[Bug c++/67200] New: Copy elision and implicit move in return performed in cases not allowed by standard

[rs2740 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67200

            Bug ID: 67200
           Summary: Copy elision and implicit move in return performed in
                    cases not allowed by standard
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

Consider:

struct A {
    A() = default;
    A(const A&) = delete;
    A(A&&) = default;
};

A f() {
    A a;
    return true ? a : a;
}

This code is ill-formed; `true ? a : a` is an lvalue of type `A`; it neither
qualifies for copy elision under [class.copy]/p31 (it is not "the name of a
nonvolatile
automatic object") nor for implicit moving under [class.copy]/p32 (it's not an
id-expression, either). Therefore, overload resolution should select the copy
constructor, which in the above example is deleted.

GCC compiles this code and in fact elides a move.