Proposed resolution:

This wording is relative to N4861.

1. Modify [atomics.types.operations] as indicated:

   void wait(T old, memory_order order = memory_order::seq_cst) const volatile noexcept;
   void wait(T old, memory_order order = memory_order::seq_cst) const noexcept;
   

   Constraints: For the volatile overload of this function, is_always_lock_free is true.

   -29- Preconditions: […]

   […]

   void notify_one() volatile noexcept;
   void notify_one() noexcept;
   

   Constraints: For the volatile overload of this function, is_always_lock_free is true.

   -32- Effects: […]

   […]

   void notify_all() volatile noexcept;
   void notify_all() noexcept;
   

   Constraints: For the volatile overload of this function, is_always_lock_free is true.

   -34- Effects: […]

   […]

2. Modify [depr.atomics.volatile], annex D, as indicated:

   If an atomic specialization has one of the following overloads, then that overload participates in overload resolution even if atomic<T>::is_always_lock_free is false:

   void store(T desired, memory_order order = memory_order::seq_cst) volatile noexcept;
   […]
   T* fetch_key(ptrdiff_t operand, memory_order order = memory_order::seq_cst) volatile noexcept;
   value_type operator++(int) volatile noexcept;
   value_type operator--(int) volatile noexcept;
   value_type operator++() volatile noexcept;
   value_type operator--() volatile noexcept;
   void wait(T old, memory_order order = memory_order::seq_cst) const volatile noexcept;
   void notify_one() volatile noexcept;
   void notify_all() volatile noexcept;
   

[ 2020-04-04 Issue Prioritization ]

Priority to 3 after reflector discussion. The suggested wording was generally accepted, but there were considerable doubts that it is necessary to add deprecated functions of the new wait/notify functions instead of declaring only the non-volatile overloads. The wish was expressed that both SG1 and LEWG should express their opinion here.

Paper P1831R1 aimed to deprecate all the atomic overloads for volatile qualified member function of std::atomic unless is_always_lock_free is true. There are a few omissions in the wording.

First, operator++ and operator-- are correctly constrained, but the deprecated overloads are not restored in Annex D, unlike the other member functions. I confirmed with the paper author this is an accidental oversight, and not an intended change of behavior for C++20.

Secondly, the wait/notify APIs were added after the initial wording For this paper was drafted, and the paper did not catch up. Again, I confirmed with the paper author that these functions should be similarly constrained and deprecated.