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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 with opt -licm with memory-ssa enabled"
href="https://bugs.llvm.org/show_bug.cgi?id=43540">43540</a>
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<tr>
<th>Summary</th>
<td>Miscompile with opt -licm with memory-ssa enabled
</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>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mikael.holmen@ericsson.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
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<pre>Created <span class=""><a href="attachment.cgi?id=22622" name="attach_22622" title="bbi-33452.ll reproducer">attachment 22622</a> <a href="attachment.cgi?id=22622&action=edit" title="bbi-33452.ll reproducer">[details]</a></span>
bbi-33452.ll reproducer
With
opt -licm -S -o - bbi-33452.ll
the store to @v_2 is erroneously hoisted out of the loop, so it's done before
the memcpy reading from @v_2.
The loop is only run one round, so the hoisting looks wrong to me.
Input:
define void @foo() {
entry:
br label %for.cond
for.cond: ; preds = %for.body, %entry
%0 = phi i16 [ %inc, %for.body ], [ 0, %entry ]
%cmp = icmp slt i16 %0, 1
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
call void @llvm.memcpy.p0i8.p0i8.i64(i8* @v_1, i8 * @v_2, i64 1, i1 false)
store i8 1, i8 * @v_2, align 1
%inc = add nsw i16 %0, 1
br label %for.cond
for.end: ; preds = %for.cond
ret void
}
Output:
@v_1 = global i8 0, align 1
@v_2 = global i8 0, align 1
define void @foo() {
entry:
store i8 1, i8* @v_2, align 1
br label %for.cond
for.cond: ; preds = %for.body, %entry
%0 = phi i16 [ %inc, %for.body ], [ 0, %entry ]
%cmp = icmp slt i16 %0, 1
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
call void @llvm.memcpy.p0i8.p0i8.i64(i8* @v_1, i8* @v_2, i64 1, i1 false)
%inc = add nsw i16 %0, 1
br label %for.cond
for.end: ; preds = %for.cond
ret void
}
; Function Attrs: argmemonly nounwind willreturn
declare void @llvm.memcpy.p0i8.p0i8.i64(i8* noalias nocapture writeonly, i8*
noalias nocapture readonly, i64, i1 immarg) #0
attributes #0 = { argmemonly nounwind willreturn }</pre>
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