public static MultiDictionary<Symbol, CSharpSyntaxNode> Analyze(CSharpCompilation compilation, MethodSymbol method, BoundNode node)
        {
            var emptyStructs = new CaptureWalkerEmptyStructTypeCache();
            var initiallyAssignedVariables = UnassignedVariablesWalker.Analyze(compilation, method, node, emptyStructs);

            var walker = new IteratorAndAsyncCaptureWalker(compilation, method, node, emptyStructs, initiallyAssignedVariables);

            bool badRegion = false;
            walker.Analyze(ref badRegion);
            Debug.Assert(!badRegion);

            var result = walker.variablesCaptured;


            if (!method.IsStatic && method.ContainingType.TypeKind == TypeKind.Struct)
            {
                // It is possible that the enclosing method only *writes* to the enclosing struct, but in that
                // case it should be considered captured anyway so that we have a proxy for it to write to.
                result.Add(method.ThisParameter, node.Syntax);
            }

            foreach (var variable in result.Keys.ToArray()) // take a snapshot, as we are modifying the underlying multidictionary
            {
                var local = variable as LocalSymbol;
                if ((object)local != null && local.RefKind != RefKind.None)
                {
                    walker.AddSpillsForRef(walker.refLocalInitializers[local], result[local]);
                }
            }

            walker.Free();
            return result;
        }

        /// <summary>
        /// Rewrite an async method into a state machine type.
        /// </summary>
        internal static BoundStatement Rewrite(
            BoundStatement body,
            MethodSymbol method,
            int methodOrdinal,
            VariableSlotAllocator slotAllocatorOpt,
            TypeCompilationState compilationState,
            DiagnosticBag diagnostics,
            out AsyncStateMachine stateMachineType)
        {
            if (!method.IsAsync)
            {
                stateMachineType = null;
                return body;
            }

            // The CLR doesn't support adding fields to structs, so in order to enable EnC in an async method we need to generate a class.
            var typeKind = compilationState.Compilation.Options.EnableEditAndContinue ? TypeKind.Class : TypeKind.Struct;

            var bodyWithAwaitLifted = AwaitExpressionSpiller.Rewrite(body, method, compilationState, diagnostics);

            stateMachineType = new AsyncStateMachine(slotAllocatorOpt, compilationState, method, methodOrdinal, typeKind);
            compilationState.ModuleBuilderOpt.CompilationState.SetStateMachineType(method, stateMachineType);
            var rewriter = new AsyncRewriter(bodyWithAwaitLifted, method, methodOrdinal, stateMachineType, slotAllocatorOpt, compilationState, diagnostics);

            if (!rewriter.VerifyPresenceOfRequiredAPIs())
            {
                return body;
            }

            return rewriter.Rewrite();
        }

 private LocalBinderFactory(MethodSymbol method, Binder enclosing)
 {
     Debug.Assert((object)method != null);
     _map = new SmallDictionary<CSharpSyntaxNode, Binder>(ReferenceEqualityComparer.Instance);
     _method = method;
     _enclosing = enclosing;
 }

        public EELocalSymbol(
            MethodSymbol method,
            ImmutableArray<Location> locations,
            string nameOpt,
            int ordinal,
            LocalDeclarationKind declarationKind,
            TypeSymbol type,
            RefKind refKind,
            bool isPinned,
            bool isCompilerGenerated,
            bool canScheduleToStack)
        {
            Debug.Assert(method != null);
            Debug.Assert(ordinal >= -1);
            Debug.Assert(!locations.IsDefault);
            Debug.Assert(type != null);

            _method = method;
            _locations = locations;
            _nameOpt = nameOpt;
            _ordinal = ordinal;
            _declarationKind = declarationKind;
            _type = type;
            _refKind = refKind;
            _isPinned = isPinned;
            _isCompilerGenerated = isCompilerGenerated;
            _canScheduleToStack = canScheduleToStack;
        }

        internal SourceAttributeData(
            SyntaxReference applicationNode,
            NamedTypeSymbol attributeClass,
            MethodSymbol attributeConstructor,
            ImmutableArray<TypedConstant> constructorArguments,
            ImmutableArray<int> constructorArgumentsSourceIndices,
            ImmutableArray<KeyValuePair<string, TypedConstant>> namedArguments,
            bool hasErrors,
            bool isConditionallyOmitted)
        {
            Debug.Assert(!isConditionallyOmitted || (object)attributeClass != null && attributeClass.IsConditional);
            Debug.Assert(!constructorArguments.IsDefault);
            Debug.Assert(!namedArguments.IsDefault);
            Debug.Assert(constructorArgumentsSourceIndices.IsDefault ||
                constructorArgumentsSourceIndices.Any() && constructorArgumentsSourceIndices.Length == constructorArguments.Length);

            this.attributeClass = attributeClass;
            this.attributeConstructor = attributeConstructor;
            this.constructorArguments = constructorArguments;
            this.constructorArgumentsSourceIndices = constructorArgumentsSourceIndices;
            this.namedArguments = namedArguments;
            this.isConditionallyOmitted = isConditionallyOmitted;
            this.hasErrors = hasErrors;
            this.applicationNode = applicationNode;
        }

        public SynthesizedImplementationMethod(
            MethodSymbol interfaceMethod,
            NamedTypeSymbol implementingType,
            string name = null,
            bool debuggerHidden = false,
            PropertySymbol associatedProperty = null,
            MethodSymbol asyncKickoffMethod = null)
        {
            //it does not make sense to add methods to substituted types
            Debug.Assert(implementingType.IsDefinition);

            this.name = name ?? ExplicitInterfaceHelpers.GetMemberName(interfaceMethod.Name, interfaceMethod.ContainingType, aliasQualifierOpt: null);
            this.interfaceMethod = interfaceMethod;
            this.implementingType = implementingType;
            this.debuggerHidden = debuggerHidden;
            this.associatedProperty = associatedProperty;
            this.explicitInterfaceImplementations = ImmutableArray.Create<MethodSymbol>(interfaceMethod);
            this.asyncKickoffMethod = asyncKickoffMethod;

            // alpha-rename to get the implementation's type parameters
            var typeMap = interfaceMethod.ContainingType.TypeSubstitution ?? TypeMap.Empty;
            typeMap.WithAlphaRename(interfaceMethod, this, out this.typeParameters);

            var substitutedInterfaceMethod = interfaceMethod.ConstructIfGeneric(this.typeParameters.Cast<TypeParameterSymbol, TypeSymbol>());
            this.returnType = substitutedInterfaceMethod.ReturnType;
            this.parameters = SynthesizedParameterSymbol.DeriveParameters(substitutedInterfaceMethod, this);
        }

        /// <summary>
        /// Return the extension method in reduced form if the extension method
        /// is applicable, and satisfies type parameter constraints, based on the
        /// "this" argument type. Otherwise, returns null.
        /// </summary>
        public static MethodSymbol Create(MethodSymbol method, TypeSymbol receiverType, Compilation compilation)
        {
            Debug.Assert(method.IsExtensionMethod && method.MethodKind != MethodKind.ReducedExtension);
            Debug.Assert(method.ParameterCount > 0);
            Debug.Assert((object)receiverType != null);

            HashSet<DiagnosticInfo> useSiteDiagnostics = null;

            method = method.InferExtensionMethodTypeArguments(receiverType, compilation, ref useSiteDiagnostics);
            if ((object)method == null)
            {
                return null;
            }

            var conversions = new TypeConversions(method.ContainingAssembly.CorLibrary);
            var conversion = conversions.ConvertExtensionMethodThisArg(method.Parameters[0].Type, receiverType, ref useSiteDiagnostics);
            if (!conversion.Exists)
            {
                return null;
            }

            if (useSiteDiagnostics != null)
            {
                foreach (var diag in useSiteDiagnostics)
                {
                    if (diag.Severity == DiagnosticSeverity.Error)
                    {
                        return null;
                    }
                }
            }

            return Create(method);
        }

        internal static void BindFieldInitializers(
            SourceMemberContainerTypeSymbol typeSymbol,
            MethodSymbol scriptCtor,
            ImmutableArray<FieldInitializers> fieldInitializers,
            bool generateDebugInfo,
            DiagnosticBag diagnostics,
            ref ProcessedFieldInitializers processedInitializers) //by ref so that we can store the results of lowering
        {
            DiagnosticBag diagsForInstanceInitializers = DiagnosticBag.GetInstance();
            try
            {
                ConsList<Imports> firstDebugImports;

                processedInitializers.BoundInitializers = BindFieldInitializers(typeSymbol, scriptCtor, fieldInitializers,
                    diagsForInstanceInitializers, generateDebugInfo, out firstDebugImports);

                processedInitializers.HasErrors = diagsForInstanceInitializers.HasAnyErrors();
                processedInitializers.FirstDebugImports = firstDebugImports;
            }
            finally
            {
                diagnostics.AddRange(diagsForInstanceInitializers);
                diagsForInstanceInitializers.Free();
            }
        }

        private BoundExpression MakePropertyGetAccess(
            SyntaxNode syntax,
            BoundExpression rewrittenReceiver,
            PropertySymbol property,
            ImmutableArray<BoundExpression> rewrittenArguments,
            MethodSymbol getMethodOpt = null,
            BoundPropertyAccess oldNodeOpt = null)
        {
            if (_inExpressionLambda && rewrittenArguments.IsEmpty)
            {
                return oldNodeOpt != null ?
                    oldNodeOpt.Update(rewrittenReceiver, property, LookupResultKind.Viable, property.Type) :
                    new BoundPropertyAccess(syntax, rewrittenReceiver, property, LookupResultKind.Viable, property.Type);
            }
            else
            {
                var getMethod = getMethodOpt ?? property.GetOwnOrInheritedGetMethod();

                Debug.Assert((object)getMethod != null);
                Debug.Assert(getMethod.ParameterCount == rewrittenArguments.Length);
                Debug.Assert(((object)getMethodOpt == null) || ReferenceEquals(getMethod, getMethodOpt));

                return BoundCall.Synthesized(
                    syntax,
                    rewrittenReceiver,
                    getMethod,
                    rewrittenArguments);
            }
        }

            internal SynthesizedLambdaMethod(NamedTypeSymbol containingType, MethodSymbol topLevelMethod, BoundLambda node, bool isStatic, TypeCompilationState compilationState)
                : base(containingType,
                       node.Symbol,
                       null,
                       node.SyntaxTree.GetReference(node.Body.Syntax),
                       node.Syntax.GetLocation(),
                       GeneratedNames.MakeLambdaMethodName(topLevelMethod.Name, compilationState.GenerateTempNumber()),
                       (containingType is LambdaFrame ? DeclarationModifiers.Internal : DeclarationModifiers.Private)
                            | (isStatic ? DeclarationModifiers.Static : 0)
                            | (node.Symbol.IsAsync ? DeclarationModifiers.Async : 0))
            {
                TypeMap typeMap;
                ImmutableArray<TypeParameterSymbol> typeParameters;
                LambdaFrame lambdaFrame;

                if (!topLevelMethod.IsGenericMethod)
                {
                    typeMap = TypeMap.Empty;
                    typeParameters = ImmutableArray<TypeParameterSymbol>.Empty;
                }
                else if ((object)(lambdaFrame = this.ContainingType as LambdaFrame) != null)
                {
                    typeMap = lambdaFrame.TypeMap;
                    typeParameters = ImmutableArray<TypeParameterSymbol>.Empty;
                }
                else
                {
                    typeMap = TypeMap.Empty.WithAlphaRename(topLevelMethod, this, out typeParameters);
                }

                AssignTypeMapAndTypeParameters(typeMap, typeParameters);
            }

        public MethodToStateMachineRewriter(
            SyntheticBoundNodeFactory F,
            MethodSymbol originalMethod,
            FieldSymbol state,
            IReadOnlySet<Symbol> variablesCaptured,
            IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> nonReusableLocalProxies,
            DiagnosticBag diagnostics,
            bool useFinalizerBookkeeping)
            : base(F.CompilationState, diagnostics)
        {
            Debug.Assert(F != null);
            Debug.Assert(originalMethod != null);
            Debug.Assert(state != null);
            Debug.Assert(nonReusableLocalProxies != null);
            Debug.Assert(diagnostics != null);
            Debug.Assert(variablesCaptured != null);

            this.F = F;
            this.stateField = state;
            this.cachedState = F.SynthesizedLocal(F.SpecialType(SpecialType.System_Int32), kind: SynthesizedLocalKind.StateMachineCachedState);
            this.useFinalizerBookkeeping = useFinalizerBookkeeping;
            this.hasFinalizerState = useFinalizerBookkeeping;
            this.originalMethod = originalMethod;
            this.variablesCaptured = variablesCaptured;

            foreach (var proxy in nonReusableLocalProxies)
            {
                this.proxies.Add(proxy.Key, proxy.Value);
            }
        }

 public AsyncStruct(MethodSymbol method)
     : base(method, GeneratedNames.MakeIteratorOrAsyncDisplayClassName(method.Name, SequenceNumber(method)), TypeKind.Struct)
 {
     // TODO: report use-site errors on these types
     this.interfaces = ImmutableArray.Create<NamedTypeSymbol>(method.DeclaringCompilation.GetWellKnownType(WellKnownType.System_Runtime_CompilerServices_IAsyncStateMachine));
     this.constructor = new SynthesizedInstanceConstructor(this);
 }

 internal ExecutableCodeBinder(CSharpSyntaxNode root, Symbol memberSymbol, Binder next, BinderFlags additionalFlags)
     : base(next, (next.Flags | additionalFlags) & ~BinderFlags.AllClearedAtExecutableCodeBoundary)
 {
     this.memberSymbol = memberSymbol;
     this.root = root;
     this.owner = memberSymbol as MethodSymbol;
 }

        // insert the implicit "return" statement at the end of the method body
        // Normally, we wouldn't bother attaching syntax trees to compiler-generated nodes, but these
        // ones are going to have sequence points.
        internal static BoundBlock AppendImplicitReturn(BoundStatement node, MethodSymbol method = null, CSharpSyntaxNode syntax = null)
        {
            if (syntax == null)
            {
                syntax = node.Syntax;
            }

            BoundStatement ret =
                (object)method != null && (object)method.IteratorElementType != null
                ? BoundYieldBreakStatement.Synthesized(syntax) as BoundStatement
                : BoundReturnStatement.Synthesized(syntax, null);

            if (syntax.Kind == SyntaxKind.Block)
            {
                var blockSyntax = (BlockSyntax)syntax;

                ret = new BoundSequencePointWithSpan(
                    blockSyntax,
                    ret,
                    blockSyntax.CloseBraceToken.Span)
                { WasCompilerGenerated = true };
            }

            switch (node.Kind)
            {
                case BoundKind.Block:
                    var block = (BoundBlock)node;
                    return block.Update(block.LocalsOpt, block.Statements.Add(ret));

                default:
                    return new BoundBlock(syntax, ImmutableArray<LocalSymbol>.Empty, ImmutableArray.Create(ret, node));
            }
        }

        internal static Func<SyntaxNode, SyntaxNode> GetEquivalentNodesMap(MethodSymbol method1, MethodSymbol method0)
        {
            var tree1 = method1.Locations[0].SourceTree;
            var tree0 = method0.Locations[0].SourceTree;
            Assert.NotEqual(tree1, tree0);

            var locals0 = GetAllLocals(method0);
            return s =>
            {
                var s1 = s;
                Assert.Equal(s1.SyntaxTree, tree1);
                foreach (var s0 in locals0)
                {
                    if (!SyntaxFactory.AreEquivalent(s0, s1))
                    {
                        continue;
                    }
                    // Make sure the containing statements are the same.
                    var p0 = GetNearestStatement(s0);
                    var p1 = GetNearestStatement(s1);
                    if (SyntaxFactory.AreEquivalent(p0, p1))
                    {
                        return s0;
                    }
                }
                return null;
            };
        }

        private ForEachEnumeratorInfo(
            TypeSymbol collectionType,
            TypeSymbol elementType,
            MethodSymbol getEnumeratorMethod,
            MethodSymbol currentPropertyGetter,
            MethodSymbol moveNextMethod,
            bool needsDisposeMethod,
            Conversion collectionConversion,
            Conversion currentConversion,
            Conversion enumeratorConversion,
            BinderFlags location)
        {
            Debug.Assert((object)collectionType != null, "Field 'collectionType' cannot be null");
            Debug.Assert((object)elementType != null, "Field 'elementType' cannot be null");
            Debug.Assert((object)getEnumeratorMethod != null, "Field 'getEnumeratorMethod' cannot be null");
            Debug.Assert((object)currentPropertyGetter != null, "Field 'currentPropertyGetter' cannot be null");
            Debug.Assert((object)moveNextMethod != null, "Field 'moveNextMethod' cannot be null");

            this.CollectionType = collectionType;
            this.ElementType = elementType;
            this.GetEnumeratorMethod = getEnumeratorMethod;
            this.CurrentPropertyGetter = currentPropertyGetter;
            this.MoveNextMethod = moveNextMethod;
            this.NeedsDisposeMethod = needsDisposeMethod;
            this.CollectionConversion = collectionConversion;
            this.CurrentConversion = currentConversion;
            this.EnumeratorConversion = enumeratorConversion;
            this.Location = location;
        }

        protected StateMachineRewriter(
            BoundStatement body,
            MethodSymbol method,
            SynthesizedContainer stateMachineType,
            VariableSlotAllocator slotAllocatorOpt,
            TypeCompilationState compilationState,
            DiagnosticBag diagnostics)
        {
            Debug.Assert(body != null);
            Debug.Assert(method != null);
            Debug.Assert(stateMachineType != null);
            Debug.Assert(compilationState != null);
            Debug.Assert(diagnostics != null);

            this.body = body;
            this.method = method;
            this.stateMachineType = stateMachineType;
            this.slotAllocatorOpt = slotAllocatorOpt;
            this.synthesizedLocalOrdinals = new SynthesizedLocalOrdinalsDispenser();
            this.diagnostics = diagnostics;

            this.F = new SyntheticBoundNodeFactory(method, body.Syntax, compilationState, diagnostics);
            Debug.Assert(F.CurrentType == method.ContainingType);
            Debug.Assert(F.Syntax == body.Syntax);
        }

        internal AsyncMethodToStateMachineRewriter(
            MethodSymbol method,
            int methodOrdinal,
            AsyncMethodBuilderMemberCollection asyncMethodBuilderMemberCollection,
            SyntheticBoundNodeFactory F,
            FieldSymbol state,
            FieldSymbol builder,
            IReadOnlySet<Symbol> hoistedVariables,
            IReadOnlyDictionary<Symbol, CapturedSymbolReplacement> nonReusableLocalProxies,
            SynthesizedLocalOrdinalsDispenser synthesizedLocalOrdinals,
            VariableSlotAllocator slotAllocatorOpt,
            int nextFreeHoistedLocalSlot,
            DiagnosticBag diagnostics)
            : base(F, method, state, hoistedVariables, nonReusableLocalProxies, synthesizedLocalOrdinals, slotAllocatorOpt, nextFreeHoistedLocalSlot, diagnostics, useFinalizerBookkeeping: false)
        {
            _method = method;
            _asyncMethodBuilderMemberCollection = asyncMethodBuilderMemberCollection;
            _asyncMethodBuilderField = builder;
            _exprReturnLabel = F.GenerateLabel("exprReturn");
            _exitLabel = F.GenerateLabel("exitLabel");

            _exprRetValue = method.IsGenericTaskReturningAsync(F.Compilation)
                ? F.SynthesizedLocal(asyncMethodBuilderMemberCollection.ResultType, syntax: F.Syntax, kind: SynthesizedLocalKind.AsyncMethodReturnValue)
                : null;

            _dynamicFactory = new LoweredDynamicOperationFactory(F, methodOrdinal);
            _awaiterFields = new Dictionary<TypeSymbol, FieldSymbol>(TypeSymbol.EqualsIgnoringDynamicComparer);
            _nextAwaiterId = slotAllocatorOpt?.PreviousAwaiterSlotCount ?? 0;
        }

        internal PlaceholderLocalBinder(
            CSharpSyntaxNode syntax,
            ImmutableArray<Alias> aliases,
            MethodSymbol containingMethod,
            EETypeNameDecoder typeNameDecoder,
            Binder next) :
            base(next)
        {
            _syntax = syntax;
            _containingMethod = containingMethod;

            var compilation = next.Compilation;
            var sourceAssembly = compilation.SourceAssembly;

            var aliasesBuilder = ArrayBuilder<LocalSymbol>.GetInstance(aliases.Length);
            var lowercaseBuilder = ImmutableDictionary.CreateBuilder<string, LocalSymbol>();
            foreach (Alias alias in aliases)
            {
                var local = PlaceholderLocalSymbol.Create(
                    typeNameDecoder,
                    containingMethod,
                    sourceAssembly,
                    alias);
                aliasesBuilder.Add(local);

                if (alias.Kind == DkmClrAliasKind.ReturnValue)
                {
                    lowercaseBuilder.Add(local.Name.ToLower(), local);
                }
            }
            _lowercaseReturnValueAliases = lowercaseBuilder.ToImmutableDictionary();
            _aliases = aliasesBuilder.ToImmutableAndFree();
        }

 public SynthesizedExplicitImplementationMethod(
     MethodSymbol interfaceMethod,
     MethodSymbol implementingMethod,
     NamedTypeSymbol implementingType) : base(interfaceMethod, implementingType)
 {
     this.implementingMethod = implementingMethod;
 }