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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 - Miscompile by -loop-bound-split (load from wrong address after split)"
href="https://bugs.llvm.org/show_bug.cgi?id=51866">51866</a>
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<th>Summary</th>
<td>Miscompile by -loop-bound-split (load from wrong address after split)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</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=25259" name="attach_25259" title="bbi-60288.ll reproducer">attachment 25259</a> <a href="attachment.cgi?id=25259&action=edit" title="bbi-60288.ll reproducer">[details]</a></span>
bbi-60288.ll reproducer
llvm commit: 0dc461441eed
Reproduce with:
opt -passes='module(loop-bound-split)' -S -o - bbi-60288.ll
In the input the loop executes 10 rounds, and for each round we read in B with
the induction variable "i" as offset.
After loop-bound-split, the loop is split in two, one for i < 5 and one for
larger i. However, in the second loop we starts over reading at offset 0 in B
instead of offset 5.
I.e. in the second loop we do
for.cond.split: ; preds =
%for.cond.split.preheader, %for.inc.split
%i.0.split = phi i16 [ %inc.split, %for.inc.split ], [ 0,
%for.cond.split.preheader ]
%exitcond.not.split = icmp eq i16 %i.0.split, 10
br i1 %exitcond.not.split, label %for.end.loopexit, label %for.body.split
for.body.split: ; preds = %for.cond.split
%cmp1.split = icmp ult i16 %i.0.split, 5
%arrayidx.split = getelementptr inbounds [10 x i16], [10 x i16]* @B, i16 0,
i16 %i.0.split
%2 = load i16, i16* %arrayidx.split, align 1
br i1 false, label %if.then.split, label %if.else.split
where %i.0.split "starts over" from 0 in the PHI and %i.0.split is used in the
gep determining where to read.
I think the PHI should be
%i.0.split = phi i16 [ %inc.split, %for.inc.split ], [ 5,
%for.cond.split.preheader ]
instead.</pre>
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