Allocate fewer TypeMaps and TypeAccumulators #9618
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test performance please |
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performance test scheduled: 17 job(s) in queue, 1 running. |
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Performance test finished successfully: Visit http://dotty-bench.epfl.ch/9618/ to see the changes. Benchmarks is based on merging with master (387c562) |
liufengyun
approved these changes
Aug 24, 2020
| def foldArgs(x: T, args: List[Type]): T = args match | ||
| case arg :: rest => foldArgs(op(x, arg), rest) | ||
| case nil => x | ||
| foldArgs(op(x, tycon), args) |
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In map and fold, do we need to recurse on typcon? The semantics is quite different from TypeMap and TypeAccumulator, and is specific to Substituters. Maybe add a note here to avoid misuse?
| } | ||
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| final class SubstThisMap(from: ClassSymbol, to: Type)(using Context) extends DeepTypeMap { | ||
| def apply(tp: Type): Type = substThis(tp, from, to, this) | ||
| def apply(tp: Type): Type = substThis(tp, from, to, this)(using mapCtx) |
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Does it mean all classes that inherit TypeMap (e.g. DeepTypeMap, ApproximatingTypeMap and AsSeenFromMap) have to write using mapCtx explicitly everywhere?
There's something problematic going on here. TypeMaps usually take a context as a parameter, which becomes a private parameter acessor field. That parameter shadows the mapCtx field inherited from TypeMap. `mapCtx` is a variable that is temporarily mutated when mapping LazyRefs. But since it is shadowed, such mutations do not affect code that is defined in the subclass of TypeMap. One fix is to explicitly pass mapCtx to all code that is called from the maps. That's what's done here for substituters. There might be other solutions as well, which have to be tried out.
This was referenced Dec 31, 2020
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Delay allocation of TypeMap and TypeAccumulators by handling common cases directly
before doing an allocation. The biggest win is handling AppliedTypes directly. This risks
creating more than one map instance, since function part and every argument might
in the end require a map. But looking at stats shows that the benefits largely outweigh
the costs.