[lworld] RFR: 8372954: [lworld] Remove old implementation of the substitutability test method [v3]

[Dan Heidinga]

On Mon, 2 Feb 2026 23:03:40 GMT, Paul Hübner <phubner at openjdk.org> wrote:

>> Hi all,
>> 
>> This change removes the old substitutability test method. The new/alt substitutability test takes the place of the legacy test, and all identifiers with "alt" are removed.
>> 
>> Testing: tiers 1-5 on Linux (x64, AArch64), macOS (x64, AArch64), Windows (x64).
>
> Paul Hübner 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 13 additional commits since the last revision:
> 
>  - Merge branch 'lworld' of https://github.com/openjdk/valhalla into JDK-8372954
>  - Missed obsolete test
>  - Years
>  - Merge branch 'lworld' of https://github.com/openjdk/valhalla into JDK-8372954
>  - substitutability contract changed
>  - Legacy handling in ProcessHandleImpl
>  - typo
>  - Test flags
>  - Dead stuff
>  - Merge branch 'JDK-8372954' of github.com:Arraying/valhalla into JDK-8372954
>  - ... and 3 more: https://git.openjdk.org/valhalla/compare/f3a1a179...29344379

Apart from adding the comment, this looks good to me

src/hotspot/share/classfile/classFileParser.cpp line 1399:

> 1397:   // one for the field the JVM injects when detecting an empty inline class
> 1398:   const int total_fields = length + num_injected + (is_inline_type ? 2 : 0)
> 1399:                            + (is_value_class ? 1 : 0);

Can you update the comment block above to include something like:

// all value classes, even abstract ones, get an additional slot for the acmp_maps field used by the substitutability check


We need something to make it clear why we're testing both inline type and value class here and what the new field is

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PR Review: https://git.openjdk.org/valhalla/pull/2012#pullrequestreview-3744873855
PR Review Comment: https://git.openjdk.org/valhalla/pull/2012#discussion_r2758735750