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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 - Failure to optimize double overflow comparison to __builtin_add_overflow"
href="https://bugs.llvm.org/show_bug.cgi?id=46432">46432</a>
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</tr>
<tr>
<th>Summary</th>
<td>Failure to optimize double overflow comparison to __builtin_add_overflow
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>gabravier@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>unsigned foo(unsigned a, unsigned b)
{
unsigned sum = a + b;
if (sum < a)
abort();
if (sum < b)
abort();
return sum;
}
This can be optimized to remove one of the two checks, or to this :
unsigned foo(unsigned a, unsigned b)
{
unsigned sum;
if (__builtin_add_overflow(a, b, &sum))
abort();
else
return sum;
}
This transformation is done by GCC, but not by LLVM.</pre>
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