diff --git a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
index 75418982ea..d38a2242e0 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_helpers.cc
@@ -918,7 +918,7 @@ bool HasNonZeroDefaultValue(const FieldDescriptor* field) {
 
 string BuildFlagsString(const FlagType flag_type,
                         const std::vector<string>& strings) {
-  if (strings.size() == 0) {
+  if (strings.empty()) {
     return GetZeroEnumNameForFlagType(flag_type);
   } else if (strings.size() == 1) {
     return strings[0];
@@ -945,7 +945,7 @@ string BuildCommentsString(const SourceLocation& location,
     lines.pop_back();
   }
   // If there are no comments, just return an empty string.
-  if (lines.size() == 0) {
+  if (lines.empty()) {
     return "";
   }
 
@@ -1405,7 +1405,7 @@ string DirectDecodeString(const string& str) {
 // static
 string TextFormatDecodeData::DecodeDataForString(const string& input_for_decode,
                                                  const string& desired_output) {
-  if ((input_for_decode.size() == 0) || (desired_output.size() == 0)) {
+  if (input_for_decode.empty() || desired_output.empty()) {
     std::cerr << "error: got empty string for making TextFormat data, input: \""
          << input_for_decode << "\", desired: \"" << desired_output << "\"."
          << std::endl;
@@ -1515,7 +1515,7 @@ bool Parser::ParseLoop() {
     ++line_;
     RemoveComment(&line);
     TrimWhitespace(&line);
-    if (line.size() == 0) {
+    if (line.empty()) {
       continue;  // Blank line.
     }
     if (!line_consumer_->ConsumeLine(line, &error_str_)) {
@@ -1622,7 +1622,7 @@ void ImportWriter::Print(io::Printer* printer) const {
 
   bool add_blank_line = false;
 
-  if (protobuf_framework_imports_.size() > 0) {
+  if (!protobuf_framework_imports_.empty()) {
     const string framework_name(ProtobufLibraryFrameworkName);
     const string cpp_symbol(ProtobufFrameworkImportSymbol(framework_name));
 
@@ -1650,7 +1650,7 @@ void ImportWriter::Print(io::Printer* printer) const {
     add_blank_line = true;
   }
 
-  if (other_framework_imports_.size() > 0) {
+  if (!other_framework_imports_.empty()) {
     if (add_blank_line) {
       printer->Print("\n");
     }
@@ -1665,7 +1665,7 @@ void ImportWriter::Print(io::Printer* printer) const {
     add_blank_line = true;
   }
 
-  if (other_imports_.size() > 0) {
+  if (!other_imports_.empty()) {
     if (add_blank_line) {
       printer->Print("\n");
     }
@@ -1717,7 +1717,7 @@ bool ImportWriter::ProtoFrameworkCollector::ConsumeLine(
 
     StringPiece proto_file = proto_file_list.substr(start, offset - start);
     TrimWhitespace(&proto_file);
-    if (proto_file.size() != 0) {
+    if (!proto_file.empty()) {
       std::map<string, string>::iterator existing_entry =
           map_->find(string(proto_file));
       if (existing_entry != map_->end()) {
diff --git a/src/google/protobuf/compiler/objectivec/objectivec_message.cc b/src/google/protobuf/compiler/objectivec/objectivec_message.cc
index 2a0e40231d..5ab5fd5b55 100644
--- a/src/google/protobuf/compiler/objectivec/objectivec_message.cc
+++ b/src/google/protobuf/compiler/objectivec/objectivec_message.cc
@@ -50,9 +50,6 @@ namespace protobuf {
 namespace compiler {
 namespace objectivec {
 
-using internal::WireFormat;
-using internal::WireFormatLite;
-
 namespace {
 struct FieldOrderingByNumber {
   inline bool operator()(const FieldDescriptor* a,
@@ -417,6 +414,7 @@ void MessageGenerator::GenerateSource(io::Printer* printer) {
         SortFieldsByStorageSize(descriptor_));
 
     std::vector<const Descriptor::ExtensionRange*> sorted_extensions;
+    sorted_extensions.reserve(descriptor_->extension_range_count());
     for (int i = 0; i < descriptor_->extension_range_count(); ++i) {
       sorted_extensions.push_back(descriptor_->extension_range(i));
     }
@@ -536,7 +534,7 @@ void MessageGenerator::GenerateSource(io::Printer* printer) {
         "                                    fieldCount:$fields_count$\n"
         "                                   storageSize:sizeof($classname$__storage_)\n"
         "                                         flags:$init_flags$];\n");
-    if (oneof_generators_.size() != 0) {
+    if (!oneof_generators_.empty()) {
       printer->Print(
           "    static const char *oneofs[] = {\n");
       for (const auto& generator : oneof_generators_) {
@@ -567,7 +565,7 @@ void MessageGenerator::GenerateSource(io::Printer* printer) {
           "    [localDescriptor setupExtraTextInfo:extraTextFormatInfo];\n"
           "#endif  // !GPBOBJC_SKIP_MESSAGE_TEXTFORMAT_EXTRAS\n");
     }
-    if (sorted_extensions.size() != 0) {
+    if (!sorted_extensions.empty()) {
       printer->Print(
           "    static const GPBExtensionRange ranges[] = {\n");
       for (int i = 0; i < sorted_extensions.size(); i++) {
@@ -589,7 +587,7 @@ void MessageGenerator::GenerateSource(io::Printer* printer) {
     }
     string suffix_added;
     ClassName(descriptor_, &suffix_added);
-    if (suffix_added.size() > 0) {
+    if (!suffix_added.empty()) {
       printer->Print(
           "    [localDescriptor setupMessageClassNameSuffix:@\"$suffix$\"];\n",
           "suffix", suffix_added);