RFR: addressing several issues in the implementation of universal tvars [v8]

[Maurizio Cimadamore]

On Wed, 8 Jun 2022 00:17:01 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> Last review iteration found several issues in the current implementation, addressing them here
>
> Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:
> 
>   merging StructuralTypeComparator and TypeArgStructComparator

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Types.java line 1378:

> 1376:         SubtypingRelation isSubtypeRelation = new SubtypingRelation();
> 1377:         class SubtypingRelation extends TypeRelation {
> 1378:             SubtypingRelationKind param;

What is this needed for? We should get into a position where subtyping is "just" subtyping, no need for having some kind of mode flag - unless I'm misunderstanding something?

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PR: https://git.openjdk.java.net/valhalla/pull/684