<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 - Why is this reload not folded away inless restrict?"
href="https://bugs.llvm.org/show_bug.cgi?id=41430">41430</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Why is this reload not folded away inless restrict?
</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>Global Analyses
</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>From IRC:
<a href="https://godbolt.org/z/oVDACU">https://godbolt.org/z/oVDACU</a>
Given:
#include <immintrin.h>
#include <inttypes.h>
void example(__m256i *dest, const __m256i *a) {
(*dest)[2] = (*a)[2];
(*dest)[3] = (*a)[3];
}
We produce:
define dso_local void @example(<4 x i64>* nocapture, <4 x i64>* nocapture
readonly) local_unnamed_addr #0 {
%3 = load <4 x i64>, <4 x i64>* %1, align 32, !tbaa !2
%4 = load <4 x i64>, <4 x i64>* %0, align 32
%5 = shufflevector <4 x i64> %4, <4 x i64> %3, <4 x i32> <i32 0, i32 1, i32
6, i32 3>
store <4 x i64> %5, <4 x i64>* %0, align 32
%6 = load <4 x i64>, <4 x i64>* %1, align 32, !tbaa !2
%7 = shufflevector <4 x i64> %5, <4 x i64> %6, <4 x i32> <i32 0, i32 1, i32
2, i32 7>
store <4 x i64> %7, <4 x i64>* %0, align 32
ret void
}
So we load a and dest, blend the 3'th element into dest from a,
store dest, load dest back, blend the 4'th element into dest from a,
and finally store dest.
Why is that intermediate reloading there? The alignment is specified.
I guess there could be a problem if they would point into overlapping
memory, but wouldn't that already be UB since that would mean one
of the pointers is misaligned?</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>