// Copyright (c) 2018, 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 vm.bytecode.gen_bytecode;

import 'package:kernel/ast.dart' hide MapEntry;
import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
import 'package:kernel/core_types.dart' show CoreTypes;
import 'package:kernel/library_index.dart' show LibraryIndex;
import 'package:kernel/transformations/constants.dart'
    show ConstantEvaluator, ConstantsBackend, EvaluationEnvironment;
import 'package:kernel/type_environment.dart' show TypeEnvironment;
import 'package:kernel/vm/constants_native_effects.dart'
    show VmConstantsBackend;
import 'package:vm/bytecode/assembler.dart';
import 'package:vm/bytecode/constant_pool.dart';
import 'package:vm/bytecode/dbc.dart';
import 'package:vm/bytecode/local_vars.dart' show LocalVariables;
import 'package:vm/metadata/bytecode.dart';

/// Flag to toggle generation of bytecode in kernel files.
const bool isKernelBytecodeEnabled = false;

/// Flag to toggle generation of bytecode in platform kernel files.
const bool isKernelBytecodeEnabledForPlatform = isKernelBytecodeEnabled;

const bool isTraceEnabled = false;

void generateBytecode(Component component, {bool strongMode: true}) {
  final coreTypes = new CoreTypes(component);
  void ignoreAmbiguousSupertypes(Class cls, Supertype a, Supertype b) {}
  final hierarchy = new ClassHierarchy(component,
      onAmbiguousSupertypes: ignoreAmbiguousSupertypes);
  final typeEnvironment =
      new TypeEnvironment(coreTypes, hierarchy, strongMode: strongMode);
  final constantsBackend = new VmConstantsBackend(null, coreTypes);
  new BytecodeGenerator(component, coreTypes, hierarchy, typeEnvironment,
          constantsBackend, strongMode)
      .visitComponent(component);
}

class BytecodeGenerator extends RecursiveVisitor<Null> {
  final Component component;
  final CoreTypes coreTypes;
  final ClassHierarchy hierarchy;
  final TypeEnvironment typeEnvironment;
  final ConstantsBackend constantsBackend;
  final bool strongMode;
  final BytecodeMetadataRepository metadata = new BytecodeMetadataRepository();

  Class enclosingClass;
  Member enclosingMember;
  BytecodeAssembler asm;
  ConstantPool cp;
  LocalVariables locals;
  ConstantEmitter constantEmitter;
  ConstantEvaluator constantEvaluator;
  Map<LabeledStatement, Label> labeledStatements;
  Map<SwitchCase, Label> switchCases;

  BytecodeGenerator(this.component, this.coreTypes, this.hierarchy,
      this.typeEnvironment, this.constantsBackend, this.strongMode) {
    component.addMetadataRepository(metadata);
  }

  @override
  visitComponent(Component node) => node.visitChildren(this);

  @override
  visitLibrary(Library node) {
    if (node.isExternal) {
      return;
    }
    visitList(node.classes, this);
    visitList(node.procedures, this);
    visitList(node.fields, this);
  }

  @override
  visitClass(Class node) {
    visitList(node.constructors, this);
    visitList(node.procedures, this);
    visitList(node.fields, this);
  }

  @override
  defaultMember(Member node) {
    if (node.isAbstract) {
      return;
    }
    try {
      if (node is Field) {
        if (node.isStatic && node.initializer != null) {
          start(node);
          if (node.isConst) {
            _genPushConstExpr(node.initializer);
          } else {
            node.initializer.accept(this);
          }
          _genReturnTOS();
          end(node);
        }
      } else if ((node is Procedure && !node.isRedirectingFactoryConstructor) ||
          (node is Constructor)) {
        start(node);
        if (node is Constructor) {
          _genConstructorInitializers(node);
        }
        node.function?.body?.accept(this);
        // TODO(alexmarkov): figure out when 'return null' should be generated.
        _genPushNull();
        _genReturnTOS();
        end(node);
      }
    } on UnsupportedOperationError catch (e) {
      if (isTraceEnabled) {
        print('Unable to generate bytecode for $node: $e');
      }
    }
  }

  LibraryIndex _libraryIndex;
  LibraryIndex get libraryIndex =>
      _libraryIndex ??= new LibraryIndex.coreLibraries(component);

  Procedure _listFromLiteral;
  Procedure get listFromLiteral => _listFromLiteral ??=
      libraryIndex.getMember('dart:core', 'List', '_fromLiteral');

  Procedure _mapFromLiteral;
  Procedure get mapFromLiteral => _mapFromLiteral ??=
      libraryIndex.getMember('dart:core', 'Map', '_fromLiteral');

  Procedure _interpolateSingle;
  Procedure get interpolateSingle => _interpolateSingle ??=
      libraryIndex.getMember('dart:core', '_StringBase', '_interpolateSingle');

  Procedure _interpolate;
  Procedure get interpolate => _interpolate ??=
      libraryIndex.getMember('dart:core', '_StringBase', '_interpolate');

  void _genConstructorInitializers(Constructor node) {
    bool isRedirecting =
        node.initializers.any((init) => init is RedirectingInitializer);
    if (!isRedirecting) {
      for (var field in node.enclosingClass.fields) {
        if (!field.isStatic &&
            field.initializer != null &&
            !node.initializers.any(
                (init) => init is FieldInitializer && init.field == field)) {
          _genFieldInitializer(field, field.initializer);
        }
      }
    }
    visitList(node.initializers, this);
  }

  void _genFieldInitializer(Field field, Expression initializer) {
    if (initializer is NullLiteral) {
      return;
    }

    asm.emitPush(locals.thisVarIndex);
    initializer.accept(this);

    // TODO(alexmarkov): assignability check

    final int cpIndex = cp.add(new ConstantFieldOffset(field));
    asm.emitStoreFieldTOS(cpIndex);
  }

  void _genArguments(Expression receiver, Arguments arguments) {
    if (arguments.types.isNotEmpty) {
      _genTypeArguments(arguments.types);
    }
    receiver?.accept(this);
    visitList(arguments.positional, this);
    arguments.named.forEach((NamedExpression ne) => ne.value.accept(this));
  }

  void _genPushNull() {
    final cpIndex = cp.add(const ConstantNull());
    asm.emitPushConstant(cpIndex);
  }

  void _genPushInt(int value) {
    int cpIndex = cp.add(new ConstantInt(value));
    asm.emitPushConstant(cpIndex);
  }

  void _genPushConstExpr(Expression expr) {
    final constant = constantEvaluator.evaluate(expr);
    asm.emitPushConstant(constant.accept(constantEmitter));
  }

  void _genReturnTOS() {
    asm.emitReturnTOS();
  }

  void _genStaticCall(
      Member target, ConstantArgDesc argDesc, int totalArgCount) {
    final argDescIndex = cp.add(argDesc);
    final icdataIndex = cp.add(new ConstantStaticICData(target, argDescIndex));

    asm.emitPushConstant(icdataIndex);
    asm.emitIndirectStaticCall(totalArgCount, argDescIndex);
  }

  void _genStaticCallWithArgs(Member target, Arguments args,
      {bool hasReceiver: false, bool alwaysPassTypeArgs: false}) {
    final ConstantArgDesc argDesc =
        new ConstantArgDesc.fromArguments(args, hasReceiver: hasReceiver);

    int totalArgCount = args.positional.length + args.named.length;
    if (hasReceiver) {
      totalArgCount++;
    }
    if (args.types.isNotEmpty || alwaysPassTypeArgs) {
      totalArgCount++;
    }

    _genStaticCall(target, argDesc, totalArgCount);
  }

  bool hasTypeParameters(List<DartType> typeArgs) {
    final findTypeParams = new FindTypeParametersVisitor();
    return typeArgs.any((t) => t.accept(findTypeParams));
  }

  bool hasInstantiatorTypeArguments(Class c) {
    return c.typeParameters.isNotEmpty ||
        (c.superclass != null && hasInstantiatorTypeArguments(c.superclass));
  }

  bool isGenericFunction(Member member) {
    final function = member.function;
    return function != null && function.typeParameters.isNotEmpty;
  }

  void _genTypeArguments(List<DartType> typeArgs, {Class instantiatingClass}) {
    int typeArgsCPIndex = cp.add(new ConstantTypeArguments(typeArgs));
    if (instantiatingClass != null) {
      typeArgsCPIndex = cp.add(new ConstantTypeArgumentsForInstanceAllocation(
          instantiatingClass, typeArgsCPIndex));
    }
    if (typeArgs.isEmpty || !hasTypeParameters(typeArgs)) {
      asm.emitPushConstant(typeArgsCPIndex);
    } else {
      // TODO(alexmarkov): try to reuse instantiator type arguments
      _genPushInstantiatorAndFunctionTypeArguments(typeArgs);
      asm.emitInstantiateTypeArgumentsTOS(1, typeArgsCPIndex);
    }
  }

  void _genPushInstantiatorAndFunctionTypeArguments(List<DartType> types) {
    // TODO(alexmarkov): do not load instantiator type arguments / function type
    // arguments if they are not needed for these particular [types].
    _genPushInstantiatorTypeArguments();
    _genPushFunctionTypeArguments();
  }

  void _genPushInstantiatorTypeArguments() {
    // TODO(alexmarkov): access from closures to up-level type arguments.
    if ((enclosingMember.isInstanceMember || enclosingMember is Constructor) &&
        hasInstantiatorTypeArguments(enclosingClass)) {
      asm.emitPush(locals.thisVarIndex);
      final int cpIndex =
          cp.add(new ConstantTypeArgumentsFieldOffset(enclosingClass));
      asm.emitLoadFieldTOS(cpIndex);
    } else {
      _genPushNull();
    }
  }

  void _genPushFunctionTypeArguments() {
    // TODO(alexmarkov): closures
    if (isGenericFunction(enclosingMember)) {
      asm.emitPush(locals.functionTypeArgsVarIndex);
    } else {
      _genPushNull();
    }
  }

  /// Generates bool condition. Returns `true` if condition is negated.
  bool _genCondition(Node condition) {
    bool negated = false;
    if (condition is Not) {
      condition = (condition as Not).operand;
      negated = true;
    }
    condition.accept(this);
    // TODO(alexmarkov): bool check
    return negated;
  }

  void _genJumpIfFalse(bool negated, Label dest) {
    asm.emitPushConstant(cp.add(new ConstantBool(true)));
    if (negated) {
      asm.emitIfEqStrictTOS(); // if ((!condition) == true) ...
    } else {
      asm.emitIfNeStrictTOS(); // if (condition != true) ...
    }
    asm.emitJump(dest); // ... then jump dest
  }

  // Duplicates value on top of the stack using temporary variable
  // corresponding to [node].
  void _genDupTOS(TreeNode node) {
    // TODO(alexmarkov): Consider introducing Dup bytecode or keeping track of
    // expression stack depth.
    final int temp = locals.tempIndex(node);
    asm.emitStoreLocal(temp);
    asm.emitPush(temp);
  }

  void start(Member node) {
    enclosingMember = node;
    enclosingClass = node.enclosingClass;
    asm = new BytecodeAssembler();
    cp = new ConstantPool();
    locals = new LocalVariables();
    constantEmitter = new ConstantEmitter(cp);
    // TODO(alexmarkov): improve caching in ConstantEvaluator and reuse it
    constantEvaluator = new ConstantEvaluator(constantsBackend, typeEnvironment,
        coreTypes, strongMode, /* enableAsserts = */ true)
      ..env = new EvaluationEnvironment();
    labeledStatements = <LabeledStatement, Label>{};
    switchCases = <SwitchCase, Label>{};

    node.accept(locals);

    if (locals.hasOptionalParameters) {
      final function = node.function;
      final int numOptionalPositional = function.positionalParameters.length -
          function.requiredParameterCount;
      final int numOptionalNamed = function.namedParameters.length;
      final int numFixed =
          locals.numParameters - (numOptionalPositional + numOptionalNamed);

      asm.emitEntryOptional(numFixed, numOptionalPositional, numOptionalNamed);

      if (numOptionalPositional != 0) {
        assert(numOptionalNamed == 0);
        for (int i = 0; i < numOptionalPositional; i++) {
          final param = function
              .positionalParameters[function.requiredParameterCount + i];
          asm.emitLoadConstant(numFixed + i, _getDefaultParamConstIndex(param));
        }
      } else {
        assert(numOptionalNamed != 0);
        for (int i = 0; i < numOptionalNamed; i++) {
          final param = function.namedParameters[i];
          asm.emitLoadConstant(
              numFixed + i, cp.add(new ConstantString(param.name)));
          asm.emitLoadConstant(numFixed + i, _getDefaultParamConstIndex(param));
        }
      }

      asm.emitFrame(locals.frameSize - locals.numParameters);
    } else {
      asm.emitEntry(locals.frameSize);
    }
    asm.emitCheckStack();

    // TODO(alexmarkov): add type checks for parameters
  }

  int _getDefaultParamConstIndex(VariableDeclaration param) {
    if (param.initializer == null) {
      return cp.add(const ConstantNull());
    }
    final constant = constantEvaluator.evaluate(param.initializer);
    return constant.accept(constantEmitter);
  }

  void _genJumpIfTrue(bool negated, Label dest) {
    _genJumpIfFalse(!negated, dest);
  }

  void end(Member node) {
    enclosingMember = null;
    enclosingClass = null;
    metadata.mapping[node] = new BytecodeMetadata(asm.bytecode, cp);
    if (isTraceEnabled) {
      print('Generated bytecode for $node');
    }
  }

  @override
  defaultTreeNode(Node node) => throw new UnsupportedOperationError(
      'Unsupported node ${node.runtimeType}');

  @override
  visitAsExpression(AsExpression node) {
    node.operand.accept(this);

    if (node.type == const DynamicType()) {
      return;
    }
    if (node.isTypeError) {
      // TODO(alexmarkov): type checks
      return;
    }
    if (hasTypeParameters([node.type])) {
      _genPushInstantiatorAndFunctionTypeArguments([node.type]);
    } else {
      _genPushNull(); // Instantiator type arguments.
      _genPushNull(); // Function type arguments.
    }
    final typeIndex = cp.add(new ConstantType(node.type));
    asm.emitPushConstant(typeIndex);
    final argDescIndex = cp.add(new ConstantArgDesc(4));
    final icdataIndex = cp.add(new ConstantICData('_as', argDescIndex));
    asm.emitInstanceCall1(4, icdataIndex);
  }

  @override
  visitBoolLiteral(BoolLiteral node) {
    final cpIndex = cp.add(new ConstantBool.fromLiteral(node));
    asm.emitPushConstant(cpIndex);
  }

  @override
  visitIntLiteral(IntLiteral node) {
    final cpIndex = cp.add(new ConstantInt.fromLiteral(node));
    asm.emitPushConstant(cpIndex);
  }

  @override
  visitDoubleLiteral(DoubleLiteral node) {
    final cpIndex = cp.add(new ConstantDouble.fromLiteral(node));
    asm.emitPushConstant(cpIndex);
  }

  @override
  visitConditionalExpression(ConditionalExpression node) {
    final Label otherwisePart = new Label();
    final Label done = new Label();
    final int temp = locals.tempIndex(node);

    final bool negated = _genCondition(node.condition);
    _genJumpIfFalse(negated, otherwisePart);

    node.then.accept(this);
    asm.emitPopLocal(temp);
    asm.emitJump(done);

    asm.bind(otherwisePart);
    node.otherwise.accept(this);
    asm.emitPopLocal(temp);

    asm.bind(done);
    asm.emitPush(temp);
  }

  @override
  visitConstructorInvocation(ConstructorInvocation node) {
    if (node.isConst) {
      _genPushConstExpr(node);
      return;
    }

    final constructedClass = node.constructedType.classNode;
    final classIndex = cp.add(new ConstantClass(constructedClass));

    if (hasInstantiatorTypeArguments(constructedClass)) {
      _genTypeArguments(node.arguments.types,
          instantiatingClass: constructedClass);
      asm.emitPushConstant(cp.add(new ConstantClass(constructedClass)));
      asm.emitAllocateT();
    } else {
      assert(node.arguments.types.isEmpty);
      asm.emitAllocate(classIndex);
    }

    _genDupTOS(node);

    // Remove type arguments as they are only passed to instance allocation,
    // and not passed to a constructor.
    final args =
        new Arguments(node.arguments.positional, named: node.arguments.named);
    _genArguments(null, args);
    _genStaticCallWithArgs(node.target, args, hasReceiver: true);
    asm.emitDrop1();
  }

//  @override
//  visitDirectMethodInvocation(DirectMethodInvocation node) {
//  }

  @override
  visitDirectPropertyGet(DirectPropertyGet node) {
    node.receiver.accept(this);
    final target = node.target;
    if (target is Field || (target is Procedure && target.isGetter)) {
      _genStaticCall(target, new ConstantArgDesc(1), 1);
    } else {
      throw new UnsupportedOperationError(
          'Unsupported DirectPropertyGet with ${target.runtimeType} $target');
    }
  }

//  @override
//  visitDirectPropertySet(DirectPropertySet node) {
//  }
//
//  @override
//  visitFunctionExpression(FunctionExpression node) {
//  }
//
//  @override
//  visitInstantiation(Instantiation node) {
//  }
//
//  @override
//  visitInvalidExpression(InvalidExpression node) {
//  }

  @override
  visitIsExpression(IsExpression node) {
    node.operand.accept(this);

    // TODO(alexmarkov): generate _simpleInstanceOf if possible

    if (hasTypeParameters([node.type])) {
      _genPushInstantiatorAndFunctionTypeArguments([node.type]);
    } else {
      _genPushNull(); // Instantiator type arguments.
      _genPushNull(); // Function type arguments.
    }
    final typeIndex = cp.add(new ConstantType(node.type));
    asm.emitPushConstant(typeIndex);
    final argDescIndex = cp.add(new ConstantArgDesc(4));
    final icdataIndex = cp.add(new ConstantICData('_instanceOf', argDescIndex));
    asm.emitInstanceCall1(4, icdataIndex);
  }

  @override
  visitLet(Let node) {
    node.variable.accept(this);
    node.body.accept(this);
  }

  @override
  visitListLiteral(ListLiteral node) {
    if (node.isConst) {
      _genPushConstExpr(node);
      return;
    }

    _genTypeArguments([node.typeArgument]);

    _genDupTOS(node);

    // TODO(alexmarkov): gen more efficient code for empty array
    _genPushInt(node.expressions.length);
    asm.emitCreateArrayTOS();
    final int temp = locals.tempIndex(node);
    asm.emitStoreLocal(temp);

    for (int i = 0; i < node.expressions.length; i++) {
      asm.emitPush(temp);
      _genPushInt(i);
      node.expressions[i].accept(this);
      // TODO(alexmarkov): assignable check
      asm.emitStoreIndexedTOS();
    }

    _genStaticCall(listFromLiteral, new ConstantArgDesc(1, numTypeArgs: 1), 2);
  }

  @override
  visitLogicalExpression(LogicalExpression node) {
    assert(node.operator == '||' || node.operator == '&&');

    final Label shortCircuit = new Label();
    final Label done = new Label();
    final int temp = locals.tempIndex(node);
    final isOR = (node.operator == '||');

    bool negated = _genCondition(node.left);
    asm.emitPushConstant(cp.add(new ConstantBool(true)));
    if (negated != isOR) {
      // OR: if (condition == true)
      // AND: if ((!condition) == true)
      asm.emitIfEqStrictTOS();
    } else {
      // OR: if ((!condition) != true)
      // AND: if (condition != true)
      asm.emitIfNeStrictTOS();
    }
    asm.emitJump(shortCircuit);

    negated = _genCondition(node.right);
    if (negated) {
      asm.emitBooleanNegateTOS();
    }
    asm.emitPopLocal(temp);
    asm.emitJump(done);

    asm.bind(shortCircuit);
    asm.emitPushConstant(cp.add(new ConstantBool(isOR)));
    asm.emitPopLocal(temp);

    asm.bind(done);
    asm.emitPush(temp);
  }

  @override
  visitMapLiteral(MapLiteral node) {
    if (node.isConst) {
      _genPushConstExpr(node);
      return;
    }

    _genTypeArguments([node.keyType, node.valueType]);

    if (node.entries.isEmpty) {
      asm.emitPushConstant(
          cp.add(new ConstantList(const DynamicType(), const [])));
    } else {
      _genTypeArguments([const DynamicType()]);
      _genPushInt(node.entries.length * 2);
      asm.emitCreateArrayTOS();

      final int temp = locals.tempIndex(node);
      asm.emitStoreLocal(temp);

      for (int i = 0; i < node.entries.length; i++) {
        // key
        asm.emitPush(temp);
        _genPushInt(i * 2);
        node.entries[i].key.accept(this);
        asm.emitStoreIndexedTOS();
        // value
        asm.emitPush(temp);
        _genPushInt(i * 2 + 1);
        node.entries[i].value.accept(this);
        asm.emitStoreIndexedTOS();
      }
    }

    _genStaticCall(mapFromLiteral, new ConstantArgDesc(1, numTypeArgs: 1), 2);
  }

  @override
  visitMethodInvocation(MethodInvocation node) {
    final args = node.arguments;
    _genArguments(node.receiver, args);
    // TODO(alexmarkov): fast path smi ops
    final argDescIndex =
        cp.add(new ConstantArgDesc.fromArguments(args, hasReceiver: true));
    final icdataIndex =
        cp.add(new ConstantICData(node.name.name, argDescIndex));
    // TODO(alexmarkov): figure out when generate InstanceCall2 (2 checked arguments).
    asm.emitInstanceCall1(
        args.positional.length + args.named.length + 1, icdataIndex);
  }

  @override
  visitPropertyGet(PropertyGet node) {
    node.receiver.accept(this);
    final argDescIndex = cp.add(new ConstantArgDesc(1));
    final icdataIndex = cp.add(
        new ConstantICData('$kGetterPrefix${node.name.name}', argDescIndex));
    asm.emitInstanceCall1(1, icdataIndex);
  }

  @override
  visitPropertySet(PropertySet node) {
    final int temp = locals.tempIndex(node);
    node.receiver.accept(this);
    node.value.accept(this);
    asm.emitStoreLocal(temp);
    final argDescIndex = cp.add(new ConstantArgDesc(2));
    final icdataIndex = cp.add(
        new ConstantICData('$kSetterPrefix${node.name.name}', argDescIndex));
    asm.emitInstanceCall1(2, icdataIndex);
    asm.emitDrop1();
    asm.emitPush(temp);
  }

  @override
  visitSuperMethodInvocation(SuperMethodInvocation node) {
    final args = node.arguments;
    _genArguments(new ThisExpression(), args);
    Member target =
        hierarchy.getDispatchTarget(enclosingClass.superclass, node.name);
    if (target == null) {
      throw new UnsupportedOperationError(
          'Unsupported SuperMethodInvocation without target');
    }
    if (target is Procedure && !target.isGetter) {
      _genStaticCallWithArgs(target, args);
    } else {
      throw new UnsupportedOperationError(
          'Unsupported SuperMethodInvocation with target ${target.runtimeType} $target');
    }
  }

  @override
  visitSuperPropertyGet(SuperPropertyGet node) {
    asm.emitPush(locals.thisVarIndex);
    Member target =
        hierarchy.getDispatchTarget(enclosingClass.superclass, node.name);
    if (target == null) {
      throw new UnsupportedOperationError(
          'Unsupported SuperPropertyGet without target');
    }
    if (target is Field || (target is Procedure && target.isGetter)) {
      _genStaticCall(target, new ConstantArgDesc(1), 1);
    } else {
      throw new UnsupportedOperationError(
          'Unsupported SuperPropertyGet with target ${target.runtimeType} $target');
    }
  }

//  @override
//  visitSuperPropertySet(SuperPropertySet node) {
//  }

  @override
  visitNot(Not node) {
    bool negated = _genCondition(node.operand);
    if (!negated) {
      asm.emitBooleanNegateTOS();
    }
  }

  @override
  visitNullLiteral(NullLiteral node) {
    final cpIndex = cp.add(const ConstantNull());
    asm.emitPushConstant(cpIndex);
  }

//  @override
//  visitRethrow(Rethrow node) {
//  }

  bool _hasTrivialInitializer(Field field) =>
      (field.initializer == null) ||
      (field.initializer is StringLiteral) ||
      (field.initializer is BoolLiteral) ||
      (field.initializer is IntLiteral) ||
      (field.initializer is NullLiteral);

  @override
  visitStaticGet(StaticGet node) {
    final target = node.target;
    if (target is Field) {
      if (target.isConst) {
        _genPushConstExpr(target.initializer);
      } else if (_hasTrivialInitializer(target)) {
        final fieldIndex = cp.add(new ConstantField(target));
        asm.emitPushConstant(
            fieldIndex); // TODO(alexmarkov): do we really need this?
        asm.emitPushStatic(fieldIndex);
      } else {
        _genStaticCall(target, new ConstantArgDesc(0), 0);
      }
    } else if (target is Procedure) {
      if (target.isGetter) {
        _genStaticCall(target, new ConstantArgDesc(0), 0);
      } else {
        final tearOffIndex = cp.add(new ConstantTearOff(target));
        asm.emitPushConstant(tearOffIndex);
      }
    } else {
      throw 'Unexpected target for StaticGet: ${target.runtimeType} $target';
    }
  }

  @override
  visitStaticInvocation(StaticInvocation node) {
    final args = node.arguments;
    bool alwaysPassTypeArgs = false;
    if (node.target.isFactory && args.types.isEmpty) {
      // VM needs type arguments for every invocation of a factory constructor.
      // TODO(alexmarkov): Why? Clean this up.
      _genPushNull();
      alwaysPassTypeArgs = true;
    }
    _genArguments(null, args);
    _genStaticCallWithArgs(node.target, args,
        alwaysPassTypeArgs: alwaysPassTypeArgs);
  }

  @override
  visitStaticSet(StaticSet node) {
    node.value.accept(this);
    _genDupTOS(node);
    final target = node.target;
    if (target is Field) {
      // TODO(alexmarkov): assignable check
      int cpIndex = cp.add(new ConstantField(target));
      asm.emitStoreStaticTOS(cpIndex);
    } else {
      _genStaticCall(target, new ConstantArgDesc(1), 1);
      asm.emitDrop1();
    }
  }

  @override
  visitStringConcatenation(StringConcatenation node) {
    if (node.expressions.length == 1) {
      node.expressions.single.accept(this);
      _genStaticCall(interpolateSingle, new ConstantArgDesc(1), 1);
    } else {
      _genPushNull();
      _genPushInt(node.expressions.length);
      asm.emitCreateArrayTOS();

      final int temp = locals.tempIndex(node);
      asm.emitStoreLocal(temp);

      for (int i = 0; i < node.expressions.length; i++) {
        asm.emitPush(temp);
        _genPushInt(i);
        node.expressions[i].accept(this);
        asm.emitStoreIndexedTOS();
      }

      _genStaticCall(interpolate, new ConstantArgDesc(1), 1);
    }
  }

  @override
  visitStringLiteral(StringLiteral node) {
    final cpIndex = cp.add(new ConstantString.fromLiteral(node));
    asm.emitPushConstant(cpIndex);
  }

  @override
  visitSymbolLiteral(SymbolLiteral node) {
    final cpIndex = cp.add(new ConstantSymbol.fromLiteral(node));
    asm.emitPushConstant(cpIndex);
  }

  @override
  visitThisExpression(ThisExpression node) {
    // TODO(alexmarkov): access to captured this from closures.
    asm.emitPush(locals.thisVarIndex);
  }

  @override
  visitThrow(Throw node) {
    node.expression.accept(this);
    asm.emitThrow(0);
  }

  @override
  visitTypeLiteral(TypeLiteral node) {
    final DartType type = node.type;
    final int typeCPIndex = cp.add(new ConstantType(type));
    if (!hasTypeParameters([type])) {
      asm.emitPushConstant(typeCPIndex);
    } else {
      _genPushInstantiatorAndFunctionTypeArguments([type]);
      asm.emitInstantiateType(typeCPIndex);
    }
  }

  @override
  visitVariableGet(VariableGet node) {
    if (node.variable.isConst) {
      _genPushConstExpr(node.variable.initializer);
    } else {
      // TODO(alexmarkov): access to captured variables.
      asm.emitPush(locals.varIndex(node.variable));
    }
  }

  @override
  visitVariableSet(VariableSet node) {
    node.value.accept(this);
    // TODO(alexmarkov): access to captured variables.
    asm.emitStoreLocal(locals.varIndex(node.variable));
  }

//  @override
//  visitLoadLibrary(LoadLibrary node) {
//  }
//
//  @override
//  visitCheckLibraryIsLoaded(CheckLibraryIsLoaded node) {
//  }
//
//  @override
//  visitVectorCreation(VectorCreation node) {
//  }
//
//  @override
//  visitVectorGet(VectorGet node) {
//  }
//
//  @override
//  visitVectorSet(VectorSet node) {
//  }
//
//  @override
//  visitVectorCopy(VectorCopy node) {
//  }
//
//  @override
//  visitClosureCreation(ClosureCreation node) {
//  }

  @override
  visitAssertStatement(AssertStatement node) {
    // TODO(alexmarkov): support asserts
  }

  @override
  visitBlock(Block node) {
    visitList(node.statements, this);
  }

  @override
  visitAssertBlock(AssertBlock node) {
    // TODO(alexmarkov): support asserts
  }

  @override
  visitBreakStatement(BreakStatement node) {
    // TODO(alexmarkov): execute all finally blocks on the way out.
    final label = labeledStatements[node.target] ??
        (throw 'Target label ${node.target} was not registered for break $node');
    asm.emitJump(label);
  }

  @override
  visitContinueSwitchStatement(ContinueSwitchStatement node) {
    // TODO(alexmarkov): execute all finally blocks on the way out.
    final label = switchCases[node.target] ??
        (throw 'Target label ${node.target} was not registered for continue-switch $node');
    asm.emitJump(label);
  }

  @override
  visitDoStatement(DoStatement node) {
    final Label join = new Label();
    asm.bind(join);

    asm.emitCheckStack();

    node.body.accept(this);

    // TODO(alexmarkov): do we need to break this critical edge in CFG?
    bool negated = _genCondition(node.condition);
    _genJumpIfTrue(negated, join);
  }

  @override
  visitEmptyStatement(EmptyStatement node) {
    // no-op
  }

  @override
  visitExpressionStatement(ExpressionStatement node) {
    node.expression.accept(this);
    asm.emitDrop1();
  }

  @override
  visitForInStatement(ForInStatement node) {
    node.iterable.accept(this);

    const kIterator = 'iterator'; // Iterable.iterator
    const kMoveNext = 'moveNext'; // Iterator.moveNext
    const kCurrent = 'current'; // Iterator.current

    asm.emitInstanceCall1(
        1,
        cp.add(new ConstantICData(
            '$kGetterPrefix$kIterator', cp.add(new ConstantArgDesc(1)))));

    final iteratorTemp = locals.tempIndex(node);
    asm.emitPopLocal(iteratorTemp);

    final Label done = new Label();
    final Label join = new Label();
    asm.bind(join);

    asm.emitCheckStack();

    asm.emitPush(iteratorTemp);
    asm.emitInstanceCall1(1,
        cp.add(new ConstantICData(kMoveNext, cp.add(new ConstantArgDesc(1)))));
    _genJumpIfFalse(/* negated = */ false, done);

    asm.emitPush(iteratorTemp);
    asm.emitInstanceCall1(1,
        cp.add(new ConstantICData(kCurrent, cp.add(new ConstantArgDesc(1)))));
    asm.emitPopLocal(locals.varIndex(node.variable));

    node.body.accept(this);

    asm.emitJump(join);

    asm.bind(done);
  }

  @override
  visitForStatement(ForStatement node) {
    visitList(node.variables, this);

    final Label done = new Label();
    final Label join = new Label();
    asm.bind(join);

    asm.emitCheckStack();

    if (node.condition != null) {
      bool negated = _genCondition(node.condition);
      _genJumpIfFalse(negated, done);
    }

    node.body.accept(this);

    for (var update in node.updates) {
      update.accept(this);
      asm.emitDrop1();
    }

    asm.emitJump(join);

    asm.bind(done);
  }

//  @override
//  visitFunctionDeclaration(FunctionDeclaration node) {
//  }

  @override
  visitIfStatement(IfStatement node) {
    final Label otherwisePart = new Label();

    final bool negated = _genCondition(node.condition);
    _genJumpIfFalse(negated, otherwisePart);

    node.then.accept(this);

    if (node.otherwise != null) {
      final Label done = new Label();
      asm.emitJump(done);
      asm.bind(otherwisePart);
      node.otherwise.accept(this);
      asm.bind(done);
    } else {
      asm.bind(otherwisePart);
    }
  }

  @override
  visitLabeledStatement(LabeledStatement node) {
    final label = new Label();
    labeledStatements[node] = label;
    node.body.accept(this);
    asm.bind(label);
    labeledStatements[node] = null;
  }

  @override
  visitReturnStatement(ReturnStatement node) {
    if (node.expression != null) {
      node.expression.accept(this);
    } else {
      _genPushNull();
    }
    asm.emitReturnTOS();
  }

  @override
  visitSwitchStatement(SwitchStatement node) {
    node.expression.accept(this);

    final int temp = locals.tempIndex(node);
    asm.emitPopLocal(temp);

    final Label done = new Label();
    final List<Label> caseLabels =
        new List<Label>.generate(node.cases.length, (_) => new Label());
    final equalsArgDesc = cp.add(new ConstantArgDesc(2));

    Label defaultLabel = done;
    for (int i = 0; i < node.cases.length; i++) {
      final SwitchCase switchCase = node.cases[i];
      final Label caseLabel = caseLabels[i];
      switchCases[switchCase] = caseLabel;

      if (switchCase.isDefault) {
        defaultLabel = caseLabel;
      } else {
        for (var expr in switchCase.expressions) {
          asm.emitPush(temp);
          _genPushConstExpr(expr);
          asm.emitInstanceCall2(
              2, cp.add(new ConstantICData('==', equalsArgDesc)));
          _genJumpIfTrue(/* negated = */ false, caseLabel);
        }
      }
    }

    asm.emitJump(defaultLabel);

    for (int i = 0; i < node.cases.length; i++) {
      final SwitchCase switchCase = node.cases[i];
      final Label caseLabel = caseLabels[i];

      asm.bind(caseLabel);
      switchCase.body.accept(this);

      // Front-end issues a compile-time error if there is a fallthrough
      // between cases. Also, default case should be the last one.
    }

    asm.bind(done);
    node.cases.forEach(switchCases.remove);
  }

//  @override
//  visitTryCatch(TryCatch node) {
//  }
//
//  @override
//  visitTryFinally(TryFinally node) {
//  }

  @override
  visitVariableDeclaration(VariableDeclaration node) {
    if (node.isConst) {
      final Constant constant = constantEvaluator.evaluate(node.initializer);
      constantEvaluator.env.addVariableValue(node, constant);
    } else {
      if (node.initializer != null) {
        node.initializer.accept(this);
      } else {
        _genPushNull();
      }
      asm.emitPopLocal(locals.varIndex(node));
    }
  }

  @override
  visitWhileStatement(WhileStatement node) {
    final Label done = new Label();
    final Label join = new Label();
    asm.bind(join);

    asm.emitCheckStack();

    bool negated = _genCondition(node.condition);
    _genJumpIfFalse(negated, done);

    node.body.accept(this);

    asm.emitJump(join);

    asm.bind(done);
  }

//  @override
//  visitYieldStatement(YieldStatement node) {
//  }

  @override
  visitFieldInitializer(FieldInitializer node) {
    _genFieldInitializer(node.field, node.value);
  }

  @override
  visitRedirectingInitializer(RedirectingInitializer node) {
    final args = node.arguments;
    assert(args.types.isEmpty);
    _genArguments(new ThisExpression(), args);
    _genStaticCallWithArgs(node.target, args, hasReceiver: true);
    asm.emitDrop1();
  }

  @override
  visitSuperInitializer(SuperInitializer node) {
    final args = node.arguments;
    assert(args.types.isEmpty);
    _genArguments(new ThisExpression(), args);
    // Re-resolve target due to partial mixin resolution.
    Member target;
    for (var replacement in enclosingClass.superclass.constructors) {
      if (node.target.name == replacement.name) {
        target = replacement;
        break;
      }
    }
    assert(target != null);
    _genStaticCallWithArgs(target, args, hasReceiver: true);
    asm.emitDrop1();
  }

//  @override
//  visitLocalInitializer(LocalInitializer node) {
//  }
//
//  @override
//  visitAssertInitializer(AssertInitializer node) {
//  }
//
//  @override
//  visitInvalidInitializer(InvalidInitializer node) {}

  @override
  visitConstantExpression(ConstantExpression node) {
    int cpIndex = node.constant.accept(constantEmitter);
    asm.emitPushConstant(cpIndex);
  }
}

class ConstantEmitter extends ConstantVisitor<int> {
  final ConstantPool cp;

  ConstantEmitter(this.cp);

  @override
  int defaultConstant(Constant node) => throw new UnsupportedOperationError(
      'Unsupported constant node ${node.runtimeType}');

  @override
  int visitNullConstant(NullConstant node) => cp.add(const ConstantNull());

  @override
  int visitBoolConstant(BoolConstant node) =>
      cp.add(new ConstantBool(node.value));

  @override
  int visitIntConstant(IntConstant node) => cp.add(new ConstantInt(node.value));

  @override
  int visitDoubleConstant(DoubleConstant node) =>
      cp.add(new ConstantDouble(node.value));

  @override
  int visitStringConstant(StringConstant node) =>
      cp.add(new ConstantString(node.value));

  @override
  int visitListConstant(ListConstant node) => cp.add(new ConstantList(
      node.typeArgument,
      new List<int>.from(node.entries.map((Constant c) => c.accept(this)))));

  @override
  int visitInstanceConstant(InstanceConstant node) =>
      cp.add(new ConstantInstance(
          node.klass,
          cp.add(new ConstantTypeArguments(node.typeArguments)),
          node.fieldValues.map<Reference, int>(
              (Reference fieldRef, Constant value) =>
                  new MapEntry(fieldRef, value.accept(this)))));

  @override
  int visitTearOffConstant(TearOffConstant node) =>
      cp.add(new ConstantTearOff(node.procedure));

//  @override
//  int visitTypeLiteralConstant(TypeLiteralConstant node) => defaultConstant(node);
}

class UnsupportedOperationError {
  final String message;
  UnsupportedOperationError(this.message);

  @override
  String toString() => message;
}

class FindTypeParametersVisitor extends DartTypeVisitor<bool> {
  bool visit(DartType type) => type.accept(this);

  @override
  bool defaultDartType(DartType node) =>
      throw 'Unexpected type ${node.runtimeType} $node';

  @override
  bool visitInvalidType(InvalidType node) => false;

  @override
  bool visitDynamicType(DynamicType node) => false;

  @override
  bool visitVoidType(VoidType node) => false;

  @override
  bool visitBottomType(BottomType node) => false;

  @override
  bool visitVectorType(VectorType node) => false;

  @override
  bool visitTypeParameterType(TypeParameterType node) => true;

  @override
  bool visitInterfaceType(InterfaceType node) =>
      node.typeArguments.any((t) => t.accept(this));

  @override
  bool visitTypedefType(TypedefType node) =>
      node.typeArguments.any((t) => t.accept(this));

  @override
  bool visitFunctionType(FunctionType node) =>
      node.typeParameters.isNotEmpty ||
      node.positionalParameters.any((t) => t.accept(this)) ||
      node.namedParameters.any((p) => p.type.accept(this));
}