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