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
  18 namespace Mono.CSharp.Nullable
  19 {
  20         public class NullableType : TypeExpr
  21         {
  22                 TypeExpr underlying;
  23
  24                 public NullableType (TypeExpr underlying, Location l)
  25                 {
  26                         this.underlying = underlying;
  27                         loc = l;
  28
  29                         eclass = ExprClass.Type;
  30                 }
  31
  32                 public NullableType (Type type, Location loc)
  33                         : this (new TypeExpression (type, loc), loc)
  34                 { }
  35
  36                 protected override TypeExpr DoResolveAsTypeStep (IMemberContext ec)
  37                 {
  38                         if (TypeManager.generic_nullable_type == null) {
  39                                 TypeManager.generic_nullable_type = TypeManager.CoreLookupType (ec.Compiler,
  40                                         "System", "Nullable`1", Kind.Struct, true);
  41                         }
  42
  43                         TypeArguments args = new TypeArguments (underlying);
  44                         GenericTypeExpr ctype = new GenericTypeExpr (TypeManager.generic_nullable_type, args, loc);
  45                         return ctype.ResolveAsTypeTerminal (ec, false);
  46                 }
  47
  48                 public override TypeExpr ResolveAsTypeTerminal (IMemberContext ec, bool silent)
  49                 {
  50                         return ResolveAsBaseTerminal (ec, silent);
  51                 }
  52         }
  53
  54         public sealed class NullableInfo
  55         {
  56                 public readonly Type Type;
  57                 public readonly Type UnderlyingType;
  58                 public MethodInfo HasValue;
  59                 public MethodInfo Value;
  60                 public MethodInfo GetValueOrDefault;
  61                 public ConstructorInfo Constructor;
  62
  63                 public NullableInfo (Type type)
  64                 {
  65                         Type = type;
  66                         UnderlyingType = TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (type) [0]);
  67
  68                         PropertyInfo has_value_pi = TypeManager.GetPredefinedProperty (type, "HasValue", Location.Null, Type.EmptyTypes);
  69                         PropertyInfo value_pi = TypeManager.GetPredefinedProperty (type, "Value", Location.Null, Type.EmptyTypes);
  70                         GetValueOrDefault = TypeManager.GetPredefinedMethod (type, "GetValueOrDefault", Location.Null, Type.EmptyTypes);
  71
  72                         HasValue = has_value_pi.GetGetMethod (false);
  73                         Value = value_pi.GetGetMethod (false);
  74
  75                         // When compiling corlib
  76                         if (TypeManager.IsBeingCompiled (type)) {
  77                                 TypeContainer tc = TypeManager.LookupGenericTypeContainer (type);
  78
  79                                 // TODO: check for correct overload
  80                                 Constructor c = ((Constructor) tc.InstanceConstructors [0]);
  81
  82                                 Constructor = TypeBuilder.GetConstructor (type, c.ConstructorBuilder);
  83                                 return;
  84                         }
  85
  86 #if MS_COMPATIBLE
  87                         if (TypeManager.IsBeingCompiled (UnderlyingType)) {
  88                                 ConstructorInfo cinfo = TypeManager.DropGenericTypeArguments (type).GetConstructors ()[0];
  89                                 Constructor = TypeBuilder.GetConstructor (type, cinfo);
  90                                 return;
  91                         }
  92 #endif
  93
  94                         Constructor = type.GetConstructor (new Type[] { UnderlyingType });
  95                 }
  96         }
  97
  98         public class Unwrap : Expression, IMemoryLocation, IAssignMethod
  99         {
 100                 Expression expr;
 101                 NullableInfo info;
 102
 103                 LocalTemporary temp;
 104                 readonly bool useDefaultValue;
 105
 106                 Unwrap (Expression expr, bool useDefaultValue)
 107                 {
 108                         this.expr = expr;
 109                         this.loc = expr.Location;
 110                         this.useDefaultValue = useDefaultValue;
 111
 112                         info = new NullableInfo (expr.Type);
 113                         type = info.UnderlyingType;
 114                         eclass = expr.eclass;
 115                 }
 116
 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 Unwrap Create (Expression expr, bool useDefaultValue)
 130                 {
 131                         return new Unwrap (expr, useDefaultValue);
 132                 }
 133
 134                 public override Expression CreateExpressionTree (ResolveContext ec)
 135                 {
 136                         return expr.CreateExpressionTree (ec);
 137                 }
 138
 139                 protected override Expression DoResolve (ResolveContext ec)
 140                 {
 141                         return this;
 142                 }
 143
 144                 public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
 145                 {
 146                         return DoResolve (ec);
 147                 }
 148
 149                 public override void Emit (EmitContext ec)
 150                 {
 151                         Store (ec);
 152                         if (useDefaultValue)
 153                                 Invocation.EmitCall (ec, false, this, info.GetValueOrDefault, null, loc);
 154                         else
 155                                 Invocation.EmitCall (ec, false, this, info.Value, null, loc);
 156                 }
 157
 158                 public void EmitCheck (EmitContext ec)
 159                 {
 160                         Store (ec);
 161                         Invocation.EmitCall (ec, false, this, info.HasValue, null, loc);
 162                 }
 163
 164                 public override bool Equals (object obj)
 165                 {
 166                         Unwrap uw = obj as Unwrap;
 167                         return uw != null && expr.Equals (uw.expr);
 168                 }
 169
 170                 public Expression Original {
 171                         get {
 172                                 return expr;
 173                         }
 174                 }
 175
 176                 public override int GetHashCode ()
 177                 {
 178                         return expr.GetHashCode ();
 179                 }
 180
 181                 public override bool IsNull {
 182                         get {
 183                                 return expr.IsNull;
 184                         }
 185                 }
 186
 187                 void Store (EmitContext ec)
 188                 {
 189                         if (expr is VariableReference)
 190                                 return;
 191
 192                         if (temp != null)
 193                                 return;
 194
 195                         expr.Emit (ec);
 196                         LocalVariable.Store (ec);
 197                 }
 198
 199                 public void Load (EmitContext ec)
 200                 {
 201                         if (expr is VariableReference)
 202                                 expr.Emit (ec);
 203                         else
 204                                 LocalVariable.Emit (ec);
 205                 }
 206
 207 #if NET_4_0
 208                 public override System.Linq.Expressions.Expression MakeExpression (BuilderContext ctx)
 209                 {
 210                         return expr.MakeExpression (ctx);
 211                 }
 212 #endif
 213
 214                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 215                 {
 216                         type = storey.MutateType (type);
 217                         info.Constructor = storey.MutateConstructor (info.Constructor);
 218                         info.HasValue = storey.MutateGenericMethod (info.HasValue);
 219                         info.GetValueOrDefault = storey.MutateGenericMethod (info.GetValueOrDefault);
 220                         info.Value = storey.MutateGenericMethod (info.Value);
 221                 }
 222
 223                 public void AddressOf (EmitContext ec, AddressOp mode)
 224                 {
 225                         IMemoryLocation ml = expr as VariableReference;
 226                         if (ml != null)
 227                                 ml.AddressOf (ec, mode);
 228                         else
 229                                 LocalVariable.AddressOf (ec, mode);
 230                 }
 231
 232                 //
 233                 // Keeps result of non-variable expression
 234                 //
 235                 LocalTemporary LocalVariable {
 236                         get {
 237                                 if (temp == null)
 238                                         temp = new LocalTemporary (info.Type);
 239                                 return temp;
 240                         }
 241                 }
 242
 243                 public void Emit (EmitContext ec, bool leave_copy)
 244                 {
 245                         if (leave_copy)
 246                                 Load (ec);
 247
 248                         Emit (ec);
 249                 }
 250
 251                 public void EmitAssign (EmitContext ec, Expression source,
 252                                         bool leave_copy, bool prepare_for_load)
 253                 {
 254                         InternalWrap wrap = new InternalWrap (source, info, loc);
 255                         ((IAssignMethod) expr).EmitAssign (ec, wrap, leave_copy, false);
 256                 }
 257
 258                 protected class InternalWrap : Expression
 259                 {
 260                         public Expression expr;
 261                         public NullableInfo info;
 262
 263                         public InternalWrap (Expression expr, NullableInfo info, Location loc)
 264                         {
 265                                 this.expr = expr;
 266                                 this.info = info;
 267                                 this.loc = loc;
 268
 269                                 type = info.Type;
 270                                 eclass = ExprClass.Value;
 271                         }
 272
 273                         public override Expression CreateExpressionTree (ResolveContext ec)
 274                         {
 275                                 throw new NotSupportedException ("ET");
 276                         }
 277
 278                         protected override Expression DoResolve (ResolveContext ec)
 279                         {
 280                                 return this;
 281                         }
 282
 283                         public override void Emit (EmitContext ec)
 284                         {
 285                                 expr.Emit (ec);
 286                                 ec.ig.Emit (OpCodes.Newobj, info.Constructor);
 287                         }
 288                 }
 289         }
 290
 291         public class Wrap : TypeCast
 292         {
 293                 readonly NullableInfo info;
 294
 295                 protected Wrap (Expression expr, Type type)
 296                         : base (expr, type)
 297                 {
 298                         info = new NullableInfo (type);
 299                         eclass = ExprClass.Value;
 300                 }
 301
 302                 public Expression Child {
 303                         get { return child; }
 304                 }
 305
 306                 public override Expression CreateExpressionTree (ResolveContext ec)
 307                 {
 308                         TypeCast child_cast = child as TypeCast;
 309                         if (child_cast != null) {
 310                                 child.Type = type;
 311                                 return child_cast.CreateExpressionTree (ec);
 312                         }
 313
 314                         return base.CreateExpressionTree (ec);
 315                 }
 316
 317                 public static Expression Create (Expression expr, Type type)
 318                 {
 319                         //
 320                         // Avoid unwraping and wraping of the same type
 321                         //
 322                         Unwrap unwrap = expr as Unwrap;
 323                         if (unwrap != null && TypeManager.IsEqual (expr.Type, TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (type) [0])))
 324                                 return unwrap.Original;
 325
 326                         return new Wrap (expr, type);
 327                 }
 328
 329                 public override void Emit (EmitContext ec)
 330                 {
 331                         child.Emit (ec);
 332                         ec.ig.Emit (OpCodes.Newobj, info.Constructor);
 333                 }
 334         }
 335
 336         //
 337         // Represents null literal lifted to nullable type
 338         //
 339         public class LiftedNull : NullConstant, IMemoryLocation
 340         {
 341                 private LiftedNull (Type nullable_type, Location loc)
 342                         : base (nullable_type, loc)
 343                 {
 344                         eclass = ExprClass.Value;
 345                 }
 346
 347                 public static Constant Create (Type nullable, Location loc)
 348                 {
 349                         return new LiftedNull (nullable, loc);
 350                 }
 351
 352                 public static Expression CreateFromExpression (ResolveContext ec, Expression e)
 353                 {
 354                         ec.Report.Warning (458, 2, e.Location, "The result of the expression is always `null' of type `{0}'",
 355                                 TypeManager.CSharpName (e.Type));
 356
 357                         return ReducedExpression.Create (Create (e.Type, e.Location), e);
 358                 }
 359
 360                 public override void Emit (EmitContext ec)
 361                 {
 362                         // TODO: generate less temporary variables
 363                         LocalTemporary value_target = new LocalTemporary (type);
 364
 365                         value_target.AddressOf (ec, AddressOp.Store);
 366                         ec.ig.Emit (OpCodes.Initobj, type);
 367                         value_target.Emit (ec);
 368                 }
 369
 370                 public void AddressOf (EmitContext ec, AddressOp Mode)
 371                 {
 372                         LocalTemporary value_target = new LocalTemporary (type);
 373
 374                         value_target.AddressOf (ec, AddressOp.Store);
 375                         ec.ig.Emit (OpCodes.Initobj, type);
 376                         ((IMemoryLocation) value_target).AddressOf (ec, Mode);
 377                 }
 378         }
 379
 380         //
 381         // Generic lifting expression, supports all S/S? -> T/T? cases
 382         //
 383         public class Lifted : Expression, IMemoryLocation
 384         {
 385                 Expression expr, null_value;
 386                 Unwrap unwrap;
 387
 388                 public Lifted (Expression expr, Unwrap unwrap, Type type)
 389                 {
 390                         this.expr = expr;
 391                         this.unwrap = unwrap;
 392                         this.loc = expr.Location;
 393                         this.type = type;
 394                 }
 395
 396                 public Lifted (Expression expr, Expression unwrap, Type type)
 397                         : this (expr, unwrap as Unwrap, type)
 398                 {
 399                 }
 400
 401                 public override Expression CreateExpressionTree (ResolveContext ec)
 402                 {
 403                         return expr.CreateExpressionTree (ec);
 404                 }
 405
 406                 protected override Expression DoResolve (ResolveContext ec)
 407                 {
 408                         //
 409                         // It's null when lifting non-nullable type
 410                         //
 411                         if (unwrap == null) {
 412                                 // S -> T? is wrap only
 413                                 if (TypeManager.IsNullableType (type))
 414                                         return Wrap.Create (expr, type);
 415
 416                                 // S -> T can be simplified
 417                                 return expr;
 418                         }
 419
 420                         // Wrap target for T?
 421                         if (TypeManager.IsNullableType (type)) {
 422                                 expr = Wrap.Create (expr, type);
 423                                 if (expr == null)
 424                                         return null;
 425
 426                                 null_value = LiftedNull.Create (type, loc);
 427                         } else {
 428                                 null_value = new NullConstant (type, loc);
 429                         }
 430
 431                         eclass = ExprClass.Value;
 432                         return this;
 433                 }
 434
 435                 public override void Emit (EmitContext ec)
 436                 {
 437                         ILGenerator ig = ec.ig;
 438                         Label is_null_label = ig.DefineLabel ();
 439                         Label end_label = ig.DefineLabel ();
 440
 441                         unwrap.EmitCheck (ec);
 442                         ig.Emit (OpCodes.Brfalse, is_null_label);
 443
 444                         expr.Emit (ec);
 445
 446                         ig.Emit (OpCodes.Br, end_label);
 447                         ig.MarkLabel (is_null_label);
 448
 449                         null_value.Emit (ec);
 450                         ig.MarkLabel (end_label);
 451                 }
 452
 453                 public void AddressOf (EmitContext ec, AddressOp mode)
 454                 {
 455                         unwrap.AddressOf (ec, mode);
 456                 }
 457         }
 458
 459         public class LiftedUnaryOperator : Unary, IMemoryLocation
 460         {
 461                 Unwrap unwrap;
 462                 Expression user_operator;
 463
 464                 public LiftedUnaryOperator (Unary.Operator op, Expression expr)
 465                         : base (op, expr)
 466                 {
 467                 }
 468
 469                 public void AddressOf (EmitContext ec, AddressOp mode)
 470                 {
 471                         unwrap.AddressOf (ec, mode);
 472                 }
 473
 474                 public override Expression CreateExpressionTree (ResolveContext ec)
 475                 {
 476                         if (user_operator != null)
 477                                 return user_operator.CreateExpressionTree (ec);
 478
 479                         if (Oper == Operator.UnaryPlus)
 480                                 return Expr.CreateExpressionTree (ec);
 481
 482                         return base.CreateExpressionTree (ec);
 483                 }
 484
 485                 protected override Expression DoResolve (ResolveContext ec)
 486                 {
 487                         unwrap = Unwrap.Create (Expr, false);
 488                         if (unwrap == null)
 489                                 return null;
 490
 491                         Expression res = base.ResolveOperator (ec, unwrap);
 492                         if (res != this) {
 493                                 if (user_operator == null)
 494                                         return res;
 495                         } else {
 496                                 res = Expr = LiftExpression (ec, Expr);
 497                         }
 498
 499                         if (res == null)
 500                                 return null;
 501
 502                         eclass = ExprClass.Value;
 503                         type = res.Type;
 504                         return this;
 505                 }
 506
 507                 public override void Emit (EmitContext ec)
 508                 {
 509                         ILGenerator ig = ec.ig;
 510                         Label is_null_label = ig.DefineLabel ();
 511                         Label end_label = ig.DefineLabel ();
 512
 513                         unwrap.EmitCheck (ec);
 514                         ig.Emit (OpCodes.Brfalse, is_null_label);
 515
 516                         NullableInfo ni = new NullableInfo (type);
 517
 518                         if (user_operator != null) {
 519                                 user_operator.Emit (ec);
 520                         } else {
 521                                 EmitOperator (ec, ni.UnderlyingType);
 522                         }
 523
 524                         ig.Emit (OpCodes.Newobj, ni.Constructor);
 525                         ig.Emit (OpCodes.Br_S, end_label);
 526
 527                         ig.MarkLabel (is_null_label);
 528                         LiftedNull.Create (type, loc).Emit (ec);
 529
 530                         ig.MarkLabel (end_label);
 531                 }
 532
 533                 Expression LiftExpression (ResolveContext ec, Expression expr)
 534                 {
 535                         TypeExpr lifted_type = new NullableType (expr.Type, expr.Location);
 536                         lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 537                         if (lifted_type == null)
 538                                 return null;
 539
 540                         expr.Type = lifted_type.Type;
 541                         return expr;
 542                 }
 543
 544                 protected override Expression ResolveEnumOperator (ResolveContext ec, Expression expr)
 545                 {
 546                         expr = base.ResolveEnumOperator (ec, expr);
 547                         if (expr == null)
 548                                 return null;
 549
 550                         Expr = LiftExpression (ec, Expr);
 551                         return LiftExpression (ec, expr);
 552                 }
 553
 554                 protected override Expression ResolveUserOperator (ResolveContext ec, Expression expr)
 555                 {
 556                         expr = base.ResolveUserOperator (ec, expr);
 557                         if (expr == null)
 558                                 return null;
 559
 560                         //
 561                         // When a user operator is of non-nullable type
 562                         //
 563                         if (Expr is Unwrap) {
 564                                 user_operator = LiftExpression (ec, expr);
 565                                 return user_operator;
 566                         }
 567
 568                         return expr;
 569                 }
 570         }
 571
 572         public class LiftedBinaryOperator : Binary
 573         {
 574                 Unwrap left_unwrap, right_unwrap;
 575                 bool left_null_lifted, right_null_lifted;
 576                 Expression left_orig, right_orig;
 577                 Expression user_operator;
 578                 ConstructorInfo wrap_ctor;
 579
 580                 public LiftedBinaryOperator (Binary.Operator op, Expression left, Expression right,
 581                                              Location loc)
 582                         : base (op, left, right)
 583                 {
 584                         this.loc = loc;
 585                 }
 586
 587                 public override Expression CreateExpressionTree (ResolveContext ec)
 588                 {
 589                         if (user_operator != null)
 590                                 return user_operator.CreateExpressionTree (ec);
 591
 592                         return base.CreateExpressionTree (ec);
 593                 }
 594
 595                 //
 596                 // CSC 2 has this behavior, it allows structs to be compared
 597                 // with the null literal *outside* of a generics context and
 598                 // inlines that as true or false.
 599                 //
 600                 Expression CreateNullConstant (ResolveContext ec, Expression expr)
 601                 {
 602                         // FIXME: Handle side effect constants
 603                         Constant c = new BoolConstant (Oper == Operator.Inequality, loc).Resolve (ec);
 604
 605                         if ((Oper & Operator.EqualityMask) != 0) {
 606                                 ec.Report.Warning (472, 2, loc, "The result of comparing value type `{0}' with null is `{1}'",
 607                                         TypeManager.CSharpName (expr.Type), c.AsString ());
 608                         } else {
 609                                 ec.Report.Warning (464, 2, loc, "The result of comparing type `{0}' with null is always `{1}'",
 610                                         TypeManager.CSharpName (expr.Type), c.AsString ());
 611                         }
 612
 613                         return ReducedExpression.Create (c, this);
 614                 }
 615
 616                 protected override Expression DoResolve (ResolveContext ec)
 617                 {
 618                         if ((Oper & Operator.LogicalMask) != 0) {
 619                                 Error_OperatorCannotBeApplied (ec, left, right);
 620                                 return null;
 621                         }
 622
 623                         bool use_default_call = (Oper & (Operator.BitwiseMask | Operator.EqualityMask)) != 0;
 624                         left_orig = left;
 625                         if (TypeManager.IsNullableType (left.Type)) {
 626                                 left = left_unwrap = Unwrap.Create (left, use_default_call);
 627                                 if (left == null)
 628                                         return null;
 629                         }
 630
 631                         right_orig = right;
 632                         if (TypeManager.IsNullableType (right.Type)) {
 633                                 right = right_unwrap = Unwrap.Create (right, use_default_call);
 634                                 if (right == null)
 635                                         return null;
 636                         }
 637
 638                         //
 639                         // Some details are in 6.4.2, 7.2.7
 640                         // Arguments can be lifted for equal operators when the return type is bool and both
 641                         // arguments are of same type
 642                         //
 643                         if (left_orig.IsNull) {
 644                                 left = right;
 645                                 left_null_lifted = true;
 646                                 type = TypeManager.bool_type;
 647                         }
 648
 649                         if (right_orig.IsNull) {
 650                                 right = left;
 651                                 right_null_lifted = true;
 652                                 type = TypeManager.bool_type;
 653                         }
 654
 655                         eclass = ExprClass.Value;
 656                         return DoResolveCore (ec, left_orig, right_orig);
 657                 }
 658
 659                 void EmitBitwiseBoolean (EmitContext ec)
 660                 {
 661                         ILGenerator ig = ec.ig;
 662
 663                         Label load_left = ig.DefineLabel ();
 664                         Label load_right = ig.DefineLabel ();
 665                         Label end_label = ig.DefineLabel ();
 666
 667                         left_unwrap.Emit (ec);
 668                         ig.Emit (OpCodes.Brtrue_S, load_right);
 669
 670                         right_unwrap.Emit (ec);
 671                         ig.Emit (OpCodes.Brtrue_S, load_left);
 672
 673                         left_unwrap.EmitCheck (ec);
 674                         ig.Emit (OpCodes.Brfalse_S, load_right);
 675
 676                         // load left
 677                         ig.MarkLabel (load_left);
 678
 679                         if (Oper == Operator.BitwiseAnd) {
 680                                 left_unwrap.Load (ec);
 681                         } else {
 682                                 right_unwrap.Load (ec);
 683                                 right_unwrap = left_unwrap;
 684                         }
 685                         ig.Emit (OpCodes.Br_S, end_label);
 686
 687                         // load right
 688                         ig.MarkLabel (load_right);
 689                         right_unwrap.Load (ec);
 690
 691                         ig.MarkLabel (end_label);
 692                 }
 693
 694                 //
 695                 // Emits optimized equality or inequality operator when possible
 696                 //
 697                 void EmitEquality (EmitContext ec)
 698                 {
 699                         ILGenerator ig = ec.ig;
 700
 701                         //
 702                         // Either left or right is null
 703                         //
 704                         if (left_unwrap != null && (right_null_lifted || right.IsNull)) {
 705                                 left_unwrap.EmitCheck (ec);
 706                                 if (Oper == Binary.Operator.Equality) {
 707                                         ig.Emit (OpCodes.Ldc_I4_0);
 708                                         ig.Emit (OpCodes.Ceq);
 709                                 }
 710                                 return;
 711                         }
 712
 713                         if (right_unwrap != null && (left_null_lifted || left.IsNull)) {
 714                                 right_unwrap.EmitCheck (ec);
 715                                 if (Oper == Binary.Operator.Equality) {
 716                                         ig.Emit (OpCodes.Ldc_I4_0);
 717                                         ig.Emit (OpCodes.Ceq);
 718                                 }
 719                                 return;
 720                         }
 721
 722                         Label dissimilar_label = ig.DefineLabel ();
 723                         Label end_label = ig.DefineLabel ();
 724
 725                         if (user_operator != null) {
 726                                 user_operator.Emit (ec);
 727                                 ig.Emit (Oper == Operator.Equality ? OpCodes.Brfalse_S : OpCodes.Brtrue_S, dissimilar_label);
 728                         } else {
 729                                 left.Emit (ec);
 730                                 right.Emit (ec);
 731
 732                                 ig.Emit (OpCodes.Bne_Un_S, dissimilar_label);
 733                         }
 734
 735                         if (left_unwrap != null)
 736                                 left_unwrap.EmitCheck (ec);
 737
 738                         if (right_unwrap != null)
 739                                 right_unwrap.EmitCheck (ec);
 740
 741                         if (left_unwrap != null && right_unwrap != null) {
 742                                 if (Oper == Operator.Inequality)
 743                                         ig.Emit (OpCodes.Xor);
 744                                 else
 745                                         ig.Emit (OpCodes.Ceq);
 746                         } else {
 747                                 if (Oper == Operator.Inequality) {
 748                                         ig.Emit (OpCodes.Ldc_I4_0);
 749                                         ig.Emit (OpCodes.Ceq);
 750                                 }
 751                         }
 752
 753                         ig.Emit (OpCodes.Br_S, end_label);
 754
 755                         ig.MarkLabel (dissimilar_label);
 756                         if (Oper == Operator.Inequality)
 757                                 ig.Emit (OpCodes.Ldc_I4_1);
 758                         else
 759                                 ig.Emit (OpCodes.Ldc_I4_0);
 760
 761                         ig.MarkLabel (end_label);
 762                 }
 763
 764                 public override void EmitBranchable (EmitContext ec, Label target, bool onTrue)
 765                 {
 766                         Emit (ec);
 767                         ec.ig.Emit (onTrue ? OpCodes.Brtrue : OpCodes.Brfalse, target);
 768                 }
 769
 770                 public override void Emit (EmitContext ec)
 771                 {
 772                         //
 773                         // Optimize same expression operation
 774                         //
 775                         if (right_unwrap != null && right.Equals (left))
 776                                 right_unwrap = left_unwrap;
 777
 778                         if (user_operator == null && IsBitwiseBoolean) {
 779                                 EmitBitwiseBoolean (ec);
 780                                 return;
 781                         }
 782
 783                         if ((Oper & Operator.EqualityMask) != 0) {
 784                                 EmitEquality (ec);
 785                                 return;
 786                         }
 787
 788                         ILGenerator ig = ec.ig;
 789
 790                         Label is_null_label = ig.DefineLabel ();
 791                         Label end_label = ig.DefineLabel ();
 792
 793                         if (left_unwrap != null) {
 794                                 left_unwrap.EmitCheck (ec);
 795                                 ig.Emit (OpCodes.Brfalse, is_null_label);
 796                         }
 797
 798                         //
 799                         // Don't emit HasValue check when left and right expressions are same
 800                         //
 801                         if (right_unwrap != null && !left.Equals (right)) {
 802                                 right_unwrap.EmitCheck (ec);
 803                                 ig.Emit (OpCodes.Brfalse, is_null_label);
 804                         }
 805
 806                         EmitOperator (ec, left.Type);
 807
 808                         if (wrap_ctor != null)
 809                                 ig.Emit (OpCodes.Newobj, wrap_ctor);
 810
 811                         ig.Emit (OpCodes.Br_S, end_label);
 812                         ig.MarkLabel (is_null_label);
 813
 814                         if ((Oper & Operator.ComparisonMask) != 0) {
 815                                 ig.Emit (OpCodes.Ldc_I4_0);
 816                         } else {
 817                                 LiftedNull.Create (type, loc).Emit (ec);
 818                         }
 819
 820                         ig.MarkLabel (end_label);
 821                 }
 822
 823                 protected override void EmitOperator (EmitContext ec, Type l)
 824                 {
 825                         if (user_operator != null) {
 826                                 user_operator.Emit (ec);
 827                                 return;
 828                         }
 829
 830                         if (TypeManager.IsNullableType (l))
 831                                 l = TypeManager.TypeToCoreType (TypeManager.GetTypeArguments (l) [0]);
 832
 833                         base.EmitOperator (ec, l);
 834                 }
 835
 836                 bool IsBitwiseBoolean {
 837                         get {
 838                                 return (Oper & Operator.BitwiseMask) != 0 && left_unwrap != null && right_unwrap != null &&
 839                                 left_unwrap.Type == TypeManager.bool_type && right_unwrap.Type == TypeManager.bool_type;
 840                         }
 841                 }
 842
 843                 Expression LiftResult (ResolveContext ec, Expression res_expr)
 844                 {
 845                         TypeExpr lifted_type;
 846
 847                         //
 848                         // Avoid double conversion
 849                         //
 850                         if (left_unwrap == null || left_null_lifted || !TypeManager.IsEqual (left_unwrap.Type, left.Type) || (left_unwrap != null && right_null_lifted)) {
 851                                 lifted_type = new NullableType (left.Type, loc);
 852                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 853                                 if (lifted_type == null)
 854                                         return null;
 855
 856                                 if (left is UserCast || left is TypeCast)
 857                                         left.Type = lifted_type.Type;
 858                                 else
 859                                         left = EmptyCast.Create (left, lifted_type.Type);
 860                         }
 861
 862                         if (right_unwrap == null || right_null_lifted || !TypeManager.IsEqual (right_unwrap.Type, right.Type) || (right_unwrap != null && left_null_lifted)) {
 863                                 lifted_type = new NullableType (right.Type, loc);
 864                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 865                                 if (lifted_type == null)
 866                                         return null;
 867
 868                                 if (right is UserCast || right is TypeCast)
 869                                         right.Type = lifted_type.Type;
 870                                 else
 871                                         right = EmptyCast.Create (right, lifted_type.Type);
 872                         }
 873
 874                         if ((Oper & Operator.ComparisonMask) == 0) {
 875                                 lifted_type = new NullableType (res_expr.Type, loc);
 876                                 lifted_type = lifted_type.ResolveAsTypeTerminal (ec, false);
 877                                 if (lifted_type == null)
 878                                         return null;
 879
 880                                 wrap_ctor = new NullableInfo (lifted_type.Type).Constructor;
 881                                 type = res_expr.Type = lifted_type.Type;
 882                         }
 883
 884                         if (left_null_lifted) {
 885                                 left = LiftedNull.Create (right.Type, left.Location);
 886
 887                                 if ((Oper & (Operator.ArithmeticMask | Operator.ShiftMask | Operator.BitwiseMask)) != 0)
 888                                         return LiftedNull.CreateFromExpression (ec, res_expr);
 889
 890                                 //
 891                                 // Value types and null comparison
 892                                 //
 893                                 if (right_unwrap == null || (Oper & Operator.RelationalMask) != 0)
 894                                         return CreateNullConstant (ec, right_orig).Resolve (ec);
 895                         }
 896
 897                         if (right_null_lifted) {
 898                                 right = LiftedNull.Create (left.Type, right.Location);
 899
 900                                 if ((Oper & (Operator.ArithmeticMask | Operator.ShiftMask | Operator.BitwiseMask)) != 0)
 901                                         return LiftedNull.CreateFromExpression (ec, res_expr);
 902
 903                                 //
 904                                 // Value types and null comparison
 905                                 //
 906                                 if (left_unwrap == null || (Oper & Operator.RelationalMask) != 0)
 907                                         return CreateNullConstant (ec, left_orig);
 908                         }
 909
 910                         return res_expr;
 911                 }
 912
 913                 protected override Expression ResolveOperatorPredefined (ResolveContext ec, Binary.PredefinedOperator [] operators, bool primitives_only, Type enum_type)
 914                 {
 915                         Expression e = base.ResolveOperatorPredefined (ec, operators, primitives_only, enum_type);
 916
 917                         if (e == this || enum_type != null)
 918                                 return LiftResult (ec, e);
 919
 920                         //
 921                         // 7.9.9 Equality operators and null
 922                         //
 923                         // The == and != operators permit one operand to be a value of a nullable type and
 924                         // the other to be the null literal, even if no predefined or user-defined operator
 925                         // (in unlifted or lifted form) exists for the operation.
 926                         //
 927                         if (e == null && (Oper & Operator.EqualityMask) != 0) {
 928                                 if ((left_null_lifted && right_unwrap != null) || (right_null_lifted && left_unwrap != null))
 929                                         return LiftResult (ec, this);
 930                         }
 931
 932                         return e;
 933                 }
 934
 935                 protected override Expression ResolveUserOperator (ResolveContext ec, Type l, Type r)
 936                 {
 937                         Expression expr = base.ResolveUserOperator (ec, l, r);
 938                         if (expr == null)
 939                                 return null;
 940
 941                         expr = LiftResult (ec, expr);
 942                         if (expr is Constant)
 943                                 return expr;
 944
 945                         type = expr.Type;
 946                         user_operator = expr;
 947                         return this;
 948                 }
 949         }
 950
 951         public class NullCoalescingOperator : Expression
 952         {
 953                 Expression left, right;
 954                 Unwrap unwrap;
 955
 956                 public NullCoalescingOperator (Expression left, Expression right, Location loc)
 957                 {
 958                         this.left = left;
 959                         this.right = right;
 960                         this.loc = loc;
 961                 }
 962
 963                 public override Expression CreateExpressionTree (ResolveContext ec)
 964                 {
 965                         if (left.Type == TypeManager.null_type)
 966                                 ec.Report.Error (845, loc, "An expression tree cannot contain a coalescing operator with null left side");
 967
 968                         UserCast uc = left as UserCast;
 969                         Expression conversion = null;
 970                         if (uc != null) {
 971                                 left = uc.Source;
 972
 973                                 Arguments c_args = new Arguments (2);
 974                                 c_args.Add (new Argument (uc.CreateExpressionTree (ec)));
 975                                 c_args.Add (new Argument (left.CreateExpressionTree (ec)));
 976                                 conversion = CreateExpressionFactoryCall (ec, "Lambda", c_args);
 977                         }
 978
 979                         Arguments args = new Arguments (3);
 980                         args.Add (new Argument (left.CreateExpressionTree (ec)));
 981                         args.Add (new Argument (right.CreateExpressionTree (ec)));
 982                         if (conversion != null)
 983                                 args.Add (new Argument (conversion));
 984
 985                         return CreateExpressionFactoryCall (ec, "Coalesce", args);
 986                 }
 987
 988                 Expression ConvertExpression (ResolveContext ec)
 989                 {
 990                         // TODO: ImplicitConversionExists should take care of this
 991                         if (left.eclass == ExprClass.MethodGroup)
 992                                 return null;
 993
 994                         Type ltype = left.Type;
 995
 996                         //
 997                         // If left is a nullable type and an implicit conversion exists from right to underlying type of left,
 998                         // the result is underlying type of left
 999                         //
1000                         if (TypeManager.IsNullableType (ltype)) {
1001                                 unwrap = Unwrap.Create (left, false);
1002                                 if (unwrap == null)
1003                                         return null;
1004
1005                                 if (Convert.ImplicitConversionExists (ec, right, unwrap.Type)) {
1006                                         left = unwrap;
1007                                         type = left.Type;
1008                                         right = Convert.ImplicitConversion (ec, right, type, loc);
1009                                         return this;
1010                                 }
1011                         } else if (TypeManager.IsReferenceType (ltype)) {
1012                                 if (Convert.ImplicitConversionExists (ec, right, ltype)) {
1013                                         //
1014                                         // Reduce (constant ?? expr) to constant
1015                                         //
1016                                         Constant lc = left as Constant;
1017                                         if (lc != null && !lc.IsDefaultValue)
1018                                                 return new SideEffectConstant (lc, right, loc).Resolve (ec);
1019
1020                                         //
1021                                         // Reduce (left ?? null) to left OR (null-constant ?? right) to right
1022                                         //
1023                                         if (right.IsNull || lc != null)
1024                                                 return ReducedExpression.Create (lc != null ? right : left, this);
1025
1026                                         right = Convert.ImplicitConversion (ec, right, ltype, loc);
1027                                         type = left.Type;
1028                                         return this;
1029                                 }
1030                         } else {
1031                                 return null;
1032                         }
1033
1034                         Type rtype = right.Type;
1035                         if (!Convert.ImplicitConversionExists (ec, unwrap != null ? unwrap : left, rtype) || right.eclass == ExprClass.MethodGroup)
1036                                 return null;
1037
1038                         //
1039                         // Reduce (null ?? right) to right
1040                         //
1041                         if (left.IsNull)
1042                                 return ReducedExpression.Create (right, this);
1043
1044                         left = Convert.ImplicitConversion (ec, unwrap != null ? unwrap : left, rtype, loc);
1045                         type = rtype;
1046                         return this;
1047                 }
1048
1049                 protected override Expression DoResolve (ResolveContext ec)
1050                 {
1051                         left = left.Resolve (ec);
1052                         right = right.Resolve (ec);
1053
1054                         if (left == null || right == null)
1055                                 return null;
1056
1057                         eclass = ExprClass.Value;
1058
1059                         Expression e = ConvertExpression (ec);
1060                         if (e == null) {
1061                                 Binary.Error_OperatorCannotBeApplied (ec, left, right, "??", loc);
1062                                 return null;
1063                         }
1064
1065                         return e;
1066                 }
1067
1068                 public override void Emit (EmitContext ec)
1069                 {
1070                         ILGenerator ig = ec.ig;
1071
1072                         Label end_label = ig.DefineLabel ();
1073
1074                         if (unwrap != null) {
1075                                 Label is_null_label = ig.DefineLabel ();
1076
1077                                 unwrap.EmitCheck (ec);
1078                                 ig.Emit (OpCodes.Brfalse, is_null_label);
1079
1080                                 left.Emit (ec);
1081                                 ig.Emit (OpCodes.Br, end_label);
1082
1083                                 ig.MarkLabel (is_null_label);
1084                                 right.Emit (ec);
1085
1086                                 ig.MarkLabel (end_label);
1087                                 return;
1088                         }
1089
1090                         left.Emit (ec);
1091
1092                         ig.Emit (OpCodes.Dup);
1093                         ig.Emit (OpCodes.Brtrue, end_label);
1094
1095                         ig.Emit (OpCodes.Pop);
1096                         right.Emit (ec);
1097
1098                         ig.MarkLabel (end_label);
1099                 }
1100
1101                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
1102                 {
1103                         left.MutateHoistedGenericType (storey);
1104                         right.MutateHoistedGenericType (storey);
1105                         type = storey.MutateType (type);
1106                 }
1107
1108                 protected override void CloneTo (CloneContext clonectx, Expression t)
1109                 {
1110                         NullCoalescingOperator target = (NullCoalescingOperator) t;
1111
1112                         target.left = left.Clone (clonectx);
1113                         target.right = right.Clone (clonectx);
1114                 }
1115         }
1116
1117         public class LiftedUnaryMutator : ExpressionStatement
1118         {
1119                 public readonly UnaryMutator.Mode Mode;
1120                 Expression expr;
1121                 UnaryMutator underlying;
1122                 Unwrap unwrap;
1123
1124                 public LiftedUnaryMutator (UnaryMutator.Mode mode, Expression expr, Location loc)
1125                 {
1126                         this.expr = expr;
1127                         this.Mode = mode;
1128                         this.loc = loc;
1129                 }
1130
1131                 public override Expression CreateExpressionTree (ResolveContext ec)
1132                 {
1133                         return new SimpleAssign (this, this).CreateExpressionTree (ec);
1134                 }
1135
1136                 protected override Expression DoResolve (ResolveContext ec)
1137                 {
1138                         expr = expr.Resolve (ec);
1139                         if (expr == null)
1140                                 return null;
1141
1142                         unwrap = Unwrap.Create (expr, false);
1143                         if (unwrap == null)
1144                                 return null;
1145
1146                         underlying = (UnaryMutator) new UnaryMutator (Mode, unwrap).Resolve (ec);
1147                         if (underlying == null)
1148                                 return null;
1149
1150
1151                         eclass = ExprClass.Value;
1152                         type = expr.Type;
1153                         return this;
1154                 }
1155
1156                 void DoEmit (EmitContext ec, bool is_expr)
1157                 {
1158                         ILGenerator ig = ec.ig;
1159                         Label is_null_label = ig.DefineLabel ();
1160                         Label end_label = ig.DefineLabel ();
1161
1162                         unwrap.EmitCheck (ec);
1163                         ig.Emit (OpCodes.Brfalse, is_null_label);
1164
1165                         if (is_expr) {
1166                                 underlying.Emit (ec);
1167                                 ig.Emit (OpCodes.Br_S, end_label);
1168                         } else {
1169                                 underlying.EmitStatement (ec);
1170                         }
1171
1172                         ig.MarkLabel (is_null_label);
1173                         if (is_expr)
1174                                 LiftedNull.Create (type, loc).Emit (ec);
1175
1176                         ig.MarkLabel (end_label);
1177                 }
1178
1179                 public override void Emit (EmitContext ec)
1180                 {
1181                         DoEmit (ec, true);
1182                 }
1183
1184                 public override void EmitStatement (EmitContext ec)
1185                 {
1186                         DoEmit (ec, false);
1187                 }
1188         }
1189 }
1190