DenseMap.h revision a76b1febd4fd258e8054395adedcbd477668d956 
1//===- llvm/ADT/DenseMap.h - Dense probed hash table ------------*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file was developed by Chris Lattner and is distributed under
6// the University of Illinois Open Source License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the DenseMap class.
11//
12//===----------------------------------------------------------------------===//
13
14#ifndef LLVM_ADT_DENSEMAP_H
15#define LLVM_ADT_DENSEMAP_H
16
17#include "llvm/Support/DataTypes.h"
18#include <cassert>
19#include <utility>
20
21namespace llvm {
22
23template<typename T>
24struct DenseMapKeyInfo {
25  //static inline T getEmptyKey();
26  //static inline T getTombstoneKey();
27  //static unsigned getHashValue(const T &Val);
28  //static bool isPod()
29};
30
31// Provide DenseMapKeyInfo for all pointers.
32template<typename T>
33struct DenseMapKeyInfo<T*> {
34  static inline T* getEmptyKey() { return (T*)-1; }
35  static inline T* getTombstoneKey() { return (T*)-2; }
36  static unsigned getHashValue(const T *PtrVal) {
37    return (unsigned)((uintptr_t)PtrVal >> 4) ^
38           (unsigned)((uintptr_t)PtrVal >> 9);
39  }
40  static bool isPod() { return true; }
41};
42
43template<typename KeyT, typename ValueT,
44         typename KeyInfoT = DenseMapKeyInfo<KeyT> >
45class DenseMapIterator;
46template<typename KeyT, typename ValueT,
47         typename KeyInfoT = DenseMapKeyInfo<KeyT> >
48class DenseMapConstIterator;
49
50template<typename KeyT, typename ValueT,
51         typename KeyInfoT = DenseMapKeyInfo<KeyT> >
52class DenseMap {
53  typedef std::pair<KeyT, ValueT> BucketT;
54  unsigned NumBuckets;
55  BucketT *Buckets;
56
57  unsigned NumEntries;
58  unsigned NumTombstones;
59  DenseMap(const DenseMap &); // not implemented.
60public:
61  explicit DenseMap(unsigned NumInitBuckets = 64) {
62    init(NumInitBuckets);
63  }
64  ~DenseMap() {
65    const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
66    for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
67      if (P->first != EmptyKey && P->first != TombstoneKey)
68        P->second.~ValueT();
69      P->first.~KeyT();
70    }
71    delete[] (char*)Buckets;
72  }
73
74  typedef DenseMapIterator<KeyT, ValueT, KeyInfoT> iterator;
75  typedef DenseMapConstIterator<KeyT, ValueT, KeyInfoT> const_iterator;
76  inline iterator begin() {
77     return iterator(Buckets, Buckets+NumBuckets);
78  }
79  inline iterator end() {
80    return iterator(Buckets+NumBuckets, Buckets+NumBuckets);
81  }
82  inline const_iterator begin() const {
83    return const_iterator(Buckets, Buckets+NumBuckets);
84  }
85  inline const_iterator end() const {
86    return const_iterator(Buckets+NumBuckets, Buckets+NumBuckets);
87  }
88
89  bool empty() const { return NumEntries == 0; }
90  unsigned size() const { return NumEntries; }
91
92  void clear() {
93    const KeyT EmptyKey = getEmptyKey(), TombstoneKey = getTombstoneKey();
94    for (BucketT *P = Buckets, *E = Buckets+NumBuckets; P != E; ++P) {
95      if (P->first != EmptyKey && P->first != TombstoneKey) {
96        P->first = EmptyKey;
97        P->second.~ValueT();
98        --NumEntries;
99      }
100    }
101    assert(NumEntries == 0 && "Node count imbalance!");
102    NumTombstones = 0;
103  }
104
105  /// count - Return true if the specified key is in the map.
106  bool count(const KeyT &Val) const {
107    BucketT *TheBucket;
108    return LookupBucketFor(Val, TheBucket);
109  }
110
111  iterator find(const KeyT &Val) const {
112    BucketT *TheBucket;
113    if (LookupBucketFor(Val, TheBucket))
114      return iterator(TheBucket, Buckets+NumBuckets);
115    return end();
116  }
117
118  bool insert(const std::pair<KeyT, ValueT> &KV) {
119    BucketT *TheBucket;
120    if (LookupBucketFor(KV.first, TheBucket))
121      return false; // Already in map.
122
123    // Otherwise, insert the new element.
124    InsertIntoBucket(KV.first, KV.second, TheBucket);
125    return true;
126  }
127
128  bool erase(const KeyT &Val) {
129    BucketT *TheBucket;
130    if (!LookupBucketFor(Val, TheBucket))
131      return false; // not in map.
132
133    TheBucket->second.~ValueT();
134    TheBucket->first = getTombstoneKey();
135    --NumEntries;
136    ++NumTombstones;
137    return true;
138  }
139  bool erase(iterator I) {
140    BucketT *TheBucket = &*I;
141    TheBucket->second.~ValueT();
142    TheBucket->first = getTombstoneKey();
143    --NumEntries;
144    ++NumTombstones;
145    return true;
146  }
147
148  ValueT &operator[](const KeyT &Key) {
149    BucketT *TheBucket;
150    if (LookupBucketFor(Key, TheBucket))
151      return TheBucket->second;
152
153    return InsertIntoBucket(Key, ValueT(), TheBucket)->second;
154  }
155
156private:
157  BucketT *InsertIntoBucket(const KeyT &Key, const ValueT &Value,
158                            BucketT *TheBucket) {
159    // If the load of the hash table is more than 3/4, or if fewer than 1/8 of
160    // the buckets are empty (meaning that many are filled with tombstones),
161    // grow the table.
162    //
163    // The later case is tricky.  For example, if we had one empty bucket with
164    // tons of tombstones, failing lookups (e.g. for insertion) would have to
165    // probe almost the entire table until it found the empty bucket.  If the
166    // table completely filled with tombstones, no lookup would ever succeed,
167    // causing infinite loops in lookup.
168    if (NumEntries*4 >= NumBuckets*3 ||
169        NumBuckets-(NumEntries+NumTombstones) < NumBuckets/8) {
170      this->grow();
171      LookupBucketFor(Key, TheBucket);
172    }
173    ++NumEntries;
174
175    // If we are writing over a tombstone, remember this.
176    if (TheBucket->first != getEmptyKey())
177      --NumTombstones;
178
179    TheBucket->first = Key;
180    new (&TheBucket->second) ValueT(Value);
181    return TheBucket;
182  }
183
184  static unsigned getHashValue(const KeyT &Val) {
185    return KeyInfoT::getHashValue(Val);
186  }
187  static const KeyT getEmptyKey() {
188    return KeyInfoT::getEmptyKey();
189  }
190  static const KeyT getTombstoneKey() {
191    return KeyInfoT::getTombstoneKey();
192  }
193
194  /// LookupBucketFor - Lookup the appropriate bucket for Val, returning it in
195  /// FoundBucket.  If the bucket contains the key and a value, this returns
196  /// true, otherwise it returns a bucket with an empty marker or tombstone and
197  /// returns false.
198  bool LookupBucketFor(const KeyT &Val, BucketT *&FoundBucket) const {
199    unsigned BucketNo = getHashValue(Val);
200    unsigned ProbeAmt = 1;
201    BucketT *BucketsPtr = Buckets;
202
203    // FoundTombstone - Keep track of whether we find a tombstone while probing.
204    BucketT *FoundTombstone = 0;
205    const KeyT EmptyKey = getEmptyKey();
206    const KeyT TombstoneKey = getTombstoneKey();
207    assert(Val != EmptyKey && Val != TombstoneKey &&
208           "Empty/Tombstone value shouldn't be inserted into map!");
209
210    while (1) {
211      BucketT *ThisBucket = BucketsPtr + (BucketNo & (NumBuckets-1));
212      // Found Val's bucket?  If so, return it.
213      if (ThisBucket->first == Val) {
214        FoundBucket = ThisBucket;
215        return true;
216      }
217
218      // If we found an empty bucket, the key doesn't exist in the set.
219      // Insert it and return the default value.
220      if (ThisBucket->first == EmptyKey) {
221        // If we've already seen a tombstone while probing, fill it in instead
222        // of the empty bucket we eventually probed to.
223        if (FoundTombstone) ThisBucket = FoundTombstone;
224        FoundBucket = FoundTombstone ? FoundTombstone : ThisBucket;
225        return false;
226      }
227
228      // If this is a tombstone, remember it.  If Val ends up not in the map, we
229      // prefer to return it than something that would require more probing.
230      if (ThisBucket->first == TombstoneKey && !FoundTombstone)
231        FoundTombstone = ThisBucket;  // Remember the first tombstone found.
232
233      // Otherwise, it's a hash collision or a tombstone, continue quadratic
234      // probing.
235      BucketNo += ProbeAmt++;
236    }
237  }
238
239  void init(unsigned InitBuckets) {
240    NumEntries = 0;
241    NumTombstones = 0;
242    NumBuckets = InitBuckets;
243    assert(InitBuckets && (InitBuckets & InitBuckets-1) == 0 &&
244           "# initial buckets must be a power of two!");
245    Buckets = (BucketT*)new char[sizeof(BucketT)*InitBuckets];
246    // Initialize all the keys to EmptyKey.
247    const KeyT EmptyKey = getEmptyKey();
248    for (unsigned i = 0; i != InitBuckets; ++i)
249      new (&Buckets[i].first) KeyT(EmptyKey);
250  }
251
252  void grow() {
253    unsigned OldNumBuckets = NumBuckets;
254    BucketT *OldBuckets = Buckets;
255
256    // Double the number of buckets.
257    NumBuckets <<= 1;
258    NumTombstones = 0;
259    Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
260
261    // Initialize all the keys to EmptyKey.
262    const KeyT EmptyKey = getEmptyKey();
263    for (unsigned i = 0, e = NumBuckets; i != e; ++i)
264      new (&Buckets[i].first) KeyT(EmptyKey);
265
266    // Insert all the old elements.
267    const KeyT TombstoneKey = getTombstoneKey();
268    for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets; B != E; ++B) {
269      if (B->first != EmptyKey && B->first != TombstoneKey) {
270        // Insert the key/value into the new table.
271        BucketT *DestBucket;
272        bool FoundVal = LookupBucketFor(B->first, DestBucket);
273        FoundVal = FoundVal; // silence warning.
274        assert(!FoundVal && "Key already in new map?");
275        DestBucket->first = B->first;
276        new (&DestBucket->second) ValueT(B->second);
277
278        // Free the value.
279        B->second.~ValueT();
280      }
281      B->first.~KeyT();
282    }
283
284    // Free the old table.
285    delete[] (char*)OldBuckets;
286  }
287};
288
289template<typename KeyT, typename ValueT, typename KeyInfoT>
290class DenseMapIterator {
291  typedef std::pair<KeyT, ValueT> BucketT;
292protected:
293  const BucketT *Ptr, *End;
294public:
295  DenseMapIterator(const BucketT *Pos, const BucketT *E) : Ptr(Pos), End(E) {
296    AdvancePastEmptyBuckets();
297  }
298
299  std::pair<KeyT, ValueT> &operator*() const {
300    return *const_cast<BucketT*>(Ptr);
301  }
302  std::pair<KeyT, ValueT> *operator->() const {
303    return const_cast<BucketT*>(Ptr);
304  }
305
306  bool operator==(const DenseMapIterator &RHS) const {
307    return Ptr == RHS.Ptr;
308  }
309  bool operator!=(const DenseMapIterator &RHS) const {
310    return Ptr != RHS.Ptr;
311  }
312
313  inline DenseMapIterator& operator++() {          // Preincrement
314    ++Ptr;
315    AdvancePastEmptyBuckets();
316    return *this;
317  }
318  DenseMapIterator operator++(int) {        // Postincrement
319    DenseMapIterator tmp = *this; ++*this; return tmp;
320  }
321
322private:
323  void AdvancePastEmptyBuckets() {
324    const KeyT Empty = KeyInfoT::getEmptyKey();
325    const KeyT Tombstone = KeyInfoT::getTombstoneKey();
326
327    while (Ptr != End && (Ptr->first == Empty || Ptr->first == Tombstone))
328      ++Ptr;
329  }
330};
331
332template<typename KeyT, typename ValueT, typename KeyInfoT>
333class DenseMapConstIterator : public DenseMapIterator<KeyT, ValueT, KeyInfoT> {
334public:
335  DenseMapConstIterator(const std::pair<KeyT, ValueT> *Pos,
336                        const std::pair<KeyT, ValueT> *E)
337    : DenseMapIterator<KeyT, ValueT>(Pos, E) {
338  }
339  const std::pair<KeyT, ValueT> &operator*() const {
340    return *this->Ptr;
341  }
342  const std::pair<KeyT, ValueT> *operator->() const {
343    return this->Ptr;
344  }
345};
346
347} // end namespace llvm
348
349#endif
350