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 ( switchIsOn, opt_SimplDoEtaReduction,
12 opt_SimplNoPreInlining,
13 dopt, DynFlag(Opt_D_dump_inlinings),
17 import SimplUtils ( mkCase, tryRhsTyLam, tryEtaExpansion,
18 simplBinder, simplBinders, simplRecIds, simplLetId,
19 SimplCont(..), DupFlag(..), mkStop, mkRhsStop,
20 contResultType, discardInline, countArgs, contIsDupable,
21 getContArgs, interestingCallContext, interestingArg, isStrictType
23 import Var ( mkSysTyVar, tyVarKind )
25 import Id ( Id, idType, idInfo, isDataConId, hasNoBinding,
26 idUnfolding, setIdUnfolding, isExportedId, isDeadBinder,
27 idDemandInfo, setIdInfo,
28 idOccInfo, setIdOccInfo,
29 zapLamIdInfo, setOneShotLambda,
31 import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker,
33 setUnfoldingInfo, atLeastArity,
36 import Demand ( isStrict )
37 import DataCon ( dataConNumInstArgs, dataConRepStrictness,
38 dataConSig, dataConArgTys
41 import PprCore ( pprParendExpr, pprCoreExpr )
42 import CoreFVs ( mustHaveLocalBinding )
43 import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons,
46 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsTrivial,
47 exprIsConApp_maybe, mkPiType, findAlt, findDefault,
48 exprType, coreAltsType, exprIsValue,
49 exprOkForSpeculation, exprArity, exprIsCheap,
50 mkCoerce, mkSCC, mkInlineMe, mkAltExpr
52 import Rules ( lookupRule )
53 import CostCentre ( currentCCS )
54 import Type ( mkTyVarTys, isUnLiftedType, seqType,
55 mkFunTy, splitTyConApp_maybe, tyConAppArgs,
58 import Subst ( mkSubst, substTy, substEnv,
59 isInScope, lookupIdSubst, simplIdInfo
61 import TyCon ( isDataTyCon, tyConDataConsIfAvailable )
62 import TysPrim ( realWorldStatePrimTy )
63 import PrelInfo ( realWorldPrimId )
65 import Maybes ( maybeToBool )
66 import Util ( zipWithEqual )
71 The guts of the simplifier is in this module, but the driver
72 loop for the simplifier is in SimplCore.lhs.
75 -----------------------------------------
76 *** IMPORTANT NOTE ***
77 -----------------------------------------
78 The simplifier used to guarantee that the output had no shadowing, but
79 it does not do so any more. (Actually, it never did!) The reason is
80 documented with simplifyArgs.
85 %************************************************************************
89 %************************************************************************
92 simplTopBinds :: [InBind] -> SimplM [OutBind]
95 = -- Put all the top-level binders into scope at the start
96 -- so that if a transformation rule has unexpectedly brought
97 -- anything into scope, then we don't get a complaint about that.
98 -- It's rather as if the top-level binders were imported.
99 simplRecIds (bindersOfBinds binds) $ \ bndrs' ->
100 simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
101 freeTick SimplifierDone `thenSmpl_`
102 returnSmpl (fromOL binds')
105 -- We need to track the zapped top-level binders, because
106 -- they should have their fragile IdInfo zapped (notably occurrence info)
107 simpl_binds [] bs = ASSERT( null bs ) returnSmpl (nilOL, panic "simplTopBinds corner")
108 simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs)
109 simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs))
113 simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId]
114 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
115 simplRecBind top_lvl pairs bndrs' thing_inside
116 = go pairs bndrs' `thenSmpl` \ (binds', (_, (binds'', res))) ->
117 returnSmpl (unitOL (Rec (flattenBinds (fromOL binds'))) `appOL` binds'', res)
119 go [] _ = thing_inside `thenSmpl` \ stuff ->
122 go ((bndr, rhs) : pairs) (bndr' : bndrs')
123 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
124 -- Don't float unboxed bindings out,
125 -- because we can't "rec" them
129 %************************************************************************
131 \subsection[Simplify-simplExpr]{The main function: simplExpr}
133 %************************************************************************
135 The reason for this OutExprStuff stuff is that we want to float *after*
136 simplifying a RHS, not before. If we do so naively we get quadratic
137 behaviour as things float out.
139 To see why it's important to do it after, consider this (real) example:
153 a -- Can't inline a this round, cos it appears twice
157 Each of the ==> steps is a round of simplification. We'd save a
158 whole round if we float first. This can cascade. Consider
163 let f = let d1 = ..d.. in \y -> e
167 in \x -> ...(\y ->e)...
169 Only in this second round can the \y be applied, and it
170 might do the same again.
174 simplExpr :: CoreExpr -> SimplM CoreExpr
175 simplExpr expr = getSubst `thenSmpl` \ subst ->
176 simplExprC expr (mkStop (substTy subst (exprType expr)))
177 -- The type in the Stop continuation is usually not used
178 -- It's only needed when discarding continuations after finding
179 -- a function that returns bottom.
180 -- Hence the lazy substitution
182 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
183 -- Simplify an expression, given a continuation
185 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
186 returnSmpl (wrapFloats floats body)
188 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
189 -- Simplify an expression, returning floated binds
191 simplExprF (Var v) cont
194 simplExprF (Lit lit) (Select _ bndr alts se cont)
195 = knownCon (Lit lit) (LitAlt lit) [] bndr alts se cont
197 simplExprF (Lit lit) cont
198 = rebuild (Lit lit) cont
200 simplExprF (App fun arg) cont
201 = getSubstEnv `thenSmpl` \ se ->
202 simplExprF fun (ApplyTo NoDup arg se cont)
204 simplExprF (Case scrut bndr alts) cont
205 = getSubstEnv `thenSmpl` \ subst_env ->
206 getSwitchChecker `thenSmpl` \ chkr ->
207 if not (switchIsOn chkr NoCaseOfCase) then
208 -- Simplify the scrutinee with a Select continuation
209 simplExprF scrut (Select NoDup bndr alts subst_env cont)
212 -- If case-of-case is off, simply simplify the case expression
213 -- in a vanilla Stop context, and rebuild the result around it
214 simplExprC scrut (Select NoDup bndr alts subst_env
215 (mkStop (contResultType cont))) `thenSmpl` \ case_expr' ->
216 rebuild case_expr' cont
219 simplExprF (Let (Rec pairs) body) cont
220 = simplRecIds (map fst pairs) $ \ bndrs' ->
221 -- NB: bndrs' don't have unfoldings or spec-envs
222 -- We add them as we go down, using simplPrags
224 simplRecBind False pairs bndrs' (simplExprF body cont)
226 simplExprF expr@(Lam _ _) cont = simplLam expr cont
228 simplExprF (Type ty) cont
229 = ASSERT( case cont of { Stop _ _ -> True; ArgOf _ _ _ -> True; other -> False } )
230 simplType ty `thenSmpl` \ ty' ->
231 rebuild (Type ty') cont
233 -- Comments about the Coerce case
234 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
235 -- It's worth checking for a coerce in the continuation,
236 -- in case we can cancel them. For example, in the initial form of a worker
237 -- we may find (coerce T (coerce S (\x.e))) y
238 -- and we'd like it to simplify to e[y/x] in one round of simplification
240 simplExprF (Note (Coerce to from) e) (CoerceIt outer_to cont)
241 = simplType from `thenSmpl` \ from' ->
242 if outer_to == from' then
243 -- The coerces cancel out
246 -- They don't cancel, but the inner one is redundant
247 simplExprF e (CoerceIt outer_to cont)
249 simplExprF (Note (Coerce to from) e) cont
250 = simplType to `thenSmpl` \ to' ->
251 simplExprF e (CoerceIt 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 (mkSCC 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 -- It's also important not to inline a worker back into a wrapper.
281 -- A wrapper looks like
282 -- wraper = inline_me (\x -> ...worker... )
283 -- Normally, the inline_me prevents the worker getting inlined into
284 -- the wrapper (initially, the worker's only call site!). But,
285 -- if the wrapper is sure to be called, the strictness analyser will
286 -- mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf
287 -- continuation. That's why the keep_inline predicate returns True for
288 -- ArgOf continuations. It shouldn't do any harm not to dissolve the
289 -- inline-me note under these circumstances
291 simplExprF (Note InlineMe e) cont
292 | keep_inline cont -- Totally boring continuation
293 = -- Don't inline inside an INLINE expression
294 setBlackList noInlineBlackList (simplExpr e) `thenSmpl` \ e' ->
295 rebuild (mkInlineMe e') cont
297 | otherwise -- Dissolve the InlineMe note if there's
298 -- an interesting context of any kind to combine with
299 -- (even a type application -- anything except Stop)
302 keep_inline (Stop _ _) = True -- See notes above
303 keep_inline (ArgOf _ _ _) = True -- about this predicate
304 keep_inline other = False
306 -- A non-recursive let is dealt with by simplNonRecBind
307 simplExprF (Let (NonRec bndr rhs) body) cont
308 = getSubstEnv `thenSmpl` \ se ->
309 simplNonRecBind bndr rhs se (contResultType cont) $
314 ---------------------------------
320 zap_it = mkLamBndrZapper fun cont
321 cont_ty = contResultType cont
323 -- Type-beta reduction
324 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
325 = ASSERT( isTyVar bndr )
326 tick (BetaReduction bndr) `thenSmpl_`
327 simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' ->
328 extendSubst bndr (DoneTy ty_arg')
331 -- Ordinary beta reduction
332 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
333 = tick (BetaReduction bndr) `thenSmpl_`
334 simplNonRecBind zapped_bndr arg arg_se cont_ty
337 zapped_bndr = zap_it bndr
340 go lam@(Lam _ _) cont = completeLam [] lam cont
342 -- Exactly enough args
343 go expr cont = simplExprF expr cont
345 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
346 -- continuation, so there are real lambdas left to put in the result
348 -- We try for eta reduction here, but *only* if we get all the
349 -- way to an exprIsTrivial expression.
350 -- We don't want to remove extra lambdas unless we are going
351 -- to avoid allocating this thing altogether
353 completeLam rev_bndrs (Lam bndr body) cont
354 = simplBinder bndr $ \ bndr' ->
355 completeLam (bndr':rev_bndrs) body cont
357 completeLam rev_bndrs body cont
358 = simplExpr body `thenSmpl` \ body' ->
359 case try_eta body' of
360 Just etad_lam -> tick (EtaReduction (head rev_bndrs)) `thenSmpl_`
361 rebuild etad_lam cont
363 Nothing -> rebuild (foldl (flip Lam) body' rev_bndrs) cont
365 -- We don't use CoreUtils.etaReduce, because we can be more
367 -- (a) we already have the binders,
368 -- (b) we can do the triviality test before computing the free vars
369 -- [in fact I take the simple path and look for just a variable]
370 -- (c) we don't want to eta-reduce a data con worker or primop
371 -- because we only have to eta-expand them later when we saturate
372 try_eta body | not opt_SimplDoEtaReduction = Nothing
373 | otherwise = go rev_bndrs body
375 go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
376 go [] body | ok_body body = Just body -- Success!
377 go _ _ = Nothing -- Failure!
379 ok_body (Var v) = not (v `elem` rev_bndrs) && not (hasNoBinding v)
380 ok_body other = False
381 ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg
383 mkLamBndrZapper :: CoreExpr -- Function
384 -> SimplCont -- The context
385 -> Id -> Id -- Use this to zap the binders
386 mkLamBndrZapper fun cont
387 | n_args >= n_params fun = \b -> b -- Enough args
388 | otherwise = \b -> zapLamIdInfo b
390 -- NB: we count all the args incl type args
391 -- so we must count all the binders (incl type lambdas)
392 n_args = countArgs cont
394 n_params (Note _ e) = n_params e
395 n_params (Lam b e) = 1 + n_params e
396 n_params other = 0::Int
400 ---------------------------------
402 simplType :: InType -> SimplM OutType
404 = getSubst `thenSmpl` \ subst ->
406 new_ty = substTy subst ty
413 %************************************************************************
417 %************************************************************************
419 @simplNonRecBind@ is used for non-recursive lets in expressions,
420 as well as true beta reduction.
422 Very similar to @simplLazyBind@, but not quite the same.
425 simplNonRecBind :: InId -- Binder
426 -> InExpr -> SubstEnv -- Arg, with its subst-env
427 -> OutType -- Type of thing computed by the context
428 -> SimplM OutExprStuff -- The body
429 -> SimplM OutExprStuff
431 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
433 = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
436 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
437 | preInlineUnconditionally False {- not black listed -} bndr
438 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
439 extendSubst bndr (ContEx rhs_se rhs) thing_inside
442 = -- Simplify the binder.
443 -- Don't use simplBinder because that doesn't keep
444 -- fragile occurrence in the substitution
445 simplLetId bndr $ \ bndr' ->
446 getSubst `thenSmpl` \ bndr_subst ->
448 -- Substitute its IdInfo (which simplLetId does not)
449 -- The appropriate substitution env is the one right here,
450 -- not rhs_se. Often they are the same, when all this
451 -- has arisen from an application (\x. E) RHS, perhaps they aren't
452 bndr'' = simplIdInfo bndr_subst (idInfo bndr) bndr'
453 bndr_ty' = idType bndr'
454 is_strict = isStrict (idDemandInfo bndr) || isStrictType bndr_ty'
456 modifyInScope bndr'' bndr'' $
458 -- Simplify the argument
459 simplValArg bndr_ty' is_strict rhs rhs_se cont_ty $ \ rhs' ->
461 -- Now complete the binding and simplify the body
462 if needsCaseBinding bndr_ty' rhs' then
463 addCaseBind bndr'' rhs' thing_inside
465 completeBinding bndr bndr'' False False rhs' thing_inside
470 simplTyArg :: InType -> SubstEnv -> SimplM OutType
472 = getInScope `thenSmpl` \ in_scope ->
474 ty_arg' = substTy (mkSubst in_scope se) ty_arg
476 seqType ty_arg' `seq`
479 simplValArg :: OutType -- rhs_ty: Type of arg; used only occasionally
480 -> Bool -- True <=> evaluate eagerly
481 -> InExpr -> SubstEnv
482 -> OutType -- cont_ty: Type of thing computed by the context
483 -> (OutExpr -> SimplM OutExprStuff)
484 -- Takes an expression of type rhs_ty,
485 -- returns an expression of type cont_ty
486 -> SimplM OutExprStuff -- An expression of type cont_ty
488 simplValArg arg_ty is_strict arg arg_se cont_ty thing_inside
490 = getEnv `thenSmpl` \ env ->
492 simplExprF arg (ArgOf NoDup cont_ty $ \ rhs' ->
493 setAllExceptInScope env $
497 = simplRhs False {- Not top level -}
498 True {- OK to float unboxed -}
505 - deals only with Ids, not TyVars
506 - take an already-simplified RHS
508 It does *not* attempt to do let-to-case. Why? Because they are used for
511 (when let-to-case is impossible)
513 - many situations where the "rhs" is known to be a WHNF
514 (so let-to-case is inappropriate).
517 completeBinding :: InId -- Binder
518 -> OutId -- New binder
519 -> Bool -- True <=> top level
520 -> Bool -- True <=> black-listed; don't inline
521 -> OutExpr -- Simplified RHS
522 -> SimplM (OutStuff a) -- Thing inside
523 -> SimplM (OutStuff a)
525 completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
526 | isDeadOcc occ_info -- This happens; for example, the case_bndr during case of
527 -- known constructor: case (a,b) of x { (p,q) -> ... }
528 -- Here x isn't mentioned in the RHS, so we don't want to
529 -- create the (dead) let-binding let x = (a,b) in ...
532 | trivial_rhs && not must_keep_binding
533 -- We're looking at a binding with a trivial RHS, so
534 -- perhaps we can discard it altogether!
536 -- NB: a loop breaker has must_keep_binding = True
537 -- and non-loop-breakers only have *forward* references
538 -- Hence, it's safe to discard the binding
540 -- NOTE: This isn't our last opportunity to inline.
541 -- We're at the binding site right now, and
542 -- we'll get another opportunity when we get to the ocurrence(s)
544 -- Note that we do this unconditional inlining only for trival RHSs.
545 -- Don't inline even WHNFs inside lambdas; doing so may
546 -- simply increase allocation when the function is called
547 -- This isn't the last chance; see NOTE above.
549 -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
550 -- Why? Because we don't even want to inline them into the
551 -- RHS of constructor arguments. See NOTE above
553 -- NB: Even NOINLINEis ignored here: if the rhs is trivial
554 -- it's best to inline it anyway. We often get a=E; b=a
555 -- from desugaring, with both a and b marked NOINLINE.
556 = -- Drop the binding
557 extendSubst old_bndr (DoneEx new_rhs) $
558 -- Use the substitution to make quite, quite sure that the substitution
559 -- will happen, since we are going to discard the binding
560 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
563 | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs,
564 not trivial_rhs && not (isUnLiftedType inner_ty)
565 -- x = coerce t e ==> c = e; x = inline_me (coerce t c)
566 -- Now x can get inlined, which moves the coercion
567 -- to the usage site. This is a bit like worker/wrapper stuff,
568 -- but it's useful to do it very promptly, so that
569 -- x = coerce T (I# 3)
573 -- This in turn means that
574 -- case (coerce Int x) of ...
576 -- Also the full-blown w/w thing isn't set up for non-functions
578 -- The (not (isUnLiftedType inner_ty)) avoids the nasty case of
579 -- x::Int = coerce Int Int# (foo y)
582 -- x::Int = coerce Int Int# v
583 -- which would be bogus because then v will be evaluated strictly.
584 -- How can this arise? Via
585 -- x::Int = case (foo y) of { ... }
586 -- followed by case elimination.
588 -- The inline_me note is so that the simplifier doesn't
589 -- just substitute c back inside x's rhs! (Typically, x will
590 -- get substituted away, but not if it's exported.)
591 = newId SLIT("c") inner_ty $ \ c_id ->
592 completeBinding c_id c_id top_lvl False inner_rhs $
593 completeBinding old_bndr new_bndr top_lvl black_listed
594 (Note InlineMe (Note coercion (Var c_id))) $
599 -- We make new IdInfo for the new binder by starting from the old binder,
600 -- doing appropriate substitutions.
601 -- Then we add arity and unfolding info to get the new binder
602 new_bndr_info = idInfo new_bndr `setArityInfo` arity_info
604 -- Add the unfolding *only* for non-loop-breakers
605 -- Making loop breakers not have an unfolding at all
606 -- means that we can avoid tests in exprIsConApp, for example.
607 -- This is important: if exprIsConApp says 'yes' for a recursive
608 -- thing, then we can get into an infinite loop
609 info_w_unf | loop_breaker = new_bndr_info
610 | otherwise = new_bndr_info `setUnfoldingInfo` mkUnfolding top_lvl new_rhs
612 final_id = new_bndr `setIdInfo` info_w_unf
614 -- These seqs forces the Id, and hence its IdInfo,
615 -- and hence any inner substitutions
617 addLetBind (NonRec final_id new_rhs) $
618 modifyInScope new_bndr final_id thing_inside
621 old_info = idInfo old_bndr
622 occ_info = occInfo old_info
623 loop_breaker = isLoopBreaker occ_info
624 trivial_rhs = exprIsTrivial new_rhs
625 must_keep_binding = black_listed || loop_breaker || isExportedId old_bndr
626 arity_info = atLeastArity (exprArity new_rhs)
631 %************************************************************************
633 \subsection{simplLazyBind}
635 %************************************************************************
637 simplLazyBind basically just simplifies the RHS of a let(rec).
638 It does two important optimisations though:
640 * It floats let(rec)s out of the RHS, even if they
641 are hidden by big lambdas
643 * It does eta expansion
646 simplLazyBind :: Bool -- True <=> top level
649 -> SimplM (OutStuff a) -- The body of the binding
650 -> SimplM (OutStuff a)
651 -- When called, the subst env is correct for the entire let-binding
652 -- and hence right for the RHS.
653 -- Also the binder has already been simplified, and hence is in scope
655 simplLazyBind top_lvl bndr bndr' rhs thing_inside
656 = getBlackList `thenSmpl` \ black_list_fn ->
658 black_listed = black_list_fn bndr
661 if preInlineUnconditionally black_listed bndr then
662 -- Inline unconditionally
663 tick (PreInlineUnconditionally bndr) `thenSmpl_`
664 getSubstEnv `thenSmpl` \ rhs_se ->
665 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
669 getSubst `thenSmpl` \ rhs_subst ->
671 -- Substitute IdInfo on binder, in the light of earlier
672 -- substitutions in this very letrec, and extend the in-scope
673 -- env so that it can see the new thing
674 bndr'' = simplIdInfo rhs_subst (idInfo bndr) bndr'
676 modifyInScope bndr'' bndr'' $
678 simplRhs top_lvl False {- Not ok to float unboxed (conservative) -}
680 rhs (substEnv rhs_subst) $ \ rhs' ->
682 -- Now compete the binding and simplify the body
683 completeBinding bndr bndr'' top_lvl black_listed rhs' thing_inside
689 simplRhs :: Bool -- True <=> Top level
690 -> Bool -- True <=> OK to float unboxed (speculative) bindings
691 -- False for (a) recursive and (b) top-level bindings
692 -> OutType -- Type of RHS; used only occasionally
693 -> InExpr -> SubstEnv
694 -> (OutExpr -> SimplM (OutStuff a))
695 -> SimplM (OutStuff a)
696 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
698 setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats1, (rhs_in_scope, rhs1)) ->
700 (floats2, rhs2) = splitFloats float_ubx floats1 rhs1
702 -- There's a subtlety here. There may be a binding (x* = e) in the
703 -- floats, where the '*' means 'will be demanded'. So is it safe
704 -- to float it out? Answer no, but it won't matter because
705 -- we only float if arg' is a WHNF,
706 -- and so there can't be any 'will be demanded' bindings in the floats.
708 WARN( any demanded_float (fromOL floats2), ppr (fromOL floats2) )
711 -- It's important that we do eta expansion on function *arguments* (which are
712 -- simplified with simplRhs), as well as let-bound right-hand sides.
713 -- Otherwise we find that things like
714 -- f (\x -> case x of I# x' -> coerce T (\ y -> ...))
715 -- get right through to the code generator as two separate lambdas,
716 -- which is a Bad Thing
717 tryRhsTyLam rhs2 `thenSmpl` \ (floats3, rhs3) ->
718 tryEtaExpansion rhs3 rhs_ty `thenSmpl` \ (floats4, rhs4) ->
720 -- Float lets if (a) we're at the top level
721 -- or (b) the resulting RHS is one we'd like to expose
722 if (top_lvl || exprIsCheap rhs4) then
723 (if (isNilOL floats2 && null floats3 && null floats4) then
726 tick LetFloatFromLet) `thenSmpl_`
728 addFloats floats2 rhs_in_scope $
729 addAuxiliaryBinds floats3 $
730 addAuxiliaryBinds floats4 $
733 -- Don't do the float
734 thing_inside (wrapFloats floats1 rhs1)
736 demanded_float (NonRec b r) = isStrict (idDemandInfo b) && not (isUnLiftedType (idType b))
737 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
738 demanded_float (Rec _) = False
740 -- If float_ubx is true we float all the bindings, otherwise
741 -- we just float until we come across an unlifted one.
742 -- Remember that the unlifted bindings in the floats are all for
743 -- guaranteed-terminating non-exception-raising unlifted things,
744 -- which we are happy to do speculatively. However, we may still
745 -- not be able to float them out, because the context
746 -- is either a Rec group, or the top level, neither of which
747 -- can tolerate them.
748 splitFloats float_ubx floats rhs
749 | float_ubx = (floats, rhs) -- Float them all
750 | otherwise = go (fromOL floats)
753 go (f:fs) | must_stay f = (nilOL, mkLets (f:fs) rhs)
754 | otherwise = case go fs of
755 (out, rhs') -> (f `consOL` out, rhs')
757 must_stay (Rec prs) = False -- No unlifted bindings in here
758 must_stay (NonRec b r) = isUnLiftedType (idType b)
763 %************************************************************************
765 \subsection{Variables}
767 %************************************************************************
771 = getSubst `thenSmpl` \ subst ->
772 case lookupIdSubst subst var of
773 DoneEx e -> zapSubstEnv (simplExprF e cont)
774 ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
775 DoneId var1 occ -> WARN( not (isInScope var1 subst) && mustHaveLocalBinding var1,
776 text "simplVar:" <+> ppr var )
777 zapSubstEnv (completeCall var1 occ cont)
778 -- The template is already simplified, so don't re-substitute.
779 -- This is VITAL. Consider
781 -- let y = \z -> ...x... in
783 -- We'll clone the inner \x, adding x->x' in the id_subst
784 -- Then when we inline y, we must *not* replace x by x' in
785 -- the inlined copy!!
787 ---------------------------------------------------------
788 -- Dealing with a call
790 completeCall var occ_info cont
791 = getBlackList `thenSmpl` \ black_list_fn ->
792 getInScope `thenSmpl` \ in_scope ->
793 getContArgs var cont `thenSmpl` \ (args, call_cont, inline_call) ->
794 getDOptsSmpl `thenSmpl` \ dflags ->
796 black_listed = black_list_fn var
797 arg_infos = [ interestingArg in_scope arg subst
798 | (arg, subst, _) <- args, isValArg arg]
800 interesting_cont = interestingCallContext (not (null args))
801 (not (null arg_infos))
804 inline_cont | inline_call = discardInline cont
807 maybe_inline = callSiteInline dflags black_listed inline_call occ_info
808 var arg_infos interesting_cont
810 -- First, look for an inlining
811 case maybe_inline of {
812 Just unfolding -- There is an inlining!
813 -> tick (UnfoldingDone var) `thenSmpl_`
814 simplExprF unfolding inline_cont
817 Nothing -> -- No inlining!
820 simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' ->
822 -- Next, look for rules or specialisations that match
824 -- It's important to simplify the args first, because the rule-matcher
825 -- doesn't do substitution as it goes. We don't want to use subst_args
826 -- (defined in the 'where') because that throws away useful occurrence info,
827 -- and perhaps-very-important specialisations.
829 -- Some functions have specialisations *and* are strict; in this case,
830 -- we don't want to inline the wrapper of the non-specialised thing; better
831 -- to call the specialised thing instead.
832 -- But the black-listing mechanism means that inlining of the wrapper
833 -- won't occur for things that have specialisations till a later phase, so
834 -- it's ok to try for inlining first.
836 -- You might think that we shouldn't apply rules for a loop breaker:
837 -- doing so might give rise to an infinite loop, because a RULE is
838 -- rather like an extra equation for the function:
839 -- RULE: f (g x) y = x+y
842 -- But it's too drastic to disable rules for loop breakers.
843 -- Even the foldr/build rule would be disabled, because foldr
844 -- is recursive, and hence a loop breaker:
845 -- foldr k z (build g) = g k z
846 -- So it's up to the programmer: rules can cause divergence
848 getSwitchChecker `thenSmpl` \ chkr ->
850 maybe_rule | switchIsOn chkr DontApplyRules = Nothing
851 | otherwise = lookupRule in_scope var args'
854 Just (rule_name, rule_rhs) ->
855 tick (RuleFired rule_name) `thenSmpl_`
857 (if dopt Opt_D_dump_inlinings dflags then
858 pprTrace "Rule fired" (vcat [
859 text "Rule:" <+> ptext rule_name,
860 text "Before:" <+> ppr var <+> sep (map pprParendExpr args'),
861 text "After: " <+> pprCoreExpr rule_rhs])
865 simplExprF rule_rhs call_cont ;
867 Nothing -> -- No rules
870 rebuild (mkApps (Var var) args') call_cont
874 ---------------------------------------------------------
875 -- Simplifying the arguments of a call
877 simplifyArgs :: Bool -- It's a data constructor
878 -> [(InExpr, SubstEnv, Bool)] -- Details of the arguments
879 -> OutType -- Type of the continuation
880 -> ([OutExpr] -> SimplM OutExprStuff)
881 -> SimplM OutExprStuff
883 -- Simplify the arguments to a call.
884 -- This part of the simplifier may break the no-shadowing invariant
886 -- f (...(\a -> e)...) (case y of (a,b) -> e')
887 -- where f is strict in its second arg
888 -- If we simplify the innermost one first we get (...(\a -> e)...)
889 -- Simplifying the second arg makes us float the case out, so we end up with
890 -- case y of (a,b) -> f (...(\a -> e)...) e'
891 -- So the output does not have the no-shadowing invariant. However, there is
892 -- no danger of getting name-capture, because when the first arg was simplified
893 -- we used an in-scope set that at least mentioned all the variables free in its
894 -- static environment, and that is enough.
896 -- We can't just do innermost first, or we'd end up with a dual problem:
897 -- case x of (a,b) -> f e (...(\a -> e')...)
899 -- I spent hours trying to recover the no-shadowing invariant, but I just could
900 -- not think of an elegant way to do it. The simplifier is already knee-deep in
901 -- continuations. We have to keep the right in-scope set around; AND we have
902 -- to get the effect that finding (error "foo") in a strict arg position will
903 -- discard the entire application and replace it with (error "foo"). Getting
904 -- all this at once is TOO HARD!
906 simplifyArgs is_data_con args cont_ty thing_inside
908 = go args thing_inside
910 | otherwise -- It's a data constructor, so we want
911 -- to switch off inlining in the arguments
912 -- If we don't do this, consider:
913 -- let x = +# p q in C {x}
914 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
915 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
916 = getBlackList `thenSmpl` \ old_bl ->
917 setBlackList noInlineBlackList $
919 setBlackList old_bl $
923 go [] thing_inside = thing_inside []
924 go (arg:args) thing_inside = simplifyArg is_data_con arg cont_ty $ \ arg' ->
926 thing_inside (arg':args')
928 simplifyArg is_data_con (Type ty_arg, se, _) cont_ty thing_inside
929 = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg ->
930 thing_inside (Type new_ty_arg)
932 simplifyArg is_data_con (val_arg, se, is_strict) cont_ty thing_inside
933 = getInScope `thenSmpl` \ in_scope ->
935 arg_ty = substTy (mkSubst in_scope se) (exprType val_arg)
937 if not is_data_con then
938 -- An ordinary function
939 simplValArg arg_ty is_strict val_arg se cont_ty thing_inside
941 -- A data constructor
942 -- simplifyArgs has already switched off inlining, so
943 -- all we have to do here is to let-bind any non-trivial argument
945 -- It's not always the case that new_arg will be trivial
947 -- where, in one pass, f gets substituted by a constructor,
948 -- but x gets substituted by an expression (assume this is the
949 -- unique occurrence of x). It doesn't really matter -- it'll get
950 -- fixed up next pass. And it happens for dictionary construction,
951 -- which mentions the wrapper constructor to start with.
952 simplValArg arg_ty is_strict val_arg se cont_ty $ \ arg' ->
954 if exprIsTrivial arg' then
957 newId SLIT("a") (exprType arg') $ \ arg_id ->
958 addNonRecBind arg_id arg' $
959 thing_inside (Var arg_id)
963 %************************************************************************
965 \subsection{Decisions about inlining}
967 %************************************************************************
969 NB: At one time I tried not pre/post-inlining top-level things,
970 even if they occur exactly once. Reason:
971 (a) some might appear as a function argument, so we simply
972 replace static allocation with dynamic allocation:
978 (b) some top level things might be black listed
980 HOWEVER, I found that some useful foldr/build fusion was lost (most
981 notably in spectral/hartel/parstof) because the foldr didn't see the build.
983 Doing the dynamic allocation isn't a big deal, in fact, but losing the
987 preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
988 -- Examines a bndr to see if it is used just once in a
989 -- completely safe way, so that it is safe to discard the binding
990 -- inline its RHS at the (unique) usage site, REGARDLESS of how
991 -- big the RHS might be. If this is the case we don't simplify
992 -- the RHS first, but just inline it un-simplified.
994 -- This is much better than first simplifying a perhaps-huge RHS
995 -- and then inlining and re-simplifying it.
997 -- NB: we don't even look at the RHS to see if it's trivial
1000 -- where x is used many times, but this is the unique occurrence
1001 -- of y. We should NOT inline x at all its uses, because then
1002 -- we'd do the same for y -- aargh! So we must base this
1003 -- pre-rhs-simplification decision solely on x's occurrences, not
1006 -- Evne RHSs labelled InlineMe aren't caught here, because
1007 -- there might be no benefit from inlining at the call site.
1009 preInlineUnconditionally black_listed bndr
1010 | black_listed || opt_SimplNoPreInlining = False
1011 | otherwise = case idOccInfo bndr of
1012 OneOcc in_lam once -> not in_lam && once
1013 -- Not inside a lambda, one occurrence ==> safe!
1019 %************************************************************************
1021 \subsection{The main rebuilder}
1023 %************************************************************************
1026 -------------------------------------------------------------------
1027 -- Finish rebuilding
1028 rebuild_done expr = returnOutStuff expr
1030 ---------------------------------------------------------
1031 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
1033 -- Stop continuation
1034 rebuild expr (Stop _ _) = rebuild_done expr
1036 -- ArgOf continuation
1037 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1039 -- ApplyTo continuation
1040 rebuild expr cont@(ApplyTo _ arg se cont')
1041 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1042 rebuild (App expr arg') cont'
1044 -- Coerce continuation
1045 rebuild expr (CoerceIt to_ty cont)
1046 = rebuild (mkCoerce to_ty (exprType expr) expr) cont
1048 -- Inline continuation
1049 rebuild expr (InlinePlease cont)
1050 = rebuild (Note InlineCall expr) cont
1052 rebuild scrut (Select _ bndr alts se cont)
1053 = rebuild_case scrut bndr alts se cont
1056 Case elimination [see the code above]
1058 Start with a simple situation:
1060 case x# of ===> e[x#/y#]
1063 (when x#, y# are of primitive type, of course). We can't (in general)
1064 do this for algebraic cases, because we might turn bottom into
1067 Actually, we generalise this idea to look for a case where we're
1068 scrutinising a variable, and we know that only the default case can
1073 other -> ...(case x of
1077 Here the inner case can be eliminated. This really only shows up in
1078 eliminating error-checking code.
1080 We also make sure that we deal with this very common case:
1085 Here we are using the case as a strict let; if x is used only once
1086 then we want to inline it. We have to be careful that this doesn't
1087 make the program terminate when it would have diverged before, so we
1089 - x is used strictly, or
1090 - e is already evaluated (it may so if e is a variable)
1092 Lastly, we generalise the transformation to handle this:
1098 We only do this for very cheaply compared r's (constructors, literals
1099 and variables). If pedantic bottoms is on, we only do it when the
1100 scrutinee is a PrimOp which can't fail.
1102 We do it *here*, looking at un-simplified alternatives, because we
1103 have to check that r doesn't mention the variables bound by the
1104 pattern in each alternative, so the binder-info is rather useful.
1106 So the case-elimination algorithm is:
1108 1. Eliminate alternatives which can't match
1110 2. Check whether all the remaining alternatives
1111 (a) do not mention in their rhs any of the variables bound in their pattern
1112 and (b) have equal rhss
1114 3. Check we can safely ditch the case:
1115 * PedanticBottoms is off,
1116 or * the scrutinee is an already-evaluated variable
1117 or * the scrutinee is a primop which is ok for speculation
1118 -- ie we want to preserve divide-by-zero errors, and
1119 -- calls to error itself!
1121 or * [Prim cases] the scrutinee is a primitive variable
1123 or * [Alg cases] the scrutinee is a variable and
1124 either * the rhs is the same variable
1125 (eg case x of C a b -> x ===> x)
1126 or * there is only one alternative, the default alternative,
1127 and the binder is used strictly in its scope.
1128 [NB this is helped by the "use default binder where
1129 possible" transformation; see below.]
1132 If so, then we can replace the case with one of the rhss.
1135 Blob of helper functions for the "case-of-something-else" situation.
1138 ---------------------------------------------------------
1139 -- Eliminate the case if possible
1141 rebuild_case scrut bndr alts se cont
1142 | maybeToBool maybe_con_app
1143 = knownCon scrut (DataAlt con) args bndr alts se cont
1145 | canEliminateCase scrut bndr alts
1146 = tick (CaseElim bndr) `thenSmpl_` (
1148 simplBinder bndr $ \ bndr' ->
1149 -- Remember to bind the case binder!
1150 completeBinding bndr bndr' False False scrut $
1151 simplExprF (head (rhssOfAlts alts)) cont)
1154 = complete_case scrut bndr alts se cont
1157 maybe_con_app = exprIsConApp_maybe scrut
1158 Just (con, args) = maybe_con_app
1160 -- See if we can get rid of the case altogether
1161 -- See the extensive notes on case-elimination above
1162 canEliminateCase scrut bndr alts
1163 = -- Check that the RHSs are all the same, and
1164 -- don't use the binders in the alternatives
1165 -- This test succeeds rapidly in the common case of
1166 -- a single DEFAULT alternative
1167 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1169 -- Check that the scrutinee can be let-bound instead of case-bound
1170 && ( exprOkForSpeculation scrut
1171 -- OK not to evaluate it
1172 -- This includes things like (==# a# b#)::Bool
1173 -- so that we simplify
1174 -- case ==# a# b# of { True -> x; False -> x }
1177 -- This particular example shows up in default methods for
1178 -- comparision operations (e.g. in (>=) for Int.Int32)
1179 || exprIsValue scrut -- It's already evaluated
1180 || var_demanded_later scrut -- It'll be demanded later
1182 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1183 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1184 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1185 -- its argument: case x of { y -> dataToTag# y }
1186 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1187 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1192 (rhs1:other_rhss) = rhssOfAlts alts
1193 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1195 var_demanded_later (Var v) = isStrict (idDemandInfo bndr) -- It's going to be evaluated later
1196 var_demanded_later other = False
1199 ---------------------------------------------------------
1200 -- Case of something else
1202 complete_case scrut case_bndr alts se cont
1203 = -- Prepare case alternatives
1204 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1205 impossible_cons alts `thenSmpl` \ better_alts ->
1207 -- Set the new subst-env in place (before dealing with the case binder)
1210 -- Deal with the case binder, and prepare the continuation;
1211 -- The new subst_env is in place
1212 prepareCaseCont better_alts cont $ \ cont' ->
1215 -- Deal with variable scrutinee
1217 getSwitchChecker `thenSmpl` \ chkr ->
1218 simplCaseBinder (switchIsOn chkr NoCaseOfCase)
1219 scrut case_bndr $ \ case_bndr' zap_occ_info ->
1221 -- Deal with the case alternatives
1222 simplAlts zap_occ_info impossible_cons
1223 case_bndr' better_alts cont' `thenSmpl` \ alts' ->
1225 mkCase scrut case_bndr' alts'
1226 ) `thenSmpl` \ case_expr ->
1228 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1229 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1230 -- that should not include these chaps!
1231 rebuild_done case_expr
1233 impossible_cons = case scrut of
1234 Var v -> otherCons (idUnfolding v)
1238 knownCon :: OutExpr -> AltCon -> [OutExpr]
1239 -> InId -> [InAlt] -> SubstEnv -> SimplCont
1240 -> SimplM OutExprStuff
1242 knownCon expr con args bndr alts se cont
1243 = -- Arguments should be atomic;
1245 WARN( not (all exprIsTrivial args),
1246 text "knownCon" <+> ppr expr )
1247 tick (KnownBranch bndr) `thenSmpl_`
1249 simplBinder bndr $ \ bndr' ->
1250 completeBinding bndr bndr' False False expr $
1251 -- Don't use completeBeta here. The expr might be
1252 -- an unboxed literal, like 3, or a variable
1253 -- whose unfolding is an unboxed literal... and
1254 -- completeBeta will just construct another case
1256 case findAlt con alts of
1257 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1260 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1263 (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
1264 extendSubstList bs (map mk real_args) $
1267 real_args = drop (dataConNumInstArgs dc) args
1268 mk (Type ty) = DoneTy ty
1269 mk other = DoneEx other
1274 prepareCaseCont :: [InAlt] -> SimplCont
1275 -> (SimplCont -> SimplM (OutStuff a))
1276 -> SimplM (OutStuff a)
1277 -- Polymorphic recursion here!
1279 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1280 prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
1281 mkDupableCont alts_ty cont thing_inside
1282 -- At one time I passed in the un-simplified type, and simplified
1283 -- it only if we needed to construct a join binder, but that
1284 -- didn't work because we have to decompse function types
1285 -- (using funResultTy) in mkDupableCont.
1288 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1289 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1290 way, there's a chance that v will now only be used once, and hence
1293 There is a time we *don't* want to do that, namely when
1294 -fno-case-of-case is on. This happens in the first simplifier pass,
1295 and enhances full laziness. Here's the bad case:
1296 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1297 If we eliminate the inner case, we trap it inside the I# v -> arm,
1298 which might prevent some full laziness happening. I've seen this
1299 in action in spectral/cichelli/Prog.hs:
1300 [(m,n) | m <- [1..max], n <- [1..max]]
1301 Hence the no_case_of_case argument
1304 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1305 in the case binder, because the case-binder now effectively occurs
1306 whenever v does. AND we have to do the same for the pattern-bound
1309 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1311 Here, b and p are dead. But when we move the argment inside the first
1312 case RHS, and eliminate the second case, we get
1314 case x or { (a,b) -> a b }
1316 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1317 happened. Hence the zap_occ_info function returned by simplCaseBinder
1320 simplCaseBinder no_case_of_case (Var v) case_bndr thing_inside
1321 | not no_case_of_case
1322 = simplBinder (zap case_bndr) $ \ case_bndr' ->
1323 modifyInScope v case_bndr' $
1324 -- We could extend the substitution instead, but it would be
1325 -- a hack because then the substitution wouldn't be idempotent
1326 -- any more (v is an OutId). And this just just as well.
1327 thing_inside case_bndr' zap
1329 zap b = b `setIdOccInfo` NoOccInfo
1331 simplCaseBinder add_eval_info other_scrut case_bndr thing_inside
1332 = simplBinder case_bndr $ \ case_bndr' ->
1333 thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
1336 prepareCaseAlts does two things:
1338 1. Remove impossible alternatives
1340 2. If the DEFAULT alternative can match only one possible constructor,
1341 then make that constructor explicit.
1343 case e of x { DEFAULT -> rhs }
1345 case e of x { (a,b) -> rhs }
1346 where the type is a single constructor type. This gives better code
1347 when rhs also scrutinises x or e.
1350 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1352 = case (findDefault filtered_alts, missing_cons) of
1354 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1355 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1357 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1359 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1361 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1362 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1363 arg_tys = dataConArgTys data_con
1364 (inst_tys ++ mkTyVarTys ex_tyvars')
1366 newIds SLIT("a") arg_tys $ \ bndrs ->
1367 returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1369 other -> returnSmpl filtered_alts
1371 -- Filter out alternatives that can't possibly match
1372 filtered_alts = case scrut_cons of
1374 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1376 missing_cons = [data_con | data_con <- tyConDataConsIfAvailable tycon,
1377 not (data_con `elem` handled_data_cons)]
1378 handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++
1379 [data_con | (DataAlt data_con, _, _) <- filtered_alts]
1382 prepareCaseAlts _ _ scrut_cons alts
1383 = returnSmpl alts -- Functions
1386 ----------------------
1387 simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
1388 = mapSmpl simpl_alt alts
1390 inst_tys' = tyConAppArgs (idType case_bndr')
1392 -- handled_cons is all the constructors that are dealt
1393 -- with, either by being impossible, or by there being an alternative
1394 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1396 simpl_alt (DEFAULT, _, rhs)
1397 = -- In the default case we record the constructors that the
1398 -- case-binder *can't* be.
1399 -- We take advantage of any OtherCon info in the case scrutinee
1400 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
1401 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1402 returnSmpl (DEFAULT, [], rhs')
1404 simpl_alt (con, vs, rhs)
1405 = -- Deal with the pattern-bound variables
1406 -- Mark the ones that are in ! positions in the data constructor
1407 -- as certainly-evaluated.
1408 -- NB: it happens that simplBinders does *not* erase the OtherCon
1409 -- form of unfolding, so it's ok to add this info before
1410 -- doing simplBinders
1411 simplBinders (add_evals con vs) $ \ vs' ->
1413 -- Bind the case-binder to (con args)
1415 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1417 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $
1418 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1419 returnSmpl (con, vs', rhs')
1422 -- add_evals records the evaluated-ness of the bound variables of
1423 -- a case pattern. This is *important*. Consider
1424 -- data T = T !Int !Int
1426 -- case x of { T a b -> T (a+1) b }
1428 -- We really must record that b is already evaluated so that we don't
1429 -- go and re-evaluate it when constructing the result.
1431 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1432 add_evals other_con vs = vs
1434 cat_evals [] [] = []
1435 cat_evals (v:vs) (str:strs)
1436 | isTyVar v = v : cat_evals vs (str:strs)
1437 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1438 | otherwise = v' : cat_evals vs strs
1444 %************************************************************************
1446 \subsection{Duplicating continuations}
1448 %************************************************************************
1451 mkDupableCont :: OutType -- Type of the thing to be given to the continuation
1453 -> (SimplCont -> SimplM (OutStuff a))
1454 -> SimplM (OutStuff a)
1455 mkDupableCont ty cont thing_inside
1456 | contIsDupable cont
1459 mkDupableCont _ (CoerceIt ty cont) thing_inside
1460 = mkDupableCont ty cont $ \ cont' ->
1461 thing_inside (CoerceIt ty cont')
1463 mkDupableCont ty (InlinePlease cont) thing_inside
1464 = mkDupableCont ty cont $ \ cont' ->
1465 thing_inside (InlinePlease cont')
1467 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1468 = -- Build the RHS of the join point
1469 newId SLIT("a") join_arg_ty ( \ arg_id ->
1470 cont_fn (Var arg_id) `thenSmpl` \ (floats, (_, rhs)) ->
1471 returnSmpl (Lam (setOneShotLambda arg_id) (wrapFloats floats rhs))
1472 ) `thenSmpl` \ join_rhs ->
1474 -- Build the join Id and continuation
1475 -- We give it a "$j" name just so that for later amusement
1476 -- we can identify any join points that don't end up as let-no-escapes
1477 -- [NOTE: the type used to be exprType join_rhs, but this seems more elegant.]
1478 newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) $ \ join_id ->
1480 new_cont = ArgOf OkToDup cont_ty
1481 (\arg' -> rebuild_done (App (Var join_id) arg'))
1484 tick (CaseOfCase join_id) `thenSmpl_`
1485 -- Want to tick here so that we go round again,
1486 -- and maybe copy or inline the code;
1487 -- not strictly CaseOf Case
1488 addLetBind (NonRec join_id join_rhs) $
1489 thing_inside new_cont
1491 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1492 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1493 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1494 if exprIsDupable arg' then
1495 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1497 newId SLIT("a") (exprType arg') $ \ bndr ->
1499 tick (CaseOfCase bndr) `thenSmpl_`
1500 -- Want to tick here so that we go round again,
1501 -- and maybe copy or inline the code;
1502 -- not strictly CaseOf Case
1504 addLetBind (NonRec bndr arg') $
1505 -- But what if the arg should be case-bound? We can't use
1506 -- addNonRecBind here because its type is too specific.
1507 -- This has been this way for a long time, so I'll leave it,
1508 -- but I can't convince myself that it's right.
1510 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont')
1513 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1514 = tick (CaseOfCase case_bndr) `thenSmpl_`
1516 simplBinder case_bndr $ \ case_bndr' ->
1517 prepareCaseCont alts cont $ \ cont' ->
1518 mkDupableAlts case_bndr case_bndr' cont' alts $ \ alts' ->
1519 returnOutStuff alts'
1520 ) `thenSmpl` \ (alt_binds, (in_scope, alts')) ->
1522 addFloats alt_binds in_scope $
1524 -- NB that the new alternatives, alts', are still InAlts, using the original
1525 -- binders. That means we can keep the case_bndr intact. This is important
1526 -- because another case-of-case might strike, and so we want to keep the
1527 -- info that the case_bndr is dead (if it is, which is often the case).
1528 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1529 -- case in I/O rich code. We aren't allowed a lambda bound
1530 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1531 thing_inside (Select OkToDup case_bndr alts' se (mkStop (contResultType cont)))
1533 mkDupableAlts :: InId -> OutId -> SimplCont -> [InAlt]
1534 -> ([InAlt] -> SimplM (OutStuff a))
1535 -> SimplM (OutStuff a)
1536 mkDupableAlts case_bndr case_bndr' cont [] thing_inside
1538 mkDupableAlts case_bndr case_bndr' cont (alt:alts) thing_inside
1539 = mkDupableAlt case_bndr case_bndr' cont alt $ \ alt' ->
1540 mkDupableAlts case_bndr case_bndr' cont alts $ \ alts' ->
1541 thing_inside (alt' : alts')
1543 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) thing_inside
1544 = simplBinders bndrs $ \ bndrs' ->
1545 simplExprC rhs cont `thenSmpl` \ rhs' ->
1547 if (case cont of { Stop _ _ -> exprIsDupable rhs'; other -> False}) then
1548 -- It is worth checking for a small RHS because otherwise we
1549 -- get extra let bindings that may cause an extra iteration of the simplifier to
1550 -- inline back in place. Quite often the rhs is just a variable or constructor.
1551 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1552 -- iterations because the version with the let bindings looked big, and so wasn't
1553 -- inlined, but after the join points had been inlined it looked smaller, and so
1556 -- But since the continuation is absorbed into the rhs, we only do this
1557 -- for a Stop continuation.
1559 -- NB: we have to check the size of rhs', not rhs.
1560 -- Duplicating a small InAlt might invalidate occurrence information
1561 -- However, if it *is* dupable, we return the *un* simplified alternative,
1562 -- because otherwise we'd need to pair it up with an empty subst-env.
1563 -- (Remember we must zap the subst-env before re-simplifying something).
1564 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1569 rhs_ty' = exprType rhs'
1570 (used_bndrs, used_bndrs')
1571 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1572 (case_bndr' : bndrs'),
1573 not (isDeadBinder bndr)]
1574 -- The new binders have lost their occurrence info,
1575 -- so we have to extract it from the old ones
1577 ( if null used_bndrs'
1578 -- If we try to lift a primitive-typed something out
1579 -- for let-binding-purposes, we will *caseify* it (!),
1580 -- with potentially-disastrous strictness results. So
1581 -- instead we turn it into a function: \v -> e
1582 -- where v::State# RealWorld#. The value passed to this function
1583 -- is realworld#, which generates (almost) no code.
1585 -- There's a slight infelicity here: we pass the overall
1586 -- case_bndr to all the join points if it's used in *any* RHS,
1587 -- because we don't know its usage in each RHS separately
1589 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1590 -- we make the join point into a function whenever used_bndrs'
1591 -- is empty. This makes the join-point more CPR friendly.
1592 -- Consider: let j = if .. then I# 3 else I# 4
1593 -- in case .. of { A -> j; B -> j; C -> ... }
1595 -- Now CPR should not w/w j because it's a thunk, so
1596 -- that means that the enclosing function can't w/w either,
1597 -- which is a lose. Here's the example that happened in practice:
1598 -- kgmod :: Int -> Int -> Int
1599 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1603 then newId SLIT("w") realWorldStatePrimTy $ \ rw_id ->
1604 returnSmpl ([rw_id], [Var realWorldPrimId])
1606 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1608 `thenSmpl` \ (final_bndrs', final_args) ->
1610 -- See comment about "$j" name above
1611 newId SLIT("$j") (foldr mkPiType rhs_ty' final_bndrs') $ \ join_bndr ->
1612 -- Notice the funky mkPiType. If the contructor has existentials
1613 -- it's possible that the join point will be abstracted over
1614 -- type varaibles as well as term variables.
1615 -- Example: Suppose we have
1616 -- data T = forall t. C [t]
1618 -- case (case e of ...) of
1619 -- C t xs::[t] -> rhs
1620 -- We get the join point
1621 -- let j :: forall t. [t] -> ...
1622 -- j = /\t \xs::[t] -> rhs
1624 -- case (case e of ...) of
1625 -- C t xs::[t] -> j t xs
1628 -- We make the lambdas into one-shot-lambdas. The
1629 -- join point is sure to be applied at most once, and doing so
1630 -- prevents the body of the join point being floated out by
1631 -- the full laziness pass
1632 really_final_bndrs = map one_shot final_bndrs'
1633 one_shot v | isId v = setOneShotLambda v
1636 addLetBind (NonRec join_bndr (mkLams really_final_bndrs rhs')) $
1637 thing_inside (con, bndrs, mkApps (Var join_bndr) final_args)