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 idNewDemandInfo, setIdInfo,
29 idOccInfo, setIdOccInfo,
30 zapLamIdInfo, setOneShotLambda,
32 import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker,
37 import NewDemand ( isStrictDmd )
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 noInlineBlackList `thenSmpl` \ bl ->
433 setBlackList bl (simplExpr e) `thenSmpl` \ e' ->
434 rebuild (mkInlineMe e') cont
436 | otherwise -- Dissolve the InlineMe note if there's
437 -- an interesting context of any kind to combine with
438 -- (even a type application -- anything except Stop)
441 keep_inline (Stop _ _) = True -- See notes above
442 keep_inline (ArgOf _ _ _) = True -- about this predicate
443 keep_inline other = False
447 %************************************************************************
451 %************************************************************************
453 @simplNonRecBind@ is used for non-recursive lets in expressions,
454 as well as true beta reduction.
456 Very similar to @simplLazyBind@, but not quite the same.
459 simplNonRecBind :: InId -- Binder
460 -> InExpr -> SubstEnv -- Arg, with its subst-env
461 -> OutType -- Type of thing computed by the context
462 -> SimplM OutExprStuff -- The body
463 -> SimplM OutExprStuff
465 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
467 = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
470 simplNonRecBind bndr rhs rhs_se cont_ty thing_inside
471 | preInlineUnconditionally False {- not black listed -} bndr
472 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
473 extendSubst bndr (ContEx rhs_se rhs) thing_inside
476 = -- Simplify the binder.
477 -- Don't use simplBinder because that doesn't keep
478 -- fragile occurrence in the substitution
479 simplLetId bndr $ \ bndr' ->
480 getSubst `thenSmpl` \ bndr_subst ->
482 -- Substitute its IdInfo (which simplLetId does not)
483 -- The appropriate substitution env is the one right here,
484 -- not rhs_se. Often they are the same, when all this
485 -- has arisen from an application (\x. E) RHS, perhaps they aren't
486 bndr'' = simplIdInfo bndr_subst (idInfo bndr) bndr'
487 bndr_ty' = idType bndr'
488 is_strict = isStrictDmd (idNewDemandInfo bndr) || isStrictType bndr_ty'
490 modifyInScope bndr'' bndr'' $
492 -- Simplify the argument
493 simplValArg bndr_ty' is_strict rhs rhs_se cont_ty $ \ rhs' ->
495 -- Now complete the binding and simplify the body
496 if needsCaseBinding bndr_ty' rhs' then
497 addCaseBind bndr'' rhs' thing_inside
499 completeBinding bndr bndr'' False False rhs' thing_inside
504 simplTyArg :: InType -> SubstEnv -> SimplM OutType
506 = getInScope `thenSmpl` \ in_scope ->
508 ty_arg' = substTy (mkSubst in_scope se) ty_arg
510 seqType ty_arg' `seq`
513 simplValArg :: OutType -- rhs_ty: Type of arg; used only occasionally
514 -> Bool -- True <=> evaluate eagerly
515 -> InExpr -> SubstEnv
516 -> OutType -- cont_ty: Type of thing computed by the context
517 -> (OutExpr -> SimplM OutExprStuff)
518 -- Takes an expression of type rhs_ty,
519 -- returns an expression of type cont_ty
520 -> SimplM OutExprStuff -- An expression of type cont_ty
522 simplValArg arg_ty is_strict arg arg_se cont_ty thing_inside
524 = getEnv `thenSmpl` \ env ->
526 simplExprF arg (ArgOf NoDup cont_ty $ \ rhs' ->
527 setAllExceptInScope env $
531 = simplRhs False {- Not top level -}
532 True {- OK to float unboxed -}
539 - deals only with Ids, not TyVars
540 - take an already-simplified RHS
542 It does *not* attempt to do let-to-case. Why? Because they are used for
545 (when let-to-case is impossible)
547 - many situations where the "rhs" is known to be a WHNF
548 (so let-to-case is inappropriate).
551 completeBinding :: InId -- Binder
552 -> OutId -- New binder
553 -> Bool -- True <=> top level
554 -> Bool -- True <=> black-listed; don't inline
555 -> OutExpr -- Simplified RHS
556 -> SimplM (OutStuff a) -- Thing inside
557 -> SimplM (OutStuff a)
559 completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
560 | isDeadOcc occ_info -- This happens; for example, the case_bndr during case of
561 -- known constructor: case (a,b) of x { (p,q) -> ... }
562 -- Here x isn't mentioned in the RHS, so we don't want to
563 -- create the (dead) let-binding let x = (a,b) in ...
566 | trivial_rhs && not must_keep_binding
567 -- We're looking at a binding with a trivial RHS, so
568 -- perhaps we can discard it altogether!
570 -- NB: a loop breaker has must_keep_binding = True
571 -- and non-loop-breakers only have *forward* references
572 -- Hence, it's safe to discard the binding
574 -- NOTE: This isn't our last opportunity to inline.
575 -- We're at the binding site right now, and
576 -- we'll get another opportunity when we get to the ocurrence(s)
578 -- Note that we do this unconditional inlining only for trival RHSs.
579 -- Don't inline even WHNFs inside lambdas; doing so may
580 -- simply increase allocation when the function is called
581 -- This isn't the last chance; see NOTE above.
583 -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
584 -- Why? Because we don't even want to inline them into the
585 -- RHS of constructor arguments. See NOTE above
587 -- NB: Even NOINLINEis ignored here: if the rhs is trivial
588 -- it's best to inline it anyway. We often get a=E; b=a
589 -- from desugaring, with both a and b marked NOINLINE.
590 = -- Drop the binding
591 extendSubst old_bndr (DoneEx new_rhs) $
592 -- Use the substitution to make quite, quite sure that the substitution
593 -- will happen, since we are going to discard the binding
594 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
597 | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs,
598 not trivial_rhs && not (isUnLiftedType inner_ty)
599 -- x = coerce t e ==> c = e; x = inline_me (coerce t c)
600 -- Now x can get inlined, which moves the coercion
601 -- to the usage site. This is a bit like worker/wrapper stuff,
602 -- but it's useful to do it very promptly, so that
603 -- x = coerce T (I# 3)
607 -- This in turn means that
608 -- case (coerce Int x) of ...
610 -- Also the full-blown w/w thing isn't set up for non-functions
612 -- The (not (isUnLiftedType inner_ty)) avoids the nasty case of
613 -- x::Int = coerce Int Int# (foo y)
616 -- x::Int = coerce Int Int# v
617 -- which would be bogus because then v will be evaluated strictly.
618 -- How can this arise? Via
619 -- x::Int = case (foo y) of { ... }
620 -- followed by case elimination.
622 -- The inline_me note is so that the simplifier doesn't
623 -- just substitute c back inside x's rhs! (Typically, x will
624 -- get substituted away, but not if it's exported.)
625 = newId SLIT("c") inner_ty $ \ c_id ->
626 completeBinding c_id c_id top_lvl False inner_rhs $
627 completeBinding old_bndr new_bndr top_lvl black_listed
628 (Note InlineMe (Note coercion (Var c_id))) $
633 -- We make new IdInfo for the new binder by starting from the old binder,
634 -- doing appropriate substitutions.
635 -- Then we add arity and unfolding info to get the new binder
636 new_bndr_info = idInfo new_bndr `setArityInfo` arity
638 -- Add the unfolding *only* for non-loop-breakers
639 -- Making loop breakers not have an unfolding at all
640 -- means that we can avoid tests in exprIsConApp, for example.
641 -- This is important: if exprIsConApp says 'yes' for a recursive
642 -- thing, then we can get into an infinite loop
643 info_w_unf | loop_breaker = new_bndr_info
644 | otherwise = new_bndr_info `setUnfoldingInfo` mkUnfolding top_lvl new_rhs
646 final_id = new_bndr `setIdInfo` info_w_unf
648 -- These seqs forces the Id, and hence its IdInfo,
649 -- and hence any inner substitutions
651 addLetBind (NonRec final_id new_rhs) $
652 modifyInScope new_bndr final_id thing_inside
655 old_info = idInfo old_bndr
656 occ_info = occInfo old_info
657 loop_breaker = isLoopBreaker occ_info
658 trivial_rhs = exprIsTrivial new_rhs
659 must_keep_binding = black_listed || loop_breaker || isExportedId old_bndr
660 arity = exprArity new_rhs
665 %************************************************************************
667 \subsection{simplLazyBind}
669 %************************************************************************
671 simplLazyBind basically just simplifies the RHS of a let(rec).
672 It does two important optimisations though:
674 * It floats let(rec)s out of the RHS, even if they
675 are hidden by big lambdas
677 * It does eta expansion
680 simplLazyBind :: Bool -- True <=> top level
683 -> SimplM (OutStuff a) -- The body of the binding
684 -> SimplM (OutStuff a)
685 -- When called, the subst env is correct for the entire let-binding
686 -- and hence right for the RHS.
687 -- Also the binder has already been simplified, and hence is in scope
689 simplLazyBind top_lvl bndr bndr' rhs thing_inside
690 = getBlackList `thenSmpl` \ black_list_fn ->
692 black_listed = black_list_fn bndr
695 if preInlineUnconditionally black_listed bndr then
696 -- Inline unconditionally
697 tick (PreInlineUnconditionally bndr) `thenSmpl_`
698 getSubstEnv `thenSmpl` \ rhs_se ->
699 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
703 getSubst `thenSmpl` \ rhs_subst ->
705 -- Substitute IdInfo on binder, in the light of earlier
706 -- substitutions in this very letrec, and extend the in-scope
707 -- env so that it can see the new thing
708 bndr'' = simplIdInfo rhs_subst (idInfo bndr) bndr'
710 modifyInScope bndr'' bndr'' $
712 simplRhs top_lvl False {- Not ok to float unboxed (conservative) -}
714 rhs (substEnv rhs_subst) $ \ rhs' ->
716 -- Now compete the binding and simplify the body
717 completeBinding bndr bndr'' top_lvl black_listed rhs' thing_inside
723 simplRhs :: Bool -- True <=> Top level
724 -> Bool -- True <=> OK to float unboxed (speculative) bindings
725 -- False for (a) recursive and (b) top-level bindings
726 -> OutType -- Type of RHS; used only occasionally
727 -> InExpr -> SubstEnv
728 -> (OutExpr -> SimplM (OutStuff a))
729 -> SimplM (OutStuff a)
730 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
732 setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats1, (rhs_in_scope, rhs1)) ->
734 (floats2, rhs2) = splitFloats float_ubx floats1 rhs1
736 -- There's a subtlety here. There may be a binding (x* = e) in the
737 -- floats, where the '*' means 'will be demanded'. So is it safe
738 -- to float it out? Answer no, but it won't matter because
739 -- we only float if arg' is a WHNF,
740 -- and so there can't be any 'will be demanded' bindings in the floats.
742 WARN( any demanded_float (fromOL floats2), ppr (filter demanded_float (fromOL floats2)) )
745 -- It's important that we do eta expansion on function *arguments* (which are
746 -- simplified with simplRhs), as well as let-bound right-hand sides.
747 -- Otherwise we find that things like
748 -- f (\x -> case x of I# x' -> coerce T (\ y -> ...))
749 -- get right through to the code generator as two separate lambdas,
750 -- which is a Bad Thing
751 tryRhsTyLam rhs2 `thenSmpl` \ (floats3, rhs3) ->
752 tryEtaExpansion rhs3 rhs_ty `thenSmpl` \ (floats4, rhs4) ->
754 -- Float lets if (a) we're at the top level
755 -- or (b) the resulting RHS is one we'd like to expose
756 if (top_lvl || exprIsCheap rhs4) then
757 (if (isNilOL floats2 && null floats3 && null floats4) then
760 tick LetFloatFromLet) `thenSmpl_`
762 addFloats floats2 rhs_in_scope $
763 addAuxiliaryBinds floats3 $
764 addAuxiliaryBinds floats4 $
767 -- Don't do the float
768 thing_inside (wrapFloats floats1 rhs1)
770 demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
771 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
772 demanded_float (Rec _) = False
774 -- If float_ubx is true we float all the bindings, otherwise
775 -- we just float until we come across an unlifted one.
776 -- Remember that the unlifted bindings in the floats are all for
777 -- guaranteed-terminating non-exception-raising unlifted things,
778 -- which we are happy to do speculatively. However, we may still
779 -- not be able to float them out, because the context
780 -- is either a Rec group, or the top level, neither of which
781 -- can tolerate them.
782 splitFloats float_ubx floats rhs
783 | float_ubx = (floats, rhs) -- Float them all
784 | otherwise = go (fromOL floats)
787 go (f:fs) | must_stay f = (nilOL, mkLets (f:fs) rhs)
788 | otherwise = case go fs of
789 (out, rhs') -> (f `consOL` out, rhs')
791 must_stay (Rec prs) = False -- No unlifted bindings in here
792 must_stay (NonRec b r) = isUnLiftedType (idType b)
797 %************************************************************************
799 \subsection{Variables}
801 %************************************************************************
805 = getSubst `thenSmpl` \ subst ->
806 case lookupIdSubst subst var of
807 DoneEx e -> zapSubstEnv (simplExprF e cont)
808 ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
809 DoneId var1 occ -> WARN( not (isInScope var1 subst) && mustHaveLocalBinding var1,
810 text "simplVar:" <+> ppr var )
811 zapSubstEnv (completeCall var1 occ cont)
812 -- The template is already simplified, so don't re-substitute.
813 -- This is VITAL. Consider
815 -- let y = \z -> ...x... in
817 -- We'll clone the inner \x, adding x->x' in the id_subst
818 -- Then when we inline y, we must *not* replace x by x' in
819 -- the inlined copy!!
821 ---------------------------------------------------------
822 -- Dealing with a call
824 completeCall var occ_info cont
825 = getBlackList `thenSmpl` \ black_list_fn ->
826 getInScope `thenSmpl` \ in_scope ->
827 getContArgs var cont `thenSmpl` \ (args, call_cont, inline_call) ->
828 getDOptsSmpl `thenSmpl` \ dflags ->
830 black_listed = black_list_fn var
831 arg_infos = [ interestingArg in_scope arg subst
832 | (arg, subst, _) <- args, isValArg arg]
834 interesting_cont = interestingCallContext (not (null args))
835 (not (null arg_infos))
838 inline_cont | inline_call = discardInline cont
841 maybe_inline = callSiteInline dflags black_listed inline_call occ_info
842 var arg_infos interesting_cont
844 -- First, look for an inlining
845 case maybe_inline of {
846 Just unfolding -- There is an inlining!
847 -> tick (UnfoldingDone var) `thenSmpl_`
848 simplExprF unfolding inline_cont
851 Nothing -> -- No inlining!
854 simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' ->
856 -- Next, look for rules or specialisations that match
858 -- It's important to simplify the args first, because the rule-matcher
859 -- doesn't do substitution as it goes. We don't want to use subst_args
860 -- (defined in the 'where') because that throws away useful occurrence info,
861 -- and perhaps-very-important specialisations.
863 -- Some functions have specialisations *and* are strict; in this case,
864 -- we don't want to inline the wrapper of the non-specialised thing; better
865 -- to call the specialised thing instead.
866 -- But the black-listing mechanism means that inlining of the wrapper
867 -- won't occur for things that have specialisations till a later phase, so
868 -- it's ok to try for inlining first.
870 -- You might think that we shouldn't apply rules for a loop breaker:
871 -- doing so might give rise to an infinite loop, because a RULE is
872 -- rather like an extra equation for the function:
873 -- RULE: f (g x) y = x+y
876 -- But it's too drastic to disable rules for loop breakers.
877 -- Even the foldr/build rule would be disabled, because foldr
878 -- is recursive, and hence a loop breaker:
879 -- foldr k z (build g) = g k z
880 -- So it's up to the programmer: rules can cause divergence
882 getSwitchChecker `thenSmpl` \ chkr ->
884 maybe_rule | switchIsOn chkr DontApplyRules = Nothing
885 | otherwise = lookupRule in_scope var args'
888 Just (rule_name, rule_rhs) ->
889 tick (RuleFired rule_name) `thenSmpl_`
891 (if dopt Opt_D_dump_inlinings dflags then
892 pprTrace "Rule fired" (vcat [
893 text "Rule:" <+> ptext rule_name,
894 text "Before:" <+> ppr var <+> sep (map pprParendExpr args'),
895 text "After: " <+> pprCoreExpr rule_rhs])
899 simplExprF rule_rhs call_cont ;
901 Nothing -> -- No rules
904 rebuild (mkApps (Var var) args') call_cont
908 ---------------------------------------------------------
909 -- Simplifying the arguments of a call
911 simplifyArgs :: Bool -- It's a data constructor
912 -> [(InExpr, SubstEnv, Bool)] -- Details of the arguments
913 -> OutType -- Type of the continuation
914 -> ([OutExpr] -> SimplM OutExprStuff)
915 -> SimplM OutExprStuff
917 -- Simplify the arguments to a call.
918 -- This part of the simplifier may break the no-shadowing invariant
920 -- f (...(\a -> e)...) (case y of (a,b) -> e')
921 -- where f is strict in its second arg
922 -- If we simplify the innermost one first we get (...(\a -> e)...)
923 -- Simplifying the second arg makes us float the case out, so we end up with
924 -- case y of (a,b) -> f (...(\a -> e)...) e'
925 -- So the output does not have the no-shadowing invariant. However, there is
926 -- no danger of getting name-capture, because when the first arg was simplified
927 -- we used an in-scope set that at least mentioned all the variables free in its
928 -- static environment, and that is enough.
930 -- We can't just do innermost first, or we'd end up with a dual problem:
931 -- case x of (a,b) -> f e (...(\a -> e')...)
933 -- I spent hours trying to recover the no-shadowing invariant, but I just could
934 -- not think of an elegant way to do it. The simplifier is already knee-deep in
935 -- continuations. We have to keep the right in-scope set around; AND we have
936 -- to get the effect that finding (error "foo") in a strict arg position will
937 -- discard the entire application and replace it with (error "foo"). Getting
938 -- all this at once is TOO HARD!
940 simplifyArgs is_data_con args cont_ty thing_inside
942 = go args thing_inside
944 | otherwise -- It's a data constructor, so we want
945 -- to switch off inlining in the arguments
946 -- If we don't do this, consider:
947 -- let x = +# p q in C {x}
948 -- Even though x get's an occurrence of 'many', its RHS looks cheap,
949 -- and there's a good chance it'll get inlined back into C's RHS. Urgh!
950 = getBlackList `thenSmpl` \ old_bl ->
951 noInlineBlackList `thenSmpl` \ ni_bl ->
954 setBlackList old_bl $
958 go [] thing_inside = thing_inside []
959 go (arg:args) thing_inside = simplifyArg is_data_con arg cont_ty $ \ arg' ->
961 thing_inside (arg':args')
963 simplifyArg is_data_con (Type ty_arg, se, _) cont_ty thing_inside
964 = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg ->
965 thing_inside (Type new_ty_arg)
967 simplifyArg is_data_con (val_arg, se, is_strict) cont_ty thing_inside
968 = getInScope `thenSmpl` \ in_scope ->
970 arg_ty = substTy (mkSubst in_scope se) (exprType val_arg)
972 if not is_data_con then
973 -- An ordinary function
974 simplValArg arg_ty is_strict val_arg se cont_ty thing_inside
976 -- A data constructor
977 -- simplifyArgs has already switched off inlining, so
978 -- all we have to do here is to let-bind any non-trivial argument
980 -- It's not always the case that new_arg will be trivial
982 -- where, in one pass, f gets substituted by a constructor,
983 -- but x gets substituted by an expression (assume this is the
984 -- unique occurrence of x). It doesn't really matter -- it'll get
985 -- fixed up next pass. And it happens for dictionary construction,
986 -- which mentions the wrapper constructor to start with.
987 simplValArg arg_ty is_strict val_arg se cont_ty $ \ arg' ->
989 if exprIsTrivial arg' then
992 newId SLIT("a") (exprType arg') $ \ arg_id ->
993 addNonRecBind arg_id arg' $
994 thing_inside (Var arg_id)
998 %************************************************************************
1000 \subsection{Decisions about inlining}
1002 %************************************************************************
1004 NB: At one time I tried not pre/post-inlining top-level things,
1005 even if they occur exactly once. Reason:
1006 (a) some might appear as a function argument, so we simply
1007 replace static allocation with dynamic allocation:
1013 (b) some top level things might be black listed
1015 HOWEVER, I found that some useful foldr/build fusion was lost (most
1016 notably in spectral/hartel/parstof) because the foldr didn't see the build.
1018 Doing the dynamic allocation isn't a big deal, in fact, but losing the
1022 preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
1023 -- Examines a bndr to see if it is used just once in a
1024 -- completely safe way, so that it is safe to discard the binding
1025 -- inline its RHS at the (unique) usage site, REGARDLESS of how
1026 -- big the RHS might be. If this is the case we don't simplify
1027 -- the RHS first, but just inline it un-simplified.
1029 -- This is much better than first simplifying a perhaps-huge RHS
1030 -- and then inlining and re-simplifying it.
1032 -- NB: we don't even look at the RHS to see if it's trivial
1035 -- where x is used many times, but this is the unique occurrence
1036 -- of y. We should NOT inline x at all its uses, because then
1037 -- we'd do the same for y -- aargh! So we must base this
1038 -- pre-rhs-simplification decision solely on x's occurrences, not
1041 -- Evne RHSs labelled InlineMe aren't caught here, because
1042 -- there might be no benefit from inlining at the call site.
1044 preInlineUnconditionally black_listed bndr
1045 | black_listed || opt_SimplNoPreInlining = False
1046 | otherwise = case idOccInfo bndr of
1047 OneOcc in_lam once -> not in_lam && once
1048 -- Not inside a lambda, one occurrence ==> safe!
1054 %************************************************************************
1056 \subsection{The main rebuilder}
1058 %************************************************************************
1061 -------------------------------------------------------------------
1062 -- Finish rebuilding
1063 rebuild_done expr = returnOutStuff expr
1065 ---------------------------------------------------------
1066 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
1068 -- Stop continuation
1069 rebuild expr (Stop _ _) = rebuild_done expr
1071 -- ArgOf continuation
1072 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1074 -- ApplyTo continuation
1075 rebuild expr cont@(ApplyTo _ arg se cont')
1076 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1077 rebuild (App expr arg') cont'
1079 -- Coerce continuation
1080 rebuild expr (CoerceIt to_ty cont)
1081 = rebuild (mkCoerce to_ty (exprType expr) expr) cont
1083 -- Inline continuation
1084 rebuild expr (InlinePlease cont)
1085 = rebuild (Note InlineCall expr) cont
1087 rebuild scrut (Select _ bndr alts se cont)
1088 = rebuild_case scrut bndr alts se cont
1091 Case elimination [see the code above]
1093 Start with a simple situation:
1095 case x# of ===> e[x#/y#]
1098 (when x#, y# are of primitive type, of course). We can't (in general)
1099 do this for algebraic cases, because we might turn bottom into
1102 Actually, we generalise this idea to look for a case where we're
1103 scrutinising a variable, and we know that only the default case can
1108 other -> ...(case x of
1112 Here the inner case can be eliminated. This really only shows up in
1113 eliminating error-checking code.
1115 We also make sure that we deal with this very common case:
1120 Here we are using the case as a strict let; if x is used only once
1121 then we want to inline it. We have to be careful that this doesn't
1122 make the program terminate when it would have diverged before, so we
1124 - x is used strictly, or
1125 - e is already evaluated (it may so if e is a variable)
1127 Lastly, we generalise the transformation to handle this:
1133 We only do this for very cheaply compared r's (constructors, literals
1134 and variables). If pedantic bottoms is on, we only do it when the
1135 scrutinee is a PrimOp which can't fail.
1137 We do it *here*, looking at un-simplified alternatives, because we
1138 have to check that r doesn't mention the variables bound by the
1139 pattern in each alternative, so the binder-info is rather useful.
1141 So the case-elimination algorithm is:
1143 1. Eliminate alternatives which can't match
1145 2. Check whether all the remaining alternatives
1146 (a) do not mention in their rhs any of the variables bound in their pattern
1147 and (b) have equal rhss
1149 3. Check we can safely ditch the case:
1150 * PedanticBottoms is off,
1151 or * the scrutinee is an already-evaluated variable
1152 or * the scrutinee is a primop which is ok for speculation
1153 -- ie we want to preserve divide-by-zero errors, and
1154 -- calls to error itself!
1156 or * [Prim cases] the scrutinee is a primitive variable
1158 or * [Alg cases] the scrutinee is a variable and
1159 either * the rhs is the same variable
1160 (eg case x of C a b -> x ===> x)
1161 or * there is only one alternative, the default alternative,
1162 and the binder is used strictly in its scope.
1163 [NB this is helped by the "use default binder where
1164 possible" transformation; see below.]
1167 If so, then we can replace the case with one of the rhss.
1170 Blob of helper functions for the "case-of-something-else" situation.
1173 ---------------------------------------------------------
1174 -- Eliminate the case if possible
1176 rebuild_case scrut bndr alts se cont
1177 | maybeToBool maybe_con_app
1178 = knownCon scrut (DataAlt con) args bndr alts se cont
1180 | canEliminateCase scrut bndr alts
1181 = tick (CaseElim bndr) `thenSmpl_` (
1183 simplBinder bndr $ \ bndr' ->
1184 -- Remember to bind the case binder!
1185 completeBinding bndr bndr' False False scrut $
1186 simplExprF (head (rhssOfAlts alts)) cont)
1189 = complete_case scrut bndr alts se cont
1192 maybe_con_app = exprIsConApp_maybe scrut
1193 Just (con, args) = maybe_con_app
1195 -- See if we can get rid of the case altogether
1196 -- See the extensive notes on case-elimination above
1197 canEliminateCase scrut bndr alts
1198 = -- Check that the RHSs are all the same, and
1199 -- don't use the binders in the alternatives
1200 -- This test succeeds rapidly in the common case of
1201 -- a single DEFAULT alternative
1202 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1204 -- Check that the scrutinee can be let-bound instead of case-bound
1205 && ( exprOkForSpeculation scrut
1206 -- OK not to evaluate it
1207 -- This includes things like (==# a# b#)::Bool
1208 -- so that we simplify
1209 -- case ==# a# b# of { True -> x; False -> x }
1212 -- This particular example shows up in default methods for
1213 -- comparision operations (e.g. in (>=) for Int.Int32)
1214 || exprIsValue scrut -- It's already evaluated
1215 || var_demanded_later scrut -- It'll be demanded later
1217 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1218 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1219 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1220 -- its argument: case x of { y -> dataToTag# y }
1221 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1222 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1227 (rhs1:other_rhss) = rhssOfAlts alts
1228 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1230 var_demanded_later (Var v) = isStrictDmd (idNewDemandInfo bndr) -- It's going to be evaluated later
1231 var_demanded_later other = False
1234 ---------------------------------------------------------
1235 -- Case of something else
1237 complete_case scrut case_bndr alts se cont
1238 = -- Prepare case alternatives
1239 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1240 impossible_cons alts `thenSmpl` \ better_alts ->
1242 -- Set the new subst-env in place (before dealing with the case binder)
1245 -- Deal with the case binder, and prepare the continuation;
1246 -- The new subst_env is in place
1247 prepareCaseCont better_alts cont $ \ cont' ->
1250 -- Deal with variable scrutinee
1252 getSwitchChecker `thenSmpl` \ chkr ->
1253 simplCaseBinder (switchIsOn chkr NoCaseOfCase)
1254 scrut case_bndr $ \ case_bndr' zap_occ_info ->
1256 -- Deal with the case alternatives
1257 simplAlts zap_occ_info impossible_cons
1258 case_bndr' better_alts cont' `thenSmpl` \ alts' ->
1260 mkCase scrut case_bndr' alts'
1261 ) `thenSmpl` \ case_expr ->
1263 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1264 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1265 -- that should not include these chaps!
1266 rebuild_done case_expr
1268 impossible_cons = case scrut of
1269 Var v -> otherCons (idUnfolding v)
1273 knownCon :: OutExpr -> AltCon -> [OutExpr]
1274 -> InId -> [InAlt] -> SubstEnv -> SimplCont
1275 -> SimplM OutExprStuff
1277 knownCon expr con args bndr alts se cont
1278 = -- Arguments should be atomic;
1280 WARN( not (all exprIsTrivial args),
1281 text "knownCon" <+> ppr expr )
1282 tick (KnownBranch bndr) `thenSmpl_`
1284 simplBinder bndr $ \ bndr' ->
1285 completeBinding bndr bndr' False False expr $
1286 -- Don't use completeBeta here. The expr might be
1287 -- an unboxed literal, like 3, or a variable
1288 -- whose unfolding is an unboxed literal... and
1289 -- completeBeta will just construct another case
1291 case findAlt con alts of
1292 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1295 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1298 (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args )
1299 extendSubstList bs (map mk real_args) $
1302 real_args = drop (dataConNumInstArgs dc) args
1303 mk (Type ty) = DoneTy ty
1304 mk other = DoneEx other
1309 prepareCaseCont :: [InAlt] -> SimplCont
1310 -> (SimplCont -> SimplM (OutStuff a))
1311 -> SimplM (OutStuff a)
1312 -- Polymorphic recursion here!
1314 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1315 prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
1316 mkDupableCont alts_ty cont thing_inside
1317 -- At one time I passed in the un-simplified type, and simplified
1318 -- it only if we needed to construct a join binder, but that
1319 -- didn't work because we have to decompse function types
1320 -- (using funResultTy) in mkDupableCont.
1323 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1324 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1325 way, there's a chance that v will now only be used once, and hence
1328 There is a time we *don't* want to do that, namely when
1329 -fno-case-of-case is on. This happens in the first simplifier pass,
1330 and enhances full laziness. Here's the bad case:
1331 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1332 If we eliminate the inner case, we trap it inside the I# v -> arm,
1333 which might prevent some full laziness happening. I've seen this
1334 in action in spectral/cichelli/Prog.hs:
1335 [(m,n) | m <- [1..max], n <- [1..max]]
1336 Hence the no_case_of_case argument
1339 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1340 in the case binder, because the case-binder now effectively occurs
1341 whenever v does. AND we have to do the same for the pattern-bound
1344 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1346 Here, b and p are dead. But when we move the argment inside the first
1347 case RHS, and eliminate the second case, we get
1349 case x or { (a,b) -> a b }
1351 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1352 happened. Hence the zap_occ_info function returned by simplCaseBinder
1355 simplCaseBinder no_case_of_case (Var v) case_bndr thing_inside
1356 | not no_case_of_case
1357 = simplBinder (zap case_bndr) $ \ case_bndr' ->
1358 modifyInScope v case_bndr' $
1359 -- We could extend the substitution instead, but it would be
1360 -- a hack because then the substitution wouldn't be idempotent
1361 -- any more (v is an OutId). And this just just as well.
1362 thing_inside case_bndr' zap
1364 zap b = b `setIdOccInfo` NoOccInfo
1366 simplCaseBinder add_eval_info other_scrut case_bndr thing_inside
1367 = simplBinder case_bndr $ \ case_bndr' ->
1368 thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
1371 prepareCaseAlts does two things:
1373 1. Remove impossible alternatives
1375 2. If the DEFAULT alternative can match only one possible constructor,
1376 then make that constructor explicit.
1378 case e of x { DEFAULT -> rhs }
1380 case e of x { (a,b) -> rhs }
1381 where the type is a single constructor type. This gives better code
1382 when rhs also scrutinises x or e.
1385 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1387 = case (findDefault filtered_alts, missing_cons) of
1389 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1390 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1392 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1394 getUniquesSmpl `thenSmpl` \ tv_uniqs ->
1396 ex_tyvars' = zipWith mk tv_uniqs ex_tyvars
1397 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1398 arg_tys = dataConArgTys data_con
1399 (inst_tys ++ mkTyVarTys ex_tyvars')
1401 newIds SLIT("a") arg_tys $ \ bndrs ->
1402 returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1404 other -> returnSmpl filtered_alts
1406 -- Filter out alternatives that can't possibly match
1407 filtered_alts = case scrut_cons of
1409 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1411 missing_cons = [data_con | data_con <- tyConDataConsIfAvailable tycon,
1412 not (data_con `elem` handled_data_cons)]
1413 handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++
1414 [data_con | (DataAlt data_con, _, _) <- filtered_alts]
1417 prepareCaseAlts _ _ scrut_cons alts
1418 = returnSmpl alts -- Functions
1421 ----------------------
1422 simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
1423 = mapSmpl simpl_alt alts
1425 inst_tys' = tyConAppArgs (idType case_bndr')
1427 -- handled_cons is all the constructors that are dealt
1428 -- with, either by being impossible, or by there being an alternative
1429 (con_alts,_) = findDefault alts
1430 handled_cons = scrut_cons ++ [con | (con,_,_) <- con_alts]
1432 simpl_alt (DEFAULT, _, rhs)
1433 = -- In the default case we record the constructors that the
1434 -- case-binder *can't* be.
1435 -- We take advantage of any OtherCon info in the case scrutinee
1436 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
1437 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1438 returnSmpl (DEFAULT, [], rhs')
1440 simpl_alt (con, vs, rhs)
1441 = -- Deal with the pattern-bound variables
1442 -- Mark the ones that are in ! positions in the data constructor
1443 -- as certainly-evaluated.
1444 -- NB: it happens that simplBinders does *not* erase the OtherCon
1445 -- form of unfolding, so it's ok to add this info before
1446 -- doing simplBinders
1447 simplBinders (add_evals con vs) $ \ vs' ->
1449 -- Bind the case-binder to (con args)
1451 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1453 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $
1454 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1455 returnSmpl (con, vs', rhs')
1458 -- add_evals records the evaluated-ness of the bound variables of
1459 -- a case pattern. This is *important*. Consider
1460 -- data T = T !Int !Int
1462 -- case x of { T a b -> T (a+1) b }
1464 -- We really must record that b is already evaluated so that we don't
1465 -- go and re-evaluate it when constructing the result.
1467 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1468 add_evals other_con vs = vs
1470 cat_evals [] [] = []
1471 cat_evals (v:vs) (str:strs)
1472 | isTyVar v = v : cat_evals vs (str:strs)
1473 | isStrictDmd str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1474 | otherwise = v' : cat_evals vs strs
1480 %************************************************************************
1482 \subsection{Duplicating continuations}
1484 %************************************************************************
1487 mkDupableCont :: OutType -- Type of the thing to be given to the continuation
1489 -> (SimplCont -> SimplM (OutStuff a))
1490 -> SimplM (OutStuff a)
1491 mkDupableCont ty cont thing_inside
1492 | contIsDupable cont
1495 mkDupableCont _ (CoerceIt ty cont) thing_inside
1496 = mkDupableCont ty cont $ \ cont' ->
1497 thing_inside (CoerceIt ty cont')
1499 mkDupableCont ty (InlinePlease cont) thing_inside
1500 = mkDupableCont ty cont $ \ cont' ->
1501 thing_inside (InlinePlease cont')
1503 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1504 = -- Build the RHS of the join point
1505 newId SLIT("a") join_arg_ty ( \ arg_id ->
1506 cont_fn (Var arg_id) `thenSmpl` \ (floats, (_, rhs)) ->
1507 returnSmpl (Lam (setOneShotLambda arg_id) (wrapFloats floats rhs))
1508 ) `thenSmpl` \ join_rhs ->
1510 -- Build the join Id and continuation
1511 -- We give it a "$j" name just so that for later amusement
1512 -- we can identify any join points that don't end up as let-no-escapes
1513 -- [NOTE: the type used to be exprType join_rhs, but this seems more elegant.]
1514 newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) $ \ join_id ->
1516 new_cont = ArgOf OkToDup cont_ty
1517 (\arg' -> rebuild_done (App (Var join_id) arg'))
1520 tick (CaseOfCase join_id) `thenSmpl_`
1521 -- Want to tick here so that we go round again,
1522 -- and maybe copy or inline the code;
1523 -- not strictly CaseOf Case
1524 addLetBind (NonRec join_id join_rhs) $
1525 thing_inside new_cont
1527 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1528 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1529 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1530 if exprIsDupable arg' then
1531 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1533 newId SLIT("a") (exprType arg') $ \ bndr ->
1535 tick (CaseOfCase bndr) `thenSmpl_`
1536 -- Want to tick here so that we go round again,
1537 -- and maybe copy or inline the code;
1538 -- not strictly CaseOf Case
1540 addLetBind (NonRec bndr arg') $
1541 -- But what if the arg should be case-bound? We can't use
1542 -- addNonRecBind here because its type is too specific.
1543 -- This has been this way for a long time, so I'll leave it,
1544 -- but I can't convince myself that it's right.
1546 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont')
1549 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1550 = tick (CaseOfCase case_bndr) `thenSmpl_`
1552 simplBinder case_bndr $ \ case_bndr' ->
1553 prepareCaseCont alts cont $ \ cont' ->
1554 mkDupableAlts case_bndr case_bndr' cont' alts $ \ alts' ->
1555 returnOutStuff alts'
1556 ) `thenSmpl` \ (alt_binds, (in_scope, alts')) ->
1558 addFloats alt_binds in_scope $
1560 -- NB that the new alternatives, alts', are still InAlts, using the original
1561 -- binders. That means we can keep the case_bndr intact. This is important
1562 -- because another case-of-case might strike, and so we want to keep the
1563 -- info that the case_bndr is dead (if it is, which is often the case).
1564 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1565 -- case in I/O rich code. We aren't allowed a lambda bound
1566 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1567 thing_inside (Select OkToDup case_bndr alts' se (mkStop (contResultType cont)))
1569 mkDupableAlts :: InId -> OutId -> SimplCont -> [InAlt]
1570 -> ([InAlt] -> SimplM (OutStuff a))
1571 -> SimplM (OutStuff a)
1572 mkDupableAlts case_bndr case_bndr' cont [] thing_inside
1574 mkDupableAlts case_bndr case_bndr' cont (alt:alts) thing_inside
1575 = mkDupableAlt case_bndr case_bndr' cont alt $ \ alt' ->
1576 mkDupableAlts case_bndr case_bndr' cont alts $ \ alts' ->
1577 thing_inside (alt' : alts')
1579 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) thing_inside
1580 = simplBinders bndrs $ \ bndrs' ->
1581 simplExprC rhs cont `thenSmpl` \ rhs' ->
1583 if (case cont of { Stop _ _ -> exprIsDupable rhs'; other -> False}) then
1584 -- It is worth checking for a small RHS because otherwise we
1585 -- get extra let bindings that may cause an extra iteration of the simplifier to
1586 -- inline back in place. Quite often the rhs is just a variable or constructor.
1587 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1588 -- iterations because the version with the let bindings looked big, and so wasn't
1589 -- inlined, but after the join points had been inlined it looked smaller, and so
1592 -- But since the continuation is absorbed into the rhs, we only do this
1593 -- for a Stop continuation.
1595 -- NB: we have to check the size of rhs', not rhs.
1596 -- Duplicating a small InAlt might invalidate occurrence information
1597 -- However, if it *is* dupable, we return the *un* simplified alternative,
1598 -- because otherwise we'd need to pair it up with an empty subst-env.
1599 -- (Remember we must zap the subst-env before re-simplifying something).
1600 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1605 rhs_ty' = exprType rhs'
1606 (used_bndrs, used_bndrs')
1607 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1608 (case_bndr' : bndrs'),
1609 not (isDeadBinder bndr)]
1610 -- The new binders have lost their occurrence info,
1611 -- so we have to extract it from the old ones
1613 ( if null used_bndrs'
1614 -- If we try to lift a primitive-typed something out
1615 -- for let-binding-purposes, we will *caseify* it (!),
1616 -- with potentially-disastrous strictness results. So
1617 -- instead we turn it into a function: \v -> e
1618 -- where v::State# RealWorld#. The value passed to this function
1619 -- is realworld#, which generates (almost) no code.
1621 -- There's a slight infelicity here: we pass the overall
1622 -- case_bndr to all the join points if it's used in *any* RHS,
1623 -- because we don't know its usage in each RHS separately
1625 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1626 -- we make the join point into a function whenever used_bndrs'
1627 -- is empty. This makes the join-point more CPR friendly.
1628 -- Consider: let j = if .. then I# 3 else I# 4
1629 -- in case .. of { A -> j; B -> j; C -> ... }
1631 -- Now CPR doesn't w/w j because it's a thunk, so
1632 -- that means that the enclosing function can't w/w either,
1633 -- which is a lose. Here's the example that happened in practice:
1634 -- kgmod :: Int -> Int -> Int
1635 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1639 -- I have seen a case alternative like this:
1640 -- True -> \v -> ...
1641 -- It's a bit silly to add the realWorld dummy arg in this case, making
1644 -- (the \v alone is enough to make CPR happy) but I think it's rare
1646 then newId SLIT("w") realWorldStatePrimTy $ \ rw_id ->
1647 returnSmpl ([rw_id], [Var realWorldPrimId])
1649 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1651 `thenSmpl` \ (final_bndrs', final_args) ->
1653 -- See comment about "$j" name above
1654 newId SLIT("$j") (foldr mkPiType rhs_ty' final_bndrs') $ \ join_bndr ->
1655 -- Notice the funky mkPiType. If the contructor has existentials
1656 -- it's possible that the join point will be abstracted over
1657 -- type varaibles as well as term variables.
1658 -- Example: Suppose we have
1659 -- data T = forall t. C [t]
1661 -- case (case e of ...) of
1662 -- C t xs::[t] -> rhs
1663 -- We get the join point
1664 -- let j :: forall t. [t] -> ...
1665 -- j = /\t \xs::[t] -> rhs
1667 -- case (case e of ...) of
1668 -- C t xs::[t] -> j t xs
1671 -- We make the lambdas into one-shot-lambdas. The
1672 -- join point is sure to be applied at most once, and doing so
1673 -- prevents the body of the join point being floated out by
1674 -- the full laziness pass
1675 really_final_bndrs = map one_shot final_bndrs'
1676 one_shot v | isId v = setOneShotLambda v
1679 addLetBind (NonRec join_bndr (mkLams really_final_bndrs rhs')) $
1680 thing_inside (con, bndrs, mkApps (Var join_bndr) final_args)