[lworld] RFR: 8341757: Field layout computation allowing atomic and nullable flattening [v2]

[Frederic Parain]

> Initial implementation of fields layouts in order to support heap flattening with JEP 401 model.
> The patch includes the generation of two new flat fields layouts: atomic and nullable.
> The patch also includes the support in the interpreter (through the access API) to access the new layouts while respecting the new semantic (on x86_64 and aarch64).
> Some areas do not support the new layouts yet, like JITs, Unsafe and arrays.
> 
> There's no automatic tests yet, but considering the impact those new layouts will have on the JVM, the priority was to make this code available to all developers as soon as possible. Automatic tests will be added in a following CR.
> 
> Fred

Frederic Parain has updated the pull request incrementally with one additional commit since the last revision:

  Fix bugs in aarch64 get_default_value_oop() method

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1275/files
  - new: https://git.openjdk.org/valhalla/pull/1275/files/ceaa7c8a..0eacc549

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1275&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1275&range=00-01

  Stats: 3 lines in 1 file changed: 1 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/valhalla/pull/1275.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1275/head:pull/1275

PR: https://git.openjdk.org/valhalla/pull/1275