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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - performance regression in LoopStrengthReduce"
href="https://llvm.org/bugs/show_bug.cgi?id=31629">31629</a>
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<th>Summary</th>
<td>performance regression in LoopStrengthReduce
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.9
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
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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>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>jeroen.dobbelaere@synopsys.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=17837" name="attach_17837" title="testcase showing bad behavior">attachment 17837</a> <a href="attachment.cgi?id=17837&action=edit" title="testcase showing bad behavior">[details]</a></span>
testcase showing bad behavior
During the 3.8-3.9 timeframe, a number of changes were done that exhibit some
severe quality-of-code regression.
For the testcase, I am using the xscale target to show the regression, but we
noticed it in our custom version of llvm. So this behavior is likely to be
present for most targets.
The main change that shows the regression is:
Author: Manuel Jacob <<a href="mailto:me@manueljacob.de">me@manueljacob.de</a>>
Date: Thu Jun 2 22:14:26 2016 +0000
[PM] Schedule InstSimplify after late LICM run, to clean up LCSSA nodes.
Summary:
The module pass pipeline includes a late LICM run after loop
unrolling. LCSSA is implicitly run as a pass dependency of LICM. However
no
cleanup pass was run after this, so the LCSSA nodes ended in the optimized
output.
Reviewers: hfinkel, mehdi_amini
Subscribers: majnemer, bruno, mzolotukhin, mehdi_amini, llvm-commits
Differential Revision: <a href="http://reviews.llvm.org/D20606">http://reviews.llvm.org/D20606</a>
git-svn-id: <a href="https://llvm.org/svn/llvm-project/llvm/trunk@271602">https://llvm.org/svn/llvm-project/llvm/trunk@271602</a>
91177308-0d34-0410-b5e6-96231b3b80d8
This change activates the instructionSimplifyPass, but, this change only allows
us to see when LoopStrengthReduce is breaking down.</pre>
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