[lworld] RFR: 8351569: [lworld] Revisit atomic access modes in flat var handles [v2]

[Maurizio Cimadamore]

On Fri, 21 Mar 2025 15:35:37 GMT, Chen Liang <liach at openjdk.org> wrote:

>> I have considered avoiding the array creation -- but that is messy because it means you have to deal with nulls directly. E.g. if either `expected` or `x` are `null`, what is their corresponding numeric configuration? Going through an array element allows the code to remain agnostic as to how nulls are represented. Another way to avoid array creation would be to have some way to unsafely get the payload of a value as a long, including null channel and everything.
>
> I think runtime support is better for down the road for this part.

We have decided to address this by adding a primitive to create a flat array with given known layout:
https://github.com/openjdk/valhalla/pull/1404

Once that API is integrated, I will rebase this PR on top of that.

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PR Review Comment: https://git.openjdk.org/valhalla/pull/1402#discussion_r2007902690