X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FFloatOut.lhs;h=fba88e77dc38ab73a775d2365b0d8f9bb59bb9fa;hp=290c62313a6ec9b81ada63a84c269a2b4a176296;hb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516;hpb=d95ce839533391e7118257537044f01cbb1d6694 diff --git a/compiler/simplCore/FloatOut.lhs b/compiler/simplCore/FloatOut.lhs index 290c623..fba88e7 100644 --- a/compiler/simplCore/FloatOut.lhs +++ b/compiler/simplCore/FloatOut.lhs @@ -10,16 +10,21 @@ module FloatOut ( floatOutwards ) where import CoreSyn 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 SetLevels ( Level(..), LevelledExpr, LevelledBind, - setLevels, ltMajLvl, ltLvl, isTopLvl ) + setLevels, isTopLvl ) import UniqSupply ( UniqSupply ) -import List ( partition ) +import Bag +import Util +import Maybes +import UniqFM import Outputable import FastString \end{code} @@ -96,10 +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} %************************************************************************ %* * @@ -135,8 +136,7 @@ floatOutwards float_sws dflags us pgm floatTopBind :: LevelledBind -> (FloatStats, [CoreBind]) floatTopBind bind = case (floatBind bind) of { (fs, floats) -> - (fs, floatsToBinds floats) - } + (fs, bagToList (flattenFloats floats)) } \end{code} %************************************************************************ @@ -145,52 +145,56 @@ floatTopBind bind %* * %************************************************************************ - \begin{code} floatBind :: LevelledBind -> (FloatStats, FloatBinds) - -floatBind (NonRec (TB name level) rhs) +floatBind (NonRec (TB var level) rhs) = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> - (fs, rhs_floats ++ [(level, NonRec name rhs')]) } -floatBind bind@(Rec pairs) - = case (unzip3 (map do_pair pairs)) of { (fss, rhss_floats, new_pairs) -> - let rhs_floats = concat rhss_floats in + -- 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'')) } - if not (isTopLvl bind_dest_lvl) then +floatBind (Rec pairs) + = case floatList do_pair pairs of { (fs, rhs_floats, new_pairs) -> + -- NB: the rhs floats may contain references to the + -- bound things. For example + -- f = ...(let v = ...f... in b) ... + if not (isTopLvl 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' ++ [(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 - -- bound things. For example - -- f = ...(let v = ...f... in b) ... - -- might get floated to + -- find that out. In our example we make a Rec thus: -- v = ...f... -- f = ... b ... - -- and hence we must (pessimistically) make all the floats recursive - -- with the top binding. Later dependency analysis will unravel it. - -- - -- 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, [(bind_dest_lvl, Rec (new_pairs ++ floatsToBindPairs rhs_floats))]) - } + case (partitionByMajorLevel dest_lvl rhs_floats) of { (floats', heres) -> + (fs, floats' `plusFloats` unitFloat dest_lvl + (Rec (floatsToBindPairs heres new_pairs))) } + else + -- For top level, no need to partition; just make them all recursive + -- (And the partition wouldn't work because they'd all end up in floats') + (fs, unitFloat dest_lvl + (Rec (floatsToBindPairs (flattenFloats rhs_floats) new_pairs))) } where - bind_dest_lvl = getBindLevel bind + (((TB _ dest_lvl), _) : _) = pairs do_pair (TB name level, rhs) = case (floatRhs level rhs) of { (fs, rhs_floats, rhs') -> - (fs, rhs_floats, (name, rhs')) - } + (fs, rhs_floats, (name, rhs')) } + +--------------- +floatList :: (a -> (FloatStats, FloatBinds, b)) -> [a] -> (FloatStats, FloatBinds, [b]) +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 `plusFloats` binds_as, b:bs) }} \end{code} + %************************************************************************ \subsection[FloatOut-Expr]{Floating in expressions} @@ -211,47 +215,20 @@ floatCaseAlt lvl arg -- Used rec rhss, and case-alternative rhss -- the rec or case alternative (fsa, floats', install heres arg') }} +----------------- 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') -> - if exprIsCheap arg' then - (fsa, floats, arg') - else - case (partitionByMajorLevel lvl floats) of { (floats', heres) -> - (fsa, floats', install heres arg') }} + = floatExpr lvl arg --- 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, [], Var v) -floatExpr _ (Type ty) = (zeroStats, [], Type ty) -floatExpr _ (Lit lit) = (zeroStats, [], Lit lit) +----------------- +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 (floatRhs lvl a) of { (fsa, floats_a, a') -> - (fse `add_stats` fsa, floats_e ++ floats_a, App e' a') }} + (fse `add_stats` fsa, floats_e `plusFloats` floats_a, App e' a') }} floatExpr _ lam@(Lam _ _) = let @@ -265,7 +242,7 @@ floatExpr _ lam@(Lam _ _) -- going to escape a value lambda. -- In particular, for one-shot lambdas we don't float things -- out; we get no saving by so doing. - partition_fn | all isTyVar bndrs = partitionByLevel + partition_fn | all isTyCoVar bndrs = partitionByLevel | otherwise = partitionByMajorLevel in case (floatExpr (last lvls) body) of { (fs, floats, body') -> @@ -282,20 +259,9 @@ 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 note expr) -- Other than SCCs = case (floatExpr lvl expr) of { (fs, floating_defns, expr') -> @@ -306,23 +272,24 @@ floatExpr lvl (Cast expr co) (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 - -- I.e. floatExpr for rhs, floatCaseAlt for 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 ++ body_floats, Let (NonRec bndr rhs') body') }} + (fs, rhs_floats `plusFloats` body_floats, Let (NonRec bndr rhs') body') }} floatExpr lvl (Let bind body) = case (floatBind bind) of { (fsb, bind_floats) -> case (floatExpr lvl body) of { (fse, body_floats, body') -> - (add_stats fsb fse, - bind_floats ++ body_floats, - body') }} + case partitionByMajorLevel lvl (bind_floats `plusFloats` body_floats) + of { (floats, heres) -> + -- See Note [Avoiding unnecessary floating] + (add_stats fsb fse, floats, install heres body') } } } 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 floatCaseAlt for the alternatives, so that we @@ -330,15 +297,43 @@ floatExpr lvl (Case scrut (TB case_bndr case_lvl) ty alts) float_alt (con, bs, 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 _ [] = (zeroStats, [], []) -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) }} \end{code} +Note [Avoiding unnecessary floating] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +In general we want to avoid floating a let unnecessarily, because +it might worsen strictness: + let + x = ...(let y = e in y+y).... +Here y is demanded. If we float it outside the lazy 'x=..' then +we'd have to zap its demand info, and it may never be restored. + +So at a 'let' we leave the binding right where the are unless +the binding will escape a value lambda. That's what the +partitionByMajorLevel does in the floatExpr (Let ...) case. + +Notice, though, that we must take care to drop any bindings +from the body of the let that depend on the staying-put bindings. + +We used instead to do the partitionByMajorLevel on the RHS of an '=', +in floatRhs. But that was quite tiresome. We needed to 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. +And even all that turned out to be very fragile, and broke +altogether when profiling got in the way. + +So now we do the partition right at the (Let..) itself. + %************************************************************************ %* * \subsection{Utility bits for floating stats} @@ -367,13 +362,9 @@ 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 :: FloatStats -> [(Level, Bind CoreBndr)] -> FloatStats -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} @@ -383,57 +374,114 @@ add_to_stats (FlS a b c) floats %* * %************************************************************************ -\begin{code} -getBindLevel :: Bind (TaggedBndr Level) -> Level -getBindLevel (NonRec (TB _ lvl) _) = lvl -getBindLevel (Rec (((TB _ lvl), _) : _)) = lvl -getBindLevel (Rec []) = panic "getBindLevel Rec []" -\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, _) = 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))) + +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 -install :: FloatBinds -> CoreExpr -> CoreExpr +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 + (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 - install_group (_, defns) body = Let defns body + 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}