[PATCH v1 0/6] libstdc++: submdspan for layout_{left,right,stride}.

[Luc Grosheintz]

Hi Tomasz,

I've finished submdspan for the padded layouts. Essentially,
it can reuse everything that's already here. There's a few
small changes.

Do you want to first review v1; or should a immediately
replace it with v2?

Thank you,
Luc


On 11/14/25 15:09, Luc Grosheintz wrote:
> This sequence of 6 patches implements submdspan for layout_left,
> layout_right and layout_stride.
> 
> The first commit is preparatory (move code, generalize code
> and fix some formatting issues). Then, each commit implements:
> 
>    - submdspan_canonicalize_slices,
>    - submdspan_extents (with review comments on previous patch),
>    - submdspan_mapping: layout_left, layout_right, layout_stride.
> 
> There's one deviation related to checking:
> 
>    0 <= slice_begin[k] <= slice_end[k] <= exts.extent(k)
> 
> explained in detail in the corresponding commit message.
> 
> The check that if slice_begin[k] == exts.extent(k) when computing the
> offset, adds a "chunk of code" that's not needed and blocks certain
> optimizations. The corresponding commit message has more details.
> 
> Luc Grosheintz (6):
>    libstdc++: Prepare mdspan-related code for submdspan.
>    libstdc++: Implement submdspan_canonicalize_slices. [PR110352]
>    libstdc++: Implement submdspan_extents. [PR110352]
>    libstdc++: Implement submdspan and submdspan_mapping for layout_left.
>      [PR110352]
>    libstdc++: Implement submdspan_mapping for layout_right. [PR110352]
>    libstdc++: Implement submdspan_mapping for layout_stride. [PR110352]
> 
>   libstdc++-v3/include/std/mdspan               | 841 +++++++++++++++++-
>   libstdc++-v3/src/c++23/std.cc.in              |   6 +-
>   .../testsuite/23_containers/mdspan/int_like.h |  34 +-
>   .../padded_traits.h => layout_traits.h}       |  65 +-
>   .../23_containers/mdspan/layouts/ctors.cc     |   2 +-
>   .../23_containers/mdspan/layouts/mapping.cc   |   2 +-
>   .../23_containers/mdspan/layouts/padded.cc    |   2 +-
>   .../mdspan/layouts/padded_neg.cc              |   2 +-
>   .../mdspan/submdspan/submdspan.cc             | 371 ++++++++
>   .../submdspan_canonicalize_slices.cc          | 212 +++++
>   .../submdspan_canonicalize_slices_neg.cc      | 208 +++++
>   .../mdspan/submdspan/submdspan_extents.cc     | 169 ++++
>   .../mdspan/submdspan/submdspan_extents_neg.cc |  48 +
>   .../mdspan/submdspan/submdspan_mapping.cc     | 160 ++++
>   .../mdspan/submdspan/submdspan_neg.cc         | 120 +++
>   15 files changed, 2194 insertions(+), 48 deletions(-)
>   rename libstdc++-v3/testsuite/23_containers/mdspan/{layouts/padded_traits.h => layout_traits.h} (70%)
>   create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan.cc
>   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
>   create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents.cc
>   create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_extents_neg.cc
>   create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_mapping.cc
>   create mode 100644 libstdc++-v3/testsuite/23_containers/mdspan/submdspan/submdspan_neg.cc
>