[PATCH] PR libstdc++/81912 make std::__iterator_category constexpr

[PATCH] PR libstdc++/81912 make std::__iterator_category constexpr

[Jonathan Wakely]

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We made the interator range access functions constexpr for C++17, but
didn't test it, and so didn't notice that std::__iterator_category
isn't constexpr. This fixes it, and improve tests a bit.

	PR libstdc++/81912
	* include/bits/stl_iterator_base_types.h (__iterator_category): Add
	constexpr for C++11 and later.
	* testsuite/24_iterators/container_access.cc: Add target selector.
	* testsuite/24_iterators/range_access.cc: Fix clause number in
	comment.
	* testsuite/24_iterators/range_access_cpp14.cc: Likewise.
	* testsuite/24_iterators/range_access_cpp17.cc: New.

Tested x86_64-linux, committed to trunk. Will backport to gcc-7-branch
too.

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commit b9061802f6c78de5182da956933754c9545c94e8
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Aug 21 11:48:52 2017 +0100

    PR libstdc++/81912 make std::__iterator_category constexpr
    
            PR libstdc++/81912
            * include/bits/stl_iterator_base_types.h (__iterator_category): Add
            constexpr for C++11 and later.
            * testsuite/24_iterators/container_access.cc: Add target selector.
            * testsuite/24_iterators/range_access.cc: Fix clause number in
            comment.
            * testsuite/24_iterators/range_access_cpp14.cc: Likewise.
            * testsuite/24_iterators/range_access_cpp17.cc: New.

diff --git a/libstdc++-v3/include/bits/stl_iterator_base_types.h b/libstdc++-v3/include/bits/stl_iterator_base_types.h
index 24ed016b91e..d2c36ed2ac3 100644
--- a/libstdc++-v3/include/bits/stl_iterator_base_types.h
+++ b/libstdc++-v3/include/bits/stl_iterator_base_types.h
@@ -200,7 +200,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    *  sugar for internal library use only.
   */
   template<typename _Iter>
-    inline typename iterator_traits<_Iter>::iterator_category
+    inline _GLIBCXX_CONSTEXPR
+    typename iterator_traits<_Iter>::iterator_category
     __iterator_category(const _Iter&)
     { return typename iterator_traits<_Iter>::iterator_category(); }
 
diff --git a/libstdc++-v3/testsuite/24_iterators/container_access.cc b/libstdc++-v3/testsuite/24_iterators/container_access.cc
index 7f60d2bda48..b8d0e80a2de 100644
--- a/libstdc++-v3/testsuite/24_iterators/container_access.cc
+++ b/libstdc++-v3/testsuite/24_iterators/container_access.cc
@@ -1,4 +1,4 @@
-// { dg-do run }
+// { dg-do run { target c++1z } }
 // { dg-options "-std=gnu++17" }
 
 // Copyright (C) 2015-2017 Free Software Foundation, Inc.
@@ -62,7 +62,6 @@ test03()
   static_assert(s == 3);
   constexpr auto e = std::empty(il3);
   static_assert(!e);
-
 }
 
 void
diff --git a/libstdc++-v3/testsuite/24_iterators/range_access.cc b/libstdc++-v3/testsuite/24_iterators/range_access.cc
index 6ae5499b0d8..5b978b630e1 100644
--- a/libstdc++-v3/testsuite/24_iterators/range_access.cc
+++ b/libstdc++-v3/testsuite/24_iterators/range_access.cc
@@ -17,7 +17,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// 24.6.5, range access [iterator.range]
+// C++ 2011 24.6.5, range access [iterator.range]
 
 #include <iterator>
 
diff --git a/libstdc++-v3/testsuite/24_iterators/range_access_cpp14.cc b/libstdc++-v3/testsuite/24_iterators/range_access_cpp14.cc
index 138b189aaa6..eb75d92a463 100644
--- a/libstdc++-v3/testsuite/24_iterators/range_access_cpp14.cc
+++ b/libstdc++-v3/testsuite/24_iterators/range_access_cpp14.cc
@@ -17,7 +17,7 @@
 // with this library; see the file COPYING3.  If not see
 // <http://www.gnu.org/licenses/>.
 
-// 24.6.5, range access [iterator.range]
+// C++ 2014 24.7, range access [iterator.range]
 
 #include <iterator>
 #include <vector>
diff --git a/libstdc++-v3/testsuite/24_iterators/range_access_cpp17.cc b/libstdc++-v3/testsuite/24_iterators/range_access_cpp17.cc
new file mode 100644
index 00000000000..1d5b0739007
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/range_access_cpp17.cc
@@ -0,0 +1,57 @@
+// { dg-do compile { target c++1z } }
+// { dg-options "-std=gnu++17" }
+
+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// C++ 2017 27.7, range access [iterator.range]
+
+#include <iterator>
+
+void
+test01()
+{
+  using std::reverse_iterator;
+  static int i[1];
+  static_assert(std::cbegin(i) == i);
+  static_assert(std::cend(i) == i+1);
+  static_assert(std::rbegin(i) == reverse_iterator<int*>(i+1));
+  static_assert(std::rend(i) == reverse_iterator<int*>(i));
+  static_assert(std::crbegin(i) == reverse_iterator<int*>(i+1));
+  static_assert(std::crend(i) == reverse_iterator<int*>(i));
+}
+
+void
+test02()
+{
+  static int i[] = { 1, 2 };
+  static_assert(std::distance(std::begin(i), std::end(i)) == 2);
+  static_assert(std::distance(std::cbegin(i), std::cend(i)) == 2);
+}
+
+void
+test03()
+{
+  using std::reverse_iterator;
+  static std::initializer_list<int> il{1};
+  static_assert(std::cbegin(il) == il.begin());
+  static_assert(std::cend(il) == il.end());
+  static_assert(std::rbegin(il) == reverse_iterator<const int*>(il.end()));
+  static_assert(std::rend(il) == reverse_iterator<const int*>(il.begin()));
+  static_assert(std::crbegin(il) == reverse_iterator<const int*>(il.end()));
+  static_assert(std::crend(il) == reverse_iterator<const int*>(il.begin()));
+}