[master] RFR: Relax array elements alignment [v8]

[Roman Kennke]

> PR #40 eliminated the Klass* word. A whole class of objects would not benefit from it, though: array elements are aligned at 8-byte-boundaries, even for element types where this is not necessary (byte, bool, char, short, int, float, compressed-objs). This means that array elements would still start at byte#16, after 8 bytes header and 4 bytes length and another 4 bytes unused gap.
> 
> This change improves the array element alignment and relaxes it such that elements can align at 4-byte boundaries.
> 
> Note about C2 changes: the code that extracts the state field (either byte, int or long array) assumed that all arrays would be equal, and asks for header size of T_INT. This would give wrong offset for T_LONG arrays.
> 
> I'm adding a test that checks correct array elements base offsets.
> 
> Testing:
>  - [x] tier1 (x86_64)
>  - [x] tier1 (x86_32)
>  - [x] tier1 (aarch64)
>  - [x] tier2 (x86_64)
>  - [x] tier2 (x86_32)
>  - [x] tier2 (aarch64)
>  - [x] tier3 (x86_64)
>  - [x] tier3 (x86_32)
>  - [x] tier3 (aarch64)

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

  Fix Z array initialization: initialize at byte granularity instead of words

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

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/41/files
  - new: https://git.openjdk.java.net/lilliput/pull/41/files/b91760a6..e416f8f2

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=41&range=07
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=41&range=06-07

  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/lilliput/pull/41.diff
  Fetch: git fetch https://git.openjdk.java.net/lilliput pull/41/head:pull/41

PR: https://git.openjdk.java.net/lilliput/pull/41