It gets 2 arguments in the "zipWith" rule but its arity was higher and the new
inliner didn't inline it sometimes, for instance here:

mpp ::  [Double] -> [Double] -> [Double] -> [Double] -> [Double]
mpp as bs cs ds = zipWith (*) (zipWith (+) as bs) (zipWith (+) cs ds)
 
This was a regression vs. 6.10.