Question about garbage collection specification

[Alex Parrill via Digitalmars-d]

On Monday, 15 June 2015 at 15:33:41 UTC, rsw0x wrote:
>
> this doesn't make any sense, it's referring to an object p (of 
> void*), not the location of p. It's setting the lsb of p to 1 
> and claiming it's undefined behavior, when it's clearly not.
>
> Unless I misunderstand it.

`p` is assumed to be a pointer. `cast(int) p` gets the integer 
representation of the pointer (though it should be `uintptr_t` 
but whatever). It then does an integer bitwise or, then converts 
the result back to a pointer.

It's undefined behavior in D because the spec just said so 
(regardless of its defined behavior in C).