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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - loop vectorizer unable to reason with trip count bounds"
href="https://bugs.llvm.org/show_bug.cgi?id=40961">40961</a>
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<th>Summary</th>
<td>loop vectorizer unable to reason with trip count bounds
</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>Other
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Loop Optimizer
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>oiskuu@gmail.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
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<pre>I see bugs <a class="bz_bug_link
bz_status_NEW "
title="NEW - Pointless loop unroll / vectorization"
href="show_bug.cgi?id=38280">38280</a>, <a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop vectorizer produces extremely poor code for pattern fills"
href="show_bug.cgi?id=37423">37423</a>, but this one is simpler still. Consider the following:
void topup(int a[], unsigned long i)
{
for (; i < 16; i++) {
a[i] = 1;
}
}
The result, compiled with -O -march=haswell
- loop is vectorized despite the small absolute limit on trip count
- vectorized part has loop step of 256 (!) and is actually unreachable</pre>
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