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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 - Missed opportunity to optimize pointer range checks"
href="https://bugs.llvm.org/show_bug.cgi?id=47053">47053</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed opportunity to optimize pointer range checks
</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>
<tr>
<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>bool f1 (char *a, char *b)
{
return (a + 16 <= b) || (b + 16 <= a);
}
Clang:
f1(char*, char*): # @f1(char*, char*)
lea rax, [rdi + 16]
cmp rax, rsi
setbe cl
add rsi, 16
cmp rsi, rdi
setbe al
or al, cl
ret
GCC:
f1(char*, char*):
add rdi, 15
sub rdi, rsi
cmp rdi, 30
seta al
ret
GCC transforms
A + size <= B || B + size <= A
to
(size_t) (A + (size - 1) - B) > (size - 1) * 2
Could be useful to optimize better RT checks from vectorizer.
Godbolt: <a href="https://godbolt.org/z/9jsKa4">https://godbolt.org/z/9jsKa4</a></pre>
</div>
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