<i18n dev> RFR: 8366178: Implement JEP 526: Lazy Constants (Second Preview)

[Per Minborg]

On Sat, 4 Oct 2025 04:13:05 GMT, Chen Liang <liach at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/Optional.java line 74:
>> 
>>> 72:      * If non-null, the value; if null, indicates no value is present
>>> 73:      */
>>> 74:     @Stable
>> 
>> Shouldn’t this also add a null sentinel to allow the folding of the empty case? Or is that irrelevant because empty would be the terminator of a chain.
>
> Usually a null sentinel is used when null indicates something different. I think maybe to allow folding the empty case, we should probably add a new annotation or a new element-value to indicate this status and properly handle it in C1/C2 (similar to the field trusting in ciField)

I've added two new benchmarks:


    private static final LazyConstant<Optional<Integer>> OPTIONAL_42 = LazyConstant.of(() -> Optional.of(42));
    private static final LazyConstant<Optional<Integer>> OPTIONAL_42_2 = LazyConstant.of(() -> Optional.of(42));
    private static final LazyConstant<Optional<Integer>> OPTIONAL_EMPTY = LazyConstant.of(Optional::empty);
    private static final LazyConstant<Optional<Integer>> OPTIONAL_EMPTY2 = LazyConstant.of(Optional::empty);
    
    ...
    
        @Benchmark
    public int staticOptional42() {
        return OPTIONAL_42.get().orElseThrow() + OPTIONAL_42_2.get().orElseThrow();
    }

    @Benchmark
    public boolean staticOptionalEmpty() {
        return OPTIONAL_EMPTY.get().isEmpty() ^ OPTIONAL_EMPTY2.get().isEmpty();
    }

    


Which gives:


Benchmark                              Mode  Cnt  Score   Error  Units
StableValueBenchmark.staticOptional42  avgt   10  0.354 ± 0.045  ns/op

Benchmark                                 Mode  Cnt  Score   Error  Units
StableValueBenchmark.staticOptionalEmpty  avgt   10  0.370 ± 0.030  ns/op


So, both `Optional` variants appears to support constant folding.

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PR Review Comment: https://git.openjdk.org/jdk/pull/27605#discussion_r2426044826