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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 --- - Performance regression in vector shuffle + pmaddwd"
href="http://llvm.org/bugs/show_bug.cgi?id=21230">21230</a>
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<th>Summary</th>
<td>Performance regression in vector shuffle + pmaddwd
</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>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>andrew.b.adams@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>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=13178" name="attach_13178" title="ll that produces worse x86 with trunk than release 3.5">attachment 13178</a> <a href="attachment.cgi?id=13178&action=edit" title="ll that produces worse x86 with trunk than release 3.5">[details]</a></span>
ll that produces worse x86 with trunk than release 3.5
The attached ll computes 3*a + 5*b where a and b are 16-bit vectors and the
result is a 32-bit vector. It does this with a clever application of pmaddwd.
It used to produce this asm with release 3.5
movdqa %xmm0, %xmm4
punpcklwd %xmm2, %xmm4
movdqa %xmm1, %xmm5
punpcklwd %xmm3, %xmm5
pmaddwd %xmm5, %xmm4
punpckhwd %xmm2, %xmm0
punpckhwd %xmm3, %xmm1
pmaddwd %xmm0, %xmm1
movdqa %xmm4, %xmm0
but produces this slower asm with trunk:
pshufd $78, %xmm0, %xmm5
punpcklwd %xmm2, %xmm0
pshufd $78, %xmm1, %xmm4
punpcklwd %xmm3, %xmm1
pmaddwd %xmm1, %xmm0
pshufd $78, %xmm2, %xmm1
punpcklwd %xmm1, %xmm5
pshufd $78, %xmm3, %xmm1
punpcklwd %xmm1, %xmm4
pmaddwd %xmm5, %xmm4
movdqa %xmm4, %xmm1</pre>
</div>
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