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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Divergence Analysis: Constant load in branch considered divergent"
href="https://llvm.org/bugs/show_bug.cgi?id=25864">25864</a>
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<th>Summary</th>
<td>Divergence Analysis: Constant load in branch considered divergent
</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>
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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>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>tstellar@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
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<pre>Created <span class=""><a href="attachment.cgi?id=15479" name="attach_15479" title="Test case">attachment 15479</a> <a href="attachment.cgi?id=15479&action=edit" title="Test case">[details]</a></span>
Test case
I've run into this issue with the DivergenceAnalysis pass, and I'm not sure if
it is a bug or if it is expected behavior. Attached is the test case, which
can be reproduced by applying this patch: <a href="http://reviews.llvm.org/D15608">http://reviews.llvm.org/D15608</a>
opt -analyze -divergence -mtriple=amdgcn-- divergent-test.ll
The output I get from the divergence analysis pass is this:
DIVERGENT: float %arg1
DIVERGENT: %tmp2 = fcmp ueq float %arg1, 0.000000e+00
DIVERGENT: br i1 %tmp2, label %bb7, label %bb3
DIVERGENT: %tmp4 = phi i1 [ false, %bb7 ], [ true, %bb ]
DIVERGENT: br i1 %tmp4, label %bb5, label %bb9
DIVERGENT: %tmp6 = call float @llvm.SI.load.const(<16 x i8> %tmp, i32 16)
^ This last line is what I think it incorrect. This is a constant load
intrinsic, which takes a non-divergent argument, so it shouldn't be divergent.
I have verified that AMDGPU's implementation of
TargetTransformInfo::isSourceOfDivergence() returns false for this intrinsic.
Based on brief debugging of the issue I think the problem may be that the
DivergenceAnalysis pass incorrectly things this test case contains a loop, but
I'm not really sure.</pre>
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