Revert r27992: some browser tests fail.

sdk/lib/_internal/compiler/implementation/inferrer/container_tracer.dart

 // Copyright (c) 2013, 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.
 
-part of type_graph_inferrer;
+library container_tracer;
+
+import '../dart2jslib.dart' hide Selector, TypedSelector;
+import '../elements/elements.dart';
+import '../tree/tree.dart';
+import '../universe/universe.dart';
+import '../util/util.dart' show Link;
+import 'simple_types_inferrer.dart'
+    show InferrerEngine, InferrerVisitor, LocalsHandler, TypeMaskSystem;
+import '../types/types.dart';
+import 'inferrer_visitor.dart';
 
 /**
  * A set of selector names that [List] implements, that we know do not
  * change the element type of the list, or let the list escape to code
  * that might change the element type.
  */
 Set<String> okSelectorsSet = new Set<String>.from(
   const <String>[
     // From Object.
     '==',
@@ skipping 103 matching lines @@
     'getRange',
     'asMap',
 
     // From JSArray.
     'checkMutable',
     'checkGrowable',
   ]);
 
 bool _VERBOSE = false;
 
-class ContainerTracerVisitor implements TypeInformationVisitor {
-  final ContainerTypeInformation container;
-  final TypeGraphInferrerEngine inferrer;
+class InferrerEngineForContainerTracer
+    implements MinimalInferrerEngine<TypeMask> {
   final Compiler compiler;
 
-  // The set of [TypeInformation] where the traced container could
-  // flow in, and operations done on them.
-  final Set<TypeInformation> allUsers = new Set<TypeInformation>();
-
-  // The list of found assignments to the container.
-  final List<TypeInformation> assignments = <TypeInformation>[];
-
-  bool enableLengthTracking = true;
+  InferrerEngineForContainerTracer(this.compiler);
+
+  TypeMask typeOfElement(Element element) {
+    return compiler.typesTask.getGuaranteedTypeOfElement(element);
+  }
+
+  TypeMask returnTypeOfElement(Element element) {
+    return compiler.typesTask.getGuaranteedReturnTypeOfElement(element);
+  }
+
+  TypeMask returnTypeOfSelector(Selector selector) {
+    return compiler.typesTask.getGuaranteedTypeOfSelector(selector);
+  }
+
+  TypeMask typeOfNode(Node node) {
+    return compiler.typesTask.getGuaranteedTypeOfNode(null, node);
+  }
+
+  Iterable<Element> getCallersOf(Element element) {
+    return compiler.typesTask.typesInferrer.getCallersOf(element);
+  }
+
+  void recordTypeOfNonFinalField(Node node,
+                                 Element field,
+                                 TypeMask type) {}
+}
+
+/**
+ * Global analysis phase that traces container instantiations in order to
+ * find their element type.
+ */
+class ContainerTracer extends CompilerTask {
+  ContainerTracer(Compiler compiler) : super(compiler);
+
+  String get name => 'List tracer';
+
+  bool analyze() {
+    measure(() {
+      if (compiler.disableTypeInference) return;
+      TypesInferrer inferrer = compiler.typesTask.typesInferrer;
+      InferrerEngineForContainerTracer engine =
+          new InferrerEngineForContainerTracer(compiler);
+
+      // Walk over all created [ContainerTypeMask].
+      inferrer.containerTypes.forEach((ContainerTypeMask mask) {
+        // The element type has already been set for const containers.
+        if (mask.elementType != null) return;
+        new TracerForConcreteContainer(mask, this, compiler, engine).run();
+      });
+    });
+  }
+}
+
+/**
+ * A tracer for a specific container.
+ */
+class TracerForConcreteContainer {
+  final Compiler compiler;
+  final ContainerTracer tracer;
+  final InferrerEngineForContainerTracer inferrer;
+  final ContainerTypeMask mask;
+
+  final Node analyzedNode;
+  final Element startElement;
+
+  final List<Element> workList = <Element>[];
+
+  /**
+   * A set of elements where this list might escape.
+   */
+  final Set<Element> escapingElements = new Set<Element>();
+
+  /**
+   * A set of selectors that both use and update the list, for example
+   * [: list[0]++; :] or [: list[0] |= 42; :].
+   */
+  final Set<Selector> constraints = new Set<Selector>();
+
+  /**
+   * A cache of setters that were already seen. Caching these
+   * selectors avoid the filtering done in [addSettersToAnalysis].
+   */
+  final Set<Selector> seenSetterSelectors = new Set<Selector>();
+
+  static const int MAX_ANALYSIS_COUNT = 11;
+
+  TypeMask potentialType;
+  int potentialLength;
+  bool isLengthTrackingDisabled = false;
   bool continueAnalyzing = true;
 
-  static const int MAX_ANALYSIS_COUNT = 11;
-  final Set<Element> analyzedElements = new Set<Element>();
-
-  ContainerTracerVisitor(this.container, inferrer)
-      : this.inferrer = inferrer, this.compiler = inferrer.compiler;
+  TracerForConcreteContainer(ContainerTypeMask mask,
+                             this.tracer,
+                             this.compiler,
+                             this.inferrer)
+      : analyzedNode = mask.allocationNode,
+        startElement = mask.allocationElement,
+        this.mask = mask;
 
   void run() {
-    // Add the assignments found at allocation site.
-    assignments.addAll(container.elementType.assignments);
-
-    // Collect the [TypeInformation] where the container can flow in,
-    // as well as the operations done on all these [TypeInformation]s.
-    List<TypeInformation> workList = <TypeInformation>[];
-    allUsers.add(container);
-    workList.add(container);
+    int analysisCount = 0;
+    workList.add(startElement);
     while (!workList.isEmpty) {
-      TypeInformation user = workList.removeLast();
-      user.users.forEach((TypeInformation info) {
-        if (allUsers.contains(info)) return;
-        allUsers.add(info);
-        analyzedElements.add(info.owner);
-        if (info.reachedBy(user, inferrer)) {
-          workList.add(info);
-        }
-      });
-      if (analyzedElements.length > MAX_ANALYSIS_COUNT) {
+      if (workList.length + analysisCount > MAX_ANALYSIS_COUNT) {
         bailout('Too many users');
         break;
       }
-    }
-
-    if (continueAnalyzing) {
-      for (TypeInformation info in allUsers) {
-        info.accept(this);
-        if (!continueAnalyzing) break;
-      }
-    }
-
-    ContainerTypeMask mask = container.type;
-    if (!enableLengthTracking
-        && (mask.forwardTo != compiler.typesTask.fixedListType)) {
-      mask.length = null;
-    }
-
-    TypeMask result = continueAnalyzing
-      ? inferrer.types.computeTypeMask(assignments)
-      : inferrer.types.dynamicType.type;
-
-    mask.elementType = result;
+      Element currentElement = workList.removeLast().implementation;
+      new ContainerTracerVisitor(currentElement, this).run();
+      if (!continueAnalyzing) break;
+      analysisCount++;
+    }
+
+    if (!continueAnalyzing) {
+      if (mask.forwardTo == compiler.typesTask.fixedListType) {
+        mask.length = potentialLength;
+      }
+      mask.elementType = compiler.typesTask.dynamicType;
+      return;
+    }
+
+    // [potentialType] can be null if we did not find any instruction
+    // that adds elements to the list.
+    if (potentialType == null) {
+      if (_VERBOSE) {
+        print('Found empty type for $analyzedNode $startElement');
+      }
+      mask.elementType = new TypeMask.nonNullEmpty();
+      return;
+    }
+
+    // Walk over the found constraints and update the type according
+    // to the selectors of these constraints.
+    for (Selector constraint in constraints) {
+      assert(constraint.isOperator());
+      constraint = new TypedSelector(potentialType, constraint);
+      potentialType = potentialType.union(
+          inferrer.returnTypeOfSelector(constraint), compiler);
+    }
     if (_VERBOSE) {
-      print('$result and ${mask.length} '
-            'for ${mask.allocationNode} ${mask.allocationElement}');
-    }
-  }
-
-  void bailout(String reason) {
+      print('$potentialType and $potentialLength '
+            'for $analyzedNode $startElement');
+    }
+    mask.elementType = potentialType;
+    mask.length = potentialLength;
+  }
+
+  void disableLengthTracking() {
+    if (mask.forwardTo == compiler.typesTask.fixedListType) {
+      // Bogus update to a fixed list.
+      return;
+    }
+    isLengthTrackingDisabled = true;
+    potentialLength = null;
+  }
+
+  void setPotentialLength(int value) {
+    if (isLengthTrackingDisabled) return;
+    potentialLength = value;
+  }
+
+  void unionPotentialTypeWith(TypeMask newType) {
+    assert(newType != null);
+    potentialType = potentialType == null
+        ? newType
+        : newType.union(potentialType, compiler);
+    if (potentialType == compiler.typesTask.dynamicType) {
+      bailout('Moved to dynamic');
+    }
+  }
+
+  void addEscapingElement(element) {
+    element = element.implementation;
+    if (escapingElements.contains(element)) return;
+    escapingElements.add(element);
+    if (element.isField() || element.isGetter() || element.isFunction()) {
+      for (Element e in inferrer.getCallersOf(element)) {
+        addElementToAnalysis(e);
+      }
+    } else if (element.isParameter()) {
+      addElementToAnalysis(element.enclosingElement);
+    } else if (element.isFieldParameter()) {
+      addEscapingElement(element.fieldElement);
+    }
+  }
+
+  void addSettersToAnalysis(Selector selector) {
+    assert(selector.isSetter());
+    if (seenSetterSelectors.contains(selector)) return;
+    seenSetterSelectors.add(selector);
+    for (var e in compiler.world.allFunctions.filter(selector)) {
+      e = e.implementation;
+      if (e.isField()) {
+        addEscapingElement(e);
+      } else {
+        FunctionSignature signature = e.computeSignature(compiler);
+        signature.forEachRequiredParameter((Element e) {
+          addEscapingElement(e);
+        });
+      }
+    }
+  }
+
+  void addElementToAnalysis(Element element) {
+    workList.add(element);
+  }
+
+  TypeMask bailout(String reason) {
     if (_VERBOSE) {
-      ContainerTypeMask mask = container.type;
-      print('Bailing out on ${mask.allocationNode} ${mask.allocationElement} '
-            'because: $reason');
+      print('Bailout on $analyzedNode $startElement because of $reason');
     }
     continueAnalyzing = false;
-    enableLengthTracking = false;
-  }
-
-  visitNarrowTypeInformation(NarrowTypeInformation info) {}
-  visitPhiElementTypeInformation(PhiElementTypeInformation info) {}
-  visitElementInContainerTypeInformation(
-      ElementInContainerTypeInformation info) {}
-  visitContainerTypeInformation(ContainerTypeInformation info) {}
-  visitConcreteTypeInformation(ConcreteTypeInformation info) {}
-
-  visitClosureCallSiteTypeInformation(ClosureCallSiteTypeInformation info) {
-    bailout('Passed to a closure');
-  }
-
-  visitStaticCallSiteTypeInformation(StaticCallSiteTypeInformation info) {
-    analyzedElements.add(info.caller);
-    Element called = info.calledElement;
-    if (called.isForeign(compiler) && called.name == const SourceString('JS')) {
-      bailout('Used in JS ${info.call}');
-    }
-  }
-
-  visitDynamicCallSiteTypeInformation(DynamicCallSiteTypeInformation info) {
-    Selector selector = info.selector;
+    return compiler.typesTask.dynamicType;
+  }
+
+  bool couldBeTheList(resolved) {
+    if (resolved is Selector) {
+      return escapingElements.any((e) {
+        return e.isInstanceMember() && resolved.applies(e, compiler);
+      });
+    } else if (resolved is Node) {
+      return analyzedNode == resolved;
+    } else {
+      assert(resolved is Element);
+      return escapingElements.contains(resolved);
+    }
+  }
+
+  void recordConstraint(Selector selector) {
+    constraints.add(selector);
+  }
+}
+
+class ContainerTracerVisitor
+    extends InferrerVisitor<TypeMask, InferrerEngineForContainerTracer> {
+  final Element analyzedElement;
+  final TracerForConcreteContainer tracer;
+  final bool visitingClosure;
+
+  ContainerTracerVisitor(element, tracer, [LocalsHandler<TypeMask> locals])
+      : super(element, tracer.inferrer, new TypeMaskSystem(tracer.compiler),
+              tracer.compiler, locals),
+        this.analyzedElement = element,
+        this.tracer = tracer,
+        visitingClosure = locals != null;
+
+  bool escaping = false;
+  bool visitingInitializers = false;
+
+  void run() {
+    compiler.withCurrentElement(analyzedElement, () {
+      visit(analyzedElement.parseNode(compiler));
+    });
+  }
+
+  /**
+   * Executes [f] and returns whether it triggered the list to escape.
+   */
+  bool visitAndCatchEscaping(Function f) {
+    bool oldEscaping = escaping;
+    escaping = false;
+    f();
+    bool foundEscaping = escaping;
+    escaping = oldEscaping;
+    return foundEscaping;
+  }
+
+  /**
+   * Visits the [arguments] of [callee], and records the parameters
+   * that could hold the container as escaping.
+   *
+   * Returns whether the container escaped.
+   */
+  bool visitArguments(Link<Node> arguments, /* Element or Selector */ callee) {
+    List<int> indices = [];
+    int index = 0;
+    for (Node node in arguments) {
+      if (visitAndCatchEscaping(() { visit(node); })) {
+        indices.add(index);
+      }
+      index++;
+    }
+    if (!indices.isEmpty) {
+      Iterable<Element> callees;
+      if (callee is Element) {
+        // No need to go further, we know the call will throw.
+        if (callee.isErroneous()) return false;
+        callees = [callee];
+      } else {
+        assert(callee is Selector);
+        callees = compiler.world.allFunctions.filter(callee);
+      }
+      for (var e in callees) {
+        e = e.implementation;
+        if (e.isField()) {
+          tracer.bailout('Passed to a closure');
+          break;
+        }
+        FunctionSignature signature = e.computeSignature(compiler);
+        index = 0;
+        int parameterIndex = 0;
+        signature.forEachRequiredParameter((Element parameter) {
+          if (index < indices.length && indices[index] == parameterIndex) {
+            tracer.addEscapingElement(parameter);
+            index++;
+          }
+          parameterIndex++;
+        });
+        if (index != indices.length) {
+          tracer.bailout('Used in a named parameter or closure');
+        }
+      }
+      return true;
+    } else {
+      return false;
+    }
+  }
+
+  TypeMask visitFunctionExpression(FunctionExpression node) {
+    FunctionElement function = elements[node];
+    if (function != analyzedElement) {
+      // Visiting a closure.
+      LocalsHandler closureLocals = new LocalsHandler<TypeMask>.from(
+          locals, node, useOtherTryBlock: false);
+      new ContainerTracerVisitor(function, tracer, closureLocals).run();
+      return types.functionType;
+    } else {
+      // Visiting [analyzedElement].
+      FunctionSignature signature = function.computeSignature(compiler);
+      signature.forEachParameter((element) {
+        locals.update(element, inferrer.typeOfElement(element), node);
+      });
+      visitingInitializers = true;
+      visit(node.initializers);
+      visitingInitializers = false;
+      visit(node.body);
+      return null;
+    }
+  }
+
+  TypeMask visitLiteralList(LiteralList node) {
+    if (node.isConst()) {
+      return inferrer.typeOfNode(node);
+    }
+    if (tracer.couldBeTheList(node)) {
+      escaping = true;
+      int length = 0;
+      for (Node element in node.elements.nodes) {
+        tracer.unionPotentialTypeWith(visit(element));
+        length++;
+      }
+      tracer.setPotentialLength(length);
+    } else {
+      node.visitChildren(this);
+    }
+    return types.growableListType;
+  }
+
+  TypeMask visitSendSet(SendSet node) {
+    bool isReceiver = visitAndCatchEscaping(() {
+      visit(node.receiver);
+    });
+    return handleSendSet(node, isReceiver);
+  }
+
+  TypeMask handleSendSet(SendSet node, bool isReceiver) {
+    TypeMask rhsType;
+    TypeMask indexType;
+
+    Selector getterSelector =
+        elements.getGetterSelectorInComplexSendSet(node);
+    Selector operatorSelector =
+        elements.getOperatorSelectorInComplexSendSet(node);
+    Selector setterSelector = elements.getSelector(node);
+
+    String op = node.assignmentOperator.source.stringValue;
+    bool isIncrementOrDecrement = op == '++' || op == '--';
+    bool isIndexEscaping = false;
+    bool isValueEscaping = false;
+    if (isIncrementOrDecrement) {
+      rhsType = types.intType;
+      if (node.isIndex) {
+        isIndexEscaping = visitAndCatchEscaping(() {
+          indexType = visit(node.arguments.head);
+        });
+      }
+    } else if (node.isIndex) {
+      isIndexEscaping = visitAndCatchEscaping(() {
+        indexType = visit(node.arguments.head);
+      });
+      isValueEscaping = visitAndCatchEscaping(() {
+        rhsType = visit(node.arguments.tail.head);
+      });
+    } else {
+      isValueEscaping = visitAndCatchEscaping(() {
+        rhsType = visit(node.arguments.head);
+      });
+    }
+
+    Element element = elements[node];
+
+    if (node.isIndex) {
+      if (isReceiver) {
+        if (op == '=') {
+          tracer.unionPotentialTypeWith(rhsType);
+        } else {
+          tracer.recordConstraint(operatorSelector);
+        }
+      } else if (isIndexEscaping || isValueEscaping) {
+        // If the index or value is escaping, iterate over all
+        // potential targets, and mark their parameter as escaping.
+        for (var e in compiler.world.allFunctions.filter(setterSelector)) {
+          e = e.implementation;
+          FunctionSignature signature = e.computeSignature(compiler);
+          int index = 0;
+          signature.forEachRequiredParameter((Element parameter) {
+            if (index == 0 && isIndexEscaping) {
+              tracer.addEscapingElement(parameter);
+            }
+            if (index == 1 && isValueEscaping) {
+              tracer.addEscapingElement(parameter);
+            }
+            index++;
+          });
+        }
+      }
+    } else if (isReceiver) {
+      if (setterSelector.name == const SourceString('length')) {
+        tracer.disableLengthTracking();
+        tracer.unionPotentialTypeWith(compiler.typesTask.nullType);
+      }
+    } else if (isValueEscaping) {
+      if (element != null
+          && element.isField()
+          && setterSelector == null
+          && !visitingInitializers) {
+        // Initializer at declaration of a field.
+        assert(analyzedElement.isField());
+        tracer.addEscapingElement(analyzedElement);
+      } else if (element != null
+                  && (!element.isInstanceMember() || visitingInitializers)) {
+        // A local, a static element, or a field in an initializer.
+        tracer.addEscapingElement(element);
+      } else {
+        tracer.addSettersToAnalysis(setterSelector);
+      }
+    }
+
+    TypeMask result;
+    if (node.isPostfix) {
+      // We don't check if [getterSelector] could be the container because
+      // a list++ will always throw.
+      result = inferrer.returnTypeOfSelector(getterSelector);
+    } else if (op != '=') {
+      // We don't check if [getterSelector] could be the container because
+      // a list += 42 will always throw.
+      result = inferrer.returnTypeOfSelector(operatorSelector);
+    } else {
+      if (isValueEscaping) {
+        escaping = true;
+      }
+      result = rhsType;
+    }
+
+    if (Elements.isLocal(element)) {
+      locals.update(element, result, node);
+    }
+
+    return result;
+  }
+
+  TypeMask visitSuperSend(Send node) {
+    Element element = elements[node];
+    if (!node.isPropertyAccess) {
+      visitArguments(node.arguments, element);
+    }
+
+    if (tracer.couldBeTheList(element)) {
+      escaping = true;
+    }
+
+    if (element.isField()) {
+      return inferrer.typeOfElement(element);
+    } else if (element.isFunction()) {
+      return inferrer.returnTypeOfElement(element);
+    } else {
+      return types.dynamicType;
+    }
+  }
+
+  TypeMask visitStaticSend(Send node) {
+    Element element = elements[node];
+
+    if (Elements.isGrowableListConstructorCall(element, node, compiler)) {
+      visitArguments(node.arguments, element);
+      if (tracer.couldBeTheList(node)) {
+        escaping = true;
+      }
+      return inferrer.typeOfNode(node);
+    } else if (Elements.isFixedListConstructorCall(element, node, compiler)) {
+      visitArguments(node.arguments, element);
+      if (tracer.couldBeTheList(node)) {
+        tracer.unionPotentialTypeWith(types.nullType);
+        escaping = true;
+        LiteralInt length = node.arguments.head.asLiteralInt();
+        if (length != null) {
+          tracer.setPotentialLength(length.value);
+        }
+      }
+      return inferrer.typeOfNode(node);
+    } else if (Elements.isFilledListConstructorCall(element, node, compiler)) {
+      if (tracer.couldBeTheList(node)) {
+        escaping = true;
+        visit(node.arguments.head);
+        TypeMask fillWithType = visit(node.arguments.tail.head);
+        tracer.unionPotentialTypeWith(fillWithType);
+        LiteralInt length = node.arguments.head.asLiteralInt();
+        if (length != null) {
+          tracer.setPotentialLength(length.value);
+        }
+      } else {
+        visitArguments(node.arguments, element);
+      }
+      return inferrer.typeOfNode(node);
+    }
+
+    bool isEscaping = visitArguments(node.arguments, element);
+
+    if (element.isForeign(compiler)) {
+      if (isEscaping) return tracer.bailout('Used in a JS');
+    }
+
+    if (tracer.couldBeTheList(element)) {
+      escaping = true;
+    }
+
+    if (element.isFunction() || element.isConstructor()) {
+      return inferrer.returnTypeOfElement(element);
+    } else {
+      // Closure call or unresolved.
+      return types.dynamicType;
+    }
+  }
+
+  TypeMask visitGetterSend(Send node) {
+    Element element = elements[node];
+    Selector selector = elements.getSelector(node);
+    if (Elements.isStaticOrTopLevelField(element)) {
+      if (tracer.couldBeTheList(element)) {
+        escaping = true;
+      }
+      return inferrer.typeOfElement(element);
+    } else if (Elements.isInstanceSend(node, elements)) {
+      return visitDynamicSend(node);
+    } else if (Elements.isStaticOrTopLevelFunction(element)) {
+      return types.functionType;
+    } else if (Elements.isErroneousElement(element)) {
+      return types.dynamicType;
+    } else if (Elements.isLocal(element)) {
+      if (tracer.couldBeTheList(element)) {
+        escaping = true;
+      }
+      return locals.use(element);
+    } else {
+      node.visitChildren(this);
+      return types.dynamicType;
+    }
+  }
+
+  TypeMask visitClosureSend(Send node) {
+    assert(node.receiver == null);
+    visit(node.selector);
+    bool isEscaping =
+        visitArguments(node.arguments, elements.getSelector(node));
+
+    if (isEscaping) return tracer.bailout('Passed to a closure');
+    return types.dynamicType;
+  }
+
+  TypeMask visitDynamicSend(Send node) {
+    bool isReceiver = visitAndCatchEscaping(() {
+      visit(node.receiver);
+    });
+    return handleDynamicSend(node, isReceiver);
+  }
+
+  TypeMask handleDynamicSend(Send node, bool isReceiver) {
+    Selector selector = elements.getSelector(node);
     String selectorName = selector.name.slowToString();
-    if (allUsers.contains(info.receiver)) {
-      if (!okSelectorsSet.contains(selectorName)) {
-        if (selector.isCall()) {
-          int positionalLength = info.arguments.positional.length;
-          if (selectorName == 'add') {
-            if (positionalLength == 1) {
-              assignments.add(info.arguments.positional[0]);
-            }
-          } else if (selectorName == 'insert') {
-            if (positionalLength == 2) {
-              assignments.add(info.arguments.positional[1]);
-            }
-          } else {
-            bailout('Used in a not-ok selector');
-            return;
+    if (isReceiver && !okSelectorsSet.contains(selectorName)) {
+      if (selector.isCall()
+          && (selectorName == 'add' || selectorName == 'insert')) {
+        TypeMask argumentType;
+        if (node.arguments.isEmpty
+            || (selectorName == 'insert' && node.arguments.tail.isEmpty)) {
+          return tracer.bailout('Invalid "add" or "insert" call on a list');
+        }
+        bool isEscaping = visitAndCatchEscaping(() {
+          argumentType = visit(node.arguments.head);
+          if (selectorName == 'insert') {
+            argumentType = visit(node.arguments.tail.head);
           }
-        } else if (selector.isIndexSet()) {
-          assignments.add(info.arguments.positional[1]);
-        } else if (!selector.isIndex()) {
-          bailout('Used in a not-ok selector');
-          return;
-        }
-      }
-      if (!doNotChangeLengthSelectorsSet.contains(selectorName)) {
-        enableLengthTracking = false;
-      }
-      if (selectorName == 'length' && selector.isSetter()) {
-        enableLengthTracking = false;
-        assignments.add(inferrer.types.nullType);
-      }
-    } else if (selector.isCall()
-               && !info.targets.every((element) => element.isFunction())) {
-      bailout('Passed to a closure');
-      return;
-    }
-  }
-
-  bool isClosure(Element element) {
-    if (!element.isFunction()) return false;
-    Element outermost = element.getOutermostEnclosingMemberOrTopLevel();
-    return outermost.declaration != element.declaration;
-  }
-
-  visitElementTypeInformation(ElementTypeInformation info) {
-    if (isClosure(info.element)) {
-      bailout('Returned from a closure');
-    }
+        });
+        if (isEscaping) {
+          return tracer.bailout('List containing itself');
+        }
+        tracer.unionPotentialTypeWith(argumentType);
+      } else {
+        return tracer.bailout('Send with the node as receiver $node');
+      }
+    } else if (!node.isPropertyAccess) {
+      visitArguments(node.arguments, selector);
+    }
+    if (isReceiver && !doNotChangeLengthSelectorsSet.contains(selectorName)) {
+      tracer.disableLengthTracking();
+    }
+    if (tracer.couldBeTheList(selector)) {
+      escaping = true;
+    }
+    return inferrer.returnTypeOfSelector(selector);
+  }
+
+  TypeMask visitReturn(Return node) {
+    if (node.expression == null) {
+      return types.nullType;
+    }
+
+    TypeMask type;
+    bool isEscaping = visitAndCatchEscaping(() {
+      type = visit(node.expression);
+    });
+
+    if (isEscaping) {
+      if (visitingClosure) {
+        tracer.bailout('Return from closure');
+      } else {
+        tracer.addEscapingElement(analyzedElement);
+      }
+    }
+    return type;
+  }
+
+  TypeMask visitForIn(ForIn node) {
+    visit(node.expression);
+    Selector iteratorSelector = elements.getIteratorSelector(node);
+    Selector currentSelector = elements.getCurrentSelector(node);
+
+    TypeMask iteratorType = inferrer.returnTypeOfSelector(iteratorSelector);
+    TypeMask currentType = inferrer.returnTypeOfSelector(currentSelector);
+
+    // We nullify the type in case there is no element in the
+    // iterable.
+    currentType = currentType.nullable();
+
+    Node identifier = node.declaredIdentifier;
+    Element element = elements[identifier];
+    if (Elements.isLocal(element)) {
+      locals.update(element, currentType, node);
+    }
+
+    return handleLoop(node, () {
+      visit(node.body);
+    });
   }
 }