Note that if the two pointers are passed to a function, and the comparison is done in the function, the results are different:

  #include <stdio.h>

  void pcmp(int *p, int *q)
  {
      printf("%p %p %d\n", (void *)p, (void *)q, p == q);
  }

  int main(void) {
    int a, b;
    int *p = &a;
    int *q = &b + 1;
    printf("%p %p %d\n", (void *)p, (void *)q, p == q);
    pcmp(p, q);
    return 0;
  }

That is giving me:

  0x7ffebac1483c 0x7ffebac1483c 0
  0x7ffebac1483c 0x7ffebac1483c 1

That's compiled with '-std=c11 -O1' as in the article. The result is the same of pcmp is moved into a separate file so that when compiling it the compiler has no knowledge of the origins of the two pointers.

I don't like this at all. It bugs me that I can get different results comparing two pointers depending on where I happen to do the comparison.