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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - SCEV createNodeForPHI is too optimistic about NSW."
href="http://llvm.org/bugs/show_bug.cgi?id=17452">17452</a>
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<th>Summary</th>
<td>SCEV createNodeForPHI is too optimistic about NSW.
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>atrick@apple.com
</td>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11329" name="attach_11329" title="Unit test">attachment 11329</a> <a href="attachment.cgi?id=11329&action=edit" title="Unit test">[details]</a></span>
Unit test
SCEV::createNodeForPhi flags an AddRec expression as NSW if the value on the
backedge is flagged nsw. It disregards whether the value has the same form as
the expression, or is merely a subexression as in:
%i.0 = phi i32 [ 0, %pre ], [ %tmp3, %loop ]
%tmp2 = add i32 %i.0, 1
%tmp3 = add nsw i32 %tmp2, 1
%check = icmp slt i32 %i.0, %N
A unit test is attached. It could be appended to nsw.ll.
I believe it would be sufficient to test if one of the BEValue's operands is
the PHINode before propagating NSW without losing any important cases.</pre>
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