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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Clang unable to optimize away constant stores to Wi/Xi"
href="https://bugs.llvm.org/show_bug.cgi?id=45192">45192</a>
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<th>Summary</th>
<td>Clang unable to optimize away constant stores to Wi/Xi
</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>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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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>glider@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, ndesaulniers@google.com, smithp352@googlemail.com, Ties.Stuij@arm.com
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<div>
<pre>I'm seeing a lot of occurrences of the following pattern when compiling an
Android 4.14 kernel with -ftrivial-var-auto-init=pattern:
ffffff8008f3686c: 3201f3e9 mov w9, #0xaaaaaaaa
// #-1431655766
ffffff8008f36870: 293327a9 stp w9, w9, [x29, #-104]
ffffff8008f36874: b201f3e9 mov x9, #0xaaaaaaaaaaaaaaaa
// #-6148914691236517206
ffffff8008f36878: a93a27a9 stp x9, x9, [x29, #-96]
ffffff8008f3687c: a93b27a9 stp x9, x9, [x29, #-80]
I suppose a more optimal code for this would be:
mov x9, #0xaaaaaaaaaaaaaaaa // #-6148914691236517206
stp w9, w9, [x29, #-104]
stp x9, x9, [x29, #-96]
stp x9, x9, [x29, #-80]</pre>
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