2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[Simplify]{The main module of the simplifier}
7 module Simplify ( simplTopBinds, simplExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( intSwitchSet, switchIsOn,
12 opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
13 opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
17 import SimplUtils ( mkCase, transformRhs, findAlt, etaCoreExpr,
18 simplBinder, simplBinders, simplIds, findDefault, mkCoerce
20 import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
23 import Id ( Id, idType, idInfo, idUnique,
24 getIdUnfolding, setIdUnfolding, isExportedId,
25 getIdSpecialisation, setIdSpecialisation,
26 getIdDemandInfo, setIdDemandInfo,
28 getIdOccInfo, setIdOccInfo,
29 zapLamIdInfo, zapFragileIdInfo,
31 setInlinePragma, mayHaveNoBinding,
32 setOneShotLambda, maybeModifyIdInfo
34 import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
35 ArityInfo(..), atLeastArity, arityLowerBound, unknownArity,
36 specInfo, inlinePragInfo, setArityInfo, setInlinePragInfo, setUnfoldingInfo
38 import Demand ( Demand, isStrict, wwLazy )
39 import Const ( isWHNFCon, conOkForAlt )
40 import ConFold ( tryPrimOp )
41 import PrimOp ( PrimOp, primOpStrictness, primOpType )
42 import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
43 import Const ( Con(..) )
44 import Name ( isLocallyDefined )
46 import CoreFVs ( exprFreeVars )
47 import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
48 callSiteInline, hasSomeUnfolding
50 import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
51 coreExprType, coreAltsType, exprArity, exprIsValue,
54 import Rules ( lookupRule )
55 import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
56 import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType, seqType,
57 mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
58 funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
60 import Subst ( Subst, mkSubst, emptySubst, substTy, substExpr,
61 substEnv, isInScope, lookupInScope, lookupIdSubst, substIdInfo
63 import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
64 import TysPrim ( realWorldStatePrimTy )
65 import PrelInfo ( realWorldPrimId )
66 import BasicTypes ( TopLevelFlag(..), isTopLevel )
67 import Maybes ( maybeToBool )
68 import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
71 import Unique ( foldrIdKey ) -- Temp
75 The guts of the simplifier is in this module, but the driver
76 loop for the simplifier is in SimplCore.lhs.
79 %************************************************************************
83 %************************************************************************
86 simplTopBinds :: [InBind] -> SimplM [OutBind]
89 = -- Put all the top-level binders into scope at the start
90 -- so that if a transformation rule has unexpectedly brought
91 -- anything into scope, then we don't get a complaint about that.
92 -- It's rather as if the top-level binders were imported.
93 simplIds (bindersOfBinds binds) $ \ bndrs' ->
94 simpl_binds binds bndrs' `thenSmpl` \ (binds', _) ->
95 freeTick SimplifierDone `thenSmpl_`
99 -- We need to track the zapped top-level binders, because
100 -- they should have their fragile IdInfo zapped (notably occurrence info)
101 simpl_binds [] bs = ASSERT( null bs ) returnSmpl ([], panic "simplTopBinds corner")
102 simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs)
103 simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs))
107 simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId]
108 -> SimplM (OutStuff a) -> SimplM (OutStuff a)
109 simplRecBind top_lvl pairs bndrs' thing_inside
110 = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
111 returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
113 go [] _ = thing_inside `thenSmpl` \ stuff ->
114 returnSmpl ([], stuff)
116 go ((bndr, rhs) : pairs) (bndr' : bndrs')
117 = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
118 -- Don't float unboxed bindings out,
119 -- because we can't "rec" them
123 %************************************************************************
125 \subsection[Simplify-simplExpr]{The main function: simplExpr}
127 %************************************************************************
130 addBind :: CoreBind -> OutStuff a -> OutStuff a
131 addBind bind (binds, res) = (bind:binds, res)
133 addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
134 addBinds [] stuff = stuff
135 addBinds binds1 (binds2, res) = (binds1++binds2, res)
138 The reason for this OutExprStuff stuff is that we want to float *after*
139 simplifying a RHS, not before. If we do so naively we get quadratic
140 behaviour as things float out.
142 To see why it's important to do it after, consider this (real) example:
156 a -- Can't inline a this round, cos it appears twice
160 Each of the ==> steps is a round of simplification. We'd save a
161 whole round if we float first. This can cascade. Consider
166 let f = let d1 = ..d.. in \y -> e
170 in \x -> ...(\y ->e)...
172 Only in this second round can the \y be applied, and it
173 might do the same again.
177 simplExpr :: CoreExpr -> SimplM CoreExpr
178 simplExpr expr = getSubst `thenSmpl` \ subst ->
179 simplExprC expr (Stop (substTy subst (coreExprType expr)))
180 -- The type in the Stop continuation is usually not used
181 -- It's only needed when discarding continuations after finding
182 -- a function that returns bottom.
183 -- Hence the lazy substitution
185 simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
186 -- Simplify an expression, given a continuation
188 simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
189 returnSmpl (mkLets floats body)
191 simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
192 -- Simplify an expression, returning floated binds
194 simplExprF (Var v) cont
197 simplExprF expr@(Con (PrimOp op) args) cont
198 = getSubstEnv `thenSmpl` \ se ->
201 (primOpStrictness op)
202 (pushArgs se args cont) $ \ args1 cont1 ->
205 -- Boring... we may have too many arguments now, so we push them back
207 args2 = ASSERT( length args1 >= n_args )
209 cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
211 -- Try the prim op simplification
212 -- It's really worth trying simplExpr again if it succeeds,
213 -- because you can find
214 -- case (eqChar# x 'a') of ...
216 -- case (case x of 'a' -> True; other -> False) of ...
217 case tryPrimOp op args2 of
218 Just e' -> zapSubstEnv (simplExprF e' cont2)
219 Nothing -> rebuild (Con (PrimOp op) args2) cont2
221 simplExprF (Con con@(DataCon _) args) cont
222 = simplConArgs args $ \ args' ->
223 rebuild (Con con args') cont
225 simplExprF expr@(Con con@(Literal _) args) cont
226 = ASSERT( null args )
229 simplExprF (App fun arg) cont
230 = getSubstEnv `thenSmpl` \ se ->
231 simplExprF fun (ApplyTo NoDup arg se cont)
233 simplExprF (Case scrut bndr alts) cont
234 = getSubstEnv `thenSmpl` \ se ->
235 simplExprF scrut (Select NoDup bndr alts se cont)
238 simplExprF (Let (Rec pairs) body) cont
239 = simplIds (map fst pairs) $ \ bndrs' ->
240 -- NB: bndrs' don't have unfoldings or spec-envs
241 -- We add them as we go down, using simplPrags
243 simplRecBind False pairs bndrs' (simplExprF body cont)
245 simplExprF expr@(Lam _ _) cont = simplLam expr cont
247 simplExprF (Type ty) cont
248 = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
249 simplType ty `thenSmpl` \ ty' ->
250 rebuild (Type ty') cont
252 -- Comments about the Coerce case
253 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
254 -- It's worth checking for a coerce in the continuation,
255 -- in case we can cancel them. For example, in the initial form of a worker
256 -- we may find (coerce T (coerce S (\x.e))) y
257 -- and we'd like it to simplify to e[y/x] in one round of simplification
259 simplExprF (Note (Coerce to from) e) (CoerceIt outer_to cont)
260 = simplType from `thenSmpl` \ from' ->
261 if outer_to == from' then
262 -- The coerces cancel out
265 -- They don't cancel, but the inner one is redundant
266 simplExprF e (CoerceIt outer_to cont)
268 simplExprF (Note (Coerce to from) e) cont
269 = simplType to `thenSmpl` \ to' ->
270 simplExprF e (CoerceIt to' cont)
272 -- hack: we only distinguish subsumed cost centre stacks for the purposes of
273 -- inlining. All other CCCSs are mapped to currentCCS.
274 simplExprF (Note (SCC cc) e) cont
275 = setEnclosingCC currentCCS $
276 simplExpr e `thenSmpl` \ e ->
277 rebuild (mkNote (SCC cc) e) cont
279 simplExprF (Note InlineCall e) cont
280 = simplExprF e (InlinePlease cont)
282 -- Comments about the InlineMe case
283 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
284 -- Don't inline in the RHS of something that has an
285 -- inline pragma. But be careful that the InScopeEnv that
286 -- we return does still have inlinings on!
288 -- It really is important to switch off inlinings. This function
289 -- may be inlinined in other modules, so we don't want to remove
290 -- (by inlining) calls to functions that have specialisations, or
291 -- that may have transformation rules in an importing scope.
292 -- E.g. {-# INLINE f #-}
294 -- and suppose that g is strict *and* has specialisations.
295 -- If we inline g's wrapper, we deny f the chance of getting
296 -- the specialised version of g when f is inlined at some call site
297 -- (perhaps in some other module).
299 simplExprF (Note InlineMe e) cont
301 Stop _ -> -- Totally boring continuation
302 -- Don't inline inside an INLINE expression
303 switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
304 rebuild (mkNote InlineMe e') cont
306 other -> -- Dissolve the InlineMe note if there's
307 -- an interesting context of any kind to combine with
308 -- (even a type application -- anything except Stop)
311 -- A non-recursive let is dealt with by simplBeta
312 simplExprF (Let (NonRec bndr rhs) body) cont
313 = getSubstEnv `thenSmpl` \ se ->
314 simplBeta bndr rhs se (contResultType cont) $
319 ---------------------------------
325 zap_it = mkLamBndrZapper fun cont
326 cont_ty = contResultType cont
328 -- Type-beta reduction
329 go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
330 = ASSERT( isTyVar bndr )
331 tick (BetaReduction bndr) `thenSmpl_`
332 getInScope `thenSmpl` \ in_scope ->
334 ty' = substTy (mkSubst in_scope arg_se) ty_arg
337 extendSubst bndr (DoneTy ty')
340 -- Ordinary beta reduction
341 go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
342 = tick (BetaReduction bndr) `thenSmpl_`
343 simplBeta zapped_bndr arg arg_se cont_ty
346 zapped_bndr = zap_it bndr
349 go lam@(Lam _ _) cont = completeLam [] lam cont
351 -- Exactly enough args
352 go expr cont = simplExprF expr cont
354 -- completeLam deals with the case where a lambda doesn't have an ApplyTo
356 -- We used to try for eta reduction here, but I found that this was
357 -- eta reducing things like
358 -- f = \x -> (coerce (\x -> e))
359 -- This made f's arity reduce, which is a bad thing, so I removed the
360 -- eta reduction at this point, and now do it only when binding
361 -- (at the call to postInlineUnconditionally
363 completeLam acc (Lam bndr body) cont
364 = simplBinder bndr $ \ bndr' ->
365 completeLam (bndr':acc) body cont
367 completeLam acc body cont
368 = simplExpr body `thenSmpl` \ body' ->
369 rebuild (foldl (flip Lam) body' acc) cont
370 -- Remember, acc is the *reversed* binders
372 mkLamBndrZapper :: CoreExpr -- Function
373 -> SimplCont -- The context
374 -> Id -> Id -- Use this to zap the binders
375 mkLamBndrZapper fun cont
376 | n_args >= n_params fun = \b -> b -- Enough args
377 | otherwise = \b -> zapLamIdInfo b
379 -- NB: we count all the args incl type args
380 -- so we must count all the binders (incl type lambdas)
381 n_args = countArgs cont
383 n_params (Note _ e) = n_params e
384 n_params (Lam b e) = 1 + n_params e
385 n_params other = 0::Int
389 ---------------------------------
390 simplConArgs makes sure that the arguments all end up being atomic.
391 That means it may generate some Lets, hence the strange type
394 simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
395 simplConArgs args thing_inside
396 = getSubst `thenSmpl` \ subst ->
397 go subst args thing_inside
399 go subst [] thing_inside
401 go subst (arg:args) thing_inside
404 arg1 = substExpr subst arg
405 -- Simplify the RHS with inlining switched off, so that
406 -- only absolutely essential things will happen.
407 -- If we don't do this, consider:
408 -- let x = e in C {x}
409 -- We end up inlining x back into C's argument,
410 -- and then let-binding it again!
412 -- It's important that the substitution *does* deal with case-binder synonyms:
413 -- case x of y { True -> (x,1) }
414 -- Here we must be sure to substitute y for x when simplifying the args of the pair,
415 -- to increase the chances of being able to inline x. The substituter will do
416 -- that because the x->y mapping is held in the in-scope set.
418 ASSERT( exprIsTrivial arg1 )
419 go subst args $ \ args1 ->
420 thing_inside (arg1 : args1)
423 = -- If the argument ain't trivial, then let-bind it
424 simplExpr arg `thenSmpl` \ arg1 ->
425 newId (coreExprType arg1) $ \ arg_id ->
426 go subst args $ \ args1 ->
427 thing_inside (Var arg_id : args1) `thenSmpl` \ res ->
428 returnSmpl (addBind (NonRec arg_id arg1) res)
429 -- I used to use completeBeta but that was wrong, because
430 -- arg_id isn't an InId
434 ---------------------------------
436 simplType :: InType -> SimplM OutType
438 = getSubst `thenSmpl` \ subst ->
440 new_ty = substTy subst ty
447 %************************************************************************
451 %************************************************************************
453 @simplBeta@ 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 simplBeta :: 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 simplBeta bndr rhs rhs_se cont_ty thing_inside
467 = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
470 simplBeta 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 RHS
477 simplBinder bndr $ \ bndr' ->
478 simplArg (idType bndr') (getIdDemandInfo bndr)
479 rhs rhs_se cont_ty $ \ rhs' ->
481 -- Now complete the binding and simplify the body
482 completeBeta bndr bndr' rhs' thing_inside
484 completeBeta bndr bndr' rhs' thing_inside
485 | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
486 -- Make a case expression instead of a let
487 -- These can arise either from the desugarer,
488 -- or from beta reductions: (\x.e) (x +# y)
489 = getInScope `thenSmpl` \ in_scope ->
490 thing_inside `thenSmpl` \ (floats, (_, body)) ->
491 returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
494 = completeBinding bndr bndr' False False rhs' thing_inside
499 simplArg :: OutType -> Demand
500 -> InExpr -> SubstEnv
501 -> OutType -- Type of thing computed by the context
502 -> (OutExpr -> SimplM OutExprStuff)
503 -> SimplM OutExprStuff
504 simplArg arg_ty demand arg arg_se cont_ty thing_inside
506 isUnLiftedType arg_ty ||
507 (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
508 -- Return true only for dictionary types where the dictionary
509 -- has more than one component (else we risk poking on the component
510 -- of a newtype dictionary)
511 = transformRhs arg `thenSmpl` \ t_arg ->
512 getEnv `thenSmpl` \ env ->
514 simplExprF t_arg (ArgOf NoDup cont_ty $ \ rhs' ->
515 setAllExceptInScope env $
516 etaFirst thing_inside rhs')
519 = simplRhs False {- Not top level -}
520 True {- OK to float unboxed -}
524 -- Do eta-reduction on the simplified RHS, if eta reduction is on
525 -- NB: etaCoreExpr only eta-reduces if that results in something trivial
526 etaFirst | opt_SimplDoEtaReduction = \ thing_inside rhs -> thing_inside (etaCoreExprToTrivial rhs)
527 | otherwise = \ thing_inside rhs -> thing_inside rhs
529 -- Try for eta reduction, but *only* if we get all
530 -- the way to an exprIsTrivial expression. We don't want to remove
531 -- extra lambdas unless we are going to avoid allocating this thing altogether
532 etaCoreExprToTrivial rhs | exprIsTrivial rhs' = rhs'
535 rhs' = etaCoreExpr rhs
540 - deals only with Ids, not TyVars
541 - take an already-simplified RHS
543 It does *not* attempt to do let-to-case. Why? Because they are used for
546 (when let-to-case is impossible)
548 - many situations where the "rhs" is known to be a WHNF
549 (so let-to-case is inappropriate).
552 completeBinding :: InId -- Binder
553 -> OutId -- New binder
554 -> Bool -- True <=> top level
555 -> Bool -- True <=> black-listed; don't inline
556 -> OutExpr -- Simplified RHS
557 -> SimplM (OutStuff a) -- Thing inside
558 -> SimplM (OutStuff a)
560 completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside
561 | (case occ_info of -- This happens; for example, the case_bndr during case of
562 IAmDead -> True -- known constructor: case (a,b) of x { (p,q) -> ... }
563 other -> False) -- Here x isn't mentioned in the RHS, so we don't want to
564 -- create the (dead) let-binding let x = (a,b) in ...
567 | postInlineUnconditionally black_listed occ_info old_bndr new_rhs
568 -- Maybe we don't need a let-binding! Maybe we can just
569 -- inline it right away. Unlike the preInlineUnconditionally case
570 -- we are allowed to look at the RHS.
572 -- NB: a loop breaker never has postInlineUnconditionally True
573 -- and non-loop-breakers only have *forward* references
574 -- Hence, it's safe to discard the binding
576 -- NB: You might think that postInlineUnconditionally is an optimisation,
578 -- let x = f Bool in (x, y)
579 -- then because of the constructor, x will not be *inlined* in the pair,
580 -- so the trivial binding will stay. But in this postInlineUnconditionally
581 -- gag we use the *substitution* to substitute (f Bool) for x, and that *will*
583 = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
584 extendSubst old_bndr (DoneEx new_rhs)
588 = getSubst `thenSmpl` \ subst ->
590 -- We make new IdInfo for the new binder by starting from the old binder,
591 -- doing appropriate substitutions.
592 -- Then we add arity and unfolding info to get the new binder
593 new_bndr_info = substIdInfo subst (idInfo old_bndr) (idInfo new_bndr)
594 `setArityInfo` ArityAtLeast (exprArity new_rhs)
595 `setUnfoldingInfo` mkUnfolding top_lvl new_rhs
597 final_id = new_bndr `setIdInfo` new_bndr_info
599 -- These seqs force the Ids, and hence the IdInfos, and hence any
600 -- inner substitutions
603 (modifyInScope new_bndr final_id thing_inside `thenSmpl` \ stuff ->
604 returnSmpl (addBind (NonRec final_id new_rhs) stuff))
607 occ_info = getIdOccInfo old_bndr
611 %************************************************************************
613 \subsection{simplLazyBind}
615 %************************************************************************
617 simplLazyBind basically just simplifies the RHS of a let(rec).
618 It does two important optimisations though:
620 * It floats let(rec)s out of the RHS, even if they
621 are hidden by big lambdas
623 * It does eta expansion
626 simplLazyBind :: Bool -- True <=> top level
629 -> SimplM (OutStuff a) -- The body of the binding
630 -> SimplM (OutStuff a)
631 -- When called, the subst env is correct for the entire let-binding
632 -- and hence right for the RHS.
633 -- Also the binder has already been simplified, and hence is in scope
635 simplLazyBind top_lvl bndr bndr' rhs thing_inside
636 = getBlackList `thenSmpl` \ black_list_fn ->
638 black_listed = black_list_fn bndr
641 if preInlineUnconditionally black_listed bndr then
642 -- Inline unconditionally
643 tick (PreInlineUnconditionally bndr) `thenSmpl_`
644 getSubstEnv `thenSmpl` \ rhs_se ->
645 (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
649 getSubstEnv `thenSmpl` \ rhs_se ->
650 simplRhs top_lvl False {- Not ok to float unboxed -}
652 rhs rhs_se $ \ rhs' ->
654 -- Now compete the binding and simplify the body
655 completeBinding bndr bndr' top_lvl black_listed rhs' thing_inside
661 simplRhs :: Bool -- True <=> Top level
662 -> Bool -- True <=> OK to float unboxed (speculative) bindings
663 -> OutType -> InExpr -> SubstEnv
664 -> (OutExpr -> SimplM (OutStuff a))
665 -> SimplM (OutStuff a)
666 simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
667 = -- Swizzle the inner lets past the big lambda (if any)
668 -- and try eta expansion
669 transformRhs rhs `thenSmpl` \ t_rhs ->
672 setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
674 -- Float lets out of RHS
676 (floats_out, rhs'') | float_ubx = (floats, rhs')
677 | otherwise = splitFloats floats rhs'
679 if (top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
680 not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
682 tickLetFloat floats_out `thenSmpl_`
685 -- There's a subtlety here. There may be a binding (x* = e) in the
686 -- floats, where the '*' means 'will be demanded'. So is it safe
687 -- to float it out? Answer no, but it won't matter because
688 -- we only float if arg' is a WHNF,
689 -- and so there can't be any 'will be demanded' bindings in the floats.
691 WARN( any demanded_float floats_out, ppr floats_out )
692 setInScope in_scope' (etaFirst thing_inside rhs'') `thenSmpl` \ stuff ->
693 -- in_scope' may be excessive, but that's OK;
694 -- it's a superset of what's in scope
695 returnSmpl (addBinds floats_out stuff)
697 -- Don't do the float
698 etaFirst thing_inside (mkLets floats rhs')
700 -- In a let-from-let float, we just tick once, arbitrarily
701 -- choosing the first floated binder to identify it
702 tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
703 tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
705 demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
706 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
707 demanded_float (Rec _) = False
709 -- Don't float any unlifted bindings out, because the context
710 -- is either a Rec group, or the top level, neither of which
711 -- can tolerate them.
712 splitFloats floats rhs
716 go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
717 | otherwise = case go fs of
718 (out, rhs') -> (f:out, rhs')
720 must_stay (Rec prs) = False -- No unlifted bindings in here
721 must_stay (NonRec b r) = isUnLiftedType (idType b)
726 %************************************************************************
728 \subsection{Variables}
730 %************************************************************************
734 = getSubst `thenSmpl` \ subst ->
735 case lookupIdSubst subst var of
736 DoneEx e -> zapSubstEnv (simplExprF e cont)
737 ContEx env1 e -> setSubstEnv env1 (simplExprF e cont)
738 DoneId var1 occ -> WARN( not (isInScope var1 subst) && isLocallyDefined var1 && not (mayHaveNoBinding var1),
739 text "simplVar:" <+> ppr var )
740 -- The mayHaveNoBinding test accouunts for the fact
741 -- that class dictionary constructors dont have top level
742 -- bindings and hence aren't in scope.
746 = getBlackList `thenSmpl` \ black_list ->
747 getInScope `thenSmpl` \ in_scope ->
748 completeCall black_list in_scope occ var cont
750 ---------------------------------------------------------
751 -- Dealing with a call
753 completeCall black_list_fn in_scope occ var cont
755 -- Look for an unfolding. There's a binding for the
756 -- thing, but perhaps we want to inline it anyway
757 | maybeToBool maybe_inline
758 = tick (UnfoldingDone var) `thenSmpl_`
759 zapSubstEnv (completeInlining var unf_template discard_inline_cont)
760 -- The template is already simplified, so don't re-substitute.
761 -- This is VITAL. Consider
763 -- let y = \z -> ...x... in
765 -- We'll clone the inner \x, adding x->x' in the id_subst
766 -- Then when we inline y, we must *not* replace x by x' in
767 -- the inlined copy!!
769 | otherwise -- No inlining
770 -- Use prepareArgs to use function strictness
771 = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
773 -- Look for rules or specialisations that match
775 -- It's important to simplify the args first, because the rule-matcher
776 -- doesn't do substitution as it goes. We don't want to use subst_args
777 -- (defined in the 'where') because that throws away useful occurrence info,
778 -- and perhaps-very-important specialisations.
780 -- Some functions have specialisations *and* are strict; in this case,
781 -- we don't want to inline the wrapper of the non-specialised thing; better
782 -- to call the specialised thing instead.
783 -- But the black-listing mechanism means that inlining of the wrapper
784 -- won't occur for things that have specialisations till a later phase, so
785 -- it's ok to try for inlining first.
786 getSwitchChecker `thenSmpl` \ chkr ->
787 if switchIsOn chkr DontApplyRules then
789 rebuild (mkApps (Var var) args') cont'
792 case lookupRule in_scope var args' of
793 Just (rule_name, rule_rhs, rule_args) ->
794 tick (RuleFired rule_name) `thenSmpl_`
795 zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args cont'))
796 -- See note above about zapping the substitution here
798 Nothing -> rebuild (mkApps (Var var) args') cont'
801 get_str var = case getIdStrictness var of
802 NoStrictnessInfo -> (repeat wwLazy, False)
803 StrictnessInfo demands result_bot -> (demands, result_bot)
805 ---------- Unfolding stuff
806 (subst_args, result_cont) = contArgs in_scope cont
807 val_args = filter isValArg subst_args
808 arg_infos = map (interestingArg in_scope) val_args
809 inline_call = contIsInline result_cont
810 interesting_cont = contIsInteresting result_cont
811 discard_inline_cont | inline_call = discardInline cont
814 maybe_inline = callSiteInline black_listed inline_call occ
815 var arg_infos interesting_cont
816 Just unf_template = maybe_inline
817 black_listed = black_list_fn var
820 -- An argument is interesting if it has *some* structure
821 -- We are here trying to avoid unfolding a function that
822 -- is applied only to variables that have no unfolding
823 -- (i.e. they are probably lambda bound): f x y z
824 -- There is little point in inlining f here.
825 interestingArg in_scope (Type _) = False
826 interestingArg in_scope (App fn (Type _)) = interestingArg in_scope fn
827 interestingArg in_scope (Var v) = hasSomeUnfolding (getIdUnfolding v')
829 v' = case lookupVarSet in_scope v of
832 interestingArg in_scope other = True
835 -- First a special case
836 -- Don't actually inline the scrutinee when we see
837 -- case x of y { .... }
838 -- and x has unfolding (C a b). Why not? Because
839 -- we get a silly binding y = C a b. If we don't
840 -- inline knownCon can directly substitute x for y instead.
841 completeInlining var (Con con con_args) (Select _ bndr alts se cont)
843 = knownCon (Var var) con con_args bndr alts se cont
845 -- Now the normal case
846 completeInlining var unfolding cont
847 = simplExprF unfolding cont
849 ----------- costCentreOk
850 -- costCentreOk checks that it's ok to inline this thing
851 -- The time it *isn't* is this:
853 -- f x = let y = E in
854 -- scc "foo" (...y...)
856 -- Here y has a "current cost centre", and we can't inline it inside "foo",
857 -- regardless of whether E is a WHNF or not.
859 costCentreOk ccs_encl cc_rhs
860 = not opt_SccProfilingOn
861 || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
862 || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
867 ---------------------------------------------------------
868 -- Preparing arguments for a call
870 prepareArgs :: SDoc -- Error message info
871 -> OutType -> ([Demand],Bool) -> SimplCont
872 -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
873 -> SimplM OutExprStuff
875 prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
876 = go [] demands orig_fun_ty orig_cont
878 not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
879 -- "No strictness info" is signalled by an infinite list of wwLazy
881 demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
882 | result_bot = fun_demands -- Enough args, and function returns bottom
883 | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
884 -- NB: demands is finite iff enough args and result_bot is True
886 -- Main game plan: loop through the arguments, simplifying
887 -- each of them in turn. We carry with us a list of demands,
888 -- and the type of the function-applied-to-earlier-args
891 go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
892 = getInScope `thenSmpl` \ in_scope ->
894 ty_arg' = substTy (mkSubst in_scope se) ty_arg
895 res_ty = applyTy fun_ty ty_arg'
897 seqType ty_arg' `seq`
898 go (Type ty_arg' : acc) ds res_ty cont
901 go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
902 = case splitFunTy_maybe fun_ty of {
903 Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
904 (thing_inside (reverse acc) cont) ;
905 Just (arg_ty, res_ty) ->
906 simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
907 go (arg':acc) ds res_ty cont }
909 -- We've run out of demands, which only happens for functions
910 -- we *know* now return bottom
912 -- * case (error "hello") of { ... }
913 -- * (error "Hello") arg
914 -- * f (error "Hello") where f is strict
916 go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
917 thing_inside (reverse acc) (discardCont cont)
919 -- We're run out of arguments
920 go acc ds fun_ty cont = thing_inside (reverse acc) cont
922 -- Boring: we must only record a tick if there was an interesting
923 -- continuation to discard. If not, we tick forever.
924 tick_case_of_error (Stop _) = returnSmpl ()
925 tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
926 tick_case_of_error other = tick BottomFound
929 %************************************************************************
931 \subsection{Decisions about inlining}
933 %************************************************************************
935 NB: At one time I tried not pre/post-inlining top-level things,
936 even if they occur exactly once. Reason:
937 (a) some might appear as a function argument, so we simply
938 replace static allocation with dynamic allocation:
944 (b) some top level things might be black listed
946 HOWEVER, I found that some useful foldr/build fusion was lost (most
947 notably in spectral/hartel/parstof) because the foldr didn't see the build.
949 Doing the dynamic allocation isn't a big deal, in fact, but losing the
953 preInlineUnconditionally :: Bool {- Black listed -} -> InId -> Bool
954 -- Examines a bndr to see if it is used just once in a
955 -- completely safe way, so that it is safe to discard the binding
956 -- inline its RHS at the (unique) usage site, REGARDLESS of how
957 -- big the RHS might be. If this is the case we don't simplify
958 -- the RHS first, but just inline it un-simplified.
960 -- This is much better than first simplifying a perhaps-huge RHS
961 -- and then inlining and re-simplifying it.
963 -- NB: we don't even look at the RHS to see if it's trivial
966 -- where x is used many times, but this is the unique occurrence
967 -- of y. We should NOT inline x at all its uses, because then
968 -- we'd do the same for y -- aargh! So we must base this
969 -- pre-rhs-simplification decision solely on x's occurrences, not
972 -- Evne RHSs labelled InlineMe aren't caught here, because
973 -- there might be no benefit from inlining at the call site.
975 preInlineUnconditionally black_listed bndr
976 | black_listed || opt_SimplNoPreInlining = False
977 | otherwise = case getIdOccInfo bndr of
978 OneOcc in_lam once -> not in_lam && once
979 -- Not inside a lambda, one occurrence ==> safe!
983 postInlineUnconditionally :: Bool -- Black listed
985 -> InId -> OutExpr -> Bool
986 -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
987 -- It returns True if it's ok to discard the binding and inline the
988 -- RHS at every use site.
990 -- NOTE: This isn't our last opportunity to inline.
991 -- We're at the binding site right now, and
992 -- we'll get another opportunity when we get to the ocurrence(s)
994 postInlineUnconditionally black_listed occ_info bndr rhs
995 | isExportedId bndr ||
997 loop_breaker = False -- Don't inline these
998 | otherwise = exprIsTrivial rhs -- Duplicating is free
999 -- Don't inline even WHNFs inside lambdas; doing so may
1000 -- simply increase allocation when the function is called
1001 -- This isn't the last chance; see NOTE above.
1003 -- NB: Even inline pragmas (e.g. IMustBeINLINEd) are ignored here
1004 -- Why? Because we don't even want to inline them into the
1005 -- RHS of constructor arguments. See NOTE above
1007 -- NB: Even NOINLINEis ignored here: if the rhs is trivial
1008 -- it's best to inline it anyway. We often get a=E; b=a
1009 -- from desugaring, with both a and b marked NOINLINE.
1011 loop_breaker = case occ_info of
1012 IAmALoopBreaker -> True
1018 %************************************************************************
1020 \subsection{The main rebuilder}
1022 %************************************************************************
1025 -------------------------------------------------------------------
1026 -- Finish rebuilding
1028 = getInScope `thenSmpl` \ in_scope ->
1029 returnSmpl ([], (in_scope, expr))
1031 ---------------------------------------------------------
1032 rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
1034 -- Stop continuation
1035 rebuild expr (Stop _) = rebuild_done expr
1037 -- ArgOf continuation
1038 rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
1040 -- ApplyTo continuation
1041 rebuild expr cont@(ApplyTo _ arg se cont')
1042 = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1043 rebuild (App expr arg') cont'
1045 -- Coerce continuation
1046 rebuild expr (CoerceIt to_ty cont)
1047 = rebuild (mkCoerce to_ty expr) cont
1049 -- Inline continuation
1050 rebuild expr (InlinePlease cont)
1051 = rebuild (Note InlineCall expr) cont
1053 -- Case of known constructor or literal
1054 rebuild expr@(Con con args) (Select _ bndr alts se cont)
1055 | conOkForAlt con -- Knocks out PrimOps and NoRepLits
1056 = knownCon expr con args bndr alts se cont
1059 ---------------------------------------------------------
1060 -- The other Select cases
1062 rebuild scrut (Select _ bndr alts se cont)
1063 | -- Check that the RHSs are all the same, and
1064 -- don't use the binders in the alternatives
1065 -- This test succeeds rapidly in the common case of
1066 -- a single DEFAULT alternative
1067 all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
1069 -- Check that the scrutinee can be let-bound instead of case-bound
1070 && ( exprOkForSpeculation scrut
1071 -- OK not to evaluate it
1072 -- This includes things like (==# a# b#)::Bool
1073 -- so that we simplify
1074 -- case ==# a# b# of { True -> x; False -> x }
1077 -- This particular example shows up in default methods for
1078 -- comparision operations (e.g. in (>=) for Int.Int32)
1079 || exprIsValue scrut -- It's already evaluated
1080 || var_demanded_later scrut -- It'll be demanded later
1082 -- || not opt_SimplPedanticBottoms) -- Or we don't care!
1083 -- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
1084 -- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
1085 -- its argument: case x of { y -> dataToTag# y }
1086 -- Here we must *not* discard the case, because dataToTag# just fetches the tag from
1087 -- the info pointer. So we'll be pedantic all the time, and see if that gives any
1091 -- && opt_SimplDoCaseElim
1092 -- [June 99; don't test this flag. The code generator dies if it sees
1093 -- case (\x.e) of f -> ...
1094 -- so better to always do it
1096 -- Get rid of the case altogether
1097 -- See the extensive notes on case-elimination below
1098 -- Remember to bind the binder though!
1099 = tick (CaseElim bndr) `thenSmpl_` (
1101 simplBinder bndr $ \ bndr' ->
1102 completeBinding bndr bndr' False False scrut $
1103 simplExprF rhs1 cont)
1106 = rebuild_case scrut bndr alts se cont
1108 (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
1109 binders_unused (_, bndrs, _) = all isDeadBinder bndrs
1111 var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
1112 var_demanded_later other = False
1115 Case elimination [see the code above]
1117 Start with a simple situation:
1119 case x# of ===> e[x#/y#]
1122 (when x#, y# are of primitive type, of course). We can't (in general)
1123 do this for algebraic cases, because we might turn bottom into
1126 Actually, we generalise this idea to look for a case where we're
1127 scrutinising a variable, and we know that only the default case can
1132 other -> ...(case x of
1136 Here the inner case can be eliminated. This really only shows up in
1137 eliminating error-checking code.
1139 We also make sure that we deal with this very common case:
1144 Here we are using the case as a strict let; if x is used only once
1145 then we want to inline it. We have to be careful that this doesn't
1146 make the program terminate when it would have diverged before, so we
1148 - x is used strictly, or
1149 - e is already evaluated (it may so if e is a variable)
1151 Lastly, we generalise the transformation to handle this:
1157 We only do this for very cheaply compared r's (constructors, literals
1158 and variables). If pedantic bottoms is on, we only do it when the
1159 scrutinee is a PrimOp which can't fail.
1161 We do it *here*, looking at un-simplified alternatives, because we
1162 have to check that r doesn't mention the variables bound by the
1163 pattern in each alternative, so the binder-info is rather useful.
1165 So the case-elimination algorithm is:
1167 1. Eliminate alternatives which can't match
1169 2. Check whether all the remaining alternatives
1170 (a) do not mention in their rhs any of the variables bound in their pattern
1171 and (b) have equal rhss
1173 3. Check we can safely ditch the case:
1174 * PedanticBottoms is off,
1175 or * the scrutinee is an already-evaluated variable
1176 or * the scrutinee is a primop which is ok for speculation
1177 -- ie we want to preserve divide-by-zero errors, and
1178 -- calls to error itself!
1180 or * [Prim cases] the scrutinee is a primitive variable
1182 or * [Alg cases] the scrutinee is a variable and
1183 either * the rhs is the same variable
1184 (eg case x of C a b -> x ===> x)
1185 or * there is only one alternative, the default alternative,
1186 and the binder is used strictly in its scope.
1187 [NB this is helped by the "use default binder where
1188 possible" transformation; see below.]
1191 If so, then we can replace the case with one of the rhss.
1194 Blob of helper functions for the "case-of-something-else" situation.
1197 ---------------------------------------------------------
1198 -- Case of something else
1200 rebuild_case scrut case_bndr alts se cont
1201 = -- Prepare case alternatives
1202 prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
1203 scrut_cons alts `thenSmpl` \ better_alts ->
1205 -- Set the new subst-env in place (before dealing with the case binder)
1208 -- Deal with the case binder, and prepare the continuation;
1209 -- The new subst_env is in place
1210 prepareCaseCont better_alts cont $ \ cont' ->
1213 -- Deal with variable scrutinee
1214 ( simplCaseBinder scrut case_bndr $ \ case_bndr' zap_occ_info ->
1216 -- Deal with the case alternatives
1217 simplAlts zap_occ_info scrut_cons
1218 case_bndr' better_alts cont' `thenSmpl` \ alts' ->
1220 mkCase scrut case_bndr' alts'
1221 ) `thenSmpl` \ case_expr ->
1223 -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
1224 -- over the rebuild_done; rebuild_done returns the in-scope set, and
1225 -- that should not include these chaps!
1226 rebuild_done case_expr
1228 -- scrut_cons tells what constructors the scrutinee can't possibly match
1229 scrut_cons = case scrut of
1230 Var v -> otherCons (getIdUnfolding v)
1234 knownCon expr con args bndr alts se cont
1235 = tick (KnownBranch bndr) `thenSmpl_`
1237 simplBinder bndr $ \ bndr' ->
1238 case findAlt con alts of
1239 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1240 completeBinding bndr bndr' False False expr $
1241 -- Don't use completeBeta here. The expr might be
1242 -- an unboxed literal, like 3, or a variable
1243 -- whose unfolding is an unboxed literal... and
1244 -- completeBeta will just construct another case
1248 (Literal lit, bs, rhs) -> ASSERT( null bs )
1249 extendSubst bndr (DoneEx expr) $
1250 -- Unconditionally substitute, because expr must
1251 -- be a variable or a literal. It can't be a
1252 -- NoRep literal because they don't occur in
1256 (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
1257 completeBinding bndr bndr' False False expr $
1259 extendSubstList bs (map mk real_args) $
1262 real_args = drop (dataConNumInstArgs dc) args
1263 mk (Type ty) = DoneTy ty
1264 mk other = DoneEx other
1269 prepareCaseCont :: [InAlt] -> SimplCont
1270 -> (SimplCont -> SimplM (OutStuff a))
1271 -> SimplM (OutStuff a)
1272 -- Polymorphic recursion here!
1274 prepareCaseCont [alt] cont thing_inside = thing_inside cont
1275 prepareCaseCont alts cont thing_inside = simplType (coreAltsType alts) `thenSmpl` \ alts_ty ->
1276 mkDupableCont alts_ty cont thing_inside
1277 -- At one time I passed in the un-simplified type, and simplified
1278 -- it only if we needed to construct a join binder, but that
1279 -- didn't work because we have to decompse function types
1280 -- (using funResultTy) in mkDupableCont.
1283 simplCaseBinder checks whether the scrutinee is a variable, v.
1284 If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
1285 that way, there's a chance that v will now only be used once, and hence inlined.
1287 If we do this, then we have to nuke any occurrence info (eg IAmDead)
1288 in the case binder, because the case-binder now effectively occurs
1289 whenever v does. AND we have to do the same for the pattern-bound
1292 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1294 Here, b and p are dead. But when we move the argment inside the first
1295 case RHS, and eliminate the second case, we get
1297 case x or { (a,b) -> a b }
1299 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1300 happened. Hence the zap_occ_info function returned by simplCaseBinder
1303 simplCaseBinder (Var v) case_bndr thing_inside
1304 = simplBinder (zap case_bndr) $ \ case_bndr' ->
1305 modifyInScope v case_bndr' $
1306 -- We could extend the substitution instead, but it would be
1307 -- a hack because then the substitution wouldn't be idempotent
1308 -- any more (v is an OutId). And this just just as well.
1309 thing_inside case_bndr' zap
1311 zap b = b `setIdOccInfo` NoOccInfo
1313 simplCaseBinder other_scrut case_bndr thing_inside
1314 = simplBinder case_bndr $ \ case_bndr' ->
1315 thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr
1318 prepareCaseAlts does two things:
1320 1. Remove impossible alternatives
1322 2. If the DEFAULT alternative can match only one possible constructor,
1323 then make that constructor explicit.
1325 case e of x { DEFAULT -> rhs }
1327 case e of x { (a,b) -> rhs }
1328 where the type is a single constructor type. This gives better code
1329 when rhs also scrutinises x or e.
1332 prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
1334 = case (findDefault filtered_alts, missing_cons) of
1336 ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
1337 -> tick (FillInCaseDefault bndr) `thenSmpl_`
1339 (_,_,ex_tyvars,_,_,_) = dataConSig data_con
1341 getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
1343 ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
1344 mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
1346 newIds (dataConArgTys
1348 (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
1349 returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
1351 other -> returnSmpl filtered_alts
1353 -- Filter out alternatives that can't possibly match
1354 filtered_alts = case scrut_cons of
1356 other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
1358 missing_cons = [data_con | data_con <- tyConDataCons tycon,
1359 not (data_con `elem` handled_data_cons)]
1360 handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
1361 [data_con | (DataCon data_con, _, _) <- filtered_alts]
1364 prepareCaseAlts _ _ scrut_cons alts
1365 = returnSmpl alts -- Functions
1368 ----------------------
1369 simplAlts zap_occ_info scrut_cons case_bndr' alts cont'
1370 = mapSmpl simpl_alt alts
1372 inst_tys' = case splitTyConApp_maybe (idType case_bndr') of
1373 Just (tycon, inst_tys) -> inst_tys
1375 -- handled_cons is all the constructors that are dealt
1376 -- with, either by being impossible, or by there being an alternative
1377 handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
1379 simpl_alt (DEFAULT, _, rhs)
1380 = -- In the default case we record the constructors that the
1381 -- case-binder *can't* be.
1382 -- We take advantage of any OtherCon info in the case scrutinee
1383 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $
1384 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1385 returnSmpl (DEFAULT, [], rhs')
1387 simpl_alt (con, vs, rhs)
1388 = -- Deal with the pattern-bound variables
1389 -- Mark the ones that are in ! positions in the data constructor
1390 -- as certainly-evaluated.
1391 -- NB: it happens that simplBinders does *not* erase the OtherCon
1392 -- form of unfolding, so it's ok to add this info before
1393 -- doing simplBinders
1394 simplBinders (add_evals con vs) $ \ vs' ->
1396 -- Bind the case-binder to (Con args)
1398 con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
1400 modifyInScope case_bndr' (case_bndr' `setIdUnfolding` mkUnfolding False con_app) $
1401 simplExprC rhs cont' `thenSmpl` \ rhs' ->
1402 returnSmpl (con, vs', rhs')
1405 -- add_evals records the evaluated-ness of the bound variables of
1406 -- a case pattern. This is *important*. Consider
1407 -- data T = T !Int !Int
1409 -- case x of { T a b -> T (a+1) b }
1411 -- We really must record that b is already evaluated so that we don't
1412 -- go and re-evaluate it when constructing the result.
1414 add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
1415 add_evals other_con vs = vs
1417 cat_evals [] [] = []
1418 cat_evals (v:vs) (str:strs)
1419 | isTyVar v = v : cat_evals vs (str:strs)
1420 | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
1421 | otherwise = v' : cat_evals vs strs
1427 %************************************************************************
1429 \subsection{Duplicating continuations}
1431 %************************************************************************
1434 mkDupableCont :: OutType -- Type of the thing to be given to the continuation
1436 -> (SimplCont -> SimplM (OutStuff a))
1437 -> SimplM (OutStuff a)
1438 mkDupableCont ty cont thing_inside
1439 | contIsDupable cont
1442 mkDupableCont _ (CoerceIt ty cont) thing_inside
1443 = mkDupableCont ty cont $ \ cont' ->
1444 thing_inside (CoerceIt ty cont')
1446 mkDupableCont ty (InlinePlease cont) thing_inside
1447 = mkDupableCont ty cont $ \ cont' ->
1448 thing_inside (InlinePlease cont')
1450 mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
1451 = -- Build the RHS of the join point
1452 newId join_arg_ty ( \ arg_id ->
1453 cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
1454 returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs))
1455 ) `thenSmpl` \ join_rhs ->
1457 -- Build the join Id and continuation
1458 newId (coreExprType join_rhs) $ \ join_id ->
1460 new_cont = ArgOf OkToDup cont_ty
1461 (\arg' -> rebuild_done (App (Var join_id) arg'))
1464 tick (CaseOfCase join_id) `thenSmpl_`
1465 -- Want to tick here so that we go round again,
1466 -- and maybe copy or inline the code;
1467 -- not strictly CaseOf Case
1468 thing_inside new_cont `thenSmpl` \ res ->
1469 returnSmpl (addBind (NonRec join_id join_rhs) res)
1471 mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
1472 = mkDupableCont (funResultTy ty) cont $ \ cont' ->
1473 setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
1474 if exprIsDupable arg' then
1475 thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
1477 newId (coreExprType arg') $ \ bndr ->
1479 tick (CaseOfCase bndr) `thenSmpl_`
1480 -- Want to tick here so that we go round again,
1481 -- and maybe copy or inline the code;
1482 -- not strictly CaseOf Case
1483 thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
1484 returnSmpl (addBind (NonRec bndr arg') res)
1486 mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
1487 = tick (CaseOfCase case_bndr) `thenSmpl_`
1489 simplBinder case_bndr $ \ case_bndr' ->
1490 prepareCaseCont alts cont $ \ cont' ->
1491 mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
1492 returnSmpl (concat alt_binds_s, alts')
1493 ) `thenSmpl` \ (alt_binds, alts') ->
1495 extendInScopes [b | NonRec b _ <- alt_binds] $
1497 -- NB that the new alternatives, alts', are still InAlts, using the original
1498 -- binders. That means we can keep the case_bndr intact. This is important
1499 -- because another case-of-case might strike, and so we want to keep the
1500 -- info that the case_bndr is dead (if it is, which is often the case).
1501 -- This is VITAL when the type of case_bndr is an unboxed pair (often the
1502 -- case in I/O rich code. We aren't allowed a lambda bound
1503 -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
1504 thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
1506 returnSmpl (addBinds alt_binds res)
1509 mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
1510 mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
1511 = simplBinders bndrs $ \ bndrs' ->
1512 simplExprC rhs cont `thenSmpl` \ rhs' ->
1514 if (case cont of { Stop _ -> exprIsDupable rhs'; other -> False}) then
1515 -- It is worth checking for a small RHS because otherwise we
1516 -- get extra let bindings that may cause an extra iteration of the simplifier to
1517 -- inline back in place. Quite often the rhs is just a variable or constructor.
1518 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1519 -- iterations because the version with the let bindings looked big, and so wasn't
1520 -- inlined, but after the join points had been inlined it looked smaller, and so
1523 -- But since the continuation is absorbed into the rhs, we only do this
1524 -- for a Stop continuation.
1526 -- NB: we have to check the size of rhs', not rhs.
1527 -- Duplicating a small InAlt might invalidate occurrence information
1528 -- However, if it *is* dupable, we return the *un* simplified alternative,
1529 -- because otherwise we'd need to pair it up with an empty subst-env.
1530 -- (Remember we must zap the subst-env before re-simplifying something).
1531 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1532 returnSmpl ([], alt)
1536 rhs_ty' = coreExprType rhs'
1537 (used_bndrs, used_bndrs')
1538 = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
1539 (case_bndr' : bndrs'),
1540 not (isDeadBinder bndr)]
1541 -- The new binders have lost their occurrence info,
1542 -- so we have to extract it from the old ones
1544 ( if null used_bndrs'
1545 -- If we try to lift a primitive-typed something out
1546 -- for let-binding-purposes, we will *caseify* it (!),
1547 -- with potentially-disastrous strictness results. So
1548 -- instead we turn it into a function: \v -> e
1549 -- where v::State# RealWorld#. The value passed to this function
1550 -- is realworld#, which generates (almost) no code.
1552 -- There's a slight infelicity here: we pass the overall
1553 -- case_bndr to all the join points if it's used in *any* RHS,
1554 -- because we don't know its usage in each RHS separately
1556 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1557 -- we make the join point into a function whenever used_bndrs'
1558 -- is empty. This makes the join-point more CPR friendly.
1559 -- Consider: let j = if .. then I# 3 else I# 4
1560 -- in case .. of { A -> j; B -> j; C -> ... }
1562 -- Now CPR should not w/w j because it's a thunk, so
1563 -- that means that the enclosing function can't w/w either,
1564 -- which is a lose. Here's the example that happened in practice:
1565 -- kgmod :: Int -> Int -> Int
1566 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1570 then newId realWorldStatePrimTy $ \ rw_id ->
1571 returnSmpl ([rw_id], [Var realWorldPrimId])
1573 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
1575 `thenSmpl` \ (final_bndrs', final_args) ->
1577 newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
1579 -- Notice that we make the lambdas into one-shot-lambdas. The
1580 -- join point is sure to be applied at most once, and doing so
1581 -- prevents the body of the join point being floated out by
1582 -- the full laziness pass
1583 returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
1584 (con, bndrs, mkApps (Var join_bndr) final_args))