| Issue |
63328
|
| Summary |
Missed optimization of std::vector access
|
| Labels |
|
| Assignees |
|
| Reporter |
hiraditya
|
I originally reported the bug in gcc but it seems clang also has the problem
```cpp
void f(int);
void g(std::vector<int> v)
{
for (std::vector<int>::size_type i = 0; i < v.size(); i++)
f( v[ i ] );
}
void h(std::vector<int> v)
{
for (std::vector<int>::const_iterator i = v.begin(); i != v.end(); ++i)
f( *i );
}
```
$ clang++ -O3
```asm
g(std::vector<int, std::allocator<int> >): # @g(std::vector<int, std::allocator<int> >)
push r14
push rbx
push rax
mov rax, qword ptr [rdi]
cmp qword ptr [rdi + 8], rax
je .LBB0_3
mov rbx, rdi
xor r14d, r14d
.LBB0_2: # =>This Inner Loop Header: Depth=1
mov edi, dword ptr [rax + 4*r14]
call f(int)@PLT
inc r14
mov rax, qword ptr [rbx]
mov rcx, qword ptr [rbx + 8]
sub rcx, rax
sar rcx, 2
cmp r14, rcx
jb .LBB0_2
.LBB0_3:
add rsp, 8
pop rbx
pop r14
ret
h(std::vector<int, std::allocator<int> >): # @h(std::vector<int, std::allocator<int> >)
push r14
push rbx
push rax
mov r14, qword ptr [rdi]
cmp r14, qword ptr [rdi + 8]
je .LBB1_3
mov rbx, rdi
.LBB1_2: # =>This Inner Loop Header: Depth=1
mov edi, dword ptr [r14]
call f(int)@PLT
add r14, 4
cmp r14, qword ptr [rbx + 8]
jne .LBB1_2
.LBB1_3:
add rsp, 8
pop rbx
pop r14
ret
```
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