I know that the subjunctive uses past tense, but does that mean there's no way to distinguish the following sentences?
I would say hello, if he were home.
I would have said hello, if he were home.
The first means that the speaker is willing to say hello, if the person is home. The second one means the speaker had the opportunity to say hello previously, but the person wasn't home.
The distinction may not seem significant, but the two sentences mean something entirely different.