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"
77 import GHC.Exts -- For `xori`
81 %************************************************************************
83 \subsection{Find the type of a Core atom/expression}
85 %************************************************************************
88 exprType :: CoreExpr -> Type
90 exprType (Var var) = idType var
91 exprType (Lit lit) = literalType lit
92 exprType (Let _ body) = exprType body
93 exprType (Case _ _ ty alts) = ty
95 = let (_, ty) = coercionKind co in ty
96 exprType (Note other_note e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 coreAltType (_,_,rhs) = exprType rhs
108 @mkPiType@ makes a (->) type or a forall type, depending on whether
109 it is given a type variable or a term variable. We cleverly use the
110 lbvarinfo field to figure out the right annotation for the arrove in
111 case of a term variable.
114 mkPiType :: Var -> Type -> Type -- The more polymorphic version
115 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
117 mkPiTypes vs ty = foldr mkPiType ty vs
120 | isId v = mkFunTy (idType v) ty
121 | otherwise = mkForAllTy v ty
125 applyTypeToArg :: Type -> CoreExpr -> Type
126 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
127 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
129 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
130 -- A more efficient version of applyTypeToArg
131 -- when we have several args
132 -- The first argument is just for debugging
133 applyTypeToArgs e op_ty [] = op_ty
135 applyTypeToArgs e op_ty (Type ty : args)
136 = -- Accumulate type arguments so we can instantiate all at once
139 go rev_tys (Type ty : args) = go (ty:rev_tys) args
140 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
142 op_ty' = applyTys op_ty (reverse rev_tys)
144 applyTypeToArgs e op_ty (other_arg : args)
145 = case (splitFunTy_maybe op_ty) of
146 Just (_, res_ty) -> applyTypeToArgs e res_ty args
147 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
152 %************************************************************************
154 \subsection{Attaching notes}
156 %************************************************************************
158 mkNote removes redundant coercions, and SCCs where possible
162 mkNote :: Note -> CoreExpr -> CoreExpr
163 mkNote (SCC cc) expr = mkSCC cc expr
164 mkNote InlineMe expr = mkInlineMe expr
165 mkNote note expr = Note note expr
169 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
170 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
171 not be *applied* to anything.
173 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
176 f = inline_me (coerce t fw)
177 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
178 We want the split, so that the coerces can cancel at the call site.
180 However, we can get left with tiresome type applications. Notably, consider
181 f = /\ a -> let t = e in (t, w)
182 Then lifting the let out of the big lambda gives
184 f = /\ a -> let t = inline_me (t' a) in (t, w)
185 The inline_me is to stop the simplifier inlining t' right back
186 into t's RHS. In the next phase we'll substitute for t (since
187 its rhs is trivial) and *then* we could get rid of the inline_me.
188 But it hardly seems worth it, so I don't bother.
191 mkInlineMe (Var v) = Var v
192 mkInlineMe e = Note InlineMe e
198 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
199 mkCoerce co (Cast expr co2)
200 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
201 (_from_ty2, to_ty2) = coercionKind co2} in
202 from_ty `coreEqType` to_ty2 )
203 mkCoerce (mkTransCoercion co2 co) expr
206 = let (from_ty, to_ty) = coercionKind co in
207 -- if to_ty `coreEqType` from_ty
210 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
215 mkSCC :: CostCentre -> Expr b -> Expr b
216 -- Note: Nested SCC's *are* preserved for the benefit of
217 -- cost centre stack profiling
218 mkSCC cc (Lit lit) = Lit lit
219 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
220 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
221 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
222 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
223 mkSCC cc expr = Note (SCC cc) expr
227 %************************************************************************
229 \subsection{Other expression construction}
231 %************************************************************************
234 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
235 -- (bindNonRec x r b) produces either
238 -- case r of x { _DEFAULT_ -> b }
240 -- depending on whether x is unlifted or not
241 -- It's used by the desugarer to avoid building bindings
242 -- that give Core Lint a heart attack. Actually the simplifier
243 -- deals with them perfectly well.
245 bindNonRec bndr rhs body
246 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
247 | otherwise = Let (NonRec bndr rhs) body
249 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
250 -- Make a case expression instead of a let
251 -- These can arise either from the desugarer,
252 -- or from beta reductions: (\x.e) (x +# y)
256 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
257 -- This guy constructs the value that the scrutinee must have
258 -- when you are in one particular branch of a case
259 mkAltExpr (DataAlt con) args inst_tys
260 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
261 mkAltExpr (LitAlt lit) [] []
264 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
265 mkIfThenElse guard then_expr else_expr
266 -- Not going to be refining, so okay to take the type of the "then" clause
267 = Case guard (mkWildId boolTy) (exprType then_expr)
268 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
269 (DataAlt trueDataCon, [], then_expr) ]
273 %************************************************************************
275 \subsection{Taking expressions apart}
277 %************************************************************************
279 The default alternative must be first, if it exists at all.
280 This makes it easy to find, though it makes matching marginally harder.
283 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
284 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
285 findDefault alts = (alts, Nothing)
287 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
290 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
291 other -> go alts panic_deflt
293 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
296 go (alt@(con1,_,_) : alts) deflt
297 = case con `cmpAltCon` con1 of
298 LT -> deflt -- Missed it already; the alts are in increasing order
300 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
302 isDefaultAlt :: CoreAlt -> Bool
303 isDefaultAlt (DEFAULT, _, _) = True
304 isDefaultAlt other = False
306 ---------------------------------
307 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
308 -- Merge preserving order; alternatives in the first arg
309 -- shadow ones in the second
310 mergeAlts [] as2 = as2
311 mergeAlts as1 [] = as1
312 mergeAlts (a1:as1) (a2:as2)
313 = case a1 `cmpAlt` a2 of
314 LT -> a1 : mergeAlts as1 (a2:as2)
315 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
316 GT -> a2 : mergeAlts (a1:as1) as2
320 %************************************************************************
322 \subsection{Figuring out things about expressions}
324 %************************************************************************
326 @exprIsTrivial@ is true of expressions we are unconditionally happy to
327 duplicate; simple variables and constants, and type
328 applications. Note that primop Ids aren't considered
331 @exprIsBottom@ is true of expressions that are guaranteed to diverge
334 There used to be a gruesome test for (hasNoBinding v) in the
336 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
337 The idea here is that a constructor worker, like $wJust, is
338 really short for (\x -> $wJust x), becuase $wJust has no binding.
339 So it should be treated like a lambda. Ditto unsaturated primops.
340 But now constructor workers are not "have-no-binding" Ids. And
341 completely un-applied primops and foreign-call Ids are sufficiently
342 rare that I plan to allow them to be duplicated and put up with
345 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
346 a) it really generates code, (and a heap object when it's
347 a function arg) to capture the cost centre
348 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
351 exprIsTrivial (Var v) = True -- See notes above
352 exprIsTrivial (Type _) = True
353 exprIsTrivial (Lit lit) = litIsTrivial lit
354 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
355 exprIsTrivial (Note (SCC _) e) = False -- See notes above
356 exprIsTrivial (Note _ e) = exprIsTrivial e
357 exprIsTrivial (Cast e co) = exprIsTrivial e
358 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
359 exprIsTrivial other = False
363 @exprIsDupable@ is true of expressions that can be duplicated at a modest
364 cost in code size. This will only happen in different case
365 branches, so there's no issue about duplicating work.
367 That is, exprIsDupable returns True of (f x) even if
368 f is very very expensive to call.
370 Its only purpose is to avoid fruitless let-binding
371 and then inlining of case join points
375 exprIsDupable (Type _) = True
376 exprIsDupable (Var v) = True
377 exprIsDupable (Lit lit) = litIsDupable lit
378 exprIsDupable (Note InlineMe e) = True
379 exprIsDupable (Note _ e) = exprIsDupable e
380 exprIsDupable (Cast e co) = exprIsDupable e
384 go (Var v) n_args = True
385 go (App f a) n_args = n_args < dupAppSize
388 go other n_args = False
391 dupAppSize = 4 -- Size of application we are prepared to duplicate
394 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
395 it is obviously in weak head normal form, or is cheap to get to WHNF.
396 [Note that that's not the same as exprIsDupable; an expression might be
397 big, and hence not dupable, but still cheap.]
399 By ``cheap'' we mean a computation we're willing to:
400 push inside a lambda, or
401 inline at more than one place
402 That might mean it gets evaluated more than once, instead of being
403 shared. The main examples of things which aren't WHNF but are
408 (where e, and all the ei are cheap)
411 (where e and b are cheap)
414 (where op is a cheap primitive operator)
417 (because we are happy to substitute it inside a lambda)
419 Notice that a variable is considered 'cheap': we can push it inside a lambda,
420 because sharing will make sure it is only evaluated once.
423 exprIsCheap :: CoreExpr -> Bool
424 exprIsCheap (Lit lit) = True
425 exprIsCheap (Type _) = True
426 exprIsCheap (Var _) = True
427 exprIsCheap (Note InlineMe e) = True
428 exprIsCheap (Note _ e) = exprIsCheap e
429 exprIsCheap (Cast e co) = exprIsCheap e
430 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
431 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
432 and [exprIsCheap rhs | (_,_,rhs) <- alts]
433 -- Experimentally, treat (case x of ...) as cheap
434 -- (and case __coerce x etc.)
435 -- This improves arities of overloaded functions where
436 -- there is only dictionary selection (no construction) involved
437 exprIsCheap (Let (NonRec x _) e)
438 | isUnLiftedType (idType x) = exprIsCheap e
440 -- strict lets always have cheap right hand sides,
441 -- and do no allocation.
443 exprIsCheap other_expr -- Applications and variables
446 -- Accumulate value arguments, then decide
447 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
448 | otherwise = go f val_args
450 go (Var f) [] = True -- Just a type application of a variable
451 -- (f t1 t2 t3) counts as WHNF
453 = case globalIdDetails f of
454 RecordSelId {} -> go_sel args
455 ClassOpId _ -> go_sel args
456 PrimOpId op -> go_primop op args
458 DataConWorkId _ -> go_pap args
459 other | length args < idArity f -> go_pap args
461 other -> isBottomingId f
462 -- Application of a function which
463 -- always gives bottom; we treat this as cheap
464 -- because it certainly doesn't need to be shared!
466 go other args = False
469 go_pap args = all exprIsTrivial args
470 -- For constructor applications and primops, check that all
471 -- the args are trivial. We don't want to treat as cheap, say,
473 -- We'll put up with one constructor application, but not dozens
476 go_primop op args = primOpIsCheap op && all exprIsCheap args
477 -- In principle we should worry about primops
478 -- that return a type variable, since the result
479 -- might be applied to something, but I'm not going
480 -- to bother to check the number of args
483 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
484 go_sel other = False -- look cheap, so we will substitute it inside a
485 -- lambda. Particularly for dictionary field selection.
486 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
487 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
490 exprOkForSpeculation returns True of an expression that it is
492 * safe to evaluate even if normal order eval might not
493 evaluate the expression at all, or
495 * safe *not* to evaluate even if normal order would do so
499 the expression guarantees to terminate,
501 without raising an exception,
502 without causing a side effect (e.g. writing a mutable variable)
504 NB: if exprIsHNF e, then exprOkForSpecuation e
507 let x = case y# +# 1# of { r# -> I# r# }
510 case y# +# 1# of { r# ->
515 We can only do this if the (y+1) is ok for speculation: it has no
516 side effects, and can't diverge or raise an exception.
519 exprOkForSpeculation :: CoreExpr -> Bool
520 exprOkForSpeculation (Lit _) = True
521 exprOkForSpeculation (Type _) = True
522 -- Tick boxes are *not* suitable for speculation
523 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
524 && not (isTickBoxOp v)
525 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
526 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
527 exprOkForSpeculation other_expr
528 = case collectArgs other_expr of
529 (Var f, args) -> spec_ok (globalIdDetails f) args
533 spec_ok (DataConWorkId _) args
534 = True -- The strictness of the constructor has already
535 -- been expressed by its "wrapper", so we don't need
536 -- to take the arguments into account
538 spec_ok (PrimOpId op) args
539 | isDivOp op, -- Special case for dividing operations that fail
540 [arg1, Lit lit] <- args -- only if the divisor is zero
541 = not (isZeroLit lit) && exprOkForSpeculation arg1
542 -- Often there is a literal divisor, and this
543 -- can get rid of a thunk in an inner looop
546 = primOpOkForSpeculation op &&
547 all exprOkForSpeculation args
548 -- A bit conservative: we don't really need
549 -- to care about lazy arguments, but this is easy
551 spec_ok other args = False
553 isDivOp :: PrimOp -> Bool
554 -- True of dyadic operators that can fail
555 -- only if the second arg is zero
556 -- This function probably belongs in PrimOp, or even in
557 -- an automagically generated file.. but it's such a
558 -- special case I thought I'd leave it here for now.
559 isDivOp IntQuotOp = True
560 isDivOp IntRemOp = True
561 isDivOp WordQuotOp = True
562 isDivOp WordRemOp = True
563 isDivOp IntegerQuotRemOp = True
564 isDivOp IntegerDivModOp = True
565 isDivOp FloatDivOp = True
566 isDivOp DoubleDivOp = True
567 isDivOp other = False
572 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
573 exprIsBottom e = go 0 e
575 -- n is the number of args
576 go n (Note _ e) = go n e
577 go n (Cast e co) = go n e
578 go n (Let _ e) = go n e
579 go n (Case e _ _ _) = go 0 e -- Just check the scrut
580 go n (App e _) = go (n+1) e
581 go n (Var v) = idAppIsBottom v n
583 go n (Lam _ _) = False
584 go n (Type _) = False
586 idAppIsBottom :: Id -> Int -> Bool
587 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
590 @exprIsHNF@ returns true for expressions that are certainly *already*
591 evaluated to *head* normal form. This is used to decide whether it's ok
594 case x of _ -> e ===> e
596 and to decide whether it's safe to discard a `seq`
598 So, it does *not* treat variables as evaluated, unless they say they are.
600 But it *does* treat partial applications and constructor applications
601 as values, even if their arguments are non-trivial, provided the argument
603 e.g. (:) (f x) (map f xs) is a value
604 map (...redex...) is a value
605 Because `seq` on such things completes immediately
607 For unlifted argument types, we have to be careful:
609 Suppose (f x) diverges; then C (f x) is not a value. However this can't
610 happen: see CoreSyn Note [CoreSyn let/app invariant]. Args of unboxed
611 type must be ok-for-speculation (or trivial).
614 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
615 exprIsHNF (Var v) -- NB: There are no value args at this point
616 = isDataConWorkId v -- Catches nullary constructors,
617 -- so that [] and () are values, for example
618 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
619 || isEvaldUnfolding (idUnfolding v)
620 -- Check the thing's unfolding; it might be bound to a value
621 -- A worry: what if an Id's unfolding is just itself:
622 -- then we could get an infinite loop...
624 exprIsHNF (Lit l) = True
625 exprIsHNF (Type ty) = True -- Types are honorary Values;
626 -- we don't mind copying them
627 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
628 exprIsHNF (Note _ e) = exprIsHNF e
629 exprIsHNF (Cast e co) = exprIsHNF e
630 exprIsHNF (App e (Type _)) = exprIsHNF e
631 exprIsHNF (App e a) = app_is_value e [a]
632 exprIsHNF other = False
634 -- There is at least one value argument
635 app_is_value (Var fun) args
636 = idArity fun > valArgCount args -- Under-applied function
637 || isDataConWorkId fun -- or data constructor
638 app_is_value (Note n f) as = app_is_value f as
639 app_is_value (Cast f _) as = app_is_value f as
640 app_is_value (App f a) as = app_is_value f (a:as)
641 app_is_value other as = False
645 -- These InstPat functions go here to avoid circularity between DataCon and Id
646 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
647 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
648 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
650 dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc
651 -- Remember to include the existential dictionaries
653 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
654 -> [FastString] -- A long enough list of FSs to use for names
655 -> [Unique] -- An equally long list of uniques, at least one for each binder
657 -> [Type] -- Types to instantiate the universally quantified tyvars
658 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
659 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
660 -- (ex_tvs, co_tvs, arg_ids),
662 -- ex_tvs are intended to be used as binders for existential type args
664 -- co_tvs are intended to be used as binders for coercion args and the kinds
665 -- of these vars have been instantiated by the inst_tys and the ex_tys
667 -- arg_ids are indended to be used as binders for value arguments, including
668 -- dicts, and their types have been instantiated with inst_tys and ex_tys
671 -- The following constructor T1
674 -- T1 :: forall b. Int -> b -> T(a,b)
677 -- has representation type
678 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
681 -- dataConInstPat fss us T1 (a1',b') will return
683 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
685 -- where the double-primed variables are created with the FastStrings and
686 -- Uniques given as fss and us
687 dataConInstPat arg_fun fss uniqs con inst_tys
688 = (ex_bndrs, co_bndrs, id_bndrs)
690 univ_tvs = dataConUnivTyVars con
691 ex_tvs = dataConExTyVars con
692 arg_tys = arg_fun con
693 eq_spec = dataConEqSpec con
694 eq_preds = eqSpecPreds eq_spec
697 n_co = length eq_spec
699 -- split the Uniques and FastStrings
700 (ex_uniqs, uniqs') = splitAt n_ex uniqs
701 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
703 (ex_fss, fss') = splitAt n_ex fss
704 (co_fss, id_fss) = splitAt n_co fss'
706 -- Make existential type variables
707 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
708 mk_ex_var uniq fs var = mkTyVar new_name kind
710 new_name = mkSysTvName uniq fs
713 -- Make the instantiating substitution
714 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
716 -- Make new coercion vars, instantiating kind
717 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
718 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
720 new_name = mkSysTvName uniq fs
721 co_kind = substTy subst (mkPredTy eq_pred)
723 -- make value vars, instantiating types
724 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcLoc
725 id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys
727 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
728 -- Returns (Just (dc, [x1..xn])) if the argument expression is
729 -- a constructor application of the form (dc x1 .. xn)
730 exprIsConApp_maybe (Cast expr co)
731 = -- Here we do the PushC reduction rule as described in the FC paper
732 case exprIsConApp_maybe expr of {
734 Just (dc, dc_args) ->
736 -- The transformation applies iff we have
737 -- (C e1 ... en) `cast` co
738 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
739 -- That is, with a T at the top of both sides
740 -- The left-hand one must be a T, because exprIsConApp returned True
741 -- but the right-hand one might not be. (Though it usually will.)
743 let (from_ty, to_ty) = coercionKind co
744 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
745 -- The inner one must be a TyConApp
747 case splitTyConApp_maybe to_ty of {
749 Just (to_tc, to_tc_arg_tys)
750 | from_tc /= to_tc -> Nothing
751 -- These two Nothing cases are possible; we might see
752 -- (C x y) `cast` (g :: T a ~ S [a]),
753 -- where S is a type function. In fact, exprIsConApp
754 -- will probably not be called in such circumstances,
755 -- but there't nothing wrong with it
759 tc_arity = tyConArity from_tc
761 (univ_args, rest1) = splitAt tc_arity dc_args
762 (ex_args, rest2) = splitAt n_ex_tvs rest1
763 (co_args, val_args) = splitAt n_cos rest2
765 arg_tys = dataConRepArgTys dc
766 dc_univ_tyvars = dataConUnivTyVars dc
767 dc_ex_tyvars = dataConExTyVars dc
768 dc_eq_spec = dataConEqSpec dc
769 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
770 n_ex_tvs = length dc_ex_tyvars
771 n_cos = length dc_eq_spec
773 -- Make the "theta" from Fig 3 of the paper
774 gammas = decomposeCo tc_arity co
775 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
776 theta = zipOpenTvSubst dc_tyvars new_tys
778 -- First we cast the existential coercion arguments
779 cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
781 `mkTransCoercion` (substTy theta ty)
782 new_co_args = zipWith cast_co dc_eq_spec co_args
784 -- ...and now value arguments
785 new_val_args = zipWith cast_arg arg_tys val_args
786 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
789 ASSERT( length univ_args == tc_arity )
790 ASSERT( from_tc == dataConTyCon dc )
791 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
792 ASSERT( all isTypeArg (univ_args ++ ex_args) )
793 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 )
795 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
799 -- We do not want to tell the world that we have a
800 -- Cons, to *stop* Case of Known Cons, which removes
802 exprIsConApp_maybe (Note (TickBox {}) expr)
804 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
808 exprIsConApp_maybe (Note _ expr)
809 = exprIsConApp_maybe expr
810 -- We ignore InlineMe notes in case we have
811 -- x = __inline_me__ (a,b)
812 -- All part of making sure that INLINE pragmas never hurt
813 -- Marcin tripped on this one when making dictionaries more inlinable
815 -- In fact, we ignore all notes. For example,
816 -- case _scc_ "foo" (C a b) of
818 -- should be optimised away, but it will be only if we look
819 -- through the SCC note.
821 exprIsConApp_maybe expr = analyse (collectArgs expr)
823 analyse (Var fun, args)
824 | Just con <- isDataConWorkId_maybe fun,
825 args `lengthAtLeast` dataConRepArity con
826 -- Might be > because the arity excludes type args
829 -- Look through unfoldings, but only cheap ones, because
830 -- we are effectively duplicating the unfolding
831 analyse (Var fun, [])
832 | let unf = idUnfolding fun,
834 = exprIsConApp_maybe (unfoldingTemplate unf)
836 analyse other = Nothing
841 %************************************************************************
843 \subsection{Eta reduction and expansion}
845 %************************************************************************
848 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
849 {- The Arity returned is the number of value args the
850 thing can be applied to without doing much work
852 exprEtaExpandArity is used when eta expanding
855 It returns 1 (or more) to:
856 case x of p -> \s -> ...
857 because for I/O ish things we really want to get that \s to the top.
858 We are prepared to evaluate x each time round the loop in order to get that
860 It's all a bit more subtle than it looks:
864 Consider one-shot lambdas
865 let x = expensive in \y z -> E
866 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
867 Hence the ArityType returned by arityType
869 2. The state-transformer hack
871 The one-shot lambda special cause is particularly important/useful for
872 IO state transformers, where we often get
873 let x = E in \ s -> ...
875 and the \s is a real-world state token abstraction. Such abstractions
876 are almost invariably 1-shot, so we want to pull the \s out, past the
877 let x=E, even if E is expensive. So we treat state-token lambdas as
878 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
880 3. Dealing with bottom
883 f = \x -> error "foo"
884 Here, arity 1 is fine. But if it is
888 then we want to get arity 2. Tecnically, this isn't quite right, because
890 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
891 do so; it improves some programs significantly, and increasing convergence
892 isn't a bad thing. Hence the ABot/ATop in ArityType.
894 Actually, the situation is worse. Consider
898 Can we eta-expand here? At first the answer looks like "yes of course", but
901 This should diverge! But if we eta-expand, it won't. Again, we ignore this
902 "problem", because being scrupulous would lose an important transformation for
908 Non-recursive newtypes are transparent, and should not get in the way.
909 We do (currently) eta-expand recursive newtypes too. So if we have, say
911 newtype T = MkT ([T] -> Int)
915 where f has arity 1. Then: etaExpandArity e = 1;
916 that is, etaExpandArity looks through the coerce.
918 When we eta-expand e to arity 1: eta_expand 1 e T
919 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
921 HOWEVER, note that if you use coerce bogusly you can ge
923 And since negate has arity 2, you might try to eta expand. But you can't
924 decopose Int to a function type. Hence the final case in eta_expand.
928 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
930 -- A limited sort of function type
931 data ArityType = AFun Bool ArityType -- True <=> one-shot
932 | ATop -- Know nothing
935 arityDepth :: ArityType -> Arity
936 arityDepth (AFun _ ty) = 1 + arityDepth ty
939 andArityType ABot at2 = at2
940 andArityType ATop at2 = ATop
941 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
942 andArityType at1 at2 = andArityType at2 at1
944 arityType :: DynFlags -> CoreExpr -> ArityType
945 -- (go1 e) = [b1,..,bn]
946 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
947 -- where bi is True <=> the lambda is one-shot
949 arityType dflags (Note n e) = arityType dflags e
950 -- Not needed any more: etaExpand is cleverer
951 -- | ok_note n = arityType dflags e
952 -- | otherwise = ATop
954 arityType dflags (Cast e co) = arityType dflags e
956 arityType dflags (Var v)
957 = mk (idArity v) (arg_tys (idType v))
959 mk :: Arity -> [Type] -> ArityType
960 -- The argument types are only to steer the "state hack"
961 -- Consider case x of
963 -- False -> \(s:RealWorld) -> e
964 -- where foo has arity 1. Then we want the state hack to
965 -- apply to foo too, so we can eta expand the case.
966 mk 0 tys | isBottomingId v = ABot
967 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
969 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
970 mk n [] = AFun False (mk (n-1) [])
972 arg_tys :: Type -> [Type] -- Ignore for-alls
974 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
975 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
978 -- Lambdas; increase arity
979 arityType dflags (Lam x e)
980 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
981 | otherwise = arityType dflags e
983 -- Applications; decrease arity
984 arityType dflags (App f (Type _)) = arityType dflags f
985 arityType dflags (App f a) = case arityType dflags f of
986 AFun one_shot xs | exprIsCheap a -> xs
989 -- Case/Let; keep arity if either the expression is cheap
990 -- or it's a 1-shot lambda
991 -- The former is not really right for Haskell
992 -- f x = case x of { (a,b) -> \y. e }
994 -- f x y = case x of { (a,b) -> e }
995 -- The difference is observable using 'seq'
996 arityType dflags (Case scrut _ _ alts)
997 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
998 xs | exprIsCheap scrut -> xs
999 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1002 arityType dflags (Let b e)
1003 = case arityType dflags e of
1004 xs | cheap_bind b -> xs
1005 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1008 cheap_bind (NonRec b e) = is_cheap (b,e)
1009 cheap_bind (Rec prs) = all is_cheap prs
1010 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1012 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1013 -- dictionary bindings. This improves arities. Thereby, it also
1014 -- means that full laziness is less prone to floating out the
1015 -- application of a function to its dictionary arguments, which
1016 -- can thereby lose opportunities for fusion. Example:
1017 -- foo :: Ord a => a -> ...
1018 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1019 -- -- So foo has arity 1
1021 -- f = \x. foo dInt $ bar x
1023 -- The (foo DInt) is floated out, and makes ineffective a RULE
1024 -- foo (bar x) = ...
1026 -- One could go further and make exprIsCheap reply True to any
1027 -- dictionary-typed expression, but that's more work.
1029 arityType dflags other = ATop
1031 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1032 ok_note InlineMe = False
1033 ok_note other = True
1034 -- Notice that we do not look through __inline_me__
1035 -- This may seem surprising, but consider
1036 -- f = _inline_me (\x -> e)
1037 -- We DO NOT want to eta expand this to
1038 -- f = \x -> (_inline_me (\x -> e)) x
1039 -- because the _inline_me gets dropped now it is applied,
1048 etaExpand :: Arity -- Result should have this number of value args
1050 -> CoreExpr -> Type -- Expression and its type
1052 -- (etaExpand n us e ty) returns an expression with
1053 -- the same meaning as 'e', but with arity 'n'.
1055 -- Given e' = etaExpand n us e ty
1057 -- ty = exprType e = exprType e'
1059 -- Note that SCCs are not treated specially. If we have
1060 -- etaExpand 2 (\x -> scc "foo" e)
1061 -- = (\xy -> (scc "foo" e) y)
1062 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1064 etaExpand n us expr ty
1065 | manifestArity expr >= n = expr -- The no-op case
1067 = eta_expand n us expr ty
1070 -- manifestArity sees how many leading value lambdas there are
1071 manifestArity :: CoreExpr -> Arity
1072 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1073 | otherwise = manifestArity e
1074 manifestArity (Note _ e) = manifestArity e
1075 manifestArity (Cast e _) = manifestArity e
1078 -- etaExpand deals with for-alls. For example:
1080 -- where E :: forall a. a -> a
1082 -- (/\b. \y::a -> E b y)
1084 -- It deals with coerces too, though they are now rare
1085 -- so perhaps the extra code isn't worth it
1087 eta_expand n us expr ty
1089 -- The ILX code generator requires eta expansion for type arguments
1090 -- too, but alas the 'n' doesn't tell us how many of them there
1091 -- may be. So we eagerly eta expand any big lambdas, and just
1092 -- cross our fingers about possible loss of sharing in the ILX case.
1093 -- The Right Thing is probably to make 'arity' include
1094 -- type variables throughout the compiler. (ToDo.)
1096 -- Saturated, so nothing to do
1099 -- Short cut for the case where there already
1100 -- is a lambda; no point in gratuitously adding more
1101 eta_expand n us (Lam v body) ty
1103 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1106 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1108 -- We used to have a special case that stepped inside Coerces here,
1109 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1110 -- = Note note (eta_expand n us e ty)
1111 -- BUT this led to an infinite loop
1112 -- Example: newtype T = MkT (Int -> Int)
1113 -- eta_expand 1 (coerce (Int->Int) e)
1114 -- --> coerce (Int->Int) (eta_expand 1 T e)
1116 -- --> coerce (Int->Int) (coerce T
1117 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1118 -- by the splitNewType_maybe case below
1121 eta_expand n us expr ty
1122 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1123 case splitForAllTy_maybe ty of {
1126 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1128 lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
1129 -- Using tv as a base retains its tyvar/covar-ness
1133 case splitFunTy_maybe ty of {
1134 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1136 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1142 -- newtype T = MkT ([T] -> Int)
1143 -- Consider eta-expanding this
1146 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1148 case splitNewTypeRepCo_maybe ty of {
1150 mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ;
1153 -- We have an expression of arity > 0, but its type isn't a function
1154 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1155 -- Essentially the programmer is playing fast and loose with types
1156 -- (Happy does this a lot). So we simply decline to eta-expand.
1161 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1162 It tells how many things the expression can be applied to before doing
1163 any work. It doesn't look inside cases, lets, etc. The idea is that
1164 exprEtaExpandArity will do the hard work, leaving something that's easy
1165 for exprArity to grapple with. In particular, Simplify uses exprArity to
1166 compute the ArityInfo for the Id.
1168 Originally I thought that it was enough just to look for top-level lambdas, but
1169 it isn't. I've seen this
1171 foo = PrelBase.timesInt
1173 We want foo to get arity 2 even though the eta-expander will leave it
1174 unchanged, in the expectation that it'll be inlined. But occasionally it
1175 isn't, because foo is blacklisted (used in a rule).
1177 Similarly, see the ok_note check in exprEtaExpandArity. So
1178 f = __inline_me (\x -> e)
1179 won't be eta-expanded.
1181 And in any case it seems more robust to have exprArity be a bit more intelligent.
1182 But note that (\x y z -> f x y z)
1183 should have arity 3, regardless of f's arity.
1186 exprArity :: CoreExpr -> Arity
1189 go (Var v) = idArity v
1190 go (Lam x e) | isId x = go e + 1
1192 go (Note n e) = go e
1193 go (Cast e _) = go e
1194 go (App e (Type t)) = go e
1195 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1196 -- NB: exprIsCheap a!
1197 -- f (fac x) does not have arity 2,
1198 -- even if f has arity 3!
1199 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1200 -- unknown, hence arity 0
1204 %************************************************************************
1206 \subsection{Equality}
1208 %************************************************************************
1210 @cheapEqExpr@ is a cheap equality test which bales out fast!
1211 True => definitely equal
1212 False => may or may not be equal
1215 cheapEqExpr :: Expr b -> Expr b -> Bool
1217 cheapEqExpr (Var v1) (Var v2) = v1==v2
1218 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1219 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1221 cheapEqExpr (App f1 a1) (App f2 a2)
1222 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1224 cheapEqExpr _ _ = False
1226 exprIsBig :: Expr b -> Bool
1227 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1228 exprIsBig (Lit _) = False
1229 exprIsBig (Var v) = False
1230 exprIsBig (Type t) = False
1231 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1232 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1233 exprIsBig other = True
1238 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1239 -- Used in rule matching, so does *not* look through
1240 -- newtypes, predicate types; hence tcEqExpr
1242 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1244 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1246 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1247 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1248 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1249 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1250 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1251 tcEqExprX env (Let (NonRec v1 r1) e1)
1252 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1253 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1254 tcEqExprX env (Let (Rec ps1) e1)
1255 (Let (Rec ps2) e2) = equalLength ps1 ps2
1256 && and (zipWith eq_rhs ps1 ps2)
1257 && tcEqExprX env' e1 e2
1259 env' = foldl2 rn_bndr2 env ps2 ps2
1260 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1261 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1262 tcEqExprX env (Case e1 v1 t1 a1)
1263 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1264 && tcEqTypeX env t1 t2
1265 && equalLength a1 a2
1266 && and (zipWith (eq_alt env') a1 a2)
1268 env' = rnBndr2 env v1 v2
1270 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1271 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1272 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1273 tcEqExprX env e1 e2 = False
1275 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1277 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1278 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1279 eq_note env other1 other2 = False
1283 %************************************************************************
1285 \subsection{The size of an expression}
1287 %************************************************************************
1290 coreBindsSize :: [CoreBind] -> Int
1291 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1293 exprSize :: CoreExpr -> Int
1294 -- A measure of the size of the expressions
1295 -- It also forces the expression pretty drastically as a side effect
1296 exprSize (Var v) = v `seq` 1
1297 exprSize (Lit lit) = lit `seq` 1
1298 exprSize (App f a) = exprSize f + exprSize a
1299 exprSize (Lam b e) = varSize b + exprSize e
1300 exprSize (Let b e) = bindSize b + exprSize e
1301 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1302 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1303 exprSize (Note n e) = noteSize n + exprSize e
1304 exprSize (Type t) = seqType t `seq` 1
1306 noteSize (SCC cc) = cc `seq` 1
1307 noteSize InlineMe = 1
1308 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1310 varSize :: Var -> Int
1311 varSize b | isTyVar b = 1
1312 | otherwise = seqType (idType b) `seq`
1313 megaSeqIdInfo (idInfo b) `seq`
1316 varsSize = foldr ((+) . varSize) 0
1318 bindSize (NonRec b e) = varSize b + exprSize e
1319 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1321 pairSize (b,e) = varSize b + exprSize e
1323 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1327 %************************************************************************
1329 \subsection{Hashing}
1331 %************************************************************************
1334 hashExpr :: CoreExpr -> Int
1335 -- Two expressions that hash to the same Int may be equal (but may not be)
1336 -- Two expressions that hash to the different Ints are definitely unequal
1338 -- But "unequal" here means "not identical"; two alpha-equivalent
1339 -- expressions may hash to the different Ints
1341 -- The emphasis is on a crude, fast hash, rather than on high precision
1343 -- We must be careful that \x.x and \y.y map to the same hash code,
1344 -- (at least if we want the above invariant to be true)
1346 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1347 -- UniqFM doesn't like negative Ints
1349 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1351 hash_expr :: HashEnv -> CoreExpr -> Word32
1352 -- Word32, because we're expecting overflows here, and overflowing
1353 -- signed types just isn't cool. In C it's even undefined.
1354 hash_expr env (Note _ e) = hash_expr env e
1355 hash_expr env (Cast e co) = hash_expr env e
1356 hash_expr env (Var v) = hashVar env v
1357 hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1358 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1359 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1360 hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
1361 hash_expr env (Case e _ _ _) = hash_expr env e
1362 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1363 hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1
1364 -- Shouldn't happen. Better to use WARN than trace, because trace
1365 -- prevents the CPR optimisation kicking in for hash_expr.
1367 fast_hash_expr env (Var v) = hashVar env v
1368 fast_hash_expr env (Type t) = fast_hash_type env t
1369 fast_hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1370 fast_hash_expr env (Cast e co) = fast_hash_expr env e
1371 fast_hash_expr env (Note n e) = fast_hash_expr env e
1372 fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1373 fast_hash_expr env other = 1
1375 fast_hash_type :: HashEnv -> Type -> Word32
1376 fast_hash_type env ty
1377 | Just tv <- getTyVar_maybe ty = hashVar env tv
1378 | Just (tc,_) <- splitTyConApp_maybe ty
1379 = fromIntegral (hashName (tyConName tc))
1382 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1383 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1385 hashVar :: HashEnv -> Var -> Word32
1387 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1390 %************************************************************************
1392 \subsection{Determining non-updatable right-hand-sides}
1394 %************************************************************************
1396 Top-level constructor applications can usually be allocated
1397 statically, but they can't if the constructor, or any of the
1398 arguments, come from another DLL (because we can't refer to static
1399 labels in other DLLs).
1401 If this happens we simply make the RHS into an updatable thunk,
1402 and 'exectute' it rather than allocating it statically.
1405 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1406 -- This function is called only on *top-level* right-hand sides
1407 -- Returns True if the RHS can be allocated statically, with
1408 -- no thunks involved at all.
1410 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1411 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1412 -- update flag on it.
1414 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1415 -- (a) a value lambda
1416 -- (b) a saturated constructor application with static args
1418 -- BUT watch out for
1419 -- (i) Any cross-DLL references kill static-ness completely
1420 -- because they must be 'executed' not statically allocated
1421 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1422 -- this is not necessary)
1424 -- (ii) We treat partial applications as redexes, because in fact we
1425 -- make a thunk for them that runs and builds a PAP
1426 -- at run-time. The only appliations that are treated as
1427 -- static are *saturated* applications of constructors.
1429 -- We used to try to be clever with nested structures like this:
1430 -- ys = (:) w ((:) w [])
1431 -- on the grounds that CorePrep will flatten ANF-ise it later.
1432 -- But supporting this special case made the function much more
1433 -- complicated, because the special case only applies if there are no
1434 -- enclosing type lambdas:
1435 -- ys = /\ a -> Foo (Baz ([] a))
1436 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1438 -- But in fact, even without -O, nested structures at top level are
1439 -- flattened by the simplifier, so we don't need to be super-clever here.
1443 -- f = \x::Int. x+7 TRUE
1444 -- p = (True,False) TRUE
1446 -- d = (fst p, False) FALSE because there's a redex inside
1447 -- (this particular one doesn't happen but...)
1449 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1450 -- n = /\a. Nil a TRUE
1452 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1455 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1456 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1458 -- b) (C x xs), where C is a contructors is updatable if the application is
1461 -- c) don't look through unfolding of f in (f x).
1463 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1464 -- them as making the RHS re-entrant (non-updatable).
1466 rhsIsStatic this_pkg rhs = is_static False rhs
1468 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1471 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1473 is_static in_arg (Note (SCC _) e) = False
1474 is_static in_arg (Note _ e) = is_static in_arg e
1475 is_static in_arg (Cast e co) = is_static in_arg e
1477 is_static in_arg (Lit lit)
1479 MachLabel _ _ -> False
1481 -- A MachLabel (foreign import "&foo") in an argument
1482 -- prevents a constructor application from being static. The
1483 -- reason is that it might give rise to unresolvable symbols
1484 -- in the object file: under Linux, references to "weak"
1485 -- symbols from the data segment give rise to "unresolvable
1486 -- relocation" errors at link time This might be due to a bug
1487 -- in the linker, but we'll work around it here anyway.
1490 is_static in_arg other_expr = go other_expr 0
1492 go (Var f) n_val_args
1493 #if mingw32_TARGET_OS
1494 | not (isDllName this_pkg (idName f))
1496 = saturated_data_con f n_val_args
1497 || (in_arg && n_val_args == 0)
1498 -- A naked un-applied variable is *not* deemed a static RHS
1500 -- Reason: better to update so that the indirection gets shorted
1501 -- out, and the true value will be seen
1502 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1503 -- are always updatable. If you do so, make sure that non-updatable
1504 -- ones have enough space for their static link field!
1506 go (App f a) n_val_args
1507 | isTypeArg a = go f n_val_args
1508 | not in_arg && is_static True a = go f (n_val_args + 1)
1509 -- The (not in_arg) checks that we aren't in a constructor argument;
1510 -- if we are, we don't allow (value) applications of any sort
1512 -- NB. In case you wonder, args are sometimes not atomic. eg.
1513 -- x = D# (1.0## /## 2.0##)
1514 -- can't float because /## can fail.
1516 go (Note (SCC _) f) n_val_args = False
1517 go (Note _ f) n_val_args = go f n_val_args
1518 go (Cast e co) n_val_args = go e n_val_args
1520 go other n_val_args = False
1522 saturated_data_con f n_val_args
1523 = case isDataConWorkId_maybe f of
1524 Just dc -> n_val_args == dataConRepArity dc