<html>
    <head>
      <base href="https://llvm.org/bugs/" />
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <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>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>loop-unroll and simplifycfg cause oscillation with phi node arguments
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libraries
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Loop Optimizer
          </td>
        </tr>

        <tr>
          <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>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </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>
        </div>
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