -2744,7 +2745,8 @@ armv6t2_deps="arm"
> armv8_deps="aarch64"
> neon_deps_any="aarch64 arm"
> intrinsics_neon_deps="neon"
> -intrinsics_sse2_deps="sse2"
> +intrinsics_sse_deps="sse"
> +intrinsics_sse2_deps="sse2 intrinsics_sse"
> vfp_deps="arm"
> vfpv3_deps="vfp"
> setend_deps="arm"
> @@ -6446,6 +6448,7 @@ elif enabled loongarch; then
> fi
>
> check_cc intrinsics_neon arm_neon.h "int16x8_t test = vdupq_n_s16(0)"
> +check_cc intrinsics_sse immintrin.h "__m128 test = _mm_setzero_ps()"
> check_cc intrinsics_sse2 emmintrin.h "__m128i test = _mm_setzero_si128()"
>
> check_ldflags -Wl,--as-needed
> diff --git a/libavutil/x86/intreadwrite.h b/libavutil/x86/intreadwrite.h
> index 9bbef00dba..6546eb016c 100644
> --- a/libavutil/x86/intreadwrite.h
> +++ b/libavutil/x86/intreadwrite.h
> @@ -22,29 +22,25 @@
> #define AVUTIL_X86_INTREADWRITE_H
>
> #include <stdint.h>
> +#if HAVE_INTRINSICS_SSE
> +#include <immintrin.h>
> +#endif

This change seems to have broken builds for x86 with Clang 16 or newer. 
(Clang 15 and lower seems to be fine.)

See e.g. 
http://fate.ffmpeg.org/log.cgi?slot=i686-mingw32-clang-trunk&time=20240711035948&log=compile 
for an example of the error. The issue is that a clang internal intrinsics 
header contains "_mm_comige_sh(__m128h A,", i.e. a parameter with the name 
"A" (which toolchain provided headers shouldn't use). This clashes with 
libavcodec/huffuyv.h, which has a "#define A 3".

This is obviously a Clang intrinsics header bug, but we can't fix the 
existing Clang 16-18 releases that are out there, so I guess what we can 
do is change our "define A" to something more elaborate. (IIRC there are 
some similar issues with names with ncurses and/or android headers too.)

// Martin

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