[Bug c/48777] New: duplicate pointers to empty structs passed as arguments to function

[Bug c/48777] New: duplicate pointers to empty structs passed as arguments to function

[mjh at edg dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48777

           Summary: duplicate pointers to empty structs passed as
                    arguments to function
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: mjh@edg.com


#if OKAY
typedef int TYPE;
#elif ALSO_OKAY
struct A { int i; };
typedef struct A TYPE;
#else
struct A {};
typedef struct A TYPE;
#endif

int f(TYPE *a1, TYPE *a2) {
  return a1 == a2;
}
int main(void) {
  TYPE a1, a2;
  return f(&a1, &a2);
}

When OKAY or ALSO_OKAY are defined, unique addresses are passed for the
arguments to "f", but when an empty struct is used, the same address is passed
for both arguments (causing the function "f" to return 1).

This regression appears to have been introduced in 4.0.0 and exists through
4.5.2 (the latest version I have).

Thanks,

Mike.

[Bug c/48777] duplicate pointers to empty structs passed as arguments to function

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48777

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-04-26 19:20:31 UTC ---
Considering empty structs are a GNU extension, this could be considered
correct.

[Bug c/48777] duplicate pointers to empty structs passed as arguments to function

[joseph at codesourcery dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48777

--- Comment #2 from joseph at codesourcery dot com <joseph at codesourcery dot com> 2011-04-26 19:48:53 UTC ---
Indeed, empty structs in GNU C (as opposed to C++) are expected to take up 
no space, and so possibly not have unique addresses.

[Bug c/48777] duplicate pointers to empty structs passed as arguments to function

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48777

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
                 CC|                            |mpolacek at gcc dot gnu.org
         Resolution|---                         |INVALID

--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Thus closing.