X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FcoreSyn%2FCoreSubst.lhs;h=9f1e20db4d20d83d95810bd15c5ffc1cbb6ed6d1;hp=582ece2124a83a8861eade2817bfdb4b59974a5a;hb=b06d623b2e367a572de5daf06d6a0b12c2740471;hpb=cb579c2b44b9e7aa6fdbda2b70a1361035ff2ef5 diff --git a/compiler/coreSyn/CoreSubst.lhs b/compiler/coreSyn/CoreSubst.lhs index 582ece2..9f1e20d 100644 --- a/compiler/coreSyn/CoreSubst.lhs +++ b/compiler/coreSyn/CoreSubst.lhs @@ -11,12 +11,12 @@ module CoreSubst ( Subst, TvSubstEnv, IdSubstEnv, InScopeSet, -- ** Substituting into expressions and related types - deShadowBinds, - substTy, substExpr, substSpec, substWorker, - lookupIdSubst, lookupTvSubst, + deShadowBinds, substSpec, substRulesForImportedIds, + substTy, substExpr, substBind, substUnfolding, + substUnfoldingSource, lookupIdSubst, lookupTvSubst, substIdOcc, -- ** Operations on substitutions - emptySubst, mkEmptySubst, mkSubst, substInScope, isEmptySubst, + emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst, extendIdSubst, extendIdSubstList, extendTvSubst, extendTvSubstList, extendSubst, extendSubstList, zapSubstEnv, extendInScope, extendInScopeList, extendInScopeIds, @@ -24,7 +24,10 @@ module CoreSubst ( -- ** Substituting and cloning binders substBndr, substBndrs, substRecBndrs, - cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs + cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs, + + -- ** Simple expression optimiser + simpleOptExpr ) where #include "HsVersions.h" @@ -32,17 +35,21 @@ module CoreSubst ( import CoreSyn import CoreFVs import CoreUtils +import OccurAnal( occurAnalyseExpr ) import qualified Type import Type ( Type, TvSubst(..), TvSubstEnv ) +import OptCoercion ( optCoercion ) import VarSet import VarEnv import Id +import Name ( Name ) import Var ( Var, TyVar, setVarUnique ) import IdInfo import Unique import UniqSupply import Maybes +import BasicTypes ( isAlwaysActive ) import Outputable import PprCore () -- Instances import FastString @@ -89,8 +96,8 @@ data Subst -- Types.TvSubstEnv -- -- INVARIANT 3: See Note [Extending the Subst] +\end{code} -{- Note [Extending the Subst] ~~~~~~~~~~~~~~~~~~~~~~~~~~ For a core Subst, which binds Ids as well, we make a different choice for Ids @@ -118,6 +125,13 @@ In consequence: so we only extend the in-scope set. Then we must look up in the in-scope 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. + 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 + itself, whose range is assumed to be correct wrt the in-scope set.) + Why do we make a different choice for the IdSubstEnv than the TvSubstEnv? * For Ids, we change the IdInfo all the time (e.g. deleting the @@ -129,8 +143,8 @@ Why do we make a different choice for the IdSubstEnv than the TvSubstEnv? * For TyVars, only coercion variables can possibly change, and they are easy to spot --} +\begin{code} -- | An environment for substituting for 'Id's type IdSubstEnv = IdEnv CoreExpr @@ -204,13 +218,22 @@ lookupIdSubst (Subst in_scope ids _) 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 ) + | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope ) 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 +-- | Simultaneously substitute for a bunch of variables +-- No left-right shadowing +-- ie the substitution for (\x \y. e) a1 a2 +-- so neither x nor y scope over a1 a2 +mkOpenSubst :: InScopeSet -> [(Var,CoreArg)] -> Subst +mkOpenSubst in_scope pairs = Subst in_scope + (mkVarEnv [(id,e) | (id, e) <- pairs, isId id]) + (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs]) + ------------------------------ isInScope :: Var -> Subst -> Bool isInScope v (Subst in_scope _ _) = v `elemInScopeSet` in_scope @@ -256,6 +279,9 @@ instance Outputable Subst where \begin{code} -- | Apply a substititon to an entire 'CoreExpr'. Rememeber, you may only -- apply the substitution /once/: see "CoreSubst#apply_once" +-- +-- 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 = go expr @@ -265,7 +291,10 @@ substExpr subst expr 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 (Cast e co) = Cast (go e) (optCoercion (getTvSubst subst) co) + -- Optimise coercions as we go; this is good, for example + -- in the RHS of rules, which are only substituted in + go (Lam bndr body) = Lam bndr' (substExpr subst' body) where (subst', bndr') = substBndr subst bndr @@ -305,6 +334,9 @@ substBind subst (Rec pairs) = (subst', Rec pairs') -- -- (Actually, within a single /type/ there might still be shadowing, because -- 'substTy' is a no-op for the empty substitution, but that's probably OK.) +-- +-- [Aug 09] This function is not used in GHC at the moment, but seems so +-- short and simple that I'm going to leave it here deShadowBinds :: [CoreBind] -> [CoreBind] deShadowBinds binds = snd (mapAccumL substBind emptySubst binds) \end{code} @@ -435,8 +467,10 @@ 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} @@ -464,53 +498,97 @@ substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo substIdInfo subst new_id info | nothing_to_do = Nothing | otherwise = Just (info `setSpecInfo` substSpec subst new_id old_rules - `setWorkerInfo` substWorker subst old_wrkr - `setUnfoldingInfo` noUnfolding) + `setUnfoldingInfo` substUnfolding subst old_unf) where old_rules = specInfo info - old_wrkr = workerInfo info - nothing_to_do = isEmptySpecInfo old_rules && - not (workerExists old_wrkr) && - not (hasUnfolding (unfoldingInfo info)) + old_unf = unfoldingInfo info + nothing_to_do = isEmptySpecInfo old_rules && isClosedUnfolding old_unf ------------------ --- | Substitutes for the 'Id's within the 'WorkerInfo' -substWorker :: Subst -> WorkerInfo -> WorkerInfo - -- Seq'ing on the returned WorkerInfo is enough to cause all the - -- substitutions to happen completely - -substWorker _ NoWorker - = NoWorker -substWorker subst (HasWorker w a) - = case lookupIdSubst subst w of - Var w1 -> HasWorker w1 a - other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr w ) - NoWorker -- Worker has got substituted away altogether - -- (This can happen if it's trivial, - -- via postInlineUnconditionally, hence warning) +-- | Substitutes for the 'Id's within an unfolding +substUnfolding :: 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_src = src }) + -- Retain an InlineRule! + | not (isInlineRuleSource src) -- Always zap a CoreUnfolding, to save substitution work + = NoUnfolding + | otherwise -- But keep an InlineRule! + = seqExpr new_tmpl `seq` + new_src `seq` + unf { uf_tmpl = new_tmpl, uf_src = new_src } + where + new_tmpl = substExpr subst tmpl + new_src = substUnfoldingSource subst src + +substUnfolding _ unf = unf -- NoUnfolding, OtherCon + +------------------- +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] + InlineRule -- 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] + InlineRule + +substUnfoldingSource _ src = src + +------------------ +substIdOcc :: Subst -> Id -> Id +-- These Ids should not be substituted to non-Ids +substIdOcc subst v = case lookupIdSubst subst v of + Var v' -> v' + other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst]) ------------------ -- | Substitutes for the 'Id's within the 'WorkerInfo' given the new function 'Id' substSpec :: Subst -> Id -> SpecInfo -> SpecInfo +substSpec subst new_id (SpecInfo rules rhs_fvs) + = seqSpecInfo new_spec `seq` new_spec + where + subst_ru_fn = const (idName new_id) + new_spec = SpecInfo (map (substRule subst subst_ru_fn) rules) + (substVarSet subst rhs_fvs) + +------------------ +substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule] +substRulesForImportedIds subst rules + = map (substRule subst (\name -> name)) rules -substSpec subst new_fn spec@(SpecInfo rules rhs_fvs) - | isEmptySubst subst - = spec - | otherwise - = seqSpecInfo new_rules `seq` new_rules +------------------ +substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule + +-- The subst_ru_fn argument is applied to substitute the ru_fn field +-- of the rule: +-- - Rules for *imported* Ids never change ru_fn +-- - Rules for *local* Ids are in the IdInfo for that Id, +-- and the ru_fn field is simply replaced by the new name +-- of the Id + +substRule _ _ rule@(BuiltinRule {}) = rule +substRule subst subst_ru_fn rule@(Rule { ru_bndrs = bndrs, ru_args = args + , ru_fn = fn_name, ru_rhs = rhs }) + = rule { ru_bndrs = bndrs', + ru_fn = subst_ru_fn fn_name, + ru_args = map (substExpr subst') args, + ru_rhs = substExpr subst' rhs } where - new_name = idName new_fn - new_rules = SpecInfo (map do_subst rules) (substVarSet subst rhs_fvs) - - do_subst rule@(BuiltinRule {}) = rule - do_subst rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs }) - = rule { ru_bndrs = bndrs', - ru_fn = new_name, -- Important: the function may have changed its name! - ru_args = map (substExpr subst') args, - ru_rhs = substExpr subst' rhs } - where - (subst', bndrs') = substBndrs subst bndrs + (subst', bndrs') = substBndrs subst bndrs ------------------ substVarSet :: Subst -> VarSet -> VarSet @@ -521,3 +599,135 @@ substVarSet subst fvs | isId fv = exprFreeVars (lookupIdSubst 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 +%* * +%************************************************************************ + +\begin{code} +simpleOptExpr :: CoreExpr -> CoreExpr +-- Do simple optimisation on an expression +-- The optimisation is very straightforward: just +-- inline non-recursive bindings that are used only once, +-- or where the RHS is trivial +-- +-- The result is NOT guaranteed occurence-analysed, becuase +-- in (let x = y in ....) we substitute for x; so y's occ-info +-- may change radically + +simpleOptExpr expr + = go init_subst (occurAnalyseExpr expr) + where + init_subst = mkEmptySubst (mkInScopeSet (exprFreeVars expr)) + -- It's potentially important to make a proper in-scope set + -- Consider let x = ..y.. in \y. ...x... + -- Then we should remember to clone y before substituting + -- for x. It's very unlikely to occur, because we probably + -- won't *be* substituting for x if it occurs inside a + -- lambda. + -- + -- 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) + + 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 + + + ---------------------- + 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' + , isAlwaysActive (idInlineActivation b) -- Note [Inline prag in simplOpt] + = Left (extendIdSubst subst b r') + + | otherwise + = Right r' + where + r' = go subst r + + ---------------------- + -- 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 +\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 \ No newline at end of file