Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_atomic_msvc.h
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_atomic_msvc.h
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_atomic_msvc.h
@@ -33,6 +33,10 @@
 extern "C" long _InterlockedExchangeAdd(  // NOLINT
     long volatile * Addend, long Value);  // NOLINT
 #pragma intrinsic(_InterlockedExchangeAdd)
+extern "C" char _InterlockedCompareExchange8(  // NOLINT
+    char volatile *Destination,                // NOLINT
+    char Exchange, char Comparand);            // NOLINT
+#pragma intrinsic(_InterlockedCompareExchange8)
 extern "C" short _InterlockedCompareExchange16(  // NOLINT
     short volatile *Destination,                 // NOLINT
     short Exchange, short Comparand);            // NOLINT
@@ -175,15 +179,13 @@
                                            u8 *cmp,
                                            u8 xchgv,
                                            memory_order mo) {
-#ifdef _WIN64
-  // TODO(wwchrome): Implement same functionality without inline asm.
-  // Inline asm not supported in Win64.
-  __debugbreak();
-  return false;
-#else
   (void)mo;
   DCHECK(!((uptr)a % sizeof(*a)));
   u8 cmpv = *cmp;
+#ifdef _WIN64
+  u8 prev = (u8)_InterlockedCompareExchange8(
+      (volatile char*)&a->val_dont_use, (char)xchgv, (char)cmpv);
+#else
   u8 prev;
   __asm {
     mov al, cmpv
@@ -192,11 +194,11 @@
     lock cmpxchg [ecx], dl
     mov prev, al
   }
+#endif
   if (prev == cmpv)
     return true;
   *cmp = prev;
   return false;
-#endif
 }
 
 INLINE bool atomic_compare_exchange_strong(volatile atomic_uintptr_t *a,