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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 - Interprocedural Sparse Conditional Constant Propagation generates incorrect code"
href="https://bugs.llvm.org/show_bug.cgi?id=39772">39772</a>
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<th>Summary</th>
<td>Interprocedural Sparse Conditional Constant Propagation generates incorrect code
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</td>
</tr>
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<th>OS</th>
<td>MacOS X
</td>
</tr>
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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>
</tr>
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<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jbush342@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=21148" name="attach_21148" title="Program that reproduces issue">attachment 21148</a> <a href="attachment.cgi?id=21148&action=edit" title="Program that reproduces issue">[details]</a></span>
Program that reproduces issue
The attached program generates incorrect code. Specifically, this clause:
if (left_height > right_height) {
return left_height + 1;
} else {
return right_height + 1;
}
Always returns 1 if it hits the else condition (left_height is not greater than
right_height). You can see the generated LLVM IR below. Note that, the phi node
will return 1 if it branches from %if.else:
if.end5: ; preds = %if.end
%cmp6 = icmp sgt i32 %call, %call1
br i1 %cmp6, label %if.then7, label %if.else
if.then7: ; preds = %if.end5
%add = add nsw i32 %call, 1
br label %cleanup
if.else: ; preds = %if.end5
br label %cleanup
cleanup: ; preds = %if.else,
%if.then7, %if.then
%retval.0 = phi i32 [ 0, %if.then ], [ %add, %if.then7 ], [ 1, %if.else ]
ret i32 %retval.0
}
If I add the parameter -mllvm -opt-bisect-limit=6, it still generates incorrect
code as above, bug if I change the parameter to 5, it no longer does, which
corresponds to this pass:
BISECT: running pass (6) Interprocedural Sparse Conditional Constant
Propagation on module (bug-min.c)
This behavior started some time between SVN revision 329504 and 346103. It
still happens as of 347515.
I don't think this is clang specific, but I couldn't figure out how to
reproduce with opt (I generated LLVM IR code from clang with -O0, but running
with opt -O3 did not seem to optimize anything).</pre>
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