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

[Claes Redestad]

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.

Another datapoint is the `MethodHandlesDropArguments.interCreate` microbenchmark which explicitly tests `MethodHandles.dropArguments` (with a minimal argument list):

Before:

Benchmark                                                                Mode  Cnt     Score    Error   Units
MethodHandlesDropArguments.interCreate                                   avgt    5   136.778 ?  1.265   ns/op
MethodHandlesDropArguments.interCreate:?gc.alloc.rate.norm               avgt    5   264.020 ?  0.021    B/op

Patch:

Benchmark                                                                Mode  Cnt     Score     Error   Units
MethodHandlesDropArguments.interCreate                                   avgt    5   120.536 ?   3.133   ns/op
MethodHandlesDropArguments.interCreate:?gc.alloc.rate.norm               avgt    5   220.818 ?  41.309    B/op

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