PowerShell-master/src/System.Management.Automation/engine/interpreter/LightCompiler.cs

/* ****************************************************************************
 *
 * Copyright (c) Microsoft Corporation.
 *
 * This source code is subject to terms and conditions of the Apache License, Version 2.0. A
 * copy of the license can be found in the License.html file at the root of this distribution. If
 * you cannot locate the Apache License, Version 2.0, please send an email to
 * dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
 * by the terms of the Apache License, Version 2.0.
 *
 * You must not remove this notice, or any other, from this software.
 *
 *
 * ***************************************************************************/

#if !CLR2
using System.Globalization;
using System.Linq;
using System.Linq.Expressions;
#endif

using System.Collections.Generic;
using System.Diagnostics;
using System.Reflection;
using AstUtils = System.Management.Automation.Interpreter.Utils;
using System.Runtime.CompilerServices;

namespace System.Management.Automation.Interpreter
{
    internal sealed class ExceptionHandler
    {
        public readonly Type ExceptionType;
        public readonly int StartIndex;
        public readonly int EndIndex;
        public readonly int LabelIndex;
        public readonly int HandlerStartIndex;
        public readonly int HandlerEndIndex;

        internal TryCatchFinallyHandler Parent = null;

        public bool IsFault { get { return ExceptionType == null; } }

        internal ExceptionHandler(int start, int end, int labelIndex, int handlerStartIndex, int handlerEndIndex, Type exceptionType)
        {
            StartIndex = start;
            EndIndex = end;
            LabelIndex = labelIndex;
            ExceptionType = exceptionType;
            HandlerStartIndex = handlerStartIndex;
            HandlerEndIndex = handlerEndIndex;
        }

        internal void SetParent(TryCatchFinallyHandler tryHandler)
        {
            Debug.Assert(Parent == null);
            Parent = tryHandler;
        }

        public bool Matches(Type exceptionType)
        {
            if (ExceptionType == null || ExceptionType.IsAssignableFrom(exceptionType))
            {
                return true;
            }

            return false;
        }

        public bool IsBetterThan(ExceptionHandler other)
        {
            if (other == null)
            {
                return true;
            }

            Debug.Assert(StartIndex == other.StartIndex && EndIndex == other.EndIndex, "we only need to compare handlers for the same try block");
            return HandlerStartIndex < other.HandlerStartIndex;
        }

        internal bool IsInsideTryBlock(int index)
        {
            return index >= StartIndex && index < EndIndex;
        }

        internal bool IsInsideCatchBlock(int index)
        {
            return index >= HandlerStartIndex && index < HandlerEndIndex;
        }

        internal bool IsInsideFinallyBlock(int index)
        {
            Debug.Assert(Parent != null);
            return Parent.IsFinallyBlockExist && index >= Parent.FinallyStartIndex && index < Parent.FinallyEndIndex;
        }

        public override string ToString()
        {
            return string.Format(
                CultureInfo.InvariantCulture,
                "{0} [{1}-{2}] [{3}->{4}]",
                IsFault ? "fault" : "catch(" + ExceptionType.Name + ")",
                StartIndex,
                EndIndex,
                HandlerStartIndex,
                HandlerEndIndex);
        }
    }

    internal sealed class TryCatchFinallyHandler
    {
        internal readonly int TryStartIndex = Instruction.UnknownInstrIndex;
        internal readonly int TryEndIndex = Instruction.UnknownInstrIndex;
        internal readonly int FinallyStartIndex = Instruction.UnknownInstrIndex;
        internal readonly int FinallyEndIndex = Instruction.UnknownInstrIndex;
        internal readonly int GotoEndTargetIndex = Instruction.UnknownInstrIndex;

        private readonly ExceptionHandler[] _handlers;

        internal bool IsFinallyBlockExist
        {
            get { return (FinallyStartIndex != Instruction.UnknownInstrIndex && FinallyEndIndex != Instruction.UnknownInstrIndex); }
        }

        internal bool IsCatchBlockExist
        {
            get { return (_handlers != null); }
        }

        /// <summary>
        /// No finally block.
        /// </summary>
        internal TryCatchFinallyHandler(int tryStart, int tryEnd, int gotoEndTargetIndex, ExceptionHandler[] handlers)
            : this(tryStart, tryEnd, gotoEndTargetIndex, Instruction.UnknownInstrIndex, Instruction.UnknownInstrIndex, handlers)
        {
            Debug.Assert(handlers != null, "catch blocks should exist");
        }

        /// <summary>
        /// No catch blocks.
        /// </summary>
        internal TryCatchFinallyHandler(int tryStart, int tryEnd, int gotoEndTargetIndex, int finallyStart, int finallyEnd)
            : this(tryStart, tryEnd, gotoEndTargetIndex, finallyStart, finallyEnd, null)
        {
            Debug.Assert(finallyStart != Instruction.UnknownInstrIndex && finallyEnd != Instruction.UnknownInstrIndex, "finally block should exist");
        }

        /// <summary>
        /// Generic constructor.
        /// </summary>
        internal TryCatchFinallyHandler(int tryStart, int tryEnd, int gotoEndLabelIndex, int finallyStart, int finallyEnd, ExceptionHandler[] handlers)
        {
            TryStartIndex = tryStart;
            TryEndIndex = tryEnd;
            FinallyStartIndex = finallyStart;
            FinallyEndIndex = finallyEnd;
            GotoEndTargetIndex = gotoEndLabelIndex;

            _handlers = handlers;

            if (_handlers != null)
            {
                for (int index = 0; index < _handlers.Length; index++)
                {
                    var handler = _handlers[index];
                    handler.SetParent(this);
                }
            }
        }

        /// <summary>
        /// Goto the index of the first instruction of the suitable catch block.
        /// </summary>
        internal int GotoHandler(InterpretedFrame frame, object exception, out ExceptionHandler handler)
        {
            Debug.Assert(_handlers != null, "we should have at least one handler if the method gets called");
            handler = Array.Find(_handlers, t => t.Matches(exception.GetType()));
            if (handler == null) { return 0; }

            return frame.Goto(handler.LabelIndex, exception, gotoExceptionHandler: true);
        }
    }

    /// <summary>
    /// The re-throw instruction will throw this exception.
    /// </summary>
    internal sealed class RethrowException : SystemException
    {
    }

    internal class DebugInfo
    {
        // TODO: readonly

        public int StartLine, EndLine;
        public int Index;
        public string FileName;
        public bool IsClear;
        private static readonly DebugInfoComparer s_debugComparer = new DebugInfoComparer();

        private sealed class DebugInfoComparer : IComparer<DebugInfo>
        {
            // We allow comparison between int and DebugInfo here
            int IComparer<DebugInfo>.Compare(DebugInfo d1, DebugInfo d2)
            {
                if (d1.Index > d2.Index) return 1;
                else if (d1.Index == d2.Index) return 0;
                else return -1;
            }
        }

        public static DebugInfo GetMatchingDebugInfo(DebugInfo[] debugInfos, int index)
        {
            // Create a faked DebugInfo to do the search
            DebugInfo d = new DebugInfo { Index = index };

            // to find the closest debug info before the current index

            int i = Array.BinarySearch<DebugInfo>(debugInfos, d, s_debugComparer);
            if (i < 0)
            {
                // ~i is the index for the first bigger element
                // if there is no bigger element, ~i is the length of the array
                i = ~i;
                if (i == 0)
                {
                    return null;
                }
                // return the last one that is smaller
                i -= 1;
            }

            return debugInfos[i];
        }

        public override string ToString()
        {
            if (IsClear)
            {
                return string.Format(CultureInfo.InvariantCulture, "{0}: clear", Index);
            }
            else
            {
                return string.Format(CultureInfo.InvariantCulture, "{0}: [{1}-{2}] '{3}'", Index, StartLine, EndLine, FileName);
            }
        }
    }

    // TODO:
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Performance", "CA1815:OverrideEqualsAndOperatorEqualsOnValueTypes")]
    internal readonly struct InterpretedFrameInfo
    {
        public readonly string MethodName;

        // TODO:
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Security", "CA2104:DoNotDeclareReadOnlyMutableReferenceTypes")]
        public readonly DebugInfo DebugInfo;

        public InterpretedFrameInfo(string methodName, DebugInfo info)
        {
            MethodName = methodName;
            DebugInfo = info;
        }

        public override string ToString()
        {
            return MethodName + (DebugInfo != null ? ": " + DebugInfo : null);
        }
    }

    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1506:AvoidExcessiveClassCoupling")]
    internal sealed class LightCompiler
    {
        internal const int DefaultCompilationThreshold = 32;

        // zero: sync compilation
        private readonly int _compilationThreshold;

        private readonly InstructionList _instructions;
        private readonly LocalVariables _locals = new LocalVariables();

        private readonly List<DebugInfo> _debugInfos = new List<DebugInfo>();
        private readonly HybridReferenceDictionary<LabelTarget, LabelInfo> _treeLabels = new HybridReferenceDictionary<LabelTarget, LabelInfo>();
        private LabelScopeInfo _labelBlock = new LabelScopeInfo(null, LabelScopeKind.Lambda);

        private readonly Stack<ParameterExpression> _exceptionForRethrowStack = new Stack<ParameterExpression>();

        // Set to true to force compilation of this lambda.
        // This disables the interpreter for this lambda. We still need to
        // walk it, however, to resolve variables closed over from the parent
        // lambdas (because they may be interpreted).
        private bool _forceCompile;

        private readonly LightCompiler _parent;

        private static readonly LocalDefinition[] s_emptyLocals = Array.Empty<LocalDefinition>();

        public LightCompiler(int compilationThreshold)
        {
            _instructions = new InstructionList();
            _compilationThreshold = compilationThreshold < 0 ? DefaultCompilationThreshold : compilationThreshold;
        }

        private LightCompiler(LightCompiler parent)
            : this(parent._compilationThreshold)
        {
            _parent = parent;
        }

        public InstructionList Instructions
        {
            get { return _instructions; }
        }

        public LocalVariables Locals
        {
            get { return _locals; }
        }

        internal static Expression Unbox(Expression strongBoxExpression)
        {
            return Expression.Field(strongBoxExpression, typeof(StrongBox<object>).GetField("Value"));
        }

        public LightDelegateCreator CompileTop(LambdaExpression node)
        {
            for (int index = 0; index < node.Parameters.Count; index++)
            {
                var p = node.Parameters[index];
                var local = _locals.DefineLocal(p, 0);
                _instructions.EmitInitializeParameter(local.Index);
            }

            Compile(node.Body);

            // pop the result of the last expression:
            if (node.Body.Type != typeof(void) && node.ReturnType == typeof(void))
            {
                _instructions.EmitPop();
            }

            Debug.Assert(_instructions.CurrentStackDepth == (node.ReturnType != typeof(void) ? 1 : 0));

            return new LightDelegateCreator(MakeInterpreter(node.Name), node);
        }

        // internal LightDelegateCreator CompileTop(LightLambdaExpression node) {
        //    foreach (var p in node.Parameters) {
        //        var local = _locals.DefineLocal(p, 0);
        //        _instructions.EmitInitializeParameter(local.Index);
        //    }
        //
        //    Compile(node.Body);
        //
        //    // pop the result of the last expression:
        //    if (node.Body.Type != typeof(void) && node.ReturnType == typeof(void)) {
        //        _instructions.EmitPop();
        //    }
        //
        //    Debug.Assert(_instructions.CurrentStackDepth == (node.ReturnType != typeof(void) ? 1 : 0));
        //
        //    return new LightDelegateCreator(MakeInterpreter(node.Name), node);
        // }

        private Interpreter MakeInterpreter(string lambdaName)
        {
            if (_forceCompile)
            {
                return null;
            }

            var debugInfos = _debugInfos.ToArray();
            return new Interpreter(lambdaName, _locals, GetBranchMapping(), _instructions.ToArray(), debugInfos, _compilationThreshold);
        }

        private void CompileConstantExpression(Expression expr)
        {
            var node = (ConstantExpression)expr;
            _instructions.EmitLoad(node.Value, node.Type);
        }

        private void CompileDefaultExpression(Expression expr)
        {
            CompileDefaultExpression(expr.Type);
        }

        private void CompileDefaultExpression(Type type)
        {
            if (type != typeof(void))
            {
                if (type.IsValueType)
                {
                    object value = ScriptingRuntimeHelpers.GetPrimitiveDefaultValue(type);
                    if (value != null)
                    {
                        _instructions.EmitLoad(value);
                    }
                    else
                    {
                        _instructions.EmitDefaultValue(type);
                    }
                }
                else
                {
                    _instructions.EmitLoad(null);
                }
            }
        }

        private LocalVariable EnsureAvailableForClosure(ParameterExpression expr)
        {
            LocalVariable local;
            if (_locals.TryGetLocalOrClosure(expr, out local))
            {
                if (!local.InClosure && !local.IsBoxed)
                {
                    _locals.Box(expr, _instructions);
                }

                return local;
            }
            else if (_parent != null)
            {
                _parent.EnsureAvailableForClosure(expr);
                return _locals.AddClosureVariable(expr);
            }
            else
            {
                throw new InvalidOperationException("unbound variable: " + expr);
            }
        }

        // private void EnsureVariable(ParameterExpression variable) {
        //    if (!_locals.ContainsVariable(variable)) {
        //        EnsureAvailableForClosure(variable);
        //    }
        // }

        private LocalVariable ResolveLocal(ParameterExpression variable)
        {
            LocalVariable local;
            if (!_locals.TryGetLocalOrClosure(variable, out local))
            {
                local = EnsureAvailableForClosure(variable);
            }

            return local;
        }

        public void CompileGetVariable(ParameterExpression variable)
        {
            LocalVariable local = ResolveLocal(variable);

            if (local.InClosure)
            {
                _instructions.EmitLoadLocalFromClosure(local.Index);
            }
            else if (local.IsBoxed)
            {
                _instructions.EmitLoadLocalBoxed(local.Index);
            }
            else
            {
                _instructions.EmitLoadLocal(local.Index);
            }

            _instructions.SetDebugCookie(variable.Name);
        }

        public void CompileGetBoxedVariable(ParameterExpression variable)
        {
            LocalVariable local = ResolveLocal(variable);

            if (local.InClosure)
            {
                _instructions.EmitLoadLocalFromClosureBoxed(local.Index);
            }
            else
            {
                Debug.Assert(local.IsBoxed);
                _instructions.EmitLoadLocal(local.Index);
            }

            _instructions.SetDebugCookie(variable.Name);
        }

        public void CompileSetVariable(ParameterExpression variable, bool isVoid)
        {
            LocalVariable local = ResolveLocal(variable);

            if (local.InClosure)
            {
                if (isVoid)
                {
                    _instructions.EmitStoreLocalToClosure(local.Index);
                }
                else
                {
                    _instructions.EmitAssignLocalToClosure(local.Index);
                }
            }
            else if (local.IsBoxed)
            {
                if (isVoid)
                {
                    _instructions.EmitStoreLocalBoxed(local.Index);
                }
                else
                {
                    _instructions.EmitAssignLocalBoxed(local.Index);
                }
            }
            else
            {
                if (isVoid)
                {
                    _instructions.EmitStoreLocal(local.Index);
                }
                else
                {
                    _instructions.EmitAssignLocal(local.Index);
                }
            }

            _instructions.SetDebugCookie(variable.Name);
        }

        public void CompileParameterExpression(Expression expr)
        {
            var node = (ParameterExpression)expr;
            CompileGetVariable(node);
        }

        private void CompileBlockExpression(Expression expr, bool asVoid)
        {
            var node = (BlockExpression)expr;
            var end = CompileBlockStart(node);

            var lastExpression = node.Expressions[node.Expressions.Count - 1];
            Compile(lastExpression, asVoid);
            CompileBlockEnd(end);
        }

        private LocalDefinition[] CompileBlockStart(BlockExpression node)
        {
            var start = _instructions.Count;

            LocalDefinition[] locals;
            var variables = node.Variables;
            if (variables.Count != 0)
            {
                // TODO: basic flow analysis so we don't have to initialize all
                // variables.
                locals = new LocalDefinition[variables.Count];
                int localCnt = 0;
                for (int index = 0; index < variables.Count; index++)
                {
                    var variable = variables[index];
                    var local = _locals.DefineLocal(variable, start);
                    locals[localCnt++] = local;

                    _instructions.EmitInitializeLocal(local.Index, variable.Type);
                    _instructions.SetDebugCookie(variable.Name);
                }
            }
            else
            {
                locals = s_emptyLocals;
            }

            for (int i = 0; i < node.Expressions.Count - 1; i++)
            {
                CompileAsVoid(node.Expressions[i]);
            }

            return locals;
        }

        private void CompileBlockEnd(LocalDefinition[] locals)
        {
            for (int index = 0; index < locals.Length; index++)
            {
                var local = locals[index];
                _locals.UndefineLocal(local, _instructions.Count);
            }
        }

        private void CompileIndexExpression(Expression expr)
        {
            var index = (IndexExpression)expr;

            // instance:
            if (index.Object != null)
            {
                Compile(index.Object);
            }

            // indexes, byref args not allowed.
            for (int i = 0; i < index.Arguments.Count; i++)
            {
                var arg = index.Arguments[i];
                Compile(arg);
            }

            if (index.Indexer != null)
            {
                _instructions.EmitCall(index.Indexer.GetMethod);
            }
            else if (index.Arguments.Count != 1)
            {
                _instructions.EmitCall(index.Object.Type.GetMethod("Get", BindingFlags.Public | BindingFlags.Instance));
            }
            else
            {
                _instructions.EmitGetArrayItem(index.Object.Type);
            }
        }

        private void CompileIndexAssignment(BinaryExpression node, bool asVoid)
        {
            var index = (IndexExpression)node.Left;

            if (!asVoid)
            {
                throw new NotImplementedException();
            }

            // instance:
            if (index.Object != null)
            {
                Compile(index.Object);
            }

            // indexes, byref args not allowed.
            for (int i = 0; i < index.Arguments.Count; i++)
            {
                var arg = index.Arguments[i];
                Compile(arg);
            }

            // value:
            Compile(node.Right);

            if (index.Indexer != null)
            {
                _instructions.EmitCall(index.Indexer.SetMethod);
            }
            else if (index.Arguments.Count != 1)
            {
                _instructions.EmitCall(index.Object.Type.GetMethod("Set", BindingFlags.Public | BindingFlags.Instance));
            }
            else
            {
                _instructions.EmitSetArrayItem(index.Object.Type);
            }
        }

        private void CompileMemberAssignment(BinaryExpression node, bool asVoid)
        {
            var member = (MemberExpression)node.Left;

            PropertyInfo pi = member.Member as PropertyInfo;
            if (pi != null)
            {
                var method = pi.SetMethod;
                if (member.Expression != null)
                {
                    Compile(member.Expression);
                }

                Compile(node.Right);

                int start = _instructions.Count;
                if (!asVoid)
                {
                    LocalDefinition local = _locals.DefineLocal(Expression.Parameter(node.Right.Type), start);
                    _instructions.EmitAssignLocal(local.Index);
                    _instructions.EmitCall(method);
                    _instructions.EmitLoadLocal(local.Index);
                    _locals.UndefineLocal(local, _instructions.Count);
                }
                else
                {
                    _instructions.EmitCall(method);
                }

                return;
            }

            FieldInfo fi = member.Member as FieldInfo;
            if (fi != null)
            {
                if (member.Expression != null)
                {
                    Compile(member.Expression);
                }

                Compile(node.Right);

                int start = _instructions.Count;
                if (!asVoid)
                {
                    LocalDefinition local = _locals.DefineLocal(Expression.Parameter(node.Right.Type), start);
                    _instructions.EmitAssignLocal(local.Index);
                    _instructions.EmitStoreField(fi);
                    _instructions.EmitLoadLocal(local.Index);
                    _locals.UndefineLocal(local, _instructions.Count);
                }
                else
                {
                    _instructions.EmitStoreField(fi);
                }

                return;
            }

            throw new NotImplementedException();
        }

        private void CompileVariableAssignment(BinaryExpression node, bool asVoid)
        {
            this.Compile(node.Right);

            var target = (ParameterExpression)node.Left;
            CompileSetVariable(target, asVoid);
        }

        private void CompileAssignBinaryExpression(Expression expr, bool asVoid)
        {
            var node = (BinaryExpression)expr;

            switch (node.Left.NodeType)
            {
                case ExpressionType.Index:
                    CompileIndexAssignment(node, asVoid);
                    break;

                case ExpressionType.MemberAccess:
                    CompileMemberAssignment(node, asVoid);
                    break;

                case ExpressionType.Parameter:
                case ExpressionType.Extension:
                    CompileVariableAssignment(node, asVoid);
                    break;

                default:
                    throw new InvalidOperationException("Invalid lvalue for assignment: " + node.Left.NodeType);
            }
        }

        private void CompileBinaryExpression(Expression expr)
        {
            var node = (BinaryExpression)expr;

            if (node.Method != null)
            {
                Compile(node.Left);
                Compile(node.Right);
                _instructions.EmitCall(node.Method);
            }
            else
            {
                switch (node.NodeType)
                {
                    case ExpressionType.ArrayIndex:
                        Debug.Assert(node.Right.Type == typeof(int));
                        Compile(node.Left);
                        Compile(node.Right);
                        _instructions.EmitGetArrayItem(node.Left.Type);
                        return;

                    case ExpressionType.Add:
                    case ExpressionType.AddChecked:
                    case ExpressionType.Subtract:
                    case ExpressionType.SubtractChecked:
                    case ExpressionType.Multiply:
                    case ExpressionType.MultiplyChecked:
                    case ExpressionType.Divide:
                        CompileArithmetic(node.NodeType, node.Left, node.Right);
                        return;

                    case ExpressionType.Equal:
                        CompileEqual(node.Left, node.Right);
                        return;

                    case ExpressionType.NotEqual:
                        CompileNotEqual(node.Left, node.Right);
                        return;

                    case ExpressionType.LessThan:
                    case ExpressionType.LessThanOrEqual:
                    case ExpressionType.GreaterThan:
                    case ExpressionType.GreaterThanOrEqual:
                        CompileComparison(node.NodeType, node.Left, node.Right);
                        return;

                    default:
                        throw new NotImplementedException(node.NodeType.ToString());
                }
            }
        }

        private void CompileEqual(Expression left, Expression right)
        {
            Debug.Assert(left.Type == right.Type ||
                         !left.Type.IsValueType && !right.Type.IsValueType);
            Compile(left);
            Compile(right);
            _instructions.EmitEqual(left.Type);
        }

        private void CompileNotEqual(Expression left, Expression right)
        {
            Debug.Assert(left.Type == right.Type ||
                         !left.Type.IsValueType && !right.Type.IsValueType);
            Compile(left);
            Compile(right);
            _instructions.EmitNotEqual(left.Type);
        }

        private void CompileComparison(ExpressionType nodeType, Expression left, Expression right)
        {
            Debug.Assert(left.Type == right.Type && TypeUtils.IsNumeric(left.Type));

            // TODO:
            // if (TypeUtils.IsNullableType(left.Type) && liftToNull) ...

            Compile(left);
            Compile(right);

            switch (nodeType)
            {
                case ExpressionType.LessThan: _instructions.EmitLessThan(left.Type); break;
                case ExpressionType.LessThanOrEqual: _instructions.EmitLessThanOrEqual(left.Type); break;
                case ExpressionType.GreaterThan: _instructions.EmitGreaterThan(left.Type); break;
                case ExpressionType.GreaterThanOrEqual: _instructions.EmitGreaterThanOrEqual(left.Type); break;
                default: throw Assert.Unreachable;
            }
        }

        private void CompileArithmetic(ExpressionType nodeType, Expression left, Expression right)
        {
            Debug.Assert(left.Type == right.Type && TypeUtils.IsArithmetic(left.Type));
            Compile(left);
            Compile(right);
            switch (nodeType)
            {
                case ExpressionType.Add: _instructions.EmitAdd(left.Type, false); break;
                case ExpressionType.AddChecked: _instructions.EmitAdd(left.Type, true); break;
                case ExpressionType.Subtract: _instructions.EmitSub(left.Type, false); break;
                case ExpressionType.SubtractChecked: _instructions.EmitSub(left.Type, true); break;
                case ExpressionType.Multiply: _instructions.EmitMul(left.Type, false); break;
                case ExpressionType.MultiplyChecked: _instructions.EmitMul(left.Type, true); break;
                case ExpressionType.Divide: _instructions.EmitDiv(left.Type); break;
                default: throw Assert.Unreachable;
            }
        }

        private void CompileConvertUnaryExpression(Expression expr)
        {
            var node = (UnaryExpression)expr;
            if (node.Method != null)
            {
                Compile(node.Operand);

                // We should be able to ignore Int32ToObject
                if (node.Method != ScriptingRuntimeHelpers.Int32ToObjectMethod)
                {
                    _instructions.EmitCall(node.Method);
                }
            }
            else if (node.Type == typeof(void))
            {
                CompileAsVoid(node.Operand);
            }
            else
            {
                Compile(node.Operand);
                CompileConvertToType(node.Operand.Type, node.Type, node.NodeType == ExpressionType.ConvertChecked);
            }
        }

        private void CompileConvertToType(Type typeFrom, Type typeTo, bool isChecked)
        {
            Debug.Assert(typeFrom != typeof(void) && typeTo != typeof(void));

            if (typeTo == typeFrom)
            {
                return;
            }

            TypeCode from = typeFrom.GetTypeCode();
            TypeCode to = typeTo.GetTypeCode();
            if (TypeUtils.IsNumeric(from) && TypeUtils.IsNumeric(to))
            {
                if (isChecked)
                {
                    _instructions.EmitNumericConvertChecked(from, to);
                }
                else
                {
                    _instructions.EmitNumericConvertUnchecked(from, to);
                }

                return;
            }

            // TODO: Conversions to a super-class or implemented interfaces are no-op.
            // A conversion to a non-implemented interface or an unrelated class, etc. should fail.
            return;
        }

        private void CompileNotExpression(UnaryExpression node)
        {
            if (node.Operand.Type == typeof(bool))
            {
                Compile(node.Operand);
                _instructions.EmitNot();
            }
            else
            {
                throw new NotImplementedException();
            }
        }

        private void CompileUnaryExpression(Expression expr)
        {
            var node = (UnaryExpression)expr;

            if (node.Method != null)
            {
                Compile(node.Operand);
                _instructions.EmitCall(node.Method);
            }
            else
            {
                switch (node.NodeType)
                {
                    case ExpressionType.Not:
                        CompileNotExpression(node);
                        return;
                    case ExpressionType.TypeAs:
                        CompileTypeAsExpression(node);
                        return;
                    default:
                        throw new NotImplementedException(node.NodeType.ToString());
                }
            }
        }

        private void CompileAndAlsoBinaryExpression(Expression expr)
        {
            CompileLogicalBinaryExpression(expr, true);
        }

        private void CompileOrElseBinaryExpression(Expression expr)
        {
            CompileLogicalBinaryExpression(expr, false);
        }

        private void CompileLogicalBinaryExpression(Expression expr, bool andAlso)
        {
            var node = (BinaryExpression)expr;
            if (node.Method != null)
            {
                throw new NotImplementedException();
            }

            Debug.Assert(node.Left.Type == node.Right.Type);

            if (node.Left.Type == typeof(bool))
            {
                var elseLabel = _instructions.MakeLabel();
                var endLabel = _instructions.MakeLabel();
                Compile(node.Left);
                if (andAlso)
                {
                    _instructions.EmitBranchFalse(elseLabel);
                }
                else
                {
                    _instructions.EmitBranchTrue(elseLabel);
                }

                Compile(node.Right);
                _instructions.EmitBranch(endLabel, false, true);
                _instructions.MarkLabel(elseLabel);
                _instructions.EmitLoad(!andAlso);
                _instructions.MarkLabel(endLabel);
                return;
            }

            Debug.Assert(node.Left.Type == typeof(bool?));
            throw new NotImplementedException();
        }

        private void CompileConditionalExpression(Expression expr, bool asVoid)
        {
            var node = (ConditionalExpression)expr;
            Compile(node.Test);

            if (node.IfTrue == AstUtils.Empty())
            {
                var endOfFalse = _instructions.MakeLabel();
                _instructions.EmitBranchTrue(endOfFalse);
                Compile(node.IfFalse, asVoid);
                _instructions.MarkLabel(endOfFalse);
            }
            else
            {
                var endOfTrue = _instructions.MakeLabel();
                _instructions.EmitBranchFalse(endOfTrue);
                Compile(node.IfTrue, asVoid);

                if (node.IfFalse != AstUtils.Empty())
                {
                    var endOfFalse = _instructions.MakeLabel();
                    _instructions.EmitBranch(endOfFalse, false, !asVoid);
                    _instructions.MarkLabel(endOfTrue);
                    Compile(node.IfFalse, asVoid);
                    _instructions.MarkLabel(endOfFalse);
                }
                else
                {
                    _instructions.MarkLabel(endOfTrue);
                }
            }
        }

        #region Loops

        private static void CompileLoopExpression(Expression expr)
        {
            //    var node = (LoopExpression)expr;
            //    var enterLoop = new EnterLoopInstruction(node, _locals, _compilationThreshold, _instructions.Count);
            //
            //    PushLabelBlock(LabelScopeKind.Statement);
            //    LabelInfo breakLabel = DefineLabel(node.BreakLabel);
            //    LabelInfo continueLabel = DefineLabel(node.ContinueLabel);
            //
            //    _instructions.MarkLabel(continueLabel.GetLabel(this));
            //
            //    // emit loop body:
            //    _instructions.Emit(enterLoop);
            //    CompileAsVoid(node.Body);
            //
            //    // emit loop branch:
            //    _instructions.EmitBranch(continueLabel.GetLabel(this), expr.Type != typeof(void), false);
            //
            //    _instructions.MarkLabel(breakLabel.GetLabel(this));
            //
            //    PopLabelBlock(LabelScopeKind.Statement);
            //
            //    enterLoop.FinishLoop(_instructions.Count);
        }

        #endregion

        private void CompileSwitchExpression(Expression expr)
        {
            var node = (SwitchExpression)expr;

            // Currently only supports int test values, with no method
            if (node.SwitchValue.Type != typeof(int) || node.Comparison != null)
            {
                throw new NotImplementedException();
            }

            // Test values must be constant
            if (!node.Cases.All(static c => c.TestValues.All(t => t is ConstantExpression)))
            {
                throw new NotImplementedException();
            }

            LabelInfo end = DefineLabel(null);
            bool hasValue = node.Type != typeof(void);

            Compile(node.SwitchValue);
            var caseDict = new Dictionary<int, int>();
            int switchIndex = _instructions.Count;
            _instructions.EmitSwitch(caseDict);

            if (node.DefaultBody != null)
            {
                Compile(node.DefaultBody);
            }
            else
            {
                Debug.Assert(!hasValue);
            }

            _instructions.EmitBranch(end.GetLabel(this), false, hasValue);

            for (int i = 0; i < node.Cases.Count; i++)
            {
                var switchCase = node.Cases[i];

                int caseOffset = _instructions.Count - switchIndex;
                for (int index = 0; index < switchCase.TestValues.Count; index++)
                {
                    var testValue = (ConstantExpression)switchCase.TestValues[index];
                    caseDict[(int)testValue.Value] = caseOffset;
                }

                Compile(switchCase.Body);

                if (i < node.Cases.Count - 1)
                {
                    _instructions.EmitBranch(end.GetLabel(this), false, hasValue);
                }
            }

            _instructions.MarkLabel(end.GetLabel(this));
        }

        private void CompileLabelExpression(Expression expr)
        {
            var node = (LabelExpression)expr;

            // If we're an immediate child of a block, our label will already
            // be defined. If not, we need to define our own block so this
            // label isn't exposed except to its own child expression.
            LabelInfo label = null;

            if (_labelBlock.Kind == LabelScopeKind.Block)
            {
                _labelBlock.TryGetLabelInfo(node.Target, out label);

                // We're in a block but didn't find our label, try switch
                if (label == null && _labelBlock.Parent.Kind == LabelScopeKind.Switch)
                {
                    _labelBlock.Parent.TryGetLabelInfo(node.Target, out label);
                }

                // if we're in a switch or block, we should've found the label
                Debug.Assert(label != null);
            }

            label ??= DefineLabel(node.Target);

            if (node.DefaultValue != null)
            {
                if (node.Target.Type == typeof(void))
                {
                    CompileAsVoid(node.DefaultValue);
                }
                else
                {
                    Compile(node.DefaultValue);
                }
            }

            _instructions.MarkLabel(label.GetLabel(this));
        }

        private void CompileGotoExpression(Expression expr)
        {
            var node = (GotoExpression)expr;
            var labelInfo = ReferenceLabel(node.Target);

            if (node.Value != null)
            {
                Compile(node.Value);
            }

            _instructions.EmitGoto(labelInfo.GetLabel(this), node.Type != typeof(void), node.Value != null && node.Value.Type != typeof(void));
        }

        public BranchLabel GetBranchLabel(LabelTarget target)
        {
            return ReferenceLabel(target).GetLabel(this);
        }

        public void PushLabelBlock(LabelScopeKind type)
        {
            _labelBlock = new LabelScopeInfo(_labelBlock, type);
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "kind")]
        public void PopLabelBlock(LabelScopeKind kind)
        {
            Debug.Assert(_labelBlock != null && _labelBlock.Kind == kind);
            _labelBlock = _labelBlock.Parent;
        }

        private LabelInfo EnsureLabel(LabelTarget node)
        {
            LabelInfo result;
            if (!_treeLabels.TryGetValue(node, out result))
            {
                _treeLabels[node] = result = new LabelInfo(node);
            }

            return result;
        }

        private LabelInfo ReferenceLabel(LabelTarget node)
        {
            LabelInfo result = EnsureLabel(node);
            result.Reference(_labelBlock);
            return result;
        }

        internal LabelInfo DefineLabel(LabelTarget node)
        {
            if (node == null)
            {
                return new LabelInfo(null);
            }

            LabelInfo result = EnsureLabel(node);
            result.Define(_labelBlock);
            return result;
        }

        private bool TryPushLabelBlock(Expression node)
        {
            // Anything that is "statement-like" -- e.g. has no associated
            // stack state can be jumped into, with the exception of try-blocks
            // We indicate this by a "Block"
            //
            // Otherwise, we push an "Expression" to indicate that it can't be
            // jumped into
            switch (node.NodeType)
            {
                default:
                    if (_labelBlock.Kind != LabelScopeKind.Expression)
                    {
                        PushLabelBlock(LabelScopeKind.Expression);
                        return true;
                    }

                    return false;
                case ExpressionType.Label:
                    // LabelExpression is a bit special, if it's directly in a
                    // block it becomes associate with the block's scope. Same
                    // thing if it's in a switch case body.
                    if (_labelBlock.Kind == LabelScopeKind.Block)
                    {
                        var label = ((LabelExpression)node).Target;
                        if (_labelBlock.ContainsTarget(label))
                        {
                            return false;
                        }

                        if (_labelBlock.Parent.Kind == LabelScopeKind.Switch &&
                            _labelBlock.Parent.ContainsTarget(label))
                        {
                            return false;
                        }
                    }

                    PushLabelBlock(LabelScopeKind.Statement);
                    return true;
                case ExpressionType.Block:
                    PushLabelBlock(LabelScopeKind.Block);
                    // Labels defined immediately in the block are valid for
                    // the whole block.
                    if (_labelBlock.Parent.Kind != LabelScopeKind.Switch)
                    {
                        DefineBlockLabels(node);
                    }

                    return true;
                case ExpressionType.Switch:
                    PushLabelBlock(LabelScopeKind.Switch);
                    // Define labels inside of the switch cases so they are in
                    // scope for the whole switch. This allows "goto case" and
                    // "goto default" to be considered as local jumps.
                    var @switch = (SwitchExpression)node;
                    for (int index = 0; index < @switch.Cases.Count; index++)
                    {
                        SwitchCase c = @switch.Cases[index];
                        DefineBlockLabels(c.Body);
                    }

                    DefineBlockLabels(@switch.DefaultBody);
                    return true;

                // Remove this when Convert(Void) goes away.
                case ExpressionType.Convert:
                    if (node.Type != typeof(void))
                    {
                        // treat it as an expression
                        goto default;
                    }

                    PushLabelBlock(LabelScopeKind.Statement);
                    return true;

                case ExpressionType.Conditional:
                case ExpressionType.Loop:
                case ExpressionType.Goto:
                    PushLabelBlock(LabelScopeKind.Statement);
                    return true;
            }
        }

        private void DefineBlockLabels(Expression node)
        {
            if (node is not BlockExpression block)
            {
                return;
            }

            for (int i = 0, n = block.Expressions.Count; i < n; i++)
            {
                Expression e = block.Expressions[i];

                var label = e as LabelExpression;
                if (label != null)
                {
                    DefineLabel(label.Target);
                }
            }
        }

        private HybridReferenceDictionary<LabelTarget, BranchLabel> GetBranchMapping()
        {
            var newLabelMapping = new HybridReferenceDictionary<LabelTarget, BranchLabel>(_treeLabels.Count);
            foreach (var kvp in _treeLabels)
            {
                newLabelMapping[kvp.Key] = kvp.Value.GetLabel(this);
            }

            return newLabelMapping;
        }

        private void CompileThrowUnaryExpression(Expression expr, bool asVoid)
        {
            var node = (UnaryExpression)expr;

            if (node.Operand == null)
            {
                CompileParameterExpression(_exceptionForRethrowStack.Peek());
                if (asVoid)
                {
                    _instructions.EmitRethrowVoid();
                }
                else
                {
                    _instructions.EmitRethrow();
                }
            }
            else
            {
                Compile(node.Operand);
                if (asVoid)
                {
                    _instructions.EmitThrowVoid();
                }
                else
                {
                    _instructions.EmitThrow();
                }
            }
        }

        // TODO: remove (replace by true fault support)
        private static bool EndsWithRethrow(Expression expr)
        {
            if (expr.NodeType == ExpressionType.Throw)
            {
                var node = (UnaryExpression)expr;
                return node.Operand == null;
            }

            BlockExpression block = expr as BlockExpression;
            if (block != null)
            {
                return EndsWithRethrow(block.Expressions[block.Expressions.Count - 1]);
            }

            return false;
        }

        // TODO: remove (replace by true fault support)
        private void CompileAsVoidRemoveRethrow(Expression expr)
        {
            int stackDepth = _instructions.CurrentStackDepth;

            if (expr.NodeType == ExpressionType.Throw)
            {
                Debug.Assert(((UnaryExpression)expr).Operand == null);
                return;
            }

            var node = (BlockExpression)expr;
            var end = CompileBlockStart(node);

            CompileAsVoidRemoveRethrow(node.Expressions[node.Expressions.Count - 1]);

            Debug.Assert(stackDepth == _instructions.CurrentStackDepth);

            CompileBlockEnd(end);
        }

        private void CompileTryExpression(Expression expr)
        {
            var node = (TryExpression)expr;

            BranchLabel end = _instructions.MakeLabel();
            BranchLabel gotoEnd = _instructions.MakeLabel();
            int tryStart = _instructions.Count;

            BranchLabel startOfFinally = null;
            if (node.Finally != null)
            {
                startOfFinally = _instructions.MakeLabel();
                _instructions.EmitEnterTryFinally(startOfFinally);
            }
            else
            {
                _instructions.EmitEnterTryCatch();
            }

            List<ExceptionHandler> exHandlers = null;
            var enterTryInstr = _instructions.GetInstruction(tryStart) as EnterTryCatchFinallyInstruction;
            Debug.Assert(enterTryInstr != null);

            PushLabelBlock(LabelScopeKind.Try);
            Compile(node.Body);

            bool hasValue = node.Body.Type != typeof(void);
            int tryEnd = _instructions.Count;

            // handlers jump here:
            _instructions.MarkLabel(gotoEnd);
            _instructions.EmitGoto(end, hasValue, hasValue);

            // keep the result on the stack:
            if (node.Handlers.Count > 0)
            {
                exHandlers = new List<ExceptionHandler>();

                // TODO: emulates faults (replace by true fault support)
                if (node.Finally == null && node.Handlers.Count == 1)
                {
                    var handler = node.Handlers[0];
                    if (handler.Filter == null && handler.Test == typeof(Exception) && handler.Variable == null)
                    {
                        if (EndsWithRethrow(handler.Body))
                        {
                            if (hasValue)
                            {
                                _instructions.EmitEnterExceptionHandlerNonVoid();
                            }
                            else
                            {
                                _instructions.EmitEnterExceptionHandlerVoid();
                            }

                            // at this point the stack balance is prepared for the hidden exception variable:
                            int handlerLabel = _instructions.MarkRuntimeLabel();
                            int handlerStart = _instructions.Count;

                            CompileAsVoidRemoveRethrow(handler.Body);
                            _instructions.EmitLeaveFault(hasValue);
                            _instructions.MarkLabel(end);

                            exHandlers.Add(new ExceptionHandler(tryStart, tryEnd, handlerLabel, handlerStart, _instructions.Count, null));
                            enterTryInstr.SetTryHandler(new TryCatchFinallyHandler(tryStart, tryEnd, gotoEnd.TargetIndex, exHandlers.ToArray()));
                            PopLabelBlock(LabelScopeKind.Try);
                            return;
                        }
                    }
                }

                for (int index = 0; index < node.Handlers.Count; index++)
                {
                    var handler = node.Handlers[index];
                    PushLabelBlock(LabelScopeKind.Catch);

                    if (handler.Filter != null)
                    {
                        // PushLabelBlock(LabelScopeKind.Filter);
                        throw new NotImplementedException();
                        // PopLabelBlock(LabelScopeKind.Filter);
                    }

                    var parameter = handler.Variable ?? Expression.Parameter(handler.Test);

                    var local = _locals.DefineLocal(parameter, _instructions.Count);
                    _exceptionForRethrowStack.Push(parameter);

                    // add a stack balancing nop instruction (exception handling pushes the current exception):
                    if (hasValue)
                    {
                        _instructions.EmitEnterExceptionHandlerNonVoid();
                    }
                    else
                    {
                        _instructions.EmitEnterExceptionHandlerVoid();
                    }

                    // at this point the stack balance is prepared for the hidden exception variable:
                    int handlerLabel = _instructions.MarkRuntimeLabel();
                    int handlerStart = _instructions.Count;

                    CompileSetVariable(parameter, true);
                    Compile(handler.Body);

                    _exceptionForRethrowStack.Pop();

                    // keep the value of the body on the stack:
                    Debug.Assert(hasValue == (handler.Body.Type != typeof(void)));
                    _instructions.EmitLeaveExceptionHandler(hasValue, gotoEnd);

                    exHandlers.Add(new ExceptionHandler(tryStart, tryEnd, handlerLabel, handlerStart,
                                                        _instructions.Count, handler.Test));
                    PopLabelBlock(LabelScopeKind.Catch);

                    _locals.UndefineLocal(local, _instructions.Count);
                }

                if (node.Fault != null)
                {
                    throw new NotImplementedException();
                }
            }

            if (node.Finally != null)
            {
                Debug.Assert(startOfFinally != null);
                PushLabelBlock(LabelScopeKind.Finally);

                _instructions.MarkLabel(startOfFinally);
                _instructions.EmitEnterFinally(startOfFinally);
                CompileAsVoid(node.Finally);
                _instructions.EmitLeaveFinally();

                enterTryInstr.SetTryHandler(
                    new TryCatchFinallyHandler(tryStart, tryEnd, gotoEnd.TargetIndex,
                        startOfFinally.TargetIndex, _instructions.Count,
                        exHandlers?.ToArray()));
                PopLabelBlock(LabelScopeKind.Finally);
            }
            else
            {
                Debug.Assert(exHandlers != null);
                enterTryInstr.SetTryHandler(
                    new TryCatchFinallyHandler(tryStart, tryEnd, gotoEnd.TargetIndex, exHandlers.ToArray()));
            }

            _instructions.MarkLabel(end);

            PopLabelBlock(LabelScopeKind.Try);
        }

        private void CompileDynamicExpression(Expression expr)
        {
            var node = (DynamicExpression)expr;

            for (int index = 0; index < node.Arguments.Count; index++)
            {
                var arg = node.Arguments[index];
                Compile(arg);
            }

            _instructions.EmitDynamic(node.DelegateType, node.Binder);
        }

        private void CompileMethodCallExpression(Expression expr)
        {
            var node = (MethodCallExpression)expr;

            var parameters = node.Method.GetParameters();

            // TODO:
            // Support pass by reference.
            // Note that LoopCompiler needs to be updated too.

            // force compilation for now for ref types
            // also could be a mutable value type, Delegate.CreateDelegate and MethodInfo.Invoke both can't handle this, we
            // need to generate code.
            var declaringType = node.Method.DeclaringType;
            if (!parameters.TrueForAll(static p => !p.ParameterType.IsByRef) ||
                (!node.Method.IsStatic && declaringType.IsValueType && !declaringType.IsPrimitive))
            {
                _forceCompile = true;
            }

            if (!node.Method.IsStatic)
            {
                Compile(node.Object);
            }

            for (int index = 0; index < node.Arguments.Count; index++)
            {
                var arg = node.Arguments[index];
                Compile(arg);
            }

            _instructions.EmitCall(node.Method, parameters);
        }

        private void CompileNewExpression(Expression expr)
        {
            var node = (NewExpression)expr;

            if (node.Constructor != null)
            {
                var parameters = node.Constructor.GetParameters();
                if (!parameters.TrueForAll(static p => !p.ParameterType.IsByRef))
                {
                    _forceCompile = true;
                }
            }

            if (node.Constructor != null)
            {
                for (int index = 0; index < node.Arguments.Count; index++)
                {
                    var arg = node.Arguments[index];
                    this.Compile(arg);
                }

                _instructions.EmitNew(node.Constructor);
            }
            else
            {
                Debug.Assert(expr.Type.IsValueType);
                _instructions.EmitDefaultValue(node.Type);
            }
        }

        private void CompileMemberExpression(Expression expr)
        {
            var node = (MemberExpression)expr;

            var member = node.Member;
            FieldInfo fi = member as FieldInfo;
            if (fi != null)
            {
                if (fi.IsLiteral)
                {
                    _instructions.EmitLoad(fi.GetValue(null), fi.FieldType);
                }
                else if (fi.IsStatic)
                {
                    if (fi.IsInitOnly)
                    {
                        _instructions.EmitLoad(fi.GetValue(null), fi.FieldType);
                    }
                    else
                    {
                        _instructions.EmitLoadField(fi);
                    }
                }
                else
                {
                    Compile(node.Expression);
                    _instructions.EmitLoadField(fi);
                }

                return;
            }

            PropertyInfo pi = member as PropertyInfo;
            if (pi != null)
            {
                var method = pi.GetMethod;
                if (node.Expression != null)
                {
                    Compile(node.Expression);
                }

                _instructions.EmitCall(method);
                return;
            }

            throw new System.NotImplementedException();
        }

        private void CompileNewArrayExpression(Expression expr)
        {
            var node = (NewArrayExpression)expr;

            for (int index = 0; index < node.Expressions.Count; index++)
            {
                var arg = node.Expressions[index];
                Compile(arg);
            }

            Type elementType = node.Type.GetElementType();
            int rank = node.Expressions.Count;

            if (node.NodeType == ExpressionType.NewArrayInit)
            {
                _instructions.EmitNewArrayInit(elementType, rank);
            }
            else if (node.NodeType == ExpressionType.NewArrayBounds)
            {
                if (rank == 1)
                {
                    _instructions.EmitNewArray(elementType);
                }
                else
                {
                    _instructions.EmitNewArrayBounds(elementType, rank);
                }
            }
            else
            {
                throw new System.NotImplementedException();
            }
        }

        private void CompileExtensionExpression(Expression expr)
        {
            var instructionProvider = expr as IInstructionProvider;
            if (instructionProvider != null)
            {
                instructionProvider.AddInstructions(this);
                return;
            }

            if (expr.CanReduce)
            {
                Compile(expr.Reduce());
            }
            else
            {
                throw new System.NotImplementedException();
            }
        }

        private void CompileDebugInfoExpression(Expression expr)
        {
            var node = (DebugInfoExpression)expr;
            int start = _instructions.Count;
            var info = new DebugInfo()
            {
                Index = start,
                FileName = node.Document.FileName,
                StartLine = node.StartLine,
                EndLine = node.EndLine,
                IsClear = node.IsClear
            };
            _debugInfos.Add(info);
        }

        private void CompileRuntimeVariablesExpression(Expression expr)
        {
            // Generates IRuntimeVariables for all requested variables
            var node = (RuntimeVariablesExpression)expr;
            for (int index = 0; index < node.Variables.Count; index++)
            {
                var variable = node.Variables[index];
                EnsureAvailableForClosure(variable);
                CompileGetBoxedVariable(variable);
            }

            _instructions.EmitNewRuntimeVariables(node.Variables.Count);
        }

        private void CompileLambdaExpression(Expression expr)
        {
            var node = (LambdaExpression)expr;
            var compiler = new LightCompiler(this);
            var creator = compiler.CompileTop(node);

            if (compiler._locals.ClosureVariables != null)
            {
                foreach (ParameterExpression variable in compiler._locals.ClosureVariables.Keys)
                {
                    CompileGetBoxedVariable(variable);
                }
            }

            _instructions.EmitCreateDelegate(creator);
        }

        private void CompileCoalesceBinaryExpression(Expression expr)
        {
            var node = (BinaryExpression)expr;

            if (TypeUtils.IsNullableType(node.Left.Type))
            {
                throw new NotImplementedException();
            }
            else if (node.Conversion != null)
            {
                throw new NotImplementedException();
            }
            else
            {
                var leftNotNull = _instructions.MakeLabel();
                Compile(node.Left);
                _instructions.EmitCoalescingBranch(leftNotNull);
                _instructions.EmitPop();
                Compile(node.Right);
                _instructions.MarkLabel(leftNotNull);
            }
        }

        private void CompileInvocationExpression(Expression expr)
        {
            var node = (InvocationExpression)expr;

            // TODO: LambdaOperand optimization (see compiler)
            if (typeof(LambdaExpression).IsAssignableFrom(node.Expression.Type))
            {
                throw new System.NotImplementedException();
            }

            // TODO: do not create a new Call Expression
            // if (PlatformAdaptationLayer.IsCompactFramework) {
            //    // Workaround for a bug in Compact Framework
            //    Compile(
            //        AstUtils.Convert(
            //            Expression.Call(
            //                node.Expression,
            //                node.Expression.Type.GetMethod("DynamicInvoke"),
            //                Expression.NewArrayInit(typeof(object), node.Arguments.Map((e) => AstUtils.Convert(e, typeof(object))))
            //            ),
            //            node.Type
            //        )
            //    );
            // } else {
            CompileMethodCallExpression(Expression.Call(node.Expression, node.Expression.Type.GetMethod("Invoke"), node.Arguments));
            // }
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "expr")]
        private void CompileListInitExpression(Expression expr)
        {
            throw new System.NotImplementedException();
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "expr")]
        private void CompileMemberInitExpression(Expression expr)
        {
            throw new System.NotImplementedException();
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "expr")]
        private void CompileQuoteUnaryExpression(Expression expr)
        {
            throw new System.NotImplementedException();
        }

        private void CompileUnboxUnaryExpression(Expression expr)
        {
            var node = (UnaryExpression)expr;
            // unboxing is a nop:
            Compile(node.Operand);
        }

        private void CompileTypeEqualExpression(Expression expr)
        {
            Debug.Assert(expr.NodeType == ExpressionType.TypeEqual);
            var node = (TypeBinaryExpression)expr;

            Compile(node.Expression);
            _instructions.EmitLoad(node.TypeOperand);
            _instructions.EmitTypeEquals();
        }

        private void CompileTypeAsExpression(UnaryExpression node)
        {
            Compile(node.Operand);
            _instructions.EmitTypeAs(node.Type);
        }

        private void CompileTypeIsExpression(Expression expr)
        {
            Debug.Assert(expr.NodeType == ExpressionType.TypeIs);
            var node = (TypeBinaryExpression)expr;

            Compile(node.Expression);

            // use TypeEqual for sealed types:
            if (node.TypeOperand.IsSealed)
            {
                _instructions.EmitLoad(node.TypeOperand);
                _instructions.EmitTypeEquals();
            }
            else
            {
                _instructions.EmitTypeIs(node.TypeOperand);
            }
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "expr")]
        private void CompileReducibleExpression(Expression expr)
        {
            throw new System.NotImplementedException();
        }

        internal void Compile(Expression expr, bool asVoid)
        {
            if (asVoid)
            {
                CompileAsVoid(expr);
            }
            else
            {
                Compile(expr);
            }
        }

        internal void CompileAsVoid(Expression expr)
        {
            bool pushLabelBlock = TryPushLabelBlock(expr);
            int startingStackDepth = _instructions.CurrentStackDepth;
            switch (expr.NodeType)
            {
                case ExpressionType.Assign:
                    CompileAssignBinaryExpression(expr, true);
                    break;

                case ExpressionType.Block:
                    CompileBlockExpression(expr, true);
                    break;

                case ExpressionType.Throw:
                    CompileThrowUnaryExpression(expr, true);
                    break;

                case ExpressionType.Constant:
                case ExpressionType.Default:
                case ExpressionType.Parameter:
                    // no-op
                    break;

                default:
                    CompileNoLabelPush(expr);
                    if (expr.Type != typeof(void))
                    {
                        _instructions.EmitPop();
                    }

                    break;
            }

            Debug.Assert(_instructions.CurrentStackDepth == startingStackDepth);
            if (pushLabelBlock)
            {
                PopLabelBlock(_labelBlock.Kind);
            }
        }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity")]
        private void CompileNoLabelPush(Expression expr)
        {
            int startingStackDepth = _instructions.CurrentStackDepth;
            switch (expr.NodeType)
            {
                case ExpressionType.Add: CompileBinaryExpression(expr); break;
                case ExpressionType.AddChecked: CompileBinaryExpression(expr); break;
                case ExpressionType.And: CompileBinaryExpression(expr); break;
                case ExpressionType.AndAlso: CompileAndAlsoBinaryExpression(expr); break;
                case ExpressionType.ArrayLength: CompileUnaryExpression(expr); break;
                case ExpressionType.ArrayIndex: CompileBinaryExpression(expr); break;
                case ExpressionType.Call: CompileMethodCallExpression(expr); break;
                case ExpressionType.Coalesce: CompileCoalesceBinaryExpression(expr); break;
                case ExpressionType.Conditional: CompileConditionalExpression(expr, expr.Type == typeof(void)); break;
                case ExpressionType.Constant: CompileConstantExpression(expr); break;
                case ExpressionType.Convert: CompileConvertUnaryExpression(expr); break;
                case ExpressionType.ConvertChecked: CompileConvertUnaryExpression(expr); break;
                case ExpressionType.Divide: CompileBinaryExpression(expr); break;
                case ExpressionType.Equal: CompileBinaryExpression(expr); break;
                case ExpressionType.ExclusiveOr: CompileBinaryExpression(expr); break;
                case ExpressionType.GreaterThan: CompileBinaryExpression(expr); break;
                case ExpressionType.GreaterThanOrEqual: CompileBinaryExpression(expr); break;
                case ExpressionType.Invoke: CompileInvocationExpression(expr); break;
                case ExpressionType.Lambda: CompileLambdaExpression(expr); break;
                case ExpressionType.LeftShift: CompileBinaryExpression(expr); break;
                case ExpressionType.LessThan: CompileBinaryExpression(expr); break;
                case ExpressionType.LessThanOrEqual: CompileBinaryExpression(expr); break;
                case ExpressionType.ListInit: CompileListInitExpression(expr); break;
                case ExpressionType.MemberAccess: CompileMemberExpression(expr); break;
                case ExpressionType.MemberInit: CompileMemberInitExpression(expr); break;
                case ExpressionType.Modulo: CompileBinaryExpression(expr); break;
                case ExpressionType.Multiply: CompileBinaryExpression(expr); break;
                case ExpressionType.MultiplyChecked: CompileBinaryExpression(expr); break;
                case ExpressionType.Negate: CompileUnaryExpression(expr); break;
                case ExpressionType.UnaryPlus: CompileUnaryExpression(expr); break;
                case ExpressionType.NegateChecked: CompileUnaryExpression(expr); break;
                case ExpressionType.New: CompileNewExpression(expr); break;
                case ExpressionType.NewArrayInit: CompileNewArrayExpression(expr); break;
                case ExpressionType.NewArrayBounds: CompileNewArrayExpression(expr); break;
                case ExpressionType.Not: CompileUnaryExpression(expr); break;
                case ExpressionType.NotEqual: CompileBinaryExpression(expr); break;
                case ExpressionType.Or: CompileBinaryExpression(expr); break;
                case ExpressionType.OrElse: CompileOrElseBinaryExpression(expr); break;
                case ExpressionType.Parameter: CompileParameterExpression(expr); break;
                case ExpressionType.Power: CompileBinaryExpression(expr); break;
                case ExpressionType.Quote: CompileQuoteUnaryExpression(expr); break;
                case ExpressionType.RightShift: CompileBinaryExpression(expr); break;
                case ExpressionType.Subtract: CompileBinaryExpression(expr); break;
                case ExpressionType.SubtractChecked: CompileBinaryExpression(expr); break;
                case ExpressionType.TypeAs: CompileUnaryExpression(expr); break;
                case ExpressionType.TypeIs: CompileTypeIsExpression(expr); break;
                case ExpressionType.Assign: CompileAssignBinaryExpression(expr, expr.Type == typeof(void)); break;
                case ExpressionType.Block: CompileBlockExpression(expr, expr.Type == typeof(void)); break;
                case ExpressionType.DebugInfo: CompileDebugInfoExpression(expr); break;
                case ExpressionType.Decrement: CompileUnaryExpression(expr); break;
                case ExpressionType.Dynamic: CompileDynamicExpression(expr); break;
                case ExpressionType.Default: CompileDefaultExpression(expr); break;
                case ExpressionType.Extension: CompileExtensionExpression(expr); break;
                case ExpressionType.Goto: CompileGotoExpression(expr); break;
                case ExpressionType.Increment: CompileUnaryExpression(expr); break;
                case ExpressionType.Index: CompileIndexExpression(expr); break;
                case ExpressionType.Label: CompileLabelExpression(expr); break;
                case ExpressionType.RuntimeVariables: CompileRuntimeVariablesExpression(expr); break;
                case ExpressionType.Loop:
                    CompileLoopExpression(expr); break;
                case ExpressionType.Switch: CompileSwitchExpression(expr); break;
                case ExpressionType.Throw: CompileThrowUnaryExpression(expr, expr.Type == typeof(void)); break;
                case ExpressionType.Try: CompileTryExpression(expr); break;
                case ExpressionType.Unbox: CompileUnboxUnaryExpression(expr); break;
                case ExpressionType.TypeEqual: CompileTypeEqualExpression(expr); break;
                case ExpressionType.OnesComplement: CompileUnaryExpression(expr); break;
                case ExpressionType.IsTrue: CompileUnaryExpression(expr); break;
                case ExpressionType.IsFalse: CompileUnaryExpression(expr); break;
                case ExpressionType.AddAssign:
                case ExpressionType.AndAssign:
                case ExpressionType.DivideAssign:
                case ExpressionType.ExclusiveOrAssign:
                case ExpressionType.LeftShiftAssign:
                case ExpressionType.ModuloAssign:
                case ExpressionType.MultiplyAssign:
                case ExpressionType.OrAssign:
                case ExpressionType.PowerAssign:
                case ExpressionType.RightShiftAssign:
                case ExpressionType.SubtractAssign:
                case ExpressionType.AddAssignChecked:
                case ExpressionType.MultiplyAssignChecked:
                case ExpressionType.SubtractAssignChecked:
                case ExpressionType.PreIncrementAssign:
                case ExpressionType.PreDecrementAssign:
                case ExpressionType.PostIncrementAssign:
                case ExpressionType.PostDecrementAssign:
                    CompileReducibleExpression(expr); break;
                default: throw Assert.Unreachable;
            }
            Debug.Assert(_instructions.CurrentStackDepth == startingStackDepth + (expr.Type == typeof(void) ? 0 : 1));
        }

        public void Compile(Expression expr)
        {
            bool pushLabelBlock = TryPushLabelBlock(expr);
            CompileNoLabelPush(expr);
            if (pushLabelBlock)
            {
                PopLabelBlock(_labelBlock.Kind);
            }
        }
    }
}