[lworld] RFR: 8345995: [lworld] Flat arrays need to be redesigned to support new flat layouts [v6]

[Frederic Parain]

> Here's a redesign of flat arrays to support multiple flat layouts (NON_ATOMIC_FLAT, ATOMIC_FLAT, NULLABLE_ATOMIC_FLAT). The patch contains a lot of cleanup and simplification of the flat arrays access code.
> 
> This patch has been tested in interpreted mode only on both x86_64 and aarch64.
> 
> Unfortunately, it currently triggers a number of failures when run with JITs enabled. After a discussion with Tobias, this PR will probably not be integrated until a patch for the JITs is available.
> 
> Regards,
> 
> Fred

Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains nine commits:

 - Fix markWord for nullable flat arrays
 - Merge remote-tracking branch 'upstream/lworld' into array_ext_hdr
 - Christian's patch to fix JIT code
 - Fix bad register usage causing mdp corruption
 - Small cleanups
 - Merge remote-tracking branch 'upstream/lworld' into array_ext_hdr
 - CDS fixes and various cleanup
 - Merge remote-tracking branch 'upstream/lworld' into array_ext_hdr
 - More flat arrays work and code cleanup

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Changes: https://git.openjdk.org/valhalla/pull/1315/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1315&range=05
  Stats: 1570 lines in 66 files changed: 939 ins; 281 del; 350 mod
  Patch: https://git.openjdk.org/valhalla/pull/1315.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1315/head:pull/1315

PR: https://git.openjdk.org/valhalla/pull/1315