Fix #9058: disable failing performance optimization during implicits lookup

[anatoliykmetyuk]

No description provided.

[anatoliykmetyuk]

test performance please

[dottybot]

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

[odersky]

Can you explain why the disabled lines violate the transitivity contract?

[odersky]

Oh, I think I see it:

object A extends B
class C extends A

Then C <: A$ and A$ <: B but we do not have C <: B.

But maybe we should just drop these two lines in compareOwner instead:

    else if (sym2.is(Module)) compareOwner(sym1, sym2.companionClass)
    else if (sym1.is(Module)) compareOwner(sym1.companionClass, sym2)

Can you try that?

[odersky]

In fact, my previous suggestion fails tastyBootstrap. But the following version should work:

  def compareOwner(sym1: Symbol, sym2: Symbol)(using Context): Int =
    if sym1 == sym2 then 0
    else if sym1.isSubClass(sym2) then 1
    else if sym2.isSubClass(sym1) then -1
    else if sym1.is(Module) && sym2.is(Module) then
      compareOwner(sym1.companionClass, sym2.companionClass)
    else 0

EDIT: It does not. Here's a counter example:

A <: B, B$ <: C
then
A$ <: B$, B$ <: C
yet not
A$ <: C

[dottybot]

Performance test finished successfully:

Visit http://dotty-bench.epfl.ch/9060/ to see the changes.

Benchmarks is based on merging with master (2116281)

[odersky]

In fact there was also somehthing wrong with prefer. Function arity should be compared before owner subclasses.

[anatoliykmetyuk]

Superseded by #9065.