Zwicky and Pullum (1983: 507) state that "n't cannot be attached to words containing simple clitics ['s/'ve], although the simple clitic 've can do so." As such, they don't think (1) is acceptable:
(1) *I'dn't be doing this unless I had to.
but
(2) I'd've smoked more dope when I was young [my example]
However, to my native ears (1) doesn't sound so unacceptable. How would one go about determining its acceptability objectively? Corpora, perhaps?
