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
20 #include "llvm/Support/DataTypes.h"
21 #include "llvm/Support/PointerLikeTypeTraits.h"
25 class SmallPtrSetIteratorImpl;
27 /// SmallPtrSetImpl - This is the common code shared among all the
28 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
29 /// for small and one for large sets.
31 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
32 /// which is treated as a simple array of pointers. When a pointer is added to
33 /// the set, the array is scanned to see if the element already exists, if not
34 /// the element is 'pushed back' onto the array. If we run out of space in the
35 /// array, we grow into the 'large set' case. SmallSet should be used when the
36 /// sets are often small. In this case, no memory allocation is used, and only
37 /// light-weight and cache-efficient scanning is used.
39 /// Large sets use a classic exponentially-probed hash table. Empty buckets are
40 /// represented with an illegal pointer value (-1) to allow null pointers to be
41 /// inserted. Tombstones are represented with another illegal pointer value
42 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
43 /// more. When this happens, the table is doubled in size.
45 class SmallPtrSetImpl {
46 friend class SmallPtrSetIteratorImpl;
48 /// CurArray - This is the current set of buckets. If it points to
49 /// SmallArray, then the set is in 'small mode'.
50 const void **CurArray;
51 /// CurArraySize - The allocated size of CurArray, always a power of two.
52 /// Note that CurArray points to an array that has CurArraySize+1 elements in
53 /// it, so that the end iterator actually points to valid memory.
54 unsigned CurArraySize;
56 // If small, this is # elts allocated consequtively
58 unsigned NumTombstones;
59 const void *SmallArray[1]; // Must be last ivar.
61 // Helper to copy construct a SmallPtrSet.
62 SmallPtrSetImpl(const SmallPtrSetImpl& that);
63 explicit SmallPtrSetImpl(unsigned SmallSize) {
64 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
65 "Initial size must be a power of two!");
66 CurArray = &SmallArray[0];
67 CurArraySize = SmallSize;
68 // The end pointer, always valid, is set to a valid element to help the
70 CurArray[SmallSize] = 0;
76 bool empty() const { return size() == 0; }
77 unsigned size() const { return NumElements; }
80 // If the capacity of the array is huge, and the # elements used is small,
82 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32)
83 return shrink_and_clear();
85 // Fill the array with empty markers.
86 memset(CurArray, -1, CurArraySize*sizeof(void*));
92 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
93 static void *getEmptyMarker() {
94 // Note that -1 is chosen to make clear() efficiently implementable with
95 // memset and because it's not a valid pointer value.
96 return reinterpret_cast<void*>(-1);
99 /// insert_imp - This returns true if the pointer was new to the set, false if
100 /// it was already in the set. This is hidden from the client so that the
101 /// derived class can check that the right type of pointer is passed in.
102 bool insert_imp(const void * Ptr);
104 /// erase_imp - If the set contains the specified pointer, remove it and
105 /// return true, otherwise return false. This is hidden from the client so
106 /// that the derived class can check that the right type of pointer is passed
108 bool erase_imp(const void * Ptr);
110 bool count_imp(const void * Ptr) const {
112 // Linear search for the item.
113 for (const void *const *APtr = SmallArray,
114 *const *E = SmallArray+NumElements; APtr != E; ++APtr)
121 return *FindBucketFor(Ptr) == Ptr;
125 bool isSmall() const { return CurArray == &SmallArray[0]; }
127 unsigned Hash(const void *Ptr) const {
128 return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1));
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.
136 void operator=(const SmallPtrSetImpl &RHS); // DO NOT IMPLEMENT.
138 void CopyFrom(const SmallPtrSetImpl &RHS);
141 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
142 /// instances of SmallPtrSetIterator.
143 class SmallPtrSetIteratorImpl {
145 const void *const *Bucket;
147 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) {
151 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
152 return Bucket == RHS.Bucket;
154 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
155 return Bucket != RHS.Bucket;
159 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
160 /// that is. This is guaranteed to stop because the end() bucket is marked
162 void AdvanceIfNotValid() {
163 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
164 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
169 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
170 template<typename PtrTy>
171 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
172 typedef PointerLikeTypeTraits<PtrTy> PtrTraits;
174 explicit SmallPtrSetIterator(const void *const *BP)
175 : SmallPtrSetIteratorImpl(BP) {}
177 // Most methods provided by baseclass.
179 const PtrTy operator*() const {
180 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket));
183 inline SmallPtrSetIterator& operator++() { // Preincrement
189 SmallPtrSetIterator operator++(int) { // Postincrement
190 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
194 /// NextPowerOfTwo - This is a helper template that rounds N up to the next
197 struct NextPowerOfTwo;
199 /// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper
200 /// template used to implement NextPowerOfTwo.
201 template<unsigned N, bool isPowerTwo>
202 struct NextPowerOfTwoH {
206 struct NextPowerOfTwoH<N, false> {
208 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
209 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
210 Val = NextPowerOfTwo<(N|(N-1)) + 1>::Val
215 struct NextPowerOfTwo {
216 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
220 /// SmallPtrSet - This class implements a set which is optimizer for holding
221 /// SmallSize or less elements. This internally rounds up SmallSize to the next
222 /// power of two if it is not already a power of two. See the comments above
223 /// SmallPtrSetImpl for details of the algorithm.
224 template<class PtrType, unsigned SmallSize>
225 class SmallPtrSet : public SmallPtrSetImpl {
226 // Make sure that SmallSize is a power of two, round up if not.
227 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
228 void *SmallArray[SmallSizePowTwo];
229 typedef PointerLikeTypeTraits<PtrType> PtrTraits;
231 SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
232 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(that) {}
234 template<typename It>
235 SmallPtrSet(It I, It E)
236 : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {
240 /// insert - This returns true if the pointer was new to the set, false if it
241 /// was already in the set.
242 bool insert(PtrType Ptr) {
243 return insert_imp(PtrTraits::getAsVoidPointer(Ptr));
246 /// erase - If the set contains the specified pointer, remove it and return
247 /// true, otherwise return false.
248 bool erase(PtrType Ptr) {
249 return erase_imp(PtrTraits::getAsVoidPointer(Ptr));
252 /// count - Return true if the specified pointer is in the set.
253 bool count(PtrType Ptr) const {
254 return count_imp(PtrTraits::getAsVoidPointer(Ptr));
257 template <typename IterT>
258 void insert(IterT I, IterT E) {
263 typedef SmallPtrSetIterator<PtrType> iterator;
264 typedef SmallPtrSetIterator<PtrType> const_iterator;
265 inline iterator begin() const {
266 return iterator(CurArray);
268 inline iterator end() const {
269 return iterator(CurArray+CurArraySize);
272 // Allow assignment from any smallptrset with the same element type even if it
273 // doesn't have the same smallsize.
274 const SmallPtrSet<PtrType, SmallSize>&
275 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) {