RFR: 8301958: Reduce Arrays.copyOf/-Range overheads [v10]

[Claes Redestad]

On Mon, 13 Feb 2023 09:59:52 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This patch adds special-cases to `Arrays.copyOf` and `Arrays.copyOfRange` to copy arrays more efficiently when exactly the whole input array is to be copied. This helps eliminate range checks and has been verified to help various String operations. Example:
>> 
>> Baseline
>> 
>> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
>> StringConstructor.newStringFromArray                      7  avgt   15  16.817 ± 0.369  ns/op
>> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  16.866 ± 0.449  ns/op
>> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  22.198 ± 0.396  ns/op
>> 
>> Patch: 
>> 
>> Benchmark                                            (size)  Mode  Cnt   Score   Error  Units
>> StringConstructor.newStringFromArray                      7  avgt   15  14.666 ± 0.336  ns/op
>> StringConstructor.newStringFromArrayWithCharset           7  avgt   15  14.582 ± 0.288  ns/op
>> StringConstructor.newStringFromArrayWithCharsetName       7  avgt   15  20.339 ± 0.328  ns/op
>
> Claes Redestad has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Address review comments

Thanks for reviewng!

I've filed https://bugs.openjdk.org/browse/JDK-8302315 to investigate the clone/arraycopy performance discrepancy. Ideally we should be able to just do `array.clone()` here and get optimal performance with less code.

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PR: https://git.openjdk.org/jdk/pull/12453