Performance improvement: Avoid most operations in interpolateUndetVars

Perform the operation only if there are qualifying type variables, which is rarely the case.
Reverted variances optimization to simpler and shorter previous implementation, because variances
is no longer hot.

2 files changed, 13 insertions, 49 deletions

diff --git a/src/dotty/tools/dotc/core/TypeOps.scala b/src/dotty/tools/dotc/core/TypeOps.scala
index 6070b4f49..272e93dd3 100644
--- a/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/src/dotty/tools/dotc/core/TypeOps.scala
@@ -113,54 +113,6 @@ trait TypeOps { this: Context =>
     }
   }
 
-  type VarianceMap = SimpleMap[TypeVar, Integer]
-
-  /** Add occurrences of type variables in type `tp` to variance map `vmap` */
-  final def addVariances(vmap: VarianceMap, tp: Type, variance: Int, include: TypeVar => Boolean, accu: VariancesAccumulator): VarianceMap = tp match {
-    case tp: TypeRef =>
-      if (tp.symbol.isStatic) vmap
-      else {
-        val prefix = tp.prefix
-        val tp1 = tp.lookupRefined(prefix, tp.name)
-        addVariances(vmap, if (tp1.exists) tp1 else prefix, variance, include, accu)
-      }
-    case tp: TermRef =>
-      if (tp.symbol.isStatic) vmap
-      else addVariances(vmap, tp.prefix, variance, include, accu)
-
-    case _: ThisType
-      | _: BoundType
-      | NoPrefix => vmap
-
-    case tp: RefinedType =>
-      addVariances(
-        addVariances(vmap, tp.parent, variance, include, accu),
-        tp.refinedInfo, variance, include, accu)
-
-    case bounds @ TypeBounds(lo, hi) if lo eq hi =>
-      addVariances(vmap, lo, variance * bounds.variance, include, accu)
-
-    case tp: TypeVar if !tp.isInstantiated && (typerState.constraint contains tp) && include(tp) =>
-      val v = vmap(tp)
-      if (v == null) vmap.updated(tp, variance)
-      else if (v == variance) vmap
-      else vmap.updated(tp, 0)
-
-    case _ =>
-      (if (accu != null) accu else new VariancesAccumulator(include)).runOver(vmap, tp, variance)
-  }
-
-  class VariancesAccumulator(include: TypeVar => Boolean) extends TypeAccumulator[VarianceMap] {
-    def apply(vmap: VarianceMap, tp: Type): VarianceMap = addVariances(vmap, tp, variance, include, this)
-    def runOver(vmap: VarianceMap, tp: Type, variance: Int): VarianceMap = {
-      val saved = this.variance
-      this.variance = variance
-      val result = foldOver(vmap, tp)
-      this.variance = saved
-      result
-    }
-  }
-
   private def enterArgBinding(formal: Symbol, info: Type, cls: ClassSymbol, decls: Scope) = {
     val lazyInfo = new LazyType { // needed so we do not force `formal`.
       def complete(denot: SymDenotation)(implicit ctx: Context): Unit = {
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 00d719acb..5c65b7ede 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -838,7 +838,19 @@ object Types {
      *  0 means: mixed or non-variant occurrences
      */
     def variances(include: TypeVar => Boolean)(implicit ctx: Context): VarianceMap = track("variances") {
-      ctx.addVariances(SimpleMap.Empty, this, +1, include, null)
+      val accu = new TypeAccumulator[VarianceMap] {
+        def apply(vmap: VarianceMap, t: Type): VarianceMap = t match {
+          case t: TypeVar
+          if !t.isInstantiated && (ctx.typerState.constraint contains t) && include(t) =>
+            val v = vmap(t)
+            if (v == null) vmap.updated(t, variance)
+            else if (v == variance) vmap
+            else vmap.updated(t, 0)
+          case _ =>
+            foldOver(vmap, t)
+        }
+      }
+      accu(SimpleMap.Empty, this)
     }
 
     /** A simplified version of this type which is equivalent wrt =:= to this type.