Re: diffcore-rename performance mode

Jeff King [off-list ref] writes:

I thought we were holding counts of hashes, in which case there _is_ no
overflow.

The raw hashval (the fingerprint recorded in struct spanhash) is
further reduced and used as an index into spahash_top.data[].
So more than one hashval can try to sit in the same slot in
spanhash_top.data[] array.