What's the meaning of torch::jit::CreateFunctionalGraphs pass?

I’ve been lately doing some experiments with torch’s JIT compiler and found no documentation on torch jit passes. The pass I’m interested in is torch::jit::CreateFunctionalGraphs (https://github.com/pytorch/pytorch/blob/558a9501fa178f47c488a608dcc79d6a5a6159af/torch/csrc/jit/passes/create_functional_graphs.cpp#L215). Could someone please help me to understand the meaning of this pass, what’s the use of it? How it works?
Thank you