[GHC] #13227: Loss of full laziness in mapFB

[GHC]

#13227: Loss of full laziness in mapFB
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        Reporter:  simonpj           |                Owner:  nomeata
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.0.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by nomeata):

 Looks like a clear win. According to perf.haskell.org (which does run
 nofib!), the only significant changes are time improvements of 3.5% for
 cacheprof and k-nucleotide:
 https://perf.haskell.org/ghc/#revision/4c5af213a9fff60ca8de2ed9f5ae28955d21beb6
 These might be spurious, as allocations do not change. But even if really
 nothing changes, as this is a simplifying commit, from this point of view
 there is no reason not do it. And I’d be happy to get rid of this rather
 squishy notion of “probably” one-shot.

 I will prepare a DR for review.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13227#comment:7>
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