lssk := LocalSlotSplitKey{name, offset, t}
	if als, ok := f.CanonicalLocalSplits[lssk]; ok {
		return als
	}
	// Note: the _ field may appear several times.  But
	// have no fear, identically-named but distinct Autos are
	// ok, albeit maybe confusing for a debugger.
	ls := f.fe.SplitSlot(name, sfx, offset, t)
	f.CanonicalLocalSplits[lssk] = &ls
	return &ls
}