For messages with all trivially copyable fields use the trivial copy of Impl_ in the copy constructor.

PiperOrigin-RevId: 686236500

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

@@ -254,6 +254,8 @@ class FieldGenerator {
   // Properties: see FieldGeneratorBase for documentation
   bool should_split() const { return impl_->should_split(); }
   bool is_trivial() const { return impl_->is_trivial(); }
+  // Returns true if the field has trivial copy construction.
+  bool has_trivial_copy() const { return is_trivial(); }
   bool has_trivial_value() const { return impl_->has_trivial_value(); }
   bool has_trivial_zero_default() const {
     return impl_->has_trivial_zero_default();

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

@@ -3049,32 +3049,18 @@ void MessageGenerator::GenerateConstexprConstructor(io::Printer* p) {
       )cc");
 }
 
-bool MessageGenerator::ImplHasCopyCtor() const {
+bool MessageGenerator::CanUseTrivialCopy() const {
   if (ShouldSplit(descriptor_, options_)) return false;
   if (HasSimpleBaseClass(descriptor_, options_)) return false;
   if (descriptor_->extension_range_count() > 0) return false;
-  if (descriptor_->real_oneof_decl_count() > 0) return false;
   if (num_weak_fields_ > 0) return false;
 
-  // If the message contains only scalar fields (ints and enums),
-  // then we can copy the entire impl_ section with a single statement.
-  for (const auto* field : optimized_order_) {
-    if (field->is_repeated()) return false;
-    if (field->is_extension()) return false;
-    switch (field->cpp_type()) {
-      case FieldDescriptor::CPPTYPE_ENUM:
-      case FieldDescriptor::CPPTYPE_INT32:
-      case FieldDescriptor::CPPTYPE_INT64:
-      case FieldDescriptor::CPPTYPE_UINT32:
-      case FieldDescriptor::CPPTYPE_UINT64:
-      case FieldDescriptor::CPPTYPE_FLOAT:
-      case FieldDescriptor::CPPTYPE_DOUBLE:
-      case FieldDescriptor::CPPTYPE_BOOL:
-        break;
-      default:
-        return false;
-    }
+  // If all fields are trivially copyable then we can use the trivial copy
+  // constructor of Impl_
+  for (const auto* field : FieldRange(descriptor_)) {
+    if (!field_generators_.get(field).has_trivial_copy()) return false;
   }
+
   return true;
 }
 
@@ -3381,13 +3367,19 @@ void MessageGenerator::GenerateStructors(io::Printer* p) {
         MergeFrom(from);
       }
     )cc");
-  } else if (ImplHasCopyCtor()) {
+  } else if (CanUseTrivialCopy()) {
     p->Emit(R"cc(
       $classname$::$classname$(
           //~ Force alignment
           ::$proto_ns$::Arena* arena, const $classname$& from)
-          : $classname$(arena) {
-        MergeFrom(from);
+#if defined(PROTOBUF_CUSTOM_VTABLE)
+          : $superclass$(arena, $classname$_class_data_.base()),
+#else   // PROTOBUF_CUSTOM_VTABLE
+          : $superclass$(arena),
+#endif  // PROTOBUF_CUSTOM_VTABLE
+            _impl_(from._impl_) {
+        _internal_metadata_.MergeFrom<$unknown_fields_type$>(
+            from._internal_metadata_);
       }
     )cc");
   } else {

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

@@ -174,8 +174,9 @@ class MessageGenerator {
   // the current message's arena, reducing `GetArena()` call churn.
   bool RequiresArena(GeneratorFunction function) const;
 
-  // Returns whether impl_ has a copy ctor.
-  bool ImplHasCopyCtor() const;
+  // Returns true if all fields are trivially copayble, and has no non-field
+  // state (eg extensions).
+  bool CanUseTrivialCopy() const;
 
   // Returns the level that this message needs ArenaDtor. If the message has
   // a field that is not arena-exclusive, it needs an ArenaDtor

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

@@ -167,8 +167,14 @@ JavaFeatures::JavaFeatures(::google::protobuf::Arena* arena)
 }
 JavaFeatures::JavaFeatures(
     ::google::protobuf::Arena* arena, const JavaFeatures& from)
-    : JavaFeatures(arena) {
-  MergeFrom(from);
+#if defined(PROTOBUF_CUSTOM_VTABLE)
+    : ::google::protobuf::Message(arena, JavaFeatures_class_data_.base()),
+#else   // PROTOBUF_CUSTOM_VTABLE
+    : ::google::protobuf::Message(arena),
+#endif  // PROTOBUF_CUSTOM_VTABLE
+      _impl_(from._impl_) {
+  _internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(
+      from._internal_metadata_);
 }
 inline PROTOBUF_NDEBUG_INLINE JavaFeatures::Impl_::Impl_(
     ::google::protobuf::internal::InternalVisibility visibility,

src/google/protobuf/cpp_features.pb.cc

@@ -167,8 +167,14 @@ CppFeatures::CppFeatures(::google::protobuf::Arena* arena)
 }
 CppFeatures::CppFeatures(
     ::google::protobuf::Arena* arena, const CppFeatures& from)
-    : CppFeatures(arena) {
-  MergeFrom(from);
+#if defined(PROTOBUF_CUSTOM_VTABLE)
+    : ::google::protobuf::Message(arena, CppFeatures_class_data_.base()),
+#else   // PROTOBUF_CUSTOM_VTABLE
+    : ::google::protobuf::Message(arena),
+#endif  // PROTOBUF_CUSTOM_VTABLE
+      _impl_(from._impl_) {
+  _internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(
+      from._internal_metadata_);
 }
 inline PROTOBUF_NDEBUG_INLINE CppFeatures::Impl_::Impl_(
     ::google::protobuf::internal::InternalVisibility visibility,

src/google/protobuf/descriptor.pb.cc

@@ -3892,8 +3892,14 @@ DescriptorProto_ReservedRange::DescriptorProto_ReservedRange(::google::protobuf:
 }
 DescriptorProto_ReservedRange::DescriptorProto_ReservedRange(
     ::google::protobuf::Arena* arena, const DescriptorProto_ReservedRange& from)
-    : DescriptorProto_ReservedRange(arena) {
-  MergeFrom(from);
+#if defined(PROTOBUF_CUSTOM_VTABLE)
+    : ::google::protobuf::Message(arena, DescriptorProto_ReservedRange_class_data_.base()),
+#else   // PROTOBUF_CUSTOM_VTABLE
+    : ::google::protobuf::Message(arena),
+#endif  // PROTOBUF_CUSTOM_VTABLE
+      _impl_(from._impl_) {
+  _internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(
+      from._internal_metadata_);
 }
 inline PROTOBUF_NDEBUG_INLINE DescriptorProto_ReservedRange::Impl_::Impl_(
     ::google::protobuf::internal::InternalVisibility visibility,
@@ -6402,8 +6408,14 @@ EnumDescriptorProto_EnumReservedRange::EnumDescriptorProto_EnumReservedRange(::g
 }
 EnumDescriptorProto_EnumReservedRange::EnumDescriptorProto_EnumReservedRange(
     ::google::protobuf::Arena* arena, const EnumDescriptorProto_EnumReservedRange& from)
-    : EnumDescriptorProto_EnumReservedRange(arena) {
-  MergeFrom(from);
+#if defined(PROTOBUF_CUSTOM_VTABLE)
+    : ::google::protobuf::Message(arena, EnumDescriptorProto_EnumReservedRange_class_data_.base()),
+#else   // PROTOBUF_CUSTOM_VTABLE
+    : ::google::protobuf::Message(arena),
+#endif  // PROTOBUF_CUSTOM_VTABLE
+      _impl_(from._impl_) {
+  _internal_metadata_.MergeFrom<::google::protobuf::UnknownFieldSet>(
+      from._internal_metadata_);
 }
 inline PROTOBUF_NDEBUG_INLINE EnumDescriptorProto_EnumReservedRange::Impl_::Impl_(
     ::google::protobuf::internal::InternalVisibility visibility,