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, switchIsOn,
12 opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
13 opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
17 import SimplUtils ( mkCase, transformRhs, findAlt,
18 simplBinder, simplBinders, simplIds, findDefault,
19 SimplCont(..), DupFlag(..), contResultType, analyseCont,
20 discardInline, countArgs, countValArgs, discardCont, contIsDupable
22 import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
25 import Id ( Id, idType, idInfo, idUnique, isDataConId, isDataConId_maybe,
26 idUnfolding, setIdUnfolding, isExportedId, isDeadBinder,
27 idSpecialisation, setIdSpecialisation,
28 idDemandInfo, setIdDemandInfo,
30 idOccInfo, setIdOccInfo,
31 zapLamIdInfo, zapFragileIdInfo,
32 idStrictness, isBottomingId,
33 setInlinePragma, mayHaveNoBinding,
34 setOneShotLambda, maybeModifyIdInfo
36 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
37 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
38 specInfo, inlinePragInfo, setArityInfo, setInlinePragInfo, setUnfoldingInfo,
41 import Demand ( Demand, isStrict, wwLazy )
42 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConRepArity,
43 dataConSig, dataConArgTys
45 import Name ( isLocallyDefined )
47 import CoreFVs ( exprFreeVars )
48 import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons, maybeUnfoldingTemplate,
49 callSiteInline, hasSomeUnfolding, noUnfolding
51 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
52 exprType, coreAltsType, exprArity, exprIsValue, idAppIsCheap,
53 exprOkForSpeculation, etaReduceExpr,
54 mkCoerce, mkSCC, mkInlineMe
56 import Rules ( lookupRule )
57 import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
58 import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType, seqType,
59 mkFunTy, splitFunTy, splitFunTys, splitFunTy_maybe,
61 funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
63 import Subst ( Subst, mkSubst, emptySubst, substTy, substExpr,
64 substEnv, isInScope, lookupIdSubst, substIdInfo
66 import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
67 import TysPrim ( realWorldStatePrimTy )
68 import PrelInfo ( realWorldPrimId )
69 import BasicTypes ( TopLevelFlag(..), isTopLevel )
70 import Maybes ( maybeToBool )
71 import Util ( zipWithEqual, lengthExceeds )
74 import Unique ( foldrIdKey ) -- Temp
78 The guts of the simplifier is in this module, but the driver
79 loop for the simplifier is in SimplCore.lhs.
82 %************************************************************************
86 %************************************************************************
89 simplTopBinds :: [InBind] -> SimplM [OutBind]
92 = -- Put all the top-level binders into scope at the start
93 -- so that if a transformation rule has unexpectedly brought
94 -- anything into scope, then we don't get a complaint about that.
95 -- It's rather as if the top-level binders were imported.
96 simplIds (bindersOfBinds binds) $ \ bndrs' ->
97 simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
98 freeTick SimplifierDone `thenSmpl_`
102 -- We need to track the zapped top-level binders, because
103 -- they should have their fragile IdInfo zapped (notably occurrence info)
104 simpl_binds [] bs = ASSERT( null bs ) returnSmpl ([], panic "simplTopBinds corner")
105 simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs)
106 simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs))
110 simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId]
111 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
112 simplRecBind top_lvl pairs bndrs' thing_inside
113 = go pairs bndrs' `thenSmpl` \ (binds', (binds'', res)) ->
114 returnSmpl (Rec (flattenBinds binds') : binds'', res)
116 go [] _ = thing_inside `thenSmpl` \ stuff ->
117 returnSmpl ([], stuff)
119 go ((bndr, rhs) : pairs) (bndr' : bndrs')
120 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
121 -- Don't float unboxed bindings out,
122 -- because we can't "rec" them
126 %************************************************************************
128 \subsection[Simplify-simplExpr]{The main function: simplExpr}
130 %************************************************************************
133 addLetBind :: OutId -> OutExpr -> SimplM (OutStuff a) -> SimplM (OutStuff a)
134 addLetBind bndr rhs thing_inside
135 = thing_inside `thenSmpl` \ (binds, res) ->
136 returnSmpl (NonRec bndr rhs : binds, res)
138 addLetBinds :: [CoreBind] -> SimplM (OutStuff a) -> SimplM (OutStuff a)
139 addLetBinds binds1 thing_inside
140 = thing_inside `thenSmpl` \ (binds2, res) ->
141 returnSmpl (binds1 ++ binds2, res)
143 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
144 -- Make a case expression instead of a let
145 -- These can arise either from the desugarer,
146 -- or from beta reductions: (\x.e) (x +# y)
148 addCaseBind bndr rhs thing_inside
149 = getInScope `thenSmpl` \ in_scope ->
150 thing_inside `thenSmpl` \ (floats, (_, body)) ->
151 returnSmpl ([], (in_scope, Case rhs bndr [(DEFAULT, [], mkLets floats body)]))
153 addNonRecBind bndr rhs thing_inside
154 -- Checks for needing a case binding
155 | needsCaseBinding (idType bndr) rhs = addCaseBind bndr rhs thing_inside
156 | otherwise = addLetBind bndr rhs thing_inside
159 The reason for this OutExprStuff stuff is that we want to float *after*
160 simplifying a RHS, not before. If we do so naively we get quadratic
161 behaviour as things float out.
163 To see why it's important to do it after, consider this (real) example:
177 a -- Can't inline a this round, cos it appears twice
181 Each of the ==> steps is a round of simplification. We'd save a
182 whole round if we float first. This can cascade. Consider
187 let f = let d1 = ..d.. in \y -> e
191 in \x -> ...(\y ->e)...
193 Only in this second round can the \y be applied, and it
194 might do the same again.
198 simplExpr :: CoreExpr -> SimplM CoreExpr
199 simplExpr expr = getSubst `thenSmpl` \ subst ->
200 simplExprC expr (Stop (substTy subst (exprType expr)))
201 -- The type in the Stop continuation is usually not used
202 -- It's only needed when discarding continuations after finding
203 -- a function that returns bottom.
204 -- Hence the lazy substitution
206 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
207 -- Simplify an expression, given a continuation
209 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
210 returnSmpl (mkLets floats body)
212 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
213 -- Simplify an expression, returning floated binds
215 simplExprF (Var v) cont
218 simplExprF (Lit lit) (Select _ bndr alts se cont)
219 = knownCon (Lit lit) (LitAlt lit) [] bndr alts se cont
221 simplExprF (Lit lit) cont
222 = rebuild (Lit lit) cont
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 = getSubst `thenSmpl` \ subst ->
230 getSwitchChecker `thenSmpl` \ chkr ->
231 if switchIsOn chkr NoCaseOfCase then
232 -- If case-of-case is off, simply simplify the scrutinee and rebuild
233 simplExprC scrut (Stop (substTy subst (idType bndr))) `thenSmpl` \ scrut' ->
234 rebuild_case False scrut' bndr alts (substEnv subst) cont
236 -- But if it's on, we simplify the scrutinee with a Select continuation
237 simplExprF scrut (Select NoDup bndr alts (substEnv subst) cont)
240 simplExprF (Let (Rec pairs) body) cont
241 = simplIds (map fst pairs) $ \ bndrs' ->
242 -- NB: bndrs' don't have unfoldings or spec-envs
243 -- We add them as we go down, using simplPrags
245 simplRecBind False pairs bndrs' (simplExprF body cont)
247 simplExprF expr@(Lam _ _) cont = simplLam expr cont
249 simplExprF (Type ty) cont
250 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
251 simplType ty `thenSmpl` \ ty' ->
252 rebuild (Type ty') cont
254 -- Comments about the Coerce case
255 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
256 -- It's worth checking for a coerce in the continuation,
257 -- in case we can cancel them. For example, in the initial form of a worker
258 -- we may find (coerce T (coerce S (\x.e))) y
259 -- and we'd like it to simplify to e[y/x] in one round of simplification
261 simplExprF (Note (Coerce to from) e) (CoerceIt outer_to cont)
262 = simplType from `thenSmpl` \ from' ->
263 if outer_to == from' then
264 -- The coerces cancel out
267 -- They don't cancel, but the inner one is redundant
268 simplExprF e (CoerceIt outer_to cont)
270 simplExprF (Note (Coerce to from) e) cont
271 = simplType to `thenSmpl` \ to' ->
272 simplExprF e (CoerceIt to' cont)
274 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
275 -- inlining. All other CCCSs are mapped to currentCCS.
276 simplExprF (Note (SCC cc) e) cont
277 = setEnclosingCC currentCCS $
278 simplExpr e `thenSmpl` \ e ->
279 rebuild (mkSCC cc e) cont
281 simplExprF (Note InlineCall e) cont
282 = simplExprF e (InlinePlease cont)
284 -- Comments about the InlineMe case
285 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
286 -- Don't inline in the RHS of something that has an
287 -- inline pragma. But be careful that the InScopeEnv that
288 -- we return does still have inlinings on!
290 -- It really is important to switch off inlinings. This function
291 -- may be inlinined in other modules, so we don't want to remove
292 -- (by inlining) calls to functions that have specialisations, or
293 -- that may have transformation rules in an importing scope.
294 -- E.g. {-# INLINE f #-}
296 -- and suppose that g is strict *and* has specialisations.
297 -- If we inline g's wrapper, we deny f the chance of getting
298 -- the specialised version of g when f is inlined at some call site
299 -- (perhaps in some other module).
301 simplExprF (Note InlineMe e) cont
303 Stop _ -> -- Totally boring continuation
304 -- Don't inline inside an INLINE expression
305 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
306 rebuild (mkInlineMe e') cont
308 other -> -- Dissolve the InlineMe note if there's
309 -- an interesting context of any kind to combine with
310 -- (even a type application -- anything except Stop)
313 -- A non-recursive let is dealt with by simplBeta
314 simplExprF (Let (NonRec bndr rhs) body) cont
315 = getSubstEnv `thenSmpl` \ se ->
316 simplBeta bndr rhs se (contResultType cont) $
321 ---------------------------------
327 zap_it = mkLamBndrZapper fun cont
328 cont_ty = contResultType cont
330 -- Type-beta reduction
331 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
332 = ASSERT( isTyVar bndr )
333 tick (BetaReduction bndr) `thenSmpl_`
334 simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' ->
335 extendSubst bndr (DoneTy ty_arg')
338 -- Ordinary beta reduction
339 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
340 = tick (BetaReduction bndr) `thenSmpl_`
341 simplBeta zapped_bndr arg arg_se cont_ty
344 zapped_bndr = zap_it bndr
347 go lam@(Lam _ _) cont = completeLam [] lam cont
349 -- Exactly enough args
350 go expr cont = simplExprF expr cont
352 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
354 -- We used to try for eta reduction here, but I found that this was
355 -- eta reducing things like
356 -- f = \x -> (coerce (\x -> e))
357 -- This made f's arity reduce, which is a bad thing, so I removed the
358 -- eta reduction at this point, and now do it only when binding
359 -- (at the call to postInlineUnconditionally)
361 completeLam acc (Lam bndr body) cont
362 = simplBinder bndr $ \ bndr' ->
363 completeLam (bndr':acc) body cont
365 completeLam acc body cont
366 = simplExpr body `thenSmpl` \ body' ->
367 rebuild (foldl (flip Lam) body' acc) cont
368 -- Remember, acc is the *reversed* binders
370 mkLamBndrZapper :: CoreExpr -- Function
371 -> SimplCont -- The context
372 -> Id -> Id -- Use this to zap the binders
373 mkLamBndrZapper fun cont
374 | n_args >= n_params fun = \b -> b -- Enough args
375 | otherwise = \b -> zapLamIdInfo b
377 -- NB: we count all the args incl type args
378 -- so we must count all the binders (incl type lambdas)
379 n_args = countArgs cont
381 n_params (Note _ e) = n_params e
382 n_params (Lam b e) = 1 + n_params e
383 n_params other = 0::Int
387 ---------------------------------
389 simplType :: InType -> SimplM OutType
391 = getSubst `thenSmpl` \ subst ->
393 new_ty = substTy subst ty
400 %************************************************************************
404 %************************************************************************
406 @simplBeta@ is used for non-recursive lets in expressions,
407 as well as true beta reduction.
409 Very similar to @simplLazyBind@, but not quite the same.
412 simplBeta :: InId -- Binder
413 -> InExpr -> SubstEnv -- Arg, with its subst-env
414 -> OutType -- Type of thing computed by the context
415 -> SimplM OutExprStuff -- The body
416 -> SimplM OutExprStuff
418 simplBeta bndr rhs rhs_se cont_ty thing_inside
420 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
423 simplBeta bndr rhs rhs_se cont_ty thing_inside
424 | preInlineUnconditionally False {- not black listed -} bndr
425 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
426 extendSubst bndr (ContEx rhs_se rhs) thing_inside
429 = -- Simplify the RHS
430 simplBinder bndr $ \ bndr' ->
431 simplValArg (idType bndr') (idDemandInfo bndr)
432 rhs rhs_se cont_ty $ \ rhs' ->
434 -- Now complete the binding and simplify the body
435 if needsCaseBinding (idType bndr') rhs' then
436 addCaseBind bndr' rhs' thing_inside
438 completeBinding bndr bndr' False False rhs' thing_inside
443 simplTyArg :: InType -> SubstEnv -> SimplM OutType
445 = getInScope `thenSmpl` \ in_scope ->
447 ty_arg' = substTy (mkSubst in_scope se) ty_arg
449 seqType ty_arg' `seq`
452 simplValArg :: OutType -- Type of arg
453 -> Demand -- Demand on the argument
454 -> InExpr -> SubstEnv
455 -> OutType -- Type of thing computed by the context
456 -> (OutExpr -> SimplM OutExprStuff)
457 -> SimplM OutExprStuff
459 simplValArg arg_ty demand arg arg_se cont_ty thing_inside
461 isUnLiftedType arg_ty ||
462 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
463 -- Return true only for dictionary types where the dictionary
464 -- has more than one component (else we risk poking on the component
465 -- of a newtype dictionary)
466 = transformRhs arg `thenSmpl` \ t_arg ->
467 getEnv `thenSmpl` \ env ->
469 simplExprF t_arg (ArgOf NoDup cont_ty $ \ rhs' ->
470 setAllExceptInScope env $
471 etaFirst thing_inside rhs')
474 = simplRhs False {- Not top level -}
475 True {- OK to float unboxed -}
479 -- Do eta-reduction on the simplified RHS, if eta reduction is on
480 -- NB: etaFirst only eta-reduces if that results in something trivial
481 etaFirst | opt_SimplDoEtaReduction = \ thing_inside rhs -> thing_inside (etaCoreExprToTrivial rhs)
482 | otherwise = \ thing_inside rhs -> thing_inside rhs
484 -- Try for eta reduction, but *only* if we get all
485 -- the way to an exprIsTrivial expression. We don't want to remove
486 -- extra lambdas unless we are going to avoid allocating this thing altogether
487 etaCoreExprToTrivial rhs | exprIsTrivial rhs' = rhs'
490 rhs' = etaReduceExpr rhs
495 - deals only with Ids, not TyVars
496 - take an already-simplified RHS
498 It does *not* attempt to do let-to-case. Why? Because they are used for
501 (when let-to-case is impossible)
503 - many situations where the "rhs" is known to be a WHNF
504 (so let-to-case is inappropriate).
507 completeBinding :: InId -- Binder
508 -> OutId -- New binder
509 -> Bool -- True <=> top level
510 -> Bool -- True <=> black-listed; don't inline
511 -> OutExpr -- Simplified RHS
512 -> SimplM (OutStuff a) -- Thing inside
513 -> SimplM (OutStuff a)
515 completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
516 | (case occ_info of -- This happens; for example, the case_bndr during case of
517 IAmDead -> True -- known constructor: case (a,b) of x { (p,q) -> ... }
518 other -> False) -- Here x isn't mentioned in the RHS, so we don't want to
519 -- create the (dead) let-binding let x = (a,b) in ...
522 | postInlineUnconditionally black_listed occ_info old_bndr new_rhs
523 -- Maybe we don't need a let-binding! Maybe we can just
524 -- inline it right away. Unlike the preInlineUnconditionally case
525 -- we are allowed to look at the RHS.
527 -- NB: a loop breaker never has postInlineUnconditionally True
528 -- and non-loop-breakers only have *forward* references
529 -- Hence, it's safe to discard the binding
531 -- NB: You might think that postInlineUnconditionally is an optimisation,
533 -- let x = f Bool in (x, y)
534 -- then because of the constructor, x will not be *inlined* in the pair,
535 -- so the trivial binding will stay. But in this postInlineUnconditionally
536 -- gag we use the *substitution* to substitute (f Bool) for x, and that *will*
538 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
539 extendSubst old_bndr (DoneEx new_rhs)
543 = getSubst `thenSmpl` \ subst ->
545 -- We make new IdInfo for the new binder by starting from the old binder,
546 -- doing appropriate substitutions.
547 -- Then we add arity and unfolding info to get the new binder
548 old_info = idInfo old_bndr
549 new_bndr_info = substIdInfo subst old_info (idInfo new_bndr)
550 `setArityInfo` ArityAtLeast (exprArity new_rhs)
551 `setUnfoldingInfo` mkUnfolding top_lvl (cprInfo old_info) new_rhs
553 final_id = new_bndr `setIdInfo` new_bndr_info
555 -- These seqs force the Ids, and hence the IdInfos, and hence any
556 -- inner substitutions
558 addLetBind final_id new_rhs $
559 modifyInScope new_bndr final_id thing_inside
562 occ_info = idOccInfo old_bndr
566 %************************************************************************
568 \subsection{simplLazyBind}
570 %************************************************************************
572 simplLazyBind basically just simplifies the RHS of a let(rec).
573 It does two important optimisations though:
575 * It floats let(rec)s out of the RHS, even if they
576 are hidden by big lambdas
578 * It does eta expansion
581 simplLazyBind :: Bool -- True <=> top level
584 -> SimplM (OutStuff a) -- The body of the binding
585 -> SimplM (OutStuff a)
586 -- When called, the subst env is correct for the entire let-binding
587 -- and hence right for the RHS.
588 -- Also the binder has already been simplified, and hence is in scope
590 simplLazyBind top_lvl bndr bndr' rhs thing_inside
591 = getBlackList `thenSmpl` \ black_list_fn ->
593 black_listed = black_list_fn bndr
596 if preInlineUnconditionally black_listed bndr then
597 -- Inline unconditionally
598 tick (PreInlineUnconditionally bndr) `thenSmpl_`
599 getSubstEnv `thenSmpl` \ rhs_se ->
600 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
604 getSubstEnv `thenSmpl` \ rhs_se ->
605 simplRhs top_lvl False {- Not ok to float unboxed -}
607 rhs rhs_se $ \ rhs' ->
609 -- Now compete the binding and simplify the body
610 completeBinding bndr bndr' top_lvl black_listed rhs' thing_inside
616 simplRhs :: Bool -- True <=> Top level
617 -> Bool -- True <=> OK to float unboxed (speculative) bindings
618 -> OutType -> InExpr -> SubstEnv
619 -> (OutExpr -> SimplM (OutStuff a))
620 -> SimplM (OutStuff a)
621 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
622 = -- Swizzle the inner lets past the big lambda (if any)
623 -- and try eta expansion
624 transformRhs rhs `thenSmpl` \ t_rhs ->
627 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
629 -- Float lets out of RHS
631 (floats_out, rhs'') | float_ubx = (floats, rhs')
632 | otherwise = splitFloats floats rhs'
634 if (top_lvl || wantToExpose 0 rhs') && -- Float lets if (a) we're at the top level
635 not (null floats_out) -- or (b) the resulting RHS is one we'd like to expose
637 tickLetFloat floats_out `thenSmpl_`
640 -- There's a subtlety here. There may be a binding (x* = e) in the
641 -- floats, where the '*' means 'will be demanded'. So is it safe
642 -- to float it out? Answer no, but it won't matter because
643 -- we only float if arg' is a WHNF,
644 -- and so there can't be any 'will be demanded' bindings in the floats.
646 WARN( any demanded_float floats_out, ppr floats_out )
647 addLetBinds floats_out $
648 setInScope in_scope' $
649 etaFirst thing_inside rhs''
650 -- in_scope' may be excessive, but that's OK;
651 -- it's a superset of what's in scope
653 -- Don't do the float
654 etaFirst thing_inside (mkLets floats rhs')
656 -- In a let-from-let float, we just tick once, arbitrarily
657 -- choosing the first floated binder to identify it
658 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
659 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
661 demanded_float (NonRec b r) = isStrict (idDemandInfo b) && not (isUnLiftedType (idType b))
662 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
663 demanded_float (Rec _) = False
665 -- Don't float any unlifted bindings out, because the context
666 -- is either a Rec group, or the top level, neither of which
667 -- can tolerate them.
668 splitFloats floats rhs
672 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
673 | otherwise = case go fs of
674 (out, rhs') -> (f:out, rhs')
676 must_stay (Rec prs) = False -- No unlifted bindings in here
677 must_stay (NonRec b r) = isUnLiftedType (idType b)
679 wantToExpose :: Int -> CoreExpr -> Bool
680 -- True for expressions that we'd like to expose at the
681 -- top level of an RHS. This includes partial applications
682 -- even if the args aren't cheap; the next pass will let-bind the
683 -- args and eta expand the partial application. So exprIsCheap won't do.
684 -- Here's the motivating example:
685 -- z = letrec g = \x y -> ...g... in g E
686 -- Even though E is a redex we'd like to float the letrec to give
687 -- g = \x y -> ...g...
689 -- Now the next use of SimplUtils.tryEtaExpansion will give
690 -- g = \x y -> ...g...
691 -- z = let v = E in \w -> g v w
692 -- And now we'll float the v to give
693 -- g = \x y -> ...g...
696 -- Which is what we want; chances are z will be inlined now.
697 wantToExpose n (Var v) = idAppIsCheap v n
698 wantToExpose n (Lit l) = True
699 wantToExpose n (Lam _ e) = ASSERT( n==0 ) True -- We won't have applied \'s
700 wantToExpose n (Note _ e) = wantToExpose n e
701 wantToExpose n (App f (Type _)) = wantToExpose n f
702 wantToExpose n (App f a) = wantToExpose (n+1) f
703 wantToExpose n other = False -- There won't be any lets
708 %************************************************************************
710 \subsection{Variables}
712 %************************************************************************
716 = getSubst `thenSmpl` \ subst ->
717 case lookupIdSubst subst var of
718 DoneEx e -> zapSubstEnv (simplExprF e cont)
719 ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
720 DoneId var1 occ -> WARN( not (isInScope var1 subst) && isLocallyDefined var1 && not (mayHaveNoBinding var1),
721 text "simplVar:" <+> ppr var )
722 -- The mayHaveNoBinding test accouunts for the fact
723 -- that class dictionary constructors dont have top level
724 -- bindings and hence aren't in scope.
725 zapSubstEnv (completeCall var1 occ cont)
726 -- The template is already simplified, so don't re-substitute.
727 -- This is VITAL. Consider
729 -- let y = \z -> ...x... in
731 -- We'll clone the inner \x, adding x->x' in the id_subst
732 -- Then when we inline y, we must *not* replace x by x' in
733 -- the inlined copy!!
735 ---------------------------------------------------------
736 -- Dealing with a call
738 completeCall var occ cont
739 = getBlackList `thenSmpl` \ black_list_fn ->
740 getSwitchChecker `thenSmpl` \ chkr ->
741 getInScope `thenSmpl` \ in_scope ->
743 black_listed = black_list_fn var
744 (arg_infos, interesting_cont, inline_call) = analyseCont in_scope cont
745 discard_inline_cont | inline_call = discardInline cont
748 maybe_inline = callSiteInline black_listed inline_call occ
749 var arg_infos interesting_cont
751 -- First, look for an inlining
753 case maybe_inline of {
754 Just unfolding -- There is an inlining!
755 -> tick (UnfoldingDone var) `thenSmpl_`
756 simplExprF unfolding discard_inline_cont
759 Nothing -> -- No inlining!
761 -- Next, look for rules or specialisations that match
763 -- It's important to simplify the args first, because the rule-matcher
764 -- doesn't do substitution as it goes. We don't want to use subst_args
765 -- (defined in the 'where') because that throws away useful occurrence info,
766 -- and perhaps-very-important specialisations.
768 -- Some functions have specialisations *and* are strict; in this case,
769 -- we don't want to inline the wrapper of the non-specialised thing; better
770 -- to call the specialised thing instead.
771 -- But the black-listing mechanism means that inlining of the wrapper
772 -- won't occur for things that have specialisations till a later phase, so
773 -- it's ok to try for inlining first.
775 prepareArgs (switchIsOn chkr NoCaseOfCase) var cont $ \ args' cont' ->
777 maybe_rule | switchIsOn chkr DontApplyRules = Nothing
778 | otherwise = lookupRule in_scope var args'
781 Just (rule_name, rule_rhs) ->
782 tick (RuleFired rule_name) `thenSmpl_`
783 simplExprF rule_rhs cont' ;
785 Nothing -> -- No rules
788 rebuild (mkApps (Var var) args') cont'
794 ---------------------------------------------------------
795 -- Preparing arguments for a call
797 prepareArgs :: Bool -- True if the no-case-of-case switch is on
798 -> OutId -> SimplCont
799 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
800 -> SimplM OutExprStuff
801 prepareArgs no_case_of_case fun orig_cont thing_inside
802 = go [] demands orig_fun_ty orig_cont
804 orig_fun_ty = idType fun
805 is_data_con = isDataConId fun
807 (demands, result_bot)
808 | no_case_of_case = ([], False) -- Ignore strictness info if the no-case-of-case
809 -- flag is on. Strictness changes evaluation order
810 -- and that can change full laziness
812 = case idStrictness fun of
813 StrictnessInfo demands result_bot
814 | not (demands `lengthExceeds` countValArgs orig_cont)
815 -> -- Enough args, use the strictness given.
816 -- For bottoming functions we used to pretend that the arg
817 -- is lazy, so that we don't treat the arg as an
818 -- interesting context. This avoids substituting
819 -- top-level bindings for (say) strings into
820 -- calls to error. But now we are more careful about
821 -- inlining lone variables, so its ok (see SimplUtils.analyseCont)
822 (demands, result_bot)
824 other -> ([], False) -- Not enough args, or no strictness
826 -- Main game plan: loop through the arguments, simplifying
827 -- each of them in turn. We carry with us a list of demands,
828 -- and the type of the function-applied-to-earlier-args
830 -- We've run out of demands, and the result is now bottom
832 -- * case (error "hello") of { ... }
833 -- * (error "Hello") arg
834 -- * f (error "Hello") where f is strict
836 go acc [] fun_ty cont
838 = tick_case_of_error cont `thenSmpl_`
839 thing_inside (reverse acc) (discardCont cont)
842 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
843 = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg ->
844 go (Type new_ty_arg : acc) ds (applyTy fun_ty new_ty_arg) cont
847 go acc ds fun_ty (ApplyTo _ val_arg se cont)
848 | not is_data_con -- Function isn't a data constructor
849 = simplValArg arg_ty dem val_arg se (contResultType cont) $ \ new_arg ->
850 go (new_arg : acc) ds' res_ty cont
852 | exprIsTrivial val_arg -- Function is a data contstructor, arg is trivial
853 = getInScope `thenSmpl` \ in_scope ->
855 new_arg = substExpr (mkSubst in_scope se) val_arg
856 -- Simplify the RHS with inlining switched off, so that
857 -- only absolutely essential things will happen.
858 -- If we don't do this, consider:
859 -- let x = +# p q in C {x}
860 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
861 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
863 -- It's important that the substitution *does* deal with case-binder synonyms:
864 -- case x of y { True -> (x,1) }
865 -- Here we must be sure to substitute y for x when simplifying the args of the pair,
866 -- to increase the chances of being able to inline x. The substituter will do
867 -- that because the x->y mapping is held in the in-scope set.
869 -- It's not always the case that the new arg will be trivial
871 -- where, in one pass, f gets substituted by a constructor,
872 -- but x gets substituted by an expression (assume this is the
873 -- unique occurrence of x). It doesn't really matter -- it'll get
874 -- fixed up next pass. And it happens for dictionary construction,
875 -- which mentions the wrapper constructor to start with.
877 go (new_arg : acc) ds' res_ty cont
880 = simplValArg arg_ty dem val_arg se (contResultType cont) $ \ new_arg ->
881 -- A data constructor whose argument is now non-trivial;
882 -- so let/case bind it.
883 newId arg_ty $ \ arg_id ->
884 addNonRecBind arg_id new_arg $
885 go (Var arg_id : acc) ds' res_ty cont
888 (arg_ty, res_ty) = splitFunTy fun_ty
889 (dem, ds') = case ds of
893 -- We're run out of arguments and the result ain't bottom
894 go acc ds fun_ty cont = thing_inside (reverse acc) cont
896 -- Boring: we must only record a tick if there was an interesting
897 -- continuation to discard. If not, we tick forever.
898 tick_case_of_error (Stop _) = returnSmpl ()
899 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
900 tick_case_of_error other = tick BottomFound
904 %************************************************************************
906 \subsection{Decisions about inlining}
908 %************************************************************************
910 NB: At one time I tried not pre/post-inlining top-level things,
911 even if they occur exactly once. Reason:
912 (a) some might appear as a function argument, so we simply
913 replace static allocation with dynamic allocation:
919 (b) some top level things might be black listed
921 HOWEVER, I found that some useful foldr/build fusion was lost (most
922 notably in spectral/hartel/parstof) because the foldr didn't see the build.
924 Doing the dynamic allocation isn't a big deal, in fact, but losing the
928 preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
929 -- Examines a bndr to see if it is used just once in a
930 -- completely safe way, so that it is safe to discard the binding
931 -- inline its RHS at the (unique) usage site, REGARDLESS of how
932 -- big the RHS might be. If this is the case we don't simplify
933 -- the RHS first, but just inline it un-simplified.
935 -- This is much better than first simplifying a perhaps-huge RHS
936 -- and then inlining and re-simplifying it.
938 -- NB: we don't even look at the RHS to see if it's trivial
941 -- where x is used many times, but this is the unique occurrence
942 -- of y. We should NOT inline x at all its uses, because then
943 -- we'd do the same for y -- aargh! So we must base this
944 -- pre-rhs-simplification decision solely on x's occurrences, not
947 -- Evne RHSs labelled InlineMe aren't caught here, because
948 -- there might be no benefit from inlining at the call site.
950 preInlineUnconditionally black_listed bndr
951 | black_listed || opt_SimplNoPreInlining = False
952 | otherwise = case idOccInfo bndr of
953 OneOcc in_lam once -> not in_lam && once
954 -- Not inside a lambda, one occurrence ==> safe!
958 postInlineUnconditionally :: Bool -- Black listed
960 -> InId -> OutExpr -> Bool
961 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
962 -- It returns True if it's ok to discard the binding and inline the
963 -- RHS at every use site.
965 -- NOTE: This isn't our last opportunity to inline.
966 -- We're at the binding site right now, and
967 -- we'll get another opportunity when we get to the ocurrence(s)
969 postInlineUnconditionally black_listed occ_info bndr rhs
970 | isExportedId bndr ||
972 loop_breaker = False -- Don't inline these
973 | otherwise = exprIsTrivial rhs -- Duplicating is free
974 -- Don't inline even WHNFs inside lambdas; doing so may
975 -- simply increase allocation when the function is called
976 -- This isn't the last chance; see NOTE above.
978 -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
979 -- Why? Because we don't even want to inline them into the
980 -- RHS of constructor arguments. See NOTE above
982 -- NB: Even NOINLINEis ignored here: if the rhs is trivial
983 -- it's best to inline it anyway. We often get a=E; b=a
984 -- from desugaring, with both a and b marked NOINLINE.
986 loop_breaker = case occ_info of
987 IAmALoopBreaker -> True
993 %************************************************************************
995 \subsection{The main rebuilder}
997 %************************************************************************
1000 -------------------------------------------------------------------
1001 -- Finish rebuilding
1003 = getInScope `thenSmpl` \ in_scope ->
1004 returnSmpl ([], (in_scope, expr))
1006 ---------------------------------------------------------
1007 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
1009 -- Stop continuation
1010 rebuild expr (Stop _) = rebuild_done expr
1012 -- ArgOf continuation
1013 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1015 -- ApplyTo continuation
1016 rebuild expr cont@(ApplyTo _ arg se cont')
1017 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1018 rebuild (App expr arg') cont'
1020 -- Coerce continuation
1021 rebuild expr (CoerceIt to_ty cont)
1022 = rebuild (mkCoerce to_ty (exprType expr) expr) cont
1024 -- Inline continuation
1025 rebuild expr (InlinePlease cont)
1026 = rebuild (Note InlineCall expr) cont
1028 rebuild scrut (Select _ bndr alts se cont)
1029 = rebuild_case True scrut bndr alts se cont
1032 Case elimination [see the code above]
1034 Start with a simple situation:
1036 case x# of ===> e[x#/y#]
1039 (when x#, y# are of primitive type, of course). We can't (in general)
1040 do this for algebraic cases, because we might turn bottom into
1043 Actually, we generalise this idea to look for a case where we're
1044 scrutinising a variable, and we know that only the default case can
1049 other -> ...(case x of
1053 Here the inner case can be eliminated. This really only shows up in
1054 eliminating error-checking code.
1056 We also make sure that we deal with this very common case:
1061 Here we are using the case as a strict let; if x is used only once
1062 then we want to inline it. We have to be careful that this doesn't
1063 make the program terminate when it would have diverged before, so we
1065 - x is used strictly, or
1066 - e is already evaluated (it may so if e is a variable)
1068 Lastly, we generalise the transformation to handle this:
1074 We only do this for very cheaply compared r's (constructors, literals
1075 and variables). If pedantic bottoms is on, we only do it when the
1076 scrutinee is a PrimOp which can't fail.
1078 We do it *here*, looking at un-simplified alternatives, because we
1079 have to check that r doesn't mention the variables bound by the
1080 pattern in each alternative, so the binder-info is rather useful.
1082 So the case-elimination algorithm is:
1084 1. Eliminate alternatives which can't match
1086 2. Check whether all the remaining alternatives
1087 (a) do not mention in their rhs any of the variables bound in their pattern
1088 and (b) have equal rhss
1090 3. Check we can safely ditch the case:
1091 * PedanticBottoms is off,
1092 or * the scrutinee is an already-evaluated variable
1093 or * the scrutinee is a primop which is ok for speculation
1094 -- ie we want to preserve divide-by-zero errors, and
1095 -- calls to error itself!
1097 or * [Prim cases] the scrutinee is a primitive variable
1099 or * [Alg cases] the scrutinee is a variable and
1100 either * the rhs is the same variable
1101 (eg case x of C a b -> x ===> x)
1102 or * there is only one alternative, the default alternative,
1103 and the binder is used strictly in its scope.
1104 [NB this is helped by the "use default binder where
1105 possible" transformation; see below.]
1108 If so, then we can replace the case with one of the rhss.
1111 Blob of helper functions for the "case-of-something-else" situation.
1114 ---------------------------------------------------------
1115 -- Eliminate the case if possible
1117 rebuild_case add_eval_info scrut bndr alts se cont
1118 | maybeToBool maybe_con_app
1119 = knownCon scrut (DataAlt con) args bndr alts se cont
1121 | canEliminateCase scrut bndr alts
1122 = tick (CaseElim bndr) `thenSmpl_` (
1124 simplBinder bndr $ \ bndr' ->
1125 -- Remember to bind the case binder!
1126 completeBinding bndr bndr' False False scrut $
1127 simplExprF (head (rhssOfAlts alts)) cont)
1130 = complete_case add_eval_info scrut bndr alts se cont
1133 maybe_con_app = analyse (collectArgs scrut)
1134 Just (con, args) = maybe_con_app
1136 analyse (Var fun, args)
1137 | maybeToBool maybe_con_app = maybe_con_app
1139 maybe_con_app = case isDataConId_maybe fun of
1140 Just con | length args >= dataConRepArity con
1141 -- Might be > because the arity excludes type args
1145 analyse (Var fun, [])
1146 = case maybeUnfoldingTemplate (idUnfolding fun) of
1148 Just unf -> analyse (collectArgs unf)
1150 analyse other = Nothing
1153 -- See if we can get rid of the case altogether
1154 -- See the extensive notes on case-elimination above
1155 canEliminateCase scrut bndr alts
1156 = -- Check that the RHSs are all the same, and
1157 -- don't use the binders in the alternatives
1158 -- This test succeeds rapidly in the common case of
1159 -- a single DEFAULT alternative
1160 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1162 -- Check that the scrutinee can be let-bound instead of case-bound
1163 && ( exprOkForSpeculation scrut
1164 -- OK not to evaluate it
1165 -- This includes things like (==# a# b#)::Bool
1166 -- so that we simplify
1167 -- case ==# a# b# of { True -> x; False -> x }
1170 -- This particular example shows up in default methods for
1171 -- comparision operations (e.g. in (>=) for Int.Int32)
1172 || exprIsValue scrut -- It's already evaluated
1173 || var_demanded_later scrut -- It'll be demanded later
1175 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1176 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1177 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1178 -- its argument: case x of { y -> dataToTag# y }
1179 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1180 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1185 (rhs1:other_rhss) = rhssOfAlts alts
1186 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1188 var_demanded_later (Var v) = isStrict (idDemandInfo bndr) -- It's going to be evaluated later
1189 var_demanded_later other = False
1192 ---------------------------------------------------------
1193 -- Case of something else
1195 complete_case add_eval_info scrut case_bndr alts se cont
1196 = -- Prepare case alternatives
1197 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1198 impossible_cons alts `thenSmpl` \ better_alts ->
1200 -- Set the new subst-env in place (before dealing with the case binder)
1203 -- Deal with the case binder, and prepare the continuation;
1204 -- The new subst_env is in place
1205 prepareCaseCont better_alts cont $ \ cont' ->
1208 -- Deal with variable scrutinee
1209 ( simplCaseBinder add_eval_info scrut case_bndr $ \ case_bndr' zap_occ_info ->
1211 -- Deal with the case alternatives
1212 simplAlts zap_occ_info impossible_cons
1213 case_bndr' better_alts cont' `thenSmpl` \ alts' ->
1215 mkCase scrut case_bndr' alts'
1216 ) `thenSmpl` \ case_expr ->
1218 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1219 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1220 -- that should not include these chaps!
1221 rebuild_done case_expr
1223 impossible_cons = case scrut of
1224 Var v -> otherCons (idUnfolding v)
1228 knownCon :: OutExpr -> AltCon -> [OutExpr]
1229 -> InId -> [InAlt] -> SubstEnv -> SimplCont
1230 -> SimplM OutExprStuff
1232 knownCon expr con args bndr alts se cont
1233 = tick (KnownBranch bndr) `thenSmpl_`
1235 simplBinder bndr $ \ bndr' ->
1236 completeBinding bndr bndr' False False expr $
1237 -- Don't use completeBeta here. The expr might be
1238 -- an unboxed literal, like 3, or a variable
1239 -- whose unfolding is an unboxed literal... and
1240 -- completeBeta will just construct another case
1242 case findAlt con alts of
1243 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1246 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1249 (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
1250 extendSubstList bs (map mk real_args) $
1253 real_args = drop (dataConNumInstArgs dc) args
1254 mk (Type ty) = DoneTy ty
1255 mk other = DoneEx other
1260 prepareCaseCont :: [InAlt] -> SimplCont
1261 -> (SimplCont -> SimplM (OutStuff a))
1262 -> SimplM (OutStuff a)
1263 -- Polymorphic recursion here!
1265 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1266 prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
1267 mkDupableCont alts_ty cont thing_inside
1268 -- At one time I passed in the un-simplified type, and simplified
1269 -- it only if we needed to construct a join binder, but that
1270 -- didn't work because we have to decompse function types
1271 -- (using funResultTy) in mkDupableCont.
1274 simplCaseBinder checks whether the scrutinee is a variable, v.
1275 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1276 that way, there's a chance that v will now only be used once, and hence inlined.
1278 There is a time we *don't* want to do that, namely when -fno-case-of-case
1279 is on. This happens in the first simplifier pass, and enhances full laziness.
1280 Here's the bad case:
1281 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1282 If we eliminate the inner case, we trap it inside the I# v -> arm,
1283 which might prevent some full laziness happening. I've seen this
1284 in action in spectral/cichelli/Prog.hs:
1285 [(m,n) | m <- [1..max], n <- [1..max]]
1286 Hence the add_eval_info argument
1289 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1290 in the case binder, because the case-binder now effectively occurs
1291 whenever v does. AND we have to do the same for the pattern-bound
1294 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1296 Here, b and p are dead. But when we move the argment inside the first
1297 case RHS, and eliminate the second case, we get
1299 case x or { (a,b) -> a b }
1301 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1302 happened. Hence the zap_occ_info function returned by simplCaseBinder
1305 simplCaseBinder add_eval_info (Var v) case_bndr thing_inside
1307 = simplBinder (zap case_bndr) $ \ case_bndr' ->
1308 modifyInScope v case_bndr' $
1309 -- We could extend the substitution instead, but it would be
1310 -- a hack because then the substitution wouldn't be idempotent
1311 -- any more (v is an OutId). And this just just as well.
1312 thing_inside case_bndr' zap
1314 zap b = b `setIdOccInfo` NoOccInfo
1316 simplCaseBinder add_eval_info other_scrut case_bndr thing_inside
1317 = simplBinder case_bndr $ \ case_bndr' ->
1318 thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
1321 prepareCaseAlts does two things:
1323 1. Remove impossible alternatives
1325 2. If the DEFAULT alternative can match only one possible constructor,
1326 then make that constructor explicit.
1328 case e of x { DEFAULT -> rhs }
1330 case e of x { (a,b) -> rhs }
1331 where the type is a single constructor type. This gives better code
1332 when rhs also scrutinises x or e.
1335 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1337 = case (findDefault filtered_alts, missing_cons) of
1339 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1340 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1342 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1344 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1346 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1347 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1349 newIds (dataConArgTys
1351 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1352 returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1354 other -> returnSmpl filtered_alts
1356 -- Filter out alternatives that can't possibly match
1357 filtered_alts = case scrut_cons of
1359 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1361 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1362 not (data_con `elem` handled_data_cons)]
1363 handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++
1364 [data_con | (DataAlt data_con, _, _) <- filtered_alts]
1367 prepareCaseAlts _ _ scrut_cons alts
1368 = returnSmpl alts -- Functions
1371 ----------------------
1372 simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
1373 = mapSmpl simpl_alt alts
1375 inst_tys' = case splitTyConApp_maybe (idType case_bndr') of
1376 Just (tycon, inst_tys) -> inst_tys
1378 -- handled_cons is all the constructors that are dealt
1379 -- with, either by being impossible, or by there being an alternative
1380 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1382 simpl_alt (DEFAULT, _, rhs)
1383 = -- In the default case we record the constructors that the
1384 -- case-binder *can't* be.
1385 -- We take advantage of any OtherCon info in the case scrutinee
1386 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
1387 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1388 returnSmpl (DEFAULT, [], rhs')
1390 simpl_alt (con, vs, rhs)
1391 = -- Deal with the pattern-bound variables
1392 -- Mark the ones that are in ! positions in the data constructor
1393 -- as certainly-evaluated.
1394 -- NB: it happens that simplBinders does *not* erase the OtherCon
1395 -- form of unfolding, so it's ok to add this info before
1396 -- doing simplBinders
1397 simplBinders (add_evals con vs) $ \ vs' ->
1399 -- Bind the case-binder to (con args)
1401 unfolding = mkUnfolding False NoCPRInfo (mkAltExpr con vs' inst_tys')
1403 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $
1404 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1405 returnSmpl (con, vs', rhs')
1408 -- add_evals records the evaluated-ness of the bound variables of
1409 -- a case pattern. This is *important*. Consider
1410 -- data T = T !Int !Int
1412 -- case x of { T a b -> T (a+1) b }
1414 -- We really must record that b is already evaluated so that we don't
1415 -- go and re-evaluate it when constructing the result.
1417 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1418 add_evals other_con vs = vs
1420 cat_evals [] [] = []
1421 cat_evals (v:vs) (str:strs)
1422 | isTyVar v = v : cat_evals vs (str:strs)
1423 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1424 | otherwise = v' : cat_evals vs strs
1430 %************************************************************************
1432 \subsection{Duplicating continuations}
1434 %************************************************************************
1437 mkDupableCont :: OutType -- Type of the thing to be given to the continuation
1439 -> (SimplCont -> SimplM (OutStuff a))
1440 -> SimplM (OutStuff a)
1441 mkDupableCont ty cont thing_inside
1442 | contIsDupable cont
1445 mkDupableCont _ (CoerceIt ty cont) thing_inside
1446 = mkDupableCont ty cont $ \ cont' ->
1447 thing_inside (CoerceIt ty cont')
1449 mkDupableCont ty (InlinePlease cont) thing_inside
1450 = mkDupableCont ty cont $ \ cont' ->
1451 thing_inside (InlinePlease cont')
1453 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1454 = -- Build the RHS of the join point
1455 newId join_arg_ty ( \ arg_id ->
1456 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1457 returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs))
1458 ) `thenSmpl` \ join_rhs ->
1460 -- Build the join Id and continuation
1461 newId (exprType join_rhs) $ \ join_id ->
1463 new_cont = ArgOf OkToDup cont_ty
1464 (\arg' -> rebuild_done (App (Var join_id) arg'))
1467 tick (CaseOfCase join_id) `thenSmpl_`
1468 -- Want to tick here so that we go round again,
1469 -- and maybe copy or inline the code;
1470 -- not strictly CaseOf Case
1471 addLetBind join_id join_rhs (thing_inside new_cont)
1473 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1474 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1475 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1476 if exprIsDupable arg' then
1477 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1479 newId (exprType arg') $ \ bndr ->
1481 tick (CaseOfCase bndr) `thenSmpl_`
1482 -- Want to tick here so that we go round again,
1483 -- and maybe copy or inline the code;
1484 -- not strictly CaseOf Case
1486 addLetBind bndr arg' $
1487 -- But what if the arg should be case-bound? We can't use
1488 -- addNonRecBind here because its type is too specific.
1489 -- This has been this way for a long time, so I'll leave it,
1490 -- but I can't convince myself that it's right.
1492 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont')
1495 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1496 = tick (CaseOfCase case_bndr) `thenSmpl_`
1498 simplBinder case_bndr $ \ case_bndr' ->
1499 prepareCaseCont alts cont $ \ cont' ->
1500 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1501 returnSmpl (concat alt_binds_s, alts')
1502 ) `thenSmpl` \ (alt_binds, alts') ->
1504 extendInScopes [b | NonRec b _ <- alt_binds] $
1506 -- NB that the new alternatives, alts', are still InAlts, using the original
1507 -- binders. That means we can keep the case_bndr intact. This is important
1508 -- because another case-of-case might strike, and so we want to keep the
1509 -- info that the case_bndr is dead (if it is, which is often the case).
1510 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1511 -- case in I/O rich code. We aren't allowed a lambda bound
1512 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1513 addLetBinds alt_binds $
1514 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont)))
1516 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1517 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1518 = simplBinders bndrs $ \ bndrs' ->
1519 simplExprC rhs cont `thenSmpl` \ rhs' ->
1521 if (case cont of { Stop _ -> exprIsDupable rhs'; other -> False}) then
1522 -- It is worth checking for a small RHS because otherwise we
1523 -- get extra let bindings that may cause an extra iteration of the simplifier to
1524 -- inline back in place. Quite often the rhs is just a variable or constructor.
1525 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1526 -- iterations because the version with the let bindings looked big, and so wasn't
1527 -- inlined, but after the join points had been inlined it looked smaller, and so
1530 -- But since the continuation is absorbed into the rhs, we only do this
1531 -- for a Stop continuation.
1533 -- NB: we have to check the size of rhs', not rhs.
1534 -- Duplicating a small InAlt might invalidate occurrence information
1535 -- However, if it *is* dupable, we return the *un* simplified alternative,
1536 -- because otherwise we'd need to pair it up with an empty subst-env.
1537 -- (Remember we must zap the subst-env before re-simplifying something).
1538 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1539 returnSmpl ([], alt)
1543 rhs_ty' = exprType rhs'
1544 (used_bndrs, used_bndrs')
1545 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1546 (case_bndr' : bndrs'),
1547 not (isDeadBinder bndr)]
1548 -- The new binders have lost their occurrence info,
1549 -- so we have to extract it from the old ones
1551 ( if null used_bndrs'
1552 -- If we try to lift a primitive-typed something out
1553 -- for let-binding-purposes, we will *caseify* it (!),
1554 -- with potentially-disastrous strictness results. So
1555 -- instead we turn it into a function: \v -> e
1556 -- where v::State# RealWorld#. The value passed to this function
1557 -- is realworld#, which generates (almost) no code.
1559 -- There's a slight infelicity here: we pass the overall
1560 -- case_bndr to all the join points if it's used in *any* RHS,
1561 -- because we don't know its usage in each RHS separately
1563 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1564 -- we make the join point into a function whenever used_bndrs'
1565 -- is empty. This makes the join-point more CPR friendly.
1566 -- Consider: let j = if .. then I# 3 else I# 4
1567 -- in case .. of { A -> j; B -> j; C -> ... }
1569 -- Now CPR should not w/w j because it's a thunk, so
1570 -- that means that the enclosing function can't w/w either,
1571 -- which is a lose. Here's the example that happened in practice:
1572 -- kgmod :: Int -> Int -> Int
1573 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1577 then newId realWorldStatePrimTy $ \ rw_id ->
1578 returnSmpl ([rw_id], [Var realWorldPrimId])
1580 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1582 `thenSmpl` \ (final_bndrs', final_args) ->
1584 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1586 -- Notice that we make the lambdas into one-shot-lambdas. The
1587 -- join point is sure to be applied at most once, and doing so
1588 -- prevents the body of the join point being floated out by
1589 -- the full laziness pass
1590 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1591 (con, bndrs, mkApps (Var join_bndr) final_args))