[GHC] #15907: memo001 causes compile time panic with fails with -O -dannot-lint

[GHC]

#15907: memo001 causes compile time panic with fails with -O -dannot-lint
-------------------------------------+-------------------------------------
           Reporter:  osa1           |             Owner:  (none)
               Type:  bug            |            Status:  new
           Priority:  normal         |         Milestone:  8.6.3
          Component:  Compiler       |           Version:  8.7
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  None/Unknown
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
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 {{{
 $ cd libraries/base/tests; ghc-stage2 memo001.hs -O -dannot-lint
 [1 of 2] Compiling Memo1            ( Memo1.lhs, Memo1.o ) [Optimisation
 flags changed]
 ghc-stage2: panic! (the 'impossible' happened)
   (GHC version 8.7.20181116 for x86_64-unknown-linux):
         idInfo
   val_a3pf
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/basicTypes/Var.hs:567:34 in ghc:Var

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

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15907>
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