<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 - Missed vectorization opportunity"
href="https://bugs.llvm.org/show_bug.cgi?id=44148">44148</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed vectorization opportunity
</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>Loop Optimizer
</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>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>#define N 512
int a[N], b[N];
int
foo (int aval)
{
int res = 0;
for (int i=0; i<N; i++)
{
if (a[i] != 0)
res = aval;
}
return res;
}
Clang -O3 -march=haswell: loop not vectorized [-Rpass-missed=loop-vectorize]
foo(int): # @foo(int)
xor eax, eax
mov rcx, -2048
.LBB0_1: # =>This Inner Loop Header: Depth=1
mov edx, dword ptr [rcx + a+2052]
or edx, dword ptr [rcx + a+2048]
or edx, dword ptr [rcx + a+2056]
or edx, dword ptr [rcx + a+2060]
or edx, dword ptr [rcx + a+2064]
or edx, dword ptr [rcx + a+2068]
or edx, dword ptr [rcx + a+2072]
or edx, dword ptr [rcx + a+2076]
cmovne eax, edi
add rcx, 32
jne .LBB0_1
ret
a:
.zero 2048
b:
.zero 2048
ICC -O3 -march=haswell:
foo(int):
xor eax, eax #10.11
vpxor ymm1, ymm1, ymm1 #13.17
xor edx, edx #11.3
vpcmpeqd ymm0, ymm0, ymm0 #10.11
..B1.2: # Preds ..B1.2 ..B1.1
vpcmpeqd ymm2, ymm1, YMMWORD PTR [a+rdx*4] #13.17
add rdx, 8 #11.3
vpxor ymm3, ymm2, ymm0 #10.11
vmovmskps ecx, ymm3 #10.11
or eax, ecx #10.11
cmp rdx, 512 #11.3
jb ..B1.2 # Prob 99% #11.3
test eax, eax #16.10
cmovne eax, edi #16.10
vzeroupper #16.10
ret #16.10
a:
b:
<a href="https://godbolt.org/z/AjRQNY">https://godbolt.org/z/AjRQNY</a>
This loop is similar, also not vectorized:
int
foo (int aval)
{
int res = 0;
for (int i=0; i<N; i++)
{
if (a[i] != 0)
res = b[i];
}
return res;
}
<a href="https://godbolt.org/z/AU_5rf">https://godbolt.org/z/AU_5rf</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>