Cleanup unused MOA code.

PiperOrigin-RevId: 495946574

src/google/protobuf/arena.cc

@@ -535,17 +535,14 @@ void ThreadSafeArena::InitializeWithPolicy(const AllocationPolicy& policy) {
 uint64_t ThreadSafeArena::GetNextLifeCycleId() {
   ThreadCache& tc = thread_cache();
   uint64_t id = tc.next_lifecycle_id;
-  // We increment lifecycle_id's by multiples of two so we can use bit 0 as
-  // a tag.
-  constexpr uint64_t kDelta = 2;
-  constexpr uint64_t kInc = ThreadCache::kPerThreadIds * kDelta;
+  constexpr uint64_t kInc = ThreadCache::kPerThreadIds;
   if (PROTOBUF_PREDICT_FALSE((id & (kInc - 1)) == 0)) {
     // On platforms that don't support uint64_t atomics we can certainly not
     // afford to increment by large intervals and expect uniqueness due to
     // wrapping, hence we only add by 1.
     id = lifecycle_id_.fetch_add(1, std::memory_order_relaxed) * kInc;
   }
-  tc.next_lifecycle_id = id + kDelta;
+  tc.next_lifecycle_id = id + 1;
   return id;
 }
 

src/google/protobuf/thread_safe_arena.h

@@ -55,13 +55,6 @@ namespace google {
 namespace protobuf {
 namespace internal {
 
-// Tag type used to invoke the constructor of message-owned arena.
-// Only message-owned arenas use this constructor for creation.
-// Such constructors are internal implementation details of the library.
-struct MessageOwned {
-  explicit MessageOwned() = default;
-};
-
 // This class provides the core Arena memory allocation library. Different
 // implementations only need to implement the public interface below.
 // Arena is not a template type as that would only be useful if all protos
@@ -72,9 +65,6 @@ class PROTOBUF_EXPORT ThreadSafeArena {
  public:
   ThreadSafeArena();
 
-  // Constructor solely used by message-owned arena.
-  explicit ThreadSafeArena(internal::MessageOwned);
-
   ThreadSafeArena(char* mem, size_t size);
 
   explicit ThreadSafeArena(void* mem, size_t size,
@@ -134,11 +124,6 @@ class PROTOBUF_EXPORT ThreadSafeArena {
   // Add object pointer and cleanup function pointer to the list.
   void AddCleanup(void* elem, void (*cleanup)(void*));
 
-  // Checks whether this arena is message-owned.
-  PROTOBUF_ALWAYS_INLINE bool IsMessageOwned() const {
-    return tag_and_id_ & kMessageOwnedArena;
-  }
-
  private:
   friend class ArenaBenchmark;
   friend class TcParser;
@@ -183,9 +168,6 @@ class PROTOBUF_EXPORT ThreadSafeArena {
   // user-provided initial block.
   SerialArena first_arena_;
 
-  // The LSB of tag_and_id_ indicates if the arena is message-owned.
-  enum : uint64_t { kMessageOwnedArena = 1 };
-
   static_assert(std::is_trivially_destructible<SerialArena>{},
                 "SerialArena needs to be trivially destructible.");
 
@@ -200,10 +182,8 @@ class PROTOBUF_EXPORT ThreadSafeArena {
   void CleanupList();
 
   inline void CacheSerialArena(SerialArena* serial) {
-    if (!IsMessageOwned()) {
-      thread_cache().last_serial_arena = serial;
-      thread_cache().last_lifecycle_id_seen = tag_and_id_;
-    }
+    thread_cache().last_serial_arena = serial;
+    thread_cache().last_lifecycle_id_seen = tag_and_id_;
   }
 
   PROTOBUF_NDEBUG_INLINE bool GetSerialArenaFast(SerialArena** arena) {