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SmallVector.h (47703B)

---

 //===- llvm/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 LLVM_ADT_SMALLVECTOR_H
 #define LLVM_ADT_SMALLVECTOR_H
 
 #ifdef _MSC_VER
 #pragma warning(push)
 #pragma warning(disable: 4267) // warning C4267: '=': conversion from 'size_t' to 'Size_T', possible loss of data
 #pragma warning(disable: 4324) // warning C4324: 'llvm::SmallVectorStorage<T,0>': structure was padded due to alignment specifier
 #pragma warning(disable: 4100) // warning C4100: 'TSize': unreferenced formal parameter
 #endif
 
 //#include "llvm/Support/Compiler.h"
 //#include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
 #include <functional>
 #include <initializer_list>
 #include <iterator>
 #include <limits>
 #include <memory>
 #include <new>
 #include <type_traits>
 #include <utility>
 
 namespace llvm {
 
 template <typename T> class ArrayRef;
 
 template <typename IteratorT> class iterator_range;
 
 template <class Iterator>
 using EnableIfConvertibleToInputIterator = std::enable_if_t<std::is_convertible<
     typename std::iterator_traits<Iterator>::iterator_category,
     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(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.
   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.
   void grow_pod(void *FirstEl, size_t MinSize, size_t TSize);
 
   /// If vector was first created with capacity 0, getFirstEl() points to the
   /// memory right after, an area unallocated. If a subsequent allocation,
   /// that grows the vector, happens to return the same pointer as getFirstEl(),
   /// get a new allocation, otherwise isSmall() will falsely return that no
   /// allocation was done (true) and the memory will not be freed in the
   /// destructor. If a VSize is given (vector size), also copy that many
   /// elements to the new allocation - used if realloca fails to increase
   /// space, and happens to allocate precisely at BeginX.
   /// This is unlikely to be called often, but resolves a memory leak when the
   /// situation does occur.
   void *replaceAllocation(void *NewElts, size_t TSize, size_t NewCapacity,
                           size_t VSize = 0);
 
 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());
     Size = 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 Size) : Base(getFirstEl(), Size) {}
 
   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();
     this->Size = this->Capacity = 0; // FIXME: Setting Capacity to 0 is suspect.
   }
 
   /// 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 (LLVM_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.
   void assertSafeToReferenceAfterClear(const T *From, const T *To) {
     if (From == To)
       return;
     this->assertSafeToReferenceAfterResize(From, 0);
     this->assertSafeToReferenceAfterResize(To - 1, 0);
   }
   template <
       class ItTy,
       std::enable_if_t<!std::is_same<std::remove_const_t<ItTy>, T *>::value,
                        bool> = false>
   void assertSafeToReferenceAfterClear(ItTy, ItTy) {}
 
   /// Check whether any part of the range will be invalidated by growing.
   void assertSafeToAddRange(const T *From, const T *To) {
     if (From == To)
       return;
     this->assertSafeToAdd(From, To - From);
     this->assertSafeToAdd(To - 1, To - From);
   }
   template <
       class ItTy,
       std::enable_if_t<!std::is_same<std::remove_const_t<ItTy>, T *>::value,
                        bool> = false>
   void assertSafeToAddRange(ItTy, ItTy) {}
 
   /// 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 (/*LLVM_LIKELY*/(NewSize <= This->capacity())) [[likely]]
       return &Elt;
 
     bool ReferencesStorage = false;
     int64_t Index = -1;
     if (!U::TakesParamByValue) {
       if (/*LLVM_UNLIKELY*/(This->isReferenceToStorage(&Elt))) [[unlikely]] {
         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 Size) : SmallVectorTemplateCommon<T>(Size) {}
 
   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->BeginX = NewElts;
   this->Capacity = 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 Size) : SmallVectorTemplateCommon<T>(Size) {}
 
   // 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) {
     // 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,
       std::enable_if_t<std::is_same<std::remove_const_t<T1>, T2>::value> * =
           nullptr) {
     // 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)
       memcpy(reinterpret_cast<void *>(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)); }
 
   /// 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();
   }
 
 public:
   void push_back(ValueParamT Elt) {
     const T *EltPtr = reserveForParamAndGetAddress(Elt);
     memcpy(reinterpret_cast<void *>(this->end()), EltPtr, 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();
   }
 
   ~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) {
     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);
   }
 
   /// 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()); }
 
   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;
     }
 
     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 (LLVM_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 /*LLVM_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 /*LLVM_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 Size)
     : SmallVectorImpl<T>(N) {
     this->resize(Size);
   }
 
   SmallVector(size_t Size, const T &Value)
     : SmallVectorImpl<T>(N) {
     this->assign(Size, 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<U, T>::value>>
   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;
   }
 
   SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(N) {
     if (!RHS.empty())
       SmallVectorImpl<T>::operator=(::std::move(RHS));
   }
 
   SmallVector(SmallVectorImpl<T> &&RHS) : SmallVectorImpl<T>(N) {
     if (!RHS.empty())
       SmallVectorImpl<T>::operator=(::std::move(RHS));
   }
 
   SmallVector &operator=(SmallVector &&RHS) {
     if (N) {
       SmallVectorImpl<T>::operator=(::std::move(RHS));
       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::remove_const_t<std::remove_reference_t<decltype(*std::begin(
         std::declval<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 {std::begin(Range), std::end(Range)};
 }
 template <typename R>
 SmallVector<ValueTypeFromRangeType<R>> to_vector(R &&Range) {
   return {std::begin(Range), std::end(Range)};
 }
 
 template <typename Out, unsigned Size, typename R>
 SmallVector<Out, Size> to_vector_of(R &&Range) {
   return {std::begin(Range), std::end(Range)};
 }
 
 template <typename Out, typename R> SmallVector<Out> to_vector_of(R &&Range) {
   return {std::begin(Range), std::end(Range)};
 }
 
 // Explicit instantiations
 extern template class llvm::SmallVectorBase<uint32_t>;
 #if SIZE_MAX > UINT32_MAX
 extern template class llvm::SmallVectorBase<uint64_t>;
 #endif
 
 } // end namespace llvm
 
 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);
   }
 
 } // end namespace std
 
 #ifdef _MSC_VER
 #pragma warning(pop)
 #endif
 
 #endif // LLVM_ADT_SMALLVECTOR_H