[libcxx-commits] [libcxx] faaeaf3 - [libc++] Implement P0493R5: Atomic minimum/maximum (#180333)
via libcxx-commits
libcxx-commits at lists.llvm.org
Tue Jul 21 04:41:55 PDT 2026
Author: Connector Switch
Date: 2026-07-21T19:41:49+08:00
New Revision: faaeaf35a50acefd4e25e092e3f720067c40afe3
URL: https://github.com/llvm/llvm-project/commit/faaeaf35a50acefd4e25e092e3f720067c40afe3
DIFF: https://github.com/llvm/llvm-project/commit/faaeaf35a50acefd4e25e092e3f720067c40afe3.diff
LOG: [libc++] Implement P0493R5: Atomic minimum/maximum (#180333)
Closes #105418.
Since gcc does not currently support `__atomic_fetch_min/max`, we use a
CAS loop in `atomic_ref` and `support/gcc.h`.
---------
Co-authored-by: Louis Dionne <ldionne.2 at gmail.com>
Added:
libcxx/test/std/atomics/atomics.ref/fetch_max.pass.cpp
libcxx/test/std/atomics/atomics.ref/fetch_min.pass.cpp
libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max.pass.cpp
libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max_explicit.pass.cpp
libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min.pass.cpp
libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min_explicit.pass.cpp
libcxx/test/support/atomic_fetch_max_helper.h
libcxx/test/support/atomic_fetch_min_helper.h
Modified:
libcxx/docs/FeatureTestMacroTable.rst
libcxx/docs/ReleaseNotes/24.rst
libcxx/docs/Status/Cxx26Papers.csv
libcxx/include/__atomic/atomic.h
libcxx/include/__atomic/atomic_ref.h
libcxx/include/__atomic/support.h
libcxx/include/__atomic/support/c11.h
libcxx/include/__atomic/support/gcc.h
libcxx/include/atomic
libcxx/include/version
libcxx/modules/std/atomic.inc
libcxx/test/std/language.support/support.limits/support.limits.general/atomic.version.compile.pass.cpp
libcxx/test/std/language.support/support.limits/support.limits.general/version.version.compile.pass.cpp
libcxx/utils/generate_feature_test_macro_components.py
Removed:
################################################################################
diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index 6bf2f35fb4212..00665332a9ed7 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -424,7 +424,7 @@ Status
---------------------------------------------------------- -----------------
``__cpp_lib_associative_heterogeneous_insertion`` *unimplemented*
---------------------------------------------------------- -----------------
- ``__cpp_lib_atomic_min_max`` *unimplemented*
+ ``__cpp_lib_atomic_min_max`` ``202403L``
---------------------------------------------------------- -----------------
``__cpp_lib_atomic_ref`` ``202603L``
---------------------------------------------------------- -----------------
diff --git a/libcxx/docs/ReleaseNotes/24.rst b/libcxx/docs/ReleaseNotes/24.rst
index bcac37b8a717f..70c704ff9d326 100644
--- a/libcxx/docs/ReleaseNotes/24.rst
+++ b/libcxx/docs/ReleaseNotes/24.rst
@@ -38,6 +38,7 @@ What's New in Libc++ 24.0.0?
Implemented Papers
------------------
+- P0493R5: Atomic minimum/maximum (`Github <https://llvm.org/PR105418>`__)
Improvements and New Features
-----------------------------
diff --git a/libcxx/docs/Status/Cxx26Papers.csv b/libcxx/docs/Status/Cxx26Papers.csv
index 916bb559f254b..7fcebd331197b 100644
--- a/libcxx/docs/Status/Cxx26Papers.csv
+++ b/libcxx/docs/Status/Cxx26Papers.csv
@@ -53,7 +53,7 @@
"`P3107R5 <https://wg21.link/P3107R5>`__","Permit an efficient implementation of ``std::print``","2024-03 (Tokyo)","","","`#105414 <https://github.com/llvm/llvm-project/issues/105414>`__",""
"`P3142R0 <https://wg21.link/P3142R0>`__","Printing Blank Lines with ``println``","2024-03 (Tokyo)","|Complete|","19","`#105415 <https://github.com/llvm/llvm-project/issues/105415>`__","Implemented as a DR against C++23."
"`P2845R8 <https://wg21.link/P2845R8>`__","Formatting of ``std::filesystem::path``","2024-03 (Tokyo)","","","`#105416 <https://github.com/llvm/llvm-project/issues/105416>`__",""
-"`P0493R5 <https://wg21.link/P0493R5>`__","Atomic minimum/maximum","2024-03 (Tokyo)","","","`#105418 <https://github.com/llvm/llvm-project/issues/105418>`__",""
+"`P0493R5 <https://wg21.link/P0493R5>`__","Atomic minimum/maximum","2024-03 (Tokyo)","|Complete|","24","`#105418 <https://github.com/llvm/llvm-project/issues/105418>`__",""
"`P2542R8 <https://wg21.link/P2542R8>`__","``views::concat``","2024-03 (Tokyo)","|Complete|","23","`#105419 <https://github.com/llvm/llvm-project/issues/105419>`__",""
"`P2591R5 <https://wg21.link/P2591R5>`__","Concatenation of strings and string views","2024-03 (Tokyo)","|Complete|","19","`#105420 <https://github.com/llvm/llvm-project/issues/105420>`__",""
"`P2248R8 <https://wg21.link/P2248R8>`__","Enabling list-initialization for algorithms","2024-03 (Tokyo)","","","`#105421 <https://github.com/llvm/llvm-project/issues/105421>`__",""
diff --git a/libcxx/include/__atomic/atomic.h b/libcxx/include/__atomic/atomic.h
index 3d0ed9cc47396..d21ebf20bf23d 100644
--- a/libcxx/include/__atomic/atomic.h
+++ b/libcxx/include/__atomic/atomic.h
@@ -16,6 +16,8 @@
#include <__atomic/is_always_lock_free.h>
#include <__atomic/memory_order.h>
#include <__atomic/support.h>
+#include <__concepts/arithmetic.h>
+#include <__concepts/same_as.h>
#include <__config>
#include <__cstddef/ptr
diff _t.h>
#include <__memory/addressof.h>
@@ -24,6 +26,7 @@
#include <__type_traits/is_function.h>
#include <__type_traits/is_integral.h>
#include <__type_traits/is_nothrow_constructible.h>
+#include <__type_traits/is_pointer.h>
#include <__type_traits/is_same.h>
#include <__type_traits/is_trivially_copyable.h>
#include <__type_traits/remove_pointer.h>
@@ -178,6 +181,20 @@ struct __atomic_base<_Tp, true> : public __atomic_base<_Tp, false> {
_LIBCPP_HIDE_FROM_ABI _Tp fetch_xor(_Tp __op, memory_order __m = memory_order_seq_cst) _NOEXCEPT {
return std::__cxx_atomic_fetch_xor(std::addressof(this->__a_), __op, __m);
}
+#if _LIBCPP_STD_VER >= 26
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_max(_Tp __op, memory_order __m = memory_order_seq_cst) volatile _NOEXCEPT {
+ return std::__cxx_atomic_fetch_max(std::addressof(this->__a_), __op, __m);
+ }
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_max(_Tp __op, memory_order __m = memory_order_seq_cst) _NOEXCEPT {
+ return std::__cxx_atomic_fetch_max(std::addressof(this->__a_), __op, __m);
+ }
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_min(_Tp __op, memory_order __m = memory_order_seq_cst) volatile _NOEXCEPT {
+ return std::__cxx_atomic_fetch_min(std::addressof(this->__a_), __op, __m);
+ }
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_min(_Tp __op, memory_order __m = memory_order_seq_cst) _NOEXCEPT {
+ return std::__cxx_atomic_fetch_min(std::addressof(this->__a_), __op, __m);
+ }
+#endif
_LIBCPP_HIDE_FROM_ABI _Tp operator++(int) volatile _NOEXCEPT { return fetch_add(_Tp(1)); }
_LIBCPP_HIDE_FROM_ABI _Tp operator++(int) _NOEXCEPT { return fetch_add(_Tp(1)); }
@@ -306,6 +323,28 @@ struct atomic<_Tp*> : public __atomic_base<_Tp*> {
return std::__cxx_atomic_fetch_sub(std::addressof(this->__a_), __op, __m);
}
+#if _LIBCPP_STD_VER >= 26
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_max(_Tp* __op, memory_order __m = memory_order_seq_cst) volatile _NOEXCEPT {
+ static_assert(!is_function<__remove_pointer_t<_Tp> >::value, "Pointer to function isn't allowed");
+ return std::__cxx_atomic_fetch_max(std::addressof(this->__a_), __op, __m);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_max(_Tp* __op, memory_order __m = memory_order_seq_cst) _NOEXCEPT {
+ static_assert(!is_function<__remove_pointer_t<_Tp> >::value, "Pointer to function isn't allowed");
+ return std::__cxx_atomic_fetch_max(std::addressof(this->__a_), __op, __m);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_min(_Tp* __op, memory_order __m = memory_order_seq_cst) volatile _NOEXCEPT {
+ static_assert(!is_function<__remove_pointer_t<_Tp> >::value, "Pointer to function isn't allowed");
+ return std::__cxx_atomic_fetch_min(std::addressof(this->__a_), __op, __m);
+ }
+
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_min(_Tp* __op, memory_order __m = memory_order_seq_cst) _NOEXCEPT {
+ static_assert(!is_function<__remove_pointer_t<_Tp> >::value, "Pointer to function isn't allowed");
+ return std::__cxx_atomic_fetch_min(std::addressof(this->__a_), __op, __m);
+ }
+#endif
+
_LIBCPP_HIDE_FROM_ABI _Tp* operator++(int) volatile _NOEXCEPT { return fetch_add(1); }
_LIBCPP_HIDE_FROM_ABI _Tp* operator++(int) _NOEXCEPT { return fetch_add(1); }
_LIBCPP_HIDE_FROM_ABI _Tp* operator--(int) volatile _NOEXCEPT { return fetch_sub(1); }
@@ -799,6 +838,68 @@ atomic_fetch_xor_explicit(atomic<_Tp>* __o, typename atomic<_Tp>::value_type __o
return __o->fetch_xor(__op, __m);
}
+#if _LIBCPP_STD_VER >= 26
+// atomic_fetch_max
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_max(volatile atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op) _NOEXCEPT {
+ return __o->fetch_max(__op);
+}
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_max(atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op) _NOEXCEPT {
+ return __o->fetch_max(__op);
+}
+
+// atomic_fetch_max_explicit
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_max_explicit(
+ volatile atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op, memory_order __m) _NOEXCEPT {
+ return __o->fetch_max(__op, __m);
+}
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp
+atomic_fetch_max_explicit(atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op, memory_order __m) _NOEXCEPT {
+ return __o->fetch_max(__op, __m);
+}
+
+// atomic_fetch_min
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_min(volatile atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op) _NOEXCEPT {
+ return __o->fetch_min(__op);
+}
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_min(atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op) _NOEXCEPT {
+ return __o->fetch_min(__op);
+}
+
+// atomic_fetch_min_explicit
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp atomic_fetch_min_explicit(
+ volatile atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op, memory_order __m) _NOEXCEPT {
+ return __o->fetch_min(__op, __m);
+}
+
+template <class _Tp>
+ requires((integral<_Tp> && !same_as<_Tp, bool>) || is_pointer_v<_Tp>)
+_LIBCPP_HIDE_FROM_ABI _Tp
+atomic_fetch_min_explicit(atomic<_Tp>* __o, typename atomic<_Tp>::value_type __op, memory_order __m) _NOEXCEPT {
+ return __o->fetch_min(__op, __m);
+}
+#endif
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ATOMIC_ATOMIC_H
diff --git a/libcxx/include/__atomic/atomic_ref.h b/libcxx/include/__atomic/atomic_ref.h
index 93f19a740ba3a..78f1f24f4c7a4 100644
--- a/libcxx/include/__atomic/atomic_ref.h
+++ b/libcxx/include/__atomic/atomic_ref.h
@@ -304,6 +304,32 @@ struct atomic_ref<_Tp> : public __atomic_ref_base<_Tp> {
_LIBCPP_HIDE_FROM_ABI _Tp fetch_xor(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
return __atomic_fetch_xor(this->__ptr_, __arg, std::__to_gcc_order(__order));
}
+# if _LIBCPP_STD_VER >= 26
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_max(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+# if __has_builtin(__atomic_fetch_max)
+ return __atomic_fetch_max(this->__ptr_, __arg, std::__to_gcc_order(__order));
+# else
+ _Tp __old = this->load(memory_order_relaxed);
+ _Tp __new;
+ do {
+ __new = __old > __arg ? __old : __arg;
+ } while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed));
+ return __old;
+# endif
+ }
+ _LIBCPP_HIDE_FROM_ABI _Tp fetch_min(_Tp __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+# if __has_builtin(__atomic_fetch_min)
+ return __atomic_fetch_min(this->__ptr_, __arg, std::__to_gcc_order(__order));
+# else
+ _Tp __old = this->load(memory_order_relaxed);
+ _Tp __new;
+ do {
+ __new = __old < __arg ? __old : __arg;
+ } while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed));
+ return __old;
+# endif
+ }
+# endif
_LIBCPP_HIDE_FROM_ABI _Tp operator++(int) const noexcept { return fetch_add(_Tp(1)); }
_LIBCPP_HIDE_FROM_ABI _Tp operator--(int) const noexcept { return fetch_sub(_Tp(1)); }
@@ -386,6 +412,26 @@ struct atomic_ref<_Tp*> : public __atomic_ref_base<_Tp*> {
_LIBCPP_HIDE_FROM_ABI _Tp* fetch_sub(ptr
diff _t __arg, memory_order __order = memory_order_seq_cst) const noexcept {
return __atomic_fetch_sub(this->__ptr_, __arg * sizeof(_Tp), std::__to_gcc_order(__order));
}
+# if _LIBCPP_STD_VER >= 26
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_max(_Tp* __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+ // TODO: Use __atomic_fetch_max once it accepts pointer arguments.
+ _Tp* __old = this->load(memory_order_relaxed);
+ _Tp* __new;
+ do {
+ __new = __old > __arg ? __old : __arg;
+ } while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed));
+ return __old;
+ }
+ _LIBCPP_HIDE_FROM_ABI _Tp* fetch_min(_Tp* __arg, memory_order __order = memory_order_seq_cst) const noexcept {
+ // TODO: Use __atomic_fetch_min once it accepts pointer arguments.
+ _Tp* __old = this->load(memory_order_relaxed);
+ _Tp* __new;
+ do {
+ __new = __old < __arg ? __old : __arg;
+ } while (!this->compare_exchange_weak(__old, __new, __order, memory_order_relaxed));
+ return __old;
+ }
+# endif
_LIBCPP_HIDE_FROM_ABI _Tp* operator++(int) const noexcept { return fetch_add(1); }
_LIBCPP_HIDE_FROM_ABI _Tp* operator--(int) const noexcept { return fetch_sub(1); }
diff --git a/libcxx/include/__atomic/support.h b/libcxx/include/__atomic/support.h
index 053ad54aa6ce5..55a93face9d83 100644
--- a/libcxx/include/__atomic/support.h
+++ b/libcxx/include/__atomic/support.h
@@ -99,6 +99,15 @@
// template <class _Tp>
// _Tp __cxx_atomic_fetch_xor(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
//
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_max(_Atmc<_Tp> volatile* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_max(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_min(_Atmc<_Tp> volatile* __a, _Tp __pattern, memory_order __order) noexcept;
+// template <class _Tp>
+// _Tp __cxx_atomic_fetch_min(_Atmc<_Tp>* __a, _Tp __pattern, memory_order __order) noexcept;
+//
// clang-format on
//
diff --git a/libcxx/include/__atomic/support/c11.h b/libcxx/include/__atomic/support/c11.h
index 1ad299882a12a..899502422570a 100644
--- a/libcxx/include/__atomic/support/c11.h
+++ b/libcxx/include/__atomic/support/c11.h
@@ -13,6 +13,8 @@
#include <__config>
#include <__cstddef/ptr
diff _t.h>
#include <__memory/addressof.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_pointer.h>
#include <__type_traits/remove_const.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -259,6 +261,81 @@ __cxx_atomic_fetch_xor(__cxx_atomic_base_impl<_Tp>* __a, _Tp __pattern, memory_o
std::addressof(__a->__a_value), __pattern, static_cast<__memory_order_underlying_t>(__order));
}
+// Clang's __c11_atomic_fetch_max/min builtins do not accept pointer
+// arguments, so dispatch to a CAS loop for pointer types.
+// TODO: Use the builtin for pointer types once Clang accepts them.
+template <class _Tp, __enable_if_t<!is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_max(__cxx_atomic_base_impl<_Tp> volatile* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ return __c11_atomic_fetch_max(
+ std::addressof(__a->__a_value), __val, static_cast<__memory_order_underlying_t>(__order));
+}
+template <class _Tp, __enable_if_t<is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_max(__cxx_atomic_base_impl<_Tp> volatile* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ _Tp __ret = std::__cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret > __val ? __ret : __val;
+ } while (
+ !std::__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+}
+
+template <class _Tp, __enable_if_t<!is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_max(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ return __c11_atomic_fetch_max(
+ std::addressof(__a->__a_value), __val, static_cast<__memory_order_underlying_t>(__order));
+}
+template <class _Tp, __enable_if_t<is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_max(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ _Tp __ret = std::__cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret > __val ? __ret : __val;
+ } while (
+ !std::__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+}
+
+template <class _Tp, __enable_if_t<!is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_min(__cxx_atomic_base_impl<_Tp> volatile* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ return __c11_atomic_fetch_min(
+ std::addressof(__a->__a_value), __val, static_cast<__memory_order_underlying_t>(__order));
+}
+template <class _Tp, __enable_if_t<is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_min(__cxx_atomic_base_impl<_Tp> volatile* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ _Tp __ret = std::__cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret < __val ? __ret : __val;
+ } while (
+ !std::__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+}
+
+template <class _Tp, __enable_if_t<!is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_min(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ return __c11_atomic_fetch_min(
+ std::addressof(__a->__a_value), __val, static_cast<__memory_order_underlying_t>(__order));
+}
+template <class _Tp, __enable_if_t<is_pointer<_Tp>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_min(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) _NOEXCEPT {
+ _Tp __ret = std::__cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret < __val ? __ret : __val;
+ } while (
+ !std::__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+}
+
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ATOMIC_SUPPORT_C11_H
diff --git a/libcxx/include/__atomic/support/gcc.h b/libcxx/include/__atomic/support/gcc.h
index 73c1b1c8070a4..37c38d25012c6 100644
--- a/libcxx/include/__atomic/support/gcc.h
+++ b/libcxx/include/__atomic/support/gcc.h
@@ -258,6 +258,64 @@ __cxx_atomic_fetch_xor(__cxx_atomic_base_impl<_Tp>* __a, _Tp __pattern, memory_o
return __atomic_fetch_xor(std::addressof(__a->__a_value), __pattern, __to_gcc_order(__order));
}
+template <typename _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_max(volatile __cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) {
+#if __has_builtin(__atomic_fetch_max)
+ return __atomic_fetch_max(std::addressof(__a->__a_value), __val, __to_gcc_order(__order));
+#else
+ _Tp __ret = __cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret > __val ? __ret : __val;
+ } while (!__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+#endif
+}
+
+template <typename _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp __cxx_atomic_fetch_max(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) {
+#if __has_builtin(__atomic_fetch_max)
+ return __atomic_fetch_max(std::addressof(__a->__a_value), __val, __to_gcc_order(__order));
+#else
+ _Tp __ret = __cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret > __val ? __ret : __val;
+ } while (!__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+#endif
+}
+
+template <typename _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__cxx_atomic_fetch_min(volatile __cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) {
+#if __has_builtin(__atomic_fetch_min)
+ return __atomic_fetch_min(std::addressof(__a->__a_value), __val, __to_gcc_order(__order));
+#else
+ _Tp __ret = __cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret < __val ? __ret : __val;
+ } while (!__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+#endif
+}
+
+template <typename _Tp>
+_LIBCPP_HIDE_FROM_ABI _Tp __cxx_atomic_fetch_min(__cxx_atomic_base_impl<_Tp>* __a, _Tp __val, memory_order __order) {
+#if __has_builtin(__atomic_fetch_min)
+ return __atomic_fetch_min(std::addressof(__a->__a_value), __val, __to_gcc_order(__order));
+#else
+ _Tp __ret = __cxx_atomic_load(__a, memory_order_relaxed);
+ _Tp __value;
+ do {
+ __value = __ret < __val ? __ret : __val;
+ } while (!__cxx_atomic_compare_exchange_weak(__a, std::addressof(__ret), __value, __order, memory_order_relaxed));
+ return __ret;
+#endif
+}
+
#define __cxx_atomic_is_lock_free(__s) __atomic_is_lock_free(__s, 0)
_LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/include/atomic b/libcxx/include/atomic
index a6a910c2f380f..a89987ebd36e6 100644
--- a/libcxx/include/atomic
+++ b/libcxx/include/atomic
@@ -164,6 +164,10 @@ struct atomic<integral>
integral fetch_or(integral op, memory_order m = memory_order_seq_cst) noexcept;
integral fetch_xor(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
integral fetch_xor(integral op, memory_order m = memory_order_seq_cst) noexcept;
+ integral fetch_max(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
+ integral fetch_max(integral op, memory_order m = memory_order_seq_cst) noexcept;
+ integral fetch_min(integral op, memory_order m = memory_order_seq_cst) volatile noexcept;
+ integral fetch_min(integral op, memory_order m = memory_order_seq_cst) noexcept;
integral operator++(int) volatile noexcept;
integral operator++(int) noexcept;
@@ -240,6 +244,10 @@ struct atomic<T*>
T* fetch_add(ptr
diff _t op, memory_order m = memory_order_seq_cst) noexcept;
T* fetch_sub(ptr
diff _t op, memory_order m = memory_order_seq_cst) volatile noexcept;
T* fetch_sub(ptr
diff _t op, memory_order m = memory_order_seq_cst) noexcept;
+ T* fetch_max(T*, memory_order = memory_order_seq_cst) volatile noexcept;
+ T* fetch_max(T*, memory_order = memory_order_seq_cst) noexcept;
+ T* fetch_min(T*, memory_order = memory_order_seq_cst) volatile noexcept;
+ T* fetch_min(T*, memory_order = memory_order_seq_cst) noexcept;
T* operator++(int) volatile noexcept;
T* operator++(int) noexcept;
@@ -441,6 +449,26 @@ template<class T>
template<class T>
T atomic_fetch_xor_explicit(atomic<T>*, atomic<T>::value_type,
memory_order) noexcept;
+template<class T>
+ T atomic_fetch_max(volatile atomic<T>*, atomic<T>::value_type) noexcept;
+template<class T>
+ T atomic_fetch_max(atomic<T>*, atomic<T>::value_type) noexcept;
+template<class T>
+ T atomic_fetch_max_explicit(volatile atomic<T>*, atomic<T>::value_type,
+ memory_order) noexcept;
+template<class T>
+ T atomic_fetch_max_explicit(atomic<T>*, atomic<T>::value_type,
+ memory_order) noexcept;
+template<class T>
+ T atomic_fetch_min(volatile atomic<T>*, atomic<T>::value_type) noexcept;
+template<class T>
+ T atomic_fetch_min(atomic<T>*, atomic<T>::value_type) noexcept;
+template<class T>
+ T atomic_fetch_min_explicit(volatile atomic<T>*, atomic<T>::value_type,
+ memory_order) noexcept;
+template<class T>
+ T atomic_fetch_min_explicit(atomic<T>*, atomic<T>::value_type,
+ memory_order) noexcept;
template<class T>
void atomic_wait(const volatile atomic<T>*, atomic<T>::value_type) noexcept; // since C++20
diff --git a/libcxx/include/version b/libcxx/include/version
index 4a6b01093641d..7545d187ca7f1 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -558,7 +558,7 @@ __cpp_lib_void_t 201411L <type_traits>
#if _LIBCPP_STD_VER >= 26
# define __cpp_lib_aligned_accessor 202411L
// # define __cpp_lib_associative_heterogeneous_insertion 202306L
-// # define __cpp_lib_atomic_min_max 202403L
+# define __cpp_lib_atomic_min_max 202403L
# undef __cpp_lib_atomic_ref
# define __cpp_lib_atomic_ref 202603L
# undef __cpp_lib_bind_front
diff --git a/libcxx/modules/std/atomic.inc b/libcxx/modules/std/atomic.inc
index 9a30fb7affe71..38321e1a1bb64 100644
--- a/libcxx/modules/std/atomic.inc
+++ b/libcxx/modules/std/atomic.inc
@@ -50,6 +50,12 @@ export namespace std {
using std::atomic_fetch_sub_explicit _LIBCPP_USING_IF_EXISTS;
using std::atomic_fetch_xor _LIBCPP_USING_IF_EXISTS;
using std::atomic_fetch_xor_explicit _LIBCPP_USING_IF_EXISTS;
+#if _LIBCPP_STD_VER >= 26
+ using std::atomic_fetch_max _LIBCPP_USING_IF_EXISTS;
+ using std::atomic_fetch_max_explicit _LIBCPP_USING_IF_EXISTS;
+ using std::atomic_fetch_min _LIBCPP_USING_IF_EXISTS;
+ using std::atomic_fetch_min_explicit _LIBCPP_USING_IF_EXISTS;
+#endif
using std::atomic_notify_all _LIBCPP_USING_IF_EXISTS;
using std::atomic_notify_one _LIBCPP_USING_IF_EXISTS;
using std::atomic_wait _LIBCPP_USING_IF_EXISTS;
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_max.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_max.pass.cpp
new file mode 100644
index 0000000000000..7302eaea570f0
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_max.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_max(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+// T* fetch_max(T*, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_fetch_max_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_max = requires(std::atomic_ref<T> const& a, T v) {
+ { a.fetch_max(v) } -> std::same_as<T>;
+ { a.fetch_max(v, std::memory_order::relaxed) } -> std::same_as<T>;
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchMax {
+ void operator()() const { static_assert(!has_fetch_max<T>); }
+};
+
+template <typename T>
+struct TestFetchMax {
+ void operator()() const {
+ static_assert((std::is_integral_v<T> || std::is_pointer_v<T>) && has_fetch_max<T>);
+
+ if constexpr (std::is_integral_v<T>) {
+ alignas(std::atomic_ref<T>::required_alignment) T x{};
+ std::atomic_ref<T> const a(x);
+
+ auto load = [&]() { return x; };
+ auto store = [&](T val) { x = val; };
+ auto max = [&](T val, auto order) { return a.fetch_max(val, order); };
+
+ ASSERT_NOEXCEPT(a.fetch_max(T(0), std::memory_order_seq_cst));
+ test_fetch_max_integral<T>(load, store, max);
+
+ } else if constexpr (std::is_pointer_v<T>) {
+ using U = std::remove_pointer_t<T>;
+ U arr[5]{};
+ alignas(std::atomic_ref<T>::required_alignment) T p{};
+ std::atomic_ref<T> const a(p);
+
+ auto load = [&]() { return p; };
+ auto store = [&](T val) { p = val; };
+ auto max = [&](T val, auto order) { return a.fetch_max(val, order); };
+
+ ASSERT_NOEXCEPT(a.fetch_max(&arr[0], std::memory_order_seq_cst));
+ test_fetch_max_pointer<U>(&arr[0], &arr[2], &arr[4], load, store, max);
+ }
+ }
+};
+
+int main(int, char**) {
+ TestEachIntegralType<TestFetchMax>()();
+ TestEachPointerType<TestFetchMax>()();
+
+ TestEachFloatingPointType<TestDoesNotHaveFetchMax>()();
+
+ TestDoesNotHaveFetchMax<bool>()();
+ TestDoesNotHaveFetchMax<UserAtomicType>()();
+ TestDoesNotHaveFetchMax<LargeUserAtomicType>()();
+
+ return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.ref/fetch_min.pass.cpp b/libcxx/test/std/atomics/atomics.ref/fetch_min.pass.cpp
new file mode 100644
index 0000000000000..e7f36363ae3a7
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.ref/fetch_min.pass.cpp
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// integral-type fetch_min(integral-type, memory_order = memory_order::seq_cst) const noexcept;
+// T* fetch_min(T*, memory_order = memory_order::seq_cst) const noexcept;
+
+#include <atomic>
+#include <cassert>
+#include <concepts>
+#include <type_traits>
+
+#include "atomic_fetch_min_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+template <typename T>
+concept has_fetch_min = requires(std::atomic_ref<T> const& a, T v) {
+ { a.fetch_min(v) } -> std::same_as<T>;
+ { a.fetch_min(v, std::memory_order::relaxed) } -> std::same_as<T>;
+};
+
+template <typename T>
+struct TestDoesNotHaveFetchMin {
+ void operator()() const { static_assert(!has_fetch_min<T>); }
+};
+
+template <typename T>
+struct TestFetchMin {
+ void operator()() const {
+ static_assert((std::is_integral_v<T> || std::is_pointer_v<T>) && has_fetch_min<T>);
+
+ if constexpr (std::is_integral_v<T>) {
+ alignas(std::atomic_ref<T>::required_alignment) T x{};
+ std::atomic_ref<T> const a(x);
+
+ auto load = [&]() { return x; };
+ auto store = [&](T val) { x = val; };
+ auto min = [&](T val, auto order) { return a.fetch_min(val, order); };
+
+ ASSERT_NOEXCEPT(a.fetch_min(T(0), std::memory_order_seq_cst));
+ test_fetch_min_integral<T>(load, store, min);
+
+ } else if constexpr (std::is_pointer_v<T>) {
+ using U = std::remove_pointer_t<T>;
+ U arr[5]{};
+ alignas(std::atomic_ref<T>::required_alignment) T p{};
+ std::atomic_ref<T> const a(p);
+
+ auto load = [&]() { return p; };
+ auto store = [&](T val) { p = val; };
+ auto min = [&](T val, auto order) { return a.fetch_min(val, order); };
+
+ ASSERT_NOEXCEPT(a.fetch_min(&arr[0], std::memory_order_seq_cst));
+ test_fetch_min_pointer<U>(&arr[0], &arr[2], &arr[4], load, store, min);
+ }
+ }
+};
+
+int main(int, char**) {
+ TestEachIntegralType<TestFetchMin>()();
+ TestEachPointerType<TestFetchMin>()();
+
+ TestEachFloatingPointType<TestDoesNotHaveFetchMin>()();
+
+ TestDoesNotHaveFetchMin<bool>()();
+ TestDoesNotHaveFetchMin<UserAtomicType>()();
+ TestDoesNotHaveFetchMin<LargeUserAtomicType>()();
+
+ return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max.pass.cpp
new file mode 100644
index 0000000000000..7b2a5715ddddd
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max.pass.cpp
@@ -0,0 +1,121 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// <atomic>
+
+// template<class T>
+// T atomic_fetch_max(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
+// template<class T>
+// constexpr T atomic_fetch_max(atomic<T>*, typename atomic<T>::value_type) noexcept;
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_fetch_max_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+#ifndef TEST_HAS_NO_THREADS
+# include <thread>
+
+# include "make_test_thread.h"
+#endif
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_impl() {
+ {
+ MaybeVolatile<std::atomic<T>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T val) { a.store(val); };
+ auto max = [&](T val, auto) { return std::atomic_fetch_max(&a, val); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_max(&a, T(0)));
+ test_fetch_max_integral<T>(load, store, max);
+ }
+
+#ifndef TEST_HAS_NO_THREADS
+ // Concurrent stress test: many threads calling atomic_fetch_max should leave
+ // the atomic at the global maximum value seen.
+ {
+ constexpr auto number_of_threads = 4;
+ constexpr auto loop = 30;
+
+ MaybeVolatile<std::atomic<T>> at(0);
+
+ std::vector<std::thread> threads;
+ threads.reserve(number_of_threads);
+ for (auto i = 0; i < number_of_threads; ++i) {
+ threads.push_back(support::make_test_thread([&at, i]() {
+ for (auto j = 0; j < loop; ++j) {
+ std::atomic_fetch_max(&at, T(i * loop + j));
+ }
+ }));
+ }
+
+ for (auto& thread : threads) {
+ thread.join();
+ }
+
+ const auto times = [](int n) {
+ T res(0);
+ for (auto i = 0; i < n; ++i) {
+ res = std::max<T>(res, i);
+ }
+ return res;
+ };
+
+ assert(at.load() == times(number_of_threads * loop));
+ }
+#endif
+}
+
+template <class T>
+struct TestFn {
+ void operator()() const {
+ test_impl<T>();
+ if constexpr (std::atomic<T>::is_always_lock_free) {
+ test_impl<T, std::add_volatile_t>();
+ }
+ }
+};
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_pointer_impl() {
+ T arr[5];
+ T* p0 = &arr[0];
+ T* p2 = &arr[2];
+ T* p4 = &arr[4];
+
+ MaybeVolatile<std::atomic<T*>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T* val) { a.store(val); };
+ auto max = [&](T* val, auto) { return std::atomic_fetch_max(&a, val); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_max(&a, p0));
+ test_fetch_max_pointer<T>(p0, p2, p4, load, store, max);
+}
+
+template <class T>
+void test_pointer() {
+ test_pointer_impl<T>();
+ if constexpr (std::atomic<T*>::is_always_lock_free) {
+ test_pointer_impl<T, std::add_volatile_t>();
+ }
+}
+
+int main(int, char**) {
+ TestEachIntegralType<TestFn>()();
+ test_pointer<int>();
+ test_pointer<char>();
+
+ return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max_explicit.pass.cpp
new file mode 100644
index 0000000000000..e811f114708c8
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_max_explicit.pass.cpp
@@ -0,0 +1,123 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// <atomic>
+
+// template<class T>
+// T atomic_fetch_max_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
+// memory_order) noexcept;
+// template<class T>
+// constexpr T atomic_fetch_max_explicit(atomic<T>*, typename atomic<T>::value_type,
+// memory_order) noexcept;
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_fetch_max_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+#ifndef TEST_HAS_NO_THREADS
+# include <thread>
+
+# include "make_test_thread.h"
+#endif
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_impl() {
+ {
+ MaybeVolatile<std::atomic<T>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T val) { a.store(val); };
+ auto max = [&](T val, auto order) { return std::atomic_fetch_max_explicit(&a, val, order); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_max_explicit(&a, T(0), std::memory_order_seq_cst));
+ test_fetch_max_integral<T>(load, store, max);
+ }
+
+#ifndef TEST_HAS_NO_THREADS
+ // Concurrent stress test: many threads calling atomic_fetch_max_explicit should
+ // leave the atomic at the global maximum value seen.
+ {
+ constexpr auto number_of_threads = 4;
+ constexpr auto loop = 30;
+
+ MaybeVolatile<std::atomic<T>> at(0);
+
+ std::vector<std::thread> threads;
+ threads.reserve(number_of_threads);
+ for (auto i = 0; i < number_of_threads; ++i) {
+ threads.push_back(support::make_test_thread([&at, i]() {
+ for (auto j = 0; j < loop; ++j) {
+ std::atomic_fetch_max_explicit(&at, T(i * loop + j), std::memory_order_relaxed);
+ }
+ }));
+ }
+
+ for (auto& thread : threads) {
+ thread.join();
+ }
+
+ const auto times = [](int n) {
+ T res(0);
+ for (auto i = 0; i < n; ++i) {
+ res = std::max<T>(res, i);
+ }
+ return res;
+ };
+
+ assert(at.load() == times(number_of_threads * loop));
+ }
+#endif
+}
+
+template <class T>
+struct TestFn {
+ void operator()() const {
+ test_impl<T>();
+ if constexpr (std::atomic<T>::is_always_lock_free) {
+ test_impl<T, std::add_volatile_t>();
+ }
+ }
+};
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_pointer_impl() {
+ T arr[5];
+ T* p0 = &arr[0];
+ T* p2 = &arr[2];
+ T* p4 = &arr[4];
+
+ MaybeVolatile<std::atomic<T*>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T* val) { a.store(val); };
+ auto max = [&](T* val, auto order) { return std::atomic_fetch_max_explicit(&a, val, order); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_max_explicit(&a, p0, std::memory_order_seq_cst));
+ test_fetch_max_pointer<T>(p0, p2, p4, load, store, max);
+}
+
+template <class T>
+void test_pointer() {
+ test_pointer_impl<T>();
+ if constexpr (std::atomic<T*>::is_always_lock_free) {
+ test_pointer_impl<T, std::add_volatile_t>();
+ }
+}
+
+int main(int, char**) {
+ TestEachIntegralType<TestFn>()();
+ test_pointer<int>();
+ test_pointer<char>();
+
+ return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min.pass.cpp
new file mode 100644
index 0000000000000..df40cc7a92c7b
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min.pass.cpp
@@ -0,0 +1,114 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// <atomic>
+
+// template<class T>
+// T atomic_fetch_min(volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
+// template<class T>
+// constexpr T atomic_fetch_min(atomic<T>*, typename atomic<T>::value_type) noexcept;
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <limits>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_fetch_min_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+#ifndef TEST_HAS_NO_THREADS
+# include <thread>
+
+# include "make_test_thread.h"
+#endif
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_impl() {
+ {
+ MaybeVolatile<std::atomic<T>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T val) { a.store(val); };
+ auto min = [&](T val, auto) { return std::atomic_fetch_min(&a, val); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_min(&a, T(0)));
+ test_fetch_min_integral<T>(load, store, min);
+ }
+
+#ifndef TEST_HAS_NO_THREADS
+ // Concurrent stress test: many threads calling atomic_fetch_min should leave
+ // the atomic at the global minimum value seen.
+ {
+ constexpr auto number_of_threads = 4;
+ constexpr auto loop = 30;
+
+ MaybeVolatile<std::atomic<T>> at(std::numeric_limits<T>::max());
+
+ std::vector<std::thread> threads;
+ threads.reserve(number_of_threads);
+ for (auto i = 0; i < number_of_threads; ++i) {
+ threads.push_back(support::make_test_thread([&at, i]() {
+ for (auto j = 0; j < loop; ++j) {
+ std::atomic_fetch_min(&at, T(i * loop + j));
+ }
+ }));
+ }
+
+ for (auto& thread : threads) {
+ thread.join();
+ }
+
+ assert(at.load() == T(0));
+ }
+#endif
+}
+
+template <class T>
+struct TestFn {
+ void operator()() const {
+ test_impl<T>();
+ if constexpr (std::atomic<T>::is_always_lock_free) {
+ test_impl<T, std::add_volatile_t>();
+ }
+ }
+};
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_pointer_impl() {
+ T arr[5];
+ T* p0 = &arr[0];
+ T* p2 = &arr[2];
+ T* p4 = &arr[4];
+
+ MaybeVolatile<std::atomic<T*>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T* val) { a.store(val); };
+ auto min = [&](T* val, auto) { return std::atomic_fetch_min(&a, val); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_min(&a, p0));
+ test_fetch_min_pointer<T>(p0, p2, p4, load, store, min);
+}
+
+template <class T>
+void test_pointer() {
+ test_pointer_impl<T>();
+ if constexpr (std::atomic<T*>::is_always_lock_free) {
+ test_pointer_impl<T, std::add_volatile_t>();
+ }
+}
+
+int main(int, char**) {
+ TestEachIntegralType<TestFn>()();
+ test_pointer<int>();
+ test_pointer<char>();
+
+ return 0;
+}
diff --git a/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min_explicit.pass.cpp b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min_explicit.pass.cpp
new file mode 100644
index 0000000000000..2295b942b86de
--- /dev/null
+++ b/libcxx/test/std/atomics/atomics.types.operations/atomics.types.operations.req/atomic_fetch_min_explicit.pass.cpp
@@ -0,0 +1,116 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// REQUIRES: std-at-least-c++26
+// XFAIL: !has-64-bit-atomics
+
+// <atomic>
+
+// template<class T>
+// T atomic_fetch_min_explicit(volatile atomic<T>*, typename atomic<T>::value_type,
+// memory_order) noexcept;
+// template<class T>
+// constexpr T atomic_fetch_min_explicit(atomic<T>*, typename atomic<T>::value_type,
+// memory_order) noexcept;
+
+#include <algorithm>
+#include <atomic>
+#include <cassert>
+#include <limits>
+#include <type_traits>
+#include <vector>
+
+#include "atomic_fetch_min_helper.h"
+#include "atomic_helpers.h"
+#include "test_macros.h"
+
+#ifndef TEST_HAS_NO_THREADS
+# include <thread>
+
+# include "make_test_thread.h"
+#endif
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_impl() {
+ {
+ MaybeVolatile<std::atomic<T>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T val) { a.store(val); };
+ auto min = [&](T val, auto order) { return std::atomic_fetch_min_explicit(&a, val, order); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_min_explicit(&a, T(0), std::memory_order_seq_cst));
+ test_fetch_min_integral<T>(load, store, min);
+ }
+
+#ifndef TEST_HAS_NO_THREADS
+ // Concurrent stress test: many threads calling atomic_fetch_min_explicit should
+ // leave the atomic at the global minimum value seen.
+ {
+ constexpr auto number_of_threads = 4;
+ constexpr auto loop = 30;
+
+ MaybeVolatile<std::atomic<T>> at(std::numeric_limits<T>::max());
+
+ std::vector<std::thread> threads;
+ threads.reserve(number_of_threads);
+ for (auto i = 0; i < number_of_threads; ++i) {
+ threads.push_back(support::make_test_thread([&at, i]() {
+ for (auto j = 0; j < loop; ++j) {
+ std::atomic_fetch_min_explicit(&at, T(i * loop + j), std::memory_order_relaxed);
+ }
+ }));
+ }
+
+ for (auto& thread : threads) {
+ thread.join();
+ }
+
+ assert(at.load() == T(0));
+ }
+#endif
+}
+
+template <class T>
+struct TestFn {
+ void operator()() const {
+ test_impl<T>();
+ if constexpr (std::atomic<T>::is_always_lock_free) {
+ test_impl<T, std::add_volatile_t>();
+ }
+ }
+};
+
+template <class T, template <class> class MaybeVolatile = std::type_identity_t>
+void test_pointer_impl() {
+ T arr[5];
+ T* p0 = &arr[0];
+ T* p2 = &arr[2];
+ T* p4 = &arr[4];
+
+ MaybeVolatile<std::atomic<T*>> a;
+ auto load = [&]() { return a.load(); };
+ auto store = [&](T* val) { a.store(val); };
+ auto min = [&](T* val, auto order) { return std::atomic_fetch_min_explicit(&a, val, order); };
+ ASSERT_NOEXCEPT(std::atomic_fetch_min_explicit(&a, p0, std::memory_order_seq_cst));
+ test_fetch_min_pointer<T>(p0, p2, p4, load, store, min);
+}
+
+template <class T>
+void test_pointer() {
+ test_pointer_impl<T>();
+ if constexpr (std::atomic<T*>::is_always_lock_free) {
+ test_pointer_impl<T, std::add_volatile_t>();
+ }
+}
+
+int main(int, char**) {
+ TestEachIntegralType<TestFn>()();
+ test_pointer<int>();
+ test_pointer<char>();
+
+ return 0;
+}
diff --git a/libcxx/test/std/language.support/support.limits/support.limits.general/atomic.version.compile.pass.cpp b/libcxx/test/std/language.support/support.limits/support.limits.general/atomic.version.compile.pass.cpp
index e62416257a696..aece31d25c249 100644
--- a/libcxx/test/std/language.support/support.limits/support.limits.general/atomic.version.compile.pass.cpp
+++ b/libcxx/test/std/language.support/support.limits/support.limits.general/atomic.version.compile.pass.cpp
@@ -339,17 +339,11 @@
# error "__cpp_lib_atomic_lock_free_type_aliases should have the value 201907L in c++26"
# endif
-# if !defined(_LIBCPP_VERSION)
-# ifndef __cpp_lib_atomic_min_max
-# error "__cpp_lib_atomic_min_max should be defined in c++26"
-# endif
-# if __cpp_lib_atomic_min_max != 202403L
-# error "__cpp_lib_atomic_min_max should have the value 202403L in c++26"
-# endif
-# else
-# ifdef __cpp_lib_atomic_min_max
-# error "__cpp_lib_atomic_min_max should not be defined because it is unimplemented in libc++!"
-# endif
+# ifndef __cpp_lib_atomic_min_max
+# error "__cpp_lib_atomic_min_max should be defined in c++26"
+# endif
+# if __cpp_lib_atomic_min_max != 202403L
+# error "__cpp_lib_atomic_min_max should have the value 202403L in c++26"
# endif
# ifndef __cpp_lib_atomic_ref
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 f2d74cc99d864..9e987346c599b 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
@@ -6434,17 +6434,11 @@
# error "__cpp_lib_atomic_lock_free_type_aliases should have the value 201907L in c++26"
# endif
-# if !defined(_LIBCPP_VERSION)
-# ifndef __cpp_lib_atomic_min_max
-# error "__cpp_lib_atomic_min_max should be defined in c++26"
-# endif
-# if __cpp_lib_atomic_min_max != 202403L
-# error "__cpp_lib_atomic_min_max should have the value 202403L in c++26"
-# endif
-# else
-# ifdef __cpp_lib_atomic_min_max
-# error "__cpp_lib_atomic_min_max should not be defined because it is unimplemented in libc++!"
-# endif
+# ifndef __cpp_lib_atomic_min_max
+# error "__cpp_lib_atomic_min_max should be defined in c++26"
+# endif
+# if __cpp_lib_atomic_min_max != 202403L
+# error "__cpp_lib_atomic_min_max should have the value 202403L in c++26"
# endif
# ifndef __cpp_lib_atomic_ref
diff --git a/libcxx/test/support/atomic_fetch_max_helper.h b/libcxx/test/support/atomic_fetch_max_helper.h
new file mode 100644
index 0000000000000..ff4bd7aa38912
--- /dev/null
+++ b/libcxx/test/support/atomic_fetch_max_helper.h
@@ -0,0 +1,147 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_STD_ATOMICS_ATOMIC_FETCH_MAX_HELPER_H
+#define TEST_STD_ATOMICS_ATOMIC_FETCH_MAX_HELPER_H
+
+#include <cassert>
+#include <type_traits>
+
+#include "test_macros.h"
+
+// Test fetch_max for integral types
+// LoadOp: () -> T - reads current value
+// StoreOp: (T) -> void - stores a value
+// MaxOp: (T, memory_order) -> T - performs fetch_max operation
+template <class T, class LoadOp, class StoreOp, class MaxOp>
+void test_fetch_max_integral(LoadOp load, StoreOp store, MaxOp max) {
+ // Test basic fetch_max (update to larger value)
+ {
+ store(T(10));
+ T old = max(T(20), std::memory_order_seq_cst);
+ assert(old == T(10));
+ assert(load() == T(20));
+ }
+
+ // Test with smaller value (no change)
+ {
+ store(T(10));
+ T old = max(T(5), std::memory_order_seq_cst);
+ assert(old == T(10));
+ assert(load() == T(10));
+ }
+
+ // Test
diff erent memory orderings
+ {
+ store(T(15));
+ T old = max(T(25), std::memory_order_seq_cst);
+ assert(old == T(15));
+ assert(load() == T(25));
+ }
+
+ {
+ store(T(10));
+ T old = max(T(25), std::memory_order_relaxed);
+ assert(old == T(10));
+ assert(load() == T(25));
+ }
+
+ {
+ store(T(10));
+ T old = max(T(30), std::memory_order_acquire);
+ assert(old == T(10));
+ assert(load() == T(30));
+ }
+
+ {
+ store(T(10));
+ T old = max(T(15), std::memory_order_release);
+ assert(old == T(10));
+ assert(load() == T(15));
+ }
+
+ {
+ store(T(10));
+ T old = max(T(22), std::memory_order_acq_rel);
+ assert(old == T(10));
+ assert(load() == T(22));
+ }
+
+ {
+ store(T(15));
+ T old = max(T(35), std::memory_order_relaxed);
+ assert(old == T(15));
+ assert(load() == T(35));
+ }
+
+ // Test return type
+ {
+ store(T(10));
+ static_assert(std::is_same_v<decltype(max(T(20), std::memory_order_seq_cst)), T>);
+ }
+}
+
+// Test fetch_max for pointer types
+// LoadOp: () -> T* - reads current pointer value
+// StoreOp: (T*) -> void - stores a pointer value
+// MaxOp: (T*, memory_order) -> T* - performs fetch_max operation
+template <class T, class LoadOp, class StoreOp, class MaxOp>
+void test_fetch_max_pointer(T* p0, T* p2, T* p4, LoadOp load, StoreOp store, MaxOp max) {
+ // Test basic fetch_max (update to larger pointer)
+ {
+ store(p2);
+ T* old = max(p4, std::memory_order_seq_cst);
+ assert(old == p2);
+ assert(load() == p4);
+ }
+
+ // Test with smaller pointer (no change)
+ {
+ store(p2);
+ T* old = max(p0, std::memory_order_seq_cst);
+ assert(old == p2);
+ assert(load() == p2);
+ }
+
+ // Test
diff erent memory orderings
+ {
+ store(p0);
+ T* old = max(p2, std::memory_order_seq_cst);
+ assert(old == p0);
+ assert(load() == p2);
+ }
+
+ {
+ store(p0);
+ T* old = max(p2, std::memory_order_relaxed);
+ assert(old == p0);
+ assert(load() == p2);
+ }
+
+ {
+ store(p0);
+ T* old = max(p4, std::memory_order_acquire);
+ assert(old == p0);
+ assert(load() == p4);
+ }
+
+ {
+ store(p0);
+ T* old = max(p4, std::memory_order_release);
+ assert(old == p0);
+ assert(load() == p4);
+ }
+
+ // Test return type
+ {
+ store(p2);
+ static_assert(std::is_same_v<decltype(max(p4, std::memory_order_seq_cst)), T*>);
+ }
+}
+
+#endif // TEST_STD_ATOMICS_ATOMIC_FETCH_MAX_HELPER_H
diff --git a/libcxx/test/support/atomic_fetch_min_helper.h b/libcxx/test/support/atomic_fetch_min_helper.h
new file mode 100644
index 0000000000000..20a3558296118
--- /dev/null
+++ b/libcxx/test/support/atomic_fetch_min_helper.h
@@ -0,0 +1,147 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef TEST_STD_ATOMICS_ATOMIC_FETCH_MIN_HELPER_H
+#define TEST_STD_ATOMICS_ATOMIC_FETCH_MIN_HELPER_H
+
+#include <cassert>
+#include <type_traits>
+
+#include "test_macros.h"
+
+// Test fetch_min for integral types
+// LoadOp: () -> T - reads current value
+// StoreOp: (T) -> void - stores a value
+// MinOp: (T, memory_order) -> T - performs fetch_min operation
+template <class T, class LoadOp, class StoreOp, class MinOp>
+void test_fetch_min_integral(LoadOp load, StoreOp store, MinOp min) {
+ // Test basic fetch_min (update to smaller value)
+ {
+ store(T(10));
+ T old = min(T(5), std::memory_order_seq_cst);
+ assert(old == T(10));
+ assert(load() == T(5));
+ }
+
+ // Test with larger value (no change)
+ {
+ store(T(10));
+ T old = min(T(20), std::memory_order_seq_cst);
+ assert(old == T(10));
+ assert(load() == T(10));
+ }
+
+ // Test
diff erent memory orderings
+ {
+ store(T(15));
+ T old = min(T(8), std::memory_order_seq_cst);
+ assert(old == T(15));
+ assert(load() == T(8));
+ }
+
+ {
+ store(T(10));
+ T old = min(T(3), std::memory_order_relaxed);
+ assert(old == T(10));
+ assert(load() == T(3));
+ }
+
+ {
+ store(T(10));
+ T old = min(T(2), std::memory_order_acquire);
+ assert(old == T(10));
+ assert(load() == T(2));
+ }
+
+ {
+ store(T(10));
+ T old = min(T(7), std::memory_order_release);
+ assert(old == T(10));
+ assert(load() == T(7));
+ }
+
+ {
+ store(T(10));
+ T old = min(T(4), std::memory_order_acq_rel);
+ assert(old == T(10));
+ assert(load() == T(4));
+ }
+
+ {
+ store(T(15));
+ T old = min(T(6), std::memory_order_relaxed);
+ assert(old == T(15));
+ assert(load() == T(6));
+ }
+
+ // Test return type
+ {
+ store(T(10));
+ static_assert(std::is_same_v<decltype(min(T(5), std::memory_order_seq_cst)), T>);
+ }
+}
+
+// Test fetch_min for pointer types
+// LoadOp: () -> T* - reads current pointer value
+// StoreOp: (T*) -> void - stores a pointer value
+// MinOp: (T*, memory_order) -> T* - performs fetch_min operation
+template <class T, class LoadOp, class StoreOp, class MinOp>
+void test_fetch_min_pointer(T* p0, T* p2, T* p4, LoadOp load, StoreOp store, MinOp min) {
+ // Test basic fetch_min (update to smaller pointer)
+ {
+ store(p2);
+ T* old = min(p0, std::memory_order_seq_cst);
+ assert(old == p2);
+ assert(load() == p0);
+ }
+
+ // Test with larger pointer (no change)
+ {
+ store(p2);
+ T* old = min(p4, std::memory_order_seq_cst);
+ assert(old == p2);
+ assert(load() == p2);
+ }
+
+ // Test
diff erent memory orderings
+ {
+ store(p4);
+ T* old = min(p2, std::memory_order_seq_cst);
+ assert(old == p4);
+ assert(load() == p2);
+ }
+
+ {
+ store(p4);
+ T* old = min(p2, std::memory_order_relaxed);
+ assert(old == p4);
+ assert(load() == p2);
+ }
+
+ {
+ store(p4);
+ T* old = min(p0, std::memory_order_acquire);
+ assert(old == p4);
+ assert(load() == p0);
+ }
+
+ {
+ store(p4);
+ T* old = min(p0, std::memory_order_release);
+ assert(old == p4);
+ assert(load() == p0);
+ }
+
+ // Test return type
+ {
+ store(p2);
+ static_assert(std::is_same_v<decltype(min(p0, std::memory_order_seq_cst)), T*>);
+ }
+}
+
+#endif // TEST_STD_ATOMICS_ATOMIC_FETCH_MIN_HELPER_H
diff --git a/libcxx/utils/generate_feature_test_macro_components.py b/libcxx/utils/generate_feature_test_macro_components.py
index f4e16078d5af0..13a5dab01b74e 100644
--- a/libcxx/utils/generate_feature_test_macro_components.py
+++ b/libcxx/utils/generate_feature_test_macro_components.py
@@ -191,7 +191,6 @@ def add_version_header(tc):
"name": "__cpp_lib_atomic_min_max",
"values": {"c++26": 202403}, # P0493R5: Atomic minimum/maximum
"headers": ["atomic"],
- "unimplemented": True,
},
{
"name": "__cpp_lib_atomic_ref",
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