GHC bug

A frog told me about this

(a ... b) xs
  | a == x
  , (l, _:r) <- break (== x) xs
  = l ++ [x]

baldur@Loki:~$ ghci -fobject-code -fdefer-typed-holes -ignore-dot-ghci /tmp/tnVL.hs
GHCi, version 8.0.1: http://www.haskell.org/ghc/  :? for help
[1 of 1] Compiling Main             ( /tmp/tnVL.hs, /tmp/tnVL.o )

/tmp/tnVL.hs:2:10: warning: [-Wtyped-holes]
    Variable not in scope: x

/tmp/tnVL.hs:3:27: warning: [-Wtyped-holes]
    Variable not in scope: x

/tmp/tnVL.hs:4:11: warning: [-Wtyped-holes]
    Variable not in scope: x
ghc: panic! (the 'impossible' happened)
  (GHC version 8.0.1 for x86_64-unknown-linux):
        StgCmmEnv: variable not found
  $dEq_a26w
  local binds for:
  $trModule
  $trModule1_r29y
  $trModule2_r2a9
  x_r2aa
  x1_r2ab
  x2_r2ac
  a2_s2ah
  b_s2ai
  xs_s2aj
  fail_s2ak

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

> 

I managed to find a more minimal example

u a | a == x = undefined

doesn't trigger error in GHCi.

Trac metadata

Trac field	Value
Version	8.0.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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