https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109443
--- Comment #17 from AK <hiraditya at msn dot com> ---
Even after vector::size() is hoisted, the codegen is sub-optimal compared to
iterator version.
```
void use_idx_const_size(std::vector<int> v) {
auto s = v.size();
for (std::vector<int>::size_type i = 0; i < s; i++)
f(v[i]);
}
```
$ g++ -O3
use_idx_const_size(std::vector<int, std::allocator<int> >):
push r12
push rbp
push rbx
mov rdx, QWORD PTR [rdi+8]
mov rax, QWORD PTR [rdi]
mov r12, rdx
sub r12, rax
sar r12, 2
cmp rax, rdx
je .L1
mov rbp, rdi
xor ebx, ebx
jmp .L3
.L6:
mov rax, QWORD PTR [rbp+0]
.L3:
mov edi, DWORD PTR [rax+rbx*4]
add rbx, 1
call f(int)
cmp rbx, r12
jb .L6
.L1:
pop rbx
pop rbp
pop r12
ret
It seems compiler is assuming that vector `v` is not loop-invariant?
