RFR: 8256011: Shenandoah: Don't resurrect finalizably reachable objects [v8]

[Roman Kennke]

> In the weak-LRB we currently return referents when it is 'marked', that is when it's either reachable strongly or through a finalizable object. This means a finalizable object can be resurrected by Reference.get(), which is wrong. Only truly strongly reachable objects should be returned by Reference.get() during weak-reference-processing. 
> 
> I had to reconsider the way we call into runtime-LRBs from generated code for these reasons:
>  - We need to distinguish phantom, weak and strong reference strength, and native vs in-heap access. Those are two orthogonal dimensions
>  - We can have strong and phantom native referents, and strong and weak in-heap referents
>  - Native referents are never compressed
> 
> Note that this depends on PR#1140.
> 
> Testing:
>  - [x] hotspot_gc_shenandoah (x86_64, x64_32, aarch64)
>  - [x] tier1 +UseShenandoahGC +ShenandoahVerify
>  - [x] tier2 +UseShenandoahGC +ShenandoahVerify

Roman Kennke has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 18 additional commits since the last revision:

 - Fix/invert condition in CmpP optimization
 - Fix after merge
 - Merge branch 'master' into JDK-8256011
 - Merge branch 'master' into JDK-8256011
 - Don't make phantom-access narrow (mistake when doing 32bit parts
 - Remove superfluous LP64 in aarch64 part
 - Fixes/missing parts for x86_64
 - Aarch64 parts
 - Whitespace changes
 - Mask decorators in hash/cmp, not in ctor
 - ... and 8 more: https://git.openjdk.java.net/jdk/compare/8d27361d...c0ee9346

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1109/files
  - new: https://git.openjdk.java.net/jdk/pull/1109/files/92a92fcd..c0ee9346

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1109&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1109&range=06-07

  Stats: 6278 lines in 184 files changed: 4337 ins; 942 del; 999 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1109.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1109/head:pull/1109

PR: https://git.openjdk.java.net/jdk/pull/1109