SmallPtrSet.h revision 2e502577ab3645ab5c54434671d299e35c2245cc
1//===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file defines the SmallPtrSet class. See the doxygen comment for 11// SmallPtrSetImpl for more details on the algorithm used. 12// 13//===----------------------------------------------------------------------===// 14 15#ifndef LLVM_ADT_SMALLPTRSET_H 16#define LLVM_ADT_SMALLPTRSET_H 17 18#include <cassert> 19#include <cstring> 20#include <iterator> 21#include "llvm/System/DataTypes.h" 22#include "llvm/Support/PointerLikeTypeTraits.h" 23 24namespace llvm { 25 26class SmallPtrSetIteratorImpl; 27 28/// SmallPtrSetImpl - This is the common code shared among all the 29/// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one 30/// for small and one for large sets. 31/// 32/// Small sets use an array of pointers allocated in the SmallPtrSet object, 33/// which is treated as a simple array of pointers. When a pointer is added to 34/// the set, the array is scanned to see if the element already exists, if not 35/// the element is 'pushed back' onto the array. If we run out of space in the 36/// array, we grow into the 'large set' case. SmallSet should be used when the 37/// sets are often small. In this case, no memory allocation is used, and only 38/// light-weight and cache-efficient scanning is used. 39/// 40/// Large sets use a classic exponentially-probed hash table. Empty buckets are 41/// represented with an illegal pointer value (-1) to allow null pointers to be 42/// inserted. Tombstones are represented with another illegal pointer value 43/// (-2), to allow deletion. The hash table is resized when the table is 3/4 or 44/// more. When this happens, the table is doubled in size. 45/// 46class SmallPtrSetImpl { 47 friend class SmallPtrSetIteratorImpl; 48protected: 49 /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'. 50 const void **SmallArray; 51 /// CurArray - This is the current set of buckets. If equal to SmallArray, 52 /// then the set is in 'small mode'. 53 const void **CurArray; 54 /// CurArraySize - The allocated size of CurArray, always a power of two. 55 /// Note that CurArray points to an array that has CurArraySize+1 elements in 56 /// it, so that the end iterator actually points to valid memory. 57 unsigned CurArraySize; 58 59 // If small, this is # elts allocated consequtively 60 unsigned NumElements; 61 unsigned NumTombstones; 62 63 // Helper to copy construct a SmallPtrSet. 64 SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that); 65 explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) : 66 SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) { 67 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 && 68 "Initial size must be a power of two!"); 69 // The end pointer, always valid, is set to a valid element to help the 70 // iterator. 71 CurArray[SmallSize] = 0; 72 clear(); 73 } 74 ~SmallPtrSetImpl(); 75 76public: 77 bool empty() const { return size() == 0; } 78 unsigned size() const { return NumElements; } 79 80 void clear() { 81 // If the capacity of the array is huge, and the # elements used is small, 82 // shrink the array. 83 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32) 84 return shrink_and_clear(); 85 86 // Fill the array with empty markers. 87 memset(CurArray, -1, CurArraySize*sizeof(void*)); 88 NumElements = 0; 89 NumTombstones = 0; 90 } 91 92protected: 93 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); } 94 static void *getEmptyMarker() { 95 // Note that -1 is chosen to make clear() efficiently implementable with 96 // memset and because it's not a valid pointer value. 97 return reinterpret_cast<void*>(-1); 98 } 99 100 /// insert_imp - This returns true if the pointer was new to the set, false if 101 /// it was already in the set. This is hidden from the client so that the 102 /// derived class can check that the right type of pointer is passed in. 103 bool insert_imp(const void * Ptr); 104 105 /// erase_imp - If the set contains the specified pointer, remove it and 106 /// return true, otherwise return false. This is hidden from the client so 107 /// that the derived class can check that the right type of pointer is passed 108 /// in. 109 bool erase_imp(const void * Ptr); 110 111 bool count_imp(const void * Ptr) const { 112 if (isSmall()) { 113 // Linear search for the item. 114 for (const void *const *APtr = SmallArray, 115 *const *E = SmallArray+NumElements; APtr != E; ++APtr) 116 if (*APtr == Ptr) 117 return true; 118 return false; 119 } 120 121 // Big set case. 122 return *FindBucketFor(Ptr) == Ptr; 123 } 124 125private: 126 bool isSmall() const { return CurArray == SmallArray; } 127 128 unsigned Hash(const void *Ptr) const { 129 return static_cast<unsigned>(((uintptr_t)Ptr >> 4) & (CurArraySize-1)); 130 } 131 const void * const *FindBucketFor(const void *Ptr) const; 132 void shrink_and_clear(); 133 134 /// Grow - Allocate a larger backing store for the buckets and move it over. 135 void Grow(); 136 137 void operator=(const SmallPtrSetImpl &RHS); // DO NOT IMPLEMENT. 138protected: 139 void CopyFrom(const SmallPtrSetImpl &RHS); 140}; 141 142/// SmallPtrSetIteratorImpl - This is the common base class shared between all 143/// instances of SmallPtrSetIterator. 144class SmallPtrSetIteratorImpl { 145protected: 146 const void *const *Bucket; 147public: 148 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) { 149 AdvanceIfNotValid(); 150 } 151 152 bool operator==(const SmallPtrSetIteratorImpl &RHS) const { 153 return Bucket == RHS.Bucket; 154 } 155 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const { 156 return Bucket != RHS.Bucket; 157 } 158 159protected: 160 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket 161 /// that is. This is guaranteed to stop because the end() bucket is marked 162 /// valid. 163 void AdvanceIfNotValid() { 164 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() || 165 *Bucket == SmallPtrSetImpl::getTombstoneMarker()) 166 ++Bucket; 167 } 168}; 169 170/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet. 171template<typename PtrTy> 172class SmallPtrSetIterator : public SmallPtrSetIteratorImpl { 173 typedef PointerLikeTypeTraits<PtrTy> PtrTraits; 174 175public: 176 typedef PtrTy value_type; 177 typedef PtrTy reference; 178 typedef PtrTy pointer; 179 typedef std::ptrdiff_t difference_type; 180 typedef std::forward_iterator_tag iterator_category; 181 182 explicit SmallPtrSetIterator(const void *const *BP) 183 : SmallPtrSetIteratorImpl(BP) {} 184 185 // Most methods provided by baseclass. 186 187 const PtrTy operator*() const { 188 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket)); 189 } 190 191 inline SmallPtrSetIterator& operator++() { // Preincrement 192 ++Bucket; 193 AdvanceIfNotValid(); 194 return *this; 195 } 196 197 SmallPtrSetIterator operator++(int) { // Postincrement 198 SmallPtrSetIterator tmp = *this; ++*this; return tmp; 199 } 200}; 201 202/// NextPowerOfTwo - This is a helper template that rounds N up to the next 203/// power of two (which means N itself if N is already a power of two). 204template<unsigned N> 205struct NextPowerOfTwo; 206 207/// NextPowerOfTwoH - If N is not a power of two, increase it. This is a helper 208/// template used to implement NextPowerOfTwo. 209template<unsigned N, bool isPowerTwo> 210struct NextPowerOfTwoH { 211 enum { Val = N }; 212}; 213template<unsigned N> 214struct NextPowerOfTwoH<N, false> { 215 enum { 216 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets 217 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111. 218 Val = NextPowerOfTwo<(N|(N-1)) + 1>::Val 219 }; 220}; 221 222template<unsigned N> 223struct NextPowerOfTwo { 224 enum { Val = NextPowerOfTwoH<N, (N&(N-1)) == 0>::Val }; 225}; 226 227 228/// SmallPtrSet - This class implements a set which is optimized for holding 229/// SmallSize or less elements. This internally rounds up SmallSize to the next 230/// power of two if it is not already a power of two. See the comments above 231/// SmallPtrSetImpl for details of the algorithm. 232template<class PtrType, unsigned SmallSize> 233class SmallPtrSet : public SmallPtrSetImpl { 234 // Make sure that SmallSize is a power of two, round up if not. 235 enum { SmallSizePowTwo = NextPowerOfTwo<SmallSize>::Val }; 236 /// SmallStorage - Fixed size storage used in 'small mode'. The extra element 237 /// ensures that the end iterator actually points to valid memory. 238 const void *SmallStorage[SmallSizePowTwo+1]; 239 typedef PointerLikeTypeTraits<PtrType> PtrTraits; 240public: 241 SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {} 242 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {} 243 244 template<typename It> 245 SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) { 246 insert(I, E); 247 } 248 249 /// insert - This returns true if the pointer was new to the set, false if it 250 /// was already in the set. 251 bool insert(PtrType Ptr) { 252 return insert_imp(PtrTraits::getAsVoidPointer(Ptr)); 253 } 254 255 /// erase - If the set contains the specified pointer, remove it and return 256 /// true, otherwise return false. 257 bool erase(PtrType Ptr) { 258 return erase_imp(PtrTraits::getAsVoidPointer(Ptr)); 259 } 260 261 /// count - Return true if the specified pointer is in the set. 262 bool count(PtrType Ptr) const { 263 return count_imp(PtrTraits::getAsVoidPointer(Ptr)); 264 } 265 266 template <typename IterT> 267 void insert(IterT I, IterT E) { 268 for (; I != E; ++I) 269 insert(*I); 270 } 271 272 typedef SmallPtrSetIterator<PtrType> iterator; 273 typedef SmallPtrSetIterator<PtrType> const_iterator; 274 inline iterator begin() const { 275 return iterator(CurArray); 276 } 277 inline iterator end() const { 278 return iterator(CurArray+CurArraySize); 279 } 280 281 // Allow assignment from any smallptrset with the same element type even if it 282 // doesn't have the same smallsize. 283 const SmallPtrSet<PtrType, SmallSize>& 284 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) { 285 CopyFrom(RHS); 286 return *this; 287 } 288 289}; 290 291} 292 293#endif 294