[Bug middle-end/108448] GCC Elides Assignment to Pointer and memcpy

[sjames at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108448

Sam James <sjames at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|needs-reduction             |
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|---                         |INVALID

--- Comment #20 from Sam James <sjames at gcc dot gnu.org> ---
This reduces to:
```
int a;

void abort();
_Bool y_map_existsStringKey_v() __attribute__((pure));
_Bool y_map_existsStringKey_v(int *m, char *, void *val_ptr) {
  char **b = val_ptr;
  *b = m;
  return 1;
}
void pthread_getspecific();
void y_assert_fail() { abort(); }
void main() {
  int *stack = 0;
  pthread_getspecific();
  if (y_map_existsStringKey_v(&a, 0, &stack))
    stack || (y_assert_fail(), 0);
}
```

y_map_existsStringKey_v is NOT a candidate for pure, as it has side-effects (it
modifies val_ptr). Indeed, dropping the pure attribute from
y_map_existsStringKey_v on the original fixes it too.