[libcxx-commits] [libcxx] [libc++] P2389R2: `dextents` Index Type Parameter (PR #97393)
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Tue Jul 2 01:01:37 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-libcxx
Author: Xiaoyang Liu (xiaoyang-sde)
<details>
<summary>Changes</summary>
## Introduction
This patch implements [P2389R2](https://wg21.link/P2389R2), which was adopted at the St. Louis meeting. It builds upon previous enhancements from [P2299R3](https://wg21.link/P2299R3), which introduced deduction guides and the `dextents` alias template. The main problem addressed is the increased verbosity of `dextents` following the parameterization of index types in [P2553R1](https://wg21.link/P2553R1). After considering and rejecting a breaking change, the paper proposes introducing a new template alias called `dims`, which simplifies the declaration of `mdspan` with dynamic extents while maintaining the option to customize the index type.
## Reference
- [P2389R2](https://wg21.link/P2389R2)
- [Draft C++ Standard: [mdspan.syn]](https://eel.is/c++draft/mdspan.syn)
- [Draft C++ Standard: [version.syn]](https://eel.is/c++draft/version.syn)
---
Full diff: https://github.com/llvm/llvm-project/pull/97393.diff
9 Files Affected:
- (modified) libcxx/docs/FeatureTestMacroTable.rst (+2)
- (modified) libcxx/docs/ReleaseNotes/19.rst (+1)
- (modified) libcxx/include/__mdspan/extents.h (+6)
- (modified) libcxx/include/mdspan (+4)
- (modified) libcxx/include/version (+3-1)
- (added) libcxx/test/std/containers/views/mdspan/extents/dims.pass.cpp (+49)
- (modified) libcxx/test/std/language.support/support.limits/support.limits.general/mdspan.version.compile.pass.cpp (+3-3)
- (modified) libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp (+2-2)
- (modified) libcxx/utils/generate_feature_test_macro_components.py (+1-1)
``````````diff
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index 72f624fa746b4..c7cdb15a7c3e1 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -440,6 +440,8 @@ Status
---------------------------------------------------------- -----------------
``__cpp_lib_linalg`` *unimplemented*
---------------------------------------------------------- -----------------
+ ``__cpp_lib_mdspan`` ``202406L``
+ ---------------------------------------------------------- -----------------
``__cpp_lib_out_ptr`` *unimplemented*
---------------------------------------------------------- -----------------
``__cpp_lib_ranges_concat`` *unimplemented*
diff --git a/libcxx/docs/ReleaseNotes/19.rst b/libcxx/docs/ReleaseNotes/19.rst
index d30021b7eb234..9d36a16df74f6 100644
--- a/libcxx/docs/ReleaseNotes/19.rst
+++ b/libcxx/docs/ReleaseNotes/19.rst
@@ -53,6 +53,7 @@ Implemented Papers
- P2713R1 - Escaping improvements in ``std::format``
- P2231R1 - Missing ``constexpr`` in ``std::optional`` and ``std::variant``
- P0019R8 - ``std::atomic_ref``
+- P2389R2 - ``dextents`` Index Type Parameter
Improvements and New Features
-----------------------------
diff --git a/libcxx/include/__mdspan/extents.h b/libcxx/include/__mdspan/extents.h
index fea0decd8c6af..27d05122a11f5 100644
--- a/libcxx/include/__mdspan/extents.h
+++ b/libcxx/include/__mdspan/extents.h
@@ -465,6 +465,12 @@ template <class... _IndexTypes>
explicit extents(_IndexTypes...) -> extents<size_t, size_t(((void)sizeof(_IndexTypes), dynamic_extent))...>;
# endif
+# if _LIBCPP_STD_VER >= 26
+// [mdspan.extents.dims], alias template `dims`
+template <size_t _Rank, class _IndexType = size_t>
+using dims = dextents<_IndexType, _Rank>;
+# endif
+
namespace __mdspan_detail {
// Helper type traits for identifying a class as extents.
diff --git a/libcxx/include/mdspan b/libcxx/include/mdspan
index 8d443f4acd1dd..aa7ba278b1aa0 100644
--- a/libcxx/include/mdspan
+++ b/libcxx/include/mdspan
@@ -20,6 +20,10 @@ namespace std {
template<class IndexType, size_t Rank>
using dextents = see below;
+ // [mdspan.extents.dims], alias template dims
+ template<size_t Rank, class IndexType = size_t>
+ using dims = see below; // since C++26
+
// [mdspan.layout], layout mapping
struct layout_left;
struct layout_right;
diff --git a/libcxx/include/version b/libcxx/include/version
index cac6eaa3b6e88..c8ea46127db82 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -156,7 +156,7 @@ __cpp_lib_make_unique 201304L <memory>
__cpp_lib_map_try_emplace 201411L <map>
__cpp_lib_math_constants 201907L <numbers>
__cpp_lib_math_special_functions 201603L <cmath>
-__cpp_lib_mdspan 202207L <mdspan>
+__cpp_lib_mdspan 202406L <mdspan>
__cpp_lib_memory_resource 201603L <memory_resource>
__cpp_lib_move_iterator_concept 202207L <iterator>
__cpp_lib_move_only_function 202110L <functional>
@@ -521,6 +521,8 @@ __cpp_lib_void_t 201411L <type_traits>
// # define __cpp_lib_hazard_pointer 202306L
// # define __cpp_lib_is_within_lifetime 202306L
// # define __cpp_lib_linalg 202311L
+# undef __cpp_lib_mdspan
+# define __cpp_lib_mdspan 202406L
# undef __cpp_lib_out_ptr
// # define __cpp_lib_out_ptr 202311L
// # define __cpp_lib_ranges_concat 202403L
diff --git a/libcxx/test/std/containers/views/mdspan/extents/dims.pass.cpp b/libcxx/test/std/containers/views/mdspan/extents/dims.pass.cpp
new file mode 100644
index 0000000000000..e74bc0e66fca1
--- /dev/null
+++ b/libcxx/test/std/containers/views/mdspan/extents/dims.pass.cpp
@@ -0,0 +1,49 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
+
+// <mdspan>
+
+// template<size_t Rank, class IndexType = size_t>
+// using dims = see below;
+//
+// Result: A type E that is a specialization of extents such that
+// E::rank() == Rank && E::rank() == E::rank_dynamic() is true,
+// and E::index_type denotes IndexType.
+
+#include <mdspan>
+#include <cstddef>
+
+#include "test_macros.h"
+
+template <class IndexType>
+void test_alias_template_dims() {
+ constexpr size_t D = std::dynamic_extent;
+ ASSERT_SAME_TYPE(std::dims<0, IndexType>, std::extents<IndexType>);
+ ASSERT_SAME_TYPE(std::dims<1, IndexType>, std::extents<IndexType, D>);
+ ASSERT_SAME_TYPE(std::dims<2, IndexType>, std::extents<IndexType, D, D>);
+ ASSERT_SAME_TYPE(std::dims<3, IndexType>, std::extents<IndexType, D, D, D>);
+ ASSERT_SAME_TYPE(std::dims<9, IndexType>, std::extents<IndexType, D, D, D, D, D, D, D, D, D>);
+}
+
+template <>
+void test_alias_template_dims<size_t>() {
+ constexpr size_t D = std::dynamic_extent;
+ ASSERT_SAME_TYPE(std::dims<0>, std::extents<size_t>);
+ ASSERT_SAME_TYPE(std::dims<1>, std::extents<size_t, D>);
+ ASSERT_SAME_TYPE(std::dims<2>, std::extents<size_t, D, D>);
+ ASSERT_SAME_TYPE(std::dims<3>, std::extents<size_t, D, D, D>);
+ ASSERT_SAME_TYPE(std::dims<9>, std::extents<size_t, D, D, D, D, D, D, D, D, D>);
+}
+
+int main(int, char**) {
+ test_alias_template_dims<int>();
+ test_alias_template_dims<unsigned int>();
+ test_alias_template_dims<size_t>();
+ return 0;
+}
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/mdspan.version.compile.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/mdspan.version.compile.pass.cpp
index 4ef3382306421..bd92562d31186 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/mdspan.version.compile.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/mdspan.version.compile.pass.cpp
@@ -17,7 +17,7 @@
/* Constant Value
__cpp_lib_freestanding_mdspan 202311L [C++26]
- __cpp_lib_mdspan 202207L [C++23]
+ __cpp_lib_mdspan 202406L [C++26]
__cpp_lib_submdspan 202306L [C++26]
*/
@@ -115,8 +115,8 @@
# ifndef __cpp_lib_mdspan
# error "__cpp_lib_mdspan should be defined in c++26"
# endif
-# if __cpp_lib_mdspan != 202207L
-# error "__cpp_lib_mdspan should have the value 202207L in c++26"
+# if __cpp_lib_mdspan != 202406L
+# error "__cpp_lib_mdspan should have the value 202406L in c++26"
# endif
# if !defined(_LIBCPP_VERSION)
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
index 32ed30e21cbbe..2a72ce97c1fbc 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
@@ -143,7 +143,7 @@
__cpp_lib_map_try_emplace 201411L [C++17]
__cpp_lib_math_constants 201907L [C++20]
__cpp_lib_math_special_functions 201603L [C++17]
- __cpp_lib_mdspan 202207L [C++23]
+ __cpp_lib_mdspan 202406L [C++26]
__cpp_lib_memory_resource 201603L [C++17]
__cpp_lib_modules 202207L [C++23]
__cpp_lib_move_iterator_concept 202207L [C++20]
@@ -7160,7 +7160,7 @@
# ifndef __cpp_lib_mdspan
# error "__cpp_lib_mdspan should be defined in c++26"
# endif
-# if __cpp_lib_mdspan != 202207L
+# if __cpp_lib_mdspan != 202406L
# error "__cpp_lib_mdspan should have the value 202207L in c++26"
# endif
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index fe5bab05195a3..89cba7169e94b 100755
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -848,7 +848,7 @@ def add_version_header(tc):
},
{
"name": "__cpp_lib_mdspan",
- "values": {"c++23": 202207},
+ "values": {"c++23": 202207, "c++26": 202406},
"headers": ["mdspan"],
},
{
``````````
</details>
https://github.com/llvm/llvm-project/pull/97393
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