X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FFloatOut.lhs;h=ba74afce7669865002b689f1843cb820b0377a91;hb=0a5613f40b0e32cf59966e6b56b807cdbe80aa7b;hp=988bd53015d53474cc51ccb94b8ddf35e5657b55;hpb=0065d5ab628975892cea1ec7303f968c3338cbe1;p=ghc-hetmet.git diff --git a/compiler/simplCore/FloatOut.lhs b/compiler/simplCore/FloatOut.lhs index 988bd53..ba74afc 100644 --- a/compiler/simplCore/FloatOut.lhs +++ b/compiler/simplCore/FloatOut.lhs @@ -8,23 +8,25 @@ \begin{code} module FloatOut ( floatOutwards ) where -#include "HsVersions.h" - import CoreSyn -import CoreUtils ( mkSCC, exprIsHNF, exprIsTrivial ) +import CoreUtils +import CoreArity ( etaExpand ) +import CoreMonad ( FloatOutSwitches(..) ) -import DynFlags ( DynFlags, DynFlag(..), FloatOutSwitches(..) ) +import DynFlags ( DynFlags, DynFlag(..) ) import ErrUtils ( dumpIfSet_dyn ) import CostCentre ( dupifyCC, CostCentre ) -import Id ( Id, idType ) +import Id ( Id, idType, idArity, isBottomingId ) import Type ( isUnLiftedType ) -import CoreLint ( showPass, endPass ) import SetLevels ( Level(..), LevelledExpr, LevelledBind, - setLevels, ltMajLvl, ltLvl, isTopLvl ) + setLevels, isTopLvl, tOP_LEVEL ) import UniqSupply ( UniqSupply ) -import List ( partition ) +import Bag +import Util +import Maybes +import UniqFM import Outputable -import Util ( notNull ) +import FastString \end{code} ----------------- @@ -99,10 +101,6 @@ vwhich might usefully be separated to @ Well, maybe. We don't do this at the moment. -\begin{code} -type FloatBind = (Level, CoreBind) -- INVARIANT: a FloatBind is always lifted -type FloatBinds = [FloatBind] -\end{code} %************************************************************************ %* * @@ -118,8 +116,6 @@ floatOutwards :: FloatOutSwitches floatOutwards float_sws dflags us pgm = do { - showPass dflags float_msg ; - let { annotated_w_levels = setLevels float_sws pgm us ; (fss, binds_s') = unzip (map floatTopBind annotated_w_levels) } ; @@ -130,29 +126,18 @@ floatOutwards float_sws dflags us pgm let { (tlets, ntlets, lams) = get_stats (sum_stats fss) }; dumpIfSet_dyn dflags Opt_D_dump_simpl_stats "FloatOut stats:" - (hcat [ int tlets, ptext SLIT(" Lets floated to top level; "), - int ntlets, ptext SLIT(" Lets floated elsewhere; from "), - int lams, ptext SLIT(" Lambda groups")]); + (hcat [ int tlets, ptext (sLit " Lets floated to top level; "), + int ntlets, ptext (sLit " Lets floated elsewhere; from "), + int lams, ptext (sLit " Lambda groups")]); - endPass dflags float_msg Opt_D_verbose_core2core (concat binds_s') - {- no specific flag for dumping float-out -} - } - where - float_msg = showSDoc (text "Float out" <+> parens (sws float_sws)) - sws (FloatOutSw lam const) = pp_not lam <+> text "lambdas" <> comma <+> - pp_not const <+> text "constants" - pp_not True = empty - pp_not False = text "not" - -floatTopBind bind@(NonRec _ _) - = case (floatBind bind) of { (fs, floats, bind') -> - (fs, floatsToBinds floats ++ [bind']) + return (concat binds_s') } -floatTopBind bind@(Rec _) - = case (floatBind bind) of { (fs, floats, Rec pairs') -> - WARN( notNull floats, ppr bind $$ ppr floats ) - (fs, [Rec (floatsToBindPairs floats ++ pairs')]) } +floatTopBind :: LevelledBind -> (FloatStats, [CoreBind]) +floatTopBind bind + = case (floatBind bind) of { (fs, floats) -> + (fs, bagToList (flattenFloats floats)) + } \end{code} %************************************************************************ @@ -161,23 +146,34 @@ floatTopBind bind@(Rec _) %* * %************************************************************************ - \begin{code} -floatBind :: LevelledBind - -> (FloatStats, FloatBinds, CoreBind) +floatBind :: LevelledBind -> (FloatStats, FloatBinds) + +floatBind (NonRec (TB var level) rhs) + = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> -floatBind (NonRec (TB name level) rhs) - = case (floatNonRecRhs level rhs) of { (fs, rhs_floats, rhs') -> - (fs, rhs_floats, NonRec name rhs') } + -- A tiresome hack: + -- see Note [Bottoming floats: eta expansion] in SetLevels + let rhs'' | isBottomingId var = etaExpand (idArity var) rhs' + | otherwise = rhs' + + in (fs, rhs_floats `plusFloats` unitFloat level (NonRec var rhs'')) } floatBind bind@(Rec pairs) = case (unzip3 (map do_pair pairs)) of { (fss, rhss_floats, new_pairs) -> - - if not (isTopLvl bind_dest_level) then - -- Standard case; the floated bindings can't mention the - -- binders, because they couldn't be escaping a major level - -- if so. - (sum_stats fss, concat rhss_floats, Rec new_pairs) + let rhs_floats = foldr1 plusFloats rhss_floats in + + if not (isTopLvl bind_dest_lvl) then + -- Find which bindings float out at least one lambda beyond this one + -- These ones can't mention the binders, because they couldn't + -- be escaping a major level if so. + -- The ones that are not going further can join the letrec; + -- they may not be mutually recursive but the occurrence analyser will + -- find that out. + case (partitionByMajorLevel bind_dest_lvl rhs_floats) of { (floats', heres) -> + (sum_stats fss, + floats' `plusFloats` unitFloat bind_dest_lvl + (Rec (floatsToBindPairs heres new_pairs))) } else -- In a recursive binding, *destined for* the top level -- (only), the rhs floats may contain references to the @@ -192,11 +188,11 @@ floatBind bind@(Rec pairs) -- This can only happen for bindings destined for the top level, -- because only then will partitionByMajorLevel allow through a binding -- that only differs in its minor level - (sum_stats fss, [], - Rec (new_pairs ++ floatsToBindPairs (concat rhss_floats))) + (sum_stats fss, unitFloat tOP_LEVEL + (Rec (floatsToBindPairs (flattenFloats rhs_floats) new_pairs))) } where - bind_dest_level = getBindLevel bind + bind_dest_lvl = getBindLevel bind do_pair (TB name level, rhs) = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> @@ -211,12 +207,12 @@ floatBind bind@(Rec pairs) %************************************************************************ \begin{code} -floatExpr, floatRhs, floatNonRecRhs +floatExpr, floatRhs, floatCaseAlt :: Level -> LevelledExpr -> (FloatStats, FloatBinds, CoreExpr) -floatRhs lvl arg -- Used rec rhss, and case-alternative rhss +floatCaseAlt lvl arg -- Used rec rhss, and case-alternative rhss = case (floatExpr lvl arg) of { (fsa, floats, arg') -> case (partitionByMajorLevel lvl floats) of { (floats', heres) -> -- Dump bindings that aren't going to escape from a lambda; @@ -224,45 +220,53 @@ floatRhs lvl arg -- Used rec rhss, and case-alternative rhss -- the rec or case alternative (fsa, floats', install heres arg') }} -floatNonRecRhs lvl arg -- Used for nested non-rec rhss, and fn args +floatRhs lvl arg -- Used for nested non-rec rhss, and fn args + -- See Note [Floating out of RHS] = case (floatExpr lvl arg) of { (fsa, floats, arg') -> - -- Dump bindings that aren't going to escape from a lambda - -- This isn't a scoping issue (the binder isn't in scope in the RHS of a non-rec binding) - -- Rather, it is to avoid floating the x binding out of - -- f (let x = e in b) - -- unnecessarily. But we first test for values or trival rhss, - -- because (in particular) we don't want to insert new bindings between - -- the "=" and the "\". E.g. - -- f = \x -> let in - -- We do not want - -- f = let in \x -> - -- (a) The simplifier will immediately float it further out, so we may - -- as well do so right now; in general, keeping rhss as manifest - -- values is good - -- (b) If a float-in pass follows immediately, it might add yet more - -- bindings just after the '='. And some of them might (correctly) - -- be strict even though the 'let f' is lazy, because f, being a value, - -- gets its demand-info zapped by the simplifier. - if exprIsHNF arg' || exprIsTrivial arg' then + if exprIsCheap arg' then (fsa, floats, arg') else case (partitionByMajorLevel lvl floats) of { (floats', heres) -> (fsa, floats', install heres arg') }} -floatExpr _ (Var v) = (zeroStats, [], Var v) -floatExpr _ (Type ty) = (zeroStats, [], Type ty) -floatExpr _ (Lit lit) = (zeroStats, [], Lit lit) +-- Note [Floating out of RHSs] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- Dump bindings that aren't going to escape from a lambda +-- This isn't a scoping issue (the binder isn't in scope in the RHS +-- of a non-rec binding) +-- Rather, it is to avoid floating the x binding out of +-- f (let x = e in b) +-- unnecessarily. But we first test for values or trival rhss, +-- because (in particular) we don't want to insert new bindings between +-- the "=" and the "\". E.g. +-- f = \x -> let in +-- We do not want +-- f = let in \x -> +-- (a) The simplifier will immediately float it further out, so we may +-- as well do so right now; in general, keeping rhss as manifest +-- values is good +-- (b) If a float-in pass follows immediately, it might add yet more +-- bindings just after the '='. And some of them might (correctly) +-- be strict even though the 'let f' is lazy, because f, being a value, +-- gets its demand-info zapped by the simplifier. +-- +-- We use exprIsCheap because that is also what's used by the simplifier +-- to decide whether to float a let out of a let + +floatExpr _ (Var v) = (zeroStats, emptyFloats, Var v) +floatExpr _ (Type ty) = (zeroStats, emptyFloats, Type ty) +floatExpr _ (Lit lit) = (zeroStats, emptyFloats, Lit lit) floatExpr lvl (App e a) = case (floatExpr lvl e) of { (fse, floats_e, e') -> - case (floatNonRecRhs lvl a) of { (fsa, floats_a, a') -> - (fse `add_stats` fsa, floats_e ++ floats_a, App e' a') }} + case (floatRhs lvl a) of { (fsa, floats_a, a') -> + (fse `add_stats` fsa, floats_e `plusFloats` floats_a, App e' a') }} -floatExpr lvl lam@(Lam _ _) +floatExpr _ lam@(Lam _ _) = let (bndrs_w_lvls, body) = collectBinders lam bndrs = [b | TB b _ <- bndrs_w_lvls] - lvls = [l | TB b l <- bndrs_w_lvls] + lvls = [l | TB _ l <- bndrs_w_lvls] -- For the all-tyvar case we are prepared to pull -- the lets out, to implement the float-out-of-big-lambda @@ -287,67 +291,55 @@ floatExpr lvl (Note note@(SCC cc) expr) -- Annotate bindings floated outwards past an scc expression -- with the cc. We mark that cc as "duplicated", though. - annotated_defns = annotate (dupifyCC cc) floating_defns + annotated_defns = wrapCostCentre (dupifyCC cc) floating_defns in (fs, annotated_defns, Note note expr') } - where - annotate :: CostCentre -> FloatBinds -> FloatBinds - - annotate dupd_cc defn_groups - = [ (level, ann_bind floater) | (level, floater) <- defn_groups ] - where - ann_bind (NonRec binder rhs) - = NonRec binder (mkSCC dupd_cc rhs) - - ann_bind (Rec pairs) - = Rec [(binder, mkSCC dupd_cc rhs) | (binder, rhs) <- pairs] - -floatExpr lvl (Note InlineMe expr) -- Other than SCCs - = case floatExpr InlineCtxt expr of { (fs, floating_defns, expr') -> - -- There can be some floating_defns, arising from - -- ordinary lets that were there all the time. It seems - -- more efficient to test once here than to avoid putting - -- them into floating_defns (which would mean testing for - -- inlineCtxt at every let) - (fs, [], Note InlineMe (install floating_defns expr')) } -- See notes in SetLevels floatExpr lvl (Note note expr) -- Other than SCCs = case (floatExpr lvl expr) of { (fs, floating_defns, expr') -> (fs, floating_defns, Note note expr') } +floatExpr lvl (Cast expr co) + = case (floatExpr lvl expr) of { (fs, floating_defns, expr') -> + (fs, floating_defns, Cast expr' co) } + floatExpr lvl (Let (NonRec (TB bndr bndr_lvl) rhs) body) - | isUnLiftedType (idType bndr) -- Treat unlifted lets just like a case - = case floatExpr lvl rhs of { (fs, rhs_floats, rhs') -> - case floatRhs bndr_lvl body of { (fs, body_floats, body') -> - (fs, rhs_floats ++ body_floats, Let (NonRec bndr rhs') body') }} + | isUnLiftedType (idType bndr) -- Treat unlifted lets just like a case + -- I.e. floatExpr for rhs, floatCaseAlt for body + = case floatExpr lvl rhs of { (_, rhs_floats, rhs') -> + case floatCaseAlt bndr_lvl body of { (fs, body_floats, body') -> + (fs, rhs_floats `plusFloats` body_floats, Let (NonRec bndr rhs') body') }} floatExpr lvl (Let bind body) - = case (floatBind bind) of { (fsb, rhs_floats, bind') -> + = case (floatBind bind) of { (fsb, bind_floats) -> case (floatExpr lvl body) of { (fse, body_floats, body') -> (add_stats fsb fse, - rhs_floats ++ [(bind_lvl, bind')] ++ body_floats, + bind_floats `plusFloats` body_floats, body') }} - where - bind_lvl = getBindLevel bind floatExpr lvl (Case scrut (TB case_bndr case_lvl) ty alts) = case floatExpr lvl scrut of { (fse, fde, scrut') -> case floatList float_alt alts of { (fsa, fda, alts') -> - (add_stats fse fsa, fda ++ fde, Case scrut' case_bndr ty alts') + (add_stats fse fsa, fda `plusFloats` fde, Case scrut' case_bndr ty alts') }} where - -- Use floatRhs for the alternatives, so that we + -- Use floatCaseAlt for the alternatives, so that we -- don't gratuitiously float bindings out of the RHSs float_alt (con, bs, rhs) - = case (floatRhs case_lvl rhs) of { (fs, rhs_floats, rhs') -> + = case (floatCaseAlt case_lvl rhs) of { (fs, rhs_floats, rhs') -> (fs, rhs_floats, (con, [b | TB b _ <- bs], rhs')) } floatList :: (a -> (FloatStats, FloatBinds, b)) -> [a] -> (FloatStats, FloatBinds, [b]) -floatList f [] = (zeroStats, [], []) +floatList _ [] = (zeroStats, emptyFloats, []) floatList f (a:as) = case f a of { (fs_a, binds_a, b) -> case floatList f as of { (fs_as, binds_as, bs) -> - (fs_a `add_stats` fs_as, binds_a ++ binds_as, b:bs) }} + (fs_a `add_stats` fs_as, binds_a `plusFloats` binds_as, b:bs) }} + +getBindLevel :: Bind (TaggedBndr Level) -> Level +getBindLevel (NonRec (TB _ lvl) _) = lvl +getBindLevel (Rec (((TB _ lvl), _) : _)) = lvl +getBindLevel (Rec []) = panic "getBindLevel Rec []" \end{code} %************************************************************************ @@ -365,21 +357,22 @@ data FloatStats Int -- Number of non-top-floats * lambda groups they've been past Int -- Number of lambda (groups) seen +get_stats :: FloatStats -> (Int, Int, Int) get_stats (FlS a b c) = (a, b, c) +zeroStats :: FloatStats zeroStats = FlS 0 0 0 +sum_stats :: [FloatStats] -> FloatStats sum_stats xs = foldr add_stats zeroStats xs +add_stats :: FloatStats -> FloatStats -> FloatStats add_stats (FlS a1 b1 c1) (FlS a2 b2 c2) = FlS (a1 + a2) (b1 + b2) (c1 + c2) -add_to_stats (FlS a b c) floats - = FlS (a + length top_floats) (b + length other_floats) (c + 1) - where - (top_floats, other_floats) = partition to_very_top floats - - to_very_top (my_lvl, _) = isTopLvl my_lvl +add_to_stats :: FloatStats -> FloatBinds -> FloatStats +add_to_stats (FlS a b c) (FB tops others) + = FlS (a + lengthBag tops) (b + lengthBag (flattenMajor others)) (c + 1) \end{code} @@ -389,55 +382,115 @@ add_to_stats (FlS a b c) floats %* * %************************************************************************ -\begin{code} -getBindLevel (NonRec (TB _ lvl) _) = lvl -getBindLevel (Rec (((TB _ lvl), _) : _)) = lvl -\end{code} +Note [Representation of FloatBinds] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The FloatBinds types is somewhat important. We can get very large numbers +of floating bindings, often all destined for the top level. A typical example +is x = [4,2,5,2,5, .... ] +Then we get lots of small expressions like (fromInteger 4), which all get +lifted to top level. + +The trouble is that + (a) we partition these floating bindings *at every binding site* + (b) SetLevels introduces a new bindings site for every float +So we had better not look at each binding at each binding site! + +That is why MajorEnv is represented as a finite map. + +We keep the bindings destined for the *top* level separate, because +we float them out even if they don't escape a *value* lambda; see +partitionByMajorLevel. + \begin{code} -partitionByMajorLevel, partitionByLevel - :: Level -- Partitioning level +type FloatBind = CoreBind -- INVARIANT: a FloatBind is always lifted - -> FloatBinds -- Defns to be divided into 2 piles... +data FloatBinds = FB !(Bag FloatBind) -- Destined for top level + !MajorEnv -- Levels other than top + -- See Note [Representation of FloatBinds] - -> (FloatBinds, -- Defns with level strictly < partition level, - FloatBinds) -- The rest +type MajorEnv = UniqFM MinorEnv -- Keyed by major level +type MinorEnv = UniqFM (Bag FloatBind) -- Keyed by minor level +flattenFloats :: FloatBinds -> Bag FloatBind +flattenFloats (FB tops others) = tops `unionBags` flattenMajor others -partitionByMajorLevel ctxt_lvl defns - = partition float_further defns - where - -- Float it if we escape a value lambda, or if we get to the top level - float_further (my_lvl, bind) = my_lvl `ltMajLvl` ctxt_lvl || isTopLvl my_lvl - -- The isTopLvl part says that if we can get to the top level, say "yes" anyway - -- This means that - -- x = f e - -- transforms to - -- lvl = e - -- x = f lvl - -- which is as it should be - -partitionByLevel ctxt_lvl defns - = partition float_further defns - where - float_further (my_lvl, _) = my_lvl `ltLvl` ctxt_lvl -\end{code} +flattenMajor :: MajorEnv -> Bag FloatBind +flattenMajor = foldUFM (unionBags . flattenMinor) emptyBag -\begin{code} -floatsToBinds :: FloatBinds -> [CoreBind] -floatsToBinds floats = map snd floats +flattenMinor :: MinorEnv -> Bag FloatBind +flattenMinor = foldUFM unionBags emptyBag -floatsToBindPairs :: FloatBinds -> [(Id,CoreExpr)] +emptyFloats :: FloatBinds +emptyFloats = FB emptyBag emptyUFM -floatsToBindPairs floats = concat (map mk_pairs floats) - where - mk_pairs (_, Rec pairs) = pairs - mk_pairs (_, NonRec binder rhs) = [(binder,rhs)] +unitFloat :: Level -> FloatBind -> FloatBinds +unitFloat lvl@(Level major minor) b + | isTopLvl lvl = FB (unitBag b) emptyUFM + | otherwise = FB emptyBag (unitUFM major (unitUFM minor (unitBag b))) -install :: FloatBinds -> CoreExpr -> CoreExpr +plusFloats :: FloatBinds -> FloatBinds -> FloatBinds +plusFloats (FB t1 b1) (FB t2 b2) = FB (t1 `unionBags` t2) (b1 `plusMajor` b2) +plusMajor :: MajorEnv -> MajorEnv -> MajorEnv +plusMajor = plusUFM_C plusMinor + +plusMinor :: MinorEnv -> MinorEnv -> MinorEnv +plusMinor = plusUFM_C unionBags + +floatsToBindPairs :: Bag FloatBind -> [(Id,CoreExpr)] -> [(Id,CoreExpr)] +floatsToBindPairs floats binds = foldrBag add binds floats + where + add (Rec pairs) binds = pairs ++ binds + add (NonRec binder rhs) binds = (binder,rhs) : binds + +install :: Bag FloatBind -> CoreExpr -> CoreExpr install defn_groups expr - = foldr install_group expr defn_groups + = foldrBag install_group expr defn_groups + where + install_group defns body = Let defns body + +partitionByMajorLevel, partitionByLevel + :: Level -- Partitioning level + -> FloatBinds -- Defns to be divided into 2 piles... + -> (FloatBinds, -- Defns with level strictly < partition level, + Bag FloatBind) -- The rest + +-- ---- partitionByMajorLevel ---- +-- Float it if we escape a value lambda, *or* if we get to the top level +-- If we can get to the top level, say "yes" anyway. This means that +-- x = f e +-- transforms to +-- lvl = e +-- x = f lvl +-- which is as it should be + +partitionByMajorLevel (Level major _) (FB tops defns) + = (FB tops outer, heres `unionBags` flattenMajor inner) where - install_group (_, defns) body = Let defns body + (outer, mb_heres, inner) = splitUFM defns major + heres = case mb_heres of + Nothing -> emptyBag + Just h -> flattenMinor h + +partitionByLevel (Level major minor) (FB tops defns) + = (FB tops (outer_maj `plusMajor` unitUFM major outer_min), + here_min `unionBags` flattenMinor inner_min + `unionBags` flattenMajor inner_maj) + + where + (outer_maj, mb_here_maj, inner_maj) = splitUFM defns major + (outer_min, mb_here_min, inner_min) = case mb_here_maj of + Nothing -> (emptyUFM, Nothing, emptyUFM) + Just min_defns -> splitUFM min_defns minor + here_min = mb_here_min `orElse` emptyBag + +wrapCostCentre :: CostCentre -> FloatBinds -> FloatBinds +wrapCostCentre cc (FB tops defns) + = FB (wrap_defns tops) (mapUFM (mapUFM wrap_defns) defns) + where + wrap_defns = mapBag wrap_one + wrap_one (NonRec binder rhs) = NonRec binder (mkSCC cc rhs) + wrap_one (Rec pairs) = Rec (mapSnd (mkSCC cc) pairs) \end{code} +