mcs/mcs/flowanalysis.cs

   1 //
   2 // flowanalyis.cs: The control flow analysis code
   3 //
   4 // Author:
   5 //   Martin Baulig (martin@ximian.com)
   6 //
   7 // (C) 2001, 2002, 2003 Ximian, Inc.
   8 //
   9
  10 using System;
  11 using System.Text;
  12 using System.Collections;
  13 using System.Reflection;
  14 using System.Reflection.Emit;
  15 using System.Diagnostics;
  16
  17 namespace Mono.CSharp
  18 {
  19         // <summary>
  20         //   A new instance of this class is created every time a new block is resolved
  21         //   and if there's branching in the block's control flow.
  22         // </summary>
  23         public abstract class FlowBranching
  24         {
  25                 // <summary>
  26                 //   The type of a FlowBranching.
  27                 // </summary>
  28                 public enum BranchingType : byte {
  29                         // Normal (conditional or toplevel) block.
  30                         Block,
  31
  32                         // Conditional.
  33                         Conditional,
  34
  35                         // A loop block.
  36                         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                                         if (num_locals > 0)
 445                                                 locals = new MyBitVector (parent.locals, CountLocals);
 446
 447                                         if (num_params > 0)
 448                                                 parameters = new MyBitVector (parent.parameters, num_params);
 449
 450                                         reachability = parent.Reachability.Clone ();
 451                                 } else {
 452                                         if (num_locals > 0)
 453                                                 locals = new MyBitVector (null, CountLocals);
 454
 455                                         if (num_params > 0)
 456                                                 parameters = new MyBitVector (null, num_params);
 457
 458                                         reachability = Reachability.Never ();
 459                                 }
 460
 461                                 id = ++next_id;
 462                         }
 463
 464                         public UsageVector (SiblingType type, UsageVector parent, Location loc)
 465                                 : this (type, parent, loc, parent.CountParameters, parent.CountLocals)
 466                         { }
 467
 468                         public UsageVector (MyBitVector parameters, MyBitVector locals,
 469                                             Reachability reachability, Location loc)
 470                         {
 471                                 this.Type = SiblingType.Block;
 472                                 this.Location = loc;
 473
 474                                 this.reachability = reachability;
 475                                 this.parameters = parameters;
 476                                 this.locals = locals;
 477
 478                                 id = ++next_id;
 479                         }
 480
 481                         // <summary>
 482                         //   This does a deep copy of the usage vector.
 483                         // </summary>
 484                         public UsageVector Clone ()
 485                         {
 486                                 UsageVector retval = new UsageVector (Type, null, Location, CountParameters, CountLocals);
 487
 488                                 if (retval.locals != null)
 489                                         retval.locals = locals.Clone ();
 490
 491                                 if (parameters != null)
 492                                         retval.parameters = parameters.Clone ();
 493
 494                                 retval.reachability = reachability.Clone ();
 495
 496                                 return retval;
 497                         }
 498
 499                         public bool IsAssigned (VariableInfo var)
 500                         {
 501                                 if (!var.IsParameter && Reachability.AlwaysBreaks)
 502                                         return true;
 503
 504                                 return var.IsAssigned (var.IsParameter ? parameters : locals);
 505                         }
 506
 507                         public void SetAssigned (VariableInfo var)
 508                         {
 509                                 if (!var.IsParameter && Reachability.AlwaysBreaks)
 510                                         return;
 511
 512                                 IsDirty = true;
 513                                 var.SetAssigned (var.IsParameter ? parameters : locals);
 514                         }
 515
 516                         public bool IsFieldAssigned (VariableInfo var, string name)
 517                         {
 518                                 if (!var.IsParameter && Reachability.AlwaysBreaks)
 519                                         return true;
 520
 521                                 return var.IsFieldAssigned (var.IsParameter ? parameters : locals, name);
 522                         }
 523
 524                         public void SetFieldAssigned (VariableInfo var, string name)
 525                         {
 526                                 if (!var.IsParameter && Reachability.AlwaysBreaks)
 527                                         return;
 528
 529                                 IsDirty = true;
 530                                 var.SetFieldAssigned (var.IsParameter ? parameters : locals, name);
 531                         }
 532
 533                         public Reachability Reachability {
 534                                 get {
 535                                         return reachability;
 536                                 }
 537                         }
 538
 539                         public void Return ()
 540                         {
 541                                 if (!reachability.IsUnreachable) {
 542                                         IsDirty = true;
 543                                         reachability.SetReturns ();
 544                                 }
 545                         }
 546
 547                         public void Break ()
 548                         {
 549                                 if (!reachability.IsUnreachable) {
 550                                         IsDirty = true;
 551                                         reachability.SetBreaks ();
 552                                 }
 553                         }
 554
 555                         public void Throw ()
 556                         {
 557                                 if (!reachability.IsUnreachable) {
 558                                         IsDirty = true;
 559                                         reachability.SetThrows ();
 560                                 }
 561                         }
 562
 563                         public void Goto ()
 564                         {
 565                                 if (!reachability.IsUnreachable) {
 566                                         IsDirty = true;
 567                                         reachability.SetBarrier ();
 568                                 }
 569                         }
 570
 571                         // <summary>
 572                         //   Merges a child branching.
 573                         // </summary>
 574                         public UsageVector MergeChild (FlowBranching branching)
 575                         {
 576                                 UsageVector result = branching.Merge ();
 577
 578                                 Report.Debug (2, "  MERGING CHILD", this, IsDirty,
 579                                               result.ParameterVector, result.LocalVector,
 580                                               result.Reachability, Type);
 581
 582                                 reachability = result.Reachability;
 583
 584                                 if (branching.Type == BranchingType.LoopBlock) {
 585                                         bool may_leave_loop = reachability.MayBreak;
 586                                         reachability.ResetBreaks ();
 587
 588                                         if (branching.Infinite && !may_leave_loop) {
 589                                                 if (reachability.Returns == FlowReturns.Sometimes) {
 590                                                         // If we're an infinite loop and do not break,
 591                                                         // the code after the loop can never be reached.
 592                                                         // However, if we may return from the loop,
 593                                                         // then we do always return (or stay in the
 594                                                         // loop forever).
 595                                                         reachability.SetReturns ();
 596                                                 }
 597
 598                                                 reachability.SetBarrier ();
 599                                         } else {
 600                                                 if (reachability.Returns == FlowReturns.Always) {
 601                                                         // We're either finite or we may leave the loop.
 602                                                         reachability.SetReturnsSometimes ();
 603                                                 }
 604                                         }
 605                                 } else if (branching.Type == BranchingType.Switch)
 606                                         reachability.ResetBreaks ();
 607
 608                                 //
 609                                 // We've now either reached the point after the branching or we will
 610                                 // never get there since we always return or always throw an exception.
 611                                 //
 612                                 // If we can reach the point after the branching, mark all locals and
 613                                 // parameters as initialized which have been initialized in all branches
 614                                 // we need to look at (see above).
 615                                 //
 616
 617                                 if ((Type == SiblingType.SwitchSection) && !reachability.IsUnreachable) {
 618                                         Report.Error (163, Location,
 619                                                       "Control cannot fall through from one " +
 620                                                       "case label to another");
 621                                         return result;
 622                                 }
 623
 624                                 if (locals != null && result.LocalVector != null)
 625                                         locals.Or (result.LocalVector);
 626
 627                                 if (result.ParameterVector != null)
 628                                         parameters.Or (result.ParameterVector);
 629
 630                                 Report.Debug (2, "  MERGING CHILD DONE", this, result);
 631
 632                                 IsDirty = true;
 633
 634                                 return result;
 635                         }
 636
 637                         protected void MergeFinally (FlowBranching branching, UsageVector f_origins,
 638                                                      MyBitVector f_params)
 639                         {
 640                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 641                                         MyBitVector temp_params = f_params.Clone ();
 642                                         temp_params.Or (vector.Parameters);
 643                                 }
 644                         }
 645
 646                         public void MergeFinally (FlowBranching branching, UsageVector f_vector,
 647                                                   UsageVector f_origins)
 648                         {
 649                                 if (parameters != null) {
 650                                         if (f_vector != null) {
 651                                                 MergeFinally (branching, f_origins, f_vector.Parameters);
 652                                                 MyBitVector.Or (ref parameters, f_vector.ParameterVector);
 653                                         } else
 654                                                 MergeFinally (branching, f_origins, parameters);
 655                                 }
 656
 657                                 if (f_vector != null && f_vector.LocalVector != null)
 658                                         MyBitVector.Or (ref locals, f_vector.LocalVector);
 659                         }
 660
 661                         // <summary>
 662                         //   Tells control flow analysis that the current code position may be reached with
 663                         //   a forward jump from any of the origins listed in `origin_vectors' which is a
 664                         //   list of UsageVectors.
 665                         //
 666                         //   This is used when resolving forward gotos - in the following example, the
 667                         //   variable `a' is uninitialized in line 8 becase this line may be reached via
 668                         //   the goto in line 4:
 669                         //
 670                         //      1     int a;
 671                         //
 672                         //      3     if (something)
 673                         //      4        goto World;
 674                         //
 675                         //      6     a = 5;
 676                         //
 677                         //      7  World:
 678                         //      8     Console.WriteLine (a);
 679                         //
 680                         // </summary>
 681                         public void MergeJumpOrigins (ICollection origin_vectors)
 682                         {
 683                                 Report.Debug (1, "  MERGING JUMP ORIGINS", this);
 684
 685                                 reachability = Reachability.Never ();
 686
 687                                 if (origin_vectors == null)
 688                                         return;
 689
 690                                 bool first = true;
 691
 692                                 foreach (UsageVector vector in origin_vectors) {
 693                                         Report.Debug (1, "    MERGING JUMP ORIGIN", vector);
 694
 695                                         if (first) {
 696                                                 if (locals != null && vector.Locals != null)
 697                                                         locals.Or (vector.locals);
 698
 699                                                 if (parameters != null)
 700                                                         parameters.Or (vector.parameters);
 701                                                 first = false;
 702                                         } else {
 703                                                 if (locals != null && vector.Locals != null)
 704                                                         locals.And (vector.locals);
 705                                                 if (parameters != null)
 706                                                         parameters.And (vector.parameters);
 707                                         }
 708
 709                                         Reachability.And (ref reachability, vector.Reachability, true);
 710                                 }
 711
 712                                 Report.Debug (1, "  MERGING JUMP ORIGINS DONE", this);
 713                         }
 714
 715                         // <summary>
 716                         //   This is used at the beginning of a finally block if there were
 717                         //   any return statements in the try block or one of the catch blocks.
 718                         // </summary>
 719                         public void MergeFinallyOrigins (UsageVector f_origins)
 720                         {
 721                                 Report.Debug (1, "  MERGING FINALLY ORIGIN", this);
 722
 723                                 reachability = Reachability.Never ();
 724
 725                                 for (UsageVector vector = f_origins; vector != null; vector = vector.Next) {
 726                                         Report.Debug (1, "    MERGING FINALLY ORIGIN", vector);
 727
 728                                         if (parameters != null)
 729                                                 parameters.And (vector.parameters);
 730
 731                                         Reachability.And (ref reachability, vector.Reachability, true);
 732                                 }
 733
 734                                 Report.Debug (1, "  MERGING FINALLY ORIGIN DONE", this);
 735                         }
 736
 737                         public void CheckOutParameters (FlowBranching branching)
 738                         {
 739                                 if (parameters != null)
 740                                         branching.CheckOutParameters (parameters, branching.Location);
 741                         }
 742
 743                         // <summary>
 744                         //   Performs an `or' operation on the locals and the parameters.
 745                         // </summary>
 746                         public void Or (UsageVector new_vector)
 747                         {
 748                                 IsDirty = true;
 749                                 locals.Or (new_vector.locals);
 750                                 if (parameters != null)
 751                                         parameters.Or (new_vector.parameters);
 752                         }
 753
 754                         // <summary>
 755                         //   Performs an `and' operation on the locals.
 756                         // </summary>
 757                         public void AndLocals (UsageVector new_vector)
 758                         {
 759                                 IsDirty = true;
 760                                 locals.And (new_vector.locals);
 761                         }
 762
 763                         public bool HasParameters {
 764                                 get {
 765                                         return parameters != null;
 766                                 }
 767                         }
 768
 769                         public bool HasLocals {
 770                                 get {
 771                                         return locals != null;
 772                                 }
 773                         }
 774
 775                         // <summary>
 776                         //   Returns a deep copy of the parameters.
 777                         // </summary>
 778                         public MyBitVector Parameters {
 779                                 get {
 780                                         if (parameters != null)
 781                                                 return parameters.Clone ();
 782                                         else
 783                                                 return null;
 784                                 }
 785                         }
 786
 787                         // <summary>
 788                         //   Returns a deep copy of the locals.
 789                         // </summary>
 790                         public MyBitVector Locals {
 791                                 get {
 792                                         if (locals != null)
 793                                                 return locals.Clone ();
 794                                         else
 795                                                 return null;
 796                                 }
 797                         }
 798
 799                         public MyBitVector ParameterVector {
 800                                 get {
 801                                         return parameters;
 802                                 }
 803                         }
 804
 805                         public MyBitVector LocalVector {
 806                                 get {
 807                                         return locals;
 808                                 }
 809                         }
 810
 811                         //
 812                         // Debugging stuff.
 813                         //
 814
 815                         public override string ToString ()
 816                         {
 817                                 StringBuilder sb = new StringBuilder ();
 818
 819                                 sb.Append ("Vector (");
 820                                 sb.Append (id);
 821                                 sb.Append (",");
 822                                 sb.Append (IsDirty);
 823                                 sb.Append (",");
 824                                 sb.Append (reachability);
 825                                 if (parameters != null) {
 826                                         sb.Append (" - ");
 827                                         sb.Append (parameters);
 828                                 }
 829                                 sb.Append (" - ");
 830                                 sb.Append (locals);
 831                                 sb.Append (")");
 832
 833                                 return sb.ToString ();
 834                         }
 835                 }
 836
 837                 // <summary>
 838                 //   Creates a new flow branching which is contained in `parent'.
 839                 //   You should only pass non-null for the `block' argument if this block
 840                 //   introduces any new variables - in this case, we need to create a new
 841                 //   usage vector with a different size than our parent's one.
 842                 // </summary>
 843                 protected FlowBranching (FlowBranching parent, BranchingType type, SiblingType stype,
 844                                          Block block, Location loc)
 845                 {
 846                         Parent = parent;
 847                         Block = block;
 848                         Location = loc;
 849                         Type = type;
 850                         id = ++next_id;
 851
 852                         UsageVector vector;
 853                         if (Block != null) {
 854                                 param_map = Block.ParameterMap;
 855                                 local_map = Block.LocalMap;
 856
 857                                 UsageVector parent_vector = parent != null ? parent.CurrentUsageVector : null;
 858                                 vector = new UsageVector (stype, parent_vector, loc, param_map.Length, local_map.Length);
 859
 860
 861                         } else {
 862                                 param_map = Parent.param_map;
 863                                 local_map = Parent.local_map;
 864                                 vector = new UsageVector (stype, Parent.CurrentUsageVector, loc);
 865                         }
 866
 867                         AddSibling (vector);
 868                 }
 869
 870                 public abstract UsageVector CurrentUsageVector {
 871                         get;
 872                 }
 873
 874                 // <summary>
 875                 //   Creates a sibling of the current usage vector.
 876                 // </summary>
 877                 public virtual void CreateSibling (SiblingType type)
 878                 {
 879                         AddSibling (new UsageVector (type, Parent.CurrentUsageVector, Location));
 880
 881                         Report.Debug (1, "  CREATED SIBLING", CurrentUsageVector);
 882                 }
 883
 884                 protected abstract void AddSibling (UsageVector uv);
 885
 886                 public abstract void Label (ArrayList origin_vectors);
 887
 888                 // <summary>
 889                 //   Check whether all `out' parameters have been assigned.
 890                 // </summary>
 891                 public void CheckOutParameters (MyBitVector parameters, Location loc)
 892                 {
 893                         for (int i = 0; i < param_map.Count; i++) {
 894                                 VariableInfo var = param_map [i];
 895
 896                                 if (var == null)
 897                                         continue;
 898
 899                                 if (var.IsAssigned (parameters))
 900                                         continue;
 901
 902                                 Report.Error (177, loc, "The out parameter `" +
 903                                               var.Name + "' must be " +
 904                                               "assigned before control leave the current method.");
 905                         }
 906                 }
 907
 908                 protected UsageVector Merge (UsageVector sibling_list)
 909                 {
 910                         if (sibling_list.Next == null)
 911                                 return sibling_list;
 912
 913                         MyBitVector locals = null;
 914                         MyBitVector parameters = null;
 915
 916                         Reachability reachability = null;
 917
 918                         Report.Debug (2, "  MERGING SIBLINGS", this, Name);
 919
 920                         for (UsageVector child = sibling_list; child != null; child = child.Next) {
 921                                 bool do_break = (Type != BranchingType.Switch) &&
 922                                         (Type != BranchingType.LoopBlock);
 923
 924                                 Report.Debug (2, "    MERGING SIBLING   ", child,
 925                                               child.ParameterVector, child.LocalVector,
 926                                               reachability, child.Reachability, do_break);
 927
 928                                 Reachability.And (ref reachability, child.Reachability, do_break);
 929
 930                                 // A local variable is initialized after a flow branching if it
 931                                 // has been initialized in all its branches which do neither
 932                                 // always return or always throw an exception.
 933                                 //
 934                                 // If a branch may return, but does not always return, then we
 935                                 // can treat it like a never-returning branch here: control will
 936                                 // only reach the code position after the branching if we did not
 937                                 // return here.
 938                                 //
 939                                 // It's important to distinguish between always and sometimes
 940                                 // returning branches here:
 941                                 //
 942                                 //    1   int a;
 943                                 //    2   if (something) {
 944                                 //    3      return;
 945                                 //    4      a = 5;
 946                                 //    5   }
 947                                 //    6   Console.WriteLine (a);
 948                                 //
 949                                 // The if block in lines 3-4 always returns, so we must not look
 950                                 // at the initialization of `a' in line 4 - thus it'll still be
 951                                 // uninitialized in line 6.
 952                                 //
 953                                 // On the other hand, the following is allowed:
 954                                 //
 955                                 //    1   int a;
 956                                 //    2   if (something)
 957                                 //    3      a = 5;
 958                                 //    4   else
 959                                 //    5      return;
 960                                 //    6   Console.WriteLine (a);
 961                                 //
 962                                 // Here, `a' is initialized in line 3 and we must not look at
 963                                 // line 5 since it always returns.
 964                                 //
 965                                 bool do_break_2 = (child.Type != SiblingType.Block) &&
 966                                         (child.Type != SiblingType.SwitchSection);
 967                                 bool unreachable = (do_break_2 && child.Reachability.AlwaysBreaks) ||
 968                                         child.Reachability.AlwaysThrows ||
 969                                         child.Reachability.AlwaysReturns ||
 970                                         child.Reachability.AlwaysHasBarrier;
 971
 972                                 Report.Debug (2, "    MERGING SIBLING #1", reachability,
 973                                               Type, child.Type, child.Reachability.IsUnreachable,
 974                                               do_break_2, unreachable);
 975
 976                                 if (!unreachable && (child.LocalVector != null))
 977                                         MyBitVector.And (ref locals, child.LocalVector);
 978
 979                                 // An `out' parameter must be assigned in all branches which do
 980                                 // not always throw an exception.
 981                                 if ((child.ParameterVector != null) && !child.Reachability.AlwaysThrows)
 982                                         MyBitVector.And (ref parameters, child.ParameterVector);
 983
 984                                 Report.Debug (2, "    MERGING SIBLING #2", parameters, locals);
 985                         }
 986
 987                         if (reachability == null)
 988                                 reachability = Reachability.Never ();
 989
 990                         Report.Debug (2, "  MERGING SIBLINGS DONE", parameters, locals,
 991                                       reachability, Infinite);
 992
 993                         return new UsageVector (parameters, locals, reachability, Location);
 994                 }
 995
 996                 protected abstract UsageVector Merge ();
 997
 998                 // <summary>
 999                 //   Merge a child branching.
1000                 // </summary>
1001                 public UsageVector MergeChild (FlowBranching child)
1002                 {
1003                         return CurrentUsageVector.MergeChild (child);
1004                 }
1005
1006                 // <summary>
1007                 //   Does the toplevel merging.
1008                 // </summary>
1009                 public Reachability MergeTopBlock ()
1010                 {
1011                         if ((Type != BranchingType.Block) || (Block == null))
1012                                 throw new NotSupportedException ();
1013
1014                         UsageVector vector = new UsageVector (
1015                                 SiblingType.Conditional, null, Location, param_map.Length, local_map.Length);
1016
1017                         UsageVector result = vector.MergeChild (this);
1018
1019                         Report.Debug (4, "MERGE TOP BLOCK", Location, vector, result.Reachability);
1020
1021                         if (vector.Reachability.Throws != FlowReturns.Always)
1022                                 CheckOutParameters (vector.Parameters, Location);
1023
1024                         return result.Reachability;
1025                 }
1026
1027                 public virtual bool InTryBlock ()
1028                 {
1029                         if (Parent != null)
1030                                 return Parent.InTryBlock ();
1031                         else
1032                                 return false;
1033                 }
1034
1035                 public virtual void AddFinallyVector (UsageVector vector)
1036                 {
1037                         if (Parent != null)
1038                                 Parent.AddFinallyVector (vector);
1039                         else
1040                                 throw new NotSupportedException ();
1041                 }
1042
1043                 public bool IsAssigned (VariableInfo vi)
1044                 {
1045                         return CurrentUsageVector.IsAssigned (vi);
1046                 }
1047
1048                 public bool IsFieldAssigned (VariableInfo vi, string field_name)
1049                 {
1050                         if (CurrentUsageVector.IsAssigned (vi))
1051                                 return true;
1052
1053                         return CurrentUsageVector.IsFieldAssigned (vi, field_name);
1054                 }
1055
1056                 public void SetAssigned (VariableInfo vi)
1057                 {
1058                         CurrentUsageVector.SetAssigned (vi);
1059                 }
1060
1061                 public void SetFieldAssigned (VariableInfo vi, string name)
1062                 {
1063                         CurrentUsageVector.SetFieldAssigned (vi, name);
1064                 }
1065
1066                 public override string ToString ()
1067                 {
1068                         StringBuilder sb = new StringBuilder ();
1069                         sb.Append (GetType ());
1070                         sb.Append (" (");
1071
1072                         sb.Append (id);
1073                         sb.Append (",");
1074                         sb.Append (Type);
1075                         if (Block != null) {
1076                                 sb.Append (" - ");
1077                                 sb.Append (Block.ID);
1078                                 sb.Append (" - ");
1079                                 sb.Append (Block.StartLocation);
1080                         }
1081                         sb.Append (" - ");
1082                         // sb.Append (Siblings.Length);
1083                         // sb.Append (" - ");
1084                         sb.Append (CurrentUsageVector);
1085                         sb.Append (")");
1086                         return sb.ToString ();
1087                 }
1088
1089                 public string Name {
1090                         get {
1091                                 return String.Format ("{0} ({1}:{2}:{3})",
1092                                                       GetType (), id, Type, Location);
1093                         }
1094                 }
1095         }
1096
1097         public class FlowBranchingBlock : FlowBranching
1098         {
1099                 UsageVector sibling_list = null;
1100
1101                 public FlowBranchingBlock (FlowBranching parent, BranchingType type, SiblingType stype,
1102                                            Block block, Location loc)
1103                         : base (parent, type, stype, block, loc)
1104                 { }
1105
1106                 public override UsageVector CurrentUsageVector {
1107                         get { return sibling_list; }
1108                 }
1109
1110                 protected override void AddSibling (UsageVector sibling)
1111                 {
1112                         sibling.Next = sibling_list;
1113                         sibling_list = sibling;
1114                 }
1115
1116                 public override void Label (ArrayList origin_vectors)
1117                 {
1118                         if (!CurrentUsageVector.Reachability.IsUnreachable) {
1119                                 if (origin_vectors == null)
1120                                         origin_vectors = new ArrayList (1);
1121                                 origin_vectors.Add (CurrentUsageVector.Clone ());
1122                         }
1123
1124                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1125                 }
1126
1127                 protected override UsageVector Merge ()
1128                 {
1129                         return Merge (sibling_list);
1130                 }
1131         }
1132
1133         public class FlowBranchingException : FlowBranching
1134         {
1135                 UsageVector current_vector;
1136                 UsageVector catch_vectors;
1137                 UsageVector finally_vector;
1138                 UsageVector finally_origins;
1139
1140                 public FlowBranchingException (FlowBranching parent, BranchingType type, Block block, Location loc)
1141                         : base (parent, type, SiblingType.Try, block, loc)
1142                 { }
1143
1144                 protected override void AddSibling (UsageVector sibling)
1145                 {
1146                         if (sibling.Type == SiblingType.Try) {
1147                                 sibling.Next = catch_vectors;
1148                                 catch_vectors = sibling;
1149                         } else if (sibling.Type == SiblingType.Catch) {
1150                                 sibling.Next = catch_vectors;
1151                                 catch_vectors = sibling;
1152                         } else if (sibling.Type == SiblingType.Finally) {
1153                                 sibling.MergeFinallyOrigins (finally_origins);
1154                                 finally_vector = sibling;
1155                         } else
1156                                 throw new InvalidOperationException ();
1157
1158                         current_vector = sibling;
1159                 }
1160
1161                 public override UsageVector CurrentUsageVector {
1162                         get { return current_vector; }
1163                 }
1164
1165                 public override bool InTryBlock ()
1166                 {
1167                         return true;
1168                 }
1169
1170                 public override void AddFinallyVector (UsageVector vector)
1171                 {
1172                         vector = vector.Clone ();
1173                         vector.Next = finally_origins;
1174                         finally_origins = vector;
1175                 }
1176
1177                 public override void Label (ArrayList origin_vectors)
1178                 {
1179                         CurrentUsageVector.MergeJumpOrigins (origin_vectors);
1180                 }
1181
1182                 protected override UsageVector Merge ()
1183                 {
1184                         UsageVector vector = Merge (catch_vectors);
1185
1186                         vector.MergeFinally (this, finally_vector, finally_origins);
1187
1188                         return vector;
1189                 }
1190         }
1191
1192         // <summary>
1193         //   This is used by the flow analysis code to keep track of the type of local variables
1194         //   and variables.
1195         //
1196         //   The flow code uses a BitVector to keep track of whether a variable has been assigned
1197         //   or not.  This is easy for fundamental types (int, char etc.) or reference types since
1198         //   you can only assign the whole variable as such.
1199         //
1200         //   For structs, we also need to keep track of all its fields.  To do this, we allocate one
1201         //   bit for the struct itself (it's used if you assign/access the whole struct) followed by
1202         //   one bit for each of its fields.
1203         //
1204         //   This class computes this `layout' for each type.
1205         // </summary>
1206         public class TypeInfo
1207         {
1208                 public readonly Type Type;
1209
1210                 // <summary>
1211                 //   Total number of bits a variable of this type consumes in the flow vector.
1212                 // </summary>
1213                 public readonly int TotalLength;
1214
1215                 // <summary>
1216                 //   Number of bits the simple fields of a variable of this type consume
1217                 //   in the flow vector.
1218                 // </summary>
1219                 public readonly int Length;
1220
1221                 // <summary>
1222                 //   This is only used by sub-structs.
1223                 // </summary>
1224                 public readonly int Offset;
1225
1226                 // <summary>
1227                 //   If this is a struct.
1228                 // </summary>
1229                 public readonly bool IsStruct;
1230
1231                 // <summary>
1232                 //   If this is a struct, all fields which are structs theirselves.
1233                 // </summary>
1234                 public TypeInfo[] SubStructInfo;
1235
1236                 protected readonly StructInfo struct_info;
1237                 private static Hashtable type_hash = new Hashtable ();
1238
1239                 public static TypeInfo GetTypeInfo (Type type)
1240                 {
1241                         TypeInfo info = (TypeInfo) type_hash [type];
1242                         if (info != null)
1243                                 return info;
1244
1245                         info = new TypeInfo (type);
1246                         type_hash.Add (type, info);
1247                         return info;
1248                 }
1249
1250                 public static TypeInfo GetTypeInfo (TypeContainer tc)
1251                 {
1252                         TypeInfo info = (TypeInfo) type_hash [tc.TypeBuilder];
1253                         if (info != null)
1254                                 return info;
1255
1256                         info = new TypeInfo (tc);
1257                         type_hash.Add (tc.TypeBuilder, info);
1258                         return info;
1259                 }
1260
1261                 private TypeInfo (Type type)
1262                 {
1263                         this.Type = type;
1264
1265                         struct_info = StructInfo.GetStructInfo (type);
1266                         if (struct_info != null) {
1267                                 Length = struct_info.Length;
1268                                 TotalLength = struct_info.TotalLength;
1269                                 SubStructInfo = struct_info.StructFields;
1270                                 IsStruct = true;
1271                         } else {
1272                                 Length = 0;
1273                                 TotalLength = 1;
1274                                 IsStruct = false;
1275                         }
1276                 }
1277
1278                 private TypeInfo (TypeContainer tc)
1279                 {
1280                         this.Type = tc.TypeBuilder;
1281
1282                         struct_info = StructInfo.GetStructInfo (tc);
1283                         if (struct_info != null) {
1284                                 Length = struct_info.Length;
1285                                 TotalLength = struct_info.TotalLength;
1286                                 SubStructInfo = struct_info.StructFields;
1287                                 IsStruct = true;
1288                         } else {
1289                                 Length = 0;
1290                                 TotalLength = 1;
1291                                 IsStruct = false;
1292                         }
1293                 }
1294
1295                 protected TypeInfo (StructInfo struct_info, int offset)
1296                 {
1297                         this.struct_info = struct_info;
1298                         this.Offset = offset;
1299                         this.Length = struct_info.Length;
1300                         this.TotalLength = struct_info.TotalLength;
1301                         this.SubStructInfo = struct_info.StructFields;
1302                         this.Type = struct_info.Type;
1303                         this.IsStruct = true;
1304                 }
1305
1306                 public int GetFieldIndex (string name)
1307                 {
1308                         if (struct_info == null)
1309                                 return 0;
1310
1311                         return struct_info [name];
1312                 }
1313
1314                 public TypeInfo GetSubStruct (string name)
1315                 {
1316                         if (struct_info == null)
1317                                 return null;
1318
1319                         return struct_info.GetStructField (name);
1320                 }
1321
1322                 // <summary>
1323                 //   A struct's constructor must always assign all fields.
1324                 //   This method checks whether it actually does so.
1325                 // </summary>
1326                 public bool IsFullyInitialized (FlowBranching branching, VariableInfo vi, Location loc)
1327                 {
1328                         if (struct_info == null)
1329                                 return true;
1330
1331                         bool ok = true;
1332                         for (int i = 0; i < struct_info.Count; i++) {
1333                                 FieldInfo field = struct_info.Fields [i];
1334
1335                                 if (!branching.IsFieldAssigned (vi, field.Name)) {
1336                                         Report.Error (171, loc,
1337                                                       "Field `" + TypeManager.CSharpName (Type) +
1338                                                       "." + field.Name + "' must be fully initialized " +
1339                                                       "before control leaves the constructor");
1340                                         ok = false;
1341                                 }
1342                         }
1343
1344                         return ok;
1345                 }
1346
1347                 public override string ToString ()
1348                 {
1349                         return String.Format ("TypeInfo ({0}:{1}:{2}:{3})",
1350                                               Type, Offset, Length, TotalLength);
1351                 }
1352
1353                 protected class StructInfo {
1354                         public readonly Type Type;
1355                         public readonly FieldInfo[] Fields;
1356                         public readonly TypeInfo[] StructFields;
1357                         public readonly int Count;
1358                         public readonly int CountPublic;
1359                         public readonly int CountNonPublic;
1360                         public readonly int Length;
1361                         public readonly int TotalLength;
1362                         public readonly bool HasStructFields;
1363
1364                         private static Hashtable field_type_hash = new Hashtable ();
1365                         private Hashtable struct_field_hash;
1366                         private Hashtable field_hash;
1367
1368                         protected bool InTransit = false;
1369
1370                         // Private constructor.  To save memory usage, we only need to create one instance
1371                         // of this class per struct type.
1372                         private StructInfo (Type type)
1373                         {
1374                                 this.Type = type;
1375
1376                                 field_type_hash.Add (type, this);
1377
1378                                 if (type is TypeBuilder) {
1379                                         TypeContainer tc = TypeManager.LookupTypeContainer (type);
1380
1381                                         ArrayList fields = tc.Fields;
1382
1383                                         ArrayList public_fields = new ArrayList ();
1384                                         ArrayList non_public_fields = new ArrayList ();
1385
1386                                         if (fields != null) {
1387                                                 foreach (Field field in fields) {
1388                                                         if ((field.ModFlags & Modifiers.STATIC) != 0)
1389                                                                 continue;
1390                                                         if ((field.ModFlags & Modifiers.PUBLIC) != 0)
1391                                                                 public_fields.Add (field.FieldBuilder);
1392                                                         else
1393                                                                 non_public_fields.Add (field.FieldBuilder);
1394                                                 }
1395                                         }
1396
1397                                         CountPublic = public_fields.Count;
1398                                         CountNonPublic = non_public_fields.Count;
1399                                         Count = CountPublic + CountNonPublic;
1400
1401                                         Fields = new FieldInfo [Count];
1402                                         public_fields.CopyTo (Fields, 0);
1403                                         non_public_fields.CopyTo (Fields, CountPublic);
1404                                 } else {
1405                                         FieldInfo[] public_fields = type.GetFields (
1406                                                 BindingFlags.Instance|BindingFlags.Public);
1407                                         FieldInfo[] non_public_fields = type.GetFields (
1408                                                 BindingFlags.Instance|BindingFlags.NonPublic);
1409
1410                                         CountPublic = public_fields.Length;
1411                                         CountNonPublic = non_public_fields.Length;
1412                                         Count = CountPublic + CountNonPublic;
1413
1414                                         Fields = new FieldInfo [Count];
1415                                         public_fields.CopyTo (Fields, 0);
1416                                         non_public_fields.CopyTo (Fields, CountPublic);
1417                                 }
1418
1419                                 struct_field_hash = new Hashtable ();
1420                                 field_hash = new Hashtable ();
1421
1422                                 Length = 0;
1423                                 StructFields = new TypeInfo [Count];
1424                                 StructInfo[] sinfo = new StructInfo [Count];
1425
1426                                 InTransit = true;
1427
1428                                 for (int i = 0; i < Count; i++) {
1429                                         FieldInfo field = (FieldInfo) Fields [i];
1430
1431                                         sinfo [i] = GetStructInfo (field.FieldType);
1432                                         if (sinfo [i] == null)
1433                                                 field_hash.Add (field.Name, ++Length);
1434                                         else if (sinfo [i].InTransit) {
1435                                                 Report.Error (523, String.Format (
1436                                                                       "Struct member '{0}.{1}' of type '{2}' causes " +
1437                                                                       "a cycle in the structure layout",
1438                                                                       type, field.Name, sinfo [i].Type));
1439                                                 sinfo [i] = null;
1440                                                 return;
1441                                         }
1442                                 }
1443
1444                                 InTransit = false;
1445
1446                                 TotalLength = Length + 1;
1447                                 for (int i = 0; i < Count; i++) {
1448                                         FieldInfo field = (FieldInfo) Fields [i];
1449
1450                                         if (sinfo [i] == null)
1451                                                 continue;
1452
1453                                         field_hash.Add (field.Name, TotalLength);
1454
1455                                         HasStructFields = true;
1456                                         StructFields [i] = new TypeInfo (sinfo [i], TotalLength);
1457                                         struct_field_hash.Add (field.Name, StructFields [i]);
1458                                         TotalLength += sinfo [i].TotalLength;
1459                                 }
1460                         }
1461
1462                         public int this [string name] {
1463                                 get {
1464                                         if (field_hash.Contains (name))
1465                                                 return (int) field_hash [name];
1466                                         else
1467                                                 return 0;
1468                                 }
1469                         }
1470
1471                         public TypeInfo GetStructField (string name)
1472                         {
1473                                 return (TypeInfo) struct_field_hash [name];
1474                         }
1475
1476                         public static StructInfo GetStructInfo (Type type)
1477                         {
1478                                 if (!TypeManager.IsValueType (type) || TypeManager.IsEnumType (type) ||
1479                                     TypeManager.IsBuiltinType (type))
1480                                         return null;
1481
1482                                 StructInfo info = (StructInfo) field_type_hash [type];
1483                                 if (info != null)
1484                                         return info;
1485
1486                                 return new StructInfo (type);
1487                         }
1488
1489                         public static StructInfo GetStructInfo (TypeContainer tc)
1490                         {
1491                                 StructInfo info = (StructInfo) field_type_hash [tc.TypeBuilder];
1492                                 if (info != null)
1493                                         return info;
1494
1495                                 return new StructInfo (tc.TypeBuilder);
1496                         }
1497                 }
1498         }
1499
1500         // <summary>
1501         //   This is used by the flow analysis code to store information about a single local variable
1502         //   or parameter.  Depending on the variable's type, we need to allocate one or more elements
1503         //   in the BitVector - if it's a fundamental or reference type, we just need to know whether
1504         //   it has been assigned or not, but for structs, we need this information for each of its fields.
1505         // </summary>
1506         public class VariableInfo {
1507                 public readonly string Name;
1508                 public readonly TypeInfo TypeInfo;
1509
1510                 // <summary>
1511                 //   The bit offset of this variable in the flow vector.
1512                 // </summary>
1513                 public readonly int Offset;
1514
1515                 // <summary>
1516                 //   The number of bits this variable needs in the flow vector.
1517                 //   The first bit always specifies whether the variable as such has been assigned while
1518                 //   the remaining bits contain this information for each of a struct's fields.
1519                 // </summary>
1520                 public readonly int Length;
1521
1522                 // <summary>
1523                 //   If this is a parameter of local variable.
1524                 // </summary>
1525                 public readonly bool IsParameter;
1526
1527                 public readonly LocalInfo LocalInfo;
1528                 public readonly int ParameterIndex;
1529
1530                 readonly VariableInfo Parent;
1531                 VariableInfo[] sub_info;
1532
1533                 protected VariableInfo (string name, Type type, int offset)
1534                 {
1535                         this.Name = name;
1536                         this.Offset = offset;
1537                         this.TypeInfo = TypeInfo.GetTypeInfo (type);
1538
1539                         Length = TypeInfo.TotalLength;
1540
1541                         Initialize ();
1542                 }
1543
1544                 protected VariableInfo (VariableInfo parent, TypeInfo type)
1545                 {
1546                         this.Name = parent.Name;
1547                         this.TypeInfo = type;
1548                         this.Offset = parent.Offset + type.Offset;
1549                         this.Parent = parent;
1550                         this.Length = type.TotalLength;
1551
1552                         this.IsParameter = parent.IsParameter;
1553                         this.LocalInfo = parent.LocalInfo;
1554                         this.ParameterIndex = parent.ParameterIndex;
1555
1556                         Initialize ();
1557                 }
1558
1559                 protected void Initialize ()
1560                 {
1561                         TypeInfo[] sub_fields = TypeInfo.SubStructInfo;
1562                         if (sub_fields != null) {
1563                                 sub_info = new VariableInfo [sub_fields.Length];
1564                                 for (int i = 0; i < sub_fields.Length; i++) {
1565                                         if (sub_fields [i] != null)
1566                                                 sub_info [i] = new VariableInfo (this, sub_fields [i]);
1567                                 }
1568                         } else
1569                                 sub_info = new VariableInfo [0];
1570                 }
1571
1572                 public VariableInfo (LocalInfo local_info, int offset)
1573                         : this (local_info.Name, local_info.VariableType, offset)
1574                 {
1575                         this.LocalInfo = local_info;
1576                         this.IsParameter = false;
1577                 }
1578
1579                 public VariableInfo (string name, Type type, int param_idx, int offset)
1580                         : this (name, type, offset)
1581                 {
1582                         this.ParameterIndex = param_idx;
1583                         this.IsParameter = true;
1584                 }
1585
1586                 public bool IsAssigned (EmitContext ec)
1587                 {
1588                         return !ec.DoFlowAnalysis || ec.CurrentBranching.IsAssigned (this);
1589                 }
1590
1591                 public bool IsAssigned (EmitContext ec, Location loc)
1592                 {
1593                         if (IsAssigned (ec))
1594                                 return true;
1595
1596                         Report.Error (165, loc,
1597                                       "Use of unassigned local variable `" + Name + "'");
1598                         ec.CurrentBranching.SetAssigned (this);
1599                         return false;
1600                 }
1601
1602                 public bool IsAssigned (MyBitVector vector)
1603                 {
1604                         if (vector [Offset])
1605                                 return true;
1606
1607                         for (VariableInfo parent = Parent; parent != null; parent = parent.Parent)
1608                                 if (vector [parent.Offset])
1609                                         return true;
1610
1611                         // Return unless this is a struct.
1612                         if (!TypeInfo.IsStruct)
1613                                 return false;
1614
1615                         // Ok, so each field must be assigned.
1616                         for (int i = 0; i < TypeInfo.Length; i++) {
1617                                 if (!vector [Offset + i + 1])
1618                                         return false;
1619                         }
1620
1621                         // Ok, now check all fields which are structs.
1622                         for (int i = 0; i < sub_info.Length; i++) {
1623                                 VariableInfo sinfo = sub_info [i];
1624                                 if (sinfo == null)
1625                                         continue;
1626
1627                                 if (!sinfo.IsAssigned (vector))
1628                                         return false;
1629                         }
1630
1631                         vector [Offset] = true;
1632                         return true;
1633                 }
1634
1635                 public void SetAssigned (EmitContext ec)
1636                 {
1637                         if (ec.DoFlowAnalysis)
1638                                 ec.CurrentBranching.SetAssigned (this);
1639                 }
1640
1641                 public void SetAssigned (MyBitVector vector)
1642                 {
1643                         vector [Offset] = true;
1644                 }
1645
1646                 public bool IsFieldAssigned (EmitContext ec, string name, Location loc)
1647                 {
1648                         if (!ec.DoFlowAnalysis || ec.CurrentBranching.IsFieldAssigned (this, name))
1649                                 return true;
1650
1651                         Report.Error (170, loc,
1652                                       "Use of possibly unassigned field `" + name + "'");
1653                         ec.CurrentBranching.SetFieldAssigned (this, name);
1654                         return false;
1655                 }
1656
1657                 public bool IsFieldAssigned (MyBitVector vector, string field_name)
1658                 {
1659                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1660
1661                         if (field_idx == 0)
1662                                 return true;
1663
1664                         return vector [Offset + field_idx];
1665                 }
1666
1667                 public void SetFieldAssigned (EmitContext ec, string name)
1668                 {
1669                         if (ec.DoFlowAnalysis)
1670                                 ec.CurrentBranching.SetFieldAssigned (this, name);
1671                 }
1672
1673                 public void SetFieldAssigned (MyBitVector vector, string field_name)
1674                 {
1675                         int field_idx = TypeInfo.GetFieldIndex (field_name);
1676
1677                         if (field_idx == 0)
1678                                 return;
1679
1680                         vector [Offset + field_idx] = true;
1681                 }
1682
1683                 public VariableInfo GetSubStruct (string name)
1684                 {
1685                         TypeInfo type = TypeInfo.GetSubStruct (name);
1686
1687                         if (type == null)
1688                                 return null;
1689
1690                         return new VariableInfo (this, type);
1691                 }
1692
1693                 public override string ToString ()
1694                 {
1695                         return String.Format ("VariableInfo ({0}:{1}:{2}:{3}:{4})",
1696                                               Name, TypeInfo, Offset, Length, IsParameter);
1697                 }
1698         }
1699
1700         // <summary>
1701         //   This is used by the flow code to hold the `layout' of the flow vector for
1702         //   all locals and all parameters (ie. we create one instance of this class for the
1703         //   locals and another one for the params).
1704         // </summary>
1705         public class VariableMap {
1706                 // <summary>
1707                 //   The number of variables in the map.
1708                 // </summary>
1709                 public readonly int Count;
1710
1711                 // <summary>
1712                 //   Total length of the flow vector for this map.
1713                 // <summary>
1714                 public readonly int Length;
1715
1716                 VariableInfo[] map;
1717
1718                 public VariableMap (InternalParameters ip)
1719                 {
1720                         Count = ip != null ? ip.Count : 0;
1721
1722                         // Dont bother allocating anything!
1723                         if (Count == 0)
1724                                 return;
1725
1726                         Length = 0;
1727
1728                         for (int i = 0; i < Count; i++) {
1729                                 Parameter.Modifier mod = ip.ParameterModifier (i);
1730
1731                                 if ((mod & Parameter.Modifier.OUT) == 0)
1732                                         continue;
1733
1734                                 // Dont allocate till we find an out var.
1735                                 if (map == null)
1736                                         map = new VariableInfo [Count];
1737
1738                                 map [i] = new VariableInfo (ip.ParameterName (i),
1739                                         TypeManager.GetElementType (ip.ParameterType (i)), i, Length);
1740
1741                                 Length += map [i].Length;
1742                         }
1743                 }
1744
1745                 public VariableMap (LocalInfo[] locals)
1746                         : this (null, locals)
1747                 { }
1748
1749                 public VariableMap (VariableMap parent, LocalInfo[] locals)
1750                 {
1751                         int offset = 0, start = 0;
1752                         if (parent != null && parent.map != null) {
1753                                 offset = parent.Length;
1754                                 start = parent.Count;
1755                         }
1756
1757                         Count = locals.Length + start;
1758
1759                         if (Count == 0)
1760                                 return;
1761
1762                         map = new VariableInfo [Count];
1763                         Length = offset;
1764
1765                         if (parent != null && parent.map != null) {
1766                                 parent.map.CopyTo (map, 0);
1767                         }
1768
1769                         for (int i = start; i < Count; i++) {
1770                                 LocalInfo li = locals [i-start];
1771
1772                                 if (li.VariableType == null)
1773                                         continue;
1774
1775                                 map [i] = li.VariableInfo = new VariableInfo (li, Length);
1776                                 Length += map [i].Length;
1777                         }
1778                 }
1779
1780                 // <summary>
1781                 //   Returns the VariableInfo for variable @index or null if we don't need to
1782                 //   compute assignment info for this variable.
1783                 // </summary>
1784                 public VariableInfo this [int index] {
1785                         get {
1786                                 if (map == null)
1787                                         return null;
1788
1789                                 return map [index];
1790                         }
1791                 }
1792
1793                 public override string ToString ()
1794                 {
1795                         return String.Format ("VariableMap ({0}:{1})", Count, Length);
1796                 }
1797         }
1798
1799         // <summary>
1800         //   This is a special bit vector which can inherit from another bit vector doing a
1801         //   copy-on-write strategy.  The inherited vector may have a smaller size than the
1802         //   current one.
1803         // </summary>
1804         public class MyBitVector {
1805                 public readonly int Count;
1806                 public readonly MyBitVector InheritsFrom;
1807
1808                 bool is_dirty;
1809                 BitArray vector;
1810
1811                 public MyBitVector (int Count)
1812                         : this (null, Count)
1813                 { }
1814
1815                 public MyBitVector (MyBitVector InheritsFrom, int Count)
1816                 {
1817                         this.InheritsFrom = InheritsFrom;
1818                         this.Count = Count;
1819                 }
1820
1821                 // <summary>
1822                 //   Checks whether this bit vector has been modified.  After setting this to true,
1823                 //   we won't use the inherited vector anymore, but our own copy of it.
1824                 // </summary>
1825                 public bool IsDirty {
1826                         get {
1827                                 return is_dirty;
1828                         }
1829
1830                         set {
1831                                 if (!is_dirty)
1832                                         initialize_vector ();
1833                         }
1834                 }
1835
1836                 // <summary>
1837                 //   Get/set bit `index' in the bit vector.
1838                 // </summary>
1839                 public bool this [int index]
1840                 {
1841                         get {
1842                                 if (index > Count)
1843                                         throw new ArgumentOutOfRangeException ();
1844
1845                                 // We're doing a "copy-on-write" strategy here; as long
1846                                 // as nobody writes to the array, we can use our parent's
1847                                 // copy instead of duplicating the vector.
1848
1849                                 if (vector != null)
1850                                         return vector [index];
1851                                 else if (InheritsFrom != null) {
1852                                         BitArray inherited = InheritsFrom.Vector;
1853
1854                                         if (index < inherited.Count)
1855                                                 return inherited [index];
1856                                         else
1857                                                 return false;
1858                                 } else
1859                                         return false;
1860                         }
1861
1862                         set {
1863                                 if (index > Count)
1864                                         throw new ArgumentOutOfRangeException ();
1865
1866                                 // Only copy the vector if we're actually modifying it.
1867
1868                                 if (this [index] != value) {
1869                                         initialize_vector ();
1870
1871                                         vector [index] = value;
1872                                 }
1873                         }
1874                 }
1875
1876                 // <summary>
1877                 //   If you explicitly convert the MyBitVector to a BitArray, you will get a deep
1878                 //   copy of the bit vector.
1879                 // </summary>
1880                 public static explicit operator BitArray (MyBitVector vector)
1881                 {
1882                         vector.initialize_vector ();
1883                         return vector.Vector;
1884                 }
1885
1886                 // <summary>
1887                 //   Performs an `or' operation on the bit vector.  The `new_vector' may have a
1888                 //   different size than the current one.
1889                 // </summary>
1890                 public void Or (MyBitVector new_vector)
1891                 {
1892                         BitArray new_array = new_vector.Vector;
1893
1894                         initialize_vector ();
1895
1896                         int upper;
1897                         if (vector.Count < new_array.Count)
1898                                 upper = vector.Count;
1899                         else
1900                                 upper = new_array.Count;
1901
1902                         for (int i = 0; i < upper; i++)
1903                                 vector [i] = vector [i] | new_array [i];
1904                 }
1905
1906                 // <summary>
1907                 //   Perfonrms an `and' operation on the bit vector.  The `new_vector' may have
1908                 //   a different size than the current one.
1909                 // </summary>
1910                 public void And (MyBitVector new_vector)
1911                 {
1912                         BitArray new_array = new_vector.Vector;
1913
1914                         initialize_vector ();
1915
1916                         int lower, upper;
1917                         if (vector.Count < new_array.Count)
1918                                 lower = upper = vector.Count;
1919                         else {
1920                                 lower = new_array.Count;
1921                                 upper = vector.Count;
1922                         }
1923
1924                         for (int i = 0; i < lower; i++)
1925                                 vector [i] = vector [i] & new_array [i];
1926
1927                         for (int i = lower; i < upper; i++)
1928                                 vector [i] = false;
1929                 }
1930
1931                 public static void And (ref MyBitVector target, MyBitVector vector)
1932                 {
1933                         if (target != null)
1934                                 target.And (vector);
1935                         else
1936                                 target = vector.Clone ();
1937                 }
1938
1939                 public static void Or (ref MyBitVector target, MyBitVector vector)
1940                 {
1941                         if (target != null)
1942                                 target.Or (vector);
1943                         else
1944                                 target = vector.Clone ();
1945                 }
1946
1947                 // <summary>
1948                 //   This does a deep copy of the bit vector.
1949                 // </summary>
1950                 public MyBitVector Clone ()
1951                 {
1952                         MyBitVector retval = new MyBitVector (Count);
1953
1954                         retval.Vector = Vector;
1955
1956                         return retval;
1957                 }
1958
1959                 BitArray Vector {
1960                         get {
1961                                 if (vector != null)
1962                                         return vector;
1963                                 else if (!is_dirty && (InheritsFrom != null))
1964                                         return InheritsFrom.Vector;
1965
1966                                 initialize_vector ();
1967
1968                                 return vector;
1969                         }
1970
1971                         set {
1972                                 initialize_vector ();
1973
1974                                 for (int i = 0; i < System.Math.Min (vector.Count, value.Count); i++)
1975                                         vector [i] = value [i];
1976                         }
1977                 }
1978
1979                 void initialize_vector ()
1980                 {
1981                         if (vector != null)
1982                                 return;
1983
1984                         vector = new BitArray (Count, false);
1985                         if (InheritsFrom != null)
1986                                 Vector = InheritsFrom.Vector;
1987
1988                         is_dirty = true;
1989                 }
1990
1991                 public override string ToString ()
1992                 {
1993                         StringBuilder sb = new StringBuilder ("{");
1994
1995                         BitArray vector = Vector;
1996                         if (!IsDirty)
1997                                 sb.Append ("=");
1998                         for (int i = 0; i < vector.Count; i++) {
1999                                 sb.Append (vector [i] ? "1" : "0");
2000                         }
2001
2002                         sb.Append ("}");
2003                         return sb.ToString ();
2004                 }
2005         }
2006 }