Function mutates_own_collection 

pub fn mutates_own_collection(op: &Op) -> bool

Whether this tier lowers op as a value-semantics mutation of a register’s own collection or Text, or of a value in its own record’s field: through an _own runtime helper that copies first only what the register’s owned flag (and, for a field, its field flag) says may be held elsewhere, so the change never reaches an alias and a loop of them runs in place.