mcs/gmcs/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                                 } else if (branching.Type == BranchingType.Switch) {
 664                                         if (new_r.MayBreak || new_r.MayReturn)
 665                                                 new_r.ResetBarrier ();
 666
 667                                         new_r.ResetBreaks ();
 668                                 }
 669
 670                                 //
 671                                 // We've now either reached the point after the branching or we will
 672                                 // never get there since we always return or always throw an exception.
 673                                 //
 674                                 // If we can reach the point after the branching, mark all locals and
 675                                 // parameters as initialized which have been initialized in all branches
 676                                 // we need to look at (see above).
 677                                 //
 678
 679                                 if ((Type == SiblingType.SwitchSection) && !new_r.IsUnreachable) {
 680                                         Report.Error (163, Location,
 681                                                       "Control cannot fall through from one " +
 682                                                               "case label to another");
 683                                         return result;
 684                                         }
 685
 686                                 if (locals != null && result.LocalVector != null)
 687                                         locals.Or (result.LocalVector);
 688
 689                                 if (result.ParameterVector != null)
 690                                         parameters.Or (result.ParameterVector);
 691
 692                                 if ((branching.Type == BranchingType.Block) && branching.Block.Implicit)
 693                                         reachability = new_r.Clone ();
 694                                 else
 695                                         reachability.Or (new_r);
 696
 697                                 Report.Debug (2, "  MERGING CHILD DONE", this, result,
 698                                               new_r, reachability);
 699
 700                                 IsDirty = true;
 701
 702                                 return result;
 703                                 }
 704
 705                         protected void MergeFinally (FlowBranching branching, UsageVector f_origins,
 706                                                      MyBitVector f_params)
 707                         {
 708                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 709                                         MyBitVector temp_params = f_params.Clone ();
 710                                         temp_params.Or (vector.Parameters);
 711                                 }
 712                         }
 713
 714                         public void MergeFinally (FlowBranching branching, UsageVector f_vector,
 715                                                   UsageVector f_origins)
 716                         {
 717                                 if (parameters != null) {
 718                                         if (f_vector != null) {
 719                                                 MergeFinally (branching, f_origins, f_vector.Parameters);
 720                                                 MyBitVector.Or (ref parameters, f_vector.ParameterVector);
 721                                         } else
 722                                                 MergeFinally (branching, f_origins, parameters);
 723                                 }
 724
 725                                 if (f_vector != null && f_vector.LocalVector != null)
 726                                         MyBitVector.Or (ref locals, f_vector.LocalVector);
 727                         }
 728
 729                         // <summary>
 730                         //   Tells control flow analysis that the current code position may be reached with
 731                         //   a forward jump from any of the origins listed in `origin_vectors' which is a
 732                         //   list of UsageVectors.
 733                         //
 734                         //   This is used when resolving forward gotos - in the following example, the
 735                         //   variable `a' is uninitialized in line 8 becase this line may be reached via
 736                         //   the goto in line 4:
 737                         //
 738                         //      1     int a;
 739                         //
 740                         //      3     if (something)
 741                         //      4        goto World;
 742                         //
 743                         //      6     a = 5;
 744                         //
 745                         //      7  World:
 746                         //      8     Console.WriteLine (a);
 747                         //
 748                         // </summary>
 749                         public void MergeJumpOrigins (UsageVector o_vectors)
 750                         {
 751                                 Report.Debug (1, "  MERGING JUMP ORIGINS", this);
 752
 753                                 reachability = Reachability.Never ();
 754
 755                                 if (o_vectors == null) {
 756                                         reachability.SetBarrier ();
 757                                         return;
 758                                 }
 759
 760                                 bool first = true;
 761
 762                                 for (UsageVector vector = o_vectors; vector != null;
 763                                      vector = vector.Next) {
 764                                         Report.Debug (1, "  MERGING JUMP ORIGIN", vector);
 765
 766                                         if (first) {
 767                                                 if (locals != null && vector.Locals != null)
 768                                                 locals.Or (vector.locals);
 769
 770                                                 if (parameters != null)
 771                                                         parameters.Or (vector.parameters);
 772                                                 first = false;
 773                                         } else {
 774                                                 if (locals != null && vector.Locals != null)
 775                                         locals.And (vector.locals);
 776                                         if (parameters != null)
 777                                                 parameters.And (vector.parameters);
 778                                 }
 779
 780                                         Reachability.And (ref reachability, vector.Reachability, true);
 781                                 }
 782
 783                                 Report.Debug (1, "  MERGING JUMP ORIGINS DONE", this);
 784                         }
 785
 786                         // <summary>
 787                         //   This is used at the beginning of a finally block if there were
 788                         //   any return statements in the try block or one of the catch blocks.
 789                         // </summary>
 790                         public void MergeFinallyOrigins (UsageVector f_origins)
 791                         {
 792                                 Report.Debug (1, "  MERGING FINALLY ORIGIN", this);
 793
 794                                 reachability = Reachability.Never ();
 795
 796                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 797                                         Report.Debug (1, "  MERGING FINALLY ORIGIN", vector);
 798
 799                                         if (parameters != null)
 800                                                 parameters.And (vector.parameters);
 801
 802                                         Reachability.And (ref reachability, vector.Reachability, true);
 803                                 }
 804
 805                                 Report.Debug (1, "  MERGING FINALLY ORIGIN DONE", this);
 806                         }
 807
 808                         public void MergeBreakOrigins (UsageVector o_vectors)
 809                         {
 810                                 Report.Debug (1, "  MERGING BREAK ORIGINS", this);
 811
 812                                 if (o_vectors == null)
 813                                         return;
 814
 815                                 bool first = true;
 816
 817                                 for (UsageVector vector = o_vectors; vector != null;
 818                                      vector = vector.Next) {
 819                                         Report.Debug (1, "    MERGING BREAK ORIGIN", vector);
 820
 821                                         if (first) {
 822                                                 if (locals != null && vector.Locals != null)
 823                                                         locals.Or (vector.locals);
 824
 825                                                 if (parameters != null)
 826                                                         parameters.Or (vector.parameters);
 827                                                 first = false;
 828                                         } else {
 829                                                 if (locals != null && vector.Locals != null)
 830                                                         locals.And (vector.locals);
 831                                                 if (parameters != null)
 832                                                         parameters.And (vector.parameters);
 833                                         }
 834                                 }
 835
 836                                 Report.Debug (1, "  MERGING BREAK ORIGINS DONE", this);
 837                         }
 838
 839                         public void CheckOutParameters (FlowBranching branching)
 840                         {
 841                                 if (parameters != null)
 842                                         branching.CheckOutParameters (parameters, branching.Location);
 843                         }
 844
 845                         // <summary>
 846                         //   Performs an `or' operation on the locals and the parameters.
 847                         // </summary>
 848                         public void Or (UsageVector new_vector)
 849                         {
 850                                 IsDirty = true;
 851                                 locals.Or (new_vector.locals);
 852                                 if (parameters != null)
 853                                         parameters.Or (new_vector.parameters);
 854                         }
 855
 856                         // <summary>
 857                         //   Performs an `and' operation on the locals.
 858                         // </summary>
 859                         public void AndLocals (UsageVector new_vector)
 860                         {
 861                                 IsDirty = true;
 862                                 locals.And (new_vector.locals);
 863                         }
 864
 865                         public bool HasParameters {
 866                                 get {
 867                                         return parameters != null;
 868                                 }
 869                         }
 870
 871                         public bool HasLocals {
 872                                 get {
 873                                         return locals != null;
 874                                 }
 875                         }
 876
 877                         // <summary>
 878                         //   Returns a deep copy of the parameters.
 879                         // </summary>
 880                         public MyBitVector Parameters {
 881                                 get {
 882                                         if (parameters != null)
 883                                                 return parameters.Clone ();
 884                                         else
 885                                                 return null;
 886                                 }
 887                         }
 888
 889                         // <summary>
 890                         //   Returns a deep copy of the locals.
 891                         // </summary>
 892                         public MyBitVector Locals {
 893                                 get {
 894                                         if (locals != null)
 895                                         return locals.Clone ();
 896                                         else
 897                                                 return null;
 898                                 }
 899                         }
 900
 901                         public MyBitVector ParameterVector {
 902                                 get {
 903                                         return parameters;
 904                                 }
 905                         }
 906
 907                         public MyBitVector LocalVector {
 908                                 get {
 909                                         return locals;
 910                                 }
 911                         }
 912
 913                         //
 914                         // Debugging stuff.
 915                         //
 916
 917                         public override string ToString ()
 918                         {
 919                                 StringBuilder sb = new StringBuilder ();
 920
 921                                 sb.Append ("Vector (");
 922                                 sb.Append (Type);
 923                                 sb.Append (",");
 924                                 sb.Append (id);
 925                                 sb.Append (",");
 926                                 sb.Append (IsDirty);
 927                                 sb.Append (",");
 928                                 sb.Append (reachability);
 929                                 if (parameters != null) {
 930                                         sb.Append (" - ");
 931                                         sb.Append (parameters);
 932                                 }
 933                                 sb.Append (" - ");
 934                                 sb.Append (locals);
 935                                 sb.Append (")");
 936
 937                                 return sb.ToString ();
 938                         }
 939                 }
 940
 941                 // <summary>
 942                 //   Creates a new flow branching which is contained in `parent'.
 943                 //   You should only pass non-null for the `block' argument if this block
 944                 //   introduces any new variables - in this case, we need to create a new
 945                 //   usage vector with a different size than our parent's one.
 946                 // </summary>
 947                 protected FlowBranching (FlowBranching parent, BranchingType type, SiblingType stype,
 948                                          Block block, Location loc)
 949                 {
 950                         Parent = parent;
 951                         Block = block;
 952                         Location = loc;
 953                         Type = type;
 954                         id = ++next_id;
 955
 956                         UsageVector vector;
 957                         if (Block != null) {
 958                                 param_map = Block.ParameterMap;
 959                                 local_map = Block.LocalMap;
 960
 961                                 UsageVector parent_vector = parent != null ? parent.CurrentUsageVector : null;
 962                                 vector = new UsageVector (
 963                                         stype, parent_vector, Block, loc,
 964                                         param_map.Length, local_map.Length);
 965                         } else {
 966                                 param_map = Parent.param_map;
 967                                 local_map = Parent.local_map;
 968                                 vector = new UsageVector (
 969                                         stype, Parent.CurrentUsageVector, null, loc);
 970                         }
 971
 972                         AddSibling (vector);
 973                 }
 974
 975                 public abstract UsageVector CurrentUsageVector {
 976                         get;
 977                 }
 978
 979                 // <summary>
 980                 //   Creates a sibling of the current usage vector.
 981                 // </summary>
 982                 public virtual void CreateSibling (Block block, SiblingType type)
 983                 {
 984                         UsageVector vector = new UsageVector (
 985                                 type, Parent.CurrentUsageVector, block, Location);
 986                         AddSibling (vector);
 987
 988                         Report.Debug (1, "  CREATED SIBLING", CurrentUsageVector);
 989                 }
 990
 991                 public void CreateSibling ()
 992                 {
 993                         CreateSibling (null, SiblingType.Conditional);
 994                 }
 995
 996                 protected abstract void AddSibling (UsageVector uv);
 997
 998                 public virtual LabeledStatement LookupLabel (string name, Location loc)
 999                 {
1000                         if (Parent != null)
1001                                 return Parent.LookupLabel (name, loc);
1002
1003                         Report.Error (
1004                                 159, loc,
1005                                 "No such label `" + name + "' in this scope");
1006                         return null;
1007                 }
1008
1009                 public abstract void Label (UsageVector origin_vectors);
1010
1011                 // <summary>
1012                 //   Check whether all `out' parameters have been assigned.
1013                 // </summary>
1014                 public void CheckOutParameters (MyBitVector parameters, Location loc)
1015                 {
1016                         for (int i = 0; i < param_map.Count; i++) {
1017                                 VariableInfo var = param_map [i];
1018
1019                                 if (var == null)
1020                                         continue;
1021
1022                                 if (var.IsAssigned (parameters))
1023                                         continue;
1024
1025                                 Report.Error (177, loc, "The out parameter `" +
1026                                               var.Name + "' must be " +
1027                                               "assigned before control leaves the current method.");
1028                         }
1029                 }
1030
1031                 protected UsageVector Merge (UsageVector sibling_list)
1032                         {
1033                         if (sibling_list.Next == null)
1034                                 return sibling_list;
1035
1036                         MyBitVector locals = null;
1037                         MyBitVector parameters = null;
1038
1039                         Reachability reachability = null;
1040
1041                         Report.Debug (2, "  MERGING SIBLINGS", this, Name);
1042
1043                         for (UsageVector child = sibling_list; child != null; child = child.Next) {
1044                                 bool do_break = (Type != BranchingType.Switch) &&
1045                                         (Type != BranchingType.Loop);
1046
1047                                 Report.Debug (2, "    MERGING SIBLING   ", child,
1048                                               child.ParameterVector, child.LocalVector,
1049                                               reachability, child.Reachability, do_break);
1050
1051                                 Reachability.And (ref reachability, child.Reachability, do_break);
1052
1053                                 // A local variable is initialized after a flow branching if it
1054                                 // has been initialized in all its branches which do neither
1055                                 // always return or always throw an exception.
1056                                 //
1057                                 // If a branch may return, but does not always return, then we
1058                                 // can treat it like a never-returning branch here: control will
1059                                 // only reach the code position after the branching if we did not
1060                                 // return here.
1061                                 //
1062                                 // It's important to distinguish between always and sometimes
1063                                 // returning branches here:
1064                                 //
1065                                 //    1   int a;
1066                                 //    2   if (something) {
1067                                 //    3      return;
1068                                 //    4      a = 5;
1069                                 //    5   }
1070                                 //    6   Console.WriteLine (a);
1071                                 //
1072                                 // The if block in lines 3-4 always returns, so we must not look
1073                                 // at the initialization of `a' in line 4 - thus it'll still be
1074                                 // uninitialized in line 6.
1075                                 //
1076                                 // On the other hand, the following is allowed:
1077                                 //
1078                                 //    1   int a;
1079                                 //    2   if (something)
1080                                 //    3      a = 5;
1081                                 //    4   else
1082                                 //    5      return;
1083                                 //    6   Console.WriteLine (a);
1084                                 //
1085                                 // Here, `a' is initialized in line 3 and we must not look at
1086                                 // line 5 since it always returns.
1087                                 //
1088                                 bool do_break_2 = (child.Type != SiblingType.Block) &&
1089                                         (child.Type != SiblingType.SwitchSection);
1090                                 bool always_throws = (child.Type != SiblingType.Try) &&
1091                                         child.Reachability.AlwaysThrows;
1092                                 bool unreachable = always_throws ||
1093                                         (do_break_2 && child.Reachability.AlwaysBreaks) ||
1094                                         child.Reachability.AlwaysReturns ||
1095                                         child.Reachability.AlwaysHasBarrier;
1096
1097                                 Report.Debug (2, "    MERGING SIBLING #1", reachability,
1098                                               Type, child.Type, child.Reachability.IsUnreachable,
1099                                               do_break_2, always_throws, unreachable);
1100
1101                                 if (!unreachable && (child.LocalVector != null))
1102                                         MyBitVector.And (ref locals, child.LocalVector);
1103
1104                                 // An `out' parameter must be assigned in all branches which do
1105                                 // not always throw an exception.
1106                                 if ((child.ParameterVector != null) && !child.Reachability.AlwaysThrows)
1107                                         MyBitVector.And (ref parameters, child.ParameterVector);
1108
1109                                 Report.Debug (2, "    MERGING SIBLING #2", parameters, locals);
1110                         }
1111
1112                         if (reachability == null)
1113                                 reachability = Reachability.Never ();
1114
1115                         Report.Debug (2, "  MERGING SIBLINGS DONE", parameters, locals,
1116                                       reachability, Infinite);
1117
1118                         return new UsageVector (
1119                                 parameters, locals, reachability, null, Location);
1120                 }
1121
1122                 protected abstract UsageVector Merge ();
1123
1124                 // <summary>
1125                 //   Merge a child branching.
1126                 // </summary>
1127                 public UsageVector MergeChild (FlowBranching child)
1128                 {
1129                         return CurrentUsageVector.MergeChild (child);
1130                 }
1131
1132                 // <summary>
1133                 //   Does the toplevel merging.
1134                 // </summary>
1135                 public Reachability MergeTopBlock ()
1136                 {
1137                         if ((Type != BranchingType.Block) || (Block == null))
1138                                 throw new NotSupportedException ();
1139
1140                         UsageVector vector = new UsageVector (
1141                                 SiblingType.Block, null, Block, Location,
1142                                 param_map.Length, local_map.Length);
1143
1144                         UsageVector result = vector.MergeChild (this);
1145
1146                         Report.Debug (4, "MERGE TOP BLOCK", Location, vector, result.Reachability);
1147
1148                         if ((vector.Reachability.Throws != FlowReturns.Always) &&
1149                             (vector.Reachability.Barrier != FlowReturns.Always))
1150                                 CheckOutParameters (vector.Parameters, Location);
1151
1152                         return result.Reachability;
1153                 }
1154
1155                 //
1156                 // Checks whether we're in a `try' block.
1157                 //
1158                 public virtual bool InTryOrCatch (bool is_return)
1159                 {
1160                         if ((Block != null) && Block.IsDestructor)
1161                                 return true;
1162                         else if (!is_return &&
1163                             ((Type == BranchingType.Loop) || (Type == BranchingType.Switch)))
1164                                 return false;
1165                         else if (Parent != null)
1166                                 return Parent.InTryOrCatch (is_return);
1167                         else
1168                                 return false;
1169                 }
1170
1171                 //
1172                 // Checks whether we're in a `catch' block.
1173                 //
1174                 public virtual bool InCatch ()
1175                 {
1176                         if (Parent != null)
1177                                 return Parent.InCatch ();
1178                         else
1179                                 return false;
1180                 }
1181
1182                 //
1183                 // Checks whether we're in a `finally' block.
1184                 //
1185                 public virtual bool InFinally (bool is_return)
1186                 {
1187                         if (!is_return &&
1188                             ((Type == BranchingType.Loop) || (Type == BranchingType.Switch)))
1189                                 return false;
1190                         else if (Parent != null)
1191                                 return Parent.InFinally (is_return);
1192                         else
1193                                 return false;
1194                 }
1195
1196                 public virtual bool InLoop ()
1197                 {
1198                         if (Type == BranchingType.Loop)
1199                                 return true;
1200                         else if (Parent != null)
1201                                 return Parent.InLoop ();
1202                         else
1203                                 return false;
1204                 }
1205
1206                 public virtual bool InSwitch ()
1207                 {
1208                         if (Type == BranchingType.Switch)
1209                                 return true;
1210                         else if (Parent != null)
1211                                 return Parent.InSwitch ();
1212                         else
1213                                 return false;
1214                 }
1215
1216                 public virtual bool BreakCrossesTryCatchBoundary ()
1217                 {
1218                         if ((Type == BranchingType.Loop) || (Type == BranchingType.Switch))
1219                                 return false;
1220                         else if (Parent != null)
1221                                 return Parent.BreakCrossesTryCatchBoundary ();
1222                         else
1223                                 return false;
1224                 }
1225
1226                 public virtual void AddFinallyVector (UsageVector vector)
1227                 {
1228                         if (Parent != null)
1229                                 Parent.AddFinallyVector (vector);
1230                         else if ((Block == null) || !Block.IsDestructor)
1231                                 throw new NotSupportedException ();
1232                 }
1233
1234                 public virtual void AddBreakVector (UsageVector vector)
1235                 {
1236                         if (Parent != null)
1237                                 Parent.AddBreakVector (vector);
1238                         else if ((Block == null) || !Block.IsDestructor)
1239                                 throw new NotSupportedException ();
1240                 }
1241
1242                 public virtual void StealFinallyClauses (ref ArrayList list)
1243                 {
1244                         if (Parent != null)
1245                                 Parent.StealFinallyClauses (ref list);
1246                 }
1247
1248                 public bool IsAssigned (VariableInfo vi)
1249                 {
1250                         return CurrentUsageVector.IsAssigned (vi);
1251                 }
1252
1253                 public bool IsFieldAssigned (VariableInfo vi, string field_name)
1254                 {
1255                         if (CurrentUsageVector.IsAssigned (vi))
1256                                 return true;
1257
1258                         return CurrentUsageVector.IsFieldAssigned (vi, field_name);
1259                 }
1260
1261                 public void SetAssigned (VariableInfo vi)
1262                 {
1263                         CurrentUsageVector.SetAssigned (vi);
1264                 }
1265
1266                 public void SetFieldAssigned (VariableInfo vi, string name)
1267                 {
1268                         CurrentUsageVector.SetFieldAssigned (vi, name);
1269                 }
1270
1271                 public override string ToString ()
1272                 {
1273                         StringBuilder sb = new StringBuilder ();
1274                         sb.Append (GetType ());
1275                         sb.Append (" (");
1276
1277                         sb.Append (id);
1278                         sb.Append (",");
1279                         sb.Append (Type);
1280                         if (Block != null) {
1281                                 sb.Append (" - ");
1282                                 sb.Append (Block.ID);
1283                                 sb.Append (" - ");
1284                                 sb.Append (Block.StartLocation);
1285                         }
1286                         sb.Append (" - ");
1287                         // sb.Append (Siblings.Length);
1288                         // sb.Append (" - ");
1289                         sb.Append (CurrentUsageVector);
1290                         sb.Append (")");
1291                         return sb.ToString ();
1292                 }
1293
1294                 public string Name {
1295                         get {
1296                                 return String.Format ("{0} ({1}:{2}:{3})",
1297                                                       GetType (), id, Type, Location);
1298                         }
1299                 }
1300         }
1301
1302         public class FlowBranchingBlock : FlowBranching
1303         {
1304                 UsageVector sibling_list = null;
1305
1306                 public FlowBranchingBlock (FlowBranching parent, BranchingType type,
1307                                            SiblingType stype, Block block, Location loc)
1308                         : base (parent, type, stype, block, loc)
1309                 { }
1310
1311                 public override UsageVector CurrentUsageVector {
1312                         get { return sibling_list; }
1313                 }
1314
1315                 protected override void AddSibling (UsageVector sibling)
1316                 {
1317                         sibling.Next = sibling_list;
1318                         sibling_list = sibling;
1319                 }
1320
1321                 public override LabeledStatement LookupLabel (string name, Location loc)
1322                 {
1323                         if (Block == null)
1324                                 return base.LookupLabel (name, loc);
1325
1326                         LabeledStatement s = Block.LookupLabel (name);
1327                         if (s != null)
1328                                 return s;
1329
1330                         return base.LookupLabel (name, loc);
1331                 }
1332
1333                 public override void Label (UsageVector origin_vectors)
1334                 {
1335                         if (!CurrentUsageVector.Reachability.IsUnreachable) {
1336                                 UsageVector vector = CurrentUsageVector.Clone ();
1337                                 vector.Next = origin_vectors;
1338                                 origin_vectors = vector;
1339                 }
1340
1341                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1342                 }
1343
1344                 protected override UsageVector Merge ()
1345                 {
1346                         return Merge (sibling_list);
1347                 }
1348         }
1349
1350         public class FlowBranchingLoop : FlowBranchingBlock
1351         {
1352                 UsageVector break_origins;
1353
1354                 public FlowBranchingLoop (FlowBranching parent, Block block, Location loc)
1355                         : base (parent, BranchingType.Loop, SiblingType.Conditional, block, loc)
1356                 { }
1357
1358                 public override void AddBreakVector (UsageVector vector)
1359                 {
1360                         vector = vector.Clone ();
1361                         vector.Next = break_origins;
1362                         break_origins = vector;
1363                 }
1364
1365                 protected override UsageVector Merge ()
1366                 {
1367                         UsageVector vector = base.Merge ();
1368
1369                         vector.MergeBreakOrigins (break_origins);
1370
1371                         return vector;
1372                 }
1373         }
1374
1375         public class FlowBranchingException : FlowBranching
1376         {
1377                 ExceptionStatement stmt;
1378                 UsageVector current_vector;
1379                 UsageVector catch_vectors;
1380                 UsageVector finally_vector;
1381                 UsageVector finally_origins;
1382                 bool emit_finally;
1383                 bool in_try;
1384
1385                 public FlowBranchingException (FlowBranching parent,
1386                                                ExceptionStatement stmt)
1387                         : base (parent, BranchingType.Exception, SiblingType.Try,
1388                                 null, stmt.loc)
1389                 {
1390                         this.stmt = stmt;
1391                         this.emit_finally = true;
1392                 }
1393
1394                 protected override void AddSibling (UsageVector sibling)
1395                 {
1396                         if (sibling.Type == SiblingType.Try) {
1397                                 sibling.Next = catch_vectors;
1398                                 catch_vectors = sibling;
1399                                 in_try = true;
1400                         } else if (sibling.Type == SiblingType.Catch) {
1401                                 sibling.Next = catch_vectors;
1402                                 catch_vectors = sibling;
1403                                 in_try = false;
1404                         } else if (sibling.Type == SiblingType.Finally) {
1405                                 sibling.MergeFinallyOrigins (finally_origins);
1406                                 finally_vector = sibling;
1407                                 in_try = false;
1408                         } else
1409                                 throw new InvalidOperationException ();
1410
1411                         current_vector = sibling;
1412                 }
1413
1414                 public override UsageVector CurrentUsageVector {
1415                         get { return current_vector; }
1416                 }
1417
1418                 public override bool InTryOrCatch (bool is_return)
1419                 {
1420                         return finally_vector == null;
1421                 }
1422
1423                 public override bool InCatch ()
1424                 {
1425                         return !in_try && (finally_vector == null);
1426                 }
1427
1428                 public override bool InFinally (bool is_return)
1429                 {
1430                         return finally_vector != null;
1431                 }
1432
1433                 public override bool BreakCrossesTryCatchBoundary ()
1434                 {
1435                         return true;
1436                 }
1437
1438                 public override void AddFinallyVector (UsageVector vector)
1439                 {
1440                         vector = vector.Clone ();
1441                         vector.Next = finally_origins;
1442                         finally_origins = vector;
1443                 }
1444
1445                 public override void StealFinallyClauses (ref ArrayList list)
1446                 {
1447                         if (list == null)
1448                                 list = new ArrayList ();
1449                         list.Add (stmt);
1450                         emit_finally = false;
1451                         base.StealFinallyClauses (ref list);
1452                 }
1453
1454                 public bool EmitFinally {
1455                         get { return emit_finally; }
1456                 }
1457
1458                 public override LabeledStatement LookupLabel (string name, Location loc)
1459                 {
1460                         if (current_vector.Block == null)
1461                                 return base.LookupLabel (name, loc);
1462
1463                         LabeledStatement s = current_vector.Block.LookupLabel (name);
1464                         if (s != null)
1465                                 return s;
1466
1467                         if (finally_vector != null) {
1468                                 Report.Error (
1469                                         157, loc, "Control can not leave the body " +
1470                                         "of the finally block");
1471                                 return null;
1472                         }
1473
1474                         return base.LookupLabel (name, loc);
1475                 }
1476
1477                 public override void Label (UsageVector origin_vectors)
1478                 {
1479                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1480                 }
1481
1482                 protected override UsageVector Merge ()
1483                 {
1484                         UsageVector vector = Merge (catch_vectors);
1485
1486                         vector.MergeFinally (this, finally_vector, finally_origins);
1487
1488                         return vector;
1489                 }
1490         }
1491
1492         // <summary>
1493         //   This is used by the flow analysis code to keep track of the type of local variables
1494         //   and variables.
1495         //
1496         //   The flow code uses a BitVector to keep track of whether a variable has been assigned
1497         //   or not.  This is easy for fundamental types (int, char etc.) or reference types since
1498         //   you can only assign the whole variable as such.
1499         //
1500         //   For structs, we also need to keep track of all its fields.  To do this, we allocate one
1501         //   bit for the struct itself (it's used if you assign/access the whole struct) followed by
1502         //   one bit for each of its fields.
1503         //
1504         //   This class computes this `layout' for each type.
1505         // </summary>
1506         public class TypeInfo
1507         {
1508                 public readonly Type Type;
1509
1510                 // <summary>
1511                 //   Total number of bits a variable of this type consumes in the flow vector.
1512                 // </summary>
1513                 public readonly int TotalLength;
1514
1515                 // <summary>
1516                 //   Number of bits the simple fields of a variable of this type consume
1517                 //   in the flow vector.
1518                 // </summary>
1519                 public readonly int Length;
1520
1521                 // <summary>
1522                 //   This is only used by sub-structs.
1523                 // </summary>
1524                 public readonly int Offset;
1525
1526                 // <summary>
1527                 //   If this is a struct.
1528                 // </summary>
1529                 public readonly bool IsStruct;
1530
1531                 // <summary>
1532                 //   If this is a struct, all fields which are structs theirselves.
1533                 // </summary>
1534                 public TypeInfo[] SubStructInfo;
1535
1536                 protected readonly StructInfo struct_info;
1537                 private static Hashtable type_hash = new Hashtable ();
1538
1539                 public static TypeInfo GetTypeInfo (Type type)
1540                 {
1541                         TypeInfo info = (TypeInfo) type_hash [type];
1542                         if (info != null)
1543                                 return info;
1544
1545                         info = new TypeInfo (type);
1546                         type_hash.Add (type, info);
1547                         return info;
1548                 }
1549
1550                 public static TypeInfo GetTypeInfo (TypeContainer tc)
1551                 {
1552                         TypeInfo info = (TypeInfo) type_hash [tc.TypeBuilder];
1553                         if (info != null)
1554                                 return info;
1555
1556                         info = new TypeInfo (tc);
1557                         type_hash.Add (tc.TypeBuilder, info);
1558                         return info;
1559                 }
1560
1561                 private TypeInfo (Type type)
1562                 {
1563                         this.Type = type;
1564
1565                         struct_info = StructInfo.GetStructInfo (type);
1566                         if (struct_info != null) {
1567                                 Length = struct_info.Length;
1568                                 TotalLength = struct_info.TotalLength;
1569                                 SubStructInfo = struct_info.StructFields;
1570                                 IsStruct = true;
1571                         } else {
1572                                 Length = 0;
1573                                 TotalLength = 1;
1574                                 IsStruct = false;
1575                         }
1576                 }
1577
1578                 private TypeInfo (TypeContainer tc)
1579                 {
1580                         this.Type = tc.TypeBuilder;
1581
1582                         struct_info = StructInfo.GetStructInfo (tc);
1583                         if (struct_info != null) {
1584                                 Length = struct_info.Length;
1585                                 TotalLength = struct_info.TotalLength;
1586                                 SubStructInfo = struct_info.StructFields;
1587                                 IsStruct = true;
1588                         } else {
1589                                 Length = 0;
1590                                 TotalLength = 1;
1591                                 IsStruct = false;
1592                         }
1593                 }
1594
1595                 protected TypeInfo (StructInfo struct_info, int offset)
1596                 {
1597                         this.struct_info = struct_info;
1598                         this.Offset = offset;
1599                         this.Length = struct_info.Length;
1600                         this.TotalLength = struct_info.TotalLength;
1601                         this.SubStructInfo = struct_info.StructFields;
1602                         this.Type = struct_info.Type;
1603                         this.IsStruct = true;
1604                 }
1605
1606                 public int GetFieldIndex (string name)
1607                 {
1608                         if (struct_info == null)
1609                                 return 0;
1610
1611                         return struct_info [name];
1612                 }
1613
1614                 public TypeInfo GetSubStruct (string name)
1615                 {
1616                         if (struct_info == null)
1617                                 return null;
1618
1619                         return struct_info.GetStructField (name);
1620                 }
1621
1622                 // <summary>
1623                 //   A struct's constructor must always assign all fields.
1624                 //   This method checks whether it actually does so.
1625                 // </summary>
1626                 public bool IsFullyInitialized (FlowBranching branching, VariableInfo vi, Location loc)
1627                 {
1628                         if (struct_info == null)
1629                                 return true;
1630
1631                         bool ok = true;
1632                         for (int i = 0; i < struct_info.Count; i++) {
1633                                 FieldInfo field = struct_info.Fields [i];
1634
1635                                 if (!branching.IsFieldAssigned (vi, field.Name)) {
1636                                         Report.Error (171, loc,
1637                                                       "Field `" + TypeManager.CSharpName (Type) +
1638                                                       "." + field.Name + "' must be fully initialized " +
1639                                                       "before control leaves the constructor");
1640                                         ok = false;
1641                                 }
1642                         }
1643
1644                         return ok;
1645                 }
1646
1647                 public override string ToString ()
1648                 {
1649                         return String.Format ("TypeInfo ({0}:{1}:{2}:{3})",
1650                                               Type, Offset, Length, TotalLength);
1651                 }
1652
1653                 protected class StructInfo {
1654                         public readonly Type Type;
1655                         public readonly FieldInfo[] Fields;
1656                         public readonly TypeInfo[] StructFields;
1657                         public readonly int Count;
1658                         public readonly int CountPublic;
1659                         public readonly int CountNonPublic;
1660                         public readonly int Length;
1661                         public readonly int TotalLength;
1662                         public readonly bool HasStructFields;
1663
1664                         private static Hashtable field_type_hash = new Hashtable ();
1665                         private Hashtable struct_field_hash;
1666                         private Hashtable field_hash;
1667
1668                         protected bool InTransit = false;
1669
1670                         // Private constructor.  To save memory usage, we only need to create one instance
1671                         // of this class per struct type.
1672                         private StructInfo (Type type)
1673                         {
1674                                 this.Type = type;
1675
1676                                 field_type_hash.Add (type, this);
1677
1678                                 if (type is TypeBuilder) {
1679                                         TypeContainer tc = TypeManager.LookupTypeContainer (type);
1680
1681                                         ArrayList fields = tc.Fields;
1682
1683                                         ArrayList public_fields = new ArrayList ();
1684                                         ArrayList non_public_fields = new ArrayList ();
1685
1686                                         if (fields != null) {
1687                                                 foreach (Field field in fields) {
1688                                                         if ((field.ModFlags & Modifiers.STATIC) != 0)
1689                                                                 continue;
1690                                                         if ((field.ModFlags & Modifiers.PUBLIC) != 0)
1691                                                                 public_fields.Add (field.FieldBuilder);
1692                                                         else
1693                                                                 non_public_fields.Add (field.FieldBuilder);
1694                                                 }
1695                                         }
1696
1697                                         CountPublic = public_fields.Count;
1698                                         CountNonPublic = non_public_fields.Count;
1699                                         Count = CountPublic + CountNonPublic;
1700
1701                                         Fields = new FieldInfo [Count];
1702                                         public_fields.CopyTo (Fields, 0);
1703                                         non_public_fields.CopyTo (Fields, CountPublic);
1704                                 } else if (type is GenericTypeParameterBuilder) {
1705                                         CountPublic = CountNonPublic = Count = 0;
1706
1707                                         Fields = new FieldInfo [0];
1708                                 } else {
1709                                         FieldInfo[] public_fields = type.GetFields (
1710                                                 BindingFlags.Instance|BindingFlags.Public);
1711                                         FieldInfo[] non_public_fields = type.GetFields (
1712                                                 BindingFlags.Instance|BindingFlags.NonPublic);
1713
1714                                         CountPublic = public_fields.Length;
1715                                         CountNonPublic = non_public_fields.Length;
1716                                         Count = CountPublic + CountNonPublic;
1717
1718                                         Fields = new FieldInfo [Count];
1719                                         public_fields.CopyTo (Fields, 0);
1720                                         non_public_fields.CopyTo (Fields, CountPublic);
1721                                 }
1722
1723                                 struct_field_hash = new Hashtable ();
1724                                 field_hash = new Hashtable ();
1725
1726                                 Length = 0;
1727                                 StructFields = new TypeInfo [Count];
1728                                 StructInfo[] sinfo = new StructInfo [Count];
1729
1730                                 InTransit = true;
1731
1732                                 for (int i = 0; i < Count; i++) {
1733                                         FieldInfo field = (FieldInfo) Fields [i];
1734
1735                                         sinfo [i] = GetStructInfo (field.FieldType);
1736                                         if (sinfo [i] == null)
1737                                                 field_hash.Add (field.Name, ++Length);
1738                                         else if (sinfo [i].InTransit) {
1739                                                 Report.Error (523, String.Format (
1740                                                                       "Struct member '{0}.{1}' of type '{2}' causes " +
1741                                                                       "a cycle in the structure layout",
1742                                                                       type, field.Name, sinfo [i].Type));
1743                                                 sinfo [i] = null;
1744                                                 return;
1745                                         }
1746                                 }
1747
1748                                 InTransit = false;
1749
1750                                 TotalLength = Length + 1;
1751                                 for (int i = 0; i < Count; i++) {
1752                                         FieldInfo field = (FieldInfo) Fields [i];
1753
1754                                         if (sinfo [i] == null)
1755                                                 continue;
1756
1757                                         field_hash.Add (field.Name, TotalLength);
1758
1759                                         HasStructFields = true;
1760                                         StructFields [i] = new TypeInfo (sinfo [i], TotalLength);
1761                                         struct_field_hash.Add (field.Name, StructFields [i]);
1762                                         TotalLength += sinfo [i].TotalLength;
1763                                 }
1764                         }
1765
1766                         public int this [string name] {
1767                                 get {
1768                                         if (field_hash.Contains (name))
1769                                                 return (int) field_hash [name];
1770                                         else
1771                                                 return 0;
1772                                 }
1773                         }
1774
1775                         public TypeInfo GetStructField (string name)
1776                         {
1777                                 return (TypeInfo) struct_field_hash [name];
1778                         }
1779
1780                         public static StructInfo GetStructInfo (Type type)
1781                         {
1782                                 if (!TypeManager.IsValueType (type) || TypeManager.IsEnumType (type) ||
1783                                     TypeManager.IsBuiltinType (type))
1784                                         return null;
1785
1786                                 StructInfo info = (StructInfo) field_type_hash [type];
1787                                 if (info != null)
1788                                         return info;
1789
1790                                 return new StructInfo (type);
1791                         }
1792
1793                         public static StructInfo GetStructInfo (TypeContainer tc)
1794                         {
1795                                 StructInfo info = (StructInfo) field_type_hash [tc.TypeBuilder];
1796                                 if (info != null)
1797                                         return info;
1798
1799                                 return new StructInfo (tc.TypeBuilder);
1800                         }
1801                 }
1802         }
1803
1804         // <summary>
1805         //   This is used by the flow analysis code to store information about a single local variable
1806         //   or parameter.  Depending on the variable's type, we need to allocate one or more elements
1807         //   in the BitVector - if it's a fundamental or reference type, we just need to know whether
1808         //   it has been assigned or not, but for structs, we need this information for each of its fields.
1809         // </summary>
1810         public class VariableInfo {
1811                 public readonly string Name;
1812                 public readonly TypeInfo TypeInfo;
1813
1814                 // <summary>
1815                 //   The bit offset of this variable in the flow vector.
1816                 // </summary>
1817                 public readonly int Offset;
1818
1819                 // <summary>
1820                 //   The number of bits this variable needs in the flow vector.
1821                 //   The first bit always specifies whether the variable as such has been assigned while
1822                 //   the remaining bits contain this information for each of a struct's fields.
1823                 // </summary>
1824                 public readonly int Length;
1825
1826                 // <summary>
1827                 //   If this is a parameter of local variable.
1828                 // </summary>
1829                 public readonly bool IsParameter;
1830
1831                 public readonly LocalInfo LocalInfo;
1832                 public readonly int ParameterIndex;
1833
1834                 readonly VariableInfo Parent;
1835                 VariableInfo[] sub_info;
1836
1837                 protected VariableInfo (string name, Type type, int offset)
1838                 {
1839                         this.Name = name;
1840                         this.Offset = offset;
1841                         this.TypeInfo = TypeInfo.GetTypeInfo (type);
1842
1843                         Length = TypeInfo.TotalLength;
1844
1845                         Initialize ();
1846                 }
1847
1848                 protected VariableInfo (VariableInfo parent, TypeInfo type)
1849                 {
1850                         this.Name = parent.Name;
1851                         this.TypeInfo = type;
1852                         this.Offset = parent.Offset + type.Offset;
1853                         this.Parent = parent;
1854                         this.Length = type.TotalLength;
1855
1856                         this.IsParameter = parent.IsParameter;
1857                         this.LocalInfo = parent.LocalInfo;
1858                         this.ParameterIndex = parent.ParameterIndex;
1859
1860                         Initialize ();
1861                 }
1862
1863                 protected void Initialize ()
1864                 {
1865                         TypeInfo[] sub_fields = TypeInfo.SubStructInfo;
1866                         if (sub_fields != null) {
1867                                 sub_info = new VariableInfo [sub_fields.Length];
1868                                 for (int i = 0; i < sub_fields.Length; i++) {
1869                                         if (sub_fields [i] != null)
1870                                                 sub_info [i] = new VariableInfo (this, sub_fields [i]);
1871                                 }
1872                         } else
1873                                 sub_info = new VariableInfo [0];
1874                 }
1875
1876                 public VariableInfo (LocalInfo local_info, int offset)
1877                         : this (local_info.Name, local_info.VariableType, offset)
1878                 {
1879                         this.LocalInfo = local_info;
1880                         this.IsParameter = false;
1881                 }
1882
1883                 public VariableInfo (string name, Type type, int param_idx, int offset)
1884                         : this (name, type, offset)
1885                 {
1886                         this.ParameterIndex = param_idx;
1887                         this.IsParameter = true;
1888                 }
1889
1890                 public bool IsAssigned (EmitContext ec)
1891                 {
1892                         return !ec.DoFlowAnalysis || ec.CurrentBranching.IsAssigned (this);
1893                 }
1894
1895                 public bool IsAssigned (EmitContext ec, Location loc)
1896                 {
1897                         if (IsAssigned (ec))
1898                                 return true;
1899
1900                         Report.Error (165, loc,
1901                                       "Use of unassigned local variable `" + Name + "'");
1902                         ec.CurrentBranching.SetAssigned (this);
1903                         return false;
1904                 }
1905
1906                 public bool IsAssigned (MyBitVector vector)
1907                 {
1908                         if (vector [Offset])
1909                                 return true;
1910
1911                         for (VariableInfo parent = Parent; parent != null; parent = parent.Parent)
1912                                 if (vector [parent.Offset])
1913                                         return true;
1914
1915                         // Return unless this is a struct.
1916                         if (!TypeInfo.IsStruct)
1917                                 return false;
1918
1919                         // Ok, so each field must be assigned.
1920                         for (int i = 0; i < TypeInfo.Length; i++) {
1921                                 if (!vector [Offset + i + 1])
1922                                         return false;
1923                         }
1924
1925                         // Ok, now check all fields which are structs.
1926                         for (int i = 0; i < sub_info.Length; i++) {
1927                                 VariableInfo sinfo = sub_info [i];
1928                                 if (sinfo == null)
1929                                         continue;
1930
1931                                 if (!sinfo.IsAssigned (vector))
1932                                         return false;
1933                         }
1934
1935                         vector [Offset] = true;
1936                         return true;
1937                 }
1938
1939                 public void SetAssigned (EmitContext ec)
1940                 {
1941                         if (ec.DoFlowAnalysis)
1942                                 ec.CurrentBranching.SetAssigned (this);
1943                 }
1944
1945                 public void SetAssigned (MyBitVector vector)
1946                 {
1947                         vector [Offset] = true;
1948                 }
1949
1950                 public bool IsFieldAssigned (EmitContext ec, string name, Location loc)
1951                 {
1952                         if (!ec.DoFlowAnalysis || ec.CurrentBranching.IsFieldAssigned (this, name))
1953                                 return true;
1954
1955                         Report.Error (170, loc,
1956                                       "Use of possibly unassigned field `" + name + "'");
1957                         ec.CurrentBranching.SetFieldAssigned (this, name);
1958                         return false;
1959                 }
1960
1961                 public bool IsFieldAssigned (MyBitVector vector, string field_name)
1962                 {
1963                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1964
1965                         if (field_idx == 0)
1966                                 return true;
1967
1968                         return vector [Offset + field_idx];
1969                 }
1970
1971                 public void SetFieldAssigned (EmitContext ec, string name)
1972                 {
1973                         if (ec.DoFlowAnalysis)
1974                                 ec.CurrentBranching.SetFieldAssigned (this, name);
1975                 }
1976
1977                 public void SetFieldAssigned (MyBitVector vector, string field_name)
1978                 {
1979                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1980
1981                         if (field_idx == 0)
1982                                 return;
1983
1984                         vector [Offset + field_idx] = true;
1985                 }
1986
1987                 public VariableInfo GetSubStruct (string name)
1988                 {
1989                         TypeInfo type = TypeInfo.GetSubStruct (name);
1990
1991                         if (type == null)
1992                                 return null;
1993
1994                         return new VariableInfo (this, type);
1995                 }
1996
1997                 public override string ToString ()
1998                 {
1999                         return String.Format ("VariableInfo ({0}:{1}:{2}:{3}:{4})",
2000                                               Name, TypeInfo, Offset, Length, IsParameter);
2001                 }
2002         }
2003
2004         // <summary>
2005         //   This is used by the flow code to hold the `layout' of the flow vector for
2006         //   all locals and all parameters (ie. we create one instance of this class for the
2007         //   locals and another one for the params).
2008         // </summary>
2009         public class VariableMap {
2010                 // <summary>
2011                 //   The number of variables in the map.
2012                 // </summary>
2013                 public readonly int Count;
2014
2015                 // <summary>
2016                 //   Total length of the flow vector for this map.
2017                 // <summary>
2018                 public readonly int Length;
2019
2020                 VariableInfo[] map;
2021
2022                 public VariableMap (InternalParameters ip)
2023                 {
2024                         Count = ip != null ? ip.Count : 0;
2025
2026                         // Dont bother allocating anything!
2027                         if (Count == 0)
2028                                 return;
2029
2030                         Length = 0;
2031
2032                         for (int i = 0; i < Count; i++) {
2033                                 Parameter.Modifier mod = ip.ParameterModifier (i);
2034
2035                                 if ((mod & Parameter.Modifier.OUT) == 0)
2036                                         continue;
2037
2038                                 // Dont allocate till we find an out var.
2039                                 if (map == null)
2040                                         map = new VariableInfo [Count];
2041
2042                                 map [i] = new VariableInfo (ip.ParameterName (i),
2043                                         TypeManager.GetElementType (ip.ParameterType (i)), i, Length);
2044
2045                                 Length += map [i].Length;
2046                         }
2047                 }
2048
2049                 public VariableMap (LocalInfo[] locals)
2050                         : this (null, locals)
2051                 { }
2052
2053                 public VariableMap (VariableMap parent, LocalInfo[] locals)
2054                 {
2055                         int offset = 0, start = 0;
2056                         if (parent != null && parent.map != null) {
2057                                 offset = parent.Length;
2058                                 start = parent.Count;
2059                         }
2060
2061                         Count = locals.Length + start;
2062
2063                         if (Count == 0)
2064                                 return;
2065
2066                         map = new VariableInfo [Count];
2067                         Length = offset;
2068
2069                         if (parent != null && parent.map != null) {
2070                                 parent.map.CopyTo (map, 0);
2071                         }
2072
2073                         for (int i = start; i < Count; i++) {
2074                                 LocalInfo li = locals [i-start];
2075
2076                                 if (li.VariableType == null)
2077                                         continue;
2078
2079                                 map [i] = li.VariableInfo = new VariableInfo (li, Length);
2080                                 Length += map [i].Length;
2081                         }
2082                 }
2083
2084                 // <summary>
2085                 //   Returns the VariableInfo for variable @index or null if we don't need to
2086                 //   compute assignment info for this variable.
2087                 // </summary>
2088                 public VariableInfo this [int index] {
2089                         get {
2090                                 if (map == null)
2091                                         return null;
2092
2093                                 return map [index];
2094                         }
2095                 }
2096
2097                 public override string ToString ()
2098                 {
2099                         return String.Format ("VariableMap ({0}:{1})", Count, Length);
2100                 }
2101         }
2102
2103         // <summary>
2104         //   This is a special bit vector which can inherit from another bit vector doing a
2105         //   copy-on-write strategy.  The inherited vector may have a smaller size than the
2106         //   current one.
2107         // </summary>
2108         public class MyBitVector {
2109                 public readonly int Count;
2110                 public readonly MyBitVector InheritsFrom;
2111
2112                 bool is_dirty;
2113                 BitArray vector;
2114
2115                 public MyBitVector (int Count)
2116                         : this (null, Count)
2117                 { }
2118
2119                 public MyBitVector (MyBitVector InheritsFrom, int Count)
2120                 {
2121                         this.InheritsFrom = InheritsFrom;
2122                         this.Count = Count;
2123                 }
2124
2125                 // <summary>
2126                 //   Checks whether this bit vector has been modified.  After setting this to true,
2127                 //   we won't use the inherited vector anymore, but our own copy of it.
2128                 // </summary>
2129                 public bool IsDirty {
2130                         get {
2131                                 return is_dirty;
2132                         }
2133
2134                         set {
2135                                 if (!is_dirty)
2136                                         initialize_vector ();
2137                         }
2138                 }
2139
2140                 // <summary>
2141                 //   Get/set bit `index' in the bit vector.
2142                 // </summary>
2143                 public bool this [int index]
2144                 {
2145                         get {
2146                                 if (index > Count)
2147                                         throw new ArgumentOutOfRangeException ();
2148
2149                                 // We're doing a "copy-on-write" strategy here; as long
2150                                 // as nobody writes to the array, we can use our parent's
2151                                 // copy instead of duplicating the vector.
2152
2153                                 if (vector != null)
2154                                         return vector [index];
2155                                 else if (InheritsFrom != null) {
2156                                         BitArray inherited = InheritsFrom.Vector;
2157
2158                                         if (index < inherited.Count)
2159                                                 return inherited [index];
2160                                         else
2161                                                 return false;
2162                                 } else
2163                                         return false;
2164                         }
2165
2166                         set {
2167                                 if (index > Count)
2168                                         throw new ArgumentOutOfRangeException ();
2169
2170                                 // Only copy the vector if we're actually modifying it.
2171
2172                                 if (this [index] != value) {
2173                                         initialize_vector ();
2174
2175                                         vector [index] = value;
2176                                 }
2177                         }
2178                 }
2179
2180                 // <summary>
2181                 //   If you explicitly convert the MyBitVector to a BitArray, you will get a deep
2182                 //   copy of the bit vector.
2183                 // </summary>
2184                 public static explicit operator BitArray (MyBitVector vector)
2185                 {
2186                         vector.initialize_vector ();
2187                         return vector.Vector;
2188                 }
2189
2190                 // <summary>
2191                 //   Performs an `or' operation on the bit vector.  The `new_vector' may have a
2192                 //   different size than the current one.
2193                 // </summary>
2194                 public void Or (MyBitVector new_vector)
2195                 {
2196                         BitArray new_array = new_vector.Vector;
2197
2198                         initialize_vector ();
2199
2200                         int upper;
2201                         if (vector.Count < new_array.Count)
2202                                 upper = vector.Count;
2203                         else
2204                                 upper = new_array.Count;
2205
2206                         for (int i = 0; i < upper; i++)
2207                                 vector [i] = vector [i] | new_array [i];
2208                 }
2209
2210                 // <summary>
2211                 //   Perfonrms an `and' operation on the bit vector.  The `new_vector' may have
2212                 //   a different size than the current one.
2213                 // </summary>
2214                 public void And (MyBitVector new_vector)
2215                 {
2216                         BitArray new_array = new_vector.Vector;
2217
2218                         initialize_vector ();
2219
2220                         int lower, upper;
2221                         if (vector.Count < new_array.Count)
2222                                 lower = upper = vector.Count;
2223                         else {
2224                                 lower = new_array.Count;
2225                                 upper = vector.Count;
2226                         }
2227
2228                         for (int i = 0; i < lower; i++)
2229                                 vector [i] = vector [i] & new_array [i];
2230
2231                         for (int i = lower; i < upper; i++)
2232                                 vector [i] = false;
2233                 }
2234
2235                 public static void And (ref MyBitVector target, MyBitVector vector)
2236                 {
2237                         if (target != null)
2238                                 target.And (vector);
2239                         else
2240                                 target = vector.Clone ();
2241                 }
2242
2243                 public static void Or (ref MyBitVector target, MyBitVector vector)
2244                 {
2245                         if (target != null)
2246                                 target.Or (vector);
2247                         else
2248                                 target = vector.Clone ();
2249                 }
2250
2251                 // <summary>
2252                 //   This does a deep copy of the bit vector.
2253                 // </summary>
2254                 public MyBitVector Clone ()
2255                 {
2256                         MyBitVector retval = new MyBitVector (Count);
2257
2258                         retval.Vector = Vector;
2259
2260                         return retval;
2261                 }
2262
2263                 BitArray Vector {
2264                         get {
2265                                 if (vector != null)
2266                                         return vector;
2267                                 else if (!is_dirty && (InheritsFrom != null))
2268                                         return InheritsFrom.Vector;
2269
2270                                 initialize_vector ();
2271
2272                                 return vector;
2273                         }
2274
2275                         set {
2276                                 initialize_vector ();
2277
2278                                 for (int i = 0; i < System.Math.Min (vector.Count, value.Count); i++)
2279                                         vector [i] = value [i];
2280                         }
2281                 }
2282
2283                 void initialize_vector ()
2284                 {
2285                         if (vector != null)
2286                                 return;
2287
2288                         vector = new BitArray (Count, false);
2289                         if (InheritsFrom != null)
2290                                 Vector = InheritsFrom.Vector;
2291
2292                         is_dirty = true;
2293                 }
2294
2295                 public override string ToString ()
2296                 {
2297                         StringBuilder sb = new StringBuilder ("{");
2298
2299                         BitArray vector = Vector;
2300                         if (!IsDirty)
2301                                 sb.Append ("=");
2302                         for (int i = 0; i < vector.Count; i++) {
2303                                 sb.Append (vector [i] ? "1" : "0");
2304                         }
2305
2306                         sb.Append ("}");
2307                         return sb.ToString ();
2308                 }
2309         }
2310 }