[lworld] RFR: 8366705: [lworld] Re-work of arrays meta-data [v4]

[Tobias Hartmann]

On Wed, 3 Sep 2025 14:43:55 GMT, Frederic Parain <fparain at openjdk.org> wrote:

>> Since the removal of Q-types and the notion that nullability was not part of the Java type, there was an awkward situation because nullable arrays of value types and null free arrays of value types had each a different Java mirror when they were in fact supposed to have the same Java type.
>> In order to accommodate to the new situation, that arrays can have properties (nullability, flatness, atomicity, etc.) that are not part of their Java type, the 1-1 relationship between the *ArrayKlass and the Java mirror must be broken.
>> The proposed solution is to dedicate one instance of ObjArrayKlass to represent the Java type of the array in the JVM, and have this instance being the counterpart of the Java mirror of the array, and have several instances of RefArrayKlass and FlatArrayKlass that represent the refinements of the Java array type. Each RefArrayKlass/FlatArrayKlass encodes the characteristic of a Java array for a given element type and a set of properties.
>
> Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 67 commits:
> 
>  - Merge branch 'array_klasses' of github.com:fparain/valhalla into array_klasses
>  - Forgot a TODO
>  - Small cleanup
>  - Merge remote-tracking branch 'upstream/lworld' into array_klasses
>  - Moved get_Klass() back to protected and updated usages
>  - Merge branch 'array_klasses' of github.com:fparain/valhalla into array_klasses
>  - Linked TODOs to JDK-8366668
>  - Multidim array fix
>  - Cleanup T_FLAT_ELEMENT related code
>  - Fix for isAssignableFrom + tests
>  - ... and 57 more: https://git.openjdk.org/valhalla/compare/22e9d5f5...527a17b6

Marked as reviewed by thartmann (Committer).

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PR Review: https://git.openjdk.org/valhalla/pull/1452#pullrequestreview-3183646545