mcs/mcs/flowanalysis.cs

   1 //
   2 // flowanalyis.cs: The control flow analysis code
   3 //
   4 // Author:
   5 //   Martin Baulig (martin@ximian.com)
   6 //
   7 // (C) 2001, 2002, 2003 Ximian, Inc.
   8 //
   9
  10 using System;
  11 using System.Text;
  12 using System.Collections;
  13 using System.Reflection;
  14 using System.Reflection.Emit;
  15 using System.Diagnostics;
  16
  17 namespace Mono.CSharp
  18 {
  19         // <summary>
  20         //   A new instance of this class is created every time a new block is resolved
  21         //   and if there's branching in the block's control flow.
  22         // </summary>
  23         public abstract class FlowBranching
  24         {
  25                 // <summary>
  26                 //   The type of a FlowBranching.
  27                 // </summary>
  28                 public enum BranchingType : byte {
  29                         // Normal (conditional or toplevel) block.
  30                         Block,
  31
  32                         // Conditional.
  33                         Conditional,
  34
  35                         // A loop block.
  36                         Loop,
  37
  38                         // Try/Catch block.
  39                         Exception,
  40
  41                         // Switch block.
  42                         Switch,
  43
  44                         // Switch section.
  45                         SwitchSection
  46                 }
  47
  48                 // <summary>
  49                 //   The type of one sibling of a branching.
  50                 // </summary>
  51                 public enum SiblingType : byte {
  52                         Block,
  53                         Conditional,
  54                         SwitchSection,
  55                         Try,
  56                         Catch,
  57                         Finally
  58                 }
  59
  60                 // <summary>
  61                 //   This is used in the control flow analysis code to specify whether the
  62                 //   current code block may return to its enclosing block before reaching
  63                 //   its end.
  64                 // </summary>
  65                 public enum FlowReturns : byte {
  66                         Undefined = 0,
  67
  68                         // It can never return.
  69                         Never,
  70
  71                         // This means that the block contains a conditional return statement
  72                         // somewhere.
  73                         Sometimes,
  74
  75                         // The code always returns, ie. there's an unconditional return / break
  76                         // statement in it.
  77                         Always
  78                 }
  79
  80                 public sealed class Reachability
  81                 {
  82                         FlowReturns returns, breaks, throws, barrier;
  83
  84                         public FlowReturns Returns {
  85                                 get { return returns; }
  86                         }
  87                         public FlowReturns Breaks {
  88                                 get { return breaks; }
  89                         }
  90                         public FlowReturns Throws {
  91                                 get { return throws; }
  92                         }
  93                         public FlowReturns Barrier {
  94                                 get { return barrier; }
  95                         }
  96                         public Reachability (FlowReturns returns, FlowReturns breaks,
  97                                              FlowReturns throws, FlowReturns barrier)
  98                         {
  99                                 this.returns = returns;
 100                                 this.breaks = breaks;
 101                                 this.throws = throws;
 102                                 this.barrier = barrier;
 103                         }
 104
 105                         public Reachability Clone ()
 106                         {
 107                                 return new Reachability (returns, breaks, throws, barrier);
 108                         }
 109
 110                         // <summary>
 111                         //   Performs an `And' operation on the FlowReturns status
 112                         //   (for instance, a block only returns Always if all its siblings
 113                         //   always return).
 114                         // </summary>
 115                         public static FlowReturns AndFlowReturns (FlowReturns a, FlowReturns b)
 116                         {
 117                                 if (a == FlowReturns.Undefined)
 118                                         return b;
 119
 120                                 switch (a) {
 121                                 case FlowReturns.Never:
 122                                         if (b == FlowReturns.Never)
 123                                                 return FlowReturns.Never;
 124                                         else
 125                                                 return FlowReturns.Sometimes;
 126
 127                                 case FlowReturns.Sometimes:
 128                                         return FlowReturns.Sometimes;
 129
 130                                 case FlowReturns.Always:
 131                                         if (b == FlowReturns.Always)
 132                                                 return FlowReturns.Always;
 133                                         else
 134                                                 return FlowReturns.Sometimes;
 135
 136                                 default:
 137                                         throw new ArgumentException ();
 138                                 }
 139                         }
 140
 141                         public static FlowReturns OrFlowReturns (FlowReturns a, FlowReturns b)
 142                         {
 143                                 if (a == FlowReturns.Undefined)
 144                                         return b;
 145
 146                                 switch (a) {
 147                                 case FlowReturns.Never:
 148                                         return b;
 149
 150                                 case FlowReturns.Sometimes:
 151                                         if (b == FlowReturns.Always)
 152                                                 return FlowReturns.Always;
 153                                         else
 154                                                 return FlowReturns.Sometimes;
 155
 156                                 case FlowReturns.Always:
 157                                         return FlowReturns.Always;
 158
 159                                 default:
 160                                         throw new ArgumentException ();
 161                                 }
 162                         }
 163
 164                         public static void And (ref Reachability a, Reachability b, bool do_break)
 165                         {
 166                                 if (a == null) {
 167                                         a = b.Clone ();
 168                                         return;
 169                                 }
 170
 171                                 //
 172                                 // `break' does not "break" in a Switch or a LoopBlock
 173                                 //
 174                                 bool a_breaks = do_break && a.AlwaysBreaks;
 175                                 bool b_breaks = do_break && b.AlwaysBreaks;
 176
 177                                 bool a_has_barrier, b_has_barrier;
 178                                 if (do_break) {
 179                                         //
 180                                         // This is the normal case: the code following a barrier
 181                                         // cannot be reached.
 182                                         //
 183                                         a_has_barrier = a.AlwaysHasBarrier;
 184                                         b_has_barrier = b.AlwaysHasBarrier;
 185                                 } else {
 186                                         //
 187                                         // Special case for Switch and LoopBlocks: we can reach the
 188                                         // code after the barrier via the `break'.
 189                                         //
 190                                         a_has_barrier = !a.AlwaysBreaks && a.AlwaysHasBarrier;
 191                                         b_has_barrier = !b.AlwaysBreaks && b.AlwaysHasBarrier;
 192                                 }
 193
 194                                 bool a_unreachable = a_breaks || a.AlwaysThrows || a_has_barrier;
 195                                 bool b_unreachable = b_breaks || b.AlwaysThrows || b_has_barrier;
 196
 197                                 //
 198                                 // Do all code paths always return ?
 199                                 //
 200                                 if (a.AlwaysReturns) {
 201                                         if (b.AlwaysReturns || b_unreachable)
 202                                                 a.returns = FlowReturns.Always;
 203                                         else
 204                                                 a.returns = FlowReturns.Sometimes;
 205                                 } else if (b.AlwaysReturns) {
 206                                         if (a.AlwaysReturns || a_unreachable)
 207                                                 a.returns = FlowReturns.Always;
 208                                         else
 209                                                 a.returns = FlowReturns.Sometimes;
 210                                 } else if (!a.MayReturn) {
 211                                         if (b.MayReturn)
 212                                                 a.returns = FlowReturns.Sometimes;
 213                                         else
 214                                                 a.returns = FlowReturns.Never;
 215                                 } else if (!b.MayReturn) {
 216                                         if (a.MayReturn)
 217                                                 a.returns = FlowReturns.Sometimes;
 218                                         else
 219                                                 a.returns = FlowReturns.Never;
 220                                 }
 221
 222                                 a.breaks = AndFlowReturns (a.breaks, b.breaks);
 223                                 a.throws = AndFlowReturns (a.throws, b.throws);
 224                                 a.barrier = AndFlowReturns (a.barrier, b.barrier);
 225
 226                                 if (a_unreachable && b_unreachable)
 227                                         a.barrier = FlowReturns.Always;
 228                                 else if (a_unreachable || b_unreachable)
 229                                         a.barrier = FlowReturns.Sometimes;
 230                                 else
 231                                         a.barrier = FlowReturns.Never;
 232                         }
 233
 234                         public void Or (Reachability b)
 235                         {
 236                                 returns = OrFlowReturns (returns, b.returns);
 237                                 breaks = OrFlowReturns (breaks, b.breaks);
 238                                 throws = OrFlowReturns (throws, b.throws);
 239                                 barrier = OrFlowReturns (barrier, b.barrier);
 240                         }
 241
 242                         public static Reachability Never ()
 243                         {
 244                                 return new Reachability (
 245                                         FlowReturns.Never, FlowReturns.Never,
 246                                         FlowReturns.Never, FlowReturns.Never);
 247                         }
 248
 249                         public FlowReturns Reachable {
 250                                 get {
 251                                         if ((returns == FlowReturns.Always) ||
 252                                             (breaks == FlowReturns.Always) ||
 253                                             (throws == FlowReturns.Always) ||
 254                                             (barrier == FlowReturns.Always))
 255                                                 return FlowReturns.Never;
 256                                         else if ((returns == FlowReturns.Never) &&
 257                                                  (breaks == FlowReturns.Never) &&
 258                                                  (throws == FlowReturns.Never) &&
 259                                                  (barrier == FlowReturns.Never))
 260                                                 return FlowReturns.Always;
 261                                         else
 262                                                 return FlowReturns.Sometimes;
 263                                 }
 264                         }
 265
 266                         public bool AlwaysBreaks {
 267                                 get { return breaks == FlowReturns.Always; }
 268                         }
 269
 270                         public bool MayBreak {
 271                                 get { return breaks != FlowReturns.Never; }
 272                         }
 273
 274                         public bool AlwaysReturns {
 275                                 get { return returns == FlowReturns.Always; }
 276                         }
 277
 278                         public bool MayReturn {
 279                                 get { return returns != FlowReturns.Never; }
 280                         }
 281
 282                         public bool AlwaysThrows {
 283                                 get { return throws == FlowReturns.Always; }
 284                         }
 285
 286                         public bool MayThrow {
 287                                 get { return throws != FlowReturns.Never; }
 288                         }
 289
 290                         public bool AlwaysHasBarrier {
 291                                 get { return barrier == FlowReturns.Always; }
 292                         }
 293
 294                         public bool MayHaveBarrier {
 295                                 get { return barrier != FlowReturns.Never; }
 296                         }
 297
 298                         public bool IsUnreachable {
 299                                 get { return Reachable == FlowReturns.Never; }
 300                         }
 301
 302                         public void SetReturns ()
 303                         {
 304                                 returns = FlowReturns.Always;
 305                         }
 306
 307                         public void SetReturnsSometimes ()
 308                         {
 309                                 returns = FlowReturns.Sometimes;
 310                         }
 311
 312                         public void SetBreaks ()
 313                         {
 314                                 breaks = FlowReturns.Always;
 315                         }
 316
 317                         public void ResetBreaks ()
 318                         {
 319                                 breaks = FlowReturns.Never;
 320                         }
 321
 322                         public void SetThrows ()
 323                         {
 324                                 throws = FlowReturns.Always;
 325                         }
 326
 327                         public void SetThrowsSometimes ()
 328                         {
 329                                 throws = FlowReturns.Sometimes;
 330                         }
 331
 332                         public void SetBarrier ()
 333                         {
 334                                 barrier = FlowReturns.Always;
 335                         }
 336
 337                         public void ResetBarrier ()
 338                         {
 339                                 barrier = FlowReturns.Never;
 340                         }
 341
 342                         static string ShortName (FlowReturns returns)
 343                         {
 344                                 switch (returns) {
 345                                 case FlowReturns.Never:
 346                                         return "N";
 347                                 case FlowReturns.Sometimes:
 348                                         return "S";
 349                                 default:
 350                                         return "A";
 351                                 }
 352                         }
 353
 354                         public override string ToString ()
 355                         {
 356                                 return String.Format ("[{0}:{1}:{2}:{3}:{4}]",
 357                                                       ShortName (returns), ShortName (breaks),
 358                                                       ShortName (throws), ShortName (barrier),
 359                                                       ShortName (Reachable));
 360                         }
 361                 }
 362
 363                 public static FlowBranching CreateBranching (FlowBranching parent, BranchingType type, Block block, Location loc)
 364                 {
 365                         switch (type) {
 366                         case BranchingType.Exception:
 367                                 throw new InvalidOperationException ();
 368
 369                         case BranchingType.Switch:
 370                                 return new FlowBranchingBlock (parent, type, SiblingType.SwitchSection, block, loc);
 371
 372                         case BranchingType.SwitchSection:
 373                                 return new FlowBranchingBlock (parent, type, SiblingType.Block, block, loc);
 374
 375                         case BranchingType.Block:
 376                                 return new FlowBranchingBlock (parent, type, SiblingType.Block, block, loc);
 377
 378                         case BranchingType.Loop:
 379                                 return new FlowBranchingLoop (parent, block, loc);
 380
 381                         default:
 382                                 return new FlowBranchingBlock (parent, type, SiblingType.Conditional, block, loc);
 383                         }
 384                 }
 385
 386                 // <summary>
 387                 //   The type of this flow branching.
 388                 // </summary>
 389                 public readonly BranchingType Type;
 390
 391                 // <summary>
 392                 //   The block this branching is contained in.  This may be null if it's not
 393                 //   a top-level block and it doesn't declare any local variables.
 394                 // </summary>
 395                 public readonly Block Block;
 396
 397                 // <summary>
 398                 //   The parent of this branching or null if this is the top-block.
 399                 // </summary>
 400                 public readonly FlowBranching Parent;
 401
 402                 // <summary>
 403                 //   Start-Location of this flow branching.
 404                 // </summary>
 405                 public readonly Location Location;
 406
 407                 // <summary>
 408                 //   If this is an infinite loop.
 409                 // </summary>
 410                 public bool Infinite;
 411
 412                 //
 413                 // Private
 414                 //
 415                 VariableMap param_map, local_map;
 416
 417                 static int next_id = 0;
 418                 int id;
 419
 420                 // <summary>
 421                 //   The vector contains a BitArray with information about which local variables
 422                 //   and parameters are already initialized at the current code position.
 423                 // </summary>
 424                 public class UsageVector {
 425                         // <summary>
 426                         //   The type of this branching.
 427                         // </summary>
 428                         public readonly SiblingType Type;
 429
 430                         // <summary>
 431                         //   Start location of this branching.
 432                         // </summary>
 433                         public readonly Location Location;
 434
 435                         // <summary>
 436                         //   This is only valid for SwitchSection, Try, Catch and Finally.
 437                         // </summary>
 438                         public readonly Block Block;
 439
 440                         // <summary>
 441                         //   If this is true, then the usage vector has been modified and must be
 442                         //   merged when we're done with this branching.
 443                         // </summary>
 444                         public bool IsDirty;
 445
 446                         // <summary>
 447                         //   The number of parameters in this block.
 448                         // </summary>
 449                         public readonly int CountParameters;
 450
 451                         // <summary>
 452                         //   The number of locals in this block.
 453                         // </summary>
 454                         public readonly int CountLocals;
 455
 456                         // <summary>
 457                         //   If not null, then we inherit our state from this vector and do a
 458                         //   copy-on-write.  If null, then we're the first sibling in a top-level
 459                         //   block and inherit from the empty vector.
 460                         // </summary>
 461                         public readonly UsageVector InheritsFrom;
 462
 463                         // <summary>
 464                         //   This is used to construct a list of UsageVector's.
 465                         // </summary>
 466                         public UsageVector Next;
 467
 468                         //
 469                         // Private.
 470                         //
 471                         MyBitVector locals, parameters;
 472                         Reachability reachability;
 473
 474                         static int next_id = 0;
 475                         int id;
 476
 477                         //
 478                         // Normally, you should not use any of these constructors.
 479                         //
 480                         public UsageVector (SiblingType type, UsageVector parent,
 481                                             Block block, Location loc,
 482                                             int num_params, int num_locals)
 483                         {
 484                                 this.Type = type;
 485                                 this.Block = block;
 486                                 this.Location = loc;
 487                                 this.InheritsFrom = parent;
 488                                 this.CountParameters = num_params;
 489                                 this.CountLocals = num_locals;
 490
 491                                 if (parent != null) {
 492                                         if (num_locals > 0)
 493                                                 locals = new MyBitVector (parent.locals, CountLocals);
 494
 495                                         if (num_params > 0)
 496                                                 parameters = new MyBitVector (parent.parameters, num_params);
 497
 498                                         reachability = parent.Reachability.Clone ();
 499                                 } else {
 500                                         if (num_locals > 0)
 501                                                 locals = new MyBitVector (null, CountLocals);
 502
 503                                         if (num_params > 0)
 504                                                 parameters = new MyBitVector (null, num_params);
 505
 506                                         reachability = Reachability.Never ();
 507                                 }
 508
 509                                 id = ++next_id;
 510                         }
 511
 512                         public UsageVector (SiblingType type, UsageVector parent,
 513                                             Block block, Location loc)
 514                                 : this (type, parent, block, loc,
 515                                         parent.CountParameters, parent.CountLocals)
 516                         { }
 517
 518                         public UsageVector (MyBitVector parameters, MyBitVector locals,
 519                                             Reachability reachability, Block block,
 520                                             Location loc)
 521                         {
 522                                 this.Type = SiblingType.Block;
 523                                 this.Location = loc;
 524                                 this.Block = block;
 525
 526                                 this.reachability = reachability;
 527                                 this.parameters = parameters;
 528                                 this.locals = locals;
 529
 530                                 id = ++next_id;
 531                         }
 532
 533                         // <summary>
 534                         //   This does a deep copy of the usage vector.
 535                         // </summary>
 536                         public UsageVector Clone ()
 537                         {
 538                                 UsageVector retval = new UsageVector (
 539                                         Type, null, Block, Location,
 540                                         CountParameters, CountLocals);
 541
 542                                 if (retval.locals != null)
 543                                         retval.locals = locals.Clone ();
 544
 545                                 if (parameters != null)
 546                                         retval.parameters = parameters.Clone ();
 547
 548                                 retval.reachability = reachability.Clone ();
 549
 550                                 return retval;
 551                         }
 552
 553                         public bool IsAssigned (VariableInfo var)
 554                         {
 555                                 if (!var.IsParameter && Reachability.IsUnreachable)
 556                                         return true;
 557
 558                                 return var.IsAssigned (var.IsParameter ? parameters : locals);
 559                         }
 560
 561                         public void SetAssigned (VariableInfo var)
 562                         {
 563                                 if (!var.IsParameter && Reachability.IsUnreachable)
 564                                         return;
 565
 566                                 IsDirty = true;
 567                                 var.SetAssigned (var.IsParameter ? parameters : locals);
 568                         }
 569
 570                         public bool IsFieldAssigned (VariableInfo var, string name)
 571                         {
 572                                 if (!var.IsParameter && Reachability.IsUnreachable)
 573                                         return true;
 574
 575                                 return var.IsFieldAssigned (var.IsParameter ? parameters : locals, name);
 576                         }
 577
 578                         public void SetFieldAssigned (VariableInfo var, string name)
 579                         {
 580                                 if (!var.IsParameter && Reachability.IsUnreachable)
 581                                         return;
 582
 583                                 IsDirty = true;
 584                                 var.SetFieldAssigned (var.IsParameter ? parameters : locals, name);
 585                         }
 586
 587                         public Reachability Reachability {
 588                                 get {
 589                                         return reachability;
 590                                 }
 591                         }
 592
 593                         public void Return ()
 594                         {
 595                                 if (!reachability.IsUnreachable) {
 596                                         IsDirty = true;
 597                                         reachability.SetReturns ();
 598                                 }
 599                         }
 600
 601                         public void Break ()
 602                         {
 603                                 if (!reachability.IsUnreachable) {
 604                                         IsDirty = true;
 605                                         reachability.SetBreaks ();
 606                                 }
 607                         }
 608
 609                         public void Throw ()
 610                         {
 611                                 if (!reachability.IsUnreachable) {
 612                                         IsDirty = true;
 613                                         reachability.SetThrows ();
 614                                 }
 615                         }
 616
 617                         public void Goto ()
 618                         {
 619                                 if (!reachability.IsUnreachable) {
 620                                         IsDirty = true;
 621                                         reachability.SetBarrier ();
 622                                 }
 623                         }
 624
 625                         // <summary>
 626                         //   Merges a child branching.
 627                         // </summary>
 628                         public UsageVector MergeChild (FlowBranching branching)
 629                         {
 630                                 UsageVector result = branching.Merge ();
 631
 632                                 Report.Debug (2, "  MERGING CHILD", this, branching, IsDirty,
 633                                               result.ParameterVector, result.LocalVector,
 634                                               result.Reachability, reachability, Type);
 635
 636                                 Reachability new_r = result.Reachability;
 637
 638                                 if (branching.Type == BranchingType.Loop) {
 639                                         bool may_leave_loop = new_r.MayBreak;
 640                                         new_r.ResetBreaks ();
 641
 642                                         if (branching.Infinite && !may_leave_loop) {
 643                                                 if (new_r.Returns == FlowReturns.Sometimes) {
 644                                                         // If we're an infinite loop and do not break,
 645                                                         // the code after the loop can never be reached.
 646                                                         // However, if we may return from the loop,
 647                                                         // then we do always return (or stay in the
 648                                                         // loop forever).
 649                                                         new_r.SetReturns ();
 650                                                 }
 651
 652                                                 new_r.SetBarrier ();
 653                                         } else {
 654                                                 if (new_r.Returns == FlowReturns.Always) {
 655                                                         // We're either finite or we may leave the loop.
 656                                                         new_r.SetReturnsSometimes ();
 657                                                 }
 658                                                 if (new_r.Throws == FlowReturns.Always) {
 659                                                         // We're either finite or we may leave the loop.
 660                                                         new_r.SetThrowsSometimes ();
 661                                                 }
 662
 663                                                 if (!new_r.MayReturn && !new_r.MayThrow)
 664                                                         new_r.ResetBarrier ();
 665                                         }
 666                                 } else if (branching.Type == BranchingType.Switch) {
 667                                         if (new_r.MayBreak || new_r.MayReturn)
 668                                                 new_r.ResetBarrier ();
 669
 670                                         new_r.ResetBreaks ();
 671                                 }
 672
 673                                 //
 674                                 // We've now either reached the point after the branching or we will
 675                                 // never get there since we always return or always throw an exception.
 676                                 //
 677                                 // If we can reach the point after the branching, mark all locals and
 678                                 // parameters as initialized which have been initialized in all branches
 679                                 // we need to look at (see above).
 680                                 //
 681
 682                                 if ((Type == SiblingType.SwitchSection) && !new_r.IsUnreachable) {
 683                                         Report.Error (163, Location,
 684                                                       "Control cannot fall through from one " +
 685                                                       "case label to another");
 686                                         return result;
 687                                 }
 688
 689                                 if (locals != null && result.LocalVector != null)
 690                                         locals.Or (result.LocalVector);
 691
 692                                 if (result.ParameterVector != null)
 693                                         parameters.Or (result.ParameterVector);
 694
 695                                 if ((branching.Type == BranchingType.Block) && branching.Block.Implicit)
 696                                         reachability = new_r.Clone ();
 697                                 else
 698                                         reachability.Or (new_r);
 699
 700                                 Report.Debug (2, "  MERGING CHILD DONE", this, result,
 701                                               new_r, reachability);
 702
 703                                 IsDirty = true;
 704
 705                                 return result;
 706                         }
 707
 708                         protected void MergeFinally (FlowBranching branching, UsageVector f_origins,
 709                                                      MyBitVector f_params)
 710                         {
 711                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 712                                         MyBitVector temp_params = f_params.Clone ();
 713                                         temp_params.Or (vector.Parameters);
 714                                 }
 715                         }
 716
 717                         public void MergeFinally (FlowBranching branching, UsageVector f_vector,
 718                                                   UsageVector f_origins)
 719                         {
 720                                 if (parameters != null) {
 721                                         if (f_vector != null) {
 722                                                 MergeFinally (branching, f_origins, f_vector.Parameters);
 723                                                 MyBitVector.Or (ref parameters, f_vector.ParameterVector);
 724                                         } else
 725                                                 MergeFinally (branching, f_origins, parameters);
 726                                 }
 727
 728                                 if (f_vector != null && f_vector.LocalVector != null)
 729                                         MyBitVector.Or (ref locals, f_vector.LocalVector);
 730                         }
 731
 732                         // <summary>
 733                         //   Tells control flow analysis that the current code position may be reached with
 734                         //   a forward jump from any of the origins listed in `origin_vectors' which is a
 735                         //   list of UsageVectors.
 736                         //
 737                         //   This is used when resolving forward gotos - in the following example, the
 738                         //   variable `a' is uninitialized in line 8 becase this line may be reached via
 739                         //   the goto in line 4:
 740                         //
 741                         //      1     int a;
 742                         //
 743                         //      3     if (something)
 744                         //      4        goto World;
 745                         //
 746                         //      6     a = 5;
 747                         //
 748                         //      7  World:
 749                         //      8     Console.WriteLine (a);
 750                         //
 751                         // </summary>
 752                         public void MergeJumpOrigins (UsageVector o_vectors)
 753                         {
 754                                 Report.Debug (1, "  MERGING JUMP ORIGINS", this);
 755
 756                                 reachability = Reachability.Never ();
 757
 758                                 if (o_vectors == null) {
 759                                         reachability.SetBarrier ();
 760                                         return;
 761                                 }
 762
 763                                 bool first = true;
 764
 765                                 for (UsageVector vector = o_vectors; vector != null;
 766                                      vector = vector.Next) {
 767                                         Report.Debug (1, "    MERGING JUMP ORIGIN", vector);
 768
 769                                         if (first) {
 770                                                 if (locals != null && vector.Locals != null)
 771                                                         locals.Or (vector.locals);
 772
 773                                                 if (parameters != null)
 774                                                         parameters.Or (vector.parameters);
 775                                                 first = false;
 776                                         } else {
 777                                                 if (locals != null && vector.Locals != null)
 778                                                         locals.And (vector.locals);
 779                                                 if (parameters != null)
 780                                                         parameters.And (vector.parameters);
 781                                         }
 782
 783                                         Reachability.And (ref reachability, vector.Reachability, true);
 784                                 }
 785
 786                                 Report.Debug (1, "  MERGING JUMP ORIGINS DONE", this);
 787                         }
 788
 789                         // <summary>
 790                         //   This is used at the beginning of a finally block if there were
 791                         //   any return statements in the try block or one of the catch blocks.
 792                         // </summary>
 793                         public void MergeFinallyOrigins (UsageVector f_origins)
 794                         {
 795                                 Report.Debug (1, "  MERGING FINALLY ORIGIN", this);
 796
 797                                 reachability = Reachability.Never ();
 798
 799                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 800                                         Report.Debug (1, "    MERGING FINALLY ORIGIN", vector);
 801
 802                                         if (parameters != null)
 803                                                 parameters.And (vector.parameters);
 804
 805                                         Reachability.And (ref reachability, vector.Reachability, true);
 806                                 }
 807
 808                                 Report.Debug (1, "  MERGING FINALLY ORIGIN DONE", this);
 809                         }
 810
 811                         public void MergeBreakOrigins (UsageVector o_vectors)
 812                         {
 813                                 Report.Debug (1, "  MERGING BREAK ORIGINS", this);
 814
 815                                 if (o_vectors == null)
 816                                         return;
 817
 818                                 bool first = true;
 819
 820                                 for (UsageVector vector = o_vectors; vector != null;
 821                                      vector = vector.Next) {
 822                                         Report.Debug (1, "    MERGING BREAK ORIGIN", vector);
 823
 824                                         if (first) {
 825                                                 if (locals != null && vector.Locals != null)
 826                                                         locals.Or (vector.locals);
 827
 828                                                 if (parameters != null)
 829                                                         parameters.Or (vector.parameters);
 830                                                 first = false;
 831                                         } else {
 832                                                 if (locals != null && vector.Locals != null)
 833                                                         locals.And (vector.locals);
 834                                                 if (parameters != null)
 835                                                         parameters.And (vector.parameters);
 836                                         }
 837                                 }
 838
 839                                 Report.Debug (1, "  MERGING BREAK ORIGINS DONE", this);
 840                         }
 841
 842                         public void CheckOutParameters (FlowBranching branching)
 843                         {
 844                                 if (parameters != null)
 845                                         branching.CheckOutParameters (parameters, branching.Location);
 846                         }
 847
 848                         // <summary>
 849                         //   Performs an `or' operation on the locals and the parameters.
 850                         // </summary>
 851                         public void Or (UsageVector new_vector)
 852                         {
 853                                 IsDirty = true;
 854                                 locals.Or (new_vector.locals);
 855                                 if (parameters != null)
 856                                         parameters.Or (new_vector.parameters);
 857                         }
 858
 859                         // <summary>
 860                         //   Performs an `and' operation on the locals.
 861                         // </summary>
 862                         public void AndLocals (UsageVector new_vector)
 863                         {
 864                                 IsDirty = true;
 865                                 locals.And (new_vector.locals);
 866                         }
 867
 868                         public bool HasParameters {
 869                                 get {
 870                                         return parameters != null;
 871                                 }
 872                         }
 873
 874                         public bool HasLocals {
 875                                 get {
 876                                         return locals != null;
 877                                 }
 878                         }
 879
 880                         // <summary>
 881                         //   Returns a deep copy of the parameters.
 882                         // </summary>
 883                         public MyBitVector Parameters {
 884                                 get {
 885                                         if (parameters != null)
 886                                                 return parameters.Clone ();
 887                                         else
 888                                                 return null;
 889                                 }
 890                         }
 891
 892                         // <summary>
 893                         //   Returns a deep copy of the locals.
 894                         // </summary>
 895                         public MyBitVector Locals {
 896                                 get {
 897                                         if (locals != null)
 898                                                 return locals.Clone ();
 899                                         else
 900                                                 return null;
 901                                 }
 902                         }
 903
 904                         public MyBitVector ParameterVector {
 905                                 get {
 906                                         return parameters;
 907                                 }
 908                         }
 909
 910                         public MyBitVector LocalVector {
 911                                 get {
 912                                         return locals;
 913                                 }
 914                         }
 915
 916                         //
 917                         // Debugging stuff.
 918                         //
 919
 920                         public override string ToString ()
 921                         {
 922                                 StringBuilder sb = new StringBuilder ();
 923
 924                                 sb.Append ("Vector (");
 925                                 sb.Append (Type);
 926                                 sb.Append (",");
 927                                 sb.Append (id);
 928                                 sb.Append (",");
 929                                 sb.Append (IsDirty);
 930                                 sb.Append (",");
 931                                 sb.Append (reachability);
 932                                 if (parameters != null) {
 933                                         sb.Append (" - ");
 934                                         sb.Append (parameters);
 935                                 }
 936                                 sb.Append (" - ");
 937                                 sb.Append (locals);
 938                                 sb.Append (")");
 939
 940                                 return sb.ToString ();
 941                         }
 942                 }
 943
 944                 // <summary>
 945                 //   Creates a new flow branching which is contained in `parent'.
 946                 //   You should only pass non-null for the `block' argument if this block
 947                 //   introduces any new variables - in this case, we need to create a new
 948                 //   usage vector with a different size than our parent's one.
 949                 // </summary>
 950                 protected FlowBranching (FlowBranching parent, BranchingType type, SiblingType stype,
 951                                          Block block, Location loc)
 952                 {
 953                         Parent = parent;
 954                         Block = block;
 955                         Location = loc;
 956                         Type = type;
 957                         id = ++next_id;
 958
 959                         UsageVector vector;
 960                         if (Block != null) {
 961                                 param_map = Block.ParameterMap;
 962                                 local_map = Block.LocalMap;
 963
 964                                 UsageVector parent_vector = parent != null ? parent.CurrentUsageVector : null;
 965                                 vector = new UsageVector (
 966                                         stype, parent_vector, Block, loc,
 967                                         param_map.Length, local_map.Length);
 968                         } else {
 969                                 param_map = Parent.param_map;
 970                                 local_map = Parent.local_map;
 971                                 vector = new UsageVector (
 972                                         stype, Parent.CurrentUsageVector, null, loc);
 973                         }
 974
 975                         AddSibling (vector);
 976                 }
 977
 978                 public abstract UsageVector CurrentUsageVector {
 979                         get;
 980                 }
 981
 982                 // <summary>
 983                 //   Creates a sibling of the current usage vector.
 984                 // </summary>
 985                 public virtual void CreateSibling (Block block, SiblingType type)
 986                 {
 987                         UsageVector vector = new UsageVector (
 988                                 type, Parent.CurrentUsageVector, block, Location);
 989                         AddSibling (vector);
 990
 991                         Report.Debug (1, "  CREATED SIBLING", CurrentUsageVector);
 992                 }
 993
 994                 public void CreateSibling ()
 995                 {
 996                         CreateSibling (null, SiblingType.Conditional);
 997                 }
 998
 999                 protected abstract void AddSibling (UsageVector uv);
1000
1001                 public virtual LabeledStatement LookupLabel (string name, Location loc)
1002                 {
1003                         if (Parent != null)
1004                                 return Parent.LookupLabel (name, loc);
1005
1006                         Report.Error (
1007                                 159, loc,
1008                                 "No such label `" + name + "' in this scope");
1009                         return null;
1010                 }
1011
1012                 public abstract void Label (UsageVector origin_vectors);
1013
1014                 // <summary>
1015                 //   Check whether all `out' parameters have been assigned.
1016                 // </summary>
1017                 public void CheckOutParameters (MyBitVector parameters, Location loc)
1018                 {
1019                         for (int i = 0; i < param_map.Count; i++) {
1020                                 VariableInfo var = param_map [i];
1021
1022                                 if (var == null)
1023                                         continue;
1024
1025                                 if (var.IsAssigned (parameters))
1026                                         continue;
1027
1028                                 Report.Error (177, loc, "The out parameter `" +
1029                                               var.Name + "' must be " +
1030                                               "assigned before control leaves the current method.");
1031                         }
1032                 }
1033
1034                 protected UsageVector Merge (UsageVector sibling_list)
1035                 {
1036                         if (sibling_list.Next == null)
1037                                 return sibling_list;
1038
1039                         MyBitVector locals = null;
1040                         MyBitVector parameters = null;
1041
1042                         Reachability reachability = null;
1043
1044                         Report.Debug (2, "  MERGING SIBLINGS", this, Name);
1045
1046                         for (UsageVector child = sibling_list; child != null; child = child.Next) {
1047                                 bool do_break = (Type != BranchingType.Switch) &&
1048                                         (Type != BranchingType.Loop);
1049
1050                                 Report.Debug (2, "    MERGING SIBLING   ", child,
1051                                               child.ParameterVector, child.LocalVector,
1052                                               reachability, child.Reachability, do_break);
1053
1054                                 Reachability.And (ref reachability, child.Reachability, do_break);
1055
1056                                 // A local variable is initialized after a flow branching if it
1057                                 // has been initialized in all its branches which do neither
1058                                 // always return or always throw an exception.
1059                                 //
1060                                 // If a branch may return, but does not always return, then we
1061                                 // can treat it like a never-returning branch here: control will
1062                                 // only reach the code position after the branching if we did not
1063                                 // return here.
1064                                 //
1065                                 // It's important to distinguish between always and sometimes
1066                                 // returning branches here:
1067                                 //
1068                                 //    1   int a;
1069                                 //    2   if (something) {
1070                                 //    3      return;
1071                                 //    4      a = 5;
1072                                 //    5   }
1073                                 //    6   Console.WriteLine (a);
1074                                 //
1075                                 // The if block in lines 3-4 always returns, so we must not look
1076                                 // at the initialization of `a' in line 4 - thus it'll still be
1077                                 // uninitialized in line 6.
1078                                 //
1079                                 // On the other hand, the following is allowed:
1080                                 //
1081                                 //    1   int a;
1082                                 //    2   if (something)
1083                                 //    3      a = 5;
1084                                 //    4   else
1085                                 //    5      return;
1086                                 //    6   Console.WriteLine (a);
1087                                 //
1088                                 // Here, `a' is initialized in line 3 and we must not look at
1089                                 // line 5 since it always returns.
1090                                 //
1091                                 bool do_break_2 = (child.Type != SiblingType.Block) &&
1092                                         (child.Type != SiblingType.SwitchSection);
1093                                 bool always_throws = (child.Type != SiblingType.Try) &&
1094                                         child.Reachability.AlwaysThrows;
1095                                 bool unreachable = always_throws ||
1096                                         (do_break_2 && child.Reachability.AlwaysBreaks) ||
1097                                         child.Reachability.AlwaysReturns ||
1098                                         child.Reachability.AlwaysHasBarrier;
1099
1100                                 Report.Debug (2, "    MERGING SIBLING #1", reachability,
1101                                               Type, child.Type, child.Reachability.IsUnreachable,
1102                                               do_break_2, always_throws, unreachable);
1103
1104                                 if (!unreachable && (child.LocalVector != null))
1105                                         MyBitVector.And (ref locals, child.LocalVector);
1106
1107                                 // An `out' parameter must be assigned in all branches which do
1108                                 // not always throw an exception.
1109                                 if ((child.ParameterVector != null) && !child.Reachability.AlwaysThrows)
1110                                         MyBitVector.And (ref parameters, child.ParameterVector);
1111
1112                                 Report.Debug (2, "    MERGING SIBLING #2", parameters, locals);
1113                         }
1114
1115                         if (reachability == null)
1116                                 reachability = Reachability.Never ();
1117
1118                         Report.Debug (2, "  MERGING SIBLINGS DONE", parameters, locals,
1119                                       reachability, Infinite);
1120
1121                         return new UsageVector (
1122                                 parameters, locals, reachability, null, Location);
1123                 }
1124
1125                 protected abstract UsageVector Merge ();
1126
1127                 // <summary>
1128                 //   Merge a child branching.
1129                 // </summary>
1130                 public UsageVector MergeChild (FlowBranching child)
1131                 {
1132                         return CurrentUsageVector.MergeChild (child);
1133                 }
1134
1135                 // <summary>
1136                 //   Does the toplevel merging.
1137                 // </summary>
1138                 public Reachability MergeTopBlock ()
1139                 {
1140                         if ((Type != BranchingType.Block) || (Block == null))
1141                                 throw new NotSupportedException ();
1142
1143                         UsageVector vector = new UsageVector (
1144                                 SiblingType.Block, null, Block, Location,
1145                                 param_map.Length, local_map.Length);
1146
1147                         UsageVector result = vector.MergeChild (this);
1148
1149                         Report.Debug (4, "MERGE TOP BLOCK", Location, vector, result.Reachability);
1150
1151                         if ((vector.Reachability.Throws != FlowReturns.Always) &&
1152                             (vector.Reachability.Barrier != FlowReturns.Always))
1153                                 CheckOutParameters (vector.Parameters, Location);
1154
1155                         return result.Reachability;
1156                 }
1157
1158                 //
1159                 // Checks whether we're in a `try' block.
1160                 //
1161                 public virtual bool InTryOrCatch (bool is_return)
1162                 {
1163                         if ((Block != null) && Block.IsDestructor)
1164                                 return true;
1165                         else if (!is_return &&
1166                             ((Type == BranchingType.Loop) || (Type == BranchingType.Switch)))
1167                                 return false;
1168                         else if (Parent != null)
1169                                 return Parent.InTryOrCatch (is_return);
1170                         else
1171                                 return false;
1172                 }
1173
1174                 //
1175                 // Checks whether we're in a `catch' block.
1176                 //
1177                 public virtual bool InCatch ()
1178                 {
1179                         if (Parent != null)
1180                                 return Parent.InCatch ();
1181                         else
1182                                 return false;
1183                 }
1184
1185                 //
1186                 // Checks whether we're in a `finally' block.
1187                 //
1188                 public virtual bool InFinally (bool is_return)
1189                 {
1190                         if (!is_return &&
1191                             ((Type == BranchingType.Loop) || (Type == BranchingType.Switch)))
1192                                 return false;
1193                         else if (Parent != null)
1194                                 return Parent.InFinally (is_return);
1195                         else
1196                                 return false;
1197                 }
1198
1199                 public virtual bool InLoop ()
1200                 {
1201                         if (Type == BranchingType.Loop)
1202                                 return true;
1203                         else if (Parent != null)
1204                                 return Parent.InLoop ();
1205                         else
1206                                 return false;
1207                 }
1208
1209                 public virtual bool InSwitch ()
1210                 {
1211                         if (Type == BranchingType.Switch)
1212                                 return true;
1213                         else if (Parent != null)
1214                                 return Parent.InSwitch ();
1215                         else
1216                                 return false;
1217                 }
1218
1219                 public virtual bool BreakCrossesTryCatchBoundary ()
1220                 {
1221                         if ((Type == BranchingType.Loop) || (Type == BranchingType.Switch))
1222                                 return false;
1223                         else if (Parent != null)
1224                                 return Parent.BreakCrossesTryCatchBoundary ();
1225                         else
1226                                 return false;
1227                 }
1228
1229                 public virtual void AddFinallyVector (UsageVector vector)
1230                 {
1231                         if (Parent != null)
1232                                 Parent.AddFinallyVector (vector);
1233                         else if ((Block == null) || !Block.IsDestructor)
1234                                 throw new NotSupportedException ();
1235                 }
1236
1237                 public virtual void AddBreakVector (UsageVector vector)
1238                 {
1239                         if (Parent != null)
1240                                 Parent.AddBreakVector (vector);
1241                         else if ((Block == null) || !Block.IsDestructor)
1242                                 throw new NotSupportedException ();
1243                 }
1244
1245                 public virtual void StealFinallyClauses (ref ArrayList list)
1246                 {
1247                         if (Parent != null)
1248                                 Parent.StealFinallyClauses (ref list);
1249                 }
1250
1251                 public bool IsAssigned (VariableInfo vi)
1252                 {
1253                         return CurrentUsageVector.IsAssigned (vi);
1254                 }
1255
1256                 public bool IsFieldAssigned (VariableInfo vi, string field_name)
1257                 {
1258                         if (CurrentUsageVector.IsAssigned (vi))
1259                                 return true;
1260
1261                         return CurrentUsageVector.IsFieldAssigned (vi, field_name);
1262                 }
1263
1264                 public void SetAssigned (VariableInfo vi)
1265                 {
1266                         CurrentUsageVector.SetAssigned (vi);
1267                 }
1268
1269                 public void SetFieldAssigned (VariableInfo vi, string name)
1270                 {
1271                         CurrentUsageVector.SetFieldAssigned (vi, name);
1272                 }
1273
1274                 public override string ToString ()
1275                 {
1276                         StringBuilder sb = new StringBuilder ();
1277                         sb.Append (GetType ());
1278                         sb.Append (" (");
1279
1280                         sb.Append (id);
1281                         sb.Append (",");
1282                         sb.Append (Type);
1283                         if (Block != null) {
1284                                 sb.Append (" - ");
1285                                 sb.Append (Block.ID);
1286                                 sb.Append (" - ");
1287                                 sb.Append (Block.StartLocation);
1288                         }
1289                         sb.Append (" - ");
1290                         // sb.Append (Siblings.Length);
1291                         // sb.Append (" - ");
1292                         sb.Append (CurrentUsageVector);
1293                         sb.Append (")");
1294                         return sb.ToString ();
1295                 }
1296
1297                 public string Name {
1298                         get {
1299                                 return String.Format ("{0} ({1}:{2}:{3})",
1300                                                       GetType (), id, Type, Location);
1301                         }
1302                 }
1303         }
1304
1305         public class FlowBranchingBlock : FlowBranching
1306         {
1307                 UsageVector sibling_list = null;
1308
1309                 public FlowBranchingBlock (FlowBranching parent, BranchingType type,
1310                                            SiblingType stype, Block block, Location loc)
1311                         : base (parent, type, stype, block, loc)
1312                 { }
1313
1314                 public override UsageVector CurrentUsageVector {
1315                         get { return sibling_list; }
1316                 }
1317
1318                 protected override void AddSibling (UsageVector sibling)
1319                 {
1320                         sibling.Next = sibling_list;
1321                         sibling_list = sibling;
1322                 }
1323
1324                 public override LabeledStatement LookupLabel (string name, Location loc)
1325                 {
1326                         if (Block == null)
1327                                 return base.LookupLabel (name, loc);
1328
1329                         LabeledStatement s = Block.LookupLabel (name);
1330                         if (s != null)
1331                                 return s;
1332
1333                         return base.LookupLabel (name, loc);
1334                 }
1335
1336                 public override void Label (UsageVector origin_vectors)
1337                 {
1338                         if (!CurrentUsageVector.Reachability.IsUnreachable) {
1339                                 UsageVector vector = CurrentUsageVector.Clone ();
1340                                 vector.Next = origin_vectors;
1341                                 origin_vectors = vector;
1342                         }
1343
1344                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1345                 }
1346
1347                 protected override UsageVector Merge ()
1348                 {
1349                         return Merge (sibling_list);
1350                 }
1351         }
1352
1353         public class FlowBranchingLoop : FlowBranchingBlock
1354         {
1355                 UsageVector break_origins;
1356
1357                 public FlowBranchingLoop (FlowBranching parent, Block block, Location loc)
1358                         : base (parent, BranchingType.Loop, SiblingType.Conditional, block, loc)
1359                 { }
1360
1361                 public override void AddBreakVector (UsageVector vector)
1362                 {
1363                         vector = vector.Clone ();
1364                         vector.Next = break_origins;
1365                         break_origins = vector;
1366                 }
1367
1368                 protected override UsageVector Merge ()
1369                 {
1370                         UsageVector vector = base.Merge ();
1371
1372                         vector.MergeBreakOrigins (break_origins);
1373
1374                         return vector;
1375                 }
1376         }
1377
1378         public class FlowBranchingException : FlowBranching
1379         {
1380                 ExceptionStatement stmt;
1381                 UsageVector current_vector;
1382                 UsageVector catch_vectors;
1383                 UsageVector finally_vector;
1384                 UsageVector finally_origins;
1385                 bool emit_finally;
1386                 bool in_try;
1387
1388                 public FlowBranchingException (FlowBranching parent,
1389                                                ExceptionStatement stmt)
1390                         : base (parent, BranchingType.Exception, SiblingType.Try,
1391                                 null, stmt.loc)
1392                 {
1393                         this.stmt = stmt;
1394                         this.emit_finally = true;
1395                 }
1396
1397                 protected override void AddSibling (UsageVector sibling)
1398                 {
1399                         if (sibling.Type == SiblingType.Try) {
1400                                 sibling.Next = catch_vectors;
1401                                 catch_vectors = sibling;
1402                                 in_try = true;
1403                         } else if (sibling.Type == SiblingType.Catch) {
1404                                 sibling.Next = catch_vectors;
1405                                 catch_vectors = sibling;
1406                                 in_try = false;
1407                         } else if (sibling.Type == SiblingType.Finally) {
1408                                 sibling.MergeFinallyOrigins (finally_origins);
1409                                 finally_vector = sibling;
1410                                 in_try = false;
1411                         } else
1412                                 throw new InvalidOperationException ();
1413
1414                         current_vector = sibling;
1415                 }
1416
1417                 public override UsageVector CurrentUsageVector {
1418                         get { return current_vector; }
1419                 }
1420
1421                 public override bool InTryOrCatch (bool is_return)
1422                 {
1423                         return finally_vector == null;
1424                 }
1425
1426                 public override bool InCatch ()
1427                 {
1428                         return !in_try && (finally_vector == null);
1429                 }
1430
1431                 public override bool InFinally (bool is_return)
1432                 {
1433                         return finally_vector != null;
1434                 }
1435
1436                 public override bool BreakCrossesTryCatchBoundary ()
1437                 {
1438                         return true;
1439                 }
1440
1441                 public override void AddFinallyVector (UsageVector vector)
1442                 {
1443                         vector = vector.Clone ();
1444                         vector.Next = finally_origins;
1445                         finally_origins = vector;
1446                 }
1447
1448                 public override void StealFinallyClauses (ref ArrayList list)
1449                 {
1450                         if (list == null)
1451                                 list = new ArrayList ();
1452                         list.Add (stmt);
1453                         emit_finally = false;
1454                         base.StealFinallyClauses (ref list);
1455                 }
1456
1457                 public bool EmitFinally {
1458                         get { return emit_finally; }
1459                 }
1460
1461                 public override LabeledStatement LookupLabel (string name, Location loc)
1462                 {
1463                         if (current_vector.Block == null)
1464                                 return base.LookupLabel (name, loc);
1465
1466                         LabeledStatement s = current_vector.Block.LookupLabel (name);
1467                         if (s != null)
1468                                 return s;
1469
1470                         if (finally_vector != null) {
1471                                 Report.Error (
1472                                         157, loc, "Control can not leave the body " +
1473                                         "of the finally block");
1474                                 return null;
1475                         }
1476
1477                         return base.LookupLabel (name, loc);
1478                 }
1479
1480                 public override void Label (UsageVector origin_vectors)
1481                 {
1482                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1483                 }
1484
1485                 protected override UsageVector Merge ()
1486                 {
1487                         UsageVector vector = Merge (catch_vectors);
1488
1489                         vector.MergeFinally (this, finally_vector, finally_origins);
1490
1491                         return vector;
1492                 }
1493         }
1494
1495         // <summary>
1496         //   This is used by the flow analysis code to keep track of the type of local variables
1497         //   and variables.
1498         //
1499         //   The flow code uses a BitVector to keep track of whether a variable has been assigned
1500         //   or not.  This is easy for fundamental types (int, char etc.) or reference types since
1501         //   you can only assign the whole variable as such.
1502         //
1503         //   For structs, we also need to keep track of all its fields.  To do this, we allocate one
1504         //   bit for the struct itself (it's used if you assign/access the whole struct) followed by
1505         //   one bit for each of its fields.
1506         //
1507         //   This class computes this `layout' for each type.
1508         // </summary>
1509         public class TypeInfo
1510         {
1511                 public readonly Type Type;
1512
1513                 // <summary>
1514                 //   Total number of bits a variable of this type consumes in the flow vector.
1515                 // </summary>
1516                 public readonly int TotalLength;
1517
1518                 // <summary>
1519                 //   Number of bits the simple fields of a variable of this type consume
1520                 //   in the flow vector.
1521                 // </summary>
1522                 public readonly int Length;
1523
1524                 // <summary>
1525                 //   This is only used by sub-structs.
1526                 // </summary>
1527                 public readonly int Offset;
1528
1529                 // <summary>
1530                 //   If this is a struct.
1531                 // </summary>
1532                 public readonly bool IsStruct;
1533
1534                 // <summary>
1535                 //   If this is a struct, all fields which are structs theirselves.
1536                 // </summary>
1537                 public TypeInfo[] SubStructInfo;
1538
1539                 protected readonly StructInfo struct_info;
1540                 private static Hashtable type_hash = new Hashtable ();
1541
1542                 public static TypeInfo GetTypeInfo (Type type)
1543                 {
1544                         TypeInfo info = (TypeInfo) type_hash [type];
1545                         if (info != null)
1546                                 return info;
1547
1548                         info = new TypeInfo (type);
1549                         type_hash.Add (type, info);
1550                         return info;
1551                 }
1552
1553                 public static TypeInfo GetTypeInfo (TypeContainer tc)
1554                 {
1555                         TypeInfo info = (TypeInfo) type_hash [tc.TypeBuilder];
1556                         if (info != null)
1557                                 return info;
1558
1559                         info = new TypeInfo (tc);
1560                         type_hash.Add (tc.TypeBuilder, info);
1561                         return info;
1562                 }
1563
1564                 private TypeInfo (Type type)
1565                 {
1566                         this.Type = type;
1567
1568                         struct_info = StructInfo.GetStructInfo (type);
1569                         if (struct_info != null) {
1570                                 Length = struct_info.Length;
1571                                 TotalLength = struct_info.TotalLength;
1572                                 SubStructInfo = struct_info.StructFields;
1573                                 IsStruct = true;
1574                         } else {
1575                                 Length = 0;
1576                                 TotalLength = 1;
1577                                 IsStruct = false;
1578                         }
1579                 }
1580
1581                 private TypeInfo (TypeContainer tc)
1582                 {
1583                         this.Type = tc.TypeBuilder;
1584
1585                         struct_info = StructInfo.GetStructInfo (tc);
1586                         if (struct_info != null) {
1587                                 Length = struct_info.Length;
1588                                 TotalLength = struct_info.TotalLength;
1589                                 SubStructInfo = struct_info.StructFields;
1590                                 IsStruct = true;
1591                         } else {
1592                                 Length = 0;
1593                                 TotalLength = 1;
1594                                 IsStruct = false;
1595                         }
1596                 }
1597
1598                 protected TypeInfo (StructInfo struct_info, int offset)
1599                 {
1600                         this.struct_info = struct_info;
1601                         this.Offset = offset;
1602                         this.Length = struct_info.Length;
1603                         this.TotalLength = struct_info.TotalLength;
1604                         this.SubStructInfo = struct_info.StructFields;
1605                         this.Type = struct_info.Type;
1606                         this.IsStruct = true;
1607                 }
1608
1609                 public int GetFieldIndex (string name)
1610                 {
1611                         if (struct_info == null)
1612                                 return 0;
1613
1614                         return struct_info [name];
1615                 }
1616
1617                 public TypeInfo GetSubStruct (string name)
1618                 {
1619                         if (struct_info == null)
1620                                 return null;
1621
1622                         return struct_info.GetStructField (name);
1623                 }
1624
1625                 // <summary>
1626                 //   A struct's constructor must always assign all fields.
1627                 //   This method checks whether it actually does so.
1628                 // </summary>
1629                 public bool IsFullyInitialized (FlowBranching branching, VariableInfo vi, Location loc)
1630                 {
1631                         if (struct_info == null)
1632                                 return true;
1633
1634                         bool ok = true;
1635                         for (int i = 0; i < struct_info.Count; i++) {
1636                                 FieldInfo field = struct_info.Fields [i];
1637
1638                                 if (!branching.IsFieldAssigned (vi, field.Name)) {
1639                                         Report.Error (171, loc,
1640                                                       "Field `" + TypeManager.CSharpName (Type) +
1641                                                       "." + field.Name + "' must be fully initialized " +
1642                                                       "before control leaves the constructor");
1643                                         ok = false;
1644                                 }
1645                         }
1646
1647                         return ok;
1648                 }
1649
1650                 public override string ToString ()
1651                 {
1652                         return String.Format ("TypeInfo ({0}:{1}:{2}:{3})",
1653                                               Type, Offset, Length, TotalLength);
1654                 }
1655
1656                 protected class StructInfo {
1657                         public readonly Type Type;
1658                         public readonly FieldInfo[] Fields;
1659                         public readonly TypeInfo[] StructFields;
1660                         public readonly int Count;
1661                         public readonly int CountPublic;
1662                         public readonly int CountNonPublic;
1663                         public readonly int Length;
1664                         public readonly int TotalLength;
1665                         public readonly bool HasStructFields;
1666
1667                         private static Hashtable field_type_hash = new Hashtable ();
1668                         private Hashtable struct_field_hash;
1669                         private Hashtable field_hash;
1670
1671                         protected bool InTransit = false;
1672
1673                         // Private constructor.  To save memory usage, we only need to create one instance
1674                         // of this class per struct type.
1675                         private StructInfo (Type type)
1676                         {
1677                                 this.Type = type;
1678
1679                                 field_type_hash.Add (type, this);
1680
1681                                 if (type is TypeBuilder) {
1682                                         TypeContainer tc = TypeManager.LookupTypeContainer (type);
1683
1684                                         ArrayList fields = null;
1685                                         if (tc != null)
1686                                                 fields = tc.Fields;
1687
1688                                         ArrayList public_fields = new ArrayList ();
1689                                         ArrayList non_public_fields = new ArrayList ();
1690
1691                                         if (fields != null) {
1692                                                 foreach (FieldMember field in fields) {
1693                                                         if ((field.ModFlags & Modifiers.STATIC) != 0)
1694                                                                 continue;
1695                                                         if ((field.ModFlags & Modifiers.PUBLIC) != 0)
1696                                                                 public_fields.Add (field.FieldBuilder);
1697                                                         else
1698                                                                 non_public_fields.Add (field.FieldBuilder);
1699                                                 }
1700                                         }
1701
1702                                         CountPublic = public_fields.Count;
1703                                         CountNonPublic = non_public_fields.Count;
1704                                         Count = CountPublic + CountNonPublic;
1705
1706                                         Fields = new FieldInfo [Count];
1707                                         public_fields.CopyTo (Fields, 0);
1708                                         non_public_fields.CopyTo (Fields, CountPublic);
1709                                 } else {
1710                                         FieldInfo[] public_fields = type.GetFields (
1711                                                 BindingFlags.Instance|BindingFlags.Public);
1712                                         FieldInfo[] non_public_fields = type.GetFields (
1713                                                 BindingFlags.Instance|BindingFlags.NonPublic);
1714
1715                                         CountPublic = public_fields.Length;
1716                                         CountNonPublic = non_public_fields.Length;
1717                                         Count = CountPublic + CountNonPublic;
1718
1719                                         Fields = new FieldInfo [Count];
1720                                         public_fields.CopyTo (Fields, 0);
1721                                         non_public_fields.CopyTo (Fields, CountPublic);
1722                                 }
1723
1724                                 struct_field_hash = new Hashtable ();
1725                                 field_hash = new Hashtable ();
1726
1727                                 Length = 0;
1728                                 StructFields = new TypeInfo [Count];
1729                                 StructInfo[] sinfo = new StructInfo [Count];
1730
1731                                 InTransit = true;
1732
1733                                 for (int i = 0; i < Count; i++) {
1734                                         FieldInfo field = (FieldInfo) Fields [i];
1735
1736                                         sinfo [i] = GetStructInfo (field.FieldType);
1737                                         if (sinfo [i] == null)
1738                                                 field_hash.Add (field.Name, ++Length);
1739                                         else if (sinfo [i].InTransit) {
1740                                                 Report.Error (523, String.Format (
1741                                                                       "Struct member '{0}.{1}' of type '{2}' causes " +
1742                                                                       "a cycle in the structure layout",
1743                                                                       type, field.Name, sinfo [i].Type));
1744                                                 sinfo [i] = null;
1745                                                 return;
1746                                         }
1747                                 }
1748
1749                                 InTransit = false;
1750
1751                                 TotalLength = Length + 1;
1752                                 for (int i = 0; i < Count; i++) {
1753                                         FieldInfo field = (FieldInfo) Fields [i];
1754
1755                                         if (sinfo [i] == null)
1756                                                 continue;
1757
1758                                         field_hash.Add (field.Name, TotalLength);
1759
1760                                         HasStructFields = true;
1761                                         StructFields [i] = new TypeInfo (sinfo [i], TotalLength);
1762                                         struct_field_hash.Add (field.Name, StructFields [i]);
1763                                         TotalLength += sinfo [i].TotalLength;
1764                                 }
1765                         }
1766
1767                         public int this [string name] {
1768                                 get {
1769                                         if (field_hash.Contains (name))
1770                                                 return (int) field_hash [name];
1771                                         else
1772                                                 return 0;
1773                                 }
1774                         }
1775
1776                         public TypeInfo GetStructField (string name)
1777                         {
1778                                 return (TypeInfo) struct_field_hash [name];
1779                         }
1780
1781                         public static StructInfo GetStructInfo (Type type)
1782                         {
1783                                 if (!TypeManager.IsValueType (type) || TypeManager.IsEnumType (type) ||
1784                                     TypeManager.IsBuiltinType (type))
1785                                         return null;
1786
1787                                 StructInfo info = (StructInfo) field_type_hash [type];
1788                                 if (info != null)
1789                                         return info;
1790
1791                                 return new StructInfo (type);
1792                         }
1793
1794                         public static StructInfo GetStructInfo (TypeContainer tc)
1795                         {
1796                                 StructInfo info = (StructInfo) field_type_hash [tc.TypeBuilder];
1797                                 if (info != null)
1798                                         return info;
1799
1800                                 return new StructInfo (tc.TypeBuilder);
1801                         }
1802                 }
1803         }
1804
1805         // <summary>
1806         //   This is used by the flow analysis code to store information about a single local variable
1807         //   or parameter.  Depending on the variable's type, we need to allocate one or more elements
1808         //   in the BitVector - if it's a fundamental or reference type, we just need to know whether
1809         //   it has been assigned or not, but for structs, we need this information for each of its fields.
1810         // </summary>
1811         public class VariableInfo {
1812                 public readonly string Name;
1813                 public readonly TypeInfo TypeInfo;
1814
1815                 // <summary>
1816                 //   The bit offset of this variable in the flow vector.
1817                 // </summary>
1818                 public readonly int Offset;
1819
1820                 // <summary>
1821                 //   The number of bits this variable needs in the flow vector.
1822                 //   The first bit always specifies whether the variable as such has been assigned while
1823                 //   the remaining bits contain this information for each of a struct's fields.
1824                 // </summary>
1825                 public readonly int Length;
1826
1827                 // <summary>
1828                 //   If this is a parameter of local variable.
1829                 // </summary>
1830                 public readonly bool IsParameter;
1831
1832                 public readonly LocalInfo LocalInfo;
1833                 public readonly int ParameterIndex;
1834
1835                 readonly VariableInfo Parent;
1836                 VariableInfo[] sub_info;
1837
1838                 protected VariableInfo (string name, Type type, int offset)
1839                 {
1840                         this.Name = name;
1841                         this.Offset = offset;
1842                         this.TypeInfo = TypeInfo.GetTypeInfo (type);
1843
1844                         Length = TypeInfo.TotalLength;
1845
1846                         Initialize ();
1847                 }
1848
1849                 protected VariableInfo (VariableInfo parent, TypeInfo type)
1850                 {
1851                         this.Name = parent.Name;
1852                         this.TypeInfo = type;
1853                         this.Offset = parent.Offset + type.Offset;
1854                         this.Parent = parent;
1855                         this.Length = type.TotalLength;
1856
1857                         this.IsParameter = parent.IsParameter;
1858                         this.LocalInfo = parent.LocalInfo;
1859                         this.ParameterIndex = parent.ParameterIndex;
1860
1861                         Initialize ();
1862                 }
1863
1864                 protected void Initialize ()
1865                 {
1866                         TypeInfo[] sub_fields = TypeInfo.SubStructInfo;
1867                         if (sub_fields != null) {
1868                                 sub_info = new VariableInfo [sub_fields.Length];
1869                                 for (int i = 0; i < sub_fields.Length; i++) {
1870                                         if (sub_fields [i] != null)
1871                                                 sub_info [i] = new VariableInfo (this, sub_fields [i]);
1872                                 }
1873                         } else
1874                                 sub_info = new VariableInfo [0];
1875                 }
1876
1877                 public VariableInfo (LocalInfo local_info, int offset)
1878                         : this (local_info.Name, local_info.VariableType, offset)
1879                 {
1880                         this.LocalInfo = local_info;
1881                         this.IsParameter = false;
1882                 }
1883
1884                 public VariableInfo (string name, Type type, int param_idx, int offset)
1885                         : this (name, type, offset)
1886                 {
1887                         this.ParameterIndex = param_idx;
1888                         this.IsParameter = true;
1889                 }
1890
1891                 public bool IsAssigned (EmitContext ec)
1892                 {
1893                         return !ec.DoFlowAnalysis || ec.CurrentBranching.IsAssigned (this);
1894                 }
1895
1896                 public bool IsAssigned (EmitContext ec, Location loc)
1897                 {
1898                         if (IsAssigned (ec))
1899                                 return true;
1900
1901                         Report.Error (165, loc,
1902                                       "Use of unassigned local variable `" + Name + "'");
1903                         ec.CurrentBranching.SetAssigned (this);
1904                         return false;
1905                 }
1906
1907                 public bool IsAssigned (MyBitVector vector)
1908                 {
1909                         if (vector [Offset])
1910                                 return true;
1911
1912                         for (VariableInfo parent = Parent; parent != null; parent = parent.Parent)
1913                                 if (vector [parent.Offset])
1914                                         return true;
1915
1916                         // Return unless this is a struct.
1917                         if (!TypeInfo.IsStruct)
1918                                 return false;
1919
1920                         // Ok, so each field must be assigned.
1921                         for (int i = 0; i < TypeInfo.Length; i++) {
1922                                 if (!vector [Offset + i + 1])
1923                                         return false;
1924                         }
1925
1926                         // Ok, now check all fields which are structs.
1927                         for (int i = 0; i < sub_info.Length; i++) {
1928                                 VariableInfo sinfo = sub_info [i];
1929                                 if (sinfo == null)
1930                                         continue;
1931
1932                                 if (!sinfo.IsAssigned (vector))
1933                                         return false;
1934                         }
1935
1936                         vector [Offset] = true;
1937                         return true;
1938                 }
1939
1940                 public void SetAssigned (EmitContext ec)
1941                 {
1942                         if (ec.DoFlowAnalysis)
1943                                 ec.CurrentBranching.SetAssigned (this);
1944                 }
1945
1946                 public void SetAssigned (MyBitVector vector)
1947                 {
1948                         vector [Offset] = true;
1949                 }
1950
1951                 public bool IsFieldAssigned (EmitContext ec, string name, Location loc)
1952                 {
1953                         if (!ec.DoFlowAnalysis || ec.CurrentBranching.IsFieldAssigned (this, name))
1954                                 return true;
1955
1956                         Report.Error (170, loc,
1957                                       "Use of possibly unassigned field `" + name + "'");
1958                         ec.CurrentBranching.SetFieldAssigned (this, name);
1959                         return false;
1960                 }
1961
1962                 public bool IsFieldAssigned (MyBitVector vector, string field_name)
1963                 {
1964                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1965
1966                         if (field_idx == 0)
1967                                 return true;
1968
1969                         return vector [Offset + field_idx];
1970                 }
1971
1972                 public void SetFieldAssigned (EmitContext ec, string name)
1973                 {
1974                         if (ec.DoFlowAnalysis)
1975                                 ec.CurrentBranching.SetFieldAssigned (this, name);
1976                 }
1977
1978                 public void SetFieldAssigned (MyBitVector vector, string field_name)
1979                 {
1980                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1981
1982                         if (field_idx == 0)
1983                                 return;
1984
1985                         vector [Offset + field_idx] = true;
1986                 }
1987
1988                 public VariableInfo GetSubStruct (string name)
1989                 {
1990                         TypeInfo type = TypeInfo.GetSubStruct (name);
1991
1992                         if (type == null)
1993                                 return null;
1994
1995                         return new VariableInfo (this, type);
1996                 }
1997
1998                 public override string ToString ()
1999                 {
2000                         return String.Format ("VariableInfo ({0}:{1}:{2}:{3}:{4})",
2001                                               Name, TypeInfo, Offset, Length, IsParameter);
2002                 }
2003         }
2004
2005         // <summary>
2006         //   This is used by the flow code to hold the `layout' of the flow vector for
2007         //   all locals and all parameters (ie. we create one instance of this class for the
2008         //   locals and another one for the params).
2009         // </summary>
2010         public class VariableMap {
2011                 // <summary>
2012                 //   The number of variables in the map.
2013                 // </summary>
2014                 public readonly int Count;
2015
2016                 // <summary>
2017                 //   Total length of the flow vector for this map.
2018                 // <summary>
2019                 public readonly int Length;
2020
2021                 VariableInfo[] map;
2022
2023                 public VariableMap (InternalParameters ip)
2024                 {
2025                         Count = ip != null ? ip.Count : 0;
2026
2027                         // Dont bother allocating anything!
2028                         if (Count == 0)
2029                                 return;
2030
2031                         Length = 0;
2032
2033                         for (int i = 0; i < Count; i++) {
2034                                 Parameter.Modifier mod = ip.ParameterModifier (i);
2035
2036                                 if ((mod & Parameter.Modifier.OUT) == 0)
2037                                         continue;
2038
2039                                 // Dont allocate till we find an out var.
2040                                 if (map == null)
2041                                         map = new VariableInfo [Count];
2042
2043                                 map [i] = new VariableInfo (ip.ParameterName (i),
2044                                         TypeManager.GetElementType (ip.ParameterType (i)), i, Length);
2045
2046                                 Length += map [i].Length;
2047                         }
2048                 }
2049
2050                 public VariableMap (LocalInfo[] locals)
2051                         : this (null, locals)
2052                 { }
2053
2054                 public VariableMap (VariableMap parent, LocalInfo[] locals)
2055                 {
2056                         int offset = 0, start = 0;
2057                         if (parent != null && parent.map != null) {
2058                                 offset = parent.Length;
2059                                 start = parent.Count;
2060                         }
2061
2062                         Count = locals.Length + start;
2063
2064                         if (Count == 0)
2065                                 return;
2066
2067                         map = new VariableInfo [Count];
2068                         Length = offset;
2069
2070                         if (parent != null && parent.map != null) {
2071                                 parent.map.CopyTo (map, 0);
2072                         }
2073
2074                         for (int i = start; i < Count; i++) {
2075                                 LocalInfo li = locals [i-start];
2076
2077                                 if (li.VariableType == null)
2078                                         continue;
2079
2080                                 map [i] = li.VariableInfo = new VariableInfo (li, Length);
2081                                 Length += map [i].Length;
2082                         }
2083                 }
2084
2085                 // <summary>
2086                 //   Returns the VariableInfo for variable @index or null if we don't need to
2087                 //   compute assignment info for this variable.
2088                 // </summary>
2089                 public VariableInfo this [int index] {
2090                         get {
2091                                 if (map == null)
2092                                         return null;
2093
2094                                 return map [index];
2095                         }
2096                 }
2097
2098                 public override string ToString ()
2099                 {
2100                         return String.Format ("VariableMap ({0}:{1})", Count, Length);
2101                 }
2102         }
2103
2104         // <summary>
2105         //   This is a special bit vector which can inherit from another bit vector doing a
2106         //   copy-on-write strategy.  The inherited vector may have a smaller size than the
2107         //   current one.
2108         // </summary>
2109         public class MyBitVector {
2110                 public readonly int Count;
2111                 public readonly MyBitVector InheritsFrom;
2112
2113                 bool is_dirty;
2114                 BitArray vector;
2115
2116                 public MyBitVector (int Count)
2117                         : this (null, Count)
2118                 { }
2119
2120                 public MyBitVector (MyBitVector InheritsFrom, int Count)
2121                 {
2122                         this.InheritsFrom = InheritsFrom;
2123                         this.Count = Count;
2124                 }
2125
2126                 // <summary>
2127                 //   Checks whether this bit vector has been modified.  After setting this to true,
2128                 //   we won't use the inherited vector anymore, but our own copy of it.
2129                 // </summary>
2130                 public bool IsDirty {
2131                         get {
2132                                 return is_dirty;
2133                         }
2134
2135                         set {
2136                                 if (!is_dirty)
2137                                         initialize_vector ();
2138                         }
2139                 }
2140
2141                 // <summary>
2142                 //   Get/set bit `index' in the bit vector.
2143                 // </summary>
2144                 public bool this [int index]
2145                 {
2146                         get {
2147                                 if (index > Count)
2148                                         throw new ArgumentOutOfRangeException ();
2149
2150                                 // We're doing a "copy-on-write" strategy here; as long
2151                                 // as nobody writes to the array, we can use our parent's
2152                                 // copy instead of duplicating the vector.
2153
2154                                 if (vector != null)
2155                                         return vector [index];
2156                                 else if (InheritsFrom != null) {
2157                                         BitArray inherited = InheritsFrom.Vector;
2158
2159                                         if (index < inherited.Count)
2160                                                 return inherited [index];
2161                                         else
2162                                                 return false;
2163                                 } else
2164                                         return false;
2165                         }
2166
2167                         set {
2168                                 if (index > Count)
2169                                         throw new ArgumentOutOfRangeException ();
2170
2171                                 // Only copy the vector if we're actually modifying it.
2172
2173                                 if (this [index] != value) {
2174                                         initialize_vector ();
2175
2176                                         vector [index] = value;
2177                                 }
2178                         }
2179                 }
2180
2181                 // <summary>
2182                 //   If you explicitly convert the MyBitVector to a BitArray, you will get a deep
2183                 //   copy of the bit vector.
2184                 // </summary>
2185                 public static explicit operator BitArray (MyBitVector vector)
2186                 {
2187                         vector.initialize_vector ();
2188                         return vector.Vector;
2189                 }
2190
2191                 // <summary>
2192                 //   Performs an `or' operation on the bit vector.  The `new_vector' may have a
2193                 //   different size than the current one.
2194                 // </summary>
2195                 public void Or (MyBitVector new_vector)
2196                 {
2197                         BitArray new_array = new_vector.Vector;
2198
2199                         initialize_vector ();
2200
2201                         int upper;
2202                         if (vector.Count < new_array.Count)
2203                                 upper = vector.Count;
2204                         else
2205                                 upper = new_array.Count;
2206
2207                         for (int i = 0; i < upper; i++)
2208                                 vector [i] = vector [i] | new_array [i];
2209                 }
2210
2211                 // <summary>
2212                 //   Perfonrms an `and' operation on the bit vector.  The `new_vector' may have
2213                 //   a different size than the current one.
2214                 // </summary>
2215                 public void And (MyBitVector new_vector)
2216                 {
2217                         BitArray new_array = new_vector.Vector;
2218
2219                         initialize_vector ();
2220
2221                         int lower, upper;
2222                         if (vector.Count < new_array.Count)
2223                                 lower = upper = vector.Count;
2224                         else {
2225                                 lower = new_array.Count;
2226                                 upper = vector.Count;
2227                         }
2228
2229                         for (int i = 0; i < lower; i++)
2230                                 vector [i] = vector [i] & new_array [i];
2231
2232                         for (int i = lower; i < upper; i++)
2233                                 vector [i] = false;
2234                 }
2235
2236                 public static void And (ref MyBitVector target, MyBitVector vector)
2237                 {
2238                         if (target != null)
2239                                 target.And (vector);
2240                         else
2241                                 target = vector.Clone ();
2242                 }
2243
2244                 public static void Or (ref MyBitVector target, MyBitVector vector)
2245                 {
2246                         if (target != null)
2247                                 target.Or (vector);
2248                         else
2249                                 target = vector.Clone ();
2250                 }
2251
2252                 // <summary>
2253                 //   This does a deep copy of the bit vector.
2254                 // </summary>
2255                 public MyBitVector Clone ()
2256                 {
2257                         MyBitVector retval = new MyBitVector (Count);
2258
2259                         retval.Vector = Vector;
2260
2261                         return retval;
2262                 }
2263
2264                 BitArray Vector {
2265                         get {
2266                                 if (vector != null)
2267                                         return vector;
2268                                 else if (!is_dirty && (InheritsFrom != null))
2269                                         return InheritsFrom.Vector;
2270
2271                                 initialize_vector ();
2272
2273                                 return vector;
2274                         }
2275
2276                         set {
2277                                 initialize_vector ();
2278
2279                                 for (int i = 0; i < System.Math.Min (vector.Count, value.Count); i++)
2280                                         vector [i] = value [i];
2281                         }
2282                 }
2283
2284                 void initialize_vector ()
2285                 {
2286                         if (vector != null)
2287                                 return;
2288
2289                         vector = new BitArray (Count, false);
2290                         if (InheritsFrom != null)
2291                                 Vector = InheritsFrom.Vector;
2292
2293                         is_dirty = true;
2294                 }
2295
2296                 public override string ToString ()
2297                 {
2298                         StringBuilder sb = new StringBuilder ("{");
2299
2300                         BitArray vector = Vector;
2301                         if (!IsDirty)
2302                                 sb.Append ("=");
2303                         for (int i = 0; i < vector.Count; i++) {
2304                                 sb.Append (vector [i] ? "1" : "0");
2305                         }
2306
2307                         sb.Append ("}");
2308                         return sb.ToString ();
2309                 }
2310         }
2311 }