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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - extra moves generated for unary SSE ops"
href="http://llvm.org/bugs/show_bug.cgi?id=22206">22206</a>
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<th>Summary</th>
<td>extra moves generated for unary SSE ops
</td>
</tr>
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<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>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
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<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>This is SSE (but not AVX) fallout from fixing correctness in <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - SQRTSS and similar scalar SSE insns are not accurately modelled"
href="show_bug.cgi?id=14221">bug 14221</a>. This
was originally reported by Michael Kuperstein in <a href="http://reviews.llvm.org/D6885">http://reviews.llvm.org/D6885</a>.
Using llc built from r225612:
$ cat sqrtss.ll
define float @sqrtss(<4 x float> %a) {
%res = tail call <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float> %a) nounwind
%new = extractelement <4 x float> %res, i32 0
%orig = extractelement <4 x float> %a, i32 0
%add = fadd float %new, %orig
ret float %add
}
declare <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float>) nounwind readnone
$ ./llc sqrtss.ll -o -
..
movaps %xmm0, %xmm1 ## copy original value because...
sqrtss %xmm1, %xmm1 ## current unary op def requires src == dst
addss %xmm0, %xmm1 ## different bug here...
movaps %xmm1, %xmm0 ## could have swapped add operands to avoid mov
retq</pre>
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