From 8c2c816cf746d70b2623412c81c50e8d96d1c13a Mon Sep 17 00:00:00 2001
From: Christopher Di Bella <cjdb@google.com>
Date: Thu, 26 Mar 2026 10:09:34 -0700
Subject: [PATCH] Reapply "[libcxx] adds `__split_buffer::__swap_layouts`"
 (#185120) (#187763)

This reverts commit 01a97050f01b6b833d3d1f22997b5009293b43a3.
---
 libcxx/include/__split_buffer    | 17 +++++++++++++++++
 libcxx/include/__vector/vector.h | 19 +++----------------
 2 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/libcxx/include/__split_buffer b/libcxx/include/__split_buffer
index 89c398e52599..27ec8b7f988d 100644
--- a/libcxx/include/__split_buffer
+++ b/libcxx/include/__split_buffer
@@ -188,6 +188,14 @@ public:
     __back_cap_  = __other.__back_cap_;
   }
 
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __swap_layouts(pointer& __begin, pointer& __end, pointer& __back_capacity) {
+    using std::swap;
+    swap(__begin_, __begin);
+    swap(__end_, __end);
+    swap(__back_cap_, __back_capacity);
+  }
+
 private:
   pointer __front_cap_ = nullptr;
   pointer __begin_     = nullptr;
@@ -336,6 +344,14 @@ public:
     __size_      = __other.__size_;
   }
 
+  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __swap_layouts(pointer& __begin, size_type& __size, size_type& __capacity) {
+    using std::swap;
+    swap(__begin_, __begin);
+    swap(__size_, __size);
+    swap(__cap_, __capacity);
+  }
+
 private:
   pointer __front_cap_ = nullptr;
   pointer __begin_     = nullptr;
@@ -447,6 +463,7 @@ public:
   using __base_type::__set_data;
   using __base_type::__set_sentinel;
   using __base_type::__set_valid_range;
+  using __base_type::__swap_layouts;
 
   using typename __base_type::__alloc_traits;
   using typename __base_type::allocator_type;
diff --git a/libcxx/include/__vector/vector.h b/libcxx/include/__vector/vector.h
index 229287b43e70..df41c102616e 100644
--- a/libcxx/include/__vector/vector.h
+++ b/libcxx/include/__vector/vector.h
@@ -814,22 +814,9 @@ private:
     return __p;
   }
 
-  _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void __swap_layouts(_SplitBuffer& __sb) {
-    auto __vector_begin    = __begin_;
-    auto __vector_sentinel = __end_;
-    auto __vector_cap      = __cap_;
-
-    auto __sb_begin    = __sb.begin();
-    auto __sb_sentinel = __sb.__raw_sentinel();
-    auto __sb_cap      = __sb.__raw_capacity();
-
-    // TODO: replace with __set_valid_range and __set_capacity when vector supports it.
-    __begin_ = __sb_begin;
-    __end_   = __sb_sentinel;
-    __cap_   = __sb_cap;
-
-    __sb.__set_valid_range(__vector_begin, __vector_sentinel);
-    __sb.__set_capacity(__vector_cap);
+  _LIBCPP_NODEBUG _LIBCPP_ALWAYS_INLINE _LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI void
+  __swap_layouts(_SplitBuffer& __sb) {
+    __sb.__swap_layouts(__begin_, __end_, __cap_);
   }
 };