[GHC] #12370: Implement LetUp in DmdAnal (or document why we do not do it)

[GHC]

#12370: Implement LetUp in DmdAnal (or document why we do not do it)
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        Reporter:  nomeata           |                Owner:
            Type:  task              |               Status:  new
        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):
       Wiki Page:                    |
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Comment (by nomeata):

 > I will separately measure if this increases the number of thunks
 determined to be one-shot. But even if it did, it does not matter much, as
 shown by nofib.

 Again, only insignificant changes, not worth mentioning. The number of
 thunks in total goes up by 0.06%, precision of the analysis is now 24.9%
 instead of 24.8%.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12370#comment:5>
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