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,
29 setInlinePragma, getInlinePragma, idMustBeINLINEd,
32 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
33 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
34 specInfo, inlinePragInfo, zapLamIdInfo
36 import Demand ( Demand, isStrict, wwLazy )
37 import Const ( isWHNFCon, conOkForAlt )
38 import ConFold ( tryPrimOp )
39 import PrimOp ( PrimOp, primOpStrictness, primOpType )
40 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
41 import Const ( Con(..) )
42 import Name ( isLocallyDefined )
44 import CoreFVs ( exprFreeVars )
45 import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
46 callSiteInline, blackListed
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,
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, substRules
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 bndr rhs (simpl_binds binds)
99 simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map fst pairs) (simpl_binds binds)
102 simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
103 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
104 simplRecBind top_lvl pairs bndrs' thing_inside
105 = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
106 returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
108 go [] _ = thing_inside `thenSmpl` \ stuff ->
109 returnSmpl ([], stuff)
111 go ((bndr, rhs) : pairs) (bndr' : bndrs')
112 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
113 -- Don't float unboxed bindings out,
114 -- because we can't "rec" them
118 %************************************************************************
120 \subsection[Simplify-simplExpr]{The main function: simplExpr}
122 %************************************************************************
125 addBind :: CoreBind -> OutStuff a -> OutStuff a
126 addBind bind (binds, res) = (bind:binds, res)
128 addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
129 addBinds [] stuff = stuff
130 addBinds binds1 (binds2, res) = (binds1++binds2, res)
133 The reason for this OutExprStuff stuff is that we want to float *after*
134 simplifying a RHS, not before. If we do so naively we get quadratic
135 behaviour as things float out.
137 To see why it's important to do it after, consider this (real) example:
151 a -- Can't inline a this round, cos it appears twice
155 Each of the ==> steps is a round of simplification. We'd save a
156 whole round if we float first. This can cascade. Consider
161 let f = let d1 = ..d.. in \y -> e
165 in \x -> ...(\y ->e)...
167 Only in this second round can the \y be applied, and it
168 might do the same again.
172 simplExpr :: CoreExpr -> SimplM CoreExpr
173 simplExpr expr = getSubst `thenSmpl` \ subst ->
174 simplExprC expr (Stop (substTy subst (coreExprType expr)))
175 -- The type in the Stop continuation is usually not used
176 -- It's only needed when discarding continuations after finding
177 -- a function that returns bottom
179 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
180 -- Simplify an expression, given a continuation
182 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
183 returnSmpl (mkLets floats body)
185 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
186 -- Simplify an expression, returning floated binds
188 simplExprF (Var v) cont
191 simplExprF expr@(Con (PrimOp op) args) cont
192 = getSubstEnv `thenSmpl` \ se ->
195 (primOpStrictness op)
196 (pushArgs se args cont) $ \ args1 cont1 ->
199 -- Boring... we may have too many arguments now, so we push them back
201 args2 = ASSERT( length args1 >= n_args )
203 cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
205 -- Try the prim op simplification
206 -- It's really worth trying simplExpr again if it succeeds,
207 -- because you can find
208 -- case (eqChar# x 'a') of ...
210 -- case (case x of 'a' -> True; other -> False) of ...
211 case tryPrimOp op args2 of
212 Just e' -> zapSubstEnv (simplExprF e' cont2)
213 Nothing -> rebuild (Con (PrimOp op) args2) cont2
215 simplExprF (Con con@(DataCon _) args) cont
216 = freeTick LeafVisit `thenSmpl_`
217 simplConArgs args ( \ args' ->
218 rebuild (Con con args') cont)
220 simplExprF expr@(Con con@(Literal _) args) cont
221 = ASSERT( null args )
222 freeTick LeafVisit `thenSmpl_`
225 simplExprF (App fun arg) cont
226 = getSubstEnv `thenSmpl` \ se ->
227 simplExprF fun (ApplyTo NoDup arg se cont)
229 simplExprF (Case scrut bndr alts) cont
230 = getSubstEnv `thenSmpl` \ se ->
231 simplExprF scrut (Select NoDup bndr alts se cont)
234 simplExprF (Let (Rec pairs) body) cont
235 = simplIds (map fst pairs) $ \ bndrs' ->
236 -- NB: bndrs' don't have unfoldings or spec-envs
237 -- We add them as we go down, using simplPrags
239 simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
241 simplExprF expr@(Lam _ _) cont = simplLam expr cont
243 simplExprF (Type ty) cont
244 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
245 simplType ty `thenSmpl` \ ty' ->
246 rebuild (Type ty') cont
248 simplExprF (Note (Coerce to from) e) cont
249 | to == from = simplExprF e cont
250 | otherwise = getSubst `thenSmpl` \ subst ->
251 simplExprF e (CoerceIt (substTy subst to) cont)
253 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
254 -- inlining. All other CCCSs are mapped to currentCCS.
255 simplExprF (Note (SCC cc) e) cont
256 = setEnclosingCC currentCCS $
257 simplExpr e `thenSmpl` \ e ->
258 rebuild (mkNote (SCC cc) e) cont
260 simplExprF (Note InlineCall e) cont
261 = simplExprF e (InlinePlease cont)
263 -- Comments about the InlineMe case
264 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
265 -- Don't inline in the RHS of something that has an
266 -- inline pragma. But be careful that the InScopeEnv that
267 -- we return does still have inlinings on!
269 -- It really is important to switch off inlinings. This function
270 -- may be inlinined in other modules, so we don't want to remove
271 -- (by inlining) calls to functions that have specialisations, or
272 -- that may have transformation rules in an importing scope.
273 -- E.g. {-# INLINE f #-}
275 -- and suppose that g is strict *and* has specialisations.
276 -- If we inline g's wrapper, we deny f the chance of getting
277 -- the specialised version of g when f is inlined at some call site
278 -- (perhaps in some other module).
280 simplExprF (Note InlineMe e) cont
282 Stop _ -> -- Totally boring continuation
283 -- Don't inline inside an INLINE expression
284 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
285 rebuild (mkNote InlineMe e') cont
287 other -> -- Dissolve the InlineMe note if there's
288 -- an interesting context of any kind to combine with
289 -- (even a type application -- anything except Stop)
292 -- A non-recursive let is dealt with by simplBeta
293 simplExprF (Let (NonRec bndr rhs) body) cont
294 = getSubstEnv `thenSmpl` \ se ->
295 simplBeta bndr rhs se (contResultType cont) $
300 ---------------------------------
306 zap_it = mkLamBndrZapper fun (countArgs cont)
307 cont_ty = contResultType cont
309 -- Type-beta reduction
310 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
311 = ASSERT( isTyVar bndr )
312 tick (BetaReduction bndr) `thenSmpl_`
313 getInScope `thenSmpl` \ in_scope ->
315 ty' = substTy (mkSubst in_scope arg_se) ty_arg
317 extendSubst bndr (DoneTy ty')
320 -- Ordinary beta reduction
321 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
322 = tick (BetaReduction bndr) `thenSmpl_`
323 simplBeta zapped_bndr arg arg_se cont_ty
326 zapped_bndr = zap_it bndr
329 go lam@(Lam _ _) cont = completeLam [] lam cont
331 -- Exactly enough args
332 go expr cont = simplExprF expr cont
335 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
336 -- continuation. Try for eta reduction, but *only* if we get all
337 -- the way to an exprIsTrivial expression.
338 -- 'acc' holds the simplified binders, in reverse order
340 completeLam acc (Lam bndr body) cont
341 = simplBinder bndr $ \ bndr' ->
342 completeLam (bndr':acc) body cont
344 completeLam acc body cont
345 = simplExpr body `thenSmpl` \ body' ->
347 case (opt_SimplDoEtaReduction, check_eta acc body') of
348 (True, Just body'') -- Eta reduce!
349 -> tick (EtaReduction (head acc)) `thenSmpl_`
352 other -> -- No eta reduction
353 rebuild (foldl (flip Lam) body' acc) cont
354 -- Remember, acc is the reversed binders
356 -- NB: the binders are reversed
357 check_eta (b : bs) (App fun arg)
358 | (varToCoreExpr b `cheapEqExpr` arg)
362 | exprIsTrivial body && -- ONLY if the body is trivial
363 not (any (`elemVarSet` body_fvs) acc)
364 = Just body -- Success!
366 body_fvs = exprFreeVars body
368 check_eta _ _ = Nothing -- Bale out
370 mkLamBndrZapper :: CoreExpr -- Function
371 -> Int -- Number of args
372 -> Id -> Id -- Use this to zap the binders
373 mkLamBndrZapper fun n_args
374 | n_args >= n_params fun = \b -> b -- Enough args
375 | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
377 n_params (Lam b e) | isId b = 1 + n_params e
378 | otherwise = n_params e
379 n_params other = 0::Int
383 ---------------------------------
384 simplConArgs makes sure that the arguments all end up being atomic.
385 That means it may generate some Lets, hence the strange type
388 simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
389 simplConArgs [] thing_inside
392 simplConArgs (arg:args) thing_inside
393 = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
394 -- Simplify the RHS with inlining switched off, so that
395 -- only absolutely essential things will happen.
397 simplConArgs args $ \ args' ->
399 -- If the argument ain't trivial, then let-bind it
400 if exprIsTrivial arg' then
401 thing_inside (arg' : args')
403 newId (coreExprType arg') $ \ arg_id ->
404 thing_inside (Var arg_id : args') `thenSmpl` \ res ->
405 returnSmpl (addBind (NonRec arg_id arg') res)
409 ---------------------------------
411 simplType :: InType -> SimplM OutType
413 = getSubst `thenSmpl` \ subst ->
414 returnSmpl (substTy subst ty)
418 %************************************************************************
422 %************************************************************************
424 @simplBeta@ is used for non-recursive lets in expressions,
425 as well as true beta reduction.
427 Very similar to @simplLazyBind@, but not quite the same.
430 simplBeta :: InId -- Binder
431 -> InExpr -> SubstEnv -- Arg, with its subst-env
432 -> OutType -- Type of thing computed by the context
433 -> SimplM OutExprStuff -- The body
434 -> SimplM OutExprStuff
436 simplBeta bndr rhs rhs_se cont_ty thing_inside
438 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
441 simplBeta bndr rhs rhs_se cont_ty thing_inside
442 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
443 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
444 extendSubst bndr (ContEx rhs_se rhs) thing_inside
447 = -- Simplify the RHS
448 simplBinder bndr $ \ bndr' ->
449 simplArg (idType bndr') (getIdDemandInfo bndr)
450 rhs rhs_se cont_ty $ \ rhs' ->
452 -- Now complete the binding and simplify the body
453 completeBeta bndr bndr' rhs' thing_inside
455 completeBeta bndr bndr' rhs' thing_inside
456 | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
457 -- Make a case expression instead of a let
458 -- These can arise either from the desugarer,
459 -- or from beta reductions: (\x.e) (x +# y)
460 = getInScope `thenSmpl` \ in_scope ->
461 thing_inside `thenSmpl` \ (floats, (_, body)) ->
462 returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
465 = completeBinding bndr bndr' rhs' thing_inside
470 simplArg :: OutType -> Demand
471 -> InExpr -> SubstEnv
472 -> OutType -- Type of thing computed by the context
473 -> (OutExpr -> SimplM OutExprStuff)
474 -> SimplM OutExprStuff
475 simplArg arg_ty demand arg arg_se cont_ty thing_inside
477 isUnLiftedType arg_ty ||
478 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
479 -- Return true only for dictionary types where the dictionary
480 -- has more than one component (else we risk poking on the component
481 -- of a newtype dictionary)
482 = getSubstEnv `thenSmpl` \ body_se ->
483 transformRhs arg `thenSmpl` \ t_arg ->
484 setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
485 setSubstEnv body_se (thing_inside arg')
486 )) -- NB: we must restore body_se before carrying on with thing_inside!!
489 = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
494 - deals only with Ids, not TyVars
495 - take an already-simplified RHS
497 It does *not* attempt to do let-to-case. Why? Because they are used for
500 (when let-to-case is impossible)
502 - many situations where the "rhs" is known to be a WHNF
503 (so let-to-case is inappropriate).
506 completeBinding :: InId -- Binder
507 -> OutId -- New binder
508 -> OutExpr -- Simplified RHS
509 -> SimplM (OutStuff a) -- Thing inside
510 -> SimplM (OutStuff a)
512 completeBinding old_bndr new_bndr new_rhs thing_inside
513 | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
514 -- known constructor: case (a,b) of x { (p,q) -> ... }
515 -- Here x isn't mentioned in the RHS, so we don't want to
516 -- create the (dead) let-binding let x = (a,b) in ...
519 | postInlineUnconditionally old_bndr new_rhs
520 -- Maybe we don't need a let-binding! Maybe we can just
521 -- inline it right away. Unlike the preInlineUnconditionally case
522 -- we are allowed to look at the RHS.
524 -- NB: a loop breaker never has postInlineUnconditionally True
525 -- and non-loop-breakers only have *forward* references
526 -- Hence, it's safe to discard the binding
527 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
528 extendSubst old_bndr (DoneEx new_rhs)
532 = getSubst `thenSmpl` \ subst ->
534 bndr_info = idInfo old_bndr
535 old_rules = specInfo bndr_info
536 new_rules = substRules subst old_rules
538 -- The new binding site Id needs its specialisations re-attached
539 bndr_w_arity = new_bndr `setIdArity` ArityAtLeast (exprArity new_rhs)
542 | isEmptyCoreRules old_rules = bndr_w_arity
543 | otherwise = bndr_w_arity `setIdSpecialisation` new_rules
545 -- At the occurrence sites we want to know the unfolding,
546 -- and the occurrence info of the original
547 -- (simplBinder cleaned up the inline prag of the original
548 -- to eliminate un-stable info, in case this expression is
549 -- simplified a second time; hence the need to reattach it)
550 occ_site_id = binding_site_id
551 `setIdUnfolding` mkUnfolding new_rhs
552 `setInlinePragma` inlinePragInfo bndr_info
554 modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
555 returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff)
559 %************************************************************************
561 \subsection{simplLazyBind}
563 %************************************************************************
565 simplLazyBind basically just simplifies the RHS of a let(rec).
566 It does two important optimisations though:
568 * It floats let(rec)s out of the RHS, even if they
569 are hidden by big lambdas
571 * It does eta expansion
574 simplLazyBind :: TopLevelFlag
577 -> SimplM (OutStuff a) -- The body of the binding
578 -> SimplM (OutStuff a)
579 -- When called, the subst env is correct for the entire let-binding
580 -- and hence right for the RHS.
581 -- Also the binder has already been simplified, and hence is in scope
583 simplLazyBind top_lvl bndr bndr' rhs thing_inside
584 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
585 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
586 getSubstEnv `thenSmpl` \ rhs_se ->
587 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
590 = -- Simplify the RHS
591 getSubstEnv `thenSmpl` \ rhs_se ->
593 simplRhs top_lvl False {- Not ok to float unboxed -}
595 rhs rhs_se $ \ rhs' ->
597 -- Now compete the binding and simplify the body
598 completeBinding bndr bndr' rhs' thing_inside
604 simplRhs :: TopLevelFlag
605 -> Bool -- True <=> OK to float unboxed (speculative) bindings
606 -> OutType -> InExpr -> SubstEnv
607 -> (OutExpr -> SimplM (OutStuff a))
608 -> SimplM (OutStuff a)
609 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
610 = -- Swizzle the inner lets past the big lambda (if any)
611 -- and try eta expansion
612 transformRhs rhs `thenSmpl` \ t_rhs ->
615 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
617 -- Float lets out of RHS
619 (floats_out, rhs'') | float_ubx = (floats, rhs')
620 | otherwise = splitFloats floats rhs'
622 if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
623 not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
625 tickLetFloat floats_out `thenSmpl_`
628 -- There's a subtlety here. There may be a binding (x* = e) in the
629 -- floats, where the '*' means 'will be demanded'. So is it safe
630 -- to float it out? Answer no, but it won't matter because
631 -- we only float if arg' is a WHNF,
632 -- and so there can't be any 'will be demanded' bindings in the floats.
634 WARN( any demanded_float floats_out, ppr floats_out )
635 setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
636 -- in_scope' may be excessive, but that's OK;
637 -- it's a superset of what's in scope
638 returnSmpl (addBinds floats_out stuff)
640 -- Don't do the float
641 thing_inside (mkLets floats rhs')
643 -- In a let-from-let float, we just tick once, arbitrarily
644 -- choosing the first floated binder to identify it
645 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
646 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
648 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
649 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
650 demanded_float (Rec _) = False
652 -- Don't float any unlifted bindings out, because the context
653 -- is either a Rec group, or the top level, neither of which
654 -- can tolerate them.
655 splitFloats floats rhs
659 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
660 | otherwise = case go fs of
661 (out, rhs') -> (f:out, rhs')
663 must_stay (Rec prs) = False -- No unlifted bindings in here
664 must_stay (NonRec b r) = isUnLiftedType (idType b)
669 %************************************************************************
671 \subsection{Variables}
673 %************************************************************************
677 = freeTick LeafVisit `thenSmpl_`
678 getSubst `thenSmpl` \ subst ->
679 case lookupSubst subst var of
680 Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
681 Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
682 Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
685 var' = case lookupInScope subst var of
689 if isLocallyDefined var && not (idMustBeINLINEd var)
690 -- The idMustBeINLINEd test accouunts for the fact
691 -- that class dictionary constructors don't have top level
692 -- bindings and hence aren't in scope.
695 pprTrace "simplVar:" (ppr var) var
700 getBlackList `thenSmpl` \ black_list ->
701 getInScope `thenSmpl` \ in_scope ->
702 completeCall black_list in_scope var' cont
704 ---------------------------------------------------------
705 -- Dealing with a call
707 completeCall black_list_fn in_scope var cont
708 -- Look for rules or specialisations that match
709 -- Do this *before* trying inlining because some functions
710 -- have specialisations *and* are strict; we don't want to
711 -- inline the wrapper of the non-specialised thing... better
712 -- to call the specialised thing instead.
713 | maybeToBool maybe_rule_match
714 = tick (RuleFired rule_name) `thenSmpl_`
715 zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args result_cont))
716 -- See note below about zapping the substitution here
718 -- Look for an unfolding. There's a binding for the
719 -- thing, but perhaps we want to inline it anyway
720 | maybeToBool maybe_inline
721 = tick (UnfoldingDone var) `thenSmpl_`
722 zapSubstEnv (completeInlining var unf_template discard_inline_cont)
723 -- The template is already simplified, so don't re-substitute.
724 -- This is VITAL. Consider
726 -- let y = \z -> ...x... in
728 -- We'll clone the inner \x, adding x->x' in the id_subst
729 -- Then when we inline y, we must *not* replace x by x' in
730 -- the inlined copy!!
732 | otherwise -- Neither rule nor inlining
733 -- Use prepareArgs to use function strictness
734 = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
735 rebuild (mkApps (Var var) args') cont'
738 get_str var = case getIdStrictness var of
739 NoStrictnessInfo -> (repeat wwLazy, False)
740 StrictnessInfo demands result_bot -> (demands, result_bot)
743 (args', result_cont) = contArgs in_scope cont
744 inline_call = contIsInline result_cont
745 interesting_cont = contIsInteresting result_cont
746 discard_inline_cont | inline_call = discardInline cont
749 ---------- Unfolding stuff
750 maybe_inline = callSiteInline black_listed inline_call
751 var args' interesting_cont
752 Just unf_template = maybe_inline
753 black_listed = black_list_fn var
755 ---------- Specialisation stuff
756 maybe_rule_match = lookupRule in_scope var args'
757 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
760 -- First a special case
761 -- Don't actually inline the scrutinee when we see
762 -- case x of y { .... }
763 -- and x has unfolding (C a b). Why not? Because
764 -- we get a silly binding y = C a b. If we don't
765 -- inline knownCon can directly substitute x for y instead.
766 completeInlining var (Con con con_args) (Select _ bndr alts se cont)
768 = knownCon (Var var) con con_args bndr alts se cont
770 -- Now the normal case
771 completeInlining var unfolding cont
772 = simplExprF unfolding cont
774 ----------- costCentreOk
775 -- costCentreOk checks that it's ok to inline this thing
776 -- The time it *isn't* is this:
778 -- f x = let y = E in
779 -- scc "foo" (...y...)
781 -- Here y has a "current cost centre", and we can't inline it inside "foo",
782 -- regardless of whether E is a WHNF or not.
784 costCentreOk ccs_encl cc_rhs
785 = not opt_SccProfilingOn
786 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
787 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
792 ---------------------------------------------------------
793 -- Preparing arguments for a call
795 prepareArgs :: SDoc -- Error message info
796 -> OutType -> ([Demand],Bool) -> SimplCont
797 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
798 -> SimplM OutExprStuff
800 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
801 = go [] demands orig_fun_ty orig_cont
803 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
804 -- "No strictness info" is signalled by an infinite list of wwLazy
806 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
807 | result_bot = fun_demands -- Enough args, and function returns bottom
808 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
809 -- NB: demands is finite iff enough args and result_bot is True
811 -- Main game plan: loop through the arguments, simplifying
812 -- each of them in turn. We carry with us a list of demands,
813 -- and the type of the function-applied-to-earlier-args
816 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
817 = getInScope `thenSmpl` \ in_scope ->
819 ty_arg' = substTy (mkSubst in_scope se) ty_arg
820 res_ty = applyTy fun_ty ty_arg'
822 go (Type ty_arg' : acc) ds res_ty cont
825 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
826 = case splitFunTy_maybe fun_ty of {
827 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
828 (thing_inside (reverse acc) cont) ;
829 Just (arg_ty, res_ty) ->
830 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
831 go (arg':acc) ds res_ty cont }
833 -- We've run out of demands, which only happens for functions
834 -- we *know* now return bottom
836 -- * case (error "hello") of { ... }
837 -- * (error "Hello") arg
838 -- * f (error "Hello") where f is strict
840 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
841 thing_inside (reverse acc) (discardCont cont)
843 -- We're run out of arguments
844 go acc ds fun_ty cont = thing_inside (reverse acc) cont
846 -- Boring: we must only record a tick if there was an interesting
847 -- continuation to discard. If not, we tick forever.
848 tick_case_of_error (Stop _) = returnSmpl ()
849 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
850 tick_case_of_error other = tick BottomFound
853 %************************************************************************
855 \subsection{Decisions about inlining}
857 %************************************************************************
860 preInlineUnconditionally :: InId -> Bool
861 -- Examines a bndr to see if it is used just once in a
862 -- completely safe way, so that it is safe to discard the binding
863 -- inline its RHS at the (unique) usage site, REGARDLESS of how
864 -- big the RHS might be. If this is the case we don't simplify
865 -- the RHS first, but just inline it un-simplified.
867 -- This is much better than first simplifying a perhaps-huge RHS
868 -- and then inlining and re-simplifying it.
870 -- NB: we don't even look at the RHS to see if it's trivial
873 -- where x is used many times, but this is the unique occurrence
874 -- of y. We should NOT inline x at all its uses, because then
875 -- we'd do the same for y -- aargh! So we must base this
876 -- pre-rhs-simplification decision solely on x's occurrences, not
879 -- Evne RHSs labelled InlineMe aren't caught here, because
880 -- there might be no benefit from inlining at the call site.
881 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
882 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
883 preInlineUnconditionally bndr
884 = case getInlinePragma bndr of
885 IMustBeINLINEd -> True
886 ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
887 -- one occurrence ==> safe!
891 postInlineUnconditionally :: InId -> OutExpr -> Bool
892 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
893 -- It returns True if it's ok to discard the binding and inline the
894 -- RHS at every use site.
896 -- NOTE: This isn't our last opportunity to inline.
897 -- We're at the binding site right now, and
898 -- we'll get another opportunity when we get to the ocurrence(s)
900 postInlineUnconditionally bndr rhs
904 = case getInlinePragma bndr of
905 IAmALoopBreaker -> False
907 ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
908 -- Don't inline even WHNFs inside lambdas; doing so may
909 -- simply increase allocation when the function is called
910 -- This isn't the last chance; see NOTE above.
912 ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
913 -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
914 -- decision about duplicating code is best left to callSiteInline
916 other -> exprIsTrivial rhs -- Duplicating is *free*
917 -- NB: Even InlineMe and IMustBeINLINEd are ignored here
918 -- Why? Because we don't even want to inline them into the
919 -- RHS of constructor arguments. See NOTE above
920 -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
921 -- it's best to inline it anyway. We often get a=E; b=a
922 -- from desugaring, with both a and b marked NOINLINE.
927 %************************************************************************
929 \subsection{The main rebuilder}
931 %************************************************************************
934 -------------------------------------------------------------------
937 = getInScope `thenSmpl` \ in_scope ->
938 returnSmpl ([], (in_scope, expr))
940 ---------------------------------------------------------
941 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
944 rebuild expr (Stop _) = rebuild_done expr
946 -- ArgOf continuation
947 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
949 -- ApplyTo continuation
950 rebuild expr cont@(ApplyTo _ arg se cont')
951 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
952 rebuild (App expr arg') cont'
954 -- Coerce continuation
955 rebuild expr (CoerceIt to_ty cont)
956 = rebuild (mkCoerce to_ty expr) cont
958 -- Inline continuation
959 rebuild expr (InlinePlease cont)
960 = rebuild (Note InlineCall expr) cont
962 -- Case of known constructor or literal
963 rebuild expr@(Con con args) (Select _ bndr alts se cont)
964 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
965 = knownCon expr con args bndr alts se cont
968 ---------------------------------------------------------
969 -- The other Select cases
971 rebuild scrut (Select _ bndr alts se cont)
972 | -- Check that the RHSs are all the same, and
973 -- don't use the binders in the alternatives
974 -- This test succeeds rapidly in the common case of
975 -- a single DEFAULT alternative
976 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
978 -- Check that the scrutinee can be let-bound instead of case-bound
979 && ( (isUnLiftedType (idType bndr) && -- It's unlifted and floatable
980 exprOkForSpeculation scrut) -- NB: scrut = an unboxed variable satisfies
981 || exprIsValue scrut -- It's already evaluated
982 || var_demanded_later scrut -- It'll be demanded later
984 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
985 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
986 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
987 -- its argument: case x of { y -> dataToTag# y }
988 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
989 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
993 -- && opt_SimplDoCaseElim
994 -- [June 99; don't test this flag. The code generator dies if it sees
995 -- case (\x.e) of f -> ...
996 -- so better to always do it
998 = -- Get rid of the case altogether
999 -- See the extensive notes on case-elimination below
1000 -- Remember to bind the binder though!
1001 tick (CaseElim bndr) `thenSmpl_` (
1003 simplBinder bndr $ \ bndr' ->
1004 completeBinding bndr bndr' scrut $
1005 simplExprF rhs1 cont)
1008 = rebuild_case scrut bndr alts se cont
1010 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1011 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1013 var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1014 var_demanded_later other = False
1017 Case elimination [see the code above]
1019 Start with a simple situation:
1021 case x# of ===> e[x#/y#]
1024 (when x#, y# are of primitive type, of course). We can't (in general)
1025 do this for algebraic cases, because we might turn bottom into
1028 Actually, we generalise this idea to look for a case where we're
1029 scrutinising a variable, and we know that only the default case can
1034 other -> ...(case x of
1038 Here the inner case can be eliminated. This really only shows up in
1039 eliminating error-checking code.
1041 We also make sure that we deal with this very common case:
1046 Here we are using the case as a strict let; if x is used only once
1047 then we want to inline it. We have to be careful that this doesn't
1048 make the program terminate when it would have diverged before, so we
1050 - x is used strictly, or
1051 - e is already evaluated (it may so if e is a variable)
1053 Lastly, we generalise the transformation to handle this:
1059 We only do this for very cheaply compared r's (constructors, literals
1060 and variables). If pedantic bottoms is on, we only do it when the
1061 scrutinee is a PrimOp which can't fail.
1063 We do it *here*, looking at un-simplified alternatives, because we
1064 have to check that r doesn't mention the variables bound by the
1065 pattern in each alternative, so the binder-info is rather useful.
1067 So the case-elimination algorithm is:
1069 1. Eliminate alternatives which can't match
1071 2. Check whether all the remaining alternatives
1072 (a) do not mention in their rhs any of the variables bound in their pattern
1073 and (b) have equal rhss
1075 3. Check we can safely ditch the case:
1076 * PedanticBottoms is off,
1077 or * the scrutinee is an already-evaluated variable
1078 or * the scrutinee is a primop which is ok for speculation
1079 -- ie we want to preserve divide-by-zero errors, and
1080 -- calls to error itself!
1082 or * [Prim cases] the scrutinee is a primitive variable
1084 or * [Alg cases] the scrutinee is a variable and
1085 either * the rhs is the same variable
1086 (eg case x of C a b -> x ===> x)
1087 or * there is only one alternative, the default alternative,
1088 and the binder is used strictly in its scope.
1089 [NB this is helped by the "use default binder where
1090 possible" transformation; see below.]
1093 If so, then we can replace the case with one of the rhss.
1096 Blob of helper functions for the "case-of-something-else" situation.
1099 ---------------------------------------------------------
1100 -- Case of something else
1102 rebuild_case scrut case_bndr alts se cont
1103 = -- Prepare case alternatives
1104 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1105 scrut_cons alts `thenSmpl` \ better_alts ->
1107 -- Set the new subst-env in place (before dealing with the case binder)
1110 -- Deal with the case binder, and prepare the continuation;
1111 -- The new subst_env is in place
1112 prepareCaseCont better_alts cont $ \ cont' ->
1115 -- Deal with variable scrutinee
1116 ( simplBinder case_bndr $ \ case_bndr' ->
1117 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1119 case_bndr'' = zap_occ_info case_bndr'
1122 -- Deal with the case alternaatives
1123 simplAlts zap_occ_info scrut_cons
1124 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1126 mkCase scrut case_bndr'' alts'
1127 ) `thenSmpl` \ case_expr ->
1129 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1130 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1131 -- that should not include these chaps!
1132 rebuild_done case_expr
1134 -- scrut_cons tells what constructors the scrutinee can't possibly match
1135 scrut_cons = case scrut of
1136 Var v -> otherCons (getIdUnfolding v)
1140 knownCon expr con args bndr alts se cont
1141 = tick (KnownBranch bndr) `thenSmpl_`
1143 simplBinder bndr $ \ bndr' ->
1144 case findAlt con alts of
1145 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1146 completeBinding bndr bndr' expr $
1147 -- Don't use completeBeta here. The expr might be
1148 -- an unboxed literal, like 3, or a variable
1149 -- whose unfolding is an unboxed literal... and
1150 -- completeBeta will just construct another case
1154 (Literal lit, bs, rhs) -> ASSERT( null bs )
1155 extendSubst bndr (DoneEx expr) $
1156 -- Unconditionally substitute, because expr must
1157 -- be a variable or a literal. It can't be a
1158 -- NoRep literal because they don't occur in
1162 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1163 completeBinding bndr bndr' expr $
1165 extendSubstList bs (map mk real_args) $
1168 real_args = drop (dataConNumInstArgs dc) args
1169 mk (Type ty) = DoneTy ty
1170 mk other = DoneEx other
1175 prepareCaseCont :: [InAlt] -> SimplCont
1176 -> (SimplCont -> SimplM (OutStuff a))
1177 -> SimplM (OutStuff a)
1178 -- Polymorphic recursion here!
1180 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1181 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1184 substForVarScrut checks whether the scrutinee is a variable, v.
1185 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1186 that way, there's a chance that v will now only be used once, and hence inlined.
1188 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1189 in the case binder, because the case-binder now effectively occurs
1190 whenever v does. AND we have to do the same for the pattern-bound
1193 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1195 Here, b and p are dead. But when we move the argment inside the first
1196 case RHS, and eliminate the second case, we get
1198 case x or { (a,b) -> a b }
1200 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1201 happened. Hence the zap_occ_info function returned by substForVarScrut
1204 substForVarScrut (Var v) case_bndr' thing_inside
1205 | isLocallyDefined v -- No point for imported things
1206 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1207 `setInlinePragma` IMustBeINLINEd) $
1208 -- We could extend the substitution instead, but it would be
1209 -- a hack because then the substitution wouldn't be idempotent
1211 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1213 substForVarScrut other_scrut case_bndr' thing_inside
1214 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1217 prepareCaseAlts does two things:
1219 1. Remove impossible alternatives
1221 2. If the DEFAULT alternative can match only one possible constructor,
1222 then make that constructor explicit.
1224 case e of x { DEFAULT -> rhs }
1226 case e of x { (a,b) -> rhs }
1227 where the type is a single constructor type. This gives better code
1228 when rhs also scrutinises x or e.
1231 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1233 = case (findDefault filtered_alts, missing_cons) of
1235 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1236 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1238 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1240 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1242 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1243 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1245 newIds (dataConArgTys
1247 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1248 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1250 other -> returnSmpl filtered_alts
1252 -- Filter out alternatives that can't possibly match
1253 filtered_alts = case scrut_cons of
1255 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1257 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1258 not (data_con `elem` handled_data_cons)]
1259 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1260 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1263 prepareCaseAlts _ _ scrut_cons alts
1264 = returnSmpl alts -- Functions
1267 ----------------------
1268 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1269 = mapSmpl simpl_alt alts
1271 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1272 Just (tycon, inst_tys) -> inst_tys
1274 -- handled_cons is all the constructors that are dealt
1275 -- with, either by being impossible, or by there being an alternative
1276 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1278 simpl_alt (DEFAULT, _, rhs)
1279 = -- In the default case we record the constructors that the
1280 -- case-binder *can't* be.
1281 -- We take advantage of any OtherCon info in the case scrutinee
1282 modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
1283 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1284 returnSmpl (DEFAULT, [], rhs')
1286 simpl_alt (con, vs, rhs)
1287 = -- Deal with the pattern-bound variables
1288 -- Mark the ones that are in ! positions in the data constructor
1289 -- as certainly-evaluated
1290 simplBinders (add_evals con vs) $ \ vs' ->
1292 -- Bind the case-binder to (Con args)
1294 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1296 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1297 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1298 returnSmpl (con, vs', rhs')
1301 -- add_evals records the evaluated-ness of the bound variables of
1302 -- a case pattern. This is *important*. Consider
1303 -- data T = T !Int !Int
1305 -- case x of { T a b -> T (a+1) b }
1307 -- We really must record that b is already evaluated so that we don't
1308 -- go and re-evaluate it when constructing the result.
1310 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1311 add_evals other_con vs = vs
1313 cat_evals [] [] = []
1314 cat_evals (v:vs) (str:strs)
1315 | isTyVar v = v : cat_evals vs (str:strs)
1316 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1317 | otherwise = v' : cat_evals vs strs
1323 %************************************************************************
1325 \subsection{Duplicating continuations}
1327 %************************************************************************
1330 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1332 -> (SimplCont -> SimplM (OutStuff a))
1333 -> SimplM (OutStuff a)
1334 mkDupableCont ty cont thing_inside
1335 | contIsDupable cont
1338 mkDupableCont _ (CoerceIt ty cont) thing_inside
1339 = mkDupableCont ty cont $ \ cont' ->
1340 thing_inside (CoerceIt ty cont')
1342 mkDupableCont ty (InlinePlease cont) thing_inside
1343 = mkDupableCont ty cont $ \ cont' ->
1344 thing_inside (InlinePlease cont')
1346 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1347 = -- Build the RHS of the join point
1348 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1349 newId join_arg_ty' ( \ arg_id ->
1350 getSwitchChecker `thenSmpl` \ chkr ->
1351 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1352 returnSmpl (Lam arg_id (mkLets binds rhs))
1353 ) `thenSmpl` \ join_rhs ->
1355 -- Build the join Id and continuation
1356 newId (coreExprType join_rhs) $ \ join_id ->
1358 new_cont = ArgOf OkToDup cont_ty
1359 (\arg' -> rebuild_done (App (Var join_id) arg'))
1362 -- Do the thing inside
1363 thing_inside new_cont `thenSmpl` \ res ->
1364 returnSmpl (addBind (NonRec join_id join_rhs) res)
1366 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1367 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1368 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1369 if exprIsDupable arg' then
1370 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1372 newId (coreExprType arg') $ \ bndr ->
1373 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1374 returnSmpl (addBind (NonRec bndr arg') res)
1376 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1377 = tick (CaseOfCase case_bndr) `thenSmpl_`
1379 simplBinder case_bndr $ \ case_bndr' ->
1380 prepareCaseCont alts cont $ \ cont' ->
1381 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1382 returnSmpl (concat alt_binds_s, alts')
1383 ) `thenSmpl` \ (alt_binds, alts') ->
1385 extendInScopes [b | NonRec b _ <- alt_binds] $
1387 -- NB that the new alternatives, alts', are still InAlts, using the original
1388 -- binders. That means we can keep the case_bndr intact. This is important
1389 -- because another case-of-case might strike, and so we want to keep the
1390 -- info that the case_bndr is dead (if it is, which is often the case).
1391 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1392 -- case in I/O rich code. We aren't allowed a lambda bound
1393 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1394 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1396 returnSmpl (addBinds alt_binds res)
1399 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1400 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1401 = -- Not worth checking whether the rhs is small; the
1402 -- inliner will inline it if so.
1403 simplBinders bndrs $ \ bndrs' ->
1404 simplExprC rhs cont `thenSmpl` \ rhs' ->
1406 rhs_ty' = coreExprType rhs'
1407 (used_bndrs, used_bndrs')
1408 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1409 (case_bndr' : bndrs'),
1410 not (isDeadBinder bndr)]
1411 -- The new binders have lost their occurrence info,
1412 -- so we have to extract it from the old ones
1414 ( if null used_bndrs'
1415 -- If we try to lift a primitive-typed something out
1416 -- for let-binding-purposes, we will *caseify* it (!),
1417 -- with potentially-disastrous strictness results. So
1418 -- instead we turn it into a function: \v -> e
1419 -- where v::State# RealWorld#. The value passed to this function
1420 -- is realworld#, which generates (almost) no code.
1422 -- There's a slight infelicity here: we pass the overall
1423 -- case_bndr to all the join points if it's used in *any* RHS,
1424 -- because we don't know its usage in each RHS separately
1426 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1427 -- we make the join point into a function whenever used_bndrs'
1428 -- is empty. This makes the join-point more CPR friendly.
1429 -- Consider: let j = if .. then I# 3 else I# 4
1430 -- in case .. of { A -> j; B -> j; C -> ... }
1432 -- Now CPR should not w/w j because it's a thunk, so
1433 -- that means that the enclosing function can't w/w either,
1434 -- which is a lose. Here's the example that happened in practice:
1435 -- kgmod :: Int -> Int -> Int
1436 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1440 then newId realWorldStatePrimTy $ \ rw_id ->
1441 returnSmpl ([rw_id], [Var realWorldPrimId])
1443 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1445 `thenSmpl` \ (final_bndrs', final_args) ->
1447 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1449 -- Notice that we make the lambdas into one-shot-lambdas. The
1450 -- join point is sure to be applied at most once, and doing so
1451 -- prevents the body of the join point being floated out by
1452 -- the full laziness pass
1453 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1454 (con, bndrs, mkApps (Var join_bndr) final_args))