[GHC] #8655: Evaluate know-to-terminate-soon thunks

[GHC]

#8655: Evaluate know-to-terminate-soon thunks
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       Reporter:  nomeata           |             Owner:  nomeata
           Type:  task              |            Status:  new
       Priority:  normal            |         Milestone:
      Component:  Compiler          |           Version:  7.6.3
       Keywords:                    |  Operating System:  Unknown/Multiple
   Architecture:  Unknown/Multiple  |   Type of failure:  None/Unknown
     Difficulty:  Unknown           |         Test Case:
     Blocked By:                    |          Blocking:
Related Tickets:                    |
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 I guess I’ll better put my interior monologue in a ticket than on ghc-
 dev...

 In order to implement nested CPR (#1600), I had to enrich the CPR type to
 keep track of whether something, when entered, will converge for sure. My
 code does not solve the halting problem, but does only simple stuff, so if
 something is known to converge, is is very likely to be cheap.

 Simon suggested to measure the effect of evaluating a let-bound thunk with
 the known-to-terminate property, as if the body was using it strictly.
 This tickets tracks this suggestion, and reports progress.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8655>
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