Function rustc_mir_transform::elaborate_drops::find_dead_unwinds

fn find_dead_unwinds<'tcx>(
    tcx: TyCtxt<'tcx>, 
    body: &Body<'tcx>, 
    env: &MoveDataParamEnv<'tcx>
) -> BitSet<BasicBlock>

Returns the set of basic blocks whose unwind edges are known to not be reachable, because they are drop terminators that can’t drop anything.