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diff --git a/include/llvm/IR/User.h b/include/llvm/IR/User.h
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+++ b/include/llvm/IR/User.h
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+//===-- llvm/User.h - User class definition ---------------------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This class defines the interface that one who uses a Value must implement.
+// Each instance of the Value class keeps track of what User's have handles
+// to it.
+//
+//  * Instructions are the largest class of Users.
+//  * Constants may be users of other constants (think arrays and stuff)
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_USER_H
+#define LLVM_USER_H
+
+#include "llvm/IR/Value.h"
+#include "llvm/Support/ErrorHandling.h"
+
+namespace llvm {
+
+/// OperandTraits - Compile-time customization of
+/// operand-related allocators and accessors
+/// for use of the User class
+template <class>
+struct OperandTraits;
+
+class User : public Value {
+  User(const User &) LLVM_DELETED_FUNCTION;
+  void *operator new(size_t) LLVM_DELETED_FUNCTION;
+  template <unsigned>
+  friend struct HungoffOperandTraits;
+  virtual void anchor();
+protected:
+  /// OperandList - This is a pointer to the array of Uses for this User.
+  /// For nodes of fixed arity (e.g. a binary operator) this array will live
+  /// prefixed to some derived class instance.  For nodes of resizable variable
+  /// arity (e.g. PHINodes, SwitchInst etc.), this memory will be dynamically
+  /// allocated and should be destroyed by the classes' virtual dtor.
+  Use *OperandList;
+
+  /// NumOperands - The number of values used by this User.
+  ///
+  unsigned NumOperands;
+
+  void *operator new(size_t s, unsigned Us);
+  User(Type *ty, unsigned vty, Use *OpList, unsigned NumOps)
+    : Value(ty, vty), OperandList(OpList), NumOperands(NumOps) {}
+  Use *allocHungoffUses(unsigned) const;
+  void dropHungoffUses() {
+    Use::zap(OperandList, OperandList + NumOperands, true);
+    OperandList = 0;
+    // Reset NumOperands so User::operator delete() does the right thing.
+    NumOperands = 0;
+  }
+public:
+  ~User() {
+    Use::zap(OperandList, OperandList + NumOperands);
+  }
+  /// operator delete - free memory allocated for User and Use objects
+  void operator delete(void *Usr);
+  /// placement delete - required by std, but never called.
+  void operator delete(void*, unsigned) {
+    llvm_unreachable("Constructor throws?");
+  }
+  /// placement delete - required by std, but never called.
+  void operator delete(void*, unsigned, bool) {
+    llvm_unreachable("Constructor throws?");
+  }
+protected:
+  template <int Idx, typename U> static Use &OpFrom(const U *that) {
+    return Idx < 0
+      ? OperandTraits<U>::op_end(const_cast<U*>(that))[Idx]
+      : OperandTraits<U>::op_begin(const_cast<U*>(that))[Idx];
+  }
+  template <int Idx> Use &Op() {
+    return OpFrom<Idx>(this);
+  }
+  template <int Idx> const Use &Op() const {
+    return OpFrom<Idx>(this);
+  }
+public:
+  Value *getOperand(unsigned i) const {
+    assert(i < NumOperands && "getOperand() out of range!");
+    return OperandList[i];
+  }
+  void setOperand(unsigned i, Value *Val) {
+    assert(i < NumOperands && "setOperand() out of range!");
+    assert((!isa<Constant>((const Value*)this) ||
+            isa<GlobalValue>((const Value*)this)) &&
+           "Cannot mutate a constant with setOperand!");
+    OperandList[i] = Val;
+  }
+  const Use &getOperandUse(unsigned i) const {
+    assert(i < NumOperands && "getOperandUse() out of range!");
+    return OperandList[i];
+  }
+  Use &getOperandUse(unsigned i) {
+    assert(i < NumOperands && "getOperandUse() out of range!");
+    return OperandList[i];
+  }
+
+  unsigned getNumOperands() const { return NumOperands; }
+
+  // ---------------------------------------------------------------------------
+  // Operand Iterator interface...
+  //
+  typedef Use*       op_iterator;
+  typedef const Use* const_op_iterator;
+
+  inline op_iterator       op_begin()       { return OperandList; }
+  inline const_op_iterator op_begin() const { return OperandList; }
+  inline op_iterator       op_end()         { return OperandList+NumOperands; }
+  inline const_op_iterator op_end()   const { return OperandList+NumOperands; }
+
+  /// Convenience iterator for directly iterating over the Values in the
+  /// OperandList
+  class value_op_iterator : public std::iterator<std::forward_iterator_tag,
+                                                 Value*> {
+    op_iterator OI;
+  public:
+    explicit value_op_iterator(Use *U) : OI(U) {}
+
+    bool operator==(const value_op_iterator &x) const {
+      return OI == x.OI;
+    }
+    bool operator!=(const value_op_iterator &x) const {
+      return !operator==(x);
+    }
+
+    /// Iterator traversal: forward iteration only
+    value_op_iterator &operator++() {          // Preincrement
+      ++OI;
+      return *this;
+    }
+    value_op_iterator operator++(int) {        // Postincrement
+      value_op_iterator tmp = *this; ++*this; return tmp;
+    }
+
+    /// Retrieve a pointer to the current Value.
+    Value *operator*() const {
+      return *OI;
+    }
+
+    Value *operator->() const { return operator*(); }
+  };
+
+  inline value_op_iterator value_op_begin() {
+    return value_op_iterator(op_begin());
+  }
+  inline value_op_iterator value_op_end() {
+    return value_op_iterator(op_end());
+  }
+
+  // dropAllReferences() - This function is in charge of "letting go" of all
+  // objects that this User refers to.  This allows one to
+  // 'delete' a whole class at a time, even though there may be circular
+  // references...  First all references are dropped, and all use counts go to
+  // zero.  Then everything is deleted for real.  Note that no operations are
+  // valid on an object that has "dropped all references", except operator
+  // delete.
+  //
+  void dropAllReferences() {
+    for (op_iterator i = op_begin(), e = op_end(); i != e; ++i)
+      i->set(0);
+  }
+
+  /// replaceUsesOfWith - Replaces all references to the "From" definition with
+  /// references to the "To" definition.
+  ///
+  void replaceUsesOfWith(Value *From, Value *To);
+
+  // Methods for support type inquiry through isa, cast, and dyn_cast:
+  static inline bool classof(const Value *V) {
+    return isa<Instruction>(V) || isa<Constant>(V);
+  }
+};
+
+template<> struct simplify_type<User::op_iterator> {
+  typedef Value* SimpleType;
+
+  static SimpleType getSimplifiedValue(const User::op_iterator &Val) {
+    return static_cast<SimpleType>(Val->get());
+  }
+};
+
+template<> struct simplify_type<const User::op_iterator>
+  : public simplify_type<User::op_iterator> {};
+
+template<> struct simplify_type<User::const_op_iterator> {
+  typedef Value* SimpleType;
+
+  static SimpleType getSimplifiedValue(const User::const_op_iterator &Val) {
+    return static_cast<SimpleType>(Val->get());
+  }
+};
+
+template<> struct simplify_type<const User::const_op_iterator>
+  : public simplify_type<User::const_op_iterator> {};
+
+
+// value_use_iterator::getOperandNo - Requires the definition of the User class.
+template<typename UserTy>
+unsigned value_use_iterator<UserTy>::getOperandNo() const {
+  return U - U->getUser()->op_begin();
+}
+
+} // End llvm namespace
+
+#endif