https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105495
--- Comment #5 from LIU Hao <lh_mouse at 126 dot com> ---
This does not trigger the issue:
```c
#define __atomic_compare_exchange(p,c,n,w,ms,mf) \
({ int __temp; \
__builtin_memcpy(&__temp, c, sizeof(*c)); \
_Bool __r = __atomic_compare_exchange(p, (__typeof__(*(c))*) &__temp, n,
w, ms, mf); \
__builtin_memcpy(c, &__temp, sizeof(*c)); \
__r; });
typedef struct { int b; } cond;
int
__MCF_batch_release_common(cond* p, int c);
int
_MCF_cond_signal_some(cond* p, int x)
{
cond c = {x}, n = {2};
__atomic_compare_exchange(p, &c, &n, 1, 0, 0);
return __MCF_batch_release_common(p, x);
}
```
which results in (godbolt https://gcc.godbolt.org/z/n68T1c6oP):
```asm
_MCF_cond_signal_some:
mov edx, 2
mov eax, esi
lock cmpxchg DWORD PTR [rdi], edx
jmp __MCF_batch_release_common
```
Effectively, we are using a `int` to provide storage for a struct of
`sizeof(int)`.
But if we use a `long` to provide storage for the struct, such issue reappears:
```c
#define __atomic_compare_exchange(p,c,n,w,ms,mf) \
({ long __temp; \
__builtin_memcpy(&__temp, c, sizeof(*c)); \
_Bool __r = __atomic_compare_exchange(p, (__typeof__(*(c))*) &__temp, n,
w, ms, mf); \
__builtin_memcpy(c, &__temp, sizeof(*c)); \
__r; });
typedef struct { int b; } cond;
int
__MCF_batch_release_common(cond* p, int c);
int
_MCF_cond_signal_some(cond* p, int x)
{
cond c = {x}, n = {2};
__atomic_compare_exchange(p, &c, &n, 1, 0, 0);
return __MCF_batch_release_common(p, x);
}
```
which results in (https://gcc.godbolt.org/z/PGof8nGd7)
```asm
_MCF_cond_signal_some:
mov edx, 2
mov eax, esi
mov DWORD PTR [rsp-16], esi
lock cmpxchg DWORD PTR [rdi], edx
je .L2
mov DWORD PTR [rsp-16], eax
.L2:
jmp __MCF_batch_release_common
```
It is also notable that with this kind of hacks, GCC is finally able to perform
TCO on the return statement.
