[GHC] #10657: Regression T2497 WAY=optasm: Simplifier ticks exhausted

[GHC]

#10657: Regression T2497 WAY=optasm: Simplifier ticks exhausted
-------------------------------------+-------------------------------------
              Reporter:  thomie      |             Owner:
                  Type:  bug         |            Status:  new
              Priority:  high        |         Milestone:  7.12.1
             Component:  Compiler    |           Version:  7.11
              Keywords:              |  Operating System:  Unknown/Multiple
          Architecture:              |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
             Test Case:              |        Blocked By:
  typecheck/should_compile/T2497     |
              Blocking:              |   Related Tickets:
Differential Revisions:              |
-------------------------------------+-------------------------------------
 {{{
 $ make TEST=T2497 WAY=optasm EXTRA_HC_OPTS=-fsimpl-tick-factor=10000
 TEST_HC=ghc-7.11.20150711
 ...
 T2497.hs:18:1: warning: Defined but not used: ‘beq’
 ghc: panic! (the 'impossible' happened)
   (GHC version 7.11.20150711 for x86_64-unknown-linux):
         Simplifier ticks exhausted
   When trying RuleFired rule 1
   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: 40000
 ...
 }}}

 The test is very small:
 {{{
 module ShouldCompile() where

 eq :: Eq a => a -> a -> Bool
 eq = (==)

 {-# RULES
     "rule 1" forall x y. x == y = y `eq` x
   #-}
 }}}


 The problem does not occur with ghc-7.10.1. Curiously the problem goes
 away when I change the module header to `module ShouldCompile where`.

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10657>
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