Add optimization to reduce extra iterations of the safe init checker.

Author: q-ata

compiler/src/dotty/tools/dotc/transform/init/Cache.scala

@@ -75,6 +75,8 @@ class Cache[Config, Res]:
    */
   protected var changed: Boolean = false
 
+  protected var cacheUsed: Boolean = false
+
   /** Used to avoid allocation, its state does not matter */
   protected given MutableTreeWrapper = new MutableTreeWrapper
 
@@ -99,7 +101,9 @@ class Cache[Config, Res]:
    */
   def cachedEval(config: Config, expr: Tree, cacheResult: Boolean, default: Res)(eval: Tree => Res): Res =
     this.get(config, expr) match
-    case Some(value) => value
+    case Some(value) =>
+      cacheUsed = true
+      value
     case None =>
       val assumeValue: Res =
         this.last.get(config, expr) match
@@ -124,6 +128,8 @@ class Cache[Config, Res]:
 
   def hasChanged = changed
 
+  def isUsed = cacheUsed
+
   /** Prepare cache for the next iteration
    *
    *  1. Reset changed flag.
@@ -132,6 +138,7 @@ class Cache[Config, Res]:
    */
   def prepareForNextIteration()(using Context) =
     this.changed = false
+    this.cacheUsed = false
     this.last = this.current
     this.current = Map.empty
 end Cache

compiler/src/dotty/tools/dotc/transform/init/Semantic.scala

@@ -1101,12 +1101,15 @@ object Semantic:
    *
    *  The class to be checked must be an instantiable concrete class.
    */
-  private def checkClass(classSym: ClassSymbol)(using Cache.Data, Context): Unit =
+  private def checkClass(classSym: ClassSymbol)(using Cache.Data, Context): Int =
     val thisRef = ThisRef(classSym)
     val tpl = classSym.defTree.asInstanceOf[TypeDef].rhs.asInstanceOf[Template]
 
+    var accum = 0
+
     @tailrec
     def iterate(): Unit = {
+      accum += 1
       given Promoted = Promoted.empty(classSym)
       given Trace = Trace.empty.add(classSym.defTree)
       given reporter: Reporter.BufferedReporter = new Reporter.BufferedReporter
@@ -1120,7 +1123,7 @@ object Semantic:
       log("checking " + classSym) { eval(tpl, thisRef, classSym) }
       reporter.errors.foreach(_.issue)
 
-      if cache.hasChanged && reporter.errors.isEmpty then
+      if cache.hasChanged && reporter.errors.isEmpty && cache.isUsed then
         // code to prepare cache and heap for next iteration
         cache.prepareForNextIteration()
         iterate()
@@ -1129,15 +1132,19 @@ object Semantic:
     }
 
     iterate()
+
+    accum - 1
   end checkClass
 
   /**
    * Check the specified concrete classes
    */
   def checkClasses(classes: List[ClassSymbol])(using Context): Unit =
+    var total = 0
     given Cache.Data()
     for classSym <- classes if isConcreteClass(classSym) do
-      checkClass(classSym)
+      total += checkClass(classSym)
+    System.err.nn.println(total)
 
 // ----- Semantic definition --------------------------------
   type ArgInfo = TraceValue[Value]