[Bug libstdc++/31246] Strange -Wunreachable-code warning with _GLIBCXX_DEBUG

["pinskia at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #1 from pinskia at gcc dot gnu dot org  2007-03-17 16:58 -------
Lets look at the IR:
;; Function __gnu_debug::_Safe_iterator<_Iterator, _Sequence>::_Safe_iterator()
[with _Iterator = __gnu_cxx::__normal_iterator<int*, __gnu_norm::vector<int,
std::allocator<int> > >, _Sequence = __gnu_debug_def::vector<int,
std::allocator<int> >]
(_ZN11__gnu_debug14_Safe_iteratorIN9__gnu_cxx17__normal_iteratorIPiN10__gnu_norm6vectorIiSaIiEEEEEN15__gnu_debug_def6vectorIiS6_EEEC4Ev
*INTERNAL* )
;; enabled by -tree-original

{
  <<cleanup_point <<< Unknown tree: expr_stmt
  __base_ctor  (&((struct _Safe_iterator<__gnu_cxx::__normal_iterator<int*,
__gnu_norm::vector<int, std::allocator<int> > >,__gnu_debug_def::vector<int,
std::allocator<int> > > *) this)->D.12082) >>>
>>;
  try
    {
      <<cleanup_point <<< Unknown tree: expr_stmt
  __comp_ctor  (&((struct _Safe_iterator<__gnu_cxx::__normal_iterator<int*,
__gnu_norm::vector<int, std::allocator<int> > >,__gnu_debug_def::vector<int,
std::allocator<int> > > *) this)->_M_current) >>>
>>;
    }
  catch
    {
      __base_dtor  ((struct _Safe_iterator_base *) this);
    }
}


and the constructor for ->M_current:
__gnu_debug::_Safe_iterator<__gnu_cxx::__normal_iterator<int*,
__gnu_norm::vector<int, std::allocator<int> > >, __gnu_debug_def::vector<int,
std::allocator<int> > >::~_Safe_iterator() (this, __in_chrg)
{
  struct _Safe_iterator_base * this.102;

  [/usr/include/c++/4.0.0/debug/safe_iterator.h : 65] {
    [/usr/include/c++/4.0.0/debug/safe_iterator.h : 65] try
      {

      }
    finally
      {
        [/usr/include/c++/4.0.0/debug/safe_iterator.h : 65] this.102 = (struct
_Safe_iterator_base *) this;
        [/usr/include/c++/4.0.0/debug/safe_iterator.h : 65] __base_dtor 
(this.102);
      }
  }
  [/usr/include/c++/4.0.0/debug/safe_iterator.h : 65] <D12095>:;
}


So the constructor for that cannot throw so the catch part is removed in both
cases.

The warning is not strange and is correct in that the __base_dtor cannot be
called ever.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31246