# cat x.c
extern void foo (void) __attribute__ ((weak));

int
main ()
{
  if (&foo)
    foo ();

  return 0;
}
# g++ -S -O -Wall x.c
x.c: In function `int main ()':
x.c:6: warning: the address of `foo ()', will always be `true'

gcc is ok. gcc 3.0 has the same bug.