Bring back checkedPeriod

Author: odersky

compiler/src/dotty/tools/dotc/core/Denotations.scala

@@ -237,6 +237,7 @@ object Denotations {
     final def validFor: Period = myValidFor
     final def validFor_=(p: Period): Unit =
       myValidFor = p
+      symbol.setCheckedPeriod(Nowhere): @unchecked
 
     /** Is this denotation different from NoDenotation or an ErrorDenotation? */
     def exists: Boolean = true

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1810,6 +1810,7 @@ object SymDenotations {
 
     /** The last denotation of this symbol */
     var lastDenot: SymDenotation = _
+    var checkedPeriod: Period = Nowhere
 
     /** Overridden in NoSymbol */
     //private[SymDenotations]
@@ -1819,11 +1820,13 @@ object SymDenotations {
     override def hashCode = common.id // for debugging
 
     /** The current denotation of this symbol */
-    def currentDenot(using Context): SymDenotation =
+    def computeDenot(using Context): SymDenotation =
       util.Stats.record("Symbol.denot")
       val valid = validFor.code
+      val now = ctx.period
+      symbol.setCheckedPeriod(now)
       // Next condition is inlined from Periods.containsSinglePhasePeriod
-      if ((valid - ctx.period.code) >>> PhaseWidth) <= (valid & PhaseMask)
+      if ((valid - now.code) >>> PhaseWidth) <= (valid & PhaseMask)
       then this
       else recomputeDenot()
 

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -113,15 +113,23 @@ object Symbols {
     private[core] def denot_=(d: SymDenotation): Unit =
       util.Stats.record("Symbol.denot_=")
       self.lastDenot = d
+      self.checkedPeriod = Nowhere
 
     /** The current denotation of this symbol */
     def denot(using Context): SymDenotation =
-      self.lastDenot.currentDenot
+      util.Stats.record("Symbol.denot")
+      val lastd = self.lastDenot
+      if self.checkedPeriod.code == ctx.period.code
+      then lastd
+      else lastd.computeDenot
 
     private[core] def setLastDenot(d: SymDenotation): SymDenotation =
       self.lastDenot = d
       d
 
+    def setCheckedPeriod(period: Period): Unit =
+      self.checkedPeriod = period
+
     /** The original denotation of this symbol, without forcing anything */
     def originDenotation: SymDenotation = self