PR libstdc++/90920 restore previous checks for empty ranges

The change in r263433 broke the contract of the __rotate functions, by no
longer accepting empty ranges. That means that callers which inlined the
old version of std::rotate (without checks) that end up linking to a new
definition of std::__rotate (also without checks) could perform a divide
by zero and crash.

This restores the old contract of the __rotate overloads.

	PR libstdc++/90920 partially revert r263433
	* include/bits/stl_algo.h (__rotate): Restore checks for empty ranges.
	(rotate): Remove checks.
	* testsuite/25_algorithms/rotate/90920.cc: New test.

From-SVN: r272489

1 files changed, 48 insertions, 0 deletions

diff --git a/libstdc++-v3/testsuite/25_algorithms/rotate/90920.cc b/libstdc++-v3/testsuite/25_algorithms/rotate/90920.cc
new file mode 100644
index 00000000000..cae3ae748d8
--- /dev/null
+++ b/libstdc++-v3/testsuite/25_algorithms/rotate/90920.cc
@@ -0,0 +1,48 @@
+// Copyright (C) 2019 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-do run }
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+namespace gnu_test
+{
+  // This is the definition from GCC 8.x, with no checks for first==middle
+  // or middle==last.
+  template<typename _ForwardIterator>
+    inline _ForwardIterator
+    rotate(_ForwardIterator __first, _ForwardIterator __middle,
+	   _ForwardIterator __last)
+    {
+      return std::__rotate(__first, __middle, __last,
+			   std::__iterator_category(__first));
+    }
+}
+
+void
+test01()
+{
+  int i = 0;
+  gnu_test::rotate(&i, &i, &i+1);
+}
+
+int
+main()
+{
+  test01();
+}