[Haskell-cafe] Code runs 7x FASTER with profiling

Brandon Allbery allbery.b at gmail.com
Fri Dec 8 23:59:01 UTC 2017

On Fri, Dec 8, 2017 at 9:18 AM, Neil Mayhew <
neil_mayhew at users.sourceforge.net> wrote:

> Good point. Having great optimization isn’t a justification for complete
> mental laziness on the part of the programmer! However, I did find the
> behaviour in this case surprising and unintuitive, given ghc’s usual
> ability to optimize things, and having it change on me when I enabled
> profiling left me wondering where to go next. The code I presented here is
> considerably simplified from the original program, and represents a lot of
> work already expended trying to get to the root of the problem.
This is actually why I (and likely SPJ) am inclined to consider it a bug;
while it might be arguable as Sven does, the counterintuitive effect when
you turn on profiling suggests that it's not intended or expected.
(Although maybe it should be; the intuition is "profiling disables
optimization" but what it really does is a bit more subtle than that overly
simplistic notion.)

brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net
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