RFR: 8287442: Reduce list to array conversions in java.lang.invoke.MethodHandles

[Rob Spoor]

On Fri, 27 May 2022 14:18:19 GMT, Claes Redestad <redestad at openjdk.org> wrote:

> In preparation of #8855 this PR refactors the conversions from `List` to array and array to `List`, reducing the number of conversions when calling `MethodHandles.dropArguments` in particular. This remove about ~5% of allocations on the `StringConcatFactoryBootstraps` microbenchmark.

src/java.base/share/classes/java/lang/invoke/MethodHandles.java line 5266:

> 5264:      */
> 5265:     public static MethodHandle dropArguments(MethodHandle target, int pos, List<Class<?>> valueTypes) {
> 5266:         return dropArguments(target, pos, valueTypes.toArray(new Class<?>[0]).clone(), true);

Isn't this call to `clone()` unnecessary, as `valueTypes.toArray` should either return the passed empty array, or a newly created array?

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PR: https://git.openjdk.java.net/jdk/pull/8923