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<base href="http://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Integrated aarch64 assembler should exchange cmp/cmn given negative immediates"
href="http://llvm.org/bugs/show_bug.cgi?id=21994">21994</a>
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<th>Summary</th>
<td>Integrated aarch64 assembler should exchange cmp/cmn given negative immediates
</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>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: AArch64
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>simon.hosie@arm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Given:
foo:
cmp x0, #-1
ret
`clang -c --target=aarch64-linux-gnu -integrated-as cmn_aarch64.s` gives:
cmn_aarch64.s:2:17: error: expected compatible register, symbol or integer in
range [0, 4095]
while `clang -c --target=aarch64-linux-gnu -no-integrated-as cmn_aarch64.s`
succeeds and gives code that disassembles to:
0000000000000000 <foo>:
0: b100041f cmn x0, #0x1
4: d65f03c0 ret
gas appears to accept negative immediates an implicitly changes the cmp to a
cmn to make the instruction legal, while llvm simply rejects the immediate. I
don't think GCC generates this. It's just handwritten assembly which stumbles
into the incompatibility.</pre>
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</p>
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