RFR: 8369654: javac OutOfMemoryError for complex intersection type [v8]

[Vicente Romero]

> Javac is throwing an OOME for the code like:
> 
> class Test {
>     interface WithMixin01<T> {}
>     // ...
>     // 20 interfaces here
>     interface WithMixin20<T> {}
> 
>     interface ClientA extends
>             WithMixin02<ClientA>,
>             WithMixin01<ClientA>,
>             WithMixin03<ClientA>,
>             WithMixin04<ClientA>,
>             WithMixin05<ClientA>,
>             WithMixin06<ClientA>,
>             WithMixin07<ClientA>,
>             WithMixin08<ClientA>,
>             WithMixin09<ClientA>,
>             WithMixin10<ClientA>,
>             WithMixin11<ClientA>,
>             WithMixin12<ClientA>,
>             WithMixin13<ClientA>,
>             WithMixin14<ClientA>,
>             WithMixin15<ClientA>,
>             WithMixin16<ClientA>,
>             WithMixin17<ClientA>,
>             WithMixin18<ClientA>,
>             WithMixin19<ClientA>,
>             WithMixin20<ClientA> {
>     }
> 
>     interface ClientB extends
>             WithMixin01<ClientB>,
>             WithMixin02<ClientB>,
>             WithMixin03<ClientB>,
>             WithMixin04<ClientB>,
>             WithMixin05<ClientB>,
>             WithMixin06<ClientB>,
>             WithMixin07<ClientB>,
>             WithMixin08<ClientB>,
>             WithMixin09<ClientB>,
>             WithMixin10<ClientB>,
>             WithMixin11<ClientB>,
>             WithMixin12<ClientB>,
>             WithMixin13<ClientB>,
>             WithMixin14<ClientB>,
>             WithMixin15<ClientB>,
>             WithMixin16<ClientB>,
>             WithMixin17<ClientB>,
>             WithMixin18<ClientB>,
>             WithMixin19<ClientB>,
>             WithMixin20<ClientB> {
>     }
> 
>     public static void main(String... args) {
>         ClientA a = null;
>         ClientB b = null;
>         String selector = "a";
>         Object o = switch (selector) {
>             case "a" -> a;
>             case "b" -> b;
>             default -> null;
>         };
>     }
> }
> 
> the reason is that after [JDK-8353565](https://bugs.openjdk.org/browse/JDK-8353565) we are using Types::lub when joining jump chains in Code. The result of the lub will be erased anyways so the proposal here is to cut in the result given by lub types that will be erased anyways. The reason for the slow lub invocation here is that in order to obtain the lub in this case, the lub method is invoked several times. Each invocation, minus the first one, with very complex types which makes them very slooooow.
> 
> TIA

Vicente Romero has updated the pull request incrementally with one additional commit since the last revision:

  simplifying code

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/28050/files
  - new: https://git.openjdk.org/jdk/pull/28050/files/cff29576..dd862d62

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=28050&range=07
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=28050&range=06-07

  Stats: 51 lines in 1 file changed: 11 ins; 29 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/28050.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28050/head:pull/28050

PR: https://git.openjdk.org/jdk/pull/28050