X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FOccurAnal.lhs;h=ad3eee0ce7345c4250a46921ac92f980649115bb;hb=2317c27bc0ca18dec43eacf87a6cf22cdf01f0f7;hp=05c57821edfcd90b4c748b58875d3a224eb37d5c;hpb=83817d01dff687643eee23218435b968ba358a25;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/OccurAnal.lhs b/ghc/compiler/simplCore/OccurAnal.lhs index 05c5782..ad3eee0 100644 --- a/ghc/compiler/simplCore/OccurAnal.lhs +++ b/ghc/compiler/simplCore/OccurAnal.lhs @@ -1,5 +1,5 @@ % -% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996 +% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % %************************************************************************ %* * @@ -12,34 +12,31 @@ core expression with (hopefully) improved usage information. \begin{code} module OccurAnal ( - occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr + occurAnalysePgm, occurAnalyseExpr ) where #include "HsVersions.h" -import BinderInfo -import CmdLineOpts ( opt_D_dump_occur_anal, SimplifierSwitch(..) ) import CoreSyn -import Digraph ( stronglyConnCompR, SCC(..) ) -import Id ( idWantsToBeINLINEd, addNoInlinePragma, nukeNoInlinePragma, - omitIfaceSigForId, isSpecPragmaId, - idType, idUnique, Id, - emptyIdSet, unionIdSets, mkIdSet, - elementOfIdSet, - addOneToIdSet, IdSet, - - IdEnv, nullIdEnv, unitIdEnv, combineIdEnvs, - delOneFromIdEnv, delManyFromIdEnv, isNullIdEnv, - mapIdEnv, lookupIdEnv, elemIdEnv, addOneToIdEnv +import CoreFVs ( idRuleVars ) +import CoreUtils ( exprIsTrivial, isDefaultAlt ) +import Id ( isDataConWorkId, isOneShotBndr, setOneShotLambda, + idOccInfo, setIdOccInfo, isLocalId, + isExportedId, idArity, + idType, idUnique, Id ) -import Specialise ( idSpecVars ) -import Name ( isExported, isLocallyDefined ) -import Type ( splitFunTy_maybe, splitForAllTys ) -import Maybes ( maybeToBool ) -import PprCore -import Unique ( u2i ) +import BasicTypes ( OccInfo(..), isOneOcc, InterestingCxt ) + +import VarSet +import VarEnv + +import Type ( isFunTy, dropForAlls ) +import Maybes ( orElse ) +import Digraph ( stronglyConnCompR, SCC(..) ) +import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey ) +import Unique ( Unique ) import UniqFM ( keysUFM ) -import Util ( zipWithEqual ) +import Util ( zipWithEqual, mapAndUnzip ) import Outputable \end{code} @@ -53,170 +50,22 @@ import Outputable Here's the externally-callable interface: \begin{code} -occurAnalyseBinds - :: [CoreBinding] -- input - -> (SimplifierSwitch -> Bool) - -> [SimplifiableCoreBinding] -- output - -occurAnalyseBinds binds simplifier_sw_chkr - | opt_D_dump_occur_anal = pprTrace "OccurAnal:" - (pprGenericBindings binds') - binds' - | otherwise = binds' +occurAnalysePgm :: [CoreBind] -> [CoreBind] +occurAnalysePgm binds + = snd (go initOccEnv binds) where - (_, _, binds') = occAnalTop initial_env binds - - initial_env = OccEnv (simplifier_sw_chkr IgnoreINLINEPragma) - (\id in_scope -> isLocallyDefined id) -- Anything local is interesting - emptyIdSet -- Not actually used -\end{code} - - -\begin{code} -occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting - -> CoreExpr - -> (IdEnv BinderInfo, -- Occ info for interesting free vars - SimplifiableCoreExpr) - -occurAnalyseExpr interesting expr - = occAnal initial_env expr - where - initial_env = OccEnv False {- Do not ignore INLINE Pragma -} - (\id locals -> interesting id || elementOfIdSet id locals) - emptyIdSet - -occurAnalyseGlobalExpr :: CoreExpr -> SimplifiableCoreExpr -occurAnalyseGlobalExpr expr - = -- Top level expr, so no interesting free vars, and - -- discard occurence info returned - snd (occurAnalyseExpr (\_ -> False) expr) -\end{code} - - -%************************************************************************ -%* * -\subsection{Top level stuff} -%* * -%************************************************************************ - -In @occAnalTop@ we do indirection-shorting. That is, if we have this: - - loc = - ... - exp = loc - -where exp is exported, and loc is not, then we replace it with this: - - loc = exp - exp = - ... - -Without this we never get rid of the exp = loc thing. -This save a gratuitous jump -(from \tr{x_exported} to \tr{x_local}), and makes strictness -information propagate better. -This used to happen in the final phase, but its tidier to do it here. - - -If more than one exported thing is equal to a local thing (i.e., the -local thing really is shared), then we do one only: -\begin{verbatim} - x_local = .... - x_exported1 = x_local - x_exported2 = x_local -==> - x_exported1 = .... - - x_exported2 = x_exported1 -\end{verbatim} - -We rely on prior eta reduction to simplify things like -\begin{verbatim} - x_exported = /\ tyvars -> x_local tyvars -==> - x_exported = x_local -\end{verbatim} -Hence,there's a possibility of leaving unchanged something like this: -\begin{verbatim} - x_local = .... - x_exported1 = x_local Int -\end{verbatim} -By the time we've thrown away the types in STG land this -could be eliminated. But I don't think it's very common -and it's dangerous to do this fiddling in STG land -because we might elminate a binding that's mentioned in the -unfolding for something. - - -\begin{code} -occAnalTop :: OccEnv -- What's in scope - -> [CoreBinding] - -> (IdEnv BinderInfo, -- Occurrence info - IdEnv Id, -- Indirection elimination info - [SimplifiableCoreBinding] - ) - -occAnalTop env [] = (emptyDetails, nullIdEnv, []) - --- Special case for eliminating indirections -occAnalTop env (NonRec exported_id (Var local_id) : binds) - | isExported exported_id && -- Only if this is exported - - isLocallyDefined local_id && -- Only if this one is defined in this - -- module, so that we *can* change its - -- binding to be the exported thing! - - not (isExported local_id) && -- Only if this one is not itself exported, - -- since the transformation will nuke it - - not (omitIfaceSigForId local_id) && -- Don't do the transformation if rhs_id is - -- something like a constructor, whose - -- definition is implicitly exported and - -- which must not vanish. - -- To illustrate the preceding check consider - -- data T = MkT Int - -- mkT = MkT - -- f x = MkT (x+1) - -- Here, we'll make a local, non-exported, defn for MkT, and without the - -- above condition we'll transform it to: - -- mkT = \x. MkT [x] - -- f = \y. mkT (y+1) - -- This is bad because mkT will get the IdDetails of MkT, and won't - -- be exported. Also the code generator won't make a definition for - -- the MkT constructor. - -- Slightly gruesome, this. - - - not (maybeToBool (lookupIdEnv ind_env local_id)) - -- Only if not already substituted for - - = -- Aha! An indirection; let's eliminate it! - (scope_usage, ind_env', binds') - where - (scope_usage, ind_env, binds') = occAnalTop env binds - ind_env' = addOneToIdEnv ind_env local_id exported_id + go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind]) + go env [] + = (emptyDetails, []) + go env (bind:binds) + = (final_usage, bind' ++ binds') + where + (bs_usage, binds') = go env binds + (final_usage, bind') = occAnalBind env bind bs_usage --- The normal case -occAnalTop env (bind : binds) - = (final_usage, ind_env, new_binds ++ binds') - where - new_env = env `addNewCands` (bindersOf bind) - (scope_usage, ind_env, binds') = occAnalTop new_env binds - (final_usage, new_binds) = occAnalBind env (zap_bind bind) scope_usage - - -- Deal with any indirections - zap_bind (NonRec bndr rhs) - | bndr `elemIdEnv` ind_env = Rec (zap (bndr,rhs)) - -- The Rec isn't strictly necessary, but it's convenient - zap_bind (Rec pairs) - | or [id `elemIdEnv` ind_env | (id,_) <- pairs] = Rec (concat (map zap pairs)) - - zap_bind bind = bind - - zap pair@(bndr,rhs) = case lookupIdEnv ind_env bndr of - Nothing -> [pair] - Just exported_id -> [(bndr, Var exported_id), - (exported_id, rhs)] +occurAnalyseExpr :: CoreExpr -> CoreExpr + -- Do occurrence analysis, and discard occurence info returned +occurAnalyseExpr expr = snd (occAnal initOccEnv expr) \end{code} @@ -230,30 +79,31 @@ Bindings ~~~~~~~~ \begin{code} -type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique, +type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached + +type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique, -- which is gotten from the Id. -type Details1 = (Id, UsageDetails, SimplifiableCoreExpr) -type Details2 = ((Id, BinderInfo), SimplifiableCoreExpr) +type Details1 = (Id, UsageDetails, CoreExpr) +type Details2 = (IdWithOccInfo, CoreExpr) occAnalBind :: OccEnv - -> CoreBinding + -> CoreBind -> UsageDetails -- Usage details of scope -> (UsageDetails, -- Of the whole let(rec) - [SimplifiableCoreBinding]) + [CoreBind]) occAnalBind env (NonRec binder rhs) body_usage - | isNeeded env body_usage binder -- It's mentioned in body + | not (binder `usedIn` body_usage) -- It's not mentioned + = (body_usage, []) + + | otherwise -- It's mentioned in the body = (final_body_usage `combineUsageDetails` rhs_usage, [NonRec tagged_binder rhs']) - | otherwise -- Not mentioned, so drop dead code - = (body_usage, []) - where - binder' = nukeNoInlinePragma binder - (rhs_usage, rhs') = occAnalRhs env binder' rhs - (final_body_usage, tagged_binder) = tagBinder body_usage binder' + (final_body_usage, tagged_binder) = tagBinder body_usage binder + (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs \end{code} Dropping dead code for recursive bindings is done in a very simple way: @@ -295,15 +145,10 @@ It isn't easy to do a perfect job in one blow. Consider occAnalBind env (Rec pairs) body_usage = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs where - pp_item (_, bndr, _) = ppr bndr - - binders = map fst pairs - new_env = env `addNewCands` binders - analysed_pairs :: [Details1] - analysed_pairs = [ (nukeNoInlinePragma bndr, rhs_usage, rhs') + analysed_pairs = [ (bndr, rhs_usage, rhs') | (bndr, rhs) <- pairs, - let (rhs_usage, rhs') = occAnalRhs new_env bndr rhs + let (rhs_usage, rhs') = occAnalRhs env bndr rhs ] sccs :: [SCC (Node Details1)] @@ -313,7 +158,7 @@ occAnalBind env (Rec pairs) body_usage ---- stuff for dependency analysis of binds ------------------------------- edges :: [Node Details1] edges = _scc_ "occAnalBind.assoc" - [ (details, IBOX(u2i (idUnique id)), edges_from rhs_usage) + [ (details, idUnique id, edges_from rhs_usage) | details@(id, rhs_usage, rhs) <- analysed_pairs ] @@ -323,10 +168,10 @@ occAnalBind env (Rec pairs) body_usage -- by just extracting the keys from the finite map. Grimy, but fast. -- Previously we had this: -- [ bndr | bndr <- bndrs, - -- maybeToBool (lookupIdEnv rhs_usage bndr)] + -- maybeToBool (lookupVarEnv rhs_usage bndr)] -- which has n**2 cost, and this meant that edges_from alone -- consumed 10% of total runtime! - edges_from :: UsageDetails -> [Int] + edges_from :: UsageDetails -> [Unique] edges_from rhs_usage = _scc_ "occAnalBind.edges_from" keysUFM rhs_usage @@ -334,10 +179,10 @@ occAnalBind env (Rec pairs) body_usage -- Non-recursive SCC do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far) - | isNeeded env body_usage bndr - = (combined_usage, new_bind : binds_so_far) - | otherwise + | not (bndr `usedIn` body_usage) = (body_usage, binds_so_far) -- Dead code + | otherwise + = (combined_usage, new_bind : binds_so_far) where total_usage = combineUsageDetails body_usage rhs_usage (combined_usage, tagged_bndr) = tagBinder total_usage bndr @@ -345,20 +190,20 @@ occAnalBind env (Rec pairs) body_usage -- Recursive SCC do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far) - | any (isNeeded env body_usage) bndrs - = (combined_usage, final_bind:binds_so_far) - | otherwise + | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage = (body_usage, binds_so_far) -- Dead code + | otherwise + = (combined_usage, final_bind:binds_so_far) where - details = [details | (details, _, _) <- cycle] - bndrs = [bndr | (bndr, _, _) <- details] - rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details] - total_usage = foldr combineUsageDetails body_usage rhs_usages - (combined_usage, tagged_binders) = tagBinders total_usage bndrs - final_bind = Rec (reOrderRec env new_cycle) - - new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_binders cycle) - mk_new_bind (bndr, occ_info) ((_, _, rhs'), key, keys) = (((bndr, occ_info), rhs'), key, keys) + details = [details | (details, _, _) <- cycle] + bndrs = [bndr | (bndr, _, _) <- details] + rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details] + total_usage = foldr combineUsageDetails body_usage rhs_usages + (combined_usage, tagged_bndrs) = tagBinders total_usage bndrs + final_bind = Rec (reOrderRec env new_cycle) + + new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle) + mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys) \end{code} @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic @@ -376,6 +221,10 @@ on the no-inline Ids then the binds are topologically sorted. This means that the simplifier will generally do a good job if it works from top bottom, recording inlinings for any Ids which aren't marked as "no-inline" as it goes. +============== +[June 98: I don't understand the following paragraphs, and I've + changed the a=b case again so that it isn't a special case any more.] + Here's a case that bit me: letrec @@ -388,6 +237,7 @@ Re-ordering doesn't change the order of bindings, but there was no loop-breaker. My solution was to make a=b bindings record b as Many, rather like INLINE bindings. Perhaps something cleverer would suffice. +=============== You might think that you can prevent non-termination simply by making sure that we simplify a recursive binding's RHS in an environment that @@ -424,42 +274,67 @@ reOrderRec env (AcyclicSCC (bind, _, _)) = [bind] -- Common case of simple self-recursion reOrderRec env (CyclicSCC [bind]) - = [((addNoInlinePragma bndr, occ_info), rhs)] + = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)] where - (((bndr, occ_info), rhs), _, _) = bind + ((tagged_bndr, rhs), _, _) = bind -reOrderRec env (CyclicSCC binds) +reOrderRec env (CyclicSCC (bind : binds)) = -- Choose a loop breaker, mark it no-inline, -- do SCC analysis on the rest, and recursively sort them out concat (map (reOrderRec env) (stronglyConnCompR unchosen)) ++ - [((addNoInlinePragma bndr, occ_info), rhs)] + [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)] where - (chosen_pair, unchosen) = choose_loop_breaker binds - ((bndr,occ_info), rhs) = chosen_pair - - -- Choosing the loop breaker; heursitic - choose_loop_breaker (bind@(details, _, _) : rest) - | not (null rest) && - bad_choice details - = (chosen, bind : unchosen) -- Don't pick it - | otherwise -- Pick it - = (details,rest) + (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds + (tagged_bndr, rhs) = chosen_pair + + -- This loop looks for the bind with the lowest score + -- to pick as the loop breaker. The rest accumulate in + choose_loop_breaker (details,_,_) loop_sc acc [] + = (details, acc) -- Done + + choose_loop_breaker loop_bind loop_sc acc (bind : binds) + | sc < loop_sc -- Lower score so pick this new one + = choose_loop_breaker bind sc (loop_bind : acc) binds + + | otherwise -- No lower so don't pick it + = choose_loop_breaker loop_bind loop_sc (bind : acc) binds where - (chosen, unchosen) = choose_loop_breaker rest - - bad_choice ((bndr, occ_info), rhs) - = var_rhs rhs -- Dont pick var RHS - || inlineMe env bndr -- Dont pick INLINE thing - || isOneFunOcc occ_info -- Dont pick single-occ thing - || not_fun_ty (idType bndr) -- Dont pick data-ty thing - - -- isOneFunOcc looks for one textual occurrence, whether inside lambda or whatever. - -- We stick to just FunOccs because if we're not going to be able - -- to inline the thing on this round it might be better to pick - -- this one as the loop breaker. Real example (the Enum Ordering instance - -- from PrelBase): + sc = score bind + + score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker + score ((bndr, rhs), _, _) + | exprIsTrivial rhs = 4 -- Practically certain to be inlined + -- Used to have also: && not (isExportedId bndr) + -- But I found this sometimes cost an extra iteration when we have + -- rec { d = (a,b); a = ...df...; b = ...df...; df = d } + -- where df is the exported dictionary. Then df makes a really + -- bad choice for loop breaker + + | not_fun_ty (idType bndr) = 3 -- Data types help with cases + -- This used to have a lower score than inlineCandidate, but + -- it's *really* helpful if dictionaries get inlined fast, + -- so I'm experimenting with giving higher priority to data-typed things + + | inlineCandidate bndr rhs = 2 -- Likely to be inlined + +-- NOT NEEDED ANY MORE [Feb06] +-- We make all rules available in all bindings, by substituting +-- the IdInfo before looking at any RHSs. I'm just leaving this +-- snippet in as a commment so we can find it again if necessary. +-- +-- | not (isEmptySpecInfo (idSpecialisation bndr)) = 1 +-- -- Avoid things with specialisations; we'd like +-- -- to take advantage of them in the subsequent bindings + + | otherwise = 0 + + inlineCandidate :: Id -> CoreExpr -> Bool + inlineCandidate id (Note InlineMe _) = True + inlineCandidate id rhs = isOneOcc (idOccInfo id) + + -- Real example (the Enum Ordering instance from PrelBase): -- rec f = \ x -> case d of (p,q,r) -> p x -- g = \ x -> case d of (p,q,r) -> q x -- d = (v, f, g) @@ -467,14 +342,9 @@ reOrderRec env (CyclicSCC binds) -- Here, f and g occur just once; but we can't inline them into d. -- On the other hand we *could* simplify those case expressions if -- we didn't stupidly choose d as the loop breaker. + -- But we won't because constructor args are marked "Many". - not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty)) - where - (_, rho_ty) = splitForAllTys ty - - -- A variable RHS - var_rhs (Var v) = True - var_rhs other_rhs = False + not_fun_ty ty = not (isFunTy (dropForAlls ty)) \end{code} @occAnalRhs@ deals with the question of bindings where the Id is marked @@ -485,36 +355,55 @@ we'll catch it next time round. At worst this costs an extra simplifier pass. ToDo: try using the occurrence info for the inline'd binder. [March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec. +[June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec. -[March 98] A new wrinkle is that if the binder has specialisations inside -it then we count the specialised Ids as "extra rhs's". That way -the "parent" keeps the specialised "children" alive. If the parent -dies (because it isn't referenced any more), then the children will -die too unless they are already referenced directly. \begin{code} occAnalRhs :: OccEnv -> Id -> CoreExpr -- Binder and rhs - -> (UsageDetails, SimplifiableCoreExpr) - -occAnalRhs env id (Var v) - | isCandidate env v - = (unitIdEnv v (markMany (funOccurrence 0)), Var v) - - | otherwise - = (emptyDetails, Var v) + -- For non-recs the binder is alrady tagged + -- with occurrence info + -> (UsageDetails, CoreExpr) occAnalRhs env id rhs - | inlineMe env id - = (mapIdEnv markMany total_usage, rhs') - - | otherwise - = (total_usage, rhs') - + = (final_usage, rhs') + where + (rhs_usage, rhs') = occAnal ctxt rhs + ctxt | certainly_inline id = env + | otherwise = rhsCtxt + -- Note that we generally use an rhsCtxt. This tells the occ anal n + -- that it's looking at an RHS, which has an effect in occAnalApp + -- + -- But there's a problem. Consider + -- x1 = a0 : [] + -- x2 = a1 : x1 + -- x3 = a2 : x2 + -- g = f x3 + -- First time round, it looks as if x1 and x2 occur as an arg of a + -- let-bound constructor ==> give them a many-occurrence. + -- But then x3 is inlined (unconditionally as it happens) and + -- next time round, x2 will be, and the next time round x1 will be + -- Result: multiple simplifier iterations. Sigh. + -- Crude solution: use rhsCtxt for things that occur just once... + + certainly_inline id = case idOccInfo id of + OneOcc in_lam one_br _ -> not in_lam && one_br + other -> False + + -- [March 98] A new wrinkle is that if the binder has specialisations inside + -- it then we count the specialised Ids as "extra rhs's". That way + -- the "parent" keeps the specialised "children" alive. If the parent + -- dies (because it isn't referenced any more), then the children will + -- die too unless they are already referenced directly. + + final_usage = addRuleUsage rhs_usage id + +addRuleUsage :: UsageDetails -> Id -> UsageDetails +-- Add the usage from RULES in Id to the usage +addRuleUsage usage id + = foldVarSet add usage (idRuleVars id) where - (rhs_usage, rhs') = occAnal env rhs - total_usage = foldr add rhs_usage (idSpecVars id) - add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info + add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info -- (i.e manyOcc) because many copies -- of the specialised thing can appear \end{code} @@ -525,17 +414,16 @@ Expressions occAnal :: OccEnv -> CoreExpr -> (UsageDetails, -- Gives info only about the "interesting" Ids - SimplifiableCoreExpr) - -occAnal env (Var v) - | isCandidate env v - = (unitIdEnv v (funOccurrence 0), Var v) - - | otherwise - = (emptyDetails, Var v) - -occAnal env (Lit lit) = (emptyDetails, Lit lit) -occAnal env (Prim op args) = (occAnalArgs env args, Prim op args) + CoreExpr) + +occAnal env (Type t) = (emptyDetails, Type t) +occAnal env (Var v) = (mkOneOcc env v False, Var v) + -- At one stage, I gathered the idRuleVars for v here too, + -- which in a way is the right thing to do. + -- Btu that went wrong right after specialisation, when + -- the *occurrences* of the overloaded function didn't have any + -- rules in them, so the *specialised* versions looked as if they + -- weren't used at all. \end{code} We regard variables that occur as constructor arguments as "dangerousToDup": @@ -554,250 +442,386 @@ If we aren't careful we duplicate the (expensive x) call! Constructors are rather like lambdas in this way. \begin{code} -occAnal env (Con con args) - = (mapIdEnv markDangerousToDup (occAnalArgs env args), - Con con args) +occAnal env expr@(Lit lit) = (emptyDetails, expr) +\end{code} + +\begin{code} +occAnal env (Note InlineMe body) + = case occAnal env body of { (usage, body') -> + (mapVarEnv markMany usage, Note InlineMe body') + } occAnal env (Note note@(SCC cc) body) - = (mapIdEnv markInsideSCC usage, Note note body') - where - (usage, body') = occAnal env body + = case occAnal env body of { (usage, body') -> + (mapVarEnv markInsideSCC usage, Note note body') + } occAnal env (Note note body) - = (usage, Note note body') - where - (usage, body') = occAnal env body + = case occAnal env body of { (usage, body') -> + (usage, Note note body') + } +\end{code} -occAnal env (App fun arg) - = (fun_usage `combineUsageDetails` arg_usage, App fun' arg) - where - (fun_usage, fun') = occAnal env fun - arg_usage = occAnalArg env arg +\begin{code} +occAnal env app@(App fun arg) + = occAnalApp env (collectArgs app) False + +-- Ignore type variables altogether +-- (a) occurrences inside type lambdas only not marked as InsideLam +-- (b) type variables not in environment + +occAnal env expr@(Lam x body) | isTyVar x + = case occAnal env body of { (body_usage, body') -> + (body_usage, Lam x body') + } -- For value lambdas we do a special hack. Consider -- (\x. \y. ...x...) -- If we did nothing, x is used inside the \y, so would be marked -- as dangerous to dup. But in the common case where the abstraction -- is applied to two arguments this is over-pessimistic. --- So instead we don't take account of the \y when dealing with x's usage; --- instead, the simplifier is careful when partially applying lambdas - -occAnal env expr@(Lam (ValBinder binder) body) - = (mapIdEnv markDangerousToDup final_usage, - foldr ( \v b -> Lam (ValBinder v) b) body' tagged_binders) +-- So instead, we just mark each binder with its occurrence +-- info in the *body* of the multiple lambda. +-- Then, the simplifier is careful when partially applying lambdas. + +occAnal env expr@(Lam _ _) + = case occAnal env_body body of { (body_usage, body') -> + let + (final_usage, tagged_binders) = tagBinders body_usage binders + -- URGH! Sept 99: we don't seem to be able to use binders' here, because + -- we get linear-typed things in the resulting program that we can't handle yet. + -- (e.g. PrelShow) TODO + + really_final_usage = if linear then + final_usage + else + mapVarEnv markInsideLam final_usage + in + (really_final_usage, + mkLams tagged_binders body') } where - (binders,body) = collectValBinders expr - (body_usage, body') = occAnal (env `addNewCands` binders) body - (final_usage, tagged_binders) = tagBinders body_usage binders - --- ANDY: WE MUST THINK ABOUT THIS! (ToDo) -occAnal env (Lam (TyBinder tyvar) body) - = case occAnal env body of { (body_usage, body') -> - (mapIdEnv markDangerousToDup body_usage, - Lam (TyBinder tyvar) body') } --- where --- (body_usage, body') = occAnal env body - -occAnal env (Case scrut alts) - = case occAnalAlts env alts of { (alts_usage, alts') -> - case occAnal env scrut of { (scrut_usage, scrut') -> - let - det = scrut_usage `combineUsageDetails` alts_usage - in - if isNullIdEnv det then - (det, Case scrut' alts') - else - (det, Case scrut' alts') }} -{- - (scrut_usage `combineUsageDetails` alts_usage, - Case scrut' alts') + env_body = vanillaCtxt -- Body is (no longer) an RhsContext + (binders, body) = collectBinders expr + binders' = oneShotGroup env binders + linear = all is_one_shot binders' + is_one_shot b = isId b && isOneShotBndr b + +occAnal env (Case scrut bndr ty alts) + = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') -> + case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts') -> + let + alts_usage = foldr1 combineAltsUsageDetails alts_usage_s + alts_usage' = addCaseBndrUsage alts_usage + (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr + total_usage = scrut_usage `combineUsageDetails` alts_usage1 + in + total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }} where - (scrut_usage, scrut') = occAnal env scrut - (alts_usage, alts') = occAnalAlts env alts --} + -- The case binder gets a usage of either "many" or "dead", never "one". + -- Reason: we like to inline single occurrences, to eliminate a binding, + -- but inlining a case binder *doesn't* eliminate a binding. + -- We *don't* want to transform + -- case x of w { (p,q) -> f w } + -- into + -- case x of w { (p,q) -> f (p,q) } + addCaseBndrUsage usage = case lookupVarEnv usage bndr of + Nothing -> usage + Just occ -> extendVarEnv usage bndr (markMany occ) + + occ_anal_scrut (Var v) (alt1 : other_alts) + | not (null other_alts) || not (isDefaultAlt alt1) + = (mkOneOcc env v True, Var v) + occ_anal_scrut scrut alts = occAnal vanillaCtxt scrut + -- No need for rhsCtxt occAnal env (Let bind body) - = case occAnal new_env body of { (body_usage, body') -> + = case occAnal env body of { (body_usage, body') -> case occAnalBind env bind body_usage of { (final_usage, new_binds) -> - (final_usage, foldr Let body' new_binds) }} -- mkCoLet* wants Core... (sigh) + (final_usage, mkLets new_binds body') }} + +occAnalArgs env args + = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') -> + (foldr combineUsageDetails emptyDetails arg_uds_s, args')} where - new_env = env `addNewCands` (bindersOf bind) --- (body_usage, body') = occAnal new_env body --- (final_usage, new_binds) = occAnalBind env bind body_usage + arg_env = vanillaCtxt \end{code} -Case alternatives -~~~~~~~~~~~~~~~~~ +Applications are dealt with specially because we want +the "build hack" to work. + \begin{code} -occAnalAlts env (AlgAlts alts deflt) - = (foldr combineAltsUsageDetails deflt_usage alts_usage, - -- Note: combine*Alts*UsageDetails... - AlgAlts alts' deflt') +-- Hack for build, fold, runST +occAnalApp env (Var fun, args) is_rhs + = case args_stuff of { (args_uds, args') -> + let + -- We mark the free vars of the argument of a constructor or PAP + -- as "many", if it is the RHS of a let(rec). + -- This means that nothing gets inlined into a constructor argument + -- position, which is what we want. Typically those constructor + -- arguments are just variables, or trivial expressions. + -- + -- This is the *whole point* of the isRhsEnv predicate + final_args_uds + | isRhsEnv env, + isDataConWorkId fun || valArgCount args < idArity fun + = mapVarEnv markMany args_uds + | otherwise = args_uds + in + (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') } where - (alts_usage, alts') = unzip (map do_alt alts) - (deflt_usage, deflt') = occAnalDeflt env deflt - - do_alt (con, args, rhs) - = (final_usage, (con, tagged_args, rhs')) - where - new_env = env `addNewCands` args - (rhs_usage, rhs') = occAnal new_env rhs - (final_usage, tagged_args) = tagBinders rhs_usage args - -occAnalAlts env (PrimAlts alts deflt) - = (foldr combineAltsUsageDetails deflt_usage alts_usage, - -- Note: combine*Alts*UsageDetails... - PrimAlts alts' deflt') + fun_uniq = idUnique fun + fun_uds = mkOneOcc env fun (valArgCount args > 0) + args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args + | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args + | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args + | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args + -- (foldr k z xs) may call k many times, but it never + -- shares a partial application of k; hence [False,True] + -- This means we can optimise + -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs + -- by floating in the v + + | otherwise = occAnalArgs env args + + +occAnalApp env (fun, args) is_rhs + = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') -> + -- The addAppCtxt is a bit cunning. One iteration of the simplifier + -- often leaves behind beta redexs like + -- (\x y -> e) a1 a2 + -- Here we would like to mark x,y as one-shot, and treat the whole + -- thing much like a let. We do this by pushing some True items + -- onto the context stack. + + case occAnalArgs env args of { (args_uds, args') -> + let + final_uds = fun_uds `combineUsageDetails` args_uds + in + (final_uds, mkApps fun' args') }} + +appSpecial :: OccEnv + -> Int -> CtxtTy -- Argument number, and context to use for it + -> [CoreExpr] + -> (UsageDetails, [CoreExpr]) +appSpecial env n ctxt args + = go n args where - (alts_usage, alts') = unzip (map do_alt alts) - (deflt_usage, deflt') = occAnalDeflt env deflt - - do_alt (lit, rhs) - = (rhs_usage, (lit, rhs')) - where - (rhs_usage, rhs') = occAnal env rhs + arg_env = vanillaCtxt -occAnalDeflt env NoDefault = (emptyDetails, NoDefault) + go n [] = (emptyDetails, []) -- Too few args -occAnalDeflt env (BindDefault binder rhs) - = (final_usage, BindDefault tagged_binder rhs') - where - new_env = env `addNewCand` binder - (rhs_usage, rhs') = occAnal new_env rhs - (final_usage, tagged_binder) = tagBinder rhs_usage binder + go 1 (arg:args) -- The magic arg + = case occAnal (setCtxt arg_env ctxt) arg of { (arg_uds, arg') -> + case occAnalArgs env args of { (args_uds, args') -> + (combineUsageDetails arg_uds args_uds, arg':args') }} + + go n (arg:args) + = case occAnal arg_env arg of { (arg_uds, arg') -> + case go (n-1) args of { (args_uds, args') -> + (combineUsageDetails arg_uds args_uds, arg':args') }} \end{code} + +Case alternatives +~~~~~~~~~~~~~~~~~ +If the case binder occurs at all, the other binders effectively do too. +For example + case e of x { (a,b) -> rhs } +is rather like + let x = (a,b) in rhs +If e turns out to be (e1,e2) we indeed get something like + let a = e1; b = e2; x = (a,b) in rhs -Atoms -~~~~~ \begin{code} -occAnalArgs :: OccEnv -> [CoreArg] -> UsageDetails - -occAnalArgs env atoms - = foldr do_one_atom emptyDetails atoms - where - do_one_atom (VarArg v) usage - | isCandidate env v = addOneOcc usage v (argOccurrence 0) - | otherwise = usage - do_one_atom other_arg usage = usage - - -occAnalArg :: OccEnv -> CoreArg -> UsageDetails - -occAnalArg env (VarArg v) - | isCandidate env v = unitDetails v (argOccurrence 0) - | otherwise = emptyDetails -occAnalArg _ _ = emptyDetails +occAnalAlt env case_bndr (con, bndrs, rhs) + = case occAnal env rhs of { (rhs_usage, rhs') -> + let + (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs + final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs + | otherwise = tagged_bndrs + -- Leave the binders untagged if the case + -- binder occurs at all; see note above + in + (final_usage, (con, final_bndrs, rhs')) } \end{code} %************************************************************************ %* * -\subsection[OccurAnal-types]{Data types} +\subsection[OccurAnal-types]{OccEnv} %* * %************************************************************************ \begin{code} -data OccEnv = - OccEnv - Bool -- IgnoreINLINEPragma flag - -- False <=> OK to use INLINEPragma information - -- True <=> ignore INLINEPragma information +data OccEnv + = OccEnv OccEncl -- Enclosing context information + CtxtTy -- Tells about linearity + +-- OccEncl is used to control whether to inline into constructor arguments +-- For example: +-- x = (p,q) -- Don't inline p or q +-- y = /\a -> (p a, q a) -- Still don't inline p or q +-- z = f (p,q) -- Do inline p,q; it may make a rule fire +-- So OccEncl tells enought about the context to know what to do when +-- we encounter a contructor application or PAP. + +data OccEncl + = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda + -- Don't inline into constructor args here + | OccVanilla -- Argument of function, body of lambda, scruintee of case etc. + -- Do inline into constructor args here + +type CtxtTy = [Bool] + -- [] No info + -- + -- True:ctxt Analysing a function-valued expression that will be + -- applied just once + -- + -- False:ctxt Analysing a function-valued expression that may + -- be applied many times; but when it is, + -- the CtxtTy inside applies - (Id -> IdSet -> Bool) -- Tells whether an Id occurrence is interesting, - -- given the set of in-scope variables +initOccEnv :: OccEnv +initOccEnv = OccEnv OccRhs [] - IdSet -- In-scope Ids +vanillaCtxt = OccEnv OccVanilla [] +rhsCtxt = OccEnv OccRhs [] +isRhsEnv (OccEnv OccRhs _) = True +isRhsEnv (OccEnv OccVanilla _) = False -addNewCands :: OccEnv -> [Id] -> OccEnv -addNewCands (OccEnv ip ifun cands) ids - = OccEnv ip ifun (cands `unionIdSets` mkIdSet ids) +setCtxt :: OccEnv -> CtxtTy -> OccEnv +setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt -addNewCand :: OccEnv -> Id -> OccEnv -addNewCand (OccEnv ip ifun cands) id - = OccEnv ip ifun (addOneToIdSet cands id) +oneShotGroup :: OccEnv -> [CoreBndr] -> [CoreBndr] + -- The result binders have one-shot-ness set that they might not have had originally. + -- This happens in (build (\cn -> e)). Here the occurrence analyser + -- linearity context knows that c,n are one-shot, and it records that fact in + -- the binder. This is useful to guide subsequent float-in/float-out tranformations -isCandidate :: OccEnv -> Id -> Bool -isCandidate (OccEnv _ ifun cands) id = ifun id cands +oneShotGroup (OccEnv encl ctxt) bndrs + = go ctxt bndrs [] + where + go ctxt [] rev_bndrs = reverse rev_bndrs -inlineMe :: OccEnv -> Id -> Bool -inlineMe env id - = {- See comments with simplIdWantsToBeINLINEd in SimplUtils.lhs - not ignore_inline_prag && - -} - idWantsToBeINLINEd id + go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs + | isId bndr = go ctxt bndrs (bndr':rev_bndrs) + where + bndr' | lin_ctxt = setOneShotLambda bndr + | otherwise = bndr + go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs) -type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage +addAppCtxt (OccEnv encl ctxt) args + = OccEnv encl (replicate (valArgCount args) True ++ ctxt) +\end{code} + +%************************************************************************ +%* * +\subsection[OccurAnal-types]{OccEnv} +%* * +%************************************************************************ + +\begin{code} +type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage combineUsageDetails, combineAltsUsageDetails :: UsageDetails -> UsageDetails -> UsageDetails combineUsageDetails usage1 usage2 - = combineIdEnvs addBinderInfo usage1 usage2 + = plusVarEnv_C addOccInfo usage1 usage2 combineAltsUsageDetails usage1 usage2 - = combineIdEnvs orBinderInfo usage1 usage2 + = plusVarEnv_C orOccInfo usage1 usage2 -addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails +addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails addOneOcc usage id info - = combineIdEnvs addBinderInfo usage (unitIdEnv id info) + = plusVarEnv_C addOccInfo usage (unitVarEnv id info) -- ToDo: make this more efficient -emptyDetails = (nullIdEnv :: UsageDetails) +emptyDetails = (emptyVarEnv :: UsageDetails) -unitDetails id info = (unitIdEnv id info :: UsageDetails) +usedIn :: Id -> UsageDetails -> Bool +v `usedIn` details = isExportedId v || v `elemVarEnv` details tagBinders :: UsageDetails -- Of scope -> [Id] -- Binders -> (UsageDetails, -- Details with binders removed - [(Id,BinderInfo)]) -- Tagged binders - -tagBinders usage binders = - let - usage' = usage `delManyFromIdEnv` binders - uss = [ (binder, usage_of usage binder) | binder <- binders ] - in - if isNullIdEnv usage' then - (usage', uss) - else - (usage', uss) -{- - = (usage `delManyFromIdEnv` binders, - [ (binder, usage_of usage binder) | binder <- binders ] - ) --} + [IdWithOccInfo]) -- Tagged binders + +tagBinders usage binders + = let + usage' = usage `delVarEnvList` binders + uss = map (setBinderOcc usage) binders + in + usage' `seq` (usage', uss) + tagBinder :: UsageDetails -- Of scope -> Id -- Binders -> (UsageDetails, -- Details with binders removed - (Id,BinderInfo)) -- Tagged binders - -tagBinder usage binder = - let - usage' = usage `delOneFromIdEnv` binder - us = usage_of usage binder - cont = - if isNullIdEnv usage' then -- Bogus test to force evaluation. - (usage', (binder, us)) - else - (usage', (binder, us)) - in - if isDeadOcc us then -- Ditto - cont - else - cont - - -usage_of usage binder - | isExported binder || isSpecPragmaId binder - = noBinderInfo -- Visible-elsewhere things count as many - | otherwise - = case (lookupIdEnv usage binder) of - Nothing -> deadOccurrence - Just info -> info - -isNeeded env usage binder = not (isDeadOcc (usage_of usage binder)) + IdWithOccInfo) -- Tagged binders + +tagBinder usage binder + = let + usage' = usage `delVarEnv` binder + binder' = setBinderOcc usage binder + in + usage' `seq` (usage', binder') + +setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr +setBinderOcc usage bndr + | isTyVar bndr = bndr + | isExportedId bndr = case idOccInfo bndr of + NoOccInfo -> bndr + other -> setIdOccInfo bndr NoOccInfo + -- Don't use local usage info for visible-elsewhere things + -- BUT *do* erase any IAmALoopBreaker annotation, because we're + -- about to re-generate it and it shouldn't be "sticky" + + | otherwise = setIdOccInfo bndr occ_info + where + occ_info = lookupVarEnv usage bndr `orElse` IAmDead \end{code} +%************************************************************************ +%* * +\subsection{Operations over OccInfo} +%* * +%************************************************************************ + +\begin{code} +mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails +mkOneOcc env id int_cxt + | isLocalId id = unitVarEnv id (OneOcc False True int_cxt) + | otherwise = emptyDetails + +markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo + +markMany IAmDead = IAmDead +markMany other = NoOccInfo + +markInsideSCC occ = markMany occ + +markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt +markInsideLam occ = occ + +addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo + +addOccInfo IAmDead info2 = info2 +addOccInfo info1 IAmDead = info1 +addOccInfo info1 info2 = NoOccInfo + +-- (orOccInfo orig new) is used +-- when combining occurrence info from branches of a case + +orOccInfo IAmDead info2 = info2 +orOccInfo info1 IAmDead = info1 +orOccInfo (OneOcc in_lam1 one_branch1 int_cxt1) + (OneOcc in_lam2 one_branch2 int_cxt2) + = OneOcc (in_lam1 || in_lam2) + False -- False, because it occurs in both branches + (int_cxt1 && int_cxt2) + +orOccInfo info1 info2 = NoOccInfo +\end{code}