RFR: 8301958: Reduce Arrays.copyOf/-Range overheads [v7]

[David Schlosnagle]

On Wed, 8 Feb 2023 00:07:14 GMT, Claes Redestad <redestad at openjdk.org> wrote:

>> This patch adds special-cases to `Arrays.copyOf` and `Arrays.copyOfRange` to clone arrays when `newLength` or range inputs span the input array. 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:
> 
>   Minimize, force inline, generalize

src/java.base/share/classes/java/util/Arrays.java line 3594:

> 3592:     public static int[] copyOf(int[] original, int newLength) {
> 3593:         if (newLength == original.length) {
> 3594:             return original.clone();

I am curious about the use of `clone ` for some primitive array types and `copyOf` using `System.arraycopy` in other types (e.g. `byte[]`). Do these types optimize differently or hit different intrinsics depending on primitive type? Is there difference in array zeroing?

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