2012-02-06 François Dumont <fdumont@gcc.gnu.org>

	* include/debug/safe_iterator.h
	(_Safe_iterator::_M_before_dereferenceable): Avoid the expensive
	creation of a _Safe_iterator instance to do the check.

From-SVN: r183941

libstdc++-v3/ChangeLog

+2012-02-06  François Dumont  <fdumont@gcc.gnu.org>
+
+	* include/debug/safe_iterator.h
+	(_Safe_iterator::_M_before_dereferenceable): Avoid the expensive
+	creation of a _Safe_iterator instance to do the check.
+
 2012-02-05  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	PR libstdc++/52104

libstdc++-v3/include/debug/safe_iterator.h

@@ -380,8 +380,12 @@ namespace __gnu_debug
       bool
       _M_before_dereferenceable() const
       {
-	_Self __it = *this;
-	return __it._M_incrementable() && (++__it)._M_dereferenceable();
+	if (this->_M_incrementable())
+	{
+	  _Iterator __base = base();
+	  return ++__base != _M_get_sequence()->_M_base().end();
+	}
+	return false;
       }
 
       /// Is the iterator incrementable?