To reduce the amount of allocation instead of:

    struct parsed_data * = parse (...);
    struct process_data * = process (..., parsed_data);
    struct foo_data * = do_foo (..., process_data);

you can do

    parse (...) {
        ...
        process (...);
        ...
    }

    process (...) {
        ...
        do_foo (...);
        ...
    }

It sounds like violating separation of concerns at first, but it has the benefit, that you can easily do procession and parsing in parallel, and all the data can become readonly. Also I was impressed when I looked at a call graph of this, since this essentially becomes the documentation of the whole program.