diff --git a/compiler/src/dotty/tools/dotc/core/Types.scala b/compiler/src/dotty/tools/dotc/core/Types.scala
index c71ad928a7d2..4a103c7787fb 100644
--- a/compiler/src/dotty/tools/dotc/core/Types.scala
+++ b/compiler/src/dotty/tools/dotc/core/Types.scala
@@ -117,9 +117,12 @@ object Types {
             case t: TypeRef =>
               !t.currentSymbol.isStatic && {
                 (t: Type).mightBeProvisional = false // break cycles
-                t.symbol.is(Provisional)
+                // We can use flagsUNSAFE here because in the worth case, we
+                // will overapproximate isProvisional by returning true if the
+                // denotation has not been completed yet.
+                t.symbol.flagsUNSAFE.is(Provisional)
                 || test(t.prefix, theAcc)
-                || t.info.match
+                || t.denot.infoOrCompleter.match
                     case info: AliasingBounds => test(info.alias, theAcc)
                     case TypeBounds(lo, hi) => test(lo, theAcc) || test(hi, theAcc)
                     case _ => false
@@ -2072,7 +2075,7 @@ object Types {
     private var myNarrow: TermRef | Null = null
     override def narrow(using Context): TermRef = {
       if (myNarrow == null) myNarrow = super.narrow
-      myNarrow.nn
+      myNarrow.uncheckedNN
     }
   }
 
@@ -3024,7 +3027,7 @@ object Types {
 
     def recThis: RecThis = {
       if (myRecThis == null) myRecThis = new RecThisImpl(this)
-      myRecThis.nn
+      myRecThis.uncheckedNN
     }
 
     override def underlying(using Context): Type = parent
@@ -3446,7 +3449,7 @@ object Types {
             case _ :: rest => newParamRef(i) :: recur(rest, i + 1)
             case _ => Nil
         myParamRefs = recur(paramNames, 0)
-      myParamRefs.nn
+      myParamRefs.uncheckedNN
     }
 
     /** Like `paramInfos` but substitute parameter references with the given arguments */
@@ -4212,7 +4215,17 @@ object Types {
     def isUnreducibleWild(using Context): Boolean =
       tycon.isLambdaSub && hasWildcardArg && !isMatchAlias
 
-    def tryCompiletimeConstantFold(using Context): Type = tycon match {
+    var myTryCompiletimeConstantFold: Type | Null = null
+    var myTryCompiletimeConstantFoldPeriod: Period = Nowhere
+
+    def tryCompiletimeConstantFold(using Context): Type =
+      if myTryCompiletimeConstantFoldPeriod != ctx.period then
+        myTryCompiletimeConstantFold = tryCompiletimeConstantFoldImpl
+        if !isProvisional then
+          myTryCompiletimeConstantFoldPeriod = ctx.period
+      myTryCompiletimeConstantFold.uncheckedNN
+
+    private def tryCompiletimeConstantFoldImpl(using Context): Type = tycon match {
       case tycon: TypeRef if defn.isCompiletimeAppliedType(tycon.symbol) =>
         extension (tp: Type) def fixForEvaluation: Type =
           tp.normalized.dealias match {
@@ -4634,7 +4647,7 @@ object Types {
     private var myRepr: Name | Null = null
     def repr(using Context): Name = {
       if (myRepr == null) myRepr = SkolemName.fresh()
-      myRepr.nn
+      myRepr.uncheckedNN
     }
 
     override def toString: String = s"Skolem($hashCode)"
@@ -4873,7 +4886,7 @@ object Types {
 
             TypeComparer.tracked(matchCases)
           }
-      myReduced.nn
+      myReduced.uncheckedNN
     }
 
     override def computeHash(bs: Binders): Int = doHash(bs, scrutinee, bound :: cases)
@@ -4932,14 +4945,14 @@ object Types {
           else if (ctx.erasedTypes) appliedRef
           else AndType(givenSelf, appliedRef)
         }
-      selfTypeCache.nn
+      selfTypeCache.uncheckedNN
     }
 
     def appliedRef(using Context): Type = {
       if (appliedRefCache == null)
         appliedRefCache =
           TypeRef(prefix, cls).appliedTo(cls.classDenot.typeParams.map(_.typeRef))
-      appliedRefCache.nn
+      appliedRefCache.uncheckedNN
     }
 
     // cached because baseType needs parents
@@ -4948,7 +4961,7 @@ object Types {
     override def parents(using Context): List[Type] = {
       if (parentsCache == null)
         parentsCache = declaredParents.mapConserve(_.asSeenFrom(prefix, cls.owner))
-      parentsCache.nn
+      parentsCache.uncheckedNN
     }
 
     protected def newLikeThis(prefix: Type, declaredParents: List[Type], decls: Scope, selfInfo: TypeOrSymbol)(using Context): ClassInfo =