// 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.

part of js_backend;

class JavaScriptItemCompilationContext extends ItemCompilationContext {
  final Set<HInstruction> boundsChecked;

  JavaScriptItemCompilationContext()
      : boundsChecked = new Set<HInstruction>();
}

class CheckedModeHelper {
  final SourceString name;

  const CheckedModeHelper(SourceString this.name);

  Element getElement(Compiler compiler) => compiler.findHelper(name);

  jsAst.Expression generateCall(SsaCodeGenerator codegen,
                                HTypeConversion node) {
    Element helperElement = getElement(codegen.compiler);
    codegen.world.registerStaticUse(helperElement);
    List<jsAst.Expression> arguments = <jsAst.Expression>[];
    codegen.use(node.checkedInput);
    arguments.add(codegen.pop());
    generateAdditionalArguments(codegen, node, arguments);
    String helperName = codegen.backend.namer.isolateAccess(helperElement);
    return new jsAst.Call(new jsAst.VariableUse(helperName), arguments);
  }

  void generateAdditionalArguments(SsaCodeGenerator codegen,
                                   HTypeConversion node,
                                   List<jsAst.Expression> arguments) {
    // No additional arguments needed.
  }
}

class PropertyCheckedModeHelper extends CheckedModeHelper {
  const PropertyCheckedModeHelper(SourceString name) : super(name);

  void generateAdditionalArguments(SsaCodeGenerator codegen,
                                   HTypeConversion node,
                                   List<jsAst.Expression> arguments) {
    DartType type = node.typeExpression;
    String additionalArgument = codegen.backend.namer.operatorIsType(type);
    arguments.add(js.string(additionalArgument));
  }
}

class TypeVariableCheckedModeHelper extends CheckedModeHelper {
  const TypeVariableCheckedModeHelper(SourceString name) : super(name);

  void generateAdditionalArguments(SsaCodeGenerator codegen,
                                   HTypeConversion node,
                                   List<jsAst.Expression> arguments) {
    assert(node.typeExpression.kind == TypeKind.TYPE_VARIABLE);
    codegen.use(node.typeRepresentation);
    arguments.add(codegen.pop());
  }
}

class SubtypeCheckedModeHelper extends CheckedModeHelper {
  const SubtypeCheckedModeHelper(SourceString name) : super(name);

  void generateAdditionalArguments(SsaCodeGenerator codegen,
                                   HTypeConversion node,
                                   List<jsAst.Expression> arguments) {
    DartType type = node.typeExpression;
    Element element = type.element;
    String isField = codegen.backend.namer.operatorIs(element);
    arguments.add(js.string(isField));
    codegen.use(node.typeRepresentation);
    arguments.add(codegen.pop());
    String asField = codegen.backend.namer.substitutionName(element);
    arguments.add(js.string(asField));
  }
}

class FunctionTypeCheckedModeHelper extends CheckedModeHelper {
  const FunctionTypeCheckedModeHelper(SourceString name) : super(name);

  void generateAdditionalArguments(SsaCodeGenerator codegen,
                                   HTypeConversion node,
                                   List<jsAst.Expression> arguments) {
    DartType type = node.typeExpression;
    String signatureName = codegen.backend.namer.getFunctionTypeName(type);
    arguments.add(js.string(signatureName));

    if (type.containsTypeVariables) {
      ClassElement contextClass = Types.getClassContext(type);
      // TODO(ahe): Creating a string here is unfortunate. It is slow (due to
      // string concatenation in the implementation), and may prevent
      // segmentation of '$'.
      String contextName = codegen.backend.namer.getNameForRti(contextClass);
      arguments.add(js.string(contextName));

      if (node.contextIsTypeArguments) {
        arguments.add(new jsAst.LiteralNull());
        codegen.use(node.context);
        arguments.add(codegen.pop());
      } else {
        codegen.use(node.context);
        arguments.add(codegen.pop());
      }
    }
  }
}

/*
 * Invariants:
 *   canInline(function) implies canInline(function, insideLoop:true)
 *   !canInline(function, insideLoop: true) implies !canInline(function)
 */
class FunctionInlineCache {
  final Map<FunctionElement, bool> canBeInlined =
      new Map<FunctionElement, bool>();

  final Map<FunctionElement, bool> canBeInlinedInsideLoop =
      new Map<FunctionElement, bool>();

  // Returns [:true:]/[:false:] if we have a cached decision.
  // Returns [:null:] otherwise.
  bool canInline(FunctionElement element, {bool insideLoop}) {
    return insideLoop ? canBeInlinedInsideLoop[element] : canBeInlined[element];
  }

  void markAsInlinable(FunctionElement element, {bool insideLoop}) {
    if (insideLoop) {
      canBeInlinedInsideLoop[element] = true;
    } else {
      // If we can inline a function outside a loop then we should do it inside
      // a loop as well.
      canBeInlined[element] = true;
      canBeInlinedInsideLoop[element] = true;
    }
  }

  void markAsNonInlinable(FunctionElement element, {bool insideLoop}) {
    if (insideLoop) {
      // If we can't inline a function inside a loop, then we should not inline
      // it outside a loop either.
      canBeInlined[element] = false;
      canBeInlinedInsideLoop[element] = false;
    } else {
      canBeInlined[element] = false;
    }
  }
}


class JavaScriptBackend extends Backend {
  SsaBuilderTask builder;
  SsaOptimizerTask optimizer;
  SsaCodeGeneratorTask generator;
  CodeEmitterTask emitter;

  /**
   * The generated code as a js AST for compiled methods.
   */
  Map<Element, jsAst.Expression> get generatedCode {
    return compiler.enqueuer.codegen.generatedCode;
  }

  /**
   * The generated code as a js AST for compiled bailout methods.
   */
  final Map<Element, jsAst.Expression> generatedBailoutCode =
      new Map<Element, jsAst.Expression>();

  FunctionInlineCache inlineCache = new FunctionInlineCache();

  ClassElement jsInterceptorClass;
  ClassElement jsStringClass;
  ClassElement jsArrayClass;
  ClassElement jsNumberClass;
  ClassElement jsIntClass;
  ClassElement jsDoubleClass;
  ClassElement jsNullClass;
  ClassElement jsBoolClass;
  ClassElement jsPlainJavaScriptObjectClass;
  ClassElement jsUnknownJavaScriptObjectClass;

  ClassElement jsIndexableClass;
  ClassElement jsMutableIndexableClass;

  ClassElement jsMutableArrayClass;
  ClassElement jsFixedArrayClass;
  ClassElement jsExtendableArrayClass;

  Element jsIndexableLength;
  Element jsArrayRemoveLast;
  Element jsArrayAdd;
  Element jsStringSplit;
  Element jsStringToString;
  Element jsStringOperatorAdd;
  Element objectEquals;

  ClassElement typeLiteralClass;
  ClassElement mapLiteralClass;
  ClassElement constMapLiteralClass;

  Element getInterceptorMethod;
  Element interceptedNames;

  /**
   * This element is a top-level variable (in generated output) that the
   * compiler initializes to a datastructure used to map from a Type to the
   * interceptor.  See declaration of `mapTypeToInterceptor` in
   * `interceptors.dart`.
   */
  Element mapTypeToInterceptor;

  HType stringType;
  HType indexablePrimitiveType;
  HType readableArrayType;
  HType mutableArrayType;
  HType fixedArrayType;
  HType extendableArrayType;

  // TODO(9577): Make it so that these are not needed when there are no native
  // classes.
  Element dispatchPropertyName;
  Element getNativeInterceptorMethod;
  Element defineNativeMethodsFinishMethod;
  bool needToInitializeDispatchProperty = false;

  bool seenAnyClass = false;

  final Namer namer;

  /**
   * Interface used to determine if an object has the JavaScript
   * indexing behavior. The interface is only visible to specific
   * libraries.
   */
  ClassElement jsIndexingBehaviorInterface;

  /**
   * A collection of selectors that must have a one shot interceptor
   * generated.
   */
  final Map<String, Selector> oneShotInterceptors;

  /**
   * The members of instantiated interceptor classes: maps a member name to the
   * list of members that have that name. This map is used by the codegen to
   * know whether a send must be intercepted or not.
   */
  final Map<SourceString, Set<Element>> interceptedElements;
  // TODO(sra): Not all methods in the Set always require an interceptor.  A
  // method may be mixed into a true interceptor *and* a plain class. For the
  // method to work on the interceptor class it needs to use the explicit
  // receiver.  This constrains the call on a known plain receiver to pass the
  // explicit receiver.  https://code.google.com/p/dart/issues/detail?id=8942

  /**
   * A map of specialized versions of the [getInterceptorMethod].
   * Since [getInterceptorMethod] is a hot method at runtime, we're
   * always specializing it based on the incoming type. The keys in
   * the map are the names of these specialized versions. Note that
   * the generic version that contains all possible type checks is
   * also stored in this map.
   */
  final Map<String, Set<ClassElement>> specializedGetInterceptors;

  /**
   * Set of classes whose methods are intercepted.
   */
  final Set<ClassElement> _interceptedClasses = new Set<ClassElement>();

  /**
   * Set of classes used as mixins on native classes.  Methods on these classes
   * might also be mixed in to non-native classes.
   */
  final Set<ClassElement> classesMixedIntoNativeClasses =
      new Set<ClassElement>();

  /**
   * Set of classes whose `operator ==` methods handle `null` themselves.
   */
  final Set<ClassElement> specialOperatorEqClasses = new Set<ClassElement>();

  List<CompilerTask> get tasks {
    return <CompilerTask>[builder, optimizer, generator, emitter];
  }

  final RuntimeTypes rti;

  /// Holds the method "disableTreeShaking" in js_mirrors when
  /// dart:mirrors has been loaded.
  FunctionElement disableTreeShakingMarker;

  /// Holds the method "preserveNames" in js_mirrors when
  /// dart:mirrors has been loaded.
  FunctionElement preserveNamesMarker;

  /// Holds the method "preserveMetadata" in js_mirrors when
  /// dart:mirrors has been loaded.
  FunctionElement preserveMetadataMarker;

  /// True if a call to preserveMetadataMarker has been seen.  This means that
  /// metadata must be retained for dart:mirrors to work correctly.
  bool mustRetainMetadata = false;

  /// True if any metadata has been retained.  This is slightly different from
  /// [mustRetainMetadata] and tells us if any metadata was retained.  For
  /// example, if [mustRetainMetadata] is true but there is no metadata in the
  /// program, this variable will stil be false.
  bool hasRetainedMetadata = false;

  /// True if a call to preserveNames has been seen.
  bool mustPreserveNames = false;

  /// True if a call to disableTreeShaking has been seen.
  bool isTreeShakingDisabled = false;

  /// True if there isn't sufficient @MirrorsUsed data.
  bool hasInsufficientMirrorsUsed = false;

  /// List of constants from metadata.  If metadata must be preserved,
  /// these constants must be registered.
  final List<Dependency> metadataConstants = <Dependency>[];

  /// List of symbols that the user has requested for reflection.
  final Set<String> symbolsUsed = new Set<String>();

  /// List of elements that the user has requested for reflection.
  final Set<Element> targetsUsed = new Set<Element>();

  /// List of annotations provided by user that indicate that the annotated
  /// element must be retained.
  final Set<Element> metaTargetsUsed = new Set<Element>();

  /// List of elements that the backend may use.
  final Set<Element> helpersUsed = new Set<Element>();


  /// Set of typedefs that are used as type literals.
  final Set<TypedefElement> typedefTypeLiterals = new Set<TypedefElement>();

  /// All the checked mode helpers.
  static const checkedModeHelpers = const [
      const CheckedModeHelper(const SourceString('voidTypeCheck')),
      const CheckedModeHelper(const SourceString('stringTypeCast')),
      const CheckedModeHelper(const SourceString('stringTypeCheck')),
      const CheckedModeHelper(const SourceString('doubleTypeCast')),
      const CheckedModeHelper(const SourceString('doubleTypeCheck')),
      const CheckedModeHelper(const SourceString('numTypeCast')),
      const CheckedModeHelper(const SourceString('numTypeCheck')),
      const CheckedModeHelper(const SourceString('boolTypeCast')),
      const CheckedModeHelper(const SourceString('boolTypeCheck')),
      const CheckedModeHelper(const SourceString('intTypeCast')),
      const CheckedModeHelper(const SourceString('intTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('numberOrStringSuperNativeTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('numberOrStringSuperNativeTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('numberOrStringSuperTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('numberOrStringSuperTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('stringSuperNativeTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('stringSuperNativeTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('stringSuperTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('stringSuperTypeCheck')),
      const CheckedModeHelper(const SourceString('listTypeCast')),
      const CheckedModeHelper(const SourceString('listTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('listSuperNativeTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('listSuperNativeTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('listSuperTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('listSuperTypeCheck')),
      const PropertyCheckedModeHelper(
          const SourceString('interceptedTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('interceptedTypeCheck')),
      const SubtypeCheckedModeHelper(
          const SourceString('subtypeCast')),
      const SubtypeCheckedModeHelper(
          const SourceString('assertSubtype')),
      const TypeVariableCheckedModeHelper(
          const SourceString('subtypeOfRuntimeTypeCast')),
      const TypeVariableCheckedModeHelper(
          const SourceString('assertSubtypeOfRuntimeType')),
      const FunctionTypeCheckedModeHelper(
          const SourceString('functionSubtypeCast')),
      const FunctionTypeCheckedModeHelper(
          const SourceString('assertFunctionSubtype')),
      const PropertyCheckedModeHelper(
          const SourceString('propertyTypeCast')),
      const PropertyCheckedModeHelper(
          const SourceString('propertyTypeCheck')) ];

  // Checked mode helpers indexed by name.
  Map<String, CheckedModeHelper> checkedModeHelperByName =
      new Map<String, CheckedModeHelper>.fromIterable(
          checkedModeHelpers,
          key: (helper) => helper.name.slowToString());

  /// Number of methods compiled before considering reflection.
  int preMirrorsMethodCount = 0;

  /// Resolution and codegen support for generating table of interceptors and
  /// constructors for custom elements.
  CustomElementsAnalysis customElementsAnalysis;

  JavaScriptBackend(Compiler compiler, bool generateSourceMap)
      : namer = determineNamer(compiler),
        oneShotInterceptors = new Map<String, Selector>(),
        interceptedElements = new Map<SourceString, Set<Element>>(),
        rti = new RuntimeTypes(compiler),
        specializedGetInterceptors = new Map<String, Set<ClassElement>>(),
        super(compiler, JAVA_SCRIPT_CONSTANT_SYSTEM) {
    emitter = new CodeEmitterTask(compiler, namer, generateSourceMap);
    builder = new SsaBuilderTask(this);
    optimizer = new SsaOptimizerTask(this);
    generator = new SsaCodeGeneratorTask(this);
    customElementsAnalysis = new CustomElementsAnalysis(this);
  }

  static Namer determineNamer(Compiler compiler) {
    return compiler.enableMinification ?
        new MinifyNamer(compiler) :
        new Namer(compiler);
  }

  bool usedByBackend(Element element) {
    if (element.isParameter()
        || element.isFieldParameter()
        || element.isField()) {
      if (usedByBackend(element.enclosingElement)) return true;
    }
    return helpersUsed.contains(element.declaration);
  }

  bool invokedReflectively(Element element) {
    if (element.isParameter() || element.isFieldParameter()) {
      if (hasInsufficientMirrorsUsed && compiler.enabledInvokeOn) return true;
      if (invokedReflectively(element.enclosingElement)) return true;
    }

    if (element.isField()) {
      if (Elements.isStaticOrTopLevel(element)
          && (element.modifiers.isFinal() || element.modifiers.isConst())) {
        return false;
      }
      if (hasInsufficientMirrorsUsed && compiler.enabledInvokeOn) return true;
    }

    return isNeededForReflection(element.declaration);
  }

  bool canBeUsedForGlobalOptimizations(Element element) {
    return !usedByBackend(element) && !invokedReflectively(element);
  }

  bool isInterceptorClass(ClassElement element) {
    if (element == null) return false;
    if (Elements.isNativeOrExtendsNative(element)) return true;
    if (interceptedClasses.contains(element)) return true;
    if (classesMixedIntoNativeClasses.contains(element)) return true;
    return false;
  }

  String registerOneShotInterceptor(Selector selector) {
    Set<ClassElement> classes = getInterceptedClassesOn(selector.name);
    String name = namer.getOneShotInterceptorName(selector, classes);
    if (!oneShotInterceptors.containsKey(name)) {
      registerSpecializedGetInterceptor(classes);
      oneShotInterceptors[name] = selector;
    }
    return name;
  }

  bool isInterceptedMethod(Element element) {
    if (!element.isInstanceMember()) return false;
    if (element.isGenerativeConstructorBody()) {
      return Elements.isNativeOrExtendsNative(element.getEnclosingClass());
    }
    return interceptedElements[element.name] != null;
  }

  bool fieldHasInterceptedGetter(Element element) {
    assert(element.isField());
    return interceptedElements[element.name] != null;
  }

  bool fieldHasInterceptedSetter(Element element) {
    assert(element.isField());
    return interceptedElements[element.name] != null;
  }

  bool isInterceptedName(SourceString name) {
    return interceptedElements[name] != null;
  }

  bool isInterceptedSelector(Selector selector) {
    return interceptedElements[selector.name] != null;
  }

  final Map<SourceString, Set<ClassElement>> interceptedClassesCache =
      new Map<SourceString, Set<ClassElement>>();

  /**
   * Returns a set of interceptor classes that contain a member named
   * [name]. Returns [:null:] if there is no class.
   */
  Set<ClassElement> getInterceptedClassesOn(SourceString name) {
    Set<Element> intercepted = interceptedElements[name];
    if (intercepted == null) return null;
    return interceptedClassesCache.putIfAbsent(name, () {
      // Populate the cache by running through all the elements and
      // determine if the given selector applies to them.
      Set<ClassElement> result = new Set<ClassElement>();
      for (Element element in intercepted) {
        ClassElement classElement = element.getEnclosingClass();
        if (Elements.isNativeOrExtendsNative(classElement)
            || interceptedClasses.contains(classElement)) {
          result.add(classElement);
        }
        if (classesMixedIntoNativeClasses.contains(classElement)) {
          Set<ClassElement> nativeSubclasses =
              nativeSubclassesOfMixin(classElement);
          if (nativeSubclasses != null) result.addAll(nativeSubclasses);
        }
      }
      return result;
    });
  }

  Set<ClassElement> nativeSubclassesOfMixin(ClassElement mixin) {
    Set<MixinApplicationElement> uses = compiler.world.mixinUses[mixin];
    if (uses == null) return null;
    Set<ClassElement> result = null;
    for (MixinApplicationElement use in uses) {
      Iterable<ClassElement> subclasses = compiler.world.subclassesOf(use);
      if (subclasses != null) {
        for (ClassElement subclass in subclasses) {
          if (Elements.isNativeOrExtendsNative(subclass)) {
            if (result == null) result = new Set<ClassElement>();
            result.add(subclass);
          }
        }
      }
    }
    return result;
  }

  bool operatorEqHandlesNullArgument(FunctionElement operatorEqfunction) {
    return specialOperatorEqClasses.contains(
        operatorEqfunction.getEnclosingClass());
  }

  void initializeHelperClasses() {
    getInterceptorMethod =
        compiler.findInterceptor(const SourceString('getInterceptor'));
    interceptedNames =
        compiler.findInterceptor(const SourceString('interceptedNames'));
    mapTypeToInterceptor =
        compiler.findInterceptor(const SourceString('mapTypeToInterceptor'));
    dispatchPropertyName =
        compiler.findInterceptor(const SourceString('dispatchPropertyName'));
    getNativeInterceptorMethod =
        compiler.findInterceptor(const SourceString('getNativeInterceptor'));
    defineNativeMethodsFinishMethod =
        compiler.findHelper(const SourceString('defineNativeMethodsFinish'));

    // These methods are overwritten with generated versions.
    inlineCache.markAsNonInlinable(getInterceptorMethod, insideLoop: true);

    List<ClassElement> classes = [
      jsInterceptorClass =
          compiler.findInterceptor(const SourceString('Interceptor')),
      jsStringClass = compiler.findInterceptor(const SourceString('JSString')),
      jsArrayClass = compiler.findInterceptor(const SourceString('JSArray')),
      // The int class must be before the double class, because the
      // emitter relies on this list for the order of type checks.
      jsIntClass = compiler.findInterceptor(const SourceString('JSInt')),
      jsDoubleClass = compiler.findInterceptor(const SourceString('JSDouble')),
      jsNumberClass = compiler.findInterceptor(const SourceString('JSNumber')),
      jsNullClass = compiler.findInterceptor(const SourceString('JSNull')),
      jsBoolClass = compiler.findInterceptor(const SourceString('JSBool')),
      jsMutableArrayClass =
          compiler.findInterceptor(const SourceString('JSMutableArray')),
      jsFixedArrayClass =
          compiler.findInterceptor(const SourceString('JSFixedArray')),
      jsExtendableArrayClass =
          compiler.findInterceptor(const SourceString('JSExtendableArray')),
      jsPlainJavaScriptObjectClass =
          compiler.findInterceptor(const SourceString('PlainJavaScriptObject')),
      jsUnknownJavaScriptObjectClass =
          compiler.findInterceptor(
              const SourceString('UnknownJavaScriptObject')),
    ];

    jsIndexableClass =
        compiler.findInterceptor(const SourceString('JSIndexable'));
    jsMutableIndexableClass =
        compiler.findInterceptor(const SourceString('JSMutableIndexable'));

    // TODO(kasperl): Some tests do not define the special JSArray
    // subclasses, so we check to see if they are defined before
    // trying to resolve them.
    if (jsFixedArrayClass != null) {
      jsFixedArrayClass.ensureResolved(compiler);
    }
    if (jsExtendableArrayClass != null) {
      jsExtendableArrayClass.ensureResolved(compiler);
    }

    jsIndexableClass.ensureResolved(compiler);
    jsIndexableLength = compiler.lookupElementIn(
        jsIndexableClass, const SourceString('length'));
    if (jsIndexableLength != null && jsIndexableLength.isAbstractField()) {
      AbstractFieldElement element = jsIndexableLength;
      jsIndexableLength = element.getter;
    }

    jsArrayClass.ensureResolved(compiler);
    jsArrayRemoveLast = compiler.lookupElementIn(
        jsArrayClass, const SourceString('removeLast'));
    jsArrayAdd = compiler.lookupElementIn(
        jsArrayClass, const SourceString('add'));

    jsStringClass.ensureResolved(compiler);
    jsStringSplit = compiler.lookupElementIn(
        jsStringClass, const SourceString('split'));
    jsStringOperatorAdd = compiler.lookupElementIn(
        jsStringClass, const SourceString('+'));
    jsStringToString = compiler.lookupElementIn(
        jsStringClass, const SourceString('toString'));

    typeLiteralClass = compiler.findHelper(const SourceString('TypeImpl'));
    mapLiteralClass =
        compiler.coreLibrary.find(const SourceString('LinkedHashMap'));
    constMapLiteralClass =
        compiler.findHelper(const SourceString('ConstantMap'));

    objectEquals = compiler.lookupElementIn(
        compiler.objectClass, const SourceString('=='));

    jsIndexingBehaviorInterface =
        compiler.findHelper(const SourceString('JavaScriptIndexingBehavior'));

    specialOperatorEqClasses
        ..add(compiler.objectClass)
        ..add(jsInterceptorClass)
        ..add(jsNullClass);

    validateInterceptorImplementsAllObjectMethods(jsInterceptorClass);

    stringType = new HBoundedType(
        new TypeMask.nonNullExact(jsStringClass));
    indexablePrimitiveType = new HBoundedType(
        new TypeMask.nonNullSubtype(jsIndexableClass));
    readableArrayType = new HBoundedType(
        new TypeMask.nonNullSubclass(jsArrayClass));
    mutableArrayType = new HBoundedType(
        new TypeMask.nonNullSubclass(jsMutableArrayClass));
    fixedArrayType = new HBoundedType(
        new TypeMask.nonNullExact(jsFixedArrayClass));
    extendableArrayType = new HBoundedType(
        new TypeMask.nonNullExact(jsExtendableArrayClass));
  }

  void validateInterceptorImplementsAllObjectMethods(
      ClassElement interceptorClass) {
    if (interceptorClass == null) return;
    interceptorClass.ensureResolved(compiler);
    compiler.objectClass.forEachMember((_, Element member) {
      if (member.isGenerativeConstructor()) return;
      Element interceptorMember = interceptorClass.lookupMember(member.name);
      // Interceptors must override all Object methods due to calling convention
      // differences.
      assert(interceptorMember.getEnclosingClass() != compiler.objectClass);
    });
  }

  void addInterceptorsForNativeClassMembers(
      ClassElement cls, Enqueuer enqueuer) {
    if (enqueuer.isResolutionQueue) {
      cls.ensureResolved(compiler);
      cls.forEachMember((ClassElement classElement, Element member) {
        if (member.isSynthesized) return;
        // All methods on [Object] are shadowed by [Interceptor].
        if (classElement == compiler.objectClass) return;
        Set<Element> set = interceptedElements.putIfAbsent(
            member.name, () => new Set<Element>());
        set.add(member);
      },
      includeSuperAndInjectedMembers: true);

      // Walk superclass chain to find mixins.
      for (; cls != null; cls = cls.superclass) {
        if (cls.isMixinApplication) {
          MixinApplicationElement mixinApplication = cls;
          classesMixedIntoNativeClasses.add(mixinApplication.mixin);
        }
      }
    }
  }

  void addInterceptors(ClassElement cls,
                       Enqueuer enqueuer,
                       TreeElements elements) {
    if (enqueuer.isResolutionQueue) {
      _interceptedClasses.add(jsInterceptorClass);
      _interceptedClasses.add(cls);
      cls.ensureResolved(compiler);
      cls.forEachMember((ClassElement classElement, Element member) {
          // All methods on [Object] are shadowed by [Interceptor].
          if (classElement == compiler.objectClass) return;
          Set<Element> set = interceptedElements.putIfAbsent(
              member.name, () => new Set<Element>());
          set.add(member);
        },
        includeSuperAndInjectedMembers: true);
    }
    enqueueClass(enqueuer, cls, elements);
  }

  Set<ClassElement> get interceptedClasses {
    assert(compiler.enqueuer.resolution.queueIsClosed);
    return _interceptedClasses;
  }

  void registerSpecializedGetInterceptor(Set<ClassElement> classes) {
    String name = namer.getInterceptorName(getInterceptorMethod, classes);
    if (classes.contains(jsInterceptorClass)) {
      // We can't use a specialized [getInterceptorMethod], so we make
      // sure we emit the one with all checks.
      specializedGetInterceptors[name] = interceptedClasses;
    } else {
      specializedGetInterceptors[name] = classes;
    }
  }

  Constant registerCompileTimeConstant(Constant constant,
                                       TreeElements elements) {
    registerCompileTimeConstantInternal(constant, elements);
    for (Constant dependency in constant.getDependencies()) {
      registerCompileTimeConstant(dependency, elements);
    }
  }

  void registerCompileTimeConstantInternal(Constant constant,
                                           TreeElements elements) {
    DartType type = constant.computeType(compiler);
    registerInstantiatedConstantType(type, elements);

    if (constant.isFunction()) {
      FunctionConstant function = constant;
      compiler.enqueuer.codegen.registerGetOfStaticFunction(function.element);
    } else if (constant.isInterceptor()) {
      // An interceptor constant references the class's prototype chain.
      InterceptorConstant interceptor = constant;
      registerInstantiatedConstantType(interceptor.dispatchedType, elements);
    } else if (constant.isType()) {
      TypeConstant typeConstant = constant;
      registerTypeLiteral(typeConstant.representedType.element,
          compiler.enqueuer.codegen, elements);
    }
  }

  void registerInstantiatedConstantType(DartType type, TreeElements elements) {
    Enqueuer enqueuer = compiler.enqueuer.codegen;
    enqueuer.registerInstantiatedType(type, elements);
    if (type is InterfaceType && !type.treatAsRaw &&
        classNeedsRti(type.element)) {
      enqueuer.registerStaticUse(getSetRuntimeTypeInfo());
    }
    if (type.element == typeImplementation) {
      // If we use a type literal in a constant, the compile time
      // constant emitter will generate a call to the createRuntimeType
      // helper so we register a use of that.
      enqueuer.registerStaticUse(getCreateRuntimeType());
    }
  }

  void registerMetadataConstant(Constant constant, TreeElements elements) {
    if (mustRetainMetadata) {
      registerCompileTimeConstant(constant, elements);
    } else {
      metadataConstants.add(new Dependency(constant, elements));
    }
  }

  void registerInstantiatedClass(ClassElement cls,
                                 Enqueuer enqueuer,
                                 TreeElements elements) {
    if (!seenAnyClass) {
      seenAnyClass = true;
      if (enqueuer.isResolutionQueue) {
        // TODO(9577): Make it so that these are not needed when there are no
        // native classes.
        enqueue(enqueuer, getNativeInterceptorMethod, elements);
        enqueue(enqueuer, defineNativeMethodsFinishMethod, elements);
        enqueueClass(enqueuer, jsInterceptorClass, compiler.globalDependencies);
      }
    }

    // Register any helper that will be needed by the backend.
    if (enqueuer.isResolutionQueue) {
      if (cls == compiler.intClass
          || cls == compiler.doubleClass
          || cls == compiler.numClass) {
        // The backend will try to optimize number operations and use the
        // `iae` helper directly.
        enqueue(enqueuer,
                compiler.findHelper(const SourceString('iae')),
                elements);
      } else if (cls == compiler.listClass
                 || cls == compiler.stringClass) {
        // The backend will try to optimize array and string access and use the
        // `ioore` and `iae` helpers directly.
        enqueue(enqueuer,
                compiler.findHelper(const SourceString('ioore')),
                elements);
        enqueue(enqueuer,
                compiler.findHelper(const SourceString('iae')),
                elements);
      } else if (cls == compiler.functionClass) {
        enqueueClass(enqueuer, compiler.closureClass, elements);
      } else if (cls == compiler.mapClass) {
        // The backend will use a literal list to initialize the entries
        // of the map.
        enqueueClass(enqueuer, compiler.listClass, elements);
        enqueueClass(enqueuer, mapLiteralClass, elements);
        enqueueInResolution(getMapMaker(), elements);
      } else if (cls == compiler.boundClosureClass) {
        // TODO(ngeoffray): Move the bound closure class in the
        // backend.
        enqueueClass(enqueuer, compiler.boundClosureClass, elements);
      }
    }
    ClassElement result = null;
    if (cls == compiler.stringClass || cls == jsStringClass) {
      addInterceptors(jsStringClass, enqueuer, elements);
    } else if (cls == compiler.listClass
               || cls == jsArrayClass
               || cls == jsFixedArrayClass
               || cls == jsExtendableArrayClass) {
      addInterceptors(jsArrayClass, enqueuer, elements);
      addInterceptors(jsMutableArrayClass, enqueuer, elements);
      addInterceptors(jsFixedArrayClass, enqueuer, elements);
      addInterceptors(jsExtendableArrayClass, enqueuer, elements);
    } else if (cls == compiler.intClass || cls == jsIntClass) {
      addInterceptors(jsIntClass, enqueuer, elements);
      addInterceptors(jsNumberClass, enqueuer, elements);
    } else if (cls == compiler.doubleClass || cls == jsDoubleClass) {
      addInterceptors(jsDoubleClass, enqueuer, elements);
      addInterceptors(jsNumberClass, enqueuer, elements);
    } else if (cls == compiler.boolClass || cls == jsBoolClass) {
      addInterceptors(jsBoolClass, enqueuer, elements);
    } else if (cls == compiler.nullClass || cls == jsNullClass) {
      addInterceptors(jsNullClass, enqueuer, elements);
    } else if (cls == compiler.numClass || cls == jsNumberClass) {
      addInterceptors(jsIntClass, enqueuer, elements);
      addInterceptors(jsDoubleClass, enqueuer, elements);
      addInterceptors(jsNumberClass, enqueuer, elements);
    } else if (cls == jsPlainJavaScriptObjectClass) {
      addInterceptors(jsPlainJavaScriptObjectClass, enqueuer, elements);
    } else if (cls == jsUnknownJavaScriptObjectClass) {
      addInterceptors(jsUnknownJavaScriptObjectClass, enqueuer, elements);
    } else if (Elements.isNativeOrExtendsNative(cls)) {
      addInterceptorsForNativeClassMembers(cls, enqueuer);
    } else if (cls == jsIndexingBehaviorInterface) {
      // These two helpers are used by the emitter and the codegen.
      // Because we cannot enqueue elements at the time of emission,
      // we make sure they are always generated.
      enqueue(
          enqueuer,
          compiler.findHelper(const SourceString('isJsIndexable')),
          elements);
      enqueue(
          enqueuer,
          compiler.findInterceptor(const SourceString('dispatchPropertyName')),
          elements);
    }

    customElementsAnalysis.registerInstantiatedClass(cls, enqueuer);
  }

  void registerUseInterceptor(Enqueuer enqueuer) {
    assert(!enqueuer.isResolutionQueue);
    if (!enqueuer.nativeEnqueuer.hasInstantiatedNativeClasses()) return;
    TreeElements elements = compiler.globalDependencies;
    enqueue(enqueuer, getNativeInterceptorMethod, elements);
    enqueue(enqueuer, defineNativeMethodsFinishMethod, elements);
    enqueueClass(enqueuer, jsPlainJavaScriptObjectClass, elements);
    needToInitializeDispatchProperty = true;
  }

  JavaScriptItemCompilationContext createItemCompilationContext() {
    return new JavaScriptItemCompilationContext();
  }

  void enqueueHelpers(ResolutionEnqueuer world, TreeElements elements) {
    // TODO(ngeoffray): Not enqueuing those two classes currently make
    // the compiler potentially crash. However, any reasonable program
    // will instantiate those two classes.
    addInterceptors(jsBoolClass, world, elements);
    addInterceptors(jsNullClass, world, elements);
    if (compiler.enableTypeAssertions) {
      // Unconditionally register the helper that checks if the
      // expression in an if/while/for is a boolean.
      // TODO(ngeoffray): Should we have the resolver register those instead?
      Element e =
          compiler.findHelper(const SourceString('boolConversionCheck'));
      if (e != null) enqueue(world, e, elements);
    }
    registerCheckedModeHelpers(elements);
  }

  onResolutionComplete() => rti.computeClassesNeedingRti();

  void registerStringInterpolation(TreeElements elements) {
    enqueueInResolution(getStringInterpolationHelper(), elements);
  }

  void registerCatchStatement(Enqueuer enqueuer, TreeElements elements) {
    void ensure(ClassElement classElement) {
      if (classElement != null) {
        enqueueClass(enqueuer, classElement, elements);
      }
    }
    enqueueInResolution(getExceptionUnwrapper(), elements);
    ensure(jsPlainJavaScriptObjectClass);
    ensure(jsUnknownJavaScriptObjectClass);
  }

  void registerThrowExpression(TreeElements elements) {
    // We don't know ahead of time whether we will need the throw in a
    // statement context or an expression context, so we register both
    // here, even though we may not need the throwExpression helper.
    enqueueInResolution(getWrapExceptionHelper(), elements);
    enqueueInResolution(getThrowExpressionHelper(), elements);
  }

  void registerLazyField(TreeElements elements) {
    enqueueInResolution(getCyclicThrowHelper(), elements);
  }

  void registerTypeLiteral(Element element,
                           Enqueuer enqueuer,
                           TreeElements elements) {
    enqueuer.registerInstantiatedClass(typeImplementation, elements);
    enqueueInResolution(getCreateRuntimeType(), elements);
    // TODO(ahe): Might want to register [element] as an instantiated class
    // when reflection is used.  However, as long as we disable tree-shaking
    // eagerly it doesn't matter.
    if (element.isTypedef()) {
      typedefTypeLiterals.add(element);
    }
    customElementsAnalysis.registerTypeLiteral(element, enqueuer);
  }

  void registerStackTraceInCatch(TreeElements elements) {
    enqueueInResolution(getTraceFromException(), elements);
  }

  void registerSetRuntimeType(TreeElements elements) {
    enqueueInResolution(getSetRuntimeTypeInfo(), elements);
  }

  void registerGetRuntimeTypeArgument(TreeElements elements) {
    enqueueInResolution(getGetRuntimeTypeArgument(), elements);
  }

  void registerGenericCallMethod(Element callMethod,
                                 Enqueuer enqueuer, TreeElements elements) {
    if (enqueuer.isResolutionQueue || methodNeedsRti(callMethod)) {
      registerComputeSignature(enqueuer, elements);
    }
  }

  void registerGenericClosure(Element closure,
                              Enqueuer enqueuer, TreeElements elements) {
    if (enqueuer.isResolutionQueue || methodNeedsRti(closure)) {
      registerComputeSignature(enqueuer, elements);
    }
  }

  void registerComputeSignature(Enqueuer enqueuer, TreeElements elements) {
    // Calls to [:computeSignature:] are generated by the emitter and we
    // therefore need to enqueue the used elements in the codegen enqueuer as
    // well as in the resolution enqueuer.
    enqueue(enqueuer, getSetRuntimeTypeInfo(), elements);
    enqueue(enqueuer, getGetRuntimeTypeInfo(), elements);
    enqueue(enqueuer, getComputeSignature(), elements);
    enqueue(enqueuer, getGetRuntimeTypeArguments(), elements);
    enqueueClass(enqueuer, compiler.listClass, elements);
  }

  void registerRuntimeType(Enqueuer enqueuer, TreeElements elements) {
    registerComputeSignature(enqueuer, elements);
    enqueueInResolution(getSetRuntimeTypeInfo(), elements);
    enqueueInResolution(getGetRuntimeTypeInfo(), elements);
    registerGetRuntimeTypeArgument(elements);
    enqueueClass(enqueuer, compiler.listClass, elements);
  }

  void registerTypeVariableExpression(TreeElements elements) {
    enqueueInResolution(getSetRuntimeTypeInfo(), elements);
    enqueueInResolution(getGetRuntimeTypeInfo(), elements);
    registerGetRuntimeTypeArgument(elements);
    enqueueClass(compiler.enqueuer.resolution, compiler.listClass, elements);
    enqueueInResolution(getRuntimeTypeToString(), elements);
    enqueueInResolution(getCreateRuntimeType(), elements);
  }

  void registerIsCheck(DartType type, Enqueuer world, TreeElements elements) {
    type = type.unalias(compiler);
    enqueueClass(world, compiler.boolClass, elements);
    bool inCheckedMode = compiler.enableTypeAssertions;
    // [registerIsCheck] is also called for checked mode checks, so we
    // need to register checked mode helpers.
    if (inCheckedMode) {
      if (!world.isResolutionQueue) {
        // All helpers are added to resolution queue in enqueueHelpers. These
        // calls to enqueueInResolution serve as assertions that the helper was
        // in fact added.
        // TODO(13155): Find a way to enqueue helpers lazily.
        CheckedModeHelper helper = getCheckedModeHelper(type, typeCast: false);
        if (helper != null) {
          enqueue(world, helper.getElement(compiler), elements);
        }
        // We also need the native variant of the check (for DOM types).
        helper = getNativeCheckedModeHelper(type, typeCast: false);
        if (helper != null) {
          enqueue(world, helper.getElement(compiler), elements);
        }
      }
    }
    bool isTypeVariable = type.kind == TypeKind.TYPE_VARIABLE;
    if (!type.treatAsRaw || type.containsTypeVariables) {
      enqueueInResolution(getSetRuntimeTypeInfo(), elements);
      enqueueInResolution(getGetRuntimeTypeInfo(), elements);
      enqueueInResolution(getGetRuntimeTypeArgument(), elements);
      if (inCheckedMode) {
        enqueueInResolution(getAssertSubtype(), elements);
      }
      enqueueInResolution(getCheckSubtype(), elements);
      if (isTypeVariable) {
        enqueueInResolution(getCheckSubtypeOfRuntimeType(), elements);
        if (inCheckedMode) {
          enqueueInResolution(getAssertSubtypeOfRuntimeType(), elements);
        }
      }
      enqueueClass(world, compiler.listClass, elements);
    }
    if (type is FunctionType) {
      enqueueInResolution(getCheckFunctionSubtype(), elements);
    }
    if (type.element.isNative()) {
      // We will neeed to add the "$is" and "$as" properties on the
      // JavaScript object prototype, so we make sure
      // [:defineProperty:] is compiled.
      enqueue(world,
              compiler.findHelper(const SourceString('defineProperty')),
              elements);
    }
  }

  void registerAsCheck(DartType type, Enqueuer world, TreeElements elements) {
    type = type.unalias(compiler);
    if (!world.isResolutionQueue) {
      // All helpers are added to resolution queue in enqueueHelpers. These
      // calls to enqueueInResolution serve as assertions that the helper was in
      // fact added.
      // TODO(13155): Find a way to enqueue helpers lazily.
      CheckedModeHelper helper = getCheckedModeHelper(type, typeCast: true);
      enqueueInResolution(helper.getElement(compiler), elements);
      // We also need the native variant of the check (for DOM types).
      helper = getNativeCheckedModeHelper(type, typeCast: true);
      if (helper != null) {
        enqueueInResolution(helper.getElement(compiler), elements);
      }
    }
  }

  void registerThrowNoSuchMethod(TreeElements elements) {
    enqueueInResolution(getThrowNoSuchMethod(), elements);
    // Also register the types of the arguments passed to this method.
    enqueueClass(compiler.enqueuer.resolution, compiler.listClass, elements);
    enqueueClass(compiler.enqueuer.resolution, compiler.stringClass, elements);
  }

  void registerThrowRuntimeError(TreeElements elements) {
    enqueueInResolution(getThrowRuntimeError(), elements);
    // Also register the types of the arguments passed to this method.
    enqueueClass(compiler.enqueuer.resolution, compiler.stringClass, elements);
  }

  void registerAbstractClassInstantiation(TreeElements elements) {
    enqueueInResolution(getThrowAbstractClassInstantiationError(), elements);
    // Also register the types of the arguments passed to this method.
    enqueueClass(compiler.enqueuer.resolution, compiler.stringClass, elements);
  }

  void registerFallThroughError(TreeElements elements) {
    enqueueInResolution(getFallThroughError(), elements);
  }

  void enableNoSuchMethod(Enqueuer world) {
    enqueue(world, getCreateInvocationMirror(), compiler.globalDependencies);
    world.registerInvocation(compiler.noSuchMethodSelector);
  }

  void registerSuperNoSuchMethod(TreeElements elements) {
    enqueueInResolution(getCreateInvocationMirror(), elements);
    enqueueInResolution(
        compiler.objectClass.lookupLocalMember(Compiler.NO_SUCH_METHOD),
        elements);
    enqueueClass(compiler.enqueuer.resolution, compiler.listClass, elements);
  }

  void registerRequiredType(DartType type, Element enclosingElement) {
    /**
     * If [argument] has type variables or is a type variable, this
     * method registers a RTI dependency between the class where the
     * type variable is defined (that is the enclosing class of the
     * current element being resolved) and the class of [annotation].
     * If the class of [annotation] requires RTI, then the class of
     * the type variable does too.
     */
    void analyzeTypeArgument(DartType annotation, DartType argument) {
      if (argument == null) return;
      if (argument.element.isTypeVariable()) {
        ClassElement enclosing = argument.element.getEnclosingClass();
        assert(enclosing == enclosingElement.getEnclosingClass().declaration);
        rti.registerRtiDependency(annotation.element, enclosing);
      } else if (argument is InterfaceType) {
        InterfaceType type = argument;
        type.typeArguments.forEach((DartType argument) {
          analyzeTypeArgument(annotation, argument);
        });
      }
    }

    if (type is InterfaceType) {
      InterfaceType itf = type;
      itf.typeArguments.forEach((DartType argument) {
        analyzeTypeArgument(type, argument);
      });
    }
    // TODO(ngeoffray): Also handle T a (in checked mode).
  }

  void registerClassUsingVariableExpression(ClassElement cls) {
    rti.classesUsingTypeVariableExpression.add(cls);
  }

  bool classNeedsRti(ClassElement cls) {
    return rti.classesNeedingRti.contains(cls.declaration) ||
        compiler.enabledRuntimeType;
  }

  bool isDefaultNoSuchMethodImplementation(Element element) {
    assert(element.name == Compiler.NO_SUCH_METHOD);
    ClassElement classElement = element.getEnclosingClass();
    return classElement == compiler.objectClass
        || classElement == jsInterceptorClass;
  }

  bool isDefaultEqualityImplementation(Element element) {
    assert(element.name == const SourceString('=='));
    ClassElement classElement = element.getEnclosingClass();
    return classElement == compiler.objectClass
        || classElement == jsInterceptorClass
        || classElement == jsNullClass;
  }

  bool methodNeedsRti(FunctionElement function) {
    return rti.methodsNeedingRti.contains(function) ||
           compiler.enabledRuntimeType;
  }

  // Enqueue [e] in [enqueuer].
  //
  // The backend must *always* call this method when enqueuing an
  // element. Calls done by the backend are not seen by global
  // optimizations, so they would make these optimizations unsound.
  // Therefore we need to collect the list of helpers the backend may
  // use.
  void enqueue(Enqueuer enqueuer, Element e, TreeElements elements) {
    if (e == null) return;
    helpersUsed.add(e.declaration);
    enqueuer.addToWorkList(e);
    elements.registerDependency(e);
  }

  void enqueueInResolution(Element e, TreeElements elements) {
    if (e == null) return;
    ResolutionEnqueuer enqueuer = compiler.enqueuer.resolution;
    enqueue(enqueuer, e, elements);
  }

  void enqueueClass(Enqueuer enqueuer, Element cls, TreeElements elements) {
    if (cls == null) return;
    helpersUsed.add(cls.declaration);
    // Both declaration and implementation may declare fields, so we
    // add both to the list of helpers.
    if (cls.declaration != cls.implementation) {
      helpersUsed.add(cls.implementation);
    }
    enqueuer.registerInstantiatedClass(cls, elements);
  }

  void registerConstantMap(TreeElements elements) {
    void enqueue(SourceString name) {
      Element e = compiler.findHelper(name);
      if (e != null) {
        enqueueClass(compiler.enqueuer.resolution, e, elements);
      }
    }

    enqueue(MapConstant.DART_CLASS);
    enqueue(MapConstant.DART_PROTO_CLASS);
    enqueue(MapConstant.DART_STRING_CLASS);
    enqueue(MapConstant.DART_GENERAL_CLASS);
  }

  void codegen(CodegenWorkItem work) {
    Element element = work.element;
    var kind = element.kind;
    if (kind == ElementKind.TYPEDEF) return;
    if (element.isConstructor() && element.getEnclosingClass() == jsNullClass) {
      // Work around a problem compiling JSNull's constructor.
      return;
    }
    if (kind.category == ElementCategory.VARIABLE) {
      Constant initialValue =
          compiler.constantHandler.getConstantForVariable(element);
      if (initialValue != null) {
        registerCompileTimeConstant(initialValue, work.resolutionTree);
        compiler.constantHandler.addCompileTimeConstantForEmission(
            initialValue);
        return;
      } else {
        // If the constant-handler was not able to produce a result we have to
        // go through the builder (below) to generate the lazy initializer for
        // the static variable.
        // We also need to register the use of the cyclic-error helper.
        compiler.enqueuer.codegen.registerStaticUse(getCyclicThrowHelper());
      }
    }

    HGraph graph = builder.build(work);
    optimizer.optimize(work, graph, false);
    if (work.allowSpeculativeOptimization
        && optimizer.trySpeculativeOptimizations(work, graph)) {
      jsAst.Expression code = generator.generateBailoutMethod(work, graph);
      generatedBailoutCode[element] = code;
      optimizer.prepareForSpeculativeOptimizations(work, graph);
      optimizer.optimize(work, graph, true);
    }
    jsAst.Expression code = generator.generateCode(work, graph);
    generatedCode[element] = code;
  }

  native.NativeEnqueuer nativeResolutionEnqueuer(Enqueuer world) {
    return new native.NativeResolutionEnqueuer(world, compiler);
  }

  native.NativeEnqueuer nativeCodegenEnqueuer(Enqueuer world) {
    return new native.NativeCodegenEnqueuer(world, compiler, emitter);
  }

  ClassElement defaultSuperclass(ClassElement element) {
    // Native classes inherit from Interceptor.
    return element.isNative() ? jsInterceptorClass : compiler.objectClass;
  }

  /**
   * Unit test hook that returns code of an element as a String.
   *
   * Invariant: [element] must be a declaration element.
   */
  String assembleCode(Element element) {
    assert(invariant(element, element.isDeclaration));
    return jsAst.prettyPrint(generatedCode[element], compiler).getText();
  }

  void assembleProgram() {
    emitter.assembleProgram();
    int totalMethodCount = generatedCode.length;
    if (totalMethodCount != preMirrorsMethodCount) {
      int mirrorCount = totalMethodCount - preMirrorsMethodCount;
      double percentage = (mirrorCount / totalMethodCount) * 100;
      compiler.reportHint(
          compiler.mainApp, MessageKind.MIRROR_BLOAT,
          {'count': mirrorCount,
           'total': totalMethodCount,
           'percentage': percentage.round()});
      for (LibraryElement library in compiler.libraries.values) {
        if (library.isInternalLibrary) continue;
        for (LibraryTag tag in library.tags) {
          Import importTag = tag.asImport();
          if (importTag == null) continue;
          LibraryElement importedLibrary = library.getLibraryFromTag(tag);
          if (importedLibrary != compiler.mirrorsLibrary) continue;
          compiler.withCurrentElement(library, () {
            compiler.reportInfo(importTag, MessageKind.MIRROR_IMPORT);
          });
        }
      }
    }
  }

  Element getImplementationClass(Element element) {
    if (element == compiler.intClass) {
      return jsIntClass;
    } else if (element == compiler.boolClass) {
      return jsBoolClass;
    } else if (element == compiler.numClass) {
      return jsNumberClass;
    } else if (element == compiler.doubleClass) {
      return jsDoubleClass;
    } else if (element == compiler.stringClass) {
      return jsStringClass;
    } else if (element == compiler.listClass) {
      return jsArrayClass;
    } else {
      return element;
    }
  }

  /**
   * Returns the checked mode helper that will be needed to do a type check/type
   * cast on [type] at runtime. Note that this method is being called both by
   * the resolver with interface types (int, String, ...), and by the SSA
   * backend with implementation types (JSInt, JSString, ...).
   */
  CheckedModeHelper getCheckedModeHelper(DartType type, {bool typeCast}) {
    return getCheckedModeHelperInternal(
        type, typeCast: typeCast, nativeCheckOnly: false);
  }

  /**
   * Returns the native checked mode helper that will be needed to do a type
   * check/type cast on [type] at runtime. If no native helper exists for
   * [type], [:null:] is returned.
   */
  CheckedModeHelper getNativeCheckedModeHelper(DartType type, {bool typeCast}) {
    return getCheckedModeHelperInternal(
        type, typeCast: typeCast, nativeCheckOnly: true);
  }

  /**
   * Returns the checked mode helper for the type check/type cast for [type]. If
   * [nativeCheckOnly] is [:true:], only names for native helpers are returned.
   */
  CheckedModeHelper getCheckedModeHelperInternal(DartType type,
                                                 {bool typeCast,
                                                  bool nativeCheckOnly}) {
    String name = getCheckedModeHelperNameInternal(type,
        typeCast: typeCast, nativeCheckOnly: nativeCheckOnly);
    if (name == null) return null;
    CheckedModeHelper helper = checkedModeHelperByName[name];
    assert(helper != null);
    return helper;
  }

  String getCheckedModeHelperNameInternal(DartType type,
                                          {bool typeCast,
                                           bool nativeCheckOnly}) {
    assert(type.kind != TypeKind.TYPEDEF);
    Element element = type.element;
    bool nativeCheck = nativeCheckOnly ||
        emitter.nativeEmitter.requiresNativeIsCheck(element);

    // TODO(13955), TODO(9731).  The test for non-primitive types should use an
    // interceptor.  The interceptor should be an argument to HTypeConversion so
    // that it can be optimized by standard interceptor optimizations.
    nativeCheck = true;

    if (type == compiler.types.voidType) {
      assert(!typeCast); // Cannot cast to void.
      if (nativeCheckOnly) return null;
      return 'voidTypeCheck';
    } else if (element == jsStringClass || element == compiler.stringClass) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'stringTypeCast'
          : 'stringTypeCheck';
    } else if (element == jsDoubleClass || element == compiler.doubleClass) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'doubleTypeCast'
          : 'doubleTypeCheck';
    } else if (element == jsNumberClass || element == compiler.numClass) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'numTypeCast'
          : 'numTypeCheck';
    } else if (element == jsBoolClass || element == compiler.boolClass) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'boolTypeCast'
          : 'boolTypeCheck';
    } else if (element == jsIntClass || element == compiler.intClass) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'intTypeCast'
          : 'intTypeCheck';
    } else if (Elements.isNumberOrStringSupertype(element, compiler)) {
      if (nativeCheck) {
        return typeCast
            ? 'numberOrStringSuperNativeTypeCast'
            : 'numberOrStringSuperNativeTypeCheck';
      } else {
        return typeCast
          ? 'numberOrStringSuperTypeCast'
          : 'numberOrStringSuperTypeCheck';
      }
    } else if (Elements.isStringOnlySupertype(element, compiler)) {
      if (nativeCheck) {
        return typeCast
            ? 'stringSuperNativeTypeCast'
            : 'stringSuperNativeTypeCheck';
      } else {
        return typeCast
            ? 'stringSuperTypeCast'
            : 'stringSuperTypeCheck';
      }
    } else if ((element == compiler.listClass || element == jsArrayClass) &&
               type.treatAsRaw) {
      if (nativeCheckOnly) return null;
      return typeCast
          ? 'listTypeCast'
          : 'listTypeCheck';
    } else {
      if (Elements.isListSupertype(element, compiler)) {
        if (nativeCheck) {
          return typeCast
              ? 'listSuperNativeTypeCast'
              : 'listSuperNativeTypeCheck';
        } else {
          return typeCast
              ? 'listSuperTypeCast'
              : 'listSuperTypeCheck';
        }
      } else {
        if (type.kind == TypeKind.INTERFACE && !type.treatAsRaw) {
          return typeCast
              ? 'subtypeCast'
              : 'assertSubtype';
        } else if (type.kind == TypeKind.TYPE_VARIABLE) {
          return typeCast
              ? 'subtypeOfRuntimeTypeCast'
              : 'assertSubtypeOfRuntimeType';
        } else if (type.kind == TypeKind.FUNCTION) {
          return typeCast
              ? 'functionSubtypeCast'
              : 'assertFunctionSubtype';
        } else {
          if (nativeCheck) {
            // TODO(karlklose): can we get rid of this branch when we use
            // interceptors?
            return typeCast
                ? 'interceptedTypeCast'
                : 'interceptedTypeCheck';
          } else {
            return typeCast
                ? 'propertyTypeCast'
                : 'propertyTypeCheck';
          }
        }
      }
    }
  }

  void registerCheckedModeHelpers(TreeElements elements) {
    // We register all the helpers in the resolution queue.
    // TODO(13155): Find a way to register fewer helpers.
    for (CheckedModeHelper helper in checkedModeHelpers) {
      enqueueInResolution(helper.getElement(compiler), elements);
    }
  }

  /**
   * Returns [:true:] if the checking of [type] is performed directly on the
   * object and not on an interceptor.
   */
  bool hasDirectCheckFor(DartType type) {
    Element element = type.element;
    return element == compiler.stringClass ||
        element == compiler.boolClass ||
        element == compiler.numClass ||
        element == compiler.intClass ||
        element == compiler.doubleClass ||
        element == jsArrayClass ||
        element == jsMutableArrayClass ||
        element == jsExtendableArrayClass ||
        element == jsFixedArrayClass;
  }

  Element getExceptionUnwrapper() {
    return compiler.findHelper(const SourceString('unwrapException'));
  }

  Element getThrowRuntimeError() {
    return compiler.findHelper(const SourceString('throwRuntimeError'));
  }

  Element getThrowAbstractClassInstantiationError() {
    return compiler.findHelper(
        const SourceString('throwAbstractClassInstantiationError'));
  }

  Element getStringInterpolationHelper() {
    return compiler.findHelper(const SourceString('S'));
  }

  Element getWrapExceptionHelper() {
    return compiler.findHelper(const SourceString(r'wrapException'));
  }

  Element getThrowExpressionHelper() {
    return compiler.findHelper(const SourceString('throwExpression'));
  }

  Element getClosureConverter() {
    return compiler.findHelper(const SourceString('convertDartClosureToJS'));
  }

  Element getTraceFromException() {
    return compiler.findHelper(const SourceString('getTraceFromException'));
  }

  Element getMapMaker() {
    return compiler.findHelper(const SourceString('makeLiteralMap'));
  }

  Element getSetRuntimeTypeInfo() {
    return compiler.findHelper(const SourceString('setRuntimeTypeInfo'));
  }

  Element getGetRuntimeTypeInfo() {
    return compiler.findHelper(const SourceString('getRuntimeTypeInfo'));
  }

  Element getComputeSignature() {
    return compiler.findHelper(const SourceString('computeSignature'));
  }

  Element getGetRuntimeTypeArguments() {
    return compiler.findHelper(const SourceString('getRuntimeTypeArguments'));
  }

  Element getGetRuntimeTypeArgument() {
    return compiler.findHelper(const SourceString('getRuntimeTypeArgument'));
  }

  Element getRuntimeTypeToString() {
    return compiler.findHelper(const SourceString('runtimeTypeToString'));
  }

  Element getCheckSubtype() {
    return compiler.findHelper(const SourceString('checkSubtype'));
  }

  Element getAssertSubtype() {
    return compiler.findHelper(const SourceString('assertSubtype'));
  }

  Element getCheckSubtypeOfRuntimeType() {
    return compiler.findHelper(const SourceString('checkSubtypeOfRuntimeType'));
  }

  Element getAssertSubtypeOfRuntimeType() {
    return compiler.findHelper(
        const SourceString('assertSubtypeOfRuntimeType'));
  }

  Element getCheckFunctionSubtype() {
    return compiler.findHelper(const SourceString('checkFunctionSubtype'));
  }

  Element getThrowNoSuchMethod() {
    return compiler.findHelper(const SourceString('throwNoSuchMethod'));
  }

  Element getCreateRuntimeType() {
    return compiler.findHelper(const SourceString('createRuntimeType'));
  }

  Element getFallThroughError() {
    return compiler.findHelper(const SourceString("getFallThroughError"));
  }

  Element getCreateInvocationMirror() {
    return compiler.findHelper(Compiler.CREATE_INVOCATION_MIRROR);
  }

  Element getCyclicThrowHelper() {
    return compiler.findHelper(const SourceString("throwCyclicInit"));
  }

  bool isNullImplementation(ClassElement cls) {
    return cls == jsNullClass;
  }

  ClassElement get intImplementation => jsIntClass;
  ClassElement get doubleImplementation => jsDoubleClass;
  ClassElement get numImplementation => jsNumberClass;
  ClassElement get stringImplementation => jsStringClass;
  ClassElement get listImplementation => jsArrayClass;
  ClassElement get constListImplementation => jsArrayClass;
  ClassElement get fixedListImplementation => jsFixedArrayClass;
  ClassElement get growableListImplementation => jsExtendableArrayClass;
  ClassElement get mapImplementation => mapLiteralClass;
  ClassElement get constMapImplementation => constMapLiteralClass;
  ClassElement get typeImplementation => typeLiteralClass;
  ClassElement get boolImplementation => jsBoolClass;
  ClassElement get nullImplementation => jsNullClass;

  void registerStaticUse(Element element, Enqueuer enqueuer) {
    if (element == disableTreeShakingMarker) {
      compiler.disableTypeInferenceForMirrors = true;
      isTreeShakingDisabled = true;
    } else if (element == preserveNamesMarker) {
      mustPreserveNames = true;
    } else if (element == preserveMetadataMarker) {
      mustRetainMetadata = true;
    }
    customElementsAnalysis.registerStaticUse(element, enqueuer);
  }

  /// Called when [:const Symbol(name):] is seen.
  void registerConstSymbol(String name, TreeElements elements) {
    symbolsUsed.add(name);
    if (name.endsWith('=')) {
      symbolsUsed.add(name.substring(0, name.length - 1));
    }
  }

  /// Called when [:new Symbol(...):] is seen.
  void registerNewSymbol(TreeElements elements) {
  }

  /// Called when resolving the `Symbol` constructor.
  void registerSymbolConstructor(TreeElements elements) {
    // Make sure that collection_dev.Symbol.validated is registered.
    assert(compiler.symbolValidatedConstructor != null);
    enqueueInResolution(compiler.symbolValidatedConstructor, elements);
  }

  /// Should [element] (a getter) be retained for reflection?
  bool shouldRetainGetter(Element element) => isNeededForReflection(element);

  /// Should [element] (a setter) be retained for reflection?
  bool shouldRetainSetter(Element element) => isNeededForReflection(element);

  /// Should [name] be retained for reflection?
  bool shouldRetainName(SourceString name) {
    if (hasInsufficientMirrorsUsed) return mustPreserveNames;
    if (name == const SourceString('')) return false;
    return symbolsUsed.contains(name.slowToString());
  }

  bool get rememberLazies => isTreeShakingDisabled;

  bool retainMetadataOf(Element element) {
    if (mustRetainMetadata) hasRetainedMetadata = true;
    if (mustRetainMetadata && isNeededForReflection(element)) {
      for (MetadataAnnotation metadata in element.metadata) {
        metadata.ensureResolved(compiler);
        compiler.constantHandler.addCompileTimeConstantForEmission(
            metadata.value);
      }
      return true;
    }
    return false;
  }

  Future onLibraryLoaded(LibraryElement library, Uri uri) {
    if (uri == Uri.parse('dart:_js_mirrors')) {
      disableTreeShakingMarker =
          library.find(const SourceString('disableTreeShaking'));
      preserveMetadataMarker =
          library.find(const SourceString('preserveMetadata'));
    } else if (uri == Uri.parse('dart:_js_names')) {
      preserveNamesMarker =
          library.find(const SourceString('preserveNames'));
    }
    return new Future.value();
  }

  void registerMirrorUsage(Set<String> symbols,
                           Set<Element> targets,
                           Set<Element> metaTargets) {
    if (symbols == null && targets == null && metaTargets == null) {
      // The user didn't specify anything, or there are imports of
      // 'dart:mirrors' without @MirrorsUsed.
      hasInsufficientMirrorsUsed = true;
      return;
    }
    if (symbols != null) symbolsUsed.addAll(symbols);
    if (targets != null) {
      for (Element target in targets) {
        if (target.isAbstractField()) {
          AbstractFieldElement field = target;
          targetsUsed.add(field.getter);
          targetsUsed.add(field.setter);
        } else {
          targetsUsed.add(target);
        }
      }
    }
    if (metaTargets != null) metaTargetsUsed.addAll(metaTargets);
  }

  /**
   * Returns `true` if [element] can be accessed through reflection, that is,
   * is in the set of elements covered by a `MirrorsUsed` annotation.
   *
   * This property is used to tag emitted elements with a marker which is
   * checked by the runtime system to throw an exception if an element is
   * accessed (invoked, get, set) that is not accessible for the reflective
   * system.
   */
  bool isAccessibleByReflection(Element element) {
    if (hasInsufficientMirrorsUsed) return true;
    return isNeededForReflection(element);
  }

  /**
   * Returns `true` if the emitter must emit the element even though there
   * is no direct use in the program, but because the reflective system may
   * need to access it.
   */
  bool isNeededForReflection(Element element) {
    if (hasInsufficientMirrorsUsed) return isTreeShakingDisabled;
    /// Record the name of [element] in [symbolsUsed]. Return true for
    /// convenience.
    bool registerNameOf(Element element) {
      symbolsUsed.add(element.name.slowToString());
      if (element.isConstructor()) {
        symbolsUsed.add(element.getEnclosingClass().name.slowToString());
      }
      return true;
    }

    Element enclosing = element.enclosingElement;
    if (enclosing != null && isNeededForReflection(enclosing)) {
      return registerNameOf(element);
    }

    if (isNeededThroughMetaTarget(element)) {
      return registerNameOf(element);
    }

    if (!targetsUsed.isEmpty && targetsUsed.contains(element)) {
      return registerNameOf(element);
    }

    if (element is ClosureClassElement) {
      // TODO(ahe): Try to fix the enclosing element of ClosureClassElement
      // instead.
      ClosureClassElement closureClass = element;
      if (isNeededForReflection(closureClass.methodElement)) {
        return registerNameOf(element);
      }
    }

    // TODO(kasperl): Consider caching this information. It is consulted
    // multiple times because of the way we deal with the enclosing element.
    return false;
  }

  /**
   * Returns `true` if the element is needed because it has an annotation
   * of a type that is used as a meta target for reflection.
   */
  bool isNeededThroughMetaTarget(Element element) {
    if (metaTargetsUsed.isEmpty) return false;
    for (Link link = element.metadata; !link.isEmpty; link = link.tail) {
      MetadataAnnotation metadata = link.head;
      // TODO(kasperl): It would be nice if we didn't have to resolve
      // all metadata but only stuff that potentially would match one
      // of the used meta targets.
      metadata.ensureResolved(compiler);
      Constant value = metadata.value;
      if (value == null) continue;
      DartType type = value.computeType(compiler);
      if (metaTargetsUsed.contains(type.element)) return true;
    }
    return false;
  }

  jsAst.Call generateIsJsIndexableCall(jsAst.Expression use1,
                                       jsAst.Expression use2) {
    String dispatchPropertyName = 'init.dispatchPropertyName';

    // We pass the dispatch property record to the isJsIndexable
    // helper rather than reading it inside the helper to increase the
    // chance of making the dispatch record access monomorphic.
    jsAst.PropertyAccess record = new jsAst.PropertyAccess(
        use2, new jsAst.VariableUse(dispatchPropertyName));

    List<jsAst.Expression> arguments = <jsAst.Expression>[use1, record];
    FunctionElement helper =
        compiler.findHelper(const SourceString('isJsIndexable'));
    String helperName = namer.isolateAccess(helper);
    return new jsAst.Call(new jsAst.VariableUse(helperName), arguments);
  }

  bool isTypedArray(TypeMask mask) {
    // Just checking for [:TypedData:] is not sufficient, as it is an
    // abstract class any user-defined class can implement. So we also
    // check for the interface [JavaScriptIndexingBehavior].
    return compiler.typedDataClass != null
        && mask.satisfies(compiler.typedDataClass, compiler)
        && mask.satisfies(jsIndexingBehaviorInterface, compiler);
  }

  /// Called when [enqueuer] is empty, but before it is closed.
  void onQueueEmpty(Enqueuer enqueuer) {
    if (!enqueuer.isResolutionQueue && preMirrorsMethodCount == 0) {
      preMirrorsMethodCount = generatedCode.length;
    }

    if (isTreeShakingDisabled) enqueuer.enqueueEverything();

    if (mustPreserveNames) compiler.log('Preserving names.');

    if (mustRetainMetadata) {
      compiler.log('Retaining metadata.');

      compiler.libraries.values.forEach(retainMetadataOf);
      for (Dependency dependency in metadataConstants) {
        registerCompileTimeConstant(
            dependency.constant, dependency.user);
      }
      metadataConstants.clear();
    }

    customElementsAnalysis.onQueueEmpty(enqueuer);
  }
}

/// Records that [constant] is used by [user.element].
class Dependency {
  final Constant constant;
  final TreeElements user;

  const Dependency(this.constant, this.user);
}

/// Used to copy metadata to the the actual constant handler.
class ConstantCopier implements ConstantVisitor {
  final ConstantHandler target;

  ConstantCopier(this.target);

  void copy(/* Constant or List<Constant> */ value) {
    if (value is Constant) {
      target.compiledConstants.add(value);
    } else {
      target.compiledConstants.addAll(value);
    }
  }

  void visitFunction(FunctionConstant constant) => copy(constant);

  void visitNull(NullConstant constant) => copy(constant);

  void visitInt(IntConstant constant) => copy(constant);

  void visitDouble(DoubleConstant constant) => copy(constant);

  void visitTrue(TrueConstant constant) => copy(constant);

  void visitFalse(FalseConstant constant) => copy(constant);

  void visitString(StringConstant constant) => copy(constant);

  void visitType(TypeConstant constant) => copy(constant);

  void visitInterceptor(InterceptorConstant constant) => copy(constant);

  void visitList(ListConstant constant) {
    copy(constant.entries);
    copy(constant);
  }
  void visitMap(MapConstant constant) {
    copy(constant.keys);
    copy(constant.values);
    copy(constant.protoValue);
    copy(constant);
  }

  void visitConstructed(ConstructedConstant constant) {
    copy(constant.fields);
    copy(constant);
  }
}