<mdspan>: More EBO (#3847)

tests/std/tests/GH_002206_unreserved_names/test.compile.pass.cpp

@@ -13,6 +13,7 @@
 #define intrinsic       3
 #define lifetimebound   4
 #define noop_dtor       5
+#define empty_bases     6
 
 #include <__msvc_all_public_headers.hpp>
 
@@ -35,3 +36,7 @@
 #if noop_dtor != 5
 #error bad macro expansion
 #endif // noop_dtor != 5
+
+#if empty_bases != 6
+#error bad macro expansion
+#endif // noop_dtor != 6

tests/std/tests/P0009R18_mdspan_default_accessor/test.cpp

@@ -27,6 +27,9 @@ constexpr void test_one(array<ElementType, 3> elems) {
     static_assert(is_trivially_copyable_v<Accessor>);
     static_assert(semiregular<Accessor>);
 
+    // Check if default_accessor is empty
+    static_assert(std::is_empty_v<Accessor>);
+
     // Check nested types
     static_assert(same_as<typename Accessor::offset_policy, Accessor>);
     static_assert(same_as<typename Accessor::element_type, ElementType>);

tests/std/tests/P0009R18_mdspan_layout_left/test.cpp

@@ -423,6 +423,10 @@ constexpr void check_correctness() {
 #endif // ^^^ !defined(__cpp_multidimensional_subscript) ^^^
     }
 
+
+#ifdef __clang__
+    if (!is_constant_evaluated()) // FIXME clang hits constexpr limit here
+#endif
     { // 3x2 matrix with column-major order
         const array values{0, 1, 2, 3, 4, 5};
         mdspan<const int, extents<int, 3, 2>, layout_left> matrix{values.data()};
@@ -444,6 +448,9 @@ constexpr void check_correctness() {
 #endif // ^^^ !defined(__cpp_multidimensional_subscript) ^^^
     }
 
+#ifdef __clang__
+    if (!is_constant_evaluated()) // FIXME clang hits constexpr limit here
+#endif
     { // 3x2x4 tensor
         const array values{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23};
         mdspan<const int, dextents<size_t, 3>, layout_left> tensor{values.data(), 3, 2, 4};
@@ -493,6 +500,12 @@ constexpr void check_correctness() {
     }
 }
 
+// When 'M::extents_type::rank_dynamic()' is equal to 0 then 'is_empty_v<M>' should be true (MSVC STL specific behavior)
+static_assert(!is_empty_v<layout_left::mapping<dextents<long long, 2>>>);
+static_assert(!is_empty_v<layout_left::mapping<extents<long long, 3, dynamic_extent>>>);
+static_assert(is_empty_v<layout_left::mapping<extents<long long, 3, 3>>>);
+static_assert(is_empty_v<layout_left::mapping<extents<long long>>>);
+
 constexpr bool test() {
     check_members_with_various_extents([]<class E>(const E& e) { check_members(e, make_index_sequence<E::rank()>{}); });
     if (!is_constant_evaluated()) { // too heavy for compile time

tests/std/tests/P0009R18_mdspan_layout_right/test.cpp

@@ -516,6 +516,12 @@ constexpr void check_correctness() {
     }
 }
 
+// When 'M::extents_type::rank_dynamic()' is equal to 0 then 'is_empty_v<M>' should be true (MSVC STL specific behavior)
+static_assert(!is_empty_v<layout_right::mapping<dextents<long, 2>>>);
+static_assert(!is_empty_v<layout_right::mapping<extents<long, 3, dynamic_extent>>>);
+static_assert(is_empty_v<layout_right::mapping<extents<long, 3, 3>>>);
+static_assert(is_empty_v<layout_right::mapping<extents<long>>>);
+
 constexpr bool test() {
     check_members_with_various_extents([]<class E>(const E& e) { check_members(e, make_index_sequence<E::rank()>{}); });
     if (!is_constant_evaluated()) { // too heavy for compile time

tests/std/tests/P0009R18_mdspan_layout_stride/test.cpp

@@ -821,6 +821,12 @@ constexpr void check_correctness() {
     }
 }
 
+// When 'M::extents_type::rank()' is equal to 0 then 'is_empty_v<M>' should be true (MSVC STL specific behavior)
+static_assert(!is_empty_v<layout_stride::mapping<dextents<long long, 2>>>);
+static_assert(!is_empty_v<layout_stride::mapping<extents<long long, 3, dynamic_extent>>>);
+static_assert(!is_empty_v<layout_stride::mapping<extents<long long, 3, 3>>>);
+static_assert(is_empty_v<layout_stride::mapping<extents<long long>>>);
+
 constexpr bool test() {
     // Check signed integers
     check_members(extents<signed char, 5>{5}, array{1});

tests/std/tests/P0009R18_mdspan_mdspan/test.cpp

@@ -1095,35 +1095,52 @@ constexpr void check_empty() {
 }
 
 constexpr void check_swap() {
-    using E   = extents<int, 3, 3>;
-    using Mds = mdspan<int, E, TrackingLayout<>, TrackingAccessor<int>>;
-    static_assert(is_nothrow_swappable_v<Mds>);
-    static_assert(!is_swappable_v<const Mds>);
-
-    int a1[9] = {1, 0, 0, 0, 1, 0, 0, 0, 1};
-    Mds mds1{TrackingDataHandle<int>{1, a1}, TrackingLayout<>::mapping<E>(1), TrackingAccessor<int>{1}};
-    int a2[9] = {3, 0, 0, 0, 3, 0, 0, 0, 3};
-    Mds mds2{TrackingDataHandle<int>{3, a2}, TrackingLayout<>::mapping<E>(3), TrackingAccessor<int>{3}};
-    swap(mds1, mds2);
-    static_assert(is_void_v<decltype(swap(mds1, mds2))>);
-
-    assert(mds1.data_handle().get_id() == 3);
-    assert(mds1.data_handle().is_swapped());
-    assert(mds1.mapping().get_id() == 3);
-    assert(mds1.mapping().is_swapped());
-    assert(mds1.accessor().get_id() == 3);
-    assert(mds1.accessor().is_swapped());
-    assert((mds1[array{1, 1}] == 3));
-    assert((mds1[array{0, 1}] == 0));
-
-    assert(mds2.data_handle().get_id() == 1);
-    assert(mds2.data_handle().is_swapped());
-    assert(mds2.mapping().get_id() == 1);
-    assert(mds2.mapping().is_swapped());
-    assert(mds2.accessor().get_id() == 1);
-    assert(mds2.accessor().is_swapped());
-    assert((mds2[array{1, 1}] == 1));
-    assert((mds2[array{0, 1}] == 0));
+    { // Check swapping with tracking types
+        using E   = extents<int, 3, 3>;
+        using Mds = mdspan<int, E, TrackingLayout<>, TrackingAccessor<int>>;
+        static_assert(is_nothrow_swappable_v<Mds>);
+        static_assert(!is_swappable_v<const Mds>);
+
+        int a1[9] = {1, 0, 0, 0, 1, 0, 0, 0, 1};
+        Mds mds1{TrackingDataHandle<int>{1, a1}, TrackingLayout<>::mapping<E>(1), TrackingAccessor<int>{1}};
+        int a2[9] = {3, 0, 0, 0, 3, 0, 0, 0, 3};
+        Mds mds2{TrackingDataHandle<int>{3, a2}, TrackingLayout<>::mapping<E>(3), TrackingAccessor<int>{3}};
+        swap(mds1, mds2);
+        static_assert(is_void_v<decltype(swap(mds1, mds2))>);
+
+        assert(mds1.data_handle().get_id() == 3);
+        assert(mds1.data_handle().is_swapped());
+        assert(mds1.mapping().get_id() == 3);
+        assert(mds1.mapping().is_swapped());
+        assert(mds1.accessor().get_id() == 3);
+        assert(mds1.accessor().is_swapped());
+        assert((mds1[array{1, 1}] == 3));
+        assert((mds1[array{0, 1}] == 0));
+
+        assert(mds2.data_handle().get_id() == 1);
+        assert(mds2.data_handle().is_swapped());
+        assert(mds2.mapping().get_id() == 1);
+        assert(mds2.mapping().is_swapped());
+        assert(mds2.accessor().get_id() == 1);
+        assert(mds2.accessor().is_swapped());
+        assert((mds2[array{1, 1}] == 1));
+        assert((mds2[array{0, 1}] == 0));
+    }
+
+    { // Check swapping with standard layout and accessor
+        using Mds = mdspan<int, extents<int, 2, 2>>;
+        static_assert(is_nothrow_swappable_v<Mds>);
+        static_assert(!is_swappable_v<const Mds>);
+
+        int diag[] = {1, 0, 0, 1};
+        Mds mds1{diag};
+        int revdiag[] = {0, 1, 1, 0};
+        Mds mds2{revdiag};
+
+        swap(mds1, mds2);
+        assert(mds1.data_handle() == revdiag);
+        assert(mds2.data_handle() == diag);
+    }
 }
 
 constexpr void check_getters() {
@@ -1316,11 +1333,33 @@ constexpr void check_deduction_guides() {
     }
 }
 
+// When
+// * 'Mds::accessor_type' is specialization of 'default_accesor', and
+// * 'Mds::layout_type' is
+//   * 'layout_left' or 'layout_right' and 'Mds::extents_type::rank_dynamic() == 0', or
+//   * 'layout_stride' and 'Mds::extents_type::rank() == 0'
+// then 'sizeof(Mds) == sizeof(void*)' (MSVC STL specific behavior).
+static_assert(sizeof(mdspan<int, extents<int, 3, 3, 3>, layout_left>) == sizeof(void*));
+static_assert(sizeof(mdspan<int, dextents<int, 3>, layout_left>) > sizeof(void*));
+static_assert(sizeof(mdspan<int, extents<int, 3, 3, 3>, layout_left, TrivialAccessor<int>>) > sizeof(void*));
+
+static_assert(sizeof(mdspan<long, extents<long, 2, 2, 2>, layout_right>) == sizeof(void*));
+static_assert(sizeof(mdspan<long, dextents<long, 2>, layout_right>) > sizeof(void*));
+static_assert(sizeof(mdspan<long, extents<long, 2, 2, 2>, layout_right, TrivialAccessor<long>>) > sizeof(void*));
+
+static_assert(sizeof(mdspan<short, extents<short>, layout_stride>) == sizeof(void*));
+static_assert(sizeof(mdspan<short, extents<short, 4, 4, 4>, layout_stride>) > sizeof(void*));
+static_assert(sizeof(mdspan<short, dextents<short, 4>, layout_stride>) > sizeof(void*));
+static_assert(sizeof(mdspan<short, extents<short, 4, 4, 4>, layout_stride, TrivialAccessor<short>>) > sizeof(void*));
+
 constexpr bool test() {
+    check_modeled_concepts_and_member_types<dextents<unsigned long long, 3>, layout_left, default_accessor>();
+    check_modeled_concepts_and_member_types<dextents<unsigned long long, 3>, layout_right, default_accessor>();
+    check_modeled_concepts_and_member_types<dextents<unsigned long long, 3>, layout_stride, default_accessor>();
+    check_modeled_concepts_and_member_types<dextents<unsigned long long, 3>, layout_left, TrackingAccessor>();
     check_modeled_concepts_and_member_types<extents<signed char, 2, 3, 5>, layout_stride, TrivialAccessor>();
     check_modeled_concepts_and_member_types<extents<unsigned short, 2, 4, dynamic_extent>, TrackingLayout<>,
         AccessorWithTrackingDataHandle>();
-    check_modeled_concepts_and_member_types<dextents<unsigned long long, 3>, layout_left, TrackingAccessor>();
     check_observers();
     check_default_constructor();
     check_defaulted_copy_and_move_constructors();