Java: Improve join-order for FunctionalInterface.

[aschackmull]

Reimplements #13357

As reported by @rvermeulen, for very large code bases the current join order (find all interface abstract methods, join with all overrides of those methods, check if the interface also inherits a concrete override) can blow up

[smowton]

lgtm if you've confirmed this results in the desired join order (first join with concrete (default) methods this interface inherits, then match against the candidate abstract method)

[aschackmull]

lgtm if you've confirmed this results in the desired join order (first join with concrete (default) methods this interface inherits, then match against the candidate abstract method)

I have. Also, that's exactly what bindingset[m] pragma[inline_late] ensures.

[aschackmull]

I've additionally added a piece of manual magic in the form of "overrides something" m.overrides(_) as that improves things quite a bit further.

[smowton]

Sounds good -- I have no intuition as to what late inlining is going to do!

[aschackmull]

I have no intuition as to what late inlining is going to do!

Late inlining means "join-order first, then inline". It works in conjunction with the bindingset, such that the bindingset provides join-order restrictions. In this case m is required to be bound before the predicate can be chosen, so something that binds m must be join-ordered before.