RFR: 8339290: Optimize ClassFile Utf8EntryImpl#writeTo [v8]

[Claes Redestad]

On Mon, 2 Sep 2024 15:27:59 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:
> 
>   typo

Thanks for focusing the benchmark! 

Even with the suggested correction to the `Unsafe` vector loop, simplifying to just a simple scalar loop seem to be a net improvement across modes. I think this method could be turned into an intrinsic piggy-backing on countPositives if we find more leverage for it (`DataOutputStream::writeUTF` is a good candidate)

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

PR Comment: https://git.openjdk.org/jdk/pull/20772#issuecomment-2325185111