libstdc++: Define __cpp_lib_execution feature test macro

This macro has never been defined by libstdc++, despite supporting the
parallel algorithms. It should have a different value for C++17 and
C++20, because P1001R2 should not be supported in C++17, but
unsequenced_policy is defined for C++17 (see PR p4702).

	* include/std/execution (__cpp_lib_execution): Define to indicate
	support for P0024R2 and P1001R2.
	* include/std/version (__cpp_lib_execution): Define.
	* testsuite/25_algorithms/pstl/feature_test.cc: Only test macro
	defined by <algorithm>, move other tests to new tests ...
	* testsuite/25_algorithms/pstl/feature_test-2.cc: New test.
	* testsuite/25_algorithms/pstl/feature_test-3.cc: New test.
	* testsuite/25_algorithms/pstl/feature_test-4.cc: New test.
	* testsuite/25_algorithms/pstl/feature_test-5.cc: New test.

libstdc++-v3/ChangeLog

 2020-04-22  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/execution (__cpp_lib_execution): Define to indicate
+	support for P0024R2 and P1001R2.
+	* include/std/version (__cpp_lib_execution): Define.
+	* testsuite/25_algorithms/pstl/feature_test.cc: Only test macro
+	defined by <algorithm>, move other tests to new tests ...
+	* testsuite/25_algorithms/pstl/feature_test-2.cc: New test.
+	* testsuite/25_algorithms/pstl/feature_test-3.cc: New test.
+	* testsuite/25_algorithms/pstl/feature_test-4.cc: New test.
+	* testsuite/25_algorithms/pstl/feature_test-5.cc: New test.
+
 	* include/bits/stl_iterator.h (__cpp_lib_array_constexpr): Define
 	different values for C++17 and C++20, to indicate different feature
 	sets. Update value for C++20 to indicate P1032R1 support.

libstdc++-v3/include/std/execution

@@ -50,6 +50,7 @@
 
 // Feature test macro for parallel algorithms
 # define __cpp_lib_parallel_algorithm 201603L
+# define __cpp_lib_execution 201902L
 
 #endif // C++17
 

libstdc++-v3/include/std/version

@@ -127,6 +127,7 @@
 #define __cpp_lib_clamp 201603
 #define __cpp_lib_constexpr_char_traits 201611
 #define __cpp_lib_enable_shared_from_this 201603
+#define __cpp_lib_execution 201902L // FIXME: should be 201603L
 #define __cpp_lib_filesystem 201703
 #define __cpp_lib_gcd 201606
 #define __cpp_lib_gcd_lcm 201606
@@ -188,6 +189,7 @@
 #define __cpp_lib_array_constexpr 201811L
 #define __cpp_lib_assume_aligned 201811L
 #define __cpp_lib_bind_front 201907L
+// FIXME: #define __cpp_lib_execution 201902L
 #define __cpp_lib_integer_comparison_functions 202002L
 #define __cpp_lib_constexpr_algorithms 201806L
 #define __cpp_lib_constexpr_complex 201711L

libstdc++-v3/testsuite/25_algorithms/pstl/feature_test-2.cc

+// Copyright (C) 2020 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++17" }
+// { dg-do preprocess { target c++17 } }
+
+#include <numeric>
+
+#ifndef __cpp_lib_parallel_algorithm
+# error "Feature-test macro for parallel algorithms missing in <numeric>"
+#elif __cpp_lib_parallel_algorithm != 201603L
+# error "Feature-test macro for parallel algorithms has wrong value in <numeric>"
+#endif

libstdc++-v3/testsuite/25_algorithms/pstl/feature_test-3.cc

+// Copyright (C) 2020 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++17" }
+// { dg-do preprocess { target c++17 } }
+
+#include <execution>
+
+#ifndef __cpp_lib_execution
+# error "Feature-test macro for execution policies is missing in <execution>"
+#elif __cpp_lib_execution != 201902L
+# error "Feature-test macro for parallel algorithms has wrong value in <execution>"
+#endif
+
+// Neither SD-6 nor C++20 requires this macro to be defined in <execution>.
+#ifndef __cpp_lib_parallel_algorithm
+# error "Feature-test macro for parallel algorithms missing in <execution>"
+#elif __cpp_lib_parallel_algorithm != 201603L
+# error "Feature-test macro for parallel algorithms has wrong value in <execution>"
+#endif

libstdc++-v3/testsuite/25_algorithms/pstl/feature_test-4.cc

+// Copyright (C) 2020 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++17" }
+// { dg-do preprocess { target c++17 } }
+
+#include <version>
+
+#ifndef __cpp_lib_parallel_algorithm
+# error "Feature-test macro for parallel algorithms missing in <version>"
+#elif __cpp_lib_parallel_algorithm != 201603L
+# error "Feature-test macro for parallel algorithms has wrong value in <version>"
+#endif
+
+#ifndef __cpp_lib_execution
+# error "Feature-test macro for execution policies is missing in <version>"
+#elif __cpp_lib_execution != 201902L
+# error "Feature-test macro for parallel algorithms has wrong value in <version>"
+#endif

libstdc++-v3/testsuite/25_algorithms/pstl/feature_test-5.cc

+// Copyright (C) 2020 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++17" }
+// { dg-do preprocess { target c++17 } }
+
+#include <memory>
+
+// Neither SD-6 nor C++20 requires this macro to be defined in <memory>.
+#ifndef __cpp_lib_parallel_algorithm
+# error "Feature-test macro for parallel algorithms missing in <memory>"
+#elif __cpp_lib_parallel_algorithm != 201603L
+# error "Feature-test macro for parallel algorithms has wrong value in <memory>"
+#endif

libstdc++-v3/testsuite/25_algorithms/pstl/feature_test.cc

@@ -19,32 +19,9 @@
 // { dg-do preprocess { target c++17 } }
 
 #include <algorithm>
+
 #ifndef __cpp_lib_parallel_algorithm
-# error "Feature-test macro for parallel algorithms missing"
+# error "Feature-test macro for parallel algorithms missing in <algorithm>"
 #elif __cpp_lib_parallel_algorithm != 201603L
 # error "Feature-test macro for parallel algorithms has wrong value in <algorithm>"
 #endif
-
-#include <numeric>
-#if __cpp_lib_parallel_algorithm != 201603L
-# error "Feature-test macro for parallel algorithms has wrong value in <numeric>"
-#endif
-
-#include <version>
-#if __cpp_lib_parallel_algorithm != 201603L
-# error "Feature-test macro for parallel algorithms has wrong value in <version>"
-#endif
-
-// The N4810 draft does not require the macro to be defined in <execution>.
-#include <memory>
-#if __cpp_lib_parallel_algorithm != 201603L
-# error "Feature-test macro for parallel algorithms has wrong value in <memory>"
-#endif
-
-// The N4810 draft does not require the macro to be defined in <execution>.
-// Include this last, because it will trigger the inclusion of TBB headers,
-// which then include <memory>, so we need to have already checked <memory>.
-#include <execution>
-#if __cpp_lib_parallel_algorithm != 201603L
-# error "Feature-test macro for parallel algorithms has wrong value in <execution>"
-#endif