[gcc r16-1471] libstdc++: Implement layout_stride from mdspan.
Tomasz Kaminski
tkaminsk@gcc.gnu.org
Thu Jun 12 09:52:02 GMT 2025
https://gcc.gnu.org/g:4fc47a8913fdcc560f1da3b66916fd3c4ce25366
commit r16-1471-g4fc47a8913fdcc560f1da3b66916fd3c4ce25366
Author: Luc Grosheintz <luc.grosheintz@gmail.com>
Date: Wed Jun 4 16:58:51 2025 +0200
libstdc++: Implement layout_stride from mdspan.
Implements the remaining parts of layout_left and layout_right; and all
of layout_stride.
The implementation of layout_stride::mapping::is_exhaustive applies
the following change to the standard:
4266. layout_stride::mapping should treat empty mappings as exhaustive
https://cplusplus.github.io/LWG/issue4266
The preconditions for layout_stride(extents, strides) are not checked.
libstdc++-v3/ChangeLog:
* include/std/mdspan (layout_stride): New class.
* src/c++23/std.cc.in: Add layout_stride.
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Diff:
---
libstdc++-v3/include/std/mdspan | 249 ++++++++++++++++++++++++++++++++++++++-
libstdc++-v3/src/c++23/std.cc.in | 3 +-
2 files changed, 250 insertions(+), 2 deletions(-)
diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 8ab7a1a52fbe..fe182c35a558 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -415,6 +415,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
class mapping;
};
+ struct layout_stride
+ {
+ template<typename _Extents>
+ class mapping;
+ };
+
namespace __mdspan
{
template<typename _Tp>
@@ -508,7 +514,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Mapping>
concept __standardized_mapping = __mapping_of<layout_left, _Mapping>
- || __mapping_of<layout_right, _Mapping>;
+ || __mapping_of<layout_right, _Mapping>
+ || __mapping_of<layout_stride, _Mapping>;
// A tag type to create internal ctors.
class __internal_ctor
@@ -554,6 +561,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: mapping(__other.extents(), __mdspan::__internal_ctor{})
{ }
+ template<typename _OExtents>
+ requires is_constructible_v<extents_type, _OExtents>
+ constexpr explicit(extents_type::rank() > 0)
+ mapping(const layout_stride::mapping<_OExtents>& __other)
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { __glibcxx_assert(*this == __other); }
+
constexpr mapping&
operator=(const mapping&) noexcept = default;
@@ -684,6 +698,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
: mapping(__other.extents(), __mdspan::__internal_ctor{})
{ }
+ template<class _OExtents>
+ requires is_constructible_v<extents_type, _OExtents>
+ constexpr explicit(extents_type::rank() > 0)
+ mapping(const layout_stride::mapping<_OExtents>& __other) noexcept
+ : mapping(__other.extents(), __mdspan::__internal_ctor{})
+ { __glibcxx_assert(*this == __other); }
+
constexpr mapping&
operator=(const mapping&) noexcept = default;
@@ -756,6 +777,232 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
[[no_unique_address]] extents_type _M_extents{};
};
+ namespace __mdspan
+ {
+ template<typename M>
+ concept __mapping_alike = requires
+ {
+ requires __is_extents<typename M::extents_type>;
+ { M::is_always_strided() } -> same_as<bool>;
+ { M::is_always_exhaustive() } -> same_as<bool>;
+ { M::is_always_unique() } -> same_as<bool>;
+ bool_constant<M::is_always_strided()>::value;
+ bool_constant<M::is_always_exhaustive()>::value;
+ bool_constant<M::is_always_unique()>::value;
+ };
+
+ template<typename _Mapping>
+ constexpr typename _Mapping::index_type
+ __offset(const _Mapping& __m) noexcept
+ {
+ using _IndexType = typename _Mapping::index_type;
+ constexpr auto __rank = _Mapping::extents_type::rank();
+
+ if constexpr (__standardized_mapping<_Mapping>)
+ return 0;
+ else if (__empty(__m.extents()))
+ return 0;
+ else
+ {
+ auto __impl = [&__m]<size_t... _Counts>(index_sequence<_Counts...>)
+ { return __m(((void) _Counts, _IndexType(0))...); };
+ return __impl(make_index_sequence<__rank>());
+ }
+ }
+
+ template<typename _Mapping, typename... _Indices>
+ constexpr typename _Mapping::index_type
+ __linear_index_strides(const _Mapping& __m, _Indices... __indices)
+ noexcept
+ {
+ using _IndexType = typename _Mapping::index_type;
+ _IndexType __res = 0;
+ if constexpr (sizeof...(__indices) > 0)
+ {
+ auto __update = [&, __pos = 0u](_IndexType __idx) mutable
+ {
+ __res += __idx * __m.stride(__pos++);
+ };
+ (__update(__indices), ...);
+ }
+ return __res;
+ }
+ }
+
+ template<typename _Extents>
+ class layout_stride::mapping
+ {
+ public:
+ using extents_type = _Extents;
+ using index_type = typename extents_type::index_type;
+ using size_type = typename extents_type::size_type;
+ using rank_type = typename extents_type::rank_type;
+ using layout_type = layout_stride;
+
+ static_assert(__mdspan::__representable_size<extents_type, index_type>,
+ "The size of extents_type must be representable as index_type");
+
+ constexpr
+ mapping() noexcept
+ {
+ // The precondition is either statically asserted, or automatically
+ // satisfied because dynamic extents are zero-initialzied.
+ size_t __stride = 1;
+ for (size_t __i = extents_type::rank(); __i > 0; --__i)
+ {
+ _M_strides[__i - 1] = index_type(__stride);
+ __stride *= size_t(_M_extents.extent(__i - 1));
+ }
+ }
+
+ constexpr
+ mapping(const mapping&) noexcept = default;
+
+ template<__mdspan::__valid_index_type<index_type> _OIndexType>
+ constexpr
+ mapping(const extents_type& __exts,
+ span<_OIndexType, extents_type::rank()> __strides) noexcept
+ : _M_extents(__exts)
+ {
+ for (size_t __i = 0; __i < extents_type::rank(); ++__i)
+ _M_strides[__i] = index_type(as_const(__strides[__i]));
+ }
+
+ template<__mdspan::__valid_index_type<index_type> _OIndexType>
+ constexpr
+ mapping(const extents_type& __exts,
+ const array<_OIndexType, extents_type::rank()>& __strides)
+ noexcept
+ : mapping(__exts,
+ span<const _OIndexType, extents_type::rank()>(__strides))
+ { }
+
+ template<__mdspan::__mapping_alike _StridedMapping>
+ requires (is_constructible_v<extents_type,
+ typename _StridedMapping::extents_type>
+ && _StridedMapping::is_always_unique()
+ && _StridedMapping::is_always_strided())
+ constexpr explicit(!(
+ is_convertible_v<typename _StridedMapping::extents_type, extents_type>
+ && __mdspan::__standardized_mapping<_StridedMapping>))
+ mapping(const _StridedMapping& __other) noexcept
+ : _M_extents(__other.extents())
+ {
+ using _OIndexType = _StridedMapping::index_type;
+ using _OExtents = _StridedMapping::extents_type;
+
+ __glibcxx_assert(__mdspan::__offset(__other) == 0);
+ static_assert(__mdspan::__representable_size<_OExtents, index_type>,
+ "The size of StridedMapping::extents_type must be representable as"
+ " index_type");
+ if constexpr (cmp_greater(numeric_limits<_OIndexType>::max(),
+ numeric_limits<index_type>::max()))
+ __glibcxx_assert(!cmp_less(numeric_limits<index_type>::max(),
+ __other.required_span_size())
+ && "other.required_span_size() must be representable"
+ " as index_type");
+ if constexpr (extents_type::rank() > 0)
+ for (size_t __i = 0; __i < extents_type::rank(); ++__i)
+ _M_strides[__i] = index_type(__other.stride(__i));
+ }
+
+ constexpr mapping&
+ operator=(const mapping&) noexcept = default;
+
+ constexpr const extents_type&
+ extents() const noexcept { return _M_extents; }
+
+ constexpr array<index_type, extents_type::rank()>
+ strides() const noexcept
+ {
+ array<index_type, extents_type::rank()> __ret;
+ for (size_t __i = 0; __i < extents_type::rank(); ++__i)
+ __ret[__i] = _M_strides[__i];
+ return __ret;
+ }
+
+ constexpr index_type
+ required_span_size() const noexcept
+ {
+ if (__mdspan::__empty(_M_extents))
+ return 0;
+
+ index_type __ret = 1;
+ for (size_t __i = 0; __i < extents_type::rank(); ++__i)
+ __ret += (_M_extents.extent(__i) - 1) * _M_strides[__i];
+ return __ret;
+ }
+
+ template<__mdspan::__valid_index_type<index_type>... _Indices>
+ requires (sizeof...(_Indices) == extents_type::rank())
+ constexpr index_type
+ operator()(_Indices... __indices) const noexcept
+ {
+ return __mdspan::__linear_index_strides(*this,
+ static_cast<index_type>(__indices)...);
+ }
+
+ static constexpr bool
+ is_always_unique() noexcept { return true; }
+
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4266. layout_stride::mapping should treat empty mappings as exhaustive
+ static constexpr bool
+ is_always_exhaustive() noexcept
+ {
+ return (_Extents::rank() == 0) || __mdspan::__contains_zero(
+ __mdspan::__static_extents<extents_type>());
+ }
+
+ static constexpr bool
+ is_always_strided() noexcept { return true; }
+
+ static constexpr bool
+ is_unique() noexcept { return true; }
+
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 4266. layout_stride::mapping should treat empty mappings as exhaustive
+ constexpr bool
+ is_exhaustive() const noexcept
+ {
+ if constexpr (!is_always_exhaustive())
+ {
+ constexpr auto __rank = extents_type::rank();
+ auto __size = __mdspan::__fwd_prod(_M_extents, __rank);
+ if(__size > 0)
+ return __size == required_span_size();
+ }
+ return true;
+ }
+
+ static constexpr bool
+ is_strided() noexcept { return true; }
+
+ constexpr index_type
+ stride(rank_type __r) const noexcept { return _M_strides[__r]; }
+
+ template<__mdspan::__mapping_alike _OMapping>
+ requires ((extents_type::rank() == _OMapping::extents_type::rank())
+ && _OMapping::is_always_strided())
+ friend constexpr bool
+ operator==(const mapping& __self, const _OMapping& __other) noexcept
+ {
+ if (__self.extents() != __other.extents())
+ return false;
+ if constexpr (extents_type::rank() > 0)
+ for (size_t __i = 0; __i < extents_type::rank(); ++__i)
+ if (!cmp_equal(__self.stride(__i), __other.stride(__i)))
+ return false;
+ return __mdspan::__offset(__other) == 0;
+ }
+
+ private:
+ using _S_strides_t = typename __array_traits<index_type,
+ extents_type::rank()>::_Type;
+ [[no_unique_address]] extents_type _M_extents;
+ [[no_unique_address]] _S_strides_t _M_strides;
+ };
+
_GLIBCXX_END_NAMESPACE_VERSION
}
#endif
diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/std.cc.in
index 5af0f7ef5e2b..109f590f1d1f 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -1842,7 +1842,8 @@ export namespace std
using std::extents;
using std::layout_left;
using std::layout_right;
- // FIXME layout_*, default_accessor and mdspan
+ using std::layout_stride;
+ // FIXME layout_left_padded, layout_right_padded, default_accessor and mdspan
}
#endif
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