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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - AA incorrect NoAlias result"
href="http://llvm.org/bugs/show_bug.cgi?id=18460">18460</a>
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<th>Summary</th>
<td>AA incorrect NoAlias result
</td>
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<tr>
<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>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Global Analyses
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>hfinkel@anl.gov
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
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<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11865" name="attach_11865" title="bugpoint reduced test case">attachment 11865</a> <a href="attachment.cgi?id=11865&action=edit" title="bugpoint reduced test case">[details]</a></span>
bugpoint reduced test case
BasicAliasAnalysis is incorrectly returning NoAlias in the following situation:
%end147 = getelementptr inbounds %"struct.llvm::LiveRange::Segment"* %v97,
i64 -1, i32 1
%end151 = getelementptr inbounds %"struct.llvm::LiveRange::Segment"* %Seg,
i64 0, i32 1
%Value.i.i.i.i.i.i = getelementptr inbounds %"class.llvm::SlotIndex"*
%end147, i64 0, i32 0, i32 0
...
%__b.__a.i = select i1 %cmp.i.i, %"class.llvm::SlotIndex"* %end151,
%"class.llvm::SlotIndex"* %end147
%v117 = getelementptr inbounds %"class.llvm::SlotIndex"* %__b.__a.i, i64 0,
i32 0, i32 0
%v118 = load i64* %v117, align 8, !tbaa !20
store i64 undef, i64* %Value.i.i.i.i.i.i, align 8, !tbaa !20
Running:
opt -tbaa -basicaa -aa-eval -evaluate-tbaa -print-no-aliases -print-may-aliases
-disable-output < bugpoint-reduced-simplified.ll
will display (near the end of the output):
NoAlias: %v118 = load i64* %v117, align 8, !tbaa !12 <-> store i64 undef,
i64* %Value.i.i.i.i.i.i, align 8, !tbaa !12
This is incorrect, essentially saying that (gep(%end147, 0, 0, 0)) does not
alias (gep(select(..., ..., %end147), 0, 0, 0)), and it certainly might!
I've attached a test case (which is derived from LLVM's LiveInterval.cpp),
which is a bugpoint-reduced file (with some manual cleanup).</pre>
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