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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 - Missing SymbolCast for explicit integer downcasts"
href="https://bugs.llvm.org/show_bug.cgi?id=39138">39138</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missing SymbolCast for explicit integer downcasts
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Static Analyzer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>dcoughlin@apple.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>adam.balogh@ericsson.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>`ExprEngine` only creates `SymbolCast` for an integer `CastExpr` if the result
is known to be truncated. However it does not create it if the result only "may
be" truncated. These casts are simply ignored which leads to incorrect results:
If `n` is of type `unsigned char` and `m` is a wider `unsigned`, then the range
of `m` is incorrect after this code:
```
assert(n >= 0xfe);
m = (unsigned char)(n + 1);
```
If `n >= 0xfe` then `n` is either `0xfe` or `0xff`, so `m` should be either
`0xff` or `0`. However, the range of `m` in this case is `[0xff..0x100]` which
means that the downcast is ignored.</pre>
</div>
</p>
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