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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 --- - may fail to recognize potential EFLAGS clobbers for compare-exchange operations"
href="http://llvm.org/bugs/show_bug.cgi?id=20376">20376</a>
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<th>Summary</th>
<td>may fail to recognize potential EFLAGS clobbers for compare-exchange operations
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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>Linux
</td>
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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
</td>
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<th>Component</th>
<td>Backend: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>peter@pcc.me.uk
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>Given the following IR:
declare void @g()
declare void @h()
declare void @i()
define void @cx(i64* %foo, i64 %bar, i64 %baz) {
%cx = cmpxchg i64* %foo, i64 %bar, i64 %baz seq_cst seq_cst
%p = extractvalue { i64, i1 } %cx, 1
call void @g()
br i1 %p, label %t, label %f
t:
call void @h()
ret void
f:
call void @i()
ret void
}
we currently generate the following x86 code for the entry block of @cx:
cx: # @cx
.cfi_startproc
# BB#0:
pushq %rax
.Ltmp0:
.cfi_def_cfa_offset 16
movq %rsi, %rax
lock
cmpxchgq %rdx, (%rdi)
callq g
jne .LBB0_2
This is clearly wrong, as the external call may clobber EFLAGS.</pre>
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