2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreUtils]{Utility functions on @Core@ syntax}
9 mkInlineMe, mkSCC, mkCoerce, mkCoerce2,
10 bindNonRec, needsCaseBinding,
11 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
13 -- Taking expressions apart
14 findDefault, findAlt, isDefaultAlt, mergeAlts,
16 -- Properties of expressions
17 exprType, coreAltType,
18 exprIsDupable, exprIsTrivial, exprIsCheap,
19 exprIsHNF,exprOkForSpeculation, exprIsBig,
20 exprIsConApp_maybe, exprIsBottom,
23 -- Arity and eta expansion
24 manifestArity, exprArity,
25 exprEtaExpandArity, etaExpand,
34 cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg
37 #include "HsVersions.h"
40 import GLAEXTS -- For `xori`
43 import CoreFVs ( exprFreeVars )
44 import PprCore ( pprCoreExpr )
46 import VarSet ( unionVarSet )
48 import Name ( hashName )
49 import Packages ( HomeModules )
51 import Packages ( isDllName )
53 import Literal ( hashLiteral, literalType, litIsDupable,
54 litIsTrivial, isZeroLit, Literal( MachLabel ) )
55 import DataCon ( DataCon, dataConRepArity, dataConInstArgTys,
56 isVanillaDataCon, dataConTyCon )
57 import PrimOp ( PrimOp(..), primOpOkForSpeculation, primOpIsCheap )
58 import Id ( Id, idType, globalIdDetails, idNewStrictness,
59 mkWildId, idArity, idName, idUnfolding, idInfo,
60 isOneShotBndr, isStateHackType, isDataConWorkId_maybe, mkSysLocal,
61 isDataConWorkId, isBottomingId
63 import IdInfo ( GlobalIdDetails(..), megaSeqIdInfo )
64 import NewDemand ( appIsBottom )
65 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
66 splitFunTy, tcEqTypeX,
67 applyTys, isUnLiftedType, seqType, mkTyVarTy,
68 splitForAllTy_maybe, isForAllTy, splitRecNewType_maybe,
69 splitTyConApp_maybe, coreEqType, funResultTy, applyTy
71 import TyCon ( tyConArity )
72 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
73 import CostCentre ( CostCentre )
74 import BasicTypes ( Arity )
75 import Unique ( Unique )
77 import TysPrim ( alphaTy ) -- Debugging only
78 import Util ( equalLength, lengthAtLeast, foldl2 )
82 %************************************************************************
84 \subsection{Find the type of a Core atom/expression}
86 %************************************************************************
89 exprType :: CoreExpr -> Type
91 exprType (Var var) = idType var
92 exprType (Lit lit) = literalType lit
93 exprType (Let _ body) = exprType body
94 exprType (Case _ _ ty alts) = ty
95 exprType (Note (Coerce ty _) e) = ty -- **! should take usage from e
96 exprType (Note other_note e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 coreAltType (_,_,rhs) = exprType rhs
108 @mkPiType@ makes a (->) type or a forall type, depending on whether
109 it is given a type variable or a term variable. We cleverly use the
110 lbvarinfo field to figure out the right annotation for the arrove in
111 case of a term variable.
114 mkPiType :: Var -> Type -> Type -- The more polymorphic version
115 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
117 mkPiTypes vs ty = foldr mkPiType ty vs
120 | isId v = mkFunTy (idType v) ty
121 | otherwise = mkForAllTy v ty
125 applyTypeToArg :: Type -> CoreExpr -> Type
126 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
127 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
129 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
130 -- A more efficient version of applyTypeToArg
131 -- when we have several args
132 -- The first argument is just for debugging
133 applyTypeToArgs e op_ty [] = op_ty
135 applyTypeToArgs e op_ty (Type ty : args)
136 = -- Accumulate type arguments so we can instantiate all at once
139 go rev_tys (Type ty : args) = go (ty:rev_tys) args
140 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
142 op_ty' = applyTys op_ty (reverse rev_tys)
144 applyTypeToArgs e op_ty (other_arg : args)
145 = case (splitFunTy_maybe op_ty) of
146 Just (_, res_ty) -> applyTypeToArgs e res_ty args
147 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
152 %************************************************************************
154 \subsection{Attaching notes}
156 %************************************************************************
158 mkNote removes redundant coercions, and SCCs where possible
162 mkNote :: Note -> CoreExpr -> CoreExpr
163 mkNote (Coerce to_ty from_ty) expr = mkCoerce2 to_ty from_ty expr
164 mkNote (SCC cc) expr = mkSCC cc expr
165 mkNote InlineMe expr = mkInlineMe expr
166 mkNote note expr = Note note expr
170 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
171 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
172 not be *applied* to anything.
174 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
177 f = inline_me (coerce t fw)
178 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
179 We want the split, so that the coerces can cancel at the call site.
181 However, we can get left with tiresome type applications. Notably, consider
182 f = /\ a -> let t = e in (t, w)
183 Then lifting the let out of the big lambda gives
185 f = /\ a -> let t = inline_me (t' a) in (t, w)
186 The inline_me is to stop the simplifier inlining t' right back
187 into t's RHS. In the next phase we'll substitute for t (since
188 its rhs is trivial) and *then* we could get rid of the inline_me.
189 But it hardly seems worth it, so I don't bother.
192 mkInlineMe (Var v) = Var v
193 mkInlineMe e = Note InlineMe e
199 mkCoerce :: Type -> CoreExpr -> CoreExpr
200 mkCoerce to_ty expr = mkCoerce2 to_ty (exprType expr) expr
202 mkCoerce2 :: Type -> Type -> CoreExpr -> CoreExpr
203 mkCoerce2 to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
204 = ASSERT( from_ty `coreEqType` to_ty2 )
205 mkCoerce2 to_ty from_ty2 expr
207 mkCoerce2 to_ty from_ty expr
208 | to_ty `coreEqType` from_ty = expr
209 | otherwise = ASSERT( from_ty `coreEqType` exprType expr )
210 Note (Coerce to_ty from_ty) expr
214 mkSCC :: CostCentre -> Expr b -> Expr b
215 -- Note: Nested SCC's *are* preserved for the benefit of
216 -- cost centre stack profiling
217 mkSCC cc (Lit lit) = Lit lit
218 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
219 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
220 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
221 mkSCC cc expr = Note (SCC cc) expr
225 %************************************************************************
227 \subsection{Other expression construction}
229 %************************************************************************
232 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
233 -- (bindNonRec x r b) produces either
236 -- case r of x { _DEFAULT_ -> b }
238 -- depending on whether x is unlifted or not
239 -- It's used by the desugarer to avoid building bindings
240 -- that give Core Lint a heart attack. Actually the simplifier
241 -- deals with them perfectly well.
243 bindNonRec bndr rhs body
244 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
245 | otherwise = Let (NonRec bndr rhs) body
247 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
248 -- Make a case expression instead of a let
249 -- These can arise either from the desugarer,
250 -- or from beta reductions: (\x.e) (x +# y)
254 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
255 -- This guy constructs the value that the scrutinee must have
256 -- when you are in one particular branch of a case
257 mkAltExpr (DataAlt con) args inst_tys
258 = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
259 mkAltExpr (LitAlt lit) [] []
262 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
263 mkIfThenElse guard then_expr else_expr
264 -- Not going to be refining, so okay to take the type of the "then" clause
265 = Case guard (mkWildId boolTy) (exprType then_expr)
266 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
267 (DataAlt trueDataCon, [], then_expr) ]
271 %************************************************************************
273 \subsection{Taking expressions apart}
275 %************************************************************************
277 The default alternative must be first, if it exists at all.
278 This makes it easy to find, though it makes matching marginally harder.
281 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
282 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
283 findDefault alts = (alts, Nothing)
285 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
288 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
289 other -> go alts panic_deflt
291 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
294 go (alt@(con1,_,_) : alts) deflt
295 = case con `cmpAltCon` con1 of
296 LT -> deflt -- Missed it already; the alts are in increasing order
298 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
300 isDefaultAlt :: CoreAlt -> Bool
301 isDefaultAlt (DEFAULT, _, _) = True
302 isDefaultAlt other = False
304 ---------------------------------
305 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
306 -- Merge preserving order; alternatives in the first arg
307 -- shadow ones in the second
308 mergeAlts [] as2 = as2
309 mergeAlts as1 [] = as1
310 mergeAlts (a1:as1) (a2:as2)
311 = case a1 `cmpAlt` a2 of
312 LT -> a1 : mergeAlts as1 (a2:as2)
313 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
314 GT -> a2 : mergeAlts (a1:as1) as2
318 %************************************************************************
320 \subsection{Figuring out things about expressions}
322 %************************************************************************
324 @exprIsTrivial@ is true of expressions we are unconditionally happy to
325 duplicate; simple variables and constants, and type
326 applications. Note that primop Ids aren't considered
329 @exprIsBottom@ is true of expressions that are guaranteed to diverge
332 There used to be a gruesome test for (hasNoBinding v) in the
334 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
335 The idea here is that a constructor worker, like $wJust, is
336 really short for (\x -> $wJust x), becuase $wJust has no binding.
337 So it should be treated like a lambda. Ditto unsaturated primops.
338 But now constructor workers are not "have-no-binding" Ids. And
339 completely un-applied primops and foreign-call Ids are sufficiently
340 rare that I plan to allow them to be duplicated and put up with
343 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
344 a) it really generates code, (and a heap object when it's
345 a function arg) to capture the cost centre
346 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
349 exprIsTrivial (Var v) = True -- See notes above
350 exprIsTrivial (Type _) = True
351 exprIsTrivial (Lit lit) = litIsTrivial lit
352 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
353 exprIsTrivial (Note (SCC _) e) = False -- See notes above
354 exprIsTrivial (Note _ e) = exprIsTrivial e
355 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
356 exprIsTrivial other = False
360 @exprIsDupable@ is true of expressions that can be duplicated at a modest
361 cost in code size. This will only happen in different case
362 branches, so there's no issue about duplicating work.
364 That is, exprIsDupable returns True of (f x) even if
365 f is very very expensive to call.
367 Its only purpose is to avoid fruitless let-binding
368 and then inlining of case join points
372 exprIsDupable (Type _) = True
373 exprIsDupable (Var v) = True
374 exprIsDupable (Lit lit) = litIsDupable lit
375 exprIsDupable (Note InlineMe e) = True
376 exprIsDupable (Note _ e) = exprIsDupable e
380 go (Var v) n_args = True
381 go (App f a) n_args = n_args < dupAppSize
384 go other n_args = False
387 dupAppSize = 4 -- Size of application we are prepared to duplicate
390 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
391 it is obviously in weak head normal form, or is cheap to get to WHNF.
392 [Note that that's not the same as exprIsDupable; an expression might be
393 big, and hence not dupable, but still cheap.]
395 By ``cheap'' we mean a computation we're willing to:
396 push inside a lambda, or
397 inline at more than one place
398 That might mean it gets evaluated more than once, instead of being
399 shared. The main examples of things which aren't WHNF but are
404 (where e, and all the ei are cheap)
407 (where e and b are cheap)
410 (where op is a cheap primitive operator)
413 (because we are happy to substitute it inside a lambda)
415 Notice that a variable is considered 'cheap': we can push it inside a lambda,
416 because sharing will make sure it is only evaluated once.
419 exprIsCheap :: CoreExpr -> Bool
420 exprIsCheap (Lit lit) = True
421 exprIsCheap (Type _) = True
422 exprIsCheap (Var _) = True
423 exprIsCheap (Note InlineMe e) = True
424 exprIsCheap (Note _ e) = exprIsCheap e
425 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
426 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
427 and [exprIsCheap rhs | (_,_,rhs) <- alts]
428 -- Experimentally, treat (case x of ...) as cheap
429 -- (and case __coerce x etc.)
430 -- This improves arities of overloaded functions where
431 -- there is only dictionary selection (no construction) involved
432 exprIsCheap (Let (NonRec x _) e)
433 | isUnLiftedType (idType x) = exprIsCheap e
435 -- strict lets always have cheap right hand sides, and
438 exprIsCheap other_expr
439 = go other_expr 0 True
441 go (Var f) n_args args_cheap
442 = (idAppIsCheap f n_args && args_cheap)
443 -- A constructor, cheap primop, or partial application
445 || idAppIsBottom f n_args
446 -- Application of a function which
447 -- always gives bottom; we treat this as cheap
448 -- because it certainly doesn't need to be shared!
450 go (App f a) n_args args_cheap
451 | not (isRuntimeArg a) = go f n_args args_cheap
452 | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
454 go other n_args args_cheap = False
456 idAppIsCheap :: Id -> Int -> Bool
457 idAppIsCheap id n_val_args
458 | n_val_args == 0 = True -- Just a type application of
459 -- a variable (f t1 t2 t3)
462 = case globalIdDetails id of
463 DataConWorkId _ -> True
464 RecordSelId {} -> n_val_args == 1 -- I'm experimenting with making record selection
465 ClassOpId _ -> n_val_args == 1 -- look cheap, so we will substitute it inside a
466 -- lambda. Particularly for dictionary field selection.
467 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
468 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
470 PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
471 -- that return a type variable, since the result
472 -- might be applied to something, but I'm not going
473 -- to bother to check the number of args
474 other -> n_val_args < idArity id
477 exprOkForSpeculation returns True of an expression that it is
479 * safe to evaluate even if normal order eval might not
480 evaluate the expression at all, or
482 * safe *not* to evaluate even if normal order would do so
486 the expression guarantees to terminate,
488 without raising an exception,
489 without causing a side effect (e.g. writing a mutable variable)
492 let x = case y# +# 1# of { r# -> I# r# }
495 case y# +# 1# of { r# ->
500 We can only do this if the (y+1) is ok for speculation: it has no
501 side effects, and can't diverge or raise an exception.
504 exprOkForSpeculation :: CoreExpr -> Bool
505 exprOkForSpeculation (Lit _) = True
506 exprOkForSpeculation (Type _) = True
507 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
508 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
509 exprOkForSpeculation other_expr
510 = case collectArgs other_expr of
511 (Var f, args) -> spec_ok (globalIdDetails f) args
515 spec_ok (DataConWorkId _) args
516 = True -- The strictness of the constructor has already
517 -- been expressed by its "wrapper", so we don't need
518 -- to take the arguments into account
520 spec_ok (PrimOpId op) args
521 | isDivOp op, -- Special case for dividing operations that fail
522 [arg1, Lit lit] <- args -- only if the divisor is zero
523 = not (isZeroLit lit) && exprOkForSpeculation arg1
524 -- Often there is a literal divisor, and this
525 -- can get rid of a thunk in an inner looop
528 = primOpOkForSpeculation op &&
529 all exprOkForSpeculation args
530 -- A bit conservative: we don't really need
531 -- to care about lazy arguments, but this is easy
533 spec_ok other args = False
535 isDivOp :: PrimOp -> Bool
536 -- True of dyadic operators that can fail
537 -- only if the second arg is zero
538 -- This function probably belongs in PrimOp, or even in
539 -- an automagically generated file.. but it's such a
540 -- special case I thought I'd leave it here for now.
541 isDivOp IntQuotOp = True
542 isDivOp IntRemOp = True
543 isDivOp WordQuotOp = True
544 isDivOp WordRemOp = True
545 isDivOp IntegerQuotRemOp = True
546 isDivOp IntegerDivModOp = True
547 isDivOp FloatDivOp = True
548 isDivOp DoubleDivOp = True
549 isDivOp other = False
554 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
555 exprIsBottom e = go 0 e
557 -- n is the number of args
558 go n (Note _ e) = go n e
559 go n (Let _ e) = go n e
560 go n (Case e _ _ _) = go 0 e -- Just check the scrut
561 go n (App e _) = go (n+1) e
562 go n (Var v) = idAppIsBottom v n
564 go n (Lam _ _) = False
565 go n (Type _) = False
567 idAppIsBottom :: Id -> Int -> Bool
568 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
571 @exprIsHNF@ returns true for expressions that are certainly *already*
572 evaluated to *head* normal form. This is used to decide whether it's ok
575 case x of _ -> e ===> e
577 and to decide whether it's safe to discard a `seq`
579 So, it does *not* treat variables as evaluated, unless they say they are.
581 But it *does* treat partial applications and constructor applications
582 as values, even if their arguments are non-trivial, provided the argument
584 e.g. (:) (f x) (map f xs) is a value
585 map (...redex...) is a value
586 Because `seq` on such things completes immediately
588 For unlifted argument types, we have to be careful:
590 Suppose (f x) diverges; then C (f x) is not a value. True, but
591 this form is illegal (see the invariants in CoreSyn). Args of unboxed
592 type must be ok-for-speculation (or trivial).
595 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
596 exprIsHNF (Var v) -- NB: There are no value args at this point
597 = isDataConWorkId v -- Catches nullary constructors,
598 -- so that [] and () are values, for example
599 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
600 || isEvaldUnfolding (idUnfolding v)
601 -- Check the thing's unfolding; it might be bound to a value
602 -- A worry: what if an Id's unfolding is just itself:
603 -- then we could get an infinite loop...
605 exprIsHNF (Lit l) = True
606 exprIsHNF (Type ty) = True -- Types are honorary Values;
607 -- we don't mind copying them
608 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
609 exprIsHNF (Note _ e) = exprIsHNF e
610 exprIsHNF (App e (Type _)) = exprIsHNF e
611 exprIsHNF (App e a) = app_is_value e [a]
612 exprIsHNF other = False
614 -- There is at least one value argument
615 app_is_value (Var fun) args
616 | isDataConWorkId fun -- Constructor apps are values
617 || idArity fun > valArgCount args -- Under-applied function
618 = check_args (idType fun) args
619 app_is_value (App f a) as = app_is_value f (a:as)
620 app_is_value other as = False
622 -- 'check_args' checks that unlifted-type args
623 -- are in fact guaranteed non-divergent
624 check_args fun_ty [] = True
625 check_args fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
626 Just (_, ty) -> check_args ty args
627 check_args fun_ty (arg : args)
628 | isUnLiftedType arg_ty = exprOkForSpeculation arg
629 | otherwise = check_args res_ty args
631 (arg_ty, res_ty) = splitFunTy fun_ty
635 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
636 exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
637 = -- Maybe this is over the top, but here we try to turn
638 -- coerce (S,T) ( x, y )
640 -- ( coerce S x, coerce T y )
641 -- This happens in anger in PrelArrExts which has a coerce
642 -- case coerce memcpy a b of
644 -- where the memcpy is in the IO monad, but the call is in
646 case exprIsConApp_maybe expr of {
650 case splitTyConApp_maybe to_ty of {
652 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
653 | not (isVanillaDataCon dc) -> Nothing
655 -- Type constructor must match
656 -- We knock out existentials to keep matters simple(r)
658 arity = tyConArity tc
659 val_args = drop arity args
660 to_arg_tys = dataConInstArgTys dc tc_arg_tys
661 mk_coerce ty arg = mkCoerce ty arg
662 new_val_args = zipWith mk_coerce to_arg_tys val_args
664 ASSERT( all isTypeArg (take arity args) )
665 ASSERT( equalLength val_args to_arg_tys )
666 Just (dc, map Type tc_arg_tys ++ new_val_args)
669 exprIsConApp_maybe (Note _ expr)
670 = exprIsConApp_maybe expr
671 -- We ignore InlineMe notes in case we have
672 -- x = __inline_me__ (a,b)
673 -- All part of making sure that INLINE pragmas never hurt
674 -- Marcin tripped on this one when making dictionaries more inlinable
676 -- In fact, we ignore all notes. For example,
677 -- case _scc_ "foo" (C a b) of
679 -- should be optimised away, but it will be only if we look
680 -- through the SCC note.
682 exprIsConApp_maybe expr = analyse (collectArgs expr)
684 analyse (Var fun, args)
685 | Just con <- isDataConWorkId_maybe fun,
686 args `lengthAtLeast` dataConRepArity con
687 -- Might be > because the arity excludes type args
690 -- Look through unfoldings, but only cheap ones, because
691 -- we are effectively duplicating the unfolding
692 analyse (Var fun, [])
693 | let unf = idUnfolding fun,
695 = exprIsConApp_maybe (unfoldingTemplate unf)
697 analyse other = Nothing
702 %************************************************************************
704 \subsection{Eta reduction and expansion}
706 %************************************************************************
709 exprEtaExpandArity :: CoreExpr -> Arity
710 {- The Arity returned is the number of value args the
711 thing can be applied to without doing much work
713 exprEtaExpandArity is used when eta expanding
716 It returns 1 (or more) to:
717 case x of p -> \s -> ...
718 because for I/O ish things we really want to get that \s to the top.
719 We are prepared to evaluate x each time round the loop in order to get that
721 It's all a bit more subtle than it looks:
725 Consider one-shot lambdas
726 let x = expensive in \y z -> E
727 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
728 Hence the ArityType returned by arityType
730 2. The state-transformer hack
732 The one-shot lambda special cause is particularly important/useful for
733 IO state transformers, where we often get
734 let x = E in \ s -> ...
736 and the \s is a real-world state token abstraction. Such abstractions
737 are almost invariably 1-shot, so we want to pull the \s out, past the
738 let x=E, even if E is expensive. So we treat state-token lambdas as
739 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
741 3. Dealing with bottom
744 f = \x -> error "foo"
745 Here, arity 1 is fine. But if it is
749 then we want to get arity 2. Tecnically, this isn't quite right, because
751 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
752 do so; it improves some programs significantly, and increasing convergence
753 isn't a bad thing. Hence the ABot/ATop in ArityType.
755 Actually, the situation is worse. Consider
759 Can we eta-expand here? At first the answer looks like "yes of course", but
762 This should diverge! But if we eta-expand, it won't. Again, we ignore this
763 "problem", because being scrupulous would lose an important transformation for
769 Non-recursive newtypes are transparent, and should not get in the way.
770 We do (currently) eta-expand recursive newtypes too. So if we have, say
772 newtype T = MkT ([T] -> Int)
776 where f has arity 1. Then: etaExpandArity e = 1;
777 that is, etaExpandArity looks through the coerce.
779 When we eta-expand e to arity 1: eta_expand 1 e T
780 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
782 HOWEVER, note that if you use coerce bogusly you can ge
784 And since negate has arity 2, you might try to eta expand. But you can't
785 decopose Int to a function type. Hence the final case in eta_expand.
789 exprEtaExpandArity e = arityDepth (arityType e)
791 -- A limited sort of function type
792 data ArityType = AFun Bool ArityType -- True <=> one-shot
793 | ATop -- Know nothing
796 arityDepth :: ArityType -> Arity
797 arityDepth (AFun _ ty) = 1 + arityDepth ty
800 andArityType ABot at2 = at2
801 andArityType ATop at2 = ATop
802 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
803 andArityType at1 at2 = andArityType at2 at1
805 arityType :: CoreExpr -> ArityType
806 -- (go1 e) = [b1,..,bn]
807 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
808 -- where bi is True <=> the lambda is one-shot
810 arityType (Note n e) = arityType e
811 -- Not needed any more: etaExpand is cleverer
812 -- | ok_note n = arityType e
813 -- | otherwise = ATop
816 = mk (idArity v) (arg_tys (idType v))
818 mk :: Arity -> [Type] -> ArityType
819 -- The argument types are only to steer the "state hack"
820 -- Consider case x of
822 -- False -> \(s:RealWorld) -> e
823 -- where foo has arity 1. Then we want the state hack to
824 -- apply to foo too, so we can eta expand the case.
825 mk 0 tys | isBottomingId v = ABot
826 | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
828 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
829 mk n [] = AFun False (mk (n-1) [])
831 arg_tys :: Type -> [Type] -- Ignore for-alls
833 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
834 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
837 -- Lambdas; increase arity
838 arityType (Lam x e) | isId x = AFun (isOneShotBndr x) (arityType e)
839 | otherwise = arityType e
841 -- Applications; decrease arity
842 arityType (App f (Type _)) = arityType f
843 arityType (App f a) = case arityType f of
844 AFun one_shot xs | exprIsCheap a -> xs
847 -- Case/Let; keep arity if either the expression is cheap
848 -- or it's a 1-shot lambda
849 -- The former is not really right for Haskell
850 -- f x = case x of { (a,b) -> \y. e }
852 -- f x y = case x of { (a,b) -> e }
853 -- The difference is observable using 'seq'
854 arityType (Case scrut _ _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
855 xs | exprIsCheap scrut -> xs
856 xs@(AFun one_shot _) | one_shot -> AFun True ATop
859 arityType (Let b e) = case arityType e of
860 xs | all exprIsCheap (rhssOfBind b) -> xs
861 xs@(AFun one_shot _) | one_shot -> AFun True ATop
864 arityType other = ATop
866 {- NOT NEEDED ANY MORE: etaExpand is cleverer
867 ok_note InlineMe = False
869 -- Notice that we do not look through __inline_me__
870 -- This may seem surprising, but consider
871 -- f = _inline_me (\x -> e)
872 -- We DO NOT want to eta expand this to
873 -- f = \x -> (_inline_me (\x -> e)) x
874 -- because the _inline_me gets dropped now it is applied,
883 etaExpand :: Arity -- Result should have this number of value args
885 -> CoreExpr -> Type -- Expression and its type
887 -- (etaExpand n us e ty) returns an expression with
888 -- the same meaning as 'e', but with arity 'n'.
890 -- Given e' = etaExpand n us e ty
892 -- ty = exprType e = exprType e'
894 -- Note that SCCs are not treated specially. If we have
895 -- etaExpand 2 (\x -> scc "foo" e)
896 -- = (\xy -> (scc "foo" e) y)
897 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
899 etaExpand n us expr ty
900 | manifestArity expr >= n = expr -- The no-op case
901 | otherwise = eta_expand n us expr ty
904 -- manifestArity sees how many leading value lambdas there are
905 manifestArity :: CoreExpr -> Arity
906 manifestArity (Lam v e) | isId v = 1 + manifestArity e
907 | otherwise = manifestArity e
908 manifestArity (Note _ e) = manifestArity e
911 -- etaExpand deals with for-alls. For example:
913 -- where E :: forall a. a -> a
915 -- (/\b. \y::a -> E b y)
917 -- It deals with coerces too, though they are now rare
918 -- so perhaps the extra code isn't worth it
920 eta_expand n us expr ty
922 -- The ILX code generator requires eta expansion for type arguments
923 -- too, but alas the 'n' doesn't tell us how many of them there
924 -- may be. So we eagerly eta expand any big lambdas, and just
925 -- cross our fingers about possible loss of sharing in the ILX case.
926 -- The Right Thing is probably to make 'arity' include
927 -- type variables throughout the compiler. (ToDo.)
929 -- Saturated, so nothing to do
932 -- Short cut for the case where there already
933 -- is a lambda; no point in gratuitously adding more
934 eta_expand n us (Lam v body) ty
936 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
939 = Lam v (eta_expand (n-1) us body (funResultTy ty))
941 -- We used to have a special case that stepped inside Coerces here,
942 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
943 -- = Note note (eta_expand n us e ty)
944 -- BUT this led to an infinite loop
945 -- Example: newtype T = MkT (Int -> Int)
946 -- eta_expand 1 (coerce (Int->Int) e)
947 -- --> coerce (Int->Int) (eta_expand 1 T e)
949 -- --> coerce (Int->Int) (coerce T
950 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
951 -- by the splitNewType_maybe case below
954 eta_expand n us expr ty
955 = case splitForAllTy_maybe ty of {
956 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
960 case splitFunTy_maybe ty of {
961 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
963 arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
969 -- newtype T = MkT ([T] -> Int)
970 -- Consider eta-expanding this
973 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
974 -- Only try this for recursive newtypes; the non-recursive kind
975 -- are transparent anyway
977 case splitRecNewType_maybe ty of {
978 Just ty' -> mkCoerce2 ty ty' (eta_expand n us (mkCoerce2 ty' ty expr) ty') ;
981 -- We have an expression of arity > 0, but its type isn't a function
982 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
983 -- Essentially the programmer is playing fast and loose with types
984 -- (Happy does this a lot). So we simply decline to eta-expand.
989 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
990 It tells how many things the expression can be applied to before doing
991 any work. It doesn't look inside cases, lets, etc. The idea is that
992 exprEtaExpandArity will do the hard work, leaving something that's easy
993 for exprArity to grapple with. In particular, Simplify uses exprArity to
994 compute the ArityInfo for the Id.
996 Originally I thought that it was enough just to look for top-level lambdas, but
997 it isn't. I've seen this
999 foo = PrelBase.timesInt
1001 We want foo to get arity 2 even though the eta-expander will leave it
1002 unchanged, in the expectation that it'll be inlined. But occasionally it
1003 isn't, because foo is blacklisted (used in a rule).
1005 Similarly, see the ok_note check in exprEtaExpandArity. So
1006 f = __inline_me (\x -> e)
1007 won't be eta-expanded.
1009 And in any case it seems more robust to have exprArity be a bit more intelligent.
1010 But note that (\x y z -> f x y z)
1011 should have arity 3, regardless of f's arity.
1014 exprArity :: CoreExpr -> Arity
1017 go (Var v) = idArity v
1018 go (Lam x e) | isId x = go e + 1
1020 go (Note n e) = go e
1021 go (App e (Type t)) = go e
1022 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1023 -- NB: exprIsCheap a!
1024 -- f (fac x) does not have arity 2,
1025 -- even if f has arity 3!
1026 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1027 -- unknown, hence arity 0
1031 %************************************************************************
1033 \subsection{Equality}
1035 %************************************************************************
1037 @cheapEqExpr@ is a cheap equality test which bales out fast!
1038 True => definitely equal
1039 False => may or may not be equal
1042 cheapEqExpr :: Expr b -> Expr b -> Bool
1044 cheapEqExpr (Var v1) (Var v2) = v1==v2
1045 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1046 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1048 cheapEqExpr (App f1 a1) (App f2 a2)
1049 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1051 cheapEqExpr _ _ = False
1053 exprIsBig :: Expr b -> Bool
1054 -- Returns True of expressions that are too big to be compared by cheapEqExpr
1055 exprIsBig (Lit _) = False
1056 exprIsBig (Var v) = False
1057 exprIsBig (Type t) = False
1058 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1059 exprIsBig other = True
1064 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1065 -- Used in rule matching, so does *not* look through
1066 -- newtypes, predicate types; hence tcEqExpr
1068 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1070 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1072 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1073 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1074 tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
1075 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1076 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1077 tcEqExprX env (Let (NonRec v1 r1) e1)
1078 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1079 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1080 tcEqExprX env (Let (Rec ps1) e1)
1081 (Let (Rec ps2) e2) = equalLength ps1 ps2
1082 && and (zipWith eq_rhs ps1 ps2)
1083 && tcEqExprX env' e1 e2
1085 env' = foldl2 rn_bndr2 env ps2 ps2
1086 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1087 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1088 tcEqExprX env (Case e1 v1 t1 a1)
1089 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1090 && tcEqTypeX env t1 t2
1091 && equalLength a1 a2
1092 && and (zipWith (eq_alt env') a1 a2)
1094 env' = rnBndr2 env v1 v2
1096 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1097 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1098 tcEqExprX env e1 e2 = False
1100 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1102 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
1103 eq_note env (Coerce t1 f1) (Coerce t2 f2) = tcEqTypeX env t1 t2 && tcEqTypeX env f1 f2
1104 eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
1105 eq_note env other1 other2 = False
1109 %************************************************************************
1111 \subsection{The size of an expression}
1113 %************************************************************************
1116 coreBindsSize :: [CoreBind] -> Int
1117 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1119 exprSize :: CoreExpr -> Int
1120 -- A measure of the size of the expressions
1121 -- It also forces the expression pretty drastically as a side effect
1122 exprSize (Var v) = v `seq` 1
1123 exprSize (Lit lit) = lit `seq` 1
1124 exprSize (App f a) = exprSize f + exprSize a
1125 exprSize (Lam b e) = varSize b + exprSize e
1126 exprSize (Let b e) = bindSize b + exprSize e
1127 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1128 exprSize (Note n e) = noteSize n + exprSize e
1129 exprSize (Type t) = seqType t `seq` 1
1131 noteSize (SCC cc) = cc `seq` 1
1132 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
1133 noteSize InlineMe = 1
1134 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1136 varSize :: Var -> Int
1137 varSize b | isTyVar b = 1
1138 | otherwise = seqType (idType b) `seq`
1139 megaSeqIdInfo (idInfo b) `seq`
1142 varsSize = foldr ((+) . varSize) 0
1144 bindSize (NonRec b e) = varSize b + exprSize e
1145 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1147 pairSize (b,e) = varSize b + exprSize e
1149 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1153 %************************************************************************
1155 \subsection{Hashing}
1157 %************************************************************************
1160 hashExpr :: CoreExpr -> Int
1161 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1164 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1166 hash_expr (Note _ e) = hash_expr e
1167 hash_expr (Let (NonRec b r) e) = hashId b
1168 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1169 hash_expr (Case _ b _ _) = hashId b
1170 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1171 hash_expr (Var v) = hashId v
1172 hash_expr (Lit lit) = hashLiteral lit
1173 hash_expr (Lam b _) = hashId b
1174 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1176 fast_hash_expr (Var v) = hashId v
1177 fast_hash_expr (Lit lit) = hashLiteral lit
1178 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1179 fast_hash_expr (App f a) = fast_hash_expr a
1180 fast_hash_expr (Lam b _) = hashId b
1181 fast_hash_expr other = 1
1184 hashId id = hashName (idName id)
1187 %************************************************************************
1189 \subsection{Determining non-updatable right-hand-sides}
1191 %************************************************************************
1193 Top-level constructor applications can usually be allocated
1194 statically, but they can't if the constructor, or any of the
1195 arguments, come from another DLL (because we can't refer to static
1196 labels in other DLLs).
1198 If this happens we simply make the RHS into an updatable thunk,
1199 and 'exectute' it rather than allocating it statically.
1202 rhsIsStatic :: HomeModules -> CoreExpr -> Bool
1203 -- This function is called only on *top-level* right-hand sides
1204 -- Returns True if the RHS can be allocated statically, with
1205 -- no thunks involved at all.
1207 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1208 -- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
1209 -- update flag on it.
1211 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1212 -- (a) a value lambda
1213 -- (b) a saturated constructor application with static args
1215 -- BUT watch out for
1216 -- (i) Any cross-DLL references kill static-ness completely
1217 -- because they must be 'executed' not statically allocated
1218 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1219 -- this is not necessary)
1221 -- (ii) We treat partial applications as redexes, because in fact we
1222 -- make a thunk for them that runs and builds a PAP
1223 -- at run-time. The only appliations that are treated as
1224 -- static are *saturated* applications of constructors.
1226 -- We used to try to be clever with nested structures like this:
1227 -- ys = (:) w ((:) w [])
1228 -- on the grounds that CorePrep will flatten ANF-ise it later.
1229 -- But supporting this special case made the function much more
1230 -- complicated, because the special case only applies if there are no
1231 -- enclosing type lambdas:
1232 -- ys = /\ a -> Foo (Baz ([] a))
1233 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1235 -- But in fact, even without -O, nested structures at top level are
1236 -- flattened by the simplifier, so we don't need to be super-clever here.
1240 -- f = \x::Int. x+7 TRUE
1241 -- p = (True,False) TRUE
1243 -- d = (fst p, False) FALSE because there's a redex inside
1244 -- (this particular one doesn't happen but...)
1246 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1247 -- n = /\a. Nil a TRUE
1249 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1252 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1253 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1255 -- b) (C x xs), where C is a contructors is updatable if the application is
1258 -- c) don't look through unfolding of f in (f x).
1260 -- When opt_RuntimeTypes is on, we keep type lambdas and treat
1261 -- them as making the RHS re-entrant (non-updatable).
1263 rhsIsStatic hmods rhs = is_static False rhs
1265 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1268 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1270 is_static in_arg (Note (SCC _) e) = False
1271 is_static in_arg (Note _ e) = is_static in_arg e
1273 is_static in_arg (Lit lit)
1275 MachLabel _ _ -> False
1277 -- A MachLabel (foreign import "&foo") in an argument
1278 -- prevents a constructor application from being static. The
1279 -- reason is that it might give rise to unresolvable symbols
1280 -- in the object file: under Linux, references to "weak"
1281 -- symbols from the data segment give rise to "unresolvable
1282 -- relocation" errors at link time This might be due to a bug
1283 -- in the linker, but we'll work around it here anyway.
1286 is_static in_arg other_expr = go other_expr 0
1288 go (Var f) n_val_args
1289 #if mingw32_TARGET_OS
1290 | not (isDllName hmods (idName f))
1292 = saturated_data_con f n_val_args
1293 || (in_arg && n_val_args == 0)
1294 -- A naked un-applied variable is *not* deemed a static RHS
1296 -- Reason: better to update so that the indirection gets shorted
1297 -- out, and the true value will be seen
1298 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1299 -- are always updatable. If you do so, make sure that non-updatable
1300 -- ones have enough space for their static link field!
1302 go (App f a) n_val_args
1303 | isTypeArg a = go f n_val_args
1304 | not in_arg && is_static True a = go f (n_val_args + 1)
1305 -- The (not in_arg) checks that we aren't in a constructor argument;
1306 -- if we are, we don't allow (value) applications of any sort
1308 -- NB. In case you wonder, args are sometimes not atomic. eg.
1309 -- x = D# (1.0## /## 2.0##)
1310 -- can't float because /## can fail.
1312 go (Note (SCC _) f) n_val_args = False
1313 go (Note _ f) n_val_args = go f n_val_args
1315 go other n_val_args = False
1317 saturated_data_con f n_val_args
1318 = case isDataConWorkId_maybe f of
1319 Just dc -> n_val_args == dataConRepArity dc