-
+%
% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[Simplify]{The main module of the simplifier}
#include "HsVersions.h"
-import CmdLineOpts ( intSwitchSet,
- opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
- opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
- opt_SimplDoCaseElim,
+import CmdLineOpts ( switchIsOn, opt_SimplDoEtaReduction,
+ opt_SimplNoPreInlining,
+ dopt, DynFlag(Opt_D_dump_inlinings),
SimplifierSwitch(..)
)
import SimplMonad
-import SimplUtils ( mkCase, transformRhs, findAlt,
- simplBinder, simplBinders, simplIds, findDefault, mkCoerce
+import SimplUtils ( mkCase, tryRhsTyLam, tryEtaExpansion,
+ simplBinder, simplBinders, simplIds,
+ SimplCont(..), DupFlag(..), mkStop, mkRhsStop,
+ contResultType, discardInline, countArgs, contIsDupable,
+ getContArgs, interestingCallContext, interestingArg, isStrictType
)
-import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
+import Var ( mkSysTyVar, tyVarKind )
import VarEnv
-import VarSet
-import Id ( Id, idType, idInfo, idUnique,
- getIdUnfolding, setIdUnfolding, isExportedId,
- getIdSpecialisation, setIdSpecialisation,
- getIdDemandInfo, setIdDemandInfo,
- getIdArity, setIdArity,
- getIdStrictness,
- setInlinePragma, getInlinePragma, idMustBeINLINEd,
- setOneShotLambda
+import Id ( Id, idType, idInfo, isDataConId, hasNoBinding,
+ idUnfolding, setIdUnfolding, isExportedId, isDeadBinder,
+ idDemandInfo, setIdInfo,
+ idOccInfo, setIdOccInfo,
+ zapLamIdInfo, setOneShotLambda,
)
-import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
- ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
- specInfo, inlinePragInfo, zapLamIdInfo
+import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker,
+ setArityInfo,
+ setUnfoldingInfo, atLeastArity,
+ occInfo
+ )
+import Demand ( isStrict )
+import DataCon ( dataConNumInstArgs, dataConRepStrictness,
+ dataConSig, dataConArgTys
)
-import Demand ( Demand, isStrict, wwLazy )
-import Const ( isWHNFCon, conOkForAlt )
-import ConFold ( tryPrimOp )
-import PrimOp ( PrimOp, primOpStrictness, primOpType )
-import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
-import Const ( Con(..) )
-import Name ( isLocallyDefined )
import CoreSyn
-import CoreFVs ( exprFreeVars )
-import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
- callSiteInline, blackListed
+import PprCore ( pprParendExpr, pprCoreExpr )
+import CoreFVs ( mustHaveLocalBinding )
+import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons,
+ callSiteInline
)
-import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
- coreExprType, coreAltsType, exprArity, exprIsValue,
- exprOkForSpeculation
+import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsTrivial,
+ exprIsConApp_maybe, mkPiType, findAlt, findDefault,
+ exprType, coreAltsType, exprIsValue,
+ exprOkForSpeculation, exprArity, exprIsCheap,
+ mkCoerce, mkSCC, mkInlineMe, mkAltExpr
)
import Rules ( lookupRule )
-import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
-import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType,
- mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
- funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
+import CostCentre ( currentCCS )
+import Type ( mkTyVarTys, isUnLiftedType, seqType,
+ mkFunTy, splitTyConApp_maybe, tyConAppArgs,
+ funResultTy
)
-import Subst ( Subst, mkSubst, emptySubst, substExpr, substTy,
- substEnv, lookupInScope, lookupSubst, substRules
+import Subst ( mkSubst, substTy,
+ isInScope, lookupIdSubst, substIdInfo
)
-import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
+import TyCon ( isDataTyCon, tyConDataConsIfAvailable )
import TysPrim ( realWorldStatePrimTy )
import PrelInfo ( realWorldPrimId )
-import BasicTypes ( TopLevelFlag(..), isTopLevel )
+import OrdList
import Maybes ( maybeToBool )
-import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
-import PprCore
+import Util ( zipWithEqual )
import Outputable
\end{code}
loop for the simplifier is in SimplCore.lhs.
+-----------------------------------------
+ *** IMPORTANT NOTE ***
+-----------------------------------------
+The simplifier used to guarantee that the output had no shadowing, but
+it does not do so any more. (Actually, it never did!) The reason is
+documented with simplifyArgs.
+
+
+
+
%************************************************************************
%* *
\subsection{Bindings}
-- so that if a transformation rule has unexpectedly brought
-- anything into scope, then we don't get a complaint about that.
-- It's rather as if the top-level binders were imported.
- extendInScopes top_binders $
- simpl_binds binds `thenSmpl` \ (binds', _) ->
- freeTick SimplifierDone `thenSmpl_`
- returnSmpl binds'
+ simplIds (bindersOfBinds binds) $ \ bndrs' ->
+ simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
+ freeTick SimplifierDone `thenSmpl_`
+ returnSmpl (fromOL binds')
where
- top_binders = bindersOfBinds binds
-
- simpl_binds [] = returnSmpl ([], panic "simplTopBinds corner")
- simpl_binds (NonRec bndr rhs : binds) = simplLazyBind TopLevel bndr bndr rhs (simpl_binds binds)
- simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map fst pairs) (simpl_binds binds)
+ -- We need to track the zapped top-level binders, because
+ -- they should have their fragile IdInfo zapped (notably occurrence info)
+ simpl_binds [] bs = ASSERT( null bs ) returnSmpl (nilOL, panic "simplTopBinds corner")
+ simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs)
+ simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs))
+ where
+ n = length pairs
-simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
+simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId]
-> SimplM (OutStuff a) -> SimplM (OutStuff a)
simplRecBind top_lvl pairs bndrs' thing_inside
- = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
- returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
+ = go pairs bndrs' `thenSmpl` \ (binds', (_, (binds'', res))) ->
+ returnSmpl (unitOL (Rec (flattenBinds (fromOL binds'))) `appOL` binds'', res)
where
go [] _ = thing_inside `thenSmpl` \ stuff ->
- returnSmpl ([], stuff)
+ returnOutStuff stuff
go ((bndr, rhs) : pairs) (bndr' : bndrs')
= simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
%* *
%************************************************************************
-\begin{code}
-addBind :: CoreBind -> OutStuff a -> OutStuff a
-addBind bind (binds, res) = (bind:binds, res)
-
-addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
-addBinds [] stuff = stuff
-addBinds binds1 (binds2, res) = (binds1++binds2, res)
-\end{code}
-
The reason for this OutExprStuff stuff is that we want to float *after*
simplifying a RHS, not before. If we do so naively we get quadratic
behaviour as things float out.
\begin{code}
simplExpr :: CoreExpr -> SimplM CoreExpr
simplExpr expr = getSubst `thenSmpl` \ subst ->
- simplExprC expr (Stop (substTy subst (coreExprType expr)))
+ simplExprC expr (mkStop (substTy subst (exprType expr)))
-- The type in the Stop continuation is usually not used
-- It's only needed when discarding continuations after finding
- -- a function that returns bottom
+ -- a function that returns bottom.
+ -- Hence the lazy substitution
simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
-- Simplify an expression, given a continuation
simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
- returnSmpl (mkLets floats body)
+ returnSmpl (wrapFloats floats body)
simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
-- Simplify an expression, returning floated binds
simplExprF (Var v) cont
= simplVar v cont
-simplExprF expr@(Con (PrimOp op) args) cont
- = getSubstEnv `thenSmpl` \ se ->
- prepareArgs (ppr op)
- (primOpType op)
- (primOpStrictness op)
- (pushArgs se args cont) $ \ args1 cont1 ->
+simplExprF (Lit lit) (Select _ bndr alts se cont)
+ = knownCon (Lit lit) (LitAlt lit) [] bndr alts se cont
- let
- -- Boring... we may have too many arguments now, so we push them back
- n_args = length args
- args2 = ASSERT( length args1 >= n_args )
- take n_args args1
- cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
- in
- -- Try the prim op simplification
- -- It's really worth trying simplExpr again if it succeeds,
- -- because you can find
- -- case (eqChar# x 'a') of ...
- -- ==>
- -- case (case x of 'a' -> True; other -> False) of ...
- case tryPrimOp op args2 of
- Just e' -> zapSubstEnv (simplExprF e' cont2)
- Nothing -> rebuild (Con (PrimOp op) args2) cont2
-
-simplExprF (Con con@(DataCon _) args) cont
- = freeTick LeafVisit `thenSmpl_`
- simplConArgs args ( \ args' ->
- rebuild (Con con args') cont)
-
-simplExprF expr@(Con con@(Literal _) args) cont
- = ASSERT( null args )
- freeTick LeafVisit `thenSmpl_`
- rebuild expr cont
+simplExprF (Lit lit) cont
+ = rebuild (Lit lit) cont
simplExprF (App fun arg) cont
= getSubstEnv `thenSmpl` \ se ->
simplExprF fun (ApplyTo NoDup arg se cont)
simplExprF (Case scrut bndr alts) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplExprF scrut (Select NoDup bndr alts se cont)
+ = getSubstEnv `thenSmpl` \ subst_env ->
+ getSwitchChecker `thenSmpl` \ chkr ->
+ if not (switchIsOn chkr NoCaseOfCase) then
+ -- Simplify the scrutinee with a Select continuation
+ simplExprF scrut (Select NoDup bndr alts subst_env cont)
+
+ else
+ -- If case-of-case is off, simply simplify the case expression
+ -- in a vanilla Stop context, and rebuild the result around it
+ simplExprC scrut (Select NoDup bndr alts subst_env
+ (mkStop (contResultType cont))) `thenSmpl` \ case_expr' ->
+ rebuild case_expr' cont
simplExprF (Let (Rec pairs) body) cont
-- NB: bndrs' don't have unfoldings or spec-envs
-- We add them as we go down, using simplPrags
- simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
+ simplRecBind False pairs bndrs' (simplExprF body cont)
simplExprF expr@(Lam _ _) cont = simplLam expr cont
simplExprF (Type ty) cont
- = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
+ = ASSERT( case cont of { Stop _ _ -> True; ArgOf _ _ _ -> True; other -> False } )
simplType ty `thenSmpl` \ ty' ->
rebuild (Type ty') cont
+-- Comments about the Coerce case
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- It's worth checking for a coerce in the continuation,
+-- in case we can cancel them. For example, in the initial form of a worker
+-- we may find (coerce T (coerce S (\x.e))) y
+-- and we'd like it to simplify to e[y/x] in one round of simplification
+
+simplExprF (Note (Coerce to from) e) (CoerceIt outer_to cont)
+ = simplType from `thenSmpl` \ from' ->
+ if outer_to == from' then
+ -- The coerces cancel out
+ simplExprF e cont
+ else
+ -- They don't cancel, but the inner one is redundant
+ simplExprF e (CoerceIt outer_to cont)
+
simplExprF (Note (Coerce to from) e) cont
- | to == from = simplExprF e cont
- | otherwise = getSubst `thenSmpl` \ subst ->
- simplExprF e (CoerceIt (substTy subst to) cont)
+ = simplType to `thenSmpl` \ to' ->
+ simplExprF e (CoerceIt to' cont)
-- hack: we only distinguish subsumed cost centre stacks for the purposes of
-- inlining. All other CCCSs are mapped to currentCCS.
simplExprF (Note (SCC cc) e) cont
= setEnclosingCC currentCCS $
simplExpr e `thenSmpl` \ e ->
- rebuild (mkNote (SCC cc) e) cont
+ rebuild (mkSCC cc e) cont
simplExprF (Note InlineCall e) cont
= simplExprF e (InlinePlease cont)
--- Comments about the InlineMe case
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+-- Comments about the InlineMe case
+-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-- Don't inline in the RHS of something that has an
-- inline pragma. But be careful that the InScopeEnv that
-- we return does still have inlinings on!
-- the specialised version of g when f is inlined at some call site
-- (perhaps in some other module).
-simplExprF (Note InlineMe e) cont
- = case cont of
- Stop _ -> -- Totally boring continuation
- -- Don't inline inside an INLINE expression
- switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
- rebuild (mkNote InlineMe e') cont
+-- It's also important not to inline a worker back into a wrapper.
+-- A wrapper looks like
+-- wraper = inline_me (\x -> ...worker... )
+-- Normally, the inline_me prevents the worker getting inlined into
+-- the wrapper (initially, the worker's only call site!). But,
+-- if the wrapper is sure to be called, the strictness analyser will
+-- mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf
+-- continuation. That's why the keep_inline predicate returns True for
+-- ArgOf continuations. It shouldn't do any harm not to dissolve the
+-- inline-me note under these circumstances
- other -> -- Dissolve the InlineMe note if there's
- -- an interesting context of any kind to combine with
- -- (even a type application -- anything except Stop)
- simplExprF e cont
+simplExprF (Note InlineMe e) cont
+ | keep_inline cont -- Totally boring continuation
+ = -- Don't inline inside an INLINE expression
+ setBlackList noInlineBlackList (simplExpr e) `thenSmpl` \ e' ->
+ rebuild (mkInlineMe e') cont
+
+ | otherwise -- Dissolve the InlineMe note if there's
+ -- an interesting context of any kind to combine with
+ -- (even a type application -- anything except Stop)
+ = simplExprF e cont
+ where
+ keep_inline (Stop _ _) = True -- See notes above
+ keep_inline (ArgOf _ _ _) = True -- about this predicate
+ keep_inline other = False
-- A non-recursive let is dealt with by simplBeta
simplExprF (Let (NonRec bndr rhs) body) cont
simplLam fun cont
= go fun cont
where
- zap_it = mkLamBndrZapper fun (countArgs cont)
+ zap_it = mkLamBndrZapper fun cont
cont_ty = contResultType cont
-- Type-beta reduction
go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
= ASSERT( isTyVar bndr )
- tick (BetaReduction bndr) `thenSmpl_`
- getInScope `thenSmpl` \ in_scope ->
- let
- ty' = substTy (mkSubst in_scope arg_se) ty_arg
- in
- extendSubst bndr (DoneTy ty')
+ tick (BetaReduction bndr) `thenSmpl_`
+ simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' ->
+ extendSubst bndr (DoneTy ty_arg')
(go body body_cont)
-- Ordinary beta reduction
-- Exactly enough args
go expr cont = simplExprF expr cont
-
-- completeLam deals with the case where a lambda doesn't have an ApplyTo
--- continuation. Try for eta reduction, but *only* if we get all
--- the way to an exprIsTrivial expression.
--- 'acc' holds the simplified binders, in reverse order
+-- continuation, so there are real lambdas left to put in the result
+
+-- We try for eta reduction here, but *only* if we get all the
+-- way to an exprIsTrivial expression.
+-- We don't want to remove extra lambdas unless we are going
+-- to avoid allocating this thing altogether
-completeLam acc (Lam bndr body) cont
+completeLam rev_bndrs (Lam bndr body) cont
= simplBinder bndr $ \ bndr' ->
- completeLam (bndr':acc) body cont
+ completeLam (bndr':rev_bndrs) body cont
-completeLam acc body cont
+completeLam rev_bndrs body cont
= simplExpr body `thenSmpl` \ body' ->
+ case try_eta body' of
+ Just etad_lam -> tick (EtaReduction (head rev_bndrs)) `thenSmpl_`
+ rebuild etad_lam cont
- case (opt_SimplDoEtaReduction, check_eta acc body') of
- (True, Just body'') -- Eta reduce!
- -> tick (EtaReduction (head acc)) `thenSmpl_`
- rebuild body'' cont
-
- other -> -- No eta reduction
- rebuild (foldl (flip Lam) body' acc) cont
- -- Remember, acc is the reversed binders
+ Nothing -> rebuild (foldl (flip Lam) body' rev_bndrs) cont
where
- -- NB: the binders are reversed
- check_eta (b : bs) (App fun arg)
- | (varToCoreExpr b `cheapEqExpr` arg)
- = check_eta bs fun
-
- check_eta [] body
- | exprIsTrivial body && -- ONLY if the body is trivial
- not (any (`elemVarSet` body_fvs) acc)
- = Just body -- Success!
- where
- body_fvs = exprFreeVars body
-
- check_eta _ _ = Nothing -- Bale out
+ -- We don't use CoreUtils.etaReduce, because we can be more
+ -- efficient here:
+ -- (a) we already have the binders,
+ -- (b) we can do the triviality test before computing the free vars
+ -- [in fact I take the simple path and look for just a variable]
+ -- (c) we don't want to eta-reduce a data con worker or primop
+ -- because we only have to eta-expand them later when we saturate
+ try_eta body | not opt_SimplDoEtaReduction = Nothing
+ | otherwise = go rev_bndrs body
+
+ go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
+ go [] body | ok_body body = Just body -- Success!
+ go _ _ = Nothing -- Failure!
+
+ ok_body (Var v) = not (v `elem` rev_bndrs) && not (hasNoBinding v)
+ ok_body other = False
+ ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg
mkLamBndrZapper :: CoreExpr -- Function
- -> Int -- Number of args
+ -> SimplCont -- The context
-> Id -> Id -- Use this to zap the binders
-mkLamBndrZapper fun n_args
+mkLamBndrZapper fun cont
| n_args >= n_params fun = \b -> b -- Enough args
- | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
+ | otherwise = \b -> zapLamIdInfo b
where
- n_params (Lam b e) | isId b = 1 + n_params e
- | otherwise = n_params e
- n_params other = 0::Int
-\end{code}
-
+ -- NB: we count all the args incl type args
+ -- so we must count all the binders (incl type lambdas)
+ n_args = countArgs cont
----------------------------------
-simplConArgs makes sure that the arguments all end up being atomic.
-That means it may generate some Lets, hence the strange type
-
-\begin{code}
-simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
-simplConArgs [] thing_inside
- = thing_inside []
-
-simplConArgs (arg:args) thing_inside
- = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
- -- Simplify the RHS with inlining switched off, so that
- -- only absolutely essential things will happen.
-
- simplConArgs args $ \ args' ->
-
- -- If the argument ain't trivial, then let-bind it
- if exprIsTrivial arg' then
- thing_inside (arg' : args')
- else
- newId (coreExprType arg') $ \ arg_id ->
- thing_inside (Var arg_id : args') `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec arg_id arg') res)
+ n_params (Note _ e) = n_params e
+ n_params (Lam b e) = 1 + n_params e
+ n_params other = 0::Int
\end{code}
simplType :: InType -> SimplM OutType
simplType ty
= getSubst `thenSmpl` \ subst ->
- returnSmpl (substTy subst ty)
+ let
+ new_ty = substTy subst ty
+ in
+ seqType new_ty `seq`
+ returnSmpl new_ty
\end{code}
#endif
simplBeta bndr rhs rhs_se cont_ty thing_inside
- | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
+ | preInlineUnconditionally False {- not black listed -} bndr
= tick (PreInlineUnconditionally bndr) `thenSmpl_`
extendSubst bndr (ContEx rhs_se rhs) thing_inside
| otherwise
- = -- Simplify the RHS
+ = -- Simplify the RHS
simplBinder bndr $ \ bndr' ->
- simplArg (idType bndr') (getIdDemandInfo bndr)
- rhs rhs_se cont_ty $ \ rhs' ->
+ let
+ bndr_ty' = idType bndr'
+ is_strict = isStrict (idDemandInfo bndr) || isStrictType bndr_ty'
+ in
+ simplValArg bndr_ty' is_strict rhs rhs_se cont_ty $ \ rhs' ->
-- Now complete the binding and simplify the body
- completeBeta bndr bndr' rhs' thing_inside
-
-completeBeta bndr bndr' rhs' thing_inside
- | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
- -- Make a case expression instead of a let
- -- These can arise either from the desugarer,
- -- or from beta reductions: (\x.e) (x +# y)
- = getInScope `thenSmpl` \ in_scope ->
- thing_inside `thenSmpl` \ (floats, (_, body)) ->
- returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
-
- | otherwise
- = completeBinding bndr bndr' rhs' thing_inside
+ if needsCaseBinding bndr_ty' rhs' then
+ addCaseBind bndr' rhs' thing_inside
+ else
+ completeBinding bndr bndr' False False rhs' thing_inside
\end{code}
\begin{code}
-simplArg :: OutType -> Demand
- -> InExpr -> SubstEnv
- -> OutType -- Type of thing computed by the context
- -> (OutExpr -> SimplM OutExprStuff)
- -> SimplM OutExprStuff
-simplArg arg_ty demand arg arg_se cont_ty thing_inside
- | isStrict demand ||
- isUnLiftedType arg_ty ||
- (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
- -- 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)
- = getSubstEnv `thenSmpl` \ body_se ->
- transformRhs arg `thenSmpl` \ t_arg ->
- setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
- setSubstEnv body_se (thing_inside arg')
- )) -- NB: we must restore body_se before carrying on with thing_inside!!
+simplTyArg :: InType -> SubstEnv -> SimplM OutType
+simplTyArg ty_arg se
+ = getInScope `thenSmpl` \ in_scope ->
+ let
+ ty_arg' = substTy (mkSubst in_scope se) ty_arg
+ in
+ seqType ty_arg' `seq`
+ returnSmpl ty_arg'
+
+simplValArg :: OutType -- rhs_ty: Type of arg; used only occasionally
+ -> Bool -- True <=> evaluate eagerly
+ -> InExpr -> SubstEnv
+ -> OutType -- cont_ty: Type of thing computed by the context
+ -> (OutExpr -> SimplM OutExprStuff)
+ -- Takes an expression of type rhs_ty,
+ -- returns an expression of type cont_ty
+ -> SimplM OutExprStuff -- An expression of type cont_ty
+
+simplValArg arg_ty is_strict arg arg_se cont_ty thing_inside
+ | is_strict
+ = getEnv `thenSmpl` \ env ->
+ setSubstEnv arg_se $
+ simplExprF arg (ArgOf NoDup cont_ty $ \ rhs' ->
+ setAllExceptInScope env $
+ thing_inside rhs')
| otherwise
- = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
+ = simplRhs False {- Not top level -}
+ True {- OK to float unboxed -}
+ arg_ty arg arg_se
+ thing_inside
\end{code}
\begin{code}
completeBinding :: InId -- Binder
-> OutId -- New binder
+ -> Bool -- True <=> top level
+ -> Bool -- True <=> black-listed; don't inline
-> OutExpr -- Simplified RHS
-> SimplM (OutStuff a) -- Thing inside
-> SimplM (OutStuff a)
-completeBinding old_bndr new_bndr new_rhs thing_inside
- | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
+completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
+ | isDeadOcc occ_info -- This happens; for example, the case_bndr during case of
-- known constructor: case (a,b) of x { (p,q) -> ... }
-- Here x isn't mentioned in the RHS, so we don't want to
-- create the (dead) let-binding let x = (a,b) in ...
= thing_inside
- | postInlineUnconditionally old_bndr new_rhs
- -- Maybe we don't need a let-binding! Maybe we can just
- -- inline it right away. Unlike the preInlineUnconditionally case
- -- we are allowed to look at the RHS.
+ | trivial_rhs && not must_keep_binding
+ -- We're looking at a binding with a trivial RHS, so
+ -- perhaps we can discard it altogether!
--
- -- NB: a loop breaker never has postInlineUnconditionally True
+ -- NB: a loop breaker has must_keep_binding = True
-- and non-loop-breakers only have *forward* references
-- Hence, it's safe to discard the binding
- = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
- extendSubst old_bndr (DoneEx new_rhs)
- thing_inside
+ --
+ -- NOTE: This isn't our last opportunity to inline.
+ -- We're at the binding site right now, and
+ -- we'll get another opportunity when we get to the ocurrence(s)
+
+ -- Note that we do this unconditional inlining only for trival RHSs.
+ -- Don't inline even WHNFs inside lambdas; doing so may
+ -- simply increase allocation when the function is called
+ -- This isn't the last chance; see NOTE above.
+ --
+ -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
+ -- Why? Because we don't even want to inline them into the
+ -- RHS of constructor arguments. See NOTE above
+ --
+ -- NB: Even NOINLINEis ignored here: if the rhs is trivial
+ -- it's best to inline it anyway. We often get a=E; b=a
+ -- from desugaring, with both a and b marked NOINLINE.
+ = -- Drop the binding
+ extendSubst old_bndr (DoneEx new_rhs) $
+ -- Use the substitution to make quite, quite sure that the substitution
+ -- will happen, since we are going to discard the binding
+ tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
+ thing_inside
+
+ | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs,
+ not trivial_rhs && not (isUnLiftedType inner_ty)
+ -- x = coerce t e ==> c = e; x = inline_me (coerce t c)
+ -- Now x can get inlined, which moves the coercion
+ -- to the usage site. This is a bit like worker/wrapper stuff,
+ -- but it's useful to do it very promptly, so that
+ -- x = coerce T (I# 3)
+ -- get's w/wd to
+ -- c = I# 3
+ -- x = coerce T c
+ -- This in turn means that
+ -- case (coerce Int x) of ...
+ -- will inline x.
+ -- Also the full-blown w/w thing isn't set up for non-functions
+ --
+ -- The (not (isUnLiftedType inner_ty)) avoids the nasty case of
+ -- x::Int = coerce Int Int# (foo y)
+ -- ==>
+ -- v::Int# = foo y
+ -- x::Int = coerce Int Int# v
+ -- which would be bogus because then v will be evaluated strictly.
+ -- How can this arise? Via
+ -- x::Int = case (foo y) of { ... }
+ -- followed by case elimination.
+ --
+ -- The inline_me note is so that the simplifier doesn't
+ -- just substitute c back inside x's rhs! (Typically, x will
+ -- get substituted away, but not if it's exported.)
+ = newId SLIT("c") inner_ty $ \ c_id ->
+ completeBinding c_id c_id top_lvl False inner_rhs $
+ completeBinding old_bndr new_bndr top_lvl black_listed
+ (Note InlineMe (Note coercion (Var c_id))) $
+ thing_inside
| otherwise
- = getSubst `thenSmpl` \ subst ->
- let
- bndr_info = idInfo old_bndr
- old_rules = specInfo bndr_info
- new_rules = substRules subst old_rules
-
- -- The new binding site Id needs its specialisations re-attached
- bndr_w_arity = new_bndr `setIdArity` ArityAtLeast (exprArity new_rhs)
-
- binding_site_id
- | isEmptyCoreRules old_rules = bndr_w_arity
- | otherwise = bndr_w_arity `setIdSpecialisation` new_rules
-
- -- At the occurrence sites we want to know the unfolding,
- -- and the occurrence info of the original
- -- (simplBinder cleaned up the inline prag of the original
- -- to eliminate un-stable info, in case this expression is
- -- simplified a second time; hence the need to reattach it)
- occ_site_id = binding_site_id
- `setIdUnfolding` mkUnfolding new_rhs
- `setInlinePragma` inlinePragInfo bndr_info
- in
- modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
- returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff)
+ = getSubst `thenSmpl` \ subst ->
+ let
+ -- We make new IdInfo for the new binder by starting from the old binder,
+ -- doing appropriate substitutions.
+ -- Then we add arity and unfolding info to get the new binder
+ new_bndr_info = substIdInfo subst old_info (idInfo new_bndr)
+ `setArityInfo` arity_info
+
+ -- Add the unfolding *only* for non-loop-breakers
+ -- Making loop breakers not have an unfolding at all
+ -- means that we can avoid tests in exprIsConApp, for example.
+ -- This is important: if exprIsConApp says 'yes' for a recursive
+ -- thing, then we can get into an infinite loop
+ info_w_unf | loop_breaker = new_bndr_info
+ | otherwise = new_bndr_info `setUnfoldingInfo` mkUnfolding top_lvl new_rhs
+
+ final_id = new_bndr `setIdInfo` info_w_unf
+ in
+ -- These seqs forces the Id, and hence its IdInfo,
+ -- and hence any inner substitutions
+ final_id `seq`
+ addLetBind (NonRec final_id new_rhs) $
+ modifyInScope new_bndr final_id thing_inside
+
+ where
+ old_info = idInfo old_bndr
+ occ_info = occInfo old_info
+ loop_breaker = isLoopBreaker occ_info
+ trivial_rhs = exprIsTrivial new_rhs
+ must_keep_binding = black_listed || loop_breaker || isExportedId old_bndr
+ arity_info = atLeastArity (exprArity new_rhs)
\end{code}
+
%************************************************************************
%* *
\subsection{simplLazyBind}
* It does eta expansion
\begin{code}
-simplLazyBind :: TopLevelFlag
+simplLazyBind :: Bool -- True <=> top level
-> InId -> OutId
-> InExpr -- The RHS
-> SimplM (OutStuff a) -- The body of the binding
-- Also the binder has already been simplified, and hence is in scope
simplLazyBind top_lvl bndr bndr' rhs thing_inside
- | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
- = tick (PreInlineUnconditionally bndr) `thenSmpl_`
- getSubstEnv `thenSmpl` \ rhs_se ->
- (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
+ = getBlackList `thenSmpl` \ black_list_fn ->
+ let
+ black_listed = black_list_fn bndr
+ in
- | otherwise
- = -- Simplify the RHS
- getSubstEnv `thenSmpl` \ rhs_se ->
+ if preInlineUnconditionally black_listed bndr then
+ -- Inline unconditionally
+ tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ getSubstEnv `thenSmpl` \ rhs_se ->
+ (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
+ else
- simplRhs top_lvl False {- Not ok to float unboxed -}
+ -- Simplify the RHS
+ getSubstEnv `thenSmpl` \ rhs_se ->
+ simplRhs top_lvl False {- Not ok to float unboxed (conservative) -}
(idType bndr')
rhs rhs_se $ \ rhs' ->
-- Now compete the binding and simplify the body
- completeBinding bndr bndr' rhs' thing_inside
+ completeBinding bndr bndr' top_lvl black_listed rhs' thing_inside
\end{code}
\begin{code}
-simplRhs :: TopLevelFlag
+simplRhs :: Bool -- True <=> Top level
-> Bool -- True <=> OK to float unboxed (speculative) bindings
- -> OutType -> InExpr -> SubstEnv
+ -- False for (a) recursive and (b) top-level bindings
+ -> OutType -- Type of RHS; used only occasionally
+ -> InExpr -> SubstEnv
-> (OutExpr -> SimplM (OutStuff a))
-> SimplM (OutStuff a)
simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
- = -- Swizzle the inner lets past the big lambda (if any)
- -- and try eta expansion
- transformRhs rhs `thenSmpl` \ t_rhs ->
-
- -- Simplify it
- setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
-
- -- Float lets out of RHS
+ = -- Simplify it
+ setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats1, (rhs_in_scope, rhs1)) ->
let
- (floats_out, rhs'') | float_ubx = (floats, rhs')
- | otherwise = splitFloats floats rhs'
+ (floats2, rhs2) = splitFloats float_ubx floats1 rhs1
in
- if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
- not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
- then
- tickLetFloat floats_out `thenSmpl_`
- -- Do the float
- --
-- There's a subtlety here. There may be a binding (x* = e) in the
-- floats, where the '*' means 'will be demanded'. So is it safe
-- to float it out? Answer no, but it won't matter because
-- we only float if arg' is a WHNF,
-- and so there can't be any 'will be demanded' bindings in the floats.
-- Hence the assert
- WARN( any demanded_float floats_out, ppr floats_out )
- setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
- -- in_scope' may be excessive, but that's OK;
- -- it's a superset of what's in scope
- returnSmpl (addBinds floats_out stuff)
+ WARN( any demanded_float (fromOL floats2), ppr (fromOL floats2) )
+
+ -- Transform the RHS
+ -- It's important that we do eta expansion on function *arguments* (which are
+ -- simplified with simplRhs), as well as let-bound right-hand sides.
+ -- Otherwise we find that things like
+ -- f (\x -> case x of I# x' -> coerce T (\ y -> ...))
+ -- get right through to the code generator as two separate lambdas,
+ -- which is a Bad Thing
+ tryRhsTyLam rhs2 `thenSmpl` \ (floats3, rhs3) ->
+ tryEtaExpansion rhs3 rhs_ty `thenSmpl` \ (floats4, rhs4) ->
+
+ -- Float lets if (a) we're at the top level
+ -- or (b) the resulting RHS is one we'd like to expose
+ if (top_lvl || exprIsCheap rhs4) then
+ (if (isNilOL floats2 && null floats3 && null floats4) then
+ returnSmpl ()
+ else
+ tick LetFloatFromLet) `thenSmpl_`
+
+ addFloats floats2 rhs_in_scope $
+ addAuxiliaryBinds floats3 $
+ addAuxiliaryBinds floats4 $
+ thing_inside rhs4
else
-- Don't do the float
- thing_inside (mkLets floats rhs')
+ thing_inside (wrapFloats floats1 rhs1)
--- In a let-from-let float, we just tick once, arbitrarily
--- choosing the first floated binder to identify it
-tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
-tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
-
-demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
+demanded_float (NonRec b r) = isStrict (idDemandInfo b) && not (isUnLiftedType (idType b))
-- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
demanded_float (Rec _) = False
--- Don't float any unlifted bindings out, because the context
+-- If float_ubx is true we float all the bindings, otherwise
+-- we just float until we come across an unlifted one.
+-- Remember that the unlifted bindings in the floats are all for
+-- guaranteed-terminating non-exception-raising unlifted things,
+-- which we are happy to do speculatively. However, we may still
+-- not be able to float them out, because the context
-- is either a Rec group, or the top level, neither of which
-- can tolerate them.
-splitFloats floats rhs
- = go floats
+splitFloats float_ubx floats rhs
+ | float_ubx = (floats, rhs) -- Float them all
+ | otherwise = go (fromOL floats)
where
- go [] = ([], rhs)
- go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
+ go [] = (nilOL, rhs)
+ go (f:fs) | must_stay f = (nilOL, mkLets (f:fs) rhs)
| otherwise = case go fs of
- (out, rhs') -> (f:out, rhs')
+ (out, rhs') -> (f `consOL` out, rhs')
must_stay (Rec prs) = False -- No unlifted bindings in here
must_stay (NonRec b r) = isUnLiftedType (idType b)
\begin{code}
simplVar var cont
- = freeTick LeafVisit `thenSmpl_`
- getSubst `thenSmpl` \ subst ->
- case lookupSubst subst var of
- Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
- Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
- Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
-
- Nothing -> let
- var' = case lookupInScope subst var of
- Just v' -> v'
- Nothing ->
-#ifdef DEBUG
- if isLocallyDefined var && not (idMustBeINLINEd var)
- -- The idMustBeINLINEd test accouunts for the fact
- -- that class dictionary constructors don't have top level
- -- bindings and hence aren't in scope.
- then
- -- Not in scope
- pprTrace "simplVar:" (ppr var) var
- else
-#endif
- var
- in
- getBlackList `thenSmpl` \ black_list ->
- getInScope `thenSmpl` \ in_scope ->
-
- prepareArgs (ppr var') (idType var') (get_str var') cont $ \ args' cont' ->
- completeCall black_list in_scope var' args' cont'
- where
- get_str var = case getIdStrictness var of
- NoStrictnessInfo -> (repeat wwLazy, False)
- StrictnessInfo demands result_bot -> (demands, result_bot)
-
-
----------------------------------------------------------
--- Preparing arguments for a call
-
-prepareArgs :: SDoc -- Error message info
- -> OutType -> ([Demand],Bool) -> SimplCont
- -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
- -> SimplM OutExprStuff
-
-prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
- = go [] demands orig_fun_ty orig_cont
- where
- not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
- -- "No strictness info" is signalled by an infinite list of wwLazy
-
- demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
- | result_bot = fun_demands -- Enough args, and function returns bottom
- | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
- -- NB: demands is finite iff enough args and result_bot is True
-
- -- Main game plan: loop through the arguments, simplifying
- -- each of them in turn. We carry with us a list of demands,
- -- and the type of the function-applied-to-earlier-args
-
- -- Type argument
- go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
- = getInScope `thenSmpl` \ in_scope ->
- let
- ty_arg' = substTy (mkSubst in_scope se) ty_arg
- res_ty = applyTy fun_ty ty_arg'
- in
- go (Type ty_arg' : acc) ds res_ty cont
-
- -- Value argument
- go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
- = case splitFunTy_maybe fun_ty of {
- Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
- (thing_inside (reverse acc) cont) ;
- Just (arg_ty, res_ty) ->
- simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
- go (arg':acc) ds res_ty cont }
-
- -- We've run out of demands, which only happens for functions
- -- we *know* now return bottom
- -- This deals with
- -- * case (error "hello") of { ... }
- -- * (error "Hello") arg
- -- * f (error "Hello") where f is strict
- -- etc
- go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
- thing_inside (reverse acc) (discardCont cont)
-
- -- We're run out of arguments
- go acc ds fun_ty cont = thing_inside (reverse acc) cont
-
--- Boring: we must only record a tick if there was an interesting
--- continuation to discard. If not, we tick forever.
-tick_case_of_error (Stop _) = returnSmpl ()
-tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
-tick_case_of_error other = tick BottomFound
-
----------------------------------------------------------
--- Dealing with a call
-
-completeCall black_list_fn in_scope var args cont
- -- Look for rules or specialisations that match
- -- Do this *before* trying inlining because some functions
- -- have specialisations *and* are strict; we don't want to
- -- inline the wrapper of the non-specialised thing... better
- -- to call the specialised thing instead.
- | maybeToBool maybe_rule_match
- = tick (RuleFired rule_name) `thenSmpl_`
- zapSubstEnv (completeApp rule_rhs rule_args cont)
- -- See note below about zapping the substitution here
-
- -- Look for an unfolding. There's a binding for the
- -- thing, but perhaps we want to inline it anyway
- | maybeToBool maybe_inline
- = tick (UnfoldingDone var) `thenSmpl_`
- zapSubstEnv (completeInlining var unf_template args (discardInlineCont cont))
+ = getSubst `thenSmpl` \ subst ->
+ case lookupIdSubst subst var of
+ DoneEx e -> zapSubstEnv (simplExprF e cont)
+ ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
+ DoneId var1 occ -> WARN( not (isInScope var1 subst) && mustHaveLocalBinding var1,
+ text "simplVar:" <+> ppr var )
+ zapSubstEnv (completeCall var1 occ cont)
-- The template is already simplified, so don't re-substitute.
-- This is VITAL. Consider
-- let x = e in
-- We'll clone the inner \x, adding x->x' in the id_subst
-- Then when we inline y, we must *not* replace x by x' in
-- the inlined copy!!
-
- | otherwise -- Neither rule nor inlining
- = rebuild (mkApps (Var var) args) cont
-
- where
- ---------- Unfolding stuff
- maybe_inline = callSiteInline black_listed inline_call
- var args interesting_cont
- Just unf_template = maybe_inline
- interesting_cont = contIsInteresting cont
- inline_call = contIsInline cont
- black_listed = black_list_fn var
-
- ---------- Specialisation stuff
- maybe_rule_match = lookupRule in_scope var args
- Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
-
-
--- First a special case
--- Don't actually inline the scrutinee when we see
--- case x of y { .... }
--- and x has unfolding (C a b). Why not? Because
--- we get a silly binding y = C a b. If we don't
--- inline knownCon can directly substitute x for y instead.
-completeInlining var (Con con con_args) args (Select _ bndr alts se cont)
- | conOkForAlt con
- = ASSERT( null args )
- knownCon (Var var) con con_args bndr alts se cont
-
--- Now the normal case
-completeInlining var unfolding args cont
- = completeApp unfolding args cont
-
--- completeApp applies a new InExpr (from an unfolding or rule)
--- to an *already simplified* set of arguments
-completeApp :: InExpr -- (\xs. body)
- -> [OutExpr] -- Args; already simplified
- -> SimplCont -- What to do with result of applicatoin
- -> SimplM OutExprStuff
-completeApp fun args cont
- = go fun args
- where
- zap_it = mkLamBndrZapper fun (length args)
- cont_ty = contResultType cont
- -- These equations are very similar to simplLam and simplBeta combined,
- -- except that they deal with already-simplified arguments
-
- -- Type argument
- go (Lam bndr fun) (Type ty:args) = tick (BetaReduction bndr) `thenSmpl_`
- extendSubst bndr (DoneTy ty)
- (go fun args)
-
- -- Value argument
- go (Lam bndr fun) (arg:args)
- | preInlineUnconditionally zapped_bndr && not opt_SimplNoPreInlining
- = tick (BetaReduction bndr) `thenSmpl_`
- tick (PreInlineUnconditionally bndr) `thenSmpl_`
- extendSubst zapped_bndr (DoneEx arg)
- (go fun args)
- | otherwise
- = tick (BetaReduction bndr) `thenSmpl_`
- simplBinder zapped_bndr ( \ bndr' ->
- completeBeta zapped_bndr bndr' arg $
- go fun args
- )
- where
- zapped_bndr = zap_it bndr
-
- -- Consumed all the lambda binders or args
- go fun args = simplExprF fun (pushArgs emptySubstEnv args cont)
-
-
------------ costCentreOk
--- costCentreOk checks that it's ok to inline this thing
--- The time it *isn't* is this:
+---------------------------------------------------------
+-- Dealing with a call
+
+completeCall var occ_info cont
+ = getBlackList `thenSmpl` \ black_list_fn ->
+ getInScope `thenSmpl` \ in_scope ->
+ getContArgs var cont `thenSmpl` \ (args, call_cont, inline_call) ->
+ getDOptsSmpl `thenSmpl` \ dflags ->
+ let
+ black_listed = black_list_fn var
+ arg_infos = [ interestingArg in_scope arg subst
+ | (arg, subst, _) <- args, isValArg arg]
+
+ interesting_cont = interestingCallContext (not (null args))
+ (not (null arg_infos))
+ call_cont
+
+ inline_cont | inline_call = discardInline cont
+ | otherwise = cont
+
+ maybe_inline = callSiteInline dflags black_listed inline_call occ_info
+ var arg_infos interesting_cont
+ in
+ -- First, look for an inlining
+ case maybe_inline of {
+ Just unfolding -- There is an inlining!
+ -> tick (UnfoldingDone var) `thenSmpl_`
+ simplExprF unfolding inline_cont
+
+ ;
+ Nothing -> -- No inlining!
+
+
+ simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' ->
+
+ -- Next, look for rules or specialisations that match
+ --
+ -- It's important to simplify the args first, because the rule-matcher
+ -- doesn't do substitution as it goes. We don't want to use subst_args
+ -- (defined in the 'where') because that throws away useful occurrence info,
+ -- and perhaps-very-important specialisations.
+ --
+ -- Some functions have specialisations *and* are strict; in this case,
+ -- we don't want to inline the wrapper of the non-specialised thing; better
+ -- to call the specialised thing instead.
+ -- But the black-listing mechanism means that inlining of the wrapper
+ -- won't occur for things that have specialisations till a later phase, so
+ -- it's ok to try for inlining first.
+ --
+ -- You might think that we shouldn't apply rules for a loop breaker:
+ -- doing so might give rise to an infinite loop, because a RULE is
+ -- rather like an extra equation for the function:
+ -- RULE: f (g x) y = x+y
+ -- Eqn: f a y = a-y
+ --
+ -- But it's too drastic to disable rules for loop breakers.
+ -- Even the foldr/build rule would be disabled, because foldr
+ -- is recursive, and hence a loop breaker:
+ -- foldr k z (build g) = g k z
+ -- So it's up to the programmer: rules can cause divergence
+
+ getSwitchChecker `thenSmpl` \ chkr ->
+ let
+ maybe_rule | switchIsOn chkr DontApplyRules = Nothing
+ | otherwise = lookupRule in_scope var args'
+ in
+ case maybe_rule of {
+ Just (rule_name, rule_rhs) ->
+ tick (RuleFired rule_name) `thenSmpl_`
+#ifdef DEBUG
+ (if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "Rule fired" (vcat [
+ text "Rule:" <+> ptext rule_name,
+ text "Before:" <+> ppr var <+> sep (map pprParendExpr args'),
+ text "After: " <+> pprCoreExpr rule_rhs])
+ else
+ id) $
+#endif
+ simplExprF rule_rhs call_cont ;
+
+ Nothing -> -- No rules
+
+ -- Done
+ rebuild (mkApps (Var var) args') call_cont
+ }}
+
+
+---------------------------------------------------------
+-- Simplifying the arguments of a call
+
+simplifyArgs :: Bool -- It's a data constructor
+ -> [(InExpr, SubstEnv, Bool)] -- Details of the arguments
+ -> OutType -- Type of the continuation
+ -> ([OutExpr] -> SimplM OutExprStuff)
+ -> SimplM OutExprStuff
+
+-- Simplify the arguments to a call.
+-- This part of the simplifier may break the no-shadowing invariant
+-- Consider
+-- f (...(\a -> e)...) (case y of (a,b) -> e')
+-- where f is strict in its second arg
+-- If we simplify the innermost one first we get (...(\a -> e)...)
+-- Simplifying the second arg makes us float the case out, so we end up with
+-- case y of (a,b) -> f (...(\a -> e)...) e'
+-- So the output does not have the no-shadowing invariant. However, there is
+-- no danger of getting name-capture, because when the first arg was simplified
+-- we used an in-scope set that at least mentioned all the variables free in its
+-- static environment, and that is enough.
--
--- f x = let y = E in
--- scc "foo" (...y...)
+-- We can't just do innermost first, or we'd end up with a dual problem:
+-- case x of (a,b) -> f e (...(\a -> e')...)
--
--- Here y has a "current cost centre", and we can't inline it inside "foo",
--- regardless of whether E is a WHNF or not.
-
-costCentreOk ccs_encl cc_rhs
- = not opt_SccProfilingOn
- || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
- || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
+-- I spent hours trying to recover the no-shadowing invariant, but I just could
+-- not think of an elegant way to do it. The simplifier is already knee-deep in
+-- continuations. We have to keep the right in-scope set around; AND we have
+-- to get the effect that finding (error "foo") in a strict arg position will
+-- discard the entire application and replace it with (error "foo"). Getting
+-- all this at once is TOO HARD!
+
+simplifyArgs is_data_con args cont_ty thing_inside
+ | not is_data_con
+ = go args thing_inside
+
+ | otherwise -- It's a data constructor, so we want
+ -- to switch off inlining in the arguments
+ -- If we don't do this, consider:
+ -- let x = +# p q in C {x}
+ -- Even though x get's an occurrence of 'many', its RHS looks cheap,
+ -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
+ = getBlackList `thenSmpl` \ old_bl ->
+ setBlackList noInlineBlackList $
+ go args $ \ args' ->
+ setBlackList old_bl $
+ thing_inside args'
+
+ where
+ go [] thing_inside = thing_inside []
+ go (arg:args) thing_inside = simplifyArg is_data_con arg cont_ty $ \ arg' ->
+ go args $ \ args' ->
+ thing_inside (arg':args')
+
+simplifyArg is_data_con (Type ty_arg, se, _) cont_ty thing_inside
+ = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg ->
+ thing_inside (Type new_ty_arg)
+
+simplifyArg is_data_con (val_arg, se, is_strict) cont_ty thing_inside
+ = getInScope `thenSmpl` \ in_scope ->
+ let
+ arg_ty = substTy (mkSubst in_scope se) (exprType val_arg)
+ in
+ if not is_data_con then
+ -- An ordinary function
+ simplValArg arg_ty is_strict val_arg se cont_ty thing_inside
+ else
+ -- A data constructor
+ -- simplifyArgs has already switched off inlining, so
+ -- all we have to do here is to let-bind any non-trivial argument
+
+ -- It's not always the case that new_arg will be trivial
+ -- Consider f x
+ -- where, in one pass, f gets substituted by a constructor,
+ -- but x gets substituted by an expression (assume this is the
+ -- unique occurrence of x). It doesn't really matter -- it'll get
+ -- fixed up next pass. And it happens for dictionary construction,
+ -- which mentions the wrapper constructor to start with.
+ simplValArg arg_ty is_strict val_arg se cont_ty $ \ arg' ->
+
+ if exprIsTrivial arg' then
+ thing_inside arg'
+ else
+ newId SLIT("a") (exprType arg') $ \ arg_id ->
+ addNonRecBind arg_id arg' $
+ thing_inside (Var arg_id)
\end{code}
%* *
%************************************************************************
+NB: At one time I tried not pre/post-inlining top-level things,
+even if they occur exactly once. Reason:
+ (a) some might appear as a function argument, so we simply
+ replace static allocation with dynamic allocation:
+ l = <...>
+ x = f l
+ becomes
+ x = f <...>
+
+ (b) some top level things might be black listed
+
+HOWEVER, I found that some useful foldr/build fusion was lost (most
+notably in spectral/hartel/parstof) because the foldr didn't see the build.
+
+Doing the dynamic allocation isn't a big deal, in fact, but losing the
+fusion can be.
+
\begin{code}
-preInlineUnconditionally :: InId -> Bool
+preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
-- Examines a bndr to see if it is used just once in a
-- completely safe way, so that it is safe to discard the binding
-- inline its RHS at the (unique) usage site, REGARDLESS of how
--
-- Evne RHSs labelled InlineMe aren't caught here, because
-- there might be no benefit from inlining at the call site.
- -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
- -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
-preInlineUnconditionally bndr
- = case getInlinePragma bndr of
- IMustBeINLINEd -> True
- ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
- -- one occurrence ==> safe!
- other -> False
-
-
-postInlineUnconditionally :: InId -> OutExpr -> Bool
- -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
- -- It returns True if it's ok to discard the binding and inline the
- -- RHS at every use site.
-
- -- NOTE: This isn't our last opportunity to inline.
- -- We're at the binding site right now, and
- -- we'll get another opportunity when we get to the ocurrence(s)
-postInlineUnconditionally bndr rhs
- | isExportedId bndr
- = False
- | otherwise
- = case getInlinePragma bndr of
- IAmALoopBreaker -> False
-
- ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
- -- Don't inline even WHNFs inside lambdas; doing so may
- -- simply increase allocation when the function is called
- -- This isn't the last chance; see NOTE above.
-
- ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
- -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
- -- decision about duplicating code is best left to callSiteInline
-
- other -> exprIsTrivial rhs -- Duplicating is *free*
- -- NB: Even InlineMe and IMustBeINLINEd are ignored here
- -- Why? Because we don't even want to inline them into the
- -- RHS of constructor arguments. See NOTE above
- -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
- -- it's best to inline it anyway. We often get a=E; b=a
- -- from desugaring, with both a and b marked NOINLINE.
+preInlineUnconditionally black_listed bndr
+ | black_listed || opt_SimplNoPreInlining = False
+ | otherwise = case idOccInfo bndr of
+ OneOcc in_lam once -> not in_lam && once
+ -- Not inside a lambda, one occurrence ==> safe!
+ other -> False
\end{code}
\begin{code}
-------------------------------------------------------------------
-- Finish rebuilding
-rebuild_done expr
- = getInScope `thenSmpl` \ in_scope ->
- returnSmpl ([], (in_scope, expr))
+rebuild_done expr = returnOutStuff expr
---------------------------------------------------------
rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
-- Stop continuation
-rebuild expr (Stop _) = rebuild_done expr
+rebuild expr (Stop _ _) = rebuild_done expr
-- ArgOf continuation
rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
-- Coerce continuation
rebuild expr (CoerceIt to_ty cont)
- = rebuild (mkCoerce to_ty expr) cont
+ = rebuild (mkCoerce to_ty (exprType expr) expr) cont
-- Inline continuation
rebuild expr (InlinePlease cont)
= rebuild (Note InlineCall expr) cont
--- Case of known constructor or literal
-rebuild expr@(Con con args) (Select _ bndr alts se cont)
- | conOkForAlt con -- Knocks out PrimOps and NoRepLits
- = knownCon expr con args bndr alts se cont
-
-
----------------------------------------------------------
--- The other Select cases
-
rebuild scrut (Select _ bndr alts se cont)
- | -- Check that the RHSs are all the same, and
- -- don't use the binders in the alternatives
- -- This test succeeds rapidly in the common case of
- -- a single DEFAULT alternative
- all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
-
- -- Check that the scrutinee can be let-bound instead of case-bound
- && ( (isUnLiftedType (idType bndr) && -- It's unlifted and floatable
- exprOkForSpeculation scrut) -- NB: scrut = an unboxed variable satisfies
- || exprIsValue scrut -- It's already evaluated
- || var_demanded_later scrut -- It'll be demanded later
-
--- || not opt_SimplPedanticBottoms) -- Or we don't care!
--- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
--- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
--- its argument: case x of { y -> dataToTag# y }
--- Here we must *not* discard the case, because dataToTag# just fetches the tag from
--- the info pointer. So we'll be pedantic all the time, and see if that gives any
--- other problems
- )
-
- && opt_SimplDoCaseElim
- = -- Get rid of the case altogether
- -- See the extensive notes on case-elimination below
- -- Remember to bind the binder though!
- tick (CaseElim bndr) `thenSmpl_` (
- setSubstEnv se $
- simplBinder bndr $ \ bndr' ->
- completeBinding bndr bndr' scrut $
- simplExprF rhs1 cont)
-
- | otherwise
= rebuild_case scrut bndr alts se cont
- where
- (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
- binders_unused (_, bndrs, _) = all isDeadBinder bndrs
-
- var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
- var_demanded_later other = False
\end{code}
Case elimination [see the code above]
\begin{code}
---------------------------------------------------------
+-- Eliminate the case if possible
+
+rebuild_case scrut bndr alts se cont
+ | maybeToBool maybe_con_app
+ = knownCon scrut (DataAlt con) args bndr alts se cont
+
+ | canEliminateCase scrut bndr alts
+ = tick (CaseElim bndr) `thenSmpl_` (
+ setSubstEnv se $
+ simplBinder bndr $ \ bndr' ->
+ -- Remember to bind the case binder!
+ completeBinding bndr bndr' False False scrut $
+ simplExprF (head (rhssOfAlts alts)) cont)
+
+ | otherwise
+ = complete_case scrut bndr alts se cont
+
+ where
+ maybe_con_app = exprIsConApp_maybe scrut
+ Just (con, args) = maybe_con_app
+
+ -- See if we can get rid of the case altogether
+ -- See the extensive notes on case-elimination above
+canEliminateCase scrut bndr alts
+ = -- Check that the RHSs are all the same, and
+ -- don't use the binders in the alternatives
+ -- This test succeeds rapidly in the common case of
+ -- a single DEFAULT alternative
+ all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
+
+ -- Check that the scrutinee can be let-bound instead of case-bound
+ && ( exprOkForSpeculation scrut
+ -- OK not to evaluate it
+ -- This includes things like (==# a# b#)::Bool
+ -- so that we simplify
+ -- case ==# a# b# of { True -> x; False -> x }
+ -- to just
+ -- x
+ -- This particular example shows up in default methods for
+ -- comparision operations (e.g. in (>=) for Int.Int32)
+ || exprIsValue scrut -- It's already evaluated
+ || var_demanded_later scrut -- It'll be demanded later
+
+-- || not opt_SimplPedanticBottoms) -- Or we don't care!
+-- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
+-- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
+-- its argument: case x of { y -> dataToTag# y }
+-- Here we must *not* discard the case, because dataToTag# just fetches the tag from
+-- the info pointer. So we'll be pedantic all the time, and see if that gives any
+-- other problems
+ )
+
+ where
+ (rhs1:other_rhss) = rhssOfAlts alts
+ binders_unused (_, bndrs, _) = all isDeadBinder bndrs
+
+ var_demanded_later (Var v) = isStrict (idDemandInfo bndr) -- It's going to be evaluated later
+ var_demanded_later other = False
+
+
+---------------------------------------------------------
-- Case of something else
-rebuild_case scrut case_bndr alts se cont
+complete_case scrut case_bndr alts se cont
= -- Prepare case alternatives
prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
- scrut_cons alts `thenSmpl` \ better_alts ->
+ impossible_cons alts `thenSmpl` \ better_alts ->
-- Set the new subst-env in place (before dealing with the case binder)
setSubstEnv se $
-- Deal with variable scrutinee
- ( simplBinder case_bndr $ \ case_bndr' ->
- substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
- let
- case_bndr'' = zap_occ_info case_bndr'
- in
+ (
+ getSwitchChecker `thenSmpl` \ chkr ->
+ simplCaseBinder (switchIsOn chkr NoCaseOfCase)
+ scrut case_bndr $ \ case_bndr' zap_occ_info ->
- -- Deal with the case alternaatives
- simplAlts zap_occ_info scrut_cons
- case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
+ -- Deal with the case alternatives
+ simplAlts zap_occ_info impossible_cons
+ case_bndr' better_alts cont' `thenSmpl` \ alts' ->
- mkCase scrut case_bndr'' alts'
+ mkCase scrut case_bndr' alts'
) `thenSmpl` \ case_expr ->
-- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
-- that should not include these chaps!
rebuild_done case_expr
where
- -- scrut_cons tells what constructors the scrutinee can't possibly match
- scrut_cons = case scrut of
- Var v -> otherCons (getIdUnfolding v)
- other -> []
+ impossible_cons = case scrut of
+ Var v -> otherCons (idUnfolding v)
+ other -> []
+
+knownCon :: OutExpr -> AltCon -> [OutExpr]
+ -> InId -> [InAlt] -> SubstEnv -> SimplCont
+ -> SimplM OutExprStuff
knownCon expr con args bndr alts se cont
- = tick (KnownBranch bndr) `thenSmpl_`
+ = -- Arguments should be atomic;
+ -- yell if not
+ WARN( not (all exprIsTrivial args),
+ text "knownCon" <+> ppr expr )
+ tick (KnownBranch bndr) `thenSmpl_`
setSubstEnv se (
simplBinder bndr $ \ bndr' ->
+ completeBinding bndr bndr' False False expr $
+ -- Don't use completeBeta here. The expr might be
+ -- an unboxed literal, like 3, or a variable
+ -- whose unfolding is an unboxed literal... and
+ -- completeBeta will just construct another case
+ -- expression!
case findAlt con alts of
(DEFAULT, bs, rhs) -> ASSERT( null bs )
- completeBinding bndr bndr' expr $
- -- Don't use completeBeta here. The expr might be
- -- an unboxed literal, like 3, or a variable
- -- whose unfolding is an unboxed literal... and
- -- completeBeta will just construct another case
- -- expression!
simplExprF rhs cont
- (Literal lit, bs, rhs) -> ASSERT( null bs )
- extendSubst bndr (DoneEx expr) $
- -- Unconditionally substitute, because expr must
- -- be a variable or a literal. It can't be a
- -- NoRep literal because they don't occur in
- -- case patterns.
+ (LitAlt lit, bs, rhs) -> ASSERT( null bs )
simplExprF rhs cont
- (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
- completeBinding bndr bndr' expr $
- -- See note above
+ (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
extendSubstList bs (map mk real_args) $
simplExprF rhs cont
where
-- Polymorphic recursion here!
prepareCaseCont [alt] cont thing_inside = thing_inside cont
-prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
+prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
+ mkDupableCont alts_ty cont thing_inside
+ -- At one time I passed in the un-simplified type, and simplified
+ -- it only if we needed to construct a join binder, but that
+ -- didn't work because we have to decompse function types
+ -- (using funResultTy) in mkDupableCont.
\end{code}
-substForVarScrut checks whether the scrutinee is a variable, v.
-If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
-that way, there's a chance that v will now only be used once, and hence inlined.
+simplCaseBinder checks whether the scrutinee is a variable, v. If so,
+try to eliminate uses of v in the RHSs in favour of case_bndr; that
+way, there's a chance that v will now only be used once, and hence
+inlined.
+
+There is a time we *don't* want to do that, namely when
+-fno-case-of-case is on. This happens in the first simplifier pass,
+and enhances full laziness. Here's the bad case:
+ f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
+If we eliminate the inner case, we trap it inside the I# v -> arm,
+which might prevent some full laziness happening. I've seen this
+in action in spectral/cichelli/Prog.hs:
+ [(m,n) | m <- [1..max], n <- [1..max]]
+Hence the no_case_of_case argument
+
If we do this, then we have to nuke any occurrence info (eg IAmDead)
in the case binder, because the case-binder now effectively occurs
case x or { (a,b) -> a b }
Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
-happened. Hence the zap_occ_info function returned by substForVarScrut
+happened. Hence the zap_occ_info function returned by simplCaseBinder
\begin{code}
-substForVarScrut (Var v) case_bndr' thing_inside
- | isLocallyDefined v -- No point for imported things
- = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
- `setInlinePragma` IMustBeINLINEd) $
+simplCaseBinder no_case_of_case (Var v) case_bndr thing_inside
+ | not no_case_of_case
+ = simplBinder (zap case_bndr) $ \ case_bndr' ->
+ modifyInScope v case_bndr' $
-- We could extend the substitution instead, but it would be
-- a hack because then the substitution wouldn't be idempotent
- -- any more.
- thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
+ -- any more (v is an OutId). And this just just as well.
+ thing_inside case_bndr' zap
+ where
+ zap b = b `setIdOccInfo` NoOccInfo
-substForVarScrut other_scrut case_bndr' thing_inside
- = thing_inside (\ bndr -> bndr) -- NoOp on bndr
+simplCaseBinder add_eval_info other_scrut case_bndr thing_inside
+ = simplBinder case_bndr $ \ case_bndr' ->
+ thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
\end{code}
prepareCaseAlts does two things:
let
ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
+ arg_tys = dataConArgTys data_con
+ (inst_tys ++ mkTyVarTys ex_tyvars')
in
- newIds (dataConArgTys
- data_con
- (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
- returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
+ newIds SLIT("a") arg_tys $ \ bndrs ->
+ returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
other -> returnSmpl filtered_alts
where
[] -> alts
other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
- missing_cons = [data_con | data_con <- tyConDataCons tycon,
+ missing_cons = [data_con | data_con <- tyConDataConsIfAvailable tycon,
not (data_con `elem` handled_data_cons)]
- handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
- [data_con | (DataCon data_con, _, _) <- filtered_alts]
+ handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++
+ [data_con | (DataAlt data_con, _, _) <- filtered_alts]
-- The default case
prepareCaseAlts _ _ scrut_cons alts
----------------------
-simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
+simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
= mapSmpl simpl_alt alts
where
- inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
- Just (tycon, inst_tys) -> inst_tys
+ inst_tys' = tyConAppArgs (idType case_bndr')
-- handled_cons is all the constructors that are dealt
-- with, either by being impossible, or by there being an alternative
= -- In the default case we record the constructors that the
-- case-binder *can't* be.
-- We take advantage of any OtherCon info in the case scrutinee
- modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
+ modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
simplExprC rhs cont' `thenSmpl` \ rhs' ->
returnSmpl (DEFAULT, [], rhs')
simpl_alt (con, vs, rhs)
= -- Deal with the pattern-bound variables
-- Mark the ones that are in ! positions in the data constructor
- -- as certainly-evaluated
- simplBinders (add_evals con vs) $ \ vs' ->
+ -- as certainly-evaluated.
+ -- NB: it happens that simplBinders does *not* erase the OtherCon
+ -- form of unfolding, so it's ok to add this info before
+ -- doing simplBinders
+ simplBinders (add_evals con vs) $ \ vs' ->
- -- Bind the case-binder to (Con args)
+ -- Bind the case-binder to (con args)
let
- con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
+ unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
in
- modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
+ modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $
simplExprC rhs cont' `thenSmpl` \ rhs' ->
returnSmpl (con, vs', rhs')
-- We really must record that b is already evaluated so that we don't
-- go and re-evaluate it when constructing the result.
- add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
+ add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
add_evals other_con vs = vs
cat_evals [] [] = []
%************************************************************************
\begin{code}
-mkDupableCont :: InType -- Type of the thing to be given to the continuation
+mkDupableCont :: OutType -- Type of the thing to be given to the continuation
-> SimplCont
-> (SimplCont -> SimplM (OutStuff a))
-> SimplM (OutStuff a)
mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
= -- Build the RHS of the join point
- simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
- newId join_arg_ty' ( \ arg_id ->
- getSwitchChecker `thenSmpl` \ chkr ->
- cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
- returnSmpl (Lam arg_id (mkLets binds rhs))
+ newId SLIT("a") join_arg_ty ( \ arg_id ->
+ cont_fn (Var arg_id) `thenSmpl` \ (floats, (_, rhs)) ->
+ returnSmpl (Lam (setOneShotLambda arg_id) (wrapFloats floats rhs))
) `thenSmpl` \ join_rhs ->
-- Build the join Id and continuation
- newId (coreExprType join_rhs) $ \ join_id ->
+ -- We give it a "$j" name just so that for later amusement
+ -- we can identify any join points that don't end up as let-no-escapes
+ -- [NOTE: the type used to be exprType join_rhs, but this seems more elegant.]
+ newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) $ \ join_id ->
let
new_cont = ArgOf OkToDup cont_ty
(\arg' -> rebuild_done (App (Var join_id) arg'))
in
-
- -- Do the thing inside
- thing_inside new_cont `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec join_id join_rhs) res)
+
+ tick (CaseOfCase join_id) `thenSmpl_`
+ -- Want to tick here so that we go round again,
+ -- and maybe copy or inline the code;
+ -- not strictly CaseOf Case
+ addLetBind (NonRec join_id join_rhs) $
+ thing_inside new_cont
mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
= mkDupableCont (funResultTy ty) cont $ \ cont' ->
if exprIsDupable arg' then
thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
else
- newId (coreExprType arg') $ \ bndr ->
- thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec bndr arg') res)
+ newId SLIT("a") (exprType arg') $ \ bndr ->
+
+ tick (CaseOfCase bndr) `thenSmpl_`
+ -- Want to tick here so that we go round again,
+ -- and maybe copy or inline the code;
+ -- not strictly CaseOf Case
+
+ addLetBind (NonRec bndr arg') $
+ -- But what if the arg should be case-bound? We can't use
+ -- addNonRecBind here because its type is too specific.
+ -- This has been this way for a long time, so I'll leave it,
+ -- but I can't convince myself that it's right.
+
+ thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont')
+
mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
= tick (CaseOfCase case_bndr) `thenSmpl_`
setSubstEnv se (
simplBinder case_bndr $ \ case_bndr' ->
prepareCaseCont alts cont $ \ cont' ->
- mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
- returnSmpl (concat alt_binds_s, alts')
- ) `thenSmpl` \ (alt_binds, alts') ->
+ mkDupableAlts case_bndr case_bndr' cont' alts $ \ alts' ->
+ returnOutStuff alts'
+ ) `thenSmpl` \ (alt_binds, (in_scope, alts')) ->
- extendInScopes [b | NonRec b _ <- alt_binds] $
+ addFloats alt_binds in_scope $
-- NB that the new alternatives, alts', are still InAlts, using the original
-- binders. That means we can keep the case_bndr intact. This is important
-- This is VITAL when the type of case_bndr is an unboxed pair (often the
-- case in I/O rich code. We aren't allowed a lambda bound
-- arg of unboxed tuple type, and indeed such a case_bndr is always dead
- thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
-
- returnSmpl (addBinds alt_binds res)
+ thing_inside (Select OkToDup case_bndr alts' se (mkStop (contResultType cont)))
+mkDupableAlts :: InId -> OutId -> SimplCont -> [InAlt]
+ -> ([InAlt] -> SimplM (OutStuff a))
+ -> SimplM (OutStuff a)
+mkDupableAlts case_bndr case_bndr' cont [] thing_inside
+ = thing_inside []
+mkDupableAlts case_bndr case_bndr' cont (alt:alts) thing_inside
+ = mkDupableAlt case_bndr case_bndr' cont alt $ \ alt' ->
+ mkDupableAlts case_bndr case_bndr' cont alts $ \ alts' ->
+ thing_inside (alt' : alts')
-mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
-mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
- = -- Not worth checking whether the rhs is small; the
- -- inliner will inline it if so.
- simplBinders bndrs $ \ bndrs' ->
+mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) thing_inside
+ = simplBinders bndrs $ \ bndrs' ->
simplExprC rhs cont `thenSmpl` \ rhs' ->
+
+ if (case cont of { Stop _ _ -> exprIsDupable rhs'; other -> False}) then
+ -- It is worth checking for a small RHS because otherwise we
+ -- get extra let bindings that may cause an extra iteration of the simplifier to
+ -- inline back in place. Quite often the rhs is just a variable or constructor.
+ -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
+ -- iterations because the version with the let bindings looked big, and so wasn't
+ -- inlined, but after the join points had been inlined it looked smaller, and so
+ -- was inlined.
+ --
+ -- But since the continuation is absorbed into the rhs, we only do this
+ -- for a Stop continuation.
+ --
+ -- NB: we have to check the size of rhs', not rhs.
+ -- Duplicating a small InAlt might invalidate occurrence information
+ -- However, if it *is* dupable, we return the *un* simplified alternative,
+ -- because otherwise we'd need to pair it up with an empty subst-env.
+ -- (Remember we must zap the subst-env before re-simplifying something).
+ -- Rather than do this we simply agree to re-simplify the original (small) thing later.
+ thing_inside alt
+
+ else
let
- rhs_ty' = coreExprType rhs'
+ rhs_ty' = exprType rhs'
(used_bndrs, used_bndrs')
= unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
(case_bndr' : bndrs'),
-- then 78
-- else 5
- then newId realWorldStatePrimTy $ \ rw_id ->
+ then newId SLIT("w") realWorldStatePrimTy $ \ rw_id ->
returnSmpl ([rw_id], [Var realWorldPrimId])
else
returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
)
`thenSmpl` \ (final_bndrs', final_args) ->
- newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
-
- -- Notice that we make the lambdas into one-shot-lambdas. The
+ -- See comment about "$j" name above
+ newId SLIT("$j") (foldr mkPiType rhs_ty' final_bndrs') $ \ join_bndr ->
+ -- Notice the funky mkPiType. If the contructor has existentials
+ -- it's possible that the join point will be abstracted over
+ -- type varaibles as well as term variables.
+ -- Example: Suppose we have
+ -- data T = forall t. C [t]
+ -- Then faced with
+ -- case (case e of ...) of
+ -- C t xs::[t] -> rhs
+ -- We get the join point
+ -- let j :: forall t. [t] -> ...
+ -- j = /\t \xs::[t] -> rhs
+ -- in
+ -- case (case e of ...) of
+ -- C t xs::[t] -> j t xs
+
+ let
+ -- We make the lambdas into one-shot-lambdas. The
-- join point is sure to be applied at most once, and doing so
-- prevents the body of the join point being floated out by
-- the full laziness pass
- returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
- (con, bndrs, mkApps (Var join_bndr) final_args))
+ really_final_bndrs = map one_shot final_bndrs'
+ one_shot v | isId v = setOneShotLambda v
+ | otherwise = v
+ in
+ addLetBind (NonRec join_bndr (mkLams really_final_bndrs rhs')) $
+ thing_inside (con, bndrs, mkApps (Var join_bndr) final_args)
\end{code}
projects / ghc-hetmet.git / blobdiff