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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - PGO leads to performance degradation"
href="https://bugs.llvm.org/show_bug.cgi?id=36303">36303</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>PGO leads to performance degradation
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>6.0
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>vleschuk@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19840" name="attach_19840" title="Code sample">attachment 19840</a> <a href="attachment.cgi?id=19840&action=edit" title="Code sample">[details]</a></span>
Code sample
I've been testing PGO with the code from the thread:
<a href="http://lists.llvm.org/pipermail/llvm-dev/2016-May/099395.html">http://lists.llvm.org/pipermail/llvm-dev/2016-May/099395.html</a>
(Code is attached).
And it appeared that using PGO (either -fprofile-instr or -fprofile) lead to
performance degradation. See the results of `{ for i in `seq 1 100`; do time
./test > /dev/null ; done ; } 2>> perf.log` below:
clang -O3: 3.12253
clang -O3 + -fprofile-use: 3.14982
clang -O3 + -fprofile-use + -mllvm -force-precise-rotation-cost : 3.14189
gcc -O3: 3.38019
gcc -O3 + -fprofile-use: 2.937
clang/llvm were built from release_60 branch, gcc version was 7.3.0.</pre>
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