[Bug c/53532] New: function call ignored when called with argument of incompatible, undefined structure

[machata at post dot cz]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53532

             Bug #: 53532
           Summary: function call ignored when called with argument of
                    incompatible, undefined structure
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: machata@post.cz


The following code...

struct aaa {};
extern int xxx(struct aaa e);
int main() {
  xxx((struct bbb) {});
  return 0;
}

... compiles without warnings and the call to xxx is ignored:
# gcc -Wall -Wextra -c foo.c
# objdump -x foo.o
[...]
Disassembly of section .text:
0000000000000000 <main>:
   0:    55                   push   %rbp
   1:    48 89 e5             mov    %rsp,%rbp
   4:    b8 00 00 00 00       mov    $0x0,%eax
   9:    5d                   pop    %rbp
   a:    c3                   retq
[...]

The code above seems invalid, and I think that gcc should reject it.

The definition of struct aaa is somehow important.  When dropped, GCC realizes
things are wrong, and complains abundantly.

# LANG=C gcc -Wall -Wextra -x c /dev/stdin
extern int xxx(struct aaa e);
int main() {
  xxx((struct bbb) {});
  return 0;
}
/dev/stdin:1:23: warning: 'struct aaa' declared inside parameter list [enabled
by default]
/dev/stdin:1:23: warning: its scope is only this definition or declaration,
which is probably not what you want [enabled by default]
/dev/stdin: In function 'main':
/dev/stdin:3:15: error: type of formal parameter 1 is incomplete

It also complains about struct bbb being incomplete, which it didn't mind at
all while aaa was there.