X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FOccurAnal.lhs;h=ba7d19295b83da21329ef12b160828fb3e4698a5;hp=d97368a2f6e3f8fd2ce74e55ce994cb1041d4510;hb=febf1ced754a3996ac1a5877dcded87828560d1c;hpb=d385c64c1684fa7d66027b6e9c6d8e581b46e923 diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs index d97368a..ba7d192 100644 --- a/compiler/simplCore/OccurAnal.lhs +++ b/compiler/simplCore/OccurAnal.lhs @@ -19,17 +19,18 @@ module OccurAnal ( import CoreSyn import CoreFVs -import Type ( tyVarsOfType ) -import CoreUtils ( exprIsTrivial, isDefaultAlt, mkCoerceI, isExpandableApp ) -import Coercion ( CoercionI(..), mkSymCoI ) +import CoreUtils ( exprIsTrivial, isDefaultAlt, isExpandableApp, mkCoerce ) import Id import NameEnv import NameSet import Name ( Name, localiseName ) import BasicTypes +import Coercion + import VarSet import VarEnv -import Var ( Var, varUnique ) +import Var + import Maybes ( orElse ) import Digraph ( SCC(..), stronglyConnCompFromEdgedVerticesR ) import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey ) @@ -52,11 +53,12 @@ import Data.List Here's the externally-callable interface: \begin{code} -occurAnalysePgm :: [CoreBind] -> [CoreRule] -> [CoreBind] -occurAnalysePgm binds rules - = snd (go (initOccEnv rules) binds) +occurAnalysePgm :: Maybe (Activation -> Bool) -> [CoreRule] + -> [CoreBind] -> [CoreBind] +occurAnalysePgm active_rule imp_rules binds + = snd (go (initOccEnv active_rule imp_rules) binds) where - initial_uds = addIdOccs emptyDetails (rulesFreeVars rules) + initial_uds = addIdOccs emptyDetails (rulesFreeVars imp_rules) -- The RULES keep things alive! go :: OccEnv -> [CoreBind] -> (UsageDetails, [CoreBind]) @@ -70,7 +72,11 @@ occurAnalysePgm binds rules occurAnalyseExpr :: CoreExpr -> CoreExpr -- Do occurrence analysis, and discard occurence info returned -occurAnalyseExpr expr = snd (occAnal (initOccEnv []) expr) +occurAnalyseExpr expr + = snd (occAnal (initOccEnv all_active_rules []) expr) + where + -- To be conservative, we say that all inlines and rules are active + all_active_rules = Just (\_ -> True) \end{code} @@ -92,18 +98,20 @@ occAnalBind :: OccEnv -- The incoming OccEnv [CoreBind]) occAnalBind env _ (NonRec binder rhs) body_usage - | isTyCoVar binder -- A type let; we don't gather usage info + | isTyVar binder -- A type let; we don't gather usage info = (body_usage, [NonRec binder rhs]) | 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 [Rules are extra RHSs] - [NonRec tagged_binder rhs']) + = (body_usage' +++ rhs_usage3, [NonRec tagged_binder rhs']) where (body_usage', tagged_binder) = tagBinder body_usage binder - (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs + (rhs_usage1, rhs') = occAnalRhs env (Just tagged_binder) rhs + rhs_usage2 = addIdOccs rhs_usage1 (idUnfoldingVars binder) + rhs_usage3 = addIdOccs rhs_usage2 (idRuleVars binder) + -- See Note [Rules are extra RHSs] and Note [Rule dependency info] \end{code} Note [Dead code] @@ -189,7 +197,7 @@ However things are made quite a bit more complicated by RULES. Remember [Rules for recursive functions] in Simplify.lhs Hence, if - f's RHS mentions g, and + f's RHS (or its INLINE template if it has one) mentions g, and g has a RULE that mentions h, and h has a RULE that mentions f @@ -198,6 +206,7 @@ However things are made quite a bit more complicated by RULES. Remember 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.) + See also Note [Finding rule RHS free vars] 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 @@ -221,7 +230,23 @@ However things are made quite a bit more complicated by RULES. Remember rec_edges for the Rec block analysis loop_breaker_edges for the loop breaker analysis - + * Note [Finding rule RHS free vars] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + Consider this real example from Data Parallel Haskell + tagZero :: Array Int -> Array Tag + {-# INLINE [1] tagZeroes #-} + tagZero xs = pmap (\x -> fromBool (x==0)) xs + + {-# RULES "tagZero" [~1] forall xs n. + pmap fromBool = tagZero xs #-} + So tagZero's RHS mentions pmap, and pmap's RULE mentions tagZero. + However, tagZero can only be inlined in phase 1 and later, while + the RULE is only active *before* phase 1. So there's no problem. + + To make this work, we look for the RHS free vars only for + *active* rules. That's the reason for the is_active argument + to idRhsRuleVars, and the occ_rule_act field of the OccEnv. + * Note [Weak loop breakers] ~~~~~~~~~~~~~~~~~~~~~~~~~ There is a last nasty wrinkle. Suppose we have @@ -234,7 +259,7 @@ However things are made quite a bit more complicated by RULES. Remember ...more... } - Remmber that we simplify the RULES before any RHS (see Note + Remember 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 @@ -259,7 +284,7 @@ However things are made quite a bit more complicated by RULES. Remember ~~~~~~~~~~~~~~~~~~~~~~~~~~~ The VarSet in a SpecInfo is used for dependency analysis in the occurrence analyser. We must track free vars in *both* lhs and rhs. - Hence use of idRuleVars, rather than idRuleRhsVars in addRuleUsage. + Hence use of idRuleVars, rather than idRuleRhsVars in occAnalBind. Why both? Consider x = y RULE f x = 4 @@ -274,6 +299,35 @@ However things are made quite a bit more complicated by RULES. Remember at the same time as the regular RHS of the function, so it should be treated *exactly* like an extra RHS. + There is a danger that we'll be sub-optimal if we see this + f = ...f... + [INLINE f = ..no f...] + where f is recursive, but the INLINE is not. This can just about + happen with a sufficiently odd set of rules; eg + + foo :: Int -> Int + {-# INLINE [1] foo #-} + foo x = x+1 + + bar :: Int -> Int + {-# INLINE [1] bar #-} + bar x = foo x + 1 + + {-# RULES "foo" [~1] forall x. foo x = bar x #-} + + Here the RULE makes bar recursive; but it's INLINE pragma remains + non-recursive. It's tempting to then say that 'bar' should not be + a loop breaker, but an attempt to do so goes wrong in two ways: + a) We may get + $df = ...$cfoo... + $cfoo = ...$df.... + [INLINE $cfoo = ...no-$df...] + But we want $cfoo to depend on $df explicitly so that we + put the bindings in the right order to inline $df in $cfoo + and perhaps break the loop altogether. (Maybe this + b) + + Example [eftInt] ~~~~~~~~~~~~~~~ @@ -311,7 +365,7 @@ This showed up when compiling Control.Concurrent.Chan.getChanContents. \begin{code} occAnalBind _ env (Rec pairs) body_usage - = foldr occAnalRec (body_usage, []) sccs + = foldr (occAnalRec env) (body_usage, []) sccs -- For a recursive group, we -- * occ-analyse all the RHSs -- * compute strongly-connected components @@ -327,13 +381,21 @@ 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, varUnique bndr, out_edges) - where - (rhs_usage, rhs') = occAnalRhs env bndr rhs - 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] + = (details, varUnique bndr, keysUFM out_edges) + where + details = ND { nd_bndr = bndr, nd_rhs = rhs' + , nd_uds = rhs_usage3, nd_inl = inl_fvs} + + (rhs_usage1, rhs') = occAnalRhs env Nothing rhs + rhs_usage2 = addIdOccs rhs_usage1 rule_fvs -- Note [Rules are extra RHSs] + rhs_usage3 = addIdOccs rhs_usage2 unf_fvs + unf = realIdUnfolding bndr -- Ignore any current loop-breaker flag + unf_fvs = stableUnfoldingVars unf + rule_fvs = idRuleVars bndr -- See Note [Rule dependency info] + + inl_fvs = rhs_fvs `unionVarSet` unf_fvs + rhs_fvs = intersectUFM_C (\b _ -> b) bndr_set rhs_usage1 + out_edges = intersectUFM_C (\b _ -> b) bndr_set rhs_usage3 -- (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 -- @@ -345,11 +407,13 @@ occAnalBind _ env (Rec pairs) body_usage -- consumed 10% of total runtime! ----------------------------- -occAnalRec :: SCC (Node Details) -> (UsageDetails, [CoreBind]) - -> (UsageDetails, [CoreBind]) +occAnalRec :: OccEnv -> 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) +occAnalRec _ (AcyclicSCC (ND { nd_bndr = bndr, nd_rhs = rhs, nd_uds = rhs_usage}, _, _)) + (body_usage, binds) | not (bndr `usedIn` body_usage) = (body_usage, binds) @@ -362,7 +426,7 @@ occAnalRec (AcyclicSCC (ND bndr rhs rhs_usage _, _, _)) (body_usage, binds) -- The Rec case is the interesting one -- See Note [Loop breaking] -occAnalRec (CyclicSCC nodes) (body_usage, binds) +occAnalRec env (CyclicSCC nodes) (body_usage, binds) | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage = (body_usage, binds) -- Dead code @@ -370,13 +434,15 @@ occAnalRec (CyclicSCC nodes) (body_usage, binds) = (final_usage, Rec pairs : binds) where - bndrs = [b | (ND b _ _ _, _, _) <- nodes] + bndrs = [b | (ND { nd_bndr = b }, _, _) <- nodes] bndr_set = mkVarSet bndrs + non_boring bndr = isId bndr && + (isStableUnfolding (realIdUnfolding bndr) || idHasRules bndr) ---------------------------- -- Tag the binders with their occurrence info total_usage = foldl add_usage body_usage nodes - add_usage usage_so_far (ND _ _ rhs_usage _, _, _) = usage_so_far +++ rhs_usage + add_usage usage_so_far (ND { nd_uds = rhs_usage }, _, _) = usage_so_far +++ rhs_usage (final_usage, tagged_nodes) = mapAccumL tag_node total_usage nodes tag_node :: UsageDetails -> Node Details -> (UsageDetails, Node Details) @@ -385,8 +451,8 @@ occAnalRec (CyclicSCC nodes) (body_usage, binds) -- 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)) + tag_node usage (details@ND { nd_bndr = bndr }, k, ks) + = (usage `delVarEnv` bndr, (details { nd_bndr = bndr2 }, k, ks)) where bndr2 | bndr `elemVarSet` all_rule_fvs = makeLoopBreaker True bndr1 | otherwise = bndr1 @@ -396,26 +462,32 @@ occAnalRec (CyclicSCC nodes) (body_usage, binds) ---------------------------- -- Now reconstruct the cycle - pairs | no_rules = reOrderCycle 0 tagged_nodes [] - | otherwise = foldr (reOrderRec 0) [] $ - stronglyConnCompFromEdgedVerticesR loop_breaker_edges + pairs | any non_boring bndrs + = foldr (reOrderRec 0) [] $ + stronglyConnCompFromEdgedVerticesR loop_breaker_edges + | otherwise + = reOrderCycle 0 tagged_nodes [] -- See Note [Choosing loop breakers] for loop_breaker_edges loop_breaker_edges = map mk_node tagged_nodes - mk_node (details@(ND _ _ _ rhs_fvs), k, _) = (details, k, new_ks) + mk_node (details@(ND { nd_inl = inl_fvs }), k, _) = (details, k, new_ks) where - new_ks = keysUFM (fst (extendFvs rule_fv_env rhs_fvs)) + new_ks = keysUFM (fst (extendFvs rule_fv_env inl_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 = transClosureFV init_rule_fvs - 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)] + rule_fv_env = transClosureFV init_rule_fvs + init_rule_fvs + | Just is_active <- occ_rule_act env -- See Note [Finding rule RHS free vars] + = [ (b, rule_fvs) + | b <- bndrs + , isId b + , let rule_fvs = idRuleRhsVars is_active b + `intersectVarSet` bndr_set + , not (isEmptyVarSet rule_fvs)] + | otherwise + = [] \end{code} @reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic @@ -455,39 +527,41 @@ 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. -data Details = ND Id -- Binder - CoreExpr -- RHS +data Details + = ND { nd_bndr :: Id -- Binder + , nd_rhs :: CoreExpr -- RHS - UsageDetails -- Full usage from RHS, - -- including *both* RULES *and* InlineRule unfolding + , nd_uds :: UsageDetails -- Usage from RHS, + -- including RULES and InlineRule unfolding - IdSet -- Other binders *from this Rec group* mentioned in - -- * the RHS - -- * any InlineRule unfolding - -- but *excluding* any RULES + , nd_inl :: IdSet -- Other binders *from this Rec group* mentioned in + } -- its InlineRule unfolding (if present) + -- AND the RHS + -- but *excluding* any RULES + -- This is the IdSet that may be used if the Id is inlined reOrderRec :: Int -> SCC (Node Details) -> [(Id,CoreExpr)] -> [(Id,CoreExpr)] -- Sorted into a plausible order. Enough of the Ids have -- IAmALoopBreaker pragmas that there are no loops left. -reOrderRec _ (AcyclicSCC (ND bndr rhs _ _, _, _)) pairs = (bndr, rhs) : pairs -reOrderRec depth (CyclicSCC cycle) pairs = reOrderCycle depth cycle pairs +reOrderRec _ (AcyclicSCC (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _)) + pairs = (bndr, rhs) : pairs +reOrderRec depth (CyclicSCC cycle) pairs = reOrderCycle depth cycle pairs reOrderCycle :: Int -> [Node Details] -> [(Id,CoreExpr)] -> [(Id,CoreExpr)] reOrderCycle _ [] _ = panic "reOrderCycle" -reOrderCycle _ [bind] pairs -- Common case of simple self-recursion - = (makeLoopBreaker False bndr, rhs) : pairs - where - (ND bndr rhs _ _, _, _) = bind +reOrderCycle _ [(ND { nd_bndr = bndr, nd_rhs = rhs }, _, _)] pairs + = -- Common case of simple self-recursion + (makeLoopBreaker False bndr, rhs) : pairs reOrderCycle depth (bind : binds) pairs = -- Choose a loop breaker, mark it no-inline, -- do SCC analysis on the rest, and recursively sort them out --- pprTrace "reOrderCycle" (ppr [b | (ND b _ _ _, _, _) <- bind:binds]) $ +-- pprTrace "reOrderCycle" (ppr [b | (ND { nd_bndr = b }, _, _) <- bind:binds]) $ foldr (reOrderRec new_depth) ([ (makeLoopBreaker False bndr, rhs) - | (ND bndr rhs _ _, _, _) <- chosen_binds] ++ pairs) + | (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _) <- chosen_binds] ++ pairs) (stronglyConnCompFromEdgedVerticesR unchosen) where (chosen_binds, unchosen) = choose_loop_breaker [bind] (score bind) [] binds @@ -519,13 +593,13 @@ reOrderCycle depth (bind : binds) pairs sc = score bind score :: Node Details -> Int -- Higher score => less likely to be picked as loop breaker - score (ND bndr rhs _ _, _, _) - | not (isId bndr) = 100 -- A type or cercion varialbe is never a loop breaker + score (ND { nd_bndr = bndr, nd_rhs = rhs }, _, _) + | not (isId bndr) = 100 -- A type or cercion variable 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, _) <- isStableUnfolding_maybe (idUnfolding bndr) + | Just inl_source <- isStableCoreUnfolding_maybe (idUnfolding bndr) = case inl_source of InlineWrapper {} -> 10 -- Note [INLINE pragmas] _other -> 3 -- Data structures are more important than this @@ -717,49 +791,27 @@ 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 + -> Maybe Id -> CoreExpr -- Binder and rhs + -- Just b => non-rec, and alrady tagged with occurrence info + -- Nothing => Rec, no occ info -> (UsageDetails, CoreExpr) - -- Returned usage details includes any INLINE rhs - -occAnalRhs env id rhs - | isId id = (addIdOccs rhs_usage (idUnfoldingVars id), rhs') - | otherwise = (rhs_usage, rhs') - -- Include occurrences for the "extra RHS" from a CoreUnfolding + -- Returned usage details covers only the RHS, + -- and *not* the RULE or INLINE template for the Id +occAnalRhs env mb_bndr rhs + = occAnal ctxt rhs where - (rhs_usage, rhs') = occAnal ctxt rhs - ctxt | certainly_inline id = env - | otherwise = rhsCtxt env - -- 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 - _ -> False -\end{code} - - - -\begin{code} -addRuleUsage :: UsageDetails -> Var -> UsageDetails --- Add the usage from RULES in Id to the usage -addRuleUsage usage var - | isId var = addIdOccs usage (idRuleVars var) - | otherwise = usage - -- idRuleVars here: see Note [Rule dependency info] + -- See Note [Cascading inlines] + ctxt = case mb_bndr of + Just b | certainly_inline b -> env + _other -> rhsCtxt env + + certainly_inline bndr -- See Note [Cascading inlines] + = case idOccInfo bndr of + OneOcc in_lam one_br _ -> not in_lam && one_br && active && not_stable + _ -> False + where + active = isAlwaysActive (idInlineActivation bndr) + not_stable = not (isStableUnfolding (idUnfolding bndr)) addIdOccs :: UsageDetails -> VarSet -> UsageDetails addIdOccs usage id_set = foldVarSet add usage id_set @@ -773,6 +825,46 @@ addIdOccs usage id_set = foldVarSet add usage id_set -- (Same goes for INLINE.) \end{code} +Note [Cascading inlines] +~~~~~~~~~~~~~~~~~~~~~~~~ +By default we use an rhsCtxt for the RHS of a binding. This tells the +occ anal n that it's looking at an RHS, which has an effect in +occAnalApp. In particular, for constructor applications, it makes +the arguments appear to have NoOccInfo, so that we don't inline into +them. Thus x = f y + k = Just x +we do not want to inline x. + +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. + +So, when analysing the RHS of x3 we notice that x3 will itself +definitely inline the next time round, and so we analyse x3's rhs in +an ordinary context, not rhsCtxt. Hence the "certainly_inline" stuff. + +Annoyingly, we have to approximiate SimplUtils.preInlineUnconditionally. +If we say "yes" when preInlineUnconditionally says "no" the simplifier iterates +indefinitely: + x = f y + k = Just x +inline ==> + k = Just (f y) +float ==> + x1 = f y + k = Just x1 + +This is worse than the slow cascade, so we only want to say "certainly_inline" +if it really is certain. Look at the note with preInlineUnconditionally +for the various clauses. + Expressions ~~~~~~~~~~~ \begin{code} @@ -781,33 +873,27 @@ occAnal :: OccEnv -> (UsageDetails, -- Gives info only about the "interesting" Ids CoreExpr) -occAnal _ (Type t) = (emptyDetails, Type t) -occAnal env (Var v) = (mkOneOcc env v False, Var v) +occAnal _ expr@(Type _) = (emptyDetails, expr) +occAnal _ expr@(Lit _) = (emptyDetails, expr) +occAnal env expr@(Var v) = (mkOneOcc env v False, expr) -- At one stage, I gathered the idRuleVars for v here too, -- which in a way is the right thing to do. -- 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. -\end{code} - -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 - (case z of {(p,q)->q}, case z of {(p,q)->q}) -\end{verbatim} - -We feel free to duplicate the WHNF (True,y), but that means -that y may be duplicated thereby. +occAnal _ (Coercion co) + = (addIdOccs emptyDetails (coVarsOfCo co), Coercion co) + -- See Note [Gather occurrences of coercion veriables] +\end{code} -If we aren't careful we duplicate the (expensive x) call! -Constructors are rather like lambdas in this way. +Note [Gather occurrences of coercion veriables] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +We need to gather info about what coercion variables appear, so that +we can sort them into the right place when doing dependency analysis. \begin{code} -occAnal _ expr@(Lit _) = (emptyDetails, expr) \end{code} \begin{code} @@ -823,7 +909,10 @@ occAnal env (Note note body) occAnal env (Cast expr co) = case occAnal env expr of { (usage, expr') -> - (markManyIf (isRhsEnv env) usage, Cast expr' co) + let usage1 = markManyIf (isRhsEnv env) usage + usage2 = addIdOccs usage1 (coVarsOfCo co) + -- See Note [Gather occurrences of coercion veriables] + in (usage2, 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. @@ -838,7 +927,7 @@ 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) | isTyCoVar x +occAnal env (Lam x body) | isTyVar x = case occAnal env body of { (body_usage, body') -> (body_usage, Lam x body') } @@ -930,6 +1019,18 @@ occAnalArgs env args Applications are dealt with specially because we want the "build hack" to work. +Note [Arguments of let-bound constructors] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider + f x = let y = expensive x in + let z = (True,y) in + (case z of {(p,q)->q}, case z of {(p,q)->q}) +We feel free to duplicate the WHNF (True,y), but that means +that y may be duplicated thereby. + +If we aren't careful we duplicate the (expensive x) call! +Constructors are rather like lambdas in this way. + \begin{code} occAnalApp :: OccEnv -> (Expr CoreBndr, [Arg CoreBndr]) @@ -945,6 +1046,7 @@ occAnalApp env (Var fun, args) -- arguments are just variables, or trivial expressions. -- -- This is the *whole point* of the isRhsEnv predicate + -- See Note [Arguments of let-bound constructors] in (fun_uds +++ final_args_uds, mkApps (Var fun) args') } where @@ -1055,7 +1157,7 @@ wrapProxy (bndr, rhs_var, co) (body_usg, 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) + rhs = mkCoerce co (Var (zapIdOccInfo rhs_var)) -- See Note [Zap case binders in proxy bindings] \end{code} @@ -1070,7 +1172,10 @@ data OccEnv = OccEnv { occ_encl :: !OccEncl -- Enclosing context information , occ_ctxt :: !CtxtTy -- Tells about linearity , occ_proxy :: ProxyEnv - , occ_rule_fvs :: ImpRuleUsage } + , occ_rule_fvs :: ImpRuleUsage + , occ_rule_act :: Maybe (Activation -> Bool) -- Nothing => Rules are inactive + -- See Note [Finding rule RHS free vars] + } ----------------------------- @@ -1102,11 +1207,14 @@ type CtxtTy = [Bool] -- be applied many times; but when it is, -- the CtxtTy inside applies -initOccEnv :: [CoreRule] -> OccEnv -initOccEnv rules = OccEnv { occ_encl = OccVanilla - , occ_ctxt = [] - , occ_proxy = PE emptyVarEnv emptyVarSet - , occ_rule_fvs = findImpRuleUsage rules } +initOccEnv :: Maybe (Activation -> Bool) -> [CoreRule] + -> OccEnv +initOccEnv active_rule imp_rules + = OccEnv { occ_encl = OccVanilla + , occ_ctxt = [] + , occ_proxy = PE emptyVarEnv emptyVarSet + , occ_rule_fvs = findImpRuleUsage active_rule imp_rules + , occ_rule_act = active_rule } vanillaCtxt :: OccEnv -> OccEnv vanillaCtxt env = env { occ_encl = OccVanilla, occ_ctxt = [] } @@ -1176,11 +1284,12 @@ that occur on the RULE's RHS. This mapping from imported Id to local Ids is held in occ_rule_fvs. \begin{code} -findImpRuleUsage :: [CoreRule] -> ImpRuleUsage +findImpRuleUsage :: Maybe (Activation -> Bool) -> [CoreRule] -> ImpRuleUsage -- Find the *local* Ids that can be reached transitively, -- via local rules, from each *imported* Id. -- Sigh: this function seems more complicated than it is really worth -findImpRuleUsage rules +findImpRuleUsage Nothing _ = emptyNameEnv +findImpRuleUsage (Just is_active) rules = mkNameEnv [ (f, mapUFM (\_ -> NoOccInfo) ls) | f <- rule_names , let ls = find_lcl_deps f @@ -1193,8 +1302,11 @@ findImpRuleUsage rules -- (f,g) means imported Id 'g' appears in RHS of -- rule for imported Id 'f', *or* does so transitively imp_deps = foldr add_imp emptyNameEnv rules - add_imp rule acc = extendNameEnv_C unionVarSet acc (ru_fn rule) - (exprSomeFreeVars keep_imp (ru_rhs rule)) + add_imp rule acc + | is_active (ruleActivation rule) + = extendNameEnv_C unionVarSet acc (ru_fn rule) + (exprSomeFreeVars keep_imp (ru_rhs rule)) + | otherwise = acc keep_imp v = isId v && (idName v `elemNameSet` rule_name_set) full_imp_deps = transClosureFV (ufmToList imp_deps) @@ -1251,9 +1363,11 @@ extendFvs env s %************************************************************************ \begin{code} -data ProxyEnv - = PE (IdEnv (Id, [(Id,CoercionI)])) VarSet - -- Main env, and its free variables (of both range and domain) +data ProxyEnv -- See Note [ProxyEnv] + = PE (IdEnv -- Domain = scrutinee variables + (Id, -- The scrutinee variable again + [(Id,Coercion)])) -- The case binders that it maps to + VarSet -- Free variables of both range and domain \end{code} Note [ProxyEnv] @@ -1396,6 +1510,17 @@ From this we want to extract the bindings Notice that later bindings may mention earlier ones, and that we need to go "both ways". +Note [Zap case binders in proxy bindings] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +From the original + case x of cb(dead) { p -> ...x... } +we will get + case x of cb(live) { p -> let x = cb in ...x... } + +Core Lint never expects to find an *occurence* of an Id marked +as Dead, so we must zap the OccInfo on cb before making the +binding x = cb. See Trac #5028. + Historical note [no-case-of-case] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We *used* to suppress the binder-swap in case expressions when @@ -1458,7 +1583,7 @@ binder-swap unconditionally and still get occurrence analysis information right. \begin{code} -extendProxyEnv :: ProxyEnv -> Id -> CoercionI -> Id -> ProxyEnv +extendProxyEnv :: ProxyEnv -> Id -> Coercion -> Id -> ProxyEnv -- (extendPE x co y) typically arises from -- case (x |> co) of y { ... } -- It extends the proxy env with the binding @@ -1471,7 +1596,7 @@ extendProxyEnv pe scrut co 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 + fvs2 = fvs1 `unionVarSet` tyCoVarsOfCo co `extendVarSet` case_bndr `extendVarSet` scrut1 @@ -1479,10 +1604,11 @@ extendProxyEnv pe scrut co case_bndr -- 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! + -- Also we don't want any INLINE or NOINLINE pragmas! ----------- -type ProxyBind = (Id, Id, CoercionI) +type ProxyBind = (Id, Id, Coercion) + -- (scrut variable, case-binder variable, coercion) getProxies :: OccEnv -> Id -> Bag ProxyBind -- Return a bunch of bindings [...(xi,ei)...] @@ -1492,7 +1618,7 @@ 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 :: IdEnv (Id, Coercion) fwd_pe = foldVarEnv add1 emptyVarEnv pe where add1 (x,ycos) env = foldr (add2 x) env ycos @@ -1506,23 +1632,23 @@ getProxies (OccEnv { occ_proxy = PE pe _ }) case_bndr go_fwd' case_bndr | Just (scrut, co) <- lookupVarEnv fwd_pe case_bndr - = unitBag (scrut, case_bndr, mkSymCoI co) + = unitBag (scrut, case_bndr, mkSymCo 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)] + lookup_bwd :: Id -> [(Id, Coercion)] -- 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 :: Id -> [(Id, Coercion)] -> Bag ProxyBind go_bwd scrut cb_cos = foldr (unionBags . go_bwd1 scrut) emptyBag cb_cos - go_bwd1 :: Id -> (Id, CoercionI) -> Bag ProxyBind + go_bwd1 :: Id -> (Id, Coercion) -> Bag ProxyBind go_bwd1 scrut (case_bndr, co) = -- pprTrace "go_bwd1" (ppr case_bndr) $ unitBag (case_bndr, scrut, co) @@ -1537,9 +1663,9 @@ mkAltEnv env scrut cb where 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] + Var v -> extendProxyEnv pe v (mkReflCo (idType v)) cb + Cast (Var v) co -> extendProxyEnv pe v co cb + _other -> trimProxyEnv pe [cb] ----------- trimOccEnv :: OccEnv -> [CoreBndr] -> OccEnv @@ -1560,12 +1686,7 @@ trimProxyEnv (PE pe fvs) 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 + extendVarSet (tyCoVarsOfCo co) cb \end{code} @@ -1632,7 +1753,7 @@ tagBinder usage binder setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr setBinderOcc usage bndr - | isTyCoVar bndr = bndr + | isTyVar bndr = bndr | isExportedId bndr = case idOccInfo bndr of NoOccInfo -> bndr _ -> setIdOccInfo bndr NoOccInfo