Index: include/bit
===================================================================
--- include/bit
+++ include/bit
@@ -88,7 +88,7 @@
 inline _LIBCPP_INLINE_VISIBILITY
 int __ctz(unsigned long long __x) {
     unsigned long __where;
-#if defined(_LIBCPP_HAS_BITSCAN64)
+#if defined(_LIBCPP_HAS_BITSCAN64) && \
     (defined(_M_AMD64) || defined(__x86_64__))
   if (_BitScanForward64(&__where, __x))
     return static_cast<int>(__where);
@@ -147,7 +147,12 @@
 
 inline _LIBCPP_INLINE_VISIBILITY int __popcount(unsigned long long __x) {
   static_assert(sizeof(unsigned long long) == 8, "");
+#if defined(_M_IX86)
+  // Win32 doesn't have __popcnt64 so emulate it with two 32 bit calls.
+  return __popcnt(__x) + __popcnt(__x >> 32);
+#else
   return __popcnt64(__x);
+#endif
 }
 
 #endif // _LIBCPP_COMPILER_MSVC