RFR: 8351565: Implement JEP 502: Stable Values (Preview) [v25]

[Maurizio Cimadamore]

On Wed, 2 Apr 2025 11:43:40 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> I didn't mean to say "this is not true, so use a `static final` instead". What I meant was more "let's not dive into VM-specific details now" (see my other comment on the topic), and just focus on semantics instead. Then let's put all the constant-folding related stuff somewhere else. I liked using non-static final fields!
>
> Basically: drop all references to "performance" and "constant folding" everywhere. And then introduce a section dedicated to that topic which talks a bit about how the content of a SV is trusted not to change by the JVM, which enables constant-folding optimizations.

The reason I'm suggesting this is that what's constant-folded is kind of a moving target, so we don't want to say/promise too much. For now, we can say that if the SV, or the stable function/collection is stored in a static/final field then its content will be constant-folded. But we know that there's other stuff in the pipeline (e.g. [this JEP](https://openjdk.org/jeps/8349536)) which will affect this picture, and enable for more constant-folding when accessing SV and stable functions/collections.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23972#discussion_r2024659484