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                         if (source == null) {
 329                                 // Ensure that we don't propagate the error as spurious "uninitialized variable" errors.
 330                                 target = target.ResolveLValue (ec, EmptyExpression.Null, Location);
 331                                 return null;
 332                         }
 333
 334                         //
 335                         // This is used in an embedded assignment.
 336                         // As an example, consider the statement "A = X = Y = Z".
 337                         //
 338                         if (is_embedded && !(source is Constant)) {
 339                                 // If this is the innermost assignment (the "Y = Z" in our example),
 340                                 // create a new temporary local, otherwise inherit that variable
 341                                 // from our child (the "X = (Y = Z)" inherits the local from the
 342                                 // "Y = Z" assignment).
 343
 344                                 if (embedded == null) {
 345                                         if (this is CompoundAssign)
 346                                                 real_temp = temp = new LocalTemporary (target.Type);
 347                                         else
 348                                                 real_temp = temp = new LocalTemporary (source.Type);
 349                                 } else
 350                                         temp = embedded.temp;
 351
 352                                 // Set the source to the new temporary variable.
 353                                 // This means that the following target.ResolveLValue () will tell
 354                                 // the target to read it's source value from that variable.
 355                                 source = temp;
 356                         }
 357
 358                         // If we have an embedded assignment, use the embedded assignment's temporary
 359                         // local variable as source.
 360                         if (embedded != null)
 361                                 source = (embedded.temp != null) ? embedded.temp : embedded.source;
 362
 363                         target = target.ResolveLValue (ec, source, Location);
 364
 365                         if (target == null)
 366                                 return null;
 367
 368                         bool same_assignment = (embedded != null) ? embedded.Target.Equals(target) : source.Equals (target);
 369                         if (same_assignment) {
 370                                 Report.Warning (1717, 3, loc, "Assignment made to same variable; did you mean to assign something else?");
 371                         }
 372
 373                         Type target_type = target.Type;
 374                         Type source_type = real_source.Type;
 375
 376                         // If we're an embedded assignment, our parent will reuse our source as its
 377                         // source, it won't read from our target.
 378                         if (is_embedded)
 379                                 type = source_type;
 380                         else
 381                                 type = target_type;
 382                         eclass = ExprClass.Value;
 383
 384                         if (target is EventExpr) {
 385                                 EventInfo ei = ((EventExpr) target).EventInfo;
 386
 387                                 Expression ml = MemberLookup (
 388                                         ec.ContainerType, ec.ContainerType, ei.Name,
 389                                         MemberTypes.Event, AllBindingFlags | BindingFlags.DeclaredOnly, loc);
 390
 391                                 if (ml == null) {
 392                                         //
 393                                         // If this is the case, then the Event does not belong
 394                                         // to this Type and so, according to the spec
 395                                         // is allowed to only appear on the left hand of
 396                                         // the += and -= operators
 397                                         //
 398                                         // Note that target will not appear as an EventExpr
 399                                         // in the case it is being referenced within the same type container;
 400                                         // it will appear as a FieldExpr in that case.
 401                                         //
 402
 403                                         if (!(source is BinaryDelegate)) {
 404                                                 error70 (ei, loc);
 405                                                 return null;
 406                                         }
 407                                 }
 408                         }
 409
 410                         if (!(target is IAssignMethod) && (target.eclass != ExprClass.EventAccess)) {
 411                                 Error_ValueAssignment (loc);
 412                                 return null;
 413                         }
 414
 415                         if ((source.eclass == ExprClass.Type) && (source is TypeExpr)) {
 416                                 source.Error_UnexpectedKind (ec.DeclContainer, "variable or value", loc);
 417                                 return null;
 418                         } else if ((RootContext.Version == LanguageVersion.ISO_1) &&
 419                                    (source is MethodGroupExpr)){
 420                                 ((MethodGroupExpr) source).ReportUsageError ();
 421                                 return null;
 422
 423                         }
 424
 425                         if (target_type == source_type){
 426                                 if (source is New && target_type.IsValueType &&
 427                                     (target.eclass != ExprClass.IndexerAccess) && (target.eclass != ExprClass.PropertyAccess)){
 428                                         New n = (New) source;
 429
 430                                         if (n.SetValueTypeVariable (target))
 431                                                 return n;
 432                                         else
 433                                                 return null;
 434                                 }
 435
 436                                 return this;
 437                         }
 438
 439                         //
 440                         // If this assignment/operator was part of a compound binary
 441                         // operator, then we allow an explicit conversion, as detailed
 442                         // in the spec.
 443                         //
 444
 445                         if (this is CompoundAssign){
 446                                 CompoundAssign a = (CompoundAssign) this;
 447
 448                                 Binary b = source as Binary;
 449                                 if (b != null){
 450                                         //
 451                                         // 1. if the source is explicitly convertible to the
 452                                         //    target_type
 453                                         //
 454
 455                                         source = Convert.ExplicitConversion (ec, source, target_type, loc);
 456                                         if (source == null){
 457                                                 a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, true);
 458                                                 return null;
 459                                         }
 460
 461                                         //
 462                                         // 2. and the original right side is implicitly convertible to
 463                                         // the type of target
 464                                         //
 465                                         if (Convert.ImplicitConversionExists (ec, a.original_source, target_type))
 466                                                 return this;
 467
 468                                         //
 469                                         // In the spec 2.4 they added: or if type of the target is int
 470                                         // and the operator is a shift operator...
 471                                         //
 472                                         if (source_type == TypeManager.int32_type &&
 473                                             (b.Oper == Binary.Operator.LeftShift || b.Oper == Binary.Operator.RightShift))
 474                                                 return this;
 475
 476                                         a.original_source.Error_ValueCannotBeConverted (ec, loc, target_type, false);
 477                                         return null;
 478                                 }
 479                         }
 480
 481                         if (source.eclass == ExprClass.MethodGroup && !TypeManager.IsDelegateType (target_type)) {
 482                                 Report.Error (428, source.Location, "Cannot convert method group `{0}' to non-delegate type `{1}'. Did you intend to invoke the method?",
 483                                         ((MethodGroupExpr)source).Name, target.GetSignatureForError ());
 484                                 return null;
 485                         }
 486
 487                         source = Convert.ImplicitConversionRequired (ec, source, target_type, loc);
 488                         if (source == null)
 489                                 return null;
 490
 491                         // If we're an embedded assignment, we need to create a new temporary variable
 492                         // for the converted value.  Our parent will use this new variable as its source.
 493                         // The same applies when we have an embedded assignment - in this case, we need
 494                         // to convert our embedded assignment's temporary local variable to the correct
 495                         // type and store it in a new temporary local.
 496                         if (is_embedded || embedded != null) {
 497                                 type = target_type;
 498                                 temp = new LocalTemporary (type);
 499                                 must_free_temp = true;
 500                         }
 501
 502                         return this;
 503                 }
 504
 505                 Expression EmitEmbedded (EmitContext ec)
 506                 {
 507                         // Emit an embedded assignment.
 508
 509                         if (real_temp != null) {
 510                                 // If we're the innermost assignment, `real_source' is the right-hand
 511                                 // expression which gets assigned to all the variables left of it.
 512                                 // Emit this expression and store its result in real_temp.
 513                                 real_source.Emit (ec);
 514                                 real_temp.Store (ec);
 515                         }
 516
 517                         if (embedded != null)
 518                                 embedded.EmitEmbedded (ec);
 519
 520                         // This happens when we've done a type conversion, in this case source will be
 521                         // the expression which does the type conversion from real_temp.
 522                         // So emit it and store the result in temp; this is the var which will be read
 523                         // by our parent.
 524                         if (temp != real_temp) {
 525                                 source.Emit (ec);
 526                                 temp.Store (ec);
 527                         }
 528
 529                         Expression temp_source = (temp != null) ? temp : source;
 530                         ((IAssignMethod) target).EmitAssign (ec, temp_source, false, false);
 531                         return temp_source;
 532                 }
 533
 534                 void ReleaseEmbedded (EmitContext ec)
 535                 {
 536                         if (embedded != null)
 537                                 embedded.ReleaseEmbedded (ec);
 538
 539                         if (real_temp != null)
 540                                 real_temp.Release (ec);
 541
 542                         if (must_free_temp)
 543                                 temp.Release (ec);
 544                 }
 545
 546                 void Emit (EmitContext ec, bool is_statement)
 547                 {
 548                         if (target is EventExpr) {
 549                                 ((EventExpr) target).EmitAddOrRemove (ec, source);
 550                                 return;
 551                         }
 552
 553                         IAssignMethod am = (IAssignMethod) target;
 554
 555                         Expression temp_source;
 556                         if (embedded != null) {
 557                                 temp_source = embedded.EmitEmbedded (ec);
 558
 559                                 if (temp != null) {
 560                                         source.Emit (ec);
 561                                         temp.Store (ec);
 562                                         temp_source = temp;
 563                                 }
 564                         } else
 565                                 temp_source = source;
 566
 567                         am.EmitAssign (ec, temp_source, !is_statement, this is CompoundAssign);
 568
 569                         if (embedded != null) {
 570                                 if (temp != null)
 571                                         temp.Release (ec);
 572                                 embedded.ReleaseEmbedded (ec);
 573                         }
 574                 }
 575
 576                 public override void Emit (EmitContext ec)
 577                 {
 578                         Emit (ec, false);
 579                 }
 580
 581                 public override void EmitStatement (EmitContext ec)
 582                 {
 583                         Emit (ec, true);
 584                 }
 585         }
 586
 587
 588         // This class implements fields and events class initializers
 589         public class FieldInitializer : Assign
 590         {
 591                 public readonly DeclSpace TypeContainer;
 592
 593                 public FieldInitializer (FieldBuilder field, Expression expression, DeclSpace container)
 594                         : base (new FieldExpr (field, expression.Location, true), expression)
 595                 {
 596                         this.TypeContainer = container;
 597                         if (!field.IsStatic)
 598                                 ((FieldExpr)target).InstanceExpression = CompilerGeneratedThis.Instance;
 599                 }
 600
 601                 public bool IsComplexInitializer {
 602                         get {
 603                                 if (embedded != null)
 604                                         return true;
 605
 606                                 return !(source is Constant);
 607                         }
 608                 }
 609
 610                 public bool IsDefaultInitializer {
 611                         get {
 612                                 Constant c = source as Constant;
 613                                 if (c == null)
 614                                         return false;
 615
 616                                 FieldExpr fe = (FieldExpr)target;
 617                                 return c.IsDefaultInitializer (fe.Type);
 618                         }
 619                 }
 620         }
 621
 622
 623         //
 624         // This class is used for compound assignments.
 625         //
 626         class CompoundAssign : Assign {
 627                 Binary.Operator op;
 628                 public Expression original_source;
 629
 630                 public CompoundAssign (Binary.Operator op, Expression target, Expression source)
 631                         : base (target, source, target.Location)
 632                 {
 633                         original_source = source;
 634                         this.op = op;
 635                 }
 636
 637                 protected CompoundAssign (CompoundAssign embedded, Location l)
 638                         : this (embedded.op, embedded.target, embedded.source)
 639                 {
 640                         this.is_embedded = true;
 641                 }
 642
 643                 protected override Assign GetEmbeddedAssign (Location loc)
 644                 {
 645                         return new CompoundAssign (this, loc);
 646                 }
 647
 648                 public override Expression DoResolve (EmitContext ec)
 649                 {
 650                         original_source = original_source.Resolve (ec);
 651                         if (original_source == null)
 652                                 return null;
 653
 654                         target = target.Resolve (ec);
 655                         if (target == null)
 656                                 return null;
 657
 658                         if (target is MethodGroupExpr){
 659                                 Error_CannotAssign (((MethodGroupExpr)target).Name, target.ExprClassName);
 660                                 return null;
 661                         }
 662                         //
 663                         // Only now we can decouple the original source/target
 664                         // into a tree, to guarantee that we do not have side
 665                         // effects.
 666                         //
 667                         source = new Binary (op, target, original_source);
 668                         return base.DoResolve (ec);
 669                 }
 670         }
 671 }