During calculation of the collection set candidates in the Remark pause, G1 uses an array of G1CollectionSetCandidateInfos. This struct holds a reference to a G1HeapRegion and some integer.

That latter integer is not needed during that calculation, and not modified at all by that process; since we delete that temporary data structure later anyway, it makes sense to not carry around the full G1CollectionSetCandidateInfo array while building the collection set candidates from marking.