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 //
   8 // (C) 2001, 2002, 2003 Ximian, Inc.
   9 // (C) 2004 Novell, Inc
  10 //
  11 using System;
  12 using System.Reflection;
  13 using System.Reflection.Emit;
  14
  15 namespace Mono.CSharp {
  16
  17         /// <summary>
  18         ///   This interface is implemented by expressions that can be assigned to.
  19         /// </summary>
  20         /// <remarks>
  21         ///   This interface is implemented by Expressions whose values can not
  22         ///   store the result on the top of the stack.
  23         ///
  24         ///   Expressions implementing this (Properties, Indexers and Arrays) would
  25         ///   perform an assignment of the Expression "source" into its final
  26         ///   location.
  27         ///
  28         ///   No values on the top of the stack are expected to be left by
  29         ///   invoking this method.
  30         /// </remarks>
  31         public interface IAssignMethod {
  32                 //
  33                 // This is an extra version of Emit. If leave_copy is `true'
  34                 // A copy of the expression will be left on the stack at the
  35                 // end of the code generated for EmitAssign
  36                 //
  37                 void Emit (EmitContext ec, bool leave_copy);
  38
  39                 //
  40                 // This method does the assignment
  41                 // `source' will be stored into the location specified by `this'
  42                 // if `leave_copy' is true, a copy of `source' will be left on the stack
  43                 // if `prepare_for_load' is true, when `source' is emitted, there will
  44                 // be data on the stack that it can use to compuatate its value. This is
  45                 // for expressions like a [f ()] ++, where you can't call `f ()' twice.
  46                 //
  47                 void EmitAssign (EmitContext ec, Expression source, bool leave_copy, bool prepare_for_load);
  48
  49                 /*
  50                 For simple assignments, this interface is very simple, EmitAssign is called with source
  51                 as the source expression and leave_copy and prepare_for_load false.
  52
  53                 For compound assignments it gets complicated.
  54
  55                 EmitAssign will be called as before, however, prepare_for_load will be
  56                 true. The @source expression will contain an expression
  57                 which calls Emit. So, the calls look like:
  58
  59                 this.EmitAssign (ec, source, false, true) ->
  60                         source.Emit (ec); ->
  61                                 [...] ->
  62                                         this.Emit (ec, false); ->
  63                                         end this.Emit (ec, false); ->
  64                                 end [...]
  65                         end source.Emit (ec);
  66                 end this.EmitAssign (ec, source, false, true)
  67
  68
  69                 When prepare_for_load is true, EmitAssign emits a `token' on the stack that
  70                 Emit will use for its state.
  71
  72                 Let's take FieldExpr as an example. assume we are emitting f ().y += 1;
  73
  74                 Here is the call tree again. This time, each call is annotated with the IL
  75                 it produces:
  76
  77                 this.EmitAssign (ec, source, false, true)
  78                         call f
  79                         dup
  80
  81                         Binary.Emit ()
  82                                 this.Emit (ec, false);
  83                                 ldfld y
  84                                 end this.Emit (ec, false);
  85
  86                                 IntConstant.Emit ()
  87                                 ldc.i4.1
  88                                 end IntConstant.Emit
  89
  90                                 add
  91                         end Binary.Emit ()
  92
  93                         stfld
  94                 end this.EmitAssign (ec, source, false, true)
  95
  96                 Observe two things:
  97                         1) EmitAssign left a token on the stack. It was the result of f ().
  98                         2) This token was used by Emit
  99
 100                 leave_copy (in both EmitAssign and Emit) tells the compiler to leave a copy
 101                 of the expression at that point in evaluation. This is used for pre/post inc/dec
 102                 and for a = x += y. Let's do the above example with leave_copy true in EmitAssign
 103
 104                 this.EmitAssign (ec, source, true, true)
 105                         call f
 106                         dup
 107
 108                         Binary.Emit ()
 109                                 this.Emit (ec, false);
 110                                 ldfld y
 111                                 end this.Emit (ec, false);
 112
 113                                 IntConstant.Emit ()
 114                                 ldc.i4.1
 115                                 end IntConstant.Emit
 116
 117                                 add
 118                         end Binary.Emit ()
 119
 120                         dup
 121                         stloc temp
 122                         stfld
 123                         ldloc temp
 124                 end this.EmitAssign (ec, source, true, true)
 125
 126                 And with it true in Emit
 127
 128                 this.EmitAssign (ec, source, false, true)
 129                         call f
 130                         dup
 131
 132                         Binary.Emit ()
 133                                 this.Emit (ec, true);
 134                                 ldfld y
 135                                 dup
 136                                 stloc temp
 137                                 end this.Emit (ec, true);
 138
 139                                 IntConstant.Emit ()
 140                                 ldc.i4.1
 141                                 end IntConstant.Emit
 142
 143                                 add
 144                         end Binary.Emit ()
 145
 146                         stfld
 147                         ldloc temp
 148                 end this.EmitAssign (ec, source, false, true)
 149
 150                 Note that these two examples are what happens for ++x and x++, respectively.
 151                 */
 152         }
 153
 154         /// <summary>
 155         ///   An Expression to hold a temporary value.
 156         /// </summary>
 157         /// <remarks>
 158         ///   The LocalTemporary class is used to hold temporary values of a given
 159         ///   type to "simulate" the expression semantics on property and indexer
 160         ///   access whose return values are void.
 161         ///
 162         ///   The local temporary is used to alter the normal flow of code generation
 163         ///   basically it creates a local variable, and its emit instruction generates
 164         ///   code to access this value, return its address or save its value.
 165         ///
 166         ///   If `is_address' is true, then the value that we store is the address to the
 167         ///   real value, and not the value itself.
 168         ///
 169         ///   This is needed for a value type, because otherwise you just end up making a
 170         ///   copy of the value on the stack and modifying it. You really need a pointer
 171         ///   to the origional value so that you can modify it in that location. This
 172         ///   Does not happen with a class because a class is a pointer -- so you always
 173         ///   get the indirection.
 174         ///
 175         ///   The `is_address' stuff is really just a hack. We need to come up with a better
 176         ///   way to handle it.
 177         /// </remarks>
 178         public class LocalTemporary : Expression, IMemoryLocation {
 179                 LocalBuilder builder;
 180                 bool is_address;
 181
 182                 public LocalTemporary (Type t) : this (t, false) {}
 183
 184                 public LocalTemporary (Type t, bool is_address)
 185                 {
 186                         type = t;
 187                         eclass = ExprClass.Value;
 188                         this.is_address = is_address;
 189                 }
 190
 191                 public LocalTemporary (LocalBuilder b, Type t)
 192                 {
 193                         type = t;
 194                         eclass = ExprClass.Value;
 195                         loc = Location.Null;
 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 Expression DoResolve (EmitContext ec)
 206                 {
 207                         return this;
 208                 }
 209
 210                 public override void Emit (EmitContext ec)
 211                 {
 212                         ILGenerator ig = ec.ig;
 213
 214                         if (builder == null)
 215                                 throw new InternalErrorException ("Emit without Store, or after Release");
 216
 217                         ig.Emit (OpCodes.Ldloc, builder);
 218                         // we need to copy from the pointer
 219                         if (is_address)
 220                                 LoadFromPtr (ig, type);
 221                 }
 222
 223                 // NB: if you have `is_address' on the stack there must
 224                 // be a managed pointer. Otherwise, it is the type from
 225                 // the ctor.
 226                 public void Store (EmitContext ec)
 227                 {
 228                         ILGenerator ig = ec.ig;
 229                         if (builder == null)
 230                                 builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);
 231
 232                         ig.Emit (OpCodes.Stloc, builder);
 233                 }
 234
 235                 public void AddressOf (EmitContext ec, AddressOp mode)
 236                 {
 237                         if (builder == null)
 238                                 builder = ec.GetTemporaryLocal (is_address ? TypeManager.GetReferenceType (type): type);
 239
 240                         // if is_address, than this is just the address anyways,
 241                         // so we just return this.
 242                         ILGenerator ig = ec.ig;
 243
 244                         if (is_address)
 245                                 ig.Emit (OpCodes.Ldloc, builder);
 246                         else
 247                                 ig.Emit (OpCodes.Ldloca, builder);
 248                 }
 249
 250                 public bool PointsToAddress {
 251                         get {
 252                                 return is_address;
 253                         }
 254                 }
 255         }
 256
 257         /// <summary>
 258         ///   The Assign node takes care of assigning the value of source into
 259         ///   the expression represented by target.
 260         /// </summary>
 261         public class Assign : ExpressionStatement {
 262                 protected Expression target, source, real_source;
 263                 protected LocalTemporary temp = null, real_temp = null;
 264                 protected Assign embedded = null;
 265                 protected bool is_embedded = false;
 266                 protected bool must_free_temp = false;
 267
 268                 public Assign (Expression target, Expression source)
 269                         : this (target, source, target.Location)
 270                 {
 271                 }
 272
 273                 public Assign (Expression target, Expression source, Location l)
 274                 {
 275                         this.target = target;
 276                         this.source = this.real_source = source;
 277                         this.loc = l;
 278                 }
 279
 280                 protected Assign (Assign embedded, Location l)
 281                         : this (embedded.target, embedded.source, l)
 282                 {
 283                         this.is_embedded = true;
 284                 }
 285
 286                 protected virtual Assign GetEmbeddedAssign (Location loc)
 287                 {
 288                         return new Assign (this, loc);
 289                 }
 290
 291                 public Expression Target {
 292                         get {
 293                                 return target;
 294                         }
 295
 296                         set {
 297                                 target = value;
 298                         }
 299                 }
 300
 301                 public Expression Source {
 302                         get {
 303                                 return source;
 304                         }
 305
 306                         set {
 307                                 source = value;
 308                         }
 309                 }
 310
 311                 public static void error70 (EventInfo ei, Location l)
 312                 {
 313                         Report.Error (70, l, "The event `" + TypeManager.CSharpSignature (ei) +
 314                                       "' can only appear on the left hand side of += or -= (except when" +
 315                                       " used from within the type `" + ei.DeclaringType + "')");
 316                 }
 317
 318                 //
 319                 // Will return either `this' or an instance of `New'.
 320                 //
 321                 public override Expression DoResolve (EmitContext ec)
 322                 {
 323                         // Create an embedded assignment if our source is an assignment.
 324                         if (source is Assign)
 325                                 source = embedded = ((Assign) source).GetEmbeddedAssign (loc);
 326
 327                         real_source = source = source.Resolve (ec);
 328
 329                         if (source == null) {
 330                                 // Ensure that we don't propagate the error as spurious "uninitialized variable" errors.
 331                                 target = target.ResolveLValue (ec, EmptyExpression.Null, Location);
 332                                 return null;
 333                         }
 334
 335                         //
 336                         // This is used in an embedded assignment.
 337                         // As an example, consider the statement "A = X = Y = Z".
 338                         //
 339                         if (is_embedded && !(source is Constant)) {
 340                                 // If this is the innermost assignment (the "Y = Z" in our example),
 341                                 // create a new temporary local, otherwise inherit that variable
 342                                 // from our child (the "X = (Y = Z)" inherits the local from the
 343                                 // "Y = Z" assignment).
 344
 345                                 if (embedded == null) {
 346                                         if (this is CompoundAssign)
 347                                                 real_temp = temp = new LocalTemporary (target.Type);
 348                                         else
 349                                                 real_temp = temp = new LocalTemporary (source.Type);
 350                                 } else
 351                                         temp = embedded.temp;
 352
 353                                 // Set the source to the new temporary variable.
 354                                 // This means that the following target.ResolveLValue () will tell
 355                                 // the target to read it's source value from that variable.
 356                                 source = temp;
 357                         }
 358
 359                         // If we have an embedded assignment, use the embedded assignment's temporary
 360                         // local variable as source.
 361                         if (embedded != null)
 362                                 source = (embedded.temp != null) ? embedded.temp : embedded.source;
 363
 364                         target = target.ResolveLValue (ec, source, Location);
 365
 366                         if (target == null)
 367                                 return null;
 368
 369                         bool same_assignment = (embedded != null) ? embedded.Target.Equals(target) : source.Equals (target);
 370                         if (same_assignment) {
 371                                 Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 372                         }
 373
 374                         Type target_type = target.Type;
 375                         Type source_type = real_source.Type;
 376
 377                         // If we're an embedded assignment, our parent will reuse our source as its
 378                         // source, it won't read from our target.
 379                         if (is_embedded)
 380                                 type = source_type;
 381                         else
 382                                 type = target_type;
 383                         eclass = ExprClass.Value;
 384
 385                         if (target is EventExpr) {
 386                                 EventInfo ei = ((EventExpr) target).EventInfo;
 387
 388                                 Expression ml = MemberLookup (
 389                                         ec.ContainerType, ec.ContainerType, ei.Name,
 390                                         MemberTypes.Event, AllBindingFlags | BindingFlags.DeclaredOnly, loc);
 391
 392                                 if (ml == null) {
 393                                         //
 394                                         // If this is the case, then the Event does not belong
 395                                         // to this Type and so, according to the spec
 396                                         // is allowed to only appear on the left hand of
 397                                         // the += and -= operators
 398                                         //
 399                                         // Note that target will not appear as an EventExpr
 400                                         // in the case it is being referenced within the same type container;
 401                                         // it will appear as a FieldExpr in that case.
 402                                         //
 403
 404                                         if (!(source is BinaryDelegate)) {
 405                                                 error70 (ei, loc);
 406                                                 return null;
 407                                         }
 408                                 }
 409                         }
 410
 411                         if (!(target is IAssignMethod) && (target.eclass != ExprClass.EventAccess)) {
 412                                 Error_ValueAssignment (loc);
 413                                 return null;
 414                         }
 415
 416                         if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
 417                                 source.Error_UnexpectedKind (ec.DeclContainer, "variable or value", loc);
 418                                 return null;
 419                         } else if ((RootContext.Version == LanguageVersion.ISO_1) &&
 420                                    (source is MethodGroupExpr)){
 421                                 ((MethodGroupExpr) source).ReportUsageError ();
 422                                 return null;
 423
 424                         }
 425
 426                         if (target_type == source_type){
 427                                 if (source is New && target_type.IsValueType &&
 428                                     (target.eclass != ExprClass.IndexerAccess) && (target.eclass != ExprClass.PropertyAccess)){
 429                                         New n = (New) source;
 430
 431                                         if (n.SetValueTypeVariable (target))
 432                                                 return n;
 433                                         else
 434                                                 return null;
 435                                 }
 436
 437                                 return this;
 438                         }
 439
 440                         //
 441                         // If this assignment/operator was part of a compound binary
 442                         // operator, then we allow an explicit conversion, as detailed
 443                         // in the spec.
 444                         //
 445
 446                         if (this is CompoundAssign){
 447                                 CompoundAssign a = (CompoundAssign) this;
 448
 449                                 Binary b = source as Binary;
 450                                 if (b != null){
 451                                         //
 452                                         // 1. if the source is explicitly convertible to the
 453                                         //    target_type
 454                                         //
 455
 456                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 457                                         if (source == null){
 458                                                 a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, true);
 459                                                 return null;
 460                                         }
 461
 462                                         //
 463                                         // 2. and the original right side is implicitly convertible to
 464                                         // the type of target
 465                                         //
 466                                         if (Convert.ImplicitConversionExists (ec, a.original_source, target_type))
 467                                                 return this;
 468
 469                                         //
 470                                         // In the spec 2.4 they added: or if type of the target is int
 471                                         // and the operator is a shift operator...
 472                                         //
 473                                         if (source_type == TypeManager.int32_type &&
 474                                             (b.Oper == Binary.Operator.LeftShift || b.Oper == Binary.Operator.RightShift))
 475                                                 return this;
 476
 477                                         a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
 478                                         return null;
 479                                 }
 480                         }
 481
 482                         if (source.eclass == ExprClass.MethodGroup && !TypeManager.IsDelegateType (target_type)) {
 483                                 Report.Error (428, source.Location, "Cannot convert method group `{0}' to non-delegate type `{1}'. Did you intend to invoke the method?",
 484                                         ((MethodGroupExpr)source).Name, target.GetSignatureForError ());
 485                                 return null;
 486                         }
 487
 488                         source = Convert.ImplicitConversionRequired (ec, source, target_type, loc);
 489                         if (source == null)
 490                                 return null;
 491
 492                         // If we're an embedded assignment, we need to create a new temporary variable
 493                         // for the converted value.  Our parent will use this new variable as its source.
 494                         // The same applies when we have an embedded assignment - in this case, we need
 495                         // to convert our embedded assignment's temporary local variable to the correct
 496                         // type and store it in a new temporary local.
 497                         if (is_embedded || embedded != null) {
 498                                 type = target_type;
 499                                 temp = new LocalTemporary (type);
 500                                 must_free_temp = true;
 501                         }
 502
 503                         return this;
 504                 }
 505
 506                 Expression EmitEmbedded (EmitContext ec)
 507                 {
 508                         // Emit an embedded assignment.
 509
 510                         if (real_temp != null) {
 511                                 // If we're the innermost assignment, `real_source' is the right-hand
 512                                 // expression which gets assigned to all the variables left of it.
 513                                 // Emit this expression and store its result in real_temp.
 514                                 real_source.Emit (ec);
 515                                 real_temp.Store (ec);
 516                         }
 517
 518                         if (embedded != null)
 519                                 embedded.EmitEmbedded (ec);
 520
 521                         // This happens when we've done a type conversion, in this case source will be
 522                         // the expression which does the type conversion from real_temp.
 523                         // So emit it and store the result in temp; this is the var which will be read
 524                         // by our parent.
 525                         if (temp != real_temp) {
 526                                 source.Emit (ec);
 527                                 temp.Store (ec);
 528                         }
 529
 530                         Expression temp_source = (temp != null) ? temp : source;
 531                         ((IAssignMethod) target).EmitAssign (ec, temp_source, false, false);
 532                         return temp_source;
 533                 }
 534
 535                 void ReleaseEmbedded (EmitContext ec)
 536                 {
 537                         if (embedded != null)
 538                                 embedded.ReleaseEmbedded (ec);
 539
 540                         if (real_temp != null)
 541                                 real_temp.Release (ec);
 542
 543                         if (must_free_temp)
 544                                 temp.Release (ec);
 545                 }
 546
 547                 void Emit (EmitContext ec, bool is_statement)
 548                 {
 549                         if (target is EventExpr) {
 550                                 ((EventExpr) target).EmitAddOrRemove (ec, source);
 551                                 return;
 552                         }
 553
 554                         IAssignMethod am = (IAssignMethod) target;
 555
 556                         Expression temp_source;
 557                         if (embedded != null) {
 558                                 temp_source = embedded.EmitEmbedded (ec);
 559
 560                                 if (temp != null) {
 561                                         source.Emit (ec);
 562                                         temp.Store (ec);
 563                                         temp_source = temp;
 564                                 }
 565                         } else
 566                                 temp_source = source;
 567
 568                         bool prepare_for_load = this is CompoundAssign && !(source is StringConcat);
 569                         am.EmitAssign (ec, temp_source, !is_statement, prepare_for_load);
 570
 571                         if (embedded != null) {
 572                                 if (temp != null)
 573                                         temp.Release (ec);
 574                                 embedded.ReleaseEmbedded (ec);
 575                         }
 576                 }
 577
 578                 public override void Emit (EmitContext ec)
 579                 {
 580                         Emit (ec, false);
 581                 }
 582
 583                 public override void EmitStatement (EmitContext ec)
 584                 {
 585                         Emit (ec, true);
 586                 }
 587
 588                 protected override void CloneTo (CloneContext clonectx, Expression t)
 589                 {
 590                         Assign _target = (Assign) t;
 591
 592                         _target.target = target.Clone (clonectx);
 593                         _target.source = source.Clone (clonectx);
 594                 }
 595         }
 596
 597
 598         // This class implements fields and events class initializers
 599         public class FieldInitializer : Assign
 600         {
 601                 public readonly DeclSpace TypeContainer;
 602
 603                 public FieldInitializer (FieldBuilder field, Expression expression, DeclSpace container)
 604                         : base (new FieldExpr (field, expression.Location, true), expression)
 605                 {
 606                         this.TypeContainer = container;
 607                         if (!field.IsStatic)
 608                                 ((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
 609                 }
 610
 611                 public bool IsComplexInitializer {
 612                         get {
 613                                 if (embedded != null)
 614                                         return true;
 615
 616                                 return !(source is Constant);
 617                         }
 618                 }
 619
 620                 public bool IsDefaultInitializer {
 621                         get {
 622                                 Constant c = source as Constant;
 623                                 if (c == null)
 624                                         return false;
 625
 626                                 FieldExpr fe = (FieldExpr)target;
 627                                 return c.IsDefaultInitializer (fe.Type);
 628                         }
 629                 }
 630         }
 631
 632
 633         //
 634         // This class is used for compound assignments.
 635         //
 636         class CompoundAssign : Assign {
 637                 Binary.Operator op;
 638                 public Expression original_source;
 639
 640                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 641                         : base (target, source, target.Location)
 642                 {
 643                         original_source = source;
 644                         this.op = op;
 645                 }
 646
 647                 protected CompoundAssign (CompoundAssign embedded, Location l)
 648                         : this (embedded.op, embedded.target, embedded.source)
 649                 {
 650                         this.is_embedded = true;
 651                 }
 652
 653                 protected override Assign GetEmbeddedAssign (Location loc)
 654                 {
 655                         return new CompoundAssign (this, loc);
 656                 }
 657
 658                 public override Expression DoResolve (EmitContext ec)
 659                 {
 660                         original_source = original_source.Resolve (ec);
 661                         if (original_source == null)
 662                                 return null;
 663
 664                         target = target.Resolve (ec);
 665                         if (target == null)
 666                                 return null;
 667
 668                         if (target is MethodGroupExpr){
 669                                 Error_CannotAssign (((MethodGroupExpr)target).Name, target.ExprClassName);
 670                                 return null;
 671                         }
 672                         //
 673                         // Only now we can decouple the original source/target
 674                         // into a tree, to guarantee that we do not have side
 675                         // effects.
 676                         //
 677                         source = new Binary (op, target, original_source);
 678                         return base.DoResolve (ec);
 679                 }
 680
 681                 protected override void CloneTo (CloneContext clonectx, Expression t)
 682                 {
 683                         CompoundAssign target = (CompoundAssign) t;
 684
 685                         target.original_source = original_source.Clone (clonectx);
 686                 }
 687         }
 688 }