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

["sylvain dot pion at sophia dot inria dot fr" <gcc-bugzilla at gcc dot gnu dot org>]

Compiling the following with "-Wunreachable-code -D_GLIBCXX_DEBUG"
--------------------------
#include <vector>

int main()
{
  std::vector<int>::iterator a;
}
--------------------------

produces the warning :

--------------------------
/usr/lib/gcc/i386-redhat-linux/4.1.1/../../../../include/c++/4.1.1/debug/safe_iterator.h:
In constructor ?__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> >]?:
/usr/lib/gcc/i386-redhat-linux/4.1.1/../../../../include/c++/4.1.1/debug/safe_iterator.h:103:
warning: will never be executed
--------------------------

I tried g++ 4.1, 4.2 and 4.3.  They all produce this annoying warning.

Looking at the code in safe_iterator.h shows nothing obviously wrong.
This might even suggest a bug in -Wunreachable-code, although I categorized
it for now in libstdc++, as I have not been able to isolate a small piece
of code that reproduces the problem.


Some other compilers tend to have the equivalent of -Wunreachable-code
by default.  It would be nice if it worked well, and if it was enabled
by -Wall or -Wextra.


-- 
           Summary: Strange -Wunreachable-code warning with _GLIBCXX_DEBUG
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: sylvain dot pion at sophia dot inria dot fr
  GCC host triplet: i686-pc-linux-gnu


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