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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 - Canonicalize OR with operands which do not have shared bits to ADD"
href="https://bugs.llvm.org/show_bug.cgi?id=42197">42197</a>
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<th>Summary</th>
<td>Canonicalize OR with operands which do not have shared bits to ADD
</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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<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>typedef unsigned char byte;
byte add_no_common_bits(byte x, byte y) {
// hint, no common bits
__builtin_assume((x & y) == 0);
return x | y;
}
byte or_no_common_bits(byte x, byte y) {
// hint, no common bits
__builtin_assume((x & y) == 0);
return x + y;
}
add_no_common_bits(unsigned char, unsigned char):
mov eax, edi
or eax, esi
ret
or_no_common_bits(unsigned char, unsigned char):
lea eax, [rsi + rdi]
ret
If we can prove that there are no shared bits between X and Y, maybe we could
turn OR to ADD.
Or ADD to OR.. not sure which form is better.</pre>
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