https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96738
Bug ID: 96738
Summary: GCC generates worse assembly than clang and It fails
to vectorized code compared to clang
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: rtl-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: euloanty at live dot com
Target Milestone: ---
https://godbolt.org/z/9K3369
#include<array>
#include<cstdint>
struct number
{
std::array<std::uint64_t,5> num;
inline constexpr std::uint64_t& operator[](std::size_t position)
noexcept
{
return num[position];
}
inline constexpr std::uint64_t const& operator[](std::size_t position)
const noexcept
{
return num[position];
}
};
number add_reduce(number const& a,number const& b) noexcept
{
constexpr auto reduce_mask_51{(static_cast<std::uint64_t>(1) << 51) - 1};
number out;
std::uint64_t c{(a[0] + b[0])>>51};
out[1] = a[1] + b[1] + c; c = (out[1] >> 51); out[1] &= reduce_mask_51;
out[2] = a[2] + b[2] + c; c = (out[2] >> 51); out[2] &= reduce_mask_51;
out[3] = a[3] + b[3] + c; c = (out[3] >> 51); out[3] &= reduce_mask_51;
out[4] = a[4] + b[4] + c; c = (out[4] >> 51); out[4] &= reduce_mask_51;
out[0] = c * 19;
return out;
}
gcc:
add_reduce(number const&, number const&):
movq (%rdx), %rax
addq (%rsi), %rax
movq %rdi, %r8
movq %rdx, %rdi
shrq $51, %rax
movq 8(%rdx), %rdx
addq 8(%rsi), %rdx
movq %rsi, %rcx
movabsq $2251799813685247, %rsi
addq %rdx, %rax
movq %rax, %rdx
shrq $51, %rax
andq %rsi, %rdx
movq %rdx, 8(%r8)
movq 16(%rdi), %rdx
addq 16(%rcx), %rdx
addq %rdx, %rax
movq %rax, %rdx
shrq $51, %rax
andq %rsi, %rdx
movq %rdx, 16(%r8)
movq 24(%rdi), %rdx
addq 24(%rcx), %rdx
addq %rax, %rdx
movq %rdx, %rax
shrq $51, %rdx
andq %rsi, %rax
movq %rax, 24(%r8)
movq 32(%rdi), %rax
addq 32(%rcx), %rax
addq %rdx, %rax
andq %rax, %rsi
shrq $51, %rax
leaq (%rax,%rax,8), %rdx
movq %rsi, 32(%r8)
leaq (%rax,%rdx,2), %rax
movq %rax, (%r8)
movq %r8, %rax
ret
clang:
add_reduce(number const&, number const&): # @add_reduce(number
const&, number const&)
movq %rdi, %rax
movq (%rdx), %rcx
movq 8(%rdx), %rdi
addq (%rsi), %rcx
shrq $51, %rcx
addq 8(%rsi), %rdi
addq %rcx, %rdi
movq %rdi, %rcx
shrq $51, %rcx
movabsq $2251799813685247, %r8 # imm = 0x7FFFFFFFFFFFF
andq %r8, %rdi
movq %rdi, 8(%rax)
movq 16(%rdx), %rdi
addq 16(%rsi), %rdi
addq %rcx, %rdi
movq %rdi, %rcx
shrq $51, %rcx
andq %r8, %rdi
movq %rdi, 16(%rax)
movq 24(%rdx), %rdi
addq 24(%rsi), %rdi
addq %rcx, %rdi
movq %rdi, %rcx
andq %r8, %rdi
movq %rdi, 24(%rax)
movq 32(%rdx), %rdx
addq 32(%rsi), %rdx
shrq $51, %rcx
addq %rcx, %rdx
movq %rdx, %rcx
shrq $51, %rcx
andq %r8, %rdx
movq %rdx, 32(%rax)
leaq (%rcx,%rcx,8), %rdx
leaq (%rcx,%rdx,2), %rcx
movq %rcx, (%rax)
retq
clang with -march=native
.LCPI0_0:
.quad 2251799813685247
add_reduce(number const&, number const&): # @add_reduce(number
const&, number const&)
movq %rdi, %rax
movq (%rdx), %rcx
movq 8(%rdx), %rdi
addq (%rsi), %rcx
shrq $51, %rcx
addq 8(%rsi), %rdi
addq %rcx, %rdi
vmovq %rdi, %xmm0
shrq $51, %rdi
movq 16(%rdx), %rcx
addq 16(%rsi), %rcx
addq %rdi, %rcx
vmovq %rcx, %xmm1
shrq $51, %rcx
movq 24(%rdx), %rdi
addq 24(%rsi), %rdi
addq %rcx, %rdi
vmovq %rdi, %xmm2
shrq $51, %rdi
movq 32(%rdx), %rcx
addq 32(%rsi), %rcx
addq %rdi, %rcx
vpunpcklqdq %xmm1, %xmm0, %xmm0 # xmm0 = xmm0[0],xmm1[0]
vmovq %rcx, %xmm1
vpunpcklqdq %xmm1, %xmm2, %xmm1 # xmm1 = xmm2[0],xmm1[0]
vinserti128 $1, %xmm1, %ymm0, %ymm0
vpandq .LCPI0_0(%rip){1to4}, %ymm0, %ymm0
shrq $51, %rcx
vmovdqu %ymm0, 8(%rax)
leaq (%rcx,%rcx,8), %rdx
leaq (%rcx,%rdx,2), %rcx
movq %rcx, (%rax)
vzeroupper
retq
