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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 --- - ExpandInlineAsm is brittle, and uses obsolete register dirflag"
href="http://llvm.org/bugs/show_bug.cgi?id=17757">17757</a>
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<th>Summary</th>
<td>ExpandInlineAsm is brittle, and uses obsolete register dirflag
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>3.2
</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>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
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<th>Reporter</th>
<td>chris@smowton.net
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=11464" name="attach_11464" title="Patch">attachment 11464</a> <a href="attachment.cgi?id=11464&action=edit" title="Patch">[details]</a></span>
Patch
X86TargetLowering::ExpandInlineAsm is supposed to raise inline assembly
functions that implement endianness swaps into llvm.bswap intrinsics. However
it only recognises the exact sequence emitted by Clang; Dragonegg (3.2) emits a
somewhat different sequence and thus doesn't get raised, inhibiting some
optimisations.
In particular, the existing function inspects the asm clobber list and expects
exactly "~{cc}", "~{dirflag}", "~{flags}", "~{fpsr}". However, GCC eliminated
{dirflag} as a seperate clobberable pseudo-register in 2006
[<a href="http://gcc.gnu.org/ml/gcc-patches/2006-12/msg00468.html">http://gcc.gnu.org/ml/gcc-patches/2006-12/msg00468.html</a>], and at least in
gcc-4.6 emits some permutation of "~{cc}", "~{flags}", "~{fpsr}". The attached
patch makes the clobber testing less brittle to allow both dragonegg and clang
code to be raised appropriately.</pre>
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