I can't see any context in the form of a discussion, it's just code, so I can't see the anticipated trade-offs etc. but I'd expect the cost of access to the Btr

I can't see any context in the form of a discussion, it's just code, so I can't see the anticipated trade-offs etc. but I'd expect the cost of access to the Btree of any decent size (that is, overflowing cache) and large fanout to be almost completely about RAM memory latency. Therefore I'd expect compiling just the tree-accessing code to be of little value. Happy to be put right though.