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 //===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
 // This file implements the newly proposed standard C++ interfaces for hashing
 // arbitrary data and building hash functions for user-defined types. This
 // interface was originally proposed in N3333[1] and is currently under review
 // for inclusion in a future TR and/or standard.
 //
 // The primary interfaces provide are comprised of one type and three functions:
 //
 //  -- 'hash_code' class is an opaque type representing the hash code for some
 //     data. It is the intended product of hashing, and can be used to implement
 //     hash tables, checksumming, and other common uses of hashes. It is not an
 //     integer type (although it can be converted to one) because it is risky
 //     to assume much about the internals of a hash_code. In particular, each
 //     execution of the program has a high probability of producing a different
 //     hash_code for a given input. Thus their values are not stable to save or
 //     persist, and should only be used during the execution for the
 //     construction of hashing datastructures.
 //
 //  -- 'hash_value' is a function designed to be overloaded for each
 //     user-defined type which wishes to be used within a hashing context. It
 //     should be overloaded within the user-defined type's namespace and found
 //     via ADL. Overloads for primitive types are provided by this library.
 //
 //  -- 'hash_combine' and 'hash_combine_range' are functions designed to aid
 //      programmers in easily and intuitively combining a set of data into
 //      a single hash_code for their object. They should only logically be used
 //      within the implementation of a 'hash_value' routine or similar context.
 //
 // Note that 'hash_combine_range' contains very special logic for hashing
 // a contiguous array of integers or pointers. This logic is *extremely* fast,
 // on a modern Intel "Gainestown" Xeon (Nehalem uarch) @2.2 GHz, these were
 // benchmarked at over 6.5 GiB/s for large keys, and <20 cycles/hash for keys
 // under 32-bytes.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_HASHING_H
 #define LLVM_ADT_HASHING_H
 
 #include "llvm/Config/abi-breaking.h"
 #include "llvm/Support/DataTypes.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/SwapByteOrder.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
 #include <cstring>
 #include <optional>
 #include <string>
 #include <tuple>
 #include <utility>
 
 namespace llvm {
 template <typename T, typename Enable> struct DenseMapInfo;
 
 /// An opaque object representing a hash code.
 ///
 /// This object represents the result of hashing some entity. It is intended to
 /// be used to implement hashtables or other hashing-based data structures.
 /// While it wraps and exposes a numeric value, this value should not be
 /// trusted to be stable or predictable across processes or executions.
 ///
 /// In order to obtain the hash_code for an object 'x':
 /// \code
 ///   using llvm::hash_value;
 ///   llvm::hash_code code = hash_value(x);
 /// \endcode
 class hash_code {
   size_t value;
 
 public:
   /// Default construct a hash_code.
   /// Note that this leaves the value uninitialized.
   hash_code() = default;
 
   /// Form a hash code directly from a numerical value.
   hash_code(size_t value) : value(value) {}
 
   /// Convert the hash code to its numerical value for use.
   /*explicit*/ operator size_t() const { return value; }
 
   friend bool operator==(const hash_code &lhs, const hash_code &rhs) {
     return lhs.value == rhs.value;
   }
   friend bool operator!=(const hash_code &lhs, const hash_code &rhs) {
     return lhs.value != rhs.value;
   }
 
   /// Allow a hash_code to be directly run through hash_value.
   friend size_t hash_value(const hash_code &code) { return code.value; }
 };
 
 /// Compute a hash_code for any integer value.
 ///
 /// Note that this function is intended to compute the same hash_code for
 /// a particular value without regard to the pre-promotion type. This is in
 /// contrast to hash_combine which may produce different hash_codes for
 /// differing argument types even if they would implicit promote to a common
 /// type without changing the value.
 template <typename T>
 std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value);
 
 /// Compute a hash_code for a pointer's address.
 ///
 /// N.B.: This hashes the *address*. Not the value and not the type.
 template <typename T> hash_code hash_value(const T *ptr);
 
 /// Compute a hash_code for a pair of objects.
 template <typename T, typename U>
 hash_code hash_value(const std::pair<T, U> &arg);
 
 /// Compute a hash_code for a tuple.
 template <typename... Ts>
 hash_code hash_value(const std::tuple<Ts...> &arg);
 
 /// Compute a hash_code for a standard string.
 template <typename T>
 hash_code hash_value(const std::basic_string<T> &arg);
 
 /// Compute a hash_code for a standard string.
 template <typename T> hash_code hash_value(const std::optional<T> &arg);
 
 // All of the implementation details of actually computing the various hash
 // code values are held within this namespace. These routines are included in
 // the header file mainly to allow inlining and constant propagation.
 namespace hashing {
 namespace detail {
 
 inline uint64_t fetch64(const char *p) {
   uint64_t result;
   memcpy(&result, p, sizeof(result));
   if (sys::IsBigEndianHost)
     sys::swapByteOrder(result);
   return result;
 }
 
 inline uint32_t fetch32(const char *p) {
   uint32_t result;
   memcpy(&result, p, sizeof(result));
   if (sys::IsBigEndianHost)
     sys::swapByteOrder(result);
   return result;
 }
 
 /// Some primes between 2^63 and 2^64 for various uses.
 static constexpr uint64_t k0 = 0xc3a5c85c97cb3127ULL;
 static constexpr uint64_t k1 = 0xb492b66fbe98f273ULL;
 static constexpr uint64_t k2 = 0x9ae16a3b2f90404fULL;
 static constexpr uint64_t k3 = 0xc949d7c7509e6557ULL;
 
 /// Bitwise right rotate.
 /// Normally this will compile to a single instruction, especially if the
 /// shift is a manifest constant.
 inline uint64_t rotate(uint64_t val, size_t shift) {
   // Avoid shifting by 64: doing so yields an undefined result.
   return shift == 0 ? val : ((val >> shift) | (val << (64 - shift)));
 }
 
 inline uint64_t shift_mix(uint64_t val) {
   return val ^ (val >> 47);
 }
 
 inline uint64_t hash_16_bytes(uint64_t low, uint64_t high) {
   // Murmur-inspired hashing.
   const uint64_t kMul = 0x9ddfea08eb382d69ULL;
   uint64_t a = (low ^ high) * kMul;
   a ^= (a >> 47);
   uint64_t b = (high ^ a) * kMul;
   b ^= (b >> 47);
   b *= kMul;
   return b;
 }
 
 inline uint64_t hash_1to3_bytes(const char *s, size_t len, uint64_t seed) {
   uint8_t a = s[0];
   uint8_t b = s[len >> 1];
   uint8_t c = s[len - 1];
   uint32_t y = static_cast<uint32_t>(a) + (static_cast<uint32_t>(b) << 8);
   uint32_t z = static_cast<uint32_t>(len) + (static_cast<uint32_t>(c) << 2);
   return shift_mix(y * k2 ^ z * k3 ^ seed) * k2;
 }
 
 inline uint64_t hash_4to8_bytes(const char *s, size_t len, uint64_t seed) {
   uint64_t a = fetch32(s);
   return hash_16_bytes(len + (a << 3), seed ^ fetch32(s + len - 4));
 }
 
 inline uint64_t hash_9to16_bytes(const char *s, size_t len, uint64_t seed) {
   uint64_t a = fetch64(s);
   uint64_t b = fetch64(s + len - 8);
   return hash_16_bytes(seed ^ a, rotate(b + len, len)) ^ b;
 }
 
 inline uint64_t hash_17to32_bytes(const char *s, size_t len, uint64_t seed) {
   uint64_t a = fetch64(s) * k1;
   uint64_t b = fetch64(s + 8);
   uint64_t c = fetch64(s + len - 8) * k2;
   uint64_t d = fetch64(s + len - 16) * k0;
   return hash_16_bytes(llvm::rotr<uint64_t>(a - b, 43) +
                            llvm::rotr<uint64_t>(c ^ seed, 30) + d,
                        a + llvm::rotr<uint64_t>(b ^ k3, 20) - c + len + seed);
 }
 
 inline uint64_t hash_33to64_bytes(const char *s, size_t len, uint64_t seed) {
   uint64_t z = fetch64(s + 24);
   uint64_t a = fetch64(s) + (len + fetch64(s + len - 16)) * k0;
   uint64_t b = llvm::rotr<uint64_t>(a + z, 52);
   uint64_t c = llvm::rotr<uint64_t>(a, 37);
   a += fetch64(s + 8);
   c += llvm::rotr<uint64_t>(a, 7);
   a += fetch64(s + 16);
   uint64_t vf = a + z;
   uint64_t vs = b + llvm::rotr<uint64_t>(a, 31) + c;
   a = fetch64(s + 16) + fetch64(s + len - 32);
   z = fetch64(s + len - 8);
   b = llvm::rotr<uint64_t>(a + z, 52);
   c = llvm::rotr<uint64_t>(a, 37);
   a += fetch64(s + len - 24);
   c += llvm::rotr<uint64_t>(a, 7);
   a += fetch64(s + len - 16);
   uint64_t wf = a + z;
   uint64_t ws = b + llvm::rotr<uint64_t>(a, 31) + c;
   uint64_t r = shift_mix((vf + ws) * k2 + (wf + vs) * k0);
   return shift_mix((seed ^ (r * k0)) + vs) * k2;
 }
 
 inline uint64_t hash_short(const char *s, size_t length, uint64_t seed) {
   if (length >= 4 && length <= 8)
     return hash_4to8_bytes(s, length, seed);
   if (length > 8 && length <= 16)
     return hash_9to16_bytes(s, length, seed);
   if (length > 16 && length <= 32)
     return hash_17to32_bytes(s, length, seed);
   if (length > 32)
     return hash_33to64_bytes(s, length, seed);
   if (length != 0)
     return hash_1to3_bytes(s, length, seed);
 
   return k2 ^ seed;
 }
 
 /// The intermediate state used during hashing.
 /// Currently, the algorithm for computing hash codes is based on CityHash and
 /// keeps 56 bytes of arbitrary state.
 struct hash_state {
   uint64_t h0 = 0, h1 = 0, h2 = 0, h3 = 0, h4 = 0, h5 = 0, h6 = 0;
 
   /// Create a new hash_state structure and initialize it based on the
   /// seed and the first 64-byte chunk.
   /// This effectively performs the initial mix.
   static hash_state create(const char *s, uint64_t seed) {
     hash_state state = {0,
                         seed,
                         hash_16_bytes(seed, k1),
                         llvm::rotr<uint64_t>(seed ^ k1, 49),
                         seed * k1,
                         shift_mix(seed),
                         0};
     state.h6 = hash_16_bytes(state.h4, state.h5);
     state.mix(s);
     return state;
   }
 
   /// Mix 32-bytes from the input sequence into the 16-bytes of 'a'
   /// and 'b', including whatever is already in 'a' and 'b'.
   static void mix_32_bytes(const char *s, uint64_t &a, uint64_t &b) {
     a += fetch64(s);
     uint64_t c = fetch64(s + 24);
     b = llvm::rotr<uint64_t>(b + a + c, 21);
     uint64_t d = a;
     a += fetch64(s + 8) + fetch64(s + 16);
     b += llvm::rotr<uint64_t>(a, 44) + d;
     a += c;
   }
 
   /// Mix in a 64-byte buffer of data.
   /// We mix all 64 bytes even when the chunk length is smaller, but we
   /// record the actual length.
   void mix(const char *s) {
     h0 = llvm::rotr<uint64_t>(h0 + h1 + h3 + fetch64(s + 8), 37) * k1;
     h1 = llvm::rotr<uint64_t>(h1 + h4 + fetch64(s + 48), 42) * k1;
     h0 ^= h6;
     h1 += h3 + fetch64(s + 40);
     h2 = llvm::rotr<uint64_t>(h2 + h5, 33) * k1;
     h3 = h4 * k1;
     h4 = h0 + h5;
     mix_32_bytes(s, h3, h4);
     h5 = h2 + h6;
     h6 = h1 + fetch64(s + 16);
     mix_32_bytes(s + 32, h5, h6);
     std::swap(h2, h0);
   }
 
   /// Compute the final 64-bit hash code value based on the current
   /// state and the length of bytes hashed.
   uint64_t finalize(size_t length) {
     return hash_16_bytes(hash_16_bytes(h3, h5) + shift_mix(h1) * k1 + h2,
                          hash_16_bytes(h4, h6) + shift_mix(length) * k1 + h0);
   }
 };
 
 /// In LLVM_ENABLE_ABI_BREAKING_CHECKS builds, the seed is non-deterministic
 /// per process (address of a function in LLVMSupport) to prevent having users
 /// depend on the particular hash values. On platforms without ASLR, this is
 /// still likely non-deterministic per build.
 inline uint64_t get_execution_seed() {
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
   return static_cast<uint64_t>(
       reinterpret_cast<uintptr_t>(&install_fatal_error_handler));
 #else
   return 0xff51afd7ed558ccdULL;
 #endif
 }
 
 
 /// Trait to indicate whether a type's bits can be hashed directly.
 ///
 /// A type trait which is true if we want to combine values for hashing by
 /// reading the underlying data. It is false if values of this type must
 /// first be passed to hash_value, and the resulting hash_codes combined.
 //
 // FIXME: We want to replace is_integral_or_enum and is_pointer here with
 // a predicate which asserts that comparing the underlying storage of two
 // values of the type for equality is equivalent to comparing the two values
 // for equality. For all the platforms we care about, this holds for integers
 // and pointers, but there are platforms where it doesn't and we would like to
 // support user-defined types which happen to satisfy this property.
 template <typename T> struct is_hashable_data
   : std::integral_constant<bool, ((is_integral_or_enum<T>::value ||
                                    std::is_pointer<T>::value) &&
                                   64 % sizeof(T) == 0)> {};
 
 // Special case std::pair to detect when both types are viable and when there
 // is no alignment-derived padding in the pair. This is a bit of a lie because
 // std::pair isn't truly POD, but it's close enough in all reasonable
 // implementations for our use case of hashing the underlying data.
 template <typename T, typename U> struct is_hashable_data<std::pair<T, U> >
   : std::integral_constant<bool, (is_hashable_data<T>::value &&
                                   is_hashable_data<U>::value &&
                                   (sizeof(T) + sizeof(U)) ==
                                    sizeof(std::pair<T, U>))> {};
 
 /// Helper to get the hashable data representation for a type.
 /// This variant is enabled when the type itself can be used.
 template <typename T>
 std::enable_if_t<is_hashable_data<T>::value, T>
 get_hashable_data(const T &value) {
   return value;
 }
 /// Helper to get the hashable data representation for a type.
 /// This variant is enabled when we must first call hash_value and use the
 /// result as our data.
 template <typename T>
 std::enable_if_t<!is_hashable_data<T>::value, size_t>
 get_hashable_data(const T &value) {
   using ::llvm::hash_value;
   return hash_value(value);
 }
 
 /// Helper to store data from a value into a buffer and advance the
 /// pointer into that buffer.
 ///
 /// This routine first checks whether there is enough space in the provided
 /// buffer, and if not immediately returns false. If there is space, it
 /// copies the underlying bytes of value into the buffer, advances the
 /// buffer_ptr past the copied bytes, and returns true.
 template <typename T>
 bool store_and_advance(char *&buffer_ptr, char *buffer_end, const T& value,
                        size_t offset = 0) {
   size_t store_size = sizeof(value) - offset;
   if (buffer_ptr + store_size > buffer_end)
     return false;
   const char *value_data = reinterpret_cast<const char *>(&value);
   memcpy(buffer_ptr, value_data + offset, store_size);
   buffer_ptr += store_size;
   return true;
 }
 
 /// Implement the combining of integral values into a hash_code.
 ///
 /// This overload is selected when the value type of the iterator is
 /// integral. Rather than computing a hash_code for each object and then
 /// combining them, this (as an optimization) directly combines the integers.
 template <typename InputIteratorT>
 hash_code hash_combine_range_impl(InputIteratorT first, InputIteratorT last) {
   const uint64_t seed = get_execution_seed();
   char buffer[64], *buffer_ptr = buffer;
   char *const buffer_end = std::end(buffer);
   while (first != last && store_and_advance(buffer_ptr, buffer_end,
                                             get_hashable_data(*first)))
     ++first;
   if (first == last)
     return hash_short(buffer, buffer_ptr - buffer, seed);
   assert(buffer_ptr == buffer_end);
 
   hash_state state = state.create(buffer, seed);
   size_t length = 64;
   while (first != last) {
     // Fill up the buffer. We don't clear it, which re-mixes the last round
     // when only a partial 64-byte chunk is left.
     buffer_ptr = buffer;
     while (first != last && store_and_advance(buffer_ptr, buffer_end,
                                               get_hashable_data(*first)))
       ++first;
 
     // Rotate the buffer if we did a partial fill in order to simulate doing
     // a mix of the last 64-bytes. That is how the algorithm works when we
     // have a contiguous byte sequence, and we want to emulate that here.
     std::rotate(buffer, buffer_ptr, buffer_end);
 
     // Mix this chunk into the current state.
     state.mix(buffer);
     length += buffer_ptr - buffer;
   };
 
   return state.finalize(length);
 }
 
 /// Implement the combining of integral values into a hash_code.
 ///
 /// This overload is selected when the value type of the iterator is integral
 /// and when the input iterator is actually a pointer. Rather than computing
 /// a hash_code for each object and then combining them, this (as an
 /// optimization) directly combines the integers. Also, because the integers
 /// are stored in contiguous memory, this routine avoids copying each value
 /// and directly reads from the underlying memory.
 template <typename ValueT>
 std::enable_if_t<is_hashable_data<ValueT>::value, hash_code>
 hash_combine_range_impl(ValueT *first, ValueT *last) {
   const uint64_t seed = get_execution_seed();
   const char *s_begin = reinterpret_cast<const char *>(first);
   const char *s_end = reinterpret_cast<const char *>(last);
   const size_t length = std::distance(s_begin, s_end);
   if (length <= 64)
     return hash_short(s_begin, length, seed);
 
   const char *s_aligned_end = s_begin + (length & ~63);
   hash_state state = state.create(s_begin, seed);
   s_begin += 64;
   while (s_begin != s_aligned_end) {
     state.mix(s_begin);
     s_begin += 64;
   }
   if (length & 63)
     state.mix(s_end - 64);
 
   return state.finalize(length);
 }
 
 } // namespace detail
 } // namespace hashing
 
 
 /// Compute a hash_code for a sequence of values.
 ///
 /// This hashes a sequence of values. It produces the same hash_code as
 /// 'hash_combine(a, b, c, ...)', but can run over arbitrary sized sequences
 /// and is significantly faster given pointers and types which can be hashed as
 /// a sequence of bytes.
 template <typename InputIteratorT>
 hash_code hash_combine_range(InputIteratorT first, InputIteratorT last) {
   return ::llvm::hashing::detail::hash_combine_range_impl(first, last);
 }
 
 
 // Implementation details for hash_combine.
 namespace hashing {
 namespace detail {
 
 /// Helper class to manage the recursive combining of hash_combine
 /// arguments.
 ///
 /// This class exists to manage the state and various calls involved in the
 /// recursive combining of arguments used in hash_combine. It is particularly
 /// useful at minimizing the code in the recursive calls to ease the pain
 /// caused by a lack of variadic functions.
 struct hash_combine_recursive_helper {
   char buffer[64] = {};
   hash_state state;
   const uint64_t seed;
 
 public:
   /// Construct a recursive hash combining helper.
   ///
   /// This sets up the state for a recursive hash combine, including getting
   /// the seed and buffer setup.
   hash_combine_recursive_helper()
     : seed(get_execution_seed()) {}
 
   /// Combine one chunk of data into the current in-flight hash.
   ///
   /// This merges one chunk of data into the hash. First it tries to buffer
   /// the data. If the buffer is full, it hashes the buffer into its
   /// hash_state, empties it, and then merges the new chunk in. This also
   /// handles cases where the data straddles the end of the buffer.
   template <typename T>
   char *combine_data(size_t &length, char *buffer_ptr, char *buffer_end, T data) {
     if (!store_and_advance(buffer_ptr, buffer_end, data)) {
       // Check for skew which prevents the buffer from being packed, and do
       // a partial store into the buffer to fill it. This is only a concern
       // with the variadic combine because that formation can have varying
       // argument types.
       size_t partial_store_size = buffer_end - buffer_ptr;
       memcpy(buffer_ptr, &data, partial_store_size);
 
       // If the store fails, our buffer is full and ready to hash. We have to
       // either initialize the hash state (on the first full buffer) or mix
       // this buffer into the existing hash state. Length tracks the *hashed*
       // length, not the buffered length.
       if (length == 0) {
         state = state.create(buffer, seed);
         length = 64;
       } else {
         // Mix this chunk into the current state and bump length up by 64.
         state.mix(buffer);
         length += 64;
       }
       // Reset the buffer_ptr to the head of the buffer for the next chunk of
       // data.
       buffer_ptr = buffer;
 
       // Try again to store into the buffer -- this cannot fail as we only
       // store types smaller than the buffer.
       if (!store_and_advance(buffer_ptr, buffer_end, data,
                              partial_store_size))
         llvm_unreachable("buffer smaller than stored type");
     }
     return buffer_ptr;
   }
 
   /// Recursive, variadic combining method.
   ///
   /// This function recurses through each argument, combining that argument
   /// into a single hash.
   template <typename T, typename ...Ts>
   hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                     const T &arg, const Ts &...args) {
     buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg));
 
     // Recurse to the next argument.
     return combine(length, buffer_ptr, buffer_end, args...);
   }
 
   /// Base case for recursive, variadic combining.
   ///
   /// The base case when combining arguments recursively is reached when all
   /// arguments have been handled. It flushes the remaining buffer and
   /// constructs a hash_code.
   hash_code combine(size_t length, char *buffer_ptr, char *buffer_end) {
     // Check whether the entire set of values fit in the buffer. If so, we'll
     // use the optimized short hashing routine and skip state entirely.
     if (length == 0)
       return hash_short(buffer, buffer_ptr - buffer, seed);
 
     // Mix the final buffer, rotating it if we did a partial fill in order to
     // simulate doing a mix of the last 64-bytes. That is how the algorithm
     // works when we have a contiguous byte sequence, and we want to emulate
     // that here.
     std::rotate(buffer, buffer_ptr, buffer_end);
 
     // Mix this chunk into the current state.
     state.mix(buffer);
     length += buffer_ptr - buffer;
 
     return state.finalize(length);
   }
 };
 
 } // namespace detail
 } // namespace hashing
 
 /// Combine values into a single hash_code.
 ///
 /// This routine accepts a varying number of arguments of any type. It will
 /// attempt to combine them into a single hash_code. For user-defined types it
 /// attempts to call a \see hash_value overload (via ADL) for the type. For
 /// integer and pointer types it directly combines their data into the
 /// resulting hash_code.
 ///
 /// The result is suitable for returning from a user's hash_value
 /// *implementation* for their user-defined type. Consumers of a type should
 /// *not* call this routine, they should instead call 'hash_value'.
 template <typename ...Ts> hash_code hash_combine(const Ts &...args) {
   // Recursively hash each argument using a helper class.
   ::llvm::hashing::detail::hash_combine_recursive_helper helper;
   return helper.combine(0, helper.buffer, helper.buffer + 64, args...);
 }
 
 // Implementation details for implementations of hash_value overloads provided
 // here.
 namespace hashing {
 namespace detail {
 
 /// Helper to hash the value of a single integer.
 ///
 /// Overloads for smaller integer types are not provided to ensure consistent
 /// behavior in the presence of integral promotions. Essentially,
 /// "hash_value('4')" and "hash_value('0' + 4)" should be the same.
 inline hash_code hash_integer_value(uint64_t value) {
   // Similar to hash_4to8_bytes but using a seed instead of length.
   const uint64_t seed = get_execution_seed();
   const char *s = reinterpret_cast<const char *>(&value);
   const uint64_t a = fetch32(s);
   return hash_16_bytes(seed + (a << 3), fetch32(s + 4));
 }
 
 } // namespace detail
 } // namespace hashing
 
 // Declared and documented above, but defined here so that any of the hashing
 // infrastructure is available.
 template <typename T>
 std::enable_if_t<is_integral_or_enum<T>::value, hash_code> hash_value(T value) {
   return ::llvm::hashing::detail::hash_integer_value(
       static_cast<uint64_t>(value));
 }
 
 // Declared and documented above, but defined here so that any of the hashing
 // infrastructure is available.
 template <typename T> hash_code hash_value(const T *ptr) {
   return ::llvm::hashing::detail::hash_integer_value(
     reinterpret_cast<uintptr_t>(ptr));
 }
 
 // Declared and documented above, but defined here so that any of the hashing
 // infrastructure is available.
 template <typename T, typename U>
 hash_code hash_value(const std::pair<T, U> &arg) {
   return hash_combine(arg.first, arg.second);
 }
 
 template <typename... Ts> hash_code hash_value(const std::tuple<Ts...> &arg) {
   return std::apply([](const auto &...xs) { return hash_combine(xs...); }, arg);
 }
 
 // Declared and documented above, but defined here so that any of the hashing
 // infrastructure is available.
 template <typename T>
 hash_code hash_value(const std::basic_string<T> &arg) {
   return hash_combine_range(arg.begin(), arg.end());
 }
 
 template <typename T> hash_code hash_value(const std::optional<T> &arg) {
   return arg ? hash_combine(true, *arg) : hash_value(false);
 }
 
 template <> struct DenseMapInfo<hash_code, void> {
   static inline hash_code getEmptyKey() { return hash_code(-1); }
   static inline hash_code getTombstoneKey() { return hash_code(-2); }
   static unsigned getHashValue(hash_code val) {
     return static_cast<unsigned>(size_t(val));
   }
   static bool isEqual(hash_code LHS, hash_code RHS) { return LHS == RHS; }
 };
 
 } // namespace llvm
 
 /// Implement std::hash so that hash_code can be used in STL containers.
 namespace std {
 
 template<>
 struct hash<llvm::hash_code> {
   size_t operator()(llvm::hash_code const& Val) const {
     return Val;
   }
 };
 
 } // namespace std;
 
 #endif

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