On 09/12/24 13:08 +0100, Giuseppe D'Angelo wrote:
For PSTL, I've just chosen to port from is_trivial to the direct equivalent, as I'm really unsure about the meaning of the code.

Yeah, I'm not sure either.

I note that the code uses std::conjunction instead of the non-portable
__and_. std::conjunction is only available in C++17 and upstream PSTL
wants to be valid as C++14 too (and maybe even C++11). But upstream
doesn't want to use our non-portable __and_ either, so we're in a bit
of a bind.

The patch is fine as-is, but it's something we might want to revisit
in future.

Could I ask you to open an issue about std::is_trivial upstream:
https://github.com/oneapi-src/oneDPL/issues
If/when they fix it, we can consider aligning with their direction.
And that might resolve the question of which aspects of triviality are
really needed here.


--
Giuseppe D'Angelo

From a24a9495976a08f19df32dddf9b0e29661aca696 Mon Sep 17 00:00:00 2001
From: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
Date: Mon, 9 Dec 2024 02:06:25 +0100
Subject: [PATCH 2/6] libstdc++: pstl: port away from is_trivial

In preparation for the deprecation of is_trivial (P3247R2).
Unfortunately I am unable to fully understand what aspect of triviality
seems to matter for these algorithms, so I just ported is_trivial to its
direct equivalent (trivially copyable + trivially default
constructible.)

libstdc++-v3/ChangeLog:

        * include/pstl/algorithm_impl.h (__remove_elements): Port away
          from is_trivial.
        (__pattern_inplace_merge): Likewise.
        * include/pstl/glue_memory_impl.h (uninitialized_copy): Likewise.
        (uninitialized_copy_n): Likewise.
        (uninitialized_move): Likewise.
        (uninitialized_move_n): Likewise.
        (uninitialized_default_construct): Likewise.
        (uninitialized_default_construct_n): Likewise.
        (uninitialized_value_construct): Likewise.
        (uninitialized_value_construct_n): 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_modifying_operations/partition.cc: 
Likewise.

Signed-off-by: Giuseppe D'Angelo <giuseppe.dang...@kdab.com>
---
libstdc++-v3/include/pstl/algorithm_impl.h    |  9 +++++---
libstdc++-v3/include/pstl/glue_memory_impl.h  | 21 ++++++++++++-------
.../pstl/uninitialized_construct.cc           |  2 +-
.../pstl/uninitialized_copy_move.cc           |  2 +-
.../pstl/uninitialized_fill_destroy.cc        |  2 +-
.../alg_modifying_operations/partition.cc     | 13 ++++++++++--
6 files changed, 33 insertions(+), 16 deletions(-)

diff --git a/libstdc++-v3/include/pstl/algorithm_impl.h 
b/libstdc++-v3/include/pstl/algorithm_impl.h
index 1403b02280f..5b1cd201094 100644
--- a/libstdc++-v3/include/pstl/algorithm_impl.h
+++ b/libstdc++-v3/include/pstl/algorithm_impl.h
@@ -1297,7 +1297,8 @@ __remove_elements(__parallel_tag<_IsVector> __tag, 
_ExecutionPolicy&& __exec, _F
                    [](_ForwardIterator __x, _Tp* __z)
                    {
                        __internal::__invoke_if_else(
-                            std::is_trivial<_Tp>(), [&]() { *__z = 
std::move(*__x); },
+                            std::conjunction<std::is_trivially_copyable<_Tp>, 
std::is_trivially_default_constructible<_Tp>>(),
+                            [&]() { *__z = std::move(*__x); },
                            [&]() { ::new (std::addressof(*__z)) 
_Tp(std::move(*__x)); });
                    },
                    _IsVector{});
@@ -1310,7 +1311,8 @@ __remove_elements(__parallel_tag<_IsVector> __tag, 
_ExecutionPolicy&& __exec, _F
            [__result, __first](_Tp* __i, _Tp* __j)
            {
                __invoke_if_else(
-                    std::is_trivial<_Tp>(), [&]() { __brick_move(__i, __j, 
__first + (__i - __result), _IsVector{}); },
+                    std::conjunction<std::is_trivially_copyable<_Tp>, 
std::is_trivially_default_constructible<_Tp>>(),
+                    [&]() { __brick_move(__i, __j, __first + (__i - __result), 
_IsVector{}); },
                    [&]() { __brick_move_destroy()(__i, __j, __first + (__i - 
__result), _IsVector{}); });
            });
        return __first + __m;
@@ -2794,7 +2796,8 @@ __pattern_inplace_merge(__parallel_tag<_IsVector> __tag, 
_ExecutionPolicy&& __ex
            auto __move_values = [](_RandomAccessIterator __x, _Tp* __z)
            {
                __internal::__invoke_if_else(
-                    std::is_trivial<_Tp>(), [&]() { *__z = std::move(*__x); },
+                    std::conjunction<std::is_trivially_copyable<_Tp>, 
std::is_trivially_default_constructible<_Tp>>(),
+                    [&]() { *__z = std::move(*__x); },
                    [&]() { ::new (std::addressof(*__z)) _Tp(std::move(*__x)); 
});
            };

diff --git a/libstdc++-v3/include/pstl/glue_memory_impl.h 
b/libstdc++-v3/include/pstl/glue_memory_impl.h
index 7850605f94a..0f37fbbf214 100644
--- a/libstdc++-v3/include/pstl/glue_memory_impl.h
+++ b/libstdc++-v3/include/pstl/glue_memory_impl.h
@@ -34,7 +34,8 @@ uninitialized_copy(_ExecutionPolicy&& __exec, _InputIterator 
__first, _InputIter
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    return __pstl::__internal::__invoke_if_else(
-        std::integral_constant < bool, std::is_trivial<_ValueType1>::value&& 
std::is_trivial<_ValueType2>::value > (),
+        std::conjunction<std::is_trivially_copyable<_ValueType1>, 
std::is_trivially_default_constructible<_ValueType1>,
+                         std::is_trivially_copyable<_ValueType2>, 
std::is_trivially_default_constructible<_ValueType2>>(),
        [&]()
        {
            return __pstl::__internal::__pattern_walk2_brick(
@@ -65,7 +66,8 @@ uninitialized_copy_n(_ExecutionPolicy&& __exec, 
_InputIterator __first, _Size __
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    return __pstl::__internal::__invoke_if_else(
-        std::integral_constant < bool, std::is_trivial<_ValueType1>::value&& 
std::is_trivial<_ValueType2>::value > (),
+        std::conjunction<std::is_trivially_copyable<_ValueType1>, 
std::is_trivially_default_constructible<_ValueType1>,
+                         std::is_trivially_copyable<_ValueType2>, 
std::is_trivially_default_constructible<_ValueType2>>(),
        [&]()
        {
            return __pstl::__internal::__pattern_walk2_brick_n(
@@ -98,7 +100,8 @@ uninitialized_move(_ExecutionPolicy&& __exec, _InputIterator 
__first, _InputIter
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    return __pstl::__internal::__invoke_if_else(
-        std::integral_constant < bool, std::is_trivial<_ValueType1>::value&& 
std::is_trivial<_ValueType2>::value > (),
+        std::conjunction<std::is_trivially_copyable<_ValueType1>, 
std::is_trivially_default_constructible<_ValueType1>,
+                         std::is_trivially_copyable<_ValueType2>, 
std::is_trivially_default_constructible<_ValueType2>>(),
        [&]()
        {
            return __pstl::__internal::__pattern_walk2_brick(
@@ -129,7 +132,8 @@ uninitialized_move_n(_ExecutionPolicy&& __exec, 
_InputIterator __first, _Size __
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    return __pstl::__internal::__invoke_if_else(
-        std::integral_constant < bool, std::is_trivial<_ValueType1>::value&& 
std::is_trivial<_ValueType2>::value > (),
+        std::conjunction<std::is_trivially_copyable<_ValueType1>, 
std::is_trivially_default_constructible<_ValueType1>,
+                         std::is_trivially_copyable<_ValueType2>, 
std::is_trivially_default_constructible<_ValueType2>>(),
        [&]()
        {
            return __pstl::__internal::__pattern_walk2_brick_n(
@@ -254,7 +258,7 @@ uninitialized_default_construct(_ExecutionPolicy&& __exec, 
_ForwardIterator __fi

    auto __dispatch_tag = __pstl::__internal::__select_backend(__exec, __first);

-    __pstl::__internal::__invoke_if_not(std::is_trivial<_ValueType>(),
+    
__pstl::__internal::__invoke_if_not(std::conjunction<std::is_trivially_copyable<_ValueType>,
 std::is_trivially_default_constructible<_ValueType>>(),
                                        [&]()
                                        {
                                            __pstl::__internal::__pattern_walk1(
@@ -273,7 +277,8 @@ uninitialized_default_construct_n(_ExecutionPolicy&& 
__exec, _ForwardIterator __
    auto __dispatch_tag = __pstl::__internal::__select_backend(__exec, __first);

    return __pstl::__internal::__invoke_if_else(
-        std::is_trivial<_ValueType>(), [&]() { return std::next(__first, __n); 
},
+        std::conjunction<std::is_trivially_copyable<_ValueType>, 
std::is_trivially_default_constructible<_ValueType>>(),
+        [&]() { return std::next(__first, __n); },
        [&]()
        {
            return __pstl::__internal::__pattern_walk1_n(
@@ -296,7 +301,7 @@ uninitialized_value_construct(_ExecutionPolicy&& __exec, 
_ForwardIterator __firs
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    __pstl::__internal::__invoke_if_else(
-        std::is_trivial<_ValueType>(),
+        std::conjunction<std::is_trivially_copyable<_ValueType>, 
std::is_trivially_default_constructible<_ValueType>>(),
        [&]()
        {
            __pstl::__internal::__pattern_walk_brick(
@@ -324,7 +329,7 @@ uninitialized_value_construct_n(_ExecutionPolicy&& __exec, 
_ForwardIterator __fi
    using __is_vector = typename decltype(__dispatch_tag)::__is_vector;

    return __pstl::__internal::__invoke_if_else(
-        std::is_trivial<_ValueType>(),
+        std::conjunction<std::is_trivially_copyable<_ValueType>, 
std::is_trivially_default_constructible<_ValueType>>(),
        [&]()
        {
            return __pstl::__internal::__pattern_walk_brick_n(
diff --git 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_construct.cc
 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_construct.cc
index 407e4885327..0bc1e3266d9 100644
--- 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_construct.cc
+++ 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_construct.cc
@@ -108,7 +108,7 @@ test_uninit_construct_by_type()
    for (size_t n = 0; n <= N; n = n <= 16 ? n + 1 : size_t(3.1415 * n))
    {
        std::unique_ptr<T[]> p(new T[n]);
-        invoke_on_all_policies(test_uninit_construct(), p.get(), std::next(p.get(), 
n), n, std::is_trivial<T>());
+        invoke_on_all_policies(test_uninit_construct(), p.get(), std::next(p.get(), n), n, 
std::conjunction<std::is_trivially_copyable<T>, 
std::is_trivially_default_constructible<T>>());
    }
}

diff --git 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_copy_move.cc
 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_copy_move.cc
index 2558147a7f1..38c1bf136df 100644
--- 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_copy_move.cc
+++ 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_copy_move.cc
@@ -128,7 +128,7 @@ test_uninitialized_copy_move_by_type()
    {
        Sequence<T> in(n, [=](size_t k) -> T { return T(k); });
        std::unique_ptr<T[]> p(new T[n]);
-        invoke_on_all_policies(test_uninitialized_copy_move(), in.begin(), in.end(), 
p.get(), n, std::is_trivial<T>());
+        invoke_on_all_policies(test_uninitialized_copy_move(), in.begin(), in.end(), p.get(), n, 
std::conjunction<std::is_trivially_copyable<T>, 
std::is_trivially_default_constructible<T>>());
    }
}

diff --git 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_fill_destroy.cc
 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_fill_destroy.cc
index fed9bdb8886..dfadb554a11 100644
--- 
a/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_fill_destroy.cc
+++ 
b/libstdc++-v3/testsuite/20_util/specialized_algorithms/pstl/uninitialized_fill_destroy.cc
@@ -83,7 +83,7 @@ test_uninitialized_fill_destroy_by_type()
    {
        std::unique_ptr<T[]> p(new T[n]);
        invoke_on_all_policies(test_uninitialized_fill_destroy(), p.get(), 
std::next(p.get(), n), T(), n,
-                               std::is_trivial<T>());
+                               std::conjunction<std::is_trivially_copyable<T>, 
std::is_trivially_default_constructible<T>>());
    }
}

diff --git 
a/libstdc++-v3/testsuite/25_algorithms/pstl/alg_modifying_operations/partition.cc
 
b/libstdc++-v3/testsuite/25_algorithms/pstl/alg_modifying_operations/partition.cc
index e13fe938d1f..58979bac2b0 100644
--- 
a/libstdc++-v3/testsuite/25_algorithms/pstl/alg_modifying_operations/partition.cc
+++ 
b/libstdc++-v3/testsuite/25_algorithms/pstl/alg_modifying_operations/partition.cc
@@ -57,15 +57,24 @@ struct DataType
    T my_val;
};

+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
+// is_trivial is deprecated in C++26
template <typename Iterator>
-typename std::enable_if<std::is_trivial<typename 
std::iterator_traits<Iterator>::value_type>::value, bool>::type
+using iterator_value_type_is_trivial = std::is_trivial<
+    typename std::iterator_traits<Iterator>::value_type
+>;
+#pragma GCC diagnostic pop
+
+template <typename Iterator>
+typename std::enable_if<iterator_value_type_is_trivial<Iterator>::value, 
bool>::type
is_equal(Iterator first, Iterator last, Iterator d_first)
{
    return std::equal(first, last, d_first);
}

template <typename Iterator>
-typename std::enable_if<!std::is_trivial<typename 
std::iterator_traits<Iterator>::value_type>::value, bool>::type
+typename std::enable_if<!iterator_value_type_is_trivial<Iterator>::value, 
bool>::type
    is_equal(Iterator, Iterator, Iterator)
{
    return true;
--
2.34.1




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