[libcxx] simplify __optional_iterator operations and add to_address utility

Author: dywoq

libcxx/include/optional

@@ -630,57 +630,55 @@ public:
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator& operator=(const __optional_iterator&) = default;
 
   _LIBCPP_HIDE_FROM_ABI constexpr reference operator*() const { return *__it_; }
-  _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const { return *__it_.operator->(); }
+  _LIBCPP_HIDE_FROM_ABI constexpr pointer operator->() const { return __it_.operator->(); } 
 
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator& operator++() noexcept {
-    __it_ = _Base();
+    ++__it_;
     return *this;
   }
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator operator++(int) noexcept {
     auto __tmp = *this;
-    __it_      = _Base();
+    ++__it_;
     return __tmp;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator& operator--() noexcept {
-    __it_ = _Base();
+    --__it_;
     return *this;
   }
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator operator--(int) noexcept {
     auto __tmp = *this;
-    __it_      = _Base();
+    --__it_;
     return __tmp;
   }
 
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator& operator+=(difference_type __n) noexcept {
-    if (__n != 0)
-      __it_ = _Base();
+    __it_ += __n;
     return *this;
   }
   _LIBCPP_HIDE_FROM_ABI constexpr __optional_iterator& operator-=(difference_type __n) noexcept {
-    if (__n != 0)
-      __it_ = _Base();
+    __it_ -= __n;
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI friend constexpr __optional_iterator
   operator+(__optional_iterator __i, difference_type __n) noexcept {
-    return (__n == 0 ? __i : __optional_iterator(_Base()));
+    return __optional_iterator(__i.__it_ + __n);
   }
   _LIBCPP_HIDE_FROM_ABI friend constexpr __optional_iterator
   operator+(difference_type __n, __optional_iterator __i) noexcept {
     return __i + __n;
   }
   _LIBCPP_HIDE_FROM_ABI friend constexpr __optional_iterator
   operator-(__optional_iterator __i, difference_type __n) noexcept {
-    return (__n == 0 ? __i : __optional_iterator(_Base()));
+    return __optional_iterator(__i.__it_ - __n);
   }
   _LIBCPP_HIDE_FROM_ABI friend constexpr difference_type
   operator-(__optional_iterator __a, __optional_iterator __b) noexcept {
-    return (__a.__it_ == __b.__it_ ? 0 : (__a.__it_ ? 1 : -1));
+    return __a.__it_ - __b.__it_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](difference_type __n) const noexcept { return *(*this + __n); }
+  _LIBCPP_HIDE_FROM_ABI constexpr reference operator[](difference_type __n) const noexcept { return *(__it_ + __n); }
 
   _LIBCPP_HIDE_FROM_ABI constexpr bool operator==(const __optional_iterator& __other) const {
     return __it_ == __other.__it_;
@@ -710,6 +708,10 @@ public:
     return __optional_iterator<const _Tp>(__wrap_iter<const _Tp*>{__it_.base()});
   }
 };
+template <typename _Tp>
+_LIBCPP_HIDE_FROM_ABI constexpr _Tp* to_address(const __optional_iterator<_Tp>& __it) noexcept {
+  return std::to_address(__it.__it_);
+}
 
 #    endif // _LIBCPP_STD_VER >= 26