message: Set field status to UNDEFINED when a new builder instance is created
  Summary: As title. No need to do this beforehand (when they have DEFAULT value).
diff: @@ -28,9 +28,16 @@ void fields_mapping(const IRInstruction* insn,
  always_assert(fregs != nullptr);
  always_assert(builder != nullptr);
  - // Set DEFAULT fields to UNDEFINED.
  + bool new_builder = false;
  + if (insn->opcode() == OPCODE_NEW_INSTANCE) {
  + if (insn->get_type() == builder->get_type()) {
  + new_builder = true;
  + }
  + }
  +
  + // Set fields to UNDEFINED if new builder instance.
  + if (new_builder) {
  for (auto& pair : fregs->field_to_reg) {
  - if (pair.second == FieldOrRegStatus::DEFAULT) {
  fregs->field_to_reg[pair.first] = FieldOrRegStatus::UNDEFINED;
  fregs->field_to_iput_insns[pair.first].clear();
  }
  