[Bug c++/58051] New: No named return value optimization when returned object is implicitly converted

[scovich at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58051

            Bug ID: 58051
           Summary: No named return value optimization when returned
                    object is implicitly converted
           Product: gcc
           Version: 4.8.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: scovich at gmail dot com

The following test case introduces an extra object copy, even though none
should be required:

// <<<--- bug.cpp --->>>
extern "C" void puts(char const *);
struct A {
    A()=default;
    A(A &&)=default;
    A(A const &) { puts("copy"); }
    ~A() { puts("~A"); }
};
struct B {
    A _a;
    B(A a) : _a((A&&)(a)) { }
};
B go() {
    A rval;
    return rval;
}
int main () { go(); }
// <<<--- end bug.cpp --->>>

(when compiled with both `gcc-4.8.1 -std=gnu++11' and `gcc-4.6.3 -std=gnu++0x')

RVO works properly if go() returns A() or std::move(rval).