From d879d44ba5685ad5b7b2faea3bcd0a274d38ebbb Mon Sep 17 00:00:00 2001
From: Yuao Ma <c8ef@outlook.com>
Date: Fri, 10 Oct 2025 22:14:21 +0800
Subject: [PATCH] libstdc++: Implement P2835R7 Expose std::atomic_ref's object
 address

This patch adds the address function to __atomic_ref_base.

libstdc++-v3/ChangeLog:

	* include/bits/atomic_base.h: Implement address().
	* include/bits/version.def: Bump version number.
	* include/bits/version.h: Regenerate.
	* testsuite/29_atomics/atomic_ref/address.cc: New test.
---
 libstdc++-v3/include/bits/atomic_base.h       |  6 +++
 libstdc++-v3/include/bits/version.def         |  4 ++
 libstdc++-v3/include/bits/version.h           |  7 ++-
 .../29_atomics/atomic_ref/address.cc          | 43 +++++++++++++++++++
 4 files changed, 59 insertions(+), 1 deletion(-)
 create mode 100644 libstdc++-v3/testsuite/29_atomics/atomic_ref/address.cc

diff --git a/libstdc++-v3/include/bits/atomic_base.h b/libstdc++-v3/include/bits/atomic_base.h
index 84661d449e2..8c7fbbc417c 100644
--- a/libstdc++-v3/include/bits/atomic_base.h
+++ b/libstdc++-v3/include/bits/atomic_base.h
@@ -1589,6 +1589,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       }
 #endif // __glibcxx_atomic_wait
 
+#if __glibcxx_atomic_ref >= 202411L
+      _GLIBCXX_ALWAYS_INLINE constexpr _Tp*
+      address() const noexcept
+      { return _M_ptr; }
+#endif // __glibcxx_atomic_ref >= 202411L
+
     protected:
       _Tp* _M_ptr;
     };
diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 83f1817bf8e..1118da4b541 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -789,6 +789,10 @@ ftms = {
 
 ftms = {
   name = atomic_ref;
+  values = {
+    v = 202411;
+    cxxmin = 26;
+  };
   values = {
     v = 201806;
     cxxmin = 20;
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 0d6692d244a..c452bbeec8e 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -880,7 +880,12 @@
 #undef __glibcxx_want_atomic_lock_free_type_aliases
 
 #if !defined(__cpp_lib_atomic_ref)
-# if (__cplusplus >= 202002L)
+# if (__cplusplus >  202302L)
+#  define __glibcxx_atomic_ref 202411L
+#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_atomic_ref)
+#   define __cpp_lib_atomic_ref 202411L
+#  endif
+# elif (__cplusplus >= 202002L)
 #  define __glibcxx_atomic_ref 201806L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_atomic_ref)
 #   define __cpp_lib_atomic_ref 201806L
diff --git a/libstdc++-v3/testsuite/29_atomics/atomic_ref/address.cc b/libstdc++-v3/testsuite/29_atomics/atomic_ref/address.cc
new file mode 100644
index 00000000000..52b3f5f131c
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_ref/address.cc
@@ -0,0 +1,43 @@
+// { dg-do run { target c++26 } }
+// { dg-require-atomic-cmpxchg-word "" }
+// { dg-add-options libatomic }
+
+#include <atomic>
+#include <memory>
+
+#include <testsuite_hooks.h>
+
+template <typename T>
+struct TestAtomicRefAddress
+{
+  void operator()() const
+  {
+    T x(T(42));
+    const std::atomic_ref<T> a(x);
+
+    static_assert(noexcept(a.address()));
+    VERIFY( std::addressof(x) == a.address() );
+  }
+};
+
+int
+main ()
+{
+  struct X { int c; };
+  TestAtomicRefAddress<X>()();
+  TestAtomicRefAddress<const X>()();
+  TestAtomicRefAddress<volatile X>()();
+  TestAtomicRefAddress<const volatile X>()();
+  TestAtomicRefAddress<int>()();
+  TestAtomicRefAddress<const int>()();
+  TestAtomicRefAddress<volatile int>()();
+  TestAtomicRefAddress<const volatile int>()();
+  TestAtomicRefAddress<float>()();
+  TestAtomicRefAddress<const float>()();
+  TestAtomicRefAddress<volatile float>()();
+  TestAtomicRefAddress<const volatile float>()();
+  TestAtomicRefAddress<char*>()();
+  TestAtomicRefAddress<char* const>()();
+  TestAtomicRefAddress<char* volatile>()();
+  TestAtomicRefAddress<char* const volatile>()();
+}
-- 
2.43.0