Implement C++20 p0879 - Constexpr for swap and swap related functions.

2019-08-14  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Implement C++20 p0879 - Constexpr for swap and swap related functions.
	* include/std/version (__cpp_lib_constexpr_swap_algorithms): New macro.
	* include/bits/algorithmfwd.h (__cpp_lib_constexpr_swap_algorithms):
	New macro.
	(iter_swap, make_heap, next_permutation, partial_sort_copy, pop_heap)
	(prev_permutation, push_heap, reverse, rotate, sort_heap, swap)
	(swap_ranges, nth_element, partial_sort, sort): Add constexpr.
	* include/bits/move.h (swap): Add constexpr.
	* include/bits/stl_algo.h (__move_median_to_first, __reverse, reverse)
	(__gcd, __rotate, rotate, __partition, __heap_select)
	(__partial_sort_copy, partial_sort_copy, __unguarded_partition)
	(__unguarded_partition_pivot, __partial_sort, __introsort_loop, __sort)
	(__introselect, __chunk_insertion_sort, next_permutation)
	(prev_permutation, partition, partial_sort, nth_element, sort)
	(__iter_swap::iter_swap, iter_swap, swap_ranges): Add constexpr.
	* include/bits/stl_algobase.h (__iter_swap::iter_swap, iter_swap)
	(swap_ranges): Add constexpr.
	* include/bits/stl_heap.h (__push_heap, push_heap, __adjust_heap,
	__pop_heap, pop_heap, __make_heap, make_heap, __sort_heap, sort_heap):
	Add constexpr.
	* include/std/type_traits (swap): Add constexpr.
	* testsuite/25_algorithms/headers/algorithm/synopsis.cc: Add constexpr.
	* testsuite/25_algorithms/iter_swap/constexpr.cc: New test.
	* testsuite/25_algorithms/make_heap/constexpr.cc: New test.
	* testsuite/25_algorithms/next_permutation/constexpr.cc: New test.
	* testsuite/25_algorithms/nth_element/constexpr.cc: New test.
	* testsuite/25_algorithms/partial_sort/constexpr.cc: New test.
	* testsuite/25_algorithms/partial_sort_copy/constexpr.cc: New test.
	* testsuite/25_algorithms/partition/constexpr.cc: New test.
	* testsuite/25_algorithms/pop_heap/constexpr.cc: New test.
	* testsuite/25_algorithms/prev_permutation/constexpr.cc: New test.
	* testsuite/25_algorithms/push_heap/constexpr.cc: New test.
	* testsuite/25_algorithms/reverse/constexpr.cc: New test.
	* testsuite/25_algorithms/rotate/constexpr.cc: New test.
	* testsuite/25_algorithms/sort/constexpr.cc: New test.
	* testsuite/25_algorithms/sort_heap/constexpr.cc: New test.
	* testsuite/25_algorithms/swap/constexpr.cc: New test.
	* testsuite/25_algorithms/swap_ranges/constexpr.cc: New test.

From-SVN: r274488

7 files changed, 83 insertions, 0 deletions

diff --git a/libstdc++-v3/include/bits/algorithmfwd.h b/libstdc++-v3/include/bits/algorithmfwd.h
index 99491db1c5e..9c511f05197 100644
--- a/libstdc++-v3/include/bits/algorithmfwd.h
+++ b/libstdc++-v3/include/bits/algorithmfwd.h
@@ -193,6 +193,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
 #if __cplusplus > 201703L
 #  define __cpp_lib_constexpr_algorithms 201711L
+#  define __cpp_lib_constexpr_swap_algorithms 201806L
 #endif
 
 #if __cplusplus >= 201103L
@@ -377,6 +378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _FIter1, typename _FIter2>
+    _GLIBCXX20_CONSTEXPR
     void
     iter_swap(_FIter1, _FIter2);
 
@@ -391,10 +393,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     lower_bound(_FIter, _FIter, const _Tp&, _Compare);
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     make_heap(_RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     make_heap(_RAIter, _RAIter, _Compare);
 
@@ -478,10 +482,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // mismatch
 
   template<typename _BIter>
+    _GLIBCXX20_CONSTEXPR
     bool
     next_permutation(_BIter, _BIter);
 
   template<typename _BIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     bool
     next_permutation(_BIter, _BIter, _Compare);
 
@@ -496,10 +502,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // partial_sort
 
   template<typename _IIter, typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     _RAIter
     partial_sort_copy(_IIter, _IIter, _RAIter, _RAIter);
 
   template<typename _IIter, typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     _RAIter
     partial_sort_copy(_IIter, _IIter, _RAIter, _RAIter, _Compare);
 
@@ -519,26 +527,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     pop_heap(_RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     pop_heap(_RAIter, _RAIter, _Compare);
 
   template<typename _BIter>
+    _GLIBCXX20_CONSTEXPR
     bool
     prev_permutation(_BIter, _BIter);
 
   template<typename _BIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     bool
     prev_permutation(_BIter, _BIter, _Compare);
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     push_heap(_RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     push_heap(_RAIter, _RAIter, _Compare);
 
@@ -579,6 +593,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // replace_if
 
   template<typename _BIter>
+    _GLIBCXX20_CONSTEXPR
     void
     reverse(_BIter, _BIter);
 
@@ -590,6 +605,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   inline namespace _V2
   {
     template<typename _FIter>
+      _GLIBCXX20_CONSTEXPR
       _FIter
       rotate(_FIter, _FIter, _FIter);
   }
@@ -613,10 +629,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 #endif
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     sort_heap(_RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     sort_heap(_RAIter, _RAIter, _Compare);
 
@@ -628,15 +646,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // For C++11 swap() is declared in <type_traits>.
 
   template<typename _Tp, size_t _Nm>
+    _GLIBCXX20_CONSTEXPR
     inline void
     swap(_Tp& __a, _Tp& __b);
 
   template<typename _Tp, size_t _Nm>
+    _GLIBCXX20_CONSTEXPR
     inline void
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm]);
 #endif
 
   template<typename _FIter1, typename _FIter2>
+    _GLIBCXX20_CONSTEXPR
     _FIter2
     swap_ranges(_FIter1, _FIter1, _FIter2);
 
@@ -783,22 +804,27 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
     mismatch(_IIter1, _IIter1, _IIter2, _BinaryPredicate);
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     nth_element(_RAIter, _RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     nth_element(_RAIter, _RAIter, _RAIter, _Compare);
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     partial_sort(_RAIter, _RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     partial_sort(_RAIter, _RAIter, _RAIter, _Compare);
 
   template<typename _BIter, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     _BIter
     partition(_BIter, _BIter, _Predicate);
 
@@ -892,10 +918,12 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
     set_union(_IIter1, _IIter1, _IIter2, _IIter2, _OIter, _Compare);
 
   template<typename _RAIter>
+    _GLIBCXX20_CONSTEXPR
     void
     sort(_RAIter, _RAIter);
 
   template<typename _RAIter, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     sort(_RAIter, _RAIter, _Compare);
 
diff --git a/libstdc++-v3/include/bits/move.h b/libstdc++-v3/include/bits/move.h
index e3ddeb563b4..d7c7068e29c 100644
--- a/libstdc++-v3/include/bits/move.h
+++ b/libstdc++-v3/include/bits/move.h
@@ -175,6 +175,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  @return   Nothing.
   */
   template<typename _Tp>
+    _GLIBCXX20_CONSTEXPR
     inline
 #if __cplusplus >= 201103L
     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
@@ -199,6 +200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // DR 809. std::swap should be overloaded for array types.
   /// Swap the contents of two arrays.
   template<typename _Tp, size_t _Nm>
+    _GLIBCXX20_CONSTEXPR
     inline
 #if __cplusplus >= 201103L
     typename enable_if<__is_swappable<_Tp>::value>::type
diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 0d707250d2e..bece93379de 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -74,6 +74,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// Swaps the median value of *__a, *__b and *__c under __comp to *__result
   template<typename _Iterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __move_median_to_first(_Iterator __result,_Iterator __a, _Iterator __b,
 			   _Iterator __c, _Compare __comp)
@@ -1162,6 +1163,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  overloaded for bidirectional iterators.
   */
   template<typename _BidirectionalIterator>
+    _GLIBCXX20_CONSTEXPR
     void
     __reverse(_BidirectionalIterator __first, _BidirectionalIterator __last,
 	      bidirectional_iterator_tag)
@@ -1182,6 +1184,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  overloaded for random access iterators.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     void
     __reverse(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	      random_access_iterator_tag)
@@ -1210,6 +1213,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  swaps @p *(__first+i) and @p *(__last-(i+1))
   */
   template<typename _BidirectionalIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     reverse(_BidirectionalIterator __first, _BidirectionalIterator __last)
     {
@@ -1263,6 +1267,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  It returns the greatest common divisor of two integer values.
   */
   template<typename _EuclideanRingElement>
+    _GLIBCXX20_CONSTEXPR
     _EuclideanRingElement
     __gcd(_EuclideanRingElement __m, _EuclideanRingElement __n)
     {
@@ -1280,6 +1285,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function for the rotate algorithm.
   template<typename _ForwardIterator>
+    _GLIBCXX20_CONSTEXPR
     _ForwardIterator
     __rotate(_ForwardIterator __first,
 	     _ForwardIterator __middle,
@@ -1321,6 +1327,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
    /// This is a helper function for the rotate algorithm.
   template<typename _BidirectionalIterator>
+    _GLIBCXX20_CONSTEXPR
     _BidirectionalIterator
     __rotate(_BidirectionalIterator __first,
 	     _BidirectionalIterator __middle,
@@ -1359,6 +1366,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function for the rotate algorithm.
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     _RandomAccessIterator
     __rotate(_RandomAccessIterator __first,
 	     _RandomAccessIterator __middle,
@@ -1465,6 +1473,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  for each @p n in the range @p [0,__last-__first).
   */
   template<typename _ForwardIterator>
+    _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     rotate(_ForwardIterator __first, _ForwardIterator __middle,
 	   _ForwardIterator __last)
@@ -1520,6 +1529,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function...
   template<typename _ForwardIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     _ForwardIterator
     __partition(_ForwardIterator __first, _ForwardIterator __last,
 		_Predicate __pred, forward_iterator_tag)
@@ -1545,6 +1555,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function...
   template<typename _BidirectionalIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     _BidirectionalIterator
     __partition(_BidirectionalIterator __first, _BidirectionalIterator __last,
 		_Predicate __pred, bidirectional_iterator_tag)
@@ -1699,6 +1710,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function for the sort routines.
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __heap_select(_RandomAccessIterator __first,
 		  _RandomAccessIterator __middle,
@@ -1714,6 +1726,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _InputIterator, typename _RandomAccessIterator,
 	   typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     _RandomAccessIterator
     __partial_sort_copy(_InputIterator __first, _InputIterator __last,
 			_RandomAccessIterator __result_first,
@@ -1768,6 +1781,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  The value returned is @p __result_first+N.
   */
   template<typename _InputIterator, typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline _RandomAccessIterator
     partial_sort_copy(_InputIterator __first, _InputIterator __last,
 		      _RandomAccessIterator __result_first,
@@ -1818,6 +1832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   */
   template<typename _InputIterator, typename _RandomAccessIterator,
 	   typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline _RandomAccessIterator
     partial_sort_copy(_InputIterator __first, _InputIterator __last,
 		      _RandomAccessIterator __result_first,
@@ -1931,6 +1946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function...
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     _RandomAccessIterator
     __unguarded_partition(_RandomAccessIterator __first,
 			  _RandomAccessIterator __last,
@@ -1952,6 +1968,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function...
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline _RandomAccessIterator
     __unguarded_partition_pivot(_RandomAccessIterator __first,
 				_RandomAccessIterator __last, _Compare __comp)
@@ -1963,6 +1980,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     __partial_sort(_RandomAccessIterator __first,
 		   _RandomAccessIterator __middle,
@@ -1975,6 +1993,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// This is a helper function for the sort routine.
   template<typename _RandomAccessIterator, typename _Size, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __introsort_loop(_RandomAccessIterator __first,
 		     _RandomAccessIterator __last,
@@ -1998,6 +2017,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // sort
 
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     __sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	   _Compare __comp)
@@ -2012,6 +2032,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _RandomAccessIterator, typename _Size, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __introselect(_RandomAccessIterator __first, _RandomAccessIterator __nth,
 		  _RandomAccessIterator __last, _Size __depth_limit,
@@ -2728,6 +2749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _RandomAccessIterator, typename _Distance,
 	   typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __chunk_insertion_sort(_RandomAccessIterator __first,
 			   _RandomAccessIterator __last,
@@ -2997,6 +3019,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  is the largest of the set, the smallest is generated and false returned.
   */
   template<typename _BidirectionalIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     next_permutation(_BidirectionalIterator __first,
 		     _BidirectionalIterator __last)
@@ -3029,6 +3052,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  smallest is generated and false returned.
   */
   template<typename _BidirectionalIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     next_permutation(_BidirectionalIterator __first,
 		     _BidirectionalIterator __last, _Compare __comp)
@@ -3098,6 +3122,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  returned.
   */
   template<typename _BidirectionalIterator>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     prev_permutation(_BidirectionalIterator __first,
 		     _BidirectionalIterator __last)
@@ -3130,6 +3155,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  the largest is generated and false returned.
   */
   template<typename _BidirectionalIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline bool
     prev_permutation(_BidirectionalIterator __first,
 		     _BidirectionalIterator __last, _Compare __comp)
@@ -4757,6 +4783,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @p stable_partition() if this is needed.
   */
   template<typename _ForwardIterator, typename _Predicate>
+    _GLIBCXX20_CONSTEXPR
     inline _ForwardIterator
     partition(_ForwardIterator __first, _ForwardIterator __last,
 	      _Predicate   __pred)
@@ -4790,6 +4817,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  the range @p [__middle,__last) then *j<*i and *k<*i are both false.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     partial_sort(_RandomAccessIterator __first,
 		 _RandomAccessIterator __middle,
@@ -4828,6 +4856,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  are both false.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     partial_sort(_RandomAccessIterator __first,
 		 _RandomAccessIterator __middle,
@@ -4864,6 +4893,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  holds that *j < *i is false.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
 		_RandomAccessIterator __last)
@@ -4903,6 +4933,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  holds that @p __comp(*j,*i) is false.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth,
 		_RandomAccessIterator __last, _Compare __comp)
@@ -4940,6 +4971,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @p stable_sort() if this is needed.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last)
     {
@@ -4970,6 +5002,7 @@ _GLIBCXX_BEGIN_NAMESPACE_ALGO
    *  @p stable_sort() if this is needed.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     sort(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	 _Compare __comp)
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index ab1ff5185d4..36bb9ccb777 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -136,6 +136,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct __iter_swap
     {
       template<typename _ForwardIterator1, typename _ForwardIterator2>
+	_GLIBCXX20_CONSTEXPR
 	static void
 	iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
 	{
@@ -151,6 +152,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     struct __iter_swap<true>
     {
       template<typename _ForwardIterator1, typename _ForwardIterator2>
+	_GLIBCXX20_CONSTEXPR
 	static void
 	iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
 	{
@@ -170,6 +172,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  iterators themselves.
   */
   template<typename _ForwardIterator1, typename _ForwardIterator2>
+    _GLIBCXX20_CONSTEXPR
     inline void
     iter_swap(_ForwardIterator1 __a, _ForwardIterator2 __b)
     {
@@ -216,6 +219,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  The ranges must not overlap.
   */
   template<typename _ForwardIterator1, typename _ForwardIterator2>
+    _GLIBCXX20_CONSTEXPR
     _ForwardIterator2
     swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1,
 		_ForwardIterator2 __first2)
diff --git a/libstdc++-v3/include/bits/stl_heap.h b/libstdc++-v3/include/bits/stl_heap.h
index d9530e66621..7eb12f04321 100644
--- a/libstdc++-v3/include/bits/stl_heap.h
+++ b/libstdc++-v3/include/bits/stl_heap.h
@@ -129,6 +129,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _RandomAccessIterator, typename _Distance, typename _Tp,
 	   typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __push_heap(_RandomAccessIterator __first,
 		_Distance __holeIndex, _Distance __topIndex, _Tp __value,
@@ -155,6 +156,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  [__first,__last) is a valid heap.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     push_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
     {
@@ -190,6 +192,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  performed using comp.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     push_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	      _Compare __comp)
@@ -215,6 +218,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _RandomAccessIterator, typename _Distance,
 	   typename _Tp, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __adjust_heap(_RandomAccessIterator __first, _Distance __holeIndex,
 		  _Distance __len, _Tp __value, _Compare __comp)
@@ -244,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     __pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	       _RandomAccessIterator __result, _Compare& __comp)
@@ -272,6 +277,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  heap.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
     {
@@ -305,6 +311,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  heap.  Comparisons are made using comp.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     pop_heap(_RandomAccessIterator __first,
 	     _RandomAccessIterator __last, _Compare __comp)
@@ -327,6 +334,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 		_Compare& __comp)
@@ -361,6 +369,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  This operation makes the elements in [__first,__last) into a heap.
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
     {
@@ -387,6 +396,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  Comparisons are made using __comp.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	      _Compare __comp)
@@ -403,6 +413,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     }
 
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     void
     __sort_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 		_Compare& __comp)
@@ -423,6 +434,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  This operation sorts the valid heap in the range [__first,__last).
   */
   template<typename _RandomAccessIterator>
+    _GLIBCXX20_CONSTEXPR
     inline void
     sort_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
     {
@@ -450,6 +462,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  Comparisons are made using __comp.
   */
   template<typename _RandomAccessIterator, typename _Compare>
+    _GLIBCXX20_CONSTEXPR
     inline void
     sort_heap(_RandomAccessIterator __first, _RandomAccessIterator __last,
 	      _Compare __comp)
diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 9428dadc9d7..b31c26ab381 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -2695,6 +2695,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { };
 
   template<typename _Tp>
+    _GLIBCXX20_CONSTEXPR
     inline
     typename enable_if<__and_<__not_<__is_tuple_like<_Tp>>,
 			      is_move_constructible<_Tp>,
@@ -2704,6 +2705,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	            is_nothrow_move_assignable<_Tp>>::value);
 
   template<typename _Tp, size_t _Nm>
+    _GLIBCXX20_CONSTEXPR
     inline
     typename enable_if<__is_swappable<_Tp>::value>::type
     swap(_Tp (&__a)[_Nm], _Tp (&__b)[_Nm])
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index 5757568d639..7f7d05fd8f2 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -154,6 +154,7 @@
 #define __cpp_lib_bind_front 201907L
 #define __cpp_lib_bounded_array_traits 201902L
 #define __cpp_lib_constexpr_algorithms 201711L
+#define __cpp_lib_constexpr_swap_algorithms 201806L
 #if __cpp_impl_destroying_delete
 # define __cpp_lib_destroying_delete 201806L
 #endif