RFR: 8369654: javac OutOfMemoryError for complex intersection type [v12]

[Maurizio Cimadamore]

On Sat, 1 Nov 2025 12:25:47 GMT, Vicente Romero <vromero at openjdk.org> wrote:

>> 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 ...
>
> Vicente Romero 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 16 additional commits since the last revision:
> 
>  - Merge branch 'master' into JDK-8369654
>  - fixing comment
>  - adding some doc
>  - delta changes
>  - simplifying code
>  - adding more array support
>  - missing supertype
>  - another change
>  - another fix
>  - minor fixes
>  - ... and 6 more: https://git.openjdk.org/jdk/compare/fc64c841...34e2d9d4

Very good -- thanks!

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

Marked as reviewed by mcimadamore (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28050#pullrequestreview-3410285240