RFR: 8332249: Micro-optimize Method.hashCode

[Sean Gwizdak]

On Tue, 28 May 2024 17:25:34 GMT, Sean Gwizdak <duke at openjdk.org> wrote:

> Improve the speed of Method.hashCode by caching the hashcode on first use. I've seen an application where Method.hashCode is a hot path, and this is a fairly simple speedup. The memory overhead is low. 
> 
> This addresses issue [JDK-8332249](https://bugs.openjdk.org/browse/JDK-8332249). 
> 
> Before:
> 
> Benchmark                         Mode  Cnt  Score   Error  Units
> # Intel Skylake
> MethodHashCode.benchmarkHashCode  avgt    5  1.843 ± 0.149  ns/op
> # Arm Neoverse N1
> MethodHashCode.benchmarkHashCode  avgt    5  2.363 ± 0.091  ns/op
> 
> 
> 
> After:
> 
> 
> Benchmark                         Mode  Cnt  Score   Error  Units
> # Intel Skylake
> MethodHashCode.benchmarkHashCode  avgt    5  1.121 ± 1.189  ns/op
> # Arm Neoverse N1
> MethodHashCode.benchmarkHashCode  avgt    5  1.001 ± 0.001  ns/op

Minor change after draft review -- moved Method hashCode benchmark into the newly created MethodBenchmark file.

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PR Comment: https://git.openjdk.org/jdk/pull/19433#issuecomment-2145806129