lemming: > > On Fri, 23 May 2008, Henning Thielemann wrote: > > >An even more advanced tool could show differences between two Core > >listings. Say I have a program which runs too slow. But if I change a > >small detail it runs significantly faster - I want to know, how did my > >change in the Haskell file modified the Core and why the speedup. > >Showing differences between Core files will certainly be complicated > >because the generated identifiers are completely different. I don't know > >whether the order of declarations is a problem. > > > >I have an example here where a program becomes faster by a factor of 10 > >with a rather small change. First I thought the slow thing must be the > >higher order function which occurs in the Core and is not inlined, but it > >is present in the slow and the fast variant of the program. > > In this special example, actually simple 'diff' spotted the critical > difference, namely a polymorphic function was called. Now I'm in a > dilemma: I can either INLINE the function, then it's whole body is copied > into main program, which is not necessary here. However this solution > would guarantee speed in every case. Or I can SPECIALISE the function, > then the function will only be called, but with polymorphism overhead > eliminated. This would only work for a restricted range of types. I'd like > to have a pragma, that tells GHC to specialise a function for every type > it is called with. >
I usually go with inlining, and get GHC as a whole program optimising compiler. -- Don _______________________________________________ Cvs-ghc mailing list Cvs-ghc@haskell.org http://www.haskell.org/mailman/listinfo/cvs-ghc
