[Haskell-cafe] ghc has problems with 'zipWith' ?

Is it possible and senseful for a compiler to extract common sub-expressions? Naively I think that for a given tree of an expression it is efficiently possible to find all common sub-trees. Referential transparency would assure that equal expressions have the same value, so they can be replaced by the same object. E.g. the example above could be automatically transformed to:

ms as = let tmp0 = zipWith (+) (zipWith (*) as tmp1) (0:tmp1) tmp1 = 1:tmp0 in tmp0

It's possible and will preserve semantics, but isn't always an optimization. http://www.haskell.org/pipermail/haskell-cafe/2003-December/005574.html