Index: docs/UndefinedBehaviorSanitizer.rst
===================================================================
--- docs/UndefinedBehaviorSanitizer.rst
+++ docs/UndefinedBehaviorSanitizer.rst
@@ -130,11 +130,11 @@
      it is often unintentional, so UBSan offers to catch it.
   -  ``-fsanitize=vla-bound``: A variable-length array whose bound
      does not evaluate to a positive value.
-  -  ``-fsanitize=vptr``: Use of an object whose vptr indicates that
-     it is of the wrong dynamic type, or that its lifetime has not
-     begun or has ended. Incompatible with ``-fno-rtti``. Link must
-     be performed by ``clang++``, not ``clang``, to make sure C++-specific
-     parts of the runtime library and C++ standard libraries are present.
+  -  ``-fsanitize=vptr``: Use of an object whose vptr indicates that it is of
+     the wrong dynamic type, or that its lifetime has not begun or has ended.
+     Incompatible with ``-fno-rtti`` and ``-fno-sanitize=null``. Link must be
+     performed by ``clang++``, not ``clang``, to make sure C++-specific parts of
+     the runtime library and C++ standard libraries are present.
 
 You can also use the following check groups:
   -  ``-fsanitize=undefined``: All of the checks listed above other than
Index: include/clang/Basic/DiagnosticDriverKinds.td
===================================================================
--- include/clang/Basic/DiagnosticDriverKinds.td
+++ include/clang/Basic/DiagnosticDriverKinds.td
@@ -230,7 +230,10 @@
   InGroup<DiagGroup<"rtti-for-exceptions">>;
 def warn_drv_disabling_vptr_no_rtti_default : Warning<
   "implicitly disabling vptr sanitizer because rtti wasn't enabled">,
-  InGroup<DiagGroup<"auto-disable-vptr-sanitizer">>;
+  InGroup<AutoDisableVptrSanitizer>;
+def warn_drv_disabling_vptr_no_null_check : Warning<
+  "implicitly disabling vptr sanitizer because null checking wasn't enabled">,
+  InGroup<AutoDisableVptrSanitizer>;
 def warn_drv_object_size_disabled_O0 : Warning<
   "the object size sanitizer has no effect at -O0, but is explicitly enabled: %0">,
   InGroup<InvalidCommandLineArgument>;
Index: include/clang/Basic/DiagnosticGroups.td
===================================================================
--- include/clang/Basic/DiagnosticGroups.td
+++ include/clang/Basic/DiagnosticGroups.td
@@ -27,6 +27,7 @@
 def GNUAutoType : DiagGroup<"gnu-auto-type">;
 def ArrayBounds : DiagGroup<"array-bounds">;
 def ArrayBoundsPointerArithmetic : DiagGroup<"array-bounds-pointer-arithmetic">;
+def AutoDisableVptrSanitizer : DiagGroup<"auto-disable-vptr-sanitizer">;
 def Availability : DiagGroup<"availability">;
 def Section : DiagGroup<"section">;
 def AutoImport : DiagGroup<"auto-import">;
Index: lib/CodeGen/CGExpr.cpp
===================================================================
--- lib/CodeGen/CGExpr.cpp
+++ lib/CodeGen/CGExpr.cpp
@@ -604,20 +604,23 @@
   auto PtrToAlloca =
       dyn_cast<llvm::AllocaInst>(Ptr->stripPointerCastsNoFollowAliases());
 
+  llvm::Value *IsNonNull = nullptr;
+  bool IsGuaranteedNonNull =
+      SkippedChecks.has(SanitizerKind::Null) || PtrToAlloca;
   bool AllowNullPointers = TCK == TCK_DowncastPointer || TCK == TCK_Upcast ||
                            TCK == TCK_UpcastToVirtualBase;
   if ((SanOpts.has(SanitizerKind::Null) || AllowNullPointers) &&
-      !SkippedChecks.has(SanitizerKind::Null) && !PtrToAlloca) {
+      !IsGuaranteedNonNull) {
     // The glvalue must not be an empty glvalue.
-    llvm::Value *IsNonNull = Builder.CreateIsNotNull(Ptr);
+    IsNonNull = Builder.CreateIsNotNull(Ptr);
 
     // The IR builder can constant-fold the null check if the pointer points to
     // a constant.
-    bool PtrIsNonNull =
+    IsGuaranteedNonNull =
         IsNonNull == llvm::ConstantInt::getTrue(getLLVMContext());
 
     // Skip the null check if the pointer is known to be non-null.
-    if (!PtrIsNonNull) {
+    if (!IsGuaranteedNonNull) {
       if (AllowNullPointers) {
         // When performing pointer casts, it's OK if the value is null.
         // Skip the remaining checks in that case.
@@ -691,12 +694,24 @@
   //    -- the [pointer or glvalue] is used to access a non-static data member
   //       or call a non-static member function
   CXXRecordDecl *RD = Ty->getAsCXXRecordDecl();
+  bool HasNullCheck = IsGuaranteedNonNull || IsNonNull;
   if (SanOpts.has(SanitizerKind::Vptr) &&
-      !SkippedChecks.has(SanitizerKind::Vptr) &&
+      !SkippedChecks.has(SanitizerKind::Vptr) && HasNullCheck &&
       (TCK == TCK_MemberAccess || TCK == TCK_MemberCall ||
        TCK == TCK_DowncastPointer || TCK == TCK_DowncastReference ||
        TCK == TCK_UpcastToVirtualBase) &&
       RD && RD->hasDefinition() && RD->isDynamicClass()) {
+    // Ensure that the pointer is non-null before loading it. If there is no
+    // compile-time guarantee, reuse the run-time null check.
+    if (!IsGuaranteedNonNull) {
+      assert(IsNonNull && "Missing run-time null check");
+      if (!Done)
+        Done = createBasicBlock("vptr.null");
+      llvm::BasicBlock *VptrNotNull = createBasicBlock("vptr.not.null");
+      Builder.CreateCondBr(IsNonNull, VptrNotNull, Done);
+      EmitBlock(VptrNotNull);
+    }
+
     // Compute a hash of the mangled name of the type.
     //
     // FIXME: This is not guaranteed to be deterministic! Move to a
Index: lib/Driver/SanitizerArgs.cpp
===================================================================
--- lib/Driver/SanitizerArgs.cpp
+++ lib/Driver/SanitizerArgs.cpp
@@ -306,6 +306,13 @@
     Kinds &= ~Vptr;
   }
 
+  // Disable -fsanitize=vptr if -fsanitize=null is not enabled (the vptr
+  // instrumentation is broken without run-time null checks).
+  if ((Kinds & Vptr) && !(Kinds & Null)) {
+    Kinds &= ~Vptr;
+    D.Diag(diag::warn_drv_disabling_vptr_no_null_check);
+  }
+
   // Check that LTO is enabled if we need it.
   if ((Kinds & NeedsLTO) && !D.isUsingLTO()) {
     D.Diag(diag::err_drv_argument_only_allowed_with)
Index: test/CodeGenCXX/catch-undef-behavior.cpp
===================================================================
--- test/CodeGenCXX/catch-undef-behavior.cpp
+++ test/CodeGenCXX/catch-undef-behavior.cpp
@@ -1,6 +1,6 @@
 // RUN: %clang_cc1 -std=c++11 -fsanitize=signed-integer-overflow,integer-divide-by-zero,float-divide-by-zero,shift-base,shift-exponent,unreachable,return,vla-bound,alignment,null,vptr,object-size,float-cast-overflow,bool,enum,array-bounds,function -fsanitize-recover=signed-integer-overflow,integer-divide-by-zero,float-divide-by-zero,shift-base,shift-exponent,vla-bound,alignment,null,vptr,object-size,float-cast-overflow,bool,enum,array-bounds,function -emit-llvm %s -o - -triple x86_64-linux-gnu | opt -instnamer -S | FileCheck %s
-// RUN: %clang_cc1 -std=c++11 -fsanitize=vptr,address -fsanitize-recover=vptr,address -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK-ASAN
-// RUN: %clang_cc1 -std=c++11 -fsanitize=vptr -fsanitize-recover=vptr -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=DOWNCAST-NULL
+// RUN: %clang_cc1 -std=c++11 -fsanitize=null,vptr,address -fsanitize-recover=null,vptr,address -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK-ASAN
+// RUN: %clang_cc1 -std=c++11 -fsanitize=null,vptr -fsanitize-recover=null,vptr -emit-llvm %s -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=DOWNCAST-NULL
 // RUN: %clang_cc1 -std=c++11 -fsanitize=function -emit-llvm %s -o - -triple x86_64-linux-gnux32 | FileCheck %s --check-prefix=CHECK-X32
 // RUN: %clang_cc1 -std=c++11 -fsanitize=function -emit-llvm %s -o - -triple i386-linux-gnu | FileCheck %s --check-prefix=CHECK-X86
 
Index: test/CodeGenCXX/ubsan-devirtualized-calls.cpp
===================================================================
--- test/CodeGenCXX/ubsan-devirtualized-calls.cpp
+++ test/CodeGenCXX/ubsan-devirtualized-calls.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -std=c++11 -triple %itanium_abi_triple -emit-llvm -fsanitize=vptr %s -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c++11 -triple %itanium_abi_triple -emit-llvm -fsanitize=null,vptr %s -o - | FileCheck %s
 
 struct Base1 {
   virtual void f1() {}
@@ -64,6 +64,11 @@
   // CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED3]] {{.*}}, i{{[0-9]+}} %[[P1]]
 
   static_cast<Base1 *>(badp)->f1(); //< No devirt, test 'badp isa Base1'.
+  // We were able to skip the null check on the first type check becuase 'p'
+  // is backed by an alloca. We can't skip the second null check because 'badp'
+  // is a (bitcast (load ...)).
+  // CHECK: call void @__ubsan_handle_type_mismatch
+  //
   // CHECK: %[[BADP1:[0-9]+]] = ptrtoint %struct.Base1* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
   // CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_BASE1]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
 }
@@ -76,6 +81,8 @@
   // CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_1]] {{.*}}, i{{[0-9]+}} %[[P1]]
 
   static_cast<Base1 *>(badp)->f1(); //< Devirt Base1::f1 to Derived4::f1.
+  // CHECK: call void @__ubsan_handle_type_mismatch
+  //
   // CHECK: %[[BADP1:[0-9]+]] = ptrtoint %struct.Derived4* {{%[0-9]+}} to i{{[0-9]+}}, !nosanitize
   // CHECK-NEXT: call void @__ubsan_handle_dynamic_type_cache{{[_a-z]*}}({{.*}} [[UBSAN_TI_DERIVED4_2]] {{.*}}, i{{[0-9]+}} %[[BADP1]]
 }
Index: test/CodeGenCXX/ubsan-type-checks.cpp
===================================================================
--- test/CodeGenCXX/ubsan-type-checks.cpp
+++ test/CodeGenCXX/ubsan-type-checks.cpp
@@ -1,6 +1,8 @@
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin10 -emit-llvm -o - %s -fsanitize=alignment | FileCheck %s -check-prefixes=ALIGN,COMMON
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin10 -emit-llvm -o - %s -fsanitize=null | FileCheck %s -check-prefixes=NULL,COMMON
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin10 -emit-llvm -o - %s -fsanitize=object-size | FileCheck %s -check-prefixes=OBJSIZE,COMMON
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin10 -emit-llvm -o - %s -fsanitize=null,vptr | FileCheck %s -check-prefixes=VPTR
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-apple-darwin10 -emit-llvm -o - %s -fsanitize=vptr | FileCheck %s -check-prefixes=NOVPTR
 
 struct A {
   // COMMON-LABEL: define linkonce_odr void @_ZN1A10do_nothingEv
@@ -27,10 +29,43 @@
   }
 };
 
-void force_irgen() {
+struct Animal {
+  virtual const char *speak() = 0;
+};
+
+struct Cat : Animal {
+  const char *speak() override { return "meow"; }
+};
+
+struct Dog : Animal {
+  const char *speak() override { return "woof"; }
+};
+
+// VPTR-LABEL: define void @_Z12invalid_castP3Cat
+void invalid_cast(Cat *cat = nullptr) {
+  // First, null check the pointer:
+  //
+  // VPTR: [[ICMP:%.*]] = icmp ne %struct.Dog* {{.*}}, null
+  // VPTR-NEXT: br i1 [[ICMP]]
+  // VPTR: call void @__ubsan_handle_type_mismatch
+  //
+  // Once we're done emitting the null check, reuse the check to see if we can
+  // proceed to the vptr check:
+  //
+  // VPTR: br i1 [[ICMP]]
+  // VPTR: call void @__ubsan_handle_dynamic_type_cache_miss
+  auto *badDog = reinterpret_cast<Dog *>(cat);
+  badDog->speak();
+}
+
+// NOVPTR-NOT: __ubsan_handle_dynamic_type_cache_miss
+int main() {
   A a;
   a.do_nothing();
 
   B b;
   b.do_nothing();
+
+  invalid_cast();
+  return 0;
 }
Index: test/CodeGenCXX/ubsan-vtable-checks.cpp
===================================================================
--- test/CodeGenCXX/ubsan-vtable-checks.cpp
+++ test/CodeGenCXX/ubsan-vtable-checks.cpp
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux -emit-llvm -fsanitize=null %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NULL --check-prefix=ITANIUM
 // RUN: %clang_cc1 -std=c++11 -triple x86_64-windows -emit-llvm -fsanitize=null %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-NULL --check-prefix=MSABI
-// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux -emit-llvm -fsanitize=vptr %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-VPTR --check-prefix=ITANIUM
-// RUN: %clang_cc1 -std=c++11 -triple x86_64-windows -emit-llvm -fsanitize=vptr %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-VPTR --check-prefix=MSABI
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-unknown-linux -emit-llvm -fsanitize=null,vptr %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-VPTR --check-prefix=ITANIUM
+// RUN: %clang_cc1 -std=c++11 -triple x86_64-windows -emit-llvm -fsanitize=null,vptr %s -o - | FileCheck %s --check-prefix=CHECK --check-prefix=CHECK-VPTR --check-prefix=MSABI
 struct T {
   virtual ~T() {}
   virtual int v() { return 1; }
Index: test/Driver/fsanitize.c
===================================================================
--- test/Driver/fsanitize.c
+++ test/Driver/fsanitize.c
@@ -58,6 +58,10 @@
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fno-rtti %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-UNDEFINED-NO-RTTI
 // CHECK-UNDEFINED-NO-RTTI-NOT: vptr
 
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=undefined -fno-sanitize=null %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-VPTR-NO-NULL
+// RUN: %clang -target x86_64-linux-gnu -fsanitize=vptr %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-VPTR-NO-NULL
+// CHECK-VPTR-NO-NULL: warning: implicitly disabling vptr sanitizer because null checking wasn't enabled
+
 // RUN: %clang -target x86_64-linux-gnu -fsanitize=address,thread -fno-rtti %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-SANA-SANT
 // CHECK-SANA-SANT: '-fsanitize=address' not allowed with '-fsanitize=thread'
 
@@ -362,8 +366,8 @@
 // RUN: %clang -target x86_64-apple-darwin10 -mmacosx-version-min=10.8 -fsanitize=vptr %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-VPTR-DARWIN-OLD
 // CHECK-VPTR-DARWIN-OLD: unsupported option '-fsanitize=vptr' for target 'x86_64-apple-darwin10'
 
-// RUN: %clang -target x86_64-apple-darwin10 -mmacosx-version-min=10.9 -fsanitize=alignment,vptr %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-VPTR-DARWIN-NEW
-// CHECK-VPTR-DARWIN-NEW: -fsanitize=alignment,vptr
+// RUN: %clang -target x86_64-apple-darwin10 -mmacosx-version-min=10.9 -fsanitize=alignment,null,vptr %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-VPTR-DARWIN-NEW
+// CHECK-VPTR-DARWIN-NEW: -fsanitize=alignment,null,vptr
 
 // RUN: %clang -target armv7-apple-ios7 -miphoneos-version-min=7.0 -fsanitize=address %s -### 2>&1 | FileCheck %s --check-prefix=CHECK-ASAN-IOS
 // CHECK-ASAN-IOS: -fsanitize=address
Index: test/Driver/rtti-options.cpp
===================================================================
--- test/Driver/rtti-options.cpp
+++ test/Driver/rtti-options.cpp
@@ -16,14 +16,14 @@
 // Make sure we only error/warn once, when trying to enable vptr and
 // undefined and have -fno-rtti
 // RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=undefined -fsanitize=vptr -fno-rtti %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-ERROR -check-prefix=CHECK-OK %s
-// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=vptr %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
-// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=vptr -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
-// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=vptr -fno-rtti %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-ERROR %s
+// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=null,vptr %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
+// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=null,vptr -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
+// RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=null,vptr -fno-rtti %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-ERROR %s
 // RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=undefined %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
 // RUN: %clang -### -c -target x86_64-unknown-linux -fsanitize=undefined -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
-// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=vptr %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-WARN %s
-// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=vptr -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
-// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=vptr -fno-rtti %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-ERROR %s
+// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=null,vptr %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-WARN %s
+// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=null,vptr -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
+// RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=null,vptr -fno-rtti %s 2>&1 | FileCheck -check-prefix=CHECK-SAN-ERROR %s
 // RUN: %clang -### -c -target x86_64-scei-ps4 -fsanitize=undefined -frtti %s 2>&1 | FileCheck -check-prefix=CHECK-OK %s
 
 // Exceptions + no/default rtti