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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - SLP vectorizer doesn't obey llvm.loop.vectorize.width=1"
href="https://bugs.llvm.org/show_bug.cgi?id=43553">43553</a>
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<th>Summary</th>
<td>SLP vectorizer doesn't obey llvm.loop.vectorize.width=1
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>9.0
</td>
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<th>Hardware</th>
<td>Other
</td>
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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>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>husseydevin@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<pre>Follow up to <a class="bz_bug_link
bz_status_NEW "
title="NEW - #pragma clang loop vectorize(disable) should actually disable vectorization"
href="show_bug.cgi?id=43539">bug 43539</a>. Code example is there.
The SLP vectorizer (plus any other passes that emit SIMD code) should always
obey the llvm.loop.vectorize.width=1 (emitted by #pragma clang loop
vectorize(disable)) or llvm.loop.vectorize.enable=false.
Currently, what happens on non-trivial loops is that the loop optimizer will
unroll (and/or interleave) the loop, and SLP will vectorize the unrolled loop.
Enabled or disabled, the loop ends up being vectorized, making this
annotation/pragma useless.</pre>
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