libstdc++: Add comparison operators to sequence containers

Some more C++20 changes from P1614R2, "The Mothership has Landed".

This implements <=> for sequence containers (and the __normal_iterator
and _Pointer_adapter class templates).

	* include/bits/forward_list.h (forward_list): Define operator<=> and
	remove redundant comparison operators for C++20.
	* include/bits/stl_bvector.h (vector<bool, Alloc>): Likewise.
	* include/bits/stl_deque.h (deque): Likewise.
	* include/bits/stl_iterator.h (__normal_iterator): Likewise.
	* include/bits/stl_list.h (list): Likewise.
	* include/bits/stl_vector.h (vector): Likewise.
	* include/debug/deque (__gnu_debug::deque): Likewise.
	* include/debug/forward_list (__gnu_debug::forward_list): Likewise.
	* include/debug/list (__gnu_debug::list): Likewise.
	* include/debug/safe_iterator.h (__gnu_debug::_Safe_iterator):
	Likewise.
	* include/debug/vector (__gnu_debug::vector): Likewise.
	* include/ext/pointer.h (__gnu_cxx::_Pointer_adapter): Define
	operator<=> for C++20.
	* testsuite/23_containers/deque/operators/cmp_c++20.cc: New test.
	* testsuite/23_containers/forward_list/cmp_c++20.cc: New test.
	* testsuite/23_containers/list/cmp_c++20.cc: New test.
	* testsuite/23_containers/vector/bool/cmp_c++20.cc: New test.
	* testsuite/23_containers/vector/cmp_c++20.cc: New test.

5 files changed, 50 insertions, 0 deletions

diff --git a/libstdc++-v3/include/debug/deque b/libstdc++-v3/include/debug/deque
index 8c6b4d14c2b..4d525bfc0aa 100644
--- a/libstdc++-v3/include/debug/deque
+++ b/libstdc++-v3/include/debug/deque
@@ -648,6 +648,12 @@ namespace __debug
 	       const deque<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Alloc>
+    constexpr __detail::__synth3way_t<_Tp>
+    operator<=>(const deque<_Tp, _Alloc>& __x, const deque<_Tp, _Alloc>& __y)
+    { return __x._M_base() <=> __y._M_base(); }
+#else
   template<typename _Tp, typename _Alloc>
     inline bool
     operator!=(const deque<_Tp, _Alloc>& __lhs,
@@ -677,6 +683,7 @@ namespace __debug
     operator>(const deque<_Tp, _Alloc>& __lhs,
 	      const deque<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Tp, typename _Alloc>
     inline void
diff --git a/libstdc++-v3/include/debug/forward_list b/libstdc++-v3/include/debug/forward_list
index f0ff62c8cb1..2fd03e70499 100644
--- a/libstdc++-v3/include/debug/forward_list
+++ b/libstdc++-v3/include/debug/forward_list
@@ -838,6 +838,13 @@ namespace __debug
 	       const forward_list<_Tp, _Alloc>& __ly)
     { return __lx._M_base() == __ly._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Alloc>
+    constexpr __detail::__synth3way_t<_Tp>
+    operator<=>(const forward_list<_Tp, _Alloc>& __x,
+		const forward_list<_Tp, _Alloc>& __y)
+    { return __x._M_base() <=> __y._M_base(); }
+#else
   template<typename _Tp, typename _Alloc>
     inline bool
     operator<(const forward_list<_Tp, _Alloc>& __lx,
@@ -870,6 +877,7 @@ namespace __debug
     operator<=(const forward_list<_Tp, _Alloc>& __lx,
 	       const forward_list<_Tp, _Alloc>& __ly)
     { return !(__ly < __lx); }
+#endif // three-way comparison
 
   /// See std::forward_list::swap().
   template<typename _Tp, typename _Alloc>
diff --git a/libstdc++-v3/include/debug/list b/libstdc++-v3/include/debug/list
index ee54ef27e57..6dd85741f81 100644
--- a/libstdc++-v3/include/debug/list
+++ b/libstdc++-v3/include/debug/list
@@ -864,6 +864,12 @@ namespace __debug
 	       const list<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Alloc>
+    constexpr __detail::__synth3way_t<_Tp>
+    operator<=>(const list<_Tp, _Alloc>& __x, const list<_Tp, _Alloc>& __y)
+    { return __x._M_base() <=> __y._M_base(); }
+#else
   template<typename _Tp, typename _Alloc>
     inline bool
     operator!=(const list<_Tp, _Alloc>& __lhs,
@@ -893,6 +899,7 @@ namespace __debug
     operator>(const list<_Tp, _Alloc>& __lhs,
 	      const list<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Tp, typename _Alloc>
     inline void
diff --git a/libstdc++-v3/include/debug/safe_iterator.h b/libstdc++-v3/include/debug/safe_iterator.h
index f746cca5fb3..687b844fd75 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -35,6 +35,9 @@
 #include <debug/safe_base.h>
 #include <bits/stl_pair.h>
 #include <ext/type_traits.h>
+#if __cplusplus > 201703L
+# include <compare>
+#endif
 
 #define _GLIBCXX_DEBUG_VERIFY_OPERANDS(_Lhs, _Rhs, _BadMsgId, _DiffMsgId) \
   _GLIBCXX_DEBUG_VERIFY(!_Lhs._M_singular() && !_Rhs._M_singular(),	\
@@ -469,6 +472,7 @@ namespace __gnu_debug
 	  return __lhs.base() == __rhs.base();
 	}
 
+#if ! __cpp_lib_three_way_comparison
       friend bool
       operator!=(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -485,6 +489,7 @@ namespace __gnu_debug
 	  _GLIBCXX_DEBUG_VERIFY_EQ_OPERANDS(__lhs, __rhs);
 	  return __lhs.base() != __rhs.base();
 	}
+#endif // three-way comparison
     };
 
   template<typename _Iterator, typename _Sequence>
@@ -805,6 +810,21 @@ namespace __gnu_debug
 	return *this;
       }
 
+#if __cpp_lib_three_way_comparison
+      friend auto
+      operator<=>(const _Self& __lhs, const _Self& __rhs) noexcept
+      {
+	_GLIBCXX_DEBUG_VERIFY_REL_OPERANDS(__lhs, __rhs);
+	return __lhs.base() <=> __rhs.base();
+      }
+
+      friend auto
+      operator<=>(const _Self& __lhs, const _OtherSelf& __rhs) noexcept
+      {
+	_GLIBCXX_DEBUG_VERIFY_REL_OPERANDS(__lhs, __rhs);
+	return __lhs.base() <=> __rhs.base();
+      }
+#else
       friend bool
       operator<(const _Self& __lhs, const _Self& __rhs) _GLIBCXX_NOEXCEPT
       {
@@ -860,6 +880,7 @@ namespace __gnu_debug
 	_GLIBCXX_DEBUG_VERIFY_REL_OPERANDS(__lhs, __rhs);
 	return __lhs.base() >= __rhs.base();
       }
+#endif // three-way comparison
 
       // _GLIBCXX_RESOLVE_LIB_DEFECTS
       // According to the resolution of DR179 not only the various comparison
diff --git a/libstdc++-v3/include/debug/vector b/libstdc++-v3/include/debug/vector
index 96772f72643..4c08ab61ce8 100644
--- a/libstdc++-v3/include/debug/vector
+++ b/libstdc++-v3/include/debug/vector
@@ -731,6 +731,12 @@ namespace __debug
 	       const vector<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Tp, typename _Alloc>
+    constexpr __detail::__synth3way_t<_Tp>
+    operator<=>(const vector<_Tp, _Alloc>& __x, const vector<_Tp, _Alloc>& __y)
+    { return __x._M_base() <=> __y._M_base(); }
+#else
   template<typename _Tp, typename _Alloc>
     inline bool
     operator!=(const vector<_Tp, _Alloc>& __lhs,
@@ -760,6 +766,7 @@ namespace __debug
     operator>(const vector<_Tp, _Alloc>& __lhs,
 	      const vector<_Tp, _Alloc>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Tp, typename _Alloc>
     inline void