[lworld] RFR: 8370880: [lworld] Split ciObjArrayKlass into ciRefArrayKlass and ciFlatArrayKlass

[Quan Anh Mai]

On Sat, 15 Nov 2025 10:54:41 GMT, Quan Anh Mai <qamai at openjdk.org> wrote:

> Hi,
> 
> This PR splits `ciObjArrayKlass` into `ciRefArrayKlass` and `ciFlatArrayKlass`, aligns the hierarchy with the corresponding types of the VM.
> 
> I also had to fix `GraphKit::cast_to_flat_array`, currently it incorrectly assumes that the cast is to an exact type, splitting into `cast_to_flat_array` and `cast_to_flat_array_exact` seems to make it clearer.
> 
> Please kindly review, thanks a lot.

There are still a lot of refactoring to be done regarding moving elements from `ciArrayKlass` to `ciObjArrayKlass` since now it is the new common ancestor of all arrays of objects.

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PR Comment: https://git.openjdk.org/valhalla/pull/1739#issuecomment-3536344109