LRB and 32-bit compressed oops

[Roland Westrelin]

> I don't think that storing fwd ptr compressed is an option. It would
> have to be decoded and re-encoded in the barrier. It would complicate
> and slow down everything else in GC. And it would gain us nothing: we
> still need the 64bits because alignment. (And we already have a
> prototype to eliminate that word...)
>
> The question was really only, can we get rid of the superfluous mov
> and register usage in the noop-decode case?

A compressed fwd ptr is a way to get rid of the extra movs. I think it
would make compiled code better overall, too.

Without a compressed fwd ptr, messing with the register allocator would
be required. I have no idea how to do that.

Roland.