dart2js cps: Replace GetLazyStatic with GetStatic.

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';
+
+/// 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 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;
+      node.replaceWith(newNode);
+    } else {
+      initializerFor[node.element] = node;
+    }
+  }
+
+  void visitSetStatic(SetStatic node) {
+    initializerFor.putIfAbsent(node.element, () => node);
+  }
+}