[PATCH v1 6/6] libstdc++: Replace numeric_limit with __int_traits in mdspan.

[Luc Grosheintz]

Using __int_traits avoids the need to include <limits> from <mdspan>.
This in turn should reduce the size of the pre-compiled <mdspan>.
Similar refactoring was carried out for PR92546. Unfortunately,

  ./gcc/xgcc -std=c++23 -P -E -x c++ - -include mdspan | wc -l

shows a decrease by 1(!) line. This is due to bits/max_size_type.h which
includes <limits>.

libstdc++-v3/ChangeLog:

        * include/std/mdspan (__valid_static_extent): Replace
        numeric_limits with __int_traits.
        (extents::_S_ctor_explicit): ditto.
        (extents::__static_quotient): ditto.
        (layout_stride::mapping::mapping): ditto.
        * testsuite/23_containers/mdspan/extents/class_mandates_neg.cc:
        Update test with additional diagnostics.

Signed-off-by: Luc Grosheintz <luc.groshei...@gmail.com>
---
 libstdc++-v3/include/std/mdspan               | 26 ++++++++++---------
 .../mdspan/extents/class_mandates_neg.cc      |  3 +++
 2 files changed, 17 insertions(+), 12 deletions(-)

diff --git a/libstdc++-v3/include/std/mdspan b/libstdc++-v3/include/std/mdspan
index 2cf572f1410..8fc853e7b5b 100644
--- a/libstdc++-v3/include/std/mdspan
+++ b/libstdc++-v3/include/std/mdspan
@@ -36,7 +36,6 @@
 #include <span>
 #include <array>
 #include <type_traits>
-#include <limits>
 #include <utility>
 
 #define __glibcxx_want_mdspan
@@ -195,7 +194,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<size_t _Extent, typename _IndexType>
       concept
       __valid_static_extent = _Extent == dynamic_extent
-       || _Extent <= numeric_limits<_IndexType>::max();
+       || _Extent <= __gnu_cxx::__int_traits<_IndexType>::__max;
 
     template<array _Extents>
       consteval size_t
@@ -306,8 +305,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
        _S_ctor_explicit()
        {
          return (_S_is_less_dynamic(_Extents, _OExtents) || ...)
-           || (numeric_limits<index_type>::max()
-               < numeric_limits<_OIndexType>::max());
+           || (__gnu_cxx::__int_traits<index_type>::__max
+               < __gnu_cxx::__int_traits<_OIndexType>::__max);
        }
 
       template<size_t... _OExtents>
@@ -515,7 +514,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     template<typename _Extents,
              typename _IndexType = typename _Extents::index_type>
       consteval _IndexType
-      __static_quotient(_IndexType __nom = numeric_limits<_IndexType>::max())
+      __static_quotient(_IndexType __nom = __gnu_cxx::__int_traits<_IndexType>
+                                                   ::__max)
       {
        auto __sta_exts = __static_extents<_Extents>();
        for (auto __factor : __sta_exts)
@@ -974,12 +974,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
          static_assert(__mdspan::__representable_size<_OExtents, index_type>,
            "The size of StridedMapping::extents_type must be representable as"
            " index_type");
-         if constexpr (cmp_greater(numeric_limits<_OIndexType>::max(),
-                                   numeric_limits<index_type>::max()))
-           __glibcxx_assert(!cmp_less(numeric_limits<index_type>::max(),
-                                      __other.required_span_size())
-               && "other.required_span_size() must be representable"
-                  " as index_type");
+         if constexpr (cmp_greater(__gnu_cxx::__int_traits<_OIndexType>::__max,
+                                   __gnu_cxx::__int_traits<index_type>::__max))
+           __glibcxx_assert(!cmp_less(
+               __gnu_cxx::__int_traits<index_type>::__max,
+               __other.required_span_size())
+             && "other.required_span_size() must be representable"
+                " as index_type");
          if constexpr (extents_type::rank() > 0)
            for (size_t __i = 0; __i < extents_type::rank(); ++__i)
              _M_strides[__i] = index_type(__other.stride(__i));
@@ -1296,7 +1297,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       size() const noexcept
       {
        __glibcxx_assert(cmp_less_equal(_M_mapping.required_span_size(),
-                                       numeric_limits<size_t>::max()));
+                                       __gnu_cxx::__int_traits<size_t>
+                                                ::__max));
        return size_type(__mdspan::__size(extents()));
       }
 
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 67d18feda96..db5cad27e52 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
@@ -12,3 +12,6 @@ std::extents<double, 1> e4;               // { dg-error "from 
here" }
 // { dg-prune-output "signed or unsigned integer" }
 // { dg-prune-output "invalid use of incomplete type" }
 // { dg-prune-output "non-constant condition for static assertion" }
+// { dg-prune-output "integer constants in boolean context" }
+// { dg-prune-output "__gnu_cxx::__numeric_traits_integer" }
+// { dg-prune-output "static assertion failed" }
-- 
2.50.0