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
18 #include "llvm/Support/Compiler.h"
19 #include "llvm/Support/DataTypes.h"
20 #include "llvm/Support/PointerLikeTypeTraits.h"
28 class SmallPtrSetIteratorImpl;
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.
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.
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.
48 class SmallPtrSetImpl {
49 friend class SmallPtrSetIteratorImpl;
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;
61 // If small, this is # elts allocated consecutively
63 unsigned NumTombstones;
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
73 CurArray[SmallSize] = 0;
79 bool empty() const { return size() == 0; }
80 unsigned size() const { return NumElements; }
83 // If the capacity of the array is huge, and the # elements used is small,
85 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
86 return shrink_and_clear();
88 // Fill the array with empty markers.
89 memset(CurArray, -1, CurArraySize*sizeof(void*));
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);
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);
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
111 bool erase_imp(const void * Ptr);
113 bool count_imp(const void * Ptr) const {
115 // Linear search for the item.
116 for (const void *const *APtr = SmallArray,
117 *const *E = SmallArray+NumElements; APtr != E; ++APtr)
124 return *FindBucketFor(Ptr) == Ptr;
128 bool isSmall() const { return CurArray == SmallArray; }
130 const void * const *FindBucketFor(const void *Ptr) const;
131 void shrink_and_clear();
133 /// Grow - Allocate a larger backing store for the buckets and move it over.
134 void Grow(unsigned NewSize);
136 void operator=(const SmallPtrSetImpl &RHS) LLVM_DELETED_FUNCTION;
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);
142 void CopyFrom(const SmallPtrSetImpl &RHS);
145 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
146 /// instances of SmallPtrSetIterator.
147 class SmallPtrSetIteratorImpl {
149 const void *const *Bucket;
151 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
155 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
156 return Bucket == RHS.Bucket;
158 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
159 return Bucket != RHS.Bucket;
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
166 void AdvanceIfNotValid() {
167 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
168 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
173 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
174 template<typename PtrTy>
175 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
176 typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
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;
185 explicit SmallPtrSetIterator(const void *const *BP)
186 : SmallPtrSetIteratorImpl(BP) {}
188 // Most methods provided by baseclass.
190 const PtrTy operator*() const {
191 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
194 inline SmallPtrSetIterator& operator++() { // Preincrement
200 SmallPtrSetIterator operator++(int) { // Postincrement
201 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
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).
208 struct RoundUpToPowerOfTwo;
210 /// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a
211 /// helper template used to implement RoundUpToPowerOfTwo.
212 template<unsigned N, bool isPowerTwo>
213 struct RoundUpToPowerOfTwoH {
217 struct RoundUpToPowerOfTwoH<N, false> {
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
226 struct RoundUpToPowerOfTwo {
227 enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
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.
235 template<class PtrType, unsigned SmallSize>
236 class 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;
244 SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {}
245 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {}
247 template<typename It>
248 SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {
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));
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));
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));
269 template <typename IterT>
270 void insert(IterT I, IterT E) {
275 typedef SmallPtrSetIterator<PtrType> iterator;
276 typedef SmallPtrSetIterator<PtrType> const_iterator;
277 inline iterator begin() const {
278 return iterator(CurArray);
280 inline iterator end() const {
281 return iterator(CurArray+CurArraySize);
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) {
292 /// swap - Swaps the elements of two sets.
293 void swap(SmallPtrSet<PtrType, SmallSize> &RHS) {
294 SmallPtrSetImpl::swap(RHS);
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) {