On 7/8/25 16:56, Tomasz Kaminski wrote:
On Thu, Jul 3, 2025 at 12:36 PM Luc Grosheintz <luc.groshei...@gmail.com>
wrote:
This commit implements and tests the function is_sufficiently_aligned
from P2897R7.
libstdc++-v3/ChangeLog:
* include/bits/align.h (is_sufficiently_aligned): New function.
* include/bits/version.def (is_sufficiently_aligned): Add.
* include/bits/version.h: Regenerate.
* include/std/memory: Add __glibcxx_want_is_sufficiently_aligned.
* src/c++23/std.cc.in (is_sufficiently_aligned): Add.
* testsuite/20_util/is_sufficiently_aligned/1.cc: New test.
* testsuite/20_util/is_sufficiently_aligned/2.cc: New test.
---
Only one small suggestion on placement of the tests. Otherwise it looks
good.
libstdc++-v3/include/bits/align.h | 16 ++++++++++
libstdc++-v3/include/bits/version.def | 8 +++++
libstdc++-v3/include/bits/version.h | 10 ++++++
libstdc++-v3/include/std/memory | 1 +
libstdc++-v3/src/c++23/std.cc.in | 1 +
.../20_util/is_sufficiently_aligned/1.cc | 31 +++++++++++++++++++
.../20_util/is_sufficiently_aligned/2.cc | 7 +++++
7 files changed, 74 insertions(+)
create mode 100644
libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/1.cc
create mode 100644
libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2.cc
diff --git a/libstdc++-v3/include/bits/align.h
b/libstdc++-v3/include/bits/align.h
index 2b40c37e033..fbbe9cb1f9c 100644
--- a/libstdc++-v3/include/bits/align.h
+++ b/libstdc++-v3/include/bits/align.h
@@ -102,6 +102,22 @@ align(size_t __align, size_t __size, void*& __ptr,
size_t& __space) noexcept
}
#endif // __glibcxx_assume_aligned
+#ifdef __glibcxx_is_sufficiently_aligned // C++ >= 26
+ /** @brief Is @a __ptr aligned to an _Align byte boundary?
+ *
+ * @tparam _Align An alignment value
+ * @tparam _Tp An object type
+ *
+ * C++26 20.2.5 [ptr.align]
+ *
+ * @ingroup memory
+ */
+ template<size_t _Align, class _Tp>
+ bool
+ is_sufficiently_aligned(_Tp* __ptr)
+ { return reinterpret_cast<__UINTPTR_TYPE__>(__ptr) % _Align == 0; }
+#endif // __glibcxx_is_sufficiently_aligned
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace
diff --git a/libstdc++-v3/include/bits/version.def
b/libstdc++-v3/include/bits/version.def
index f4ba501c403..a2695e67716 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -732,6 +732,14 @@ ftms = {
};
};
+ftms = {
+ name = is_sufficiently_aligned;
+ values = {
+ v = 202411;
+ cxxmin = 26;
+ };
+};
+
ftms = {
name = atomic_flag_test;
values = {
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index dc8ac07be16..1b17a965239 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -815,6 +815,16 @@
#endif /* !defined(__cpp_lib_assume_aligned) &&
defined(__glibcxx_want_assume_aligned) */
#undef __glibcxx_want_assume_aligned
+#if !defined(__cpp_lib_is_sufficiently_aligned)
+# if (__cplusplus > 202302L)
+# define __glibcxx_is_sufficiently_aligned 202411L
+# if defined(__glibcxx_want_all) ||
defined(__glibcxx_want_is_sufficiently_aligned)
+# define __cpp_lib_is_sufficiently_aligned 202411L
+# endif
+# endif
+#endif /* !defined(__cpp_lib_is_sufficiently_aligned) &&
defined(__glibcxx_want_is_sufficiently_aligned) */
+#undef __glibcxx_want_is_sufficiently_aligned
+
#if !defined(__cpp_lib_atomic_flag_test)
# if (__cplusplus >= 202002L)
# define __glibcxx_atomic_flag_test 201907L
diff --git a/libstdc++-v3/include/std/memory
b/libstdc++-v3/include/std/memory
index 1da03b3ea6a..ff342ff35f3 100644
--- a/libstdc++-v3/include/std/memory
+++ b/libstdc++-v3/include/std/memory
@@ -110,6 +110,7 @@
#define __glibcxx_want_constexpr_memory
#define __glibcxx_want_enable_shared_from_this
#define __glibcxx_want_indirect
+#define __glibcxx_want_is_sufficiently_aligned
#define __glibcxx_want_make_unique
#define __glibcxx_want_out_ptr
#define __glibcxx_want_parallel_algorithm
diff --git a/libstdc++-v3/src/c++23/std.cc.in b/libstdc++-v3/src/c++23/
std.cc.in
index e692caaa5f9..6f4214ed3a7 100644
--- a/libstdc++-v3/src/c++23/std.cc.in
+++ b/libstdc++-v3/src/c++23/std.cc.in
@@ -1864,6 +1864,7 @@ export namespace std
using std::allocator_arg_t;
using std::allocator_traits;
using std::assume_aligned;
+ using std::is_sufficiently_aligned;
using std::make_obj_using_allocator;
using std::pointer_traits;
using std::to_address;
diff --git a/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/1.cc
b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/1.cc
new file mode 100644
index 00000000000..4c2738b57db
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/1.cc
@@ -0,0 +1,31 @@
+// { dg-do run { target c++26 } }
+
+#include <memory>
+#include <array>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+ constexpr size_t N = 4;
+ constexpr size_t M = 2*N + 1;
+ alignas(N) std::array<char, M> buffer{};
+
+ auto* ptr = buffer.data();
+ VERIFY(std::is_sufficiently_aligned<1>(ptr+0));
+ VERIFY(std::is_sufficiently_aligned<1>(ptr+1));
+
+ VERIFY(std::is_sufficiently_aligned<2>(ptr+0));
+ VERIFY(!std::is_sufficiently_aligned<2>(ptr+1));
+ VERIFY(std::is_sufficiently_aligned<2>(ptr+2));
+
+ for (size_t i = 0; i < M; ++i)
+ VERIFY(std::is_sufficiently_aligned<N>(ptr + i) == (i % N == 0));
+}
+
+int
+main()
+{
+ test01();
+ return 0;
+}
diff --git a/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2.cc
b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2.cc
new file mode 100644
index 00000000000..8e0f4c07661
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_sufficiently_aligned/2.cc
@@ -0,0 +1,7 @@
+// { dg-do compile { target c++26 } }
+
+#include <memory>
+
+#ifndef __cpp_lib_is_sufficiently_aligned
+#error "Missing FTM"
+#endif
I would integrate that into 1.cc file directly. I do not think we need a
separate test.
Now I know they're called version.cc it's easier to find others. There's
testsuite/20_util/headers/memory/version.cc
which checks:
__cpp_lib_allocator_traits_is_always_equal
__cpp_lib_addressof_constexpr
That feels like the place to also put this one. It's use of dejagnu is
neat too:
// { dg-do preprocess { target c++17 } }
// { dg-add-options no_pch }
Now I'm tempted to adjust mdspan/version.cc accordingly.
--
2.49.0
