[lworld] RFR: 8375320: [lworld] Revert System.identityHashcode for value objects to non AltSubstitutability version

[Roger Riggs]

On Wed, 14 Jan 2026 21:57:37 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> Restore the unconditional use of value_object_hash_code_method. 
> The Alt hashcode method based on the Unsafe.getFieldMap is not used.
> System.identityHashCode uses ValueObjectMethods.valueObjectHashCode() implemented using the original method-handle implementation.

A quick review would get this broken change reverted.

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PR Comment: https://git.openjdk.org/valhalla/pull/1907#issuecomment-3756067323