Delete CPS IR

pkg/compiler/lib/src/tree_ir/tree_ir_nodes.dart

-// Copyright (c) 2014, 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.
-
-library tree_ir_nodes;
-
-import '../constants/values.dart' as values;
-import '../dart_types.dart' show DartType, InterfaceType, TypeVariableType;
-import '../elements/elements.dart';
-import '../io/source_information.dart' show SourceInformation;
-import '../types/types.dart' show TypeMask;
-import '../universe/selector.dart' show Selector;
-
-import '../cps_ir/builtin_operator.dart';
-export '../cps_ir/builtin_operator.dart';
-import '../cps_ir/cps_ir_nodes.dart' show TypeExpressionKind;
-export '../cps_ir/cps_ir_nodes.dart' show TypeExpressionKind;
-
-// These imports are only used for the JavaScript specific nodes.  If we want to
-// support more than one native backend, we should probably create better
-// abstractions for native code and its type and effect system.
-import '../js/js.dart' as js show Template;
-import '../native/native.dart' as native show NativeBehavior;
-import '../types/types.dart' as types show TypeMask;
-
-// The Tree language is the target of translation out of the CPS-based IR.
-//
-// The translation from CPS to Dart consists of several stages.  Among the
-// stages are translation to direct style, translation out of SSA, eliminating
-// unnecessary names, recognizing high-level control constructs.  Combining
-// these separate concerns is complicated and the constraints of the CPS-based
-// language do not permit a multi-stage translation.
-//
-// For that reason, CPS is translated to the direct-style language Tree.
-// Translation out of SSA, unnaming, and control-flow, as well as 'instruction
-// selection' are performed on the Tree language.
-//
-// In contrast to the CPS-based IR, non-primitive expressions can be named and
-// arguments (to calls, primitives, and blocks) can be arbitrary expressions.
-//
-// Additionally, variables are considered in scope within inner functions;
-// closure variables are thus handled directly instead of using ref cells.
-
-/**
- * The base class of all Tree nodes.
- */
-abstract class Node {
-  /// Workaround for a slow Object.hashCode in the VM.
-  static int _usedHashCodes = 0;
-  final int hashCode = ++_usedHashCodes;
-}
-
-/**
- * The base class of [Expression]s.
- */
-abstract class Expression extends Node {
-  accept(ExpressionVisitor v);
-  accept1(ExpressionVisitor1 v, arg);
-
-  SourceInformation get sourceInformation => null;
-}
-
-abstract class Statement extends Node {
-  Statement get next;
-  void set next(Statement s);
-  accept(StatementVisitor v);
-  accept1(StatementVisitor1 v, arg);
-}
-
-/**
- * Labels name [LabeledStatement]s.
- */
-class Label {
-  /// Number of [Break] or [Continue] statements that target this label.
-  /// The [Break] constructor will increment this automatically, but the
-  /// counter must be decremented by hand when a [Break] becomes orphaned.
-  int useCount = 0;
-
-  /// The [LabeledStatement] or [WhileTrue] binding this label.
-  JumpTarget binding;
-}
-
-/**
- * A local variable in the tree IR.
- *
- * All tree IR variables are mutable.
- *
- * To use a variable as an expression, reference it from a [VariableUse], with
- * one [VariableUse] per expression.
- *
- * [Variable]s are reference counted. The node constructors [VariableUse],
- * [Assign], [FunctionDefinition], and [Try] automatically update the reference
- * count for their variables, but when transforming the tree, the transformer
- * is responsible for updating reference counts.
- */
-class Variable extends Node {
-  /// Function that declares this variable.
-  ExecutableElement host;
-
-  /// [Entity] used for synthesizing a name for the variable.
-  /// Different variables may have the same entity. May be null.
-  Entity element;
-
-  /// Number of places where this variable occurs in a [VariableUse].
-  int readCount = 0;
-
-  /// Number of places where this variable occurs as:
-  /// - left-hand of an [Assign]
-  /// - parameter in a [FunctionDefinition]
-  /// - catch parameter in a [Try]
-  int writeCount = 0;
-
-  /// True if an inner JS function might access this variable through a
-  /// [ForeignCode] node.
-  bool isCaptured = false;
-
-  Variable(this.host, this.element) {
-    assert(host != null);
-  }
-
-  String toString() =>
-      element == null ? 'Variable.${hashCode}' : element.toString();
-}
-
-/// Read the value of a variable.
-class VariableUse extends Expression {
-  Variable variable;
-  SourceInformation sourceInformation;
-
-  /// Creates a use of [variable] and updates its `readCount`.
-  VariableUse(this.variable, {this.sourceInformation}) {
-    variable.readCount++;
-  }
-
-  accept(ExpressionVisitor visitor) => visitor.visitVariableUse(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitVariableUse(this, arg);
-  }
-}
-
-class Assign extends Expression {
-  Variable variable;
-  Expression value;
-  SourceInformation sourceInformation;
-
-  Assign(this.variable, this.value, {this.sourceInformation}) {
-    variable.writeCount++;
-  }
-
-  accept(ExpressionVisitor v) => v.visitAssign(this);
-  accept1(ExpressionVisitor1 v, arg) => v.visitAssign(this, arg);
-
-  static ExpressionStatement makeStatement(Variable variable, Expression value,
-      [Statement next]) {
-    return new ExpressionStatement(new Assign(variable, value), next);
-  }
-}
-
-/**
- * Common interface for invocations with arguments.
- */
-abstract class Invoke {
-  List<Expression> get arguments;
-}
-
-/**
- * A call to a static function or getter/setter to a static field.
- *
- * In contrast to the CPS-based IR, the arguments can be arbitrary expressions.
- */
-class InvokeStatic extends Expression implements Invoke {
-  final Entity target;
-  final List<Expression> arguments;
-  final Selector selector;
-  final SourceInformation sourceInformation;
-
-  InvokeStatic(this.target, this.selector, this.arguments,
-      [this.sourceInformation]);
-
-  accept(ExpressionVisitor visitor) => visitor.visitInvokeStatic(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitInvokeStatic(this, arg);
-  }
-}
-
-/**
- * A call to a method, operator, getter, setter or index getter/setter.
- *
- * If [receiver] is `null`, an error is thrown before the arguments are
- * evaluated. This corresponds to the JS evaluation order.
- */
-class InvokeMethod extends Expression implements Invoke {
-  Expression receiver;
-  final Selector selector;
-  final TypeMask mask;
-  final List<Expression> arguments;
-  final SourceInformation sourceInformation;
-
-  /// If true, it is known that the receiver cannot be `null`.
-  bool receiverIsNotNull = false;
-
-  InvokeMethod(this.receiver, this.selector, this.mask, this.arguments,
-      this.sourceInformation) {
-    assert(receiver != null);
-  }
-
-  accept(ExpressionVisitor visitor) => visitor.visitInvokeMethod(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitInvokeMethod(this, arg);
-  }
-}
-
-/// Invoke [target] on [receiver], bypassing ordinary dispatch semantics.
-///
-/// Since the [receiver] is not used for method lookup, it may be `null`
-/// without an error being thrown.
-class InvokeMethodDirectly extends Expression implements Invoke {
-  Expression receiver;
-  final Element target;
-  final Selector selector;
-  final List<Expression> arguments;
-  final SourceInformation sourceInformation;
-
-  InvokeMethodDirectly(this.receiver, this.target, this.selector,
-      this.arguments, this.sourceInformation);
-
-  bool get isTearOff => selector.isGetter && !target.isGetter;
-
-  accept(ExpressionVisitor visitor) => visitor.visitInvokeMethodDirectly(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitInvokeMethodDirectly(this, arg);
-  }
-}
-
-/**
- * Call to a factory or generative constructor.
- */
-class InvokeConstructor extends Expression implements Invoke {
-  final DartType type;
-  final FunctionElement target;
-  final List<Expression> arguments;
-  final Selector selector;
-  final SourceInformation sourceInformation;
-
-  /// TODO(karlklose): get rid of this field.  Instead use the constant's
-  /// expression to find the constructor to be called in dart2dart.
-  final values.ConstantValue constant;
-
-  InvokeConstructor(this.type, this.target, this.selector, this.arguments,
-      this.sourceInformation,
-      [this.constant]);
-
-  ClassElement get targetClass => target.enclosingElement;
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitInvokeConstructor(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitInvokeConstructor(this, arg);
-  }
-}
-
-/// Call a method using a one-shot interceptor.
-///
-/// There is no explicit receiver, the first argument serves that purpose.
-class OneShotInterceptor extends Expression implements Invoke {
-  final Selector selector;
-  final TypeMask mask;
-  final List<Expression> arguments;
-  final SourceInformation sourceInformation;
-
-  OneShotInterceptor(
-      this.selector, this.mask, this.arguments, this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) => visitor.visitOneShotInterceptor(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitOneShotInterceptor(this, arg);
-  }
-}
-
-/**
- * A constant.
- */
-class Constant extends Expression {
-  final values.ConstantValue value;
-  final SourceInformation sourceInformation;
-
-  Constant(this.value, {this.sourceInformation});
-
-  Constant.bool(values.BoolConstantValue constantValue)
-      : value = constantValue,
-        sourceInformation = null;
-
-  accept(ExpressionVisitor visitor) => visitor.visitConstant(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitConstant(this, arg);
-
-  String toString() => 'Constant(value=${value.toStructuredText()})';
-}
-
-class This extends Expression {
-  accept(ExpressionVisitor visitor) => visitor.visitThis(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitThis(this, arg);
-}
-
-class LiteralList extends Expression {
-  final InterfaceType type;
-  final List<Expression> values;
-
-  LiteralList(this.type, this.values);
-
-  accept(ExpressionVisitor visitor) => visitor.visitLiteralList(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitLiteralList(this, arg);
-  }
-}
-
-/// Type test or type cast.
-///
-/// Note that if this is a type test, then [type] cannot be `Object`, `dynamic`,
-/// or the `Null` type. These cases are compiled to other node types.
-class TypeOperator extends Expression {
-  Expression value;
-  final DartType type;
-  final List<Expression> typeArguments;
-  final bool isTypeTest;
-
-  TypeOperator(this.value, this.type, this.typeArguments,
-      {bool this.isTypeTest});
-
-  accept(ExpressionVisitor visitor) => visitor.visitTypeOperator(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitTypeOperator(this, arg);
-  }
-
-  String get operator => isTypeTest ? 'is' : 'as';
-}
-
-/**
- * Apply a built-in operator.
- *
- * It must be known that the arguments have the proper types.
- * Null is not a valid argument to any of the built-in operators.
- */
-class ApplyBuiltinOperator extends Expression {
-  BuiltinOperator operator;
-  List<Expression> arguments;
-  SourceInformation sourceInformation;
-
-  ApplyBuiltinOperator(this.operator, this.arguments, this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitApplyBuiltinOperator(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitApplyBuiltinOperator(this, arg);
-  }
-}
-
-class ApplyBuiltinMethod extends Expression {
-  BuiltinMethod method;
-  Expression receiver;
-  List<Expression> arguments;
-
-  bool receiverIsNotNull;
-
-  ApplyBuiltinMethod(this.method, this.receiver, this.arguments,
-      {this.receiverIsNotNull: false});
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitApplyBuiltinMethod(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitApplyBuiltinMethod(this, arg);
-  }
-}
-
-/// A conditional expression.
-class Conditional extends Expression {
-  Expression condition;
-  Expression thenExpression;
-  Expression elseExpression;
-
-  Conditional(this.condition, this.thenExpression, this.elseExpression);
-
-  accept(ExpressionVisitor visitor) => visitor.visitConditional(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitConditional(this, arg);
-  }
-
-  String toString() => 'Conditional(condition=$condition,thenExpression='
-      '$thenExpression,elseExpression=$elseExpression)';
-}
-
-/// An && or || expression. The operator is internally represented as a boolean
-/// [isAnd] to simplify rewriting of logical operators.
-/// Note the result of && and || is one of the arguments, which might not be
-/// boolean. 'ShortCircuitOperator' might have been a better name.
-class LogicalOperator extends Expression {
-  Expression left;
-  bool isAnd;
-  Expression right;
-
-  LogicalOperator(this.left, this.right, this.isAnd);
-  LogicalOperator.and(this.left, this.right) : isAnd = true;
-  LogicalOperator.or(this.left, this.right) : isAnd = false;
-
-  String get operator => isAnd ? '&&' : '||';
-
-  accept(ExpressionVisitor visitor) => visitor.visitLogicalOperator(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitLogicalOperator(this, arg);
-  }
-
-  String toString() => 'LogicalOperator(left=$left,right=$right,isAnd=$isAnd)';
-}
-
-/// Logical negation.
-// TODO(asgerf): Replace this class with the IsFalsy builtin operator?
-//               Right now the tree builder compiles IsFalsy to Not.
-class Not extends Expression {
-  Expression operand;
-
-  Not(this.operand);
-
-  accept(ExpressionVisitor visitor) => visitor.visitNot(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitNot(this, arg);
-}
-
-/// A [LabeledStatement] or [WhileTrue] or [For].
-abstract class JumpTarget extends Statement {
-  Label get label;
-  Statement get body;
-}
-
-/**
- * A labeled statement.  Breaks to the label within the labeled statement
- * target the successor statement.
- */
-class LabeledStatement extends JumpTarget {
-  Statement next;
-  final Label label;
-  Statement body;
-
-  LabeledStatement(this.label, this.body, this.next) {
-    assert(label.binding == null);
-    label.binding = this;
-  }
-
-  accept(StatementVisitor visitor) => visitor.visitLabeledStatement(this);
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitLabeledStatement(this, arg);
-  }
-}
-
-/// A [WhileTrue] or [For] loop.
-abstract class Loop extends JumpTarget {}
-
-/**
- * A labeled while(true) loop.
- */
-class WhileTrue extends Loop {
-  final Label label;
-  Statement body;
-
-  WhileTrue(this.label, this.body) {
-    assert(label.binding == null);
-    label.binding = this;
-  }
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  accept(StatementVisitor visitor) => visitor.visitWhileTrue(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitWhileTrue(this, arg);
-}
-
-/**
- * A loop with a condition and update expressions. If there are any update
- * expressions, this generates a for loop, otherwise a while loop.
- *
- * When the condition is false, control resumes at the [next] statement.
- *
- * It is NOT valid to target this statement with a [Break].
- * The only way to reach [next] is for the condition to evaluate to false.
- *
- * [For] statements are introduced in the [LoopRewriter] and are
- * assumed not to occur before then.
- */
-class For extends Loop {
-  final Label label;
-  Expression condition;
-  List<Expression> updates;
-  Statement body;
-  Statement next;
-
-  For(this.label, this.condition, this.updates, this.body, this.next) {
-    assert(label.binding == null);
-    label.binding = this;
-  }
-
-  accept(StatementVisitor visitor) => visitor.visitFor(this);
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitFor(this, arg);
-  }
-}
-
-/// A [Break] or [Continue] statement.
-abstract class Jump extends Statement {
-  Label get target;
-}
-
-/**
- * A break from an enclosing [LabeledStatement].  The break targets the
- * labeled statement's successor statement.
- */
-class Break extends Jump {
-  final Label target;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  Break(this.target) {
-    ++target.useCount;
-  }
-
-  accept(StatementVisitor visitor) => visitor.visitBreak(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitBreak(this, arg);
-}
-
-/**
- * A continue to an enclosing [WhileTrue] or [For] loop.
- * The continue targets the loop's body.
- */
-class Continue extends Jump {
-  final Label target;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  Continue(this.target) {
-    ++target.useCount;
-  }
-
-  accept(StatementVisitor visitor) => visitor.visitContinue(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitContinue(this, arg);
-}
-
-/**
- * A return exit from the function.
- *
- * In contrast to the CPS-based IR, the return value is an arbitrary
- * expression.
- */
-class Return extends Statement {
-  /// Should not be null. Use [Constant] with [NullConstantValue] for void
-  /// returns.
-  /// Even in constructors this holds true. Take special care when translating
-  /// back to dart, where `return null;` in a constructor is an error.
-  Expression value;
-  SourceInformation sourceInformation;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  Return(this.value, {this.sourceInformation});
-
-  accept(StatementVisitor visitor) => visitor.visitReturn(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitReturn(this, arg);
-}
-
-/// A throw statement.
-///
-/// In the Tree IR, throw is a statement (like JavaScript and unlike Dart).
-/// It does not have a successor statement.
-class Throw extends Statement {
-  Expression value;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  Throw(this.value);
-
-  accept(StatementVisitor visitor) => visitor.visitThrow(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitThrow(this, arg);
-}
-
-/**
- * A conditional branch based on the true value of an [Expression].
- */
-class If extends Statement {
-  Expression condition;
-  Statement thenStatement;
-  Statement elseStatement;
-  SourceInformation sourceInformation;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  If(this.condition, this.thenStatement, this.elseStatement,
-      this.sourceInformation);
-
-  accept(StatementVisitor visitor) => visitor.visitIf(this);
-  accept1(StatementVisitor1 visitor, arg) => visitor.visitIf(this, arg);
-}
-
-class ExpressionStatement extends Statement {
-  Statement next;
-  Expression expression;
-
-  ExpressionStatement(this.expression, this.next);
-
-  accept(StatementVisitor visitor) => visitor.visitExpressionStatement(this);
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitExpressionStatement(this, arg);
-  }
-}
-
-class Try extends Statement {
-  Statement tryBody;
-  List<Variable> catchParameters;
-  Statement catchBody;
-
-  Statement get next => null;
-  void set next(Statement s) => throw 'UNREACHABLE';
-
-  Try(this.tryBody, this.catchParameters, this.catchBody) {
-    for (Variable variable in catchParameters) {
-      variable.writeCount++; // Being a catch parameter counts as a write.
-    }
-  }
-
-  accept(StatementVisitor visitor) => visitor.visitTry(this);
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitTry(this, arg);
-  }
-}
-
-/// A statement that is known to be unreachable.
-class Unreachable extends Statement {
-  Statement get next => null;
-  void set next(Statement value) => throw 'UNREACHABLE';
-
-  accept(StatementVisitor visitor) => visitor.visitUnreachable(this);
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitUnreachable(this, arg);
-  }
-}
-
-class FunctionDefinition extends Node {
-  final ExecutableElement element;
-  final List<Variable> parameters;
-  final SourceInformation sourceInformation;
-  Statement body;
-
-  /// Creates a function definition and updates `writeCount` for [parameters].
-  FunctionDefinition(this.element, this.parameters, this.body,
-      {this.sourceInformation}) {
-    for (Variable param in parameters) {
-      param.writeCount++; // Being a parameter counts as a write.
-    }
-  }
-}
-
-class CreateBox extends Expression {
-  accept(ExpressionVisitor visitor) => visitor.visitCreateBox(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitCreateBox(this, arg);
-}
-
-class CreateInstance extends Expression {
-  ClassElement classElement;
-  List<Expression> arguments;
-  Expression typeInformation;
-  SourceInformation sourceInformation;
-
-  CreateInstance(this.classElement, this.arguments, this.typeInformation,
-      this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) => visitor.visitCreateInstance(this);
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitCreateInstance(this, arg);
-  }
-}
-
-class GetField extends Expression {
-  Expression object;
-  Element field;
-  bool objectIsNotNull;
-  SourceInformation sourceInformation;
-
-  GetField(this.object, this.field, this.sourceInformation,
-      {this.objectIsNotNull: false});
-
-  accept(ExpressionVisitor visitor) => visitor.visitGetField(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitGetField(this, arg);
-}
-
-class SetField extends Expression {
-  Expression object;
-  Element field;
-  Expression value;
-  SourceInformation sourceInformation;
-
-  /// If non-null, this is a compound assignment to the field, using the given
-  /// operator.  The operator must be a compoundable operator.
-  BuiltinOperator compound;
-
-  SetField(this.object, this.field, this.value, this.sourceInformation,
-      {this.compound});
-
-  accept(ExpressionVisitor visitor) => visitor.visitSetField(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitSetField(this, arg);
-}
-
-/// Read the type test property from [object]. The value is truthy/fasly rather
-/// than bool. [object] must not be `null`.
-class GetTypeTestProperty extends Expression {
-  Expression object;
-  DartType dartType;
-
-  GetTypeTestProperty(this.object, this.dartType);
-
-  accept(ExpressionVisitor visitor) => visitor.visitGetTypeTestProperty(this);
-  accept1(ExpressionVisitor1 visitor, arg) =>
-      visitor.visitGetTypeTestProperty(this, arg);
-}
-
-/// Read the value of a field, possibly provoking its initializer to evaluate,
-/// or tear off a static method.
-class GetStatic extends Expression {
-  Element element;
-  SourceInformation sourceInformation;
-  bool useLazyGetter = false;
-
-  GetStatic(this.element, this.sourceInformation);
-
-  GetStatic.lazy(this.element, this.sourceInformation) : useLazyGetter = true;
-
-  accept(ExpressionVisitor visitor) => visitor.visitGetStatic(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitGetStatic(this, arg);
-}
-
-class SetStatic extends Expression {
-  Element element;
-  Expression value;
-  SourceInformation sourceInformation;
-  BuiltinOperator compound;
-
-  SetStatic(this.element, this.value, this.sourceInformation, {this.compound});
-
-  accept(ExpressionVisitor visitor) => visitor.visitSetStatic(this);
-  accept1(ExpressionVisitor1 visitor, arg) => visitor.visitSetStatic(this, arg);
-}
-
-class GetLength extends Expression {
-  Expression object;
-
-  GetLength(this.object);
-
-  accept(ExpressionVisitor v) => v.visitGetLength(this);
-  accept1(ExpressionVisitor1 v, arg) => v.visitGetLength(this, arg);
-}
-
-class GetIndex extends Expression {
-  Expression object;
-  Expression index;
-
-  GetIndex(this.object, this.index);
-
-  accept(ExpressionVisitor v) => v.visitGetIndex(this);
-  accept1(ExpressionVisitor1 v, arg) => v.visitGetIndex(this, arg);
-}
-
-class SetIndex extends Expression {
-  Expression object;
-  Expression index;
-  Expression value;
-  BuiltinOperator compound;
-
-  SetIndex(this.object, this.index, this.value, {this.compound});
-
-  accept(ExpressionVisitor v) => v.visitSetIndex(this);
-  accept1(ExpressionVisitor1 v, arg) => v.visitSetIndex(this, arg);
-}
-
-class ReifyRuntimeType extends Expression {
-  Expression value;
-  SourceInformation sourceInformation;
-
-  ReifyRuntimeType(this.value, this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitReifyRuntimeType(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitReifyRuntimeType(this, arg);
-  }
-}
-
-class ReadTypeVariable extends Expression {
-  final TypeVariableType variable;
-  Expression target;
-  final SourceInformation sourceInformation;
-
-  ReadTypeVariable(this.variable, this.target, this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitReadTypeVariable(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitReadTypeVariable(this, arg);
-  }
-}
-
-class CreateInvocationMirror extends Expression {
-  final Selector selector;
-  final List<Expression> arguments;
-
-  CreateInvocationMirror(this.selector, this.arguments);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitCreateInvocationMirror(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitCreateInvocationMirror(this, arg);
-  }
-}
-
-class Interceptor extends Expression {
-  Expression input;
-  Set<ClassElement> interceptedClasses;
-  final SourceInformation sourceInformation;
-
-  Interceptor(this.input, this.interceptedClasses, this.sourceInformation);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitInterceptor(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitInterceptor(this, arg);
-  }
-}
-
-class ForeignCode extends Node {
-  final js.Template codeTemplate;
-  final types.TypeMask type;
-  final List<Expression> arguments;
-  final native.NativeBehavior nativeBehavior;
-  final List<bool> nullableArguments; // One 'bit' per argument.
-  final Element dependency;
-  final SourceInformation sourceInformation;
-
-  ForeignCode(this.codeTemplate, this.type, this.arguments, this.nativeBehavior,
-      this.nullableArguments, this.dependency, this.sourceInformation) {
-    assert(arguments.length == nullableArguments.length);
-  }
-}
-
-class ForeignExpression extends ForeignCode implements Expression {
-  ForeignExpression(
-      js.Template codeTemplate,
-      types.TypeMask type,
-      List<Expression> arguments,
-      native.NativeBehavior nativeBehavior,
-      List<bool> nullableArguments,
-      Element dependency,
-      SourceInformation sourceInformation)
-      : super(codeTemplate, type, arguments, nativeBehavior, nullableArguments,
-            dependency, sourceInformation);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitForeignExpression(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitForeignExpression(this, arg);
-  }
-}
-
-class ForeignStatement extends ForeignCode implements Statement {
-  ForeignStatement(
-      js.Template codeTemplate,
-      types.TypeMask type,
-      List<Expression> arguments,
-      native.NativeBehavior nativeBehavior,
-      List<bool> nullableArguments,
-      Element dependency,
-      SourceInformation sourceInformation)
-      : super(codeTemplate, type, arguments, nativeBehavior, nullableArguments,
-            dependency, sourceInformation);
-
-  accept(StatementVisitor visitor) {
-    return visitor.visitForeignStatement(this);
-  }
-
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitForeignStatement(this, arg);
-  }
-
-  @override
-  Statement get next => null;
-
-  @override
-  void set next(Statement s) => throw 'UNREACHABLE';
-}
-
-/// Denotes the internal representation of [dartType], where all type variables
-/// are replaced by the values in [arguments].
-/// (See documentation on the TypeExpression CPS node for more details.)
-class TypeExpression extends Expression {
-  final TypeExpressionKind kind;
-  final DartType dartType;
-  final List<Expression> arguments;
-
-  TypeExpression(this.kind, this.dartType, this.arguments);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitTypeExpression(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitTypeExpression(this, arg);
-  }
-}
-
-class Await extends Expression {
-  Expression input;
-
-  Await(this.input);
-
-  accept(ExpressionVisitor visitor) {
-    return visitor.visitAwait(this);
-  }
-
-  accept1(ExpressionVisitor1 visitor, arg) {
-    return visitor.visitAwait(this, arg);
-  }
-}
-
-class Yield extends Statement {
-  Statement next;
-  Expression input;
-  final bool hasStar;
-
-  Yield(this.input, this.hasStar, this.next);
-
-  accept(StatementVisitor visitor) {
-    return visitor.visitYield(this);
-  }
-
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitYield(this, arg);
-  }
-}
-
-class ReceiverCheck extends Statement {
-  Expression condition;
-  Expression value;
-  Selector selector;
-  bool useSelector;
-  bool useInvoke;
-  Statement next;
-  SourceInformation sourceInformation;
-
-  ReceiverCheck(
-      {this.condition,
-      this.value,
-      this.selector,
-      this.useSelector,
-      this.useInvoke,
-      this.next,
-      this.sourceInformation});
-
-  accept(StatementVisitor visitor) {
-    return visitor.visitReceiverCheck(this);
-  }
-
-  accept1(StatementVisitor1 visitor, arg) {
-    return visitor.visitReceiverCheck(this, arg);
-  }
-}
-
-abstract class ExpressionVisitor<E> {
-  E visitExpression(Expression node) => node.accept(this);
-  E visitVariableUse(VariableUse node);
-  E visitAssign(Assign node);
-  E visitInvokeStatic(InvokeStatic node);
-  E visitInvokeMethod(InvokeMethod node);
-  E visitInvokeMethodDirectly(InvokeMethodDirectly node);
-  E visitInvokeConstructor(InvokeConstructor node);
-  E visitOneShotInterceptor(OneShotInterceptor node);
-  E visitConstant(Constant node);
-  E visitThis(This node);
-  E visitConditional(Conditional node);
-  E visitLogicalOperator(LogicalOperator node);
-  E visitNot(Not node);
-  E visitLiteralList(LiteralList node);
-  E visitTypeOperator(TypeOperator node);
-  E visitGetField(GetField node);
-  E visitSetField(SetField node);
-  E visitGetStatic(GetStatic node);
-  E visitSetStatic(SetStatic node);
-  E visitGetTypeTestProperty(GetTypeTestProperty node);
-  E visitCreateBox(CreateBox node);
-  E visitCreateInstance(CreateInstance node);
-  E visitReifyRuntimeType(ReifyRuntimeType node);
-  E visitReadTypeVariable(ReadTypeVariable node);
-  E visitTypeExpression(TypeExpression node);
-  E visitCreateInvocationMirror(CreateInvocationMirror node);
-  E visitInterceptor(Interceptor node);
-  E visitApplyBuiltinOperator(ApplyBuiltinOperator node);
-  E visitApplyBuiltinMethod(ApplyBuiltinMethod node);
-  E visitForeignExpression(ForeignExpression node);
-  E visitGetLength(GetLength node);
-  E visitGetIndex(GetIndex node);
-  E visitSetIndex(SetIndex node);
-  E visitAwait(Await node);
-}
-
-abstract class ExpressionVisitor1<E, A> {
-  E visitExpression(Expression node, A arg) => node.accept1(this, arg);
-  E visitVariableUse(VariableUse node, A arg);
-  E visitAssign(Assign node, A arg);
-  E visitInvokeStatic(InvokeStatic node, A arg);
-  E visitInvokeMethod(InvokeMethod node, A arg);
-  E visitInvokeMethodDirectly(InvokeMethodDirectly node, A arg);
-  E visitInvokeConstructor(InvokeConstructor node, A arg);
-  E visitOneShotInterceptor(OneShotInterceptor node, A arg);
-  E visitConstant(Constant node, A arg);
-  E visitThis(This node, A arg);
-  E visitConditional(Conditional node, A arg);
-  E visitLogicalOperator(LogicalOperator node, A arg);
-  E visitNot(Not node, A arg);
-  E visitLiteralList(LiteralList node, A arg);
-  E visitTypeOperator(TypeOperator node, A arg);
-  E visitGetField(GetField node, A arg);
-  E visitSetField(SetField node, A arg);
-  E visitGetStatic(GetStatic node, A arg);
-  E visitSetStatic(SetStatic node, A arg);
-  E visitGetTypeTestProperty(GetTypeTestProperty node, A arg);
-  E visitCreateBox(CreateBox node, A arg);
-  E visitCreateInstance(CreateInstance node, A arg);
-  E visitReifyRuntimeType(ReifyRuntimeType node, A arg);
-  E visitReadTypeVariable(ReadTypeVariable node, A arg);
-  E visitTypeExpression(TypeExpression node, A arg);
-  E visitCreateInvocationMirror(CreateInvocationMirror node, A arg);
-  E visitInterceptor(Interceptor node, A arg);
-  E visitApplyBuiltinOperator(ApplyBuiltinOperator node, A arg);
-  E visitApplyBuiltinMethod(ApplyBuiltinMethod node, A arg);
-  E visitForeignExpression(ForeignExpression node, A arg);
-  E visitGetLength(GetLength node, A arg);
-  E visitGetIndex(GetIndex node, A arg);
-  E visitSetIndex(SetIndex node, A arg);
-  E visitAwait(Await node, A arg);
-}
-
-abstract class StatementVisitor<S> {
-  S visitStatement(Statement node) => node.accept(this);
-  S visitLabeledStatement(LabeledStatement node);
-  S visitReturn(Return node);
-  S visitThrow(Throw node);
-  S visitBreak(Break node);
-  S visitContinue(Continue node);
-  S visitIf(If node);
-  S visitWhileTrue(WhileTrue node);
-  S visitFor(For node);
-  S visitExpressionStatement(ExpressionStatement node);
-  S visitTry(Try node);
-  S visitUnreachable(Unreachable node);
-  S visitForeignStatement(ForeignStatement node);
-  S visitYield(Yield node);
-  S visitReceiverCheck(ReceiverCheck node);
-}
-
-abstract class StatementVisitor1<S, A> {
-  S visitStatement(Statement node, A arg) => node.accept1(this, arg);
-  S visitLabeledStatement(LabeledStatement node, A arg);
-  S visitReturn(Return node, A arg);
-  S visitThrow(Throw node, A arg);
-  S visitBreak(Break node, A arg);
-  S visitContinue(Continue node, A arg);
-  S visitIf(If node, A arg);
-  S visitWhileTrue(WhileTrue node, A arg);
-  S visitFor(For node, A arg);
-  S visitExpressionStatement(ExpressionStatement node, A arg);
-  S visitTry(Try node, A arg);
-  S visitUnreachable(Unreachable node, A arg);
-  S visitForeignStatement(ForeignStatement node, A arg);
-  S visitYield(Yield node, A arg);
-  S visitReceiverCheck(ReceiverCheck node, A arg);
-}
-
-abstract class RecursiveVisitor implements StatementVisitor, ExpressionVisitor {
-  visitExpression(Expression e) => e.accept(this);
-  visitStatement(Statement s) => s.accept(this);
-
-  visitVariable(Variable variable) {}
-
-  visitVariableUse(VariableUse node) {
-    visitVariable(node.variable);
-  }
-
-  visitAssign(Assign node) {
-    visitVariable(node.variable);
-    visitExpression(node.value);
-  }
-
-  visitInvokeStatic(InvokeStatic node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitInvokeMethod(InvokeMethod node) {
-    visitExpression(node.receiver);
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitInvokeMethodDirectly(InvokeMethodDirectly node) {
-    visitExpression(node.receiver);
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitInvokeConstructor(InvokeConstructor node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitOneShotInterceptor(OneShotInterceptor node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitConstant(Constant node) {}
-
-  visitThis(This node) {}
-
-  visitConditional(Conditional node) {
-    visitExpression(node.condition);
-    visitExpression(node.thenExpression);
-    visitExpression(node.elseExpression);
-  }
-
-  visitLogicalOperator(LogicalOperator node) {
-    visitExpression(node.left);
-    visitExpression(node.right);
-  }
-
-  visitNot(Not node) {
-    visitExpression(node.operand);
-  }
-
-  visitLiteralList(LiteralList node) {
-    node.values.forEach(visitExpression);
-  }
-
-  visitTypeOperator(TypeOperator node) {
-    visitExpression(node.value);
-    node.typeArguments.forEach(visitExpression);
-  }
-
-  visitLabeledStatement(LabeledStatement node) {
-    visitStatement(node.body);
-    visitStatement(node.next);
-  }
-
-  visitReturn(Return node) {
-    visitExpression(node.value);
-  }
-
-  visitThrow(Throw node) {
-    visitExpression(node.value);
-  }
-
-  visitBreak(Break node) {}
-
-  visitContinue(Continue node) {}
-
-  visitIf(If node) {
-    visitExpression(node.condition);
-    visitStatement(node.thenStatement);
-    visitStatement(node.elseStatement);
-  }
-
-  visitWhileTrue(WhileTrue node) {
-    visitStatement(node.body);
-  }
-
-  visitFor(For node) {
-    visitExpression(node.condition);
-    node.updates.forEach(visitExpression);
-    visitStatement(node.body);
-    visitStatement(node.next);
-  }
-
-  visitExpressionStatement(ExpressionStatement inputNode) {
-    // Iterate over chains of expression statements to avoid deep recursion.
-    Statement node = inputNode;
-    while (node is ExpressionStatement) {
-      ExpressionStatement stmt = node;
-      visitExpression(stmt.expression);
-      node = stmt.next;
-    }
-    visitStatement(node);
-  }
-
-  visitTry(Try node) {
-    visitStatement(node.tryBody);
-    visitStatement(node.catchBody);
-  }
-
-  visitGetField(GetField node) {
-    visitExpression(node.object);
-  }
-
-  visitSetField(SetField node) {
-    visitExpression(node.object);
-    visitExpression(node.value);
-  }
-
-  visitGetStatic(GetStatic node) {}
-
-  visitSetStatic(SetStatic node) {
-    visitExpression(node.value);
-  }
-
-  visitGetTypeTestProperty(GetTypeTestProperty node) {
-    visitExpression(node.object);
-  }
-
-  visitCreateBox(CreateBox node) {}
-
-  visitCreateInstance(CreateInstance node) {
-    node.arguments.forEach(visitExpression);
-    if (node.typeInformation != null) visitExpression(node.typeInformation);
-  }
-
-  visitReifyRuntimeType(ReifyRuntimeType node) {
-    visitExpression(node.value);
-  }
-
-  visitReadTypeVariable(ReadTypeVariable node) {
-    visitExpression(node.target);
-  }
-
-  visitTypeExpression(TypeExpression node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitCreateInvocationMirror(CreateInvocationMirror node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitUnreachable(Unreachable node) {}
-
-  visitApplyBuiltinOperator(ApplyBuiltinOperator node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitApplyBuiltinMethod(ApplyBuiltinMethod node) {
-    visitExpression(node.receiver);
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitInterceptor(Interceptor node) {
-    visitExpression(node.input);
-  }
-
-  visitForeignCode(ForeignCode node) {
-    node.arguments.forEach(visitExpression);
-  }
-
-  visitForeignExpression(ForeignExpression node) => visitForeignCode(node);
-  visitForeignStatement(ForeignStatement node) => visitForeignCode(node);
-
-  visitGetLength(GetLength node) {
-    visitExpression(node.object);
-  }
-
-  visitGetIndex(GetIndex node) {
-    visitExpression(node.object);
-    visitExpression(node.index);
-  }
-
-  visitSetIndex(SetIndex node) {
-    visitExpression(node.object);
-    visitExpression(node.index);
-    visitExpression(node.value);
-  }
-
-  visitAwait(Await node) {
-    visitExpression(node.input);
-  }
-
-  visitYield(Yield node) {
-    visitExpression(node.input);
-    visitStatement(node.next);
-  }
-
-  visitReceiverCheck(ReceiverCheck node) {
-    if (node.condition != null) visitExpression(node.condition);
-    visitExpression(node.value);
-    visitStatement(node.next);
-  }
-}
-
-abstract class Transformer
-    implements ExpressionVisitor<Expression>, StatementVisitor<Statement> {
-  Expression visitExpression(Expression e) => e.accept(this);
-  Statement visitStatement(Statement s) => s.accept(this);
-}
-
-class RecursiveTransformer extends Transformer {
-  void _replaceExpressions(List<Expression> list) {
-    for (int i = 0; i < list.length; i++) {
-      list[i] = visitExpression(list[i]);
-    }
-  }
-
-  visitVariableUse(VariableUse node) => node;
-
-  visitAssign(Assign node) {
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitInvokeStatic(InvokeStatic node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitInvokeMethod(InvokeMethod node) {
-    node.receiver = visitExpression(node.receiver);
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitInvokeMethodDirectly(InvokeMethodDirectly node) {
-    node.receiver = visitExpression(node.receiver);
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitInvokeConstructor(InvokeConstructor node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitOneShotInterceptor(OneShotInterceptor node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitConstant(Constant node) => node;
-
-  visitThis(This node) => node;
-
-  visitConditional(Conditional node) {
-    node.condition = visitExpression(node.condition);
-    node.thenExpression = visitExpression(node.thenExpression);
-    node.elseExpression = visitExpression(node.elseExpression);
-    return node;
-  }
-
-  visitLogicalOperator(LogicalOperator node) {
-    node.left = visitExpression(node.left);
-    node.right = visitExpression(node.right);
-    return node;
-  }
-
-  visitNot(Not node) {
-    node.operand = visitExpression(node.operand);
-    return node;
-  }
-
-  visitLiteralList(LiteralList node) {
-    _replaceExpressions(node.values);
-    return node;
-  }
-
-  visitTypeOperator(TypeOperator node) {
-    node.value = visitExpression(node.value);
-    _replaceExpressions(node.typeArguments);
-    return node;
-  }
-
-  visitLabeledStatement(LabeledStatement node) {
-    node.body = visitStatement(node.body);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  visitReturn(Return node) {
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitThrow(Throw node) {
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitBreak(Break node) => node;
-
-  visitContinue(Continue node) => node;
-
-  visitIf(If node) {
-    node.condition = visitExpression(node.condition);
-    node.thenStatement = visitStatement(node.thenStatement);
-    node.elseStatement = visitStatement(node.elseStatement);
-    return node;
-  }
-
-  visitWhileTrue(WhileTrue node) {
-    node.body = visitStatement(node.body);
-    return node;
-  }
-
-  visitFor(For node) {
-    node.condition = visitExpression(node.condition);
-    _replaceExpressions(node.updates);
-    node.body = visitStatement(node.body);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  visitExpressionStatement(ExpressionStatement node) {
-    // Iterate over chains of expression statements to avoid deep recursion.
-    Statement first = node;
-    while (true) {
-      node.expression = visitExpression(node.expression);
-      if (node.next is ExpressionStatement) {
-        node = node.next;
-      } else {
-        break;
-      }
-    }
-    node.next = visitStatement(node.next);
-    return first;
-  }
-
-  visitTry(Try node) {
-    node.tryBody = visitStatement(node.tryBody);
-    node.catchBody = visitStatement(node.catchBody);
-    return node;
-  }
-
-  visitGetField(GetField node) {
-    node.object = visitExpression(node.object);
-    return node;
-  }
-
-  visitSetField(SetField node) {
-    node.object = visitExpression(node.object);
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitGetStatic(GetStatic node) => node;
-
-  visitSetStatic(SetStatic node) {
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitGetTypeTestProperty(GetTypeTestProperty node) {
-    node.object = visitExpression(node.object);
-    return node;
-  }
-
-  visitCreateBox(CreateBox node) => node;
-
-  visitCreateInstance(CreateInstance node) {
-    _replaceExpressions(node.arguments);
-    if (node.typeInformation != null) {
-      node.typeInformation = visitExpression(node.typeInformation);
-    }
-    return node;
-  }
-
-  visitReifyRuntimeType(ReifyRuntimeType node) {
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitReadTypeVariable(ReadTypeVariable node) {
-    node.target = visitExpression(node.target);
-    return node;
-  }
-
-  visitTypeExpression(TypeExpression node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitCreateInvocationMirror(CreateInvocationMirror node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitForeignExpression(ForeignExpression node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitForeignStatement(ForeignStatement node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitUnreachable(Unreachable node) {
-    return node;
-  }
-
-  visitApplyBuiltinOperator(ApplyBuiltinOperator node) {
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitApplyBuiltinMethod(ApplyBuiltinMethod node) {
-    node.receiver = visitExpression(node.receiver);
-    _replaceExpressions(node.arguments);
-    return node;
-  }
-
-  visitInterceptor(Interceptor node) {
-    node.input = visitExpression(node.input);
-    return node;
-  }
-
-  visitGetLength(GetLength node) {
-    node.object = visitExpression(node.object);
-    return node;
-  }
-
-  visitGetIndex(GetIndex node) {
-    node.object = visitExpression(node.object);
-    node.index = visitExpression(node.index);
-    return node;
-  }
-
-  visitSetIndex(SetIndex node) {
-    node.object = visitExpression(node.object);
-    node.index = visitExpression(node.index);
-    node.value = visitExpression(node.value);
-    return node;
-  }
-
-  visitAwait(Await node) {
-    node.input = visitExpression(node.input);
-    return node;
-  }
-
-  visitYield(Yield node) {
-    node.input = visitExpression(node.input);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-
-  visitReceiverCheck(ReceiverCheck node) {
-    if (node.condition != null) {
-      node.condition = visitExpression(node.condition);
-    }
-    node.value = visitExpression(node.value);
-    node.next = visitStatement(node.next);
-    return node;
-  }
-}
-
-class FallthroughTarget {
-  final Statement target;
-  int useCount = 0;
-
-  FallthroughTarget(this.target);
-}
-
-/// A stack machine for tracking fallthrough while traversing the Tree IR.
-class FallthroughStack {
-  final List<FallthroughTarget> _stack = <FallthroughTarget>[
-    new FallthroughTarget(null)
-  ];
-
-  /// Set a new fallthrough target.
-  void push(Statement newFallthrough) {
-    _stack.add(new FallthroughTarget(newFallthrough));
-  }
-
-  /// Remove the current fallthrough target.
-  void pop() {
-    _stack.removeLast();
-  }
-
-  /// The current fallthrough target, or `null` if control will fall over
-  /// the end of the method.
-  Statement get target => _stack.last.target;
-
-  /// Number of uses of the current fallthrough target.
-  int get useCount => _stack.last.useCount;
-
-  /// Indicate that a statement will fall through to the current fallthrough
-  /// target.
-  void use() {
-    ++_stack.last.useCount;
-  }
-}