RFR: 8355177: Speed up StringBuilder::append(char[]) via UTF16::compress & Unsafe::copyMemory [v4]

[Markus KARG]

On Fri, 2 May 2025 03:49:39 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> In BufferedReader.readLine and other similar scenarios, we need to use StringBuilder.append(char[]) to build the string.
>> 
>> For these scenarios, we can use the intrinsic method StringUTF16.compress and Unsafe.copyMemory instead of the character copy of the char-by-char loop to improve the speed.
>
> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains seven commits:
> 
>  - Merge remote-tracking branch 'upstream/master' into optim_sb_append_chars_202504
>    
>    # Conflicts:
>    #	src/java.base/share/classes/java/lang/AbstractStringBuilder.java
>  - Merge remote-tracking branch 'upstream/master' into optim_sb_append_chars_202504
>    
>    # Conflicts:
>    #	src/java.base/share/classes/java/lang/StringUTF16.java
>  - putCharsUnchecked
>  - copyright
>  - Using StringUTF16.compress to speed up LATIN1 StringBuilder append(char[])
>  - Using Unsafe.copyMemory to speed up UTF16 StringBuilder append(char[])
>  - add append(char[]) benchmark

> ```java
> >         char[] ca = new char[end - off];
> ```
> 
> Your code here has a memory allocation, which may cause slowdown

This is exactly what I wanted to express with my posting.

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PR Comment: https://git.openjdk.org/jdk/pull/24773#issuecomment-2846485487