[GHC] #8766: length [Integer] is twice as slow but length [Int] is 10 times faster

[GHC]

#8766: length [Integer] is twice as slow but length [Int] is 10 times faster
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        Reporter:  George                   |            Owner:
            Type:  bug                      |           Status:  new
        Priority:  normal                   |        Milestone:
       Component:  Compiler                 |          Version:  7.8.1-rc1
      Resolution:                           |         Keywords:
Operating System:  Unknown/Multiple         |     Architecture:
 Type of failure:  Runtime performance bug  |  Unknown/Multiple
       Test Case:                           |       Difficulty:  Unknown
        Blocking:                           |       Blocked By:
                                            |  Related Tickets:
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Comment (by nomeata):

 Ok, with this change (i.e. a special `eftIntegerFB`) I get good results:
 Run time decreases from 16.3s in 7.6.3 to 11.7s in GHC HEAD. But if I use
 `-fno-call-arity` (Call arity analysis is not in 7.8), I still get 23s,
 which is still a regression over 16s, but better than the 30 I got with
 the unmodified library code.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8766#comment:7>
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