This project actually uses Yosys. From a quick glance at the code, this tool essentially uses Yosys for the heavy-duty logic stuff [1], resulting in a JSON-based logic definition using a couple of standard cells (DFF, MUX, arithmetic, etc.) that verilog2factorio parses [2] and translates into predefined Factorio blueprints. The only part that I couldn't find would be laying out the cells into the overall blueprint (and performing routing).

[1] https://github.com/Redcrafter/verilog2factorio/blob/9691b702...

[2] https://github.com/Redcrafter/verilog2factorio/blob/9691b702...

You don't need much understanding in advance to develop a novel backend, since you are forced and guided to learn the whole language as you try to write the backend and start pattern matching on the data structures.