dart2js cps: Refactor tracking of side effects.

pkg/compiler/lib/src/cps_ir/eagerly_load_statics.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.cps_ir.eagerly_load_statics;
 
 import 'cps_ir_nodes.dart';
 import 'optimizers.dart' show Pass;
 import '../elements/elements.dart';
+import 'cps_fragment.dart';
 
 /// Replaces [GetLazyStatic] with [GetStatic] when the static field is known
 /// to have been initialized.
 ///
 /// Apart from [GetStatic] generating better code, this improves the side-effect
 /// analysis in the [GVN] pass, since [GetStatic] has no effects.
 class EagerlyLoadStatics extends TrampolineRecursiveVisitor implements Pass {
   String get passName => 'Eagerly load statics';
 
   Map<FieldElement, Primitive> initializerFor = <FieldElement, Primitive>{};
 
   final Map<Continuation, Map<FieldElement, Primitive>> initializersAt =
       <Continuation, Map<FieldElement, Primitive>>{};
 
   static Map<FieldElement, Primitive> cloneFieldMap(
         Map<FieldElement, Primitive> map) {
     return new Map<FieldElement, Primitive>.from(map);
   }
 
   void rewrite(FunctionDefinition node) {
     visit(node.body);
   }
 
+  Expression traverseLetPrim(LetPrim node) {
+    Expression next = node.body;
+    visit(node.primitive);
+    return next;
+  }
+
   Expression traverseLetCont(LetCont node) {
     for (Continuation cont in node.continuations) {
       initializersAt[cont] = cloneFieldMap(initializerFor);
       push(cont);
     }
     return node.body;
   }
 
   Expression traverseLetHandler(LetHandler node) {
     initializersAt[node.handler] = cloneFieldMap(initializerFor);
     push(node.handler);
     return node.body;
   }
 
   Expression traverseContinuation(Continuation cont) {
     initializerFor = initializersAt[cont];
     return cont.body;
   }
 
   void visitGetLazyStatic(GetLazyStatic node) {
     Primitive initializer = initializerFor[node.element];
-    if (initializer != null) {
-      GetStatic newNode = new GetStatic.witnessed(node.element, initializer,
-          node.sourceInformation);
-      newNode.type = node.type;
+    if (initializer is GetLazyStatic && initializer.isFinal) {
+      // No reason to create a GetStatic when the field is final.
+      node.replaceWithFragment(new CpsFragment(), initializer);
+    } else if (initializer != null) {
+      GetStatic newNode = new GetStatic.witnessed(node.element,
+          initializer, sourceInformation: node.sourceInformation)
+          ..type = node.type;
       node.replaceWith(newNode);
     } else {
       initializerFor[node.element] = node;
     }
   }
 
   void visitSetStatic(SetStatic node) {
     initializerFor.putIfAbsent(node.element, () => node);
   }
 }