[Haskell-cafe] GHC Optimization seriously hurting performance by unsharing.
ky3 at atamo.com
Wed Apr 9 05:11:41 UTC 2014
On Tue, Apr 8, 2014 at 12:55 PM, Michael Karcher <
mkarcher at mkarcher.dialup.fu-berlin.de> wrote:
> > let bigset = fromAscList testdata
> finally query the membership of the number 5 several times. This happens
> to be reasonably fast if compiled without optimization, but goes down to
> dog slow if compiled with optimization, as the set building process is
> hoisted into the loop and thus performed 10 times.
> > replicateM_ 10 . print . member 5 $ bigset
Isn't this 'hoisting into the loop' a case of over-aggressive inlining, a
known pitfall of -O2 ?
What happens with plain -O, which is the recommended general-purpose
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