Index: libcxx/include/__algorithm/copy_n.h
===================================================================
--- libcxx/include/__algorithm/copy_n.h
+++ libcxx/include/__algorithm/copy_n.h
@@ -57,9 +57,10 @@
 >::type
 copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)
 {
+    typedef typename iterator_traits<_InputIterator>::difference_type difference_type;
     typedef decltype(_VSTD::__convert_to_integral(__orig_n)) _IntegralSize;
     _IntegralSize __n = __orig_n;
-    return _VSTD::copy(__first, __first + __n, __result);
+    return _VSTD::copy(__first, __first + difference_type(__n), __result);
 }
 
 _LIBCPP_END_NAMESPACE_STD
Index: libcxx/include/__algorithm/find_end.h
===================================================================
--- libcxx/include/__algorithm/find_end.h
+++ libcxx/include/__algorithm/find_end.h
@@ -95,14 +95,16 @@
 _LIBCPP_CONSTEXPR_AFTER_CXX11 _RandomAccessIterator1 __find_end(
     _RandomAccessIterator1 __first1, _RandomAccessIterator1 __last1, _RandomAccessIterator2 __first2,
     _RandomAccessIterator2 __last2, _BinaryPredicate __pred, random_access_iterator_tag, random_access_iterator_tag) {
+  typedef typename iterator_traits<_RandomAccessIterator1>::difference_type _D1;
+  typedef typename iterator_traits<_RandomAccessIterator2>::difference_type _D2;
   // Take advantage of knowing source and pattern lengths.  Stop short when source is smaller than pattern
-  typename iterator_traits<_RandomAccessIterator2>::difference_type __len2 = __last2 - __first2;
+  _D2 __len2 = __last2 - __first2;
   if (__len2 == 0)
     return __last1;
-  typename iterator_traits<_RandomAccessIterator1>::difference_type __len1 = __last1 - __first1;
+  _D1 __len1 = __last1 - __first1;
   if (__len1 < __len2)
     return __last1;
-  const _RandomAccessIterator1 __s = __first1 + (__len2 - 1); // End of pattern match can't go before here
+  const _RandomAccessIterator1 __s = __first1 + _D1(__len2 - 1); // End of pattern match can't go before here
   _RandomAccessIterator1 __l1 = __last1;
   _RandomAccessIterator2 __l2 = __last2;
   --__l2;
Index: libcxx/include/__algorithm/search.h
===================================================================
--- libcxx/include/__algorithm/search.h
+++ libcxx/include/__algorithm/search.h
@@ -68,7 +68,7 @@
   const _D1 __len1 = __last1 - __first1;
   if (__len1 < __len2)
     return _VSTD::make_pair(__last1, __last1);
-  const _RandomAccessIterator1 __s = __last1 - (__len2 - 1); // Start of pattern match can't go beyond here
+  const _RandomAccessIterator1 __s = __last1 - _D1(__len2 - 1); // Start of pattern match can't go beyond here
 
   while (true) {
     while (true) {
@@ -83,7 +83,7 @@
     _RandomAccessIterator2 __m2 = __first2;
     while (true) {
       if (++__m2 == __last2)
-        return _VSTD::make_pair(__first1, __first1 + __len2);
+        return _VSTD::make_pair(__first1, __first1 + _D1(__len2));
       ++__m1; // no need to check range on __m1 because __s guarantees we have enough source
       if (!__pred(*__m1, *__m2)) {
         ++__first1;
Index: libcxx/include/__algorithm/search_n.h
===================================================================
--- libcxx/include/__algorithm/search_n.h
+++ libcxx/include/__algorithm/search_n.h
@@ -59,12 +59,13 @@
                                                                _RandomAccessIterator __last, _Size __count,
                                                                const _Tp& __value_, _BinaryPredicate __pred,
                                                                random_access_iterator_tag) {
+  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
   if (__count <= 0)
     return __first;
   _Size __len = static_cast<_Size>(__last - __first);
   if (__len < __count)
     return __last;
-  const _RandomAccessIterator __s = __last - (__count - 1); // Start of pattern match can't go beyond here
+  const _RandomAccessIterator __s = __last - difference_type(__count - 1); // Start of pattern match can't go beyond here
   while (true) {
     // Find first element in sequence that matchs __value_, with a mininum of loop checks
     while (true) {
Index: libcxx/include/__algorithm/sift_down.h
===================================================================
--- libcxx/include/__algorithm/sift_down.h
+++ libcxx/include/__algorithm/sift_down.h
@@ -38,7 +38,7 @@
     __child = 2 * __child + 1;
     _RandomAccessIterator __child_i = __first + __child;
 
-    if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + 1))) {
+    if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
         // right-child exists and is greater than left-child
         ++__child_i;
         ++__child;
@@ -63,7 +63,7 @@
         __child = 2 * __child + 1;
         __child_i = __first + __child;
 
-        if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + 1))) {
+        if ((__child + 1) < __len && __comp(*__child_i, *(__child_i + difference_type(1)))) {
             // right-child exists and is greater than left-child
             ++__child_i;
             ++__child;
Index: libcxx/include/__algorithm/sort.h
===================================================================
--- libcxx/include/__algorithm/sort.h
+++ libcxx/include/__algorithm/sort.h
@@ -156,10 +156,11 @@
 void
 __insertion_sort_3(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp)
 {
+    typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
     typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
-    _RandomAccessIterator __j = __first+2;
-    _VSTD::__sort3<_Compare>(__first, __first+1, __j, __comp);
-    for (_RandomAccessIterator __i = __j+1; __i != __last; ++__i)
+    _RandomAccessIterator __j = __first+difference_type(2);
+    _VSTD::__sort3<_Compare>(__first, __first+difference_type(1), __j, __comp);
+    for (_RandomAccessIterator __i = __j+difference_type(1); __i != __last; ++__i)
     {
         if (__comp(*__i, *__j))
         {
@@ -181,6 +182,7 @@
 bool
 __insertion_sort_incomplete(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp)
 {
+    typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
     switch (__last - __first)
     {
     case 0:
@@ -191,21 +193,21 @@
             swap(*__first, *__last);
         return true;
     case 3:
-        _VSTD::__sort3<_Compare>(__first, __first+1, --__last, __comp);
+        _VSTD::__sort3<_Compare>(__first, __first+difference_type(1), --__last, __comp);
         return true;
     case 4:
-        _VSTD::__sort4<_Compare>(__first, __first+1, __first+2, --__last, __comp);
+        _VSTD::__sort4<_Compare>(__first, __first+difference_type(1), __first+difference_type(2), --__last, __comp);
         return true;
     case 5:
-        _VSTD::__sort5<_Compare>(__first, __first+1, __first+2, __first+3, --__last, __comp);
+        _VSTD::__sort5<_Compare>(__first, __first+difference_type(1), __first+difference_type(2), __first+difference_type(3), --__last, __comp);
         return true;
     }
     typedef typename iterator_traits<_RandomAccessIterator>::value_type value_type;
-    _RandomAccessIterator __j = __first+2;
-    _VSTD::__sort3<_Compare>(__first, __first+1, __j, __comp);
+    _RandomAccessIterator __j = __first+difference_type(2);
+    _VSTD::__sort3<_Compare>(__first, __first+difference_type(1), __j, __comp);
     const unsigned __limit = 8;
     unsigned __count = 0;
-    for (_RandomAccessIterator __i = __j+1; __i != __last; ++__i)
+    for (_RandomAccessIterator __i = __j+difference_type(1); __i != __last; ++__i)
     {
         if (__comp(*__i, *__j))
         {
@@ -283,13 +285,13 @@
                 swap(*__first, *__last);
             return;
         case 3:
-            _VSTD::__sort3<_Compare>(__first, __first+1, --__last, __comp);
+            _VSTD::__sort3<_Compare>(__first, __first+difference_type(1), --__last, __comp);
             return;
         case 4:
-            _VSTD::__sort4<_Compare>(__first, __first+1, __first+2, --__last, __comp);
+            _VSTD::__sort4<_Compare>(__first, __first+difference_type(1), __first+difference_type(2), --__last, __comp);
             return;
         case 5:
-            _VSTD::__sort5<_Compare>(__first, __first+1, __first+2, __first+3, --__last, __comp);
+            _VSTD::__sort5<_Compare>(__first, __first+difference_type(1), __first+difference_type(2), __first+difference_type(3), --__last, __comp);
             return;
         }
         if (__len <= __limit)
@@ -421,7 +423,7 @@
         if (__n_swaps == 0)
         {
             bool __fs = _VSTD::__insertion_sort_incomplete<_Compare>(__first, __i, __comp);
-            if (_VSTD::__insertion_sort_incomplete<_Compare>(__i+1, __last, __comp))
+            if (_VSTD::__insertion_sort_incomplete<_Compare>(__i+difference_type(1), __last, __comp))
             {
                 if (__fs)
                     return;
@@ -446,7 +448,7 @@
         }
         else
         {
-            _VSTD::__sort<_Compare>(__i+1, __last, __comp);
+            _VSTD::__sort<_Compare>(__i+difference_type(1), __last, __comp);
             // _VSTD::__sort<_Compare>(__first, __i, __comp);
             __last = __i;
         }
Index: libcxx/test/std/algorithms/robust_re_difference_type.compile.pass.cpp
===================================================================
--- libcxx/test/std/algorithms/robust_re_difference_type.compile.pass.cpp
+++ libcxx/test/std/algorithms/robust_re_difference_type.compile.pass.cpp
@@ -77,6 +77,7 @@
     auto mid = PickyIterator<void**, long>(a+5);
     auto last = PickyIterator<void**, long>(a+10);
     auto first2 = PickyIterator<void**, long long>(b);
+    auto mid2 = PickyIterator<void**, long long>(b+5);
     auto last2 = PickyIterator<void**, long long>(b+10);
     void *value = nullptr;
     int count = 1;
@@ -84,7 +85,7 @@
     (void)std::all_of(first, last, [](void*){ return true; });
     (void)std::any_of(first, last, [](void*){ return true; });
     (void)std::copy(first, last, first2);
-    // TODO FIXME (void)std::copy_n(first, count, first2);
+    (void)std::copy_n(first, count, first2);
     (void)std::copy_backward(first, last, last2);
     (void)std::count(first, last, value);
     (void)std::count_if(first, last, [](void*){ return true; });
@@ -132,7 +133,7 @@
     (void)std::binary_search(first, last, value);
     (void)std::equal(first, last, first2);
     (void)std::equal_range(first, last, value);
-    // TODO FIXME (void)std::find_end(first, last, first2, mid2);
+    (void)std::find_end(first, last, first2, mid2);
     (void)std::includes(first, last, first2, last2);
     NOT_CONSTEVAL( (void)std::inplace_merge(first, mid, last); )
     (void)std::is_heap(first, last);
@@ -143,7 +144,7 @@
     (void)std::lexicographical_compare(first, last, first2, last2);
     // TODO: lexicographical_compare_three_way
     (void)std::lower_bound(first, last, value);
-    // TODO FIXME (void)std::make_heap(first, last);
+    (void)std::make_heap(first, last);
     (void)std::max(value, value);
     (void)std::max({ value, value });
     (void)std::max_element(first, last);
@@ -157,19 +158,19 @@
     (void)std::mismatch(first, last, first2);
     (void)std::next_permutation(first, last);
     (void)std::nth_element(first, mid, last);
-    // TODO FIXME (void)std::partial_sort(first, mid, last);
-    // TODO FIXME (void)std::partial_sort_copy(first, last, first2, mid2);
-    // TODO FIXME (void)std::pop_heap(first, last);
+    (void)std::partial_sort(first, mid, last);
+    (void)std::partial_sort_copy(first, last, first2, mid2);
+    (void)std::pop_heap(first, last);
     (void)std::prev_permutation(first, last);
     (void)std::push_heap(first, last);
-    // TODO FIXME (void)std::search(first, last, first2, mid2);
-    // TODO FIXME (void)std::search_n(first, last, count, value);
+    (void)std::search(first, last, first2, mid2);
+    (void)std::search_n(first, last, count, value);
     (void)std::set_difference(first, mid, mid, last, first2);
     (void)std::set_intersection(first, mid, mid, last, first2);
     (void)std::set_symmetric_difference(first, mid, mid, last, first2);
     (void)std::set_union(first, mid, mid, last, first2);
-    // TODO FIXME (void)std::sort(first, mid, last);
-    // TODO FIXME (void)std::sort_heap(first, last);
+    (void)std::sort(first, last);
+    (void)std::sort_heap(first, last);
     NOT_CONSTEVAL( (void)std::stable_sort(first, last); )
     (void)std::unique(first, last);
     (void)std::unique_copy(first, last, first2);
@@ -188,7 +189,7 @@
     (void)std::binary_search(first, last, value, std::less<void*>());
     (void)std::equal(first, last, first2, std::equal_to<void*>());
     (void)std::equal_range(first, last, value, std::less<void*>());
-    // TODO FIXME (void)std::find_end(first, last, first2, mid2, std::equal_to<void*>());
+    (void)std::find_end(first, last, first2, mid2, std::equal_to<void*>());
     (void)std::includes(first, last, first2, last2, std::less<void*>());
     NOT_CONSTEVAL( (void)std::inplace_merge(first, mid, last, std::less<void*>()); )
     (void)std::is_heap(first, last, std::less<void*>());
@@ -199,7 +200,7 @@
     (void)std::lexicographical_compare(first, last, first2, last2, std::less<void*>());
     // TODO: lexicographical_compare_three_way
     (void)std::lower_bound(first, last, value, std::less<void*>());
-    // TODO FIXME (void)std::make_heap(first, last, std::less<void*>());
+    (void)std::make_heap(first, last, std::less<void*>());
     (void)std::max(value, value, std::less<void*>());
     (void)std::max({ value, value }, std::less<void*>());
     (void)std::max_element(first, last, std::less<void*>());
@@ -213,19 +214,19 @@
     (void)std::mismatch(first, last, first2, std::equal_to<void*>());
     (void)std::next_permutation(first, last, std::less<void*>());
     (void)std::nth_element(first, mid, last, std::less<void*>());
-    // TODO FIXME (void)std::partial_sort(first, mid, last, std::less<void*>());
-    // TODO FIXME (void)std::partial_sort_copy(first, last, first2, mid2, std::less<void*>());
-    // TODO FIXME (void)std::pop_heap(first, last, std::less<void*>());
+    (void)std::partial_sort(first, mid, last, std::less<void*>());
+    (void)std::partial_sort_copy(first, last, first2, mid2, std::less<void*>());
+    (void)std::pop_heap(first, last, std::less<void*>());
     (void)std::prev_permutation(first, last, std::less<void*>());
     (void)std::push_heap(first, last, std::less<void*>());
-    // TODO FIXME (void)std::search(first, last, first2, mid2, std::equal_to<void*>());
-    // TODO FIXME (void)std::search_n(first, last, count, value, std::equal_to<void*>());
+    (void)std::search(first, last, first2, mid2, std::equal_to<void*>());
+    (void)std::search_n(first, last, count, value, std::equal_to<void*>());
     (void)std::set_difference(first, mid, mid, last, first2, std::less<void*>());
     (void)std::set_intersection(first, mid, mid, last, first2, std::less<void*>());
     (void)std::set_symmetric_difference(first, mid, mid, last, first2, std::less<void*>());
     (void)std::set_union(first, mid, mid, last, first2, std::less<void*>());
-    // TODO FIXME (void)std::sort(first, mid, last, std::less<void*>());
-    // TODO FIXME (void)std::sort_heap(first, last, std::less<void*>());
+    (void)std::sort(first, last, std::less<void*>());
+    (void)std::sort_heap(first, last, std::less<void*>());
     NOT_CONSTEVAL( (void)std::stable_sort(first, last, std::less<void*>()); )
     (void)std::unique(first, last, std::equal_to<void*>());
     (void)std::unique_copy(first, last, first2, std::equal_to<void*>());