2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
11 mkInlineMe, mkSCC, mkCoerce,
12 bindNonRec, needsCaseBinding,
13 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
15 -- Taking expressions apart
16 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
18 -- Properties of expressions
19 exprType, coreAltType,
20 exprIsDupable, exprIsTrivial, exprIsCheap,
21 exprIsHNF,exprOkForSpeculation, exprIsBig,
22 exprIsConApp_maybe, exprIsBottom,
25 -- Arity and eta expansion
26 manifestArity, exprArity,
27 exprEtaExpandArity, etaExpand,
36 cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg,
38 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
41 #include "HsVersions.h"
77 import GHC.Exts -- For `xori`
81 %************************************************************************
83 \subsection{Find the type of a Core atom/expression}
85 %************************************************************************
88 exprType :: CoreExpr -> Type
90 exprType (Var var) = idType var
91 exprType (Lit lit) = literalType lit
92 exprType (Let _ body) = exprType body
93 exprType (Case _ _ ty alts) = ty
94 exprType (Cast e co) = snd (coercionKind co)
95 exprType (Note other_note e) = exprType e
96 exprType (Lam binder expr) = mkPiType binder (exprType expr)
98 = case collectArgs e of
99 (fun, args) -> applyTypeToArgs e (exprType fun) args
101 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
103 coreAltType :: CoreAlt -> Type
104 coreAltType (_,_,rhs) = exprType rhs
107 @mkPiType@ makes a (->) type or a forall type, depending on whether
108 it is given a type variable or a term variable. We cleverly use the
109 lbvarinfo field to figure out the right annotation for the arrove in
110 case of a term variable.
113 mkPiType :: Var -> Type -> Type -- The more polymorphic version
114 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
116 mkPiTypes vs ty = foldr mkPiType ty vs
119 | isId v = mkFunTy (idType v) ty
120 | otherwise = mkForAllTy v ty
124 applyTypeToArg :: Type -> CoreExpr -> Type
125 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
126 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
128 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
129 -- A more efficient version of applyTypeToArg
130 -- when we have several args
131 -- The first argument is just for debugging
132 applyTypeToArgs e op_ty [] = op_ty
134 applyTypeToArgs e op_ty (Type ty : args)
135 = -- Accumulate type arguments so we can instantiate all at once
138 go rev_tys (Type ty : args) = go (ty:rev_tys) args
139 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
141 op_ty' = applyTys op_ty (reverse rev_tys)
143 applyTypeToArgs e op_ty (other_arg : args)
144 = case (splitFunTy_maybe op_ty) of
145 Just (_, res_ty) -> applyTypeToArgs e res_ty args
146 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
151 %************************************************************************
153 \subsection{Attaching notes}
155 %************************************************************************
157 mkNote removes redundant coercions, and SCCs where possible
161 mkNote :: Note -> CoreExpr -> CoreExpr
162 mkNote (SCC cc) expr = mkSCC cc expr
163 mkNote InlineMe expr = mkInlineMe expr
164 mkNote note expr = Note note expr
168 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
169 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
170 not be *applied* to anything.
172 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
175 f = inline_me (coerce t fw)
176 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
177 We want the split, so that the coerces can cancel at the call site.
179 However, we can get left with tiresome type applications. Notably, consider
180 f = /\ a -> let t = e in (t, w)
181 Then lifting the let out of the big lambda gives
183 f = /\ a -> let t = inline_me (t' a) in (t, w)
184 The inline_me is to stop the simplifier inlining t' right back
185 into t's RHS. In the next phase we'll substitute for t (since
186 its rhs is trivial) and *then* we could get rid of the inline_me.
187 But it hardly seems worth it, so I don't bother.
190 mkInlineMe (Var v) = Var v
191 mkInlineMe e = Note InlineMe e
197 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
198 mkCoerce co (Cast expr co2)
199 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
200 (_from_ty2, to_ty2) = coercionKind co2} in
201 from_ty `coreEqType` to_ty2 )
202 mkCoerce (mkTransCoercion co2 co) expr
205 = let (from_ty, to_ty) = coercionKind co in
206 -- if to_ty `coreEqType` from_ty
209 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
214 mkSCC :: CostCentre -> Expr b -> Expr b
215 -- Note: Nested SCC's *are* preserved for the benefit of
216 -- cost centre stack profiling
217 mkSCC cc (Lit lit) = Lit lit
218 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
219 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
220 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
221 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
222 mkSCC cc expr = Note (SCC cc) expr
226 %************************************************************************
228 \subsection{Other expression construction}
230 %************************************************************************
233 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
234 -- (bindNonRec x r b) produces either
237 -- case r of x { _DEFAULT_ -> b }
239 -- depending on whether x is unlifted or not
240 -- It's used by the desugarer to avoid building bindings
241 -- that give Core Lint a heart attack. Actually the simplifier
242 -- deals with them perfectly well.
244 bindNonRec bndr rhs body
245 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
246 | otherwise = Let (NonRec bndr rhs) body
248 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
249 -- Make a case expression instead of a let
250 -- These can arise either from the desugarer,
251 -- or from beta reductions: (\x.e) (x +# y)
255 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
256 -- This guy constructs the value that the scrutinee must have
257 -- when you are in one particular branch of a case
258 mkAltExpr (DataAlt con) args inst_tys
259 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
260 mkAltExpr (LitAlt lit) [] []
263 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
264 mkIfThenElse guard then_expr else_expr
265 -- Not going to be refining, so okay to take the type of the "then" clause
266 = Case guard (mkWildId boolTy) (exprType then_expr)
267 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
268 (DataAlt trueDataCon, [], then_expr) ]
272 %************************************************************************
274 \subsection{Taking expressions apart}
276 %************************************************************************
278 The default alternative must be first, if it exists at all.
279 This makes it easy to find, though it makes matching marginally harder.
282 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
283 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
284 findDefault alts = (alts, Nothing)
286 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
289 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
290 other -> go alts panic_deflt
292 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
295 go (alt@(con1,_,_) : alts) deflt
296 = case con `cmpAltCon` con1 of
297 LT -> deflt -- Missed it already; the alts are in increasing order
299 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
301 isDefaultAlt :: CoreAlt -> Bool
302 isDefaultAlt (DEFAULT, _, _) = True
303 isDefaultAlt other = False
305 ---------------------------------
306 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
307 -- Merge preserving order; alternatives in the first arg
308 -- shadow ones in the second
309 mergeAlts [] as2 = as2
310 mergeAlts as1 [] = as1
311 mergeAlts (a1:as1) (a2:as2)
312 = case a1 `cmpAlt` a2 of
313 LT -> a1 : mergeAlts as1 (a2:as2)
314 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
315 GT -> a2 : mergeAlts (a1:as1) as2
318 ---------------------------------
319 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
320 -- Given case (C a b x y) of
322 -- we want to drop the leading type argument of the scrutinee
323 -- leaving the arguments to match agains the pattern
325 trimConArgs DEFAULT args = ASSERT( null args ) []
326 trimConArgs (LitAlt lit) args = ASSERT( null args ) []
327 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
331 %************************************************************************
333 \subsection{Figuring out things about expressions}
335 %************************************************************************
337 @exprIsTrivial@ is true of expressions we are unconditionally happy to
338 duplicate; simple variables and constants, and type
339 applications. Note that primop Ids aren't considered
342 @exprIsBottom@ is true of expressions that are guaranteed to diverge
345 There used to be a gruesome test for (hasNoBinding v) in the
347 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
348 The idea here is that a constructor worker, like $wJust, is
349 really short for (\x -> $wJust x), becuase $wJust has no binding.
350 So it should be treated like a lambda. Ditto unsaturated primops.
351 But now constructor workers are not "have-no-binding" Ids. And
352 completely un-applied primops and foreign-call Ids are sufficiently
353 rare that I plan to allow them to be duplicated and put up with
356 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
357 a) it really generates code, (and a heap object when it's
358 a function arg) to capture the cost centre
359 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
362 exprIsTrivial (Var v) = True -- See notes above
363 exprIsTrivial (Type _) = True
364 exprIsTrivial (Lit lit) = litIsTrivial lit
365 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
366 exprIsTrivial (Note (SCC _) e) = False -- See notes above
367 exprIsTrivial (Note _ e) = exprIsTrivial e
368 exprIsTrivial (Cast e co) = exprIsTrivial e
369 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
370 exprIsTrivial other = False
374 @exprIsDupable@ is true of expressions that can be duplicated at a modest
375 cost in code size. This will only happen in different case
376 branches, so there's no issue about duplicating work.
378 That is, exprIsDupable returns True of (f x) even if
379 f is very very expensive to call.
381 Its only purpose is to avoid fruitless let-binding
382 and then inlining of case join points
386 exprIsDupable (Type _) = True
387 exprIsDupable (Var v) = True
388 exprIsDupable (Lit lit) = litIsDupable lit
389 exprIsDupable (Note InlineMe e) = True
390 exprIsDupable (Note _ e) = exprIsDupable e
391 exprIsDupable (Cast e co) = exprIsDupable e
395 go (Var v) n_args = True
396 go (App f a) n_args = n_args < dupAppSize
399 go other n_args = False
402 dupAppSize = 4 -- Size of application we are prepared to duplicate
405 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
406 it is obviously in weak head normal form, or is cheap to get to WHNF.
407 [Note that that's not the same as exprIsDupable; an expression might be
408 big, and hence not dupable, but still cheap.]
410 By ``cheap'' we mean a computation we're willing to:
411 push inside a lambda, or
412 inline at more than one place
413 That might mean it gets evaluated more than once, instead of being
414 shared. The main examples of things which aren't WHNF but are
419 (where e, and all the ei are cheap)
422 (where e and b are cheap)
425 (where op is a cheap primitive operator)
428 (because we are happy to substitute it inside a lambda)
430 Notice that a variable is considered 'cheap': we can push it inside a lambda,
431 because sharing will make sure it is only evaluated once.
434 exprIsCheap :: CoreExpr -> Bool
435 exprIsCheap (Lit lit) = True
436 exprIsCheap (Type _) = True
437 exprIsCheap (Var _) = True
438 exprIsCheap (Note InlineMe e) = True
439 exprIsCheap (Note _ e) = exprIsCheap e
440 exprIsCheap (Cast e co) = exprIsCheap e
441 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
442 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
443 and [exprIsCheap rhs | (_,_,rhs) <- alts]
444 -- Experimentally, treat (case x of ...) as cheap
445 -- (and case __coerce x etc.)
446 -- This improves arities of overloaded functions where
447 -- there is only dictionary selection (no construction) involved
448 exprIsCheap (Let (NonRec x _) e)
449 | isUnLiftedType (idType x) = exprIsCheap e
451 -- strict lets always have cheap right hand sides,
452 -- and do no allocation.
454 exprIsCheap other_expr -- Applications and variables
457 -- Accumulate value arguments, then decide
458 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
459 | otherwise = go f val_args
461 go (Var f) [] = True -- Just a type application of a variable
462 -- (f t1 t2 t3) counts as WHNF
464 = case globalIdDetails f of
465 RecordSelId {} -> go_sel args
466 ClassOpId _ -> go_sel args
467 PrimOpId op -> go_primop op args
469 DataConWorkId _ -> go_pap args
470 other | length args < idArity f -> go_pap args
472 other -> isBottomingId f
473 -- Application of a function which
474 -- always gives bottom; we treat this as cheap
475 -- because it certainly doesn't need to be shared!
477 go other args = False
480 go_pap args = all exprIsTrivial args
481 -- For constructor applications and primops, check that all
482 -- the args are trivial. We don't want to treat as cheap, say,
484 -- We'll put up with one constructor application, but not dozens
487 go_primop op args = primOpIsCheap op && all exprIsCheap args
488 -- In principle we should worry about primops
489 -- that return a type variable, since the result
490 -- might be applied to something, but I'm not going
491 -- to bother to check the number of args
494 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
495 go_sel other = False -- look cheap, so we will substitute it inside a
496 -- lambda. Particularly for dictionary field selection.
497 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
498 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
501 exprOkForSpeculation returns True of an expression that it is
503 * safe to evaluate even if normal order eval might not
504 evaluate the expression at all, or
506 * safe *not* to evaluate even if normal order would do so
510 the expression guarantees to terminate,
512 without raising an exception,
513 without causing a side effect (e.g. writing a mutable variable)
515 NB: if exprIsHNF e, then exprOkForSpecuation e
518 let x = case y# +# 1# of { r# -> I# r# }
521 case y# +# 1# of { r# ->
526 We can only do this if the (y+1) is ok for speculation: it has no
527 side effects, and can't diverge or raise an exception.
530 exprOkForSpeculation :: CoreExpr -> Bool
531 exprOkForSpeculation (Lit _) = True
532 exprOkForSpeculation (Type _) = True
533 -- Tick boxes are *not* suitable for speculation
534 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
535 && not (isTickBoxOp 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. However this can't
621 happen: see CoreSyn Note [CoreSyn let/app invariant]. 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 = idArity fun > valArgCount args -- Under-applied function
648 || isDataConWorkId fun -- or data constructor
649 app_is_value (Note n f) as = app_is_value f as
650 app_is_value (Cast f _) as = app_is_value f as
651 app_is_value (App f a) as = app_is_value f (a:as)
652 app_is_value other as = False
656 -- These InstPat functions go here to avoid circularity between DataCon and Id
657 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
658 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
659 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
661 dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc
662 -- Remember to include the existential dictionaries
664 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
665 -> [FastString] -- A long enough list of FSs to use for names
666 -> [Unique] -- An equally long list of uniques, at least one for each binder
668 -> [Type] -- Types to instantiate the universally quantified tyvars
669 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
670 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
671 -- (ex_tvs, co_tvs, arg_ids),
673 -- ex_tvs are intended to be used as binders for existential type args
675 -- co_tvs are intended to be used as binders for coercion args and the kinds
676 -- of these vars have been instantiated by the inst_tys and the ex_tys
678 -- arg_ids are indended to be used as binders for value arguments, including
679 -- dicts, and their types have been instantiated with inst_tys and ex_tys
682 -- The following constructor T1
685 -- T1 :: forall b. Int -> b -> T(a,b)
688 -- has representation type
689 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
692 -- dataConInstPat fss us T1 (a1',b') will return
694 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
696 -- where the double-primed variables are created with the FastStrings and
697 -- Uniques given as fss and us
698 dataConInstPat arg_fun fss uniqs con inst_tys
699 = (ex_bndrs, co_bndrs, id_bndrs)
701 univ_tvs = dataConUnivTyVars con
702 ex_tvs = dataConExTyVars con
703 arg_tys = arg_fun con
704 eq_spec = dataConEqSpec con
705 eq_preds = eqSpecPreds eq_spec
708 n_co = length eq_spec
710 -- split the Uniques and FastStrings
711 (ex_uniqs, uniqs') = splitAt n_ex uniqs
712 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
714 (ex_fss, fss') = splitAt n_ex fss
715 (co_fss, id_fss) = splitAt n_co fss'
717 -- Make existential type variables
718 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
719 mk_ex_var uniq fs var = mkTyVar new_name kind
721 new_name = mkSysTvName uniq fs
724 -- Make the instantiating substitution
725 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
727 -- Make new coercion vars, instantiating kind
728 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
729 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
731 new_name = mkSysTvName uniq fs
732 co_kind = substTy subst (mkPredTy eq_pred)
734 -- make value vars, instantiating types
735 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcLoc
736 id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys
738 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
739 -- Returns (Just (dc, [x1..xn])) if the argument expression is
740 -- a constructor application of the form (dc x1 .. xn)
741 exprIsConApp_maybe (Cast expr co)
742 = -- Here we do the PushC reduction rule as described in the FC paper
743 case exprIsConApp_maybe expr of {
745 Just (dc, dc_args) ->
747 -- The transformation applies iff we have
748 -- (C e1 ... en) `cast` co
749 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
750 -- That is, with a T at the top of both sides
751 -- The left-hand one must be a T, because exprIsConApp returned True
752 -- but the right-hand one might not be. (Though it usually will.)
754 let (from_ty, to_ty) = coercionKind co
755 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
756 -- The inner one must be a TyConApp
758 case splitTyConApp_maybe to_ty of {
760 Just (to_tc, to_tc_arg_tys)
761 | from_tc /= to_tc -> Nothing
762 -- These two Nothing cases are possible; we might see
763 -- (C x y) `cast` (g :: T a ~ S [a]),
764 -- where S is a type function. In fact, exprIsConApp
765 -- will probably not be called in such circumstances,
766 -- but there't nothing wrong with it
770 tc_arity = tyConArity from_tc
772 (univ_args, rest1) = splitAt tc_arity dc_args
773 (ex_args, rest2) = splitAt n_ex_tvs rest1
774 (co_args, val_args) = splitAt n_cos rest2
776 arg_tys = dataConRepArgTys dc
777 dc_univ_tyvars = dataConUnivTyVars dc
778 dc_ex_tyvars = dataConExTyVars dc
779 dc_eq_spec = dataConEqSpec dc
780 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
781 n_ex_tvs = length dc_ex_tyvars
782 n_cos = length dc_eq_spec
784 -- Make the "theta" from Fig 3 of the paper
785 gammas = decomposeCo tc_arity co
786 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
787 theta = zipOpenTvSubst dc_tyvars new_tys
789 -- First we cast the existential coercion arguments
790 cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
792 `mkTransCoercion` (substTy theta ty)
793 new_co_args = zipWith cast_co dc_eq_spec co_args
795 -- ...and now value arguments
796 new_val_args = zipWith cast_arg arg_tys val_args
797 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
800 ASSERT( length univ_args == tc_arity )
801 ASSERT( from_tc == dataConTyCon dc )
802 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
803 ASSERT( all isTypeArg (univ_args ++ ex_args) )
804 ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
806 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
810 -- We do not want to tell the world that we have a
811 -- Cons, to *stop* Case of Known Cons, which removes
813 exprIsConApp_maybe (Note (TickBox {}) expr)
815 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
819 exprIsConApp_maybe (Note _ expr)
820 = exprIsConApp_maybe expr
821 -- We ignore InlineMe notes in case we have
822 -- x = __inline_me__ (a,b)
823 -- All part of making sure that INLINE pragmas never hurt
824 -- Marcin tripped on this one when making dictionaries more inlinable
826 -- In fact, we ignore all notes. For example,
827 -- case _scc_ "foo" (C a b) of
829 -- should be optimised away, but it will be only if we look
830 -- through the SCC note.
832 exprIsConApp_maybe expr = analyse (collectArgs expr)
834 analyse (Var fun, args)
835 | Just con <- isDataConWorkId_maybe fun,
836 args `lengthAtLeast` dataConRepArity con
837 -- Might be > because the arity excludes type args
840 -- Look through unfoldings, but only cheap ones, because
841 -- we are effectively duplicating the unfolding
842 analyse (Var fun, [])
843 | let unf = idUnfolding fun,
845 = exprIsConApp_maybe (unfoldingTemplate unf)
847 analyse other = Nothing
852 %************************************************************************
854 \subsection{Eta reduction and expansion}
856 %************************************************************************
859 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
860 {- The Arity returned is the number of value args the
861 thing can be applied to without doing much work
863 exprEtaExpandArity is used when eta expanding
866 It returns 1 (or more) to:
867 case x of p -> \s -> ...
868 because for I/O ish things we really want to get that \s to the top.
869 We are prepared to evaluate x each time round the loop in order to get that
871 It's all a bit more subtle than it looks:
875 Consider one-shot lambdas
876 let x = expensive in \y z -> E
877 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
878 Hence the ArityType returned by arityType
880 2. The state-transformer hack
882 The one-shot lambda special cause is particularly important/useful for
883 IO state transformers, where we often get
884 let x = E in \ s -> ...
886 and the \s is a real-world state token abstraction. Such abstractions
887 are almost invariably 1-shot, so we want to pull the \s out, past the
888 let x=E, even if E is expensive. So we treat state-token lambdas as
889 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
891 3. Dealing with bottom
894 f = \x -> error "foo"
895 Here, arity 1 is fine. But if it is
899 then we want to get arity 2. Tecnically, this isn't quite right, because
901 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
902 do so; it improves some programs significantly, and increasing convergence
903 isn't a bad thing. Hence the ABot/ATop in ArityType.
905 Actually, the situation is worse. Consider
909 Can we eta-expand here? At first the answer looks like "yes of course", but
912 This should diverge! But if we eta-expand, it won't. Again, we ignore this
913 "problem", because being scrupulous would lose an important transformation for
919 Non-recursive newtypes are transparent, and should not get in the way.
920 We do (currently) eta-expand recursive newtypes too. So if we have, say
922 newtype T = MkT ([T] -> Int)
926 where f has arity 1. Then: etaExpandArity e = 1;
927 that is, etaExpandArity looks through the coerce.
929 When we eta-expand e to arity 1: eta_expand 1 e T
930 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
932 HOWEVER, note that if you use coerce bogusly you can ge
934 And since negate has arity 2, you might try to eta expand. But you can't
935 decopose Int to a function type. Hence the final case in eta_expand.
939 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
941 -- A limited sort of function type
942 data ArityType = AFun Bool ArityType -- True <=> one-shot
943 | ATop -- Know nothing
946 arityDepth :: ArityType -> Arity
947 arityDepth (AFun _ ty) = 1 + arityDepth ty
950 andArityType ABot at2 = at2
951 andArityType ATop at2 = ATop
952 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
953 andArityType at1 at2 = andArityType at2 at1
955 arityType :: DynFlags -> CoreExpr -> ArityType
956 -- (go1 e) = [b1,..,bn]
957 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
958 -- where bi is True <=> the lambda is one-shot
960 arityType dflags (Note n e) = arityType dflags e
961 -- Not needed any more: etaExpand is cleverer
962 -- | ok_note n = arityType dflags e
963 -- | otherwise = ATop
965 arityType dflags (Cast e co) = arityType dflags e
967 arityType dflags (Var v)
968 = mk (idArity v) (arg_tys (idType v))
970 mk :: Arity -> [Type] -> ArityType
971 -- The argument types are only to steer the "state hack"
972 -- Consider case x of
974 -- False -> \(s:RealWorld) -> e
975 -- where foo has arity 1. Then we want the state hack to
976 -- apply to foo too, so we can eta expand the case.
977 mk 0 tys | isBottomingId v = ABot
978 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
980 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
981 mk n [] = AFun False (mk (n-1) [])
983 arg_tys :: Type -> [Type] -- Ignore for-alls
985 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
986 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
989 -- Lambdas; increase arity
990 arityType dflags (Lam x e)
991 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
992 | otherwise = arityType dflags e
994 -- Applications; decrease arity
995 arityType dflags (App f (Type _)) = arityType dflags f
996 arityType dflags (App f a) = case arityType dflags f of
997 AFun one_shot xs | exprIsCheap a -> xs
1000 -- Case/Let; keep arity if either the expression is cheap
1001 -- or it's a 1-shot lambda
1002 -- The former is not really right for Haskell
1003 -- f x = case x of { (a,b) -> \y. e }
1005 -- f x y = case x of { (a,b) -> e }
1006 -- The difference is observable using 'seq'
1007 arityType dflags (Case scrut _ _ alts)
1008 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1009 xs | exprIsCheap scrut -> xs
1010 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1013 arityType dflags (Let b e)
1014 = case arityType dflags e of
1015 xs | cheap_bind b -> xs
1016 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1019 cheap_bind (NonRec b e) = is_cheap (b,e)
1020 cheap_bind (Rec prs) = all is_cheap prs
1021 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1023 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1024 -- dictionary bindings. This improves arities. Thereby, it also
1025 -- means that full laziness is less prone to floating out the
1026 -- application of a function to its dictionary arguments, which
1027 -- can thereby lose opportunities for fusion. Example:
1028 -- foo :: Ord a => a -> ...
1029 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1030 -- -- So foo has arity 1
1032 -- f = \x. foo dInt $ bar x
1034 -- The (foo DInt) is floated out, and makes ineffective a RULE
1035 -- foo (bar x) = ...
1037 -- One could go further and make exprIsCheap reply True to any
1038 -- dictionary-typed expression, but that's more work.
1040 arityType dflags other = ATop
1042 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1043 ok_note InlineMe = False
1044 ok_note other = True
1045 -- Notice that we do not look through __inline_me__
1046 -- This may seem surprising, but consider
1047 -- f = _inline_me (\x -> e)
1048 -- We DO NOT want to eta expand this to
1049 -- f = \x -> (_inline_me (\x -> e)) x
1050 -- because the _inline_me gets dropped now it is applied,
1059 etaExpand :: Arity -- Result should have this number of value args
1061 -> CoreExpr -> Type -- Expression and its type
1063 -- (etaExpand n us e ty) returns an expression with
1064 -- the same meaning as 'e', but with arity 'n'.
1066 -- Given e' = etaExpand n us e ty
1068 -- ty = exprType e = exprType e'
1070 -- Note that SCCs are not treated specially. If we have
1071 -- etaExpand 2 (\x -> scc "foo" e)
1072 -- = (\xy -> (scc "foo" e) y)
1073 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1075 etaExpand n us expr ty
1076 | manifestArity expr >= n = expr -- The no-op case
1078 = eta_expand n us expr ty
1081 -- manifestArity sees how many leading value lambdas there are
1082 manifestArity :: CoreExpr -> Arity
1083 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1084 | otherwise = manifestArity e
1085 manifestArity (Note _ e) = manifestArity e
1086 manifestArity (Cast e _) = manifestArity e
1089 -- etaExpand deals with for-alls. For example:
1091 -- where E :: forall a. a -> a
1093 -- (/\b. \y::a -> E b y)
1095 -- It deals with coerces too, though they are now rare
1096 -- so perhaps the extra code isn't worth it
1098 eta_expand n us expr ty
1100 -- The ILX code generator requires eta expansion for type arguments
1101 -- too, but alas the 'n' doesn't tell us how many of them there
1102 -- may be. So we eagerly eta expand any big lambdas, and just
1103 -- cross our fingers about possible loss of sharing in the ILX case.
1104 -- The Right Thing is probably to make 'arity' include
1105 -- type variables throughout the compiler. (ToDo.)
1107 -- Saturated, so nothing to do
1110 -- Short cut for the case where there already
1111 -- is a lambda; no point in gratuitously adding more
1112 eta_expand n us (Lam v body) ty
1114 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1117 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1119 -- We used to have a special case that stepped inside Coerces here,
1120 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1121 -- = Note note (eta_expand n us e ty)
1122 -- BUT this led to an infinite loop
1123 -- Example: newtype T = MkT (Int -> Int)
1124 -- eta_expand 1 (coerce (Int->Int) e)
1125 -- --> coerce (Int->Int) (eta_expand 1 T e)
1127 -- --> coerce (Int->Int) (coerce T
1128 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1129 -- by the splitNewType_maybe case below
1132 eta_expand n us expr ty
1133 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1134 case splitForAllTy_maybe ty of {
1137 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1139 lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
1140 -- Using tv as a base retains its tyvar/covar-ness
1144 case splitFunTy_maybe ty of {
1145 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1147 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1153 -- newtype T = MkT ([T] -> Int)
1154 -- Consider eta-expanding this
1157 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1159 case splitNewTypeRepCo_maybe ty of {
1161 mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ;
1164 -- We have an expression of arity > 0, but its type isn't a function
1165 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1166 -- Essentially the programmer is playing fast and loose with types
1167 -- (Happy does this a lot). So we simply decline to eta-expand.
1172 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1173 It tells how many things the expression can be applied to before doing
1174 any work. It doesn't look inside cases, lets, etc. The idea is that
1175 exprEtaExpandArity will do the hard work, leaving something that's easy
1176 for exprArity to grapple with. In particular, Simplify uses exprArity to
1177 compute the ArityInfo for the Id.
1179 Originally I thought that it was enough just to look for top-level lambdas, but
1180 it isn't. I've seen this
1182 foo = PrelBase.timesInt
1184 We want foo to get arity 2 even though the eta-expander will leave it
1185 unchanged, in the expectation that it'll be inlined. But occasionally it
1186 isn't, because foo is blacklisted (used in a rule).
1188 Similarly, see the ok_note check in exprEtaExpandArity. So
1189 f = __inline_me (\x -> e)
1190 won't be eta-expanded.
1192 And in any case it seems more robust to have exprArity be a bit more intelligent.
1193 But note that (\x y z -> f x y z)
1194 should have arity 3, regardless of f's arity.
1197 exprArity :: CoreExpr -> Arity
1200 go (Var v) = idArity v
1201 go (Lam x e) | isId x = go e + 1
1203 go (Note n e) = go e
1204 go (Cast e _) = go e
1205 go (App e (Type t)) = go e
1206 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1207 -- NB: exprIsCheap a!
1208 -- f (fac x) does not have arity 2,
1209 -- even if f has arity 3!
1210 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1211 -- unknown, hence arity 0
1215 %************************************************************************
1217 \subsection{Equality}
1219 %************************************************************************
1221 @cheapEqExpr@ is a cheap equality test which bales out fast!
1222 True => definitely equal
1223 False => may or may not be equal
1226 cheapEqExpr :: Expr b -> Expr b -> Bool
1228 cheapEqExpr (Var v1) (Var v2) = v1==v2
1229 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1230 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1232 cheapEqExpr (App f1 a1) (App f2 a2)
1233 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1235 cheapEqExpr _ _ = False
1237 exprIsBig :: Expr b -> Bool
1238 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1239 exprIsBig (Lit _) = False
1240 exprIsBig (Var v) = False
1241 exprIsBig (Type t) = False
1242 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1243 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1244 exprIsBig other = True
1249 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1250 -- Used in rule matching, so does *not* look through
1251 -- newtypes, predicate types; hence tcEqExpr
1253 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1255 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1257 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1258 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1259 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1260 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1261 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1262 tcEqExprX env (Let (NonRec v1 r1) e1)
1263 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1264 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1265 tcEqExprX env (Let (Rec ps1) e1)
1266 (Let (Rec ps2) e2) = equalLength ps1 ps2
1267 && and (zipWith eq_rhs ps1 ps2)
1268 && tcEqExprX env' e1 e2
1270 env' = foldl2 rn_bndr2 env ps2 ps2
1271 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1272 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1273 tcEqExprX env (Case e1 v1 t1 a1)
1274 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1275 && tcEqTypeX env t1 t2
1276 && equalLength a1 a2
1277 && and (zipWith (eq_alt env') a1 a2)
1279 env' = rnBndr2 env v1 v2
1281 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1282 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1283 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1284 tcEqExprX env e1 e2 = False
1286 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1288 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1289 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1290 eq_note env other1 other2 = False
1294 %************************************************************************
1296 \subsection{The size of an expression}
1298 %************************************************************************
1301 coreBindsSize :: [CoreBind] -> Int
1302 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1304 exprSize :: CoreExpr -> Int
1305 -- A measure of the size of the expressions
1306 -- It also forces the expression pretty drastically as a side effect
1307 exprSize (Var v) = v `seq` 1
1308 exprSize (Lit lit) = lit `seq` 1
1309 exprSize (App f a) = exprSize f + exprSize a
1310 exprSize (Lam b e) = varSize b + exprSize e
1311 exprSize (Let b e) = bindSize b + exprSize e
1312 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1313 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1314 exprSize (Note n e) = noteSize n + exprSize e
1315 exprSize (Type t) = seqType t `seq` 1
1317 noteSize (SCC cc) = cc `seq` 1
1318 noteSize InlineMe = 1
1319 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1321 varSize :: Var -> Int
1322 varSize b | isTyVar b = 1
1323 | otherwise = seqType (idType b) `seq`
1324 megaSeqIdInfo (idInfo b) `seq`
1327 varsSize = foldr ((+) . varSize) 0
1329 bindSize (NonRec b e) = varSize b + exprSize e
1330 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1332 pairSize (b,e) = varSize b + exprSize e
1334 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1338 %************************************************************************
1340 \subsection{Hashing}
1342 %************************************************************************
1345 hashExpr :: CoreExpr -> Int
1346 -- Two expressions that hash to the same Int may be equal (but may not be)
1347 -- Two expressions that hash to the different Ints are definitely unequal
1349 -- But "unequal" here means "not identical"; two alpha-equivalent
1350 -- expressions may hash to the different Ints
1352 -- The emphasis is on a crude, fast hash, rather than on high precision
1354 -- We must be careful that \x.x and \y.y map to the same hash code,
1355 -- (at least if we want the above invariant to be true)
1357 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1358 -- UniqFM doesn't like negative Ints
1360 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1362 hash_expr :: HashEnv -> CoreExpr -> Word32
1363 -- Word32, because we're expecting overflows here, and overflowing
1364 -- signed types just isn't cool. In C it's even undefined.
1365 hash_expr env (Note _ e) = hash_expr env e
1366 hash_expr env (Cast e co) = hash_expr env e
1367 hash_expr env (Var v) = hashVar env v
1368 hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1369 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1370 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1371 hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
1372 hash_expr env (Case e _ _ _) = hash_expr env e
1373 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1374 hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1
1375 -- Shouldn't happen. Better to use WARN than trace, because trace
1376 -- prevents the CPR optimisation kicking in for hash_expr.
1378 fast_hash_expr env (Var v) = hashVar env v
1379 fast_hash_expr env (Type t) = fast_hash_type env t
1380 fast_hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1381 fast_hash_expr env (Cast e co) = fast_hash_expr env e
1382 fast_hash_expr env (Note n e) = fast_hash_expr env e
1383 fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1384 fast_hash_expr env other = 1
1386 fast_hash_type :: HashEnv -> Type -> Word32
1387 fast_hash_type env ty
1388 | Just tv <- getTyVar_maybe ty = hashVar env tv
1389 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1390 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1393 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1394 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1396 hashVar :: HashEnv -> Var -> Word32
1398 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1401 %************************************************************************
1403 \subsection{Determining non-updatable right-hand-sides}
1405 %************************************************************************
1407 Top-level constructor applications can usually be allocated
1408 statically, but they can't if the constructor, or any of the
1409 arguments, come from another DLL (because we can't refer to static
1410 labels in other DLLs).
1412 If this happens we simply make the RHS into an updatable thunk,
1413 and 'exectute' it rather than allocating it statically.
1416 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1417 -- This function is called only on *top-level* right-hand sides
1418 -- Returns True if the RHS can be allocated statically, with
1419 -- no thunks involved at all.
1421 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1422 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1423 -- update flag on it.
1425 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1426 -- (a) a value lambda
1427 -- (b) a saturated constructor application with static args
1429 -- BUT watch out for
1430 -- (i) Any cross-DLL references kill static-ness completely
1431 -- because they must be 'executed' not statically allocated
1432 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1433 -- this is not necessary)
1435 -- (ii) We treat partial applications as redexes, because in fact we
1436 -- make a thunk for them that runs and builds a PAP
1437 -- at run-time. The only appliations that are treated as
1438 -- static are *saturated* applications of constructors.
1440 -- We used to try to be clever with nested structures like this:
1441 -- ys = (:) w ((:) w [])
1442 -- on the grounds that CorePrep will flatten ANF-ise it later.
1443 -- But supporting this special case made the function much more
1444 -- complicated, because the special case only applies if there are no
1445 -- enclosing type lambdas:
1446 -- ys = /\ a -> Foo (Baz ([] a))
1447 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1449 -- But in fact, even without -O, nested structures at top level are
1450 -- flattened by the simplifier, so we don't need to be super-clever here.
1454 -- f = \x::Int. x+7 TRUE
1455 -- p = (True,False) TRUE
1457 -- d = (fst p, False) FALSE because there's a redex inside
1458 -- (this particular one doesn't happen but...)
1460 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1461 -- n = /\a. Nil a TRUE
1463 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1466 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1467 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1469 -- b) (C x xs), where C is a contructors is updatable if the application is
1472 -- c) don't look through unfolding of f in (f x).
1474 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1475 -- them as making the RHS re-entrant (non-updatable).
1477 rhsIsStatic this_pkg rhs = is_static False rhs
1479 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1482 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1484 is_static in_arg (Note (SCC _) e) = False
1485 is_static in_arg (Note _ e) = is_static in_arg e
1486 is_static in_arg (Cast e co) = is_static in_arg e
1488 is_static in_arg (Lit lit)
1490 MachLabel _ _ -> False
1492 -- A MachLabel (foreign import "&foo") in an argument
1493 -- prevents a constructor application from being static. The
1494 -- reason is that it might give rise to unresolvable symbols
1495 -- in the object file: under Linux, references to "weak"
1496 -- symbols from the data segment give rise to "unresolvable
1497 -- relocation" errors at link time This might be due to a bug
1498 -- in the linker, but we'll work around it here anyway.
1501 is_static in_arg other_expr = go other_expr 0
1503 go (Var f) n_val_args
1504 #if mingw32_TARGET_OS
1505 | not (isDllName this_pkg (idName f))
1507 = saturated_data_con f n_val_args
1508 || (in_arg && n_val_args == 0)
1509 -- A naked un-applied variable is *not* deemed a static RHS
1511 -- Reason: better to update so that the indirection gets shorted
1512 -- out, and the true value will be seen
1513 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1514 -- are always updatable. If you do so, make sure that non-updatable
1515 -- ones have enough space for their static link field!
1517 go (App f a) n_val_args
1518 | isTypeArg a = go f n_val_args
1519 | not in_arg && is_static True a = go f (n_val_args + 1)
1520 -- The (not in_arg) checks that we aren't in a constructor argument;
1521 -- if we are, we don't allow (value) applications of any sort
1523 -- NB. In case you wonder, args are sometimes not atomic. eg.
1524 -- x = D# (1.0## /## 2.0##)
1525 -- can't float because /## can fail.
1527 go (Note (SCC _) f) n_val_args = False
1528 go (Note _ f) n_val_args = go f n_val_args
1529 go (Cast e co) n_val_args = go e n_val_args
1531 go other n_val_args = False
1533 saturated_data_con f n_val_args
1534 = case isDataConWorkId_maybe f of
1535 Just dc -> n_val_args == dataConRepArity dc