<html>
<head>
<base href="http://llvm.org/bugs/" />
</head>
<body><span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span> changed
<a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED --- - can't delete empty, terminating, strided loop"
href="http://llvm.org/bugs/show_bug.cgi?id=19183">bug 19183</a>
<br>
<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>RESOLVED
</td>
<td>REOPENED
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>FIXED
</td>
<td>---
</td>
</tr></table>
<p>
<div>
<b><a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED --- - can't delete empty, terminating, strided loop"
href="http://llvm.org/bugs/show_bug.cgi?id=19183#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED --- - can't delete empty, terminating, strided loop"
href="http://llvm.org/bugs/show_bug.cgi?id=19183">bug 19183</a>
from <span class="vcard"><a class="email" href="mailto:richard-llvm@metafoo.co.uk" title="Richard Smith <richard-llvm@metafoo.co.uk>"> <span class="fn">Richard Smith</span></a>
</span></b>
<pre>Thanks!
Sadly, this isn't enough to clean up the mess left behind by the vectorizer
(presumably because the vectorization happens too late). This testcase still
leaves behind a do-nothing loop:
#include <memory>
#include <cstring>
long test(int iters, int len, int sticky)
{
const int block_size = 0x1000;
const int blocks = len / block_size;
std::unique_ptr<char[]> source(new char[blocks * block_size]);
std::unique_ptr<char[]> destination(new char[blocks * block_size]);
for (int i = 0; i < iters; ++i) {
char *psrc = source.get();
char *pdst = destination.get();
for (int block = 0; block < blocks; ++block) {
memcpy(psrc, pdst, block_size);
psrc += block_size;
pdst += block_size;
if (sticky) {
psrc -= block_size;
pdst -= block_size;
}
}
}
return long(iters) * blocks * block_size;
}
Running opt a second time on the output of clang -O3 -emit-llvm does remove the
do-nothing loop now, though.
(We should really be able to delete the entire function body, but that's a
separate issue...)</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>