niter_base simplification

[FranÃois Dumont <frs dot dumont at gmail dot com>]

Hello

    I don't know if I am missing something but I think __niter_base 
could be simplified to remove usage of _Iter_base. Additionally I 
overload it to also remove __normal_iterator layer even if behind a 
reverse_iterator or move_iterator, might help compiler to optimize code, 
no ? If not, might allow other algo optimization in the future...

    I prefered to provide a __make_reverse_iterator to allow the latter 
in C++11 and not only in C++14. Is it fine to do it this way or do you 
prefer to simply get rid of all this part ?

    * include/bits/cpp_type_traits.h (__gnu_cxx::__normal_iterator): 
Delete.
    * include/bits/stl_algobase.h (std::__niter_base): Adapt.
    * include/bits/stl_iterator.h (__make_reverse_iterator): New in C++11.
    (std::__niter_base): Overloads for std::reverse_iterator,
    __gnu_cxx::__normal_iterator and std::move_iterator.

Tested under Linux x86_64. I checked that std::copy still ends up 
calling __builtin_memmove when used on vector iterators.

FranÃois

diff --git a/libstdc++-v3/include/bits/cpp_type_traits.h b/libstdc++-v3/include/bits/cpp_type_traits.h
index 8c6bb7f..2142917 100644
--- a/libstdc++-v3/include/bits/cpp_type_traits.h
+++ b/libstdc++-v3/include/bits/cpp_type_traits.h
@@ -64,17 +64,6 @@
 // removed.
 //
 
-// Forward declaration hack, should really include this from somewhere.
-namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
-{
-_GLIBCXX_BEGIN_NAMESPACE_VERSION
-
-  template<typename _Iterator, typename _Container>
-    class __normal_iterator;
-
-_GLIBCXX_END_NAMESPACE_VERSION
-} // namespace
-
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -331,24 +320,6 @@ __INT_N(__GLIBCXX_TYPE_INT_N_3)
     };
 
   //
-  // Normal iterator type
-  //
-  template<typename _Tp>
-    struct __is_normal_iterator
-    {
-      enum { __value = 0 };
-      typedef __false_type __type;
-    };
-
-  template<typename _Iterator, typename _Container>
-    struct __is_normal_iterator< __gnu_cxx::__normal_iterator<_Iterator,
-							      _Container> >
-    {
-      enum { __value = 1 };
-      typedef __true_type __type;
-    };
-
-  //
   // An arithmetic type is an integer type or a floating point type
   //
   template<typename _Tp>
diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h
index 0bcb133..73eea6b 100644
--- a/libstdc++-v3/include/bits/stl_algobase.h
+++ b/libstdc++-v3/include/bits/stl_algobase.h
@@ -270,17 +270,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       return __a;
     }
 
-  // If _Iterator is a __normal_iterator return its base (a plain pointer,
-  // normally) otherwise return it untouched.  See copy, fill, ... 
+  // Fallback implementation of the function used to remove the
+  // __normal_iterator wrapper. See copy, fill, ...
   template<typename _Iterator>
-    struct _Niter_base
-    : _Iter_base<_Iterator, __is_normal_iterator<_Iterator>::__value>
-    { };
-
-  template<typename _Iterator>
-    inline typename _Niter_base<_Iterator>::iterator_type
+    inline _Iterator
     __niter_base(_Iterator __it)
-    { return std::_Niter_base<_Iterator>::_S_base(__it); }
+    { return __it; }
 
   // Likewise, for move_iterator.
   template<typename _Iterator>
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 4a9189e..3aad9f3 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -390,7 +390,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     { return __y.base() - __x.base(); }
   //@}
 
-#if __cplusplus > 201103L
+#if __cplusplus == 201103L
+  template<typename _Iterator>
+    inline reverse_iterator<_Iterator>
+    __make_reverse_iterator(_Iterator __i)
+    { return reverse_iterator<_Iterator>(__i); }
+
+# define _GLIBCXX_MAKE_REVERSE_ITERATOR(_Iter) \
+  std::__make_reverse_iterator(_Iter)
+#elif __cplusplus > 201103L
 #define __cpp_lib_make_reverse_iterator 201402
 
   // _GLIBCXX_RESOLVE_LIB_DEFECTS
@@ -400,6 +408,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     inline reverse_iterator<_Iterator>
     make_reverse_iterator(_Iterator __i)
     { return reverse_iterator<_Iterator>(__i); }
+
+# define _GLIBCXX_MAKE_REVERSE_ITERATOR(_Iter) \
+  std::make_reverse_iterator(_Iter)
+#endif
+
+#if __cplusplus >= 201103L
+  template<typename _Iterator>
+    auto
+    __niter_base(reverse_iterator<_Iterator> __it)
+    -> decltype(_GLIBCXX_MAKE_REVERSE_ITERATOR(__niter_base(__it.base())))
+    { return _GLIBCXX_MAKE_REVERSE_ITERATOR(__niter_base(__it.base())); }
 #endif
 
   // 24.4.2.2.1 back_insert_iterator
@@ -979,6 +998,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace
 
+namespace std _GLIBCXX_VISIBILITY(default)
+{
+_GLIBCXX_BEGIN_NAMESPACE_VERSION
+
+  template<typename _Iterator, typename _Container>
+    _Iterator
+    __niter_base(__gnu_cxx::__normal_iterator<_Iterator, _Container> __it)
+    { return __it.base(); }
+
+_GLIBCXX_END_NAMESPACE_VERSION
+} // namespace
+
 #if __cplusplus >= 201103L
 
 namespace std _GLIBCXX_VISIBILITY(default)
@@ -1212,6 +1243,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   // @} group iterators
 
+  template<typename _Iterator>
+    auto
+    __niter_base(move_iterator<_Iterator> __it)
+    -> decltype(make_move_iterator(__niter_base(__it.base())))
+    { return make_move_iterator(__niter_base(__it.base())); }
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace