[GHC] #9565: T3500b exhaust simplifier ticks (loops?) on WAY=optasm

[GHC]

#9565: T3500b exhaust simplifier ticks (loops?) on WAY=optasm
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              Reporter:  slyfox      |            Owner:
                  Type:  bug         |           Status:  new
              Priority:  normal      |        Milestone:
             Component:  Compiler    |          Version:  7.9
            Resolution:              |         Keywords:
      Operating System:              |     Architecture:  x86_64 (amd64)
  Unknown/Multiple                   |       Difficulty:  Unknown
       Type of failure:  Compile-    |       Blocked By:
  time crash                         |  Related Tickets:
             Test Case:  T3500b      |
              Blocking:              |
Differential Revisions:              |
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Comment (by carter):

 could this be an instance of the known issue about recursive types
 interacting with the inliner?
 https://www.haskell.org/ghc/docs/7.8.3/html/users_guide/bugs.html see the
 second item there


 if i change the program to
 {{{

 {-# LANGUAGE TypeFamilies, FlexibleContexts, UndecidableInstances #-}

 module Main where

 newtype Mu f = Mu (f (Mu f))

 type family Id m
 type instance Id m = m

 instance Show (Id (f (Mu f))) => Show (Mu f) where
     show (Mu f) = show f
     {-# NOINLINE show #-}

 showMu :: Mu (Either ()) -> String
 showMu = show

 item :: Mu (Either ())
 item = Mu (Right (Mu (Left ())))

 main = print (showMu item)
 }}}

 that is, I mark the show instance NOINLINE, the problem goes away.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9565#comment:1>
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