Fall back to direct subtype comparison at the end in dropIfSuper and dropIfSub

[noti0na1]

Improve compiling in #20516.

We need to be careful to check branches of AndTypes and OrTypes in correct order, see discussion in issue #20516.

Fall back to direct subtype comparison at the end in dropIfSuper and dropIfSub.

We may need to improve subtype checking for large intersections further to be able to fully test the example.

Currently, tests/pos-deep-subtype/i20516.scala compiles in 5s with this PR, and in 40s on the main branch.

[noti0na1]

test performance please

[dottybot]

performance test scheduled: 1 job(s) in queue, 0 running.

[dottybot]

Performance test finished successfully:

Visit https://dotty-bench.epfl.ch/20523/ to see the changes.

Benchmarks is based on merging with main (dea3d10)

[odersky]

The code changes look reasonable, but we should check they don't introduce a performance regression elsewhere. Have a look at the discussion #20034. Can you run the test cases mentioned there and check whether they become significantly slower?

[noti0na1]

Can you run the test cases mentioned there and check whether they become significantly slower?

@odersky I compared the compiling time of i19907_*.scala, i12915.scala, i7034.scala, and other tests in deep-subtype between my fix and the main branch, and there is no difference.

[odersky]

OK, looks all good then.