2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreUtils]{Utility functions on @Core@ syntax}
9 mkNote, mkInlineMe, mkSCC, mkCoerce,
10 bindNonRec, needsCaseBinding,
11 mkIfThenElse, mkAltExpr, mkPiType,
13 -- Taking expressions apart
14 findDefault, findAlt, hasDefault,
16 -- Properties of expressions
17 exprType, coreAltsType,
18 exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
19 exprIsValue,exprOkForSpeculation, exprIsBig,
20 exprIsConApp_maybe, exprIsAtom,
21 idAppIsBottom, idAppIsCheap,
24 -- Arity and eta expansion
25 manifestArity, exprArity,
26 exprEtaExpandArity, etaExpand,
35 cheapEqExpr, eqExpr, applyTypeToArgs
38 #include "HsVersions.h"
41 import GlaExts -- For `xori`
44 import PprCore ( pprCoreExpr )
45 import Var ( Var, isId, isTyVar )
47 import Name ( hashName )
48 import Literal ( hashLiteral, literalType, litIsDupable )
49 import DataCon ( DataCon, dataConRepArity, dataConArgTys, isExistentialDataCon, dataConTyCon )
50 import PrimOp ( primOpOkForSpeculation, primOpIsCheap )
51 import Id ( Id, idType, globalIdDetails, idNewStrictness, idLBVarInfo,
52 mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda,
53 isDataConId_maybe, mkSysLocal, isDataConId, isBottomingId
55 import IdInfo ( LBVarInfo(..),
58 import NewDemand ( appIsBottom )
59 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe, splitFunTy,
60 applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy,
61 splitForAllTy_maybe, isForAllTy, splitNewType_maybe,
62 splitTyConApp_maybe, eqType, funResultTy, applyTy
64 import TyCon ( tyConArity )
65 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
66 import CostCentre ( CostCentre )
67 import BasicTypes ( Arity )
68 import Unique ( Unique )
70 import TysPrim ( alphaTy ) -- Debugging only
74 %************************************************************************
76 \subsection{Find the type of a Core atom/expression}
78 %************************************************************************
81 exprType :: CoreExpr -> Type
83 exprType (Var var) = idType var
84 exprType (Lit lit) = literalType lit
85 exprType (Let _ body) = exprType body
86 exprType (Case _ _ alts) = coreAltsType alts
87 exprType (Note (Coerce ty _) e) = ty -- **! should take usage from e
88 exprType (Note other_note e) = exprType e
89 exprType (Lam binder expr) = mkPiType binder (exprType expr)
91 = case collectArgs e of
92 (fun, args) -> applyTypeToArgs e (exprType fun) args
94 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
96 coreAltsType :: [CoreAlt] -> Type
97 coreAltsType ((_,_,rhs) : _) = exprType rhs
100 @mkPiType@ makes a (->) type or a forall type, depending on whether
101 it is given a type variable or a term variable. We cleverly use the
102 lbvarinfo field to figure out the right annotation for the arrove in
103 case of a term variable.
106 mkPiType :: Var -> Type -> Type -- The more polymorphic version doesn't work...
107 mkPiType v ty | isId v = (case idLBVarInfo v of
108 LBVarInfo u -> mkUTy u
110 mkFunTy (idType v) ty
111 | isTyVar v = mkForAllTy v ty
115 -- The first argument is just for debugging
116 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
117 applyTypeToArgs e op_ty [] = op_ty
119 applyTypeToArgs e op_ty (Type ty : args)
120 = -- Accumulate type arguments so we can instantiate all at once
121 applyTypeToArgs e (applyTys op_ty tys) rest_args
123 (tys, rest_args) = go [ty] args
124 go tys (Type ty : args) = go (ty:tys) args
125 go tys rest_args = (reverse tys, rest_args)
127 applyTypeToArgs e op_ty (other_arg : args)
128 = case (splitFunTy_maybe op_ty) of
129 Just (_, res_ty) -> applyTypeToArgs e res_ty args
130 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
135 %************************************************************************
137 \subsection{Attaching notes}
139 %************************************************************************
141 mkNote removes redundant coercions, and SCCs where possible
144 mkNote :: Note -> CoreExpr -> CoreExpr
145 mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr
146 mkNote (SCC cc) expr = mkSCC cc expr
147 mkNote InlineMe expr = mkInlineMe expr
148 mkNote note expr = Note note expr
150 -- Slide InlineCall in around the function
151 -- No longer necessary I think (SLPJ Apr 99)
152 -- mkNote InlineCall (App f a) = App (mkNote InlineCall f) a
153 -- mkNote InlineCall (Var v) = Note InlineCall (Var v)
154 -- mkNote InlineCall expr = expr
157 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
158 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
159 not be *applied* to anything.
161 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
164 f = inline_me (coerce t fw)
165 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
166 We want the split, so that the coerces can cancel at the call site.
168 However, we can get left with tiresome type applications. Notably, consider
169 f = /\ a -> let t = e in (t, w)
170 Then lifting the let out of the big lambda gives
172 f = /\ a -> let t = inline_me (t' a) in (t, w)
173 The inline_me is to stop the simplifier inlining t' right back
174 into t's RHS. In the next phase we'll substitute for t (since
175 its rhs is trivial) and *then* we could get rid of the inline_me.
176 But it hardly seems worth it, so I don't bother.
179 mkInlineMe (Var v) = Var v
180 mkInlineMe e = Note InlineMe e
186 mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr
188 mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
189 = ASSERT( from_ty `eqType` to_ty2 )
190 mkCoerce to_ty from_ty2 expr
192 mkCoerce to_ty from_ty expr
193 | to_ty `eqType` from_ty = expr
194 | otherwise = ASSERT( from_ty `eqType` exprType expr )
195 Note (Coerce to_ty from_ty) expr
199 mkSCC :: CostCentre -> Expr b -> Expr b
200 -- Note: Nested SCC's *are* preserved for the benefit of
201 -- cost centre stack profiling
202 mkSCC cc (Lit lit) = Lit lit
203 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
204 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
205 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
206 mkSCC cc expr = Note (SCC cc) expr
210 %************************************************************************
212 \subsection{Other expression construction}
214 %************************************************************************
217 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
218 -- (bindNonRec x r b) produces either
221 -- case r of x { _DEFAULT_ -> b }
223 -- depending on whether x is unlifted or not
224 -- It's used by the desugarer to avoid building bindings
225 -- that give Core Lint a heart attack. Actually the simplifier
226 -- deals with them perfectly well.
227 bindNonRec bndr rhs body
228 | needsCaseBinding (idType bndr) rhs = Case rhs bndr [(DEFAULT,[],body)]
229 | otherwise = Let (NonRec bndr rhs) body
231 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
232 -- Make a case expression instead of a let
233 -- These can arise either from the desugarer,
234 -- or from beta reductions: (\x.e) (x +# y)
238 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
239 -- This guy constructs the value that the scrutinee must have
240 -- when you are in one particular branch of a case
241 mkAltExpr (DataAlt con) args inst_tys
242 = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
243 mkAltExpr (LitAlt lit) [] []
246 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
247 mkIfThenElse guard then_expr else_expr
248 = Case guard (mkWildId boolTy)
249 [ (DataAlt trueDataCon, [], then_expr),
250 (DataAlt falseDataCon, [], else_expr) ]
254 %************************************************************************
256 \subsection{Taking expressions apart}
258 %************************************************************************
260 The default alternative must be first, if it exists at all.
261 This makes it easy to find, though it makes matching marginally harder.
264 hasDefault :: [CoreAlt] -> Bool
265 hasDefault ((DEFAULT,_,_) : alts) = True
268 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
269 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
270 findDefault alts = (alts, Nothing)
272 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
275 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
276 other -> go alts panic_deflt
279 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
282 go (alt@(con1,_,_) : alts) deflt | con == con1 = alt
283 | otherwise = ASSERT( not (con1 == DEFAULT) )
288 %************************************************************************
290 \subsection{Figuring out things about expressions}
292 %************************************************************************
294 @exprIsTrivial@ is true of expressions we are unconditionally happy to
295 duplicate; simple variables and constants, and type
296 applications. Note that primop Ids aren't considered
299 @exprIsBottom@ is true of expressions that are guaranteed to diverge
302 There used to be a gruesome test for (hasNoBinding v) in the
304 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
305 The idea here is that a constructor worker, like $wJust, is
306 really short for (\x -> $wJust x), becuase $wJust has no binding.
307 So it should be treated like a lambda. Ditto unsaturated primops.
308 But now constructor workers are not "have-no-binding" Ids. And
309 completely un-applied primops and foreign-call Ids are sufficiently
310 rare that I plan to allow them to be duplicated and put up with
314 exprIsTrivial (Var v) = True -- See notes above
315 exprIsTrivial (Type _) = True
316 exprIsTrivial (Lit lit) = True
317 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
318 exprIsTrivial (Note _ e) = exprIsTrivial e
319 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
320 exprIsTrivial other = False
322 exprIsAtom :: CoreExpr -> Bool
323 -- Used to decide whether to let-binding an STG argument
324 -- when compiling to ILX => type applications are not allowed
325 exprIsAtom (Var v) = True -- primOpIsDupable?
326 exprIsAtom (Lit lit) = True
327 exprIsAtom (Type ty) = True
328 exprIsAtom (Note (SCC _) e) = False
329 exprIsAtom (Note _ e) = exprIsAtom e
330 exprIsAtom other = False
334 @exprIsDupable@ is true of expressions that can be duplicated at a modest
335 cost in code size. This will only happen in different case
336 branches, so there's no issue about duplicating work.
338 That is, exprIsDupable returns True of (f x) even if
339 f is very very expensive to call.
341 Its only purpose is to avoid fruitless let-binding
342 and then inlining of case join points
346 exprIsDupable (Type _) = True
347 exprIsDupable (Var v) = True
348 exprIsDupable (Lit lit) = litIsDupable lit
349 exprIsDupable (Note InlineMe e) = True
350 exprIsDupable (Note _ e) = exprIsDupable e
354 go (Var v) n_args = True
355 go (App f a) n_args = n_args < dupAppSize
358 go other n_args = False
361 dupAppSize = 4 -- Size of application we are prepared to duplicate
364 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
365 it is obviously in weak head normal form, or is cheap to get to WHNF.
366 [Note that that's not the same as exprIsDupable; an expression might be
367 big, and hence not dupable, but still cheap.]
369 By ``cheap'' we mean a computation we're willing to:
370 push inside a lambda, or
371 inline at more than one place
372 That might mean it gets evaluated more than once, instead of being
373 shared. The main examples of things which aren't WHNF but are
378 (where e, and all the ei are cheap)
381 (where e and b are cheap)
384 (where op is a cheap primitive operator)
387 (because we are happy to substitute it inside a lambda)
389 Notice that a variable is considered 'cheap': we can push it inside a lambda,
390 because sharing will make sure it is only evaluated once.
393 exprIsCheap :: CoreExpr -> Bool
394 exprIsCheap (Lit lit) = True
395 exprIsCheap (Type _) = True
396 exprIsCheap (Var _) = True
397 exprIsCheap (Note InlineMe e) = True
398 exprIsCheap (Note _ e) = exprIsCheap e
399 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
400 exprIsCheap (Case e _ alts) = exprIsCheap e &&
401 and [exprIsCheap rhs | (_,_,rhs) <- alts]
402 -- Experimentally, treat (case x of ...) as cheap
403 -- (and case __coerce x etc.)
404 -- This improves arities of overloaded functions where
405 -- there is only dictionary selection (no construction) involved
406 exprIsCheap (Let (NonRec x _) e)
407 | isUnLiftedType (idType x) = exprIsCheap e
409 -- strict lets always have cheap right hand sides, and
412 exprIsCheap other_expr
413 = go other_expr 0 True
415 go (Var f) n_args args_cheap
416 = (idAppIsCheap f n_args && args_cheap)
417 -- A constructor, cheap primop, or partial application
419 || idAppIsBottom f n_args
420 -- Application of a function which
421 -- always gives bottom; we treat this as cheap
422 -- because it certainly doesn't need to be shared!
424 go (App f a) n_args args_cheap
425 | not (isRuntimeArg a) = go f n_args args_cheap
426 | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
428 go other n_args args_cheap = False
430 idAppIsCheap :: Id -> Int -> Bool
431 idAppIsCheap id n_val_args
432 | n_val_args == 0 = True -- Just a type application of
433 -- a variable (f t1 t2 t3)
435 | otherwise = case globalIdDetails id of
437 RecordSelId _ -> True -- I'm experimenting with making record selection
438 -- look cheap, so we will substitute it inside a
439 -- lambda. Particularly for dictionary field selection
441 PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
442 -- that return a type variable, since the result
443 -- might be applied to something, but I'm not going
444 -- to bother to check the number of args
445 other -> n_val_args < idArity id
448 exprOkForSpeculation returns True of an expression that it is
450 * safe to evaluate even if normal order eval might not
451 evaluate the expression at all, or
453 * safe *not* to evaluate even if normal order would do so
457 the expression guarantees to terminate,
459 without raising an exception,
460 without causing a side effect (e.g. writing a mutable variable)
463 let x = case y# +# 1# of { r# -> I# r# }
466 case y# +# 1# of { r# ->
471 We can only do this if the (y+1) is ok for speculation: it has no
472 side effects, and can't diverge or raise an exception.
475 exprOkForSpeculation :: CoreExpr -> Bool
476 exprOkForSpeculation (Lit _) = True
477 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
478 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
479 exprOkForSpeculation other_expr
480 = go other_expr 0 True
482 go (Var f) n_args args_ok
483 = case globalIdDetails f of
484 DataConId _ -> True -- The strictness of the constructor has already
485 -- been expressed by its "wrapper", so we don't need
486 -- to take the arguments into account
488 PrimOpId op -> primOpOkForSpeculation op && args_ok
489 -- A bit conservative: we don't really need
490 -- to care about lazy arguments, but this is easy
494 go (App f a) n_args args_ok
495 | not (isRuntimeArg a) = go f n_args args_ok
496 | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok)
498 go other n_args args_ok = False
503 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
504 exprIsBottom e = go 0 e
506 -- n is the number of args
507 go n (Note _ e) = go n e
508 go n (Let _ e) = go n e
509 go n (Case e _ _) = go 0 e -- Just check the scrut
510 go n (App e _) = go (n+1) e
511 go n (Var v) = idAppIsBottom v n
513 go n (Lam _ _) = False
515 idAppIsBottom :: Id -> Int -> Bool
516 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
519 @exprIsValue@ returns true for expressions that are certainly *already*
520 evaluated to *head* normal form. This is used to decide whether it's ok
523 case x of _ -> e ===> e
525 and to decide whether it's safe to discard a `seq`
527 So, it does *not* treat variables as evaluated, unless they say they are.
529 But it *does* treat partial applications and constructor applications
530 as values, even if their arguments are non-trivial, provided the argument
532 e.g. (:) (f x) (map f xs) is a value
533 map (...redex...) is a value
534 Because `seq` on such things completes immediately
536 For unlifted argument types, we have to be careful:
538 Suppose (f x) diverges; then C (f x) is not a value. True, but
539 this form is illegal (see the invariants in CoreSyn). Args of unboxed
540 type must be ok-for-speculation (or trivial).
543 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
544 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
546 exprIsValue (Lit l) = True
547 exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
548 exprIsValue (Note _ e) = exprIsValue e
549 exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v)
550 -- The idArity case catches data cons and primops that
551 -- don't have unfoldings
552 -- A worry: what if an Id's unfolding is just itself:
553 -- then we could get an infinite loop...
554 exprIsValue other_expr
555 | (Var fun, args) <- collectArgs other_expr,
556 isDataConId fun || valArgCount args < idArity fun
557 = check (idType fun) args
561 -- 'check' checks that unlifted-type args are in
562 -- fact guaranteed non-divergent
563 check fun_ty [] = True
564 check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
565 Just (_, ty) -> check ty args
566 check fun_ty (arg : args)
567 | isUnLiftedType arg_ty = exprOkForSpeculation arg
568 | otherwise = check res_ty args
570 (arg_ty, res_ty) = splitFunTy fun_ty
574 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
575 exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
576 = -- Maybe this is over the top, but here we try to turn
577 -- coerce (S,T) ( x, y )
579 -- ( coerce S x, coerce T y )
580 -- This happens in anger in PrelArrExts which has a coerce
581 -- case coerce memcpy a b of
583 -- where the memcpy is in the IO monad, but the call is in
585 case exprIsConApp_maybe expr of {
589 case splitTyConApp_maybe to_ty of {
591 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
592 | isExistentialDataCon dc -> Nothing
594 -- Type constructor must match
595 -- We knock out existentials to keep matters simple(r)
597 arity = tyConArity tc
598 val_args = drop arity args
599 to_arg_tys = dataConArgTys dc tc_arg_tys
600 mk_coerce ty arg = mkCoerce ty (exprType arg) arg
601 new_val_args = zipWith mk_coerce to_arg_tys val_args
603 ASSERT( all isTypeArg (take arity args) )
604 ASSERT( length val_args == length to_arg_tys )
605 Just (dc, map Type tc_arg_tys ++ new_val_args)
608 exprIsConApp_maybe (Note _ expr)
609 = exprIsConApp_maybe expr
610 -- We ignore InlineMe notes in case we have
611 -- x = __inline_me__ (a,b)
612 -- All part of making sure that INLINE pragmas never hurt
613 -- Marcin tripped on this one when making dictionaries more inlinable
615 -- In fact, we ignore all notes. For example,
616 -- case _scc_ "foo" (C a b) of
618 -- should be optimised away, but it will be only if we look
619 -- through the SCC note.
621 exprIsConApp_maybe expr = analyse (collectArgs expr)
623 analyse (Var fun, args)
624 | Just con <- isDataConId_maybe fun,
625 length args >= dataConRepArity con
626 -- Might be > because the arity excludes type args
629 -- Look through unfoldings, but only cheap ones, because
630 -- we are effectively duplicating the unfolding
631 analyse (Var fun, [])
632 | let unf = idUnfolding fun,
634 = exprIsConApp_maybe (unfoldingTemplate unf)
636 analyse other = Nothing
641 %************************************************************************
643 \subsection{Eta reduction and expansion}
645 %************************************************************************
648 exprEtaExpandArity :: CoreExpr -> Arity
649 -- The Int is number of value args the thing can be
650 -- applied to without doing much work
652 -- This is used when eta expanding
653 -- e ==> \xy -> e x y
655 -- It returns 1 (or more) to:
656 -- case x of p -> \s -> ...
657 -- because for I/O ish things we really want to get that \s to the top.
658 -- We are prepared to evaluate x each time round the loop in order to get that
660 -- It's all a bit more subtle than it looks. Consider one-shot lambdas
661 -- let x = expensive in \y z -> E
662 -- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
663 -- Hence the ArityType returned by arityType
665 -- NB: this is particularly important/useful for IO state
666 -- transformers, where we often get
667 -- let x = E in \ s -> ...
668 -- and the \s is a real-world state token abstraction. Such
669 -- abstractions are almost invariably 1-shot, so we want to
670 -- pull the \s out, past the let x=E.
671 -- The hack is in Id.isOneShotLambda
674 -- f = \x -> error "foo"
675 -- Here, arity 1 is fine. But if it is
676 -- f = \x -> case e of
677 -- True -> error "foo"
678 -- False -> \y -> x+y
679 -- then we want to get arity 2.
680 -- Hence the ABot/ATop in ArityType
683 exprEtaExpandArity e = arityDepth (arityType e)
685 -- A limited sort of function type
686 data ArityType = AFun Bool ArityType -- True <=> one-shot
687 | ATop -- Know nothing
690 arityDepth :: ArityType -> Arity
691 arityDepth (AFun _ ty) = 1 + arityDepth ty
694 andArityType ABot at2 = at2
695 andArityType ATop at2 = ATop
696 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
697 andArityType at1 at2 = andArityType at2 at1
699 arityType :: CoreExpr -> ArityType
700 -- (go1 e) = [b1,..,bn]
701 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
702 -- where bi is True <=> the lambda is one-shot
704 arityType (Note n e) = arityType e
705 -- Not needed any more: etaExpand is cleverer
706 -- | ok_note n = arityType e
707 -- | otherwise = ATop
712 mk :: Arity -> ArityType
713 mk 0 | isBottomingId v = ABot
715 mk n = AFun False (mk (n-1))
717 -- When the type of the Id encodes one-shot-ness,
718 -- use the idinfo here
720 -- Lambdas; increase arity
721 arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e)
722 | otherwise = arityType e
724 -- Applications; decrease arity
725 arityType (App f (Type _)) = arityType f
726 arityType (App f a) = case arityType f of
727 AFun one_shot xs | one_shot -> xs
728 | exprIsCheap a -> xs
731 -- Case/Let; keep arity if either the expression is cheap
732 -- or it's a 1-shot lambda
733 arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
734 xs@(AFun one_shot _) | one_shot -> xs
735 xs | exprIsCheap scrut -> xs
738 arityType (Let b e) = case arityType e of
739 xs@(AFun one_shot _) | one_shot -> xs
740 xs | all exprIsCheap (rhssOfBind b) -> xs
743 arityType other = ATop
745 {- NOT NEEDED ANY MORE: etaExpand is cleverer
746 ok_note InlineMe = False
748 -- Notice that we do not look through __inline_me__
749 -- This may seem surprising, but consider
750 -- f = _inline_me (\x -> e)
751 -- We DO NOT want to eta expand this to
752 -- f = \x -> (_inline_me (\x -> e)) x
753 -- because the _inline_me gets dropped now it is applied,
762 etaExpand :: Arity -- Result should have this number of value args
764 -> CoreExpr -> Type -- Expression and its type
766 -- (etaExpand n us e ty) returns an expression with
767 -- the same meaning as 'e', but with arity 'n'.
769 -- Given e' = etaExpand n us e ty
771 -- ty = exprType e = exprType e'
773 etaExpand n us expr ty
774 | manifestArity expr >= n = expr -- The no-op case
775 | otherwise = eta_expand n us expr ty
778 -- manifestArity sees how many leading value lambdas there are
779 manifestArity :: CoreExpr -> Arity
780 manifestArity (Lam v e) | isId v = 1 + manifestArity e
781 | otherwise = manifestArity e
782 manifestArity (Note _ e) = manifestArity e
785 -- etaExpand deals with for-alls. For example:
787 -- where E :: forall a. a -> a
789 -- (/\b. \y::a -> E b y)
791 -- It deals with coerces too, though they are now rare
792 -- so perhaps the extra code isn't worth it
794 eta_expand n us expr ty
796 -- The ILX code generator requires eta expansion for type arguments
797 -- too, but alas the 'n' doesn't tell us how many of them there
798 -- may be. So we eagerly eta expand any big lambdas, and just
799 -- cross our fingers about possible loss of sharing in the
801 -- The Right Thing is probably to make 'arity' include
802 -- type variables throughout the compiler. (ToDo.)
804 -- Saturated, so nothing to do
807 eta_expand n us (Note note@(Coerce _ ty) e) _
808 = Note note (eta_expand n us e ty)
810 -- Use mkNote so that _scc_s get pushed inside any lambdas that
811 -- are generated as part of the eta expansion. We rely on this
812 -- behaviour in CorePrep, when we eta expand an already-prepped RHS.
813 eta_expand n us (Note note e) ty
814 = mkNote note (eta_expand n us e ty)
816 -- Short cut for the case where there already
817 -- is a lambda; no point in gratuitously adding more
818 eta_expand n us (Lam v body) ty
820 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
823 = Lam v (eta_expand (n-1) us body (funResultTy ty))
825 eta_expand n us expr ty
826 = case splitForAllTy_maybe ty of {
827 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
831 case splitFunTy_maybe ty of {
832 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
834 arg1 = mkSysLocal SLIT("eta") uniq arg_ty
839 case splitNewType_maybe ty of {
840 Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ;
841 Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
845 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
846 It tells how many things the expression can be applied to before doing
847 any work. It doesn't look inside cases, lets, etc. The idea is that
848 exprEtaExpandArity will do the hard work, leaving something that's easy
849 for exprArity to grapple with. In particular, Simplify uses exprArity to
850 compute the ArityInfo for the Id.
852 Originally I thought that it was enough just to look for top-level lambdas, but
853 it isn't. I've seen this
855 foo = PrelBase.timesInt
857 We want foo to get arity 2 even though the eta-expander will leave it
858 unchanged, in the expectation that it'll be inlined. But occasionally it
859 isn't, because foo is blacklisted (used in a rule).
861 Similarly, see the ok_note check in exprEtaExpandArity. So
862 f = __inline_me (\x -> e)
863 won't be eta-expanded.
865 And in any case it seems more robust to have exprArity be a bit more intelligent.
866 But note that (\x y z -> f x y z)
867 should have arity 3, regardless of f's arity.
870 exprArity :: CoreExpr -> Arity
873 go (Var v) = idArity v
874 go (Lam x e) | isId x = go e + 1
877 go (App e (Type t)) = go e
878 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
879 -- NB: exprIsCheap a!
880 -- f (fac x) does not have arity 2,
881 -- even if f has arity 3!
882 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
883 -- unknown, hence arity 0
888 %************************************************************************
890 \subsection{Equality}
892 %************************************************************************
894 @cheapEqExpr@ is a cheap equality test which bales out fast!
895 True => definitely equal
896 False => may or may not be equal
899 cheapEqExpr :: Expr b -> Expr b -> Bool
901 cheapEqExpr (Var v1) (Var v2) = v1==v2
902 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
903 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
905 cheapEqExpr (App f1 a1) (App f2 a2)
906 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
908 cheapEqExpr _ _ = False
910 exprIsBig :: Expr b -> Bool
911 -- Returns True of expressions that are too big to be compared by cheapEqExpr
912 exprIsBig (Lit _) = False
913 exprIsBig (Var v) = False
914 exprIsBig (Type t) = False
915 exprIsBig (App f a) = exprIsBig f || exprIsBig a
916 exprIsBig other = True
921 eqExpr :: CoreExpr -> CoreExpr -> Bool
922 -- Works ok at more general type, but only needed at CoreExpr
923 -- Used in rule matching, so when we find a type we use
924 -- eqTcType, which doesn't look through newtypes
925 -- [And it doesn't risk falling into a black hole either.]
927 = eq emptyVarEnv e1 e2
929 -- The "env" maps variables in e1 to variables in ty2
930 -- So when comparing lambdas etc,
931 -- we in effect substitute v2 for v1 in e1 before continuing
932 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
933 Just v1' -> v1' == v2
936 eq env (Lit lit1) (Lit lit2) = lit1 == lit2
937 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
938 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
939 eq env (Let (NonRec v1 r1) e1)
940 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
941 eq env (Let (Rec ps1) e1)
942 (Let (Rec ps2) e2) = length ps1 == length ps2 &&
943 and (zipWith eq_rhs ps1 ps2) &&
946 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
947 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
948 eq env (Case e1 v1 a1)
949 (Case e2 v2 a2) = eq env e1 e2 &&
950 length a1 == length a2 &&
951 and (zipWith (eq_alt env') a1 a2)
953 env' = extendVarEnv env v1 v2
955 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
956 eq env (Type t1) (Type t2) = t1 `eqType` t2
959 eq_list env [] [] = True
960 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
961 eq_list env es1 es2 = False
963 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
964 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
966 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
967 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2
968 eq_note env InlineCall InlineCall = True
969 eq_note env other1 other2 = False
973 %************************************************************************
975 \subsection{The size of an expression}
977 %************************************************************************
980 coreBindsSize :: [CoreBind] -> Int
981 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
983 exprSize :: CoreExpr -> Int
984 -- A measure of the size of the expressions
985 -- It also forces the expression pretty drastically as a side effect
986 exprSize (Var v) = varSize v
987 exprSize (Lit lit) = lit `seq` 1
988 exprSize (App f a) = exprSize f + exprSize a
989 exprSize (Lam b e) = varSize b + exprSize e
990 exprSize (Let b e) = bindSize b + exprSize e
991 exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
992 exprSize (Note n e) = noteSize n + exprSize e
993 exprSize (Type t) = seqType t `seq` 1
995 noteSize (SCC cc) = cc `seq` 1
996 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
997 noteSize InlineCall = 1
998 noteSize InlineMe = 1
1000 varSize :: Var -> Int
1001 varSize b | isTyVar b = 1
1002 | otherwise = seqType (idType b) `seq`
1003 megaSeqIdInfo (idInfo b) `seq`
1006 varsSize = foldr ((+) . varSize) 0
1008 bindSize (NonRec b e) = varSize b + exprSize e
1009 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1011 pairSize (b,e) = varSize b + exprSize e
1013 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1017 %************************************************************************
1019 \subsection{Hashing}
1021 %************************************************************************
1024 hashExpr :: CoreExpr -> Int
1025 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1028 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1030 hash_expr (Note _ e) = hash_expr e
1031 hash_expr (Let (NonRec b r) e) = hashId b
1032 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1033 hash_expr (Case _ b _) = hashId b
1034 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1035 hash_expr (Var v) = hashId v
1036 hash_expr (Lit lit) = hashLiteral lit
1037 hash_expr (Lam b _) = hashId b
1038 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1040 fast_hash_expr (Var v) = hashId v
1041 fast_hash_expr (Lit lit) = hashLiteral lit
1042 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1043 fast_hash_expr (App f a) = fast_hash_expr a
1044 fast_hash_expr (Lam b _) = hashId b
1045 fast_hash_expr other = 1
1048 hashId id = hashName (idName id)