In ordinary C, without a garbage collector, I'd be baffled to find an implementation where one could not:

    1) Cast a pointer to an integer of sufficient size.
    2) Xor that integer with another value.
    3) Xor the result with the same value.
    4) Cast back to a pointer.
    5) Dereference.

It's sufficiently corner-case that I am not certain what the standard says about it. In any event, pointers matter when coding in assembly, where language standards aren't even relevant.