X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=fb7257739f6168482dbd46a6e90e205dd3b62de5;hb=08652e67c4d5d9a40687f93c286021a867c1bca0;hp=77c586158bbe13b8d17b7a2069d4ade849f4dfd9;hpb=ad94d40948668032189ad22a0ad741ac1f645f50;p=ghc-hetmet.git diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs index 77c5861..fb72577 100644 --- a/compiler/simplCore/OccurAnal.lhs +++ b/compiler/simplCore/OccurAnal.lhs @@ -2,47 +2,37 @@ % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % %************************************************************************ -%* * +%* * \section[OccurAnal]{Occurrence analysis pass} -%* * +%* * %************************************************************************ The occurrence analyser re-typechecks a core expression, returning a new core expression with (hopefully) improved usage information. \begin{code} -{-# OPTIONS -w #-} --- The above warning supression flag is a temporary kludge. --- While working on this module you are encouraged to remove it and fix --- any warnings in the module. See --- http://hackage.haskell.org/trac/ghc/wiki/CodingStyle#Warnings --- for details - module OccurAnal ( - occurAnalysePgm, occurAnalyseExpr + occurAnalysePgm, occurAnalyseExpr ) where #include "HsVersions.h" import CoreSyn -import CoreFVs ( idRuleVars ) -import CoreUtils ( exprIsTrivial, isDefaultAlt ) -import Id ( isDataConWorkId, isOneShotBndr, setOneShotLambda, - idOccInfo, setIdOccInfo, isLocalId, - isExportedId, idArity, idHasRules, - idUnique, Id - ) -import BasicTypes ( OccInfo(..), isOneOcc, InterestingCxt ) +import CoreFVs +import CoreUtils ( exprIsTrivial, isDefaultAlt ) +import Id +import IdInfo +import BasicTypes import VarSet import VarEnv -import Maybes ( orElse ) -import Digraph ( stronglyConnCompR, SCC(..) ) -import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey ) -import Unique ( Unique ) -import UniqFM ( keysUFM, intersectsUFM ) -import Util ( mapAndUnzip ) +import Maybes ( orElse ) +import Digraph ( stronglyConnCompR, SCC(..) ) +import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey ) +import Unique ( Unique ) +import UniqFM ( keysUFM, intersectUFM_C, foldUFM_Directly ) +import Util ( mapAndUnzip ) import Outputable import Data.List @@ -50,9 +40,9 @@ import Data.List %************************************************************************ -%* * +%* * \subsection[OccurAnal-main]{Counting occurrences: main function} -%* * +%* * %************************************************************************ Here's the externally-callable interface: @@ -63,24 +53,24 @@ occurAnalysePgm binds = snd (go initOccEnv binds) where 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 + go _ [] + = (emptyDetails, []) + go env (bind:binds) + = (final_usage, bind' ++ binds') + where + (bs_usage, binds') = go env binds + (final_usage, bind') = occAnalBind env bind bs_usage occurAnalyseExpr :: CoreExpr -> CoreExpr - -- Do occurrence analysis, and discard occurence info returned + -- Do occurrence analysis, and discard occurence info returned occurAnalyseExpr expr = snd (occAnal initOccEnv expr) \end{code} %************************************************************************ -%* * +%* * \subsection[OccurAnal-main]{Counting occurrences: main function} -%* * +%* * %************************************************************************ Bindings @@ -88,144 +78,343 @@ Bindings \begin{code} occAnalBind :: OccEnv - -> CoreBind - -> UsageDetails -- Usage details of scope - -> (UsageDetails, -- Of the whole let(rec) - [CoreBind]) + -> CoreBind + -> UsageDetails -- Usage details of scope + -> (UsageDetails, -- Of the whole let(rec) + [CoreBind]) occAnalBind env (NonRec binder rhs) body_usage - | not (binder `usedIn` body_usage) -- It's not mentioned + | not (binder `usedIn` body_usage) -- It's not mentioned = (body_usage, []) - | otherwise -- It's mentioned in the body - = (body_usage' +++ addRuleUsage rhs_usage binder, -- Note [RulesOnly] + | otherwise -- It's mentioned in the body + = (body_usage' +++ addRuleUsage rhs_usage binder, -- Note [Rules are extra RHSs] [NonRec tagged_binder rhs']) where (body_usage', tagged_binder) = tagBinder body_usage binder - (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs + (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs \end{code} +Note [Dead code] +~~~~~~~~~~~~~~~~ Dropping dead code for recursive bindings is done in a very simple way: - the entire set of bindings is dropped if none of its binders are - mentioned in its body; otherwise none are. + the entire set of bindings is dropped if none of its binders are + mentioned in its body; otherwise none are. This seems to miss an obvious improvement. -@ - letrec f = ...g... - g = ...f... - in - ...g... + letrec f = ...g... + g = ...f... + in + ...g... ===> + letrec f = ...g... + g = ...(...g...)... + in + ...g... + +Now 'f' is unused! But it's OK! Dependency analysis will sort this +out into a letrec for 'g' and a 'let' for 'f', and then 'f' will get +dropped. It isn't easy to do a perfect job in one blow. Consider + + letrec f = ...g... + g = ...h... + h = ...k... + k = ...m... + m = ...m... + in + ...m... + + +Note [Loop breaking and RULES] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Loop breaking is surprisingly subtle. First read the section 4 of +"Secrets of the GHC inliner". This describes our basic plan. + +However things are made quite a bit more complicated by RULES. Remember + + * Note [Rules are extra RHSs] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~ + A RULE for 'f' is like an extra RHS for 'f'. 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). + + To that end, we build a Rec group for each cyclic strongly + connected component, + *treating f's rules as extra RHSs for 'f'*. + + When we make the Rec groups we include variables free in *either* + LHS *or* RHS of the rule. The former might seems silly, but see + Note [Rule dependency info]. + + So in Example [eftInt], eftInt and eftIntFB will be put in the + same Rec, even though their 'main' RHSs are both non-recursive. + + * Note [Rules are visible in their own rec group] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + We want the rules for 'f' to be visible in f's right-hand side. + And we'd like them to be visible in other functions in f's Rec + group. E.g. in Example [Specialisation rules] we want f' rule + to be visible in both f's RHS, and fs's RHS. + + This means that we must simplify the RULEs first, before looking + at any of the definitions. This is done by Simplify.simplRecBind, + when it calls addLetIdInfo. + + * Note [Choosing loop breakers] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + We avoid infinite inlinings by choosing loop breakers, and + ensuring that a loop breaker cuts each loop. But what is a + "loop"? In particular, a RULES is like an equation for 'f' that + is *always* inlined if it are applicable. We do *not* disable + rules for loop-breakers. It's up to whoever makes the rules to + make sure that the rules themselves alwasys terminate. See Note + [Rules for recursive functions] in Simplify.lhs + + Hence, if + f's RHS mentions g, and + g has a RULE that mentions h, and + h has a RULE that mentions f + + then we *must* choose f to be a loop breaker. In general, take the + free variables of f's RHS, and augment it with all the variables + reachable by RULES from those starting points. That is the whole + reason for computing rule_fv_env in occAnalBind. (Of course we + only consider free vars that are also binders in this Rec group.) + + Note that when we compute this rule_fv_env, we only consider variables + free in the *RHS* of the rule, in contrast to the way we build the + Rec group in the first place (Note [Rule dependency info]) + + Note that in Example [eftInt], *neither* eftInt *nor* eftIntFB is + chosen as a loop breaker, because their RHSs don't mention each other. + And indeed both can be inlined safely. + + Note that the edges of the graph we use for computing loop breakers + are not the same as the edges we use for computing the Rec blocks. + That's why we compute + rec_edges for the Rec block analysis + loop_breaker_edges for the loop breaker analysis + + + * Note [Weak loop breakers] + ~~~~~~~~~~~~~~~~~~~~~~~~~ + There is a last nasty wrinkle. Suppose we have + + Rec { f = f_rhs + RULE f [] = g + + h = h_rhs + g = h + ...more... + } + + Remmber that we simplify the RULES before any RHS (see Note + [Rules are visible in their own rec group] above). + + So we must *not* postInlineUnconditionally 'g', even though + its RHS turns out to be trivial. (I'm assuming that 'g' is + not choosen as a loop breaker.) + + We "solve" this by making g a "weak" or "rules-only" loop breaker, + with OccInfo = IAmLoopBreaker True. A normal "strong" loop breaker + has IAmLoopBreaker False. So + + Inline postInlineUnconditinoally + IAmLoopBreaker False no no + IAmLoopBreaker True yes no + other yes yes + + The **sole** reason for this kind of loop breaker is so that + postInlineUnconditionally does not fire. Ugh. + + * Note [Rule dependency info] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~ + The VarSet in a SpecInfo is used for dependency analysis in the + occurrence analyser. We must track free vars in *both* lhs and rhs. Why both? + Consider + x = y + RULE f x = 4 + Then if we substitute y for x, we'd better do so in the + rule's LHS too, so we'd better ensure the dependency is respected + + +Example [eftInt] +~~~~~~~~~~~~~~~ +Example (from GHC.Enum): - letrec f = ...g... - g = ...(...g...)... - in - ...g... -@ + eftInt :: Int# -> Int# -> [Int] + eftInt x y = ...(non-recursive)... -Now @f@ is unused. But dependency analysis will sort this out into a -@letrec@ for @g@ and a @let@ for @f@, and then @f@ will get dropped. -It isn't easy to do a perfect job in one blow. Consider + {-# INLINE [0] eftIntFB #-} + eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r + eftIntFB c n x y = ...(non-recursive)... -@ - letrec f = ...g... - g = ...h... - h = ...k... - k = ...m... - m = ...m... - in - ...m... -@ + {-# RULES + "eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y) + "eftIntList" [1] eftIntFB (:) [] = eftInt + #-} + +Example [Specialisation rules] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this group, which is typical of what SpecConstr builds: + + fs a = ....f (C a).... + f x = ....f (C a).... + {-# RULE f (C a) = fs a #-} + +So 'f' and 'fs' are in the same Rec group (since f refers to fs via its RULE). + +But watch out! If 'fs' is not chosen as a loop breaker, we may get an infinite loop: + - the RULE is applied in f's RHS (see Note [Self-recursive rules] in Simplify + - fs is inlined (say it's small) + - now there's another opportunity to apply the RULE + +This showed up when compiling Control.Concurrent.Chan.getChanContents. \begin{code} occAnalBind env (Rec pairs) body_usage - = foldr ({-# SCC "occAnalBind.dofinal" #-} do_final_bind) (body_usage, []) sccs + = foldr occAnalRec (body_usage, []) sccs + -- For a recursive group, we + -- * occ-analyse all the RHSs + -- * compute strongly-connected components + -- * feed those components to occAnalRec where - analysed_pairs :: [Details] - analysed_pairs = [ (bndr, rhs_usage, rhs') - | (bndr, rhs) <- pairs, - let (rhs_usage, rhs') = occAnalRhs env bndr rhs - ] + -------------Dependency analysis ------------------------------ + bndr_set = mkVarSet (map fst pairs) sccs :: [SCC (Node Details)] - sccs = {-# SCC "occAnalBind.scc" #-} stronglyConnCompR edges - - - ---- stuff for dependency analysis of binds ------------------------------- - edges :: [Node Details] - edges = {-# SCC "occAnalBind.assoc" #-} - [ (details, idUnique id, edges_from id rhs_usage) - | details@(id, rhs_usage, rhs) <- analysed_pairs - ] - - -- (a -> b) means a mentions b - -- Given the usage details (a UFM that gives occ info for each free var of - -- the RHS) we can get the list of free vars -- or rather their Int keys -- - -- by just extracting the keys from the finite map. Grimy, but fast. - -- Previously we had this: - -- [ bndr | bndr <- bndrs, - -- maybeToBool (lookupVarEnv rhs_usage bndr)] - -- which has n**2 cost, and this meant that edges_from alone - -- consumed 10% of total runtime! - edges_from :: Id -> UsageDetails -> [Unique] - edges_from bndr rhs_usage = {-# SCC "occAnalBind.edges_from" #-} - keysUFM (addRuleUsage rhs_usage bndr) - - ---- Stuff to "re-constitute" bindings from dependency-analysis info ------ - - -- Non-recursive SCC - do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far) - | not (bndr `usedIn` body_usage) - = (body_usage, binds_so_far) -- Dead code - | otherwise - = (body_usage' +++ addRuleUsage rhs_usage bndr, new_bind : binds_so_far) - where - (body_usage', tagged_bndr) = tagBinder body_usage bndr - new_bind = NonRec tagged_bndr rhs' - - -- Recursive SCC - do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far) - | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage - = (body_usage, binds_so_far) -- Dead code - | otherwise -- If any is used, they all are - = (final_usage, final_bind : binds_so_far) + sccs = {-# SCC "occAnalBind.scc" #-} stronglyConnCompR rec_edges + + rec_edges :: [Node Details] + rec_edges = {-# SCC "occAnalBind.assoc" #-} map make_node pairs + + make_node (bndr, rhs) + = (ND bndr rhs' rhs_usage rhs_fvs, idUnique bndr, out_edges) + where + (rhs_usage, rhs') = occAnalRhs env bndr rhs + rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage + out_edges = keysUFM (rhs_fvs `unionVarSet` idRuleVars bndr) + -- (a -> b) means a mentions b + -- Given the usage details (a UFM that gives occ info for each free var of + -- the RHS) we can get the list of free vars -- or rather their Int keys -- + -- by just extracting the keys from the finite map. Grimy, but fast. + -- Previously we had this: + -- [ bndr | bndr <- bndrs, + -- maybeToBool (lookupVarEnv rhs_usage bndr)] + -- which has n**2 cost, and this meant that edges_from alone + -- consumed 10% of total runtime! + +----------------------------- +occAnalRec :: SCC (Node Details) -> (UsageDetails, [CoreBind]) + -> (UsageDetails, [CoreBind]) + + -- The NonRec case is just like a Let (NonRec ...) above +occAnalRec (AcyclicSCC (ND bndr rhs rhs_usage _, _, _)) (body_usage, binds) + | not (bndr `usedIn` body_usage) + = (body_usage, binds) + + | otherwise -- It's mentioned in the body + = (body_usage' +++ addRuleUsage rhs_usage bndr, -- Note [Rules are extra RHSs] + NonRec tagged_bndr rhs : binds) + where + (body_usage', tagged_bndr) = tagBinder body_usage bndr + + + -- The Rec case is the interesting one + -- See Note [Loop breaking] +occAnalRec (CyclicSCC nodes) (body_usage, binds) + | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage + = (body_usage, binds) -- Dead code + + | otherwise -- At this point we always build a single Rec + = (final_usage, Rec pairs : binds) + + where + bndrs = [b | (ND b _ _ _, _, _) <- nodes] + bndr_set = mkVarSet bndrs + + ---------------------------- + -- Tag the binders with their occurrence info + total_usage = foldl add_usage body_usage nodes + add_usage body_usage (ND bndr _ rhs_usage _, _, _) + = body_usage +++ addRuleUsage rhs_usage bndr + (final_usage, tagged_nodes) = mapAccumL tag_node total_usage nodes + + tag_node :: UsageDetails -> Node Details -> (UsageDetails, Node Details) + -- (a) Tag the binders in the details with occ info + -- (b) Mark the binder with "weak loop-breaker" OccInfo + -- saying "no preInlineUnconditionally" if it is used + -- in any rule (lhs or rhs) of the recursive group + -- See Note [Weak loop breakers] + tag_node usage (ND bndr rhs rhs_usage rhs_fvs, k, ks) + = (usage `delVarEnv` bndr, (ND bndr2 rhs rhs_usage rhs_fvs, k, ks)) where - details = [details | (details, _, _) <- cycle] - bndrs = [bndr | (bndr, _, _) <- details] - bndr_usages = [addRuleUsage rhs_usage bndr | (bndr, rhs_usage, _) <- details] - total_usage = foldr (+++) body_usage bndr_usages - (final_usage, tagged_cycle) = mapAccumL tag_bind total_usage cycle - tag_bind usg ((bndr,rhs_usg,rhs),k,ks) = (usg', ((bndr',rhs_usg,rhs),k,ks)) - where - (usg', bndr') = tagBinder usg bndr - final_bind = Rec (reOrderCycle (mkVarSet bndrs) tagged_cycle) - -{- An alternative; rebuild the edges. No semantic difference, but perf might change - - -- Hopefully 'bndrs' is a relatively small group now - -- Now get ready for the loop-breaking phase - -- We've done dead-code elimination already, so no worries about un-referenced binders - keys = map idUnique bndrs - mk_node tagged_bndr (_, rhs_usage, rhs') - = ((tagged_bndr, rhs'), idUnique tagged_bndr, used) - where - used = [key | key <- keys, used_outside_rule rhs_usage key ] - - used_outside_rule usage uniq = case lookupUFM_Directly usage uniq of - Nothing -> False - Just RulesOnly -> False -- Ignore rules - other -> True --} + bndr2 | bndr `elemVarSet` all_rule_fvs = makeLoopBreaker True bndr1 + | otherwise = bndr1 + bndr1 = setBinderOcc usage bndr + all_rule_fvs = bndr_set `intersectVarSet` foldr (unionVarSet . idRuleVars) + emptyVarSet bndrs + + ---------------------------- + -- Now reconstruct the cycle + pairs | no_rules = reOrderCycle tagged_nodes + | otherwise = concatMap reOrderRec (stronglyConnCompR loop_breaker_edges) + + -- See Note [Choosing loop breakers] for looop_breaker_edges + loop_breaker_edges = map mk_node tagged_nodes + mk_node (details@(ND _ _ _ rhs_fvs), k, _) = (details, k, new_ks) + where + new_ks = keysUFM (extendFvs rule_fv_env rhs_fvs rhs_fvs) + + ------------------------------------ + rule_fv_env :: IdEnv IdSet -- Variables from this group mentioned in RHS of rules + -- Domain is *subset* of bound vars (others have no rule fvs) + rule_fv_env = rule_loop init_rule_fvs + + no_rules = null init_rule_fvs + init_rule_fvs = [(b, rule_fvs) + | b <- bndrs + , let rule_fvs = idRuleRhsVars b `intersectVarSet` bndr_set + , not (isEmptyVarSet rule_fvs)] + + rule_loop :: [(Id,IdSet)] -> IdEnv IdSet -- Finds fixpoint + rule_loop fv_list + | no_change = env + | otherwise = rule_loop new_fv_list + where + env = mkVarEnv init_rule_fvs + (no_change, new_fv_list) = mapAccumL bump True fv_list + bump no_change (b,fvs) + | new_fvs `subVarSet` fvs = (no_change, (b,fvs)) + | otherwise = (False, (b,new_fvs `unionVarSet` fvs)) + where + new_fvs = extendFvs env emptyVarSet fvs + +idRuleRhsVars :: Id -> VarSet +-- Just the variables free on the *rhs* of a rule +-- See Note [Choosing loop breakers] +idRuleRhsVars id = foldr (unionVarSet . ruleRhsFreeVars) emptyVarSet (idCoreRules id) + +extendFvs :: IdEnv IdSet -> IdSet -> IdSet -> IdSet +-- (extendFVs env fvs s) returns (fvs `union` env(s)) +extendFvs env fvs id_set + = foldUFM_Directly add fvs id_set + where + add uniq _ fvs + = case lookupVarEnv_Directly env uniq of + Just fvs' -> fvs' `unionVarSet` fvs + Nothing -> fvs \end{code} @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic strongly connected component (there's guaranteed to be a cycle). It returns the -same pairs, but - a) in a better order, - b) with some of the Ids having a IAmALoopBreaker pragma +same pairs, but + a) in a better order, + b) with some of the Ids having a IAmALoopBreaker pragma The "loop-breaker" Ids are sufficient to break all cycles in the SCC. This means that the simplifier can guarantee not to loop provided it never records an inlining @@ -237,16 +426,16 @@ 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.] +[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 - a = b - b = \x. BIG - in - ...a...a...a.... + letrec + a = b + b = \x. BIG + in + ...a...a...a.... Re-ordering doesn't change the order of bindings, but there was no loop-breaker. @@ -258,146 +447,135 @@ Perhaps something cleverer would suffice. \begin{code} type Node details = (details, Unique, [Unique]) -- The Ints are gotten from the Unique, -- which is gotten from the Id. -type Details = (Id, UsageDetails, CoreExpr) - -reOrderRec :: IdSet -- Binders of this group - -> SCC (Node Details) - -> [(Id,CoreExpr)] +data Details = ND Id -- Binder + CoreExpr -- RHS + UsageDetails -- Full usage from RHS (*not* including rules) + IdSet -- Other binders from this Rec group mentioned on RHS + -- (derivable from UsageDetails but cached here) + +reOrderRec :: SCC (Node Details) + -> [(Id,CoreExpr)] -- Sorted into a plausible order. Enough of the Ids have --- IAmALoopBreaker pragmas that there are no loops left. -reOrderRec bndrs (AcyclicSCC ((bndr, _, rhs), _, _)) = [(bndr, rhs)] -reOrderRec bndrs (CyclicSCC cycle) = reOrderCycle bndrs cycle +-- IAmALoopBreaker pragmas that there are no loops left. +reOrderRec (AcyclicSCC (ND bndr rhs _ _, _, _)) = [(bndr, rhs)] +reOrderRec (CyclicSCC cycle) = reOrderCycle cycle -reOrderCycle :: IdSet -> [Node Details] -> [(Id,CoreExpr)] -reOrderCycle bndrs [] +reOrderCycle :: [Node Details] -> [(Id,CoreExpr)] +reOrderCycle [] = panic "reOrderCycle" -reOrderCycle bndrs [bind] -- Common case of simple self-recursion - = [(makeLoopBreaker bndrs rhs_usg bndr, rhs)] +reOrderCycle [bind] -- Common case of simple self-recursion + = [(makeLoopBreaker False bndr, rhs)] where - ((bndr, rhs_usg, rhs), _, _) = bind + (ND bndr rhs _ _, _, _) = bind -reOrderCycle bndrs (bind : binds) - = -- Choose a loop breaker, mark it no-inline, - -- do SCC analysis on the rest, and recursively sort them out - concatMap (reOrderRec bndrs) (stronglyConnCompR unchosen) ++ - [(makeLoopBreaker bndrs rhs_usg bndr, rhs)] +reOrderCycle (bind : binds) + = -- Choose a loop breaker, mark it no-inline, + -- do SCC analysis on the rest, and recursively sort them out + concatMap reOrderRec (stronglyConnCompR unchosen) ++ + [(makeLoopBreaker False bndr, rhs)] where (chosen_bind, unchosen) = choose_loop_breaker bind (score bind) [] binds - (bndr, rhs_usg, rhs) = chosen_bind + ND bndr rhs _ _ = chosen_bind - -- 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 + -- 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 + | 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 - sc = score bind - - score :: Node Details -> 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 - - | idHasRules bndr = 3 - -- Avoid things with specialisations; we'd like - -- to take advantage of them in the subsequent bindings - -- Also vital to avoid risk of divergence: - -- Note [Recursive rules] - - | inlineCandidate bndr rhs = 2 -- Likely to be inlined - -- Note [Inline candidates] - - | is_con_app rhs = 1 -- Data types help with cases - - | otherwise = 0 + | otherwise -- No lower so don't pick it + = choose_loop_breaker loop_bind loop_sc (bind : acc) binds + where + sc = score bind + + score :: Node Details -> Int -- Higher score => less likely to be picked as loop breaker + score (ND bndr rhs _ _, _, _) + | workerExists (idWorkerInfo bndr) = 10 + -- Note [Worker inline loop] + + | 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 + + | is_con_app rhs = 2 -- Data types help with cases + -- Note [conapp] + +-- If an Id is marked "never inline" then it makes a great loop breaker +-- The only reason for not checking that here is that it is rare +-- and I've never seen a situation where it makes a difference, +-- so it probably isn't worth the time to test on every binder +-- | isNeverActive (idInlinePragma bndr) = -10 + + | inlineCandidate bndr rhs = 1 -- Likely to be inlined + -- Note [Inline candidates] + + | 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) - -- - -- 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". - - -- Cheap and cheerful; the simplifer moves casts out of the way - -- The lambda case is important to spot x = /\a. C (f a) - -- which comes up when C is a dictionary constructor and - -- f is a default method. - -- Example: the instance for Show (ST s a) in GHC.ST - -- - -- However we *also* treat (\x. C p q) as a con-app-like thing, - -- Note [Closure conversion] + inlineCandidate _ (Note InlineMe _) = True + inlineCandidate id _ = isOneOcc (idOccInfo id) + + -- Note [conapp] + -- + -- It's really really important to inline dictionaries. Real + -- example (the Enum Ordering instance from GHC.Base): + -- + -- 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) + -- + -- 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". + -- Inlining dictionaries is really essential to unravelling + -- the loops in static numeric dictionaries, see GHC.Float. + + -- Cheap and cheerful; the simplifer moves casts out of the way + -- The lambda case is important to spot x = /\a. C (f a) + -- which comes up when C is a dictionary constructor and + -- f is a default method. + -- Example: the instance for Show (ST s a) in GHC.ST + -- + -- However we *also* treat (\x. C p q) as a con-app-like thing, + -- Note [Closure conversion] is_con_app (Var v) = isDataConWorkId v is_con_app (App f _) = is_con_app f - is_con_app (Lam b e) = is_con_app e + is_con_app (Lam _ e) = is_con_app e is_con_app (Note _ e) = is_con_app e - is_con_app other = False - -makeLoopBreaker :: VarSet -- Binders of this group - -> UsageDetails -- Usage of this rhs (neglecting rules) - -> Id -> Id --- Set the loop-breaker flag, recording whether the thing occurs only in --- the RHS of a RULE (in this recursive group) -makeLoopBreaker bndrs rhs_usg bndr - = setIdOccInfo bndr (IAmALoopBreaker rules_only) - where - rules_only = bndrs `intersectsUFM` rhs_usg + is_con_app _ = False + +makeLoopBreaker :: Bool -> Id -> Id +-- Set the loop-breaker flag +-- See Note [Weak loop breakers] +makeLoopBreaker weak bndr = setIdOccInfo bndr (IAmALoopBreaker weak) \end{code} -Note [Inline candidates] +Note [Worker inline loop] ~~~~~~~~~~~~~~~~~~~~~~~~ -At one point I gave is_con_app a higher score than inline-candidate, -on the grounds that "it's *really* helpful if dictionaries get inlined fast". -However a nofib run revealed no change if they were swapped so that -inline-candidate has the higher score. And it's important that it does, -else you can get a bad worker-wrapper split thus: +Never choose a wrapper as the loop breaker! Because +wrappers get auto-generated inlinings when importing, and +that can lead to an infinite inlining loop. For example: rec { - $wfoo x = ....foo x.... - - {-loop brk-} foo x = ...$wfoo x... - } -But we *want* the wrapper to be inlined! If it isn't, the interface -file sees the unfolding for $wfoo, and sees that foo is strict (and -hence it gets an auto-generated wrapper. Result: an infinite inlining -in the importing scope. So be a bit careful if you change this. A -good example is Tree.repTree in nofib/spectral/minimax. If is_con_app -has the higher score, then compiling Game.hs goes into an infinite loop. - -Note [Recursive rules] -~~~~~~~~~~~~~~~~~~~~~~ -Consider this group, which is typical of what SpecConstr builds: + $wfoo x = ....foo x.... - fs a = ....f (C a).... - f x = ....f (C a).... - {-# RULE f (C a) = fs a #-} - -So 'f' and 'fs' are mutually recursive. If we choose 'fs' as the loop breaker, -all is well; the RULE is applied, and 'fs' becomes self-recursive. + {-loop brk-} foo x = ...$wfoo x... + } -But if we choose 'f' as the loop breaker, we may get an infinite loop: - - the RULE is applied in f's RHS (see Note [Self-recursive rules] in Simplify - - fs is inlined (say it's small) - - now there's another opportunity to apply the RULE - -So it's very important to choose the RULE-variable as the loop breaker. -This showed up when compiling Control.Concurrent.Chan.getChanContents. +The interface file sees the unfolding for $wfoo, and sees that foo is +strict (and hence it gets an auto-generated wrapper). Result: an +infinite inlining in the importing scope. So be a bit careful if you +change this. A good example is Tree.repTree in +nofib/spectral/minimax. If the repTree wrapper is chosen as the loop +breaker then compiling Game.hs goes into an infinite loop (this +happened when we gave is_con_app a lower score than inline candidates). Note [Closure conversion] ~~~~~~~~~~~~~~~~~~~~~~~~~ @@ -414,8 +592,8 @@ which generated code like this: ; plus1 _ n = Clo plus2 n - ; plus2 Zero n = n - ; plus2 (Succ m) n = Succ (plus $: m $: n) } + ; plus2 Zero n = n + ; plus2 (Succ m) n = Succ (plus $: m $: n) } If we inline 'plus' and 'plus1', everything unravels nicely. But if we choose 'plus1' as the loop breaker (which is entirely possible @@ -435,92 +613,62 @@ ToDo: try using the occurrence info for the inline'd binder. \begin{code} occAnalRhs :: OccEnv - -> Id -> CoreExpr -- Binder and rhs - -- For non-recs the binder is alrady tagged - -- with occurrence info - -> (UsageDetails, CoreExpr) + -> Id -> CoreExpr -- Binder and rhs + -- For non-recs the binder is alrady tagged + -- with occurrence info + -> (UsageDetails, CoreExpr) occAnalRhs env id rhs = occAnal ctxt rhs where 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... + | 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 + OneOcc in_lam one_br _ -> not in_lam && one_br + _ -> False \end{code} -Note [RulesOnly] -~~~~~~~~~~~~~~~~~~ -If the binder has RULES 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. - -That's the basic idea. However in a recursive situation we want to be a bit -cleverer. Example (from GHC.Enum): - - eftInt :: Int# -> Int# -> [Int] - eftInt x y = ...(non-recursive)... - - {-# INLINE [0] eftIntFB #-} - eftIntFB :: (Int -> r -> r) -> r -> Int# -> Int# -> r - eftIntFB c n x y = ...(non-recursive)... - - {-# RULES - "eftInt" [~1] forall x y. eftInt x y = build (\ c n -> eftIntFB c n x y) - "eftIntList" [1] eftIntFB (:) [] = eftInt - #-} - -The two look mutually recursive only because of their RULES; we don't want -that to inhibit inlining! - -So when we identify a LoopBreaker, we mark it to say whether it only mentions -the other binders in its recursive group in a RULE. If so, we can inline it, -because doing so will not expose new occurrences of binders in its group. \begin{code} - addRuleUsage :: UsageDetails -> Id -> UsageDetails -- Add the usage from RULES in Id to the usage addRuleUsage usage id = foldVarSet add usage (idRuleVars id) where - 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 + 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} Expressions ~~~~~~~~~~~ \begin{code} occAnal :: OccEnv - -> CoreExpr - -> (UsageDetails, -- Gives info only about the "interesting" Ids - CoreExpr) + -> CoreExpr + -> (UsageDetails, -- Gives info only about the "interesting" Ids + CoreExpr) -occAnal env (Type t) = (emptyDetails, Type t) +occAnal _ (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 + -- But 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. @@ -530,8 +678,8 @@ We regard variables that occur as constructor arguments as "dangerousToDup": \begin{verbatim} module A where -f x = let y = expensive x in - let z = (True,y) in +f x = let y = expensive x in + let z = (True,y) in (case z of {(p,q)->q}, case z of {(p,q)->q}) \end{verbatim} @@ -542,16 +690,16 @@ If we aren't careful we duplicate the (expensive x) call! Constructors are rather like lambdas in this way. \begin{code} -occAnal env expr@(Lit lit) = (emptyDetails, expr) +occAnal _ expr@(Lit _) = (emptyDetails, expr) \end{code} \begin{code} occAnal env (Note InlineMe body) - = case occAnal env body of { (usage, body') -> + = case occAnal env body of { (usage, body') -> (mapVarEnv markMany usage, Note InlineMe body') } -occAnal env (Note note@(SCC cc) body) +occAnal env (Note note@(SCC _) body) = case occAnal env body of { (usage, body') -> (mapVarEnv markInsideSCC usage, Note note body') } @@ -564,27 +712,27 @@ occAnal env (Note note body) occAnal env (Cast expr co) = case occAnal env expr of { (usage, expr') -> (markRhsUds env True usage, Cast expr' co) - -- If we see let x = y `cast` co - -- then mark y as 'Many' so that we don't - -- immediately inline y again. + -- If we see let x = y `cast` co + -- then mark y as 'Many' so that we don't + -- immediately inline y again. } \end{code} \begin{code} -occAnal env app@(App fun arg) - = occAnalApp env (collectArgs app) False +occAnal env app@(App _ _) + = occAnalApp env (collectArgs app) -- 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 +occAnal env (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...) +-- (\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. @@ -596,63 +744,64 @@ 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 + -- 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 - env_body = vanillaCtxt -- Body is (no longer) an RhsContext + env_body = vanillaCtxt -- Body is (no longer) an RhsContext (binders, body) = collectBinders expr - binders' = oneShotGroup env binders - linear = all is_one_shot binders' + 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 alt_env bndr) alts of { (alts_usage_s, alts') -> + = case occ_anal_scrut scrut alts of { (scrut_usage, scrut') -> + case mapAndUnzip (occAnalAlt alt_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 + alts_usage = foldr1 combineAltsUsageDetails alts_usage_s + alts_usage' = addCaseBndrUsage alts_usage + (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr total_usage = scrut_usage +++ alts_usage1 in total_usage `seq` (total_usage, Case scrut' tagged_bndr ty alts') }} where - -- 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) } + -- 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) + Nothing -> usage + Just occ -> extendVarEnv usage bndr (markMany occ) alt_env = setVanillaCtxt env - -- Consider x = case v of { True -> (p,q); ... } - -- Then it's fine to inline p and q + -- Consider x = case v of { True -> (p,q); ... } + -- Then it's fine to inline p and q 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 + | 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 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, mkLets new_binds body') }} -occAnalArgs env args - = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') -> +occAnalArgs :: OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr]) +occAnalArgs _env args + = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') -> (foldr (+++) emptyDetails arg_uds_s, args')} where arg_env = vanillaCtxt @@ -662,7 +811,10 @@ Applications are dealt with specially because we want the "build hack" to work. \begin{code} -occAnalApp env (Var fun, args) is_rhs +occAnalApp :: OccEnv + -> (Expr CoreBndr, [Arg CoreBndr]) + -> (UsageDetails, Expr CoreBndr) +occAnalApp env (Var fun, args) = case args_stuff of { (args_uds, args') -> let final_args_uds = markRhsUds env is_pap args_uds @@ -673,41 +825,41 @@ occAnalApp env (Var fun, args) is_rhs fun_uds = mkOneOcc env fun (valArgCount args > 0) is_pap = isDataConWorkId fun || valArgCount args < idArity fun - -- Hack for build, fold, runST - 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') -> + -- Hack for build, fold, runST + 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) + = 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 +++ args_uds + final_uds = fun_uds +++ args_uds in (final_uds, mkApps fun' args') }} - -markRhsUds :: OccEnv -- Check if this is a RhsEnv - -> Bool -- and this is true - -> UsageDetails -- The do markMany on this - -> UsageDetails --- We mark the free vars of the argument of a constructor or PAP + +markRhsUds :: OccEnv -- Check if this is a RhsEnv + -> Bool -- and this is true + -> UsageDetails -- The do markMany on this + -> UsageDetails +-- 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 @@ -716,57 +868,61 @@ markRhsUds :: OccEnv -- Check if this is a RhsEnv -- This is the *whole point* of the isRhsEnv predicate markRhsUds env is_pap arg_uds | isRhsEnv env && is_pap = mapVarEnv markMany arg_uds - | otherwise = arg_uds + | otherwise = arg_uds -appSpecial :: OccEnv - -> Int -> CtxtTy -- Argument number, and context to use for it - -> [CoreExpr] - -> (UsageDetails, [CoreExpr]) +appSpecial :: OccEnv + -> Int -> CtxtTy -- Argument number, and context to use for it + -> [CoreExpr] + -> (UsageDetails, [CoreExpr]) appSpecial env n ctxt args = go n args where arg_env = vanillaCtxt - go n [] = (emptyDetails, []) -- Too few args + go _ [] = (emptyDetails, []) -- Too few args + + 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') -> + (arg_uds +++ args_uds, arg':args') }} - 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') -> - (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') -> - (arg_uds +++ args_uds, arg':args') }} + = case occAnal arg_env arg of { (arg_uds, arg') -> + case go (n-1) args of { (args_uds, args') -> + (arg_uds +++ args_uds, arg':args') }} \end{code} - + Case alternatives ~~~~~~~~~~~~~~~~~ -If the case binder occurs at all, the other binders effectively do too. +If the case binder occurs at all, the other binders effectively do too. For example - case e of x { (a,b) -> rhs } + case e of x { (a,b) -> rhs } is rather like - let x = (a,b) in rhs + 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 + let a = e1; b = e2; x = (a,b) in rhs Note [Aug 06]: I don't think this is necessary any more, and it helpe - to know when binders are unused. See esp the call to - isDeadBinder in Simplify.mkDupableAlt + to know when binders are unused. See esp the call to + isDeadBinder in Simplify.mkDupableAlt \begin{code} -occAnalAlt env case_bndr (con, bndrs, rhs) +occAnalAlt :: OccEnv + -> CoreBndr + -> CoreAlt + -> (UsageDetails, Alt IdWithOccInfo) +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 = tagged_bndrs -- See Note [Aug06] above + final_bndrs = tagged_bndrs -- See Note [Aug06] above {- - 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 + 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')) } @@ -774,90 +930,95 @@ occAnalAlt env case_bndr (con, bndrs, rhs) %************************************************************************ -%* * +%* * \subsection[OccurAnal-types]{OccEnv} -%* * +%* * %************************************************************************ \begin{code} data OccEnv - = OccEnv OccEncl -- Enclosing context information - CtxtTy -- Tells about linearity + = 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 +-- 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 + = 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 + -- [] 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 initOccEnv :: OccEnv initOccEnv = OccEnv OccRhs [] +vanillaCtxt :: OccEnv vanillaCtxt = OccEnv OccVanilla [] + +rhsCtxt :: OccEnv rhsCtxt = OccEnv OccRhs [] +isRhsEnv :: OccEnv -> Bool isRhsEnv (OccEnv OccRhs _) = True isRhsEnv (OccEnv OccVanilla _) = False setVanillaCtxt :: OccEnv -> OccEnv setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty -setVanillaCtxt other_env = other_env +setVanillaCtxt other_env = other_env setCtxt :: OccEnv -> CtxtTy -> OccEnv setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt 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 + -- 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 -oneShotGroup (OccEnv encl ctxt) bndrs +oneShotGroup (OccEnv _encl ctxt) bndrs = go ctxt bndrs [] where - go ctxt [] rev_bndrs = reverse rev_bndrs + go _ [] rev_bndrs = reverse rev_bndrs go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs - | isId bndr = go ctxt bndrs (bndr':rev_bndrs) - where - bndr' | lin_ctxt = setOneShotLambda bndr - | otherwise = bndr + | 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) -addAppCtxt (OccEnv encl ctxt) args +addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv +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 +type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage (+++), combineAltsUsageDetails - :: UsageDetails -> UsageDetails -> UsageDetails + :: UsageDetails -> UsageDetails -> UsageDetails (+++) usage1 usage2 = plusVarEnv_C addOccInfo usage1 usage2 @@ -868,8 +1029,9 @@ combineAltsUsageDetails usage1 usage2 addOneOcc :: UsageDetails -> Id -> OccInfo -> UsageDetails addOneOcc usage id info = plusVarEnv_C addOccInfo usage (unitVarEnv id info) - -- ToDo: make this more efficient + -- ToDo: make this more efficient +emptyDetails :: UsageDetails emptyDetails = (emptyVarEnv :: UsageDetails) usedIn :: Id -> UsageDetails -> Bool @@ -877,10 +1039,10 @@ v `usedIn` details = isExportedId v || v `elemVarEnv` details type IdWithOccInfo = Id -tagBinders :: UsageDetails -- Of scope - -> [Id] -- Binders - -> (UsageDetails, -- Details with binders removed - [IdWithOccInfo]) -- Tagged binders +tagBinders :: UsageDetails -- Of scope + -> [Id] -- Binders + -> (UsageDetails, -- Details with binders removed + [IdWithOccInfo]) -- Tagged binders tagBinders usage binders = let @@ -889,10 +1051,10 @@ tagBinders usage binders in usage' `seq` (usage', uss) -tagBinder :: UsageDetails -- Of scope - -> Id -- Binders - -> (UsageDetails, -- Details with binders removed - IdWithOccInfo) -- Tagged binders +tagBinder :: UsageDetails -- Of scope + -> Id -- Binders + -> (UsageDetails, -- Details with binders removed + IdWithOccInfo) -- Tagged binders tagBinder usage binder = let @@ -905,12 +1067,12 @@ 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" - + NoOccInfo -> bndr + _ -> 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 @@ -918,42 +1080,42 @@ setBinderOcc usage bndr %************************************************************************ -%* * +%* * \subsection{Operations over OccInfo} -%* * +%* * %************************************************************************ \begin{code} mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails -mkOneOcc env id int_cxt +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 +markMany _ = NoOccInfo markInsideSCC occ = markMany occ markInsideLam (OneOcc _ one_br int_cxt) = OneOcc True one_br int_cxt -markInsideLam occ = occ +markInsideLam occ = occ addOccInfo, orOccInfo :: OccInfo -> OccInfo -> OccInfo addOccInfo IAmDead info2 = info2 addOccInfo info1 IAmDead = info1 -addOccInfo info1 info2 = NoOccInfo +addOccInfo _ _ = 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) +orOccInfo (OneOcc in_lam1 _ int_cxt1) + (OneOcc in_lam2 _ int_cxt2) = OneOcc (in_lam1 || in_lam2) - False -- False, because it occurs in both branches - (int_cxt1 && int_cxt2) -orOccInfo info1 info2 = NoOccInfo + False -- False, because it occurs in both branches + (int_cxt1 && int_cxt2) +orOccInfo _ _ = NoOccInfo \end{code}