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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - llvm.assume blocks vectorizer predication"
href="https://bugs.llvm.org/show_bug.cgi?id=43620">43620</a>
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<th>Summary</th>
<td>llvm.assume blocks vectorizer predication
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>benny.kra@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>ayal.zaks@intel.com, hfinkel@anl.gov, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>$ cat t.cc
void foo(float *__restrict a, float *__restrict b, int n) {
for (int i = 0; i != n; ++i) {
float x = 1;
if (i < 495616) {
x = 23;
} else if (i < 991232) {
x = 42;
} else {
__builtin_unreachable();
}
b[i] = a[i] * x;
}
}
This only gets vectorized if I remove the __builtin_unreachable, but that
shouldn't affect vectorization at all. The unreachable gets converted into an
llvm.assume by SimplifyCFG but LV doesn't understand that it's not blocking
predication.
Godbolt: <a href="https://godbolt.org/z/PYp4wa">https://godbolt.org/z/PYp4wa</a></pre>
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</p>
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