From 699d71150a45f9fc4173f39dadc740465b854595 Mon Sep 17 00:00:00 2001
From: achabense <60953653+achabense@users.noreply.github.com>
Date: Wed, 10 Sep 2025 21:19:14 +0800
Subject: [PATCH 1/4] benchmark

---
 benchmarks/CMakeLists.txt   |  1 +
 benchmarks/src/any_swap.cpp | 42 +++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+)
 create mode 100644 benchmarks/src/any_swap.cpp

diff --git a/benchmarks/CMakeLists.txt b/benchmarks/CMakeLists.txt
index caab5625c60..eefc7869042 100644
--- a/benchmarks/CMakeLists.txt
+++ b/benchmarks/CMakeLists.txt
@@ -102,6 +102,7 @@ endfunction()
 
 add_benchmark(adjacent_difference src/adjacent_difference.cpp)
 add_benchmark(adjacent_find src/adjacent_find.cpp)
+add_benchmark(any_swap src/any_swap.cpp)
 add_benchmark(bitset_from_string src/bitset_from_string.cpp)
 add_benchmark(bitset_to_string src/bitset_to_string.cpp)
 add_benchmark(efficient_nonlocking_print src/efficient_nonlocking_print.cpp)
diff --git a/benchmarks/src/any_swap.cpp b/benchmarks/src/any_swap.cpp
new file mode 100644
index 00000000000..4d2ec21744d
--- /dev/null
+++ b/benchmarks/src/any_swap.cpp
@@ -0,0 +1,42 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <any>
+#include <array>
+#include <benchmark/benchmark.h>
+#include <type_traits>
+
+using trivial = std::array<int, 2>;
+static_assert(std::is_trivially_copyable_v<trivial>);
+
+struct small {
+    std::array<int, 4> c{};
+    small()                            = default;
+    small(const small&)                = default;
+    small& operator=(const small&)     = default;
+    small(small&&) noexcept            = default;
+    small& operator=(small&&) noexcept = default;
+    ~small() {}
+};
+static_assert(!std::is_trivially_copyable_v<small>);
+static_assert(std::is_nothrow_move_constructible_v<small>);
+
+using large = std::array<int, 32>;
+
+template <class T>
+void bm(benchmark::State& state) {
+    std::any a = T{};
+    std::any b = T{};
+
+    for (auto _ : state) {
+        a.swap(b);
+        benchmark::DoNotOptimize(a);
+        benchmark::DoNotOptimize(b);
+    }
+}
+
+BENCHMARK(bm<trivial>);
+BENCHMARK(bm<small>);
+BENCHMARK(bm<large>);
+
+BENCHMARK_MAIN();

From 2944511990a373f97c46f052e750e32760ecf04d Mon Sep 17 00:00:00 2001
From: achabense <60953653+achabense@users.noreply.github.com>
Date: Wed, 10 Sep 2025 21:20:36 +0800
Subject: [PATCH 2/4] Step 1

---
 stl/inc/any | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/stl/inc/any b/stl/inc/any
index 2f33cb0545d..4a2f798d53d 100644
--- a/stl/inc/any
+++ b/stl/inc/any
@@ -230,7 +230,9 @@ public:
     }
 
     void swap(any& _That) noexcept {
-        _That = _STD exchange(*this, _STD move(_That));
+        any _Old = _STD move(*this);
+        *this    = _STD move(_That);
+        _That    = _STD move(_Old);
     }
 
     // Observers [any.observers]

From 5567c9c5703b4040f2c004a20ca26a40a549ff39 Mon Sep 17 00:00:00 2001
From: achabense <60953653+achabense@users.noreply.github.com>
Date: Wed, 10 Sep 2025 21:22:00 +0800
Subject: [PATCH 3/4] Step 2

---
 stl/inc/any | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/stl/inc/any b/stl/inc/any
index 4a2f798d53d..d0e2ea6a4ca 100644
--- a/stl/inc/any
+++ b/stl/inc/any
@@ -231,8 +231,9 @@ public:
 
     void swap(any& _That) noexcept {
         any _Old = _STD move(*this);
-        *this    = _STD move(_That);
-        _That    = _STD move(_Old);
+        _Assign(_STD move(_That));
+        _That.reset();
+        _That._Move_from(_Old);
     }
 
     // Observers [any.observers]

From c1ca587440c7c63b4e20357704fb4c5464a08c4e Mon Sep 17 00:00:00 2001
From: "Stephan T. Lavavej" <stl@microsoft.com>
Date: Fri, 3 Oct 2025 09:23:52 -0700
Subject: [PATCH 4/4] Avoid another move construction.

---
 stl/inc/any | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/stl/inc/any b/stl/inc/any
index d0e2ea6a4ca..9aba1b3fb41 100644
--- a/stl/inc/any
+++ b/stl/inc/any
@@ -231,7 +231,8 @@ public:
 
     void swap(any& _That) noexcept {
         any _Old = _STD move(*this);
-        _Assign(_STD move(_That));
+        reset();
+        _Move_from(_That);
         _That.reset();
         _That._Move_from(_Old);
     }