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,
36 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
39 #include "HsVersions.h"
42 import GLAEXTS -- For `xori`
45 import CoreFVs ( exprFreeVars )
46 import PprCore ( pprCoreExpr )
47 import Var ( Var, TyVar, CoVar, isCoVar, tyVarKind, mkCoVar, mkTyVar )
48 import OccName ( mkVarOccFS )
49 import VarSet ( unionVarSet )
51 import Name ( hashName, mkSysTvName )
53 import Packages ( isDllName )
55 import Literal ( hashLiteral, literalType, litIsDupable,
56 litIsTrivial, isZeroLit, Literal( MachLabel ) )
57 import DataCon ( DataCon, dataConRepArity, eqSpecPreds,
58 dataConTyCon, dataConRepArgTys,
59 dataConUnivTyVars, dataConExTyVars, dataConEqSpec,
60 dataConOrigArgTys, dataConTheta )
61 import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
62 import Id ( Id, idType, globalIdDetails, idNewStrictness,
63 mkWildId, idArity, idName, idUnfolding, idInfo,
64 isOneShotBndr, isStateHackType, isDataConWorkId_maybe, mkSysLocal,
65 isDataConWorkId, isBottomingId, isDictId
67 import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo )
68 import NewDemand ( appIsBottom )
69 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
70 splitFunTy, tcEqTypeX,
71 applyTys, isUnLiftedType, seqType, mkTyVarTy,
72 splitForAllTy_maybe, isForAllTy,
73 splitTyConApp_maybe, coreEqType, funResultTy, applyTy,
76 import Coercion ( Coercion, mkTransCoercion, coercionKind,
77 splitNewTypeRepCo_maybe, mkSymCoercion,
78 decomposeCo, coercionKindPredTy,
80 import TyCon ( tyConArity )
81 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
82 import CostCentre ( CostCentre )
83 import BasicTypes ( Arity )
84 import PackageConfig ( PackageId )
85 import Unique ( Unique )
87 import DynFlags ( DynFlags, DynFlag(Opt_DictsCheap), dopt )
88 import TysPrim ( alphaTy ) -- Debugging only
89 import Util ( equalLength, lengthAtLeast, foldl2 )
90 import FastString ( FastString )
94 %************************************************************************
96 \subsection{Find the type of a Core atom/expression}
98 %************************************************************************
101 exprType :: CoreExpr -> Type
103 exprType (Var var) = idType var
104 exprType (Lit lit) = literalType lit
105 exprType (Let _ body) = exprType body
106 exprType (Case _ _ ty alts) = ty
108 = let (_, ty) = coercionKind co in ty
109 exprType (Note other_note e) = exprType e
110 exprType (Lam binder expr) = mkPiType binder (exprType expr)
112 = case collectArgs e of
113 (fun, args) -> applyTypeToArgs e (exprType fun) args
115 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
117 coreAltType :: CoreAlt -> Type
118 coreAltType (_,_,rhs) = exprType rhs
121 @mkPiType@ makes a (->) type or a forall type, depending on whether
122 it is given a type variable or a term variable. We cleverly use the
123 lbvarinfo field to figure out the right annotation for the arrove in
124 case of a term variable.
127 mkPiType :: Var -> Type -> Type -- The more polymorphic version
128 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
130 mkPiTypes vs ty = foldr mkPiType ty vs
133 | isId v = mkFunTy (idType v) ty
134 | otherwise = mkForAllTy v ty
138 applyTypeToArg :: Type -> CoreExpr -> Type
139 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
140 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
142 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
143 -- A more efficient version of applyTypeToArg
144 -- when we have several args
145 -- The first argument is just for debugging
146 applyTypeToArgs e op_ty [] = op_ty
148 applyTypeToArgs e op_ty (Type ty : args)
149 = -- Accumulate type arguments so we can instantiate all at once
152 go rev_tys (Type ty : args) = go (ty:rev_tys) args
153 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
155 op_ty' = applyTys op_ty (reverse rev_tys)
157 applyTypeToArgs e op_ty (other_arg : args)
158 = case (splitFunTy_maybe op_ty) of
159 Just (_, res_ty) -> applyTypeToArgs e res_ty args
160 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
165 %************************************************************************
167 \subsection{Attaching notes}
169 %************************************************************************
171 mkNote removes redundant coercions, and SCCs where possible
175 mkNote :: Note -> CoreExpr -> CoreExpr
176 mkNote (SCC cc) expr = mkSCC cc expr
177 mkNote InlineMe expr = mkInlineMe expr
178 mkNote note expr = Note note expr
182 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
183 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
184 not be *applied* to anything.
186 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
189 f = inline_me (coerce t fw)
190 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
191 We want the split, so that the coerces can cancel at the call site.
193 However, we can get left with tiresome type applications. Notably, consider
194 f = /\ a -> let t = e in (t, w)
195 Then lifting the let out of the big lambda gives
197 f = /\ a -> let t = inline_me (t' a) in (t, w)
198 The inline_me is to stop the simplifier inlining t' right back
199 into t's RHS. In the next phase we'll substitute for t (since
200 its rhs is trivial) and *then* we could get rid of the inline_me.
201 But it hardly seems worth it, so I don't bother.
204 mkInlineMe (Var v) = Var v
205 mkInlineMe e = Note InlineMe e
211 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
212 mkCoerce co (Cast expr co2)
213 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
214 (_from_ty2, to_ty2) = coercionKind co2} in
215 from_ty `coreEqType` to_ty2 )
216 mkCoerce (mkTransCoercion co2 co) expr
219 = let (from_ty, to_ty) = coercionKind co in
220 -- if to_ty `coreEqType` from_ty
223 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
228 mkSCC :: CostCentre -> Expr b -> Expr b
229 -- Note: Nested SCC's *are* preserved for the benefit of
230 -- cost centre stack profiling
231 mkSCC cc (Lit lit) = Lit lit
232 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
233 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
234 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
235 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
236 mkSCC cc expr = Note (SCC cc) expr
240 %************************************************************************
242 \subsection{Other expression construction}
244 %************************************************************************
247 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
248 -- (bindNonRec x r b) produces either
251 -- case r of x { _DEFAULT_ -> b }
253 -- depending on whether x is unlifted or not
254 -- It's used by the desugarer to avoid building bindings
255 -- that give Core Lint a heart attack. Actually the simplifier
256 -- deals with them perfectly well.
258 bindNonRec bndr rhs body
259 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
260 | otherwise = Let (NonRec bndr rhs) body
262 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
263 -- Make a case expression instead of a let
264 -- These can arise either from the desugarer,
265 -- or from beta reductions: (\x.e) (x +# y)
269 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
270 -- This guy constructs the value that the scrutinee must have
271 -- when you are in one particular branch of a case
272 mkAltExpr (DataAlt con) args inst_tys
273 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
274 mkAltExpr (LitAlt lit) [] []
277 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
278 mkIfThenElse guard then_expr else_expr
279 -- Not going to be refining, so okay to take the type of the "then" clause
280 = Case guard (mkWildId boolTy) (exprType then_expr)
281 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
282 (DataAlt trueDataCon, [], then_expr) ]
286 %************************************************************************
288 \subsection{Taking expressions apart}
290 %************************************************************************
292 The default alternative must be first, if it exists at all.
293 This makes it easy to find, though it makes matching marginally harder.
296 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
297 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
298 findDefault alts = (alts, Nothing)
300 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
303 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
304 other -> go alts panic_deflt
306 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
309 go (alt@(con1,_,_) : alts) deflt
310 = case con `cmpAltCon` con1 of
311 LT -> deflt -- Missed it already; the alts are in increasing order
313 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
315 isDefaultAlt :: CoreAlt -> Bool
316 isDefaultAlt (DEFAULT, _, _) = True
317 isDefaultAlt other = False
319 ---------------------------------
320 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
321 -- Merge preserving order; alternatives in the first arg
322 -- shadow ones in the second
323 mergeAlts [] as2 = as2
324 mergeAlts as1 [] = as1
325 mergeAlts (a1:as1) (a2:as2)
326 = case a1 `cmpAlt` a2 of
327 LT -> a1 : mergeAlts as1 (a2:as2)
328 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
329 GT -> a2 : mergeAlts (a1:as1) as2
333 %************************************************************************
335 \subsection{Figuring out things about expressions}
337 %************************************************************************
339 @exprIsTrivial@ is true of expressions we are unconditionally happy to
340 duplicate; simple variables and constants, and type
341 applications. Note that primop Ids aren't considered
344 @exprIsBottom@ is true of expressions that are guaranteed to diverge
347 There used to be a gruesome test for (hasNoBinding v) in the
349 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
350 The idea here is that a constructor worker, like $wJust, is
351 really short for (\x -> $wJust x), becuase $wJust has no binding.
352 So it should be treated like a lambda. Ditto unsaturated primops.
353 But now constructor workers are not "have-no-binding" Ids. And
354 completely un-applied primops and foreign-call Ids are sufficiently
355 rare that I plan to allow them to be duplicated and put up with
358 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
359 a) it really generates code, (and a heap object when it's
360 a function arg) to capture the cost centre
361 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
364 exprIsTrivial (Var v) = True -- See notes above
365 exprIsTrivial (Type _) = True
366 exprIsTrivial (Lit lit) = litIsTrivial lit
367 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
368 exprIsTrivial (Note (SCC _) e) = False -- See notes above
369 exprIsTrivial (Note _ e) = exprIsTrivial e
370 exprIsTrivial (Cast e co) = exprIsTrivial e
371 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
372 exprIsTrivial other = False
376 @exprIsDupable@ is true of expressions that can be duplicated at a modest
377 cost in code size. This will only happen in different case
378 branches, so there's no issue about duplicating work.
380 That is, exprIsDupable returns True of (f x) even if
381 f is very very expensive to call.
383 Its only purpose is to avoid fruitless let-binding
384 and then inlining of case join points
388 exprIsDupable (Type _) = True
389 exprIsDupable (Var v) = True
390 exprIsDupable (Lit lit) = litIsDupable lit
391 exprIsDupable (Note InlineMe e) = True
392 exprIsDupable (Note _ e) = exprIsDupable e
393 exprIsDupable (Cast e co) = exprIsDupable e
397 go (Var v) n_args = True
398 go (App f a) n_args = n_args < dupAppSize
401 go other n_args = False
404 dupAppSize = 4 -- Size of application we are prepared to duplicate
407 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
408 it is obviously in weak head normal form, or is cheap to get to WHNF.
409 [Note that that's not the same as exprIsDupable; an expression might be
410 big, and hence not dupable, but still cheap.]
412 By ``cheap'' we mean a computation we're willing to:
413 push inside a lambda, or
414 inline at more than one place
415 That might mean it gets evaluated more than once, instead of being
416 shared. The main examples of things which aren't WHNF but are
421 (where e, and all the ei are cheap)
424 (where e and b are cheap)
427 (where op is a cheap primitive operator)
430 (because we are happy to substitute it inside a lambda)
432 Notice that a variable is considered 'cheap': we can push it inside a lambda,
433 because sharing will make sure it is only evaluated once.
436 exprIsCheap :: CoreExpr -> Bool
437 exprIsCheap (Lit lit) = True
438 exprIsCheap (Type _) = True
439 exprIsCheap (Var _) = True
440 exprIsCheap (Note InlineMe e) = True
441 exprIsCheap (Note _ e) = exprIsCheap e
442 exprIsCheap (Cast e co) = exprIsCheap e
443 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
444 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
445 and [exprIsCheap rhs | (_,_,rhs) <- alts]
446 -- Experimentally, treat (case x of ...) as cheap
447 -- (and case __coerce x etc.)
448 -- This improves arities of overloaded functions where
449 -- there is only dictionary selection (no construction) involved
450 exprIsCheap (Let (NonRec x _) e)
451 | isUnLiftedType (idType x) = exprIsCheap e
453 -- strict lets always have cheap right hand sides,
454 -- and do no allocation.
456 exprIsCheap other_expr -- Applications and variables
459 -- Accumulate value arguments, then decide
460 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
461 | otherwise = go f val_args
463 go (Var f) [] = True -- Just a type application of a variable
464 -- (f t1 t2 t3) counts as WHNF
466 = case globalIdDetails f of
467 RecordSelId {} -> go_sel args
468 ClassOpId _ -> go_sel args
469 PrimOpId op -> go_primop op args
471 DataConWorkId _ -> go_pap args
472 other | length args < idArity f -> go_pap args
474 other -> isBottomingId f
475 -- Application of a function which
476 -- always gives bottom; we treat this as cheap
477 -- because it certainly doesn't need to be shared!
479 go other args = False
482 go_pap args = all exprIsTrivial args
483 -- For constructor applications and primops, check that all
484 -- the args are trivial. We don't want to treat as cheap, say,
486 -- We'll put up with one constructor application, but not dozens
489 go_primop op args = primOpIsCheap op && all exprIsCheap args
490 -- In principle we should worry about primops
491 -- that return a type variable, since the result
492 -- might be applied to something, but I'm not going
493 -- to bother to check the number of args
496 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
497 go_sel other = False -- look cheap, so we will substitute it inside a
498 -- lambda. Particularly for dictionary field selection.
499 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
500 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
503 exprOkForSpeculation returns True of an expression that it is
505 * safe to evaluate even if normal order eval might not
506 evaluate the expression at all, or
508 * safe *not* to evaluate even if normal order would do so
512 the expression guarantees to terminate,
514 without raising an exception,
515 without causing a side effect (e.g. writing a mutable variable)
517 NB: if exprIsHNF e, then exprOkForSpecuation e
520 let x = case y# +# 1# of { r# -> I# r# }
523 case y# +# 1# of { r# ->
528 We can only do this if the (y+1) is ok for speculation: it has no
529 side effects, and can't diverge or raise an exception.
532 exprOkForSpeculation :: CoreExpr -> Bool
533 exprOkForSpeculation (Lit _) = True
534 exprOkForSpeculation (Type _) = True
535 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
536 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
537 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
538 exprOkForSpeculation other_expr
539 = case collectArgs other_expr of
540 (Var f, args) -> spec_ok (globalIdDetails f) args
544 spec_ok (DataConWorkId _) args
545 = True -- The strictness of the constructor has already
546 -- been expressed by its "wrapper", so we don't need
547 -- to take the arguments into account
549 spec_ok (PrimOpId op) args
550 | isDivOp op, -- Special case for dividing operations that fail
551 [arg1, Lit lit] <- args -- only if the divisor is zero
552 = not (isZeroLit lit) && exprOkForSpeculation arg1
553 -- Often there is a literal divisor, and this
554 -- can get rid of a thunk in an inner looop
557 = primOpOkForSpeculation op &&
558 all exprOkForSpeculation args
559 -- A bit conservative: we don't really need
560 -- to care about lazy arguments, but this is easy
562 spec_ok other args = False
564 isDivOp :: PrimOp -> Bool
565 -- True of dyadic operators that can fail
566 -- only if the second arg is zero
567 -- This function probably belongs in PrimOp, or even in
568 -- an automagically generated file.. but it's such a
569 -- special case I thought I'd leave it here for now.
570 isDivOp IntQuotOp = True
571 isDivOp IntRemOp = True
572 isDivOp WordQuotOp = True
573 isDivOp WordRemOp = True
574 isDivOp IntegerQuotRemOp = True
575 isDivOp IntegerDivModOp = True
576 isDivOp FloatDivOp = True
577 isDivOp DoubleDivOp = True
578 isDivOp other = False
583 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
584 exprIsBottom e = go 0 e
586 -- n is the number of args
587 go n (Note _ e) = go n e
588 go n (Cast e co) = go n e
589 go n (Let _ e) = go n e
590 go n (Case e _ _ _) = go 0 e -- Just check the scrut
591 go n (App e _) = go (n+1) e
592 go n (Var v) = idAppIsBottom v n
594 go n (Lam _ _) = False
595 go n (Type _) = False
597 idAppIsBottom :: Id -> Int -> Bool
598 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
601 @exprIsHNF@ returns true for expressions that are certainly *already*
602 evaluated to *head* normal form. This is used to decide whether it's ok
605 case x of _ -> e ===> e
607 and to decide whether it's safe to discard a `seq`
609 So, it does *not* treat variables as evaluated, unless they say they are.
611 But it *does* treat partial applications and constructor applications
612 as values, even if their arguments are non-trivial, provided the argument
614 e.g. (:) (f x) (map f xs) is a value
615 map (...redex...) is a value
616 Because `seq` on such things completes immediately
618 For unlifted argument types, we have to be careful:
620 Suppose (f x) diverges; then C (f x) is not a value. True, but
621 this form is illegal (see the invariants in CoreSyn). Args of unboxed
622 type must be ok-for-speculation (or trivial).
625 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
626 exprIsHNF (Var v) -- NB: There are no value args at this point
627 = isDataConWorkId v -- Catches nullary constructors,
628 -- so that [] and () are values, for example
629 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
630 || isEvaldUnfolding (idUnfolding v)
631 -- Check the thing's unfolding; it might be bound to a value
632 -- A worry: what if an Id's unfolding is just itself:
633 -- then we could get an infinite loop...
635 exprIsHNF (Lit l) = True
636 exprIsHNF (Type ty) = True -- Types are honorary Values;
637 -- we don't mind copying them
638 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
639 exprIsHNF (Note _ e) = exprIsHNF e
640 exprIsHNF (Cast e co) = exprIsHNF e
641 exprIsHNF (App e (Type _)) = exprIsHNF e
642 exprIsHNF (App e a) = app_is_value e [a]
643 exprIsHNF other = False
645 -- There is at least one value argument
646 app_is_value (Var fun) args
647 | isDataConWorkId fun -- Constructor apps are values
648 || idArity fun > valArgCount args -- Under-applied function
649 = check_args (idType fun) args
650 app_is_value (App f a) as = app_is_value f (a:as)
651 app_is_value other as = False
653 -- 'check_args' checks that unlifted-type args
654 -- are in fact guaranteed non-divergent
655 check_args fun_ty [] = True
656 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
657 Just (_, ty) -> check_args ty args
658 check_args fun_ty (arg : args)
659 | isUnLiftedType arg_ty = exprOkForSpeculation arg
660 | otherwise = check_args res_ty args
662 (arg_ty, res_ty) = splitFunTy fun_ty
666 -- deep applies a TyConApp coercion as a substitution to a reflexive coercion
667 -- deepCast t [a1,...,an] co corresponds to deep(t, [a1,...,an], co) from
669 deepCast :: Type -> [TyVar] -> Coercion -> Coercion
670 deepCast ty tyVars co
671 = ASSERT( let {(lty, rty) = coercionKind co;
672 Just (tc1, lArgs) = splitTyConApp_maybe lty;
673 Just (tc2, rArgs) = splitTyConApp_maybe rty}
675 tc1 == tc2 && length lArgs == length rArgs &&
676 length lArgs == length tyVars )
677 substTyWith tyVars coArgs ty
679 -- coArgs = [right (left (left co)), right (left co), right co]
680 coArgs = decomposeCo (length tyVars) co
682 -- These InstPat functions go here to avoid circularity between DataCon and Id
683 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
684 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
685 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
687 dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc
688 -- Remember to include the existential dictionaries
690 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
691 -> [FastString] -- A long enough list of FSs to use for names
692 -> [Unique] -- An equally long list of uniques, at least one for each binder
694 -> [Type] -- Types to instantiate the universally quantified tyvars
695 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
696 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
697 -- (ex_tvs, co_tvs, arg_ids),
699 -- ex_tvs are intended to be used as binders for existential type args
701 -- co_tvs are intended to be used as binders for coercion args and the kinds
702 -- of these vars have been instantiated by the inst_tys and the ex_tys
704 -- arg_ids are indended to be used as binders for value arguments, including
705 -- dicts, and their types have been instantiated with inst_tys and ex_tys
708 -- The following constructor T1
711 -- T1 :: forall b. Int -> b -> T(a,b)
714 -- has representation type
715 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
718 -- dataConInstPat fss us T1 (a1',b') will return
720 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
722 -- where the double-primed variables are created with the FastStrings and
723 -- Uniques given as fss and us
724 dataConInstPat arg_fun fss uniqs con inst_tys
725 = (ex_bndrs, co_bndrs, id_bndrs)
727 univ_tvs = dataConUnivTyVars con
728 ex_tvs = dataConExTyVars con
729 arg_tys = arg_fun con
730 eq_spec = dataConEqSpec con
731 eq_preds = eqSpecPreds eq_spec
734 n_co = length eq_spec
736 -- split the Uniques and FastStrings
737 (ex_uniqs, uniqs') = splitAt n_ex uniqs
738 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
740 (ex_fss, fss') = splitAt n_ex fss
741 (co_fss, id_fss) = splitAt n_co fss'
743 -- make existential type variables
744 mk_ex_var uniq fs var = mkTyVar new_name kind
746 new_name = mkSysTvName uniq fs
749 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
751 -- make the instantiation substitution
752 inst_subst = substTyWith (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
754 -- make new coercion vars, instantiating kind
755 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
757 new_name = mkSysTvName uniq fs
758 co_kind = inst_subst (mkPredTy eq_pred)
760 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
762 -- make value vars, instantiating types
763 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (inst_subst ty) noSrcLoc
764 id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys
766 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
767 -- Returns (Just (dc, [x1..xn])) if the argument expression is
768 -- a constructor application of the form (dc x1 .. xn)
769 exprIsConApp_maybe (Cast expr co)
770 = -- Maybe this is over the top, but here we try to turn
771 -- coerce (S,T) ( x, y )
773 -- ( coerce S x, coerce T y )
774 -- This happens in anger in PrelArrExts which has a coerce
775 -- case coerce memcpy a b of
777 -- where the memcpy is in the IO monad, but the call is in
779 case exprIsConApp_maybe expr of {
783 let (from_ty, to_ty) = coercionKind co in
785 case splitTyConApp_maybe to_ty of {
787 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
788 -- | not (isVanillaDataCon dc) -> Nothing
790 -- Type constructor must match datacon
792 case splitTyConApp_maybe from_ty of {
794 Just (tc', tc_arg_tys') | tc /= tc' -> Nothing
795 -- Both sides of coercion must have the same type constructor
799 -- here we do the PushC reduction rule as described in the FC paper
800 arity = tyConArity tc
801 n_ex_tvs = length dc_ex_tyvars
803 (_univ_args, rest) = splitAt arity args
804 (ex_args, val_args) = splitAt n_ex_tvs rest
806 arg_tys = dataConRepArgTys dc
807 dc_tyvars = dataConUnivTyVars dc
808 dc_ex_tyvars = dataConExTyVars dc
810 deep arg_ty = deepCast arg_ty dc_tyvars co
812 -- first we appropriately cast the value arguments
813 new_val_args = zipWith mkCoerce (map deep arg_tys) val_args
815 -- then we cast the existential coercion arguments
816 orig_tvs = dc_tyvars ++ dc_ex_tyvars
817 gammas = decomposeCo arity co
818 new_tys = gammas ++ (map (\ (Type t) -> t) ex_args)
819 theta = substTyWith orig_tvs new_tys
822 , (ty1, ty2) <- splitCoercionKind (tyVarKind tv)
823 = Type $ mkTransCoercion (mkSymCoercion (theta ty1))
824 (mkTransCoercion ty (theta ty2))
827 new_ex_args = zipWith cast_ty dc_ex_tyvars ex_args
830 ASSERT( all isTypeArg (take arity args) )
831 ASSERT( equalLength val_args arg_tys )
832 Just (dc, map Type tc_arg_tys ++ new_ex_args ++ new_val_args)
835 exprIsConApp_maybe (Note _ expr)
836 = exprIsConApp_maybe expr
837 -- We ignore InlineMe notes in case we have
838 -- x = __inline_me__ (a,b)
839 -- All part of making sure that INLINE pragmas never hurt
840 -- Marcin tripped on this one when making dictionaries more inlinable
842 -- In fact, we ignore all notes. For example,
843 -- case _scc_ "foo" (C a b) of
845 -- should be optimised away, but it will be only if we look
846 -- through the SCC note.
848 exprIsConApp_maybe expr = analyse (collectArgs expr)
850 analyse (Var fun, args)
851 | Just con <- isDataConWorkId_maybe fun,
852 args `lengthAtLeast` dataConRepArity con
853 -- Might be > because the arity excludes type args
856 -- Look through unfoldings, but only cheap ones, because
857 -- we are effectively duplicating the unfolding
858 analyse (Var fun, [])
859 | let unf = idUnfolding fun,
861 = exprIsConApp_maybe (unfoldingTemplate unf)
863 analyse other = Nothing
868 %************************************************************************
870 \subsection{Eta reduction and expansion}
872 %************************************************************************
875 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
876 {- The Arity returned is the number of value args the
877 thing can be applied to without doing much work
879 exprEtaExpandArity is used when eta expanding
882 It returns 1 (or more) to:
883 case x of p -> \s -> ...
884 because for I/O ish things we really want to get that \s to the top.
885 We are prepared to evaluate x each time round the loop in order to get that
887 It's all a bit more subtle than it looks:
891 Consider one-shot lambdas
892 let x = expensive in \y z -> E
893 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
894 Hence the ArityType returned by arityType
896 2. The state-transformer hack
898 The one-shot lambda special cause is particularly important/useful for
899 IO state transformers, where we often get
900 let x = E in \ s -> ...
902 and the \s is a real-world state token abstraction. Such abstractions
903 are almost invariably 1-shot, so we want to pull the \s out, past the
904 let x=E, even if E is expensive. So we treat state-token lambdas as
905 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
907 3. Dealing with bottom
910 f = \x -> error "foo"
911 Here, arity 1 is fine. But if it is
915 then we want to get arity 2. Tecnically, this isn't quite right, because
917 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
918 do so; it improves some programs significantly, and increasing convergence
919 isn't a bad thing. Hence the ABot/ATop in ArityType.
921 Actually, the situation is worse. Consider
925 Can we eta-expand here? At first the answer looks like "yes of course", but
928 This should diverge! But if we eta-expand, it won't. Again, we ignore this
929 "problem", because being scrupulous would lose an important transformation for
935 Non-recursive newtypes are transparent, and should not get in the way.
936 We do (currently) eta-expand recursive newtypes too. So if we have, say
938 newtype T = MkT ([T] -> Int)
942 where f has arity 1. Then: etaExpandArity e = 1;
943 that is, etaExpandArity looks through the coerce.
945 When we eta-expand e to arity 1: eta_expand 1 e T
946 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
948 HOWEVER, note that if you use coerce bogusly you can ge
950 And since negate has arity 2, you might try to eta expand. But you can't
951 decopose Int to a function type. Hence the final case in eta_expand.
955 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
957 -- A limited sort of function type
958 data ArityType = AFun Bool ArityType -- True <=> one-shot
959 | ATop -- Know nothing
962 arityDepth :: ArityType -> Arity
963 arityDepth (AFun _ ty) = 1 + arityDepth ty
966 andArityType ABot at2 = at2
967 andArityType ATop at2 = ATop
968 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
969 andArityType at1 at2 = andArityType at2 at1
971 arityType :: DynFlags -> CoreExpr -> ArityType
972 -- (go1 e) = [b1,..,bn]
973 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
974 -- where bi is True <=> the lambda is one-shot
976 arityType dflags (Note n e) = arityType dflags e
977 -- Not needed any more: etaExpand is cleverer
978 -- | ok_note n = arityType dflags e
979 -- | otherwise = ATop
981 arityType dflags (Cast e co) = arityType dflags e
983 arityType dflags (Var v)
984 = mk (idArity v) (arg_tys (idType v))
986 mk :: Arity -> [Type] -> ArityType
987 -- The argument types are only to steer the "state hack"
988 -- Consider case x of
990 -- False -> \(s:RealWorld) -> e
991 -- where foo has arity 1. Then we want the state hack to
992 -- apply to foo too, so we can eta expand the case.
993 mk 0 tys | isBottomingId v = ABot
994 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
996 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
997 mk n [] = AFun False (mk (n-1) [])
999 arg_tys :: Type -> [Type] -- Ignore for-alls
1001 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1002 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1005 -- Lambdas; increase arity
1006 arityType dflags (Lam x e)
1007 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1008 | otherwise = arityType dflags e
1010 -- Applications; decrease arity
1011 arityType dflags (App f (Type _)) = arityType dflags f
1012 arityType dflags (App f a) = case arityType dflags f of
1013 AFun one_shot xs | exprIsCheap a -> xs
1016 -- Case/Let; keep arity if either the expression is cheap
1017 -- or it's a 1-shot lambda
1018 -- The former is not really right for Haskell
1019 -- f x = case x of { (a,b) -> \y. e }
1021 -- f x y = case x of { (a,b) -> e }
1022 -- The difference is observable using 'seq'
1023 arityType dflags (Case scrut _ _ alts)
1024 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1025 xs | exprIsCheap scrut -> xs
1026 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1029 arityType dflags (Let b e)
1030 = case arityType dflags e of
1031 xs | cheap_bind b -> xs
1032 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1035 cheap_bind (NonRec b e) = is_cheap (b,e)
1036 cheap_bind (Rec prs) = all is_cheap prs
1037 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1039 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1040 -- dictionary bindings. This improves arities. Thereby, it also
1041 -- means that full laziness is less prone to floating out the
1042 -- application of a function to its dictionary arguments, which
1043 -- can thereby lose opportunities for fusion. Example:
1044 -- foo :: Ord a => a -> ...
1045 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1046 -- -- So foo has arity 1
1048 -- f = \x. foo dInt $ bar x
1050 -- The (foo DInt) is floated out, and makes ineffective a RULE
1051 -- foo (bar x) = ...
1053 -- One could go further and make exprIsCheap reply True to any
1054 -- dictionary-typed expression, but that's more work.
1056 arityType dflags other = ATop
1058 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1059 ok_note InlineMe = False
1060 ok_note other = True
1061 -- Notice that we do not look through __inline_me__
1062 -- This may seem surprising, but consider
1063 -- f = _inline_me (\x -> e)
1064 -- We DO NOT want to eta expand this to
1065 -- f = \x -> (_inline_me (\x -> e)) x
1066 -- because the _inline_me gets dropped now it is applied,
1075 etaExpand :: Arity -- Result should have this number of value args
1077 -> CoreExpr -> Type -- Expression and its type
1079 -- (etaExpand n us e ty) returns an expression with
1080 -- the same meaning as 'e', but with arity 'n'.
1082 -- Given e' = etaExpand n us e ty
1084 -- ty = exprType e = exprType e'
1086 -- Note that SCCs are not treated specially. If we have
1087 -- etaExpand 2 (\x -> scc "foo" e)
1088 -- = (\xy -> (scc "foo" e) y)
1089 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1091 etaExpand n us expr ty
1092 | manifestArity expr >= n = expr -- The no-op case
1094 = eta_expand n us expr ty
1097 -- manifestArity sees how many leading value lambdas there are
1098 manifestArity :: CoreExpr -> Arity
1099 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1100 | otherwise = manifestArity e
1101 manifestArity (Note _ e) = manifestArity e
1102 manifestArity (Cast e _) = manifestArity e
1105 -- etaExpand deals with for-alls. For example:
1107 -- where E :: forall a. a -> a
1109 -- (/\b. \y::a -> E b y)
1111 -- It deals with coerces too, though they are now rare
1112 -- so perhaps the extra code isn't worth it
1114 eta_expand n us expr ty
1116 -- The ILX code generator requires eta expansion for type arguments
1117 -- too, but alas the 'n' doesn't tell us how many of them there
1118 -- may be. So we eagerly eta expand any big lambdas, and just
1119 -- cross our fingers about possible loss of sharing in the ILX case.
1120 -- The Right Thing is probably to make 'arity' include
1121 -- type variables throughout the compiler. (ToDo.)
1123 -- Saturated, so nothing to do
1126 -- Short cut for the case where there already
1127 -- is a lambda; no point in gratuitously adding more
1128 eta_expand n us (Lam v body) ty
1130 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1133 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1135 -- We used to have a special case that stepped inside Coerces here,
1136 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1137 -- = Note note (eta_expand n us e ty)
1138 -- BUT this led to an infinite loop
1139 -- Example: newtype T = MkT (Int -> Int)
1140 -- eta_expand 1 (coerce (Int->Int) e)
1141 -- --> coerce (Int->Int) (eta_expand 1 T e)
1143 -- --> coerce (Int->Int) (coerce T
1144 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1145 -- by the splitNewType_maybe case below
1148 eta_expand n us expr ty
1149 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1150 case splitForAllTy_maybe ty of {
1153 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1155 lam_tv = mkTyVar (mkSysTvName uniq FSLIT("etaT")) (tyVarKind tv)
1159 case splitFunTy_maybe ty of {
1160 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1162 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1168 -- newtype T = MkT ([T] -> Int)
1169 -- Consider eta-expanding this
1172 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1174 case splitNewTypeRepCo_maybe ty of {
1176 mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ;
1179 -- We have an expression of arity > 0, but its type isn't a function
1180 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1181 -- Essentially the programmer is playing fast and loose with types
1182 -- (Happy does this a lot). So we simply decline to eta-expand.
1187 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1188 It tells how many things the expression can be applied to before doing
1189 any work. It doesn't look inside cases, lets, etc. The idea is that
1190 exprEtaExpandArity will do the hard work, leaving something that's easy
1191 for exprArity to grapple with. In particular, Simplify uses exprArity to
1192 compute the ArityInfo for the Id.
1194 Originally I thought that it was enough just to look for top-level lambdas, but
1195 it isn't. I've seen this
1197 foo = PrelBase.timesInt
1199 We want foo to get arity 2 even though the eta-expander will leave it
1200 unchanged, in the expectation that it'll be inlined. But occasionally it
1201 isn't, because foo is blacklisted (used in a rule).
1203 Similarly, see the ok_note check in exprEtaExpandArity. So
1204 f = __inline_me (\x -> e)
1205 won't be eta-expanded.
1207 And in any case it seems more robust to have exprArity be a bit more intelligent.
1208 But note that (\x y z -> f x y z)
1209 should have arity 3, regardless of f's arity.
1212 exprArity :: CoreExpr -> Arity
1215 go (Var v) = idArity v
1216 go (Lam x e) | isId x = go e + 1
1218 go (Note n e) = go e
1219 go (Cast e _) = go e
1220 go (App e (Type t)) = go e
1221 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1222 -- NB: exprIsCheap a!
1223 -- f (fac x) does not have arity 2,
1224 -- even if f has arity 3!
1225 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1226 -- unknown, hence arity 0
1230 %************************************************************************
1232 \subsection{Equality}
1234 %************************************************************************
1236 @cheapEqExpr@ is a cheap equality test which bales out fast!
1237 True => definitely equal
1238 False => may or may not be equal
1241 cheapEqExpr :: Expr b -> Expr b -> Bool
1243 cheapEqExpr (Var v1) (Var v2) = v1==v2
1244 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1245 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1247 cheapEqExpr (App f1 a1) (App f2 a2)
1248 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1250 cheapEqExpr _ _ = False
1252 exprIsBig :: Expr b -> Bool
1253 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1254 exprIsBig (Lit _) = False
1255 exprIsBig (Var v) = False
1256 exprIsBig (Type t) = False
1257 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1258 exprIsBig other = True
1263 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1264 -- Used in rule matching, so does *not* look through
1265 -- newtypes, predicate types; hence tcEqExpr
1267 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1269 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1271 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1272 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1273 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1274 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1275 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1276 tcEqExprX env (Let (NonRec v1 r1) e1)
1277 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1278 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1279 tcEqExprX env (Let (Rec ps1) e1)
1280 (Let (Rec ps2) e2) = equalLength ps1 ps2
1281 && and (zipWith eq_rhs ps1 ps2)
1282 && tcEqExprX env' e1 e2
1284 env' = foldl2 rn_bndr2 env ps2 ps2
1285 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1286 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1287 tcEqExprX env (Case e1 v1 t1 a1)
1288 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1289 && tcEqTypeX env t1 t2
1290 && equalLength a1 a2
1291 && and (zipWith (eq_alt env') a1 a2)
1293 env' = rnBndr2 env v1 v2
1295 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1296 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1297 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1298 tcEqExprX env e1 e2 = False
1300 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1302 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1303 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1304 eq_note env other1 other2 = False
1308 %************************************************************************
1310 \subsection{The size of an expression}
1312 %************************************************************************
1315 coreBindsSize :: [CoreBind] -> Int
1316 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1318 exprSize :: CoreExpr -> Int
1319 -- A measure of the size of the expressions
1320 -- It also forces the expression pretty drastically as a side effect
1321 exprSize (Var v) = v `seq` 1
1322 exprSize (Lit lit) = lit `seq` 1
1323 exprSize (App f a) = exprSize f + exprSize a
1324 exprSize (Lam b e) = varSize b + exprSize e
1325 exprSize (Let b e) = bindSize b + exprSize e
1326 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1327 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1328 exprSize (Note n e) = noteSize n + exprSize e
1329 exprSize (Type t) = seqType t `seq` 1
1331 noteSize (SCC cc) = cc `seq` 1
1332 noteSize InlineMe = 1
1333 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1335 varSize :: Var -> Int
1336 varSize b | isTyVar b = 1
1337 | otherwise = seqType (idType b) `seq`
1338 megaSeqIdInfo (idInfo b) `seq`
1341 varsSize = foldr ((+) . varSize) 0
1343 bindSize (NonRec b e) = varSize b + exprSize e
1344 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1346 pairSize (b,e) = varSize b + exprSize e
1348 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1352 %************************************************************************
1354 \subsection{Hashing}
1356 %************************************************************************
1359 hashExpr :: CoreExpr -> Int
1360 -- Two expressions that hash to the same Int may be equal (but may not be)
1361 -- Two expressions that hash to the different Ints are definitely unequal
1363 -- But "unequal" here means "not identical"; two alpha-equivalent
1364 -- expressions may hash to the different Ints
1366 -- The emphasis is on a crude, fast hash, rather than on high precision
1368 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1371 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1373 hash_expr (Note _ e) = hash_expr e
1374 hash_expr (Cast e co) = hash_expr e
1375 hash_expr (Let (NonRec b r) e) = hashId b
1376 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1377 hash_expr (Case _ b _ _) = hashId b
1378 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1379 hash_expr (Var v) = hashId v
1380 hash_expr (Lit lit) = hashLiteral lit
1381 hash_expr (Lam b _) = hashId b
1382 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1384 fast_hash_expr (Var v) = hashId v
1385 fast_hash_expr (Lit lit) = hashLiteral lit
1386 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1387 fast_hash_expr (App f a) = fast_hash_expr a
1388 fast_hash_expr (Lam b _) = hashId b
1389 fast_hash_expr other = 1
1392 hashId id = hashName (idName id)
1395 %************************************************************************
1397 \subsection{Determining non-updatable right-hand-sides}
1399 %************************************************************************
1401 Top-level constructor applications can usually be allocated
1402 statically, but they can't if the constructor, or any of the
1403 arguments, come from another DLL (because we can't refer to static
1404 labels in other DLLs).
1406 If this happens we simply make the RHS into an updatable thunk,
1407 and 'exectute' it rather than allocating it statically.
1410 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1411 -- This function is called only on *top-level* right-hand sides
1412 -- Returns True if the RHS can be allocated statically, with
1413 -- no thunks involved at all.
1415 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1416 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1417 -- update flag on it.
1419 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1420 -- (a) a value lambda
1421 -- (b) a saturated constructor application with static args
1423 -- BUT watch out for
1424 -- (i) Any cross-DLL references kill static-ness completely
1425 -- because they must be 'executed' not statically allocated
1426 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1427 -- this is not necessary)
1429 -- (ii) We treat partial applications as redexes, because in fact we
1430 -- make a thunk for them that runs and builds a PAP
1431 -- at run-time. The only appliations that are treated as
1432 -- static are *saturated* applications of constructors.
1434 -- We used to try to be clever with nested structures like this:
1435 -- ys = (:) w ((:) w [])
1436 -- on the grounds that CorePrep will flatten ANF-ise it later.
1437 -- But supporting this special case made the function much more
1438 -- complicated, because the special case only applies if there are no
1439 -- enclosing type lambdas:
1440 -- ys = /\ a -> Foo (Baz ([] a))
1441 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1443 -- But in fact, even without -O, nested structures at top level are
1444 -- flattened by the simplifier, so we don't need to be super-clever here.
1448 -- f = \x::Int. x+7 TRUE
1449 -- p = (True,False) TRUE
1451 -- d = (fst p, False) FALSE because there's a redex inside
1452 -- (this particular one doesn't happen but...)
1454 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1455 -- n = /\a. Nil a TRUE
1457 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1460 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1461 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1463 -- b) (C x xs), where C is a contructors is updatable if the application is
1466 -- c) don't look through unfolding of f in (f x).
1468 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1469 -- them as making the RHS re-entrant (non-updatable).
1471 rhsIsStatic this_pkg rhs = is_static False rhs
1473 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1476 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1478 is_static in_arg (Note (SCC _) e) = False
1479 is_static in_arg (Note _ e) = is_static in_arg e
1480 is_static in_arg (Cast e co) = is_static in_arg e
1482 is_static in_arg (Lit lit)
1484 MachLabel _ _ -> False
1486 -- A MachLabel (foreign import "&foo") in an argument
1487 -- prevents a constructor application from being static. The
1488 -- reason is that it might give rise to unresolvable symbols
1489 -- in the object file: under Linux, references to "weak"
1490 -- symbols from the data segment give rise to "unresolvable
1491 -- relocation" errors at link time This might be due to a bug
1492 -- in the linker, but we'll work around it here anyway.
1495 is_static in_arg other_expr = go other_expr 0
1497 go (Var f) n_val_args
1498 #if mingw32_TARGET_OS
1499 | not (isDllName this_pkg (idName f))
1501 = saturated_data_con f n_val_args
1502 || (in_arg && n_val_args == 0)
1503 -- A naked un-applied variable is *not* deemed a static RHS
1505 -- Reason: better to update so that the indirection gets shorted
1506 -- out, and the true value will be seen
1507 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1508 -- are always updatable. If you do so, make sure that non-updatable
1509 -- ones have enough space for their static link field!
1511 go (App f a) n_val_args
1512 | isTypeArg a = go f n_val_args
1513 | not in_arg && is_static True a = go f (n_val_args + 1)
1514 -- The (not in_arg) checks that we aren't in a constructor argument;
1515 -- if we are, we don't allow (value) applications of any sort
1517 -- NB. In case you wonder, args are sometimes not atomic. eg.
1518 -- x = D# (1.0## /## 2.0##)
1519 -- can't float because /## can fail.
1521 go (Note (SCC _) f) n_val_args = False
1522 go (Note _ f) n_val_args = go f n_val_args
1523 go (Cast e co) n_val_args = go e n_val_args
1525 go other n_val_args = False
1527 saturated_data_con f n_val_args
1528 = case isDataConWorkId_maybe f of
1529 Just dc -> n_val_args == dataConRepArity dc