cross module optimization issues

[pepe]

On 28/11/2008, at 15:46, Simon Peyton-Jones wrote:

> The $f2 comes from the instance Monad (IterateeGM ...).
> print_lines uses a specialised version of that instance, namely
>        Monad (IterateeGM el IO)
> The fact that print_lines uses it makes GHC generate a specialised  
> version of the instance decl.
>
> Even in the absence of print_lines you can generate the specialised  
> instance thus
>
> instance Monad m => Monad (IterateeGM el m) where
>    {-# SPECIALISE instance Monad (IterateeGM el IO) #-}
>        ... methods...
>
> does that help?


Once Simon and Neil dig the issue and analyze it, the reason seems  
evident.
But this thread reminds of why writing high performance Haskell code  
is regarded as a black art outside the community (well, and sometimes  
inside too).

Wouldn't a JIT version of GHC be a great thing to have?
Or would a backend for LLVM be already beneficial enough?


Cheers
pepe