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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - -Rpass-missed=loop-vectorize says nothing at all for outer loops"
href="https://llvm.org/bugs/show_bug.cgi?id=28374">28374</a>
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<th>Summary</th>
<td>-Rpass-missed=loop-vectorize says nothing at all for outer loops
</td>
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<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>MacOS X
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>sean@rogue-research.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=16662" name="attach_16662" title="Repro case">attachment 16662</a> <a href="attachment.cgi?id=16662&action=edit" title="Repro case">[details]</a></span>
Repro case
Consider:
--------test.c-------
#include <stdio.h>
int foo(int *A, int *B, int n) {
#pragma clang loop vectorize(enable)
for (int k = 0; k < n; ++k)
{
unsigned sum = 0;
#pragma clang loop vectorize(enable)
for (int i = 0; i < n; ++i)
sum += A[i] + 5;
printf("%i", sum);
}
return 0;
}
---------------
$ clang --version
clang version 3.9.0 (trunk 274259)
$ clang -S -fvectorize -O3 -Rpass=loop-vectorize -Rpass-missed=loop-vectorize
-Rpass-analysis=loop-vectorize ~/Desktop/test.c
/Users/sean/Desktop/test.c:11:4: remark: vectorized loop (vectorization width:
4, interleaved count: 2) [-Rpass=loop-vectorize]
for (int i = 0; i < n; ++i)
^
It helpfully says it vectorized the inner loop, but says *nothing* about the
outer loop (despite the #pragma even).
Adam Nemet said on cfe-dev that "the vectorizer does not visit outer loops and
the diagnostics is emitted in the vectorizer so we don’t get a chance to report
anything."
For a user trying to audit/tweak his loops to be vectorization-friendly, it's
frustrating that the flags that are supposed to report if/why a loop has/has
not been vectorized are not behaving reliably.</pre>
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