Nested function call and RVO.

[Rodolfo Federico Gamarra]

Hi all,

I have been reviewing the RVO optimization technique and came across
with a nested function call where I hoped this optmization to work as
well.
I compiled the following snippet with
  g++ -O3     main.cc   -o main
and got as result
A()
N()
A(A&)

Is there any fundamental reason for this optimization not to happen in
this case? I was hoping to get only one object constructed at all. The
relevant passage in the standard seems to me is "12.8 - Copying class
objects (15)".
// main.cc
#include <iostream>
using namespace std;
struct A {
  A()                       { cout << "A()\n";                  }
  A(const A& a)             { cout << "A(const A&)\n";          }
  A(A& a)                   { cout << "A(A&)\n";                }
  A& operator=(const A& a)  { cout << "operator=(const A&)\n";  }
  void N()                  { cout << "N()\n";                  }
};
A   AlternativeA(A a)       { a.N(); return a;                  }
A   FactoryA()              { return A();                       }
int main()                  { A a = AlternativeA(FactoryA());   }
//eof

Thanks a lot for your help in advance.
--
Rodolfo Federico Gamarra