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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 out comparison when very narrow range is already known"
href="https://bugs.llvm.org/show_bug.cgi?id=48408">48408</a>
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<th>Summary</th>
<td>Failure to optimize out comparison when very narrow range is already known
</td>
</tr>
<tr>
<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>
</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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<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>#ifndef __clang__
__attribute__((always_inline)) inline void __builtin_assume(bool condition)
{
if (!condition)
__builtin_unreachable();
}
#endif
bool f(int a)
{
__builtin_assume((a == -1) || (a == 0));
return a < -1;
}
This can be optimized to `return false;`. This transformation is done by GCC,
but not by LLVM.
See also Godbolt comparison here : <a href="https://godbolt.org/z/8x5x89">https://godbolt.org/z/8x5x89</a></pre>
</div>
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