https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114342
Bug ID: 114342
Summary: suboptimal codegen of vector::vector(range)
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: hiraditya at msn dot com
Target Milestone: ---
#include<vector>
#include <ranges>
std::vector<int> td() {
int arr[]{-5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10,
15, -5, 10, 15,-5, 10, 15 -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5,
10, 15, -5, 10, 15, -5, 10,-5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5,
10, 15, -5, 10,-5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5,
10,-5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10,-5, 10,
15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10, 15, -5, 10,};
auto b = std::ranges::begin(arr);
auto e = std::ranges::end(arr);
std::vector<int> dd(b, e);
return dd;
}
What is the reason for calling `rep movsq` twice?
$ gcc -O3 -std=c++23
```
td():
push rbp
mov esi, OFFSET FLAT:.LC0
mov ecx, 55
pxor xmm0, xmm0
push rbx
mov rbx, rdi
sub rsp, 456
mov QWORD PTR [rbx+16], 0
mov rbp, rsp
movups XMMWORD PTR [rbx], xmm0
mov rdi, rbp
rep movsq
mov eax, DWORD PTR [rsi]
mov DWORD PTR [rdi], eax
mov edi, 444
call operator new(unsigned long)
lea rdx, [rax+444]
mov QWORD PTR [rbx], rax
lea rdi, [rax+8]
mov rsi, rbp
mov QWORD PTR [rbx+16], rdx
mov rcx, QWORD PTR [rsp]
and rdi, -8
mov QWORD PTR [rax], rcx
mov rcx, QWORD PTR [rsp+436]
mov QWORD PTR [rax+436], rcx
sub rax, rdi
sub rsi, rax
add eax, 444
shr eax, 3
mov ecx, eax
mov rax, rbx
rep movsq
mov QWORD PTR [rbx+8], rdx
add rsp, 456
pop rbx
pop rbp
ret
mov rbp, rax
jmp .L2
td() [clone .cold]:
.L2:
mov rdi, QWORD PTR [rbx]
mov rsi, QWORD PTR [rbx+16]
sub rsi, rdi
test rdi, rdi
je .L3
call operator delete(void*, unsigned long)
.L3:
mov rdi, rbp
call _Unwind_Resume
```
https://godbolt.org/z/5333db8Px
