isLoading variable replaced with a flag for performance reasons

Author: anatoliykmetyuk

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

@@ -406,6 +406,11 @@ object Flags {
   /** A denotation that is valid in all run-ids */
   val (Permanent @ _, _, _) = newFlags(61, "<permanent>")
 
+  /** Denotation is being loaded. If `Completing` is not set,
+   *  this means this denotation was loaded from an external file.
+   */
+  val (Loading @ _, _, _) = newFlags(62, "<loading>")
+
 // --------- Combined Flag Sets and Conjunctions ----------------------
 
   /** All possible flags */

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

@@ -149,16 +149,6 @@ object SymDenotations {
     private var myPrivateWithin: Symbol = initPrivateWithin
     private var myAnnotations: List[Annotation] = Nil
 
-    private[this] var isLoading = false
-    private[this] var wasLoaded = false
-
-    def startedLoading() =
-      isLoading = true
-
-    def finishedLoading() =
-      isLoading = false
-      wasLoaded = true
-
     /** The owner of the symbol; overridden in NoDenotation */
     def owner: Symbol = maybeOwner
 
@@ -171,12 +161,19 @@ object SymDenotations {
     private[dotc] final def flagsUNSAFE: FlagSet = myFlags
 
     private def setMyFlags(flags: FlagSet) =
-      lazy val immutableFlags = if wasLoaded then AfterLoadFlags else FromStartFlags
+      lazy val immutableFlags = if myInfo.isInstanceOf[SymbolLoader] then AfterLoadFlags else FromStartFlags
       lazy val changedImmutableFlags = (myFlags ^ flags) & immutableFlags
-      if myFlags.is(Touched) && !isLoading then assert(changedImmutableFlags.isEmpty,
+      if myFlags.is(Touched, butNot = Loading) then assert(changedImmutableFlags.isEmpty,
         s"Illegal mutation of flags ${changedImmutableFlags.flagsString} on completion of $this")
       myFlags = flags
 
+    final def startedLoading() =
+      myFlags |= Loading
+
+    final def finishedLoading() =
+      myFlags &~= Loading
+
+
     final def flagsString(implicit ctx: Context): String = flags.flagsString
 
     /** Adapt flag set to this denotation's term or type nature */