Forgot to commit
[mono.git] / mcs / mcs / flowanalysis.cs
index 89d1fe00b47464700d9cd06d729a16c934c38a88..2213d36e59eacb468a4ba34648963c64140dc6bc 100644 (file)
@@ -5,7 +5,8 @@
 //   Martin Baulig (martin@ximian.com)
 //   Raja R Harinath (rharinath@novell.com)
 //
-// (C) 2001, 2002, 2003 Ximian, Inc.
+// Copyright 2001, 2002, 2003 Ximian, Inc.
+// Copyright 2003-2008 Novell, Inc.
 //
 
 using System;
@@ -42,14 +43,20 @@ namespace Mono.CSharp
                        // part of a block headed by a jump target
                        Labeled,
 
-                       // Try/Catch block.
+                       // TryCatch block.
+                       TryCatch,
+
+                       // TryFinally, Using, Lock, CollectionForeach
                        Exception,
 
                        // Switch block.
                        Switch,
 
                        // The toplevel block of a function
-                       Toplevel
+                       Toplevel,
+
+                       // An iterator block
+                       Iterator
                }
 
                // <summary>
@@ -70,6 +77,7 @@ namespace Mono.CSharp
                        case BranchingType.Exception:
                        case BranchingType.Labeled:
                        case BranchingType.Toplevel:
+                       case BranchingType.TryCatch:
                                throw new InvalidOperationException ();
 
                        case BranchingType.Switch:
@@ -306,6 +314,10 @@ namespace Mono.CSharp
 
                                locals |= child.locals;
 
+                               // throw away un-necessary information about variables in child blocks
+                               if (locals.Count != CountLocals)
+                                       locals = new MyBitVector (locals, CountLocals);
+
                                if (overwrite)
                                        is_unreachable = new_isunr;
                                else
@@ -396,32 +408,19 @@ namespace Mono.CSharp
 
                protected abstract UsageVector Merge ();
 
-               // <summary>
-               //   Merge a child branching.
-               // </summary>
                public UsageVector MergeChild (FlowBranching child)
                {
-                       bool overwrite = false;
-
-                       switch (child.Type) {
-                       case BranchingType.Labeled:
-                               overwrite = true;
-                               break;
-                       case BranchingType.Block:
-                               if (child.Block != null && child.Block != child.Block.Explicit)
-                                       overwrite = true;
-                               break;
-                       }
-
-                       Report.Debug (2, "  MERGING CHILD", this, child);
-                       UsageVector result = CurrentUsageVector.MergeChild (child.Merge (), overwrite);
-                       Report.Debug (2, "  MERGING CHILD DONE", this, result);
-                       return result;
+                       return CurrentUsageVector.MergeChild (child.Merge (), true);
                }
 
-               public virtual bool InTryWithCatch ()
+               public virtual bool CheckRethrow (Location loc)
+               {
+                       return Parent.CheckRethrow (loc);
+               }
+
+               public virtual bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
                {
-                       return Parent.InTryWithCatch ();
+                       return Parent.AddResumePoint (stmt, loc, out pc);
                }
 
                // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
@@ -437,9 +436,9 @@ namespace Mono.CSharp
                }
 
                // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
-               public virtual bool AddReturnOrigin (UsageVector vector, Location loc)
+               public virtual bool AddReturnOrigin (UsageVector vector, ExitStatement stmt)
                {
-                       return Parent.AddReturnOrigin (vector, loc);
+                       return Parent.AddReturnOrigin (vector, stmt);
                }
 
                // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
@@ -448,12 +447,6 @@ namespace Mono.CSharp
                        return Parent.AddGotoOrigin (vector, goto_stmt);
                }
 
-               // returns true if we crossed an unwind-protected region (try/catch/finally, lock, using, ...)
-               public virtual bool StealFinallyClauses (ref ArrayList list)
-               {
-                       return Parent.StealFinallyClauses (ref list);
-               }
-
                public bool IsAssigned (VariableInfo vi)
                {
                        return CurrentUsageVector.IsAssigned (vi, false);
@@ -517,7 +510,7 @@ namespace Mono.CSharp
 
                protected override void AddSibling (UsageVector sibling)
                {
-                       if (sibling.Type == SiblingType.Block && sibling_list != null)
+                       if (sibling_list != null && sibling_list.Type == SiblingType.Block)
                                throw new InternalErrorException ("Blocks don't have sibling flow paths");
                        sibling.Next = sibling_list;
                        sibling_list = sibling;
@@ -638,6 +631,22 @@ namespace Mono.CSharp
                }
        }
 
+       public class FlowBranchingIterator : FlowBranchingBlock
+       {
+               Iterator iterator;
+               public FlowBranchingIterator (FlowBranching parent, Iterator iterator)
+                       : base (parent, BranchingType.Iterator, SiblingType.Block, null, iterator.Location)
+               {
+                       this.iterator = iterator;
+               }
+
+               public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
+               {
+                       pc = iterator.AddResumePoint (stmt);
+                       return false;
+               }
+       }
+
        public class FlowBranchingToplevel : FlowBranchingBlock
        {
                UsageVector return_origins;
@@ -647,11 +656,17 @@ namespace Mono.CSharp
                {
                }
 
-               public override bool InTryWithCatch ()
+               public override bool CheckRethrow (Location loc)
                {
+                       Report.Error (156, loc, "A throw statement with no arguments is not allowed outside of a catch clause");
                        return false;
                }
 
+               public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
+               {
+                       throw new InternalErrorException ("A yield in a non-iterator block");
+               }
+
                public override bool AddBreakOrigin (UsageVector vector, Location loc)
                {
                        Report.Error (139, loc, "No enclosing loop out of which to break or continue");
@@ -664,20 +679,15 @@ namespace Mono.CSharp
                        return false;
                }
 
-               public override bool AddReturnOrigin (UsageVector vector, Location loc)
+               public override bool AddReturnOrigin (UsageVector vector, ExitStatement stmt)
                {
                        vector = vector.Clone ();
-                       vector.Location = loc;
+                       vector.Location = stmt.loc;
                        vector.Next = return_origins;
                        return_origins = vector;
                        return false;
                }
 
-               public override bool StealFinallyClauses (ref ArrayList list)
-               {
-                       return false;
-               }
-
                public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
                {
                        string name = goto_stmt.Target;
@@ -714,32 +724,146 @@ namespace Mono.CSharp
                }
        }
 
+       public class FlowBranchingTryCatch : FlowBranchingBlock
+       {
+               TryCatch stmt;
+               public FlowBranchingTryCatch (FlowBranching parent, TryCatch stmt)
+                       : base (parent, BranchingType.Block, SiblingType.Try, null, stmt.loc)
+               {
+                       this.stmt = stmt;
+               }
+
+               public override bool CheckRethrow (Location loc)
+               {
+                       return CurrentUsageVector.Next != null || Parent.CheckRethrow (loc);
+               }
+
+               public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
+               {
+                       int errors = Report.Errors;
+                       Parent.AddResumePoint (stmt, loc, out pc);
+                       if (errors == Report.Errors) {
+                               if (CurrentUsageVector.Next == null)
+                                       Report.Error (1626, loc, "Cannot yield a value in the body of a try block with a catch clause");
+                               else
+                                       Report.Error (1631, loc, "Cannot yield a value in the body of a catch clause");
+                       }
+                       return true;
+               }
+
+               public override bool AddBreakOrigin (UsageVector vector, Location loc)
+               {
+                       Parent.AddBreakOrigin (vector, loc);
+                       stmt.SomeCodeFollows ();
+                       return true;
+               }
+
+               public override bool AddContinueOrigin (UsageVector vector, Location loc)
+               {
+                       Parent.AddContinueOrigin (vector, loc);
+                       stmt.SomeCodeFollows ();
+                       return true;
+               }
+
+               public override bool AddReturnOrigin (UsageVector vector, ExitStatement exit_stmt)
+               {
+                       Parent.AddReturnOrigin (vector, exit_stmt);
+                       stmt.SomeCodeFollows ();
+                       return true;
+               }
+
+               public override bool AddGotoOrigin (UsageVector vector, Goto goto_stmt)
+               {
+                       Parent.AddGotoOrigin (vector, goto_stmt);
+                       return true;
+               }
+       }
+
        public class FlowBranchingException : FlowBranching
        {
                ExceptionStatement stmt;
                UsageVector current_vector;
-               UsageVector catch_vectors;
+               UsageVector try_vector;
                UsageVector finally_vector;
 
-               UsageVector break_origins;
-               UsageVector continue_origins;
-               UsageVector return_origins;
-               GotoOrigin goto_origins;
-
-               class GotoOrigin {
-                       public GotoOrigin Next;
-                       public Goto GotoStmt;
-                       public UsageVector Vector;
+               abstract class SavedOrigin {
+                       public readonly SavedOrigin Next;
+                       public readonly UsageVector Vector;
 
-                       public GotoOrigin (UsageVector vector, Goto goto_stmt, GotoOrigin next)
+                       protected SavedOrigin (SavedOrigin next, UsageVector vector)
                        {
-                               Vector = vector;
-                               GotoStmt = goto_stmt;
                                Next = next;
+                               Vector = vector.Clone ();
+                       }
+
+                       protected abstract void DoPropagateFinally (FlowBranching parent);
+                       public void PropagateFinally (UsageVector finally_vector, FlowBranching parent)
+                       {
+                               if (finally_vector != null)
+                                       Vector.MergeChild (finally_vector, false);
+                               DoPropagateFinally (parent);
+                       }
+               }
+
+               class BreakOrigin : SavedOrigin {
+                       Location Loc;
+                       public BreakOrigin (SavedOrigin next, UsageVector vector, Location loc)
+                               : base (next, vector)
+                       {
+                               Loc = loc;
+                       }
+
+                       protected override void DoPropagateFinally (FlowBranching parent)
+                       {
+                               parent.AddBreakOrigin (Vector, Loc);
+                       }
+               }
+
+               class ContinueOrigin : SavedOrigin {
+                       Location Loc;
+                       public ContinueOrigin (SavedOrigin next, UsageVector vector, Location loc)
+                               : base (next, vector)
+                       {
+                               Loc = loc;
+                       }
+
+                       protected override void DoPropagateFinally (FlowBranching parent)
+                       {
+                               parent.AddContinueOrigin (Vector, Loc);
+                       }
+               }
+
+               class ReturnOrigin : SavedOrigin {
+                       public ExitStatement Stmt;
+
+                       public ReturnOrigin (SavedOrigin next, UsageVector vector, ExitStatement stmt)
+                               : base (next, vector)
+                       {
+                               Stmt = stmt;
+                       }
+
+                       protected override void DoPropagateFinally (FlowBranching parent)
+                       {
+                               parent.AddReturnOrigin (Vector, Stmt);
                        }
                }
 
-               bool emit_finally;
+               class GotoOrigin : SavedOrigin {
+                       public Goto Stmt;
+
+                       public GotoOrigin (SavedOrigin next, UsageVector vector, Goto stmt)
+                               : base (next, vector)
+                       {
+                               Stmt = stmt;
+                       }
+
+                       protected override void DoPropagateFinally (FlowBranching parent)
+                       {
+                               parent.AddGotoOrigin (Vector, Stmt);
+                       }
+               }
+
+               SavedOrigin saved_origins;
 
                public FlowBranchingException (FlowBranching parent,
                                               ExceptionStatement stmt)
@@ -747,16 +871,13 @@ namespace Mono.CSharp
                                null, stmt.loc)
                {
                        this.stmt = stmt;
-                       this.emit_finally = true;
                }
 
                protected override void AddSibling (UsageVector sibling)
                {
                        switch (sibling.Type) {
                        case SiblingType.Try:
-                       case SiblingType.Catch:
-                               sibling.Next = catch_vectors;
-                               catch_vectors = sibling;
+                               try_vector = sibling;
                                break;
                        case SiblingType.Finally:
                                finally_vector = sibling;
@@ -771,65 +892,74 @@ namespace Mono.CSharp
                        get { return current_vector; }
                }
 
-               public override bool InTryWithCatch ()
+               public override bool CheckRethrow (Location loc)
                {
-                       if (finally_vector == null) {
-                               Try t = stmt as Try;
-                               if (t != null && t.HasCatch)
-                                       return true;
-                       }
+                       if (!Parent.CheckRethrow (loc))
+                               return false;
+                       if (finally_vector == null)
+                               return true;
+                       Report.Error (724, loc, "A throw statement with no arguments is not allowed inside of a finally clause nested inside of the innermost catch clause");
+                       return false;
+               }
 
-                       return base.InTryWithCatch ();
+               public override bool AddResumePoint (ResumableStatement stmt, Location loc, out int pc)
+               {
+                       int errors = Report.Errors;
+                       Parent.AddResumePoint (this.stmt, loc, out pc);
+                       if (errors == Report.Errors) {
+                               if (finally_vector == null)
+                                       this.stmt.AddResumePoint (stmt, pc);
+                               else
+                                       Report.Error (1625, loc, "Cannot yield in the body of a finally clause");
+                       }
+                       return true;
                }
 
                public override bool AddBreakOrigin (UsageVector vector, Location loc)
                {
-                       vector = vector.Clone ();
                        if (finally_vector != null) {
-                               vector.MergeChild (finally_vector, false);
                                int errors = Report.Errors;
                                Parent.AddBreakOrigin (vector, loc);
                                if (errors == Report.Errors)
                                        Report.Error (157, loc, "Control cannot leave the body of a finally clause");
                        } else {
-                               vector.Location = loc;
-                               vector.Next = break_origins;
-                               break_origins = vector;
+                               saved_origins = new BreakOrigin (saved_origins, vector, loc);
                        }
+
+                       // either the loop test or a back jump will follow code
+                       stmt.SomeCodeFollows ();
                        return true;
                }
 
                public override bool AddContinueOrigin (UsageVector vector, Location loc)
                {
-                       vector = vector.Clone ();
                        if (finally_vector != null) {
-                               vector.MergeChild (finally_vector, false);
                                int errors = Report.Errors;
                                Parent.AddContinueOrigin (vector, loc);
                                if (errors == Report.Errors)
                                        Report.Error (157, loc, "Control cannot leave the body of a finally clause");
                        } else {
-                               vector.Location = loc;
-                               vector.Next = continue_origins;
-                               continue_origins = vector;
+                               saved_origins = new ContinueOrigin (saved_origins, vector, loc);
                        }
+
+                       // either the loop test or a back jump will follow code
+                       stmt.SomeCodeFollows ();
                        return true;
                }
 
-               public override bool AddReturnOrigin (UsageVector vector, Location loc)
+               public override bool AddReturnOrigin (UsageVector vector, ExitStatement exit_stmt)
                {
-                       vector = vector.Clone ();
                        if (finally_vector != null) {
-                               vector.MergeChild (finally_vector, false);
                                int errors = Report.Errors;
-                               Parent.AddReturnOrigin (vector, loc);
+                               Parent.AddReturnOrigin (vector, exit_stmt);
                                if (errors == Report.Errors)
-                                       Report.Error (157, loc, "Control cannot leave the body of a finally clause");
+                                       exit_stmt.Error_FinallyClause ();
                        } else {
-                               vector.Location = loc;
-                               vector.Next = return_origins;
-                               return_origins = vector;
+                               saved_origins = new ReturnOrigin (saved_origins, vector, exit_stmt);
                        }
+
+                       // sets ec.NeedReturnLabel()
+                       stmt.SomeCodeFollows ();
                        return true;
                }
 
@@ -839,65 +969,26 @@ namespace Mono.CSharp
                        if (s != null)
                                throw new InternalErrorException ("Shouldn't get here");
 
-                       vector = vector.Clone ();
                        if (finally_vector != null) {
-                               vector.MergeChild (finally_vector, false);
                                int errors = Report.Errors;
                                Parent.AddGotoOrigin (vector, goto_stmt);
                                if (errors == Report.Errors)
                                        Report.Error (157, goto_stmt.loc, "Control cannot leave the body of a finally clause");
                        } else {
-                               goto_origins = new GotoOrigin (vector, goto_stmt, goto_origins);
+                               saved_origins = new GotoOrigin (saved_origins, vector, goto_stmt);
                        }
                        return true;
                }
 
-               public override bool StealFinallyClauses (ref ArrayList list)
-               {
-                       if (list == null)
-                               list = new ArrayList ();
-                       list.Add (stmt);
-                       emit_finally = false;
-                       base.StealFinallyClauses (ref list);
-                       return true;
-               }
-
-               public bool EmitFinally {
-                       get { return emit_finally; }
-               }
-
                protected override UsageVector Merge ()
                {
-                       Report.Debug (2, "  MERGING TRY/CATCH", Name);
-                       UsageVector vector = UsageVector.MergeSiblings (catch_vectors, Location);
-                       Report.Debug (2, "  MERGING TRY/CATCH DONE", vector);
+                       UsageVector vector = try_vector.Clone ();
 
                        if (finally_vector != null)
                                vector.MergeChild (finally_vector, false);
 
-                       for (UsageVector origin = break_origins; origin != null; origin = origin.Next) {
-                               if (finally_vector != null)
-                                       origin.MergeChild (finally_vector, false);
-                               Parent.AddBreakOrigin (origin, origin.Location);
-                       }
-
-                       for (UsageVector origin = continue_origins; origin != null; origin = origin.Next) {
-                               if (finally_vector != null)
-                                       origin.MergeChild (finally_vector, false);
-                               Parent.AddContinueOrigin (origin, origin.Location);
-                       }
-
-                       for (UsageVector origin = return_origins; origin != null; origin = origin.Next) {
-                               if (finally_vector != null)
-                                       origin.MergeChild (finally_vector, false);
-                               Parent.AddReturnOrigin (origin, origin.Location);
-                       }
-
-                       for (GotoOrigin origin = goto_origins; origin != null; origin = origin.Next) {
-                               if (finally_vector != null)
-                                       origin.Vector.MergeChild (finally_vector, false);
-                               Parent.AddGotoOrigin (origin.Vector, origin.GotoStmt);
-                       }
+                       for (SavedOrigin origin = saved_origins; origin != null; origin = origin.Next)
+                               origin.PropagateFinally (finally_vector, Parent);
 
                        return vector;
                }
@@ -947,8 +1038,19 @@ namespace Mono.CSharp
                // </summary>
                public TypeInfo[] SubStructInfo;
 
-               protected readonly StructInfo struct_info;
-               private static Hashtable type_hash = new Hashtable ();
+               readonly StructInfo struct_info;
+               private static Hashtable type_hash;
+               
+               static TypeInfo ()
+               {
+                       Reset ();
+               }
+               
+               public static void Reset ()
+               {
+                       type_hash = new Hashtable ();
+                       StructInfo.field_type_hash = new Hashtable ();
+               }
 
                public static TypeInfo GetTypeInfo (Type type)
                {
@@ -1006,7 +1108,7 @@ namespace Mono.CSharp
                        }
                }
 
-               protected TypeInfo (StructInfo struct_info, int offset)
+               TypeInfo (StructInfo struct_info, int offset)
                {
                        this.struct_info = struct_info;
                        this.Offset = offset;
@@ -1047,9 +1149,16 @@ namespace Mono.CSharp
                                FieldInfo field = struct_info.Fields [i];
 
                                if (!branching.IsFieldAssigned (vi, field.Name)) {
-                                       Report.Error (171, loc,
-                                               "Field `{0}' must be fully assigned before control leaves the constructor",
-                                               TypeManager.GetFullNameSignature (field));
+                                       FieldBase fb = TypeManager.GetField (field);
+                                       if (fb is Property.BackingField) {
+                                               Report.Error (843, loc,
+                                                       "An automatically implemented property `{0}' must be fully assigned before control leaves the constructor. Consider calling default contructor",
+                                                       fb.GetSignatureForError ());
+                                       } else {
+                                               Report.Error (171, loc,
+                                                       "Field `{0}' must be fully assigned before control leaves the constructor",
+                                                       TypeManager.GetFullNameSignature (field));
+                                       }
                                        ok = false;
                                }
                        }
@@ -1063,7 +1172,7 @@ namespace Mono.CSharp
                                              Type, Offset, Length, TotalLength);
                }
 
-               protected class StructInfo {
+               class StructInfo {
                        public readonly Type Type;
                        public readonly FieldInfo[] Fields;
                        public readonly TypeInfo[] StructFields;
@@ -1074,7 +1183,7 @@ namespace Mono.CSharp
                        public readonly int TotalLength;
                        public readonly bool HasStructFields;
 
-                       private static Hashtable field_type_hash = new Hashtable ();
+                       public static Hashtable field_type_hash;
                        private Hashtable struct_field_hash;
                        private Hashtable field_hash;
 
@@ -1088,16 +1197,18 @@ namespace Mono.CSharp
 
                                field_type_hash.Add (type, this);
 
-                               if (type is TypeBuilder) {
-                                       TypeContainer tc = TypeManager.LookupTypeContainer (type);
-
-                                       ArrayList fields = null;
-                                       if (tc != null)
-                                               fields = tc.Fields;
+                               if (type.Module == RootContext.ToplevelTypes.Builder) {
+                                       TypeContainer tc = TypeManager.LookupTypeContainer (TypeManager.DropGenericTypeArguments (type));
 
                                        ArrayList public_fields = new ArrayList ();
                                        ArrayList non_public_fields = new ArrayList ();
 
+                                       //
+                                       // TODO: tc != null is needed because FixedBuffers are not cached
+                                       //
+                                       if (tc != null) {                                       
+                                       ArrayList fields = tc.Fields;
+
                                        if (fields != null) {
                                                foreach (FieldBase field in fields) {
                                                        if ((field.ModFlags & Modifiers.STATIC) != 0)
@@ -1108,6 +1219,7 @@ namespace Mono.CSharp
                                                                non_public_fields.Add (field.FieldBuilder);
                                                }
                                        }
+                                       }
 
                                        CountPublic = public_fields.Count;
                                        CountNonPublic = non_public_fields.Count;
@@ -1116,12 +1228,10 @@ namespace Mono.CSharp
                                        Fields = new FieldInfo [Count];
                                        public_fields.CopyTo (Fields, 0);
                                        non_public_fields.CopyTo (Fields, CountPublic);
-#if GMCS_SOURCE
                                } else if (type is GenericTypeParameterBuilder) {
                                        CountPublic = CountNonPublic = Count = 0;
 
                                        Fields = new FieldInfo [0];
-#endif
                                } else {
                                        FieldInfo[] public_fields = type.GetFields (
                                                BindingFlags.Instance|BindingFlags.Public);
@@ -1200,6 +1310,9 @@ namespace Mono.CSharp
                                    TypeManager.IsBuiltinType (type))
                                        return null;
 
+                               if (TypeManager.IsGenericParameter (type))
+                                       return null;
+
                                StructInfo info = (StructInfo) field_type_hash [type];
                                if (info != null)
                                        return info;
@@ -1250,6 +1363,11 @@ namespace Mono.CSharp
                readonly VariableInfo Parent;
                VariableInfo[] sub_info;
 
+               bool is_ever_assigned;
+               public bool IsEverAssigned {
+                       get { return is_ever_assigned; }
+               }
+
                protected VariableInfo (string name, Type type, int offset)
                {
                        this.Name = name;
@@ -1295,8 +1413,8 @@ namespace Mono.CSharp
                        this.IsParameter = false;
                }
 
-               public VariableInfo (Parameters ip, int i, int offset)
-                       : this (ip.ParameterName (i), TypeManager.GetElementType (ip.ParameterType (i)), offset)
+               public VariableInfo (ParametersCompiled ip, int i, int offset)
+                       : this (ip.FixedParameters [i].Name, ip.Types [i], offset)
                {
                        this.IsParameter = true;
                }
@@ -1357,6 +1475,7 @@ namespace Mono.CSharp
                        }
 
                        vector [Offset] = true;
+                       is_ever_assigned = true;
                        return true;
                }
 
@@ -1372,6 +1491,7 @@ namespace Mono.CSharp
                                vector [Offset] = true;
                        else
                                vector.SetRange (Offset, Length);
+                       is_ever_assigned = true;
                }
 
                public bool IsFieldAssigned (EmitContext ec, string name, Location loc)
@@ -1411,6 +1531,7 @@ namespace Mono.CSharp
                                return;
 
                        vector [Offset + field_idx] = true;
+                       is_ever_assigned = true;
                }
 
                public VariableInfo GetSubStruct (string name)
@@ -1453,21 +1574,27 @@ namespace Mono.CSharp
                public MyBitVector (MyBitVector InheritsFrom, int Count)
                {
                        if (InheritsFrom != null)
-                               shared = InheritsFrom.Shared;
+                               shared = InheritsFrom.MakeShared (Count);
 
                        this.Count = Count;
                }
 
-               // Use this accessor to get a shareable copy of the underlying BitArray representation
-               BitArray Shared {
-                       get {
-                               // Post-condition: vector == null
-                               if (shared == null) {
-                                       shared = vector;
-                                       vector = null;
-                               }
-                               return shared;
+               BitArray MakeShared (int new_count)
+               {
+                       // Post-condition: vector == null
+
+                       // ensure we don't leak out dirty bits from the BitVector we inherited from
+                       if (new_count > Count &&
+                           ((shared != null && shared.Count > Count) ||
+                            (shared == null && vector == null)))
+                               initialize_vector ();
+
+                       if (vector != null) {
+                               shared = vector;
+                               vector = null;
                        }
+
+                       return shared;
                }
 
                // <summary>
@@ -1476,7 +1603,9 @@ namespace Mono.CSharp
                public bool this [int index] {
                        get {
                                if (index >= Count)
-                                       throw new ArgumentOutOfRangeException ();
+                                       // FIXME: Disabled due to missing anonymous method flow analysis
+                                       // throw new ArgumentOutOfRangeException ();
+                                       return true; 
 
                                if (vector != null)
                                        return vector [index];
@@ -1566,7 +1695,7 @@ namespace Mono.CSharp
                        if (Count == o.Count) {
                                if (vector == null) {
                                        if (shared == null) {
-                                               shared = new_vector.Shared;
+                                               shared = new_vector.MakeShared (Count);
                                                return this;
                                        }
                                        initialize_vector ();
@@ -1652,7 +1781,7 @@ namespace Mono.CSharp
                        // Don't clobber Empty
                        if (Count == 0)
                                return;
-                       shared = value ? null : Empty.Shared;
+                       shared = value ? null : Empty.MakeShared (Count);
                        vector = null;
                }