It has been suggested in some quarters that had have, followed by a past participle, is a regionalism that has no place in standard English grammar.
If I had have known you were coming, I would have been prepared, or If I'd have known you were coming, I would have been prepared, mean essentially the same as If I had known you were coming….. But the former is often used for emphasis, and it sounds perfectly idiomatic to me.
So is had have seen etc. grammatically correct?
Best Answer
The had have construction in an if-clause is an example of what is commonly called the double perfect. This extract from grammar.about.com cites The Cambridge Grammar of the English Language's discussion of the usage, which it calls non-standard:
There's an extended discussion of the issue in Counterfactuality in non-standard subjunctive conditionals. The authors claim that there is a semantic difference between the standard and non-standard forms. Here is their opening section which offers references to possible explanations for the 'extra piece of morphology'.