From 46e63634f767be3b92a76932d1ba3a0f562dc941 Mon Sep 17 00:00:00 2001
From: Yuao Ma <c8ef@outlook.com>
Date: Fri, 10 Oct 2025 23:14:48 +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       | 12 ++++++
 libstdc++-v3/include/bits/version.def         |  4 ++
 libstdc++-v3/include/bits/version.h           |  7 +++-
 .../29_atomics/atomic_ref/address.cc          | 39 +++++++++++++++++++
 4 files changed, 61 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..0f3f6b1925d 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 const _Tp*
+      address() const noexcept
+      { return _M_ptr; }
+#endif // __glibcxx_atomic_ref >= 202411L
+
     protected:
       _Tp* _M_ptr;
     };
@@ -1672,6 +1678,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	__atomic_impl::notify_all(this->_M_ptr);
       }
 #endif // __glibcxx_atomic_wait
+
+#if __glibcxx_atomic_ref >= 202411L
+      _GLIBCXX_ALWAYS_INLINE constexpr _Tp*
+      address() const noexcept
+      { return this->_M_ptr; }
+#endif // __glibcxx_atomic_ref >= 202411L
     };
 
   template<typename _Tp,
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..42a080af55e
--- /dev/null
+++ b/libstdc++-v3/testsuite/29_atomics/atomic_ref/address.cc
@@ -0,0 +1,39 @@
+// { dg-do run { target c++26 } }
+// { dg-require-atomic-cmpxchg-word "" }
+// { dg-add-options libatomic }
+
+#include <atomic>
+#include <memory>
+#include <type_traits>
+
+#include <testsuite_hooks.h>
+
+template <typename T>
+void testAtomicRefAddress()
+{
+  T x(T(42));
+  const std::atomic_ref<T> a(x);
+
+  static_assert( noexcept(a.address()) );
+  static_assert( std::is_same_v<decltype(a.address()), T*> );
+  VERIFY( std::addressof(x) == a.address() );
+}
+
+template <typename T>
+void testAtomicRefAddressForCV()
+{
+  testAtomicRefAddress<T>();
+  testAtomicRefAddress<const T>();
+  testAtomicRefAddress<volatile T>();
+  testAtomicRefAddress<const volatile T>();
+}
+
+int
+main ()
+{
+  struct X { int c; };
+  testAtomicRefAddressForCV<X>();
+  testAtomicRefAddressForCV<int>();
+  testAtomicRefAddressForCV<float>();
+  testAtomicRefAddressForCV<char*>();
+}
-- 
2.43.0