[FFmpeg-devel] Don't use _tzcnt instrinics with clang for windows w/o BMI.

[Matt Oliver]

On 25 October 2017 at 07:15, Dale Curtis <dalecurtis at chromium.org> wrote:

> Technically _tzcnt* intrinsics are only available when the BMI
> instruction set is present. However the instruction encoding
> degrades to "rep bsf" on older processors.
>
> Clang for Windows debatably restricts the _tzcnt* instrinics behind
> the __BMI__ architecture define, so check for its presence or
> exclude the usage of these intrinics when clang is present.
>
> See also:
> https://ffmpeg.org/pipermail/ffmpeg-devel/2015-November/183404.html
> https://bugs.llvm.org/show_bug.cgi?id=30506
> http://lists.llvm.org/pipermail/cfe-dev/2016-October/051034.html
>
> Signed-off-by: Dale Curtis <dalecurtis at chromium.org


LGTM