[master] RFR: Relax array elements alignment [v6]

[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.
> 
> GHA seems to see 3 new test failures (timeouts), but only on Windows(x64). I ran the same test on a different Windows machine (all of compiler/c2/irTests) and could not reproduce the failures. They do look like timeouts on GHA, maybe it's just too long-running tests?
> 
> Those are the GHA/Windows failing tests:
> compiler/c2/irTests/TestAutoVectorization2DArray.java 
> compiler/c2/irTests/TestIRAbs.java 
> compiler/c2/irTests/TestStripMiningDropsSafepoint.java 
> 
> 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:

  Thomas' suggestions

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

Changes:
  - all: https://git.openjdk.java.net/lilliput/pull/41/files
  - new: https://git.openjdk.java.net/lilliput/pull/41/files/e021859a..99802a7d

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=lilliput&pr=41&range=05
 - incr: https://webrevs.openjdk.java.net/?repo=lilliput&pr=41&range=04-05

  Stats: 43 lines in 15 files changed: 3 ins; 12 del; 28 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