Implement the <tuple> part of C++20 p1032 Misc constexpr bits.

2019-11-15  Edward Smith-Rowland  <3dw4rd@verizon.net>

	Implement the <tuple> part of C++20 p1032 Misc constexpr bits.
	* include/std/tuple (_Head_base, _Tuple_impl(allocator_arg_t,...)
	(_M_assign, tuple(allocator_arg_t,...), _Inherited, operator=, _M_swap)
	(swap, pair(piecewise_construct_t,): Constexpr.
	* (__uses_alloc0::_Sink::operator=, __uses_alloc_t): Constexpr.
	* testsuite/20_util/tuple/cons/constexpr_allocator_arg_t.cc: New test.
	* testsuite/20_util/tuple/constexpr_swap.cc : New test.
	* testsuite/20_util/uses_allocator/69293_neg.cc: Extra error for C++20.
	* testsuite/20_util/uses_allocator/cons_neg.cc: : Extra error for C++20.

From-SVN: r278331

libstdc++-v3/ChangeLog

+2019-11-15  Edward Smith-Rowland  <3dw4rd@verizon.net>
+
+	Implement the <tuple> part of C++20 p1032 Misc constexpr bits.
+	* include/std/tuple (_Head_base, _Tuple_impl(allocator_arg_t,...)
+	(_M_assign, tuple(allocator_arg_t,...), _Inherited, operator=, _M_swap)
+	(swap, pair(piecewise_construct_t,): Constexpr.
+	* (__uses_alloc0::_Sink::operator=, __uses_alloc_t): Constexpr.
+	* testsuite/20_util/tuple/cons/constexpr_allocator_arg_t.cc: New test.
+	* testsuite/20_util/tuple/constexpr_swap.cc : New test.
+	* testsuite/20_util/uses_allocator/69293_neg.cc: Extra error for C++20.
+	* testsuite/20_util/uses_allocator/cons_neg.cc: : Extra error for C++20.
+
 2019-11-15  Jonathan Wakely  <jwakely@redhat.com>
 
 	* include/std/stop_token: Reduce header dependencies by including

libstdc++-v3/testsuite/20_util/tuple/cons/constexpr_allocator_arg_t.cc

+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+//
+// 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/>.
+
+#include <memory>
+#include <tuple>
+
+const std::allocator<int> alloc{};
+
+constexpr bool
+test_tuple()
+{
+  auto ok = true;
+
+  std::tuple<int, double, double> ta(std::allocator_arg, alloc);
+  std::tuple<int, double, double> tb(std::allocator_arg, alloc, 0, 3.456, 6.789);
+  std::tuple<int, double, double> tc(std::allocator_arg, alloc, 0, 3.456f, 6.789f);
+  std::tuple<int, double, double> td(std::allocator_arg, alloc, tb);
+  std::tuple<int, double, double> te(std::allocator_arg, alloc, std::move(tb));
+
+  std::tuple<int, float, float> tf(std::allocator_arg, alloc, 0, 3.456f, 6.789f);
+  std::tuple<int, double, double> tg(std::allocator_arg, alloc, tf);
+  std::tuple<int, double, double> th(std::allocator_arg, alloc, std::move(tf));
+
+  std::pair<int, float> pf(12, 3.142f);
+  std::tuple<int, double> ti(std::allocator_arg, alloc, pf);
+  std::tuple<int, double> tj(std::allocator_arg, alloc, std::move(pf));
+
+  return ok;
+}
+
+static_assert(test_tuple());

libstdc++-v3/testsuite/20_util/tuple/constexpr_swap.cc

+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+//
+// 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/>.
+
+#include <tuple>
+
+constexpr bool
+test_tuple()
+{
+  auto ok = true;
+
+  std::tuple<int, double, double> t1(1, 3.1415, 2.7182);
+  std::tuple<int, double, double> t2(1, 4.1234, 3.3333);
+  t1.swap(t2);
+  std::swap(t1, t2);
+
+  return ok;
+}
+
+static_assert(test_tuple());

libstdc++-v3/testsuite/20_util/uses_allocator/69293_neg.cc

@@ -45,4 +45,5 @@ test01()
   alloc_type a;
   std::tuple<X> t(std::allocator_arg, a); // this is required to be ill-formed
   // { dg-error "failed: .* uses_allocator is true" "" { target *-*-* } 0 }
+  // { dg-error "no matching function for call" "" { target c++2a } 0 }
 }

libstdc++-v3/testsuite/20_util/uses_allocator/cons_neg.cc

@@ -44,3 +44,4 @@ void test01()
   tuple<Type> t(allocator_arg, a, 1);
 }
 // { dg-error "failed: .* uses_allocator is true" "" { target *-*-* } 0 }
+// { dg-error "no matching function for call" "" { target c++2a } 0 }