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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - -mtune when targeting AArch64 can incorrectly affect the architecture version code is generated for"
href="https://bugs.llvm.org/show_bug.cgi?id=34625">34625</a>
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<th>Summary</th>
<td>-mtune when targeting AArch64 can incorrectly affect the architecture version code is generated for
</td>
</tr>
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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>
</tr>
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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
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>kristof.beyls@arm.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>$ cat t.c
int f(int *a, int b, int c) {
return __sync_val_compare_and_swap (a, b, c);
}
# cas[al] is an instruction introduced in armv8.1, so with the below command
line, generation of the cas instruction is OK (-march=armv8.1a):
$ clang -target aarch64-linux-gnu -march=armv8.1a -S t.c -O2 -o- | grep cas
casal w1, w2, [x0]
# thunderx2t99 is a cpu implementing armv8.1a, so generation of the cas
instruction is OK in the below command line (mcpu=thunderx2t99):
$ clang -target aarch64-linux-gnu -mcpu=thunderx2t99 -march=armv8a -S t.c -O2
-o- | grep cas
casal w1, w2, [x0]
# mtune shouldn't affect the architecture version targeted, so in the below
command line (march=armv8a mtune=thunderx2t99), the cas instruction should not
have been generated:
$ clang -target aarch64-linux-gnu -mtune=thunderx2t99 -march=armv8a -S t.c -O2
-o- | grep cas
casal w1, w2, [x0]</pre>
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