mcs/mcs/assign.cs

   1 //
   2 // assign.cs: Assignments.
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Martin Baulig (martin@ximian.com)
   7 //   Marek Safar (marek.safar@gmail.com)
   8 //
   9 // Dual licensed under the terms of the MIT X11 or GNU GPL
  10 //
  11 // Copyright 2001, 2002, 2003 Ximian, Inc.
  12 // Copyright 2004-2008 Novell, Inc
  13 // Copyright 2011 Xamarin Inc
  14 //
  15 using System;
  16
  17 #if STATIC
  18 using IKVM.Reflection.Emit;
  19 #else
  20 using System.Reflection.Emit;
  21 #endif
  22
  23 namespace Mono.CSharp {
  24
  25         /// <summary>
  26         ///   This interface is implemented by expressions that can be assigned to.
  27         /// </summary>
  28         /// <remarks>
  29         ///   This interface is implemented by Expressions whose values can not
  30         ///   store the result on the top of the stack.
  31         ///
  32         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  33         ///   perform an assignment of the Expression "source" into its final
  34         ///   location.
  35         ///
  36         ///   No values on the top of the stack are expected to be left by
  37         ///   invoking this method.
  38         /// </remarks>
  39         public interface IAssignMethod {
  40                 //
  41                 // This is an extra version of Emit. If leave_copy is `true'
  42                 // A copy of the expression will be left on the stack at the
  43                 // end of the code generated for EmitAssign
  44                 //
  45                 void Emit (EmitContext ec, bool leave_copy);
  46
  47                 //
  48                 // This method does the assignment
  49                 // `source' will be stored into the location specified by `this'
  50                 // if `leave_copy' is true, a copy of `source' will be left on the stack
  51                 // if `prepare_for_load' is true, when `source' is emitted, there will
  52                 // be data on the stack that it can use to compuatate its value. This is
  53                 // for expressions like a [f ()] ++, where you can't call `f ()' twice.
  54                 //
  55                 void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool isCompound);
  56
  57                 /*
  58                 For simple assignments, this interface is very simple, EmitAssign is called with source
  59                 as the source expression and leave_copy and prepare_for_load false.
  60
  61                 For compound assignments it gets complicated.
  62
  63                 EmitAssign will be called as before, however, prepare_for_load will be
  64                 true. The @source expression will contain an expression
  65                 which calls Emit. So, the calls look like:
  66
  67                 this.EmitAssign (ec, source, false, true) ->
  68                         source.Emit (ec); ->
  69                                 [...] ->
  70                                         this.Emit (ec, false); ->
  71                                         end this.Emit (ec, false); ->
  72                                 end [...]
  73                         end source.Emit (ec);
  74                 end this.EmitAssign (ec, source, false, true)
  75
  76
  77                 When prepare_for_load is true, EmitAssign emits a `token' on the stack that
  78                 Emit will use for its state.
  79
  80                 Let's take FieldExpr as an example. assume we are emitting f ().y += 1;
  81
  82                 Here is the call tree again. This time, each call is annotated with the IL
  83                 it produces:
  84
  85                 this.EmitAssign (ec, source, false, true)
  86                         call f
  87                         dup
  88
  89                         Binary.Emit ()
  90                                 this.Emit (ec, false);
  91                                 ldfld y
  92                                 end this.Emit (ec, false);
  93
  94                                 IntConstant.Emit ()
  95                                 ldc.i4.1
  96                                 end IntConstant.Emit
  97
  98                                 add
  99                         end Binary.Emit ()
 100
 101                         stfld
 102                 end this.EmitAssign (ec, source, false, true)
 103
 104                 Observe two things:
 105                         1) EmitAssign left a token on the stack. It was the result of f ().
 106                         2) This token was used by Emit
 107
 108                 leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
 109                 of the expression at that point in evaluation. This is used for pre/post inc/dec
 110                 and for a = x += y. Let's do the above example with leave_copy true in EmitAssign
 111
 112                 this.EmitAssign (ec, source, true, true)
 113                         call f
 114                         dup
 115
 116                         Binary.Emit ()
 117                                 this.Emit (ec, false);
 118                                 ldfld y
 119                                 end this.Emit (ec, false);
 120
 121                                 IntConstant.Emit ()
 122                                 ldc.i4.1
 123                                 end IntConstant.Emit
 124
 125                                 add
 126                         end Binary.Emit ()
 127
 128                         dup
 129                         stloc temp
 130                         stfld
 131                         ldloc temp
 132                 end this.EmitAssign (ec, source, true, true)
 133
 134                 And with it true in Emit
 135
 136                 this.EmitAssign (ec, source, false, true)
 137                         call f
 138                         dup
 139
 140                         Binary.Emit ()
 141                                 this.Emit (ec, true);
 142                                 ldfld y
 143                                 dup
 144                                 stloc temp
 145                                 end this.Emit (ec, true);
 146
 147                                 IntConstant.Emit ()
 148                                 ldc.i4.1
 149                                 end IntConstant.Emit
 150
 151                                 add
 152                         end Binary.Emit ()
 153
 154                         stfld
 155                         ldloc temp
 156                 end this.EmitAssign (ec, source, false, true)
 157
 158                 Note that these two examples are what happens for ++x and x++, respectively.
 159                 */
 160         }
 161
 162         /// <summary>
 163         ///   An Expression to hold a temporary value.
 164         /// </summary>
 165         /// <remarks>
 166         ///   The LocalTemporary class is used to hold temporary values of a given
 167         ///   type to "simulate" the expression semantics. The local variable is
 168         ///   never captured.
 169         ///
 170         ///   The local temporary is used to alter the normal flow of code generation
 171         ///   basically it creates a local variable, and its emit instruction generates
 172         ///   code to access this value, return its address or save its value.
 173         ///
 174         ///   If `is_address' is true, then the value that we store is the address to the
 175         ///   real value, and not the value itself.
 176         ///
 177         ///   This is needed for a value type, because otherwise you just end up making a
 178         ///   copy of the value on the stack and modifying it. You really need a pointer
 179         ///   to the origional value so that you can modify it in that location. This
 180         ///   Does not happen with a class because a class is a pointer -- so you always
 181         ///   get the indirection.
 182         ///
 183         /// </remarks>
 184         public class LocalTemporary : Expression, IMemoryLocation, IAssignMethod {
 185                 LocalBuilder builder;
 186
 187                 public LocalTemporary (TypeSpec t)
 188                 {
 189                         type = t;
 190                         eclass = ExprClass.Value;
 191                 }
 192
 193                 public LocalTemporary (LocalBuilder b, TypeSpec t)
 194                         : this (t)
 195                 {
 196                         builder = b;
 197                 }
 198
 199                 public void Release (EmitContext ec)
 200                 {
 201                         ec.FreeTemporaryLocal (builder, type);
 202                         builder = null;
 203                 }
 204
 205                 public override bool ContainsEmitWithAwait ()
 206                 {
 207                         return false;
 208                 }
 209
 210                 public override Expression CreateExpressionTree (ResolveContext ec)
 211                 {
 212                         Arguments args = new Arguments (1);
 213                         args.Add (new Argument (this));
 214                         return CreateExpressionFactoryCall (ec, "Constant", args);
 215                 }
 216
 217                 protected override Expression DoResolve (ResolveContext ec)
 218                 {
 219                         return this;
 220                 }
 221
 222                 public override Expression DoResolveLValue (ResolveContext ec, Expression right_side)
 223                 {
 224                         return this;
 225                 }
 226
 227                 public override void Emit (EmitContext ec)
 228                 {
 229                         if (builder == null)
 230                                 throw new InternalErrorException ("Emit without Store, or after Release");
 231
 232                         ec.Emit (OpCodes.Ldloc, builder);
 233                 }
 234
 235                 #region IAssignMethod Members
 236
 237                 public void Emit (EmitContext ec, bool leave_copy)
 238                 {
 239                         Emit (ec);
 240
 241                         if (leave_copy)
 242                                 Emit (ec);
 243                 }
 244
 245                 public void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool isCompound)
 246                 {
 247                         if (isCompound)
 248                                 throw new NotImplementedException ();
 249
 250                         source.Emit (ec);
 251
 252                         Store (ec);
 253
 254                         if (leave_copy)
 255                                 Emit (ec);
 256                 }
 257
 258                 #endregion
 259
 260                 public LocalBuilder Builder {
 261                         get { return builder; }
 262                 }
 263
 264                 public void Store (EmitContext ec)
 265                 {
 266                         if (builder == null)
 267                                 builder = ec.GetTemporaryLocal (type);
 268
 269                         ec.Emit (OpCodes.Stloc, builder);
 270                 }
 271
 272                 public void AddressOf (EmitContext ec, AddressOp mode)
 273                 {
 274                         if (builder == null)
 275                                 builder = ec.GetTemporaryLocal (type);
 276
 277                         if (builder.LocalType.IsByRef) {
 278                                 //
 279                                 // if is_address, than this is just the address anyways,
 280                                 // so we just return this.
 281                                 //
 282                                 ec.Emit (OpCodes.Ldloc, builder);
 283                         } else {
 284                                 ec.Emit (OpCodes.Ldloca, builder);
 285                         }
 286                 }
 287         }
 288
 289         /// <summary>
 290         ///   The Assign node takes care of assigning the value of source into
 291         ///   the expression represented by target.
 292         /// </summary>
 293         public abstract class Assign : ExpressionStatement {
 294                 protected Expression target, source;
 295
 296                 protected Assign (Expression target, Expression source, Location loc)
 297                 {
 298                         this.target = target;
 299                         this.source = source;
 300                         this.loc = loc;
 301                 }
 302
 303                 public Expression Target {
 304                         get { return target; }
 305                 }
 306
 307                 public Expression Source {
 308                         get {
 309                                 return source;
 310                         }
 311                 }
 312
 313                 public override Location StartLocation {
 314                         get {
 315                                 return target.StartLocation;
 316                         }
 317                 }
 318
 319                 public override bool ContainsEmitWithAwait ()
 320                 {
 321                         return target.ContainsEmitWithAwait () || source.ContainsEmitWithAwait ();
 322                 }
 323
 324                 public override Expression CreateExpressionTree (ResolveContext ec)
 325                 {
 326                         ec.Report.Error (832, loc, "An expression tree cannot contain an assignment operator");
 327                         return null;
 328                 }
 329
 330                 protected override Expression DoResolve (ResolveContext ec)
 331                 {
 332                         bool ok = true;
 333                         source = source.Resolve (ec);
 334
 335                         if (source == null) {
 336                                 ok = false;
 337                                 source = ErrorExpression.Instance;
 338                         }
 339
 340                         target = target.ResolveLValue (ec, source);
 341
 342                         if (target == null || !ok)
 343                                 return null;
 344
 345                         TypeSpec target_type = target.Type;
 346                         TypeSpec source_type = source.Type;
 347
 348                         eclass = ExprClass.Value;
 349                         type = target_type;
 350
 351                         if (!(target is IAssignMethod)) {
 352                                 target.Error_ValueAssignment (ec, source);
 353                                 return null;
 354                         }
 355
 356                         if (target_type != source_type) {
 357                                 Expression resolved = ResolveConversions (ec);
 358
 359                                 if (resolved != this)
 360                                         return resolved;
 361                         }
 362
 363                         return this;
 364                 }
 365
 366 #if NET_4_0 || MOBILE_DYNAMIC
 367                 public override System.Linq.Expressions.Expression MakeExpression (BuilderContext ctx)
 368                 {
 369                         var tassign = target as IDynamicAssign;
 370                         if (tassign == null)
 371                                 throw new InternalErrorException (target.GetType () + " does not support dynamic assignment");
 372
 373                         var target_object = tassign.MakeAssignExpression (ctx, source);
 374
 375                         //
 376                         // Some hacking is needed as DLR does not support void type and requires
 377                         // always have object convertible return type to support caching and chaining
 378                         //
 379                         // We do this by introducing an explicit block which returns RHS value when
 380                         // available or null
 381                         //
 382                         if (target_object.NodeType == System.Linq.Expressions.ExpressionType.Block)
 383                                 return target_object;
 384
 385                         System.Linq.Expressions.UnaryExpression source_object;
 386                         if (ctx.HasSet (BuilderContext.Options.CheckedScope)) {
 387                                 source_object = System.Linq.Expressions.Expression.ConvertChecked (source.MakeExpression (ctx), target_object.Type);
 388                         } else {
 389                                 source_object = System.Linq.Expressions.Expression.Convert (source.MakeExpression (ctx), target_object.Type);
 390                         }
 391
 392                         return System.Linq.Expressions.Expression.Assign (target_object, source_object);
 393                 }
 394 #endif
 395                 protected virtual Expression ResolveConversions (ResolveContext ec)
 396                 {
 397                         source = Convert.ImplicitConversionRequired (ec, source, target.Type, source.Location);
 398                         if (source == null)
 399                                 return null;
 400
 401                         return this;
 402                 }
 403
 404                 void Emit (EmitContext ec, bool is_statement)
 405                 {
 406                         IAssignMethod t = (IAssignMethod) target;
 407                         t.EmitAssign (ec, source, !is_statement, this is CompoundAssign);
 408                 }
 409
 410                 public override void Emit (EmitContext ec)
 411                 {
 412                         Emit (ec, false);
 413                 }
 414
 415                 public override void EmitStatement (EmitContext ec)
 416                 {
 417                         Emit (ec, true);
 418                 }
 419
 420                 public override void FlowAnalysis (FlowAnalysisContext fc)
 421                 {
 422                         source.FlowAnalysis (fc);
 423
 424                         if (target is ArrayAccess || target is IndexerExpr || target is PropertyExpr)
 425                                 target.FlowAnalysis (fc);
 426                 }
 427
 428                 protected override void CloneTo (CloneContext clonectx, Expression t)
 429                 {
 430                         Assign _target = (Assign) t;
 431
 432                         _target.target = target.Clone (clonectx);
 433                         _target.source = source.Clone (clonectx);
 434                 }
 435
 436                 public override object Accept (StructuralVisitor visitor)
 437                 {
 438                         return visitor.Visit (this);
 439                 }
 440         }
 441
 442         public class SimpleAssign : Assign
 443         {
 444                 public SimpleAssign (Expression target, Expression source)
 445                         : this (target, source, target.Location)
 446                 {
 447                 }
 448
 449                 public SimpleAssign (Expression target, Expression source, Location loc)
 450                         : base (target, source, loc)
 451                 {
 452                 }
 453
 454                 bool CheckEqualAssign (Expression t)
 455                 {
 456                         if (source is Assign) {
 457                                 Assign a = (Assign) source;
 458                                 if (t.Equals (a.Target))
 459                                         return true;
 460                                 return a is SimpleAssign && ((SimpleAssign) a).CheckEqualAssign (t);
 461                         }
 462                         return t.Equals (source);
 463                 }
 464
 465                 protected override Expression DoResolve (ResolveContext ec)
 466                 {
 467                         Expression e = base.DoResolve (ec);
 468                         if (e == null || e != this)
 469                                 return e;
 470
 471                         if (CheckEqualAssign (target))
 472                                 ec.Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 473
 474                         return this;
 475                 }
 476
 477                 public override void FlowAnalysis (FlowAnalysisContext fc)
 478                 {
 479                         base.FlowAnalysis (fc);
 480
 481                         var vr = target as VariableReference;
 482                         if (vr != null) {
 483                                 if (vr.VariableInfo != null)
 484                                         fc.SetVariableAssigned (vr.VariableInfo);
 485
 486                                 return;
 487                         }
 488
 489                         var fe = target as FieldExpr;
 490                         if (fe != null) {
 491                                 fe.SetFieldAssigned (fc);
 492                                 return;
 493                         }
 494                 }
 495
 496                 public override void MarkReachable (Reachability rc)
 497                 {
 498                         var es = source as ExpressionStatement;
 499                         if (es != null)
 500                                 es.MarkReachable (rc);
 501                 }
 502         }
 503
 504         public class RuntimeExplicitAssign : Assign
 505         {
 506                 public RuntimeExplicitAssign (Expression target, Expression source)
 507                         : base (target, source, target.Location)
 508                 {
 509                 }
 510
 511                 protected override Expression ResolveConversions (ResolveContext ec)
 512                 {
 513                         source = EmptyCast.Create (source, target.Type);
 514                         return this;
 515                 }
 516         }
 517
 518         //
 519         // Compiler generated assign
 520         //
 521         class CompilerAssign : Assign
 522         {
 523                 public CompilerAssign (Expression target, Expression source, Location loc)
 524                         : base (target, source, loc)
 525                 {
 526                         if (target.Type != null) {
 527                                 type = target.Type;
 528                                 eclass = ExprClass.Value;
 529                         }
 530                 }
 531
 532                 protected override Expression DoResolve (ResolveContext ec)
 533                 {
 534                         var expr = base.DoResolve (ec);
 535                         var vr = target as VariableReference;
 536                         if (vr != null && vr.VariableInfo != null)
 537                                 vr.VariableInfo.IsEverAssigned = false;
 538
 539                         return expr;
 540                 }
 541
 542                 public void UpdateSource (Expression source)
 543                 {
 544                         base.source = source;
 545                 }
 546         }
 547
 548         //
 549         // Implements fields and events class initializers
 550         //
 551         public class FieldInitializer : Assign
 552         {
 553                 //
 554                 // Field initializers are tricky for partial classes. They have to
 555                 // share same constructor (block) for expression trees resolve but
 556                 // they have they own resolve scope
 557                 //
 558                 sealed class FieldInitializerContext : BlockContext
 559                 {
 560                         readonly ExplicitBlock ctor_block;
 561
 562                         public FieldInitializerContext (IMemberContext mc, BlockContext constructorContext)
 563                                 : base (mc, null, constructorContext.ReturnType)
 564                         {
 565                                 flags |= Options.FieldInitializerScope | Options.ConstructorScope;
 566                                 this.ctor_block = constructorContext.CurrentBlock.Explicit;
 567
 568                                 if (ctor_block.IsCompilerGenerated)
 569                                         CurrentBlock = ctor_block;
 570                         }
 571
 572                         public override ExplicitBlock ConstructorBlock {
 573                             get {
 574                                 return ctor_block;
 575                             }
 576                         }
 577                 }
 578
 579                 //
 580                 // Keep resolved value because field initializers have their own rules
 581                 //
 582                 ExpressionStatement resolved;
 583                 FieldBase mc;
 584
 585                 public FieldInitializer (FieldBase mc, Expression expression, Location loc)
 586                         : base (new FieldExpr (mc.Spec, expression.Location), expression, loc)
 587                 {
 588                         this.mc = mc;
 589                         if (!mc.IsStatic)
 590                                 ((FieldExpr)target).InstanceExpression = new CompilerGeneratedThis (mc.CurrentType, expression.Location);
 591                 }
 592
 593                 public int AssignmentOffset { get; private set; }
 594
 595                 public FieldBase Field {
 596                         get {
 597                                 return mc;
 598                         }
 599                 }
 600
 601                 public override Location StartLocation {
 602                         get {
 603                                 return loc;
 604                         }
 605                 }
 606
 607                 protected override Expression DoResolve (ResolveContext rc)
 608                 {
 609                         // Field initializer can be resolved (fail) many times
 610                         if (source == null)
 611                                 return null;
 612
 613                         if (resolved == null) {
 614                                 var bc = (BlockContext) rc;
 615                                 var ctx = new FieldInitializerContext (mc, bc);
 616                                 resolved = base.DoResolve (ctx) as ExpressionStatement;
 617                                 AssignmentOffset = ctx.AssignmentInfoOffset - bc.AssignmentInfoOffset;
 618                         }
 619
 620                         return resolved;
 621                 }
 622
 623                 public override void EmitStatement (EmitContext ec)
 624                 {
 625                         if (resolved == null)
 626                                 return;
 627
 628                         //
 629                         // Emit sequence symbol info even if we are in compiler generated
 630                         // block to allow debugging field initializers when constructor is
 631                         // compiler generated
 632                         //
 633                         if (ec.HasSet (BuilderContext.Options.OmitDebugInfo) && ec.HasMethodSymbolBuilder) {
 634                                 using (ec.With (BuilderContext.Options.OmitDebugInfo, false)) {
 635                                         ec.Mark (loc);
 636                                 }
 637                         }
 638
 639                         if (resolved != this)
 640                                 resolved.EmitStatement (ec);
 641                         else
 642                                 base.EmitStatement (ec);
 643                 }
 644
 645                 public override void FlowAnalysis (FlowAnalysisContext fc)
 646                 {
 647                         source.FlowAnalysis (fc);
 648                         ((FieldExpr) target).SetFieldAssigned (fc);
 649                 }
 650
 651                 public bool IsDefaultInitializer {
 652                         get {
 653                                 Constant c = source as Constant;
 654                                 if (c == null)
 655                                         return false;
 656
 657                                 FieldExpr fe = (FieldExpr)target;
 658                                 return c.IsDefaultInitializer (fe.Type);
 659                         }
 660                 }
 661
 662                 public override bool IsSideEffectFree {
 663                         get {
 664                                 return source.IsSideEffectFree;
 665                         }
 666                 }
 667         }
 668
 669         class PrimaryConstructorAssign : SimpleAssign
 670         {
 671                 readonly Field field;
 672                 readonly Parameter parameter;
 673
 674                 public PrimaryConstructorAssign (Field field, Parameter parameter)
 675                         : base (null, null, parameter.Location)
 676                 {
 677                         this.field = field;
 678                         this.parameter = parameter;
 679                 }
 680
 681                 protected override Expression DoResolve (ResolveContext rc)
 682                 {
 683                         target = new FieldExpr (field, loc);
 684                         source = rc.CurrentBlock.ParametersBlock.GetParameterInfo (parameter).CreateReferenceExpression (rc, loc);
 685                         return base.DoResolve (rc);
 686                 }
 687
 688                 public override void EmitStatement (EmitContext ec)
 689                 {
 690                         using (ec.With (BuilderContext.Options.OmitDebugInfo, true)) {
 691                                 base.EmitStatement (ec);
 692                         }
 693                 }
 694         }
 695
 696         //
 697         // This class is used for compound assignments.
 698         //
 699         public class CompoundAssign : Assign
 700         {
 701                 // This is just a hack implemented for arrays only
 702                 public sealed class TargetExpression : Expression
 703                 {
 704                         readonly Expression child;
 705
 706                         public TargetExpression (Expression child)
 707                         {
 708                                 this.child = child;
 709                                 this.loc = child.Location;
 710                         }
 711
 712                         public override bool ContainsEmitWithAwait ()
 713                         {
 714                                 return child.ContainsEmitWithAwait ();
 715                         }
 716
 717                         public override Expression CreateExpressionTree (ResolveContext ec)
 718                         {
 719                                 throw new NotSupportedException ("ET");
 720                         }
 721
 722                         protected override Expression DoResolve (ResolveContext ec)
 723                         {
 724                                 type = child.Type;
 725                                 eclass = ExprClass.Value;
 726                                 return this;
 727                         }
 728
 729                         public override void Emit (EmitContext ec)
 730                         {
 731                                 child.Emit (ec);
 732                         }
 733
 734                         public override Expression EmitToField (EmitContext ec)
 735                         {
 736                                 return child.EmitToField (ec);
 737                         }
 738                 }
 739
 740                 // Used for underlying binary operator
 741                 readonly Binary.Operator op;
 742                 Expression right;
 743                 Expression left;
 744
 745                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 746                         : base (target, source, target.Location)
 747                 {
 748                         right = source;
 749                         this.op = op;
 750                 }
 751
 752                 public CompoundAssign (Binary.Operator op, Expression target, Expression source, Expression left)
 753                         : this (op, target, source)
 754                 {
 755                         this.left = left;
 756                 }
 757
 758                 public Binary.Operator Operator {
 759                         get {
 760                                 return op;
 761                         }
 762                 }
 763
 764                 protected override Expression DoResolve (ResolveContext ec)
 765                 {
 766                         right = right.Resolve (ec);
 767                         if (right == null)
 768                                 return null;
 769
 770                         MemberAccess ma = target as MemberAccess;
 771                         using (ec.Set (ResolveContext.Options.CompoundAssignmentScope)) {
 772                                 target = target.Resolve (ec);
 773                         }
 774
 775                         if (target == null)
 776                                 return null;
 777
 778                         if (target is MethodGroupExpr){
 779                                 ec.Report.Error (1656, loc,
 780                                         "Cannot assign to `{0}' because it is a `{1}'",
 781                                         ((MethodGroupExpr)target).Name, target.ExprClassName);
 782                                 return null;
 783                         }
 784
 785                         var event_expr = target as EventExpr;
 786                         if (event_expr != null) {
 787                                 source = Convert.ImplicitConversionRequired (ec, right, target.Type, loc);
 788                                 if (source == null)
 789                                         return null;
 790
 791                                 Expression rside;
 792                                 if (op == Binary.Operator.Addition)
 793                                         rside = EmptyExpression.EventAddition;
 794                                 else if (op == Binary.Operator.Subtraction)
 795                                         rside = EmptyExpression.EventSubtraction;
 796                                 else
 797                                         rside = null;
 798
 799                                 target = target.ResolveLValue (ec, rside);
 800                                 if (target == null)
 801                                         return null;
 802
 803                                 eclass = ExprClass.Value;
 804                                 type = event_expr.Operator.ReturnType;
 805                                 return this;
 806                         }
 807
 808                         //
 809                         // Only now we can decouple the original source/target
 810                         // into a tree, to guarantee that we do not have side
 811                         // effects.
 812                         //
 813                         if (left == null)
 814                                 left = new TargetExpression (target);
 815
 816                         source = new Binary (op, left, right, true);
 817
 818                         if (target is DynamicMemberAssignable) {
 819                                 Arguments targs = ((DynamicMemberAssignable) target).Arguments;
 820                                 source = source.Resolve (ec);
 821
 822                                 Arguments args = new Arguments (targs.Count + 1);
 823                                 args.AddRange (targs);
 824                                 args.Add (new Argument (source));
 825
 826                                 var binder_flags = CSharpBinderFlags.ValueFromCompoundAssignment;
 827
 828                                 //
 829                                 // Compound assignment does target conversion using additional method
 830                                 // call, set checked context as the binary operation can overflow
 831                                 //
 832                                 if (ec.HasSet (ResolveContext.Options.CheckedScope))
 833                                         binder_flags |= CSharpBinderFlags.CheckedContext;
 834
 835                                 if (target is DynamicMemberBinder) {
 836                                         source = new DynamicMemberBinder (ma.Name, binder_flags, args, loc).Resolve (ec);
 837
 838                                         // Handles possible event addition/subtraction
 839                                         if (op == Binary.Operator.Addition || op == Binary.Operator.Subtraction) {
 840                                                 args = new Arguments (targs.Count + 1);
 841                                                 args.AddRange (targs);
 842                                                 args.Add (new Argument (right));
 843                                                 string method_prefix = op == Binary.Operator.Addition ?
 844                                                         Event.AEventAccessor.AddPrefix : Event.AEventAccessor.RemovePrefix;
 845
 846                                                 var invoke = DynamicInvocation.CreateSpecialNameInvoke (
 847                                                         new MemberAccess (right, method_prefix + ma.Name, loc), args, loc).Resolve (ec);
 848
 849                                                 args = new Arguments (targs.Count);
 850                                                 args.AddRange (targs);
 851                                                 source = new DynamicEventCompoundAssign (ma.Name, args,
 852                                                         (ExpressionStatement) source, (ExpressionStatement) invoke, loc).Resolve (ec);
 853                                         }
 854                                 } else {
 855                                         source = new DynamicIndexBinder (binder_flags, args, loc).Resolve (ec);
 856                                 }
 857
 858                                 return source;
 859                         }
 860
 861                         return base.DoResolve (ec);
 862                 }
 863
 864                 public override void FlowAnalysis (FlowAnalysisContext fc)
 865                 {
 866                         target.FlowAnalysis (fc);
 867                         source.FlowAnalysis (fc);
 868                 }
 869
 870                 protected override Expression ResolveConversions (ResolveContext ec)
 871                 {
 872                         //
 873                         // LAMESPEC: Under dynamic context no target conversion is happening
 874                         // This allows more natual dynamic behaviour but breaks compatibility
 875                         // with static binding
 876                         //
 877                         if (target is RuntimeValueExpression)
 878                                 return this;
 879
 880                         TypeSpec target_type = target.Type;
 881
 882                         //
 883                         // 1. the return type is implicitly convertible to the type of target
 884                         //
 885                         if (Convert.ImplicitConversionExists (ec, source, target_type)) {
 886                                 source = Convert.ImplicitConversion (ec, source, target_type, loc);
 887                                 return this;
 888                         }
 889
 890                         //
 891                         // Otherwise, if the selected operator is a predefined operator
 892                         //
 893                         Binary b = source as Binary;
 894                         if (b == null) {
 895                                 if (source is ReducedExpression)
 896                                         b = ((ReducedExpression) source).OriginalExpression as Binary;
 897                                 else if (source is ReducedExpression.ReducedConstantExpression) {
 898                                         b = ((ReducedExpression.ReducedConstantExpression) source).OriginalExpression as Binary;
 899                                 } else if (source is Nullable.LiftedBinaryOperator) {
 900                                         var po = ((Nullable.LiftedBinaryOperator) source);
 901                                         if (po.UserOperator == null)
 902                                                 b = po.Binary;
 903                                 } else if (source is TypeCast) {
 904                                         b = ((TypeCast) source).Child as Binary;
 905                                 }
 906                         }
 907
 908                         if (b != null) {
 909                                 //
 910                                 // 2a. the operator is a shift operator
 911                                 //
 912                                 // 2b. the return type is explicitly convertible to the type of x, and
 913                                 // y is implicitly convertible to the type of x
 914                                 //
 915                                 if ((b.Oper & Binary.Operator.ShiftMask) != 0 ||
 916                                         Convert.ImplicitConversionExists (ec, right, target_type)) {
 917                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 918                                         return this;
 919                                 }
 920                         }
 921
 922                         if (source.Type.BuiltinType == BuiltinTypeSpec.Type.Dynamic) {
 923                                 Arguments arg = new Arguments (1);
 924                                 arg.Add (new Argument (source));
 925                                 return new SimpleAssign (target, new DynamicConversion (target_type, CSharpBinderFlags.ConvertExplicit, arg, loc), loc).Resolve (ec);
 926                         }
 927
 928                         right.Error_ValueCannotBeConverted (ec, target_type, false);
 929                         return null;
 930                 }
 931
 932                 protected override void CloneTo (CloneContext clonectx, Expression t)
 933                 {
 934                         CompoundAssign ctarget = (CompoundAssign) t;
 935
 936                         ctarget.right = ctarget.source = source.Clone (clonectx);
 937                         ctarget.target = target.Clone (clonectx);
 938                 }
 939
 940                 public override object Accept (StructuralVisitor visitor)
 941                 {
 942                         return visitor.Visit (this);
 943                 }
 944         }
 945 }