X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=include%2Fllvm%2FADT%2FDenseMap.h;h=e18be8963d48bda4032b4425b5a41762e062754b;hb=d6a2aab53e3c4fcd53399cfa6f66d62913e53663;hp=577c4a21c5ba8a5998facde9d26189457b40c952;hpb=6e94c00ab29e654125e845f3bce692a3764c1c11;p=oota-llvm.git

diff --git a/include/llvm/ADT/DenseMap.h b/include/llvm/ADT/DenseMap.h
index 577c4a21c5b..e18be8963d4 100644
--- a/include/llvm/ADT/DenseMap.h
+++ b/include/llvm/ADT/DenseMap.h
@@ -2,8 +2,8 @@
 //
 //                     The LLVM Compiler Infrastructure
 //
-// This file was developed by Chris Lattner and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 //
@@ -14,98 +14,364 @@
 #ifndef LLVM_ADT_DENSEMAP_H
 #define LLVM_ADT_DENSEMAP_H
 
-#include "llvm/Support/DataTypes.h"
+#include "llvm/Support/PointerLikeTypeTraits.h"
+#include "llvm/Support/MathExtras.h"
 #include <cassert>
+#include <utility>
+#include <new>
 
 namespace llvm {
-  
+
 template<typename T>
-struct DenseMapKeyInfo {
+struct DenseMapInfo {
   //static inline T getEmptyKey();
   //static inline T getTombstoneKey();
   //static unsigned getHashValue(const T &Val);
+  //static bool isEqual(const T &LHS, const T &RHS);
   //static bool isPod()
 };
 
+// Provide DenseMapInfo for all pointers.
 template<typename T>
-struct DenseMapKeyInfo<T*> {
-  static inline T* getEmptyKey() { return (T*)-1; }
-  static inline T* getTombstoneKey() { return (T*)-2; }
+struct DenseMapInfo<T*> {
+  static inline T* getEmptyKey() {
+    intptr_t Val = -1;
+    Val <<= PointerLikeTypeTraits<T*>::NumLowBitsAvailable;
+    return reinterpret_cast<T*>(Val);
+  }
+  static inline T* getTombstoneKey() {
+    intptr_t Val = -2;
+    Val <<= PointerLikeTypeTraits<T*>::NumLowBitsAvailable;
+    return reinterpret_cast<T*>(Val);
+  }
   static unsigned getHashValue(const T *PtrVal) {
-    return (unsigned)((uintptr_t)PtrVal >> 4) ^
-           (unsigned)((uintptr_t)PtrVal >> 9);
+    return (unsigned((uintptr_t)PtrVal) >> 4) ^
+           (unsigned((uintptr_t)PtrVal) >> 9);
   }
+  static bool isEqual(const T *LHS, const T *RHS) { return LHS == RHS; }
   static bool isPod() { return true; }
 };
 
+// Provide DenseMapInfo for chars.
+template<> struct DenseMapInfo<char> {
+  static inline char getEmptyKey() { return ~0; }
+  static inline char getTombstoneKey() { return ~0 - 1; }
+  static unsigned getHashValue(const char& Val) { return Val * 37; }
+  static bool isPod() { return true; }
+  static bool isEqual(const char &LHS, const char &RHS) {
+    return LHS == RHS;
+  }
+};
+  
+// Provide DenseMapInfo for unsigned ints.
+template<> struct DenseMapInfo<unsigned> {
+  static inline unsigned getEmptyKey() { return ~0; }
+  static inline unsigned getTombstoneKey() { return ~0 - 1; }
+  static unsigned getHashValue(const unsigned& Val) { return Val * 37; }
+  static bool isPod() { return true; }
+  static bool isEqual(const unsigned& LHS, const unsigned& RHS) {
+  return LHS == RHS;
+  }
+};
 
-template<typename KeyT, typename ValueT>
+// Provide DenseMapInfo for unsigned longs.
+template<> struct DenseMapInfo<unsigned long> {
+  static inline unsigned long getEmptyKey() { return ~0L; }
+  static inline unsigned long getTombstoneKey() { return ~0L - 1L; }
+  static unsigned getHashValue(const unsigned long& Val) {
+    return (unsigned)(Val * 37L);
+  }
+  static bool isPod() { return true; }
+  static bool isEqual(const unsigned long& LHS, const unsigned long& RHS) {
+  return LHS == RHS;
+  }
+};
+
+// Provide DenseMapInfo for all pairs whose members have info.
+template<typename T, typename U>
+struct DenseMapInfo<std::pair<T, U> > {
+  typedef std::pair<T, U> Pair;
+  typedef DenseMapInfo<T> FirstInfo;
+  typedef DenseMapInfo<U> SecondInfo;
+
+  static inline Pair getEmptyKey() {
+    return std::make_pair(FirstInfo::getEmptyKey(),
+                          SecondInfo::getEmptyKey());
+  }
+  static inline Pair getTombstoneKey() {
+    return std::make_pair(FirstInfo::getTombstoneKey(),
+                            SecondInfo::getEmptyKey());
+  }
+  static unsigned getHashValue(const Pair& PairVal) {
+    uint64_t key = (uint64_t)FirstInfo::getHashValue(PairVal.first) << 32
+          | (uint64_t)SecondInfo::getHashValue(PairVal.second);
+    key += ~(key << 32);
+    key ^= (key >> 22);
+    key += ~(key << 13);
+    key ^= (key >> 8);
+    key += (key << 3);
+    key ^= (key >> 15);
+    key += ~(key << 27);
+    key ^= (key >> 31);
+    return (unsigned)key;
+  }
+  static bool isEqual(const Pair& LHS, const Pair& RHS) { return LHS == RHS; }
+  static bool isPod() { return FirstInfo::isPod() && SecondInfo::isPod(); }
+};
+
+template<typename KeyT, typename ValueT,
+         typename KeyInfoT = DenseMapInfo<KeyT>,
+         typename ValueInfoT = DenseMapInfo<ValueT> >
+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>,
+         typename ValueInfoT = DenseMapInfo<ValueT> >
 class DenseMap {
-  struct BucketT { KeyT Key; ValueT Value; };
+  typedef std::pair<KeyT, ValueT> BucketT;
   unsigned NumBuckets;
   BucketT *Buckets;
-  
+
   unsigned NumEntries;
-  DenseMap(const DenseMap &); // not implemented.
+  unsigned NumTombstones;
 public:
-  explicit DenseMap(unsigned NumInitBuckets = 8) {
+  typedef KeyT key_type;
+  typedef ValueT mapped_type;
+  typedef BucketT value_type;
+
+  DenseMap(const DenseMap& other) {
+    NumBuckets = 0;
+    CopyFrom(other);
+  }
+
+  explicit DenseMap(unsigned NumInitBuckets = 64) {
     init(NumInitBuckets);
   }
+
   ~DenseMap() {
     const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
     for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
-      if (P->Key != EmptyKey && P->Key != TombstoneKey)
-        P->Value.~ValueT();
-      P->Key.~KeyT();
+      if (!KeyInfoT::isEqual(P->first, EmptyKey) &&
+          !KeyInfoT::isEqual(P->first, TombstoneKey))
+        P->second.~ValueT();
+      P->first.~KeyT();
     }
-    delete[] (char*)Buckets;
+    operator delete(Buckets);
   }
-  
+
+  typedef DenseMapIterator<KeyT, ValueT, KeyInfoT> iterator;
+  typedef DenseMapConstIterator<KeyT, ValueT, KeyInfoT> const_iterator;
+  inline iterator begin() {
+     return iterator(Buckets, Buckets+NumBuckets);
+  }
+  inline iterator end() {
+    return iterator(Buckets+NumBuckets, Buckets+NumBuckets);
+  }
+  inline const_iterator begin() const {
+    return const_iterator(Buckets, Buckets+NumBuckets);
+  }
+  inline const_iterator end() const {
+    return const_iterator(Buckets+NumBuckets, Buckets+NumBuckets);
+  }
+
+  bool empty() const { return NumEntries == 0; }
   unsigned size() const { return NumEntries; }
-  
+
+  /// Grow the densemap so that it has at least Size buckets. Does not shrink
+  void resize(size_t Size) { grow(Size); }
+
   void clear() {
+    // If the capacity of the array is huge, and the # elements used is small,
+    // shrink the array.
+    if (NumEntries * 4 < NumBuckets && NumBuckets > 64) {
+      shrink_and_clear();
+      return;
+    }
+
     const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
     for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
-      if (P->Key != EmptyKey && P->Key != TombstoneKey) {
-        P->Key = EmptyKey;
-        P->Value.~ValueT();
-        --NumEntries;
+      if (!KeyInfoT::isEqual(P->first, EmptyKey)) {
+        if (!KeyInfoT::isEqual(P->first, TombstoneKey)) {
+          P->second.~ValueT();
+          --NumEntries;
+        }
+        P->first = EmptyKey;
       }
     }
     assert(NumEntries == 0 && "Node count imbalance!");
+    NumTombstones = 0;
   }
-  
+
   /// count - Return true if the specified key is in the map.
   bool count(const KeyT &Val) const {
     BucketT *TheBucket;
     return LookupBucketFor(Val, TheBucket);
   }
-  
-  ValueT &operator[](const KeyT &Val) {
+
+  iterator find(const KeyT &Val) {
+    BucketT *TheBucket;
+    if (LookupBucketFor(Val, TheBucket))
+      return iterator(TheBucket, Buckets+NumBuckets);
+    return end();
+  }
+  const_iterator find(const KeyT &Val) const {
     BucketT *TheBucket;
     if (LookupBucketFor(Val, TheBucket))
-      return TheBucket->Value;
+      return const_iterator(TheBucket, Buckets+NumBuckets);
+    return end();
+  }
+
+  /// lookup - Return the entry for the specified key, or a default
+  /// constructed value if no such entry exists.
+  ValueT lookup(const KeyT &Val) const {
+    BucketT *TheBucket;
+    if (LookupBucketFor(Val, TheBucket))
+      return TheBucket->second;
+    return ValueT();
+  }
+
+  std::pair<iterator, bool> insert(const std::pair<KeyT, ValueT> &KV) {
+    BucketT *TheBucket;
+    if (LookupBucketFor(KV.first, TheBucket))
+      return std::make_pair(iterator(TheBucket, Buckets+NumBuckets),
+                            false); // Already in map.
+
+    // Otherwise, insert the new element.
+    TheBucket = InsertIntoBucket(KV.first, KV.second, TheBucket);
+    return std::make_pair(iterator(TheBucket, Buckets+NumBuckets),
+                          true);
+  }
+
+  /// insert - Range insertion of pairs.
+  template<typename InputIt>
+  void insert(InputIt I, InputIt E) {
+    for (; I != E; ++I)
+      insert(*I);
+  }
+
+
+  bool erase(const KeyT &Val) {
+    BucketT *TheBucket;
+    if (!LookupBucketFor(Val, TheBucket))
+      return false; // not in map.
+
+    TheBucket->second.~ValueT();
+    TheBucket->first = getTombstoneKey();
+    --NumEntries;
+    ++NumTombstones;
+    return true;
+  }
+  bool erase(iterator I) {
+    BucketT *TheBucket = &*I;
+    TheBucket->second.~ValueT();
+    TheBucket->first = getTombstoneKey();
+    --NumEntries;
+    ++NumTombstones;
+    return true;
+  }
+
+  value_type& FindAndConstruct(const KeyT &Key) {
+    BucketT *TheBucket;
+    if (LookupBucketFor(Key, TheBucket))
+      return *TheBucket;
+
+    return *InsertIntoBucket(Key, ValueT(), TheBucket);
+  }
+
+  ValueT &operator[](const KeyT &Key) {
+    return FindAndConstruct(Key).second;
+  }
+
+  DenseMap& operator=(const DenseMap& other) {
+    CopyFrom(other);
+    return *this;
+  }
 
-    // If the load of the hash table is more than 3/4, grow it.
-    if (NumEntries*4 >= NumBuckets*3) {
-      this->grow();
-      LookupBucketFor(Val, TheBucket);
+  /// isPointerIntoBucketsArray - Return true if the specified pointer points
+  /// somewhere into the DenseMap's array of buckets (i.e. either to a key or
+  /// value in the DenseMap).
+  bool isPointerIntoBucketsArray(const void *Ptr) const {
+    return Ptr >= Buckets && Ptr < Buckets+NumBuckets;
+  }
+
+  /// getPointerIntoBucketsArray() - Return an opaque pointer into the buckets
+  /// array.  In conjunction with the previous method, this can be used to
+  /// determine whether an insertion caused the DenseMap to reallocate.
+  const void *getPointerIntoBucketsArray() const { return Buckets; }
+
+private:
+  void CopyFrom(const DenseMap& other) {
+    if (NumBuckets != 0 && (!KeyInfoT::isPod() || !ValueInfoT::isPod())) {
+      const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
+      for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
+        if (!KeyInfoT::isEqual(P->first, EmptyKey) &&
+            !KeyInfoT::isEqual(P->first, TombstoneKey))
+          P->second.~ValueT();
+        P->first.~KeyT();
+      }
     }
+
+    NumEntries = other.NumEntries;
+    NumTombstones = other.NumTombstones;
+
+    if (NumBuckets)
+      operator delete(Buckets);
+    Buckets = static_cast<BucketT*>(operator new(sizeof(BucketT) *
+                                                 other.NumBuckets));
+
+    if (KeyInfoT::isPod() && ValueInfoT::isPod())
+      memcpy(Buckets, other.Buckets, other.NumBuckets * sizeof(BucketT));
+    else
+      for (size_t i = 0; i < other.NumBuckets; ++i) {
+        new (&Buckets[i].first) KeyT(other.Buckets[i].first);
+        if (!KeyInfoT::isEqual(Buckets[i].first, getEmptyKey()) &&
+            !KeyInfoT::isEqual(Buckets[i].first, getTombstoneKey()))
+          new (&Buckets[i].second) ValueT(other.Buckets[i].second);
+      }
+    NumBuckets = other.NumBuckets;
+  }
+
+  BucketT *InsertIntoBucket(const KeyT &Key, const ValueT &Value,
+                            BucketT *TheBucket) {
+    // If the load of the hash table is more than 3/4, or if fewer than 1/8 of
+    // the buckets are empty (meaning that many are filled with tombstones),
+    // grow the table.
+    //
+    // The later case is tricky.  For example, if we had one empty bucket with
+    // tons of tombstones, failing lookups (e.g. for insertion) would have to
+    // probe almost the entire table until it found the empty bucket.  If the
+    // table completely filled with tombstones, no lookup would ever succeed,
+    // causing infinite loops in lookup.
     ++NumEntries;
-    TheBucket->Key = Val;
-    new (&TheBucket->Value) ValueT();
-    return TheBucket->Value;
+    if (NumEntries*4 >= NumBuckets*3 ||
+        NumBuckets-(NumEntries+NumTombstones) < NumBuckets/8) {
+      this->grow(NumBuckets * 2);
+      LookupBucketFor(Key, TheBucket);
+    }
+
+    // If we are writing over a tombstone, remember this.
+    if (!KeyInfoT::isEqual(TheBucket->first, getEmptyKey()))
+      --NumTombstones;
+
+    TheBucket->first = Key;
+    new (&TheBucket->second) ValueT(Value);
+    return TheBucket;
   }
-  
-private:
-  unsigned getHashValue(const KeyT &Val) const {
-    return DenseMapKeyInfo<KeyT>::getHashValue(Val);
+
+  static unsigned getHashValue(const KeyT &Val) {
+    return KeyInfoT::getHashValue(Val);
   }
-  const KeyT getEmptyKey() const { return DenseMapKeyInfo<KeyT>::getEmptyKey();}
-  const KeyT getTombstoneKey() const {
-    return DenseMapKeyInfo<KeyT>::getTombstoneKey();
+  static const KeyT getEmptyKey() {
+    return KeyInfoT::getEmptyKey();
   }
-  
+  static const KeyT getTombstoneKey() {
+    return KeyInfoT::getTombstoneKey();
+  }
+
   /// LookupBucketFor - Lookup the appropriate bucket for Val, returning it in
   /// FoundBucket.  If the bucket contains the key and a value, this returns
   /// true, otherwise it returns a bucket with an empty marker or tombstone and
@@ -114,37 +380,38 @@ private:
     unsigned BucketNo = getHashValue(Val);
     unsigned ProbeAmt = 1;
     BucketT *BucketsPtr = Buckets;
-    
+
     // FoundTombstone - Keep track of whether we find a tombstone while probing.
     BucketT *FoundTombstone = 0;
     const KeyT EmptyKey = getEmptyKey();
     const KeyT TombstoneKey = getTombstoneKey();
-    assert(Val != EmptyKey && Val != TombstoneKey &&
+    assert(!KeyInfoT::isEqual(Val, EmptyKey) &&
+           !KeyInfoT::isEqual(Val, TombstoneKey) &&
            "Empty/Tombstone value shouldn't be inserted into map!");
-      
+
     while (1) {
       BucketT *ThisBucket = BucketsPtr + (BucketNo & (NumBuckets-1));
       // Found Val's bucket?  If so, return it.
-      if (ThisBucket->Key == Val) {
+      if (KeyInfoT::isEqual(ThisBucket->first, Val)) {
         FoundBucket = ThisBucket;
         return true;
       }
-      
+
       // If we found an empty bucket, the key doesn't exist in the set.
       // Insert it and return the default value.
-      if (ThisBucket->Key == EmptyKey) {
+      if (KeyInfoT::isEqual(ThisBucket->first, EmptyKey)) {
         // If we've already seen a tombstone while probing, fill it in instead
         // of the empty bucket we eventually probed to.
         if (FoundTombstone) ThisBucket = FoundTombstone;
         FoundBucket = FoundTombstone ? FoundTombstone : ThisBucket;
         return false;
       }
-      
+
       // If this is a tombstone, remember it.  If Val ends up not in the map, we
       // prefer to return it than something that would require more probing.
-      if (ThisBucket->Key == TombstoneKey && !FoundTombstone)
+      if (KeyInfoT::isEqual(ThisBucket->first, TombstoneKey) && !FoundTombstone)
         FoundTombstone = ThisBucket;  // Remember the first tombstone found.
-      
+
       // Otherwise, it's a hash collision or a tombstone, continue quadratic
       // probing.
       BucketNo += ProbeAmt++;
@@ -153,48 +420,148 @@ private:
 
   void init(unsigned InitBuckets) {
     NumEntries = 0;
+    NumTombstones = 0;
     NumBuckets = InitBuckets;
-    assert(InitBuckets && (InitBuckets & InitBuckets-1) == 0 &&
+    assert(InitBuckets && (InitBuckets & (InitBuckets-1)) == 0 &&
            "# initial buckets must be a power of two!");
-    Buckets = (BucketT*)new char[sizeof(BucketT)*InitBuckets];
+    Buckets = static_cast<BucketT*>(operator new(sizeof(BucketT)*InitBuckets));
     // Initialize all the keys to EmptyKey.
     const KeyT EmptyKey = getEmptyKey();
     for (unsigned i = 0; i != InitBuckets; ++i)
-      new (&Buckets[i].Key) KeyT(EmptyKey);
+      new (&Buckets[i].first) KeyT(EmptyKey);
   }
-  
-  void grow() {
+
+  void grow(unsigned AtLeast) {
     unsigned OldNumBuckets = NumBuckets;
     BucketT *OldBuckets = Buckets;
-    
+
     // Double the number of buckets.
-    NumBuckets <<= 1;
-    Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
+    while (NumBuckets <= AtLeast)
+      NumBuckets <<= 1;
+    NumTombstones = 0;
+    Buckets = static_cast<BucketT*>(operator new(sizeof(BucketT)*NumBuckets));
 
     // Initialize all the keys to EmptyKey.
     const KeyT EmptyKey = getEmptyKey();
     for (unsigned i = 0, e = NumBuckets; i != e; ++i)
-      new (&Buckets[i].Key) KeyT(EmptyKey);
+      new (&Buckets[i].first) KeyT(EmptyKey);
 
     // Insert all the old elements.
     const KeyT TombstoneKey = getTombstoneKey();
     for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets; B != E; ++B) {
-      if (B->Key != EmptyKey && B->Key != TombstoneKey) {
+      if (!KeyInfoT::isEqual(B->first, EmptyKey) &&
+          !KeyInfoT::isEqual(B->first, TombstoneKey)) {
         // Insert the key/value into the new table.
         BucketT *DestBucket;
-        bool FoundVal = LookupBucketFor(B->Key, DestBucket);
+        bool FoundVal = LookupBucketFor(B->first, DestBucket);
+        FoundVal = FoundVal; // silence warning.
         assert(!FoundVal && "Key already in new map?");
-        DestBucket->Key = B->Key;
-        new (&DestBucket->Value) ValueT(B->Value);
-        
+        DestBucket->first = B->first;
+        new (&DestBucket->second) ValueT(B->second);
+
         // Free the value.
-        B->Value.~ValueT();
+        B->second.~ValueT();
       }
-      B->Key.~KeyT();
+      B->first.~KeyT();
     }
-    
+
     // Free the old table.
-    delete[] (char*)OldBuckets;
+    operator delete(OldBuckets);
+  }
+
+  void shrink_and_clear() {
+    unsigned OldNumBuckets = NumBuckets;
+    BucketT *OldBuckets = Buckets;
+
+    // Reduce the number of buckets.
+    NumBuckets = NumEntries > 32 ? 1 << (Log2_32_Ceil(NumEntries) + 1)
+                                 : 64;
+    NumTombstones = 0;
+    Buckets = static_cast<BucketT*>(operator new(sizeof(BucketT)*NumBuckets));
+
+    // Initialize all the keys to EmptyKey.
+    const KeyT EmptyKey = getEmptyKey();
+    for (unsigned i = 0, e = NumBuckets; i != e; ++i)
+      new (&Buckets[i].first) KeyT(EmptyKey);
+
+    // Free the old buckets.
+    const KeyT TombstoneKey = getTombstoneKey();
+    for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets; B != E; ++B) {
+      if (!KeyInfoT::isEqual(B->first, EmptyKey) &&
+          !KeyInfoT::isEqual(B->first, TombstoneKey)) {
+        // Free the value.
+        B->second.~ValueT();
+      }
+      B->first.~KeyT();
+    }
+
+    // Free the old table.
+    operator delete(OldBuckets);
+
+    NumEntries = 0;
+  }
+};
+
+template<typename KeyT, typename ValueT, typename KeyInfoT, typename ValueInfoT>
+class DenseMapIterator {
+  typedef std::pair<KeyT, ValueT> BucketT;
+protected:
+  const BucketT *Ptr, *End;
+public:
+  DenseMapIterator(void) : Ptr(0), End(0) {}
+
+  DenseMapIterator(const BucketT *Pos, const BucketT *E) : Ptr(Pos), End(E) {
+    AdvancePastEmptyBuckets();
+  }
+
+  std::pair<KeyT, ValueT> &operator*() const {
+    return *const_cast<BucketT*>(Ptr);
+  }
+  std::pair<KeyT, ValueT> *operator->() const {
+    return const_cast<BucketT*>(Ptr);
+  }
+
+  bool operator==(const DenseMapIterator &RHS) const {
+    return Ptr == RHS.Ptr;
+  }
+  bool operator!=(const DenseMapIterator &RHS) const {
+    return Ptr != RHS.Ptr;
+  }
+
+  inline DenseMapIterator& operator++() {          // Preincrement
+    ++Ptr;
+    AdvancePastEmptyBuckets();
+    return *this;
+  }
+  DenseMapIterator operator++(int) {        // Postincrement
+    DenseMapIterator tmp = *this; ++*this; return tmp;
+  }
+
+private:
+  void AdvancePastEmptyBuckets() {
+    const KeyT Empty = KeyInfoT::getEmptyKey();
+    const KeyT Tombstone = KeyInfoT::getTombstoneKey();
+
+    while (Ptr != End &&
+           (KeyInfoT::isEqual(Ptr->first, Empty) ||
+            KeyInfoT::isEqual(Ptr->first, Tombstone)))
+      ++Ptr;
+  }
+};
+
+template<typename KeyT, typename ValueT, typename KeyInfoT, typename ValueInfoT>
+class DenseMapConstIterator : public DenseMapIterator<KeyT, ValueT, KeyInfoT> {
+public:
+  DenseMapConstIterator(void) : 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;
   }
 };