Index: lib/builtins/int_lib.h
===================================================================
--- lib/builtins/int_lib.h
+++ lib/builtins/int_lib.h
@@ -78,4 +78,40 @@
 COMPILER_RT_ABI tu_int __udivmodti4(tu_int a, tu_int b, tu_int* rem);
 #endif
 
+/* Definitions for builtins unavailable on MSVC */
+#ifdef _MSC_VER
+#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;
+    }
+}
+
+uint32_t __inline __builtin_clzl(uint64_t value) {
+    return __builtin_clzll(value);
+}
+#endif
+
 #endif /* INT_LIB_H */