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)
  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 ContainsEmitWithAwait ()
 439                 {
 440                         return unwrap.ContainsEmitWithAwait ();
 441                 }
 442
 443                 public override Expression CreateExpressionTree (ResolveContext ec)
 444                 {
 445                         return expr.CreateExpressionTree (ec);
 446                 }
 447
 448                 protected override Expression DoResolve (ResolveContext ec)
 449                 {
 450                         //
 451                         // It's null when lifting non-nullable type
 452                         //
 453                         if (unwrap == null) {
 454                                 // S -> T? is wrap only
 455                                 if (type.IsNullableType)
 456                                         return Wrap.Create (expr, type);
 457
 458                                 // S -> T can be simplified
 459                                 return expr;
 460                         }
 461
 462                         // Wrap target for T?
 463                         if (type.IsNullableType) {
 464                                 if (!expr.Type.IsNullableType) {
 465                                         expr = Wrap.Create (expr, type);
 466                                         if (expr == null)
 467                                                 return null;
 468                                 }
 469
 470                                 null_value = LiftedNull.Create (type, loc);
 471                         } else if (TypeSpec.IsValueType (type)) {
 472                                 null_value = LiftedNull.Create (type, loc);
 473                         } else {
 474                                 null_value = new NullConstant (type, loc);
 475                         }
 476
 477                         eclass = ExprClass.Value;
 478                         return this;
 479                 }
 480
 481                 public override void Emit (EmitContext ec)
 482                 {
 483                         Label is_null_label = ec.DefineLabel ();
 484                         Label end_label = ec.DefineLabel ();
 485
 486                         unwrap.EmitCheck (ec);
 487                         ec.Emit (OpCodes.Brfalse, is_null_label);
 488
 489                         expr.Emit (ec);
 490
 491                         ec.Emit (OpCodes.Br, end_label);
 492                         ec.MarkLabel (is_null_label);
 493
 494                         null_value.Emit (ec);
 495
 496                         ec.MarkLabel (end_label);
 497                 }
 498
 499                 public override void FlowAnalysis (FlowAnalysisContext fc)
 500                 {
 501                         expr.FlowAnalysis (fc);
 502                 }
 503
 504                 public void AddressOf (EmitContext ec, AddressOp mode)
 505                 {
 506                         unwrap.AddressOf (ec, mode);
 507                 }
 508         }
 509
 510         public class LiftedUnaryOperator : Unary, IMemoryLocation
 511         {
 512                 Unwrap unwrap;
 513                 Expression user_operator;
 514
 515                 public LiftedUnaryOperator (Unary.Operator op, Expression expr, Location loc)
 516                         : base (op, expr, loc)
 517                 {
 518                 }
 519
 520                 public void AddressOf (EmitContext ec, AddressOp mode)
 521                 {
 522                         unwrap.AddressOf (ec, mode);
 523                 }
 524
 525                 public override Expression CreateExpressionTree (ResolveContext ec)
 526                 {
 527                         if (user_operator != null)
 528                                 return user_operator.CreateExpressionTree (ec);
 529
 530                         if (Oper == Operator.UnaryPlus)
 531                                 return Expr.CreateExpressionTree (ec);
 532
 533                         return base.CreateExpressionTree (ec);
 534                 }
 535
 536                 protected override Expression DoResolve (ResolveContext ec)
 537                 {
 538                         unwrap = Unwrap.Create (Expr, false);
 539                         if (unwrap == null)
 540                                 return null;
 541
 542                         Expression res = base.ResolveOperator (ec, unwrap);
 543                         if (res == null) {
 544                                 Error_OperatorCannotBeApplied (ec, loc, OperName (Oper), Expr.Type);
 545                                 return null;
 546                         }
 547
 548                         if (res != this) {
 549                                 if (user_operator == null)
 550                                         return res;
 551                         } else {
 552                                 res = Expr = LiftExpression (ec, Expr);
 553                         }
 554
 555                         if (res == null)
 556                                 return null;
 557
 558                         eclass = ExprClass.Value;
 559                         type = res.Type;
 560                         return this;
 561                 }
 562
 563                 public override void Emit (EmitContext ec)
 564                 {
 565                         Label is_null_label = ec.DefineLabel ();
 566                         Label end_label = ec.DefineLabel ();
 567
 568                         unwrap.EmitCheck (ec);
 569                         ec.Emit (OpCodes.Brfalse, is_null_label);
 570
 571                         if (user_operator != null) {
 572                                 user_operator.Emit (ec);
 573                         } else {
 574                                 EmitOperator (ec, NullableInfo.GetUnderlyingType (type));
 575                         }
 576
 577                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 578                         ec.Emit (OpCodes.Br_S, end_label);
 579
 580                         ec.MarkLabel (is_null_label);
 581                         LiftedNull.Create (type, loc).Emit (ec);
 582
 583                         ec.MarkLabel (end_label);
 584                 }
 585
 586                 static Expression LiftExpression (ResolveContext ec, Expression expr)
 587                 {
 588                         var lifted_type = new NullableType (expr.Type, expr.Location);
 589                         if (lifted_type.ResolveAsType (ec) == null)
 590                                 return null;
 591
 592                         expr.Type = lifted_type.Type;
 593                         return expr;
 594                 }
 595
 596                 protected override Expression ResolveEnumOperator (ResolveContext ec, Expression expr, TypeSpec[] predefined)
 597                 {
 598                         expr = base.ResolveEnumOperator (ec, expr, predefined);
 599                         if (expr == null)
 600                                 return null;
 601
 602                         Expr = LiftExpression (ec, Expr);
 603                         return LiftExpression (ec, expr);
 604                 }
 605
 606                 protected override Expression ResolveUserOperator (ResolveContext ec, Expression expr)
 607                 {
 608                         expr = base.ResolveUserOperator (ec, expr);
 609                         if (expr == null)
 610                                 return null;
 611
 612                         //
 613                         // When a user operator is of non-nullable type
 614                         //
 615                         if (Expr is Unwrap) {
 616                                 user_operator = LiftExpression (ec, expr);
 617                                 return user_operator;
 618                         }
 619
 620                         return expr;
 621                 }
 622         }
 623
 624         //
 625         // Lifted version of binary operators
 626         //
 627         class LiftedBinaryOperator : Expression
 628         {
 629                 public LiftedBinaryOperator (Binary b)
 630                 {
 631                         this.Binary = b;
 632                         this.loc = b.Location;
 633                 }
 634
 635                 public Binary Binary { get; private set; }
 636
 637                 public Expression Left { get; set; }
 638
 639                 public Expression Right { get; set; }
 640
 641                 public Unwrap UnwrapLeft { get; set; }
 642
 643                 public Unwrap UnwrapRight { get; set; }
 644
 645                 public MethodSpec UserOperator { get; set; }
 646
 647                 bool IsBitwiseBoolean {
 648                         get {
 649                                 return (Binary.Oper == Binary.Operator.BitwiseAnd || Binary.Oper == Binary.Operator.BitwiseOr) &&
 650                                 ((UnwrapLeft != null && UnwrapLeft.Type.BuiltinType == BuiltinTypeSpec.Type.Bool) ||
 651                                  (UnwrapRight != null && UnwrapRight.Type.BuiltinType == BuiltinTypeSpec.Type.Bool));
 652                         }
 653                 }
 654
 655                 public override bool ContainsEmitWithAwait ()
 656                 {
 657                         return Left.ContainsEmitWithAwait () || Right.ContainsEmitWithAwait ();
 658                 }
 659
 660                 public override Expression CreateExpressionTree (ResolveContext rc)
 661                 {
 662                         if (UserOperator != null) {
 663                                 Arguments args = new Arguments (2);
 664                                 args.Add (new Argument (Binary.Left));
 665                                 args.Add (new Argument (Binary.Right));
 666
 667                                 var method = new UserOperatorCall (UserOperator, args, Binary.CreateExpressionTree, loc);
 668                                 return method.CreateExpressionTree (rc);
 669                         }
 670
 671                         return Binary.CreateExpressionTree (rc);
 672                 }
 673
 674                 protected override Expression DoResolve (ResolveContext rc)
 675                 {
 676                         if (rc.IsRuntimeBinder) {
 677                                 if (UnwrapLeft == null && !Left.Type.IsNullableType)
 678                                         Left = LiftOperand (rc, Left);
 679
 680                                 if (UnwrapRight == null && !Right.Type.IsNullableType)
 681                                         Right = LiftOperand (rc, Right);
 682                         } else {
 683                                 if (UnwrapLeft == null && Left != null && Left.Type.IsNullableType) {
 684                                         Left = Unwrap.CreateUnwrapped (Left);
 685                                         UnwrapLeft = Left as Unwrap;
 686                                 }
 687
 688                                 if (UnwrapRight == null && Right != null && Right.Type.IsNullableType) {
 689                                         Right = Unwrap.CreateUnwrapped (Right);
 690                                         UnwrapRight = Right as Unwrap;
 691                                 }
 692                         }
 693
 694                         type = Binary.Type;
 695                         eclass = Binary.eclass;
 696
 697                         return this;
 698                 }
 699
 700                 Expression LiftOperand (ResolveContext rc, Expression expr)
 701                 {
 702                         TypeSpec type;
 703                         if (expr.IsNull) {
 704                                 type = Left.IsNull ? Right.Type : Left.Type;
 705                         } else {
 706                                 type = expr.Type;
 707                         }
 708
 709                         if (!type.IsNullableType)
 710                                 type = NullableInfo.MakeType (rc.Module, type);
 711
 712                         return Wrap.Create (expr, type);
 713                 }
 714
 715                 public override void Emit (EmitContext ec)
 716                 {
 717                         if (IsBitwiseBoolean && UserOperator == null) {
 718                                 EmitBitwiseBoolean (ec);
 719                                 return;
 720                         }
 721
 722                         if ((Binary.Oper & Binary.Operator.EqualityMask) != 0) {
 723                                 EmitEquality (ec);
 724                                 return;
 725                         }
 726
 727                         Label is_null_label = ec.DefineLabel ();
 728                         Label end_label = ec.DefineLabel ();
 729
 730                         if (ec.HasSet (BuilderContext.Options.AsyncBody) && Right.ContainsEmitWithAwait ()) {
 731                                 Left = Left.EmitToField (ec);
 732                                 Right = Right.EmitToField (ec);
 733                         }
 734
 735                         if (UnwrapLeft != null) {
 736                                 UnwrapLeft.EmitCheck (ec);
 737                         }
 738
 739                         //
 740                         // Don't emit HasValue check when left and right expressions are same
 741                         //
 742                         if (UnwrapRight != null && !Binary.Left.Equals (Binary.Right)) {
 743                                 UnwrapRight.EmitCheck (ec);
 744                                 if (UnwrapLeft != null) {
 745                                         ec.Emit (OpCodes.And);
 746                                 }
 747                         }
 748
 749                         ec.Emit (OpCodes.Brfalse, is_null_label);
 750
 751                         if (UserOperator != null) {
 752                                 var args = new Arguments (2);
 753                                 args.Add (new Argument (Left));
 754                                 args.Add (new Argument (Right));
 755
 756                                 var call = new CallEmitter ();
 757                                 call.EmitPredefined (ec, UserOperator, args);
 758                         } else {
 759                                 Binary.EmitOperator (ec, Left, Right);
 760                         }
 761
 762                         //
 763                         // Wrap the result when the operator return type is nullable type
 764                         //
 765                         if (type.IsNullableType)
 766                                 ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 767
 768                         ec.Emit (OpCodes.Br_S, end_label);
 769                         ec.MarkLabel (is_null_label);
 770
 771                         if ((Binary.Oper & Binary.Operator.ComparisonMask) != 0) {
 772                                 ec.EmitInt (0);
 773                         } else {
 774                                 LiftedNull.Create (type, loc).Emit (ec);
 775                         }
 776
 777                         ec.MarkLabel (end_label);
 778                 }
 779
 780                 void EmitBitwiseBoolean (EmitContext ec)
 781                 {
 782                         Label load_left = ec.DefineLabel ();
 783                         Label load_right = ec.DefineLabel ();
 784                         Label end_label = ec.DefineLabel ();
 785                         Label is_null_label = ec.DefineLabel ();
 786
 787                         bool or = Binary.Oper == Binary.Operator.BitwiseOr;
 788
 789                         //
 790                         // Both operands are bool? types
 791                         //
 792                         if (UnwrapLeft != null && UnwrapRight != null) {
 793                                 if (ec.HasSet (BuilderContext.Options.AsyncBody) && Binary.Right.ContainsEmitWithAwait ()) {
 794                                         Left = Left.EmitToField (ec);
 795                                         Right = Right.EmitToField (ec);
 796                                 } else {
 797                                         UnwrapLeft.Store (ec);
 798                                         UnwrapRight.Store (ec);
 799                                 }
 800
 801                                 Left.Emit (ec);
 802                                 ec.Emit (OpCodes.Brtrue_S, load_right);
 803
 804                                 Right.Emit (ec);
 805                                 ec.Emit (OpCodes.Brtrue_S, load_left);
 806
 807                                 UnwrapLeft.EmitCheck (ec);
 808                                 ec.Emit (OpCodes.Brfalse_S, load_right);
 809
 810                                 // load left
 811                                 ec.MarkLabel (load_left);
 812                                 if (or)
 813                                         UnwrapRight.Load (ec);
 814                                 else
 815                                         UnwrapLeft.Load (ec);
 816
 817                                 ec.Emit (OpCodes.Br_S, end_label);
 818
 819                                 // load right
 820                                 ec.MarkLabel (load_right);
 821                                 if (or)
 822                                         UnwrapLeft.Load (ec);
 823                                 else
 824                                         UnwrapRight.Load (ec);
 825
 826                                 ec.MarkLabel (end_label);
 827                                 return;
 828                         }
 829
 830                         //
 831                         // Faster version when one operand is bool
 832                         //
 833                         if (UnwrapLeft == null) {
 834                                 //
 835                                 // (bool, bool?)
 836                                 //
 837                                 // Optimizes remaining (false & bool?), (true | bool?) which are not easy to handle
 838                                 // in binary expression reduction
 839                                 //
 840                                 var c = Left as BoolConstant;
 841                                 if (c != null) {
 842                                         // Keep evaluation order
 843                                         UnwrapRight.Store (ec);
 844
 845                                         ec.EmitInt (or ? 1 : 0);
 846                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 847                                 } else if (Left.IsNull) {
 848                                         UnwrapRight.Emit (ec);
 849                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, is_null_label);
 850
 851                                         UnwrapRight.Load (ec);
 852                                         ec.Emit (OpCodes.Br_S, end_label);
 853
 854                                         ec.MarkLabel (is_null_label);
 855                                         LiftedNull.Create (type, loc).Emit (ec);
 856                                 } else {
 857                                         Left.Emit (ec);
 858                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, load_right);
 859
 860                                         ec.EmitInt (or ? 1 : 0);
 861                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 862
 863                                         ec.Emit (OpCodes.Br_S, end_label);
 864
 865                                         ec.MarkLabel (load_right);
 866                                         UnwrapRight.Original.Emit (ec);
 867                                 }
 868                         } else {
 869                                 //
 870                                 // (bool?, bool)
 871                                 //
 872                                 // Keep left-right evaluation order
 873                                 UnwrapLeft.Store (ec);
 874
 875                                 //
 876                                 // Optimizes remaining (bool? & false), (bool? | true) which are not easy to handle
 877                                 // in binary expression reduction
 878                                 //
 879                                 var c = Right as BoolConstant;
 880                                 if (c != null) {
 881                                         ec.EmitInt (or ? 1 : 0);
 882                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 883                                 } else if (Right.IsNull) {
 884                                         UnwrapLeft.Emit (ec);
 885                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, is_null_label);
 886
 887                                         UnwrapLeft.Load (ec);
 888                                         ec.Emit (OpCodes.Br_S, end_label);
 889
 890                                         ec.MarkLabel (is_null_label);
 891                                         LiftedNull.Create (type, loc).Emit (ec);
 892                                 } else {
 893                                         Right.Emit (ec);
 894                                         ec.Emit (or ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, load_right);
 895
 896                                         ec.EmitInt (or ? 1 : 0);
 897                                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
 898
 899                                         ec.Emit (OpCodes.Br_S, end_label);
 900
 901                                         ec.MarkLabel (load_right);
 902
 903                                         UnwrapLeft.Load (ec);
 904                                 }
 905                         }
 906
 907                         ec.MarkLabel (end_label);
 908                 }
 909
 910                 //
 911                 // Emits optimized equality or inequality operator when possible
 912                 //
 913                 void EmitEquality (EmitContext ec)
 914                 {
 915                         //
 916                         // Either left or right is null
 917                         //
 918                         if (UnwrapLeft != null && Binary.Right.IsNull) { // TODO: Optimize for EmitBranchable
 919                                 //
 920                                 // left.HasValue == false
 921                                 //
 922                                 UnwrapLeft.EmitCheck (ec);
 923                                 if (Binary.Oper == Binary.Operator.Equality) {
 924                                         ec.EmitInt (0);
 925                                         ec.Emit (OpCodes.Ceq);
 926                                 }
 927                                 return;
 928                         }
 929
 930                         if (UnwrapRight != null && Binary.Left.IsNull) {
 931                                 //
 932                                 // right.HasValue == false
 933                                 //
 934                                 UnwrapRight.EmitCheck (ec);
 935                                 if (Binary.Oper == Binary.Operator.Equality) {
 936                                         ec.EmitInt (0);
 937                                         ec.Emit (OpCodes.Ceq);
 938                                 }
 939                                 return;
 940                         }
 941
 942                         Label dissimilar_label = ec.DefineLabel ();
 943                         Label end_label = ec.DefineLabel ();
 944
 945                         if (UserOperator != null) {
 946                                 var left = Left;
 947
 948                                 if (UnwrapLeft != null) {
 949                                         UnwrapLeft.EmitCheck (ec);
 950                                 } else {
 951                                         // Keep evaluation order same
 952                                         if (!(Left is VariableReference)) {
 953                                                 Left.Emit (ec);
 954                                                 var lt = new LocalTemporary (Left.Type);
 955                                                 lt.Store (ec);
 956                                                 left = lt;
 957                                         }
 958                                 }
 959
 960                                 if (UnwrapRight != null) {
 961                                         UnwrapRight.EmitCheck (ec);
 962
 963                                         if (UnwrapLeft != null) {
 964                                                 ec.Emit (OpCodes.Bne_Un, dissimilar_label);
 965
 966                                                 Label compare_label = ec.DefineLabel ();
 967                                                 UnwrapLeft.EmitCheck (ec);
 968                                                 ec.Emit (OpCodes.Brtrue, compare_label);
 969
 970                                                 if (Binary.Oper == Binary.Operator.Equality)
 971                                                         ec.EmitInt (1);
 972                                                 else
 973                                                         ec.EmitInt (0);
 974
 975                                                 ec.Emit (OpCodes.Br, end_label);
 976
 977                                                 ec.MarkLabel (compare_label);
 978                                         } else {
 979                                                 ec.Emit (OpCodes.Brfalse, dissimilar_label);
 980                                         }
 981                                 } else {
 982                                         ec.Emit (OpCodes.Brfalse, dissimilar_label);
 983                                 }
 984
 985                                 var args = new Arguments (2);
 986                                 args.Add (new Argument (left));
 987                                 args.Add (new Argument (Right));
 988
 989                                 var call = new CallEmitter ();
 990                                 call.EmitPredefined (ec, UserOperator, args);
 991                         } else {
 992                                 if (ec.HasSet (BuilderContext.Options.AsyncBody) && Binary.Right.ContainsEmitWithAwait ()) {
 993                                         Left = Left.EmitToField (ec);
 994                                         Right = Right.EmitToField (ec);
 995                                 }
 996
 997                                 //
 998                                 // Emit underlying value comparison first.
 999                                 //
1000                                 // For this code: int? a = 1; bool b = a == 1;
1001                                 //
1002                                 // We emit something similar to this. Expressions with side effects have local
1003                                 // variable created by Unwrap expression
1004                                 //
1005                                 //      left.GetValueOrDefault ()
1006                                 //      right
1007                                 //      bne.un.s   dissimilar_label
1008                                 //  left.HasValue
1009                                 //      br.s       end_label
1010                                 // dissimilar_label:
1011                                 //      ldc.i4.0
1012                                 // end_label:
1013                                 //
1014
1015                                 Left.Emit (ec);
1016                                 Right.Emit (ec);
1017
1018                                 ec.Emit (OpCodes.Bne_Un_S, dissimilar_label);
1019
1020                                 //
1021                                 // Check both left and right expressions for Unwrap call in which
1022                                 // case we need to run get_HasValue() check because the type is
1023                                 // nullable and could have null value
1024                                 //
1025                                 if (UnwrapLeft != null)
1026                                         UnwrapLeft.EmitCheck (ec);
1027
1028                                 if (UnwrapRight != null)
1029                                         UnwrapRight.EmitCheck (ec);
1030
1031                                 if (UnwrapLeft != null && UnwrapRight != null) {
1032                                         if (Binary.Oper == Binary.Operator.Inequality)
1033                                                 ec.Emit (OpCodes.Xor);
1034                                         else
1035                                                 ec.Emit (OpCodes.Ceq);
1036                                 } else {
1037                                         if (Binary.Oper == Binary.Operator.Inequality) {
1038                                                 ec.EmitInt (0);
1039                                                 ec.Emit (OpCodes.Ceq);
1040                                         }
1041                                 }
1042                         }
1043
1044                         ec.Emit (OpCodes.Br_S, end_label);
1045
1046                         ec.MarkLabel (dissimilar_label);
1047                         if (Binary.Oper == Binary.Operator.Inequality)
1048                                 ec.EmitInt (1);
1049                         else
1050                                 ec.EmitInt (0);
1051
1052                         ec.MarkLabel (end_label);
1053                 }
1054
1055                 public override void FlowAnalysis (FlowAnalysisContext fc)
1056                 {
1057                         Binary.FlowAnalysis (fc);
1058                 }
1059
1060                 public override SLE.Expression MakeExpression (BuilderContext ctx)
1061                 {
1062                         return Binary.MakeExpression (ctx, Left, Right);
1063                 }
1064         }
1065
1066         public class NullCoalescingOperator : Expression
1067         {
1068                 Expression left, right;
1069                 Unwrap unwrap;
1070
1071                 public NullCoalescingOperator (Expression left, Expression right)
1072                 {
1073                         this.left = left;
1074                         this.right = right;
1075                         this.loc = left.Location;
1076                 }
1077
1078                 public Expression LeftExpression {
1079                         get {
1080                                 return left;
1081                         }
1082                 }
1083
1084                 public Expression RightExpression {
1085                         get {
1086                                 return right;
1087                         }
1088                 }
1089
1090                 public override Expression CreateExpressionTree (ResolveContext ec)
1091                 {
1092                         if (left is NullLiteral)
1093                                 ec.Report.Error (845, loc, "An expression tree cannot contain a coalescing operator with null left side");
1094
1095                         UserCast uc = left as UserCast;
1096                         Expression conversion = null;
1097                         if (uc != null) {
1098                                 left = uc.Source;
1099
1100                                 Arguments c_args = new Arguments (2);
1101                                 c_args.Add (new Argument (uc.CreateExpressionTree (ec)));
1102                                 c_args.Add (new Argument (left.CreateExpressionTree (ec)));
1103                                 conversion = CreateExpressionFactoryCall (ec, "Lambda", c_args);
1104                         }
1105
1106                         Arguments args = new Arguments (3);
1107                         args.Add (new Argument (left.CreateExpressionTree (ec)));
1108                         args.Add (new Argument (right.CreateExpressionTree (ec)));
1109                         if (conversion != null)
1110                                 args.Add (new Argument (conversion));
1111
1112                         return CreateExpressionFactoryCall (ec, "Coalesce", args);
1113                 }
1114
1115                 Expression ConvertExpression (ResolveContext ec)
1116                 {
1117                         // TODO: ImplicitConversionExists should take care of this
1118                         if (left.eclass == ExprClass.MethodGroup)
1119                                 return null;
1120
1121                         TypeSpec ltype = left.Type;
1122
1123                         //
1124                         // If left is a nullable type and an implicit conversion exists from right to underlying type of left,
1125                         // the result is underlying type of left
1126                         //
1127                         if (ltype.IsNullableType) {
1128                                 unwrap = Unwrap.Create (left, false);
1129                                 if (unwrap == null)
1130                                         return null;
1131
1132                                 //
1133                                 // Reduce (left ?? null) to left
1134                                 //
1135                                 if (right.IsNull)
1136                                         return ReducedExpression.Create (left, this);
1137
1138                                 if (Convert.ImplicitConversionExists (ec, right, unwrap.Type)) {
1139                                         left = unwrap;
1140                                         ltype = left.Type;
1141
1142                                         //
1143                                         // If right is a dynamic expression, the result type is dynamic
1144                                         //
1145                                         if (right.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1146                                                 type = right.Type;
1147
1148                                                 // Need to box underlying value type
1149                                                 left = Convert.ImplicitBoxingConversion (left, ltype, type);
1150                                                 return this;
1151                                         }
1152
1153                                         right = Convert.ImplicitConversion (ec, right, ltype, loc);
1154                                         type = ltype;
1155                                         return this;
1156                                 }
1157                         } else if (TypeSpec.IsReferenceType (ltype)) {
1158                                 if (Convert.ImplicitConversionExists (ec, right, ltype)) {
1159                                         //
1160                                         // If right is a dynamic expression, the result type is dynamic
1161                                         //
1162                                         if (right.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
1163                                                 type = right.Type;
1164                                                 return this;
1165                                         }
1166
1167                                         //
1168                                         // Reduce ("foo" ?? expr) to expression
1169                                         //
1170                                         Constant lc = left as Constant;
1171                                         if (lc != null && !lc.IsDefaultValue)
1172                                                 return ReducedExpression.Create (lc, this, false);
1173
1174                                         //
1175                                         // Reduce (left ?? null) to left OR (null-constant ?? right) to right
1176                                         //
1177                                         if (right.IsNull || lc != null) {
1178                                                 //
1179                                                 // Special case null ?? null
1180                                                 //
1181                                                 if (right.IsNull && ltype == right.Type)
1182                                                         return null;
1183
1184                                                 return ReducedExpression.Create (lc != null ? right : left, this, false);
1185                                         }
1186
1187                                         right = Convert.ImplicitConversion (ec, right, ltype, loc);
1188                                         type = ltype;
1189                                         return this;
1190                                 }
1191                         } else {
1192                                 return null;
1193                         }
1194
1195                         TypeSpec rtype = right.Type;
1196                         if (!Convert.ImplicitConversionExists (ec, unwrap ?? left, rtype) || right.eclass == ExprClass.MethodGroup)
1197                                 return null;
1198
1199                         //
1200                         // Reduce (null ?? right) to right
1201                         //
1202                         if (left.IsNull)
1203                                 return ReducedExpression.Create (right, this, false).Resolve (ec);
1204
1205                         left = Convert.ImplicitConversion (ec, unwrap ?? left, rtype, loc);
1206
1207                         if (TypeSpec.IsValueType (left.Type) && !left.Type.IsNullableType) {
1208                                 Warning_UnreachableExpression (ec, right.Location);
1209                                 return ReducedExpression.Create (left, this, false).Resolve (ec);
1210                         }
1211
1212                         type = rtype;
1213                         return this;
1214                 }
1215
1216                 public override bool ContainsEmitWithAwait ()
1217                 {
1218                         if (unwrap != null)
1219                                 return unwrap.ContainsEmitWithAwait () || right.ContainsEmitWithAwait ();
1220
1221                         return left.ContainsEmitWithAwait () || right.ContainsEmitWithAwait ();
1222                 }
1223
1224                 protected override Expression DoResolve (ResolveContext ec)
1225                 {
1226                         left = left.Resolve (ec);
1227                         right = right.Resolve (ec);
1228
1229                         if (left == null || right == null)
1230                                 return null;
1231
1232                         eclass = ExprClass.Value;
1233
1234                         Expression e = ConvertExpression (ec);
1235                         if (e == null) {
1236                                 Binary.Error_OperatorCannotBeApplied (ec, left, right, "??", loc);
1237                                 return null;
1238                         }
1239
1240                         return e;
1241                 }
1242
1243                 public override void Emit (EmitContext ec)
1244                 {
1245                         Label end_label = ec.DefineLabel ();
1246
1247                         if (unwrap != null) {
1248                                 Label is_null_label = ec.DefineLabel ();
1249
1250                                 unwrap.EmitCheck (ec);
1251                                 ec.Emit (OpCodes.Brfalse, is_null_label);
1252
1253                                 //
1254                                 // When both expressions are nullable the unwrap
1255                                 // is needed only for null check not for value uwrap
1256                                 //
1257                                 if (type.IsNullableType && TypeSpecComparer.IsEqual (NullableInfo.GetUnderlyingType (type), unwrap.Type))
1258                                         unwrap.Load (ec);
1259                                 else
1260                                         left.Emit (ec);
1261
1262                                 ec.Emit (OpCodes.Br, end_label);
1263
1264                                 ec.MarkLabel (is_null_label);
1265                                 right.Emit (ec);
1266
1267                                 ec.MarkLabel (end_label);
1268                                 return;
1269                         }
1270
1271                         left.Emit (ec);
1272                         ec.Emit (OpCodes.Dup);
1273
1274                         // Only to make verifier happy
1275                         if (left.Type.IsGenericParameter)
1276                                 ec.Emit (OpCodes.Box, left.Type);
1277
1278                         ec.Emit (OpCodes.Brtrue, end_label);
1279
1280                         ec.Emit (OpCodes.Pop);
1281                         right.Emit (ec);
1282
1283                         ec.MarkLabel (end_label);
1284                 }
1285
1286                 public override void FlowAnalysis (FlowAnalysisContext fc)
1287                 {
1288                         left.FlowAnalysis (fc);
1289                         var left_da = fc.BranchDefiniteAssignment ();
1290                         right.FlowAnalysis (fc);
1291                         fc.DefiniteAssignment = left_da;
1292                 }
1293
1294                 protected override void CloneTo (CloneContext clonectx, Expression t)
1295                 {
1296                         NullCoalescingOperator target = (NullCoalescingOperator) t;
1297
1298                         target.left = left.Clone (clonectx);
1299                         target.right = right.Clone (clonectx);
1300                 }
1301
1302                 public override object Accept (StructuralVisitor visitor)
1303                 {
1304                         return visitor.Visit (this);
1305                 }
1306         }
1307
1308         class LiftedUnaryMutator : UnaryMutator
1309         {
1310                 public LiftedUnaryMutator (Mode mode, Expression expr, Location loc)
1311                         : base (mode, expr, loc)
1312                 {
1313                 }
1314
1315                 protected override Expression DoResolve (ResolveContext ec)
1316                 {
1317                         var orig_expr = expr;
1318
1319                         expr = Unwrap.Create (expr);
1320
1321                         var res = base.DoResolveOperation (ec);
1322
1323                         expr = orig_expr;
1324                         type = expr.Type;
1325
1326                         return res;
1327                 }
1328
1329                 protected override void EmitOperation (EmitContext ec)
1330                 {
1331                         Label is_null_label = ec.DefineLabel ();
1332                         Label end_label = ec.DefineLabel ();
1333
1334                         LocalTemporary lt = new LocalTemporary (type);
1335
1336                         // Value is on the stack
1337                         lt.Store (ec);
1338
1339                         var call = new CallEmitter ();
1340                         call.InstanceExpression = lt;
1341                         call.EmitPredefined (ec, NullableInfo.GetHasValue (expr.Type), null);
1342
1343                         ec.Emit (OpCodes.Brfalse, is_null_label);
1344
1345                         call = new CallEmitter ();
1346                         call.InstanceExpression = lt;
1347                         call.EmitPredefined (ec, NullableInfo.GetGetValueOrDefault (expr.Type), null);
1348
1349                         lt.Release (ec);
1350
1351                         base.EmitOperation (ec);
1352
1353                         ec.Emit (OpCodes.Newobj, NullableInfo.GetConstructor (type));
1354                         ec.Emit (OpCodes.Br_S, end_label);
1355
1356                         ec.MarkLabel (is_null_label);
1357                         LiftedNull.Create (type, loc).Emit (ec);
1358
1359                         ec.MarkLabel (end_label);
1360                 }
1361         }
1362 }
1363