diff --git a/include/llvm/ADT/DenseMap.h b/include/llvm/ADT/DenseMap.h
index 52354b7f222..83299478e92 100644
--- a/include/llvm/ADT/DenseMap.h
+++ b/include/llvm/ADT/DenseMap.h
@@ -14,8 +14,9 @@
 #ifndef LLVM_ADT_DENSEMAP_H
 #define LLVM_ADT_DENSEMAP_H
 
-#include "llvm/Support/PointerLikeTypeTraits.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/PointerLikeTypeTraits.h"
+#include "llvm/Support/type_traits.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include <iterator>
 #include <new>
@@ -27,12 +28,8 @@ namespace llvm {
 
 template<typename KeyT, typename ValueT,
          typename KeyInfoT = DenseMapInfo<KeyT>,
-         typename ValueInfoT = DenseMapInfo<ValueT> >
+         typename ValueInfoT = DenseMapInfo<ValueT>, bool IsConst = false>
 class DenseMapIterator;
-template<typename KeyT, typename ValueT,
-         typename KeyInfoT = DenseMapInfo<KeyT>,
-         typename ValueInfoT = DenseMapInfo<ValueT> >
-class DenseMapConstIterator;
 
 template<typename KeyT, typename ValueT,
          typename KeyInfoT = DenseMapInfo<KeyT>,
@@ -73,7 +70,8 @@ public:
   }
 
   typedef DenseMapIterator<KeyT, ValueT, KeyInfoT> iterator;
-  typedef DenseMapConstIterator<KeyT, ValueT, KeyInfoT> const_iterator;
+  typedef DenseMapIterator<KeyT, ValueT,
+                           KeyInfoT, ValueInfoT, true> const_iterator;
   inline iterator begin() {
      return iterator(Buckets, Buckets+NumBuckets);
   }
@@ -426,32 +424,47 @@ private:
   }
 };
 
-template<typename KeyT, typename ValueT, typename KeyInfoT, typename ValueInfoT>
-class DenseMapIterator : 
-      public std::iterator<std::forward_iterator_tag, std::pair<KeyT, ValueT>,
-                          ptrdiff_t> {
-  typedef std::pair<KeyT, ValueT> BucketT;
-protected:
-  const BucketT *Ptr, *End;
+template<typename KeyT, typename ValueT,
+         typename KeyInfoT, typename ValueInfoT, bool IsConst>
+class DenseMapIterator {
+  typedef std::pair<KeyT, ValueT> Bucket;
+  typedef DenseMapIterator<KeyT, ValueT,
+                           KeyInfoT, ValueInfoT, true> ConstIterator;
+  friend class DenseMapIterator<KeyT, ValueT, KeyInfoT, ValueInfoT, true>;
+public:
+  typedef ptrdiff_t difference_type;
+  typedef typename conditional<IsConst, const Bucket, Bucket>::type value_type;
+  typedef value_type *pointer;
+  typedef value_type &reference;
+  typedef std::forward_iterator_tag iterator_category;
+private:
+  pointer Ptr, End;
 public:
   DenseMapIterator() : Ptr(0), End(0) {}
 
-  DenseMapIterator(const BucketT *Pos, const BucketT *E) : Ptr(Pos), End(E) {
+  DenseMapIterator(pointer Pos, pointer E) : Ptr(Pos), End(E) {
     AdvancePastEmptyBuckets();
   }
 
-  std::pair<KeyT, ValueT> &operator*() const {
-    return *const_cast<BucketT*>(Ptr);
+  // If IsConst is true this is a converting constructor from iterator to
+  // const_iterator and the default copy constructor is used.
+  // Otherwise this is a copy constructor for iterator.
+  DenseMapIterator(const DenseMapIterator<KeyT, ValueT,
+                                          KeyInfoT, ValueInfoT, false>& I)
+    : Ptr(I.Ptr), End(I.End) {}
+
+  reference operator*() const {
+    return *Ptr;
   }
-  std::pair<KeyT, ValueT> *operator->() const {
-    return const_cast<BucketT*>(Ptr);
+  pointer operator->() const {
+    return Ptr;
   }
 
-  bool operator==(const DenseMapIterator &RHS) const {
-    return Ptr == RHS.Ptr;
+  bool operator==(const ConstIterator &RHS) const {
+    return Ptr == RHS.operator->();
   }
-  bool operator!=(const DenseMapIterator &RHS) const {
-    return Ptr != RHS.Ptr;
+  bool operator!=(const ConstIterator &RHS) const {
+    return Ptr != RHS.operator->();
   }
 
   inline DenseMapIterator& operator++() {  // Preincrement
@@ -475,22 +488,6 @@ private:
   }
 };
 
-template<typename KeyT, typename ValueT, typename KeyInfoT, typename ValueInfoT>
-class DenseMapConstIterator : public DenseMapIterator<KeyT, ValueT, KeyInfoT> {
-public:
-  DenseMapConstIterator() : DenseMapIterator<KeyT, ValueT, KeyInfoT>() {}
-  DenseMapConstIterator(const std::pair<KeyT, ValueT> *Pos,
-                        const std::pair<KeyT, ValueT> *E)
-    : DenseMapIterator<KeyT, ValueT, KeyInfoT>(Pos, E) {
-  }
-  const std::pair<KeyT, ValueT> &operator*() const {
-    return *this->Ptr;
-  }
-  const std::pair<KeyT, ValueT> *operator->() const {
-    return this->Ptr;
-  }
-};
-
 } // end namespace llvm
 
 #endif
diff --git a/include/llvm/Analysis/SparsePropagation.h b/include/llvm/Analysis/SparsePropagation.h
index 820e1bd1e43..677d41d80b2 100644
--- a/include/llvm/Analysis/SparsePropagation.h
+++ b/include/llvm/Analysis/SparsePropagation.h
@@ -153,7 +153,7 @@ public:
   /// value.  If an value is not in the map, it is returned as untracked,
   /// unlike the getOrInitValueState method.
   LatticeVal getLatticeState(Value *V) const {
-    DenseMap<Value*, LatticeVal>::iterator I = ValueState.find(V);
+    DenseMap<Value*, LatticeVal>::const_iterator I = ValueState.find(V);
     return I != ValueState.end() ? I->second : LatticeFunc->getUntrackedVal();
   }
   
diff --git a/include/llvm/Support/type_traits.h b/include/llvm/Support/type_traits.h
index cfaae4b8419..ce916b5fcc6 100644
--- a/include/llvm/Support/type_traits.h
+++ b/include/llvm/Support/type_traits.h
@@ -96,6 +96,12 @@ template <typename T> struct remove_pointer<T*volatile> { typedef T type; };
 template <typename T> struct remove_pointer<T*const volatile> {
     typedef T type; };
 
+template <bool, typename T, typename F>
+struct conditional { typedef T type; };
+
+template <typename T, typename F>
+struct conditional<false, T, F> { typedef F type; };
+
 }
 
 #endif
diff --git a/lib/Analysis/IPA/Andersens.cpp b/lib/Analysis/IPA/Andersens.cpp
index 17f304c0211..40a8cd5b23e 100644
--- a/lib/Analysis/IPA/Andersens.cpp
+++ b/lib/Analysis/IPA/Andersens.cpp
@@ -518,7 +518,7 @@ namespace {
     /// getObject - Return the node corresponding to the memory object for the
     /// specified global or allocation instruction.
     unsigned getObject(Value *V) const {
-      DenseMap<Value*, unsigned>::iterator I = ObjectNodes.find(V);
+      DenseMap<Value*, unsigned>::const_iterator I = ObjectNodes.find(V);
       assert(I != ObjectNodes.end() &&
              "Value does not have an object in the points-to graph!");
       return I->second;
@@ -527,7 +527,7 @@ namespace {
     /// getReturnNode - Return the node representing the return value for the
     /// specified function.
     unsigned getReturnNode(Function *F) const {
-      DenseMap<Function*, unsigned>::iterator I = ReturnNodes.find(F);
+      DenseMap<Function*, unsigned>::const_iterator I = ReturnNodes.find(F);
       assert(I != ReturnNodes.end() && "Function does not return a value!");
       return I->second;
     }
@@ -535,7 +535,7 @@ namespace {
     /// getVarargNode - Return the node representing the variable arguments
     /// formal for the specified function.
     unsigned getVarargNode(Function *F) const {
-      DenseMap<Function*, unsigned>::iterator I = VarargNodes.find(F);
+      DenseMap<Function*, unsigned>::const_iterator I = VarargNodes.find(F);
       assert(I != VarargNodes.end() && "Function does not take var args!");
       return I->second;
     }
diff --git a/lib/CodeGen/AsmPrinter/DwarfException.cpp b/lib/CodeGen/AsmPrinter/DwarfException.cpp
index 6c03b559b77..8c1c0c98ec4 100644
--- a/lib/CodeGen/AsmPrinter/DwarfException.cpp
+++ b/lib/CodeGen/AsmPrinter/DwarfException.cpp
@@ -497,7 +497,7 @@ ComputeCallSiteTable(SmallVectorImpl<CallSiteEntry> &CallSites,
         SawPotentiallyThrowing = false;
 
       // Beginning of a new try-range?
-      RangeMapType::iterator L = PadMap.find(BeginLabel);
+      RangeMapType::const_iterator L = PadMap.find(BeginLabel);
       if (L == PadMap.end())
         // Nope, it was just some random label.
         continue;
diff --git a/lib/CodeGen/PreAllocSplitting.cpp b/lib/CodeGen/PreAllocSplitting.cpp
index 374ae667938..e23024c085a 100644
--- a/lib/CodeGen/PreAllocSplitting.cpp
+++ b/lib/CodeGen/PreAllocSplitting.cpp
@@ -366,10 +366,10 @@ PreAllocSplitting::IsAvailableInStack(MachineBasicBlock *DefMBB,
   if (!DefMBB)
     return false;
 
-  DenseMap<unsigned, int>::iterator I = IntervalSSMap.find(Reg);
+  DenseMap<unsigned, int>::const_iterator I = IntervalSSMap.find(Reg);
   if (I == IntervalSSMap.end())
     return false;
-  DenseMap<SlotIndex, SlotIndex>::iterator
+  DenseMap<SlotIndex, SlotIndex>::const_iterator
     II = Def2SpillMap.find(DefIndex);
   if (II == Def2SpillMap.end())
     return false;
diff --git a/lib/CodeGen/SlotIndexes.cpp b/lib/CodeGen/SlotIndexes.cpp
index 9519114b5a3..7365ec1b9a0 100644
--- a/lib/CodeGen/SlotIndexes.cpp
+++ b/lib/CodeGen/SlotIndexes.cpp
@@ -201,7 +201,7 @@ void SlotIndexes::dump() const {
     }
   }
 
-  for (MBB2IdxMap::iterator itr = mbb2IdxMap.begin();
+  for (MBB2IdxMap::const_iterator itr = mbb2IdxMap.begin();
        itr != mbb2IdxMap.end(); ++itr) {
     errs() << "MBB " << itr->first->getNumber() << " (" << itr->first << ") - ["
            << itr->second.first << ", " << itr->second.second << "]\n";
diff --git a/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp b/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
index e9e5d34ba51..c0084be9179 100644
--- a/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
+++ b/lib/Target/MSP430/MSP430ISelDAGToDAG.cpp
@@ -364,7 +364,7 @@ bool MSP430DAGToDAGISel::IsLegalAndProfitableToFold(SDNode *N, SDNode *U,
   /// TokenFactor by PreprocessForRMW. Query the map Store => Load1 (created
   /// during preprocessing) to determine whether it's legal to introduce such
   /// "cycle" for a moment.
-  DenseMap<SDNode*, SDNode*>::iterator I = RMWStores.find(Root);
+  DenseMap<SDNode*, SDNode*>::const_iterator I = RMWStores.find(Root);
   if (I != RMWStores.end() && I->second == N)
     return true;
 
diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 87bc10d9fe0..c7d9aaa9d54 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -2170,7 +2170,7 @@ X86InstrInfo::foldMemoryOperandImpl(MachineFunction &MF,
   // If table selected...
   if (OpcodeTablePtr) {
     // Find the Opcode to fuse
-    DenseMap<unsigned*, std::pair<unsigned,unsigned> >::iterator I =
+    DenseMap<unsigned*, std::pair<unsigned,unsigned> >::const_iterator I =
       OpcodeTablePtr->find((unsigned*)MI->getOpcode());
     if (I != OpcodeTablePtr->end()) {
       unsigned Opcode = I->second.first;
@@ -2402,7 +2402,7 @@ bool X86InstrInfo::canFoldMemoryOperand(const MachineInstr *MI,
   
   if (OpcodeTablePtr) {
     // Find the Opcode to fuse
-    DenseMap<unsigned*, std::pair<unsigned,unsigned> >::iterator I =
+    DenseMap<unsigned*, std::pair<unsigned,unsigned> >::const_iterator I =
       OpcodeTablePtr->find((unsigned*)Opc);
     if (I != OpcodeTablePtr->end())
       return true;
@@ -2413,7 +2413,7 @@ bool X86InstrInfo::canFoldMemoryOperand(const MachineInstr *MI,
 bool X86InstrInfo::unfoldMemoryOperand(MachineFunction &MF, MachineInstr *MI,
                                 unsigned Reg, bool UnfoldLoad, bool UnfoldStore,
                                 SmallVectorImpl<MachineInstr*> &NewMIs) const {
-  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::iterator I =
+  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::const_iterator I =
     MemOp2RegOpTable.find((unsigned*)MI->getOpcode());
   if (I == MemOp2RegOpTable.end())
     return false;
@@ -2530,7 +2530,7 @@ X86InstrInfo::unfoldMemoryOperand(SelectionDAG &DAG, SDNode *N,
   if (!N->isMachineOpcode())
     return false;
 
-  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::iterator I =
+  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::const_iterator I =
     MemOp2RegOpTable.find((unsigned*)N->getMachineOpcode());
   if (I == MemOp2RegOpTable.end())
     return false;
@@ -2623,7 +2623,7 @@ X86InstrInfo::unfoldMemoryOperand(SelectionDAG &DAG, SDNode *N,
 unsigned X86InstrInfo::getOpcodeAfterMemoryUnfold(unsigned Opc,
                                       bool UnfoldLoad, bool UnfoldStore,
                                       unsigned *LoadRegIndex) const {
-  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::iterator I =
+  DenseMap<unsigned*, std::pair<unsigned,unsigned> >::const_iterator I =
     MemOp2RegOpTable.find((unsigned*)Opc);
   if (I == MemOp2RegOpTable.end())
     return 0;
diff --git a/lib/Transforms/Scalar/ABCD.cpp b/lib/Transforms/Scalar/ABCD.cpp
index 3ceda0cbec3..e58fa636047 100644
--- a/lib/Transforms/Scalar/ABCD.cpp
+++ b/lib/Transforms/Scalar/ABCD.cpp
@@ -1049,7 +1049,7 @@ void ABCD::InequalityGraph::printHeader(raw_ostream &OS, Function &F) const {
 
 /// Prints the body of the dot file
 void ABCD::InequalityGraph::printBody(raw_ostream &OS) const {
-  DenseMap<Value *, SmallPtrSet<Edge *, 16> >::iterator begin =
+  DenseMap<Value *, SmallPtrSet<Edge *, 16> >::const_iterator begin =
       graph.begin(), end = graph.end();
 
   for (; begin != end ; ++begin) {
diff --git a/lib/Transforms/Scalar/GVN.cpp b/lib/Transforms/Scalar/GVN.cpp
index 0e3f7507da8..30ab8286d24 100644
--- a/lib/Transforms/Scalar/GVN.cpp
+++ b/lib/Transforms/Scalar/GVN.cpp
@@ -624,7 +624,7 @@ uint32_t ValueTable::lookup_or_add(Value *V) {
 /// lookup - Returns the value number of the specified value. Fails if
 /// the value has not yet been numbered.
 uint32_t ValueTable::lookup(Value *V) const {
-  DenseMap<Value*, uint32_t>::iterator VI = valueNumbering.find(V);
+  DenseMap<Value*, uint32_t>::const_iterator VI = valueNumbering.find(V);
   assert(VI != valueNumbering.end() && "Value not numbered?");
   return VI->second;
 }
@@ -644,7 +644,7 @@ void ValueTable::erase(Value *V) {
 /// verifyRemoved - Verify that the value is removed from all internal data
 /// structures.
 void ValueTable::verifyRemoved(const Value *V) const {
-  for (DenseMap<Value*, uint32_t>::iterator
+  for (DenseMap<Value*, uint32_t>::const_iterator
          I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
     assert(I->first != V && "Inst still occurs in value numbering map!");
   }
@@ -2011,12 +2011,12 @@ void GVN::verifyRemoved(const Instruction *Inst) const {
 
   // Walk through the value number scope to make sure the instruction isn't
   // ferreted away in it.
-  for (DenseMap<BasicBlock*, ValueNumberScope*>::iterator
+  for (DenseMap<BasicBlock*, ValueNumberScope*>::const_iterator
          I = localAvail.begin(), E = localAvail.end(); I != E; ++I) {
     const ValueNumberScope *VNS = I->second;
 
     while (VNS) {
-      for (DenseMap<uint32_t, Value*>::iterator
+      for (DenseMap<uint32_t, Value*>::const_iterator
              II = VNS->table.begin(), IE = VNS->table.end(); II != IE; ++II) {
         assert(II->second != Inst && "Inst still in value numbering scope!");
       }
diff --git a/lib/Transforms/Scalar/SCCVN.cpp b/lib/Transforms/Scalar/SCCVN.cpp
index c047fca9938..8dd718ab218 100644
--- a/lib/Transforms/Scalar/SCCVN.cpp
+++ b/lib/Transforms/Scalar/SCCVN.cpp
@@ -507,7 +507,7 @@ void ValueTable::erase(Value *V) {
 /// verifyRemoved - Verify that the value is removed from all internal data
 /// structures.
 void ValueTable::verifyRemoved(const Value *V) const {
-  for (DenseMap<Value*, uint32_t>::iterator
+  for (DenseMap<Value*, uint32_t>::const_iterator
          I = valueNumbering.begin(), E = valueNumbering.end(); I != E; ++I) {
     assert(I->first != V && "Inst still occurs in value numbering map!");
   }
diff --git a/lib/VMCore/Metadata.cpp b/lib/VMCore/Metadata.cpp
index 4fadfed503b..c84afb2ea09 100644
--- a/lib/VMCore/Metadata.cpp
+++ b/lib/VMCore/Metadata.cpp
@@ -341,11 +341,11 @@ MDNode *MetadataContextImpl::getMD(unsigned MDKind, const Instruction *Inst) {
 /// getMDs - Get the metadata attached to an Instruction.
 void MetadataContextImpl::
 getMDs(const Instruction *Inst, SmallVectorImpl<MDPairTy> &MDs) const {
-  MDStoreTy::iterator I = MetadataStore.find(Inst);
+  MDStoreTy::const_iterator I = MetadataStore.find(Inst);
   if (I == MetadataStore.end())
     return;
   MDs.resize(I->second.size());
-  for (MDMapTy::iterator MI = I->second.begin(), ME = I->second.end();
+  for (MDMapTy::const_iterator MI = I->second.begin(), ME = I->second.end();
        MI != ME; ++MI)
     // MD kinds are numbered from 1.
     MDs[MI->first - 1] = std::make_pair(MI->first, MI->second);
diff --git a/unittests/ADT/DenseMapTest.cpp b/unittests/ADT/DenseMapTest.cpp
index 15a5379fb8d..afac651a6b2 100644
--- a/unittests/ADT/DenseMapTest.cpp
+++ b/unittests/ADT/DenseMapTest.cpp
@@ -164,4 +164,16 @@ TEST_F(DenseMapTest, IterationTest) {
   }
 }
 
+// const_iterator test
+TEST_F(DenseMapTest, ConstIteratorTest) {
+  // Check conversion from iterator to const_iterator.
+  DenseMap<uint32_t, uint32_t>::iterator it = uintMap.begin();
+  DenseMap<uint32_t, uint32_t>::const_iterator cit(it);
+  EXPECT_TRUE(it == cit);
+
+  // Check copying of const_iterators.
+  DenseMap<uint32_t, uint32_t>::const_iterator cit2(cit);
+  EXPECT_TRUE(cit == cit2);
+}
+
 }