[lworld] RFR: 8370450: [lworld] Alternate implementation of the substitutability test method [v2]

[Roger Riggs]

On Wed, 22 Oct 2025 18:17:30 GMT, Frederic Parain <fparain at openjdk.org> wrote:

>> This is an alternate version of the substitutability method.
>> To use it, add -Xshare:off -XX:+UseAltSubstitutabilityMethod to the command line of the Valhalla VM in preview mode.
>
> Frederic Parain has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains two commits:
> 
>  - Merge remote-tracking branch 'upstream/lworld' into new_acmp
>  - Add alternate version of the substitutability method

When comparing the oops, do they need some additional handling?
Supposing for example, they are buffered value objects (from different sources).
It seems necessary to recurse (effectively) with those oops/refs.

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PR Comment: https://git.openjdk.org/valhalla/pull/1695#issuecomment-3438994804