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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 - Manually unrolled loop generates better code (elided memcpy) than llvm unrolled version"
href="https://bugs.llvm.org/show_bug.cgi?id=40011">40011</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Manually unrolled loop generates better code (elided memcpy) than llvm unrolled version
</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>All
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jmuizelaar@mozilla.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>The following code:
struct L {
double f[9];
};
template<class T>
struct Allocation {
T *vec;
void init(T s) {
*vec = s;
}
};
void foo(Allocation<L> a) {
L s;
s.f[0] = 1;
s.f[1] = 1;
s.f[2] = 1;
s.f[3] = 1;
s.f[4] = 1;
s.f[5] = 1;
s.f[6] = 1;
s.f[7] = 1;
s.f[8] = 1;
a.init(s);
}
void bar(Allocation<L> a) {
L s;
for (int i=0; i<9; i++) {
s.f[i] = 1;
}
a.init(s);
}
compiles to:
.LCPI0_0:
.quad 4607182418800017408 # double 1
.quad 4607182418800017408 # double 1
foo(Allocation<L>): # @foo(Allocation<L>)
movaps xmm0, xmmword ptr [rip + .LCPI0_0] # xmm0 = [1.0E+0,1.0E+0]
movups xmmword ptr [rdi], xmm0
movups xmmword ptr [rdi + 16], xmm0
movups xmmword ptr [rdi + 32], xmm0
movups xmmword ptr [rdi + 48], xmm0
movabs rax, 4607182418800017408
mov qword ptr [rdi + 64], rax
ret
.LCPI1_0:
.quad 4607182418800017408 # double 1
.quad 4607182418800017408 # double 1
bar(Allocation<L>): # @bar(Allocation<L>)
movaps xmm0, xmmword ptr [rip + .LCPI1_0] # xmm0 = [1.0E+0,1.0E+0]
movaps xmmword ptr [rsp - 72], xmm0
movaps xmmword ptr [rsp - 56], xmm0
movaps xmmword ptr [rsp - 40], xmm0
movaps xmmword ptr [rsp - 24], xmm0
movabs rax, 4607182418800017408
mov qword ptr [rsp - 8], rax
mov qword ptr [rdi + 64], rax
movaps xmm0, xmmword ptr [rsp - 24]
movups xmmword ptr [rdi + 48], xmm0
movaps xmm0, xmmword ptr [rsp - 40]
movups xmmword ptr [rdi + 32], xmm0
movaps xmm0, xmmword ptr [rsp - 56]
movups xmmword ptr [rdi + 16], xmm0
movaps xmm0, xmmword ptr [rsp - 72]
movups xmmword ptr [rdi], xmm0
ret
The manually unrolled foo elides the memcpy, bar keeps it.</pre>
</div>
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