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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - AArch64: EON instruction not selected efficiently"
href="http://llvm.org/bugs/show_bug.cgi?id=22751">22751</a>
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<th>Summary</th>
<td>AArch64: EON instruction not selected efficiently
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: AArch64
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>james.molloy@arm.com
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>The following code snippet should produce an EON instruction in both A64 and
A32:
unsigned long
f(unsigned long a, unsigned long b, unsigned long c) {
return (a ^ ~(b << 4));
}
On A64 and A32, we get two instructions produced:
eor x8, x0, x1, lsl #4
mvn x0, x8
I think this is because SDAG canonicalises the expression into "~(a ^ b << 4)",
which we don't recognize as a pattern for EON.</pre>
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</p>
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