[master] RFR: Load Klass from header, C1/x86 implementation [v4]

[Roman Kennke]

> This implements loading the Klass* from object header (instead of dedicated Klass* field) in C1 generated code. It introduces a new C1 LIR opcode (LoadKlass) and related CodeStub for the slow-path runtime-call.
> 
> The original implementation was brittle in that it emits the decode_klass() whenever it encounters a load that is T_ADDRESS and from klass_offset_in_bytes() (e.g. 4 or 8). Lucky that we did not seem to emit any unrelated such loads. This new implementation uses a dedicated C1 op instead, and expands this to the corresponding load of the header word, and call into slow-path upon fast-path-failure, in the LIR assembler.
> 
> Testing:
>  - [x] tier1 (x86_64,x86_32)
>  - [x] tier2 (x86_64,x86_32)
>  - [x] tier3 (x86_64,x86_32)
>  - [ ] tier4 (x86_64,x86_32)

Roman Kennke has updated the pull request incrementally with one additional commit since the last revision:

  Basic aarch64 implementation

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

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/20/files
  - new: https://git.openjdk.java.net/lilliput/pull/20/files/f7c0dfef..ee89ba25

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=20&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=20&range=02-03

  Stats: 26 lines in 2 files changed: 14 ins; 11 del; 1 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/20.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/20/head:pull/20

PR: https://git.openjdk.java.net/lilliput/pull/20