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

lib/compiler/implementation/compiler.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 WorkItem {
   final Element element;
   TreeElements resolutionTree;
   Function run;
   bool allowSpeculativeOptimization = true;
   List<HTypeGuard> guards = const <HTypeGuard>[];
@@ skipping 15 matching lines @@
   }
 
   String codegen(Compiler compiler) {
     return compiler.codegen(this);
   }
 }
 
 class Compiler implements DiagnosticListener {
   Queue<WorkItem> worklist;
   Universe universe;
+  World world;
   String assembledCode;
   Namer namer;
   Types types;
   bool enableTypeAssertions = false;
 
   final Tracer tracer;
 
   CompilerTask measuredTask;
   Element _currentElement;
   LibraryElement coreLibrary;
@@ skipping 47 matching lines @@
   static final SourceString START_ROOT_ISOLATE =
       const SourceString('startRootIsolate');
   bool enabledNoSuchMethod = false;
 
   bool workListIsClosed = false;
 
   Stopwatch codegenProgress;
 
   Compiler([this.tracer = const Tracer()])
       : universe = new Universe(),
+        world = new World(),
         worklist = new Queue<WorkItem>(),
         codegenProgress = new Stopwatch.start() {
     namer = new Namer(this);
     constantHandler = new ConstantHandler(this);
     scanner = new ScannerTask(this);
     dietParser = new DietParserTask(this);
     parser = new ParserTask(this);
     validator = new TreeValidatorTask(this);
     resolver = new ResolverTask(this);
     checker = new TypeCheckerTask(this);
@@ skipping 180 matching lines @@
           cancel('main is not a function', element: main);
         }
         FunctionElement mainMethod = main;
         FunctionSignature parameters = mainMethod.computeSignature(this);
         if (parameters.parameterCount > 0) {
           cancel('main cannot have parameters', element: mainMethod);
         }
       });
     }
     native.processNativeClasses(this, universe.libraries.getValues());
+    computeSubclasses();

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

Could we move this code to world? That would seem logical to me. Maybe something
like:

world.populate(universe.libraries);

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

Done.

     enqueue(new WorkItem.toCompile(main));
     codegenProgress.reset();
     while (!worklist.isEmpty()) {
       WorkItem work = worklist.removeLast();
       withCurrentElement(work.element, () => (work.run)(this));
     }
     workListIsClosed = true;
     assert(enqueuer.checkNoEnqueuedInvokedInstanceMethods());
     enqueuer.registerFieldClosureInvocations();
     emitter.assembleProgram();
     if (!worklist.isEmpty()) {
       internalErrorOnElement(worklist.first().element,
                              "work list is not empty");
     }
   }
 
+  void addSubtypes(ClassElement cls) {
+    for (Type type in cls.allSupertypes) {
+      List<Element> subtypes = world.subtypes.putIfAbsent(
+        type.element,
+        () => <ClassElement>[]);
+      subtypes.add(cls);
+    }
+  }
+
+  void computeSubclasses() {
+    universe.libraries.getValues().forEach((LibraryElement library) {
+      for (Link<Element> link = library.topLevelElements;
+           !link.isEmpty();
+           link = link.tail) {
+        Element element = link.head;
+        if (!element.isClass()) continue;
+        ClassElement cls = element;
+        resolveClass(cls);
+        addSubtypes(cls);
+      }
+    });
+  }
+
   TreeElements analyzeElement(Element element) {
     assert(parser !== null);
     Node tree = parser.parse(element);
     validator.validate(tree);
     TreeElements elements = resolver.resolve(element);
     checker.check(tree, elements);
     return elements;
   }
 
   TreeElements analyze(WorkItem work) {
@@ skipping 239 matching lines @@
   }
 }
 
 class SourceSpan {
   final Uri uri;
   final int begin;
   final int end;
 
   const SourceSpan(this.uri, this.begin, this.end);
 }