<utility>: Remove self swap check from pair.

stl/inc/utility

@@ -441,21 +441,17 @@ struct pair { // store a pair of values
  _CONSTEXPR20 void swap(pair& _Right) noexcept(
  _Is_nothrow_swappable<_Ty1>::value && _Is_nothrow_swappable<_Ty2>::value) {
  using _STD swap;
- if (this != _STD addressof(_Right)) {
- swap(first, _Right.first); // intentional ADL
- swap(second, _Right.second); // intentional ADL
- }
+ swap(first, _Right.first); // intentional ADL
+ swap(second, _Right.second); // intentional ADL
  }
 
 #if _HAS_CXX23
  template <int = 0> // see GH-3013
  constexpr void swap(const pair& _Right) const
  noexcept(is_nothrow_swappable_v<const _Ty1> && is_nothrow_swappable_v<const _Ty2>) {
  using _STD swap;
- if (this != _STD addressof(_Right)) {
- swap(first, _Right.first); // intentional ADL
- swap(second, _Right.second); // intentional ADL
- }
+ swap(first, _Right.first); // intentional ADL
+ swap(second, _Right.second); // intentional ADL
  }
 #endif // _HAS_CXX23
 

tests/std/tests/GH_004597_self_swap/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_20_matrix.lst

tests/std/tests/GH_004597_self_swap/test.cpp

@@ -0,0 +1,61 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <utility>
+
+// Test GH-4597 "<utility>: Side effects in self-swaps of pair are skipped"
+struct swap_counter {
+ unsigned int* pcnt_ = nullptr;
+
+ friend constexpr void swap(swap_counter& lhs, swap_counter& rhs) noexcept {
+ std::swap(lhs.pcnt_, rhs.pcnt_);
+ if (lhs.pcnt_ != nullptr) {
+ ++(*lhs.pcnt_);
+ }
+ if (rhs.pcnt_ != nullptr) {
+ ++(*rhs.pcnt_);
+ }
+ }
+
+ constexpr bool operator==(unsigned int x) const {
+ return *pcnt_ == x;
+ }
+};
+
+
+void test_gh_4595() {
+ {
+ static_assert([] {
+ unsigned int cnt{};
+ std::pair<swap_counter, int> pr{swap_counter{&cnt}, 0};
+ pr.swap(pr);
+ return (cnt == 2u) && (pr.first == 2u) && (pr.second == 0);
+ }());
+ }
+
+ {
+ static_assert([] {
+ unsigned int cnt{};
+ std::pair<swap_counter, int> p1{swap_counter{&cnt}, 0};
+ std::pair<swap_counter, int> p2{swap_counter{&cnt}, 1};
+ p1.swap(p2);
+ return (cnt == 2u) && (p1.first == 2u) && (p1.second == 1) && (p2.first == 2u) && (p2.second == 0);
+ }());
+ }
+
+ {
+ static_assert([] {
+ unsigned int c1{};
+ unsigned int c2{2};
+ std::pair<swap_counter, int> p1{swap_counter{&c1}, 1};
+ std::pair<swap_counter, int> p2{swap_counter{&c2}, 3};
+ p1.swap(p2);
+ return (c1 == 1u) && (c2 == 3u) && (p1.first == 3u) && (p1.second == 3) && (p2.first == 1u)
+ && (p2.second == 1);
+ }());
+ }
+}
+
+int main() {
+ test_gh_4595();
+}