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, mkPiTypes,
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, 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
109 mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
111 mkPiTypes vs ty = foldr mkPiType ty vs
114 | isId v = mkFunTy (idType v) ty
115 | otherwise = mkForAllTy v ty
119 applyTypeToArg :: Type -> CoreExpr -> Type
120 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
121 applyTypeToArg fun_ty other_arg = funResultTy fun_ty
123 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
124 -- A more efficient version of applyTypeToArg
125 -- when we have several args
126 -- The first argument is just for debugging
127 applyTypeToArgs e op_ty [] = op_ty
129 applyTypeToArgs e op_ty (Type ty : args)
130 = -- Accumulate type arguments so we can instantiate all at once
133 go rev_tys (Type ty : args) = go (ty:rev_tys) args
134 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
136 op_ty' = applyTys op_ty (reverse rev_tys)
138 applyTypeToArgs e op_ty (other_arg : args)
139 = case (splitFunTy_maybe op_ty) of
140 Just (_, res_ty) -> applyTypeToArgs e res_ty args
141 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
146 %************************************************************************
148 \subsection{Attaching notes}
150 %************************************************************************
152 mkNote removes redundant coercions, and SCCs where possible
155 mkNote :: Note -> CoreExpr -> CoreExpr
156 mkNote (Coerce to_ty from_ty) expr = mkCoerce to_ty from_ty expr
157 mkNote (SCC cc) expr = mkSCC cc expr
158 mkNote InlineMe expr = mkInlineMe expr
159 mkNote note expr = Note note expr
161 -- Slide InlineCall in around the function
162 -- No longer necessary I think (SLPJ Apr 99)
163 -- mkNote InlineCall (App f a) = App (mkNote InlineCall f) a
164 -- mkNote InlineCall (Var v) = Note InlineCall (Var v)
165 -- mkNote InlineCall expr = expr
168 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
169 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
170 not be *applied* to anything.
172 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
175 f = inline_me (coerce t fw)
176 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
177 We want the split, so that the coerces can cancel at the call site.
179 However, we can get left with tiresome type applications. Notably, consider
180 f = /\ a -> let t = e in (t, w)
181 Then lifting the let out of the big lambda gives
183 f = /\ a -> let t = inline_me (t' a) in (t, w)
184 The inline_me is to stop the simplifier inlining t' right back
185 into t's RHS. In the next phase we'll substitute for t (since
186 its rhs is trivial) and *then* we could get rid of the inline_me.
187 But it hardly seems worth it, so I don't bother.
190 mkInlineMe (Var v) = Var v
191 mkInlineMe e = Note InlineMe e
197 mkCoerce :: Type -> Type -> CoreExpr -> CoreExpr
199 mkCoerce to_ty from_ty (Note (Coerce to_ty2 from_ty2) expr)
200 = ASSERT( from_ty `eqType` to_ty2 )
201 mkCoerce to_ty from_ty2 expr
203 mkCoerce to_ty from_ty expr
204 | to_ty `eqType` from_ty = expr
205 | otherwise = ASSERT( from_ty `eqType` exprType expr )
206 Note (Coerce to_ty from_ty) expr
210 mkSCC :: CostCentre -> Expr b -> Expr b
211 -- Note: Nested SCC's *are* preserved for the benefit of
212 -- cost centre stack profiling
213 mkSCC cc (Lit lit) = Lit lit
214 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
215 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
216 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
217 mkSCC cc expr = Note (SCC cc) expr
221 %************************************************************************
223 \subsection{Other expression construction}
225 %************************************************************************
228 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
229 -- (bindNonRec x r b) produces either
232 -- case r of x { _DEFAULT_ -> b }
234 -- depending on whether x is unlifted or not
235 -- It's used by the desugarer to avoid building bindings
236 -- that give Core Lint a heart attack. Actually the simplifier
237 -- deals with them perfectly well.
238 bindNonRec bndr rhs body
239 | needsCaseBinding (idType bndr) rhs = Case rhs bndr [(DEFAULT,[],body)]
240 | otherwise = Let (NonRec bndr rhs) body
242 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
243 -- Make a case expression instead of a let
244 -- These can arise either from the desugarer,
245 -- or from beta reductions: (\x.e) (x +# y)
249 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
250 -- This guy constructs the value that the scrutinee must have
251 -- when you are in one particular branch of a case
252 mkAltExpr (DataAlt con) args inst_tys
253 = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
254 mkAltExpr (LitAlt lit) [] []
257 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
258 mkIfThenElse guard then_expr else_expr
259 = Case guard (mkWildId boolTy)
260 [ (DataAlt trueDataCon, [], then_expr),
261 (DataAlt falseDataCon, [], else_expr) ]
265 %************************************************************************
267 \subsection{Taking expressions apart}
269 %************************************************************************
271 The default alternative must be first, if it exists at all.
272 This makes it easy to find, though it makes matching marginally harder.
275 hasDefault :: [CoreAlt] -> Bool
276 hasDefault ((DEFAULT,_,_) : alts) = True
279 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
280 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
281 findDefault alts = (alts, Nothing)
283 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
286 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
287 other -> go alts panic_deflt
290 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
293 go (alt@(con1,_,_) : alts) deflt | con == con1 = alt
294 | otherwise = ASSERT( not (con1 == DEFAULT) )
299 %************************************************************************
301 \subsection{Figuring out things about expressions}
303 %************************************************************************
305 @exprIsTrivial@ is true of expressions we are unconditionally happy to
306 duplicate; simple variables and constants, and type
307 applications. Note that primop Ids aren't considered
310 @exprIsBottom@ is true of expressions that are guaranteed to diverge
313 There used to be a gruesome test for (hasNoBinding v) in the
315 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
316 The idea here is that a constructor worker, like $wJust, is
317 really short for (\x -> $wJust x), becuase $wJust has no binding.
318 So it should be treated like a lambda. Ditto unsaturated primops.
319 But now constructor workers are not "have-no-binding" Ids. And
320 completely un-applied primops and foreign-call Ids are sufficiently
321 rare that I plan to allow them to be duplicated and put up with
325 exprIsTrivial (Var v) = True -- See notes above
326 exprIsTrivial (Type _) = True
327 exprIsTrivial (Lit lit) = True
328 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
329 exprIsTrivial (Note _ e) = exprIsTrivial e
330 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
331 exprIsTrivial other = False
333 exprIsAtom :: CoreExpr -> Bool
334 -- Used to decide whether to let-binding an STG argument
335 -- when compiling to ILX => type applications are not allowed
336 exprIsAtom (Var v) = True -- primOpIsDupable?
337 exprIsAtom (Lit lit) = True
338 exprIsAtom (Type ty) = True
339 exprIsAtom (Note (SCC _) e) = False
340 exprIsAtom (Note _ e) = exprIsAtom e
341 exprIsAtom other = False
345 @exprIsDupable@ is true of expressions that can be duplicated at a modest
346 cost in code size. This will only happen in different case
347 branches, so there's no issue about duplicating work.
349 That is, exprIsDupable returns True of (f x) even if
350 f is very very expensive to call.
352 Its only purpose is to avoid fruitless let-binding
353 and then inlining of case join points
357 exprIsDupable (Type _) = True
358 exprIsDupable (Var v) = True
359 exprIsDupable (Lit lit) = litIsDupable lit
360 exprIsDupable (Note InlineMe e) = True
361 exprIsDupable (Note _ e) = exprIsDupable e
365 go (Var v) n_args = True
366 go (App f a) n_args = n_args < dupAppSize
369 go other n_args = False
372 dupAppSize = 4 -- Size of application we are prepared to duplicate
375 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
376 it is obviously in weak head normal form, or is cheap to get to WHNF.
377 [Note that that's not the same as exprIsDupable; an expression might be
378 big, and hence not dupable, but still cheap.]
380 By ``cheap'' we mean a computation we're willing to:
381 push inside a lambda, or
382 inline at more than one place
383 That might mean it gets evaluated more than once, instead of being
384 shared. The main examples of things which aren't WHNF but are
389 (where e, and all the ei are cheap)
392 (where e and b are cheap)
395 (where op is a cheap primitive operator)
398 (because we are happy to substitute it inside a lambda)
400 Notice that a variable is considered 'cheap': we can push it inside a lambda,
401 because sharing will make sure it is only evaluated once.
404 exprIsCheap :: CoreExpr -> Bool
405 exprIsCheap (Lit lit) = True
406 exprIsCheap (Type _) = True
407 exprIsCheap (Var _) = True
408 exprIsCheap (Note InlineMe e) = True
409 exprIsCheap (Note _ e) = exprIsCheap e
410 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
411 exprIsCheap (Case e _ alts) = exprIsCheap e &&
412 and [exprIsCheap rhs | (_,_,rhs) <- alts]
413 -- Experimentally, treat (case x of ...) as cheap
414 -- (and case __coerce x etc.)
415 -- This improves arities of overloaded functions where
416 -- there is only dictionary selection (no construction) involved
417 exprIsCheap (Let (NonRec x _) e)
418 | isUnLiftedType (idType x) = exprIsCheap e
420 -- strict lets always have cheap right hand sides, and
423 exprIsCheap other_expr
424 = go other_expr 0 True
426 go (Var f) n_args args_cheap
427 = (idAppIsCheap f n_args && args_cheap)
428 -- A constructor, cheap primop, or partial application
430 || idAppIsBottom f n_args
431 -- Application of a function which
432 -- always gives bottom; we treat this as cheap
433 -- because it certainly doesn't need to be shared!
435 go (App f a) n_args args_cheap
436 | not (isRuntimeArg a) = go f n_args args_cheap
437 | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
439 go other n_args args_cheap = False
441 idAppIsCheap :: Id -> Int -> Bool
442 idAppIsCheap id n_val_args
443 | n_val_args == 0 = True -- Just a type application of
444 -- a variable (f t1 t2 t3)
446 | otherwise = case globalIdDetails id of
448 RecordSelId _ -> True -- I'm experimenting with making record selection
449 -- look cheap, so we will substitute it inside a
450 -- lambda. Particularly for dictionary field selection
452 PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
453 -- that return a type variable, since the result
454 -- might be applied to something, but I'm not going
455 -- to bother to check the number of args
456 other -> n_val_args < idArity id
459 exprOkForSpeculation returns True of an expression that it is
461 * safe to evaluate even if normal order eval might not
462 evaluate the expression at all, or
464 * safe *not* to evaluate even if normal order would do so
468 the expression guarantees to terminate,
470 without raising an exception,
471 without causing a side effect (e.g. writing a mutable variable)
474 let x = case y# +# 1# of { r# -> I# r# }
477 case y# +# 1# of { r# ->
482 We can only do this if the (y+1) is ok for speculation: it has no
483 side effects, and can't diverge or raise an exception.
486 exprOkForSpeculation :: CoreExpr -> Bool
487 exprOkForSpeculation (Lit _) = True
488 exprOkForSpeculation (Type _) = True
489 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
490 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
491 exprOkForSpeculation other_expr
492 = case collectArgs other_expr of
493 (Var f, args) -> spec_ok (globalIdDetails f) args
497 spec_ok (DataConId _) args
498 = True -- The strictness of the constructor has already
499 -- been expressed by its "wrapper", so we don't need
500 -- to take the arguments into account
502 spec_ok (PrimOpId op) args
503 | isDivOp op, -- Special case for dividing operations that fail
504 [arg1, Lit lit] <- args -- only if the divisor is zero
505 = not (isZeroLit lit) && exprOkForSpeculation arg1
506 -- Often there is a literal divisor, and this
507 -- can get rid of a thunk in an inner looop
510 = primOpOkForSpeculation op &&
511 all exprOkForSpeculation args
512 -- A bit conservative: we don't really need
513 -- to care about lazy arguments, but this is easy
515 spec_ok other args = False
517 isDivOp :: PrimOp -> Bool
518 -- True of dyadic operators that can fail
519 -- only if the second arg is zero
520 -- This function probably belongs in PrimOp, or even in
521 -- an automagically generated file.. but it's such a
522 -- special case I thought I'd leave it here for now.
523 isDivOp IntQuotOp = True
524 isDivOp IntRemOp = True
525 isDivOp WordQuotOp = True
526 isDivOp WordRemOp = True
527 isDivOp IntegerQuotRemOp = True
528 isDivOp IntegerDivModOp = True
529 isDivOp FloatDivOp = True
530 isDivOp DoubleDivOp = True
531 isDivOp other = False
536 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
537 exprIsBottom e = go 0 e
539 -- n is the number of args
540 go n (Note _ e) = go n e
541 go n (Let _ e) = go n e
542 go n (Case e _ _) = go 0 e -- Just check the scrut
543 go n (App e _) = go (n+1) e
544 go n (Var v) = idAppIsBottom v n
546 go n (Lam _ _) = False
548 idAppIsBottom :: Id -> Int -> Bool
549 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
552 @exprIsValue@ returns true for expressions that are certainly *already*
553 evaluated to *head* normal form. This is used to decide whether it's ok
556 case x of _ -> e ===> e
558 and to decide whether it's safe to discard a `seq`
560 So, it does *not* treat variables as evaluated, unless they say they are.
562 But it *does* treat partial applications and constructor applications
563 as values, even if their arguments are non-trivial, provided the argument
565 e.g. (:) (f x) (map f xs) is a value
566 map (...redex...) is a value
567 Because `seq` on such things completes immediately
569 For unlifted argument types, we have to be careful:
571 Suppose (f x) diverges; then C (f x) is not a value. True, but
572 this form is illegal (see the invariants in CoreSyn). Args of unboxed
573 type must be ok-for-speculation (or trivial).
576 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
577 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
579 exprIsValue (Lit l) = True
580 exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
581 exprIsValue (Note _ e) = exprIsValue e
582 exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v)
583 -- The idArity case catches data cons and primops that
584 -- don't have unfoldings
585 -- A worry: what if an Id's unfolding is just itself:
586 -- then we could get an infinite loop...
587 exprIsValue other_expr
588 | (Var fun, args) <- collectArgs other_expr,
589 isDataConId fun || valArgCount args < idArity fun
590 = check (idType fun) args
594 -- 'check' checks that unlifted-type args are in
595 -- fact guaranteed non-divergent
596 check fun_ty [] = True
597 check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
598 Just (_, ty) -> check ty args
599 check fun_ty (arg : args)
600 | isUnLiftedType arg_ty = exprOkForSpeculation arg
601 | otherwise = check res_ty args
603 (arg_ty, res_ty) = splitFunTy fun_ty
607 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
608 exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
609 = -- Maybe this is over the top, but here we try to turn
610 -- coerce (S,T) ( x, y )
612 -- ( coerce S x, coerce T y )
613 -- This happens in anger in PrelArrExts which has a coerce
614 -- case coerce memcpy a b of
616 -- where the memcpy is in the IO monad, but the call is in
618 case exprIsConApp_maybe expr of {
622 case splitTyConApp_maybe to_ty of {
624 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
625 | isExistentialDataCon dc -> Nothing
627 -- Type constructor must match
628 -- We knock out existentials to keep matters simple(r)
630 arity = tyConArity tc
631 val_args = drop arity args
632 to_arg_tys = dataConArgTys dc tc_arg_tys
633 mk_coerce ty arg = mkCoerce ty (exprType arg) arg
634 new_val_args = zipWith mk_coerce to_arg_tys val_args
636 ASSERT( all isTypeArg (take arity args) )
637 ASSERT( equalLength val_args to_arg_tys )
638 Just (dc, map Type tc_arg_tys ++ new_val_args)
641 exprIsConApp_maybe (Note _ expr)
642 = exprIsConApp_maybe expr
643 -- We ignore InlineMe notes in case we have
644 -- x = __inline_me__ (a,b)
645 -- All part of making sure that INLINE pragmas never hurt
646 -- Marcin tripped on this one when making dictionaries more inlinable
648 -- In fact, we ignore all notes. For example,
649 -- case _scc_ "foo" (C a b) of
651 -- should be optimised away, but it will be only if we look
652 -- through the SCC note.
654 exprIsConApp_maybe expr = analyse (collectArgs expr)
656 analyse (Var fun, args)
657 | Just con <- isDataConId_maybe fun,
658 args `lengthAtLeast` dataConRepArity con
659 -- Might be > because the arity excludes type args
662 -- Look through unfoldings, but only cheap ones, because
663 -- we are effectively duplicating the unfolding
664 analyse (Var fun, [])
665 | let unf = idUnfolding fun,
667 = exprIsConApp_maybe (unfoldingTemplate unf)
669 analyse other = Nothing
674 %************************************************************************
676 \subsection{Eta reduction and expansion}
678 %************************************************************************
681 exprEtaExpandArity :: CoreExpr -> Arity
682 -- The Int is number of value args the thing can be
683 -- applied to without doing much work
685 -- This is used when eta expanding
686 -- e ==> \xy -> e x y
688 -- It returns 1 (or more) to:
689 -- case x of p -> \s -> ...
690 -- because for I/O ish things we really want to get that \s to the top.
691 -- We are prepared to evaluate x each time round the loop in order to get that
693 -- It's all a bit more subtle than it looks. Consider one-shot lambdas
694 -- let x = expensive in \y z -> E
695 -- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
696 -- Hence the ArityType returned by arityType
698 -- NB: this is particularly important/useful for IO state
699 -- transformers, where we often get
700 -- let x = E in \ s -> ...
701 -- and the \s is a real-world state token abstraction. Such
702 -- abstractions are almost invariably 1-shot, so we want to
703 -- pull the \s out, past the let x=E.
704 -- The hack is in Id.isOneShotLambda
707 -- f = \x -> error "foo"
708 -- Here, arity 1 is fine. But if it is
709 -- f = \x -> case e of
710 -- True -> error "foo"
711 -- False -> \y -> x+y
712 -- then we want to get arity 2.
713 -- Hence the ABot/ATop in ArityType
716 exprEtaExpandArity e = arityDepth (arityType e)
718 -- A limited sort of function type
719 data ArityType = AFun Bool ArityType -- True <=> one-shot
720 | ATop -- Know nothing
723 arityDepth :: ArityType -> Arity
724 arityDepth (AFun _ ty) = 1 + arityDepth ty
727 andArityType ABot at2 = at2
728 andArityType ATop at2 = ATop
729 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
730 andArityType at1 at2 = andArityType at2 at1
732 arityType :: CoreExpr -> ArityType
733 -- (go1 e) = [b1,..,bn]
734 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
735 -- where bi is True <=> the lambda is one-shot
737 arityType (Note n e) = arityType e
738 -- Not needed any more: etaExpand is cleverer
739 -- | ok_note n = arityType e
740 -- | otherwise = ATop
745 mk :: Arity -> ArityType
746 mk 0 | isBottomingId v = ABot
748 mk n = AFun False (mk (n-1))
750 -- When the type of the Id encodes one-shot-ness,
751 -- use the idinfo here
753 -- Lambdas; increase arity
754 arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e)
755 | otherwise = arityType e
757 -- Applications; decrease arity
758 arityType (App f (Type _)) = arityType f
759 arityType (App f a) = case arityType f of
760 AFun one_shot xs | one_shot -> xs
761 | exprIsCheap a -> xs
764 -- Case/Let; keep arity if either the expression is cheap
765 -- or it's a 1-shot lambda
766 arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
767 xs@(AFun one_shot _) | one_shot -> xs
768 xs | exprIsCheap scrut -> xs
771 arityType (Let b e) = case arityType e of
772 xs@(AFun one_shot _) | one_shot -> xs
773 xs | all exprIsCheap (rhssOfBind b) -> xs
776 arityType other = ATop
778 {- NOT NEEDED ANY MORE: etaExpand is cleverer
779 ok_note InlineMe = False
781 -- Notice that we do not look through __inline_me__
782 -- This may seem surprising, but consider
783 -- f = _inline_me (\x -> e)
784 -- We DO NOT want to eta expand this to
785 -- f = \x -> (_inline_me (\x -> e)) x
786 -- because the _inline_me gets dropped now it is applied,
795 etaExpand :: Arity -- Result should have this number of value args
797 -> CoreExpr -> Type -- Expression and its type
799 -- (etaExpand n us e ty) returns an expression with
800 -- the same meaning as 'e', but with arity 'n'.
802 -- Given e' = etaExpand n us e ty
804 -- ty = exprType e = exprType e'
806 etaExpand n us expr ty
807 | manifestArity expr >= n = expr -- The no-op case
808 | otherwise = eta_expand n us expr ty
811 -- manifestArity sees how many leading value lambdas there are
812 manifestArity :: CoreExpr -> Arity
813 manifestArity (Lam v e) | isId v = 1 + manifestArity e
814 | otherwise = manifestArity e
815 manifestArity (Note _ e) = manifestArity e
818 -- etaExpand deals with for-alls. For example:
820 -- where E :: forall a. a -> a
822 -- (/\b. \y::a -> E b y)
824 -- It deals with coerces too, though they are now rare
825 -- so perhaps the extra code isn't worth it
827 eta_expand n us expr ty
829 -- The ILX code generator requires eta expansion for type arguments
830 -- too, but alas the 'n' doesn't tell us how many of them there
831 -- may be. So we eagerly eta expand any big lambdas, and just
832 -- cross our fingers about possible loss of sharing in the
834 -- The Right Thing is probably to make 'arity' include
835 -- type variables throughout the compiler. (ToDo.)
837 -- Saturated, so nothing to do
840 eta_expand n us (Note note@(Coerce _ ty) e) _
841 = Note note (eta_expand n us e ty)
843 -- Use mkNote so that _scc_s get pushed inside any lambdas that
844 -- are generated as part of the eta expansion. We rely on this
845 -- behaviour in CorePrep, when we eta expand an already-prepped RHS.
846 eta_expand n us (Note note e) ty
847 = mkNote note (eta_expand n us e ty)
849 -- Short cut for the case where there already
850 -- is a lambda; no point in gratuitously adding more
851 eta_expand n us (Lam v body) ty
853 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
856 = Lam v (eta_expand (n-1) us body (funResultTy ty))
858 eta_expand n us expr ty
859 = case splitForAllTy_maybe ty of {
860 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
864 case splitFunTy_maybe ty of {
865 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
867 arg1 = mkSysLocal SLIT("eta") uniq arg_ty
872 case splitNewType_maybe ty of {
873 Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ;
874 Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
878 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
879 It tells how many things the expression can be applied to before doing
880 any work. It doesn't look inside cases, lets, etc. The idea is that
881 exprEtaExpandArity will do the hard work, leaving something that's easy
882 for exprArity to grapple with. In particular, Simplify uses exprArity to
883 compute the ArityInfo for the Id.
885 Originally I thought that it was enough just to look for top-level lambdas, but
886 it isn't. I've seen this
888 foo = PrelBase.timesInt
890 We want foo to get arity 2 even though the eta-expander will leave it
891 unchanged, in the expectation that it'll be inlined. But occasionally it
892 isn't, because foo is blacklisted (used in a rule).
894 Similarly, see the ok_note check in exprEtaExpandArity. So
895 f = __inline_me (\x -> e)
896 won't be eta-expanded.
898 And in any case it seems more robust to have exprArity be a bit more intelligent.
899 But note that (\x y z -> f x y z)
900 should have arity 3, regardless of f's arity.
903 exprArity :: CoreExpr -> Arity
906 go (Var v) = idArity v
907 go (Lam x e) | isId x = go e + 1
910 go (App e (Type t)) = go e
911 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
912 -- NB: exprIsCheap a!
913 -- f (fac x) does not have arity 2,
914 -- even if f has arity 3!
915 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
916 -- unknown, hence arity 0
920 %************************************************************************
922 \subsection{Equality}
924 %************************************************************************
926 @cheapEqExpr@ is a cheap equality test which bales out fast!
927 True => definitely equal
928 False => may or may not be equal
931 cheapEqExpr :: Expr b -> Expr b -> Bool
933 cheapEqExpr (Var v1) (Var v2) = v1==v2
934 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
935 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
937 cheapEqExpr (App f1 a1) (App f2 a2)
938 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
940 cheapEqExpr _ _ = False
942 exprIsBig :: Expr b -> Bool
943 -- Returns True of expressions that are too big to be compared by cheapEqExpr
944 exprIsBig (Lit _) = False
945 exprIsBig (Var v) = False
946 exprIsBig (Type t) = False
947 exprIsBig (App f a) = exprIsBig f || exprIsBig a
948 exprIsBig other = True
953 eqExpr :: CoreExpr -> CoreExpr -> Bool
954 -- Works ok at more general type, but only needed at CoreExpr
955 -- Used in rule matching, so when we find a type we use
956 -- eqTcType, which doesn't look through newtypes
957 -- [And it doesn't risk falling into a black hole either.]
959 = eq emptyVarEnv e1 e2
961 -- The "env" maps variables in e1 to variables in ty2
962 -- So when comparing lambdas etc,
963 -- we in effect substitute v2 for v1 in e1 before continuing
964 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
965 Just v1' -> v1' == v2
968 eq env (Lit lit1) (Lit lit2) = lit1 == lit2
969 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
970 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
971 eq env (Let (NonRec v1 r1) e1)
972 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
973 eq env (Let (Rec ps1) e1)
974 (Let (Rec ps2) e2) = equalLength ps1 ps2 &&
975 and (zipWith eq_rhs ps1 ps2) &&
978 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
979 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
980 eq env (Case e1 v1 a1)
981 (Case e2 v2 a2) = eq env e1 e2 &&
983 and (zipWith (eq_alt env') a1 a2)
985 env' = extendVarEnv env v1 v2
987 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
988 eq env (Type t1) (Type t2) = t1 `eqType` t2
991 eq_list env [] [] = True
992 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
993 eq_list env es1 es2 = False
995 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
996 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
998 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
999 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2
1000 eq_note env InlineCall InlineCall = True
1001 eq_note env other1 other2 = False
1005 %************************************************************************
1007 \subsection{The size of an expression}
1009 %************************************************************************
1012 coreBindsSize :: [CoreBind] -> Int
1013 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1015 exprSize :: CoreExpr -> Int
1016 -- A measure of the size of the expressions
1017 -- It also forces the expression pretty drastically as a side effect
1018 exprSize (Var v) = v `seq` 1
1019 exprSize (Lit lit) = lit `seq` 1
1020 exprSize (App f a) = exprSize f + exprSize a
1021 exprSize (Lam b e) = varSize b + exprSize e
1022 exprSize (Let b e) = bindSize b + exprSize e
1023 exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
1024 exprSize (Note n e) = noteSize n + exprSize e
1025 exprSize (Type t) = seqType t `seq` 1
1027 noteSize (SCC cc) = cc `seq` 1
1028 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
1029 noteSize InlineCall = 1
1030 noteSize InlineMe = 1
1032 varSize :: Var -> Int
1033 varSize b | isTyVar b = 1
1034 | otherwise = seqType (idType b) `seq`
1035 megaSeqIdInfo (idInfo b) `seq`
1038 varsSize = foldr ((+) . varSize) 0
1040 bindSize (NonRec b e) = varSize b + exprSize e
1041 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1043 pairSize (b,e) = varSize b + exprSize e
1045 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1049 %************************************************************************
1051 \subsection{Hashing}
1053 %************************************************************************
1056 hashExpr :: CoreExpr -> Int
1057 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1060 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1062 hash_expr (Note _ e) = hash_expr e
1063 hash_expr (Let (NonRec b r) e) = hashId b
1064 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1065 hash_expr (Case _ b _) = hashId b
1066 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1067 hash_expr (Var v) = hashId v
1068 hash_expr (Lit lit) = hashLiteral lit
1069 hash_expr (Lam b _) = hashId b
1070 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1072 fast_hash_expr (Var v) = hashId v
1073 fast_hash_expr (Lit lit) = hashLiteral lit
1074 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1075 fast_hash_expr (App f a) = fast_hash_expr a
1076 fast_hash_expr (Lam b _) = hashId b
1077 fast_hash_expr other = 1
1080 hashId id = hashName (idName id)