[Bug c/128163] wrong code at -O1: store through the pointer argument of an [[unsequenced]] function declared without a prototype is ignored

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=128163

Drea Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2026-10-25
           Keywords|documentation               |wrong-code

--- Comment #8 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.

The problem is this check in handle_unsequenced_attribute:
```
  for (tree argtype = TYPE_ARG_TYPES (fntype); argtype;
       argtype = TREE_CHAIN (argtype))
    /* If any of the arguments have pointer or reference type, just
       add the attribute alone.  */
    if (POINTER_TYPE_P (TREE_VALUE (argtype)))
      return NULL_TREE;

```

Is wrong for var-args functions.  Also wrong for the non-prototype functions.