Improve _GLIBCXX_DEBUG safe iterator range size computation.

	* include/debug/forward_list
	(_Sequence_traits<__debug::forward_list<>>::_S_size): Returns __dp_sign
	distance when not empty.
	* include/debug/list (_Sequence_traits<__debug::list<>>::_S_size):
	Likewise.
	* include/debug/helper_functions.h (__dp_sign_max_size): New
	_Distance_precision enum entry.
	(__valid_range_aux(_IIte, _IIte, _Distance_traits<>::__type,
	__false_type)): Adapt.
	* include/debug/safe_iterator.tcc
	(_Safe_iterator<>::_M_get_distance_to(const _Safe_iterator&)): Review
	distance computation.

From-SVN: r276600

libstdc++-v3/ChangeLog

+2019-10-04  François Dumont  <fdumont@gcc.gnu.org>
+
+	* include/debug/forward_list
+	(_Sequence_traits<__debug::forward_list<>>::_S_size): Returns __dp_sign
+	distance when not empty.
+	* include/debug/list (_Sequence_traits<__debug::list<>>::_S_size):
+	Likewise.
+	* include/debug/helper_functions.h (__dp_sign_max_size): New
+	_Distance_precision enum entry.
+	(__valid_range_aux(_IIte, _IIte, _Distance_traits<>::__type,
+	__false_type)): Adapt.
+	* include/debug/safe_iterator.tcc
+	(_Safe_iterator<>::_M_get_distance_to(const _Safe_iterator&)): Review
+	distance computation.
+
 2019-10-04  Jonathan Wakely  <jwakely@redhat.com>
 
 	PR libstdc++/81091

libstdc++-v3/include/debug/forward_list

@@ -911,7 +911,7 @@ namespace __gnu_debug
       _S_size(const std::__debug::forward_list<_Tp, _Alloc>& __seq)
       {
 	return __seq.empty()
-	  ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_equality);
+	  ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_sign);
       }
     };
 

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

@@ -50,10 +50,11 @@ namespace __gnu_debug
    */
   enum _Distance_precision
     {
-      __dp_none,	// Not even an iterator type
-      __dp_equality,	//< Can compare iterator equality, only
-      __dp_sign,	//< Can determine equality and ordering
-      __dp_exact	//< Can determine distance precisely
+      __dp_none,		// Not even an iterator type
+      __dp_equality,		//< Can compare iterator equality, only
+      __dp_sign,		//< Can determine equality and ordering
+      __dp_sign_max_size,	//< __dp_sign and gives max range size
+      __dp_exact		//< Can determine distance precisely
     };
 
   template<typename _Iterator,
@@ -176,6 +177,7 @@ namespace __gnu_debug
 	    return true;
 	  break;
 	case __dp_sign:
+	case __dp_sign_max_size:
 	case __dp_exact:
 	  return __dist.first >= 0;
 	}

libstdc++-v3/include/debug/list

@@ -916,7 +916,7 @@ namespace __gnu_debug
       _S_size(const std::__debug::list<_Tp, _Alloc>& __seq)
       {
 	return __seq.empty()
-	  ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_equality);
+	  ? std::make_pair(0, __dp_exact) : std::make_pair(1, __dp_sign);
       }
     };
 #endif

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

@@ -113,18 +113,22 @@ namespace __gnu_debug
     _Safe_iterator<_Iterator, _Sequence, _Category>::
     _M_get_distance_to(const _Safe_iterator& __rhs) const
     {
-      typedef typename _Distance_traits<_Iterator>::__type _Diff;
+      typedef typename _Distance_traits<_Iterator>::__type _Dist;
       typedef _Sequence_traits<_Sequence> _SeqTraits;
 
-      if (this->base() == __rhs.base())
-	return std::make_pair(0, __dp_exact);
+      _Dist __base_dist = __get_distance(this->base(), __rhs.base());
+      if (__base_dist.second == __dp_exact)
+	return __base_dist;
 
+      _Dist __seq_dist = _SeqTraits::_S_size(*this->_M_get_sequence());
       if (this->_M_is_before_begin())
 	{
 	  if (__rhs._M_is_begin())
 	    return std::make_pair(1, __dp_exact);
 
-	  return std::make_pair(1, __dp_sign);
+	  return __seq_dist.second == __dp_exact
+	    ? std::make_pair(__seq_dist.first + 1, __dp_exact)
+	    : __seq_dist;
 	}
 
       if (this->_M_is_begin())
@@ -133,30 +137,42 @@ namespace __gnu_debug
 	    return std::make_pair(-1, __dp_exact);
 
 	  if (__rhs._M_is_end())
-	    return _SeqTraits::_S_size(*this->_M_get_sequence());
+	    return __seq_dist;
 
-	  return std::make_pair(1, __dp_sign);
+	  return std::make_pair(__seq_dist.first,
+				__seq_dist.second == __dp_exact
+				? __dp_sign_max_size : __seq_dist.second);
 	}
 
       if (this->_M_is_end())
 	{
 	  if (__rhs._M_is_before_begin())
-	    return std::make_pair(-1, __dp_exact);
+	    return __seq_dist.second == __dp_exact
+	      ? std::make_pair(-__seq_dist.first - 1, __dp_exact)
+	      : std::make_pair(-__seq_dist.first, __dp_sign);
 
 	  if (__rhs._M_is_begin())
-	    {
-	      _Diff __diff = _SeqTraits::_S_size(*this->_M_get_sequence());
-	      return std::make_pair(-__diff.first, __diff.second);
-	    }
+	    return std::make_pair(-__seq_dist.first, __seq_dist.second);
 
-	  return std::make_pair(-1, __dp_sign);
+	  return std::make_pair(-__seq_dist.first,
+				__seq_dist.second == __dp_exact
+				? __dp_sign_max_size : __seq_dist.second);
 	}
 
-      if (__rhs._M_is_before_begin() || __rhs._M_is_begin())
-	return std::make_pair(-1, __dp_sign);
+      if (__rhs._M_is_before_begin())
+	return __seq_dist.second == __dp_exact
+	  ? std::make_pair(__seq_dist.first - 1, __dp_exact)
+	  : std::make_pair(-__seq_dist.first, __dp_sign);
+
+      if (__rhs._M_is_begin())
+	return std::make_pair(-__seq_dist.first,
+			      __seq_dist.second == __dp_exact
+			      ? __dp_sign_max_size : __seq_dist.second);
 
       if (__rhs._M_is_end())
-	return std::make_pair(1, __dp_sign);
+	return std::make_pair(__seq_dist.first,
+			      __seq_dist.second == __dp_exact
+			      ? __dp_sign_max_size : __seq_dist.second);
 
       return std::make_pair(1, __dp_equality);
     }