RFC: Draft JEP: Generational ZGC

[Florian Weimer]

* Stefan Karlsson:

> Hi Leslie,
>
> Could you test if this branch compiles as expected?
> https://github.com/stefank/jdk/tree/zgc_generational_found_old_initialization
>
> I asked around and it seems like array initialization uses 
> copy-initialization of the elements, and that older GCCs didn't take the 
> opportunity to convert the copying into move operations. Or something 
> along those lines. I've restructured the code to prevent that problem.

GCC 10 needs this patch as well.

I think the proper fix is to add a move constructor to CHeapBitMap
(and move assignment as well):

  CHeapBitMap(CHeapBitMap &&) = default;
  CHeapBitMap &operator=(CHeapBitMap &&) = default;

I don't see any pointers-to-self in the class definition (or its base
class), so it should work, but I only have limited means to test this.

At least it's building with the two lines added, and basic smoke
testing shows nothing amiss.  But I don't know how quickly bugs in
this area would blow up in practice.