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, dataConRepOccInstPat
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, setVarUnique,
48 mkCoVar, mkTyVar, mkCoVar )
49 import OccName ( OccName, occNameFS, mkVarOcc )
50 import VarSet ( unionVarSet )
52 import Name ( hashName, mkSysTvName )
54 import Packages ( isDllName )
56 import Literal ( hashLiteral, literalType, litIsDupable,
57 litIsTrivial, isZeroLit, Literal( MachLabel ) )
58 import DataCon ( DataCon, dataConRepArity, eqSpecPreds,
59 isVanillaDataCon, dataConTyCon, dataConRepArgTys,
60 dataConUnivTyVars, dataConExTyVars, dataConEqSpec,
62 import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
63 import Id ( Id, idType, globalIdDetails, idNewStrictness,
64 mkWildId, idArity, idName, idUnfolding, idInfo,
65 isOneShotBndr, isStateHackType, isDataConWorkId_maybe, mkSysLocal,
66 isDataConWorkId, isBottomingId, isDictId
68 import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo )
69 import NewDemand ( appIsBottom )
70 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
71 splitFunTy, tcEqTypeX,
72 applyTys, isUnLiftedType, seqType, mkTyVarTy,
73 splitForAllTy_maybe, isForAllTy, splitRecNewType_maybe,
74 splitTyConApp_maybe, coreEqType, funResultTy, applyTy,
77 import Coercion ( Coercion, mkTransCoercion, coercionKind,
78 splitNewTypeRepCo_maybe, mkSymCoercion, mkLeftCoercion,
79 mkRightCoercion, decomposeCo, coercionKindPredTy,
80 splitCoercionKind, mkEqPred )
81 import TyCon ( tyConArity )
82 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
83 import CostCentre ( CostCentre )
84 import BasicTypes ( Arity )
85 import PackageConfig ( PackageId )
86 import Unique ( Unique )
88 import DynFlags ( DynFlags, DynFlag(Opt_DictsCheap), dopt )
89 import TysPrim ( alphaTy ) -- Debugging only
90 import Util ( equalLength, lengthAtLeast, foldl2 )
91 import FastString ( mkFastString )
95 %************************************************************************
97 \subsection{Find the type of a Core atom/expression}
99 %************************************************************************
102 exprType :: CoreExpr -> Type
104 exprType (Var var) = idType var
105 exprType (Lit lit) = literalType lit
106 exprType (Let _ body) = exprType body
107 exprType (Case _ _ ty alts) = ty
109 = let (_, ty) = coercionKind co in ty
110 exprType (Note other_note e) = exprType e
111 exprType (Lam binder expr) = mkPiType binder (exprType expr)
113 = case collectArgs e of
114 (fun, args) -> applyTypeToArgs e (exprType fun) args
116 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
118 coreAltType :: CoreAlt -> Type
119 coreAltType (_,_,rhs) = exprType rhs
122 @mkPiType@ makes a (->) type or a forall type, depending on whether
123 it is given a type variable or a term variable. We cleverly use the
124 lbvarinfo field to figure out the right annotation for the arrove in
125 case of a term variable.
128 mkPiType :: Var -> Type -> Type -- The more polymorphic version
129 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
131 mkPiTypes vs ty = foldr mkPiType ty vs
134 | isId v = mkFunTy (idType v) ty
135 | otherwise = mkForAllTy v ty
139 applyTypeToArg :: Type -> CoreExpr -> Type
140 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
141 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
143 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
144 -- A more efficient version of applyTypeToArg
145 -- when we have several args
146 -- The first argument is just for debugging
147 applyTypeToArgs e op_ty [] = op_ty
149 applyTypeToArgs e op_ty (Type ty : args)
150 = -- Accumulate type arguments so we can instantiate all at once
153 go rev_tys (Type ty : args) = go (ty:rev_tys) args
154 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
156 op_ty' = applyTys op_ty (reverse rev_tys)
158 applyTypeToArgs e op_ty (other_arg : args)
159 = case (splitFunTy_maybe op_ty) of
160 Just (_, res_ty) -> applyTypeToArgs e res_ty args
161 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
166 %************************************************************************
168 \subsection{Attaching notes}
170 %************************************************************************
172 mkNote removes redundant coercions, and SCCs where possible
176 mkNote :: Note -> CoreExpr -> CoreExpr
177 mkNote (SCC cc) expr = mkSCC cc expr
178 mkNote InlineMe expr = mkInlineMe expr
179 mkNote note expr = Note note expr
183 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
184 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
185 not be *applied* to anything.
187 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
190 f = inline_me (coerce t fw)
191 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
192 We want the split, so that the coerces can cancel at the call site.
194 However, we can get left with tiresome type applications. Notably, consider
195 f = /\ a -> let t = e in (t, w)
196 Then lifting the let out of the big lambda gives
198 f = /\ a -> let t = inline_me (t' a) in (t, w)
199 The inline_me is to stop the simplifier inlining t' right back
200 into t's RHS. In the next phase we'll substitute for t (since
201 its rhs is trivial) and *then* we could get rid of the inline_me.
202 But it hardly seems worth it, so I don't bother.
205 mkInlineMe (Var v) = Var v
206 mkInlineMe e = Note InlineMe e
212 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
213 mkCoerce co (Cast expr co2)
214 = ASSERT(let { (from_ty, to_ty) = coercionKind co;
215 (from_ty2, to_ty2) = coercionKind co2} in
216 from_ty `coreEqType` to_ty2 )
217 mkCoerce (mkTransCoercion co2 co) expr
220 = let (from_ty, to_ty) = coercionKind co in
221 -- if to_ty `coreEqType` from_ty
224 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
229 mkSCC :: CostCentre -> Expr b -> Expr b
230 -- Note: Nested SCC's *are* preserved for the benefit of
231 -- cost centre stack profiling
232 mkSCC cc (Lit lit) = Lit lit
233 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
234 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
235 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
236 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
237 mkSCC cc expr = Note (SCC cc) expr
241 %************************************************************************
243 \subsection{Other expression construction}
245 %************************************************************************
248 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
249 -- (bindNonRec x r b) produces either
252 -- case r of x { _DEFAULT_ -> b }
254 -- depending on whether x is unlifted or not
255 -- It's used by the desugarer to avoid building bindings
256 -- that give Core Lint a heart attack. Actually the simplifier
257 -- deals with them perfectly well.
259 bindNonRec bndr rhs body
260 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
261 | otherwise = Let (NonRec bndr rhs) body
263 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
264 -- Make a case expression instead of a let
265 -- These can arise either from the desugarer,
266 -- or from beta reductions: (\x.e) (x +# y)
270 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
271 -- This guy constructs the value that the scrutinee must have
272 -- when you are in one particular branch of a case
273 mkAltExpr (DataAlt con) args inst_tys
274 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
275 mkAltExpr (LitAlt lit) [] []
278 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
279 mkIfThenElse guard then_expr else_expr
280 -- Not going to be refining, so okay to take the type of the "then" clause
281 = Case guard (mkWildId boolTy) (exprType then_expr)
282 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
283 (DataAlt trueDataCon, [], then_expr) ]
287 %************************************************************************
289 \subsection{Taking expressions apart}
291 %************************************************************************
293 The default alternative must be first, if it exists at all.
294 This makes it easy to find, though it makes matching marginally harder.
297 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
298 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
299 findDefault alts = (alts, Nothing)
301 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
304 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
305 other -> go alts panic_deflt
307 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
310 go (alt@(con1,_,_) : alts) deflt
311 = case con `cmpAltCon` con1 of
312 LT -> deflt -- Missed it already; the alts are in increasing order
314 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
316 isDefaultAlt :: CoreAlt -> Bool
317 isDefaultAlt (DEFAULT, _, _) = True
318 isDefaultAlt other = False
320 ---------------------------------
321 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
322 -- Merge preserving order; alternatives in the first arg
323 -- shadow ones in the second
324 mergeAlts [] as2 = as2
325 mergeAlts as1 [] = as1
326 mergeAlts (a1:as1) (a2:as2)
327 = case a1 `cmpAlt` a2 of
328 LT -> a1 : mergeAlts as1 (a2:as2)
329 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
330 GT -> a2 : mergeAlts (a1:as1) as2
334 %************************************************************************
336 \subsection{Figuring out things about expressions}
338 %************************************************************************
340 @exprIsTrivial@ is true of expressions we are unconditionally happy to
341 duplicate; simple variables and constants, and type
342 applications. Note that primop Ids aren't considered
345 @exprIsBottom@ is true of expressions that are guaranteed to diverge
348 There used to be a gruesome test for (hasNoBinding v) in the
350 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
351 The idea here is that a constructor worker, like $wJust, is
352 really short for (\x -> $wJust x), becuase $wJust has no binding.
353 So it should be treated like a lambda. Ditto unsaturated primops.
354 But now constructor workers are not "have-no-binding" Ids. And
355 completely un-applied primops and foreign-call Ids are sufficiently
356 rare that I plan to allow them to be duplicated and put up with
359 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
360 a) it really generates code, (and a heap object when it's
361 a function arg) to capture the cost centre
362 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
365 exprIsTrivial (Var v) = True -- See notes above
366 exprIsTrivial (Type _) = True
367 exprIsTrivial (Lit lit) = litIsTrivial lit
368 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
369 exprIsTrivial (Note (SCC _) e) = False -- See notes above
370 exprIsTrivial (Note _ e) = exprIsTrivial e
371 exprIsTrivial (Cast e co) = exprIsTrivial e
372 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
373 exprIsTrivial other = False
377 @exprIsDupable@ is true of expressions that can be duplicated at a modest
378 cost in code size. This will only happen in different case
379 branches, so there's no issue about duplicating work.
381 That is, exprIsDupable returns True of (f x) even if
382 f is very very expensive to call.
384 Its only purpose is to avoid fruitless let-binding
385 and then inlining of case join points
389 exprIsDupable (Type _) = True
390 exprIsDupable (Var v) = True
391 exprIsDupable (Lit lit) = litIsDupable lit
392 exprIsDupable (Note InlineMe e) = True
393 exprIsDupable (Note _ e) = exprIsDupable e
394 exprIsDupable (Cast e co) = exprIsDupable e
398 go (Var v) n_args = True
399 go (App f a) n_args = n_args < dupAppSize
402 go other n_args = False
405 dupAppSize = 4 -- Size of application we are prepared to duplicate
408 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
409 it is obviously in weak head normal form, or is cheap to get to WHNF.
410 [Note that that's not the same as exprIsDupable; an expression might be
411 big, and hence not dupable, but still cheap.]
413 By ``cheap'' we mean a computation we're willing to:
414 push inside a lambda, or
415 inline at more than one place
416 That might mean it gets evaluated more than once, instead of being
417 shared. The main examples of things which aren't WHNF but are
422 (where e, and all the ei are cheap)
425 (where e and b are cheap)
428 (where op is a cheap primitive operator)
431 (because we are happy to substitute it inside a lambda)
433 Notice that a variable is considered 'cheap': we can push it inside a lambda,
434 because sharing will make sure it is only evaluated once.
437 exprIsCheap :: CoreExpr -> Bool
438 exprIsCheap (Lit lit) = True
439 exprIsCheap (Type _) = True
440 exprIsCheap (Var _) = True
441 exprIsCheap (Note InlineMe e) = True
442 exprIsCheap (Note _ e) = exprIsCheap e
443 exprIsCheap (Cast e co) = exprIsCheap e
444 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
445 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
446 and [exprIsCheap rhs | (_,_,rhs) <- alts]
447 -- Experimentally, treat (case x of ...) as cheap
448 -- (and case __coerce x etc.)
449 -- This improves arities of overloaded functions where
450 -- there is only dictionary selection (no construction) involved
451 exprIsCheap (Let (NonRec x _) e)
452 | isUnLiftedType (idType x) = exprIsCheap e
454 -- strict lets always have cheap right hand sides,
455 -- and do no allocation.
457 exprIsCheap other_expr -- Applications and variables
460 -- Accumulate value arguments, then decide
461 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
462 | otherwise = go f val_args
464 go (Var f) [] = True -- Just a type application of a variable
465 -- (f t1 t2 t3) counts as WHNF
467 = case globalIdDetails f of
468 RecordSelId {} -> go_sel args
469 ClassOpId _ -> go_sel args
470 PrimOpId op -> go_primop op args
472 DataConWorkId _ -> go_pap args
473 other | length args < idArity f -> go_pap args
475 other -> isBottomingId f
476 -- Application of a function which
477 -- always gives bottom; we treat this as cheap
478 -- because it certainly doesn't need to be shared!
480 go other args = False
483 go_pap args = all exprIsTrivial args
484 -- For constructor applications and primops, check that all
485 -- the args are trivial. We don't want to treat as cheap, say,
487 -- We'll put up with one constructor application, but not dozens
490 go_primop op args = primOpIsCheap op && all exprIsCheap args
491 -- In principle we should worry about primops
492 -- that return a type variable, since the result
493 -- might be applied to something, but I'm not going
494 -- to bother to check the number of args
497 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
498 go_sel other = False -- look cheap, so we will substitute it inside a
499 -- lambda. Particularly for dictionary field selection.
500 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
501 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
504 exprOkForSpeculation returns True of an expression that it is
506 * safe to evaluate even if normal order eval might not
507 evaluate the expression at all, or
509 * safe *not* to evaluate even if normal order would do so
513 the expression guarantees to terminate,
515 without raising an exception,
516 without causing a side effect (e.g. writing a mutable variable)
518 NB: if exprIsHNF e, then exprOkForSpecuation e
521 let x = case y# +# 1# of { r# -> I# r# }
524 case y# +# 1# of { r# ->
529 We can only do this if the (y+1) is ok for speculation: it has no
530 side effects, and can't diverge or raise an exception.
533 exprOkForSpeculation :: CoreExpr -> Bool
534 exprOkForSpeculation (Lit _) = True
535 exprOkForSpeculation (Type _) = True
536 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
537 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
538 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
539 exprOkForSpeculation other_expr
540 = case collectArgs other_expr of
541 (Var f, args) -> spec_ok (globalIdDetails f) args
545 spec_ok (DataConWorkId _) args
546 = True -- The strictness of the constructor has already
547 -- been expressed by its "wrapper", so we don't need
548 -- to take the arguments into account
550 spec_ok (PrimOpId op) args
551 | isDivOp op, -- Special case for dividing operations that fail
552 [arg1, Lit lit] <- args -- only if the divisor is zero
553 = not (isZeroLit lit) && exprOkForSpeculation arg1
554 -- Often there is a literal divisor, and this
555 -- can get rid of a thunk in an inner looop
558 = primOpOkForSpeculation op &&
559 all exprOkForSpeculation args
560 -- A bit conservative: we don't really need
561 -- to care about lazy arguments, but this is easy
563 spec_ok other args = False
565 isDivOp :: PrimOp -> Bool
566 -- True of dyadic operators that can fail
567 -- only if the second arg is zero
568 -- This function probably belongs in PrimOp, or even in
569 -- an automagically generated file.. but it's such a
570 -- special case I thought I'd leave it here for now.
571 isDivOp IntQuotOp = True
572 isDivOp IntRemOp = True
573 isDivOp WordQuotOp = True
574 isDivOp WordRemOp = True
575 isDivOp IntegerQuotRemOp = True
576 isDivOp IntegerDivModOp = True
577 isDivOp FloatDivOp = True
578 isDivOp DoubleDivOp = True
579 isDivOp other = False
584 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
585 exprIsBottom e = go 0 e
587 -- n is the number of args
588 go n (Note _ e) = go n e
589 go n (Cast e co) = go n e
590 go n (Let _ e) = go n e
591 go n (Case e _ _ _) = go 0 e -- Just check the scrut
592 go n (App e _) = go (n+1) e
593 go n (Var v) = idAppIsBottom v n
595 go n (Lam _ _) = False
596 go n (Type _) = False
598 idAppIsBottom :: Id -> Int -> Bool
599 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
602 @exprIsHNF@ returns true for expressions that are certainly *already*
603 evaluated to *head* normal form. This is used to decide whether it's ok
606 case x of _ -> e ===> e
608 and to decide whether it's safe to discard a `seq`
610 So, it does *not* treat variables as evaluated, unless they say they are.
612 But it *does* treat partial applications and constructor applications
613 as values, even if their arguments are non-trivial, provided the argument
615 e.g. (:) (f x) (map f xs) is a value
616 map (...redex...) is a value
617 Because `seq` on such things completes immediately
619 For unlifted argument types, we have to be careful:
621 Suppose (f x) diverges; then C (f x) is not a value. True, but
622 this form is illegal (see the invariants in CoreSyn). Args of unboxed
623 type must be ok-for-speculation (or trivial).
626 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
627 exprIsHNF (Var v) -- NB: There are no value args at this point
628 = isDataConWorkId v -- Catches nullary constructors,
629 -- so that [] and () are values, for example
630 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
631 || isEvaldUnfolding (idUnfolding v)
632 -- Check the thing's unfolding; it might be bound to a value
633 -- A worry: what if an Id's unfolding is just itself:
634 -- then we could get an infinite loop...
636 exprIsHNF (Lit l) = True
637 exprIsHNF (Type ty) = True -- Types are honorary Values;
638 -- we don't mind copying them
639 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
640 exprIsHNF (Note _ e) = exprIsHNF e
641 exprIsHNF (Cast e co) = exprIsHNF e
642 exprIsHNF (App e (Type _)) = exprIsHNF e
643 exprIsHNF (App e a) = app_is_value e [a]
644 exprIsHNF other = False
646 -- There is at least one value argument
647 app_is_value (Var fun) args
648 | isDataConWorkId fun -- Constructor apps are values
649 || idArity fun > valArgCount args -- Under-applied function
650 = check_args (idType fun) args
651 app_is_value (App f a) as = app_is_value f (a:as)
652 app_is_value other as = False
654 -- 'check_args' checks that unlifted-type args
655 -- are in fact guaranteed non-divergent
656 check_args fun_ty [] = True
657 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
658 Just (_, ty) -> check_args ty args
659 check_args fun_ty (arg : args)
660 | isUnLiftedType arg_ty = exprOkForSpeculation arg
661 | otherwise = check_args res_ty args
663 (arg_ty, res_ty) = splitFunTy fun_ty
667 -- deep applies a TyConApp coercion as a substitution to a reflexive coercion
668 -- deepCast t [a1,...,an] co corresponds to deep(t, [a1,...,an], co) from
670 deepCast :: Type -> [TyVar] -> Coercion -> Coercion
671 deepCast ty tyVars co
672 = ASSERT( let {(lty, rty) = coercionKind co;
673 Just (tc1, lArgs) = splitTyConApp_maybe lty;
674 Just (tc2, rArgs) = splitTyConApp_maybe rty}
676 tc1 == tc2 && length lArgs == length rArgs &&
677 length lArgs == length tyVars )
678 substTyWith tyVars coArgs ty
680 -- coArgs = [right (left (left co)), right (left co), right co]
681 coArgs = decomposeCo (length tyVars) co
683 -- These InstPat functions go here to avoid circularity between DataCon and Id
684 dataConOrigInstPat = dataConInstPat dataConOrigArgTys
685 dataConRepInstPat = dataConInstPat dataConRepArgTys
686 dataConRepOccInstPat = dataConOccInstPat dataConRepArgTys
688 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
689 -> [Unique] -- A long enough list of uniques, at least one for each binder
691 -> [Type] -- Types to instantiate the universally quantified tyvars
692 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
693 -- dataConInstPat us con inst_tys returns a triple (ex_tvs, co_tvs, arg_ids),
695 -- ex_tvs are intended to be used as binders for existential type args
697 -- co_tvs are intended to be used as binders for coercion args and the kinds
698 -- of these vars have been instantiated by the inst_tys and the ex_tys
700 -- arg_ids are indended to be used as binders for value arguments, including
701 -- dicts, and have their types instantiated with inst_tys and ex_tys
704 -- The following constructor T1
707 -- T1 :: forall b. Int -> b -> T(a,b)
710 -- has representation type
711 -- forall a. forall a1. forall a2. forall b. (a :=: (a1,a2)) =>
714 -- dataConInstPat us T1 (a1',a2') will return
716 -- ([a1'', a2'', b''],[c :: (a1',a2'):=:(a1'',a2'')],[x :: Int,y :: b''])
718 -- where the double-primed variables are created from the unique list input
719 dataConInstPat arg_fun uniqs con inst_tys
720 = dataConOccInstPat arg_fun uniqs occs con inst_tys
722 -- dataConOccInstPat doesn't actually make use of the OccName directly for
723 -- existential and coercion variable binders, so it is right to just
724 -- use the VarName namespace for all of the OccNames
726 mk_occs n = mkVarOcc ("ipv" ++ show n) : mk_occs (n+1)
728 dataConOccInstPat :: (DataCon -> [Type]) -- function used to find arg tys
729 -> [Unique] -- A long enough list of uniques, at least one for each binder
730 -> [OccName] -- An equally long list of OccNames to use
732 -> [Type] -- Types to instantiate the universally quantified tyvars
733 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
734 -- This function actually does the job specified in the comment for
735 -- dataConInstPat, but uses the specified list of OccNames. This is
736 -- is necessary for use in e.g. tcIfaceDataAlt
737 dataConOccInstPat arg_fun uniqs occs con inst_tys
738 = (ex_bndrs, co_bndrs, id_bndrs)
740 univ_tvs = dataConUnivTyVars con
741 ex_tvs = dataConExTyVars con
742 arg_tys = arg_fun con
743 eq_spec = dataConEqSpec con
744 eq_preds = eqSpecPreds eq_spec
747 n_co = length eq_spec
748 n_id = length arg_tys
750 -- split the Uniques and OccNames
751 (ex_uniqs, uniqs') = splitAt n_ex uniqs
752 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
754 (ex_occs, occs') = splitAt n_ex occs
755 (co_occs, id_occs) = splitAt n_co occs'
757 -- make existential type variables
758 mk_ex_var uniq occ var = mkTyVar new_name kind
760 new_name = mkSysTvName uniq (occNameFS occ)
763 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_occs ex_tvs
765 -- make the instantiation substitution
766 inst_subst = substTyWith (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
768 -- make new coercion vars, instantiating kind
769 mk_co_var uniq occ eq_pred = mkCoVar new_name (inst_subst (mkPredTy eq_pred))
771 new_name = mkSysTvName uniq (occNameFS occ)
773 co_bndrs = zipWith3 mk_co_var co_uniqs co_occs eq_preds
775 -- make value vars, instantiating types
776 mk_id_var uniq occ ty = mkUserLocal occ uniq (inst_subst ty) noSrcLoc
777 id_bndrs = zipWith3 mk_id_var id_uniqs id_occs arg_tys
779 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
780 -- Returns (Just (dc, [x1..xn])) if the argument expression is
781 -- a constructor application of the form (dc x1 .. xn)
783 exprIsConApp_maybe (Cast expr co)
784 = -- Maybe this is over the top, but here we try to turn
785 -- coerce (S,T) ( x, y )
787 -- ( coerce S x, coerce T y )
788 -- This happens in anger in PrelArrExts which has a coerce
789 -- case coerce memcpy a b of
791 -- where the memcpy is in the IO monad, but the call is in
793 case exprIsConApp_maybe expr of {
797 let (from_ty, to_ty) = coercionKind co in
799 case splitTyConApp_maybe to_ty of {
801 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
802 -- | not (isVanillaDataCon dc) -> Nothing
804 -- Type constructor must match datacon
806 case splitTyConApp_maybe from_ty of {
808 Just (tc', tc_arg_tys') | tc /= tc' -> Nothing
809 -- Both sides of coercion must have the same type constructor
813 -- here we do the PushC reduction rule as described in the FC paper
814 arity = tyConArity tc
815 n_ex_tvs = length dc_ex_tyvars
817 (univ_args, rest) = splitAt arity args
818 (ex_args, val_args) = splitAt n_ex_tvs rest
820 arg_tys = dataConRepArgTys dc
821 dc_tyvars = dataConUnivTyVars dc
822 dc_ex_tyvars = dataConExTyVars dc
824 deep arg_ty = deepCast arg_ty dc_tyvars co
826 -- first we appropriately cast the value arguments
827 arg_cos = map deep arg_tys
828 new_val_args = zipWith mkCoerce (map deep arg_tys) val_args
830 -- then we cast the existential coercion arguments
831 orig_tvs = dc_tyvars ++ dc_ex_tyvars
832 gammas = decomposeCo arity co
833 new_tys = gammas ++ (map (\ (Type t) -> t) ex_args)
834 theta = substTyWith orig_tvs new_tys
837 , (ty1, ty2) <- splitCoercionKind (tyVarKind tv)
838 = Type $ mkTransCoercion (mkSymCoercion (theta ty1))
839 (mkTransCoercion ty (theta ty2))
842 new_ex_args = zipWith cast_ty dc_ex_tyvars ex_args
845 ASSERT( all isTypeArg (take arity args) )
846 ASSERT( equalLength val_args arg_tys )
847 Just (dc, map Type tc_arg_tys ++ new_ex_args ++ new_val_args)
850 exprIsConApp_maybe (Note _ expr)
851 = exprIsConApp_maybe expr
852 -- We ignore InlineMe notes in case we have
853 -- x = __inline_me__ (a,b)
854 -- All part of making sure that INLINE pragmas never hurt
855 -- Marcin tripped on this one when making dictionaries more inlinable
857 -- In fact, we ignore all notes. For example,
858 -- case _scc_ "foo" (C a b) of
860 -- should be optimised away, but it will be only if we look
861 -- through the SCC note.
863 exprIsConApp_maybe expr = analyse (collectArgs expr)
865 analyse (Var fun, args)
866 | Just con <- isDataConWorkId_maybe fun,
867 args `lengthAtLeast` dataConRepArity con
868 -- Might be > because the arity excludes type args
871 -- Look through unfoldings, but only cheap ones, because
872 -- we are effectively duplicating the unfolding
873 analyse (Var fun, [])
874 | let unf = idUnfolding fun,
876 = exprIsConApp_maybe (unfoldingTemplate unf)
878 analyse other = Nothing
883 %************************************************************************
885 \subsection{Eta reduction and expansion}
887 %************************************************************************
890 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
891 {- The Arity returned is the number of value args the
892 thing can be applied to without doing much work
894 exprEtaExpandArity is used when eta expanding
897 It returns 1 (or more) to:
898 case x of p -> \s -> ...
899 because for I/O ish things we really want to get that \s to the top.
900 We are prepared to evaluate x each time round the loop in order to get that
902 It's all a bit more subtle than it looks:
906 Consider one-shot lambdas
907 let x = expensive in \y z -> E
908 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
909 Hence the ArityType returned by arityType
911 2. The state-transformer hack
913 The one-shot lambda special cause is particularly important/useful for
914 IO state transformers, where we often get
915 let x = E in \ s -> ...
917 and the \s is a real-world state token abstraction. Such abstractions
918 are almost invariably 1-shot, so we want to pull the \s out, past the
919 let x=E, even if E is expensive. So we treat state-token lambdas as
920 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
922 3. Dealing with bottom
925 f = \x -> error "foo"
926 Here, arity 1 is fine. But if it is
930 then we want to get arity 2. Tecnically, this isn't quite right, because
932 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
933 do so; it improves some programs significantly, and increasing convergence
934 isn't a bad thing. Hence the ABot/ATop in ArityType.
936 Actually, the situation is worse. Consider
940 Can we eta-expand here? At first the answer looks like "yes of course", but
943 This should diverge! But if we eta-expand, it won't. Again, we ignore this
944 "problem", because being scrupulous would lose an important transformation for
950 Non-recursive newtypes are transparent, and should not get in the way.
951 We do (currently) eta-expand recursive newtypes too. So if we have, say
953 newtype T = MkT ([T] -> Int)
957 where f has arity 1. Then: etaExpandArity e = 1;
958 that is, etaExpandArity looks through the coerce.
960 When we eta-expand e to arity 1: eta_expand 1 e T
961 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
963 HOWEVER, note that if you use coerce bogusly you can ge
965 And since negate has arity 2, you might try to eta expand. But you can't
966 decopose Int to a function type. Hence the final case in eta_expand.
970 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
972 -- A limited sort of function type
973 data ArityType = AFun Bool ArityType -- True <=> one-shot
974 | ATop -- Know nothing
977 arityDepth :: ArityType -> Arity
978 arityDepth (AFun _ ty) = 1 + arityDepth ty
981 andArityType ABot at2 = at2
982 andArityType ATop at2 = ATop
983 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
984 andArityType at1 at2 = andArityType at2 at1
986 arityType :: DynFlags -> CoreExpr -> ArityType
987 -- (go1 e) = [b1,..,bn]
988 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
989 -- where bi is True <=> the lambda is one-shot
991 arityType dflags (Note n e) = arityType dflags e
992 -- Not needed any more: etaExpand is cleverer
993 -- | ok_note n = arityType dflags e
994 -- | otherwise = ATop
996 arityType dflags (Cast e co) = arityType dflags e
998 arityType dflags (Var v)
999 = mk (idArity v) (arg_tys (idType v))
1001 mk :: Arity -> [Type] -> ArityType
1002 -- The argument types are only to steer the "state hack"
1003 -- Consider case x of
1005 -- False -> \(s:RealWorld) -> e
1006 -- where foo has arity 1. Then we want the state hack to
1007 -- apply to foo too, so we can eta expand the case.
1008 mk 0 tys | isBottomingId v = ABot
1009 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
1011 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
1012 mk n [] = AFun False (mk (n-1) [])
1014 arg_tys :: Type -> [Type] -- Ignore for-alls
1016 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1017 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1020 -- Lambdas; increase arity
1021 arityType dflags (Lam x e)
1022 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1023 | otherwise = arityType dflags e
1025 -- Applications; decrease arity
1026 arityType dflags (App f (Type _)) = arityType dflags f
1027 arityType dflags (App f a) = case arityType dflags f of
1028 AFun one_shot xs | exprIsCheap a -> xs
1031 -- Case/Let; keep arity if either the expression is cheap
1032 -- or it's a 1-shot lambda
1033 -- The former is not really right for Haskell
1034 -- f x = case x of { (a,b) -> \y. e }
1036 -- f x y = case x of { (a,b) -> e }
1037 -- The difference is observable using 'seq'
1038 arityType dflags (Case scrut _ _ alts)
1039 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1040 xs | exprIsCheap scrut -> xs
1041 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1044 arityType dflags (Let b e)
1045 = case arityType dflags e of
1046 xs | cheap_bind b -> xs
1047 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1050 cheap_bind (NonRec b e) = is_cheap (b,e)
1051 cheap_bind (Rec prs) = all is_cheap prs
1052 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1054 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1055 -- dictionary bindings. This improves arities. Thereby, it also
1056 -- means that full laziness is less prone to floating out the
1057 -- application of a function to its dictionary arguments, which
1058 -- can thereby lose opportunities for fusion. Example:
1059 -- foo :: Ord a => a -> ...
1060 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1061 -- -- So foo has arity 1
1063 -- f = \x. foo dInt $ bar x
1065 -- The (foo DInt) is floated out, and makes ineffective a RULE
1066 -- foo (bar x) = ...
1068 -- One could go further and make exprIsCheap reply True to any
1069 -- dictionary-typed expression, but that's more work.
1071 arityType dflags other = ATop
1073 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1074 ok_note InlineMe = False
1075 ok_note other = True
1076 -- Notice that we do not look through __inline_me__
1077 -- This may seem surprising, but consider
1078 -- f = _inline_me (\x -> e)
1079 -- We DO NOT want to eta expand this to
1080 -- f = \x -> (_inline_me (\x -> e)) x
1081 -- because the _inline_me gets dropped now it is applied,
1090 etaExpand :: Arity -- Result should have this number of value args
1092 -> CoreExpr -> Type -- Expression and its type
1094 -- (etaExpand n us e ty) returns an expression with
1095 -- the same meaning as 'e', but with arity 'n'.
1097 -- Given e' = etaExpand n us e ty
1099 -- ty = exprType e = exprType e'
1101 -- Note that SCCs are not treated specially. If we have
1102 -- etaExpand 2 (\x -> scc "foo" e)
1103 -- = (\xy -> (scc "foo" e) y)
1104 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1106 etaExpand n us expr ty
1107 | manifestArity expr >= n = expr -- The no-op case
1109 = eta_expand n us expr ty
1112 -- manifestArity sees how many leading value lambdas there are
1113 manifestArity :: CoreExpr -> Arity
1114 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1115 | otherwise = manifestArity e
1116 manifestArity (Note _ e) = manifestArity e
1117 manifestArity (Cast e _) = manifestArity e
1120 -- etaExpand deals with for-alls. For example:
1122 -- where E :: forall a. a -> a
1124 -- (/\b. \y::a -> E b y)
1126 -- It deals with coerces too, though they are now rare
1127 -- so perhaps the extra code isn't worth it
1129 eta_expand n us expr ty
1131 -- The ILX code generator requires eta expansion for type arguments
1132 -- too, but alas the 'n' doesn't tell us how many of them there
1133 -- may be. So we eagerly eta expand any big lambdas, and just
1134 -- cross our fingers about possible loss of sharing in the ILX case.
1135 -- The Right Thing is probably to make 'arity' include
1136 -- type variables throughout the compiler. (ToDo.)
1138 -- Saturated, so nothing to do
1141 -- Short cut for the case where there already
1142 -- is a lambda; no point in gratuitously adding more
1143 eta_expand n us (Lam v body) ty
1145 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1148 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1150 -- We used to have a special case that stepped inside Coerces here,
1151 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1152 -- = Note note (eta_expand n us e ty)
1153 -- BUT this led to an infinite loop
1154 -- Example: newtype T = MkT (Int -> Int)
1155 -- eta_expand 1 (coerce (Int->Int) e)
1156 -- --> coerce (Int->Int) (eta_expand 1 T e)
1158 -- --> coerce (Int->Int) (coerce T
1159 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1160 -- by the splitNewType_maybe case below
1163 eta_expand n us expr ty
1164 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1165 case splitForAllTy_maybe ty of {
1168 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1170 lam_tv = mkTyVar (mkSysTvName uniq FSLIT("etaT")) (tyVarKind tv)
1174 case splitFunTy_maybe ty of {
1175 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1177 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1183 -- newtype T = MkT ([T] -> Int)
1184 -- Consider eta-expanding this
1187 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1189 case splitNewTypeRepCo_maybe ty of {
1191 mkCoerce co (eta_expand n us (mkCoerce (mkSymCoercion co) expr) ty1) ;
1194 -- We have an expression of arity > 0, but its type isn't a function
1195 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1196 -- Essentially the programmer is playing fast and loose with types
1197 -- (Happy does this a lot). So we simply decline to eta-expand.
1202 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1203 It tells how many things the expression can be applied to before doing
1204 any work. It doesn't look inside cases, lets, etc. The idea is that
1205 exprEtaExpandArity will do the hard work, leaving something that's easy
1206 for exprArity to grapple with. In particular, Simplify uses exprArity to
1207 compute the ArityInfo for the Id.
1209 Originally I thought that it was enough just to look for top-level lambdas, but
1210 it isn't. I've seen this
1212 foo = PrelBase.timesInt
1214 We want foo to get arity 2 even though the eta-expander will leave it
1215 unchanged, in the expectation that it'll be inlined. But occasionally it
1216 isn't, because foo is blacklisted (used in a rule).
1218 Similarly, see the ok_note check in exprEtaExpandArity. So
1219 f = __inline_me (\x -> e)
1220 won't be eta-expanded.
1222 And in any case it seems more robust to have exprArity be a bit more intelligent.
1223 But note that (\x y z -> f x y z)
1224 should have arity 3, regardless of f's arity.
1227 exprArity :: CoreExpr -> Arity
1230 go (Var v) = idArity v
1231 go (Lam x e) | isId x = go e + 1
1233 go (Note n e) = go e
1234 go (Cast e _) = go e
1235 go (App e (Type t)) = go e
1236 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1237 -- NB: exprIsCheap a!
1238 -- f (fac x) does not have arity 2,
1239 -- even if f has arity 3!
1240 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1241 -- unknown, hence arity 0
1245 %************************************************************************
1247 \subsection{Equality}
1249 %************************************************************************
1251 @cheapEqExpr@ is a cheap equality test which bales out fast!
1252 True => definitely equal
1253 False => may or may not be equal
1256 cheapEqExpr :: Expr b -> Expr b -> Bool
1258 cheapEqExpr (Var v1) (Var v2) = v1==v2
1259 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1260 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1262 cheapEqExpr (App f1 a1) (App f2 a2)
1263 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1265 cheapEqExpr _ _ = False
1267 exprIsBig :: Expr b -> Bool
1268 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1269 exprIsBig (Lit _) = False
1270 exprIsBig (Var v) = False
1271 exprIsBig (Type t) = False
1272 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1273 exprIsBig other = True
1278 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1279 -- Used in rule matching, so does *not* look through
1280 -- newtypes, predicate types; hence tcEqExpr
1282 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1284 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1286 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1287 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1288 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1289 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1290 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1291 tcEqExprX env (Let (NonRec v1 r1) e1)
1292 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1293 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1294 tcEqExprX env (Let (Rec ps1) e1)
1295 (Let (Rec ps2) e2) = equalLength ps1 ps2
1296 && and (zipWith eq_rhs ps1 ps2)
1297 && tcEqExprX env' e1 e2
1299 env' = foldl2 rn_bndr2 env ps2 ps2
1300 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1301 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1302 tcEqExprX env (Case e1 v1 t1 a1)
1303 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1304 && tcEqTypeX env t1 t2
1305 && equalLength a1 a2
1306 && and (zipWith (eq_alt env') a1 a2)
1308 env' = rnBndr2 env v1 v2
1310 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1311 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1312 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1313 tcEqExprX env e1 e2 = False
1315 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1317 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1318 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1319 eq_note env other1 other2 = False
1323 %************************************************************************
1325 \subsection{The size of an expression}
1327 %************************************************************************
1330 coreBindsSize :: [CoreBind] -> Int
1331 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1333 exprSize :: CoreExpr -> Int
1334 -- A measure of the size of the expressions
1335 -- It also forces the expression pretty drastically as a side effect
1336 exprSize (Var v) = v `seq` 1
1337 exprSize (Lit lit) = lit `seq` 1
1338 exprSize (App f a) = exprSize f + exprSize a
1339 exprSize (Lam b e) = varSize b + exprSize e
1340 exprSize (Let b e) = bindSize b + exprSize e
1341 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1342 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1343 exprSize (Note n e) = noteSize n + exprSize e
1344 exprSize (Type t) = seqType t `seq` 1
1346 noteSize (SCC cc) = cc `seq` 1
1347 noteSize InlineMe = 1
1348 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1350 varSize :: Var -> Int
1351 varSize b | isTyVar b = 1
1352 | otherwise = seqType (idType b) `seq`
1353 megaSeqIdInfo (idInfo b) `seq`
1356 varsSize = foldr ((+) . varSize) 0
1358 bindSize (NonRec b e) = varSize b + exprSize e
1359 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1361 pairSize (b,e) = varSize b + exprSize e
1363 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1367 %************************************************************************
1369 \subsection{Hashing}
1371 %************************************************************************
1374 hashExpr :: CoreExpr -> Int
1375 -- Two expressions that hash to the same Int may be equal (but may not be)
1376 -- Two expressions that hash to the different Ints are definitely unequal
1378 -- But "unequal" here means "not identical"; two alpha-equivalent
1379 -- expressions may hash to the different Ints
1381 -- The emphasis is on a crude, fast hash, rather than on high precision
1383 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1386 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1388 hash_expr (Note _ e) = hash_expr e
1389 hash_expr (Cast e co) = hash_expr e
1390 hash_expr (Let (NonRec b r) e) = hashId b
1391 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1392 hash_expr (Case _ b _ _) = hashId b
1393 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1394 hash_expr (Var v) = hashId v
1395 hash_expr (Lit lit) = hashLiteral lit
1396 hash_expr (Lam b _) = hashId b
1397 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1399 fast_hash_expr (Var v) = hashId v
1400 fast_hash_expr (Lit lit) = hashLiteral lit
1401 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1402 fast_hash_expr (App f a) = fast_hash_expr a
1403 fast_hash_expr (Lam b _) = hashId b
1404 fast_hash_expr other = 1
1407 hashId id = hashName (idName id)
1410 %************************************************************************
1412 \subsection{Determining non-updatable right-hand-sides}
1414 %************************************************************************
1416 Top-level constructor applications can usually be allocated
1417 statically, but they can't if the constructor, or any of the
1418 arguments, come from another DLL (because we can't refer to static
1419 labels in other DLLs).
1421 If this happens we simply make the RHS into an updatable thunk,
1422 and 'exectute' it rather than allocating it statically.
1425 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1426 -- This function is called only on *top-level* right-hand sides
1427 -- Returns True if the RHS can be allocated statically, with
1428 -- no thunks involved at all.
1430 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1431 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1432 -- update flag on it.
1434 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1435 -- (a) a value lambda
1436 -- (b) a saturated constructor application with static args
1438 -- BUT watch out for
1439 -- (i) Any cross-DLL references kill static-ness completely
1440 -- because they must be 'executed' not statically allocated
1441 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1442 -- this is not necessary)
1444 -- (ii) We treat partial applications as redexes, because in fact we
1445 -- make a thunk for them that runs and builds a PAP
1446 -- at run-time. The only appliations that are treated as
1447 -- static are *saturated* applications of constructors.
1449 -- We used to try to be clever with nested structures like this:
1450 -- ys = (:) w ((:) w [])
1451 -- on the grounds that CorePrep will flatten ANF-ise it later.
1452 -- But supporting this special case made the function much more
1453 -- complicated, because the special case only applies if there are no
1454 -- enclosing type lambdas:
1455 -- ys = /\ a -> Foo (Baz ([] a))
1456 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1458 -- But in fact, even without -O, nested structures at top level are
1459 -- flattened by the simplifier, so we don't need to be super-clever here.
1463 -- f = \x::Int. x+7 TRUE
1464 -- p = (True,False) TRUE
1466 -- d = (fst p, False) FALSE because there's a redex inside
1467 -- (this particular one doesn't happen but...)
1469 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1470 -- n = /\a. Nil a TRUE
1472 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1475 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1476 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1478 -- b) (C x xs), where C is a contructors is updatable if the application is
1481 -- c) don't look through unfolding of f in (f x).
1483 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1484 -- them as making the RHS re-entrant (non-updatable).
1486 rhsIsStatic this_pkg rhs = is_static False rhs
1488 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1491 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1493 is_static in_arg (Note (SCC _) e) = False
1494 is_static in_arg (Note _ e) = is_static in_arg e
1495 is_static in_arg (Cast e co) = is_static in_arg e
1497 is_static in_arg (Lit lit)
1499 MachLabel _ _ -> False
1501 -- A MachLabel (foreign import "&foo") in an argument
1502 -- prevents a constructor application from being static. The
1503 -- reason is that it might give rise to unresolvable symbols
1504 -- in the object file: under Linux, references to "weak"
1505 -- symbols from the data segment give rise to "unresolvable
1506 -- relocation" errors at link time This might be due to a bug
1507 -- in the linker, but we'll work around it here anyway.
1510 is_static in_arg other_expr = go other_expr 0
1512 go (Var f) n_val_args
1513 #if mingw32_TARGET_OS
1514 | not (isDllName this_pkg (idName f))
1516 = saturated_data_con f n_val_args
1517 || (in_arg && n_val_args == 0)
1518 -- A naked un-applied variable is *not* deemed a static RHS
1520 -- Reason: better to update so that the indirection gets shorted
1521 -- out, and the true value will be seen
1522 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1523 -- are always updatable. If you do so, make sure that non-updatable
1524 -- ones have enough space for their static link field!
1526 go (App f a) n_val_args
1527 | isTypeArg a = go f n_val_args
1528 | not in_arg && is_static True a = go f (n_val_args + 1)
1529 -- The (not in_arg) checks that we aren't in a constructor argument;
1530 -- if we are, we don't allow (value) applications of any sort
1532 -- NB. In case you wonder, args are sometimes not atomic. eg.
1533 -- x = D# (1.0## /## 2.0##)
1534 -- can't float because /## can fail.
1536 go (Note (SCC _) f) n_val_args = False
1537 go (Note _ f) n_val_args = go f n_val_args
1538 go (Cast e co) n_val_args = go e n_val_args
1540 go other n_val_args = False
1542 saturated_data_con f n_val_args
1543 = case isDataConWorkId_maybe f of
1544 Just dc -> n_val_args == dataConRepArity dc