diff --git a/llvm/cmake/modules/HandleLLVMOptions.cmake b/llvm/cmake/modules/HandleLLVMOptions.cmake
--- a/llvm/cmake/modules/HandleLLVMOptions.cmake
+++ b/llvm/cmake/modules/HandleLLVMOptions.cmake
@@ -849,7 +849,7 @@
 endif()
 
 macro(append_common_sanitizer_flags)
-  if (NOT MSVC)
+  if (NOT MSVC OR CLANG_CL)
     # Append -fno-omit-frame-pointer and turn on debug info to get better
     # stack traces.
     add_flag_if_supported("-fno-omit-frame-pointer" FNO_OMIT_FRAME_POINTER)
@@ -928,23 +928,18 @@
       message(FATAL_ERROR "This sanitizer not yet supported in a MinGW environment: ${LLVM_USE_SANITIZER}")
     endif()
   elseif(MSVC)
-    if (LLVM_USE_SANITIZER STREQUAL "Address")
-      append_common_sanitizer_flags()
-      append("/fsanitize=address" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
-      if (NOT CLANG_CL)
-        # Not compatible with /RTC flags.
-        foreach (flags_opt_to_scrub
-            CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE} CMAKE_C_FLAGS_${uppercase_CMAKE_BUILD_TYPE})
-          string (REGEX REPLACE "(^| )/RTC[1csu]*($| )" " "
-            "${flags_opt_to_scrub}" "${${flags_opt_to_scrub}}")
-        endforeach()
+    if (NOT LLVM_USE_SANITIZER MATCHES "^(Address|Undefined|Address;Undefined|Undefined;Address)$")
+      message(FATAL_ERROR "This sanitizer not yet supported in the MSVC environment: ${LLVM_USE_SANITIZER}")
+    endif()
+    append_common_sanitizer_flags()
+    if (LINKER_IS_LLD_LINK)
+      if (LLVM_HOST_TRIPLE MATCHES "i[2-6]86-.*")
+        set(arch "i386")
+      else()
+        set(arch "x86_64")
       endif()
-      if (LINKER_IS_LLD_LINK)
-        if (LLVM_HOST_TRIPLE MATCHES "i[2-6]86-.*")
-          set(arch "i386")
-        else()
-          set(arch "x86_64")
-        endif()
+      # Prepare ASAN runtime if needed
+      if (LLVM_USE_SANITIZER MATCHES ".*Address.*")
         if (${LLVM_USE_CRT_${uppercase_CMAKE_BUILD_TYPE}} MATCHES "^(MT|MTd)$")
           append("/wholearchive:clang_rt.asan-${arch}.lib /wholearchive:clang_rt.asan_cxx-${arch}.lib"
             CMAKE_EXE_LINKER_FLAGS)
@@ -955,8 +950,25 @@
             CMAKE_EXE_LINKER_FLAGS CMAKE_MODULE_LINKER_FLAGS CMAKE_SHARED_LINKER_FLAGS)
         endif()
       endif()
-    else()
-      message(FATAL_ERROR "This sanitizer not yet supported in the MSVC environment: ${LLVM_USE_SANITIZER}")
+    endif()
+    if (LLVM_USE_SANITIZER MATCHES ".*Address.*")
+      if (NOT CLANG_CL)
+        append("/fsanitize=address" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+        # Not compatible with /RTC flags.
+        foreach (flags_opt_to_scrub
+            CMAKE_CXX_FLAGS_${uppercase_CMAKE_BUILD_TYPE} CMAKE_C_FLAGS_${uppercase_CMAKE_BUILD_TYPE})
+          string (REGEX REPLACE "(^| )/RTC[1csu]*($| )" " "
+            "${flags_opt_to_scrub}" "${${flags_opt_to_scrub}}")
+        endforeach()
+      else()
+        append("-fsanitize=address" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+      endif()
+    endif()
+    if (LLVM_USE_SANITIZER MATCHES ".*Undefined.*")
+      if (NOT CLANG_CL)
+        message(FATAL_ERROR "This sanitizer is only supported by clang-cl: Undefined")
+      endif()
+      append(${LLVM_UBSAN_FLAGS} CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
     endif()
   else()
     message(FATAL_ERROR "LLVM_USE_SANITIZER is not supported on this platform.")
diff --git a/llvm/include/llvm/ADT/EpochTracker.h b/llvm/include/llvm/ADT/EpochTracker.h
--- a/llvm/include/llvm/ADT/EpochTracker.h
+++ b/llvm/include/llvm/ADT/EpochTracker.h
@@ -23,6 +23,7 @@
 namespace llvm {
 
 #if LLVM_ENABLE_ABI_BREAKING_CHECKS
+#define LLVM_DEBUGEPOCHBASE_HANDLEBASE_EMPTYBASE
 
 /// A base class for data structure classes wishing to make iterators
 /// ("handles") pointing into themselves fail-fast.  When building without
@@ -78,6 +79,11 @@
 };
 
 #else
+#ifdef _MSC_VER
+#define LLVM_DEBUGEPOCHBASE_HANDLEBASE_EMPTYBASE __declspec(empty_bases)
+#else
+#define LLVM_DEBUGEPOCHBASE_HANDLEBASE_EMPTYBASE
+#endif // _MSC_VER
 
 class DebugEpochBase {
 public:
diff --git a/llvm/include/llvm/ADT/SmallPtrSet.h b/llvm/include/llvm/ADT/SmallPtrSet.h
--- a/llvm/include/llvm/ADT/SmallPtrSet.h
+++ b/llvm/include/llvm/ADT/SmallPtrSet.h
@@ -264,8 +264,9 @@
 
 /// SmallPtrSetIterator - This implements a const_iterator for SmallPtrSet.
 template <typename PtrTy>
-class SmallPtrSetIterator : public SmallPtrSetIteratorImpl,
-                            DebugEpochBase::HandleBase {
+class LLVM_DEBUGEPOCHBASE_HANDLEBASE_EMPTYBASE SmallPtrSetIterator
+    : public SmallPtrSetIteratorImpl,
+      DebugEpochBase::HandleBase {
   using PtrTraits = PointerLikeTypeTraits<PtrTy>;
 
 public:
diff --git a/llvm/include/llvm/ADT/StringMap.h b/llvm/include/llvm/ADT/StringMap.h
--- a/llvm/include/llvm/ADT/StringMap.h
+++ b/llvm/include/llvm/ADT/StringMap.h
@@ -107,8 +107,9 @@
 /// funky memory allocation and hashing things to make it extremely efficient,
 /// storing the string data *after* the value in the map.
 template <typename ValueTy, typename AllocatorTy = MallocAllocator>
-class StringMap : public StringMapImpl,
-                  private detail::AllocatorHolder<AllocatorTy> {
+class LLVM_ALLOCATORHOLDER_EMPTYBASE StringMap
+    : public StringMapImpl,
+      private detail::AllocatorHolder<AllocatorTy> {
   using AllocTy = detail::AllocatorHolder<AllocatorTy>;
 
 public:
diff --git a/llvm/include/llvm/Support/AllocatorBase.h b/llvm/include/llvm/Support/AllocatorBase.h
--- a/llvm/include/llvm/Support/AllocatorBase.h
+++ b/llvm/include/llvm/Support/AllocatorBase.h
@@ -19,6 +19,12 @@
 #ifndef LLVM_SUPPORT_ALLOCATORBASE_H
 #define LLVM_SUPPORT_ALLOCATORBASE_H
 
+#ifdef _MSC_VER
+#define LLVM_ALLOCATORHOLDER_EMPTYBASE __declspec(empty_bases)
+#else
+#define LLVM_ALLOCATORHOLDER_EMPTYBASE
+#endif // _MSC_VER
+
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/MemAlloc.h"
 #include <type_traits>