Shortcuts that benefit from generic builtins

Author: marcauberer

libcxx/include/__bit/countl.h

@@ -74,6 +74,9 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countl_zero(_Tp __t) _
   if (__t == 0)
     return numeric_limits<_Tp>::digits;
 
+#if __has_builtin(__builtin_clzg)
+  return __builtin_clzg(__t) - (numeric_limits<unsigned>::digits - numeric_limits<_Tp>::digits);
+#else
   if (sizeof(_Tp) <= sizeof(unsigned int))
     return std::__libcpp_clz(static_cast<unsigned int>(__t)) -
            (numeric_limits<unsigned int>::digits - numeric_limits<_Tp>::digits);
@@ -95,6 +98,7 @@ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __countl_zero(_Tp __t) _
     }
     return __ret + __iter;
   }
+#endif // __has_builtin(__builtin_clzg)
 }
 
 #if _LIBCPP_STD_VER >= 20

libcxx/include/__bit/countr.h

@@ -52,6 +52,9 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __coun
   if (__t == 0)
     return numeric_limits<_Tp>::digits;
 
+#if __has_builtin(__builtin_ctz)
+  return __builtin_ctz(__t);
+#else
   if (sizeof(_Tp) <= sizeof(unsigned int))
     return std::__libcpp_ctz(static_cast<unsigned int>(__t));
   else if (sizeof(_Tp) <= sizeof(unsigned long))
@@ -67,6 +70,7 @@ _LIBCPP_NODISCARD _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 int __coun
     }
     return __ret + std::__libcpp_ctz(static_cast<unsigned long long>(__t));
   }
+#endif // __has_builtin(__builtin_ctz)
 }
 
 #if _LIBCPP_STD_VER >= 20

libcxx/include/__bit/popcount.h

@@ -51,6 +51,9 @@ inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR int __libcpp_popcount(unsigned lo
 
 template <__libcpp_unsigned_integer _Tp>
 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int popcount(_Tp __t) noexcept {
+#  if __has_builtin(__builtin_popcount)
+  return __builtin_popcount(__t);
+#  else
   if (sizeof(_Tp) <= sizeof(unsigned int))
     return std::__libcpp_popcount(static_cast<unsigned int>(__t));
   else if (sizeof(_Tp) <= sizeof(unsigned long))
@@ -65,6 +68,7 @@ _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr int popcount(_Tp __t) noex
     }
     return __ret;
   }
+#  endif // __has_builtin(__builtin_popcount)
 }
 
 #endif // _LIBCPP_STD_VER >= 20