Strange compilation behavior

Daniel Fischer at
Sun Dec 9 18:43:57 EST 2007

Am Montag, 10. Dezember 2007 00:29 schrieb Chad Scherrer:
> Hello,
> I'm using ghc 6.6.1 under Ubuntu Gutsy on a Pentium 4 machine, and I
> was working to get some code running in an acceptable time. I was
> surprised to find that turning on profiling switches made the code run
> over 40x faster!
> Here's the first run, using ghc --make -O2:
> 88.03user 0.08system 1:28.16elapsed 99%CPU (0avgtext+0avgdata
> 0maxresident)k 0inputs+0outputs (0major+13517minor)pagefaults 0swaps
> And with ghc --make -O2 -prof -auto-all:
> 2.33user 0.07system 0:02.41elapsed 99%CPU (0avgtext+0avgdata 0maxresident)k
> 0inputs+0outputs (0major+17712minor)pagefaults 0swaps
> Otherwise everything is the same! Is this something anyone else has
> run into? I'm not sure if it might have been fixed in 6.8.1, but
> something funny is going on here.
> Thanks,
> Chad

Might be ticket #1934, though -O2 -prof -auto-all resulted in an incorrect 
programme for me, which ran in 0.00s. Try also ghc --make -O -prof -auto-all 
and ghc --make -O2 -prof -auto
For me, both these combinations produced correct programmes which took 
reasonable time. If it's the same for you, it probably is the same bug, which 
did not show with 6.8.1.


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