<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Slow handling of vectorized loop epilogue"
href="https://bugs.llvm.org/show_bug.cgi?id=46119">46119</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Slow handling of vectorized loop epilogue
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>elrodc@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I have benchmarks here:
<a href="https://chriselrod.github.io/LoopVectorization.jl/latest/examples/dot_product/">https://chriselrod.github.io/LoopVectorization.jl/latest/examples/dot_product/</a>
Showing poor performance of Julia and Clang-compiled functions whenever the
epilogue is long.
Optimized by LLVM:
<a href="https://godbolt.org/z/kfzhK2">https://godbolt.org/z/kfzhK2</a>
Faster version:
<a href="https://godbolt.org/z/C5f7by">https://godbolt.org/z/C5f7by</a>
Benchmarks on a 10980xe, summing dot products of 4096 vectors with random
lengths uniformly distributed between 1 and...
32:
Default: 50.925 microseconds
Fast: 30.677 microseconds
64:
Default: 64.971 microseconds
Fast: 40.321 microseconds
96:
Default: 70.463 microseconds
Fast: 48.614 microseconds
128:
Default: 78.189 microseconds
Fast: 52.912 microseconds
LLVM's current behavior takes about 50% longer than using masks + SIMD
instructions on the epilogue for randomly sized vectors of length 1,...N where
N is 32, 64, 96, or 128 on this architecture.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>