1//===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===//
2//
3//                     The LLVM Compiler Infrastructure
4//
5// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
7//
8//===----------------------------------------------------------------------===//
9//
10// This file defines the SmallPtrSet class.  See the doxygen comment for
11// SmallPtrSetImpl for more details on the algorithm used.
12//
13//===----------------------------------------------------------------------===//
14
15#ifndef LLVM_ADT_SMALLPTRSET_H
16#define LLVM_ADT_SMALLPTRSET_H
17
18#include "llvm/Support/Compiler.h"
19#include "llvm/Support/DataTypes.h"
20#include "llvm/Support/PointerLikeTypeTraits.h"
21#include <cassert>
22#include <cstddef>
23#include <cstring>
24#include <iterator>
25
26namespace llvm {
27
28class SmallPtrSetIteratorImpl;
29
30/// SmallPtrSetImpl - This is the common code shared among all the
31/// SmallPtrSet<>'s, which is almost everything.  SmallPtrSet has two modes, one
32/// for small and one for large sets.
33///
34/// Small sets use an array of pointers allocated in the SmallPtrSet object,
35/// which is treated as a simple array of pointers.  When a pointer is added to
36/// the set, the array is scanned to see if the element already exists, if not
37/// the element is 'pushed back' onto the array.  If we run out of space in the
38/// array, we grow into the 'large set' case.  SmallSet should be used when the
39/// sets are often small.  In this case, no memory allocation is used, and only
40/// light-weight and cache-efficient scanning is used.
41///
42/// Large sets use a classic exponentially-probed hash table.  Empty buckets are
43/// represented with an illegal pointer value (-1) to allow null pointers to be
44/// inserted.  Tombstones are represented with another illegal pointer value
45/// (-2), to allow deletion.  The hash table is resized when the table is 3/4 or
46/// more.  When this happens, the table is doubled in size.
47///
48class SmallPtrSetImpl {
49  friend class SmallPtrSetIteratorImpl;
50protected:
51  /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'.
52  const void **SmallArray;
53  /// CurArray - This is the current set of buckets.  If equal to SmallArray,
54  /// then the set is in 'small mode'.
55  const void **CurArray;
56  /// CurArraySize - The allocated size of CurArray, always a power of two.
57  /// Note that CurArray points to an array that has CurArraySize+1 elements in
58  /// it, so that the end iterator actually points to valid memory.
59  unsigned CurArraySize;
60
61  // If small, this is # elts allocated consecutively
62  unsigned NumElements;
63  unsigned NumTombstones;
64
65  // Helper to copy construct a SmallPtrSet.
66  SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that);
67  explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) :
68    SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
69    assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
70           "Initial size must be a power of two!");
71    // The end pointer, always valid, is set to a valid element to help the
72    // iterator.
73    CurArray[SmallSize] = 0;
74    clear();
75  }
76  ~SmallPtrSetImpl();
77
78public:
79  bool empty() const { return size() == 0; }
80  unsigned size() const { return NumElements; }
81
82  void clear() {
83    // If the capacity of the array is huge, and the # elements used is small,
84    // shrink the array.
85    if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
86      return shrink_and_clear();
87
88    // Fill the array with empty markers.
89    memset(CurArray, -1, CurArraySize*sizeof(void*));
90    NumElements = 0;
91    NumTombstones = 0;
92  }
93
94protected:
95  static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
96  static void *getEmptyMarker() {
97    // Note that -1 is chosen to make clear() efficiently implementable with
98    // memset and because it's not a valid pointer value.
99    return reinterpret_cast<void*>(-1);
100  }
101
102  /// insert_imp - This returns true if the pointer was new to the set, false if
103  /// it was already in the set.  This is hidden from the client so that the
104  /// derived class can check that the right type of pointer is passed in.
105  bool insert_imp(const void * Ptr);
106
107  /// erase_imp - If the set contains the specified pointer, remove it and
108  /// return true, otherwise return false.  This is hidden from the client so
109  /// that the derived class can check that the right type of pointer is passed
110  /// in.
111  bool erase_imp(const void * Ptr);
112
113  bool count_imp(const void * Ptr) const {
114    if (isSmall()) {
115      // Linear search for the item.
116      for (const void *const *APtr = SmallArray,
117                      *const *E = SmallArray+NumElements; APtr != E; ++APtr)
118        if (*APtr == Ptr)
119          return true;
120      return false;
121    }
122
123    // Big set case.
124    return *FindBucketFor(Ptr) == Ptr;
125  }
126
127private:
128  bool isSmall() const { return CurArray == SmallArray; }
129
130  const void * const *FindBucketFor(const void *Ptr) const;
131  void shrink_and_clear();
132
133  /// Grow - Allocate a larger backing store for the buckets and move it over.
134  void Grow(unsigned NewSize);
135
136  void operator=(const SmallPtrSetImpl &RHS) LLVM_DELETED_FUNCTION;
137protected:
138  /// swap - Swaps the elements of two sets.
139  /// Note: This method assumes that both sets have the same small size.
140  void swap(SmallPtrSetImpl &RHS);
141
142  void CopyFrom(const SmallPtrSetImpl &RHS);
143};
144
145/// SmallPtrSetIteratorImpl - This is the common base class shared between all
146/// instances of SmallPtrSetIterator.
147class SmallPtrSetIteratorImpl {
148protected:
149  const void *const *Bucket;
150public:
151  explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
152    AdvanceIfNotValid();
153  }
154
155  bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
156    return Bucket == RHS.Bucket;
157  }
158  bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
159    return Bucket != RHS.Bucket;
160  }
161
162protected:
163  /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
164  /// that is.   This is guaranteed to stop because the end() bucket is marked
165  /// valid.
166  void AdvanceIfNotValid() {
167    while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
168           *Bucket == SmallPtrSetImpl::getTombstoneMarker())
169      ++Bucket;
170  }
171};
172
173/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
174template<typename PtrTy>
175class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
176  typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
177
178public:
179  typedef PtrTy                     value_type;
180  typedef PtrTy                     reference;
181  typedef PtrTy                     pointer;
182  typedef std::ptrdiff_t            difference_type;
183  typedef std::forward_iterator_tag iterator_category;
184
185  explicit SmallPtrSetIterator(const void *const *BP)
186    : SmallPtrSetIteratorImpl(BP) {}
187
188  // Most methods provided by baseclass.
189
190  const PtrTy operator*() const {
191    return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
192  }
193
194  inline SmallPtrSetIterator& operator++() {          // Preincrement
195    ++Bucket;
196    AdvanceIfNotValid();
197    return *this;
198  }
199
200  SmallPtrSetIterator operator++(int) {        // Postincrement
201    SmallPtrSetIterator tmp = *this; ++*this; return tmp;
202  }
203};
204
205/// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next
206/// power of two (which means N itself if N is already a power of two).
207template<unsigned N>
208struct RoundUpToPowerOfTwo;
209
210/// RoundUpToPowerOfTwoH - If N is not a power of two, increase it.  This is a
211/// helper template used to implement RoundUpToPowerOfTwo.
212template<unsigned N, bool isPowerTwo>
213struct RoundUpToPowerOfTwoH {
214  enum { Val = N };
215};
216template<unsigned N>
217struct RoundUpToPowerOfTwoH<N, false> {
218  enum {
219    // We could just use NextVal = N+1, but this converges faster.  N|(N-1) sets
220    // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
221    Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val
222  };
223};
224
225template<unsigned N>
226struct RoundUpToPowerOfTwo {
227  enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
228};
229
230
231/// SmallPtrSet - This class implements a set which is optimized for holding
232/// SmallSize or less elements.  This internally rounds up SmallSize to the next
233/// power of two if it is not already a power of two.  See the comments above
234/// SmallPtrSetImpl for details of the algorithm.
235template<class PtrType, unsigned SmallSize>
236class SmallPtrSet : public SmallPtrSetImpl {
237  // Make sure that SmallSize is a power of two, round up if not.
238  enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
239  /// SmallStorage - Fixed size storage used in 'small mode'.  The extra element
240  /// ensures that the end iterator actually points to valid memory.
241  const void *SmallStorage[SmallSizePowTwo+1];
242  typedef PointerLikeTypeTraits<PtrType> PtrTraits;
243public:
244  SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {}
245  SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {}
246
247  template<typename It>
248  SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {
249    insert(I, E);
250  }
251
252  /// insert - This returns true if the pointer was new to the set, false if it
253  /// was already in the set.
254  bool insert(PtrType Ptr) {
255    return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
256  }
257
258  /// erase - If the set contains the specified pointer, remove it and return
259  /// true, otherwise return false.
260  bool erase(PtrType Ptr) {
261    return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
262  }
263
264  /// count - Return true if the specified pointer is in the set.
265  bool count(PtrType Ptr) const {
266    return count_imp(PtrTraits::getAsVoidPointer(Ptr));
267  }
268
269  template <typename IterT>
270  void insert(IterT I, IterT E) {
271    for (; I != E; ++I)
272      insert(*I);
273  }
274
275  typedef SmallPtrSetIterator<PtrType> iterator;
276  typedef SmallPtrSetIterator<PtrType> const_iterator;
277  inline iterator begin() const {
278    return iterator(CurArray);
279  }
280  inline iterator end() const {
281    return iterator(CurArray+CurArraySize);
282  }
283
284  // Allow assignment from any smallptrset with the same element type even if it
285  // doesn't have the same smallsize.
286  const SmallPtrSet<PtrType, SmallSize>&
287  operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
288    CopyFrom(RHS);
289    return *this;
290  }
291
292  /// swap - Swaps the elements of two sets.
293  void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
294    SmallPtrSetImpl::swap(RHS);
295  }
296};
297
298}
299
300namespace std {
301  /// Implement std::swap in terms of SmallPtrSet swap.
302  template<class T, unsigned N>
303  inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) {
304    LHS.swap(RHS);
305  }
306}
307
308#endif
309