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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - [AArch64] r226200 can emit illegal thumb2 instruction: "sub sp, r12, #80"" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23772&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=zcyh0vJRfD4XaDEoTq8YHIIUthWcZQ_94FLN1bsUTfk&s=WaDi5oQLERTxmhJ0tbxG1P1tEbm9AqopoaolI7rbXek&e=">23772</a>
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<th>Summary</th>
<td>[AArch64] r226200 can emit illegal thumb2 instruction: "sub sp, r12, #80"
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<th>Product</th>
<td>new-bugs
</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>Linux
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>new bugs
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>zhaoshiz@codeaurora.org
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<th>CC</th>
<td>apazos@codeaurora.org, hfinkel@anl.gov, llvmbugs@cs.uiuc.edu, mcrosier@codeaurora.org
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<th>Classification</th>
<td>Unclassified
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<p>
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<pre>r226200 allows coalescing into SP but missed a corner case:
%vreg907<def> = COPY %SP; GPRnopc:%vreg907
%vreg908<def> = t2SUBri %vreg907, 80, pred:14, pred:%noreg, opt:%noreg;
GPRnopc:%vreg908,%vreg907
%SP<def> = COPY %vreg908; GPRnopc:%vreg908
When %vreg908 is coalesced into SP but %vreg907 is not, it's likely to emit an
illegal instruction:
sub sp, r12, #80
In Thumb2, we can only use SP as Rd if and only if Rn is also SP. This patch,
when trying remove "%SP<def> = COPY %vreg908", checks if %vreg907 is SP
already. If not, be conservative and do not coalesce %vreg908 into SP.
<a href="https://urldefense.proofpoint.com/v2/url?u=http-3A__reviews.llvm.org_D10287&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=zcyh0vJRfD4XaDEoTq8YHIIUthWcZQ_94FLN1bsUTfk&s=9YTGUt9IB7ZmBwKhRP7jnYMsCGOosLvW53SUYnm23pw&e=">http://reviews.llvm.org/D10287</a></pre>
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</p>
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