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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Bad optimization of simple switch"
href="https://bugs.llvm.org/show_bug.cgi?id=45683">45683</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Bad optimization of simple switch
</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>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<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>int f(unsigned x)
{
switch (x)
{
case 0:
return 1;
case 1:
return 2;
}
}
This gets optimized to some rather weird code (uses `sbb` on x86) when it could
just be optimized to `return x + 1`. See here for an example of the bad
generation : <a href="https://godbolt.org/z/2fQmpH">https://godbolt.org/z/2fQmpH</a>
Maybe we could change the translation of `select` (as it is used in the IR this
translates to) in order to detect cases such as this and optimize them properly
?</pre>
</div>
</p>
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