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diff --git a/include/llvm/Support/ValueHandle.h b/include/llvm/Support/ValueHandle.h
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+++ b/include/llvm/Support/ValueHandle.h
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+//===- llvm/Support/ValueHandle.h - Value Smart Pointer classes -*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file declares the ValueHandle class and its sub-classes.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_VALUEHANDLE_H
+#define LLVM_SUPPORT_VALUEHANDLE_H
+
+#include "llvm/ADT/PointerIntPair.h"
+#include "llvm/Value.h"
+
+namespace llvm {
+class ValueHandleBase;
+
+// ValueHandleBase** is only 4-byte aligned.
+template<>
+class PointerLikeTypeTraits<ValueHandleBase**> {
+public:
+  static inline void *getAsVoidPointer(ValueHandleBase** P) { return P; }
+  static inline ValueHandleBase **getFromVoidPointer(void *P) {
+    return static_cast<ValueHandleBase**>(P);
+  }
+  enum { NumLowBitsAvailable = 2 };
+};
+
+/// ValueHandleBase - This is the common base class of value handles.
+/// ValueHandle's are smart pointers to Value's that have special behavior when
+/// the value is deleted or ReplaceAllUsesWith'd.  See the specific handles
+/// below for details.
+///
+class ValueHandleBase {
+  friend class Value;
+protected:
+  /// HandleBaseKind - This indicates what sub class the handle actually is.
+  /// This is to avoid having a vtable for the light-weight handle pointers. The
+  /// fully general Callback version does have a vtable.
+  enum HandleBaseKind {
+    Assert,
+    Weak,
+    Callback
+  };
+private:
+  
+  PointerIntPair<ValueHandleBase**, 2, HandleBaseKind> PrevPair;
+  ValueHandleBase *Next;
+  Value *VP;
+public:
+  explicit ValueHandleBase(HandleBaseKind Kind)
+    : PrevPair(0, Kind), Next(0), VP(0) {}
+  ValueHandleBase(HandleBaseKind Kind, Value *V)
+    : PrevPair(0, Kind), Next(0), VP(V) {
+    if (V)
+      AddToUseList();
+  }
+  ValueHandleBase(HandleBaseKind Kind, const ValueHandleBase &RHS)
+    : PrevPair(0, Kind), Next(0), VP(RHS.VP) {
+    if (VP)
+      AddToExistingUseList(RHS.getPrevPtr());
+  }
+  ~ValueHandleBase() {
+    if (VP)
+      RemoveFromUseList();   
+  }
+  
+  Value *operator=(Value *RHS) {
+    if (VP == RHS) return RHS;
+    if (VP) RemoveFromUseList();
+    VP = RHS;
+    if (VP) AddToUseList();
+    return RHS;
+  }
+
+  Value *operator=(const ValueHandleBase &RHS) {
+    if (VP == RHS.VP) return RHS.VP;
+    if (VP) RemoveFromUseList();
+    VP = RHS.VP;
+    if (VP) AddToExistingUseList(RHS.getPrevPtr());
+    return VP;
+  }
+  
+  Value *operator->() const { return getValPtr(); }
+  Value &operator*() const { return *getValPtr(); }
+
+protected:
+  Value *getValPtr() const { return VP; }
+private:
+  // Callbacks made from Value.
+  static void ValueIsDeleted(Value *V);
+  static void ValueIsRAUWd(Value *Old, Value *New);
+  
+  // Internal implementation details.
+  ValueHandleBase **getPrevPtr() const { return PrevPair.getPointer(); }
+  HandleBaseKind getKind() const { return PrevPair.getInt(); }
+  void setPrevPtr(ValueHandleBase **Ptr) { PrevPair.setPointer(Ptr); }
+  
+  /// AddToUseList - Add this ValueHandle to the use list for VP, where List is
+  /// known to point into the existing use list.
+  void AddToExistingUseList(ValueHandleBase **List);
+  
+  /// AddToUseList - Add this ValueHandle to the use list for VP.
+  void AddToUseList();
+  /// RemoveFromUseList - Remove this ValueHandle from its current use list.
+  void RemoveFromUseList();
+};
+  
+/// WeakVH - This is a value handle that tries hard to point to a Value, even
+/// across RAUW operations, but will null itself out if the value is destroyed.
+/// this is useful for advisory sorts of information, but should not be used as
+/// the key of a map (since the map would have to rearrange itself when the
+/// pointer changes).
+class WeakVH : public ValueHandleBase {
+public:
+  WeakVH() : ValueHandleBase(Weak) {}
+  WeakVH(Value *P) : ValueHandleBase(Weak, P) {}
+  WeakVH(const WeakVH &RHS)
+    : ValueHandleBase(Weak, RHS) {}
+
+  operator Value*() const {
+    return getValPtr();
+  }
+};
+
+// Specialize simplify_type to allow WeakVH to participate in
+// dyn_cast, isa, etc.
+template<typename From> struct simplify_type;
+template<> struct simplify_type<const WeakVH> {
+  typedef Value* SimpleType;
+  static SimpleType getSimplifiedValue(const WeakVH &WVH) {
+    return static_cast<Value *>(WVH);
+  }
+};
+template<> struct simplify_type<WeakVH> : public simplify_type<const WeakVH> {};
+
+/// AssertingVH - This is a Value Handle that points to a value and asserts out
+/// if the value is destroyed while the handle is still live.  This is very
+/// useful for catching dangling pointer bugs and other things which can be
+/// non-obvious.  One particularly useful place to use this is as the Key of a
+/// map.  Dangling pointer bugs often lead to really subtle bugs that only occur
+/// if another object happens to get allocated to the same address as the old
+/// one.  Using an AssertingVH ensures that an assert is triggered as soon as
+/// the bad delete occurs.
+///
+/// Note that an AssertingVH handle does *not* follow values across RAUW
+/// operations.  This means that RAUW's need to explicitly update the
+/// AssertingVH's as it moves.  This is required because in non-assert mode this
+/// class turns into a trivial wrapper around a pointer.
+template <typename ValueTy>
+class AssertingVH 
+#ifndef NDEBUG
+  : public ValueHandleBase
+#endif
+  {
+
+#ifndef NDEBUG
+  ValueTy *getValPtr() const {
+    return static_cast<ValueTy*>(ValueHandleBase::getValPtr());
+  }
+  void setValPtr(ValueTy *P) {
+    ValueHandleBase::operator=(P);
+  }
+#else
+  ValueTy *ThePtr;
+  ValueTy *getValPtr() const { return ThePtr; }
+  void setValPtr(ValueTy *P) { ThePtr = P; }
+#endif
+
+public:
+#ifndef NDEBUG
+  AssertingVH() : ValueHandleBase(Assert) {}
+  AssertingVH(ValueTy *P) : ValueHandleBase(Assert, P) {}
+  AssertingVH(const AssertingVH &RHS) : ValueHandleBase(Assert, RHS) {}
+#else
+  AssertingVH() : ThePtr(0) {}
+  AssertingVH(ValueTy *P) : ThePtr(P) {}
+#endif
+
+  operator ValueTy*() const {
+    return getValPtr();
+  }
+
+  ValueTy *operator=(ValueTy *RHS) {
+    setValPtr(RHS);
+    return getValPtr();
+  }
+  ValueTy *operator=(AssertingVH<ValueTy> &RHS) {
+    setValPtr(RHS.getValPtr());
+    return getValPtr();
+  }
+
+  ValueTy *operator->() const { return getValPtr(); }
+  ValueTy &operator*() const { return *getValPtr(); }
+};
+
+// Specialize simplify_type to allow AssertingVH to participate in
+// dyn_cast, isa, etc.
+template<typename From> struct simplify_type;
+template<> struct simplify_type<const AssertingVH<Value> > {
+  typedef Value* SimpleType;
+  static SimpleType getSimplifiedValue(const AssertingVH<Value> &AVH) {
+    return static_cast<Value *>(AVH);
+  }
+};
+template<> struct simplify_type<AssertingVH<Value> >
+  : public simplify_type<const AssertingVH<Value> > {};
+
+/// CallbackVH - This is a value handle that allows subclasses to define
+/// callbacks that run when the underlying Value has RAUW called on it or is
+/// destroyed.  This class can be used as the key of a map, as long as the user
+/// takes it out of the map before calling setValPtr() (since the map has to
+/// rearrange itself when the pointer changes).  Unlike ValueHandleBase, this
+/// class has a vtable and a virtual destructor.
+class CallbackVH : public ValueHandleBase {
+protected:
+  CallbackVH(const CallbackVH &RHS)
+    : ValueHandleBase(Callback, RHS) {}
+
+  virtual ~CallbackVH();
+
+  void setValPtr(Value *P) {
+    ValueHandleBase::operator=(P);
+  }
+
+public:
+  CallbackVH() : ValueHandleBase(Callback) {}
+  CallbackVH(Value *P) : ValueHandleBase(Callback, P) {}
+
+  operator Value*() const {
+    return getValPtr();
+  }
+
+  /// Called when this->getValPtr() is destroyed, inside ~Value(), so you may
+  /// call any non-virtual Value method on getValPtr(), but no subclass methods.
+  /// If WeakVH were implemented as a CallbackVH, it would use this method to
+  /// call setValPtr(NULL).  AssertingVH would use this method to cause an
+  /// assertion failure.
+  ///
+  /// All implementations must remove the reference from this object to the
+  /// Value that's being destroyed.
+  virtual void deleted() {
+    setValPtr(NULL);
+  }
+
+  /// Called when this->getValPtr()->replaceAllUsesWith(new_value) is called,
+  /// _before_ any of the uses have actually been replaced.  If WeakVH were
+  /// implemented as a CallbackVH, it would use this method to call
+  /// setValPtr(new_value).  AssertingVH would do nothing in this method.
+  virtual void allUsesReplacedWith(Value *new_value) {}
+};
+
+// Specialize simplify_type to allow CallbackVH to participate in
+// dyn_cast, isa, etc.
+template<typename From> struct simplify_type;
+template<> struct simplify_type<const CallbackVH> {
+  typedef Value* SimpleType;
+  static SimpleType getSimplifiedValue(const CallbackVH &CVH) {
+    return static_cast<Value *>(CVH);
+  }
+};
+template<> struct simplify_type<CallbackVH>
+  : public simplify_type<const CallbackVH> {};
+
+} // End llvm namespace
+
+#endif