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 pull request now contains four commits:
> 
>  - 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

src/jdk.compiler/share/classes/com/sun/tools/javac/jvm/Target.java line 210:

> 208:      * instance state.
> 209:      */
> 210:     public boolean omitUnusedPrivateSyntheticEnclosingInstanceFields() {

nit: what about a shorter name for this one?

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