11.4.8 sweep_bit_vectors_1

Bit vectors are also one of the rare types that are malloced individually. Consequently, while sweeping, all further needless bit vectors must be freed by hand. This is done, as one might imagine, the expected way: since they are all registered in a list called all_bit_vectors, all elements of that list are traversed, all unmarked bit vectors are unlinked by calling xfree and all of them become unmarked. In addition, the bookkeeping information used for garbage collector’s output purposes is updated.