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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 --- - LoopDistribute domtree handling gives eternal loop"
href="https://llvm.org/bugs/show_bug.cgi?id=30958">30958</a>
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<th>Summary</th>
<td>LoopDistribute domtree handling gives eternal loop
</td>
</tr>
<tr>
<th>Product</th>
<td>tools
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>opt
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>jesper.antonsson@ericsson.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=17572" name="attach_17572" title="Small program provoking the bug">attachment 17572</a> <a href="attachment.cgi?id=17572&action=edit" title="Small program provoking the bug">[details]</a></span>
Small program provoking the bug
Opt gets stuck in an eternal loop with the attached small program, using these
flags:
opt -simplifycfg -loop-distribute -instcombine loopdist_simplified.ll
The reason is that the LoopDistribute pass mess up the dominator tree and
introduce a cycle, so when the instcombiner needs to walk the dominator tree it
gets stuck in a tight eternal loop:
Program received signal SIGINT, Interrupt.
llvm::DominatorTreeBase<llvm::BasicBlock>::dominatedBySlowTreeWalk
(this=0x343d570, A=0x345e5e0, B=0x3455b70)
at ../include/llvm/Support/GenericDomTree.h:220
220 B = IDom; // Walk up the tree
If we use this command line:
opt -loop-distribute -verify-dom-info loopdist_simplified.ll
... the verifier complains:
DominatorTree for function: f is not up to date!
Computed:
=============================--------------------------------
Inorder Dominator Tree: DFSNumbers invalid: 0 slow queries.
[1] %0 {0,5}
Actual:
=============================--------------------------------
Inorder Dominator Tree:
[1] %0 {0,17}
[2] %bb1 {1,16}
[3] %bb2.lver.check {2,15}
[4] %bb2.ph.lver.orig {3,6}
[5] %bb2.lver.orig {4,5}
[4] %bb2.ph.ldist1 {7,14}
[5] %bb2.ldist1 {8,13}
[6] %bb2.ph {9,12}
[7] %bb2 {10,11}</pre>
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