Index: llvm/include/llvm/ADT/PointerUnion.h
===================================================================
--- llvm/include/llvm/ADT/PointerUnion.h
+++ llvm/include/llvm/ADT/PointerUnion.h
@@ -18,6 +18,7 @@
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/ADT/PointerIntPair.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/PointerLikeTypeTraits.h"
 #include <algorithm>
 #include <cassert>
@@ -87,6 +88,9 @@
   };
 }
 
+// This is a forward declaration of CastInfoPointerUnionImpl
+// Refer to its definition below for further details
+template <typename... PTs> struct CastInfoPointerUnionImpl;
 /// A discriminated union of two or more pointer types, with the discriminator
 /// in the low bit of the pointer.
 ///
@@ -122,6 +126,11 @@
   using First = TypeAtIndex<0, PTs...>;
   using Base = typename PointerUnion::PointerUnionMembers;
 
+  /// This is needed to give the CastInfo implementation below access
+  /// to protected members.
+  /// Refer to its definition for further details.
+  friend struct CastInfoPointerUnionImpl<PTs...>;
+
 public:
   PointerUnion() = default;
 
@@ -134,25 +143,24 @@
 
   explicit operator bool() const { return !isNull(); }
 
+  // FIXME: Replace the uses of is(), get() and dyn_cast() with
+  //        isa<T>, cast<T> and the llvm::dyn_cast<T>
+
   /// Test if the Union currently holds the type matching T.
-  template <typename T> bool is() const {
-    return this->Val.getInt() == FirstIndexOfType<T, PTs...>::value;
-  }
+  template <typename T> inline bool is() const { return isa<T>(*this); }
 
   /// Returns the value of the specified pointer type.
   ///
   /// If the specified pointer type is incorrect, assert.
-  template <typename T> T get() const {
-    assert(is<T>() && "Invalid accessor called");
-    return PointerLikeTypeTraits<T>::getFromVoidPointer(this->Val.getPointer());
+  template <typename T> inline T get() const {
+    assert(isa<T>(*this) && "Invalid accessor called");
+    return cast<T>(*this);
   }
 
   /// Returns the current pointer if it is of the specified pointer type,
   /// otherwise returns null.
-  template <typename T> T dyn_cast() const {
-    if (is<T>())
-      return get<T>();
-    return T();
+  template <typename T> inline T dyn_cast() const {
+    return llvm::dyn_cast<T>(*this);
   }
 
   /// If the union is set to the first pointer type get an address pointing to
@@ -205,6 +213,52 @@
   return lhs.getOpaqueValue() < rhs.getOpaqueValue();
 }
 
+/// We can't (at least, at this moment with C++14) declare CastInfo
+/// as a friend of PointerUnion like this:
+/// ```
+///   template<typename To>
+///   friend struct CastInfo<To, PointerUnion<PTs...>>;
+/// ```
+/// The compiler complains 'Partial specialization cannot be declared as a
+/// friend'.
+/// So we define this struct to be a bridge between CastInfo and
+/// PointerUnion.
+template <typename... PTs> struct CastInfoPointerUnionImpl {
+  using From = PointerUnion<PTs...>;
+
+  template <typename To> static inline bool isPossible(From &F) {
+    return F.Val.getInt() == FirstIndexOfType<To, PTs...>::value;
+  }
+
+  template <typename To> static To doCast(From &F) {
+    assert(isPossible<To>(F) && "cast to an incompatible type !");
+    return PointerLikeTypeTraits<To>::getFromVoidPointer(F.Val.getPointer());
+  }
+};
+
+// Specialization of CastInfo for PointerUnion
+template <typename To, typename... PTs>
+struct CastInfo<To, PointerUnion<PTs...>>
+    : public DefaultDoCastIfPossible<To, PointerUnion<PTs...>,
+                                     CastInfo<To, PointerUnion<PTs...>>> {
+  using From = PointerUnion<PTs...>;
+  using Impl = CastInfoPointerUnionImpl<PTs...>;
+
+  static inline bool isPossible(From &f) {
+    return Impl::template isPossible<To>(f);
+  }
+
+  static To doCast(From &f) { return Impl::template doCast<To>(f); }
+
+  static inline To castFailed() { return To(); }
+};
+
+template <typename To, typename... PTs>
+struct CastInfo<To, const PointerUnion<PTs...>>
+    : public ConstStrippingForwardingCast<To, const PointerUnion<PTs...>,
+                                          CastInfo<To, PointerUnion<PTs...>>> {
+};
+
 // Teach SmallPtrSet that PointerUnion is "basically a pointer", that has
 // # low bits available = min(PT1bits,PT2bits)-1.
 template <typename ...PTs>
Index: llvm/unittests/ADT/PointerUnionTest.cpp
===================================================================
--- llvm/unittests/ADT/PointerUnionTest.cpp
+++ llvm/unittests/ADT/PointerUnionTest.cpp
@@ -156,4 +156,136 @@
   EXPECT_TRUE((void *)n.getAddrOfPtr1() == (void *)&n);
 }
 
+TEST_F(PointerUnionTest, NewCastInfra) {
+  // test isa<>
+  EXPECT_TRUE(isa<float *>(a));
+  EXPECT_TRUE(isa<int *>(b));
+  EXPECT_TRUE(isa<int *>(c));
+  EXPECT_TRUE(isa<int *>(n));
+  EXPECT_TRUE(isa<int *>(i3));
+  EXPECT_TRUE(isa<float *>(f3));
+  EXPECT_TRUE(isa<long long *>(l3));
+  EXPECT_TRUE(isa<int *>(i4));
+  EXPECT_TRUE(isa<float *>(f4));
+  EXPECT_TRUE(isa<long long *>(l4));
+  EXPECT_TRUE(isa<double *>(d4));
+  EXPECT_TRUE(isa<int *>(i4null));
+  EXPECT_TRUE(isa<float *>(f4null));
+  EXPECT_TRUE(isa<long long *>(l4null));
+  EXPECT_TRUE(isa<double *>(d4null));
+  EXPECT_FALSE(isa<int *>(a));
+  EXPECT_FALSE(isa<float *>(b));
+  EXPECT_FALSE(isa<float *>(c));
+  EXPECT_FALSE(isa<float *>(n));
+  EXPECT_FALSE(isa<float *>(i3));
+  EXPECT_FALSE(isa<long long *>(i3));
+  EXPECT_FALSE(isa<int *>(f3));
+  EXPECT_FALSE(isa<long long *>(f3));
+  EXPECT_FALSE(isa<int *>(l3));
+  EXPECT_FALSE(isa<float *>(l3));
+  EXPECT_FALSE(isa<float *>(i4));
+  EXPECT_FALSE(isa<long long *>(i4));
+  EXPECT_FALSE(isa<double *>(i4));
+  EXPECT_FALSE(isa<int *>(f4));
+  EXPECT_FALSE(isa<long long *>(f4));
+  EXPECT_FALSE(isa<double *>(f4));
+  EXPECT_FALSE(isa<int *>(l4));
+  EXPECT_FALSE(isa<float *>(l4));
+  EXPECT_FALSE(isa<double *>(l4));
+  EXPECT_FALSE(isa<int *>(d4));
+  EXPECT_FALSE(isa<float *>(d4));
+  EXPECT_FALSE(isa<long long *>(d4));
+  EXPECT_FALSE(isa<float *>(i4null));
+  EXPECT_FALSE(isa<long long *>(i4null));
+  EXPECT_FALSE(isa<double *>(i4null));
+  EXPECT_FALSE(isa<int *>(f4null));
+  EXPECT_FALSE(isa<long long *>(f4null));
+  EXPECT_FALSE(isa<double *>(f4null));
+  EXPECT_FALSE(isa<int *>(l4null));
+  EXPECT_FALSE(isa<float *>(l4null));
+  EXPECT_FALSE(isa<double *>(l4null));
+  EXPECT_FALSE(isa<int *>(d4null));
+  EXPECT_FALSE(isa<float *>(d4null));
+  EXPECT_FALSE(isa<long long *>(d4null));
+
+  // test cast<>
+  EXPECT_EQ(cast<float *>(a), &f);
+  EXPECT_EQ(cast<int *>(b), &i);
+  EXPECT_EQ(cast<int *>(c), &i);
+  EXPECT_EQ(cast<int *>(i3), &i);
+  EXPECT_EQ(cast<float *>(f3), &f);
+  EXPECT_EQ(cast<long long *>(l3), &l);
+  EXPECT_EQ(cast<int *>(i4), &i);
+  EXPECT_EQ(cast<float *>(f4), &f);
+  EXPECT_EQ(cast<long long *>(l4), &l);
+  EXPECT_EQ(cast<double *>(d4), &d);
+
+  // test dyn_cast
+  EXPECT_EQ(dyn_cast<int *>(a), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(a), &f);
+  EXPECT_EQ(dyn_cast<int *>(b), &i);
+  EXPECT_EQ(dyn_cast<float *>(b), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(c), &i);
+  EXPECT_EQ(dyn_cast<float *>(c), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(n), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(n), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(i3), &i);
+  EXPECT_EQ(dyn_cast<float *>(i3), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(i3), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(f3), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(f3), &f);
+  EXPECT_EQ(dyn_cast<long long *>(f3), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(l3), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(l3), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(l3), &l);
+  EXPECT_EQ(dyn_cast<int *>(i4), &i);
+  EXPECT_EQ(dyn_cast<float *>(i4), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(i4), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(i4), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(f4), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(f4), &f);
+  EXPECT_EQ(dyn_cast<long long *>(f4), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(f4), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(l4), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(l4), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(l4), &l);
+  EXPECT_EQ(dyn_cast<double *>(l4), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(d4), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(d4), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(d4), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(d4), &d);
+  EXPECT_EQ(dyn_cast<int *>(i4null), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(i4null), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(i4null), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(i4null), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(f4null), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(f4null), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(f4null), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(f4null), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(l4null), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(l4null), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(l4null), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(l4null), nullptr);
+  EXPECT_EQ(dyn_cast<int *>(d4null), nullptr);
+  EXPECT_EQ(dyn_cast<float *>(d4null), nullptr);
+  EXPECT_EQ(dyn_cast<long long *>(d4null), nullptr);
+  EXPECT_EQ(dyn_cast<double *>(d4null), nullptr);
+
+  // test for const
+  const PU4 constd4(&d);
+  EXPECT_TRUE(isa<double *>(constd4));
+  EXPECT_FALSE(isa<int *>(constd4));
+  EXPECT_EQ(cast<double *>(constd4), &d);
+  EXPECT_EQ(dyn_cast<long long *>(constd4), nullptr);
+
+  auto *result1 = cast<double *>(constd4);
+  static_assert(std::is_same<double *, decltype(result1)>::value,
+                "type mismatch for cast with PointerUnion");
+
+  PointerUnion<int *, const double *> constd2(&d);
+  auto *result2 = cast<const double *>(d);
+  static_assert(std::is_same<const double *, decltype(result2)>::value,
+                "type mismatch for cast with PointerUnion");
+}
+
 } // end anonymous namespace