[PATCH 1/3] libstdc++: Apply the move_iterator changes described in P1207R4

[Patrick Palka]

These changes are needed for some of the tests in the constrained algorithm
patch, because they use move_iterator with an uncopyable output_iterator.  The
other changes described in the paper are already applied, it seems.

libstdc++-v3/ChangeLog:

        * include/bits/stl_iterator.h (move_iterator::move_iterator): Move the
        iterator when initializing _M_current.
        (move_iterator::base): Split into two overloads differing in
        ref-qualifiers as in P1207R4.
---
 libstdc++-v3/include/bits/stl_iterator.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/libstdc++-v3/include/bits/stl_iterator.h 
b/libstdc++-v3/include/bits/stl_iterator.h
index 784d200d22f..1a288a5c785 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1166,7 +1166,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       explicit _GLIBCXX17_CONSTEXPR
       move_iterator(iterator_type __i)
-      : _M_current(__i) { }
+      : _M_current(std::move(__i)) { }
 
       template<typename _Iter>
        _GLIBCXX17_CONSTEXPR
@@ -1174,9 +1174,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        : _M_current(__i.base()) { }
 
       _GLIBCXX17_CONSTEXPR iterator_type
-      base() const
+      base() const &
+#if __cplusplus > 201703L && __cpp_lib_concepts
+       requires copy_constructible<iterator_type>
+#endif
       { return _M_current; }
 
+      _GLIBCXX17_CONSTEXPR iterator_type
+      base() &&
+      { return std::move(_M_current); }
+
       _GLIBCXX17_CONSTEXPR reference
       operator*() const
       { return static_cast<reference>(*_M_current); }
-- 
2.25.0.114.g5b0ca878e0