Cache the result of "is_repeated" on its own bit to avoid having to read and

compare the label.
This query is very common when handling descriptors.

PiperOrigin-RevId: 623857268

src/google/protobuf/descriptor.cc

@@ -6500,6 +6500,7 @@ void DescriptorBuilder::BuildFieldOrExtension(const FieldDescriptorProto& proto,
       absl::implicit_cast<int>(proto.type()));
   result->label_ = static_cast<FieldDescriptor::Label>(
       absl::implicit_cast<int>(proto.label()));
+  result->is_repeated_ = result->label_ == FieldDescriptor::LABEL_REPEATED;
 
   if (result->label() == FieldDescriptor::LABEL_REQUIRED) {
     // An extension cannot have a required field (b/13365836).

src/google/protobuf/descriptor.h

@@ -1084,6 +1084,7 @@ class PROTOBUF_EXPORT FieldDescriptor : private internal::SymbolBase,
   bool has_json_name_ : 1;
   bool is_extension_ : 1;
   bool is_oneof_ : 1;
+  bool is_repeated_ : 1;  // Redundant with label_, but it is queried a lot.
 
   // Actually a `Label` but stored as uint8_t to save space.
   uint8_t label_ : 2;
@@ -2686,7 +2687,8 @@ inline bool FieldDescriptor::is_optional() const {
 }
 
 inline bool FieldDescriptor::is_repeated() const {
-  return label() == LABEL_REPEATED;
+  ABSL_DCHECK_EQ(is_repeated_, label() == LABEL_REPEATED);
+  return is_repeated_;
 }
 
 inline bool FieldDescriptor::is_packable() const {