[FFmpeg-devel] [PATCH] x86/intmath: allow the source operand for icc/icl ff_ctzll to be a memory location

[Ganesh Ajjanagadde]

On Sat, Oct 24, 2015 at 6:08 PM, James Almer <jamrial at gmail.com> wrote:
> This gives the compiler some flexibility
>
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavutil/x86/intmath.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/libavutil/x86/intmath.h b/libavutil/x86/intmath.h
> index 7881e3c..10d3e7f 100644
> --- a/libavutil/x86/intmath.h
> +++ b/libavutil/x86/intmath.h
> @@ -36,7 +36,7 @@ static av_always_inline av_const int ff_ctzll_x86(long long v)
>  {
>  #   if ARCH_X86_64
>      uint64_t c;
> -    __asm__("bsfq %1,%0" : "=r" (c) : "r" (v));
> +    __asm__ ("bsfq %1,%0" : "=r" (c) : "rm" (v));
>      return c;
>  #   else
>      return ((uint32_t)v == 0) ? _bit_scan_forward((uint32_t)(v >> 32)) + 32 : _bit_scan_forward((uint32_t)v);
> --
> 2.6.2

This question may be silly, but can you clarify when this asm code is
used instead of __builtin_ctzll? For instance, I think on GNU/Linux,
x86-64, sufficiently modern GCC (even with asm enabled), we should
always use the builtin: the compiler knows best what to do with its
builtin.

>
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