1 //===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file is distributed under the University of Illinois Open Source
6 // License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This file defines the SmallPtrSet class. See the doxygen comment for
11 // SmallPtrSetImpl for more details on the algorithm used.
13 //===----------------------------------------------------------------------===//
15 #ifndef LLVM_ADT_SMALLPTRSET_H
16 #define LLVM_ADT_SMALLPTRSET_H
21 #include "llvm/System/DataTypes.h"
22 #include "llvm/Support/PointerLikeTypeTraits.h"
26 class SmallPtrSetIteratorImpl;
28 /// SmallPtrSetImpl - This is the common code shared among all the
29 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
30 /// for small and one for large sets.
32 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
33 /// which is treated as a simple array of pointers. When a pointer is added to
34 /// the set, the array is scanned to see if the element already exists, if not
35 /// the element is 'pushed back' onto the array. If we run out of space in the
36 /// array, we grow into the 'large set' case. SmallSet should be used when the
37 /// sets are often small. In this case, no memory allocation is used, and only
38 /// light-weight and cache-efficient scanning is used.
40 /// Large sets use a classic exponentially-probed hash table. Empty buckets are
41 /// represented with an illegal pointer value (-1) to allow null pointers to be
42 /// inserted. Tombstones are represented with another illegal pointer value
43 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
44 /// more. When this happens, the table is doubled in size.
46 class SmallPtrSetImpl {
47 friend class SmallPtrSetIteratorImpl;
49 /// CurArray - This is the current set of buckets. If it points to
50 /// SmallArray, then the set is in 'small mode'.
51 const void **CurArray;
52 /// CurArraySize - The allocated size of CurArray, always a power of two.
53 /// Note that CurArray points to an array that has CurArraySize+1 elements in
54 /// it, so that the end iterator actually points to valid memory.
55 unsigned CurArraySize;
57 // If small, this is # elts allocated consequtively
59 unsigned NumTombstones;
60 const void *SmallArray[1]; // Must be last ivar.
62 // Helper to copy construct a SmallPtrSet.
63 SmallPtrSetImpl(const SmallPtrSetImpl& that);
64 explicit SmallPtrSetImpl(unsigned SmallSize) {
65 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
66 "Initial size must be a power of two!");
67 CurArray = &SmallArray[0];
68 CurArraySize = SmallSize;
69 // The end pointer, always valid, is set to a valid element to help the
71 CurArray[SmallSize] = 0;
77 bool empty() const { return size() == 0; }
78 unsigned size() const { return NumElements; }
81 // If the capacity of the array is huge, and the # elements used is small,
83 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
84 return shrink_and_clear();
86 // Fill the array with empty markers.
87 memset(CurArray, -1, CurArraySize*sizeof(void*));
93 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
94 static void *getEmptyMarker() {
95 // Note that -1 is chosen to make clear() efficiently implementable with
96 // memset and because it's not a valid pointer value.
97 return reinterpret_cast<void*>(-1);
100 /// insert_imp - This returns true if the pointer was new to the set, false if
101 /// it was already in the set. This is hidden from the client so that the
102 /// derived class can check that the right type of pointer is passed in.
103 bool insert_imp(const void * Ptr);
105 /// erase_imp - If the set contains the specified pointer, remove it and
106 /// return true, otherwise return false. This is hidden from the client so
107 /// that the derived class can check that the right type of pointer is passed
109 bool erase_imp(const void * Ptr);
111 bool count_imp(const void * Ptr) const {
113 // Linear search for the item.
114 for (const void *const *APtr = SmallArray,
115 *const *E = SmallArray+NumElements; APtr != E; ++APtr)
122 return *FindBucketFor(Ptr) == Ptr;
126 bool isSmall() const { return CurArray == &SmallArray[0]; }
128 unsigned Hash(const void *Ptr) const {
129 return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1));
131 const void * const *FindBucketFor(const void *Ptr) const;
132 void shrink_and_clear();
134 /// Grow - Allocate a larger backing store for the buckets and move it over.
137 void operator=(const SmallPtrSetImpl &RHS); // DO NOT IMPLEMENT.
139 void CopyFrom(const SmallPtrSetImpl &RHS);
142 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
143 /// instances of SmallPtrSetIterator.
144 class SmallPtrSetIteratorImpl {
146 const void *const *Bucket;
148 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
152 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
153 return Bucket == RHS.Bucket;
155 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
156 return Bucket != RHS.Bucket;
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
163 void AdvanceIfNotValid() {
164 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
165 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
170 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
171 template<typename PtrTy>
172 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
173 typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
176 typedef PtrTy value_type;
177 typedef PtrTy reference;
178 typedef PtrTy pointer;
179 typedef std::ptrdiff_t difference_type;
180 typedef std::forward_iterator_tag iterator_category;
182 explicit SmallPtrSetIterator(const void *const *BP)
183 : SmallPtrSetIteratorImpl(BP) {}
185 // Most methods provided by baseclass.
187 const PtrTy operator*() const {
188 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
191 inline SmallPtrSetIterator& operator++() { // Preincrement
197 SmallPtrSetIterator operator++(int) { // Postincrement
198 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
202 /// NextPowerOfTwo - This is a helper template that rounds N up to the next
205 struct NextPowerOfTwo;
207 /// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper
208 /// template used to implement NextPowerOfTwo.
209 template<unsigned N, bool isPowerTwo>
210 struct NextPowerOfTwoH {
214 struct NextPowerOfTwoH<N, false> {
216 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
217 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
218 Val = NextPowerOfTwo<(N|(N-1)) + 1>::Val
223 struct NextPowerOfTwo {
224 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
228 /// SmallPtrSet - This class implements a set which is optimizer for holding
229 /// SmallSize or less elements. This internally rounds up SmallSize to the next
230 /// power of two if it is not already a power of two. See the comments above
231 /// SmallPtrSetImpl for details of the algorithm.
232 template<class PtrType, unsigned SmallSize>
233 class SmallPtrSet : public SmallPtrSetImpl {
234 // Make sure that SmallSize is a power of two, round up if not.
235 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
236 void *SmallArray[SmallSizePowTwo];
237 typedef PointerLikeTypeTraits<PtrType> PtrTraits;
239 SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
240 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(that) {}
242 template<typename It>
243 SmallPtrSet(It I, It E)
244 : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {
248 /// insert - This returns true if the pointer was new to the set, false if it
249 /// was already in the set.
250 bool insert(PtrType Ptr) {
251 return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
254 /// erase - If the set contains the specified pointer, remove it and return
255 /// true, otherwise return false.
256 bool erase(PtrType Ptr) {
257 return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
260 /// count - Return true if the specified pointer is in the set.
261 bool count(PtrType Ptr) const {
262 return count_imp(PtrTraits::getAsVoidPointer(Ptr));
265 template <typename IterT>
266 void insert(IterT I, IterT E) {
271 typedef SmallPtrSetIterator<PtrType> iterator;
272 typedef SmallPtrSetIterator<PtrType> const_iterator;
273 inline iterator begin() const {
274 return iterator(CurArray);
276 inline iterator end() const {
277 return iterator(CurArray+CurArraySize);
280 // Allow assignment from any smallptrset with the same element type even if it
281 // doesn't have the same smallsize.
282 const SmallPtrSet<PtrType, SmallSize>&
283 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {