RFR: 8302818: Optimize wrapper sets and immutable sets of Enums [v5]

[Tingjun Yuan]

On Tue, 21 Feb 2023 03:39:46 GMT, Tingjun Yuan <duke at openjdk.org> wrote:

>> Currently, the two subclasses of `java.util.EnumSet` optimize bulk operations when the argument is also a `EnumSet`, but there is no such optimization for wrapper sets (returned by `Collections.unmodifiableSet`, `Collections.synchronizedSet`, etc.) and immutable sets (returned by `Set.of` methods) of `Enum`s.
>> 
>> This PR introduces optimization classes for these situations.  No public APIs are changed.
>
> Tingjun Yuan has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Set.copyOf: need defensive copy

Thanks again for reviewing. Correct me if I'm wrong.

@cl4es I need to add these new wrapper classes `{Unmodifiable,Synchronized}{Regular,Jumbo}EnumSet` to implement interfaces `{Regular,Jumbo}EnumSetCompatible`, just like `*RandomAccessList` which appear to implement `RandomAccess`. I don't think removing these wrapper classes and introducing accessors is a good idea, because I will have to check for the wrapper classes in bulk operation methods, which are used more frequently.

@pavelrappo `{Unmodifiable,Sychronized}Set` also have subclasses implementing `SortedSet` and `NavigableSet`, I'm not sure whether `instanceof` is safe for these subclasses.

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PR Comment: https://git.openjdk.org/jdk/pull/12498#issuecomment-1478658361