[gcc r16-3650] libstdc++: Adjust span/mdspan CTAD for P2781R9.
Tomasz Kaminski
tkaminsk@gcc.gnu.org
Mon Sep 8 07:41:27 GMT 2025
https://gcc.gnu.org/g:71711f8ac3af615fec197e4eb71d0bee8ef44a23
commit r16-3650-g71711f8ac3af615fec197e4eb71d0bee8ef44a23
Author: Luc Grosheintz <luc.grosheintz@gmail.com>
Date: Thu Sep 4 14:20:29 2025 +0200
libstdc++: Adjust span/mdspan CTAD for P2781R9.
A usecase for P2781R9 is more ergonomic creation of span and mdspan with
mixed static and dynamic extents, e.g.:
span(ptr, cw<3>)
extents(cw<3>, 5, cw<7>)
mdspan(ptr, cw<3>, 5, cw<7>)
should be deduced as:
span<..., 3>
extents<..., 3, dyn, 7>
mdspan<..., extents<..., 3, dyn, 7>>
The change required is to strip cv-qualifiers and references from
`_Tp::value`, because of:
template<_CwFixedValue _X, typename>
struct constant_wrapper : _CwOperators
{
static constexpr const auto& value = _X._M_data;
libstdc++-v3/ChangeLog:
* include/std/span (__integral_constant_like): Allow the member
`value` of a constant wrapping type to be a const reference of
an integer.
* testsuite/23_containers/mdspan/extents/misc.cc: Add test for
cw and constant_wrapper.
* testsuite/23_containers/mdspan/mdspan.cc: Ditto.
* testsuite/23_containers/span/deduction.cc: Ditto.
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
Diff:
---
libstdc++-v3/include/std/span | 3 ++-
.../testsuite/23_containers/mdspan/extents/misc.cc | 22 +++++++++++++++------
.../testsuite/23_containers/mdspan/mdspan.cc | 23 +++++++++++++++-------
.../testsuite/23_containers/span/deduction.cc | 20 ++++++++++++++++++-
4 files changed, 53 insertions(+), 15 deletions(-)
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index 44f9b36a7efe..f9aa3c77e8e1 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -480,7 +480,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
namespace __detail
{
template<typename _Tp>
- concept __integral_constant_like = is_integral_v<decltype(_Tp::value)>
+ concept __integral_constant_like =
+ is_integral_v<remove_cvref_t<decltype(_Tp::value)>>
&& !is_same_v<bool, remove_const_t<decltype(_Tp::value)>>
&& convertible_to<_Tp, decltype(_Tp::value)>
&& equality_comparable_with<_Tp, decltype(_Tp::value)>
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
index 8a43a682004d..94086653a745 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/extents/misc.cc
@@ -98,7 +98,7 @@ test_deduction(Extents... exts)
}
constexpr bool
-test_integral_constant_deduction()
+test_deduction_from_constant()
{
auto verify = [](auto actual, auto expected)
{
@@ -106,13 +106,23 @@ test_integral_constant_deduction()
VERIFY(actual == expected);
};
- constexpr auto c1 = std::integral_constant<size_t, 1>{};
- constexpr auto c2 = std::integral_constant<int, 2>{};
+ constexpr auto i1 = std::integral_constant<size_t, 1>{};
+ constexpr auto i2 = std::integral_constant<int, 2>{};
verify(std::extents(1), std::extents<size_t, dyn>{1});
- verify(std::extents(c1), std::extents<size_t, 1>{});
+ verify(std::extents(i1), std::extents<size_t, 1>{});
+ verify(std::extents(i2), std::extents<size_t, 2>{});
+ verify(std::extents(std::true_type{}, 2), std::dextents<size_t, 2>{1, 2});
+ verify(std::extents(std::false_type{}, 2), std::dextents<size_t, 2>{0, 2});
+
+#if __glibcxx_constant_wrapper
+ constexpr auto c2 = std::constant_wrapper<2>{};
+ verify(std::extents(c2), std::extents<size_t, 2>{});
+ verify(std::extents(1, c2), std::extents<size_t, dyn, 2>{1});
verify(std::extents(c2), std::extents<size_t, 2>{});
- verify(std::extents(c1, 2), std::extents<size_t, 1, dyn>{2});
+ verify(std::extents(1, c2), std::extents<size_t, dyn, 2>{1});
+ verify(std::extents(std::cw<true>, c2), std::extents<size_t, 1, 2>{});
+#endif
return true;
}
@@ -123,7 +133,7 @@ test_deduction_all()
test_deduction<1>(1);
test_deduction<2>(1.0, 2.0f);
test_deduction<3>(int(1), short(2), size_t(3));
- test_integral_constant_deduction();
+ test_deduction_from_constant();
return true;
}
diff --git a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
index bdfc6ebcf561..ca100b4f314a 100644
--- a/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
+++ b/libstdc++-v3/testsuite/23_containers/mdspan/mdspan.cc
@@ -280,7 +280,7 @@ test_from_pointer_and_shape()
}
constexpr bool
-test_from_pointer_and_integral_constant()
+test_from_pointer_and_constant()
{
std::array<double, 6> buffer{};
double * ptr = buffer.data();
@@ -292,12 +292,21 @@ test_from_pointer_and_integral_constant()
VERIFY(actual.extents() == expected.extents());
};
- auto c3 = std::integral_constant<int, 3>{};
- auto c6 = std::integral_constant<int, 6>{};
+ auto i3 = std::integral_constant<int, 3>{};
+ auto i6 = std::integral_constant<int, 6>{};
verify(std::mdspan(ptr, 6), std::extents(6));
- verify(std::mdspan(ptr, c6), std::extents(c6));
- verify(std::mdspan(ptr, 2, c3), std::extents(2, c3));
+ verify(std::mdspan(ptr, i6), std::extents(i6));
+ verify(std::mdspan(ptr, 2, i3), std::extents(2, i3));
+ verify(std::mdspan(ptr, std::true_type{}, i3), std::extents(1, i3));
+
+#if __glibcxx_constant_wrapper
+ auto c3 = std::constant_wrapper<3>{};
+ verify(std::mdspan(ptr, 2, c3), std::extents(2, i3));
+ verify(std::mdspan(ptr, 2, std::cw<3>), std::extents(2, i3));
+ verify(std::mdspan(ptr, std::cw<true>, std::cw<3>),
+ std::extents(std::cw<1>, i3));
+#endif
return true;
}
@@ -729,8 +738,8 @@ main()
test_from_pointer_and_shape();
static_assert(test_from_pointer_and_shape());
- test_from_pointer_and_integral_constant();
- static_assert(test_from_pointer_and_integral_constant());
+ test_from_pointer_and_constant();
+ static_assert(test_from_pointer_and_constant());
test_from_extents();
static_assert(test_from_extents());
diff --git a/libstdc++-v3/testsuite/23_containers/span/deduction.cc b/libstdc++-v3/testsuite/23_containers/span/deduction.cc
index c66db90222e6..e958ad5d6db0 100644
--- a/libstdc++-v3/testsuite/23_containers/span/deduction.cc
+++ b/libstdc++-v3/testsuite/23_containers/span/deduction.cc
@@ -82,5 +82,23 @@ test01()
static_assert( is_dynamic_span<int>(s12) );
std::span s13(a.data(), std::integral_constant<size_t, 3>{});
- static_assert( is_static_span<long, 3>(s13));
+ static_assert( is_static_span<long, 3>(s13) );
+
+ std::span s14(a.data(), true);
+ static_assert( is_dynamic_span<long>(s14) );
+
+ std::span s15(a.data(), std::true_type{});
+ static_assert( is_dynamic_span<long>(s15) );
+
+#if __glibcxx_constant_wrapper
+ auto c5 = std::constant_wrapper<5>{};
+ std::span s16(a.data(), c5);
+ static_assert( is_static_span<long, 5>(s16) );
+
+ std::span s17(a.data(), std::cw<4>);
+ static_assert( is_static_span<long, 4>(s17) );
+
+ std::span s18(a.data(), std::cw<true>);
+ static_assert( is_static_span<long, 1>(s18) );
+#endif
}
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