Superfluous seq no eliminated

Program:

foo :: Int -> Int
foo 0 = 0
foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)

GHC generates this code:

T.$wfoo =
  \ (ww_slm :: GHC.Prim.Int#) ->
    case ww_slm of ds_XkE {
      __DEFAULT ->
        case case GHC.Prim.<# ds_XkE 5 of _ {
               GHC.Bool.False -> lvl1_rlG; GHC.Bool.True -> lvl_rlE
             }
        of _ { __DEFAULT ->
        T.$wfoo (GHC.Prim.-# ds_XkE 1)
        };
      0 -> 0
    }

Note that the seq is still there although it is a nop. This actually occurs in stream fusion code.

Trac metadata

Trac field	Value
Version	6.13
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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