2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[Simplify]{The main module of the simplifier}
7 module Simplify ( simplTopBinds, simplExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( intSwitchSet,
12 opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
13 opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
17 import SimplUtils ( mkCase, transformRhs, findAlt,
18 simplBinder, simplBinders, simplIds, findDefault, mkCoerce
20 import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
23 import Id ( Id, idType, idInfo, idUnique,
24 getIdUnfolding, setIdUnfolding, isExportedId,
25 getIdSpecialisation, setIdSpecialisation,
26 getIdDemandInfo, setIdDemandInfo,
27 getIdArity, setIdArity, setIdInfo,
29 setInlinePragma, getInlinePragma, idMustBeINLINEd,
30 setOneShotLambda, maybeModifyIdInfo
32 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
33 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity, zapFragileIdInfo,
34 specInfo, inlinePragInfo, zapLamIdInfo, setArityInfo, setInlinePragInfo, setUnfoldingInfo
36 import Demand ( Demand, isStrict, wwLazy )
37 import Const ( isWHNFCon, conOkForAlt )
38 import ConFold ( tryPrimOp )
39 import PrimOp ( PrimOp, primOpStrictness, primOpType )
40 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
41 import Const ( Con(..) )
42 import Name ( isLocallyDefined )
44 import CoreFVs ( exprFreeVars )
45 import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
46 callSiteInline, blackListed, hasSomeUnfolding
48 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
49 coreExprType, coreAltsType, exprArity, exprIsValue,
52 import Rules ( lookupRule )
53 import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
54 import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType, seqType,
55 mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
56 funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
58 import Subst ( Subst, mkSubst, emptySubst, substExpr, substTy,
59 substEnv, lookupInScope, lookupSubst, substIdInfo
61 import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
62 import TysPrim ( realWorldStatePrimTy )
63 import PrelInfo ( realWorldPrimId )
64 import BasicTypes ( TopLevelFlag(..), isTopLevel )
65 import Maybes ( maybeToBool )
66 import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
72 The guts of the simplifier is in this module, but the driver
73 loop for the simplifier is in SimplCore.lhs.
76 %************************************************************************
80 %************************************************************************
83 simplTopBinds :: [InBind] -> SimplM [OutBind]
86 = -- Put all the top-level binders into scope at the start
87 -- so that if a transformation rule has unexpectedly brought
88 -- anything into scope, then we don't get a complaint about that.
89 -- It's rather as if the top-level binders were imported.
90 extendInScopes top_binders $
91 simpl_binds binds `thenSmpl` \ (binds', _) ->
92 freeTick SimplifierDone `thenSmpl_`
95 top_binders = bindersOfBinds binds
97 simpl_binds [] = returnSmpl ([], panic "simplTopBinds corner")
98 simpl_binds (NonRec bndr rhs : binds) = simplLazyBind TopLevel bndr (zap bndr) rhs (simpl_binds binds)
99 simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map (zap . fst) pairs) (simpl_binds binds)
101 zap id = maybeModifyIdInfo zapFragileIdInfo id
105 simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
106 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
107 simplRecBind top_lvl pairs bndrs' thing_inside
108 = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
109 returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
111 go [] _ = thing_inside `thenSmpl` \ stuff ->
112 returnSmpl ([], stuff)
114 go ((bndr, rhs) : pairs) (bndr' : bndrs')
115 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
116 -- Don't float unboxed bindings out,
117 -- because we can't "rec" them
121 %************************************************************************
123 \subsection[Simplify-simplExpr]{The main function: simplExpr}
125 %************************************************************************
128 addBind :: CoreBind -> OutStuff a -> OutStuff a
129 addBind bind (binds, res) = (bind:binds, res)
131 addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
132 addBinds [] stuff = stuff
133 addBinds binds1 (binds2, res) = (binds1++binds2, res)
136 The reason for this OutExprStuff stuff is that we want to float *after*
137 simplifying a RHS, not before. If we do so naively we get quadratic
138 behaviour as things float out.
140 To see why it's important to do it after, consider this (real) example:
154 a -- Can't inline a this round, cos it appears twice
158 Each of the ==> steps is a round of simplification. We'd save a
159 whole round if we float first. This can cascade. Consider
164 let f = let d1 = ..d.. in \y -> e
168 in \x -> ...(\y ->e)...
170 Only in this second round can the \y be applied, and it
171 might do the same again.
175 simplExpr :: CoreExpr -> SimplM CoreExpr
176 simplExpr expr = getSubst `thenSmpl` \ subst ->
177 simplExprC expr (Stop (substTy subst (coreExprType expr)))
178 -- The type in the Stop continuation is usually not used
179 -- It's only needed when discarding continuations after finding
180 -- a function that returns bottom.
181 -- Hence the lazy substitution
183 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
184 -- Simplify an expression, given a continuation
186 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
187 returnSmpl (mkLets floats body)
189 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
190 -- Simplify an expression, returning floated binds
192 simplExprF (Var v) cont
195 simplExprF expr@(Con (PrimOp op) args) cont
196 = getSubstEnv `thenSmpl` \ se ->
199 (primOpStrictness op)
200 (pushArgs se args cont) $ \ args1 cont1 ->
203 -- Boring... we may have too many arguments now, so we push them back
205 args2 = ASSERT( length args1 >= n_args )
207 cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
209 -- Try the prim op simplification
210 -- It's really worth trying simplExpr again if it succeeds,
211 -- because you can find
212 -- case (eqChar# x 'a') of ...
214 -- case (case x of 'a' -> True; other -> False) of ...
215 case tryPrimOp op args2 of
216 Just e' -> zapSubstEnv (simplExprF e' cont2)
217 Nothing -> rebuild (Con (PrimOp op) args2) cont2
219 simplExprF (Con con@(DataCon _) args) cont
220 = simplConArgs args ( \ args' ->
221 rebuild (Con con args') cont)
223 simplExprF expr@(Con con@(Literal _) args) cont
224 = ASSERT( null args )
227 simplExprF (App fun arg) cont
228 = getSubstEnv `thenSmpl` \ se ->
229 simplExprF fun (ApplyTo NoDup arg se cont)
231 simplExprF (Case scrut bndr alts) cont
232 = getSubstEnv `thenSmpl` \ se ->
233 simplExprF scrut (Select NoDup bndr alts se cont)
236 simplExprF (Let (Rec pairs) body) cont
237 = simplIds (map fst pairs) $ \ bndrs' ->
238 -- NB: bndrs' don't have unfoldings or spec-envs
239 -- We add them as we go down, using simplPrags
241 simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
243 simplExprF expr@(Lam _ _) cont = simplLam expr cont
245 simplExprF (Type ty) cont
246 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
247 simplType ty `thenSmpl` \ ty' ->
248 rebuild (Type ty') cont
250 simplExprF (Note (Coerce to from) e) cont
251 | to == from = simplExprF e cont
252 | otherwise = simplType to `thenSmpl` \ to' ->
253 simplExprF e (CoerceIt to' cont)
255 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
256 -- inlining. All other CCCSs are mapped to currentCCS.
257 simplExprF (Note (SCC cc) e) cont
258 = setEnclosingCC currentCCS $
259 simplExpr e `thenSmpl` \ e ->
260 rebuild (mkNote (SCC cc) e) cont
262 simplExprF (Note InlineCall e) cont
263 = simplExprF e (InlinePlease cont)
265 -- Comments about the InlineMe case
266 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
267 -- Don't inline in the RHS of something that has an
268 -- inline pragma. But be careful that the InScopeEnv that
269 -- we return does still have inlinings on!
271 -- It really is important to switch off inlinings. This function
272 -- may be inlinined in other modules, so we don't want to remove
273 -- (by inlining) calls to functions that have specialisations, or
274 -- that may have transformation rules in an importing scope.
275 -- E.g. {-# INLINE f #-}
277 -- and suppose that g is strict *and* has specialisations.
278 -- If we inline g's wrapper, we deny f the chance of getting
279 -- the specialised version of g when f is inlined at some call site
280 -- (perhaps in some other module).
282 simplExprF (Note InlineMe e) cont
284 Stop _ -> -- Totally boring continuation
285 -- Don't inline inside an INLINE expression
286 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
287 rebuild (mkNote InlineMe e') cont
289 other -> -- Dissolve the InlineMe note if there's
290 -- an interesting context of any kind to combine with
291 -- (even a type application -- anything except Stop)
294 -- A non-recursive let is dealt with by simplBeta
295 simplExprF (Let (NonRec bndr rhs) body) cont
296 = getSubstEnv `thenSmpl` \ se ->
297 simplBeta bndr rhs se (contResultType cont) $
302 ---------------------------------
308 zap_it = mkLamBndrZapper fun (countArgs cont)
309 cont_ty = contResultType cont
311 -- Type-beta reduction
312 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
313 = ASSERT( isTyVar bndr )
314 tick (BetaReduction bndr) `thenSmpl_`
315 getInScope `thenSmpl` \ in_scope ->
317 ty' = substTy (mkSubst in_scope arg_se) ty_arg
320 extendSubst bndr (DoneTy ty')
323 -- Ordinary beta reduction
324 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
325 = tick (BetaReduction bndr) `thenSmpl_`
326 simplBeta zapped_bndr arg arg_se cont_ty
329 zapped_bndr = zap_it bndr
332 go lam@(Lam _ _) cont = completeLam [] lam cont
334 -- Exactly enough args
335 go expr cont = simplExprF expr cont
338 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
339 -- continuation. Try for eta reduction, but *only* if we get all
340 -- the way to an exprIsTrivial expression.
341 -- 'acc' holds the simplified binders, in reverse order
343 completeLam acc (Lam bndr body) cont
344 = simplBinder bndr $ \ bndr' ->
345 completeLam (bndr':acc) body cont
347 completeLam acc body cont
348 = simplExpr body `thenSmpl` \ body' ->
350 case (opt_SimplDoEtaReduction, check_eta acc body') of
351 (True, Just body'') -- Eta reduce!
352 -> tick (EtaReduction (head acc)) `thenSmpl_`
355 other -> -- No eta reduction
356 rebuild (foldl (flip Lam) body' acc) cont
357 -- Remember, acc is the reversed binders
359 -- NB: the binders are reversed
360 check_eta (b : bs) (App fun arg)
361 | (varToCoreExpr b `cheapEqExpr` arg)
365 | exprIsTrivial body && -- ONLY if the body is trivial
366 not (any (`elemVarSet` body_fvs) acc)
367 = Just body -- Success!
369 body_fvs = exprFreeVars body
371 check_eta _ _ = Nothing -- Bale out
373 mkLamBndrZapper :: CoreExpr -- Function
374 -> Int -- Number of args
375 -> Id -> Id -- Use this to zap the binders
376 mkLamBndrZapper fun n_args
377 | n_args >= n_params fun = \b -> b -- Enough args
378 | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
380 n_params (Lam b e) | isId b = 1 + n_params e
381 | otherwise = n_params e
382 n_params other = 0::Int
386 ---------------------------------
387 simplConArgs makes sure that the arguments all end up being atomic.
388 That means it may generate some Lets, hence the strange type
391 simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
392 simplConArgs [] thing_inside
395 simplConArgs (arg:args) thing_inside
396 = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
397 -- Simplify the RHS with inlining switched off, so that
398 -- only absolutely essential things will happen.
400 simplConArgs args $ \ args' ->
402 -- If the argument ain't trivial, then let-bind it
403 if exprIsTrivial arg' then
404 thing_inside (arg' : args')
406 newId (coreExprType arg') $ \ arg_id ->
407 thing_inside (Var arg_id : args') `thenSmpl` \ res ->
408 returnSmpl (addBind (NonRec arg_id arg') res)
412 ---------------------------------
414 simplType :: InType -> SimplM OutType
416 = getSubst `thenSmpl` \ subst ->
418 new_ty = substTy subst ty
425 %************************************************************************
429 %************************************************************************
431 @simplBeta@ is used for non-recursive lets in expressions,
432 as well as true beta reduction.
434 Very similar to @simplLazyBind@, but not quite the same.
437 simplBeta :: InId -- Binder
438 -> InExpr -> SubstEnv -- Arg, with its subst-env
439 -> OutType -- Type of thing computed by the context
440 -> SimplM OutExprStuff -- The body
441 -> SimplM OutExprStuff
443 simplBeta bndr rhs rhs_se cont_ty thing_inside
445 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
448 simplBeta bndr rhs rhs_se cont_ty thing_inside
449 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
450 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
451 extendSubst bndr (ContEx rhs_se rhs) thing_inside
454 = -- Simplify the RHS
455 simplBinder bndr $ \ bndr' ->
456 simplArg (idType bndr') (getIdDemandInfo bndr)
457 rhs rhs_se cont_ty $ \ rhs' ->
459 -- Now complete the binding and simplify the body
460 completeBeta bndr bndr' rhs' thing_inside
462 completeBeta bndr bndr' rhs' thing_inside
463 | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
464 -- Make a case expression instead of a let
465 -- These can arise either from the desugarer,
466 -- or from beta reductions: (\x.e) (x +# y)
467 = getInScope `thenSmpl` \ in_scope ->
468 thing_inside `thenSmpl` \ (floats, (_, body)) ->
469 returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
472 = completeBinding bndr bndr' rhs' thing_inside
477 simplArg :: OutType -> Demand
478 -> InExpr -> SubstEnv
479 -> OutType -- Type of thing computed by the context
480 -> (OutExpr -> SimplM OutExprStuff)
481 -> SimplM OutExprStuff
482 simplArg arg_ty demand arg arg_se cont_ty thing_inside
484 isUnLiftedType arg_ty ||
485 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
486 -- Return true only for dictionary types where the dictionary
487 -- has more than one component (else we risk poking on the component
488 -- of a newtype dictionary)
489 = getSubstEnv `thenSmpl` \ body_se ->
490 transformRhs arg `thenSmpl` \ t_arg ->
491 setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
492 setSubstEnv body_se (thing_inside arg')
493 )) -- NB: we must restore body_se before carrying on with thing_inside!!
496 = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
501 - deals only with Ids, not TyVars
502 - take an already-simplified RHS
504 It does *not* attempt to do let-to-case. Why? Because they are used for
507 (when let-to-case is impossible)
509 - many situations where the "rhs" is known to be a WHNF
510 (so let-to-case is inappropriate).
513 completeBinding :: InId -- Binder
514 -> OutId -- New binder
515 -> OutExpr -- Simplified RHS
516 -> SimplM (OutStuff a) -- Thing inside
517 -> SimplM (OutStuff a)
519 completeBinding old_bndr new_bndr new_rhs thing_inside
520 | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
521 -- known constructor: case (a,b) of x { (p,q) -> ... }
522 -- Here x isn't mentioned in the RHS, so we don't want to
523 -- create the (dead) let-binding let x = (a,b) in ...
526 | postInlineUnconditionally old_bndr new_rhs
527 -- Maybe we don't need a let-binding! Maybe we can just
528 -- inline it right away. Unlike the preInlineUnconditionally case
529 -- we are allowed to look at the RHS.
531 -- NB: a loop breaker never has postInlineUnconditionally True
532 -- and non-loop-breakers only have *forward* references
533 -- Hence, it's safe to discard the binding
534 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
535 extendSubst old_bndr (DoneEx new_rhs)
539 = getSubst `thenSmpl` \ subst ->
541 -- We make new IdInfo for the new binder by starting from the old binder,
542 -- doing appropriate substitutions,
543 new_bndr_info = substIdInfo subst (idInfo old_bndr) (idInfo new_bndr)
544 `setArityInfo` ArityAtLeast (exprArity new_rhs)
546 -- At the *binding* site we use the new binder info
547 binding_site_id = new_bndr `setIdInfo` new_bndr_info
549 -- At the *occurrence* sites we want to know the unfolding
550 -- We also want the occurrence info of the *original*
551 occ_site_id = new_bndr `setIdInfo`
552 (new_bndr_info `setUnfoldingInfo` mkUnfolding new_rhs
553 `setInlinePragInfo` getInlinePragma old_bndr)
555 -- These seqs force the Ids, and hence the IdInfos, and hence any
556 -- inner substitutions
557 binding_site_id `seq`
560 (modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
561 returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff))
565 %************************************************************************
567 \subsection{simplLazyBind}
569 %************************************************************************
571 simplLazyBind basically just simplifies the RHS of a let(rec).
572 It does two important optimisations though:
574 * It floats let(rec)s out of the RHS, even if they
575 are hidden by big lambdas
577 * It does eta expansion
580 simplLazyBind :: TopLevelFlag
583 -> SimplM (OutStuff a) -- The body of the binding
584 -> SimplM (OutStuff a)
585 -- When called, the subst env is correct for the entire let-binding
586 -- and hence right for the RHS.
587 -- Also the binder has already been simplified, and hence is in scope
589 simplLazyBind top_lvl bndr bndr' rhs thing_inside
590 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
591 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
592 getSubstEnv `thenSmpl` \ rhs_se ->
593 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
596 = -- Simplify the RHS
597 getSubstEnv `thenSmpl` \ rhs_se ->
599 simplRhs top_lvl False {- Not ok to float unboxed -}
601 rhs rhs_se $ \ rhs' ->
603 -- Now compete the binding and simplify the body
604 completeBinding bndr bndr' rhs' thing_inside
610 simplRhs :: TopLevelFlag
611 -> Bool -- True <=> OK to float unboxed (speculative) bindings
612 -> OutType -> InExpr -> SubstEnv
613 -> (OutExpr -> SimplM (OutStuff a))
614 -> SimplM (OutStuff a)
615 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
616 = -- Swizzle the inner lets past the big lambda (if any)
617 -- and try eta expansion
618 transformRhs rhs `thenSmpl` \ t_rhs ->
621 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
623 -- Float lets out of RHS
625 (floats_out, rhs'') | float_ubx = (floats, rhs')
626 | otherwise = splitFloats floats rhs'
628 if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
629 not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
631 tickLetFloat floats_out `thenSmpl_`
634 -- There's a subtlety here. There may be a binding (x* = e) in the
635 -- floats, where the '*' means 'will be demanded'. So is it safe
636 -- to float it out? Answer no, but it won't matter because
637 -- we only float if arg' is a WHNF,
638 -- and so there can't be any 'will be demanded' bindings in the floats.
640 WARN( any demanded_float floats_out, ppr floats_out )
641 setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
642 -- in_scope' may be excessive, but that's OK;
643 -- it's a superset of what's in scope
644 returnSmpl (addBinds floats_out stuff)
646 -- Don't do the float
647 thing_inside (mkLets floats rhs')
649 -- In a let-from-let float, we just tick once, arbitrarily
650 -- choosing the first floated binder to identify it
651 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
652 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
654 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
655 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
656 demanded_float (Rec _) = False
658 -- Don't float any unlifted bindings out, because the context
659 -- is either a Rec group, or the top level, neither of which
660 -- can tolerate them.
661 splitFloats floats rhs
665 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
666 | otherwise = case go fs of
667 (out, rhs') -> (f:out, rhs')
669 must_stay (Rec prs) = False -- No unlifted bindings in here
670 must_stay (NonRec b r) = isUnLiftedType (idType b)
675 %************************************************************************
677 \subsection{Variables}
679 %************************************************************************
683 = getSubst `thenSmpl` \ subst ->
684 case lookupSubst subst var of
685 Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
686 Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
687 Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
690 var' = case lookupInScope subst var of
694 if isLocallyDefined var && not (idMustBeINLINEd var)
695 -- The idMustBeINLINEd test accouunts for the fact
696 -- that class dictionary constructors don't have top level
697 -- bindings and hence aren't in scope.
700 pprTrace "simplVar:" (ppr var) var
705 getBlackList `thenSmpl` \ black_list ->
706 getInScope `thenSmpl` \ in_scope ->
707 completeCall black_list in_scope var var' cont
709 ---------------------------------------------------------
710 -- Dealing with a call
712 completeCall black_list_fn in_scope orig_var var cont
713 -- For reasons I'm not very clear about, it's important *not* to plug 'var',
714 -- which is replete with an inlining in its IdInfo, into the resulting expression
715 -- Doing so results in a significant space leak.
716 -- Instead we pass orig_var, which has no inlinings etc.
718 -- Look for rules or specialisations that match
719 -- Do this *before* trying inlining because some functions
720 -- have specialisations *and* are strict; we don't want to
721 -- inline the wrapper of the non-specialised thing... better
722 -- to call the specialised thing instead.
723 | maybeToBool maybe_rule_match
724 = tick (RuleFired rule_name) `thenSmpl_`
725 zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args result_cont))
726 -- See note below about zapping the substitution here
728 -- Look for an unfolding. There's a binding for the
729 -- thing, but perhaps we want to inline it anyway
730 | maybeToBool maybe_inline
731 = tick (UnfoldingDone var) `thenSmpl_`
732 zapSubstEnv (completeInlining orig_var unf_template discard_inline_cont)
733 -- The template is already simplified, so don't re-substitute.
734 -- This is VITAL. Consider
736 -- let y = \z -> ...x... in
738 -- We'll clone the inner \x, adding x->x' in the id_subst
739 -- Then when we inline y, we must *not* replace x by x' in
740 -- the inlined copy!!
742 | otherwise -- Neither rule nor inlining
743 -- Use prepareArgs to use function strictness
744 = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
745 rebuild (mkApps (Var orig_var) args') cont'
748 get_str var = case getIdStrictness var of
749 NoStrictnessInfo -> (repeat wwLazy, False)
750 StrictnessInfo demands result_bot -> (demands, result_bot)
753 (args', result_cont) = contArgs in_scope cont
754 val_args = filter isValArg args'
755 arg_infos = map (interestingArg in_scope) val_args
756 inline_call = contIsInline result_cont
757 interesting_cont = contIsInteresting result_cont
758 discard_inline_cont | inline_call = discardInline cont
761 ---------- Unfolding stuff
762 maybe_inline = callSiteInline black_listed inline_call
763 var arg_infos interesting_cont
764 Just unf_template = maybe_inline
765 black_listed = black_list_fn var
767 ---------- Specialisation stuff
768 maybe_rule_match = lookupRule in_scope var args'
769 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
773 -- An argument is interesting if it has *some* structure
774 -- We are here trying to avoid unfolding a function that
775 -- is applied only to variables that have no unfolding
776 -- (i.e. they are probably lambda bound): f x y z
777 -- There is little point in inlining f here.
778 interestingArg in_scope (Type _) = False
779 interestingArg in_scope (App fn (Type _)) = interestingArg in_scope fn
780 interestingArg in_scope (Var v) = hasSomeUnfolding (getIdUnfolding v')
782 v' = case lookupVarSet in_scope v of
785 interestingArg in_scope other = True
788 -- First a special case
789 -- Don't actually inline the scrutinee when we see
790 -- case x of y { .... }
791 -- and x has unfolding (C a b). Why not? Because
792 -- we get a silly binding y = C a b. If we don't
793 -- inline knownCon can directly substitute x for y instead.
794 completeInlining var (Con con con_args) (Select _ bndr alts se cont)
796 = knownCon (Var var) con con_args bndr alts se cont
798 -- Now the normal case
799 completeInlining var unfolding cont
800 = simplExprF unfolding cont
802 ----------- costCentreOk
803 -- costCentreOk checks that it's ok to inline this thing
804 -- The time it *isn't* is this:
806 -- f x = let y = E in
807 -- scc "foo" (...y...)
809 -- Here y has a "current cost centre", and we can't inline it inside "foo",
810 -- regardless of whether E is a WHNF or not.
812 costCentreOk ccs_encl cc_rhs
813 = not opt_SccProfilingOn
814 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
815 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
820 ---------------------------------------------------------
821 -- Preparing arguments for a call
823 prepareArgs :: SDoc -- Error message info
824 -> OutType -> ([Demand],Bool) -> SimplCont
825 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
826 -> SimplM OutExprStuff
828 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
829 = go [] demands orig_fun_ty orig_cont
831 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
832 -- "No strictness info" is signalled by an infinite list of wwLazy
834 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
835 | result_bot = fun_demands -- Enough args, and function returns bottom
836 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
837 -- NB: demands is finite iff enough args and result_bot is True
839 -- Main game plan: loop through the arguments, simplifying
840 -- each of them in turn. We carry with us a list of demands,
841 -- and the type of the function-applied-to-earlier-args
844 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
845 = getInScope `thenSmpl` \ in_scope ->
847 ty_arg' = substTy (mkSubst in_scope se) ty_arg
848 res_ty = applyTy fun_ty ty_arg'
850 seqType ty_arg' `seq`
851 go (Type ty_arg' : acc) ds res_ty cont
854 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
855 = case splitFunTy_maybe fun_ty of {
856 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
857 (thing_inside (reverse acc) cont) ;
858 Just (arg_ty, res_ty) ->
859 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
860 go (arg':acc) ds res_ty cont }
862 -- We've run out of demands, which only happens for functions
863 -- we *know* now return bottom
865 -- * case (error "hello") of { ... }
866 -- * (error "Hello") arg
867 -- * f (error "Hello") where f is strict
869 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
870 thing_inside (reverse acc) (discardCont cont)
872 -- We're run out of arguments
873 go acc ds fun_ty cont = thing_inside (reverse acc) cont
875 -- Boring: we must only record a tick if there was an interesting
876 -- continuation to discard. If not, we tick forever.
877 tick_case_of_error (Stop _) = returnSmpl ()
878 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
879 tick_case_of_error other = tick BottomFound
882 %************************************************************************
884 \subsection{Decisions about inlining}
886 %************************************************************************
889 preInlineUnconditionally :: InId -> Bool
890 -- Examines a bndr to see if it is used just once in a
891 -- completely safe way, so that it is safe to discard the binding
892 -- inline its RHS at the (unique) usage site, REGARDLESS of how
893 -- big the RHS might be. If this is the case we don't simplify
894 -- the RHS first, but just inline it un-simplified.
896 -- This is much better than first simplifying a perhaps-huge RHS
897 -- and then inlining and re-simplifying it.
899 -- NB: we don't even look at the RHS to see if it's trivial
902 -- where x is used many times, but this is the unique occurrence
903 -- of y. We should NOT inline x at all its uses, because then
904 -- we'd do the same for y -- aargh! So we must base this
905 -- pre-rhs-simplification decision solely on x's occurrences, not
908 -- Evne RHSs labelled InlineMe aren't caught here, because
909 -- there might be no benefit from inlining at the call site.
910 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
911 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
912 preInlineUnconditionally bndr
913 = case getInlinePragma bndr of
914 IMustBeINLINEd -> True
915 ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
916 -- one occurrence ==> safe!
920 postInlineUnconditionally :: InId -> OutExpr -> Bool
921 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
922 -- It returns True if it's ok to discard the binding and inline the
923 -- RHS at every use site.
925 -- NOTE: This isn't our last opportunity to inline.
926 -- We're at the binding site right now, and
927 -- we'll get another opportunity when we get to the ocurrence(s)
929 postInlineUnconditionally bndr rhs
933 = case getInlinePragma bndr of
934 IAmALoopBreaker -> False
936 ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
937 -- Don't inline even WHNFs inside lambdas; doing so may
938 -- simply increase allocation when the function is called
939 -- This isn't the last chance; see NOTE above.
941 ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
942 -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
943 -- decision about duplicating code is best left to callSiteInline
945 other -> exprIsTrivial rhs -- Duplicating is *free*
946 -- NB: Even InlineMe and IMustBeINLINEd are ignored here
947 -- Why? Because we don't even want to inline them into the
948 -- RHS of constructor arguments. See NOTE above
949 -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
950 -- it's best to inline it anyway. We often get a=E; b=a
951 -- from desugaring, with both a and b marked NOINLINE.
956 %************************************************************************
958 \subsection{The main rebuilder}
960 %************************************************************************
963 -------------------------------------------------------------------
966 = getInScope `thenSmpl` \ in_scope ->
967 returnSmpl ([], (in_scope, expr))
969 ---------------------------------------------------------
970 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
973 rebuild expr (Stop _) = rebuild_done expr
975 -- ArgOf continuation
976 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
978 -- ApplyTo continuation
979 rebuild expr cont@(ApplyTo _ arg se cont')
980 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
981 rebuild (App expr arg') cont'
983 -- Coerce continuation
984 rebuild expr (CoerceIt to_ty cont)
985 = rebuild (mkCoerce to_ty expr) cont
987 -- Inline continuation
988 rebuild expr (InlinePlease cont)
989 = rebuild (Note InlineCall expr) cont
991 -- Case of known constructor or literal
992 rebuild expr@(Con con args) (Select _ bndr alts se cont)
993 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
994 = knownCon expr con args bndr alts se cont
997 ---------------------------------------------------------
998 -- The other Select cases
1000 rebuild scrut (Select _ bndr alts se cont)
1001 | -- Check that the RHSs are all the same, and
1002 -- don't use the binders in the alternatives
1003 -- This test succeeds rapidly in the common case of
1004 -- a single DEFAULT alternative
1005 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1007 -- Check that the scrutinee can be let-bound instead of case-bound
1008 && ( exprOkForSpeculation scrut
1009 -- OK not to evaluate it
1010 -- This includes things like (==# a# b#)::Bool
1011 -- so that we simplify
1012 -- case ==# a# b# of { True -> x; False -> x }
1015 -- This particular example shows up in default methods for
1016 -- comparision operations (e.g. in (>=) for Int.Int32)
1017 || exprIsValue scrut -- It's already evaluated
1018 || var_demanded_later scrut -- It'll be demanded later
1020 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1021 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1022 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1023 -- its argument: case x of { y -> dataToTag# y }
1024 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1025 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1029 -- && opt_SimplDoCaseElim
1030 -- [June 99; don't test this flag. The code generator dies if it sees
1031 -- case (\x.e) of f -> ...
1032 -- so better to always do it
1034 -- Get rid of the case altogether
1035 -- See the extensive notes on case-elimination below
1036 -- Remember to bind the binder though!
1037 = tick (CaseElim bndr) `thenSmpl_` (
1039 simplBinder bndr $ \ bndr' ->
1040 completeBinding bndr bndr' scrut $
1041 simplExprF rhs1 cont)
1044 = rebuild_case scrut bndr alts se cont
1046 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1047 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1049 var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1050 var_demanded_later other = False
1053 Case elimination [see the code above]
1055 Start with a simple situation:
1057 case x# of ===> e[x#/y#]
1060 (when x#, y# are of primitive type, of course). We can't (in general)
1061 do this for algebraic cases, because we might turn bottom into
1064 Actually, we generalise this idea to look for a case where we're
1065 scrutinising a variable, and we know that only the default case can
1070 other -> ...(case x of
1074 Here the inner case can be eliminated. This really only shows up in
1075 eliminating error-checking code.
1077 We also make sure that we deal with this very common case:
1082 Here we are using the case as a strict let; if x is used only once
1083 then we want to inline it. We have to be careful that this doesn't
1084 make the program terminate when it would have diverged before, so we
1086 - x is used strictly, or
1087 - e is already evaluated (it may so if e is a variable)
1089 Lastly, we generalise the transformation to handle this:
1095 We only do this for very cheaply compared r's (constructors, literals
1096 and variables). If pedantic bottoms is on, we only do it when the
1097 scrutinee is a PrimOp which can't fail.
1099 We do it *here*, looking at un-simplified alternatives, because we
1100 have to check that r doesn't mention the variables bound by the
1101 pattern in each alternative, so the binder-info is rather useful.
1103 So the case-elimination algorithm is:
1105 1. Eliminate alternatives which can't match
1107 2. Check whether all the remaining alternatives
1108 (a) do not mention in their rhs any of the variables bound in their pattern
1109 and (b) have equal rhss
1111 3. Check we can safely ditch the case:
1112 * PedanticBottoms is off,
1113 or * the scrutinee is an already-evaluated variable
1114 or * the scrutinee is a primop which is ok for speculation
1115 -- ie we want to preserve divide-by-zero errors, and
1116 -- calls to error itself!
1118 or * [Prim cases] the scrutinee is a primitive variable
1120 or * [Alg cases] the scrutinee is a variable and
1121 either * the rhs is the same variable
1122 (eg case x of C a b -> x ===> x)
1123 or * there is only one alternative, the default alternative,
1124 and the binder is used strictly in its scope.
1125 [NB this is helped by the "use default binder where
1126 possible" transformation; see below.]
1129 If so, then we can replace the case with one of the rhss.
1132 Blob of helper functions for the "case-of-something-else" situation.
1135 ---------------------------------------------------------
1136 -- Case of something else
1138 rebuild_case scrut case_bndr alts se cont
1139 = -- Prepare case alternatives
1140 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1141 scrut_cons alts `thenSmpl` \ better_alts ->
1143 -- Set the new subst-env in place (before dealing with the case binder)
1146 -- Deal with the case binder, and prepare the continuation;
1147 -- The new subst_env is in place
1148 prepareCaseCont better_alts cont $ \ cont' ->
1151 -- Deal with variable scrutinee
1152 ( simplBinder case_bndr $ \ case_bndr' ->
1153 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1155 case_bndr'' = zap_occ_info case_bndr'
1158 -- Deal with the case alternaatives
1159 simplAlts zap_occ_info scrut_cons
1160 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1162 mkCase scrut case_bndr'' alts'
1163 ) `thenSmpl` \ case_expr ->
1165 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1166 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1167 -- that should not include these chaps!
1168 rebuild_done case_expr
1170 -- scrut_cons tells what constructors the scrutinee can't possibly match
1171 scrut_cons = case scrut of
1172 Var v -> otherCons (getIdUnfolding v)
1176 knownCon expr con args bndr alts se cont
1177 = tick (KnownBranch bndr) `thenSmpl_`
1179 simplBinder bndr $ \ bndr' ->
1180 case findAlt con alts of
1181 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1182 completeBinding bndr bndr' expr $
1183 -- Don't use completeBeta here. The expr might be
1184 -- an unboxed literal, like 3, or a variable
1185 -- whose unfolding is an unboxed literal... and
1186 -- completeBeta will just construct another case
1190 (Literal lit, bs, rhs) -> ASSERT( null bs )
1191 extendSubst bndr (DoneEx expr) $
1192 -- Unconditionally substitute, because expr must
1193 -- be a variable or a literal. It can't be a
1194 -- NoRep literal because they don't occur in
1198 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1199 completeBinding bndr bndr' expr $
1201 extendSubstList bs (map mk real_args) $
1204 real_args = drop (dataConNumInstArgs dc) args
1205 mk (Type ty) = DoneTy ty
1206 mk other = DoneEx other
1211 prepareCaseCont :: [InAlt] -> SimplCont
1212 -> (SimplCont -> SimplM (OutStuff a))
1213 -> SimplM (OutStuff a)
1214 -- Polymorphic recursion here!
1216 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1217 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1220 substForVarScrut checks whether the scrutinee is a variable, v.
1221 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1222 that way, there's a chance that v will now only be used once, and hence inlined.
1224 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1225 in the case binder, because the case-binder now effectively occurs
1226 whenever v does. AND we have to do the same for the pattern-bound
1229 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1231 Here, b and p are dead. But when we move the argment inside the first
1232 case RHS, and eliminate the second case, we get
1234 case x or { (a,b) -> a b }
1236 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1237 happened. Hence the zap_occ_info function returned by substForVarScrut
1240 substForVarScrut (Var v) case_bndr' thing_inside
1241 | isLocallyDefined v -- No point for imported things
1242 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1243 `setInlinePragma` IMustBeINLINEd) $
1244 -- We could extend the substitution instead, but it would be
1245 -- a hack because then the substitution wouldn't be idempotent
1247 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1249 substForVarScrut other_scrut case_bndr' thing_inside
1250 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1253 prepareCaseAlts does two things:
1255 1. Remove impossible alternatives
1257 2. If the DEFAULT alternative can match only one possible constructor,
1258 then make that constructor explicit.
1260 case e of x { DEFAULT -> rhs }
1262 case e of x { (a,b) -> rhs }
1263 where the type is a single constructor type. This gives better code
1264 when rhs also scrutinises x or e.
1267 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1269 = case (findDefault filtered_alts, missing_cons) of
1271 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1272 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1274 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1276 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1278 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1279 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1281 newIds (dataConArgTys
1283 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1284 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1286 other -> returnSmpl filtered_alts
1288 -- Filter out alternatives that can't possibly match
1289 filtered_alts = case scrut_cons of
1291 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1293 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1294 not (data_con `elem` handled_data_cons)]
1295 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1296 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1299 prepareCaseAlts _ _ scrut_cons alts
1300 = returnSmpl alts -- Functions
1303 ----------------------
1304 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1305 = mapSmpl simpl_alt alts
1307 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1308 Just (tycon, inst_tys) -> inst_tys
1310 -- handled_cons is all the constructors that are dealt
1311 -- with, either by being impossible, or by there being an alternative
1312 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1314 simpl_alt (DEFAULT, _, rhs)
1315 = -- In the default case we record the constructors that the
1316 -- case-binder *can't* be.
1317 -- We take advantage of any OtherCon info in the case scrutinee
1318 modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
1319 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1320 returnSmpl (DEFAULT, [], rhs')
1322 simpl_alt (con, vs, rhs)
1323 = -- Deal with the pattern-bound variables
1324 -- Mark the ones that are in ! positions in the data constructor
1325 -- as certainly-evaluated
1326 simplBinders (add_evals con vs) $ \ vs' ->
1328 -- Bind the case-binder to (Con args)
1330 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1332 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1333 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1334 returnSmpl (con, vs', rhs')
1337 -- add_evals records the evaluated-ness of the bound variables of
1338 -- a case pattern. This is *important*. Consider
1339 -- data T = T !Int !Int
1341 -- case x of { T a b -> T (a+1) b }
1343 -- We really must record that b is already evaluated so that we don't
1344 -- go and re-evaluate it when constructing the result.
1346 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1347 add_evals other_con vs = vs
1349 cat_evals [] [] = []
1350 cat_evals (v:vs) (str:strs)
1351 | isTyVar v = v : cat_evals vs (str:strs)
1352 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1353 | otherwise = v' : cat_evals vs strs
1359 %************************************************************************
1361 \subsection{Duplicating continuations}
1363 %************************************************************************
1366 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1368 -> (SimplCont -> SimplM (OutStuff a))
1369 -> SimplM (OutStuff a)
1370 mkDupableCont ty cont thing_inside
1371 | contIsDupable cont
1374 mkDupableCont _ (CoerceIt ty cont) thing_inside
1375 = mkDupableCont ty cont $ \ cont' ->
1376 thing_inside (CoerceIt ty cont')
1378 mkDupableCont ty (InlinePlease cont) thing_inside
1379 = mkDupableCont ty cont $ \ cont' ->
1380 thing_inside (InlinePlease cont')
1382 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1383 = -- Build the RHS of the join point
1384 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1385 newId join_arg_ty' ( \ arg_id ->
1386 getSwitchChecker `thenSmpl` \ chkr ->
1387 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1388 returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs))
1389 ) `thenSmpl` \ join_rhs ->
1391 -- Build the join Id and continuation
1392 newId (coreExprType join_rhs) $ \ join_id ->
1394 new_cont = ArgOf OkToDup cont_ty
1395 (\arg' -> rebuild_done (App (Var join_id) arg'))
1398 -- Do the thing inside
1399 thing_inside new_cont `thenSmpl` \ res ->
1400 returnSmpl (addBind (NonRec join_id join_rhs) res)
1402 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1403 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1404 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1405 if exprIsDupable arg' then
1406 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1408 newId (coreExprType arg') $ \ bndr ->
1409 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1410 returnSmpl (addBind (NonRec bndr arg') res)
1412 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1413 = tick (CaseOfCase case_bndr) `thenSmpl_`
1415 simplBinder case_bndr $ \ case_bndr' ->
1416 prepareCaseCont alts cont $ \ cont' ->
1417 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1418 returnSmpl (concat alt_binds_s, alts')
1419 ) `thenSmpl` \ (alt_binds, alts') ->
1421 extendInScopes [b | NonRec b _ <- alt_binds] $
1423 -- NB that the new alternatives, alts', are still InAlts, using the original
1424 -- binders. That means we can keep the case_bndr intact. This is important
1425 -- because another case-of-case might strike, and so we want to keep the
1426 -- info that the case_bndr is dead (if it is, which is often the case).
1427 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1428 -- case in I/O rich code. We aren't allowed a lambda bound
1429 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1430 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1432 returnSmpl (addBinds alt_binds res)
1435 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1436 mkDupableAlt case_bndr case_bndr' (Stop _) alt@(con, bndrs, rhs)
1438 = -- It is worth checking for a small RHS because otherwise we
1439 -- get extra let bindings that may cause an extra iteration of the simplifier to
1440 -- inline back in place. Quite often the rhs is just a variable or constructor.
1441 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1442 -- iterations because the version with the let bindings looked big, and so wasn't
1443 -- inlined, but after the join points had been inlined it looked smaller, and so
1446 -- But since the continuation is absorbed into the rhs, we only do this
1447 -- for a Stop continuation.
1448 returnSmpl ([], alt)
1450 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1452 = -- Not worth checking whether the rhs is small; the
1453 -- inliner will inline it if so.
1454 simplBinders bndrs $ \ bndrs' ->
1455 simplExprC rhs cont `thenSmpl` \ rhs' ->
1457 rhs_ty' = coreExprType rhs'
1458 (used_bndrs, used_bndrs')
1459 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1460 (case_bndr' : bndrs'),
1461 not (isDeadBinder bndr)]
1462 -- The new binders have lost their occurrence info,
1463 -- so we have to extract it from the old ones
1465 ( if null used_bndrs'
1466 -- If we try to lift a primitive-typed something out
1467 -- for let-binding-purposes, we will *caseify* it (!),
1468 -- with potentially-disastrous strictness results. So
1469 -- instead we turn it into a function: \v -> e
1470 -- where v::State# RealWorld#. The value passed to this function
1471 -- is realworld#, which generates (almost) no code.
1473 -- There's a slight infelicity here: we pass the overall
1474 -- case_bndr to all the join points if it's used in *any* RHS,
1475 -- because we don't know its usage in each RHS separately
1477 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1478 -- we make the join point into a function whenever used_bndrs'
1479 -- is empty. This makes the join-point more CPR friendly.
1480 -- Consider: let j = if .. then I# 3 else I# 4
1481 -- in case .. of { A -> j; B -> j; C -> ... }
1483 -- Now CPR should not w/w j because it's a thunk, so
1484 -- that means that the enclosing function can't w/w either,
1485 -- which is a lose. Here's the example that happened in practice:
1486 -- kgmod :: Int -> Int -> Int
1487 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1491 then newId realWorldStatePrimTy $ \ rw_id ->
1492 returnSmpl ([rw_id], [Var realWorldPrimId])
1494 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1496 `thenSmpl` \ (final_bndrs', final_args) ->
1498 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1500 -- Notice that we make the lambdas into one-shot-lambdas. The
1501 -- join point is sure to be applied at most once, and doing so
1502 -- prevents the body of the join point being floated out by
1503 -- the full laziness pass
1504 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1505 (con, bndrs, mkApps (Var join_bndr) final_args))