Index: include/clang/Basic/Attr.td
===================================================================
--- include/clang/Basic/Attr.td
+++ include/clang/Basic/Attr.td
@@ -1403,6 +1403,13 @@
   let Documentation = [NoSanitizeMemoryDocs];
 }
 
+// Attribute to disable UBSan vptr checks.
+def NoSanitizeVptr : InheritableAttr {
+  let Spellings = [GNU<"no_sanitize_vptr">];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [NoSanitizeVptrDocs];
+}
+
 // C/C++ Thread safety attributes (e.g. for deadlock, data race checking)
 
 def GuardedVar : InheritableAttr {
Index: include/clang/Basic/AttrDocs.td
===================================================================
--- include/clang/Basic/AttrDocs.td
+++ include/clang/Basic/AttrDocs.td
@@ -958,6 +958,15 @@
   }];
 }
 
+def NoSanitizeVptrDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+Use ``__attribute__((no_sanitize_vptr))`` on a function declaration to
+specify that dynamic vptr checks (e.g. checks for bad downcasting) should not
+be inserted.
+  }];
+}
+
 def DocCatTypeSafety : DocumentationCategory<"Type Safety Checking"> {
   let Content = [{
 Clang supports additional attributes to enable checking type safety properties
Index: lib/CodeGen/CGExpr.cpp
===================================================================
--- lib/CodeGen/CGExpr.cpp
+++ lib/CodeGen/CGExpr.cpp
@@ -580,7 +580,8 @@
       (TCK == TCK_MemberAccess || TCK == TCK_MemberCall ||
        TCK == TCK_DowncastPointer || TCK == TCK_DowncastReference ||
        TCK == TCK_UpcastToVirtualBase) &&
-      RD && RD->hasDefinition() && RD->isDynamicClass()) {
+      RD && RD->hasDefinition() && RD->isDynamicClass() &&
+      !CurFuncDecl->hasAttr<NoSanitizeVptrAttr>()) {
     // Compute a hash of the mangled name of the type.
     //
     // FIXME: This is not guaranteed to be deterministic! Move to a
Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -4772,6 +4772,9 @@
   case AttributeList::AT_NoSanitizeMemory:
     handleSimpleAttribute<NoSanitizeMemoryAttr>(S, D, Attr);
     break;
+  case AttributeList::AT_NoSanitizeVptr:
+    handleSimpleAttribute<NoSanitizeVptrAttr>(S, D, Attr);
+    break;
   case AttributeList::AT_GuardedBy:
     handleGuardedByAttr(S, D, Attr);
     break;
Index: test/CodeGen/no-sanitize-vptr.cpp
===================================================================
--- /dev/null
+++ test/CodeGen/no-sanitize-vptr.cpp
@@ -0,0 +1,23 @@
+// Verify ubsan doesn't emit checks for functions with the no_sanitize_vptr attribute.
+// RUN: %clang_cc1 -fsanitize=vptr -emit-llvm %s -o - | FileCheck %s
+
+class Bar {
+public:
+  virtual ~Bar() {}
+};
+class Foo : public Bar {};
+
+Bar bar;
+
+Foo *testfunc1(Bar *bar) {
+  // CHECK: testfunc1
+  // CHECK: call void @__ubsan_handle_dynamic_type_cache_miss
+  return static_cast<Foo*>(bar); // down-casting
+  // CHECK: ret
+}
+__attribute__((no_sanitize_vptr)) Foo *testfunc2(Bar *bar) {
+  // CHECK: testfunc2
+  // CHECK-NOT: call void @__ubsan_handle_dynamic_type_cache_miss
+  return static_cast<Foo*>(bar); // down-casting
+  // CHECK: ret
+}
Index: test/SemaCXX/attr-no-sanitize-vptr.cpp
===================================================================
--- /dev/null
+++ test/SemaCXX/attr-no-sanitize-vptr.cpp
@@ -0,0 +1,37 @@
+// RUN: %clang_cc1 -fsyntax-only -verify  %s
+
+#define NO_SANITIZE_VPTR __attribute__((no_sanitize_vptr))
+
+#if !__has_attribute(no_sanitize_vptr)
+#error "Should support no_sanitize_vptr"
+#endif
+
+void noanal_fun() NO_SANITIZE_VPTR;
+
+void noanal_fun_args() __attribute__((no_sanitize_vptr(1))); // \
+  // expected-error {{'no_sanitize_vptr' attribute takes no arguments}}
+
+int noanal_testfn(int y) NO_SANITIZE_VPTR;
+
+int noanal_testfn(int y) {
+  int x NO_SANITIZE_VPTR = y; // \
+    // expected-error {{'no_sanitize_vptr' attribute only applies to functions}}
+  return x;
+}
+
+int noanal_test_var NO_SANITIZE_VPTR; // \
+  // expected-error {{'no_sanitize_vptr' attribute only applies to functions}}
+
+class NoanalFoo {
+ private:
+  int test_field NO_SANITIZE_VPTR; // \
+    // expected-error {{'no_sanitize_vptr' attribute only applies to functions}}
+  void test_method() NO_SANITIZE_VPTR;
+};
+
+class NO_SANITIZE_VPTR NoanalTestClass { // \
+  // expected-error {{'no_sanitize_vptr' attribute only applies to functions}}
+};
+
+void noanal_fun_params(int lvar NO_SANITIZE_VPTR); // \
+  // expected-error {{'no_sanitize_vptr' attribute only applies to functions}}