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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - AArch64 backend ignores failure ordering for cmpxchg"
href="https://bugs.llvm.org/show_bug.cgi?id=50512">50512</a>
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<th>Summary</th>
<td>AArch64 backend ignores failure ordering for cmpxchg
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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>enhancement
</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>efriedma@quicinc.com
</td>
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<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
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<p>
<div>
<pre><a href="https://godbolt.org/z/jvnYzrPce">https://godbolt.org/z/jvnYzrPce</a>
For the following testcase:
#include <stdatomic.h>
void test(_Atomic(int) *a, int b) {
atomic_compare_exchange_weak_explicit(a, &b, 1, memory_order_relaxed,
memory_order_seq_cst); // undefined!
}
We generate (with --target=aarch64 -O2 -march=armv8.2-a):
test:
mov w8, #1
cas w1, w8, [x0]
ret
This is pretty clearly wrong, especially with the most recent updates to the
C++ standard.</pre>
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