mcs/mcs/nullable.cs

   1 //
   2 // nullable.cs: Nullable types support
   3 //
   4 // Authors: Martin Baulig (martin@ximian.com)
   5 //          Miguel de Icaza (miguel@ximian.com)
   6 //          Marek Safar (marek.safar@gmail.com)
   7 //
   8 // Dual licensed under the terms of the MIT X11 or GNU GPL
   9 //
  10 // Copyright 2001, 2002, 2003 Ximian, Inc (http://www.ximian.com)
  11 // Copyright 2004-2008 Novell, Inc
  12 // Copyright 2011 Xamarin Inc
  13 //
  14
  15 using System;
  16 using SLE = System.Linq.Expressions;
  17
  18 #if STATIC
  19 using IKVM.Reflection.Emit;
  20 #else
  21 using System.Reflection.Emit;
  22 #endif
  23
  24 namespace Mono.CSharp.Nullable
  25 {
  26         public class NullableType : TypeExpr
  27         {
  28                 readonly TypeSpec underlying;
  29
  30                 public NullableType (TypeSpec type, Location loc)
  31                 {
  32                         this.underlying = type;
  33                         this.loc = loc;
  34                 }
  35
  36                 public override TypeSpec ResolveAsType (IMemberContext ec, bool allowUnboundTypeArguments = false)
  37                 {
  38                         eclass = ExprClass.Type;
  39
  40                         var otype = ec.Module.PredefinedTypes.Nullable.Resolve ();
  41                         if (otype == null)
  42                                 return null;
  43
  44                         TypeArguments args = new TypeArguments (new TypeExpression (underlying, loc));
  45                         GenericTypeExpr ctype = new GenericTypeExpr (otype, args, loc);
  46
  47                         type = ctype.ResolveAsType (ec);
  48                         return type;
  49                 }
  50         }
  51
  52         static class NullableInfo
  53         {
  54                 public static MethodSpec GetConstructor (TypeSpec nullableType)
  55                 {
  56                         return (MethodSpec) MemberCache.FindMember (nullableType,
  57                                 MemberFilter.Constructor (ParametersCompiled.CreateFullyResolved (GetUnderlyingType (nullableType))), BindingRestriction.DeclaredOnly);
  58                 }
  59
  60                 public static MethodSpec GetHasValue (TypeSpec nullableType)
  61                 {
  62                         return (MethodSpec) MemberCache.FindMember (nullableType,
  63                                 MemberFilter.Method ("get_HasValue", 0, ParametersCompiled.EmptyReadOnlyParameters, null), BindingRestriction.None);
  64                 }
  65
  66                 public static MethodSpec GetGetValueOrDefault (TypeSpec nullableType)
  67                 {
  68                         return (MethodSpec) MemberCache.FindMember (nullableType,
  69                                 MemberFilter.Method ("GetValueOrDefault", 0, ParametersCompiled.EmptyReadOnlyParameters, null), BindingRestriction.None);
  70                 }
  71
  72                 //
  73                 // Don't use unless really required for correctness, see Unwrap::Emit
  74                 //
  75                 public static MethodSpec GetValue (TypeSpec nullableType)
  76                 {
  77                         return (MethodSpec) MemberCache.FindMember (nullableType,
  78                                 MemberFilter.Method ("get_Value", 0, ParametersCompiled.EmptyReadOnlyParameters, null), BindingRestriction.None);
  79                 }
  80
  81                 public static TypeSpec GetUnderlyingType (TypeSpec nullableType)
  82                 {
  83                         return ((InflatedTypeSpec) nullableType).TypeArguments[0];
  84                 }
  85
  86                 public static TypeSpec GetEnumUnderlyingType (ModuleContainer module, TypeSpec nullableEnum)
  87                 {
  88                         return MakeType (module, EnumSpec.GetUnderlyingType (GetUnderlyingType (nullableEnum)));
  89                 }
  90
  91                 public static TypeSpec MakeType (ModuleContainer module, TypeSpec underlyingType)
  92                 {
  93                         return module.PredefinedTypes.Nullable.TypeSpec.MakeGenericType (module,
  94                                 new[] { underlyingType });
  95
  96                 }
  97         }
  98
  99         public class Unwrap : Expression, IMemoryLocation
 100         {
 101                 Expression expr;
 102
 103                 LocalTemporary temp;
 104                 Expression temp_field;
 105                 readonly bool useDefaultValue;
 106
 107                 public Unwrap (Expression expr, bool useDefaultValue = true)
 108                 {
 109                         this.expr = expr;
 110                         this.loc = expr.Location;
 111                         this.useDefaultValue = useDefaultValue;
 112
 113                         type = NullableInfo.GetUnderlyingType (expr.Type);
 114                         eclass = expr.eclass;
 115                 }
 116
 117                 public override bool ContainsEmitWithAwait ()
 118                 {
 119                         return expr.ContainsEmitWithAwait ();
 120                 }
 121
 122                 // TODO: REMOVE
 123                 public static Expression Create (Expression expr)
 124                 {
 125                         //
 126                         // Avoid unwraping and wraping of same type
 127                         //
 128                         Wrap wrap = expr as Wrap;
 129                         if (wrap != null)
 130                                 return wrap.Child;
 131
 132                         return Create (expr, false);
 133                 }
 134
 135                 public static Expression CreateUnwrapped (Expression expr)
 136                 {
 137                         //
 138                         // Avoid unwraping and wraping of same type
 139                         //
 140                         Wrap wrap = expr as Wrap;
 141                         if (wrap != null)
 142                                 return wrap.Child;
 143
 144                         return Create (expr, true);
 145                 }
 146
 147                 public static Unwrap Create (Expression expr, bool useDefaultValue)
 148                 {
 149                         return new Unwrap (expr, useDefaultValue);
 150                 }
 151
 152                 public override Expression CreateExpressionTree (ResolveContext ec)
 153                 {
 154                         return expr.CreateExpressionTree (ec);
 155                 }
 156
 157                 protected override Expression DoResolve (ResolveContext ec)
 158                 {
 159                         return this;
 160                 }
 161
 162                 public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
 163                 {
 164                         expr = expr.DoResolveLValue (ec, right_side);
 165                         return this;
 166                 }
 167
 168                 public override void Emit (EmitContext ec)
 169                 {
 170                         Store (ec);
 171
 172                         var call = new CallEmitter ();
 173                         call.InstanceExpression = this;
 174
 175                         //
 176                         // Using GetGetValueOrDefault is prefered because JIT can possibly
 177                         // inline it whereas Value property contains a throw which is very
 178                         // unlikely to be inlined
 179                         //
 180                         if (useDefaultValue)
 181                                 call.EmitPredefined (ec, NullableInfo.GetGetValueOrDefault (expr.Type), null);
 182                         else
 183                                 call.EmitPredefined (ec, NullableInfo.GetValue (expr.Type), null);
 184                 }
 185
 186                 public void EmitCheck (EmitContext ec)
 187                 {
 188                         Store (ec);
 189
 190                         var call = new CallEmitter ();
 191                         call.InstanceExpression = this;
 192
 193                         call.EmitPredefined (ec, NullableInfo.GetHasValue (expr.Type), null);
 194                 }
 195
 196                 public override void EmitSideEffect (EmitContext ec)
 197                 {
 198                         expr.EmitSideEffect (ec);
 199                 }
 200
 201                 public override Expression EmitToField (EmitContext ec)
 202                 {
 203                         if (temp_field == null)
 204                                 temp_field = this.expr.EmitToField (ec);
 205
 206                         return this;
 207                 }
 208
 209                 public override bool Equals (object obj)
 210                 {
 211                         Unwrap uw = obj as Unwrap;
 212                         return uw != null && expr.Equals (uw.expr);
 213                 }
 214
 215                 public override void FlowAnalysis (FlowAnalysisContext fc)
 216                 {
 217                         expr.FlowAnalysis (fc);
 218                 }
 219
 220                 public Expression Original {
 221                         get {
 222                                 return expr;
 223                         }
 224                 }
 225
 226                 public override int GetHashCode ()
 227                 {
 228                         return expr.GetHashCode ();
 229                 }
 230
 231                 public override bool IsNull {
 232                         get {
 233                                 return expr.IsNull;
 234                         }
 235                 }
 236
 237                 public void Store (EmitContext ec)
 238                 {
 239                         if (temp != null || temp_field != null)
 240                                 return;
 241
 242                         if (expr is VariableReference)
 243                                 return;
 244
 245                         expr.Emit (ec);
 246                         LocalVariable.Store (ec);
 247                 }
 248
 249                 public void Load (EmitContext ec)
 250                 {
 251                         if (temp_field != null)
 252                                 temp_field.Emit (ec);
 253                         else if (expr is VariableReference)
 254                                 expr.Emit (ec);
 255                         else
 256                                 LocalVariable.Emit (ec);
 257                 }
 258
 259                 public override SLE.Expression MakeExpression (BuilderContext ctx)
 260                 {
 261                         return expr.MakeExpression (ctx);
 262                 }
 263
 264                 public void AddressOf (EmitContext ec, AddressOp mode)
 265                 {
 266                         IMemoryLocation ml;
 267
 268                         if (temp_field != null) {
 269                                 ml = temp_field as IMemoryLocation;
 270                                 if (ml == null) {
 271                                         var lt = new LocalTemporary (temp_field.Type);
 272                                         temp_field.Emit (ec);
 273                                         lt.Store (ec);
 274                                         ml = lt;
 275                                 }
 276                         } else {
 277                                 ml = expr as VariableReference;
 278                         }
 279
 280                         if (ml != null)
 281                                 ml.AddressOf (ec, mode);
 282                         else
 283                                 LocalVariable.AddressOf (ec, mode);
 284                 }
 285
 286                 //
 287                 // Keeps result of non-variable expression
 288                 //
 289                 LocalTemporary LocalVariable {
 290                         get {
 291                                 if (temp == null && temp_field == null)
 292                                         temp = new LocalTemporary (expr.Type);
 293                                 return temp;
 294                         }
 295                 }
 296         }
 297
 298         //
 299         // Calls get_Value method on nullable expression
 300         //
 301         public class UnwrapCall : CompositeExpression
 302         {
 303                 public UnwrapCall (Expression expr)
 304                         : base (expr)
 305                 {
 306                 }
 307
 308                 protected override Expression DoResolve (ResolveContext rc)
 309                 {
 310                         base.DoResolve (rc);
 311
 312                         if (type != null)
 313                                 type = NullableInfo.GetUnderlyingType (type);
 314
 315                         return this;
 316                 }
 317
 318                 public override void Emit (EmitContext ec)
 319                 {
 320                         var call = new CallEmitter ();
 321                         call.InstanceExpression = Child;
 322                         call.EmitPredefined (ec, NullableInfo.GetValue (Child.Type), null);
 323                 }
 324         }
 325
 326         public class Wrap : TypeCast
 327         {
 328                 private Wrap (Expression expr, TypeSpec type)
 329                         : base (expr, type)
 330                 {
 331                         eclass = ExprClass.Value;
 332                 }
 333
 334                 public override Expression CreateExpressionTree (ResolveContext ec)
 335                 {
 336                         TypeCast child_cast = child as TypeCast;
 337                         if (child_cast != null) {
 338                                 child.Type = type;
 339                                 return child_cast.CreateExpressionTree (ec);
 340                         }
 341
 342                         var user_cast = child as UserCast;
 343                         if (user_cast != null) {
 344                                 child.Type = type;
 345                                 return user_cast.CreateExpressionTree (ec);
 346                         }
 347
 348                         return base.CreateExpressionTree (ec);
 349                 }
 350
 351                 public static Expression Create (Expression expr, TypeSpec type)
 352                 {
 353                         //
 354                         // Avoid unwraping and wraping of the same type
 355                         //
 356                         Unwrap unwrap = expr as Unwrap;
 357                         if (unwrap != null && expr.Type == NullableInfo.GetUnderlyingType (type))
 358                                 return unwrap.Original;
 359
 360                         return new Wrap (expr, type);
 361                 }
 362
 363                 public override void Emit (EmitContext ec)
 364                 {
 365                         child.Emit (ec);
 366                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 367                 }
 368         }
 369
 370         //
 371         // Represents null literal lifted to nullable type
 372         //
 373         public class LiftedNull : NullConstant, IMemoryLocation
 374         {
 375                 private LiftedNull (TypeSpec nullable_type, Location loc)
 376                         : base (nullable_type, loc)
 377                 {
 378                         eclass = ExprClass.Value;
 379                 }
 380
 381                 public static Constant Create (TypeSpec nullable, Location loc)
 382                 {
 383                         return new LiftedNull (nullable, loc);
 384                 }
 385
 386                 public static Constant CreateFromExpression (ResolveContext rc, Expression e)
 387                 {
 388                         if (!rc.HasSet (ResolveContext.Options.ExpressionTreeConversion)) {
 389                                 rc.Report.Warning (458, 2, e.Location, "The result of the expression is always `null' of type `{0}'",
 390                                         e.Type.GetSignatureForError ());
 391                         }
 392
 393                         return ReducedExpression.Create (Create (e.Type, e.Location), e);
 394                 }
 395
 396                 public override void Emit (EmitContext ec)
 397                 {
 398                         // TODO: generate less temporary variables
 399                         LocalTemporary value_target = new LocalTemporary (type);
 400
 401                         value_target.AddressOf (ec, AddressOp.Store);
 402                         ec.Emit (OpCodes.Initobj, type);
 403                         value_target.Emit (ec);
 404                         value_target.Release (ec);
 405                 }
 406
 407                 public void AddressOf (EmitContext ec, AddressOp Mode)
 408                 {
 409                         LocalTemporary value_target = new LocalTemporary (type);
 410
 411                         value_target.AddressOf (ec, AddressOp.Store);
 412                         ec.Emit (OpCodes.Initobj, type);
 413                         value_target.AddressOf (ec, Mode);
 414                 }
 415         }
 416
 417         //
 418         // Generic lifting expression, supports all S/S? -> T/T? cases
 419         //
 420         public class LiftedConversion : Expression, IMemoryLocation
 421         {
 422                 Expression expr, null_value;
 423                 Unwrap unwrap;
 424
 425                 public LiftedConversion (Expression expr, Unwrap unwrap, TypeSpec type)
 426                 {
 427                         this.expr = expr;
 428                         this.unwrap = unwrap;
 429                         this.loc = expr.Location;
 430                         this.type = type;
 431                 }
 432
 433                 public LiftedConversion (Expression expr, Expression unwrap, TypeSpec type)
 434                         : this (expr, unwrap as Unwrap, type)
 435                 {
 436                 }
 437
 438                 public override bool IsNull {
 439                         get {
 440                                 return expr.IsNull;
 441                         }
 442                 }
 443
 444                 public override bool ContainsEmitWithAwait ()
 445                 {
 446                         return unwrap.ContainsEmitWithAwait ();
 447                 }
 448
 449                 public override Expression CreateExpressionTree (ResolveContext ec)
 450                 {
 451                         return expr.CreateExpressionTree (ec);
 452                 }
 453
 454                 protected override Expression DoResolve (ResolveContext ec)
 455                 {
 456                         //
 457                         // It's null when lifting non-nullable type
 458                         //
 459                         if (unwrap == null) {
 460                                 // S -> T? is wrap only
 461                                 if (type.IsNullableType)
 462                                         return Wrap.Create (expr, type);
 463
 464                                 // S -> T can be simplified
 465                                 return expr;
 466                         }
 467
 468                         // Wrap target for T?
 469                         if (type.IsNullableType) {
 470                                 if (!expr.Type.IsNullableType) {
 471                                         expr = Wrap.Create (expr, type);
 472                                         if (expr == null)
 473                                                 return null;
 474                                 }
 475
 476                                 null_value = LiftedNull.Create (type, loc);
 477                         } else if (TypeSpec.IsValueType (type)) {
 478                                 null_value = LiftedNull.Create (type, loc);
 479                         } else {
 480                                 null_value = new NullConstant (type, loc);
 481                         }
 482
 483                         eclass = ExprClass.Value;
 484                         return this;
 485                 }
 486
 487                 public override void Emit (EmitContext ec)
 488                 {
 489                         Label is_null_label = ec.DefineLabel ();
 490                         Label end_label = ec.DefineLabel ();
 491
 492                         unwrap.EmitCheck (ec);
 493                         ec.Emit (OpCodes.Brfalse, is_null_label);
 494
 495                         expr.Emit (ec);
 496
 497                         ec.Emit (OpCodes.Br, end_label);
 498                         ec.MarkLabel (is_null_label);
 499
 500                         null_value.Emit (ec);
 501
 502                         ec.MarkLabel (end_label);
 503                 }
 504
 505                 public override void FlowAnalysis (FlowAnalysisContext fc)
 506                 {
 507                         expr.FlowAnalysis (fc);
 508                 }
 509
 510                 public void AddressOf (EmitContext ec, AddressOp mode)
 511                 {
 512                         unwrap.AddressOf (ec, mode);
 513                 }
 514         }
 515
 516         public class LiftedUnaryOperator : Unary, IMemoryLocation
 517         {
 518                 Unwrap unwrap;
 519                 Expression user_operator;
 520
 521                 public LiftedUnaryOperator (Unary.Operator op, Expression expr, Location loc)
 522                         : base (op, expr, loc)
 523                 {
 524                 }
 525
 526                 public void AddressOf (EmitContext ec, AddressOp mode)
 527                 {
 528                         unwrap.AddressOf (ec, mode);
 529                 }
 530
 531                 public override Expression CreateExpressionTree (ResolveContext ec)
 532                 {
 533                         if (user_operator != null)
 534                                 return user_operator.CreateExpressionTree (ec);
 535
 536                         if (Oper == Operator.UnaryPlus)
 537                                 return Expr.CreateExpressionTree (ec);
 538
 539                         return base.CreateExpressionTree (ec);
 540                 }
 541
 542                 protected override Expression DoResolve (ResolveContext ec)
 543                 {
 544                         unwrap = Unwrap.Create (Expr, false);
 545                         if (unwrap == null)
 546                                 return null;
 547
 548                         Expression res = base.ResolveOperator (ec, unwrap);
 549                         if (res == null) {
 550                                 Error_OperatorCannotBeApplied (ec, loc, OperName (Oper), Expr.Type);
 551                                 return null;
 552                         }
 553
 554                         if (res != this) {
 555                                 if (user_operator == null)
 556                                         return res;
 557                         } else {
 558                                 res = Expr = LiftExpression (ec, Expr);
 559                         }
 560
 561                         if (res == null)
 562                                 return null;
 563
 564                         eclass = ExprClass.Value;
 565                         type = res.Type;
 566                         return this;
 567                 }
 568
 569                 public override void Emit (EmitContext ec)
 570                 {
 571                         Label is_null_label = ec.DefineLabel ();
 572                         Label end_label = ec.DefineLabel ();
 573
 574                         unwrap.EmitCheck (ec);
 575                         ec.Emit (OpCodes.Brfalse, is_null_label);
 576
 577                         if (user_operator != null) {
 578                                 user_operator.Emit (ec);
 579                         } else {
 580                                 EmitOperator (ec, NullableInfo.GetUnderlyingType (type));
 581                         }
 582
 583                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 584                         ec.Emit (OpCodes.Br_S, end_label);
 585
 586                         ec.MarkLabel (is_null_label);
 587                         LiftedNull.Create (type, loc).Emit (ec);
 588
 589                         ec.MarkLabel (end_label);
 590                 }
 591
 592                 static Expression LiftExpression (ResolveContext ec, Expression expr)
 593                 {
 594                         var lifted_type = new NullableType (expr.Type, expr.Location);
 595                         if (lifted_type.ResolveAsType (ec) == null)
 596                                 return null;
 597
 598                         expr.Type = lifted_type.Type;
 599                         return expr;
 600                 }
 601
 602                 protected override Expression ResolveEnumOperator (ResolveContext ec, Expression expr, TypeSpec[] predefined)
 603                 {
 604                         expr = base.ResolveEnumOperator (ec, expr, predefined);
 605                         if (expr == null)
 606                                 return null;
 607
 608                         Expr = LiftExpression (ec, Expr);
 609                         return LiftExpression (ec, expr);
 610                 }
 611
 612                 protected override Expression ResolveUserOperator (ResolveContext ec, Expression expr)
 613                 {
 614                         expr = base.ResolveUserOperator (ec, expr);
 615                         if (expr == null)
 616                                 return null;
 617
 618                         //
 619                         // When a user operator is of non-nullable type
 620                         //
 621                         if (Expr is Unwrap) {
 622                                 user_operator = LiftExpression (ec, expr);
 623                                 return user_operator;
 624                         }
 625
 626                         return expr;
 627                 }
 628         }
 629
 630         //
 631         // Lifted version of binary operators
 632         //
 633         class LiftedBinaryOperator : Expression
 634         {
 635                 public LiftedBinaryOperator (Binary b)
 636                 {
 637                         this.Binary = b;
 638                         this.loc = b.Location;
 639                 }
 640
 641                 public Binary Binary { get; private set; }
 642
 643                 public Expression Left { get; set; }
 644
 645                 public Expression Right { get; set; }
 646
 647                 public Unwrap UnwrapLeft { get; set; }
 648
 649                 public Unwrap UnwrapRight { get; set; }
 650
 651                 public MethodSpec UserOperator { get; set; }
 652
 653                 bool IsBitwiseBoolean {
 654                         get {
 655                                 return (Binary.Oper == Binary.Operator.BitwiseAnd || Binary.Oper == Binary.Operator.BitwiseOr) &&
 656                                 ((UnwrapLeft != null && UnwrapLeft.Type.BuiltinType == BuiltinTypeSpec.Type.Bool) ||
 657                                  (UnwrapRight != null && UnwrapRight.Type.BuiltinType == BuiltinTypeSpec.Type.Bool));
 658                         }
 659                 }
 660
 661                 public override bool ContainsEmitWithAwait ()
 662                 {
 663                         return Left.ContainsEmitWithAwait () || Right.ContainsEmitWithAwait ();
 664                 }
 665
 666                 public override Expression CreateExpressionTree (ResolveContext rc)
 667                 {
 668                         if (UserOperator != null) {
 669                                 Arguments args = new Arguments (2);
 670                                 args.Add (new Argument (Binary.Left));
 671                                 args.Add (new Argument (Binary.Right));
 672
 673                                 var method = new UserOperatorCall (UserOperator, args, Binary.CreateExpressionTree, loc);
 674                                 return method.CreateExpressionTree (rc);
 675                         }
 676
 677                         return Binary.CreateExpressionTree (rc);
 678                 }
 679
 680                 protected override Expression DoResolve (ResolveContext rc)
 681                 {
 682                         if (rc.IsRuntimeBinder) {
 683                                 if (UnwrapLeft == null && !Left.Type.IsNullableType)
 684                                         Left = LiftOperand (rc, Left);
 685
 686                                 if (UnwrapRight == null && !Right.Type.IsNullableType)
 687                                         Right = LiftOperand (rc, Right);
 688                         } else {
 689                                 if (UnwrapLeft == null && Left != null && Left.Type.IsNullableType) {
 690                                         Left = Unwrap.CreateUnwrapped (Left);
 691                                         UnwrapLeft = Left as Unwrap;
 692                                 }
 693
 694                                 if (UnwrapRight == null && Right != null && Right.Type.IsNullableType) {
 695                                         Right = Unwrap.CreateUnwrapped (Right);
 696                                         UnwrapRight = Right as Unwrap;
 697                                 }
 698                         }
 699
 700                         type = Binary.Type;
 701                         eclass = Binary.eclass;
 702
 703                         return this;
 704                 }
 705
 706                 Expression LiftOperand (ResolveContext rc, Expression expr)
 707                 {
 708                         TypeSpec type;
 709                         if (expr.IsNull) {
 710                                 type = Left.IsNull ? Right.Type : Left.Type;
 711                         } else {
 712                                 type = expr.Type;
 713                         }
 714
 715                         if (!type.IsNullableType)
 716                                 type = NullableInfo.MakeType (rc.Module, type);
 717
 718                         return Wrap.Create (expr, type);
 719                 }
 720
 721                 public override void Emit (EmitContext ec)
 722                 {
 723                         if (IsBitwiseBoolean && UserOperator == null) {
 724                                 EmitBitwiseBoolean (ec);
 725                                 return;
 726                         }
 727
 728                         if ((Binary.Oper & Binary.Operator.EqualityMask) != 0) {
 729                                 EmitEquality (ec);
 730                                 return;
 731                         }
 732
 733                         Label is_null_label = ec.DefineLabel ();
 734                         Label end_label = ec.DefineLabel ();
 735
 736                         if (ec.HasSet (BuilderContext.Options.AsyncBody) && Right.ContainsEmitWithAwait ()) {
 737                                 Left = Left.EmitToField (ec);
 738                                 Right = Right.EmitToField (ec);
 739                         }
 740
 741                         if (UnwrapLeft != null) {
 742                                 UnwrapLeft.EmitCheck (ec);
 743                         }
 744
 745                         //
 746                         // Don't emit HasValue check when left and right expressions are same
 747                         //
 748                         if (UnwrapRight != null && !Binary.Left.Equals (Binary.Right)) {
 749                                 UnwrapRight.EmitCheck (ec);
 750                                 if (UnwrapLeft != null) {
 751                                         ec.Emit (OpCodes.And);
 752                                 }
 753                         }
 754
 755                         ec.Emit (OpCodes.Brfalse, is_null_label);
 756
 757                         if (UserOperator != null) {
 758                                 var args = new Arguments (2);
 759                                 args.Add (new Argument (Left));
 760                                 args.Add (new Argument (Right));
 761
 762                                 var call = new CallEmitter ();
 763                                 call.EmitPredefined (ec, UserOperator, args);
 764                         } else {
 765                                 Binary.EmitOperator (ec, Left, Right);
 766                         }
 767
 768                         //
 769                         // Wrap the result when the operator return type is nullable type
 770                         //
 771                         if (type.IsNullableType)
 772                                 ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 773
 774                         ec.Emit (OpCodes.Br_S, end_label);
 775                         ec.MarkLabel (is_null_label);
 776
 777                         if ((Binary.Oper & Binary.Operator.ComparisonMask) != 0) {
 778                                 ec.EmitInt (0);
 779                         } else {
 780                                 LiftedNull.Create (type, loc).Emit (ec);
 781                         }
 782
 783                         ec.MarkLabel (end_label);
 784                 }
 785
 786                 void EmitBitwiseBoolean (EmitContext ec)
 787                 {
 788                         Label load_left = ec.DefineLabel ();
 789                         Label load_right = ec.DefineLabel ();
 790                         Label end_label = ec.DefineLabel ();
 791                         Label is_null_label = ec.DefineLabel ();
 792
 793                         bool or = Binary.Oper == Binary.Operator.BitwiseOr;
 794
 795                         //
 796                         // Both operands are bool? types
 797                         //
 798                         if ((UnwrapLeft != null && !Left.IsNull) && (UnwrapRight != null && !Right.IsNull)) {
 799                                 if (ec.HasSet (BuilderContext.Options.AsyncBody) && Binary.Right.ContainsEmitWithAwait ()) {
 800                                         Left = Left.EmitToField (ec);
 801                                         Right = Right.EmitToField (ec);
 802                                 } else {
 803                                         UnwrapLeft.Store (ec);
 804                                         UnwrapRight.Store (ec);
 805                                 }
 806
 807                                 Left.Emit (ec);
 808                                 ec.Emit (OpCodes.Brtrue_S, load_right);
 809
 810                                 Right.Emit (ec);
 811                                 ec.Emit (OpCodes.Brtrue_S, load_left);
 812
 813                                 UnwrapLeft.EmitCheck (ec);
 814                                 ec.Emit (OpCodes.Brfalse_S, load_right);
 815
 816                                 // load left
 817                                 ec.MarkLabel (load_left);
 818                                 if (or)
 819                                         UnwrapRight.Load (ec);
 820                                 else
 821                                         UnwrapLeft.Load (ec);
 822
 823                                 ec.Emit (OpCodes.Br_S, end_label);
 824
 825                                 // load right
 826                                 ec.MarkLabel (load_right);
 827                                 if (or)
 828                                         UnwrapLeft.Load (ec);
 829                                 else
 830                                         UnwrapRight.Load (ec);
 831
 832                                 ec.MarkLabel (end_label);
 833                                 return;
 834                         }
 835
 836                         //
 837                         // Faster version when one operand is bool
 838                         //
 839                         if (UnwrapLeft == null) {
 840                                 //
 841                                 // (bool, bool?)
 842                                 //
 843                                 // Optimizes remaining (false & bool?), (true | bool?) which are not easy to handle
 844                                 // in binary expression reduction
 845                                 //
 846                                 var c = Left as BoolConstant;
 847                                 if (c != null) {
 848                                         // Keep evaluation order
 849                                         UnwrapRight.Store (ec);
 850
 851                                         ec.EmitInt (or ? 1 : 0);
 852                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 853                                 } else if (Left.IsNull) {
 854                                         UnwrapRight.Emit (ec);
 855                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, is_null_label);
 856
 857                                         UnwrapRight.Load (ec);
 858                                         ec.Emit (OpCodes.Br_S, end_label);
 859
 860                                         ec.MarkLabel (is_null_label);
 861                                         LiftedNull.Create (type, loc).Emit (ec);
 862                                 } else {
 863                                         Left.Emit (ec);
 864                                         UnwrapRight.Store (ec);
 865
 866                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, load_right);
 867
 868                                         ec.EmitInt (or ? 1 : 0);
 869                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 870
 871                                         ec.Emit (OpCodes.Br_S, end_label);
 872
 873                                         ec.MarkLabel (load_right);
 874                                         UnwrapRight.Load (ec);
 875                                 }
 876                         } else {
 877                                 //
 878                                 // (bool?, bool)
 879                                 //
 880                                 // Keep left-right evaluation order
 881                                 UnwrapLeft.Store (ec);
 882
 883                                 //
 884                                 // Optimizes remaining (bool? & false), (bool? | true) which are not easy to handle
 885                                 // in binary expression reduction
 886                                 //
 887                                 var c = Right as BoolConstant;
 888                                 if (c != null) {
 889                                         ec.EmitInt (or ? 1 : 0);
 890                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 891                                 } else if (Right.IsNull) {
 892                                         UnwrapLeft.Emit (ec);
 893                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, is_null_label);
 894
 895                                         UnwrapLeft.Load (ec);
 896                                         ec.Emit (OpCodes.Br_S, end_label);
 897
 898                                         ec.MarkLabel (is_null_label);
 899                                         LiftedNull.Create (type, loc).Emit (ec);
 900                                 } else if (Left.IsNull && UnwrapRight != null) {
 901                                         UnwrapRight.Emit (ec);
 902
 903                                         ec.Emit (or ? OpCodes.Brtrue_S : OpCodes.Brfalse_S, load_right);
 904
 905                                         LiftedNull.Create (type, loc).Emit (ec);
 906
 907                                         ec.Emit (OpCodes.Br_S, end_label);
 908
 909                                         ec.MarkLabel (load_right);
 910
 911                                         UnwrapRight.Load (ec);
 912                                 } else {
 913                                         Right.Emit (ec);
 914                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, load_left);
 915
 916                                         ec.EmitInt (or ? 1 : 0);
 917                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 918
 919                                         ec.Emit (OpCodes.Br_S, end_label);
 920
 921                                         ec.MarkLabel (load_left);
 922
 923                                         UnwrapLeft.Load (ec);
 924                                 }
 925                         }
 926
 927                         ec.MarkLabel (end_label);
 928                 }
 929
 930                 //
 931                 // Emits optimized equality or inequality operator when possible
 932                 //
 933                 void EmitEquality (EmitContext ec)
 934                 {
 935                         //
 936                         // Either left or right is null
 937                         //
 938                         if (UnwrapLeft != null && Binary.Right.IsNull) { // TODO: Optimize for EmitBranchable
 939                                 //
 940                                 // left.HasValue == false
 941                                 //
 942                                 UnwrapLeft.EmitCheck (ec);
 943                                 if (Binary.Oper == Binary.Operator.Equality) {
 944                                         ec.EmitInt (0);
 945                                         ec.Emit (OpCodes.Ceq);
 946                                 }
 947                                 return;
 948                         }
 949
 950                         if (UnwrapRight != null && Binary.Left.IsNull) {
 951                                 //
 952                                 // right.HasValue == false
 953                                 //
 954                                 UnwrapRight.EmitCheck (ec);
 955                                 if (Binary.Oper == Binary.Operator.Equality) {
 956                                         ec.EmitInt (0);
 957                                         ec.Emit (OpCodes.Ceq);
 958                                 }
 959                                 return;
 960                         }
 961
 962                         Label dissimilar_label = ec.DefineLabel ();
 963                         Label end_label = ec.DefineLabel ();
 964
 965                         if (UserOperator != null) {
 966                                 var left = Left;
 967
 968                                 if (UnwrapLeft != null) {
 969                                         UnwrapLeft.EmitCheck (ec);
 970                                 } else {
 971                                         // Keep evaluation order same
 972                                         if (!(Left is VariableReference)) {
 973                                                 Left.Emit (ec);
 974                                                 var lt = new LocalTemporary (Left.Type);
 975                                                 lt.Store (ec);
 976                                                 left = lt;
 977                                         }
 978                                 }
 979
 980                                 if (UnwrapRight != null) {
 981                                         UnwrapRight.EmitCheck (ec);
 982
 983                                         if (UnwrapLeft != null) {
 984                                                 ec.Emit (OpCodes.Bne_Un, dissimilar_label);
 985
 986                                                 Label compare_label = ec.DefineLabel ();
 987                                                 UnwrapLeft.EmitCheck (ec);
 988                                                 ec.Emit (OpCodes.Brtrue, compare_label);
 989
 990                                                 if (Binary.Oper == Binary.Operator.Equality)
 991                                                         ec.EmitInt (1);
 992                                                 else
 993                                                         ec.EmitInt (0);
 994
 995                                                 ec.Emit (OpCodes.Br, end_label);
 996
 997                                                 ec.MarkLabel (compare_label);
 998                                         } else {
 999                                                 ec.Emit (OpCodes.Brfalse, dissimilar_label);
1000                                         }
1001                                 } else {
1002                                         ec.Emit (OpCodes.Brfalse, dissimilar_label);
1003                                 }
1004
1005                                 var args = new Arguments (2);
1006                                 args.Add (new Argument (left));
1007                                 args.Add (new Argument (Right));
1008
1009                                 var call = new CallEmitter ();
1010                                 call.EmitPredefined (ec, UserOperator, args);
1011                         } else {
1012                                 if (ec.HasSet (BuilderContext.Options.AsyncBody) && Binary.Right.ContainsEmitWithAwait ()) {
1013                                         Left = Left.EmitToField (ec);
1014                                         Right = Right.EmitToField (ec);
1015                                 }
1016
1017                                 //
1018                                 // Emit underlying value comparison first.
1019                                 //
1020                                 // For this code: int? a = 1; bool b = a == 1;
1021                                 //
1022                                 // We emit something similar to this. Expressions with side effects have local
1023                                 // variable created by Unwrap expression
1024                                 //
1025                                 //      left.GetValueOrDefault ()
1026                                 //      right
1027                                 //      bne.un.s   dissimilar_label
1028                                 //  left.HasValue
1029                                 //      br.s       end_label
1030                                 // dissimilar_label:
1031                                 //      ldc.i4.0
1032                                 // end_label:
1033                                 //
1034
1035                                 Left.Emit (ec);
1036                                 Right.Emit (ec);
1037
1038                                 ec.Emit (OpCodes.Bne_Un_S, dissimilar_label);
1039
1040                                 //
1041                                 // Check both left and right expressions for Unwrap call in which
1042                                 // case we need to run get_HasValue() check because the type is
1043                                 // nullable and could have null value
1044                                 //
1045                                 if (UnwrapLeft != null)
1046                                         UnwrapLeft.EmitCheck (ec);
1047
1048                                 if (UnwrapRight != null)
1049                                         UnwrapRight.EmitCheck (ec);
1050
1051                                 if (UnwrapLeft != null && UnwrapRight != null) {
1052                                         if (Binary.Oper == Binary.Operator.Inequality)
1053                                                 ec.Emit (OpCodes.Xor);
1054                                         else
1055                                                 ec.Emit (OpCodes.Ceq);
1056                                 } else {
1057                                         if (Binary.Oper == Binary.Operator.Inequality) {
1058                                                 ec.EmitInt (0);
1059                                                 ec.Emit (OpCodes.Ceq);
1060                                         }
1061                                 }
1062                         }
1063
1064                         ec.Emit (OpCodes.Br_S, end_label);
1065
1066                         ec.MarkLabel (dissimilar_label);
1067                         if (Binary.Oper == Binary.Operator.Inequality)
1068                                 ec.EmitInt (1);
1069                         else
1070                                 ec.EmitInt (0);
1071
1072                         ec.MarkLabel (end_label);
1073                 }
1074
1075                 public override void FlowAnalysis (FlowAnalysisContext fc)
1076                 {
1077                         Binary.FlowAnalysis (fc);
1078                 }
1079
1080                 public override SLE.Expression MakeExpression (BuilderContext ctx)
1081                 {
1082                         return Binary.MakeExpression (ctx, Left, Right);
1083                 }
1084         }
1085
1086         public class NullCoalescingOperator : Expression
1087         {
1088                 Expression left, right;
1089                 Unwrap unwrap;
1090                 bool user_conversion_left;
1091
1092                 public NullCoalescingOperator (Expression left, Expression right)
1093                 {
1094                         this.left = left;
1095                         this.right = right;
1096                         this.loc = left.Location;
1097                 }
1098
1099                 public Expression LeftExpression {
1100                         get {
1101                                 return left;
1102                         }
1103                 }
1104
1105                 public Expression RightExpression {
1106                         get {
1107                                 return right;
1108                         }
1109                 }
1110
1111                 public override Expression CreateExpressionTree (ResolveContext ec)
1112                 {
1113                         if (left is NullLiteral)
1114                                 ec.Report.Error (845, loc, "An expression tree cannot contain a coalescing operator with null left side");
1115
1116                         UserCast uc = left as UserCast;
1117                         Expression conversion = null;
1118                         if (uc != null) {
1119                                 left = uc.Source;
1120
1121                                 Arguments c_args = new Arguments (2);
1122                                 c_args.Add (new Argument (uc.CreateExpressionTree (ec)));
1123                                 c_args.Add (new Argument (left.CreateExpressionTree (ec)));
1124                                 conversion = CreateExpressionFactoryCall (ec, "Lambda", c_args);
1125                         }
1126
1127                         Arguments args = new Arguments (3);
1128                         args.Add (new Argument (left.CreateExpressionTree (ec)));
1129                         args.Add (new Argument (right.CreateExpressionTree (ec)));
1130                         if (conversion != null)
1131                                 args.Add (new Argument (conversion));
1132
1133                         return CreateExpressionFactoryCall (ec, "Coalesce", args);
1134                 }
1135
1136                 Expression ConvertExpression (ResolveContext ec)
1137                 {
1138                         // TODO: ImplicitConversionExists should take care of this
1139                         if (left.eclass == ExprClass.MethodGroup)
1140                                 return null;
1141
1142                         TypeSpec ltype = left.Type;
1143
1144                         //
1145                         // If left is a nullable type and an implicit conversion exists from right to underlying type of left,
1146                         // the result is underlying type of left
1147                         //
1148                         if (ltype.IsNullableType) {
1149                                 unwrap = Unwrap.Create (left, false);
1150                                 if (unwrap == null)
1151                                         return null;
1152
1153                                 //
1154                                 // Reduce (left ?? null) to left
1155                                 //
1156                                 if (right.IsNull)
1157                                         return ReducedExpression.Create (left, this);
1158
1159                                 Expression conv;
1160                                 if (right.Type.IsNullableType) {
1161                                         conv = right.Type == ltype ? right : Convert.ImplicitNulableConversion (ec, right, ltype);
1162                                         if (conv != null) {
1163                                                 right = conv;
1164                                                 type = ltype;
1165                                                 return this;
1166                                         }
1167                                 } else {
1168                                         conv = Convert.ImplicitConversion (ec, right, unwrap.Type, loc);
1169                                         if (conv != null) {
1170                                                 left = unwrap;
1171                                                 ltype = left.Type;
1172
1173                                                 //
1174                                                 // If right is a dynamic expression, the result type is dynamic
1175                                                 //
1176                                                 if (right.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1177                                                         type = right.Type;
1178
1179                                                         // Need to box underlying value type
1180                                                         left = Convert.ImplicitBoxingConversion (left, ltype, type);
1181                                                         return this;
1182                                                 }
1183
1184                                                 right = conv;
1185                                                 type = ltype;
1186                                                 return this;
1187                                         }
1188                                 }
1189                         } else if (TypeSpec.IsReferenceType (ltype)) {
1190                                 if (Convert.ImplicitConversionExists (ec, right, ltype)) {
1191                                         //
1192                                         // If right is a dynamic expression, the result type is dynamic
1193                                         //
1194                                         if (right.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1195                                                 type = right.Type;
1196                                                 return this;
1197                                         }
1198
1199                                         //
1200                                         // Reduce ("foo" ?? expr) to expression
1201                                         //
1202                                         Constant lc = left as Constant;
1203                                         if (lc != null && !lc.IsDefaultValue)
1204                                                 return ReducedExpression.Create (lc, this, false);
1205
1206                                         //
1207                                         // Reduce (left ?? null) to left OR (null-constant ?? right) to right
1208                                         //
1209                                         if (right.IsNull || lc != null) {
1210                                                 //
1211                                                 // Special case null ?? null
1212                                                 //
1213                                                 if (right.IsNull && ltype == right.Type)
1214                                                         return null;
1215
1216                                                 return ReducedExpression.Create (lc != null ? right : left, this, false);
1217                                         }
1218
1219                                         right = Convert.ImplicitConversion (ec, right, ltype, loc);
1220                                         type = ltype;
1221                                         return this;
1222                                 }
1223                         } else {
1224                                 return null;
1225                         }
1226
1227                         TypeSpec rtype = right.Type;
1228                         if (!Convert.ImplicitConversionExists (ec, unwrap ?? left, rtype) || right.eclass == ExprClass.MethodGroup)
1229                                 return null;
1230
1231                         //
1232                         // Reduce (null ?? right) to right
1233                         //
1234                         if (left.IsNull)
1235                                 return ReducedExpression.Create (right, this, false).Resolve (ec);
1236
1237                         left = Convert.ImplicitConversion (ec, unwrap ?? left, rtype, loc);
1238                         user_conversion_left = left is UserCast;
1239                         type = rtype;
1240                         return this;
1241                 }
1242
1243                 public override bool ContainsEmitWithAwait ()
1244                 {
1245                         if (unwrap != null)
1246                                 return unwrap.ContainsEmitWithAwait () || right.ContainsEmitWithAwait ();
1247
1248                         return left.ContainsEmitWithAwait () || right.ContainsEmitWithAwait ();
1249                 }
1250
1251                 protected override Expression DoResolve (ResolveContext ec)
1252                 {
1253                         left = left.Resolve (ec);
1254                         right = right.Resolve (ec);
1255
1256                         if (left == null || right == null)
1257                                 return null;
1258
1259                         eclass = ExprClass.Value;
1260
1261                         Expression e = ConvertExpression (ec);
1262                         if (e == null) {
1263                                 Binary.Error_OperatorCannotBeApplied (ec, left, right, "??", loc);
1264                                 return null;
1265                         }
1266
1267                         return e;
1268                 }
1269
1270                 public override void Emit (EmitContext ec)
1271                 {
1272                         Label end_label = ec.DefineLabel ();
1273
1274                         if (unwrap != null) {
1275                                 Label is_null_label = ec.DefineLabel ();
1276
1277                                 unwrap.EmitCheck (ec);
1278                                 ec.Emit (OpCodes.Brfalse, is_null_label);
1279
1280                                 //
1281                                 // When both expressions are nullable the unwrap
1282                                 // is needed only for null check not for value uwrap
1283                                 //
1284                                 if (type.IsNullableType && TypeSpecComparer.IsEqual (NullableInfo.GetUnderlyingType (type), unwrap.Type))
1285                                         unwrap.Load (ec);
1286                                 else
1287                                         left.Emit (ec);
1288
1289                                 ec.Emit (OpCodes.Br, end_label);
1290
1291                                 ec.MarkLabel (is_null_label);
1292                                 right.Emit (ec);
1293
1294                                 ec.MarkLabel (end_label);
1295                                 return;
1296                         }
1297
1298                         //
1299                         // Null check is done on original expression not after expression is converted to
1300                         // result type. This is in most cases same but when user conversion is involved
1301                         // we can end up in situation when user operator does the null handling which is
1302                         // not what the operator is supposed to do.
1303                         // There is tricky case where cast of left expression is meant to be cast of
1304                         // whole source expression (null check is done on it) and cast from right-to-left
1305                         // conversion needs to do null check on unconverted source expression.
1306                         //
1307                         if (user_conversion_left) {
1308                                 var op_expr = (UserCast) left;
1309
1310                                 op_expr.Source.Emit (ec);
1311                                 LocalTemporary temp;
1312
1313                                 // TODO: More load kinds can be special cased
1314                                 if (!(op_expr.Source is VariableReference)) {
1315                                         temp = new LocalTemporary (op_expr.Source.Type);
1316                                         temp.Store (ec);
1317                                         temp.Emit (ec);
1318                                         op_expr.Source = temp;
1319                                 } else {
1320                                         temp = null;
1321                                 }
1322
1323                                 var right_label = ec.DefineLabel ();
1324                                 ec.Emit (OpCodes.Brfalse_S, right_label);
1325                                 left.Emit (ec);
1326                                 ec.Emit (OpCodes.Br, end_label);
1327                                 ec.MarkLabel (right_label);
1328
1329                                 if (temp != null)
1330                                         temp.Release (ec);
1331                         } else {
1332                                 //
1333                                 // Common case where expression is not modified before null check and
1334                                 // we generate better/smaller code
1335                                 //
1336                                 left.Emit (ec);
1337                                 ec.Emit (OpCodes.Dup);
1338
1339                                 // Only to make verifier happy
1340                                 if (left.Type.IsGenericParameter)
1341                                         ec.Emit (OpCodes.Box, left.Type);
1342
1343                                 ec.Emit (OpCodes.Brtrue, end_label);
1344
1345                                 ec.Emit (OpCodes.Pop);
1346                         }
1347
1348                         right.Emit (ec);
1349
1350                         ec.MarkLabel (end_label);
1351                 }
1352
1353                 public override void FlowAnalysis (FlowAnalysisContext fc)
1354                 {
1355                         left.FlowAnalysis (fc);
1356                         var left_da = fc.BranchDefiniteAssignment ();
1357                         right.FlowAnalysis (fc);
1358                         fc.DefiniteAssignment = left_da;
1359                 }
1360
1361                 protected override void CloneTo (CloneContext clonectx, Expression t)
1362                 {
1363                         NullCoalescingOperator target = (NullCoalescingOperator) t;
1364
1365                         target.left = left.Clone (clonectx);
1366                         target.right = right.Clone (clonectx);
1367                 }
1368
1369                 public override object Accept (StructuralVisitor visitor)
1370                 {
1371                         return visitor.Visit (this);
1372                 }
1373         }
1374
1375         class LiftedUnaryMutator : UnaryMutator
1376         {
1377                 public LiftedUnaryMutator (Mode mode, Expression expr, Location loc)
1378                         : base (mode, expr, loc)
1379                 {
1380                 }
1381
1382                 protected override Expression DoResolve (ResolveContext ec)
1383                 {
1384                         var orig_expr = expr;
1385
1386                         expr = Unwrap.Create (expr);
1387
1388                         var res = base.DoResolveOperation (ec);
1389
1390                         expr = orig_expr;
1391                         type = expr.Type;
1392
1393                         return res;
1394                 }
1395
1396                 protected override void EmitOperation (EmitContext ec)
1397                 {
1398                         Label is_null_label = ec.DefineLabel ();
1399                         Label end_label = ec.DefineLabel ();
1400
1401                         LocalTemporary lt = new LocalTemporary (type);
1402
1403                         // Value is on the stack
1404                         lt.Store (ec);
1405
1406                         var call = new CallEmitter ();
1407                         call.InstanceExpression = lt;
1408                         call.EmitPredefined (ec, NullableInfo.GetHasValue (expr.Type), null);
1409
1410                         ec.Emit (OpCodes.Brfalse, is_null_label);
1411
1412                         call = new CallEmitter ();
1413                         call.InstanceExpression = lt;
1414                         call.EmitPredefined (ec, NullableInfo.GetGetValueOrDefault (expr.Type), null);
1415
1416                         lt.Release (ec);
1417
1418                         base.EmitOperation (ec);
1419
1420                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
1421                         ec.Emit (OpCodes.Br_S, end_label);
1422
1423                         ec.MarkLabel (is_null_label);
1424                         LiftedNull.Create (type, loc).Emit (ec);
1425
1426                         ec.MarkLabel (end_label);
1427                 }
1428         }
1429 }
1430