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