Alex Hoppen 640cfac61c [CodeComplete] Compute type relations for global cached results ...

Computing the type relation for every item in the code completion cache is way to expensive (~4x slowdown for global completion that imports `SwiftUI`). Instead, compute a type’s supertypes (protocol conformances and superclasses) once and write their USRs to the cache. To compute a type relation we can then check if the contextual type is in the completion item’s supertypes.

This reduces the overhead of computing the type relations (again global completion that imports `SwiftUI`) to ~6% – measured by instructions executed.

Technically, we might miss some conversions like
- retroactive conformances inside another module (because we can’t cache them if that other module isn’t imported)
- complex generic conversions (just too complicated to model using USRs)

Because of this, we never report an `unrelated` type relation for global items but always default to `unknown`.

But I believe this change covers the most common cases and is a good tradeoff between accuracy and performance.

rdar://83846531

2022-03-01 09:16:23 +01:00

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