[GHC] #9740: D380 caused fft2 regressions

[GHC]

#9740: D380 caused fft2 regressions
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       Reporter:  dfeuer             |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:  7.10.1
      Component:  Compiler           |                 Version:  7.8.3
       Keywords:                     |        Operating System:
   Architecture:  Unknown/Multiple   |  Unknown/Multiple
     Difficulty:  Easy (less than 1  |         Type of failure:  Runtime
  hour)                              |  performance bug
     Blocked By:                     |               Test Case:
Related Tickets:                     |                Blocking:
                                     |  Differential Revisions:  Phab:D390
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 When I got rid of the hand-unboxing in GHC.List, I missed the fact that a
 `take` helper function took an unboxed value and was therefore strict.
 When I changed that to a regular function, I didn't make it strict, and
 this caused a regression in fft2 and (I believe) also a test suite perf
 test. The function is properly strictified in D390.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9740>
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