is_null_pointer_constant
int is_null1 = is_null_pointer_constant(left);
int is_null2 = is_null_pointer_constant(right);
int is_null1 = is_null_pointer_constant(*cond);
int is_null2 = is_null_pointer_constant(expr->cond_false);
int is_null = is_null_pointer_constant(*rp);
!is_null_pointer_constant(source) && Wcast_to_as)