RFR: 8350607: Consolidate MethodHandles::zero into MethodHandles::constant [v2]

[Chen Liang]

On Tue, 25 Feb 2025 21:38:58 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> Chen Liang has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   We no longer load DelegateMH as we no longer rebind
>
> src/java.base/share/classes/java/lang/invoke/MethodHandleImpl.java line 2241:
> 
>> 2239:         var form = constantForm(basicType);
>> 2240: 
>> 2241:         if (type.isPrimitive()) {
> 
> I think you could simplify this using `Wrapper.forBasicType`; all variants should be able to use `wrapper.convert`

The cast is not performed if the `type` is an interface; this is a behavioral disparity with the old `value = ptype.cast(value);` in `insertArguments`.

> src/java.base/share/classes/java/lang/invoke/MethodHandles.java line 4874:
> 
>> 4872:         Objects.requireNonNull(type);
>> 4873:         return type.isPrimitive() ? primitiveZero(Wrapper.forPrimitiveType(type))
>> 4874:                 : MethodHandleImpl.makeConstantReturning(type, null);
> 
> Not sure if it's important but the existing impl would cache `zero(Object.class)` while this new impl won't. Behaviorally neutral for any other reference type, though.

`type == Object.class` can use the primitive path, but I am too lazy to add another of this check.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23706#discussion_r1970611614
PR Review Comment: https://git.openjdk.org/jdk/pull/23706#discussion_r1970616917