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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 --- - Exponential output growth introduced in the IndVarsSimplify pass"
href="https://llvm.org/bugs/show_bug.cgi?id=28166">28166</a>
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<th>Summary</th>
<td>Exponential output growth introduced in the IndVarsSimplify pass
</td>
</tr>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>3.8
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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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>
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<th>Component</th>
<td>new bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>david.stenberg@ericsson.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>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=16565" name="attach_16565" title="Reproducer">attachment 16565</a> <a href="attachment.cgi?id=16565&action=edit" title="Reproducer">[details]</a></span>
Reproducer
When running opt:
opt -S -Oz -O1 bugpoint-reduced-simplified.ll
with the attached bugpoint-reduced-simplified.ll file, the resulting output
file seems to grow exponentially with the number of loop iterations (40 in the
bugpoint-reduced-simplified.ll), as seen here for N=20, 21, and 22:
$ du -h out-*
74M out-20.ll
148M out-21.ll
295M out-22.ll
The problem seems to be introduced in the Induction Variable Simplification
pass, where the condition for the br instruction in bb3 grows:
N = 1:
br i1 icmp sge (i16 ptrtoint (i16* @bar to i16), i16 0),
label %bb4.preheader, label %bb5
N = 2:
br i1 icmp sge (i16 xor (i16 zext (i1 icmp sge
(i16 ptrtoint (i16* @bar to i16), i16 0) to i16),
i16 ptrtoint (i16* @bar to i16)), i16 zext (i1 icmp sge
(i16 ptrtoint (i16* @bar to i16), i16 0) to i16)),
label %bb4.preheader, label %bb5
And so on.
The issue might be related to how the passes are executed, as passing any
combination of the -O[z123] flags triggers the issue. When passing just one of
the flags, the issue is not seen.</pre>
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