RFR: 8271623: Omit enclosing instance fields from inner classes that don't use it [v4]

[Vicente Romero]

On Mon, 15 Nov 2021 20:18:06 GMT, Liam Miller-Cushon <cushon at openjdk.org> wrote:

>> This change omits the synthetic `this$0` field from inner classes that do not access any enclosing instance state.
>
> Liam Miller-Cushon 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 four additional commits since the last revision:
> 
>  - Don't remove enclosing instance fields from serializable classes without serialVersionUIDs
>  - Enable enclosing instance optimization for --release 18 and newer
>  - Add a test case with nested inner classes
>  - 8271623: Omit enclosing instance fields from inner classes that don't use it

made a first review of the code, looks good, still I would like to give another pass on it. Comment, do you still need to force the access to the outer class in all the test cases or does it make sense to provide a new golden file for some of them when applicable?

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PR: https://git.openjdk.java.net/jdk/pull/4966