2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[Simplify]{The main module of the simplifier}
7 module Simplify ( simplTopBinds, simplExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( intSwitchSet,
12 opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
13 opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
18 import SimplUtils ( mkCase, transformRhs, findAlt,
19 simplBinder, simplBinders, simplIds, findDefault, mkCoerce
21 import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
24 import Id ( Id, idType, idInfo, idUnique,
25 getIdUnfolding, setIdUnfolding, isExportedId,
26 getIdSpecialisation, setIdSpecialisation,
27 getIdDemandInfo, setIdDemandInfo,
28 getIdArity, setIdArity,
30 setInlinePragma, getInlinePragma, idMustBeINLINEd,
33 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
34 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
35 specInfo, inlinePragInfo, zapLamIdInfo
37 import Demand ( Demand, isStrict, wwLazy )
38 import Const ( isWHNFCon, conOkForAlt )
39 import ConFold ( tryPrimOp )
40 import PrimOp ( PrimOp, primOpStrictness, primOpType )
41 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
42 import Const ( Con(..) )
43 import Name ( isLocallyDefined )
45 import CoreFVs ( exprFreeVars )
46 import CoreUnfold ( Unfolding(..), mkUnfolding, callSiteInline,
47 isEvaldUnfolding, blackListed )
48 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsWHNF, 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 || exprIsWHNF rhs') && -- Float lets if (a) we're at the top level
623 not (null floats_out) -- or (b) it exposes a HNF
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 ->
703 prepareArgs (ppr var') (idType var') (get_str var') cont $ \ args' cont' ->
704 completeCall black_list in_scope var' args' cont'
706 get_str var = case getIdStrictness var of
707 NoStrictnessInfo -> (repeat wwLazy, False)
708 StrictnessInfo demands result_bot -> (demands, result_bot)
711 ---------------------------------------------------------
712 -- Preparing arguments for a call
714 prepareArgs :: SDoc -- Error message info
715 -> OutType -> ([Demand],Bool) -> SimplCont
716 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
717 -> SimplM OutExprStuff
719 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
720 = go [] demands orig_fun_ty orig_cont
722 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
723 -- "No strictness info" is signalled by an infinite list of wwLazy
725 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
726 | result_bot = fun_demands -- Enough args, and function returns bottom
727 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
728 -- NB: demands is finite iff enough args and result_bot is True
730 -- Main game plan: loop through the arguments, simplifying
731 -- each of them in turn. We carry with us a list of demands,
732 -- and the type of the function-applied-to-earlier-args
735 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
736 = getInScope `thenSmpl` \ in_scope ->
738 ty_arg' = substTy (mkSubst in_scope se) ty_arg
739 res_ty = applyTy fun_ty ty_arg'
741 go (Type ty_arg' : acc) ds res_ty cont
744 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
745 = case splitFunTy_maybe fun_ty of {
746 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
747 (thing_inside (reverse acc) cont) ;
748 Just (arg_ty, res_ty) ->
749 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
750 go (arg':acc) ds res_ty cont }
752 -- We've run out of demands, which only happens for functions
753 -- we *know* now return bottom
755 -- * case (error "hello") of { ... }
756 -- * (error "Hello") arg
757 -- * f (error "Hello") where f is strict
759 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
760 thing_inside (reverse acc) (discardCont cont)
762 -- We're run out of arguments
763 go acc ds fun_ty cont = thing_inside (reverse acc) cont
765 -- Boring: we must only record a tick if there was an interesting
766 -- continuation to discard. If not, we tick forever.
767 tick_case_of_error (Stop _) = returnSmpl ()
768 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
769 tick_case_of_error other = tick BottomFound
771 ---------------------------------------------------------
772 -- Dealing with a call
774 completeCall black_list_fn in_scope var args cont
775 -- Look for rules or specialisations that match
776 -- Do this *before* trying inlining because some functions
777 -- have specialisations *and* are strict; we don't want to
778 -- inline the wrapper of the non-specialised thing... better
779 -- to call the specialised thing instead.
780 | maybeToBool maybe_rule_match
781 = tick (RuleFired rule_name) `thenSmpl_`
782 zapSubstEnv (completeApp rule_rhs rule_args cont)
783 -- See note below about zapping the substitution here
785 -- Look for an unfolding. There's a binding for the
786 -- thing, but perhaps we want to inline it anyway
787 | maybeToBool maybe_inline
788 = tick (UnfoldingDone var) `thenSmpl_`
789 zapSubstEnv (completeInlining var unf_template args (discardInlineCont cont))
790 -- The template is already simplified, so don't re-substitute.
791 -- This is VITAL. Consider
793 -- let y = \z -> ...x... in
795 -- We'll clone the inner \x, adding x->x' in the id_subst
796 -- Then when we inline y, we must *not* replace x by x' in
797 -- the inlined copy!!
799 | otherwise -- Neither rule nor inlining
800 = rebuild (mkApps (Var var) args) cont
803 ---------- Unfolding stuff
804 maybe_inline = callSiteInline black_listed inline_call
805 var args interesting_cont
806 Just unf_template = maybe_inline
807 interesting_cont = contIsInteresting cont
808 inline_call = contIsInline cont
809 black_listed = black_list_fn var
811 ---------- Specialisation stuff
812 maybe_rule_match = lookupRule in_scope var args
813 Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
816 -- First a special case
817 -- Don't actually inline the scrutinee when we see
818 -- case x of y { .... }
819 -- and x has unfolding (C a b). Why not? Because
820 -- we get a silly binding y = C a b. If we don't
821 -- inline knownCon can directly substitute x for y instead.
822 completeInlining var (Con con con_args) args (Select _ bndr alts se cont)
824 = ASSERT( null args )
825 knownCon (Var var) con con_args bndr alts se cont
827 -- Now the normal case
828 completeInlining var unfolding args cont
829 = completeApp unfolding args cont
831 -- completeApp applies a new InExpr (from an unfolding or rule)
832 -- to an *already simplified* set of arguments
833 completeApp :: InExpr -- (\xs. body)
834 -> [OutExpr] -- Args; already simplified
835 -> SimplCont -- What to do with result of applicatoin
836 -> SimplM OutExprStuff
837 completeApp fun args cont
840 zap_it = mkLamBndrZapper fun (length args)
841 cont_ty = contResultType cont
843 -- These equations are very similar to simplLam and simplBeta combined,
844 -- except that they deal with already-simplified arguments
847 go (Lam bndr fun) (Type ty:args) = tick (BetaReduction bndr) `thenSmpl_`
848 extendSubst bndr (DoneTy ty)
852 go (Lam bndr fun) (arg:args)
853 | preInlineUnconditionally zapped_bndr && not opt_SimplNoPreInlining
854 = tick (BetaReduction bndr) `thenSmpl_`
855 tick (PreInlineUnconditionally bndr) `thenSmpl_`
856 extendSubst zapped_bndr (DoneEx arg)
859 = tick (BetaReduction bndr) `thenSmpl_`
860 simplBinder zapped_bndr ( \ bndr' ->
861 completeBeta zapped_bndr bndr' arg $
865 zapped_bndr = zap_it bndr
867 -- Consumed all the lambda binders or args
868 go fun args = simplExprF fun (pushArgs emptySubstEnv args cont)
871 ----------- costCentreOk
872 -- costCentreOk checks that it's ok to inline this thing
873 -- The time it *isn't* is this:
875 -- f x = let y = E in
876 -- scc "foo" (...y...)
878 -- Here y has a "current cost centre", and we can't inline it inside "foo",
879 -- regardless of whether E is a WHNF or not.
881 costCentreOk ccs_encl cc_rhs
882 = not opt_SccProfilingOn
883 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
884 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
888 %************************************************************************
890 \subsection{Decisions about inlining}
892 %************************************************************************
895 preInlineUnconditionally :: InId -> Bool
896 -- Examines a bndr to see if it is used just once in a
897 -- completely safe way, so that it is safe to discard the binding
898 -- inline its RHS at the (unique) usage site, REGARDLESS of how
899 -- big the RHS might be. If this is the case we don't simplify
900 -- the RHS first, but just inline it un-simplified.
902 -- This is much better than first simplifying a perhaps-huge RHS
903 -- and then inlining and re-simplifying it.
905 -- NB: we don't even look at the RHS to see if it's trivial
908 -- where x is used many times, but this is the unique occurrence
909 -- of y. We should NOT inline x at all its uses, because then
910 -- we'd do the same for y -- aargh! So we must base this
911 -- pre-rhs-simplification decision solely on x's occurrences, not
914 -- Evne RHSs labelled InlineMe aren't caught here, because
915 -- there might be no benefit from inlining at the call site.
916 -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
917 -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
918 preInlineUnconditionally bndr
919 = case getInlinePragma bndr of
920 IMustBeINLINEd -> True
921 ICanSafelyBeINLINEd NotInsideLam 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.
962 %************************************************************************
964 \subsection{The main rebuilder}
966 %************************************************************************
969 -------------------------------------------------------------------
972 = getInScope `thenSmpl` \ in_scope ->
973 returnSmpl ([], (in_scope, expr))
975 ---------------------------------------------------------
976 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
979 rebuild expr (Stop _) = rebuild_done expr
981 -- ArgOf continuation
982 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
984 -- ApplyTo continuation
985 rebuild expr cont@(ApplyTo _ arg se cont')
986 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
987 rebuild (App expr arg') cont'
989 -- Coerce continuation
990 rebuild expr (CoerceIt to_ty cont)
991 = rebuild (mkCoerce to_ty expr) cont
993 -- Inline continuation
994 rebuild expr (InlinePlease cont)
995 = rebuild (Note InlineCall expr) cont
997 -- Case of known constructor or literal
998 rebuild expr@(Con con args) (Select _ bndr alts se cont)
999 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
1000 = knownCon expr con args bndr alts se cont
1003 ---------------------------------------------------------
1004 -- The other Select cases
1006 rebuild scrut (Select _ bndr alts se cont)
1007 | -- Check that the RHSs are all the same, and
1008 -- don't use the binders in the alternatives
1009 -- This test succeeds rapidly in the common case of
1010 -- a single DEFAULT alternative
1011 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1013 -- Check that the scrutinee can be let-bound instead of case-bound
1014 && ( (isUnLiftedType (idType bndr) && -- It's unlifted and floatable
1015 exprOkForSpeculation scrut) -- NB: scrut = an unboxed variable satisfies
1016 || is_a_value scrut -- It's a value
1018 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1019 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1020 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1021 -- its argument: case x of { y -> dataToTag# y }
1022 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1023 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1027 && opt_SimplDoCaseElim
1028 = -- Get rid of the case altogether
1029 -- See the extensive notes on case-elimination below
1030 -- Remember to bind the binder though!
1031 tick (CaseElim bndr) `thenSmpl_` (
1033 simplBinder bndr $ \ bndr' ->
1034 completeBinding bndr bndr' scrut $
1035 simplExprF rhs1 cont)
1038 = rebuild_case scrut bndr alts se cont
1040 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1041 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1043 -- Check whether or not scrut is known to be evaluted
1044 is_a_value (Var v) = isEvaldUnfolding (getIdUnfolding v) -- It's been evaluated
1045 || isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1046 is_a_value scrut = exprIsValue scrut
1049 Case elimination [see the code above]
1051 Start with a simple situation:
1053 case x# of ===> e[x#/y#]
1056 (when x#, y# are of primitive type, of course). We can't (in general)
1057 do this for algebraic cases, because we might turn bottom into
1060 Actually, we generalise this idea to look for a case where we're
1061 scrutinising a variable, and we know that only the default case can
1066 other -> ...(case x of
1070 Here the inner case can be eliminated. This really only shows up in
1071 eliminating error-checking code.
1073 We also make sure that we deal with this very common case:
1078 Here we are using the case as a strict let; if x is used only once
1079 then we want to inline it. We have to be careful that this doesn't
1080 make the program terminate when it would have diverged before, so we
1082 - x is used strictly, or
1083 - e is already evaluated (it may so if e is a variable)
1085 Lastly, we generalise the transformation to handle this:
1091 We only do this for very cheaply compared r's (constructors, literals
1092 and variables). If pedantic bottoms is on, we only do it when the
1093 scrutinee is a PrimOp which can't fail.
1095 We do it *here*, looking at un-simplified alternatives, because we
1096 have to check that r doesn't mention the variables bound by the
1097 pattern in each alternative, so the binder-info is rather useful.
1099 So the case-elimination algorithm is:
1101 1. Eliminate alternatives which can't match
1103 2. Check whether all the remaining alternatives
1104 (a) do not mention in their rhs any of the variables bound in their pattern
1105 and (b) have equal rhss
1107 3. Check we can safely ditch the case:
1108 * PedanticBottoms is off,
1109 or * the scrutinee is an already-evaluated variable
1110 or * the scrutinee is a primop which is ok for speculation
1111 -- ie we want to preserve divide-by-zero errors, and
1112 -- calls to error itself!
1114 or * [Prim cases] the scrutinee is a primitive variable
1116 or * [Alg cases] the scrutinee is a variable and
1117 either * the rhs is the same variable
1118 (eg case x of C a b -> x ===> x)
1119 or * there is only one alternative, the default alternative,
1120 and the binder is used strictly in its scope.
1121 [NB this is helped by the "use default binder where
1122 possible" transformation; see below.]
1125 If so, then we can replace the case with one of the rhss.
1128 Blob of helper functions for the "case-of-something-else" situation.
1131 ---------------------------------------------------------
1132 -- Case of something else
1134 rebuild_case scrut case_bndr alts se cont
1135 = -- Prepare case alternatives
1136 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1137 scrut_cons alts `thenSmpl` \ better_alts ->
1139 -- Set the new subst-env in place (before dealing with the case binder)
1142 -- Deal with the case binder, and prepare the continuation;
1143 -- The new subst_env is in place
1144 prepareCaseCont better_alts cont $ \ cont' ->
1147 -- Deal with variable scrutinee
1148 ( simplBinder case_bndr $ \ case_bndr' ->
1149 substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
1151 case_bndr'' = zap_occ_info case_bndr'
1154 -- Deal with the case alternaatives
1155 simplAlts zap_occ_info scrut_cons
1156 case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
1158 mkCase scrut case_bndr'' alts'
1159 ) `thenSmpl` \ case_expr ->
1161 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1162 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1163 -- that should not include these chaps!
1164 rebuild_done case_expr
1166 -- scrut_cons tells what constructors the scrutinee can't possibly match
1167 scrut_cons = case scrut of
1168 Var v -> case getIdUnfolding v of
1169 OtherCon cons -> cons
1174 knownCon expr con args bndr alts se cont
1175 = tick (KnownBranch bndr) `thenSmpl_`
1177 simplBinder bndr $ \ bndr' ->
1178 case findAlt con alts of
1179 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1180 completeBinding bndr bndr' expr $
1181 -- Don't use completeBeta here. The expr might be
1182 -- an unboxed literal, like 3, or a variable
1183 -- whose unfolding is an unboxed literal... and
1184 -- completeBeta will just construct another case
1188 (Literal lit, bs, rhs) -> ASSERT( null bs )
1189 extendSubst bndr (DoneEx expr) $
1190 -- Unconditionally substitute, because expr must
1191 -- be a variable or a literal. It can't be a
1192 -- NoRep literal because they don't occur in
1196 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1197 completeBinding bndr bndr' expr $
1199 extendSubstList bs (map mk real_args) $
1202 real_args = drop (dataConNumInstArgs dc) args
1203 mk (Type ty) = DoneTy ty
1204 mk other = DoneEx other
1209 prepareCaseCont :: [InAlt] -> SimplCont
1210 -> (SimplCont -> SimplM (OutStuff a))
1211 -> SimplM (OutStuff a)
1212 -- Polymorphic recursion here!
1214 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1215 prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
1218 substForVarScrut checks whether the scrutinee is a variable, v.
1219 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1220 that way, there's a chance that v will now only be used once, and hence inlined.
1222 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1223 in the case binder, because the case-binder now effectively occurs
1224 whenever v does. AND we have to do the same for the pattern-bound
1227 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1229 Here, b and p are dead. But when we move the argment inside the first
1230 case RHS, and eliminate the second case, we get
1232 case x or { (a,b) -> a b }
1234 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1235 happened. Hence the zap_occ_info function returned by substForVarScrut
1238 substForVarScrut (Var v) case_bndr' thing_inside
1239 | isLocallyDefined v -- No point for imported things
1240 = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
1241 `setInlinePragma` IMustBeINLINEd) $
1242 -- We could extend the substitution instead, but it would be
1243 -- a hack because then the substitution wouldn't be idempotent
1245 thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
1247 substForVarScrut other_scrut case_bndr' thing_inside
1248 = thing_inside (\ bndr -> bndr) -- NoOp on bndr
1251 prepareCaseAlts does two things:
1253 1. Remove impossible alternatives
1255 2. If the DEFAULT alternative can match only one possible constructor,
1256 then make that constructor explicit.
1258 case e of x { DEFAULT -> rhs }
1260 case e of x { (a,b) -> rhs }
1261 where the type is a single constructor type. This gives better code
1262 when rhs also scrutinises x or e.
1265 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1267 = case (findDefault filtered_alts, missing_cons) of
1269 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1270 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1272 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1274 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1276 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1277 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1279 newIds (dataConArgTys
1281 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1282 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1284 other -> returnSmpl filtered_alts
1286 -- Filter out alternatives that can't possibly match
1287 filtered_alts = case scrut_cons of
1289 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1291 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1292 not (data_con `elem` handled_data_cons)]
1293 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1294 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1297 prepareCaseAlts _ _ scrut_cons alts
1298 = returnSmpl alts -- Functions
1301 ----------------------
1302 simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
1303 = mapSmpl simpl_alt alts
1305 inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
1306 Just (tycon, inst_tys) -> inst_tys
1308 -- handled_cons is all the constructors that are dealt
1309 -- with, either by being impossible, or by there being an alternative
1310 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1312 simpl_alt (DEFAULT, _, rhs)
1313 = -- In the default case we record the constructors that the
1314 -- case-binder *can't* be.
1315 -- We take advantage of any OtherCon info in the case scrutinee
1316 modifyInScope (case_bndr'' `setIdUnfolding` OtherCon handled_cons) $
1317 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1318 returnSmpl (DEFAULT, [], rhs')
1320 simpl_alt (con, vs, rhs)
1321 = -- Deal with the pattern-bound variables
1322 -- Mark the ones that are in ! positions in the data constructor
1323 -- as certainly-evaluated
1324 simplBinders (add_evals con vs) $ \ vs' ->
1326 -- Bind the case-binder to (Con args)
1328 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1330 modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
1331 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1332 returnSmpl (con, vs', rhs')
1335 -- add_evals records the evaluated-ness of the bound variables of
1336 -- a case pattern. This is *important*. Consider
1337 -- data T = T !Int !Int
1339 -- case x of { T a b -> T (a+1) b }
1341 -- We really must record that b is already evaluated so that we don't
1342 -- go and re-evaluate it when constructing the result.
1344 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1345 add_evals other_con vs = vs
1347 cat_evals [] [] = []
1348 cat_evals (v:vs) (str:strs)
1349 | isTyVar v = v : cat_evals vs (str:strs)
1350 | isStrict str = (v' `setIdUnfolding` OtherCon []) : cat_evals vs strs
1351 | otherwise = v' : cat_evals vs strs
1357 %************************************************************************
1359 \subsection{Duplicating continuations}
1361 %************************************************************************
1364 mkDupableCont :: InType -- Type of the thing to be given to the continuation
1366 -> (SimplCont -> SimplM (OutStuff a))
1367 -> SimplM (OutStuff a)
1368 mkDupableCont ty cont thing_inside
1369 | contIsDupable cont
1372 mkDupableCont _ (CoerceIt ty cont) thing_inside
1373 = mkDupableCont ty cont $ \ cont' ->
1374 thing_inside (CoerceIt ty cont')
1376 mkDupableCont ty (InlinePlease cont) thing_inside
1377 = mkDupableCont ty cont $ \ cont' ->
1378 thing_inside (InlinePlease cont')
1380 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1381 = -- Build the RHS of the join point
1382 simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
1383 newId join_arg_ty' ( \ arg_id ->
1384 getSwitchChecker `thenSmpl` \ chkr ->
1385 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1386 returnSmpl (Lam arg_id (mkLets binds rhs))
1387 ) `thenSmpl` \ join_rhs ->
1389 -- Build the join Id and continuation
1390 newId (coreExprType join_rhs) $ \ join_id ->
1392 new_cont = ArgOf OkToDup cont_ty
1393 (\arg' -> rebuild_done (App (Var join_id) arg'))
1396 -- Do the thing inside
1397 thing_inside new_cont `thenSmpl` \ res ->
1398 returnSmpl (addBind (NonRec join_id join_rhs) res)
1400 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1401 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1402 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1403 if exprIsDupable arg' then
1404 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1406 newId (coreExprType arg') $ \ bndr ->
1407 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1408 returnSmpl (addBind (NonRec bndr arg') res)
1410 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1411 = tick (CaseOfCase case_bndr) `thenSmpl_`
1413 simplBinder case_bndr $ \ case_bndr' ->
1414 prepareCaseCont alts cont $ \ cont' ->
1415 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1416 returnSmpl (concat alt_binds_s, alts')
1417 ) `thenSmpl` \ (alt_binds, alts') ->
1419 extendInScopes [b | NonRec b _ <- alt_binds] $
1421 -- NB that the new alternatives, alts', are still InAlts, using the original
1422 -- binders. That means we can keep the case_bndr intact. This is important
1423 -- because another case-of-case might strike, and so we want to keep the
1424 -- info that the case_bndr is dead (if it is, which is often the case).
1425 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1426 -- case in I/O rich code. We aren't allowed a lambda bound
1427 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1428 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1430 returnSmpl (addBinds alt_binds res)
1433 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1434 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1435 = -- Not worth checking whether the rhs is small; the
1436 -- inliner will inline it if so.
1437 simplBinders bndrs $ \ bndrs' ->
1438 simplExprC rhs cont `thenSmpl` \ rhs' ->
1440 rhs_ty' = coreExprType rhs'
1441 (used_bndrs, used_bndrs')
1442 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1443 (case_bndr' : bndrs'),
1444 not (isDeadBinder bndr)]
1445 -- The new binders have lost their occurrence info,
1446 -- so we have to extract it from the old ones
1448 ( if null used_bndrs'
1449 -- If we try to lift a primitive-typed something out
1450 -- for let-binding-purposes, we will *caseify* it (!),
1451 -- with potentially-disastrous strictness results. So
1452 -- instead we turn it into a function: \v -> e
1453 -- where v::State# RealWorld#. The value passed to this function
1454 -- is realworld#, which generates (almost) no code.
1456 -- There's a slight infelicity here: we pass the overall
1457 -- case_bndr to all the join points if it's used in *any* RHS,
1458 -- because we don't know its usage in each RHS separately
1460 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1461 -- we make the join point into a function whenever used_bndrs'
1462 -- is empty. This makes the join-point more CPR friendly.
1463 -- Consider: let j = if .. then I# 3 else I# 4
1464 -- in case .. of { A -> j; B -> j; C -> ... }
1466 -- Now CPR should not w/w j because it's a thunk, so
1467 -- that means that the enclosing function can't w/w either,
1468 -- which is a lose. Here's the example that happened in practice:
1469 -- kgmod :: Int -> Int -> Int
1470 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
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 ->
1483 -- Notice that we make the lambdas into one-shot-lambdas. The
1484 -- join point is sure to be applied at most once, and doing so
1485 -- prevents the body of the join point being floated out by
1486 -- the full laziness pass
1487 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1488 (con, bndrs, mkApps (Var join_bndr) final_args))