libstdc++: Prepare mdspan-related code for submdspan.

The changes needed for submdspan are:

  * In submdspan related code the user-defined integer-like
    types need to be copy- and move-constructable.

  * The traits for writing tests that work with both left- and right,
    possibly padded, layouts will also be useful for submdspan.
    Therefore, this code is moved up and generalized.

  * Move __offset further up in <mdspan> and fix some formatting
    mistakes.

libstdc++-v3/ChangeLog:

	* include/std/mdspan: Improve formatting and placement.
	* testsuite/23_containers/mdspan/int_like.h: Optionally,
	add move- and copy-ctors.
	* testsuite/23_containers/mdspan/layouts/padded_traits.h: Move to...
	* testsuite/23_containers/mdspan/layout_traits.h: ...here.
	* testsuite/23_containers/mdspan/layouts/ctors.cc: Fix include.
	* testsuite/23_containers/mdspan/layouts/mapping.cc: Ditto.
	* testsuite/23_containers/mdspan/layouts/padded.cc: Ditto.
	* testsuite/23_containers/mdspan/layouts/padded_neg.cc: Ditto.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
Signed-off-by: Luc Grosheintz <luc.grosheintz@gmail.com>

libstdc++-v3/include/std/mdspan

@@ -345,7 +345,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   inline constexpr full_extent_t full_extent{};
 
   template<typename _OffsetType, typename _ExtentType, typename _StrideType>
-    struct strided_slice {
+    struct strided_slice
+    {
       static_assert(__is_standard_integer<_OffsetType>::value
 	|| __detail::__integral_constant_like<_OffsetType>);
       static_assert(__is_standard_integer<_ExtentType>::value
@@ -368,7 +369,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       [[no_unique_address]] _Mapping mapping = _Mapping();
       size_t offset{};
     };
-#endif
+#endif // __glibcxx_submdspan
 
   template<typename _IndexType, size_t... _Extents>
     class extents
@@ -553,7 +554,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       __fwd_prod(const _Extents& __exts, size_t __begin, size_t __end) noexcept
       {
 	size_t __sta_prod = [__begin, __end] {
-	  span<const size_t> __sta_exts = __static_extents<_Extents>(__begin, __end);
+	  span<const size_t> __sta_exts
+	    = __static_extents<_Extents>(__begin, __end);
 	  size_t __ret = 1;
 	  for(auto __ext : __sta_exts)
 	    if (__ext != dynamic_extent)
@@ -769,7 +771,8 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
     template<typename _Layout, typename _Mapping>
       concept __mapping_of =
-	is_same_v<typename _Layout::template mapping<typename _Mapping::extents_type>,
+	is_same_v<typename _Layout::template mapping<
+		    typename _Mapping::extents_type>,
 		  _Mapping>;
 
     template<template<size_t> typename _Layout, typename _Mapping>
@@ -804,6 +807,25 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     // A tag type to create internal ctors.
     class __internal_ctor
     { };
+
+    template<typename _Mapping>
+      constexpr typename _Mapping::index_type
+      __offset(const _Mapping& __m) noexcept
+      {
+	using _IndexType = typename _Mapping::index_type;
+	constexpr auto __rank = _Mapping::extents_type::rank();
+
+	if constexpr (__standardized_mapping<_Mapping>)
+	  return 0;
+	else if (__empty(__m.extents()))
+	  return 0;
+	else
+	  {
+	    auto __impl = [&__m]<size_t... _Counts>(index_sequence<_Counts...>)
+	      { return __m(((void) _Counts, _IndexType(0))...); };
+	    return __impl(make_index_sequence<__rank>());
+	  }
+      }
   }
 
   template<typename _Extents>
@@ -1136,25 +1158,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	bool_constant<_Mp::is_always_unique()>::value;
       };
 
-    template<typename _Mapping>
-      constexpr typename _Mapping::index_type
-      __offset(const _Mapping& __m) noexcept
-      {
-	using _IndexType = typename _Mapping::index_type;
-	constexpr auto __rank = _Mapping::extents_type::rank();
-
-	if constexpr (__standardized_mapping<_Mapping>)
-	  return 0;
-	else if (__empty(__m.extents()))
-	  return 0;
-	else
-	  {
-	    auto __impl = [&__m]<size_t... _Counts>(index_sequence<_Counts...>)
-	      { return __m(((void) _Counts, _IndexType(0))...); };
-	    return __impl(make_index_sequence<__rank>());
-	  }
-      }
-
     template<typename _Mapping, typename... _Indices>
       constexpr typename _Mapping::index_type
       __linear_index_strides(const _Mapping& __m, _Indices... __indices)

libstdc++-v3/testsuite/23_containers/mdspan/int_like.h

@@ -9,7 +9,7 @@ enum class CustomIndexKind
   RValue,
 };
 
-template<CustomIndexKind Kind>
+template<CustomIndexKind Kind, bool Copyable = false>
   class CustomIndexType
   {
   public:
@@ -18,15 +18,24 @@ template<CustomIndexKind Kind>
     : value(i)
     { }
 
-    CustomIndexType() = delete;
-    CustomIndexType(const CustomIndexType&) = delete;
-    CustomIndexType(CustomIndexType&&) = delete;
+    CustomIndexType() requires(Copyable) = default;
+    CustomIndexType() requires(!Copyable) = delete;
 
-    const CustomIndexType&
-    operator=(const CustomIndexType&) = delete;
+    CustomIndexType(const CustomIndexType&) requires(Copyable) = default;
+    CustomIndexType(const CustomIndexType&) requires(!Copyable) = delete;
 
-    const CustomIndexType&
-    operator=(CustomIndexType&&) = delete;
+    CustomIndexType(CustomIndexType&&) requires(Copyable) = default;
+    CustomIndexType(CustomIndexType&&) requires(!Copyable) = delete;
+
+    CustomIndexType&
+    operator=(const CustomIndexType&) requires(Copyable) = default;
+    CustomIndexType&
+    operator=(const CustomIndexType&) requires(!Copyable) = delete;
+
+    CustomIndexType&
+    operator=(CustomIndexType&&) requires(Copyable) = default;
+    CustomIndexType&
+    operator=(CustomIndexType&&) requires(!Copyable) = delete;
 
     constexpr
     operator int() const noexcept

libstdc++-v3/testsuite/23_containers/mdspan/layout_traits.h

@@ -1,8 +1,14 @@
-#ifndef TEST_MDSPAN_PADDED_TRAITS_H
-#define TEST_MDSPAN_PADDED_TRAITS_H
+#ifndef TEST_MDSPAN_LAYOUT_TRAITS_H
+#define TEST_MDSPAN_LAYOUT_TRAITS_H
 
 #include <algorithm>
 
+enum class PaddingSide
+{
+  Left,
+  Right
+};
+
 template<typename Layout>
   constexpr static bool is_left_padded = false;
 
@@ -26,6 +32,18 @@ template<typename Layout>
   is_padded_layout = is_left_padded<Layout> || is_right_padded<Layout>;
 
 #if __cplusplus > 202302L
+template<PaddingSide Side, typename Layout>
+  constexpr bool
+  is_same_padded;
+
+template<typename Layout>
+  constexpr bool
+  is_same_padded<PaddingSide::Left, Layout> = is_left_padded<Layout>;
+
+template<typename Layout>
+  constexpr bool
+  is_same_padded<PaddingSide::Right, Layout> = is_right_padded<Layout>;
+
 template<typename Extents>
   constexpr auto
   dynamic_extents_array(const Extents& exts)
@@ -36,12 +54,6 @@ template<typename Extents>
     return ret;
   }
 
-enum class PaddingSide
-{
-  Left,
-  Right
-};
-
 struct DeducePaddingSide
 {
   template<template<size_t> typename Layout>
@@ -58,7 +70,9 @@ struct DeducePaddingSide
     constexpr static PaddingSide
     from_typename()
     {
-      if constexpr (is_left_padded<Layout>)
+      if constexpr (std::same_as<Layout, std::layout_left>)
+	return PaddingSide::Left;
+      else if constexpr (is_left_padded<Layout>)
 	return PaddingSide::Left;
       else
 	return PaddingSide::Right;
@@ -84,8 +98,18 @@ template<>
 
     template<typename T, size_t N>
       constexpr static std::array<T, N>
-      make_array(const std::array<T, N>& expected)
-      { return expected; }
+      make_array(const std::array<T, N>& a)
+      { return a; }
+
+    template<typename... Indices>
+      constexpr static auto
+      make_indices(Indices... indices)
+      { return std::array{indices...}; }
+
+    template<typename... Ts>
+      constexpr static std::tuple<Ts...>
+      make_tuple(const std::tuple<Ts...>& tup)
+      { return tup; }
 
     template<typename Mapping>
       constexpr static auto
@@ -128,6 +152,25 @@ template<>
 	return a;
       }
 
+    template<typename... Indices>
+      constexpr static auto
+      make_indices(Indices... indices)
+      { return make_array(std::array{indices...}); }
+
+    template<typename... Ts>
+      constexpr static auto
+      make_tuple(const std::tuple<Ts...>& tup)
+      {
+	constexpr size_t rank = sizeof...(Ts);
+	auto impl = [&]<size_t... I>(std::index_sequence<I...>)
+	{
+	  auto idx = [rank](size_t i) consteval
+	  { return rank - 1 - i; };
+	  return std::tuple<Ts...[idx(I)]...>{get<idx(I)>(tup)...};
+	};
+	return impl(std::make_index_sequence<rank>());
+      }
+
     template<typename Mapping>
       constexpr static auto
       padded_stride(const Mapping& m)

libstdc++-v3/testsuite/23_containers/mdspan/layouts/ctors.cc

@@ -1,7 +1,7 @@
 // { dg-do run { target c++23 } }
 #include <mdspan>
 
-#include "padded_traits.h"
+#include "../layout_traits.h"
 #include <cstdint>
 #include <testsuite_hooks.h>
 

libstdc++-v3/testsuite/23_containers/mdspan/layouts/mapping.cc

@@ -2,7 +2,7 @@
 #include <mdspan>
 
 #include "../int_like.h"
-#include "padded_traits.h"
+#include "../layout_traits.h"
 #include <cstdint>
 #include <testsuite_hooks.h>
 

libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded.cc

@@ -3,7 +3,7 @@
 
 #include <cstdint>
 #include "../int_like.h"
-#include "padded_traits.h"
+#include "../layout_traits.h"
 #include <testsuite_hooks.h>
 
 constexpr size_t dyn = std::dynamic_extent;

libstdc++-v3/testsuite/23_containers/mdspan/layouts/padded_neg.cc

@@ -1,7 +1,7 @@
 // { dg-do compile { target c++26 } }
 #include <mdspan>
 
-#include "padded_traits.h"
+#include "../layout_traits.h"
 #include <cstdint>
 
 constexpr size_t dyn = std::dynamic_extent;