text: //===- llvm/ADT/SmallVector.h - 'Normally small' vectors --------*- C++ -*-===//
  //
  //                     The LLVM Compiler Infrastructure
  //
  // This file is distributed under the University of Illinois Open Source
  // License. See LICENSE.TXT for details.
  //
  //===----------------------------------------------------------------------===//
  //
  // This file defines the SmallVector class.
  //
  //===----------------------------------------------------------------------===//
  
  #ifndef LLVM_ADT_SMALLVECTOR_H
  #define LLVM_ADT_SMALLVECTOR_H
  
  #include "llvm/ADT/iterator_range.h"
  #include "llvm/Support/AlignOf.h"
  #include "llvm/Support/Compiler.h"
  #include "llvm/Support/MathExtras.h"
  #include "llvm/Support/type_traits.h"
  #include <algorithm>
  #include <cassert>
  #include <cstddef>
  #include <cstdlib>
  #include <cstring>
  #include <iterator>
  #include <memory>
  
  namespace llvm {
  
  /// This is all the non-templated stuff common to all SmallVectors.
  class SmallVectorBase {
  protected:
    void *BeginX, *EndX, *CapacityX;
  
  protected:
    SmallVectorBase(void *FirstEl, size_t Size)
      : BeginX(FirstEl), EndX(FirstEl), CapacityX((char*)FirstEl+Size) {}
  
    /// This is an implementation of the grow() method which only works
    /// on POD-like data types and is out of line to reduce code duplication.
    void grow_pod(void *FirstEl, size_t MinSizeInBytes, size_t TSize);
  
  public:
    /// This returns size()*sizeof(T).
    size_t size_in_bytes() const {
      return size_t((char*)EndX - (char*)BeginX);
    }
  
    /// capacity_in_bytes - This returns capacity()*sizeof(T).
    size_t capacity_in_bytes() const {
      return size_t((char*)CapacityX - (char*)BeginX);
    }
  
    bool LLVM_ATTRIBUTE_UNUSED_RESULT empty() const { return BeginX == EndX; }
  };
  
  template <typename T, unsigned N> struct SmallVectorStorage;
  
  /// This is the part of SmallVectorTemplateBase which does not depend on whether
  /// the type T is a POD. The extra dummy template argument is used by ArrayRef
  /// to avoid unnecessarily requiring T to be complete.
  template <typename T, typename = void>
  class SmallVectorTemplateCommon : public SmallVectorBase {
  private:
    template <typename, unsigned> friend struct SmallVectorStorage;
  
    // Allocate raw space for N elements of type T.  If T has a ctor or dtor, we
    // don't want it to be automatically run, so we need to represent the space as
    // something else.  Use an array of char of sufficient alignment.
    typedef llvm::AlignedCharArrayUnion<T> U;
    U FirstEl;
    // Space after 'FirstEl' is clobbered, do not add any instance vars after it.
  
  protected:
    SmallVectorTemplateCommon(size_t Size) : SmallVectorBase(&FirstEl, Size) {}
  
    void grow_pod(size_t MinSizeInBytes, size_t TSize) {
      SmallVectorBase::grow_pod(&FirstEl, MinSizeInBytes, TSize);
    }
  
    /// Return true if this is a smallvector which has not had dynamic
    /// memory allocated for it.
    bool isSmall() const {
      return BeginX == static_cast<const void*>(&FirstEl);
    }
  
    /// Put this vector in a state of being small.
    void resetToSmall() {
      BeginX = EndX = CapacityX = &FirstEl;
    }
  
    void setEnd(T *P) { this->EndX = P; }
  public:
    typedef size_t size_type;
    typedef ptrdiff_t difference_type;
    typedef T value_type;
    typedef T *iterator;
    typedef const T *const_iterator;
  
    typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
    typedef std::reverse_iterator<iterator> reverse_iterator;
  
    typedef T &reference;
    typedef const T &const_reference;
    typedef T *pointer;
    typedef const T *const_pointer;
  
    // forward iterator creation methods.
    iterator begin() { return (iterator)this->BeginX; }
    const_iterator begin() const { return (const_iterator)this->BeginX; }
    iterator end() { return (iterator)this->EndX; }
    const_iterator end() const { return (const_iterator)this->EndX; }
  protected:
    iterator capacity_ptr() { return (iterator)this->CapacityX; }
    const_iterator capacity_ptr() const { return (const_iterator)this->CapacityX;}
  public:
  
    // reverse iterator creation methods.
    reverse_iterator rbegin()            { return reverse_iterator(end()); }
    const_reverse_iterator rbegin() const{ return const_reverse_iterator(end()); }
    reverse_iterator rend()              { return reverse_iterator(begin()); }
    const_reverse_iterator rend() const { return const_reverse_iterator(begin());}
  
    size_type size() const { return end()-begin(); }
    size_type max_size() const { return size_type(-1) / sizeof(T); }
  
    /// Return the total number of elements in the currently allocated buffer.
    size_t capacity() const { return capacity_ptr() - begin(); }
  
    /// Return a pointer to the vector's buffer, even if empty().
    pointer data() { return pointer(begin()); }
    /// Return a pointer to the vector's buffer, even if empty().
    const_pointer data() const { return const_pointer(begin()); }
  
    reference operator[](size_type idx) {
      assert(idx < size());
      return begin()[idx];
    }
    const_reference operator[](size_type idx) const {
      assert(idx < size());
      return begin()[idx];
    }
  
    reference front() {
      assert(!empty());
      return begin()[0];
    }
    const_reference front() const {
      assert(!empty());
      return begin()[0];
    }
  
    reference back() {
      assert(!empty());
      return end()[-1];
    }
    const_reference back() const {
      assert(!empty());
      return end()[-1];
    }
  };
  
  /// SmallVectorTemplateBase<isPodLike = false> - This is where we put method
  /// implementations that are designed to work with non-POD-like T's.
  template <typename T, bool isPodLike>
  class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
  protected:
    SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
  
    static void destroy_range(T *S, T *E) {
      while (S != E) {
        --E;
        E->~T();
      }
    }
  
    /// Use move-assignment to move the range [I, E) onto the
    /// objects starting with "Dest".  This is just <memory>'s
    /// std::move, but not all stdlibs actually provide that.
    template<typename It1, typename It2>
    static It2 move(It1 I, It1 E, It2 Dest) {
      for (; I != E; ++I, ++Dest)
        *Dest = ::std::move(*I);
      return Dest;
    }
  
    /// Use move-assignment to move the range
    /// [I, E) onto the objects ending at "Dest", moving objects
    /// in reverse order.  This is just <algorithm>'s
    /// std::move_backward, but not all stdlibs actually provide that.
    template<typename It1, typename It2>
    static It2 move_backward(It1 I, It1 E, It2 Dest) {
      while (I != E)
        *--Dest = ::std::move(*--E);
      return Dest;
    }
  
    /// Move the range [I, E) into the uninitialized memory starting with "Dest",
    /// constructing elements as needed.
    template<typename It1, typename It2>
    static void uninitialized_move(It1 I, It1 E, It2 Dest) {
      for (; I != E; ++I, ++Dest)
        ::new ((void*) &*Dest) T(::std::move(*I));
    }
  
    /// Copy the range [I, E) onto the uninitialized memory starting with "Dest",
    /// constructing elements as needed.
    template<typename It1, typename It2>
    static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
      std::uninitialized_copy(I, E, Dest);
    }
  
    /// Grow the allocated memory (without initializing new elements), doubling
    /// the size of the allocated memory. Guarantees space for at least one more
    /// element, or MinSize more elements if specified.
    void grow(size_t MinSize = 0);
  
  public:
    void push_back(const T &Elt) {
      if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void*) this->end()) T(Elt);
      this->setEnd(this->end()+1);
    }
  
    void push_back(T &&Elt) {
      if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void*) this->end()) T(::std::move(Elt));
      this->setEnd(this->end()+1);
    }
  
    void pop_back() {
      this->setEnd(this->end()-1);
      this->end()->~T();
    }
  
  #if LLVM_HAS_VARIADIC_TEMPLATES
    template <typename... ArgTypes> void emplace_back(ArgTypes &&... Args) {
      if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      ::new ((void *)this->end()) T(std::forward<ArgTypes>(Args)...);
      this->setEnd(this->end() + 1);
    }
  #else
  private:
    template <typename Constructor> void emplace_back_impl(Constructor construct) {
      if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      construct((void *)this->end());
      this->setEnd(this->end() + 1);
    }
  
  public:
    void emplace_back() {
      emplace_back_impl([](void *Mem) { ::new (Mem) T(); });
    }
    template <typename T1> void emplace_back(T1 &&A1) {
      emplace_back_impl([&](void *Mem) { ::new (Mem) T(std::forward<T1>(A1)); });
    }
    template <typename T1, typename T2> void emplace_back(T1 &&A1, T2 &&A2) {
      emplace_back_impl([&](void *Mem) {
        ::new (Mem) T(std::forward<T1>(A1), std::forward<T2>(A2));
      });
    }
    template <typename T1, typename T2, typename T3>
    void emplace_back(T1 &&A1, T2 &&A2, T3 &&A3) {
      T(std::forward<T1>(A1), std::forward<T2>(A2), std::forward<T3>(A3));
      emplace_back_impl([&](void *Mem) {
        ::new (Mem)
            T(std::forward<T1>(A1), std::forward<T2>(A2), std::forward<T3>(A3));
      });
    }
    template <typename T1, typename T2, typename T3, typename T4>
    void emplace_back(T1 &&A1, T2 &&A2, T3 &&A3, T4 &&A4) {
      emplace_back_impl([&](void *Mem) {
        ::new (Mem) T(std::forward<T1>(A1), std::forward<T2>(A2),
                      std::forward<T3>(A3), std::forward<T4>(A4));
      });
    }
  #endif // LLVM_HAS_VARIADIC_TEMPLATES
  };
  
  // Define this out-of-line to dissuade the C++ compiler from inlining it.
  template <typename T, bool isPodLike>
  void SmallVectorTemplateBase<T, isPodLike>::grow(size_t MinSize) {
    size_t CurCapacity = this->capacity();
    size_t CurSize = this->size();
    // Always grow, even from zero.
    size_t NewCapacity = size_t(NextPowerOf2(CurCapacity+2));
    if (NewCapacity < MinSize)
      NewCapacity = MinSize;
    T *NewElts = static_cast<T*>(malloc(NewCapacity*sizeof(T)));
  
    // Move the elements over.
    this->uninitialized_move(this->begin(), this->end(), NewElts);
  
    // Destroy the original elements.
    destroy_range(this->begin(), this->end());
  
    // If this wasn't grown from the inline copy, deallocate the old space.
    if (!this->isSmall())
      free(this->begin());
  
    this->setEnd(NewElts+CurSize);
    this->BeginX = NewElts;
    this->CapacityX = this->begin()+NewCapacity;
  }
  
  
  /// SmallVectorTemplateBase<isPodLike = true> - This is where we put method
  /// implementations that are designed to work with POD-like T's.
  template <typename T>
  class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
  protected:
    SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
  
    // No need to do a destroy loop for POD's.
    static void destroy_range(T *, T *) {}
  
    /// Use move-assignment to move the range [I, E) onto the
    /// objects starting with "Dest".  For PODs, this is just memcpy.
    template<typename It1, typename It2>
    static It2 move(It1 I, It1 E, It2 Dest) {
      return ::std::copy(I, E, Dest);
    }
  
    /// Use move-assignment to move the range [I, E) onto the objects ending at
    /// "Dest", moving objects in reverse order.
    template<typename It1, typename It2>
    static It2 move_backward(It1 I, It1 E, It2 Dest) {
      return ::std::copy_backward(I, E, Dest);
    }
  
    /// Move the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template<typename It1, typename It2>
    static void uninitialized_move(It1 I, It1 E, It2 Dest) {
      // Just do a copy.
      uninitialized_copy(I, E, Dest);
    }
  
    /// Copy the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template<typename It1, typename It2>
    static void uninitialized_copy(It1 I, It1 E, It2 Dest) {
      // Arbitrary iterator types; just use the basic implementation.
      std::uninitialized_copy(I, E, Dest);
    }
  
    /// Copy the range [I, E) onto the uninitialized memory
    /// starting with "Dest", constructing elements into it as needed.
    template<typename T1, typename T2>
    static void uninitialized_copy(T1 *I, T1 *E, T2 *Dest) {
      // Use memcpy for PODs iterated by pointers (which includes SmallVector
      // iterators): std::uninitialized_copy optimizes to memmove, but we can
      // use memcpy here.
      memcpy(Dest, I, (E-I)*sizeof(T));
    }
  
    /// Double the size of the allocated memory, guaranteeing space for at
    /// least one more element or MinSize if specified.
    void grow(size_t MinSize = 0) {
      this->grow_pod(MinSize*sizeof(T), sizeof(T));
    }
  public:
    void push_back(const T &Elt) {
      if (LLVM_UNLIKELY(this->EndX >= this->CapacityX))
        this->grow();
      memcpy(this->end(), &Elt, sizeof(T));
      this->setEnd(this->end()+1);
    }
  
    void pop_back() {
      this->setEnd(this->end()-1);
    }
  };
  
  
  /// This class consists of common code factored out of the SmallVector class to
  /// reduce code duplication based on the SmallVector 'N' template parameter.
  template <typename T>
  class SmallVectorImpl : public SmallVectorTemplateBase<T, isPodLike<T>::value> {
    typedef SmallVectorTemplateBase<T, isPodLike<T>::value > SuperClass;
  
    SmallVectorImpl(const SmallVectorImpl&) LLVM_DELETED_FUNCTION;
  public:
    typedef typename SuperClass::iterator iterator;
    typedef typename SuperClass::size_type size_type;
  
  protected:
    // Default ctor - Initialize to empty.
    explicit SmallVectorImpl(unsigned N)
      : SmallVectorTemplateBase<T, isPodLike<T>::value>(N*sizeof(T)) {
    }
  
  public:
    ~SmallVectorImpl() {
      // Destroy the constructed elements in the vector.
      this->destroy_range(this->begin(), this->end());
  
      // If this wasn't grown from the inline copy, deallocate the old space.
      if (!this->isSmall())
        free(this->begin());
    }
  
  
    void clear() {
      this->destroy_range(this->begin(), this->end());
      this->EndX = this->BeginX;
    }
  
    void resize(size_type N) {
      if (N < this->size()) {
        this->destroy_range(this->begin()+N, this->end());
        this->setEnd(this->begin()+N);
      } else if (N > this->size()) {
        if (this->capacity() < N)
          this->grow(N);
        for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
          new (&*I) T();
        this->setEnd(this->begin()+N);
      }
    }
  
    void resize(size_type N, const T &NV) {
      if (N < this->size()) {
        this->destroy_range(this->begin()+N, this->end());
        this->setEnd(this->begin()+N);
      } else if (N > this->size()) {
        if (this->capacity() < N)
          this->grow(N);
        std::uninitialized_fill(this->end(), this->begin()+N, NV);
        this->setEnd(this->begin()+N);
      }
    }
  
    void reserve(size_type N) {
      if (this->capacity() < N)
        this->grow(N);
    }
  
    T LLVM_ATTRIBUTE_UNUSED_RESULT pop_back_val() {
      T Result = ::std::move(this->back());
      this->pop_back();
      return Result;
    }
  
    void swap(SmallVectorImpl &RHS);
  
    /// Add the specified range to the end of the SmallVector.
    template<typename in_iter>
    void append(in_iter in_start, in_iter in_end) {
      size_type NumInputs = std::distance(in_start, in_end);
      // Grow allocated space if needed.
      if (NumInputs > size_type(this->capacity_ptr()-this->end()))
        this->grow(this->size()+NumInputs);
  
      // Copy the new elements over.
      // TODO: NEED To compile time dispatch on whether in_iter is a random access
      // iterator to use the fast uninitialized_copy.
      std::uninitialized_copy(in_start, in_end, this->end());
      this->setEnd(this->end() + NumInputs);
    }
  
    /// Add the specified range to the end of the SmallVector.
    void append(size_type NumInputs, const T &Elt) {
      // Grow allocated space if needed.
      if (NumInputs > size_type(this->capacity_ptr()-this->end()))
        this->grow(this->size()+NumInputs);
  
      // Copy the new elements over.
      std::uninitialized_fill_n(this->end(), NumInputs, Elt);
      this->setEnd(this->end() + NumInputs);
    }
  
    void assign(size_type NumElts, const T &Elt) {
      clear();
      if (this->capacity() < NumElts)
        this->grow(NumElts);
      this->setEnd(this->begin()+NumElts);
      std::uninitialized_fill(this->begin(), this->end(), Elt);
    }
  
    iterator erase(iterator I) {
      assert(I >= this->begin() && "Iterator to erase is out of bounds.");
      assert(I < this->end() && "Erasing at past-the-end iterator.");
  
      iterator N = I;
      // Shift all elts down one.
      this->move(I+1, this->end(), I);
      // Drop the last elt.
      this->pop_back();
      return(N);
    }
  
    iterator erase(iterator S, iterator E) {
      assert(S >= this->begin() && "Range to erase is out of bounds.");
      assert(S <= E && "Trying to erase invalid range.");
      assert(E <= this->end() && "Trying to erase past the end.");
  
      iterator N = S;
      // Shift all elts down.
      iterator I = this->move(E, this->end(), S);
      // Drop the last elts.
      this->destroy_range(I, this->end());
      this->setEnd(I);
      return(N);
    }
  
    iterator insert(iterator I, T &&Elt) {
      if (I == this->end()) {  // Important special case for empty vector.
        this->push_back(::std::move(Elt));
        return this->end()-1;
      }
  
      assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      assert(I <= this->end() && "Inserting past the end of the vector.");
  
      if (this->EndX >= this->CapacityX) {
        size_t EltNo = I-this->begin();
        this->grow();
        I = this->begin()+EltNo;
      }
  
      ::new ((void*) this->end()) T(::std::move(this->back()));
      // Push everything else over.
      this->move_backward(I, this->end()-1, this->end());
      this->setEnd(this->end()+1);
  
      // If we just moved the element we're inserting, be sure to update
      // the reference.
      T *EltPtr = &Elt;
      if (I <= EltPtr && EltPtr < this->EndX)
        ++EltPtr;
  
      *I = ::std::move(*EltPtr);
      return I;
    }
  
    iterator insert(iterator I, const T &Elt) {
      if (I == this->end()) {  // Important special case for empty vector.
        this->push_back(Elt);
        return this->end()-1;
      }
  
      assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      assert(I <= this->end() && "Inserting past the end of the vector.");
  
      if (this->EndX >= this->CapacityX) {
        size_t EltNo = I-this->begin();
        this->grow();
        I = this->begin()+EltNo;
      }
      ::new ((void*) this->end()) T(std::move(this->back()));
      // Push everything else over.
      this->move_backward(I, this->end()-1, this->end());
      this->setEnd(this->end()+1);
  
      // If we just moved the element we're inserting, be sure to update
      // the reference.
      const T *EltPtr = &Elt;
      if (I <= EltPtr && EltPtr < this->EndX)
        ++EltPtr;
  
      *I = *EltPtr;
      return I;
    }
  
    iterator insert(iterator I, size_type NumToInsert, const T &Elt) {
      // Convert iterator to elt# to avoid invalidating iterator when we reserve()
      size_t InsertElt = I - this->begin();
  
      if (I == this->end()) {  // Important special case for empty vector.
        append(NumToInsert, Elt);
        return this->begin()+InsertElt;
      }
  
      assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      assert(I <= this->end() && "Inserting past the end of the vector.");
  
      // Ensure there is enough space.
      reserve(this->size() + NumToInsert);
  
      // Uninvalidate the iterator.
      I = this->begin()+InsertElt;
  
      // If there are more elements between the insertion point and the end of the
      // range than there are being inserted, we can use a simple approach to
      // insertion.  Since we already reserved space, we know that this won't
      // reallocate the vector.
      if (size_t(this->end()-I) >= NumToInsert) {
        T *OldEnd = this->end();
        append(std::move_iterator<iterator>(this->end() - NumToInsert),
               std::move_iterator<iterator>(this->end()));
  
        // Copy the existing elements that get replaced.
        this->move_backward(I, OldEnd-NumToInsert, OldEnd);
  
        std::fill_n(I, NumToInsert, Elt);
        return I;
      }
  
      // Otherwise, we're inserting more elements than exist already, and we're
      // not inserting at the end.
  
      // Move over the elements that we're about to overwrite.
      T *OldEnd = this->end();
      this->setEnd(this->end() + NumToInsert);
      size_t NumOverwritten = OldEnd-I;
      this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);
  
      // Replace the overwritten part.
      std::fill_n(I, NumOverwritten, Elt);
  
      // Insert the non-overwritten middle part.
      std::uninitialized_fill_n(OldEnd, NumToInsert-NumOverwritten, Elt);
      return I;
    }
  
    template<typename ItTy>
    iterator insert(iterator I, ItTy From, ItTy To) {
      // Convert iterator to elt# to avoid invalidating iterator when we reserve()
      size_t InsertElt = I - this->begin();
  
      if (I == this->end()) {  // Important special case for empty vector.
        append(From, To);
        return this->begin()+InsertElt;
      }
  
      assert(I >= this->begin() && "Insertion iterator is out of bounds.");
      assert(I <= this->end() && "Inserting past the end of the vector.");
  
      size_t NumToInsert = std::distance(From, To);
  
      // Ensure there is enough space.
      reserve(this->size() + NumToInsert);
  
      // Uninvalidate the iterator.
      I = this->begin()+InsertElt;
  
      // If there are more elements between the insertion point and the end of the
      // range than there are being inserted, we can use a simple approach to
      // insertion.  Since we already reserved space, we know that this won't
      // reallocate the vector.
      if (size_t(this->end()-I) >= NumToInsert) {
        T *OldEnd = this->end();
        append(std::move_iterator<iterator>(this->end() - NumToInsert),
               std::move_iterator<iterator>(this->end()));
  
        // Copy the existing elements that get replaced.
        this->move_backward(I, OldEnd-NumToInsert, OldEnd);
  
        std::copy(From, To, I);
        return I;
      }
  
      // Otherwise, we're inserting more elements than exist already, and we're
      // not inserting at the end.
  
      // Move over the elements that we're about to overwrite.
      T *OldEnd = this->end();
      this->setEnd(this->end() + NumToInsert);
      size_t NumOverwritten = OldEnd-I;
      this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);
  
      // Replace the overwritten part.
      for (T *J = I; NumOverwritten > 0; --NumOverwritten) {
        *J = *From;
        ++J; ++From;
      }
  
      // Insert the non-overwritten middle part.
      this->uninitialized_copy(From, To, OldEnd);
      return I;
    }
  
    SmallVectorImpl &operator=(const SmallVectorImpl &RHS);
  
    SmallVectorImpl &operator=(SmallVectorImpl &&RHS);
  
    bool operator==(const SmallVectorImpl &RHS) const {
      if (this->size() != RHS.size()) return false;
      return std::equal(this->begin(), this->end(), RHS.begin());
    }
    bool operator!=(const SmallVectorImpl &RHS) const {
      return !(*this == RHS);
    }
  
    bool operator<(const SmallVectorImpl &RHS) const {
      return std::lexicographical_compare(this->begin(), this->end(),
                                          RHS.begin(), RHS.end());
    }
  
    /// Set the array size to \p N, which the current array must have enough
    /// capacity for.
    ///
    /// This does not construct or destroy any elements in the vector.
    ///
    /// Clients can use this in conjunction with capacity() to write past the end
    /// of the buffer when they know that more elements are available, and only
    /// update the size later. This avoids the cost of value initializing elements
    /// which will only be overwritten.
    void set_size(size_type N) {
      assert(N <= this->capacity());
      this->setEnd(this->begin() + N);
    }
  };
  
  
  template <typename T>
  void SmallVectorImpl<T>::swap(SmallVectorImpl<T> &RHS) {
    if (this == &RHS) return;
  
    // We can only avoid copying elements if neither vector is small.
    if (!this->isSmall() && !RHS.isSmall()) {
      std::swap(this->BeginX, RHS.BeginX);
      std::swap(this->EndX, RHS.EndX);
      std::swap(this->CapacityX, RHS.CapacityX);
      return;
    }
    if (RHS.size() > this->capacity())
      this->grow(RHS.size());
    if (this->size() > RHS.capacity())
      RHS.grow(this->size());
  
    // Swap the shared elements.
    size_t NumShared = this->size();
    if (NumShared > RHS.size()) NumShared = RHS.size();
    for (size_type i = 0; i != NumShared; ++i)
      std::swap((*this)[i], RHS[i]);
  
    // Copy over the extra elts.
    if (this->size() > RHS.size()) {
      size_t EltDiff = this->size() - RHS.size();
      this->uninitialized_copy(this->begin()+NumShared, this->end(), RHS.end());
      RHS.setEnd(RHS.end()+EltDiff);
      this->destroy_range(this->begin()+NumShared, this->end());
      this->setEnd(this->begin()+NumShared);
    } else if (RHS.size() > this->size()) {
      size_t EltDiff = RHS.size() - this->size();
      this->uninitialized_copy(RHS.begin()+NumShared, RHS.end(), this->end());
      this->setEnd(this->end() + EltDiff);
      this->destroy_range(RHS.begin()+NumShared, RHS.end());
      RHS.setEnd(RHS.begin()+NumShared);
    }
  }
  
  template <typename T>
  SmallVectorImpl<T> &SmallVectorImpl<T>::
    operator=(const SmallVectorImpl<T> &RHS) {
    // Avoid self-assignment.
    if (this == &RHS) return *this;
  
    // If we already have sufficient space, assign the common elements, then
    // destroy any excess.
    size_t RHSSize = RHS.size();
    size_t CurSize = this->size();
    if (CurSize >= RHSSize) {
      // Assign common elements.
      iterator NewEnd;
      if (RHSSize)
        NewEnd = std::copy(RHS.begin(), RHS.begin()+RHSSize, this->begin());
      else
        NewEnd = this->begin();
  
      // Destroy excess elements.
      this->destroy_range(NewEnd, this->end());
  
      // Trim.
      this->setEnd(NewEnd);
      return *this;
    }
  
    // If we have to grow to have enough elements, destroy the current elements.
    // This allows us to avoid copying them during the grow.
    // FIXME: don't do this if they're efficiently moveable.
    if (this->capacity() < RHSSize) {
      // Destroy current elements.
      this->destroy_range(this->begin(), this->end());
      this->setEnd(this->begin());
      CurSize = 0;
      this->grow(RHSSize);
    } else if (CurSize) {
      // Otherwise, use assignment for the already-constructed elements.
      std::copy(RHS.begin(), RHS.begin()+CurSize, this->begin());
    }
  
    // Copy construct the new elements in place.
    this->uninitialized_copy(RHS.begin()+CurSize, RHS.end(),
                             this->begin()+CurSize);
  
    // Set end.
    this->setEnd(this->begin()+RHSSize);
    return *this;
  }
  
  template <typename T>
  SmallVectorImpl<T> &SmallVectorImpl<T>::operator=(SmallVectorImpl<T> &&RHS) {
    // Avoid self-assignment.
    if (this == &RHS) return *this;
  
    // If the RHS isn't small, clear this vector and then steal its buffer.
    if (!RHS.isSmall()) {
      this->destroy_range(this->begin(), this->end());
      if (!this->isSmall()) free(this->begin());
      this->BeginX = RHS.BeginX;
      this->EndX = RHS.EndX;
      this->CapacityX = RHS.CapacityX;
      RHS.resetToSmall();
      return *this;
    }
  
    // If we already have sufficient space, assign the common elements, then
    // destroy any excess.
    size_t RHSSize = RHS.size();
    size_t CurSize = this->size();
    if (CurSize >= RHSSize) {
      // Assign common elements.
      iterator NewEnd = this->begin();
      if (RHSSize)
        NewEnd = this->move(RHS.begin(), RHS.end(), NewEnd);
  
      // Destroy excess elements and trim the bounds.
      this->destroy_range(NewEnd, this->end());
      this->setEnd(NewEnd);
  
      // Clear the RHS.
      RHS.clear();
  
      return *this;
    }
  
    // If we have to grow to have enough elements, destroy the current elements.
    // This allows us to avoid copying them during the grow.
    // FIXME: this may not actually make any sense if we can efficiently move
    // elements.
    if (this->capacity() < RHSSize) {
      // Destroy current elements.
      this->destroy_range(this->begin(), this->end());
      this->setEnd(this->begin());
      CurSize = 0;
      this->grow(RHSSize);
    } else if (CurSize) {
      // Otherwise, use assignment for the already-constructed elements.
      this->move(RHS.begin(), RHS.begin()+CurSize, this->begin());
    }
  
    // Move-construct the new elements in place.
    this->uninitialized_move(RHS.begin()+CurSize, RHS.end(),
                             this->begin()+CurSize);
  
    // Set end.
    this->setEnd(this->begin()+RHSSize);
  
    RHS.clear();
    return *this;
  }
  
  /// Storage for the SmallVector elements which aren't contained in
  /// SmallVectorTemplateCommon. There are 'N-1' elements here. The remaining '1'
  /// element is in the base class. This is specialized for the N=1 and N=0 cases
  /// to avoid allocating unnecessary storage.
  template <typename T, unsigned N>
  struct SmallVectorStorage {
    typename SmallVectorTemplateCommon<T>::U InlineElts[N - 1];
  };
  template <typename T> struct SmallVectorStorage<T, 1> {};
  template <typename T> struct SmallVectorStorage<T, 0> {};
  
  /// This is a 'vector' (really, a variable-sized array), optimized
  /// for the case when the array is small.  It contains some number of elements
  /// in-place, which allows it to avoid heap allocation when the actual number of
  /// elements is below that threshold.  This allows normal "small" cases to be
  /// fast without losing generality for large inputs.
  ///
  /// Note that this does not attempt to be exception safe.
  ///
  template <typename T, unsigned N>
  class SmallVector : public SmallVectorImpl<T> {
    /// Inline space for elements which aren't stored in the base class.
    SmallVectorStorage<T, N> Storage;
  public:
    SmallVector() : SmallVectorImpl<T>(N) {
    }
  
    explicit SmallVector(size_t Size, const T &Value = T())
      : SmallVectorImpl<T>(N) {
      this->assign(Size, Value);
    }
  
    template<typename ItTy>
    SmallVector(ItTy S, ItTy E) : SmallVectorImpl<T>(N) {
      this->append(S, E);
    }
  
    template <typename RangeTy>
    explicit SmallVector(const llvm::iterator_range<RangeTy> R)
        : SmallVectorImpl<T>(N) {
      this->append(R.begin(), R.end());
    }
  
    SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(N) {
      if (!RHS.empty())
        SmallVectorImpl<T>::operator=(RHS);
    }
  
    const SmallVector &operator=(const SmallVector &RHS) {
      SmallVectorImpl<T>::operator=(RHS);
      return *this;
    }
  
    SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(N) {
      if (!RHS.empty())
        SmallVectorImpl<T>::operator=(::std::move(RHS));
    }
  
    const SmallVector &operator=(SmallVector &&RHS) {
      SmallVectorImpl<T>::operator=(::std::move(RHS));
      return *this;
    }
  };
  
  template<typename T, unsigned N>
  static inline size_t capacity_in_bytes(const SmallVector<T, N> &X) {
    return X.capacity_in_bytes();
  }
  
  } // End llvm namespace
  
  namespace std {
    /// Implement std::swap in terms of SmallVector swap.
    template<typename T>
    inline void
    swap(llvm::SmallVectorImpl<T> &LHS, llvm::SmallVectorImpl<T> &RHS) {
      LHS.swap(RHS);
    }
  
    /// Implement std::swap in terms of SmallVector swap.
    template<typename T, unsigned N>
    inline void
    swap(llvm::SmallVector<T, N> &LHS, llvm::SmallVector<T, N> &RHS) {
      LHS.swap(RHS);
    }
  }
  
  #endif
  