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

[Jorn Vernee]

On Mon, 24 Feb 2025 23:45:37 GMT, Chen Liang <liach at openjdk.org> wrote:

>> LF editor spins classes, this avoids the spinning overhead and should speed up non-capturing lambdas too.
>> 
>> There may need to be additional intrinsic work for MH combinator lf bytecode generation.
>
> 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/LambdaForm.java line 1658:

> 1656:         var carrier = argument(0, L_TYPE).withConstraint(species); // BMH bound with data
> 1657:         Name[] constNames = new Name[] { carrier, new Name(species.getterFunction(0), carrier) };
> 1658:         return LF_constant[type.ordinal()] = create(1, constNames, Kind.CONSTANT);

I think this caching logic should be in `constantForm`, which also does the cache lookup.

src/java.base/share/classes/java/lang/invoke/LambdaFormEditor.java line 972:

> 970:                 callFilter = null;
> 971:             else
> 972:                 callFilter = new Name(LambdaForm.identity(newType), newType.btWrapper.zero());

Maybe we could have a `Name` constructor that just takes an `Object` and returns it like this.

test/hotspot/jtreg/runtime/cds/appcds/dynamicArchive/TestDynamicRegenerateHolderClasses.java line 42:

> 40:     static String CHECK_MESSAGES[] = {"java.lang.invoke.Invokers$Holder source: shared objects file (top)",
> 41:                                       "java.lang.invoke.DirectMethodHandle$Holder source: shared objects file (top)",
> 42:                                       "java.lang.invoke.DelegatingMethodHandle$Holder source: shared objects file (top)",

I don't understand why this change is needed. Could you please explain it?

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PR Review Comment: https://git.openjdk.org/jdk/pull/23706#discussion_r1979282388
PR Review Comment: https://git.openjdk.org/jdk/pull/23706#discussion_r1979441441
PR Review Comment: https://git.openjdk.org/jdk/pull/23706#discussion_r1979454377