Index: llvm/include/llvm/Support/Casting.h
===================================================================
--- llvm/include/llvm/Support/Casting.h
+++ llvm/include/llvm/Support/Casting.h
@@ -358,6 +358,41 @@
   return (Val && isa<X>(Val)) ? cast<X>(Val) : nullptr;
 }
 
+// unique_dyn_cast<X> - Given a unique_ptr<Y>, try to return a unique_ptr<X>,
+// taking ownership of the input pointer iff isa<X>(Val) is true.  If the
+// cast is successful, From refers to nullptr on exit and the casted value
+// is returned.  If the cast is unsuccessful, the function returns nullptr
+// and From is unchanged.
+template <class X, class Y>
+LLVM_NODISCARD inline auto unique_dyn_cast(std::unique_ptr<Y> &Val)
+    -> decltype(cast<X>(Val)) {
+  if (!isa<X>(Val))
+    return nullptr;
+  return cast<X>(std::move(Val));
+}
+
+template <class X, class Y>
+LLVM_NODISCARD inline auto unique_dyn_cast(std::unique_ptr<Y> &&Val)
+    -> decltype(cast<X>(Val)) {
+  return unique_dyn_cast<X, Y>(Val);
+}
+
+// dyn_cast_or_null<X> - Functionally identical to unique_dyn_cast, except that
+// a null value is accepted.
+template <class X, class Y>
+LLVM_NODISCARD inline auto unique_dyn_cast_or_null(std::unique_ptr<Y> &Val)
+    -> decltype(cast<X>(Val)) {
+  if (!Val)
+    return nullptr;
+  return unique_dyn_cast(Val);
+}
+
+template <class X, class Y>
+LLVM_NODISCARD inline auto unique_dyn_cast_or_null(std::unique_ptr<Y> &&Val)
+    -> decltype(cast<X>(Val)) {
+  return unique_dyn_cast_or_null<X, Y>(Val);
+}
+
 } // End llvm namespace
 
 #endif
Index: llvm/unittests/Support/Casting.cpp
===================================================================
--- llvm/unittests/Support/Casting.cpp
+++ llvm/unittests/Support/Casting.cpp
@@ -40,6 +40,14 @@
     }*/
 };
 
+struct base {
+  virtual ~base() {}
+};
+
+struct derived : public base {
+  static bool classof(const base *B) { return true; }
+};
+
 template <> struct isa_impl<foo, bar> {
   static inline bool doit(const bar &Val) {
     dbgs() << "Classof: " << &Val << "\n";
@@ -47,6 +55,10 @@
   }
 };
 
+template <typename T> struct isa_impl<foo, T> {
+  static inline bool doit(const T &Val) { return false; }
+};
+
 foo *bar::baz() {
     return cast<foo>(this);
 }
@@ -176,6 +188,58 @@
   EXPECT_NE(F5, null_foo);
 }
 
+std::unique_ptr<derived> newd() { return llvm::make_unique<derived>(); }
+std::unique_ptr<base> newb() { return llvm::make_unique<derived>(); }
+
+TEST(CastingTest, unique_dyn_cast) {
+  derived *OrigD = nullptr;
+  auto D = llvm::make_unique<derived>();
+  OrigD = D.get();
+
+  // Converting from D to itself is valid, it should return a new unique_ptr
+  // and the old one should become nullptr.
+  auto NewD = unique_dyn_cast<derived>(D);
+  ASSERT_EQ(OrigD, NewD.get());
+  ASSERT_EQ(nullptr, D);
+
+  // Converting from D to B is valid, B should have a value and D should be
+  // nullptr.
+  auto B = unique_dyn_cast<base>(NewD);
+  ASSERT_EQ(OrigD, B.get());
+  ASSERT_EQ(nullptr, NewD);
+
+  // Converting from B to itself is valid, it should return a new unique_ptr
+  // and the old one should become nullptr.
+  auto NewB = unique_dyn_cast<base>(B);
+  ASSERT_EQ(OrigD, NewB.get());
+  ASSERT_EQ(nullptr, B);
+
+  // Converting from B to D is valid, D should have a value and B should be
+  // nullptr;
+  D = unique_dyn_cast<derived>(NewB);
+  ASSERT_EQ(OrigD, D.get());
+  ASSERT_EQ(nullptr, NewB);
+
+  // Converting between unrelated types should fail.  The original value should
+  // remain unchanged and it should return nullptr.
+  auto F = unique_dyn_cast<foo>(D);
+  ASSERT_EQ(nullptr, F);
+  ASSERT_EQ(OrigD, D.get());
+
+  // All of the above should also hold for temporaries.
+  auto D2 = unique_dyn_cast<derived>(newd());
+  EXPECT_NE(nullptr, D2);
+
+  auto B2 = unique_dyn_cast<derived>(newb());
+  EXPECT_NE(nullptr, B2);
+
+  auto B3 = unique_dyn_cast<base>(newb());
+  EXPECT_NE(nullptr, B3);
+
+  auto F2 = unique_dyn_cast<foo>(newb());
+  EXPECT_EQ(nullptr, F2);
+}
+
 // These lines are errors...
 //foo *F20 = cast<foo>(B2);  // Yields const foo*
 //foo &F21 = cast<foo>(B3);  // Yields const foo&