Two pointers that point to members of different arrays can not be aliases, even if the offsets within arrays are not known.

Example:

In the code fragment below, the specific objects pointed to by p and q are not known, but they are members of different arrays, and therefore can not be aliased.

int a[], b[];

void f (int i, int j)
{
  int *p, *q;
  int x, y;
  p = &a[i];
  q = &b[j];
  x = *(q + 3);
  *p = 5;
  y = *(q + 3);
  g (x, y);
}

Since p and q are not aliased, the second reference to *(q + 3) can be eliminated, as shown below.

int a[], b[];

void f(int i, int j)
{
  int *p, *q;
  int x, y;
  p = &a[i];
  q = &b[j];
  x = *(q + 3);
  *p = 5;
  g (x, x);
}

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