2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
11 mkInlineMe, mkSCC, mkCoerce,
12 bindNonRec, needsCaseBinding,
13 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
15 -- Taking expressions apart
16 findDefault, findAlt, isDefaultAlt, mergeAlts,
18 -- Properties of expressions
19 exprType, coreAltType,
20 exprIsDupable, exprIsTrivial, exprIsCheap,
21 exprIsHNF,exprOkForSpeculation, exprIsBig,
22 exprIsConApp_maybe, exprIsBottom,
25 -- Arity and eta expansion
26 manifestArity, exprArity,
27 exprEtaExpandArity, etaExpand,
36 cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg,
38 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
41 #include "HsVersions.h"
74 import GHC.Exts -- For `xori`
78 %************************************************************************
80 \subsection{Find the type of a Core atom/expression}
82 %************************************************************************
85 exprType :: CoreExpr -> Type
87 exprType (Var var) = idType var
88 exprType (Lit lit) = literalType lit
89 exprType (Let _ body) = exprType body
90 exprType (Case _ _ ty alts) = ty
92 = let (_, ty) = coercionKind co in ty
93 exprType (Note other_note e) = exprType e
94 exprType (Lam binder expr) = mkPiType binder (exprType expr)
96 = case collectArgs e of
97 (fun, args) -> applyTypeToArgs e (exprType fun) args
99 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
101 coreAltType :: CoreAlt -> Type
102 coreAltType (_,_,rhs) = exprType rhs
105 @mkPiType@ makes a (->) type or a forall type, depending on whether
106 it is given a type variable or a term variable. We cleverly use the
107 lbvarinfo field to figure out the right annotation for the arrove in
108 case of a term variable.
111 mkPiType :: Var -> Type -> Type -- The more polymorphic version
112 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
114 mkPiTypes vs ty = foldr mkPiType ty vs
117 | isId v = mkFunTy (idType v) ty
118 | otherwise = mkForAllTy v ty
122 applyTypeToArg :: Type -> CoreExpr -> Type
123 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
124 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
126 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
127 -- A more efficient version of applyTypeToArg
128 -- when we have several args
129 -- The first argument is just for debugging
130 applyTypeToArgs e op_ty [] = op_ty
132 applyTypeToArgs e op_ty (Type ty : args)
133 = -- Accumulate type arguments so we can instantiate all at once
136 go rev_tys (Type ty : args) = go (ty:rev_tys) args
137 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
139 op_ty' = applyTys op_ty (reverse rev_tys)
141 applyTypeToArgs e op_ty (other_arg : args)
142 = case (splitFunTy_maybe op_ty) of
143 Just (_, res_ty) -> applyTypeToArgs e res_ty args
144 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
149 %************************************************************************
151 \subsection{Attaching notes}
153 %************************************************************************
155 mkNote removes redundant coercions, and SCCs where possible
159 mkNote :: Note -> CoreExpr -> CoreExpr
160 mkNote (SCC cc) expr = mkSCC cc expr
161 mkNote InlineMe expr = mkInlineMe expr
162 mkNote note expr = Note note expr
166 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
167 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
168 not be *applied* to anything.
170 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
173 f = inline_me (coerce t fw)
174 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
175 We want the split, so that the coerces can cancel at the call site.
177 However, we can get left with tiresome type applications. Notably, consider
178 f = /\ a -> let t = e in (t, w)
179 Then lifting the let out of the big lambda gives
181 f = /\ a -> let t = inline_me (t' a) in (t, w)
182 The inline_me is to stop the simplifier inlining t' right back
183 into t's RHS. In the next phase we'll substitute for t (since
184 its rhs is trivial) and *then* we could get rid of the inline_me.
185 But it hardly seems worth it, so I don't bother.
188 mkInlineMe (Var v) = Var v
189 mkInlineMe e = Note InlineMe e
195 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
196 mkCoerce co (Cast expr co2)
197 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
198 (_from_ty2, to_ty2) = coercionKind co2} in
199 from_ty `coreEqType` to_ty2 )
200 mkCoerce (mkTransCoercion co2 co) expr
203 = let (from_ty, to_ty) = coercionKind co in
204 -- if to_ty `coreEqType` from_ty
207 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
212 mkSCC :: CostCentre -> Expr b -> Expr b
213 -- Note: Nested SCC's *are* preserved for the benefit of
214 -- cost centre stack profiling
215 mkSCC cc (Lit lit) = Lit lit
216 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
217 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
218 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
219 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
220 mkSCC cc expr = Note (SCC cc) expr
224 %************************************************************************
226 \subsection{Other expression construction}
228 %************************************************************************
231 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
232 -- (bindNonRec x r b) produces either
235 -- case r of x { _DEFAULT_ -> b }
237 -- depending on whether x is unlifted or not
238 -- It's used by the desugarer to avoid building bindings
239 -- that give Core Lint a heart attack. Actually the simplifier
240 -- deals with them perfectly well.
242 bindNonRec bndr rhs body
243 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
244 | otherwise = Let (NonRec bndr rhs) body
246 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
247 -- Make a case expression instead of a let
248 -- These can arise either from the desugarer,
249 -- or from beta reductions: (\x.e) (x +# y)
253 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
254 -- This guy constructs the value that the scrutinee must have
255 -- when you are in one particular branch of a case
256 mkAltExpr (DataAlt con) args inst_tys
257 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
258 mkAltExpr (LitAlt lit) [] []
261 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
262 mkIfThenElse guard then_expr else_expr
263 -- Not going to be refining, so okay to take the type of the "then" clause
264 = Case guard (mkWildId boolTy) (exprType then_expr)
265 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
266 (DataAlt trueDataCon, [], then_expr) ]
270 %************************************************************************
272 \subsection{Taking expressions apart}
274 %************************************************************************
276 The default alternative must be first, if it exists at all.
277 This makes it easy to find, though it makes matching marginally harder.
280 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
281 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
282 findDefault alts = (alts, Nothing)
284 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
287 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
288 other -> go alts panic_deflt
290 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
293 go (alt@(con1,_,_) : alts) deflt
294 = case con `cmpAltCon` con1 of
295 LT -> deflt -- Missed it already; the alts are in increasing order
297 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
299 isDefaultAlt :: CoreAlt -> Bool
300 isDefaultAlt (DEFAULT, _, _) = True
301 isDefaultAlt other = False
303 ---------------------------------
304 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
305 -- Merge preserving order; alternatives in the first arg
306 -- shadow ones in the second
307 mergeAlts [] as2 = as2
308 mergeAlts as1 [] = as1
309 mergeAlts (a1:as1) (a2:as2)
310 = case a1 `cmpAlt` a2 of
311 LT -> a1 : mergeAlts as1 (a2:as2)
312 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
313 GT -> a2 : mergeAlts (a1:as1) as2
317 %************************************************************************
319 \subsection{Figuring out things about expressions}
321 %************************************************************************
323 @exprIsTrivial@ is true of expressions we are unconditionally happy to
324 duplicate; simple variables and constants, and type
325 applications. Note that primop Ids aren't considered
328 @exprIsBottom@ is true of expressions that are guaranteed to diverge
331 There used to be a gruesome test for (hasNoBinding v) in the
333 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
334 The idea here is that a constructor worker, like $wJust, is
335 really short for (\x -> $wJust x), becuase $wJust has no binding.
336 So it should be treated like a lambda. Ditto unsaturated primops.
337 But now constructor workers are not "have-no-binding" Ids. And
338 completely un-applied primops and foreign-call Ids are sufficiently
339 rare that I plan to allow them to be duplicated and put up with
342 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
343 a) it really generates code, (and a heap object when it's
344 a function arg) to capture the cost centre
345 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
348 exprIsTrivial (Var v) = True -- See notes above
349 exprIsTrivial (Type _) = True
350 exprIsTrivial (Lit lit) = litIsTrivial lit
351 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
352 exprIsTrivial (Note (SCC _) e) = False -- See notes above
353 exprIsTrivial (Note _ e) = exprIsTrivial e
354 exprIsTrivial (Cast e co) = exprIsTrivial e
355 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
356 exprIsTrivial other = False
360 @exprIsDupable@ is true of expressions that can be duplicated at a modest
361 cost in code size. This will only happen in different case
362 branches, so there's no issue about duplicating work.
364 That is, exprIsDupable returns True of (f x) even if
365 f is very very expensive to call.
367 Its only purpose is to avoid fruitless let-binding
368 and then inlining of case join points
372 exprIsDupable (Type _) = True
373 exprIsDupable (Var v) = True
374 exprIsDupable (Lit lit) = litIsDupable lit
375 exprIsDupable (Note InlineMe e) = True
376 exprIsDupable (Note _ e) = exprIsDupable e
377 exprIsDupable (Cast e co) = exprIsDupable e
381 go (Var v) n_args = True
382 go (App f a) n_args = n_args < dupAppSize
385 go other n_args = False
388 dupAppSize = 4 -- Size of application we are prepared to duplicate
391 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
392 it is obviously in weak head normal form, or is cheap to get to WHNF.
393 [Note that that's not the same as exprIsDupable; an expression might be
394 big, and hence not dupable, but still cheap.]
396 By ``cheap'' we mean a computation we're willing to:
397 push inside a lambda, or
398 inline at more than one place
399 That might mean it gets evaluated more than once, instead of being
400 shared. The main examples of things which aren't WHNF but are
405 (where e, and all the ei are cheap)
408 (where e and b are cheap)
411 (where op is a cheap primitive operator)
414 (because we are happy to substitute it inside a lambda)
416 Notice that a variable is considered 'cheap': we can push it inside a lambda,
417 because sharing will make sure it is only evaluated once.
420 exprIsCheap :: CoreExpr -> Bool
421 exprIsCheap (Lit lit) = True
422 exprIsCheap (Type _) = True
423 exprIsCheap (Var _) = True
424 exprIsCheap (Note InlineMe e) = True
425 exprIsCheap (Note _ e) = exprIsCheap e
426 exprIsCheap (Cast e co) = exprIsCheap e
427 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
428 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
429 and [exprIsCheap rhs | (_,_,rhs) <- alts]
430 -- Experimentally, treat (case x of ...) as cheap
431 -- (and case __coerce x etc.)
432 -- This improves arities of overloaded functions where
433 -- there is only dictionary selection (no construction) involved
434 exprIsCheap (Let (NonRec x _) e)
435 | isUnLiftedType (idType x) = exprIsCheap e
437 -- strict lets always have cheap right hand sides,
438 -- and do no allocation.
440 exprIsCheap other_expr -- Applications and variables
443 -- Accumulate value arguments, then decide
444 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
445 | otherwise = go f val_args
447 go (Var f) [] = True -- Just a type application of a variable
448 -- (f t1 t2 t3) counts as WHNF
450 = case globalIdDetails f of
451 RecordSelId {} -> go_sel args
452 ClassOpId _ -> go_sel args
453 PrimOpId op -> go_primop op args
455 DataConWorkId _ -> go_pap args
456 other | length args < idArity f -> go_pap args
458 other -> isBottomingId f
459 -- Application of a function which
460 -- always gives bottom; we treat this as cheap
461 -- because it certainly doesn't need to be shared!
463 go other args = False
466 go_pap args = all exprIsTrivial args
467 -- For constructor applications and primops, check that all
468 -- the args are trivial. We don't want to treat as cheap, say,
470 -- We'll put up with one constructor application, but not dozens
473 go_primop op args = primOpIsCheap op && all exprIsCheap args
474 -- In principle we should worry about primops
475 -- that return a type variable, since the result
476 -- might be applied to something, but I'm not going
477 -- to bother to check the number of args
480 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
481 go_sel other = False -- look cheap, so we will substitute it inside a
482 -- lambda. Particularly for dictionary field selection.
483 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
484 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
487 exprOkForSpeculation returns True of an expression that it is
489 * safe to evaluate even if normal order eval might not
490 evaluate the expression at all, or
492 * safe *not* to evaluate even if normal order would do so
496 the expression guarantees to terminate,
498 without raising an exception,
499 without causing a side effect (e.g. writing a mutable variable)
501 NB: if exprIsHNF e, then exprOkForSpecuation e
504 let x = case y# +# 1# of { r# -> I# r# }
507 case y# +# 1# of { r# ->
512 We can only do this if the (y+1) is ok for speculation: it has no
513 side effects, and can't diverge or raise an exception.
516 exprOkForSpeculation :: CoreExpr -> Bool
517 exprOkForSpeculation (Lit _) = True
518 exprOkForSpeculation (Type _) = True
519 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
520 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
521 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
522 exprOkForSpeculation other_expr
523 = case collectArgs other_expr of
524 (Var f, args) -> spec_ok (globalIdDetails f) args
528 spec_ok (DataConWorkId _) args
529 = True -- The strictness of the constructor has already
530 -- been expressed by its "wrapper", so we don't need
531 -- to take the arguments into account
533 spec_ok (PrimOpId op) args
534 | isDivOp op, -- Special case for dividing operations that fail
535 [arg1, Lit lit] <- args -- only if the divisor is zero
536 = not (isZeroLit lit) && exprOkForSpeculation arg1
537 -- Often there is a literal divisor, and this
538 -- can get rid of a thunk in an inner looop
541 = primOpOkForSpeculation op &&
542 all exprOkForSpeculation args
543 -- A bit conservative: we don't really need
544 -- to care about lazy arguments, but this is easy
546 spec_ok other args = False
548 isDivOp :: PrimOp -> Bool
549 -- True of dyadic operators that can fail
550 -- only if the second arg is zero
551 -- This function probably belongs in PrimOp, or even in
552 -- an automagically generated file.. but it's such a
553 -- special case I thought I'd leave it here for now.
554 isDivOp IntQuotOp = True
555 isDivOp IntRemOp = True
556 isDivOp WordQuotOp = True
557 isDivOp WordRemOp = True
558 isDivOp IntegerQuotRemOp = True
559 isDivOp IntegerDivModOp = True
560 isDivOp FloatDivOp = True
561 isDivOp DoubleDivOp = True
562 isDivOp other = False
567 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
568 exprIsBottom e = go 0 e
570 -- n is the number of args
571 go n (Note _ e) = go n e
572 go n (Cast e co) = go n e
573 go n (Let _ e) = go n e
574 go n (Case e _ _ _) = go 0 e -- Just check the scrut
575 go n (App e _) = go (n+1) e
576 go n (Var v) = idAppIsBottom v n
578 go n (Lam _ _) = False
579 go n (Type _) = False
581 idAppIsBottom :: Id -> Int -> Bool
582 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
585 @exprIsHNF@ returns true for expressions that are certainly *already*
586 evaluated to *head* normal form. This is used to decide whether it's ok
589 case x of _ -> e ===> e
591 and to decide whether it's safe to discard a `seq`
593 So, it does *not* treat variables as evaluated, unless they say they are.
595 But it *does* treat partial applications and constructor applications
596 as values, even if their arguments are non-trivial, provided the argument
598 e.g. (:) (f x) (map f xs) is a value
599 map (...redex...) is a value
600 Because `seq` on such things completes immediately
602 For unlifted argument types, we have to be careful:
604 Suppose (f x) diverges; then C (f x) is not a value. True, but
605 this form is illegal (see the invariants in CoreSyn). Args of unboxed
606 type must be ok-for-speculation (or trivial).
609 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
610 exprIsHNF (Var v) -- NB: There are no value args at this point
611 = isDataConWorkId v -- Catches nullary constructors,
612 -- so that [] and () are values, for example
613 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
614 || isEvaldUnfolding (idUnfolding v)
615 -- Check the thing's unfolding; it might be bound to a value
616 -- A worry: what if an Id's unfolding is just itself:
617 -- then we could get an infinite loop...
619 exprIsHNF (Lit l) = True
620 exprIsHNF (Type ty) = True -- Types are honorary Values;
621 -- we don't mind copying them
622 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
623 exprIsHNF (Note (TickBox {}) _)
625 exprIsHNF (Note (BinaryTickBox {}) _)
627 exprIsHNF (Note _ e) = exprIsHNF e
628 exprIsHNF (Cast e co) = exprIsHNF e
629 exprIsHNF (App e (Type _)) = exprIsHNF e
630 exprIsHNF (App e a) = app_is_value e [a]
631 exprIsHNF other = False
633 -- There is at least one value argument
634 app_is_value (Var fun) args
635 | isDataConWorkId fun -- Constructor apps are values
636 || idArity fun > valArgCount args -- Under-applied function
637 = check_args (idType fun) args
638 app_is_value (App f a) as = app_is_value f (a:as)
639 app_is_value other as = False
641 -- 'check_args' checks that unlifted-type args
642 -- are in fact guaranteed non-divergent
643 check_args fun_ty [] = True
644 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
645 Just (_, ty) -> check_args ty args
646 check_args fun_ty (arg : args)
647 | isUnLiftedType arg_ty = exprOkForSpeculation arg
648 | otherwise = check_args res_ty args
650 (arg_ty, res_ty) = splitFunTy fun_ty
654 -- These InstPat functions go here to avoid circularity between DataCon and Id
655 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
656 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
657 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
659 dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc
660 -- Remember to include the existential dictionaries
662 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
663 -> [FastString] -- A long enough list of FSs to use for names
664 -> [Unique] -- An equally long list of uniques, at least one for each binder
666 -> [Type] -- Types to instantiate the universally quantified tyvars
667 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
668 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
669 -- (ex_tvs, co_tvs, arg_ids),
671 -- ex_tvs are intended to be used as binders for existential type args
673 -- co_tvs are intended to be used as binders for coercion args and the kinds
674 -- of these vars have been instantiated by the inst_tys and the ex_tys
676 -- arg_ids are indended to be used as binders for value arguments, including
677 -- dicts, and their types have been instantiated with inst_tys and ex_tys
680 -- The following constructor T1
683 -- T1 :: forall b. Int -> b -> T(a,b)
686 -- has representation type
687 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
690 -- dataConInstPat fss us T1 (a1',b') will return
692 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
694 -- where the double-primed variables are created with the FastStrings and
695 -- Uniques given as fss and us
696 dataConInstPat arg_fun fss uniqs con inst_tys
697 = (ex_bndrs, co_bndrs, id_bndrs)
699 univ_tvs = dataConUnivTyVars con
700 ex_tvs = dataConExTyVars con
701 arg_tys = arg_fun con
702 eq_spec = dataConEqSpec con
703 eq_preds = eqSpecPreds eq_spec
706 n_co = length eq_spec
708 -- split the Uniques and FastStrings
709 (ex_uniqs, uniqs') = splitAt n_ex uniqs
710 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
712 (ex_fss, fss') = splitAt n_ex fss
713 (co_fss, id_fss) = splitAt n_co fss'
715 -- Make existential type variables
716 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
717 mk_ex_var uniq fs var = mkTyVar new_name kind
719 new_name = mkSysTvName uniq fs
722 -- Make the instantiating substitution
723 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
725 -- Make new coercion vars, instantiating kind
726 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
727 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
729 new_name = mkSysTvName uniq fs
730 co_kind = substTy subst (mkPredTy eq_pred)
732 -- make value vars, instantiating types
733 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcLoc
734 id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys
736 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
737 -- Returns (Just (dc, [x1..xn])) if the argument expression is
738 -- a constructor application of the form (dc x1 .. xn)
739 exprIsConApp_maybe (Cast expr co)
740 = -- Here we do the PushC reduction rule as described in the FC paper
741 case exprIsConApp_maybe expr of {
743 Just (dc, dc_args) ->
745 -- The transformation applies iff we have
746 -- (C e1 ... en) `cast` co
747 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
748 -- That is, with a T at the top of both sides
749 -- The left-hand one must be a T, because exprIsConApp returned True
750 -- but the right-hand one might not be. (Though it usually will.)
752 let (from_ty, to_ty) = coercionKind co
753 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
754 -- The inner one must be a TyConApp
756 case splitTyConApp_maybe to_ty of {
758 Just (to_tc, to_tc_arg_tys)
759 | from_tc /= to_tc -> Nothing
760 -- These two Nothing cases are possible; we might see
761 -- (C x y) `cast` (g :: T a ~ S [a]),
762 -- where S is a type function. In fact, exprIsConApp
763 -- will probably not be called in such circumstances,
764 -- but there't nothing wrong with it
768 tc_arity = tyConArity from_tc
770 (univ_args, rest1) = splitAt tc_arity dc_args
771 (ex_args, rest2) = splitAt n_ex_tvs rest1
772 (co_args, val_args) = splitAt n_cos rest2
774 arg_tys = dataConRepArgTys dc
775 dc_univ_tyvars = dataConUnivTyVars dc
776 dc_ex_tyvars = dataConExTyVars dc
777 dc_eq_spec = dataConEqSpec dc
778 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
779 n_ex_tvs = length dc_ex_tyvars
780 n_cos = length dc_eq_spec
782 -- Make the "theta" from Fig 3 of the paper
783 gammas = decomposeCo tc_arity co
784 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
785 theta = zipOpenTvSubst dc_tyvars new_tys
787 -- First we cast the existential coercion arguments
788 cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
790 `mkTransCoercion` (substTy theta ty)
791 new_co_args = zipWith cast_co dc_eq_spec co_args
793 -- ...and now value arguments
794 new_val_args = zipWith cast_arg arg_tys val_args
795 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
798 ASSERT( length univ_args == tc_arity )
799 ASSERT( from_tc == dataConTyCon dc )
800 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
801 ASSERT( all isTypeArg (univ_args ++ ex_args) )
802 ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
804 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
807 -- We do not want to tell the world that we have a
808 -- Cons, to *stop* Case of Known Cons, which removes
810 exprIsConApp_maybe (Note (TickBox {}) expr)
812 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
815 exprIsConApp_maybe (Note _ expr)
816 = exprIsConApp_maybe expr
817 -- We ignore InlineMe notes in case we have
818 -- x = __inline_me__ (a,b)
819 -- All part of making sure that INLINE pragmas never hurt
820 -- Marcin tripped on this one when making dictionaries more inlinable
822 -- In fact, we ignore all notes. For example,
823 -- case _scc_ "foo" (C a b) of
825 -- should be optimised away, but it will be only if we look
826 -- through the SCC note.
828 exprIsConApp_maybe expr = analyse (collectArgs expr)
830 analyse (Var fun, args)
831 | Just con <- isDataConWorkId_maybe fun,
832 args `lengthAtLeast` dataConRepArity con
833 -- Might be > because the arity excludes type args
836 -- Look through unfoldings, but only cheap ones, because
837 -- we are effectively duplicating the unfolding
838 analyse (Var fun, [])
839 | let unf = idUnfolding fun,
841 = exprIsConApp_maybe (unfoldingTemplate unf)
843 analyse other = Nothing
848 %************************************************************************
850 \subsection{Eta reduction and expansion}
852 %************************************************************************
855 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
856 {- The Arity returned is the number of value args the
857 thing can be applied to without doing much work
859 exprEtaExpandArity is used when eta expanding
862 It returns 1 (or more) to:
863 case x of p -> \s -> ...
864 because for I/O ish things we really want to get that \s to the top.
865 We are prepared to evaluate x each time round the loop in order to get that
867 It's all a bit more subtle than it looks:
871 Consider one-shot lambdas
872 let x = expensive in \y z -> E
873 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
874 Hence the ArityType returned by arityType
876 2. The state-transformer hack
878 The one-shot lambda special cause is particularly important/useful for
879 IO state transformers, where we often get
880 let x = E in \ s -> ...
882 and the \s is a real-world state token abstraction. Such abstractions
883 are almost invariably 1-shot, so we want to pull the \s out, past the
884 let x=E, even if E is expensive. So we treat state-token lambdas as
885 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
887 3. Dealing with bottom
890 f = \x -> error "foo"
891 Here, arity 1 is fine. But if it is
895 then we want to get arity 2. Tecnically, this isn't quite right, because
897 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
898 do so; it improves some programs significantly, and increasing convergence
899 isn't a bad thing. Hence the ABot/ATop in ArityType.
901 Actually, the situation is worse. Consider
905 Can we eta-expand here? At first the answer looks like "yes of course", but
908 This should diverge! But if we eta-expand, it won't. Again, we ignore this
909 "problem", because being scrupulous would lose an important transformation for
915 Non-recursive newtypes are transparent, and should not get in the way.
916 We do (currently) eta-expand recursive newtypes too. So if we have, say
918 newtype T = MkT ([T] -> Int)
922 where f has arity 1. Then: etaExpandArity e = 1;
923 that is, etaExpandArity looks through the coerce.
925 When we eta-expand e to arity 1: eta_expand 1 e T
926 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
928 HOWEVER, note that if you use coerce bogusly you can ge
930 And since negate has arity 2, you might try to eta expand. But you can't
931 decopose Int to a function type. Hence the final case in eta_expand.
935 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
937 -- A limited sort of function type
938 data ArityType = AFun Bool ArityType -- True <=> one-shot
939 | ATop -- Know nothing
942 arityDepth :: ArityType -> Arity
943 arityDepth (AFun _ ty) = 1 + arityDepth ty
946 andArityType ABot at2 = at2
947 andArityType ATop at2 = ATop
948 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
949 andArityType at1 at2 = andArityType at2 at1
951 arityType :: DynFlags -> CoreExpr -> ArityType
952 -- (go1 e) = [b1,..,bn]
953 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
954 -- where bi is True <=> the lambda is one-shot
956 arityType dflags (Note n e) = arityType dflags e
957 -- Not needed any more: etaExpand is cleverer
958 -- | ok_note n = arityType dflags e
959 -- | otherwise = ATop
961 arityType dflags (Cast e co) = arityType dflags e
963 arityType dflags (Var v)
964 = mk (idArity v) (arg_tys (idType v))
966 mk :: Arity -> [Type] -> ArityType
967 -- The argument types are only to steer the "state hack"
968 -- Consider case x of
970 -- False -> \(s:RealWorld) -> e
971 -- where foo has arity 1. Then we want the state hack to
972 -- apply to foo too, so we can eta expand the case.
973 mk 0 tys | isBottomingId v = ABot
974 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
976 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
977 mk n [] = AFun False (mk (n-1) [])
979 arg_tys :: Type -> [Type] -- Ignore for-alls
981 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
982 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
985 -- Lambdas; increase arity
986 arityType dflags (Lam x e)
987 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
988 | otherwise = arityType dflags e
990 -- Applications; decrease arity
991 arityType dflags (App f (Type _)) = arityType dflags f
992 arityType dflags (App f a) = case arityType dflags f of
993 AFun one_shot xs | exprIsCheap a -> xs
996 -- Case/Let; keep arity if either the expression is cheap
997 -- or it's a 1-shot lambda
998 -- The former is not really right for Haskell
999 -- f x = case x of { (a,b) -> \y. e }
1001 -- f x y = case x of { (a,b) -> e }
1002 -- The difference is observable using 'seq'
1003 arityType dflags (Case scrut _ _ alts)
1004 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1005 xs | exprIsCheap scrut -> xs
1006 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1009 arityType dflags (Let b e)
1010 = case arityType dflags e of
1011 xs | cheap_bind b -> xs
1012 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1015 cheap_bind (NonRec b e) = is_cheap (b,e)
1016 cheap_bind (Rec prs) = all is_cheap prs
1017 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1019 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1020 -- dictionary bindings. This improves arities. Thereby, it also
1021 -- means that full laziness is less prone to floating out the
1022 -- application of a function to its dictionary arguments, which
1023 -- can thereby lose opportunities for fusion. Example:
1024 -- foo :: Ord a => a -> ...
1025 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1026 -- -- So foo has arity 1
1028 -- f = \x. foo dInt $ bar x
1030 -- The (foo DInt) is floated out, and makes ineffective a RULE
1031 -- foo (bar x) = ...
1033 -- One could go further and make exprIsCheap reply True to any
1034 -- dictionary-typed expression, but that's more work.
1036 arityType dflags other = ATop
1038 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1039 ok_note InlineMe = False
1040 ok_note other = True
1041 -- Notice that we do not look through __inline_me__
1042 -- This may seem surprising, but consider
1043 -- f = _inline_me (\x -> e)
1044 -- We DO NOT want to eta expand this to
1045 -- f = \x -> (_inline_me (\x -> e)) x
1046 -- because the _inline_me gets dropped now it is applied,
1055 etaExpand :: Arity -- Result should have this number of value args
1057 -> CoreExpr -> Type -- Expression and its type
1059 -- (etaExpand n us e ty) returns an expression with
1060 -- the same meaning as 'e', but with arity 'n'.
1062 -- Given e' = etaExpand n us e ty
1064 -- ty = exprType e = exprType e'
1066 -- Note that SCCs are not treated specially. If we have
1067 -- etaExpand 2 (\x -> scc "foo" e)
1068 -- = (\xy -> (scc "foo" e) y)
1069 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1071 etaExpand n us expr ty
1072 | manifestArity expr >= n = expr -- The no-op case
1074 = eta_expand n us expr ty
1077 -- manifestArity sees how many leading value lambdas there are
1078 manifestArity :: CoreExpr -> Arity
1079 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1080 | otherwise = manifestArity e
1081 manifestArity (Note _ e) = manifestArity e
1082 manifestArity (Cast e _) = manifestArity e
1085 -- etaExpand deals with for-alls. For example:
1087 -- where E :: forall a. a -> a
1089 -- (/\b. \y::a -> E b y)
1091 -- It deals with coerces too, though they are now rare
1092 -- so perhaps the extra code isn't worth it
1094 eta_expand n us expr ty
1096 -- The ILX code generator requires eta expansion for type arguments
1097 -- too, but alas the 'n' doesn't tell us how many of them there
1098 -- may be. So we eagerly eta expand any big lambdas, and just
1099 -- cross our fingers about possible loss of sharing in the ILX case.
1100 -- The Right Thing is probably to make 'arity' include
1101 -- type variables throughout the compiler. (ToDo.)
1103 -- Saturated, so nothing to do
1106 -- Short cut for the case where there already
1107 -- is a lambda; no point in gratuitously adding more
1108 eta_expand n us (Lam v body) ty
1110 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1113 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1115 -- We used to have a special case that stepped inside Coerces here,
1116 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1117 -- = Note note (eta_expand n us e ty)
1118 -- BUT this led to an infinite loop
1119 -- Example: newtype T = MkT (Int -> Int)
1120 -- eta_expand 1 (coerce (Int->Int) e)
1121 -- --> coerce (Int->Int) (eta_expand 1 T e)
1123 -- --> coerce (Int->Int) (coerce T
1124 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1125 -- by the splitNewType_maybe case below
1128 eta_expand n us expr ty
1129 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1130 case splitForAllTy_maybe ty of {
1133 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1135 lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
1136 -- Using tv as a base retains its tyvar/covar-ness
1140 case splitFunTy_maybe ty of {
1141 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1143 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1149 -- newtype T = MkT ([T] -> Int)
1150 -- Consider eta-expanding this
1153 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1155 case splitNewTypeRepCo_maybe ty of {
1157 mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ;
1160 -- We have an expression of arity > 0, but its type isn't a function
1161 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1162 -- Essentially the programmer is playing fast and loose with types
1163 -- (Happy does this a lot). So we simply decline to eta-expand.
1168 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1169 It tells how many things the expression can be applied to before doing
1170 any work. It doesn't look inside cases, lets, etc. The idea is that
1171 exprEtaExpandArity will do the hard work, leaving something that's easy
1172 for exprArity to grapple with. In particular, Simplify uses exprArity to
1173 compute the ArityInfo for the Id.
1175 Originally I thought that it was enough just to look for top-level lambdas, but
1176 it isn't. I've seen this
1178 foo = PrelBase.timesInt
1180 We want foo to get arity 2 even though the eta-expander will leave it
1181 unchanged, in the expectation that it'll be inlined. But occasionally it
1182 isn't, because foo is blacklisted (used in a rule).
1184 Similarly, see the ok_note check in exprEtaExpandArity. So
1185 f = __inline_me (\x -> e)
1186 won't be eta-expanded.
1188 And in any case it seems more robust to have exprArity be a bit more intelligent.
1189 But note that (\x y z -> f x y z)
1190 should have arity 3, regardless of f's arity.
1193 exprArity :: CoreExpr -> Arity
1196 go (Var v) = idArity v
1197 go (Lam x e) | isId x = go e + 1
1199 go (Note (TickBox {}) _) = 0
1200 go (Note (BinaryTickBox {}) _)
1202 go (Note n e) = go e
1203 go (Cast e _) = go e
1204 go (App e (Type t)) = go e
1205 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1206 -- NB: exprIsCheap a!
1207 -- f (fac x) does not have arity 2,
1208 -- even if f has arity 3!
1209 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1210 -- unknown, hence arity 0
1214 %************************************************************************
1216 \subsection{Equality}
1218 %************************************************************************
1220 @cheapEqExpr@ is a cheap equality test which bales out fast!
1221 True => definitely equal
1222 False => may or may not be equal
1225 cheapEqExpr :: Expr b -> Expr b -> Bool
1227 cheapEqExpr (Var v1) (Var v2) = v1==v2
1228 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1229 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1231 cheapEqExpr (App f1 a1) (App f2 a2)
1232 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1234 cheapEqExpr _ _ = False
1236 exprIsBig :: Expr b -> Bool
1237 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1238 exprIsBig (Lit _) = False
1239 exprIsBig (Var v) = False
1240 exprIsBig (Type t) = False
1241 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1242 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1243 exprIsBig other = True
1248 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1249 -- Used in rule matching, so does *not* look through
1250 -- newtypes, predicate types; hence tcEqExpr
1252 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1254 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1256 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1257 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1258 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1259 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1260 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1261 tcEqExprX env (Let (NonRec v1 r1) e1)
1262 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1263 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1264 tcEqExprX env (Let (Rec ps1) e1)
1265 (Let (Rec ps2) e2) = equalLength ps1 ps2
1266 && and (zipWith eq_rhs ps1 ps2)
1267 && tcEqExprX env' e1 e2
1269 env' = foldl2 rn_bndr2 env ps2 ps2
1270 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1271 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1272 tcEqExprX env (Case e1 v1 t1 a1)
1273 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1274 && tcEqTypeX env t1 t2
1275 && equalLength a1 a2
1276 && and (zipWith (eq_alt env') a1 a2)
1278 env' = rnBndr2 env v1 v2
1280 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1281 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1282 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1283 tcEqExprX env e1 e2 = False
1285 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1287 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1288 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1289 eq_note env other1 other2 = False
1293 %************************************************************************
1295 \subsection{The size of an expression}
1297 %************************************************************************
1300 coreBindsSize :: [CoreBind] -> Int
1301 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1303 exprSize :: CoreExpr -> Int
1304 -- A measure of the size of the expressions
1305 -- It also forces the expression pretty drastically as a side effect
1306 exprSize (Var v) = v `seq` 1
1307 exprSize (Lit lit) = lit `seq` 1
1308 exprSize (App f a) = exprSize f + exprSize a
1309 exprSize (Lam b e) = varSize b + exprSize e
1310 exprSize (Let b e) = bindSize b + exprSize e
1311 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1312 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1313 exprSize (Note n e) = noteSize n + exprSize e
1314 exprSize (Type t) = seqType t `seq` 1
1316 noteSize (SCC cc) = cc `seq` 1
1317 noteSize InlineMe = 1
1318 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1319 noteSize (TickBox m n) = m `seq` n `seq` 1
1320 noteSize (BinaryTickBox m t e) = m `seq` t `seq` e `seq` 1
1322 varSize :: Var -> Int
1323 varSize b | isTyVar b = 1
1324 | otherwise = seqType (idType b) `seq`
1325 megaSeqIdInfo (idInfo b) `seq`
1328 varsSize = foldr ((+) . varSize) 0
1330 bindSize (NonRec b e) = varSize b + exprSize e
1331 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1333 pairSize (b,e) = varSize b + exprSize e
1335 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1339 %************************************************************************
1341 \subsection{Hashing}
1343 %************************************************************************
1346 hashExpr :: CoreExpr -> Int
1347 -- Two expressions that hash to the same Int may be equal (but may not be)
1348 -- Two expressions that hash to the different Ints are definitely unequal
1350 -- But "unequal" here means "not identical"; two alpha-equivalent
1351 -- expressions may hash to the different Ints
1353 -- The emphasis is on a crude, fast hash, rather than on high precision
1355 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1358 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1360 hash_expr (Note _ e) = hash_expr e
1361 hash_expr (Cast e co) = hash_expr e
1362 hash_expr (Let (NonRec b r) e) = hashId b
1363 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1364 hash_expr (Case _ b _ _) = hashId b
1365 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1366 hash_expr (Var v) = hashId v
1367 hash_expr (Lit lit) = hashLiteral lit
1368 hash_expr (Lam b _) = hashId b
1369 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1371 fast_hash_expr (Var v) = hashId v
1372 fast_hash_expr (Lit lit) = hashLiteral lit
1373 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1374 fast_hash_expr (App f a) = fast_hash_expr a
1375 fast_hash_expr (Lam b _) = hashId b
1376 fast_hash_expr other = 1
1379 hashId id = hashName (idName id)
1382 %************************************************************************
1384 \subsection{Determining non-updatable right-hand-sides}
1386 %************************************************************************
1388 Top-level constructor applications can usually be allocated
1389 statically, but they can't if the constructor, or any of the
1390 arguments, come from another DLL (because we can't refer to static
1391 labels in other DLLs).
1393 If this happens we simply make the RHS into an updatable thunk,
1394 and 'exectute' it rather than allocating it statically.
1397 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1398 -- This function is called only on *top-level* right-hand sides
1399 -- Returns True if the RHS can be allocated statically, with
1400 -- no thunks involved at all.
1402 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1403 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1404 -- update flag on it.
1406 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1407 -- (a) a value lambda
1408 -- (b) a saturated constructor application with static args
1410 -- BUT watch out for
1411 -- (i) Any cross-DLL references kill static-ness completely
1412 -- because they must be 'executed' not statically allocated
1413 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1414 -- this is not necessary)
1416 -- (ii) We treat partial applications as redexes, because in fact we
1417 -- make a thunk for them that runs and builds a PAP
1418 -- at run-time. The only appliations that are treated as
1419 -- static are *saturated* applications of constructors.
1421 -- We used to try to be clever with nested structures like this:
1422 -- ys = (:) w ((:) w [])
1423 -- on the grounds that CorePrep will flatten ANF-ise it later.
1424 -- But supporting this special case made the function much more
1425 -- complicated, because the special case only applies if there are no
1426 -- enclosing type lambdas:
1427 -- ys = /\ a -> Foo (Baz ([] a))
1428 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1430 -- But in fact, even without -O, nested structures at top level are
1431 -- flattened by the simplifier, so we don't need to be super-clever here.
1435 -- f = \x::Int. x+7 TRUE
1436 -- p = (True,False) TRUE
1438 -- d = (fst p, False) FALSE because there's a redex inside
1439 -- (this particular one doesn't happen but...)
1441 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1442 -- n = /\a. Nil a TRUE
1444 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1447 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1448 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1450 -- b) (C x xs), where C is a contructors is updatable if the application is
1453 -- c) don't look through unfolding of f in (f x).
1455 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1456 -- them as making the RHS re-entrant (non-updatable).
1458 rhsIsStatic this_pkg rhs = is_static False rhs
1460 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1463 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1465 is_static in_arg (Note (SCC _) e) = False
1466 is_static in_arg (Note (TickBox {}) e) = False
1467 is_static in_arg (Note (BinaryTickBox {}) e) = False
1468 is_static in_arg (Note _ e) = is_static in_arg e
1469 is_static in_arg (Cast e co) = is_static in_arg e
1471 is_static in_arg (Lit lit)
1473 MachLabel _ _ -> False
1475 -- A MachLabel (foreign import "&foo") in an argument
1476 -- prevents a constructor application from being static. The
1477 -- reason is that it might give rise to unresolvable symbols
1478 -- in the object file: under Linux, references to "weak"
1479 -- symbols from the data segment give rise to "unresolvable
1480 -- relocation" errors at link time This might be due to a bug
1481 -- in the linker, but we'll work around it here anyway.
1484 is_static in_arg other_expr = go other_expr 0
1486 go (Var f) n_val_args
1487 #if mingw32_TARGET_OS
1488 | not (isDllName this_pkg (idName f))
1490 = saturated_data_con f n_val_args
1491 || (in_arg && n_val_args == 0)
1492 -- A naked un-applied variable is *not* deemed a static RHS
1494 -- Reason: better to update so that the indirection gets shorted
1495 -- out, and the true value will be seen
1496 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1497 -- are always updatable. If you do so, make sure that non-updatable
1498 -- ones have enough space for their static link field!
1500 go (App f a) n_val_args
1501 | isTypeArg a = go f n_val_args
1502 | not in_arg && is_static True a = go f (n_val_args + 1)
1503 -- The (not in_arg) checks that we aren't in a constructor argument;
1504 -- if we are, we don't allow (value) applications of any sort
1506 -- NB. In case you wonder, args are sometimes not atomic. eg.
1507 -- x = D# (1.0## /## 2.0##)
1508 -- can't float because /## can fail.
1510 go (Note (SCC _) f) n_val_args = False
1511 go (Note _ f) n_val_args = go f n_val_args
1512 go (Cast e co) n_val_args = go e n_val_args
1514 go other n_val_args = False
1516 saturated_data_con f n_val_args
1517 = case isDataConWorkId_maybe f of
1518 Just dc -> n_val_args == dataConRepArity dc