RFR: 8339168: Optimize ClassFile Util slotSize [v6]

[Claes Redestad]

On Wed, 4 Sep 2024 23:25:30 GMT, Shaojin Wen <swen at openjdk.org> wrote:

>> A small optimization to improve the performance of jdk.internal.classfile.impl.Util#slotSize/isDoubleSlot
>
> Shaojin Wen has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'upstream/master' into optim_util_slotSize_20240828
>  - Merge remote-tracking branch 'upstream/master' into optim_util_slotSize_20240828
>  - suggestion from @cl4es
>  - add benchmark
>  - suggestion from @liach & @cl4es
>  - Suggestions from @cl4es
>  - optimize slotSize & isDoubleSlot

I don't think this microbenchmark is worth it. 

It's fine as an experiment and to motivate and include numbers for this PR, but micros we commit into the OpenJDK should limit themselves to public APIs (unless it's critical to have an isolated test for some reason).

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Changes requested by redestad (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/20747#pullrequestreview-2281613017