Index: llvm/include/llvm/ADT/PointerUnion.h
===================================================================
--- llvm/include/llvm/ADT/PointerUnion.h
+++ llvm/include/llvm/ADT/PointerUnion.h
@@ -160,10 +160,11 @@
               void *, pointer_union_detail::bitsRequired(sizeof...(PTs)), int,
               pointer_union_detail::PointerUnionUIntTraits<PTs...>>,
           0, PTs...> {
-  // The first type is special in some ways, but we don't want PointerUnion to
-  // be a 'template <typename First, typename ...Rest>' because it's much more
-  // convenient to have a name for the whole pack. So split off the first type
-  // here.
+  // The first type is special because we want to directly cast a pointer to a
+  // default-initialized union to a pointer to the first type. But we don't
+  // want PointerUnion to be a 'template <typename First, typename ...Rest>'
+  // because it's much more convenient to have a name for the whole pack. So
+  // split off the first type here.
   using First = typename pointer_union_detail::GetFirstType<PTs...>::type;
   using Base = typename PointerUnion::PointerUnionMembers;
 
@@ -175,12 +176,7 @@
 
   /// Test if the pointer held in the union is null, regardless of
   /// which type it is.
-  bool isNull() const {
-    // Convert from the void* to one of the pointer types, to make sure that
-    // we recursively strip off low bits if we have a nested PointerUnion.
-    return !PointerLikeTypeTraits<First>::getFromVoidPointer(
-        this->Val.getPointer());
-  }
+  bool isNull() const { return !this->Val.getPointer(); }
 
   explicit operator bool() const { return !isNull(); }
 
@@ -219,7 +215,8 @@
   First *getAddrOfPtr1() {
     assert(is<First>() && "Val is not the first pointer");
     assert(
-        get<First>() == this->Val.getPointer() &&
+        PointerLikeTypeTraits<First>::getAsVoidPointer(get<First>())
+        == this->Val.getPointer() &&
         "Can't get the address because PointerLikeTypeTraits changes the ptr");
     return const_cast<First *>(
         reinterpret_cast<const First *>(this->Val.getAddrOfPointer()));
Index: llvm/include/llvm/ADT/TinyPtrVector.h
===================================================================
--- llvm/include/llvm/ADT/TinyPtrVector.h
+++ llvm/include/llvm/ADT/TinyPtrVector.h
@@ -31,6 +31,10 @@
 public:
   using VecTy = SmallVector<EltTy, 4>;
   using value_type = typename VecTy::value_type;
+  // EltTy must be the first pointer type so that is<EltTy> is true for the
+  // default-constructed PtrUnion. This allows an empty TinyPtrVector to
+  // naturally vend a begin/end iterator of type EltTy* without an additional
+  // check for the empty state.
   using PtrUnion = PointerUnion<EltTy, VecTy *>;
 
 private:
@@ -96,14 +100,14 @@
       if (RHS.Val.template is<EltTy>()) {
         V->clear();
         V->push_back(RHS.front());
-        RHS.Val = (EltTy)nullptr;
+        RHS.Val = EltTy();
         return *this;
       }
       delete V;
     }
 
     Val = RHS.Val;
-    RHS.Val = (EltTy)nullptr;
+    RHS.Val = EltTy();
     return *this;
   }
 
@@ -213,9 +217,9 @@
 
   EltTy operator[](unsigned i) const {
     assert(!Val.isNull() && "can't index into an empty vector");
-    if (EltTy V = Val.template dyn_cast<EltTy>()) {
+    if (Val.template is<EltTy>()) {
       assert(i == 0 && "tinyvector index out of range");
-      return V;
+      return Val.template get<EltTy>();
     }
 
     assert(i < Val.template get<VecTy*>()->size() &&
@@ -225,29 +229,29 @@
 
   EltTy front() const {
     assert(!empty() && "vector empty");
-    if (EltTy V = Val.template dyn_cast<EltTy>())
-      return V;
+    if (Val.template is<EltTy>())
+      return Val.template get<EltTy>();
     return Val.template get<VecTy*>()->front();
   }
 
   EltTy back() const {
     assert(!empty() && "vector empty");
-    if (EltTy V = Val.template dyn_cast<EltTy>())
-      return V;
+    if (Val.template is<EltTy>())
+      return Val.template get<EltTy>();
     return Val.template get<VecTy*>()->back();
   }
 
   void push_back(EltTy NewVal) {
-    assert(NewVal && "Can't add a null value");
-
     // If we have nothing, add something.
     if (Val.isNull()) {
       Val = NewVal;
+      assert(!Val.isNull() && "Can't add a null value");
       return;
     }
 
     // If we have a single value, convert to a vector.
-    if (EltTy V = Val.template dyn_cast<EltTy>()) {
+    if (Val.template is<EltTy>()) {
+      EltTy V = Val.template get<EltTy>();
       Val = new VecTy();
       Val.template get<VecTy*>()->push_back(V);
     }
@@ -267,7 +271,7 @@
   void clear() {
     // If we have a single value, convert to empty.
     if (Val.template is<EltTy>()) {
-      Val = (EltTy)nullptr;
+      Val = EltTy();
     } else if (VecTy *Vec = Val.template dyn_cast<VecTy*>()) {
       // If we have a vector form, just clear it.
       Vec->clear();
@@ -282,7 +286,7 @@
     // If we have a single value, convert to empty.
     if (Val.template is<EltTy>()) {
       if (I == begin())
-        Val = (EltTy)nullptr;
+        Val = EltTy();
     } else if (VecTy *Vec = Val.template dyn_cast<VecTy*>()) {
       // multiple items in a vector; just do the erase, there is no
       // benefit to collapsing back to a pointer
@@ -298,7 +302,7 @@
 
     if (Val.template is<EltTy>()) {
       if (S == begin() && S != E)
-        Val = (EltTy)nullptr;
+        Val = EltTy();
     } else if (VecTy *Vec = Val.template dyn_cast<VecTy*>()) {
       return Vec->erase(S, E);
     }
@@ -313,7 +317,8 @@
       return std::prev(end());
     }
     assert(!Val.isNull() && "Null value with non-end insert iterator.");
-    if (EltTy V = Val.template dyn_cast<EltTy>()) {
+    if (Val.template is<EltTy>()) {
+      EltTy V = Val.template get<EltTy>();
       assert(I == begin());
       Val = Elt;
       push_back(V);
@@ -339,7 +344,8 @@
       }
 
       Val = new VecTy();
-    } else if (EltTy V = Val.template dyn_cast<EltTy>()) {
+    } else if (Val.template is<EltTy>()) {
+      EltTy V = Val.template get<EltTy>();
       Val = new VecTy();
       Val.template get<VecTy*>()->push_back(V);
     }
Index: llvm/unittests/ADT/PointerUnionTest.cpp
===================================================================
--- llvm/unittests/ADT/PointerUnionTest.cpp
+++ llvm/unittests/ADT/PointerUnionTest.cpp
@@ -13,14 +13,28 @@
 namespace {
 
 typedef PointerUnion<int *, float *> PU;
+typedef PointerUnion3<int *, float *, long long *> PU3;
+typedef PointerUnion4<int *, float *, long long *, double *> PU4;
 
 struct PointerUnionTest : public testing::Test {
   float f;
   int i;
+  double d;
+  long long l;
 
   PU a, b, c, n;
-
-  PointerUnionTest() : f(3.14f), i(42), a(&f), b(&i), c(&i), n() {}
+  PU3 i3, f3, l3;
+  PU4 i4, f4, l4, d4;
+  PU4 i4null, f4null, l4null, d4null;
+
+  PointerUnionTest() : f(3.14f), i(42), d(3.14), l(42),
+                       a(&f), b(&i), c(&i), n(),
+                       i3(&i), f3(&f), l3(&l),
+                       i4(&i), f4(&f), l4(&l), d4(&d),
+                       i4null((int *)nullptr), f4null((float *)nullptr),
+                       l4null((long long *) nullptr),
+                       d4null((double *)nullptr)
+  {}
 };
 
 TEST_F(PointerUnionTest, Comparison) {
@@ -32,6 +46,19 @@
   EXPECT_FALSE(b != c);
   EXPECT_TRUE(b != n);
   EXPECT_FALSE(b == n);
+  EXPECT_TRUE(i3 == i3);
+  EXPECT_FALSE(i3 != i3);
+  EXPECT_TRUE(i3 != f3);
+  EXPECT_TRUE(f3 != l3);
+  EXPECT_TRUE(i4 == i4);
+  EXPECT_FALSE(i4 != i4);
+  EXPECT_TRUE(i4 != f4);
+  EXPECT_TRUE(i4 != l4);
+  EXPECT_TRUE(f4 != l4);
+  EXPECT_TRUE(l4 != d4);
+  EXPECT_TRUE(i4null != f4null);
+  EXPECT_TRUE(i4null != l4null);
+  EXPECT_TRUE(i4null != d4null);
 }
 
 TEST_F(PointerUnionTest, Null) {
@@ -51,6 +78,17 @@
   b = nullptr;
   EXPECT_EQ(n, b);
   EXPECT_NE(b, c);
+  EXPECT_FALSE(i3.isNull());
+  EXPECT_FALSE(f3.isNull());
+  EXPECT_FALSE(l3.isNull());
+  EXPECT_FALSE(i4.isNull());
+  EXPECT_FALSE(f4.isNull());
+  EXPECT_FALSE(l4.isNull());
+  EXPECT_FALSE(d4.isNull());
+  EXPECT_TRUE(i4null.isNull());
+  EXPECT_TRUE(f4null.isNull());
+  EXPECT_TRUE(l4null.isNull());
+  EXPECT_TRUE(d4null.isNull());
 }
 
 TEST_F(PointerUnionTest, Is) {
@@ -60,6 +98,17 @@
   EXPECT_FALSE(b.is<float *>());
   EXPECT_TRUE(n.is<int *>());
   EXPECT_FALSE(n.is<float *>());
+  EXPECT_TRUE(i3.is<int *>());
+  EXPECT_TRUE(f3.is<float *>());
+  EXPECT_TRUE(l3.is<long long *>());
+  EXPECT_TRUE(i4.is<int *>());
+  EXPECT_TRUE(f4.is<float *>());
+  EXPECT_TRUE(l4.is<long long *>());
+  EXPECT_TRUE(d4.is<double *>());
+  EXPECT_TRUE(i4null.is<int *>());
+  EXPECT_TRUE(f4null.is<float *>());
+  EXPECT_TRUE(l4null.is<long long *>());
+  EXPECT_TRUE(d4null.is<double *>());
 }
 
 TEST_F(PointerUnionTest, Get) {
@@ -105,4 +154,9 @@
   EXPECT_TRUE(a != PU8(&a0));
 }
 
+TEST_F(PointerUnionTest, GetAddrOfPtr1) {
+  EXPECT_TRUE((void *)b.getAddrOfPtr1() == (void *)&b);
+  EXPECT_TRUE((void *)n.getAddrOfPtr1() == (void *)&n);
+}
+
 } // end anonymous namespace
Index: llvm/unittests/ADT/TinyPtrVectorTest.cpp
===================================================================
--- llvm/unittests/ADT/TinyPtrVectorTest.cpp
+++ llvm/unittests/ADT/TinyPtrVectorTest.cpp
@@ -22,12 +22,21 @@
 using namespace llvm;
 
 namespace {
+template <typename T> struct RemovePointer : std::remove_pointer<T> {};
+
+template <typename PointerTy, unsigned IntBits, typename IntType,
+          typename PtrTraits, typename Info>
+struct RemovePointer<
+    PointerIntPair<PointerTy, IntBits, IntType, PtrTraits, Info>> {
+  typedef typename RemovePointer<PointerTy>::type type;
+};
 
 template <typename VectorT>
 class TinyPtrVectorTest : public testing::Test {
 protected:
   typedef typename VectorT::value_type PtrT;
-  typedef typename std::remove_pointer<PtrT>::type ValueT;
+  typedef typename RemovePointer<PtrT>::type ValueT;
+  using PtrTraits = PointerLikeTypeTraits<PtrT>;
 
   VectorT V;
   VectorT V2;
@@ -37,11 +46,13 @@
 
   TinyPtrVectorTest() {
     for (size_t i = 0, e = array_lengthof(TestValues); i != e; ++i)
-      TestPtrs.push_back(&TestValues[i]);
+      TestPtrs.push_back(PtrT(&TestValues[i]));
 
     std::shuffle(TestPtrs.begin(), TestPtrs.end(), std::mt19937{});
   }
 
+  PtrT makePtr(ValueT *V) { return PtrT(V); }
+
   ArrayRef<PtrT> testArray(size_t N) {
     return makeArrayRef(&TestPtrs[0], N);
   }
@@ -70,7 +81,8 @@
 };
 
 typedef ::testing::Types<TinyPtrVector<int*>,
-                         TinyPtrVector<double*>
+                         TinyPtrVector<double*>,
+                         TinyPtrVector<PointerIntPair<int *, 1>>
                          > TinyPtrVectorTestTypes;
 TYPED_TEST_CASE(TinyPtrVectorTest, TinyPtrVectorTestTypes);
 
@@ -95,8 +107,8 @@
   this->expectValues(this->V, this->testArray(4));
   this->V.pop_back();
   this->expectValues(this->V, this->testArray(3));
-  this->TestPtrs[3] = &this->TestValues[42];
-  this->TestPtrs[4] = &this->TestValues[43];
+  this->TestPtrs[3] = this->makePtr(&this->TestValues[42]);
+  this->TestPtrs[4] = this->makePtr(&this->TestValues[43]);
   this->V.push_back(this->TestPtrs[3]);
   this->expectValues(this->V, this->testArray(4));
   this->V.push_back(this->TestPtrs[4]);