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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 some limit bounds patterns based on __builtin_assume"
href="https://bugs.llvm.org/show_bug.cgi?id=45682">45682</a>
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<th>Summary</th>
<td>Failure to optimize some limit bounds patterns based on __builtin_assume
</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>
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<th>Priority</th>
<td>P
</td>
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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>#include <limits.h>
#ifdef __clang__
#define assume __builtin_assume
#else
inline void assume(bool x)
{
if (!x)
__builtin_unreachable();
}
#endif
void g();
void f(int x, int y)
{
assume(y > 0);
x += y;
if (x == -INT_MAX - 1)
g();
}
`f` is optimized to doing nothing by gcc, clang does the check even though `y >
0` means the last condition is always false. Sample comparison here :
<a href="https://godbolt.org/z/x-cuqX">https://godbolt.org/z/x-cuqX</a></pre>
</div>
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