pkg/dart2wasm/lib/code_generator.dart

// Copyright (c) 2022, 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.

import 'dart:collection' show LinkedHashMap;

import 'package:kernel/ast.dart';
import 'package:kernel/type_environment.dart';
import 'package:wasm_builder/wasm_builder.dart' as w;

import 'async.dart';
import 'class_info.dart';
import 'closures.dart';
import 'dispatch_table.dart';
import 'dynamic_forwarders.dart';
import 'intrinsics.dart';
import 'param_info.dart';
import 'records.dart';
import 'reference_extensions.dart';
import 'sync_star.dart';
import 'translator.dart';
import 'types.dart';

abstract class CodeGenerator {
  // The two parameters here are used for inlining:
  //
  // If the user
  //
  //   * inlines the code, it will provide locals and a return label
  //
  //   * doesn't inline (i.e. makes new function with this code) it will provide
  //     the parameters of the function and no return label.
  //
  void generate(List<w.Local> paramLocals, w.Label? returnLabel);

  // TODO(kustermann): Remove this again.
  Closures get closures;
}

/// Main code generator for member bodies.
///
/// The [generate] method first collects all local functions and function
/// expressions in the body and then generates code for the body. Code for the
/// local functions and function expressions must be generated separately by
/// calling the [generateLambda] method on all lambdas in [closures].
///
/// A new [CodeGenerator] object must be created for each new member or lambda.
///
/// Every visitor method for an expression takes in the Wasm type that it is
/// expected to leave on the stack (or the special [voidMarker] to indicate that
/// it should leave nothing). It returns what it actually left on the stack. The
/// code generation for every expression or subexpression is done via the [wrap]
/// method, which emits appropriate conversion code if the produced type is not
/// a subtype of the expected type.
abstract class AstCodeGenerator
    extends ExpressionVisitor1<w.ValueType, w.ValueType>
    with ExpressionVisitor1DefaultMixin<w.ValueType, w.ValueType>
    implements InitializerVisitor<void>, StatementVisitor<void>, CodeGenerator {
  final Translator translator;
  final w.FunctionType functionType;
  final w.InstructionsBuilder b;
  final Member enclosingMember;

  // To be initialized in `generate()`
  late final List<w.Local> paramLocals;
  late final w.Label? returnLabel;

  late final Intrinsifier intrinsifier = Intrinsifier(this);
  late final StaticTypeContext typeContext =
      StaticTypeContext(enclosingMember, translator.typeEnvironment);

  @override
  late final Closures closures;

  bool exceptionLocationPrinted = false;

  final Map<VariableDeclaration, w.Local> locals = {};
  w.Local? thisLocal;
  w.Local? preciseThisLocal;
  w.Local? returnValueLocal;
  final Map<TypeParameter, w.Local> typeLocals = {};

  // Maps a classes' fields to corresponding locals so that we can update the
  // local directly if a field has both a default value and a FieldInitializer.
  final Map<Field, w.Local> fieldLocals = {};

  /// Finalizers to run on `return`.
  final List<TryBlockFinalizer> returnFinalizers = [];

  /// Finalizers to run on a `break`. `breakFinalizers[L].last` (which should
  /// always be present) is the `br` target for the label `L` that will run the
  /// finalizers, or break out of the loop.
  final LinkedHashMap<LabeledStatement, List<w.Label>> breakFinalizers =
      LinkedHashMap();

  final List<w.Label> tryLabels = [];

  final Map<SwitchCase, w.Label> switchLabels = {};

  /// Maps a switch statement to the information used when doing a backward
  /// jump to one of the cases in the switch statement
  final Map<SwitchStatement, SwitchBackwardJumpInfo> switchBackwardJumpInfos =
      {};

  /// Create a code generator for a member or one of its lambdas.
  AstCodeGenerator(
      this.translator, this.functionType, this.b, this.enclosingMember);

  w.ModuleBuilder get m => translator.m;

  List<w.ValueType> get outputs => functionType.outputs;

  w.ValueType get returnType => translator.outputOrVoid(outputs);

  TranslatorOptions get options => translator.options;

  w.ValueType get voidMarker => translator.voidMarker;

  Types get types => translator.types;

  w.ValueType translateType(DartType type) => translator.translateType(type);

  w.Local addLocal(w.ValueType type) {
    return b.addLocal(type);
  }

  DartType dartTypeOf(Expression exp) {
    return exp.getStaticType(typeContext);
  }

  void unimplemented(
      TreeNode node, Object message, List<w.ValueType> expectedTypes) {
    final text = "Not implemented: $message at ${node.location}";
    print(text);
    b.comment(text);
    b.block(const [], expectedTypes);
    b.unreachable();
    b.end();
  }

  @override
  w.ValueType defaultExpression(Expression node, w.ValueType expectedType) {
    unimplemented(
        node, node.runtimeType, [if (expectedType != voidMarker) expectedType]);
    return expectedType;
  }

  Source? _sourceMapSource;
  int _sourceMapFileOffset = TreeNode.noOffset;

  /// Update the [Source] for the AST nodes being compiled.
  ///
  /// The [Source] is used to resolve [TreeNode.fileOffset]s to file URI, line,
  /// and column numbers, to be able to generate source mappings, in
  /// [setSourceMapFileOffset].
  ///
  /// Setting this `null` disables source mapping for the instructions being
  /// generated.
  ///
  /// This should be called before [setSourceMapFileOffset] as the file offset
  /// passed to that function is resolved using the [Source].
  ///
  /// Returns the old [Source], which can be used to restore the source mapping
  /// after visiting a sub-tree.
  Source? setSourceMapSource(Source? source) {
    final old = _sourceMapSource;
    _sourceMapSource = source;
    return old;
  }

  /// Update the source location of the AST nodes being compiled in the source
  /// map.
  ///
  /// When the offset is [TreeNode.noOffset], this disables mapping the
  /// generated instructions.
  ///
  /// Returns the old file offset, which can be used to restore the source
  /// mapping after vising a sub-tree.
  int setSourceMapFileOffset(int fileOffset) {
    if (!b.recordSourceMaps) {
      final old = _sourceMapFileOffset;
      _sourceMapFileOffset = fileOffset;
      return old;
    }
    if (fileOffset == TreeNode.noOffset) {
      b.stopSourceMapping();
      final old = _sourceMapFileOffset;
      _sourceMapFileOffset = fileOffset;
      return old;
    }
    final source = _sourceMapSource!;
    final fileUri = source.fileUri!;
    final location = source.getLocation(fileUri, fileOffset);
    final old = _sourceMapFileOffset;
    _sourceMapFileOffset = fileOffset;
    b.startSourceMapping(fileUri, location.line - 1, location.column - 1,
        enclosingMember.name.text);
    return old;
  }

  /// Calls [setSourceMapSource] and [setSourceMapFileOffset].
  (Source?, int) setSourceMapSourceAndFileOffset(
      Source? source, int fileOffset) {
    final oldSource = setSourceMapSource(source);
    final oldFileOffset = setSourceMapFileOffset(fileOffset);
    return (oldSource, oldFileOffset);
  }

  /// Generate code while preventing recursive inlining.
  @override
  void generate(List<w.Local> paramLocals, w.Label? returnLabel) {
    this.paramLocals = paramLocals;
    this.returnLabel = returnLabel;

    translator.membersBeingGenerated.add(enclosingMember);
    generateInternal();
    translator.membersBeingGenerated.remove(enclosingMember);
  }

  void generateInternal();

  void _setupLocalParameters(Member member, ParameterInfo paramInfo,
      int parameterOffset, int implicitParams,
      {bool isForwarder = false}) {
    List<TypeParameter> typeParameters = member is Constructor
        ? member.enclosingClass.typeParameters
        : member.function!.typeParameters;
    for (int i = 0; i < typeParameters.length; i++) {
      final typeParameter = typeParameters[i];
      typeLocals[typeParameter] = paramLocals[parameterOffset + i];
    }
    if (!translator.options.omitImplicitTypeChecks) {
      for (int i = 0; i < typeParameters.length; i++) {
        final typeParameter = typeParameters[i];
        if (typeParameter.isCovariantByClass &&
            typeParameter.bound != translator.coreTypes.objectNullableRawType) {
          _generateTypeArgumentBoundCheck(typeParameter.name!,
              typeLocals[typeParameter]!, typeParameter.bound);
        }
      }
    }

    void setupParamLocal(VariableDeclaration variable, int index,
        Constant? defaultValue, bool isRequired) {
      w.Local local = paramLocals[implicitParams + index];
      if (defaultValue == ParameterInfo.defaultValueSentinel) {
        // The default value for this parameter differs between implementations
        // within the same selector. This means that callers will pass the
        // default value sentinel to indicate that the parameter is not given.
        // The callee must check for the sentinel value and substitute the
        // actual default value.
        //
        // NOTE: The default sentinel is a dummy instance of the wasm type of
        // the parameter in the function signature. This type may be a super
        // type of the kind of arguments we actually see in practice.
        // (e.g. we may know that only nullable one byte strings can flow into
        // the argument, but the wasm type may be of object type). So we first
        // have to handle sentinel before we can downcast the value.
        b.local_get(local);
        translator.constants.instantiateConstant(
            b, ParameterInfo.defaultValueSentinel, local.type);
        b.ref_eq();
        b.if_();
        wrap(variable.initializer!, local.type);
        b.local_set(local);
        b.end();
      }
      if (!isForwarder) {
        // TFA may have inferred a very precise type for the incoming arguments,
        // but the wasm function parameter type may not reflect this (e.g. due
        // to upper-bounding in dispatch table row building)
        // => This means, we may need to do a downcast here.
        final incomingArgumentType =
            translator.translateTypeOfParameter(variable, isRequired);
        if (!local.type.isSubtypeOf(incomingArgumentType)) {
          final newLocal = addLocal(incomingArgumentType);
          b.local_get(local);
          translator.convertType(b, local.type, newLocal.type);
          b.local_set(newLocal);
          local = newLocal;
        }
      }
      if (!translator.options.omitImplicitTypeChecks) {
        if (variable.isCovariantByClass || variable.isCovariantByDeclaration) {
          final boxedType = variable.type.isPotentiallyNullable
              ? translator.topInfo.nullableType
              : translator.topInfo.nonNullableType;
          w.Local operand = local;
          if (!operand.type.isSubtypeOf(boxedType)) {
            final boxedOperand = addLocal(boxedType);
            b.local_get(operand);
            translator.convertType(b, operand.type, boxedOperand.type);
            b.local_set(boxedOperand);
            operand = boxedOperand;
          }
          b.local_get(operand);
          _generateArgumentTypeCheck(
            variable.name!,
            operand.type as w.RefType,
            variable.type,
          );
        }
      }
      if (!isForwarder && !variable.isFinal) {
        // We now have a precise local that can contain the values passed by
        // callers, but the body may assign less precise types to this variable,
        // so we may introduce another local variable that is less precise.
        // => Binaryen will simplify the above downcast and this upcast.
        final variableType = translator.translateTypeOfLocalVariable(variable);
        if (!variableType.isSubtypeOf(local.type)) {
          w.Local newLocal = addLocal(variableType);
          b.local_get(local);
          translator.convertType(b, local.type, newLocal.type);
          b.local_set(newLocal);
          local = newLocal;
        }
      }

      locals[variable] = local;
    }

    final memberFunction = member.function!;
    List<VariableDeclaration> positional = memberFunction.positionalParameters;
    for (int i = 0; i < positional.length; i++) {
      final bool isRequired = i < memberFunction.requiredParameterCount;
      setupParamLocal(positional[i], i, paramInfo.positional[i], isRequired);
    }
    List<VariableDeclaration> named = memberFunction.namedParameters;
    for (var param in named) {
      setupParamLocal(param, paramInfo.nameIndex[param.name]!,
          paramInfo.named[param.name], param.isRequired);
    }

    // For all parameters whose Wasm type has been forced to `externref` due to
    // this function being an export, internalize and cast the parameter to the
    // canonical representation type for its Dart type.
    locals.forEach((parameter, local) {
      DartType parameterType = parameter.type;
      if (local.type == w.RefType.extern(nullable: true) &&
          !(parameterType is InterfaceType &&
              parameterType.classNode == translator.wasmExternRefClass)) {
        w.Local newLocal = addLocal(translateType(parameterType));
        b.local_get(local);
        translator.convertType(b, local.type, newLocal.type);
        b.local_set(newLocal);
        locals[parameter] = newLocal;
      }
    });
  }

  void setupParameters(Reference reference, {bool isForwarder = false}) {
    Member member = reference.asMember;
    ParameterInfo paramInfo = translator.paramInfoForDirectCall(reference);

    int parameterOffset = _initializeThis(reference);
    int implicitParams = parameterOffset + paramInfo.typeParamCount;

    _setupLocalParameters(member, paramInfo, parameterOffset, implicitParams,
        isForwarder: isForwarder);
  }

  void setupParametersAndContexts(Member member) {
    setupParameters(member.reference);

    closures.findCaptures(member);
    closures.collectContexts(member);
    closures.buildContexts();

    allocateContext(member.function!);
    captureParameters();
  }

  void _setupDefaultFieldValues(ClassInfo info) {
    fieldLocals.clear();

    for (Field field in info.cls!.fields) {
      if (field.isInstanceMember && field.initializer != null) {
        final source = field.enclosingComponent!.uriToSource[field.fileUri]!;
        final (oldSource, oldFileOffset) =
            setSourceMapSourceAndFileOffset(source, field.fileOffset);

        int fieldIndex = translator.fieldIndex[field]!;
        w.Local local = addLocal(info.struct.fields[fieldIndex].type.unpacked);

        wrap(field.initializer!, info.struct.fields[fieldIndex].type.unpacked);
        b.local_set(local);
        fieldLocals[field] = local;

        setSourceMapSourceAndFileOffset(oldSource, oldFileOffset);
      }
    }
  }

  List<w.Local> _getConstructorArgumentLocals(Reference target,
      [reverse = false]) {
    Constructor member = target.asConstructor;
    List<w.Local> constructorArgs = [];

    List<TypeParameter> typeParameters = member.enclosingClass.typeParameters;

    for (int i = 0; i < typeParameters.length; i++) {
      constructorArgs.add(typeLocals[typeParameters[i]]!);
    }

    List<VariableDeclaration> positional = member.function.positionalParameters;
    for (VariableDeclaration pos in positional) {
      constructorArgs.add(locals[pos]!);
    }

    Map<String, w.Local> namedArgs = {};
    List<VariableDeclaration> named = member.function.namedParameters;
    for (VariableDeclaration param in named) {
      namedArgs[param.name!] = locals[param]!;
    }

    final ParameterInfo paramInfo = translator.paramInfoForDirectCall(target);

    for (String name in paramInfo.names) {
      w.Local namedLocal = namedArgs[name]!;
      constructorArgs.add(namedLocal);
    }

    if (reverse) {
      return constructorArgs.reversed.toList();
    }

    return constructorArgs;
  }

  void setupLambdaParametersAndContexts(Lambda lambda) {
    FunctionNode functionNode = lambda.functionNode;
    _initializeContextLocals(functionNode);

    int paramIndex = 1;
    for (TypeParameter typeParam in functionNode.typeParameters) {
      typeLocals[typeParam] = paramLocals[paramIndex++];
    }
    for (VariableDeclaration param in functionNode.positionalParameters) {
      locals[param] = paramLocals[paramIndex++];
    }
    for (VariableDeclaration param in functionNode.namedParameters) {
      locals[param] = paramLocals[paramIndex++];
    }

    allocateContext(functionNode);
    captureParameters();
  }

  /// Initialize locals containing `this` in constructors and instance members.
  /// Returns the number of parameter locals taken up by the receiver parameter,
  /// i.e. the parameter offset for the first type parameter (or the first
  /// parameter if there are no type parameters).
  int _initializeThis(Reference reference) {
    Member member = reference.asMember;
    final hasThis =
        member.isInstanceMember || reference.isConstructorBodyReference;
    if (hasThis) {
      thisLocal = paramLocals[0];
      final preciseThisType = translator.preciseThisFor(member);
      if (translator.needsConversion(thisLocal!.type, preciseThisType)) {
        preciseThisLocal = addLocal(preciseThisType);
        b.local_get(thisLocal!);
        translator.convertType(b, thisLocal!.type, preciseThisType);
        b.local_set(preciseThisLocal!);
      } else {
        preciseThisLocal = thisLocal!;
      }
      return 1;
    }
    return 0;
  }

  /// Initialize locals pointing to every context in the context chain of a
  /// closure, plus the locals containing `this` if `this` is captured by the
  /// closure.
  void _initializeContextLocals(TreeNode node, {int contextParamIndex = 0}) {
    Context? context;

    if (node is Constructor) {
      // The context parameter is for the constructor context.
      context = closures.contexts[node];
    } else {
      assert(node is FunctionNode);
      // The context parameter is for the parent context.
      context = closures.contexts[node]?.parent;
    }

    if (context != null) {
      assert(!context.isEmpty);
      w.RefType contextType = w.RefType.def(context.struct, nullable: false);

      b.local_get(paramLocals[contextParamIndex]);
      b.ref_cast(contextType);

      while (true) {
        w.Local contextLocal = addLocal(contextType);
        context!.currentLocal = contextLocal;

        if (context.parent != null || context.containsThis) {
          b.local_tee(contextLocal);
        } else {
          b.local_set(contextLocal);
        }

        if (context.containsThis) {
          thisLocal = addLocal(context
              .struct.fields[context.thisFieldIndex].type.unpacked
              .withNullability(false));
          preciseThisLocal = thisLocal;

          b.struct_get(context.struct, context.thisFieldIndex);
          b.ref_as_non_null();
          b.local_set(thisLocal!);

          if (context.parent != null) {
            b.local_get(contextLocal);
          }
        }

        if (context.parent == null) break;

        b.struct_get(context.struct, context.parentFieldIndex);
        b.ref_as_non_null();
        context = context.parent!;
        contextType = w.RefType.def(context.struct, nullable: false);
      }
    }
  }

  void _implicitReturn() {
    if (outputs.isNotEmpty) {
      w.ValueType returnType = outputs.single;
      if (returnType is w.RefType && returnType.nullable) {
        // Dart body may have an implicit return null.
        b.ref_null(returnType.heapType.bottomType);
      } else {
        b.comment("Unreachable implicit return");
        b.unreachable();
      }
    }
  }

  void allocateContext(TreeNode node) {
    Context? context = closures.contexts[node];
    if (context != null && !context.isEmpty) {
      w.Local contextLocal =
          addLocal(w.RefType.def(context.struct, nullable: true));
      context.currentLocal = contextLocal;
      b.struct_new_default(context.struct);
      b.local_set(contextLocal);
      if (context.containsThis) {
        b.local_get(contextLocal);
        b.local_get(preciseThisLocal!);
        b.struct_set(context.struct, context.thisFieldIndex);
      }
      if (context.parent != null) {
        w.Local parentLocal = context.parent!.currentLocal;
        b.local_get(contextLocal);
        b.local_get(parentLocal);
        b.struct_set(context.struct, context.parentFieldIndex);
      }
    }
  }

  void captureParameters() {
    locals.forEach((variable, local) {
      Capture? capture = closures.captures[variable];
      if (capture != null) {
        b.local_get(capture.context.currentLocal);
        b.local_get(local);
        translator.convertType(b, local.type, capture.type);
        b.struct_set(capture.context.struct, capture.fieldIndex);
      }
    });
    typeLocals.forEach((parameter, local) {
      Capture? capture = closures.captures[parameter];
      if (capture != null) {
        b.local_get(capture.context.currentLocal);
        b.local_get(local);
        translator.convertType(b, local.type, capture.type);
        b.struct_set(capture.context.struct, capture.fieldIndex);
      }
    });
  }

  /// Helper function to throw a Wasm ref downcast error.
  void throwWasmRefError(String expected) {
    _emitString(expected);
    call(translator.stackTraceCurrent.reference);
    call(translator.throwWasmRefError.reference);
    b.unreachable();
  }

  /// Generates code for an expression plus conversion code to convert the
  /// result to the expected type if needed. All expression code generation goes
  /// through this method.
  w.ValueType wrap(Expression node, w.ValueType expectedType) {
    var sourceUpdated = false;
    Source? oldSource;
    if (node is FileUriNode) {
      final source =
          node.enclosingComponent!.uriToSource[(node as FileUriNode).fileUri]!;
      oldSource = setSourceMapSource(source);
      sourceUpdated = true;
    }
    final oldFileOffset = setSourceMapFileOffset(node.fileOffset);
    try {
      w.ValueType resultType = node.accept1(this, expectedType);
      translator.convertType(b, resultType, expectedType);
      return expectedType;
    } catch (_) {
      _printLocation(node);
      rethrow;
    } finally {
      if (sourceUpdated) {
        setSourceMapSource(oldSource);
      }
      setSourceMapFileOffset(oldFileOffset);
    }
  }

  void visitStatement(Statement node) {
    final oldFileOffset = setSourceMapFileOffset(node.fileOffset);
    try {
      node.accept(this);
    } catch (_) {
      _printLocation(node);
      rethrow;
    } finally {
      setSourceMapFileOffset(oldFileOffset);
    }
  }

  void visitInitializer(Initializer node) {
    try {
      node.accept(this);
    } catch (_) {
      _printLocation(node);
      rethrow;
    }
  }

  void _printLocation(TreeNode node) {
    if (!exceptionLocationPrinted) {
      print("Exception in ${node.runtimeType} at ${node.location}");
      exceptionLocationPrinted = true;
    }
  }

  List<w.ValueType> call(Reference target) {
    w.FunctionType targetFunctionType =
        translator.signatureForDirectCall(target);
    final inliningCodeGen =
        translator.getInliningCodeGenerator(target, targetFunctionType, b);
    if (inliningCodeGen != null) {
      List<w.Local> inlinedLocals =
          targetFunctionType.inputs.map((t) => addLocal(t)).toList();
      for (w.Local local in inlinedLocals.reversed) {
        b.local_set(local);
      }
      w.Label block = b.block(const [], targetFunctionType.outputs);
      b.comment("Inlined ${target.asMember}");
      inliningCodeGen.generate(inlinedLocals, block);
      return targetFunctionType.outputs;
    } else {
      w.BaseFunction targetFunction = translator.functions.getFunction(target);
      String access =
          target.isGetter ? "get" : (target.isSetter ? "set" : "call");
      b.comment("Direct $access of '${target.asMember}'");
      b.call(targetFunction);
      return targetFunction.type.outputs;
    }
  }

  @override
  void visitInvalidInitializer(InvalidInitializer node) {}

  @override
  void visitAssertInitializer(AssertInitializer node) {
    visitStatement(node.statement);
  }

  @override
  void visitLocalInitializer(LocalInitializer node) {
    visitStatement(node.variable);
  }

  @override
  void visitFieldInitializer(FieldInitializer node) {
    Class cls = (node.parent as Constructor).enclosingClass;
    w.StructType struct = translator.classInfo[cls]!.struct;
    Field field = node.field;
    int fieldIndex = translator.fieldIndex[field]!;

    w.Local? local = fieldLocals[field];

    local ??= addLocal(struct.fields[fieldIndex].type.unpacked);

    wrap(node.value, struct.fields[fieldIndex].type.unpacked);
    b.local_set(local);
    fieldLocals[field] = local;
  }

  @override
  void visitRedirectingInitializer(RedirectingInitializer node) {
    Class cls = (node.parent as Constructor).enclosingClass;

    for (TypeParameter typeParam in cls.typeParameters) {
      types.makeType(
          this, TypeParameterType(typeParam, Nullability.nonNullable));
    }

    final targetMember = node.targetReference.asMember;
    final target = targetMember.initializerReference;
    _visitArguments(node.arguments, translator.signatureForDirectCall(target),
        translator.paramInfoForDirectCall(target), cls.typeParameters.length);

    b.comment("Direct call of '$targetMember Redirected Initializer'");
    call(target);
  }

  @override
  void visitSuperInitializer(SuperInitializer node) {
    Supertype? supertype =
        (node.parent as Constructor).enclosingClass.supertype;
    Supertype? supersupertype = node.target.enclosingClass.supertype;

    // Skip calls to the constructor for Object, as this is empty
    if (supersupertype != null) {
      for (DartType typeArg in supertype!.typeArguments) {
        types.makeType(this, typeArg);
      }

      final targetMember = node.targetReference.asMember;
      final target = targetMember.initializerReference;
      _visitArguments(
          node.arguments,
          translator.signatureForDirectCall(target),
          translator.paramInfoForDirectCall(target),
          supertype.typeArguments.length);

      b.comment("Direct call of '$targetMember Initializer'");
      call(target);
    }
  }

  @override
  void visitBlock(Block node) {
    for (Statement statement in node.statements) {
      visitStatement(statement);
    }
  }

  @override
  void visitLabeledStatement(LabeledStatement node) {
    w.Label label = b.block();
    breakFinalizers[node] = <w.Label>[label];
    visitStatement(node.body);
    breakFinalizers.remove(node);
    b.end();
  }

  @override
  void visitBreakStatement(BreakStatement node) {
    b.br(breakFinalizers[node.target]!.last);
  }

  @override
  void visitVariableDeclaration(VariableDeclaration node) {
    final w.ValueType type = translator.translateTypeOfLocalVariable(node);
    w.Local? local;
    Capture? capture = closures.captures[node];
    if (capture == null || !capture.written) {
      local = addLocal(type);
      locals[node] = local;
    }

    // Handle variable initialization. Nullable variables have an implicit
    // initializer.
    if (node.initializer != null ||
        node.type.nullability == Nullability.nullable) {
      Expression initializer =
          node.initializer ?? ConstantExpression(NullConstant());
      if (capture != null) {
        w.ValueType expectedType = capture.written ? capture.type : local!.type;
        b.local_get(capture.context.currentLocal);
        wrap(initializer, expectedType);
        if (!capture.written) {
          b.local_tee(local!);
        }
        b.struct_set(capture.context.struct, capture.fieldIndex);
      } else {
        wrap(initializer, local!.type);
        b.local_set(local);
      }
    } else if (local != null && !local.type.defaultable) {
      // Uninitialized variable
      translator.globals.instantiateDummyValue(b, local.type);
      b.local_set(local);
    }
  }

  /// Initialize a variable [node] to an initial value which must be left on
  /// the stack by [pushInitialValue].
  ///
  /// This is similar to [visitVariableDeclaration] but it gives more control
  /// over how the variable is initialized.
  void initializeVariable(
      VariableDeclaration node, void Function() pushInitialValue) {
    final w.ValueType type = translator.translateTypeOfLocalVariable(node);
    w.Local? local;
    final Capture? capture = closures.captures[node];
    if (capture == null || !capture.written) {
      local = addLocal(type);
      locals[node] = local;
    }

    if (capture != null) {
      b.local_get(capture.context.currentLocal);
      pushInitialValue();
      if (!capture.written) {
        b.local_tee(local!);
      }
      b.struct_set(capture.context.struct, capture.fieldIndex);
    } else {
      pushInitialValue();
      b.local_set(local!);
    }
  }

  @override
  void visitEmptyStatement(EmptyStatement node) {}

  @override
  void visitAssertStatement(AssertStatement node) {
    if (options.enableAsserts) {
      w.Label assertBlock = b.block();
      wrap(node.condition, w.NumType.i32);
      b.br_if(assertBlock);

      Expression? message = node.message;
      if (message != null) {
        wrap(message, translator.topInfo.nullableType);
      } else {
        b.ref_null(w.HeapType.none);
      }
      final Location? location = node.location;
      final stringClass = translator.options.jsCompatibility
          ? translator.jsStringClass
          : translator.stringBaseClass;
      final w.RefType stringRefType =
          translator.classInfo[stringClass]!.nullableType;
      if (location != null) {
        translator.constants.instantiateConstant(
          b,
          StringConstant(location.file.toString()),
          stringRefType,
        );
        b.i64_const(location.line);
        b.i64_const(location.column);
        final String sourceString =
            node.enclosingComponent!.uriToSource[location.file]!.text;
        final String conditionString = sourceString.substring(
            node.conditionStartOffset, node.conditionEndOffset);
        translator.constants.instantiateConstant(
          b,
          StringConstant(conditionString),
          stringRefType,
        );
      } else {
        b.ref_null(stringRefType.heapType);
        b.i64_const(0);
        b.i64_const(0);
        b.ref_null(stringRefType.heapType);
      }

      call(translator.throwAssertionError.reference);

      b.unreachable();
      b.end();
    }
  }

  @override
  void visitAssertBlock(AssertBlock node) {
    if (!options.enableAsserts) return;

    for (Statement statement in node.statements) {
      visitStatement(statement);
    }
  }

  @override
  void visitTryCatch(TryCatch node) {
    // It is not valid dart to have a try without a catch.
    assert(node.catches.isNotEmpty);

    // We lower a [TryCatch] to a wasm try block.
    w.Label try_ = b.try_();
    visitStatement(node.body);
    b.br(try_);

    // Note: We must wait to add the try block to the [tryLabels] stack until
    // after we have visited the body of the try. This is to handle the case of
    // a rethrow nested within a try nested within a catch, that is we need the
    // rethrow to target the last try block with a catch.
    tryLabels.add(try_);

    // Stash the original exception in a local so we can push it back onto the
    // stack after each type test. Also, store the stack trace in a local.
    w.Local thrownException = addLocal(translator.topInfo.nonNullableType);
    w.Local thrownStackTrace =
        addLocal(translator.stackTraceInfo.repr.nonNullableType);

    void emitCatchBlock(Catch catch_, bool emitGuard) {
      // For each catch node:
      //   1) Create a block for the catch.
      //   2) Push the caught exception onto the stack.
      //   3) Add a type test based on the guard of the catch.
      //   4) If the test fails, we jump to the next catch. Otherwise, we
      //      execute the body of the catch.
      w.Label catchBlock = b.block();
      DartType guard = catch_.guard;

      // Only emit the type test if the guard is not [Object].
      if (emitGuard) {
        b.local_get(thrownException);
        types.emitIsTest(this, guard,
            translator.coreTypes.objectNonNullableRawType, catch_.location);
        b.i32_eqz();
        b.br_if(catchBlock);
      }

      final VariableDeclaration? exceptionDeclaration = catch_.exception;
      if (exceptionDeclaration != null) {
        initializeVariable(exceptionDeclaration, () {
          b.local_get(thrownException);
          // Type test passed, downcast the exception to the expected type.
          translator.convertType(
            b,
            thrownException.type,
            translator.translateType(exceptionDeclaration.type),
          );
        });
      }

      final VariableDeclaration? stackTraceDeclaration = catch_.stackTrace;
      if (stackTraceDeclaration != null) {
        initializeVariable(
            stackTraceDeclaration, () => b.local_get(thrownStackTrace));
      }

      visitStatement(catch_.body);

      // Jump out of the try entirely if we enter any catch block.
      b.br(try_);
      b.end(); // end catchBlock.
    }

    // Insert a catch instruction which will catch any thrown Dart
    // exceptions.
    b.catch_(translator.exceptionTag);

    b.local_set(thrownStackTrace);
    b.local_set(thrownException);
    for (final Catch catch_ in node.catches) {
      // Only insert type checks if the guard is not `Object`
      final bool shouldEmitGuard =
          catch_.guard != translator.coreTypes.objectNonNullableRawType;
      emitCatchBlock(catch_, shouldEmitGuard);
      if (!shouldEmitGuard) {
        // If we didn't emit a guard, we won't ever fall through to the
        // following catch blocks.
        break;
      }
    }
    // Rethrow if all the catch blocks fall through
    b.rethrow_(try_);

    // If we have a catches that are generic enough to catch a JavaScript
    // error, we need to put that into a catch_all block.
    final Iterable<Catch> catchAllCatches = node.catches
        .where((c) => guardCanMatchJSException(translator, c.guard));

    if (catchAllCatches.isNotEmpty) {
      // This catches any objects that aren't dart exceptions, such as
      // JavaScript exceptions or objects.
      b.catch_all();

      // We can't inspect the thrown object in a catch_all and get a stack
      // trace, so we just attach the current stack trace.
      call(translator.stackTraceCurrent.reference);
      b.local_set(thrownStackTrace);

      // We create a generic JavaScript error in this case.
      call(translator.javaScriptErrorFactory.reference);
      b.local_set(thrownException);

      for (final c in catchAllCatches) {
        // Type guards based on a type parameter are special, in that we cannot
        // statically determine whether a JavaScript error will always satisfy
        // the guard, so we should emit the type checking code for it. All
        // other guards will always match a JavaScript error, however, so no
        // need to emit type checks for those.
        final bool shouldEmitGuard = c.guard is TypeParameterType;
        emitCatchBlock(c, shouldEmitGuard);
        if (!shouldEmitGuard) {
          // If we didn't emit a guard, we won't ever fall through to the
          // following catch blocks.
          break;
        }
      }

      // Rethrow if the catch block falls through
      b.rethrow_(try_);
    }

    tryLabels.removeLast();
    b.end(); // end try_.
  }

  @override
  void visitTryFinally(TryFinally node) {
    // We lower a [TryFinally] to a number of nested blocks, depending on how
    // many different code paths we have that run the finally block.
    //
    // We emit the finalizer once in a catch, to handle the case where the try
    // throws. Once outside of the catch, to handle the case where the try does
    // not throw. If there is a return within the try block, then we emit the
    // finalizer one more time along with logic to continue walking up the
    // stack.
    //
    // A `break L` can run more than one finalizer, and each of those
    // finalizers will need to be run in a different `try` block. So for each
    // wrapping label we generate a block to run the finalizer on `break` and
    // then branch to the right Wasm block to either run the next finalizer or
    // break.

    // The block for the try-finally statement. Used as `br` target in normal
    // execution after the finalizer (no throws, returns, or breaks).
    w.Label tryFinallyBlock = b.block();

    // Create one block for each wrapping label.
    for (final labelBlocks in breakFinalizers.values.toList().reversed) {
      labelBlocks.add(b.block());
    }

    // Continuation of this block runs the finalizer and returns (or jumps to
    // the next finalizer block). Used as `br` target on `return`.
    w.Label returnFinalizerBlock = b.block();
    returnFinalizers.add(TryBlockFinalizer(returnFinalizerBlock));

    w.Label tryBlock = b.try_();
    visitStatement(node.body);

    final bool mustHandleReturn =
        returnFinalizers.removeLast().mustHandleReturn;

    // `break` statements in the current finalizer and the rest will not run
    // the current finalizer, update the `break` targets.
    final removedBreakTargets = <LabeledStatement, w.Label>{};
    for (final breakFinalizerEntry in breakFinalizers.entries) {
      removedBreakTargets[breakFinalizerEntry.key] =
          breakFinalizerEntry.value.removeLast();
    }

    // Handle Dart exceptions.
    b.catch_(translator.exceptionTag);
    visitStatement(node.finalizer);
    b.rethrow_(tryBlock);

    // Handle JS exceptions.
    b.catch_all();
    visitStatement(node.finalizer);
    b.rethrow_(tryBlock);

    b.end(); // tryBlock

    // Run finalizer on normal execution (no breaks, throws, or returns).
    visitStatement(node.finalizer);
    b.br(tryFinallyBlock);
    b.end(); // returnFinalizerBlock

    // Run the finalizer on `return`.
    if (mustHandleReturn) {
      visitStatement(node.finalizer);
      if (returnFinalizers.isNotEmpty) {
        b.br(returnFinalizers.last.label);
      } else {
        if (returnValueLocal != null) {
          b.local_get(returnValueLocal!);
          translator.convertType(b, returnValueLocal!.type, returnType);
        }
        _returnFromFunction();
      }
    }

    // Generate finalizers for `break`s in the `try` block.
    for (final removedBreakTargetEntry in removedBreakTargets.entries) {
      b.end();
      visitStatement(node.finalizer);
      b.br(breakFinalizers[removedBreakTargetEntry.key]!.last);
    }

    b.end(); // tryFinallyBlock
  }

  @override
  void visitExpressionStatement(ExpressionStatement node) {
    wrap(node.expression, voidMarker);
  }

  bool _hasLogicalOperator(Expression condition) {
    while (condition is Not) {
      condition = condition.operand;
    }
    return condition is LogicalExpression;
  }

  void branchIf(Expression? condition, w.Label target,
      {required bool negated}) {
    if (condition == null) {
      if (!negated) b.br(target);
      return;
    }
    while (condition is Not) {
      negated = !negated;
      condition = condition.operand;
    }
    if (condition is LogicalExpression) {
      bool isConjunctive =
          (condition.operatorEnum == LogicalExpressionOperator.AND) ^ negated;
      if (isConjunctive) {
        w.Label conditionBlock = b.block();
        branchIf(condition.left, conditionBlock, negated: !negated);
        branchIf(condition.right, target, negated: negated);
        b.end();
      } else {
        branchIf(condition.left, target, negated: negated);
        branchIf(condition.right, target, negated: negated);
      }
    } else {
      wrap(condition!, w.NumType.i32);
      if (negated) {
        b.i32_eqz();
      }
      b.br_if(target);
    }
  }

  void _conditional(Expression condition, void Function() then,
      void Function()? otherwise, List<w.ValueType> result) {
    if (!_hasLogicalOperator(condition)) {
      // Simple condition
      wrap(condition, w.NumType.i32);
      b.if_(const [], result);
      then();
      if (otherwise != null) {
        b.else_();
        otherwise();
      }
      b.end();
    } else {
      // Complex condition
      w.Label ifBlock = b.block(const [], result);
      if (otherwise != null) {
        w.Label elseBlock = b.block();
        branchIf(condition, elseBlock, negated: true);
        then();
        b.br(ifBlock);
        b.end();
        otherwise();
      } else {
        branchIf(condition, ifBlock, negated: true);
        then();
      }
      b.end();
    }
  }

  @override
  void visitIfStatement(IfStatement node) {
    _conditional(
        node.condition,
        () => visitStatement(node.then),
        node.otherwise != null ? () => visitStatement(node.otherwise!) : null,
        const []);
  }

  @override
  void visitDoStatement(DoStatement node) {
    w.Label loop = b.loop();
    allocateContext(node);
    visitStatement(node.body);
    branchIf(node.condition, loop, negated: false);
    b.end();
  }

  @override
  void visitWhileStatement(WhileStatement node) {
    w.Label block = b.block();
    w.Label loop = b.loop();
    branchIf(node.condition, block, negated: true);
    allocateContext(node);
    visitStatement(node.body);
    b.br(loop);
    b.end();
    b.end();
  }

  @override
  void visitForStatement(ForStatement node) {
    allocateContext(node);
    for (VariableDeclaration variable in node.variables) {
      visitStatement(variable);
    }
    w.Label block = b.block();
    w.Label loop = b.loop();
    branchIf(node.condition, block, negated: true);
    visitStatement(node.body);

    emitForStatementUpdate(node);

    b.br(loop);
    b.end();
    b.end();
  }

  void emitForStatementUpdate(ForStatement node) {
    Context? context = closures.contexts[node];
    if (context != null && !context.isEmpty) {
      // Create a new context for each iteration of the loop.
      w.Local oldContext = context.currentLocal;
      allocateContext(node);
      w.Local newContext = context.currentLocal;

      // Copy the values of captured loop variables to the new context.
      for (VariableDeclaration variable in node.variables) {
        Capture? capture = closures.captures[variable];
        if (capture != null) {
          assert(capture.context == context);
          b.local_get(newContext);
          b.local_get(oldContext);
          b.struct_get(context.struct, capture.fieldIndex);
          b.struct_set(context.struct, capture.fieldIndex);
        }
      }

      // Update the context local to point to the new context.
      b.local_get(newContext);
      b.local_set(oldContext);
    }

    for (Expression update in node.updates) {
      wrap(update, voidMarker);
    }
  }

  @override
  void visitForInStatement(ForInStatement node) {
    throw "ForInStatement should have been desugared: $node";
  }

  /// Handle the return from this function, either by jumping to [returnLabel]
  /// in the case this function was inlined or just inserting a return
  /// instruction.
  void _returnFromFunction() {
    if (returnLabel != null) {
      b.br(returnLabel!);
    } else {
      b.return_();
    }
  }

  @override
  void visitReturnStatement(ReturnStatement node) {
    Expression? expression = node.expression;
    if (expression != null) {
      wrap(expression, returnType);
    } else {
      translator.convertType(b, voidMarker, returnType);
    }

    // If we are wrapped in a [TryFinally] node then we have to run finalizers
    // as the stack unwinds. When we get to the top of the finalizer stack, we
    // will handle the return using [returnValueLocal] if this function returns
    // a value.
    if (returnFinalizers.isNotEmpty) {
      for (TryBlockFinalizer finalizer in returnFinalizers) {
        finalizer.mustHandleReturn = true;
      }
      if (returnType != voidMarker) {
        // Since the flow of the return value through the returnValueLocal
        // crosses control-flow constructs, the local needs to always have a
        // defaultable type in order for the Wasm code to validate.
        returnValueLocal ??= addLocal(returnType.withNullability(true));
        b.local_set(returnValueLocal!);
      }
      b.br(returnFinalizers.last.label);
    } else {
      _returnFromFunction();
    }
  }

  @override
  void visitSwitchStatement(SwitchStatement node) {
    // If we have an empty switch, just evaluate the expression for any
    // potential side effects. In this case, the return type does not matter.
    if (node.cases.isEmpty) {
      wrap(node.expression, voidMarker);
      return;
    }

    final switchInfo = SwitchInfo(this, node);

    bool isNullable = dartTypeOf(node.expression).isPotentiallyNullable;

    // When the type is nullable we use two variables: one for the nullable
    // value, one after the null check, with non-nullable type.
    w.Local switchValueNonNullableLocal = addLocal(switchInfo.nonNullableType);
    w.Local? switchValueNullableLocal =
        isNullable ? addLocal(switchInfo.nullableType) : null;

    // Initialize switch value local
    wrap(node.expression,
        isNullable ? switchInfo.nullableType : switchInfo.nonNullableType);
    b.local_set(
        isNullable ? switchValueNullableLocal! : switchValueNonNullableLocal);

    // Special cases
    SwitchCase? defaultCase = switchInfo.defaultCase;
    SwitchCase? nullCase = switchInfo.nullCase;

    // Create `loop` for backward jumps
    w.Label loopLabel = b.loop();

    // Set `switchValueLocal` for backward jumps
    w.Local switchValueLocal =
        isNullable ? switchValueNullableLocal! : switchValueNonNullableLocal;

    // Add backward jump info
    switchBackwardJumpInfos[node] =
        SwitchBackwardJumpInfo(switchValueLocal, loopLabel);

    // Set up blocks, in reverse order of cases so they end in forward order
    w.Label doneLabel = b.block();
    for (SwitchCase c in node.cases.reversed) {
      switchLabels[c] = b.block();
    }

    // Compute value and handle null
    if (isNullable) {
      w.Label nullLabel = nullCase != null
          ? switchLabels[nullCase]!
          : defaultCase != null
              ? switchLabels[defaultCase]!
              : doneLabel;
      b.local_get(switchValueNullableLocal!);
      b.br_on_null(nullLabel);
      translator.convertType(b, switchInfo.nullableType.withNullability(false),
          switchInfo.nonNullableType);
      b.local_set(switchValueNonNullableLocal);
    }

    // Compare against all case values
    for (SwitchCase c in node.cases) {
      for (Expression exp in c.expressions) {
        if (exp is NullLiteral ||
            exp is ConstantExpression && exp.constant is NullConstant) {
          // Null already checked, skip
        } else {
          switchInfo.compare(
            switchValueNonNullableLocal,
            () => wrap(exp, switchInfo.nonNullableType),
          );
          b.br_if(switchLabels[c]!);
        }
      }
    }

    // No explicit cases matched
    if (node.isExplicitlyExhaustive) {
      b.unreachable();
    } else {
      w.Label defaultLabel =
          defaultCase != null ? switchLabels[defaultCase]! : doneLabel;
      b.br(defaultLabel);
    }

    // Emit case bodies
    for (SwitchCase c in node.cases) {
      b.end();
      // Remove backward jump target from forward jump labels
      switchLabels.remove(c);

      // Create a `loop` in default case to allow backward jumps to it
      if (c.isDefault) {
        switchBackwardJumpInfos[node]!.defaultLoopLabel = b.loop();
      }

      visitStatement(c.body);

      if (c.isDefault) {
        b.end(); // defaultLoopLabel
      }

      b.br(doneLabel);
    }
    b.end(); // doneLabel
    b.end(); // loopLabel

    // Remove backward jump info
    final removed = switchBackwardJumpInfos.remove(node);
    assert(removed != null);
  }

  @override
  void visitContinueSwitchStatement(ContinueSwitchStatement node) {
    w.Label? label = switchLabels[node.target];
    if (label != null) {
      b.br(label);
    } else {
      // Backward jump. Find the case literal in jump target, set the switched
      // values to the jump target's value, and loop.
      final SwitchCase targetSwitchCase = node.target;
      final SwitchStatement targetSwitch =
          targetSwitchCase.parent! as SwitchStatement;
      final SwitchBackwardJumpInfo targetInfo =
          switchBackwardJumpInfos[targetSwitch]!;
      if (targetSwitchCase.expressions.isEmpty) {
        // Default case
        assert(targetSwitchCase.isDefault);
        b.br(targetInfo.defaultLoopLabel!);
        return;
      }
      final Expression targetValue =
          targetSwitchCase.expressions[0]; // pick any of the values
      wrap(targetValue, targetInfo.switchValueLocal.type);
      b.local_set(targetInfo.switchValueLocal);
      b.br(targetInfo.loopLabel);
    }
  }

  @override
  void visitYieldStatement(YieldStatement node) {
    unimplemented(node, node.runtimeType, const []);
  }

  @override
  w.ValueType visitAwaitExpression(
      AwaitExpression node, w.ValueType expectedType) {
    throw 'Await expression in code generator: $node (${node.location})';
  }

  @override
  w.ValueType visitBlockExpression(
      BlockExpression node, w.ValueType expectedType) {
    visitStatement(node.body);
    return wrap(node.value, expectedType);
  }

  @override
  w.ValueType visitLet(Let node, w.ValueType expectedType) {
    visitStatement(node.variable);
    return wrap(node.body, expectedType);
  }

  @override
  w.ValueType visitThisExpression(
      ThisExpression node, w.ValueType expectedType) {
    return visitThis(expectedType);
  }

  w.ValueType visitThis(w.ValueType expectedType) {
    w.ValueType thisType = thisLocal!.type;
    w.ValueType preciseThisType = preciseThisLocal!.type;
    assert(!thisType.nullable);
    assert(!preciseThisType.nullable);
    if (thisType.isSubtypeOf(expectedType)) {
      b.local_get(thisLocal!);
      return thisType;
    }
    if (preciseThisType.isSubtypeOf(expectedType)) {
      b.local_get(preciseThisLocal!);
      return preciseThisType;
    }
    // A user of `this` may have more precise type information, in which case
    // we downcast it here.
    b.local_get(thisLocal!);
    translator.convertType(b, thisType, expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitConstructorInvocation(
      ConstructorInvocation node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult =
        intrinsifier.generateConstructorIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    ClassInfo info = translator.classInfo[node.target.enclosingClass]!;
    translator.functions.recordClassAllocation(info.classId);

    final target = node.targetReference;
    _visitArguments(node.arguments, translator.signatureForDirectCall(target),
        translator.paramInfoForDirectCall(target), 0);

    return call(target).single;
  }

  @override
  w.ValueType visitStaticInvocation(
      StaticInvocation node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult = intrinsifier.generateStaticIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    final target = node.targetReference;
    _visitArguments(node.arguments, translator.signatureForDirectCall(target),
        translator.paramInfoForDirectCall(target), 0);
    return translator.outputOrVoid(call(target));
  }

  Member _lookupSuperTarget(Member interfaceTarget, {required bool setter}) {
    return translator.hierarchy.getDispatchTarget(
        enclosingMember.enclosingClass!.superclass!, interfaceTarget.name,
        setter: setter)!;
  }

  @override
  w.ValueType visitSuperMethodInvocation(
      SuperMethodInvocation node, w.ValueType expectedType) {
    Reference target =
        _lookupSuperTarget(node.interfaceTarget, setter: false).reference;
    w.FunctionType targetFunctionType =
        translator.signatureForDirectCall(target);
    final w.ValueType receiverType = translator.preciseThisFor(target.asMember);

    // When calling `==` and the argument is potentially nullable, check if the
    // argument is `null`.
    if (node.name.text == '==') {
      assert(node.arguments.positional.length == 1);
      assert(node.arguments.named.isEmpty);
      final argument = node.arguments.positional[0];
      if (dartTypeOf(argument).isPotentiallyNullable) {
        w.Label resultBlock = b.block(const [], const [w.NumType.i32]);

        w.ValueType argumentType = targetFunctionType.inputs[1];
        // `==` arguments are non-nullable.
        assert(argumentType.nullable == false);

        final argumentNullBlock = b.block(const [], const []);

        visitThis(receiverType);
        wrap(argument, argumentType.withNullability(true));
        b.br_on_null(argumentNullBlock);

        final resultType = translator.outputOrVoid(call(target));
        // `super ==` should return bool.
        assert(resultType == w.NumType.i32);
        b.br(resultBlock);

        b.end(); // argumentNullBlock

        b.i32_const(0); // false
        b.br(resultBlock);

        b.end(); // resultBlock
        return w.NumType.i32;
      }
    }

    visitThis(receiverType);
    _visitArguments(node.arguments, translator.signatureForDirectCall(target),
        translator.paramInfoForDirectCall(target), 1);
    return translator.outputOrVoid(call(target));
  }

  @override
  w.ValueType visitInstanceInvocation(
      InstanceInvocation node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult = intrinsifier.generateInstanceIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    w.ValueType callWithNullCheck(
        Procedure target, void Function(w.ValueType) onNull) {
      late w.Label done;
      final w.ValueType resultType =
          _virtualCall(node, target, _VirtualCallKind.Call, (signature) {
        done = b.block(const [], signature.outputs);
        final w.Label nullReceiver = b.block();
        wrap(node.receiver, translator.topInfo.nullableType);
        b.br_on_null(nullReceiver);
      }, (w.FunctionType signature, ParameterInfo paramInfo) {
        _visitArguments(node.arguments, signature, paramInfo, 1);
      });
      b.br(done);
      b.end(); // end nullReceiver
      onNull(resultType);
      b.end();
      return resultType;
    }

    final Procedure target = node.interfaceTarget;
    if (node.kind == InstanceAccessKind.Object) {
      switch (target.name.text) {
        case "toString":
          return callWithNullCheck(
              target, (resultType) => wrap(StringLiteral("null"), resultType));
        case "noSuchMethod":
          return callWithNullCheck(target, (resultType) {
            final target = node.interfaceTargetReference;
            final signature = translator.signatureForDirectCall(target);
            final paramInfo = translator.paramInfoForDirectCall(target);

            // Object? receiver
            b.ref_null(translator.topInfo.struct);
            // Invocation invocation
            _visitArguments(node.arguments, signature, paramInfo, 1);
            call(translator.noSuchMethodErrorThrowWithInvocation.reference);
          });
        default:
          unimplemented(node, "Nullable invocation of ${target.name.text}",
              [if (expectedType != voidMarker) expectedType]);
          return expectedType;
      }
    }

    Member? singleTarget = translator.singleTarget(node);
    if (singleTarget != null) {
      final target = singleTarget.reference;
      final signature = translator.signatureForDirectCall(target);
      final paramInfo = translator.paramInfoForDirectCall(target);
      wrap(node.receiver, signature.inputs.first);
      _visitArguments(node.arguments, signature, paramInfo, 1);

      return translator.outputOrVoid(call(target));
    }
    return _virtualCall(node, target, _VirtualCallKind.Call,
        (signature) => wrap(node.receiver, signature.inputs.first),
        (w.FunctionType signature, ParameterInfo paramInfo) {
      _visitArguments(node.arguments, signature, paramInfo, 1);
    });
  }

  @override
  w.ValueType visitDynamicInvocation(
      DynamicInvocation node, w.ValueType expectedType) {
    // Call dynamic invocation forwarder
    final receiver = node.receiver;
    final typeArguments = node.arguments.types;
    final positionalArguments = node.arguments.positional;
    final namedArguments = node.arguments.named;
    final forwarder = translator.dynamicForwarders
        .getDynamicInvocationForwarder(node.name.text);

    // Evaluate receiver
    wrap(receiver, translator.topInfo.nullableType);
    final nullableReceiverLocal = addLocal(translator.topInfo.nullableType);
    b.local_set(nullableReceiverLocal);

    // Evaluate type arguments.
    final typeArgsLocal = addLocal(
        makeArray(translator.typeArrayType, typeArguments.length,
            (elementType, elementIdx) {
      translator.types.makeType(this, typeArguments[elementIdx]);
    }));
    b.local_set(typeArgsLocal);

    // Evaluate positional arguments
    final positionalArgsLocal = addLocal(makeArray(
        translator.nullableObjectArrayType, positionalArguments.length,
        (elementType, elementIdx) {
      wrap(positionalArguments[elementIdx], elementType);
    }));
    b.local_set(positionalArgsLocal);

    // Evaluate named arguments. The arguments need to be evaluated in the
    // order they appear in the AST, but need to be sorted based on names in
    // the argument list passed to the dynamic forwarder. Create a local for
    // each argument to allow adding values to the list in expected order.
    final List<MapEntry<String, w.Local>> namedArgumentLocals = [];
    for (final namedArgument in namedArguments) {
      wrap(namedArgument.value, translator.topInfo.nullableType);
      final argumentLocal = addLocal(translator.topInfo.nullableType);
      b.local_set(argumentLocal);
      namedArgumentLocals.add(MapEntry(namedArgument.name, argumentLocal));
    }
    namedArgumentLocals.sort((e1, e2) => e1.key.compareTo(e2.key));

    // Create named argument array
    final namedArgsLocal = addLocal(
        makeArray(translator.nullableObjectArrayType, namedArguments.length * 2,
            (elementType, elementIdx) {
      if (elementIdx % 2 == 0) {
        final name = namedArgumentLocals[elementIdx ~/ 2].key;
        final w.ValueType symbolValueType =
            translator.classInfo[translator.symbolClass]!.nonNullableType;
        translator.constants.instantiateConstant(
            b, SymbolConstant(name, null), symbolValueType);
      } else {
        final local = namedArgumentLocals[elementIdx ~/ 2].value;
        b.local_get(local);
      }
    }));
    b.local_set(namedArgsLocal);

    final nullBlock = b.block([], [translator.topInfo.nonNullableType]);
    b.local_get(nullableReceiverLocal);
    b.br_on_non_null(nullBlock);
    // Throw `NoSuchMethodError`. Normally this needs to happen via instance
    // invocation of `noSuchMethod` (done in [_callNoSuchMethod]), but we don't
    // have a `Null` class in dart2wasm so we throw directly.
    b.local_get(nullableReceiverLocal);
    createInvocationObject(translator, b, forwarder.memberName, typeArgsLocal,
        positionalArgsLocal, namedArgsLocal);

    call(translator.noSuchMethodErrorThrowWithInvocation.reference);
    b.unreachable();
    b.end(); // nullBlock

    b.local_get(typeArgsLocal);
    b.local_get(positionalArgsLocal);
    b.local_get(namedArgsLocal);
    b.call(forwarder.function);

    return translator.topInfo.nullableType;
  }

  @override
  w.ValueType visitEqualsCall(EqualsCall node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult = intrinsifier.generateEqualsIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    Member? singleTarget = translator.singleTarget(node);
    if (singleTarget == translator.coreTypes.objectEquals) {
      // Plain reference comparison
      wrap(node.left, w.RefType.eq(nullable: true));
      wrap(node.right, w.RefType.eq(nullable: true));
      b.ref_eq();
    } else {
      // Check operands for null, then call implementation
      bool leftNullable = dartTypeOf(node.left).isPotentiallyNullable;
      bool rightNullable = dartTypeOf(node.right).isPotentiallyNullable;
      w.RefType leftType = translator.topInfo.typeWithNullability(leftNullable);
      w.RefType rightType =
          translator.topInfo.typeWithNullability(rightNullable);
      w.Local leftLocal = addLocal(leftType);
      w.Local rightLocal = addLocal(rightType);
      w.Label? operandNull;
      w.Label? done;
      if (leftNullable || rightNullable) {
        done = b.block(const [], const [w.NumType.i32]);
        operandNull = b.block();
      }
      wrap(node.left, leftLocal.type);
      b.local_set(leftLocal);
      wrap(node.right, rightLocal.type);
      if (rightNullable) {
        b.local_tee(rightLocal);
        b.br_on_null(operandNull!);
        b.drop();
      } else {
        b.local_set(rightLocal);
      }

      void left([_]) {
        b.local_get(leftLocal);
        if (leftNullable) {
          b.br_on_null(operandNull!);
        }
      }

      void right([_, __]) {
        b.local_get(rightLocal);
        if (rightNullable) {
          b.ref_as_non_null();
        }
      }

      if (singleTarget != null) {
        left();
        right();
        call(singleTarget.reference);
      } else {
        _virtualCall(
          node,
          node.interfaceTarget,
          _VirtualCallKind.Call,
          left,
          right,
        );
      }
      if (leftNullable || rightNullable) {
        b.br(done!);
        b.end(); // operandNull
        if (leftNullable && rightNullable) {
          // Both sides nullable - compare references
          b.local_get(leftLocal);
          b.local_get(rightLocal);
          b.ref_eq();
        } else {
          // Only one side nullable - not equal if one is null
          b.i32_const(0);
        }
        b.end(); // done
      }
    }
    return w.NumType.i32;
  }

  @override
  w.ValueType visitEqualsNull(EqualsNull node, w.ValueType expectedType) {
    wrap(node.expression, const w.RefType.any(nullable: true));
    b.ref_is_null();
    return w.NumType.i32;
  }

  w.ValueType _virtualCall(
      TreeNode node,
      Member interfaceTarget,
      _VirtualCallKind kind,
      void Function(w.FunctionType signature) pushReceiver,
      void Function(w.FunctionType signature, ParameterInfo) pushArguments) {
    SelectorInfo selector = translator.dispatchTable.selectorForTarget(
        interfaceTarget.referenceAs(
            getter: kind.isGetter, setter: kind.isSetter));
    assert(selector.name == interfaceTarget.name.text);

    pushReceiver(selector.signature);

    if (selector.targetRanges.length == 1) {
      assert(selector.staticDispatchRanges.length == 1);
      final target = selector.targetRanges[0].target;
      final signature = translator.signatureForDirectCall(target);
      final paramInfo = translator.paramInfoForDirectCall(target);
      pushArguments(signature, paramInfo);
      return translator.outputOrVoid(call(target));
    }

    if (selector.targetRanges.isEmpty) {
      // Unreachable call
      b.comment("Virtual call of ${selector.name} with no targets"
          " at ${node.location}");
      pushArguments(selector.signature, selector.paramInfo);
      for (int i = 0; i < selector.signature.inputs.length; ++i) {
        b.drop();
      }
      b.block(const [], selector.signature.outputs);
      b.unreachable();
      b.end();
      return translator.outputOrVoid(selector.signature.outputs);
    }

    // Receiver is already on stack.
    w.Local receiverVar = addLocal(selector.signature.inputs.first);
    assert(!receiverVar.type.nullable);
    b.local_tee(receiverVar);
    pushArguments(selector.signature, selector.paramInfo);

    if (selector.staticDispatchRanges.isNotEmpty) {
      final polymorphicDispatcher =
          translator.polymorphicDispatchers.getPolymorphicDispatcher(selector);
      b.call(polymorphicDispatcher);
    } else {
      final offset = selector.offset!;
      b.comment("Instance $kind of '${selector.name}'");
      b.local_get(receiverVar);
      b.struct_get(translator.topInfo.struct, FieldIndex.classId);
      if (offset != 0) {
        b.i32_const(offset);
        b.i32_add();
      }
      b.call_indirect(selector.signature, translator.dispatchTable.wasmTable);

      translator.functions.recordSelectorUse(selector);
    }

    return translator.outputOrVoid(selector.signature.outputs);
  }

  @override
  w.ValueType visitVariableGet(VariableGet node, w.ValueType expectedType) {
    w.Local? local = locals[node.variable];
    Capture? capture = closures.captures[node.variable];
    if (capture != null) {
      if (!capture.written && local != null) {
        b.local_get(local);
        return local.type;
      } else {
        b.local_get(capture.context.currentLocal);
        b.struct_get(capture.context.struct, capture.fieldIndex);
        return capture.type;
      }
    } else {
      if (local == null) {
        throw "Read of undefined variable ${node.variable}";
      }
      b.local_get(local);
      return local.type;
    }
  }

  @override
  w.ValueType visitVariableSet(VariableSet node, w.ValueType expectedType) {
    w.Local? local = locals[node.variable];
    Capture? capture = closures.captures[node.variable];
    bool preserved = expectedType != voidMarker;
    if (capture != null) {
      assert(capture.written);
      b.local_get(capture.context.currentLocal);
      wrap(node.value, capture.type);
      if (preserved) {
        w.Local temp = addLocal(capture.type);
        b.local_tee(temp);
        b.struct_set(capture.context.struct, capture.fieldIndex);
        b.local_get(temp);
        return temp.type;
      } else {
        b.struct_set(capture.context.struct, capture.fieldIndex);
        return voidMarker;
      }
    } else {
      if (local == null) {
        throw "Write of undefined variable ${node.variable}";
      }
      wrap(node.value, local.type);
      if (preserved) {
        b.local_tee(local);
        return local.type;
      } else {
        b.local_set(local);
        return voidMarker;
      }
    }
  }

  @override
  w.ValueType visitStaticGet(StaticGet node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult =
        intrinsifier.generateStaticGetterIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    Member target = node.target;
    if (target is Field) {
      return translator.globals.readGlobal(b, target);
    } else {
      return translator.outputOrVoid(call(target.reference));
    }
  }

  @override
  w.ValueType visitStaticTearOff(StaticTearOff node, w.ValueType expectedType) {
    translator.constants.instantiateConstant(
        b, StaticTearOffConstant(node.target), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitStaticSet(StaticSet node, w.ValueType expectedType) {
    bool preserved = expectedType != voidMarker;
    Member target = node.target;
    if (target is Field) {
      w.Global global = translator.globals.getGlobal(target);
      w.Global? flag = translator.globals.getGlobalInitializedFlag(target);
      wrap(node.value, global.type.type);
      b.global_set(global);
      if (flag != null) {
        b.i32_const(1); // true
        b.global_set(flag);
      }
      if (preserved) {
        b.global_get(global);
        return global.type.type;
      } else {
        return voidMarker;
      }
    } else {
      w.FunctionType targetFunctionType =
          translator.signatureForDirectCall(target.reference);
      w.ValueType paramType = targetFunctionType.inputs.single;
      wrap(node.value, paramType);
      w.Local? temp;
      if (preserved) {
        temp = addLocal(paramType);
        b.local_tee(temp);
      }
      call(target.reference);
      if (preserved) {
        b.local_get(temp!);
        return temp.type;
      } else {
        return voidMarker;
      }
    }
  }

  @override
  w.ValueType visitSuperPropertyGet(
      SuperPropertyGet node, w.ValueType expectedType) {
    Member target = _lookupSuperTarget(node.interfaceTarget, setter: false);
    if (target is Procedure && !target.isGetter) {
      // Super tear-off
      w.StructType closureStruct = _pushClosure(
          translator.getTearOffClosure(target),
          translator.getTearOffType(target),
          () => visitThis(w.RefType.struct(nullable: false)));
      return w.RefType.def(closureStruct, nullable: false);
    }
    return _directGet(target, ThisExpression(), () => null);
  }

  @override
  w.ValueType visitSuperPropertySet(
      SuperPropertySet node, w.ValueType expectedType) {
    Member target = _lookupSuperTarget(node.interfaceTarget, setter: true);
    return _directSet(target, ThisExpression(), node.value,
        preserved: expectedType != voidMarker);
  }

  @override
  w.ValueType visitInstanceGet(InstanceGet node, w.ValueType expectedType) {
    Member target = node.interfaceTarget;
    if (node.kind == InstanceAccessKind.Object) {
      late w.Label doneLabel;
      w.ValueType resultType =
          _virtualCall(node, target, _VirtualCallKind.Get, (signature) {
        doneLabel = b.block(const [], signature.outputs);
        w.Label nullLabel = b.block();
        wrap(node.receiver, translator.topInfo.nullableType);
        b.br_on_null(nullLabel);
      }, (_, __) {});
      b.br(doneLabel);
      b.end(); // nullLabel
      switch (target.name.text) {
        case "hashCode":
          b.i64_const(2011);
          break;
        case "runtimeType":
          wrap(ConstantExpression(TypeLiteralConstant(NullType())), resultType);
          break;
        default:
          unimplemented(
              node, "Nullable get of ${target.name.text}", [resultType]);
          break;
      }
      b.end(); // doneLabel
      return resultType;
    }
    Member? singleTarget = translator.singleTarget(node);
    if (singleTarget != null) {
      return _directGet(singleTarget, node.receiver,
          () => intrinsifier.generateInstanceGetterIntrinsic(node));
    } else {
      return _virtualCall(
          node,
          target,
          _VirtualCallKind.Get,
          (signature) => wrap(node.receiver, signature.inputs.first),
          (_, __) {});
    }
  }

  @override
  w.ValueType visitDynamicGet(DynamicGet node, w.ValueType expectedType) {
    final receiver = node.receiver;
    final forwarder =
        translator.dynamicForwarders.getDynamicGetForwarder(node.name.text);

    // Evaluate receiver
    wrap(receiver, translator.topInfo.nullableType);
    final nullableReceiverLocal = addLocal(translator.topInfo.nullableType);
    b.local_set(nullableReceiverLocal);

    final nullBlock = b.block([], [translator.topInfo.nonNullableType]);
    b.local_get(nullableReceiverLocal);
    b.br_on_non_null(nullBlock);
    // Throw `NoSuchMethodError`. Normally this needs to happen via instance
    // invocation of `noSuchMethod` (done in [_callNoSuchMethod]), but we don't
    // have a `Null` class in dart2wasm so we throw directly.
    b.local_get(nullableReceiverLocal);
    createGetterInvocationObject(translator, b, forwarder.memberName);

    call(translator.noSuchMethodErrorThrowWithInvocation.reference);
    b.unreachable();
    b.end(); // nullBlock

    // Call get forwarder
    b.call(forwarder.function);

    return translator.topInfo.nullableType;
  }

  @override
  w.ValueType visitDynamicSet(DynamicSet node, w.ValueType expectedType) {
    final receiver = node.receiver;
    final value = node.value;
    final forwarder =
        translator.dynamicForwarders.getDynamicSetForwarder(node.name.text);

    // Evaluate receiver
    wrap(receiver, translator.topInfo.nullableType);
    final nullableReceiverLocal = addLocal(translator.topInfo.nullableType);
    b.local_set(nullableReceiverLocal);

    // Evaluate positional arg
    wrap(value, translator.topInfo.nullableType);
    final positionalArgLocal = addLocal(translator.topInfo.nullableType);
    b.local_set(positionalArgLocal);

    final nullBlock = b.block([], [translator.topInfo.nonNullableType]);
    b.local_get(nullableReceiverLocal);
    b.br_on_non_null(nullBlock);
    // Throw `NoSuchMethodError`. Normally this needs to happen via instance
    // invocation of `noSuchMethod` (done in [_callNoSuchMethod]), but we don't
    // have a `Null` class in dart2wasm so we throw directly.
    b.local_get(nullableReceiverLocal);
    createSetterInvocationObject(
        translator, b, forwarder.memberName, positionalArgLocal);

    call(translator.noSuchMethodErrorThrowWithInvocation.reference);
    b.unreachable();
    b.end(); // nullBlock

    // Call set forwarder
    b.local_get(positionalArgLocal);
    b.call(forwarder.function);

    return translator.topInfo.nullableType;
  }

  w.ValueType _directGet(
      Member target, Expression receiver, w.ValueType? Function() intrinsify) {
    w.ValueType? intrinsicResult = intrinsify();
    if (intrinsicResult != null) return intrinsicResult;

    if (target is Field) {
      ClassInfo info = translator.classInfo[target.enclosingClass]!;
      int fieldIndex = translator.fieldIndex[target]!;
      w.ValueType receiverType = info.nonNullableType;
      w.ValueType fieldType = info.struct.fields[fieldIndex].type.unpacked;
      wrap(receiver, receiverType);
      b.struct_get(info.struct, fieldIndex);
      return fieldType;
    } else {
      // Instance call of getter
      assert(target is Procedure && target.isGetter);
      w.FunctionType targetFunctionType =
          translator.signatureForDirectCall(target.reference);
      wrap(receiver, targetFunctionType.inputs.single);
      return translator.outputOrVoid(call(target.reference));
    }
  }

  @override
  w.ValueType visitInstanceTearOff(
      InstanceTearOff node, w.ValueType expectedType) {
    Member target = node.interfaceTarget;

    if (node.kind == InstanceAccessKind.Object) {
      late w.Label doneLabel;
      w.ValueType resultType =
          _virtualCall(node, target, _VirtualCallKind.Get, (signature) {
        doneLabel = b.block(const [], signature.outputs);
        w.Label nullLabel = b.block();
        wrap(node.receiver, translator.topInfo.nullableType);
        b.br_on_null(nullLabel);
        translator.convertType(
            b, translator.topInfo.nullableType, signature.inputs[0]);
      }, (_, __) {});
      b.br(doneLabel);
      b.end(); // nullLabel
      switch (target.name.text) {
        case "toString":
          wrap(
              ConstantExpression(
                  StaticTearOffConstant(translator.nullToString)),
              resultType);
          break;
        case "noSuchMethod":
          wrap(
              ConstantExpression(
                  StaticTearOffConstant(translator.nullNoSuchMethod)),
              resultType);
          break;
        default:
          unimplemented(
              node, "Nullable tear-off of ${target.name.text}", [resultType]);
          break;
      }
      b.end(); // doneLabel
      return resultType;
    }

    return _virtualCall(node, target, _VirtualCallKind.Get,
        (signature) => wrap(node.receiver, signature.inputs.first), (_, __) {});
  }

  @override
  w.ValueType visitInstanceSet(InstanceSet node, w.ValueType expectedType) {
    bool preserved = expectedType != voidMarker;
    w.Local? temp;
    Member? singleTarget = translator.singleTarget(node);
    if (singleTarget != null) {
      return _directSet(singleTarget, node.receiver, node.value,
          preserved: preserved);
    } else {
      _virtualCall(node, node.interfaceTarget, _VirtualCallKind.Set,
          (signature) => wrap(node.receiver, signature.inputs.first),
          (signature, _) {
        w.ValueType paramType = signature.inputs.last;
        wrap(node.value, paramType);
        if (preserved) {
          temp = addLocal(paramType);
          b.local_tee(temp!);
        }
      });
      if (preserved) {
        b.local_get(temp!);
        return temp!.type;
      } else {
        return voidMarker;
      }
    }
  }

  w.ValueType _directSet(Member target, Expression receiver, Expression value,
      {required bool preserved}) {
    w.Local? temp;
    if (target is Field) {
      ClassInfo info = translator.classInfo[target.enclosingClass]!;
      int fieldIndex = translator.fieldIndex[target]!;
      w.ValueType receiverType = info.nonNullableType;
      w.ValueType fieldType = info.struct.fields[fieldIndex].type.unpacked;
      wrap(receiver, receiverType);
      wrap(value, fieldType);
      if (preserved) {
        temp = addLocal(fieldType);
        b.local_tee(temp);
      }
      b.struct_set(info.struct, fieldIndex);
    } else {
      w.FunctionType targetFunctionType =
          translator.signatureForDirectCall(target.reference);
      w.ValueType paramType = targetFunctionType.inputs.last;
      wrap(receiver, targetFunctionType.inputs.first);
      wrap(value, paramType);
      if (preserved) {
        temp = addLocal(paramType);
        b.local_tee(temp);
      }
      call(target.reference);
    }
    if (preserved) {
      b.local_get(temp!);
      return temp.type;
    } else {
      return voidMarker;
    }
  }

  @override
  void visitFunctionDeclaration(FunctionDeclaration node) {
    Capture? capture = closures.captures[node.variable];
    bool locallyClosurized = closures.closurizedFunctions.contains(node);
    if (capture != null || locallyClosurized) {
      if (capture != null) {
        b.local_get(capture.context.currentLocal);
      }
      w.StructType struct = _instantiateClosure(node.function);
      if (locallyClosurized) {
        w.Local local = addLocal(w.RefType.def(struct, nullable: false));
        locals[node.variable] = local;
        if (capture != null) {
          b.local_tee(local);
        } else {
          b.local_set(local);
        }
      }
      if (capture != null) {
        b.struct_set(capture.context.struct, capture.fieldIndex);
      }
    }
  }

  @override
  w.ValueType visitFunctionExpression(
      FunctionExpression node, w.ValueType expectedType) {
    w.StructType struct = _instantiateClosure(node.function);
    return w.RefType.def(struct, nullable: false);
  }

  w.StructType _instantiateClosure(FunctionNode functionNode) {
    Lambda lambda = closures.lambdas[functionNode]!;
    ClosureImplementation closure = translator.getClosure(
        functionNode,
        lambda.function,
        ParameterInfo.fromLocalFunction(functionNode),
        "closure wrapper at ${functionNode.location}");
    return _pushClosure(
        closure,
        functionNode.computeFunctionType(Nullability.nonNullable),
        () => _pushContext(functionNode));
  }

  w.StructType _pushClosure(ClosureImplementation closure,
      DartType functionType, void Function() pushContext) {
    w.StructType struct = closure.representation.closureStruct;

    ClassInfo info = translator.closureInfo;
    translator.functions.recordClassAllocation(info.classId);

    b.i32_const(info.classId);
    b.i32_const(initialIdentityHash);
    pushContext();
    b.global_get(closure.vtable);
    types.makeType(this, functionType);
    b.struct_new(struct);

    return struct;
  }

  void _pushContext(FunctionNode functionNode) {
    Context? context = closures.contexts[functionNode]?.parent;
    if (context != null) {
      assert(!context.isEmpty);
      b.local_get(context.currentLocal);
      if (context.currentLocal.type.nullable) {
        b.ref_as_non_null();
      }
    } else {
      b.global_get(translator.globals.dummyStructGlobal); // Dummy context
    }
  }

  @override
  w.ValueType visitFunctionInvocation(
      FunctionInvocation node, w.ValueType expectedType) {
    w.ValueType? intrinsicResult =
        intrinsifier.generateFunctionCallIntrinsic(node);
    if (intrinsicResult != null) return intrinsicResult;

    if (node.kind == FunctionAccessKind.Function) {
      // Type of function is `Function`, without the argument types.
      return visitDynamicInvocation(
          DynamicInvocation(DynamicAccessKind.Dynamic, node.receiver, node.name,
              node.arguments),
          expectedType);
    }

    final Expression receiver = node.receiver;
    final Arguments arguments = node.arguments;

    int typeCount = arguments.types.length;
    int posArgCount = arguments.positional.length;
    List<String> argNames = arguments.named.map((a) => a.name).toList()..sort();
    ClosureRepresentation? representation = translator.closureLayouter
        .getClosureRepresentation(typeCount, posArgCount, argNames);
    if (representation == null) {
      // This is a dynamic function call with a signature that matches no
      // functions in the program.
      b.unreachable();
      return translator.topInfo.nullableType;
    }

    // Evaluate receiver
    w.StructType struct = representation.closureStruct;
    w.Local temp = addLocal(w.RefType.def(struct, nullable: false));
    wrap(receiver, temp.type);
    b.local_tee(temp);
    b.struct_get(struct, FieldIndex.closureContext);

    // Type arguments
    for (DartType typeArg in arguments.types) {
      types.makeType(this, typeArg);
    }

    // Positional arguments
    for (Expression arg in arguments.positional) {
      wrap(arg, translator.topInfo.nullableType);
    }

    // Named arguments
    final Map<String, w.Local> namedLocals = {};
    for (final namedArg in arguments.named) {
      final w.Local namedLocal = addLocal(translator.topInfo.nullableType);
      namedLocals[namedArg.name] = namedLocal;
      wrap(namedArg.value, namedLocal.type);
      b.local_set(namedLocal);
    }
    for (String name in argNames) {
      b.local_get(namedLocals[name]!);
    }

    // Call entry point in vtable
    int vtableFieldIndex =
        representation.fieldIndexForSignature(posArgCount, argNames);
    w.FunctionType functionType =
        representation.getVtableFieldType(vtableFieldIndex);
    b.local_get(temp);
    b.struct_get(struct, FieldIndex.closureVtable);
    b.struct_get(representation.vtableStruct, vtableFieldIndex);
    b.call_ref(functionType);
    return translator.topInfo.nullableType;
  }

  @override
  w.ValueType visitLocalFunctionInvocation(
      LocalFunctionInvocation node, w.ValueType expectedType) {
    var decl = node.variable.parent as FunctionDeclaration;
    Lambda lambda = closures.lambdas[decl.function]!;
    _pushContext(decl.function);
    Arguments arguments = node.arguments;
    visitArgumentsLists(arguments.positional, lambda.function.type,
        ParameterInfo.fromLocalFunction(decl.function), 1,
        typeArguments: arguments.types, named: arguments.named);
    b.comment("Local call of ${decl.variable.name}");
    b.call(lambda.function);
    return translator.outputOrVoid(lambda.function.type.outputs);
  }

  @override
  w.ValueType visitInstantiation(Instantiation node, w.ValueType expectedType) {
    DartType type = dartTypeOf(node.expression);
    if (type is FunctionType) {
      int typeCount = type.typeParameters.length;
      int posArgCount = type.positionalParameters.length;
      List<String> argNames = type.namedParameters.map((a) => a.name).toList();
      ClosureRepresentation representation = translator.closureLayouter
          .getClosureRepresentation(typeCount, posArgCount, argNames)!;

      // Operand closure
      w.RefType closureType =
          w.RefType.def(representation.closureStruct, nullable: false);
      w.Local closureTemp = addLocal(closureType);
      wrap(node.expression, closureType);
      b.local_tee(closureTemp);

      // Type arguments
      for (DartType typeArg in node.typeArguments) {
        types.makeType(this, typeArg);
      }

      // Instantiation function
      b.local_get(closureTemp);
      b.struct_get(representation.closureStruct, FieldIndex.closureVtable);
      b.struct_get(
          representation.vtableStruct, FieldIndex.vtableInstantiationFunction);

      // Call instantiation function
      b.call_ref(representation.instantiationFunctionType);
      return representation.instantiationFunctionType.outputs.single;
    } else {
      // Only other alternative is `NeverType`.
      assert(type is NeverType);
      b.unreachable();
      return voidMarker;
    }
  }

  @override
  w.ValueType visitLogicalExpression(
      LogicalExpression node, w.ValueType expectedType) {
    _conditional(node, () => b.i32_const(1), () => b.i32_const(0),
        const [w.NumType.i32]);
    return w.NumType.i32;
  }

  @override
  w.ValueType visitNot(Not node, w.ValueType expectedType) {
    wrap(node.operand, w.NumType.i32);
    b.i32_eqz();
    return w.NumType.i32;
  }

  @override
  w.ValueType visitConditionalExpression(
      ConditionalExpression node, w.ValueType expectedType) {
    _conditional(
        node.condition,
        () => wrap(node.then, expectedType),
        () => wrap(node.otherwise, expectedType),
        [if (expectedType != voidMarker) expectedType]);
    return expectedType;
  }

  @override
  w.ValueType visitNullCheck(NullCheck node, w.ValueType expectedType) {
    return _nullCheck(node.operand, translator.throwNullCheckError);
  }

  w.ValueType _nullCheck(Expression operand, Procedure errorProcedure) {
    w.ValueType operandType = translator.translateType(dartTypeOf(operand));
    w.ValueType nonNullOperandType = operandType.withNullability(false);
    w.Label nullCheckBlock = b.block(const [], [nonNullOperandType]);
    wrap(operand, operandType);

    // We lower a null check to a br_on_non_null, throwing a [TypeError] in the
    // null case.
    b.br_on_non_null(nullCheckBlock);
    call(translator.stackTraceCurrent.reference);
    call(errorProcedure.reference);
    b.unreachable();
    b.end();
    return nonNullOperandType;
  }

  void visitArgumentsLists(List<Expression> positional,
      w.FunctionType signature, ParameterInfo paramInfo, int signatureOffset,
      {List<DartType> typeArguments = const [],
      List<NamedExpression> named = const []}) {
    for (int i = 0; i < typeArguments.length; i++) {
      types.makeType(this, typeArguments[i]);
    }
    signatureOffset += typeArguments.length;
    for (int i = 0; i < positional.length; i++) {
      wrap(positional[i], signature.inputs[signatureOffset + i]);
    }
    // Default values for positional parameters
    for (int i = positional.length; i < paramInfo.positional.length; i++) {
      final w.ValueType type = signature.inputs[signatureOffset + i];
      translator.constants
          .instantiateConstant(b, paramInfo.positional[i]!, type);
    }
    // Named arguments
    final Map<String, w.Local> namedLocals = {};
    for (var namedArg in named) {
      final w.ValueType type = signature
          .inputs[signatureOffset + paramInfo.nameIndex[namedArg.name]!];
      final w.Local namedLocal = addLocal(type);
      namedLocals[namedArg.name] = namedLocal;
      wrap(namedArg.value, namedLocal.type);
      b.local_set(namedLocal);
    }
    for (String name in paramInfo.names) {
      w.Local? namedLocal = namedLocals[name];
      final w.ValueType type =
          signature.inputs[signatureOffset + paramInfo.nameIndex[name]!];
      if (namedLocal != null) {
        b.local_get(namedLocal);
      } else {
        translator.constants
            .instantiateConstant(b, paramInfo.named[name]!, type);
      }
    }
  }

  void _visitArguments(Arguments node, w.FunctionType signature,
      ParameterInfo paramInfo, int signatureOffset) {
    visitArgumentsLists(node.positional, signature, paramInfo, signatureOffset,
        typeArguments: node.types, named: node.named);
  }

  @override
  w.ValueType visitStringConcatenation(
      StringConcatenation node, w.ValueType expectedType) {
    bool isConstantString(Expression expr) =>
        expr is StringLiteral ||
        (expr is ConstantExpression && expr.constant is StringConstant);

    String extractConstantString(Expression expr) {
      if (expr is StringLiteral) {
        return expr.value;
      } else {
        return ((expr as ConstantExpression).constant as StringConstant).value;
      }
    }

    if (node.expressions.every(isConstantString)) {
      StringBuffer result = StringBuffer();
      for (final expr in node.expressions) {
        result.write(extractConstantString(expr));
      }
      final expr = StringLiteral(result.toString());
      return visitStringLiteral(expr, expectedType);
    }

    late final Procedure target;

    final expressions = node.expressions;
    // We have special cases for 1/2/3/4 arguments in non-JSCM mode.
    if (!translator.options.jsCompatibility && expressions.length <= 4) {
      final nullableObjectType =
          translator.translateType(translator.coreTypes.objectNullableRawType);
      for (final expression in expressions) {
        wrap(expression, nullableObjectType);
      }
      if (expressions.length == 1) {
        target = translator.stringInterpolate1;
      } else if (expressions.length == 2) {
        target = translator.stringInterpolate2;
      } else if (expressions.length == 3) {
        target = translator.stringInterpolate3;
      } else {
        assert(expressions.length == 4);
        target = translator.stringInterpolate4;
      }
    } else {
      final nullableObjectType = translator.coreTypes.objectNullableRawType;
      makeArrayFromExpressions(node.expressions, nullableObjectType);
      target = translator.options.jsCompatibility
          ? translator.jsStringInterpolate
          : translator.stringInterpolate;
    }

    return translator.outputOrVoid(call(target.reference));
  }

  @override
  w.ValueType visitThrow(Throw node, w.ValueType expectedType) {
    // Front-end wraps the argument with `as Object` when necessary, so we can
    // assume non-nullable here.
    assert(!dartTypeOf(node.expression).isPotentiallyNullable);
    wrap(node.expression, translator.topInfo.nonNullableType);
    call(translator.errorThrowWithCurrentStackTrace.reference);
    b.unreachable();
    return expectedType;
  }

  @override
  w.ValueType visitRethrow(Rethrow node, w.ValueType expectedType) {
    b.rethrow_(tryLabels.last);
    return expectedType;
  }

  @override
  w.ValueType visitConstantExpression(
      ConstantExpression node, w.ValueType expectedType) {
    translator.constants.instantiateConstant(b, node.constant, expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitNullLiteral(NullLiteral node, w.ValueType expectedType) {
    translator.constants.instantiateConstant(b, NullConstant(), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitStringLiteral(StringLiteral node, w.ValueType expectedType) {
    translator.constants
        .instantiateConstant(b, StringConstant(node.value), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitBoolLiteral(BoolLiteral node, w.ValueType expectedType) {
    translator.constants
        .instantiateConstant(b, BoolConstant(node.value), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitIntLiteral(IntLiteral node, w.ValueType expectedType) {
    translator.constants
        .instantiateConstant(b, IntConstant(node.value), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitDoubleLiteral(DoubleLiteral node, w.ValueType expectedType) {
    translator.constants
        .instantiateConstant(b, DoubleConstant(node.value), expectedType);
    return expectedType;
  }

  @override
  w.ValueType visitListLiteral(ListLiteral node, w.ValueType expectedType) {
    final useSharedCreator = types.isTypeConstant(node.typeArgument);

    final passType = !useSharedCreator;
    final passArray = node.expressions.isNotEmpty;

    final targetReference = passArray
        ? translator.growableListFromWasmArray.reference
        : translator.growableListEmpty.reference;

    final w.BaseFunction target = useSharedCreator
        ? translator.partialInstantiator.getOneTypeArgumentForwarder(
            targetReference,
            node.typeArgument,
            'create${passArray ? '' : 'Empty'}List<${node.typeArgument}>')
        : translator.functions.getFunction(targetReference);

    if (passType) {
      types.makeType(this, node.typeArgument);
    }
    if (passArray) {
      makeArrayFromExpressions(node.expressions,
          translator.coreTypes.objectRawType(Nullability.nullable));
    }

    b.call(target);
    return target.type.outputs.single;
  }

  w.ValueType makeArrayFromExpressions(
      List<Expression> expressions, InterfaceType elementType) {
    return makeArray(
        translator.arrayTypeForDartType(elementType), expressions.length,
        (w.ValueType type, int i) {
      wrap(expressions[i], type);
    });
  }

  w.ValueType makeArray(w.ArrayType arrayType, int length,
      void Function(w.ValueType, int) generateItem) {
    return translator.makeArray(b, arrayType, length, generateItem);
  }

  @override
  w.ValueType visitMapLiteral(MapLiteral node, w.ValueType expectedType) {
    final useSharedCreator = types.isTypeConstant(node.keyType) &&
        types.isTypeConstant(node.valueType);

    final passTypes = !useSharedCreator;
    final passArray = node.entries.isNotEmpty;

    final targetReference = passArray
        ? translator.mapFromWasmArray.reference
        : translator.mapFactory.reference;

    final w.BaseFunction target = useSharedCreator
        ? translator.partialInstantiator.getTwoTypeArgumentForwarder(
            targetReference,
            node.keyType,
            node.valueType,
            'create${passArray ? '' : 'Empty'}Map<${node.keyType}, ${node.valueType}>')
        : translator.functions.getFunction(targetReference);

    if (passTypes) {
      types.makeType(this, node.keyType);
      types.makeType(this, node.valueType);
    }
    if (passArray) {
      makeArray(translator.nullableObjectArrayType, 2 * node.entries.length,
          (elementType, elementIndex) {
        final index = elementIndex ~/ 2;
        final entry = node.entries[index];
        if (elementIndex % 2 == 0) {
          wrap(entry.key, elementType);
        } else {
          wrap(entry.value, elementType);
        }
      });
    }
    b.call(target);
    return target.type.outputs.single;
  }

  @override
  w.ValueType visitSetLiteral(SetLiteral node, w.ValueType expectedType) {
    final useSharedCreator = types.isTypeConstant(node.typeArgument);

    final passType = !useSharedCreator;
    final passArray = node.expressions.isNotEmpty;

    final targetReference = passArray
        ? translator.setFromWasmArray.reference
        : translator.setFactory.reference;

    final w.BaseFunction target = useSharedCreator
        ? translator.partialInstantiator.getOneTypeArgumentForwarder(
            targetReference,
            node.typeArgument,
            'create${passArray ? '' : 'Empty'}Set<${node.typeArgument}>')
        : translator.functions.getFunction(targetReference);

    if (passType) {
      types.makeType(this, node.typeArgument);
    }
    if (passArray) {
      makeArrayFromExpressions(node.expressions,
          translator.coreTypes.objectRawType(Nullability.nullable));
    }
    b.call(target);
    return target.type.outputs.single;
  }

  @override
  w.ValueType visitTypeLiteral(TypeLiteral node, w.ValueType expectedType) {
    return types.makeType(this, node.type);
  }

  @override
  w.ValueType visitIsExpression(IsExpression node, w.ValueType expectedType) {
    final operandType = dartTypeOf(node.operand);
    final boxedOperandType = operandType.isPotentiallyNullable
        ? translator.topInfo.nullableType
        : translator.topInfo.nonNullableType;
    wrap(node.operand, boxedOperandType);
    types.emitIsTest(this, node.type, operandType, node.location);
    return w.NumType.i32;
  }

  @override
  w.ValueType visitAsExpression(AsExpression node, w.ValueType expectedType) {
    if (translator.options.omitExplicitTypeChecks || node.isUnchecked) {
      return wrap(node.operand, expectedType);
    }

    final operandType = dartTypeOf(node.operand);
    final boxedOperandType = operandType.isPotentiallyNullable
        ? translator.topInfo.nullableType
        : translator.topInfo.nonNullableType;
    wrap(node.operand, boxedOperandType);
    return types.emitAsCheck(
        this, node.type, operandType, boxedOperandType, node.location);
  }

  @override
  w.ValueType visitLoadLibrary(LoadLibrary node, w.ValueType expectedType) {
    LibraryDependency import = node.import;
    _emitString(import.enclosingLibrary.importUri.toString());
    _emitString(import.name!);
    return translator.outputOrVoid(call(translator.loadLibrary.reference));
  }

  @override
  w.ValueType visitCheckLibraryIsLoaded(
      CheckLibraryIsLoaded node, w.ValueType expectedType) {
    LibraryDependency import = node.import;
    _emitString(import.enclosingLibrary.importUri.toString());
    _emitString(import.name!);
    return translator
        .outputOrVoid(call(translator.checkLibraryIsLoaded.reference));
  }

  /// Pushes the `_Type` object for a function or class type parameter to the
  /// stack and returns the value type of the object.
  w.ValueType instantiateTypeParameter(TypeParameter parameter) {
    w.ValueType resultType;

    w.Local? local = typeLocals[parameter];
    Capture? capture = closures.captures[parameter];
    if (local != null) {
      b.local_get(local);
      resultType = local.type;
    } else if (capture != null) {
      Capture capture = closures.captures[parameter]!;
      b.local_get(capture.context.currentLocal);
      b.struct_get(capture.context.struct, capture.fieldIndex);
      resultType = capture.type;
    } else {
      Class cls = parameter.declaration as Class;
      ClassInfo info = translator.classInfo[cls]!;
      int fieldIndex = translator.typeParameterIndex[parameter]!;
      visitThis(info.nonNullableType);
      b.struct_get(info.struct, fieldIndex);
      resultType = info.struct.fields[fieldIndex].type.unpacked;
    }