From f8e0ff7f33338c2874b75e45e4ea5abbfafb954c Mon Sep 17 00:00:00 2001
From: Evan Brown <ezb@google.com>
Date: Mon, 3 Oct 2022 10:51:40 -0700
Subject: Use trivial relocation for transfers in swisstable and b-tree.

PiperOrigin-RevId: 478547898
Change-Id: Ie20cd0a49df042be912888ee238333a5f5fa0404
---
 absl/container/internal/container_memory.h | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

(limited to 'absl/container/internal/container_memory.h')

diff --git a/absl/container/internal/container_memory.h b/absl/container/internal/container_memory.h
index 00e9f6d7..c29c533b 100644
--- a/absl/container/internal/container_memory.h
+++ b/absl/container/internal/container_memory.h
@@ -17,6 +17,7 @@
 
 #include <cassert>
 #include <cstddef>
+#include <cstring>
 #include <memory>
 #include <new>
 #include <tuple>
@@ -340,7 +341,8 @@ template <class K, class V>
 struct map_slot_policy {
   using slot_type = map_slot_type<K, V>;
   using value_type = std::pair<const K, V>;
-  using mutable_value_type = std::pair<K, V>;
+  using mutable_value_type =
+      std::pair<absl::remove_const_t<K>, absl::remove_const_t<V>>;
 
  private:
   static void emplace(slot_type* slot) {
@@ -424,6 +426,15 @@ struct map_slot_policy {
   static void transfer(Allocator* alloc, slot_type* new_slot,
                        slot_type* old_slot) {
     emplace(new_slot);
+#if defined(__cpp_lib_launder) && __cpp_lib_launder >= 201606
+    if (absl::is_trivially_relocatable<value_type>()) {
+      // TODO(b/247130232): remove cast after fixing class-memaccess warning.
+      std::memcpy(static_cast<void*>(std::launder(&new_slot->value)),
+                  &old_slot->value, sizeof(value_type));
+      return;
+    }
+#endif
+
     if (kMutableKeys::value) {
       absl::allocator_traits<Allocator>::construct(
           *alloc, &new_slot->mutable_value, std::move(old_slot->mutable_value));
-- 
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