[Haskell-cafe] Re: speed: ghc vs gcc

[Don Stewart]

dons:
> bulat.ziganshin:
> > Hello Achim,
> > 
> > Friday, February 20, 2009, 11:44:49 PM, you wrote:
> > 
> > >> > Turning this into a ticket with associated test will:
> > >> 
> > >> but why you think that this is untypical and needs a ticket? ;)
> > >> 
> > > Bulat, you are right in every aspect. You never did anything wrong.
> > 
> > Achim, this is simplest code one can imagine. so when Simon will go to
> > check ghc optimizations, he will try it without any reports. but
> > Simon, unlike Don, never said that ghc may be compared to gcc. Don, on
> > the other hand, say this everyday. when he is asked for code that
> > shows this, he declined to answer. so - why YOU think that ghc
> > generates fast code and this example is something unusual? can you
> > provide any *technical* arguments or will continue to make personal
> > attacks together with Don?
> 
> Bulat, you misunderstand, it is not personal! We just want something to
> work on. Something specific.
> 
> For example, you've identified loop unrolling as something that could
> very profitably be improved in GHC, and Claus even wrote a prototype to
> see what kind of speedups to guess. 
> 
> This is a great contribution!  Now we know where to hunt.

And just to summarise what we have seen:

    ghc -O2 naive left fold                    15.680
    gcc -O0                                     4.500
    ghc manual recursion -fasm                  1.328
    ghc manual recursion                        1.035
    ghc naive left fold "stream fusion"         0.967
    gcc -O1                                     0.892
    ghc "-funroll-loops" -D8                    0.623
    gcc -O3 -funroll-loops                      0.318
    ghc "-funroll-loops" -D64                   0.088

So what did we learn here?

-- Don