[Mono-bugs] [Bug 398325] New: [PATCH] Use of unassigned local variable not recognized for variables declared after end of scope of an assigned variable

[bugzilla_noreply at novell.com]

https://bugzilla.novell.com/show_bug.cgi?id=398325


           Summary: [PATCH] Use of unassigned local variable not recognized
                    for variables declared after end of scope of an assigned
                    variable
           Product: Mono: Compilers
           Version: SVN
          Platform: x86-64
        OS/Version: Windows Vista
            Status: NEW
          Keywords: patch
          Severity: Normal
          Priority: P5 - None
         Component: C#
        AssignedTo: mono-bugs at lists.ximian.com
        ReportedBy: Moritz.Kroll at gmx.de
         QAContact: mono-bugs at lists.ximian.com
          Found By: ---


Description of Problem:
The following code compiles without an error:

class test
{
        static void Main(string[] args)
        {
                {
                        int x = 8;
                }
                string y;
                args[0] = y;    // use of unassigned variable y
        }
}

This happens for two reasons:
 - The UsageVector is not shortened to the number of variables available in the
outer block, when a flow branching ends, and
 - when a MyBitVector is inherited from a smaller vector which inherits from a
larger vector, the values of the old larger vector are used instead of false
values.


Fix:

Index: flowanalysis.cs
===================================================================
--- flowanalysis.cs     (revision 105252)
+++ flowanalysis.cs     (working copy)
@@ -287,6 +287,11 @@
                                return new UsageVector (locals, is_unreachable,
null, loc);
                        }

+                       public void Shorten (int newSize)
+                       {
+                               locals = locals.Shorten (newSize);
+                       }
+
                        // <summary>
                        //   Merges a child branching.
                        // </summary>
@@ -406,7 +411,9 @@

                public UsageVector MergeChild (FlowBranching child)
                {
-                       return CurrentUsageVector.MergeChild (child.Merge (),
true);
+                       UsageVector result = CurrentUsageVector.MergeChild
(child.Merge (), true);
+                       CurrentUsageVector.Shorten
(CurrentUsageVector.CountLocals);
+                       return result;
                }

                public virtual bool CheckRethrow (Location loc)
@@ -1556,10 +1563,21 @@

                public MyBitVector (MyBitVector InheritsFrom, int Count)
                {
+                       this.Count = Count;
+
                        if (InheritsFrom != null)
-                               shared = InheritsFrom.Shared;
-
-                       this.Count = Count;
+                       {
+                               if (Count > InheritsFrom.Count)
+                               {
+                                       // Create a new larger vector and
initialize lower bits with InheritsFrom
+                                       // and rest with false
+                                       for (int i = 0; i < InheritsFrom.Count;
i++)
+                                               this[i] = InheritsFrom[i];
+                                       for (int i = InheritsFrom.Count; i <
Count; i++)
+                                               this[i] = false;
+                               }
+                               else shared = InheritsFrom.Shared;
+                       }
                }

                // Use this accessor to get a shareable copy of the underlying
BitArray representation
@@ -1602,6 +1620,21 @@
                }

                // <summary>
+               //   Shortens the bit vector to the given number of bits.
+               //   An exception is thrown if the new number of bits is
greater than the current.
+               // </summary>
+               public MyBitVector Shorten (int newCount)
+               {
+                       if (newCount > Count)
+                               throw new ArgumentOutOfRangeException ();
+
+                       if (newCount == Count)
+                               return this;
+
+                       return new MyBitVector (this, newCount);
+               }
+
+               // <summary>
                //   Performs an `or' operation on the bit vector.  The
`new_vector' may have a
                //   different size than the current one.
                // </summary>


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