[Bug c++/80456] New: calling constexpr member function from volatile-qualified member function: error: ‘this’ is not a constant expression

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80456

            Bug ID: 80456
           Summary: calling constexpr member function from
                    volatile-qualified member function: error: ‘this’ is
                    not a constant expression
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

This valid code is rejected:

struct A {
  static constexpr bool test() noexcept { return true; }

  void f() volatile {
    constexpr bool b = test();
  }
};

void g() {
  A a;
  a.f();
}

vol.cc: In member function ‘void A::f() volatile’:
vol.cc:5:29: error: ‘this’ is not a constant expression
     constexpr bool b = test();
                             ^

This complicates adding static assertions to std::atomic<T*>, as it has lots of
volatile-qualified member functions which need to enforce requirements.