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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - new pass manager performance regression: loop unswitch for omnetpp"
href="https://bugs.llvm.org/show_bug.cgi?id=49128">49128</a>
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<th>Summary</th>
<td>new pass manager performance regression: loop unswitch for omnetpp
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<th>Product</th>
<td>new-bugs
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>Sanne.Wouda@arm.com
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>We're seeing a regression on omnetpp (both spec 2006 and 2017, -8% and -7%
respectively) as a result of the new pass manager switch. This is AArch64 on a
Neoverse-N1, with -flto -mcpu=native -fomit-frame-pointer.
This seems to boil down to a recent patch to LoopUnswitch
(<a href="https://reviews.llvm.org/D93764">https://reviews.llvm.org/D93764</a>) which implemented partial loop unswitching.
However, the new pass manager uses SimpleLoopUnswitch and does not benefit from
this improvement.
AFAIU, LoopUnswitch is incompatible with the new pass manager, so the
improvement to LoopUnswitch needs to be ported to SimpleLoopUnswitch.</pre>
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