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

[GHC]

#9565: T3500b exhaust simplifier ticks (loops?) on WAY=optasm
-------------------------------------+-------------------------------------
       Reporter:  slyfox             |                   Owner:
           Type:  bug                |                  Status:  new
       Priority:  normal             |               Milestone:
      Component:  Compiler           |                 Version:  7.9
       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:
-------------------------------------+-------------------------------------
 {{{
 $ make fulltest TEST="T3500b" WAY=optasm

 =====> T3500b(optasm) 3767 of 4101 [0, 0, 0]
 cd ./typecheck/should_run && '/home/slyfox/dev/git/ghc-
 validate/inplace/bin/ghc-stage2' -fforce-recomp -dcore-lint -dcmm-lint
 -dno-debug-output -no-user-package-db -rtsopts -fno-ghci-history -o T3500b
 T3500b.hs -O -fasm   >T3500b.comp.stderr 2>&1
 Compile failed (status 256) errors were:
 [1 of 1] Compiling Main             ( T3500b.hs, T3500b.o )
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 7.9.20140907 for x86_64-unknown-linux):
         Simplifier ticks exhausted
     When trying RuleFired foldr/augment
     To increase the limit, use -fsimpl-tick-factor=N (default 100)
     If you need to do this, let GHC HQ know, and what factor you needed
     To see detailed counts use -ddump-simpl-stats
     Total ticks: 12441

 Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
 }}}

 Attempt to increase '''-fsimpl-tick-factor''' does not help copiling
 sample.
 Looks like infinite inlining pass.

 The test source itself:
 {{{#!hs
 {-# 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

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

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

 main = print (showMu item)
 }}}

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