X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FFloatIn.lhs;h=b9f44c95c12854e9c54f1be1d5d71b62daf639c0;hp=e32a8ea1601c41c1977467f9f7739f774f90b4b4;hb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516;hpb=8100cd4395e46ae747be4298c181a4730d6206bc diff --git a/compiler/simplCore/FloatIn.lhs b/compiler/simplCore/FloatIn.lhs index e32a8ea..b9f44c9 100644 --- a/compiler/simplCore/FloatIn.lhs +++ b/compiler/simplCore/FloatIn.lhs @@ -16,16 +16,15 @@ module FloatIn ( floatInwards ) where #include "HsVersions.h" -import DynFlags ( DynFlags, DynFlag(..) ) import CoreSyn import CoreUtils ( exprIsHNF, exprIsDupable ) -import CoreLint ( showPass, endPass ) -import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf ) -import Id ( isOneShotBndr ) -import Var ( Id, idType ) +import CoreFVs ( CoreExprWithFVs, freeVars, freeVarsOf, idRuleAndUnfoldingVars ) +import Id ( isOneShotBndr, idType ) +import Var import Type ( isUnLiftedType ) import VarSet import Util ( zipEqual, zipWithEqual, count ) +import UniqFM import Outputable \end{code} @@ -33,16 +32,8 @@ Top-level interface function, @floatInwards@. Note that we do not actually float any bindings downwards from the top-level. \begin{code} -floatInwards :: DynFlags -> [CoreBind] -> IO [CoreBind] - -floatInwards dflags binds - = do { - showPass dflags "Float inwards"; - let { binds' = map fi_top_bind binds }; - endPass dflags "Float inwards" Opt_D_verbose_core2core binds' - {- no specific flag for dumping float-in -} - } - +floatInwards :: [CoreBind] -> [CoreBind] +floatInwards = map fi_top_bind where fi_top_bind (NonRec binder rhs) = NonRec binder (fiExpr [] (freeVars rhs)) @@ -124,7 +115,7 @@ the closure for a is not built. type FreeVarsSet = IdSet type FloatingBinds = [(CoreBind, FreeVarsSet)] - -- In reverse dependency order (innermost bindiner first) + -- In reverse dependency order (innermost binder first) -- The FreeVarsSet is the free variables of the binding. In the case -- of recursive bindings, the set doesn't include the bound @@ -142,7 +133,7 @@ fiExpr to_drop (_, AnnType ty) = ASSERT( null to_drop ) fiExpr to_drop (_, AnnCast expr co) = Cast (fiExpr to_drop expr) co -- Just float in past coercion -fiExpr to_drop (_, AnnLit lit) = Lit lit +fiExpr _ (_, AnnLit lit) = Lit lit \end{code} Applications: we do float inside applications, mainly because we @@ -156,8 +147,8 @@ fiExpr to_drop (_,AnnApp fun arg) [drop_here, fun_drop, arg_drop] = sepBindsByDropPoint False [freeVarsOf fun, freeVarsOf arg] to_drop \end{code} -We are careful about lambdas: - +Note [Floating in past a lambda group] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * We must be careful about floating inside inside a value lambda. That risks losing laziness. The float-out pass might rescue us, but then again it might not. @@ -173,24 +164,30 @@ We are careful about lambdas: This is bad as now f is an updatable closure (update PAP) and has arity 0. +* Hack alert! We only float in through one-shot lambdas, + not (as you might guess) through lone big lambdas. + Reason: we float *out* past big lambdas (see the test in the Lam + case of FloatOut.floatExpr) and we don't want to float straight + back in again. + + It *is* important to float into one-shot lambdas, however; + see the remarks with noFloatIntoRhs. + So we treat lambda in groups, using the following rule: - Float inside a group of lambdas only if - they are all either type lambdas or one-shot lambdas. + Float in if (a) there is at least one Id, + and (b) there are no non-one-shot Ids + + Otherwise drop all the bindings outside the group. - Otherwise drop all the bindings outside the group. +This is what the 'go' function in the AnnLam case is doing. + +Urk! if all are tyvars, and we don't float in, we may miss an + opportunity to float inside a nested case branch \begin{code} - -- Hack alert! We only float in through one-shot lambdas, - -- not (as you might guess) through big lambdas. - -- Reason: we float *out* past big lambdas (see the test in the Lam - -- case of FloatOut.floatExpr) and we don't want to float straight - -- back in again. - -- - -- It *is* important to float into one-shot lambdas, however; - -- see the remarks with noFloatIntoRhs. fiExpr to_drop lam@(_, AnnLam _ _) - | all is_one_shot bndrs -- Float in + | go False bndrs -- Float in = mkLams bndrs (fiExpr to_drop body) | otherwise -- Dump it all here @@ -198,6 +195,12 @@ fiExpr to_drop lam@(_, AnnLam _ _) where (bndrs, body) = collectAnnBndrs lam + + go seen_one_shot_id [] = seen_one_shot_id + go seen_one_shot_id (b:bs) + | isTyCoVar b = go seen_one_shot_id bs + | isOneShotBndr b = go True bs + | otherwise = False -- Give up at a non-one-shot Id \end{code} We don't float lets inwards past an SCC. @@ -206,14 +209,10 @@ We don't float lets inwards past an SCC. cc, change current cc to the new one and float binds into expr. \begin{code} -fiExpr to_drop (_, AnnNote note@(SCC cc) expr) +fiExpr to_drop (_, AnnNote note@(SCC _) expr) = -- Wimp out for now mkCoLets' to_drop (Note note (fiExpr [] expr)) -fiExpr to_drop (_, AnnNote InlineMe expr) - = -- Ditto... don't float anything into an INLINE expression - mkCoLets' to_drop (Note InlineMe (fiExpr [] expr)) - fiExpr to_drop (_, AnnNote note@(CoreNote _) expr) = Note note (fiExpr to_drop expr) \end{code} @@ -240,66 +239,86 @@ So: rather than drop \tr{w}'s binding here, we add it onto the list of things to drop in the outer let's body, and let nature take its course. +Note [extra_fvs (1): avoid floating into RHS] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consdider let x=\y....t... in body. We do not necessarily want to float +a binding for t into the RHS, because it'll immediately be floated out +again. (It won't go inside the lambda else we risk losing work.) +In letrec, we need to be more careful still. We don't want to transform + let x# = y# +# 1# + in + letrec f = \z. ...x#...f... + in ... +into + letrec f = let x# = y# +# 1# in \z. ...x#...f... in ... +because now we can't float the let out again, because a letrec +can't have unboxed bindings. + +So we make "extra_fvs" which is the rhs_fvs of such bindings, and +arrange to dump bindings that bind extra_fvs before the entire let. + +Note [extra_fvs (s): free variables of rules] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + let x{rule mentioning y} = rhs in body +Here y is not free in rhs or body; but we still want to dump bindings +that bind y outside the let. So we augment extra_fvs with the +idRuleAndUnfoldingVars of x. No need for type variables, hence not using +idFreeVars. + + \begin{code} fiExpr to_drop (_,AnnLet (AnnNonRec id rhs@(rhs_fvs, ann_rhs)) body) = fiExpr new_to_drop body where body_fvs = freeVarsOf body - final_body_fvs | noFloatIntoRhs ann_rhs - || isUnLiftedType (idType id) = body_fvs `unionVarSet` rhs_fvs - | otherwise = body_fvs - -- See commments with letrec below + rule_fvs = idRuleAndUnfoldingVars id -- See Note [extra_fvs (2): free variables of rules] + extra_fvs | noFloatIntoRhs ann_rhs + || isUnLiftedType (idType id) = rule_fvs `unionVarSet` rhs_fvs + | otherwise = rule_fvs + -- See Note [extra_fvs (2): avoid floating into RHS] -- No point in floating in only to float straight out again -- Ditto ok-for-speculation unlifted RHSs - [shared_binds, rhs_binds, body_binds] = sepBindsByDropPoint False [rhs_fvs, final_body_fvs] to_drop + [shared_binds, extra_binds, rhs_binds, body_binds] + = sepBindsByDropPoint False [extra_fvs, rhs_fvs, body_fvs] to_drop new_to_drop = body_binds ++ -- the bindings used only in the body [(NonRec id rhs', rhs_fvs')] ++ -- the new binding itself + extra_binds ++ -- bindings from extra_fvs shared_binds -- the bindings used both in rhs and body -- Push rhs_binds into the right hand side of the binding rhs' = fiExpr rhs_binds rhs - rhs_fvs' = rhs_fvs `unionVarSet` floatedBindsFVs rhs_binds + rhs_fvs' = rhs_fvs `unionVarSet` floatedBindsFVs rhs_binds `unionVarSet` rule_fvs + -- Don't forget the rule_fvs; the binding mentions them! fiExpr to_drop (_,AnnLet (AnnRec bindings) body) = fiExpr new_to_drop body where - rhss = map snd bindings - + (ids, rhss) = unzip bindings rhss_fvs = map freeVarsOf rhss body_fvs = freeVarsOf body - -- Add to body_fvs the free vars of any RHS that has - -- a lambda at the top. This has the effect of making it seem - -- that such things are used in the body as well, and hence prevents - -- them getting floated in. The big idea is to avoid turning: - -- let x# = y# +# 1# - -- in - -- letrec f = \z. ...x#...f... - -- in ... - -- into - -- letrec f = let x# = y# +# 1# in \z. ...x#...f... in ... - -- - -- Because now we can't float the let out again, because a letrec - -- can't have unboxed bindings. - - final_body_fvs = foldr (unionVarSet . get_extras) body_fvs rhss - get_extras (rhs_fvs, rhs) | noFloatIntoRhs rhs = rhs_fvs - | otherwise = emptyVarSet - - (shared_binds:body_binds:rhss_binds) = sepBindsByDropPoint False (final_body_fvs:rhss_fvs) to_drop - - new_to_drop = -- the bindings used only in the body - body_binds ++ - -- the new binding itself + -- See Note [extra_fvs (1,2)] + rule_fvs = foldr (unionVarSet . idRuleAndUnfoldingVars) emptyVarSet ids + extra_fvs = rule_fvs `unionVarSet` + unionVarSets [ fvs | (fvs, rhs) <- rhss + , noFloatIntoRhs rhs ] + + (shared_binds:extra_binds:body_binds:rhss_binds) + = sepBindsByDropPoint False (extra_fvs:body_fvs:rhss_fvs) to_drop + + new_to_drop = body_binds ++ -- the bindings used only in the body [(Rec (fi_bind rhss_binds bindings), rhs_fvs')] ++ - -- the bindings used both in rhs and body or in more than one rhs - shared_binds + -- The new binding itself + extra_binds ++ -- Note [extra_fvs (1,2)] + shared_binds -- Used in more than one place - rhs_fvs' = unionVarSet (unionVarSets rhss_fvs) - (unionVarSets (map floatedBindsFVs rhss_binds)) + rhs_fvs' = unionVarSets rhss_fvs `unionVarSet` + unionVarSets (map floatedBindsFVs rhss_binds) `unionVarSet` + rule_fvs -- Don't forget the rule variables! -- Push rhs_binds into the right hand side of the binding fi_bind :: [FloatingBinds] -- one per "drop pt" conjured w/ fvs_of_rhss @@ -331,14 +350,14 @@ fiExpr to_drop (_, AnnCase scrut case_bndr ty alts) scrut_fvs = freeVarsOf scrut alts_fvs = map alt_fvs alts all_alts_fvs = unionVarSets alts_fvs - alt_fvs (con, args, rhs) = foldl delVarSet (freeVarsOf rhs) (case_bndr:args) + alt_fvs (_con, args, rhs) = foldl delVarSet (freeVarsOf rhs) (case_bndr:args) -- Delete case_bndr and args from free vars of rhs -- to get free vars of alt fi_alt to_drop (con, args, rhs) = (con, args, fiExpr to_drop rhs) -noFloatIntoRhs (AnnNote InlineMe _) = True -noFloatIntoRhs (AnnLam b _) = not (is_one_shot b) +noFloatIntoRhs :: AnnExpr' Var (UniqFM Var) -> Bool +noFloatIntoRhs (AnnLam b _) = not (is_one_shot b) -- IMPORTANT: don't say 'True' for a RHS with a one-shot lambda at the top. -- This makes a big difference for things like -- f x# = let x = I# x# @@ -350,6 +369,7 @@ noFloatIntoRhs (AnnLam b _) = not (is_one_shot b) noFloatIntoRhs rhs = exprIsHNF (deAnnotate' rhs) -- We'd just float right back out again... +is_one_shot :: Var -> Bool is_one_shot b = isId b && isOneShotBndr b \end{code} @@ -392,8 +412,8 @@ sepBindsByDropPoint type DropBox = (FreeVarsSet, FloatingBinds) -sepBindsByDropPoint is_case drop_pts [] - = [] : [[] | p <- drop_pts] -- cut to the chase scene; it happens +sepBindsByDropPoint _is_case drop_pts [] + = [] : [[] | _ <- drop_pts] -- cut to the chase scene; it happens sepBindsByDropPoint is_case drop_pts floaters = go floaters (map (\fvs -> (fvs, [])) (emptyVarSet : drop_pts)) @@ -411,7 +431,7 @@ sepBindsByDropPoint is_case drop_pts floaters -- "here" means the group of bindings dropped at the top of the fork (used_here : used_in_flags) = [ any (`elemVarSet` fvs) (bindersOf bind) - | (fvs, drops) <- drop_boxes] + | (fvs, _) <- drop_boxes] drop_here = used_here || not can_push @@ -444,6 +464,8 @@ sepBindsByDropPoint is_case drop_pts floaters insert_maybe box True = insert box insert_maybe box False = box + go _ _ = panic "sepBindsByDropPoint/go" + floatedBindsFVs :: FloatingBinds -> FreeVarsSet floatedBindsFVs binds = unionVarSets (map snd binds) @@ -452,6 +474,7 @@ mkCoLets' :: FloatingBinds -> CoreExpr -> CoreExpr mkCoLets' to_drop e = foldl (flip (Let . fst)) e to_drop -- Remember to_drop is in *reverse* dependency order +bindIsDupable :: Bind CoreBndr -> Bool bindIsDupable (Rec prs) = all (exprIsDupable . snd) prs -bindIsDupable (NonRec b r) = exprIsDupable r +bindIsDupable (NonRec _ r) = exprIsDupable r \end{code}