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(llvm::rotr<uint64_t>(a - b, 43) + 223 llvm::rotr<uint64_t>(c ^ seed, 30) + d, 224 a + llvm::rotr<uint64_t>(b ^ k3, 20) - c + len + seed); 225 } 226 227 inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) { 228 uint64_t z = fetch64(s + 24); 229 uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0; 230 uint64_t b = llvm::rotr<uint64_t>(a + z, 52); 231 uint64_t c = llvm::rotr<uint64_t>(a, 37); 232 a += fetch64(s + 8); 233 c += llvm::rotr<uint64_t>(a, 7); 234 a += fetch64(s + 16); 235 uint64_t vf = a + z; 236 uint64_t vs = b + llvm::rotr<uint64_t>(a, 31) + c; 237 a = fetch64(s + 16) + fetch64(s + len - 32); 238 z = fetch64(s + len - 8); 239 b = llvm::rotr<uint64_t>(a + z, 52); 240 c = llvm::rotr<uint64_t>(a, 37); 241 a += fetch64(s + len - 24); 242 c += llvm::rotr<uint64_t>(a, 7); 243 a += fetch64(s + len - 16); 244 uint64_t wf = a + z; 245 uint64_t ws = b + llvm::rotr<uint64_t>(a, 31) + c; 246 uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0); 247 return shift_mix((seed ^ (r * k0)) + vs) * k2; 248 } 249 250 inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) { 251 if (length >= 4 && length <= 8) 252 return hash_4to8_bytes(s, length, seed); 253 if (length > 8 && length <= 16) 254 return hash_9to16_bytes(s, length, seed); 255 if (length > 16 && length <= 32) 256 return hash_17to32_bytes(s, length, seed); 257 if (length > 32) 258 return hash_33to64_bytes(s, length, seed); 259 if (length != 0) 260 return hash_1to3_bytes(s, length, seed); 261 262 return k2 ^ seed; 263 } 264 265 /// The intermediate state used during hashing. 266 /// Currently, the algorithm for computing hash codes is based on CityHash and 267 /// keeps 56 bytes of arbitrary state. 268 struct hash_state { 269 uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0; 270 271 /// Create a new hash_state structure and initialize it based on the 272 /// seed and the first 64-byte chunk. 273 /// This effectively performs the initial mix. 274 static hash_state create(const char *s, uint64_t seed) { 275 hash_state state = {0, 276 seed, 277 hash_16_bytes(seed, k1), 278 llvm::rotr<uint64_t>(seed ^ k1, 49), 279 seed * k1, 280 shift_mix(seed), 281 0}; 282 state.h6 = hash_16_bytes(state.h4, state.h5); 283 state.mix(s); 284 return state; 285 } 286 287 /// Mix 32-bytes from the input sequence into the 16-bytes of 'a' 288 /// and 'b', including whatever is already in 'a' and 'b'. 289 static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) { 290 a += fetch64(s); 291 uint64_t c = fetch64(s + 24); 292 b = llvm::rotr<uint64_t>(b + a + c, 21); 293 uint64_t d = a; 294 a += fetch64(s + 8) + fetch64(s + 16); 295 b += llvm::rotr<uint64_t>(a, 44) + d; 296 a += c; 297 } 298 299 /// Mix in a 64-byte buffer of data. 300 /// We mix all 64 bytes even when the chunk length is smaller, but we 301 /// record the actual length. 302 void mix(const char *s) { 303 h0 = llvm::rotr<uint64_t>(h0 + h1 + h3 + fetch64(s + 8), 37) * k1; 304 h1 = llvm::rotr<uint64_t>(h1 + h4 + fetch64(s + 48), 42) * k1; 305 h0 ^= h6; 306 h1 += h3 + fetch64(s + 40); 307 h2 = llvm::rotr<uint64_t>(h2 + h5, 33) * k1; 308 h3 = h4 * k1; 309 h4 = h0 + h5; 310 mix_32_bytes(s, h3, h4); 311 h5 = h2 + h6; 312 h6 = h1 + fetch64(s + 16); 313 mix_32_bytes(s + 32, h5, h6); 314 std::swap(h2, h0); 315 } 316 317 /// Compute the final 64-bit hash code value based on the current 318 /// state and the length of bytes hashed. 319 uint64_t finalize(size_t length) { 320 return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2, 321 hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0); 322 } 323 }; 324 325 326 /// A global, fixed seed-override variable. 327 /// 328 /// This variable can be set using the \see llvm::set_fixed_execution_seed 329 /// function. See that function for details. Do not, under any circumstances, 330 /// set or read this variable. 331 extern uint64_t fixed_seed_override; 332 333 inline uint64_t get_execution_seed() { 334 // FIXME: This needs to be a per-execution seed. This is just a placeholder 335 // implementation. Switching to a per-execution seed is likely to flush out 336 // instability bugs and so will happen as its own commit. 337 // 338 // However, if there is a fixed seed override set the first time this is 339 // called, return that instead of the per-execution seed. 340 const uint64_t seed_prime = 0xff51afd7ed558ccdULL; 341 static uint64_t seed = fixed_seed_override ? fixed_seed_override : seed_prime; 342 return seed; 343 } 344 345 346 /// Trait to indicate whether a type's bits can be hashed directly. 347 /// 348 /// A type trait which is true if we want to combine values for hashing by 349 /// reading the underlying data. It is false if values of this type must 350 /// first be passed to hash_value, and the resulting hash_codes combined. 351 // 352 // FIXME: We want to replace is_integral_or_enum and is_pointer here with 353 // a predicate which asserts that comparing the underlying storage of two 354 // values of the type for equality is equivalent to comparing the two values 355 // for equality. For all the platforms we care about, this holds for integers 356 // and pointers, but there are platforms where it doesn't and we would like to 357 // support user-defined types which happen to satisfy this property. 358 template <typename T> struct is_hashable_data 359 : std::integral_constant<bool, ((is_integral_or_enum<T>::value || 360 std::is_pointer<T>::value) && 361 64 % sizeof(T) == 0)> {}; 362 363 // Special case std::pair to detect when both types are viable and when there 364 // is no alignment-derived padding in the pair. This is a bit of a lie because 365 // std::pair isn't truly POD, but it's close enough in all reasonable 366 // implementations for our use case of hashing the underlying data. 367 template <typename T, typename U> struct is_hashable_data<std::pair<T, U> > 368 : std::integral_constant<bool, (is_hashable_data<T>::value && 369 is_hashable_data<U>::value && 370 (sizeof(T) + sizeof(U)) == 371 sizeof(std::pair<T, U>))> {}; 372 373 /// Helper to get the hashable data representation for a type. 374 /// This variant is enabled when the type itself can be used. 375 template <typename T> 376 std::enable_if_t<is_hashable_data<T>::value, T> 377 get_hashable_data(const T &value) { 378 return value; 379 } 380 /// Helper to get the hashable data representation for a type. 381 /// This variant is enabled when we must first call hash_value and use the 382 /// result as our data. 383 template <typename T> 384 std::enable_if_t<!is_hashable_data<T>::value, size_t> 385 get_hashable_data(const T &value) { 386 using ::llvm::hash_value; 387 return hash_value(value); 388 } 389 390 /// Helper to store data from a value into a buffer and advance the 391 /// pointer into that buffer. 392 /// 393 /// This routine first checks whether there is enough space in the provided 394 /// buffer, and if not immediately returns false. If there is space, it 395 /// copies the underlying bytes of value into the buffer, advances the 396 /// buffer_ptr past the copied bytes, and returns true. 397 template <typename T> 398 bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value, 399 size_t offset = 0) { 400 size_t store_size = sizeof(value) - offset; 401 if (buffer_ptr + store_size > buffer_end) 402 return false; 403 const char *value_data = reinterpret_cast<const char *>(&value); 404 memcpy(buffer_ptr, value_data + offset, store_size); 405 buffer_ptr += store_size; 406 return true; 407 } 408 409 /// Implement the combining of integral values into a hash_code. 410 /// 411 /// This overload is selected when the value type of the iterator is 412 /// integral. Rather than computing a hash_code for each object and then 413 /// combining them, this (as an optimization) directly combines the integers. 414 template <typename InputIteratorT> 415 hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) { 416 const uint64_t seed = get_execution_seed(); 417 char buffer[64], *buffer_ptr = buffer; 418 char *const buffer_end = std::end(buffer); 419 while (first != last && store_and_advance(buffer_ptr, buffer_end, 420 get_hashable_data(*first))) 421 ++first; 422 if (first == last) 423 return hash_short(buffer, buffer_ptr - buffer, seed); 424 assert(buffer_ptr == buffer_end); 425 426 hash_state state = state.create(buffer, seed); 427 size_t length = 64; 428 while (first != last) { 429 // Fill up the buffer. We don't clear it, which re-mixes the last round 430 // when only a partial 64-byte chunk is left. 431 buffer_ptr = buffer; 432 while (first != last && store_and_advance(buffer_ptr, buffer_end, 433 get_hashable_data(*first))) 434 ++first; 435 436 // Rotate the buffer if we did a partial fill in order to simulate doing 437 // a mix of the last 64-bytes. That is how the algorithm works when we 438 // have a contiguous byte sequence, and we want to emulate that here. 439 std::rotate(buffer, buffer_ptr, buffer_end); 440 441 // Mix this chunk into the current state. 442 state.mix(buffer); 443 length += buffer_ptr - buffer; 444 }; 445 446 return state.finalize(length); 447 } 448 449 /// Implement the combining of integral values into a hash_code. 450 /// 451 /// This overload is selected when the value type of the iterator is integral 452 /// and when the input iterator is actually a pointer. Rather than computing 453 /// a hash_code for each object and then combining them, this (as an 454 /// optimization) directly combines the integers. Also, because the integers 455 /// are stored in contiguous memory, this routine avoids copying each value 456 /// and directly reads from the underlying memory. 457 template <typename ValueT> 458 std::enable_if_t<is_hashable_data<ValueT>::value, hash_code> 459 hash_combine_range_impl(ValueT *first, ValueT *last) { 460 const uint64_t seed = get_execution_seed(); 461 const char *s_begin = reinterpret_cast<const char *>(first); 462 const char *s_end = reinterpret_cast<const char *>(last); 463 const size_t length = std::distance(s_begin, s_end); 464 if (length <= 64) 465 return hash_short(s_begin, length, seed); 466 467 const char *s_aligned_end = s_begin + (length & ~63); 468 hash_state state = state.create(s_begin, seed); 469 s_begin += 64; 470 while (s_begin != s_aligned_end) { 471 state.mix(s_begin); 472 s_begin += 64; 473 } 474 if (length & 63) 475 state.mix(s_end - 64); 476 477 return state.finalize(length); 478 } 479 480 } // namespace detail 481 } // namespace hashing 482 483 484 /// Compute a hash_code for a sequence of values. 485 /// 486 /// This hashes a sequence of values. It produces the same hash_code as 487 /// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences 488 /// and is significantly faster given pointers and types which can be hashed as 489 /// a sequence of bytes. 490 template <typename InputIteratorT> 491 hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) { 492 return ::llvm::hashing::detail::hash_combine_range_impl(first, last); 493 } 494 495 496 // Implementation details for hash_combine. 497 namespace hashing { 498 namespace detail { 499 500 /// Helper class to manage the recursive combining of hash_combine 501 /// arguments. 502 /// 503 /// This class exists to manage the state and various calls involved in the 504 /// recursive combining of arguments used in hash_combine. It is particularly 505 /// useful at minimizing the code in the recursive calls to ease the pain 506 /// caused by a lack of variadic functions. 507 struct hash_combine_recursive_helper { 508 char buffer[64] = {}; 509 hash_state state; 510 const uint64_t seed; 511 512 public: 513 /// Construct a recursive hash combining helper. 514 /// 515 /// This sets up the state for a recursive hash combine, including getting 516 /// the seed and buffer setup. 517 hash_combine_recursive_helper() 518 : seed(get_execution_seed()) {} 519 520 /// Combine one chunk of data into the current in-flight hash. 521 /// 522 /// This merges one chunk of data into the hash. First it tries to buffer 523 /// the data. If the buffer is full, it hashes the buffer into its 524 /// hash_state, empties it, and then merges the new chunk in. This also 525 /// handles cases where the data straddles the end of the buffer. 526 template <typename T> 527 char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) { 528 if (!store_and_advance(buffer_ptr, buffer_end, data)) { 529 // Check for skew which prevents the buffer from being packed, and do 530 // a partial store into the buffer to fill it. This is only a concern 531 // with the variadic combine because that formation can have varying 532 // argument types. 533 size_t partial_store_size = buffer_end - buffer_ptr; 534 memcpy(buffer_ptr, &data, partial_store_size); 535 536 // If the store fails, our buffer is full and ready to hash. We have to 537 // either initialize the hash state (on the first full buffer) or mix 538 // this buffer into the existing hash state. Length tracks the *hashed* 539 // length, not the buffered length. 540 if (length == 0) { 541 state = state.create(buffer, seed); 542 length = 64; 543 } else { 544 // Mix this chunk into the current state and bump length up by 64. 545 state.mix(buffer); 546 length += 64; 547 } 548 // Reset the buffer_ptr to the head of the buffer for the next chunk of 549 // data. 550 buffer_ptr = buffer; 551 552 // Try again to store into the buffer -- this cannot fail as we only 553 // store types smaller than the buffer. 554 if (!store_and_advance(buffer_ptr, buffer_end, data, 555 partial_store_size)) 556 llvm_unreachable("buffer smaller than stored type"); 557 } 558 return buffer_ptr; 559 } 560 561 /// Recursive, variadic combining method. 562 /// 563 /// This function recurses through each argument, combining that argument 564 /// into a single hash. 565 template <typename T, typename ...Ts> 566 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end, 567 const T &arg, const Ts &...args) { 568 buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg)); 569 570 // Recurse to the next argument. 571 return combine(length, buffer_ptr, buffer_end, args...); 572 } 573 574 /// Base case for recursive, variadic combining. 575 /// 576 /// The base case when combining arguments recursively is reached when all 577 /// arguments have been handled. It flushes the remaining buffer and 578 /// constructs a hash_code. 579 hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) { 580 // Check whether the entire set of values fit in the buffer. If so, we'll 581 // use the optimized short hashing routine and skip state entirely. 582 if (length == 0) 583 return hash_short(buffer, buffer_ptr - buffer, seed); 584 585 // Mix the final buffer, rotating it if we did a partial fill in order to 586 // simulate doing a mix of the last 64-bytes. That is how the algorithm 587 // works when we have a contiguous byte sequence, and we want to emulate 588 // that here. 589 std::rotate(buffer, buffer_ptr, buffer_end); 590 591 // Mix this chunk into the current state. 592 state.mix(buffer); 593 length += buffer_ptr - buffer; 594 595 return state.finalize(length); 596 } 597 }; 598 599 } // namespace detail 600 } // namespace hashing 601 602 /// Combine values into a single hash_code. 603 /// 604 /// This routine accepts a varying number of arguments of any type. It will 605 /// attempt to combine them into a single hash_code. For user-defined types it 606 /// attempts to call a \see hash_value overload (via ADL) for the type. For 607 /// integer and pointer types it directly combines their data into the 608 /// resulting hash_code. 609 /// 610 /// The result is suitable for returning from a user's hash_value 611 /// *implementation* for their user-defined type. Consumers of a type should 612 /// *not* call this routine, they should instead call 'hash_value'. 613 template <typename ...Ts> hash_code hash_combine(const Ts &...args) { 614 // Recursively hash each argument using a helper class. 615 ::llvm::hashing::detail::hash_combine_recursive_helper helper; 616 return helper.combine(0, helper.buffer, helper.buffer + 64, args...); 617 } 618 619 // Implementation details for implementations of hash_value overloads provided 620 // here. 621 namespace hashing { 622 namespace detail { 623 624 /// Helper to hash the value of a single integer. 625 /// 626 /// Overloads for smaller integer types are not provided to ensure consistent 627 /// behavior in the presence of integral promotions. Essentially, 628 /// "hash_value('4')" and "hash_value('0' + 4)" should be the same. 629 inline hash_code hash_integer_value(uint64_t value) { 630 // Similar to hash_4to8_bytes but using a seed instead of length. 631 const uint64_t seed = get_execution_seed(); 632 const char *s = reinterpret_cast<const char *>(&value); 633 const uint64_t a = fetch32(s); 634 return hash_16_bytes(seed + (a << 3), fetch32(s + 4)); 635 } 636 637 } // namespace detail 638 } // namespace hashing 639 640 // Declared and documented above, but defined here so that any of the hashing 641 // infrastructure is available. 642 template <typename T> 643 std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value) { 644 return ::llvm::hashing::detail::hash_integer_value( 645 static_cast<uint64_t>(value)); 646 } 647 648 // Declared and documented above, but defined here so that any of the hashing 649 // infrastructure is available. 650 template <typename T> hash_code hash_value(const T *ptr) { 651 return ::llvm::hashing::detail::hash_integer_value( 652 reinterpret_cast<uintptr_t>(ptr)); 653 } 654 655 // Declared and documented above, but defined here so that any of the hashing 656 // infrastructure is available. 657 template <typename T, typename U> 658 hash_code hash_value(const std::pair<T, U> &arg) { 659 return hash_combine(arg.first, arg.second); 660 } 661 662 template <typename... Ts> hash_code hash_value(const std::tuple<Ts...> &arg) { 663 return std::apply([](const auto &...xs) { return hash_combine(xs...); }, arg); 664 } 665 666 // Declared and documented above, but defined here so that any of the hashing 667 // infrastructure is available. 668 template <typename T> 669 hash_code hash_value(const std::basic_string<T> &arg) { 670 return hash_combine_range(arg.begin(), arg.end()); 671 } 672 673 template <typename T> hash_code hash_value(const std::optional<T> &arg) { 674 return arg ? hash_combine(true, *arg) : hash_value(false); 675 } 676 677 template <> struct DenseMapInfo<hash_code, void> { 678 static inline hash_code getEmptyKey() { return hash_code(-1); } 679 static inline hash_code getTombstoneKey() { return hash_code(-2); } 680 static unsigned getHashValue(hash_code val) { return val; } 681 static bool isEqual(hash_code LHS, hash_code RHS) { return LHS == RHS; } 682 }; 683 684 } // namespace llvm 685 686 #endif 687