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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Windows: Cannot compile code that includes ppl.h with SSE2 disabled due to _mm_pause usage"
href="https://bugs.llvm.org/show_bug.cgi?id=34079">34079</a>
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<th>Summary</th>
<td>Windows: Cannot compile code that includes ppl.h with SSE2 disabled due to _mm_pause usage
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>5.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Frontend
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
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<th>Reporter</th>
<td>reupenllvm@forward.cat
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>If SSE2 is disabled (/arch:IA32 in VC), with an X86 target compiling code that
includes VC header ppl.h will result in errors such as:
(ClCompile target) ->
C:\Program Files (x86)\Microsoft Visual Studio
14.0\VC\include\concrt.h(636,21): error : '_mm_pause' needs target feature sse2
[F:\foobar2000\columns_ui\ui_helpers\ui_helpers.vcxproj]
C:\Program Files (x86)\Microsoft Visual Studio
14.0\VC\include\concrt.h(710,17): error : '_mm_pause' needs target feature sse2
[F:\foobar2000\columns_ui\ui_helpers\ui_helpers.vcxproj]
I was about to report this problem to Microsoft, but on reading the Intel and
AMD docs for the PAUSE instruction, they say (respectively):
>From <a href="https://software.intel.com/en-us/node/524249">https://software.intel.com/en-us/node/524249</a>:
Since PAUSE is backwards compatible to all existing IA-32 architecture-based
processor generations, a test for processor type (a CPUID test) is not needed.
All legacy processors execute PAUSE instruction as a NOP, but in processors
that use the PAUSE instruction as a hint there can be significant performance
benefit.
>From <a href="https://support.amd.com/TechDocs/24594.pdf">https://support.amd.com/TechDocs/24594.pdf</a>:
Processors that do not support PAUSE treat this opcode as a NOP instruction
The Microsoft compiler doesn't complain about the use of _mm_pause() with SSE2
disabled (and it generates PAUSE instructions).</pre>
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