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