llvm::HashBuilder< HasherT, Endianness > Class Template Reference

Interface to help hash various types through a hasher type. More...

#include "llvm/Support/HashBuilder.h"

Inheritance diagram for llvm::HashBuilder< HasherT, Endianness >:

Public Types
template<typename T>
using	HasAddHashT
template<typename T>
using	HasByteSwapT
Public Types inherited from llvm::HashBuilderBase< HasherT >
template<typename HasherT_ = HasherT>
using	HashResultTy = decltype(std::declval<HasherT_ &>().final())

Public Member Functions
	HashBuilder (HasherT &Hasher)
template<typename... ArgTypes>
	HashBuilder (ArgTypes &&...Args)
template<typename T>
std::enable_if_t< hashbuilder_detail::IsHashableData< T >::value, HashBuilder & >	add (T Value)
	Implement hashing for hashable data types, e.g. integral or enum values.
template<typename T>
HashBuilder &	add (ArrayRef< T > Value)
	Support hashing ArrayRef.
HashBuilder &	add (StringRef Value)
	Support hashing StringRef.
template<typename T>
std::enable_if_t< is_detected< HasAddHashT, T >::value &&!hashbuilder_detail::IsHashableData< T >::value, HashBuilder & >	add (const T &Value)
	Implement hashing for user-defined structs.
template<typename T1, typename T2>
HashBuilder &	add (const std::pair< T1, T2 > &Value)
template<typename... Ts>
HashBuilder &	add (const std::tuple< Ts... > &Arg)
template<typename... Ts>
std::enable_if_t<(sizeof...(Ts) > 1), HashBuilder & >	add (const Ts &...Args)
	A convenenience variadic helper.
template<typename ForwardIteratorT>
HashBuilder &	addRange (ForwardIteratorT First, ForwardIteratorT Last)
template<typename RangeT>
HashBuilder &	addRange (const RangeT &Range)
template<typename ForwardIteratorT>
HashBuilder &	addRangeElements (ForwardIteratorT First, ForwardIteratorT Last)
template<typename RangeT>
HashBuilder &	addRangeElements (const RangeT &Range)
template<typename T>
std::enable_if_t< is_detected< HasByteSwapT, T >::value, HashBuilder & >	adjustForEndiannessAndAdd (const T &Value)
	Adjust Value for the target endianness and add it to the hash.
Public Member Functions inherited from llvm::HashBuilderBase< HasherT >
HasherT &	getHasher ()
void	update (ArrayRef< uint8_t > Data)
	Forward to HasherT::update(ArrayRef<uint8_t>).
void	update (StringRef Data)
	Forward to HasherT::update(ArrayRef<uint8_t>).
template<typename HasherT_ = HasherT>
HashResultTy< HasherT_ >	final ()
	Forward to HasherT::final() if available.
template<typename HasherT_ = HasherT>
HashResultTy< HasherT_ >	result ()
	Forward to HasherT::result() if available.

Additional Inherited Members
Protected Member Functions inherited from llvm::HashBuilderBase< HasherT >
	HashBuilderBase (HasherT &Hasher)
template<typename... ArgTypes>
	HashBuilderBase (ArgTypes &&...Args)

Detailed Description

template<typename HasherT, llvm::endianness Endianness>
class llvm::HashBuilder< HasherT, Endianness >

Interface to help hash various types through a hasher type.

Via provided specializations of add, addRange, and addRangeElements functions, various types (e.g. ArrayRef, StringRef, etc.) can be hashed without requiring any knowledge of hashed types from the hasher type.

The only method expected from the templated hasher type HasherT is:

• void update(ArrayRef<uint8_t> Data)

Additionally, the following methods will be forwarded to the hasher type:

• decltype(std::declval<HasherT &>().final()) final()
• decltype(std::declval<HasherT &>().result()) result()

From a user point of view, the interface provides the following:

• template<typename T> add(const T &Value) The add function implements hashing of various types.
• template <typename ItT> void addRange(ItT First, ItT Last) The addRange function is designed to aid hashing a range of values. It explicitly adds the size of the range in the hash.
• template <typename ItT> void addRangeElements(ItT First, ItT Last) The addRangeElements function is also designed to aid hashing a range of values. In contrast to addRange, it ignores the size of the range, behaving as if elements were added one at a time with add.

User-defined struct types can participate in this interface by providing an addHash templated function. See the associated template specialization for details.

This interface does not impose requirements on the hasher update(ArrayRef<uint8_t> Data) method. We want to avoid collisions for variable-size types; for example for

builder.add({1});
builder.add({2, 3});

and

builder.add({1, 2});
builder.add({3});

. Thus, specializations of add and addHash for variable-size types must not assume that the hasher type considers the size as part of the hash; they must explicitly add the size to the hash. See for example specializations for ArrayRef and StringRef.

Additionally, since types are eventually forwarded to the hasher's void update(ArrayRef<uint8_t>) method, endianness plays a role in the hash computation (for example when computing add((int)123)). Specifiying a non-native Endianness template parameter allows to compute stable hash across platforms with different endianness.

Definition at line 137 of file HashBuilder.h.

Member Typedef Documentation

HasAddHashT

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

using llvm::HashBuilder< HasherT, Endianness >::HasAddHashT

Initial value:

 
      decltype(addHash(std::declval<HashBuilder &>(), std::declval<T &>()))

Definition at line 206 of file HashBuilder.h.

HasByteSwapT

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

using llvm::HashBuilder< HasherT, Endianness >::HasByteSwapT

Initial value:

 decltype(support::endian::byte_swap(
      std::declval<T &>(), llvm::endianness::little))

Definition at line 348 of file HashBuilder.h.

Constructor & Destructor Documentation

HashBuilder() [1/2]

template<typename HasherT, llvm::endianness Endianness>

llvm::HashBuilder< HasherT, Endianness >::HashBuilder ( HasherT & Hasher )

inlineexplicit

Definition at line 139 of file HashBuilder.h.

HashBuilder() [2/2]

template<typename HasherT, llvm::endianness Endianness>

template<typename... ArgTypes>

llvm::HashBuilder< HasherT, Endianness >::HashBuilder ( ArgTypes &&... Args )

inlineexplicit

Definition at line 141 of file HashBuilder.h.

Member Function Documentation

add() [1/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::add ( ArrayRef< T > Value )

inline

Support hashing ArrayRef.

Value.size() is taken into account to ensure cases like

builder.add({1});
builder.add({2, 3});

and

builder.add({1, 2});
builder.add({3});

do not collide.

Definition at line 164 of file HashBuilder.h.

add() [2/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename T1, typename T2>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::add ( const std::pair< T1, T2 > & Value )

inline

Definition at line 301 of file HashBuilder.h.

add() [3/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename... Ts>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::add ( const std::tuple< Ts... > & Arg )

inline

Definition at line 305 of file HashBuilder.h.

add() [4/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

std::enable_if_t< is_detected< HasAddHashT, T >::value &&!hashbuilder_detail::IsHashableData< T >::value, HashBuilder & > llvm::HashBuilder< HasherT, Endianness >::add ( const T & Value )

inline

Implement hashing for user-defined structs.

Any user-define struct can participate in hashing via HashBuilder by providing a addHash templated function.

template <typename HasherT, llvm::endianness Endianness>
void addHash(HashBuilder<HasherT, Endianness> &HBuilder,
             const UserDefinedStruct &Value);

For example:

struct SimpleStruct {
  char c;
  int i;
};
 
template <typename HasherT, llvm::endianness Endianness>
void addHash(HashBuilder<HasherT, Endianness> &HBuilder,
             const SimpleStruct &Value) {
  HBuilder.add(Value.c);
  HBuilder.add(Value.i);
}

To avoid endianness issues, specializations of addHash should generally rely on exising add, addRange, and addRangeElements functions. If directly using update, an implementation must correctly handle endianness.

struct __attribute__ ((packed)) StructWithFastHash {
  int I;
  char C;
 
  // If possible, we want to hash both `I` and `C` in a single
  // `update` call for performance concerns.
  template <typename HasherT, llvm::endianness Endianness>
  friend void addHash(HashBuilder<HasherT, Endianness> &HBuilder,
                      const StructWithFastHash &Value) {
    if (Endianness == llvm::endianness::native) {
      HBuilder.update(ArrayRef(
          reinterpret_cast<const uint8_t *>(&Value), sizeof(Value)));
    } else {
      // Rely on existing `add` methods to handle endianness.
      HBuilder.add(Value.I);
      HBuilder.add(Value.C);
    }
  }
};

To avoid collisions, specialization of addHash for variable-size types must take the size into account.

For example:

struct CustomContainer {
private:
  size_t Size;
  int Elements[100];
 
public:
  CustomContainer(size_t Size) : Size(Size) {
    for (size_t I = 0; I != Size; ++I)
      Elements[I] = I;
  }
  template <typename HasherT, llvm::endianness Endianness>
  friend void addHash(HashBuilder<HasherT, Endianness> &HBuilder,
                      const CustomContainer &Value) {
    if (Endianness == llvm::endianness::native) {
      HBuilder.update(ArrayRef(
          reinterpret_cast<const uint8_t *>(&Value.Size),
          sizeof(Value.Size) + Value.Size * sizeof(Value.Elements[0])));
    } else {
      // `addRange` will take care of encoding the size.
      HBuilder.addRange(&Value.Elements[0], &Value.Elements[0] +
      Value.Size);
    }
  }
};

Definition at line 295 of file HashBuilder.h.

add() [5/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename... Ts>

std::enable_if_t<(sizeof...(Ts) > 1), HashBuilder & > llvm::HashBuilder< HasherT, Endianness >::add ( const Ts &... Args )

inline

A convenenience variadic helper.

It simply iterates over its arguments, in order.

add(Arg1, Arg2);

is equivalent to

add(Arg1)
add(Arg2)

Definition at line 321 of file HashBuilder.h.

add() [6/7]

template<typename HasherT, llvm::endianness Endianness>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::add ( StringRef Value )

inline

Support hashing StringRef.

Value.size() is taken into account to ensure cases like

builder.add("a");
builder.add("bc");

and

builder.add("ab");
builder.add("c");

do not collide.

Definition at line 194 of file HashBuilder.h.

add() [7/7]

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

std::enable_if_t< hashbuilder_detail::IsHashableData< T >::value, HashBuilder & > llvm::HashBuilder< HasherT, Endianness >::add ( T Value )

inline

Implement hashing for hashable data types, e.g. integral or enum values.

Definition at line 147 of file HashBuilder.h.

Referenced by llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add(), llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add(), llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add(), llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add(), llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add(), llvm::VersionTuple::addHash, llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::addRange(), llvm::memprof::computeFullStackId(), computeStackId(), and llvm::hash_value().

addRange() [1/2]

template<typename HasherT, llvm::endianness Endianness>

template<typename RangeT>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::addRange ( const RangeT & Range )

inline

Definition at line 331 of file HashBuilder.h.

addRange() [2/2]

template<typename HasherT, llvm::endianness Endianness>

template<typename ForwardIteratorT>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::addRange ( ForwardIteratorT First, ForwardIteratorT Last )

inline

Definition at line 326 of file HashBuilder.h.

Referenced by llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::addRange().

addRangeElements() [1/2]

template<typename HasherT, llvm::endianness Endianness>

template<typename RangeT>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::addRangeElements ( const RangeT & Range )

inline

Definition at line 343 of file HashBuilder.h.

addRangeElements() [2/2]

template<typename HasherT, llvm::endianness Endianness>

template<typename ForwardIteratorT>

HashBuilder & llvm::HashBuilder< HasherT, Endianness >::addRangeElements ( ForwardIteratorT First, ForwardIteratorT Last )

inline

Definition at line 336 of file HashBuilder.h.

Referenced by llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::addRange(), and llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::addRangeElements().

adjustForEndiannessAndAdd()

template<typename HasherT, llvm::endianness Endianness>

template<typename T>

std::enable_if_t< is_detected< HasByteSwapT, T >::value, HashBuilder & > llvm::HashBuilder< HasherT, Endianness >::adjustForEndiannessAndAdd ( const T & Value )

inline

Adjust Value for the target endianness and add it to the hash.

Definition at line 353 of file HashBuilder.h.

Referenced by llvm::HashBuilder< hashbuilder_detail::HashCodeHasher, llvm::endianness::native >::add().

---

The documentation for this class was generated from the following file:

• include/llvm/Support/HashBuilder.h