[master] RFR: Only include Mark Word when required [v3]

[Julian Waters]

> WIP
> 
> Discussion: https://bugs.openjdk.java.net/browse/JDK-8198331
> 
> Current goals and dependencies (To help keep track)
> - [x] 2 bit identity Hash Code
> - [ ] Elimination of locking from the Mark Word entirely (Hopefully)
> - [ ] 5 bit GC section (4 bit object age, 1 bit forwarding state)
> - [ ] No Mark Word in header until required
> - [ ] Support and optimizations for objects guaranteed to not have a Mark Word (May depend on Valhalla for the GC section)

Julian Waters has updated the pull request incrementally with one additional commit since the last revision:

  Don't initially allocate the Mark Word

-------------

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/47/files
  - new: https://git.openjdk.java.net/lilliput/pull/47/files/56f74f5c..3d4dcd8f

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=47&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=47&range=01-02

  Stats: 6 lines in 2 files changed: 5 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/47.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/47/head:pull/47

PR: https://git.openjdk.java.net/lilliput/pull/47