diff --git a/compiler-rt/lib/profile/InstrProfilingPort.h b/compiler-rt/lib/profile/InstrProfilingPort.h
--- a/compiler-rt/lib/profile/InstrProfilingPort.h
+++ b/compiler-rt/lib/profile/InstrProfilingPort.h
@@ -24,11 +24,17 @@
 #define COMPILER_RT_ALWAYS_INLINE __forceinline
 #define COMPILER_RT_CLEANUP(x)
 #elif __GNUC__
-#define COMPILER_RT_ALIGNAS(x) __attribute__((aligned(x)))
+#ifdef _WIN32
+#define COMPILER_RT_FTRUNCATE(f, l) _chsize(fileno(f), l)
+#define COMPILER_RT_VISIBILITY
+#define COMPILER_RT_WEAK __attribute__((selectany))
+#else
+#define COMPILER_RT_FTRUNCATE(f, l) ftruncate(fileno(f), l)
 #define COMPILER_RT_VISIBILITY __attribute__((visibility("hidden")))
 #define COMPILER_RT_WEAK __attribute__((weak))
+#endif
+#define COMPILER_RT_ALIGNAS(x) __attribute__((aligned(x)))
 #define COMPILER_RT_ALLOCA __builtin_alloca
-#define COMPILER_RT_FTRUNCATE(f,l) ftruncate(fileno(f),l)
 #define COMPILER_RT_ALWAYS_INLINE inline __attribute((always_inline))
 #define COMPILER_RT_CLEANUP(x) __attribute__((cleanup(x)))
 #endif