https://llvm.org/bugs/show_bug.cgi?id=30506
Bug ID: 30506
Summary: <intrin.h> does not declare _tzcnt_u32
Product: new-bugs
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: new bugs
Assignee: unassignedb...@nondot.org
Reporter: froy...@gmail.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
Firefox's copy of FFmpeg includes <intrin.h> on MSVC to get access to
_tzcnt_u32:
https://dxr.mozilla.org/mozilla-central/source/media/ffvpx/libavutil/x86/intmath.h#26
This is the same as upstream:
https://github.com/FFmpeg/FFmpeg/blob/master/libavutil/x86/intmath.h#L26
Upstream FFmpeg used to include <immintrin.h> for the same purpose
(<immintrin.h> declares it in MSVC, which is included by MSVC's <intrin.h>),
until that was discovered to not work on older MSVC installations:
https://github.com/FFmpeg/FFmpeg/commit/f98417451291a3ff6719d739b5e904e0b7bf404b
Unfortunately, clang-cl's <intrin.h> doesn't declare _tzcnt_u32, which breaks
compiling Firefox.
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