[GHC] #8173: GHC uses nub

[GHC]

#8173: GHC uses nub
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        Reporter:  nh2               |            Owner:  leroux
            Type:  bug               |           Status:  closed
        Priority:  normal            |        Milestone:
       Component:  Compiler          |          Version:  7.6.3
      Resolution:  wontfix           |         Keywords:
Operating System:  Unknown/Multiple  |     Architecture:  Unknown/Multiple
 Type of failure:  Compile-time      |       Difficulty:  Moderate (less
  performance bug                    |  than a day)
       Test Case:                    |       Blocked By:
        Blocking:                    |  Related Tickets:
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Comment (by simonpj):

 Don't give up so easily :-)

 Did you look at the amount of heap the compiler ''allocated''?  It's
 easily discoverable (eg use `+RTS -s`, and it's in the nofib logs too,
 though I don't think `nofib-analyse` looks for it.  (You could fix `nofib-
 analyse` so that it does.)

 The point is that reducing allocation is almost always good; and it is a
 FAR more repeatable number than runtime, for which it is hard to measure
 small differences.  My bet is that `ordNub` will be a tiny win in most
 cases.

 The other thing is that while using `ordNub` may not benefit typical
 programs, it may have a dramatic effect on some weird program which
 happens to produce very long lists for `nub` to digest.  Provided using
 `ordNub` doesn't slow things down for typical programs (use allocation
 numbers to check) I'm all for using it so that the edge cases don't fall
 off a cliff.

 Simon

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8173#comment:13>
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