Re: move constructors likely a requirement

[John W. Eaton]

On 9/5/19 7:59 AM, Carlo De Falco wrote:
> > Il giorno 4 set 2019, alle ore 20:14, John W. Eaton <address@hidden> ha scritto:
> >
> > If I understand correctly, -Wpessimizing-move is supposed to be implied when 
> > compiling C++ code with GCC and using -Wall.
> If I understand correctly, copy elision is mandated by the standard only since 
> c++14, while we are using c++11.
> Could it be possible that gcc and clang have different criteria to decide 
> whether to make the optimization?

I compiled the following program with g++ 9 (the version that introduced 
the -Wpessimizing-move warning option) using both -std=c++17 and no -std 
option (defaults to c++14) and the warnings are the same in both cases.

#include <utility>

struct T {
  void show () { }
};

T fn ()
{
  T t1;

  // No warning from GCC here.
  T t2 = std::move (T ());

  t2.show ();

  // GCC does warn here.
  return std::move (t1);
}

jwe