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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 - LoopIdiom does not produce memcpy/memset with runtime checks if pointers may alias"
href="https://bugs.llvm.org/show_bug.cgi?id=51550">51550</a>
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<th>Summary</th>
<td>LoopIdiom does not produce memcpy/memset with runtime checks if pointers may alias
</td>
</tr>
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<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>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>typedef __SIZE_TYPE__ size_t;
void idiom_memcpy_aliasing(unsigned char * dst, size_t d_len, unsigned char
*src)
{
// no restrict, possible aliasing
unsigned char *d_end = dst + d_len;
// icc seems to produce memcpy when alias checks are OK and d_len j < 96,
jumps to trivial copy loop otherwise.
while (dst < d_end)
*dst++ = *src++;
}
ICC -O2+ is able to do this kind of transformation.
<a href="https://godbolt.org/z/eK1P4YjMf">https://godbolt.org/z/eK1P4YjMf</a></pre>
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