[master] RFR: JDK-8301786: [Lilliput] Failing CompressedClassPointerEncoding.java [v2]

[Thomas Stuefe]

> This fixes and expands runtime/CompressedOops/CompressedClassPointerEncoding.java.
> 
> Test had been broken by integration of [JDK-8294677](https://bugs.openjdk.org/browse/JDK-8294677), but to my embarrassment, I found that the test had never actually been finished, some vital checks were missing.
> 
> I fixed all that, clarified comments, and also changed the test to have multiple sub tests. I manually tested on x64 and aarch64.
> 
> On aarch64, I tried to test both `xor` and `movk` encoding modes but was unable to test latter - the lowest valid encoding base that would trigger `movk` mode is `0xa00_00000000`, and the kernel on my Raspi box is compiled for max. 39 bits for virtual user space addresses. That makes mapping at higher addresses fail. See comment in test.
> 
> There is more work to be done for aarch64: runtime/CompressedOops/CompressedClassPointerEncoding.java asserts. I opened https://bugs.openjdk.org/browse/JDK-8301880 to track that.

Thomas Stuefe has updated the pull request incrementally with one additional commit since the last revision:

  Feedback Alexey; massage comments

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

Changes:
  - all: https://git.openjdk.org/lilliput/pull/72/files
  - new: https://git.openjdk.org/lilliput/pull/72/files/be6b5575..bda987ca

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=lilliput&pr=72&range=01
 - incr: https://webrevs.openjdk.org/?repo=lilliput&pr=72&range=00-01

  Stats: 17 lines in 1 file changed: 0 ins; 3 del; 14 mod
  Patch: https://git.openjdk.org/lilliput/pull/72.diff
  Fetch: git fetch https://git.openjdk.org/lilliput pull/72/head:pull/72

PR: https://git.openjdk.org/lilliput/pull/72