Remove unnecessary cast

Author: winner245

libcxx/include/__bit_reference

@@ -68,26 +68,23 @@ struct __size_difference_type_traits<_Cp, __void_t<typename _Cp::difference_type
 // cast back to the unsigned `_StorageType`.
 
 // Creates a mask of type `_StorageType` with a specified number of leading zeros (__clz) and sets all remaining
-// bits to one
+// bits to one.
 template <class _StorageType>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _StorageType __trailing_mask(unsigned __clz) {
   static_assert(is_unsigned<_StorageType>::value, "__trailing_mask only works with unsigned types");
-  return static_cast<_StorageType>(static_cast<_StorageType>(~static_cast<_StorageType>(0)) >> __clz);
+  return _StorageType(~_StorageType(0)) >> __clz;
 }
 
 // Creates a mask of type `_StorageType` with a specified number of leading zeros (__clz), a specified number of
-// trailing zeros (__ctz), and sets all bits in between to one
+// trailing zeros (__ctz), and sets all bits in between to one.
 template <class _StorageType>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _StorageType __middle_mask(unsigned __clz, unsigned __ctz) {
   static_assert(is_unsigned<_StorageType>::value, "__middle_mask only works with unsigned types");
-  return static_cast<_StorageType>(
-      static_cast<_StorageType>(static_cast<_StorageType>(~static_cast<_StorageType>(0)) << __ctz) &
-      std::__trailing_mask<_StorageType>(__clz));
+  return _StorageType(_StorageType(~_StorageType(0)) << __ctz) & std::__trailing_mask<_StorageType>(__clz);
 }
 
 // This function is designed to operate correctly even for smaller integral types like `uint8_t`, `uint16_t`,
-// or `unsigned short`. Casting back to _StorageType is crucial to prevent undefined behavior that can arise
-// from integral promotions.
+// or `unsigned short`.
 // See https://github.com/llvm/llvm-project/pull/122410.
 template <class _StoragePointer>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
@@ -97,8 +94,7 @@ __fill_masked_range(_StoragePointer __word, unsigned __clz, unsigned __ctz, bool
   using _StorageType = typename pointer_traits<_StoragePointer>::element_type;
   _LIBCPP_ASSERT_VALID_INPUT_RANGE(
       __ctz + __clz < sizeof(_StorageType) * CHAR_BIT, "__fill_masked_range called with invalid range");
-  _StorageType __m = static_cast<_StorageType>(static_cast<_StorageType>(~static_cast<_StorageType>(0)) >> __clz) &
-                     static_cast<_StorageType>(static_cast<_StorageType>(~static_cast<_StorageType>(0)) << __ctz);
+  _StorageType __m = std::__middle_mask<_StorageType>(__clz, __ctz);
   if (__fill_val)
     *__word |= __m;
   else