[GHC] #15648: Core Lint error with source-level unboxed equality

[GHC]

#15648: Core Lint error with source-level unboxed equality
-------------------------------------+-------------------------------------
        Reporter:  RyanGlScott       |                Owner:  (none)
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.4.3
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:  #15209            |  Differential Rev(s):
       Wiki Page:                    |
-------------------------------------+-------------------------------------

Comment (by RyanGlScott):

 More shenanigans: if you put this at the end of `Bug.hs`:

 {{{#!hs
 main :: IO ()
 main = case ueqSym @Bool @Bool of
          _ -> mkLegit `seq` print ()
 }}}

 Then you'll get an outright panic when you compile it:

 {{{
 $ /opt/ghc/8.6.1/bin/ghc -O2 -fforce-recomp Bug.hs
 [1 of 2] Compiling Foo              ( Foo.hs, Foo.o )
 [2 of 2] Compiling Bug              ( Bug.hs, Bug.o )
 ghc: panic! (the 'impossible' happened)
   (GHC version 8.6.0.20180907 for x86_64-unknown-linux):
         StgCmmEnv: variable not found
   x_a5Pc
   local binds for:
   main
   $tc'Jank
   $trModule
   $tc'Jank2
   $tc'Jank1
   $tc'Jank3
   $tc'Legit
   $tc'Legit2
   $tc'Legit1
   $tc'Legit3
   $tcJankyEquality
   $tcJankyEquality1
   $tcJankyEquality2
   $tcLegitEquality
   $tcLegitEquality1
   $tcLegitEquality2
   $trModule3
   $trModule1
   $trModule2
   $trModule4
   main1
   $WLegit
   $krep_r6Fh
   $krep1_r6Fi
   $krep2_r6Fj
   $krep3_r6Fk
   $krep4_r6Fl
   $krep5_r6Fm
   $krep6_r6Fn
   $krep7_r6Fo
   $krep8_r6Fp
   $krep9_r6Fq
   Call stack:
       CallStack (from HasCallStack):
         callStackDoc, called at compiler/utils/Outputable.hs:1160:37 in
 ghc:Outputable
         pprPanic, called at compiler/codeGen/StgCmmEnv.hs:149:9 in
 ghc:StgCmmEnv
 }}}

-- 
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15648#comment:2>
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