[PATCH v2 02/10] libstdc++: Implement submdspan_canonicalize_slices. [PR110352]
Luc Grosheintz
luc.grosheintz@gmail.com
Thu Nov 20 19:05:49 GMT 2025
On 11/20/25 15:26, Tomasz Kaminski wrote:
> On Tue, Nov 18, 2025 at 3:32 PM Luc Grosheintz <luc.grosheintz@gmail.com>
> wrote:
>
>> Implements submdspan_canonicalize_slices as described in P3663 and adds
>> it to the std module.
>>
>> PR libstdc++/110352
>>
>> libstdc++-v3/ChangeLog:
>>
>> * include/std/mdspan (submdspan_canonicalize_slices): New
>> function.
>> * src/c++23/std.cc.in (submdspan_canonicalize_slices): Add.
>> *
>> testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc:
>> New test.
>> *
>> testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc:
>> New test.
>>
>> Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
>> ---
>>
> The implementation looks good, but has a lot of type checks are not needed:
> __valid_XXX concepts should not look into the types, as
> canonicalization guarantees that the
> argument has such types, so I would remove them and inline the few >0
> checks into the corresponding
> __assert_valid_index, and also rename the functions to just __valid_index.
> The standard specifies the requirements, because we need to describe what
> needs to be accepted by
> user defined mappings, and we just reuse them from Mandates, knowing that
> they describe more, that
> need to be checked. The assumption is that implementation will skip the
> ones that are already guaranteed.
The reason we have them is because there's a user-facing function
that accepts only canonicalized slices:
submdspan_mapping
I think this way things will break nicer when a user passes in non-
canonical collapsing index types, e.g. uint8_t or integral_constant.
Personally, I like the "safety net" it provides to users.
In fact, I read the standard as requiring that for non-canonical slices
calling submdspan_mapping should be ill-formed. The reasoning is:
1. The mapping passed to submdspan models sliceable-mapping.
2. "LayoutMapping models sliceable-mapping" is defined as "LayoutMapping
meets the sliceable layout mapping requirements".
3. A type M meets the sliceable layout mapping requirements if,
- the expression submdspan_mapping(m, invalid_slices...) is ill-formed
- ...
Admittedly, this is slightly odd because we have both:
- A type LayoutMapping satisfies sliceable-mapping
- A type LayoutMapping models sliceable-mapping
and the two mean different things. I don't know why we need the
satisfies version.
AFAICT, we're only allowed to pass a standardized mapping to
submdspan if it models sliceable-mapping. Hence, we must write
submdspan_mapping in such a way that it rejects non-canonical
slices. We do it like this:
template<__mdspan::__valid_canonical_slice_type<index_type>... _Slices>
requires (...)
friend constexpr auto
submdspan_mapping(const mapping& __mapping, _Slices... __slices);
Does this make any sense?
>
> Also, the P3663 paper added support to use any destructruturable type (auto
> [a, b] = slice) as slice type,
> so we should test for aggregates. So we should test for structures that do
> not have members. I have added
> some suggestions below.
>
> I would also add a single test (not covering all cases) for array<int, 2>.
>
>
> libstdc++-v3/include/std/mdspan | 199 ++++++++++++++++
>> libstdc++-v3/src/c++23/std.cc.in | 1 +
>> .../submdspan_canonicalize_slices.cc | 212 ++++++++++++++++++
>> .../submdspan_canonicalize_slices_neg.cc | 208 +++++++++++++++++
>> 4 files changed, 620 insertions(+)
>> create mode 100644
>> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
>> create mode 100644
>> libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
>>
>> diff --git a/libstdc++-v3/include/std/mdspan
>> b/libstdc++-v3/include/std/mdspan
>> index 0a49f24fd3f..70656bcdd01 100644
>> --- a/libstdc++-v3/include/std/mdspan
>> +++ b/libstdc++-v3/include/std/mdspan
>> @@ -33,20 +33,21 @@
>> #pragma GCC system_header
>> #endif
>>
>> #include <span>
>> #include <array>
>> #include <type_traits>
>> #include <utility>
>>
>> #if __cplusplus > 202302L
> Include `bit/version.h` before the headers,
> and use __glibcxx_submdspan to guard including a tuple.
>
>
>> #include <bits/align.h>
>> +#include <tuple>
>> #endif
>>
>> #define __glibcxx_want_mdspan
>> #define __glibcxx_want_aligned_accessor
>> #define __glibcxx_want_submdspan
>> #include <bits/version.h>
>>
>> #ifdef __glibcxx_mdspan
>>
>> namespace std _GLIBCXX_VISIBILITY(default)
>> @@ -819,20 +820,204 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> 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>());
>> }
>> }
>> +
>> +#ifdef __glibcxx_submdspan
>>
> I would preffer if would put this just before submdspan_canonical_slices,
> in single
> if def block. I.e. reopen namespace twice.
>
>> + template<typename _Tp>
>> + inline constexpr bool __is_strided_slice = false;
>>
> Here and below, constexpr variable are automatically inline.
>
>> +
>> + template<typename _OffsetType, typename _ExtentType, typename
>> _StrideType>
>> + inline constexpr bool __is_strided_slice<strided_slice<_OffsetType,
>> + _ExtentType, _StrideType>> = true;
>> +
>> + template<typename _IndexType, typename _OIndexType>
>> + consteval bool
>> + __is_representable_integer(_OIndexType __value)
>> + {
>>
> This is consteval function, so it always evalauted at compile time, so we
> do not need
> to do if constexpr check, so I think we can just say:
> return !std::cmp_less(__value, __min) && !std::cmp_greater(__value,
> __ma);
>
>
>> + constexpr auto __min = __gnu_cxx::__int_traits<_IndexType>::__min;
>> + constexpr auto __omin =
>> __gnu_cxx::__int_traits<_OIndexType>::__min;
>> + constexpr auto __max = __gnu_cxx::__int_traits<_IndexType>::__max;
>> + constexpr auto __omax =
>> __gnu_cxx::__int_traits<_OIndexType>::__max;
>> +
>> + if constexpr (std::cmp_less(__omin, __min))
>> + if(std::cmp_less(__value, __min))
>> + return false;
>> + if constexpr (std::cmp_greater(__omax, __max))
>> + if(std::cmp_greater(__value, __max))
>> + return false;
>> + return true;
>> + }
>> +
>> + template<typename _IndexType, typename _Slice>
>> + constexpr auto
>> + __canonical_index(_Slice&& __slice)
>> + {
>> + if constexpr (__detail::__integral_constant_like<_Slice>)
>> + {
>> +
>> static_assert(__is_representable_integer<_IndexType>(_Slice::value));
>> + static_assert(std::cmp_greater_equal(_Slice::value, 0));
>> + return std::cw<_IndexType(_Slice::value)>;
>> + }
>> + else
>> + return __index_type_cast<_IndexType>(std::move(__slice));
>> + }
>> +
>> + template<typename _Tp>
>> + inline constexpr bool __is_constant_wrapper = false;
>> +
>> + template<_CwFixedValue _Xv, typename _Tp>
>> + inline constexpr bool __is_constant_wrapper<constant_wrapper<_Xv,
>> _Tp>>
>> + = true;
>> +
>> + template<typename _Slice, typename _IndexType>
>> + concept __valid_canonical_index_type = same_as<_Slice, _IndexType>
>> + || (__is_constant_wrapper<_Slice>
>> + && same_as<typename _Slice::value_type, _IndexType>
>> + && (_Slice::value >= 0));
>> +
>> + template<typename _Slice, typename _IndexType>
>> + concept __valid_strided_slice_type = __is_strided_slice<_Slice>
>> + && __valid_canonical_index_type<typename _Slice::offset_type,
>> _IndexType>
>> + && __valid_canonical_index_type<typename _Slice::extent_type,
>> _IndexType>
>> + && __valid_canonical_index_type<typename _Slice::stride_type,
>> _IndexType>
>> + && (!(__is_constant_wrapper<typename _Slice::extent_type>
>> + && __is_constant_wrapper<typename _Slice::stride_type>)
>> + || (_Slice::stride_type::value > 0));
>> +
>> + template<typename _Slice, typename _IndexType>
>> + concept __valid_canonical_slice_type = same_as<_Slice, _IndexType>
>> + || same_as<_Slice, full_extent_t>
>> + || __valid_strided_slice_type<_Slice, _IndexType>
>> + || __valid_canonical_index_type<_Slice, _IndexType>;
>>
> Because the slices are canonicalized, we do not need to validate the types,
> (we know exactly what was produced), so I think we can simply remove this
> concept,
> and move relevant checks to corresponding __valid functions.
>
>> +
>> + template<typename _IndexType, typename _Slice>
>> + constexpr auto
>> + __slice_cast(_Slice&& __slice)
>> + {
>> + using _SliceType = remove_cvref_t<_Slice>;
>> + if constexpr (is_convertible_v<_SliceType, full_extent_t>)
>> + return static_cast<full_extent_t>(std::move(__slice));
>> + else if constexpr (is_convertible_v<_SliceType, _IndexType>)
>> + return __canonical_index<_IndexType>(std::move(__slice));
>> + else if constexpr (__is_strided_slice<_SliceType>)
>> + {
>> + auto __extent = __canonical_index<_IndexType>(
>> + std::move(__slice.extent));
>> + auto __offset = __canonical_index<_IndexType>(
>> + std::move(__slice.offset));
>> + if constexpr (is_same_v<decltype(__extent),
>> + constant_wrapper<_IndexType(0)>>)
>> + return strided_slice{
>> + .offset = __offset,
>> + .extent = __extent,
>> + .stride = cw<_IndexType(1)>
>> + };
>> + else
>> + return strided_slice{
>> + .offset = __offset,
>> + .extent = __extent,
>> + .stride = __canonical_index<_IndexType>(
>> + std::move(__slice.stride))
>> + };
>> + }
>> + else
>> + {
>> + auto [__sbegin, __send] = std::move(__slice);
>> + auto __offset =
>> __canonical_index<_IndexType>(std::move(__sbegin));
>> + auto __end = __canonical_index<_IndexType>(std::move(__send));
>> + return strided_slice{
>> + .offset = __offset,
>> + .extent = __canonical_index<_IndexType>(__end - __offset),
>> + .stride = cw<_IndexType(1)>
>> + };
>> + }
>> + }
>> +
>> + template<typename _IndexType, size_t _Extent, typename _OIndexType>
>> + constexpr void
>> + __assert_valid_index(const extents<_IndexType, _Extent>& __ext,
>> + const _OIndexType& __idx)
>>
> + {
>>
>
>
>> + if constexpr (__is_constant_wrapper<_OIndexType>
>> + && _Extent != dynamic_extent)
>>
> And the static_assert(_OIndexType::value) would be hre.
>
>> + static_assert(std::cmp_less_equal(_OIndexType::value,
>> _Extent));
>>
> We know that __value is of type _IndexType so we can just use <.
>
>> + else
>> + __glibcxx_assert(std::cmp_less_equal(
>> + static_cast<_IndexType>(__idx), __ext.extent(0)));
>>
> Same here.
>
>> + }
>> +
>> + template<typename _IndexType, size_t _Extent, typename _Slice>
>> + constexpr void
>> + __assert_valid_slice(const extents<_IndexType, _Extent>& __ext,
>> + const _Slice& __slice)
>> + {
>> + static_assert(__valid_canonical_slice_type<_Slice, _IndexType>);
The above looks pointless, but canonicalization doesn't produce valid
slice types, e.g. it's possible for a constant_wrapper to be out-of-range.
Therefore, to avoid having two concepts (and needing names for both), it
uses __valid_canonical_slice_type.
>> +
>> + if constexpr (__is_strided_slice<_Slice>)
>> + {
>> + if constexpr (!(__is_constant_wrapper<typename
>> _Slice::extent_type>
>> + && __is_constant_wrapper<typename
>> _Slice::stride_type>))
>> + __glibcxx_assert(__slice.extent == 0 || __slice.stride > 0);
>>
> Similar places static assert for concepts here.
>
>> +
>> + // DEVIATION: For empty slices, P3663r3 does not allow us to
>> check
>> + // that this is less than or equal to the k-th extent (at
>> runtime).
>> + // We're only allowed to check if __slice.offset,
>> __slice.extent
>> + // are constant wrappers and __ext is a static extent.
>> + __assert_valid_index(__ext, __slice.offset);
>> + __assert_valid_index(__ext, __slice.extent);
>>
> I would put them before looking into stride, so at beginning.
>
>> +
>> + if constexpr (__is_constant_wrapper<typename
>> _Slice::offset_type>
>> + && __is_constant_wrapper<typename _Slice::extent_type>
>> + && _Extent != dynamic_extent)
>> + static_assert(std::cmp_greater_equal(
>> + _Extent - _Slice::offset_type::value,
>> + _Slice::extent_type::value));
>> + else
>> + __glibcxx_assert(__ext.extent(0) - __slice.offset
>> + >= __slice.extent);
>> + }
>>
> The last else constexpr could be replaced with:
> if constexpr (!is_samve_v<_Slice, _FullExtents>)
> __assert_valid_index(__ext, __slice.offset);
> If it is not strided slice, or full_extent, it must be single index.
>
>> + else if constexpr (__is_constant_wrapper<_Slice>
>> + && _Extent != dynamic_extent)
>> + static_assert(std::cmp_less(_Slice::value, _Extent));
>> + else if constexpr (convertible_to<_Slice, _IndexType>)
>> + __glibcxx_assert(__slice < __ext.extent(0));
>> + }
>> +
>> + template<size_t _Index, typename _Extents>
>> + constexpr auto
>> + __extract_extent(const _Extents& __exts)
>> + {
>> + using _IndexType = typename _Extents::index_type;
>> + return extents<_IndexType, _Extents::static_extent(_Index)>{
>> + __exts.extent(_Index)};
>> + }
>> +
>> + template<typename _Extents, typename... _Slices>
>> + constexpr void
>> + __assert_valid_slices(const _Extents& __exts, const _Slices&...
>> __slices)
>> + {
>> + constexpr auto __rank = _Extents::rank();
>> + auto __impl = [&]<size_t... _Is>(index_sequence<_Is...>)
>> + {
>> + ((__assert_valid_slice(__extract_extent<_Is>(__exts),
>> + __slices...[_Is])),...);
>> + };
>> + __impl(make_index_sequence<__rank>());
>> + }
>> +#endif // __glibcxx_submdspan
>> }
>>
>> template<typename _Extents>
>> class layout_left::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;
>> @@ -2492,14 +2677,28 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> -> mdspan<_ElementType, typename _MappingType::extents_type,
>> typename _MappingType::layout_type>;
>>
>> template<typename _MappingType, typename _AccessorType>
>> mdspan(const typename _AccessorType::data_handle_type&, const
>> _MappingType&,
>> const _AccessorType&)
>> -> mdspan<typename _AccessorType::element_type,
>> typename _MappingType::extents_type,
>> typename _MappingType::layout_type, _AccessorType>;
>>
>> +#if __glibcxx_submdspan
>> + template<typename _IndexType, size_t... _Extents, typename... _Slices>
>> + requires (sizeof...(_Extents) == sizeof...(_Slices))
>> + constexpr auto
>> + submdspan_canonicalize_slices(const extents<_IndexType, _Extents...>&
>> __exts,
>> + _Slices... __raw_slices)
>> + {
>> + auto [...__slices]
>> + = make_tuple(__mdspan::__slice_cast<_IndexType>(__raw_slices)...);
>> + __mdspan::__assert_valid_slices(__exts, __slices...);
>> + return make_tuple(__slices...);
>> + }
>> +#endif // __glibcxx_submdspan
>> +
>> _GLIBCXX_END_NAMESPACE_VERSION
>> }
>> #endif
>> #endif
>> diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
>> std.cc.in
>> index dd458a230e6..63b3d183bf5 100644
>> --- a/libstdc++-v3/src/c++23/std.cc.in
>> +++ b/libstdc++-v3/src/c++23/std.cc.in
>> @@ -1874,20 +1874,21 @@ export namespace std
>> using std::aligned_accessor;
>> #endif
>> using std::mdspan;
>> #if __glibcxx_padded_layouts
>> using std::layout_left_padded;
>> using std::layout_right_padded;
>> using std::strided_slice;
>> using std::full_extent_t;
>> using std::full_extent;
>> using std::submdspan_mapping_result;
>> + using std::submdspan_canonicalize_slices;
>> #endif
>> // FIXME submdspan_extents, mdsubspan
>> }
>> #endif
>>
>> // 20.2 <memory>
>> export namespace std
>> {
>> using std::align;
>> using std::allocator;
>> diff --git
>> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
>> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
>> new file mode 100644
>> index 00000000000..1dec3548c1d
>> --- /dev/null
>> +++
>> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices.cc
>> @@ -0,0 +1,212 @@
>> +// { dg-do run { target c++26 } }
>> +#include <mdspan>
>> +
>> +#include <testsuite_hooks.h>
>> +#include <cstddef>
>> +#include <cstdint>
>> +
>> +constexpr size_t dyn = std::dynamic_extent;
>> +
>> +template<typename Extents, typename CInt>
>> + constexpr bool
>> + check_collapsing(Extents exts, CInt ci_raw)
>> + {
>> + using IndexType = typename Extents::index_type;
>> + auto ci_expected = std::cw<IndexType{ci_raw.value}>;
>> + auto [ci] = std::submdspan_canonicalize_slices(exts, ci_raw);
>> + static_assert(std::same_as<decltype(ci), decltype(ci_expected)>);
>> + VERIFY(std::cmp_equal(ci.value, ci_raw.value));
>> +
>> + auto [i] = std::submdspan_canonicalize_slices(exts, ci_raw.value);
>> + static_assert(std::same_as<decltype(i), IndexType>);
>> + VERIFY(std::cmp_equal(i, ci_raw.value));
>> + return true;
>> + }
>> +
>> +template<typename Extents>
>> + constexpr bool
>> + test_scalar(Extents exts)
>> + {
>> + using IndexType = typename Extents::index_type;
>> +
>> + check_collapsing(exts, std::cw<uint8_t{0}>);
>> + check_collapsing(exts, std::cw<IndexType{0}>);
>> +
>> + check_collapsing(exts, std::cw<uint8_t{4}>);
>> + check_collapsing(exts, std::cw<IndexType{4}>);
>> + return true;
>> + }
>> +
>> +constexpr bool
>> +test_scalar()
>> +{
>> + test_scalar(std::extents<int, dyn>{5});
>> + test_scalar(std::extents<int, 5>{});
>> + test_scalar(std::extents<unsigned int, dyn>{5});
>> + test_scalar(std::extents<unsigned int, 5>{});
>> + return true;
>> +}
>> +
>> +constexpr void
>> +assert_same(auto lhs, auto rhs)
>> +{
>> + static_assert(std::same_as<decltype(lhs), decltype(rhs)>);
>> + VERIFY(lhs == rhs);
>> +}
>> +
>> +template<template<typename, typename> typename Pair>
>> + constexpr bool
>> + test_pair(auto exts, auto cbegin, auto cend, auto coffset, auto cextent)
>> + {
>> + using IndexType = typename decltype(exts)::index_type;
>> + auto c1 = std::cw<IndexType{1}>;
>> +
>> + auto raw_cc = Pair{cbegin, cend};
>> + auto [cc] = std::submdspan_canonicalize_slices(exts, raw_cc);
>> + assert_same(cc.offset, coffset);
>> + assert_same(cc.extent, cextent);
>> + assert_same(cc.stride, c1);
>> +
>> + auto raw_cd = Pair{cbegin, cend.value};
>> + auto [cd] = std::submdspan_canonicalize_slices(exts, raw_cd);
>> + assert_same(cd.offset, coffset);
>> + assert_same(cd.extent, cextent.value);
>> + assert_same(cd.stride, c1);
>> +
>> + auto raw_dc = Pair{cbegin.value, cend};
>> + auto [dc] = std::submdspan_canonicalize_slices(exts, raw_dc);
>> + assert_same(dc.offset, coffset.value);
>> + assert_same(dc.extent, cextent.value);
>> + assert_same(dc.stride, c1);
>> +
>> + auto raw_dd = Pair{cbegin.value, cend.value};
>> + auto [dd] = std::submdspan_canonicalize_slices(exts, raw_dd);
>> + assert_same(dd.offset, coffset.value);
>> + assert_same(dd.extent, cextent.value);
>> + assert_same(dd.stride, c1);
>> + return true;
>> + }
>> +
>> +template<template<typename, typename> typename Pair>
>> + constexpr bool
>> + test_pair()
>> + {
>> + test_pair<Pair>(std::extents<int, dyn>{5}, std::cw<uint8_t{2}>,
>> + std::cw<uint8_t{5}>, std::cw<2>, std::cw<3>);
>> + test_pair<Pair>(std::extents<int, 5>{}, std::cw<uint8_t{2}>,
>> + std::cw<uint8_t{5}>, std::cw<2>, std::cw<3>);
>> + test_pair<Pair>(std::extents<int, 0>{}, std::cw<uint8_t{0}>,
>> + std::cw<uint8_t{0}>, std::cw<0>, std::cw<0>);
>> + test_pair<Pair>(std::extents<int, dyn>{0}, std::cw<uint8_t{0}>,
>> + std::cw<uint8_t{0}>, std::cw<0>, std::cw<0>);
>> + return true;
>> + }
>> +
>> +constexpr bool
>> +test_pair_all()
>> +{
>> + test_pair<std::pair>();
>> + test_pair<std::tuple>();
>>
> The new code support also usual aggregates, so please add a test for
> following:
> template<typename T, typename U>
> struct Aggregate {
> T t;
> U u;
> };
>
> It should work out of the box with the syntax you are using.
>
>
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_strided_slice(auto exts, auto co, auto ce, auto cs)
>> +{
>> + using IndexType = decltype(exts)::index_type;
>> +
>> + auto coffset = std::cw<IndexType{co.value}>;
>> + auto cextent = std::cw<IndexType{ce.value}>;
>> + auto cstride = std::cw<IndexType{cs.value}>;
>> +
>> + auto raw_ccc = std::strided_slice{co, ce, cs};
>> + auto [ccc] = std::submdspan_canonicalize_slices(exts, raw_ccc);
>> + assert_same(ccc.offset, coffset);
>> + assert_same(ccc.extent, cextent);
>> + assert_same(ccc.stride, cstride);
>> +
>> + auto raw_dcc = std::strided_slice{co.value, ce, cs};
>> + auto [dcc] = std::submdspan_canonicalize_slices(exts, raw_dcc);
>> + assert_same(dcc.offset, coffset.value);
>> + assert_same(dcc.extent, cextent);
>> + assert_same(dcc.stride, cstride);
>> +
>> + auto raw_cdc = std::strided_slice{co, ce.value, cs};
>> + auto [cdc] = std::submdspan_canonicalize_slices(exts, raw_cdc);
>> + assert_same(cdc.offset, coffset);
>> + assert_same(cdc.extent, cextent.value);
>> + assert_same(cdc.stride, cstride);
>> +
>> + auto raw_ccd = std::strided_slice{co, ce, cs.value};
>> + auto [ccd] = std::submdspan_canonicalize_slices(exts, raw_ccd);
>> + assert_same(ccd.offset, coffset);
>> + assert_same(ccd.extent, cextent);
>> + assert_same(ccd.stride, cstride.value);
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_strided_slice()
>> +{
>> + auto run = [](auto exts)
>> + {
>> + auto cs = std::cw<uint8_t{9}>;
>> + test_strided_slice(exts, std::cw<uint8_t{2}>, std::cw<uint8_t{3}>,
>> cs);
>> + test_strided_slice(exts, std::cw<uint8_t{0}>, std::cw<uint8_t{5}>,
>> cs);
>> + };
>> +
>> + run(std::extents<int, 5>{});
>> + run(std::extents<int, dyn>{5});
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_strided_slice_zero_extent(auto exts, auto cs)
>> +{
>> + using IndexType = typename decltype(exts)::index_type;
>> + auto c0 = std::cw<uint8_t{0}>;
>> + auto raw_ccc = std::strided_slice{c0, c0, cs};
>> + auto [ccc] = std::submdspan_canonicalize_slices(exts, raw_ccc);
>> + assert_same(ccc.stride, std::cw<IndexType{1}>);
>> +
>> + auto raw_ccd = std::strided_slice{c0, c0, cs.value};
>> + auto [ccd] = std::submdspan_canonicalize_slices(exts, raw_ccd);
>> + assert_same(ccd.stride, std::cw<IndexType{1}>);
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_strided_slice_zero_extent(auto exts)
>> +{
>> + test_strided_slice_zero_extent(exts, std::cw<uint8_t{0}>);
>> + test_strided_slice_zero_extent(exts, std::cw<uint8_t{9}>);
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_strided_slice_zero_extent()
>> +{
>> + test_strided_slice_zero_extent(std::extents<int, 0>{});
>> + test_strided_slice_zero_extent(std::extents<int, dyn>{0});
>> + test_strided_slice_zero_extent(std::extents<int, 5>{});
>> + test_strided_slice_zero_extent(std::extents<int, dyn>{5});
>> + return true;
>> +}
>> +
>> +constexpr bool
>> +test_all()
>> +{
>> + test_scalar();
>> + test_pair_all();
>> + test_strided_slice();
>> + test_strided_slice_zero_extent();
>> + return true;
>> +}
>> +
>> +int
>> +main()
>> +{
>> + test_all();
>> + static_assert(test_all());
>> + return 0;
>> +}
>> diff --git
>> a/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
>> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
>> new file mode 100644
>> index 00000000000..94bca183aa3
>> --- /dev/null
>> +++
>> b/libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_canonicalize_slices_neg.cc
>> @@ -0,0 +1,208 @@
>> +// { dg-do compile { target c++26 } }
>> +#include <mdspan>
>> +
>> +#include <cstdint>
>> +
>> +constexpr size_t dyn = std::dynamic_extent;
>> +
>> +constexpr auto dyn_empty = std::extents<int32_t, dyn>{0};
>> +constexpr auto sta_empty = std::extents<uint32_t, 0>{};
>> +
>> +constexpr auto dyn_uexts = std::extents<uint8_t, dyn>{5};
>> +constexpr auto sta_uexts = std::extents<uint16_t, 5>{5};
>> +constexpr auto dyn_sexts = std::extents<int8_t, dyn>{5};
>> +constexpr auto sta_sexts = std::extents<int16_t, 5>{5};
>> +
>> +constexpr bool
>> +test_rank_mismatch()
>> +{
>> + auto exts = std::extents(1);
>> + std::submdspan_canonicalize_slices(exts, 0, 0); // { dg-error "no
>> matching" }
>> + return true;
>> +}
>> +
>> +template<typename Int, typename Extents>
>> +constexpr bool
>> +test_under1(Int i1, Extents exts)
>> +{
>> + auto [s1] = std::submdspan_canonicalize_slices(exts, i1);
>> + return true;
>> +}
>> +
>> +static_assert(test_under1(-1, dyn_sexts)); // { dg-error "expansion of"
>> }
>> +static_assert(test_under1(-1, dyn_uexts)); // { dg-error "expansion of"
>> }
>> +static_assert(test_under1(-1, sta_sexts)); // { dg-error "expansion of"
>> }
>> +static_assert(test_under1(-1, sta_uexts)); // { dg-error "expansion of"
>> }
>> +
>> +static_assert(test_under1(std::cw<-1>, dyn_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under1(std::cw<-1>, dyn_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under1(std::cw<-1>, sta_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under1(std::cw<-1>, sta_uexts)); // { dg-error
>> "required from" }
>> +
>> +template<typename Int, typename Extents>
>> +constexpr bool
>> +test_over1(Int i1, Extents exts)
>> +{
>> + auto [s1] = std::submdspan_canonicalize_slices(exts, i1);
>> + return true;
>> +}
>> +
>> +static_assert(test_over1(0, dyn_empty)); // { dg-error "expansion of" }
>> +static_assert(test_over1(0, sta_empty)); // { dg-error "expansion of" }
>> +static_assert(test_over1(5, dyn_sexts)); // { dg-error "expansion of" }
>> +static_assert(test_over1(5, dyn_uexts)); // { dg-error "expansion of" }
>> +static_assert(test_over1(5, sta_sexts)); // { dg-error "expansion of" }
>> +static_assert(test_over1(5, sta_uexts)); // { dg-error "expansion of" }
>> +
>> +static_assert(test_over1(std::cw<0>, dyn_empty)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over1(std::cw<0>, sta_empty)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over1(std::cw<5>, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over1(std::cw<5>, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over1(std::cw<5>, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over1(std::cw<5>, sta_uexts)); // { dg-error
>> "expansion of" }
>> +
>> +template<typename Offset, typename Extent, typename Stride, typename
>> Extents>
>> + constexpr bool
>> + test_under2(Offset o, Extent e, Stride s, Extents exts)
>> + {
>> + std::submdspan_canonicalize_slices(exts, std::strided_slice{o, e, s});
>> + return true;
>> + }
>> +
>> +constexpr auto i8_1 = int8_t{1};
>> +
>> +static_assert(test_under2(-i8_1, 0, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, -i8_1, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, 1, -i8_1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(-i8_1, 0, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, -i8_1, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, 1, -i8_1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(-i8_1, 0, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, -i8_1, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, 1, -i8_1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(-i8_1, 0, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, -i8_1, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_under2(0, 1, -i8_1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +
>> +constexpr auto c_i8_m1 = std::cw<int8_t{-1}>;
>> +constexpr auto c_i16_m1 = std::cw<int16_t{-1}>;
>> +constexpr auto c_i64_m1 = std::cw<int64_t{-1}>;
>> +
>> +static_assert(test_under2(c_i8_m1, 0, 1, dyn_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, c_i16_m1, 1, dyn_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, 1, c_i64_m1, dyn_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(c_i8_m1, 0, 1, dyn_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, c_i16_m1, 1, dyn_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, 1, c_i64_m1, dyn_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(c_i8_m1, 0, 1, sta_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, c_i16_m1, 1, sta_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, 1, c_i64_m1, sta_uexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(c_i8_m1, 0, 1, sta_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, c_i16_m1, 1, sta_sexts)); // { dg-error
>> "required from" }
>> +static_assert(test_under2(0, 1, c_i64_m1, sta_sexts)); // { dg-error
>> "required from" }
>> +
>> +template<typename Offset, typename Extent, typename Stride, typename
>> Extents>
>> + constexpr bool
>> + test_over2(Offset o, Extent e, Stride s, Extents exts)
>> + {
>> + std::submdspan_canonicalize_slices(exts, std::strided_slice{o, e, s});
>> + return true;
>> + }
>> +
>> +constexpr auto i8_6 = int8_t{6};
>> +constexpr auto c_i8_6 = std::cw<int8_t{6}>;
>> +constexpr auto c2 = std::cw<2>;
>> +constexpr auto c4 = std::cw<4>;
>> +
>> +static_assert(test_over2(i8_6, 0, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, i8_6, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, 4, 0, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c_i8_6, 0, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, c_i8_6, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, 4, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, c4, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, c4, 1, dyn_uexts)); // { dg-error
>> "expansion of" }
>> +
>> +static_assert(test_over2(i8_6, 0, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, i8_6, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, 4, 0, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c_i8_6, 0, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, c_i8_6, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, 4, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, c4, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, c4, 1, dyn_sexts)); // { dg-error
>> "expansion of" }
>> +
>> +static_assert(test_over2(i8_6, 0, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, i8_6, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, 4, 0, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c_i8_6, 0, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, c_i8_6, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, 4, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, c4, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, c4, 1, sta_uexts)); // { dg-error
>> "expansion of" }
>> +
>> +static_assert(test_over2(i8_6, 0, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, i8_6, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, 4, 0, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c_i8_6, 0, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(0, c_i8_6, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, 4, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(2, c4, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +static_assert(test_over2(c2, c4, 1, sta_sexts)); // { dg-error
>> "expansion of" }
>> +
>> +// Checks the precondition: offset + extent <= exts.extent(0) for unsigned
>> +// index_type when offset + extent overflows.
>> +constexpr bool
>> +test_overflow1(auto o, auto e)
>> +{
>> + auto exts = std::extents<uint8_t, dyn>{255};
>> + auto slice = std::strided_slice{o, e, 1};
>> + std::submdspan_canonicalize_slices(exts, slice);
>> + return true;
>> +}
>> +
>> +static_assert(test_overflow1(128, 128)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow1(std::cw<128>, 128)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow1(128, std::cw<128>)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow1(std::cw<128>, std::cw<128>)); // { dg-error
>> "expansion of" }
>> +
>> +constexpr bool
>> +test_overflow2(auto b, auto e)
>> +{
>> + auto exts = std::extents<uint8_t, dyn>{255};
>> + auto slice = std::pair{b, e};
>> + std::submdspan_canonicalize_slices(exts, slice);
>> + return true;
>> +}
>> +
>> +static_assert(test_overflow2(5, 4)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow2(std::cw<5>, 4)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow2(5, std::cw<4>)); // { dg-error
>> "expansion of" }
>> +static_assert(test_overflow2(std::cw<5>, std::cw<4>)); // { dg-error
>> "expansion of" }
>> +
>> +constexpr auto u8_4 = uint8_t{4};
>> +constexpr auto u8_5 = uint8_t{5};
>> +static_assert(test_overflow2(u8_5, u8_4)); // {
>> dg-error "expansion of" }
>> +static_assert(test_overflow2(std::cw<u8_5>, u8_4)); // {
>> dg-error "expansion of" }
>> +static_assert(test_overflow2(u8_5, std::cw<u8_4>)); // {
>> dg-error "expansion of" }
>> +static_assert(test_overflow2(std::cw<u8_5>, std::cw<u8_4>)); // {
>> dg-error "expansion of" }
>> +
>> +constexpr bool
>> +test_invalid(auto e, auto s)
>> +{
>> + auto exts = std::extents(5);
>> + auto slice = std::strided_slice(0, e, s);
>> + std::submdspan_canonicalize_slices(exts, slice);
>> + return true;
>> +}
>> +
>> +static_assert(test_invalid(3, 0)); // { dg-error
>> "expansion of" }
>> +static_assert(test_invalid(3, std::cw<0>)); // { dg-error
>> "expansion of" }
>> +static_assert(test_invalid(3, std::cw<0>)); // { dg-error
>> "expansion of" }
>> +static_assert(test_invalid(std::cw<3>, std::cw<0>)); // { dg-error
>> "expansion of" }
>> +
>> +
>> +// { dg-prune-output "static assertion failed" }
>> +// { dg-prune-output "__glibcxx_assert_fail" }
>> +// { dg-prune-output "__glibcxx_assert" }
>> +// { dg-prune-output "non-constant condition" }
>> --
>> 2.51.2
>>
>>
>
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