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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - wrong results with union and strict-aliasing"
href="http://llvm.org/bugs/show_bug.cgi?id=21725">21725</a>
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<th>Summary</th>
<td>wrong results with union and strict-aliasing
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>3.4
</td>
</tr>
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<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>Global Analyses
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>bruno-llvm@defraine.net
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</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=13420" name="attach_13420" title="test.c">attachment 13420</a> <a href="attachment.cgi?id=13420&action=edit" title="test.c">[details]</a></span>
test.c
The following testcase produces wrong results with '-O1' and higher (tested
with llvm-3.4 and llvm-3.5).
Disabling 'strict-aliasing' makes the problem go away.
We do believe that the behavior should be the same with and without
strict-aliasing.
It seems that initially, the write to 'u.s' is moved out of the loop.
(more exactly, after the loop)
Later on the loop is removed, with only the write to 'up->i' remaining.
As the store to 'u.s' is still following, the end result is not what we expect
to see.</pre>
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