Here are the data structures with brief descriptions:

Cbackend_params	This structure contains parameters that should be propagated to the libFirm parameter set
Ci_call_record	An intrinsic call record
Ci_instr_record	An intrinsic instruction record
Ci_record	An intrinsic record
Cir_asm_constraint	A input/output constraint attribute
Cloop_element	Loop elements: loop nodes and ir nodes
Cpmap_entry	A key, value pair
Cpset_entry	The entry of a pset, representing an element pointer in the set and its meta-information
Cset_entry	The entry of a set, representing an element in the set and its meta-information
Csrc_loc_t	A sourcecode location
Cvararg_params	This structure holds the information on how the backend implements variadic functions
Cvrp_attr	VRP information for a single node