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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Failure to thread extractelement through phi w/undef"
href="https://bugs.llvm.org/show_bug.cgi?id=38988">38988</a>
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<th>Summary</th>
<td>Failure to thread extractelement through phi w/undef
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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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>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>listmail@philipreames.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>$cat test.ll
define i32 @test(i1 %c, i32* nocapture readonly %p) {
br i1 %c, label %cond.load, label %else
cond.load: ; preds = %0
%1 = load i32, i32* %p, align 4
%2 = insertelement <1 x i32> undef, i32 %1, i32 0
br label %else
else: ; preds = %0, %cond.load
%res.phi.select = phi <1 x i32> [ %2, %cond.load ], [ undef, %0 ]
%3 = extractelement <1 x i32> %res.phi.select, i32 0
ret i32 %3
}
$opt -O3 test.ll -S
(same as input)
We should be producing:
define i32 @test(i1 %c, i32* nocapture readonly %p) {
br i1 %c, label %cond.load, label %else
cond.load:
%1 = load i32, i32* %p, align 4
br label %else
else:
%ret = phi i32 [%1, %cond.load], [undef, %0]
ret i32 %ret
}</pre>
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