Index: llvm/include/llvm/ADT/SmallVector.h
===================================================================
--- llvm/include/llvm/ADT/SmallVector.h
+++ llvm/include/llvm/ADT/SmallVector.h
@@ -136,11 +136,20 @@
     this->Size = this->Capacity = 0; // FIXME: Setting Capacity to 0 is suspect.
   }
 
-  void assertSafeToPush(const void *Elt) {
-    assert(
-        (Elt < begin() || Elt >= end() || this->size() < this->capacity()) &&
-        "Attempting to push_back to the vector an element of the vector without"
-        " enough space reserved");
+  /// Check whether Elt will be invalidated by resizing the vector to NewSize.
+  void assertSafeToReferenceAfterResize(const void *Elt, size_t NewSize) {
+    assert((Elt >= this->end() ||
+            (NewSize <= this->size()
+                 ? Elt < this->begin() + NewSize
+                 : (Elt < this->begin() || NewSize <= this->capacity()))) &&
+           "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) {
+    return this->assertSafeToReferenceAfterResize(Elt, this->size() + N);
   }
 
 public:
@@ -226,7 +235,14 @@
                              (is_trivially_move_constructible<T>::value) &&
                              std::is_trivially_destructible<T>::value>
 class SmallVectorTemplateBase : public SmallVectorTemplateCommon<T> {
+public:
+  /// Take parameters by reference (not by value) since T is not trivially
+  /// copyable.
+  static constexpr bool TakesParamByValue = false;
+
 protected:
+  using ValueParamT = const T &;
+
   SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
 
   static void destroy_range(T *S, T *E) {
@@ -257,8 +273,9 @@
   void grow(size_t MinSize = 0);
 
 public:
-  void push_back(const T &Elt) {
-    this->assertSafeToPush(&Elt);
+  void push_back(ValueParamT Elt) {
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt);
     if (LLVM_UNLIKELY(this->size() >= this->capacity()))
       this->grow();
     ::new ((void*) this->end()) T(Elt);
@@ -266,7 +283,7 @@
   }
 
   void push_back(T &&Elt) {
-    this->assertSafeToPush(&Elt);
+    this->assertSafeToAdd(&Elt);
     if (LLVM_UNLIKELY(this->size() >= this->capacity()))
       this->grow();
     ::new ((void*) this->end()) T(::std::move(Elt));
@@ -319,7 +336,16 @@
 /// skipping destruction.
 template <typename T>
 class SmallVectorTemplateBase<T, true> : public SmallVectorTemplateCommon<T> {
+public:
+  /// Take parameters by value when T is small since it's trivially copyable.
+  static constexpr bool TakesParamByValue =
+      std::conditional<sizeof(T) <= 2 * sizeof(void *), std::true_type,
+                       std::false_type>::type::value;
+
 protected:
+  using ValueParamT =
+      typename std::conditional<TakesParamByValue, T, const T &>::type;
+
   SmallVectorTemplateBase(size_t Size) : SmallVectorTemplateCommon<T>(Size) {}
 
   // No need to do a destroy loop for POD's.
@@ -361,8 +387,9 @@
   void grow(size_t MinSize = 0) { this->grow_pod(MinSize, sizeof(T)); }
 
 public:
-  void push_back(const T &Elt) {
-    this->assertSafeToPush(&Elt);
+  void push_back(ValueParamT Elt) {
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt);
     if (LLVM_UNLIKELY(this->size() >= this->capacity()))
       this->grow();
     memcpy(reinterpret_cast<void *>(this->end()), &Elt, sizeof(T));
@@ -384,7 +411,11 @@
   using reference = typename SuperClass::reference;
   using size_type = typename SuperClass::size_type;
 
+  using SmallVectorTemplateBase<T>::TakesParamByValue;
+
 protected:
+  using ValueParamT = typename SmallVectorTemplateBase<T>::ValueParamT;
+
   // Default ctor - Initialize to empty.
   explicit SmallVectorImpl(unsigned N)
       : SmallVectorTemplateBase<T>(N) {}
@@ -417,7 +448,9 @@
     }
   }
 
-  void resize(size_type N, const T &NV) {
+  void resize(size_type N, ValueParamT NV) {
+    if (!TakesParamByValue)
+      this->assertSafeToReferenceAfterResize(&NV, N);
     if (N < this->size()) {
       this->destroy_range(this->begin()+N, this->end());
       this->set_size(N);
@@ -463,7 +496,9 @@
   }
 
   /// Append \p NumInputs copies of \p Elt to the end.
-  void append(size_type NumInputs, const T &Elt) {
+  void append(size_type NumInputs, ValueParamT Elt) {
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt, NumInputs);
     if (NumInputs > this->capacity() - this->size())
       this->grow(this->size()+NumInputs);
 
@@ -478,7 +513,9 @@
   // FIXME: Consider assigning over existing elements, rather than clearing &
   // re-initializing them - for all assign(...) variants.
 
-  void assign(size_type NumElts, const T &Elt) {
+  void assign(size_type NumElts, ValueParamT Elt) {
+    if (!TakesParamByValue)
+      this->assertSafeToReferenceAfterResize(&Elt, 0);
     clear();
     if (this->capacity() < NumElts)
       this->grow(NumElts);
@@ -533,7 +570,14 @@
     return(N);
   }
 
-  iterator insert(iterator I, T &&Elt) {
+  // Use a mock template argument to allow use of enable_if for disabling this
+  // version of insert when ValueParamT is the same as T.
+  template <class IteratorT>
+  iterator insert(IteratorT I1, T &&Elt,
+                  typename std::enable_if_t<
+                      std::is_convertible<IteratorT, iterator>::value &&
+                      !TakesParamByValue> * = 0) {
+    iterator I = I1;
     if (I == this->end()) {  // Important special case for empty vector.
       this->push_back(::std::move(Elt));
       return this->end()-1;
@@ -542,6 +586,10 @@
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
+    // Check that adding an element won't invalidate Elt.
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt);
+
     if (this->size() >= this->capacity()) {
       size_t EltNo = I-this->begin();
       this->grow();
@@ -563,7 +611,7 @@
     return I;
   }
 
-  iterator insert(iterator I, const T &Elt) {
+  iterator insert(iterator I, ValueParamT Elt) {
     if (I == this->end()) {  // Important special case for empty vector.
       this->push_back(Elt);
       return this->end()-1;
@@ -572,6 +620,10 @@
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
+    // Check that adding an element won't invalidate Elt.
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt);
+
     if (this->size() >= this->capacity()) {
       size_t EltNo = I-this->begin();
       this->grow();
@@ -583,16 +635,17 @@
     this->set_size(this->size() + 1);
 
     // If we just moved the element we're inserting, be sure to update
-    // the reference.
+    // the reference. The check for TakesParamByValue is redundant but can
+    // be resolved at compile-time.
     const T *EltPtr = &Elt;
-    if (I <= EltPtr && EltPtr < this->end())
+    if (!TakesParamByValue && I <= EltPtr && EltPtr < this->end())
       ++EltPtr;
 
     *I = *EltPtr;
     return I;
   }
 
-  iterator insert(iterator I, size_type NumToInsert, const T &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();
 
@@ -604,6 +657,10 @@
     assert(I >= this->begin() && "Insertion iterator is out of bounds.");
     assert(I <= this->end() && "Inserting past the end of the vector.");
 
+    // Check that adding NumToInsert elements won't invalidate Elt.
+    if (!TakesParamByValue)
+      this->assertSafeToAdd(&Elt, NumToInsert);
+
     // Ensure there is enough space.
     reserve(this->size() + NumToInsert);
 
@@ -905,6 +962,8 @@
 template <typename T, unsigned N>
 class LLVM_GSL_OWNER SmallVector : public SmallVectorImpl<T>,
                                    SmallVectorStorage<T, N> {
+  using ValueParamT = typename SmallVectorImpl<T>::ValueParamT;
+
 public:
   SmallVector() : SmallVectorImpl<T>(N) {}
 
@@ -913,8 +972,8 @@
     this->destroy_range(this->begin(), this->end());
   }
 
-  explicit SmallVector(size_t Size, const T &Value = T())
-    : SmallVectorImpl<T>(N) {
+  explicit SmallVector(size_t Size, ValueParamT Value = T())
+      : SmallVectorImpl<T>(N) {
     this->assign(Size, Value);
   }
 
Index: llvm/unittests/ADT/SmallVectorTest.cpp
===================================================================
--- llvm/unittests/ADT/SmallVectorTest.cpp
+++ llvm/unittests/ADT/SmallVectorTest.cpp
@@ -252,8 +252,13 @@
   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]);
+  // Insert at beginning. Take a copy when necessary to avoid having the
+  // element invalidated by growth.
+  if (this->theVector.capacity() < 3)
+    this->theVector.insert(this->theVector.begin(),
+                           Constructable(this->theVector[1]));
+  else
+    this->theVector.insert(this->theVector.begin(), this->theVector[1]);
   this->assertValuesInOrder(this->theVector, 3u, 2, 1, 2);
 
   // Pop one element
@@ -999,4 +1004,131 @@
   EXPECT_TRUE(makeArrayRef(V2).equals({4, 5, 3, 2}));
 }
 
+template <class VectorT>
+class SmallVectorTakesParameterByValueTest : public SmallVectorTestBase {
+protected:
+  bool TakesParamByValue = VectorT::TakesParamByValue;
+  const char *AssertionMessage =
+      "Attempting to reference an element of the vector in an operation \" "
+      "\"that invalidates it";
+
+  VectorT V;
+
+  template <typename T, unsigned N>
+  static unsigned NumBuiltinElts(const SmallVector<T, N> &) {
+    return N;
+  }
+
+  void SetUp() override {
+    SmallVectorTestBase::SetUp();
+
+    // Fill up the small size so that insertions move the elements.
+    V.push_back(0);
+  }
+};
+
+static_assert(SmallVectorImpl<int>::TakesParamByValue,
+              "int should be trivially copyable and small enough");
+static_assert(!SmallVectorImpl<Constructable>::TakesParamByValue,
+              "Constructable should not be trivially copyable");
+using SmallVectorTakesParameterByValueTestTypes =
+    ::testing::Types<SmallVector<int, 1>, SmallVector<Constructable, 1>>;
+
+TYPED_TEST_CASE(SmallVectorTakesParameterByValueTest,
+                SmallVectorTakesParameterByValueTestTypes);
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, PushBack) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.push_back(V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.push_back(V.back()), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, PushBackMoved) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.push_back(std::move(V.back()));
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.push_back(std::move(V.back())), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, Resize) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.resize(2, V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.resize(2, V.back()), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, Append) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.append(1, V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.append(1, V.back()), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, Assign) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.assign(1, V.back());
+    V.assign(2, V.back());
+    V.assign(3, V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  // Regardless of capacity, assign should never reference an internal element.
+  EXPECT_DEATH(V.assign(1, V.back()), this->AssertionMessage);
+  EXPECT_DEATH(V.assign(2, V.back()), this->AssertionMessage);
+  EXPECT_DEATH(V.assign(3, V.back()), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, Insert) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.insert(V.begin(), V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.insert(V.begin(), V.back()), this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, InsertMoved) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.insert(V.begin(), std::move(V.back()));
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.insert(V.begin(), std::move(V.back())),
+               this->AssertionMessage);
+#endif
+}
+
+TYPED_TEST(SmallVectorTakesParameterByValueTest, InsertN) {
+  auto &V = this->V;
+  if (this->TakesParamByValue) {
+    V.insert(V.begin(), 2, V.back());
+    return;
+  }
+#if !defined(NDEBUG) && GTEST_HAS_DEATH_TEST
+  EXPECT_DEATH(V.insert(V.begin(), 2, V.back()), this->AssertionMessage);
+#endif
+}
+
 } // end namespace
Index: llvm/utils/TableGen/CodeGenSchedule.cpp
===================================================================
--- llvm/utils/TableGen/CodeGenSchedule.cpp
+++ llvm/utils/TableGen/CodeGenSchedule.cpp
@@ -1540,6 +1540,7 @@
   if (SchedRW.IsVariadic) {
     unsigned OperIdx = RWSequences.size()-1;
     // Make N-1 copies of this transition's last sequence.
+    RWSequences.reserve(RWSequences.size() + SelectedRWs.size() - 1);
     RWSequences.insert(RWSequences.end(), SelectedRWs.size() - 1,
                        RWSequences[OperIdx]);
     // Push each of the N elements of the SelectedRWs onto a copy of the last
@@ -1625,6 +1626,7 @@
       //    any transition with compatible CPU ID.
       // In such case we create new empty transition with zero (AnyCPU)
       // index.
+      TransVec.reserve(TransVec.size() + 1);
       TransVec.emplace_back(TransVec[StartIdx].PredTerm);
       TransVec.back().ReadSequences.emplace_back();
       CollectAndAddVariants(TransVec.size() - 1, SchedRW);