Remove unused MOA code.

PiperOrigin-RevId: 494296827

src/google/protobuf/arena.cc

@@ -461,12 +461,6 @@ ABSL_CONST_INIT PROTOBUF_THREAD_LOCAL
 
 ThreadSafeArena::ThreadSafeArena() : first_arena_(*this) { Init(); }
 
-// Constructor solely used by message-owned arena.
-ThreadSafeArena::ThreadSafeArena(internal::MessageOwned)
-    : tag_and_id_(kMessageOwnedArena), first_arena_(*this) {
-  Init();
-}
-
 ThreadSafeArena::ThreadSafeArena(char* mem, size_t size)
     : first_arena_(FirstSerialArena{}, FirstBlock(mem, size), *this) {
   Init();
@@ -608,16 +602,10 @@ void ThreadSafeArena::AddSerialArena(void* id, SerialArena* serial) {
 }
 
 void ThreadSafeArena::Init() {
-  const bool message_owned = IsMessageOwned();
-  if (!message_owned) {
-    // Message-owned arenas bypass thread cache and do not need life cycle ID.
-    tag_and_id_ = GetNextLifeCycleId();
-  } else {
-    GOOGLE_DCHECK_EQ(tag_and_id_, kMessageOwnedArena);
-  }
+  // Message-owned arenas bypass thread cache and do not need life cycle ID.
+  tag_and_id_ = GetNextLifeCycleId();
   arena_stats_ = Sample();
   head_.store(SentrySerialArenaChunk(), std::memory_order_relaxed);
-  GOOGLE_DCHECK_EQ(message_owned, IsMessageOwned());
   first_owner_ = &thread_cache();
 
   // Record allocation for the first block that was either user-provided or

src/google/protobuf/arena.h

@@ -505,14 +505,6 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
     return InternalHelper<T>::GetArenaForAllocation(p);
   }
 
-  // Creates message-owned arena.  For internal use only.
-  static Arena* InternalCreateMessageOwnedArena() {
-    return new Arena(internal::MessageOwned{});
-  }
-
-  // Checks whether this arena is message-owned.  For internal use only.
-  bool InternalIsMessageOwnedArena() { return IsMessageOwned(); }
-
   // Helper typetraits that indicates support for arenas in a type T at compile
   // time. This is public only to allow construction of higher-level templated
   // utilities.
@@ -534,14 +526,6 @@ class PROTOBUF_EXPORT PROTOBUF_ALIGNAS(8) Arena final {
  private:
   internal::ThreadSafeArena impl_;
 
-  // Constructor solely used by message-owned arena.
-  inline Arena(internal::MessageOwned) : impl_(internal::MessageOwned{}) {}
-
-  // Checks whether this arena is message-owned.
-  PROTOBUF_ALWAYS_INLINE bool IsMessageOwned() const {
-    return impl_.IsMessageOwned();
-  }
-
   void ReturnArrayMemory(void* p, size_t size) {
     impl_.ReturnArrayMemory(p, size);
   }

src/google/protobuf/arena_impl.h

@@ -387,13 +387,6 @@ class PROTOBUF_EXPORT SerialArena {
   static constexpr size_t kBlockHeaderSize = AlignUpTo8(sizeof(ArenaBlock));
 };
 
-// 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
@@ -404,9 +397,6 @@ 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,
@@ -466,11 +456,6 @@ 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;
@@ -515,9 +500,6 @@ 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.");
 
@@ -532,10 +514,8 @@ 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) {

src/google/protobuf/compiler/cpp/string_field.cc

@@ -116,9 +116,7 @@ void StringFieldGenerator::GeneratePrivateMembers(io::Printer* printer) const {
     format("::$proto_ns$::internal::ArenaStringPtr $name$_;\n");
   } else {
     // Skips the automatic destruction; rather calls it explicitly if
-    // allocating arena is null. This is required to support message-owned
-    // arena (go/path-to-arenas) where a root proto is destroyed but
-    // InlinedStringField may have arena-allocated memory.
+    // allocating arena is null.
     format("::$proto_ns$::internal::InlinedStringField $name$_;\n");
   }
 }
@@ -497,9 +495,7 @@ void StringFieldGenerator::GenerateDestructorCode(io::Printer* printer) const {
     return;
   }
   // Explicitly calls ~InlinedStringField as its automatic call is disabled.
-  // Destructor has been implicitly skipped as a union, and even the
-  // message-owned arena is enabled, arena could still be missing for
-  // Arena::CreateMessage(nullptr).
+  // Destructor has been implicitly skipped as a union.
   GOOGLE_ABSL_DCHECK(!ShouldSplit(descriptor_, options_));
   format("$field$.~InlinedStringField();\n");
 }

src/google/protobuf/generated_message_reflection.cc

@@ -342,13 +342,6 @@ size_t Reflection::SpaceUsedLong(const Message& message) const {
 
   total_size += GetUnknownFields(message).SpaceUsedExcludingSelfLong();
 
-  // If this message owns an arena, add any unused space that's been allocated.
-  auto* arena = Arena::InternalGetArenaForAllocation(&message);
-  if (arena != nullptr && Arena::InternalGetOwningArena(&message) == nullptr &&
-      arena->InternalIsMessageOwnedArena()) {
-    total_size += arena->SpaceAllocated() - arena->SpaceUsed();
-  }
-
   if (schema_.HasExtensionSet()) {
     total_size += GetExtensionSet(message).SpaceUsedExcludingSelfLong();
   }

src/google/protobuf/map.h

@@ -1227,9 +1227,7 @@ class Map {
           key_type>::type;
       Node* node = this->template Alloc<Node>(1);
       // Even when arena is nullptr, CreateInArenaStorage is still used to
-      // ensure the arena of submessage will be consistent. Otherwise,
-      // submessage may have its own arena when message-owned arena is enabled.
-      // Note: This only works if `Key` is not arena constructible.
+      // ensure the arena of submessage will be consistent.
       Arena::CreateInArenaStorage(const_cast<Key*>(&node->kv.first),
                                   this->alloc_.arena(),
                                   static_cast<TypeToInit>(std::forward<K>(k)));

src/google/protobuf/repeated_field.h

@@ -288,15 +288,7 @@ class RepeatedField final {
   iterator erase(const_iterator first, const_iterator last);
 
   // Gets the Arena on which this RepeatedField stores its elements.
-  // Message-owned arenas are not exposed by this method, which will return
-  // nullptr for messages owned by MOAs.
-  inline Arena* GetArena() const {
-    Arena* arena = GetOwningArena();
-    if (arena == nullptr || arena->InternalIsMessageOwnedArena()) {
-      return nullptr;
-    }
-    return arena;
-  }
+  inline Arena* GetArena() const { return GetOwningArena(); }
 
   // For internal use only.
   //

src/google/protobuf/repeated_ptr_field.h

@@ -640,15 +640,7 @@ class PROTOBUF_EXPORT RepeatedPtrFieldBase {
   }
 
   // Gets the Arena on which this RepeatedPtrField stores its elements.
-  // Message-owned arenas are not exposed by this method, which will return
-  // nullptr for messages owned by MOAs.
-  inline Arena* GetArena() const {
-    Arena* arena = GetOwningArena();
-    if (arena == nullptr || arena->InternalIsMessageOwnedArena()) {
-      return nullptr;
-    }
-    return arena;
-  }
+  inline Arena* GetArena() const { return GetOwningArena(); }
 
  protected:
   inline Arena* GetOwningArena() const { return arena_; }