X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreSubst.lhs;h=a229b8c4e986496c41732ed22cd41bdb93d8d723;hp=3fe48009a8b3f9e474ab957ec23c871bc5feb438;hb=a3bab0506498db41853543558c52a4fda0d183af;hpb=794c2f4c8829ba3166c9bdb471856bc00c21f001 diff --git a/compiler/coreSyn/CoreSubst.lhs b/compiler/coreSyn/CoreSubst.lhs index 3fe4800..a229b8c 100644 --- a/compiler/coreSyn/CoreSubst.lhs +++ b/compiler/coreSyn/CoreSubst.lhs @@ -12,22 +12,24 @@ module CoreSubst ( -- ** Substituting into expressions and related types deShadowBinds, substSpec, substRulesForImportedIds, - substTy, substExpr, substBind, substUnfolding, - substInlineRuleGuidance, lookupIdSubst, lookupTvSubst, substIdOcc, + substTy, substExpr, substExprSC, substBind, substBindSC, + substUnfolding, substUnfoldingSC, + substUnfoldingSource, lookupIdSubst, lookupTvSubst, substIdOcc, -- ** Operations on substitutions emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst, extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList, extendSubst, extendSubstList, zapSubstEnv, - extendInScope, extendInScopeList, extendInScopeIds, - isInScope, + addInScopeSet, extendInScope, extendInScopeList, extendInScopeIds, + isInScope, setInScope, + delBndr, delBndrs, -- ** Substituting and cloning binders substBndr, substBndrs, substRecBndrs, cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs, -- ** Simple expression optimiser - simpleOptExpr + simpleOptPgm, simpleOptExpr, simpleOptExprWith ) where #include "HsVersions.h" @@ -35,10 +37,13 @@ module CoreSubst ( import CoreSyn import CoreFVs import CoreUtils -import OccurAnal( occurAnalyseExpr ) +import PprCore +import OccurAnal( occurAnalyseExpr, occurAnalysePgm ) import qualified Type import Type ( Type, TvSubst(..), TvSubstEnv ) +import Coercion ( isIdentityCoercion ) +import OptCoercion ( optCoercion ) import VarSet import VarEnv import Id @@ -48,6 +53,9 @@ import IdInfo import Unique import UniqSupply import Maybes +import ErrUtils +import DynFlags ( DynFlags, DynFlag(..) ) +import BasicTypes ( isAlwaysActive ) import Outputable import PprCore () -- Instances import FastString @@ -109,12 +117,14 @@ For Ids, we have a different invariant In consequence: -* In substIdBndr, we extend the IdSubstEnv only when the unique changes +* If the TvSubstEnv and IdSubstEnv are both empty, substExpr would be a + no-op, so substExprSC ("short cut") does nothing. + + However, substExpr still goes ahead and substitutes. Reason: we may + want to replace existing Ids with new ones from the in-scope set, to + avoid space leaks. -* If the TvSubstEnv and IdSubstEnv are both empty, substExpr does nothing - (Note that the above rule for substIdBndr maintains this property. If - the incoming envts are both empty, then substituting the type and - IdInfo can't change anything.) +* In substIdBndr, we extend the IdSubstEnv only when the unique changes * In lookupIdSubst, we *must* look up the Id in the in-scope set, because it may contain non-trivial changes. Example: @@ -124,7 +134,7 @@ In consequence: set when we find the occurrence of x. * The requirement to look up the Id in the in-scope set means that we - must NOT take no-op short cut in the case the substitution is empty. + must NOT take no-op short cut when the IdSubst is empty. We must still look up every Id in the in-scope set. * (However, we don't need to do so for expressions found in the IdSubst @@ -200,7 +210,7 @@ extendTvSubstList (Subst in_scope ids tvs) prs = Subst in_scope ids (extendVarEn -- 'extendIdSubst' and 'extendTvSubst' extendSubst :: Subst -> Var -> CoreArg -> Subst extendSubst (Subst in_scope ids tvs) tv (Type ty) - = ASSERT( isTyVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty) + = ASSERT( isTyCoVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty) extendSubst (Subst in_scope ids tvs) id expr = ASSERT( isId id ) Subst in_scope (extendVarEnv ids id expr) tvs @@ -210,19 +220,30 @@ extendSubstList subst [] = subst extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs -- | Find the substitution for an 'Id' in the 'Subst' -lookupIdSubst :: Subst -> Id -> CoreExpr -lookupIdSubst (Subst in_scope ids _) v +lookupIdSubst :: SDoc -> Subst -> Id -> CoreExpr +lookupIdSubst doc (Subst in_scope ids _) v | not (isLocalId v) = Var v | Just e <- lookupVarEnv ids v = e | Just v' <- lookupInScope in_scope v = Var v' -- Vital! See Note [Extending the Subst] - | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope ) + | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope $$ doc) Var v -- | Find the substitution for a 'TyVar' in the 'Subst' lookupTvSubst :: Subst -> TyVar -> Type lookupTvSubst (Subst _ _ tvs) v = lookupVarEnv tvs v `orElse` Type.mkTyVarTy v +delBndr :: Subst -> Var -> Subst +delBndr (Subst in_scope tvs ids) v + | isId v = Subst in_scope tvs (delVarEnv ids v) + | otherwise = Subst in_scope (delVarEnv tvs v) ids + +delBndrs :: Subst -> [Var] -> Subst +delBndrs (Subst in_scope tvs ids) vs + = Subst in_scope (delVarEnvList tvs vs_tv) (delVarEnvList ids vs_id) + where + (vs_id, vs_tv) = partition isId vs + -- | Simultaneously substitute for a bunch of variables -- No left-right shadowing -- ie the substitution for (\x \y. e) a1 a2 @@ -236,7 +257,14 @@ mkOpenSubst in_scope pairs = Subst in_scope isInScope :: Var -> Subst -> Bool isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope --- | Add the 'Var' to the in-scope set: as a side effect, removes any existing substitutions for it +-- | Add the 'Var' to the in-scope set, but do not remove +-- any existing substitutions for it +addInScopeSet :: Subst -> VarSet -> Subst +addInScopeSet (Subst in_scope ids tvs) vs + = Subst (in_scope `extendInScopeSetSet` vs) ids tvs + +-- | Add the 'Var' to the in-scope set: as a side effect, +-- and remove any existing substitutions for it extendInScope :: Subst -> Var -> Subst extendInScope (Subst in_scope ids tvs) v = Subst (in_scope `extendInScopeSet` v) @@ -254,6 +282,9 @@ extendInScopeIds :: Subst -> [Id] -> Subst extendInScopeIds (Subst in_scope ids tvs) vs = Subst (in_scope `extendInScopeSetList` vs) (ids `delVarEnvList` vs) tvs + +setInScope :: Subst -> InScopeSet -> Subst +setInScope (Subst _ ids tvs) in_scope = Subst in_scope ids tvs \end{code} Pretty printing, for debugging only @@ -280,21 +311,36 @@ instance Outputable Subst where -- -- Do *not* attempt to short-cut in the case of an empty substitution! -- See Note [Extending the Subst] -substExpr :: Subst -> CoreExpr -> CoreExpr -substExpr subst expr +substExprSC :: SDoc -> Subst -> CoreExpr -> CoreExpr +substExprSC _doc subst orig_expr + | isEmptySubst subst = orig_expr + | otherwise = -- pprTrace "enter subst-expr" (doc $$ ppr orig_expr) $ + subst_expr subst orig_expr + +substExpr :: SDoc -> Subst -> CoreExpr -> CoreExpr +substExpr _doc subst orig_expr = subst_expr subst orig_expr + +subst_expr :: Subst -> CoreExpr -> CoreExpr +subst_expr subst expr = go expr where - go (Var v) = lookupIdSubst subst v + go (Var v) = lookupIdSubst (text "subst_expr") subst v go (Type ty) = Type (substTy subst ty) go (Lit lit) = Lit lit go (App fun arg) = App (go fun) (go arg) go (Note note e) = Note (go_note note) (go e) - go (Cast e co) = Cast (go e) (substTy subst co) - go (Lam bndr body) = Lam bndr' (substExpr subst' body) + go (Cast e co) = Cast (go e) (optCoercion (getTvSubst subst) co) + -- Do not optimise even identity coercions + -- Reason: substitution applies to the LHS of RULES, and + -- if you "optimise" an identity coercion, you may + -- lose a binder. We optimise the LHS of rules at + -- construction time + + go (Lam bndr body) = Lam bndr' (subst_expr subst' body) where (subst', bndr') = substBndr subst bndr - go (Let bind body) = Let bind' (substExpr subst' body) + go (Let bind body) = Let bind' (subst_expr subst' body) where (subst', bind') = substBind subst bind @@ -302,7 +348,7 @@ substExpr subst expr where (subst', bndr') = substBndr subst bndr - go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs) + go_alt subst (con, bndrs, rhs) = (con, bndrs', subst_expr subst' rhs) where (subst', bndrs') = substBndrs subst bndrs @@ -310,16 +356,32 @@ substExpr subst expr -- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst' -- that should be used by subsequent substitutons. -substBind :: Subst -> CoreBind -> (Subst, CoreBind) -substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs)) +substBind, substBindSC :: Subst -> CoreBind -> (Subst, CoreBind) + +substBindSC subst bind -- Short-cut if the substitution is empty + | not (isEmptySubst subst) + = substBind subst bind + | otherwise + = case bind of + NonRec bndr rhs -> (subst', NonRec bndr' rhs) + where + (subst', bndr') = substBndr subst bndr + Rec pairs -> (subst', Rec (bndrs' `zip` rhss')) + where + (bndrs, rhss) = unzip pairs + (subst', bndrs') = substRecBndrs subst bndrs + rhss' | isEmptySubst subst' = rhss + | otherwise = map (subst_expr subst') rhss + +substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (subst_expr subst rhs)) where (subst', bndr') = substBndr subst bndr -substBind subst (Rec pairs) = (subst', Rec pairs') +substBind subst (Rec pairs) = (subst', Rec (bndrs' `zip` rhss')) where - (subst', bndrs') = substRecBndrs subst (map fst pairs) - pairs' = bndrs' `zip` rhss' - rhss' = map (substExpr subst' . snd) pairs + (bndrs, rhss) = unzip pairs + (subst', bndrs') = substRecBndrs subst bndrs + rhss' = map (subst_expr subst') rhss \end{code} \begin{code} @@ -354,8 +416,8 @@ preserve occ info in rules. -- 'IdInfo' is preserved by this process, although it is substituted into appropriately. substBndr :: Subst -> Var -> (Subst, Var) substBndr subst bndr - | isTyVar bndr = substTyVarBndr subst bndr - | otherwise = substIdBndr subst subst bndr + | isTyCoVar bndr = substTyVarBndr subst bndr + | otherwise = substIdBndr (text "var-bndr") subst subst bndr -- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right substBndrs :: Subst -> [Var] -> (Subst, [Var]) @@ -366,18 +428,20 @@ substRecBndrs :: Subst -> [Id] -> (Subst, [Id]) substRecBndrs subst bndrs = (new_subst, new_bndrs) where -- Here's the reason we need to pass rec_subst to subst_id - (new_subst, new_bndrs) = mapAccumL (substIdBndr new_subst) subst bndrs + (new_subst, new_bndrs) = mapAccumL (substIdBndr (text "rec-bndr") new_subst) subst bndrs \end{code} \begin{code} -substIdBndr :: Subst -- ^ Substitution to use for the IdInfo +substIdBndr :: SDoc + -> Subst -- ^ Substitution to use for the IdInfo -> Subst -> Id -- ^ Substitition and Id to transform -> (Subst, Id) -- ^ Transformed pair -- NB: unfolding may be zapped -substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id - = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id) +substIdBndr _doc rec_subst subst@(Subst in_scope env tvs) old_id + = -- pprTrace "substIdBndr" (doc $$ ppr old_id $$ ppr in_scope) $ + (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id) where id1 = uniqAway in_scope old_id -- id1 is cloned if necessary id2 | no_type_change = id1 @@ -409,7 +473,7 @@ It also unconditionally zaps the OccInfo. \begin{code} -- | Very similar to 'substBndr', but it always allocates a new 'Unique' for --- each variable in its output and removes all 'IdInfo' +-- each variable in its output. It substitutes the IdInfo though. cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id) cloneIdBndr subst us old_id = clone_id subst subst (old_id, uniqFromSupply us) @@ -462,8 +526,10 @@ substTyVarBndr (Subst in_scope id_env tv_env) tv -- | See 'Type.substTy' substTy :: Subst -> Type -> Type -substTy (Subst in_scope _id_env tv_env) ty - = Type.substTy (TvSubst in_scope tv_env) ty +substTy subst ty = Type.substTy (getTvSubst subst) ty + +getTvSubst :: Subst -> TvSubst +getTvSubst (Subst in_scope _id_env tv_env) = TvSubst in_scope tv_env \end{code} @@ -486,7 +552,6 @@ substIdType subst@(Subst _ _ tv_env) id ------------------ -- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'. --- Always zaps the unfolding, to save substitution work substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo substIdInfo subst new_id info | nothing_to_do = Nothing @@ -500,41 +565,58 @@ substIdInfo subst new_id info ------------------ -- | Substitutes for the 'Id's within an unfolding -substUnfolding :: Subst -> Unfolding -> Unfolding +substUnfolding, substUnfoldingSC :: Subst -> Unfolding -> Unfolding -- Seq'ing on the returned Unfolding is enough to cause -- all the substitutions to happen completely -substUnfolding subst (DFunUnfolding con args) - = DFunUnfolding con (map (substExpr subst) args) -substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_guidance = guide@(InlineRule {}) }) +substUnfoldingSC subst unf -- Short-cut version + | isEmptySubst subst = unf + | otherwise = substUnfolding subst unf + +substUnfolding subst (DFunUnfolding ar con args) + = DFunUnfolding ar con (map subst_arg args) + where + subst_arg = fmap (substExpr (text "dfun-unf") subst) + +substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_src = src }) -- Retain an InlineRule! + | not (isStableSource src) -- Zap an unstable unfolding, to save substitution work + = NoUnfolding + | otherwise -- But keep a stable one! = seqExpr new_tmpl `seq` - new_mb_wkr `seq` - unf { uf_tmpl = new_tmpl, uf_guidance = guide { ug_ir_info = new_mb_wkr } } + new_src `seq` + unf { uf_tmpl = new_tmpl, uf_src = new_src } where - new_tmpl = substExpr subst tmpl - new_mb_wkr = substInlineRuleGuidance subst (ug_ir_info guide) + new_tmpl = substExpr (text "subst-unf") subst tmpl + new_src = substUnfoldingSource subst src -substUnfolding _ (CoreUnfolding {}) = NoUnfolding -- Discard - -- Always zap a CoreUnfolding, to save substitution work - -substUnfolding _ unf = unf -- Otherwise no substitution to do +substUnfolding _ unf = unf -- NoUnfolding, OtherCon ------------------- -substInlineRuleGuidance :: Subst -> InlineRuleInfo -> InlineRuleInfo -substInlineRuleGuidance subst (InlWrapper wkr) - = case lookupIdSubst subst wkr of - Var w1 -> InlWrapper w1 - other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr wkr ) - InlUnSat -- Worker has got substituted away altogether - -- (This can happen if it's trivial, via - -- postInlineUnconditionally, hence only warning) -substInlineRuleGuidance _ info = info +substUnfoldingSource :: Subst -> UnfoldingSource -> UnfoldingSource +substUnfoldingSource (Subst in_scope ids _) (InlineWrapper wkr) + | Just wkr_expr <- lookupVarEnv ids wkr + = case wkr_expr of + Var w1 -> InlineWrapper w1 + _other -> -- WARN( True, text "Interesting! CoreSubst.substWorker1:" <+> ppr wkr + -- <+> ifPprDebug (equals <+> ppr wkr_expr) ) + -- Note [Worker inlining] + InlineStable -- It's not a wrapper any more, but still inline it! + + | Just w1 <- lookupInScope in_scope wkr = InlineWrapper w1 + | otherwise = -- WARN( True, text "Interesting! CoreSubst.substWorker2:" <+> ppr wkr ) + -- This can legitimately happen. The worker has been inlined and + -- dropped as dead code, because we don't treat the UnfoldingSource + -- as an "occurrence". + -- Note [Worker inlining] + InlineStable + +substUnfoldingSource _ src = src ------------------ substIdOcc :: Subst -> Id -> Id -- These Ids should not be substituted to non-Ids -substIdOcc subst v = case lookupIdSubst subst v of +substIdOcc subst v = case lookupIdSubst (text "substIdOcc") subst v of Var v' -> v' other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst]) @@ -551,7 +633,9 @@ substSpec subst new_id (SpecInfo rules rhs_fvs) ------------------ substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule] substRulesForImportedIds subst rules - = map (substRule subst (\name -> name)) rules + = map (substRule subst not_needed) rules + where + not_needed name = pprPanic "substRulesForImportedIds" (ppr name) ------------------ substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule @@ -565,11 +649,16 @@ substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule substRule _ _ rule@(BuiltinRule {}) = rule substRule subst subst_ru_fn rule@(Rule { ru_bndrs = bndrs, ru_args = args - , ru_fn = fn_name, ru_rhs = rhs }) + , ru_fn = fn_name, ru_rhs = rhs + , ru_local = is_local }) = rule { ru_bndrs = bndrs', - ru_fn = subst_ru_fn fn_name, - ru_args = map (substExpr subst') args, - ru_rhs = substExpr subst' rhs } + ru_fn = if is_local + then subst_ru_fn fn_name + else fn_name, + ru_args = map (substExpr (text "subst-rule" <+> ppr fn_name) subst') args, + ru_rhs = simpleOptExprWith subst' rhs } + -- Do simple optimisation on RHS, in case substitution lets + -- you improve it. The real simplifier never gets to look at it. where (subst', bndrs') = substBndrs subst bndrs @@ -579,10 +668,22 @@ substVarSet subst fvs = foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs where subst_fv subst fv - | isId fv = exprFreeVars (lookupIdSubst subst fv) + | isId fv = exprFreeVars (lookupIdSubst (text "substVarSet") subst fv) | otherwise = Type.tyVarsOfType (lookupTvSubst subst fv) \end{code} +Note [Worker inlining] +~~~~~~~~~~~~~~~~~~~~~~ +A worker can get sustituted away entirely. + - it might be trivial + - it might simply be very small +We do not treat an InlWrapper as an 'occurrence' in the occurence +analyser, so it's possible that the worker is not even in scope any more. + +In all all these cases we simply drop the special case, returning to +InlVanilla. The WARN is just so I can see if it happens a lot. + + %************************************************************************ %* * The Very Simple Optimiser @@ -601,7 +702,8 @@ simpleOptExpr :: CoreExpr -> CoreExpr -- may change radically simpleOptExpr expr - = go init_subst (occurAnalyseExpr expr) + = -- pprTrace "simpleOptExpr" (ppr init_subst $$ ppr expr) + simpleOptExprWith init_subst expr where init_subst = mkEmptySubst (mkInScopeSet (exprFreeVars expr)) -- It's potentially important to make a proper in-scope set @@ -614,71 +716,207 @@ simpleOptExpr expr -- It's a bit painful to call exprFreeVars, because it makes -- three passes instead of two (occ-anal, and go) - go subst (Var v) = lookupIdSubst subst v - go subst (App e1 e2) = App (go subst e1) (go subst e2) - go subst (Type ty) = Type (substTy subst ty) - go _ (Lit lit) = Lit lit - go subst (Note note e) = Note note (go subst e) - go subst (Cast e co) = Cast (go subst e) (substTy subst co) - go subst (Let bind body) = go_let subst bind body - go subst (Lam bndr body) = Lam bndr' (go subst' body) - where - (subst', bndr') = substBndr subst bndr - - go subst (Case e b ty as) = Case (go subst e) b' - (substTy subst ty) - (map (go_alt subst') as) - where - (subst', b') = substBndr subst b - - - ---------------------- - go_alt subst (con, bndrs, rhs) = (con, bndrs', go subst' rhs) - where - (subst', bndrs') = substBndrs subst bndrs - - ---------------------- - go_let subst (Rec prs) body - = Let (Rec (reverse rev_prs')) (go subst'' body) - where - (subst', bndrs') = substRecBndrs subst (map fst prs) - (subst'', rev_prs') = foldl do_pr (subst', []) (prs `zip` bndrs') - do_pr (subst, prs) ((b,r), b') = case go_bind subst b r of - Left subst' -> (subst', prs) - Right r' -> (subst, (b',r'):prs) +simpleOptExprWith :: Subst -> InExpr -> OutExpr +simpleOptExprWith subst expr = simple_opt_expr subst (occurAnalyseExpr expr) - go_let subst (NonRec b r) body - = case go_bind subst b r of - Left subst' -> go subst' body - Right r' -> Let (NonRec b' r') (go subst' body) - where - (subst', b') = substBndr subst b +---------------------- +simpleOptPgm :: DynFlags -> [CoreBind] -> [CoreRule] -> IO ([CoreBind], [CoreRule]) +simpleOptPgm dflags binds rules + = do { dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis" + (pprCoreBindings occ_anald_binds); + ; return (reverse binds', substRulesForImportedIds subst' rules) } + where + occ_anald_binds = occurAnalysePgm Nothing {- No rules active -} + rules binds + (subst', binds') = foldl do_one (emptySubst, []) occ_anald_binds + + do_one (subst, binds') bind + = case simple_opt_bind subst bind of + (subst', Nothing) -> (subst', binds') + (subst', Just bind') -> (subst', bind':binds') + +---------------------- +type InVar = Var +type OutVar = Var +type InId = Id +type OutId = Id +type InExpr = CoreExpr +type OutExpr = CoreExpr + +-- In these functions the substitution maps InVar -> OutExpr + +---------------------- +simple_opt_expr :: Subst -> InExpr -> OutExpr +simple_opt_expr subst expr + = go expr + where + go (Var v) = lookupIdSubst (text "simpleOptExpr") subst v + go (App e1 e2) = simple_app subst e1 [go e2] + go (Type ty) = Type (substTy subst ty) + go (Lit lit) = Lit lit + go (Note note e) = Note note (go e) + go (Cast e co) | isIdentityCoercion co' = go e + | otherwise = Cast (go e) co' + where + co' = substTy subst co + + go (Let bind body) = case simple_opt_bind subst bind of + (subst', Nothing) -> simple_opt_expr subst' body + (subst', Just bind) -> Let bind (simple_opt_expr subst' body) + + go lam@(Lam {}) = go_lam [] subst lam + go (Case e b ty as) = Case (go e) b' (substTy subst ty) + (map (go_alt subst') as) + where + (subst', b') = subst_opt_bndr subst b ---------------------- - go_bind :: Subst -> Var -> CoreExpr -> Either Subst CoreExpr - -- (go_bind subst old_var old_rhs) - -- either extends subst with (old_var -> new_rhs) - -- or return new_rhs for a binding new_var = new_rhs - go_bind subst b r - | Type ty <- r - , isTyVar b -- let a::* = TYPE ty in - = Left (extendTvSubst subst b (substTy subst ty)) - - | isId b -- let x = e in - , safe_to_inline (idOccInfo b) || exprIsTrivial r' - = Left (extendIdSubst subst b r') - - | otherwise - = Right r' + go_alt subst (con, bndrs, rhs) + = (con, bndrs', simple_opt_expr subst' rhs) where - r' = go subst r + (subst', bndrs') = subst_opt_bndrs subst bndrs ---------------------- + -- go_lam tries eta reduction + go_lam bs' subst (Lam b e) + = go_lam (b':bs') subst' e + where + (subst', b') = subst_opt_bndr subst b + go_lam bs' subst e + | Just etad_e <- tryEtaReduce bs e' = etad_e + | otherwise = mkLams bs e' + where + bs = reverse bs' + e' = simple_opt_expr subst e + +---------------------- +-- simple_app collects arguments for beta reduction +simple_app :: Subst -> InExpr -> [OutExpr] -> CoreExpr +simple_app subst (App e1 e2) as + = simple_app subst e1 (simple_opt_expr subst e2 : as) +simple_app subst (Lam b e) (a:as) + = case maybe_substitute subst b a of + Just ext_subst -> simple_app ext_subst e as + Nothing -> Let (NonRec b2 a) (simple_app subst' e as) + where + (subst', b') = subst_opt_bndr subst b + b2 = add_info subst' b b' +simple_app subst e as + = foldl App (simple_opt_expr subst e) as + +---------------------- +simple_opt_bind :: Subst -> CoreBind -> (Subst, Maybe CoreBind) +simple_opt_bind subst (Rec prs) + = (subst'', Just (Rec (reverse rev_prs'))) + where + (subst', bndrs') = subst_opt_bndrs subst (map fst prs) + (subst'', rev_prs') = foldl do_pr (subst', []) (prs `zip` bndrs') + do_pr (subst, prs) ((b,r), b') + = case maybe_substitute subst b r2 of + Just subst' -> (subst', prs) + Nothing -> (subst, (b2,r2):prs) + where + b2 = add_info subst b b' + r2 = simple_opt_expr subst r + +simple_opt_bind subst (NonRec b r) + = case maybe_substitute subst b r' of + Just ext_subst -> (ext_subst, Nothing) + Nothing -> (subst', Just (NonRec b2 r')) + where + r' = simple_opt_expr subst r + (subst', b') = subst_opt_bndr subst b + b2 = add_info subst' b b' + +---------------------- +maybe_substitute :: Subst -> InVar -> OutExpr -> Maybe Subst + -- (maybe_substitute subst in_var out_rhs) + -- either extends subst with (in_var -> out_rhs) + -- or returns Nothing +maybe_substitute subst b r + | Type ty <- r -- let a::* = TYPE ty in + = ASSERT( isTyCoVar b ) + Just (extendTvSubst subst b ty) + + | isId b -- let x = e in + , safe_to_inline (idOccInfo b) + , isAlwaysActive (idInlineActivation b) -- Note [Inline prag in simplOpt] + , not (isStableUnfolding (idUnfolding b)) + , not (isExportedId b) + = Just (extendIdSubst subst b r) + + | otherwise + = Nothing + where -- Unconditionally safe to inline safe_to_inline :: OccInfo -> Bool - safe_to_inline IAmDead = True - safe_to_inline (OneOcc in_lam one_br _) = not in_lam && one_br safe_to_inline (IAmALoopBreaker {}) = False - safe_to_inline NoOccInfo = False + safe_to_inline IAmDead = True + safe_to_inline (OneOcc in_lam one_br _) = (not in_lam && one_br) || exprIsTrivial r + safe_to_inline NoOccInfo = exprIsTrivial r + +---------------------- +subst_opt_bndr :: Subst -> InVar -> (Subst, OutVar) +subst_opt_bndr subst bndr + | isTyCoVar bndr = substTyVarBndr subst bndr + | otherwise = subst_opt_id_bndr subst bndr + +subst_opt_id_bndr :: Subst -> InId -> (Subst, OutId) +-- Nuke all fragile IdInfo, unfolding, and RULES; +-- it gets added back later by add_info +-- Rather like SimplEnv.substIdBndr +-- +-- It's important to zap fragile OccInfo (which CoreSubst.SubstIdBndr +-- carefully does not do) because simplOptExpr invalidates it + +subst_opt_id_bndr subst@(Subst in_scope id_subst tv_subst) old_id + = (Subst new_in_scope new_id_subst tv_subst, new_id) + where + id1 = uniqAway in_scope old_id + id2 = setIdType id1 (substTy subst (idType old_id)) + new_id = zapFragileIdInfo id2 -- Zaps rules, worker-info, unfolding + -- and fragile OccInfo + new_in_scope = in_scope `extendInScopeSet` new_id + + -- Extend the substitution if the unique has changed, + -- or there's some useful occurrence information + -- See the notes with substTyVarBndr for the delSubstEnv + new_id_subst | new_id /= old_id + = extendVarEnv id_subst old_id (Var new_id) + | otherwise + = delVarEnv id_subst old_id + +---------------------- +subst_opt_bndrs :: Subst -> [InVar] -> (Subst, [OutVar]) +subst_opt_bndrs subst bndrs + = mapAccumL subst_opt_bndr subst bndrs + +---------------------- +add_info :: Subst -> InVar -> OutVar -> OutVar +add_info subst old_bndr new_bndr + | isTyCoVar old_bndr = new_bndr + | otherwise = maybeModifyIdInfo mb_new_info new_bndr + where + mb_new_info = substIdInfo subst new_bndr (idInfo old_bndr) \end{code} + +Note [Inline prag in simplOpt] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If there's an INLINE/NOINLINE pragma that restricts the phase in +which the binder can be inlined, we don't inline here; after all, +we don't know what phase we're in. Here's an example + + foo :: Int -> Int -> Int + {-# INLINE foo #-} + foo m n = inner m + where + {-# INLINE [1] inner #-} + inner m = m+n + + bar :: Int -> Int + bar n = foo n 1 + +When inlining 'foo' in 'bar' we want the let-binding for 'inner' +to remain visible until Phase 1 +