RFR(L): 8064457: Introduce compressed oops mode "disjoint base" and improve compressed heap handling.

[Lindenmaier, Goetz]

Hi,

I need to improve a row of things around compressed oops heap handling
to achieve good performance on ppc.
I prepared a first webrev for review:
http://cr.openjdk.java.net/~goetz/webrevs/8064457-disjoint/webrev.00/

A detailed technical description of the change is in the webrev and according bug.

If requested, I will split the change into parts with more respective less impact on
non-ppc platforms.

The change is derived from well-tested code in our VM.  Originally it was
crafted to require the least changes of  VM coding, I changed it to be better
streamlined with the VM.
I tested this change to deliver heaps at about the same addresses as before.
Heap addresses mostly differ in lower bits.  In some cases (Solaris 5.11) a heap
in a better compressed oops mode is found, though.
I ran (and adapted) test/runtime/CompressedOops and gc/arguments/TestUseCompressedOops*.

Best regards,
  Goetz.