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, mkCoerceI,
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 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
199 mkCoerceI (ACo co) e = mkCoerce co e
201 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
202 mkCoerce co (Cast expr co2)
203 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
204 (_from_ty2, to_ty2) = coercionKind co2} in
205 from_ty `coreEqType` to_ty2 )
206 mkCoerce (mkTransCoercion co2 co) expr
209 = let (from_ty, to_ty) = coercionKind co in
210 -- if to_ty `coreEqType` from_ty
213 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
218 mkSCC :: CostCentre -> Expr b -> Expr b
219 -- Note: Nested SCC's *are* preserved for the benefit of
220 -- cost centre stack profiling
221 mkSCC cc (Lit lit) = Lit lit
222 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
223 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
224 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
225 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
226 mkSCC cc expr = Note (SCC cc) expr
230 %************************************************************************
232 \subsection{Other expression construction}
234 %************************************************************************
237 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
238 -- (bindNonRec x r b) produces either
241 -- case r of x { _DEFAULT_ -> b }
243 -- depending on whether x is unlifted or not
244 -- It's used by the desugarer to avoid building bindings
245 -- that give Core Lint a heart attack. Actually the simplifier
246 -- deals with them perfectly well.
248 bindNonRec bndr rhs body
249 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
250 | otherwise = Let (NonRec bndr rhs) body
252 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
253 -- Make a case expression instead of a let
254 -- These can arise either from the desugarer,
255 -- or from beta reductions: (\x.e) (x +# y)
259 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
260 -- This guy constructs the value that the scrutinee must have
261 -- when you are in one particular branch of a case
262 mkAltExpr (DataAlt con) args inst_tys
263 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
264 mkAltExpr (LitAlt lit) [] []
266 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
267 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
269 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
270 mkIfThenElse guard then_expr else_expr
271 -- Not going to be refining, so okay to take the type of the "then" clause
272 = Case guard (mkWildId boolTy) (exprType then_expr)
273 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
274 (DataAlt trueDataCon, [], then_expr) ]
278 %************************************************************************
280 \subsection{Taking expressions apart}
282 %************************************************************************
284 The default alternative must be first, if it exists at all.
285 This makes it easy to find, though it makes matching marginally harder.
288 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
289 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
290 findDefault alts = (alts, Nothing)
292 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
295 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
296 other -> go alts panic_deflt
298 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
301 go (alt@(con1,_,_) : alts) deflt
302 = case con `cmpAltCon` con1 of
303 LT -> deflt -- Missed it already; the alts are in increasing order
305 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
307 isDefaultAlt :: CoreAlt -> Bool
308 isDefaultAlt (DEFAULT, _, _) = True
309 isDefaultAlt other = False
311 ---------------------------------
312 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
313 -- Merge preserving order; alternatives in the first arg
314 -- shadow ones in the second
315 mergeAlts [] as2 = as2
316 mergeAlts as1 [] = as1
317 mergeAlts (a1:as1) (a2:as2)
318 = case a1 `cmpAlt` a2 of
319 LT -> a1 : mergeAlts as1 (a2:as2)
320 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
321 GT -> a2 : mergeAlts (a1:as1) as2
324 ---------------------------------
325 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
326 -- Given case (C a b x y) of
328 -- we want to drop the leading type argument of the scrutinee
329 -- leaving the arguments to match agains the pattern
331 trimConArgs DEFAULT args = ASSERT( null args ) []
332 trimConArgs (LitAlt lit) args = ASSERT( null args ) []
333 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
337 %************************************************************************
339 \subsection{Figuring out things about expressions}
341 %************************************************************************
343 @exprIsTrivial@ is true of expressions we are unconditionally happy to
344 duplicate; simple variables and constants, and type
345 applications. Note that primop Ids aren't considered
348 @exprIsBottom@ is true of expressions that are guaranteed to diverge
351 There used to be a gruesome test for (hasNoBinding v) in the
353 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
354 The idea here is that a constructor worker, like $wJust, is
355 really short for (\x -> $wJust x), becuase $wJust has no binding.
356 So it should be treated like a lambda. Ditto unsaturated primops.
357 But now constructor workers are not "have-no-binding" Ids. And
358 completely un-applied primops and foreign-call Ids are sufficiently
359 rare that I plan to allow them to be duplicated and put up with
362 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
363 a) it really generates code, (and a heap object when it's
364 a function arg) to capture the cost centre
365 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
368 exprIsTrivial (Var v) = True -- See notes above
369 exprIsTrivial (Type _) = True
370 exprIsTrivial (Lit lit) = litIsTrivial lit
371 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
372 exprIsTrivial (Note (SCC _) e) = False -- See notes above
373 exprIsTrivial (Note _ e) = exprIsTrivial e
374 exprIsTrivial (Cast e co) = exprIsTrivial e
375 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
376 exprIsTrivial other = False
380 @exprIsDupable@ is true of expressions that can be duplicated at a modest
381 cost in code size. This will only happen in different case
382 branches, so there's no issue about duplicating work.
384 That is, exprIsDupable returns True of (f x) even if
385 f is very very expensive to call.
387 Its only purpose is to avoid fruitless let-binding
388 and then inlining of case join points
392 exprIsDupable (Type _) = True
393 exprIsDupable (Var v) = True
394 exprIsDupable (Lit lit) = litIsDupable lit
395 exprIsDupable (Note InlineMe e) = True
396 exprIsDupable (Note _ e) = exprIsDupable e
397 exprIsDupable (Cast e co) = exprIsDupable e
401 go (Var v) n_args = True
402 go (App f a) n_args = n_args < dupAppSize
405 go other n_args = False
408 dupAppSize = 4 -- Size of application we are prepared to duplicate
411 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
412 it is obviously in weak head normal form, or is cheap to get to WHNF.
413 [Note that that's not the same as exprIsDupable; an expression might be
414 big, and hence not dupable, but still cheap.]
416 By ``cheap'' we mean a computation we're willing to:
417 push inside a lambda, or
418 inline at more than one place
419 That might mean it gets evaluated more than once, instead of being
420 shared. The main examples of things which aren't WHNF but are
425 (where e, and all the ei are cheap)
428 (where e and b are cheap)
431 (where op is a cheap primitive operator)
434 (because we are happy to substitute it inside a lambda)
436 Notice that a variable is considered 'cheap': we can push it inside a lambda,
437 because sharing will make sure it is only evaluated once.
440 exprIsCheap :: CoreExpr -> Bool
441 exprIsCheap (Lit lit) = True
442 exprIsCheap (Type _) = True
443 exprIsCheap (Var _) = True
444 exprIsCheap (Note InlineMe e) = True
445 exprIsCheap (Note _ e) = exprIsCheap e
446 exprIsCheap (Cast e co) = exprIsCheap e
447 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
448 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
449 and [exprIsCheap rhs | (_,_,rhs) <- alts]
450 -- Experimentally, treat (case x of ...) as cheap
451 -- (and case __coerce x etc.)
452 -- This improves arities of overloaded functions where
453 -- there is only dictionary selection (no construction) involved
454 exprIsCheap (Let (NonRec x _) e)
455 | isUnLiftedType (idType x) = exprIsCheap e
457 -- strict lets always have cheap right hand sides,
458 -- and do no allocation.
460 exprIsCheap other_expr -- Applications and variables
463 -- Accumulate value arguments, then decide
464 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
465 | otherwise = go f val_args
467 go (Var f) [] = True -- Just a type application of a variable
468 -- (f t1 t2 t3) counts as WHNF
470 = case globalIdDetails f of
471 RecordSelId {} -> go_sel args
472 ClassOpId _ -> go_sel args
473 PrimOpId op -> go_primop op args
475 DataConWorkId _ -> go_pap args
476 other | length args < idArity f -> go_pap args
478 other -> isBottomingId f
479 -- Application of a function which
480 -- always gives bottom; we treat this as cheap
481 -- because it certainly doesn't need to be shared!
483 go other args = False
486 go_pap args = all exprIsTrivial args
487 -- For constructor applications and primops, check that all
488 -- the args are trivial. We don't want to treat as cheap, say,
490 -- We'll put up with one constructor application, but not dozens
493 go_primop op args = primOpIsCheap op && all exprIsCheap args
494 -- In principle we should worry about primops
495 -- that return a type variable, since the result
496 -- might be applied to something, but I'm not going
497 -- to bother to check the number of args
500 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
501 go_sel other = False -- look cheap, so we will substitute it inside a
502 -- lambda. Particularly for dictionary field selection.
503 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
504 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
507 exprOkForSpeculation returns True of an expression that it is
509 * safe to evaluate even if normal order eval might not
510 evaluate the expression at all, or
512 * safe *not* to evaluate even if normal order would do so
516 the expression guarantees to terminate,
518 without raising an exception,
519 without causing a side effect (e.g. writing a mutable variable)
521 NB: if exprIsHNF e, then exprOkForSpecuation e
524 let x = case y# +# 1# of { r# -> I# r# }
527 case y# +# 1# of { r# ->
532 We can only do this if the (y+1) is ok for speculation: it has no
533 side effects, and can't diverge or raise an exception.
536 exprOkForSpeculation :: CoreExpr -> Bool
537 exprOkForSpeculation (Lit _) = True
538 exprOkForSpeculation (Type _) = True
539 -- Tick boxes are *not* suitable for speculation
540 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
541 && not (isTickBoxOp v)
542 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
543 exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
544 exprOkForSpeculation other_expr
545 = case collectArgs other_expr of
546 (Var f, args) -> spec_ok (globalIdDetails f) args
550 spec_ok (DataConWorkId _) args
551 = True -- The strictness of the constructor has already
552 -- been expressed by its "wrapper", so we don't need
553 -- to take the arguments into account
555 spec_ok (PrimOpId op) args
556 | isDivOp op, -- Special case for dividing operations that fail
557 [arg1, Lit lit] <- args -- only if the divisor is zero
558 = not (isZeroLit lit) && exprOkForSpeculation arg1
559 -- Often there is a literal divisor, and this
560 -- can get rid of a thunk in an inner looop
563 = primOpOkForSpeculation op &&
564 all exprOkForSpeculation args
565 -- A bit conservative: we don't really need
566 -- to care about lazy arguments, but this is easy
568 spec_ok other args = False
570 isDivOp :: PrimOp -> Bool
571 -- True of dyadic operators that can fail
572 -- only if the second arg is zero
573 -- This function probably belongs in PrimOp, or even in
574 -- an automagically generated file.. but it's such a
575 -- special case I thought I'd leave it here for now.
576 isDivOp IntQuotOp = True
577 isDivOp IntRemOp = True
578 isDivOp WordQuotOp = True
579 isDivOp WordRemOp = True
580 isDivOp IntegerQuotRemOp = True
581 isDivOp IntegerDivModOp = True
582 isDivOp FloatDivOp = True
583 isDivOp DoubleDivOp = True
584 isDivOp other = False
589 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
590 exprIsBottom e = go 0 e
592 -- n is the number of args
593 go n (Note _ e) = go n e
594 go n (Cast e co) = go n e
595 go n (Let _ e) = go n e
596 go n (Case e _ _ _) = go 0 e -- Just check the scrut
597 go n (App e _) = go (n+1) e
598 go n (Var v) = idAppIsBottom v n
600 go n (Lam _ _) = False
601 go n (Type _) = False
603 idAppIsBottom :: Id -> Int -> Bool
604 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
607 @exprIsHNF@ returns true for expressions that are certainly *already*
608 evaluated to *head* normal form. This is used to decide whether it's ok
611 case x of _ -> e ===> e
613 and to decide whether it's safe to discard a `seq`
615 So, it does *not* treat variables as evaluated, unless they say they are.
617 But it *does* treat partial applications and constructor applications
618 as values, even if their arguments are non-trivial, provided the argument
620 e.g. (:) (f x) (map f xs) is a value
621 map (...redex...) is a value
622 Because `seq` on such things completes immediately
624 For unlifted argument types, we have to be careful:
626 Suppose (f x) diverges; then C (f x) is not a value. However this can't
627 happen: see CoreSyn Note [CoreSyn let/app invariant]. Args of unboxed
628 type must be ok-for-speculation (or trivial).
631 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
632 exprIsHNF (Var v) -- NB: There are no value args at this point
633 = isDataConWorkId v -- Catches nullary constructors,
634 -- so that [] and () are values, for example
635 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
636 || isEvaldUnfolding (idUnfolding v)
637 -- Check the thing's unfolding; it might be bound to a value
638 -- A worry: what if an Id's unfolding is just itself:
639 -- then we could get an infinite loop...
641 exprIsHNF (Lit l) = True
642 exprIsHNF (Type ty) = True -- Types are honorary Values;
643 -- we don't mind copying them
644 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
645 exprIsHNF (Note _ e) = exprIsHNF e
646 exprIsHNF (Cast e co) = exprIsHNF e
647 exprIsHNF (App e (Type _)) = exprIsHNF e
648 exprIsHNF (App e a) = app_is_value e [a]
649 exprIsHNF other = False
651 -- There is at least one value argument
652 app_is_value (Var fun) args
653 = idArity fun > valArgCount args -- Under-applied function
654 || isDataConWorkId fun -- or data constructor
655 app_is_value (Note n f) as = app_is_value f as
656 app_is_value (Cast f _) as = app_is_value f as
657 app_is_value (App f a) as = app_is_value f (a:as)
658 app_is_value other as = False
662 -- These InstPat functions go here to avoid circularity between DataCon and Id
663 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
664 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
665 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
667 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
668 -- Remember to include the existential dictionaries
670 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
671 -> [FastString] -- A long enough list of FSs to use for names
672 -> [Unique] -- An equally long list of uniques, at least one for each binder
674 -> [Type] -- Types to instantiate the universally quantified tyvars
675 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
676 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
677 -- (ex_tvs, co_tvs, arg_ids),
679 -- ex_tvs are intended to be used as binders for existential type args
681 -- co_tvs are intended to be used as binders for coercion args and the kinds
682 -- of these vars have been instantiated by the inst_tys and the ex_tys
683 -- The co_tvs include both GADT equalities (dcEqSpec) and
684 -- programmer-specified equalities (dcEqTheta)
686 -- arg_ids are indended to be used as binders for value arguments,
687 -- and their types have been instantiated with inst_tys and ex_tys
688 -- The arg_ids include both dicts (dcDictTheta) and
689 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
692 -- The following constructor T1
695 -- T1 :: forall b. Int -> b -> T(a,b)
698 -- has representation type
699 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
702 -- dataConInstPat fss us T1 (a1',b') will return
704 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
706 -- where the double-primed variables are created with the FastStrings and
707 -- Uniques given as fss and us
708 dataConInstPat arg_fun fss uniqs con inst_tys
709 = (ex_bndrs, co_bndrs, arg_ids)
711 univ_tvs = dataConUnivTyVars con
712 ex_tvs = dataConExTyVars con
713 arg_tys = arg_fun con
714 eq_spec = dataConEqSpec con
715 eq_theta = dataConEqTheta con
716 eq_preds = eqSpecPreds eq_spec ++ eq_theta
719 n_co = length eq_preds
721 -- split the Uniques and FastStrings
722 (ex_uniqs, uniqs') = splitAt n_ex uniqs
723 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
725 (ex_fss, fss') = splitAt n_ex fss
726 (co_fss, id_fss) = splitAt n_co fss'
728 -- Make existential type variables
729 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
730 mk_ex_var uniq fs var = mkTyVar new_name kind
732 new_name = mkSysTvName uniq fs
735 -- Make the instantiating substitution
736 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
738 -- Make new coercion vars, instantiating kind
739 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
740 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
742 new_name = mkSysTvName uniq fs
743 co_kind = substTy subst (mkPredTy eq_pred)
745 -- make value vars, instantiating types
746 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
747 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
749 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
750 -- Returns (Just (dc, [x1..xn])) if the argument expression is
751 -- a constructor application of the form (dc x1 .. xn)
752 exprIsConApp_maybe (Cast expr co)
753 = -- Here we do the PushC reduction rule as described in the FC paper
754 case exprIsConApp_maybe expr of {
756 Just (dc, dc_args) ->
758 -- The transformation applies iff we have
759 -- (C e1 ... en) `cast` co
760 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
761 -- That is, with a T at the top of both sides
762 -- The left-hand one must be a T, because exprIsConApp returned True
763 -- but the right-hand one might not be. (Though it usually will.)
765 let (from_ty, to_ty) = coercionKind co
766 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
767 -- The inner one must be a TyConApp
769 case splitTyConApp_maybe to_ty of {
771 Just (to_tc, to_tc_arg_tys)
772 | from_tc /= to_tc -> Nothing
773 -- These two Nothing cases are possible; we might see
774 -- (C x y) `cast` (g :: T a ~ S [a]),
775 -- where S is a type function. In fact, exprIsConApp
776 -- will probably not be called in such circumstances,
777 -- but there't nothing wrong with it
781 tc_arity = tyConArity from_tc
783 (univ_args, rest1) = splitAt tc_arity dc_args
784 (ex_args, rest2) = splitAt n_ex_tvs rest1
785 (co_args, val_args) = splitAt n_cos rest2
787 arg_tys = dataConRepArgTys dc
788 dc_univ_tyvars = dataConUnivTyVars dc
789 dc_ex_tyvars = dataConExTyVars dc
790 dc_eq_spec = dataConEqSpec dc
791 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
792 n_ex_tvs = length dc_ex_tyvars
793 n_cos = length dc_eq_spec
795 -- Make the "theta" from Fig 3 of the paper
796 gammas = decomposeCo tc_arity co
797 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
798 theta = zipOpenTvSubst dc_tyvars new_tys
800 -- First we cast the existential coercion arguments
801 cast_co (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
803 `mkTransCoercion` (substTy theta ty)
804 new_co_args = zipWith cast_co dc_eq_spec co_args
806 -- ...and now value arguments
807 new_val_args = zipWith cast_arg arg_tys val_args
808 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
811 ASSERT( length univ_args == tc_arity )
812 ASSERT( from_tc == dataConTyCon dc )
813 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
814 ASSERT( all isTypeArg (univ_args ++ ex_args) )
815 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 )
817 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
821 -- We do not want to tell the world that we have a
822 -- Cons, to *stop* Case of Known Cons, which removes
824 exprIsConApp_maybe (Note (TickBox {}) expr)
826 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
830 exprIsConApp_maybe (Note _ expr)
831 = exprIsConApp_maybe expr
832 -- We ignore InlineMe notes in case we have
833 -- x = __inline_me__ (a,b)
834 -- All part of making sure that INLINE pragmas never hurt
835 -- Marcin tripped on this one when making dictionaries more inlinable
837 -- In fact, we ignore all notes. For example,
838 -- case _scc_ "foo" (C a b) of
840 -- should be optimised away, but it will be only if we look
841 -- through the SCC note.
843 exprIsConApp_maybe expr = analyse (collectArgs expr)
845 analyse (Var fun, args)
846 | Just con <- isDataConWorkId_maybe fun,
847 args `lengthAtLeast` dataConRepArity con
848 -- Might be > because the arity excludes type args
851 -- Look through unfoldings, but only cheap ones, because
852 -- we are effectively duplicating the unfolding
853 analyse (Var fun, [])
854 | let unf = idUnfolding fun,
856 = exprIsConApp_maybe (unfoldingTemplate unf)
858 analyse other = Nothing
863 %************************************************************************
865 \subsection{Eta reduction and expansion}
867 %************************************************************************
870 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
871 {- The Arity returned is the number of value args the
872 thing can be applied to without doing much work
874 exprEtaExpandArity is used when eta expanding
877 It returns 1 (or more) to:
878 case x of p -> \s -> ...
879 because for I/O ish things we really want to get that \s to the top.
880 We are prepared to evaluate x each time round the loop in order to get that
882 It's all a bit more subtle than it looks:
886 Consider one-shot lambdas
887 let x = expensive in \y z -> E
888 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
889 Hence the ArityType returned by arityType
891 2. The state-transformer hack
893 The one-shot lambda special cause is particularly important/useful for
894 IO state transformers, where we often get
895 let x = E in \ s -> ...
897 and the \s is a real-world state token abstraction. Such abstractions
898 are almost invariably 1-shot, so we want to pull the \s out, past the
899 let x=E, even if E is expensive. So we treat state-token lambdas as
900 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
902 3. Dealing with bottom
905 f = \x -> error "foo"
906 Here, arity 1 is fine. But if it is
910 then we want to get arity 2. Tecnically, this isn't quite right, because
912 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
913 do so; it improves some programs significantly, and increasing convergence
914 isn't a bad thing. Hence the ABot/ATop in ArityType.
916 Actually, the situation is worse. Consider
920 Can we eta-expand here? At first the answer looks like "yes of course", but
923 This should diverge! But if we eta-expand, it won't. Again, we ignore this
924 "problem", because being scrupulous would lose an important transformation for
930 Non-recursive newtypes are transparent, and should not get in the way.
931 We do (currently) eta-expand recursive newtypes too. So if we have, say
933 newtype T = MkT ([T] -> Int)
937 where f has arity 1. Then: etaExpandArity e = 1;
938 that is, etaExpandArity looks through the coerce.
940 When we eta-expand e to arity 1: eta_expand 1 e T
941 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
943 HOWEVER, note that if you use coerce bogusly you can ge
945 And since negate has arity 2, you might try to eta expand. But you can't
946 decopose Int to a function type. Hence the final case in eta_expand.
950 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
952 -- A limited sort of function type
953 data ArityType = AFun Bool ArityType -- True <=> one-shot
954 | ATop -- Know nothing
957 arityDepth :: ArityType -> Arity
958 arityDepth (AFun _ ty) = 1 + arityDepth ty
961 andArityType ABot at2 = at2
962 andArityType ATop at2 = ATop
963 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
964 andArityType at1 at2 = andArityType at2 at1
966 arityType :: DynFlags -> CoreExpr -> ArityType
967 -- (go1 e) = [b1,..,bn]
968 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
969 -- where bi is True <=> the lambda is one-shot
971 arityType dflags (Note n e) = arityType dflags e
972 -- Not needed any more: etaExpand is cleverer
973 -- | ok_note n = arityType dflags e
974 -- | otherwise = ATop
976 arityType dflags (Cast e co) = arityType dflags e
978 arityType dflags (Var v)
979 = mk (idArity v) (arg_tys (idType v))
981 mk :: Arity -> [Type] -> ArityType
982 -- The argument types are only to steer the "state hack"
983 -- Consider case x of
985 -- False -> \(s:RealWorld) -> e
986 -- where foo has arity 1. Then we want the state hack to
987 -- apply to foo too, so we can eta expand the case.
988 mk 0 tys | isBottomingId v = ABot
989 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
991 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
992 mk n [] = AFun False (mk (n-1) [])
994 arg_tys :: Type -> [Type] -- Ignore for-alls
996 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
997 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1000 -- Lambdas; increase arity
1001 arityType dflags (Lam x e)
1002 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1003 | otherwise = arityType dflags e
1005 -- Applications; decrease arity
1006 arityType dflags (App f (Type _)) = arityType dflags f
1007 arityType dflags (App f a) = case arityType dflags f of
1008 AFun one_shot xs | exprIsCheap a -> xs
1011 -- Case/Let; keep arity if either the expression is cheap
1012 -- or it's a 1-shot lambda
1013 -- The former is not really right for Haskell
1014 -- f x = case x of { (a,b) -> \y. e }
1016 -- f x y = case x of { (a,b) -> e }
1017 -- The difference is observable using 'seq'
1018 arityType dflags (Case scrut _ _ alts)
1019 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1020 xs | exprIsCheap scrut -> xs
1021 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1024 arityType dflags (Let b e)
1025 = case arityType dflags e of
1026 xs | cheap_bind b -> xs
1027 xs@(AFun one_shot _) | one_shot -> AFun True ATop
1030 cheap_bind (NonRec b e) = is_cheap (b,e)
1031 cheap_bind (Rec prs) = all is_cheap prs
1032 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1034 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1035 -- dictionary bindings. This improves arities. Thereby, it also
1036 -- means that full laziness is less prone to floating out the
1037 -- application of a function to its dictionary arguments, which
1038 -- can thereby lose opportunities for fusion. Example:
1039 -- foo :: Ord a => a -> ...
1040 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1041 -- -- So foo has arity 1
1043 -- f = \x. foo dInt $ bar x
1045 -- The (foo DInt) is floated out, and makes ineffective a RULE
1046 -- foo (bar x) = ...
1048 -- One could go further and make exprIsCheap reply True to any
1049 -- dictionary-typed expression, but that's more work.
1051 arityType dflags other = ATop
1053 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1054 ok_note InlineMe = False
1055 ok_note other = True
1056 -- Notice that we do not look through __inline_me__
1057 -- This may seem surprising, but consider
1058 -- f = _inline_me (\x -> e)
1059 -- We DO NOT want to eta expand this to
1060 -- f = \x -> (_inline_me (\x -> e)) x
1061 -- because the _inline_me gets dropped now it is applied,
1070 etaExpand :: Arity -- Result should have this number of value args
1072 -> CoreExpr -> Type -- Expression and its type
1074 -- (etaExpand n us e ty) returns an expression with
1075 -- the same meaning as 'e', but with arity 'n'.
1077 -- Given e' = etaExpand n us e ty
1079 -- ty = exprType e = exprType e'
1081 -- Note that SCCs are not treated specially. If we have
1082 -- etaExpand 2 (\x -> scc "foo" e)
1083 -- = (\xy -> (scc "foo" e) y)
1084 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1086 etaExpand n us expr ty
1087 | manifestArity expr >= n = expr -- The no-op case
1089 = eta_expand n us expr ty
1092 -- manifestArity sees how many leading value lambdas there are
1093 manifestArity :: CoreExpr -> Arity
1094 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1095 | otherwise = manifestArity e
1096 manifestArity (Note _ e) = manifestArity e
1097 manifestArity (Cast e _) = manifestArity e
1100 -- etaExpand deals with for-alls. For example:
1102 -- where E :: forall a. a -> a
1104 -- (/\b. \y::a -> E b y)
1106 -- It deals with coerces too, though they are now rare
1107 -- so perhaps the extra code isn't worth it
1109 eta_expand n us expr ty
1111 -- The ILX code generator requires eta expansion for type arguments
1112 -- too, but alas the 'n' doesn't tell us how many of them there
1113 -- may be. So we eagerly eta expand any big lambdas, and just
1114 -- cross our fingers about possible loss of sharing in the ILX case.
1115 -- The Right Thing is probably to make 'arity' include
1116 -- type variables throughout the compiler. (ToDo.)
1118 -- Saturated, so nothing to do
1121 -- Short cut for the case where there already
1122 -- is a lambda; no point in gratuitously adding more
1123 eta_expand n us (Lam v body) ty
1125 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1128 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1130 -- We used to have a special case that stepped inside Coerces here,
1131 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1132 -- = Note note (eta_expand n us e ty)
1133 -- BUT this led to an infinite loop
1134 -- Example: newtype T = MkT (Int -> Int)
1135 -- eta_expand 1 (coerce (Int->Int) e)
1136 -- --> coerce (Int->Int) (eta_expand 1 T e)
1138 -- --> coerce (Int->Int) (coerce T
1139 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1140 -- by the splitNewType_maybe case below
1143 eta_expand n us expr ty
1144 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1145 case splitForAllTy_maybe ty of {
1148 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1150 lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
1151 -- Using tv as a base retains its tyvar/covar-ness
1155 case splitFunTy_maybe ty of {
1156 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1158 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
1164 -- newtype T = MkT ([T] -> Int)
1165 -- Consider eta-expanding this
1168 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1170 case splitNewTypeRepCo_maybe ty of {
1171 Just(ty1,co) -> mkCoerce (mkSymCoercion co)
1172 (eta_expand n us (mkCoerce co expr) ty1) ;
1175 -- We have an expression of arity > 0, but its type isn't a function
1176 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1177 -- Essentially the programmer is playing fast and loose with types
1178 -- (Happy does this a lot). So we simply decline to eta-expand.
1183 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1184 It tells how many things the expression can be applied to before doing
1185 any work. It doesn't look inside cases, lets, etc. The idea is that
1186 exprEtaExpandArity will do the hard work, leaving something that's easy
1187 for exprArity to grapple with. In particular, Simplify uses exprArity to
1188 compute the ArityInfo for the Id.
1190 Originally I thought that it was enough just to look for top-level lambdas, but
1191 it isn't. I've seen this
1193 foo = PrelBase.timesInt
1195 We want foo to get arity 2 even though the eta-expander will leave it
1196 unchanged, in the expectation that it'll be inlined. But occasionally it
1197 isn't, because foo is blacklisted (used in a rule).
1199 Similarly, see the ok_note check in exprEtaExpandArity. So
1200 f = __inline_me (\x -> e)
1201 won't be eta-expanded.
1203 And in any case it seems more robust to have exprArity be a bit more intelligent.
1204 But note that (\x y z -> f x y z)
1205 should have arity 3, regardless of f's arity.
1208 exprArity :: CoreExpr -> Arity
1211 go (Var v) = idArity v
1212 go (Lam x e) | isId x = go e + 1
1214 go (Note n e) = go e
1215 go (Cast e _) = go e
1216 go (App e (Type t)) = go e
1217 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1218 -- NB: exprIsCheap a!
1219 -- f (fac x) does not have arity 2,
1220 -- even if f has arity 3!
1221 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1222 -- unknown, hence arity 0
1226 %************************************************************************
1228 \subsection{Equality}
1230 %************************************************************************
1232 @cheapEqExpr@ is a cheap equality test which bales out fast!
1233 True => definitely equal
1234 False => may or may not be equal
1237 cheapEqExpr :: Expr b -> Expr b -> Bool
1239 cheapEqExpr (Var v1) (Var v2) = v1==v2
1240 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1241 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1243 cheapEqExpr (App f1 a1) (App f2 a2)
1244 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1246 cheapEqExpr _ _ = False
1248 exprIsBig :: Expr b -> Bool
1249 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1250 exprIsBig (Lit _) = False
1251 exprIsBig (Var v) = False
1252 exprIsBig (Type t) = False
1253 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1254 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1255 exprIsBig other = True
1260 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1261 -- Used in rule matching, so does *not* look through
1262 -- newtypes, predicate types; hence tcEqExpr
1264 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1266 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1268 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1269 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1270 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1271 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1272 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1273 tcEqExprX env (Let (NonRec v1 r1) e1)
1274 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1275 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1276 tcEqExprX env (Let (Rec ps1) e1)
1277 (Let (Rec ps2) e2) = equalLength ps1 ps2
1278 && and (zipWith eq_rhs ps1 ps2)
1279 && tcEqExprX env' e1 e2
1281 env' = foldl2 rn_bndr2 env ps2 ps2
1282 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1283 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1284 tcEqExprX env (Case e1 v1 t1 a1)
1285 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1286 && tcEqTypeX env t1 t2
1287 && equalLength a1 a2
1288 && and (zipWith (eq_alt env') a1 a2)
1290 env' = rnBndr2 env v1 v2
1292 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1293 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1294 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1295 tcEqExprX env e1 e2 = False
1297 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1299 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1300 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1301 eq_note env other1 other2 = False
1305 %************************************************************************
1307 \subsection{The size of an expression}
1309 %************************************************************************
1312 coreBindsSize :: [CoreBind] -> Int
1313 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1315 exprSize :: CoreExpr -> Int
1316 -- A measure of the size of the expressions
1317 -- It also forces the expression pretty drastically as a side effect
1318 exprSize (Var v) = v `seq` 1
1319 exprSize (Lit lit) = lit `seq` 1
1320 exprSize (App f a) = exprSize f + exprSize a
1321 exprSize (Lam b e) = varSize b + exprSize e
1322 exprSize (Let b e) = bindSize b + exprSize e
1323 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1324 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1325 exprSize (Note n e) = noteSize n + exprSize e
1326 exprSize (Type t) = seqType t `seq` 1
1328 noteSize (SCC cc) = cc `seq` 1
1329 noteSize InlineMe = 1
1330 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1332 varSize :: Var -> Int
1333 varSize b | isTyVar b = 1
1334 | otherwise = seqType (idType b) `seq`
1335 megaSeqIdInfo (idInfo b) `seq`
1338 varsSize = foldr ((+) . varSize) 0
1340 bindSize (NonRec b e) = varSize b + exprSize e
1341 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1343 pairSize (b,e) = varSize b + exprSize e
1345 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1349 %************************************************************************
1351 \subsection{Hashing}
1353 %************************************************************************
1356 hashExpr :: CoreExpr -> Int
1357 -- Two expressions that hash to the same Int may be equal (but may not be)
1358 -- Two expressions that hash to the different Ints are definitely unequal
1360 -- But "unequal" here means "not identical"; two alpha-equivalent
1361 -- expressions may hash to the different Ints
1363 -- The emphasis is on a crude, fast hash, rather than on high precision
1365 -- We must be careful that \x.x and \y.y map to the same hash code,
1366 -- (at least if we want the above invariant to be true)
1368 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1369 -- UniqFM doesn't like negative Ints
1371 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1373 hash_expr :: HashEnv -> CoreExpr -> Word32
1374 -- Word32, because we're expecting overflows here, and overflowing
1375 -- signed types just isn't cool. In C it's even undefined.
1376 hash_expr env (Note _ e) = hash_expr env e
1377 hash_expr env (Cast e co) = hash_expr env e
1378 hash_expr env (Var v) = hashVar env v
1379 hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1380 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1381 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1382 hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
1383 hash_expr env (Case e _ _ _) = hash_expr env e
1384 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1385 hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1
1386 -- Shouldn't happen. Better to use WARN than trace, because trace
1387 -- prevents the CPR optimisation kicking in for hash_expr.
1389 fast_hash_expr env (Var v) = hashVar env v
1390 fast_hash_expr env (Type t) = fast_hash_type env t
1391 fast_hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
1392 fast_hash_expr env (Cast e co) = fast_hash_expr env e
1393 fast_hash_expr env (Note n e) = fast_hash_expr env e
1394 fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1395 fast_hash_expr env other = 1
1397 fast_hash_type :: HashEnv -> Type -> Word32
1398 fast_hash_type env ty
1399 | Just tv <- getTyVar_maybe ty = hashVar env tv
1400 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1401 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1404 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1405 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1407 hashVar :: HashEnv -> Var -> Word32
1409 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1412 %************************************************************************
1414 \subsection{Determining non-updatable right-hand-sides}
1416 %************************************************************************
1418 Top-level constructor applications can usually be allocated
1419 statically, but they can't if the constructor, or any of the
1420 arguments, come from another DLL (because we can't refer to static
1421 labels in other DLLs).
1423 If this happens we simply make the RHS into an updatable thunk,
1424 and 'exectute' it rather than allocating it statically.
1427 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1428 -- This function is called only on *top-level* right-hand sides
1429 -- Returns True if the RHS can be allocated statically, with
1430 -- no thunks involved at all.
1432 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1433 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1434 -- update flag on it.
1436 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1437 -- (a) a value lambda
1438 -- (b) a saturated constructor application with static args
1440 -- BUT watch out for
1441 -- (i) Any cross-DLL references kill static-ness completely
1442 -- because they must be 'executed' not statically allocated
1443 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1444 -- this is not necessary)
1446 -- (ii) We treat partial applications as redexes, because in fact we
1447 -- make a thunk for them that runs and builds a PAP
1448 -- at run-time. The only appliations that are treated as
1449 -- static are *saturated* applications of constructors.
1451 -- We used to try to be clever with nested structures like this:
1452 -- ys = (:) w ((:) w [])
1453 -- on the grounds that CorePrep will flatten ANF-ise it later.
1454 -- But supporting this special case made the function much more
1455 -- complicated, because the special case only applies if there are no
1456 -- enclosing type lambdas:
1457 -- ys = /\ a -> Foo (Baz ([] a))
1458 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1460 -- But in fact, even without -O, nested structures at top level are
1461 -- flattened by the simplifier, so we don't need to be super-clever here.
1465 -- f = \x::Int. x+7 TRUE
1466 -- p = (True,False) TRUE
1468 -- d = (fst p, False) FALSE because there's a redex inside
1469 -- (this particular one doesn't happen but...)
1471 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1472 -- n = /\a. Nil a TRUE
1474 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1477 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1478 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1480 -- b) (C x xs), where C is a contructors is updatable if the application is
1483 -- c) don't look through unfolding of f in (f x).
1485 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1486 -- them as making the RHS re-entrant (non-updatable).
1488 rhsIsStatic this_pkg rhs = is_static False rhs
1490 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1493 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1495 is_static in_arg (Note (SCC _) e) = False
1496 is_static in_arg (Note _ e) = is_static in_arg e
1497 is_static in_arg (Cast e co) = is_static in_arg e
1499 is_static in_arg (Lit lit)
1501 MachLabel _ _ -> False
1503 -- A MachLabel (foreign import "&foo") in an argument
1504 -- prevents a constructor application from being static. The
1505 -- reason is that it might give rise to unresolvable symbols
1506 -- in the object file: under Linux, references to "weak"
1507 -- symbols from the data segment give rise to "unresolvable
1508 -- relocation" errors at link time This might be due to a bug
1509 -- in the linker, but we'll work around it here anyway.
1512 is_static in_arg other_expr = go other_expr 0
1514 go (Var f) n_val_args
1515 #if mingw32_TARGET_OS
1516 | not (isDllName this_pkg (idName f))
1518 = saturated_data_con f n_val_args
1519 || (in_arg && n_val_args == 0)
1520 -- A naked un-applied variable is *not* deemed a static RHS
1522 -- Reason: better to update so that the indirection gets shorted
1523 -- out, and the true value will be seen
1524 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1525 -- are always updatable. If you do so, make sure that non-updatable
1526 -- ones have enough space for their static link field!
1528 go (App f a) n_val_args
1529 | isTypeArg a = go f n_val_args
1530 | not in_arg && is_static True a = go f (n_val_args + 1)
1531 -- The (not in_arg) checks that we aren't in a constructor argument;
1532 -- if we are, we don't allow (value) applications of any sort
1534 -- NB. In case you wonder, args are sometimes not atomic. eg.
1535 -- x = D# (1.0## /## 2.0##)
1536 -- can't float because /## can fail.
1538 go (Note (SCC _) f) n_val_args = False
1539 go (Note _ f) n_val_args = go f n_val_args
1540 go (Cast e co) n_val_args = go e n_val_args
1542 go other n_val_args = False
1544 saturated_data_con f n_val_args
1545 = case isDataConWorkId_maybe f of
1546 Just dc -> n_val_args == dataConRepArity dc