diff --git a/include/llvm/Metadata.h b/include/llvm/Metadata.h
index d16b7dc..2ea00e0 100644
--- a/include/llvm/Metadata.h
+++ b/include/llvm/Metadata.h
@@ -20,8 +20,6 @@
 #include "llvm/Type.h"
 #include "llvm/ADT/FoldingSet.h"
 #include "llvm/ADT/SmallVector.h"
-#include "llvm/ADT/DenseMap.h"
-#include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/ilist_node.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ValueHandle.h"
@@ -30,6 +28,7 @@
 class Constant;
 class Instruction;
 class LLVMContext;
+class MetadataContextImpl;
 
 //===----------------------------------------------------------------------===//
 // MetadataBase  - A base class for MDNode, MDString and NamedMDNode.
@@ -224,20 +223,15 @@
 /// must start with an alphabet. The regular expression used to check name
 /// is [a-zA-Z$._][a-zA-Z$._0-9]*
 class MetadataContext {
+  // DO NOT IMPLEMENT
+  MetadataContext(MetadataContext&);
+  void operator=(MetadataContext&);
+
+  MetadataContextImpl *const pImpl;
 public:
-  typedef std::pair<unsigned, TrackingVH<MDNode> > MDPairTy;
-  typedef SmallVector<MDPairTy, 2> MDMapTy;
-  typedef DenseMap<const Instruction *, MDMapTy> MDStoreTy;
-  friend class BitcodeReader;
-private:
+  MetadataContext();
+  ~MetadataContext();
 
-  /// MetadataStore - Collection of metadata used in this context.
-  MDStoreTy MetadataStore;
-
-  /// MDHandlerNames - Map to hold metadata handler names.
-  StringMap<unsigned> MDHandlerNames;
-
-public:
   /// registerMDKind - Register a new metadata kind and return its ID.
   /// A metadata kind can be registered only once. 
   unsigned registerMDKind(StringRef Name);
@@ -254,7 +248,8 @@
   MDNode *getMD(unsigned Kind, const Instruction *Inst);
 
   /// getMDs - Get the metadata attached to an Instruction.
-  void getMDs(const Instruction *Inst, SmallVectorImpl<MDPairTy> &MDs) const;
+  void getMDs(const Instruction *Inst, 
+        SmallVectorImpl<std::pair<unsigned, TrackingVH<MDNode> > > &MDs) const;
 
   /// addMD - Attach the metadata of given kind to an Instruction.
   void addMD(unsigned Kind, MDNode *Node, Instruction *Inst);
@@ -276,9 +271,7 @@
   /// ValueIsDeleted - This handler is used to update metadata store
   /// when a value is deleted.
   void ValueIsDeleted(const Value *) {}
-  void ValueIsDeleted(Instruction *Inst) {
-    removeAllMetadata(Inst);
-  }
+  void ValueIsDeleted(Instruction *Inst);
   void ValueIsRAUWd(Value *V1, Value *V2);
 
   /// ValueIsCloned - This handler is used to update metadata store
diff --git a/include/llvm/Value.h b/include/llvm/Value.h
index 6b393f6..c09fdfb 100644
--- a/include/llvm/Value.h
+++ b/include/llvm/Value.h
@@ -42,7 +42,7 @@
 class AssemblyAnnotationWriter;
 class ValueHandleBase;
 class LLVMContext;
-class MetadataContext;
+class MetadataContextImpl;
 
 //===----------------------------------------------------------------------===//
 //                                 Value Class
@@ -83,7 +83,7 @@
   friend class ValueSymbolTable; // Allow ValueSymbolTable to directly mod Name.
   friend class SymbolTable;      // Allow SymbolTable to directly poke Name.
   friend class ValueHandleBase;
-  friend class MetadataContext;
+  friend class MetadataContextImpl;
   friend class AbstractTypeUser;
   ValueName *Name;
 
diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 7f3be2b..3a385cb 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -840,7 +840,15 @@
       for (unsigned i = 1; i != RecordLength; ++i)
         Name[i-1] = Record[i];
       MetadataContext &TheMetadata = Context.getMetadata();
-      TheMetadata.MDHandlerNames[Name.str()] = Kind;
+      unsigned ExistingKind = TheMetadata.getMDKind(Name.str());
+      if (ExistingKind == 0) {
+        unsigned NewKind = TheMetadata.registerMDKind(Name.str());
+        assert (Kind == NewKind 
+                && "Unable to handle custom metadata mismatch!");
+      } else {
+        assert (ExistingKind == Kind 
+                && "Unable to handle custom metadata mismatch!");
+      }
       break;
     }
     }
diff --git a/lib/VMCore/Metadata.cpp b/lib/VMCore/Metadata.cpp
index fdac408..ad9653f 100644
--- a/lib/VMCore/Metadata.cpp
+++ b/lib/VMCore/Metadata.cpp
@@ -16,6 +16,8 @@
 #include "llvm/LLVMContext.h"
 #include "llvm/Module.h"
 #include "llvm/Instruction.h"
+#include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/StringMap.h"
 #include "SymbolTableListTraitsImpl.h"
 using namespace llvm;
 
@@ -182,48 +184,91 @@
 }
 
 //===----------------------------------------------------------------------===//
-// MetadataContext implementation.
+// MetadataContextImpl implementation.
 //
+namespace llvm {
+class MetadataContextImpl {
+public:
+  typedef std::pair<unsigned, TrackingVH<MDNode> > MDPairTy;
+  typedef SmallVector<MDPairTy, 2> MDMapTy;
+  typedef DenseMap<const Instruction *, MDMapTy> MDStoreTy;
+  friend class BitcodeReader;
+private:
+
+  /// MetadataStore - Collection of metadata used in this context.
+  MDStoreTy MetadataStore;
+
+  /// MDHandlerNames - Map to hold metadata handler names.
+  StringMap<unsigned> MDHandlerNames;
+
+public:
+  /// registerMDKind - Register a new metadata kind and return its ID.
+  /// A metadata kind can be registered only once. 
+  unsigned registerMDKind(StringRef Name);
+
+  /// getMDKind - Return metadata kind. If the requested metadata kind
+  /// is not registered then return 0.
+  unsigned getMDKind(StringRef Name) const;
+
+  /// getMD - Get the metadata of given kind attached to an Instruction.
+  /// If the metadata is not found then return 0.
+  MDNode *getMD(unsigned Kind, const Instruction *Inst);
+
+  /// getMDs - Get the metadata attached to an Instruction.
+  void getMDs(const Instruction *Inst, SmallVectorImpl<MDPairTy> &MDs) const;
+
+  /// addMD - Attach the metadata of given kind to an Instruction.
+  void addMD(unsigned Kind, MDNode *Node, Instruction *Inst);
+  
+  /// removeMD - Remove metadata of given kind attached with an instuction.
+  void removeMD(unsigned Kind, Instruction *Inst);
+  
+  /// removeAllMetadata - Remove all metadata attached with an instruction.
+  void removeAllMetadata(Instruction *Inst);
+
+  /// copyMD - If metadata is attached with Instruction In1 then attach
+  /// the same metadata to In2.
+  void copyMD(Instruction *In1, Instruction *In2);
+
+  /// getHandlerNames - Populate client supplied smallvector using custome
+  /// metadata name and ID.
+  void getHandlerNames(SmallVectorImpl<std::pair<unsigned, StringRef> >&) const;
+
+  /// ValueIsDeleted - This handler is used to update metadata store
+  /// when a value is deleted.
+  void ValueIsDeleted(const Value *) {}
+  void ValueIsDeleted(Instruction *Inst) {
+    removeAllMetadata(Inst);
+  }
+  void ValueIsRAUWd(Value *V1, Value *V2);
+
+  /// ValueIsCloned - This handler is used to update metadata store
+  /// when In1 is cloned to create In2.
+  void ValueIsCloned(const Instruction *In1, Instruction *In2);
+};
+}
 
 /// registerMDKind - Register a new metadata kind and return its ID.
 /// A metadata kind can be registered only once. 
-unsigned MetadataContext::registerMDKind(StringRef Name) {
-  assert(isValidName(Name) && "Invalid custome metadata name!");
+unsigned MetadataContextImpl::registerMDKind(StringRef Name) {
   unsigned Count = MDHandlerNames.size();
   assert(MDHandlerNames.count(Name) == 0 && "Already registered MDKind!");
   return MDHandlerNames[Name] = Count + 1;
 }
 
-/// isValidName - Return true if Name is a valid custom metadata handler name.
-bool MetadataContext::isValidName(StringRef MDName) {
-  if (MDName.empty())
-    return false;
-
-  if (!isalpha(MDName[0]))
-    return false;
-
-  for (StringRef::iterator I = MDName.begin() + 1, E = MDName.end(); I != E;
-       ++I) {
-    if (!isalnum(*I) && *I != '_' && *I != '-' && *I != '.')
-        return false;
-  }
-  return true;
-}
-
 /// getMDKind - Return metadata kind. If the requested metadata kind
 /// is not registered then return 0.
-unsigned MetadataContext::getMDKind(StringRef Name) const {
+unsigned MetadataContextImpl::getMDKind(StringRef Name) const {
   StringMap<unsigned>::const_iterator I = MDHandlerNames.find(Name);
-  if (I == MDHandlerNames.end()) {
-    assert(isValidName(Name) && "Invalid custome metadata name!");
+  if (I == MDHandlerNames.end())
     return 0;
-  }
 
   return I->getValue();
 }
 
 /// addMD - Attach the metadata of given kind to an Instruction.
-void MetadataContext::addMD(unsigned MDKind, MDNode *Node, Instruction *Inst) {
+void MetadataContextImpl::addMD(unsigned MDKind, MDNode *Node, 
+                                Instruction *Inst) {
   assert(Node && "Invalid null MDNode");
   Inst->HasMetadata = true;
   MDMapTy &Info = MetadataStore[Inst];
@@ -247,7 +292,7 @@
 }
 
 /// removeMD - Remove metadata of given kind attached with an instuction.
-void MetadataContext::removeMD(unsigned Kind, Instruction *Inst) {
+void MetadataContextImpl::removeMD(unsigned Kind, Instruction *Inst) {
   MDStoreTy::iterator I = MetadataStore.find(Inst);
   if (I == MetadataStore.end())
     return;
@@ -263,14 +308,14 @@
 }
   
 /// removeAllMetadata - Remove all metadata attached with an instruction.
-void MetadataContext::removeAllMetadata(Instruction *Inst) {
+void MetadataContextImpl::removeAllMetadata(Instruction *Inst) {
   MetadataStore.erase(Inst);
   Inst->HasMetadata = false;
 }
 
 /// copyMD - If metadata is attached with Instruction In1 then attach
 /// the same metadata to In2.
-void MetadataContext::copyMD(Instruction *In1, Instruction *In2) {
+void MetadataContextImpl::copyMD(Instruction *In1, Instruction *In2) {
   assert(In1 && In2 && "Invalid instruction!");
   MDMapTy &In1Info = MetadataStore[In1];
   if (In1Info.empty())
@@ -282,7 +327,7 @@
 
 /// getMD - Get the metadata of given kind attached to an Instruction.
 /// If the metadata is not found then return 0.
-MDNode *MetadataContext::getMD(unsigned MDKind, const Instruction *Inst) {
+MDNode *MetadataContextImpl::getMD(unsigned MDKind, const Instruction *Inst) {
   MDMapTy &Info = MetadataStore[Inst];
   if (Info.empty())
     return NULL;
@@ -294,7 +339,7 @@
 }
 
 /// getMDs - Get the metadata attached to an Instruction.
-void MetadataContext::
+void MetadataContextImpl::
 getMDs(const Instruction *Inst, SmallVectorImpl<MDPairTy> &MDs) const {
   MDStoreTy::iterator I = MetadataStore.find(Inst);
   if (I == MetadataStore.end())
@@ -307,7 +352,7 @@
 
 /// getHandlerNames - Populate client supplied smallvector using custome
 /// metadata name and ID.
-void MetadataContext::
+void MetadataContextImpl::
 getHandlerNames(SmallVectorImpl<std::pair<unsigned, StringRef> >&Names) const {
   for (StringMap<unsigned>::const_iterator I = MDHandlerNames.begin(),
          E = MDHandlerNames.end(); I != E; ++I) 
@@ -317,7 +362,8 @@
 
 /// ValueIsCloned - This handler is used to update metadata store
 /// when In1 is cloned to create In2.
-void MetadataContext::ValueIsCloned(const Instruction *In1, Instruction *In2) {
+void MetadataContextImpl::ValueIsCloned(const Instruction *In1, 
+                                        Instruction *In2) {
   // Find Metadata handles for In1.
   MDStoreTy::iterator I = MetadataStore.find(In1);
   assert(I != MetadataStore.end() && "Invalid custom metadata info!");
@@ -332,7 +378,7 @@
 
 /// ValueIsRAUWd - This handler is used when V1's all uses are replaced by
 /// V2.
-void MetadataContext::ValueIsRAUWd(Value *V1, Value *V2) {
+void MetadataContextImpl::ValueIsRAUWd(Value *V1, Value *V2) {
   Instruction *I1 = dyn_cast<Instruction>(V1);
   Instruction *I2 = dyn_cast<Instruction>(V2);
   if (!I1 || !I2)
@@ -342,3 +388,94 @@
   ValueIsCloned(I1, I2);
 }
 
+//===----------------------------------------------------------------------===//
+// MetadataContext implementation.
+//
+MetadataContext::MetadataContext() 
+  : pImpl(new MetadataContextImpl()) { }
+MetadataContext::~MetadataContext() { delete pImpl; }
+
+/// isValidName - Return true if Name is a valid custom metadata handler name.
+bool MetadataContext::isValidName(StringRef MDName) {
+  if (MDName.empty())
+    return false;
+
+  if (!isalpha(MDName[0]))
+    return false;
+
+  for (StringRef::iterator I = MDName.begin() + 1, E = MDName.end(); I != E;
+       ++I) {
+    if (!isalnum(*I) && *I != '_' && *I != '-' && *I != '.')
+        return false;
+  }
+  return true;
+}
+
+/// registerMDKind - Register a new metadata kind and return its ID.
+/// A metadata kind can be registered only once. 
+unsigned MetadataContext::registerMDKind(StringRef Name) {
+  assert(isValidName(Name) && "Invalid custome metadata name!");
+  return pImpl->registerMDKind(Name);
+}
+
+/// getMDKind - Return metadata kind. If the requested metadata kind
+/// is not registered then return 0.
+unsigned MetadataContext::getMDKind(StringRef Name) const {
+  return pImpl->getMDKind(Name);
+}
+
+/// getMD - Get the metadata of given kind attached to an Instruction.
+/// If the metadata is not found then return 0.
+MDNode *MetadataContext::getMD(unsigned Kind, const Instruction *Inst) {
+  return pImpl->getMD(Kind, Inst);
+}
+
+/// getMDs - Get the metadata attached to an Instruction.
+void MetadataContext::
+getMDs(const Instruction *Inst, 
+       SmallVectorImpl<std::pair<unsigned, TrackingVH<MDNode> > > &MDs) const {
+  return pImpl->getMDs(Inst, MDs);
+}
+
+/// addMD - Attach the metadata of given kind to an Instruction.
+void MetadataContext::addMD(unsigned Kind, MDNode *Node, Instruction *Inst) {
+  pImpl->addMD(Kind, Node, Inst);
+}
+  
+/// removeMD - Remove metadata of given kind attached with an instuction.
+void MetadataContext::removeMD(unsigned Kind, Instruction *Inst) {
+  pImpl->removeMD(Kind, Inst);
+}
+  
+/// removeAllMetadata - Remove all metadata attached with an instruction.
+void MetadataContext::removeAllMetadata(Instruction *Inst) {
+  pImpl->removeAllMetadata(Inst);
+}
+
+/// copyMD - If metadata is attached with Instruction In1 then attach
+/// the same metadata to In2.
+void MetadataContext::copyMD(Instruction *In1, Instruction *In2) {
+  pImpl->copyMD(In1, In2);
+}
+
+/// getHandlerNames - Populate client supplied smallvector using custome
+/// metadata name and ID.
+void MetadataContext::
+getHandlerNames(SmallVectorImpl<std::pair<unsigned, StringRef> >&N) const {
+  pImpl->getHandlerNames(N);
+}
+
+/// ValueIsDeleted - This handler is used to update metadata store
+/// when a value is deleted.
+void MetadataContext::ValueIsDeleted(Instruction *Inst) {
+  pImpl->ValueIsDeleted(Inst);
+}
+void MetadataContext::ValueIsRAUWd(Value *V1, Value *V2) {
+  pImpl->ValueIsRAUWd(V1, V2);
+}
+
+/// ValueIsCloned - This handler is used to update metadata store
+/// when In1 is cloned to create In2.
+void MetadataContext::ValueIsCloned(const Instruction *In1, Instruction *In2) {
+  pImpl->ValueIsCloned(In1, In2);
+}
diff --git a/lib/VMCore/Pass.cpp b/lib/VMCore/Pass.cpp
index a2831d3..a17eed8 100644
--- a/lib/VMCore/Pass.cpp
+++ b/lib/VMCore/Pass.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Module.h"
 #include "llvm/ModuleProvider.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/StringMap.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/raw_ostream.h"
 #include "llvm/System/Atomic.h"