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

[Frederic Parain]

On Wed, 3 Sep 2025 16:56:50 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> 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
>
> src/hotspot/share/oops/klass.hpp line 473:
> 
>> 471:   static const unsigned int _lh_array_tag_type_value = 0Xfffffffc;
>> 472:   static const unsigned int _lh_array_tag_flat_value = 0Xfffffffa;
>> 473:   static const unsigned int _lh_array_tag_ref_value  = 0Xfffffff8;
> 
> So there is no more layout_helper value for objArray, right?  Only flat and ref values?

Correct. The layout_helper provides information about the layout of an allocated Java array. ObjArrayKlass instances cannot contain details about a particular layout.

> src/hotspot/share/prims/jni.cpp line 2400:
> 
>> 2398:    oop v = JNIHandles::resolve(value);
>> 2399:    if (a->is_within_bounds(index)) {
>> 2400:     // TODO FIXME Temporary hack, to be removed when FlatArrayKlass is made a sub-class of ObjArrayKlass
> 
> You've done this.  Can this be cleaned up here?

Fixed

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

PR Review Comment: https://git.openjdk.org/valhalla/pull/1452#discussion_r2322782948
PR Review Comment: https://git.openjdk.org/valhalla/pull/1452#discussion_r2322785360