I am doing a research about NLP and I am using RNN (Recurrent Neural Network) or CNN (Convolutional Neural Network) to encode a sentence into a vector. When using CNN, the training time is significantly smaller than RNN. It is natural to me to think that CNN is faster than RNN because it does not build the relationship between hidden vectors of each timesteps, so it takes less time to feed forward and back propagate. However, this question was asked recently by another person and I do not have any evidence to support my intuition.
Is there any evidence or results about comparing the speed of CNN and RNN, especially on NLP tasks?