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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Multiplication of a float vector by -1 should be transformed to an XOR of sign bits."
href="http://llvm.org/bugs/show_bug.cgi?id=18532">18532</a>
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<th>Summary</th>
<td>Multiplication of a float vector by -1 should be transformed to an XOR of sign bits.
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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>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Common Code Generator Code
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nick@indigorenderer.com
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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>According to <a href="http://software.intel.com/sites/landingpage/IntrinsicsGuide/">http://software.intel.com/sites/landingpage/IntrinsicsGuide/</a> ,
_mm_mul_ps has a latency of 4 or 5 cycles, and mm_xor_ps has a latency of 1
cycle.
Therefore, when multiplying a float vector by -1, it's probably a good idea to
turn the multiplication into an XOR of the sign bits.
Multiplying a vector by -1 is quite common in 3D vector maths when negating
vectors.</pre>
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