1 //===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- 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 implements the newly proposed standard C++ interfaces for hashing 10 // arbitrary data and building hash functions for user-defined types. This 11 // interface was originally proposed in N3333[1] and is currently under review 12 // for inclusion in a future TR and/or standard. 13 // 14 // The primary interfaces provide are comprised of one type and three functions: 15 // 16 // -- 'hash_code' class is an opaque type representing the hash code for some 17 // data. It is the intended product of hashing, and can be used to implement 18 // hash tables, checksumming, and other common uses of hashes. It is not an 19 // integer type (although it can be converted to one) because it is risky 20 // to assume much about the internals of a hash_code. In particular, each 21 // execution of the program has a high probability of producing a different 22 // hash_code for a given input. Thus their values are not stable to save or 23 // persist, and should only be used during the execution for the 24 // construction of hashing datastructures. 25 // 26 // -- 'hash_value' is a function designed to be overloaded for each 27 // user-defined type which wishes to be used within a hashing context. It 28 // should be overloaded within the user-defined type's namespace and found 29 // via ADL. Overloads for primitive types are provided by this library. 30 // 31 // -- 'hash_combine' and 'hash_combine_range' are functions designed to aid 32 // programmers in easily and intuitively combining a set of data into 33 // a single hash_code for their object. They should only logically be used 34 // within the implementation of a 'hash_value' routine or similar context. 35 // 36 // Note that 'hash_combine_range' contains very special logic for hashing 37 // a contiguous array of integers or pointers. This logic is *extremely* fast, 38 // on a modern Intel "Gainestown" Xeon (Nehalem uarch) @2.2 GHz, these were 39 // benchmarked at over 6.5 GiB/s for large keys, and <20 cycles/hash for keys 40 // under 32-bytes. 41 // 42 //===----------------------------------------------------------------------===// 43 44 #ifndef LLVM_ADT_HASHING_H 45 #define LLVM_ADT_HASHING_H 46 47 #include "llvm/Support/DataTypes.h" 48 #include "llvm/Support/ErrorHandling.h" 49 #include "llvm/Support/SwapByteOrder.h" 50 #include "llvm/Support/type_traits.h" 51 #include <algorithm> 52 #include <cassert> 53 #include <cstring> 54 #include <optional> 55 #include <string> 56 #include <tuple> 57 #include <utility> 58 59 namespace llvm { 60 template <typename T, typename Enable> struct DenseMapInfo; 61 62 /// An opaque object representing a hash code. 63 /// 64 /// This object represents the result of hashing some entity. It is intended to 65 /// be used to implement hashtables or other hashing-based data structures. 66 /// While it wraps and exposes a numeric value, this value should not be 67 /// trusted to be stable or predictable across processes or executions. 68 /// 69 /// In order to obtain the hash_code for an object 'x': 70 /// \code 71 /// using llvm::hash_value; 72 /// llvm::hash_code code = hash_value(x); 73 /// \endcode 74 class hash_code { 75 size_t value; 76 77 public: 78 /// Default construct a hash_code. 79 /// Note that this leaves the value uninitialized. 80 hash_code() = default; 81 82 /// Form a hash code directly from a numerical value. 83 hash_code(size_t value) : value(value) {} 84 85 /// Convert the hash code to its numerical value for use. 86 /*explicit*/ operator size_t() const { return value; } 87 88 friend bool operator==(const hash_code &lhs, const hash_code &rhs) { 89 return lhs.value == rhs.value; 90 } 91 friend bool operator!=(const hash_code &lhs, const hash_code &rhs) { 92 return lhs.value != rhs.value; 93 } 94 95 /// Allow a hash_code to be directly run through hash_value. 96 friend size_t hash_value(const hash_code &code) { return code.value; } 97 }; 98 99 /// Compute a hash_code for any integer value. 100 /// 101 /// Note that this function is intended to compute the same hash_code for 102 /// a particular value without regard to the pre-promotion type. This is in 103 /// contrast to hash_combine which may produce different hash_codes for 104 /// differing argument types even if they would implicit promote to a common 105 /// type without changing the value. 106 template <typename T> 107 std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value); 108 109 /// Compute a hash_code for a pointer's address. 110 /// 111 /// N.B.: This hashes the *address*. Not the value and not the type. 112 template <typename T> hash_code hash_value(const T *ptr); 113 114 /// Compute a hash_code for a pair of objects. 115 template <typename T, typename U> 116 hash_code hash_value(const std::pair<T, U> &arg); 117 118 /// Compute a hash_code for a tuple. 119 template <typename... Ts> 120 hash_code hash_value(const std::tuple<Ts...> &arg); 121 122 /// Compute a hash_code for a standard string. 123 template <typename T> 124 hash_code hash_value(const std::basic_string<T> &arg); 125 126 /// Compute a hash_code for a standard string. 127 template <typename T> hash_code hash_value(const std::optional<T> &arg); 128 129 /// Override the execution seed with a fixed value. 130 /// 131 /// This hashing library uses a per-execution seed designed to change on each 132 /// run with high probability in order to ensure that the hash codes are not 133 /// attackable and to ensure that output which is intended to be stable does 134 /// not rely on the particulars of the hash codes produced. 135 /// 136 /// That said, there are use cases where it is important to be able to 137 /// reproduce *exactly* a specific behavior. To that end, we provide a function 138 /// which will forcibly set the seed to a fixed value. This must be done at the 139 /// start of the program, before any hashes are computed. Also, it cannot be 140 /// undone. This makes it thread-hostile and very hard to use outside of 141 /// immediately on start of a simple program designed for reproducible 142 /// behavior. 143 void set_fixed_execution_hash_seed(uint64_t fixed_value); 144 145 146 // All of the implementation details of actually computing the various hash 147 // code values are held within this namespace. These routines are included in 148 // the header file mainly to allow inlining and constant propagation. 149 namespace hashing { 150 namespace detail { 151 152 inline uint64_t fetch64(const char *p) { 153 uint64_t result; 154 memcpy(&result, p, sizeof(result)); 155 if (sys::IsBigEndianHost) 156 sys::swapByteOrder(result); 157 return result; 158 } 159 160 inline uint32_t fetch32(const char *p) { 161 uint32_t result; 162 memcpy(&result, p, sizeof(result)); 163 if (sys::IsBigEndianHost) 164 sys::swapByteOrder(result); 165 return result; 166 } 167 168 /// Some primes between 2^63 and 2^64 for various uses. 169 static constexpr uint64_t k0 = 0xc3a5c85c97cb3127ULL; 170 static constexpr uint64_t k1 = 0xb492b66fbe98f273ULL; 171 static constexpr uint64_t k2 = 0x9ae16a3b2f90404fULL; 172 static constexpr uint64_t k3 = 0xc949d7c7509e6557ULL; 173 174 /// Bitwise right rotate. 175 /// Normally this will compile to a single instruction, especially if the 176 /// shift is a manifest constant. 177 inline uint64_t rotate(uint64_t val, size_t shift) { 178 // Avoid shifting by 64: doing so yields an undefined result. 179 return shift == 0 ? val : ((val >> shift) | (val << (64 - shift))); 180 } 181 182 inline uint64_t shift_mix(uint64_t val) { 183 return val ^ (val >> 47); 184 } 185 186 inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) { 187 // Murmur-inspired hashing. 188 const uint64_t kMul = 0x9ddfea08eb382d69ULL; 189 uint64_t a = (low ^ high) * kMul; 190 a ^= (a >> 47); 191 uint64_t b = (high ^ a) * kMul; 192 b ^= (b >> 47); 193 b *= kMul; 194 return b; 195 } 196 197 inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) { 198 uint8_t a = s[0]; 199 uint8_t b = s[len >> 1]; 200 uint8_t c = s[len - 1]; 201 uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8); 202 uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2); 203 return shift_mix(y * k2 ^ z * k3 ^ seed) * k2; 204 } 205 206 inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) { 207 uint64_t a = fetch32(s); 208 return hash_16_bytes(len + (a << 3), seed ^ fetch32(s + len - 4)); 209 } 210 211 inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) { 212 uint64_t a = fetch64(s); 213 uint64_t b = fetch64(s + len - 8); 214 return hash_16_bytes(seed ^ a, rotate(b + len, len)) ^ b; 215 } 216 217 inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) { 218 uint64_t a = fetch64(s) * k1; 219 uint64_t b = fetch64(s + 8); 220 uint64_t c = fetch64(s + len - 8) * k2; 221 uint64_t d = fetch64(s + len - 16) * k0; 222 return hash_16_bytes(rotate(a - b, 43) + rotate(c ^ seed, 30) + d, 223 a + rotate(b ^ k3, 20) - c + len + seed); 224 } 225 226 inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) { 227 uint64_t z = fetch64(s + 24); 228 uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0; 229 uint64_t b = rotate(a + z, 52); 230 uint64_t c = rotate(a, 37); 231 a += fetch64(s + 8); 232 c += rotate(a, 7); 233 a += fetch64(s + 16); 234 uint64_t vf = a + z; 235 uint64_t vs = b + rotate(a, 31) + c; 236 a = fetch64(s + 16) + fetch64(s + len - 32); 237 z = fetch64(s + len - 8); 238 b = rotate(a + z, 52); 239 c = rotate(a, 37); 240 a += fetch64(s + len - 24); 241 c += rotate(a, 7); 242 a += fetch64(s + len - 16); 243 uint64_t wf = a + z; 244 uint64_t ws = b + rotate(a, 31) + c; 245 uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0); 246 return shift_mix((seed ^ (r * k0)) + vs) * k2; 247 } 248 249 inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) { 250 if (length >= 4 && length <= 8) 251 return hash_4to8_bytes(s, length, seed); 252 if (length > 8 && length <= 16) 253 return hash_9to16_bytes(s, length, seed); 254 if (length > 16 && length <= 32) 255 return hash_17to32_bytes(s, length, seed); 256 if (length > 32) 257 return hash_33to64_bytes(s, length, seed); 258 if (length != 0) 259 return hash_1to3_bytes(s, length, seed); 260 261 return k2 ^ seed; 262 } 263 264 /// The intermediate state used during hashing. 265 /// Currently, the algorithm for computing hash codes is based on CityHash and 266 /// keeps 56 bytes of arbitrary state. 267 struct hash_state { 268 uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0; 269 270 /// Create a new hash_state structure and initialize it based on the 271 /// seed and the first 64-byte chunk. 272 /// This effectively performs the initial mix. 273 static hash_state create(const char *s, uint64_t seed) { 274 hash_state state = { 275 0, seed, hash_16_bytes(seed, k1), rotate(seed ^ k1, 49), 276 seed * k1, shift_mix(seed), 0 }; 277 state.h6 = hash_16_bytes(state.h4, state.h5); 278 state.mix(s); 279 return state; 280 } 281 282 /// Mix 32-bytes from the input sequence into the 16-bytes of 'a' 283 /// and 'b', including whatever is already in 'a' and 'b'. 284 static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) { 285 a += fetch64(s); 286 uint64_t c = fetch64(s + 24); 287 b = rotate(b + a + c, 21); 288 uint64_t d = a; 289 a += fetch64(s + 8) + fetch64(s + 16); 290 b += rotate(a, 44) + d; 291 a += c; 292 } 293 294 /// Mix in a 64-byte buffer of data. 295 /// We mix all 64 bytes even when the chunk length is smaller, but we 296 /// record the actual length. 297 void mix(const char *s) { 298 h0 = rotate(h0 + h1 + h3 + fetch64(s + 8), 37) * k1; 299 h1 = rotate(h1 + h4 + fetch64(s + 48), 42) * k1; 300 h0 ^= h6; 301 h1 += h3 + fetch64(s + 40); 302 h2 = rotate(h2 + h5, 33) * k1; 303 h3 = h4 * k1; 304 h4 = h0 + h5; 305 mix_32_bytes(s, h3, h4); 306 h5 = h2 + h6; 307 h6 = h1 + fetch64(s + 16); 308 mix_32_bytes(s + 32, h5, h6); 309 std::swap(h2, h0); 310 } 311 312 /// Compute the final 64-bit hash code value based on the current 313 /// state and the length of bytes hashed. 314 uint64_t finalize(size_t length) { 315 return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2, 316 hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0); 317 } 318 }; 319 320 321 /// A global, fixed seed-override variable. 322 /// 323 /// This variable can be set using the \see llvm::set_fixed_execution_seed 324 /// function. See that function for details. Do not, under any circumstances, 325 /// set or read this variable. 326 extern uint64_t fixed_seed_override; 327 328 inline uint64_t get_execution_seed() { 329 // FIXME: This needs to be a per-execution seed. This is just a placeholder 330 // implementation. Switching to a per-execution seed is likely to flush out 331 // instability bugs and so will happen as its own commit. 332 // 333 // However, if there is a fixed seed override set the first time this is 334 // called, return that instead of the per-execution seed. 335 const uint64_t seed_prime = 0xff51afd7ed558ccdULL; 336 static uint64_t seed = fixed_seed_override ? fixed_seed_override : seed_prime; 337 return seed; 338 } 339 340 341 /// Trait to indicate whether a type's bits can be hashed directly. 342 /// 343 /// A type trait which is true if we want to combine values for hashing by 344 /// reading the underlying data. It is false if values of this type must 345 /// first be passed to hash_value, and the resulting hash_codes combined. 346 // 347 // FIXME: We want to replace is_integral_or_enum and is_pointer here with 348 // a predicate which asserts that comparing the underlying storage of two 349 // values of the type for equality is equivalent to comparing the two values 350 // for equality. For all the platforms we care about, this holds for integers 351 // and pointers, but there are platforms where it doesn't and we would like to 352 // support user-defined types which happen to satisfy this property. 353 template <typename T> struct is_hashable_data 354 : std::integral_constant<bool, ((is_integral_or_enum<T>::value || 355 std::is_pointer<T>::value) && 356 64 % sizeof(T) == 0)> {}; 357 358 // Special case std::pair to detect when both types are viable and when there 359 // is no alignment-derived padding in the pair. This is a bit of a lie because 360 // std::pair isn't truly POD, but it's close enough in all reasonable 361 // implementations for our use case of hashing the underlying data. 362 template <typename T, typename U> struct is_hashable_data<std::pair<T, U> > 363 : std::integral_constant<bool, (is_hashable_data<T>::value && 364 is_hashable_data<U>::value && 365 (sizeof(T) + sizeof(U)) == 366 sizeof(std::pair<T, U>))> {}; 367 368 /// Helper to get the hashable data representation for a type. 369 /// This variant is enabled when the type itself can be used. 370 template <typename T> 371 std::enable_if_t<is_hashable_data<T>::value, T> 372 get_hashable_data(const T &value) { 373 return value; 374 } 375 /// Helper to get the hashable data representation for a type. 376 /// This variant is enabled when we must first call hash_value and use the 377 /// result as our data. 378 template <typename T> 379 std::enable_if_t<!is_hashable_data<T>::value, size_t> 380 get_hashable_data(const T &value) { 381 using ::llvm::hash_value; 382 return hash_value(value); 383 } 384 385 /// Helper to store data from a value into a buffer and advance the 386 /// pointer into that buffer. 387 /// 388 /// This routine first checks whether there is enough space in the provided 389 /// buffer, and if not immediately returns false. If there is space, it 390 /// copies the underlying bytes of value into the buffer, advances the 391 /// buffer_ptr past the copied bytes, and returns true. 392 template <typename T> 393 bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value, 394 size_t offset = 0) { 395 size_t store_size = sizeof(value) - offset; 396 if (buffer_ptr + store_size > buffer_end) 397 return false; 398 const char *value_data = reinterpret_cast<const char *>(&value); 399 memcpy(buffer_ptr, value_data + offset, store_size); 400 buffer_ptr += store_size; 401 return true; 402 } 403 404 /// Implement the combining of integral values into a hash_code. 405 /// 406 /// This overload is selected when the value type of the iterator is 407 /// integral. Rather than computing a hash_code for each object and then 408 /// combining them, this (as an optimization) directly combines the integers. 409 template <typename InputIteratorT> 410 hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) { 411 const uint64_t seed = get_execution_seed(); 412 char buffer[64], *buffer_ptr = buffer; 413 char *const buffer_end = std::end(buffer); 414 while (first != last && store_and_advance(buffer_ptr, buffer_end, 415 get_hashable_data(*first))) 416 ++first; 417 if (first == last) 418 return hash_short(buffer, buffer_ptr - buffer, seed); 419 assert(buffer_ptr == buffer_end); 420 421 hash_state state = state.create(buffer, seed); 422 size_t length = 64; 423 while (first != last) { 424 // Fill up the buffer. We don't clear it, which re-mixes the last round 425 // when only a partial 64-byte chunk is left. 426 buffer_ptr = buffer; 427 while (first != last && store_and_advance(buffer_ptr, buffer_end, 428 get_hashable_data(*first))) 429 ++first; 430 431 // Rotate the buffer if we did a partial fill in order to simulate doing 432 // a mix of the last 64-bytes. That is how the algorithm works when we 433 // have a contiguous byte sequence, and we want to emulate that here. 434 std::rotate(buffer, buffer_ptr, buffer_end); 435 436 // Mix this chunk into the current state. 437 state.mix(buffer); 438 length += buffer_ptr - buffer; 439 }; 440 441 return state.finalize(length); 442 } 443 444 /// Implement the combining of integral values into a hash_code. 445 /// 446 /// This overload is selected when the value type of the iterator is integral 447 /// and when the input iterator is actually a pointer. Rather than computing 448 /// a hash_code for each object and then combining them, this (as an 449 /// optimization) directly combines the integers. Also, because the integers 450 /// are stored in contiguous memory, this routine avoids copying each value 451 /// and directly reads from the underlying memory. 452 template <typename ValueT> 453 std::enable_if_t<is_hashable_data<ValueT>::value, hash_code> 454 hash_combine_range_impl(ValueT *first, ValueT *last) { 455 const uint64_t seed = get_execution_seed(); 456 const char *s_begin = reinterpret_cast<const char *>(first); 457 const char *s_end = reinterpret_cast<const char *>(last); 458 const size_t length = std::distance(s_begin, s_end); 459 if (length <= 64) 460 return hash_short(s_begin, length, seed); 461 462 const char *s_aligned_end = s_begin + (length & ~63); 463 hash_state state = state.create(s_begin, seed); 464 s_begin += 64; 465 while (s_begin != s_aligned_end) { 466 state.mix(s_begin); 467 s_begin += 64; 468 } 469 if (length & 63) 470 state.mix(s_end - 64); 471 472 return state.finalize(length); 473 } 474 475 } // namespace detail 476 } // namespace hashing 477 478 479 /// Compute a hash_code for a sequence of values. 480 /// 481 /// This hashes a sequence of values. It produces the same hash_code as 482 /// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences 483 /// and is significantly faster given pointers and types which can be hashed as 484 /// a sequence of bytes. 485 template <typename InputIteratorT> 486 hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) { 487 return ::llvm::hashing::detail::hash_combine_range_impl(first, last); 488 } 489 490 491 // Implementation details for hash_combine. 492 namespace hashing { 493 namespace detail { 494 495 /// Helper class to manage the recursive combining of hash_combine 496 /// arguments. 497 /// 498 /// This class exists to manage the state and various calls involved in the 499 /// recursive combining of arguments used in hash_combine. It is particularly 500 /// useful at minimizing the code in the recursive calls to ease the pain 501 /// caused by a lack of variadic functions. 502 struct hash_combine_recursive_helper { 503 char buffer[64] = {}; 504 hash_state state; 505 const uint64_t seed; 506 507 public: 508 /// Construct a recursive hash combining helper. 509 /// 510 /// This sets up the state for a recursive hash combine, including getting 511 /// the seed and buffer setup. 512 hash_combine_recursive_helper() 513 : seed(get_execution_seed()) {} 514 515 /// Combine one chunk of data into the current in-flight hash. 516 /// 517 /// This merges one chunk of data into the hash. First it tries to buffer 518 /// the data. If the buffer is full, it hashes the buffer into its 519 /// hash_state, empties it, and then merges the new chunk in. This also 520 /// handles cases where the data straddles the end of the buffer. 521 template <typename T> 522 char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) { 523 if (!store_and_advance(buffer_ptr, buffer_end, data)) { 524 // Check for skew which prevents the buffer from being packed, and do 525 // a partial store into the buffer to fill it. This is only a concern 526 // with the variadic combine because that formation can have varying 527 // argument types. 528 size_t partial_store_size = buffer_end - buffer_ptr; 529 memcpy(buffer_ptr, &data, partial_store_size); 530 531 // If the store fails, our buffer is full and ready to hash. We have to 532 // either initialize the hash state (on the first full buffer) or mix 533 // this buffer into the existing hash state. Length tracks the *hashed* 534 // length, not the buffered length. 535 if (length == 0) { 536 state = state.create(buffer, seed); 537 length = 64; 538 } else { 539 // Mix this chunk into the current state and bump length up by 64. 540 state.mix(buffer); 541 length += 64; 542 } 543 // Reset the buffer_ptr to the head of the buffer for the next chunk of 544 // data. 545 buffer_ptr = buffer; 546 547 // Try again to store into the buffer -- this cannot fail as we only 548 // store types smaller than the buffer. 549 if (!store_and_advance(buffer_ptr, buffer_end, data, 550 partial_store_size)) 551 llvm_unreachable("buffer smaller than stored type"); 552 } 553 return buffer_ptr; 554 } 555 556 /// Recursive, variadic combining method. 557 /// 558 /// This function recurses through each argument, combining that argument 559 /// into a single hash. 560 template <typename T, typename ...Ts> 561 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end, 562 const T &arg, const Ts &...args) { 563 buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg)); 564 565 // Recurse to the next argument. 566 return combine(length, buffer_ptr, buffer_end, args...); 567 } 568 569 /// Base case for recursive, variadic combining. 570 /// 571 /// The base case when combining arguments recursively is reached when all 572 /// arguments have been handled. It flushes the remaining buffer and 573 /// constructs a hash_code. 574 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) { 575 // Check whether the entire set of values fit in the buffer. If so, we'll 576 // use the optimized short hashing routine and skip state entirely. 577 if (length == 0) 578 return hash_short(buffer, buffer_ptr - buffer, seed); 579 580 // Mix the final buffer, rotating it if we did a partial fill in order to 581 // simulate doing a mix of the last 64-bytes. That is how the algorithm 582 // works when we have a contiguous byte sequence, and we want to emulate 583 // that here. 584 std::rotate(buffer, buffer_ptr, buffer_end); 585 586 // Mix this chunk into the current state. 587 state.mix(buffer); 588 length += buffer_ptr - buffer; 589 590 return state.finalize(length); 591 } 592 }; 593 594 } // namespace detail 595 } // namespace hashing 596 597 /// Combine values into a single hash_code. 598 /// 599 /// This routine accepts a varying number of arguments of any type. It will 600 /// attempt to combine them into a single hash_code. For user-defined types it 601 /// attempts to call a \see hash_value overload (via ADL) for the type. For 602 /// integer and pointer types it directly combines their data into the 603 /// resulting hash_code. 604 /// 605 /// The result is suitable for returning from a user's hash_value 606 /// *implementation* for their user-defined type. Consumers of a type should 607 /// *not* call this routine, they should instead call 'hash_value'. 608 template <typename ...Ts> hash_code hash_combine(const Ts &...args) { 609 // Recursively hash each argument using a helper class. 610 ::llvm::hashing::detail::hash_combine_recursive_helper helper; 611 return helper.combine(0, helper.buffer, helper.buffer + 64, args...); 612 } 613 614 // Implementation details for implementations of hash_value overloads provided 615 // here. 616 namespace hashing { 617 namespace detail { 618 619 /// Helper to hash the value of a single integer. 620 /// 621 /// Overloads for smaller integer types are not provided to ensure consistent 622 /// behavior in the presence of integral promotions. Essentially, 623 /// "hash_value('4')" and "hash_value('0' + 4)" should be the same. 624 inline hash_code hash_integer_value(uint64_t value) { 625 // Similar to hash_4to8_bytes but using a seed instead of length. 626 const uint64_t seed = get_execution_seed(); 627 const char *s = reinterpret_cast<const char *>(&value); 628 const uint64_t a = fetch32(s); 629 return hash_16_bytes(seed + (a << 3), fetch32(s + 4)); 630 } 631 632 } // namespace detail 633 } // namespace hashing 634 635 // Declared and documented above, but defined here so that any of the hashing 636 // infrastructure is available. 637 template <typename T> 638 std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value) { 639 return ::llvm::hashing::detail::hash_integer_value( 640 static_cast<uint64_t>(value)); 641 } 642 643 // Declared and documented above, but defined here so that any of the hashing 644 // infrastructure is available. 645 template <typename T> hash_code hash_value(const T *ptr) { 646 return ::llvm::hashing::detail::hash_integer_value( 647 reinterpret_cast<uintptr_t>(ptr)); 648 } 649 650 // Declared and documented above, but defined here so that any of the hashing 651 // infrastructure is available. 652 template <typename T, typename U> 653 hash_code hash_value(const std::pair<T, U> &arg) { 654 return hash_combine(arg.first, arg.second); 655 } 656 657 template <typename... Ts> hash_code hash_value(const std::tuple<Ts...> &arg) { 658 return std::apply([](const auto &...xs) { return hash_combine(xs...); }, arg); 659 } 660 661 // Declared and documented above, but defined here so that any of the hashing 662 // infrastructure is available. 663 template <typename T> 664 hash_code hash_value(const std::basic_string<T> &arg) { 665 return hash_combine_range(arg.begin(), arg.end()); 666 } 667 668 template <typename T> hash_code hash_value(const std::optional<T> &arg) { 669 return arg ? hash_combine(true, *arg) : hash_value(false); 670 } 671 672 template <> struct DenseMapInfo<hash_code, void> { 673 static inline hash_code getEmptyKey() { return hash_code(-1); } 674 static inline hash_code getTombstoneKey() { return hash_code(-2); } 675 static unsigned getHashValue(hash_code val) { return val; } 676 static bool isEqual(hash_code LHS, hash_code RHS) { return LHS == RHS; } 677 }; 678 679 } // namespace llvm 680 681 #endif 682