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
22 #include "llvm/Support/DataTypes.h"
23 #include "llvm/Support/PointerLikeTypeTraits.h"
27 class SmallPtrSetIteratorImpl;
29 /// SmallPtrSetImpl - This is the common code shared among all the
30 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
31 /// for small and one for large sets.
33 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
34 /// which is treated as a simple array of pointers. When a pointer is added to
35 /// the set, the array is scanned to see if the element already exists, if not
36 /// the element is 'pushed back' onto the array. If we run out of space in the
37 /// array, we grow into the 'large set' case. SmallSet should be used when the
38 /// sets are often small. In this case, no memory allocation is used, and only
39 /// light-weight and cache-efficient scanning is used.
41 /// Large sets use a classic exponentially-probed hash table. Empty buckets are
42 /// represented with an illegal pointer value (-1) to allow null pointers to be
43 /// inserted. Tombstones are represented with another illegal pointer value
44 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
45 /// more. When this happens, the table is doubled in size.
47 class SmallPtrSetImpl {
48 friend class SmallPtrSetIteratorImpl;
50 /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'.
51 const void **SmallArray;
52 /// CurArray - This is the current set of buckets. If equal to SmallArray,
53 /// then the set is in 'small mode'.
54 const void **CurArray;
55 /// CurArraySize - The allocated size of CurArray, always a power of two.
56 /// Note that CurArray points to an array that has CurArraySize+1 elements in
57 /// it, so that the end iterator actually points to valid memory.
58 unsigned CurArraySize;
60 // If small, this is # elts allocated consequtively
62 unsigned NumTombstones;
64 // Helper to copy construct a SmallPtrSet.
65 SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that);
66 explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) :
67 SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) {
68 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
69 "Initial size must be a power of two!");
70 // The end pointer, always valid, is set to a valid element to help the
72 CurArray[SmallSize] = 0;
78 bool empty() const { return size() == 0; }
79 unsigned size() const { return NumElements; }
82 // If the capacity of the array is huge, and the # elements used is small,
84 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
85 return shrink_and_clear();
87 // Fill the array with empty markers.
88 memset(CurArray, -1, CurArraySize*sizeof(void*));
94 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
95 static void *getEmptyMarker() {
96 // Note that -1 is chosen to make clear() efficiently implementable with
97 // memset and because it's not a valid pointer value.
98 return reinterpret_cast<void*>(-1);
101 /// insert_imp - This returns true if the pointer was new to the set, false if
102 /// it was already in the set. This is hidden from the client so that the
103 /// derived class can check that the right type of pointer is passed in.
104 bool insert_imp(const void * Ptr);
106 /// erase_imp - If the set contains the specified pointer, remove it and
107 /// return true, otherwise return false. This is hidden from the client so
108 /// that the derived class can check that the right type of pointer is passed
110 bool erase_imp(const void * Ptr);
112 bool count_imp(const void * Ptr) const {
114 // Linear search for the item.
115 for (const void *const *APtr = SmallArray,
116 *const *E = SmallArray+NumElements; APtr != E; ++APtr)
123 return *FindBucketFor(Ptr) == Ptr;
127 bool isSmall() const { return CurArray == SmallArray; }
129 unsigned Hash(const void *Ptr) const {
130 return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1));
132 const void * const *FindBucketFor(const void *Ptr) const;
133 void shrink_and_clear();
135 /// Grow - Allocate a larger backing store for the buckets and move it over.
138 void operator=(const SmallPtrSetImpl &RHS); // DO NOT IMPLEMENT.
140 void CopyFrom(const SmallPtrSetImpl &RHS);
143 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
144 /// instances of SmallPtrSetIterator.
145 class SmallPtrSetIteratorImpl {
147 const void *const *Bucket;
149 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
153 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
154 return Bucket == RHS.Bucket;
156 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
157 return Bucket != RHS.Bucket;
161 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
162 /// that is. This is guaranteed to stop because the end() bucket is marked
164 void AdvanceIfNotValid() {
165 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
166 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
171 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
172 template<typename PtrTy>
173 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
174 typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
177 typedef PtrTy value_type;
178 typedef PtrTy reference;
179 typedef PtrTy pointer;
180 typedef std::ptrdiff_t difference_type;
181 typedef std::forward_iterator_tag iterator_category;
183 explicit SmallPtrSetIterator(const void *const *BP)
184 : SmallPtrSetIteratorImpl(BP) {}
186 // Most methods provided by baseclass.
188 const PtrTy operator*() const {
189 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
192 inline SmallPtrSetIterator& operator++() { // Preincrement
198 SmallPtrSetIterator operator++(int) { // Postincrement
199 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
203 /// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next
204 /// power of two (which means N itself if N is already a power of two).
206 struct RoundUpToPowerOfTwo;
208 /// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a
209 /// helper template used to implement RoundUpToPowerOfTwo.
210 template<unsigned N, bool isPowerTwo>
211 struct RoundUpToPowerOfTwoH {
215 struct RoundUpToPowerOfTwoH<N, false> {
217 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
218 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
219 Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val
224 struct RoundUpToPowerOfTwo {
225 enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
229 /// SmallPtrSet - This class implements a set which is optimized for holding
230 /// SmallSize or less elements. This internally rounds up SmallSize to the next
231 /// power of two if it is not already a power of two. See the comments above
232 /// SmallPtrSetImpl for details of the algorithm.
233 template<class PtrType, unsigned SmallSize>
234 class SmallPtrSet : public SmallPtrSetImpl {
235 // Make sure that SmallSize is a power of two, round up if not.
236 enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val };
237 /// SmallStorage - Fixed size storage used in 'small mode'. The extra element
238 /// ensures that the end iterator actually points to valid memory.
239 const void *SmallStorage[SmallSizePowTwo+1];
240 typedef PointerLikeTypeTraits<PtrType> PtrTraits;
242 SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {}
243 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {}
245 template<typename It>
246 SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {
250 /// insert - This returns true if the pointer was new to the set, false if it
251 /// was already in the set.
252 bool insert(PtrType Ptr) {
253 return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
256 /// erase - If the set contains the specified pointer, remove it and return
257 /// true, otherwise return false.
258 bool erase(PtrType Ptr) {
259 return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
262 /// count - Return true if the specified pointer is in the set.
263 bool count(PtrType Ptr) const {
264 return count_imp(PtrTraits::getAsVoidPointer(Ptr));
267 template <typename IterT>
268 void insert(IterT I, IterT E) {
273 typedef SmallPtrSetIterator<PtrType> iterator;
274 typedef SmallPtrSetIterator<PtrType> const_iterator;
275 inline iterator begin() const {
276 return iterator(CurArray);
278 inline iterator end() const {
279 return iterator(CurArray+CurArraySize);
282 // Allow assignment from any smallptrset with the same element type even if it
283 // doesn't have the same smallsize.
284 const SmallPtrSet<PtrType, SmallSize>&
285 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {