[Haskell-cafe] Re: speed: ghc vs gcc
dons at galois.com
Fri Feb 20 16:43:46 EST 2009
> > 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?
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