[Bug c++/39875] New: [4.5 regression] Wrong "value computed is not used" warning

["bangerth at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

I think this is from after 4.4 branched:
----------------------
template <typename TT> struct InputIterator
{
    InputIterator ()
      {
        TT i;
        (void)*i;           // require dereference operator
      }
};

InputIterator<int *> i;
---------------------

> c++ -c deal.II/source/dofs/dof_renumbering.cc  -W -Wall
deal.II/source/dofs/dof_renumbering.cc: In constructor
'InputIterator<TT>::InputIterator() [with TT = int*]':
deal.II/source/dofs/dof_renumbering.cc:10:   instantiated from here
deal.II/source/dofs/dof_renumbering.cc:6: warning: value computed is not used

That's obviously bogus, the compiler warns about a statement that is
explicitly cast to 'void' so there is no computed value any more.

The code is culled from boost's concepts checks, so this is going to hit
quite a number of people.

W.


-- 
           Summary: [4.5 regression] Wrong "value computed is not used"
                    warning
           Product: gcc
           Version: 4.5.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bangerth at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39875