RFR: 8338930: StringConcatFactory hardCoded string concatenation strategy [v2]

[Shaojin Wen]

On Sun, 25 Aug 2024 12:12:42 GMT, Shaojin Wen <duke 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:
> 
>   Revert "Optimize the construction of MethodType and MethodTypeDesc to reduce memory allocation"
>   
>   This reverts commit 3bed7290f5cb987e86407f698fb0598f19d65628.

If the number of parameters is greater than 2, the probability of reuse may not be high. Using hard-coded constants can avoid the use of forceinline.

>From this PR, adding hard-coded constants only requires a small change, which may be a good solution.

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PR Comment: https://git.openjdk.org/jdk/pull/20675#issuecomment-2308823147