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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Miscompile with opt -licm -dse (due to bad memoryssa?)"
href="https://bugs.llvm.org/show_bug.cgi?id=49859">49859</a>
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<th>Summary</th>
<td>Miscompile with opt -licm -dse (due to bad memoryssa?)
</td>
</tr>
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<th>Product</th>
<td>libraries
</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>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>mikael.holmen@ericsson.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=24721" name="attach_24721" title="bbi-54825_man_red.ll reproducer">attachment 24721</a> <a href="attachment.cgi?id=24721&action=edit" title="bbi-54825_man_red.ll reproducer">[details]</a></span>
bbi-54825_man_red.ll reproducer
Running
opt -enable-new-pm=0 -licm -dse bbi-54825_man_red.ll -S -o -
all stores to %sum are removed by dse. this then makes
%3 = load i8, i8* %sum, align 1
get the wrong value.
If we instead run
opt -enable-new-pm=0 -licm bbi-54825_man_red.ll -S -o - | opt -enable-new-pm=0
-dse -S -o -
several stores to %sum remains.
The same thing happens if we remove
AU.addPreserved<MemorySSAWrapperPass>();
from LICM.cpp.
Thus I think that LICM doesn't update memoryssa information as it should.
This looks very similar to an old bug:
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Incorrect MemorySSA result after LICM"
href="show_bug.cgi?id=45927">https://bugs.llvm.org/show_bug.cgi?id=45927</a></pre>
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