X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=a37b5f16bddd97991e343d352f3d2175064d0f60;hp=91e34f879e48e75a2025fc78ebed6187555a536a;hb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516;hpb=72462499b891d5779c19f3bda03f96e24f9554ae diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs index 91e34f8..a37b5f1 100644 --- a/compiler/simplCore/OccurAnal.lhs +++ b/compiler/simplCore/OccurAnal.lhs @@ -19,23 +19,26 @@ module OccurAnal ( import CoreSyn import CoreFVs -import CoreUtils ( exprIsTrivial, isDefaultAlt ) -import Coercion ( mkSymCoercion ) +import Type ( tyVarsOfType ) +import CoreUtils ( exprIsTrivial, isDefaultAlt, mkCoerceI, isExpandableApp ) +import Coercion ( CoercionI(..), mkSymCoI ) import Id import Name ( localiseName ) import BasicTypes import VarSet import VarEnv +import Var ( Var, varUnique ) import Maybes ( orElse ) import Digraph ( SCC(..), stronglyConnCompFromEdgedVerticesR ) import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey ) import Unique ( Unique ) import UniqFM ( keysUFM, intersectUFM_C, foldUFM_Directly ) -import Util ( mapAndUnzip ) +import Util ( mapAndUnzip, filterOut ) +import Bag import Outputable - +import FastString import Data.List \end{code} @@ -63,7 +66,7 @@ occurAnalysePgm binds rules = (final_usage, bind' ++ binds') where (bs_usage, binds') = go env binds - (final_usage, bind') = occAnalBind env bind bs_usage + (final_usage, bind') = occAnalBind env env bind bs_usage occurAnalyseExpr :: CoreExpr -> CoreExpr -- Do occurrence analysis, and discard occurence info returned @@ -81,14 +84,15 @@ Bindings ~~~~~~~~ \begin{code} -occAnalBind :: OccEnv +occAnalBind :: OccEnv -- The incoming OccEnv + -> OccEnv -- Same, but trimmed by (binderOf bind) -> CoreBind -> UsageDetails -- Usage details of scope -> (UsageDetails, -- Of the whole let(rec) [CoreBind]) -occAnalBind env (NonRec binder rhs) body_usage - | isTyVar binder -- A type let; we don't gather usage info +occAnalBind env _ (NonRec binder rhs) body_usage + | isTyCoVar binder -- A type let; we don't gather usage info = (body_usage, [NonRec binder rhs]) | not (binder `usedIn` body_usage) -- It's not mentioned @@ -177,7 +181,7 @@ However things are made quite a bit more complicated by RULES. Remember "loop"? In particular, a RULE is like an equation for 'f' that is *always* inlined if it is 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 + make sure that the rules themselves always terminate. See Note [Rules for recursive functions] in Simplify.lhs Hence, if @@ -294,7 +298,7 @@ This showed up when compiling Control.Concurrent.Chan.getChanContents. \begin{code} -occAnalBind env (Rec pairs) body_usage +occAnalBind _ env (Rec pairs) body_usage = foldr occAnalRec (body_usage, []) sccs -- For a recursive group, we -- * occ-analyse all the RHSs @@ -311,12 +315,13 @@ occAnalBind env (Rec pairs) body_usage rec_edges = {-# SCC "occAnalBind.assoc" #-} map make_node pairs make_node (bndr, rhs) - = (ND bndr rhs' all_rhs_usage rhs_fvs, idUnique bndr, out_edges) + = (ND bndr rhs' all_rhs_usage rhs_fvs, varUnique bndr, out_edges) where (rhs_usage, rhs') = occAnalRhs env bndr rhs - all_rhs_usage = addRuleUsage rhs_usage bndr -- Note [Rules are extra RHSs] - rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage - out_edges = keysUFM (rhs_fvs `unionVarSet` idRuleVars bndr) + all_rhs_usage = addIdOccs rhs_usage rule_vars -- Note [Rules are extra RHSs] + rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage + out_edges = keysUFM (rhs_fvs `unionVarSet` rule_vars) + rule_vars = idRuleVars bndr -- See Note [Rule dependency info] -- (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 -- @@ -397,6 +402,7 @@ occAnalRec (CyclicSCC nodes) (body_usage, binds) no_rules = null init_rule_fvs init_rule_fvs = [(b, rule_fvs) | b <- bndrs + , isId b , let rule_fvs = idRuleRhsVars b `intersectVarSet` bndr_set , not (isEmptyVarSet rule_fvs)] @@ -526,23 +532,30 @@ reOrderCycle depth (bind : binds) pairs score :: Node Details -> Int -- Higher score => less likely to be picked as loop breaker score (ND bndr rhs _ _, _, _) - | exprIsTrivial rhs = 10 -- Practically certain to be inlined + | not (isId bndr) = 100 -- A type or cercion varialbe is never a loop breaker + + | isDFunId bndr = 9 -- Never choose a DFun as a loop breaker + -- Note [DFuns should not be loop breakers] + + | Just (inl_source, _) <- isInlineRule_maybe (idUnfolding bndr) + = case inl_source of + InlineWrapper {} -> 10 -- Note [INLINE pragmas] + _other -> 3 -- Data structures are more important than this + -- so that dictionary/method recursion unravels + -- Note that this case hits all InlineRule things, so we + -- never look at 'rhs for InlineRule stuff. That's right, because + -- 'rhs' is irrelevant for inlining things with an InlineRule + + | is_con_app rhs = 5 -- Data types help with cases: Note [Constructor applications] + + | exprIsTrivial rhs = 10 -- 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 - | Just inl_rule_info <- isInlineRule_maybe (idUnfolding bndr) - = case inl_rule_info of - InlWrapper {} -> 10 -- Note [INLINE pragmas] - _other -> 3 -- Data structures are more important than this - -- so that dictionary/method recursion unravels - - | is_con_app rhs = 5 -- Data types help with cases - -- Includes dict funs - -- Note [Constructor applictions] - + -- 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, @@ -551,12 +564,11 @@ reOrderCycle depth (bind : binds) pairs | isOneOcc (idOccInfo bndr) = 2 -- Likely to be inlined - | canUnfold (idUnfolding bndr) = 1 - -- the Id has some kind of unfolding + | canUnfold (realIdUnfolding bndr) = 1 + -- The Id has some kind of unfolding + -- Ignore loop-breaker-ness here because that is what we are setting! | otherwise = 0 - where - -- Checking for a constructor application -- Cheap and cheerful; the simplifer moves casts out of the way @@ -575,7 +587,8 @@ reOrderCycle depth (bind : binds) pairs makeLoopBreaker :: Bool -> Id -> Id -- Set the loop-breaker flag: see Note [Weak loop breakers] -makeLoopBreaker weak bndr = setIdOccInfo bndr (IAmALoopBreaker weak) +makeLoopBreaker weak bndr + = ASSERT2( isId bndr, ppr bndr ) setIdOccInfo bndr (IAmALoopBreaker weak) \end{code} Note [Complexity of loop breaking] @@ -615,13 +628,14 @@ linear in the number of instance declarations. Note [INLINE pragmas] ~~~~~~~~~~~~~~~~~~~~~ -Never choose a function with an INLINE pramga as the loop breaker! +Avoid choosing a function with an INLINE pramga as the loop breaker! If such a function is mutually-recursive with a non-INLINE thing, then the latter should be the loop-breaker. -A particular case is wrappers generated by the demand analyser. -If you make then into a loop breaker you may get an infinite -inlining loop. For example: +Usually this is just a question of optimisation. But a particularly +bad case is wrappers generated by the demand analyser: if you make +then into a loop breaker you may get an infinite inlining loop. For +example: rec { $wfoo x = ....foo x.... @@ -645,6 +659,24 @@ happened when we gave is_con_app a lower score than inline candidates: Here we do *not* want to choose 'repTree' as the loop breaker. +Note [DFuns should not be loop breakers] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +It's particularly bad to make a DFun into a loop breaker. See +Note [How instance declarations are translated] in TcInstDcls + +We give DFuns a higher score than ordinary CONLIKE things because +if there's a choice we want the DFun to be the non-looop breker. Eg + +rec { sc = /\ a \$dC. $fBWrap (T a) ($fCT @ a $dC) + + $fCT :: forall a_afE. (Roman.C a_afE) => Roman.C (Roman.T a_afE) + {-# DFUN #-} + $fCT = /\a \$dC. MkD (T a) ((sc @ a $dC) |> blah) ($ctoF @ a $dC) + } + +Here 'sc' (the superclass) looks CONLIKE, but we'll never get to it +if we can't unravel the DFun first. + Note [Constructor applications] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ It's really really important to inline dictionaries. Real @@ -704,7 +736,8 @@ occAnalRhs :: OccEnv -- Returned usage details includes any INLINE rhs occAnalRhs env id rhs - = (addIdOccs rhs_usage (idUnfoldingVars id), rhs') + | isId id = (addIdOccs rhs_usage (idUnfoldingVars id), rhs') + | otherwise = (rhs_usage, rhs') -- Include occurrences for the "extra RHS" from a CoreUnfolding where (rhs_usage, rhs') = occAnal ctxt rhs @@ -733,9 +766,11 @@ occAnalRhs env id rhs \begin{code} -addRuleUsage :: UsageDetails -> Id -> UsageDetails +addRuleUsage :: UsageDetails -> Var -> UsageDetails -- Add the usage from RULES in Id to the usage -addRuleUsage usage id = addIdOccs usage (idRuleVars id) +addRuleUsage usage var + | isId var = addIdOccs usage (idRuleVars var) + | otherwise = usage -- idRuleVars here: see Note [Rule dependency info] addIdOccs :: UsageDetails -> VarSet -> UsageDetails @@ -800,7 +835,7 @@ occAnal env (Note note body) occAnal env (Cast expr co) = case occAnal env expr of { (usage, expr') -> - (markRhsUds env True usage, Cast expr' co) + (markManyIf (isRhsEnv env) 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. @@ -815,7 +850,7 @@ occAnal env app@(App _ _) -- (a) occurrences inside type lambdas only not marked as InsideLam -- (b) type variables not in environment -occAnal env (Lam x body) | isTyVar x +occAnal env (Lam x body) | isTyCoVar x = case occAnal env body of { (body_usage, body') -> (body_usage, Lam x body') } @@ -847,7 +882,8 @@ occAnal env expr@(Lam _ _) (really_final_usage, mkLams tagged_binders body') } where - env_body = vanillaCtxt env -- Body is (no longer) an RhsContext + env_body = vanillaCtxt (trimOccEnv env binders) + -- Body is (no longer) an RhsContext (binders, body) = collectBinders expr binders' = oneShotGroup env binders linear = all is_one_shot binders' @@ -877,16 +913,8 @@ occAnal env (Case scrut bndr ty alts) Nothing -> (usage, setIdOccInfo bndr IAmDead) Just _ -> (usage `delVarEnv` bndr, setIdOccInfo bndr NoOccInfo) - alt_env = mkAltEnv env bndr_swap - -- Consider x = case v of { True -> (p,q); ... } - -- Then it's fine to inline p and q - - bndr_swap = case scrut of - Var v -> Just (v, Var bndr) - Cast (Var v) co -> Just (v, Cast (Var bndr) (mkSymCoercion co)) - _other -> Nothing - - occ_anal_alt = occAnalAlt alt_env bndr bndr_swap + alt_env = mkAltEnv env scrut bndr + occ_anal_alt = occAnalAlt alt_env bndr occ_anal_scrut (Var v) (alt1 : other_alts) | not (null other_alts) || not (isDefaultAlt alt1) @@ -897,9 +925,11 @@ occAnal env (Case scrut bndr ty alts) = occAnal (vanillaCtxt env) scrut -- No need for rhsCtxt occAnal env (Let bind body) - = case occAnal env body of { (body_usage, body') -> - case occAnalBind env bind body_usage of { (final_usage, new_binds) -> + = case occAnal env_body body of { (body_usage, body') -> + case occAnalBind env env_body bind body_usage of { (final_usage, new_binds) -> (final_usage, mkLets new_binds body') }} + where + env_body = trimOccEnv env (bindersOf bind) occAnalArgs :: OccEnv -> [CoreExpr] -> (UsageDetails, [CoreExpr]) occAnalArgs env args @@ -919,14 +949,23 @@ occAnalApp :: OccEnv occAnalApp env (Var fun, args) = case args_stuff of { (args_uds, args') -> let - final_args_uds = markRhsUds env is_pap args_uds + final_args_uds = markManyIf (isRhsEnv env && is_exp) args_uds + -- 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 in (fun_uds +++ final_args_uds, mkApps (Var fun) args') } where fun_uniq = idUnique fun fun_uds = mkOneOcc env fun (valArgCount args > 0) - is_pap = isConLikeId fun || valArgCount args < idArity fun + is_exp = isExpandableApp fun (valArgCount args) -- See Note [CONLIKE pragma] in BasicTypes + -- The definition of is_exp should match that in + -- Simplify.prepareRhs -- Hack for build, fold, runST args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args @@ -958,21 +997,11 @@ occAnalApp env (fun, args) (final_uds, mkApps fun' args') }} -markRhsUds :: OccEnv -- Check if this is a RhsEnv - -> Bool -- and this is true - -> UsageDetails -- The do markMany on this +markManyIf :: Bool -- If this is true + -> UsageDetails -- Then 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 --- arguments are just variables, or trivial expressions. --- --- 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 - +markManyIf True uds = mapVarEnv markMany uds +markManyIf False uds = uds appSpecial :: OccEnv -> Int -> CtxtTy -- Argument number, and context to use for it @@ -997,6 +1026,192 @@ appSpecial env n ctxt args \end{code} +Note [Binders in case alternatives] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + case x of y { (a,b) -> f y } +We treat 'a', 'b' as dead, because they don't physically occur in the +case alternative. (Indeed, a variable is dead iff it doesn't occur in +its scope in the output of OccAnal.) It really helps to know when +binders are unused. See esp the call to isDeadBinder in +Simplify.mkDupableAlt + +In this example, though, the Simplifier will bring 'a' and 'b' back to +life, beause it binds 'y' to (a,b) (imagine got inlined and +scrutinised y). + +\begin{code} +occAnalAlt :: OccEnv + -> CoreBndr + -> CoreAlt + -> (UsageDetails, Alt IdWithOccInfo) +occAnalAlt env case_bndr (con, bndrs, rhs) + = let + env' = trimOccEnv env bndrs + in + case occAnal env' rhs of { (rhs_usage1, rhs1) -> + let + proxies = getProxies env' case_bndr + (rhs_usage2, rhs2) = foldrBag wrapProxy (rhs_usage1, rhs1) proxies + (alt_usg, tagged_bndrs) = tagLamBinders rhs_usage2 bndrs + bndrs' = tagged_bndrs -- See Note [Binders in case alternatives] + in + (alt_usg, (con, bndrs', rhs2)) } + +wrapProxy :: ProxyBind -> (UsageDetails, CoreExpr) -> (UsageDetails, CoreExpr) +wrapProxy (bndr, rhs_var, co) (body_usg, body) + | not (bndr `usedIn` body_usg) + = (body_usg, body) + | otherwise + = (body_usg' +++ rhs_usg, Let (NonRec tagged_bndr rhs) body) + where + (body_usg', tagged_bndr) = tagBinder body_usg bndr + rhs_usg = unitVarEnv rhs_var NoOccInfo -- We don't need exact info + rhs = mkCoerceI co (Var rhs_var) +\end{code} + + +%************************************************************************ +%* * + OccEnv +%* * +%************************************************************************ + +\begin{code} +data OccEnv + = OccEnv { occ_encl :: !OccEncl -- Enclosing context information + , occ_ctxt :: !CtxtTy -- Tells about linearity + , occ_proxy :: ProxyEnv } + + +----------------------------- +-- 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 + +instance Outputable OccEncl where + ppr OccRhs = ptext (sLit "occRhs") + ppr OccVanilla = ptext (sLit "occVanilla") + +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 + +initOccEnv :: OccEnv +initOccEnv = OccEnv { occ_encl = OccVanilla + , occ_ctxt = [] + , occ_proxy = PE emptyVarEnv emptyVarSet } + +vanillaCtxt :: OccEnv -> OccEnv +vanillaCtxt env = OccEnv { occ_encl = OccVanilla + , occ_ctxt = [] + , occ_proxy = occ_proxy env } + +rhsCtxt :: OccEnv -> OccEnv +rhsCtxt env = OccEnv { occ_encl = OccRhs, occ_ctxt = [] + , occ_proxy = occ_proxy env } + +setCtxtTy :: OccEnv -> CtxtTy -> OccEnv +setCtxtTy env ctxt = env { occ_ctxt = ctxt } + +isRhsEnv :: OccEnv -> Bool +isRhsEnv (OccEnv { occ_encl = OccRhs }) = True +isRhsEnv (OccEnv { occ_encl = OccVanilla }) = False + +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 + +oneShotGroup (OccEnv { occ_ctxt = ctxt }) bndrs + = go ctxt bndrs [] + where + 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 + + go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs) + +addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv +addAppCtxt env@(OccEnv { occ_ctxt = ctxt }) args + = env { occ_ctxt = replicate (valArgCount args) True ++ ctxt } +\end{code} + +%************************************************************************ +%* * + ProxyEnv +%* * +%************************************************************************ + +\begin{code} +data ProxyEnv + = PE (IdEnv (Id, [(Id,CoercionI)])) VarSet + -- Main env, and its free variables (of both range and domain) +\end{code} + +Note [ProxyEnv] +~~~~~~~~~~~~~~~ +The ProxyEnv keeps track of the connection between case binders and +scrutinee. Specifically, if + sc |-> (sc, [...(cb, co)...]) +is a binding in the ProxyEnv, then + cb = sc |> coi +Typically we add such a binding when encountering the case expression + case (sc |> coi) of cb { ... } + +Things to note: + * The domain of the ProxyEnv is the variable (or casted variable) + scrutinees of enclosing cases. This is additionally used + to ensure we gather occurrence info even for GlobalId scrutinees; + see Note [Binder swap for GlobalId scrutinee] + + * The ProxyEnv is just an optimisation; you can throw away any + element without losing correctness. And we do so when pushing + it inside a binding (see trimProxyEnv). + + * Once scrutinee might map to many case binders: Eg + case sc of cb1 { DEFAULT -> ....case sc of cb2 { ... } .. } + +INVARIANTS + * If sc1 |-> (sc2, [...(cb, co)...]), then sc1==sc2 + It's a UniqFM and we sometimes need the domain Id + + * Any particular case binder 'cb' occurs only once in entire range + + * No loops + +The Main Reason for having a ProxyEnv is so that when we encounter + case e of cb { pi -> ri } +we can find all the in-scope variables derivable from 'cb', +and effectively add let-bindings for them thus: + case e of cb { pi -> let { x = ..cb..; y = ...cb.. } + in ri } +The function getProxies finds these bindings; then we +add just the necessary ones, using wrapProxy. + +More info under Note [Binder swap] + Note [Binder swap] ~~~~~~~~~~~~~~~~~~ We do these two transformations right here: @@ -1052,22 +1267,50 @@ same simplifier pass that reduced (f v) to v. I think this is just too bad. CSE will recover some of it. +Note [Case of cast] +~~~~~~~~~~~~~~~~~~~ +Consider case (x `cast` co) of b { I# -> + ... (case (x `cast` co) of {...}) ... +We'd like to eliminate the inner case. That is the motivation for +equation (2) in Note [Binder swap]. When we get to the inner case, we +inline x, cancel the casts, and away we go. + Note [Binder swap on GlobalId scrutinees] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When the scrutinee is a GlobalId we must take care in two ways i) In order to *know* whether 'x' occurs free in the RHS, we need its occurrence info. BUT, we don't gather occurrence info for - GlobalIds. That's what the (small) occ_scrut_ids set in OccEnv is + GlobalIds. That's one use for the (small) occ_proxy env in OccEnv is for: it says "gather occurrence info for these. ii) We must call localiseId on 'x' first, in case it's a GlobalId, or has an External Name. See, for example, SimplEnv Note [Global Ids in the substitution]. +Note [getProxies is subtle] +~~~~~~~~~~~~~~~~~~~~~~~~~~~ +The code for getProxies isn't all that obvious. Consider + + case v |> cov of x { DEFAULT -> + case x |> cox1 of y { DEFAULT -> + case x |> cox2 of z { DEFAULT -> r + +These will give us a ProxyEnv looking like: + x |-> (x, [(y, cox1), (z, cox2)]) + v |-> (v, [(x, cov)]) + +From this we want to extract the bindings + x = z |> sym cox2 + v = x |> sym cov + y = x |> cox1 + +Notice that later bindings may mention earlier ones, and that +we need to go "both ways". + Historical note [no-case-of-case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -We *used* to suppress the binder-swap in case expressoins when +We *used* to suppress the binder-swap in case expressions when -fno-case-of-case is on. Old remarks: "This happens in the first simplifier pass, and enhances full laziness. Here's the bad case: @@ -1126,160 +1369,118 @@ It's fixed by doing the binder-swap in OccAnal because we can do the binder-swap unconditionally and still get occurrence analysis information right. -Note [Case of cast] -~~~~~~~~~~~~~~~~~~~ -Consider case (x `cast` co) of b { I# -> - ... (case (x `cast` co) of {...}) ... -We'd like to eliminate the inner case. That is the motivation for -equation (2) in Note [Binder swap]. When we get to the inner case, we -inline x, cancel the casts, and away we go. - -Note [Binders in case alternatives] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Consider - case x of y { (a,b) -> f y } -We treat 'a', 'b' as dead, because they don't physically occur in the -case alternative. (Indeed, a variable is dead iff it doesn't occur in -its scope in the output of OccAnal.) It really helps to know when -binders are unused. See esp the call to isDeadBinder in -Simplify.mkDupableAlt - -In this example, though, the Simplifier will bring 'a' and 'b' back to -life, beause it binds 'y' to (a,b) (imagine got inlined and -scrutinised y). - -\begin{code} -occAnalAlt :: OccEnv - -> CoreBndr - -> Maybe (Id, CoreExpr) -- Note [Binder swap] - -> CoreAlt - -> (UsageDetails, Alt IdWithOccInfo) -occAnalAlt env case_bndr mb_scrut_var (con, bndrs, rhs) - = case occAnal env rhs of { (rhs_usage, rhs') -> - let - (alt_usg, tagged_bndrs) = tagLamBinders rhs_usage bndrs - bndrs' = tagged_bndrs -- See Note [Binders in case alternatives] - in - case mb_scrut_var of - Just (scrut_var, scrut_rhs) -- See Note [Binder swap] - | scrut_var `localUsedIn` alt_usg -- (a) Fast path, usually false - , not (any shadowing bndrs) -- (b) - -> (addOneOcc usg_wo_scrut case_bndr NoOccInfo, - -- See Note [Case binder usage] for the NoOccInfo - (con, bndrs', Let (NonRec scrut_var2 scrut_rhs) rhs')) - where - scrut_var1 = mkLocalId (localiseName (idName scrut_var)) (idType scrut_var) - -- Localise the scrut_var before shadowing it; we're making a - -- new binding for it, and it might have an External Name, or - -- even be a GlobalId; Note [Binder swap on GlobalId scrutinees] - -- Also we don't want any INLILNE or NOINLINE pragmas! - - (usg_wo_scrut, scrut_var2) = tagBinder alt_usg scrut_var1 - shadowing bndr = bndr `elemVarSet` rhs_fvs - rhs_fvs = exprFreeVars scrut_rhs - - _other -> (alt_usg, (con, bndrs', rhs')) } -\end{code} - - -%************************************************************************ -%* * -\subsection[OccurAnal-types]{OccEnv} -%* * -%************************************************************************ - \begin{code} -data OccEnv - = OccEnv { occ_encl :: !OccEncl -- Enclosing context information - , occ_ctxt :: !CtxtTy -- Tells about linearity - , occ_scrut_ids :: !GblScrutIds } - -type GblScrutIds = IdSet -- GlobalIds that are scrutinised, and for which - -- we want to gather occurence info; see - -- Note [Binder swap for GlobalId scrutinee] - -- No need to prune this if there's a shadowing binding - -- because it's OK for it to be too big - --- 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 - -initOccEnv :: OccEnv -initOccEnv = OccEnv { occ_encl = OccVanilla - , occ_ctxt = [] - , occ_scrut_ids = emptyVarSet } - -vanillaCtxt :: OccEnv -> OccEnv -vanillaCtxt env = OccEnv { occ_encl = OccVanilla, occ_ctxt = [] - , occ_scrut_ids = occ_scrut_ids env } - -rhsCtxt :: OccEnv -> OccEnv -rhsCtxt env = OccEnv { occ_encl = OccRhs, occ_ctxt = [] - , occ_scrut_ids = occ_scrut_ids env } - -mkAltEnv :: OccEnv -> Maybe (Id, CoreExpr) -> OccEnv +extendProxyEnv :: ProxyEnv -> Id -> CoercionI -> Id -> ProxyEnv +-- (extendPE x co y) typically arises from +-- case (x |> co) of y { ... } +-- It extends the proxy env with the binding +-- y = x |> co +extendProxyEnv pe scrut co case_bndr + | scrut == case_bndr = PE env1 fvs1 -- If case_bndr shadows scrut, + | otherwise = PE env2 fvs2 -- don't extend + where + PE env1 fvs1 = trimProxyEnv pe [case_bndr] + env2 = extendVarEnv_Acc add single env1 scrut1 (case_bndr,co) + single cb_co = (scrut1, [cb_co]) + add cb_co (x, cb_cos) = (x, cb_co:cb_cos) + fvs2 = fvs1 `unionVarSet` freeVarsCoI co + `extendVarSet` case_bndr + `extendVarSet` scrut1 + + scrut1 = mkLocalId (localiseName (idName scrut)) (idType scrut) + -- Localise the scrut_var before shadowing it; we're making a + -- new binding for it, and it might have an External Name, or + -- even be a GlobalId; Note [Binder swap on GlobalId scrutinees] + -- Also we don't want any INLILNE or NOINLINE pragmas! + +----------- +type ProxyBind = (Id, Id, CoercionI) + +getProxies :: OccEnv -> Id -> Bag ProxyBind +-- Return a bunch of bindings [...(xi,ei)...] +-- such that let { ...; xi=ei; ... } binds the xi using y alone +-- See Note [getProxies is subtle] +getProxies (OccEnv { occ_proxy = PE pe _ }) case_bndr + = -- pprTrace "wrapProxies" (ppr case_bndr) $ + go_fwd case_bndr + where + fwd_pe :: IdEnv (Id, CoercionI) + fwd_pe = foldVarEnv add1 emptyVarEnv pe + where + add1 (x,ycos) env = foldr (add2 x) env ycos + add2 x (y,co) env = extendVarEnv env y (x,co) + + go_fwd :: Id -> Bag ProxyBind + -- Return bindings derivable from case_bndr + go_fwd case_bndr = -- pprTrace "go_fwd" (vcat [ppr case_bndr, text "fwd_pe =" <+> ppr fwd_pe, + -- text "pe =" <+> ppr pe]) $ + go_fwd' case_bndr + + go_fwd' case_bndr + | Just (scrut, co) <- lookupVarEnv fwd_pe case_bndr + = unitBag (scrut, case_bndr, mkSymCoI co) + `unionBags` go_fwd scrut + `unionBags` go_bwd scrut [pr | pr@(cb,_) <- lookup_bwd scrut + , cb /= case_bndr] + | otherwise + = emptyBag + + lookup_bwd :: Id -> [(Id, CoercionI)] + -- Return case_bndrs that are connected to scrut + lookup_bwd scrut = case lookupVarEnv pe scrut of + Nothing -> [] + Just (_, cb_cos) -> cb_cos + + go_bwd :: Id -> [(Id, CoercionI)] -> Bag ProxyBind + go_bwd scrut cb_cos = foldr (unionBags . go_bwd1 scrut) emptyBag cb_cos + + go_bwd1 :: Id -> (Id, CoercionI) -> Bag ProxyBind + go_bwd1 scrut (case_bndr, co) + = -- pprTrace "go_bwd1" (ppr case_bndr) $ + unitBag (case_bndr, scrut, co) + `unionBags` go_bwd case_bndr (lookup_bwd case_bndr) + +----------- +mkAltEnv :: OccEnv -> CoreExpr -> Id -> OccEnv -- Does two things: a) makes the occ_ctxt = OccVanilla --- b) extends the scrut_ids if necessary -mkAltEnv env (Just (scrut_id, _)) - | not (isLocalId scrut_id) - = OccEnv { occ_encl = OccVanilla - , occ_scrut_ids = extendVarSet (occ_scrut_ids env) scrut_id - , occ_ctxt = occ_ctxt env } -mkAltEnv env _ - | isRhsEnv env = env { occ_encl = OccVanilla } - | otherwise = env - -setCtxtTy :: OccEnv -> CtxtTy -> OccEnv -setCtxtTy env ctxt = env { occ_ctxt = ctxt } - -isRhsEnv :: OccEnv -> Bool -isRhsEnv (OccEnv { occ_encl = OccRhs }) = True -isRhsEnv (OccEnv { occ_encl = OccVanilla }) = False - -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 - -oneShotGroup (OccEnv { occ_ctxt = ctxt }) bndrs - = go ctxt bndrs [] +-- b) extends the ProxyEnv if possible +mkAltEnv env scrut cb + = env { occ_encl = OccVanilla, occ_proxy = pe' } where - 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 - - go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs) - -addAppCtxt :: OccEnv -> [Arg CoreBndr] -> OccEnv -addAppCtxt env@(OccEnv { occ_ctxt = ctxt }) args - = env { occ_ctxt = replicate (valArgCount args) True ++ ctxt } + pe = occ_proxy env + pe' = case scrut of + Var v -> extendProxyEnv pe v (IdCo (idType v)) cb + Cast (Var v) co -> extendProxyEnv pe v (ACo co) cb + _other -> trimProxyEnv pe [cb] + +----------- +trimOccEnv :: OccEnv -> [CoreBndr] -> OccEnv +trimOccEnv env bndrs = env { occ_proxy = trimProxyEnv (occ_proxy env) bndrs } + +----------- +trimProxyEnv :: ProxyEnv -> [CoreBndr] -> ProxyEnv +-- We are about to push this ProxyEnv inside a binding for 'bndrs' +-- So dump any ProxyEnv bindings which mention any of the bndrs +trimProxyEnv (PE pe fvs) bndrs + | not (bndr_set `intersectsVarSet` fvs) + = PE pe fvs + | otherwise + = PE pe' (fvs `minusVarSet` bndr_set) + where + pe' = mapVarEnv trim pe + bndr_set = mkVarSet bndrs + trim (scrut, cb_cos) | scrut `elemVarSet` bndr_set = (scrut, []) + | otherwise = (scrut, filterOut discard cb_cos) + discard (cb,co) = bndr_set `intersectsVarSet` + extendVarSet (freeVarsCoI co) cb + +----------- +freeVarsCoI :: CoercionI -> VarSet +freeVarsCoI (IdCo t) = tyVarsOfType t +freeVarsCoI (ACo co) = tyVarsOfType co \end{code} + %************************************************************************ %* * \subsection[OccurAnal-types]{OccEnv} @@ -1308,9 +1509,8 @@ addOneOcc usage id info emptyDetails :: UsageDetails emptyDetails = (emptyVarEnv :: UsageDetails) -localUsedIn, usedIn :: Id -> UsageDetails -> Bool -v `localUsedIn` details = v `elemVarEnv` details -v `usedIn` details = isExportedId v || v `localUsedIn` details +usedIn :: Id -> UsageDetails -> Bool +v `usedIn` details = isExportedId v || v `elemVarEnv` details type IdWithOccInfo = Id @@ -1344,7 +1544,7 @@ tagBinder usage binder setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr setBinderOcc usage bndr - | isTyVar bndr = bndr + | isTyCoVar bndr = bndr | isExportedId bndr = case idOccInfo bndr of NoOccInfo -> bndr _ -> setIdOccInfo bndr NoOccInfo @@ -1368,8 +1568,9 @@ setBinderOcc usage bndr mkOneOcc :: OccEnv -> Id -> InterestingCxt -> UsageDetails mkOneOcc env id int_cxt | isLocalId id = unitVarEnv id (OneOcc False True int_cxt) - | id `elemVarSet` occ_scrut_ids env = unitVarEnv id NoOccInfo - | otherwise = emptyDetails + | PE env _ <- occ_proxy env + , id `elemVarEnv` env = unitVarEnv id NoOccInfo + | otherwise = emptyDetails markMany, markInsideLam, markInsideSCC :: OccInfo -> OccInfo