Well, another solution (which I believe is common) is to just tenure the young object (and recursively tenure objects reachable from it) if the write barrier trips, which preserves the precision.

There isn't anything fundamental to generational GC that requires imprecision. It's an implementation detail. In fact, David Ungar's original generational GC paper from 1984 [1] uses precise remembered sets. GHC's GC [2] among others uses precise remembered sets.

[1]: https://people.cs.umass.edu/~emery/classes/cmpsci691s-fall20...

[2]: https://ghc.haskell.org/trac/ghc/wiki/Commentary/Rts/Storage...