Restrict keyword questions

How far does the guarantee that an object is not accessed through another
pointer go? I mean, all examples I have seen are simple stuff like:

int f (int *restrict x, int *restrict y)
{
*x = 0;
*y = 1;
return *x;
}

Ok, the "return *x" can be optimised to "return 0" in this case, but what
happens if we add a function call:...