https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81456
LIU Hao <lh_mouse at 126 dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |lh_mouse at 126 dot com
--- Comment #12 from LIU Hao <lh_mouse at 126 dot com> ---
Is this the same issue?
https://gcc.godbolt.org/z/sTs3E9EP1
```
struct stack
{
void** base;
unsigned int top, cap;
};
struct context
{
void* data;
stack* st;
};
int
clear_stack(context& ctx)
{
ctx.st->top = 0;
return 0;
}
```
GCC reuses RAX for `ctx.st` and the return value, so an extra XOR is generated:
```
clear_stack(context&):
mov rax,QWORD PTR [rdi+0x8]
xor edx,edx <-- this would be unnecessary if
`xor eax, eax` was lifted here
mov DWORD PTR [rax+0x8],edx
xor eax,eax
ret
```
as in
```
clear_stack_2(context&):
mov rcx,QWORD PTR [rdi+0x8] # 48 8b 4f 08
xor eax,eax # 31 c0
mov DWORD PTR [rcx+0x8],eax # 89 41 08
ret # c3
```
