pub fn replace_if_possible<'tcx, V, L>( table: &mut UnificationTable<InPlace<ConstVid<'tcx>, V, L>>, c: &'tcx Const<'tcx>) -> &'tcx Const<'tcx> where V: VecLike<Delegate<ConstVid<'tcx>>>, L: UndoLogs<UndoLog<Delegate<ConstVid<'tcx>>>>,