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
20 #include "llvm/Support/DataTypes.h"
24 /// SmallPtrSetImpl - This is the common code shared among all the
25 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one
26 /// for small and one for large sets.
28 /// Small sets use an array of pointers allocated in the SmallPtrSet object,
29 /// which is treated as a simple array of pointers. When a pointer is added to
30 /// the set, the array is scanned to see if the element already exists, if not
31 /// the element is 'pushed back' onto the array. If we run out of space in the
32 /// array, we grow into the 'large set' case. SmallSet should be used when the
33 /// sets are often small. In this case, no memory allocation is used, and only
34 /// light-weight and cache-efficient scanning is used.
36 /// Large sets use a classic exponentially-probed hash table. Empty buckets are
37 /// represented with an illegal pointer value (-1) to allow null pointers to be
38 /// inserted. Tombstones are represented with another illegal pointer value
39 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or
40 /// more. When this happens, the table is doubled in size.
42 class SmallPtrSetImpl {
44 /// CurArray - This is the current set of buckets. If it points to
45 /// SmallArray, then the set is in 'small mode'.
47 /// CurArraySize - The allocated size of CurArray, always a power of two.
48 /// Note that CurArray points to an array that has CurArraySize+1 elements in
49 /// it, so that the end iterator actually points to valid memory.
50 unsigned CurArraySize;
52 // If small, this is # elts allocated consequtively
54 void *SmallArray[1]; // Must be last ivar.
56 SmallPtrSetImpl(unsigned SmallSize) {
57 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
58 "Initial size must be a power of two!");
59 CurArray = &SmallArray[0];
60 CurArraySize = SmallSize;
61 // The end pointer, always valid, is set to a valid element to help the
63 CurArray[SmallSize] = 0;
71 bool empty() const { return size() == 0; }
72 unsigned size() const { return NumElements; }
74 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
75 static void *getEmptyMarker() {
76 // Note that -1 is chosen to make clear() efficiently implementable with
77 // memset and because it's not a valid pointer value.
78 return reinterpret_cast<void*>(-1);
82 // Fill the array with empty markers.
83 memset(CurArray, -1, CurArraySize*sizeof(void*));
87 /// insert - This returns true if the pointer was new to the set, false if it
88 /// was already in the set.
89 bool insert(void *Ptr);
91 /// erase - If the set contains the specified pointer, remove it and return
92 /// true, otherwise return false.
93 bool erase(void *Ptr);
95 bool count(void *Ptr) const {
97 // Linear search for the item.
98 for (void *const *APtr = SmallArray, *const *E = SmallArray+NumElements;
106 return *FindBucketFor(Ptr) == Ptr;
110 bool isSmall() const { return CurArray == &SmallArray[0]; }
112 unsigned Hash(void *Ptr) const {
113 return ((uintptr_t)Ptr >> 4) & (CurArraySize-1);
115 void * const *FindBucketFor(void *Ptr) const;
117 /// Grow - Allocate a larger backing store for the buckets and move it over.
121 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
122 /// instances of SmallPtrSetIterator.
123 class SmallPtrSetIteratorImpl {
127 SmallPtrSetIteratorImpl(void *const *BP) : Bucket(BP) {
131 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
132 return Bucket == RHS.Bucket;
134 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
135 return Bucket != RHS.Bucket;
139 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
140 /// that is. This is guaranteed to stop because the end() bucket is marked
142 void AdvanceIfNotValid() {
143 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
144 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
149 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
150 template<typename PtrTy>
151 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
153 SmallPtrSetIterator(void *const *BP) : SmallPtrSetIteratorImpl(BP) {}
155 // Most methods provided by baseclass.
157 PtrTy operator*() const {
158 return static_cast<PtrTy>(*Bucket);
161 inline SmallPtrSetIterator& operator++() { // Preincrement
167 SmallPtrSetIterator operator++(int) { // Postincrement
168 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
172 /// NextPowerOfTwo - This is a helper template that rounds N up to the next
175 struct NextPowerOfTwo;
177 /// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper
178 /// template used to implement NextPowerOfTwo.
179 template<unsigned N, bool isPowerTwo>
180 struct NextPowerOfTwoH {
184 struct NextPowerOfTwoH<N, false> {
186 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
187 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
188 NextVal = (N|(N-1)) + 1,
189 Val = NextPowerOfTwo<NextVal>::Val
194 struct NextPowerOfTwo {
195 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
199 /// SmallPtrSet - This class implements a set which is optimizer for holding
200 /// SmallSize or less elements. This internally rounds up SmallSize to the next
201 /// power of two if it is not already a power of two. See the comments above
202 /// SmallPtrSetImpl for details of the algorithm.
203 template<class PtrType, unsigned SmallSize>
204 class SmallPtrSet : public SmallPtrSetImpl {
205 // Make sure that SmallSize is a power of two, round up if not.
206 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
207 void *SmallArray[SmallSizePowTwo];
209 SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
211 typedef SmallPtrSetIterator<PtrType> iterator;
212 typedef SmallPtrSetIterator<PtrType> const_iterator;
213 inline iterator begin() const {
214 return iterator(CurArray);
216 inline iterator end() const {
217 return iterator(CurArray+CurArraySize);