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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - <intrin.h> does not declare _tzcnt_u32"
href="https://llvm.org/bugs/show_bug.cgi?id=30506">30506</a>
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<th>Summary</th>
<td><intrin.h> does not declare _tzcnt_u32
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>froydnj@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Firefox's copy of FFmpeg includes <intrin.h> on MSVC to get access to
_tzcnt_u32:
<a href="https://dxr.mozilla.org/mozilla-central/source/media/ffvpx/libavutil/x86/intmath.h#26">https://dxr.mozilla.org/mozilla-central/source/media/ffvpx/libavutil/x86/intmath.h#26</a>
This is the same as upstream:
<a href="https://github.com/FFmpeg/FFmpeg/blob/master/libavutil/x86/intmath.h#L26">https://github.com/FFmpeg/FFmpeg/blob/master/libavutil/x86/intmath.h#L26</a>
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:
<a href="https://github.com/FFmpeg/FFmpeg/commit/f98417451291a3ff6719d739b5e904e0b7bf404b">https://github.com/FFmpeg/FFmpeg/commit/f98417451291a3ff6719d739b5e904e0b7bf404b</a>
Unfortunately, clang-cl's <intrin.h> doesn't declare _tzcnt_u32, which breaks
compiling Firefox.</pre>
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