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