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

Matt Oliver protogonoi at gmail.com
Wed Oct 25 19:39:57 EEST 2017

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


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