[patch] libstdc++/64646 fix 4-iterator overload of std::is_permutation

[Jonathan Wakely <jwakely at redhat dot com>]

Fix a past-the-end dereference in the new C++14 version of
is_permutation. This only affects C++14 mode, but fixes a new function
that exists entirely because it's meant to be safer than the C++98
version ... but it isn't safer if it goes past-the-end!

Tested x86_64-linux, committed to 4.9 and trunk.

commit dd920757d437ffa60a0f9b008e57507d4c8ee831
Author: redi <redi@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Sun Jan 18 16:31:06 2015 +0000

    	PR libstdc++/64646
    	* include/bits/stl_algo.h (__is_permutation): Also test for reaching
    	end of the second range.
    	* testsuite/25_algorithms/is_permutation/64646.cc: New.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@219821 138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/libstdc++-v3/include/bits/stl_algo.h b/libstdc++-v3/include/bits/stl_algo.h
index 3325b94..c27c092 100644
--- a/libstdc++-v3/include/bits/stl_algo.h
+++ b/libstdc++-v3/include/bits/stl_algo.h
@@ -3601,7 +3601,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // Efficiently compare identical prefixes:  O(N) if sequences
       // have the same elements in the same order.
-      for (; __first1 != __last1; ++__first1, ++__first2)
+      for (; __first1 != __last1 && __first2 != __last2;
+	  ++__first1, ++__first2)
 	if (!__pred(__first1, __first2))
 	  break;
 
diff --git a/libstdc++-v3/testsuite/25_algorithms/is_permutation/64646.cc b/libstdc++-v3/testsuite/25_algorithms/is_permutation/64646.cc
new file mode 100644
index 0000000..799a18c
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/is_permutation/64646.cc
@@ -0,0 +1,35 @@
+// Copyright (C) 2015 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/>.
+
+// { dg-options "-std=gnu++14" }
+
+#include <algorithm>
+#include <forward_list>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::forward_list<int> l1{0}, l2;
+  VERIFY( !std::is_permutation(l1.begin(), l1.end(), l2.begin(), l2.end()) );
+}
+
+int
+main()
+{
+  test01();
+}