[Bug c++/20624] New: wrong "control reaches end of non-void function" warning

["oliverst at online dot de" <gcc-bugzilla at gcc dot gnu dot org>]

If you compile this code 

#include <fstream>

void test()
{
 	 std::ifstream in;
}

against the actual CVS version of STLport 5.0
(http://www.breaken.de/temp/STLport.zip) you get this warning:

  In member function 'typename stlp_std::basic_filebuf<_CharT,
_Traits>::pos_type stlp_std::basic_filebuf<_CharT, _Traits>::seekoff(typename
_Traits::off_type, int, int) [with _CharT = char, _Traits =
stlp_std::char_traits<char>]': 
372 C:\cvs\STLport\stlport\stl\_fstream.c [Warning] control reaches end of
non-void function 

Because the STLport is very complex I wasn't able to reduce the code properly.
Maybe it can already be done by just posting the function causing it:

template <class _CharT, class _Traits>
__BF_pos_type__
basic_filebuf<_CharT, _Traits>::seekoff(off_type __off,
                                        ios_base::seekdir __whence,
                                        ios_base::openmode /* dummy */) {
  if (this->is_open() &&
      (__off == 0 || (_M_constant_width && this->_M_base._M_in_binary_mode()))) {

    if (!_M_seek_init(__off != 0 || __whence != ios_base::cur))
      return pos_type(-1);

    // Seek to beginning or end, regardless of whether we're in input mode.
    if (__whence == ios_base::beg || __whence == ios_base::end)
      return _M_seek_return(_M_base._M_seek(_M_width * __off, __whence),
                            _State_type());

    // Seek relative to current position.  Complicated if we're in input mode.
    else if (__whence == ios_base::cur) {

      if (!_M_in_input_mode)
        return _M_seek_return(_M_base._M_seek(_M_width * __off, __whence),
                              _State_type());
      else if (_M_mmap_base != 0) {
        // __off is relative to gptr().  We need to do a bit of arithmetic
        // to get an offset relative to the external file pointer.
        streamoff __adjust = _M_mmap_len - (this->gptr() - (_CharT*) _M_mmap_base);

        // if __off == 0, we do not need to exit input mode and to shift file
pointer
        if (__off == 0) {
          return pos_type(_M_base._M_seek(0, ios_base::cur) - __adjust);
        }
        else
          return _M_seek_return(_M_base._M_seek(__off - __adjust,
ios_base::cur), _State_type());
      }
      else if (_M_constant_width) { // Get or set the position.  

        streamoff __iadj = _M_width * (this->gptr() - this->eback());
        
        // Compensate for offset relative to gptr versus offset relative
        // to external pointer.  For a text-oriented stream, where the 
        // compensation is more than just pointer arithmetic, we may get
        // but not set the current position.
        
        if (__iadj <= _M_ext_buf_end - _M_ext_buf) {
          
          streamoff __eadj =  _M_base._M_get_offset(_M_ext_buf + __iadj,
_M_ext_buf_end);

          if (__off == 0) {
            return pos_type(_M_base._M_seek(0, ios_base::cur) - __eadj);
          }  else {
            return _M_seek_return(_M_base._M_seek(__off - __eadj,
ios_base::cur), _State_type());
          }
        }
        else
          return pos_type(-1);
      }
      else {                    // Get the position.  Encoding is var width.
        // Get position in internal buffer.
        ptrdiff_t __ipos = this->gptr() - this->eback();
        
        // Get corresponding position in external buffer.
        _State_type __state = _M_state;
        int __epos = _M_codecvt->length(__state, _M_ext_buf, _M_ext_buf_end,
                                        __ipos);

        // Sanity check (expensive): make sure __epos is the right answer.
        _State_type __tmp_state = _M_state;
        _Filebuf_Tmp_Buf<_CharT> __buf(__ipos);
        _CharT* __ibegin = __buf._M_ptr;
        _CharT* __inext  = __ibegin;

        const char* __dummy;
        typename _Codecvt::result __status
          = _M_codecvt->in(__tmp_state,
                           _M_ext_buf, _M_ext_buf + __epos, __dummy,
                           __ibegin, __ibegin + __ipos, __inext);
        if (__status != _Codecvt::error &&
            (__status == _Codecvt::noconv ||
             (__inext == __ibegin + __ipos &&
              equal(this->gptr(), this->eback(), __ibegin,
                    _Eq_traits<traits_type>())))) {
          // Get the current position (at the end of the external buffer),
          // then adjust it.  Again, it might be a text-oriented stream.
          streamoff __cur = _M_base._M_seek(0, ios_base::cur);
          streamoff __adj =
            _M_base._M_get_offset(_M_ext_buf, _M_ext_buf + __epos) -
            _M_base._M_get_offset(_M_ext_buf, _M_ext_buf_end);
          if (__cur != -1 && __cur + __adj >= 0)
            return _M_seek_return(__cur + __adj, __state);
          else
            return pos_type(-1);
        }
        else                    // We failed the sanity check.
          return pos_type(-1);
      }
    }
    else                        // Unrecognized value for __whence.
      return pos_type(-1);
  }
  else
    return pos_type(-1);
}

I also got another piece of code, that also causes a wrong warning, but I wasn't
able to reduce that code either.

I am using

Target: i686-pc-mingw32
Configured with: /datal/gcc/gcc/configure --prefix=/datal/gcc/build/wingcc
--build=i686-pc-linux-gnu --host=i686-pc-mingw32 --target=i686-pc-mingw32
--enable-languages=c,c++,java --with-gcc --with-gnu-as --with-gnu-ld
--enable-threads=win32 --disable-nls --disable-win32-registry --disable-shared
--disable-debug --without-newlib --enable-libgcj --disable-java-awt --without-x
--enable-java-gc=boehm --disable-libgcj-debug --enable-interpreter
--enable-hash-synchronization --enable-sjlj-exceptions --enable-libgcj-multifile
--enable-libgcj-mingw-osapi=ansi
Thread model: win32
gcc version 4.0.0 20050320 (prerelease)

-- 
           Summary: wrong "control reaches end of non-void function" warning
           Product: gcc
           Version: 4.0.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: oliverst at online dot de
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20624