RFR: 8259776: Remove ParallelGC non-CAS oldgen allocation [v3]

[Kim Barrett]

> Please review this change to ParallelGC oldgen allocation.  There were two
> variants, one using CAS on the _top member of the mutable space, the other
> requiring locking or other forms of mutual exclusion.
> 
> We don't need both variants.  The non-CAS variant is only used in a few
> places, where the cost of an extra CAS doesn't matter.  What does matter is
> that having two variants, which must not be used concurrently, makes the
> code larger, more complex, and harder to verify.  (This change came out of
> analyzing JDK-8259271.  No problems were found (or expected), so this change
> is not expected to impact that bug.  But because of the two variants, the
> possibility of unexpected interact needed to be examined.)
> 
> The non-CAS allocation support has been removed, with PSOldGen::allocate now
> implemented using the CAS-based allocation.  The cas_ prefix naming
> convention is retained for the internals for clarity.
> 
> While looking at this, noticed and removed a couple of lingering references
> to the class AdjoiningGenerations, which no longer exists after JDK-8243146.
> 
> Testing:
> mach5 tier1-5

Kim Barrett has updated the pull request incrementally with one additional commit since the last revision:

  move oldgen alloc with size policy recording to heap object

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/2101/files
  - new: https://git.openjdk.java.net/jdk/pull/2101/files/ed7e2b26..994c0eb6

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=2101&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=2101&range=01-02

  Stats: 31 lines in 4 files changed: 12 ins; 14 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2101.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2101/head:pull/2101

PR: https://git.openjdk.java.net/jdk/pull/2101