RFR: 8333893: Optimization for StringBuilder append boolean & null [v4]

[Claes Redestad]

On Tue, 11 Jun 2024 11:35:28 GMT, Shaojin Wen <duke at openjdk.org> wrote:

>> After PR https://github.com/openjdk/jdk/pull/16245, C2 optimizes stores into primitive arrays by combining values ​​into larger stores.
>> 
>> This PR rewrites the code of appendNull and append(boolean) methods so that these two methods can be optimized by C2.
>
> Shaojin Wen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   revert

Agreed we should look at obsoleting the `_putCharStringU` intrinsic. This is best done separately. If performance with the intrinsic disabled looks good here then I think this PR is good to go, even if temporarily subpar on the UTF16 tests. The microbenchmark will then serve as an extra verification step to show that disabling/removing the intrinsic is beneficial.

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PR Comment: https://git.openjdk.org/jdk/pull/19626#issuecomment-2162962297