Revert "Move dart2js from sdk/lib/_internal/compiler to pkg/compiler"

pkg/compiler/lib/src/inferrer/type_graph_nodes.dart

Index: pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
diff --git a/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart b/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
deleted file mode 100644
index 8941c7bc28b0ddfdf7233193c09f88c60e833317..0000000000000000000000000000000000000000
--- a/pkg/compiler/lib/src/inferrer/type_graph_nodes.dart
+++ /dev/null
@@ -1,1537 +0,0 @@
-// 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;
-
-/**
- * Common class for all nodes in the graph. The current nodes are:
- *
- * - Concrete types
- * - Elements
- * - Call sites
- * - Narrowing instructions
- * - Phi instructions
- * - Containers (for lists)
- * - Type of the element in a container
- *
- * A node has a set of assignments and users. Assignments are used to
- * compute the type of the node ([TypeInformation.computeType]). Users are
- * added to the inferrer's work queue when the type of the node
- * changes.
- */
-abstract class TypeInformation {
-  Set<TypeInformation> users;
-  var /* List|ParameterAssignments */ _assignments;
-
-  /// The type the inferrer has found for this [TypeInformation].
-  /// Initially empty.
-  TypeMask type = const TypeMask.nonNullEmpty();
-
-  /// The graph node of the member this [TypeInformation] node belongs to.
-  final MemberTypeInformation context;
-
-  /// The element this [TypeInformation] node belongs to.
-  MemberElement get contextMember => context == null ? null : context.element;
-
-  Iterable<TypeInformation> get assignments => _assignments;
-
-  /// We abandon inference in certain cases (complex cyclic flow, native
-  /// behaviours, etc.). In some case, we might resume inference in the
-  /// closure tracer, which is handled by checking whether [assignments] has
-  /// been set to [STOP_TRACKING_ASSIGNMENTS_MARKER].
-  bool abandonInferencing = false;
-  bool get mightResume =>
-      !identical(assignments, STOP_TRACKING_ASSIGNMENTS_MARKER);
-
-  /// Number of times this [TypeInformation] has changed type.
-  int refineCount = 0;
-
-  /// Whether this [TypeInformation] is currently in the inferrer's
-  /// work queue.
-  bool inQueue = false;
-
-  /// Used to disable enqueueing of type informations where we know that their
-  /// type will not change for other reasons than being stable. For example,
-  /// if inference is disabled for a type and it is hardwired to dynamic, this
-  /// is set to true to spare recomputing dynamic again and again. Changing this
-  /// to false should never change inference outcome, just make is slower.
-  bool doNotEnqueue = false;
-
-  /// Whether this [TypeInformation] has a stable [type] that will not
-  /// change.
-  bool isStable = false;
-
-  // TypeInformations are unique.
-  static int staticHashCode = 0;
-  final int hashCode = staticHashCode++;
-
-  bool get isConcrete => false;
-
-  TypeInformation(this.context) : _assignments = <TypeInformation>[],
-                                  users = new Setlet<TypeInformation>();
-
-  TypeInformation.noAssignments(this.context)
-      : _assignments = const <TypeInformation>[],
-        users = new Setlet<TypeInformation>();
-
-  TypeInformation.untracked()
-      : _assignments = const <TypeInformation>[],
-        users = const ImmutableEmptySet(),
-        context = null;
-
-  TypeInformation.withAssignments(this.context, this._assignments)
-      : users = new Setlet<TypeInformation>();
-
-  void addUser(TypeInformation user) {
-    assert(!user.isConcrete);
-    users.add(user);
-  }
-
-  void removeUser(TypeInformation user) {
-    assert(!user.isConcrete);
-    users.remove(user);
-  }
-
-  // The below is not a compile time constant to make it differentiable
-  // from other empty lists of [TypeInformation].
-  static final STOP_TRACKING_ASSIGNMENTS_MARKER = new List<TypeInformation>(0);
-
-  bool areAssignmentsTracked() {
-    return assignments != STOP_TRACKING_ASSIGNMENTS_MARKER;
-  }
-
-  void addAssignment(TypeInformation assignment) {
-    // Cheap one-level cycle detection.
-    if (assignment == this) return;
-    if (areAssignmentsTracked()) {
-      _assignments.add(assignment);
-    }
-    // Even if we abandon inferencing on this [TypeInformation] we
-    // need to collect the users, so that phases that track where
-    // elements flow in still work.
-    assignment.addUser(this);
-  }
-
-  void removeAssignment(TypeInformation assignment) {
-    if (!abandonInferencing || mightResume) {
-      _assignments.remove(assignment);
-    }
-    // We can have multiple assignments of the same [TypeInformation].
-    if (!assignments.contains(assignment)) {
-      assignment.removeUser(this);
-    }
-  }
-
-  TypeMask refine(TypeGraphInferrerEngine inferrer) {
-    return abandonInferencing ? safeType(inferrer) : computeType(inferrer);
-  }
-
-  /**
-   * Computes a new type for this [TypeInformation] node depending on its
-   * potentially updated inputs.
-   */
-  TypeMask computeType(TypeGraphInferrerEngine inferrer);
-
-  /**
-   * Returns an approximation for this [TypeInformation] node that is always
-   * safe to use. Used when abandoning inference on a node.
-   */
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) {
-    return inferrer.types.dynamicType.type;
-  }
-
-  void giveUp(TypeGraphInferrerEngine inferrer, {bool clearAssignments: true}) {
-    abandonInferencing = true;
-    // Do not remove [this] as a user of nodes in [assignments],
-    // because our tracing analysis could be interested in tracing
-    // this node.
-    if (clearAssignments) _assignments = STOP_TRACKING_ASSIGNMENTS_MARKER;
-    // Do not remove users because our tracing analysis could be
-    // interested in tracing the users of this node.
-  }
-
-  void clear() {
-    _assignments = STOP_TRACKING_ASSIGNMENTS_MARKER;
-    users = const ImmutableEmptySet();
-  }
-
-  /// Reset the analysis of this node by making its type empty.
-
-  bool reset(TypeGraphInferrerEngine inferrer) {
-    if (abandonInferencing) return false;
-    type = const TypeMask.nonNullEmpty();
-    refineCount = 0;
-    return true;
-  }
-
-  accept(TypeInformationVisitor visitor);
-
-  /// The [Element] where this [TypeInformation] was created. May be
-  /// for some [TypeInformation] nodes, where we do not need to store
-  /// the information.
-  Element get owner => null;
-
-  /// Returns whether the type cannot change after it has been
-  /// inferred.
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return !mightResume && assignments.every((e) => e.isStable);
-  }
-
-  void removeAndClearReferences(TypeGraphInferrerEngine inferrer) {
-    assignments.forEach((info) { info.removeUser(this); });
-  }
-
-  void stabilize(TypeGraphInferrerEngine inferrer) {
-    removeAndClearReferences(inferrer);
-    // Do not remove users because the tracing analysis could be interested
-    // in tracing the users of this node.
-    _assignments = STOP_TRACKING_ASSIGNMENTS_MARKER;
-    abandonInferencing = true;
-    isStable = true;
-  }
-
-  void maybeResume() {
-    if (!mightResume) return;
-    abandonInferencing = false;
-    doNotEnqueue = false;
-  }
-}
-
-abstract class ApplyableTypeInformation implements TypeInformation {
-  bool mightBePassedToFunctionApply = false;
-}
-
-/**
- * Marker node used only during tree construction but not during actual type
- * refinement.
- *
- * Currently, this is used to give a type to an optional parameter even before
- * the corresponding default expression has been analyzed. See
- * [getDefaultTypeOfParameter] and [setDefaultTypeOfParameter] for details.
- */
-class PlaceholderTypeInformation extends TypeInformation {
-  PlaceholderTypeInformation(MemberTypeInformation context) : super(context);
-
-  void accept(TypeInformationVisitor visitor) {
-    throw new UnsupportedError("Cannot visit placeholder");
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    throw new UnsupportedError("Cannot refine placeholder");
-  }
-
-  toString() => "Placeholder [$hashCode]";
-}
-
-/**
- * Parameters of instance functions behave differently than other
- * elements because the inferrer may remove assignments. This happens
- * when the receiver of a dynamic call site can be refined
- * to a type where we know more about which instance method is being
- * called.
- */
-class ParameterAssignments extends IterableBase<TypeInformation> {
-  final Map<TypeInformation, int> assignments =
-      new Map<TypeInformation, int>();
-
-  void remove(TypeInformation info) {
-    int existing = assignments[info];
-    if (existing == null) return;
-    if (existing == 1) {
-      assignments.remove(info);
-    } else {
-      assignments[info] = existing - 1;
-    }
-  }
-
-  void add(TypeInformation info) {
-    int existing = assignments[info];
-    if (existing == null) {
-      assignments[info] = 1;
-    } else {
-      assignments[info] = existing + 1;
-    }
-  }
-
-  void replace(TypeInformation old, TypeInformation replacement) {
-    int existing = assignments[old];
-    if (existing != null) {
-      int other = assignments[replacement];
-      if (other != null) existing += other;
-      assignments[replacement] = existing;
-      assignments.remove(old);
-    }
-  }
-
-  Iterator<TypeInformation> get iterator => assignments.keys.iterator;
-  Iterable<TypeInformation> where(Function f) => assignments.keys.where(f);
-
-  bool contains(TypeInformation info) => assignments.containsKey(info);
-
-  String toString() => assignments.keys.toList().toString();
-}
-
-/**
- * A node representing a resolved element of the program. The kind of
- * elements that need an [ElementTypeInformation] are:
- *
- * - Functions (including getters and setters)
- * - Constructors (factory or generative)
- * - Fields
- * - Parameters
- * - Local variables mutated in closures
- *
- * The [ElementTypeInformation] of a function and a constructor is its
- * return type.
- *
- * Note that a few elements of these kinds must be treated specially,
- * and they are dealt in [ElementTypeInformation.handleSpecialCases]:
- *
- * - Parameters of closures, [noSuchMethod] and [call] instance
- *   methods: we currently do not infer types for those.
- *
- * - Fields and parameters being assigned by synthesized calls done by
- *   the backend: we do not know what types the backend will use.
- *
- * - Native functions and fields: because native methods contain no Dart
- *   code, and native fields do not have Dart assignments, we just
- *   trust their type annotation.
- *
- */
-abstract class ElementTypeInformation extends TypeInformation {
-  final Element element;
-
-  /// Marker to disable inference for closures in [handleSpecialCases].
-  bool disableInferenceForClosures = true;
-
-  factory ElementTypeInformation(Element element, TypeInformationSystem types) {
-    if (element.isParameter || element.isInitializingFormal) {
-      ParameterElement parameter = element;
-      if (parameter.functionDeclaration.isInstanceMember) {
-        return new ParameterTypeInformation._instanceMember(element, types);
-      }
-      return new ParameterTypeInformation._internal(element, types);
-    }
-    return new MemberTypeInformation._internal(element);
-  }
-
-  ElementTypeInformation._internal(MemberTypeInformation context, this.element)
-      : super(context);
-  ElementTypeInformation._withAssignments(MemberTypeInformation context,
-      this.element, assignments)
-      : super.withAssignments(context, assignments);
-}
-
-/**
- * A node representing members in the broadest sense:
- *
- * - Functions
- * - Constructors
- * - Fields (also synthetic ones due to closures)
- * - Local functions (closures)
- *
- * These should never be created directly but instead are constructed by
- * the [ElementTypeInformation] factory.
- */
-class MemberTypeInformation extends ElementTypeInformation
-    with ApplyableTypeInformation {
-  TypedElement get element => super.element;
-
-  /**
-   * If [element] is a function, [closurizedCount] is the number of
-   * times it is closurized. The value gets updated while infering.
-   */
-  int closurizedCount = 0;
-
-  /**
-   * This map contains the callers of [element]. It stores all unique call sites
-   * to enable counting the global number of call sites of [element].
-   *
-   * A call site is either an AST [ast.Node], a [cps_ir.Node] or in the case of
-   * synthesized calls, an [Element] (see uses of [synthesizeForwardingCall]
-   * in [SimpleTypeInferrerVisitor]).
-   */
-  final Map<Element, Setlet<Spannable>> _callers = new Map<Element, Setlet>();
-
-  MemberTypeInformation._internal(Element element)
-      : super._internal(null, element);
-
-  void addCall(Element caller, Spannable node) {
-    assert(node is ast.Node || node is cps_ir.Node || node is Element);
-    _callers.putIfAbsent(caller, () => new Setlet()).add(node);
-  }
-
-  void removeCall(Element caller, node) {
-    Setlet calls = _callers[caller];
-    if (calls == null) return;
-    calls.remove(node);
-    if (calls.isEmpty) {
-      _callers.remove(caller);
-    }
-  }
-
-  Iterable<Element> get callers => _callers.keys;
-
-  bool isCalledOnce() {
-    int count = 0;
-    for (var set in _callers.values) {
-      count += set.length;
-      if (count > 1) return false;
-    }
-    return count == 1;
-  }
-
-  bool get isClosurized => closurizedCount > 0;
-
-  // Closurized methods never become stable to ensure that the information in
-  // [users] is accurate. The inference stops tracking users for stable types.
-  // Note that we only override the getter, the setter will still modify the
-  // state of the [isStable] field inhertied from [TypeInformation].
-  bool get isStable => super.isStable && !isClosurized;
-
-  TypeMask handleSpecialCases(TypeGraphInferrerEngine inferrer) {
-    if (element.isField &&
-        !inferrer.compiler.backend.canBeUsedForGlobalOptimizations(element)) {
-      // Do not infer types for fields being assigned by synthesized calls.
-      giveUp(inferrer);
-      return safeType(inferrer);
-    }
-    if (inferrer.isNativeElement(element)) {
-      // Use the type annotation as the type for native elements. We
-      // also give up on inferring to make sure this element never
-      // goes in the work queue.
-      giveUp(inferrer);
-      if (element.isField) {
-        return inferrer.typeOfNativeBehavior(
-            native.NativeBehavior.ofFieldLoad(element, inferrer.compiler)).type;
-      } else {
-        assert(element.isFunction ||
-               element.isGetter ||
-               element.isSetter);
-        TypedElement typedElement = element;
-        var elementType = typedElement.type;
-        if (elementType.kind != TypeKind.FUNCTION) {
-          return safeType(inferrer);
-        } else {
-          return inferrer.typeOfNativeBehavior(
-              native.NativeBehavior.ofMethod(element, inferrer.compiler)).type;
-        }
-      }
-    }
-
-    Compiler compiler = inferrer.compiler;
-    if (element.declaration == compiler.intEnvironment) {
-      giveUp(inferrer);
-      return compiler.typesTask.intType.nullable();
-    } else if (element.declaration == compiler.boolEnvironment) {
-      giveUp(inferrer);
-      return compiler.typesTask.boolType.nullable();
-    } else if (element.declaration == compiler.stringEnvironment) {
-      giveUp(inferrer);
-      return compiler.typesTask.stringType.nullable();
-    }
-    return null;
-  }
-
-  TypeMask potentiallyNarrowType(TypeMask mask,
-                                 TypeGraphInferrerEngine inferrer) {
-    Compiler compiler = inferrer.compiler;
-    if (!compiler.trustTypeAnnotations && !compiler.enableTypeAssertions) {
-      return mask;
-    }
-    if (element.isGenerativeConstructor ||
-        element.isSetter) {
-      return mask;
-    }
-    if (element.isField) {
-      return new TypeMaskSystem(compiler).narrowType(mask, element.type);
-    }
-    assert(element.isFunction ||
-           element.isGetter ||
-           element.isFactoryConstructor);
-
-    FunctionType type = element.type;
-    return new TypeMaskSystem(compiler).narrowType(mask, type.returnType);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    TypeMask special = handleSpecialCases(inferrer);
-    if (special != null) return potentiallyNarrowType(special, inferrer);
-    return potentiallyNarrowType(
-        inferrer.types.computeTypeMask(assignments), inferrer);
-  }
-
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) {
-    return potentiallyNarrowType(super.safeType(inferrer), inferrer);
-  }
-
-  String toString() => 'MemberElement $element $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitMemberTypeInformation(this);
-  }
-
-  Element get owner => element.outermostEnclosingMemberOrTopLevel;
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    // The number of assignments of non-final fields is
-    // not stable. Therefore such a field cannot be stable.
-    if (element.isField && !(element.isConst || element.isFinal)) {
-      return false;
-    }
-
-    if (element.isFunction) return false;
-
-    return super.hasStableType(inferrer);
-  }
-}
-
-/**
- * A node representing parameters:
- *
- * - Parameters
- * - Initializing formals
- *
- * These should never be created directly but instead are constructed by
- * the [ElementTypeInformation] factory.
- */
-class ParameterTypeInformation extends ElementTypeInformation {
-  ParameterElement get element => super.element;
-
-  ParameterTypeInformation._internal(ParameterElement element,
-                                     TypeInformationSystem types)
-      : super._internal(types.getInferredTypeOf(element.functionDeclaration),
-                        element) {
-    assert(!element.functionDeclaration.isInstanceMember);
-  }
-
-  ParameterTypeInformation._instanceMember(ParameterElement element,
-                                           TypeInformationSystem types)
-      : super._withAssignments(
-          types.getInferredTypeOf(element.functionDeclaration),
-          element,
-          new ParameterAssignments()) {
-    assert(element.functionDeclaration.isInstanceMember);
-  }
-
-  bool isTearOffClosureParameter = false;
-
-  void tagAsTearOffClosureParameter(TypeGraphInferrerEngine inferrer) {
-    assert(element.isParameter);
-    isTearOffClosureParameter = true;
-  }
-
-  // TODO(herhut): Cleanup into one conditional.
-  TypeMask handleSpecialCases(TypeGraphInferrerEngine inferrer) {
-    if (!inferrer.compiler.backend.canBeUsedForGlobalOptimizations(element)) {
-      // Do not infer types for fields and parameters being assigned
-      // by synthesized calls.
-      giveUp(inferrer);
-      return safeType(inferrer);
-    }
-
-    // The below do not apply to parameters of constructors, so skip
-    // initializing formals.
-    if (element.isInitializingFormal) return null;
-
-    FunctionElement function = element.functionDeclaration;
-    if ((isTearOffClosureParameter || function.isLocal) &&
-        disableInferenceForClosures) {
-      // Do not infer types for parameters of closures. We do not
-      // clear the assignments in case the closure is successfully
-      // traced.
-      giveUp(inferrer, clearAssignments: false);
-      return safeType(inferrer);
-    }
-    if (function.isInstanceMember &&
-        (function.name == Compiler.NO_SUCH_METHOD ||
-        (function.name == Compiler.CALL_OPERATOR_NAME &&
-         disableInferenceForClosures))) {
-      // Do not infer types for parameters of [noSuchMethod] and
-      // [call] instance methods.
-      giveUp(inferrer);
-      return safeType(inferrer);
-    }
-    if (function == inferrer.mainElement) {
-      // The implicit call to main is not seen by the inferrer,
-      // therefore we explicitly set the type of its parameters as
-      // dynamic.
-      // TODO(14566): synthesize a call instead to get the exact
-      // types.
-      giveUp(inferrer);
-      return safeType(inferrer);
-    }
-
-    return null;
-  }
-
-  TypeMask potentiallyNarrowType(TypeMask mask,
-                                 TypeGraphInferrerEngine inferrer) {
-    Compiler compiler = inferrer.compiler;
-    if (!compiler.trustTypeAnnotations) {
-      return mask;
-    }
-    // When type assertions are enabled (aka checked mode), we have to always
-    // ignore type annotations to ensure that the checks are actually inserted
-    // into the function body and retained until runtime.
-    assert(!compiler.enableTypeAssertions);
-    return new TypeMaskSystem(compiler).narrowType(mask, element.type);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    TypeMask special = handleSpecialCases(inferrer);
-    if (special != null) return special;
-    return potentiallyNarrowType(inferrer.types.computeTypeMask(assignments),
-                                 inferrer);
-  }
-
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) {
-    return potentiallyNarrowType(super.safeType(inferrer), inferrer);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    // The number of assignments of parameters of instance methods is
-    // not stable. Therefore such a parameter cannot be stable.
-    if (element.functionDeclaration.isInstanceMember) {
-      return false;
-    }
-    return super.hasStableType(inferrer);
-  }
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitParameterTypeInformation(this);
-  }
-
-  String toString() => 'ParameterElement $element $type';
-}
-
-/**
- * A [CallSiteTypeInformation] is a call found in the AST, or a
- * synthesized call for implicit calls in Dart (such as forwarding
- * factories). The [call] field is a [ast.Node] for the former, and an
- * [Element] for the latter.
- *
- * In the inferrer graph, [CallSiteTypeInformation] nodes do not have
- * any assignment. They rely on the [caller] field for static calls,
- * and [selector] and [receiver] fields for dynamic calls.
- */
-abstract class CallSiteTypeInformation extends TypeInformation
-    with ApplyableTypeInformation {
-  final Spannable call;
-  final Element caller;
-  final Selector selector;
-  final ArgumentsTypes arguments;
-  final bool inLoop;
-
-  CallSiteTypeInformation(
-      MemberTypeInformation context,
-      this.call,
-      this.caller,
-      this.selector,
-      this.arguments,
-      this.inLoop) : super.noAssignments(context);
-
-  String toString() => 'Call site $call $type';
-
-  /// Add [this] to the graph being computed by [engine].
-  void addToGraph(TypeGraphInferrerEngine engine);
-
-  /// Return an iterable over the targets of this call.
-  Iterable<Element> get callees;
-
-  Element get owner => caller;
-}
-
-class StaticCallSiteTypeInformation extends CallSiteTypeInformation {
-  final Element calledElement;
-
-  StaticCallSiteTypeInformation(
-      MemberTypeInformation context,
-      Spannable call,
-      Element enclosing,
-      this.calledElement,
-      Selector selector,
-      ArgumentsTypes arguments,
-      bool inLoop)
-      : super(context, call, enclosing, selector, arguments, inLoop);
-
-  void addToGraph(TypeGraphInferrerEngine inferrer) {
-    MemberTypeInformation callee =
-        inferrer.types.getInferredTypeOf(calledElement);
-    callee.addCall(caller, call);
-    callee.addUser(this);
-    if (arguments != null) {
-      arguments.forEach((info) => info.addUser(this));
-    }
-    inferrer.updateParameterAssignments(
-        this, calledElement, arguments, selector, remove: false,
-        addToQueue: false);
-  }
-
-  bool get isSynthesized {
-    // Some calls do not have a corresponding node, for example
-    // fowarding factory constructors, or synthesized super
-    // constructor calls. We synthesize these calls but do
-    // not create a selector for them.
-    return selector == null;
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    if (isSynthesized) {
-      assert(arguments != null);
-      return inferrer.types.getInferredTypeOf(calledElement).type;
-    } else {
-      return inferrer.typeOfElementWithSelector(calledElement, selector).type;
-    }
-  }
-
-  Iterable<Element> get callees => [calledElement.implementation];
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitStaticCallSiteTypeInformation(this);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return inferrer.types.getInferredTypeOf(calledElement).isStable &&
-        (arguments == null || arguments.every((info) => info.isStable)) &&
-        super.hasStableType(inferrer);
-  }
-
-  void removeAndClearReferences(TypeGraphInferrerEngine inferrer) {
-    ElementTypeInformation callee =
-        inferrer.types.getInferredTypeOf(calledElement);
-    callee.removeUser(this);
-    if (arguments != null) {
-      arguments.forEach((info) => info.removeUser(this));
-    }
-    super.removeAndClearReferences(inferrer);
-  }
-}
-
-class DynamicCallSiteTypeInformation extends CallSiteTypeInformation {
-  final TypeInformation receiver;
-  /// Cached targets of this call.
-  Iterable<Element> targets;
-
-  DynamicCallSiteTypeInformation(
-      MemberTypeInformation context,
-      Spannable call,
-      Element enclosing,
-      Selector selector,
-      this.receiver,
-      ArgumentsTypes arguments,
-      bool inLoop)
-      : super(context, call, enclosing, selector, arguments, inLoop);
-
-  void addToGraph(TypeGraphInferrerEngine inferrer) {
-    assert(receiver != null);
-    Selector typedSelector = computeTypedSelector(inferrer);
-    targets = inferrer.compiler.world.allFunctions.filter(typedSelector);
-    receiver.addUser(this);
-    if (arguments != null) {
-      arguments.forEach((info) => info.addUser(this));
-    }
-    for (Element element in targets) {
-      MemberTypeInformation callee = inferrer.types.getInferredTypeOf(element);
-      callee.addCall(caller, call);
-      callee.addUser(this);
-      inferrer.updateParameterAssignments(
-          this, element, arguments, typedSelector, remove: false,
-          addToQueue: false);
-    }
-  }
-
-  Iterable<Element> get callees => targets.map((e) => e.implementation);
-
-  Selector computeTypedSelector(TypeGraphInferrerEngine inferrer) {
-    TypeMask receiverType = receiver.type;
-
-    if (selector.mask != receiverType) {
-      return receiverType == inferrer.compiler.typesTask.dynamicType
-          ? selector.asUntyped
-          : new TypedSelector(receiverType, selector, inferrer.classWorld);
-    } else {
-      return selector;
-    }
-  }
-
-  bool get targetsIncludeNoSuchMethod {
-    return targets.any((Element e) {
-      return e is FunctionElement &&
-             e.isInstanceMember &&
-             e.name == Compiler.NO_SUCH_METHOD;
-    });
-  }
-
-  /**
-   * We optimize certain operations on the [int] class because we know
-   * more about their return type than the actual Dart code. For
-   * example, we know int + int returns an int. The Dart code for
-   * [int.operator+] only says it returns a [num].
-   */
-  TypeInformation handleIntrisifiedSelector(Selector selector,
-                                            TypeGraphInferrerEngine inferrer) {
-    ClassWorld classWorld = inferrer.classWorld;
-    if (!classWorld.backend.intImplementation.isResolved) return null;
-    TypeMask emptyType = const TypeMask.nonNullEmpty();
-    if (selector.mask == null) return null;
-    if (!selector.mask.containsOnlyInt(classWorld)) {
-      return null;
-    }
-    if (!selector.isCall && !selector.isOperator) return null;
-    if (!arguments.named.isEmpty) return null;
-    if (arguments.positional.length > 1) return null;
-
-    ClassElement uint31Implementation = classWorld.backend.uint31Implementation;
-    bool isInt(info) => info.type.containsOnlyInt(classWorld);
-    bool isEmpty(info) => info.type == emptyType;
-    bool isUInt31(info) {
-      return info.type.satisfies(uint31Implementation, classWorld);
-    }
-    bool isPositiveInt(info) {
-      return info.type.satisfies(
-          classWorld.backend.positiveIntImplementation, classWorld);
-    }
-
-    String name = selector.name;
-    // We are optimizing for the cases that are not expressed in the
-    // Dart code, for example:
-    // int + int -> int
-    // uint31 | uint31 -> uint31
-    if (name == '*' || name == '+' || name == '%' || name == 'remainder' ||
-        name == '~/') {
-      if (isPositiveInt(receiver) &&
-          arguments.hasOnePositionalArgumentThatMatches(isPositiveInt)) {
-        return inferrer.types.positiveIntType;
-      } else if (arguments.hasOnePositionalArgumentThatMatches(isInt)) {
-        return inferrer.types.intType;
-      } else if (arguments.hasOnePositionalArgumentThatMatches(isEmpty)) {
-        return inferrer.types.nonNullEmptyType;
-      } else {
-        return null;
-      }
-    } else if (name == '|' || name == '^') {
-      if (isUInt31(receiver) &&
-          arguments.hasOnePositionalArgumentThatMatches(isUInt31)) {
-        return inferrer.types.uint31Type;
-      }
-    } else if (name == '>>') {
-      if (isUInt31(receiver)) {
-        return inferrer.types.uint31Type;
-      }
-    } else if (name == '&') {
-      if (isUInt31(receiver) ||
-          arguments.hasOnePositionalArgumentThatMatches(isUInt31)) {
-        return inferrer.types.uint31Type;
-      }
-    } else if (name == 'unary-') {
-      // The receiver being an int, the return value will also be an
-      // int.
-      return inferrer.types.intType;
-    } else if (name == '-') {
-      if (arguments.hasOnePositionalArgumentThatMatches(isInt)) {
-        return inferrer.types.intType;
-      } else if (arguments.hasOnePositionalArgumentThatMatches(isEmpty)) {
-        return inferrer.types.nonNullEmptyType;
-      }
-      return null;
-    } else if (name == 'abs') {
-      return arguments.hasNoArguments() ? inferrer.types.positiveIntType : null;
-    }
-    return null;
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    Iterable<Element> oldTargets = targets;
-    Selector typedSelector = computeTypedSelector(inferrer);
-    inferrer.updateSelectorInTree(caller, call, typedSelector);
-
-    Compiler compiler = inferrer.compiler;
-    Selector selectorToUse = typedSelector.extendIfReachesAll(compiler);
-    bool canReachAll = compiler.enabledInvokeOn &&
-        (selectorToUse != typedSelector);
-
-    // If this call could potentially reach all methods that satisfy
-    // the untyped selector (through noSuchMethod's `Invocation`
-    // and a call to `delegate`), we iterate over all these methods to
-    // update their parameter types.
-    targets = compiler.world.allFunctions.filter(selectorToUse);
-    Iterable<Element> typedTargets = canReachAll
-        ? compiler.world.allFunctions.filter(typedSelector)
-        : targets;
-
-    // Walk over the found targets, and compute the joined union type mask
-    // for all these targets.
-    TypeMask newType = inferrer.types.joinTypeMasks(targets.map((element) {
-      if (!oldTargets.contains(element)) {
-        MemberTypeInformation callee =
-            inferrer.types.getInferredTypeOf(element);
-        callee.addCall(caller, call);
-        callee.addUser(this);
-        inferrer.updateParameterAssignments(
-            this, element, arguments, typedSelector, remove: false,
-            addToQueue: true);
-      }
-
-      // If [canReachAll] is true, then we are iterating over all
-      // targets that satisfy the untyped selector. We skip the return
-      // type of the targets that can only be reached through
-      // `Invocation.delegate`. Note that the `noSuchMethod` targets
-      // are included in [typedTargets].
-      if (canReachAll && !typedTargets.contains(element)) {
-        return const TypeMask.nonNullEmpty();
-      }
-
-      if (inferrer.returnsListElementType(typedSelector)) {
-        ContainerTypeMask mask = receiver.type;
-        return mask.elementType;
-      } else if (inferrer.returnsMapValueType(typedSelector)) {
-        if (typedSelector.mask.isDictionary &&
-            arguments.positional[0].type.isValue) {
-          DictionaryTypeMask mask = typedSelector.mask;
-          ValueTypeMask arg = arguments.positional[0].type;
-          String key = arg.value;
-          if (mask.typeMap.containsKey(key)) {
-            if (_VERBOSE) {
-              print("Dictionary lookup for $key yields ${mask.typeMap[key]}.");
-            }
-            return mask.typeMap[key];
-          } else {
-            // The typeMap is precise, so if we do not find the key, the lookup
-            // will be [null] at runtime.
-            if (_VERBOSE) {
-              print("Dictionary lookup for $key yields [null].");
-            }
-            return inferrer.types.nullType.type;
-          }
-        }
-        MapTypeMask mask = typedSelector.mask;
-        if (_VERBOSE) {
-          print("Map lookup for $typedSelector yields ${mask.valueType}.");
-        }
-        return mask.valueType;
-      } else {
-        TypeInformation info =
-            handleIntrisifiedSelector(typedSelector, inferrer);
-        if (info != null) return info.type;
-        return inferrer.typeOfElementWithSelector(element, typedSelector).type;
-      }
-    }));
-
-    // Walk over the old targets, and remove calls that cannot happen
-    // anymore.
-    oldTargets.forEach((element) {
-      if (!targets.contains(element)) {
-        MemberTypeInformation callee =
-            inferrer.types.getInferredTypeOf(element);
-        callee.removeCall(caller, call);
-        callee.removeUser(this);
-        inferrer.updateParameterAssignments(
-            this, element, arguments, typedSelector, remove: true,
-            addToQueue: true);
-      }
-    });
-
-    return newType;
-  }
-
-  void giveUp(TypeGraphInferrerEngine inferrer, {bool clearAssignments: true}) {
-    if (!abandonInferencing) {
-      inferrer.updateSelectorInTree(caller, call, selector);
-      Iterable<Element> oldTargets = targets;
-      targets = inferrer.compiler.world.allFunctions.filter(selector);
-      for (Element element in targets) {
-        if (!oldTargets.contains(element)) {
-          MemberTypeInformation callee =
-              inferrer.types.getInferredTypeOf(element);
-          callee.addCall(caller, call);
-          inferrer.updateParameterAssignments(
-              this, element, arguments, selector, remove: false,
-              addToQueue: true);
-        }
-      }
-    }
-    super.giveUp(inferrer, clearAssignments: clearAssignments);
-  }
-
-  void removeAndClearReferences(TypeGraphInferrerEngine inferrer) {
-    for (Element element in targets) {
-      ElementTypeInformation callee = inferrer.types.getInferredTypeOf(element);
-      callee.removeUser(this);
-    }
-    if (arguments != null) {
-      arguments.forEach((info) => info.removeUser(this));
-    }
-    super.removeAndClearReferences(inferrer);
-  }
-
-  String toString() => 'Call site $call on ${receiver.type} $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitDynamicCallSiteTypeInformation(this);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return receiver.isStable &&
-        targets.every(
-            (element) => inferrer.types.getInferredTypeOf(element).isStable) &&
-        (arguments == null || arguments.every((info) => info.isStable)) &&
-        super.hasStableType(inferrer);
-  }
-}
-
-class ClosureCallSiteTypeInformation extends CallSiteTypeInformation {
-  final TypeInformation closure;
-
-  ClosureCallSiteTypeInformation(
-      MemberTypeInformation context,
-      Spannable call,
-      Element enclosing,
-      Selector selector,
-      this.closure,
-      ArgumentsTypes arguments,
-      bool inLoop)
-      : super(context, call, enclosing, selector, arguments, inLoop);
-
-  void addToGraph(TypeGraphInferrerEngine inferrer) {
-    arguments.forEach((info) => info.addUser(this));
-    closure.addUser(this);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) => safeType(inferrer);
-
-  Iterable<Element> get callees {
-    throw new UnsupportedError("Cannot compute callees of a closure call.");
-  }
-
-  String toString() => 'Closure call $call on $closure';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitClosureCallSiteTypeInformation(this);
-  }
-
-  void removeAndClearReferences(TypeGraphInferrerEngine inferrer) {
-    // This method is a placeholder for the following comment:
-    // We should maintain the information that the closure is a user
-    // of its arguments because we do not check that the arguments
-    // have a stable type for a closure call to be stable; our tracing
-    // analysis want to know whether an (non-stable) argument is
-    // passed to a closure.
-    return super.removeAndClearReferences(inferrer);
-  }
-}
-
-/**
- * A [ConcreteTypeInformation] represents a type that needed
- * to be materialized during the creation of the graph. For example,
- * literals, [:this:] or [:super:] need a [ConcreteTypeInformation].
- *
- * [ConcreteTypeInformation] nodes have no assignment. Also, to save
- * on memory, we do not add users to [ConcreteTypeInformation] nodes,
- * because we know such node will never be refined to a different
- * type.
- */
-class ConcreteTypeInformation extends TypeInformation {
-  ConcreteTypeInformation(TypeMask type) : super.untracked() {
-    this.type = type;
-    this.isStable = true;
-  }
-
-  bool get isConcrete => true;
-
-  void addUser(TypeInformation user) {
-    // Nothing to do, a concrete type does not get updated so never
-    // needs to notify its users.
-  }
-
-  void removeUser(TypeInformation user) {
-  }
-
-  void addAssignment(TypeInformation assignment) {
-    throw "Not supported";
-  }
-
-  void removeAssignment(TypeInformation assignment) {
-    throw "Not supported";
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) => type;
-
-  bool reset(TypeGraphInferrerEngine inferrer) {
-    throw "Not supported";
-  }
-
-  String toString() => 'Type $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitConcreteTypeInformation(this);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) => true;
-}
-
-class StringLiteralTypeInformation extends ConcreteTypeInformation {
-  final ast.DartString value;
-
-  StringLiteralTypeInformation(value, TypeMask mask)
-      : super(new ValueTypeMask(mask, value.slowToString())),
-        this.value = value;
-
-  String asString() => value.slowToString();
-  String toString() => 'Type $type value ${value.slowToString()}';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitStringLiteralTypeInformation(this);
-  }
-}
-
-/**
- * A [NarrowTypeInformation] narrows a [TypeInformation] to a type,
- * represented in [typeAnnotation].
- *
- * A [NarrowTypeInformation] node has only one assignment: the
- * [TypeInformation] it narrows.
- *
- * [NarrowTypeInformation] nodes are created for:
- *
- * - Code after `is` and `as` checks, where we have more information
- *   on the type of the right hand side of the expression.
- *
- * - Code after a dynamic call, where we have more information on the
- *   type of the receiver: it can only be of a class that holds a
- *   potential target of this dynamic call.
- *
- * - In checked mode, after a type annotation, we have more
- *   information on the type of a local.
- */
-class NarrowTypeInformation extends TypeInformation {
-  final TypeMask typeAnnotation;
-
-  NarrowTypeInformation(TypeInformation narrowedType, this.typeAnnotation)
-      : super(narrowedType.context) {
-    addAssignment(narrowedType);
-  }
-
-  addAssignment(TypeInformation info) {
-    super.addAssignment(info);
-    assert(assignments.length == 1);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    TypeMask input = assignments.first.type;
-    TypeMask intersection = input.intersection(typeAnnotation,
-        inferrer.classWorld);
-    if (_ANOMALY_WARN) {
-      if (!input.containsMask(intersection, inferrer.classWorld) ||
-          !typeAnnotation.containsMask(intersection, inferrer.classWorld)) {
-        print("ANOMALY WARNING: narrowed $input to $intersection via "
-            "$typeAnnotation");
-      }
-    }
-    return intersection;
-  }
-
-  String toString() {
-    return 'Narrow to $typeAnnotation $type';
-  }
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitNarrowTypeInformation(this);
-  }
-}
-
-/**
- * An [InferredTypeInformation] is a [TypeInformation] that
- * defaults to the dynamic type until it is marked as beeing
- * inferred, at which point it computes its type based on
- * its assignments.
- */
-abstract class InferredTypeInformation extends TypeInformation {
-  /** Whether the element type in that container has been inferred. */
-  bool inferred = false;
-
-  InferredTypeInformation(MemberTypeInformation context,
-                          TypeInformation parentType)
-      : super(context) {
-    if (parentType != null) addAssignment(parentType);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    if (!inferred) return safeType(inferrer);
-    return inferrer.types.computeTypeMask(assignments);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return inferred && super.hasStableType(inferrer);
-  }
-}
-
-/**
- * A [ListTypeInformation] is a [TypeInformation] created
- * for each `List` instantiations.
- */
-class ListTypeInformation extends TypeInformation
-    with TracedTypeInformation {
-  final ElementInContainerTypeInformation elementType;
-
-  /** The container type before it is inferred. */
-  final ContainerTypeMask originalType;
-
-  /** The length at the allocation site. */
-  final int originalLength;
-
-  /** The length after the container has been traced. */
-  int inferredLength;
-
-  /**
-   * Whether this list goes through a growable check.
-   * We conservatively assume it does.
-   */
-  bool checksGrowable = true;
-
-  ListTypeInformation(MemberTypeInformation context,
-                      this.originalType,
-                      this.elementType,
-                      this.originalLength)
-      : super(context) {
-    type = originalType;
-    inferredLength = originalType.length;
-    elementType.addUser(this);
-  }
-
-  String toString() => 'List type $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitListTypeInformation(this);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return elementType.isStable && super.hasStableType(inferrer);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    var mask = type;
-    if (!mask.isContainer ||
-        mask.elementType != elementType.type ||
-        mask.length != inferredLength) {
-      return new ContainerTypeMask(originalType.forwardTo,
-                                   originalType.allocationNode,
-                                   originalType.allocationElement,
-                                   elementType.type,
-                                   inferredLength);
-    }
-    return mask;
-  }
-
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) => originalType;
-}
-
-/**
- * An [ElementInContainerTypeInformation] holds the common type of the
- * elements in a [ListTypeInformation].
- */
-class ElementInContainerTypeInformation extends InferredTypeInformation {
-  ElementInContainerTypeInformation(MemberTypeInformation context,
-      elementType)
-      : super(context, elementType);
-
-  String toString() => 'Element in container $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitElementInContainerTypeInformation(this);
-  }
-}
-
-/**
- * A [MapTypeInformation] is a [TypeInformation] created
- * for maps.
- */
-class MapTypeInformation extends TypeInformation
-    with TracedTypeInformation {
-  // When in Dictionary mode, this map tracks the type of the values that
-  // have been assigned to a specific [String] key.
-  final Map<String, ValueInMapTypeInformation> typeInfoMap = {};
-  // These fields track the overall type of the keys/values in the map.
-  final KeyInMapTypeInformation keyType;
-  final ValueInMapTypeInformation valueType;
-  final MapTypeMask originalType;
-
-  // Set to false if a statically unknown key flows into this map.
-  bool _allKeysAreStrings = true;
-
-  bool get inDictionaryMode => !bailedOut && _allKeysAreStrings;
-
-  MapTypeInformation(MemberTypeInformation context,
-                     this.originalType,
-                     this.keyType,
-                     this.valueType)
-      : super(context) {
-    keyType.addUser(this);
-    valueType.addUser(this);
-    type = originalType;
-  }
-
-  TypeInformation addEntryAssignment(TypeInformation key,
-                                     TypeInformation value,
-                                     [bool nonNull = false]) {
-    TypeInformation newInfo = null;
-    if (_allKeysAreStrings && key is StringLiteralTypeInformation) {
-      String keyString = key.asString();
-      typeInfoMap.putIfAbsent(keyString, () {
-          newInfo = new ValueInMapTypeInformation(context, null, nonNull);
-          return newInfo;
-      });
-      typeInfoMap[keyString].addAssignment(value);
-    } else {
-      _allKeysAreStrings = false;
-      typeInfoMap.clear();
-    }
-    keyType.addAssignment(key);
-    valueType.addAssignment(value);
-    if (newInfo != null) newInfo.addUser(this);
-
-    return newInfo;
-  }
-
-  List<TypeInformation> addMapAssignment(MapTypeInformation other) {
-    List<TypeInformation> newInfos = <TypeInformation>[];
-    if (_allKeysAreStrings && other.inDictionaryMode) {
-      other.typeInfoMap.forEach((keyString, value) {
-        typeInfoMap.putIfAbsent(keyString, () {
-          TypeInformation newInfo =
-              new ValueInMapTypeInformation(context, null, false);
-          newInfos.add(newInfo);
-          return newInfo;
-        });
-        typeInfoMap[keyString].addAssignment(value);
-      });
-    } else {
-      _allKeysAreStrings = false;
-      typeInfoMap.clear();
-    }
-    keyType.addAssignment(other.keyType);
-    valueType.addAssignment(other.valueType);
-
-    return newInfos;
-  }
-
-  markAsInferred() {
-    keyType.inferred = valueType.inferred = true;
-    typeInfoMap.values.forEach((v) => v.inferred = true);
-  }
-
-  addAssignment(TypeInformation other) {
-    throw "not supported";
-  }
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitMapTypeInformation(this);
-  }
-
-  TypeMask toTypeMask(TypeGraphInferrerEngine inferrer) {
-    if (inDictionaryMode) {
-      Map<String, TypeMask> mappings = new Map<String, TypeMask>();
-      for (var key in typeInfoMap.keys) {
-        mappings[key] = typeInfoMap[key].type;
-      }
-      return new DictionaryTypeMask(originalType.forwardTo,
-                                    originalType.allocationNode,
-                                    originalType.allocationElement,
-                                    keyType.type,
-                                    valueType.type,
-                                    mappings);
-    } else {
-      return new MapTypeMask(originalType.forwardTo,
-                             originalType.allocationNode,
-                             originalType.allocationElement,
-                             keyType.type,
-                             valueType.type);
-    }
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    if (type.isDictionary != inDictionaryMode) {
-      return toTypeMask(inferrer);
-    } else if (type.isDictionary) {
-      assert(inDictionaryMode);
-      DictionaryTypeMask mask = type;
-      for (var key in typeInfoMap.keys) {
-        TypeInformation value = typeInfoMap[key];
-        if (!mask.typeMap.containsKey(key) &&
-            !value.type.containsAll(inferrer.classWorld) &&
-            !value.type.isNullable) {
-          return toTypeMask(inferrer);
-        }
-        if (mask.typeMap[key] != typeInfoMap[key].type) {
-          return toTypeMask(inferrer);
-        }
-      }
-    } else if (type.isMap) {
-      MapTypeMask mask = type;
-      if (mask.keyType != keyType.type ||
-          mask.valueType != valueType.type) {
-        return toTypeMask(inferrer);
-      }
-    } else {
-      return toTypeMask(inferrer);
-    }
-
-    return type;
-  }
-
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) => originalType;
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return keyType.isStable &&
-           valueType.isStable &&
-           super.hasStableType(inferrer);
-  }
-
-  String toString() {
-    return 'Map $type (K:$keyType, V:$valueType) contents $typeInfoMap';
-  }
-}
-
-/**
- * A [KeyInMapTypeInformation] holds the common type
- * for the keys in a [MapTypeInformation]
- */
-class KeyInMapTypeInformation extends InferredTypeInformation {
-  KeyInMapTypeInformation(MemberTypeInformation context,
-      TypeInformation keyType)
-      : super(context, keyType);
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitKeyInMapTypeInformation(this);
-  }
-
-  String toString() => 'Key in Map $type';
-}
-
-/**
- * A [ValueInMapTypeInformation] holds the common type
- * for the values in a [MapTypeInformation]
- */
-class ValueInMapTypeInformation extends InferredTypeInformation {
-  // [nonNull] is set to true if this value is known to be part of the map.
-  // Note that only values assigned to a specific key value in dictionary
-  // mode can ever be marked as [nonNull].
-  final bool nonNull;
-
-  ValueInMapTypeInformation(MemberTypeInformation context,
-      TypeInformation valueType, [this.nonNull = false])
-      : super(context, valueType);
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitValueInMapTypeInformation(this);
-  }
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    return nonNull ? super.computeType(inferrer)
-                   : super.computeType(inferrer).nullable();
-  }
-
-  String toString() => 'Value in Map $type';
-}
-
-/**
- * A [PhiElementTypeInformation] is an union of
- * [ElementTypeInformation], that is local to a method.
- */
-class PhiElementTypeInformation extends TypeInformation {
-  final ast.Node branchNode;
-  final bool isLoopPhi;
-  final Local variable;
-
-  PhiElementTypeInformation(MemberTypeInformation context, this.branchNode,
-                            this.isLoopPhi, this.variable)
-      : super(context);
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) {
-    return inferrer.types.computeTypeMask(assignments);
-  }
-
-  String toString() => 'Phi $variable $type';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitPhiElementTypeInformation(this);
-  }
-}
-
-class ClosureTypeInformation extends TypeInformation
-    with ApplyableTypeInformation {
-  final ast.Node node;
-  final Element element;
-
-  ClosureTypeInformation(MemberTypeInformation context, this.node,
-                         this.element)
-      : super(context);
-
-  TypeMask computeType(TypeGraphInferrerEngine inferrer) => safeType(inferrer);
-
-  TypeMask safeType(TypeGraphInferrerEngine inferrer) {
-    return inferrer.types.functionType.type;
-  }
-
-  String toString() => 'Closure $element';
-
-  accept(TypeInformationVisitor visitor) {
-    return visitor.visitClosureTypeInformation(this);
-  }
-
-  bool hasStableType(TypeGraphInferrerEngine inferrer) {
-    return false;
-  }
-}
-
-/**
- * Mixin for [TypeInformation] nodes that can bail out during tracing.
- */
-abstract class TracedTypeInformation implements TypeInformation {
-  /// Set to false once analysis has succeeded.
-  bool bailedOut = true;
-  /// Set to true once analysis is completed.
-  bool analyzed = false;
-
-  Set<TypeInformation> _flowsInto;
-
-  /**
-   * The set of [TypeInformation] nodes where values from the traced node could
-   * flow in.
-   */
-  Set<TypeInformation> get flowsInto {
-    return (_flowsInto == null) ? const ImmutableEmptySet<TypeInformation>()
-                                : _flowsInto;
-  }
-
-  /**
-   * Adds [nodes] to the sets of values this [TracedTypeInformation] flows into.
-   */
-  void addFlowsIntoTargets(Iterable<TypeInformation> nodes) {
-    if (_flowsInto == null) {
-      _flowsInto = nodes.toSet();
-    } else {
-      _flowsInto.addAll(nodes);
-    }
-  }
-}
-
-abstract class TypeInformationVisitor<T> {
-  T visitNarrowTypeInformation(NarrowTypeInformation info);
-  T visitPhiElementTypeInformation(PhiElementTypeInformation info);
-  T visitElementInContainerTypeInformation(
-      ElementInContainerTypeInformation info);
-  T visitKeyInMapTypeInformation(KeyInMapTypeInformation info);
-  T visitValueInMapTypeInformation(ValueInMapTypeInformation info);
-  T visitListTypeInformation(ListTypeInformation info);
-  T visitMapTypeInformation(MapTypeInformation info);
-  T visitConcreteTypeInformation(ConcreteTypeInformation info);
-  T visitStringLiteralTypeInformation(StringLiteralTypeInformation info);
-  T visitClosureCallSiteTypeInformation(ClosureCallSiteTypeInformation info);
-  T visitStaticCallSiteTypeInformation(StaticCallSiteTypeInformation info);
-  T visitDynamicCallSiteTypeInformation(DynamicCallSiteTypeInformation info);
-  T visitMemberTypeInformation(MemberTypeInformation info);
-  T visitParameterTypeInformation(ParameterTypeInformation info);
-  T visitClosureTypeInformation(ClosureTypeInformation info);
-}