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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [AArch64] Aliases of WZR/XZR are not considered constant"
href="https://llvm.org/bugs/show_bug.cgi?id=25457">25457</a>
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<th>Summary</th>
<td>[AArch64] Aliases of WZR/XZR are not considered constant
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
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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>mcrosier@codeaurora.org
</td>
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<th>CC</th>
<td>haicheng@codeaurora.org, james.molloy@arm.com, llvm-bugs@lists.llvm.org, t.p.northover@gmail.com
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>The alias registers of WZR/XZR are WZR_W0, W30_WZR, LR_XZR, and XZR_X0. None
of these aliases are marked as constant, so WZR/XZR is not considered as
constant.
The %wzr_w0 alias was added here:
<a href="http://reviews.llvm.org/rL238818">http://reviews.llvm.org/rL238818</a>
One practical implication is that in passes such as machine-cse and
machine-sink an instruction such as %v = copy %wzr cannot be moved because llvm
thinks %wzr is not a constant physical register.</pre>
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