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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - possible bad code generation"
href="https://llvm.org/bugs/show_bug.cgi?id=31614">31614</a>
</td>
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<tr>
<th>Summary</th>
<td>possible bad code generation
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>3.9
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>clay.trychta@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>Created <span class=""><a href="attachment.cgi?id=17832" name="attach_17832" title="repro">attachment 17832</a> <a href="attachment.cgi?id=17832&action=edit" title="repro">[details]</a></span>
repro
When compiling the attached code with -O2 -std=c++14 the generated assembly
seems to be incorrect (I tried to rule out undefined behavior, but if I missed
something please let me know).
Specifically, test_function starts with some code that seems like it can
randomly set al to 0 or 1 depending on rax:
test rax, rax
setns al
The other instance of test/setns also seems suspicious.
Some more details can be found here:
<a href="http://stackoverflow.com/questions/41597341/mapping-c-to-assembly">http://stackoverflow.com/questions/41597341/mapping-c-to-assembly</a>
<a href="https://godbolt.org/g/ccrV7m">https://godbolt.org/g/ccrV7m</a>
Please let me know if you need any other information.</pre>
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