/*
 R *CC-Project

 Copyright (C) 2026 Richard Qin

 This file is part of RCC-Project.

 RCC-Project is free software; you can redistribute it and/or modify it under
 the terms of the GNU General Public License as published by the Free
 Software Foundation; either version 3 of the License, or (at your option) any
 later version.

 RCC-Project is distributed in the hope that it will be useful, but WITHOUT ANY
 WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
 PARTICULAR PURPOSE. See the GNU General Public License for more details.

 You should have received a copy of the GNU General Public License along with
 RCC-Project; see the file COPYING. If not see
 <http://www.gnu.org/licenses/>.
 */

//===- rcc/ADT/SmallVector.h - 'Normally small' vectors --------*- 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
//
//===----------------------------------------------------------------------===//
///
/// \file
/// This file defines the SmallVector class.
///
//===----------------------------------------------------------------------===//

#ifndef RCC_ADT_SMALLVECTOR_H
#define RCC_ADT_SMALLVECTOR_H

#include "CoreLib/Compiler/Compiler.h"
#include <algorithm>
#include <cassert>
#include <cstddef>
#include <cstdint>
#include <cstdlib>
#include <cstring>
#include <functional>
#include <initializer_list>
#include <iterator>
#include <limits>
#include <memory>
#include <new>
#include <ranges>
#include <type_traits>
#include <utility>

namespace rcc
{

template <typename T> class ArrayRef;

template <typename IteratorT> class iterator_range;

template <class Iterator, class Tag>
using HasIteratorTag = std::is_convertible<
    typename std::iterator_traits<Iterator>::iterator_category, Tag>;

template <class Iterator>
using EnableIfConvertibleToInputIterator =
    std::enable_if_t<HasIteratorTag<Iterator, std::input_iterator_tag>::value>;

/// This is all the stuff common to all SmallVectors.
///
/// The template parameter specifies the type which should be used to hold the
/// Size and Capacity of the SmallVector, so it can be adjusted.
/// Using 32 bit size is desirable to shrink the size of the SmallVector.
/// Using 64 bit size is desirable for cases like SmallVector<char>, where a
/// 32 bit size would limit the vector to ~4GB. SmallVectors are used for
/// buffering bitcode output - which can exceed 4GB.
template <class Size_T> class SmallVectorBase
{
protected:
  void *BeginX;
  Size_T Size = 0, Capacity;

  /// The maximum value of the Size_T used.
  static constexpr size_t
  SizeTypeMax ()
  {
    return std::numeric_limits<Size_T>::max ();
  }

  SmallVectorBase () = delete;
  SmallVectorBase (void *FirstEl, size_t TotalCapacity)
      : BeginX (FirstEl), Capacity (static_cast<Size_T> (TotalCapacity))
  {
  }

  /// This is a helper for \a grow() that's out of line to reduce code
  /// duplication.  This function will report a fatal error if it can't grow at
  /// least to \p MinSize.
  RCC_ABI void *
  mallocForGrow (void *FirstEl, size_t MinSize, size_t TSize,
                 size_t &NewCapacity);

  /// 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.
  /// This function will report a fatal error if it cannot increase capacity.
  RCC_ABI void
  grow_pod (void *FirstEl, size_t MinSize, size_t TSize);

public:
  size_t
  size () const
  {
    return Size;
  }
  size_t
  capacity () const
  {
    return Capacity;
  }

  [[nodiscard]] bool
  empty () const
  {
    return !Size;
  }

protected:
  /// 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.
  void
  set_size (size_t N)
  {
    assert (N <= capacity ()); // implies no overflow in assignment
    Size = static_cast<Size_T> (N);
  }

  /// Set the array data pointer to \p Begin and capacity to \p N.
  ///
  /// This does not construct or destroy any elements in the vector.
  //  This does not clean up any existing allocation.
  void
  set_allocation_range (void *Begin, size_t N)
  {
    assert (N <= SizeTypeMax ());
    BeginX = Begin;
    Capacity = static_cast<Size_T> (N);
  }
};

template <class T>
using SmallVectorSizeType =
    std::conditional_t<sizeof (T) < 4 && sizeof (void *) >= 8, uint64_t,
                       uint32_t>;

/// Figure out the offset of the first element.
template <class T, typename = void> struct SmallVectorAlignmentAndSize
{
  alignas (SmallVectorBase<SmallVectorSizeType<T>>) char Base[sizeof (
      SmallVectorBase<SmallVectorSizeType<T>>)];
  alignas (T) char FirstEl[sizeof (T)];
};

/// 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<SmallVectorSizeType<T>>
{
  using Base = SmallVectorBase<SmallVectorSizeType<T>>;

protected:
  /// Find the address of the first element.  For this pointer math to be valid
  /// with small-size of 0 for T with lots of alignment, it's important that
  /// SmallVectorStorage is properly-aligned even for small-size of 0.
  void *
  getFirstEl () const
  {
    return const_cast<void *> (reinterpret_cast<const void *> (
        reinterpret_cast<const char *> (this) +
        offsetof (SmallVectorAlignmentAndSize<T>, FirstEl)));
  }
  // Space after 'FirstEl' is clobbered, do not add any instance vars after it.

  SmallVectorTemplateCommon (size_t SizeArg) : Base (getFirstEl (), SizeArg)
  {
  }

  void
  grow_pod (size_t MinSize, size_t TSize)
  {
    Base::grow_pod (getFirstEl (), MinSize, TSize);
  }

  /// Return true if this is a smallvector which has not had dynamic
  /// memory allocated for it.
  bool
  isSmall () const
  {
    return this->BeginX == getFirstEl ();
  }

  /// Put this vector in a state of being small.
  void
  resetToSmall ()
  {
    this->BeginX = getFirstEl ();
    // The inline capacity is unknown here. SmallVector restores it when moving
    // from the same concrete type; moves through SmallVectorImpl leave it at 0.
    this->Size = this->Capacity = 0;
  }

  /// Return true if V is an internal reference to the given range.
  bool
  isReferenceToRange (const void *V, const void *First, const void *Last) const
  {
    // Use std::less to avoid UB.
    std::less<> LessThan;
    return !LessThan (V, First) && LessThan (V, Last);
  }

  /// Return true if V is an internal reference to this vector.
  bool
  isReferenceToStorage (const void *V) const
  {
    return isReferenceToRange (V, this->begin (), this->end ());
  }

  /// Return true if First and Last form a valid (possibly empty) range in this
  /// vector's storage.
  bool
  isRangeInStorage (const void *First, const void *Last) const
  {
    // Use std::less to avoid UB.
    std::less<> LessThan;
    return !LessThan (First, this->begin ()) && !LessThan (Last, First) &&
           !LessThan (this->end (), Last);
  }

  /// Return true unless Elt will be invalidated by resizing the vector to
  /// NewSize.
  bool
  isSafeToReferenceAfterResize (const void *Elt, size_t NewSize)
  {
    // Past the end.
    if (RCC_LIKELY (!isReferenceToStorage (Elt)))
    {
      return true;
    }

    // Return false if Elt will be destroyed by shrinking.
    if (NewSize <= this->size ())
    {
      return Elt < this->begin () + NewSize;
    }

    // Return false if we need to grow.
    return NewSize <= this->capacity ();
  }

  /// Check whether Elt will be invalidated by resizing the vector to NewSize.
  void
  assertSafeToReferenceAfterResize (const void *Elt, size_t NewSize)
  {
    assert (isSafeToReferenceAfterResize (Elt, NewSize) &&
            "Attempting to reference an element of the vector in an operation "
            "that invalidates it");
  }

  /// Check whether Elt will be invalidated by increasing the size of the
  /// vector by N.
  void
  assertSafeToAdd (const void *Elt, size_t N = 1)
  {
    this->assertSafeToReferenceAfterResize (Elt, this->size () + N);
  }

  /// Check whether any part of the range will be invalidated by clearing.
  template <class ItTy>
  void
  assertSafeToReferenceAfterClear (ItTy From, ItTy To)
  {
    if constexpr (std::is_pointer_v<ItTy> &&
                  std::is_same_v<
                      std::remove_const_t<std::remove_pointer_t<ItTy>>,
                      std::remove_const_t<T>>)
    {
      if (From == To)
      {
        return;
      }
      this->assertSafeToReferenceAfterResize (From, 0);
      this->assertSafeToReferenceAfterResize (To - 1, 0);
    }
    (void)From;
    (void)To;
  }

  /// Check whether any part of the range will be invalidated by growing.
  template <class ItTy>
  void
  assertSafeToAddRange (ItTy From, ItTy To)
  {
    if constexpr (std::is_pointer_v<ItTy> &&
                  std::is_same_v<std::remove_cv_t<std::remove_pointer_t<ItTy>>,
                                 T>)
    {
      if (From == To)
      {
        return;
      }
      this->assertSafeToAdd (From, To - From);
      this->assertSafeToAdd (To - 1, To - From);
    }
    (void)From;
    (void)To;
  }

  /// Reserve enough space to add one element, and return the updated element
  /// pointer in case it was a reference to the storage.
  template <class U>
  static const T *
  reserveForParamAndGetAddressImpl (U *This, const T &Elt, size_t N)
  {
    size_t NewSize = This->size () + N;
    if (RCC_LIKELY (NewSize <= This->capacity ()))
    {
      return &Elt;
    }

    bool ReferencesStorage = false;
    int64_t Index = -1;
    if (!U::TakesParamByValue)
    {
      if (RCC_UNLIKELY (This->isReferenceToStorage (&Elt)))
      {
        ReferencesStorage = true;
        Index = &Elt - This->begin ();
      }
    }
    This->grow (NewSize);
    return ReferencesStorage ? This->begin () + Index : &Elt;
  }

public:
  using size_type = size_t;
  using difference_type = ptrdiff_t;
  using value_type = T;
  using iterator = T *;
  using const_iterator = const T *;

  using const_reverse_iterator = std::reverse_iterator<const_iterator>;
  using reverse_iterator = std::reverse_iterator<iterator>;

  using reference = T &;
  using const_reference = const T &;
  using pointer = T *;
  using const_pointer = const T *;

  using Base::capacity;
  using Base::empty;
  using Base::size;

  // forward iterator creation methods.
  iterator
  begin ()
  {
    return (iterator)this->BeginX;
  }
  const_iterator
  begin () const
  {
    return (const_iterator)this->BeginX;
  }
  iterator
  end ()
  {
    return begin () + size ();
  }
  const_iterator
  end () const
  {
    return begin () + size ();
  }

  // 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_in_bytes () const
  {
    return size () * sizeof (T);
  }
  size_type
  max_size () const
  {
    return std::min (this->SizeTypeMax (), size_type (-1) / sizeof (T));
  }

  size_t
  capacity_in_bytes () const
  {
    return capacity () * sizeof (T);
  }

  /// 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<TriviallyCopyable = false> - This is where we put
/// method implementations that are designed to work with non-trivial T's.
///
/// We approximate is_trivially_copyable with trivial move/copy construction and
/// trivial destruction. While the standard doesn't specify that you're allowed
/// copy these types with memcpy, there is no way for the type to observe this.
/// This catches the important case of std::pair<POD, POD>, which is not
/// trivially assignable.
template <typename T, bool = (std::is_trivially_copy_constructible<T>::value) &&
                             (std::is_trivially_move_constructible<T>::value) &&
                             std::is_trivially_destructible<T>::value>
class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T>
{
  friend class SmallVectorTemplateCommon<T>;

protected:
  static constexpr bool TakesParamByValue = false;
  using ValueParamT = const T &;

  SmallVectorTemplateBase (size_t SizeArg)
      : SmallVectorTemplateCommon<T> (SizeArg)
  {
  }

  static void
  destroy_range (T *S, T *E)
  {
    while (S != E)
    {
      --E;
      E->~T ();
    }
  }

  /// 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)
  {
    std::uninitialized_move (I, E, Dest);
  }

  /// 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);

  /// Create a new allocation big enough for \p MinSize and pass back its size
  /// in \p NewCapacity. This is the first section of \a grow().
  T *
  mallocForGrow (size_t MinSize, size_t &NewCapacity);

  /// Move existing elements over to the new allocation \p NewElts, the middle
  /// section of \a grow().
  void
  moveElementsForGrow (T *NewElts);

  /// Transfer ownership of the allocation, finishing up \a grow().
  void
  takeAllocationForGrow (T *NewElts, size_t NewCapacity);

  /// Reserve enough space to add one element, and return the updated element
  /// pointer in case it was a reference to the storage.
  const T *
  reserveForParamAndGetAddress (const T &Elt, size_t N = 1)
  {
    return this->reserveForParamAndGetAddressImpl (this, Elt, N);
  }

  /// Reserve enough space to add one element, and return the updated element
  /// pointer in case it was a reference to the storage.
  T *
  reserveForParamAndGetAddress (T &Elt, size_t N = 1)
  {
    return const_cast<T *> (
        this->reserveForParamAndGetAddressImpl (this, Elt, N));
  }

  static T &&
  forward_value_param (T &&V)
  {
    return std::move (V);
  }
  static const T &
  forward_value_param (const T &V)
  {
    return V;
  }

  void
  growAndAssign (size_t NumElts, const T &Elt)
  {
    // Grow manually in case Elt is an internal reference.
    size_t NewCapacity;
    T *NewElts = mallocForGrow (NumElts, NewCapacity);
    std::uninitialized_fill_n (NewElts, NumElts, Elt);
    this->destroy_range (this->begin (), this->end ());
    takeAllocationForGrow (NewElts, NewCapacity);
    this->set_size (NumElts);
  }

  template <typename... ArgTypes>
  T &
  growAndEmplaceBack (ArgTypes &&...Args)
  {
    // Grow manually in case one of Args is an internal reference.
    size_t NewCapacity;
    T *NewElts = mallocForGrow (0, NewCapacity);
    ::new ((void *)(NewElts + this->size ()))
        T (std::forward<ArgTypes> (Args)...);
    moveElementsForGrow (NewElts);
    takeAllocationForGrow (NewElts, NewCapacity);
    this->set_size (this->size () + 1);
    return this->back ();
  }

public:
  void
  push_back (const T &Elt)
  {
    const T *EltPtr = reserveForParamAndGetAddress (Elt);
    ::new ((void *)this->end ()) T (*EltPtr);
    this->set_size (this->size () + 1);
  }

  void
  push_back (T &&Elt)
  {
    T *EltPtr = reserveForParamAndGetAddress (Elt);
    ::new ((void *)this->end ()) T (::std::move (*EltPtr));
    this->set_size (this->size () + 1);
  }

  void
  pop_back ()
  {
    this->set_size (this->size () - 1);
    this->end ()->~T ();
  }
};

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void
SmallVectorTemplateBase<T, TriviallyCopyable>::grow (size_t MinSize)
{
  size_t NewCapacity;
  T *NewElts = mallocForGrow (MinSize, NewCapacity);
  moveElementsForGrow (NewElts);
  takeAllocationForGrow (NewElts, NewCapacity);
}

template <typename T, bool TriviallyCopyable>
T *
SmallVectorTemplateBase<T, TriviallyCopyable>::mallocForGrow (
    size_t MinSize, size_t &NewCapacity)
{
  return static_cast<T *> (
      SmallVectorBase<SmallVectorSizeType<T>>::mallocForGrow (
          this->getFirstEl (), MinSize, sizeof (T), NewCapacity));
}

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void
SmallVectorTemplateBase<T, TriviallyCopyable>::moveElementsForGrow (T *NewElts)
{
  // Move the elements over.
  this->uninitialized_move (this->begin (), this->end (), NewElts);

  // Destroy the original elements.
  destroy_range (this->begin (), this->end ());
}

// Define this out-of-line to dissuade the C++ compiler from inlining it.
template <typename T, bool TriviallyCopyable>
void
SmallVectorTemplateBase<T, TriviallyCopyable>::takeAllocationForGrow (
    T *NewElts, size_t NewCapacity)
{
  // If this wasn't grown from the inline copy, deallocate the old space.
  if (!this->isSmall ())
  {
    free (this->begin ());
  }

  this->set_allocation_range (NewElts, NewCapacity);
}

/// SmallVectorTemplateBase<TriviallyCopyable = true> - This is where we put
/// method implementations that are designed to work with trivially copyable
/// T's. This allows using memcpy in place of copy/move construction and
/// skipping destruction.
template <typename T>
class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T>
{
  friend class SmallVectorTemplateCommon<T>;

protected:
  /// True if it's cheap enough to take parameters by value. Doing so avoids
  /// overhead related to mitigations for reference invalidation.
  static constexpr bool TakesParamByValue = sizeof (T) <= 2 * sizeof (void *);

  /// Either const T& or T, depending on whether it's cheap enough to take
  /// parameters by value.
  using ValueParamT = std::conditional_t<TakesParamByValue, T, const T &>;

  SmallVectorTemplateBase (size_t SizeArg)
      : SmallVectorTemplateCommon<T> (SizeArg)
  {
  }

  // No need to do a destroy loop for POD's.
  static void
  destroy_range (T *, T *)
  {
  }

  /// 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)
  {
    if constexpr (std::is_pointer_v<It1> && std::is_pointer_v<It2> &&
                  std::is_same_v<
                      std::remove_const_t<std::remove_pointer_t<It1>>,
                      std::remove_pointer_t<It2>>)
    {
      // Use memcpy for PODs iterated by pointers (which includes SmallVector
      // iterators): std::uninitialized_copy optimizes to memmove, but we can
      // use memcpy here. Note that I and E are iterators and thus might be
      // invalid for memcpy if they are equal.
      if (I != E)
      {
        std::memcpy (reinterpret_cast<void *> (Dest), I, (E - I) * sizeof (T));
      }
    }
    else
    {
      // Arbitrary iterator types; just use the basic implementation.
      std::uninitialized_copy (I, E, Dest);
    }
  }

  /// 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));
  }

  /// Reserve enough space to add one element, and return the updated element
  /// pointer in case it was a reference to the storage.
  const T *
  reserveForParamAndGetAddress (const T &Elt, size_t N = 1)
  {
    return this->reserveForParamAndGetAddressImpl (this, Elt, N);
  }

  /// Reserve enough space to add one element, and return the updated element
  /// pointer in case it was a reference to the storage.
  T *
  reserveForParamAndGetAddress (T &Elt, size_t N = 1)
  {
    return const_cast<T *> (
        this->reserveForParamAndGetAddressImpl (this, Elt, N));
  }

  /// Copy \p V or return a reference, depending on \a ValueParamT.
  static ValueParamT
  forward_value_param (ValueParamT V)
  {
    return V;
  }

  void
  growAndAssign (size_t NumElts, T Elt)
  {
    // Elt has been copied in case it's an internal reference, side-stepping
    // reference invalidation problems without losing the realloc optimization.
    this->set_size (0);
    this->grow (NumElts);
    std::uninitialized_fill_n (this->begin (), NumElts, Elt);
    this->set_size (NumElts);
  }

  template <typename... ArgTypes>
  T &
  growAndEmplaceBack (ArgTypes &&...Args)
  {
    // Use push_back with a copy in case Args has an internal reference,
    // side-stepping reference invalidation problems without losing the realloc
    // optimization.
    push_back (T (std::forward<ArgTypes> (Args)...));
    return this->back ();
  }

  // Out-of-line slow path so the inline push_back needs no callee-saved
  // registers or stack frame on its hot path.
  RCC_ATTRIBUTE_NOINLINE void
  growAndPushBack (ValueParamT Elt)
  {
    // Copy in case Elt is an internal reference invalidated by grow.
    T Tmp = Elt;
    this->grow (this->size () + 1);
    std::memcpy (reinterpret_cast<void *> (this->end ()), &Tmp, sizeof (T));
    this->set_size (this->size () + 1);
  }

public:
  void
  push_back (ValueParamT Elt)
  {
    if (RCC_UNLIKELY (this->size () >= this->capacity ()))
    {
      return growAndPushBack (Elt);
    }
    std::memcpy (reinterpret_cast<void *> (this->end ()), &Elt, sizeof (T));
    this->set_size (this->size () + 1);
  }

  void
  pop_back ()
  {
    this->set_size (this->size () - 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>
{
  using SuperClass = SmallVectorTemplateBase<T>;

public:
  using iterator = typename SuperClass::iterator;
  using const_iterator = typename SuperClass::const_iterator;
  using reference = typename SuperClass::reference;
  using size_type = typename SuperClass::size_type;

protected:
  using SmallVectorTemplateBase<T>::TakesParamByValue;
  using ValueParamT = typename SuperClass::ValueParamT;

  // Default ctor - Initialize to empty.
  explicit SmallVectorImpl (unsigned N) : SmallVectorTemplateBase<T> (N)
  {
  }

  void
  assignRemote (SmallVectorImpl &&RHS)
  {
    this->destroy_range (this->begin (), this->end ());
    if (!this->isSmall ())
    {
      free (this->begin ());
    }
    this->BeginX = RHS.BeginX;
    this->Size = RHS.Size;
    this->Capacity = RHS.Capacity;
    RHS.resetToSmall ();
  }

  void
  moveConstructFrom (SmallVectorImpl &&RHS)
  {
    assert (this->empty () && "move construction requires an empty vector");
    if (!RHS.isSmall ())
    {
      assignRemote (std::move (RHS));
      return;
    }

    // Construct inline elements directly instead of requiring T to be move
    // assignable through the general move-assignment implementation.
    size_type RHSSize = RHS.size ();
    reserve (RHSSize);
    this->uninitialized_move (RHS.begin (), RHS.end (), this->begin ());
    this->set_size (RHSSize);
    RHS.clear ();
  }

  ~SmallVectorImpl ()
  {
    // Subclass has already destructed this vector's elements.
    // If this wasn't grown from the inline copy, deallocate the old space.
    if (!this->isSmall ())
    {
      free (this->begin ());
    }
  }

public:
  SmallVectorImpl (const SmallVectorImpl &) = delete;

  void
  clear ()
  {
    this->destroy_range (this->begin (), this->end ());
    this->Size = 0;
  }

private:
  // Make set_size() private to avoid misuse in subclasses.
  using SuperClass::set_size;

  template <bool ForOverwrite>
  void
  resizeImpl (size_type N)
  {
    if (N == this->size ())
    {
      return;
    }

    if (N < this->size ())
    {
      this->truncate (N);
      return;
    }

    this->reserve (N);
    for (auto I = this->end (), E = this->begin () + N; I != E; ++I)
    {
      if (ForOverwrite)
      {
        new (&*I) T;
      }
      else
      {
        new (&*I) T ();
      }
    }
    this->set_size (N);
  }

public:
  void
  resize (size_type N)
  {
    resizeImpl<false> (N);
  }

  /// Like resize, but \ref T is POD, the new values won't be initialized.
  void
  resize_for_overwrite (size_type N)
  {
    resizeImpl<true> (N);
  }

  /// Like resize, but requires that \p N is less than \a size().
  void
  truncate (size_type N)
  {
    assert (this->size () >= N && "Cannot increase size with truncate");
    this->destroy_range (this->begin () + N, this->end ());
    this->set_size (N);
  }

  void
  resize (size_type N, ValueParamT NV)
  {
    if (N == this->size ())
    {
      return;
    }

    if (N < this->size ())
    {
      this->truncate (N);
      return;
    }

    // N > this->size(). Defer to append.
    this->append (N - this->size (), NV);
  }

  void
  reserve (size_type N)
  {
    if (this->capacity () < N)
    {
      this->grow (N);
    }
  }

  void
  pop_back_n (size_type NumItems)
  {
    assert (this->size () >= NumItems);
    truncate (this->size () - NumItems);
  }

  [[nodiscard]] T
  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 ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
  void
  append (ItTy in_start, ItTy in_end)
  {
    if constexpr (HasIteratorTag<ItTy, std::forward_iterator_tag>::value)
    {
      this->assertSafeToAddRange (in_start, in_end);
      size_type NumInputs = std::distance (in_start, in_end);
      this->reserve (this->size () + NumInputs);
      this->uninitialized_copy (in_start, in_end, this->end ());
      this->set_size (this->size () + NumInputs);
    }
    else
    {
      // Input iterator, we can't know ahead how many elements we'll add.
      for (; in_start != in_end; ++in_start)
      {
        this->emplace_back (*in_start);
      }
    }
  }

  /// Append \p NumInputs copies of \p Elt to the end.
  void
  append (size_type NumInputs, ValueParamT Elt)
  {
    const T *EltPtr = this->reserveForParamAndGetAddress (Elt, NumInputs);
    std::uninitialized_fill_n (this->end (), NumInputs, *EltPtr);
    this->set_size (this->size () + NumInputs);
  }

  void
  append (std::initializer_list<T> IL)
  {
    append (IL.begin (), IL.end ());
  }

  void
  append (const SmallVectorImpl &RHS)
  {
    append (RHS.begin (), RHS.end ());
  }

  void
  assign (size_type NumElts, ValueParamT Elt)
  {
    // Note that Elt could be an internal reference.
    if (NumElts > this->capacity ())
    {
      this->growAndAssign (NumElts, Elt);
      return;
    }

    // Assign over existing elements.
    std::fill_n (this->begin (), std::min (NumElts, this->size ()), Elt);
    if (NumElts > this->size ())
    {
      std::uninitialized_fill_n (this->end (), NumElts - this->size (), Elt);
    }
    else if (NumElts < this->size ())
    {
      this->destroy_range (this->begin () + NumElts, this->end ());
    }
    this->set_size (NumElts);
  }

  // FIXME: Consider assigning over existing elements, rather than clearing &
  // re-initializing them - for all assign(...) variants.

  template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
  void
  assign (ItTy in_start, ItTy in_end)
  {
    this->assertSafeToReferenceAfterClear (in_start, in_end);
    clear ();
    append (in_start, in_end);
  }

  void
  assign (std::initializer_list<T> IL)
  {
    clear ();
    append (IL);
  }

  void
  assign (const SmallVectorImpl &RHS)
  {
    assign (RHS.begin (), RHS.end ());
  }

  template <typename U,
            typename = std::enable_if_t<std::is_convertible_v<U, T>>>
  void
  assign (ArrayRef<U> AR)
  {
    assign (AR.begin (), AR.end ());
  }

  iterator
  erase (const_iterator CI)
  {
    // Just cast away constness because this is a non-const member function.
    iterator I = const_cast<iterator> (CI);

    assert (this->isReferenceToStorage (CI) &&
            "Iterator to erase is out of bounds.");

    iterator N = I;
    // Shift all elts down one.
    std::move (I + 1, this->end (), I);
    // Drop the last elt.
    this->pop_back ();
    return (N);
  }

  iterator
  erase (const_iterator CS, const_iterator CE)
  {
    // Just cast away constness because this is a non-const member function.
    iterator S = const_cast<iterator> (CS);
    iterator E = const_cast<iterator> (CE);

    assert (this->isRangeInStorage (S, E) &&
            "Range to erase is out of bounds.");

    iterator N = S;
    // Shift all elts down.
    iterator I = std::move (E, this->end (), S);
    // Drop the last elts.
    this->destroy_range (I, this->end ());
    this->set_size (I - this->begin ());
    return (N);
  }

private:
  template <class ArgType>
  iterator
  insert_one_impl (iterator I, ArgType &&Elt)
  {
    // Callers ensure that ArgType is derived from T.
    static_assert (
        std::is_same<std::remove_const_t<std::remove_reference_t<ArgType>>,
                     T>::value,
        "ArgType must be derived from T!");

    if (I == this->end ())
    { // Important special case for empty vector.
      this->push_back (::std::forward<ArgType> (Elt));
      return this->end () - 1;
    }

    assert (this->isReferenceToStorage (I) &&
            "Insertion iterator is out of bounds.");

    // Grow if necessary.
    size_t Index = I - this->begin ();
    std::remove_reference_t<ArgType> *EltPtr =
        this->reserveForParamAndGetAddress (Elt);
    I = this->begin () + Index;

    ::new ((void *)this->end ()) T (::std::move (this->back ()));
    // Push everything else over.
    std::move_backward (I, this->end () - 1, this->end ());
    this->set_size (this->size () + 1);

    // If we just moved the element we're inserting, be sure to update
    // the reference (never happens if TakesParamByValue).
    static_assert (!TakesParamByValue || std::is_same<ArgType, T>::value,
                   "ArgType must be 'T' when taking by value!");
    if (!TakesParamByValue &&
        this->isReferenceToRange (EltPtr, I, this->end ()))
    {
      ++EltPtr;
    }

    *I = ::std::forward<ArgType> (*EltPtr);
    return I;
  }

public:
  iterator
  insert (iterator I, T &&Elt)
  {
    return insert_one_impl (I, this->forward_value_param (std::move (Elt)));
  }

  iterator
  insert (iterator I, const T &Elt)
  {
    return insert_one_impl (I, this->forward_value_param (Elt));
  }

  iterator
  insert (iterator I, size_type NumToInsert, ValueParamT 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 (this->isReferenceToStorage (I) &&
            "Insertion iterator is out of bounds.");

    // Ensure there is enough space, and get the (maybe updated) address of
    // Elt.
    const T *EltPtr = this->reserveForParamAndGetAddress (Elt, 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.
      std::move_backward (I, OldEnd - NumToInsert, OldEnd);

      // If we just moved the element we're inserting, be sure to update
      // the reference (never happens if TakesParamByValue).
      if (!TakesParamByValue && I <= EltPtr && EltPtr < this->end ())
      {
        EltPtr += NumToInsert;
      }

      std::fill_n (I, NumToInsert, *EltPtr);
      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->set_size (this->size () + NumToInsert);
    size_t NumOverwritten = OldEnd - I;
    this->uninitialized_move (I, OldEnd, this->end () - NumOverwritten);

    // If we just moved the element we're inserting, be sure to update
    // the reference (never happens if TakesParamByValue).
    if (!TakesParamByValue && I <= EltPtr && EltPtr < this->end ())
    {
      EltPtr += NumToInsert;
    }

    // Replace the overwritten part.
    std::fill_n (I, NumOverwritten, *EltPtr);

    // Insert the non-overwritten middle part.
    std::uninitialized_fill_n (OldEnd, NumToInsert - NumOverwritten, *EltPtr);
    return I;
  }

  template <typename ItTy, typename = EnableIfConvertibleToInputIterator<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;
    }

    if constexpr (!HasIteratorTag<ItTy, std::forward_iterator_tag>::value)
    {
      // For input iterators, we don't know the number of elements to insert.
      size_t OldSize = this->size ();
      append (From, To);
      I = this->begin () + InsertElt; // Uninvalidate the iterator.
      std::rotate (I, this->begin () + OldSize, this->end ());
      return I;
    }

    assert (this->isReferenceToStorage (I) &&
            "Insertion iterator is out of bounds.");

    // Check that the reserve that follows doesn't invalidate the iterators.
    this->assertSafeToAddRange (From, To);

    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.
      std::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->set_size (this->size () + 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;
  }

  void
  insert (iterator I, std::initializer_list<T> IL)
  {
    insert (I, IL.begin (), IL.end ());
  }

  template <typename... ArgTypes>
  reference
  emplace_back (ArgTypes &&...Args)
  {
    if (RCC_UNLIKELY (this->size () >= this->capacity ()))
    {
      return this->growAndEmplaceBack (std::forward<ArgTypes> (Args)...);
    }

    ::new ((void *)this->end ()) T (std::forward<ArgTypes> (Args)...);
    this->set_size (this->size () + 1);
    return this->back ();
  }

  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 ());
  }
  bool
  operator> (const SmallVectorImpl &RHS) const
  {
    return RHS < *this;
  }
  bool
  operator<= (const SmallVectorImpl &RHS) const
  {
    return !(*this > RHS);
  }
  bool
  operator>= (const SmallVectorImpl &RHS) const
  {
    return !(*this < RHS);
  }
};

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->Size, RHS.Size);
    std::swap (this->Capacity, RHS.Capacity);
    return;
  }
  this->reserve (RHS.size ());
  RHS.reserve (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.set_size (RHS.size () + EltDiff);
    this->destroy_range (this->begin () + NumShared, this->end ());
    this->set_size (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->set_size (this->size () + EltDiff);
    this->destroy_range (RHS.begin () + NumShared, RHS.end ());
    RHS.set_size (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->set_size (RHSSize);
    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->clear ();
    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->set_size (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->assignRemote (std::move (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 = this->begin ();
    if (RHSSize)
    {
      NewEnd = std::move (RHS.begin (), RHS.end (), NewEnd);
    }

    // Destroy excess elements and trim the bounds.
    this->destroy_range (NewEnd, this->end ());
    this->set_size (RHSSize);

    // 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->clear ();
    CurSize = 0;
    this->grow (RHSSize);
  }
  else if (CurSize)
  {
    // Otherwise, use assignment for the already-constructed elements.
    std::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->set_size (RHSSize);

  RHS.clear ();
  return *this;
}

/// Storage for the SmallVector elements.  This is specialized for the N=0 case
/// to avoid allocating unnecessary storage.
template <typename T, unsigned N> struct SmallVectorStorage
{
  alignas (T) char InlineElts[N * sizeof (T)];
};

/// We need the storage to be properly aligned even for small-size of 0 so that
/// the pointer math in \a SmallVectorTemplateCommon::getFirstEl() is
/// well-defined.
template <typename T> struct alignas (T) SmallVectorStorage<T, 0>
{
};

/// Forward declaration of SmallVector so that
/// calculateSmallVectorDefaultInlinedElements can reference
/// `sizeof(SmallVector<T, 0>)`.
template <typename T, unsigned N> class RCC_GSL_OWNER SmallVector;

/// Helper class for calculating the default number of inline elements for
/// `SmallVector<T>`.
///
/// This should be migrated to a constexpr function when our minimum
/// compiler support is enough for multi-statement constexpr functions.
template <typename T> struct CalculateSmallVectorDefaultInlinedElements
{
  // Parameter controlling the default number of inlined elements
  // for `SmallVector<T>`.
  //
  // The default number of inlined elements ensures that
  // 1. There is at least one inlined element.
  // 2. `sizeof(SmallVector<T>) <= kPreferredSmallVectorSizeof` unless
  // it contradicts 1.
  static constexpr size_t kPreferredSmallVectorSizeof = 64;

  // static_assert that sizeof(T) is not "too big".
  //
  // Because our policy guarantees at least one inlined element, it is possible
  // for an arbitrarily large inlined element to allocate an arbitrarily large
  // amount of inline storage. We generally consider it an antipattern for a
  // SmallVector to allocate an excessive amount of inline storage, so we want
  // to call attention to these cases and make sure that users are making an
  // intentional decision if they request a lot of inline storage.
  //
  // We want this assertion to trigger in pathological cases, but otherwise
  // not be too easy to hit. To accomplish that, the cutoff is actually somewhat
  // larger than kPreferredSmallVectorSizeof (otherwise,
  // `SmallVector<SmallVector<T>>` would be one easy way to trip it, and that
  // pattern seems useful in practice).
  //
  // One wrinkle is that this assertion is in theory non-portable, since
  // sizeof(T) is in general platform-dependent. However, we don't expect this
  // to be much of an issue, because most LLVM development happens on 64-bit
  // hosts, and therefore sizeof(T) is expected to *decrease* when compiled for
  // 32-bit hosts, dodging the issue. The reverse situation, where development
  // happens on a 32-bit host and then fails due to sizeof(T) *increasing* on a
  // 64-bit host, is expected to be very rare.
  static_assert (
      sizeof (T) <= 256,
      "You are trying to use a default number of inlined elements for "
      "`SmallVector<T>` but `sizeof(T)` is really big! Please use an "
      "explicit number of inlined elements with `SmallVector<T, N>` to make "
      "sure you really want that much inline storage.");

  // Discount the size of the header itself when calculating the maximum inline
  // bytes.
  static constexpr size_t PreferredInlineBytes =
      kPreferredSmallVectorSizeof - sizeof (SmallVector<T, 0>);
  static constexpr size_t NumElementsThatFit =
      PreferredInlineBytes / sizeof (T);
  static constexpr size_t value =
      NumElementsThatFit == 0 ? 1 : NumElementsThatFit;
};

/// 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
/// In the absence of a well-motivated choice for the number of inlined
/// elements \p N, it is recommended to use \c SmallVector<T> (that is,
/// omitting the \p N). This will choose a default number of inlined elements
/// reasonable for allocation on the stack (for example, trying to keep \c
/// sizeof(SmallVector<T>) around 64 bytes).
///
/// \warning This does not attempt to be exception safe.
///
/// \see https://llvm.org/docs/ProgrammersManual.html#llvm-adt-smallvector-h
template <typename T,
          unsigned N = CalculateSmallVectorDefaultInlinedElements<T>::value>
class RCC_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
                                  SmallVectorStorage<T, N>
{
public:
  SmallVector () : SmallVectorImpl<T> (N)
  {
  }

  ~SmallVector ()
  {
    // Destroy the constructed elements in the vector.
    this->destroy_range (this->begin (), this->end ());
  }

  explicit SmallVector (size_t SizeArg) : SmallVectorImpl<T> (N)
  {
    this->resize (SizeArg);
  }

  SmallVector (size_t SizeArg, const T &Value) : SmallVectorImpl<T> (N)
  {
    this->assign (SizeArg, Value);
  }

  template <typename ItTy, typename = EnableIfConvertibleToInputIterator<ItTy>>
  SmallVector (ItTy S, ItTy E) : SmallVectorImpl<T> (N)
  {
    this->append (S, E);
  }

  template <typename RangeTy>
  explicit SmallVector (const iterator_range<RangeTy> &R)
      : SmallVectorImpl<T> (N)
  {
    this->append (R.begin (), R.end ());
  }

  SmallVector (std::initializer_list<T> IL) : SmallVectorImpl<T> (N)
  {
    this->append (IL);
  }

  template <typename U,
            typename = std::enable_if_t<std::is_convertible_v<U, T>>>
  explicit SmallVector (ArrayRef<U> A) : SmallVectorImpl<T> (N)
  {
    this->append (A.begin (), A.end ());
  }

  SmallVector (const SmallVector &RHS) : SmallVectorImpl<T> (N)
  {
    if (!RHS.empty ())
    {
      SmallVectorImpl<T>::operator= (RHS);
    }
  }

  SmallVector &
  operator= (const SmallVector &RHS)
  {
    SmallVectorImpl<T>::operator= (RHS);
    return *this;
  }

  // Reuse the move-assignment instantiation for trivially move-assignable
  // elements. Calling moveConstructFrom unconditionally would emit an
  // additional per-T wrapper at -O0, increasing object size.
  // std::is_move_assignable_v<T> is too broad: it can be a false positive for
  // types with an unconstrained assignment operator whose body is ill-formed.
  SmallVector (SmallVector &&RHS) : SmallVectorImpl<T> (N)
  {
    if (!RHS.empty ())
    {
      bool StoleAllocation = N > 0 && !RHS.isSmall ();
      if constexpr (std::is_trivially_move_assignable_v<T>)
      {
        SmallVectorImpl<T>::operator= (::std::move (RHS));
      }
      else
      {
        this->moveConstructFrom (::std::move (RHS));
      }
      if constexpr (N > 0)
      {
        if (StoleAllocation)
        {
          RHS.set_allocation_range (RHS.begin (), N);
        }
      }
    }
  }

  SmallVector (SmallVectorImpl<T> &&RHS) : SmallVectorImpl<T> (N)
  {
    if (!RHS.empty ())
    {
      if constexpr (std::is_trivially_move_assignable_v<T>)
      {
        SmallVectorImpl<T>::operator= (::std::move (RHS));
      }
      else
      {
        this->moveConstructFrom (::std::move (RHS));
      }
    }
  }

  SmallVector &
  operator= (SmallVector &&RHS)
  {
    if (N)
    {
      bool StoleAllocation = this != &RHS && !RHS.isSmall ();
      SmallVectorImpl<T>::operator= (::std::move (RHS));
      // Restore the inline capacity after stealing RHS's allocation.
      if (StoleAllocation)
      {
        RHS.set_allocation_range (RHS.begin (), N);
      }
      return *this;
    }
    // SmallVectorImpl<T>::operator= does not leverage N==0. Optimize the
    // case.
    if (this == &RHS)
    {
      return *this;
    }
    if (RHS.empty ())
    {
      this->destroy_range (this->begin (), this->end ());
      this->Size = 0;
    }
    else
    {
      this->assignRemote (std::move (RHS));
    }
    return *this;
  }

  SmallVector &
  operator= (SmallVectorImpl<T> &&RHS)
  {
    SmallVectorImpl<T>::operator= (::std::move (RHS));
    return *this;
  }

  SmallVector &
  operator= (std::initializer_list<T> IL)
  {
    this->assign (IL);
    return *this;
  }
};

template <typename T, unsigned N>
inline size_t
capacity_in_bytes (const SmallVector<T, N> &X)
{
  return X.capacity_in_bytes ();
}

template <typename RangeType>
using ValueTypeFromRangeType = std::ranges::range_value_t<RangeType>;

/// Given a range of type R, iterate the entire range and return a
/// SmallVector with elements of the vector.  This is useful, for example,
/// when you want to iterate a range and then sort the results.
template <unsigned Size, typename R>
SmallVector<ValueTypeFromRangeType<R>, Size>
to_vector (R &&Range)
{
  return SmallVector<ValueTypeFromRangeType<R>, Size> (
      std::ranges::begin (Range), std::ranges::end (Range));
}
template <typename R>
SmallVector<ValueTypeFromRangeType<R>>
to_vector (R &&Range)
{
  return SmallVector<ValueTypeFromRangeType<R>> (std::ranges::begin (Range),
                                                 std::ranges::end (Range));
}

template <typename Out, unsigned Size, typename R>
SmallVector<Out, Size>
to_vector_of (R &&Range)
{
  return SmallVector<Out, Size> (std::ranges::begin (Range),
                                 std::ranges::end (Range));
}

template <typename Out, typename R>
SmallVector<Out>
to_vector_of (R &&Range)
{
  return SmallVector<Out> (std::ranges::begin (Range),
                           std::ranges::end (Range));
}

// Explicit instantiations
extern template class rcc::SmallVectorBase<uint32_t>;
#if SIZE_MAX > UINT32_MAX
extern template class rcc::SmallVectorBase<uint64_t>;
#endif

} // end namespace rcc

namespace std
{

template <typename T, unsigned N> struct hash<rcc::SmallVector<T, N>>
{
  size_t
  operator() (const rcc::SmallVector<T, N> &Value) const
  {
    size_t Seed = 0;
    for (const T &Element : Value)
    {
      size_t ElementHash = std::hash<T>{}(Element);
      Seed ^= ElementHash + static_cast<size_t> (0x9e3779b9U) + (Seed << 6) +
              (Seed >> 2);
    }
    return Seed;
  }
};

/// Implement std::swap in terms of SmallVector swap.
template <typename T>
inline void
swap (rcc::SmallVectorImpl<T> &LHS, rcc::SmallVectorImpl<T> &RHS)
{
  LHS.swap (RHS);
}

/// Implement std::swap in terms of SmallVector swap.
template <typename T, unsigned N>
inline void
swap (rcc::SmallVector<T, N> &LHS, rcc::SmallVector<T, N> &RHS)
{
  LHS.swap (RHS);
}

} // end namespace std

#endif // RCC_ADT_SMALLVECTOR_H