[lworld] RFR: 8370880: [lworld] Split ciObjArrayKlass into ciRefArrayKlass and ciFlatArrayKlass [v2]

[Quan Anh Mai]

On Mon, 17 Nov 2025 14:38:02 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.
>
> Quan Anh Mai has updated the pull request incrementally with one additional commit since the last revision:
> 
>   can only infer klass if exact

Thanks for your testing. Unfortunately, the issue cuts pretty deep. We have multiple potential inconsistencies when dealing with `_klass` such as when trying to obtain a flat `TypeAryPtr` from a non-flat `TypeAryPtr`. I think it can be addressed as follow-up issues. To fix the immediate crash, I choose to fix a particular issue, that is we can only compute the `_klass` if we have `klass_is_exact`.

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PR Comment: https://git.openjdk.org/valhalla/pull/1739#issuecomment-3542204909