RFR: 8338930: StringConcatFactory hardCoded string concatenation strategy [v10]

[Claes Redestad]

On Sun, 8 Sep 2024 05:01:53 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> This is a follow-up to PR #20273, which improves performance when the number of parameters exceeds 20.
>> 
>> When the number of parameters is large, the possibility of reuse will be lower, so we can use the static concat method and write the length and coder directly into the bytecode to solve the performance regression problem.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   from @ExE-Boss 's suggestion

I think this is a reasonable addition and could prove to be an interesting tuning in some applications. But I'd prefer this to be an opt-in feature initially, i.e. setting `java.lang.invoke.StringConcat.cacheThreshold` default value to something like 256. Get the opt-in feature out into a release, advertise its presence, battle-test it and see if there's a sweet spot that we might converge towards as a default with empirical data.

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Changes requested by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20675#pullrequestreview-2288571602