1 //===- llvm/ADT/SmallPtrSet.h - 'Normally small' pointer set ----*- C++ -*-===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 // 9 // This file defines the SmallPtrSet class. See the doxygen comment for 10 // SmallPtrSetImplBase for more details on the algorithm used. 11 // 12 //===----------------------------------------------------------------------===// 13 14 #ifndef LLVM_ADT_SMALLPTRSET_H 15 #define LLVM_ADT_SMALLPTRSET_H 16 17 #include "llvm/ADT/EpochTracker.h" 18 #include "llvm/Support/Compiler.h" 19 #include "llvm/Support/ReverseIteration.h" 20 #include "llvm/Support/type_traits.h" 21 #include <cassert> 22 #include <cstddef> 23 #include <cstdlib> 24 #include <cstring> 25 #include <initializer_list> 26 #include <iterator> 27 #include <utility> 28 29 namespace llvm { 30 31 /// SmallPtrSetImplBase - This is the common code shared among all the 32 /// SmallPtrSet<>'s, which is almost everything. SmallPtrSet has two modes, one 33 /// for small and one for large sets. 34 /// 35 /// Small sets use an array of pointers allocated in the SmallPtrSet object, 36 /// which is treated as a simple array of pointers. When a pointer is added to 37 /// the set, the array is scanned to see if the element already exists, if not 38 /// the element is 'pushed back' onto the array. If we run out of space in the 39 /// array, we grow into the 'large set' case. SmallSet should be used when the 40 /// sets are often small. In this case, no memory allocation is used, and only 41 /// light-weight and cache-efficient scanning is used. 42 /// 43 /// Large sets use a classic exponentially-probed hash table. Empty buckets are 44 /// represented with an illegal pointer value (-1) to allow null pointers to be 45 /// inserted. Tombstones are represented with another illegal pointer value 46 /// (-2), to allow deletion. The hash table is resized when the table is 3/4 or 47 /// more. When this happens, the table is doubled in size. 48 /// 49 class SmallPtrSetImplBase : public DebugEpochBase { 50 friend class SmallPtrSetIteratorImpl; 51 52 protected: 53 /// SmallArray - Points to a fixed size set of buckets, used in 'small mode'. 54 const void **SmallArray; 55 /// CurArray - This is the current set of buckets. If equal to SmallArray, 56 /// then the set is in 'small mode'. 57 const void **CurArray; 58 /// CurArraySize - The allocated size of CurArray, always a power of two. 59 unsigned CurArraySize; 60 61 /// Number of elements in CurArray that contain a value or are a tombstone. 62 /// If small, all these elements are at the beginning of CurArray and the rest 63 /// is uninitialized. 64 unsigned NumNonEmpty; 65 /// Number of tombstones in CurArray. 66 unsigned NumTombstones; 67 68 // Helpers to copy and move construct a SmallPtrSet. 69 SmallPtrSetImplBase(const void **SmallStorage, 70 const SmallPtrSetImplBase &that); 71 SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize, 72 SmallPtrSetImplBase &&that); 73 74 explicit SmallPtrSetImplBase(const void **SmallStorage, unsigned SmallSize) 75 : SmallArray(SmallStorage), CurArray(SmallStorage), 76 CurArraySize(SmallSize), NumNonEmpty(0), NumTombstones(0) { 77 assert(SmallSize && (SmallSize & (SmallSize-1)) == 0 && 78 "Initial size must be a power of two!"); 79 } 80 81 ~SmallPtrSetImplBase() { 82 if (!isSmall()) 83 free(CurArray); 84 } 85 86 public: 87 using size_type = unsigned; 88 89 SmallPtrSetImplBase &operator=(const SmallPtrSetImplBase &) = delete; 90 91 LLVM_NODISCARD bool empty() const { return size() == 0; } 92 size_type size() const { return NumNonEmpty - NumTombstones; } 93 94 void clear() { 95 incrementEpoch(); 96 // If the capacity of the array is huge, and the # elements used is small, 97 // shrink the array. 98 if (!isSmall()) { 99 if (size() * 4 < CurArraySize && CurArraySize > 32) 100 return shrink_and_clear(); 101 // Fill the array with empty markers. 102 memset(CurArray, -1, CurArraySize * sizeof(void *)); 103 } 104 105 NumNonEmpty = 0; 106 NumTombstones = 0; 107 } 108 109 protected: 110 static void *getTombstoneMarker() { return reinterpret_cast<void*>(-2); } 111 112 static void *getEmptyMarker() { 113 // Note that -1 is chosen to make clear() efficiently implementable with 114 // memset and because it's not a valid pointer value. 115 return reinterpret_cast<void*>(-1); 116 } 117 118 const void **EndPointer() const { 119 return isSmall() ? CurArray + NumNonEmpty : CurArray + CurArraySize; 120 } 121 122 /// insert_imp - This returns true if the pointer was new to the set, false if 123 /// it was already in the set. This is hidden from the client so that the 124 /// derived class can check that the right type of pointer is passed in. 125 std::pair<const void *const *, bool> insert_imp(const void *Ptr) { 126 if (isSmall()) { 127 // Check to see if it is already in the set. 128 const void **LastTombstone = nullptr; 129 for (const void **APtr = SmallArray, **E = SmallArray + NumNonEmpty; 130 APtr != E; ++APtr) { 131 const void *Value = *APtr; 132 if (Value == Ptr) 133 return std::make_pair(APtr, false); 134 if (Value == getTombstoneMarker()) 135 LastTombstone = APtr; 136 } 137 138 // Did we find any tombstone marker? 139 if (LastTombstone != nullptr) { 140 *LastTombstone = Ptr; 141 --NumTombstones; 142 incrementEpoch(); 143 return std::make_pair(LastTombstone, true); 144 } 145 146 // Nope, there isn't. If we stay small, just 'pushback' now. 147 if (NumNonEmpty < CurArraySize) { 148 SmallArray[NumNonEmpty++] = Ptr; 149 incrementEpoch(); 150 return std::make_pair(SmallArray + (NumNonEmpty - 1), true); 151 } 152 // Otherwise, hit the big set case, which will call grow. 153 } 154 return insert_imp_big(Ptr); 155 } 156 157 /// erase_imp - If the set contains the specified pointer, remove it and 158 /// return true, otherwise return false. This is hidden from the client so 159 /// that the derived class can check that the right type of pointer is passed 160 /// in. 161 bool erase_imp(const void * Ptr) { 162 const void *const *P = find_imp(Ptr); 163 if (P == EndPointer()) 164 return false; 165 166 const void **Loc = const_cast<const void **>(P); 167 assert(*Loc == Ptr && "broken find!"); 168 *Loc = getTombstoneMarker(); 169 NumTombstones++; 170 return true; 171 } 172 173 /// Returns the raw pointer needed to construct an iterator. If element not 174 /// found, this will be EndPointer. Otherwise, it will be a pointer to the 175 /// slot which stores Ptr; 176 const void *const * find_imp(const void * Ptr) const { 177 if (isSmall()) { 178 // Linear search for the item. 179 for (const void *const *APtr = SmallArray, 180 *const *E = SmallArray + NumNonEmpty; APtr != E; ++APtr) 181 if (*APtr == Ptr) 182 return APtr; 183 return EndPointer(); 184 } 185 186 // Big set case. 187 auto *Bucket = FindBucketFor(Ptr); 188 if (*Bucket == Ptr) 189 return Bucket; 190 return EndPointer(); 191 } 192 193 private: 194 bool isSmall() const { return CurArray == SmallArray; } 195 196 std::pair<const void *const *, bool> insert_imp_big(const void *Ptr); 197 198 const void * const *FindBucketFor(const void *Ptr) const; 199 void shrink_and_clear(); 200 201 /// Grow - Allocate a larger backing store for the buckets and move it over. 202 void Grow(unsigned NewSize); 203 204 protected: 205 /// swap - Swaps the elements of two sets. 206 /// Note: This method assumes that both sets have the same small size. 207 void swap(SmallPtrSetImplBase &RHS); 208 209 void CopyFrom(const SmallPtrSetImplBase &RHS); 210 void MoveFrom(unsigned SmallSize, SmallPtrSetImplBase &&RHS); 211 212 private: 213 /// Code shared by MoveFrom() and move constructor. 214 void MoveHelper(unsigned SmallSize, SmallPtrSetImplBase &&RHS); 215 /// Code shared by CopyFrom() and copy constructor. 216 void CopyHelper(const SmallPtrSetImplBase &RHS); 217 }; 218 219 /// SmallPtrSetIteratorImpl - This is the common base class shared between all 220 /// instances of SmallPtrSetIterator. 221 class SmallPtrSetIteratorImpl { 222 protected: 223 const void *const *Bucket; 224 const void *const *End; 225 226 public: 227 explicit SmallPtrSetIteratorImpl(const void *const *BP, const void*const *E) 228 : Bucket(BP), End(E) { 229 if (shouldReverseIterate()) { 230 RetreatIfNotValid(); 231 return; 232 } 233 AdvanceIfNotValid(); 234 } 235 236 bool operator==(const SmallPtrSetIteratorImpl &RHS) const { 237 return Bucket == RHS.Bucket; 238 } 239 bool operator!=(const SmallPtrSetIteratorImpl &RHS) const { 240 return Bucket != RHS.Bucket; 241 } 242 243 protected: 244 /// AdvanceIfNotValid - If the current bucket isn't valid, advance to a bucket 245 /// that is. This is guaranteed to stop because the end() bucket is marked 246 /// valid. 247 void AdvanceIfNotValid() { 248 assert(Bucket <= End); 249 while (Bucket != End && 250 (*Bucket == SmallPtrSetImplBase::getEmptyMarker() || 251 *Bucket == SmallPtrSetImplBase::getTombstoneMarker())) 252 ++Bucket; 253 } 254 void RetreatIfNotValid() { 255 assert(Bucket >= End); 256 while (Bucket != End && 257 (Bucket[-1] == SmallPtrSetImplBase::getEmptyMarker() || 258 Bucket[-1] == SmallPtrSetImplBase::getTombstoneMarker())) { 259 --Bucket; 260 } 261 } 262 }; 263 264 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet. 265 template <typename PtrTy> 266 class SmallPtrSetIterator : public SmallPtrSetIteratorImpl, 267 DebugEpochBase::HandleBase { 268 using PtrTraits = PointerLikeTypeTraits<PtrTy>; 269 270 public: 271 using value_type = PtrTy; 272 using reference = PtrTy; 273 using pointer = PtrTy; 274 using difference_type = std::ptrdiff_t; 275 using iterator_category = std::forward_iterator_tag; 276 277 explicit SmallPtrSetIterator(const void *const *BP, const void *const *E, 278 const DebugEpochBase &Epoch) 279 : SmallPtrSetIteratorImpl(BP, E), DebugEpochBase::HandleBase(&Epoch) {} 280 281 // Most methods are provided by the base class. 282 283 const PtrTy operator*() const { 284 assert(isHandleInSync() && "invalid iterator access!"); 285 if (shouldReverseIterate()) { 286 assert(Bucket > End); 287 return PtrTraits::getFromVoidPointer(const_cast<void *>(Bucket[-1])); 288 } 289 assert(Bucket < End); 290 return PtrTraits::getFromVoidPointer(const_cast<void*>(*Bucket)); 291 } 292 293 inline SmallPtrSetIterator& operator++() { // Preincrement 294 assert(isHandleInSync() && "invalid iterator access!"); 295 if (shouldReverseIterate()) { 296 --Bucket; 297 RetreatIfNotValid(); 298 return *this; 299 } 300 ++Bucket; 301 AdvanceIfNotValid(); 302 return *this; 303 } 304 305 SmallPtrSetIterator operator++(int) { // Postincrement 306 SmallPtrSetIterator tmp = *this; 307 ++*this; 308 return tmp; 309 } 310 }; 311 312 /// RoundUpToPowerOfTwo - This is a helper template that rounds N up to the next 313 /// power of two (which means N itself if N is already a power of two). 314 template<unsigned N> 315 struct RoundUpToPowerOfTwo; 316 317 /// RoundUpToPowerOfTwoH - If N is not a power of two, increase it. This is a 318 /// helper template used to implement RoundUpToPowerOfTwo. 319 template<unsigned N, bool isPowerTwo> 320 struct RoundUpToPowerOfTwoH { 321 enum { Val = N }; 322 }; 323 template<unsigned N> 324 struct RoundUpToPowerOfTwoH<N, false> { 325 enum { 326 // We could just use NextVal = N+1, but this converges faster. N|(N-1) sets 327 // the right-most zero bits to one all at once, e.g. 0b0011000 -> 0b0011111. 328 Val = RoundUpToPowerOfTwo<(N|(N-1)) + 1>::Val 329 }; 330 }; 331 332 template<unsigned N> 333 struct RoundUpToPowerOfTwo { 334 enum { Val = RoundUpToPowerOfTwoH<N, (N&(N-1)) == 0>::Val }; 335 }; 336 337 /// A templated base class for \c SmallPtrSet which provides the 338 /// typesafe interface that is common across all small sizes. 339 /// 340 /// This is particularly useful for passing around between interface boundaries 341 /// to avoid encoding a particular small size in the interface boundary. 342 template <typename PtrType> 343 class SmallPtrSetImpl : public SmallPtrSetImplBase { 344 using ConstPtrType = typename add_const_past_pointer<PtrType>::type; 345 using PtrTraits = PointerLikeTypeTraits<PtrType>; 346 using ConstPtrTraits = PointerLikeTypeTraits<ConstPtrType>; 347 348 protected: 349 // Forward constructors to the base. 350 using SmallPtrSetImplBase::SmallPtrSetImplBase; 351 352 public: 353 using iterator = SmallPtrSetIterator<PtrType>; 354 using const_iterator = SmallPtrSetIterator<PtrType>; 355 using key_type = ConstPtrType; 356 using value_type = PtrType; 357 358 SmallPtrSetImpl(const SmallPtrSetImpl &) = delete; 359 360 /// Inserts Ptr if and only if there is no element in the container equal to 361 /// Ptr. The bool component of the returned pair is true if and only if the 362 /// insertion takes place, and the iterator component of the pair points to 363 /// the element equal to Ptr. 364 std::pair<iterator, bool> insert(PtrType Ptr) { 365 auto p = insert_imp(PtrTraits::getAsVoidPointer(Ptr)); 366 return std::make_pair(makeIterator(p.first), p.second); 367 } 368 369 /// erase - If the set contains the specified pointer, remove it and return 370 /// true, otherwise return false. 371 bool erase(PtrType Ptr) { 372 return erase_imp(PtrTraits::getAsVoidPointer(Ptr)); 373 } 374 /// count - Return 1 if the specified pointer is in the set, 0 otherwise. 375 size_type count(ConstPtrType Ptr) const { 376 return find_imp(ConstPtrTraits::getAsVoidPointer(Ptr)) != EndPointer(); 377 } 378 iterator find(ConstPtrType Ptr) const { 379 return makeIterator(find_imp(ConstPtrTraits::getAsVoidPointer(Ptr))); 380 } 381 382 template <typename IterT> 383 void insert(IterT I, IterT E) { 384 for (; I != E; ++I) 385 insert(*I); 386 } 387 388 void insert(std::initializer_list<PtrType> IL) { 389 insert(IL.begin(), IL.end()); 390 } 391 392 iterator begin() const { 393 if (shouldReverseIterate()) 394 return makeIterator(EndPointer() - 1); 395 return makeIterator(CurArray); 396 } 397 iterator end() const { return makeIterator(EndPointer()); } 398 399 private: 400 /// Create an iterator that dereferences to same place as the given pointer. 401 iterator makeIterator(const void *const *P) const { 402 if (shouldReverseIterate()) 403 return iterator(P == EndPointer() ? CurArray : P + 1, CurArray, *this); 404 return iterator(P, EndPointer(), *this); 405 } 406 }; 407 408 /// Equality comparison for SmallPtrSet. 409 /// 410 /// Iterates over elements of LHS confirming that each value from LHS is also in 411 /// RHS, and that no additional values are in RHS. 412 template <typename PtrType> 413 bool operator==(const SmallPtrSetImpl<PtrType> &LHS, 414 const SmallPtrSetImpl<PtrType> &RHS) { 415 if (LHS.size() != RHS.size()) 416 return false; 417 418 for (const auto *KV : LHS) 419 if (!RHS.count(KV)) 420 return false; 421 422 return true; 423 } 424 425 /// Inequality comparison for SmallPtrSet. 426 /// 427 /// Equivalent to !(LHS == RHS). 428 template <typename PtrType> 429 bool operator!=(const SmallPtrSetImpl<PtrType> &LHS, 430 const SmallPtrSetImpl<PtrType> &RHS) { 431 return !(LHS == RHS); 432 } 433 434 /// SmallPtrSet - This class implements a set which is optimized for holding 435 /// SmallSize or less elements. This internally rounds up SmallSize to the next 436 /// power of two if it is not already a power of two. See the comments above 437 /// SmallPtrSetImplBase for details of the algorithm. 438 template<class PtrType, unsigned SmallSize> 439 class SmallPtrSet : public SmallPtrSetImpl<PtrType> { 440 // In small mode SmallPtrSet uses linear search for the elements, so it is 441 // not a good idea to choose this value too high. You may consider using a 442 // DenseSet<> instead if you expect many elements in the set. 443 static_assert(SmallSize <= 32, "SmallSize should be small"); 444 445 using BaseT = SmallPtrSetImpl<PtrType>; 446 447 // Make sure that SmallSize is a power of two, round up if not. 448 enum { SmallSizePowTwo = RoundUpToPowerOfTwo<SmallSize>::Val }; 449 /// SmallStorage - Fixed size storage used in 'small mode'. 450 const void *SmallStorage[SmallSizePowTwo]; 451 452 public: 453 SmallPtrSet() : BaseT(SmallStorage, SmallSizePowTwo) {} 454 SmallPtrSet(const SmallPtrSet &that) : BaseT(SmallStorage, that) {} 455 SmallPtrSet(SmallPtrSet &&that) 456 : BaseT(SmallStorage, SmallSizePowTwo, std::move(that)) {} 457 458 template<typename It> 459 SmallPtrSet(It I, It E) : BaseT(SmallStorage, SmallSizePowTwo) { 460 this->insert(I, E); 461 } 462 463 SmallPtrSet(std::initializer_list<PtrType> IL) 464 : BaseT(SmallStorage, SmallSizePowTwo) { 465 this->insert(IL.begin(), IL.end()); 466 } 467 468 SmallPtrSet<PtrType, SmallSize> & 469 operator=(const SmallPtrSet<PtrType, SmallSize> &RHS) { 470 if (&RHS != this) 471 this->CopyFrom(RHS); 472 return *this; 473 } 474 475 SmallPtrSet<PtrType, SmallSize> & 476 operator=(SmallPtrSet<PtrType, SmallSize> &&RHS) { 477 if (&RHS != this) 478 this->MoveFrom(SmallSizePowTwo, std::move(RHS)); 479 return *this; 480 } 481 482 SmallPtrSet<PtrType, SmallSize> & 483 operator=(std::initializer_list<PtrType> IL) { 484 this->clear(); 485 this->insert(IL.begin(), IL.end()); 486 return *this; 487 } 488 489 /// swap - Swaps the elements of two sets. 490 void swap(SmallPtrSet<PtrType, SmallSize> &RHS) { 491 SmallPtrSetImplBase::swap(RHS); 492 } 493 }; 494 495 } // end namespace llvm 496 497 namespace std { 498 499 /// Implement std::swap in terms of SmallPtrSet swap. 500 template<class T, unsigned N> 501 inline void swap(llvm::SmallPtrSet<T, N> &LHS, llvm::SmallPtrSet<T, N> &RHS) { 502 LHS.swap(RHS); 503 } 504 505 } // end namespace std 506 507 #endif // LLVM_ADT_SMALLPTRSET_H 508