message: Adds RELU6 to the list of cheap operations for potential recompute in memory_optimizer.
diff: @@ -48,13 +48,12 @@ const char* kRecomputationTargetNamePrefix = "gradients/";
  // TODO(allenl): Replace this list with a cost model.
  std::unordered_set<string> GetCheapToRecomputeOps() {
  std::unordered_set<string> cheap_ops = {
  - "Add", "AddN", "BiasAdd",
  - "Cast", "Fill", "FloorDiv",
  - "FloorMod", "FusedBatchNorm", "Mul",
  - "Neg", "RealDiv", "Reciprocal",
  - "Relu", "Reshape", "Rsqrt",
  - "Sqrt", "Square", "SquaredDifference",
  - "Sub", "Tile", "Transpose"};
  + "Add", "AddN", "BiasAdd", "Cast",
  + "Fill", "FloorDiv", "FloorMod", "FusedBatchNorm",
  + "Mul", "Neg", "RealDiv", "Reciprocal",
  + "Relu", "Relu6", "Reshape", "Rsqrt",
  + "Sqrt", "Square", "SquaredDifference", "Sub",
  + "Tile", "Transpose"};
  return cheap_ops;
  }
  