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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [MIPS] unoptimized __atomic_compare_exchange hangs on Octeon"
href="https://bugs.llvm.org/show_bug.cgi?id=32020">32020</a>
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<th>Summary</th>
<td>[MIPS] unoptimized __atomic_compare_exchange hangs on Octeon
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>4.0
</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
</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: MIPS
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>james410@cowgill.org.uk
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>Hi,
Testcase:
<span class="quote">> int main(void)
> {
> volatile int obj = 1;
> int x = obj;
>
> __atomic_compare_exchange_n(&obj, &x, 0, 1, __ATOMIC_RELAXED, __ATOMIC_RELAXED);
> }</span >
Compiling with:
clang-4.0 -O0 test.c -otes
Running "test" hangs on Cavium Octeon machines. The bug does not occur if -O1
is used.
The generated assembly contains this loop:
<span class="quote">> .LBB0_1:
> ld $1, 16($fp)
> ll $2, 0($1)
> lw $3, 32($fp)
> sw $2, 12($fp)
> bne $2, $3, .LBB0_3
> nop
> lw $1, 28($fp)
> ld $2, 16($fp)
> sc $1, 0($2)
> beqz $1, .LBB0_1
> nop</span >
However the Octeon processor manual states that _any_ store will cause a
subsequent sc instruction to fail and therefore this above loop will never
complete on Octeon.
Thanks,
James</pre>
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