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
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(..), mkUnfolding, callSiteInline,
46 isEvaldUnfolding, blackListed )
47 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsWHNF, exprIsTrivial,
48 coreExprType, coreAltsType, exprArity,
51 import Rules ( lookupRule )
52 import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
53 import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType,
54 mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
55 funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
57 import Subst ( Subst, mkSubst, emptySubst, substExpr, substTy,
58 substEnv, lookupInScope, lookupSubst, substRules
60 import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
61 import TysPrim ( realWorldStatePrimTy )
62 import PrelInfo ( realWorldPrimId )
63 import BasicTypes ( TopLevelFlag(..), isTopLevel )
64 import Maybes ( maybeToBool )
65 import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
71 The guts of the simplifier is in this module, but the driver
72 loop for the simplifier is in SimplCore.lhs.
75 %************************************************************************
79 %************************************************************************
82 simplTopBinds :: [InBind] -> SimplM [OutBind]
85 = -- Put all the top-level binders into scope at the start
86 -- so that if a transformation rule has unexpectedly brought
87 -- anything into scope, then we don't get a complaint about that.
88 -- It's rather as if the top-level binders were imported.
89 extendInScopes top_binders $
90 simpl_binds binds `thenSmpl` \ (binds', _) ->
91 freeTick SimplifierDone `thenSmpl_`
94 top_binders = bindersOfBinds binds
96 simpl_binds [] = returnSmpl ([], panic "simplTopBinds corner")
97 simpl_binds (NonRec bndr rhs : binds) = simplLazyBind TopLevel bndr bndr rhs (simpl_binds binds)
98 simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map fst pairs) (simpl_binds binds)
101 simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
102 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
103 simplRecBind top_lvl pairs bndrs' thing_inside
104 = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
105 returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
107 go [] _ = thing_inside `thenSmpl` \ stuff ->
108 returnSmpl ([], stuff)
110 go ((bndr, rhs) : pairs) (bndr' : bndrs')
111 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
112 -- Don't float unboxed bindings out,
113 -- because we can't "rec" them
117 %************************************************************************
119 \subsection[Simplify-simplExpr]{The main function: simplExpr}
121 %************************************************************************
124 addBind :: CoreBind -> OutStuff a -> OutStuff a
125 addBind bind (binds, res) = (bind:binds, res)
127 addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
128 addBinds [] stuff = stuff
129 addBinds binds1 (binds2, res) = (binds1++binds2, res)
132 The reason for this OutExprStuff stuff is that we want to float *after*
133 simplifying a RHS, not before. If we do so naively we get quadratic
134 behaviour as things float out.
136 To see why it's important to do it after, consider this (real) example:
150 a -- Can't inline a this round, cos it appears twice
154 Each of the ==> steps is a round of simplification. We'd save a
155 whole round if we float first. This can cascade. Consider
160 let f = let d1 = ..d.. in \y -> e
164 in \x -> ...(\y ->e)...
166 Only in this second round can the \y be applied, and it
167 might do the same again.
171 simplExpr :: CoreExpr -> SimplM CoreExpr
172 simplExpr expr = getSubst `thenSmpl` \ subst ->
173 simplExprC expr (Stop (substTy subst (coreExprType expr)))
174 -- The type in the Stop continuation is usually not used
175 -- It's only needed when discarding continuations after finding
176 -- a function that returns bottom
178 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
179 -- Simplify an expression, given a continuation
181 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
182 returnSmpl (mkLets floats body)
184 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
185 -- Simplify an expression, returning floated binds
187 simplExprF (Var v) cont
190 simplExprF expr@(Con (PrimOp op) args) cont
191 = getSubstEnv `thenSmpl` \ se ->
194 (primOpStrictness op)
195 (pushArgs se args cont) $ \ args1 cont1 ->
198 -- Boring... we may have too many arguments now, so we push them back
200 args2 = ASSERT( length args1 >= n_args )
202 cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
204 -- Try the prim op simplification
205 -- It's really worth trying simplExpr again if it succeeds,
206 -- because you can find
207 -- case (eqChar# x 'a') of ...
209 -- case (case x of 'a' -> True; other -> False) of ...
210 case tryPrimOp op args2 of
211 Just e' -> zapSubstEnv (simplExprF e' cont2)
212 Nothing -> rebuild (Con (PrimOp op) args2) cont2
214 simplExprF (Con con@(DataCon _) args) cont
215 = freeTick LeafVisit `thenSmpl_`
216 simplConArgs args ( \ args' ->
217 rebuild (Con con args') cont)
219 simplExprF expr@(Con con@(Literal _) args) cont
220 = ASSERT( null args )
221 freeTick LeafVisit `thenSmpl_`
224 simplExprF (App fun arg) cont
225 = getSubstEnv `thenSmpl` \ se ->
226 simplExprF fun (ApplyTo NoDup arg se cont)
228 simplExprF (Case scrut bndr alts) cont
229 = getSubstEnv `thenSmpl` \ se ->
230 simplExprF scrut (Select NoDup bndr alts se cont)
233 simplExprF (Let (Rec pairs) body) cont
234 = simplIds (map fst pairs) $ \ bndrs' ->
235 -- NB: bndrs' don't have unfoldings or spec-envs
236 -- We add them as we go down, using simplPrags
238 simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
240 simplExprF expr@(Lam _ _) cont = simplLam expr cont
242 simplExprF (Type ty) cont
243 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
244 simplType ty `thenSmpl` \ ty' ->
245 rebuild (Type ty') cont
247 simplExprF (Note (Coerce to from) e) cont
248 | to == from = simplExprF e cont
249 | otherwise = getSubst `thenSmpl` \ subst ->
250 simplExprF e (CoerceIt (substTy subst to) cont)
252 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
253 -- inlining. All other CCCSs are mapped to currentCCS.
254 simplExprF (Note (SCC cc) e) cont
255 = setEnclosingCC currentCCS $
256 simplExpr e `thenSmpl` \ e ->
257 rebuild (mkNote (SCC cc) e) cont
259 simplExprF (Note InlineCall e) cont
260 = simplExprF e (InlinePlease cont)
262 -- Comments about the InlineMe case
263 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
264 -- Don't inline in the RHS of something that has an
265 -- inline pragma. But be careful that the InScopeEnv that
266 -- we return does still have inlinings on!
268 -- It really is important to switch off inlinings. This function
269 -- may be inlinined in other modules, so we don't want to remove
270 -- (by inlining) calls to functions that have specialisations, or
271 -- that may have transformation rules in an importing scope.
272 -- E.g. {-# INLINE f #-}
274 -- and suppose that g is strict *and* has specialisations.
275 -- If we inline g's wrapper, we deny f the chance of getting
276 -- the specialised version of g when f is inlined at some call site
277 -- (perhaps in some other module).
279 simplExprF (Note InlineMe e) cont
281 Stop _ -> -- Totally boring continuation
282 -- Don't inline inside an INLINE expression
283 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
284 rebuild (mkNote InlineMe e') cont
286 other -> -- Dissolve the InlineMe note if there's
287 -- an interesting context of any kind to combine with
288 -- (even a type application -- anything except Stop)
291 -- A non-recursive let is dealt with by simplBeta
292 simplExprF (Let (NonRec bndr rhs) body) cont
293 = getSubstEnv `thenSmpl` \ se ->
294 simplBeta bndr rhs se (contResultType cont) $
299 ---------------------------------
305 zap_it = mkLamBndrZapper fun (countArgs cont)
306 cont_ty = contResultType cont
308 -- Type-beta reduction
309 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
310 = ASSERT( isTyVar bndr )
311 tick (BetaReduction bndr) `thenSmpl_`
312 getInScope `thenSmpl` \ in_scope ->
314 ty' = substTy (mkSubst in_scope arg_se) ty_arg
316 extendSubst bndr (DoneTy ty')
319 -- Ordinary beta reduction
320 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
321 = tick (BetaReduction bndr) `thenSmpl_`
322 simplBeta zapped_bndr arg arg_se cont_ty
325 zapped_bndr = zap_it bndr
328 go lam@(Lam _ _) cont = completeLam [] lam cont
330 -- Exactly enough args
331 go expr cont = simplExprF expr cont
334 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
335 -- continuation. Try for eta reduction, but *only* if we get all
336 -- the way to an exprIsTrivial expression.
337 -- 'acc' holds the simplified binders, in reverse order
339 completeLam acc (Lam bndr body) cont
340 = simplBinder bndr $ \ bndr' ->
341 completeLam (bndr':acc) body cont
343 completeLam acc body cont
344 = simplExpr body `thenSmpl` \ body' ->
346 case (opt_SimplDoEtaReduction, check_eta acc body') of
347 (True, Just body'') -- Eta reduce!
348 -> tick (EtaReduction (head acc)) `thenSmpl_`
351 other -> -- No eta reduction
352 rebuild (foldl (flip Lam) body' acc) cont
353 -- Remember, acc is the reversed binders
355 -- NB: the binders are reversed
356 check_eta (b : bs) (App fun arg)
357 | (varToCoreExpr b `cheapEqExpr` arg)
361 | exprIsTrivial body && -- ONLY if the body is trivial
362 not (any (`elemVarSet` body_fvs) acc)
363 = Just body -- Success!
365 body_fvs = exprFreeVars body
367 check_eta _ _ = Nothing -- Bale out
369 mkLamBndrZapper :: CoreExpr -- Function
370 -> Int -- Number of args
371 -> Id -> Id -- Use this to zap the binders
372 mkLamBndrZapper fun n_args
373 | saturated fun n_args = \b -> b
374 | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
376 saturated (Lam b e) 0 = False
377 saturated (Lam b e) n = saturated e (n-1)
382 ---------------------------------
383 simplConArgs makes sure that the arguments all end up being atomic.
384 That means it may generate some Lets, hence the strange type
387 simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
388 simplConArgs [] thing_inside
391 simplConArgs (arg:args) thing_inside
392 = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
393 -- Simplify the RHS with inlining switched off, so that
394 -- only absolutely essential things will happen.
396 simplConArgs args $ \ args' ->
398 -- If the argument ain't trivial, then let-bind it
399 if exprIsTrivial arg' then
400 thing_inside (arg' : args')
402 newId (coreExprType arg') $ \ arg_id ->
403 thing_inside (Var arg_id : args') `thenSmpl` \ res ->
404 returnSmpl (addBind (NonRec arg_id arg') res)
408 ---------------------------------
410 simplType :: InType -> SimplM OutType
412 = getSubst `thenSmpl` \ subst ->
413 returnSmpl (substTy subst ty)
417 %************************************************************************
421 %************************************************************************
423 @simplBeta@ is used for non-recursive lets in expressions,
424 as well as true beta reduction.
426 Very similar to @simplLazyBind@, but not quite the same.
429 simplBeta :: InId -- Binder
430 -> InExpr -> SubstEnv -- Arg, with its subst-env
431 -> OutType -- Type of thing computed by the context
432 -> SimplM OutExprStuff -- The body
433 -> SimplM OutExprStuff
435 simplBeta bndr rhs rhs_se cont_ty thing_inside
437 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
440 simplBeta bndr rhs rhs_se cont_ty thing_inside
441 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
442 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
443 extendSubst bndr (ContEx rhs_se rhs) thing_inside
446 = -- Simplify the RHS
447 simplBinder bndr $ \ bndr' ->
448 simplArg (idType bndr') (getIdDemandInfo bndr)
449 rhs rhs_se cont_ty $ \ rhs' ->
451 -- Now complete the binding and simplify the body
452 completeBeta bndr bndr' rhs' thing_inside
454 completeBeta bndr bndr' rhs' thing_inside
455 | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
456 -- Make a case expression instead of a let
457 -- These can arise either from the desugarer,
458 -- or from beta reductions: (\x.e) (x +# y)
459 = getInScope `thenSmpl` \ in_scope ->
460 thing_inside `thenSmpl` \ (floats, (_, body)) ->
461 returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
464 = completeBinding bndr bndr' rhs' thing_inside
469 simplArg :: OutType -> Demand
470 -> InExpr -> SubstEnv
471 -> OutType -- Type of thing computed by the context
472 -> (OutExpr -> SimplM OutExprStuff)
473 -> SimplM OutExprStuff
474 simplArg arg_ty demand arg arg_se cont_ty thing_inside
476 isUnLiftedType arg_ty ||
477 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
478 -- Return true only for dictionary types where the dictionary
479 -- has more than one component (else we risk poking on the component
480 -- of a newtype dictionary)
481 = getSubstEnv `thenSmpl` \ body_se ->
482 transformRhs arg `thenSmpl` \ t_arg ->
483 setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
484 setSubstEnv body_se (thing_inside arg')
485 )) -- NB: we must restore body_se before carrying on with thing_inside!!
488 = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
493 - deals only with Ids, not TyVars
494 - take an already-simplified RHS
496 It does *not* attempt to do let-to-case. Why? Because they are used for
499 (when let-to-case is impossible)
501 - many situations where the "rhs" is known to be a WHNF
502 (so let-to-case is inappropriate).
505 completeBinding :: InId -- Binder
506 -> OutId -- New binder
507 -> OutExpr -- Simplified RHS
508 -> SimplM (OutStuff a) -- Thing inside
509 -> SimplM (OutStuff a)
511 completeBinding old_bndr new_bndr new_rhs thing_inside
512 | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
513 -- known constructor: case (a,b) of x { (p,q) -> ... }
514 -- Here x isn't mentioned in the RHS, so we don't want to
515 -- create the (dead) let-binding let x = (a,b) in ...
518 | postInlineUnconditionally old_bndr new_rhs
519 -- Maybe we don't need a let-binding! Maybe we can just
520 -- inline it right away. Unlike the preInlineUnconditionally case
521 -- we are allowed to look at the RHS.
523 -- NB: a loop breaker never has postInlineUnconditionally True
524 -- and non-loop-breakers only have *forward* references
525 -- Hence, it's safe to discard the binding
526 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
527 extendSubst old_bndr (DoneEx new_rhs)
531 = getSubst `thenSmpl` \ subst ->
533 bndr_info = idInfo old_bndr
534 old_rules = specInfo bndr_info
535 new_rules = substRules subst old_rules
537 -- The new binding site Id needs its specialisations re-attached
538 bndr_w_arity = new_bndr `setIdArity` ArityAtLeast (exprArity new_rhs)
541 | isEmptyCoreRules old_rules = bndr_w_arity
542 | otherwise = bndr_w_arity `setIdSpecialisation` new_rules
544 -- At the occurrence sites we want to know the unfolding,
545 -- and the occurrence info of the original
546 -- (simplBinder cleaned up the inline prag of the original
547 -- to eliminate un-stable info, in case this expression is
548 -- simplified a second time; hence the need to reattach it)
549 occ_site_id = binding_site_id
550 `setIdUnfolding` mkUnfolding new_rhs
551 `setInlinePragma` inlinePragInfo bndr_info
553 modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
554 returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff)
558 %************************************************************************
560 \subsection{simplLazyBind}
562 %************************************************************************
564 simplLazyBind basically just simplifies the RHS of a let(rec).
565 It does two important optimisations though:
567 * It floats let(rec)s out of the RHS, even if they
568 are hidden by big lambdas
570 * It does eta expansion
573 simplLazyBind :: TopLevelFlag
576 -> SimplM (OutStuff a) -- The body of the binding
577 -> SimplM (OutStuff a)
578 -- When called, the subst env is correct for the entire let-binding
579 -- and hence right for the RHS.
580 -- Also the binder has already been simplified, and hence is in scope
582 simplLazyBind top_lvl bndr bndr' rhs thing_inside
583 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
584 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
585 getSubstEnv `thenSmpl` \ rhs_se ->
586 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
589 = -- Simplify the RHS
590 getSubstEnv `thenSmpl` \ rhs_se ->
592 simplRhs top_lvl False {- Not ok to float unboxed -}
594 rhs rhs_se $ \ rhs' ->
596 -- Now compete the binding and simplify the body
597 completeBinding bndr bndr' rhs' thing_inside
603 simplRhs :: TopLevelFlag
604 -> Bool -- True <=> OK to float unboxed (speculative) bindings
605 -> OutType -> InExpr -> SubstEnv
606 -> (OutExpr -> SimplM (OutStuff a))
607 -> SimplM (OutStuff a)
608 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
609 = -- Swizzle the inner lets past the big lambda (if any)
610 -- and try eta expansion
611 transformRhs rhs `thenSmpl` \ t_rhs ->
614 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
616 -- Float lets out of RHS
618 (floats_out, rhs'') | float_ubx = (floats, rhs')
619 | otherwise = splitFloats floats rhs'
621 if (isTopLevel top_lvl || exprIsWHNF rhs') && -- Float lets if (a) we're at the top level
622 not (null floats_out) -- or (b) it exposes a HNF
624 tickLetFloat floats_out `thenSmpl_`
627 -- There's a subtlety here. There may be a binding (x* = e) in the
628 -- floats, where the '*' means 'will be demanded'. So is it safe
629 -- to float it out? Answer no, but it won't matter because
630 -- we only float if arg' is a WHNF,
631 -- and so there can't be any 'will be demanded' bindings in the floats.
633 WARN( any demanded_float floats_out, ppr floats_out )
634 setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
635 -- in_scope' may be excessive, but that's OK;
636 -- it's a superset of what's in scope
637 returnSmpl (addBinds floats_out stuff)
639 -- Don't do the float
640 thing_inside (mkLets floats rhs')
642 -- In a let-from-let float, we just tick once, arbitrarily
643 -- choosing the first floated binder to identify it
644 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
645 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
647 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
648 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
649 demanded_float (Rec _) = False
651 -- Don't float any unlifted bindings out, because the context
652 -- is either a Rec group, or the top level, neither of which
653 -- can tolerate them.
654 splitFloats floats rhs
658 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
659 | otherwise = case go fs of
660 (out, rhs') -> (f:out, rhs')
662 must_stay (Rec prs) = False -- No unlifted bindings in here
663 must_stay (NonRec b r) = isUnLiftedType (idType b)
668 %************************************************************************
670 \subsection{Variables}
672 %************************************************************************
676 = freeTick LeafVisit `thenSmpl_`
677 getSubst `thenSmpl` \ subst ->
678 case lookupSubst subst var of
679 Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
680 Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
681 Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
684 var' = case lookupInScope subst var of
688 if isLocallyDefined var && not (idMustBeINLINEd var)
689 -- The idMustBeINLINEd test accouunts for the fact
690 -- that class method selectors don't have top level
691 -- bindings and hence aren't in scope.
694 pprTrace "simplVar:" (ppr var) var
699 getBlackList `thenSmpl` \ black_list ->
700 getInScope `thenSmpl` \ in_scope ->
702 prepareArgs (ppr var') (idType var') (get_str var') cont $ \ args' cont' ->
703 completeCall black_list in_scope var' args' cont'
705 get_str var = case getIdStrictness var of
706 NoStrictnessInfo -> (repeat wwLazy, False)
707 StrictnessInfo demands result_bot -> (demands, result_bot)
710 ---------------------------------------------------------
711 -- Preparing arguments for a call
713 prepareArgs :: SDoc -- Error message info
714 -> OutType -> ([Demand],Bool) -> SimplCont
715 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
716 -> SimplM OutExprStuff
718 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
719 = go [] demands orig_fun_ty orig_cont
721 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
722 -- "No strictness info" is signalled by an infinite list of wwLazy
724 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
725 | result_bot = fun_demands -- Enough args, and function returns bottom
726 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
727 -- NB: demands is finite iff enough args and result_bot is True
729 -- Main game plan: loop through the arguments, simplifying
730 -- each of them in turn. We carry with us a list of demands,
731 -- and the type of the function-applied-to-earlier-args
734 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
735 = getInScope `thenSmpl` \ in_scope ->
737 ty_arg' = substTy (mkSubst in_scope se) ty_arg
738 res_ty = applyTy fun_ty ty_arg'
740 go (Type ty_arg' : acc) ds res_ty cont
743 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
744 = case splitFunTy_maybe fun_ty of {
745 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
746 (thing_inside (reverse acc) cont) ;
747 Just (arg_ty, res_ty) ->
748 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
749 go (arg':acc) ds res_ty cont }
751 -- We've run out of demands, which only happens for functions
752 -- we *know* now return bottom
754 -- * case (error "hello") of { ... }
755 -- * (error "Hello") arg
756 -- * f (error "Hello") where f is strict
758 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
759 thing_inside (reverse acc) (discardCont cont)
761 -- We're run out of arguments
762 go acc ds fun_ty cont = thing_inside (reverse acc) cont
764 -- Boring: we must only record a tick if there was an interesting
765 -- continuation to discard. If not, we tick forever.
766 tick_case_of_error (Stop _) = returnSmpl ()
767 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
768 tick_case_of_error other = tick BottomFound
770 ---------------------------------------------------------
771 -- Dealing with a call
773 completeCall black_list_fn in_scope var args cont
774 -- Look for rules or specialisations that match
775 -- Do this *before* trying inlining because some functions
776 -- have specialisations *and* are strict; we don't want to
777 -- inline the wrapper of the non-specialised thing... better
778 -- to call the specialised thing instead.
779 | maybeToBool maybe_rule_match
780 = tick (RuleFired rule_name) `thenSmpl_`
781 zapSubstEnv (completeApp rule_rhs rule_args cont)
782 -- See note below about zapping the substitution here
784 -- Look for an unfolding. There's a binding for the
785 -- thing, but perhaps we want to inline it anyway
786 | maybeToBool maybe_inline
787 = tick (UnfoldingDone var) `thenSmpl_`
788 zapSubstEnv (completeInlining var unf_template args (discardInlineCont cont))
789 -- The template is already simplified, so don't re-substitute.
790 -- This is VITAL. Consider
792 -- let y = \z -> ...x... in
794 -- We'll clone the inner \x, adding x->x' in the id_subst
795 -- Then when we inline y, we must *not* replace x by x' in
796 -- the inlined copy!!
798 | otherwise -- Neither rule nor inlining
799 = rebuild (mkApps (Var var) args) cont
802 ---------- Unfolding stuff
803 maybe_inline = callSiteInline black_listed inline_call
804 var args interesting_cont
805 Just unf_template = maybe_inline
806 interesting_cont = contIsInteresting cont
807 inline_call = contIsInline cont
808 black_listed = black_list_fn var
810 ---------- Specialisation stuff
811 maybe_rule_match = lookupRule in_scope var args
812 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
815 -- First a special case
816 -- Don't actually inline the scrutinee when we see
817 -- case x of y { .... }
818 -- and x has unfolding (C a b). Why not? Because
819 -- we get a silly binding y = C a b. If we don't
820 -- inline knownCon can directly substitute x for y instead.
821 completeInlining var (Con con con_args) args (Select _ bndr alts se cont)
823 = ASSERT( null args )
824 knownCon (Var var) con con_args bndr alts se cont
826 -- Now the normal case
827 completeInlining var unfolding args cont
828 = completeApp unfolding args cont
830 -- completeApp applies a new InExpr (from an unfolding or rule)
831 -- to an *already simplified* set of arguments
832 completeApp :: InExpr -- (\xs. body)
833 -> [OutExpr] -- Args; already simplified
834 -> SimplCont -- What to do with result of applicatoin
835 -> SimplM OutExprStuff
836 completeApp fun args cont
839 zap_it = mkLamBndrZapper fun (length args)
840 cont_ty = contResultType cont
842 -- These equations are very similar to simplLam and simplBeta combined,
843 -- except that they deal with already-simplified arguments
846 go (Lam bndr fun) (Type ty:args) = tick (BetaReduction bndr) `thenSmpl_`
847 extendSubst bndr (DoneTy ty)
851 go (Lam bndr fun) (arg:args)
852 | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
853 = tick (BetaReduction bndr) `thenSmpl_`
854 tick (PreInlineUnconditionally bndr) `thenSmpl_`
855 extendSubst bndr (DoneEx arg)
858 = tick (BetaReduction bndr) `thenSmpl_`
859 simplBinder zapped_bndr ( \ bndr' ->
860 completeBeta zapped_bndr bndr' arg $
864 zapped_bndr = zap_it bndr
866 -- Consumed all the lambda binders or args
867 go fun args = simplExprF fun (pushArgs emptySubstEnv args cont)
870 ----------- costCentreOk
871 -- costCentreOk checks that it's ok to inline this thing
872 -- The time it *isn't* is this:
874 -- f x = let y = E in
875 -- scc "foo" (...y...)
877 -- Here y has a "current cost centre", and we can't inline it inside "foo",
878 -- regardless of whether E is a WHNF or not.
880 costCentreOk ccs_encl cc_rhs
881 = not opt_SccProfilingOn
882 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
883 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
887 %************************************************************************
889 \subsection{Decisions about inlining}
891 %************************************************************************
894 preInlineUnconditionally :: InId -> Bool
895 -- Examines a bndr to see if it is used just once in a
896 -- completely safe way, so that it is safe to discard the binding
897 -- inline its RHS at the (unique) usage site, REGARDLESS of how
898 -- big the RHS might be. If this is the case we don't simplify
899 -- the RHS first, but just inline it un-simplified.
901 -- This is much better than first simplifying a perhaps-huge RHS
902 -- and then inlining and re-simplifying it.
904 -- NB: we don't even look at the RHS to see if it's trivial
907 -- where x is used many times, but this is the unique occurrence
908 -- of y. We should NOT inline x at all its uses, because then
909 -- we'd do the same for y -- aargh! So we must base this
910 -- pre-rhs-simplification decision solely on x's occurrences, not
913 -- Evne RHSs labelled InlineMe aren't caught here, because
914 -- there might be no benefit from inlining at the call site.
915 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
916 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
917 preInlineUnconditionally bndr
918 = case getInlinePragma bndr of
919 IMustBeINLINEd -> True
920 ICanSafelyBeINLINEd InsideLam _ -> False
921 ICanSafelyBeINLINEd not_in_lam True -> True -- Not inside a lambda,
922 -- one occurrence ==> safe!
926 postInlineUnconditionally :: InId -> OutExpr -> Bool
927 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
928 -- It returns True if it's ok to discard the binding and inline the
929 -- RHS at every use site.
931 -- NOTE: This isn't our last opportunity to inline.
932 -- We're at the binding site right now, and
933 -- we'll get another opportunity when we get to the ocurrence(s)
935 postInlineUnconditionally bndr rhs
939 = case getInlinePragma bndr of
940 IAmALoopBreaker -> False
942 ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
943 -- Don't inline even WHNFs inside lambdas; doing so may
944 -- simply increase allocation when the function is called
945 -- This isn't the last chance; see NOTE above.
947 ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
948 -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
949 -- decision about duplicating code is best left to callSiteInline
951 other -> exprIsTrivial rhs -- Duplicating is *free*
952 -- NB: Even InlineMe and IMustBeINLINEd are ignored here
953 -- Why? Because we don't even want to inline them into the
954 -- RHS of constructor arguments. See NOTE above
955 -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
956 -- it's best to inline it anyway. We often get a=E; b=a
957 -- from desugaring, with both a and b marked NOINLINE.
961 inlineCase bndr scrut
962 = exprIsTrivial scrut -- Duplication is free
963 && ( isUnLiftedType (idType bndr)
964 || scrut_is_evald_var -- So dropping the case won't change termination
965 || isStrict (getIdDemandInfo bndr) -- It's going to get evaluated later, so again
966 -- termination doesn't change
967 || not opt_SimplPedanticBottoms) -- Or we don't care!
969 -- Check whether or not scrut is known to be evaluted
970 -- It's not going to be a visible value (else the previous
971 -- blob would apply) so we just check the variable case
972 scrut_is_evald_var = case scrut of
973 Var v -> isEvaldUnfolding (getIdUnfolding v)
979 %************************************************************************
981 \subsection{The main rebuilder}
983 %************************************************************************
986 -------------------------------------------------------------------
989 = getInScope `thenSmpl` \ in_scope ->
990 returnSmpl ([], (in_scope, expr))
992 ---------------------------------------------------------
993 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
996 rebuild expr (Stop _) = rebuild_done expr
998 -- ArgOf continuation
999 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1001 -- ApplyTo continuation
1002 rebuild expr cont@(ApplyTo _ arg se cont')
1003 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1004 rebuild (App expr arg') cont'
1006 -- Coerce continuation
1007 rebuild expr (CoerceIt to_ty cont)
1008 = rebuild (mkCoerce to_ty expr) cont
1010 -- Inline continuation
1011 rebuild expr (InlinePlease cont)
1012 = rebuild (Note InlineCall expr) cont
1014 -- Case of known constructor or literal
1015 rebuild expr@(Con con args) (Select _ bndr alts se cont)
1016 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
1017 = knownCon expr con args bndr alts se cont
1019 -- Case of other value (e.g. a partial application or lambda)
1020 -- Turn it back into a let
1021 rebuild scrut (Select _ bndr ((DEFAULT, bs, rhs):alts) se cont)
1022 | isUnLiftedType (idType bndr) && exprOkForSpeculation scrut
1024 = ASSERT( null bs && null alts )
1026 simplBinder bndr $ \ bndr' ->
1027 completeBinding bndr bndr' scrut $
1031 ---------------------------------------------------------
1032 -- The other Select cases
1034 rebuild scrut (Select _ bndr alts se cont)
1035 | all (cheapEqExpr rhs1) other_rhss
1036 && inlineCase bndr scrut
1037 && all binders_unused alts
1038 && opt_SimplDoCaseElim
1039 = -- Get rid of the case altogether
1040 -- See the extensive notes on case-elimination below
1041 -- Remember to bind the binder though!
1042 tick (CaseElim bndr) `thenSmpl_`
1044 extendSubst bndr (DoneEx scrut) $
1045 simplExprF rhs1 cont
1048 = rebuild_case scrut bndr alts se cont
1050 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1051 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1054 Case elimination [see the code above]
1056 Start with a simple situation:
1058 case x# of ===> e[x#/y#]
1061 (when x#, y# are of primitive type, of course). We can't (in general)
1062 do this for algebraic cases, because we might turn bottom into
1065 Actually, we generalise this idea to look for a case where we're
1066 scrutinising a variable, and we know that only the default case can
1071 other -> ...(case x of
1075 Here the inner case can be eliminated. This really only shows up in
1076 eliminating error-checking code.
1078 We also make sure that we deal with this very common case:
1083 Here we are using the case as a strict let; if x is used only once
1084 then we want to inline it. We have to be careful that this doesn't
1085 make the program terminate when it would have diverged before, so we
1087 - x is used strictly, or
1088 - e is already evaluated (it may so if e is a variable)
1090 Lastly, we generalise the transformation to handle this:
1096 We only do this for very cheaply compared r's (constructors, literals
1097 and variables). If pedantic bottoms is on, we only do it when the
1098 scrutinee is a PrimOp which can't fail.
1100 We do it *here*, looking at un-simplified alternatives, because we
1101 have to check that r doesn't mention the variables bound by the
1102 pattern in each alternative, so the binder-info is rather useful.
1104 So the case-elimination algorithm is:
1106 1. Eliminate alternatives which can't match
1108 2. Check whether all the remaining alternatives
1109 (a) do not mention in their rhs any of the variables bound in their pattern
1110 and (b) have equal rhss
1112 3. Check we can safely ditch the case:
1113 * PedanticBottoms is off,
1114 or * the scrutinee is an already-evaluated variable
1115 or * the scrutinee is a primop which is ok for speculation
1116 -- ie we want to preserve divide-by-zero errors, and
1117 -- calls to error itself!
1119 or * [Prim cases] the scrutinee is a primitive variable
1121 or * [Alg cases] the scrutinee is a variable and
1122 either * the rhs is the same variable
1123 (eg case x of C a b -> x ===> x)
1124 or * there is only one alternative, the default alternative,
1125 and the binder is used strictly in its scope.
1126 [NB this is helped by the "use default binder where
1127 possible" transformation; see below.]
1130 If so, then we can replace the case with one of the rhss.
1133 Blob of helper functions for the "case-of-something-else" situation.
1136 ---------------------------------------------------------
1137 -- Case of something else
1139 rebuild_case scrut case_bndr alts se cont
1140 = -- Prepare case alternatives
1141 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1142 scrut_cons alts `thenSmpl` \ better_alts ->
1144 -- Set the new subst-env in place (before dealing with the case binder)
1147 -- Deal with the case binder, and prepare the continuation;
1148 -- The new subst_env is in place
1149 prepareCaseCont better_alts cont $ \ cont' ->
1152 -- Deal with variable scrutinee
1153 ( simplBinder case_bndr $ \ case_bndr' ->
1154 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1156 case_bndr'' = zap_occ_info case_bndr'
1159 -- Deal with the case alternaatives
1160 simplAlts zap_occ_info scrut_cons
1161 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1163 mkCase scrut case_bndr'' alts'
1164 ) `thenSmpl` \ case_expr ->
1166 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1167 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1168 -- that should not include these chaps!
1169 rebuild_done case_expr
1171 -- scrut_cons tells what constructors the scrutinee can't possibly match
1172 scrut_cons = case scrut of
1173 Var v -> case getIdUnfolding v of
1174 OtherCon cons -> cons
1179 knownCon expr con args bndr alts se cont
1180 = tick (KnownBranch bndr) `thenSmpl_`
1182 simplBinder bndr $ \ bndr' ->
1183 case findAlt con alts of
1184 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1185 completeBinding bndr bndr' expr $
1186 -- Don't use completeBeta here. The expr might be
1187 -- an unboxed literal, like 3, or a variable
1188 -- whose unfolding is an unboxed literal... and
1189 -- completeBeta will just construct another case
1193 (Literal lit, bs, rhs) -> ASSERT( null bs )
1194 extendSubst bndr (DoneEx expr) $
1195 -- Unconditionally substitute, because expr must
1196 -- be a variable or a literal. It can't be a
1197 -- NoRep literal because they don't occur in
1201 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1202 completeBinding bndr bndr' expr $
1204 extendSubstList bs (map mk real_args) $
1207 real_args = drop (dataConNumInstArgs dc) args
1208 mk (Type ty) = DoneTy ty
1209 mk other = DoneEx other
1214 prepareCaseCont :: [InAlt] -> SimplCont
1215 -> (SimplCont -> SimplM (OutStuff a))
1216 -> SimplM (OutStuff a)
1217 -- Polymorphic recursion here!
1219 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1220 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1223 substForVarScrut checks whether the scrutinee is a variable, v.
1224 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1225 that way, there's a chance that v will now only be used once, and hence inlined.
1227 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1228 in the case binder, because the case-binder now effectively occurs
1229 whenever v does. AND we have to do the same for the pattern-bound
1232 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1234 Here, b and p are dead. But when we move the argment inside the first
1235 case RHS, and eliminate the second case, we get
1237 case x or { (a,b) -> a b }
1239 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1240 happened. Hence the zap_occ_info function returned by substForVarScrut
1243 substForVarScrut (Var v) case_bndr' thing_inside
1244 | isLocallyDefined v -- No point for imported things
1245 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1246 `setInlinePragma` IMustBeINLINEd) $
1247 -- We could extend the substitution instead, but it would be
1248 -- a hack because then the substitution wouldn't be idempotent
1250 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1252 substForVarScrut other_scrut case_bndr' thing_inside
1253 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1256 prepareCaseAlts does two things:
1258 1. Remove impossible alternatives
1260 2. If the DEFAULT alternative can match only one possible constructor,
1261 then make that constructor explicit.
1263 case e of x { DEFAULT -> rhs }
1265 case e of x { (a,b) -> rhs }
1266 where the type is a single constructor type. This gives better code
1267 when rhs also scrutinises x or e.
1270 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1272 = case (findDefault filtered_alts, missing_cons) of
1274 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1275 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1277 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1279 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1281 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1282 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1284 newIds (dataConArgTys
1286 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1287 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1289 other -> returnSmpl filtered_alts
1291 -- Filter out alternatives that can't possibly match
1292 filtered_alts = case scrut_cons of
1294 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1296 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1297 not (data_con `elem` handled_data_cons)]
1298 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1299 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1302 prepareCaseAlts _ _ scrut_cons alts
1303 = returnSmpl alts -- Functions
1306 ----------------------
1307 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1308 = mapSmpl simpl_alt alts
1310 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1311 Just (tycon, inst_tys) -> inst_tys
1313 -- handled_cons is all the constructors that are dealt
1314 -- with, either by being impossible, or by there being an alternative
1315 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1317 simpl_alt (DEFAULT, _, rhs)
1318 = -- In the default case we record the constructors that the
1319 -- case-binder *can't* be.
1320 -- We take advantage of any OtherCon info in the case scrutinee
1321 modifyInScope (case_bndr'' `setIdUnfolding` OtherCon handled_cons) $
1322 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1323 returnSmpl (DEFAULT, [], rhs')
1325 simpl_alt (con, vs, rhs)
1326 = -- Deal with the pattern-bound variables
1327 -- Mark the ones that are in ! positions in the data constructor
1328 -- as certainly-evaluated
1329 simplBinders (add_evals con vs) $ \ vs' ->
1331 -- Bind the case-binder to (Con args)
1333 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1335 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1336 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1337 returnSmpl (con, vs', rhs')
1340 -- add_evals records the evaluated-ness of the bound variables of
1341 -- a case pattern. This is *important*. Consider
1342 -- data T = T !Int !Int
1344 -- case x of { T a b -> T (a+1) b }
1346 -- We really must record that b is already evaluated so that we don't
1347 -- go and re-evaluate it when constructing the result.
1349 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1350 add_evals other_con vs = vs
1352 cat_evals [] [] = []
1353 cat_evals (v:vs) (str:strs)
1354 | isTyVar v = v : cat_evals vs (str:strs)
1355 | isStrict str = (v' `setIdUnfolding` OtherCon []) : cat_evals vs strs
1356 | otherwise = v' : cat_evals vs strs
1362 %************************************************************************
1364 \subsection{Duplicating continuations}
1366 %************************************************************************
1369 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1371 -> (SimplCont -> SimplM (OutStuff a))
1372 -> SimplM (OutStuff a)
1373 mkDupableCont ty cont thing_inside
1374 | contIsDupable cont
1377 mkDupableCont _ (CoerceIt ty cont) thing_inside
1378 = mkDupableCont ty cont $ \ cont' ->
1379 thing_inside (CoerceIt ty cont')
1381 mkDupableCont ty (InlinePlease cont) thing_inside
1382 = mkDupableCont ty cont $ \ cont' ->
1383 thing_inside (InlinePlease cont')
1385 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1386 = -- Build the RHS of the join point
1387 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1388 newId join_arg_ty' ( \ arg_id ->
1389 getSwitchChecker `thenSmpl` \ chkr ->
1390 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1391 returnSmpl (Lam arg_id (mkLets binds rhs))
1392 ) `thenSmpl` \ join_rhs ->
1394 -- Build the join Id and continuation
1395 newId (coreExprType join_rhs) $ \ join_id ->
1397 new_cont = ArgOf OkToDup cont_ty
1398 (\arg' -> rebuild_done (App (Var join_id) arg'))
1401 -- Do the thing inside
1402 thing_inside new_cont `thenSmpl` \ res ->
1403 returnSmpl (addBind (NonRec join_id join_rhs) res)
1405 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1406 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1407 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1408 if exprIsDupable arg' then
1409 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1411 newId (coreExprType arg') $ \ bndr ->
1412 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1413 returnSmpl (addBind (NonRec bndr arg') res)
1415 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1416 = tick (CaseOfCase case_bndr) `thenSmpl_`
1418 simplBinder case_bndr $ \ case_bndr' ->
1419 prepareCaseCont alts cont $ \ cont' ->
1420 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1421 returnSmpl (concat alt_binds_s, alts')
1422 ) `thenSmpl` \ (alt_binds, alts') ->
1424 extendInScopes [b | NonRec b _ <- alt_binds] $
1426 -- NB that the new alternatives, alts', are still InAlts, using the original
1427 -- binders. That means we can keep the case_bndr intact. This is important
1428 -- because another case-of-case might strike, and so we want to keep the
1429 -- info that the case_bndr is dead (if it is, which is often the case).
1430 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1431 -- case in I/O rich code. We aren't allowed a lambda bound
1432 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1433 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1435 returnSmpl (addBinds alt_binds res)
1438 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1439 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1440 = -- Not worth checking whether the rhs is small; the
1441 -- inliner will inline it if so.
1442 simplBinders bndrs $ \ bndrs' ->
1443 simplExprC rhs cont `thenSmpl` \ rhs' ->
1445 rhs_ty' = coreExprType rhs'
1446 (used_bndrs, used_bndrs')
1447 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1448 (case_bndr' : bndrs'),
1449 not (isDeadBinder bndr)]
1450 -- The new binders have lost their occurrence info,
1451 -- so we have to extract it from the old ones
1453 ( if null used_bndrs'
1454 -- If we try to lift a primitive-typed something out
1455 -- for let-binding-purposes, we will *caseify* it (!),
1456 -- with potentially-disastrous strictness results. So
1457 -- instead we turn it into a function: \v -> e
1458 -- where v::State# RealWorld#. The value passed to this function
1459 -- is realworld#, which generates (almost) no code.
1461 -- There's a slight infelicity here: we pass the overall
1462 -- case_bndr to all the join points if it's used in *any* RHS,
1463 -- because we don't know its usage in each RHS separately
1465 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1466 -- we make the join point into a function whenever used_bndrs'
1467 -- is empty. This makes the join-point more CPR friendly.
1468 -- Consider: let j = if .. then I# 3 else I# 4
1469 -- in case .. of { A -> j; B -> j; C -> ... }
1471 -- Now CPR should not w/w j because it's a thunk, so
1472 -- that means that the enclosing function can't w/w either,
1473 -- which is a BIG LOSE. This actually happens in practice
1474 then newId realWorldStatePrimTy $ \ rw_id ->
1475 returnSmpl ([rw_id], [Var realWorldPrimId])
1477 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1479 `thenSmpl` \ (final_bndrs', final_args) ->
1481 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1482 returnSmpl ([NonRec join_bndr (mkLams final_bndrs' rhs')],
1483 (con, bndrs, mkApps (Var join_bndr) final_args))