Devirtualize CheckTypeAndMergeFrom and use the existing function from

ClassData.
This removes a virtual function and reduces binary size.

PiperOrigin-RevId: 634413330

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

@@ -1713,10 +1713,14 @@ void MessageGenerator::GenerateClassDefinition(io::Printer* p) {
             }
           } else {
             p->Emit(R"cc(
-              void CheckTypeAndMergeFrom(
-                  const ::$proto_ns$::MessageLite& from) final;
               void CopyFrom(const $classname$& from);
-              void MergeFrom(const $classname$& from);
+              void MergeFrom(const $classname$& from) { $classname$::MergeImpl(*this, from); }
+
+              private:
+              static void MergeImpl(::$proto_ns$::MessageLite& to_msg,
+                                    const ::$proto_ns$::MessageLite& from_msg);
+
+              public:
             )cc");
           }
 
@@ -2240,9 +2244,6 @@ void MessageGenerator::GenerateClassMethods(io::Printer* p) {
     GenerateByteSize(p);
     p->Emit("\n");
 
-    GenerateMergeFrom(p);
-    p->Emit("\n");
-
     GenerateClassSpecificMergeImpl(p);
     p->Emit("\n");
 
@@ -3698,10 +3699,10 @@ void MessageGenerator::GenerateClassData(io::Printer* p) {
                         $table$,
                         $on_demand_register_arena_dtor$,
                         $is_initialized$,
+                        &$classname$::MergeImpl,
                         PROTOBUF_FIELD_OFFSET($classname$, $cached_size$),
                         false,
                     },
-                    &$classname$::MergeImpl,
                     &$classname$::kDescriptorMethods,
                     &$desc_table$,
                     $tracker_on_get_metadata$,
@@ -3727,6 +3728,7 @@ void MessageGenerator::GenerateClassData(io::Printer* p) {
                         &_table_.header,
                         $on_demand_register_arena_dtor$,
                         $is_initialized$,
+                        &$classname$::MergeImpl,
                         PROTOBUF_FIELD_OFFSET($classname$, $cached_size$),
                         true,
                     },
@@ -3739,22 +3741,6 @@ void MessageGenerator::GenerateClassData(io::Printer* p) {
   }
 }
 
-void MessageGenerator::GenerateMergeFrom(io::Printer* p) {
-  Formatter format(p);
-
-  if (!HasDescriptorMethods(descriptor_->file(), options_)) {
-    // Generate CheckTypeAndMergeFrom().
-    // We pass `*this` instead of `default_instance()` to allow for ICF.
-    p->Emit(R"cc(
-      void $classname$::CheckTypeAndMergeFrom(
-          const ::$proto_ns$::MessageLite& from) {
-        $pbi$::AssertDownCast(from, *this);
-        MergeFrom(static_cast<const $classname$&>(from));
-      }
-    )cc");
-  }
-}
-
 bool MessageGenerator::RequiresArena(GeneratorFunction function) const {
   for (const FieldDescriptor* field : FieldRange(descriptor_)) {
     if (field_generators_.get(field).RequiresArena(function)) {
@@ -3769,20 +3755,12 @@ void MessageGenerator::GenerateClassSpecificMergeImpl(io::Printer* p) {
   // Generate the class-specific MergeFrom, which avoids the ABSL_CHECK and
   // cast.
   Formatter format(p);
-  if (!HasDescriptorMethods(descriptor_->file(), options_)) {
+  format(
-    // For messages that don't inherit from Message, just implement MergeFrom
+      "void $classname$::MergeImpl(::$proto_ns$::MessageLite& to_msg, const "
-    // directly.
+      "::$proto_ns$::MessageLite& from_msg) {\n"
-    format(
+      "$WeakDescriptorSelfPin$"
-        "void $classname$::MergeFrom(const $classname$& from) {\n"
+      "  auto* const _this = static_cast<$classname$*>(&to_msg);\n"
-        "  $classname$* const _this = this;\n");
+      "  auto& from = static_cast<const $classname$&>(from_msg);\n");
-  } else {
-    format(
-        "void $classname$::MergeImpl(::$proto_ns$::MessageLite& to_msg, const "
-        "::$proto_ns$::MessageLite& from_msg) {\n"
-        "$WeakDescriptorSelfPin$"
-        "  auto* const _this = static_cast<$classname$*>(&to_msg);\n"
-        "  auto& from = static_cast<const $classname$&>(from_msg);\n");
-  }
   format.Indent();
   if (RequiresArena(GeneratorFunction::kMergeFrom)) {
     p->Emit(R"cc(

src/google/protobuf/compiler/cpp/message.h

@@ -126,7 +126,6 @@ class MessageGenerator {
   void GenerateMapEntryClassDefinition(io::Printer* p);
   void GenerateAnyMethodDefinition(io::Printer* p);
   void GenerateImplDefinition(io::Printer* p);
-  void GenerateMergeFrom(io::Printer* p);
   void GenerateClassSpecificMergeImpl(io::Printer* p);
   void GenerateCopyFrom(io::Printer* p);
   void GenerateSwap(io::Printer* p);

src/google/protobuf/compiler/java/java_features.pb.cc

@@ -191,10 +191,10 @@ JavaFeatures::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &JavaFeatures::MergeImpl,
               PROTOBUF_FIELD_OFFSET(JavaFeatures, _impl_._cached_size_),
               false,
           },
-          &JavaFeatures::MergeImpl,
           &JavaFeatures::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcompiler_2fjava_2fjava_5ffeatures_2eproto,
           nullptr,  // tracker
@@ -316,7 +316,6 @@ PROTOBUF_NOINLINE void JavaFeatures::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void JavaFeatures::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<JavaFeatures*>(&to_msg);
   auto& from = static_cast<const JavaFeatures&>(from_msg);

src/google/protobuf/compiler/plugin.pb.cc

@@ -367,10 +367,10 @@ Version::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &Version::MergeImpl,
               PROTOBUF_FIELD_OFFSET(Version, _impl_._cached_size_),
               false,
           },
-          &Version::MergeImpl,
           &Version::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcompiler_2fplugin_2eproto,
           nullptr,  // tracker
@@ -536,7 +536,6 @@ PROTOBUF_NOINLINE void Version::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void Version::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<Version*>(&to_msg);
   auto& from = static_cast<const Version&>(from_msg);
@@ -672,10 +671,10 @@ CodeGeneratorRequest::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               CodeGeneratorRequest::IsInitializedImpl,
+              &CodeGeneratorRequest::MergeImpl,
               PROTOBUF_FIELD_OFFSET(CodeGeneratorRequest, _impl_._cached_size_),
               false,
           },
-          &CodeGeneratorRequest::MergeImpl,
           &CodeGeneratorRequest::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcompiler_2fplugin_2eproto,
           nullptr,  // tracker
@@ -884,7 +883,6 @@ PROTOBUF_NOINLINE void CodeGeneratorRequest::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void CodeGeneratorRequest::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<CodeGeneratorRequest*>(&to_msg);
   auto& from = static_cast<const CodeGeneratorRequest&>(from_msg);
@@ -1030,10 +1028,10 @@ CodeGeneratorResponse_File::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &CodeGeneratorResponse_File::MergeImpl,
               PROTOBUF_FIELD_OFFSET(CodeGeneratorResponse_File, _impl_._cached_size_),
               false,
           },
-          &CodeGeneratorResponse_File::MergeImpl,
           &CodeGeneratorResponse_File::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcompiler_2fplugin_2eproto,
           nullptr,  // tracker
@@ -1209,7 +1207,6 @@ PROTOBUF_NOINLINE void CodeGeneratorResponse_File::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void CodeGeneratorResponse_File::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<CodeGeneratorResponse_File*>(&to_msg);
   auto& from = static_cast<const CodeGeneratorResponse_File&>(from_msg);
@@ -1344,10 +1341,10 @@ CodeGeneratorResponse::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &CodeGeneratorResponse::MergeImpl,
               PROTOBUF_FIELD_OFFSET(CodeGeneratorResponse, _impl_._cached_size_),
               false,
           },
-          &CodeGeneratorResponse::MergeImpl,
           &CodeGeneratorResponse::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcompiler_2fplugin_2eproto,
           nullptr,  // tracker
@@ -1543,7 +1540,6 @@ PROTOBUF_NOINLINE void CodeGeneratorResponse::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void CodeGeneratorResponse::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<CodeGeneratorResponse*>(&to_msg);
   auto& from = static_cast<const CodeGeneratorResponse&>(from_msg);

src/google/protobuf/cpp_features.pb.cc

@@ -186,10 +186,10 @@ CppFeatures::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &CppFeatures::MergeImpl,
               PROTOBUF_FIELD_OFFSET(CppFeatures, _impl_._cached_size_),
               false,
           },
-          &CppFeatures::MergeImpl,
           &CppFeatures::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fcpp_5ffeatures_2eproto,
           nullptr,  // tracker
@@ -311,7 +311,6 @@ PROTOBUF_NOINLINE void CppFeatures::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void CppFeatures::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<CppFeatures*>(&to_msg);
   auto& from = static_cast<const CppFeatures&>(from_msg);

src/google/protobuf/descriptor.pb.cc

@@ -2451,10 +2451,10 @@ FileDescriptorSet::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FileDescriptorSet::IsInitializedImpl,
+              &FileDescriptorSet::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FileDescriptorSet, _impl_._cached_size_),
               false,
           },
-          &FileDescriptorSet::MergeImpl,
           &FileDescriptorSet::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -2556,7 +2556,6 @@ PROTOBUF_NOINLINE void FileDescriptorSet::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FileDescriptorSet::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FileDescriptorSet*>(&to_msg);
   auto& from = static_cast<const FileDescriptorSet&>(from_msg);
@@ -2692,10 +2691,10 @@ FileDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FileDescriptorProto::IsInitializedImpl,
+              &FileDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FileDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &FileDescriptorProto::MergeImpl,
           &FileDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -3093,7 +3092,6 @@ PROTOBUF_NOINLINE void FileDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FileDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FileDescriptorProto*>(&to_msg);
   auto& from = static_cast<const FileDescriptorProto&>(from_msg);
@@ -3279,10 +3277,10 @@ DescriptorProto_ExtensionRange::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               DescriptorProto_ExtensionRange::IsInitializedImpl,
+              &DescriptorProto_ExtensionRange::MergeImpl,
               PROTOBUF_FIELD_OFFSET(DescriptorProto_ExtensionRange, _impl_._cached_size_),
               false,
           },
-          &DescriptorProto_ExtensionRange::MergeImpl,
           &DescriptorProto_ExtensionRange::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -3426,7 +3424,6 @@ PROTOBUF_NOINLINE void DescriptorProto_ExtensionRange::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void DescriptorProto_ExtensionRange::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<DescriptorProto_ExtensionRange*>(&to_msg);
   auto& from = static_cast<const DescriptorProto_ExtensionRange&>(from_msg);
@@ -3541,10 +3538,10 @@ DescriptorProto_ReservedRange::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &DescriptorProto_ReservedRange::MergeImpl,
               PROTOBUF_FIELD_OFFSET(DescriptorProto_ReservedRange, _impl_._cached_size_),
               false,
           },
-          &DescriptorProto_ReservedRange::MergeImpl,
           &DescriptorProto_ReservedRange::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -3666,7 +3663,6 @@ PROTOBUF_NOINLINE void DescriptorProto_ReservedRange::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void DescriptorProto_ReservedRange::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<DescriptorProto_ReservedRange*>(&to_msg);
   auto& from = static_cast<const DescriptorProto_ReservedRange&>(from_msg);
@@ -3795,10 +3791,10 @@ DescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               DescriptorProto::IsInitializedImpl,
+              &DescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(DescriptorProto, _impl_._cached_size_),
               false,
           },
-          &DescriptorProto::MergeImpl,
           &DescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -4141,7 +4137,6 @@ PROTOBUF_NOINLINE void DescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void DescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<DescriptorProto*>(&to_msg);
   auto& from = static_cast<const DescriptorProto&>(from_msg);
@@ -4312,10 +4307,10 @@ ExtensionRangeOptions_Declaration::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &ExtensionRangeOptions_Declaration::MergeImpl,
               PROTOBUF_FIELD_OFFSET(ExtensionRangeOptions_Declaration, _impl_._cached_size_),
               false,
           },
-          &ExtensionRangeOptions_Declaration::MergeImpl,
           &ExtensionRangeOptions_Declaration::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -4506,7 +4501,6 @@ PROTOBUF_NOINLINE void ExtensionRangeOptions_Declaration::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void ExtensionRangeOptions_Declaration::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<ExtensionRangeOptions_Declaration*>(&to_msg);
   auto& from = static_cast<const ExtensionRangeOptions_Declaration&>(from_msg);
@@ -4638,10 +4632,10 @@ ExtensionRangeOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               ExtensionRangeOptions::IsInitializedImpl,
+              &ExtensionRangeOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(ExtensionRangeOptions, _impl_._cached_size_),
               false,
           },
-          &ExtensionRangeOptions::MergeImpl,
           &ExtensionRangeOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -4829,7 +4823,6 @@ PROTOBUF_NOINLINE void ExtensionRangeOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void ExtensionRangeOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<ExtensionRangeOptions*>(&to_msg);
   auto& from = static_cast<const ExtensionRangeOptions&>(from_msg);
@@ -4997,10 +4990,10 @@ FieldDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FieldDescriptorProto::IsInitializedImpl,
+              &FieldDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FieldDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &FieldDescriptorProto::MergeImpl,
           &FieldDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -5327,7 +5320,6 @@ PROTOBUF_NOINLINE void FieldDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FieldDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FieldDescriptorProto*>(&to_msg);
   auto& from = static_cast<const FieldDescriptorProto&>(from_msg);
@@ -5491,10 +5483,10 @@ OneofDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               OneofDescriptorProto::IsInitializedImpl,
+              &OneofDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(OneofDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &OneofDescriptorProto::MergeImpl,
           &OneofDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -5623,7 +5615,6 @@ PROTOBUF_NOINLINE void OneofDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void OneofDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<OneofDescriptorProto*>(&to_msg);
   auto& from = static_cast<const OneofDescriptorProto&>(from_msg);
@@ -5733,10 +5724,10 @@ EnumDescriptorProto_EnumReservedRange::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &EnumDescriptorProto_EnumReservedRange::MergeImpl,
               PROTOBUF_FIELD_OFFSET(EnumDescriptorProto_EnumReservedRange, _impl_._cached_size_),
               false,
           },
-          &EnumDescriptorProto_EnumReservedRange::MergeImpl,
           &EnumDescriptorProto_EnumReservedRange::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -5858,7 +5849,6 @@ PROTOBUF_NOINLINE void EnumDescriptorProto_EnumReservedRange::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void EnumDescriptorProto_EnumReservedRange::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<EnumDescriptorProto_EnumReservedRange*>(&to_msg);
   auto& from = static_cast<const EnumDescriptorProto_EnumReservedRange&>(from_msg);
@@ -5977,10 +5967,10 @@ EnumDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               EnumDescriptorProto::IsInitializedImpl,
+              &EnumDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(EnumDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &EnumDescriptorProto::MergeImpl,
           &EnumDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -6190,7 +6180,6 @@ PROTOBUF_NOINLINE void EnumDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void EnumDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<EnumDescriptorProto*>(&to_msg);
   auto& from = static_cast<const EnumDescriptorProto&>(from_msg);
@@ -6332,10 +6321,10 @@ EnumValueDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               EnumValueDescriptorProto::IsInitializedImpl,
+              &EnumValueDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(EnumValueDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &EnumValueDescriptorProto::MergeImpl,
           &EnumValueDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -6484,7 +6473,6 @@ PROTOBUF_NOINLINE void EnumValueDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void EnumValueDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<EnumValueDescriptorProto*>(&to_msg);
   auto& from = static_cast<const EnumValueDescriptorProto&>(from_msg);
@@ -6620,10 +6608,10 @@ ServiceDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               ServiceDescriptorProto::IsInitializedImpl,
+              &ServiceDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(ServiceDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &ServiceDescriptorProto::MergeImpl,
           &ServiceDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -6781,7 +6769,6 @@ PROTOBUF_NOINLINE void ServiceDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void ServiceDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<ServiceDescriptorProto*>(&to_msg);
   auto& from = static_cast<const ServiceDescriptorProto&>(from_msg);
@@ -6930,10 +6917,10 @@ MethodDescriptorProto::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               MethodDescriptorProto::IsInitializedImpl,
+              &MethodDescriptorProto::MergeImpl,
               PROTOBUF_FIELD_OFFSET(MethodDescriptorProto, _impl_._cached_size_),
               false,
           },
-          &MethodDescriptorProto::MergeImpl,
           &MethodDescriptorProto::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -7147,7 +7134,6 @@ PROTOBUF_NOINLINE void MethodDescriptorProto::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void MethodDescriptorProto::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<MethodDescriptorProto*>(&to_msg);
   auto& from = static_cast<const MethodDescriptorProto&>(from_msg);
@@ -7338,10 +7324,10 @@ FileOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FileOptions::IsInitializedImpl,
+              &FileOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FileOptions, _impl_._cached_size_),
               false,
           },
-          &FileOptions::MergeImpl,
           &FileOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -7889,7 +7875,6 @@ PROTOBUF_NOINLINE void FileOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FileOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FileOptions*>(&to_msg);
   auto& from = static_cast<const FileOptions&>(from_msg);
@@ -8112,10 +8097,10 @@ MessageOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               MessageOptions::IsInitializedImpl,
+              &MessageOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(MessageOptions, _impl_._cached_size_),
               false,
           },
-          &MessageOptions::MergeImpl,
           &MessageOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -8339,7 +8324,6 @@ PROTOBUF_NOINLINE void MessageOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void MessageOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<MessageOptions*>(&to_msg);
   auto& from = static_cast<const MessageOptions&>(from_msg);
@@ -8486,10 +8470,10 @@ FieldOptions_EditionDefault::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &FieldOptions_EditionDefault::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FieldOptions_EditionDefault, _impl_._cached_size_),
               false,
           },
-          &FieldOptions_EditionDefault::MergeImpl,
           &FieldOptions_EditionDefault::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -8614,7 +8598,6 @@ PROTOBUF_NOINLINE void FieldOptions_EditionDefault::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FieldOptions_EditionDefault::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FieldOptions_EditionDefault*>(&to_msg);
   auto& from = static_cast<const FieldOptions_EditionDefault&>(from_msg);
@@ -8732,10 +8715,10 @@ FieldOptions_FeatureSupport::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &FieldOptions_FeatureSupport::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FieldOptions_FeatureSupport, _impl_._cached_size_),
               false,
           },
-          &FieldOptions_FeatureSupport::MergeImpl,
           &FieldOptions_FeatureSupport::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -8902,7 +8885,6 @@ PROTOBUF_NOINLINE void FieldOptions_FeatureSupport::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FieldOptions_FeatureSupport::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FieldOptions_FeatureSupport*>(&to_msg);
   auto& from = static_cast<const FieldOptions_FeatureSupport&>(from_msg);
@@ -9046,10 +9028,10 @@ FieldOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FieldOptions::IsInitializedImpl,
+              &FieldOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FieldOptions, _impl_._cached_size_),
               false,
           },
-          &FieldOptions::MergeImpl,
           &FieldOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -9429,7 +9411,6 @@ PROTOBUF_NOINLINE void FieldOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FieldOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FieldOptions*>(&to_msg);
   auto& from = static_cast<const FieldOptions&>(from_msg);
@@ -9610,10 +9591,10 @@ OneofOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               OneofOptions::IsInitializedImpl,
+              &OneofOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(OneofOptions, _impl_._cached_size_),
               false,
           },
-          &OneofOptions::MergeImpl,
           &OneofOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -9752,7 +9733,6 @@ PROTOBUF_NOINLINE void OneofOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void OneofOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<OneofOptions*>(&to_msg);
   auto& from = static_cast<const OneofOptions&>(from_msg);
@@ -9895,10 +9875,10 @@ EnumOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               EnumOptions::IsInitializedImpl,
+              &EnumOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(EnumOptions, _impl_._cached_size_),
               false,
           },
-          &EnumOptions::MergeImpl,
           &EnumOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -10090,7 +10070,6 @@ PROTOBUF_NOINLINE void EnumOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void EnumOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<EnumOptions*>(&to_msg);
   auto& from = static_cast<const EnumOptions&>(from_msg);
@@ -10249,10 +10228,10 @@ EnumValueOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               EnumValueOptions::IsInitializedImpl,
+              &EnumValueOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(EnumValueOptions, _impl_._cached_size_),
               false,
           },
-          &EnumValueOptions::MergeImpl,
           &EnumValueOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -10430,7 +10409,6 @@ PROTOBUF_NOINLINE void EnumValueOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void EnumValueOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<EnumValueOptions*>(&to_msg);
   auto& from = static_cast<const EnumValueOptions&>(from_msg);
@@ -10580,10 +10558,10 @@ ServiceOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               ServiceOptions::IsInitializedImpl,
+              &ServiceOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(ServiceOptions, _impl_._cached_size_),
               false,
           },
-          &ServiceOptions::MergeImpl,
           &ServiceOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -10740,7 +10718,6 @@ PROTOBUF_NOINLINE void ServiceOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void ServiceOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<ServiceOptions*>(&to_msg);
   auto& from = static_cast<const ServiceOptions&>(from_msg);
@@ -10893,10 +10870,10 @@ MethodOptions::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               MethodOptions::IsInitializedImpl,
+              &MethodOptions::MergeImpl,
               PROTOBUF_FIELD_OFFSET(MethodOptions, _impl_._cached_size_),
               false,
           },
-          &MethodOptions::MergeImpl,
           &MethodOptions::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -11079,7 +11056,6 @@ PROTOBUF_NOINLINE void MethodOptions::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void MethodOptions::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<MethodOptions*>(&to_msg);
   auto& from = static_cast<const MethodOptions&>(from_msg);
@@ -11220,10 +11196,10 @@ UninterpretedOption_NamePart::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               UninterpretedOption_NamePart::IsInitializedImpl,
+              &UninterpretedOption_NamePart::MergeImpl,
               PROTOBUF_FIELD_OFFSET(UninterpretedOption_NamePart, _impl_._cached_size_),
               false,
           },
-          &UninterpretedOption_NamePart::MergeImpl,
           &UninterpretedOption_NamePart::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -11347,7 +11323,6 @@ PROTOBUF_NOINLINE void UninterpretedOption_NamePart::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void UninterpretedOption_NamePart::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<UninterpretedOption_NamePart*>(&to_msg);
   auto& from = static_cast<const UninterpretedOption_NamePart&>(from_msg);
@@ -11481,10 +11456,10 @@ UninterpretedOption::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               UninterpretedOption::IsInitializedImpl,
+              &UninterpretedOption::MergeImpl,
               PROTOBUF_FIELD_OFFSET(UninterpretedOption, _impl_._cached_size_),
               false,
           },
-          &UninterpretedOption::MergeImpl,
           &UninterpretedOption::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -11721,7 +11696,6 @@ PROTOBUF_NOINLINE void UninterpretedOption::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void UninterpretedOption::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<UninterpretedOption*>(&to_msg);
   auto& from = static_cast<const UninterpretedOption&>(from_msg);
@@ -11868,10 +11842,10 @@ FeatureSet::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FeatureSet::IsInitializedImpl,
+              &FeatureSet::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FeatureSet, _impl_._cached_size_),
               false,
           },
-          &FeatureSet::MergeImpl,
           &FeatureSet::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -12077,7 +12051,6 @@ PROTOBUF_NOINLINE void FeatureSet::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FeatureSet::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FeatureSet*>(&to_msg);
   auto& from = static_cast<const FeatureSet&>(from_msg);
@@ -12220,10 +12193,10 @@ FeatureSetDefaults_FeatureSetEditionDefault::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FeatureSetDefaults_FeatureSetEditionDefault::IsInitializedImpl,
+              &FeatureSetDefaults_FeatureSetEditionDefault::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FeatureSetDefaults_FeatureSetEditionDefault, _impl_._cached_size_),
               false,
           },
-          &FeatureSetDefaults_FeatureSetEditionDefault::MergeImpl,
           &FeatureSetDefaults_FeatureSetEditionDefault::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -12370,7 +12343,6 @@ PROTOBUF_NOINLINE void FeatureSetDefaults_FeatureSetEditionDefault::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FeatureSetDefaults_FeatureSetEditionDefault::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FeatureSetDefaults_FeatureSetEditionDefault*>(&to_msg);
   auto& from = static_cast<const FeatureSetDefaults_FeatureSetEditionDefault&>(from_msg);
@@ -12516,10 +12488,10 @@ FeatureSetDefaults::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               FeatureSetDefaults::IsInitializedImpl,
+              &FeatureSetDefaults::MergeImpl,
               PROTOBUF_FIELD_OFFSET(FeatureSetDefaults, _impl_._cached_size_),
               false,
           },
-          &FeatureSetDefaults::MergeImpl,
           &FeatureSetDefaults::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -12667,7 +12639,6 @@ PROTOBUF_NOINLINE void FeatureSetDefaults::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void FeatureSetDefaults::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<FeatureSetDefaults*>(&to_msg);
   auto& from = static_cast<const FeatureSetDefaults&>(from_msg);
@@ -12797,10 +12768,10 @@ SourceCodeInfo_Location::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &SourceCodeInfo_Location::MergeImpl,
               PROTOBUF_FIELD_OFFSET(SourceCodeInfo_Location, _impl_._cached_size_),
               false,
           },
-          &SourceCodeInfo_Location::MergeImpl,
           &SourceCodeInfo_Location::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -13018,7 +12989,6 @@ PROTOBUF_NOINLINE void SourceCodeInfo_Location::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void SourceCodeInfo_Location::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<SourceCodeInfo_Location*>(&to_msg);
   auto& from = static_cast<const SourceCodeInfo_Location&>(from_msg);
@@ -13123,10 +13093,10 @@ SourceCodeInfo::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &SourceCodeInfo::MergeImpl,
               PROTOBUF_FIELD_OFFSET(SourceCodeInfo, _impl_._cached_size_),
               false,
           },
-          &SourceCodeInfo::MergeImpl,
           &SourceCodeInfo::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -13228,7 +13198,6 @@ PROTOBUF_NOINLINE void SourceCodeInfo::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void SourceCodeInfo::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<SourceCodeInfo*>(&to_msg);
   auto& from = static_cast<const SourceCodeInfo&>(from_msg);
@@ -13338,10 +13307,10 @@ GeneratedCodeInfo_Annotation::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &GeneratedCodeInfo_Annotation::MergeImpl,
               PROTOBUF_FIELD_OFFSET(GeneratedCodeInfo_Annotation, _impl_._cached_size_),
               false,
           },
-          &GeneratedCodeInfo_Annotation::MergeImpl,
           &GeneratedCodeInfo_Annotation::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -13540,7 +13509,6 @@ PROTOBUF_NOINLINE void GeneratedCodeInfo_Annotation::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void GeneratedCodeInfo_Annotation::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<GeneratedCodeInfo_Annotation*>(&to_msg);
   auto& from = static_cast<const GeneratedCodeInfo_Annotation&>(from_msg);
@@ -13652,10 +13620,10 @@ GeneratedCodeInfo::GetClassData() const {
               &_table_.header,
               nullptr,  // OnDemandRegisterArenaDtor
               nullptr,  // IsInitialized
+              &GeneratedCodeInfo::MergeImpl,
               PROTOBUF_FIELD_OFFSET(GeneratedCodeInfo, _impl_._cached_size_),
               false,
           },
-          &GeneratedCodeInfo::MergeImpl,
           &GeneratedCodeInfo::kDescriptorMethods,
           &descriptor_table_google_2fprotobuf_2fdescriptor_2eproto,
           nullptr,  // tracker
@@ -13757,7 +13725,6 @@ PROTOBUF_NOINLINE void GeneratedCodeInfo::Clear() {
   return MaybeComputeUnknownFieldsSize(total_size, &_impl_._cached_size_);
 }
 
-
 void GeneratedCodeInfo::MergeImpl(::google::protobuf::MessageLite& to_msg, const ::google::protobuf::MessageLite& from_msg) {
   auto* const _this = static_cast<GeneratedCodeInfo*>(&to_msg);
   auto& from = static_cast<const GeneratedCodeInfo&>(from_msg);

src/google/protobuf/dynamic_message.cc

@@ -273,10 +273,10 @@ struct DynamicMessageFactory::TypeInfo {
           nullptr,  // tc_table
           nullptr,  // on_demand_register_arena_dtor
           DynamicMessage::IsInitializedImpl,
+          &DynamicMessage::MergeImpl,
           PROTOBUF_FIELD_OFFSET(DynamicMessage, cached_byte_size_),
           false,
       },
-      &DynamicMessage::MergeImpl,
       &DynamicMessage::kDescriptorMethods,
       nullptr,  // descriptor_table
       nullptr,  // get_metadata_tracker

src/google/protobuf/implicit_weak_message.cc

@@ -7,6 +7,8 @@
 
 #include "google/protobuf/implicit_weak_message.h"
 
+#include <string>
+
 #include "google/protobuf/generated_message_tctable_decl.h"
 #include "google/protobuf/message_lite.h"
 #include "google/protobuf/parse_context.h"
@@ -25,6 +27,15 @@ const char* ImplicitWeakMessage::ParseImpl(ImplicitWeakMessage* msg,
   return ctx->AppendString(ptr, msg->data_);
 }
 
+void ImplicitWeakMessage::MergeImpl(MessageLite& self,
+                                    const MessageLite& other) {
+  const std::string* other_data =
+      static_cast<const ImplicitWeakMessage&>(other).data_;
+  if (other_data != nullptr) {
+    static_cast<ImplicitWeakMessage&>(self).data_->append(*other_data);
+  }
+}
+
 struct ImplicitWeakMessageDefaultType {
   constexpr ImplicitWeakMessageDefaultType()
       : instance(ConstantInitialized{}) {}
@@ -55,6 +66,7 @@ const MessageLite::ClassData* ImplicitWeakMessage::GetClassData() const {
           &table.header,
           nullptr,  // on_demand_register_arena_dtor
           nullptr,  // is_initialized (always true)
+          MergeImpl,
           PROTOBUF_FIELD_OFFSET(ImplicitWeakMessage, cached_size_),
           true,
       },

src/google/protobuf/implicit_weak_message.h

@@ -64,14 +64,6 @@ class PROTOBUF_EXPORT ImplicitWeakMessage : public MessageLite {
 
   void Clear() override { data_->clear(); }
 
-  void CheckTypeAndMergeFrom(const MessageLite& other) override {
-    const std::string* other_data =
-        static_cast<const ImplicitWeakMessage&>(other).data_;
-    if (other_data != nullptr) {
-      data_->append(*other_data);
-    }
-  }
-
   size_t ByteSizeLong() const override {
     size_t size = data_ == nullptr ? 0 : data_->size();
     cached_size_.Set(internal::ToCachedSize(size));
@@ -92,6 +84,7 @@ class PROTOBUF_EXPORT ImplicitWeakMessage : public MessageLite {
  private:
   static const char* ParseImpl(ImplicitWeakMessage* msg, const char* ptr,
                                ParseContext* ctx);
+  static void MergeImpl(MessageLite&, const MessageLite&);
 
   // This std::string is allocated on the heap, but we use a raw pointer so that
   // the default instance can be constant-initialized. In the const methods, we

src/google/protobuf/message.cc

@@ -80,10 +80,6 @@ void Message::MergeFrom(const Message& from) {
   }
 }
 
-void Message::CheckTypeAndMergeFrom(const MessageLite& other) {
-  MergeFrom(DownCastToMessage(other));
-}
-
 void Message::CopyFrom(const Message& from) {
   if (&from == this) return;
 

src/google/protobuf/message.h

@@ -345,7 +345,6 @@ class PROTOBUF_EXPORT Message : public MessageLite {
 
   void Clear() override;
 
-  void CheckTypeAndMergeFrom(const MessageLite& other) override;
   size_t ByteSizeLong() const override;
   uint8_t* _InternalSerialize(uint8_t* target,
                               io::EpsCopyOutputStream* stream) const override;

src/google/protobuf/message_lite.cc

@@ -45,6 +45,16 @@
 namespace google {
 namespace protobuf {
 
+void MessageLite::CheckTypeAndMergeFrom(const MessageLite& other) {
+  auto* data = GetClassData();
+  auto* other_data = other.GetClassData();
+
+  ABSL_CHECK_EQ(data, other_data)
+      << "Invalid call to CheckTypeAndMergeFrom between types " << GetTypeName()
+      << " and " << other.GetTypeName();
+  data->merge_to_from(*this, other);
+}
+
 bool MessageLite::IsInitialized() const {
   auto* data = GetClassData();
   return data->is_initialized != nullptr ? data->is_initialized(*this) : true;

src/google/protobuf/message_lite.h

@@ -255,7 +255,7 @@ class PROTOBUF_EXPORT MessageLite {
 
   // If |other| is the exact same class as this, calls MergeFrom(). Otherwise,
   // results are undefined (probably crash).
-  virtual void CheckTypeAndMergeFrom(const MessageLite& other) = 0;
+  void CheckTypeAndMergeFrom(const MessageLite& other);
 
   // These methods return a human-readable summary of the message. Note that
   // since the MessageLite interface does not support reflection, there is very
@@ -560,6 +560,7 @@ class PROTOBUF_EXPORT MessageLite {
     const internal::TcParseTableBase* tc_table;
     void (*on_demand_register_arena_dtor)(MessageLite& msg, Arena& arena);
     bool (*is_initialized)(const MessageLite&);
+    void (*merge_to_from)(MessageLite& to, const MessageLite& from_msg);
 
     // Offset of the CachedSize member.
     uint32_t cached_size_offset;
@@ -567,25 +568,17 @@ class PROTOBUF_EXPORT MessageLite {
     // char[] just beyond the ClassData.
     bool is_lite;
 
-    // XXX REMOVE XXX
-    constexpr ClassData(const internal::TcParseTableBase* tc_table,
-                        void (*on_demand_register_arena_dtor)(MessageLite&,
-                                                              Arena&),
-                        uint32_t cached_size_offset, bool is_lite)
-        : tc_table(tc_table),
-          on_demand_register_arena_dtor(on_demand_register_arena_dtor),
-          is_initialized(nullptr),
-          cached_size_offset(cached_size_offset),
-          is_lite(is_lite) {}
-
     constexpr ClassData(const internal::TcParseTableBase* tc_table,
                         void (*on_demand_register_arena_dtor)(MessageLite&,
                                                               Arena&),
                         bool (*is_initialized)(const MessageLite&),
+                        void (*merge_to_from)(MessageLite& to,
+                                              const MessageLite& from_msg),
                         uint32_t cached_size_offset, bool is_lite)
         : tc_table(tc_table),
           on_demand_register_arena_dtor(on_demand_register_arena_dtor),
           is_initialized(is_initialized),
+          merge_to_from(merge_to_from),
           cached_size_offset(cached_size_offset),
           is_lite(is_lite) {}
 
@@ -603,13 +596,10 @@ class PROTOBUF_EXPORT MessageLite {
   };
   struct ClassDataFull : ClassData {
     constexpr ClassDataFull(ClassData base,
-                            void (*merge_to_from)(MessageLite& to,
-                                                  const MessageLite& from_msg),
                             const DescriptorMethods* descriptor_methods,
                             const internal::DescriptorTable* descriptor_table,
                             void (*get_metadata_tracker)())
         : ClassData(base),
-          merge_to_from(merge_to_from),
           descriptor_methods(descriptor_methods),
           descriptor_table(descriptor_table),
           reflection(),
@@ -618,7 +608,6 @@ class PROTOBUF_EXPORT MessageLite {
 
     constexpr const ClassData* base() const { return this; }
 
-    void (*merge_to_from)(MessageLite& to, const MessageLite& from_msg);
     const DescriptorMethods* descriptor_methods;
 
     // Codegen types will provide a DescriptorTable to do lazy