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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [SLP] SLP vectorizer change causes performance loss"
href="https://bugs.llvm.org/show_bug.cgi?id=46261">46261</a>
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<th>Summary</th>
<td>[SLP] SLP vectorizer change causes performance loss
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</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>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>Wolfgang_Pieb@playstation.sony.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Created <span class=""><a href="attachment.cgi?id=23593" name="attach_23593" title="Test case">attachment 23593</a> <a href="attachment.cgi?id=23593&action=edit" title="Test case">[details]</a></span>
Test case
After the commit
<a href="https://github.com/llvm/llvm-project/commit/6a18a9548761b266b28a49f705a568677c24b59b">https://github.com/llvm/llvm-project/commit/6a18a9548761b266b28a49f705a568677c24b59b</a>
the attached test experiences a roughly 50% slowdown.
Compile with clang -O2 -march=btver2.
The IR dump after SLP shows that, before the commit, a substantial number of
shuffle instructions are present, e.g.
%shuffle = shufflevector <2 x float> %14, <2 x float> undef, <4 x i32> <i32 0,
i32 0, i32 0, i32 1>
whereas after the commit, the IR dump does not show any.</pre>
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</p>
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