id	summary	reporter	owner	description	type	status	priority	milestone	component	version	resolution	keywords	cc	os	architecture	failure	difficulty	testcase	blockedby	blocking	related
6087	Join points need strictness analysis	simonpj		"I came across this code in the `nofib/spectral` progam `knights`, in the code for `KnightHeuristic.possibleMoves`:
{{{
let {
  $j_sU3
    :: GHC.Types.Int -> GHC.Types.Int -> [KnightHeuristic.Direction]
  [LclId, Arity=2]
  $j_sU3 =
    \ (ww2_sRl :: GHC.Types.Int) (ww3_sRm :: GHC.Types.Int) ->
      case ww2_sRl of ww4_XQY { GHC.Types.I# ww5_sQU ->
      case GHC.Prim.>=# ww5_sQU 1 of _ {
        GHC.Types.False -> go1_azF ys_azM;
        GHC.Types.True ->
          case ds1_azR of _ { GHC.Types.I# y1_azp ->
          case GHC.Prim.<=# ww5_sQU y1_azp of _ {
            GHC.Types.False -> go1_azF ys_azM;
            GHC.Types.True ->
              case ww3_sRm of wild6_XAB { GHC.Types.I# x_XAE ->
              case GHC.Prim.>=# x_XAE 1 of _ {
                GHC.Types.False -> go1_azF ys_azM;
                GHC.Types.True ->
                  case GHC.Prim.<=# x_XAE y1_azp of _ {
                    GHC.Types.False -> go1_azF ys_azM;
                    GHC.Types.True ->
                      case GHC.List.notElem
                             @ ChessSetList.Tile
                             ChessSetList.isSquareFree_$dEq
                             (ww4_XQY, wild6_XAB)
                             wild2_azW
                      of _ {
                        GHC.Types.False -> go1_azF ys_azM;
                        GHC.Types.True ->
                          GHC.Types.:
                            @ KnightHeuristic.Direction y_azL (go1_azF ys_azM)
                      }
                  }
              }
              }
          }
          }
      }
      } } in
case y_azL of _ {
  KnightHeuristic.UL ->
    $j_sU3
      (case ww_sQJ of _ { GHC.Types.I# x_aya ->
       GHC.Types.I# (GHC.Prim.-# x_aya 1)
       })
      (case ww1_sQK of _ { GHC.Types.I# x_aya ->
       GHC.Types.I# (GHC.Prim.-# x_aya 2)
       });
  KnightHeuristic.UR ->
    $j_sU3
      (case ww_sQJ of _ { GHC.Types.I# x_ayl ->
       GHC.Types.I# (GHC.Prim.+# x_ayl 1)
       })
      (case ww1_sQK of _ { GHC.Types.I# x_aya ->
       GHC.Types.I# (GHC.Prim.-# x_aya 2)
       });

...lots more similar case alternatives follow...
}}}
Just look at all those `Int`s getting boxed, and the immediately unboxed by the join point!  The strictness analyser would spot this easily, but presumably the join point is constructed after strictness analysis.

There must be an opportunity here to run a later strictness analysis pass."	bug	new	normal	7.6.2	Compiler	7.4.1			stefan@…	Unknown/Multiple	Unknown/Multiple	Runtime performance bug	Unknown