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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 --- - loop-unroll and simplifycfg cause oscillation with phi node arguments"
href="https://llvm.org/bugs/show_bug.cgi?id=27523">27523</a>
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<th>Summary</th>
<td>loop-unroll and simplifycfg cause oscillation with phi node arguments
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nwilson20@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=16269" name="attach_16269" title="scfg_loop_unroll.ll">attachment 16269</a> <a href="attachment.cgi?id=16269&action=edit" title="scfg_loop_unroll.ll">[details]</a></span>
scfg_loop_unroll.ll
When using the flags -simplifycfg and -loop-unroll on the attached IR
(scfg_loop_unroll.ll) the phi nodes will keep flipping. This was produced by
using the attached IR and using the output as input back to opt.
For example:
$./opt -simplifycfg -loop-unroll -S scfg_loop_unroll.ll > out1.ll
$ ./opt -simplifycfg -loop-unroll -S out1.ll > out2.ll
$./opt -simplifycfg -loop-unroll -S out2.ll > out3.ll
$diff out2.ll out1.ll
1c1
< ; ModuleID = 'out1.ll'
---
<span class="quote">> ; ModuleID = 'simplifycfg_loop-unroll_osc.ll'</span >
130c130
< %.ph = phi i32 [ %3, %if.then20 ], [ undef, %if.end27 ]
---
<span class="quote">> %.ph = phi i32 [ undef, %if.end27 ], [ %3, %if.then20 ]</span >
$diff out3.ll out2.ll
1c1
< ; ModuleID = 'out2.ll'
---
<span class="quote">> ; ModuleID = 'out1.ll'</span >
130c130
< %.ph = phi i32 [ undef, %if.end27 ], [ %3, %if.then20 ]
---
<span class="quote">> %.ph = phi i32 [ %3, %if.then20 ], [ undef, %if.end27 ]</span ></pre>
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