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 //===- ArrayRef.h - Array Reference Wrapper ---------------------*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_ARRAYREF_H
 #define LLVM_ADT_ARRAYREF_H
 
 #include "llvm/ADT/Hashing.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Compiler.h"
 #include <algorithm>
 #include <array>
 #include <cassert>
 #include <cstddef>
 #include <initializer_list>
 #include <iterator>
 #include <memory>
 #include <type_traits>
 #include <vector>
 
 namespace llvm {
   template<typename T> class [[nodiscard]] MutableArrayRef;
 
   /// ArrayRef - Represent a constant reference to an array (0 or more elements
   /// consecutively in memory), i.e. a start pointer and a length.  It allows
   /// various APIs to take consecutive elements easily and conveniently.
   ///
   /// This class does not own the underlying data, it is expected to be used in
   /// situations where the data resides in some other buffer, whose lifetime
   /// extends past that of the ArrayRef. For this reason, it is not in general
   /// safe to store an ArrayRef.
   ///
   /// This is intended to be trivially copyable, so it should be passed by
   /// value.
   template<typename T>
   class LLVM_GSL_POINTER [[nodiscard]] ArrayRef {
   public:
     using value_type = T;
     using pointer = value_type *;
     using const_pointer = const value_type *;
     using reference = value_type &;
     using const_reference = const value_type &;
     using iterator = const_pointer;
     using const_iterator = const_pointer;
     using reverse_iterator = std::reverse_iterator<iterator>;
     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
     using size_type = size_t;
     using difference_type = ptrdiff_t;
 
   private:
     /// The start of the array, in an external buffer.
     const T *Data = nullptr;
 
     /// The number of elements.
     size_type Length = 0;
 
   public:
     /// @name Constructors
     /// @{
 
     /// Construct an empty ArrayRef.
     /*implicit*/ ArrayRef() = default;
 
     /// Construct an empty ArrayRef from std::nullopt.
     /*implicit*/ ArrayRef(std::nullopt_t) {}
 
     /// Construct an ArrayRef from a single element.
     /*implicit*/ ArrayRef(const T &OneElt LLVM_LIFETIME_BOUND)
         : Data(&OneElt), Length(1) {}
 
     /// Construct an ArrayRef from a pointer and length.
     constexpr /*implicit*/ ArrayRef(const T *data LLVM_LIFETIME_BOUND,
                                     size_t length)
         : Data(data), Length(length) {}
 
     /// Construct an ArrayRef from a range.
     constexpr ArrayRef(const T *begin LLVM_LIFETIME_BOUND, const T *end)
         : Data(begin), Length(end - begin) {
       assert(begin <= end);
     }
 
     /// Construct an ArrayRef from a SmallVector. This is templated in order to
     /// avoid instantiating SmallVectorTemplateCommon<T> whenever we
     /// copy-construct an ArrayRef.
     template<typename U>
     /*implicit*/ ArrayRef(const SmallVectorTemplateCommon<T, U> &Vec)
       : Data(Vec.data()), Length(Vec.size()) {
     }
 
     /// Construct an ArrayRef from a std::vector.
     template<typename A>
     /*implicit*/ ArrayRef(const std::vector<T, A> &Vec)
       : Data(Vec.data()), Length(Vec.size()) {}
 
     /// Construct an ArrayRef from a std::array
     template <size_t N>
     /*implicit*/ constexpr ArrayRef(const std::array<T, N> &Arr)
         : Data(Arr.data()), Length(N) {}
 
     /// Construct an ArrayRef from a C array.
     template <size_t N>
     /*implicit*/ constexpr ArrayRef(const T (&Arr LLVM_LIFETIME_BOUND)[N])
         : Data(Arr), Length(N) {}
 
     /// Construct an ArrayRef from a std::initializer_list.
 #if LLVM_GNUC_PREREQ(9, 0, 0)
 // Disable gcc's warning in this constructor as it generates an enormous amount
 // of messages. Anyone using ArrayRef should already be aware of the fact that
 // it does not do lifetime extension.
 #pragma GCC diagnostic push
 #pragma GCC diagnostic ignored "-Winit-list-lifetime"
 #endif
     constexpr /*implicit*/ ArrayRef(
         std::initializer_list<T> Vec LLVM_LIFETIME_BOUND)
         : Data(Vec.begin() == Vec.end() ? (T *)nullptr : Vec.begin()),
           Length(Vec.size()) {}
 #if LLVM_GNUC_PREREQ(9, 0, 0)
 #pragma GCC diagnostic pop
 #endif
 
     /// Construct an ArrayRef<const T*> from ArrayRef<T*>. This uses SFINAE to
     /// ensure that only ArrayRefs of pointers can be converted.
     template <typename U>
     ArrayRef(const ArrayRef<U *> &A,
              std::enable_if_t<std::is_convertible<U *const *, T const *>::value>
                  * = nullptr)
         : Data(A.data()), Length(A.size()) {}
 
     /// Construct an ArrayRef<const T*> from a SmallVector<T*>. This is
     /// templated in order to avoid instantiating SmallVectorTemplateCommon<T>
     /// whenever we copy-construct an ArrayRef.
     template <typename U, typename DummyT>
     /*implicit*/ ArrayRef(
         const SmallVectorTemplateCommon<U *, DummyT> &Vec,
         std::enable_if_t<std::is_convertible<U *const *, T const *>::value> * =
             nullptr)
         : Data(Vec.data()), Length(Vec.size()) {}
 
     /// Construct an ArrayRef<const T*> from std::vector<T*>. This uses SFINAE
     /// to ensure that only vectors of pointers can be converted.
     template <typename U, typename A>
     ArrayRef(const std::vector<U *, A> &Vec,
              std::enable_if_t<std::is_convertible<U *const *, T const *>::value>
                  * = nullptr)
         : Data(Vec.data()), Length(Vec.size()) {}
 
     /// @}
     /// @name Simple Operations
     /// @{
 
     iterator begin() const { return Data; }
     iterator end() const { return Data + Length; }
 
     reverse_iterator rbegin() const { return reverse_iterator(end()); }
     reverse_iterator rend() const { return reverse_iterator(begin()); }
 
     /// empty - Check if the array is empty.
     bool empty() const { return Length == 0; }
 
     const T *data() const { return Data; }
 
     /// size - Get the array size.
     size_t size() const { return Length; }
 
     /// front - Get the first element.
     const T &front() const {
       assert(!empty());
       return Data[0];
     }
 
     /// back - Get the last element.
     const T &back() const {
       assert(!empty());
       return Data[Length-1];
     }
 
     // copy - Allocate copy in Allocator and return ArrayRef<T> to it.
     template <typename Allocator> MutableArrayRef<T> copy(Allocator &A) {
       T *Buff = A.template Allocate<T>(Length);
       std::uninitialized_copy(begin(), end(), Buff);
       return MutableArrayRef<T>(Buff, Length);
     }
 
     /// equals - Check for element-wise equality.
     bool equals(ArrayRef RHS) const {
       if (Length != RHS.Length)
         return false;
       return std::equal(begin(), end(), RHS.begin());
     }
 
     /// slice(n, m) - Chop off the first N elements of the array, and keep M
     /// elements in the array.
     ArrayRef<T> slice(size_t N, size_t M) const {
       assert(N+M <= size() && "Invalid specifier");
       return ArrayRef<T>(data()+N, M);
     }
 
     /// slice(n) - Chop off the first N elements of the array.
     ArrayRef<T> slice(size_t N) const { return drop_front(N); }
 
     /// Drop the first \p N elements of the array.
     ArrayRef<T> drop_front(size_t N = 1) const {
       assert(size() >= N && "Dropping more elements than exist");
       return slice(N, size() - N);
     }
 
     /// Drop the last \p N elements of the array.
     ArrayRef<T> drop_back(size_t N = 1) const {
       assert(size() >= N && "Dropping more elements than exist");
       return slice(0, size() - N);
     }
 
     /// Return a copy of *this with the first N elements satisfying the
     /// given predicate removed.
     template <class PredicateT> ArrayRef<T> drop_while(PredicateT Pred) const {
       return ArrayRef<T>(find_if_not(*this, Pred), end());
     }
 
     /// Return a copy of *this with the first N elements not satisfying
     /// the given predicate removed.
     template <class PredicateT> ArrayRef<T> drop_until(PredicateT Pred) const {
       return ArrayRef<T>(find_if(*this, Pred), end());
     }
 
     /// Return a copy of *this with only the first \p N elements.
     ArrayRef<T> take_front(size_t N = 1) const {
       if (N >= size())
         return *this;
       return drop_back(size() - N);
     }
 
     /// Return a copy of *this with only the last \p N elements.
     ArrayRef<T> take_back(size_t N = 1) const {
       if (N >= size())
         return *this;
       return drop_front(size() - N);
     }
 
     /// Return the first N elements of this Array that satisfy the given
     /// predicate.
     template <class PredicateT> ArrayRef<T> take_while(PredicateT Pred) const {
       return ArrayRef<T>(begin(), find_if_not(*this, Pred));
     }
 
     /// Return the first N elements of this Array that don't satisfy the
     /// given predicate.
     template <class PredicateT> ArrayRef<T> take_until(PredicateT Pred) const {
       return ArrayRef<T>(begin(), find_if(*this, Pred));
     }
 
     /// @}
     /// @name Operator Overloads
     /// @{
     const T &operator[](size_t Index) const {
       assert(Index < Length && "Invalid index!");
       return Data[Index];
     }
 
     /// Disallow accidental assignment from a temporary.
     ///
     /// The declaration here is extra complicated so that "arrayRef = {}"
     /// continues to select the move assignment operator.
     template <typename U>
     std::enable_if_t<std::is_same<U, T>::value, ArrayRef<T>> &
     operator=(U &&Temporary) = delete;
 
     /// Disallow accidental assignment from a temporary.
     ///
     /// The declaration here is extra complicated so that "arrayRef = {}"
     /// continues to select the move assignment operator.
     template <typename U>
     std::enable_if_t<std::is_same<U, T>::value, ArrayRef<T>> &
     operator=(std::initializer_list<U>) = delete;
 
     /// @}
     /// @name Expensive Operations
     /// @{
     std::vector<T> vec() const {
       return std::vector<T>(Data, Data+Length);
     }
 
     /// @}
     /// @name Conversion operators
     /// @{
     operator std::vector<T>() const {
       return std::vector<T>(Data, Data+Length);
     }
 
     /// @}
   };
 
   /// MutableArrayRef - Represent a mutable reference to an array (0 or more
   /// elements consecutively in memory), i.e. a start pointer and a length.  It
   /// allows various APIs to take and modify consecutive elements easily and
   /// conveniently.
   ///
   /// This class does not own the underlying data, it is expected to be used in
   /// situations where the data resides in some other buffer, whose lifetime
   /// extends past that of the MutableArrayRef. For this reason, it is not in
   /// general safe to store a MutableArrayRef.
   ///
   /// This is intended to be trivially copyable, so it should be passed by
   /// value.
   template<typename T>
   class [[nodiscard]] MutableArrayRef : public ArrayRef<T> {
   public:
     using value_type = T;
     using pointer = value_type *;
     using const_pointer = const value_type *;
     using reference = value_type &;
     using const_reference = const value_type &;
     using iterator = pointer;
     using const_iterator = const_pointer;
     using reverse_iterator = std::reverse_iterator<iterator>;
     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
     using size_type = size_t;
     using difference_type = ptrdiff_t;
 
     /// Construct an empty MutableArrayRef.
     /*implicit*/ MutableArrayRef() = default;
 
     /// Construct an empty MutableArrayRef from std::nullopt.
     /*implicit*/ MutableArrayRef(std::nullopt_t) : ArrayRef<T>() {}
 
     /// Construct a MutableArrayRef from a single element.
     /*implicit*/ MutableArrayRef(T &OneElt) : ArrayRef<T>(OneElt) {}
 
     /// Construct a MutableArrayRef from a pointer and length.
     /*implicit*/ MutableArrayRef(T *data, size_t length)
       : ArrayRef<T>(data, length) {}
 
     /// Construct a MutableArrayRef from a range.
     MutableArrayRef(T *begin, T *end) : ArrayRef<T>(begin, end) {}
 
     /// Construct a MutableArrayRef from a SmallVector.
     /*implicit*/ MutableArrayRef(SmallVectorImpl<T> &Vec)
     : ArrayRef<T>(Vec) {}
 
     /// Construct a MutableArrayRef from a std::vector.
     /*implicit*/ MutableArrayRef(std::vector<T> &Vec)
     : ArrayRef<T>(Vec) {}
 
     /// Construct a MutableArrayRef from a std::array
     template <size_t N>
     /*implicit*/ constexpr MutableArrayRef(std::array<T, N> &Arr)
         : ArrayRef<T>(Arr) {}
 
     /// Construct a MutableArrayRef from a C array.
     template <size_t N>
     /*implicit*/ constexpr MutableArrayRef(T (&Arr)[N]) : ArrayRef<T>(Arr) {}
 
     T *data() const { return const_cast<T*>(ArrayRef<T>::data()); }
 
     iterator begin() const { return data(); }
     iterator end() const { return data() + this->size(); }
 
     reverse_iterator rbegin() const { return reverse_iterator(end()); }
     reverse_iterator rend() const { return reverse_iterator(begin()); }
 
     /// front - Get the first element.
     T &front() const {
       assert(!this->empty());
       return data()[0];
     }
 
     /// back - Get the last element.
     T &back() const {
       assert(!this->empty());
       return data()[this->size()-1];
     }
 
     /// slice(n, m) - Chop off the first N elements of the array, and keep M
     /// elements in the array.
     MutableArrayRef<T> slice(size_t N, size_t M) const {
       assert(N + M <= this->size() && "Invalid specifier");
       return MutableArrayRef<T>(this->data() + N, M);
     }
 
     /// slice(n) - Chop off the first N elements of the array.
     MutableArrayRef<T> slice(size_t N) const {
       return slice(N, this->size() - N);
     }
 
     /// Drop the first \p N elements of the array.
     MutableArrayRef<T> drop_front(size_t N = 1) const {
       assert(this->size() >= N && "Dropping more elements than exist");
       return slice(N, this->size() - N);
     }
 
     MutableArrayRef<T> drop_back(size_t N = 1) const {
       assert(this->size() >= N && "Dropping more elements than exist");
       return slice(0, this->size() - N);
     }
 
     /// Return a copy of *this with the first N elements satisfying the
     /// given predicate removed.
     template <class PredicateT>
     MutableArrayRef<T> drop_while(PredicateT Pred) const {
       return MutableArrayRef<T>(find_if_not(*this, Pred), end());
     }
 
     /// Return a copy of *this with the first N elements not satisfying
     /// the given predicate removed.
     template <class PredicateT>
     MutableArrayRef<T> drop_until(PredicateT Pred) const {
       return MutableArrayRef<T>(find_if(*this, Pred), end());
     }
 
     /// Return a copy of *this with only the first \p N elements.
     MutableArrayRef<T> take_front(size_t N = 1) const {
       if (N >= this->size())
         return *this;
       return drop_back(this->size() - N);
     }
 
     /// Return a copy of *this with only the last \p N elements.
     MutableArrayRef<T> take_back(size_t N = 1) const {
       if (N >= this->size())
         return *this;
       return drop_front(this->size() - N);
     }
 
     /// Return the first N elements of this Array that satisfy the given
     /// predicate.
     template <class PredicateT>
     MutableArrayRef<T> take_while(PredicateT Pred) const {
       return MutableArrayRef<T>(begin(), find_if_not(*this, Pred));
     }
 
     /// Return the first N elements of this Array that don't satisfy the
     /// given predicate.
     template <class PredicateT>
     MutableArrayRef<T> take_until(PredicateT Pred) const {
       return MutableArrayRef<T>(begin(), find_if(*this, Pred));
     }
 
     /// @}
     /// @name Operator Overloads
     /// @{
     T &operator[](size_t Index) const {
       assert(Index < this->size() && "Invalid index!");
       return data()[Index];
     }
   };
 
   /// This is a MutableArrayRef that owns its array.
   template <typename T> class OwningArrayRef : public MutableArrayRef<T> {
   public:
     OwningArrayRef() = default;
     OwningArrayRef(size_t Size) : MutableArrayRef<T>(new T[Size], Size) {}
 
     OwningArrayRef(ArrayRef<T> Data)
         : MutableArrayRef<T>(new T[Data.size()], Data.size()) {
       std::copy(Data.begin(), Data.end(), this->begin());
     }
 
     OwningArrayRef(OwningArrayRef &&Other) { *this = std::move(Other); }
 
     OwningArrayRef &operator=(OwningArrayRef &&Other) {
       delete[] this->data();
       this->MutableArrayRef<T>::operator=(Other);
       Other.MutableArrayRef<T>::operator=(MutableArrayRef<T>());
       return *this;
     }
 
     ~OwningArrayRef() { delete[] this->data(); }
   };
 
   /// @name ArrayRef Deduction guides
   /// @{
   /// Deduction guide to construct an ArrayRef from a single element.
   template <typename T> ArrayRef(const T &OneElt) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a pointer and length
   template <typename T> ArrayRef(const T *data, size_t length) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a range
   template <typename T> ArrayRef(const T *data, const T *end) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a SmallVector
   template <typename T> ArrayRef(const SmallVectorImpl<T> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a SmallVector
   template <typename T, unsigned N>
   ArrayRef(const SmallVector<T, N> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a std::vector
   template <typename T> ArrayRef(const std::vector<T> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a std::array
   template <typename T, std::size_t N>
   ArrayRef(const std::array<T, N> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from an ArrayRef (const)
   template <typename T> ArrayRef(const ArrayRef<T> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from an ArrayRef
   template <typename T> ArrayRef(ArrayRef<T> &Vec) -> ArrayRef<T>;
 
   /// Deduction guide to construct an ArrayRef from a C array.
   template <typename T, size_t N> ArrayRef(const T (&Arr)[N]) -> ArrayRef<T>;
 
   /// @}
 
   /// @name MutableArrayRef Deduction guides
   /// @{
   /// Deduction guide to construct a `MutableArrayRef` from a single element
   template <class T> MutableArrayRef(T &OneElt) -> MutableArrayRef<T>;
 
   /// Deduction guide to construct a `MutableArrayRef` from a pointer and
   /// length.
   template <class T>
   MutableArrayRef(T *data, size_t length) -> MutableArrayRef<T>;
 
   /// Deduction guide to construct a `MutableArrayRef` from a `SmallVector`.
   template <class T>
   MutableArrayRef(SmallVectorImpl<T> &Vec) -> MutableArrayRef<T>;
 
   template <class T, unsigned N>
   MutableArrayRef(SmallVector<T, N> &Vec) -> MutableArrayRef<T>;
 
   /// Deduction guide to construct a `MutableArrayRef` from a `std::vector`.
   template <class T> MutableArrayRef(std::vector<T> &Vec) -> MutableArrayRef<T>;
 
   /// Deduction guide to construct a `MutableArrayRef` from a `std::array`.
   template <class T, std::size_t N>
   MutableArrayRef(std::array<T, N> &Vec) -> MutableArrayRef<T>;
 
   /// Deduction guide to construct a `MutableArrayRef` from a C array.
   template <typename T, size_t N>
   MutableArrayRef(T (&Arr)[N]) -> MutableArrayRef<T>;
 
   /// @}
   /// @name ArrayRef Comparison Operators
   /// @{
 
   template<typename T>
   inline bool operator==(ArrayRef<T> LHS, ArrayRef<T> RHS) {
     return LHS.equals(RHS);
   }
 
   template <typename T>
   inline bool operator==(SmallVectorImpl<T> &LHS, ArrayRef<T> RHS) {
     return ArrayRef<T>(LHS).equals(RHS);
   }
 
   template <typename T>
   inline bool operator!=(ArrayRef<T> LHS, ArrayRef<T> RHS) {
     return !(LHS == RHS);
   }
 
   template <typename T>
   inline bool operator!=(SmallVectorImpl<T> &LHS, ArrayRef<T> RHS) {
     return !(LHS == RHS);
   }
 
   /// @}
 
   template <typename T> hash_code hash_value(ArrayRef<T> S) {
     return hash_combine_range(S.begin(), S.end());
   }
 
   // Provide DenseMapInfo for ArrayRefs.
   template <typename T> struct DenseMapInfo<ArrayRef<T>, void> {
     static inline ArrayRef<T> getEmptyKey() {
       return ArrayRef<T>(
           reinterpret_cast<const T *>(~static_cast<uintptr_t>(0)), size_t(0));
     }
 
     static inline ArrayRef<T> getTombstoneKey() {
       return ArrayRef<T>(
           reinterpret_cast<const T *>(~static_cast<uintptr_t>(1)), size_t(0));
     }
 
     static unsigned getHashValue(ArrayRef<T> Val) {
       assert(Val.data() != getEmptyKey().data() &&
              "Cannot hash the empty key!");
       assert(Val.data() != getTombstoneKey().data() &&
              "Cannot hash the tombstone key!");
       return (unsigned)(hash_value(Val));
     }
 
     static bool isEqual(ArrayRef<T> LHS, ArrayRef<T> RHS) {
       if (RHS.data() == getEmptyKey().data())
         return LHS.data() == getEmptyKey().data();
       if (RHS.data() == getTombstoneKey().data())
         return LHS.data() == getTombstoneKey().data();
       return LHS == RHS;
     }
   };
 
 } // end namespace llvm
 
 #endif // LLVM_ADT_ARRAYREF_H

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