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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - llvm and gcc disagree on who supports x86 cmpxchg16b"
href="http://llvm.org/bugs/show_bug.cgi?id=17485">17485</a>
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<th>Summary</th>
<td>llvm and gcc disagree on who supports x86 cmpxchg16b
</td>
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<th>Product</th>
<td>new-bugs
</td>
</tr>
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<th>Version</th>
<td>unspecified
</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>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>nicholas@mxc.ca
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>There are three architectures, k8-sse3 opteron-sse3 and athlon64-sse3 for which
gcc does not define __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 , but llvm's X86.td
claims they do support the cmpxchg16b instruction. What's the cause of this
discrepancy?
We should either:
a) Remove CPUXCHG16B from the architectures in X86.td because the CPUs don't
support it. It's just an LLVM bug.
b) Add __GCC_HAVE_SYNC_COMPARE_AND_SWAP_16 in clang for those architectures
because they do support it. It's just a GCC bug.
c) Leave it as is, but add a comment explaining why. Does the CPU support it
but we need to not define the macro for GCC compatibility? Does the CPU support
it but with some horrible flaw?</pre>
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</p>
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