'You needn't have said that,' my wife answered.

needn't have done,不必做什么(但事实上却已经做了)
'You needn't have said that,' my wife answered.
说明已经那样说了,所以用needn't have.
类似的shouldn't have none 不应该做什么(实际上已经做了)
例:
You needn't have come so early.
你不必这么早就来了.(已经来了)
You shouldn't have been late for the meeting.
你那次会议不应该迟到(实际上已经迟到了)