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

[Jonathan Wakely]

On Mon, 7 Jul 2025 at 10:13, Tomasz Kaminski <tkaminsk@redhat.com> wrote:
>
>
>
> 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.

Thanks, OK for trunk with that change.


>>
>>
>> > +         {
>> > +           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
>> >
>>