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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Suboptimal code after vectorization of not unrolled loop with 8 iterations"
href="https://bugs.llvm.org/show_bug.cgi?id=42411">42411</a>
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<th>Summary</th>
<td>Suboptimal code after vectorization of not unrolled loop with 8 iterations
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Loop Optimizer
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Found in PR42410.
void foo (int *__restrict arr1, int *__restrict arr2)
{
for (int i = 0; i < 8; i++)
arr1[i] += arr2[i];
}
Clang -O3 -march=skylake -fno-unroll-loops
foo(int*, int*): # @foo(int*, int*)
xor eax, eax
.LBB0_1: # =>This Inner Loop Header: Depth=1
vmovdqu ymm0, ymmword ptr [rdi + 4*rax]
vpaddd ymm0, ymm0, ymmword ptr [rsi + 4*rax]
vmovdqu ymmword ptr [rdi + 4*rax], ymm0
add rax, 8
cmp rax, 8
jne .LBB0_1
vzeroupper
ret
GCC / ICC produces with same flags:
foo(int*, int*):
vmovdqu ymm0, YMMWORD PTR [rdi] #6.5
vpaddd ymm1, ymm0, YMMWORD PTR [rsi] #6.5
vmovdqu YMMWORD PTR [rdi], ymm1 #6.5
vzeroupper #7.1
ret</pre>
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