2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
18 mkInlineMe, mkSCC, mkCoerce, mkCoerceI,
19 bindNonRec, needsCaseBinding,
20 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
22 -- Taking expressions apart
23 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
25 -- Properties of expressions
26 exprType, coreAltType,
27 exprIsDupable, exprIsTrivial, exprIsCheap,
28 exprIsHNF,exprOkForSpeculation, exprIsBig,
29 exprIsConApp_maybe, exprIsBottom,
32 -- Arity and eta expansion
33 manifestArity, exprArity,
34 exprEtaExpandArity, etaExpand,
43 cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg,
45 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
48 #include "HsVersions.h"
84 import GHC.Exts -- For `xori`
88 %************************************************************************
90 \subsection{Find the type of a Core atom/expression}
92 %************************************************************************
95 exprType :: CoreExpr -> Type
97 exprType (Var var) = idType var
98 exprType (Lit lit) = literalType lit
99 exprType (Let _ body) = exprType body
100 exprType (Case _ _ ty alts) = ty
101 exprType (Cast e co) = snd (coercionKind co)
102 exprType (Note other_note e) = exprType e
103 exprType (Lam binder expr) = mkPiType binder (exprType expr)
105 = case collectArgs e of
106 (fun, args) -> applyTypeToArgs e (exprType fun) args
108 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
110 coreAltType :: CoreAlt -> Type
111 coreAltType (_,_,rhs) = exprType rhs
114 @mkPiType@ makes a (->) type or a forall type, depending on whether
115 it is given a type variable or a term variable. We cleverly use the
116 lbvarinfo field to figure out the right annotation for the arrove in
117 case of a term variable.
120 mkPiType :: Var -> Type -> Type -- The more polymorphic version
121 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
123 mkPiTypes vs ty = foldr mkPiType ty vs
126 | isId v = mkFunTy (idType v) ty
127 | otherwise = mkForAllTy v ty
131 applyTypeToArg :: Type -> CoreExpr -> Type
132 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
133 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
135 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
136 -- A more efficient version of applyTypeToArg
137 -- when we have several args
138 -- The first argument is just for debugging
139 applyTypeToArgs e op_ty [] = op_ty
141 applyTypeToArgs e op_ty (Type ty : args)
142 = -- Accumulate type arguments so we can instantiate all at once
145 go rev_tys (Type ty : args) = go (ty:rev_tys) args
146 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
148 op_ty' = applyTys op_ty (reverse rev_tys)
150 applyTypeToArgs e op_ty (other_arg : args)
151 = case (splitFunTy_maybe op_ty) of
152 Just (_, res_ty) -> applyTypeToArgs e res_ty args
153 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
158 %************************************************************************
160 \subsection{Attaching notes}
162 %************************************************************************
164 mkNote removes redundant coercions, and SCCs where possible
168 mkNote :: Note -> CoreExpr -> CoreExpr
169 mkNote (SCC cc) expr = mkSCC cc expr
170 mkNote InlineMe expr = mkInlineMe expr
171 mkNote note expr = Note note expr
175 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
176 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
177 not be *applied* to anything.
179 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
182 f = inline_me (coerce t fw)
183 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
184 We want the split, so that the coerces can cancel at the call site.
186 However, we can get left with tiresome type applications. Notably, consider
187 f = /\ a -> let t = e in (t, w)
188 Then lifting the let out of the big lambda gives
190 f = /\ a -> let t = inline_me (t' a) in (t, w)
191 The inline_me is to stop the simplifier inlining t' right back
192 into t's RHS. In the next phase we'll substitute for t (since
193 its rhs is trivial) and *then* we could get rid of the inline_me.
194 But it hardly seems worth it, so I don't bother.
197 mkInlineMe (Var v) = Var v
198 mkInlineMe e = Note InlineMe e
204 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
206 mkCoerceI (ACo co) e = mkCoerce co e
208 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
209 mkCoerce co (Cast expr co2)
210 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
211 (_from_ty2, to_ty2) = coercionKind co2} in
212 from_ty `coreEqType` to_ty2 )
213 mkCoerce (mkTransCoercion co2 co) expr
216 = let (from_ty, to_ty) = coercionKind co in
217 -- if to_ty `coreEqType` from_ty
220 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
225 mkSCC :: CostCentre -> Expr b -> Expr b
226 -- Note: Nested SCC's *are* preserved for the benefit of
227 -- cost centre stack profiling
228 mkSCC cc (Lit lit) = Lit lit
229 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
230 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
231 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
232 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
233 mkSCC cc expr = Note (SCC cc) expr
237 %************************************************************************
239 \subsection{Other expression construction}
241 %************************************************************************
244 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
245 -- (bindNonRec x r b) produces either
248 -- case r of x { _DEFAULT_ -> b }
250 -- depending on whether x is unlifted or not
251 -- It's used by the desugarer to avoid building bindings
252 -- that give Core Lint a heart attack. Actually the simplifier
253 -- deals with them perfectly well.
255 bindNonRec bndr rhs body
256 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
257 | otherwise = Let (NonRec bndr rhs) body
259 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
260 -- Make a case expression instead of a let
261 -- These can arise either from the desugarer,
262 -- or from beta reductions: (\x.e) (x +# y)
266 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
267 -- This guy constructs the value that the scrutinee must have
268 -- when you are in one particular branch of a case
269 mkAltExpr (DataAlt con) args inst_tys
270 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
271 mkAltExpr (LitAlt lit) [] []
273 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
274 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
276 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
277 mkIfThenElse guard then_expr else_expr
278 -- Not going to be refining, so okay to take the type of the "then" clause
279 = Case guard (mkWildId boolTy) (exprType then_expr)
280 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
281 (DataAlt trueDataCon, [], then_expr) ]
285 %************************************************************************
287 \subsection{Taking expressions apart}
289 %************************************************************************
291 The default alternative must be first, if it exists at all.
292 This makes it easy to find, though it makes matching marginally harder.
295 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
296 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
297 findDefault alts = (alts, Nothing)
299 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
302 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
303 other -> go alts panic_deflt
305 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
308 go (alt@(con1,_,_) : alts) deflt
309 = case con `cmpAltCon` con1 of
310 LT -> deflt -- Missed it already; the alts are in increasing order
312 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
314 isDefaultAlt :: CoreAlt -> Bool
315 isDefaultAlt (DEFAULT, _, _) = True
316 isDefaultAlt other = False
318 ---------------------------------
319 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
320 -- Merge preserving order; alternatives in the first arg
321 -- shadow ones in the second
322 mergeAlts [] as2 = as2
323 mergeAlts as1 [] = as1
324 mergeAlts (a1:as1) (a2:as2)
325 = case a1 `cmpAlt` a2 of
326 LT -> a1 : mergeAlts as1 (a2:as2)
327 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
328 GT -> a2 : mergeAlts (a1:as1) as2
331 ---------------------------------
332 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
333 -- Given case (C a b x y) of
335 -- we want to drop the leading type argument of the scrutinee
336 -- leaving the arguments to match agains the pattern
338 trimConArgs DEFAULT args = ASSERT( null args ) []
339 trimConArgs (LitAlt lit) args = ASSERT( null args ) []
340 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
344 %************************************************************************
346 \subsection{Figuring out things about expressions}
348 %************************************************************************
350 @exprIsTrivial@ is true of expressions we are unconditionally happy to
351 duplicate; simple variables and constants, and type
352 applications. Note that primop Ids aren't considered
355 @exprIsBottom@ is true of expressions that are guaranteed to diverge
358 There used to be a gruesome test for (hasNoBinding v) in the
360 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
361 The idea here is that a constructor worker, like $wJust, is
362 really short for (\x -> $wJust x), becuase $wJust has no binding.
363 So it should be treated like a lambda. Ditto unsaturated primops.
364 But now constructor workers are not "have-no-binding" Ids. And
365 completely un-applied primops and foreign-call Ids are sufficiently
366 rare that I plan to allow them to be duplicated and put up with
369 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
370 a) it really generates code, (and a heap object when it's
371 a function arg) to capture the cost centre
372 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
375 exprIsTrivial (Var v) = True -- See notes above
376 exprIsTrivial (Type _) = True
377 exprIsTrivial (Lit lit) = litIsTrivial lit
378 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
379 exprIsTrivial (Note (SCC _) e) = False -- See notes above
380 exprIsTrivial (Note _ e) = exprIsTrivial e
381 exprIsTrivial (Cast e co) = exprIsTrivial e
382 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
383 exprIsTrivial other = False
387 @exprIsDupable@ is true of expressions that can be duplicated at a modest
388 cost in code size. This will only happen in different case
389 branches, so there's no issue about duplicating work.
391 That is, exprIsDupable returns True of (f x) even if
392 f is very very expensive to call.
394 Its only purpose is to avoid fruitless let-binding
395 and then inlining of case join points
399 exprIsDupable (Type _) = True
400 exprIsDupable (Var v) = True
401 exprIsDupable (Lit lit) = litIsDupable lit
402 exprIsDupable (Note InlineMe e) = True
403 exprIsDupable (Note _ e) = exprIsDupable e
404 exprIsDupable (Cast e co) = exprIsDupable e
408 go (Var v) n_args = True
409 go (App f a) n_args = n_args < dupAppSize
412 go other n_args = False
415 dupAppSize = 4 -- Size of application we are prepared to duplicate
418 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
419 it is obviously in weak head normal form, or is cheap to get to WHNF.
420 [Note that that's not the same as exprIsDupable; an expression might be
421 big, and hence not dupable, but still cheap.]
423 By ``cheap'' we mean a computation we're willing to:
424 push inside a lambda, or
425 inline at more than one place
426 That might mean it gets evaluated more than once, instead of being
427 shared. The main examples of things which aren't WHNF but are
432 (where e, and all the ei are cheap)
435 (where e and b are cheap)
438 (where op is a cheap primitive operator)
441 (because we are happy to substitute it inside a lambda)
443 Notice that a variable is considered 'cheap': we can push it inside a lambda,
444 because sharing will make sure it is only evaluated once.
447 exprIsCheap :: CoreExpr -> Bool
448 exprIsCheap (Lit lit) = True
449 exprIsCheap (Type _) = True
450 exprIsCheap (Var _) = True
451 exprIsCheap (Note InlineMe e) = True
452 exprIsCheap (Note _ e) = exprIsCheap e
453 exprIsCheap (Cast e co) = exprIsCheap e
454 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
455 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
456 and [exprIsCheap rhs | (_,_,rhs) <- alts]
457 -- Experimentally, treat (case x of ...) as cheap
458 -- (and case __coerce x etc.)
459 -- This improves arities of overloaded functions where
460 -- there is only dictionary selection (no construction) involved
461 exprIsCheap (Let (NonRec x _) e)
462 | isUnLiftedType (idType x) = exprIsCheap e
464 -- strict lets always have cheap right hand sides,
465 -- and do no allocation.
467 exprIsCheap other_expr -- Applications and variables
470 -- Accumulate value arguments, then decide
471 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
472 | otherwise = go f val_args
474 go (Var f) [] = True -- Just a type application of a variable
475 -- (f t1 t2 t3) counts as WHNF
477 = case globalIdDetails f of
478 RecordSelId {} -> go_sel args
479 ClassOpId _ -> go_sel args
480 PrimOpId op -> go_primop op args
482 DataConWorkId _ -> go_pap args
483 other | length args < idArity f -> go_pap args
485 other -> isBottomingId f
486 -- Application of a function which
487 -- always gives bottom; we treat this as cheap
488 -- because it certainly doesn't need to be shared!
490 go other args = False
493 go_pap args = all exprIsTrivial args
494 -- For constructor applications and primops, check that all
495 -- the args are trivial. We don't want to treat as cheap, say,
497 -- We'll put up with one constructor application, but not dozens
500 go_primop op args = primOpIsCheap op && all exprIsCheap args
501 -- In principle we should worry about primops
502 -- that return a type variable, since the result
503 -- might be applied to something, but I'm not going
504 -- to bother to check the number of args
507 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
508 go_sel other = False -- look cheap, so we will substitute it inside a
509 -- lambda. Particularly for dictionary field selection.
510 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
511 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
514 exprOkForSpeculation returns True of an expression that it is
516 * safe to evaluate even if normal order eval might not
517 evaluate the expression at all, or
519 * safe *not* to evaluate even if normal order would do so
523 the expression guarantees to terminate,
525 without raising an exception,
526 without causing a side effect (e.g. writing a mutable variable)
528 NB: if exprIsHNF e, then exprOkForSpecuation e
531 let x = case y# +# 1# of { r# -> I# r# }
534 case y# +# 1# of { r# ->
539 We can only do this if the (y+1) is ok for speculation: it has no
540 side effects, and can't diverge or raise an exception.
543 exprOkForSpeculation :: CoreExpr -> Bool
544 exprOkForSpeculation (Lit _) = True
545 exprOkForSpeculation (Type _) = True
546 -- Tick boxes are *not* suitable for speculation
547 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
548 && not (isTickBoxOp v)
549 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
550 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
551 exprOkForSpeculation other_expr
552 = case collectArgs other_expr of
553 (Var f, args) -> spec_ok (globalIdDetails f) args
557 spec_ok (DataConWorkId _) args
558 = True -- The strictness of the constructor has already
559 -- been expressed by its "wrapper", so we don't need
560 -- to take the arguments into account
562 spec_ok (PrimOpId op) args
563 | isDivOp op, -- Special case for dividing operations that fail
564 [arg1, Lit lit] <- args -- only if the divisor is zero
565 = not (isZeroLit lit) && exprOkForSpeculation arg1
566 -- Often there is a literal divisor, and this
567 -- can get rid of a thunk in an inner looop
570 = primOpOkForSpeculation op &&
571 all exprOkForSpeculation args
572 -- A bit conservative: we don't really need
573 -- to care about lazy arguments, but this is easy
575 spec_ok other args = False
577 isDivOp :: PrimOp -> Bool
578 -- True of dyadic operators that can fail
579 -- only if the second arg is zero
580 -- This function probably belongs in PrimOp, or even in
581 -- an automagically generated file.. but it's such a
582 -- special case I thought I'd leave it here for now.
583 isDivOp IntQuotOp = True
584 isDivOp IntRemOp = True
585 isDivOp WordQuotOp = True
586 isDivOp WordRemOp = True
587 isDivOp IntegerQuotRemOp = True
588 isDivOp IntegerDivModOp = True
589 isDivOp FloatDivOp = True
590 isDivOp DoubleDivOp = True
591 isDivOp other = False
596 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
597 exprIsBottom e = go 0 e
599 -- n is the number of args
600 go n (Note _ e) = go n e
601 go n (Cast e co) = go n e
602 go n (Let _ e) = go n e
603 go n (Case e _ _ _) = go 0 e -- Just check the scrut
604 go n (App e _) = go (n+1) e
605 go n (Var v) = idAppIsBottom v n
607 go n (Lam _ _) = False
608 go n (Type _) = False
610 idAppIsBottom :: Id -> Int -> Bool
611 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
614 @exprIsHNF@ returns true for expressions that are certainly *already*
615 evaluated to *head* normal form. This is used to decide whether it's ok
618 case x of _ -> e ===> e
620 and to decide whether it's safe to discard a `seq`
622 So, it does *not* treat variables as evaluated, unless they say they are.
624 But it *does* treat partial applications and constructor applications
625 as values, even if their arguments are non-trivial, provided the argument
627 e.g. (:) (f x) (map f xs) is a value
628 map (...redex...) is a value
629 Because `seq` on such things completes immediately
631 For unlifted argument types, we have to be careful:
633 Suppose (f x) diverges; then C (f x) is not a value. However this can't
634 happen: see CoreSyn Note [CoreSyn let/app invariant]. Args of unboxed
635 type must be ok-for-speculation (or trivial).
638 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
639 exprIsHNF (Var v) -- NB: There are no value args at this point
640 = isDataConWorkId v -- Catches nullary constructors,
641 -- so that [] and () are values, for example
642 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
643 || isEvaldUnfolding (idUnfolding v)
644 -- Check the thing's unfolding; it might be bound to a value
645 -- A worry: what if an Id's unfolding is just itself:
646 -- then we could get an infinite loop...
648 exprIsHNF (Lit l) = True
649 exprIsHNF (Type ty) = True -- Types are honorary Values;
650 -- we don't mind copying them
651 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
652 exprIsHNF (Note _ e) = exprIsHNF e
653 exprIsHNF (Cast e co) = exprIsHNF e
654 exprIsHNF (App e (Type _)) = exprIsHNF e
655 exprIsHNF (App e a) = app_is_value e [a]
656 exprIsHNF other = False
658 -- There is at least one value argument
659 app_is_value (Var fun) args
660 = idArity fun > valArgCount args -- Under-applied function
661 || isDataConWorkId fun -- or data constructor
662 app_is_value (Note n f) as = app_is_value f as
663 app_is_value (Cast f _) as = app_is_value f as
664 app_is_value (App f a) as = app_is_value f (a:as)
665 app_is_value other as = False
669 -- These InstPat functions go here to avoid circularity between DataCon and Id
670 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
671 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
672 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
674 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
675 -- Remember to include the existential dictionaries
677 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
678 -> [FastString] -- A long enough list of FSs to use for names
679 -> [Unique] -- An equally long list of uniques, at least one for each binder
681 -> [Type] -- Types to instantiate the universally quantified tyvars
682 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
683 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
684 -- (ex_tvs, co_tvs, arg_ids),
686 -- ex_tvs are intended to be used as binders for existential type args
688 -- co_tvs are intended to be used as binders for coercion args and the kinds
689 -- of these vars have been instantiated by the inst_tys and the ex_tys
690 -- The co_tvs include both GADT equalities (dcEqSpec) and
691 -- programmer-specified equalities (dcEqTheta)
693 -- arg_ids are indended to be used as binders for value arguments,
694 -- and their types have been instantiated with inst_tys and ex_tys
695 -- The arg_ids include both dicts (dcDictTheta) and
696 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
699 -- The following constructor T1
702 -- T1 :: forall b. Int -> b -> T(a,b)
705 -- has representation type
706 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
709 -- dataConInstPat fss us T1 (a1',b') will return
711 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
713 -- where the double-primed variables are created with the FastStrings and
714 -- Uniques given as fss and us
715 dataConInstPat arg_fun fss uniqs con inst_tys
716 = (ex_bndrs, co_bndrs, arg_ids)
718 univ_tvs = dataConUnivTyVars con
719 ex_tvs = dataConExTyVars con
720 arg_tys = arg_fun con
721 eq_spec = dataConEqSpec con
722 eq_theta = dataConEqTheta con
723 eq_preds = eqSpecPreds eq_spec ++ eq_theta
726 n_co = length eq_preds
728 -- split the Uniques and FastStrings
729 (ex_uniqs, uniqs') = splitAt n_ex uniqs
730 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
732 (ex_fss, fss') = splitAt n_ex fss
733 (co_fss, id_fss) = splitAt n_co fss'
735 -- Make existential type variables
736 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
737 mk_ex_var uniq fs var = mkTyVar new_name kind
739 new_name = mkSysTvName uniq fs
742 -- Make the instantiating substitution
743 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
745 -- Make new coercion vars, instantiating kind
746 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
747 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
749 new_name = mkSysTvName uniq fs
750 co_kind = substTy subst (mkPredTy eq_pred)
752 -- make value vars, instantiating types
753 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
754 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
756 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
757 -- Returns (Just (dc, [x1..xn])) if the argument expression is
758 -- a constructor application of the form (dc x1 .. xn)
759 exprIsConApp_maybe (Cast expr co)
760 = -- Here we do the PushC reduction rule as described in the FC paper
761 case exprIsConApp_maybe expr of {
763 Just (dc, dc_args) ->
765 -- The transformation applies iff we have
766 -- (C e1 ... en) `cast` co
767 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
768 -- That is, with a T at the top of both sides
769 -- The left-hand one must be a T, because exprIsConApp returned True
770 -- but the right-hand one might not be. (Though it usually will.)
772 let (from_ty, to_ty) = coercionKind co
773 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
774 -- The inner one must be a TyConApp
776 case splitTyConApp_maybe to_ty of {
778 Just (to_tc, to_tc_arg_tys)
779 | from_tc /= to_tc -> Nothing
780 -- These two Nothing cases are possible; we might see
781 -- (C x y) `cast` (g :: T a ~ S [a]),
782 -- where S is a type function. In fact, exprIsConApp
783 -- will probably not be called in such circumstances,
784 -- but there't nothing wrong with it
788 tc_arity = tyConArity from_tc
790 (univ_args, rest1) = splitAt tc_arity dc_args
791 (ex_args, rest2) = splitAt n_ex_tvs rest1
792 (co_args, val_args) = splitAt n_cos rest2
794 arg_tys = dataConRepArgTys dc
795 dc_univ_tyvars = dataConUnivTyVars dc
796 dc_ex_tyvars = dataConExTyVars dc
797 dc_eq_spec = dataConEqSpec dc
798 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
799 n_ex_tvs = length dc_ex_tyvars
800 n_cos = length dc_eq_spec
802 -- Make the "theta" from Fig 3 of the paper
803 gammas = decomposeCo tc_arity co
804 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
805 theta = zipOpenTvSubst dc_tyvars new_tys
807 -- First we cast the existential coercion arguments
808 cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
810 `mkTransCoercion` (substTy theta ty)
811 new_co_args = zipWith cast_co dc_eq_spec co_args
813 -- ...and now value arguments
814 new_val_args = zipWith cast_arg arg_tys val_args
815 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
818 ASSERT( length univ_args == tc_arity )
819 ASSERT( from_tc == dataConTyCon dc )
820 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
821 ASSERT( all isTypeArg (univ_args ++ ex_args) )
822 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 )
824 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
828 -- We do not want to tell the world that we have a
829 -- Cons, to *stop* Case of Known Cons, which removes
831 exprIsConApp_maybe (Note (TickBox {}) expr)
833 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
837 exprIsConApp_maybe (Note _ expr)
838 = exprIsConApp_maybe expr
839 -- We ignore InlineMe notes in case we have
840 -- x = __inline_me__ (a,b)
841 -- All part of making sure that INLINE pragmas never hurt
842 -- Marcin tripped on this one when making dictionaries more inlinable
844 -- In fact, we ignore all notes. For example,
845 -- case _scc_ "foo" (C a b) of
847 -- should be optimised away, but it will be only if we look
848 -- through the SCC note.
850 exprIsConApp_maybe expr = analyse (collectArgs expr)
852 analyse (Var fun, args)
853 | Just con <- isDataConWorkId_maybe fun,
854 args `lengthAtLeast` dataConRepArity con
855 -- Might be > because the arity excludes type args
858 -- Look through unfoldings, but only cheap ones, because
859 -- we are effectively duplicating the unfolding
860 analyse (Var fun, [])
861 | let unf = idUnfolding fun,
863 = exprIsConApp_maybe (unfoldingTemplate unf)
865 analyse other = Nothing
870 %************************************************************************
872 \subsection{Eta reduction and expansion}
874 %************************************************************************
877 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
878 {- The Arity returned is the number of value args the
879 thing can be applied to without doing much work
881 exprEtaExpandArity is used when eta expanding
884 It returns 1 (or more) to:
885 case x of p -> \s -> ...
886 because for I/O ish things we really want to get that \s to the top.
887 We are prepared to evaluate x each time round the loop in order to get that
889 It's all a bit more subtle than it looks:
893 Consider one-shot lambdas
894 let x = expensive in \y z -> E
895 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
896 Hence the ArityType returned by arityType
898 2. The state-transformer hack
900 The one-shot lambda special cause is particularly important/useful for
901 IO state transformers, where we often get
902 let x = E in \ s -> ...
904 and the \s is a real-world state token abstraction. Such abstractions
905 are almost invariably 1-shot, so we want to pull the \s out, past the
906 let x=E, even if E is expensive. So we treat state-token lambdas as
907 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
909 3. Dealing with bottom
912 f = \x -> error "foo"
913 Here, arity 1 is fine. But if it is
917 then we want to get arity 2. Tecnically, this isn't quite right, because
919 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
920 do so; it improves some programs significantly, and increasing convergence
921 isn't a bad thing. Hence the ABot/ATop in ArityType.
923 Actually, the situation is worse. Consider
927 Can we eta-expand here? At first the answer looks like "yes of course", but
930 This should diverge! But if we eta-expand, it won't. Again, we ignore this
931 "problem", because being scrupulous would lose an important transformation for
937 Non-recursive newtypes are transparent, and should not get in the way.
938 We do (currently) eta-expand recursive newtypes too. So if we have, say
940 newtype T = MkT ([T] -> Int)
944 where f has arity 1. Then: etaExpandArity e = 1;
945 that is, etaExpandArity looks through the coerce.
947 When we eta-expand e to arity 1: eta_expand 1 e T
948 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
950 HOWEVER, note that if you use coerce bogusly you can ge
952 And since negate has arity 2, you might try to eta expand. But you can't
953 decopose Int to a function type. Hence the final case in eta_expand.
957 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
959 -- A limited sort of function type
960 data ArityType = AFun Bool ArityType -- True <=> one-shot
961 | ATop -- Know nothing
964 arityDepth :: ArityType -> Arity
965 arityDepth (AFun _ ty) = 1 + arityDepth ty
968 andArityType ABot at2 = at2
969 andArityType ATop at2 = ATop
970 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
971 andArityType at1 at2 = andArityType at2 at1
973 arityType :: DynFlags -> CoreExpr -> ArityType
974 -- (go1 e) = [b1,..,bn]
975 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
976 -- where bi is True <=> the lambda is one-shot
978 arityType dflags (Note n e) = arityType dflags e
979 -- Not needed any more: etaExpand is cleverer
980 -- | ok_note n = arityType dflags e
981 -- | otherwise = ATop
983 arityType dflags (Cast e co) = arityType dflags e
985 arityType dflags (Var v)
986 = mk (idArity v) (arg_tys (idType v))
988 mk :: Arity -> [Type] -> ArityType
989 -- The argument types are only to steer the "state hack"
990 -- Consider case x of
992 -- False -> \(s:RealWorld) -> e
993 -- where foo has arity 1. Then we want the state hack to
994 -- apply to foo too, so we can eta expand the case.
995 mk 0 tys | isBottomingId v = ABot
996 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
998 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
999 mk n [] = AFun False (mk (n-1) [])
1001 arg_tys :: Type -> [Type] -- Ignore for-alls
1003 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1004 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1007 -- Lambdas; increase arity
1008 arityType dflags (Lam x e)
1009 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1010 | otherwise = arityType dflags e
1012 -- Applications; decrease arity
1013 arityType dflags (App f (Type _)) = arityType dflags f
1014 arityType dflags (App f a) = case arityType dflags f of
1015 AFun one_shot xs | exprIsCheap a -> xs
1018 -- Case/Let; keep arity if either the expression is cheap
1019 -- or it's a 1-shot lambda
1020 -- The former is not really right for Haskell
1021 -- f x = case x of { (a,b) -> \y. e }
1023 -- f x y = case x of { (a,b) -> e }
1024 -- The difference is observable using 'seq'
1025 arityType dflags (Case scrut _ _ alts)
1026 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1027 xs | exprIsCheap scrut -> xs
1028 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1031 arityType dflags (Let b e)
1032 = case arityType dflags e of
1033 xs | cheap_bind b -> xs
1034 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1037 cheap_bind (NonRec b e) = is_cheap (b,e)
1038 cheap_bind (Rec prs) = all is_cheap prs
1039 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1041 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1042 -- dictionary bindings. This improves arities. Thereby, it also
1043 -- means that full laziness is less prone to floating out the
1044 -- application of a function to its dictionary arguments, which
1045 -- can thereby lose opportunities for fusion. Example:
1046 -- foo :: Ord a => a -> ...
1047 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1048 -- -- So foo has arity 1
1050 -- f = \x. foo dInt $ bar x
1052 -- The (foo DInt) is floated out, and makes ineffective a RULE
1053 -- foo (bar x) = ...
1055 -- One could go further and make exprIsCheap reply True to any
1056 -- dictionary-typed expression, but that's more work.
1058 arityType dflags other = ATop
1060 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1061 ok_note InlineMe = False
1062 ok_note other = True
1063 -- Notice that we do not look through __inline_me__
1064 -- This may seem surprising, but consider
1065 -- f = _inline_me (\x -> e)
1066 -- We DO NOT want to eta expand this to
1067 -- f = \x -> (_inline_me (\x -> e)) x
1068 -- because the _inline_me gets dropped now it is applied,
1077 etaExpand :: Arity -- Result should have this number of value args
1079 -> CoreExpr -> Type -- Expression and its type
1081 -- (etaExpand n us e ty) returns an expression with
1082 -- the same meaning as 'e', but with arity 'n'.
1084 -- Given e' = etaExpand n us e ty
1086 -- ty = exprType e = exprType e'
1088 -- Note that SCCs are not treated specially. If we have
1089 -- etaExpand 2 (\x -> scc "foo" e)
1090 -- = (\xy -> (scc "foo" e) y)
1091 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1093 etaExpand n us expr ty
1094 | manifestArity expr >= n = expr -- The no-op case
1096 = eta_expand n us expr ty
1099 -- manifestArity sees how many leading value lambdas there are
1100 manifestArity :: CoreExpr -> Arity
1101 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1102 | otherwise = manifestArity e
1103 manifestArity (Note _ e) = manifestArity e
1104 manifestArity (Cast e _) = manifestArity e
1107 -- etaExpand deals with for-alls. For example:
1109 -- where E :: forall a. a -> a
1111 -- (/\b. \y::a -> E b y)
1113 -- It deals with coerces too, though they are now rare
1114 -- so perhaps the extra code isn't worth it
1116 eta_expand n us expr ty
1118 -- The ILX code generator requires eta expansion for type arguments
1119 -- too, but alas the 'n' doesn't tell us how many of them there
1120 -- may be. So we eagerly eta expand any big lambdas, and just
1121 -- cross our fingers about possible loss of sharing in the ILX case.
1122 -- The Right Thing is probably to make 'arity' include
1123 -- type variables throughout the compiler. (ToDo.)
1125 -- Saturated, so nothing to do
1128 -- Short cut for the case where there already
1129 -- is a lambda; no point in gratuitously adding more
1130 eta_expand n us (Lam v body) ty
1132 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1135 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1137 -- We used to have a special case that stepped inside Coerces here,
1138 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1139 -- = Note note (eta_expand n us e ty)
1140 -- BUT this led to an infinite loop
1141 -- Example: newtype T = MkT (Int -> Int)
1142 -- eta_expand 1 (coerce (Int->Int) e)
1143 -- --> coerce (Int->Int) (eta_expand 1 T e)
1145 -- --> coerce (Int->Int) (coerce T
1146 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1147 -- by the splitNewType_maybe case below
1150 eta_expand n us expr ty
1151 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1152 case splitForAllTy_maybe ty of {
1155 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1157 lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
1158 -- Using tv as a base retains its tyvar/covar-ness
1162 case splitFunTy_maybe ty of {
1163 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1165 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1171 -- newtype T = MkT ([T] -> Int)
1172 -- Consider eta-expanding this
1175 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1177 case splitNewTypeRepCo_maybe ty of {
1178 Just(ty1,co) -> mkCoerce (mkSymCoercion co)
1179 (eta_expand n us (mkCoerce co expr) ty1) ;
1182 -- We have an expression of arity > 0, but its type isn't a function
1183 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1184 -- Essentially the programmer is playing fast and loose with types
1185 -- (Happy does this a lot). So we simply decline to eta-expand.
1190 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1191 It tells how many things the expression can be applied to before doing
1192 any work. It doesn't look inside cases, lets, etc. The idea is that
1193 exprEtaExpandArity will do the hard work, leaving something that's easy
1194 for exprArity to grapple with. In particular, Simplify uses exprArity to
1195 compute the ArityInfo for the Id.
1197 Originally I thought that it was enough just to look for top-level lambdas, but
1198 it isn't. I've seen this
1200 foo = PrelBase.timesInt
1202 We want foo to get arity 2 even though the eta-expander will leave it
1203 unchanged, in the expectation that it'll be inlined. But occasionally it
1204 isn't, because foo is blacklisted (used in a rule).
1206 Similarly, see the ok_note check in exprEtaExpandArity. So
1207 f = __inline_me (\x -> e)
1208 won't be eta-expanded.
1210 And in any case it seems more robust to have exprArity be a bit more intelligent.
1211 But note that (\x y z -> f x y z)
1212 should have arity 3, regardless of f's arity.
1215 exprArity :: CoreExpr -> Arity
1218 go (Var v) = idArity v
1219 go (Lam x e) | isId x = go e + 1
1221 go (Note n e) = go e
1222 go (Cast e _) = go e
1223 go (App e (Type t)) = go e
1224 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1225 -- NB: exprIsCheap a!
1226 -- f (fac x) does not have arity 2,
1227 -- even if f has arity 3!
1228 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1229 -- unknown, hence arity 0
1233 %************************************************************************
1235 \subsection{Equality}
1237 %************************************************************************
1239 @cheapEqExpr@ is a cheap equality test which bales out fast!
1240 True => definitely equal
1241 False => may or may not be equal
1244 cheapEqExpr :: Expr b -> Expr b -> Bool
1246 cheapEqExpr (Var v1) (Var v2) = v1==v2
1247 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1248 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1250 cheapEqExpr (App f1 a1) (App f2 a2)
1251 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1253 cheapEqExpr _ _ = False
1255 exprIsBig :: Expr b -> Bool
1256 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1257 exprIsBig (Lit _) = False
1258 exprIsBig (Var v) = False
1259 exprIsBig (Type t) = False
1260 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1261 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1262 exprIsBig other = True
1267 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1268 -- Used in rule matching, so does *not* look through
1269 -- newtypes, predicate types; hence tcEqExpr
1271 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1273 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1275 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1276 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1277 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1278 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1279 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1280 tcEqExprX env (Let (NonRec v1 r1) e1)
1281 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1282 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1283 tcEqExprX env (Let (Rec ps1) e1)
1284 (Let (Rec ps2) e2) = equalLength ps1 ps2
1285 && and (zipWith eq_rhs ps1 ps2)
1286 && tcEqExprX env' e1 e2
1288 env' = foldl2 rn_bndr2 env ps2 ps2
1289 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1290 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1291 tcEqExprX env (Case e1 v1 t1 a1)
1292 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1293 && tcEqTypeX env t1 t2
1294 && equalLength a1 a2
1295 && and (zipWith (eq_alt env') a1 a2)
1297 env' = rnBndr2 env v1 v2
1299 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1300 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1301 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1302 tcEqExprX env e1 e2 = False
1304 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1306 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1307 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1308 eq_note env other1 other2 = False
1312 %************************************************************************
1314 \subsection{The size of an expression}
1316 %************************************************************************
1319 coreBindsSize :: [CoreBind] -> Int
1320 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1322 exprSize :: CoreExpr -> Int
1323 -- A measure of the size of the expressions
1324 -- It also forces the expression pretty drastically as a side effect
1325 exprSize (Var v) = v `seq` 1
1326 exprSize (Lit lit) = lit `seq` 1
1327 exprSize (App f a) = exprSize f + exprSize a
1328 exprSize (Lam b e) = varSize b + exprSize e
1329 exprSize (Let b e) = bindSize b + exprSize e
1330 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1331 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1332 exprSize (Note n e) = noteSize n + exprSize e
1333 exprSize (Type t) = seqType t `seq` 1
1335 noteSize (SCC cc) = cc `seq` 1
1336 noteSize InlineMe = 1
1337 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1339 varSize :: Var -> Int
1340 varSize b | isTyVar b = 1
1341 | otherwise = seqType (idType b) `seq`
1342 megaSeqIdInfo (idInfo b) `seq`
1345 varsSize = foldr ((+) . varSize) 0
1347 bindSize (NonRec b e) = varSize b + exprSize e
1348 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1350 pairSize (b,e) = varSize b + exprSize e
1352 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1356 %************************************************************************
1358 \subsection{Hashing}
1360 %************************************************************************
1363 hashExpr :: CoreExpr -> Int
1364 -- Two expressions that hash to the same Int may be equal (but may not be)
1365 -- Two expressions that hash to the different Ints are definitely unequal
1367 -- But "unequal" here means "not identical"; two alpha-equivalent
1368 -- expressions may hash to the different Ints
1370 -- The emphasis is on a crude, fast hash, rather than on high precision
1372 -- We must be careful that \x.x and \y.y map to the same hash code,
1373 -- (at least if we want the above invariant to be true)
1375 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1376 -- UniqFM doesn't like negative Ints
1378 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1380 hash_expr :: HashEnv -> CoreExpr -> Word32
1381 -- Word32, because we're expecting overflows here, and overflowing
1382 -- signed types just isn't cool. In C it's even undefined.
1383 hash_expr env (Note _ e) = hash_expr env e
1384 hash_expr env (Cast e co) = hash_expr env e
1385 hash_expr env (Var v) = hashVar env v
1386 hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1387 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1388 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1389 hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
1390 hash_expr env (Case e _ _ _) = hash_expr env e
1391 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1392 hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1
1393 -- Shouldn't happen. Better to use WARN than trace, because trace
1394 -- prevents the CPR optimisation kicking in for hash_expr.
1396 fast_hash_expr env (Var v) = hashVar env v
1397 fast_hash_expr env (Type t) = fast_hash_type env t
1398 fast_hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1399 fast_hash_expr env (Cast e co) = fast_hash_expr env e
1400 fast_hash_expr env (Note n e) = fast_hash_expr env e
1401 fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1402 fast_hash_expr env other = 1
1404 fast_hash_type :: HashEnv -> Type -> Word32
1405 fast_hash_type env ty
1406 | Just tv <- getTyVar_maybe ty = hashVar env tv
1407 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1408 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1411 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1412 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1414 hashVar :: HashEnv -> Var -> Word32
1416 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1419 %************************************************************************
1421 \subsection{Determining non-updatable right-hand-sides}
1423 %************************************************************************
1425 Top-level constructor applications can usually be allocated
1426 statically, but they can't if the constructor, or any of the
1427 arguments, come from another DLL (because we can't refer to static
1428 labels in other DLLs).
1430 If this happens we simply make the RHS into an updatable thunk,
1431 and 'exectute' it rather than allocating it statically.
1434 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1435 -- This function is called only on *top-level* right-hand sides
1436 -- Returns True if the RHS can be allocated statically, with
1437 -- no thunks involved at all.
1439 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1440 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1441 -- update flag on it.
1443 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1444 -- (a) a value lambda
1445 -- (b) a saturated constructor application with static args
1447 -- BUT watch out for
1448 -- (i) Any cross-DLL references kill static-ness completely
1449 -- because they must be 'executed' not statically allocated
1450 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1451 -- this is not necessary)
1453 -- (ii) We treat partial applications as redexes, because in fact we
1454 -- make a thunk for them that runs and builds a PAP
1455 -- at run-time. The only appliations that are treated as
1456 -- static are *saturated* applications of constructors.
1458 -- We used to try to be clever with nested structures like this:
1459 -- ys = (:) w ((:) w [])
1460 -- on the grounds that CorePrep will flatten ANF-ise it later.
1461 -- But supporting this special case made the function much more
1462 -- complicated, because the special case only applies if there are no
1463 -- enclosing type lambdas:
1464 -- ys = /\ a -> Foo (Baz ([] a))
1465 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1467 -- But in fact, even without -O, nested structures at top level are
1468 -- flattened by the simplifier, so we don't need to be super-clever here.
1472 -- f = \x::Int. x+7 TRUE
1473 -- p = (True,False) TRUE
1475 -- d = (fst p, False) FALSE because there's a redex inside
1476 -- (this particular one doesn't happen but...)
1478 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1479 -- n = /\a. Nil a TRUE
1481 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1484 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1485 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1487 -- b) (C x xs), where C is a contructors is updatable if the application is
1490 -- c) don't look through unfolding of f in (f x).
1492 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1493 -- them as making the RHS re-entrant (non-updatable).
1495 rhsIsStatic this_pkg rhs = is_static False rhs
1497 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1500 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1502 is_static in_arg (Note (SCC _) e) = False
1503 is_static in_arg (Note _ e) = is_static in_arg e
1504 is_static in_arg (Cast e co) = is_static in_arg e
1506 is_static in_arg (Lit lit)
1508 MachLabel _ _ -> False
1510 -- A MachLabel (foreign import "&foo") in an argument
1511 -- prevents a constructor application from being static. The
1512 -- reason is that it might give rise to unresolvable symbols
1513 -- in the object file: under Linux, references to "weak"
1514 -- symbols from the data segment give rise to "unresolvable
1515 -- relocation" errors at link time This might be due to a bug
1516 -- in the linker, but we'll work around it here anyway.
1519 is_static in_arg other_expr = go other_expr 0
1521 go (Var f) n_val_args
1522 #if mingw32_TARGET_OS
1523 | not (isDllName this_pkg (idName f))
1525 = saturated_data_con f n_val_args
1526 || (in_arg && n_val_args == 0)
1527 -- A naked un-applied variable is *not* deemed a static RHS
1529 -- Reason: better to update so that the indirection gets shorted
1530 -- out, and the true value will be seen
1531 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1532 -- are always updatable. If you do so, make sure that non-updatable
1533 -- ones have enough space for their static link field!
1535 go (App f a) n_val_args
1536 | isTypeArg a = go f n_val_args
1537 | not in_arg && is_static True a = go f (n_val_args + 1)
1538 -- The (not in_arg) checks that we aren't in a constructor argument;
1539 -- if we are, we don't allow (value) applications of any sort
1541 -- NB. In case you wonder, args are sometimes not atomic. eg.
1542 -- x = D# (1.0## /## 2.0##)
1543 -- can't float because /## can fail.
1545 go (Note (SCC _) f) n_val_args = False
1546 go (Note _ f) n_val_args = go f n_val_args
1547 go (Cast e co) n_val_args = go e n_val_args
1549 go other n_val_args = False
1551 saturated_data_con f n_val_args
1552 = case isDataConWorkId_maybe f of
1553 Just dc -> n_val_args == dataConRepArity dc