[GHC] #8457: -ffull-laziness does more harm than good

[GHC]

#8457: -ffull-laziness does more harm than good
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        Reporter:  errge             |            Owner:
            Type:  bug               |           Status:  new
        Priority:  high              |        Milestone:  7.8.1
       Component:  Compiler          |          Version:  7.7
      Resolution:                    |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  None/Unknown      |       Difficulty:  Unknown
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by errge):

 Hi Simon,

 Thanks for pointing me towards this 'Nestedly Organized Future Improving
 Benchmarks', they seem to be great. :)

 I followed http://ghc.haskell.org/trac/ghc/wiki/Building/RunningNoFib and
 the results are here:
 https://github.com/errge/notlazy/blob/master/nofib.txt

 There are some outliers in both directions, but the overall picture seems
 to me as kind of "nothing changing".  Even more if you deduce the noise
 introduced by the outliers.

 It may be meaningful to have a look on fulsom, hidden, parser and parstof;
 these are the examples where the optimization did very good and it would
 be interesting to see whether it's easy to reintroduce the necessary
 sharing by hand.  OTOH, I'm not really in the mood to debug thousand of
 lines of old school haskell written in '93 by academics. :-)  If we get
 really bored, maybe will take a look...

 And there are some outliers on the negative side: constraints, bspt and
 integer.  It'd be interesting to see here if the optimization introduced
 sharing or other performance bugs can is easy to workaround or not in
 these cases.

 My opinion about turning this off didn't change, but I can always just
 turn off myself, so feel free to either fix this or mark the bug as
 invalid.

 If there are more benchmarks to run, I'm happy to run them.

 Gergely

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8457#comment:5>
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