Index: cmake/config-ix.cmake
===================================================================
--- cmake/config-ix.cmake
+++ cmake/config-ix.cmake
@@ -181,7 +181,11 @@
       test_target_arch(i686 __i686__ "-m32")
       test_target_arch(i386 __i386__ "-m32")
     else()
-      test_target_arch(i386 "" "")
+      if (CMAKE_SIZEOF_VOID_P EQUAL 4)
+        test_target_arch(i386 "" "")
+      else()
+        test_target_arch(x86_64 "" "")
+      endif()
     endif()
   elseif("${LLVM_NATIVE_ARCH}" STREQUAL "PowerPC")
     TEST_BIG_ENDIAN(HOST_IS_BIG_ENDIAN)
@@ -267,13 +271,14 @@
 
 if (SANITIZER_COMMON_SUPPORTED_ARCH AND NOT LLVM_USE_SANITIZER AND
     (OS_NAME MATCHES "Android|Darwin|Linux|FreeBSD" OR
-    (OS_NAME MATCHES "Windows" AND MSVC AND CMAKE_SIZEOF_VOID_P EQUAL 4)))
+    (OS_NAME MATCHES "Windows" AND MSVC)))
   set(COMPILER_RT_HAS_SANITIZER_COMMON TRUE)
 else()
   set(COMPILER_RT_HAS_SANITIZER_COMMON FALSE)
 endif()
 
-if (COMPILER_RT_HAS_SANITIZER_COMMON AND ASAN_SUPPORTED_ARCH)
+if (COMPILER_RT_HAS_SANITIZER_COMMON AND ASAN_SUPPORTED_ARCH AND
+    (NOT OS_NAME MATCHES "Windows" OR CMAKE_SIZEOF_VOID_P EQUAL 4))
   set(COMPILER_RT_HAS_ASAN TRUE)
 else()
   set(COMPILER_RT_HAS_ASAN FALSE)
@@ -323,7 +328,7 @@
 endif()
 
 if (COMPILER_RT_HAS_SANITIZER_COMMON AND UBSAN_SUPPORTED_ARCH AND
-    OS_NAME MATCHES "Darwin|Linux|FreeBSD")
+    OS_NAME MATCHES "Darwin|Linux|FreeBSD|Windows")
   set(COMPILER_RT_HAS_UBSAN TRUE)
 else()
   set(COMPILER_RT_HAS_UBSAN FALSE)
Index: lib/sanitizer_common/sanitizer_atomic_msvc.h
===================================================================
--- lib/sanitizer_common/sanitizer_atomic_msvc.h
+++ lib/sanitizer_common/sanitizer_atomic_msvc.h
@@ -21,6 +21,15 @@
 #pragma intrinsic(_mm_mfence)
 extern "C" void _mm_pause();
 #pragma intrinsic(_mm_pause)
+extern "C" char _InterlockedExchange8(   // NOLINT
+    char volatile *Addend, char Value);  // NOLINT
+#pragma intrinsic(_InterlockedExchange8)
+extern "C" short _InterlockedExchange16(   // NOLINT
+    short volatile *Addend, short Value);  // NOLINT
+#pragma intrinsic(_InterlockedExchange16)
+extern "C" long _InterlockedExchange(    // NOLINT
+    long volatile *Addend, long Value);  // NOLINT
+#pragma intrinsic(_InterlockedExchange)
 extern "C" long _InterlockedExchangeAdd(  // NOLINT
     long volatile * Addend, long Value);  // NOLINT
 #pragma intrinsic(_InterlockedExchangeAdd)
@@ -145,28 +154,25 @@
     u8 v, memory_order mo) {
   (void)mo;
   DCHECK(!((uptr)a % sizeof(*a)));
-  __asm {
-    mov eax, a
-    mov cl, v
-    xchg [eax], cl  // NOLINT
-    mov v, cl
-  }
-  return v;
+  return (u8)_InterlockedExchange8((volatile char*)&a->val_dont_use, v);
 }
 
 INLINE u16 atomic_exchange(volatile atomic_uint16_t *a,
     u16 v, memory_order mo) {
   (void)mo;
   DCHECK(!((uptr)a % sizeof(*a)));
-  __asm {
-    mov eax, a
-    mov cx, v
-    xchg [eax], cx  // NOLINT
-    mov v, cx
-  }
-  return v;
+  return (u16)_InterlockedExchange16((volatile short*)&a->val_dont_use, v);
+}
+
+INLINE u32 atomic_exchange(volatile atomic_uint32_t *a,
+    u32 v, memory_order mo) {
+  (void)mo;
+  DCHECK(!((uptr)a % sizeof(*a)));
+  return (u32)_InterlockedExchange((volatile long*)&a->val_dont_use, v);
 }
 
+#ifndef _WIN64
+
 INLINE bool atomic_compare_exchange_strong(volatile atomic_uint8_t *a,
                                            u8 *cmp,
                                            u8 xchgv,
@@ -188,6 +194,8 @@
   return false;
 }
 
+#endif
+
 INLINE bool atomic_compare_exchange_strong(volatile atomic_uintptr_t *a,
                                            uptr *cmp,
                                            uptr xchg,
Index: lib/sanitizer_common/sanitizer_common.h
===================================================================
--- lib/sanitizer_common/sanitizer_common.h
+++ lib/sanitizer_common/sanitizer_common.h
@@ -383,7 +383,7 @@
   uptr up = MostSignificantSetBitIndex(size);
   CHECK(size < (1ULL << (up + 1)));
   CHECK(size > (1ULL << up));
-  return 1UL << (up + 1);
+  return 1ULL << (up + 1);
 }
 
 INLINE uptr RoundUpTo(uptr size, uptr boundary) {
@@ -659,8 +659,7 @@
 // memset/memcpy/etc.
 static inline void SanitizerBreakOptimization(void *arg) {
 #if _MSC_VER
-  // FIXME: make sure this is actually enough.
-  __asm;
+  _ReadWriteBarrier();
 #else
   __asm__ __volatile__("" : : "r" (arg) : "memory");
 #endif
Index: lib/ubsan/ubsan_diag.cc
===================================================================
--- lib/ubsan/ubsan_diag.cc
+++ lib/ubsan/ubsan_diag.cc
@@ -186,7 +186,11 @@
         // FIXME: Support floating-point formatting in sanitizer_common's
         //        printf, and stop using snprintf here.
         char Buffer[32];
+#if SANITIZER_WINDOWS
+        sprintf_s(Buffer, sizeof(Buffer), "%Lg", (long double)A.Float);
+#else
         snprintf(Buffer, sizeof(Buffer), "%Lg", (long double)A.Float);
+#endif
         Printf("%s", Buffer);
         break;
       }
Index: lib/ubsan/ubsan_flags.cc
===================================================================
--- lib/ubsan/ubsan_flags.cc
+++ lib/ubsan/ubsan_flags.cc
@@ -64,11 +64,18 @@
 
 }  // namespace __ubsan
 
-#if !SANITIZER_SUPPORTS_WEAK_HOOKS
 extern "C" {
+
+#if !SANITIZER_SUPPORTS_WEAK_HOOKS
 SANITIZER_INTERFACE_ATTRIBUTE SANITIZER_WEAK_ATTRIBUTE
 const char *__ubsan_default_options() { return ""; }
-}  // extern "C"
 #endif
 
+#if SANITIZER_WINDOWS
+const char *__ubsan_default_default_options() { return ""; }
+#pragma comment(linker, "/alternatename:__ubsan_default_options=__ubsan_default_default_options")
+#endif
+
+}  // extern "C"
+
 #endif  // CAN_SANITIZE_UB
Index: lib/ubsan/ubsan_platform.h
===================================================================
--- lib/ubsan/ubsan_platform.h
+++ lib/ubsan/ubsan_platform.h
@@ -16,7 +16,8 @@
 // Other platforms should be easy to add, and probably work as-is.
 #if (defined(__linux__) || defined(__FreeBSD__) || defined(__APPLE__)) && \
     (defined(__x86_64__) || defined(__i386__) || defined(__arm__) || \
-     defined(__aarch64__) || defined(__mips__) || defined(__powerpc64__))
+     defined(__aarch64__) || defined(__mips__) || defined(__powerpc64__)) || \
+     defined(_WIN32)
 # define CAN_SANITIZE_UB 1
 #else
 # define CAN_SANITIZE_UB 0