Index: lib/builtins/int_lib.h
===================================================================
--- lib/builtins/int_lib.h
+++ lib/builtins/int_lib.h
@@ -88,4 +88,35 @@
 COMPILER_RT_ABI tu_int __udivmodti4(tu_int a, tu_int b, tu_int* rem);
 #endif
 
+/* Definitions for builtins unavailable on MSVC */
+#if defined(_MSC_VER) && !defined(__clang__)
+#include <intrin.h>
+
+uint32_t __inline __builtin_ctz(uint32_t value) {
+  uint32_t trailing_zero = 0;
+  if (_BitScanForward(&trailing_zero, value))
+    return trailing_zero;
+  else
+    return 32;
+}
+
+uint32_t __inline __builtin_clz(uint32_t value) {
+  uint32_t leading_zero = 0;
+  if (_BitScanReverse(&leading_zero, value))
+    return 31 - leading_zero;
+  else
+    return 32;
+}
+
+uint32_t __inline __builtin_clzll(uint64_t value) {
+  uint32_t leading_zero = 0;
+  if (_BitScanReverse64(&leading_zero, value))
+    return 63 - leading_zero;
+  else
+    return 64;
+}
+
+#define __builtin_clzl __builtin_clzll
+#endif
+
 #endif /* INT_LIB_H */