[perf][5/5] Replace IValue::toString()->string() with IValue::toStringRef() (#2700)

Summary:
Pull Request resolved: https://github.com/pytorch/audio/pull/2700

ATT for pytorch/audio

Reviewed By: mthrok

Differential Revision: D39707243

fbshipit-source-id: 1dc2a5a9fe913a9071e6df679e39d632b75212fb

examples/libtorchaudio/speech_recognition/transcribe.cpp

@@ -34,6 +34,6 @@ int main(int argc, char* argv[]) {
   auto emission = encoder.forward({waveform});
   std::cout << "Generating the transcription" << std::endl;
   auto result = decoder.forward({emission});
-  std::cout << result.toString()->string() << std::endl;
+  std::cout << result.toStringRef() << std::endl;
   std::cout << "Done." << std::endl;
 }

examples/libtorchaudio/speech_recognition/transcribe_list.cpp

@@ -57,7 +57,7 @@ int main(int argc, char* argv[]) {
     t_encode += std::chrono::duration_cast<std::chrono::milliseconds>(t1 - t0);
     t_decode += std::chrono::duration_cast<std::chrono::milliseconds>(t2 - t1);
 
-    auto hypothesis = result.toString()->string();
+    auto hypothesis = result.toStringRef();
     output_hyp << hypothesis << " (" << id << ")" << std::endl;
     output_ref << reference << " (" << id << ")" << std::endl;
     std::cout << id << '\t' << hypothesis << std::endl;