[PATCH v3 2/5] libstdc++: Check prerequisite of extents::extents.

[Tomasz Kaminski]

On Mon, Jul 7, 2025 at 11:09 AM Jonathan Wakely <jwakely@redhat.com> wrote:

> On Fri, 4 Jul 2025 at 09:30, Luc Grosheintz <luc.grosheintz@gmail.com>
> wrote:
> >
> > Previously the prerequisite of the extents ctors that
> >
> >     static_extent(i) == dynamic_extent || extent(i) == other.extent(i).
> >
> > was not checked. This commit adds the __glibcxx_assert and test them.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/std/mdspan (extents): Check prerequisite of the ctor
> that
> >         static_extent(i) == dynamic_extent || extent(i) ==
> other.extent(i).
> >         * testsuite/23_containers/mdspan/extents/class_mandates_neg.cc:
> >         Test the implemented prerequisite.
> >
> > Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>
> > ---
> >  libstdc++-v3/include/std/mdspan               | 13 +++++++
> >  .../mdspan/extents/class_mandates_neg.cc      |  2 ++
> >  .../mdspan/extents/extents_mismatch_neg.cc    | 35 +++++++++++++++++++
> >  3 files changed, 50 insertions(+)
> >  create mode 100644
> libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
> >
> > diff --git a/libstdc++-v3/include/std/mdspan
> b/libstdc++-v3/include/std/mdspan
> > index cf20553aaa5..1d6cdc93d80 100644
> > --- a/libstdc++-v3/include/std/mdspan
> > +++ b/libstdc++-v3/include/std/mdspan
> > @@ -110,10 +110,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >             return __se;
> >         }
> >
> > +       template<size_t _OtherRank, typename _GetOtherExtent>
> > +         constexpr bool
> > +         _S_is_compatible_extents(_GetOtherExtent __get_extent) noexcept
>
> Was this intended to be a static member function?
>
Yes, it should be. I will also adjust that locally.

>
> > +         {
> > +           if constexpr (_OtherRank == _S_rank)
> > +             for (size_t __i = 0; __i < _S_rank; ++__i)
> > +               if (_Extents[__i] != dynamic_extent
> > +                   && !cmp_equal(_Extents[__i],
> _S_int_cast(__get_extent(__i))))
> > +                 return false;
> > +           return true;
> > +         }
> > +
> >         template<size_t _OtherRank, typename _GetOtherExtent>
> >           constexpr void
> >           _M_init_dynamic_extents(_GetOtherExtent __get_extent) noexcept
> >           {
> > +
>  __glibcxx_assert(_S_is_compatible_extents<_OtherRank>(__get_extent));
> >             for (size_t __i = 0; __i < _S_rank_dynamic; ++__i)
> >               {
> >                 size_t __di = __i;
> > diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
> > index f9c1c019666..67d18feda96 100644
> > ---
> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
> > +++
> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/class_mandates_neg.cc
> > @@ -7,6 +7,8 @@ std::extents<uint8_t, size_t(1) << 9> e1; // { dg-error
> "from here" }
> >  std::extents<char, 1> e2;                 // { dg-error "from here" }
> >  std::extents<bool, 1> e3;                 // { dg-error "from here" }
> >  std::extents<double, 1> e4;               // { dg-error "from here" }
> > +
> >  // { dg-prune-output "dynamic or representable as IndexType" }
> >  // { dg-prune-output "signed or unsigned integer" }
> >  // { dg-prune-output "invalid use of incomplete type" }
> > +// { dg-prune-output "non-constant condition for static assertion" }
> > diff --git
> a/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
> > new file mode 100644
> > index 00000000000..b35e5310d41
> > --- /dev/null
> > +++
> b/libstdc++-v3/testsuite/23_containers/mdspan/extents/extents_mismatch_neg.cc
> > @@ -0,0 +1,35 @@
> > +// { dg-do compile { target c++23 } }
> > +#include<mdspan>
> > +
> > +#include <cstdint>
> > +
> > +constexpr size_t dyn = std::dynamic_extent;
> > +
> > +constexpr bool
> > +test_dyn2sta_extents_mismatch_00()
> > +{
> > +  auto e0 = std::extents<int, dyn>{1};
> > +  [[maybe_unused]] auto e1 = std::extents<int, 2>{e0};        // {
> dg-error "expansion of" }
> > +  return true;
> > +}
> > +static_assert(test_dyn2sta_extents_mismatch_00());            // {
> dg-error "expansion of" }
> > +
> > +constexpr bool
> > +test_dyn2sta_extents_mismatch_01()
> > +{
> > +  [[maybe_unused]] auto e = std::extents<int, 1, dyn>{2, 2}; // {
> dg-error "expansion of" }
> > +  return true;
> > +}
> > +static_assert(test_dyn2sta_extents_mismatch_01());           // {
> dg-error "expansion of" }
> > +
> > +constexpr bool
> > +test_dyn2sta_extents_mismatch_02()
> > +{
> > +  std::array<int, 2> exts{2, 2};
> > +  [[maybe_unused]] auto e = std::extents<int, 1, dyn>{exts}; // {
> dg-error "expansion of" }
> > +  return true;
> > +}
> > +static_assert(test_dyn2sta_extents_mismatch_02());           // {
> dg-error "expansion of" }
> > +
> > +// { dg-prune-output "non-constant condition for static assertion" }
> > +// { dg-prune-output "__glibcxx_assert" }
> > --
> > 2.49.0
> >
>
>
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