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, isCoVar, tyVarKind )
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,
56 dataConUnivTyVars, dataConExTyVars )
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 splitNewTypeRepCo_maybe, mkSymCoercion, mkLeftCoercion,
74 mkRightCoercion, decomposeCo, coercionKindTyConApp,
76 import TyCon ( tyConArity )
77 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
78 import CostCentre ( CostCentre )
79 import BasicTypes ( Arity )
80 import PackageConfig ( PackageId )
81 import Unique ( Unique )
83 import DynFlags ( DynFlags, DynFlag(Opt_DictsCheap), dopt )
84 import TysPrim ( alphaTy ) -- Debugging only
85 import Util ( equalLength, lengthAtLeast, foldl2 )
89 %************************************************************************
91 \subsection{Find the type of a Core atom/expression}
93 %************************************************************************
96 exprType :: CoreExpr -> Type
98 exprType (Var var) = idType var
99 exprType (Lit lit) = literalType lit
100 exprType (Let _ body) = exprType body
101 exprType (Case _ _ ty alts) = ty
103 = let (_, ty) = coercionKind co in ty
104 exprType (Note other_note e) = exprType e
105 exprType (Lam binder expr) = mkPiType binder (exprType expr)
107 = case collectArgs e of
108 (fun, args) -> applyTypeToArgs e (exprType fun) args
110 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
112 coreAltType :: CoreAlt -> Type
113 coreAltType (_,_,rhs) = exprType rhs
116 @mkPiType@ makes a (->) type or a forall type, depending on whether
117 it is given a type variable or a term variable. We cleverly use the
118 lbvarinfo field to figure out the right annotation for the arrove in
119 case of a term variable.
122 mkPiType :: Var -> Type -> Type -- The more polymorphic version
123 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
125 mkPiTypes vs ty = foldr mkPiType ty vs
128 | isId v = mkFunTy (idType v) ty
129 | otherwise = mkForAllTy v ty
133 applyTypeToArg :: Type -> CoreExpr -> Type
134 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
135 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
137 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
138 -- A more efficient version of applyTypeToArg
139 -- when we have several args
140 -- The first argument is just for debugging
141 applyTypeToArgs e op_ty [] = op_ty
143 applyTypeToArgs e op_ty (Type ty : args)
144 = -- Accumulate type arguments so we can instantiate all at once
147 go rev_tys (Type ty : args) = go (ty:rev_tys) args
148 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
150 op_ty' = applyTys op_ty (reverse rev_tys)
152 applyTypeToArgs e op_ty (other_arg : args)
153 = case (splitFunTy_maybe op_ty) of
154 Just (_, res_ty) -> applyTypeToArgs e res_ty args
155 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
160 %************************************************************************
162 \subsection{Attaching notes}
164 %************************************************************************
166 mkNote removes redundant coercions, and SCCs where possible
170 mkNote :: Note -> CoreExpr -> CoreExpr
171 mkNote (SCC cc) expr = mkSCC cc expr
172 mkNote InlineMe expr = mkInlineMe expr
173 mkNote note expr = Note note expr
177 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
178 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
179 not be *applied* to anything.
181 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
184 f = inline_me (coerce t fw)
185 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
186 We want the split, so that the coerces can cancel at the call site.
188 However, we can get left with tiresome type applications. Notably, consider
189 f = /\ a -> let t = e in (t, w)
190 Then lifting the let out of the big lambda gives
192 f = /\ a -> let t = inline_me (t' a) in (t, w)
193 The inline_me is to stop the simplifier inlining t' right back
194 into t's RHS. In the next phase we'll substitute for t (since
195 its rhs is trivial) and *then* we could get rid of the inline_me.
196 But it hardly seems worth it, so I don't bother.
199 mkInlineMe (Var v) = Var v
200 mkInlineMe e = Note InlineMe e
206 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
207 mkCoerce co (Cast expr co2)
208 = ASSERT(let { (from_ty, to_ty) = coercionKind co;
209 (from_ty2, to_ty2) = coercionKind co2} in
210 from_ty `coreEqType` to_ty2 )
211 mkCoerce (mkTransCoercion co2 co) expr
214 = let (from_ty, to_ty) = coercionKind co in
215 -- if to_ty `coreEqType` from_ty
218 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindTyConApp co))
223 mkSCC :: CostCentre -> Expr b -> Expr b
224 -- Note: Nested SCC's *are* preserved for the benefit of
225 -- cost centre stack profiling
226 mkSCC cc (Lit lit) = Lit lit
227 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
228 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
229 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
230 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
231 mkSCC cc expr = Note (SCC cc) expr
235 %************************************************************************
237 \subsection{Other expression construction}
239 %************************************************************************
242 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
243 -- (bindNonRec x r b) produces either
246 -- case r of x { _DEFAULT_ -> b }
248 -- depending on whether x is unlifted or not
249 -- It's used by the desugarer to avoid building bindings
250 -- that give Core Lint a heart attack. Actually the simplifier
251 -- deals with them perfectly well.
253 bindNonRec bndr rhs body
254 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
255 | otherwise = Let (NonRec bndr rhs) body
257 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
258 -- Make a case expression instead of a let
259 -- These can arise either from the desugarer,
260 -- or from beta reductions: (\x.e) (x +# y)
264 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
265 -- This guy constructs the value that the scrutinee must have
266 -- when you are in one particular branch of a case
267 mkAltExpr (DataAlt con) args inst_tys
268 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
269 mkAltExpr (LitAlt lit) [] []
272 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
273 mkIfThenElse guard then_expr else_expr
274 -- Not going to be refining, so okay to take the type of the "then" clause
275 = Case guard (mkWildId boolTy) (exprType then_expr)
276 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
277 (DataAlt trueDataCon, [], then_expr) ]
281 %************************************************************************
283 \subsection{Taking expressions apart}
285 %************************************************************************
287 The default alternative must be first, if it exists at all.
288 This makes it easy to find, though it makes matching marginally harder.
291 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
292 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
293 findDefault alts = (alts, Nothing)
295 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
298 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
299 other -> go alts panic_deflt
301 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
304 go (alt@(con1,_,_) : alts) deflt
305 = case con `cmpAltCon` con1 of
306 LT -> deflt -- Missed it already; the alts are in increasing order
308 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
310 isDefaultAlt :: CoreAlt -> Bool
311 isDefaultAlt (DEFAULT, _, _) = True
312 isDefaultAlt other = False
314 ---------------------------------
315 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
316 -- Merge preserving order; alternatives in the first arg
317 -- shadow ones in the second
318 mergeAlts [] as2 = as2
319 mergeAlts as1 [] = as1
320 mergeAlts (a1:as1) (a2:as2)
321 = case a1 `cmpAlt` a2 of
322 LT -> a1 : mergeAlts as1 (a2:as2)
323 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
324 GT -> a2 : mergeAlts (a1:as1) as2
328 %************************************************************************
330 \subsection{Figuring out things about expressions}
332 %************************************************************************
334 @exprIsTrivial@ is true of expressions we are unconditionally happy to
335 duplicate; simple variables and constants, and type
336 applications. Note that primop Ids aren't considered
339 @exprIsBottom@ is true of expressions that are guaranteed to diverge
342 There used to be a gruesome test for (hasNoBinding v) in the
344 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
345 The idea here is that a constructor worker, like $wJust, is
346 really short for (\x -> $wJust x), becuase $wJust has no binding.
347 So it should be treated like a lambda. Ditto unsaturated primops.
348 But now constructor workers are not "have-no-binding" Ids. And
349 completely un-applied primops and foreign-call Ids are sufficiently
350 rare that I plan to allow them to be duplicated and put up with
353 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
354 a) it really generates code, (and a heap object when it's
355 a function arg) to capture the cost centre
356 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
359 exprIsTrivial (Var v) = True -- See notes above
360 exprIsTrivial (Type _) = True
361 exprIsTrivial (Lit lit) = litIsTrivial lit
362 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
363 exprIsTrivial (Note (SCC _) e) = False -- See notes above
364 exprIsTrivial (Note _ e) = exprIsTrivial e
365 exprIsTrivial (Cast e co) = exprIsTrivial e
366 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
367 exprIsTrivial other = False
371 @exprIsDupable@ is true of expressions that can be duplicated at a modest
372 cost in code size. This will only happen in different case
373 branches, so there's no issue about duplicating work.
375 That is, exprIsDupable returns True of (f x) even if
376 f is very very expensive to call.
378 Its only purpose is to avoid fruitless let-binding
379 and then inlining of case join points
383 exprIsDupable (Type _) = True
384 exprIsDupable (Var v) = True
385 exprIsDupable (Lit lit) = litIsDupable lit
386 exprIsDupable (Note InlineMe e) = True
387 exprIsDupable (Note _ e) = exprIsDupable e
388 exprIsDupable (Cast e co) = exprIsDupable e
392 go (Var v) n_args = True
393 go (App f a) n_args = n_args < dupAppSize
396 go other n_args = False
399 dupAppSize = 4 -- Size of application we are prepared to duplicate
402 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
403 it is obviously in weak head normal form, or is cheap to get to WHNF.
404 [Note that that's not the same as exprIsDupable; an expression might be
405 big, and hence not dupable, but still cheap.]
407 By ``cheap'' we mean a computation we're willing to:
408 push inside a lambda, or
409 inline at more than one place
410 That might mean it gets evaluated more than once, instead of being
411 shared. The main examples of things which aren't WHNF but are
416 (where e, and all the ei are cheap)
419 (where e and b are cheap)
422 (where op is a cheap primitive operator)
425 (because we are happy to substitute it inside a lambda)
427 Notice that a variable is considered 'cheap': we can push it inside a lambda,
428 because sharing will make sure it is only evaluated once.
431 exprIsCheap :: CoreExpr -> Bool
432 exprIsCheap (Lit lit) = True
433 exprIsCheap (Type _) = True
434 exprIsCheap (Var _) = True
435 exprIsCheap (Note InlineMe e) = True
436 exprIsCheap (Note _ e) = exprIsCheap e
437 exprIsCheap (Cast e co) = exprIsCheap e
438 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
439 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
440 and [exprIsCheap rhs | (_,_,rhs) <- alts]
441 -- Experimentally, treat (case x of ...) as cheap
442 -- (and case __coerce x etc.)
443 -- This improves arities of overloaded functions where
444 -- there is only dictionary selection (no construction) involved
445 exprIsCheap (Let (NonRec x _) e)
446 | isUnLiftedType (idType x) = exprIsCheap e
448 -- strict lets always have cheap right hand sides,
449 -- and do no allocation.
451 exprIsCheap other_expr -- Applications and variables
454 -- Accumulate value arguments, then decide
455 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
456 | otherwise = go f val_args
458 go (Var f) [] = True -- Just a type application of a variable
459 -- (f t1 t2 t3) counts as WHNF
461 = case globalIdDetails f of
462 RecordSelId {} -> go_sel args
463 ClassOpId _ -> go_sel args
464 PrimOpId op -> go_primop op args
466 DataConWorkId _ -> go_pap args
467 other | length args < idArity f -> go_pap args
469 other -> isBottomingId f
470 -- Application of a function which
471 -- always gives bottom; we treat this as cheap
472 -- because it certainly doesn't need to be shared!
474 go other args = False
477 go_pap args = all exprIsTrivial args
478 -- For constructor applications and primops, check that all
479 -- the args are trivial. We don't want to treat as cheap, say,
481 -- We'll put up with one constructor application, but not dozens
484 go_primop op args = primOpIsCheap op && all exprIsCheap args
485 -- In principle we should worry about primops
486 -- that return a type variable, since the result
487 -- might be applied to something, but I'm not going
488 -- to bother to check the number of args
491 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
492 go_sel other = False -- look cheap, so we will substitute it inside a
493 -- lambda. Particularly for dictionary field selection.
494 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
495 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
498 exprOkForSpeculation returns True of an expression that it is
500 * safe to evaluate even if normal order eval might not
501 evaluate the expression at all, or
503 * safe *not* to evaluate even if normal order would do so
507 the expression guarantees to terminate,
509 without raising an exception,
510 without causing a side effect (e.g. writing a mutable variable)
512 NB: if exprIsHNF e, then exprOkForSpecuation e
515 let x = case y# +# 1# of { r# -> I# r# }
518 case y# +# 1# of { r# ->
523 We can only do this if the (y+1) is ok for speculation: it has no
524 side effects, and can't diverge or raise an exception.
527 exprOkForSpeculation :: CoreExpr -> Bool
528 exprOkForSpeculation (Lit _) = True
529 exprOkForSpeculation (Type _) = True
530 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
531 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
532 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
533 exprOkForSpeculation other_expr
534 = case collectArgs other_expr of
535 (Var f, args) -> spec_ok (globalIdDetails f) args
539 spec_ok (DataConWorkId _) args
540 = True -- The strictness of the constructor has already
541 -- been expressed by its "wrapper", so we don't need
542 -- to take the arguments into account
544 spec_ok (PrimOpId op) args
545 | isDivOp op, -- Special case for dividing operations that fail
546 [arg1, Lit lit] <- args -- only if the divisor is zero
547 = not (isZeroLit lit) && exprOkForSpeculation arg1
548 -- Often there is a literal divisor, and this
549 -- can get rid of a thunk in an inner looop
552 = primOpOkForSpeculation op &&
553 all exprOkForSpeculation args
554 -- A bit conservative: we don't really need
555 -- to care about lazy arguments, but this is easy
557 spec_ok other args = False
559 isDivOp :: PrimOp -> Bool
560 -- True of dyadic operators that can fail
561 -- only if the second arg is zero
562 -- This function probably belongs in PrimOp, or even in
563 -- an automagically generated file.. but it's such a
564 -- special case I thought I'd leave it here for now.
565 isDivOp IntQuotOp = True
566 isDivOp IntRemOp = True
567 isDivOp WordQuotOp = True
568 isDivOp WordRemOp = True
569 isDivOp IntegerQuotRemOp = True
570 isDivOp IntegerDivModOp = True
571 isDivOp FloatDivOp = True
572 isDivOp DoubleDivOp = True
573 isDivOp other = False
578 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
579 exprIsBottom e = go 0 e
581 -- n is the number of args
582 go n (Note _ e) = go n e
583 go n (Cast e co) = go n e
584 go n (Let _ e) = go n e
585 go n (Case e _ _ _) = go 0 e -- Just check the scrut
586 go n (App e _) = go (n+1) e
587 go n (Var v) = idAppIsBottom v n
589 go n (Lam _ _) = False
590 go n (Type _) = False
592 idAppIsBottom :: Id -> Int -> Bool
593 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
596 @exprIsHNF@ returns true for expressions that are certainly *already*
597 evaluated to *head* normal form. This is used to decide whether it's ok
600 case x of _ -> e ===> e
602 and to decide whether it's safe to discard a `seq`
604 So, it does *not* treat variables as evaluated, unless they say they are.
606 But it *does* treat partial applications and constructor applications
607 as values, even if their arguments are non-trivial, provided the argument
609 e.g. (:) (f x) (map f xs) is a value
610 map (...redex...) is a value
611 Because `seq` on such things completes immediately
613 For unlifted argument types, we have to be careful:
615 Suppose (f x) diverges; then C (f x) is not a value. True, but
616 this form is illegal (see the invariants in CoreSyn). Args of unboxed
617 type must be ok-for-speculation (or trivial).
620 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
621 exprIsHNF (Var v) -- NB: There are no value args at this point
622 = isDataConWorkId v -- Catches nullary constructors,
623 -- so that [] and () are values, for example
624 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
625 || isEvaldUnfolding (idUnfolding v)
626 -- Check the thing's unfolding; it might be bound to a value
627 -- A worry: what if an Id's unfolding is just itself:
628 -- then we could get an infinite loop...
630 exprIsHNF (Lit l) = True
631 exprIsHNF (Type ty) = True -- Types are honorary Values;
632 -- we don't mind copying them
633 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
634 exprIsHNF (Note _ e) = exprIsHNF e
635 exprIsHNF (Cast e co) = exprIsHNF e
636 exprIsHNF (App e (Type _)) = exprIsHNF e
637 exprIsHNF (App e a) = app_is_value e [a]
638 exprIsHNF other = False
640 -- There is at least one value argument
641 app_is_value (Var fun) args
642 | isDataConWorkId fun -- Constructor apps are values
643 || idArity fun > valArgCount args -- Under-applied function
644 = check_args (idType fun) args
645 app_is_value (App f a) as = app_is_value f (a:as)
646 app_is_value other as = False
648 -- 'check_args' checks that unlifted-type args
649 -- are in fact guaranteed non-divergent
650 check_args fun_ty [] = True
651 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
652 Just (_, ty) -> check_args ty args
653 check_args fun_ty (arg : args)
654 | isUnLiftedType arg_ty = exprOkForSpeculation arg
655 | otherwise = check_args res_ty args
657 (arg_ty, res_ty) = splitFunTy fun_ty
661 -- deep applies a TyConApp coercion as a substitution to a reflexive coercion
662 -- deepCast t [a1,...,an] co corresponds to deep(t, [a1,...,an], co) from
664 deepCast :: Type -> [TyVar] -> Coercion -> Coercion
665 deepCast ty tyVars co
666 = ASSERT( let {(lty, rty) = coercionKind co;
667 Just (tc1, lArgs) = splitTyConApp_maybe lty;
668 Just (tc2, rArgs) = splitTyConApp_maybe rty}
670 tc1 == tc2 && length lArgs == length rArgs &&
671 length lArgs == length tyVars )
672 substTyWith tyVars coArgs ty
674 -- coArgs = [right (left (left co)), right (left co), right co]
675 coArgs = decomposeCo (length tyVars) co
677 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
678 -- Returns (Just (dc, [x1..xn])) if the argument expression is
679 -- a constructor application of the form (dc x1 .. xn)
681 exprIsConApp_maybe (Cast expr co)
682 = -- Maybe this is over the top, but here we try to turn
683 -- coerce (S,T) ( x, y )
685 -- ( coerce S x, coerce T y )
686 -- This happens in anger in PrelArrExts which has a coerce
687 -- case coerce memcpy a b of
689 -- where the memcpy is in the IO monad, but the call is in
691 case exprIsConApp_maybe expr of {
695 let (from_ty, to_ty) = coercionKind co in
697 case splitTyConApp_maybe to_ty of {
699 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
700 -- | not (isVanillaDataCon dc) -> Nothing
702 -- Type constructor must match datacon
704 case splitTyConApp_maybe from_ty of {
706 Just (tc', tc_arg_tys') | tc /= tc' -> Nothing
707 -- Both sides of coercion must have the same type constructor
711 -- here we do the PushC reduction rule as described in the FC paper
712 arity = tyConArity tc
713 n_ex_tvs = length dc_ex_tyvars
715 (univ_args, rest) = splitAt arity args
716 (ex_args, val_args) = splitAt n_ex_tvs rest
718 arg_tys = dataConRepArgTys dc
719 dc_tyvars = dataConUnivTyVars dc
720 dc_ex_tyvars = dataConExTyVars dc
722 deep arg_ty = deepCast arg_ty dc_tyvars co
724 -- first we appropriately cast the value arguments
725 arg_cos = map deep arg_tys
726 new_val_args = zipWith mkCoerce (map deep arg_tys) val_args
728 -- then we cast the existential coercion arguments
729 orig_tvs = dc_tyvars ++ dc_ex_tyvars
730 gammas = decomposeCo arity co
731 new_tys = gammas ++ (map (\ (Type t) -> t) ex_args)
732 theta = substTyWith orig_tvs new_tys
735 , (ty1, ty2) <- splitCoercionKind (tyVarKind tv)
736 = Type $ mkTransCoercion (mkSymCoercion (theta ty1))
737 (mkTransCoercion ty (theta ty2))
740 new_ex_args = zipWith cast_ty dc_ex_tyvars ex_args
743 ASSERT( all isTypeArg (take arity args) )
744 ASSERT( equalLength val_args arg_tys )
745 Just (dc, map Type tc_arg_tys ++ new_ex_args ++ new_val_args)
748 exprIsConApp_maybe (Note _ expr)
749 = exprIsConApp_maybe expr
750 -- We ignore InlineMe notes in case we have
751 -- x = __inline_me__ (a,b)
752 -- All part of making sure that INLINE pragmas never hurt
753 -- Marcin tripped on this one when making dictionaries more inlinable
755 -- In fact, we ignore all notes. For example,
756 -- case _scc_ "foo" (C a b) of
758 -- should be optimised away, but it will be only if we look
759 -- through the SCC note.
761 exprIsConApp_maybe expr = analyse (collectArgs expr)
763 analyse (Var fun, args)
764 | Just con <- isDataConWorkId_maybe fun,
765 args `lengthAtLeast` dataConRepArity con
766 -- Might be > because the arity excludes type args
769 -- Look through unfoldings, but only cheap ones, because
770 -- we are effectively duplicating the unfolding
771 analyse (Var fun, [])
772 | let unf = idUnfolding fun,
774 = exprIsConApp_maybe (unfoldingTemplate unf)
776 analyse other = Nothing
781 %************************************************************************
783 \subsection{Eta reduction and expansion}
785 %************************************************************************
788 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
789 {- The Arity returned is the number of value args the
790 thing can be applied to without doing much work
792 exprEtaExpandArity is used when eta expanding
795 It returns 1 (or more) to:
796 case x of p -> \s -> ...
797 because for I/O ish things we really want to get that \s to the top.
798 We are prepared to evaluate x each time round the loop in order to get that
800 It's all a bit more subtle than it looks:
804 Consider one-shot lambdas
805 let x = expensive in \y z -> E
806 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
807 Hence the ArityType returned by arityType
809 2. The state-transformer hack
811 The one-shot lambda special cause is particularly important/useful for
812 IO state transformers, where we often get
813 let x = E in \ s -> ...
815 and the \s is a real-world state token abstraction. Such abstractions
816 are almost invariably 1-shot, so we want to pull the \s out, past the
817 let x=E, even if E is expensive. So we treat state-token lambdas as
818 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
820 3. Dealing with bottom
823 f = \x -> error "foo"
824 Here, arity 1 is fine. But if it is
828 then we want to get arity 2. Tecnically, this isn't quite right, because
830 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
831 do so; it improves some programs significantly, and increasing convergence
832 isn't a bad thing. Hence the ABot/ATop in ArityType.
834 Actually, the situation is worse. Consider
838 Can we eta-expand here? At first the answer looks like "yes of course", but
841 This should diverge! But if we eta-expand, it won't. Again, we ignore this
842 "problem", because being scrupulous would lose an important transformation for
848 Non-recursive newtypes are transparent, and should not get in the way.
849 We do (currently) eta-expand recursive newtypes too. So if we have, say
851 newtype T = MkT ([T] -> Int)
855 where f has arity 1. Then: etaExpandArity e = 1;
856 that is, etaExpandArity looks through the coerce.
858 When we eta-expand e to arity 1: eta_expand 1 e T
859 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
861 HOWEVER, note that if you use coerce bogusly you can ge
863 And since negate has arity 2, you might try to eta expand. But you can't
864 decopose Int to a function type. Hence the final case in eta_expand.
868 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
870 -- A limited sort of function type
871 data ArityType = AFun Bool ArityType -- True <=> one-shot
872 | ATop -- Know nothing
875 arityDepth :: ArityType -> Arity
876 arityDepth (AFun _ ty) = 1 + arityDepth ty
879 andArityType ABot at2 = at2
880 andArityType ATop at2 = ATop
881 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
882 andArityType at1 at2 = andArityType at2 at1
884 arityType :: DynFlags -> CoreExpr -> ArityType
885 -- (go1 e) = [b1,..,bn]
886 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
887 -- where bi is True <=> the lambda is one-shot
889 arityType dflags (Note n e) = arityType dflags e
890 -- Not needed any more: etaExpand is cleverer
891 -- | ok_note n = arityType dflags e
892 -- | otherwise = ATop
894 arityType dflags (Cast e co) = arityType dflags e
896 arityType dflags (Var v)
897 = mk (idArity v) (arg_tys (idType v))
899 mk :: Arity -> [Type] -> ArityType
900 -- The argument types are only to steer the "state hack"
901 -- Consider case x of
903 -- False -> \(s:RealWorld) -> e
904 -- where foo has arity 1. Then we want the state hack to
905 -- apply to foo too, so we can eta expand the case.
906 mk 0 tys | isBottomingId v = ABot
907 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
909 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
910 mk n [] = AFun False (mk (n-1) [])
912 arg_tys :: Type -> [Type] -- Ignore for-alls
914 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
915 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
918 -- Lambdas; increase arity
919 arityType dflags (Lam x e)
920 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
921 | otherwise = arityType dflags e
923 -- Applications; decrease arity
924 arityType dflags (App f (Type _)) = arityType dflags f
925 arityType dflags (App f a) = case arityType dflags f of
926 AFun one_shot xs | exprIsCheap a -> xs
929 -- Case/Let; keep arity if either the expression is cheap
930 -- or it's a 1-shot lambda
931 -- The former is not really right for Haskell
932 -- f x = case x of { (a,b) -> \y. e }
934 -- f x y = case x of { (a,b) -> e }
935 -- The difference is observable using 'seq'
936 arityType dflags (Case scrut _ _ alts)
937 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
938 xs | exprIsCheap scrut -> xs
939 xs@(AFun one_shot _) | one_shot -> AFun True ATop
942 arityType dflags (Let b e)
943 = case arityType dflags e of
944 xs | cheap_bind b -> xs
945 xs@(AFun one_shot _) | one_shot -> AFun True ATop
948 cheap_bind (NonRec b e) = is_cheap (b,e)
949 cheap_bind (Rec prs) = all is_cheap prs
950 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
952 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
953 -- dictionary bindings. This improves arities. Thereby, it also
954 -- means that full laziness is less prone to floating out the
955 -- application of a function to its dictionary arguments, which
956 -- can thereby lose opportunities for fusion. Example:
957 -- foo :: Ord a => a -> ...
958 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
959 -- -- So foo has arity 1
961 -- f = \x. foo dInt $ bar x
963 -- The (foo DInt) is floated out, and makes ineffective a RULE
966 -- One could go further and make exprIsCheap reply True to any
967 -- dictionary-typed expression, but that's more work.
969 arityType dflags other = ATop
971 {- NOT NEEDED ANY MORE: etaExpand is cleverer
972 ok_note InlineMe = False
974 -- Notice that we do not look through __inline_me__
975 -- This may seem surprising, but consider
976 -- f = _inline_me (\x -> e)
977 -- We DO NOT want to eta expand this to
978 -- f = \x -> (_inline_me (\x -> e)) x
979 -- because the _inline_me gets dropped now it is applied,
988 etaExpand :: Arity -- Result should have this number of value args
990 -> CoreExpr -> Type -- Expression and its type
992 -- (etaExpand n us e ty) returns an expression with
993 -- the same meaning as 'e', but with arity 'n'.
995 -- Given e' = etaExpand n us e ty
997 -- ty = exprType e = exprType e'
999 -- Note that SCCs are not treated specially. If we have
1000 -- etaExpand 2 (\x -> scc "foo" e)
1001 -- = (\xy -> (scc "foo" e) y)
1002 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1004 etaExpand n us expr ty
1005 | manifestArity expr >= n = expr -- The no-op case
1007 = eta_expand n us expr ty
1010 -- manifestArity sees how many leading value lambdas there are
1011 manifestArity :: CoreExpr -> Arity
1012 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1013 | otherwise = manifestArity e
1014 manifestArity (Note _ e) = manifestArity e
1015 manifestArity (Cast e _) = manifestArity e
1018 -- etaExpand deals with for-alls. For example:
1020 -- where E :: forall a. a -> a
1022 -- (/\b. \y::a -> E b y)
1024 -- It deals with coerces too, though they are now rare
1025 -- so perhaps the extra code isn't worth it
1027 eta_expand n us expr ty
1029 -- The ILX code generator requires eta expansion for type arguments
1030 -- too, but alas the 'n' doesn't tell us how many of them there
1031 -- may be. So we eagerly eta expand any big lambdas, and just
1032 -- cross our fingers about possible loss of sharing in the ILX case.
1033 -- The Right Thing is probably to make 'arity' include
1034 -- type variables throughout the compiler. (ToDo.)
1036 -- Saturated, so nothing to do
1039 -- Short cut for the case where there already
1040 -- is a lambda; no point in gratuitously adding more
1041 eta_expand n us (Lam v body) ty
1043 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1046 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1048 -- We used to have a special case that stepped inside Coerces here,
1049 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1050 -- = Note note (eta_expand n us e ty)
1051 -- BUT this led to an infinite loop
1052 -- Example: newtype T = MkT (Int -> Int)
1053 -- eta_expand 1 (coerce (Int->Int) e)
1054 -- --> coerce (Int->Int) (eta_expand 1 T e)
1056 -- --> coerce (Int->Int) (coerce T
1057 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1058 -- by the splitNewType_maybe case below
1061 eta_expand n us expr ty
1062 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1063 case splitForAllTy_maybe ty of {
1064 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
1068 case splitFunTy_maybe ty of {
1069 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1071 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1077 -- newtype T = MkT ([T] -> Int)
1078 -- Consider eta-expanding this
1081 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1083 case splitNewTypeRepCo_maybe ty of {
1085 mkCoerce co (eta_expand n us (mkCoerce (mkSymCoercion co) expr) ty1) ;
1088 -- We have an expression of arity > 0, but its type isn't a function
1089 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1090 -- Essentially the programmer is playing fast and loose with types
1091 -- (Happy does this a lot). So we simply decline to eta-expand.
1096 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1097 It tells how many things the expression can be applied to before doing
1098 any work. It doesn't look inside cases, lets, etc. The idea is that
1099 exprEtaExpandArity will do the hard work, leaving something that's easy
1100 for exprArity to grapple with. In particular, Simplify uses exprArity to
1101 compute the ArityInfo for the Id.
1103 Originally I thought that it was enough just to look for top-level lambdas, but
1104 it isn't. I've seen this
1106 foo = PrelBase.timesInt
1108 We want foo to get arity 2 even though the eta-expander will leave it
1109 unchanged, in the expectation that it'll be inlined. But occasionally it
1110 isn't, because foo is blacklisted (used in a rule).
1112 Similarly, see the ok_note check in exprEtaExpandArity. So
1113 f = __inline_me (\x -> e)
1114 won't be eta-expanded.
1116 And in any case it seems more robust to have exprArity be a bit more intelligent.
1117 But note that (\x y z -> f x y z)
1118 should have arity 3, regardless of f's arity.
1121 exprArity :: CoreExpr -> Arity
1124 go (Var v) = idArity v
1125 go (Lam x e) | isId x = go e + 1
1127 go (Note n e) = go e
1128 go (Cast e _) = go e
1129 go (App e (Type t)) = go e
1130 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1131 -- NB: exprIsCheap a!
1132 -- f (fac x) does not have arity 2,
1133 -- even if f has arity 3!
1134 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1135 -- unknown, hence arity 0
1139 %************************************************************************
1141 \subsection{Equality}
1143 %************************************************************************
1145 @cheapEqExpr@ is a cheap equality test which bales out fast!
1146 True => definitely equal
1147 False => may or may not be equal
1150 cheapEqExpr :: Expr b -> Expr b -> Bool
1152 cheapEqExpr (Var v1) (Var v2) = v1==v2
1153 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1154 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1156 cheapEqExpr (App f1 a1) (App f2 a2)
1157 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1159 cheapEqExpr _ _ = False
1161 exprIsBig :: Expr b -> Bool
1162 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1163 exprIsBig (Lit _) = False
1164 exprIsBig (Var v) = False
1165 exprIsBig (Type t) = False
1166 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1167 exprIsBig other = True
1172 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1173 -- Used in rule matching, so does *not* look through
1174 -- newtypes, predicate types; hence tcEqExpr
1176 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1178 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1180 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1181 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1182 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1183 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1184 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1185 tcEqExprX env (Let (NonRec v1 r1) e1)
1186 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1187 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1188 tcEqExprX env (Let (Rec ps1) e1)
1189 (Let (Rec ps2) e2) = equalLength ps1 ps2
1190 && and (zipWith eq_rhs ps1 ps2)
1191 && tcEqExprX env' e1 e2
1193 env' = foldl2 rn_bndr2 env ps2 ps2
1194 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1195 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1196 tcEqExprX env (Case e1 v1 t1 a1)
1197 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1198 && tcEqTypeX env t1 t2
1199 && equalLength a1 a2
1200 && and (zipWith (eq_alt env') a1 a2)
1202 env' = rnBndr2 env v1 v2
1204 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1205 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1206 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1207 tcEqExprX env e1 e2 = False
1209 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1211 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1212 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1213 eq_note env other1 other2 = False
1217 %************************************************************************
1219 \subsection{The size of an expression}
1221 %************************************************************************
1224 coreBindsSize :: [CoreBind] -> Int
1225 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1227 exprSize :: CoreExpr -> Int
1228 -- A measure of the size of the expressions
1229 -- It also forces the expression pretty drastically as a side effect
1230 exprSize (Var v) = v `seq` 1
1231 exprSize (Lit lit) = lit `seq` 1
1232 exprSize (App f a) = exprSize f + exprSize a
1233 exprSize (Lam b e) = varSize b + exprSize e
1234 exprSize (Let b e) = bindSize b + exprSize e
1235 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1236 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1237 exprSize (Note n e) = noteSize n + exprSize e
1238 exprSize (Type t) = seqType t `seq` 1
1240 noteSize (SCC cc) = cc `seq` 1
1241 noteSize InlineMe = 1
1242 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1244 varSize :: Var -> Int
1245 varSize b | isTyVar b = 1
1246 | otherwise = seqType (idType b) `seq`
1247 megaSeqIdInfo (idInfo b) `seq`
1250 varsSize = foldr ((+) . varSize) 0
1252 bindSize (NonRec b e) = varSize b + exprSize e
1253 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1255 pairSize (b,e) = varSize b + exprSize e
1257 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1261 %************************************************************************
1263 \subsection{Hashing}
1265 %************************************************************************
1268 hashExpr :: CoreExpr -> Int
1269 -- Two expressions that hash to the same Int may be equal (but may not be)
1270 -- Two expressions that hash to the different Ints are definitely unequal
1272 -- But "unequal" here means "not identical"; two alpha-equivalent
1273 -- expressions may hash to the different Ints
1275 -- The emphasis is on a crude, fast hash, rather than on high precision
1277 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1280 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1282 hash_expr (Note _ e) = hash_expr e
1283 hash_expr (Cast e co) = hash_expr e
1284 hash_expr (Let (NonRec b r) e) = hashId b
1285 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1286 hash_expr (Case _ b _ _) = hashId b
1287 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1288 hash_expr (Var v) = hashId v
1289 hash_expr (Lit lit) = hashLiteral lit
1290 hash_expr (Lam b _) = hashId b
1291 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1293 fast_hash_expr (Var v) = hashId v
1294 fast_hash_expr (Lit lit) = hashLiteral lit
1295 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1296 fast_hash_expr (App f a) = fast_hash_expr a
1297 fast_hash_expr (Lam b _) = hashId b
1298 fast_hash_expr other = 1
1301 hashId id = hashName (idName id)
1304 %************************************************************************
1306 \subsection{Determining non-updatable right-hand-sides}
1308 %************************************************************************
1310 Top-level constructor applications can usually be allocated
1311 statically, but they can't if the constructor, or any of the
1312 arguments, come from another DLL (because we can't refer to static
1313 labels in other DLLs).
1315 If this happens we simply make the RHS into an updatable thunk,
1316 and 'exectute' it rather than allocating it statically.
1319 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1320 -- This function is called only on *top-level* right-hand sides
1321 -- Returns True if the RHS can be allocated statically, with
1322 -- no thunks involved at all.
1324 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1325 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1326 -- update flag on it.
1328 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1329 -- (a) a value lambda
1330 -- (b) a saturated constructor application with static args
1332 -- BUT watch out for
1333 -- (i) Any cross-DLL references kill static-ness completely
1334 -- because they must be 'executed' not statically allocated
1335 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1336 -- this is not necessary)
1338 -- (ii) We treat partial applications as redexes, because in fact we
1339 -- make a thunk for them that runs and builds a PAP
1340 -- at run-time. The only appliations that are treated as
1341 -- static are *saturated* applications of constructors.
1343 -- We used to try to be clever with nested structures like this:
1344 -- ys = (:) w ((:) w [])
1345 -- on the grounds that CorePrep will flatten ANF-ise it later.
1346 -- But supporting this special case made the function much more
1347 -- complicated, because the special case only applies if there are no
1348 -- enclosing type lambdas:
1349 -- ys = /\ a -> Foo (Baz ([] a))
1350 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1352 -- But in fact, even without -O, nested structures at top level are
1353 -- flattened by the simplifier, so we don't need to be super-clever here.
1357 -- f = \x::Int. x+7 TRUE
1358 -- p = (True,False) TRUE
1360 -- d = (fst p, False) FALSE because there's a redex inside
1361 -- (this particular one doesn't happen but...)
1363 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1364 -- n = /\a. Nil a TRUE
1366 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1369 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1370 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1372 -- b) (C x xs), where C is a contructors is updatable if the application is
1375 -- c) don't look through unfolding of f in (f x).
1377 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1378 -- them as making the RHS re-entrant (non-updatable).
1380 rhsIsStatic this_pkg rhs = is_static False rhs
1382 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1385 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1387 is_static in_arg (Note (SCC _) e) = False
1388 is_static in_arg (Note _ e) = is_static in_arg e
1389 is_static in_arg (Cast e co) = is_static in_arg e
1391 is_static in_arg (Lit lit)
1393 MachLabel _ _ -> False
1395 -- A MachLabel (foreign import "&foo") in an argument
1396 -- prevents a constructor application from being static. The
1397 -- reason is that it might give rise to unresolvable symbols
1398 -- in the object file: under Linux, references to "weak"
1399 -- symbols from the data segment give rise to "unresolvable
1400 -- relocation" errors at link time This might be due to a bug
1401 -- in the linker, but we'll work around it here anyway.
1404 is_static in_arg other_expr = go other_expr 0
1406 go (Var f) n_val_args
1407 #if mingw32_TARGET_OS
1408 | not (isDllName this_pkg (idName f))
1410 = saturated_data_con f n_val_args
1411 || (in_arg && n_val_args == 0)
1412 -- A naked un-applied variable is *not* deemed a static RHS
1414 -- Reason: better to update so that the indirection gets shorted
1415 -- out, and the true value will be seen
1416 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1417 -- are always updatable. If you do so, make sure that non-updatable
1418 -- ones have enough space for their static link field!
1420 go (App f a) n_val_args
1421 | isTypeArg a = go f n_val_args
1422 | not in_arg && is_static True a = go f (n_val_args + 1)
1423 -- The (not in_arg) checks that we aren't in a constructor argument;
1424 -- if we are, we don't allow (value) applications of any sort
1426 -- NB. In case you wonder, args are sometimes not atomic. eg.
1427 -- x = D# (1.0## /## 2.0##)
1428 -- can't float because /## can fail.
1430 go (Note (SCC _) f) n_val_args = False
1431 go (Note _ f) n_val_args = go f n_val_args
1432 go (Cast e co) n_val_args = go e n_val_args
1434 go other n_val_args = False
1436 saturated_data_con f n_val_args
1437 = case isDataConWorkId_maybe f of
1438 Just dc -> n_val_args == dataConRepArity dc