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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Loop vectorizer causes crash when compiler -"
href="https://bugs.llvm.org/show_bug.cgi?id=47308">47308</a>
</td>
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<th>Summary</th>
<td>Loop vectorizer causes crash when compiler -
</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>
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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>normal
</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>
<tr>
<th>Reporter</th>
<td>praharen@ualberta.ca
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>compile command:
./clang -Os -mllvm -force-vector-width=4 bug_test.c -S -emit-llvm -o bug_os.ll
source:
bug_test.c
include <stdio.h>
int a;
int main(void) {
int d = -1;
#pragma clang loop vectorize(assume_safety)
for (int i = 0; i < 49; ++i) {
a |= d;
d = i;
}
return 0;
}
The issue is in LoopVectorize.cpp in
LoopVectorizationPlanner::collectTriviallyDeadInstructions. The induction phi
for variable 'c' is marked as dead code here as it is the only use of induction
phi 'd'. Maybe a fix would add a check to ensure the use is not a phi of a
different induction variable. The phi statement being marked as dead code means
it does not get a vectorization recipe and the vector loop body ends up
referring to the original scalar induction variable %c in the vector loop body.
But %c is not defined yet. This causes the assertion in
InnerLoopVectorizer::fixupIVUsers to fail: "Expected LCSSA form".</pre>
</div>
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