libstdc++: Synchronize PSTL with upstream

This patch rebases the C++17 parallel algorithms implementation (pstl)
against the current upstream version, commit 843c12d.

This version does not currently include the recently added OpenMP
backend, that will be considered for a future version.

libstdc++-v3/ChangeLog:
	* include/pstl/algorithm_fwd.h: Synchronize with upstream.
	* include/pstl/algorithm_impl.h: Likewise.
	* include/pstl/execution_defs.h: Likewise.
	* include/pstl/execution_impl.h: Likewise.
	* include/pstl/glue_algorithm_impl.h: Likewise.
	* include/pstl/glue_execution_defs.h: Likewise.
	* include/pstl/glue_memory_impl.h: Likewise.
	* include/pstl/glue_numeric_impl.h: Likewise.
	* include/pstl/memory_impl.h: Likewise.
	* include/pstl/numeric_fwd.h: Likewise.
	* include/pstl/numeric_impl.h: Likewise.
	* include/pstl/parallel_backend.h: Likewise.
	* include/pstl/parallel_backend_serial.h: Likewise.
	* include/pstl/parallel_backend_tbb.h: Likewise.
	* include/pstl/parallel_impl.h: Likewise.
	* include/pstl/pstl_config.h: Likewise.
	* include/pstl/unseq_backend_simd.h: Likewise.
	* include/pstl/utils.h: Likewise.
	* testsuite/20_util/specialized_algorithms/pstl/uninitialized_construct.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/pstl/uninitialized_copy_move.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/pstl/uninitialized_fill_destroy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_merge/inplace_merge.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_merge/merge.cc: Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/copy_if.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/copy_move.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/fill.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/generate.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/is_partitioned.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/partition.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/partition_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/remove.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/remove_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/replace.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/replace_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/rotate.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/rotate_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/swap_ranges.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/transform_binary.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/transform_unary.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/unique.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_modifying_operations/unique_copy_equal.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/adjacent_find.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/all_of.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/any_of.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/count.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/equal.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/find.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/find_end.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/find_first_of.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/find_if.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/for_each.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/mismatch.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/none_of.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/nth_element.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/reverse.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/reverse_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_nonmodifying/search_n.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/includes.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/is_heap.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/is_sorted.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/lexicographical_compare.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/minmax_element.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/partial_sort.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/partial_sort_copy.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/set.cc:
	Likewise.
	* testsuite/25_algorithms/pstl/alg_sorting/sort.cc:
	Likewise.
	* testsuite/26_numerics/pstl/numeric_ops/adjacent_difference.cc:
	Likewise.
	* testsuite/26_numerics/pstl/numeric_ops/reduce.cc:
	Likewise.
	* testsuite/26_numerics/pstl/numeric_ops/scan.cc:
	Likewise.
	* testsuite/26_numerics/pstl/numeric_ops/transform_reduce.cc:
	Likewise.
	* testsuite/26_numerics/pstl/numeric_ops/transform_scan.cc:
	Likewise.
	* testsuite/util/pstl/test_utils.h:
	Likewise.

libstdc++-v3/include/pstl/execution_defs.h

@@ -22,88 +22,20 @@ inline namespace v1
 // 2.4, Sequential execution policy
 class sequenced_policy
 {
-  public:
-    // For internal use only
-    static constexpr std::false_type
-    __allow_unsequenced()
-    {
-        return std::false_type{};
-    }
-    static constexpr std::false_type
-    __allow_vector()
-    {
-        return std::false_type{};
-    }
-    static constexpr std::false_type
-    __allow_parallel()
-    {
-        return std::false_type{};
-    }
 };
 
 // 2.5, Parallel execution policy
 class parallel_policy
 {
-  public:
-    // For internal use only
-    static constexpr std::false_type
-    __allow_unsequenced()
-    {
-        return std::false_type{};
-    }
-    static constexpr std::false_type
-    __allow_vector()
-    {
-        return std::false_type{};
-    }
-    static constexpr std::true_type
-    __allow_parallel()
-    {
-        return std::true_type{};
-    }
 };
 
 // 2.6, Parallel+Vector execution policy
 class parallel_unsequenced_policy
 {
-  public:
-    // For internal use only
-    static constexpr std::true_type
-    __allow_unsequenced()
-    {
-        return std::true_type{};
-    }
-    static constexpr std::true_type
-    __allow_vector()
-    {
-        return std::true_type{};
-    }
-    static constexpr std::true_type
-    __allow_parallel()
-    {
-        return std::true_type{};
-    }
 };
 
 class unsequenced_policy
 {
-  public:
-    // For internal use only
-    static constexpr std::true_type
-    __allow_unsequenced()
-    {
-        return std::true_type{};
-    }
-    static constexpr std::true_type
-    __allow_vector()
-    {
-        return std::true_type{};
-    }
-    static constexpr std::false_type
-    __allow_parallel()
-    {
-        return std::false_type{};
-    }
 };
 
 // 2.8, Execution policy objects
@@ -135,7 +67,7 @@ struct is_execution_policy<__pstl::execution::unsequenced_policy> : std::true_ty
 {
 };
 
-#if _PSTL_CPP14_VARIABLE_TEMPLATES_PRESENT
+#if defined (_PSTL_CPP14_VARIABLE_TEMPLATES_PRESENT)
 template <class _Tp>
 constexpr bool is_execution_policy_v = __pstl::execution::is_execution_policy<_Tp>::value;
 #endif
@@ -155,6 +87,12 @@ using __enable_if_execution_policy =
     typename std::enable_if<__pstl::execution::is_execution_policy<typename std::decay<_ExecPolicy>::type>::value,
                             _Tp>::type;
 #endif
+
+template <class _IsVector>
+struct __serial_tag;
+template <class _IsVector>
+struct __parallel_tag;
+
 } // namespace __internal
 
 } // namespace __pstl

libstdc++-v3/include/pstl/execution_impl.h

@@ -20,140 +20,79 @@ namespace __pstl
 namespace __internal
 {
 
-using namespace __pstl::execution;
+template <typename _IteratorTag, typename... _IteratorTypes>
+using __are_iterators_of = std::conjunction<
+    std::is_base_of<_IteratorTag, typename std::iterator_traits<std::decay_t<_IteratorTypes>>::iterator_category>...>;
 
-/* predicate */
+template <typename... _IteratorTypes>
+using __are_random_access_iterators = __are_iterators_of<std::random_access_iterator_tag, _IteratorTypes...>;
 
-template <typename _Tp>
-std::false_type __lazy_and(_Tp, std::false_type)
-{
-    return std::false_type{};
-}
-
-template <typename _Tp>
-inline _Tp
-__lazy_and(_Tp __a, std::true_type)
-{
-    return __a;
-}
-
-template <typename _Tp>
-std::true_type __lazy_or(_Tp, std::true_type)
-{
-    return std::true_type{};
-}
-
-template <typename _Tp>
-inline _Tp
-__lazy_or(_Tp __a, std::false_type)
-{
-    return __a;
-}
-
-/* iterator */
-template <typename _IteratorType, typename... _OtherIteratorTypes>
-struct __is_random_access_iterator
-{
-    static constexpr bool value = __internal::__is_random_access_iterator<_IteratorType>::value &&
-                                  __internal::__is_random_access_iterator<_OtherIteratorTypes...>::value;
-    typedef std::integral_constant<bool, value> type;
-};
-
-template <typename _IteratorType>
-struct __is_random_access_iterator<_IteratorType>
-    : std::is_same<typename std::iterator_traits<_IteratorType>::iterator_category, std::random_access_iterator_tag>
+struct __serial_backend_tag
 {
 };
-
-/* policy */
-template <typename _Policy>
-struct __policy_traits
+struct __tbb_backend_tag
 {
 };
-
-template <>
-struct __policy_traits<sequenced_policy>
+struct __openmp_backend_tag
 {
-    typedef std::false_type allow_parallel;
-    typedef std::false_type allow_unsequenced;
-    typedef std::false_type allow_vector;
 };
 
-template <>
-struct __policy_traits<unsequenced_policy>
-{
-    typedef std::false_type allow_parallel;
-    typedef std::true_type allow_unsequenced;
-    typedef std::true_type allow_vector;
-};
+#if defined(_PSTL_PAR_BACKEND_TBB)
+using __par_backend_tag = __tbb_backend_tag;
+#elif defined(_PSTL_PAR_BACKEND_OPENMP)
+using __par_backend_tag = __openmp_backend_tag;
+#elif defined(_PSTL_PAR_BACKEND_SERIAL)
+using __par_backend_tag = __serial_backend_tag;
+#else
+#    error "A parallel backend must be specified";
+#endif
 
-template <>
-struct __policy_traits<parallel_policy>
+template <class _IsVector>
+struct __serial_tag
 {
-    typedef std::true_type allow_parallel;
-    typedef std::false_type allow_unsequenced;
-    typedef std::false_type allow_vector;
+    using __is_vector = _IsVector;
 };
 
-template <>
-struct __policy_traits<parallel_unsequenced_policy>
+template <class _IsVector>
+struct __parallel_tag
 {
-    typedef std::true_type allow_parallel;
-    typedef std::true_type allow_unsequenced;
-    typedef std::true_type allow_vector;
+    using __is_vector = _IsVector;
+    // backend tag can be change depending on
+    // TBB availability in the environment
+    using __backend_tag = __par_backend_tag;
 };
 
-template <typename _ExecutionPolicy>
-using __collector_t =
-    typename __internal::__policy_traits<typename std::decay<_ExecutionPolicy>::type>::__collector_type;
-
-template <typename _ExecutionPolicy>
-using __allow_vector =
-    typename __internal::__policy_traits<typename std::decay<_ExecutionPolicy>::type>::__allow_vector;
+template <class _IsVector, class... _IteratorTypes>
+using __tag_type = typename std::conditional<__internal::__are_random_access_iterators<_IteratorTypes...>::value,
+                                             __parallel_tag<_IsVector>, __serial_tag<_IsVector>>::type;
 
-template <typename _ExecutionPolicy>
-using __allow_unsequenced =
-    typename __internal::__policy_traits<typename std::decay<_ExecutionPolicy>::type>::__allow_unsequenced;
-
-template <typename _ExecutionPolicy>
-using __allow_parallel =
-    typename __internal::__policy_traits<typename std::decay<_ExecutionPolicy>::type>::__allow_parallel;
-
-template <typename _ExecutionPolicy, typename... _IteratorTypes>
-auto
-__is_vectorization_preferred(_ExecutionPolicy&& __exec)
-    -> decltype(__internal::__lazy_and(__exec.__allow_vector(),
-                                       typename __internal::__is_random_access_iterator<_IteratorTypes...>::type()))
+template <class... _IteratorTypes>
+__serial_tag</*_IsVector = */ std::false_type>
+__select_backend(__pstl::execution::sequenced_policy, _IteratorTypes&&...)
 {
-    return __internal::__lazy_and(__exec.__allow_vector(),
-                                  typename __internal::__is_random_access_iterator<_IteratorTypes...>::type());
+    return {};
 }
 
-template <typename _ExecutionPolicy, typename... _IteratorTypes>
-auto
-__is_parallelization_preferred(_ExecutionPolicy&& __exec)
-    -> decltype(__internal::__lazy_and(__exec.__allow_parallel(),
-                                       typename __internal::__is_random_access_iterator<_IteratorTypes...>::type()))
+template <class... _IteratorTypes>
+__serial_tag<__internal::__are_random_access_iterators<_IteratorTypes...>>
+__select_backend(__pstl::execution::unsequenced_policy, _IteratorTypes&&...)
 {
-    return __internal::__lazy_and(__exec.__allow_parallel(),
-                                  typename __internal::__is_random_access_iterator<_IteratorTypes...>::type());
+    return {};
 }
 
-template <typename __policy, typename... _IteratorTypes>
-struct __prefer_unsequenced_tag
+template <class... _IteratorTypes>
+__tag_type</*_IsVector = */ std::false_type, _IteratorTypes...>
+__select_backend(__pstl::execution::parallel_policy, _IteratorTypes&&...)
 {
-    static constexpr bool value = __internal::__allow_unsequenced<__policy>::value &&
-                                  __internal::__is_random_access_iterator<_IteratorTypes...>::value;
-    typedef std::integral_constant<bool, value> type;
-};
+    return {};
+}
 
-template <typename __policy, typename... _IteratorTypes>
-struct __prefer_parallel_tag
+template <class... _IteratorTypes>
+__tag_type<__internal::__are_random_access_iterators<_IteratorTypes...>, _IteratorTypes...>
+__select_backend(__pstl::execution::parallel_unsequenced_policy, _IteratorTypes&&...)
 {
-    static constexpr bool value = __internal::__allow_parallel<__policy>::value &&
-                                  __internal::__is_random_access_iterator<_IteratorTypes...>::value;
-    typedef std::integral_constant<bool, value> type;
-};
+    return {};
+}
 
 } // namespace __internal
 } // namespace __pstl