[GHC] #11731: Simplifier: Inlining trivial let can lose sharing

[GHC]

#11731: Simplifier: Inlining trivial let can lose sharing
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        Reporter:  nomeata           |                Owner:
            Type:  bug               |               Status:  patch
        Priority:  normal            |            Milestone:
       Component:  Compiler          |              Version:  8.1
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):  Phab:D2073
       Wiki Page:                    |
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Comment (by simonpj):

 > One clear implementation would have been to adjust the calls to
 `setIdDemandInfo` in `DmdAnal`, but that would go wrong because of the
 Cunning Plan with fixed-point iteration, where later iterations use the
 existing annotations.

 Well imagine that the demand analyser simply NEVER attributed single-use
 to anything; e.g. `mkOnceUsedDmd` returned `Use Many ...`.  Then we'd get
 no useful use-once info from the analyser so we wouldn't need to erase it.

 Not sure if it's worth it.  There are other occurrence of the string `Use
 One` in `Demand`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11731#comment:36>
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