RFR: 8336831: Optimize StringConcatHelper.simpleConcat [v6]

[Chen Liang]

On Tue, 23 Jul 2024 12:16:00 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> Currently simpleConcat is implemented using mix and prepend, but in this simple scenario, it can be implemented in a simpler way and can improve performance.
>
> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:
> 
>  - merge from master
>  - Merge remote-tracking branch 'upstream/master' into optim_simple_concat_202407
>    
>    # Conflicts:
>    #	src/java.base/share/classes/java/lang/StringConcatHelper.java
>  - Update src/java.base/share/classes/java/lang/String.java
>    
>    Co-authored-by: Chen Liang <liach at openjdk.org>
>  - add comments
>  - handle null argument
>  - extract a common doConcat handling both non-empty strings
>  - share newArray
>  - copyright 2024
>  - optimize String.concat

Merge conflict fix looks good.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20253#pullrequestreview-2193860085