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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - 256bit AVX vectorization sometimes forgets about 128bit packed instructions"
href="https://llvm.org/bugs/show_bug.cgi?id=28457">28457</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>256bit AVX vectorization sometimes forgets about 128bit packed instructions
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.8
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nowak-llvm@tepeserwery.pl
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Compiled with: -O3 -ffast-math -Rpass=loop- -fslp-vectorize-aggressive -msse
-msse2 -msse3 -mssse3 -msse4 -msse4.1 -mavx
f1 is correctly vectorized with both 256 and 128 bit packed instructions.
f2 is correctly vectorized with 256 bit packed instructions but remaining 4
iterations are handled with scalar instructions instead of 128 bit packed.
void f1(float *__restrict__ q __attribute__((align_value(32))), float
*__restrict__ p __attribute__((align_value(32)))) {
for (unsigned int i = 0; i < (8 * 1 + 4); ++i) {
// remark: completely unrolled loop with 12 iterations
q[i] = p[i] + 1.0f;
}
}
void f2(float *__restrict__ q __attribute__((align_value(32))), float
*__restrict__ p __attribute__((align_value(32)))) {
for (unsigned int i = 0; i < (8 * 5 + 4); ++i) {
// remark: vectorized loop (vectorization width: 8, interleaved count: 1)
// remark: completely unrolled loop with 5 iterations
// remark: completely unrolled loop with 4 iterations
q[i] = p[i] + 1.0f;
}
}
f1(float*, float*): # @f1(float*, float*)
vmovaps (%rsi), %ymm0
vaddps .LCPI0_0(%rip), %ymm0, %ymm0
vmovaps %ymm0, (%rdi)
vmovaps 32(%rsi), %xmm0
vaddps .LCPI0_1(%rip), %xmm0, %xmm0
vmovaps %xmm0, 32(%rdi)
vzeroupper
retq
f2(float*, float*): # @f2(float*, float*)
vmovaps .LCPI1_0(%rip), %ymm0 # ymm0 =
[1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00,1.000000e+00]
vaddps (%rsi), %ymm0, %ymm1
vmovaps %ymm1, (%rdi)
vaddps 32(%rsi), %ymm0, %ymm1
vmovaps %ymm1, 32(%rdi)
vaddps 64(%rsi), %ymm0, %ymm1
vmovaps %ymm1, 64(%rdi)
vaddps 96(%rsi), %ymm0, %ymm1
vmovaps %ymm1, 96(%rdi)
vaddps 128(%rsi), %ymm0, %ymm0
vmovaps %ymm0, 128(%rdi)
vmovss .LCPI1_1(%rip), %xmm0 # xmm0 = mem[0],zero,zero,zero
vaddss 160(%rsi), %xmm0, %xmm1
vmovss %xmm1, 160(%rdi)
vaddss 164(%rsi), %xmm0, %xmm1
vmovss %xmm1, 164(%rdi)
vaddss 168(%rsi), %xmm0, %xmm1
vmovss %xmm1, 168(%rdi)
vaddss 172(%rsi), %xmm0, %xmm0
vmovss %xmm0, 172(%rdi)
vzeroupper</pre>
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