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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Vector extract placement causes 37% regression on fp-convert."
href="http://llvm.org/bugs/show_bug.cgi?id=19258">19258</a>
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<th>Summary</th>
<td>Vector extract placement causes 37% regression on fp-convert.
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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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
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<th>Reporter</th>
<td>atrick@apple.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>This LNT tester:
<a href="http://llvm.org/perf/db_default/v4/nts/graph?plot.0=34.161.2&highlight_run=23986">http://llvm.org/perf/db_default/v4/nts/graph?plot.0=34.161.2&highlight_run=23986</a>
Showed a 37% regression on fp-convert after this checkin:
---
Author: atrick
Date: Mon Mar 24 21:18:47 2014
New Revision: 204699
URL: <a href="http://llvm.org/viewvc/llvm-project?rev=204699&view=rev">http://llvm.org/viewvc/llvm-project?rev=204699&view=rev</a>
Log:
SLP vectorizer: Don't hoist vector extracts of phis.
Extracts coming from phis were being hoisted, while all others were
sunk to their uses. This was inconsistent and didn't seem to serve a
purpose. Changing all extracts to be sunk to uses is a prerequisite
for adding block frequency to the SLP vectorizer's cost model.
---
My own benchmarking on darwin/x86_64/sandybridge showed a slight improvement
after this checkin: (2.6 vs 2.8s).
If someone can reproduce the regression and show what caused it, we should
definitely teach the vectorizer to avoid the problem.</pre>
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