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