<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 - Some remainder checks on loop IV can be simplified by having another IV"
href="https://bugs.llvm.org/show_bug.cgi?id=44703">44703</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Some remainder checks on loop IV can be simplified by having another IV
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>void reinit();
void work(int p);
void entry(int width) {
for (int p = 0; p < 8; ++p) {
if (p % 3 == 2)
reinit();
work(p);
}
}
Depending on the loop (what is `work()`, is loop unrolled, etc),
this 'rem' operation can end up being measurably costly.
But this can be instead rewritten as
void reinit();
void work(int p);
void entry(int width) {
int u = 0;
for (int p = 0; p < 8; ++p, ++u) {
if (u == 2) {
reinit();
u = -1;
}
work(p);
}
}
.. at the cost of extra induction variable.
<a href="https://godbolt.org/z/EdiSHi">https://godbolt.org/z/EdiSHi</a></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>