[lworld] RFR: 8375441: [lworld] C2: assert(is_instance()) failed: bad cast [v5]

[Marc Chevalier]

On Mon, 16 Feb 2026 08:11:27 GMT, Marc Chevalier <mchevalier at openjdk.org> wrote:

>> Some code added by [JDK-8372700](https://bugs.openjdk.org/browse/JDK-8372700) can compute the constant value of a field of a (flatten) element in a flat array. We get a crash when the element of the array is known to be `null`, and so the field doesn't exist.
>> 
>> So, let's just check in `ciConstant ciFlatArray::field_value(int index, ciField* field)` whether we get a null constant before interpreting it as a `ciInstance` and trying to retrieve a field from there. This should be enough since a `ciObject` is (directly) derived by `ciNullObject`, `ciInstance` and `ciArray`. Since we are looking up a value of a flat array, an element cannot be a `ciArray` (arrays have identities and can't be contained in a flat array). After looking up whether the flat array element is null, the `obj->as_instance()` cast acts as an assert, should we ever add another derived class from `ciObject`.
>> 
>> In case of a null array element, `field_value` simply returns an invalid `ciConstant`.
>> 
>> Tested with tier1,tier2,tier3,hs-precheckin-comp,hs-comp-stress,valhalla-comp-stress. Looks good.
>> 
>> Thanks,
>> Marc
>
> Marc Chevalier has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains 19 additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'origin/lworld' into JDK-8375441.review
>  - Merge remote-tracking branch 'origin/lworld' into JDK-8375441.review
>  - Unproblem-list
>  - Merge remote-tracking branch 'origin/lworld' into JDK-8375441.review
>  - More
>  - Addressing more comments
>  - Merge
>  - Some reviews
>  - Details
>  - exception handling
>  - ... and 9 more: https://git.openjdk.org/valhalla/compare/02b9d6dc...90f8677d

Thanks @merykitty and @TobiHartmann for reviews!

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PR Comment: https://git.openjdk.org/valhalla/pull/1923#issuecomment-3907076604