message: Enable loop-invariant node motion in the Grappler loop optimizer.
  Thanks to the team at Alibaba, who contributed the original version of this code.
diff: @@ -52,14 +52,11 @@ class LoopOptimizer : public GraphOptimizer {
  // Granular control for loop optimizer stages.
  struct LoopOptimizerOptions {
  - bool enable_loop_invariant_node_motion = false;
  + bool enable_loop_invariant_node_motion = true;
  bool enable_stack_push_removal = true;
  static LoopOptimizerOptions Default(RewriterConfig::Toggle opt_level) {
  LoopOptimizerOptions options;
  - if (opt_level == RewriterConfig::AGGRESSIVE) {
  - options.enable_loop_invariant_node_motion = true;
  - }
  return options;
  }
  };
  