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 //
  13
  14 using System;
  15 using System.Reflection;
  16 using System.Reflection.Emit;
  17 using System.Collections;
  18
  19 namespace Mono.CSharp.Nullable
  20 {
  21         public class NullableType : TypeExpr
  22         {
  23                 TypeExpr underlying;
  24
  25                 public NullableType (TypeExpr underlying, Location l)
  26                 {
  27                         this.underlying = underlying;
  28                         loc = l;
  29
  30                         eclass = ExprClass.Type;
  31                 }
  32
  33                 public NullableType (Type type, Location loc)
  34                         : this (new TypeExpression (type, loc), loc)
  35                 { }
  36
  37                 protected override TypeExpr DoResolveAsTypeStep (IResolveContext ec)
  38                 {
  39                         if (TypeManager.generic_nullable_type == null) {
  40                                 TypeManager.generic_nullable_type = TypeManager.CoreLookupType (
  41                                         "System", "Nullable`1", Kind.Struct, true);
  42                         }
  43
  44                         TypeArguments args = new TypeArguments (underlying);
  45                         GenericTypeExpr ctype = new GenericTypeExpr (TypeManager.generic_nullable_type, args, loc);
  46                         return ctype.ResolveAsTypeTerminal (ec, false);
  47                 }
  48
  49                 public override TypeExpr ResolveAsTypeTerminal (IResolveContext ec, bool silent)
  50                 {
  51                         return ResolveAsBaseTerminal (ec, silent);
  52                 }
  53         }
  54
  55         public sealed class NullableInfo
  56         {
  57                 public readonly Type Type;
  58                 public readonly Type UnderlyingType;
  59                 public MethodInfo HasValue;
  60                 public MethodInfo Value;
  61                 public MethodInfo GetValueOrDefault;
  62                 public ConstructorInfo Constructor;
  63
  64                 public NullableInfo (Type type)
  65                 {
  66                         Type = type;
  67                         UnderlyingType = TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (type) [0]);
  68
  69                         PropertyInfo has_value_pi = TypeManager.GetPredefinedProperty (type, "HasValue", Location.Null, Type.EmptyTypes);
  70                         PropertyInfo value_pi = TypeManager.GetPredefinedProperty (type, "Value", Location.Null, Type.EmptyTypes);
  71                         GetValueOrDefault = TypeManager.GetPredefinedMethod (type, "GetValueOrDefault", Location.Null, Type.EmptyTypes);
  72
  73                         HasValue = has_value_pi.GetGetMethod (false);
  74                         Value = value_pi.GetGetMethod (false);
  75
  76                         // When compiling corlib
  77                         if (type.Module == RootContext.ToplevelTypes.Builder) {
  78                                 TypeContainer tc = TypeManager.LookupGenericTypeContainer (type);
  79
  80                                 // TODO: check for correct overload
  81                                 Constructor c = ((Constructor) tc.InstanceConstructors [0]);
  82
  83 #if GMCS_SOURCE
  84                                 Constructor = TypeBuilder.GetConstructor (type, c.ConstructorBuilder);
  85 #endif
  86                                 return;
  87                         }
  88
  89                         Constructor = type.GetConstructor (new Type[] { UnderlyingType });
  90                 }
  91         }
  92
  93         public class Unwrap : Expression, IMemoryLocation, IAssignMethod
  94         {
  95                 Expression expr;
  96                 NullableInfo info;
  97
  98                 LocalTemporary temp;
  99                 readonly bool useDefaultValue;
 100
 101                 Unwrap (Expression expr, bool useDefaultValue)
 102                 {
 103                         this.expr = expr;
 104                         this.loc = expr.Location;
 105                         this.useDefaultValue = useDefaultValue;
 106
 107                         info = new NullableInfo (expr.Type);
 108                         type = info.UnderlyingType;
 109                         eclass = expr.eclass;
 110                 }
 111
 112                 public static Expression Create (Expression expr)
 113                 {
 114                         //
 115                         // Avoid unwraping and wraping of same type
 116                         //
 117                         Wrap wrap = expr as Wrap;
 118                         if (wrap != null)
 119                                 return wrap.Child;
 120
 121                         return Create (expr, false);
 122                 }
 123
 124                 public static Unwrap Create (Expression expr, bool useDefaultValue)
 125                 {
 126                         return new Unwrap (expr, useDefaultValue);
 127                 }
 128
 129                 public override Expression CreateExpressionTree (EmitContext ec)
 130                 {
 131                         return expr.CreateExpressionTree (ec);
 132                 }
 133
 134                 public override Expression DoResolve (EmitContext ec)
 135                 {
 136                         return this;
 137                 }
 138
 139                 public override Expression DoResolveLValue (EmitContext ec, Expression right_side)
 140                 {
 141                         return DoResolve (ec);
 142                 }
 143
 144                 public override void Emit (EmitContext ec)
 145                 {
 146                         Store (ec);
 147                         if (useDefaultValue)
 148                                 Invocation.EmitCall (ec, false, this, info.GetValueOrDefault, null, loc);
 149                         else
 150                                 Invocation.EmitCall (ec, false, this, info.Value, null, loc);
 151                 }
 152
 153                 public void EmitCheck (EmitContext ec)
 154                 {
 155                         Store (ec);
 156                         Invocation.EmitCall (ec, false, this, info.HasValue, null, loc);
 157                 }
 158
 159                 public override bool Equals (object obj)
 160                 {
 161                         Unwrap uw = obj as Unwrap;
 162                         return uw != null && expr.Equals (uw.expr);
 163                 }
 164
 165                 public Expression Original {
 166                         get {
 167                                 return expr;
 168                         }
 169                 }
 170
 171                 public override int GetHashCode ()
 172                 {
 173                         return expr.GetHashCode ();
 174                 }
 175
 176                 public override bool IsNull {
 177                         get {
 178                                 return expr.IsNull;
 179                         }
 180                 }
 181
 182                 void Store (EmitContext ec)
 183                 {
 184                         if (expr is VariableReference)
 185                                 return;
 186
 187                         if (temp != null)
 188                                 return;
 189
 190                         expr.Emit (ec);
 191                         LocalVariable.Store (ec);
 192                 }
 193
 194                 public void Load (EmitContext ec)
 195                 {
 196                         if (expr is VariableReference)
 197                                 expr.Emit (ec);
 198                         else
 199                                 LocalVariable.Emit (ec);
 200                 }
 201
 202                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 203                 {
 204                         type = storey.MutateType (type);
 205                         info.Constructor = storey.MutateConstructor (info.Constructor);
 206                         info.HasValue = storey.MutateGenericMethod (info.HasValue);
 207                         info.GetValueOrDefault = storey.MutateGenericMethod (info.GetValueOrDefault);
 208                         info.Value = storey.MutateGenericMethod (info.Value);
 209                 }
 210
 211                 public void AddressOf (EmitContext ec, AddressOp mode)
 212                 {
 213                         IMemoryLocation ml = expr as VariableReference;
 214                         if (ml != null)
 215                                 ml.AddressOf (ec, mode);
 216                         else
 217                                 LocalVariable.AddressOf (ec, mode);
 218                 }
 219
 220                 //
 221                 // Keeps result of non-variable expression
 222                 //
 223                 LocalTemporary LocalVariable {
 224                         get {
 225                                 if (temp == null)
 226                                         temp = new LocalTemporary (info.Type);
 227                                 return temp;
 228                         }
 229                 }
 230
 231                 public void Emit (EmitContext ec, bool leave_copy)
 232                 {
 233                         if (leave_copy)
 234                                 Load (ec);
 235
 236                         Emit (ec);
 237                 }
 238
 239                 public void EmitAssign (EmitContext ec, Expression source,
 240                                         bool leave_copy, bool prepare_for_load)
 241                 {
 242                         InternalWrap wrap = new InternalWrap (source, info, loc);
 243                         ((IAssignMethod) expr).EmitAssign (ec, wrap, leave_copy, false);
 244                 }
 245
 246                 protected class InternalWrap : Expression
 247                 {
 248                         public Expression expr;
 249                         public NullableInfo info;
 250
 251                         public InternalWrap (Expression expr, NullableInfo info, Location loc)
 252                         {
 253                                 this.expr = expr;
 254                                 this.info = info;
 255                                 this.loc = loc;
 256
 257                                 type = info.Type;
 258                                 eclass = ExprClass.Value;
 259                         }
 260
 261                         public override Expression CreateExpressionTree (EmitContext ec)
 262                         {
 263                                 throw new NotSupportedException ("ET");
 264                         }
 265
 266                         public override Expression DoResolve (EmitContext ec)
 267                         {
 268                                 return this;
 269                         }
 270
 271                         public override void Emit (EmitContext ec)
 272                         {
 273                                 expr.Emit (ec);
 274                                 ec.ig.Emit (OpCodes.Newobj, info.Constructor);
 275                         }
 276                 }
 277         }
 278
 279         public class Wrap : TypeCast
 280         {
 281                 readonly NullableInfo info;
 282
 283                 protected Wrap (Expression expr, Type type)
 284                         : base (expr, type)
 285                 {
 286                         info = new NullableInfo (type);
 287                         eclass = ExprClass.Value;
 288                 }
 289
 290                 public Expression Child {
 291                         get { return child; }
 292                 }
 293
 294                 public override Expression CreateExpressionTree (EmitContext ec)
 295                 {
 296                         TypeCast child_cast = child as TypeCast;
 297                         if (child_cast != null) {
 298                                 child.Type = type;
 299                                 return child_cast.CreateExpressionTree (ec);
 300                         }
 301
 302                         return base.CreateExpressionTree (ec);
 303                 }
 304
 305                 public static Expression Create (Expression expr, Type type)
 306                 {
 307                         //
 308                         // Avoid unwraping and wraping of the same type
 309                         //
 310                         Unwrap unwrap = expr as Unwrap;
 311                         if (unwrap != null && TypeManager.IsEqual (expr.Type, TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (type) [0])))
 312                                 return unwrap.Original;
 313
 314                         return new Wrap (expr, type);
 315                 }
 316
 317                 public override void Emit (EmitContext ec)
 318                 {
 319                         child.Emit (ec);
 320                         ec.ig.Emit (OpCodes.Newobj, info.Constructor);
 321                 }
 322         }
 323
 324         //
 325         // Represents null literal lifted to nullable type
 326         //
 327         public class LiftedNull : EmptyConstantCast, IMemoryLocation
 328         {
 329                 private LiftedNull (Type nullable_type, Location loc)
 330                         : base (new NullLiteral (loc), nullable_type)
 331                 {
 332                         eclass = ExprClass.Value;
 333                 }
 334
 335                 public static Constant Create (Type nullable, Location loc)
 336                 {
 337                         return new LiftedNull (nullable, loc);
 338                 }
 339
 340                 public static Expression CreateFromExpression (Expression e)
 341                 {
 342                         Report.Warning (458, 2, e.Location, "The result of the expression is always `null' of type `{0}'",
 343                                 TypeManager.CSharpName (e.Type));
 344
 345                         return ReducedExpression.Create (Create (e.Type, e.Location), e);
 346                 }
 347
 348                 public override Expression CreateExpressionTree (EmitContext ec)
 349                 {
 350                         Arguments args = new Arguments (2);
 351                         args.Add (new Argument (this));
 352                         args.Add (new Argument (new TypeOf (new TypeExpression (type, loc), loc)));
 353
 354                         return CreateExpressionFactoryCall ("Constant", args);
 355                 }
 356
 357                 public override void Emit (EmitContext ec)
 358                 {
 359                         // TODO: generate less temporary variables
 360                         LocalTemporary value_target = new LocalTemporary (type);
 361
 362                         value_target.AddressOf (ec, AddressOp.Store);
 363                         ec.ig.Emit (OpCodes.Initobj, type);
 364                         value_target.Emit (ec);
 365                 }
 366
 367                 public void AddressOf (EmitContext ec, AddressOp Mode)
 368                 {
 369                         LocalTemporary value_target = new LocalTemporary (type);
 370
 371                         value_target.AddressOf (ec, AddressOp.Store);
 372                         ec.ig.Emit (OpCodes.Initobj, type);
 373                         ((IMemoryLocation) value_target).AddressOf (ec, Mode);
 374                 }
 375         }
 376
 377         public class Lifted : Expression, IMemoryLocation
 378         {
 379                 Expression expr, wrap, null_value;
 380                 Unwrap unwrap;
 381
 382                 public Lifted (Expression expr, Unwrap unwrap, Type type)
 383                 {
 384                         this.expr = expr;
 385                         this.unwrap = unwrap;
 386                         this.loc = expr.Location;
 387                         this.type = type;
 388                 }
 389
 390                 public Lifted (Expression expr, Expression unwrap, Type type)
 391                         : this (expr, unwrap as Unwrap, type)
 392                 {
 393                 }
 394
 395                 public override Expression CreateExpressionTree (EmitContext ec)
 396                 {
 397                         return wrap.CreateExpressionTree (ec);
 398                 }
 399
 400                 public override Expression DoResolve (EmitContext ec)
 401                 {
 402                         wrap = Wrap.Create (expr, type);
 403                         if (wrap == null)
 404                                 return null;
 405
 406                         //
 407                         // It's null when lifted conversion is transparent
 408                         //
 409                         if (unwrap == null)
 410                                 return wrap;
 411
 412                         null_value = LiftedNull.Create (type, loc);
 413
 414                         eclass = ExprClass.Value;
 415                         return this;
 416                 }
 417
 418                 public override void Emit (EmitContext ec)
 419                 {
 420                         ILGenerator ig = ec.ig;
 421                         Label is_null_label = ig.DefineLabel ();
 422                         Label end_label = ig.DefineLabel ();
 423
 424                         unwrap.EmitCheck (ec);
 425                         ig.Emit (OpCodes.Brfalse, is_null_label);
 426
 427                         wrap.Emit (ec);
 428                         ig.Emit (OpCodes.Br, end_label);
 429
 430                         ig.MarkLabel (is_null_label);
 431                         null_value.Emit (ec);
 432
 433                         ig.MarkLabel (end_label);
 434                 }
 435
 436                 public void AddressOf (EmitContext ec, AddressOp mode)
 437                 {
 438                         unwrap.AddressOf (ec, mode);
 439                 }
 440         }
 441
 442         public class LiftedUnaryOperator : Unary, IMemoryLocation
 443         {
 444                 Unwrap unwrap;
 445                 Expression user_operator;
 446
 447                 public LiftedUnaryOperator (Unary.Operator op, Expression expr)
 448                         : base (op, expr)
 449                 {
 450                 }
 451
 452                 public void AddressOf (EmitContext ec, AddressOp mode)
 453                 {
 454                         unwrap.AddressOf (ec, mode);
 455                 }
 456
 457                 public override Expression CreateExpressionTree (EmitContext ec)
 458                 {
 459                         if (user_operator != null)
 460                                 return user_operator.CreateExpressionTree (ec);
 461
 462                         if (Oper == Operator.UnaryPlus)
 463                                 return Expr.CreateExpressionTree (ec);
 464
 465                         return base.CreateExpressionTree (ec);
 466                 }
 467
 468                 public override Expression DoResolve (EmitContext ec)
 469                 {
 470                         if (eclass != ExprClass.Invalid)
 471                                 return this;
 472
 473                         unwrap = Unwrap.Create (Expr, false);
 474                         if (unwrap == null)
 475                                 return null;
 476
 477                         Expression res = base.ResolveOperator (ec, unwrap);
 478                         if (res != this) {
 479                                 if (user_operator == null)
 480                                         return res;
 481                         } else {
 482                                 res = Expr = LiftExpression (ec, Expr);
 483                         }
 484
 485                         if (res == null)
 486                                 return null;
 487
 488                         eclass = ExprClass.Value;
 489                         type = res.Type;
 490                         return this;
 491                 }
 492
 493                 public override void Emit (EmitContext ec)
 494                 {
 495                         ILGenerator ig = ec.ig;
 496                         Label is_null_label = ig.DefineLabel ();
 497                         Label end_label = ig.DefineLabel ();
 498
 499                         unwrap.EmitCheck (ec);
 500                         ig.Emit (OpCodes.Brfalse, is_null_label);
 501
 502                         NullableInfo ni = new NullableInfo (type);
 503
 504                         if (user_operator != null) {
 505                                 user_operator.Emit (ec);
 506                         } else {
 507                                 EmitOperator (ec, ni.UnderlyingType);
 508                         }
 509
 510                         ig.Emit (OpCodes.Newobj, ni.Constructor);
 511                         ig.Emit (OpCodes.Br_S, end_label);
 512
 513                         ig.MarkLabel (is_null_label);
 514                         LiftedNull.Create (type, loc).Emit (ec);
 515
 516                         ig.MarkLabel (end_label);
 517                 }
 518
 519                 Expression LiftExpression (EmitContext ec, Expression expr)
 520                 {
 521                         TypeExpr lifted_type = new NullableType (expr.Type, expr.Location);
 522                         lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 523                         if (lifted_type == null)
 524                                 return null;
 525
 526                         expr.Type = lifted_type.Type;
 527                         return expr;
 528                 }
 529
 530                 protected override Expression ResolveEnumOperator (EmitContext ec, Expression expr)
 531                 {
 532                         expr = base.ResolveEnumOperator (ec, expr);
 533                         if (expr == null)
 534                                 return null;
 535
 536                         Expr = LiftExpression (ec, Expr);
 537                         return LiftExpression (ec, expr);
 538                 }
 539
 540                 protected override Expression ResolveUserOperator (EmitContext ec, Expression expr)
 541                 {
 542                         expr = base.ResolveUserOperator (ec, expr);
 543                         if (expr == null)
 544                                 return null;
 545
 546                         //
 547                         // When a user operator is of non-nullable type
 548                         //
 549                         if (Expr is Unwrap) {
 550                                 user_operator = LiftExpression (ec, expr);
 551                                 return user_operator;
 552                         }
 553
 554                         return expr;
 555                 }
 556         }
 557
 558         public class LiftedBinaryOperator : Binary
 559         {
 560                 Unwrap left_unwrap, right_unwrap;
 561                 bool left_null_lifted, right_null_lifted;
 562                 Expression left_orig, right_orig;
 563                 Expression user_operator;
 564                 ConstructorInfo wrap_ctor;
 565
 566                 public LiftedBinaryOperator (Binary.Operator op, Expression left, Expression right,
 567                                              Location loc)
 568                         : base (op, left, right)
 569                 {
 570                         this.loc = loc;
 571                 }
 572
 573                 public override Expression CreateExpressionTree (EmitContext ec)
 574                 {
 575                         if (user_operator != null)
 576                                 return user_operator.CreateExpressionTree (ec);
 577
 578                         return base.CreateExpressionTree (ec);
 579                 }
 580
 581                 //
 582                 // CSC 2 has this behavior, it allows structs to be compared
 583                 // with the null literal *outside* of a generics context and
 584                 // inlines that as true or false.
 585                 //
 586                 Expression CreateNullConstant (Expression expr)
 587                 {
 588                         // FIXME: Handle side effect constants
 589                         Constant c = new BoolConstant (Oper == Operator.Inequality, loc);
 590
 591                         if ((Oper & Operator.EqualityMask) != 0) {
 592                                 Report.Warning (472, 2, loc, "The result of comparing value type `{0}' with null is `{1}'",
 593                                                 expr.GetSignatureForError (), c.AsString ());
 594                         } else {
 595                                 Report.Warning (464, 2, loc, "The result of comparing type `{0}' with null is always `{1}'",
 596                                                 expr.GetSignatureForError (), c.AsString ());
 597                         }
 598
 599                         return ReducedExpression.Create (c, this);
 600                 }
 601
 602                 public override Expression DoResolve (EmitContext ec)
 603                 {
 604                         if (eclass != ExprClass.Invalid)
 605                                 return this;
 606
 607                         if ((Oper & Operator.LogicalMask) != 0) {
 608                                 Error_OperatorCannotBeApplied (left, right);
 609                                 return null;
 610                         }
 611
 612                         bool use_default_call = (Oper & (Operator.BitwiseMask | Operator.EqualityMask)) != 0;
 613                         left_orig = left;
 614                         if (TypeManager.IsNullableType (left.Type)) {
 615                                 left = left_unwrap = Unwrap.Create (left, use_default_call);
 616                                 if (left == null)
 617                                         return null;
 618                         }
 619
 620                         right_orig = right;
 621                         if (TypeManager.IsNullableType (right.Type)) {
 622                                 right = right_unwrap = Unwrap.Create (right, use_default_call);
 623                                 if (right == null)
 624                                         return null;
 625                         }
 626
 627                         //
 628                         // Some details are in 6.4.2, 7.2.7
 629                         // Arguments can be lifted for equal operators when the return type is bool and both
 630                         // arguments are of same type
 631                         //
 632                         if (left_orig.IsNull) {
 633                                 left = right;
 634                                 left_null_lifted = true;
 635                                 type = TypeManager.bool_type;
 636                         }
 637
 638                         if (right_orig.IsNull) {
 639                                 right = left;
 640                                 right_null_lifted = true;
 641                                 type = TypeManager.bool_type;
 642                         }
 643
 644                         eclass = ExprClass.Value;
 645                         return DoResolveCore (ec, left_orig, right_orig);
 646                 }
 647
 648                 void EmitBitwiseBoolean (EmitContext ec)
 649                 {
 650                         ILGenerator ig = ec.ig;
 651
 652                         Label load_left = ig.DefineLabel ();
 653                         Label load_right = ig.DefineLabel ();
 654                         Label end_label = ig.DefineLabel ();
 655
 656                         left_unwrap.Emit (ec);
 657                         ig.Emit (OpCodes.Brtrue_S, load_right);
 658
 659                         right_unwrap.Emit (ec);
 660                         ig.Emit (OpCodes.Brtrue_S, load_left);
 661
 662                         left_unwrap.EmitCheck (ec);
 663                         ig.Emit (OpCodes.Brfalse_S, load_right);
 664
 665                         // load left
 666                         ig.MarkLabel (load_left);
 667
 668                         if (Oper == Operator.BitwiseAnd) {
 669                                 left_unwrap.Load (ec);
 670                         } else {
 671                                 right_unwrap.Load (ec);
 672                                 right_unwrap = left_unwrap;
 673                         }
 674                         ig.Emit (OpCodes.Br_S, end_label);
 675
 676                         // load right
 677                         ig.MarkLabel (load_right);
 678                         right_unwrap.Load (ec);
 679
 680                         ig.MarkLabel (end_label);
 681                 }
 682
 683                 //
 684                 // Emits optimized equality or inequality operator when possible
 685                 //
 686                 void EmitEquality (EmitContext ec)
 687                 {
 688                         ILGenerator ig = ec.ig;
 689
 690                         //
 691                         // Either left or right is null
 692                         //
 693                         if (left_unwrap != null && (right_null_lifted || right.IsNull)) {
 694                                 left_unwrap.EmitCheck (ec);
 695                                 if (Oper == Binary.Operator.Equality) {
 696                                         ig.Emit (OpCodes.Ldc_I4_0);
 697                                         ig.Emit (OpCodes.Ceq);
 698                                 }
 699                                 return;
 700                         }
 701
 702                         if (right_unwrap != null && (left_null_lifted || left.IsNull)) {
 703                                 right_unwrap.EmitCheck (ec);
 704                                 if (Oper == Binary.Operator.Equality) {
 705                                         ig.Emit (OpCodes.Ldc_I4_0);
 706                                         ig.Emit (OpCodes.Ceq);
 707                                 }
 708                                 return;
 709                         }
 710
 711                         Label dissimilar_label = ig.DefineLabel ();
 712                         Label end_label = ig.DefineLabel ();
 713
 714                         if (user_operator != null) {
 715                                 user_operator.Emit (ec);
 716                                 ig.Emit (Oper == Operator.Equality ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, dissimilar_label);
 717                         } else {
 718                                 left.Emit (ec);
 719                                 right.Emit (ec);
 720
 721                                 ig.Emit (OpCodes.Bne_Un_S, dissimilar_label);
 722                         }
 723
 724                         if (left_unwrap != null)
 725                                 left_unwrap.EmitCheck (ec);
 726
 727                         if (right_unwrap != null)
 728                                 right_unwrap.EmitCheck (ec);
 729
 730                         if (left_unwrap != null && right_unwrap != null) {
 731                                 if (Oper == Operator.Inequality)
 732                                         ig.Emit (OpCodes.Xor);
 733                                 else
 734                                         ig.Emit (OpCodes.Ceq);
 735                         } else {
 736                                 if (Oper == Operator.Inequality) {
 737                                         ig.Emit (OpCodes.Ldc_I4_0);
 738                                         ig.Emit (OpCodes.Ceq);
 739                                 }
 740                         }
 741
 742                         ig.Emit (OpCodes.Br_S, end_label);
 743
 744                         ig.MarkLabel (dissimilar_label);
 745                         if (Oper == Operator.Inequality)
 746                                 ig.Emit (OpCodes.Ldc_I4_1);
 747                         else
 748                                 ig.Emit (OpCodes.Ldc_I4_0);
 749
 750                         ig.MarkLabel (end_label);
 751                 }
 752
 753                 public override void EmitBranchable (EmitContext ec, Label target, bool onTrue)
 754                 {
 755                         Emit (ec);
 756                         ec.ig.Emit (onTrue ? OpCodes.Brtrue : OpCodes.Brfalse, target);
 757                 }
 758
 759                 public override void Emit (EmitContext ec)
 760                 {
 761                         //
 762                         // Optimize same expression operation
 763                         //
 764                         if (right_unwrap != null && right.Equals (left))
 765                                 right_unwrap = left_unwrap;
 766
 767                         if (user_operator == null && IsBitwiseBoolean) {
 768                                 EmitBitwiseBoolean (ec);
 769                                 return;
 770                         }
 771
 772                         if ((Oper & Operator.EqualityMask) != 0) {
 773                                 EmitEquality (ec);
 774                                 return;
 775                         }
 776
 777                         ILGenerator ig = ec.ig;
 778
 779                         Label is_null_label = ig.DefineLabel ();
 780                         Label end_label = ig.DefineLabel ();
 781
 782                         if (left_unwrap != null) {
 783                                 left_unwrap.EmitCheck (ec);
 784                                 ig.Emit (OpCodes.Brfalse, is_null_label);
 785                         }
 786
 787                         //
 788                         // Don't emit HasValue check when left and right expressions are same
 789                         //
 790                         if (right_unwrap != null && !left.Equals (right)) {
 791                                 right_unwrap.EmitCheck (ec);
 792                                 ig.Emit (OpCodes.Brfalse, is_null_label);
 793                         }
 794
 795                         EmitOperator (ec, left.Type);
 796
 797                         if (wrap_ctor != null)
 798                                 ig.Emit (OpCodes.Newobj, wrap_ctor);
 799
 800                         ig.Emit (OpCodes.Br_S, end_label);
 801                         ig.MarkLabel (is_null_label);
 802
 803                         if ((Oper & Operator.ComparisonMask) != 0) {
 804                                 ig.Emit (OpCodes.Ldc_I4_0);
 805                         } else {
 806                                 LiftedNull.Create (type, loc).Emit (ec);
 807                         }
 808
 809                         ig.MarkLabel (end_label);
 810                 }
 811
 812                 protected override void EmitOperator (EmitContext ec, Type l)
 813                 {
 814                         if (user_operator != null) {
 815                                 user_operator.Emit (ec);
 816                                 return;
 817                         }
 818
 819                         if (TypeManager.IsNullableType (l))
 820                                 l = TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (l) [0]);
 821
 822                         base.EmitOperator (ec, l);
 823                 }
 824
 825                 bool IsBitwiseBoolean {
 826                         get {
 827                                 return (Oper & Operator.BitwiseMask) != 0 && left_unwrap != null && right_unwrap != null &&
 828                                 left_unwrap.Type == TypeManager.bool_type && right_unwrap.Type == TypeManager.bool_type;
 829                         }
 830                 }
 831
 832                 Expression LiftResult (EmitContext ec, Expression res_expr)
 833                 {
 834                         TypeExpr lifted_type;
 835
 836                         //
 837                         // Avoid double conversion
 838                         //
 839                         if (left_unwrap == null || left_null_lifted || !TypeManager.IsEqual (left_unwrap.Type, left.Type) || (left_unwrap != null && right_null_lifted)) {
 840                                 lifted_type = new NullableType (left.Type, loc);
 841                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 842                                 if (lifted_type == null)
 843                                         return null;
 844
 845                                 if (left is UserCast || left is TypeCast)
 846                                         left.Type = lifted_type.Type;
 847                                 else
 848                                         left = EmptyCast.Create (left, lifted_type.Type);
 849                         }
 850
 851                         if (right_unwrap == null || right_null_lifted || !TypeManager.IsEqual (right_unwrap.Type, right.Type) || (right_unwrap != null && left_null_lifted)) {
 852                                 lifted_type = new NullableType (right.Type, loc);
 853                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 854                                 if (lifted_type == null)
 855                                         return null;
 856
 857                                 if (right is UserCast || right is TypeCast)
 858                                         right.Type = lifted_type.Type;
 859                                 else
 860                                         right = EmptyCast.Create (right, lifted_type.Type);
 861                         }
 862
 863                         if ((Oper & Operator.ComparisonMask) == 0) {
 864                                 lifted_type = new NullableType (res_expr.Type, loc);
 865                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 866                                 if (lifted_type == null)
 867                                         return null;
 868
 869                                 wrap_ctor = new NullableInfo (lifted_type.Type).Constructor;
 870                                 type = res_expr.Type = lifted_type.Type;
 871                         }
 872
 873                         if (left_null_lifted) {
 874                                 left = LiftedNull.Create (right.Type, left.Location);
 875
 876                                 if ((Oper & (Operator.ArithmeticMask | Operator.ShiftMask)) != 0)
 877                                         return LiftedNull.CreateFromExpression (res_expr);
 878
 879                                 //
 880                                 // Value types and null comparison
 881                                 //
 882                                 if (right_unwrap == null || (Oper & Operator.RelationalMask) != 0)
 883                                         return CreateNullConstant (right_orig).Resolve (ec);
 884                         }
 885
 886                         if (right_null_lifted) {
 887                                 right = LiftedNull.Create (left.Type, right.Location);
 888
 889                                 if ((Oper & (Operator.ArithmeticMask | Operator.ShiftMask)) != 0)
 890                                         return LiftedNull.CreateFromExpression (res_expr);
 891
 892                                 //
 893                                 // Value types and null comparison
 894                                 //
 895                                 if (left_unwrap == null || (Oper & Operator.RelationalMask) != 0)
 896                                         return CreateNullConstant (left_orig).Resolve (ec);
 897                         }
 898
 899                         return res_expr;
 900                 }
 901
 902                 protected override Expression ResolveOperatorPredefined (EmitContext ec, Binary.PredefinedOperator [] operators, bool primitives_only, Type enum_type)
 903                 {
 904                         Expression e = base.ResolveOperatorPredefined (ec, operators, primitives_only, enum_type);
 905
 906                         if (e == this || enum_type != null)
 907                                 return LiftResult (ec, e);
 908
 909                         //
 910                         // 7.9.9 Equality operators and null
 911                         //
 912                         // The == and != operators permit one operand to be a value of a nullable type and
 913                         // the other to be the null literal, even if no predefined or user-defined operator
 914                         // (in unlifted or lifted form) exists for the operation.
 915                         //
 916                         if (e == null && (Oper & Operator.EqualityMask) != 0) {
 917                                 if ((left_null_lifted && right_unwrap != null) || (right_null_lifted && left_unwrap != null))
 918                                         return LiftResult (ec, this);
 919                         }
 920
 921                         return e;
 922                 }
 923
 924                 protected override Expression ResolveUserOperator (EmitContext ec, Type l, Type r)
 925                 {
 926                         Expression expr = base.ResolveUserOperator (ec, l, r);
 927                         if (expr == null)
 928                                 return null;
 929
 930                         expr = LiftResult (ec, expr);
 931                         if (expr is Constant)
 932                                 return expr;
 933
 934                         type = expr.Type;
 935                         user_operator = expr;
 936                         return this;
 937                 }
 938         }
 939
 940         public class NullCoalescingOperator : Expression
 941         {
 942                 Expression left, right;
 943                 Unwrap unwrap;
 944
 945                 public NullCoalescingOperator (Expression left, Expression right, Location loc)
 946                 {
 947                         this.left = left;
 948                         this.right = right;
 949                         this.loc = loc;
 950                 }
 951
 952                 public override Expression CreateExpressionTree (EmitContext ec)
 953                 {
 954                         if (left.Type == TypeManager.null_type)
 955                                 Report.Error (845, loc, "An expression tree cannot contain a coalescing operator with null left side");
 956
 957                         UserCast uc = left as UserCast;
 958                         Expression conversion = null;
 959                         if (uc != null) {
 960                                 left = uc.Source;
 961
 962                                 Arguments c_args = new Arguments (2);
 963                                 c_args.Add (new Argument (uc.CreateExpressionTree (ec)));
 964                                 c_args.Add (new Argument (left.CreateExpressionTree (ec)));
 965                                 conversion = CreateExpressionFactoryCall ("Lambda", c_args);
 966                         }
 967
 968                         Arguments args = new Arguments (3);
 969                         args.Add (new Argument (left.CreateExpressionTree (ec)));
 970                         args.Add (new Argument (right.CreateExpressionTree (ec)));
 971                         if (conversion != null)
 972                                 args.Add (new Argument (conversion));
 973
 974                         return CreateExpressionFactoryCall ("Coalesce", args);
 975                 }
 976
 977                 Expression ConvertExpression (EmitContext ec)
 978                 {
 979                         // TODO: ImplicitConversionExists should take care of this
 980                         if (left.eclass == ExprClass.MethodGroup)
 981                                 return null;
 982
 983                         Type ltype = left.Type;
 984
 985                         //
 986                         // If left is a nullable type and an implicit conversion exists from right to underlying type of left,
 987                         // the result is underlying type of left
 988                         //
 989                         if (TypeManager.IsNullableType (ltype)) {
 990                                 unwrap = Unwrap.Create (left, false);
 991                                 if (unwrap == null)
 992                                         return null;
 993
 994                                 if (Convert.ImplicitConversionExists (ec, right, unwrap.Type)) {
 995                                         left = unwrap;
 996                                         type = left.Type;
 997                                         right = Convert.ImplicitConversion (ec, right, type, loc);
 998                                         return this;
 999                                 }
1000                         } else if (TypeManager.IsReferenceType (ltype)) {
1001                                 if (Convert.ImplicitConversionExists (ec, right, ltype)) {
1002                                         //
1003                                         // Reduce (constant ?? expr) to constant
1004                                         //
1005                                         Constant lc = left as Constant;
1006                                         if (lc != null && !lc.IsDefaultValue)
1007                                                 return new SideEffectConstant (lc, right, loc).Resolve (ec);
1008
1009                                         //
1010                                         // Reduce (left ?? null) to left OR (null-constant ?? right) to right
1011                                         //
1012                                         if (right.IsNull || lc != null)
1013                                                 return ReducedExpression.Create (lc != null ? right : left, this).Resolve (ec);
1014
1015                                         right = Convert.ImplicitConversion (ec, right, ltype, loc);
1016                                         type = left.Type;
1017                                         return this;
1018                                 }
1019                         } else {
1020                                 return null;
1021                         }
1022
1023                         Type rtype = right.Type;
1024                         if (!Convert.ImplicitConversionExists (ec, unwrap != null ? unwrap : left, rtype) || right.eclass == ExprClass.MethodGroup)
1025                                 return null;
1026
1027                         //
1028                         // Reduce (null ?? right) to right
1029                         //
1030                         if (left.IsNull)
1031                                 return ReducedExpression.Create (right, this).Resolve (ec);
1032
1033                         left = Convert.ImplicitConversion (ec, unwrap != null ? unwrap : left, rtype, loc);
1034                         type = rtype;
1035                         return this;
1036                 }
1037
1038                 public override Expression DoResolve (EmitContext ec)
1039                 {
1040                         if (eclass != ExprClass.Invalid)
1041                                 return this;
1042
1043                         left = left.Resolve (ec);
1044                         right = right.Resolve (ec);
1045
1046                         if (left == null || right == null)
1047                                 return null;
1048
1049                         eclass = ExprClass.Value;
1050
1051                         Expression e = ConvertExpression (ec);
1052                         if (e == null) {
1053                                 Binary.Error_OperatorCannotBeApplied (left, right, "??", loc);
1054                                 return null;
1055                         }
1056
1057                         return e;
1058                 }
1059
1060                 public override void Emit (EmitContext ec)
1061                 {
1062                         ILGenerator ig = ec.ig;
1063
1064                         Label end_label = ig.DefineLabel ();
1065
1066                         if (unwrap != null) {
1067                                 Label is_null_label = ig.DefineLabel ();
1068
1069                                 unwrap.EmitCheck (ec);
1070                                 ig.Emit (OpCodes.Brfalse, is_null_label);
1071
1072                                 left.Emit (ec);
1073                                 ig.Emit (OpCodes.Br, end_label);
1074
1075                                 ig.MarkLabel (is_null_label);
1076                                 right.Emit (ec);
1077
1078                                 ig.MarkLabel (end_label);
1079                                 return;
1080                         }
1081
1082                         left.Emit (ec);
1083
1084                         ig.Emit (OpCodes.Dup);
1085                         ig.Emit (OpCodes.Brtrue, end_label);
1086
1087                         ig.Emit (OpCodes.Pop);
1088                         right.Emit (ec);
1089
1090                         ig.MarkLabel (end_label);
1091                 }
1092
1093                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
1094                 {
1095                         left.MutateHoistedGenericType (storey);
1096                         right.MutateHoistedGenericType (storey);
1097                         type = storey.MutateType (type);
1098                 }
1099
1100                 protected override void CloneTo (CloneContext clonectx, Expression t)
1101                 {
1102                         NullCoalescingOperator target = (NullCoalescingOperator) t;
1103
1104                         target.left = left.Clone (clonectx);
1105                         target.right = right.Clone (clonectx);
1106                 }
1107         }
1108
1109         public class LiftedUnaryMutator : ExpressionStatement
1110         {
1111                 public readonly UnaryMutator.Mode Mode;
1112                 Expression expr;
1113                 UnaryMutator underlying;
1114                 Unwrap unwrap;
1115
1116                 public LiftedUnaryMutator (UnaryMutator.Mode mode, Expression expr, Location loc)
1117                 {
1118                         this.expr = expr;
1119                         this.Mode = mode;
1120                         this.loc = loc;
1121
1122                         eclass = ExprClass.Value;
1123                 }
1124
1125                 public override Expression CreateExpressionTree (EmitContext ec)
1126                 {
1127                         return new SimpleAssign (this, this).CreateExpressionTree (ec);
1128                 }
1129
1130                 public override Expression DoResolve (EmitContext ec)
1131                 {
1132                         expr = expr.Resolve (ec);
1133                         if (expr == null)
1134                                 return null;
1135
1136                         unwrap = Unwrap.Create (expr, false);
1137                         if (unwrap == null)
1138                                 return null;
1139
1140                         underlying = (UnaryMutator) new UnaryMutator (Mode, unwrap).Resolve (ec);
1141                         if (underlying == null)
1142                                 return null;
1143
1144                         type = expr.Type;
1145                         return this;
1146                 }
1147
1148                 void DoEmit (EmitContext ec, bool is_expr)
1149                 {
1150                         ILGenerator ig = ec.ig;
1151                         Label is_null_label = ig.DefineLabel ();
1152                         Label end_label = ig.DefineLabel ();
1153
1154                         unwrap.EmitCheck (ec);
1155                         ig.Emit (OpCodes.Brfalse, is_null_label);
1156
1157                         if (is_expr) {
1158                                 underlying.Emit (ec);
1159                                 ig.Emit (OpCodes.Br_S, end_label);
1160                         } else {
1161                                 underlying.EmitStatement (ec);
1162                         }
1163
1164                         ig.MarkLabel (is_null_label);
1165                         if (is_expr)
1166                                 LiftedNull.Create (type, loc).Emit (ec);
1167
1168                         ig.MarkLabel (end_label);
1169                 }
1170
1171                 public override void Emit (EmitContext ec)
1172                 {
1173                         DoEmit (ec, true);
1174                 }
1175
1176                 public override void EmitStatement (EmitContext ec)
1177                 {
1178                         DoEmit (ec, false);
1179                 }
1180         }
1181 }
1182