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 <cstddef> 20#include <cstring> 21#include <iterator> 22#include "llvm/Support/DataTypes.h" 23#include "llvm/Support/PointerLikeTypeTraits.h" 24 25namespace llvm { 26 27class SmallPtrSetIteratorImpl; 28 29/// SmallPtrSetImpl - This is the common code shared among all the 30/// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one 31/// for small and one for large sets. 32/// 33/// Small sets use an array of pointers allocated in the SmallPtrSet object, 34/// which is treated as a simple array of pointers. When a pointer is added to 35/// the set, the array is scanned to see if the element already exists, if not 36/// the element is 'pushed back' onto the array. If we run out of space in the 37/// array, we grow into the 'large set' case. SmallSet should be used when the 38/// sets are often small. In this case, no memory allocation is used, and only 39/// light-weight and cache-efficient scanning is used. 40/// 41/// Large sets use a classic exponentially-probed hash table. Empty buckets are 42/// represented with an illegal pointer value (-1) to allow null pointers to be 43/// inserted. Tombstones are represented with another illegal pointer value 44/// (-2), to allow deletion. The hash table is resized when the table is 3/4 or 45/// more. When this happens, the table is doubled in size. 46/// 47class SmallPtrSetImpl { 48 friend class SmallPtrSetIteratorImpl; 49protected: 50 /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'. 51 const void **SmallArray; 52 /// CurArray - This is the current set of buckets. If equal to SmallArray, 53 /// then the set is in 'small mode'. 54 const void **CurArray; 55 /// CurArraySize - The allocated size of CurArray, always a power of two. 56 /// Note that CurArray points to an array that has CurArraySize+1 elements in 57 /// it, so that the end iterator actually points to valid memory. 58 unsigned CurArraySize; 59 60 // If small, this is # elts allocated consecutively 61 unsigned NumElements; 62 unsigned NumTombstones; 63 64 // Helper to copy construct a SmallPtrSet. 65 SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that); 66 explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) : 67 SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) { 68 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 && 69 "Initial size must be a power of two!"); 70 // The end pointer, always valid, is set to a valid element to help the 71 // iterator. 72 CurArray[SmallSize] = 0; 73 clear(); 74 } 75 ~SmallPtrSetImpl(); 76 77public: 78 bool empty() const { return size() == 0; } 79 unsigned size() const { return NumElements; } 80 81 void clear() { 82 // If the capacity of the array is huge, and the # elements used is small, 83 // shrink the array. 84 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32) 85 return shrink_and_clear(); 86 87 // Fill the array with empty markers. 88 memset(CurArray, -1, CurArraySize*sizeof(void*)); 89 NumElements = 0; 90 NumTombstones = 0; 91 } 92 93protected: 94 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); } 95 static void *getEmptyMarker() { 96 // Note that -1 is chosen to make clear() efficiently implementable with 97 // memset and because it's not a valid pointer value. 98 return reinterpret_cast<void*>(-1); 99 } 100 101 /// insert_imp - This returns true if the pointer was new to the set, false if 102 /// it was already in the set. This is hidden from the client so that the 103 /// derived class can check that the right type of pointer is passed in. 104 bool insert_imp(const void * Ptr); 105 106 /// erase_imp - If the set contains the specified pointer, remove it and 107 /// return true, otherwise return false. This is hidden from the client so 108 /// that the derived class can check that the right type of pointer is passed 109 /// in. 110 bool erase_imp(const void * Ptr); 111 112 bool count_imp(const void * Ptr) const { 113 if (isSmall()) { 114 // Linear search for the item. 115 for (const void *const *APtr = SmallArray, 116 *const *E = SmallArray+NumElements; APtr != E; ++APtr) 117 if (*APtr == Ptr) 118 return true; 119 return false; 120 } 121 122 // Big set case. 123 return *FindBucketFor(Ptr) == Ptr; 124 } 125 126private: 127 bool isSmall() const { return CurArray == SmallArray; } 128 129 const void * const *FindBucketFor(const void *Ptr) const; 130 void shrink_and_clear(); 131 132 /// Grow - Allocate a larger backing store for the buckets and move it over. 133 void Grow(unsigned NewSize); 134 135 void operator=(const SmallPtrSetImpl &RHS); // DO NOT IMPLEMENT. 136protected: 137 /// swap - Swaps the elements of two sets. 138 /// Note: This method assumes that both sets have the same small size. 139 void swap(SmallPtrSetImpl &RHS); 140 141 void CopyFrom(const SmallPtrSetImpl &RHS); 142}; 143 144/// SmallPtrSetIteratorImpl - This is the common base class shared between all 145/// instances of SmallPtrSetIterator. 146class SmallPtrSetIteratorImpl { 147protected: 148 const void *const *Bucket; 149public: 150 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) { 151 AdvanceIfNotValid(); 152 } 153 154 bool operator==(const SmallPtrSetIteratorImpl &RHS) const { 155 return Bucket == RHS.Bucket; 156 } 157 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const { 158 return Bucket != RHS.Bucket; 159 } 160 161protected: 162 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket 163 /// that is. This is guaranteed to stop because the end() bucket is marked 164 /// valid. 165 void AdvanceIfNotValid() { 166 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() || 167 *Bucket == SmallPtrSetImpl::getTombstoneMarker()) 168 ++Bucket; 169 } 170}; 171 172/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet. 173template<typename PtrTy> 174class SmallPtrSetIterator : public SmallPtrSetIteratorImpl { 175 typedef PointerLikeTypeTraits<PtrTy> PtrTraits; 176 177public: 178 typedef PtrTy value_type; 179 typedef PtrTy reference; 180 typedef PtrTy pointer; 181 typedef std::ptrdiff_t difference_type; 182 typedef std::forward_iterator_tag iterator_category; 183 184 explicit SmallPtrSetIterator(const void *const *BP) 185 : SmallPtrSetIteratorImpl(BP) {} 186 187 // Most methods provided by baseclass. 188 189 const PtrTy operator*() const { 190 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket)); 191 } 192 193 inline SmallPtrSetIterator& operator++() { // Preincrement 194 ++Bucket; 195 AdvanceIfNotValid(); 196 return *this; 197 } 198 199 SmallPtrSetIterator operator++(int) { // Postincrement 200 SmallPtrSetIterator tmp = *this; ++*this; return tmp; 201 } 202}; 203 204/// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next 205/// power of two (which means N itself if N is already a power of two). 206template<unsigned N> 207struct RoundUpToPowerOfTwo; 208 209/// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a 210/// helper template used to implement RoundUpToPowerOfTwo. 211template<unsigned N, bool isPowerTwo> 212struct RoundUpToPowerOfTwoH { 213 enum { Val = N }; 214}; 215template<unsigned N> 216struct RoundUpToPowerOfTwoH<N, false> { 217 enum { 218 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets 219 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111. 220 Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val 221 }; 222}; 223 224template<unsigned N> 225struct RoundUpToPowerOfTwo { 226 enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val }; 227}; 228 229 230/// SmallPtrSet - This class implements a set which is optimized for holding 231/// SmallSize or less elements. This internally rounds up SmallSize to the next 232/// power of two if it is not already a power of two. See the comments above 233/// SmallPtrSetImpl for details of the algorithm. 234template<class PtrType, unsigned SmallSize> 235class SmallPtrSet : public SmallPtrSetImpl { 236 // Make sure that SmallSize is a power of two, round up if not. 237 enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val }; 238 /// SmallStorage - Fixed size storage used in 'small mode'. The extra element 239 /// ensures that the end iterator actually points to valid memory. 240 const void *SmallStorage[SmallSizePowTwo+1]; 241 typedef PointerLikeTypeTraits<PtrType> PtrTraits; 242public: 243 SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {} 244 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {} 245 246 template<typename It> 247 SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) { 248 insert(I, E); 249 } 250 251 /// insert - This returns true if the pointer was new to the set, false if it 252 /// was already in the set. 253 bool insert(PtrType Ptr) { 254 return insert_imp(PtrTraits::getAsVoidPointer(Ptr)); 255 } 256 257 /// erase - If the set contains the specified pointer, remove it and return 258 /// true, otherwise return false. 259 bool erase(PtrType Ptr) { 260 return erase_imp(PtrTraits::getAsVoidPointer(Ptr)); 261 } 262 263 /// count - Return true if the specified pointer is in the set. 264 bool count(PtrType Ptr) const { 265 return count_imp(PtrTraits::getAsVoidPointer(Ptr)); 266 } 267 268 template <typename IterT> 269 void insert(IterT I, IterT E) { 270 for (; I != E; ++I) 271 insert(*I); 272 } 273 274 typedef SmallPtrSetIterator<PtrType> iterator; 275 typedef SmallPtrSetIterator<PtrType> const_iterator; 276 inline iterator begin() const { 277 return iterator(CurArray); 278 } 279 inline iterator end() const { 280 return iterator(CurArray+CurArraySize); 281 } 282 283 // Allow assignment from any smallptrset with the same element type even if it 284 // doesn't have the same smallsize. 285 const SmallPtrSet<PtrType, SmallSize>& 286 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) { 287 CopyFrom(RHS); 288 return *this; 289 } 290 291 /// swap - Swaps the elements of two sets. 292 void swap(SmallPtrSet<PtrType, SmallSize> &RHS) { 293 SmallPtrSetImpl::swap(RHS); 294 } 295}; 296 297} 298 299namespace std { 300 /// Implement std::swap in terms of SmallPtrSet swap. 301 template<class T, unsigned N> 302 inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) { 303 LHS.swap(RHS); 304 } 305} 306 307#endif 308