clang is a bit more sane:

   > cc pointereq.c 
   > ./a.out 
   0x7ffee83163b8 0x7ffee83163b8 1
   > cc -O pointereq.c 
   > ./a.out 
   0x7ffeeeb8b3b8 0x7ffeeeb8b3c0 0

So without optimization, the pointers are the same and compare as equal. With optimization, the pointers compare as not equal. At first that seemed horrible, until I saw the pointers actually are not the same. Since I don't recall any guarantees about stack layout, that seems perfectly fine.

   > cat pointereq.c 
   
   #include <stdio.h>
   
   int main(void) {
     int a, b;
     int *p = &a;
     int *q = &b + 1;
     printf("%p %p %d\n", (void *)p, (void *)q, p == q);
     return 0;
   }