id,summary,reporter,owner,description,type,status,priority,milestone,version,resolution,keywords,cc
47,Fusion broken with ghc7-rc2,choener,,"Hi,

maybe it is too late but GHCi, version 7.0.0.20101028 (ghc7 rc2) seems to badly break fusion.

Consider this program:
{{{
module Main where

import qualified Data.Vector.Unboxed as VU



mk :: Int -> VU.Vector Int
mk k = {-# CORE ""VUmk"" #-} VU.enumFromN 1 k
{-# INLINE mk #-}

join1 :: Int -> VU.Vector Int
join1 k = {-# CORE ""VUjoin"" #-} VU.zipWith (\k l -> k+l) (VU.map (\k -> k+1) $ mk k) (VU.map (\k -> k*5) $ mk k)
{-# INLINE join1 #-}

join2 :: Int -> VU.Vector Int
join2 k = {-# CORE ""VUjoin2"" #-} VU.map (\k -> k+1) $ mk k
{-# INLINE join2 #-}

main = do
  print $ {-# CORE ""VUsum1"" #-} VU.sum $ join1 20
  print $ {-# CORE ""VUsum2"" #-} VU.sum $ join2 20
  print $ {-# CORE ""VUsum3"" #-} VU.sum $ VU.map (\k -> k+1) $ VU.enumFromN (1 :: Int) 20
}}}

where I wanted to see if 'join1' produces good code -- if yes then I could split some calculations up more easily.

What ghc 6.12.3 produces is this:
{{{
main_$s$wfoldlM'_loop1 =
  \ (sc_s1Oe :: Int#)
    (sc1_s1Of :: Int#)
    (sc2_s1Og :: Int#) ->
    case ># sc_s1Oe 0 of _ {
      False -> sc2_s1Og;
      True ->
        main_$s$wfoldlM'_loop1
          (-# sc_s1Oe 1)
          (+# sc1_s1Of 1)
          (+# sc2_s1Og (+# sc1_s1Of 1))
    }

main3 :: String
GblId

main3 =
  case __core_note ""VUsum2""
       (case main_$s$wfoldlM'_loop1 20 1 0 of ww_s1MG { __DEFAULT ->
        I# ww_s1MG
        })
  of _ { I# ww_a1Iu ->
  $wshowSignedInt 0 ww_a1Iu ([] @ Char)
  }
}}}

So far, so good. Now comes rc2:

{{{
main3 =
  case __core_note ""VUsum2""
       (case (__core_note ""VUmk""
              (runSTRep
                 @ (Data.Vector.Unboxed.Base.Vector Int) main4))
             `cast` (trans
                       Data.Vector.Unboxed.Base.TFCo:R:VectorInt
                       Data.Vector.Unboxed.Base.NTCo:R:VectorInt
                     :: Data.Vector.Unboxed.Base.Vector Int
                          ~
                        Data.Vector.Primitive.Vector Int)
        of _ { Data.Vector.Primitive.Vector ipv_s2oo ipv1_s2op ipv2_s2oq ->
        letrec {
          $s$wfoldlM'_loop_s2Bw [Occ=LoopBreaker]
            :: Int# -> Int# -> Int#

          $s$wfoldlM'_loop_s2Bw =
            \ (sc_s2yG :: Int#) (sc1_s2yH :: Int#) ->
              case >=# sc_s2yG ipv1_s2op of _ {
                False ->
                  $s$wfoldlM'_loop_s2Bw
                    (+# sc_s2yG 1)
                    (+#
                       sc1_s2yH
                       (+#
                          (indexIntArray# ipv2_s2oq (+# ipv_s2oo sc_s2yG))
                          1));
                True -> sc1_s2yH
              }; } in
        case $s$wfoldlM'_loop_s2Bw 0 0 of ww_s2vB { __DEFAULT ->
        I# ww_s2vB
        }
        })
  of _ { I# ww_a2r6 ->
  $wshowSignedInt 0 ww_a2r6 ([] @ Char)
  }
}}}

This seems rather bad ;-)

I'd like to hear that it's my fault and I should better learn how to use ghc.",defect,closed,blocker,,0.7,invalid,ghc7-rc2,