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,
18 import SimplUtils ( mkCase, transformRhs, findAlt,
19 simplBinder, simplBinders, simplIds, findDefault, mkCoerce
21 import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
24 import Id ( Id, idType, idInfo, idUnique,
25 getIdUnfolding, setIdUnfolding, isExportedId,
26 getIdSpecialisation, setIdSpecialisation,
27 getIdDemandInfo, setIdDemandInfo,
28 getIdArity, setIdArity,
30 setInlinePragma, getInlinePragma, idMustBeINLINEd,
33 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
34 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
35 specInfo, inlinePragInfo, zapLamIdInfo
37 import Demand ( Demand, isStrict, wwLazy )
38 import Const ( isWHNFCon, conOkForAlt )
39 import ConFold ( tryPrimOp )
40 import PrimOp ( PrimOp, primOpStrictness, primOpType )
41 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
42 import Const ( Con(..) )
43 import Name ( isLocallyDefined )
45 import CoreFVs ( exprFreeVars )
46 import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
47 callSiteInline, blackListed
49 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
50 coreExprType, coreAltsType, exprArity, exprIsValue,
53 import Rules ( lookupRule )
54 import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
55 import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType,
56 mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
57 funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
59 import Subst ( Subst, mkSubst, emptySubst, substExpr, substTy,
60 substEnv, lookupInScope, lookupSubst, substRules
62 import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
63 import TysPrim ( realWorldStatePrimTy )
64 import PrelInfo ( realWorldPrimId )
65 import BasicTypes ( TopLevelFlag(..), isTopLevel )
66 import Maybes ( maybeToBool )
67 import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
73 The guts of the simplifier is in this module, but the driver
74 loop for the simplifier is in SimplCore.lhs.
77 %************************************************************************
81 %************************************************************************
84 simplTopBinds :: [InBind] -> SimplM [OutBind]
87 = -- Put all the top-level binders into scope at the start
88 -- so that if a transformation rule has unexpectedly brought
89 -- anything into scope, then we don't get a complaint about that.
90 -- It's rather as if the top-level binders were imported.
91 extendInScopes top_binders $
92 simpl_binds binds `thenSmpl` \ (binds', _) ->
93 freeTick SimplifierDone `thenSmpl_`
96 top_binders = bindersOfBinds binds
98 simpl_binds [] = returnSmpl ([], panic "simplTopBinds corner")
99 simpl_binds (NonRec bndr rhs : binds) = simplLazyBind TopLevel bndr bndr rhs (simpl_binds binds)
100 simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map fst pairs) (simpl_binds binds)
103 simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
104 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
105 simplRecBind top_lvl pairs bndrs' thing_inside
106 = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
107 returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
109 go [] _ = thing_inside `thenSmpl` \ stuff ->
110 returnSmpl ([], stuff)
112 go ((bndr, rhs) : pairs) (bndr' : bndrs')
113 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
114 -- Don't float unboxed bindings out,
115 -- because we can't "rec" them
119 %************************************************************************
121 \subsection[Simplify-simplExpr]{The main function: simplExpr}
123 %************************************************************************
126 addBind :: CoreBind -> OutStuff a -> OutStuff a
127 addBind bind (binds, res) = (bind:binds, res)
129 addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
130 addBinds [] stuff = stuff
131 addBinds binds1 (binds2, res) = (binds1++binds2, res)
134 The reason for this OutExprStuff stuff is that we want to float *after*
135 simplifying a RHS, not before. If we do so naively we get quadratic
136 behaviour as things float out.
138 To see why it's important to do it after, consider this (real) example:
152 a -- Can't inline a this round, cos it appears twice
156 Each of the ==> steps is a round of simplification. We'd save a
157 whole round if we float first. This can cascade. Consider
162 let f = let d1 = ..d.. in \y -> e
166 in \x -> ...(\y ->e)...
168 Only in this second round can the \y be applied, and it
169 might do the same again.
173 simplExpr :: CoreExpr -> SimplM CoreExpr
174 simplExpr expr = getSubst `thenSmpl` \ subst ->
175 simplExprC expr (Stop (substTy subst (coreExprType expr)))
176 -- The type in the Stop continuation is usually not used
177 -- It's only needed when discarding continuations after finding
178 -- a function that returns bottom
180 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
181 -- Simplify an expression, given a continuation
183 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
184 returnSmpl (mkLets floats body)
186 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
187 -- Simplify an expression, returning floated binds
189 simplExprF (Var v) cont
192 simplExprF expr@(Con (PrimOp op) args) cont
193 = getSubstEnv `thenSmpl` \ se ->
196 (primOpStrictness op)
197 (pushArgs se args cont) $ \ args1 cont1 ->
200 -- Boring... we may have too many arguments now, so we push them back
202 args2 = ASSERT( length args1 >= n_args )
204 cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
206 -- Try the prim op simplification
207 -- It's really worth trying simplExpr again if it succeeds,
208 -- because you can find
209 -- case (eqChar# x 'a') of ...
211 -- case (case x of 'a' -> True; other -> False) of ...
212 case tryPrimOp op args2 of
213 Just e' -> zapSubstEnv (simplExprF e' cont2)
214 Nothing -> rebuild (Con (PrimOp op) args2) cont2
216 simplExprF (Con con@(DataCon _) args) cont
217 = freeTick LeafVisit `thenSmpl_`
218 simplConArgs args ( \ args' ->
219 rebuild (Con con args') cont)
221 simplExprF expr@(Con con@(Literal _) args) cont
222 = ASSERT( null args )
223 freeTick LeafVisit `thenSmpl_`
226 simplExprF (App fun arg) cont
227 = getSubstEnv `thenSmpl` \ se ->
228 simplExprF fun (ApplyTo NoDup arg se cont)
230 simplExprF (Case scrut bndr alts) cont
231 = getSubstEnv `thenSmpl` \ se ->
232 simplExprF scrut (Select NoDup bndr alts se cont)
235 simplExprF (Let (Rec pairs) body) cont
236 = simplIds (map fst pairs) $ \ bndrs' ->
237 -- NB: bndrs' don't have unfoldings or spec-envs
238 -- We add them as we go down, using simplPrags
240 simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
242 simplExprF expr@(Lam _ _) cont = simplLam expr cont
244 simplExprF (Type ty) cont
245 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
246 simplType ty `thenSmpl` \ ty' ->
247 rebuild (Type ty') cont
249 simplExprF (Note (Coerce to from) e) cont
250 | to == from = simplExprF e cont
251 | otherwise = getSubst `thenSmpl` \ subst ->
252 simplExprF e (CoerceIt (substTy subst to) cont)
254 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
255 -- inlining. All other CCCSs are mapped to currentCCS.
256 simplExprF (Note (SCC cc) e) cont
257 = setEnclosingCC currentCCS $
258 simplExpr e `thenSmpl` \ e ->
259 rebuild (mkNote (SCC cc) e) cont
261 simplExprF (Note InlineCall e) cont
262 = simplExprF e (InlinePlease cont)
264 -- Comments about the InlineMe case
265 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
266 -- Don't inline in the RHS of something that has an
267 -- inline pragma. But be careful that the InScopeEnv that
268 -- we return does still have inlinings on!
270 -- It really is important to switch off inlinings. This function
271 -- may be inlinined in other modules, so we don't want to remove
272 -- (by inlining) calls to functions that have specialisations, or
273 -- that may have transformation rules in an importing scope.
274 -- E.g. {-# INLINE f #-}
276 -- and suppose that g is strict *and* has specialisations.
277 -- If we inline g's wrapper, we deny f the chance of getting
278 -- the specialised version of g when f is inlined at some call site
279 -- (perhaps in some other module).
281 simplExprF (Note InlineMe e) cont
283 Stop _ -> -- Totally boring continuation
284 -- Don't inline inside an INLINE expression
285 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
286 rebuild (mkNote InlineMe e') cont
288 other -> -- Dissolve the InlineMe note if there's
289 -- an interesting context of any kind to combine with
290 -- (even a type application -- anything except Stop)
293 -- A non-recursive let is dealt with by simplBeta
294 simplExprF (Let (NonRec bndr rhs) body) cont
295 = getSubstEnv `thenSmpl` \ se ->
296 simplBeta bndr rhs se (contResultType cont) $
301 ---------------------------------
307 zap_it = mkLamBndrZapper fun (countArgs cont)
308 cont_ty = contResultType cont
310 -- Type-beta reduction
311 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
312 = ASSERT( isTyVar bndr )
313 tick (BetaReduction bndr) `thenSmpl_`
314 getInScope `thenSmpl` \ in_scope ->
316 ty' = substTy (mkSubst in_scope arg_se) ty_arg
318 extendSubst bndr (DoneTy ty')
321 -- Ordinary beta reduction
322 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
323 = tick (BetaReduction bndr) `thenSmpl_`
324 simplBeta zapped_bndr arg arg_se cont_ty
327 zapped_bndr = zap_it bndr
330 go lam@(Lam _ _) cont = completeLam [] lam cont
332 -- Exactly enough args
333 go expr cont = simplExprF expr cont
336 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
337 -- continuation. Try for eta reduction, but *only* if we get all
338 -- the way to an exprIsTrivial expression.
339 -- 'acc' holds the simplified binders, in reverse order
341 completeLam acc (Lam bndr body) cont
342 = simplBinder bndr $ \ bndr' ->
343 completeLam (bndr':acc) body cont
345 completeLam acc body cont
346 = simplExpr body `thenSmpl` \ body' ->
348 case (opt_SimplDoEtaReduction, check_eta acc body') of
349 (True, Just body'') -- Eta reduce!
350 -> tick (EtaReduction (head acc)) `thenSmpl_`
353 other -> -- No eta reduction
354 rebuild (foldl (flip Lam) body' acc) cont
355 -- Remember, acc is the reversed binders
357 -- NB: the binders are reversed
358 check_eta (b : bs) (App fun arg)
359 | (varToCoreExpr b `cheapEqExpr` arg)
363 | exprIsTrivial body && -- ONLY if the body is trivial
364 not (any (`elemVarSet` body_fvs) acc)
365 = Just body -- Success!
367 body_fvs = exprFreeVars body
369 check_eta _ _ = Nothing -- Bale out
371 mkLamBndrZapper :: CoreExpr -- Function
372 -> Int -- Number of args
373 -> Id -> Id -- Use this to zap the binders
374 mkLamBndrZapper fun n_args
375 | n_args >= n_params fun = \b -> b -- Enough args
376 | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
378 n_params (Lam b e) | isId b = 1 + n_params e
379 | otherwise = n_params e
380 n_params other = 0::Int
384 ---------------------------------
385 simplConArgs makes sure that the arguments all end up being atomic.
386 That means it may generate some Lets, hence the strange type
389 simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
390 simplConArgs [] thing_inside
393 simplConArgs (arg:args) thing_inside
394 = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
395 -- Simplify the RHS with inlining switched off, so that
396 -- only absolutely essential things will happen.
398 simplConArgs args $ \ args' ->
400 -- If the argument ain't trivial, then let-bind it
401 if exprIsTrivial arg' then
402 thing_inside (arg' : args')
404 newId (coreExprType arg') $ \ arg_id ->
405 thing_inside (Var arg_id : args') `thenSmpl` \ res ->
406 returnSmpl (addBind (NonRec arg_id arg') res)
410 ---------------------------------
412 simplType :: InType -> SimplM OutType
414 = getSubst `thenSmpl` \ subst ->
415 returnSmpl (substTy subst ty)
419 %************************************************************************
423 %************************************************************************
425 @simplBeta@ is used for non-recursive lets in expressions,
426 as well as true beta reduction.
428 Very similar to @simplLazyBind@, but not quite the same.
431 simplBeta :: InId -- Binder
432 -> InExpr -> SubstEnv -- Arg, with its subst-env
433 -> OutType -- Type of thing computed by the context
434 -> SimplM OutExprStuff -- The body
435 -> SimplM OutExprStuff
437 simplBeta bndr rhs rhs_se cont_ty thing_inside
439 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
442 simplBeta bndr rhs rhs_se cont_ty thing_inside
443 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
444 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
445 extendSubst bndr (ContEx rhs_se rhs) thing_inside
448 = -- Simplify the RHS
449 simplBinder bndr $ \ bndr' ->
450 simplArg (idType bndr') (getIdDemandInfo bndr)
451 rhs rhs_se cont_ty $ \ rhs' ->
453 -- Now complete the binding and simplify the body
454 completeBeta bndr bndr' rhs' thing_inside
456 completeBeta bndr bndr' rhs' thing_inside
457 | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
458 -- Make a case expression instead of a let
459 -- These can arise either from the desugarer,
460 -- or from beta reductions: (\x.e) (x +# y)
461 = getInScope `thenSmpl` \ in_scope ->
462 thing_inside `thenSmpl` \ (floats, (_, body)) ->
463 returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
466 = completeBinding bndr bndr' rhs' thing_inside
471 simplArg :: OutType -> Demand
472 -> InExpr -> SubstEnv
473 -> OutType -- Type of thing computed by the context
474 -> (OutExpr -> SimplM OutExprStuff)
475 -> SimplM OutExprStuff
476 simplArg arg_ty demand arg arg_se cont_ty thing_inside
478 isUnLiftedType arg_ty ||
479 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
480 -- Return true only for dictionary types where the dictionary
481 -- has more than one component (else we risk poking on the component
482 -- of a newtype dictionary)
483 = getSubstEnv `thenSmpl` \ body_se ->
484 transformRhs arg `thenSmpl` \ t_arg ->
485 setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
486 setSubstEnv body_se (thing_inside arg')
487 )) -- NB: we must restore body_se before carrying on with thing_inside!!
490 = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
495 - deals only with Ids, not TyVars
496 - take an already-simplified RHS
498 It does *not* attempt to do let-to-case. Why? Because they are used for
501 (when let-to-case is impossible)
503 - many situations where the "rhs" is known to be a WHNF
504 (so let-to-case is inappropriate).
507 completeBinding :: InId -- Binder
508 -> OutId -- New binder
509 -> OutExpr -- Simplified RHS
510 -> SimplM (OutStuff a) -- Thing inside
511 -> SimplM (OutStuff a)
513 completeBinding old_bndr new_bndr new_rhs thing_inside
514 | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
515 -- known constructor: case (a,b) of x { (p,q) -> ... }
516 -- Here x isn't mentioned in the RHS, so we don't want to
517 -- create the (dead) let-binding let x = (a,b) in ...
520 | postInlineUnconditionally old_bndr new_rhs
521 -- Maybe we don't need a let-binding! Maybe we can just
522 -- inline it right away. Unlike the preInlineUnconditionally case
523 -- we are allowed to look at the RHS.
525 -- NB: a loop breaker never has postInlineUnconditionally True
526 -- and non-loop-breakers only have *forward* references
527 -- Hence, it's safe to discard the binding
528 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
529 extendSubst old_bndr (DoneEx new_rhs)
533 = getSubst `thenSmpl` \ subst ->
535 bndr_info = idInfo old_bndr
536 old_rules = specInfo bndr_info
537 new_rules = substRules subst old_rules
539 -- The new binding site Id needs its specialisations re-attached
540 bndr_w_arity = new_bndr `setIdArity` ArityAtLeast (exprArity new_rhs)
543 | isEmptyCoreRules old_rules = bndr_w_arity
544 | otherwise = bndr_w_arity `setIdSpecialisation` new_rules
546 -- At the occurrence sites we want to know the unfolding,
547 -- and the occurrence info of the original
548 -- (simplBinder cleaned up the inline prag of the original
549 -- to eliminate un-stable info, in case this expression is
550 -- simplified a second time; hence the need to reattach it)
551 occ_site_id = binding_site_id
552 `setIdUnfolding` mkUnfolding new_rhs
553 `setInlinePragma` inlinePragInfo bndr_info
555 modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
556 returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff)
560 %************************************************************************
562 \subsection{simplLazyBind}
564 %************************************************************************
566 simplLazyBind basically just simplifies the RHS of a let(rec).
567 It does two important optimisations though:
569 * It floats let(rec)s out of the RHS, even if they
570 are hidden by big lambdas
572 * It does eta expansion
575 simplLazyBind :: TopLevelFlag
578 -> SimplM (OutStuff a) -- The body of the binding
579 -> SimplM (OutStuff a)
580 -- When called, the subst env is correct for the entire let-binding
581 -- and hence right for the RHS.
582 -- Also the binder has already been simplified, and hence is in scope
584 simplLazyBind top_lvl bndr bndr' rhs thing_inside
585 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
586 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
587 getSubstEnv `thenSmpl` \ rhs_se ->
588 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
591 = -- Simplify the RHS
592 getSubstEnv `thenSmpl` \ rhs_se ->
594 simplRhs top_lvl False {- Not ok to float unboxed -}
596 rhs rhs_se $ \ rhs' ->
598 -- Now compete the binding and simplify the body
599 completeBinding bndr bndr' rhs' thing_inside
605 simplRhs :: TopLevelFlag
606 -> Bool -- True <=> OK to float unboxed (speculative) bindings
607 -> OutType -> InExpr -> SubstEnv
608 -> (OutExpr -> SimplM (OutStuff a))
609 -> SimplM (OutStuff a)
610 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
611 = -- Swizzle the inner lets past the big lambda (if any)
612 -- and try eta expansion
613 transformRhs rhs `thenSmpl` \ t_rhs ->
616 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
618 -- Float lets out of RHS
620 (floats_out, rhs'') | float_ubx = (floats, rhs')
621 | otherwise = splitFloats floats rhs'
623 if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
624 not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
626 tickLetFloat floats_out `thenSmpl_`
629 -- There's a subtlety here. There may be a binding (x* = e) in the
630 -- floats, where the '*' means 'will be demanded'. So is it safe
631 -- to float it out? Answer no, but it won't matter because
632 -- we only float if arg' is a WHNF,
633 -- and so there can't be any 'will be demanded' bindings in the floats.
635 WARN( any demanded_float floats_out, ppr floats_out )
636 setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
637 -- in_scope' may be excessive, but that's OK;
638 -- it's a superset of what's in scope
639 returnSmpl (addBinds floats_out stuff)
641 -- Don't do the float
642 thing_inside (mkLets floats rhs')
644 -- In a let-from-let float, we just tick once, arbitrarily
645 -- choosing the first floated binder to identify it
646 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
647 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
649 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
650 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
651 demanded_float (Rec _) = False
653 -- Don't float any unlifted bindings out, because the context
654 -- is either a Rec group, or the top level, neither of which
655 -- can tolerate them.
656 splitFloats floats rhs
660 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
661 | otherwise = case go fs of
662 (out, rhs') -> (f:out, rhs')
664 must_stay (Rec prs) = False -- No unlifted bindings in here
665 must_stay (NonRec b r) = isUnLiftedType (idType b)
670 %************************************************************************
672 \subsection{Variables}
674 %************************************************************************
678 = freeTick LeafVisit `thenSmpl_`
679 getSubst `thenSmpl` \ subst ->
680 case lookupSubst subst var of
681 Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
682 Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
683 Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
686 var' = case lookupInScope subst var of
690 if isLocallyDefined var && not (idMustBeINLINEd var)
691 -- The idMustBeINLINEd test accouunts for the fact
692 -- that class dictionary constructors don't have top level
693 -- bindings and hence aren't in scope.
696 pprTrace "simplVar:" (ppr var) var
701 getBlackList `thenSmpl` \ black_list ->
702 getInScope `thenSmpl` \ in_scope ->
703 completeCall black_list in_scope var' cont
705 ---------------------------------------------------------
706 -- Dealing with a call
708 completeCall black_list_fn in_scope var cont
709 -- Look for rules or specialisations that match
710 -- Do this *before* trying inlining because some functions
711 -- have specialisations *and* are strict; we don't want to
712 -- inline the wrapper of the non-specialised thing... better
713 -- to call the specialised thing instead.
714 | maybeToBool maybe_rule_match
715 = tick (RuleFired rule_name) `thenSmpl_`
716 zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args result_cont))
717 -- See note below about zapping the substitution here
719 -- Look for an unfolding. There's a binding for the
720 -- thing, but perhaps we want to inline it anyway
721 | maybeToBool maybe_inline
722 = tick (UnfoldingDone var) `thenSmpl_`
723 zapSubstEnv (completeInlining var unf_template discard_inline_cont)
724 -- The template is already simplified, so don't re-substitute.
725 -- This is VITAL. Consider
727 -- let y = \z -> ...x... in
729 -- We'll clone the inner \x, adding x->x' in the id_subst
730 -- Then when we inline y, we must *not* replace x by x' in
731 -- the inlined copy!!
733 | otherwise -- Neither rule nor inlining
734 -- Use prepareArgs to use function strictness
735 = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
736 rebuild (mkApps (Var var) args') cont'
739 get_str var = case getIdStrictness var of
740 NoStrictnessInfo -> (repeat wwLazy, False)
741 StrictnessInfo demands result_bot -> (demands, result_bot)
744 (args', result_cont) = contArgs in_scope cont
745 inline_call = contIsInline result_cont
746 interesting_cont = contIsInteresting result_cont
747 discard_inline_cont | inline_call = discardInline cont
750 ---------- Unfolding stuff
751 maybe_inline = callSiteInline black_listed inline_call
752 var args' interesting_cont
753 Just unf_template = maybe_inline
754 black_listed = black_list_fn var
756 ---------- Specialisation stuff
757 maybe_rule_match = lookupRule in_scope var args'
758 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
761 -- First a special case
762 -- Don't actually inline the scrutinee when we see
763 -- case x of y { .... }
764 -- and x has unfolding (C a b). Why not? Because
765 -- we get a silly binding y = C a b. If we don't
766 -- inline knownCon can directly substitute x for y instead.
767 completeInlining var (Con con con_args) (Select _ bndr alts se cont)
769 = knownCon (Var var) con con_args bndr alts se cont
771 -- Now the normal case
772 completeInlining var unfolding cont
773 = simplExprF unfolding cont
775 ----------- costCentreOk
776 -- costCentreOk checks that it's ok to inline this thing
777 -- The time it *isn't* is this:
779 -- f x = let y = E in
780 -- scc "foo" (...y...)
782 -- Here y has a "current cost centre", and we can't inline it inside "foo",
783 -- regardless of whether E is a WHNF or not.
785 costCentreOk ccs_encl cc_rhs
786 = not opt_SccProfilingOn
787 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
788 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
793 ---------------------------------------------------------
794 -- Preparing arguments for a call
796 prepareArgs :: SDoc -- Error message info
797 -> OutType -> ([Demand],Bool) -> SimplCont
798 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
799 -> SimplM OutExprStuff
801 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
802 = go [] demands orig_fun_ty orig_cont
804 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
805 -- "No strictness info" is signalled by an infinite list of wwLazy
807 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
808 | result_bot = fun_demands -- Enough args, and function returns bottom
809 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
810 -- NB: demands is finite iff enough args and result_bot is True
812 -- Main game plan: loop through the arguments, simplifying
813 -- each of them in turn. We carry with us a list of demands,
814 -- and the type of the function-applied-to-earlier-args
817 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
818 = getInScope `thenSmpl` \ in_scope ->
820 ty_arg' = substTy (mkSubst in_scope se) ty_arg
821 res_ty = applyTy fun_ty ty_arg'
823 go (Type ty_arg' : acc) ds res_ty cont
826 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
827 = case splitFunTy_maybe fun_ty of {
828 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
829 (thing_inside (reverse acc) cont) ;
830 Just (arg_ty, res_ty) ->
831 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
832 go (arg':acc) ds res_ty cont }
834 -- We've run out of demands, which only happens for functions
835 -- we *know* now return bottom
837 -- * case (error "hello") of { ... }
838 -- * (error "Hello") arg
839 -- * f (error "Hello") where f is strict
841 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
842 thing_inside (reverse acc) (discardCont cont)
844 -- We're run out of arguments
845 go acc ds fun_ty cont = thing_inside (reverse acc) cont
847 -- Boring: we must only record a tick if there was an interesting
848 -- continuation to discard. If not, we tick forever.
849 tick_case_of_error (Stop _) = returnSmpl ()
850 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
851 tick_case_of_error other = tick BottomFound
854 %************************************************************************
856 \subsection{Decisions about inlining}
858 %************************************************************************
861 preInlineUnconditionally :: InId -> Bool
862 -- Examines a bndr to see if it is used just once in a
863 -- completely safe way, so that it is safe to discard the binding
864 -- inline its RHS at the (unique) usage site, REGARDLESS of how
865 -- big the RHS might be. If this is the case we don't simplify
866 -- the RHS first, but just inline it un-simplified.
868 -- This is much better than first simplifying a perhaps-huge RHS
869 -- and then inlining and re-simplifying it.
871 -- NB: we don't even look at the RHS to see if it's trivial
874 -- where x is used many times, but this is the unique occurrence
875 -- of y. We should NOT inline x at all its uses, because then
876 -- we'd do the same for y -- aargh! So we must base this
877 -- pre-rhs-simplification decision solely on x's occurrences, not
880 -- Evne RHSs labelled InlineMe aren't caught here, because
881 -- there might be no benefit from inlining at the call site.
882 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
883 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
884 preInlineUnconditionally bndr
885 = case getInlinePragma bndr of
886 IMustBeINLINEd -> True
887 ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
888 -- one occurrence ==> safe!
892 postInlineUnconditionally :: InId -> OutExpr -> Bool
893 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
894 -- It returns True if it's ok to discard the binding and inline the
895 -- RHS at every use site.
897 -- NOTE: This isn't our last opportunity to inline.
898 -- We're at the binding site right now, and
899 -- we'll get another opportunity when we get to the ocurrence(s)
901 postInlineUnconditionally bndr rhs
905 = case getInlinePragma bndr of
906 IAmALoopBreaker -> False
908 ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
909 -- Don't inline even WHNFs inside lambdas; doing so may
910 -- simply increase allocation when the function is called
911 -- This isn't the last chance; see NOTE above.
913 ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
914 -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
915 -- decision about duplicating code is best left to callSiteInline
917 other -> exprIsTrivial rhs -- Duplicating is *free*
918 -- NB: Even InlineMe and IMustBeINLINEd are ignored here
919 -- Why? Because we don't even want to inline them into the
920 -- RHS of constructor arguments. See NOTE above
921 -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
922 -- it's best to inline it anyway. We often get a=E; b=a
923 -- from desugaring, with both a and b marked NOINLINE.
928 %************************************************************************
930 \subsection{The main rebuilder}
932 %************************************************************************
935 -------------------------------------------------------------------
938 = getInScope `thenSmpl` \ in_scope ->
939 returnSmpl ([], (in_scope, expr))
941 ---------------------------------------------------------
942 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
945 rebuild expr (Stop _) = rebuild_done expr
947 -- ArgOf continuation
948 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
950 -- ApplyTo continuation
951 rebuild expr cont@(ApplyTo _ arg se cont')
952 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
953 rebuild (App expr arg') cont'
955 -- Coerce continuation
956 rebuild expr (CoerceIt to_ty cont)
957 = rebuild (mkCoerce to_ty expr) cont
959 -- Inline continuation
960 rebuild expr (InlinePlease cont)
961 = rebuild (Note InlineCall expr) cont
963 -- Case of known constructor or literal
964 rebuild expr@(Con con args) (Select _ bndr alts se cont)
965 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
966 = knownCon expr con args bndr alts se cont
969 ---------------------------------------------------------
970 -- The other Select cases
972 rebuild scrut (Select _ bndr alts se cont)
973 | -- Check that the RHSs are all the same, and
974 -- don't use the binders in the alternatives
975 -- This test succeeds rapidly in the common case of
976 -- a single DEFAULT alternative
977 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
979 -- Check that the scrutinee can be let-bound instead of case-bound
980 && ( (isUnLiftedType (idType bndr) && -- It's unlifted and floatable
981 exprOkForSpeculation scrut) -- NB: scrut = an unboxed variable satisfies
982 || exprIsValue scrut -- It's already evaluated
983 || var_demanded_later scrut -- It'll be demanded later
985 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
986 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
987 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
988 -- its argument: case x of { y -> dataToTag# y }
989 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
990 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
994 && opt_SimplDoCaseElim
995 = -- Get rid of the case altogether
996 -- See the extensive notes on case-elimination below
997 -- Remember to bind the binder though!
998 tick (CaseElim bndr) `thenSmpl_` (
1000 simplBinder bndr $ \ bndr' ->
1001 completeBinding bndr bndr' scrut $
1002 simplExprF rhs1 cont)
1005 = rebuild_case scrut bndr alts se cont
1007 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1008 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1010 var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1011 var_demanded_later other = False
1014 Case elimination [see the code above]
1016 Start with a simple situation:
1018 case x# of ===> e[x#/y#]
1021 (when x#, y# are of primitive type, of course). We can't (in general)
1022 do this for algebraic cases, because we might turn bottom into
1025 Actually, we generalise this idea to look for a case where we're
1026 scrutinising a variable, and we know that only the default case can
1031 other -> ...(case x of
1035 Here the inner case can be eliminated. This really only shows up in
1036 eliminating error-checking code.
1038 We also make sure that we deal with this very common case:
1043 Here we are using the case as a strict let; if x is used only once
1044 then we want to inline it. We have to be careful that this doesn't
1045 make the program terminate when it would have diverged before, so we
1047 - x is used strictly, or
1048 - e is already evaluated (it may so if e is a variable)
1050 Lastly, we generalise the transformation to handle this:
1056 We only do this for very cheaply compared r's (constructors, literals
1057 and variables). If pedantic bottoms is on, we only do it when the
1058 scrutinee is a PrimOp which can't fail.
1060 We do it *here*, looking at un-simplified alternatives, because we
1061 have to check that r doesn't mention the variables bound by the
1062 pattern in each alternative, so the binder-info is rather useful.
1064 So the case-elimination algorithm is:
1066 1. Eliminate alternatives which can't match
1068 2. Check whether all the remaining alternatives
1069 (a) do not mention in their rhs any of the variables bound in their pattern
1070 and (b) have equal rhss
1072 3. Check we can safely ditch the case:
1073 * PedanticBottoms is off,
1074 or * the scrutinee is an already-evaluated variable
1075 or * the scrutinee is a primop which is ok for speculation
1076 -- ie we want to preserve divide-by-zero errors, and
1077 -- calls to error itself!
1079 or * [Prim cases] the scrutinee is a primitive variable
1081 or * [Alg cases] the scrutinee is a variable and
1082 either * the rhs is the same variable
1083 (eg case x of C a b -> x ===> x)
1084 or * there is only one alternative, the default alternative,
1085 and the binder is used strictly in its scope.
1086 [NB this is helped by the "use default binder where
1087 possible" transformation; see below.]
1090 If so, then we can replace the case with one of the rhss.
1093 Blob of helper functions for the "case-of-something-else" situation.
1096 ---------------------------------------------------------
1097 -- Case of something else
1099 rebuild_case scrut case_bndr alts se cont
1100 = -- Prepare case alternatives
1101 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1102 scrut_cons alts `thenSmpl` \ better_alts ->
1104 -- Set the new subst-env in place (before dealing with the case binder)
1107 -- Deal with the case binder, and prepare the continuation;
1108 -- The new subst_env is in place
1109 prepareCaseCont better_alts cont $ \ cont' ->
1112 -- Deal with variable scrutinee
1113 ( simplBinder case_bndr $ \ case_bndr' ->
1114 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1116 case_bndr'' = zap_occ_info case_bndr'
1119 -- Deal with the case alternaatives
1120 simplAlts zap_occ_info scrut_cons
1121 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1123 mkCase scrut case_bndr'' alts'
1124 ) `thenSmpl` \ case_expr ->
1126 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1127 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1128 -- that should not include these chaps!
1129 rebuild_done case_expr
1131 -- scrut_cons tells what constructors the scrutinee can't possibly match
1132 scrut_cons = case scrut of
1133 Var v -> otherCons (getIdUnfolding v)
1137 knownCon expr con args bndr alts se cont
1138 = tick (KnownBranch bndr) `thenSmpl_`
1140 simplBinder bndr $ \ bndr' ->
1141 case findAlt con alts of
1142 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1143 completeBinding bndr bndr' expr $
1144 -- Don't use completeBeta here. The expr might be
1145 -- an unboxed literal, like 3, or a variable
1146 -- whose unfolding is an unboxed literal... and
1147 -- completeBeta will just construct another case
1151 (Literal lit, bs, rhs) -> ASSERT( null bs )
1152 extendSubst bndr (DoneEx expr) $
1153 -- Unconditionally substitute, because expr must
1154 -- be a variable or a literal. It can't be a
1155 -- NoRep literal because they don't occur in
1159 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1160 completeBinding bndr bndr' expr $
1162 extendSubstList bs (map mk real_args) $
1165 real_args = drop (dataConNumInstArgs dc) args
1166 mk (Type ty) = DoneTy ty
1167 mk other = DoneEx other
1172 prepareCaseCont :: [InAlt] -> SimplCont
1173 -> (SimplCont -> SimplM (OutStuff a))
1174 -> SimplM (OutStuff a)
1175 -- Polymorphic recursion here!
1177 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1178 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1181 substForVarScrut checks whether the scrutinee is a variable, v.
1182 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1183 that way, there's a chance that v will now only be used once, and hence inlined.
1185 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1186 in the case binder, because the case-binder now effectively occurs
1187 whenever v does. AND we have to do the same for the pattern-bound
1190 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1192 Here, b and p are dead. But when we move the argment inside the first
1193 case RHS, and eliminate the second case, we get
1195 case x or { (a,b) -> a b }
1197 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1198 happened. Hence the zap_occ_info function returned by substForVarScrut
1201 substForVarScrut (Var v) case_bndr' thing_inside
1202 | isLocallyDefined v -- No point for imported things
1203 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1204 `setInlinePragma` IMustBeINLINEd) $
1205 -- We could extend the substitution instead, but it would be
1206 -- a hack because then the substitution wouldn't be idempotent
1208 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1210 substForVarScrut other_scrut case_bndr' thing_inside
1211 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1214 prepareCaseAlts does two things:
1216 1. Remove impossible alternatives
1218 2. If the DEFAULT alternative can match only one possible constructor,
1219 then make that constructor explicit.
1221 case e of x { DEFAULT -> rhs }
1223 case e of x { (a,b) -> rhs }
1224 where the type is a single constructor type. This gives better code
1225 when rhs also scrutinises x or e.
1228 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1230 = case (findDefault filtered_alts, missing_cons) of
1232 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1233 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1235 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1237 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1239 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1240 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1242 newIds (dataConArgTys
1244 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1245 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1247 other -> returnSmpl filtered_alts
1249 -- Filter out alternatives that can't possibly match
1250 filtered_alts = case scrut_cons of
1252 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1254 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1255 not (data_con `elem` handled_data_cons)]
1256 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1257 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1260 prepareCaseAlts _ _ scrut_cons alts
1261 = returnSmpl alts -- Functions
1264 ----------------------
1265 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1266 = mapSmpl simpl_alt alts
1268 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1269 Just (tycon, inst_tys) -> inst_tys
1271 -- handled_cons is all the constructors that are dealt
1272 -- with, either by being impossible, or by there being an alternative
1273 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1275 simpl_alt (DEFAULT, _, rhs)
1276 = -- In the default case we record the constructors that the
1277 -- case-binder *can't* be.
1278 -- We take advantage of any OtherCon info in the case scrutinee
1279 modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
1280 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1281 returnSmpl (DEFAULT, [], rhs')
1283 simpl_alt (con, vs, rhs)
1284 = -- Deal with the pattern-bound variables
1285 -- Mark the ones that are in ! positions in the data constructor
1286 -- as certainly-evaluated
1287 simplBinders (add_evals con vs) $ \ vs' ->
1289 -- Bind the case-binder to (Con args)
1291 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1293 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1294 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1295 returnSmpl (con, vs', rhs')
1298 -- add_evals records the evaluated-ness of the bound variables of
1299 -- a case pattern. This is *important*. Consider
1300 -- data T = T !Int !Int
1302 -- case x of { T a b -> T (a+1) b }
1304 -- We really must record that b is already evaluated so that we don't
1305 -- go and re-evaluate it when constructing the result.
1307 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1308 add_evals other_con vs = vs
1310 cat_evals [] [] = []
1311 cat_evals (v:vs) (str:strs)
1312 | isTyVar v = v : cat_evals vs (str:strs)
1313 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1314 | otherwise = v' : cat_evals vs strs
1320 %************************************************************************
1322 \subsection{Duplicating continuations}
1324 %************************************************************************
1327 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1329 -> (SimplCont -> SimplM (OutStuff a))
1330 -> SimplM (OutStuff a)
1331 mkDupableCont ty cont thing_inside
1332 | contIsDupable cont
1335 mkDupableCont _ (CoerceIt ty cont) thing_inside
1336 = mkDupableCont ty cont $ \ cont' ->
1337 thing_inside (CoerceIt ty cont')
1339 mkDupableCont ty (InlinePlease cont) thing_inside
1340 = mkDupableCont ty cont $ \ cont' ->
1341 thing_inside (InlinePlease cont')
1343 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1344 = -- Build the RHS of the join point
1345 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1346 newId join_arg_ty' ( \ arg_id ->
1347 getSwitchChecker `thenSmpl` \ chkr ->
1348 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1349 returnSmpl (Lam arg_id (mkLets binds rhs))
1350 ) `thenSmpl` \ join_rhs ->
1352 -- Build the join Id and continuation
1353 newId (coreExprType join_rhs) $ \ join_id ->
1355 new_cont = ArgOf OkToDup cont_ty
1356 (\arg' -> rebuild_done (App (Var join_id) arg'))
1359 -- Do the thing inside
1360 thing_inside new_cont `thenSmpl` \ res ->
1361 returnSmpl (addBind (NonRec join_id join_rhs) res)
1363 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1364 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1365 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1366 if exprIsDupable arg' then
1367 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1369 newId (coreExprType arg') $ \ bndr ->
1370 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1371 returnSmpl (addBind (NonRec bndr arg') res)
1373 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1374 = tick (CaseOfCase case_bndr) `thenSmpl_`
1376 simplBinder case_bndr $ \ case_bndr' ->
1377 prepareCaseCont alts cont $ \ cont' ->
1378 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1379 returnSmpl (concat alt_binds_s, alts')
1380 ) `thenSmpl` \ (alt_binds, alts') ->
1382 extendInScopes [b | NonRec b _ <- alt_binds] $
1384 -- NB that the new alternatives, alts', are still InAlts, using the original
1385 -- binders. That means we can keep the case_bndr intact. This is important
1386 -- because another case-of-case might strike, and so we want to keep the
1387 -- info that the case_bndr is dead (if it is, which is often the case).
1388 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1389 -- case in I/O rich code. We aren't allowed a lambda bound
1390 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1391 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1393 returnSmpl (addBinds alt_binds res)
1396 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1397 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1398 = -- Not worth checking whether the rhs is small; the
1399 -- inliner will inline it if so.
1400 simplBinders bndrs $ \ bndrs' ->
1401 simplExprC rhs cont `thenSmpl` \ rhs' ->
1403 rhs_ty' = coreExprType rhs'
1404 (used_bndrs, used_bndrs')
1405 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1406 (case_bndr' : bndrs'),
1407 not (isDeadBinder bndr)]
1408 -- The new binders have lost their occurrence info,
1409 -- so we have to extract it from the old ones
1411 ( if null used_bndrs'
1412 -- If we try to lift a primitive-typed something out
1413 -- for let-binding-purposes, we will *caseify* it (!),
1414 -- with potentially-disastrous strictness results. So
1415 -- instead we turn it into a function: \v -> e
1416 -- where v::State# RealWorld#. The value passed to this function
1417 -- is realworld#, which generates (almost) no code.
1419 -- There's a slight infelicity here: we pass the overall
1420 -- case_bndr to all the join points if it's used in *any* RHS,
1421 -- because we don't know its usage in each RHS separately
1423 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1424 -- we make the join point into a function whenever used_bndrs'
1425 -- is empty. This makes the join-point more CPR friendly.
1426 -- Consider: let j = if .. then I# 3 else I# 4
1427 -- in case .. of { A -> j; B -> j; C -> ... }
1429 -- Now CPR should not w/w j because it's a thunk, so
1430 -- that means that the enclosing function can't w/w either,
1431 -- which is a lose. Here's the example that happened in practice:
1432 -- kgmod :: Int -> Int -> Int
1433 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1437 then newId realWorldStatePrimTy $ \ rw_id ->
1438 returnSmpl ([rw_id], [Var realWorldPrimId])
1440 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1442 `thenSmpl` \ (final_bndrs', final_args) ->
1444 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1446 -- Notice that we make the lambdas into one-shot-lambdas. The
1447 -- join point is sure to be applied at most once, and doing so
1448 -- prevents the body of the join point being floated out by
1449 -- the full laziness pass
1450 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1451 (con, bndrs, mkApps (Var join_bndr) final_args))