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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Undefined behavior in int division with INT_MIN param"
href="https://bugs.llvm.org/show_bug.cgi?id=47973">47973</a>
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<th>Summary</th>
<td>Undefined behavior in int division with INT_MIN param
</td>
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<th>Product</th>
<td>compiler-rt
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>builtins
</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>ayshekuran@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>In the implementation for software integer division a/b (and mod a%b) in
int_div_impl.inc, the absolute values of a and b are calculated like so:
a = (a ^ s_a) - s_a;
(The variable s_a is -1 or 0 depending on the signedness of a.)
In the case where a (or b) is INT_MIN, this can mean that we calculate INT_MAX
+ 1 in signed integer operations. Calculating these as unsigned integers would
avoid this undefined behaviour.
In a similar fashion, the return statement can result in unsigned underflow
because it substracts s_a which gets promoted to unsigned UINT_MAX due to the
COMPUTE_UDIV being unsigned. Rewriting it as + (-s_a) would remove the
undefined behaviour.</pre>
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</p>
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