X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSimplUtils.lhs;h=501dd60ec9c538413b545b7c60d592264428422b;hb=08002107c35bdf124b1e3814d42734d82e392d45;hp=d346292c332ca9ca4bf968ee58b4b2ef59cd93d8;hpb=ff755dd9a0a0ad2f106c323852553ea247f16141;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/SimplUtils.lhs b/ghc/compiler/simplCore/SimplUtils.lhs index d346292..501dd60 100644 --- a/ghc/compiler/simplCore/SimplUtils.lhs +++ b/ghc/compiler/simplCore/SimplUtils.lhs @@ -5,39 +5,48 @@ \begin{code} module SimplUtils ( - simplBinder, simplBinders, simplIds, - transformRhs, - mkCase, findAlt, findDefault, + simplBinder, simplBinders, simplRecIds, simplLetId, + tryRhsTyLam, tryEtaExpansion, + mkCase, -- The continuation type SimplCont(..), DupFlag(..), contIsDupable, contResultType, - pushArgs, discardCont, countValArgs, countArgs, - analyseCont, discardInline + countValArgs, countArgs, mkRhsStop, mkStop, + getContArgs, interestingCallContext, interestingArg, isStrictType, discardInline ) where #include "HsVersions.h" -import CmdLineOpts ( opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge ) +import CmdLineOpts ( switchIsOn, SimplifierSwitch(..), + opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge, opt_DictsStrict, + opt_UF_UpdateInPlace + ) import CoreSyn -import CoreUnfold ( isValueUnfolding ) -import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, exprEtaExpandArity, bindNonRec ) -import Subst ( InScopeSet, mkSubst, substBndrs, substBndr, substIds, lookupIdSubst ) -import Id ( Id, idType, isId, idName, - idOccInfo, idUnfolding, - mkId, idInfo +import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, + etaExpand, exprEtaExpandArity, bindNonRec, mkCoerce, + findDefault + ) +import Subst ( InScopeSet, mkSubst, substExpr ) +import qualified Subst ( simplBndrs, simplBndr, simplLetId ) +import Id ( idType, idName, + idUnfolding, idStrictness, + mkLocalId, idInfo ) -import IdInfo ( arityLowerBound, setOccInfo, vanillaIdInfo ) +import IdInfo ( StrictnessInfo(..) ) import Maybes ( maybeToBool, catMaybes ) -import Name ( isLocalName, setNameUnique ) +import Name ( setNameUnique ) +import Demand ( isStrict ) import SimplMonad -import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys, seqType, repType, - splitTyConApp_maybe, mkTyVarTys, applyTys, splitFunTys, mkFunTys +import Type ( Type, mkForAllTys, seqType, repType, + splitTyConApp_maybe, tyConAppArgs, mkTyVarTys, + isDictTy, isDataType, isUnLiftedType, + splitRepFunTys ) import TyCon ( tyConDataConsIfAvailable ) import DataCon ( dataConRepArity ) -import VarSet -import VarEnv ( SubstEnv, SubstResult(..) ) +import VarEnv ( SubstEnv ) +import Util ( lengthExceeds, mapAccumL ) import Outputable \end{code} @@ -50,7 +59,10 @@ import Outputable \begin{code} data SimplCont -- Strict contexts - = Stop OutType -- Type of the result + = Stop OutType -- Type of the result + Bool -- True => This is the RHS of a thunk whose type suggests + -- that update-in-place would be possible + -- (This makes the inliner a little keener.) | CoerceIt OutType -- The To-type, simplified SimplCont @@ -69,14 +81,15 @@ data SimplCont -- Strict contexts | ArgOf DupFlag -- An arbitrary strict context: the argument -- of a strict function, or a primitive-arg fn -- or a PrimOp - OutType -- The type of the expression being sought by the context + OutType -- cont_ty: the type of the expression being sought by the context -- f (error "foo") ==> coerce t (error "foo") -- when f is strict -- We need to know the type t, to which to coerce. (OutExpr -> SimplM OutExprStuff) -- What to do with the result + -- The result expression in the OutExprStuff has type cont_ty instance Outputable SimplCont where - ppr (Stop _) = ptext SLIT("Stop") + ppr (Stop _ _) = ptext SLIT("Stop") ppr (ApplyTo dup arg se cont) = (ptext SLIT("ApplyTo") <+> ppr dup <+> ppr arg) $$ ppr cont ppr (ArgOf dup _ _) = ptext SLIT("ArgOf...") <+> ppr dup ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$ @@ -90,8 +103,16 @@ instance Outputable DupFlag where ppr OkToDup = ptext SLIT("ok") ppr NoDup = ptext SLIT("nodup") + +------------------- +mkRhsStop, mkStop :: OutType -> SimplCont +mkStop ty = Stop ty False +mkRhsStop ty = Stop ty (canUpdateInPlace ty) + + +------------------- contIsDupable :: SimplCont -> Bool -contIsDupable (Stop _) = True +contIsDupable (Stop _ _) = True contIsDupable (ApplyTo OkToDup _ _ _) = True contIsDupable (ArgOf OkToDup _ _) = True contIsDupable (Select OkToDup _ _ _ _) = True @@ -99,25 +120,37 @@ contIsDupable (CoerceIt _ cont) = contIsDupable cont contIsDupable (InlinePlease cont) = contIsDupable cont contIsDupable other = False -pushArgs :: SubstEnv -> [InExpr] -> SimplCont -> SimplCont -pushArgs se [] cont = cont -pushArgs se (arg:args) cont = ApplyTo NoDup arg se (pushArgs se args cont) +------------------- +discardInline :: SimplCont -> SimplCont +discardInline (InlinePlease cont) = cont +discardInline (ApplyTo d e s cont) = ApplyTo d e s (discardInline cont) +discardInline cont = cont + +------------------- +discardableCont :: SimplCont -> Bool +discardableCont (Stop _ _) = False +discardableCont (CoerceIt _ cont) = discardableCont cont +discardableCont (InlinePlease cont) = discardableCont cont +discardableCont other = True discardCont :: SimplCont -- A continuation, expecting -> SimplCont -- Replace the continuation with a suitable coerce -discardCont (Stop to_ty) = Stop to_ty -discardCont cont = CoerceIt to_ty (Stop to_ty) - where - to_ty = contResultType cont +discardCont cont = case cont of + Stop to_ty _ -> cont + other -> CoerceIt to_ty (mkStop to_ty) + where + to_ty = contResultType cont +------------------- contResultType :: SimplCont -> OutType -contResultType (Stop to_ty) = to_ty +contResultType (Stop to_ty _) = to_ty contResultType (ArgOf _ to_ty _) = to_ty contResultType (ApplyTo _ _ _ cont) = contResultType cont contResultType (CoerceIt _ cont) = contResultType cont contResultType (InlinePlease cont) = contResultType cont contResultType (Select _ _ _ _ cont) = contResultType cont +------------------- countValArgs :: SimplCont -> Int countValArgs (ApplyTo _ (Type ty) se cont) = countValArgs cont countValArgs (ApplyTo _ val_arg se cont) = 1 + countValArgs cont @@ -129,8 +162,133 @@ countArgs other = 0 \end{code} -Comment about analyseCont -~~~~~~~~~~~~~~~~~~~~~~~~~ +\begin{code} +getContArgs :: OutId -> SimplCont + -> SimplM ([(InExpr, SubstEnv, Bool)], -- Arguments; the Bool is true for strict args + SimplCont, -- Remaining continuation + Bool) -- Whether we came across an InlineCall +-- getContArgs id k = (args, k', inl) +-- args are the leading ApplyTo items in k +-- (i.e. outermost comes first) +-- augmented with demand info from the functionn +getContArgs fun orig_cont + = getSwitchChecker `thenSmpl` \ chkr -> + let + -- Ignore strictness info if the no-case-of-case + -- flag is on. Strictness changes evaluation order + -- and that can change full laziness + stricts | switchIsOn chkr NoCaseOfCase = vanilla_stricts + | otherwise = computed_stricts + in + go [] stricts False orig_cont + where + ---------------------------- + + -- Type argument + go acc ss inl (ApplyTo _ arg@(Type _) se cont) + = go ((arg,se,False) : acc) ss inl cont + -- NB: don't bother to instantiate the function type + + -- Value argument + go acc (s:ss) inl (ApplyTo _ arg se cont) + = go ((arg,se,s) : acc) ss inl cont + + -- An Inline continuation + go acc ss inl (InlinePlease cont) + = go acc ss True cont + + -- We're run out of arguments, or else we've run out of demands + -- The latter only happens if the result is guaranteed bottom + -- This is the case for + -- * case (error "hello") of { ... } + -- * (error "Hello") arg + -- * f (error "Hello") where f is strict + -- etc + go acc ss inl cont + | null ss && discardableCont cont = tick BottomFound `thenSmpl_` + returnSmpl (reverse acc, discardCont cont, inl) + | otherwise = returnSmpl (reverse acc, cont, inl) + + ---------------------------- + vanilla_stricts, computed_stricts :: [Bool] + vanilla_stricts = repeat False + computed_stricts = zipWith (||) fun_stricts arg_stricts + + ---------------------------- + (val_arg_tys, _) = splitRepFunTys (idType fun) + arg_stricts = map isStrictType val_arg_tys ++ repeat False + -- These argument types are used as a cheap and cheerful way to find + -- unboxed arguments, which must be strict. But it's an InType + -- and so there might be a type variable where we expect a function + -- type (the substitution hasn't happened yet). And we don't bother + -- doing the type applications for a polymorphic function. + -- Hence the split*Rep*FunTys + + ---------------------------- + -- If fun_stricts is finite, it means the function returns bottom + -- after that number of value args have been consumed + -- Otherwise it's infinite, extended with False + fun_stricts + = case idStrictness fun of + StrictnessInfo demands result_bot + | not (demands `lengthExceeds` countValArgs orig_cont) + -> -- Enough args, use the strictness given. + -- For bottoming functions we used to pretend that the arg + -- is lazy, so that we don't treat the arg as an + -- interesting context. This avoids substituting + -- top-level bindings for (say) strings into + -- calls to error. But now we are more careful about + -- inlining lone variables, so its ok (see SimplUtils.analyseCont) + if result_bot then + map isStrict demands -- Finite => result is bottom + else + map isStrict demands ++ vanilla_stricts + + other -> vanilla_stricts -- Not enough args, or no strictness + + +------------------- +isStrictType :: Type -> Bool + -- isStrictType computes whether an argument (or let RHS) should + -- be computed strictly or lazily, based only on its type +isStrictType ty + | isUnLiftedType ty = True + | opt_DictsStrict && isDictTy ty && isDataType ty = True + | otherwise = False + -- Return true only for dictionary types where the dictionary + -- has more than one component (else we risk poking on the component + -- of a newtype dictionary) + +------------------- +interestingArg :: InScopeSet -> InExpr -> SubstEnv -> Bool + -- An argument is interesting if it has *some* structure + -- We are here trying to avoid unfolding a function that + -- is applied only to variables that have no unfolding + -- (i.e. they are probably lambda bound): f x y z + -- There is little point in inlining f here. +interestingArg in_scope arg subst + = analyse (substExpr (mkSubst in_scope subst) arg) + -- 'analyse' only looks at the top part of the result + -- and substExpr is lazy, so this isn't nearly as brutal + -- as it looks. + where + analyse (Var v) = hasSomeUnfolding (idUnfolding v) + -- Was: isValueUnfolding (idUnfolding v') + -- But that seems over-pessimistic + analyse (Type _) = False + analyse (App fn (Type _)) = analyse fn + analyse (Note _ a) = analyse a + analyse other = True + -- Consider let x = 3 in f x + -- The substitution will contain (x -> ContEx 3), and we want to + -- to say that x is an interesting argument. + -- But consider also (\x. f x y) y + -- The substitution will contain (x -> ContEx y), and we want to say + -- that x is not interesting (assuming y has no unfolding) +\end{code} + +Comment about interestingCallContext +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ We want to avoid inlining an expression where there can't possibly be any gain, such as in an argument position. Hence, if the continuation is interesting (eg. a case scrutinee, application etc.) then we @@ -163,13 +321,9 @@ contIsInteresting looks for case expressions with just a single default case. \begin{code} -analyseCont :: InScopeSet -> SimplCont - -> ([Bool], -- Arg-info flags; one for each value argument - Bool, -- Context of the result of the call is interesting - Bool) -- There was an InlinePlease - -analyseCont in_scope cont - = case cont of +interestingCallContext :: Bool -- False <=> no args at all + -> Bool -- False <=> no value args + -> SimplCont -> Bool -- The "lone-variable" case is important. I spent ages -- messing about with unsatisfactory varaints, but this is nice. -- The idea is that if a variable appear all alone @@ -177,11 +331,15 @@ analyseCont in_scope cont -- as scrutinee of a case Select -- as arg of a strict fn ArgOf -- then we should not inline it (unless there is some other reason, - -- e.g. is is the sole occurrence). - -- Why not? At least in the case-scrutinee situation, turning - -- case x of y -> ... + -- e.g. is is the sole occurrence). We achieve this by making + -- interestingCallContext return False for a lone variable. + -- + -- Why? At least in the case-scrutinee situation, turning + -- let x = (a,b) in case x of y -> ... -- into - -- let y = (a,b) in ... + -- let x = (a,b) in case (a,b) of y -> ... + -- and thence to + -- let x = (a,b) in let y = (a,b) in ... -- is bad if the binding for x will remain. -- -- Another example: I discovered that strings @@ -194,62 +352,30 @@ analyseCont in_scope cont -- the context can ``see'' the unfolding of the variable (e.g. case or a RULE) -- so there's no gain. -- - -- However, even a type application isn't a lone variable. Consider + -- However, even a type application or coercion isn't a lone variable. + -- Consider -- case $fMonadST @ RealWorld of { :DMonad a b c -> c } -- We had better inline that sucker! The case won't see through it. - - (Stop _) -> boring_result -- Don't inline a lone variable - (Select _ _ _ _ _) -> boring_result -- Ditto - (ArgOf _ _ _) -> boring_result -- Ditto - (ApplyTo _ (Type _) _ cont) -> analyse_ty_app cont - other -> analyse_app cont + -- + -- For now, I'm treating treating a variable applied to types + -- in a *lazy* context "lone". The motivating example was + -- f = /\a. \x. BIG + -- g = /\a. \y. h (f a) + -- There's no advantage in inlining f here, and perhaps + -- a significant disadvantage. Hence some_val_args in the Stop case + +interestingCallContext some_args some_val_args cont + = interesting cont where - boring_result = ([], False, False) - - -- For now, I'm treating not treating a variable applied to types as - -- "lone". The motivating example was - -- f = /\a. \x. BIG - -- g = /\a. \y. h (f a) - -- There's no advantage in inlining f here, and perhaps - -- a significant disadvantage. - analyse_ty_app (Stop _) = boring_result - analyse_ty_app (ArgOf _ _ _) = boring_result - analyse_ty_app (Select _ _ _ _ _) = ([], True, False) -- See the $fMonadST example above - analyse_ty_app (ApplyTo _ (Type _) _ cont) = analyse_ty_app cont - analyse_ty_app cont = analyse_app cont - - analyse_app (InlinePlease cont) - = case analyse_app cont of - (infos, icont, inline) -> (infos, icont, True) - - analyse_app (ApplyTo _ arg subst cont) - | isValArg arg = case analyse_app cont of - (infos, icont, inline) -> (analyse_arg subst arg : infos, icont, inline) - | otherwise = analyse_app cont - - analyse_app cont = ([], interesting_call_context cont, False) - - -- An argument is interesting if it has *some* structure - -- We are here trying to avoid unfolding a function that - -- is applied only to variables that have no unfolding - -- (i.e. they are probably lambda bound): f x y z - -- There is little point in inlining f here. - analyse_arg :: SubstEnv -> InExpr -> Bool - analyse_arg subst (Var v) = case lookupIdSubst (mkSubst in_scope subst) v of - DoneId v' _ -> isValueUnfolding (idUnfolding v') - other -> False - analyse_arg subst (Type _) = False - analyse_arg subst (App fn (Type _)) = analyse_arg subst fn - analyse_arg subst (Note _ a) = analyse_arg subst a - analyse_arg subst other = True - - interesting_call_context (Stop ty) = canUpdateInPlace ty - interesting_call_context (InlinePlease _) = True - interesting_call_context (Select _ _ _ _ _) = True - interesting_call_context (CoerceIt _ cont) = interesting_call_context cont - interesting_call_context (ApplyTo _ (Type _) _ cont) = interesting_call_context cont - interesting_call_context (ApplyTo _ _ _ _) = True - interesting_call_context (ArgOf _ _ _) = True + interesting (InlinePlease _) = True + interesting (Select _ _ _ _ _) = some_args + interesting (ApplyTo _ _ _ _) = True -- Can happen if we have (coerce t (f x)) y + -- Perhaps True is a bit over-keen, but I've + -- seen (coerce f) x, where f has an INLINE prag, + -- So we have to give some motivaiton for inlining it + interesting (ArgOf _ _ _) = some_val_args + interesting (Stop ty upd_in_place) = some_val_args && upd_in_place + interesting (CoerceIt _ cont) = interesting cont -- If this call is the arg of a strict function, the context -- is a bit interesting. If we inline here, we may get useful -- evaluation information to avoid repeated evals: e.g. @@ -266,11 +392,8 @@ analyseCont in_scope cont -- the context for (f x) is not totally uninteresting. -discardInline :: SimplCont -> SimplCont -discardInline (InlinePlease cont) = cont -discardInline (ApplyTo d e s cont) = ApplyTo d e s (discardInline cont) -discardInline cont = cont - +------------------- +canUpdateInPlace :: Type -> Bool -- Consider let x = in ... -- If returns an explicit constructor, we might be able -- to do update in place. So we treat even a thunk RHS context @@ -281,7 +404,10 @@ discardInline cont = cont -- Note the repType: we want to look through newtypes for this purpose -canUpdateInPlace ty = case splitTyConApp_maybe (repType ty) of { +canUpdateInPlace ty + | not opt_UF_UpdateInPlace = False + | otherwise + = case splitTyConApp_maybe (repType ty) of { Nothing -> False ; Just (tycon, _) -> @@ -306,7 +432,7 @@ simplBinders :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a simplBinders bndrs thing_inside = getSubst `thenSmpl` \ subst -> let - (subst', bndrs') = substBndrs subst bndrs + (subst', bndrs') = Subst.simplBndrs subst bndrs in seqBndrs bndrs' `seq` setSubst subst' (thing_inside bndrs') @@ -315,23 +441,29 @@ simplBinder :: InBinder -> (OutBinder -> SimplM a) -> SimplM a simplBinder bndr thing_inside = getSubst `thenSmpl` \ subst -> let - (subst', bndr') = substBndr subst bndr + (subst', bndr') = Subst.simplBndr subst bndr in seqBndr bndr' `seq` setSubst subst' (thing_inside bndr') --- Same semantics as simplBinders, but a little less --- plumbing and hence a little more efficient. --- Maybe not worth the candle? -simplIds :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a -simplIds ids thing_inside +simplRecIds :: [InBinder] -> ([OutBinder] -> SimplM a) -> SimplM a +simplRecIds ids thing_inside = getSubst `thenSmpl` \ subst -> let - (subst', bndrs') = substIds subst ids + (subst', ids') = mapAccumL Subst.simplLetId subst ids in - seqBndrs bndrs' `seq` - setSubst subst' (thing_inside bndrs') + seqBndrs ids' `seq` + setSubst subst' (thing_inside ids') + +simplLetId :: InBinder -> (OutBinder -> SimplM a) -> SimplM a +simplLetId id thing_inside + = getSubst `thenSmpl` \ subst -> + let + (subst', id') = Subst.simplLetId subst id + in + seqBndr id' `seq` + setSubst subst' (thing_inside id') seqBndrs [] = () seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs @@ -345,25 +477,6 @@ seqBndr b | isTyVar b = b `seq` () %************************************************************************ %* * -\subsection{Transform a RHS} -%* * -%************************************************************************ - -Try (a) eta expansion - (b) type-lambda swizzling - -\begin{code} -transformRhs :: InExpr -> SimplM InExpr -transformRhs rhs - = tryEtaExpansion body `thenSmpl` \ body' -> - mkRhsTyLam tyvars body' - where - (tyvars, body) = collectTyBinders rhs -\end{code} - - -%************************************************************************ -%* * \subsection{Local tyvar-lifting} %* * %************************************************************************ @@ -391,7 +504,7 @@ let-floating. This optimisation is CRUCIAL in eliminating the junk introduced by desugaring mutually recursive definitions. Don't eliminate it lightly! -So far as the implemtation is concerned: +So far as the implementation is concerned: Invariant: go F e = /\tvs -> F e @@ -433,28 +546,39 @@ as we would normally do. \begin{code} -mkRhsTyLam tyvars body -- Only does something if there's a let - | null tyvars || not (worth_it body) -- inside a type lambda, and a WHNF inside that - = returnSmpl (mkLams tyvars body) +tryRhsTyLam :: OutExpr -> SimplM ([OutBind], OutExpr) + +tryRhsTyLam rhs -- Only does something if there's a let + | null tyvars || not (worth_it body) -- inside a type lambda, + = returnSmpl ([], rhs) -- and a WHNF inside that + | otherwise - = go (\x -> x) body + = go (\x -> x) body `thenSmpl` \ (binds, body') -> + returnSmpl (binds, mkLams tyvars body') + where - worth_it (Let _ e) = whnf_in_middle e - worth_it other = False + (tyvars, body) = collectTyBinders rhs + + worth_it e@(Let _ _) = whnf_in_middle e + worth_it e = False + + whnf_in_middle (Let (NonRec x rhs) e) | isUnLiftedType (idType x) = False whnf_in_middle (Let _ e) = whnf_in_middle e whnf_in_middle e = exprIsCheap e - main_tyvar_set = mkVarSet tyvars - - go fn (Let bind@(NonRec var rhs) body) | exprIsTrivial rhs + go fn (Let bind@(NonRec var rhs) body) + | exprIsTrivial rhs = go (fn . Let bind) body - go fn (Let bind@(NonRec var rhs) body) + go fn (Let (NonRec var rhs) body) = mk_poly tyvars_here var `thenSmpl` \ (var', rhs') -> - go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ body' -> - returnSmpl (Let (NonRec var' (mkLams tyvars_here (fn rhs))) body') + go (fn . Let (mk_silly_bind var rhs')) body `thenSmpl` \ (binds, body') -> + returnSmpl (NonRec var' (mkLams tyvars_here (fn rhs)) : binds, body') + where tyvars_here = tyvars + -- main_tyvar_set = mkVarSet tyvars + -- var_ty = idType var -- varSetElems (main_tyvar_set `intersectVarSet` tyVarsOfType var_ty) -- tyvars_here was an attempt to reduce the number of tyvars -- wrt which the new binding is abstracted. But the naive @@ -472,63 +596,65 @@ mkRhsTyLam tyvars body -- Only does something if there's a let -- abstracting wrt *all* the tyvars. We'll see if that -- gives rise to problems. SLPJ June 98 - var_ty = idType var - go fn (Let (Rec prs) body) = mapAndUnzipSmpl (mk_poly tyvars_here) vars `thenSmpl` \ (vars', rhss') -> let - gn body = fn $ foldr Let body (zipWith mk_silly_bind vars rhss') + gn body = fn (foldr Let body (zipWith mk_silly_bind vars rhss')) + new_bind = Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss]) in - go gn body `thenSmpl` \ body' -> - returnSmpl (Let (Rec (vars' `zip` [mkLams tyvars_here (gn rhs) | rhs <- rhss])) body') + go gn body `thenSmpl` \ (binds, body') -> + returnSmpl (new_bind : binds, body') where (vars,rhss) = unzip prs tyvars_here = tyvars -- varSetElems (main_tyvar_set `intersectVarSet` tyVarsOfTypes var_tys) + -- var_tys = map idType vars -- See notes with tyvars_here above - var_tys = map idType vars - - go fn body = returnSmpl (mkLams tyvars (fn body)) + go fn body = returnSmpl ([], fn body) mk_poly tyvars_here var = getUniqueSmpl `thenSmpl` \ uniq -> let poly_name = setNameUnique (idName var) uniq -- Keep same name poly_ty = mkForAllTys tyvars_here (idType var) -- But new type of course + poly_id = mkLocalId poly_name poly_ty - -- It's crucial to copy the occInfo of the original var, because - -- we're looking at occurrence-analysed but as yet unsimplified code! - -- In particular, we mustn't lose the loop breakers. + -- In the olden days, it was crucial to copy the occInfo of the original var, + -- because we were looking at occurrence-analysed but as yet unsimplified code! + -- In particular, we mustn't lose the loop breakers. BUT NOW we are looking + -- at already simplified code, so it doesn't matter -- -- It's even right to retain single-occurrence or dead-var info: -- Suppose we started with /\a -> let x = E in B - -- where x occurs once in E. Then we transform to: + -- where x occurs once in B. Then we transform to: -- let x' = /\a -> E in /\a -> let x* = x' a in B -- where x* has an INLINE prag on it. Now, once x* is inlined, - -- the occurrences of x' will be just the occurrences originaly + -- the occurrences of x' will be just the occurrences originally -- pinned on x. - poly_info = vanillaIdInfo `setOccInfo` idOccInfo var - - poly_id = mkId poly_name poly_ty poly_info in returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here)) - mk_silly_bind var rhs = NonRec var rhs - -- The Inline note is really important! If we don't say - -- INLINE on these silly little bindings then look what happens! + mk_silly_bind var rhs = NonRec var (Note InlineMe rhs) -- Suppose we start with: -- - -- x = let g = /\a -> \x -> f x x - -- in - -- /\ b -> let g* = g b in E + -- x = /\ a -> let g = G in E + -- + -- Then we'll float to get + -- + -- x = let poly_g = /\ a -> G + -- in /\ a -> let g = poly_g a in E + -- + -- But now the occurrence analyser will see just one occurrence + -- of poly_g, not inside a lambda, so the simplifier will + -- PreInlineUnconditionally poly_g back into g! Badk to square 1! + -- (I used to think that the "don't inline lone occurrences" stuff + -- would stop this happening, but since it's the *only* occurrence, + -- PreInlineUnconditionally kicks in first!) -- - -- Then: * the binding for g gets floated out - -- * but then it gets inlined into the rhs of g* - -- * then the binding for g* is floated out of the /\b - -- * so we're back to square one - -- The silly binding for g* must be INLINEd, so that - -- we simply substitute for g* throughout. + -- Solution: put an INLINE note on g's RHS, so that poly_g seems + -- to appear many times. (NB: mkInlineMe eliminates + -- such notes on trivial RHSs, so do it manually.) \end{code} @@ -541,91 +667,68 @@ mkRhsTyLam tyvars body -- Only does something if there's a let Try eta expansion for RHSs We go for: - \x1..xn -> N ==> \x1..xn y1..ym -> N y1..ym - AND - N E1..En ==> let z1=E1 .. zn=En in \y1..ym -> N z1..zn y1..ym + Case 1 f = \x1..xn -> N ==> f = \x1..xn y1..ym -> N y1..ym + (n >= 0) + OR + Case 2 f = N E1..En ==> z1=E1 + (n > 0) .. + zn=En + f = \y1..ym -> N z1..zn y1..ym -where (in both cases) N is a NORMAL FORM (i.e. no redexes anywhere) -wanting a suitable number of extra args. +where (in both cases) -NB: the Ei may have unlifted type, but the simplifier (which is applied -to the result) deals OK with this. + * The xi can include type variables -There is no point in looking for a combination of the two, -because that would leave use with some lets sandwiched between lambdas; -that's what the final test in the first equation is for. + * The yi are all value variables + + * N is a NORMAL FORM (i.e. no redexes anywhere) + wanting a suitable number of extra args. + + * the Ei must not have unlifted type + +There is no point in looking for a combination of the two, because +that would leave use with some lets sandwiched between lambdas; that's +what the final test in the first equation is for. + +In Case 1, we may have to sandwich some coerces between the lambdas +to make the types work. exprEtaExpandArity looks through coerces +when computing arity; and etaExpand adds the coerces as necessary when +actually computing the expansion. \begin{code} -tryEtaExpansion :: InExpr -> SimplM InExpr -tryEtaExpansion rhs - | not opt_SimplDoLambdaEtaExpansion - || exprIsTrivial rhs -- Don't eta-expand a trival RHS - || null y_tys -- No useful expansion - || not (null x_bndrs || and trivial_args) -- Not (no x-binders or no z-binds) - = returnSmpl rhs - - | otherwise -- Consider eta expansion - = newIds SLIT("y") y_tys $ ( \ y_bndrs -> - tick (EtaExpansion (head y_bndrs)) `thenSmpl_` - mapAndUnzipSmpl bind_z_arg (args `zip` trivial_args) `thenSmpl` (\ (maybe_z_binds, z_args) -> - returnSmpl (mkLams x_bndrs $ - mkLets (catMaybes maybe_z_binds) $ - mkLams y_bndrs $ - mkApps (mkApps fun z_args) (map Var y_bndrs)))) - where - (x_bndrs, body) = collectValBinders rhs - (fun, args) = collectArgs body - trivial_args = map exprIsTrivial args - fun_arity = exprEtaExpandArity fun +tryEtaExpansion :: OutExpr -> OutType -> SimplM ([OutBind], OutExpr) +tryEtaExpansion rhs rhs_ty + | not opt_SimplDoLambdaEtaExpansion -- Not if switched off + || exprIsTrivial rhs -- Not if RHS is trivial + || final_arity == 0 -- Not if arity is zero + = returnSmpl ([], rhs) + + | n_val_args == 0 && not arity_is_manifest + = -- Some lambdas but not enough: case 1 + getUniqSupplySmpl `thenSmpl` \ us -> + returnSmpl ([], etaExpand final_arity us rhs rhs_ty) + + | n_val_args > 0 && not (any cant_bind arg_infos) + = -- Partial application: case 2 + mapAndUnzipSmpl bind_z_arg arg_infos `thenSmpl` \ (maybe_z_binds, z_args) -> + getUniqSupplySmpl `thenSmpl` \ us -> + returnSmpl (catMaybes maybe_z_binds, + etaExpand final_arity us (mkApps fun z_args) rhs_ty) - bind_z_arg (arg, trivial_arg) + | otherwise + = returnSmpl ([], rhs) + where + (fun, args) = collectArgs rhs + n_val_args = valArgCount args + (fun_arity, arity_is_manifest) = exprEtaExpandArity fun + final_arity = 0 `max` (fun_arity - n_val_args) + arg_infos = [(arg, exprType arg, exprIsTrivial arg) | arg <- args] + cant_bind (_, ty, triv) = not triv && isUnLiftedType ty + + bind_z_arg (arg, arg_ty, trivial_arg) | trivial_arg = returnSmpl (Nothing, arg) - | otherwise = newId SLIT("z") (exprType arg) $ \ z -> + | otherwise = newId SLIT("z") arg_ty $ \ z -> returnSmpl (Just (NonRec z arg), Var z) - - -- Note: I used to try to avoid the exprType call by using - -- the type of the binder. But this type doesn't necessarily - -- belong to the same substitution environment as this rhs; - -- and we are going to make extra term binders (y_bndrs) from the type - -- which will be processed with the rhs substitution environment. - -- This only went wrong in a mind bendingly complicated case. - (potential_extra_arg_tys, inner_ty) = splitFunTys (exprType body) - - y_tys :: [InType] - y_tys = take no_extras_wanted potential_extra_arg_tys - - no_extras_wanted :: Int - no_extras_wanted = 0 `max` - - -- We used to expand the arity to the previous arity fo the - -- function; but this is pretty dangerous. Consdier - -- f = \xy -> e - -- so that f has arity 2. Now float something into f's RHS: - -- f = let z = BIG in \xy -> e - -- The last thing we want to do now is to put some lambdas - -- outside, to get - -- f = \xy -> let z = BIG in e - -- - -- (bndr_arity - no_of_xs) `max` - - -- See if the body could obviously do with more args - (fun_arity - valArgCount args) - --- This case is now deal with by exprEtaExpandArity - -- Finally, see if it's a state transformer, and xs is non-null - -- (so it's also a function not a thunk) in which - -- case we eta-expand on principle! This can waste work, - -- but usually doesn't. - -- I originally checked for a singleton type [ty] in this case - -- but then I found a situation in which I had - -- \ x -> let {..} in \ s -> f (...) s - -- AND f RETURNED A FUNCTION. That is, 's' wasn't the only - -- potential extra arg. --- case (x_bndrs, potential_extra_arg_tys) of --- (_:_, ty:_) -> case splitTyConApp_maybe ty of --- Just (tycon,_) | tycon == statePrimTyCon -> 1 --- other -> 0 --- other -> 0 \end{code} @@ -704,15 +807,28 @@ and similar friends. mkCase scrut case_bndr alts | all identity_alt alts = tick (CaseIdentity case_bndr) `thenSmpl_` - returnSmpl scrut + returnSmpl (re_note scrut) where - identity_alt (DEFAULT, [], Var v) = v == case_bndr - identity_alt (DataAlt con, args, rhs) = cheapEqExpr rhs - (mkConApp con (map Type arg_tys ++ map varToCoreExpr args)) - identity_alt other = False - - arg_tys = case splitTyConApp_maybe (idType case_bndr) of - Just (tycon, arg_tys) -> arg_tys + identity_alt (con, args, rhs) = de_note rhs `cheapEqExpr` identity_rhs con args + + identity_rhs (DataAlt con) args = mkConApp con (arg_tys ++ map varToCoreExpr args) + identity_rhs (LitAlt lit) _ = Lit lit + identity_rhs DEFAULT _ = Var case_bndr + + arg_tys = map Type (tyConAppArgs (idType case_bndr)) + + -- We've seen this: + -- case coerce T e of x { _ -> coerce T' x } + -- And we definitely want to eliminate this case! + -- So we throw away notes from the RHS, and reconstruct + -- (at least an approximation) at the other end + de_note (Note _ e) = de_note e + de_note e = e + + -- re_note wraps a coerce if it might be necessary + re_note scrut = case head alts of + (_,_,rhs1@(Note _ _)) -> mkCoerce (exprType rhs1) (idType case_bndr) scrut + other -> scrut \end{code} The catch-all case @@ -723,22 +839,3 @@ mkCase other_scrut case_bndr other_alts \end{code} -\begin{code} -findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr) -findDefault [] = ([], Nothing) -findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null alts && null args ) - ([], Just rhs) -findDefault (alt : alts) = case findDefault alts of - (alts', deflt) -> (alt : alts', deflt) - -findAlt :: AltCon -> [CoreAlt] -> CoreAlt -findAlt con alts - = go alts - where - go [] = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts)) - go (alt : alts) | matches alt = alt - | otherwise = go alts - - matches (DEFAULT, _, _) = True - matches (con1, _, _) = con == con1 -\end{code}