#14079: Failure to do CPR in the presence of a local letrec -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): When `e` is small we don't to w/w; insteead we inline the function bodily at all call sites. If you make it bigger, thus {{{ {-# NOINLINE dummy #-} dummy x = x e :: (Int, Int) -> Int -> Int -> (Int, Int) e x y n = je x y where je !x y | y > 0 = x | otherwise = je x (dummy y + dummy n) }}} then `e` is big enough, and full w/w happens. Actually it looks fine to me. All the right things are happening. So is ther a bug here at all? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14079#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14079: Failure to do CPR in the presence of a local letrec -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): I don't get this. I tried {{{ {-# LANGUAGE BangPatterns #-} module T14079 where e1 :: (Int, Int) -> Int -> (Int, Int) e1 !x y | y > 0 = x | otherwise = e1 x (y + 1) e2 :: (Int, Int) -> Int -> Int -> (Int, Int) e2 x y n = je x y where je !x y | y > 0 = x | otherwise = je x (y + n) }}} As you say I get a w/w split for `e1`. So if `e1` is called applied to two arguments I'll inline the wrapper and good things will happen. For for `e1` I get something good too {{{ e2 :: (Int, Int) -> Int -> Int -> (Int, Int) [GblId, Arity=3, Caf=NoCafRefs, Str=m, Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=3,unsat_ok=True,boring_ok=False) Tmpl= \ (x_a1VH [Occ=Once] :: (Int, Int)) (y_a1VI [Occ=Once] :: Int) (n_a1VJ [Occ=OnceL!] :: Int) -> joinrec { je_s2nz [Occ=LoopBreakerT[2]] :: (Int, Int) -> Int -> (Int, Int) [LclId[JoinId(2)], Arity=2, Unf=OtherCon []] je_s2nz (x1_a1VL [Occ=Once!] :: (Int, Int)) (y1_a1VM [Occ=Once!] :: Int) = case x1_a1VL of x2_X1VS { (_ [Occ=Dead], _ [Occ=Dead]) -> case y1_a1VM of { GHC.Types.I# x3_a2mT -> case GHC.Prim.># x3_a2mT 0# of { __DEFAULT -> jump je_s2nz x2_X1VS (case n_a1VJ of { GHC.Types.I# y2_a2nf [Occ=Once] -> GHC.Types.I# (GHC.Prim.+# x3_a2mT y2_a2nf) }); 1# -> x2_X1VS } } }; } in jump je_s2nz x_a1VH y_a1VI}] e2 = \ (x_a1VH :: (Int, Int)) (y_a1VI :: Int) (n_a1VJ :: Int) -> case x_a1VH of { (ww1_s2ox, ww2_s2oy) -> case y_a1VI of { GHC.Types.I# ww4_s2oC -> joinrec { $wje_s2oE [InlPrag=[0], Occ=LoopBreaker] :: Int -> Int -> GHC.Prim.Int# -> (Int, Int) [LclId[JoinId(3)], Arity=3, Str=m, Unf=OtherCon []] $wje_s2oE (ww5_X2oV :: Int) (ww6_X2oX :: Int) (ww7_X2p2 :: GHC.Prim.Int#) = case GHC.Prim.># ww7_X2p2 0# of { __DEFAULT -> case n_a1VJ of { GHC.Types.I# y1_a2nf -> jump $wje_s2oE ww5_X2oV ww6_X2oX (GHC.Prim.+# ww7_X2p2 y1_a2nf) }; 1# -> (ww5_X2oV, ww6_X2oX) }; } in jump $wje_s2oE ww1_s2ox ww2_s2oy ww4_s2oC } } }}} `e2`'s strictness signature says that it has the CPR property. It doesn't have a w/w split, but it'll be inlined wherever it is used. Just to check, I tried this {{{ f1 x y = e1 x (y+1) f2 x y n = e2 x (y+t) n where t = length (reverse (reverse (reverse (reverse (reverse (reverse [1..n])))))) }}} The definition `t` is just make `f2` big enough so that the strictness analyser will do a w/w split for it. Sure enough, good things happen {{{ T14079.$wf2 [InlPrag=[0]] :: Int -> Int -> GHC.Prim.Int# -> GHC.Prim.Int# -> (# Int, Int #) [GblId, Arity=4, Caf=NoCafRefs, Str=, Unf=Unf{Src=<vanilla>, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=IF_ARGS [0 0 0 0] 289 0}] T14079.$wf2 = \ (ww_s30e :: Int) (ww1_s30f :: Int) (ww2_s30j :: GHC.Prim.Int#) (ww3_s30n :: GHC.Prim.Int#) -> case GHC.List.$wlenAcc @ Int (GHC.List.reverse1 @ Int (GHC.List.reverse1 @ Int (GHC.List.reverse1 @ Int (GHC.List.reverse1 @ Int (GHC.List.reverse1 @ Int (GHC.List.reverse1 @ Int (GHC.Enum.eftInt 1# ww3_s30n) (GHC.Types.[] @ Int)) (GHC.Types.[] @ Int)) (GHC.Types.[] @ Int)) (GHC.Types.[] @ Int)) (GHC.Types.[] @ Int)) (GHC.Types.[] @ Int)) 0# of ww4_a2Yy { __DEFAULT -> joinrec { $wje_s308 [InlPrag=[0], Occ=LoopBreaker] :: Int -> Int -> GHC.Prim.Int# -> (# Int, Int #) [LclId[JoinId(3)], Arity=3, Str=, Unf=OtherCon []] $wje_s308 (ww5_s301 :: Int) (ww6_s302 :: Int) (ww7_s306 :: GHC.Prim.Int#) = case GHC.Prim.># ww7_s306 0# of { __DEFAULT -> jump $wje_s308 ww5_s301 ww6_s302 (GHC.Prim.+# ww7_s306 ww3_s30n); 1# -> (# ww5_s301, ww6_s302 #) }; } in jump $wje_s308 ww_s30e ww1_s30f (GHC.Prim.+# ww2_s30j ww4_a2Yy) } -- RHS size: {terms: 22, types: 23, coercions: 0, joins: 0/0} f2 [InlPrag=INLINE[0]] :: (Int, Int) -> Int -> Int -> (Int, Int) [GblId, Arity=3, Caf=NoCafRefs, Str=m, Unf=Unf{Src=InlineStable, TopLvl=True, Value=True, ConLike=True, WorkFree=True, Expandable=True, Guidance=ALWAYS_IF(arity=3,unsat_ok=True,boring_ok=False) Tmpl= \ (w_s309 [Occ=Once!] :: (Int, Int)) (w1_s30a [Occ=Once!] :: Int) (w2_s30b [Occ=Once!] :: Int) -> case w_s309 of { (ww1_s30e [Occ=Once], ww2_s30f [Occ=Once]) -> case w1_s30a of { GHC.Types.I# ww4_s30j [Occ=Once] -> case w2_s30b of { GHC.Types.I# ww6_s30n [Occ=Once] -> case T14079.$wf2 ww1_s30e ww2_s30f ww4_s30j ww6_s30n of { (# ww8_s30I [Occ=Once], ww9_s30J [Occ=Once] #) -> (ww8_s30I, ww9_s30J) } } } }}] f2 = \ (w_s309 :: (Int, Int)) (w1_s30a :: Int) (w2_s30b :: Int) -> case w_s309 of { (ww1_s30e, ww2_s30f) -> case w1_s30a of { GHC.Types.I# ww4_s30j -> case w2_s30b of { GHC.Types.I# ww6_s30n -> case T14079.$wf2 ww1_s30e ww2_s30f ww4_s30j ww6_s30n of { (# ww8_s30I, ww9_s30J #) -> (ww8_s30I, ww9_s30J) } } } } }}} This all looks fine to me. Are you sure there is a problem here? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14079#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#14079: Failure to do CPR in the presence of a local letrec -------------------------------------+------------------------------------- Reporter: nomeata | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: invalid | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by nomeata): * status: new => closed * resolution: => invalid -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14079#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler