1  extern void abort(void);
       2  void foo(int *p)
       3  {
       4    int x;
       5    int y;
       6    x = *p;
       7    *p = 0;
       8    y = *p;
       9    if (x != y)
      10      return;
      11    abort ();
      12  }
      13  
      14  int main()
      15  {
      16    int a = 1;
      17    foo(&a);
      18    return 0;
      19  }