--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/gcc/testsuite/g++.dg/opt/pr50747-2_0.C	Fri Oct 27 22:46:09 2017 +0900
@@ -0,0 +1,112 @@
+// { dg-do compile }
+// { dg-require-effective-target lto }
+// { dg-options "-w -fpermissive -fno-implicit-templates -flto" }
+
+namespace std {
+    typedef long unsigned int size_t;
+    template<typename _Alloc>     class allocator;
+    template<class _CharT>     struct char_traits;
+    template<typename _CharT, typename _Traits = char_traits<_CharT> >     class basic_ostream;
+    template<typename _CharT, typename _Traits = char_traits<_CharT>,     typename _Alloc = allocator<_CharT> >     class basic_ostringstream;
+}
+extern "C++" {
+    namespace std {
+	class exception   {
+	};
+    };
+}
+namespace __gnu_cxx __attribute__ ((__visibility__ ("default"))) {
+    template<typename _Tp>     class new_allocator     {
+    };
+}
+namespace std __attribute__ ((__visibility__ ("default"))) {
+    template<typename _Tp>     class allocator: public __gnu_cxx::new_allocator<_Tp>     {
+    public:       typedef size_t size_type;
+		  template<typename _Tp1>         struct rebind         {
+		      typedef allocator<_Tp1> other;
+		  };
+    };
+    template<typename _CharT, typename _Traits, typename _Alloc>     class basic_string     {
+	typedef typename _Alloc::template rebind<_CharT>::other _CharT_alloc_type;
+	typedef typename _CharT_alloc_type::size_type size_type;
+    private:       struct _Rep_base       {
+		   };
+		   struct _Rep : _Rep_base       {
+		       _CharT*  _M_refdata() throw()  {
+		       }
+		   };
+		   struct _Alloc_hider : _Alloc       {
+		       _Alloc_hider(_CharT* __dat, const _Alloc& __a)  : _Alloc(__a), _M_p(__dat) {
+		       }
+		       _CharT* _M_p;
+		   };
+    private:       mutable _Alloc_hider _M_dataplus;
+		   static _Rep&       _S_empty_rep()       {
+		   }
+    public:       basic_string()       : _M_dataplus(_S_empty_rep()._M_refdata(), _Alloc()) {
+		  }
+		  template<class _InputIterator>         basic_string(_InputIterator __beg, _InputIterator __end,        const _Alloc& __a = _Alloc());
+		  static _CharT*       _S_construct(size_type __req, _CharT __c, const _Alloc& __a);
+    };
+    template<typename _CharT, typename _Traits, typename _Alloc>     inline basic_ostream<_CharT, _Traits>&     operator<<(basic_ostream<_CharT, _Traits>& __os,         const basic_string<_CharT, _Traits, _Alloc>& __str)     {
+    }
+    template<typename _CharT, typename _Traits, typename _Alloc>     template<typename _InputIterator>     basic_string<_CharT, _Traits, _Alloc>::     basic_string(_InputIterator __beg, _InputIterator __end, const _Alloc& __a)     : _M_dataplus(_S_construct(__beg, __end, __a), __a)     {
+    };
+    enum _Ios_Openmode     {
+	_S_app = 1L << 0,       _S_ate = 1L << 1,       _S_bin = 1L << 2,       _S_in = 1L << 3,       _S_out = 1L << 4,       _S_trunc = 1L << 5,       _S_ios_openmode_end = 1L << 16     };
+    class ios_base   {
+    public:     class failure : public exception     {
+		};
+		typedef _Ios_Openmode openmode;
+		static const openmode in = _S_in;
+		static const openmode out = _S_out;
+    };
+    template<typename _CharT, typename _Traits>     class basic_streambuf     {
+    public:       typedef _CharT char_type;
+		  char_type*       egptr() const {
+		  }
+		  char_type*       pbase() const {
+		  }
+		  char_type*       pptr() const {
+		  }
+    };
+    template<typename _CharT, typename _Traits>     class basic_ios : public ios_base     {
+    };
+    template<typename _CharT, typename _Traits>     class basic_ostream : virtual public basic_ios<_CharT, _Traits>     {
+    };
+    template<typename _CharT, typename _Traits, typename _Alloc>     class basic_stringbuf : public basic_streambuf<_CharT, _Traits>     {
+    public:       typedef _CharT char_type;
+		  typedef _Traits traits_type;
+		  typedef basic_streambuf<char_type, traits_type> __streambuf_type;
+		  typedef basic_string<char_type, _Traits, _Alloc> __string_type;
+    protected:       ios_base::openmode _M_mode;
+		     __string_type _M_string;
+    public:       explicit       basic_stringbuf(ios_base::openmode __mode = ios_base::in | ios_base::out)       : __streambuf_type(), _M_mode(__mode), _M_string()       {
+		  }
+		  __string_type       str() const       {
+		      __string_type __ret;
+		      if (this->pptr())    {
+			  if (this->pptr() > this->egptr())        __ret = __string_type(this->pbase(), this->pptr());
+		      }
+		  }
+    };
+    template <typename _CharT, typename _Traits, typename _Alloc>     class basic_ostringstream : public basic_ostream<_CharT, _Traits>     {
+    public:       typedef _CharT char_type;
+		  typedef _Traits traits_type;
+		  typedef basic_string<_CharT, _Traits, _Alloc> __string_type;
+		  typedef basic_stringbuf<_CharT, _Traits, _Alloc> __stringbuf_type;
+		  typedef basic_ostream<char_type, traits_type> __ostream_type;
+    private:       __stringbuf_type _M_stringbuf;
+    public:       explicit       basic_ostringstream(ios_base::openmode __mode = ios_base::out)       : __ostream_type(), _M_stringbuf(__mode | ios_base::out)       {
+		  }
+		   __string_type       str() const       {
+		       return _M_stringbuf.str();
+		   }
+    };
+    template<typename _Tp> class complex;
+    template<typename _Tp, typename _CharT, class _Traits>     basic_ostream<_CharT, _Traits>&     operator<<(basic_ostream<_CharT, _Traits>& __os, const complex<_Tp>& __x)     {
+	basic_ostringstream<_CharT, _Traits> __s;
+	return __os << __s.str();
+    };
+    template     basic_ostream<wchar_t, char_traits<wchar_t> >&     operator<<(basic_ostream<wchar_t, char_traits<wchar_t> >&,                const complex<long double>&);
+}