[Bug tree-optimization/65752] Too strong optimizations int -> pointer casts

["pinskia at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65752

--- Comment #39 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Alexander Cherepanov from comment #38)
> IMHO this bug is not specific to integers and boils down to this: when a
> check for equality ignores provenance for some reason, phiopt nevertheless
> will replace one variable by another with the wrong provenance.
> 
> Integers are surely compared without regard to prevenance. That's one case.
> Another case is a comparison of two pointers when one of the lost its
> provenance info. E.g. the program (somewhat based on pr61502):
> 
>   #include <stdint.h>
>   #include <stdio.h>
>   
>   int main()
>   {
>     int y, x = 0;
>     int *volatile v = &x;
>     int *xp = v;
>     int *i = &y + 1;
>   
>     if (xp != i) {
>       printf("hello\n");
>       xp = i;
>     }
>   
>     *xp = 15;
>   
>     printf("%d\n", x);
>   }
>   
> prints 0 for me with gcc 5.2.0 -O2.

Except the above testcase is invalid/undefined as &y + 1 is undefined if
deferenced and &x and &y + 1 cannot be compared in a defined sense as both
deals with two different arrays.