scrutinee constant folding produces wrong answer when remapped values are out of bounds

This program should output 2, but in 8.1 with -O enabled it outputs 3. The problem is with the way that scrutinee constant folding rewrites the case.

f :: Word -> Word
f n = case n+1 of
       0 -> 2
       _ -> 3
{-# NOINLINE f #-}
main = print (f (-1))

Core with 8.1 and -O:

f [InlPrag=NOINLINE] :: Word -> Word
[GblId, Arity=1, Caf=NoCafRefs, Str=<S(S),1*U(1*U)>m]
f =
  \ (n_ay2 :: Word) ->
    case n_ay2 of { GHC.Types.W# x#_a1SL ->
    case x#_a1SL of {
      __DEFAULT -> lvl_r4lD;
      -1## -> lvl1_r4mD
    }
    }

Apparently -1## isn't okay: it needs to be 9223372036854775807##.

Trac metadata

Trac field	Value
Version	8.1
Type	Bug
TypeOfFailure	OtherFailure
Priority	highest
Resolution	Unresolved
Component	Compiler
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