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

[Luc Grosheintz]

On 7/7/25 11:13, Tomasz Kaminski wrote:

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

On Fri, 4 Jul 2025 at 09:30, Luc Grosheintz <luc.groshei...@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.groshei...@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.

Indeed it should have been. Thanks!

+         {
+           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