-
+%
% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[Simplify]{The main module of the simplifier}
\begin{code}
-module Simplify ( simplBind ) where
+module Simplify ( simplTopBinds, simplExpr ) where
#include "HsVersions.h"
-import CmdLineOpts ( switchIsOn, opt_SccProfilingOn, opt_PprStyle_Debug,
- opt_NoPreInlining, opt_DictsStrict, opt_D_dump_inlinings,
+import CmdLineOpts ( switchIsOn, opt_SimplDoEtaReduction,
+ opt_SimplNoPreInlining,
+ dopt, DynFlag(Opt_D_dump_inlinings),
SimplifierSwitch(..)
)
import SimplMonad
-import SimplUtils ( mkCase, etaCoreExpr, etaExpandCount, findAlt, mkRhsTyLam,
- simplBinder, simplBinders, simplIds, findDefault
+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 )
+import Var ( mkSysTyVar, tyVarKind )
import VarEnv
-import VarSet
-import Id ( Id, idType,
- getIdUnfolding, setIdUnfolding,
- getIdSpecialisation, setIdSpecialisation,
- getIdDemandInfo, setIdDemandInfo,
- getIdArity, setIdArity,
- getIdStrictness,
- setInlinePragma, getInlinePragma, idMustBeINLINEd,
- idWantsToBeINLINEd
+import Id ( Id, idType, idInfo, isDataConId, hasNoBinding,
+ idUnfolding, setIdUnfolding, isExportedId, isDeadBinder,
+ idDemandInfo, setIdInfo,
+ idOccInfo, setIdOccInfo,
+ zapLamIdInfo, setOneShotLambda,
+ )
+import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker,
+ setArityInfo,
+ setUnfoldingInfo, atLeastArity,
+ occInfo
)
-import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
- ArityInfo, atLeastArity, arityLowerBound, unknownArity
+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 )
-import DataCon ( DataCon, dataConNumInstArgs, dataConStrictMarks, dataConSig, dataConArgTys )
-import Const ( Con(..) )
-import MagicUFs ( applyMagicUnfoldingFun )
-import Name ( isExported, isLocallyDefined )
import CoreSyn
-import CoreUnfold ( Unfolding(..), UnfoldingGuidance(..),
- mkUnfolding, smallEnoughToInline,
- isEvaldUnfolding, unfoldAlways
+import PprCore ( pprParendExpr, pprCoreExpr )
+import CoreFVs ( mustHaveLocalBinding )
+import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons,
+ callSiteInline
)
-import CoreUtils ( IdSubst, SubstCoreExpr(..),
- cheapEqExpr, exprIsDupable, exprIsWHNF, exprIsTrivial,
- coreExprType, coreAltsType, exprIsCheap, substExpr,
- FormSummary(..), mkFormSummary, whnfOrBottom
+import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsTrivial,
+ exprIsConApp_maybe, mkPiType, findAlt, findDefault,
+ exprType, coreAltsType, exprIsValue,
+ exprOkForSpeculation, exprArity, exprIsCheap,
+ mkCoerce, mkSCC, mkInlineMe, mkAltExpr
)
-import SpecEnv ( lookupSpecEnv, isEmptySpecEnv, substSpecEnv )
-import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
-import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType, fullSubstTy,
- mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
- applyTy, applyTys, funResultTy, isDictTy, isDataType
+import Rules ( lookupRule )
+import CostCentre ( currentCCS )
+import Type ( mkTyVarTys, isUnLiftedType, seqType,
+ mkFunTy, splitTyConApp_maybe, tyConAppArgs,
+ funResultTy
)
-import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
+import Subst ( mkSubst, substTy,
+ isInScope, lookupIdSubst, substIdInfo
+ )
+import TyCon ( isDataTyCon, tyConDataConsIfAvailable )
import TysPrim ( realWorldStatePrimTy )
-import PrelVals ( realWorldPrimId )
-import BasicTypes ( StrictnessMark(..) )
+import PrelInfo ( realWorldPrimId )
+import OrdList
import Maybes ( maybeToBool )
-import Util ( zipWithEqual, stretchZipEqual )
-import PprCore
+import Util ( zipWithEqual )
import Outputable
\end{code}
The guts of the simplifier is in this module, but the driver
-loop for the simplifier is in SimplPgm.lhs.
+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[Simplify-simplExpr]{The main function: simplExpr}
+\subsection{Bindings}
%* *
%************************************************************************
\begin{code}
-addBind :: CoreBind -> OutStuff a -> OutStuff a
-addBind bind (binds, res) = (bind:binds, res)
+simplTopBinds :: [InBind] -> SimplM [OutBind]
+
+simplTopBinds binds
+ = -- Put all the top-level binders into scope at the start
+ -- 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.
+ simplIds (bindersOfBinds binds) $ \ bndrs' ->
+ simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
+ freeTick SimplifierDone `thenSmpl_`
+ returnSmpl (fromOL binds')
+ where
-addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
-addBinds [] stuff = stuff
-addBinds binds1 (binds2, res) = (binds1++binds2, res)
+ -- 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 :: Bool -> [(InId, InExpr)] -> [OutId]
+ -> SimplM (OutStuff a) -> SimplM (OutStuff a)
+simplRecBind top_lvl pairs bndrs' thing_inside
+ = go pairs bndrs' `thenSmpl` \ (binds', (_, (binds'', res))) ->
+ returnSmpl (unitOL (Rec (flattenBinds (fromOL binds'))) `appOL` binds'', res)
+ where
+ go [] _ = thing_inside `thenSmpl` \ stuff ->
+ returnOutStuff stuff
+
+ go ((bndr, rhs) : pairs) (bndr' : bndrs')
+ = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
+ -- Don't float unboxed bindings out,
+ -- because we can't "rec" them
\end{code}
+
+%************************************************************************
+%* *
+\subsection[Simplify-simplExpr]{The main function: simplExpr}
+%* *
+%************************************************************************
+
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 -> SimplCont -> SimplM CoreExpr
-simplExpr expr cont = simplExprB expr cont `thenSmpl` \ (binds, (_, body)) ->
- returnSmpl (mkLetBinds binds body)
+simplExpr :: CoreExpr -> SimplM CoreExpr
+simplExpr expr = getSubst `thenSmpl` \ subst ->
+ 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.
+ -- Hence the lazy substitution
-simplExprB :: InExpr -> SimplCont -> SimplM OutExprStuff
+simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
+ -- Simplify an expression, given a continuation
-simplExprB (Note InlineCall (Var v)) cont
- = simplVar True v cont
+simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
+ returnSmpl (wrapFloats floats body)
-simplExprB (Var v) cont
- = simplVar False v cont
+simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
+ -- Simplify an expression, returning floated binds
-simplExprB expr@(Con (PrimOp op) args) cont
- = simplType (coreExprType expr) `thenSmpl` \ expr_ty ->
- getInScope `thenSmpl` \ in_scope ->
- getSubstEnv `thenSmpl` \ se ->
- let
- (val_arg_demands, _) = primOpStrictness op
-
- -- Main game plan: loop through the arguments, simplifying
- -- each of them with an ArgOf continuation. Getting the right
- -- cont_ty in the ArgOf continuation is a bit of a nuisance.
- go [] ds args' = rebuild_primop (reverse args')
- go (arg:args) ds args'
- | isTypeArg arg = setSubstEnv se (simplArg arg) `thenSmpl` \ arg' ->
- go args ds (arg':args')
- go (arg:args) (d:ds) args'
- | not (isStrict d) = setSubstEnv se (simplArg arg) `thenSmpl` \ arg' ->
- go args ds (arg':args')
- | otherwise = setSubstEnv se (simplExprB arg (mk_cont args ds args'))
-
- cont_ty = contResultType in_scope expr_ty cont
- mk_cont args ds args' = ArgOf NoDup (\ arg' -> go args ds (arg':args')) cont_ty
- in
- go args val_arg_demands []
- where
+simplExprF (Var v) cont
+ = simplVar v cont
- rebuild_primop args'
- = -- 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 args' of
- Just e' -> zapSubstEnv (simplExprB e' cont)
- Nothing -> rebuild (Con (PrimOp op) args') cont
-
-simplExprB (Con con@(DataCon _) args) cont
- = simplConArgs args $ \ args' ->
- rebuild (Con con args') cont
-
-simplExprB expr@(Con con@(Literal _) args) cont
- = ASSERT( null args )
- rebuild expr cont
-
-simplExprB (App fun arg) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplExprB fun (ApplyTo NoDup arg se cont)
+simplExprF (Lit lit) (Select _ bndr alts se cont)
+ = knownCon (Lit lit) (LitAlt lit) [] bndr alts se cont
+
+simplExprF (Lit lit) cont
+ = rebuild (Lit lit) cont
-simplExprB (Case scrut bndr alts) cont
+simplExprF (App fun arg) cont
= getSubstEnv `thenSmpl` \ se ->
- simplExprB scrut (Select NoDup bndr alts se cont)
+ simplExprF fun (ApplyTo NoDup arg se cont)
-simplExprB (Note (Coerce to from) e) cont
- | to == from = simplExprB e cont
- | otherwise = getSubstEnv `thenSmpl` \ se ->
- simplExprB e (CoerceIt NoDup to se cont)
+simplExprF (Case scrut bndr alts) 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)
--- hack: we only distinguish subsumed cost centre stacks for the purposes of
--- inlining. All other CCCSs are mapped to currentCCS.
-simplExprB (Note (SCC cc) e) cont
- = setEnclosingCC currentCCS $
- simplExpr e Stop `thenSmpl` \ e ->
- rebuild (mkNote (SCC cc) e) 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
-simplExprB (Note note e) cont
- = simplExpr e Stop `thenSmpl` \ e' ->
- rebuild (mkNote note e') cont
--- A non-recursive let is dealt with by simplBeta
-simplExprB (Let (NonRec bndr rhs) body) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplBeta bndr rhs se body cont
-
-simplExprB (Let (Rec pairs) body) cont
- = simplRecBind pairs (simplExprB body cont)
-
--- Type-beta reduction
-simplExprB expr@(Lam bndr body) cont@(ApplyTo _ (Type ty_arg) arg_se body_cont)
- = ASSERT( isTyVar bndr )
- tick BetaReduction `thenSmpl_`
- setSubstEnv arg_se (simplType ty_arg) `thenSmpl` \ ty' ->
- extendTySubst bndr ty' $
- simplExprB body body_cont
-
--- Ordinary beta reduction
-simplExprB expr@(Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
- = tick BetaReduction `thenSmpl_`
- simplBeta bndr' arg arg_se body body_cont
- where
- bndr' = zapLambdaBndr bndr body body_cont
+simplExprF (Let (Rec pairs) body) cont
+ = simplIds (map fst pairs) $ \ bndrs' ->
+ -- NB: bndrs' don't have unfoldings or spec-envs
+ -- We add them as we go down, using simplPrags
-simplExprB (Lam bndr body) cont
- = simplBinder bndr $ \ bndr' ->
- simplExpr body Stop `thenSmpl` \ body' ->
- rebuild (Lam bndr' body') cont
+ simplRecBind False pairs bndrs' (simplExprF body cont)
-simplExprB (Type ty) cont
- = ASSERT( case cont of { Stop -> True; ArgOf _ _ _ -> True; other -> False } )
+simplExprF expr@(Lam _ _) cont = simplLam expr cont
+
+simplExprF (Type ty) cont
+ = ASSERT( case cont of { Stop _ _ -> True; ArgOf _ _ _ -> True; other -> False } )
simplType ty `thenSmpl` \ ty' ->
rebuild (Type ty') cont
-\end{code}
+-- 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)
----------------------------------
-\begin{code}
-simplArg :: InArg -> SimplM OutArg
-simplArg arg = simplExpr arg Stop
+simplExprF (Note (Coerce to from) e) 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 (mkSCC cc e) cont
+
+simplExprF (Note InlineCall e) cont
+ = simplExprF e (InlinePlease cont)
+
+-- 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!
+--
+-- It really is important to switch off inlinings. This function
+-- may be inlinined in other modules, so we don't want to remove
+-- (by inlining) calls to functions that have specialisations, or
+-- that may have transformation rules in an importing scope.
+-- E.g. {-# INLINE f #-}
+-- f x = ...g...
+-- and suppose that g is strict *and* has specialisations.
+-- If we inline g's wrapper, we deny f the chance of getting
+-- the specialised version of g when f is inlined at some call site
+-- (perhaps in some other module).
+
+-- 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
+
+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
+ = getSubstEnv `thenSmpl` \ se ->
+ simplBeta bndr rhs se (contResultType cont) $
+ simplExprF body cont
\end{code}
+
---------------------------------
-simplConArgs makes sure that the arguments all end up being atomic.
-That means it may generate some Lets, hence the
\begin{code}
-simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
-simplConArgs [] thing_inside
- = thing_inside []
+simplLam fun cont
+ = go fun cont
+ where
+ 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_`
+ simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' ->
+ extendSubst bndr (DoneTy ty_arg')
+ (go body body_cont)
+
+ -- Ordinary beta reduction
+ go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
+ = tick (BetaReduction bndr) `thenSmpl_`
+ simplBeta zapped_bndr arg arg_se cont_ty
+ (go body body_cont)
+ where
+ zapped_bndr = zap_it bndr
+
+ -- Not enough args
+ go lam@(Lam _ _) cont = completeLam [] lam cont
+
+ -- Exactly enough args
+ go expr cont = simplExprF expr cont
+
+-- completeLam deals with the case where a lambda doesn't have an ApplyTo
+-- 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 rev_bndrs (Lam bndr body) cont
+ = simplBinder bndr $ \ bndr' ->
+ completeLam (bndr':rev_bndrs) body cont
-simplConArgs (arg:args) thing_inside
- = switchOffInlining (simplArg arg) `thenSmpl` \ arg' ->
- -- Simplify the RHS with inlining switched off, so that
- -- only absolutely essential things will happen.
+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
- simplConArgs args $ \ args' ->
+ Nothing -> rebuild (foldl (flip Lam) body' rev_bndrs) cont
+ where
+ -- 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
+ -> SimplCont -- The context
+ -> Id -> Id -- Use this to zap the binders
+mkLamBndrZapper fun cont
+ | n_args >= n_params fun = \b -> b -- Enough args
+ | otherwise = \b -> zapLamIdInfo b
+ where
+ -- NB: we count all the args incl type args
+ -- so we must count all the binders (incl type lambdas)
+ n_args = countArgs cont
- -- 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}
\begin{code}
simplType :: InType -> SimplM OutType
simplType ty
- = getTyEnv `thenSmpl` \ (ty_subst, in_scope) ->
- returnSmpl (fullSubstTy ty_subst in_scope ty)
+ = getSubst `thenSmpl` \ subst ->
+ let
+ new_ty = substTy subst ty
+ in
+ seqType new_ty `seq`
+ returnSmpl new_ty
\end{code}
-\begin{code}
--- Find out whether the lambda is saturated,
--- if not zap the over-optimistic info in the binder
-
-zapLambdaBndr bndr body body_cont
- | isTyVar bndr || safe_info || definitely_saturated 20 body body_cont
- -- The "20" is to catch pathalogical cases with bazillions of arguments
- -- because we are using an n**2 algorithm here
- = bndr -- No need to zap
- | otherwise
- = setInlinePragma (setIdDemandInfo bndr wwLazy)
- safe_inline_prag
-
- where
- inline_prag = getInlinePragma bndr
- demand = getIdDemandInfo bndr
-
- safe_info = is_safe_inline_prag && not (isStrict demand)
-
- is_safe_inline_prag = case inline_prag of
- ICanSafelyBeINLINEd StrictOcc nalts -> False
- ICanSafelyBeINLINEd LazyOcc nalts -> False
- other -> True
-
- safe_inline_prag = case inline_prag of
- ICanSafelyBeINLINEd _ nalts
- -> ICanSafelyBeINLINEd InsideLam nalts
- other -> inline_prag
-
- definitely_saturated :: Int -> CoreExpr -> SimplCont -> Bool
- definitely_saturated 0 _ _ = False -- Too expensive to find out
- definitely_saturated n (Lam _ body) (ApplyTo _ _ _ cont) = definitely_saturated (n-1) body cont
- definitely_saturated n (Lam _ _) other_cont = False
- definitely_saturated n _ _ = True
-\end{code}
-
%************************************************************************
%* *
-\subsection{Variables}
+\subsection{Binding}
%* *
%************************************************************************
-Coercions
-~~~~~~~~~
-\begin{code}
-simplVar inline_call var cont
- = getValEnv `thenSmpl` \ (id_subst, in_scope) ->
- case lookupVarEnv id_subst var of
- Just (Done e)
- -> zapSubstEnv (simplExprB e cont)
-
- Just (SubstMe e ty_subst id_subst)
- -> setSubstEnv (ty_subst, id_subst) (simplExprB e cont)
-
- Nothing -> let
- var' = case lookupVarSet in_scope var of
- Just v' -> v'
- Nothing ->
-#ifdef DEBUG
- if isLocallyDefined var && not (idMustBeINLINEd var) then
- -- Not in scope
- pprTrace "simplVar:" (ppr var) var
- else
-#endif
- var
- in
- getSwitchChecker `thenSmpl` \ sw_chkr ->
- completeVar sw_chkr in_scope inline_call var' cont
-
-completeVar sw_chkr in_scope inline_call var cont
-
-{- MAGIC UNFOLDINGS NOT USED NOW
- | maybeToBool maybe_magic_result
- = tick MagicUnfold `thenSmpl_`
- magic_result
--}
- -- Look for existing specialisations before trying inlining
- | maybeToBool maybe_specialisation
- = tick SpecialisationDone `thenSmpl_`
- setSubstEnv (spec_bindings, emptyVarEnv) (
- -- See note below about zapping the substitution here
-
- simplExprB spec_template remaining_cont
- )
-
- -- 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.
- | has_unfolding && var_is_case_scrutinee && unfolding_is_constr
- = knownCon (Var var) con con_args cont
-
- -- Look for an unfolding. There's a binding for the
- -- thing, but perhaps we want to inline it anyway
- | has_unfolding && (inline_call || ok_to_inline)
- = getEnclosingCC `thenSmpl` \ encl_cc ->
- if must_be_unfolded || costCentreOk encl_cc var
- then -- OK to unfold
+@simplBeta@ is used for non-recursive lets in expressions,
+as well as true beta reduction.
- tickUnfold var `thenSmpl_` (
+Very similar to @simplLazyBind@, but not quite the same.
- zapSubstEnv $
- -- The template is already simplified, so don't re-substitute.
- -- This is VITAL. Consider
- -- let x = e in
- -- let y = \z -> ...x... in
- -- \ x -> ...y...
- -- 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!!
-#ifdef DEBUG
- if opt_D_dump_inlinings then
- pprTrace "Inlining:" (ppr var <+> ppr unf_template) $
- simplExprB unf_template cont
- else
-#endif
- simplExprB unf_template cont
- )
- else
+\begin{code}
+simplBeta :: InId -- Binder
+ -> InExpr -> SubstEnv -- Arg, with its subst-env
+ -> OutType -- Type of thing computed by the context
+ -> SimplM OutExprStuff -- The body
+ -> SimplM OutExprStuff
#ifdef DEBUG
- pprTrace "Inlining disallowed due to CC:\n" (ppr encl_cc <+> ppr unf_template <+> ppr (coreExprCc unf_template)) $
+simplBeta bndr rhs rhs_se cont_ty thing_inside
+ | isTyVar bndr
+ = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
#endif
- -- Can't unfold because of bad cost centre
- rebuild (Var var) cont
- | inline_call -- There was an InlineCall note, but we didn't inline!
- = rebuild (Note InlineCall (Var var)) cont
+simplBeta bndr rhs rhs_se cont_ty thing_inside
+ | preInlineUnconditionally False {- not black listed -} bndr
+ = tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ extendSubst bndr (ContEx rhs_se rhs) thing_inside
| otherwise
- = rebuild (Var var) cont
-
- where
- unfolding = getIdUnfolding var
-
-{- MAGIC UNFOLDINGS NOT USED CURRENTLY
- ---------- Magic unfolding stuff
- maybe_magic_result = case unfolding of
- MagicUnfolding _ magic_fn -> applyMagicUnfoldingFun magic_fn
- cont
- other -> Nothing
- Just magic_result = maybe_magic_result
--}
-
- ---------- Unfolding stuff
- has_unfolding = case unfolding of
- CoreUnfolding _ _ _ -> True
- other -> False
- CoreUnfolding form guidance unf_template = unfolding
-
- -- overrides cost-centre business
- must_be_unfolded = case getInlinePragma var of
- IMustBeINLINEd -> True
- _ -> False
-
- ok_to_inline = okToInline sw_chkr in_scope var form guidance cont
- unfolding_is_constr = case unf_template of
- Con con _ -> conOkForAlt con
- other -> False
- Con con con_args = unf_template
-
- ---------- Specialisation stuff
- ty_args = initial_ty_args cont
- remaining_cont = drop_ty_args cont
- maybe_specialisation = lookupSpecEnv (ppr var) (getIdSpecialisation var) ty_args
- Just (spec_bindings, spec_template) = maybe_specialisation
-
- initial_ty_args (ApplyTo _ (Type ty) (ty_subst,_) cont)
- = fullSubstTy ty_subst in_scope ty : initial_ty_args cont
- -- Having to do the substitution here is a bit of a bore
- initial_ty_args other_cont = []
-
- drop_ty_args (ApplyTo _ (Type _) _ cont) = drop_ty_args cont
- drop_ty_args other_cont = other_cont
-
- ---------- Switches
-
- var_is_case_scrutinee = case cont of
- Select _ _ _ _ _ -> True
- other -> False
-
------------ costCentreOk
--- costCentreOk checks that it's ok to inline this thing
--- The time it *isn't* is this:
---
--- f x = let y = E in
--- scc "foo" (...y...)
---
--- Here y has a "current cost centre", and we can't inline it inside "foo",
--- regardless of whether E is a WHNF or not.
---
--- We can inline a top-level binding anywhere.
-
-costCentreOk ccs_encl x
- = not opt_SccProfilingOn
- || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
- || not (isLocallyDefined x)
-\end{code}
+ = -- Simplify the RHS
+ simplBinder bndr $ \ bndr' ->
+ 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
+ if needsCaseBinding bndr_ty' rhs' then
+ addCaseBind bndr' rhs' thing_inside
+ else
+ completeBinding bndr bndr' False False rhs' thing_inside
+\end{code}
-%************************************************************************
-%* *
-\subsection{Bindings}
-%* *
-%************************************************************************
\begin{code}
-simplBind :: InBind -> SimplM (OutStuff a) -> SimplM (OutStuff a)
+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 False {- Not top level -}
+ True {- OK to float unboxed -}
+ arg_ty arg arg_se
+ thing_inside
+\end{code}
-simplBind (NonRec bndr rhs) thing_inside
- = simplTopRhs bndr rhs `thenSmpl` \ (binds, in_scope, rhs', arity) ->
- setInScope in_scope $
- completeBindNonRec (bndr `setIdArity` arity) rhs' thing_inside `thenSmpl` \ stuff ->
- returnSmpl (addBinds binds stuff)
-simplBind (Rec pairs) thing_inside
- = simplRecBind pairs thing_inside
- -- The assymetry between the two cases is a bit unclean
+completeBinding
+ - deals only with Ids, not TyVars
+ - take an already-simplified RHS
-simplRecBind :: [(InId, InExpr)] -> SimplM (OutStuff a) -> SimplM (OutStuff a)
-simplRecBind pairs thing_inside
- = simplIds (map fst pairs) $ \ bndrs' ->
- -- NB: bndrs' don't have unfoldings or spec-envs
- -- We add them as we go down, using simplPrags
+It does *not* attempt to do let-to-case. Why? Because they are used for
- go (pairs `zip` bndrs') `thenSmpl` \ (pairs', stuff) ->
- returnSmpl (addBind (Rec pairs') stuff)
- where
- go [] = thing_inside `thenSmpl` \ stuff ->
- returnSmpl ([], stuff)
+ - top-level bindings
+ (when let-to-case is impossible)
- go (((bndr, rhs), bndr') : pairs)
- = simplTopRhs bndr rhs `thenSmpl` \ (rhs_binds, in_scope, rhs', arity) ->
- setInScope in_scope $
- completeBindRec bndr (bndr' `setIdArity` arity)
- rhs' (go pairs) `thenSmpl` \ (pairs', stuff) ->
- returnSmpl (flatten rhs_binds pairs', stuff)
+ - many situations where the "rhs" is known to be a WHNF
+ (so let-to-case is inappropriate).
- flatten (NonRec b r : binds) prs = (b,r) : flatten binds prs
- flatten (Rec prs1 : binds) prs2 = prs1 ++ flatten binds prs2
- flatten [] prs = prs
+\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 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
-completeBindRec bndr bndr' rhs' thing_inside
- | postInlineUnconditionally bndr etad_rhs
- -- NB: a loop breaker never has postInlineUnconditionally True
+ | 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 has must_keep_binding = True
-- and non-loop-breakers only have *forward* references
-- Hence, it's safe to discard the binding
- = tick PostInlineUnconditionally `thenSmpl_`
- extendIdSubst bndr (Done etad_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
- = -- Here's the only difference from completeBindNonRec: we
- -- don't do simplBinder first, because we've already
- -- done simplBinder on the recursive binders
- simplPrags bndr bndr' etad_rhs `thenSmpl` \ bndr'' ->
- modifyInScope bndr'' $
- thing_inside `thenSmpl` \ (pairs, res) ->
- returnSmpl ((bndr'', etad_rhs) : pairs, res)
+ = 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
- etad_rhs = etaCoreExpr rhs'
-\end{code}
+ 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{Right hand sides}
+\subsection{simplLazyBind}
%* *
%************************************************************************
-simplRhs basically just simplifies the RHS of a let(rec).
+simplLazyBind basically just simplifies the RHS of a let(rec).
It does two important optimisations though:
* It floats let(rec)s out of the RHS, even if they
* It does eta expansion
\begin{code}
-simplTopRhs :: InId -> InExpr
- -> SimplM ([OutBind], InScopeEnv, OutExpr, ArityInfo)
-simplTopRhs bndr rhs
- = getSubstEnv `thenSmpl` \ bndr_se ->
- simplRhs bndr bndr_se rhs
-
-simplRhs bndr bndr_se rhs
- | idWantsToBeINLINEd bndr -- 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!
- = switchOffInlining (simplExpr rhs Stop) `thenSmpl` \ rhs' ->
- getInScope `thenSmpl` \ in_scope ->
- returnSmpl ([], in_scope, rhs', unknownArity)
-
- | otherwise
- = -- Swizzle the inner lets past the big lambda (if any)
- mkRhsTyLam rhs `thenSmpl` \ swizzled_rhs ->
-
- -- Simplify the swizzled RHS
- simplRhs2 bndr bndr_se swizzled_rhs `thenSmpl` \ (floats, (in_scope, rhs', arity)) ->
-
- if not (null floats) && exprIsWHNF rhs' then -- Do the float
- tick LetFloatFromLet `thenSmpl_`
- returnSmpl (floats, in_scope, rhs', arity)
- else -- Don't do it
- getInScope `thenSmpl` \ in_scope ->
- returnSmpl ([], in_scope, mkLetBinds floats rhs', arity)
-\end{code}
-
----------------------------------------------------------
- Try eta expansion for RHSs
-
-We need to pass in the substitution environment for the RHS, because
-it might be different to the current one (see simplBeta, as called
-from simplExpr for an applied lambda). The binder needs to
+simplLazyBind :: Bool -- True <=> top level
+ -> InId -> OutId
+ -> InExpr -- The RHS
+ -> SimplM (OutStuff a) -- The body of the binding
+ -> SimplM (OutStuff a)
+-- When called, the subst env is correct for the entire let-binding
+-- and hence right for the RHS.
+-- Also the binder has already been simplified, and hence is in scope
-\begin{code}
-simplRhs2 bndr bndr_se (Let bind body)
- = simplBind bind (simplRhs2 bndr bndr_se body)
-
-simplRhs2 bndr bndr_se rhs
- | null ids -- Prevent eta expansion for both thunks
- -- (would lose sharing) and variables (nothing gained).
- -- To see why we ignore it for thunks, consider
- -- let f = lookup env key in (f 1, f 2)
- -- We'd better not eta expand f just because it is
- -- always applied!
- --
- -- Also if there isn't a lambda at the top we use
- -- simplExprB so that we can do (more) let-floating
- = simplExprB rhs Stop `thenSmpl` \ (binds, (in_scope, rhs')) ->
- returnSmpl (binds, (in_scope, rhs', unknownArity))
-
- | otherwise -- Consider eta expansion
- = getSwitchChecker `thenSmpl` \ sw_chkr ->
- getInScope `thenSmpl` \ in_scope ->
- simplBinders tyvars $ \ tyvars' ->
- simplBinders ids $ \ ids' ->
-
- if switchIsOn sw_chkr SimplDoLambdaEtaExpansion
- && not (null extra_arg_tys)
- then
- tick EtaExpansion `thenSmpl_`
- setSubstEnv bndr_se (mapSmpl simplType extra_arg_tys)
- `thenSmpl` \ extra_arg_tys' ->
- newIds extra_arg_tys' $ \ extra_bndrs' ->
- simplExpr body (mk_cont extra_bndrs') `thenSmpl` \ body' ->
- let
- expanded_rhs = mkLams tyvars'
- $ mkLams ids'
- $ mkLams extra_bndrs' body'
- expanded_arity = atLeastArity (no_of_ids + no_of_extras)
- in
- returnSmpl ([], (in_scope, expanded_rhs, expanded_arity))
+simplLazyBind top_lvl bndr bndr' rhs thing_inside
+ = getBlackList `thenSmpl` \ black_list_fn ->
+ let
+ black_listed = black_list_fn bndr
+ in
+ 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
- simplExpr body Stop `thenSmpl` \ body' ->
- let
- unexpanded_rhs = mkLams tyvars'
- $ mkLams ids' body'
- unexpanded_arity = atLeastArity no_of_ids
- in
- returnSmpl ([], (in_scope, unexpanded_rhs, unexpanded_arity))
-
- where
- (tyvars, ids, body) = collectTyAndValBinders rhs
- no_of_ids = length ids
-
- potential_extra_arg_tys :: [InType] -- NB: InType
- potential_extra_arg_tys = case splitFunTys (applyTys (idType bndr) (mkTyVarTys tyvars)) of
- (arg_tys, _) -> drop no_of_ids arg_tys
- extra_arg_tys :: [InType]
- extra_arg_tys = take no_extras_wanted potential_extra_arg_tys
- no_of_extras = length extra_arg_tys
+ -- Simplify the RHS
+ getSubstEnv `thenSmpl` \ rhs_se ->
+ simplRhs top_lvl False {- Not ok to float unboxed (conservative) -}
+ (idType bndr')
+ rhs rhs_se $ \ rhs' ->
- no_extras_wanted = -- Use information about how many args the fn is applied to
- (arity - no_of_ids) `max`
+ -- Now compete the binding and simplify the body
+ completeBinding bndr bndr' top_lvl black_listed rhs' thing_inside
+\end{code}
- -- See if the body could obviously do with more args
- etaExpandCount body `max`
- -- Finally, see if it's a state transformer, in which
- -- case we eta-expand on principle! This can waste work,
- -- but usually doesn't
- case potential_extra_arg_tys of
- [ty] | ty == realWorldStatePrimTy -> 1
- other -> 0
- arity = arityLowerBound (getIdArity bndr)
+\begin{code}
+simplRhs :: Bool -- True <=> Top level
+ -> Bool -- True <=> OK to float unboxed (speculative) bindings
+ -- 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
+ = -- Simplify it
+ setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats1, (rhs_in_scope, rhs1)) ->
+ let
+ (floats2, rhs2) = splitFloats float_ubx floats1 rhs1
+ in
+ -- 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 (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 (wrapFloats floats1 rhs1)
+
+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
+
+-- 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 float_ubx floats rhs
+ | float_ubx = (floats, rhs) -- Float them all
+ | otherwise = go (fromOL floats)
+ where
+ go [] = (nilOL, rhs)
+ go (f:fs) | must_stay f = (nilOL, mkLets (f:fs) rhs)
+ | otherwise = case go fs of
+ (out, rhs') -> (f `consOL` out, rhs')
- mk_cont [] = Stop
- mk_cont (b:bs) = ApplyTo OkToDup (Var b) emptySubstEnv (mk_cont bs)
+ must_stay (Rec prs) = False -- No unlifted bindings in here
+ must_stay (NonRec b r) = isUnLiftedType (idType b)
\end{code}
+
%************************************************************************
%* *
-\subsection{Binding}
+\subsection{Variables}
%* *
%************************************************************************
\begin{code}
-simplBeta :: InId -- Binder
- -> InExpr -> SubstEnv -- Arg, with its subst-env
- -> InExpr -> SimplCont -- Lambda body
- -> SimplM OutExprStuff
-#ifdef DEBUG
-simplBeta bndr rhs rhs_se body cont
- | isTyVar bndr
- = pprPanic "simplBeta" ((ppr bndr <+> ppr rhs) $$ ppr cont)
-#endif
+simplVar var 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
+ -- let y = \z -> ...x... in
+ -- \ x -> ...y...
+ -- 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!!
-simplBeta bndr rhs rhs_se body cont
- | isUnLiftedType bndr_ty
- || (isStrict (getIdDemandInfo bndr) || is_dict bndr) && not (exprIsWHNF rhs)
- = tick Let2Case `thenSmpl_`
- getSubstEnv `thenSmpl` \ body_se ->
- setSubstEnv rhs_se $
- simplExprB rhs (Select NoDup bndr [(DEFAULT, [], body)] body_se cont)
+---------------------------------------------------------
+-- Dealing with a call
- | preInlineUnconditionally bndr && not opt_NoPreInlining
- = tick PreInlineUnconditionally `thenSmpl_`
- case rhs_se of { (ty_subst, id_subst) ->
- extendIdSubst bndr (SubstMe rhs ty_subst id_subst) $
- simplExprB body cont }
+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]
- | otherwise
- = getSubstEnv `thenSmpl` \ bndr_se ->
- setSubstEnv rhs_se (simplRhs bndr bndr_se rhs)
- `thenSmpl` \ (floats, in_scope, rhs', arity) ->
- setInScope in_scope $
- completeBindNonRec (bndr `setIdArity` arity) rhs' (
- simplExprB body cont
- ) `thenSmpl` \ stuff ->
- returnSmpl (addBinds floats stuff)
- where
- -- 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)
- is_dict bndr = opt_DictsStrict && isDictTy bndr_ty && isDataType bndr_ty
- bndr_ty = idType bndr
-\end{code}
+ interesting_cont = interestingCallContext (not (null args))
+ (not (null arg_infos))
+ call_cont
+ inline_cont | inline_call = discardInline cont
+ | otherwise = cont
-completeBindNonRec
- - deals only with Ids, not TyVars
- - take an already-simplified RHS
- - always produce let bindings
+ 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
-It does *not* attempt to do let-to-case. Why? Because they are used for
+ ;
+ Nothing -> -- No inlining!
- - top-level bindings
- (when let-to-case is impossible)
- - many situations where the "rhs" is known to be a WHNF
- (so let-to-case is inappropriate).
+ simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' ->
-\begin{code}
-completeBindNonRec :: InId -- Binder
- -> OutExpr -- Simplified RHS
- -> SimplM (OutStuff a) -- Thing inside
- -> SimplM (OutStuff a)
-completeBindNonRec bndr rhs thing_inside
- | isDeadBinder bndr -- 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
+ -- 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
- | postInlineUnconditionally bndr etad_rhs
- = tick PostInlineUnconditionally `thenSmpl_`
- extendIdSubst bndr (Done etad_rhs)
- thing_inside
-
- | otherwise -- Note that we use etad_rhs here
- -- This gives maximum chance for a remaining binding
- -- to be zapped by the indirection zapper in OccurAnal
- = simplBinder bndr $ \ bndr' ->
- simplPrags bndr bndr' etad_rhs `thenSmpl` \ bndr'' ->
- modifyInScope bndr'' $
- thing_inside `thenSmpl` \ stuff ->
- returnSmpl (addBind (NonRec bndr'' etad_rhs) stuff)
- where
- etad_rhs = etaCoreExpr rhs
+ 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
--- (simplPrags old_bndr new_bndr new_rhs) does two things
--- (a) it attaches the new unfolding to new_bndr
--- (b) it grabs the SpecEnv from old_bndr, applies the current
--- substitution to it, and attaches it to new_bndr
--- The assumption is that new_bndr, which is produced by simplBinder
--- has no unfolding or specenv.
+ -- Done
+ rebuild (mkApps (Var var) args') call_cont
+ }}
-simplPrags old_bndr new_bndr new_rhs
- | isEmptySpecEnv spec_env
- = returnSmpl (bndr_w_unfolding)
- | otherwise
- = getSimplBinderStuff `thenSmpl` \ (ty_subst, id_subst, in_scope, us) ->
+---------------------------------------------------------
+-- 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.
+--
+-- 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')...)
+--
+-- 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
- spec_env' = substSpecEnv ty_subst in_scope (subst_val id_subst) spec_env
- final_bndr = bndr_w_unfolding `setIdSpecialisation` spec_env'
+ arg_ty = substTy (mkSubst in_scope se) (exprType val_arg)
in
- returnSmpl final_bndr
- where
- bndr_w_unfolding = new_bndr `setIdUnfolding` mkUnfolding new_rhs
+ 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}
- spec_env = getIdSpecialisation old_bndr
- subst_val id_subst ty_subst in_scope expr
- = substExpr ty_subst id_subst in_scope expr
-\end{code}
+
+%************************************************************************
+%* *
+\subsection{Decisions about inlining}
+%* *
+%************************************************************************
+
+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
-- we'd do the same for y -- aargh! So we must base this
-- pre-rhs-simplification decision solely on x's occurrences, not
-- on its rhs.
-preInlineUnconditionally bndr
- = case getInlinePragma bndr of
- ICanSafelyBeINLINEd InsideLam _ -> False
- ICanSafelyBeINLINEd not_in_lam 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
- | isExported bndr
- = False
- | otherwise
- = case getInlinePragma bndr of
- IAmALoopBreaker -> False
- IMustNotBeINLINEd -> False
- IAmASpecPragmaId -> False -- Don't discard SpecPrag Ids
-
- ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
- -- Don't inline even WHNFs inside lambdas; this
- -- isn't the last chance; see NOTE above.
-
- ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsDupable rhs
-
- other -> exprIsTrivial rhs -- Duplicating is *free*
- -- NB: Even IWantToBeINLINEd and IMustBeINLINEd are ignored here
- -- Why? Because we don't even want to inline them into the
- -- RHS of constructor arguments. See NOTE above
-
-inlineCase bndr scrut
- = case getInlinePragma bndr of
- -- Not expecting IAmALoopBreaker etc; this is a case binder!
-
- ICanSafelyBeINLINEd StrictOcc one_branch
- -> one_branch || exprIsDupable scrut
- -- This case is the entire reason we distinguish StrictOcc from LazyOcc
- -- We want eliminate the "case" only if we aren't going to
- -- build a thunk instead, and that's what StrictOcc finds
- -- For example:
- -- case (f x) of y { DEFAULT -> g y }
- -- Here we DO NOT WANT:
- -- g (f x)
- -- *even* if g is strict. We want to avoid constructing the
- -- thunk for (f x)! So y gets a LazyOcc.
-
- other -> exprIsTrivial scrut -- Duplication is free
- && ( isUnLiftedType (idType bndr)
- || scrut_is_evald_var -- So dropping the case won't change termination
- || isStrict (getIdDemandInfo bndr)) -- It's going to get evaluated later, so again
- -- termination doesn't change
- where
- -- Check whether or not scrut is known to be evaluted
- -- It's not going to be a visible value (else the previous
- -- blob would apply) so we just check the variable case
- scrut_is_evald_var = case scrut of
- Var v -> isEvaldUnfolding (getIdUnfolding v)
- other -> False
+ --
+ -- Evne RHSs labelled InlineMe aren't caught here, because
+ -- there might be no benefit from inlining at the call site.
+
+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}
-okToInline is used at call sites, so it is a bit more generous.
-It's a very important function that embodies lots of heuristics.
-
-\begin{code}
-okToInline :: SwitchChecker
- -> InScopeEnv
- -> Id -- The Id
- -> FormSummary -- The thing is WHNF or bottom;
- -> UnfoldingGuidance
- -> SimplCont
- -> Bool -- True <=> inline it
-
--- A non-WHNF can be inlined if it doesn't occur inside a lambda,
--- and occurs exactly once or
--- occurs once in each branch of a case and is small
---
--- If the thing is in WHNF, there's no danger of duplicating work,
--- so we can inline if it occurs once, or is small
-
-okToInline sw_chkr in_scope id form guidance cont
- =
-#ifdef DEBUG
- if opt_D_dump_inlinings then
- pprTrace "Considering inlining"
- (ppr id <+> vcat [text "inline prag:" <+> ppr inline_prag,
- text "whnf" <+> ppr whnf,
- text "small enough" <+> ppr small_enough,
- text "some benefit" <+> ppr some_benefit,
- text "arg evals" <+> ppr arg_evals,
- text "result scrut" <+> ppr result_scrut,
- text "ANSWER =" <+> if result then text "YES" else text "NO"])
- result
- else
-#endif
- result
- where
- result =
- case inline_prag of
- IAmDead -> pprTrace "okToInline: dead" (ppr id) False
- IAmASpecPragmaId -> False
- IMustNotBeINLINEd -> False
- IAmALoopBreaker -> False
- IMustBeINLINEd -> True -- If "essential_unfoldings_only" is true we do no inlinings at all,
- -- EXCEPT for things that absolutely have to be done
- -- (see comments with idMustBeINLINEd)
- IWantToBeINLINEd -> inlinings_enabled
- ICanSafelyBeINLINEd inside_lam one_branch
- -> inlinings_enabled && (unfold_always || consider_single inside_lam one_branch)
- NoInlinePragInfo -> inlinings_enabled && (unfold_always || consider_multi)
-
- inlinings_enabled = not (switchIsOn sw_chkr EssentialUnfoldingsOnly)
- unfold_always = unfoldAlways guidance
-
- -- Consider benefit for ICanSafelyBeINLINEd
- consider_single inside_lam one_branch
- = (small_enough || one_branch) && some_benefit && (whnf || not_inside_lam)
- where
- not_inside_lam = case inside_lam of {InsideLam -> False; other -> True}
-
- -- Consider benefit for NoInlinePragInfo
- consider_multi = whnf && small_enough && some_benefit
- -- We could consider using exprIsCheap here,
- -- as in postInlineUnconditionally, but unlike the latter we wouldn't
- -- necessarily eliminate a thunk; and the "form" doesn't tell
- -- us that.
-
- inline_prag = getInlinePragma id
- whnf = whnfOrBottom form
- small_enough = smallEnoughToInline id arg_evals result_scrut guidance
- (arg_evals, result_scrut) = get_evals cont
-
- -- some_benefit checks that *something* interesting happens to
- -- the variable after it's inlined.
- some_benefit = contIsInteresting cont
-
- -- Finding out whether the args are evaluated. This isn't completely easy
- -- because the args are not yet simplified, so we have to peek into them.
- get_evals (ApplyTo _ arg (te,ve) cont)
- | isValArg arg = case get_evals cont of
- (args, res) -> (get_arg_eval arg ve : args, res)
- | otherwise = get_evals cont
-
- get_evals (Select _ _ _ _ _) = ([], True)
- get_evals other = ([], False)
-
- get_arg_eval (Con con _) ve = isWHNFCon con
- get_arg_eval (Var v) ve = case lookupVarEnv ve v of
- Just (SubstMe e' _ ve') -> get_arg_eval e' ve'
- Just (Done (Con con _)) -> isWHNFCon con
- Just (Done (Var v')) -> get_var_eval v'
- Just (Done other) -> False
- Nothing -> get_var_eval v
- get_arg_eval other ve = False
-
- get_var_eval v = case lookupVarSet in_scope v of
- Just v' -> isEvaldUnfolding (getIdUnfolding v')
- Nothing -> isEvaldUnfolding (getIdUnfolding v)
-
-
-contIsInteresting :: SimplCont -> Bool
-contIsInteresting Stop = False
-contIsInteresting (ArgOf _ _ _) = False
-contIsInteresting (ApplyTo _ (Type _) _ cont) = contIsInteresting cont
-contIsInteresting (CoerceIt _ _ _ cont) = contIsInteresting cont
-
--- See notes below on why a case with only a DEFAULT case is not intersting
--- contIsInteresting (Select _ _ [(DEFAULT,_,_)] _ _) = False
-
-contIsInteresting _ = True
-\end{code}
-
-Comment about some_benefit above
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-
-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
-inline, otherwise we don't.
-
-Previously some_benefit used to return True only if the variable was
-applied to some value arguments. This didn't work:
-
- let x = _coerce_ (T Int) Int (I# 3) in
- case _coerce_ Int (T Int) x of
- I# y -> ....
-
-we want to inline x, but can't see that it's a constructor in a case
-scrutinee position, and some_benefit is False.
-
-Another example:
-
-dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t)
-
-.... case dMonadST _@_ x0 of (a,b,c) -> ....
-
-we'd really like to inline dMonadST here, but we *don't* want to
-inline if the case expression is just
-
- case x of y { DEFAULT -> ... }
-
-since we can just eliminate this case instead (x is in WHNF). Similar
-applies when x is bound to a lambda expression. Hence
-contIsInteresting looks for case expressions with just a single
-default case.
%************************************************************************
\begin{code}
-------------------------------------------------------------------
-rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
-
-rebuild expr cont
- = tick LeavesExamined `thenSmpl_`
- case expr of
- Var v -> case getIdStrictness v of
- NoStrictnessInfo -> do_rebuild expr cont
- StrictnessInfo demands result_bot -> ASSERT( not (null demands) || result_bot )
- -- If this happened we'd get an infinite loop
- rebuild_strict demands result_bot expr (idType v) cont
- other -> do_rebuild expr cont
-
-rebuild_done expr
- = getInScope `thenSmpl` \ in_scope ->
- returnSmpl ([], (in_scope, expr))
+-- Finish rebuilding
+rebuild_done expr = returnOutStuff expr
---------------------------------------------------------
--- Stop continuation
-
-do_rebuild expr Stop = rebuild_done expr
+rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
+-- Stop continuation
+rebuild expr (Stop _ _) = rebuild_done expr
----------------------------------------------------------
-- ArgOf continuation
+rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
-do_rebuild expr (ArgOf _ cont_fn _) = cont_fn expr
-
----------------------------------------------------------
-- ApplyTo continuation
+rebuild expr cont@(ApplyTo _ arg se cont')
+ = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
+ rebuild (App expr arg') cont'
-do_rebuild expr cont@(ApplyTo _ arg se cont')
- = setSubstEnv se (simplArg arg) `thenSmpl` \ arg' ->
- do_rebuild (App expr arg') cont'
-
-
----------------------------------------------------------
-- Coerce continuation
+rebuild expr (CoerceIt to_ty cont)
+ = rebuild (mkCoerce to_ty (exprType expr) expr) cont
-do_rebuild expr (CoerceIt _ to_ty se cont)
- = setSubstEnv se $
- simplType to_ty `thenSmpl` \ to_ty' ->
- do_rebuild (mk_coerce to_ty' expr) cont
-
-
----------------------------------------------------------
--- Case of known constructor or literal
-
-do_rebuild expr@(Con con args) cont@(Select _ _ _ _ _)
- | conOkForAlt con -- Knocks out PrimOps and NoRepLits
- = knownCon expr con args cont
-
+-- Inline continuation
+rebuild expr (InlinePlease cont)
+ = rebuild (Note InlineCall expr) cont
----------------------------------------------------------
-
--- Case of other value (e.g. a partial application or lambda)
--- Turn it back into a let
-
-do_rebuild expr (Select _ bndr ((DEFAULT, bs, rhs):alts) se cont)
- | case mkFormSummary expr of { ValueForm -> True; other -> False }
- = ASSERT( null bs && null alts )
- tick Case2Let `thenSmpl_`
- setSubstEnv se (
- completeBindNonRec bndr expr $
- simplExprB rhs cont
- )
-
-
----------------------------------------------------------
--- The other Select cases
-
-do_rebuild scrut (Select _ bndr alts se cont)
- = getSwitchChecker `thenSmpl` \ chkr ->
-
- if all (cheapEqExpr rhs1) other_rhss
- && inlineCase bndr scrut
- && all binders_unused alts
- && switchIsOn chkr SimplDoCaseElim
- then
- -- Get rid of the case altogether
- -- See the extensive notes on case-elimination below
- -- Remember to bind the binder though!
- tick CaseElim `thenSmpl_`
- setSubstEnv se (
- extendIdSubst bndr (Done scrut) $
- simplExprB rhs1 cont
- )
-
- else
- rebuild_case chkr scrut bndr alts se cont
- where
- (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
- binders_unused (_, bndrs, _) = all isDeadBinder bndrs
+rebuild scrut (Select _ bndr alts se cont)
+ = rebuild_case scrut bndr alts se cont
\end{code}
Case elimination [see the code above]
If so, then we can replace the case with one of the rhss.
+Blob of helper functions for the "case-of-something-else" situation.
+
\begin{code}
---------------------------------------------------------
--- Rebuiling a function with strictness info
--- This just a version of do_rebuild, enhanced with info about
--- the strictness of the thing being rebuilt.
-
-rebuild_strict :: [Demand] -> Bool -- Stricness info
- -> OutExpr -> OutType -- Function and type
- -> SimplCont -- Continuation
- -> SimplM OutExprStuff
-
-rebuild_strict [] True fun fun_ty cont = rebuild_bot fun fun_ty cont
-rebuild_strict [] False fun fun_ty cont = do_rebuild fun cont
-
-rebuild_strict ds result_bot fun fun_ty (CoerceIt _ to_ty se cont)
- = setSubstEnv se $
- simplType to_ty `thenSmpl` \ to_ty' ->
- rebuild_strict ds result_bot (mk_coerce to_ty' fun) to_ty' cont
-
-rebuild_strict ds result_bot fun fun_ty (ApplyTo _ (Type ty_arg) se cont)
- -- Type arg; don't consume a demand
- = setSubstEnv se (simplType ty_arg) `thenSmpl` \ ty_arg' ->
- rebuild_strict ds result_bot (App fun (Type ty_arg'))
- (applyTy fun_ty ty_arg') cont
-
-rebuild_strict (d:ds) result_bot fun fun_ty (ApplyTo _ val_arg se cont)
- | isStrict d || isUnLiftedType arg_ty
- -- Strict value argument
- = getInScope `thenSmpl` \ in_scope ->
- let
- cont_ty = contResultType in_scope res_ty cont
- in
- setSubstEnv se (simplExprB val_arg (ArgOf NoDup cont_fn cont_ty))
+-- Eliminate the case if possible
- | otherwise -- Lazy value argument
- = setSubstEnv se (simplArg val_arg) `thenSmpl` \ val_arg' ->
- cont_fn val_arg'
+rebuild_case scrut bndr alts se cont
+ | maybeToBool maybe_con_app
+ = knownCon scrut (DataAlt con) args bndr alts se cont
- where
- Just (arg_ty, res_ty) = splitFunTy_maybe fun_ty
- cont_fn arg' = rebuild_strict ds result_bot
- (App fun arg') res_ty
- 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)
-rebuild_strict ds result_bot fun fun_ty cont = do_rebuild fun cont
+ | otherwise
+ = complete_case scrut bndr alts se cont
----------------------------------------------------------
--- Dealing with
--- * case (error "hello") of { ... }
--- * (error "Hello") arg
--- * f (error "Hello") where f is strict
--- etc
-
-rebuild_bot expr expr_ty Stop -- No coerce needed
- = rebuild_done expr
-
-rebuild_bot expr expr_ty (CoerceIt _ to_ty se Stop) -- Don't "tick" on this,
- -- else simplifier never stops
- = setSubstEnv se $
- simplType to_ty `thenSmpl` \ to_ty' ->
- rebuild_done (mkNote (Coerce to_ty' expr_ty) expr)
-
-rebuild_bot expr expr_ty cont -- Abandon the (strict) continuation,
- -- and just return expr
- = tick CaseOfError `thenSmpl_`
- getInScope `thenSmpl` \ in_scope ->
- let
- result_ty = contResultType in_scope expr_ty cont
- in
- rebuild_done (mkNote (Coerce result_ty expr_ty) expr)
+ 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
+ )
-mk_coerce to_ty (Note (Coerce _ from_ty) expr) = Note (Coerce to_ty from_ty) expr
-mk_coerce to_ty expr = Note (Coerce to_ty (coreExprType expr)) expr
-\end{code}
+ 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
-Blob of helper functions for the "case-of-something-else" situation.
-\begin{code}
---------------------------------------------------------
-- Case of something else
-rebuild_case sw_chkr scrut case_bndr alts se cont
+complete_case scrut case_bndr alts se cont
= -- Prepare case alternatives
- prepareCaseAlts (splitTyConApp_maybe (idType case_bndr))
- scrut_cons alts `thenSmpl` \ better_alts ->
+ prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
+ impossible_cons alts `thenSmpl` \ better_alts ->
-- Set the new subst-env in place (before dealing with the case binder)
setSubstEnv se $
-- Deal with the case binder, and prepare the continuation;
-- The new subst_env is in place
- simplBinder case_bndr $ \ case_bndr' ->
prepareCaseCont better_alts cont $ \ cont' ->
-- Deal with variable scrutinee
- 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 sw_chkr scrut case_bndr'' alts' `thenSmpl` \ case_expr ->
+ mkCase scrut case_bndr' alts'
+ ) `thenSmpl` \ case_expr ->
+
+ -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
+ -- over the rebuild_done; rebuild_done returns the in-scope set, and
+ -- 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 -> case getIdUnfolding v of
- OtherCon cons -> cons
- other -> []
- other -> []
-
-
-knownCon expr con args (Select _ bndr alts se cont)
- = tick KnownBranch `thenSmpl_`
- setSubstEnv se (
+ 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
+ = -- 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 )
- completeBindNonRec bndr expr $
- simplExprB rhs cont
-
- (Literal lit, bs, rhs) -> ASSERT( null bs )
- extendIdSubst bndr (Done 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.
- simplExprB rhs cont
-
- (DataCon dc, bs, rhs) -> completeBindNonRec bndr expr $
- extend bs real_args $
- simplExprB rhs cont
+ simplExprF rhs cont
+
+ (LitAlt lit, bs, rhs) -> ASSERT( null bs )
+ simplExprF rhs cont
+
+ (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
+ extendSubstList bs (map mk real_args) $
+ simplExprF rhs cont
where
- real_args = drop (dataConNumInstArgs dc) args
+ real_args = drop (dataConNumInstArgs dc) args
+ mk (Type ty) = DoneTy ty
+ mk other = DoneEx other
)
- where
- extend [] [] thing_inside = thing_inside
- extend (b:bs) (arg:args) thing_inside = extendIdSubst b (Done arg) $
- extend bs args thing_inside
\end{code}
\begin{code}
-- 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
Here, b and p are dead. But when we move the argment inside the first
case RHS, and eliminate the second case, we get
- case x or { (a,b) -> a b
+ 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:
when rhs also scrutinises x or e.
\begin{code}
-prepareCaseAlts (Just (tycon, inst_tys)) scrut_cons alts
+prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
| isDataTyCon tycon
= case (findDefault filtered_alts, missing_cons) of
((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
- -> tick FillInCaseDefault `thenSmpl_`
+ -> tick (FillInCaseDefault bndr) `thenSmpl_`
let
(_,_,ex_tyvars,_,_,_) = dataConSig data_con
in
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
+prepareCaseAlts _ _ scrut_cons alts
= returnSmpl alts -- Functions
----------------------
-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` OtherCon handled_cons) $
- simplExpr rhs cont' `thenSmpl` \ rhs' ->
+ 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) $
- simplExpr rhs cont' `thenSmpl` \ rhs' ->
+ 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 (dataConStrictMarks dc)
+ add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
add_evals other_con vs = vs
cat_evals [] [] = []
cat_evals (v:vs) (str:strs)
- | isTyVar v = v : cat_evals vs (str:strs)
- | otherwise =
- case str of
- MarkedStrict ->
- (zap_occ_info v `setIdUnfolding` OtherCon [])
- : cat_evals vs strs
- MarkedUnboxed con _ ->
- cat_evals (v:vs) (dataConStrictMarks con ++ strs)
- NotMarkedStrict -> zap_occ_info v : cat_evals vs strs
+ | isTyVar v = v : cat_evals vs (str:strs)
+ | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
+ | otherwise = v' : cat_evals vs strs
+ where
+ v' = zap_occ_info v
\end{code}
-
%************************************************************************
%* *
\subsection{Duplicating continuations}
%************************************************************************
\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)
| contIsDupable cont
= thing_inside cont
-mkDupableCont _ (CoerceIt _ ty se cont) thing_inside
+mkDupableCont _ (CoerceIt ty cont) thing_inside
+ = mkDupableCont ty cont $ \ cont' ->
+ thing_inside (CoerceIt ty cont')
+
+mkDupableCont ty (InlinePlease cont) thing_inside
= mkDupableCont ty cont $ \ cont' ->
- thing_inside (CoerceIt OkToDup ty se cont')
+ thing_inside (InlinePlease cont')
-mkDupableCont join_arg_ty (ArgOf _ cont_fn res_ty) thing_inside
+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 (mkLetBinds 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
+ new_cont = ArgOf OkToDup cont_ty
(\arg' -> rebuild_done (App (Var join_id) arg'))
- res_ty
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' ->
- setSubstEnv se (simplArg arg) `thenSmpl` \ arg' ->
+ setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
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 `thenSmpl_` (
- setSubstEnv se (
- simplBinder case_bndr $ \ case_bndr' ->
- prepareCaseCont alts cont $ \ cont' ->
- mapAndUnzipSmpl (mkDupableAlt case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
- returnSmpl (concat alt_binds_s, (case_bndr', alts'))
- ) `thenSmpl` \ (alt_binds, (case_bndr', alts')) ->
-
- extendInScopes [b | NonRec b _ <- alt_binds] $
- thing_inside (Select OkToDup case_bndr' alts' emptySubstEnv Stop) `thenSmpl` \ res ->
- returnSmpl (addBinds alt_binds res)
- )
+ = tick (CaseOfCase case_bndr) `thenSmpl_`
+ setSubstEnv se (
+ simplBinder case_bndr $ \ case_bndr' ->
+ prepareCaseCont alts cont $ \ cont' ->
+ mkDupableAlts case_bndr case_bndr' cont' alts $ \ alts' ->
+ returnOutStuff alts'
+ ) `thenSmpl` \ (alt_binds, (in_scope, alts')) ->
+
+ 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
+ -- because another case-of-case might strike, and so we want to keep the
+ -- info that the case_bndr is dead (if it is, which is often the case).
+ -- 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 (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 :: OutId -> SimplCont -> InAlt -> SimplM (OutStuff CoreAlt)
-mkDupableAlt case_bndr' cont alt@(con, bndrs, rhs)
+mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) thing_inside
= simplBinders bndrs $ \ bndrs' ->
- simplExpr rhs cont `thenSmpl` \ rhs' ->
- if exprIsDupable rhs' then
- -- It's small, so don't bother to let-bind it
- returnSmpl ([], (con, bndrs', rhs'))
+ 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
- -- It's big, so let-bind it
let
- rhs_ty' = coreExprType rhs'
- used_bndrs' = filter (not . isDeadBinder) (case_bndr' : bndrs')
+ rhs_ty' = exprType rhs'
+ (used_bndrs, used_bndrs')
+ = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
+ (case_bndr' : bndrs'),
+ not (isDeadBinder bndr)]
+ -- The new binders have lost their occurrence info,
+ -- so we have to extract it from the old ones
in
- ( if null used_bndrs' && isUnLiftedType rhs_ty'
- then newId realWorldStatePrimTy $ \ rw_id ->
- returnSmpl ([rw_id], [varToCoreExpr realWorldPrimId])
- else
- returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
- )
- `thenSmpl` \ (final_bndrs', final_args) ->
-
+ ( if null used_bndrs'
-- If we try to lift a primitive-typed something out
-- for let-binding-purposes, we will *caseify* it (!),
-- with potentially-disastrous strictness results. So
-- case_bndr to all the join points if it's used in *any* RHS,
-- because we don't know its usage in each RHS separately
- newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
- returnSmpl ([NonRec join_bndr (mkLams final_bndrs' rhs')],
- (con, bndrs', mkApps (Var join_bndr) final_args))
+ -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
+ -- we make the join point into a function whenever used_bndrs'
+ -- is empty. This makes the join-point more CPR friendly.
+ -- Consider: let j = if .. then I# 3 else I# 4
+ -- in case .. of { A -> j; B -> j; C -> ... }
+ --
+ -- Now CPR should not w/w j because it's a thunk, so
+ -- that means that the enclosing function can't w/w either,
+ -- which is a lose. Here's the example that happened in practice:
+ -- kgmod :: Int -> Int -> Int
+ -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
+ -- then 78
+ -- else 5
+
+ 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) ->
+
+ -- 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
+ 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