RFR: 8295555: Primitive wrapper caches could be `@Stable`

[Per Minborg]

On Mon, 12 Jun 2023 14:25:42 GMT, Per Minborg <pminborg at openjdk.org> wrote:

> This PR proposes adding `@Stable` to certain wrapper classes' cache arrays (e.g. `Integer` and `Long`).
> 
> Comments are welcome as to how to improve the VM's handling now that the backing cache array is `@Stable`. Are there simplifications to be made or are there other optimizations we might add?

The performance is similar with this PR compared to the base line:

Before:

Benchmark         (size)  Mode  Cnt  Score   Error  Units
Integers.valueOf     500  avgt   15  0.652 ± 0.003  ns/op


After

Benchmark         (size)  Mode  Cnt  Score   Error  Units
Integers.valueOf     500  avgt   15  0.649 ± 0.003  ns/op



    @State(Scope.Thread)
    public static class Data {
       int value = 42;
    }
    
    ...
    
    @Benchmark
    public void valueOf(Data data, Blackhole bh) {
        bh.consume(Integer.valueOf(data.value));
    }

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PR Comment: https://git.openjdk.org/jdk/pull/14418#issuecomment-1587463431