Index: include/clang/Basic/Builtins.def
===================================================================
--- include/clang/Basic/Builtins.def
+++ include/clang/Basic/Builtins.def
@@ -483,6 +483,7 @@
 BUILTIN(__builtin_vsprintf, "ic*cC*a", "nFP:1:")
 BUILTIN(__builtin_vsnprintf, "ic*zcC*a", "nFP:2:")
 BUILTIN(__builtin_thread_pointer, "v*", "nc")
+BUILTIN(__builtin_launder, "v*v*", "nt")
 
 // GCC exception builtins
 BUILTIN(__builtin_eh_return, "vzv*", "r") // FIXME: Takes intptr_t, not size_t!
Index: include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- include/clang/Basic/DiagnosticSemaKinds.td
+++ include/clang/Basic/DiagnosticSemaKinds.td
@@ -9332,6 +9332,10 @@
   InGroup<ShadowField>, DefaultIgnore;
 def note_shadow_field : Note<"declared here">;
 
+def err_builtin_launder_invalid_arg : Error<
+  "%select{non-pointer|function pointer|void pointer}0 argument to "
+  "'__builtin_launder' is not allowed">;
+
 def err_target_required_in_redecl : Error<
   "function declaration is missing 'target' attribute in a multiversioned "
   "function">;
Index: lib/AST/ExprConstant.cpp
===================================================================
--- lib/AST/ExprConstant.cpp
+++ lib/AST/ExprConstant.cpp
@@ -5895,7 +5895,8 @@
 
     return true;
   }
-
+  case Builtin::BI__builtin_launder:
+    return evaluatePointer(E->getArg(0), Result);
   case Builtin::BIstrchr:
   case Builtin::BIwcschr:
   case Builtin::BImemchr:
Index: lib/CodeGen/CGBuiltin.cpp
===================================================================
--- lib/CodeGen/CGBuiltin.cpp
+++ lib/CodeGen/CGBuiltin.cpp
@@ -1882,6 +1882,17 @@
 
     return RValue::get(nullptr);
   }
+  case Builtin::BI__builtin_launder: {
+    const Expr *Arg = E->getArg(0);
+    QualType ArgTy = Arg->getType()->getPointeeType();
+    Value *Ptr = EmitScalarExpr(Arg);
+    const auto *Record = ArgTy->getAsCXXRecordDecl();
+    if (CGM.getCodeGenOpts().StrictVTablePointers && Record &&
+        Record->isDynamicClass())
+      Ptr = Builder.CreateInvariantGroupBarrier(Ptr);
+
+    return RValue::get(Ptr);
+  }
   case Builtin::BI__sync_fetch_and_add:
   case Builtin::BI__sync_fetch_and_sub:
   case Builtin::BI__sync_fetch_and_or:
Index: lib/Sema/SemaChecking.cpp
===================================================================
--- lib/Sema/SemaChecking.cpp
+++ lib/Sema/SemaChecking.cpp
@@ -850,6 +850,41 @@
   return false;
 }
 
+static ExprResult SemaBuiltinLaunder(Sema &S, CallExpr *TheCall) {
+  if (checkArgCount(S, TheCall, 1))
+    return ExprError();
+
+  QualType ArgTy = TheCall->getArg(0)->getType();
+  TheCall->setType(ArgTy);
+
+  int DiagSelect = [&]() {
+    if (!ArgTy->isPointerType())
+      return 0;
+    if (ArgTy->isFunctionPointerType())
+      return 1;
+    if (ArgTy->isVoidPointerType())
+      return 2;
+    return -1;
+  }();
+  if (DiagSelect != -1) {
+    S.Diag(TheCall->getLocStart(), diag::err_builtin_launder_invalid_arg)
+        << DiagSelect << TheCall->getSourceRange();
+    return ExprError();
+  }
+
+  assert(ArgTy->getPointeeType()->isObjectType() && "Unhandled non-object pointer case");
+
+  InitializedEntity Entity =
+      InitializedEntity::InitializeParameter(S.Context, ArgTy, false);
+  ExprResult Arg = TheCall->getArg(0);
+  Arg = S.PerformCopyInitialization(Entity, SourceLocation(), Arg);
+  if (Arg.isInvalid())
+    return ExprError();
+  TheCall->setArg(0, Arg.get());
+
+  return TheCall;
+}
+
 ExprResult
 Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
                                CallExpr *TheCall) {
@@ -967,6 +1002,8 @@
     if (checkArgCount(*this, TheCall, 1)) return true;
     TheCall->setType(Context.IntTy);
     break;
+  case Builtin::BI__builtin_launder:
+    return SemaBuiltinLaunder(*this, TheCall);
   case Builtin::BI__sync_fetch_and_add:
   case Builtin::BI__sync_fetch_and_add_1:
   case Builtin::BI__sync_fetch_and_add_2:
Index: test/CodeGen/builtins.c
===================================================================
--- test/CodeGen/builtins.c
+++ test/CodeGen/builtins.c
@@ -132,6 +132,8 @@
   R(extract_return_addr, (&N));
   P(signbit, (1.0));
 
+  R(launder, (&N));
+
   return 0;
 }
 
@@ -396,6 +398,18 @@
   return __builtin_readcyclecounter();
 }
 
+/// __builtin_launder should be a NOP in C since there are no vtables.
+// CHECK-LABEL: define void @test_builtin_launder
+void test_builtin_launder(int *p) {
+  // CHECK: entry
+  // CHECK-NEXT: %p.addr = alloca i32*
+  // CHECK-NEXT: %d = alloca i32*
+  // CHECK-NEXT: store i32* %p, i32** %p.addr, align 8
+  // CHECK-NEXT: [[TMP:%.*]] = load i32*, i32** %p.addr
+  // CHECK-NEXT: store i32* [[TMP]], i32** %d
+  int *d = __builtin_launder(p);
+}
+
 // Behavior of __builtin_os_log differs between platforms, so only test on X86
 #ifdef __x86_64__
 
Index: test/CodeGenCXX/builtin-launder.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/builtin-launder.cpp
@@ -0,0 +1,147 @@
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -emit-llvm -fstrict-vtable-pointers -o - %s \
+// RUN: | FileCheck --check-prefixes=CHECK,CHECK-STRICT %s
+// RUN: %clang_cc1 -triple=x86_64-linux-gnu -emit-llvm -o - %s \
+// RUN: | FileCheck --check-prefixes=CHECK,CHECK-NONSTRICT %s
+
+//===----------------------------------------------------------------------===//
+//                            Positive Cases
+//===----------------------------------------------------------------------===//
+
+struct TestVirtualFn {
+  virtual void foo() {}
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_virtual_fn
+extern "C" void test_builtin_launder_virtual_fn(TestVirtualFn *p) {
+  // CHECK: entry
+  // CHECK-NEXT: %p.addr = alloca [[TYPE:%.*]], align 8
+  // CHECK-NEXT: %d = alloca [[TYPE]]
+  // CHECK-NEXT: store [[TYPE]] %p, [[TYPE]]* %p.addr
+  // CHECK-NEXT: [[TMP0:%.*]] = load [[TYPE]], [[TYPE]]* %p.addr
+
+  // CHECK-NONSTRICT-NEXT: store [[TYPE]] [[TMP0]], [[TYPE]]* %d
+
+  // CHECK-STRICT-NEXT: [[TMP1:%.*]] = bitcast [[TYPE]] [[TMP0]] to i8*
+  // CHECK-STRICT-NEXT: [[TMP2:%.*]] = call i8* @llvm.invariant.group.barrier.p0i8(i8* [[TMP1]])
+  // CHECK-STRICT-NEXT: [[TMP3:%.*]] = bitcast i8* [[TMP2]] to [[TYPE]]
+  // CHECK-STRICT-NEXT: store [[TYPE]] [[TMP3]], [[TYPE]]* %d
+
+  // CHECK-NEXT: ret void
+  TestVirtualFn *d = __builtin_launder(p);
+}
+
+struct TestPolyBase : TestVirtualFn {
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_poly_base
+extern "C" void test_builtin_launder_poly_base(TestPolyBase *p) {
+  // CHECK-STRICT-NOT: ret void
+  // CHECK-STRICT: @llvm.invariant.group.barrier
+
+  // CHECK-NONSTRICT-NOT: @llvm.invariant.group.barrier
+
+  // CHECK: ret void
+  TestPolyBase *d = __builtin_launder(p);
+}
+
+struct TestBase {};
+struct TestVirtualBase : virtual TestBase {};
+
+// CHECK-LABEL: define void @test_builtin_launder_virtual_base
+extern "C" void test_builtin_launder_virtual_base(TestVirtualBase *p) {
+  // CHECK-STRICT-NOT: ret void
+  // CHECK-STRICT: @llvm.invariant.group.barrier
+
+  // CHECK-NONSTRICT-NOT: @llvm.invariant.group.barrier
+
+  // CHECK: ret void
+  TestVirtualBase *d = __builtin_launder(p);
+}
+
+//===----------------------------------------------------------------------===//
+//                            Negative Cases
+//===----------------------------------------------------------------------===//
+
+// CHECK-LABEL: define void @test_builtin_launder_ommitted_one
+extern "C" void test_builtin_launder_ommitted_one(int *p) {
+  // CHECK: entry
+  // CHECK-NEXT: %p.addr = alloca i32*
+  // CHECK-NEXT: %d = alloca i32*
+  // CHECK-NEXT: store i32* %p, i32** %p.addr, align 8
+  // CHECK-NEXT: [[TMP:%.*]] = load i32*, i32** %p.addr
+  // CHECK-NEXT: store i32* [[TMP]], i32** %d
+  // CHECK-NEXT: ret void
+  int *d = __builtin_launder(p);
+}
+
+struct TestNoInvariant {
+  int x;
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_ommitted_two
+extern "C" void test_builtin_launder_ommitted_two(TestNoInvariant *p) {
+  // CHECK: entry
+  // CHECK-NEXT: %p.addr = alloca [[TYPE:%.*]], align 8
+  // CHECK-NEXT: %d = alloca [[TYPE]]
+  // CHECK-NEXT: store [[TYPE]] %p, [[TYPE]]* %p.addr
+  // CHECK-NEXT: [[TMP:%.*]] = load [[TYPE]], [[TYPE]]* %p.addr
+  // CHECK-NEXT: store [[TYPE]] [[TMP]], [[TYPE]]* %d
+  // CHECK-NEXT: ret void
+  TestNoInvariant *d = __builtin_launder(p);
+}
+
+/// The test cases in this namespace technically need to be laundered according
+/// to the language in the standard (ie they have const or reference subobjects)
+/// but LLVM doesn't currently optimize on these cases -- so Clang emits
+/// __builtin_launder as a nop.
+namespace pessimizing_cases {
+
+struct TestConstMember {
+  const int x;
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_const_member
+extern "C" void test_builtin_launder_const_member(TestConstMember *p) {
+  // CHECK: entry
+  // CHECK-NOT: @llvm.invariant.group.barrier
+  // CHECK: ret void
+  TestConstMember *d = __builtin_launder(p);
+}
+
+struct TestConstSubobject {
+  TestConstMember x;
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_const_subobject
+extern "C" void test_builtin_launder_const_subobject(TestConstSubobject *p) {
+  // CHECK: entry
+  // CHECK-NOT: @llvm.invariant.group.barrier
+  // CHECK: ret void
+  TestConstSubobject *d = __builtin_launder(p);
+}
+
+struct TestConstObject {
+  const struct TestConstMember x;
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_const_object
+extern "C" void test_builtin_launder_const_object(TestConstObject *p) {
+  // CHECK: entry
+  // CHECK-NOT: @llvm.invariant.group.barrier
+  // CHECK: ret void
+  TestConstObject *d = __builtin_launder(p);
+}
+
+struct TestReferenceMember {
+  int &x;
+};
+
+// CHECK-LABEL: define void @test_builtin_launder_reference_member
+extern "C" void test_builtin_launder_reference_member(TestReferenceMember *p) {
+  // CHECK: entry
+  // CHECK-NOT: @llvm.invariant.group.barrier
+  // CHECK: ret void
+  TestReferenceMember *d = __builtin_launder(p);
+}
+
+} // namespace pessimizing_cases
Index: test/Preprocessor/feature_tests.c
===================================================================
--- test/Preprocessor/feature_tests.c
+++ test/Preprocessor/feature_tests.c
@@ -14,6 +14,7 @@
      !__has_builtin(__builtin_convertvector) || \
      !__has_builtin(__builtin_trap) || \
      !__has_builtin(__c11_atomic_init) || \
+     !__has_builtin(__builtin_launder) || \
      !__has_feature(attribute_analyzer_noreturn) || \
      !__has_feature(attribute_overloadable)
 #error Clang should have these
Index: test/Sema/builtins.c
===================================================================
--- test/Sema/builtins.c
+++ test/Sema/builtins.c
@@ -248,3 +248,21 @@
 
     return buf;
 }
+
+typedef void (fn_t)(int);
+
+void test_builtin_launder(char *p, void *vp, const void *cvp,
+                          const volatile int *ip, float *restrict fp,
+                          fn_t *fn) {
+  __builtin_launder(); // expected-error {{too few arguments to function call, expected 1, have 0}}
+  __builtin_launder(p, p); // expected-error {{too many arguments to function call, expected 1, have 2}}
+  int x;
+  __builtin_launder(x); // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+  char *d = __builtin_launder(p);
+  __builtin_launder(vp);  // expected-error {{void pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(cvp); // expected-error {{void pointer argument to '__builtin_launder' is not allowed}}
+  const volatile int *id = __builtin_launder(ip);
+  int *id2 = __builtin_launder(ip); // expected-warning {{discards qualifiers}}
+  float *fd = __builtin_launder(fp);
+  __builtin_launder(fn); // expected-error {{function pointer argument to '__builtin_launder' is not allowed}}
+}
Index: test/SemaCXX/builtins.cpp
===================================================================
--- test/SemaCXX/builtins.cpp
+++ test/SemaCXX/builtins.cpp
@@ -53,3 +53,71 @@
 void synchronize_args() {
   __sync_synchronize(0); // expected-error {{too many arguments}}
 }
+
+namespace test_launder {
+
+struct Dummy {};
+
+using FnType = int(char);
+using MemFnType = int (Dummy::*)(char);
+using ConstMemFnType = int (Dummy::*)() const;
+
+void foo() {}
+
+void test_builtin_launder_diags(void *vp, const void *cvp, FnType *fnp,
+                                MemFnType mfp, ConstMemFnType cmfp) {
+  __builtin_launder(vp);   // expected-error {{void pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(cvp);  // expected-error {{void pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(fnp);  // expected-error {{function pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(mfp);  // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(cmfp); // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+  (void)__builtin_launder(&fnp);
+  __builtin_launder(42);      // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(nullptr); // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+  __builtin_launder(foo)      // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+}
+
+void test_builtin_launder(char *p, const volatile int *ip, const float *&fp,
+                          double *__restrict dp) {
+  int x;
+  __builtin_launder(x); // expected-error {{non-pointer argument to '__builtin_launder' is not allowed}}
+#define TEST_TYPE(Ptr, Type) \
+  static_assert(__is_same(decltype(__builtin_launder(Ptr)), Type), "expected same type")
+  TEST_TYPE(p, char*);
+  TEST_TYPE(ip, const volatile int*);
+  TEST_TYPE(fp, const float*);
+  TEST_TYPE(dp, double *__restrict);
+#undef TEST_TYPE
+  char *d = __builtin_launder(p);
+  const volatile int *id = __builtin_launder(ip);
+  int *id2 = __builtin_launder(ip); // expected-error {{cannot initialize a variable of type 'int *' with an rvalue of type 'const volatile int *'}}
+  const float* fd = __builtin_launder(fp);
+}
+
+template <class Tp>
+constexpr Tp *test_constexpr_launder(Tp *tp) {
+  return __builtin_launder(tp);
+}
+constexpr int const_int = 42;
+constexpr int const_int2 = 101;
+constexpr const int *const_ptr = test_constexpr_launder(&const_int);
+static_assert(&const_int == const_ptr, "");
+static_assert(const_ptr != test_constexpr_launder(&const_int2), "");
+
+void test_non_constexpr() {
+  constexpr int i = 42;                            // expected-note {{declared here}}
+  constexpr const int *ip = __builtin_launder(&i); // expected-error {{constexpr variable 'ip' must be initialized by a constant expression}}
+  // expected-note@-1 {{pointer to 'i' is not a constant expression}}
+}
+
+constexpr bool test_in_constexpr(const int &i) {
+  return (__builtin_launder(&i) == &i);
+}
+static_assert(test_in_constexpr(const_int), "");
+void f() {
+  constexpr int i = 42;
+  // FIXME: Should this work? Since `&i` doesn't.
+  static_assert(test_in_constexpr(i), "");
+}
+
+} // end namespace test_launder