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