mcs/mcs/flowanalysis.cs

   1 //
   2 // flowanalyis.cs: The control flow analysis code
   3 //
   4 // Author:
   5 //   Martin Baulig (martin@ximian.com)
   6 //   Raja R Harinath (rharinath@novell.com)
   7 //
   8 // Copyright 2001, 2002, 2003 Ximian, Inc.
   9 // Copyright 2003-2008 Novell, Inc.
  10 //
  11
  12 using System;
  13 using System.Text;
  14 using System.Collections.Generic;
  15
  16 namespace Mono.CSharp
  17 {
  18         // <summary>
  19         //   A new instance of this class is created every time a new block is resolved
  20         //   and if there's branching in the block's control flow.
  21         // </summary>
  22         public abstract class FlowBranching
  23         {
  24                 // <summary>
  25                 //   The type of a FlowBranching.
  26                 // </summary>
  27                 public enum BranchingType : byte {
  28                         // Normal (conditional or toplevel) block.
  29                         Block,
  30
  31                         // Conditional.
  32                         Conditional,
  33
  34                         // A loop block.
  35                         Loop,
  36
  37                         // The statement embedded inside a loop
  38                         Embedded,
  39
  40                         // part of a block headed by a jump target
  41                         Labeled,
  42
  43                         // TryCatch block.
  44                         TryCatch,
  45
  46                         // TryFinally, Using, Lock, CollectionForeach
  47                         Exception,
  48
  49                         // Switch block.
  50                         Switch,
  51
  52                         // The toplevel block of a function
  53                         Toplevel,
  54
  55                         // An iterator block
  56                         Iterator
  57                 }
  58
  59                 // <summary>
  60                 //   The type of one sibling of a branching.
  61                 // </summary>
  62                 public enum SiblingType : byte {
  63                         Block,
  64                         Conditional,
  65                         SwitchSection,
  66                         Try,
  67                         Catch,
  68                         Finally
  69                 }
  70
  71                 public static FlowBranching CreateBranching (FlowBranching parent, BranchingType type, Block block, Location loc)
  72                 {
  73                         switch (type) {
  74                         case BranchingType.Exception:
  75                         case BranchingType.Labeled:
  76                         case BranchingType.Toplevel:
  77                         case BranchingType.TryCatch:
  78                                 throw new InvalidOperationException ();
  79
  80                         case BranchingType.Switch:
  81                                 return new FlowBranchingBreakable (parent, type, SiblingType.SwitchSection, block, loc);
  82
  83                         case BranchingType.Block:
  84                                 return new FlowBranchingBlock (parent, type, SiblingType.Block, block, loc);
  85
  86                         case BranchingType.Loop:
  87                                 return new FlowBranchingBreakable (parent, type, SiblingType.Conditional, block, loc);
  88
  89                         case BranchingType.Embedded:
  90                                 return new FlowBranchingContinuable (parent, type, SiblingType.Conditional, block, loc);
  91
  92                         default:
  93                                 return new FlowBranchingBlock (parent, type, SiblingType.Conditional, block, loc);
  94                         }
  95                 }
  96
  97                 // <summary>
  98                 //   The type of this flow branching.
  99                 // </summary>
 100                 public readonly BranchingType Type;
 101
 102                 // <summary>
 103                 //   The block this branching is contained in.  This may be null if it's not
 104                 //   a top-level block and it doesn't declare any local variables.
 105                 // </summary>
 106                 public readonly Block Block;
 107
 108                 // <summary>
 109                 //   The parent of this branching or null if this is the top-block.
 110                 // </summary>
 111                 public readonly FlowBranching Parent;
 112
 113                 // <summary>
 114                 //   Start-Location of this flow branching.
 115                 // </summary>
 116                 public readonly Location Location;
 117
 118                 static int next_id = 0;
 119                 int id;
 120
 121                 // <summary>
 122                 //   The vector contains a BitArray with information about which local variables
 123                 //   and parameters are already initialized at the current code position.
 124                 // </summary>
 125                 public class UsageVector {
 126                         // <summary>
 127                         //   The type of this branching.
 128                         // </summary>
 129                         public readonly SiblingType Type;
 130
 131                         // <summary>
 132                         //   Start location of this branching.
 133                         // </summary>
 134                         public Location Location;
 135
 136                         // <summary>
 137                         //   This is only valid for SwitchSection, Try, Catch and Finally.
 138                         // </summary>
 139                         public readonly Block Block;
 140
 141                         // <summary>
 142                         //   The number of locals in this block.
 143                         // </summary>
 144                         public readonly int CountLocals;
 145
 146                         // <summary>
 147                         //   If not null, then we inherit our state from this vector and do a
 148                         //   copy-on-write.  If null, then we're the first sibling in a top-level
 149                         //   block and inherit from the empty vector.
 150                         // </summary>
 151                         public readonly UsageVector InheritsFrom;
 152
 153                         // <summary>
 154                         //   This is used to construct a list of UsageVector's.
 155                         // </summary>
 156                         public UsageVector Next;
 157
 158                         //
 159                         // Private.
 160                         //
 161                         MyBitVector locals;
 162                         bool is_unreachable;
 163
 164                         static int next_id = 0;
 165                         int id;
 166
 167                         //
 168                         // Normally, you should not use any of these constructors.
 169                         //
 170                         public UsageVector (SiblingType type, UsageVector parent, Block block, Location loc, int num_locals)
 171                         {
 172                                 this.Type = type;
 173                                 this.Block = block;
 174                                 this.Location = loc;
 175                                 this.InheritsFrom = parent;
 176                                 this.CountLocals = num_locals;
 177
 178                                 locals = num_locals == 0
 179                                         ? MyBitVector.Empty
 180                                         : new MyBitVector (parent == null ? MyBitVector.Empty : parent.locals, num_locals);
 181
 182                                 if (parent != null)
 183                                         is_unreachable = parent.is_unreachable;
 184
 185                                 id = ++next_id;
 186
 187                         }
 188
 189                         public UsageVector (SiblingType type, UsageVector parent, Block block, Location loc)
 190                                 : this (type, parent, block, loc, parent.CountLocals)
 191                         { }
 192
 193                         private UsageVector (MyBitVector locals, bool is_unreachable, Block block, Location loc)
 194                         {
 195                                 this.Type = SiblingType.Block;
 196                                 this.Location = loc;
 197                                 this.Block = block;
 198
 199                                 this.is_unreachable = is_unreachable;
 200
 201                                 this.locals = locals;
 202
 203                                 id = ++next_id;
 204
 205                         }
 206
 207                         // <summary>
 208                         //   This does a deep copy of the usage vector.
 209                         // </summary>
 210                         public UsageVector Clone ()
 211                         {
 212                                 UsageVector retval = new UsageVector (Type, null, Block, Location, CountLocals);
 213
 214                                 retval.locals = locals.Clone ();
 215                                 retval.is_unreachable = is_unreachable;
 216
 217                                 return retval;
 218                         }
 219
 220                         public bool IsAssigned (VariableInfo var, bool ignoreReachability)
 221                         {
 222                                 if (!ignoreReachability && !var.IsParameter && IsUnreachable)
 223                                         return true;
 224
 225                                 return var.IsAssigned (locals);
 226                         }
 227
 228                         public void SetAssigned (VariableInfo var)
 229                         {
 230                                 if (!var.IsParameter && IsUnreachable)
 231                                         return;
 232
 233                                 var.SetAssigned (locals);
 234                         }
 235
 236                         public bool IsFieldAssigned (VariableInfo var, string name)
 237                         {
 238                                 if (!var.IsParameter && IsUnreachable)
 239                                         return true;
 240
 241                                 return var.IsFieldAssigned (locals, name);
 242                         }
 243
 244                         public void SetFieldAssigned (VariableInfo var, string name)
 245                         {
 246                                 if (!var.IsParameter && IsUnreachable)
 247                                         return;
 248
 249                                 var.SetFieldAssigned (locals, name);
 250                         }
 251
 252                         public bool IsUnreachable {
 253                                 get { return is_unreachable; }
 254                         }
 255
 256                         public void ResetBarrier ()
 257                         {
 258                                 is_unreachable = false;
 259                         }
 260
 261                         public void Goto ()
 262                         {
 263                                 is_unreachable = true;
 264                         }
 265
 266                         public static UsageVector MergeSiblings (UsageVector sibling_list, Location loc)
 267                         {
 268                                 if (sibling_list.Next == null)
 269                                         return sibling_list;
 270
 271                                 MyBitVector locals = null;
 272                                 bool is_unreachable = sibling_list.is_unreachable;
 273
 274                                 if (!sibling_list.IsUnreachable)
 275                                         locals &= sibling_list.locals;
 276
 277                                 for (UsageVector child = sibling_list.Next; child != null; child = child.Next) {
 278                                         is_unreachable &= child.is_unreachable;
 279
 280                                         if (!child.IsUnreachable)
 281                                                 locals &= child.locals;
 282                                 }
 283
 284                                 return new UsageVector (locals, is_unreachable, null, loc);
 285                         }
 286
 287                         // <summary>
 288                         //   Merges a child branching.
 289                         // </summary>
 290                         public UsageVector MergeChild (UsageVector child, bool overwrite)
 291                         {
 292                                 Report.Debug (2, "    MERGING CHILD EFFECTS", this, child, Type);
 293
 294                                 bool new_isunr = child.is_unreachable;
 295
 296                                 //
 297                                 // We've now either reached the point after the branching or we will
 298                                 // never get there since we always return or always throw an exception.
 299                                 //
 300                                 // If we can reach the point after the branching, mark all locals and
 301                                 // parameters as initialized which have been initialized in all branches
 302                                 // we need to look at (see above).
 303                                 //
 304
 305                                 if ((Type == SiblingType.SwitchSection) && !new_isunr) {
 306                                         Report.Error (163, Location,
 307                                                       "Control cannot fall through from one " +
 308                                                       "case label to another");
 309                                         return child;
 310                                 }
 311
 312                                 locals |= child.locals;
 313
 314                                 // throw away un-necessary information about variables in child blocks
 315                                 if (locals.Count != CountLocals)
 316                                         locals = new MyBitVector (locals, CountLocals);
 317
 318                                 if (overwrite)
 319                                         is_unreachable = new_isunr;
 320                                 else
 321                                         is_unreachable |= new_isunr;
 322
 323                                 return child;
 324                         }
 325
 326                         public void MergeOrigins (UsageVector o_vectors)
 327                         {
 328                                 Report.Debug (1, "  MERGING BREAK ORIGINS", this);
 329
 330                                 if (o_vectors == null)
 331                                         return;
 332
 333                                 if (IsUnreachable && locals != null)
 334                                         locals.SetAll (true);
 335
 336                                 for (UsageVector vector = o_vectors; vector != null; vector = vector.Next) {
 337                                         Report.Debug (1, "    MERGING BREAK ORIGIN", vector);
 338                                         if (vector.IsUnreachable)
 339                                                 continue;
 340                                         locals &= vector.locals;
 341                                         is_unreachable &= vector.is_unreachable;
 342                                 }
 343
 344                                 Report.Debug (1, "  MERGING BREAK ORIGINS DONE", this);
 345                         }
 346
 347                         //
 348                         // Debugging stuff.
 349                         //
 350
 351                         public override string ToString ()
 352                         {
 353                                 return String.Format ("Vector ({0},{1},{2}-{3})", Type, id, is_unreachable, locals);
 354                         }
 355                 }
 356
 357                 // <summary>
 358                 //   Creates a new flow branching which is contained in `parent'.
 359                 //   You should only pass non-null for the `block' argument if this block
 360                 //   introduces any new variables - in this case, we need to create a new
 361                 //   usage vector with a different size than our parent's one.
 362                 // </summary>
 363                 protected FlowBranching (FlowBranching parent, BranchingType type, SiblingType stype,
 364                                          Block block, Location loc)
 365                 {
 366                         Parent = parent;
 367                         Block = block;
 368                         Location = loc;
 369                         Type = type;
 370                         id = ++next_id;
 371
 372                         UsageVector vector;
 373                         if (Block != null) {
 374                                 UsageVector parent_vector = parent != null ? parent.CurrentUsageVector : null;
 375                                 vector = new UsageVector (stype, parent_vector, Block, loc, Block.AssignableSlots);
 376                         } else {
 377                                 vector = new UsageVector (stype, Parent.CurrentUsageVector, null, loc);
 378                         }
 379
 380                         AddSibling (vector);
 381                 }
 382
 383                 public abstract UsageVector CurrentUsageVector {
 384                         get;
 385                 }
 386
 387                 // <summary>
 388                 //   Creates a sibling of the current usage vector.
 389                 // </summary>
 390                 public virtual void CreateSibling (Block block, SiblingType type)
 391                 {
 392                         UsageVector vector = new UsageVector (
 393                                 type, Parent.CurrentUsageVector, block, Location);
 394                         AddSibling (vector);
 395
 396                         Report.Debug (1, "  CREATED SIBLING", CurrentUsageVector);
 397                 }
 398
 399                 public void CreateSibling ()
 400                 {
 401                         CreateSibling (null, SiblingType.Conditional);
 402                 }
 403
 404                 protected abstract void AddSibling (UsageVector uv);
 405
 406                 protected abstract UsageVector Merge ();
 407
 408                 public UsageVector MergeChild (FlowBranching child)
 409                 {
 410                         return CurrentUsageVector.MergeChild (child.Merge (), true);
 411                 }
 412
 413                 public virtual bool CheckRethrow (Location loc)
 414                 {
 415                         return Parent.CheckRethrow (loc);
 416                 }
 417
 418                 public virtual bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
 419                 {
 420                         return Parent.AddResumePoint (stmt, loc, out pc);
 421                 }
 422
 423                 // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
 424                 public virtual bool AddBreakOrigin (UsageVector vector, Location loc)
 425                 {
 426                         return Parent.AddBreakOrigin (vector, loc);
 427                 }
 428
 429                 // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
 430                 public virtual bool AddContinueOrigin (UsageVector vector, Location loc)
 431                 {
 432                         return Parent.AddContinueOrigin (vector, loc);
 433                 }
 434
 435                 // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
 436                 public virtual bool AddReturnOrigin (UsageVector vector, ExitStatement stmt)
 437                 {
 438                         return Parent.AddReturnOrigin (vector, stmt);
 439                 }
 440
 441                 // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
 442                 public virtual bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 443                 {
 444                         return Parent.AddGotoOrigin (vector, goto_stmt);
 445                 }
 446
 447                 public bool IsAssigned (VariableInfo vi)
 448                 {
 449                         return CurrentUsageVector.IsAssigned (vi, false);
 450                 }
 451
 452                 public bool IsFieldAssigned (VariableInfo vi, string field_name)
 453                 {
 454                         return CurrentUsageVector.IsAssigned (vi, false) || CurrentUsageVector.IsFieldAssigned (vi, field_name);
 455                 }
 456
 457                 protected static Report Report {
 458                         get { return RootContext.ToplevelTypes.Compiler.Report; }
 459                 }
 460
 461                 public void SetAssigned (VariableInfo vi)
 462                 {
 463                         CurrentUsageVector.SetAssigned (vi);
 464                 }
 465
 466                 public void SetFieldAssigned (VariableInfo vi, string name)
 467                 {
 468                         CurrentUsageVector.SetFieldAssigned (vi, name);
 469                 }
 470
 471 #if DEBUG
 472                 public override string ToString ()
 473                 {
 474                         StringBuilder sb = new StringBuilder ();
 475                         sb.Append (GetType ());
 476                         sb.Append (" (");
 477
 478                         sb.Append (id);
 479                         sb.Append (",");
 480                         sb.Append (Type);
 481                         if (Block != null) {
 482                                 sb.Append (" - ");
 483                                 sb.Append (Block.ID);
 484                                 sb.Append (" - ");
 485                                 sb.Append (Block.StartLocation);
 486                         }
 487                         sb.Append (" - ");
 488                         // sb.Append (Siblings.Length);
 489                         // sb.Append (" - ");
 490                         sb.Append (CurrentUsageVector);
 491                         sb.Append (")");
 492                         return sb.ToString ();
 493                 }
 494 #endif
 495
 496                 public string Name {
 497                         get { return String.Format ("{0} ({1}:{2}:{3})", GetType (), id, Type, Location); }
 498                 }
 499         }
 500
 501         public class FlowBranchingBlock : FlowBranching
 502         {
 503                 UsageVector sibling_list = null;
 504
 505                 public FlowBranchingBlock (FlowBranching parent, BranchingType type,
 506                                            SiblingType stype, Block block, Location loc)
 507                         : base (parent, type, stype, block, loc)
 508                 { }
 509
 510                 public override UsageVector CurrentUsageVector {
 511                         get { return sibling_list; }
 512                 }
 513
 514                 protected override void AddSibling (UsageVector sibling)
 515                 {
 516                         if (sibling_list != null && sibling_list.Type == SiblingType.Block)
 517                                 throw new InternalErrorException ("Blocks don't have sibling flow paths");
 518                         sibling.Next = sibling_list;
 519                         sibling_list = sibling;
 520                 }
 521
 522                 public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 523                 {
 524                         LabeledStatement stmt = Block == null ? null : Block.LookupLabel (goto_stmt.Target);
 525                         if (stmt == null)
 526                                 return Parent.AddGotoOrigin (vector, goto_stmt);
 527
 528                         // forward jump
 529                         goto_stmt.SetResolvedTarget (stmt);
 530                         stmt.AddUsageVector (vector);
 531                         return false;
 532                 }
 533
 534                 public static void Error_UnknownLabel (Location loc, string label, Report Report)
 535                 {
 536                         Report.Error(159, loc, "The label `{0}:' could not be found within the scope of the goto statement",
 537                                 label);
 538                 }
 539
 540                 protected override UsageVector Merge ()
 541                 {
 542                         Report.Debug (2, "  MERGING SIBLINGS", Name);
 543                         UsageVector vector = UsageVector.MergeSiblings (sibling_list, Location);
 544                         Report.Debug (2, "  MERGING SIBLINGS DONE", Name, vector);
 545                         return vector;
 546                 }
 547         }
 548
 549         public class FlowBranchingBreakable : FlowBranchingBlock
 550         {
 551                 UsageVector break_origins;
 552
 553                 public FlowBranchingBreakable (FlowBranching parent, BranchingType type, SiblingType stype, Block block, Location loc)
 554                         : base (parent, type, stype, block, loc)
 555                 { }
 556
 557                 public override bool AddBreakOrigin (UsageVector vector, Location loc)
 558                 {
 559                         vector = vector.Clone ();
 560                         vector.Next = break_origins;
 561                         break_origins = vector;
 562                         return false;
 563                 }
 564
 565                 protected override UsageVector Merge ()
 566                 {
 567                         UsageVector vector = base.Merge ();
 568                         vector.MergeOrigins (break_origins);
 569                         return vector;
 570                 }
 571         }
 572
 573         public class FlowBranchingContinuable : FlowBranchingBlock
 574         {
 575                 UsageVector continue_origins;
 576
 577                 public FlowBranchingContinuable (FlowBranching parent, BranchingType type, SiblingType stype, Block block, Location loc)
 578                         : base (parent, type, stype, block, loc)
 579                 { }
 580
 581                 public override bool AddContinueOrigin (UsageVector vector, Location loc)
 582                 {
 583                         vector = vector.Clone ();
 584                         vector.Next = continue_origins;
 585                         continue_origins = vector;
 586                         return false;
 587                 }
 588
 589                 protected override UsageVector Merge ()
 590                 {
 591                         UsageVector vector = base.Merge ();
 592                         vector.MergeOrigins (continue_origins);
 593                         return vector;
 594                 }
 595         }
 596
 597         public class FlowBranchingLabeled : FlowBranchingBlock
 598         {
 599                 LabeledStatement stmt;
 600                 UsageVector actual;
 601
 602                 public FlowBranchingLabeled (FlowBranching parent, LabeledStatement stmt)
 603                         : base (parent, BranchingType.Labeled, SiblingType.Conditional, null, stmt.loc)
 604                 {
 605                         this.stmt = stmt;
 606                         CurrentUsageVector.MergeOrigins (stmt.JumpOrigins);
 607                         actual = CurrentUsageVector.Clone ();
 608
 609                         // stand-in for backward jumps
 610                         CurrentUsageVector.ResetBarrier ();
 611                 }
 612
 613                 public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 614                 {
 615                         if (goto_stmt.Target != stmt.Name)
 616                                 return Parent.AddGotoOrigin (vector, goto_stmt);
 617
 618                         // backward jump
 619                         goto_stmt.SetResolvedTarget (stmt);
 620                         actual.MergeOrigins (vector.Clone ());
 621
 622                         return false;
 623                 }
 624
 625                 protected override UsageVector Merge ()
 626                 {
 627                         UsageVector vector = base.Merge ();
 628
 629                         if (actual.IsUnreachable)
 630                                 Report.Warning (162, 2, stmt.loc, "Unreachable code detected");
 631
 632                         actual.MergeChild (vector, false);
 633                         return actual;
 634                 }
 635         }
 636
 637         public class FlowBranchingIterator : FlowBranchingBlock
 638         {
 639                 Iterator iterator;
 640                 public FlowBranchingIterator (FlowBranching parent, Iterator iterator)
 641                         : base (parent, BranchingType.Iterator, SiblingType.Block, iterator.Block, iterator.Location)
 642                 {
 643                         this.iterator = iterator;
 644                 }
 645
 646                 public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
 647                 {
 648                         pc = iterator.AddResumePoint (stmt);
 649                         return false;
 650                 }
 651         }
 652
 653         public class FlowBranchingToplevel : FlowBranchingBlock
 654         {
 655                 UsageVector return_origins;
 656
 657                 public FlowBranchingToplevel (FlowBranching parent, ParametersBlock stmt)
 658                         : base (parent, BranchingType.Toplevel, SiblingType.Conditional, stmt, stmt.loc)
 659                 {
 660                 }
 661
 662                 public override bool CheckRethrow (Location loc)
 663                 {
 664                         Report.Error (156, loc, "A throw statement with no arguments is not allowed outside of a catch clause");
 665                         return false;
 666                 }
 667
 668                 public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
 669                 {
 670                         throw new InternalErrorException ("A yield in a non-iterator block");
 671                 }
 672
 673                 public override bool AddBreakOrigin (UsageVector vector, Location loc)
 674                 {
 675                         Report.Error (139, loc, "No enclosing loop out of which to break or continue");
 676                         return false;
 677                 }
 678
 679                 public override bool AddContinueOrigin (UsageVector vector, Location loc)
 680                 {
 681                         Report.Error (139, loc, "No enclosing loop out of which to break or continue");
 682                         return false;
 683                 }
 684
 685                 public override bool AddReturnOrigin (UsageVector vector, ExitStatement stmt)
 686                 {
 687                         vector = vector.Clone ();
 688                         vector.Location = stmt.loc;
 689                         vector.Next = return_origins;
 690                         return_origins = vector;
 691                         return false;
 692                 }
 693
 694                 public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 695                 {
 696                         string name = goto_stmt.Target;
 697                         LabeledStatement s = Block.LookupLabel (name);
 698                         if (s != null)
 699                                 throw new InternalErrorException ("Shouldn't get here");
 700
 701                         if (Parent == null) {
 702                                 Error_UnknownLabel (goto_stmt.loc, name, Report);
 703                                 return false;
 704                         }
 705
 706                         int errors = Report.Errors;
 707                         Parent.AddGotoOrigin (vector, goto_stmt);
 708                         if (errors == Report.Errors)
 709                                 Report.Error (1632, goto_stmt.loc, "Control cannot leave the body of an anonymous method");
 710                         return false;
 711                 }
 712
 713                 protected override UsageVector Merge ()
 714                 {
 715                         for (UsageVector origin = return_origins; origin != null; origin = origin.Next)
 716                                 Block.ParametersBlock.CheckOutParameters (origin, origin.Location);
 717
 718                         UsageVector vector = base.Merge ();
 719                         Block.ParametersBlock.CheckOutParameters (vector, Block.loc);
 720                         // Note: we _do_not_ merge in the return origins
 721                         return vector;
 722                 }
 723
 724                 public bool End ()
 725                 {
 726                         return Merge ().IsUnreachable;
 727                 }
 728         }
 729
 730         public class FlowBranchingTryCatch : FlowBranchingBlock
 731         {
 732                 TryCatch stmt;
 733                 public FlowBranchingTryCatch (FlowBranching parent, TryCatch stmt)
 734                         : base (parent, BranchingType.Block, SiblingType.Try, null, stmt.loc)
 735                 {
 736                         this.stmt = stmt;
 737                 }
 738
 739                 public override bool CheckRethrow (Location loc)
 740                 {
 741                         return CurrentUsageVector.Next != null || Parent.CheckRethrow (loc);
 742                 }
 743
 744                 public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
 745                 {
 746                         int errors = Report.Errors;
 747                         Parent.AddResumePoint (stmt, loc, out pc);
 748                         if (errors == Report.Errors) {
 749                                 if (CurrentUsageVector.Next == null)
 750                                         Report.Error (1626, loc, "Cannot yield a value in the body of a try block with a catch clause");
 751                                 else
 752                                         Report.Error (1631, loc, "Cannot yield a value in the body of a catch clause");
 753                         }
 754                         return true;
 755                 }
 756
 757                 public override bool AddBreakOrigin (UsageVector vector, Location loc)
 758                 {
 759                         Parent.AddBreakOrigin (vector, loc);
 760                         stmt.SomeCodeFollows ();
 761                         return true;
 762                 }
 763
 764                 public override bool AddContinueOrigin (UsageVector vector, Location loc)
 765                 {
 766                         Parent.AddContinueOrigin (vector, loc);
 767                         stmt.SomeCodeFollows ();
 768                         return true;
 769                 }
 770
 771                 public override bool AddReturnOrigin (UsageVector vector, ExitStatement exit_stmt)
 772                 {
 773                         Parent.AddReturnOrigin (vector, exit_stmt);
 774                         stmt.SomeCodeFollows ();
 775                         return true;
 776                 }
 777
 778                 public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 779                 {
 780                         Parent.AddGotoOrigin (vector, goto_stmt);
 781                         return true;
 782                 }
 783         }
 784
 785         public class FlowBranchingException : FlowBranching
 786         {
 787                 ExceptionStatement stmt;
 788                 UsageVector current_vector;
 789                 UsageVector try_vector;
 790                 UsageVector finally_vector;
 791
 792                 abstract class SavedOrigin {
 793                         public readonly SavedOrigin Next;
 794                         public readonly UsageVector Vector;
 795
 796                         protected SavedOrigin (SavedOrigin next, UsageVector vector)
 797                         {
 798                                 Next = next;
 799                                 Vector = vector.Clone ();
 800                         }
 801
 802                         protected abstract void DoPropagateFinally (FlowBranching parent);
 803                         public void PropagateFinally (UsageVector finally_vector, FlowBranching parent)
 804                         {
 805                                 if (finally_vector != null)
 806                                         Vector.MergeChild (finally_vector, false);
 807                                 DoPropagateFinally (parent);
 808                         }
 809                 }
 810
 811                 class BreakOrigin : SavedOrigin {
 812                         Location Loc;
 813                         public BreakOrigin (SavedOrigin next, UsageVector vector, Location loc)
 814                                 : base (next, vector)
 815                         {
 816                                 Loc = loc;
 817                         }
 818
 819                         protected override void DoPropagateFinally (FlowBranching parent)
 820                         {
 821                                 parent.AddBreakOrigin (Vector, Loc);
 822                         }
 823                 }
 824
 825                 class ContinueOrigin : SavedOrigin {
 826                         Location Loc;
 827                         public ContinueOrigin (SavedOrigin next, UsageVector vector, Location loc)
 828                                 : base (next, vector)
 829                         {
 830                                 Loc = loc;
 831                         }
 832
 833                         protected override void DoPropagateFinally (FlowBranching parent)
 834                         {
 835                                 parent.AddContinueOrigin (Vector, Loc);
 836                         }
 837                 }
 838
 839                 class ReturnOrigin : SavedOrigin {
 840                         public ExitStatement Stmt;
 841
 842                         public ReturnOrigin (SavedOrigin next, UsageVector vector, ExitStatement stmt)
 843                                 : base (next, vector)
 844                         {
 845                                 Stmt = stmt;
 846                         }
 847
 848                         protected override void DoPropagateFinally (FlowBranching parent)
 849                         {
 850                                 parent.AddReturnOrigin (Vector, Stmt);
 851                         }
 852                 }
 853
 854                 class GotoOrigin : SavedOrigin {
 855                         public Goto Stmt;
 856
 857                         public GotoOrigin (SavedOrigin next, UsageVector vector, Goto stmt)
 858                                 : base (next, vector)
 859                         {
 860                                 Stmt = stmt;
 861                         }
 862
 863                         protected override void DoPropagateFinally (FlowBranching parent)
 864                         {
 865                                 parent.AddGotoOrigin (Vector, Stmt);
 866                         }
 867                 }
 868
 869                 SavedOrigin saved_origins;
 870
 871                 public FlowBranchingException (FlowBranching parent,
 872                                                ExceptionStatement stmt)
 873                         : base (parent, BranchingType.Exception, SiblingType.Try,
 874                                 null, stmt.loc)
 875                 {
 876                         this.stmt = stmt;
 877                 }
 878
 879                 protected override void AddSibling (UsageVector sibling)
 880                 {
 881                         switch (sibling.Type) {
 882                         case SiblingType.Try:
 883                                 try_vector = sibling;
 884                                 break;
 885                         case SiblingType.Finally:
 886                                 finally_vector = sibling;
 887                                 break;
 888                         default:
 889                                 throw new InvalidOperationException ();
 890                         }
 891                         current_vector = sibling;
 892                 }
 893
 894                 public override UsageVector CurrentUsageVector {
 895                         get { return current_vector; }
 896                 }
 897
 898                 public override bool CheckRethrow (Location loc)
 899                 {
 900                         if (!Parent.CheckRethrow (loc))
 901                                 return false;
 902                         if (finally_vector == null)
 903                                 return true;
 904                         Report.Error (724, loc, "A throw statement with no arguments is not allowed inside of a finally clause nested inside of the innermost catch clause");
 905                         return false;
 906                 }
 907
 908                 public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
 909                 {
 910                         int errors = Report.Errors;
 911                         Parent.AddResumePoint (this.stmt, loc, out pc);
 912                         if (errors == Report.Errors) {
 913                                 if (finally_vector == null)
 914                                         this.stmt.AddResumePoint (stmt, pc);
 915                                 else
 916                                         Report.Error (1625, loc, "Cannot yield in the body of a finally clause");
 917                         }
 918                         return true;
 919                 }
 920
 921                 public override bool AddBreakOrigin (UsageVector vector, Location loc)
 922                 {
 923                         if (finally_vector != null) {
 924                                 int errors = Report.Errors;
 925                                 Parent.AddBreakOrigin (vector, loc);
 926                                 if (errors == Report.Errors)
 927                                         Report.Error (157, loc, "Control cannot leave the body of a finally clause");
 928                         } else {
 929                                 saved_origins = new BreakOrigin (saved_origins, vector, loc);
 930                         }
 931
 932                         // either the loop test or a back jump will follow code
 933                         stmt.SomeCodeFollows ();
 934                         return true;
 935                 }
 936
 937                 public override bool AddContinueOrigin (UsageVector vector, Location loc)
 938                 {
 939                         if (finally_vector != null) {
 940                                 int errors = Report.Errors;
 941                                 Parent.AddContinueOrigin (vector, loc);
 942                                 if (errors == Report.Errors)
 943                                         Report.Error (157, loc, "Control cannot leave the body of a finally clause");
 944                         } else {
 945                                 saved_origins = new ContinueOrigin (saved_origins, vector, loc);
 946                         }
 947
 948                         // either the loop test or a back jump will follow code
 949                         stmt.SomeCodeFollows ();
 950                         return true;
 951                 }
 952
 953                 public override bool AddReturnOrigin (UsageVector vector, ExitStatement exit_stmt)
 954                 {
 955                         if (finally_vector != null) {
 956                                 int errors = Report.Errors;
 957                                 Parent.AddReturnOrigin (vector, exit_stmt);
 958                                 if (errors == Report.Errors)
 959                                         exit_stmt.Error_FinallyClause (Report);
 960                         } else {
 961                                 saved_origins = new ReturnOrigin (saved_origins, vector, exit_stmt);
 962                         }
 963
 964                         // sets ec.NeedReturnLabel()
 965                         stmt.SomeCodeFollows ();
 966                         return true;
 967                 }
 968
 969                 public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
 970                 {
 971                         LabeledStatement s = current_vector.Block == null ? null : current_vector.Block.LookupLabel (goto_stmt.Target);
 972                         if (s != null)
 973                                 throw new InternalErrorException ("Shouldn't get here");
 974
 975                         if (finally_vector != null) {
 976                                 int errors = Report.Errors;
 977                                 Parent.AddGotoOrigin (vector, goto_stmt);
 978                                 if (errors == Report.Errors)
 979                                         Report.Error (157, goto_stmt.loc, "Control cannot leave the body of a finally clause");
 980                         } else {
 981                                 saved_origins = new GotoOrigin (saved_origins, vector, goto_stmt);
 982                         }
 983                         return true;
 984                 }
 985
 986                 protected override UsageVector Merge ()
 987                 {
 988                         UsageVector vector = try_vector.Clone ();
 989
 990                         if (finally_vector != null)
 991                                 vector.MergeChild (finally_vector, false);
 992
 993                         for (SavedOrigin origin = saved_origins; origin != null; origin = origin.Next)
 994                                 origin.PropagateFinally (finally_vector, Parent);
 995
 996                         return vector;
 997                 }
 998         }
 999
1000         // <summary>
1001         //   This is used by the flow analysis code to keep track of the type of local variables
1002         //   and variables.
1003         //
1004         //   The flow code uses a BitVector to keep track of whether a variable has been assigned
1005         //   or not.  This is easy for fundamental types (int, char etc.) or reference types since
1006         //   you can only assign the whole variable as such.
1007         //
1008         //   For structs, we also need to keep track of all its fields.  To do this, we allocate one
1009         //   bit for the struct itself (it's used if you assign/access the whole struct) followed by
1010         //   one bit for each of its fields.
1011         //
1012         //   This class computes this `layout' for each type.
1013         // </summary>
1014         public class TypeInfo
1015         {
1016                 public readonly TypeSpec Type;
1017
1018                 // <summary>
1019                 //   Total number of bits a variable of this type consumes in the flow vector.
1020                 // </summary>
1021                 public readonly int TotalLength;
1022
1023                 // <summary>
1024                 //   Number of bits the simple fields of a variable of this type consume
1025                 //   in the flow vector.
1026                 // </summary>
1027                 public readonly int Length;
1028
1029                 // <summary>
1030                 //   This is only used by sub-structs.
1031                 // </summary>
1032                 public readonly int Offset;
1033
1034                 // <summary>
1035                 //   If this is a struct.
1036                 // </summary>
1037                 public readonly bool IsStruct;
1038
1039                 // <summary>
1040                 //   If this is a struct, all fields which are structs theirselves.
1041                 // </summary>
1042                 public TypeInfo[] SubStructInfo;
1043
1044                 readonly StructInfo struct_info;
1045                 private static Dictionary<TypeSpec, TypeInfo> type_hash;
1046
1047                 static TypeInfo ()
1048                 {
1049                         Reset ();
1050                 }
1051
1052                 public static void Reset ()
1053                 {
1054                         type_hash = new Dictionary<TypeSpec, TypeInfo> ();
1055                         StructInfo.field_type_hash = new Dictionary<TypeSpec, StructInfo> ();
1056                 }
1057
1058                 public static TypeInfo GetTypeInfo (TypeSpec type)
1059                 {
1060                         TypeInfo info;
1061                         if (type_hash.TryGetValue (type, out info))
1062                                 return info;
1063
1064                         info = new TypeInfo (type);
1065                         type_hash.Add (type, info);
1066                         return info;
1067                 }
1068
1069                 private TypeInfo (TypeSpec type)
1070                 {
1071                         this.Type = type;
1072
1073                         struct_info = StructInfo.GetStructInfo (type);
1074                         if (struct_info != null) {
1075                                 Length = struct_info.Length;
1076                                 TotalLength = struct_info.TotalLength;
1077                                 SubStructInfo = struct_info.StructFields;
1078                                 IsStruct = true;
1079                         } else {
1080                                 Length = 0;
1081                                 TotalLength = 1;
1082                                 IsStruct = false;
1083                         }
1084                 }
1085
1086                 TypeInfo (StructInfo struct_info, int offset)
1087                 {
1088                         this.struct_info = struct_info;
1089                         this.Offset = offset;
1090                         this.Length = struct_info.Length;
1091                         this.TotalLength = struct_info.TotalLength;
1092                         this.SubStructInfo = struct_info.StructFields;
1093                         this.Type = struct_info.Type;
1094                         this.IsStruct = true;
1095                 }
1096
1097                 public int GetFieldIndex (string name)
1098                 {
1099                         if (struct_info == null)
1100                                 return 0;
1101
1102                         return struct_info [name];
1103                 }
1104
1105                 public TypeInfo GetSubStruct (string name)
1106                 {
1107                         if (struct_info == null)
1108                                 return null;
1109
1110                         return struct_info.GetStructField (name);
1111                 }
1112
1113                 // <summary>
1114                 //   A struct's constructor must always assign all fields.
1115                 //   This method checks whether it actually does so.
1116                 // </summary>
1117                 public bool IsFullyInitialized (BlockContext ec, VariableInfo vi, Location loc)
1118                 {
1119                         if (struct_info == null)
1120                                 return true;
1121
1122                         bool ok = true;
1123                         FlowBranching branching = ec.CurrentBranching;
1124                         for (int i = 0; i < struct_info.Count; i++) {
1125                                 var field = struct_info.Fields [i];
1126
1127                                 if (!branching.IsFieldAssigned (vi, field.Name)) {
1128                                         if (field.MemberDefinition is Property.BackingField) {
1129                                                 ec.Report.Error (843, loc,
1130                                                         "An automatically implemented property `{0}' must be fully assigned before control leaves the constructor. Consider calling the default struct contructor from a constructor initializer",
1131                                                         field.GetSignatureForError ());
1132                                         } else {
1133                                                 ec.Report.Error (171, loc,
1134                                                         "Field `{0}' must be fully assigned before control leaves the constructor",
1135                                                         field.GetSignatureForError ());
1136                                         }
1137                                         ok = false;
1138                                 }
1139                         }
1140
1141                         return ok;
1142                 }
1143
1144                 public override string ToString ()
1145                 {
1146                         return String.Format ("TypeInfo ({0}:{1}:{2}:{3})",
1147                                               Type, Offset, Length, TotalLength);
1148                 }
1149
1150                 class StructInfo {
1151                         public readonly TypeSpec Type;
1152                         public readonly FieldSpec[] Fields;
1153                         public readonly TypeInfo[] StructFields;
1154                         public readonly int Count;
1155                         public readonly int CountPublic;
1156                         public readonly int CountNonPublic;
1157                         public readonly int Length;
1158                         public readonly int TotalLength;
1159                         public readonly bool HasStructFields;
1160
1161                         public static Dictionary<TypeSpec, StructInfo> field_type_hash;
1162                         private Dictionary<string, TypeInfo> struct_field_hash;
1163                         private Dictionary<string, int> field_hash;
1164
1165                         protected bool InTransit = false;
1166
1167                         // Private constructor.  To save memory usage, we only need to create one instance
1168                         // of this class per struct type.
1169                         private StructInfo (TypeSpec type)
1170                         {
1171                                 this.Type = type;
1172
1173                                 field_type_hash.Add (type, this);
1174
1175                                 TypeContainer tc = type.MemberDefinition as TypeContainer;
1176
1177                                 var public_fields = new List<FieldSpec> ();
1178                                 var non_public_fields = new List<FieldSpec> ();
1179
1180                                 if (tc != null) {
1181                                         var fields = tc.Fields;
1182
1183                                         if (fields != null) {
1184                                                 foreach (FieldBase field in fields) {
1185                                                         if ((field.ModFlags & Modifiers.STATIC) != 0)
1186                                                                 continue;
1187                                                         if ((field.ModFlags & Modifiers.PUBLIC) != 0)
1188                                                                 public_fields.Add (field.Spec);
1189                                                         else
1190                                                                 non_public_fields.Add (field.Spec);
1191                                                 }
1192                                         }
1193                                 }
1194
1195                                 CountPublic = public_fields.Count;
1196                                 CountNonPublic = non_public_fields.Count;
1197                                 Count = CountPublic + CountNonPublic;
1198
1199                                 Fields = new FieldSpec[Count];
1200                                 public_fields.CopyTo (Fields, 0);
1201                                 non_public_fields.CopyTo (Fields, CountPublic);
1202
1203                                 struct_field_hash = new Dictionary<string, TypeInfo> ();
1204                                 field_hash = new Dictionary<string, int> ();
1205
1206                                 Length = 0;
1207                                 StructFields = new TypeInfo [Count];
1208                                 StructInfo[] sinfo = new StructInfo [Count];
1209
1210                                 InTransit = true;
1211
1212                                 for (int i = 0; i < Count; i++) {
1213                                         var field = Fields [i];
1214
1215                                         sinfo [i] = GetStructInfo (field.MemberType);
1216                                         if (sinfo [i] == null)
1217                                                 field_hash.Add (field.Name, ++Length);
1218                                         else if (sinfo [i].InTransit) {
1219                                                 sinfo [i] = null;
1220                                                 return;
1221                                         }
1222                                 }
1223
1224                                 InTransit = false;
1225
1226                                 TotalLength = Length + 1;
1227                                 for (int i = 0; i < Count; i++) {
1228                                         var field = Fields [i];
1229
1230                                         if (sinfo [i] == null)
1231                                                 continue;
1232
1233                                         field_hash.Add (field.Name, TotalLength);
1234
1235                                         HasStructFields = true;
1236                                         StructFields [i] = new TypeInfo (sinfo [i], TotalLength);
1237                                         struct_field_hash.Add (field.Name, StructFields [i]);
1238                                         TotalLength += sinfo [i].TotalLength;
1239                                 }
1240                         }
1241
1242                         public int this [string name] {
1243                                 get {
1244                                         int val;
1245                                         if (!field_hash.TryGetValue (name, out val))
1246                                                 return 0;
1247
1248                                         return val;
1249                                 }
1250                         }
1251
1252                         public TypeInfo GetStructField (string name)
1253                         {
1254                                 TypeInfo ti;
1255                                 if (struct_field_hash.TryGetValue (name, out ti))
1256                                         return ti;
1257
1258                                 return null;
1259                         }
1260
1261                         public static StructInfo GetStructInfo (TypeSpec type)
1262                         {
1263                                 if (!type.IsStruct || TypeManager.IsBuiltinType (type))
1264                                         return null;
1265
1266                                 StructInfo info;
1267                                 if (field_type_hash.TryGetValue (type, out info))
1268                                         return info;
1269
1270                                 return new StructInfo (type);
1271                         }
1272                 }
1273         }
1274
1275         // <summary>
1276         //   This is used by the flow analysis code to store information about a single local variable
1277         //   or parameter.  Depending on the variable's type, we need to allocate one or more elements
1278         //   in the BitVector - if it's a fundamental or reference type, we just need to know whether
1279         //   it has been assigned or not, but for structs, we need this information for each of its fields.
1280         // </summary>
1281         public class VariableInfo {
1282                 public readonly string Name;
1283                 public readonly TypeInfo TypeInfo;
1284
1285                 // <summary>
1286                 //   The bit offset of this variable in the flow vector.
1287                 // </summary>
1288                 public readonly int Offset;
1289
1290                 // <summary>
1291                 //   The number of bits this variable needs in the flow vector.
1292                 //   The first bit always specifies whether the variable as such has been assigned while
1293                 //   the remaining bits contain this information for each of a struct's fields.
1294                 // </summary>
1295                 public readonly int Length;
1296
1297                 // <summary>
1298                 //   If this is a parameter of local variable.
1299                 // </summary>
1300                 public readonly bool IsParameter;
1301
1302                 public readonly LocalVariable LocalInfo;
1303
1304                 readonly VariableInfo Parent;
1305                 VariableInfo[] sub_info;
1306
1307                 bool is_ever_assigned;
1308                 public bool IsEverAssigned {
1309                         get { return is_ever_assigned; }
1310                 }
1311
1312                 protected VariableInfo (string name, TypeSpec type, int offset)
1313                 {
1314                         this.Name = name;
1315                         this.Offset = offset;
1316                         this.TypeInfo = TypeInfo.GetTypeInfo (type);
1317
1318                         Length = TypeInfo.TotalLength;
1319
1320                         Initialize ();
1321                 }
1322
1323                 protected VariableInfo (VariableInfo parent, TypeInfo type)
1324                 {
1325                         this.Name = parent.Name;
1326                         this.TypeInfo = type;
1327                         this.Offset = parent.Offset + type.Offset;
1328                         this.Parent = parent;
1329                         this.Length = type.TotalLength;
1330
1331                         this.IsParameter = parent.IsParameter;
1332                         this.LocalInfo = parent.LocalInfo;
1333
1334                         Initialize ();
1335                 }
1336
1337                 protected void Initialize ()
1338                 {
1339                         TypeInfo[] sub_fields = TypeInfo.SubStructInfo;
1340                         if (sub_fields != null) {
1341                                 sub_info = new VariableInfo [sub_fields.Length];
1342                                 for (int i = 0; i < sub_fields.Length; i++) {
1343                                         if (sub_fields [i] != null)
1344                                                 sub_info [i] = new VariableInfo (this, sub_fields [i]);
1345                                 }
1346                         } else
1347                                 sub_info = new VariableInfo [0];
1348                 }
1349
1350                 public VariableInfo (LocalVariable local_info, int offset)
1351                         : this (local_info.Name, local_info.Type, offset)
1352                 {
1353                         this.LocalInfo = local_info;
1354                         this.IsParameter = false;
1355                 }
1356
1357                 public VariableInfo (ParametersCompiled ip, int i, int offset)
1358                         : this (ip.FixedParameters [i].Name, ip.Types [i], offset)
1359                 {
1360                         this.IsParameter = true;
1361                 }
1362
1363                 public bool IsAssigned (ResolveContext ec)
1364                 {
1365                         return !ec.DoFlowAnalysis ||
1366                                 (ec.OmitStructFlowAnalysis && TypeInfo.Type.IsStruct) ||
1367                                 ec.CurrentBranching.IsAssigned (this);
1368                 }
1369
1370                 public bool IsAssigned (ResolveContext ec, Location loc)
1371                 {
1372                         if (IsAssigned (ec))
1373                                 return true;
1374
1375                         ec.Report.Error (165, loc,
1376                                       "Use of unassigned local variable `" + Name + "'");
1377                         ec.CurrentBranching.SetAssigned (this);
1378                         return false;
1379                 }
1380
1381                 public bool IsAssigned (MyBitVector vector)
1382                 {
1383                         if (vector == null)
1384                                 return true;
1385
1386                         if (vector [Offset])
1387                                 return true;
1388
1389                         // FIXME: Fix SetFieldAssigned to set the whole range like SetAssigned below. Then, get rid of this stanza
1390                         for (VariableInfo parent = Parent; parent != null; parent = parent.Parent) {
1391                                 if (vector [parent.Offset]) {
1392                                         // 'parent' is assigned, but someone forgot to note that all its components are assigned too
1393                                         parent.SetAssigned (vector);
1394                                         return true;
1395                                 }
1396                         }
1397
1398                         // Return unless this is a struct.
1399                         if (!TypeInfo.IsStruct)
1400                                 return false;
1401
1402                         // Ok, so each field must be assigned.
1403                         for (int i = 0; i < TypeInfo.Length; i++) {
1404                                 if (!vector [Offset + i + 1])
1405                                         return false;
1406                         }
1407
1408                         // Ok, now check all fields which are structs.
1409                         for (int i = 0; i < sub_info.Length; i++) {
1410                                 VariableInfo sinfo = sub_info [i];
1411                                 if (sinfo == null)
1412                                         continue;
1413
1414                                 if (!sinfo.IsAssigned (vector))
1415                                         return false;
1416                         }
1417
1418                         vector [Offset] = true;
1419                         is_ever_assigned = true;
1420                         return true;
1421                 }
1422
1423                 public void SetAssigned (ResolveContext ec)
1424                 {
1425                         if (ec.DoFlowAnalysis)
1426                                 ec.CurrentBranching.SetAssigned (this);
1427                 }
1428
1429                 public void SetAssigned (MyBitVector vector)
1430                 {
1431                         if (Length == 1)
1432                                 vector [Offset] = true;
1433                         else
1434                                 vector.SetRange (Offset, Length);
1435                         is_ever_assigned = true;
1436                 }
1437
1438                 public bool IsFieldAssigned (ResolveContext ec, string name, Location loc)
1439                 {
1440                         if (!ec.DoFlowAnalysis ||
1441                                 ec.OmitStructFlowAnalysis && TypeInfo.IsStruct ||
1442                                 ec.CurrentBranching.IsFieldAssigned (this, name))
1443                                 return true;
1444
1445                         ec.Report.Error (170, loc,
1446                                       "Use of possibly unassigned field `" + name + "'");
1447                         ec.CurrentBranching.SetFieldAssigned (this, name);
1448                         return false;
1449                 }
1450
1451                 public bool IsFieldAssigned (MyBitVector vector, string field_name)
1452                 {
1453                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1454
1455                         if (field_idx == 0)
1456                                 return true;
1457
1458                         return vector [Offset + field_idx];
1459                 }
1460
1461                 public void SetFieldAssigned (ResolveContext ec, string name)
1462                 {
1463                         if (ec.DoFlowAnalysis)
1464                                 ec.CurrentBranching.SetFieldAssigned (this, name);
1465                 }
1466
1467                 public void SetFieldAssigned (MyBitVector vector, string field_name)
1468                 {
1469                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1470
1471                         if (field_idx == 0)
1472                                 return;
1473
1474                         vector [Offset + field_idx] = true;
1475                         is_ever_assigned = true;
1476                 }
1477
1478                 public VariableInfo GetSubStruct (string name)
1479                 {
1480                         TypeInfo type = TypeInfo.GetSubStruct (name);
1481
1482                         if (type == null)
1483                                 return null;
1484
1485                         return new VariableInfo (this, type);
1486                 }
1487
1488                 public override string ToString ()
1489                 {
1490                         return String.Format ("VariableInfo ({0}:{1}:{2}:{3}:{4})",
1491                                               Name, TypeInfo, Offset, Length, IsParameter);
1492                 }
1493         }
1494
1495         // <summary>
1496         //   This is a special bit vector which can inherit from another bit vector doing a
1497         //   copy-on-write strategy.  The inherited vector may have a smaller size than the
1498         //   current one.
1499         // </summary>
1500         public class MyBitVector {
1501                 public readonly int Count;
1502                 public static readonly MyBitVector Empty = new MyBitVector ();
1503
1504                 // Invariant: vector != null => vector.Count == Count
1505                 // Invariant: vector == null || shared == null
1506                 //            i.e., at most one of 'vector' and 'shared' can be non-null.  They can both be null -- that means all-ones
1507                 // The object in 'shared' cannot be modified, while 'vector' can be freely modified
1508                 System.Collections.BitArray vector, shared;
1509
1510                 MyBitVector ()
1511                 {
1512                         shared = new System.Collections.BitArray (0, false);
1513                 }
1514
1515                 public MyBitVector (MyBitVector InheritsFrom, int Count)
1516                 {
1517                         if (InheritsFrom != null)
1518                                 shared = InheritsFrom.MakeShared (Count);
1519
1520                         this.Count = Count;
1521                 }
1522
1523                 System.Collections.BitArray MakeShared (int new_count)
1524                 {
1525                         // Post-condition: vector == null
1526
1527                         // ensure we don't leak out dirty bits from the BitVector we inherited from
1528                         if (new_count > Count &&
1529                             ((shared != null && shared.Count > Count) ||
1530                              (shared == null && vector == null)))
1531                                 initialize_vector ();
1532
1533                         if (vector != null) {
1534                                 shared = vector;
1535                                 vector = null;
1536                         }
1537
1538                         return shared;
1539                 }
1540
1541                 // <summary>
1542                 //   Get/set bit `index' in the bit vector.
1543                 // </summary>
1544                 public bool this [int index] {
1545                         get {
1546                                 if (index >= Count)
1547                                         // FIXME: Disabled due to missing anonymous method flow analysis
1548                                         // throw new ArgumentOutOfRangeException ();
1549                                         return true;
1550
1551                                 if (vector != null)
1552                                         return vector [index];
1553                                 if (shared == null)
1554                                         return true;
1555                                 if (index < shared.Count)
1556                                         return shared [index];
1557                                 return false;
1558                         }
1559
1560                         set {
1561                                 // Only copy the vector if we're actually modifying it.
1562                                 if (this [index] != value) {
1563                                         if (vector == null)
1564                                                 initialize_vector ();
1565                                         vector [index] = value;
1566                                 }
1567                         }
1568                 }
1569
1570                 // <summary>
1571                 //   Performs an `or' operation on the bit vector.  The `new_vector' may have a
1572                 //   different size than the current one.
1573                 // </summary>
1574                 private MyBitVector Or (MyBitVector new_vector)
1575                 {
1576                         if (Count == 0 || new_vector.Count == 0)
1577                                 return this;
1578
1579                         var o = new_vector.vector != null ? new_vector.vector : new_vector.shared;
1580
1581                         if (o == null) {
1582                                 int n = new_vector.Count;
1583                                 if (n < Count) {
1584                                         for (int i = 0; i < n; ++i)
1585                                                 this [i] = true;
1586                                 } else {
1587                                         SetAll (true);
1588                                 }
1589                                 return this;
1590                         }
1591
1592                         if (Count == o.Count) {
1593                                 if (vector == null) {
1594                                         if (shared == null)
1595                                                 return this;
1596                                         initialize_vector ();
1597                                 }
1598                                 vector.Or (o);
1599                                 return this;
1600                         }
1601
1602                         int min = o.Count;
1603                         if (Count < min)
1604                                 min = Count;
1605
1606                         for (int i = 0; i < min; i++) {
1607                                 if (o [i])
1608                                         this [i] = true;
1609                         }
1610
1611                         return this;
1612                 }
1613
1614                 // <summary>
1615                 //   Performs an `and' operation on the bit vector.  The `new_vector' may have
1616                 //   a different size than the current one.
1617                 // </summary>
1618                 private MyBitVector And (MyBitVector new_vector)
1619                 {
1620                         if (Count == 0)
1621                                 return this;
1622
1623                         var o = new_vector.vector != null ? new_vector.vector : new_vector.shared;
1624
1625                         if (o == null) {
1626                                 for (int i = new_vector.Count; i < Count; ++i)
1627                                         this [i] = false;
1628                                 return this;
1629                         }
1630
1631                         if (o.Count == 0) {
1632                                 SetAll (false);
1633                                 return this;
1634                         }
1635
1636                         if (Count == o.Count) {
1637                                 if (vector == null) {
1638                                         if (shared == null) {
1639                                                 shared = new_vector.MakeShared (Count);
1640                                                 return this;
1641                                         }
1642                                         initialize_vector ();
1643                                 }
1644                                 vector.And (o);
1645                                 return this;
1646                         }
1647
1648                         int min = o.Count;
1649                         if (Count < min)
1650                                 min = Count;
1651
1652                         for (int i = 0; i < min; i++) {
1653                                 if (! o [i])
1654                                         this [i] = false;
1655                         }
1656
1657                         for (int i = min; i < Count; i++)
1658                                 this [i] = false;
1659
1660                         return this;
1661                 }
1662
1663                 public static MyBitVector operator & (MyBitVector a, MyBitVector b)
1664                 {
1665                         if (a == b)
1666                                 return a;
1667                         if (a == null)
1668                                 return b.Clone ();
1669                         if (b == null)
1670                                 return a.Clone ();
1671                         if (a.Count > b.Count)
1672                                 return a.Clone ().And (b);
1673                         else
1674                                 return b.Clone ().And (a);
1675                 }
1676
1677                 public static MyBitVector operator | (MyBitVector a, MyBitVector b)
1678                 {
1679                         if (a == b)
1680                                 return a;
1681                         if (a == null)
1682                                 return new MyBitVector (null, b.Count);
1683                         if (b == null)
1684                                 return new MyBitVector (null, a.Count);
1685                         if (a.Count > b.Count)
1686                                 return a.Clone ().Or (b);
1687                         else
1688                                 return b.Clone ().Or (a);
1689                 }
1690
1691                 public MyBitVector Clone ()
1692                 {
1693                         return Count == 0 ? Empty : new MyBitVector (this, Count);
1694                 }
1695
1696                 public void SetRange (int offset, int length)
1697                 {
1698                         if (offset > Count || offset + length > Count)
1699                                 throw new ArgumentOutOfRangeException ("flow-analysis");
1700
1701                         if (shared == null && vector == null)
1702                                 return;
1703
1704                         int i = 0;
1705                         if (shared != null) {
1706                                 if (offset + length <= shared.Count) {
1707                                         for (; i < length; ++i)
1708                                                 if (!shared [i+offset])
1709                                                     break;
1710                                         if (i == length)
1711                                                 return;
1712                                 }
1713                                 initialize_vector ();
1714                         }
1715                         for (; i < length; ++i)
1716                                 vector [i+offset] = true;
1717
1718                 }
1719
1720                 public void SetAll (bool value)
1721                 {
1722                         // Don't clobber Empty
1723                         if (Count == 0)
1724                                 return;
1725                         shared = value ? null : Empty.MakeShared (Count);
1726                         vector = null;
1727                 }
1728
1729                 void initialize_vector ()
1730                 {
1731                         // Post-condition: vector != null
1732                         if (shared == null) {
1733                                 vector = new System.Collections.BitArray (Count, true);
1734                                 return;
1735                         }
1736
1737                         vector = new System.Collections.BitArray (shared);
1738                         if (Count != vector.Count)
1739                                 vector.Length = Count;
1740                         shared = null;
1741                 }
1742
1743                 StringBuilder Dump (StringBuilder sb)
1744                 {
1745                         var dump = vector == null ? shared : vector;
1746                         if (dump == null)
1747                                 return sb.Append ("/");
1748                         if (dump == shared)
1749                                 sb.Append ("=");
1750                         for (int i = 0; i < dump.Count; i++)
1751                                 sb.Append (dump [i] ? "1" : "0");
1752                         return sb;
1753                 }
1754
1755                 public override string ToString ()
1756                 {
1757                         return Dump (new StringBuilder ("{")).Append ("}").ToString ();
1758                 }
1759         }
1760 }