add - add objects to the design

yosys> help add
add <command> [selection]
This command adds objects to the design. It operates on all fully selected
modules. So e.g. 'add -wire foo' will add a wire foo to all selected modules.
add {-wire|-input|-inout|-output} <name> <width> [selection]
Add a wire (input, inout, output port) with the given name and width. The
command will fail if the object exists already and has different properties
than the object to be created.
add -global_input <name> <width> [selection]
Like 'add -input', but also connect the signal between instances of the
selected modules.
add {-assert|-assume|-live|-fair|-cover} <name1> [-if <name2>]
Add an $assert, $assume, etc. cell connected to a wire named name1, with its
enable signal optionally connected to a wire named name2 (default: 1'b1).
add -mod <name[s]>
Add module[s] with the specified name[s].