// since it emits PCDATA for the stack map at the call (calls are safe points).
func (s *State) PrepareCall(v *ssa.Value) {
	idx := s.livenessMap.Get(v)
	if !idx.StackMapValid() {
		// See Liveness.hasStackMap.
		if sym, ok := v.Aux.(*ssa.AuxCall); !ok || !(sym.Fn == ir.Syms.WBZero || sym.Fn == ir.Syms.WBMove) {
			base.Fatalf("missing stack map index for %v", v.LongString())
		}
	}