Incorrect submdspan with full_extent_t with g++-16 and C++26

#include <mdspan/mdspan.hpp>
#include <type_traits>
#include <utility>

using FE = Kokkos::full_extent_t;
using X = decltype(Kokkos::submdspan_extents(
    Kokkos::extents<size_t, 10, 5, 2>{}, FE{}, FE{}, FE{}));

static_assert(X::rank() == 3);
static_assert(X::static_extent(0) == 10);
static_assert(X::static_extent(1) == 5);
static_assert(X::static_extent(2) == 2);

int main() {}

fails wth g++-16 in C++26 mode with

/tmp/cmake_example.cpp:10:35: error: static assertion failed
   10 | static_assert(X::static_extent(0) == 10);
      |               ~~~~~~~~~~~~~~~~~~~~^~~~~
  • the comparison reduces to '(18446744073709551615 == 10)'
/tmp/cmake_example.cpp:11:35: error: static assertion failed
   11 | static_assert(X::static_extent(1) == 5);
      |               ~~~~~~~~~~~~~~~~~~~~^~~~
  • the comparison reduces to '(18446744073709551615 == 5)'
/tmp/cmake_example.cpp:12:35: error: static assertion failed
   12 | static_assert(X::static_extent(2) == 2);
      |               ~~~~~~~~~~~~~~~~~~~~^~~~
  • the comparison reduces to '(18446744073709551615 == 2)'

since constant_wrapper isn't derived from integral_constant anymore.
A quick fix would be

diff --git a/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp b/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
index 429877e7d..380032786 100644
--- a/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
+++ b/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
@@ -170,6 +171,24 @@ struct StaticExtentFromRange<integral_constant<Integral0, val0>,
   constexpr static size_t value = val1 - val0;
 };
 
+template <class Integral0, Integral0 val0, auto val1, class Integral1>
+struct StaticExtentFromRange<integral_constant<Integral0, val0>,
+                             constant_wrapper<val1, Integral1>>
+    : StaticExtentFromRange<integral_constant<Integral0, val0>,
+                            integral_constant<Integral1, static_cast<Integral1>(val1)>> {};
+
+template <auto val0, class Integral0, class Integral1, Integral1 val1>
+struct StaticExtentFromRange<constant_wrapper<val0, Integral0>,
+                             integral_constant<Integral1, val1>>
+    : StaticExtentFromRange<integral_constant<Integral0, static_cast<Integral0>(val0)>,
+                            integral_constant<Integral1, val1>> {};
+
+template <auto val0, class Integral0, auto val1, class Integral1>
+struct StaticExtentFromRange<constant_wrapper<val0, Integral0>,
+                             constant_wrapper<val1, Integral1>>
+    : StaticExtentFromRange<integral_constant<Integral0, static_cast<Integral0>(val0)>,
+                            integral_constant<Integral1, static_cast<Integral1>(val1)>> {};
+
 // compute new static extent from strided_slice, preserving static
 // knowledge
 template <class Arg0, class Arg1> struct StaticExtentFromStridedRange {
@@ -188,6 +207,24 @@ struct StaticExtentFromStridedRange<integral_constant<Integral0, val0>,
   constexpr static size_t value = val0 > 0 ? 1 + (val0 - 1) / val1 : 0;
 };
 
+template <class Integral0, Integral0 val0, auto val1, class Integral1>
+struct StaticExtentFromStridedRange<integral_constant<Integral0, val0>,
+                                    constant_wrapper<val1, Integral1>>
+    : StaticExtentFromStridedRange<integral_constant<Integral0, val0>,
+                                   integral_constant<Integral1, static_cast<Integral1>(val1)>> {};
+
+template <auto val0, class Integral0, class Integral1, Integral1 val1>
+struct StaticExtentFromStridedRange<constant_wrapper<val0, Integral0>,
+                                    integral_constant<Integral1, val1>>
+    : StaticExtentFromStridedRange<integral_constant<Integral0, static_cast<Integral0>(val0)>,
+                                   integral_constant<Integral1, val1>> {};
+
+template <auto val0, class Integral0, auto val1, class Integral1>
+struct StaticExtentFromStridedRange<constant_wrapper<val0, Integral0>,
+                                    constant_wrapper<val1, Integral1>>
+    : StaticExtentFromStridedRange<integral_constant<Integral0, static_cast<Integral0>(val0)>,
+                                   integral_constant<Integral1, static_cast<Integral1>(val1)>> {};
+
 // creates new extents through recursive calls to next_extent member function
 // next_extent has different overloads for different types of stride specifiers
 template <size_t K, class Extents, size_t... NewExtents>

diff --git a/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp b/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
index 429877e7d..6b4c7c09d 100644
--- a/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
+++ b/tpls/mdspan/include/experimental/__p2630_bits/submdspan_extents.hpp
@@ -158,16 +158,11 @@ template <class Arg0, class Arg1> struct StaticExtentFromRange {
   constexpr static size_t value = dynamic_extent;
 };
 
-template <class Integral0, Integral0 val0, class Integral1, Integral1 val1>
-struct StaticExtentFromRange<std::integral_constant<Integral0, val0>,
-                             std::integral_constant<Integral1, val1>> {
-  constexpr static size_t value = val1 - val0;
-};
-
-template <class Integral0, Integral0 val0, class Integral1, Integral1 val1>
-struct StaticExtentFromRange<integral_constant<Integral0, val0>,
-                             integral_constant<Integral1, val1>> {
-  constexpr static size_t value = val1 - val0;
+template <class IntegralConstantLike0, class IntegralConstantLike1>
+requires (integral_constant_like<IntegralConstantLike0> && integral_constant_like<IntegralConstantLike0>) 
+struct StaticExtentFromRange<IntegralConstantLike0,
+                             IntegralConstantLike1> {
+  constexpr static size_t value = IntegralConstantLike1::value - IntegralConstantLike0::value;
 };
 
 // compute new static extent from strided_slice, preserving static
@@ -176,16 +171,11 @@ template <class Arg0, class Arg1> struct StaticExtentFromStridedRange {
   constexpr static size_t value = dynamic_extent;
 };
 
-template <class Integral0, Integral0 val0, class Integral1, Integral1 val1>
-struct StaticExtentFromStridedRange<std::integral_constant<Integral0, val0>,
-                                    std::integral_constant<Integral1, val1>> {
-  constexpr static size_t value = val0 > 0 ? 1 + (val0 - 1) / val1 : 0;
-};
-
-template <class Integral0, Integral0 val0, class Integral1, Integral1 val1>
-struct StaticExtentFromStridedRange<integral_constant<Integral0, val0>,
-                                    integral_constant<Integral1, val1>> {
-  constexpr static size_t value = val0 > 0 ? 1 + (val0 - 1) / val1 : 0;
+template <class IntegralConstantLike0, class IntegralConstantLike1>
+requires (integral_constant_like<IntegralConstantLike0> && integral_constant_like<IntegralConstantLike0>)   
+struct StaticExtentFromStridedRange<IntegralConstantLike0,
+                                   IntegralConstantLike1> {
+  constexpr static size_t value = IntegralConstantLike0::value > 0 ? 1 + (IntegralConstantLike0::value - 1) / IntegralConstantLike1::value : 0;
 };
 
 // creates new extents through recursive calls to next_extent member function

would also fix it.

#488 addresses this and a few other issues which popped up.

Navigation Menu

Repository navigation

Incorrect submdspan with full_extent_t with g++-16 and C++26 #485

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Incorrect submdspan with full_extent_t with g++-16 and C++26 #485

Description

Activity

masterleinad commented on Oct 16, 2026

crtrott commented on Oct 16, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions