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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - LLVM fails to use flags from atomic instructions"
href="http://llvm.org/bugs/show_bug.cgi?id=20841">20841</a>
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<th>Summary</th>
<td>LLVM fails to use flags from atomic instructions
</td>
</tr>
<tr>
<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>
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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: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>david.majnemer@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>consider:
define zeroext i1 @f(i32* %x) {
entry:
%0 = atomicrmw add i32* %x, i32 1 seq_cst
%cmp = icmp ne i32 %0, 0
ret i1 %cmp
}
this gets CodeGen'd as:
movl $1, %eax
lock
xaddl %eax, (%rdi)
testl %eax, %eax
setne %al
retq
Note that the ZF flag was already set from the xadd instruction, the test
instruction is redundant.</pre>
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