Optimization beyond the Module Border

[Don Stewart]

bbr:
> Simon Peyton-Jones wrote:
> 
> > GHC does a lot of cross-module inlining already, and *does* write stuff into interface files, provided you use -O.
> 
> I used -O4. Is that the bad thing?

There's nothing about -O2 

However, I think that's ok -- it clamps -ON | N>2 to -O2


> > I'm always interested in performance differences of a factor of 15 though!  Can you supply an example (as small as poss) for us to look at?
> 
> Yes certainly, although small will be a big problem, I guess.
> I admit that the factor 15 is a bit dubious since the fast run-time was
> so small (1.88 sec vs. 0.112 sec).
> 
> I will see what I can do on the morrow.

I'd be interested in any progress here -- we noticed issues with
optimisations in the stream fusion package across module boundaries
that we never tracked down. If there's some key things not firing,
that would be good to know.