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 unsigned NumTombstones;
55 void *SmallArray[1]; // Must be last ivar.
57 SmallPtrSetImpl(unsigned SmallSize) {
58 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 &&
59 "Initial size must be a power of two!");
60 CurArray = &SmallArray[0];
61 CurArraySize = SmallSize;
62 // The end pointer, always valid, is set to a valid element to help the
64 CurArray[SmallSize] = 0;
72 bool empty() const { return size() == 0; }
73 unsigned size() const { return NumElements; }
75 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); }
76 static void *getEmptyMarker() {
77 // Note that -1 is chosen to make clear() efficiently implementable with
78 // memset and because it's not a valid pointer value.
79 return reinterpret_cast<void*>(-1);
83 // Fill the array with empty markers.
84 memset(CurArray, -1, CurArraySize*sizeof(void*));
89 /// insert - This returns true if the pointer was new to the set, false if it
90 /// was already in the set.
91 bool insert(void *Ptr);
93 /// erase - If the set contains the specified pointer, remove it and return
94 /// true, otherwise return false.
95 bool erase(void *Ptr);
97 bool count(void *Ptr) const {
99 // Linear search for the item.
100 for (void *const *APtr = SmallArray, *const *E = SmallArray+NumElements;
108 return *FindBucketFor(Ptr) == Ptr;
112 bool isSmall() const { return CurArray == &SmallArray[0]; }
114 unsigned Hash(void *Ptr) const {
115 return ((uintptr_t)Ptr >> 4) & (CurArraySize-1);
117 void * const *FindBucketFor(void *Ptr) const;
119 /// Grow - Allocate a larger backing store for the buckets and move it over.
123 /// SmallPtrSetIteratorImpl - This is the common base class shared between all
124 /// instances of SmallPtrSetIterator.
125 class SmallPtrSetIteratorImpl {
129 SmallPtrSetIteratorImpl(void *const *BP) : Bucket(BP) {
133 bool operator==(const SmallPtrSetIteratorImpl &RHS) const {
134 return Bucket == RHS.Bucket;
136 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const {
137 return Bucket != RHS.Bucket;
141 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket
142 /// that is. This is guaranteed to stop because the end() bucket is marked
144 void AdvanceIfNotValid() {
145 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() ||
146 *Bucket == SmallPtrSetImpl::getTombstoneMarker())
151 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
152 template<typename PtrTy>
153 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl {
155 SmallPtrSetIterator(void *const *BP) : SmallPtrSetIteratorImpl(BP) {}
157 // Most methods provided by baseclass.
159 PtrTy operator*() const {
160 return static_cast<PtrTy>(*Bucket);
163 inline SmallPtrSetIterator& operator++() { // Preincrement
169 SmallPtrSetIterator operator++(int) { // Postincrement
170 SmallPtrSetIterator tmp = *this; ++*this; return tmp;
174 /// NextPowerOfTwo - This is a helper template that rounds N up to the next
177 struct NextPowerOfTwo;
179 /// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper
180 /// template used to implement NextPowerOfTwo.
181 template<unsigned N, bool isPowerTwo>
182 struct NextPowerOfTwoH {
186 struct NextPowerOfTwoH<N, false> {
188 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets
189 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111.
190 Val = NextPowerOfTwo<(N|(N-1)) + 1>::Val
195 struct NextPowerOfTwo {
196 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val };
200 /// SmallPtrSet - This class implements a set which is optimizer for holding
201 /// SmallSize or less elements. This internally rounds up SmallSize to the next
202 /// power of two if it is not already a power of two. See the comments above
203 /// SmallPtrSetImpl for details of the algorithm.
204 template<class PtrType, unsigned SmallSize>
205 class SmallPtrSet : public SmallPtrSetImpl {
206 // Make sure that SmallSize is a power of two, round up if not.
207 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val };
208 void *SmallArray[SmallSizePowTwo];
210 SmallPtrSet() : SmallPtrSetImpl(NextPowerOfTwo<SmallSizePowTwo>::Val) {}
212 typedef SmallPtrSetIterator<PtrType> iterator;
213 typedef SmallPtrSetIterator<PtrType> const_iterator;
214 inline iterator begin() const {
215 return iterator(CurArray);
217 inline iterator end() const {
218 return iterator(CurArray+CurArraySize);