Start creating a MemberSet abstraction, and use it to fold getters/setters into field accesses.

lib/compiler/implementation/world.dart

+// Copyright (c) 2012, 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.
+
+class World {
+  final Map<ClassElement, Set<ClassElement>> subtypes;
+
+  World() : subtypes = new Map<ClassElement, Set<ClassElement>>();
+
+  /**
+   * Returns a [MemberSet] that contains the possible targets of a
+   * selector named [member] on a receiver whose type is [type].
+   */
+  MemberSet memberSetFor(Type type, SourceString member) {

[kasperl, 2012/05/09 11:13:03]

I'm not sure this functionality needs to be exposed directly to the optimizer.

[ngeoffray, 2012/05/09 11:34:22]

Made it library private.

+    ClassElement cls = type.element;
+    MemberSet result = new MemberSet(member);
+    Element element = cls.lookupMember(member);
+    if (element !== null) result.add(element);
+
+    Set<ClassElement> subtypes = subtypes[cls];
+    if (subtypes !== null) {
+      for (ClassElement sub in subtypes) {
+        element = sub.lookupLocalMember(member);
+        if (element !== null) result.add(element);
+      }
+    }
+    return result;
+  }
+}
+
+/**
+ * A [MemberSet] contains all the possible targets for a selector.
+ */
+class MemberSet {
+  final Set<Element> elements;
+  final SourceString name;
+
+  MemberSet(SourceString this.name) : elements = new Set<Element>();
+
+  void add(Element element) {
+    elements.add(element);
+  }
+
+  bool isEmpty() => elements.isEmpty();
+
+  bool hasJustFields() {
+    return elements.every((Element element) => element.isField());
+  }
+}