<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 - [AArch64] use rev16 with load/store merging patterns"
href="https://bugs.llvm.org/show_bug.cgi?id=46694">46694</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[AArch64] use rev16 with load/store merging patterns
</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>All
</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>Backend: AArch64
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>spatel+llvm@rotateright.com
</td>
</tr>
<tr>
<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
</td>
</tr></table>
<p>
<div>
<pre>struct edge {
unsigned char from;
unsigned char to;
};
void reverse_edge_inplace(struct edge *e) {
unsigned char tmp = e->from;
e->from = e->to;
e->to = tmp;
}
void reverse_edge_src_dst(const struct edge *src, struct edge *dst) {
struct edge e = *src;
unsigned char tmp = e.from;
e.from = e.to;
e.to = tmp;
*dst = e;
}
This is the same example as <a class="bz_bug_link
bz_status_NEW "
title="NEW - Missed rotate opportunity"
href="show_bug.cgi?id=41098">bug 41098</a> but targeted specifically at an AArch64
opportunity:
<a href="https://godbolt.org/z/xbaf3M">https://godbolt.org/z/xbaf3M</a>
As seen in the gcc output, we can trade 1 load + 1 store for a rev16:
ldrb w8, [x0, #1]
ldrb w9, [x0]
strb w8, [x0]
strb w9, [x0, #1]
vs.
ldrh w1, [x0]
rev16 w1, w1
strh w1, [x0]</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>