<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang generating memcpy with source/destination overlap"
href="https://bugs.llvm.org/show_bug.cgi?id=31993">31993</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>clang generating memcpy with source/destination overlap
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</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>
<tr>
<th>Component</th>
<td>new bugs
</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>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=18001" name="attach_18001" title="reproducer">attachment 18001</a> <a href="attachment.cgi?id=18001&action=edit" title="reproducer">[details]</a></span>
reproducer
With
clang -S -emit-llvm tr13026.c -o tr13026.ll
we get this memcpy call in the output
call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @s to i8*),
i8* bitcast (%struct.anon* @s to i8*), i64 4, i32 4, i1 false)
where the dest and source arguments are the same, and thus clearly overlap.
However, in the documentation:
<a href="http://llvm.org/docs/LangRef.html#llvm-memcpy-intrinsic">http://llvm.org/docs/LangRef.html#llvm-memcpy-intrinsic</a>
it says:
"The ‘llvm.memcpy.*‘ intrinsics copy a block of memory from the source location
to the destination location, which are not allowed to overlap."
And if running lint on the output:
opt -S -lint -o tr13026.opt.ll tr13026.ll
we get a warning about it:
Undefined behavior: memcpy source and destination overlap
call void @llvm.memcpy.p0i8.p0i8.i64(i8* bitcast (%struct.anon* @s to i8*),
i8* bitcast (%struct.anon* @s to i8*), i64 4, i32 4, i1 false)</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>