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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 - [SLP] getVectorElementSize() is slow"
href="https://bugs.llvm.org/show_bug.cgi?id=45269">45269</a>
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<tr>
<th>Summary</th>
<td>[SLP] getVectorElementSize() is slow
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nikita.ppv@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Compiling shared_sha256.c from test-suite:
clang -DNDEBUG -O3 -w -Werror=date-time -save-stats=obj -DHAVE_CONFIG_H
-I/home/nikic/llvm-test-suite/MultiSource/Applications/ClamAV
-I/home/nikic/llvm-test-suite/MultiSource/Applications/ClamAV/zlib
-DDONT_LOCK_DBDIRS -DC_LINUX -DFPU_WORDS_BIGENDIAN=0 -DWORDS_BIGENDIAN=0
-save-stats=obj -MD -MT
MultiSource/Applications/ClamAV/CMakeFiles/clamscan.dir/shared_sha256.c.o -MF
MultiSource/Applications/ClamAV/CMakeFiles/clamscan.dir/shared_sha256.c.o.d -o
MultiSource/Applications/ClamAV/CMakeFiles/clamscan.dir/shared_sha256.c.o -c
../MultiSource/Applications/ClamAV/shared_sha256.c
50% of the time is taken up by SLP vectorization, with 35% inside
getVectorElementSize().
The function for reference:
<a href="https://github.com/llvm/llvm-project/blob/601d25cb736d8b67e642faa06f9e956c67fd25d9/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp#L5299">https://github.com/llvm/llvm-project/blob/601d25cb736d8b67e642faa06f9e956c67fd25d9/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp#L5299</a>
It performs a full instruction scan starting from a root, which may end up
visiting a very large number of instructions.
Is it possible to limit this walk in some way?</pre>
</div>
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