Experimenting with outline methods

svgbo.diff

diff --git a/llvm/include/llvm/ADT/SmallVector.h b/llvm/include/llvm/ADT/SmallVector.h
index c3c6a366dab..40d21b7d1d3 100644
--- a/llvm/include/llvm/ADT/SmallVector.h
+++ b/llvm/include/llvm/ADT/SmallVector.h
@@ -1,995 +1,1284 @@
 //===- 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
 //
 //===----------------------------------------------------------------------===//
 //
 // This file defines the SmallVector class.
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_ADT_SMALLVECTOR_H
 #define LLVM_ADT_SMALLVECTOR_H
 
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/AlignOf.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/MemAlloc.h"
 #include "llvm/Support/type_traits.h"
 #include <algorithm>
 #include <cassert>
 #include <cstddef>
 #include <cstdlib>
 #include <cstring>
 #include <initializer_list>
 #include <iterator>
 #include <limits>
 #include <memory>
 #include <new>
 #include <type_traits>
 #include <utility>
 
 namespace llvm {
 
 /// 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 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);
 
+  size_t grow_size(size_t MinSize = 0) {
+    // Ensure we can fit the new capacity.
+    // This is only going to be applicable when the capacity is 32 bit.
+    if (MinSize > this->SizeTypeMax())
+      report_size_overflow(MinSize);
+
+    // Ensure we can meet the guarantee of space for at least one more element.
+    // The above check alone will not catch the case where grow is called with a
+    // default MinSize of 0, but the current capacity cannot be increased.
+    // This is only going to be applicable when the capacity is 32 bit.
+    if (capacity() == SizeTypeMax())
+      report_at_maximum_capacity();
+    // Always grow, even from zero.
+    size_t NewCapacity = size_t(NextPowerOf2(capacity() + 2));
+    return std::min(std::max(NewCapacity, MinSize), SizeTypeMax());
+  }
+
   /// Report that MinSize doesn't fit into this vector's size type. Throws
   /// std::length_error or calls report_fatal_error.
   LLVM_ATTRIBUTE_NORETURN static void report_size_overflow(size_t MinSize);
   /// Report that this vector is already at maximum capacity. Throws
   /// std::length_error or calls report_fatal_error.
   LLVM_ATTRIBUTE_NORETURN static void report_at_maximum_capacity();
 
 public:
   size_t size() const { return Size; }
   size_t capacity() const { return Capacity; }
 
   LLVM_NODISCARD bool empty() const { return !Size; }
 
   /// Set the array size to \p N, which the current array must have enough
   /// capacity for.
   ///
   /// This does not construct or destroy any elements in the vector.
   ///
   /// Clients can use this in conjunction with capacity() to write past the end
   /// of the buffer when they know that more elements are available, and only
   /// update the size later. This avoids the cost of value initializing elements
   /// which will only be overwritten.
   void set_size(size_t N) {
     assert(N <= capacity());
     Size = N;
   }
 };
 
 template <class T>
 using SmallVectorSizeType =
     typename std::conditional<sizeof(T) < 4 && sizeof(void *) >= 8, uint64_t,
                               uint32_t>::type;
 
 /// Figure out the offset of the first element.
 template <class T, typename = void> struct SmallVectorAlignmentAndSize {
   AlignedCharArrayUnion<SmallVectorBase<SmallVectorSizeType<T>>> Base;
   AlignedCharArrayUnion<T> FirstEl;
 };
 
+namespace detail {
+template <typename Size_T> class GrowBufferBase;
+} // namespace detail
+
 /// 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>>;
+  friend class detail::GrowBufferBase<SmallVectorSizeType<T>>;
 
   /// 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.
 
 protected:
   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.
   }
 
 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];
   }
 };
 
+namespace detail {
+template <typename T>
+static constexpr bool
+    is_pod_like_v = (is_trivially_copy_constructible<T>::value) &&
+                    (is_trivially_move_constructible<T>::value) &&
+                    std::is_trivially_destructible<T>::value;
+
+template <typename Size_T> class GrowBufferBase {
+public:
+  GrowBufferBase(Size_T Size, Size_T Capacity, Size_T TSize)
+      : Size(Size), Capacity(Capacity) {
+    BeginX = llvm::safe_malloc(Capacity * TSize);
+  }
+
+  ~GrowBufferBase() {
+    assert(BeginX == nullptr && "Buffers haven't been swapped out");
+  }
+
+  Size_T size() const { return Size; }
+  Size_T capacity() const { return Capacity; }
+
+protected:
+  void *BeginX;
+  Size_T Size, Capacity;
+
+  void increaseSize(Size_T NumItems = 1) { Size += NumItems; }
+  void setSize(Size_T NewSize) { Size = NewSize; }
+
+  template <typename T> void take_buffers(SmallVectorTemplateCommon<T> &Vec) {
+    if (!Vec.isSmall())
+      free(Vec.begin());
+    Vec.BeginX = BeginX;
+    Vec.Size = Size;
+    Vec.Capacity = Capacity;
+    BeginX = nullptr;
+    Size = 0U;
+    Capacity = 0U;
+  }
+};
+
+template <typename T, bool = is_pod_like_v<T>>
+class GrowBuffer : public GrowBufferBase<SmallVectorSizeType<T>> {
+public:
+  using Size_T = SmallVectorSizeType<T>;
+  using Base = GrowBufferBase<Size_T>;
+
+  using Base::capacity;
+  using Base::increaseSize;
+  using Base::size;
+
+  GrowBuffer(Size_T Size, Size_T Capacity) : Base(Size, Capacity, sizeof(T)) {}
+
+  T *begin() { return static_cast<T *>(this->BeginX); }
+  T *end() { return begin() + size(); }
+
+  void default_construct_at_end(Size_T Count) {
+    assert((size() + Count) <= capacity() && "Overflowed GrowBuffer storage");
+    T *First = end();
+    increaseSize(Count);
+    T *Last = end();
+    for (; First != Last; ++First) {
+      ::new (static_cast<void *>(First)) T;
+    }
+  }
+
+  void push(const T &Elt) {
+    assert(size() < capacity() && "Overflowed GrowBuffer storage");
+    ::new (static_cast<void *>(end())) T(Elt);
+    increaseSize();
+  }
+
+  void push(T &&Elt) {
+    assert(size() < capacity() && "Overflowed GrowBuffer storage");
+    ::new (static_cast<void *>(end())) T(std::move(Elt));
+    increaseSize();
+  }
+
+  template <typename... ArgTypes> void emplace(ArgTypes &&...Args) {
+    assert(size() < capacity() && "Overflowed GrowBuffer storage");
+    ::new (static_cast<void *>(end())) T(std::forward<ArgTypes>(Args)...);
+    increaseSize();
+  }
+
+  void append(Size_T Count, const T &Elt) {
+    assert((size() + Count) <= capacity() && "Overflowed GrowBuffer storage");
+    std::uninitialized_fill_n(end(), Count, Elt);
+    increaseSize(Count);
+  }
+
+  template <typename in_iter,
+            typename = std::enable_if_t<std::is_convertible<
+                typename std::iterator_traits<in_iter>::iterator_category,
+                std::input_iterator_tag>::value>>
+  void append(in_iter Start, in_iter End) {
+    assert(size() + std::distance(Start, End) <= capacity() &&
+           "Overflowed GrowBuffer storage");
+    T *NewEnd = std::uninitialized_copy(Start, End, end());
+    this->setSize(NewEnd - begin());
+  }
+
+  void swap_out_buffer(SmallVectorTemplateCommon<T> &Vec);
+
+  void swap_out_split_buffer(SmallVectorTemplateCommon<T> &Vec,
+                             Size_T SplitIndex);
+};
+template <typename T>
+class GrowBuffer<T, true> : public GrowBufferBase<SmallVectorSizeType<T>> {
+public:
+  using Size_T = SmallVectorSizeType<T>;
+  using Base = GrowBufferBase<Size_T>;
+
+  using Base::capacity;
+  using Base::increaseSize;
+  using Base::size;
+
+  GrowBuffer(Size_T Size, Size_T Capacity) : Base(Size, Capacity, sizeof(T)) {}
+
+  T *begin() { return static_cast<T *>(this->BeginX); }
+  T *end() { return begin() + size(); }
+
+  void default_construct_at_end(Size_T Count) {
+    assert((size() + Count) <= capacity() && "Overflowed GrowBuffer storage");
+    // No need to do any construction here.
+    increaseSize(Count);
+  }
+
+  void push(const T &Elt) {
+    assert(size() < capacity() && "Overflowed GrowBuffer storage");
+    memcpy(end(), &Elt, sizeof(Elt));
+    increaseSize();
+  }
+
+  template <typename... ArgTypes> void emplace(ArgTypes &&...Args) {
+    assert(size() < capacity() && "Overflowed GrowBuffer storage");
+    ::new ((void *)end()) T(std::forward<ArgTypes>(Args)...);
+    increaseSize();
+  }
+
+  template <typename in_iter,
+            typename = std::enable_if_t<std::is_convertible<
+                typename std::iterator_traits<in_iter>::iterator_category,
+                std::input_iterator_tag>::value>>
+  void append(in_iter Start, in_iter End) {
+    assert(size() + std::distance(Start, End) <= capacity() &&
+           "Overflowed GrowBuffer storage");
+    T *NewEnd = std::uninitialized_copy(Start, End, end());
+    this->setSize(NewEnd - begin());
+  }
+
+  void append(T *Start, T *End) {
+    Size_T NumItems = End - Start;
+    assert(size() + NumItems <= capacity() && "Overflowed GrowBuffer storage");
+    memcpy(end(), Start, NumItems * sizeof(T));
+    increaseSize(NumItems);
+  }
+
+  void append(Size_T Count, const T &Elt) {
+    assert((size() + Count) <= capacity() && "Overflowed GrowBuffer storage");
+    T *First = end();
+    increaseSize(Count);
+    T *Last = end();
+    for (; First != Last; ++First) {
+      memcpy(First, &Elt, sizeof(Elt));
+    }
+  }
+
+  void swap_out_buffer(SmallVectorTemplateCommon<T> &Vec);
+
+  void swap_out_split_buffer(SmallVectorTemplateCommon<T> &Vec,
+                             Size_T SplitIndex);
+};
+
+template <typename T, bool TriviallyCopyable>
+void GrowBuffer<T, TriviallyCopyable>::swap_out_buffer(
+    SmallVectorTemplateCommon<T> &Vec) {
+  std::uninitialized_copy(std::make_move_iterator(Vec.rbegin()),
+                          std::make_move_iterator(Vec.rend()),
+                          std::reverse_iterator<T *>(begin() + Vec.size()));
+  // Destory the items in the old vector.
+  for (T &Item : Vec)
+    Item.~T();
+  this->take_buffers(Vec);
+}
+
+template <typename T, bool TriviallyCopyable>
+void GrowBuffer<T, TriviallyCopyable>::swap_out_split_buffer(
+    SmallVectorTemplateCommon<T> &Vec, Size_T SplitIndex) {
+  std::uninitialized_copy(std::make_move_iterator(std::reverse_iterator<T *>(
+                              Vec.begin() + SplitIndex)),
+                          std::make_move_iterator(Vec.rend()),
+                          std::reverse_iterator<T *>(begin() + SplitIndex));
+  std::uninitialized_copy(std::make_move_iterator(&Vec[SplitIndex]),
+                          std::make_move_iterator(Vec.end()), end());
+  increaseSize(Vec.size() - SplitIndex);
+  // Destory the items in the old vector.
+  for (T &Item : Vec)
+    Item.~T();
+  this->take_buffers(Vec);
+}
+
+template <typename T>
+void GrowBuffer<T, true>::swap_out_buffer(SmallVectorTemplateCommon<T> &Vec) {
+  memcpy(begin(), Vec.begin(), Vec.size_in_bytes());
+  this->take_buffers(Vec);
+}
+
+template <typename T>
+void GrowBuffer<T, true>::swap_out_split_buffer(
+    SmallVectorTemplateCommon<T> &Vec, Size_T SplitIndex) {
+  memcpy(begin(), Vec.begin(), SplitIndex * sizeof(T));
+  memcpy(end(), &Vec[SplitIndex], (Vec.size() - SplitIndex) * sizeof(T));
+  increaseSize(Vec.size() - SplitIndex);
+  this->take_buffers(Vec);
+}
+
+} // namespace detail
+
 /// 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 = (is_trivially_copy_constructible<T>::value) &&
-                             (is_trivially_move_constructible<T>::value) &&
-                             std::is_trivially_destructible<T>::value>
+template <typename T, bool = detail::is_pod_like_v<T>>
 class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
 protected:
   SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
 
   static void destroy_range(T *S, T *E) {
     while (S != E) {
       --E;
       E->~T();
     }
   }
 
   /// 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_copy(std::make_move_iterator(I),
                             std::make_move_iterator(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);
 
 public:
   void push_back(const T &Elt) {
-    if (LLVM_UNLIKELY(this->size() >= this->capacity()))
-      this->grow();
+    if (LLVM_UNLIKELY(this->size() >= this->capacity())) {
+      detail::GrowBuffer<T> Buffer(this->size(), this->grow_size());
+      Buffer.push(Elt);
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
     ::new ((void*) this->end()) T(Elt);
     this->set_size(this->size() + 1);
   }
 
   void push_back(T &&Elt) {
-    if (LLVM_UNLIKELY(this->size() >= this->capacity()))
-      this->grow();
+    if (LLVM_UNLIKELY(this->size() >= this->capacity())) {
+      detail::GrowBuffer<T> Buffer(this->size(), this->grow_size());
+      Buffer.push(std::move(Elt));
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
     ::new ((void*) this->end()) T(::std::move(Elt));
     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) {
-  // Ensure we can fit the new capacity.
-  // This is only going to be applicable when the capacity is 32 bit.
-  if (MinSize > this->SizeTypeMax())
-    this->report_size_overflow(MinSize);
-
-  // Ensure we can meet the guarantee of space for at least one more element.
-  // The above check alone will not catch the case where grow is called with a
-  // default MinSize of 0, but the current capacity cannot be increased.
-  // This is only going to be applicable when the capacity is 32 bit.
-  if (this->capacity() == this->SizeTypeMax())
-    this->report_at_maximum_capacity();
-
-  // Always grow, even from zero.
-  size_t NewCapacity = size_t(NextPowerOf2(this->capacity() + 2));
-  NewCapacity = std::min(std::max(NewCapacity, MinSize), this->SizeTypeMax());
+  size_t NewCapacity = this->grow_size(MinSize);
   T *NewElts = static_cast<T*>(llvm::safe_malloc(NewCapacity*sizeof(T)));
 
   // Move the elements over.
   this->uninitialized_move(this->begin(), this->end(), NewElts);
 
   // Destroy the original elements.
   destroy_range(this->begin(), this->end());
 
   // If this wasn't grown from the inline copy, deallocate the old space.
   if (!this->isSmall())
     free(this->begin());
 
   this->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> {
 protected:
   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<typename std::remove_const<T1>::type,
                                     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)); }
 
 public:
   void push_back(const T &Elt) {
-    if (LLVM_UNLIKELY(this->size() >= this->capacity()))
-      this->grow();
+    if (LLVM_UNLIKELY(this->size() >= this->capacity())) {
+      detail::GrowBuffer<T> Buffer(this->size(), this->grow_size());
+      Buffer.push(Elt);
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
     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:
   // Default ctor - Initialize to empty.
   explicit SmallVectorImpl(unsigned N)
       : SmallVectorTemplateBase<T>(N) {}
 
 public:
   SmallVectorImpl(const SmallVectorImpl &) = delete;
 
   ~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());
   }
 
   void clear() {
     this->destroy_range(this->begin(), this->end());
     this->Size = 0;
   }
 
   void resize(size_type N) {
     if (N < this->size()) {
       this->destroy_range(this->begin()+N, this->end());
       this->set_size(N);
     } else if (N > this->size()) {
       if (this->capacity() < N)
         this->grow(N);
       for (auto I = this->end(), E = this->begin() + N; I != E; ++I)
         new (&*I) T();
       this->set_size(N);
     }
   }
 
   void resize(size_type N, const T &NV) {
     if (N < this->size()) {
       this->destroy_range(this->begin()+N, this->end());
       this->set_size(N);
     } else if (N > this->size()) {
-      if (this->capacity() < N)
-        this->grow(N);
+      if (this->capacity() < N) {
+        detail::GrowBuffer<T> Buffer(this->size(), this->grow_size(N));
+        Buffer.append(N - this->size(), NV);
+        Buffer.swap_out_buffer(*this);
+        return;
+      }
       std::uninitialized_fill(this->end(), this->begin()+N, NV);
       this->set_size(N);
     }
   }
 
   void reserve(size_type N) {
     if (this->capacity() < N)
       this->grow(N);
   }
 
   LLVM_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 in_iter,
             typename = std::enable_if_t<std::is_convertible<
                 typename std::iterator_traits<in_iter>::iterator_category,
                 std::input_iterator_tag>::value>>
   void append(in_iter in_start, in_iter in_end) {
     size_type NumInputs = std::distance(in_start, in_end);
-    if (NumInputs > this->capacity() - this->size())
-      this->grow(this->size()+NumInputs);
+    if (NumInputs > this->capacity() - this->size()) {
+      detail::GrowBuffer<T> Buffer(this->size(),
+                                   this->grow_size(this->size() + NumInputs));
+      Buffer.append(in_start, in_end);
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
 
     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, const T &Elt) {
-    if (NumInputs > this->capacity() - this->size())
-      this->grow(this->size()+NumInputs);
+    if (NumInputs > this->capacity() - this->size()) {
+      detail::GrowBuffer<T> Buffer(this->size(),
+                                   this->grow_size(this->size() + NumInputs));
+      Buffer.append(NumInputs, Elt);
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
 
     std::uninitialized_fill_n(this->end(), NumInputs, Elt);
     this->set_size(this->size() + NumInputs);
   }
 
   void append(std::initializer_list<T> IL) {
     append(IL.begin(), IL.end());
   }
 
   // FIXME: Consider assigning over existing elements, rather than clearing &
   // re-initializing them - for all assign(...) variants.
 
   void assign(size_type NumElts, const T &Elt) {
-    clear();
-    if (this->capacity() < NumElts)
-      this->grow(NumElts);
-    this->set_size(NumElts);
-    std::uninitialized_fill(this->begin(), this->end(), Elt);
+    if (this->capacity() < NumElts) {
+      detail::GrowBuffer<T> Buffer(0, this->grow_size(NumElts));
+      Buffer.append(NumElts, Elt);
+      this->clear();
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
+    if (NumElts == this->size()) {
+      std::fill(this->begin(), this->end(), Elt);
+    } else if (NumElts < this->size()) {
+      this->destroy_range(this->begin() + NumElts, this->end());
+      this->set_size(NumElts);
+      std::fill(this->begin(), this->end(), Elt);
+    } else {
+      std::fill(this->begin(), this->end(), Elt);
+      std::uninitialized_fill_n(this->end(), NumElts - this->size(), Elt);
+      this->set_size(NumElts);
+    }
   }
 
   template <typename in_iter,
             typename = std::enable_if_t<std::is_convertible<
                 typename std::iterator_traits<in_iter>::iterator_category,
                 std::input_iterator_tag>::value>>
   void assign(in_iter in_start, in_iter in_end) {
-    clear();
-    append(in_start, in_end);
+    size_type NumElts = std::distance(in_start, in_end);
+    if (this->capacity() < NumElts) {
+      detail::GrowBuffer<T> Buffer(0, this->grow_size(NumElts));
+      Buffer.append(in_start, in_end);
+      this->clear();
+      Buffer.swap_out_buffer(*this);
+      return;
+    }
+    if (NumElts == this->size()) {
+      std::copy(in_start, in_end, this->begin());
+    } else if (NumElts < this->size()) {
+      this->destroy_range(this->begin() + NumElts, this->end());
+      this->set_size(NumElts);
+      std::copy(in_start, in_end, this->begin());
+    } else {
+      for (auto &I : *this)
+        I = *in_start++;
+      this->uninitialized_copy(in_start, in_end, this->end());
+      this->set_size(NumElts);
+    }
   }
 
-  void assign(std::initializer_list<T> IL) {
-    clear();
-    append(IL);
-  }
+  void assign(std::initializer_list<T> IL) { assign(IL.begin(), IL.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(I >= this->begin() && "Iterator to erase is out of bounds.");
     assert(I < this->end() && "Erasing at past-the-end iterator.");
 
     iterator N = I;
     // Shift all elts down one.
     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(S >= this->begin() && "Range to erase is out of bounds.");
     assert(S <= E && "Trying to erase invalid range.");
     assert(E <= this->end() && "Trying to erase past the end.");
 
     iterator N = S;
     // Shift all elts down.
     iterator I = std::move(E, this->end(), S);
     // Drop the last elts.
     this->destroy_range(I, this->end());
     this->set_size(I - this->begin());
     return(N);
   }
 
   iterator insert(iterator I, T &&Elt) {
     if (I == this->end()) {  // Important special case for empty vector.
       this->push_back(::std::move(Elt));
       return this->end()-1;
     }
 
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
     if (this->size() >= this->capacity()) {
       size_t EltNo = I-this->begin();
-      this->grow();
-      I = this->begin()+EltNo;
+      detail::GrowBuffer<T> Buffer(EltNo, this->grow_size());
+      Buffer.push(std::move(Elt));
+      Buffer.swap_out_split_buffer(*this, EltNo);
+      return this->begin() + EltNo;
     }
 
     ::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.
     T *EltPtr = &Elt;
     if (I <= EltPtr && EltPtr < this->end())
       ++EltPtr;
 
     *I = ::std::move(*EltPtr);
     return I;
   }
 
   iterator insert(iterator I, const T &Elt) {
     if (I == this->end()) {  // Important special case for empty vector.
       this->push_back(Elt);
       return this->end()-1;
     }
 
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
     if (this->size() >= this->capacity()) {
       size_t EltNo = I-this->begin();
-      this->grow();
-      I = this->begin()+EltNo;
+      detail::GrowBuffer<T> Buffer(EltNo, this->grow_size());
+      Buffer.push(Elt);
+      Buffer.swap_out_split_buffer(*this, EltNo);
+      return this->begin() + EltNo;
     }
     ::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.
     const T *EltPtr = &Elt;
     if (I <= EltPtr && EltPtr < this->end())
       ++EltPtr;
 
     *I = *EltPtr;
     return I;
   }
 
   iterator insert(iterator I, size_type NumToInsert, const T &Elt) {
     // Convert iterator to elt# to avoid invalidating iterator when we reserve()
     size_t InsertElt = I - this->begin();
 
     if (I == this->end()) {  // Important special case for empty vector.
       append(NumToInsert, Elt);
       return this->begin()+InsertElt;
     }
 
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
-    // Ensure there is enough space.
-    reserve(this->size() + NumToInsert);
-
-    // Uninvalidate the iterator.
-    I = this->begin()+InsertElt;
+    if ((this->size() + NumToInsert) > this->capacity()) {
+      detail::GrowBuffer<T> Buffer(InsertElt,
+                                   this->grow_size(this->size() + NumToInsert));
+      Buffer.append(NumToInsert, Elt);
+      Buffer.swap_out_split_buffer(*this, InsertElt);
+      return 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::fill_n(I, NumToInsert, Elt);
       return I;
     }
 
     // Otherwise, we're inserting more elements than exist already, and we're
     // not inserting at the end.
 
     // Move over the elements that we're about to overwrite.
     T *OldEnd = this->end();
     this->set_size(this->size() + NumToInsert);
     size_t NumOverwritten = OldEnd-I;
     this->uninitialized_move(I, OldEnd, this->end()-NumOverwritten);
 
     // Replace the overwritten part.
     std::fill_n(I, NumOverwritten, Elt);
 
     // Insert the non-overwritten middle part.
     std::uninitialized_fill_n(OldEnd, NumToInsert-NumOverwritten, Elt);
     return I;
   }
 
   template <typename ItTy,
             typename = std::enable_if_t<std::is_convertible<
                 typename std::iterator_traits<ItTy>::iterator_category,
                 std::input_iterator_tag>::value>>
   iterator insert(iterator I, ItTy From, ItTy To) {
     // Convert iterator to elt# to avoid invalidating iterator when we reserve()
     size_t InsertElt = I - this->begin();
 
     if (I == this->end()) {  // Important special case for empty vector.
       append(From, To);
       return this->begin()+InsertElt;
     }
 
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
     size_t NumToInsert = std::distance(From, To);
 
-    // Ensure there is enough space.
-    reserve(this->size() + NumToInsert);
-
-    // Uninvalidate the iterator.
-    I = this->begin()+InsertElt;
+    if ((this->size() + NumToInsert) > this->capacity()) {
+      detail::GrowBuffer<T> Buffer(InsertElt,
+                                   this->grow_size(this->size() + NumToInsert));
+      Buffer.append(From, To);
+      Buffer.swap_out_split_buffer(*this, InsertElt);
+      return 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()))
-      this->grow();
-    ::new ((void *)this->end()) T(std::forward<ArgTypes>(Args)...);
-    this->set_size(this->size() + 1);
+    if (LLVM_UNLIKELY(this->size() >= this->capacity())) {
+      detail::GrowBuffer<T> Buffer(this->size(), this->grow_size());
+      Buffer.emplace(std::forward<ArgTypes>(Args)...);
+      Buffer.swap_out_buffer(*this);
+    } else {
+      ::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());
   }
 };
 
 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;
   }
   if (RHS.size() > this->capacity())
     this->grow(RHS.size());
   if (this->size() > RHS.capacity())
     RHS.grow(this->size());
 
   // Swap the shared elements.
   size_t NumShared = this->size();
   if (NumShared > RHS.size()) NumShared = RHS.size();
   for (size_type i = 0; i != NumShared; ++i)
     std::swap((*this)[i], RHS[i]);
 
   // Copy over the extra elts.
   if (this->size() > RHS.size()) {
     size_t EltDiff = this->size() - RHS.size();
     this->uninitialized_copy(this->begin()+NumShared, this->end(), RHS.end());
     RHS.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->destroy_range(this->begin(), this->end());
     this->set_size(0);
     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->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();
     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->destroy_range(this->begin(), this->end());
     this->set_size(0);
     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 {
   AlignedCharArrayUnion<T> InlineElts[N];
 };
 
 /// 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(alignof(T)) SmallVectorStorage<T, 0> {};
 
 /// This is a 'vector' (really, a variable-sized array), optimized
 /// for the case when the array is small.  It contains some number of elements
 /// in-place, which allows it to avoid heap allocation when the actual number of
 /// elements is below that threshold.  This allows normal "small" cases to be
 /// fast without losing generality for large inputs.
 ///
 /// Note that this does not attempt to be exception safe.
 ///
 template <typename T, unsigned N>
 class 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, const T &Value = T())
     : SmallVectorImpl<T>(N) {
     this->assign(Size, Value);
   }
 
   template <typename ItTy,
             typename = std::enable_if_t<std::is_convertible<
                 typename std::iterator_traits<ItTy>::iterator_category,
                 std::input_iterator_tag>::value>>
   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->assign(IL);
   }
 
   SmallVector(const SmallVector &RHS) : SmallVectorImpl<T>(N) {
     if (!RHS.empty())
       SmallVectorImpl<T>::operator=(RHS);
   }
 
   const SmallVector &operator=(const SmallVector &RHS) {
     SmallVectorImpl<T>::operator=(RHS);
     return *this;
   }
 
   SmallVector(SmallVector &&RHS) : SmallVectorImpl<T>(N) {
     if (!RHS.empty())
       SmallVectorImpl<T>::operator=(::std::move(RHS));
   }
 
   SmallVector(SmallVectorImpl<T> &&RHS) : SmallVectorImpl<T>(N) {
     if (!RHS.empty())
       SmallVectorImpl<T>::operator=(::std::move(RHS));
   }
 
   const SmallVector &operator=(SmallVector &&RHS) {
     SmallVectorImpl<T>::operator=(::std::move(RHS));
     return *this;
   }
 
   const SmallVector &operator=(SmallVectorImpl<T> &&RHS) {
     SmallVectorImpl<T>::operator=(::std::move(RHS));
     return *this;
   }
 
   const 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();
 }
 
 /// 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<typename std::remove_const<typename std::remove_reference<
                 decltype(*std::begin(std::declval<R &>()))>::type>::type,
             Size>
 to_vector(R &&Range) {
   return {std::begin(Range), std::end(Range)};
 }
 
 } // 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
 
 #endif // LLVM_ADT_SMALLVECTOR_H
diff --git a/llvm/unittests/ADT/SmallVectorTest.cpp b/llvm/unittests/ADT/SmallVectorTest.cpp
index dbe404869e2..a69a6a501ff 100644
--- a/llvm/unittests/ADT/SmallVectorTest.cpp
+++ b/llvm/unittests/ADT/SmallVectorTest.cpp
@@ -1,1003 +1,1038 @@
 //===- llvm/unittest/ADT/SmallVectorTest.cpp ------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 //
 // SmallVector unit tests.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Support/Compiler.h"
 #include "gtest/gtest.h"
 #include <list>
 #include <stdarg.h>
 
 using namespace llvm;
 
 namespace {
 
 /// A helper class that counts the total number of constructor and
 /// destructor calls.
 class Constructable {
 private:
   static int numConstructorCalls;
   static int numMoveConstructorCalls;
   static int numCopyConstructorCalls;
   static int numDestructorCalls;
   static int numAssignmentCalls;
   static int numMoveAssignmentCalls;
   static int numCopyAssignmentCalls;
+  enum class ObjectState { Destroyed = 0, Constructed, MovedFrom };
 
-  bool constructed;
+  ObjectState State;
   int value;
 
 public:
-  Constructable() : constructed(true), value(0) {
+  Constructable() : State(ObjectState::Constructed), value(0) {
     ++numConstructorCalls;
   }
 
-  Constructable(int val) : constructed(true), value(val) {
+  Constructable(int val) : State(ObjectState::Constructed), value(val) {
     ++numConstructorCalls;
   }
 
-  Constructable(const Constructable & src) : constructed(true) {
+  Constructable(const Constructable &src) : State(src.State) {
+    EXPECT_EQ(State, ObjectState::Constructed);
     value = src.value;
     ++numConstructorCalls;
     ++numCopyConstructorCalls;
   }
 
-  Constructable(Constructable && src) : constructed(true) {
+  Constructable(Constructable &&src) : State(src.State) {
+    EXPECT_EQ(State, ObjectState::Constructed);
     value = src.value;
+    src.State = ObjectState::MovedFrom;
     ++numConstructorCalls;
     ++numMoveConstructorCalls;
   }
 
   ~Constructable() {
-    EXPECT_TRUE(constructed);
+    EXPECT_NE(State, ObjectState::Destroyed);
     ++numDestructorCalls;
-    constructed = false;
+    State = ObjectState::Destroyed;
   }
 
   Constructable & operator=(const Constructable & src) {
-    EXPECT_TRUE(constructed);
+    EXPECT_NE(State, ObjectState::Destroyed);
+    EXPECT_EQ(src.State, ObjectState::Constructed);
+    State = src.State;
     value = src.value;
     ++numAssignmentCalls;
     ++numCopyAssignmentCalls;
     return *this;
   }
 
   Constructable & operator=(Constructable && src) {
-    EXPECT_TRUE(constructed);
+    EXPECT_NE(State, ObjectState::Destroyed);
+    EXPECT_EQ(src.State, ObjectState::Constructed);
+    State = src.State;
     value = src.value;
+    src.State = ObjectState::MovedFrom;
     ++numAssignmentCalls;
     ++numMoveAssignmentCalls;
     return *this;
   }
 
   int getValue() const {
+    EXPECT_EQ(State, ObjectState::Constructed);
     return abs(value);
   }
 
   static void reset() {
     numConstructorCalls = 0;
     numMoveConstructorCalls = 0;
     numCopyConstructorCalls = 0;
     numDestructorCalls = 0;
     numAssignmentCalls = 0;
     numMoveAssignmentCalls = 0;
     numCopyAssignmentCalls = 0;
   }
 
   static int getNumConstructorCalls() {
     return numConstructorCalls;
   }
 
   static int getNumMoveConstructorCalls() {
     return numMoveConstructorCalls;
   }
 
   static int getNumCopyConstructorCalls() {
     return numCopyConstructorCalls;
   }
 
   static int getNumDestructorCalls() {
     return numDestructorCalls;
   }
 
   static int getNumAssignmentCalls() {
     return numAssignmentCalls;
   }
 
   static int getNumMoveAssignmentCalls() {
     return numMoveAssignmentCalls;
   }
 
   static int getNumCopyAssignmentCalls() {
     return numCopyAssignmentCalls;
   }
 
   friend bool operator==(const Constructable & c0, const Constructable & c1) {
     return c0.getValue() == c1.getValue();
   }
 
   friend bool LLVM_ATTRIBUTE_UNUSED
   operator!=(const Constructable & c0, const Constructable & c1) {
     return c0.getValue() != c1.getValue();
   }
 };
 
 int Constructable::numConstructorCalls;
 int Constructable::numCopyConstructorCalls;
 int Constructable::numMoveConstructorCalls;
 int Constructable::numDestructorCalls;
 int Constructable::numAssignmentCalls;
 int Constructable::numCopyAssignmentCalls;
 int Constructable::numMoveAssignmentCalls;
 
 struct NonCopyable {
   NonCopyable() {}
   NonCopyable(NonCopyable &&) {}
   NonCopyable &operator=(NonCopyable &&) { return *this; }
 private:
   NonCopyable(const NonCopyable &) = delete;
   NonCopyable &operator=(const NonCopyable &) = delete;
 };
 
 LLVM_ATTRIBUTE_USED void CompileTest() {
   SmallVector<NonCopyable, 0> V;
   V.resize(42);
 }
 
 class SmallVectorTestBase : public testing::Test {
 protected:
   void SetUp() override { Constructable::reset(); }
 
   template <typename VectorT>
   void assertEmpty(VectorT & v) {
     // Size tests
     EXPECT_EQ(0u, v.size());
     EXPECT_TRUE(v.empty());
 
     // Iterator tests
     EXPECT_TRUE(v.begin() == v.end());
   }
 
   // Assert that v contains the specified values, in order.
   template <typename VectorT>
   void assertValuesInOrder(VectorT & v, size_t size, ...) {
     EXPECT_EQ(size, v.size());
 
     va_list ap;
     va_start(ap, size);
     for (size_t i = 0; i < size; ++i) {
       int value = va_arg(ap, int);
       EXPECT_EQ(value, v[i].getValue());
     }
 
     va_end(ap);
   }
 
   // Generate a sequence of values to initialize the vector.
   template <typename VectorT>
   void makeSequence(VectorT & v, int start, int end) {
     for (int i = start; i <= end; ++i) {
       v.push_back(Constructable(i));
     }
   }
 };
 
 // Test fixture class
 template <typename VectorT>
 class SmallVectorTest : public SmallVectorTestBase {
 protected:
   VectorT theVector;
   VectorT otherVector;
 };
 
 
 typedef ::testing::Types<SmallVector<Constructable, 0>,
                          SmallVector<Constructable, 1>,
                          SmallVector<Constructable, 2>,
                          SmallVector<Constructable, 4>,
                          SmallVector<Constructable, 5>
                          > SmallVectorTestTypes;
 TYPED_TEST_CASE(SmallVectorTest, SmallVectorTestTypes);
 
 // Constructor test.
 TYPED_TEST(SmallVectorTest, ConstructorNonIterTest) {
   SCOPED_TRACE("ConstructorTest");
   this->theVector = SmallVector<Constructable, 2>(2, 2);
   this->assertValuesInOrder(this->theVector, 2u, 2, 2);
 }
 
 // Constructor test.
 TYPED_TEST(SmallVectorTest, ConstructorIterTest) {
   SCOPED_TRACE("ConstructorTest");
   int arr[] = {1, 2, 3};
   this->theVector =
       SmallVector<Constructable, 4>(std::begin(arr), std::end(arr));
   this->assertValuesInOrder(this->theVector, 3u, 1, 2, 3);
 }
 
 // New vector test.
 TYPED_TEST(SmallVectorTest, EmptyVectorTest) {
   SCOPED_TRACE("EmptyVectorTest");
   this->assertEmpty(this->theVector);
   EXPECT_TRUE(this->theVector.rbegin() == this->theVector.rend());
   EXPECT_EQ(0, Constructable::getNumConstructorCalls());
   EXPECT_EQ(0, Constructable::getNumDestructorCalls());
 }
 
 // Simple insertions and deletions.
 TYPED_TEST(SmallVectorTest, PushPopTest) {
   SCOPED_TRACE("PushPopTest");
 
   // Track whether the vector will potentially have to grow.
   bool RequiresGrowth = this->theVector.capacity() < 3;
 
   // Push an element
   this->theVector.push_back(Constructable(1));
 
   // Size tests
   this->assertValuesInOrder(this->theVector, 1u, 1);
   EXPECT_FALSE(this->theVector.begin() == this->theVector.end());
   EXPECT_FALSE(this->theVector.empty());
 
   // Push another element
   this->theVector.push_back(Constructable(2));
   this->assertValuesInOrder(this->theVector, 2u, 1, 2);
 
   // Insert at beginning
   this->theVector.insert(this->theVector.begin(), this->theVector[1]);
   this->assertValuesInOrder(this->theVector, 3u, 2, 1, 2);
 
   // Pop one element
   this->theVector.pop_back();
   this->assertValuesInOrder(this->theVector, 2u, 2, 1);
 
   // Pop remaining elements
   this->theVector.pop_back();
   this->theVector.pop_back();
   this->assertEmpty(this->theVector);
 
   // Check number of constructor calls. Should be 2 for each list element,
   // one for the argument to push_back, one for the argument to insert,
   // and one for the list element itself.
   if (!RequiresGrowth) {
     EXPECT_EQ(5, Constructable::getNumConstructorCalls());
     EXPECT_EQ(5, Constructable::getNumDestructorCalls());
   } else {
     // If we had to grow the vector, these only have a lower bound, but should
     // always be equal.
     EXPECT_LE(5, Constructable::getNumConstructorCalls());
     EXPECT_EQ(Constructable::getNumConstructorCalls(),
               Constructable::getNumDestructorCalls());
   }
 }
 
 // Clear test.
 TYPED_TEST(SmallVectorTest, ClearTest) {
   SCOPED_TRACE("ClearTest");
 
   this->theVector.reserve(2);
   this->makeSequence(this->theVector, 1, 2);
   this->theVector.clear();
 
   this->assertEmpty(this->theVector);
   EXPECT_EQ(4, Constructable::getNumConstructorCalls());
   EXPECT_EQ(4, Constructable::getNumDestructorCalls());
 }
 
 // Resize smaller test.
 TYPED_TEST(SmallVectorTest, ResizeShrinkTest) {
   SCOPED_TRACE("ResizeShrinkTest");
 
   this->theVector.reserve(3);
   this->makeSequence(this->theVector, 1, 3);
   this->theVector.resize(1);
 
   this->assertValuesInOrder(this->theVector, 1u, 1);
   EXPECT_EQ(6, Constructable::getNumConstructorCalls());
   EXPECT_EQ(5, Constructable::getNumDestructorCalls());
 }
 
 // Resize bigger test.
 TYPED_TEST(SmallVectorTest, ResizeGrowTest) {
   SCOPED_TRACE("ResizeGrowTest");
 
   this->theVector.resize(2);
 
   EXPECT_EQ(2, Constructable::getNumConstructorCalls());
   EXPECT_EQ(0, Constructable::getNumDestructorCalls());
   EXPECT_EQ(2u, this->theVector.size());
 }
 
 TYPED_TEST(SmallVectorTest, ResizeWithElementsTest) {
   this->theVector.resize(2);
 
   Constructable::reset();
 
   this->theVector.resize(4);
 
   size_t Ctors = Constructable::getNumConstructorCalls();
   EXPECT_TRUE(Ctors == 2 || Ctors == 4);
   size_t MoveCtors = Constructable::getNumMoveConstructorCalls();
   EXPECT_TRUE(MoveCtors == 0 || MoveCtors == 2);
   size_t Dtors = Constructable::getNumDestructorCalls();
   EXPECT_TRUE(Dtors == 0 || Dtors == 2);
 }
 
 // Resize with fill value.
 TYPED_TEST(SmallVectorTest, ResizeFillTest) {
   SCOPED_TRACE("ResizeFillTest");
 
   this->theVector.resize(3, Constructable(77));
   this->assertValuesInOrder(this->theVector, 3u, 77, 77, 77);
 }
 
 // Overflow past fixed size.
 TYPED_TEST(SmallVectorTest, OverflowTest) {
   SCOPED_TRACE("OverflowTest");
 
   // Push more elements than the fixed size.
   this->makeSequence(this->theVector, 1, 10);
 
   // Test size and values.
   EXPECT_EQ(10u, this->theVector.size());
   for (int i = 0; i < 10; ++i) {
     EXPECT_EQ(i+1, this->theVector[i].getValue());
   }
 
   // Now resize back to fixed size.
   this->theVector.resize(1);
 
   this->assertValuesInOrder(this->theVector, 1u, 1);
 }
 
 // Iteration tests.
 TYPED_TEST(SmallVectorTest, IterationTest) {
   this->makeSequence(this->theVector, 1, 2);
 
   // Forward Iteration
   typename TypeParam::iterator it = this->theVector.begin();
   EXPECT_TRUE(*it == this->theVector.front());
   EXPECT_TRUE(*it == this->theVector[0]);
   EXPECT_EQ(1, it->getValue());
   ++it;
   EXPECT_TRUE(*it == this->theVector[1]);
   EXPECT_TRUE(*it == this->theVector.back());
   EXPECT_EQ(2, it->getValue());
   ++it;
   EXPECT_TRUE(it == this->theVector.end());
   --it;
   EXPECT_TRUE(*it == this->theVector[1]);
   EXPECT_EQ(2, it->getValue());
   --it;
   EXPECT_TRUE(*it == this->theVector[0]);
   EXPECT_EQ(1, it->getValue());
 
   // Reverse Iteration
   typename TypeParam::reverse_iterator rit = this->theVector.rbegin();
   EXPECT_TRUE(*rit == this->theVector[1]);
   EXPECT_EQ(2, rit->getValue());
   ++rit;
   EXPECT_TRUE(*rit == this->theVector[0]);
   EXPECT_EQ(1, rit->getValue());
   ++rit;
   EXPECT_TRUE(rit == this->theVector.rend());
   --rit;
   EXPECT_TRUE(*rit == this->theVector[0]);
   EXPECT_EQ(1, rit->getValue());
   --rit;
   EXPECT_TRUE(*rit == this->theVector[1]);
   EXPECT_EQ(2, rit->getValue());
 }
 
 // Swap test.
 TYPED_TEST(SmallVectorTest, SwapTest) {
   SCOPED_TRACE("SwapTest");
 
   this->makeSequence(this->theVector, 1, 2);
   std::swap(this->theVector, this->otherVector);
 
   this->assertEmpty(this->theVector);
   this->assertValuesInOrder(this->otherVector, 2u, 1, 2);
 }
 
 // Append test
 TYPED_TEST(SmallVectorTest, AppendTest) {
   SCOPED_TRACE("AppendTest");
 
   this->makeSequence(this->otherVector, 2, 3);
 
   this->theVector.push_back(Constructable(1));
   this->theVector.append(this->otherVector.begin(), this->otherVector.end());
 
   this->assertValuesInOrder(this->theVector, 3u, 1, 2, 3);
 }
 
 // Append repeated test
 TYPED_TEST(SmallVectorTest, AppendRepeatedTest) {
   SCOPED_TRACE("AppendRepeatedTest");
 
   this->theVector.push_back(Constructable(1));
   this->theVector.append(2, Constructable(77));
   this->assertValuesInOrder(this->theVector, 3u, 1, 77, 77);
 }
 
 // Append test
 TYPED_TEST(SmallVectorTest, AppendNonIterTest) {
   SCOPED_TRACE("AppendRepeatedTest");
 
   this->theVector.push_back(Constructable(1));
   this->theVector.append(2, 7);
   this->assertValuesInOrder(this->theVector, 3u, 1, 7, 7);
 }
 
 struct output_iterator {
   typedef std::output_iterator_tag iterator_category;
   typedef int value_type;
   typedef int difference_type;
   typedef value_type *pointer;
   typedef value_type &reference;
   operator int() { return 2; }
   operator Constructable() { return 7; }
 };
 
 TYPED_TEST(SmallVectorTest, AppendRepeatedNonForwardIterator) {
   SCOPED_TRACE("AppendRepeatedTest");
 
   this->theVector.push_back(Constructable(1));
   this->theVector.append(output_iterator(), output_iterator());
   this->assertValuesInOrder(this->theVector, 3u, 1, 7, 7);
 }
 
 // Assign test
 TYPED_TEST(SmallVectorTest, AssignTest) {
   SCOPED_TRACE("AssignTest");
 
   this->theVector.push_back(Constructable(1));
+  Constructable::reset();
   this->theVector.assign(2, Constructable(77));
   this->assertValuesInOrder(this->theVector, 2u, 77, 77);
+  EXPECT_EQ(Constructable::getNumCopyAssignmentCalls() +
+                Constructable::getNumCopyConstructorCalls(),
+            2);
 }
 
 // Assign test
 TYPED_TEST(SmallVectorTest, AssignRangeTest) {
   SCOPED_TRACE("AssignTest");
 
   this->theVector.push_back(Constructable(1));
   int arr[] = {1, 2, 3};
   this->theVector.assign(std::begin(arr), std::end(arr));
   this->assertValuesInOrder(this->theVector, 3u, 1, 2, 3);
 }
 
 // Assign test
 TYPED_TEST(SmallVectorTest, AssignNonIterTest) {
   SCOPED_TRACE("AssignTest");
 
   this->theVector.push_back(Constructable(1));
+  Constructable::reset();
   this->theVector.assign(2, 7);
   this->assertValuesInOrder(this->theVector, 2u, 7, 7);
+  EXPECT_EQ(Constructable::getNumCopyAssignmentCalls() +
+                Constructable::getNumCopyConstructorCalls(),
+            2);
 }
 
 // Move-assign test
 TYPED_TEST(SmallVectorTest, MoveAssignTest) {
   SCOPED_TRACE("MoveAssignTest");
 
   // Set up our vector with a single element, but enough capacity for 4.
   this->theVector.reserve(4);
   this->theVector.push_back(Constructable(1));
   
   // Set up the other vector with 2 elements.
   this->otherVector.push_back(Constructable(2));
   this->otherVector.push_back(Constructable(3));
 
   // Move-assign from the other vector.
   this->theVector = std::move(this->otherVector);
 
   // Make sure we have the right result.
   this->assertValuesInOrder(this->theVector, 2u, 2, 3);
 
   // Make sure the # of constructor/destructor calls line up. There
   // are two live objects after clearing the other vector.
   this->otherVector.clear();
   EXPECT_EQ(Constructable::getNumConstructorCalls()-2, 
             Constructable::getNumDestructorCalls());
 
   // There shouldn't be any live objects any more.
   this->theVector.clear();
   EXPECT_EQ(Constructable::getNumConstructorCalls(), 
             Constructable::getNumDestructorCalls());
 }
 
 // Erase a single element
 TYPED_TEST(SmallVectorTest, EraseTest) {
   SCOPED_TRACE("EraseTest");
 
   this->makeSequence(this->theVector, 1, 3);
   const auto &theConstVector = this->theVector;
   this->theVector.erase(theConstVector.begin());
   this->assertValuesInOrder(this->theVector, 2u, 2, 3);
 }
 
 // Erase a range of elements
 TYPED_TEST(SmallVectorTest, EraseRangeTest) {
   SCOPED_TRACE("EraseRangeTest");
 
   this->makeSequence(this->theVector, 1, 3);
   const auto &theConstVector = this->theVector;
   this->theVector.erase(theConstVector.begin(), theConstVector.begin() + 2);
   this->assertValuesInOrder(this->theVector, 1u, 3);
 }
 
 // Insert a single element.
 TYPED_TEST(SmallVectorTest, InsertTest) {
   SCOPED_TRACE("InsertTest");
 
   this->makeSequence(this->theVector, 1, 3);
   typename TypeParam::iterator I =
     this->theVector.insert(this->theVector.begin() + 1, Constructable(77));
   EXPECT_EQ(this->theVector.begin() + 1, I);
   this->assertValuesInOrder(this->theVector, 4u, 1, 77, 2, 3);
 }
 
 // Insert a copy of a single element.
 TYPED_TEST(SmallVectorTest, InsertCopy) {
   SCOPED_TRACE("InsertTest");
 
   this->makeSequence(this->theVector, 1, 3);
   Constructable C(77);
   typename TypeParam::iterator I =
       this->theVector.insert(this->theVector.begin() + 1, C);
   EXPECT_EQ(this->theVector.begin() + 1, I);
   this->assertValuesInOrder(this->theVector, 4u, 1, 77, 2, 3);
 }
 
 // Insert repeated elements.
 TYPED_TEST(SmallVectorTest, InsertRepeatedTest) {
   SCOPED_TRACE("InsertRepeatedTest");
 
   this->makeSequence(this->theVector, 1, 4);
   Constructable::reset();
+  bool RequiresGrowth = this->theVector.capacity() < 6;
   auto I =
       this->theVector.insert(this->theVector.begin() + 1, 2, Constructable(16));
-  // Move construct the top element into newly allocated space, and optionally
-  // reallocate the whole buffer, move constructing into it.
-  // FIXME: This is inefficient, we shouldn't move things into newly allocated
-  // space, then move them up/around, there should only be 2 or 4 move
-  // constructions here.
-  EXPECT_TRUE(Constructable::getNumMoveConstructorCalls() == 2 ||
-              Constructable::getNumMoveConstructorCalls() == 6);
-  // Move assign the next two to shift them up and make a gap.
-  EXPECT_EQ(1, Constructable::getNumMoveAssignmentCalls());
-  // Copy construct the two new elements from the parameter.
-  EXPECT_EQ(2, Constructable::getNumCopyAssignmentCalls());
-  // All without any copy construction.
-  EXPECT_EQ(0, Constructable::getNumCopyConstructorCalls());
+
+  if (RequiresGrowth) {
+    // Moving [1] and [2,3,4] into the new storage.
+    EXPECT_EQ(4, Constructable::getNumMoveConstructorCalls());
+    // Copy construct the new elements directly into the new storage.
+    EXPECT_EQ(2, Constructable::getNumCopyConstructorCalls());
+    // Nothing is move or copy assigned in the growth case.
+    EXPECT_EQ(0, Constructable::getNumMoveAssignmentCalls());
+    EXPECT_EQ(0, Constructable::getNumCopyAssignmentCalls());
+  } else {
+    // Shifting [3,4] down 2 blocks into uninitialized storage.
+    EXPECT_EQ(2, Constructable::getNumMoveConstructorCalls());
+    // Shifting [2] into where [4] lived.
+    EXPECT_EQ(1, Constructable::getNumMoveAssignmentCalls());
+    // Copy assign the two new elements inside the buffer.
+    EXPECT_EQ(2, Constructable::getNumCopyAssignmentCalls());
+    EXPECT_EQ(0, Constructable::getNumCopyConstructorCalls());
+  }
+
   EXPECT_EQ(this->theVector.begin() + 1, I);
   this->assertValuesInOrder(this->theVector, 6u, 1, 16, 16, 2, 3, 4);
 }
 
 TYPED_TEST(SmallVectorTest, InsertRepeatedNonIterTest) {
   SCOPED_TRACE("InsertRepeatedTest");
 
   this->makeSequence(this->theVector, 1, 4);
   Constructable::reset();
   auto I = this->theVector.insert(this->theVector.begin() + 1, 2, 7);
   EXPECT_EQ(this->theVector.begin() + 1, I);
   this->assertValuesInOrder(this->theVector, 6u, 1, 7, 7, 2, 3, 4);
 }
 
 TYPED_TEST(SmallVectorTest, InsertRepeatedAtEndTest) {
   SCOPED_TRACE("InsertRepeatedTest");
 
   this->makeSequence(this->theVector, 1, 4);
   Constructable::reset();
   auto I = this->theVector.insert(this->theVector.end(), 2, Constructable(16));
   // Just copy construct them into newly allocated space
   EXPECT_EQ(2, Constructable::getNumCopyConstructorCalls());
   // Move everything across if reallocation is needed.
   EXPECT_TRUE(Constructable::getNumMoveConstructorCalls() == 0 ||
               Constructable::getNumMoveConstructorCalls() == 4);
   // Without ever moving or copying anything else.
   EXPECT_EQ(0, Constructable::getNumCopyAssignmentCalls());
   EXPECT_EQ(0, Constructable::getNumMoveAssignmentCalls());
 
   EXPECT_EQ(this->theVector.begin() + 4, I);
   this->assertValuesInOrder(this->theVector, 6u, 1, 2, 3, 4, 16, 16);
 }
 
 TYPED_TEST(SmallVectorTest, InsertRepeatedEmptyTest) {
   SCOPED_TRACE("InsertRepeatedTest");
 
   this->makeSequence(this->theVector, 10, 15);
 
   // Empty insert.
   EXPECT_EQ(this->theVector.end(),
             this->theVector.insert(this->theVector.end(),
                                    0, Constructable(42)));
   EXPECT_EQ(this->theVector.begin() + 1,
             this->theVector.insert(this->theVector.begin() + 1,
                                    0, Constructable(42)));
 }
 
 // Insert range.
 TYPED_TEST(SmallVectorTest, InsertRangeTest) {
   SCOPED_TRACE("InsertRangeTest");
 
   Constructable Arr[3] =
     { Constructable(77), Constructable(77), Constructable(77) };
 
   this->makeSequence(this->theVector, 1, 3);
   Constructable::reset();
+  bool RequiresGrowth = this->theVector.capacity() < 6;
   auto I = this->theVector.insert(this->theVector.begin() + 1, Arr, Arr + 3);
-  // Move construct the top 3 elements into newly allocated space.
-  // Possibly move the whole sequence into new space first.
-  // FIXME: This is inefficient, we shouldn't move things into newly allocated
-  // space, then move them up/around, there should only be 2 or 3 move
-  // constructions here.
-  EXPECT_TRUE(Constructable::getNumMoveConstructorCalls() == 2 ||
-              Constructable::getNumMoveConstructorCalls() == 5);
-  // Copy assign the lower 2 new elements into existing space.
-  EXPECT_EQ(2, Constructable::getNumCopyAssignmentCalls());
-  // Copy construct the third element into newly allocated space.
-  EXPECT_EQ(1, Constructable::getNumCopyConstructorCalls());
+
+  if (RequiresGrowth) {
+    // Moving [1] and [2,3] into the new storage.
+    EXPECT_EQ(3, Constructable::getNumMoveConstructorCalls());
+    // Copy construct the 3 items from Arr into the new storage.
+    EXPECT_EQ(3, Constructable::getNumCopyConstructorCalls());
+    // Nothing is move or copy assigned in the growth case.
+    EXPECT_EQ(0, Constructable::getNumMoveAssignmentCalls());
+    EXPECT_EQ(0, Constructable::getNumCopyAssignmentCalls());
+  } else {
+    // Shifting [2,3] down 3 blocks into uninitialized storage.
+    EXPECT_EQ(2, Constructable::getNumMoveConstructorCalls());
+    // Copy assign the lower 2 new elements into existing storage.
+    EXPECT_EQ(2, Constructable::getNumCopyAssignmentCalls());
+    // Copy construct the third element into uninitialized storage.
+    EXPECT_EQ(1, Constructable::getNumCopyConstructorCalls());
+    // Nothing needs to be move assigned here as the only items that need
+    // shifting, are shifted into uninitialized storage.
+    EXPECT_EQ(0, Constructable::getNumMoveAssignmentCalls());
+  }
   EXPECT_EQ(this->theVector.begin() + 1, I);
   this->assertValuesInOrder(this->theVector, 6u, 1, 77, 77, 77, 2, 3);
 }
 
 
 TYPED_TEST(SmallVectorTest, InsertRangeAtEndTest) {
   SCOPED_TRACE("InsertRangeTest");
 
   Constructable Arr[3] =
     { Constructable(77), Constructable(77), Constructable(77) };
 
   this->makeSequence(this->theVector, 1, 3);
 
   // Insert at end.
   Constructable::reset();
   auto I = this->theVector.insert(this->theVector.end(), Arr, Arr+3);
   // Copy construct the 3 elements into new space at the top.
   EXPECT_EQ(3, Constructable::getNumCopyConstructorCalls());
   // Don't copy/move anything else.
   EXPECT_EQ(0, Constructable::getNumCopyAssignmentCalls());
   // Reallocation might occur, causing all elements to be moved into the new
   // buffer.
   EXPECT_TRUE(Constructable::getNumMoveConstructorCalls() == 0 ||
               Constructable::getNumMoveConstructorCalls() == 3);
   EXPECT_EQ(0, Constructable::getNumMoveAssignmentCalls());
   EXPECT_EQ(this->theVector.begin() + 3, I);
   this->assertValuesInOrder(this->theVector, 6u,
                             1, 2, 3, 77, 77, 77);
 }
 
 TYPED_TEST(SmallVectorTest, InsertEmptyRangeTest) {
   SCOPED_TRACE("InsertRangeTest");
 
   this->makeSequence(this->theVector, 1, 3);
 
   // Empty insert.
   EXPECT_EQ(this->theVector.end(),
             this->theVector.insert(this->theVector.end(),
                                    this->theVector.begin(),
                                    this->theVector.begin()));
   EXPECT_EQ(this->theVector.begin() + 1,
             this->theVector.insert(this->theVector.begin() + 1,
                                    this->theVector.begin(),
                                    this->theVector.begin()));
 }
 
 // Comparison tests.
 TYPED_TEST(SmallVectorTest, ComparisonTest) {
   SCOPED_TRACE("ComparisonTest");
 
   this->makeSequence(this->theVector, 1, 3);
   this->makeSequence(this->otherVector, 1, 3);
 
   EXPECT_TRUE(this->theVector == this->otherVector);
   EXPECT_FALSE(this->theVector != this->otherVector);
 
   this->otherVector.clear();
   this->makeSequence(this->otherVector, 2, 4);
 
   EXPECT_FALSE(this->theVector == this->otherVector);
   EXPECT_TRUE(this->theVector != this->otherVector);
 }
 
 // Constant vector tests.
 TYPED_TEST(SmallVectorTest, ConstVectorTest) {
   const TypeParam constVector;
 
   EXPECT_EQ(0u, constVector.size());
   EXPECT_TRUE(constVector.empty());
   EXPECT_TRUE(constVector.begin() == constVector.end());
 }
 
 // Direct array access.
 TYPED_TEST(SmallVectorTest, DirectVectorTest) {
   EXPECT_EQ(0u, this->theVector.size());
   this->theVector.reserve(4);
   EXPECT_LE(4u, this->theVector.capacity());
   EXPECT_EQ(0, Constructable::getNumConstructorCalls());
   this->theVector.push_back(1);
   this->theVector.push_back(2);
   this->theVector.push_back(3);
   this->theVector.push_back(4);
   EXPECT_EQ(4u, this->theVector.size());
   EXPECT_EQ(8, Constructable::getNumConstructorCalls());
   EXPECT_EQ(1, this->theVector[0].getValue());
   EXPECT_EQ(2, this->theVector[1].getValue());
   EXPECT_EQ(3, this->theVector[2].getValue());
   EXPECT_EQ(4, this->theVector[3].getValue());
 }
 
 TYPED_TEST(SmallVectorTest, IteratorTest) {
   std::list<int> L;
   this->theVector.insert(this->theVector.end(), L.begin(), L.end());
 }
 
 template <typename InvalidType> class DualSmallVectorsTest;
 
 template <typename VectorT1, typename VectorT2>
 class DualSmallVectorsTest<std::pair<VectorT1, VectorT2>> : public SmallVectorTestBase {
 protected:
   VectorT1 theVector;
   VectorT2 otherVector;
 
   template <typename T, unsigned N>
   static unsigned NumBuiltinElts(const SmallVector<T, N>&) { return N; }
 };
 
 typedef ::testing::Types<
     // Small mode -> Small mode.
     std::pair<SmallVector<Constructable, 4>, SmallVector<Constructable, 4>>,
     // Small mode -> Big mode.
     std::pair<SmallVector<Constructable, 4>, SmallVector<Constructable, 2>>,
     // Big mode -> Small mode.
     std::pair<SmallVector<Constructable, 2>, SmallVector<Constructable, 4>>,
     // Big mode -> Big mode.
     std::pair<SmallVector<Constructable, 2>, SmallVector<Constructable, 2>>
   > DualSmallVectorTestTypes;
 
 TYPED_TEST_CASE(DualSmallVectorsTest, DualSmallVectorTestTypes);
 
 TYPED_TEST(DualSmallVectorsTest, MoveAssignment) {
   SCOPED_TRACE("MoveAssignTest-DualVectorTypes");
 
   // Set up our vector with four elements.
   for (unsigned I = 0; I < 4; ++I)
     this->otherVector.push_back(Constructable(I));
 
   const Constructable *OrigDataPtr = this->otherVector.data();
 
   // Move-assign from the other vector.
   this->theVector =
     std::move(static_cast<SmallVectorImpl<Constructable>&>(this->otherVector));
 
   // Make sure we have the right result.
   this->assertValuesInOrder(this->theVector, 4u, 0, 1, 2, 3);
 
   // Make sure the # of constructor/destructor calls line up. There
   // are two live objects after clearing the other vector.
   this->otherVector.clear();
   EXPECT_EQ(Constructable::getNumConstructorCalls()-4,
             Constructable::getNumDestructorCalls());
 
   // If the source vector (otherVector) was in small-mode, assert that we just
   // moved the data pointer over.
   EXPECT_TRUE(this->NumBuiltinElts(this->otherVector) == 4 ||
               this->theVector.data() == OrigDataPtr);
 
   // There shouldn't be any live objects any more.
   this->theVector.clear();
   EXPECT_EQ(Constructable::getNumConstructorCalls(),
             Constructable::getNumDestructorCalls());
 
   // We shouldn't have copied anything in this whole process.
   EXPECT_EQ(Constructable::getNumCopyConstructorCalls(), 0);
 }
 
 struct notassignable {
   int &x;
   notassignable(int &x) : x(x) {}
 };
 
 TEST(SmallVectorCustomTest, NoAssignTest) {
   int x = 0;
   SmallVector<notassignable, 2> vec;
   vec.push_back(notassignable(x));
   x = 42;
   EXPECT_EQ(42, vec.pop_back_val().x);
 }
 
 struct MovedFrom {
   bool hasValue;
   MovedFrom() : hasValue(true) {
   }
   MovedFrom(MovedFrom&& m) : hasValue(m.hasValue) {
     m.hasValue = false;
   }
   MovedFrom &operator=(MovedFrom&& m) {
     hasValue = m.hasValue;
     m.hasValue = false;
     return *this;
   }
 };
 
 TEST(SmallVectorTest, MidInsert) {
   SmallVector<MovedFrom, 3> v;
   v.push_back(MovedFrom());
   v.insert(v.begin(), MovedFrom());
   for (MovedFrom &m : v)
     EXPECT_TRUE(m.hasValue);
 }
 
 enum EmplaceableArgState {
   EAS_Defaulted,
   EAS_Arg,
   EAS_LValue,
   EAS_RValue,
   EAS_Failure
 };
 template <int I> struct EmplaceableArg {
   EmplaceableArgState State;
   EmplaceableArg() : State(EAS_Defaulted) {}
   EmplaceableArg(EmplaceableArg &&X)
       : State(X.State == EAS_Arg ? EAS_RValue : EAS_Failure) {}
   EmplaceableArg(EmplaceableArg &X)
       : State(X.State == EAS_Arg ? EAS_LValue : EAS_Failure) {}
 
   explicit EmplaceableArg(bool) : State(EAS_Arg) {}
 
 private:
   EmplaceableArg &operator=(EmplaceableArg &&) = delete;
   EmplaceableArg &operator=(const EmplaceableArg &) = delete;
 };
 
 enum EmplaceableState { ES_Emplaced, ES_Moved };
 struct Emplaceable {
   EmplaceableArg<0> A0;
   EmplaceableArg<1> A1;
   EmplaceableArg<2> A2;
   EmplaceableArg<3> A3;
   EmplaceableState State;
 
   Emplaceable() : State(ES_Emplaced) {}
 
   template <class A0Ty>
   explicit Emplaceable(A0Ty &&A0)
       : A0(std::forward<A0Ty>(A0)), State(ES_Emplaced) {}
 
   template <class A0Ty, class A1Ty>
   Emplaceable(A0Ty &&A0, A1Ty &&A1)
       : A0(std::forward<A0Ty>(A0)), A1(std::forward<A1Ty>(A1)),
         State(ES_Emplaced) {}
 
   template <class A0Ty, class A1Ty, class A2Ty>
   Emplaceable(A0Ty &&A0, A1Ty &&A1, A2Ty &&A2)
       : A0(std::forward<A0Ty>(A0)), A1(std::forward<A1Ty>(A1)),
         A2(std::forward<A2Ty>(A2)), State(ES_Emplaced) {}
 
   template <class A0Ty, class A1Ty, class A2Ty, class A3Ty>
   Emplaceable(A0Ty &&A0, A1Ty &&A1, A2Ty &&A2, A3Ty &&A3)
       : A0(std::forward<A0Ty>(A0)), A1(std::forward<A1Ty>(A1)),
         A2(std::forward<A2Ty>(A2)), A3(std::forward<A3Ty>(A3)),
         State(ES_Emplaced) {}
 
   Emplaceable(Emplaceable &&) : State(ES_Moved) {}
   Emplaceable &operator=(Emplaceable &&) {
     State = ES_Moved;
     return *this;
   }
 
 private:
   Emplaceable(const Emplaceable &) = delete;
   Emplaceable &operator=(const Emplaceable &) = delete;
 };
 
 TEST(SmallVectorTest, EmplaceBack) {
   EmplaceableArg<0> A0(true);
   EmplaceableArg<1> A1(true);
   EmplaceableArg<2> A2(true);
   EmplaceableArg<3> A3(true);
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back();
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_Defaulted);
     EXPECT_TRUE(back.A1.State == EAS_Defaulted);
     EXPECT_TRUE(back.A2.State == EAS_Defaulted);
     EXPECT_TRUE(back.A3.State == EAS_Defaulted);
   }
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back(std::move(A0));
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_RValue);
     EXPECT_TRUE(back.A1.State == EAS_Defaulted);
     EXPECT_TRUE(back.A2.State == EAS_Defaulted);
     EXPECT_TRUE(back.A3.State == EAS_Defaulted);
   }
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back(A0);
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_LValue);
     EXPECT_TRUE(back.A1.State == EAS_Defaulted);
     EXPECT_TRUE(back.A2.State == EAS_Defaulted);
     EXPECT_TRUE(back.A3.State == EAS_Defaulted);
   }
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back(A0, A1);
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_LValue);
     EXPECT_TRUE(back.A1.State == EAS_LValue);
     EXPECT_TRUE(back.A2.State == EAS_Defaulted);
     EXPECT_TRUE(back.A3.State == EAS_Defaulted);
   }
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back(std::move(A0), std::move(A1));
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_RValue);
     EXPECT_TRUE(back.A1.State == EAS_RValue);
     EXPECT_TRUE(back.A2.State == EAS_Defaulted);
     EXPECT_TRUE(back.A3.State == EAS_Defaulted);
   }
   {
     SmallVector<Emplaceable, 3> V;
     Emplaceable &back = V.emplace_back(std::move(A0), A1, std::move(A2), A3);
     EXPECT_TRUE(&back == &V.back());
     EXPECT_TRUE(V.size() == 1);
     EXPECT_TRUE(back.State == ES_Emplaced);
     EXPECT_TRUE(back.A0.State == EAS_RValue);
     EXPECT_TRUE(back.A1.State == EAS_LValue);
     EXPECT_TRUE(back.A2.State == EAS_RValue);
     EXPECT_TRUE(back.A3.State == EAS_LValue);
   }
   {
     SmallVector<int, 1> V;
     V.emplace_back();
     V.emplace_back(42);
     EXPECT_EQ(2U, V.size());
     EXPECT_EQ(0, V[0]);
     EXPECT_EQ(42, V[1]);
   }
 }
 
 TEST(SmallVectorTest, InitializerList) {
   SmallVector<int, 2> V1 = {};
   EXPECT_TRUE(V1.empty());
   V1 = {0, 0};
   EXPECT_TRUE(makeArrayRef(V1).equals({0, 0}));
   V1 = {-1, -1};
   EXPECT_TRUE(makeArrayRef(V1).equals({-1, -1}));
 
   SmallVector<int, 2> V2 = {1, 2, 3, 4};
   EXPECT_TRUE(makeArrayRef(V2).equals({1, 2, 3, 4}));
   V2.assign({4});
   EXPECT_TRUE(makeArrayRef(V2).equals({4}));
   V2.append({3, 2});
   EXPECT_TRUE(makeArrayRef(V2).equals({4, 3, 2}));
   V2.insert(V2.begin() + 1, 5);
   EXPECT_TRUE(makeArrayRef(V2).equals({4, 5, 3, 2}));
 }
 
 } // end namespace