<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 - Codegen regression between 10 and 11 with -mprefer-vector-width=512"
href="https://bugs.llvm.org/show_bug.cgi?id=49931">49931</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Codegen regression between 10 and 11 with -mprefer-vector-width=512
</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>Windows NT
</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: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>typedef unsigned char uint8_t;
void foo( uint8_t *__restrict dst, uint8_t *__restrict src )
{
for( int x = 0; x < 16; x++ )
dst[x] = (dst[x]-src[x])>>2;
}
Clang flags: -O3 -mavx512vnni -mprefer-vector-width=512
See the change in the use of ZMM registers.
LLVM 11+:
foo(unsigned char*, unsigned char*): #
@foo(unsigned char*, unsigned char*)
vpmovzxbw ymm0, xmmword ptr [rdi] # ymm0 =
mem[0],zero,mem[1],zero,mem[2],zero,mem[3],zero,mem[4],zero,mem[5],zero,mem[6],zero,mem[7],zero,mem[8],zero,mem[9],zero,mem[10],zero,mem[11],zero,mem[12],zero,mem[13],zero,mem[14],zero,mem[15],zero
vpmovzxbw ymm1, xmmword ptr [rsi] # ymm1 =
mem[0],zero,mem[1],zero,mem[2],zero,mem[3],zero,mem[4],zero,mem[5],zero,mem[6],zero,mem[7],zero,mem[8],zero,mem[9],zero,mem[10],zero,mem[11],zero,mem[12],zero,mem[13],zero,mem[14],zero,mem[15],zero
vpsubw ymm0, ymm0, ymm1
vpsrlw ymm0, ymm0, 2
vpmovzxwd zmm0, ymm0 # zmm0 =
ymm0[0],zero,ymm0[1],zero,ymm0[2],zero,ymm0[3],zero,ymm0[4],zero,ymm0[5],zero,ymm0[6],zero,ymm0[7],zero,ymm0[8],zero,ymm0[9],zero,ymm0[10],zero,ymm0[11],zero,ymm0[12],zero,ymm0[13],zero,ymm0[14],zero,ymm0[15],zero
vpmovdb xmmword ptr [rdi], zmm0
vzeroupper
ret
LLVM 10:
foo(unsigned char*, unsigned char*): #
@foo(unsigned char*, unsigned char*)
vpmovzxbd zmm0, xmmword ptr [rdi] # zmm0 =
mem[0],zero,zero,zero,mem[1],zero,zero,zero,mem[2],zero,zero,zero,mem[3],zero,zero,zero,mem[4],zero,zero,zero,mem[5],zero,zero,zero,mem[6],zero,zero,zero,mem[7],zero,zero,zero,mem[8],zero,zero,zero,mem[9],zero,zero,zero,mem[10],zero,zero,zero,mem[11],zero,zero,zero,mem[12],zero,zero,zero,mem[13],zero,zero,zero,mem[14],zero,zero,zero,mem[15],zero,zero,zero
vpmovzxbd zmm1, xmmword ptr [rsi] # zmm1 =
mem[0],zero,zero,zero,mem[1],zero,zero,zero,mem[2],zero,zero,zero,mem[3],zero,zero,zero,mem[4],zero,zero,zero,mem[5],zero,zero,zero,mem[6],zero,zero,zero,mem[7],zero,zero,zero,mem[8],zero,zero,zero,mem[9],zero,zero,zero,mem[10],zero,zero,zero,mem[11],zero,zero,zero,mem[12],zero,zero,zero,mem[13],zero,zero,zero,mem[14],zero,zero,zero,mem[15],zero,zero,zero
vpsubd zmm0, zmm0, zmm1
vpsrld zmm0, zmm0, 2
vpmovdb xmmword ptr [rdi], zmm0
vzeroupper
ret
Godbolt:
<a href="https://godbolt.org/z/4zPv8rMvP">https://godbolt.org/z/4zPv8rMvP</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>