Can you bounds check dynamically sized arrays? For example, a function that receives the size as a separate argument?

    double f(double *xs, int n){
        return xs[g()];
    }

Yes. In my hypothetical world where the C compiler makes use of the VLA declaration in the function arguments, it would certainly be possible for the compiler to insert automatic bounds checking in this case:

  double f(xs, n)
    double xs[n];
    size_t n;
  {
    size_t _tmp0 = g();   /* temporary var created by compiler */
    assert(_tmp0 < n);    /* bounds check inserted by compiler */
    return xs[_tmp0];
  }

The key to making this possible is telling the compiler about the relationship between double* xs and size_t n; once the compiler has the knowledge that the type of xs is double [n] (array of double with first dimension n) it would be able to automatically insert dynamic bounds checks.

> dynamically sized arrays

Yes. What you can't do is associate bounds information with some specific pointer to an array, but this will work, for instance:

  int *x = malloc(2 * sizeof(int));
  x[1]; //ok
  x[2]; //runtime error