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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - trivial static loop is not eliminated with -Os"
href="https://bugs.llvm.org/show_bug.cgi?id=40040">40040</a>
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<th>Summary</th>
<td>trivial static loop is not eliminated with -Os
</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>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Common Code Generator Code
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>trass3r@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>void foo(int* a)
{
for (int i = 0; i < 8; ++i)
a[i] = 1;
}
$ clang -Os -march=haswell
xor eax, eax
vbroadcastss ymm0, dword ptr [rip + .LCPI0_0] # ymm0 =
[1,1,1,1,1,1,1,1]
mov ecx, 8
.LBB0_1: # =>This Inner Loop Header: Depth=1
vmovups ymmword ptr [rdi + 4*rax], ymm0
add rax, 8
cmp rax, rcx
jne .LBB0_1
<a href="https://godbolt.org/z/Q2Se1r">https://godbolt.org/z/Q2Se1r</a>
It also happens with -O2 -fno-unroll-loops and -Os -funroll-loops.
You can also change the loop body, e.g. ++a[i].</pre>
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