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  unsigned CurArraySize;
58
59  // If small, this is # elts allocated consecutively
60  unsigned NumElements;
61  unsigned NumTombstones;
62
63  // Helper to copy construct a SmallPtrSet.
64  SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that);
65  explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) :
66    SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
67    assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
68           "Initial size must be a power of two!");
69    clear();
70  }
71  ~SmallPtrSetImpl();
72
73public:
74  bool empty() const { return size() == 0; }
75  unsigned size() const { return NumElements; }
76
77  void clear() {
78    // If the capacity of the array is huge, and the # elements used is small,
79    // shrink the array.
80    if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
81      return shrink_and_clear();
82
83    // Fill the array with empty markers.
84    memset(CurArray, -1, CurArraySize*sizeof(void*));
85    NumElements = 0;
86    NumTombstones = 0;
87  }
88
89protected:
90  static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
91  static void *getEmptyMarker() {
92    // Note that -1 is chosen to make clear() efficiently implementable with
93    // memset and because it's not a valid pointer value.
94    return reinterpret_cast<void*>(-1);
95  }
96
97  /// insert_imp - This returns true if the pointer was new to the set, false if
98  /// it was already in the set.  This is hidden from the client so that the
99  /// derived class can check that the right type of pointer is passed in.
100  bool insert_imp(const void * Ptr);
101
102  /// erase_imp - If the set contains the specified pointer, remove it and
103  /// return true, otherwise return false.  This is hidden from the client so
104  /// that the derived class can check that the right type of pointer is passed
105  /// in.
106  bool erase_imp(const void * Ptr);
107
108  bool count_imp(const void * Ptr) const {
109    if (isSmall()) {
110      // Linear search for the item.
111      for (const void *const *APtr = SmallArray,
112                      *const *E = SmallArray+NumElements; APtr != E; ++APtr)
113        if (*APtr == Ptr)
114          return true;
115      return false;
116    }
117
118    // Big set case.
119    return *FindBucketFor(Ptr) == Ptr;
120  }
121
122private:
123  bool isSmall() const { return CurArray == SmallArray; }
124
125  const void * const *FindBucketFor(const void *Ptr) const;
126  void shrink_and_clear();
127
128  /// Grow - Allocate a larger backing store for the buckets and move it over.
129  void Grow(unsigned NewSize);
130
131  void operator=(const SmallPtrSetImpl &RHS) LLVM_DELETED_FUNCTION;
132protected:
133  /// swap - Swaps the elements of two sets.
134  /// Note: This method assumes that both sets have the same small size.
135  void swap(SmallPtrSetImpl &RHS);
136
137  void CopyFrom(const SmallPtrSetImpl &RHS);
138};
139
140/// SmallPtrSetIteratorImpl - This is the common base class shared between all
141/// instances of SmallPtrSetIterator.
142class SmallPtrSetIteratorImpl {
143protected:
144  const void *const *Bucket;
145  const void *const *End;
146public:
147  explicit SmallPtrSetIteratorImpl(const void *const *BP, const void*const *E)
148    : Bucket(BP), End(E) {
149      AdvanceIfNotValid();
150  }
151
152  bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
153    return Bucket == RHS.Bucket;
154  }
155  bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
156    return Bucket != RHS.Bucket;
157  }
158
159protected:
160  /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
161  /// that is.   This is guaranteed to stop because the end() bucket is marked
162  /// valid.
163  void AdvanceIfNotValid() {
164    assert(Bucket <= End);
165    while (Bucket != End &&
166           (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
167            *Bucket == SmallPtrSetImpl::getTombstoneMarker()))
168      ++Bucket;
169  }
170};
171
172/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
173template<typename PtrTy>
174class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
175  typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
176
177public:
178  typedef PtrTy                     value_type;
179  typedef PtrTy                     reference;
180  typedef PtrTy                     pointer;
181  typedef std::ptrdiff_t            difference_type;
182  typedef std::forward_iterator_tag iterator_category;
183
184  explicit SmallPtrSetIterator(const void *const *BP, const void *const *E)
185    : SmallPtrSetIteratorImpl(BP, E) {}
186
187  // Most methods provided by baseclass.
188
189  const PtrTy operator*() const {
190    assert(Bucket < End);
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'.
240  const void *SmallStorage[SmallSizePowTwo];
241  typedef PointerLikeTypeTraits<PtrType> PtrTraits;
242public:
243  SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {}
244  SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {}
245
246  template<typename It>
247  SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {
248    insert(I, E);
249  }
250
251  /// insert - This returns true if the pointer was new to the set, false if it
252  /// was already in the set.
253  bool insert(PtrType Ptr) {
254    return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
255  }
256
257  /// erase - If the set contains the specified pointer, remove it and return
258  /// true, otherwise return false.
259  bool erase(PtrType Ptr) {
260    return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
261  }
262
263  /// count - Return true if the specified pointer is in the set.
264  bool count(PtrType Ptr) const {
265    return count_imp(PtrTraits::getAsVoidPointer(Ptr));
266  }
267
268  template <typename IterT>
269  void insert(IterT I, IterT E) {
270    for (; I != E; ++I)
271      insert(*I);
272  }
273
274  typedef SmallPtrSetIterator<PtrType> iterator;
275  typedef SmallPtrSetIterator<PtrType> const_iterator;
276  inline iterator begin() const {
277    return iterator(CurArray, CurArray+CurArraySize);
278  }
279  inline iterator end() const {
280    return iterator(CurArray+CurArraySize, CurArray+CurArraySize);
281  }
282
283  // Allow assignment from any smallptrset with the same element type even if it
284  // doesn't have the same smallsize.
285  const SmallPtrSet<PtrType, SmallSize>&
286  operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {
287    CopyFrom(RHS);
288    return *this;
289  }
290
291  /// swap - Swaps the elements of two sets.
292  void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
293    SmallPtrSetImpl::swap(RHS);
294  }
295};
296
297}
298
299namespace std {
300  /// Implement std::swap in terms of SmallPtrSet swap.
301  template<class T, unsigned N>
302  inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) {
303    LHS.swap(RHS);
304  }
305}
306
307#endif
308