#5075: CPR optimisation for sum types if only one constructor is used ---------------------------------+------------------------------------------ Reporter: batterseapower | Owner: simonpj Type: feature request | Status: patch Priority: normal | Milestone: 7.6.2 Component: Compiler | Version: 7.0.3 Keywords: | Os: Unknown/Multiple Architecture: Unknown/Multiple | Failure: None/Unknown Difficulty: Unknown | Testcase: Blockedby: | Blocking: Related: | ---------------------------------+------------------------------------------ Comment(by nfrisby): Confirmed: the Just gets ww'd-away with this core2core pipeline: SpecConstr, simpl, stranal, wwsplit, simpl. {{{ Rec { $w$s$wloop $w$s$wloop = \ w_sqX w1_sqY -> case w_sqX of ds_Xng { __DEFAULT -> $w$s$wloop (-# ds_Xng 1) (case w1_sqY of _ { I# x_anM -> I# (+# x_anM 1) }); 0 -> (# w1_sqY #) } end Rec } loop_$s$wloop [InlPrag=INLINE[0]] :: ... [... Str=DmdType <S,U><L,U(U)>m2, Unf=Unf{Src=Worker=$w$s$wloop,...}] loop_$s$wloop = \ w_sqX w1_sqY -> case $w$s$wloop w_sqX w1_sqY of _ { (# ww1_sr4 #) -> Just ww1_sr4 } Rec { loop_$s$wloop1 loop_$s$wloop1 = \ sc_sqe -> case sc_sqe of ds_Xng { __DEFAULT -> loop_$s$wloop1 (-# ds_Xng 1); 0 -> Nothing } end Rec } }}} That's an impressive prefix, "$w$s$w". In case any reader is wondering, the second argument to the loop gets unboxed if a strict variant of Maybe is used. Thanks again for the compact example. -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5075#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler