Pointer top 16 bits use

[Claude via Digitalmars-d]

On Saturday, 7 May 2016 at 06:08:01 UTC, Nicholas Wilson wrote:
> In Dicebot's DConf talk he mentioned that it is possible to use 
> the top 16 bits for tagging pointers and the associated risks.
>
> Regarding the GC not seeing a pointer if the top 16 bits are 
> used, whats to stop us from changing the GC to (or adding an 
> option to) ignore those bits when checking?
>
> I imagine that it would cause a lot more false pointers, but 
> when we get precise GC that problem would go away.

I would not rely on it *at all* actually, even now. I do not 
think it would make D portable to every system (let's not only 
consider x86 architecture).
We don't know how a system would choose to map physical memory 
and hardware devices to virtual memory.