diff --git a/libcxx/include/algorithm b/libcxx/include/algorithm
index c00845f6404b..3dda30d15108 100644
--- a/libcxx/include/algorithm
+++ b/libcxx/include/algorithm
@@ -236,19 +236,19 @@ template <class OutputIterator, class Size, class Generator>
     generate_n(OutputIterator first, Size n, Generator gen);
 
 template <class ForwardIterator, class T>
-    ForwardIterator
+    constexpr ForwardIterator     // constexpr in C++20
     remove(ForwardIterator first, ForwardIterator last, const T& value);
 
 template <class ForwardIterator, class Predicate>
-    ForwardIterator
+    constexpr ForwardIterator     // constexpr in C++20
     remove_if(ForwardIterator first, ForwardIterator last, Predicate pred);
 
 template <class InputIterator, class OutputIterator, class T>
-    OutputIterator
+    constexpr OutputIterator     // constexpr in C++20
     remove_copy(InputIterator first, InputIterator last, OutputIterator result, const T& value);
 
 template <class InputIterator, class OutputIterator, class Predicate>
-    OutputIterator
+    constexpr OutputIterator     // constexpr in C++20
     remove_copy_if(InputIterator first, InputIterator last, OutputIterator result, Predicate pred);
 
 template <class ForwardIterator>
@@ -272,7 +272,7 @@ template <class BidirectionalIterator>
     reverse(BidirectionalIterator first, BidirectionalIterator last);
 
 template <class BidirectionalIterator, class OutputIterator>
-    OutputIterator
+    constexpr OutputIterator       // constexpr in C++20
     reverse_copy(BidirectionalIterator first, BidirectionalIterator last, OutputIterator result);
 
 template <class ForwardIterator>
@@ -2098,7 +2098,7 @@ generate_n(_OutputIterator __first, _Size __orig_n, _Generator __gen)
 // remove
 
 template <class _ForwardIterator, class _Tp>
-_ForwardIterator
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
 remove(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value_)
 {
     __first = _VSTD::find(__first, __last, __value_);
@@ -2120,7 +2120,7 @@ remove(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value_)
 // remove_if
 
 template <class _ForwardIterator, class _Predicate>
-_ForwardIterator
+_LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator
 remove_if(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred)
 {
     __first = _VSTD::find_if<_ForwardIterator, typename add_lvalue_reference<_Predicate>::type>
@@ -2143,7 +2143,7 @@ remove_if(_ForwardIterator __first, _ForwardIterator __last, _Predicate __pred)
 // remove_copy
 
 template <class _InputIterator, class _OutputIterator, class _Tp>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 _OutputIterator
 remove_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __result, const _Tp& __value_)
 {
@@ -2161,7 +2161,7 @@ remove_copy(_InputIterator __first, _InputIterator __last, _OutputIterator __res
 // remove_copy_if
 
 template <class _InputIterator, class _OutputIterator, class _Predicate>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 _OutputIterator
 remove_copy_if(_InputIterator __first, _InputIterator __last, _OutputIterator __result, _Predicate __pred)
 {
@@ -2327,7 +2327,7 @@ reverse(_BidirectionalIterator __first, _BidirectionalIterator __last)
 // reverse_copy
 
 template <class _BidirectionalIterator, class _OutputIterator>
-inline _LIBCPP_INLINE_VISIBILITY
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17
 _OutputIterator
 reverse_copy(_BidirectionalIterator __first, _BidirectionalIterator __last, _OutputIterator __result)
 {
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove.pass.cpp
index a77a9eddb191..557984f3900c 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove.pass.cpp
@@ -12,7 +12,7 @@
 // template<ForwardIterator Iter, class T>
 //   requires OutputIterator<Iter, RvalueOf<Iter::reference>::type>
 //         && HasEqualTo<Iter::value_type, T>
-//   Iter
+//   constexpr Iter         // constexpr after C++17
 //   remove(Iter first, Iter last, const T& value);
 
 #include <algorithm>
@@ -22,6 +22,18 @@
 #include "test_macros.h"
 #include "test_iterators.h"
 
+#if TEST_STD_VER > 17
+TEST_CONSTEXPR bool test_constexpr() {
+    int ia[] = {1, 3, 5, 2, 5, 6};
+    
+    auto it = std::remove(std::begin(ia), std::end(ia), 5);
+
+    return (std::begin(ia) + std::size(ia) - 2) == it  // we removed two elements
+        && std::none_of(std::begin(ia), it, [](int a) {return a == 5; })
+           ;
+    }
+#endif
+
 template <class Iter>
 void
 test()
@@ -75,4 +87,8 @@ int main()
     test1<random_access_iterator<std::unique_ptr<int>*> >();
     test1<std::unique_ptr<int>*>();
 #endif // TEST_STD_VER >= 11
+
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr());
+#endif
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy.pass.cpp
index bf5f79cf8359..ae7b34184264 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy.pass.cpp
@@ -11,14 +11,29 @@
 
 // template<InputIterator InIter, OutputIterator<auto, InIter::reference> OutIter, class T>
 //   requires HasEqualTo<InIter::value_type, T>
-//   OutIter
+//   constexpr OutIter         // constexpr after C++17
 //   remove_copy(InIter first, InIter last, OutIter result, const T& value);
 
 #include <algorithm>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_iterators.h"
 
+#if TEST_STD_VER > 17
+TEST_CONSTEXPR bool test_constexpr() {
+    int ia[] = {1, 3, 5, 2, 5, 6};
+    int ib[std::size(ia)] = {0};
+    
+    auto it = std::remove_copy(std::begin(ia), std::end(ia), std::begin(ib), 5);
+
+    return std::distance(std::begin(ib), it) == (std::size(ia) - 2)   // we removed two elements
+        && std::none_of(std::begin(ib), it, [](int a) {return a == 5;})
+        && std::all_of (it, std::end(ib),   [](int a) {return a == 0;})
+           ;
+    }
+#endif
+
 template <class InIter, class OutIter>
 void
 test()
@@ -67,4 +82,8 @@ int main()
     test<const int*, bidirectional_iterator<int*> >();
     test<const int*, random_access_iterator<int*> >();
     test<const int*, int*>();
+
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr());
+#endif
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy_if.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy_if.pass.cpp
index 8532998eb08d..111c59eb795b 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy_if.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_copy_if.pass.cpp
@@ -12,16 +12,31 @@
 // template<InputIterator InIter, OutputIterator<auto, InIter::reference> OutIter,
 //          Predicate<auto, InIter::value_type> Pred>
 //   requires CopyConstructible<Pred>
-//   OutIter
+//   constexpr OutIter         // constexpr after C++17
 //   remove_copy_if(InIter first, InIter last, OutIter result, Pred pred);
 
 #include <algorithm>
 #include <functional>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_iterators.h"
 
-bool equalToTwo(int v) { return v == 2; }
+TEST_CONSTEXPR bool equalToTwo(int v) { return v == 2; }
+
+#if TEST_STD_VER > 17
+TEST_CONSTEXPR bool test_constexpr() {
+    int ia[] = {1, 3, 5, 2, 5, 6};
+    int ib[std::size(ia)] = {0};
+    
+    auto it = std::remove_copy_if(std::begin(ia), std::end(ia), std::begin(ib), equalToTwo);
+
+    return std::distance(std::begin(ib), it) == (std::size(ia) - 1)   // we removed one element
+        && std::none_of(std::begin(ib), it, equalToTwo)
+        && std::all_of (it, std::end(ib), [](int a) {return a == 0;})
+           ;
+    }
+#endif
 
 template <class InIter, class OutIter>
 void
@@ -72,4 +87,8 @@ int main()
     test<const int*, bidirectional_iterator<int*> >();
     test<const int*, random_access_iterator<int*> >();
     test<const int*, int*>();
+
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr());
+#endif
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_if.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_if.pass.cpp
index c40f3e727836..d8123ee4540c 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_if.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.remove/remove_if.pass.cpp
@@ -12,7 +12,7 @@
 // template<ForwardIterator Iter, Predicate<auto, Iter::value_type> Pred>
 //   requires OutputIterator<Iter, RvalueOf<Iter::reference>::type>
 //         && CopyConstructible<Pred>
-//   Iter
+//   constexpr Iter         // constexpr after C++17
 //   remove_if(Iter first, Iter last, Pred pred);
 
 #include <algorithm>
@@ -24,7 +24,19 @@
 #include "test_iterators.h"
 #include "counting_predicates.hpp"
 
-bool equal2 ( int i ) { return i == 2; }
+TEST_CONSTEXPR bool equal2 ( int i ) { return i == 2; }
+
+#if TEST_STD_VER > 17
+TEST_CONSTEXPR bool test_constexpr() {
+    int ia[] = {1, 3, 5, 2, 5, 6};
+    
+    auto it = std::remove_if(std::begin(ia), std::end(ia), equal2);
+
+    return (std::begin(ia) + std::size(ia) - 1) == it  // we removed one element
+        && std::none_of(std::begin(ia), it, equal2)
+           ;
+    }
+#endif
 
 template <class Iter>
 void
@@ -90,4 +102,8 @@ int main()
     test1<random_access_iterator<std::unique_ptr<int>*> >();
     test1<std::unique_ptr<int>*>();
 #endif // TEST_STD_VER >= 11
+
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr());
+#endif
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.reverse/reverse_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.reverse/reverse_copy.pass.cpp
index 70840d187bfb..ec9aa9e94ab8 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.reverse/reverse_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.reverse/reverse_copy.pass.cpp
@@ -10,14 +10,28 @@
 // <algorithm>
 
 // template<BidirectionalIterator InIter, OutputIterator<auto, InIter::reference> OutIter>
-//   OutIter
+//   constexpr OutIter          // constexpr after C++17
 //   reverse_copy(InIter first, InIter last, OutIter result);
 
 #include <algorithm>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_iterators.h"
 
+#if TEST_STD_VER > 17
+TEST_CONSTEXPR bool test_constexpr() {
+    int ia[] = {1, 3, 5, 2, 5, 6};
+    int ib[std::size(ia)] = {0};
+    
+    auto it = std::reverse_copy(std::begin(ia), std::end(ia), std::begin(ib));
+
+    return std::distance(std::begin(ib), it) == std::size(ia)
+        && std::equal   (std::begin(ia), std::end(ia), std::rbegin(ib))
+           ;
+    }
+#endif
+
 template <class InIter, class OutIter>
 void
 test()
@@ -78,4 +92,8 @@ int main()
     test<const int*, bidirectional_iterator<int*> >();
     test<const int*, random_access_iterator<int*> >();
     test<const int*, int*>();
+
+#if TEST_STD_VER > 17
+    static_assert(test_constexpr());
+#endif
 }
diff --git a/libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate_copy.pass.cpp b/libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate_copy.pass.cpp
index f2ad535a2f99..2294c79b5fad 100644
--- a/libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate_copy.pass.cpp
+++ b/libcxx/test/std/algorithms/alg.modifying.operations/alg.rotate/rotate_copy.pass.cpp
@@ -10,14 +10,31 @@
 // <algorithm>
 
 // template<ForwardIterator InIter, OutputIterator<auto, InIter::reference> OutIter>
-//   OutIter
+//   constexpr OutIter          // constexpr after C++17
 //   rotate_copy(InIter first, InIter middle, InIter last, OutIter result);
 
 #include <algorithm>
 #include <cassert>
 
+#include "test_macros.h"
 #include "test_iterators.h"
 
+// #if TEST_STD_VER > 17
+// TEST_CONSTEXPR bool test_constexpr() {
+//     int ia[] = {1, 3, 5, 2, 5, 6};
+//     int ib[std::size(ia)] = {0};
+//     
+//     const size_t N = 2;
+//     const auto middle = std::begin(ia) + N;
+//     auto it = std::rotate_copy(std::begin(ia), middle, std::end(ia), std::begin(ib));
+// 
+//     return std::distance(std::begin(ib), it) == std::size(ia)
+//         && std::equal   (std::begin(ia), middle,       std::begin(ib) + std::size(ia) - N)
+//         && std::equal   (middle,         std::end(ia), std::begin(ib))
+//            ;
+//     }
+// #endif
+
 template <class InIter, class OutIter>
 void
 test()
@@ -131,4 +148,8 @@ int main()
     test<const int*, bidirectional_iterator<int*> >();
     test<const int*, random_access_iterator<int*> >();
     test<const int*, int*>();
+
+// #if TEST_STD_VER > 17
+//    static_assert(test_constexpr());
+// #endif
 }