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, applyTypeToArg
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, isZeroLit )
49 import DataCon ( DataCon, dataConRepArity, dataConArgTys, isExistentialDataCon, dataConTyCon )
50 import PrimOp ( 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,
65 import TyCon ( tyConArity )
66 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
67 import CostCentre ( CostCentre )
68 import BasicTypes ( Arity )
69 import Unique ( Unique )
71 import TysPrim ( alphaTy ) -- Debugging only
72 import Util ( equalLength, lengthAtLeast )
76 %************************************************************************
78 \subsection{Find the type of a Core atom/expression}
80 %************************************************************************
83 exprType :: CoreExpr -> Type
85 exprType (Var var) = idType var
86 exprType (Lit lit) = literalType lit
87 exprType (Let _ body) = exprType body
88 exprType (Case _ _ alts) = coreAltsType alts
89 exprType (Note (Coerce ty _) e) = ty -- **! should take usage from e
90 exprType (Note other_note e) = exprType e
91 exprType (Lam binder expr) = mkPiType binder (exprType expr)
93 = case collectArgs e of
94 (fun, args) -> applyTypeToArgs e (exprType fun) args
96 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
98 coreAltsType :: [CoreAlt] -> Type
99 coreAltsType ((_,_,rhs) : _) = exprType rhs
102 @mkPiType@ makes a (->) type or a forall type, depending on whether
103 it is given a type variable or a term variable. We cleverly use the
104 lbvarinfo field to figure out the right annotation for the arrove in
105 case of a term variable.
108 mkPiType :: Var -> Type -> Type -- The more polymorphic version doesn't work...
109 mkPiType v ty | isId v = (case idLBVarInfo v of
110 LBVarInfo u -> mkUTy u
112 mkFunTy (idType v) ty
113 | isTyVar v = mkForAllTy v ty
117 applyTypeToArg :: Type -> CoreExpr -> Type
118 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
119 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
121 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
122 -- A more efficient version of applyTypeToArg
123 -- when we have several args
124 -- The first argument is just for debugging
125 applyTypeToArgs e op_ty [] = op_ty
127 applyTypeToArgs e op_ty (Type ty : args)
128 = -- Accumulate type arguments so we can instantiate all at once
131 go rev_tys (Type ty : args) = go (ty:rev_tys) args
132 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
134 op_ty' = applyTys op_ty (reverse rev_tys)
136 applyTypeToArgs e op_ty (other_arg : args)
137 = case (splitFunTy_maybe op_ty) of
138 Just (_, res_ty) -> applyTypeToArgs e res_ty args
139 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
144 %************************************************************************
146 \subsection{Attaching notes}
148 %************************************************************************
150 mkNote removes redundant coercions, and SCCs where possible
153 mkNote :: Note -> CoreExpr -> CoreExpr
154 mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr
155 mkNote (SCC cc) expr = mkSCC cc expr
156 mkNote InlineMe expr = mkInlineMe expr
157 mkNote note expr = Note note expr
159 -- Slide InlineCall in around the function
160 -- No longer necessary I think (SLPJ Apr 99)
161 -- mkNote InlineCall (App f a) = App (mkNote InlineCall f) a
162 -- mkNote InlineCall (Var v) = Note InlineCall (Var v)
163 -- mkNote InlineCall expr = expr
166 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
167 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
168 not be *applied* to anything.
170 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
173 f = inline_me (coerce t fw)
174 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
175 We want the split, so that the coerces can cancel at the call site.
177 However, we can get left with tiresome type applications. Notably, consider
178 f = /\ a -> let t = e in (t, w)
179 Then lifting the let out of the big lambda gives
181 f = /\ a -> let t = inline_me (t' a) in (t, w)
182 The inline_me is to stop the simplifier inlining t' right back
183 into t's RHS. In the next phase we'll substitute for t (since
184 its rhs is trivial) and *then* we could get rid of the inline_me.
185 But it hardly seems worth it, so I don't bother.
188 mkInlineMe (Var v) = Var v
189 mkInlineMe e = Note InlineMe e
195 mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr
197 mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
198 = ASSERT( from_ty `eqType` to_ty2 )
199 mkCoerce to_ty from_ty2 expr
201 mkCoerce to_ty from_ty expr
202 | to_ty `eqType` from_ty = expr
203 | otherwise = ASSERT( from_ty `eqType` exprType expr )
204 Note (Coerce to_ty from_ty) expr
208 mkSCC :: CostCentre -> Expr b -> Expr b
209 -- Note: Nested SCC's *are* preserved for the benefit of
210 -- cost centre stack profiling
211 mkSCC cc (Lit lit) = Lit lit
212 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
213 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
214 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
215 mkSCC cc expr = Note (SCC cc) expr
219 %************************************************************************
221 \subsection{Other expression construction}
223 %************************************************************************
226 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
227 -- (bindNonRec x r b) produces either
230 -- case r of x { _DEFAULT_ -> b }
232 -- depending on whether x is unlifted or not
233 -- It's used by the desugarer to avoid building bindings
234 -- that give Core Lint a heart attack. Actually the simplifier
235 -- deals with them perfectly well.
236 bindNonRec bndr rhs body
237 | needsCaseBinding (idType bndr) rhs = Case rhs bndr [(DEFAULT,[],body)]
238 | otherwise = Let (NonRec bndr rhs) body
240 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
241 -- Make a case expression instead of a let
242 -- These can arise either from the desugarer,
243 -- or from beta reductions: (\x.e) (x +# y)
247 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
248 -- This guy constructs the value that the scrutinee must have
249 -- when you are in one particular branch of a case
250 mkAltExpr (DataAlt con) args inst_tys
251 = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
252 mkAltExpr (LitAlt lit) [] []
255 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
256 mkIfThenElse guard then_expr else_expr
257 = Case guard (mkWildId boolTy)
258 [ (DataAlt trueDataCon, [], then_expr),
259 (DataAlt falseDataCon, [], else_expr) ]
263 %************************************************************************
265 \subsection{Taking expressions apart}
267 %************************************************************************
269 The default alternative must be first, if it exists at all.
270 This makes it easy to find, though it makes matching marginally harder.
273 hasDefault :: [CoreAlt] -> Bool
274 hasDefault ((DEFAULT,_,_) : alts) = True
277 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
278 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
279 findDefault alts = (alts, Nothing)
281 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
284 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
285 other -> go alts panic_deflt
288 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
291 go (alt@(con1,_,_) : alts) deflt | con == con1 = alt
292 | otherwise = ASSERT( not (con1 == DEFAULT) )
297 %************************************************************************
299 \subsection{Figuring out things about expressions}
301 %************************************************************************
303 @exprIsTrivial@ is true of expressions we are unconditionally happy to
304 duplicate; simple variables and constants, and type
305 applications. Note that primop Ids aren't considered
308 @exprIsBottom@ is true of expressions that are guaranteed to diverge
311 There used to be a gruesome test for (hasNoBinding v) in the
313 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
314 The idea here is that a constructor worker, like $wJust, is
315 really short for (\x -> $wJust x), becuase $wJust has no binding.
316 So it should be treated like a lambda. Ditto unsaturated primops.
317 But now constructor workers are not "have-no-binding" Ids. And
318 completely un-applied primops and foreign-call Ids are sufficiently
319 rare that I plan to allow them to be duplicated and put up with
323 exprIsTrivial (Var v) = True -- See notes above
324 exprIsTrivial (Type _) = True
325 exprIsTrivial (Lit lit) = True
326 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
327 exprIsTrivial (Note _ e) = exprIsTrivial e
328 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
329 exprIsTrivial other = False
331 exprIsAtom :: CoreExpr -> Bool
332 -- Used to decide whether to let-binding an STG argument
333 -- when compiling to ILX => type applications are not allowed
334 exprIsAtom (Var v) = True -- primOpIsDupable?
335 exprIsAtom (Lit lit) = True
336 exprIsAtom (Type ty) = True
337 exprIsAtom (Note (SCC _) e) = False
338 exprIsAtom (Note _ e) = exprIsAtom e
339 exprIsAtom other = False
343 @exprIsDupable@ is true of expressions that can be duplicated at a modest
344 cost in code size. This will only happen in different case
345 branches, so there's no issue about duplicating work.
347 That is, exprIsDupable returns True of (f x) even if
348 f is very very expensive to call.
350 Its only purpose is to avoid fruitless let-binding
351 and then inlining of case join points
355 exprIsDupable (Type _) = True
356 exprIsDupable (Var v) = True
357 exprIsDupable (Lit lit) = litIsDupable lit
358 exprIsDupable (Note InlineMe e) = True
359 exprIsDupable (Note _ e) = exprIsDupable e
363 go (Var v) n_args = True
364 go (App f a) n_args = n_args < dupAppSize
367 go other n_args = False
370 dupAppSize = 4 -- Size of application we are prepared to duplicate
373 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
374 it is obviously in weak head normal form, or is cheap to get to WHNF.
375 [Note that that's not the same as exprIsDupable; an expression might be
376 big, and hence not dupable, but still cheap.]
378 By ``cheap'' we mean a computation we're willing to:
379 push inside a lambda, or
380 inline at more than one place
381 That might mean it gets evaluated more than once, instead of being
382 shared. The main examples of things which aren't WHNF but are
387 (where e, and all the ei are cheap)
390 (where e and b are cheap)
393 (where op is a cheap primitive operator)
396 (because we are happy to substitute it inside a lambda)
398 Notice that a variable is considered 'cheap': we can push it inside a lambda,
399 because sharing will make sure it is only evaluated once.
402 exprIsCheap :: CoreExpr -> Bool
403 exprIsCheap (Lit lit) = True
404 exprIsCheap (Type _) = True
405 exprIsCheap (Var _) = True
406 exprIsCheap (Note InlineMe e) = True
407 exprIsCheap (Note _ e) = exprIsCheap e
408 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
409 exprIsCheap (Case e _ alts) = exprIsCheap e &&
410 and [exprIsCheap rhs | (_,_,rhs) <- alts]
411 -- Experimentally, treat (case x of ...) as cheap
412 -- (and case __coerce x etc.)
413 -- This improves arities of overloaded functions where
414 -- there is only dictionary selection (no construction) involved
415 exprIsCheap (Let (NonRec x _) e)
416 | isUnLiftedType (idType x) = exprIsCheap e
418 -- strict lets always have cheap right hand sides, and
421 exprIsCheap other_expr
422 = go other_expr 0 True
424 go (Var f) n_args args_cheap
425 = (idAppIsCheap f n_args && args_cheap)
426 -- A constructor, cheap primop, or partial application
428 || idAppIsBottom f n_args
429 -- Application of a function which
430 -- always gives bottom; we treat this as cheap
431 -- because it certainly doesn't need to be shared!
433 go (App f a) n_args args_cheap
434 | not (isRuntimeArg a) = go f n_args args_cheap
435 | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
437 go other n_args args_cheap = False
439 idAppIsCheap :: Id -> Int -> Bool
440 idAppIsCheap id n_val_args
441 | n_val_args == 0 = True -- Just a type application of
442 -- a variable (f t1 t2 t3)
444 | otherwise = case globalIdDetails id of
446 RecordSelId _ -> True -- I'm experimenting with making record selection
447 -- look cheap, so we will substitute it inside a
448 -- lambda. Particularly for dictionary field selection
450 PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
451 -- that return a type variable, since the result
452 -- might be applied to something, but I'm not going
453 -- to bother to check the number of args
454 other -> n_val_args < idArity id
457 exprOkForSpeculation returns True of an expression that it is
459 * safe to evaluate even if normal order eval might not
460 evaluate the expression at all, or
462 * safe *not* to evaluate even if normal order would do so
466 the expression guarantees to terminate,
468 without raising an exception,
469 without causing a side effect (e.g. writing a mutable variable)
472 let x = case y# +# 1# of { r# -> I# r# }
475 case y# +# 1# of { r# ->
480 We can only do this if the (y+1) is ok for speculation: it has no
481 side effects, and can't diverge or raise an exception.
484 exprOkForSpeculation :: CoreExpr -> Bool
485 exprOkForSpeculation (Lit _) = True
486 exprOkForSpeculation (Type _) = True
487 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
488 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
489 exprOkForSpeculation other_expr
490 = case collectArgs other_expr of
491 (Var f, args) -> spec_ok (globalIdDetails f) args
495 spec_ok (DataConId _) args
496 = True -- The strictness of the constructor has already
497 -- been expressed by its "wrapper", so we don't need
498 -- to take the arguments into account
500 spec_ok (PrimOpId op) args
501 | isDivOp op, -- Special case for dividing operations that fail
502 [arg1, Lit lit] <- args -- only if the divisor is zero
503 = not (isZeroLit lit) && exprOkForSpeculation arg1
504 -- Often there is a literal divisor, and this
505 -- can get rid of a thunk in an inner looop
508 = primOpOkForSpeculation op &&
509 all exprOkForSpeculation args
510 -- A bit conservative: we don't really need
511 -- to care about lazy arguments, but this is easy
513 spec_ok other args = False
515 isDivOp :: PrimOp -> Bool
516 -- True of dyadic operators that can fail
517 -- only if the second arg is zero
518 -- This function probably belongs in PrimOp, or even in
519 -- an automagically generated file.. but it's such a
520 -- special case I thought I'd leave it here for now.
521 isDivOp IntQuotOp = True
522 isDivOp IntRemOp = True
523 isDivOp WordQuotOp = True
524 isDivOp WordRemOp = True
525 isDivOp IntegerQuotRemOp = True
526 isDivOp IntegerDivModOp = True
527 isDivOp FloatDivOp = True
528 isDivOp DoubleDivOp = True
529 isDivOp other = False
534 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
535 exprIsBottom e = go 0 e
537 -- n is the number of args
538 go n (Note _ e) = go n e
539 go n (Let _ e) = go n e
540 go n (Case e _ _) = go 0 e -- Just check the scrut
541 go n (App e _) = go (n+1) e
542 go n (Var v) = idAppIsBottom v n
544 go n (Lam _ _) = False
546 idAppIsBottom :: Id -> Int -> Bool
547 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
550 @exprIsValue@ returns true for expressions that are certainly *already*
551 evaluated to *head* normal form. This is used to decide whether it's ok
554 case x of _ -> e ===> e
556 and to decide whether it's safe to discard a `seq`
558 So, it does *not* treat variables as evaluated, unless they say they are.
560 But it *does* treat partial applications and constructor applications
561 as values, even if their arguments are non-trivial, provided the argument
563 e.g. (:) (f x) (map f xs) is a value
564 map (...redex...) is a value
565 Because `seq` on such things completes immediately
567 For unlifted argument types, we have to be careful:
569 Suppose (f x) diverges; then C (f x) is not a value. True, but
570 this form is illegal (see the invariants in CoreSyn). Args of unboxed
571 type must be ok-for-speculation (or trivial).
574 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
575 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
577 exprIsValue (Lit l) = True
578 exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
579 exprIsValue (Note _ e) = exprIsValue e
580 exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v)
581 -- The idArity case catches data cons and primops that
582 -- don't have unfoldings
583 -- A worry: what if an Id's unfolding is just itself:
584 -- then we could get an infinite loop...
585 exprIsValue other_expr
586 | (Var fun, args) <- collectArgs other_expr,
587 isDataConId fun || valArgCount args < idArity fun
588 = check (idType fun) args
592 -- 'check' checks that unlifted-type args are in
593 -- fact guaranteed non-divergent
594 check fun_ty [] = True
595 check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
596 Just (_, ty) -> check ty args
597 check fun_ty (arg : args)
598 | isUnLiftedType arg_ty = exprOkForSpeculation arg
599 | otherwise = check res_ty args
601 (arg_ty, res_ty) = splitFunTy fun_ty
605 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
606 exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
607 = -- Maybe this is over the top, but here we try to turn
608 -- coerce (S,T) ( x, y )
610 -- ( coerce S x, coerce T y )
611 -- This happens in anger in PrelArrExts which has a coerce
612 -- case coerce memcpy a b of
614 -- where the memcpy is in the IO monad, but the call is in
616 case exprIsConApp_maybe expr of {
620 case splitTyConApp_maybe to_ty of {
622 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
623 | isExistentialDataCon dc -> Nothing
625 -- Type constructor must match
626 -- We knock out existentials to keep matters simple(r)
628 arity = tyConArity tc
629 val_args = drop arity args
630 to_arg_tys = dataConArgTys dc tc_arg_tys
631 mk_coerce ty arg = mkCoerce ty (exprType arg) arg
632 new_val_args = zipWith mk_coerce to_arg_tys val_args
634 ASSERT( all isTypeArg (take arity args) )
635 ASSERT( equalLength val_args to_arg_tys )
636 Just (dc, map Type tc_arg_tys ++ new_val_args)
639 exprIsConApp_maybe (Note _ expr)
640 = exprIsConApp_maybe expr
641 -- We ignore InlineMe notes in case we have
642 -- x = __inline_me__ (a,b)
643 -- All part of making sure that INLINE pragmas never hurt
644 -- Marcin tripped on this one when making dictionaries more inlinable
646 -- In fact, we ignore all notes. For example,
647 -- case _scc_ "foo" (C a b) of
649 -- should be optimised away, but it will be only if we look
650 -- through the SCC note.
652 exprIsConApp_maybe expr = analyse (collectArgs expr)
654 analyse (Var fun, args)
655 | Just con <- isDataConId_maybe fun,
656 args `lengthAtLeast` dataConRepArity con
657 -- Might be > because the arity excludes type args
660 -- Look through unfoldings, but only cheap ones, because
661 -- we are effectively duplicating the unfolding
662 analyse (Var fun, [])
663 | let unf = idUnfolding fun,
665 = exprIsConApp_maybe (unfoldingTemplate unf)
667 analyse other = Nothing
672 %************************************************************************
674 \subsection{Eta reduction and expansion}
676 %************************************************************************
679 exprEtaExpandArity :: CoreExpr -> Arity
680 -- The Int is number of value args the thing can be
681 -- applied to without doing much work
683 -- This is used when eta expanding
684 -- e ==> \xy -> e x y
686 -- It returns 1 (or more) to:
687 -- case x of p -> \s -> ...
688 -- because for I/O ish things we really want to get that \s to the top.
689 -- We are prepared to evaluate x each time round the loop in order to get that
691 -- It's all a bit more subtle than it looks. Consider one-shot lambdas
692 -- let x = expensive in \y z -> E
693 -- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
694 -- Hence the ArityType returned by arityType
696 -- NB: this is particularly important/useful for IO state
697 -- transformers, where we often get
698 -- let x = E in \ s -> ...
699 -- and the \s is a real-world state token abstraction. Such
700 -- abstractions are almost invariably 1-shot, so we want to
701 -- pull the \s out, past the let x=E.
702 -- The hack is in Id.isOneShotLambda
705 -- f = \x -> error "foo"
706 -- Here, arity 1 is fine. But if it is
707 -- f = \x -> case e of
708 -- True -> error "foo"
709 -- False -> \y -> x+y
710 -- then we want to get arity 2.
711 -- Hence the ABot/ATop in ArityType
714 exprEtaExpandArity e = arityDepth (arityType e)
716 -- A limited sort of function type
717 data ArityType = AFun Bool ArityType -- True <=> one-shot
718 | ATop -- Know nothing
721 arityDepth :: ArityType -> Arity
722 arityDepth (AFun _ ty) = 1 + arityDepth ty
725 andArityType ABot at2 = at2
726 andArityType ATop at2 = ATop
727 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
728 andArityType at1 at2 = andArityType at2 at1
730 arityType :: CoreExpr -> ArityType
731 -- (go1 e) = [b1,..,bn]
732 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
733 -- where bi is True <=> the lambda is one-shot
735 arityType (Note n e) = arityType e
736 -- Not needed any more: etaExpand is cleverer
737 -- | ok_note n = arityType e
738 -- | otherwise = ATop
743 mk :: Arity -> ArityType
744 mk 0 | isBottomingId v = ABot
746 mk n = AFun False (mk (n-1))
748 -- When the type of the Id encodes one-shot-ness,
749 -- use the idinfo here
751 -- Lambdas; increase arity
752 arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e)
753 | otherwise = arityType e
755 -- Applications; decrease arity
756 arityType (App f (Type _)) = arityType f
757 arityType (App f a) = case arityType f of
758 AFun one_shot xs | one_shot -> xs
759 | exprIsCheap a -> xs
762 -- Case/Let; keep arity if either the expression is cheap
763 -- or it's a 1-shot lambda
764 arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
765 xs@(AFun one_shot _) | one_shot -> xs
766 xs | exprIsCheap scrut -> xs
769 arityType (Let b e) = case arityType e of
770 xs@(AFun one_shot _) | one_shot -> xs
771 xs | all exprIsCheap (rhssOfBind b) -> xs
774 arityType other = ATop
776 {- NOT NEEDED ANY MORE: etaExpand is cleverer
777 ok_note InlineMe = False
779 -- Notice that we do not look through __inline_me__
780 -- This may seem surprising, but consider
781 -- f = _inline_me (\x -> e)
782 -- We DO NOT want to eta expand this to
783 -- f = \x -> (_inline_me (\x -> e)) x
784 -- because the _inline_me gets dropped now it is applied,
793 etaExpand :: Arity -- Result should have this number of value args
795 -> CoreExpr -> Type -- Expression and its type
797 -- (etaExpand n us e ty) returns an expression with
798 -- the same meaning as 'e', but with arity 'n'.
800 -- Given e' = etaExpand n us e ty
802 -- ty = exprType e = exprType e'
804 etaExpand n us expr ty
805 | manifestArity expr >= n = expr -- The no-op case
806 | otherwise = eta_expand n us expr ty
809 -- manifestArity sees how many leading value lambdas there are
810 manifestArity :: CoreExpr -> Arity
811 manifestArity (Lam v e) | isId v = 1 + manifestArity e
812 | otherwise = manifestArity e
813 manifestArity (Note _ e) = manifestArity e
816 -- etaExpand deals with for-alls. For example:
818 -- where E :: forall a. a -> a
820 -- (/\b. \y::a -> E b y)
822 -- It deals with coerces too, though they are now rare
823 -- so perhaps the extra code isn't worth it
825 eta_expand n us expr ty
827 -- The ILX code generator requires eta expansion for type arguments
828 -- too, but alas the 'n' doesn't tell us how many of them there
829 -- may be. So we eagerly eta expand any big lambdas, and just
830 -- cross our fingers about possible loss of sharing in the
832 -- The Right Thing is probably to make 'arity' include
833 -- type variables throughout the compiler. (ToDo.)
835 -- Saturated, so nothing to do
838 eta_expand n us (Note note@(Coerce _ ty) e) _
839 = Note note (eta_expand n us e ty)
841 -- Use mkNote so that _scc_s get pushed inside any lambdas that
842 -- are generated as part of the eta expansion. We rely on this
843 -- behaviour in CorePrep, when we eta expand an already-prepped RHS.
844 eta_expand n us (Note note e) ty
845 = mkNote note (eta_expand n us e ty)
847 -- Short cut for the case where there already
848 -- is a lambda; no point in gratuitously adding more
849 eta_expand n us (Lam v body) ty
851 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
854 = Lam v (eta_expand (n-1) us body (funResultTy ty))
856 eta_expand n us expr ty
857 = case splitForAllTy_maybe ty of {
858 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
862 case splitFunTy_maybe ty of {
863 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
865 arg1 = mkSysLocal SLIT("eta") uniq arg_ty
870 case splitNewType_maybe ty of {
871 Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ;
872 Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
876 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
877 It tells how many things the expression can be applied to before doing
878 any work. It doesn't look inside cases, lets, etc. The idea is that
879 exprEtaExpandArity will do the hard work, leaving something that's easy
880 for exprArity to grapple with. In particular, Simplify uses exprArity to
881 compute the ArityInfo for the Id.
883 Originally I thought that it was enough just to look for top-level lambdas, but
884 it isn't. I've seen this
886 foo = PrelBase.timesInt
888 We want foo to get arity 2 even though the eta-expander will leave it
889 unchanged, in the expectation that it'll be inlined. But occasionally it
890 isn't, because foo is blacklisted (used in a rule).
892 Similarly, see the ok_note check in exprEtaExpandArity. So
893 f = __inline_me (\x -> e)
894 won't be eta-expanded.
896 And in any case it seems more robust to have exprArity be a bit more intelligent.
897 But note that (\x y z -> f x y z)
898 should have arity 3, regardless of f's arity.
901 exprArity :: CoreExpr -> Arity
904 go (Var v) = idArity v
905 go (Lam x e) | isId x = go e + 1
908 go (App e (Type t)) = go e
909 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
910 -- NB: exprIsCheap a!
911 -- f (fac x) does not have arity 2,
912 -- even if f has arity 3!
913 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
914 -- unknown, hence arity 0
919 %************************************************************************
921 \subsection{Equality}
923 %************************************************************************
925 @cheapEqExpr@ is a cheap equality test which bales out fast!
926 True => definitely equal
927 False => may or may not be equal
930 cheapEqExpr :: Expr b -> Expr b -> Bool
932 cheapEqExpr (Var v1) (Var v2) = v1==v2
933 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
934 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
936 cheapEqExpr (App f1 a1) (App f2 a2)
937 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
939 cheapEqExpr _ _ = False
941 exprIsBig :: Expr b -> Bool
942 -- Returns True of expressions that are too big to be compared by cheapEqExpr
943 exprIsBig (Lit _) = False
944 exprIsBig (Var v) = False
945 exprIsBig (Type t) = False
946 exprIsBig (App f a) = exprIsBig f || exprIsBig a
947 exprIsBig other = True
952 eqExpr :: CoreExpr -> CoreExpr -> Bool
953 -- Works ok at more general type, but only needed at CoreExpr
954 -- Used in rule matching, so when we find a type we use
955 -- eqTcType, which doesn't look through newtypes
956 -- [And it doesn't risk falling into a black hole either.]
958 = eq emptyVarEnv e1 e2
960 -- The "env" maps variables in e1 to variables in ty2
961 -- So when comparing lambdas etc,
962 -- we in effect substitute v2 for v1 in e1 before continuing
963 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
964 Just v1' -> v1' == v2
967 eq env (Lit lit1) (Lit lit2) = lit1 == lit2
968 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
969 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
970 eq env (Let (NonRec v1 r1) e1)
971 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
972 eq env (Let (Rec ps1) e1)
973 (Let (Rec ps2) e2) = equalLength ps1 ps2 &&
974 and (zipWith eq_rhs ps1 ps2) &&
977 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
978 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
979 eq env (Case e1 v1 a1)
980 (Case e2 v2 a2) = eq env e1 e2 &&
982 and (zipWith (eq_alt env') a1 a2)
984 env' = extendVarEnv env v1 v2
986 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
987 eq env (Type t1) (Type t2) = t1 `eqType` t2
990 eq_list env [] [] = True
991 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
992 eq_list env es1 es2 = False
994 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
995 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
997 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
998 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2
999 eq_note env InlineCall InlineCall = True
1000 eq_note env other1 other2 = False
1004 %************************************************************************
1006 \subsection{The size of an expression}
1008 %************************************************************************
1011 coreBindsSize :: [CoreBind] -> Int
1012 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1014 exprSize :: CoreExpr -> Int
1015 -- A measure of the size of the expressions
1016 -- It also forces the expression pretty drastically as a side effect
1017 exprSize (Var v) = varSize v
1018 exprSize (Lit lit) = lit `seq` 1
1019 exprSize (App f a) = exprSize f + exprSize a
1020 exprSize (Lam b e) = varSize b + exprSize e
1021 exprSize (Let b e) = bindSize b + exprSize e
1022 exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
1023 exprSize (Note n e) = noteSize n + exprSize e
1024 exprSize (Type t) = seqType t `seq` 1
1026 noteSize (SCC cc) = cc `seq` 1
1027 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
1028 noteSize InlineCall = 1
1029 noteSize InlineMe = 1
1031 varSize :: Var -> Int
1032 varSize b | isTyVar b = 1
1033 | otherwise = seqType (idType b) `seq`
1034 megaSeqIdInfo (idInfo b) `seq`
1037 varsSize = foldr ((+) . varSize) 0
1039 bindSize (NonRec b e) = varSize b + exprSize e
1040 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1042 pairSize (b,e) = varSize b + exprSize e
1044 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1048 %************************************************************************
1050 \subsection{Hashing}
1052 %************************************************************************
1055 hashExpr :: CoreExpr -> Int
1056 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1059 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1061 hash_expr (Note _ e) = hash_expr e
1062 hash_expr (Let (NonRec b r) e) = hashId b
1063 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1064 hash_expr (Case _ b _) = hashId b
1065 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1066 hash_expr (Var v) = hashId v
1067 hash_expr (Lit lit) = hashLiteral lit
1068 hash_expr (Lam b _) = hashId b
1069 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1071 fast_hash_expr (Var v) = hashId v
1072 fast_hash_expr (Lit lit) = hashLiteral lit
1073 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1074 fast_hash_expr (App f a) = fast_hash_expr a
1075 fast_hash_expr (Lam b _) = hashId b
1076 fast_hash_expr other = 1
1079 hashId id = hashName (idName id)