https://bugs.llvm.org/show_bug.cgi?id=40011
Bug ID: 40011
Summary: Manually unrolled loop generates better code (elided
memcpy) than llvm unrolled version
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: unassignedb...@nondot.org
Reporter: jmuizel...@mozilla.com
CC: llvm-bugs@lists.llvm.org
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.
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