mcs/mcs/iterators.cs

   1 //
   2 // iterators.cs: Support for implementing iterators
   3 //
   4 // Author:
   5 //   Miguel de Icaza (miguel@ximian.com)
   6 //   Marek Safar (marek.safar@gmail.com)
   7 //
   8 // Dual licensed under the terms of the MIT X11 or GNU GPL
   9 // Copyright 2003 Ximian, Inc.
  10 // Copyright 2003-2008 Novell, Inc.
  11 //
  12
  13 // TODO:
  14 //    Flow analysis for Yield.
  15 //
  16
  17 using System;
  18 using System.Collections;
  19 using System.Reflection;
  20 using System.Reflection.Emit;
  21
  22 namespace Mono.CSharp {
  23
  24         public class Yield : ResumableStatement {
  25                 Expression expr;
  26                 bool unwind_protect;
  27
  28                 int resume_pc;
  29
  30                 public Yield (Expression expr, Location l)
  31                 {
  32                         this.expr = expr;
  33                         loc = l;
  34                 }
  35
  36                 public static bool CheckContext (EmitContext ec, Location loc)
  37                 {
  38                         for (Block block = ec.CurrentBlock; block != null; block = block.Parent) {
  39                                 if (!block.Unsafe)
  40                                         continue;
  41
  42                                 Report.Error (1629, loc, "Unsafe code may not appear in iterators");
  43                                 return false;
  44                         }
  45
  46                         //
  47                         // We can't use `ec.InUnsafe' here because it's allowed to have an iterator
  48                         // inside an unsafe class.  See test-martin-29.cs for an example.
  49                         //
  50                         if (!ec.CurrentAnonymousMethod.IsIterator) {
  51                                 Report.Error (1621, loc,
  52                                               "The yield statement cannot be used inside " +
  53                                               "anonymous method blocks");
  54                                 return false;
  55                         }
  56
  57                         return true;
  58                 }
  59
  60                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
  61                 {
  62                         expr.MutateHoistedGenericType (storey);
  63                 }
  64
  65                 public override bool Resolve (EmitContext ec)
  66                 {
  67                         expr = expr.Resolve (ec);
  68                         if (expr == null)
  69                                 return false;
  70
  71                         Report.Debug (64, "RESOLVE YIELD #1", this, ec, expr, expr.GetType (),
  72                                       ec.CurrentAnonymousMethod, ec.CurrentIterator);
  73
  74                         if (!CheckContext (ec, loc))
  75                                 return false;
  76
  77                         Iterator iterator = ec.CurrentIterator;
  78                         if (expr.Type != iterator.OriginalIteratorType) {
  79                                 expr = Convert.ImplicitConversionRequired (
  80                                         ec, expr, iterator.OriginalIteratorType, loc);
  81                                 if (expr == null)
  82                                         return false;
  83                         }
  84
  85                         if (!ec.CurrentBranching.CurrentUsageVector.IsUnreachable)
  86                                 unwind_protect = ec.CurrentBranching.AddResumePoint (this, loc, out resume_pc);
  87
  88                         return true;
  89                 }
  90
  91                 protected override void DoEmit (EmitContext ec)
  92                 {
  93                         ec.CurrentIterator.MarkYield (ec, expr, resume_pc, unwind_protect, resume_point);
  94                 }
  95
  96                 protected override void CloneTo (CloneContext clonectx, Statement t)
  97                 {
  98                         Yield target = (Yield) t;
  99
 100                         target.expr = expr.Clone (clonectx);
 101                 }
 102         }
 103
 104         public class YieldBreak : ExitStatement {
 105                 public YieldBreak (Location l)
 106                 {
 107                         loc = l;
 108                 }
 109
 110                 public override void Error_FinallyClause ()
 111                 {
 112                         Report.Error (1625, loc, "Cannot yield in the body of a finally clause");
 113                 }
 114
 115                 protected override void CloneTo (CloneContext clonectx, Statement target)
 116                 {
 117                         throw new NotSupportedException ();
 118                 }
 119
 120                 protected override bool DoResolve (EmitContext ec)
 121                 {
 122                         return Yield.CheckContext (ec, loc);
 123                 }
 124
 125                 protected override void DoEmit (EmitContext ec)
 126                 {
 127                         ec.CurrentIterator.EmitYieldBreak (ec.ig, unwind_protect);
 128                 }
 129
 130                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 131                 {
 132                         // nothing to do
 133                 }
 134         }
 135
 136         //
 137         // Wraps method block into iterator wrapper block
 138         //
 139         class IteratorStatement : Statement
 140         {
 141                 Iterator iterator;
 142                 ExplicitBlock original_block;
 143
 144                 public IteratorStatement (Iterator iterator, ExplicitBlock original_block)
 145                 {
 146                         this.iterator = iterator;
 147                         this.original_block = original_block;
 148                         this.loc = iterator.Location;
 149                 }
 150
 151                 protected override void CloneTo (CloneContext clonectx, Statement target)
 152                 {
 153                         IteratorStatement t = (IteratorStatement) target;
 154                         t.original_block = (ExplicitBlock) original_block.Clone (clonectx);
 155                         t.iterator = (Iterator) iterator.Clone (clonectx);
 156                 }
 157
 158                 public override bool Resolve (EmitContext ec)
 159                 {
 160                         ec.StartFlowBranching (iterator);
 161                         bool ok = original_block.Resolve (ec);
 162                         ec.EndFlowBranching ();
 163                         return ok;
 164                 }
 165
 166                 protected override void DoEmit (EmitContext ec)
 167                 {
 168                         iterator.EmitMoveNext (ec, original_block);
 169                 }
 170
 171                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 172                 {
 173                         original_block.MutateHoistedGenericType (storey);
 174                         iterator.MutateHoistedGenericType (storey);
 175                 }
 176         }
 177
 178         public class IteratorStorey : AnonymousMethodStorey
 179         {
 180                 class IteratorMethod : Method
 181                 {
 182                         readonly IteratorStorey host;
 183
 184                         public IteratorMethod (IteratorStorey host, FullNamedExpression returnType, int mod, MemberName name)
 185                                 : base (host, null, returnType, mod | Modifiers.DEBUGGER_HIDDEN | Modifiers.COMPILER_GENERATED,
 186                                   name, Parameters.EmptyReadOnlyParameters, null)
 187                         {
 188                                 this.host = host;
 189
 190                                 Block = new ToplevelBlock (host.Iterator.Container.Toplevel, null, Location);
 191                         }
 192
 193                         public override EmitContext CreateEmitContext (DeclSpace tc, ILGenerator ig)
 194                         {
 195                                 EmitContext ec = new EmitContext (
 196                                         this, tc, this.ds, Location, ig, MemberType, ModFlags, false);
 197
 198                                 ec.CurrentAnonymousMethod = host.Iterator;
 199                                 return ec;
 200                         }
 201                 }
 202
 203                 class GetEnumeratorMethod : IteratorMethod
 204                 {
 205                         sealed class GetEnumeratorStatement : Statement
 206                         {
 207                                 IteratorStorey host;
 208                                 IteratorMethod host_method;
 209
 210                                 Expression new_storey;
 211
 212                                 public GetEnumeratorStatement (IteratorStorey host, IteratorMethod host_method)
 213                                 {
 214                                         this.host = host;
 215                                         this.host_method = host_method;
 216                                         loc = host_method.Location;
 217                                 }
 218
 219                                 protected override void CloneTo (CloneContext clonectx, Statement target)
 220                                 {
 221                                         throw new NotSupportedException ();
 222                                 }
 223
 224                                 public override bool Resolve (EmitContext ec)
 225                                 {
 226                                         TypeExpression storey_type_expr = new TypeExpression (host.TypeBuilder, loc);
 227                                         ArrayList init = null;
 228                                         if (host.hoisted_this != null) {
 229                                                 init = new ArrayList (host.hoisted_params == null ? 1 : host.HoistedParameters.Count + 1);
 230                                                 HoistedThis ht = host.hoisted_this;
 231                                                 FieldExpr from = new FieldExpr (ht.Field.FieldBuilder, loc);
 232                                                 from.InstanceExpression = CompilerGeneratedThis.Instance;
 233                                                 init.Add (new ElementInitializer (ht.Field.Name, from, loc));
 234                                         }
 235
 236                                         if (host.hoisted_params != null) {
 237                                                 if (init == null)
 238                                                         init = new ArrayList (host.HoistedParameters.Count);
 239
 240                                                 for (int i = 0; i < host.hoisted_params.Count; ++i) {
 241                                                         HoistedParameter hp = (HoistedParameter) host.hoisted_params [i];
 242                                                         HoistedParameter hp_cp = (HoistedParameter) host.hoisted_params_copy [i];
 243
 244                                                         FieldExpr from = new FieldExpr (hp_cp.Field.FieldBuilder, loc);
 245                                                         from.InstanceExpression = CompilerGeneratedThis.Instance;
 246
 247                                                         init.Add (new ElementInitializer (hp.Field.Name, from, loc));
 248                                                 }
 249                                         }
 250
 251                                         if (init != null) {
 252                                                 new_storey = new NewInitialize (storey_type_expr, new ArrayList (0),
 253                                                         new CollectionOrObjectInitializers (init, loc), loc);
 254                                         } else {
 255                                                 new_storey = new New (storey_type_expr, new ArrayList (0), loc);
 256                                         }
 257
 258                                         new_storey = new_storey.Resolve (ec);
 259                                         if (new_storey != null)
 260                                                 new_storey = Convert.ImplicitConversionRequired (ec, new_storey, host_method.MemberType, loc);
 261
 262                                         if (TypeManager.int_interlocked_compare_exchange == null) {
 263                                                 Type t = TypeManager.CoreLookupType ("System.Threading", "Interlocked", Kind.Class, true);
 264                                                 if (t != null) {
 265                                                         TypeManager.int_interlocked_compare_exchange = TypeManager.GetPredefinedMethod (
 266                                                                 t, "CompareExchange", loc, TypeManager.int32_type,
 267                                                                 TypeManager.int32_type, TypeManager.int32_type);
 268                                                 }
 269                                         }
 270
 271                                         ec.CurrentBranching.CurrentUsageVector.Goto ();
 272                                         return true;
 273                                 }
 274
 275                                 protected override void DoEmit (EmitContext ec)
 276                                 {
 277                                         ILGenerator ig = ec.ig;
 278                                         Label label_init = ig.DefineLabel ();
 279
 280                                         ig.Emit (OpCodes.Ldarg_0);
 281                                         ig.Emit (OpCodes.Ldflda, host.PC.FieldBuilder);
 282                                         IntConstant.EmitInt (ig, (int) Iterator.State.Start);
 283                                         IntConstant.EmitInt (ig, (int) Iterator.State.Uninitialized);
 284                                         ig.Emit (OpCodes.Call, TypeManager.int_interlocked_compare_exchange);
 285
 286                                         IntConstant.EmitInt (ig, (int) Iterator.State.Uninitialized);
 287                                         ig.Emit (OpCodes.Bne_Un_S, label_init);
 288
 289                                         ig.Emit (OpCodes.Ldarg_0);
 290                                         ig.Emit (OpCodes.Ret);
 291
 292                                         ig.MarkLabel (label_init);
 293
 294                                         new_storey.Emit (ec);
 295                                         ig.Emit (OpCodes.Ret);
 296                                 }
 297
 298                                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 299                                 {
 300                                         throw new NotSupportedException ();
 301                                 }
 302                         }
 303
 304                         public GetEnumeratorMethod (IteratorStorey host, FullNamedExpression returnType, MemberName name)
 305                                 : base (host, returnType, 0, name)
 306                         {
 307                                 Block.AddStatement (new GetEnumeratorStatement (host, this));
 308                         }
 309                 }
 310
 311                 class DisposeMethod : IteratorMethod
 312                 {
 313                         sealed class DisposeMethodStatement : Statement
 314                         {
 315                                 Iterator iterator;
 316
 317                                 public DisposeMethodStatement (Iterator iterator)
 318                                 {
 319                                         this.iterator = iterator;
 320                                         this.loc = iterator.Location;
 321                                 }
 322
 323                                 protected override void CloneTo (CloneContext clonectx, Statement target)
 324                                 {
 325                                         throw new NotSupportedException ();
 326                                 }
 327
 328                                 public override bool Resolve (EmitContext ec)
 329                                 {
 330                                         return true;
 331                                 }
 332
 333                                 protected override void DoEmit (EmitContext ec)
 334                                 {
 335                                         iterator.EmitDispose (ec);
 336                                 }
 337
 338                                 public override void MutateHoistedGenericType (AnonymousMethodStorey storey)
 339                                 {
 340                                         throw new NotSupportedException ();
 341                                 }
 342                         }
 343
 344                         public DisposeMethod (IteratorStorey host)
 345                                 : base (host, TypeManager.system_void_expr, Modifiers.PUBLIC, new MemberName ("Dispose", host.Location))
 346                         {
 347                                 host.AddMethod (this);
 348
 349                                 Block = new ToplevelBlock (host.Iterator.Container, null, Location);
 350                                 Block.AddStatement (new DisposeMethodStatement (host.Iterator));
 351                         }
 352                 }
 353
 354                 //
 355                 // Uses Method as method info
 356                 //
 357                 class DynamicMethodGroupExpr : MethodGroupExpr
 358                 {
 359                         readonly Method method;
 360
 361                         public DynamicMethodGroupExpr (Method method, Location loc)
 362                                 : base (null, loc)
 363                         {
 364                                 this.method = method;
 365                         }
 366
 367                         public override Expression DoResolve (EmitContext ec)
 368                         {
 369                                 Methods = new MethodBase [] { method.MethodBuilder };
 370                                 type = method.Parent.TypeBuilder;
 371                                 InstanceExpression = new CompilerGeneratedThis (type, Location);
 372                                 return base.DoResolve (ec);
 373                         }
 374                 }
 375
 376                 class DynamicFieldExpr : FieldExpr
 377                 {
 378                         readonly Field field;
 379
 380                         public DynamicFieldExpr (Field field, Location loc)
 381                                 : base (loc)
 382                         {
 383                                 this.field = field;
 384                         }
 385
 386                         public override Expression DoResolve (EmitContext ec)
 387                         {
 388                                 FieldInfo = field.FieldBuilder;
 389                                 type = TypeManager.TypeToCoreType (FieldInfo.FieldType);
 390                                 InstanceExpression = new CompilerGeneratedThis (type, Location);
 391                                 return base.DoResolve (ec);
 392                         }
 393                 }
 394
 395                 public readonly Iterator Iterator;
 396
 397                 TypeExpr iterator_type_expr;
 398                 Field pc_field;
 399                 Field current_field;
 400
 401                 TypeExpr enumerator_type;
 402                 TypeExpr enumerable_type;
 403 #if GMCS_SOURCE
 404                 TypeArguments generic_args;
 405                 TypeExpr generic_enumerator_type;
 406                 TypeExpr generic_enumerable_type;
 407 #else
 408                 const TypeArguments generic_args = null;
 409 #endif
 410
 411                 ArrayList hoisted_params_copy;
 412                 int local_name_idx;
 413
 414                 public IteratorStorey (Iterator iterator)
 415                         : base (iterator.Container.Toplevel, iterator.Host,
 416                           iterator.OriginalMethod as MemberBase, iterator.GenericMethod, "Iterator")
 417                 {
 418                         this.Iterator = iterator;
 419                         HasHoistedVariables = true;
 420                 }
 421
 422                 public Field PC {
 423                         get { return pc_field; }
 424                 }
 425
 426                 public Field CurrentField {
 427                         get { return current_field; }
 428                 }
 429
 430                 public ArrayList HoistedParameters {
 431                         get { return hoisted_params; }
 432                 }
 433
 434                 protected override TypeExpr [] ResolveBaseTypes (out TypeExpr base_class)
 435                 {
 436                         iterator_type_expr = new TypeExpression (MutateType (Iterator.OriginalIteratorType), Location);
 437
 438 #if GMCS_SOURCE
 439                         generic_args = new TypeArguments (iterator_type_expr);
 440 #endif
 441
 442                         ArrayList list = new ArrayList ();
 443                         if (Iterator.IsEnumerable) {
 444                                 enumerable_type = new TypeExpression (
 445                                         TypeManager.ienumerable_type, Location);
 446                                 list.Add (enumerable_type);
 447
 448 #if GMCS_SOURCE
 449                                 generic_enumerable_type = new GenericTypeExpr (
 450                                         TypeManager.generic_ienumerable_type,
 451                                         generic_args, Location);
 452                                 list.Add (generic_enumerable_type);
 453 #endif
 454                         }
 455
 456                         enumerator_type = new TypeExpression (
 457                                 TypeManager.ienumerator_type, Location);
 458                         list.Add (enumerator_type);
 459
 460                         list.Add (new TypeExpression (TypeManager.idisposable_type, Location));
 461
 462 #if GMCS_SOURCE
 463                         generic_enumerator_type = new GenericTypeExpr (
 464                                 TypeManager.generic_ienumerator_type,
 465                                 generic_args, Location);
 466                         list.Add (generic_enumerator_type);
 467 #endif
 468
 469                         type_bases = list;
 470
 471                         return base.ResolveBaseTypes (out base_class);
 472                 }
 473
 474                 protected override string GetVariableMangledName (LocalInfo local_info)
 475                 {
 476                         return "<" + local_info.Name + ">__" + local_name_idx++.ToString ();
 477                 }
 478
 479                 public void DefineIteratorMembers ()
 480                 {
 481                         pc_field = AddCompilerGeneratedField ("$PC", TypeManager.system_int32_expr);
 482                         current_field = AddCompilerGeneratedField ("$current", iterator_type_expr);
 483
 484                         if (hoisted_params != null) {
 485                                 //
 486                                 // Iterators are independent, each GetEnumerator call has to
 487                                 // create same enumerator therefore we have to keep original values
 488                                 // around for re-initialization
 489                                 //
 490                                 // TODO: Do it for assigned/modified parameters only
 491                                 //
 492                                 hoisted_params_copy = new ArrayList (hoisted_params.Count);
 493                                 foreach (HoistedParameter hp in hoisted_params) {
 494                                         hoisted_params_copy.Add (new HoistedParameter (hp, "<$>" + hp.Field.Name));
 495                                 }
 496                         }
 497
 498 #if GMCS_SOURCE
 499                         Define_Current (true);
 500 #endif
 501                         Define_Current (false);
 502                         new DisposeMethod (this);
 503                         Define_Reset ();
 504
 505                         if (Iterator.IsEnumerable) {
 506                                 MemberName name = new MemberName (
 507                                         new MemberName ("System.Collections.IEnumerable", Location), "GetEnumerator", Location);
 508
 509 #if GMCS_SOURCE
 510                                 Method get_enumerator = new IteratorMethod (this, enumerator_type, 0, name);
 511
 512                                 name = new MemberName (
 513                                         new MemberName ("System.Collections.Generic.IEnumerable", generic_args, Location), "GetEnumerator", Location);
 514                                 Method gget_enumerator = new GetEnumeratorMethod (this, generic_enumerator_type, name);
 515
 516                                 //
 517                                 // Just call generic GetEnumerator implementation
 518                                 //
 519                                 get_enumerator.Block.AddStatement (
 520                                         new Return (new Invocation (new DynamicMethodGroupExpr (gget_enumerator, Location), new ArrayList (0)), Location));
 521
 522                                 AddMethod (get_enumerator);
 523                                 AddMethod (gget_enumerator);
 524 #else
 525                                 AddMethod (new GetEnumeratorMethod (this, enumerator_type, name));
 526 #endif
 527                         }
 528                 }
 529
 530                 protected override void EmitHoistedParameters (EmitContext ec, ArrayList hoisted)
 531                 {
 532                         base.EmitHoistedParameters (ec, hoisted);
 533                         base.EmitHoistedParameters (ec, hoisted_params_copy);
 534                 }
 535
 536                 void Define_Current (bool is_generic)
 537                 {
 538                         MemberName left;
 539                         TypeExpr type;
 540
 541                         if (is_generic) {
 542                                 left = new MemberName (
 543                                         "System.Collections.Generic.IEnumerator",
 544                                         generic_args, Location);
 545                                 type = iterator_type_expr;
 546                         } else {
 547                                 left = new MemberName ("System.Collections.IEnumerator", Location);
 548                                 type = TypeManager.system_object_expr;
 549                         }
 550
 551                         MemberName name = new MemberName (left, "Current", Location);
 552
 553                         ToplevelBlock get_block = new ToplevelBlock (Location);
 554                         get_block.AddStatement (new Return (new DynamicFieldExpr (CurrentField, Location), Location));
 555
 556                         Accessor getter = new Accessor (get_block, 0, null, null, Location);
 557
 558                         Property current = new Property (
 559                                 this, type, Modifiers.DEBUGGER_HIDDEN, name, null, getter, null, false);
 560                         AddProperty (current);
 561                 }
 562
 563                 void Define_Reset ()
 564                 {
 565                         Method reset = new Method (
 566                                 this, null, TypeManager.system_void_expr,
 567                                 Modifiers.PUBLIC | Modifiers.DEBUGGER_HIDDEN,
 568                                 new MemberName ("Reset", Location),
 569                                 Parameters.EmptyReadOnlyParameters, null);
 570                         AddMethod (reset);
 571
 572                         reset.Block = new ToplevelBlock (Location);
 573
 574                         TypeExpr ex_type = new TypeLookupExpression ("System.NotSupportedException");
 575                         reset.Block.AddStatement (new Throw (new New (ex_type, null, Location), Location));
 576                 }
 577         }
 578
 579         //
 580         // Iterators are implemented as hidden anonymous block
 581         //
 582         public class Iterator : AnonymousExpression {
 583                 public readonly IMethodData OriginalMethod;
 584                 AnonymousMethodMethod method;
 585                 public readonly TypeContainer Host;
 586                 public readonly bool IsEnumerable;
 587
 588                 //
 589                 // The state as we generate the iterator
 590                 //
 591                 Label move_next_ok, move_next_error;
 592                 LocalBuilder skip_finally, current_pc;
 593
 594                 public LocalBuilder SkipFinally {
 595                         get { return skip_finally; }
 596                 }
 597
 598                 public LocalBuilder CurrentPC {
 599                         get { return current_pc; }
 600                 }
 601
 602                 public Block Container {
 603                         get { return OriginalMethod.Block; }
 604                 }
 605
 606                 public GenericMethod GenericMethod {
 607                         get { return OriginalMethod.GenericMethod; }
 608                 }
 609
 610                 public readonly Type OriginalIteratorType;
 611
 612                 readonly IteratorStorey IteratorHost;
 613
 614                 public enum State {
 615                         Running = -3, // Used only in CurrentPC, never stored into $PC
 616                         Uninitialized = -2,
 617                         After = -1,
 618                         Start = 0
 619                 }
 620
 621                 public override void AddStoreyReference (AnonymousMethodStorey storey)
 622                 {
 623                         // do nothing
 624                 }
 625
 626                 public void EmitYieldBreak (ILGenerator ig, bool unwind_protect)
 627                 {
 628                         ig.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, move_next_error);
 629                 }
 630
 631                 void EmitMoveNext_NoResumePoints (EmitContext ec, Block original_block)
 632                 {
 633                         ILGenerator ig = ec.ig;
 634
 635                         ig.Emit (OpCodes.Ldarg_0);
 636                         ig.Emit (OpCodes.Ldfld, IteratorHost.PC.FieldBuilder);
 637
 638                         ig.Emit (OpCodes.Ldarg_0);
 639                         IntConstant.EmitInt (ig, (int) State.After);
 640                         ig.Emit (OpCodes.Stfld, IteratorHost.PC.FieldBuilder);
 641
 642                         // We only care if the PC is zero (start executing) or non-zero (don't do anything)
 643                         ig.Emit (OpCodes.Brtrue, move_next_error);
 644
 645                         SymbolWriter.StartIteratorBody (ec.ig);
 646                         original_block.Emit (ec);
 647                         SymbolWriter.EndIteratorBody (ec.ig);
 648
 649                         ig.MarkLabel (move_next_error);
 650                         ig.Emit (OpCodes.Ldc_I4_0);
 651                         ig.Emit (OpCodes.Ret);
 652                 }
 653
 654                 internal void EmitMoveNext (EmitContext ec, Block original_block)
 655                 {
 656                         ILGenerator ig = ec.ig;
 657
 658                         move_next_ok = ig.DefineLabel ();
 659                         move_next_error = ig.DefineLabel ();
 660
 661                         if (resume_points == null) {
 662                                 EmitMoveNext_NoResumePoints (ec, original_block);
 663                                 return;
 664                         }
 665
 666                         current_pc = ec.GetTemporaryLocal (TypeManager.uint32_type);
 667                         ig.Emit (OpCodes.Ldarg_0);
 668                         ig.Emit (OpCodes.Ldfld, IteratorHost.PC.FieldBuilder);
 669                         ig.Emit (OpCodes.Stloc, current_pc);
 670
 671                         // We're actually in state 'running', but this is as good a PC value as any if there's an abnormal exit
 672                         ig.Emit (OpCodes.Ldarg_0);
 673                         IntConstant.EmitInt (ig, (int) State.After);
 674                         ig.Emit (OpCodes.Stfld, IteratorHost.PC.FieldBuilder);
 675
 676                         Label [] labels = new Label [1 + resume_points.Count];
 677                         labels [0] = ig.DefineLabel ();
 678
 679                         bool need_skip_finally = false;
 680                         for (int i = 0; i < resume_points.Count; ++i) {
 681                                 ResumableStatement s = (ResumableStatement) resume_points [i];
 682                                 need_skip_finally |= s is ExceptionStatement;
 683                                 labels [i+1] = s.PrepareForEmit (ec);
 684                         }
 685
 686                         if (need_skip_finally) {
 687                                 skip_finally = ec.GetTemporaryLocal (TypeManager.bool_type);
 688                                 ig.Emit (OpCodes.Ldc_I4_0);
 689                                 ig.Emit (OpCodes.Stloc, skip_finally);
 690                         }
 691
 692                         SymbolWriter.StartIteratorDispatcher (ec.ig);
 693                         ig.Emit (OpCodes.Ldloc, current_pc);
 694                         ig.Emit (OpCodes.Switch, labels);
 695
 696                         ig.Emit (OpCodes.Br, move_next_error);
 697                         SymbolWriter.EndIteratorDispatcher (ec.ig);
 698
 699                         ig.MarkLabel (labels [0]);
 700
 701                         SymbolWriter.StartIteratorBody (ec.ig);
 702                         original_block.Emit (ec);
 703                         SymbolWriter.EndIteratorBody (ec.ig);
 704
 705                         SymbolWriter.StartIteratorDispatcher (ec.ig);
 706
 707                         ig.Emit (OpCodes.Ldarg_0);
 708                         IntConstant.EmitInt (ig, (int) State.After);
 709                         ig.Emit (OpCodes.Stfld, IteratorHost.PC.FieldBuilder);
 710
 711                         ig.MarkLabel (move_next_error);
 712                         ig.Emit (OpCodes.Ldc_I4_0);
 713                         ig.Emit (OpCodes.Ret);
 714
 715                         ig.MarkLabel (move_next_ok);
 716                         ig.Emit (OpCodes.Ldc_I4_1);
 717                         ig.Emit (OpCodes.Ret);
 718
 719                         SymbolWriter.EndIteratorDispatcher (ec.ig);
 720                 }
 721
 722                 public void EmitDispose (EmitContext ec)
 723                 {
 724                         ILGenerator ig = ec.ig;
 725
 726                         Label end = ig.DefineLabel ();
 727
 728                         Label [] labels = null;
 729                         int n_resume_points = resume_points == null ? 0 : resume_points.Count;
 730                         for (int i = 0; i < n_resume_points; ++i) {
 731                                 ResumableStatement s = (ResumableStatement) resume_points [i];
 732                                 Label ret = s.PrepareForDispose (ec, end);
 733                                 if (ret.Equals (end) && labels == null)
 734                                         continue;
 735                                 if (labels == null) {
 736                                         labels = new Label [resume_points.Count + 1];
 737                                         for (int j = 0; j <= i; ++j)
 738                                                 labels [j] = end;
 739                                 }
 740                                 labels [i+1] = ret;
 741                         }
 742
 743                         if (labels != null) {
 744                                 current_pc = ec.GetTemporaryLocal (TypeManager.uint32_type);
 745                                 ig.Emit (OpCodes.Ldarg_0);
 746                                 ig.Emit (OpCodes.Ldfld, IteratorHost.PC.FieldBuilder);
 747                                 ig.Emit (OpCodes.Stloc, current_pc);
 748                         }
 749
 750                         ig.Emit (OpCodes.Ldarg_0);
 751                         IntConstant.EmitInt (ig, (int) State.After);
 752                         ig.Emit (OpCodes.Stfld, IteratorHost.PC.FieldBuilder);
 753
 754                         if (labels != null) {
 755                                 //SymbolWriter.StartIteratorDispatcher (ec.ig);
 756                                 ig.Emit (OpCodes.Ldloc, current_pc);
 757                                 ig.Emit (OpCodes.Switch, labels);
 758                                 //SymbolWriter.EndIteratorDispatcher (ec.ig);
 759
 760                                 foreach (ResumableStatement s in resume_points)
 761                                         s.EmitForDispose (ec, this, end, true);
 762                         }
 763
 764                         ig.MarkLabel (end);
 765                 }
 766
 767
 768                 ArrayList resume_points;
 769                 public int AddResumePoint (ResumableStatement stmt)
 770                 {
 771                         if (resume_points == null)
 772                                 resume_points = new ArrayList ();
 773                         resume_points.Add (stmt);
 774                         return resume_points.Count;
 775                 }
 776
 777                 //
 778                 // Called back from Yield
 779                 //
 780                 public void MarkYield (EmitContext ec, Expression expr, int resume_pc, bool unwind_protect, Label resume_point)
 781                 {
 782                         ILGenerator ig = ec.ig;
 783
 784                         // Store the new current
 785                         ig.Emit (OpCodes.Ldarg_0);
 786                         expr.Emit (ec);
 787                         ig.Emit (OpCodes.Stfld, IteratorHost.CurrentField.FieldBuilder);
 788
 789                         // store resume program-counter
 790                         ig.Emit (OpCodes.Ldarg_0);
 791                         IntConstant.EmitInt (ig, resume_pc);
 792                         ig.Emit (OpCodes.Stfld, IteratorHost.PC.FieldBuilder);
 793
 794                         // mark finally blocks as disabled
 795                         if (unwind_protect && skip_finally != null) {
 796                                 ig.Emit (OpCodes.Ldc_I4_1);
 797                                 ig.Emit (OpCodes.Stloc, skip_finally);
 798                         }
 799
 800                         // Return ok
 801                         ig.Emit (unwind_protect ? OpCodes.Leave : OpCodes.Br, move_next_ok);
 802
 803                         ig.MarkLabel (resume_point);
 804                 }
 805
 806                 public override string ContainerType {
 807                         get { return "iterator"; }
 808                 }
 809
 810                 public override bool IsIterator {
 811                         get { return true; }
 812                 }
 813
 814                 public override AnonymousMethodStorey Storey {
 815                         get { return IteratorHost; }
 816                 }
 817
 818                 //
 819                 // Our constructor
 820                 //
 821                 private Iterator (IMethodData method, TypeContainer host, Type iterator_type, bool is_enumerable)
 822                         : base (
 823                                 new ToplevelBlock (method.Block, Parameters.EmptyReadOnlyParameters, method.Block.StartLocation),
 824                                 TypeManager.bool_type,
 825                                 method.Location)
 826                 {
 827                         this.OriginalMethod = method;
 828                         this.OriginalIteratorType = iterator_type;
 829                         this.IsEnumerable = is_enumerable;
 830                         this.Host = host;
 831
 832                         IteratorHost = Block.ChangeToIterator (this, method.Block);
 833                 }
 834
 835                 public override string GetSignatureForError ()
 836                 {
 837                         return OriginalMethod.GetSignatureForError ();
 838                 }
 839
 840                 public override Expression DoResolve (EmitContext ec)
 841                 {
 842                         method = new AnonymousMethodMethod (Storey,
 843                                 this, Storey, null, TypeManager.system_boolean_expr,
 844                                 Modifiers.PUBLIC, OriginalMethod.GetSignatureForError (),
 845                                 new MemberName ("MoveNext", Location),
 846                                 Parameters.EmptyReadOnlyParameters);
 847
 848                         if (!Compatible (ec))
 849                                 return null;
 850
 851                         IteratorHost.DefineIteratorMembers ();
 852
 853                         eclass = ExprClass.Value;
 854                         type = ec.ReturnType;
 855                         return this;
 856                 }
 857
 858                 public override void Emit (EmitContext ec)
 859                 {
 860                         //
 861                         // Load Iterator storey instance
 862                         //
 863                         method.Storey.Instance.Emit (ec);
 864
 865                         //
 866                         // Initialize iterator PC when it's unitialized
 867                         //
 868                         if (IsEnumerable) {
 869                                 ILGenerator ig = ec.ig;
 870                                 ig.Emit (OpCodes.Dup);
 871                                 IntConstant.EmitInt (ig, (int)State.Uninitialized);
 872
 873                                 FieldInfo field = IteratorHost.PC.FieldBuilder;
 874 #if GMCS_SOURCE
 875                                 if (Storey.MemberName.IsGeneric)
 876                                         field = TypeBuilder.GetField (Storey.Instance.Type, field);
 877 #endif
 878                                 ig.Emit (OpCodes.Stfld, field);
 879                         }
 880                 }
 881
 882                 public override Expression CreateExpressionTree (EmitContext ec)
 883                 {
 884                         throw new NotSupportedException ("ET");
 885                 }
 886
 887                 public static void CreateIterator (IMethodData method, TypeContainer parent, int modifiers)
 888                 {
 889                         bool is_enumerable;
 890                         Type iterator_type;
 891
 892                         Type ret = method.ReturnType;
 893                         if (ret == null)
 894                                 return;
 895
 896                         if (!CheckType (ret, out iterator_type, out is_enumerable)) {
 897                                 Report.Error (1624, method.Location,
 898                                               "The body of `{0}' cannot be an iterator block " +
 899                                               "because `{1}' is not an iterator interface type",
 900                                               method.GetSignatureForError (),
 901                                               TypeManager.CSharpName (ret));
 902                                 return;
 903                         }
 904
 905                         Parameters parameters = method.ParameterInfo;
 906                         for (int i = 0; i < parameters.Count; i++) {
 907                                 Parameter p = parameters [i];
 908                                 Parameter.Modifier mod = p.ModFlags;
 909                                 if ((mod & Parameter.Modifier.ISBYREF) != 0) {
 910                                         Report.Error (1623, p.Location,
 911                                                 "Iterators cannot have ref or out parameters");
 912                                         return;
 913                                 }
 914
 915                                 if ((mod & Parameter.Modifier.ARGLIST) != 0) {
 916                                         Report.Error (1636, method.Location,
 917                                                 "__arglist is not allowed in parameter list of iterators");
 918                                         return;
 919                                 }
 920
 921                                 if (parameters.Types [i].IsPointer) {
 922                                         Report.Error (1637, p.Location,
 923                                                           "Iterators cannot have unsafe parameters or " +
 924                                                           "yield types");
 925                                         return;
 926                                 }
 927                         }
 928
 929                         if ((modifiers & Modifiers.UNSAFE) != 0) {
 930                                 Report.Error (1629, method.Location, "Unsafe code may not appear in iterators");
 931                                 return;
 932                         }
 933
 934                         Iterator iter = new Iterator (method, parent, iterator_type, is_enumerable);
 935                         iter.Storey.DefineType ();
 936                 }
 937
 938                 static bool CheckType (Type ret, out Type original_iterator_type, out bool is_enumerable)
 939                 {
 940                         original_iterator_type = null;
 941                         is_enumerable = false;
 942
 943                         if (ret == TypeManager.ienumerable_type) {
 944                                 original_iterator_type = TypeManager.object_type;
 945                                 is_enumerable = true;
 946                                 return true;
 947                         }
 948                         if (ret == TypeManager.ienumerator_type) {
 949                                 original_iterator_type = TypeManager.object_type;
 950                                 is_enumerable = false;
 951                                 return true;
 952                         }
 953
 954                         if (!TypeManager.IsGenericType (ret))
 955                                 return false;
 956
 957                         Type[] args = TypeManager.GetTypeArguments (ret);
 958                         if (args.Length != 1)
 959                                 return false;
 960
 961                         Type gt = TypeManager.DropGenericTypeArguments (ret);
 962                         if (gt == TypeManager.generic_ienumerable_type) {
 963                                 original_iterator_type = args [0];
 964                                 is_enumerable = true;
 965                                 return true;
 966                         }
 967
 968                         if (gt == TypeManager.generic_ienumerator_type) {
 969                                 original_iterator_type = args [0];
 970                                 is_enumerable = false;
 971                                 return true;
 972                         }
 973
 974                         return false;
 975                 }
 976         }
 977 }
 978