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 "llvm/Support/Compiler.h" 19#include "llvm/Support/DataTypes.h" 20#include "llvm/Support/PointerLikeTypeTraits.h" 21#include <cassert> 22#include <cstddef> 23#include <cstring> 24#include <iterator> 25 26namespace llvm { 27 28class SmallPtrSetIteratorImpl; 29 30/// SmallPtrSetImpl - This is the common code shared among all the 31/// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one 32/// for small and one for large sets. 33/// 34/// Small sets use an array of pointers allocated in the SmallPtrSet object, 35/// which is treated as a simple array of pointers. When a pointer is added to 36/// the set, the array is scanned to see if the element already exists, if not 37/// the element is 'pushed back' onto the array. If we run out of space in the 38/// array, we grow into the 'large set' case. SmallSet should be used when the 39/// sets are often small. In this case, no memory allocation is used, and only 40/// light-weight and cache-efficient scanning is used. 41/// 42/// Large sets use a classic exponentially-probed hash table. Empty buckets are 43/// represented with an illegal pointer value (-1) to allow null pointers to be 44/// inserted. Tombstones are represented with another illegal pointer value 45/// (-2), to allow deletion. The hash table is resized when the table is 3/4 or 46/// more. When this happens, the table is doubled in size. 47/// 48class SmallPtrSetImpl { 49 friend class SmallPtrSetIteratorImpl; 50protected: 51 /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'. 52 const void **SmallArray; 53 /// CurArray - This is the current set of buckets. If equal to SmallArray, 54 /// then the set is in 'small mode'. 55 const void **CurArray; 56 /// CurArraySize - The allocated size of CurArray, always a power of two. 57 /// Note that CurArray points to an array that has CurArraySize+1 elements in 58 /// it, so that the end iterator actually points to valid memory. 59 unsigned CurArraySize; 60 61 // If small, this is # elts allocated consecutively 62 unsigned NumElements; 63 unsigned NumTombstones; 64 65 // Helper to copy construct a SmallPtrSet. 66 SmallPtrSetImpl(const void **SmallStorage, const SmallPtrSetImpl& that); 67 explicit SmallPtrSetImpl(const void **SmallStorage, unsigned SmallSize) : 68 SmallArray(SmallStorage), CurArray(SmallStorage), CurArraySize(SmallSize) { 69 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 && 70 "Initial size must be a power of two!"); 71 // The end pointer, always valid, is set to a valid element to help the 72 // iterator. 73 CurArray[SmallSize] = 0; 74 clear(); 75 } 76 ~SmallPtrSetImpl(); 77 78public: 79 bool empty() const { return size() == 0; } 80 unsigned size() const { return NumElements; } 81 82 void clear() { 83 // If the capacity of the array is huge, and the # elements used is small, 84 // shrink the array. 85 if (!isSmall() && NumElements*4 < CurArraySize && CurArraySize > 32) 86 return shrink_and_clear(); 87 88 // Fill the array with empty markers. 89 memset(CurArray, -1, CurArraySize*sizeof(void*)); 90 NumElements = 0; 91 NumTombstones = 0; 92 } 93 94protected: 95 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); } 96 static void *getEmptyMarker() { 97 // Note that -1 is chosen to make clear() efficiently implementable with 98 // memset and because it's not a valid pointer value. 99 return reinterpret_cast<void*>(-1); 100 } 101 102 /// insert_imp - This returns true if the pointer was new to the set, false if 103 /// it was already in the set. This is hidden from the client so that the 104 /// derived class can check that the right type of pointer is passed in. 105 bool insert_imp(const void * Ptr); 106 107 /// erase_imp - If the set contains the specified pointer, remove it and 108 /// return true, otherwise return false. This is hidden from the client so 109 /// that the derived class can check that the right type of pointer is passed 110 /// in. 111 bool erase_imp(const void * Ptr); 112 113 bool count_imp(const void * Ptr) const { 114 if (isSmall()) { 115 // Linear search for the item. 116 for (const void *const *APtr = SmallArray, 117 *const *E = SmallArray+NumElements; APtr != E; ++APtr) 118 if (*APtr == Ptr) 119 return true; 120 return false; 121 } 122 123 // Big set case. 124 return *FindBucketFor(Ptr) == Ptr; 125 } 126 127private: 128 bool isSmall() const { return CurArray == SmallArray; } 129 130 const void * const *FindBucketFor(const void *Ptr) const; 131 void shrink_and_clear(); 132 133 /// Grow - Allocate a larger backing store for the buckets and move it over. 134 void Grow(unsigned NewSize); 135 136 void operator=(const SmallPtrSetImpl &RHS) LLVM_DELETED_FUNCTION; 137protected: 138 /// swap - Swaps the elements of two sets. 139 /// Note: This method assumes that both sets have the same small size. 140 void swap(SmallPtrSetImpl &RHS); 141 142 void CopyFrom(const SmallPtrSetImpl &RHS); 143}; 144 145/// SmallPtrSetIteratorImpl - This is the common base class shared between all 146/// instances of SmallPtrSetIterator. 147class SmallPtrSetIteratorImpl { 148protected: 149 const void *const *Bucket; 150public: 151 explicit SmallPtrSetIteratorImpl(const void *const *BP) : Bucket(BP) { 152 AdvanceIfNotValid(); 153 } 154 155 bool operator==(const SmallPtrSetIteratorImpl &RHS) const { 156 return Bucket == RHS.Bucket; 157 } 158 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const { 159 return Bucket != RHS.Bucket; 160 } 161 162protected: 163 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket 164 /// that is. This is guaranteed to stop because the end() bucket is marked 165 /// valid. 166 void AdvanceIfNotValid() { 167 while (*Bucket == SmallPtrSetImpl::getEmptyMarker() || 168 *Bucket == SmallPtrSetImpl::getTombstoneMarker()) 169 ++Bucket; 170 } 171}; 172 173/// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet. 174template<typename PtrTy> 175class SmallPtrSetIterator : public SmallPtrSetIteratorImpl { 176 typedef PointerLikeTypeTraits<PtrTy> PtrTraits; 177 178public: 179 typedef PtrTy value_type; 180 typedef PtrTy reference; 181 typedef PtrTy pointer; 182 typedef std::ptrdiff_t difference_type; 183 typedef std::forward_iterator_tag iterator_category; 184 185 explicit SmallPtrSetIterator(const void *const *BP) 186 : SmallPtrSetIteratorImpl(BP) {} 187 188 // Most methods provided by baseclass. 189 190 const PtrTy operator*() const { 191 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket)); 192 } 193 194 inline SmallPtrSetIterator& operator++() { // Preincrement 195 ++Bucket; 196 AdvanceIfNotValid(); 197 return *this; 198 } 199 200 SmallPtrSetIterator operator++(int) { // Postincrement 201 SmallPtrSetIterator tmp = *this; ++*this; return tmp; 202 } 203}; 204 205/// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next 206/// power of two (which means N itself if N is already a power of two). 207template<unsigned N> 208struct RoundUpToPowerOfTwo; 209 210/// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a 211/// helper template used to implement RoundUpToPowerOfTwo. 212template<unsigned N, bool isPowerTwo> 213struct RoundUpToPowerOfTwoH { 214 enum { Val = N }; 215}; 216template<unsigned N> 217struct RoundUpToPowerOfTwoH<N, false> { 218 enum { 219 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets 220 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111. 221 Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val 222 }; 223}; 224 225template<unsigned N> 226struct RoundUpToPowerOfTwo { 227 enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val }; 228}; 229 230 231/// SmallPtrSet - This class implements a set which is optimized for holding 232/// SmallSize or less elements. This internally rounds up SmallSize to the next 233/// power of two if it is not already a power of two. See the comments above 234/// SmallPtrSetImpl for details of the algorithm. 235template<class PtrType, unsigned SmallSize> 236class SmallPtrSet : public SmallPtrSetImpl { 237 // Make sure that SmallSize is a power of two, round up if not. 238 enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val }; 239 /// SmallStorage - Fixed size storage used in 'small mode'. The extra element 240 /// ensures that the end iterator actually points to valid memory. 241 const void *SmallStorage[SmallSizePowTwo+1]; 242 typedef PointerLikeTypeTraits<PtrType> PtrTraits; 243public: 244 SmallPtrSet() : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) {} 245 SmallPtrSet(const SmallPtrSet &that) : SmallPtrSetImpl(SmallStorage, that) {} 246 247 template<typename It> 248 SmallPtrSet(It I, It E) : SmallPtrSetImpl(SmallStorage, SmallSizePowTwo) { 249 insert(I, E); 250 } 251 252 /// insert - This returns true if the pointer was new to the set, false if it 253 /// was already in the set. 254 bool insert(PtrType Ptr) { 255 return insert_imp(PtrTraits::getAsVoidPointer(Ptr)); 256 } 257 258 /// erase - If the set contains the specified pointer, remove it and return 259 /// true, otherwise return false. 260 bool erase(PtrType Ptr) { 261 return erase_imp(PtrTraits::getAsVoidPointer(Ptr)); 262 } 263 264 /// count - Return true if the specified pointer is in the set. 265 bool count(PtrType Ptr) const { 266 return count_imp(PtrTraits::getAsVoidPointer(Ptr)); 267 } 268 269 template <typename IterT> 270 void insert(IterT I, IterT E) { 271 for (; I != E; ++I) 272 insert(*I); 273 } 274 275 typedef SmallPtrSetIterator<PtrType> iterator; 276 typedef SmallPtrSetIterator<PtrType> const_iterator; 277 inline iterator begin() const { 278 return iterator(CurArray); 279 } 280 inline iterator end() const { 281 return iterator(CurArray+CurArraySize); 282 } 283 284 // Allow assignment from any smallptrset with the same element type even if it 285 // doesn't have the same smallsize. 286 const SmallPtrSet<PtrType, SmallSize>& 287 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) { 288 CopyFrom(RHS); 289 return *this; 290 } 291 292 /// swap - Swaps the elements of two sets. 293 void swap(SmallPtrSet<PtrType, SmallSize> &RHS) { 294 SmallPtrSetImpl::swap(RHS); 295 } 296}; 297 298} 299 300namespace std { 301 /// Implement std::swap in terms of SmallPtrSet swap. 302 template<class T, unsigned N> 303 inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) { 304 LHS.swap(RHS); 305 } 306} 307 308#endif 309