<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] Incorrect optimization to sqrdmlah"
href="https://bugs.llvm.org/show_bug.cgi?id=52419">52419</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[AArch64] Incorrect optimization to sqrdmlah
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</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>jamie.cunliffe@arm.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>Currently sqrdmulh followed by an sqadd can be optimized into sqrdmlah when the
rdm target feature is provided which is incorrect for a small number of values.
#include <arm_neon.h>
#include <stdio.h>
int main(int argc, char **argv) {
int32x2_t a = {static_cast<int32_t>(0x80000000),
static_cast<int32_t>(0x80000000)};
int32x2_t b = {static_cast<int32_t>(0x80000000),
static_cast<int32_t>(0x80000000)};
int32x2_t c = {static_cast<int32_t>(0x80000000),
static_cast<int32_t>(0x80000000)};
auto val = vqadd_s32(a, vqrdmulh_s32(b, c));
printf("%d,%d\n", vget_lane_s32(val, 0), vget_lane_s32(val, 1));
return 0;
}
When compiling that with clang++ -march=armv8a+rdm -O2 test.cpp it would
optimize it into sqrdmlah and output: 0,0.
However, when compiling with clang++ -O2 test.cpp to get the sqrdmulh sqadd it
would actually be -1,-1
This also appears to be how the vqrdmlah intrinsics are currently implemented.</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>