RFR: 8339290: Optimize ClassFile Utf8EntryImpl#writeTo [v2]

[Claes Redestad]

On Fri, 30 Aug 2024 05:24:58 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> Use fast path for ascii characters 1 to 127 to improve the performance of writing Utf8Entry to BufferWriter.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   add comments

Do you have any benchmark numbers of note to support this?

src/java.base/share/classes/java/lang/StringCoding.java line 37:

> 35:     private StringCoding() { }
> 36: 
> 37:     public static boolean hasNegativeOrZeros(byte[] ba) {

Wait a second.. since you're only interested in and calling this when `s.coder == LATIN1` then values can't be negative. Which means all you really need is something like this:


  public static boolean isLatin1WithNoZeros(String s) {
      return s.isLatin() && s.indexOf(0) < 0;
  }


`indexOf` have intrinsic support and might perform better than a simple for-loop.

src/java.base/share/classes/java/lang/System.java line 2598:

> 2596: 
> 2597:             public boolean hasNegativeOrZeros(String s) {
> 2598:                 return s.coder() == String.UTF16 || StringCoding.hasNegativeOrZeros(s.value());

Avoid adding logic to methods in `*Access` bridges, define `hasNonPositives(String s)` (or `isLatin1WithNoZeros(String)`) in `StringCoding` instead.

-------------

Changes requested by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20772#pullrequestreview-2272579498
PR Review Comment: https://git.openjdk.org/jdk/pull/20772#discussion_r1738816044
PR Review Comment: https://git.openjdk.org/jdk/pull/20772#discussion_r1738821539