Remove redundant __constexpr_addressof function

The std::__addressof function is always constexpr, even in C++14, so we
can just use that.

	* include/experimental/bits/lfts_config.h: Improve doc markup.
	* include/experimental/optional: Improve docs.
	(_Has_addressof_mem, _Has_addressof_free, _Has_addressof)
	(__constexpr_addressof): Remove.
	(optional::operator->()): Use std::__addressof().
	* include/std/optional (optional::operator->()): Adjust whitespace.
	* testsuite/experimental/optional/constexpr/observers/2.cc: Check
	that operator-> is still constexpr with overloaded operator&. Change
	to compile-only test.
	* testsuite/experimental/optional/constexpr/observers/3.cc: Change to
	compile-only test.

From-SVN: r270826

libstdc++-v3/ChangeLog

 2019-05-02  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/experimental/bits/lfts_config.h: Improve doc markup.
+	* include/experimental/optional: Improve docs.
+	(_Has_addressof_mem, _Has_addressof_free, _Has_addressof)
+	(__constexpr_addressof): Remove.
+	(optional::operator->()): Use std::__addressof().
+	* include/std/optional (optional::operator->()): Adjust whitespace.
+	* testsuite/experimental/optional/constexpr/observers/2.cc: Check
+	that operator-> is still constexpr with overloaded operator&. Change
+	to compile-only test.
+	* testsuite/experimental/optional/constexpr/observers/3.cc: Change to
+	compile-only test.
+
 	* include/bits/shared_ptr.h: Improve docs.
 	* include/bits/shared_ptr_atomic.h: Likewise.
 	* include/bits/unique_ptr.h: Likewise. Adjust whitespace.

libstdc++-v3/include/experimental/bits/lfts_config.h

@@ -36,9 +36,8 @@
    * Components defined by the _C++ Extensions for Library Fundamentals_
    * Technical Specification, versions 1 and 2.
    *
-   * ISO/IEC TS 19568:2015 C++ Extensions for Library Fundamentals
-   *
-   * ISO/IEC TS 19568:2017 C++ Extensions for Library Fundamentals, Version 2
+   * - ISO/IEC TS 19568:2015 C++ Extensions for Library Fundamentals
+   * - ISO/IEC TS 19568:2017 C++ Extensions for Library Fundamentals, Version 2
    */
 
 #if _GLIBCXX_INLINE_VERSION

libstdc++-v3/include/experimental/optional

@@ -112,6 +112,8 @@ inline namespace fundamentals_v1
     virtual ~bad_optional_access() noexcept = default;
   };
 
+  /// @cond undocumented
+
   void
   __throw_bad_optional_access(const char*)
   __attribute__((__noreturn__));
@@ -121,59 +123,6 @@ inline namespace fundamentals_v1
   __throw_bad_optional_access(const char* __s)
   { _GLIBCXX_THROW_OR_ABORT(bad_optional_access(__s)); }
 
-#ifndef __cpp_lib_addressof_constexpr
-  template<typename _Tp, typename = void>
-    struct _Has_addressof_mem : std::false_type { };
-
-  template<typename _Tp>
-    struct _Has_addressof_mem<_Tp,
-         __void_t<decltype( std::declval<const _Tp&>().operator&() )>
-      >
-    : std::true_type { };
-
-  template<typename _Tp, typename = void>
-    struct _Has_addressof_free : std::false_type { };
-
-  template<typename _Tp>
-    struct _Has_addressof_free<_Tp,
-         __void_t<decltype( operator&(std::declval<const _Tp&>()) )>
-      >
-    : std::true_type { };
-
-  /**
-    * @brief Trait that detects the presence of an overloaded unary operator&.
-    *
-    * Practically speaking this detects the presence of such an operator when
-    * called on a const-qualified lvalue (e.g.
-    * declval<const _Tp&>().operator&()).
-    */
-  template<typename _Tp>
-    struct _Has_addressof
-    : std::__or_<_Has_addressof_mem<_Tp>, _Has_addressof_free<_Tp>>::type
-    { };
-
-  /**
-    * @brief An overload that attempts to take the address of an lvalue as a
-    * constant expression. Falls back to __addressof in the presence of an
-    * overloaded addressof operator (unary operator&), in which case the call
-    * will not be a constant expression.
-    */
-  template<typename _Tp>
-    constexpr
-    enable_if_t<!_Has_addressof<_Tp>::value, _Tp*>
-    __constexpr_addressof(_Tp& __t)
-    { return &__t; }
-
-  /**
-    * @brief Fallback overload that defers to __addressof.
-    */
-  template<typename _Tp>
-    inline
-    enable_if_t<_Has_addressof<_Tp>::value, _Tp*>
-    __constexpr_addressof(_Tp& __t)
-    { return std::__addressof(__t); }
-#endif // __cpp_lib_addressof_constexpr
-
   /**
     * @brief Class template that holds the necessary state for @ref optional
     * and that has the responsibility for construction and the special members.
@@ -452,9 +401,6 @@ inline namespace fundamentals_v1
       bool _M_engaged = false;
     };
 
-  template<typename _Tp>
-  class optional;
-
   template<typename _Tp, typename _Up>
     using __converts_from_optional =
       __or_<is_constructible<_Tp, const optional<_Up>&>,
@@ -473,6 +419,8 @@ inline namespace fundamentals_v1
 	    is_assignable<_Tp&, const optional<_Up>&&>,
 	    is_assignable<_Tp&, optional<_Up>&&>>;
 
+  /// @endcond
+
   /**
     * @brief Class template for optional values.
     */
@@ -698,13 +646,7 @@ inline namespace fundamentals_v1
       // [X.Y.4.5] Observers.
       constexpr const _Tp*
       operator->() const
-      {
-#ifndef __cpp_lib_addressof_constexpr
-	return __constexpr_addressof(this->_M_get());
-#else
-	return std::__addressof(this->_M_get());
-#endif
-      }
+      { return std::__addressof(this->_M_get()); }
 
       _Tp*
       operator->()
@@ -796,6 +738,8 @@ inline namespace fundamentals_v1
 	}
     };
 
+  /// @relates experimental::optional @{
+
   // [X.Y.8] Comparisons between optional values.
   template<typename _Tp>
     constexpr bool
@@ -966,11 +910,14 @@ inline namespace fundamentals_v1
     make_optional(_Tp&& __t)
     { return optional<decay_t<_Tp>> { std::forward<_Tp>(__t) }; }
 
+  // @} relates experimental::optional
   // @} group optional
 } // namespace fundamentals_v1
 } // namespace experimental
 
   // [X.Y.12]
+  /// std::hash partial specialization for experimental::optional
+  /// @relates experimental::optional
   template<typename _Tp>
     struct hash<experimental::optional<_Tp>>
     {

libstdc++-v3/include/std/optional

@@ -888,8 +888,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       operator->() const
       { return std::__addressof(this->_M_get()); }
 
-      constexpr
-      _Tp*
+      constexpr _Tp*
       operator->()
       { return std::__addressof(this->_M_get()); }
 

libstdc++-v3/testsuite/experimental/optional/constexpr/observers/2.cc

-// { dg-do run { target c++14 } }
+// { dg-do compile { target c++14 } }
 
 // Copyright (C) 2013-2019 Free Software Foundation, Inc.
 //
@@ -23,7 +23,7 @@ struct value_type
 {
   int i;
 
-  void* operator&() { return nullptr; } // N.B. non-const
+  void* operator&() const { return nullptr; }
 };
 
 int main()

libstdc++-v3/testsuite/experimental/optional/constexpr/observers/3.cc

-// { dg-do run { target c++14 } }
+// { dg-do compile { target c++14 } }
 
 // Copyright (C) 2013-2019 Free Software Foundation, Inc.
 //