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, 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' False 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 -> Bool -- True <=> black-listed; don't inline
516 -> OutExpr -- Simplified RHS
517 -> SimplM (OutStuff a) -- Thing inside
518 -> SimplM (OutStuff a)
520 completeBinding old_bndr new_bndr black_listed new_rhs thing_inside
521 | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
522 -- known constructor: case (a,b) of x { (p,q) -> ... }
523 -- Here x isn't mentioned in the RHS, so we don't want to
524 -- create the (dead) let-binding let x = (a,b) in ...
527 | not black_listed && postInlineUnconditionally old_bndr new_rhs
528 -- Maybe we don't need a let-binding! Maybe we can just
529 -- inline it right away. Unlike the preInlineUnconditionally case
530 -- we are allowed to look at the RHS.
532 -- NB: a loop breaker never has postInlineUnconditionally True
533 -- and non-loop-breakers only have *forward* references
534 -- Hence, it's safe to discard the binding
535 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
536 extendSubst old_bndr (DoneEx new_rhs)
540 = getSubst `thenSmpl` \ subst ->
542 -- We make new IdInfo for the new binder by starting from the old binder,
543 -- doing appropriate substitutions,
544 new_bndr_info = substIdInfo subst (idInfo old_bndr) (idInfo new_bndr)
545 `setArityInfo` ArityAtLeast (exprArity new_rhs)
547 -- At the *binding* site we use the new binder info
548 binding_site_id = new_bndr `setIdInfo` new_bndr_info
550 -- At the *occurrence* sites we want to know the unfolding
551 -- We also want the occurrence info of the *original*
552 occ_site_id = new_bndr `setIdInfo`
553 (new_bndr_info `setUnfoldingInfo` mkUnfolding new_rhs
554 `setInlinePragInfo` getInlinePragma old_bndr)
556 -- These seqs force the Ids, and hence the IdInfos, and hence any
557 -- inner substitutions
558 binding_site_id `seq`
561 (modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
562 returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff))
566 %************************************************************************
568 \subsection{simplLazyBind}
570 %************************************************************************
572 simplLazyBind basically just simplifies the RHS of a let(rec).
573 It does two important optimisations though:
575 * It floats let(rec)s out of the RHS, even if they
576 are hidden by big lambdas
578 * It does eta expansion
581 simplLazyBind :: TopLevelFlag
584 -> SimplM (OutStuff a) -- The body of the binding
585 -> SimplM (OutStuff a)
586 -- When called, the subst env is correct for the entire let-binding
587 -- and hence right for the RHS.
588 -- Also the binder has already been simplified, and hence is in scope
590 simplLazyBind top_lvl bndr bndr' rhs thing_inside
591 = getBlackList `thenSmpl` \ black_list_fn ->
593 black_listed = isTopLevel top_lvl && black_list_fn bndr
594 -- Only top level things can be black listed, so the
595 -- first test gets us 'False' without having to call
596 -- the function, in the common case.
598 if not black_listed &&
599 preInlineUnconditionally bndr &&
600 not opt_SimplNoPreInlining
602 tick (PreInlineUnconditionally bndr) `thenSmpl_`
603 getSubstEnv `thenSmpl` \ rhs_se ->
604 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
606 else -- Simplify the RHS
607 getSubstEnv `thenSmpl` \ rhs_se ->
608 simplRhs top_lvl False {- Not ok to float unboxed -}
610 rhs rhs_se $ \ rhs' ->
612 -- Now compete the binding and simplify the body
613 completeBinding bndr bndr' black_listed rhs' thing_inside
619 simplRhs :: TopLevelFlag
620 -> Bool -- True <=> OK to float unboxed (speculative) bindings
621 -> OutType -> InExpr -> SubstEnv
622 -> (OutExpr -> SimplM (OutStuff a))
623 -> SimplM (OutStuff a)
624 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
625 = -- Swizzle the inner lets past the big lambda (if any)
626 -- and try eta expansion
627 transformRhs rhs `thenSmpl` \ t_rhs ->
630 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
632 -- Float lets out of RHS
634 (floats_out, rhs'') | float_ubx = (floats, rhs')
635 | otherwise = splitFloats floats rhs'
637 if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
638 not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
640 tickLetFloat floats_out `thenSmpl_`
643 -- There's a subtlety here. There may be a binding (x* = e) in the
644 -- floats, where the '*' means 'will be demanded'. So is it safe
645 -- to float it out? Answer no, but it won't matter because
646 -- we only float if arg' is a WHNF,
647 -- and so there can't be any 'will be demanded' bindings in the floats.
649 WARN( any demanded_float floats_out, ppr floats_out )
650 setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
651 -- in_scope' may be excessive, but that's OK;
652 -- it's a superset of what's in scope
653 returnSmpl (addBinds floats_out stuff)
655 -- Don't do the float
656 thing_inside (mkLets floats rhs')
658 -- In a let-from-let float, we just tick once, arbitrarily
659 -- choosing the first floated binder to identify it
660 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
661 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
663 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
664 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
665 demanded_float (Rec _) = False
667 -- Don't float any unlifted bindings out, because the context
668 -- is either a Rec group, or the top level, neither of which
669 -- can tolerate them.
670 splitFloats floats rhs
674 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
675 | otherwise = case go fs of
676 (out, rhs') -> (f:out, rhs')
678 must_stay (Rec prs) = False -- No unlifted bindings in here
679 must_stay (NonRec b r) = isUnLiftedType (idType b)
684 %************************************************************************
686 \subsection{Variables}
688 %************************************************************************
692 = getSubst `thenSmpl` \ subst ->
693 case lookupSubst subst var of
694 Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
695 Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
696 Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
699 var' = case lookupInScope subst var of
703 if isLocallyDefined var && not (idMustBeINLINEd var)
704 -- The idMustBeINLINEd test accouunts for the fact
705 -- that class dictionary constructors don't have top level
706 -- bindings and hence aren't in scope.
709 pprTrace "simplVar:" (ppr var) var
714 getBlackList `thenSmpl` \ black_list ->
715 getInScope `thenSmpl` \ in_scope ->
716 completeCall black_list in_scope var var' cont
718 ---------------------------------------------------------
719 -- Dealing with a call
721 completeCall black_list_fn in_scope orig_var var cont
722 -- For reasons I'm not very clear about, it's important *not* to plug 'var',
723 -- which is replete with an inlining in its IdInfo, into the resulting expression
724 -- Doing so results in a significant space leak.
725 -- Instead we pass orig_var, which has no inlinings etc.
727 -- Look for rules or specialisations that match
728 -- Do this *before* trying inlining because some functions
729 -- have specialisations *and* are strict; we don't want to
730 -- inline the wrapper of the non-specialised thing... better
731 -- to call the specialised thing instead.
732 | maybeToBool maybe_rule_match
733 = tick (RuleFired rule_name) `thenSmpl_`
734 zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args result_cont))
735 -- See note below about zapping the substitution here
737 -- Look for an unfolding. There's a binding for the
738 -- thing, but perhaps we want to inline it anyway
739 | maybeToBool maybe_inline
740 = tick (UnfoldingDone var) `thenSmpl_`
741 zapSubstEnv (completeInlining orig_var unf_template discard_inline_cont)
742 -- The template is already simplified, so don't re-substitute.
743 -- This is VITAL. Consider
745 -- let y = \z -> ...x... in
747 -- We'll clone the inner \x, adding x->x' in the id_subst
748 -- Then when we inline y, we must *not* replace x by x' in
749 -- the inlined copy!!
751 | otherwise -- Neither rule nor inlining
752 -- Use prepareArgs to use function strictness
753 = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
754 rebuild (mkApps (Var orig_var) args') cont'
757 get_str var = case getIdStrictness var of
758 NoStrictnessInfo -> (repeat wwLazy, False)
759 StrictnessInfo demands result_bot -> (demands, result_bot)
762 (args', result_cont) = contArgs in_scope cont
763 val_args = filter isValArg args'
764 arg_infos = map (interestingArg in_scope) val_args
765 inline_call = contIsInline result_cont
766 interesting_cont = contIsInteresting result_cont
767 discard_inline_cont | inline_call = discardInline cont
770 ---------- Unfolding stuff
771 maybe_inline = callSiteInline black_listed inline_call
772 var arg_infos interesting_cont
773 Just unf_template = maybe_inline
774 black_listed = black_list_fn var
776 ---------- Specialisation stuff
777 maybe_rule_match = lookupRule in_scope var args'
778 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
782 -- An argument is interesting if it has *some* structure
783 -- We are here trying to avoid unfolding a function that
784 -- is applied only to variables that have no unfolding
785 -- (i.e. they are probably lambda bound): f x y z
786 -- There is little point in inlining f here.
787 interestingArg in_scope (Type _) = False
788 interestingArg in_scope (App fn (Type _)) = interestingArg in_scope fn
789 interestingArg in_scope (Var v) = hasSomeUnfolding (getIdUnfolding v')
791 v' = case lookupVarSet in_scope v of
794 interestingArg in_scope other = True
797 -- First a special case
798 -- Don't actually inline the scrutinee when we see
799 -- case x of y { .... }
800 -- and x has unfolding (C a b). Why not? Because
801 -- we get a silly binding y = C a b. If we don't
802 -- inline knownCon can directly substitute x for y instead.
803 completeInlining var (Con con con_args) (Select _ bndr alts se cont)
805 = knownCon (Var var) con con_args bndr alts se cont
807 -- Now the normal case
808 completeInlining var unfolding cont
809 = simplExprF unfolding cont
811 ----------- costCentreOk
812 -- costCentreOk checks that it's ok to inline this thing
813 -- The time it *isn't* is this:
815 -- f x = let y = E in
816 -- scc "foo" (...y...)
818 -- Here y has a "current cost centre", and we can't inline it inside "foo",
819 -- regardless of whether E is a WHNF or not.
821 costCentreOk ccs_encl cc_rhs
822 = not opt_SccProfilingOn
823 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
824 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
829 ---------------------------------------------------------
830 -- Preparing arguments for a call
832 prepareArgs :: SDoc -- Error message info
833 -> OutType -> ([Demand],Bool) -> SimplCont
834 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
835 -> SimplM OutExprStuff
837 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
838 = go [] demands orig_fun_ty orig_cont
840 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
841 -- "No strictness info" is signalled by an infinite list of wwLazy
843 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
844 | result_bot = fun_demands -- Enough args, and function returns bottom
845 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
846 -- NB: demands is finite iff enough args and result_bot is True
848 -- Main game plan: loop through the arguments, simplifying
849 -- each of them in turn. We carry with us a list of demands,
850 -- and the type of the function-applied-to-earlier-args
853 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
854 = getInScope `thenSmpl` \ in_scope ->
856 ty_arg' = substTy (mkSubst in_scope se) ty_arg
857 res_ty = applyTy fun_ty ty_arg'
859 seqType ty_arg' `seq`
860 go (Type ty_arg' : acc) ds res_ty cont
863 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
864 = case splitFunTy_maybe fun_ty of {
865 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
866 (thing_inside (reverse acc) cont) ;
867 Just (arg_ty, res_ty) ->
868 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
869 go (arg':acc) ds res_ty cont }
871 -- We've run out of demands, which only happens for functions
872 -- we *know* now return bottom
874 -- * case (error "hello") of { ... }
875 -- * (error "Hello") arg
876 -- * f (error "Hello") where f is strict
878 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
879 thing_inside (reverse acc) (discardCont cont)
881 -- We're run out of arguments
882 go acc ds fun_ty cont = thing_inside (reverse acc) cont
884 -- Boring: we must only record a tick if there was an interesting
885 -- continuation to discard. If not, we tick forever.
886 tick_case_of_error (Stop _) = returnSmpl ()
887 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
888 tick_case_of_error other = tick BottomFound
891 %************************************************************************
893 \subsection{Decisions about inlining}
895 %************************************************************************
898 preInlineUnconditionally :: InId -> Bool
899 -- Examines a bndr to see if it is used just once in a
900 -- completely safe way, so that it is safe to discard the binding
901 -- inline its RHS at the (unique) usage site, REGARDLESS of how
902 -- big the RHS might be. If this is the case we don't simplify
903 -- the RHS first, but just inline it un-simplified.
905 -- This is much better than first simplifying a perhaps-huge RHS
906 -- and then inlining and re-simplifying it.
908 -- NB: we don't even look at the RHS to see if it's trivial
911 -- where x is used many times, but this is the unique occurrence
912 -- of y. We should NOT inline x at all its uses, because then
913 -- we'd do the same for y -- aargh! So we must base this
914 -- pre-rhs-simplification decision solely on x's occurrences, not
917 -- Evne RHSs labelled InlineMe aren't caught here, because
918 -- there might be no benefit from inlining at the call site.
919 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
920 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
921 preInlineUnconditionally bndr
922 = case getInlinePragma bndr of
923 IMustBeINLINEd -> True
924 ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
925 -- one occurrence ==> safe!
929 postInlineUnconditionally :: InId -> OutExpr -> Bool
930 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
931 -- It returns True if it's ok to discard the binding and inline the
932 -- RHS at every use site.
934 -- NOTE: This isn't our last opportunity to inline.
935 -- We're at the binding site right now, and
936 -- we'll get another opportunity when we get to the ocurrence(s)
938 postInlineUnconditionally bndr rhs
942 = case getInlinePragma bndr of
943 IAmALoopBreaker -> False
945 ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
946 -- Don't inline even WHNFs inside lambdas; doing so may
947 -- simply increase allocation when the function is called
948 -- This isn't the last chance; see NOTE above.
950 ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
951 -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
952 -- decision about duplicating code is best left to callSiteInline
954 other -> exprIsTrivial rhs -- Duplicating is *free*
955 -- NB: Even InlineMe and IMustBeINLINEd are ignored here
956 -- Why? Because we don't even want to inline them into the
957 -- RHS of constructor arguments. See NOTE above
958 -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
959 -- it's best to inline it anyway. We often get a=E; b=a
960 -- from desugaring, with both a and b marked NOINLINE.
965 %************************************************************************
967 \subsection{The main rebuilder}
969 %************************************************************************
972 -------------------------------------------------------------------
975 = getInScope `thenSmpl` \ in_scope ->
976 returnSmpl ([], (in_scope, expr))
978 ---------------------------------------------------------
979 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
982 rebuild expr (Stop _) = rebuild_done expr
984 -- ArgOf continuation
985 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
987 -- ApplyTo continuation
988 rebuild expr cont@(ApplyTo _ arg se cont')
989 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
990 rebuild (App expr arg') cont'
992 -- Coerce continuation
993 rebuild expr (CoerceIt to_ty cont)
994 = rebuild (mkCoerce to_ty expr) cont
996 -- Inline continuation
997 rebuild expr (InlinePlease cont)
998 = rebuild (Note InlineCall expr) cont
1000 -- Case of known constructor or literal
1001 rebuild expr@(Con con args) (Select _ bndr alts se cont)
1002 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
1003 = knownCon expr con args bndr alts se cont
1006 ---------------------------------------------------------
1007 -- The other Select cases
1009 rebuild scrut (Select _ bndr alts se cont)
1010 | -- Check that the RHSs are all the same, and
1011 -- don't use the binders in the alternatives
1012 -- This test succeeds rapidly in the common case of
1013 -- a single DEFAULT alternative
1014 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1016 -- Check that the scrutinee can be let-bound instead of case-bound
1017 && ( exprOkForSpeculation scrut
1018 -- OK not to evaluate it
1019 -- This includes things like (==# a# b#)::Bool
1020 -- so that we simplify
1021 -- case ==# a# b# of { True -> x; False -> x }
1024 -- This particular example shows up in default methods for
1025 -- comparision operations (e.g. in (>=) for Int.Int32)
1026 || exprIsValue scrut -- It's already evaluated
1027 || var_demanded_later scrut -- It'll be demanded later
1029 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1030 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1031 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1032 -- its argument: case x of { y -> dataToTag# y }
1033 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1034 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1038 -- && opt_SimplDoCaseElim
1039 -- [June 99; don't test this flag. The code generator dies if it sees
1040 -- case (\x.e) of f -> ...
1041 -- so better to always do it
1043 -- Get rid of the case altogether
1044 -- See the extensive notes on case-elimination below
1045 -- Remember to bind the binder though!
1046 = tick (CaseElim bndr) `thenSmpl_` (
1048 simplBinder bndr $ \ bndr' ->
1049 completeBinding bndr bndr' False scrut $
1050 simplExprF rhs1 cont)
1053 = rebuild_case scrut bndr alts se cont
1055 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1056 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1058 var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1059 var_demanded_later other = False
1062 Case elimination [see the code above]
1064 Start with a simple situation:
1066 case x# of ===> e[x#/y#]
1069 (when x#, y# are of primitive type, of course). We can't (in general)
1070 do this for algebraic cases, because we might turn bottom into
1073 Actually, we generalise this idea to look for a case where we're
1074 scrutinising a variable, and we know that only the default case can
1079 other -> ...(case x of
1083 Here the inner case can be eliminated. This really only shows up in
1084 eliminating error-checking code.
1086 We also make sure that we deal with this very common case:
1091 Here we are using the case as a strict let; if x is used only once
1092 then we want to inline it. We have to be careful that this doesn't
1093 make the program terminate when it would have diverged before, so we
1095 - x is used strictly, or
1096 - e is already evaluated (it may so if e is a variable)
1098 Lastly, we generalise the transformation to handle this:
1104 We only do this for very cheaply compared r's (constructors, literals
1105 and variables). If pedantic bottoms is on, we only do it when the
1106 scrutinee is a PrimOp which can't fail.
1108 We do it *here*, looking at un-simplified alternatives, because we
1109 have to check that r doesn't mention the variables bound by the
1110 pattern in each alternative, so the binder-info is rather useful.
1112 So the case-elimination algorithm is:
1114 1. Eliminate alternatives which can't match
1116 2. Check whether all the remaining alternatives
1117 (a) do not mention in their rhs any of the variables bound in their pattern
1118 and (b) have equal rhss
1120 3. Check we can safely ditch the case:
1121 * PedanticBottoms is off,
1122 or * the scrutinee is an already-evaluated variable
1123 or * the scrutinee is a primop which is ok for speculation
1124 -- ie we want to preserve divide-by-zero errors, and
1125 -- calls to error itself!
1127 or * [Prim cases] the scrutinee is a primitive variable
1129 or * [Alg cases] the scrutinee is a variable and
1130 either * the rhs is the same variable
1131 (eg case x of C a b -> x ===> x)
1132 or * there is only one alternative, the default alternative,
1133 and the binder is used strictly in its scope.
1134 [NB this is helped by the "use default binder where
1135 possible" transformation; see below.]
1138 If so, then we can replace the case with one of the rhss.
1141 Blob of helper functions for the "case-of-something-else" situation.
1144 ---------------------------------------------------------
1145 -- Case of something else
1147 rebuild_case scrut case_bndr alts se cont
1148 = -- Prepare case alternatives
1149 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1150 scrut_cons alts `thenSmpl` \ better_alts ->
1152 -- Set the new subst-env in place (before dealing with the case binder)
1155 -- Deal with the case binder, and prepare the continuation;
1156 -- The new subst_env is in place
1157 prepareCaseCont better_alts cont $ \ cont' ->
1160 -- Deal with variable scrutinee
1161 ( simplBinder case_bndr $ \ case_bndr' ->
1162 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1164 case_bndr'' = zap_occ_info case_bndr'
1167 -- Deal with the case alternaatives
1168 simplAlts zap_occ_info scrut_cons
1169 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1171 mkCase scrut case_bndr'' alts'
1172 ) `thenSmpl` \ case_expr ->
1174 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1175 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1176 -- that should not include these chaps!
1177 rebuild_done case_expr
1179 -- scrut_cons tells what constructors the scrutinee can't possibly match
1180 scrut_cons = case scrut of
1181 Var v -> otherCons (getIdUnfolding v)
1185 knownCon expr con args bndr alts se cont
1186 = tick (KnownBranch bndr) `thenSmpl_`
1188 simplBinder bndr $ \ bndr' ->
1189 case findAlt con alts of
1190 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1191 completeBinding bndr bndr' False expr $
1192 -- Don't use completeBeta here. The expr might be
1193 -- an unboxed literal, like 3, or a variable
1194 -- whose unfolding is an unboxed literal... and
1195 -- completeBeta will just construct another case
1199 (Literal lit, bs, rhs) -> ASSERT( null bs )
1200 extendSubst bndr (DoneEx expr) $
1201 -- Unconditionally substitute, because expr must
1202 -- be a variable or a literal. It can't be a
1203 -- NoRep literal because they don't occur in
1207 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1208 completeBinding bndr bndr' False expr $
1210 extendSubstList bs (map mk real_args) $
1213 real_args = drop (dataConNumInstArgs dc) args
1214 mk (Type ty) = DoneTy ty
1215 mk other = DoneEx other
1220 prepareCaseCont :: [InAlt] -> SimplCont
1221 -> (SimplCont -> SimplM (OutStuff a))
1222 -> SimplM (OutStuff a)
1223 -- Polymorphic recursion here!
1225 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1226 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1229 substForVarScrut checks whether the scrutinee is a variable, v.
1230 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1231 that way, there's a chance that v will now only be used once, and hence inlined.
1233 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1234 in the case binder, because the case-binder now effectively occurs
1235 whenever v does. AND we have to do the same for the pattern-bound
1238 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1240 Here, b and p are dead. But when we move the argment inside the first
1241 case RHS, and eliminate the second case, we get
1243 case x or { (a,b) -> a b }
1245 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1246 happened. Hence the zap_occ_info function returned by substForVarScrut
1249 substForVarScrut (Var v) case_bndr' thing_inside
1250 | isLocallyDefined v -- No point for imported things
1251 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1252 `setInlinePragma` IMustBeINLINEd) $
1253 -- We could extend the substitution instead, but it would be
1254 -- a hack because then the substitution wouldn't be idempotent
1256 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1258 substForVarScrut other_scrut case_bndr' thing_inside
1259 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1262 prepareCaseAlts does two things:
1264 1. Remove impossible alternatives
1266 2. If the DEFAULT alternative can match only one possible constructor,
1267 then make that constructor explicit.
1269 case e of x { DEFAULT -> rhs }
1271 case e of x { (a,b) -> rhs }
1272 where the type is a single constructor type. This gives better code
1273 when rhs also scrutinises x or e.
1276 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1278 = case (findDefault filtered_alts, missing_cons) of
1280 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1281 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1283 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1285 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1287 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1288 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1290 newIds (dataConArgTys
1292 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1293 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1295 other -> returnSmpl filtered_alts
1297 -- Filter out alternatives that can't possibly match
1298 filtered_alts = case scrut_cons of
1300 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1302 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1303 not (data_con `elem` handled_data_cons)]
1304 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1305 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1308 prepareCaseAlts _ _ scrut_cons alts
1309 = returnSmpl alts -- Functions
1312 ----------------------
1313 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1314 = mapSmpl simpl_alt alts
1316 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1317 Just (tycon, inst_tys) -> inst_tys
1319 -- handled_cons is all the constructors that are dealt
1320 -- with, either by being impossible, or by there being an alternative
1321 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1323 simpl_alt (DEFAULT, _, rhs)
1324 = -- In the default case we record the constructors that the
1325 -- case-binder *can't* be.
1326 -- We take advantage of any OtherCon info in the case scrutinee
1327 modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
1328 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1329 returnSmpl (DEFAULT, [], rhs')
1331 simpl_alt (con, vs, rhs)
1332 = -- Deal with the pattern-bound variables
1333 -- Mark the ones that are in ! positions in the data constructor
1334 -- as certainly-evaluated
1335 simplBinders (add_evals con vs) $ \ vs' ->
1337 -- Bind the case-binder to (Con args)
1339 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1341 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1342 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1343 returnSmpl (con, vs', rhs')
1346 -- add_evals records the evaluated-ness of the bound variables of
1347 -- a case pattern. This is *important*. Consider
1348 -- data T = T !Int !Int
1350 -- case x of { T a b -> T (a+1) b }
1352 -- We really must record that b is already evaluated so that we don't
1353 -- go and re-evaluate it when constructing the result.
1355 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1356 add_evals other_con vs = vs
1358 cat_evals [] [] = []
1359 cat_evals (v:vs) (str:strs)
1360 | isTyVar v = v : cat_evals vs (str:strs)
1361 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1362 | otherwise = v' : cat_evals vs strs
1368 %************************************************************************
1370 \subsection{Duplicating continuations}
1372 %************************************************************************
1375 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1377 -> (SimplCont -> SimplM (OutStuff a))
1378 -> SimplM (OutStuff a)
1379 mkDupableCont ty cont thing_inside
1380 | contIsDupable cont
1383 mkDupableCont _ (CoerceIt ty cont) thing_inside
1384 = mkDupableCont ty cont $ \ cont' ->
1385 thing_inside (CoerceIt ty cont')
1387 mkDupableCont ty (InlinePlease cont) thing_inside
1388 = mkDupableCont ty cont $ \ cont' ->
1389 thing_inside (InlinePlease cont')
1391 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1392 = -- Build the RHS of the join point
1393 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1394 newId join_arg_ty' ( \ arg_id ->
1395 getSwitchChecker `thenSmpl` \ chkr ->
1396 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1397 returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs))
1398 ) `thenSmpl` \ join_rhs ->
1400 -- Build the join Id and continuation
1401 newId (coreExprType join_rhs) $ \ join_id ->
1403 new_cont = ArgOf OkToDup cont_ty
1404 (\arg' -> rebuild_done (App (Var join_id) arg'))
1407 -- Do the thing inside
1408 thing_inside new_cont `thenSmpl` \ res ->
1409 returnSmpl (addBind (NonRec join_id join_rhs) res)
1411 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1412 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1413 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1414 if exprIsDupable arg' then
1415 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1417 newId (coreExprType arg') $ \ bndr ->
1418 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1419 returnSmpl (addBind (NonRec bndr arg') res)
1421 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1422 = tick (CaseOfCase case_bndr) `thenSmpl_`
1424 simplBinder case_bndr $ \ case_bndr' ->
1425 prepareCaseCont alts cont $ \ cont' ->
1426 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1427 returnSmpl (concat alt_binds_s, alts')
1428 ) `thenSmpl` \ (alt_binds, alts') ->
1430 extendInScopes [b | NonRec b _ <- alt_binds] $
1432 -- NB that the new alternatives, alts', are still InAlts, using the original
1433 -- binders. That means we can keep the case_bndr intact. This is important
1434 -- because another case-of-case might strike, and so we want to keep the
1435 -- info that the case_bndr is dead (if it is, which is often the case).
1436 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1437 -- case in I/O rich code. We aren't allowed a lambda bound
1438 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1439 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1441 returnSmpl (addBinds alt_binds res)
1444 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1445 mkDupableAlt case_bndr case_bndr' (Stop _) alt@(con, bndrs, rhs)
1447 = -- It is worth checking for a small RHS because otherwise we
1448 -- get extra let bindings that may cause an extra iteration of the simplifier to
1449 -- inline back in place. Quite often the rhs is just a variable or constructor.
1450 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1451 -- iterations because the version with the let bindings looked big, and so wasn't
1452 -- inlined, but after the join points had been inlined it looked smaller, and so
1455 -- But since the continuation is absorbed into the rhs, we only do this
1456 -- for a Stop continuation.
1457 returnSmpl ([], alt)
1459 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1461 = -- Not worth checking whether the rhs is small; the
1462 -- inliner will inline it if so.
1463 simplBinders bndrs $ \ bndrs' ->
1464 simplExprC rhs cont `thenSmpl` \ rhs' ->
1466 rhs_ty' = coreExprType rhs'
1467 (used_bndrs, used_bndrs')
1468 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1469 (case_bndr' : bndrs'),
1470 not (isDeadBinder bndr)]
1471 -- The new binders have lost their occurrence info,
1472 -- so we have to extract it from the old ones
1474 ( if null used_bndrs'
1475 -- If we try to lift a primitive-typed something out
1476 -- for let-binding-purposes, we will *caseify* it (!),
1477 -- with potentially-disastrous strictness results. So
1478 -- instead we turn it into a function: \v -> e
1479 -- where v::State# RealWorld#. The value passed to this function
1480 -- is realworld#, which generates (almost) no code.
1482 -- There's a slight infelicity here: we pass the overall
1483 -- case_bndr to all the join points if it's used in *any* RHS,
1484 -- because we don't know its usage in each RHS separately
1486 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1487 -- we make the join point into a function whenever used_bndrs'
1488 -- is empty. This makes the join-point more CPR friendly.
1489 -- Consider: let j = if .. then I# 3 else I# 4
1490 -- in case .. of { A -> j; B -> j; C -> ... }
1492 -- Now CPR should not w/w j because it's a thunk, so
1493 -- that means that the enclosing function can't w/w either,
1494 -- which is a lose. Here's the example that happened in practice:
1495 -- kgmod :: Int -> Int -> Int
1496 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1500 then newId realWorldStatePrimTy $ \ rw_id ->
1501 returnSmpl ([rw_id], [Var realWorldPrimId])
1503 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1505 `thenSmpl` \ (final_bndrs', final_args) ->
1507 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1509 -- Notice that we make the lambdas into one-shot-lambdas. The
1510 -- join point is sure to be applied at most once, and doing so
1511 -- prevents the body of the join point being floated out by
1512 -- the full laziness pass
1513 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1514 (con, bndrs, mkApps (Var join_bndr) final_args))