ADT: Allow up to 18 arguments in hash_combine()

[oota-llvm.git] / include / llvm / ADT / Hashing.h

//===-- llvm/ADT/Hashing.h - Utilities for hashing --------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/Support/DataTypes.h"
#include "llvm/Support/Host.h"
#include "llvm/Support/SwapByteOrder.h"
#include "llvm/Support/type_traits.h"
#include <algorithm>
#include <cassert>
#include <cstring>
#include <iterator>
#include <utility>

// Allow detecting C++11 feature availability when building with Clang without
// breaking other compilers.
#ifndef __has_feature
# define __has_feature(x) 0
#endif

namespace llvm {

/// \brief 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:
  /// \brief Default construct a hash_code.
  /// Note that this leaves the value uninitialized.
  hash_code() {}

  /// \brief Form a hash code directly from a numerical value.
  hash_code(size_t value) : value(value) {}

  /// \brief 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;
  }

  /// \brief Allow a hash_code to be directly run through hash_value.
  friend size_t hash_value(const hash_code &code) { return code.value; }
};

/// \brief 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>
typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type
hash_value(T value);

/// \brief 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);

/// \brief Compute a hash_code for a pair of objects.
template <typename T, typename U>
hash_code hash_value(const std::pair<T, U> &arg);

/// \brief Compute a hash_code for a standard string.
template <typename T>
hash_code hash_value(const std::basic_string<T> &arg);


/// \brief Override the execution seed with a fixed value.
///
/// This hashing library uses a per-execution seed designed to change on each
/// run with high probability in order to ensure that the hash codes are not
/// attackable and to ensure that output which is intended to be stable does
/// not rely on the particulars of the hash codes produced.
///
/// That said, there are use cases where it is important to be able to
/// reproduce *exactly* a specific behavior. To that end, we provide a function
/// which will forcibly set the seed to a fixed value. This must be done at the
/// start of the program, before any hashes are computed. Also, it cannot be
/// undone. This makes it thread-hostile and very hard to use outside of
/// immediately on start of a simple program designed for reproducible
/// behavior.
void set_fixed_execution_hash_seed(size_t fixed_value);


// 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 const uint64_t k0 = 0xc3a5c85c97cb3127ULL;
static const uint64_t k1 = 0xb492b66fbe98f273ULL;
static const uint64_t k2 = 0x9ae16a3b2f90404fULL;
static const uint64_t k3 = 0xc949d7c7509e6557ULL;

/// \brief 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 = 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(rotate(a - b, 43) + rotate(c ^ seed, 30) + d,
                       a + rotate(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 = rotate(a + z, 52);
  uint64_t c = rotate(a, 37);
  a += fetch64(s + 8);
  c += rotate(a, 7);
  a += fetch64(s + 16);
  uint64_t vf = a + z;
  uint64_t vs = b + rotate(a, 31) + c;
  a = fetch64(s + 16) + fetch64(s + len - 32);
  z = fetch64(s + len - 8);
  b = rotate(a + z, 52);
  c = rotate(a, 37);
  a += fetch64(s + len - 24);
  c += rotate(a, 7);
  a += fetch64(s + len - 16);
  uint64_t wf = a + z;
  uint64_t ws = b + rotate(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;
}

/// \brief 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, h1, h2, h3, h4, h5, h6;

  /// \brief 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), rotate(seed ^ k1, 49),
      seed * k1, shift_mix(seed), 0 };
    state.h6 = hash_16_bytes(state.h4, state.h5);
    state.mix(s);
    return state;
  }

  /// \brief 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 = rotate(b + a + c, 21);
    uint64_t d = a;
    a += fetch64(s + 8) + fetch64(s + 16);
    b += rotate(a, 44) + d;
    a += c;
  }

  /// \brief 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 = rotate(h0 + h1 + h3 + fetch64(s + 8), 37) * k1;
    h1 = rotate(h1 + h4 + fetch64(s + 48), 42) * k1;
    h0 ^= h6;
    h1 += h3 + fetch64(s + 40);
    h2 = rotate(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);
  }

  /// \brief 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);
  }
};


/// \brief A global, fixed seed-override variable.
///
/// This variable can be set using the \see llvm::set_fixed_execution_seed
/// function. See that function for details. Do not, under any circumstances,
/// set or read this variable.
extern size_t fixed_seed_override;

inline size_t get_execution_seed() {
  // FIXME: This needs to be a per-execution seed. This is just a placeholder
  // implementation. Switching to a per-execution seed is likely to flush out
  // instability bugs and so will happen as its own commit.
  //
  // However, if there is a fixed seed override set the first time this is
  // called, return that instead of the per-execution seed.
  const uint64_t seed_prime = 0xff51afd7ed558ccdULL;
  static size_t seed = fixed_seed_override ? fixed_seed_override
                                           : (size_t)seed_prime;
  return seed;
}


/// \brief 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>))> {};

/// \brief Helper to get the hashable data representation for a type.
/// This variant is enabled when the type itself can be used.
template <typename T>
typename std::enable_if<is_hashable_data<T>::value, T>::type
get_hashable_data(const T &value) {
  return value;
}
/// \brief 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>
typename std::enable_if<!is_hashable_data<T>::value, size_t>::type
get_hashable_data(const T &value) {
  using ::llvm::hash_value;
  return hash_value(value);
}

/// \brief 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;
}

/// \brief 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 size_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);
}

/// \brief 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>
typename std::enable_if<is_hashable_data<ValueT>::value, hash_code>::type
hash_combine_range_impl(ValueT *first, ValueT *last) {
  const size_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


/// \brief 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 {

/// \brief 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 size_t seed;

public:
  /// \brief 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()) {}

  /// \brief 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))
        abort();
    }
    return buffer_ptr;
  }

#if defined(__has_feature) && __has_feature(__cxx_variadic_templates__)

  /// \brief 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...);
  }

#else
  // Manually expanded recursive combining methods. See variadic above for
  // documentation.

  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13, typename T14,
            typename T15, typename T16, typename T17, typename T18>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13, const T14 &arg14, const T15 &arg15,
                    const T16 &arg16, const T17 &arg17, const T18 &arg18) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15,
                   arg16, arg17, arg18);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13, typename T14,
            typename T15, typename T16, typename T17>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13, const T14 &arg14, const T15 &arg15,
                    const T16 &arg16, const T17 &arg17) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15,
                   arg16, arg17);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13, typename T14,
            typename T15, typename T16>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13, const T14 &arg14, const T15 &arg15,
                    const T16 &arg16) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15,
                   arg16);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13, typename T14,
            typename T15>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13, const T14 &arg14, const T15 &arg15) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14, arg15);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13, typename T14>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13, const T14 &arg14) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13, arg14);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12, typename T13>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12,
                    const T13 &arg13) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12, arg13);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11, typename T12>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11, const T12 &arg12) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11, arg12);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10,
            typename T11>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10, const T11 &arg11) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10, arg11);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9, typename T10>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9,
                    const T10 &arg10) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9, arg10);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8, typename T9>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8, const T9 &arg9) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8, arg9);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7, typename T8>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7, const T8 &arg8) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7, arg8);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6, typename T7>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6,
                    const T7 &arg7) {
    buffer_ptr =
        combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6,
                   arg7);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5,
            typename T6>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5, const T6 &arg6) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5, arg6);
  }
  template <typename T1, typename T2, typename T3, typename T4, typename T5>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4, const T5 &arg5) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4, arg5);
  }
  template <typename T1, typename T2, typename T3, typename T4>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3,
                    const T4 &arg4) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3, arg4);
  }
  template <typename T1, typename T2, typename T3>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2, const T3 &arg3) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2, arg3);
  }
  template <typename T1, typename T2>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1, const T2 &arg2) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end, arg2);
  }
  template <typename T1>
  hash_code combine(size_t length, char *buffer_ptr, char *buffer_end,
                    const T1 &arg1) {
    buffer_ptr = combine_data(length, buffer_ptr, buffer_end, get_hashable_data(arg1));
    return combine(length, buffer_ptr, buffer_end);
  }

#endif

  /// \brief 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


#if __has_feature(__cxx_variadic_templates__)

/// \brief 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...);
}

#else

// What follows are manually exploded overloads for each argument width. See
// the above variadic definition for documentation and specification.

template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13, typename T14, typename T15,
          typename T16, typename T17, typename T18>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13, const T14 &arg14, const T15 &arg15,
                       const T16 &arg16, const T17 &arg17, const T18 &arg18) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13, arg14, arg15, arg16, arg17, arg18);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13, typename T14, typename T15,
          typename T16, typename T17>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13, const T14 &arg14, const T15 &arg15,
                       const T16 &arg16, const T17 &arg17) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13, arg14, arg15, arg16, arg17);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13, typename T14, typename T15,
          typename T16>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13, const T14 &arg14, const T15 &arg15,
                       const T16 &arg16) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13, arg14, arg15, arg16);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13, typename T14, typename T15>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13, const T14 &arg14, const T15 &arg15) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13, arg14, arg15);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13, typename T14>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13, const T14 &arg14) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13, arg14);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12, typename T13>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12,
                       const T13 &arg13) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11, arg12,
                        arg13);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11, typename T12>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11, const T12 &arg12) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11,
                        arg12);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10,
          typename T11>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10, const T11 &arg11) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10, arg11);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9, typename T10>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9,
                       const T10 &arg10) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9, arg10);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8, typename T9>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8, const T9 &arg9) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8, arg9);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7, typename T8>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7, const T8 &arg8) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7, arg8);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6, typename T7>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6,
                       const T7 &arg7) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3,
                        arg4, arg5, arg6, arg7);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5,
          typename T6>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5, const T6 &arg6) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64,
                        arg1, arg2, arg3, arg4, arg5, arg6);
}
template <typename T1, typename T2, typename T3, typename T4, typename T5>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4, const T5 &arg5) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64,
                        arg1, arg2, arg3, arg4, arg5);
}
template <typename T1, typename T2, typename T3, typename T4>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3,
                       const T4 &arg4) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64,
                        arg1, arg2, arg3, arg4);
}
template <typename T1, typename T2, typename T3>
hash_code hash_combine(const T1 &arg1, const T2 &arg2, const T3 &arg3) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2, arg3);
}
template <typename T1, typename T2>
hash_code hash_combine(const T1 &arg1, const T2 &arg2) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1, arg2);
}
template <typename T1>
hash_code hash_combine(const T1 &arg1) {
  ::llvm::hashing::detail::hash_combine_recursive_helper helper;
  return helper.combine(0, helper.buffer, helper.buffer + 64, arg1);
}

#endif


// Implementation details for implementations of hash_value overloads provided
// here.
namespace hashing {
namespace detail {

/// \brief 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>
typename std::enable_if<is_integral_or_enum<T>::value, hash_code>::type
hash_value(T value) {
  return ::llvm::hashing::detail::hash_integer_value(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);
}

// 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());
}

} // namespace llvm

#endif