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, mustHaveLocalBinding )
25 import Literal ( Literal )
26 import Id ( Id, idType, idInfo, isDataConId, hasNoBinding,
27 idUnfolding, setIdUnfolding, isExportedId, isDeadBinder,
28 idDemandInfo, setIdInfo,
29 idOccInfo, setIdOccInfo,
30 zapLamIdInfo, setOneShotLambda,
32 import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker,
34 setUnfoldingInfo, atLeastArity,
37 import Demand ( isStrict )
38 import DataCon ( dataConNumInstArgs, dataConRepStrictness,
39 dataConSig, dataConArgTys
42 import PprCore ( pprParendExpr, pprCoreExpr )
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,
56 funResultTy, splitFunTy_maybe, splitFunTy, eqType
58 import Subst ( mkSubst, substTy, substEnv, substExpr,
59 isInScope, lookupIdSubst, simplIdInfo
61 import TyCon ( isDataTyCon, tyConDataConsIfAvailable )
62 import TysPrim ( realWorldStatePrimTy )
63 import PrelInfo ( realWorldPrimId )
65 import Maybes ( maybeToBool )
70 The guts of the simplifier is in this module, but the driver
71 loop for the simplifier is in SimplCore.lhs.
74 -----------------------------------------
75 *** IMPORTANT NOTE ***
76 -----------------------------------------
77 The simplifier used to guarantee that the output had no shadowing, but
78 it does not do so any more. (Actually, it never did!) The reason is
79 documented with simplifyArgs.
84 %************************************************************************
88 %************************************************************************
91 simplTopBinds :: [InBind] -> SimplM [OutBind]
94 = -- Put all the top-level binders into scope at the start
95 -- so that if a transformation rule has unexpectedly brought
96 -- anything into scope, then we don't get a complaint about that.
97 -- It's rather as if the top-level binders were imported.
98 simplRecIds (bindersOfBinds binds) $ \ bndrs' ->
99 simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
100 freeTick SimplifierDone `thenSmpl_`
101 returnSmpl (fromOL binds')
104 -- We need to track the zapped top-level binders, because
105 -- they should have their fragile IdInfo zapped (notably occurrence info)
106 simpl_binds [] bs = ASSERT( null bs ) returnSmpl (nilOL, panic "simplTopBinds corner")
107 simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs)
108 simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs))
112 simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId]
113 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
114 simplRecBind top_lvl pairs bndrs' thing_inside
115 = go pairs bndrs' `thenSmpl` \ (binds', (_, (binds'', res))) ->
116 returnSmpl (unitOL (Rec (flattenBinds (fromOL binds'))) `appOL` binds'', res)
118 go [] _ = thing_inside `thenSmpl` \ stuff ->
121 go ((bndr, rhs) : pairs) (bndr' : bndrs')
122 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
123 -- Don't float unboxed bindings out,
124 -- because we can't "rec" them
128 %************************************************************************
130 \subsection[Simplify-simplExpr]{The main function: simplExpr}
132 %************************************************************************
134 The reason for this OutExprStuff stuff is that we want to float *after*
135 simplifying a RHS, not before. If we do so naively we get quadratic
136 behaviour as things float out.
138 To see why it's important to do it after, consider this (real) example:
152 a -- Can't inline a this round, cos it appears twice
156 Each of the ==> steps is a round of simplification. We'd save a
157 whole round if we float first. This can cascade. Consider
162 let f = let d1 = ..d.. in \y -> e
166 in \x -> ...(\y ->e)...
168 Only in this second round can the \y be applied, and it
169 might do the same again.
173 simplExpr :: CoreExpr -> SimplM CoreExpr
174 simplExpr expr = getSubst `thenSmpl` \ subst ->
175 simplExprC expr (mkStop (substTy subst (exprType expr)))
176 -- The type in the Stop continuation is usually not used
177 -- It's only needed when discarding continuations after finding
178 -- a function that returns bottom.
179 -- Hence the lazy substitution
181 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
182 -- Simplify an expression, given a continuation
184 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
185 returnSmpl (wrapFloats floats body)
187 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
188 -- Simplify an expression, returning floated binds
190 simplExprF (Var v) cont = simplVar v cont
191 simplExprF (Lit lit) cont = simplLit lit cont
192 simplExprF expr@(Lam _ _) cont = simplLam expr cont
193 simplExprF (Note note expr) cont = simplNote note expr cont
195 simplExprF (App fun arg) cont
196 = getSubstEnv `thenSmpl` \ se ->
197 simplExprF fun (ApplyTo NoDup arg se cont)
199 simplExprF (Type ty) cont
200 = ASSERT( case cont of { Stop _ _ -> True; ArgOf _ _ _ -> True; other -> False } )
201 simplType ty `thenSmpl` \ ty' ->
202 rebuild (Type ty') 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
218 simplExprF (Let (Rec pairs) body) cont
219 = simplRecIds (map fst pairs) $ \ bndrs' ->
220 -- NB: bndrs' don't have unfoldings or spec-envs
221 -- We add them as we go down, using simplPrags
223 simplRecBind False pairs bndrs' (simplExprF body cont)
225 -- A non-recursive let is dealt with by simplNonRecBind
226 simplExprF (Let (NonRec bndr rhs) body) cont
227 = getSubstEnv `thenSmpl` \ se ->
228 simplNonRecBind bndr rhs se (contResultType cont) $
232 ---------------------------------
233 simplType :: InType -> SimplM OutType
235 = getSubst `thenSmpl` \ subst ->
237 new_ty = substTy subst ty
242 ---------------------------------
243 simplLit :: Literal -> SimplCont -> SimplM OutExprStuff
245 simplLit lit (Select _ bndr alts se cont)
246 = knownCon (Lit lit) (LitAlt lit) [] bndr alts se cont
248 simplLit lit cont = rebuild (Lit lit) cont
252 %************************************************************************
256 %************************************************************************
262 zap_it = mkLamBndrZapper fun cont
263 cont_ty = contResultType cont
265 -- Type-beta reduction
266 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
267 = ASSERT( isTyVar bndr )
268 tick (BetaReduction bndr) `thenSmpl_`
269 simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' ->
270 extendSubst bndr (DoneTy ty_arg')
273 -- Ordinary beta reduction
274 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
275 = tick (BetaReduction bndr) `thenSmpl_`
276 simplNonRecBind zapped_bndr arg arg_se cont_ty
279 zapped_bndr = zap_it bndr
282 go lam@(Lam _ _) cont = completeLam [] lam cont
284 -- Exactly enough args
285 go expr cont = simplExprF expr cont
287 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
288 -- continuation, so there are real lambdas left to put in the result
290 -- We try for eta reduction here, but *only* if we get all the
291 -- way to an exprIsTrivial expression.
292 -- We don't want to remove extra lambdas unless we are going
293 -- to avoid allocating this thing altogether
295 completeLam rev_bndrs (Lam bndr body) cont
296 = simplBinder bndr $ \ bndr' ->
297 completeLam (bndr':rev_bndrs) body cont
299 completeLam rev_bndrs body cont
300 = simplExpr body `thenSmpl` \ body' ->
301 case try_eta body' of
302 Just etad_lam -> tick (EtaReduction (head rev_bndrs)) `thenSmpl_`
303 rebuild etad_lam cont
305 Nothing -> rebuild (foldl (flip Lam) body' rev_bndrs) cont
307 -- We don't use CoreUtils.etaReduce, because we can be more
309 -- (a) we already have the binders,
310 -- (b) we can do the triviality test before computing the free vars
311 -- [in fact I take the simple path and look for just a variable]
312 -- (c) we don't want to eta-reduce a data con worker or primop
313 -- because we only have to eta-expand them later when we saturate
314 try_eta body | not opt_SimplDoEtaReduction = Nothing
315 | otherwise = go rev_bndrs body
317 go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
318 go [] body | ok_body body = Just body -- Success!
319 go _ _ = Nothing -- Failure!
321 ok_body (Var v) = not (v `elem` rev_bndrs) && not (hasNoBinding v)
322 ok_body other = False
323 ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg
325 mkLamBndrZapper :: CoreExpr -- Function
326 -> SimplCont -- The context
327 -> Id -> Id -- Use this to zap the binders
328 mkLamBndrZapper fun cont
329 | n_args >= n_params fun = \b -> b -- Enough args
330 | otherwise = \b -> zapLamIdInfo b
332 -- NB: we count all the args incl type args
333 -- so we must count all the binders (incl type lambdas)
334 n_args = countArgs cont
336 n_params (Note _ e) = n_params e
337 n_params (Lam b e) = 1 + n_params e
338 n_params other = 0::Int
342 %************************************************************************
346 %************************************************************************
349 simplNote (Coerce to from) body cont
350 = getInScope `thenSmpl` \ in_scope ->
352 addCoerce s1 k1 (CoerceIt t1 cont)
353 -- coerce T1 S1 (coerce S1 K1 e)
356 -- coerce T1 K1 e, otherwise
358 -- For example, in the initial form of a worker
359 -- we may find (coerce T (coerce S (\x.e))) y
360 -- and we'd like it to simplify to e[y/x] in one round
362 | t1 `eqType` k1 = cont -- The coerces cancel out
363 | otherwise = CoerceIt t1 cont -- They don't cancel, but
364 -- the inner one is redundant
366 addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
367 | Just (s1, s2) <- splitFunTy_maybe s1s2
368 -- (coerce (T1->T2) (S1->S2) F) E
370 -- coerce T2 S2 (F (coerce S1 T1 E))
372 -- t1t2 must be a function type, T1->T2
373 -- but s1s2 might conceivably not be
375 -- When we build the ApplyTo we can't mix the out-types
376 -- with the InExpr in the argument, so we simply substitute
377 -- to make it all consistent. This isn't a common case.
379 (t1,t2) = splitFunTy t1t2
380 new_arg = mkCoerce s1 t1 (substExpr (mkSubst in_scope arg_se) arg)
382 ApplyTo dup new_arg emptySubstEnv (addCoerce t2 s2 cont)
384 addCoerce to' _ cont = CoerceIt to' cont
386 simplType to `thenSmpl` \ to' ->
387 simplType from `thenSmpl` \ from' ->
388 simplExprF body (addCoerce to' from' cont)
391 -- Hack: we only distinguish subsumed cost centre stacks for the purposes of
392 -- inlining. All other CCCSs are mapped to currentCCS.
393 simplNote (SCC cc) e cont
394 = setEnclosingCC currentCCS $
395 simplExpr e `thenSmpl` \ e ->
396 rebuild (mkSCC cc e) cont
398 simplNote InlineCall e cont
399 = simplExprF e (InlinePlease cont)
401 -- Comments about the InlineMe case
402 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
403 -- Don't inline in the RHS of something that has an
404 -- inline pragma. But be careful that the InScopeEnv that
405 -- we return does still have inlinings on!
407 -- It really is important to switch off inlinings. This function
408 -- may be inlinined in other modules, so we don't want to remove
409 -- (by inlining) calls to functions that have specialisations, or
410 -- that may have transformation rules in an importing scope.
411 -- E.g. {-# INLINE f #-}
413 -- and suppose that g is strict *and* has specialisations.
414 -- If we inline g's wrapper, we deny f the chance of getting
415 -- the specialised version of g when f is inlined at some call site
416 -- (perhaps in some other module).
418 -- It's also important not to inline a worker back into a wrapper.
419 -- A wrapper looks like
420 -- wraper = inline_me (\x -> ...worker... )
421 -- Normally, the inline_me prevents the worker getting inlined into
422 -- the wrapper (initially, the worker's only call site!). But,
423 -- if the wrapper is sure to be called, the strictness analyser will
424 -- mark it 'demanded', so when the RHS is simplified, it'll get an ArgOf
425 -- continuation. That's why the keep_inline predicate returns True for
426 -- ArgOf continuations. It shouldn't do any harm not to dissolve the
427 -- inline-me note under these circumstances
429 simplNote InlineMe e cont
430 | keep_inline cont -- Totally boring continuation
431 = -- Don't inline inside an INLINE expression
432 setBlackList noInlineBlackList (simplExpr e) `thenSmpl` \ e' ->
433 rebuild (mkInlineMe e') cont
435 | otherwise -- Dissolve the InlineMe note if there's
436 -- an interesting context of any kind to combine with
437 -- (even a type application -- anything except Stop)
440 keep_inline (Stop _ _) = True -- See notes above
441 keep_inline (ArgOf _ _ _) = True -- about this predicate
442 keep_inline other = False
446 %************************************************************************
450 %************************************************************************
452 @simplNonRecBind@ is used for non-recursive lets in expressions,
453 as well as true beta reduction.
455 Very similar to @simplLazyBind@, but not quite the same.
458 simplNonRecBind :: InId -- Binder
459 -> InExpr -> SubstEnv -- Arg, with its subst-env
460 -> OutType -- Type of thing computed by the context
461 -> SimplM OutExprStuff -- The body
462 -> SimplM OutExprStuff
464 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
466 = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
469 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
470 | preInlineUnconditionally False {- not black listed -} bndr
471 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
472 extendSubst bndr (ContEx rhs_se rhs) thing_inside
475 = -- Simplify the binder.
476 -- Don't use simplBinder because that doesn't keep
477 -- fragile occurrence in the substitution
478 simplLetId bndr $ \ bndr' ->
479 getSubst `thenSmpl` \ bndr_subst ->
481 -- Substitute its IdInfo (which simplLetId does not)
482 -- The appropriate substitution env is the one right here,
483 -- not rhs_se. Often they are the same, when all this
484 -- has arisen from an application (\x. E) RHS, perhaps they aren't
485 bndr'' = simplIdInfo bndr_subst (idInfo bndr) bndr'
486 bndr_ty' = idType bndr'
487 is_strict = isStrict (idDemandInfo bndr) || isStrictType bndr_ty'
489 modifyInScope bndr'' bndr'' $
491 -- Simplify the argument
492 simplValArg bndr_ty' is_strict rhs rhs_se cont_ty $ \ rhs' ->
494 -- Now complete the binding and simplify the body
495 if needsCaseBinding bndr_ty' rhs' then
496 addCaseBind bndr'' rhs' thing_inside
498 completeBinding bndr bndr'' False False rhs' thing_inside
503 simplTyArg :: InType -> SubstEnv -> SimplM OutType
505 = getInScope `thenSmpl` \ in_scope ->
507 ty_arg' = substTy (mkSubst in_scope se) ty_arg
509 seqType ty_arg' `seq`
512 simplValArg :: OutType -- rhs_ty: Type of arg; used only occasionally
513 -> Bool -- True <=> evaluate eagerly
514 -> InExpr -> SubstEnv
515 -> OutType -- cont_ty: Type of thing computed by the context
516 -> (OutExpr -> SimplM OutExprStuff)
517 -- Takes an expression of type rhs_ty,
518 -- returns an expression of type cont_ty
519 -> SimplM OutExprStuff -- An expression of type cont_ty
521 simplValArg arg_ty is_strict arg arg_se cont_ty thing_inside
523 = getEnv `thenSmpl` \ env ->
525 simplExprF arg (ArgOf NoDup cont_ty $ \ rhs' ->
526 setAllExceptInScope env $
530 = simplRhs False {- Not top level -}
531 True {- OK to float unboxed -}
538 - deals only with Ids, not TyVars
539 - take an already-simplified RHS
541 It does *not* attempt to do let-to-case. Why? Because they are used for
544 (when let-to-case is impossible)
546 - many situations where the "rhs" is known to be a WHNF
547 (so let-to-case is inappropriate).
550 completeBinding :: InId -- Binder
551 -> OutId -- New binder
552 -> Bool -- True <=> top level
553 -> Bool -- True <=> black-listed; don't inline
554 -> OutExpr -- Simplified RHS
555 -> SimplM (OutStuff a) -- Thing inside
556 -> SimplM (OutStuff a)
558 completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
559 | isDeadOcc occ_info -- This happens; for example, the case_bndr during case of
560 -- known constructor: case (a,b) of x { (p,q) -> ... }
561 -- Here x isn't mentioned in the RHS, so we don't want to
562 -- create the (dead) let-binding let x = (a,b) in ...
565 | trivial_rhs && not must_keep_binding
566 -- We're looking at a binding with a trivial RHS, so
567 -- perhaps we can discard it altogether!
569 -- NB: a loop breaker has must_keep_binding = True
570 -- and non-loop-breakers only have *forward* references
571 -- Hence, it's safe to discard the binding
573 -- NOTE: This isn't our last opportunity to inline.
574 -- We're at the binding site right now, and
575 -- we'll get another opportunity when we get to the ocurrence(s)
577 -- Note that we do this unconditional inlining only for trival RHSs.
578 -- Don't inline even WHNFs inside lambdas; doing so may
579 -- simply increase allocation when the function is called
580 -- This isn't the last chance; see NOTE above.
582 -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
583 -- Why? Because we don't even want to inline them into the
584 -- RHS of constructor arguments. See NOTE above
586 -- NB: Even NOINLINEis ignored here: if the rhs is trivial
587 -- it's best to inline it anyway. We often get a=E; b=a
588 -- from desugaring, with both a and b marked NOINLINE.
589 = -- Drop the binding
590 extendSubst old_bndr (DoneEx new_rhs) $
591 -- Use the substitution to make quite, quite sure that the substitution
592 -- will happen, since we are going to discard the binding
593 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
596 | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs,
597 not trivial_rhs && not (isUnLiftedType inner_ty)
598 -- x = coerce t e ==> c = e; x = inline_me (coerce t c)
599 -- Now x can get inlined, which moves the coercion
600 -- to the usage site. This is a bit like worker/wrapper stuff,
601 -- but it's useful to do it very promptly, so that
602 -- x = coerce T (I# 3)
606 -- This in turn means that
607 -- case (coerce Int x) of ...
609 -- Also the full-blown w/w thing isn't set up for non-functions
611 -- The (not (isUnLiftedType inner_ty)) avoids the nasty case of
612 -- x::Int = coerce Int Int# (foo y)
615 -- x::Int = coerce Int Int# v
616 -- which would be bogus because then v will be evaluated strictly.
617 -- How can this arise? Via
618 -- x::Int = case (foo y) of { ... }
619 -- followed by case elimination.
621 -- The inline_me note is so that the simplifier doesn't
622 -- just substitute c back inside x's rhs! (Typically, x will
623 -- get substituted away, but not if it's exported.)
624 = newId SLIT("c") inner_ty $ \ c_id ->
625 completeBinding c_id c_id top_lvl False inner_rhs $
626 completeBinding old_bndr new_bndr top_lvl black_listed
627 (Note InlineMe (Note coercion (Var c_id))) $
632 -- We make new IdInfo for the new binder by starting from the old binder,
633 -- doing appropriate substitutions.
634 -- Then we add arity and unfolding info to get the new binder
635 new_bndr_info = idInfo new_bndr `setArityInfo` arity_info
637 -- Add the unfolding *only* for non-loop-breakers
638 -- Making loop breakers not have an unfolding at all
639 -- means that we can avoid tests in exprIsConApp, for example.
640 -- This is important: if exprIsConApp says 'yes' for a recursive
641 -- thing, then we can get into an infinite loop
642 info_w_unf | loop_breaker = new_bndr_info
643 | otherwise = new_bndr_info `setUnfoldingInfo` mkUnfolding top_lvl new_rhs
645 final_id = new_bndr `setIdInfo` info_w_unf
647 -- These seqs forces the Id, and hence its IdInfo,
648 -- and hence any inner substitutions
650 addLetBind (NonRec final_id new_rhs) $
651 modifyInScope new_bndr final_id thing_inside
654 old_info = idInfo old_bndr
655 occ_info = occInfo old_info
656 loop_breaker = isLoopBreaker occ_info
657 trivial_rhs = exprIsTrivial new_rhs
658 must_keep_binding = black_listed || loop_breaker || isExportedId old_bndr
659 arity_info = atLeastArity (exprArity new_rhs)
664 %************************************************************************
666 \subsection{simplLazyBind}
668 %************************************************************************
670 simplLazyBind basically just simplifies the RHS of a let(rec).
671 It does two important optimisations though:
673 * It floats let(rec)s out of the RHS, even if they
674 are hidden by big lambdas
676 * It does eta expansion
679 simplLazyBind :: Bool -- True <=> top level
682 -> SimplM (OutStuff a) -- The body of the binding
683 -> SimplM (OutStuff a)
684 -- When called, the subst env is correct for the entire let-binding
685 -- and hence right for the RHS.
686 -- Also the binder has already been simplified, and hence is in scope
688 simplLazyBind top_lvl bndr bndr' rhs thing_inside
689 = getBlackList `thenSmpl` \ black_list_fn ->
691 black_listed = black_list_fn bndr
694 if preInlineUnconditionally black_listed bndr then
695 -- Inline unconditionally
696 tick (PreInlineUnconditionally bndr) `thenSmpl_`
697 getSubstEnv `thenSmpl` \ rhs_se ->
698 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
702 getSubst `thenSmpl` \ rhs_subst ->
704 -- Substitute IdInfo on binder, in the light of earlier
705 -- substitutions in this very letrec, and extend the in-scope
706 -- env so that it can see the new thing
707 bndr'' = simplIdInfo rhs_subst (idInfo bndr) bndr'
709 modifyInScope bndr'' bndr'' $
711 simplRhs top_lvl False {- Not ok to float unboxed (conservative) -}
713 rhs (substEnv rhs_subst) $ \ rhs' ->
715 -- Now compete the binding and simplify the body
716 completeBinding bndr bndr'' top_lvl black_listed rhs' thing_inside
722 simplRhs :: Bool -- True <=> Top level
723 -> Bool -- True <=> OK to float unboxed (speculative) bindings
724 -- False for (a) recursive and (b) top-level bindings
725 -> OutType -- Type of RHS; used only occasionally
726 -> InExpr -> SubstEnv
727 -> (OutExpr -> SimplM (OutStuff a))
728 -> SimplM (OutStuff a)
729 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
731 setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats1, (rhs_in_scope, rhs1)) ->
733 (floats2, rhs2) = splitFloats float_ubx floats1 rhs1
735 -- There's a subtlety here. There may be a binding (x* = e) in the
736 -- floats, where the '*' means 'will be demanded'. So is it safe
737 -- to float it out? Answer no, but it won't matter because
738 -- we only float if arg' is a WHNF,
739 -- and so there can't be any 'will be demanded' bindings in the floats.
741 WARN( any demanded_float (fromOL floats2), ppr (fromOL floats2) )
744 -- It's important that we do eta expansion on function *arguments* (which are
745 -- simplified with simplRhs), as well as let-bound right-hand sides.
746 -- Otherwise we find that things like
747 -- f (\x -> case x of I# x' -> coerce T (\ y -> ...))
748 -- get right through to the code generator as two separate lambdas,
749 -- which is a Bad Thing
750 tryRhsTyLam rhs2 `thenSmpl` \ (floats3, rhs3) ->
751 tryEtaExpansion rhs3 rhs_ty `thenSmpl` \ (floats4, rhs4) ->
753 -- Float lets if (a) we're at the top level
754 -- or (b) the resulting RHS is one we'd like to expose
755 if (top_lvl || exprIsCheap rhs4) then
756 (if (isNilOL floats2 && null floats3 && null floats4) then
759 tick LetFloatFromLet) `thenSmpl_`
761 addFloats floats2 rhs_in_scope $
762 addAuxiliaryBinds floats3 $
763 addAuxiliaryBinds floats4 $
766 -- Don't do the float
767 thing_inside (wrapFloats floats1 rhs1)
769 demanded_float (NonRec b r) = isStrict (idDemandInfo b) && not (isUnLiftedType (idType b))
770 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
771 demanded_float (Rec _) = False
773 -- If float_ubx is true we float all the bindings, otherwise
774 -- we just float until we come across an unlifted one.
775 -- Remember that the unlifted bindings in the floats are all for
776 -- guaranteed-terminating non-exception-raising unlifted things,
777 -- which we are happy to do speculatively. However, we may still
778 -- not be able to float them out, because the context
779 -- is either a Rec group, or the top level, neither of which
780 -- can tolerate them.
781 splitFloats float_ubx floats rhs
782 | float_ubx = (floats, rhs) -- Float them all
783 | otherwise = go (fromOL floats)
786 go (f:fs) | must_stay f = (nilOL, mkLets (f:fs) rhs)
787 | otherwise = case go fs of
788 (out, rhs') -> (f `consOL` out, rhs')
790 must_stay (Rec prs) = False -- No unlifted bindings in here
791 must_stay (NonRec b r) = isUnLiftedType (idType b)
796 %************************************************************************
798 \subsection{Variables}
800 %************************************************************************
804 = getSubst `thenSmpl` \ subst ->
805 case lookupIdSubst subst var of
806 DoneEx e -> zapSubstEnv (simplExprF e cont)
807 ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
808 DoneId var1 occ -> WARN( not (isInScope var1 subst) && mustHaveLocalBinding var1,
809 text "simplVar:" <+> ppr var )
810 zapSubstEnv (completeCall var1 occ cont)
811 -- The template is already simplified, so don't re-substitute.
812 -- This is VITAL. Consider
814 -- let y = \z -> ...x... in
816 -- We'll clone the inner \x, adding x->x' in the id_subst
817 -- Then when we inline y, we must *not* replace x by x' in
818 -- the inlined copy!!
820 ---------------------------------------------------------
821 -- Dealing with a call
823 completeCall var occ_info cont
824 = getBlackList `thenSmpl` \ black_list_fn ->
825 getInScope `thenSmpl` \ in_scope ->
826 getContArgs var cont `thenSmpl` \ (args, call_cont, inline_call) ->
827 getDOptsSmpl `thenSmpl` \ dflags ->
829 black_listed = black_list_fn var
830 arg_infos = [ interestingArg in_scope arg subst
831 | (arg, subst, _) <- args, isValArg arg]
833 interesting_cont = interestingCallContext (not (null args))
834 (not (null arg_infos))
837 inline_cont | inline_call = discardInline cont
840 maybe_inline = callSiteInline dflags black_listed inline_call occ_info
841 var arg_infos interesting_cont
843 -- First, look for an inlining
844 case maybe_inline of {
845 Just unfolding -- There is an inlining!
846 -> tick (UnfoldingDone var) `thenSmpl_`
847 simplExprF unfolding inline_cont
850 Nothing -> -- No inlining!
853 simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' ->
855 -- Next, look for rules or specialisations that match
857 -- It's important to simplify the args first, because the rule-matcher
858 -- doesn't do substitution as it goes. We don't want to use subst_args
859 -- (defined in the 'where') because that throws away useful occurrence info,
860 -- and perhaps-very-important specialisations.
862 -- Some functions have specialisations *and* are strict; in this case,
863 -- we don't want to inline the wrapper of the non-specialised thing; better
864 -- to call the specialised thing instead.
865 -- But the black-listing mechanism means that inlining of the wrapper
866 -- won't occur for things that have specialisations till a later phase, so
867 -- it's ok to try for inlining first.
869 -- You might think that we shouldn't apply rules for a loop breaker:
870 -- doing so might give rise to an infinite loop, because a RULE is
871 -- rather like an extra equation for the function:
872 -- RULE: f (g x) y = x+y
875 -- But it's too drastic to disable rules for loop breakers.
876 -- Even the foldr/build rule would be disabled, because foldr
877 -- is recursive, and hence a loop breaker:
878 -- foldr k z (build g) = g k z
879 -- So it's up to the programmer: rules can cause divergence
881 getSwitchChecker `thenSmpl` \ chkr ->
883 maybe_rule | switchIsOn chkr DontApplyRules = Nothing
884 | otherwise = lookupRule in_scope var args'
887 Just (rule_name, rule_rhs) ->
888 tick (RuleFired rule_name) `thenSmpl_`
890 (if dopt Opt_D_dump_inlinings dflags then
891 pprTrace "Rule fired" (vcat [
892 text "Rule:" <+> ptext rule_name,
893 text "Before:" <+> ppr var <+> sep (map pprParendExpr args'),
894 text "After: " <+> pprCoreExpr rule_rhs])
898 simplExprF rule_rhs call_cont ;
900 Nothing -> -- No rules
903 rebuild (mkApps (Var var) args') call_cont
907 ---------------------------------------------------------
908 -- Simplifying the arguments of a call
910 simplifyArgs :: Bool -- It's a data constructor
911 -> [(InExpr, SubstEnv, Bool)] -- Details of the arguments
912 -> OutType -- Type of the continuation
913 -> ([OutExpr] -> SimplM OutExprStuff)
914 -> SimplM OutExprStuff
916 -- Simplify the arguments to a call.
917 -- This part of the simplifier may break the no-shadowing invariant
919 -- f (...(\a -> e)...) (case y of (a,b) -> e')
920 -- where f is strict in its second arg
921 -- If we simplify the innermost one first we get (...(\a -> e)...)
922 -- Simplifying the second arg makes us float the case out, so we end up with
923 -- case y of (a,b) -> f (...(\a -> e)...) e'
924 -- So the output does not have the no-shadowing invariant. However, there is
925 -- no danger of getting name-capture, because when the first arg was simplified
926 -- we used an in-scope set that at least mentioned all the variables free in its
927 -- static environment, and that is enough.
929 -- We can't just do innermost first, or we'd end up with a dual problem:
930 -- case x of (a,b) -> f e (...(\a -> e')...)
932 -- I spent hours trying to recover the no-shadowing invariant, but I just could
933 -- not think of an elegant way to do it. The simplifier is already knee-deep in
934 -- continuations. We have to keep the right in-scope set around; AND we have
935 -- to get the effect that finding (error "foo") in a strict arg position will
936 -- discard the entire application and replace it with (error "foo"). Getting
937 -- all this at once is TOO HARD!
939 simplifyArgs is_data_con args cont_ty thing_inside
941 = go args thing_inside
943 | otherwise -- It's a data constructor, so we want
944 -- to switch off inlining in the arguments
945 -- If we don't do this, consider:
946 -- let x = +# p q in C {x}
947 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
948 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
949 = getBlackList `thenSmpl` \ old_bl ->
950 setBlackList noInlineBlackList $
952 setBlackList old_bl $
956 go [] thing_inside = thing_inside []
957 go (arg:args) thing_inside = simplifyArg is_data_con arg cont_ty $ \ arg' ->
959 thing_inside (arg':args')
961 simplifyArg is_data_con (Type ty_arg, se, _) cont_ty thing_inside
962 = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg ->
963 thing_inside (Type new_ty_arg)
965 simplifyArg is_data_con (val_arg, se, is_strict) cont_ty thing_inside
966 = getInScope `thenSmpl` \ in_scope ->
968 arg_ty = substTy (mkSubst in_scope se) (exprType val_arg)
970 if not is_data_con then
971 -- An ordinary function
972 simplValArg arg_ty is_strict val_arg se cont_ty thing_inside
974 -- A data constructor
975 -- simplifyArgs has already switched off inlining, so
976 -- all we have to do here is to let-bind any non-trivial argument
978 -- It's not always the case that new_arg will be trivial
980 -- where, in one pass, f gets substituted by a constructor,
981 -- but x gets substituted by an expression (assume this is the
982 -- unique occurrence of x). It doesn't really matter -- it'll get
983 -- fixed up next pass. And it happens for dictionary construction,
984 -- which mentions the wrapper constructor to start with.
985 simplValArg arg_ty is_strict val_arg se cont_ty $ \ arg' ->
987 if exprIsTrivial arg' then
990 newId SLIT("a") (exprType arg') $ \ arg_id ->
991 addNonRecBind arg_id arg' $
992 thing_inside (Var arg_id)
996 %************************************************************************
998 \subsection{Decisions about inlining}
1000 %************************************************************************
1002 NB: At one time I tried not pre/post-inlining top-level things,
1003 even if they occur exactly once. Reason:
1004 (a) some might appear as a function argument, so we simply
1005 replace static allocation with dynamic allocation:
1011 (b) some top level things might be black listed
1013 HOWEVER, I found that some useful foldr/build fusion was lost (most
1014 notably in spectral/hartel/parstof) because the foldr didn't see the build.
1016 Doing the dynamic allocation isn't a big deal, in fact, but losing the
1020 preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
1021 -- Examines a bndr to see if it is used just once in a
1022 -- completely safe way, so that it is safe to discard the binding
1023 -- inline its RHS at the (unique) usage site, REGARDLESS of how
1024 -- big the RHS might be. If this is the case we don't simplify
1025 -- the RHS first, but just inline it un-simplified.
1027 -- This is much better than first simplifying a perhaps-huge RHS
1028 -- and then inlining and re-simplifying it.
1030 -- NB: we don't even look at the RHS to see if it's trivial
1033 -- where x is used many times, but this is the unique occurrence
1034 -- of y. We should NOT inline x at all its uses, because then
1035 -- we'd do the same for y -- aargh! So we must base this
1036 -- pre-rhs-simplification decision solely on x's occurrences, not
1039 -- Evne RHSs labelled InlineMe aren't caught here, because
1040 -- there might be no benefit from inlining at the call site.
1042 preInlineUnconditionally black_listed bndr
1043 | black_listed || opt_SimplNoPreInlining = False
1044 | otherwise = case idOccInfo bndr of
1045 OneOcc in_lam once -> not in_lam && once
1046 -- Not inside a lambda, one occurrence ==> safe!
1052 %************************************************************************
1054 \subsection{The main rebuilder}
1056 %************************************************************************
1059 -------------------------------------------------------------------
1060 -- Finish rebuilding
1061 rebuild_done expr = returnOutStuff expr
1063 ---------------------------------------------------------
1064 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
1066 -- Stop continuation
1067 rebuild expr (Stop _ _) = rebuild_done expr
1069 -- ArgOf continuation
1070 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1072 -- ApplyTo continuation
1073 rebuild expr cont@(ApplyTo _ arg se cont')
1074 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1075 rebuild (App expr arg') cont'
1077 -- Coerce continuation
1078 rebuild expr (CoerceIt to_ty cont)
1079 = rebuild (mkCoerce to_ty (exprType expr) expr) cont
1081 -- Inline continuation
1082 rebuild expr (InlinePlease cont)
1083 = rebuild (Note InlineCall expr) cont
1085 rebuild scrut (Select _ bndr alts se cont)
1086 = rebuild_case scrut bndr alts se cont
1089 Case elimination [see the code above]
1091 Start with a simple situation:
1093 case x# of ===> e[x#/y#]
1096 (when x#, y# are of primitive type, of course). We can't (in general)
1097 do this for algebraic cases, because we might turn bottom into
1100 Actually, we generalise this idea to look for a case where we're
1101 scrutinising a variable, and we know that only the default case can
1106 other -> ...(case x of
1110 Here the inner case can be eliminated. This really only shows up in
1111 eliminating error-checking code.
1113 We also make sure that we deal with this very common case:
1118 Here we are using the case as a strict let; if x is used only once
1119 then we want to inline it. We have to be careful that this doesn't
1120 make the program terminate when it would have diverged before, so we
1122 - x is used strictly, or
1123 - e is already evaluated (it may so if e is a variable)
1125 Lastly, we generalise the transformation to handle this:
1131 We only do this for very cheaply compared r's (constructors, literals
1132 and variables). If pedantic bottoms is on, we only do it when the
1133 scrutinee is a PrimOp which can't fail.
1135 We do it *here*, looking at un-simplified alternatives, because we
1136 have to check that r doesn't mention the variables bound by the
1137 pattern in each alternative, so the binder-info is rather useful.
1139 So the case-elimination algorithm is:
1141 1. Eliminate alternatives which can't match
1143 2. Check whether all the remaining alternatives
1144 (a) do not mention in their rhs any of the variables bound in their pattern
1145 and (b) have equal rhss
1147 3. Check we can safely ditch the case:
1148 * PedanticBottoms is off,
1149 or * the scrutinee is an already-evaluated variable
1150 or * the scrutinee is a primop which is ok for speculation
1151 -- ie we want to preserve divide-by-zero errors, and
1152 -- calls to error itself!
1154 or * [Prim cases] the scrutinee is a primitive variable
1156 or * [Alg cases] the scrutinee is a variable and
1157 either * the rhs is the same variable
1158 (eg case x of C a b -> x ===> x)
1159 or * there is only one alternative, the default alternative,
1160 and the binder is used strictly in its scope.
1161 [NB this is helped by the "use default binder where
1162 possible" transformation; see below.]
1165 If so, then we can replace the case with one of the rhss.
1168 Blob of helper functions for the "case-of-something-else" situation.
1171 ---------------------------------------------------------
1172 -- Eliminate the case if possible
1174 rebuild_case scrut bndr alts se cont
1175 | maybeToBool maybe_con_app
1176 = knownCon scrut (DataAlt con) args bndr alts se cont
1178 | canEliminateCase scrut bndr alts
1179 = tick (CaseElim bndr) `thenSmpl_` (
1181 simplBinder bndr $ \ bndr' ->
1182 -- Remember to bind the case binder!
1183 completeBinding bndr bndr' False False scrut $
1184 simplExprF (head (rhssOfAlts alts)) cont)
1187 = complete_case scrut bndr alts se cont
1190 maybe_con_app = exprIsConApp_maybe scrut
1191 Just (con, args) = maybe_con_app
1193 -- See if we can get rid of the case altogether
1194 -- See the extensive notes on case-elimination above
1195 canEliminateCase scrut bndr alts
1196 = -- Check that the RHSs are all the same, and
1197 -- don't use the binders in the alternatives
1198 -- This test succeeds rapidly in the common case of
1199 -- a single DEFAULT alternative
1200 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1202 -- Check that the scrutinee can be let-bound instead of case-bound
1203 && ( exprOkForSpeculation scrut
1204 -- OK not to evaluate it
1205 -- This includes things like (==# a# b#)::Bool
1206 -- so that we simplify
1207 -- case ==# a# b# of { True -> x; False -> x }
1210 -- This particular example shows up in default methods for
1211 -- comparision operations (e.g. in (>=) for Int.Int32)
1212 || exprIsValue scrut -- It's already evaluated
1213 || var_demanded_later scrut -- It'll be demanded later
1215 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1216 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1217 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1218 -- its argument: case x of { y -> dataToTag# y }
1219 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1220 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1225 (rhs1:other_rhss) = rhssOfAlts alts
1226 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1228 var_demanded_later (Var v) = isStrict (idDemandInfo bndr) -- It's going to be evaluated later
1229 var_demanded_later other = False
1232 ---------------------------------------------------------
1233 -- Case of something else
1235 complete_case scrut case_bndr alts se cont
1236 = -- Prepare case alternatives
1237 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1238 impossible_cons alts `thenSmpl` \ better_alts ->
1240 -- Set the new subst-env in place (before dealing with the case binder)
1243 -- Deal with the case binder, and prepare the continuation;
1244 -- The new subst_env is in place
1245 prepareCaseCont better_alts cont $ \ cont' ->
1248 -- Deal with variable scrutinee
1250 getSwitchChecker `thenSmpl` \ chkr ->
1251 simplCaseBinder (switchIsOn chkr NoCaseOfCase)
1252 scrut case_bndr $ \ case_bndr' zap_occ_info ->
1254 -- Deal with the case alternatives
1255 simplAlts zap_occ_info impossible_cons
1256 case_bndr' better_alts cont' `thenSmpl` \ alts' ->
1258 mkCase scrut case_bndr' alts'
1259 ) `thenSmpl` \ case_expr ->
1261 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1262 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1263 -- that should not include these chaps!
1264 rebuild_done case_expr
1266 impossible_cons = case scrut of
1267 Var v -> otherCons (idUnfolding v)
1271 knownCon :: OutExpr -> AltCon -> [OutExpr]
1272 -> InId -> [InAlt] -> SubstEnv -> SimplCont
1273 -> SimplM OutExprStuff
1275 knownCon expr con args bndr alts se cont
1276 = -- Arguments should be atomic;
1278 WARN( not (all exprIsTrivial args),
1279 text "knownCon" <+> ppr expr )
1280 tick (KnownBranch bndr) `thenSmpl_`
1282 simplBinder bndr $ \ bndr' ->
1283 completeBinding bndr bndr' False False expr $
1284 -- Don't use completeBeta here. The expr might be
1285 -- an unboxed literal, like 3, or a variable
1286 -- whose unfolding is an unboxed literal... and
1287 -- completeBeta will just construct another case
1289 case findAlt con alts of
1290 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1293 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1296 (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
1297 extendSubstList bs (map mk real_args) $
1300 real_args = drop (dataConNumInstArgs dc) args
1301 mk (Type ty) = DoneTy ty
1302 mk other = DoneEx other
1307 prepareCaseCont :: [InAlt] -> SimplCont
1308 -> (SimplCont -> SimplM (OutStuff a))
1309 -> SimplM (OutStuff a)
1310 -- Polymorphic recursion here!
1312 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1313 prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
1314 mkDupableCont alts_ty cont thing_inside
1315 -- At one time I passed in the un-simplified type, and simplified
1316 -- it only if we needed to construct a join binder, but that
1317 -- didn't work because we have to decompse function types
1318 -- (using funResultTy) in mkDupableCont.
1321 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1322 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1323 way, there's a chance that v will now only be used once, and hence
1326 There is a time we *don't* want to do that, namely when
1327 -fno-case-of-case is on. This happens in the first simplifier pass,
1328 and enhances full laziness. Here's the bad case:
1329 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1330 If we eliminate the inner case, we trap it inside the I# v -> arm,
1331 which might prevent some full laziness happening. I've seen this
1332 in action in spectral/cichelli/Prog.hs:
1333 [(m,n) | m <- [1..max], n <- [1..max]]
1334 Hence the no_case_of_case argument
1337 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1338 in the case binder, because the case-binder now effectively occurs
1339 whenever v does. AND we have to do the same for the pattern-bound
1342 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1344 Here, b and p are dead. But when we move the argment inside the first
1345 case RHS, and eliminate the second case, we get
1347 case x or { (a,b) -> a b }
1349 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1350 happened. Hence the zap_occ_info function returned by simplCaseBinder
1353 simplCaseBinder no_case_of_case (Var v) case_bndr thing_inside
1354 | not no_case_of_case
1355 = simplBinder (zap case_bndr) $ \ case_bndr' ->
1356 modifyInScope v case_bndr' $
1357 -- We could extend the substitution instead, but it would be
1358 -- a hack because then the substitution wouldn't be idempotent
1359 -- any more (v is an OutId). And this just just as well.
1360 thing_inside case_bndr' zap
1362 zap b = b `setIdOccInfo` NoOccInfo
1364 simplCaseBinder add_eval_info other_scrut case_bndr thing_inside
1365 = simplBinder case_bndr $ \ case_bndr' ->
1366 thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
1369 prepareCaseAlts does two things:
1371 1. Remove impossible alternatives
1373 2. If the DEFAULT alternative can match only one possible constructor,
1374 then make that constructor explicit.
1376 case e of x { DEFAULT -> rhs }
1378 case e of x { (a,b) -> rhs }
1379 where the type is a single constructor type. This gives better code
1380 when rhs also scrutinises x or e.
1383 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1385 = case (findDefault filtered_alts, missing_cons) of
1387 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1388 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1390 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1392 getUniquesSmpl `thenSmpl` \ tv_uniqs ->
1394 ex_tyvars' = zipWith mk tv_uniqs ex_tyvars
1395 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1396 arg_tys = dataConArgTys data_con
1397 (inst_tys ++ mkTyVarTys ex_tyvars')
1399 newIds SLIT("a") arg_tys $ \ bndrs ->
1400 returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1402 other -> returnSmpl filtered_alts
1404 -- Filter out alternatives that can't possibly match
1405 filtered_alts = case scrut_cons of
1407 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1409 missing_cons = [data_con | data_con <- tyConDataConsIfAvailable tycon,
1410 not (data_con `elem` handled_data_cons)]
1411 handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++
1412 [data_con | (DataAlt data_con, _, _) <- filtered_alts]
1415 prepareCaseAlts _ _ scrut_cons alts
1416 = returnSmpl alts -- Functions
1419 ----------------------
1420 simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
1421 = mapSmpl simpl_alt alts
1423 inst_tys' = tyConAppArgs (idType case_bndr')
1425 -- handled_cons is all the constructors that are dealt
1426 -- with, either by being impossible, or by there being an alternative
1427 (con_alts,_) = findDefault alts
1428 handled_cons = scrut_cons ++ [con | (con,_,_) <- con_alts]
1430 simpl_alt (DEFAULT, _, rhs)
1431 = -- In the default case we record the constructors that the
1432 -- case-binder *can't* be.
1433 -- We take advantage of any OtherCon info in the case scrutinee
1434 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
1435 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1436 returnSmpl (DEFAULT, [], rhs')
1438 simpl_alt (con, vs, rhs)
1439 = -- Deal with the pattern-bound variables
1440 -- Mark the ones that are in ! positions in the data constructor
1441 -- as certainly-evaluated.
1442 -- NB: it happens that simplBinders does *not* erase the OtherCon
1443 -- form of unfolding, so it's ok to add this info before
1444 -- doing simplBinders
1445 simplBinders (add_evals con vs) $ \ vs' ->
1447 -- Bind the case-binder to (con args)
1449 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1451 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $
1452 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1453 returnSmpl (con, vs', rhs')
1456 -- add_evals records the evaluated-ness of the bound variables of
1457 -- a case pattern. This is *important*. Consider
1458 -- data T = T !Int !Int
1460 -- case x of { T a b -> T (a+1) b }
1462 -- We really must record that b is already evaluated so that we don't
1463 -- go and re-evaluate it when constructing the result.
1465 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1466 add_evals other_con vs = vs
1468 cat_evals [] [] = []
1469 cat_evals (v:vs) (str:strs)
1470 | isTyVar v = v : cat_evals vs (str:strs)
1471 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1472 | otherwise = v' : cat_evals vs strs
1478 %************************************************************************
1480 \subsection{Duplicating continuations}
1482 %************************************************************************
1485 mkDupableCont :: OutType -- Type of the thing to be given to the continuation
1487 -> (SimplCont -> SimplM (OutStuff a))
1488 -> SimplM (OutStuff a)
1489 mkDupableCont ty cont thing_inside
1490 | contIsDupable cont
1493 mkDupableCont _ (CoerceIt ty cont) thing_inside
1494 = mkDupableCont ty cont $ \ cont' ->
1495 thing_inside (CoerceIt ty cont')
1497 mkDupableCont ty (InlinePlease cont) thing_inside
1498 = mkDupableCont ty cont $ \ cont' ->
1499 thing_inside (InlinePlease cont')
1501 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1502 = -- Build the RHS of the join point
1503 newId SLIT("a") join_arg_ty ( \ arg_id ->
1504 cont_fn (Var arg_id) `thenSmpl` \ (floats, (_, rhs)) ->
1505 returnSmpl (Lam (setOneShotLambda arg_id) (wrapFloats floats rhs))
1506 ) `thenSmpl` \ join_rhs ->
1508 -- Build the join Id and continuation
1509 -- We give it a "$j" name just so that for later amusement
1510 -- we can identify any join points that don't end up as let-no-escapes
1511 -- [NOTE: the type used to be exprType join_rhs, but this seems more elegant.]
1512 newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) $ \ join_id ->
1514 new_cont = ArgOf OkToDup cont_ty
1515 (\arg' -> rebuild_done (App (Var join_id) arg'))
1518 tick (CaseOfCase join_id) `thenSmpl_`
1519 -- Want to tick here so that we go round again,
1520 -- and maybe copy or inline the code;
1521 -- not strictly CaseOf Case
1522 addLetBind (NonRec join_id join_rhs) $
1523 thing_inside new_cont
1525 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1526 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1527 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1528 if exprIsDupable arg' then
1529 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1531 newId SLIT("a") (exprType arg') $ \ bndr ->
1533 tick (CaseOfCase bndr) `thenSmpl_`
1534 -- Want to tick here so that we go round again,
1535 -- and maybe copy or inline the code;
1536 -- not strictly CaseOf Case
1538 addLetBind (NonRec bndr arg') $
1539 -- But what if the arg should be case-bound? We can't use
1540 -- addNonRecBind here because its type is too specific.
1541 -- This has been this way for a long time, so I'll leave it,
1542 -- but I can't convince myself that it's right.
1544 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont')
1547 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1548 = tick (CaseOfCase case_bndr) `thenSmpl_`
1550 simplBinder case_bndr $ \ case_bndr' ->
1551 prepareCaseCont alts cont $ \ cont' ->
1552 mkDupableAlts case_bndr case_bndr' cont' alts $ \ alts' ->
1553 returnOutStuff alts'
1554 ) `thenSmpl` \ (alt_binds, (in_scope, alts')) ->
1556 addFloats alt_binds in_scope $
1558 -- NB that the new alternatives, alts', are still InAlts, using the original
1559 -- binders. That means we can keep the case_bndr intact. This is important
1560 -- because another case-of-case might strike, and so we want to keep the
1561 -- info that the case_bndr is dead (if it is, which is often the case).
1562 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1563 -- case in I/O rich code. We aren't allowed a lambda bound
1564 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1565 thing_inside (Select OkToDup case_bndr alts' se (mkStop (contResultType cont)))
1567 mkDupableAlts :: InId -> OutId -> SimplCont -> [InAlt]
1568 -> ([InAlt] -> SimplM (OutStuff a))
1569 -> SimplM (OutStuff a)
1570 mkDupableAlts case_bndr case_bndr' cont [] thing_inside
1572 mkDupableAlts case_bndr case_bndr' cont (alt:alts) thing_inside
1573 = mkDupableAlt case_bndr case_bndr' cont alt $ \ alt' ->
1574 mkDupableAlts case_bndr case_bndr' cont alts $ \ alts' ->
1575 thing_inside (alt' : alts')
1577 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) thing_inside
1578 = simplBinders bndrs $ \ bndrs' ->
1579 simplExprC rhs cont `thenSmpl` \ rhs' ->
1581 if (case cont of { Stop _ _ -> exprIsDupable rhs'; other -> False}) then
1582 -- It is worth checking for a small RHS because otherwise we
1583 -- get extra let bindings that may cause an extra iteration of the simplifier to
1584 -- inline back in place. Quite often the rhs is just a variable or constructor.
1585 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1586 -- iterations because the version with the let bindings looked big, and so wasn't
1587 -- inlined, but after the join points had been inlined it looked smaller, and so
1590 -- But since the continuation is absorbed into the rhs, we only do this
1591 -- for a Stop continuation.
1593 -- NB: we have to check the size of rhs', not rhs.
1594 -- Duplicating a small InAlt might invalidate occurrence information
1595 -- However, if it *is* dupable, we return the *un* simplified alternative,
1596 -- because otherwise we'd need to pair it up with an empty subst-env.
1597 -- (Remember we must zap the subst-env before re-simplifying something).
1598 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1603 rhs_ty' = exprType rhs'
1604 (used_bndrs, used_bndrs')
1605 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1606 (case_bndr' : bndrs'),
1607 not (isDeadBinder bndr)]
1608 -- The new binders have lost their occurrence info,
1609 -- so we have to extract it from the old ones
1611 ( if null used_bndrs'
1612 -- If we try to lift a primitive-typed something out
1613 -- for let-binding-purposes, we will *caseify* it (!),
1614 -- with potentially-disastrous strictness results. So
1615 -- instead we turn it into a function: \v -> e
1616 -- where v::State# RealWorld#. The value passed to this function
1617 -- is realworld#, which generates (almost) no code.
1619 -- There's a slight infelicity here: we pass the overall
1620 -- case_bndr to all the join points if it's used in *any* RHS,
1621 -- because we don't know its usage in each RHS separately
1623 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1624 -- we make the join point into a function whenever used_bndrs'
1625 -- is empty. This makes the join-point more CPR friendly.
1626 -- Consider: let j = if .. then I# 3 else I# 4
1627 -- in case .. of { A -> j; B -> j; C -> ... }
1629 -- Now CPR doesn't w/w j because it's a thunk, so
1630 -- that means that the enclosing function can't w/w either,
1631 -- which is a lose. Here's the example that happened in practice:
1632 -- kgmod :: Int -> Int -> Int
1633 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1637 -- I have seen a case alternative like this:
1638 -- True -> \v -> ...
1639 -- It's a bit silly to add the realWorld dummy arg in this case, making
1642 -- (the \v alone is enough to make CPR happy) but I think it's rare
1644 then newId SLIT("w") realWorldStatePrimTy $ \ rw_id ->
1645 returnSmpl ([rw_id], [Var realWorldPrimId])
1647 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1649 `thenSmpl` \ (final_bndrs', final_args) ->
1651 -- See comment about "$j" name above
1652 newId SLIT("$j") (foldr mkPiType rhs_ty' final_bndrs') $ \ join_bndr ->
1653 -- Notice the funky mkPiType. If the contructor has existentials
1654 -- it's possible that the join point will be abstracted over
1655 -- type varaibles as well as term variables.
1656 -- Example: Suppose we have
1657 -- data T = forall t. C [t]
1659 -- case (case e of ...) of
1660 -- C t xs::[t] -> rhs
1661 -- We get the join point
1662 -- let j :: forall t. [t] -> ...
1663 -- j = /\t \xs::[t] -> rhs
1665 -- case (case e of ...) of
1666 -- C t xs::[t] -> j t xs
1669 -- We make the lambdas into one-shot-lambdas. The
1670 -- join point is sure to be applied at most once, and doing so
1671 -- prevents the body of the join point being floated out by
1672 -- the full laziness pass
1673 really_final_bndrs = map one_shot final_bndrs'
1674 one_shot v | isId v = setOneShotLambda v
1677 addLetBind (NonRec join_bndr (mkLams really_final_bndrs rhs')) $
1678 thing_inside (con, bndrs, mkApps (Var join_bndr) final_args)