Reuse current ProvisionalState if it is still valid

Author: noti0na1

Diff for: compiler/src/dotty/tools/dotc/core/Types.scala

@@ -109,6 +109,12 @@ object Types extends TypeUtils {
     /** A cache indicating whether the type was still provisional, last time we checked */
     @sharable private var mightBeProvisional = true
 
+    // The provisonal state of a type stores the parts which could be changed and
+    // their info at a given point.
+    // For example, a `TypeVar` is provisional until it is permanently instantiated,
+    // and its info is the current instantiation.
+    type ProvisionalState = util.HashMap[Type, Type] | Null
+
     /** Is this type still provisional? This is the case if the type contains, or depends on,
      *  uninstantiated type variables or type symbols that have the Provisional flag set.
      *  This is an antimonotonic property - once a type is not provisional, it stays so forever.
@@ -120,13 +126,28 @@ object Types extends TypeUtils {
      */
     def isProvisional(using Context): Boolean = mightBeProvisional && currentProvisionalState != null
 
-    // The provisonal state of a type stores the parts which might be changed and their
-    // info at a given point.
-    // For example, a `TypeVar` is provisional until it is permently instantiated,
-    // and its info is the current instantiation.
-    type ProvisionalState = util.HashMap[Type, Type] | Null
+    private var myCurrentProvisionalState: ProvisionalState = null
+
+    private def isCurrentProvisionalStateValid(using Context): Boolean =
+      myCurrentProvisionalState != null
+      && myCurrentProvisionalState.uncheckedNN.iterator.forall: (tp, info) =>
+        tp.mightBeProvisional && tp.match
+          case tp: TypeRef =>
+            if tp.currentSymbol.isProvisional then tp eq info
+            else !tp.currentSymbol.isStatic && (tp.denot.infoOrCompleter eq info)
+          case tp: TypeVar =>
+            !tp.isPermanentlyInstantiated
+            && {
+              val inst = tp.instanceOpt
+              if inst.exists then inst eq info
+              else tp eq info
+            }
+          case tp: LazyRef =>
+            !tp.completed && (tp eq info)
+          case _ => false
 
     def currentProvisionalState(using Context): ProvisionalState =
+      if isCurrentProvisionalStateValid then return myCurrentProvisionalState
       var state: ProvisionalState = null
       inline def record(tp: Type, info: Type): Unit =
         if state == null then state = util.HashMap()
@@ -197,6 +218,7 @@ object Types extends TypeUtils {
         t.mightBeProvisional
       end test
       test(this, null)
+      myCurrentProvisionalState = state
       state
     end currentProvisionalState