1 //===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by Chris Lattner and is distributed under
6 // the University of Illinois Open Source 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
23 /// SmallPtrSetImpl - This is the common code shared among all the
24 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
25 /// for small and one for large sets.
27 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
28 /// which is treated as a simple array of pointers. When a pointer is added to
29 /// the set, the array is scanned to see if the element already exists, if not
30 /// the element is 'pushed back' onto the array. If we run out of space in the
31 /// array, we grow into the 'large set' case. SmallSet should be used when the
32 /// sets are often small. In this case, no memory allocation is used, and only
33 /// light-weight and cache-efficient scanning is used.
35 /// Large sets use a classic exponentially-probed hash table. Empty buckets are
36 /// represented with an illegal pointer value (-1) to allow null pointers to be
37 /// inserted. Tombstones are represented with another illegal pointer value
38 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
39 /// more. When this happens, the table is doubled in size.
41 class SmallPtrSetImpl {
43 /// CurArray - This is the current set of buckets. If it points to
44 /// SmallArray, then the set is in 'small mode'.
46 /// CurArraySize - The allocated size of CurArray, always a power of two.
47 /// Note that CurArray points to an array that has CurArraySize+1 elements in
48 /// it, so that the end iterator actually points to valid memory.
49 unsigned CurArraySize;
51 // If small, this is # elts allocated consequtively
53 void *SmallArray[1]; // Must be last ivar.
55 SmallPtrSetImpl(unsigned SmallSize) {
56 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
57 "Initial size must be a power of two!");
58 CurArray = &SmallArray[0];
59 CurArraySize = SmallSize;
60 // The end pointer, always valid, is set to a valid element to help the
62 CurArray[SmallSize] = 0;
70 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
71 static void *getEmptyMarker() {
72 // Note that -1 is chosen to make clear() efficiently implementable with
73 // memset and because it's not a valid pointer value.
74 return reinterpret_cast<void*>(-1);
78 // Fill the array with empty markers.
79 memset(CurArray, -1, CurArraySize*sizeof(void*));
83 /// insert - This returns true if the pointer was new to the set, false if it
84 /// was already in the set.
85 bool insert(void *Ptr);
87 /// erase - If the set contains the specified pointer, remove it and return
88 /// true, otherwise return false.
89 bool erase(void *Ptr);
91 bool count(void *Ptr) const {
93 // Linear search for the item.
94 for (void *const *APtr = SmallArray, *const *E = SmallArray+NumElements;
102 return *FindBucketFor(Ptr) == Ptr;
106 bool isSmall() const { return CurArray == &SmallArray[0]; }
108 unsigned Hash(void *Ptr) const {
109 return ((uintptr_t)Ptr >> 4) & (CurArraySize-1);
111 void * const *FindBucketFor(void *Ptr) const;
113 /// Grow - Allocate a larger backing store for the buckets and move it over.
117 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
118 /// instances of SmallPtrSetIterator.
119 class SmallPtrSetIteratorImpl {
123 SmallPtrSetIteratorImpl(void *const *BP) : Bucket(BP) {
127 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
128 return Bucket == RHS.Bucket;
130 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
131 return Bucket != RHS.Bucket;
135 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
136 /// that is. This is guaranteed to stop because the end() bucket is marked
138 void AdvanceIfNotValid() {
139 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
140 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
145 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
146 template<typename PtrTy>
147 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
149 SmallPtrSetIterator(void *const *BP) : SmallPtrSetIteratorImpl(BP) {}
151 // Most methods provided by baseclass.
153 PtrTy operator*() const {
154 return static_cast<PtrTy>(*Bucket);
157 inline SmallPtrSetIterator& operator++() { // Preincrement
163 SmallPtrSetIterator operator++(int) { // Postincrement
164 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
168 /// NextPowerOfTwo - This is a helper template that rounds N up to the next
171 struct NextPowerOfTwo;
173 /// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper
174 /// template used to implement NextPowerOfTwo.
175 template<unsigned N, bool isPowerTwo>
176 struct NextPowerOfTwoH {
180 struct NextPowerOfTwoH<N, false> {
182 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
183 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
184 NextVal = (N|(N-1)) + 1,
185 Val = NextPowerOfTwo<NextVal>::Val
190 struct NextPowerOfTwo {
191 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
195 /// SmallPtrSet - This class implements a set which is optimizer for holding
196 /// SmallSize or less elements. This internally rounds up SmallSize to the next
197 /// power of two if it is not already a power of two. See the comments above
198 /// SmallPtrSetImpl for details of the algorithm.
199 template<class PtrType, unsigned SmallSize>
200 class SmallPtrSet : public SmallPtrSetImpl {
201 // Make sure that SmallSize is a power of two, round up if not.
202 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
203 void *SmallArray[SmallSizePowTwo];
205 SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
207 typedef SmallPtrSetIterator<PtrType> iterator;
208 typedef SmallPtrSetIterator<PtrType> const_iterator;
209 inline iterator begin() const {
210 return iterator(CurArray);
212 inline iterator end() const {
213 return iterator(CurArray+CurArraySize);