Some more small optimizations

compiler/src/dotty/tools/dotc/transform/Memoize.scala

@@ -101,19 +101,8 @@ import Decorators._
         cpy.installAfter(thisTransform)
       }
 
-    lazy val field = sym.field.orElse(newField).asTerm
-
-    def adaptToField(tree: Tree): Tree =
-      if (tree.isEmpty) tree else tree.ensureConforms(field.info.widen)
-
     val NoFieldNeeded = Lazy | Deferred | JavaDefined | (if (ctx.settings.YnoInline.value) EmptyFlags else Inline)
 
-    def isErasableBottomField(cls: Symbol): Boolean = {
-      // TODO: For Scala.js, return false if this field is in a js.Object unless it is an ErasedPhantomClass.
-      !field.isVolatile &&
-      ((cls eq defn.NothingClass) || (cls eq defn.NullClass) || (cls eq defn.BoxedUnitClass) || (cls eq defn.ErasedPhantomClass))
-    }
-
     def erasedBottomTree(sym: Symbol) = {
       if (sym eq defn.NothingClass) Throw(Literal(Constant(null)))
       else if (sym eq defn.NullClass) Literal(Constant(null))
@@ -125,7 +114,18 @@ import Decorators._
       }
     }
 
-    if (sym.is(Accessor, butNot = NoFieldNeeded))
+    if (sym.is(Accessor, butNot = NoFieldNeeded)) {
+      val field = sym.field.orElse(newField).asTerm
+
+      def adaptToField(tree: Tree): Tree =
+        if (tree.isEmpty) tree else tree.ensureConforms(field.info.widen)
+
+      def isErasableBottomField(cls: Symbol): Boolean = {
+        // TODO: For Scala.js, return false if this field is in a js.Object unless it is an ErasedPhantomClass.
+        !field.isVolatile &&
+        ((cls eq defn.NothingClass) || (cls eq defn.NullClass) || (cls eq defn.BoxedUnitClass) || (cls eq defn.ErasedPhantomClass))
+      }
+
       if (sym.isGetter) {
         var rhs = tree.rhs.changeOwnerAfter(sym, field, thisTransform)
         if (isWildcardArg(rhs)) rhs = EmptyTree
@@ -151,6 +151,7 @@ import Decorators._
       }
       else tree // curiously, some accessors from Scala2 have ' ' suffixes. They count as
                 // neither getters nor setters
+    }
     else tree
   }
 }

compiler/src/dotty/tools/dotc/transform/TreeTransform.scala

@@ -196,10 +196,12 @@ object TreeTransforms {
       }
   }
 
-  @sharable val NoTransform = new TreeTransform {
+  private class NoTreeTransform extends TreeTransform {
     def phase = unsupported("phase")
   }
 
+  @sharable val NoTransform: TreeTransform = new NoTreeTransform
+
   type Mutator[T] = (TreeTransform, T, Context) => TreeTransform
 
   class TransformerInfo(val transformers: Array[TreeTransform], val nx: NXTransformations, val group: TreeTransformer)
@@ -209,15 +211,29 @@ object TreeTransforms {
    *  @see NXTransformations.index for format of plan
    */
   class NXTransformations {
+    private val clsMethodsCache = new java.util.IdentityHashMap[Class[_], Array[java.lang.reflect.Method]]
 
+    // TODO: We spend too much time here. See if we can call it less or make it faster,
+    // e.g. by checking `cls.getMethod(name, ...).getDeclaringClass != classOf[TreeTransform]` instead.
     private def hasRedefinedMethod(cls: Class[_], name: String): Boolean = {
-      val clsMethods = cls.getDeclaredMethods
+      if (cls.eq(classOf[TreeTransform]) || cls.eq(classOf[NoTreeTransform]) ||
+          cls.eq(classOf[MiniPhaseTransform]))
+        return false
+
+      // Class#getDeclaredMethods is slow, so we cache its output
+      var clsMethods = clsMethodsCache.get(cls)
+      if (clsMethods eq null) {
+        clsMethods = cls.getDeclaredMethods
+        clsMethodsCache.put(cls, clsMethods)
+      }
+
       var i = clsMethods.length - 1
       while (i >= 0) {
         if (clsMethods(i).getName == name)
-          return cls != classOf[TreeTransform]
+          return true
         i -= 1
       }
+
       hasRedefinedMethod(cls.getSuperclass, name)
     }