[PATCH v2 0/8] libstdc++: Sequence of improvements to <mdspan>.

[Tomasz Kaminski]

The patch series is now on trunk, and will continue with the next series
soon.
Thank you for the contributions, and I am looking forward to the next
patches for review.

On Wed, Aug 20, 2025 at 6:54 PM Jonathan Wakely <jwakely@redhat.com> wrote:

> On 03/08/25 22:57 +0200, Luc Grosheintz wrote:
> >The combined effect of this sequence of change is:
> >
> >  * a reduction in the number of template instantiations, by
> >    - avoiding needless dependency of IndexType,
> >    - special formulas for low-rank extents,
> >    - special formulas for (nearly) fully dynamic extents.
> >
> >  * improved code quality, by
> >    - precomputing partial products of the static extents,
> >    - special cases for low-rank extents,
> >    - rewriting the condition E[i] == dynamic_extent in a more
> >      optimizer friendly manner.
> >    - effectively loop-unrolling extents::operator==.
> >
> >While simplistic micro-benchmarking shows the effectiveness of these
> >changes, likely the stronger argument is presented in each commit:
> >  a) each change removes needless complexity,
> >  b) before/after examples of generated code show the effectiveness.
> >
> >Luc Grosheintz (8):
> >  libstdc++: Reduce template instantiations in <mdspan>.
> >  libstdc++: Precompute products of static extents.
> >  libstdc++: Improve low-rank layout_{left,right}::stride.
> >  libstdc++: Improve fully dynamic extents in mdspan.
> >  libstdc++: Improve nearly fully dynamic extents in mdspan.
> >  libstdc++: Reduce indirection in extents::extent.
> >  libstdc++: Improve extents::operator==.
> >  libstdc++: Replace numeric_limit with __int_traits in mdspan.
> >
> > libstdc++-v3/include/std/mdspan               | 282 +++++++++++++-----
> > .../mdspan/extents/class_mandates_neg.cc      |   3 +
> > 2 files changed, 208 insertions(+), 77 deletions(-)
>
> I've now reviewed all the patches in this series, with all Tomasz's v3
> patches making adjustments, and the whole series is OK for trunk.
>
> Some really nice codegen improvemens here, thanks!
>
>
>
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