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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - Availability of SSE detrimental to code performance"
href="https://llvm.org/bugs/show_bug.cgi?id=26837">26837</a>
</td>
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<tr>
<th>Summary</th>
<td>Availability of SSE detrimental to code performance
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>3.8
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<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>tulipawn@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The following Rust playpen snippet (possible to see IR or ASM interactively)
<a href="http://is.gd/FrGoDm">http://is.gd/FrGoDm</a>
produces the following benchmark results, depending on codegen options:
Pentium2
test folds1 ... bench: 736 ns/iter (+/- 5)
test folds2 ... bench: 731 ns/iter (+/- 1)
Pentium3 (or +sse)
test folds1 ... bench: 932 ns/iter (+/- 2)
test folds2 ... bench: 933 ns/iter (+/- 8)
Pentium4 (or +sse2)
running 2 tests
test folds1 ... bench: 249 ns/iter (+/- 1)
test folds2 ... bench: 733 ns/iter (+/- 6)
It seems availability of SSE2 enables successful vectorisation, whereas of SSE
makes the code slower. The latter shouldn't happen.</pre>
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