DenseMap.h revision 569b935e6b23c4a0e4ebb2c96603974310ef0587 
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) {
112    BucketT *TheBucket;
113    if (LookupBucketFor(Val, TheBucket))
114      return iterator(TheBucket, Buckets+NumBuckets);
115    return end();
116  }
117  const_iterator find(const KeyT &Val) const {
118    BucketT *TheBucket;
119    if (LookupBucketFor(Val, TheBucket))
120      return const_iterator(TheBucket, Buckets+NumBuckets);
121    return end();
122  }
123
124  bool insert(const std::pair<KeyT, ValueT> &KV) {
125    BucketT *TheBucket;
126    if (LookupBucketFor(KV.first, TheBucket))
127      return false; // Already in map.
128
129    // Otherwise, insert the new element.
130    InsertIntoBucket(KV.first, KV.second, TheBucket);
131    return true;
132  }
133
134  bool erase(const KeyT &Val) {
135    BucketT *TheBucket;
136    if (!LookupBucketFor(Val, TheBucket))
137      return false; // not in map.
138
139    TheBucket->second.~ValueT();
140    TheBucket->first = getTombstoneKey();
141    --NumEntries;
142    ++NumTombstones;
143    return true;
144  }
145  bool erase(iterator I) {
146    BucketT *TheBucket = &*I;
147    TheBucket->second.~ValueT();
148    TheBucket->first = getTombstoneKey();
149    --NumEntries;
150    ++NumTombstones;
151    return true;
152  }
153
154  ValueT &operator[](const KeyT &Key) {
155    BucketT *TheBucket;
156    if (LookupBucketFor(Key, TheBucket))
157      return TheBucket->second;
158
159    return InsertIntoBucket(Key, ValueT(), TheBucket)->second;
160  }
161
162private:
163  BucketT *InsertIntoBucket(const KeyT &Key, const ValueT &Value,
164                            BucketT *TheBucket) {
165    // If the load of the hash table is more than 3/4, or if fewer than 1/8 of
166    // the buckets are empty (meaning that many are filled with tombstones),
167    // grow the table.
168    //
169    // The later case is tricky.  For example, if we had one empty bucket with
170    // tons of tombstones, failing lookups (e.g. for insertion) would have to
171    // probe almost the entire table until it found the empty bucket.  If the
172    // table completely filled with tombstones, no lookup would ever succeed,
173    // causing infinite loops in lookup.
174    if (NumEntries*4 >= NumBuckets*3 ||
175        NumBuckets-(NumEntries+NumTombstones) < NumBuckets/8) {
176      this->grow();
177      LookupBucketFor(Key, TheBucket);
178    }
179    ++NumEntries;
180
181    // If we are writing over a tombstone, remember this.
182    if (TheBucket->first != getEmptyKey())
183      --NumTombstones;
184
185    TheBucket->first = Key;
186    new (&TheBucket->second) ValueT(Value);
187    return TheBucket;
188  }
189
190  static unsigned getHashValue(const KeyT &Val) {
191    return KeyInfoT::getHashValue(Val);
192  }
193  static const KeyT getEmptyKey() {
194    return KeyInfoT::getEmptyKey();
195  }
196  static const KeyT getTombstoneKey() {
197    return KeyInfoT::getTombstoneKey();
198  }
199
200  /// LookupBucketFor - Lookup the appropriate bucket for Val, returning it in
201  /// FoundBucket.  If the bucket contains the key and a value, this returns
202  /// true, otherwise it returns a bucket with an empty marker or tombstone and
203  /// returns false.
204  bool LookupBucketFor(const KeyT &Val, BucketT *&FoundBucket) const {
205    unsigned BucketNo = getHashValue(Val);
206    unsigned ProbeAmt = 1;
207    BucketT *BucketsPtr = Buckets;
208
209    // FoundTombstone - Keep track of whether we find a tombstone while probing.
210    BucketT *FoundTombstone = 0;
211    const KeyT EmptyKey = getEmptyKey();
212    const KeyT TombstoneKey = getTombstoneKey();
213    assert(Val != EmptyKey && Val != TombstoneKey &&
214           "Empty/Tombstone value shouldn't be inserted into map!");
215
216    while (1) {
217      BucketT *ThisBucket = BucketsPtr + (BucketNo & (NumBuckets-1));
218      // Found Val's bucket?  If so, return it.
219      if (ThisBucket->first == Val) {
220        FoundBucket = ThisBucket;
221        return true;
222      }
223
224      // If we found an empty bucket, the key doesn't exist in the set.
225      // Insert it and return the default value.
226      if (ThisBucket->first == EmptyKey) {
227        // If we've already seen a tombstone while probing, fill it in instead
228        // of the empty bucket we eventually probed to.
229        if (FoundTombstone) ThisBucket = FoundTombstone;
230        FoundBucket = FoundTombstone ? FoundTombstone : ThisBucket;
231        return false;
232      }
233
234      // If this is a tombstone, remember it.  If Val ends up not in the map, we
235      // prefer to return it than something that would require more probing.
236      if (ThisBucket->first == TombstoneKey && !FoundTombstone)
237        FoundTombstone = ThisBucket;  // Remember the first tombstone found.
238
239      // Otherwise, it's a hash collision or a tombstone, continue quadratic
240      // probing.
241      BucketNo += ProbeAmt++;
242    }
243  }
244
245  void init(unsigned InitBuckets) {
246    NumEntries = 0;
247    NumTombstones = 0;
248    NumBuckets = InitBuckets;
249    assert(InitBuckets && (InitBuckets & InitBuckets-1) == 0 &&
250           "# initial buckets must be a power of two!");
251    Buckets = (BucketT*)new char[sizeof(BucketT)*InitBuckets];
252    // Initialize all the keys to EmptyKey.
253    const KeyT EmptyKey = getEmptyKey();
254    for (unsigned i = 0; i != InitBuckets; ++i)
255      new (&Buckets[i].first) KeyT(EmptyKey);
256  }
257
258  void grow() {
259    unsigned OldNumBuckets = NumBuckets;
260    BucketT *OldBuckets = Buckets;
261
262    // Double the number of buckets.
263    NumBuckets <<= 1;
264    NumTombstones = 0;
265    Buckets = (BucketT*)new char[sizeof(BucketT)*NumBuckets];
266
267    // Initialize all the keys to EmptyKey.
268    const KeyT EmptyKey = getEmptyKey();
269    for (unsigned i = 0, e = NumBuckets; i != e; ++i)
270      new (&Buckets[i].first) KeyT(EmptyKey);
271
272    // Insert all the old elements.
273    const KeyT TombstoneKey = getTombstoneKey();
274    for (BucketT *B = OldBuckets, *E = OldBuckets+OldNumBuckets; B != E; ++B) {
275      if (B->first != EmptyKey && B->first != TombstoneKey) {
276        // Insert the key/value into the new table.
277        BucketT *DestBucket;
278        bool FoundVal = LookupBucketFor(B->first, DestBucket);
279        FoundVal = FoundVal; // silence warning.
280        assert(!FoundVal && "Key already in new map?");
281        DestBucket->first = B->first;
282        new (&DestBucket->second) ValueT(B->second);
283
284        // Free the value.
285        B->second.~ValueT();
286      }
287      B->first.~KeyT();
288    }
289
290    // Free the old table.
291    delete[] (char*)OldBuckets;
292  }
293};
294
295template<typename KeyT, typename ValueT, typename KeyInfoT>
296class DenseMapIterator {
297  typedef std::pair<KeyT, ValueT> BucketT;
298protected:
299  const BucketT *Ptr, *End;
300public:
301  DenseMapIterator(const BucketT *Pos, const BucketT *E) : Ptr(Pos), End(E) {
302    AdvancePastEmptyBuckets();
303  }
304
305  std::pair<KeyT, ValueT> &operator*() const {
306    return *const_cast<BucketT*>(Ptr);
307  }
308  std::pair<KeyT, ValueT> *operator->() const {
309    return const_cast<BucketT*>(Ptr);
310  }
311
312  bool operator==(const DenseMapIterator &RHS) const {
313    return Ptr == RHS.Ptr;
314  }
315  bool operator!=(const DenseMapIterator &RHS) const {
316    return Ptr != RHS.Ptr;
317  }
318
319  inline DenseMapIterator& operator++() {          // Preincrement
320    ++Ptr;
321    AdvancePastEmptyBuckets();
322    return *this;
323  }
324  DenseMapIterator operator++(int) {        // Postincrement
325    DenseMapIterator tmp = *this; ++*this; return tmp;
326  }
327
328private:
329  void AdvancePastEmptyBuckets() {
330    const KeyT Empty = KeyInfoT::getEmptyKey();
331    const KeyT Tombstone = KeyInfoT::getTombstoneKey();
332
333    while (Ptr != End && (Ptr->first == Empty || Ptr->first == Tombstone))
334      ++Ptr;
335  }
336};
337
338template<typename KeyT, typename ValueT, typename KeyInfoT>
339class DenseMapConstIterator : public DenseMapIterator<KeyT, ValueT, KeyInfoT> {
340public:
341  DenseMapConstIterator(const std::pair<KeyT, ValueT> *Pos,
342                        const std::pair<KeyT, ValueT> *E)
343    : DenseMapIterator<KeyT, ValueT, KeyInfoT>(Pos, E) {
344  }
345  const std::pair<KeyT, ValueT> &operator*() const {
346    return *this->Ptr;
347  }
348  const std::pair<KeyT, ValueT> *operator->() const {
349    return this->Ptr;
350  }
351};
352
353} // end namespace llvm
354
355#endif
356