2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreUtils]{Utility functions on @Core@ syntax}
9 mkInlineMe, mkSCC, mkCoerce,
10 bindNonRec, needsCaseBinding,
11 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
13 -- Taking expressions apart
14 findDefault, findAlt, isDefaultAlt, mergeAlts,
16 -- Properties of expressions
17 exprType, coreAltType,
18 exprIsDupable, exprIsTrivial, exprIsCheap,
19 exprIsHNF,exprOkForSpeculation, exprIsBig,
20 exprIsConApp_maybe, exprIsBottom,
23 -- Arity and eta expansion
24 manifestArity, exprArity,
25 exprEtaExpandArity, etaExpand,
34 cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg
37 #include "HsVersions.h"
40 import GLAEXTS -- For `xori`
43 import CoreFVs ( exprFreeVars )
44 import PprCore ( pprCoreExpr )
45 import Var ( Var, TyVar )
46 import VarSet ( unionVarSet )
48 import Name ( hashName )
50 import Packages ( isDllName )
52 import Literal ( hashLiteral, literalType, litIsDupable,
53 litIsTrivial, isZeroLit, Literal( MachLabel ) )
54 import DataCon ( DataCon, dataConRepArity,
55 isVanillaDataCon, dataConTyCon, dataConRepArgTys,
57 import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
58 import Id ( Id, idType, globalIdDetails, idNewStrictness,
59 mkWildId, idArity, idName, idUnfolding, idInfo,
60 isOneShotBndr, isStateHackType, isDataConWorkId_maybe, mkSysLocal,
61 isDataConWorkId, isBottomingId, isDictId
63 import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo )
64 import NewDemand ( appIsBottom )
65 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
66 splitFunTy, tcEqTypeX,
67 applyTys, isUnLiftedType, seqType, mkTyVarTy,
68 splitForAllTy_maybe, isForAllTy, splitRecNewType_maybe,
69 splitTyConApp_maybe, coreEqType, funResultTy, applyTy,
72 import Coercion ( Coercion, mkTransCoercion, coercionKind,
73 splitRecNewTypeCo_maybe, mkSymCoercion, mkLeftCoercion,
74 mkRightCoercion, decomposeCo, coercionKindTyConApp )
75 import TyCon ( tyConArity )
76 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
77 import CostCentre ( CostCentre )
78 import BasicTypes ( Arity )
79 import PackageConfig ( PackageId )
80 import Unique ( Unique )
82 import DynFlags ( DynFlags, DynFlag(Opt_DictsCheap), dopt )
83 import TysPrim ( alphaTy ) -- Debugging only
84 import Util ( equalLength, lengthAtLeast, foldl2 )
88 %************************************************************************
90 \subsection{Find the type of a Core atom/expression}
92 %************************************************************************
95 exprType :: CoreExpr -> Type
97 exprType (Var var) = idType var
98 exprType (Lit lit) = literalType lit
99 exprType (Let _ body) = exprType body
100 exprType (Case _ _ ty alts) = ty
102 = let (_, ty) = coercionKind co in ty
103 exprType (Note other_note e) = exprType e
104 exprType (Lam binder expr) = mkPiType binder (exprType expr)
106 = case collectArgs e of
107 (fun, args) -> applyTypeToArgs e (exprType fun) args
109 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
111 coreAltType :: CoreAlt -> Type
112 coreAltType (_,_,rhs) = exprType rhs
115 @mkPiType@ makes a (->) type or a forall type, depending on whether
116 it is given a type variable or a term variable. We cleverly use the
117 lbvarinfo field to figure out the right annotation for the arrove in
118 case of a term variable.
121 mkPiType :: Var -> Type -> Type -- The more polymorphic version
122 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
124 mkPiTypes vs ty = foldr mkPiType ty vs
127 | isId v = mkFunTy (idType v) ty
128 | otherwise = mkForAllTy v ty
132 applyTypeToArg :: Type -> CoreExpr -> Type
133 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
134 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
136 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
137 -- A more efficient version of applyTypeToArg
138 -- when we have several args
139 -- The first argument is just for debugging
140 applyTypeToArgs e op_ty [] = op_ty
142 applyTypeToArgs e op_ty (Type ty : args)
143 = -- Accumulate type arguments so we can instantiate all at once
146 go rev_tys (Type ty : args) = go (ty:rev_tys) args
147 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
149 op_ty' = applyTys op_ty (reverse rev_tys)
151 applyTypeToArgs e op_ty (other_arg : args)
152 = case (splitFunTy_maybe op_ty) of
153 Just (_, res_ty) -> applyTypeToArgs e res_ty args
154 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
159 %************************************************************************
161 \subsection{Attaching notes}
163 %************************************************************************
165 mkNote removes redundant coercions, and SCCs where possible
169 mkNote :: Note -> CoreExpr -> CoreExpr
170 mkNote (SCC cc) expr = mkSCC cc expr
171 mkNote InlineMe expr = mkInlineMe expr
172 mkNote note expr = Note note expr
176 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
177 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
178 not be *applied* to anything.
180 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
183 f = inline_me (coerce t fw)
184 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
185 We want the split, so that the coerces can cancel at the call site.
187 However, we can get left with tiresome type applications. Notably, consider
188 f = /\ a -> let t = e in (t, w)
189 Then lifting the let out of the big lambda gives
191 f = /\ a -> let t = inline_me (t' a) in (t, w)
192 The inline_me is to stop the simplifier inlining t' right back
193 into t's RHS. In the next phase we'll substitute for t (since
194 its rhs is trivial) and *then* we could get rid of the inline_me.
195 But it hardly seems worth it, so I don't bother.
198 mkInlineMe (Var v) = Var v
199 mkInlineMe e = Note InlineMe e
205 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
206 mkCoerce co (Cast expr co2)
207 = ASSERT(let { (from_ty, to_ty) = coercionKind co;
208 (from_ty2, to_ty2) = coercionKind co2} in
209 from_ty `coreEqType` to_ty2 )
210 mkCoerce (mkTransCoercion co2 co) expr
213 = let (from_ty, to_ty) = coercionKind co in
214 -- if to_ty `coreEqType` from_ty
217 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindTyConApp co))
222 mkSCC :: CostCentre -> Expr b -> Expr b
223 -- Note: Nested SCC's *are* preserved for the benefit of
224 -- cost centre stack profiling
225 mkSCC cc (Lit lit) = Lit lit
226 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
227 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
228 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
229 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
230 mkSCC cc expr = Note (SCC cc) expr
234 %************************************************************************
236 \subsection{Other expression construction}
238 %************************************************************************
241 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
242 -- (bindNonRec x r b) produces either
245 -- case r of x { _DEFAULT_ -> b }
247 -- depending on whether x is unlifted or not
248 -- It's used by the desugarer to avoid building bindings
249 -- that give Core Lint a heart attack. Actually the simplifier
250 -- deals with them perfectly well.
252 bindNonRec bndr rhs body
253 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
254 | otherwise = Let (NonRec bndr rhs) body
256 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
257 -- Make a case expression instead of a let
258 -- These can arise either from the desugarer,
259 -- or from beta reductions: (\x.e) (x +# y)
263 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
264 -- This guy constructs the value that the scrutinee must have
265 -- when you are in one particular branch of a case
266 mkAltExpr (DataAlt con) args inst_tys
267 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
268 mkAltExpr (LitAlt lit) [] []
271 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
272 mkIfThenElse guard then_expr else_expr
273 -- Not going to be refining, so okay to take the type of the "then" clause
274 = Case guard (mkWildId boolTy) (exprType then_expr)
275 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
276 (DataAlt trueDataCon, [], then_expr) ]
280 %************************************************************************
282 \subsection{Taking expressions apart}
284 %************************************************************************
286 The default alternative must be first, if it exists at all.
287 This makes it easy to find, though it makes matching marginally harder.
290 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
291 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
292 findDefault alts = (alts, Nothing)
294 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
297 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
298 other -> go alts panic_deflt
300 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
303 go (alt@(con1,_,_) : alts) deflt
304 = case con `cmpAltCon` con1 of
305 LT -> deflt -- Missed it already; the alts are in increasing order
307 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
309 isDefaultAlt :: CoreAlt -> Bool
310 isDefaultAlt (DEFAULT, _, _) = True
311 isDefaultAlt other = False
313 ---------------------------------
314 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
315 -- Merge preserving order; alternatives in the first arg
316 -- shadow ones in the second
317 mergeAlts [] as2 = as2
318 mergeAlts as1 [] = as1
319 mergeAlts (a1:as1) (a2:as2)
320 = case a1 `cmpAlt` a2 of
321 LT -> a1 : mergeAlts as1 (a2:as2)
322 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
323 GT -> a2 : mergeAlts (a1:as1) as2
327 %************************************************************************
329 \subsection{Figuring out things about expressions}
331 %************************************************************************
333 @exprIsTrivial@ is true of expressions we are unconditionally happy to
334 duplicate; simple variables and constants, and type
335 applications. Note that primop Ids aren't considered
338 @exprIsBottom@ is true of expressions that are guaranteed to diverge
341 There used to be a gruesome test for (hasNoBinding v) in the
343 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
344 The idea here is that a constructor worker, like $wJust, is
345 really short for (\x -> $wJust x), becuase $wJust has no binding.
346 So it should be treated like a lambda. Ditto unsaturated primops.
347 But now constructor workers are not "have-no-binding" Ids. And
348 completely un-applied primops and foreign-call Ids are sufficiently
349 rare that I plan to allow them to be duplicated and put up with
352 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
353 a) it really generates code, (and a heap object when it's
354 a function arg) to capture the cost centre
355 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
358 exprIsTrivial (Var v) = True -- See notes above
359 exprIsTrivial (Type _) = True
360 exprIsTrivial (Lit lit) = litIsTrivial lit
361 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
362 exprIsTrivial (Note (SCC _) e) = False -- See notes above
363 exprIsTrivial (Note _ e) = exprIsTrivial e
364 exprIsTrivial (Cast e co) = exprIsTrivial e
365 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
366 exprIsTrivial other = False
370 @exprIsDupable@ is true of expressions that can be duplicated at a modest
371 cost in code size. This will only happen in different case
372 branches, so there's no issue about duplicating work.
374 That is, exprIsDupable returns True of (f x) even if
375 f is very very expensive to call.
377 Its only purpose is to avoid fruitless let-binding
378 and then inlining of case join points
382 exprIsDupable (Type _) = True
383 exprIsDupable (Var v) = True
384 exprIsDupable (Lit lit) = litIsDupable lit
385 exprIsDupable (Note InlineMe e) = True
386 exprIsDupable (Note _ e) = exprIsDupable e
387 exprIsDupable (Cast e co) = exprIsDupable e
391 go (Var v) n_args = True
392 go (App f a) n_args = n_args < dupAppSize
395 go other n_args = False
398 dupAppSize = 4 -- Size of application we are prepared to duplicate
401 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
402 it is obviously in weak head normal form, or is cheap to get to WHNF.
403 [Note that that's not the same as exprIsDupable; an expression might be
404 big, and hence not dupable, but still cheap.]
406 By ``cheap'' we mean a computation we're willing to:
407 push inside a lambda, or
408 inline at more than one place
409 That might mean it gets evaluated more than once, instead of being
410 shared. The main examples of things which aren't WHNF but are
415 (where e, and all the ei are cheap)
418 (where e and b are cheap)
421 (where op is a cheap primitive operator)
424 (because we are happy to substitute it inside a lambda)
426 Notice that a variable is considered 'cheap': we can push it inside a lambda,
427 because sharing will make sure it is only evaluated once.
430 exprIsCheap :: CoreExpr -> Bool
431 exprIsCheap (Lit lit) = True
432 exprIsCheap (Type _) = True
433 exprIsCheap (Var _) = True
434 exprIsCheap (Note InlineMe e) = True
435 exprIsCheap (Note _ e) = exprIsCheap e
436 exprIsCheap (Cast e co) = exprIsCheap e
437 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
438 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
439 and [exprIsCheap rhs | (_,_,rhs) <- alts]
440 -- Experimentally, treat (case x of ...) as cheap
441 -- (and case __coerce x etc.)
442 -- This improves arities of overloaded functions where
443 -- there is only dictionary selection (no construction) involved
444 exprIsCheap (Let (NonRec x _) e)
445 | isUnLiftedType (idType x) = exprIsCheap e
447 -- strict lets always have cheap right hand sides,
448 -- and do no allocation.
450 exprIsCheap other_expr -- Applications and variables
453 -- Accumulate value arguments, then decide
454 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
455 | otherwise = go f val_args
457 go (Var f) [] = True -- Just a type application of a variable
458 -- (f t1 t2 t3) counts as WHNF
460 = case globalIdDetails f of
461 RecordSelId {} -> go_sel args
462 ClassOpId _ -> go_sel args
463 PrimOpId op -> go_primop op args
465 DataConWorkId _ -> go_pap args
466 other | length args < idArity f -> go_pap args
468 other -> isBottomingId f
469 -- Application of a function which
470 -- always gives bottom; we treat this as cheap
471 -- because it certainly doesn't need to be shared!
473 go other args = False
476 go_pap args = all exprIsTrivial args
477 -- For constructor applications and primops, check that all
478 -- the args are trivial. We don't want to treat as cheap, say,
480 -- We'll put up with one constructor application, but not dozens
483 go_primop op args = primOpIsCheap op && all exprIsCheap args
484 -- In principle we should worry about primops
485 -- that return a type variable, since the result
486 -- might be applied to something, but I'm not going
487 -- to bother to check the number of args
490 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
491 go_sel other = False -- look cheap, so we will substitute it inside a
492 -- lambda. Particularly for dictionary field selection.
493 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
494 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
497 exprOkForSpeculation returns True of an expression that it is
499 * safe to evaluate even if normal order eval might not
500 evaluate the expression at all, or
502 * safe *not* to evaluate even if normal order would do so
506 the expression guarantees to terminate,
508 without raising an exception,
509 without causing a side effect (e.g. writing a mutable variable)
511 NB: if exprIsHNF e, then exprOkForSpecuation e
514 let x = case y# +# 1# of { r# -> I# r# }
517 case y# +# 1# of { r# ->
522 We can only do this if the (y+1) is ok for speculation: it has no
523 side effects, and can't diverge or raise an exception.
526 exprOkForSpeculation :: CoreExpr -> Bool
527 exprOkForSpeculation (Lit _) = True
528 exprOkForSpeculation (Type _) = True
529 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
530 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
531 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
532 exprOkForSpeculation other_expr
533 = case collectArgs other_expr of
534 (Var f, args) -> spec_ok (globalIdDetails f) args
538 spec_ok (DataConWorkId _) args
539 = True -- The strictness of the constructor has already
540 -- been expressed by its "wrapper", so we don't need
541 -- to take the arguments into account
543 spec_ok (PrimOpId op) args
544 | isDivOp op, -- Special case for dividing operations that fail
545 [arg1, Lit lit] <- args -- only if the divisor is zero
546 = not (isZeroLit lit) && exprOkForSpeculation arg1
547 -- Often there is a literal divisor, and this
548 -- can get rid of a thunk in an inner looop
551 = primOpOkForSpeculation op &&
552 all exprOkForSpeculation args
553 -- A bit conservative: we don't really need
554 -- to care about lazy arguments, but this is easy
556 spec_ok other args = False
558 isDivOp :: PrimOp -> Bool
559 -- True of dyadic operators that can fail
560 -- only if the second arg is zero
561 -- This function probably belongs in PrimOp, or even in
562 -- an automagically generated file.. but it's such a
563 -- special case I thought I'd leave it here for now.
564 isDivOp IntQuotOp = True
565 isDivOp IntRemOp = True
566 isDivOp WordQuotOp = True
567 isDivOp WordRemOp = True
568 isDivOp IntegerQuotRemOp = True
569 isDivOp IntegerDivModOp = True
570 isDivOp FloatDivOp = True
571 isDivOp DoubleDivOp = True
572 isDivOp other = False
577 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
578 exprIsBottom e = go 0 e
580 -- n is the number of args
581 go n (Note _ e) = go n e
582 go n (Cast e co) = go n e
583 go n (Let _ e) = go n e
584 go n (Case e _ _ _) = go 0 e -- Just check the scrut
585 go n (App e _) = go (n+1) e
586 go n (Var v) = idAppIsBottom v n
588 go n (Lam _ _) = False
589 go n (Type _) = False
591 idAppIsBottom :: Id -> Int -> Bool
592 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
595 @exprIsHNF@ returns true for expressions that are certainly *already*
596 evaluated to *head* normal form. This is used to decide whether it's ok
599 case x of _ -> e ===> e
601 and to decide whether it's safe to discard a `seq`
603 So, it does *not* treat variables as evaluated, unless they say they are.
605 But it *does* treat partial applications and constructor applications
606 as values, even if their arguments are non-trivial, provided the argument
608 e.g. (:) (f x) (map f xs) is a value
609 map (...redex...) is a value
610 Because `seq` on such things completes immediately
612 For unlifted argument types, we have to be careful:
614 Suppose (f x) diverges; then C (f x) is not a value. True, but
615 this form is illegal (see the invariants in CoreSyn). Args of unboxed
616 type must be ok-for-speculation (or trivial).
619 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
620 exprIsHNF (Var v) -- NB: There are no value args at this point
621 = isDataConWorkId v -- Catches nullary constructors,
622 -- so that [] and () are values, for example
623 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
624 || isEvaldUnfolding (idUnfolding v)
625 -- Check the thing's unfolding; it might be bound to a value
626 -- A worry: what if an Id's unfolding is just itself:
627 -- then we could get an infinite loop...
629 exprIsHNF (Lit l) = True
630 exprIsHNF (Type ty) = True -- Types are honorary Values;
631 -- we don't mind copying them
632 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
633 exprIsHNF (Note _ e) = exprIsHNF e
634 exprIsHNF (Cast e co) = exprIsHNF e
635 exprIsHNF (App e (Type _)) = exprIsHNF e
636 exprIsHNF (App e a) = app_is_value e [a]
637 exprIsHNF other = False
639 -- There is at least one value argument
640 app_is_value (Var fun) args
641 | isDataConWorkId fun -- Constructor apps are values
642 || idArity fun > valArgCount args -- Under-applied function
643 = check_args (idType fun) args
644 app_is_value (App f a) as = app_is_value f (a:as)
645 app_is_value other as = False
647 -- 'check_args' checks that unlifted-type args
648 -- are in fact guaranteed non-divergent
649 check_args fun_ty [] = True
650 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
651 Just (_, ty) -> check_args ty args
652 check_args fun_ty (arg : args)
653 | isUnLiftedType arg_ty = exprOkForSpeculation arg
654 | otherwise = check_args res_ty args
656 (arg_ty, res_ty) = splitFunTy fun_ty
660 -- deep applies a TyConApp coercion as a substitution to a reflexive coercion
661 -- deepCast t [a1,...,an] co corresponds to deep(t, [a1,...,an], co) from
663 deepCast :: Type -> [TyVar] -> Coercion -> Coercion
664 deepCast ty tyVars co
665 = ASSERT( let {(lty, rty) = coercionKind co;
666 Just (tc1, lArgs) = splitTyConApp_maybe lty;
667 Just (tc2, rArgs) = splitTyConApp_maybe rty}
669 tc1 == tc2 && length lArgs == length rArgs &&
670 length lArgs == length tyVars )
671 substTyWith tyVars coArgs ty
673 -- coArgs = [right (left (left co)), right (left co), right co]
674 coArgs = decomposeCo (length tyVars) co
676 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
677 -- Returns (Just (dc, [x1..xn])) if the argument expression is
678 -- a constructor application of the form (dc x1 .. xn)
680 exprIsConApp_maybe (Cast expr co)
681 = -- Maybe this is over the top, but here we try to turn
682 -- coerce (S,T) ( x, y )
684 -- ( coerce S x, coerce T y )
685 -- This happens in anger in PrelArrExts which has a coerce
686 -- case coerce memcpy a b of
688 -- where the memcpy is in the IO monad, but the call is in
690 let (from_ty, to_ty) = coercionKind co in
691 case exprIsConApp_maybe expr of {
695 case splitTyConApp_maybe to_ty of {
697 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
698 | not (isVanillaDataCon dc) -> Nothing
700 -- Type constructor must match
701 -- We knock out existentials to keep matters simple(r)
703 arity = tyConArity tc
704 val_args = drop arity args
705 arg_tys = dataConRepArgTys dc
706 dc_tyvars = dataConUnivTyVars dc
707 deep arg_ty = deepCast arg_ty dc_tyvars co
708 new_val_args = zipWith mkCoerce (map deep arg_tys) val_args
710 ASSERT( all isTypeArg (take arity args) )
711 ASSERT( equalLength val_args arg_tys )
712 Just (dc, map Type tc_arg_tys ++ new_val_args)
715 exprIsConApp_maybe (Note _ expr)
716 = exprIsConApp_maybe expr
717 -- We ignore InlineMe notes in case we have
718 -- x = __inline_me__ (a,b)
719 -- All part of making sure that INLINE pragmas never hurt
720 -- Marcin tripped on this one when making dictionaries more inlinable
722 -- In fact, we ignore all notes. For example,
723 -- case _scc_ "foo" (C a b) of
725 -- should be optimised away, but it will be only if we look
726 -- through the SCC note.
728 exprIsConApp_maybe expr = analyse (collectArgs expr)
730 analyse (Var fun, args)
731 | Just con <- isDataConWorkId_maybe fun,
732 args `lengthAtLeast` dataConRepArity con
733 -- Might be > because the arity excludes type args
736 -- Look through unfoldings, but only cheap ones, because
737 -- we are effectively duplicating the unfolding
738 analyse (Var fun, [])
739 | let unf = idUnfolding fun,
741 = exprIsConApp_maybe (unfoldingTemplate unf)
743 analyse other = Nothing
748 %************************************************************************
750 \subsection{Eta reduction and expansion}
752 %************************************************************************
755 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
756 {- The Arity returned is the number of value args the
757 thing can be applied to without doing much work
759 exprEtaExpandArity is used when eta expanding
762 It returns 1 (or more) to:
763 case x of p -> \s -> ...
764 because for I/O ish things we really want to get that \s to the top.
765 We are prepared to evaluate x each time round the loop in order to get that
767 It's all a bit more subtle than it looks:
771 Consider one-shot lambdas
772 let x = expensive in \y z -> E
773 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
774 Hence the ArityType returned by arityType
776 2. The state-transformer hack
778 The one-shot lambda special cause is particularly important/useful for
779 IO state transformers, where we often get
780 let x = E in \ s -> ...
782 and the \s is a real-world state token abstraction. Such abstractions
783 are almost invariably 1-shot, so we want to pull the \s out, past the
784 let x=E, even if E is expensive. So we treat state-token lambdas as
785 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
787 3. Dealing with bottom
790 f = \x -> error "foo"
791 Here, arity 1 is fine. But if it is
795 then we want to get arity 2. Tecnically, this isn't quite right, because
797 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
798 do so; it improves some programs significantly, and increasing convergence
799 isn't a bad thing. Hence the ABot/ATop in ArityType.
801 Actually, the situation is worse. Consider
805 Can we eta-expand here? At first the answer looks like "yes of course", but
808 This should diverge! But if we eta-expand, it won't. Again, we ignore this
809 "problem", because being scrupulous would lose an important transformation for
815 Non-recursive newtypes are transparent, and should not get in the way.
816 We do (currently) eta-expand recursive newtypes too. So if we have, say
818 newtype T = MkT ([T] -> Int)
822 where f has arity 1. Then: etaExpandArity e = 1;
823 that is, etaExpandArity looks through the coerce.
825 When we eta-expand e to arity 1: eta_expand 1 e T
826 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
828 HOWEVER, note that if you use coerce bogusly you can ge
830 And since negate has arity 2, you might try to eta expand. But you can't
831 decopose Int to a function type. Hence the final case in eta_expand.
835 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
837 -- A limited sort of function type
838 data ArityType = AFun Bool ArityType -- True <=> one-shot
839 | ATop -- Know nothing
842 arityDepth :: ArityType -> Arity
843 arityDepth (AFun _ ty) = 1 + arityDepth ty
846 andArityType ABot at2 = at2
847 andArityType ATop at2 = ATop
848 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
849 andArityType at1 at2 = andArityType at2 at1
851 arityType :: DynFlags -> CoreExpr -> ArityType
852 -- (go1 e) = [b1,..,bn]
853 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
854 -- where bi is True <=> the lambda is one-shot
856 arityType dflags (Note n e) = arityType dflags e
857 -- Not needed any more: etaExpand is cleverer
858 -- | ok_note n = arityType dflags e
859 -- | otherwise = ATop
861 arityType dflags (Cast e co) = arityType dflags e
863 arityType dflags (Var v)
864 = mk (idArity v) (arg_tys (idType v))
866 mk :: Arity -> [Type] -> ArityType
867 -- The argument types are only to steer the "state hack"
868 -- Consider case x of
870 -- False -> \(s:RealWorld) -> e
871 -- where foo has arity 1. Then we want the state hack to
872 -- apply to foo too, so we can eta expand the case.
873 mk 0 tys | isBottomingId v = ABot
874 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
876 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
877 mk n [] = AFun False (mk (n-1) [])
879 arg_tys :: Type -> [Type] -- Ignore for-alls
881 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
882 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
885 -- Lambdas; increase arity
886 arityType dflags (Lam x e)
887 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
888 | otherwise = arityType dflags e
890 -- Applications; decrease arity
891 arityType dflags (App f (Type _)) = arityType dflags f
892 arityType dflags (App f a) = case arityType dflags f of
893 AFun one_shot xs | exprIsCheap a -> xs
896 -- Case/Let; keep arity if either the expression is cheap
897 -- or it's a 1-shot lambda
898 -- The former is not really right for Haskell
899 -- f x = case x of { (a,b) -> \y. e }
901 -- f x y = case x of { (a,b) -> e }
902 -- The difference is observable using 'seq'
903 arityType dflags (Case scrut _ _ alts)
904 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
905 xs | exprIsCheap scrut -> xs
906 xs@(AFun one_shot _) | one_shot -> AFun True ATop
909 arityType dflags (Let b e)
910 = case arityType dflags e of
911 xs | cheap_bind b -> xs
912 xs@(AFun one_shot _) | one_shot -> AFun True ATop
915 cheap_bind (NonRec b e) = is_cheap (b,e)
916 cheap_bind (Rec prs) = all is_cheap prs
917 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
919 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
920 -- dictionary bindings. This improves arities. Thereby, it also
921 -- means that full laziness is less prone to floating out the
922 -- application of a function to its dictionary arguments, which
923 -- can thereby lose opportunities for fusion. Example:
924 -- foo :: Ord a => a -> ...
925 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
926 -- -- So foo has arity 1
928 -- f = \x. foo dInt $ bar x
930 -- The (foo DInt) is floated out, and makes ineffective a RULE
933 -- One could go further and make exprIsCheap reply True to any
934 -- dictionary-typed expression, but that's more work.
936 arityType dflags other = ATop
938 {- NOT NEEDED ANY MORE: etaExpand is cleverer
939 ok_note InlineMe = False
941 -- Notice that we do not look through __inline_me__
942 -- This may seem surprising, but consider
943 -- f = _inline_me (\x -> e)
944 -- We DO NOT want to eta expand this to
945 -- f = \x -> (_inline_me (\x -> e)) x
946 -- because the _inline_me gets dropped now it is applied,
955 etaExpand :: Arity -- Result should have this number of value args
957 -> CoreExpr -> Type -- Expression and its type
959 -- (etaExpand n us e ty) returns an expression with
960 -- the same meaning as 'e', but with arity 'n'.
962 -- Given e' = etaExpand n us e ty
964 -- ty = exprType e = exprType e'
966 -- Note that SCCs are not treated specially. If we have
967 -- etaExpand 2 (\x -> scc "foo" e)
968 -- = (\xy -> (scc "foo" e) y)
969 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
971 etaExpand n us expr ty
972 | manifestArity expr >= n = expr -- The no-op case
974 = eta_expand n us expr ty
977 -- manifestArity sees how many leading value lambdas there are
978 manifestArity :: CoreExpr -> Arity
979 manifestArity (Lam v e) | isId v = 1 + manifestArity e
980 | otherwise = manifestArity e
981 manifestArity (Note _ e) = manifestArity e
982 manifestArity (Cast e _) = manifestArity e
985 -- etaExpand deals with for-alls. For example:
987 -- where E :: forall a. a -> a
989 -- (/\b. \y::a -> E b y)
991 -- It deals with coerces too, though they are now rare
992 -- so perhaps the extra code isn't worth it
994 eta_expand n us expr ty
996 -- The ILX code generator requires eta expansion for type arguments
997 -- too, but alas the 'n' doesn't tell us how many of them there
998 -- may be. So we eagerly eta expand any big lambdas, and just
999 -- cross our fingers about possible loss of sharing in the ILX case.
1000 -- The Right Thing is probably to make 'arity' include
1001 -- type variables throughout the compiler. (ToDo.)
1003 -- Saturated, so nothing to do
1006 -- Short cut for the case where there already
1007 -- is a lambda; no point in gratuitously adding more
1008 eta_expand n us (Lam v body) ty
1010 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1013 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1015 -- We used to have a special case that stepped inside Coerces here,
1016 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1017 -- = Note note (eta_expand n us e ty)
1018 -- BUT this led to an infinite loop
1019 -- Example: newtype T = MkT (Int -> Int)
1020 -- eta_expand 1 (coerce (Int->Int) e)
1021 -- --> coerce (Int->Int) (eta_expand 1 T e)
1023 -- --> coerce (Int->Int) (coerce T
1024 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1025 -- by the splitNewType_maybe case below
1028 eta_expand n us expr ty
1029 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1030 case splitForAllTy_maybe ty of {
1031 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
1035 case splitFunTy_maybe ty of {
1036 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1038 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1044 -- newtype T = MkT ([T] -> Int)
1045 -- Consider eta-expanding this
1048 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1050 case splitRecNewTypeCo_maybe ty of {
1052 mkCoerce co (eta_expand n us (mkCoerce (mkSymCoercion co) expr) ty1) ;
1055 -- We have an expression of arity > 0, but its type isn't a function
1056 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1057 -- Essentially the programmer is playing fast and loose with types
1058 -- (Happy does this a lot). So we simply decline to eta-expand.
1063 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1064 It tells how many things the expression can be applied to before doing
1065 any work. It doesn't look inside cases, lets, etc. The idea is that
1066 exprEtaExpandArity will do the hard work, leaving something that's easy
1067 for exprArity to grapple with. In particular, Simplify uses exprArity to
1068 compute the ArityInfo for the Id.
1070 Originally I thought that it was enough just to look for top-level lambdas, but
1071 it isn't. I've seen this
1073 foo = PrelBase.timesInt
1075 We want foo to get arity 2 even though the eta-expander will leave it
1076 unchanged, in the expectation that it'll be inlined. But occasionally it
1077 isn't, because foo is blacklisted (used in a rule).
1079 Similarly, see the ok_note check in exprEtaExpandArity. So
1080 f = __inline_me (\x -> e)
1081 won't be eta-expanded.
1083 And in any case it seems more robust to have exprArity be a bit more intelligent.
1084 But note that (\x y z -> f x y z)
1085 should have arity 3, regardless of f's arity.
1088 exprArity :: CoreExpr -> Arity
1091 go (Var v) = idArity v
1092 go (Lam x e) | isId x = go e + 1
1094 go (Note n e) = go e
1095 go (Cast e _) = go e
1096 go (App e (Type t)) = go e
1097 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1098 -- NB: exprIsCheap a!
1099 -- f (fac x) does not have arity 2,
1100 -- even if f has arity 3!
1101 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1102 -- unknown, hence arity 0
1106 %************************************************************************
1108 \subsection{Equality}
1110 %************************************************************************
1112 @cheapEqExpr@ is a cheap equality test which bales out fast!
1113 True => definitely equal
1114 False => may or may not be equal
1117 cheapEqExpr :: Expr b -> Expr b -> Bool
1119 cheapEqExpr (Var v1) (Var v2) = v1==v2
1120 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1121 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1123 cheapEqExpr (App f1 a1) (App f2 a2)
1124 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1126 cheapEqExpr _ _ = False
1128 exprIsBig :: Expr b -> Bool
1129 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1130 exprIsBig (Lit _) = False
1131 exprIsBig (Var v) = False
1132 exprIsBig (Type t) = False
1133 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1134 exprIsBig other = True
1139 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1140 -- Used in rule matching, so does *not* look through
1141 -- newtypes, predicate types; hence tcEqExpr
1143 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1145 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1147 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1148 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1149 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1150 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1151 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1152 tcEqExprX env (Let (NonRec v1 r1) e1)
1153 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1154 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1155 tcEqExprX env (Let (Rec ps1) e1)
1156 (Let (Rec ps2) e2) = equalLength ps1 ps2
1157 && and (zipWith eq_rhs ps1 ps2)
1158 && tcEqExprX env' e1 e2
1160 env' = foldl2 rn_bndr2 env ps2 ps2
1161 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1162 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1163 tcEqExprX env (Case e1 v1 t1 a1)
1164 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1165 && tcEqTypeX env t1 t2
1166 && equalLength a1 a2
1167 && and (zipWith (eq_alt env') a1 a2)
1169 env' = rnBndr2 env v1 v2
1171 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1172 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1173 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1174 tcEqExprX env e1 e2 = False
1176 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1178 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1179 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1180 eq_note env other1 other2 = False
1184 %************************************************************************
1186 \subsection{The size of an expression}
1188 %************************************************************************
1191 coreBindsSize :: [CoreBind] -> Int
1192 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1194 exprSize :: CoreExpr -> Int
1195 -- A measure of the size of the expressions
1196 -- It also forces the expression pretty drastically as a side effect
1197 exprSize (Var v) = v `seq` 1
1198 exprSize (Lit lit) = lit `seq` 1
1199 exprSize (App f a) = exprSize f + exprSize a
1200 exprSize (Lam b e) = varSize b + exprSize e
1201 exprSize (Let b e) = bindSize b + exprSize e
1202 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1203 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1204 exprSize (Note n e) = noteSize n + exprSize e
1205 exprSize (Type t) = seqType t `seq` 1
1207 noteSize (SCC cc) = cc `seq` 1
1208 noteSize InlineMe = 1
1209 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1211 varSize :: Var -> Int
1212 varSize b | isTyVar b = 1
1213 | otherwise = seqType (idType b) `seq`
1214 megaSeqIdInfo (idInfo b) `seq`
1217 varsSize = foldr ((+) . varSize) 0
1219 bindSize (NonRec b e) = varSize b + exprSize e
1220 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1222 pairSize (b,e) = varSize b + exprSize e
1224 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1228 %************************************************************************
1230 \subsection{Hashing}
1232 %************************************************************************
1235 hashExpr :: CoreExpr -> Int
1236 -- Two expressions that hash to the same Int may be equal (but may not be)
1237 -- Two expressions that hash to the different Ints are definitely unequal
1239 -- But "unequal" here means "not identical"; two alpha-equivalent
1240 -- expressions may hash to the different Ints
1242 -- The emphasis is on a crude, fast hash, rather than on high precision
1244 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1247 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1249 hash_expr (Note _ e) = hash_expr e
1250 hash_expr (Cast e co) = hash_expr e
1251 hash_expr (Let (NonRec b r) e) = hashId b
1252 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1253 hash_expr (Case _ b _ _) = hashId b
1254 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1255 hash_expr (Var v) = hashId v
1256 hash_expr (Lit lit) = hashLiteral lit
1257 hash_expr (Lam b _) = hashId b
1258 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1260 fast_hash_expr (Var v) = hashId v
1261 fast_hash_expr (Lit lit) = hashLiteral lit
1262 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1263 fast_hash_expr (App f a) = fast_hash_expr a
1264 fast_hash_expr (Lam b _) = hashId b
1265 fast_hash_expr other = 1
1268 hashId id = hashName (idName id)
1271 %************************************************************************
1273 \subsection{Determining non-updatable right-hand-sides}
1275 %************************************************************************
1277 Top-level constructor applications can usually be allocated
1278 statically, but they can't if the constructor, or any of the
1279 arguments, come from another DLL (because we can't refer to static
1280 labels in other DLLs).
1282 If this happens we simply make the RHS into an updatable thunk,
1283 and 'exectute' it rather than allocating it statically.
1286 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1287 -- This function is called only on *top-level* right-hand sides
1288 -- Returns True if the RHS can be allocated statically, with
1289 -- no thunks involved at all.
1291 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1292 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1293 -- update flag on it.
1295 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1296 -- (a) a value lambda
1297 -- (b) a saturated constructor application with static args
1299 -- BUT watch out for
1300 -- (i) Any cross-DLL references kill static-ness completely
1301 -- because they must be 'executed' not statically allocated
1302 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1303 -- this is not necessary)
1305 -- (ii) We treat partial applications as redexes, because in fact we
1306 -- make a thunk for them that runs and builds a PAP
1307 -- at run-time. The only appliations that are treated as
1308 -- static are *saturated* applications of constructors.
1310 -- We used to try to be clever with nested structures like this:
1311 -- ys = (:) w ((:) w [])
1312 -- on the grounds that CorePrep will flatten ANF-ise it later.
1313 -- But supporting this special case made the function much more
1314 -- complicated, because the special case only applies if there are no
1315 -- enclosing type lambdas:
1316 -- ys = /\ a -> Foo (Baz ([] a))
1317 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1319 -- But in fact, even without -O, nested structures at top level are
1320 -- flattened by the simplifier, so we don't need to be super-clever here.
1324 -- f = \x::Int. x+7 TRUE
1325 -- p = (True,False) TRUE
1327 -- d = (fst p, False) FALSE because there's a redex inside
1328 -- (this particular one doesn't happen but...)
1330 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1331 -- n = /\a. Nil a TRUE
1333 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1336 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1337 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1339 -- b) (C x xs), where C is a contructors is updatable if the application is
1342 -- c) don't look through unfolding of f in (f x).
1344 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1345 -- them as making the RHS re-entrant (non-updatable).
1347 rhsIsStatic this_pkg rhs = is_static False rhs
1349 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1352 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1354 is_static in_arg (Note (SCC _) e) = False
1355 is_static in_arg (Note _ e) = is_static in_arg e
1356 is_static in_arg (Cast e co) = is_static in_arg e
1358 is_static in_arg (Lit lit)
1360 MachLabel _ _ -> False
1362 -- A MachLabel (foreign import "&foo") in an argument
1363 -- prevents a constructor application from being static. The
1364 -- reason is that it might give rise to unresolvable symbols
1365 -- in the object file: under Linux, references to "weak"
1366 -- symbols from the data segment give rise to "unresolvable
1367 -- relocation" errors at link time This might be due to a bug
1368 -- in the linker, but we'll work around it here anyway.
1371 is_static in_arg other_expr = go other_expr 0
1373 go (Var f) n_val_args
1374 #if mingw32_TARGET_OS
1375 | not (isDllName this_pkg (idName f))
1377 = saturated_data_con f n_val_args
1378 || (in_arg && n_val_args == 0)
1379 -- A naked un-applied variable is *not* deemed a static RHS
1381 -- Reason: better to update so that the indirection gets shorted
1382 -- out, and the true value will be seen
1383 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1384 -- are always updatable. If you do so, make sure that non-updatable
1385 -- ones have enough space for their static link field!
1387 go (App f a) n_val_args
1388 | isTypeArg a = go f n_val_args
1389 | not in_arg && is_static True a = go f (n_val_args + 1)
1390 -- The (not in_arg) checks that we aren't in a constructor argument;
1391 -- if we are, we don't allow (value) applications of any sort
1393 -- NB. In case you wonder, args are sometimes not atomic. eg.
1394 -- x = D# (1.0## /## 2.0##)
1395 -- can't float because /## can fail.
1397 go (Note (SCC _) f) n_val_args = False
1398 go (Note _ f) n_val_args = go f n_val_args
1399 go (Cast e co) n_val_args = go e n_val_args
1401 go other n_val_args = False
1403 saturated_data_con f n_val_args
1404 = case isDataConWorkId_maybe f of
1405 Just dc -> n_val_args == dataConRepArity dc