[lworld] RFR: 8370714: [lworld] Reimplement System.identityHashCode for Value Objects

[Chen Liang]

On Fri, 5 Dec 2025 21:24:41 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

> The alternate hashcode compution is enabled when the alternate subsitutability method is enabled with: `-XX:+UseAltSubstitutabilityMethod`. 
> The IdentityHashCode is computed using the map of field offsets and sizes from Unsafe. 
> The basis of hashCode is the the hashCode of the object's class mixing in the values from the memory where the fields are placed and the hashCode of each reference.
> 
> The changes to Hotspot invoke the original or the alternate Java method based on the VM `UseAltSubstitutabilityMethod` command line flag.

Ok

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Marked as reviewed by liach (Committer).

PR Review: https://git.openjdk.org/valhalla/pull/1773#pullrequestreview-3546806156