[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
      Resolution:                    |         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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Comment (by nomeata):

 The first attempt was a bit naive; doing proper detection of surely
 converging expressions is a bit more involved. Some notes at the
 [wiki:NestedCPR#Convergesdetection] wiki page. Unfortunately it makes
 stuff that was safe before (such as removing variables from the
 environment of a strictness signature) not safe any more, so I expect it
 to take more work until the code is actually correct – currently, simple
 tests work, but `ghc-stage2` diverges while eating up memory very fast.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8655#comment:7>
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