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, 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
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 (Type _) = True
478 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
479 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
480 exprOkForSpeculation other_expr
481 = case collectArgs other_expr of
482 (Var f, args) -> spec_ok (globalIdDetails f) args
486 spec_ok (DataConId _) args
487 = True -- The strictness of the constructor has already
488 -- been expressed by its "wrapper", so we don't need
489 -- to take the arguments into account
491 spec_ok (PrimOpId op) args
492 | isDivOp op, -- Special case for dividing operations that fail
493 [arg1, Lit lit] <- args -- only if the divisor is zero
494 = not (isZeroLit lit) && exprOkForSpeculation arg1
495 -- Often there is a literal divisor, and this
496 -- can get rid of a thunk in an inner looop
499 = primOpOkForSpeculation op &&
500 all exprOkForSpeculation args
501 -- A bit conservative: we don't really need
502 -- to care about lazy arguments, but this is easy
504 spec_ok other args = False
506 isDivOp :: PrimOp -> Bool
507 -- True of dyadic operators that can fail
508 -- only if the second arg is zero
509 -- This function probably belongs in PrimOp, or even in
510 -- an automagically generated file.. but it's such a
511 -- special case I thought I'd leave it here for now.
512 isDivOp IntQuotOp = True
513 isDivOp IntRemOp = True
514 isDivOp WordQuotOp = True
515 isDivOp WordRemOp = True
516 isDivOp IntegerQuotRemOp = True
517 isDivOp IntegerDivModOp = True
518 isDivOp FloatDivOp = True
519 isDivOp DoubleDivOp = True
520 isDivOp other = False
525 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
526 exprIsBottom e = go 0 e
528 -- n is the number of args
529 go n (Note _ e) = go n e
530 go n (Let _ e) = go n e
531 go n (Case e _ _) = go 0 e -- Just check the scrut
532 go n (App e _) = go (n+1) e
533 go n (Var v) = idAppIsBottom v n
535 go n (Lam _ _) = False
537 idAppIsBottom :: Id -> Int -> Bool
538 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
541 @exprIsValue@ returns true for expressions that are certainly *already*
542 evaluated to *head* normal form. This is used to decide whether it's ok
545 case x of _ -> e ===> e
547 and to decide whether it's safe to discard a `seq`
549 So, it does *not* treat variables as evaluated, unless they say they are.
551 But it *does* treat partial applications and constructor applications
552 as values, even if their arguments are non-trivial, provided the argument
554 e.g. (:) (f x) (map f xs) is a value
555 map (...redex...) is a value
556 Because `seq` on such things completes immediately
558 For unlifted argument types, we have to be careful:
560 Suppose (f x) diverges; then C (f x) is not a value. True, but
561 this form is illegal (see the invariants in CoreSyn). Args of unboxed
562 type must be ok-for-speculation (or trivial).
565 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
566 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
568 exprIsValue (Lit l) = True
569 exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
570 exprIsValue (Note _ e) = exprIsValue e
571 exprIsValue (Var v) = idArity v > 0 || isEvaldUnfolding (idUnfolding v)
572 -- The idArity case catches data cons and primops that
573 -- don't have unfoldings
574 -- A worry: what if an Id's unfolding is just itself:
575 -- then we could get an infinite loop...
576 exprIsValue other_expr
577 | (Var fun, args) <- collectArgs other_expr,
578 isDataConId fun || valArgCount args < idArity fun
579 = check (idType fun) args
583 -- 'check' checks that unlifted-type args are in
584 -- fact guaranteed non-divergent
585 check fun_ty [] = True
586 check fun_ty (Type _ : args) = case splitForAllTy_maybe fun_ty of
587 Just (_, ty) -> check ty args
588 check fun_ty (arg : args)
589 | isUnLiftedType arg_ty = exprOkForSpeculation arg
590 | otherwise = check res_ty args
592 (arg_ty, res_ty) = splitFunTy fun_ty
596 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
597 exprIsConApp_maybe (Note (Coerce to_ty from_ty) expr)
598 = -- Maybe this is over the top, but here we try to turn
599 -- coerce (S,T) ( x, y )
601 -- ( coerce S x, coerce T y )
602 -- This happens in anger in PrelArrExts which has a coerce
603 -- case coerce memcpy a b of
605 -- where the memcpy is in the IO monad, but the call is in
607 case exprIsConApp_maybe expr of {
611 case splitTyConApp_maybe to_ty of {
613 Just (tc, tc_arg_tys) | tc /= dataConTyCon dc -> Nothing
614 | isExistentialDataCon dc -> Nothing
616 -- Type constructor must match
617 -- We knock out existentials to keep matters simple(r)
619 arity = tyConArity tc
620 val_args = drop arity args
621 to_arg_tys = dataConArgTys dc tc_arg_tys
622 mk_coerce ty arg = mkCoerce ty (exprType arg) arg
623 new_val_args = zipWith mk_coerce to_arg_tys val_args
625 ASSERT( all isTypeArg (take arity args) )
626 ASSERT( length val_args == length to_arg_tys )
627 Just (dc, map Type tc_arg_tys ++ new_val_args)
630 exprIsConApp_maybe (Note _ expr)
631 = exprIsConApp_maybe expr
632 -- We ignore InlineMe notes in case we have
633 -- x = __inline_me__ (a,b)
634 -- All part of making sure that INLINE pragmas never hurt
635 -- Marcin tripped on this one when making dictionaries more inlinable
637 -- In fact, we ignore all notes. For example,
638 -- case _scc_ "foo" (C a b) of
640 -- should be optimised away, but it will be only if we look
641 -- through the SCC note.
643 exprIsConApp_maybe expr = analyse (collectArgs expr)
645 analyse (Var fun, args)
646 | Just con <- isDataConId_maybe fun,
647 length args >= dataConRepArity con
648 -- Might be > because the arity excludes type args
651 -- Look through unfoldings, but only cheap ones, because
652 -- we are effectively duplicating the unfolding
653 analyse (Var fun, [])
654 | let unf = idUnfolding fun,
656 = exprIsConApp_maybe (unfoldingTemplate unf)
658 analyse other = Nothing
663 %************************************************************************
665 \subsection{Eta reduction and expansion}
667 %************************************************************************
670 exprEtaExpandArity :: CoreExpr -> Arity
671 -- The Int is number of value args the thing can be
672 -- applied to without doing much work
674 -- This is used when eta expanding
675 -- e ==> \xy -> e x y
677 -- It returns 1 (or more) to:
678 -- case x of p -> \s -> ...
679 -- because for I/O ish things we really want to get that \s to the top.
680 -- We are prepared to evaluate x each time round the loop in order to get that
682 -- It's all a bit more subtle than it looks. Consider one-shot lambdas
683 -- let x = expensive in \y z -> E
684 -- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
685 -- Hence the ArityType returned by arityType
687 -- NB: this is particularly important/useful for IO state
688 -- transformers, where we often get
689 -- let x = E in \ s -> ...
690 -- and the \s is a real-world state token abstraction. Such
691 -- abstractions are almost invariably 1-shot, so we want to
692 -- pull the \s out, past the let x=E.
693 -- The hack is in Id.isOneShotLambda
696 -- f = \x -> error "foo"
697 -- Here, arity 1 is fine. But if it is
698 -- f = \x -> case e of
699 -- True -> error "foo"
700 -- False -> \y -> x+y
701 -- then we want to get arity 2.
702 -- Hence the ABot/ATop in ArityType
705 exprEtaExpandArity e = arityDepth (arityType e)
707 -- A limited sort of function type
708 data ArityType = AFun Bool ArityType -- True <=> one-shot
709 | ATop -- Know nothing
712 arityDepth :: ArityType -> Arity
713 arityDepth (AFun _ ty) = 1 + arityDepth ty
716 andArityType ABot at2 = at2
717 andArityType ATop at2 = ATop
718 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
719 andArityType at1 at2 = andArityType at2 at1
721 arityType :: CoreExpr -> ArityType
722 -- (go1 e) = [b1,..,bn]
723 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
724 -- where bi is True <=> the lambda is one-shot
726 arityType (Note n e) = arityType e
727 -- Not needed any more: etaExpand is cleverer
728 -- | ok_note n = arityType e
729 -- | otherwise = ATop
734 mk :: Arity -> ArityType
735 mk 0 | isBottomingId v = ABot
737 mk n = AFun False (mk (n-1))
739 -- When the type of the Id encodes one-shot-ness,
740 -- use the idinfo here
742 -- Lambdas; increase arity
743 arityType (Lam x e) | isId x = AFun (isOneShotLambda x) (arityType e)
744 | otherwise = arityType e
746 -- Applications; decrease arity
747 arityType (App f (Type _)) = arityType f
748 arityType (App f a) = case arityType f of
749 AFun one_shot xs | one_shot -> xs
750 | exprIsCheap a -> xs
753 -- Case/Let; keep arity if either the expression is cheap
754 -- or it's a 1-shot lambda
755 arityType (Case scrut _ alts) = case foldr1 andArityType [arityType rhs | (_,_,rhs) <- alts] of
756 xs@(AFun one_shot _) | one_shot -> xs
757 xs | exprIsCheap scrut -> xs
760 arityType (Let b e) = case arityType e of
761 xs@(AFun one_shot _) | one_shot -> xs
762 xs | all exprIsCheap (rhssOfBind b) -> xs
765 arityType other = ATop
767 {- NOT NEEDED ANY MORE: etaExpand is cleverer
768 ok_note InlineMe = False
770 -- Notice that we do not look through __inline_me__
771 -- This may seem surprising, but consider
772 -- f = _inline_me (\x -> e)
773 -- We DO NOT want to eta expand this to
774 -- f = \x -> (_inline_me (\x -> e)) x
775 -- because the _inline_me gets dropped now it is applied,
784 etaExpand :: Arity -- Result should have this number of value args
786 -> CoreExpr -> Type -- Expression and its type
788 -- (etaExpand n us e ty) returns an expression with
789 -- the same meaning as 'e', but with arity 'n'.
791 -- Given e' = etaExpand n us e ty
793 -- ty = exprType e = exprType e'
795 etaExpand n us expr ty
796 | manifestArity expr >= n = expr -- The no-op case
797 | otherwise = eta_expand n us expr ty
800 -- manifestArity sees how many leading value lambdas there are
801 manifestArity :: CoreExpr -> Arity
802 manifestArity (Lam v e) | isId v = 1 + manifestArity e
803 | otherwise = manifestArity e
804 manifestArity (Note _ e) = manifestArity e
807 -- etaExpand deals with for-alls. For example:
809 -- where E :: forall a. a -> a
811 -- (/\b. \y::a -> E b y)
813 -- It deals with coerces too, though they are now rare
814 -- so perhaps the extra code isn't worth it
816 eta_expand n us expr ty
818 -- The ILX code generator requires eta expansion for type arguments
819 -- too, but alas the 'n' doesn't tell us how many of them there
820 -- may be. So we eagerly eta expand any big lambdas, and just
821 -- cross our fingers about possible loss of sharing in the
823 -- The Right Thing is probably to make 'arity' include
824 -- type variables throughout the compiler. (ToDo.)
826 -- Saturated, so nothing to do
829 eta_expand n us (Note note@(Coerce _ ty) e) _
830 = Note note (eta_expand n us e ty)
832 -- Use mkNote so that _scc_s get pushed inside any lambdas that
833 -- are generated as part of the eta expansion. We rely on this
834 -- behaviour in CorePrep, when we eta expand an already-prepped RHS.
835 eta_expand n us (Note note e) ty
836 = mkNote note (eta_expand n us e ty)
838 -- Short cut for the case where there already
839 -- is a lambda; no point in gratuitously adding more
840 eta_expand n us (Lam v body) ty
842 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
845 = Lam v (eta_expand (n-1) us body (funResultTy ty))
847 eta_expand n us expr ty
848 = case splitForAllTy_maybe ty of {
849 Just (tv,ty') -> Lam tv (eta_expand n us (App expr (Type (mkTyVarTy tv))) ty')
853 case splitFunTy_maybe ty of {
854 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
856 arg1 = mkSysLocal SLIT("eta") uniq arg_ty
861 case splitNewType_maybe ty of {
862 Just ty' -> mkCoerce ty ty' (eta_expand n us (mkCoerce ty' ty expr) ty') ;
863 Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
867 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
868 It tells how many things the expression can be applied to before doing
869 any work. It doesn't look inside cases, lets, etc. The idea is that
870 exprEtaExpandArity will do the hard work, leaving something that's easy
871 for exprArity to grapple with. In particular, Simplify uses exprArity to
872 compute the ArityInfo for the Id.
874 Originally I thought that it was enough just to look for top-level lambdas, but
875 it isn't. I've seen this
877 foo = PrelBase.timesInt
879 We want foo to get arity 2 even though the eta-expander will leave it
880 unchanged, in the expectation that it'll be inlined. But occasionally it
881 isn't, because foo is blacklisted (used in a rule).
883 Similarly, see the ok_note check in exprEtaExpandArity. So
884 f = __inline_me (\x -> e)
885 won't be eta-expanded.
887 And in any case it seems more robust to have exprArity be a bit more intelligent.
888 But note that (\x y z -> f x y z)
889 should have arity 3, regardless of f's arity.
892 exprArity :: CoreExpr -> Arity
895 go (Var v) = idArity v
896 go (Lam x e) | isId x = go e + 1
899 go (App e (Type t)) = go e
900 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
901 -- NB: exprIsCheap a!
902 -- f (fac x) does not have arity 2,
903 -- even if f has arity 3!
904 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
905 -- unknown, hence arity 0
910 %************************************************************************
912 \subsection{Equality}
914 %************************************************************************
916 @cheapEqExpr@ is a cheap equality test which bales out fast!
917 True => definitely equal
918 False => may or may not be equal
921 cheapEqExpr :: Expr b -> Expr b -> Bool
923 cheapEqExpr (Var v1) (Var v2) = v1==v2
924 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
925 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
927 cheapEqExpr (App f1 a1) (App f2 a2)
928 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
930 cheapEqExpr _ _ = False
932 exprIsBig :: Expr b -> Bool
933 -- Returns True of expressions that are too big to be compared by cheapEqExpr
934 exprIsBig (Lit _) = False
935 exprIsBig (Var v) = False
936 exprIsBig (Type t) = False
937 exprIsBig (App f a) = exprIsBig f || exprIsBig a
938 exprIsBig other = True
943 eqExpr :: CoreExpr -> CoreExpr -> Bool
944 -- Works ok at more general type, but only needed at CoreExpr
945 -- Used in rule matching, so when we find a type we use
946 -- eqTcType, which doesn't look through newtypes
947 -- [And it doesn't risk falling into a black hole either.]
949 = eq emptyVarEnv e1 e2
951 -- The "env" maps variables in e1 to variables in ty2
952 -- So when comparing lambdas etc,
953 -- we in effect substitute v2 for v1 in e1 before continuing
954 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
955 Just v1' -> v1' == v2
958 eq env (Lit lit1) (Lit lit2) = lit1 == lit2
959 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
960 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
961 eq env (Let (NonRec v1 r1) e1)
962 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
963 eq env (Let (Rec ps1) e1)
964 (Let (Rec ps2) e2) = length ps1 == length ps2 &&
965 and (zipWith eq_rhs ps1 ps2) &&
968 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
969 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
970 eq env (Case e1 v1 a1)
971 (Case e2 v2 a2) = eq env e1 e2 &&
972 length a1 == length a2 &&
973 and (zipWith (eq_alt env') a1 a2)
975 env' = extendVarEnv env v1 v2
977 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
978 eq env (Type t1) (Type t2) = t1 `eqType` t2
981 eq_list env [] [] = True
982 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
983 eq_list env es1 es2 = False
985 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
986 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
988 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
989 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1 `eqType` t2 && f1 `eqType` f2
990 eq_note env InlineCall InlineCall = True
991 eq_note env other1 other2 = False
995 %************************************************************************
997 \subsection{The size of an expression}
999 %************************************************************************
1002 coreBindsSize :: [CoreBind] -> Int
1003 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1005 exprSize :: CoreExpr -> Int
1006 -- A measure of the size of the expressions
1007 -- It also forces the expression pretty drastically as a side effect
1008 exprSize (Var v) = varSize v
1009 exprSize (Lit lit) = lit `seq` 1
1010 exprSize (App f a) = exprSize f + exprSize a
1011 exprSize (Lam b e) = varSize b + exprSize e
1012 exprSize (Let b e) = bindSize b + exprSize e
1013 exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
1014 exprSize (Note n e) = noteSize n + exprSize e
1015 exprSize (Type t) = seqType t `seq` 1
1017 noteSize (SCC cc) = cc `seq` 1
1018 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
1019 noteSize InlineCall = 1
1020 noteSize InlineMe = 1
1022 varSize :: Var -> Int
1023 varSize b | isTyVar b = 1
1024 | otherwise = seqType (idType b) `seq`
1025 megaSeqIdInfo (idInfo b) `seq`
1028 varsSize = foldr ((+) . varSize) 0
1030 bindSize (NonRec b e) = varSize b + exprSize e
1031 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1033 pairSize (b,e) = varSize b + exprSize e
1035 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1039 %************************************************************************
1041 \subsection{Hashing}
1043 %************************************************************************
1046 hashExpr :: CoreExpr -> Int
1047 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
1050 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
1052 hash_expr (Note _ e) = hash_expr e
1053 hash_expr (Let (NonRec b r) e) = hashId b
1054 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
1055 hash_expr (Case _ b _) = hashId b
1056 hash_expr (App f e) = hash_expr f * fast_hash_expr e
1057 hash_expr (Var v) = hashId v
1058 hash_expr (Lit lit) = hashLiteral lit
1059 hash_expr (Lam b _) = hashId b
1060 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
1062 fast_hash_expr (Var v) = hashId v
1063 fast_hash_expr (Lit lit) = hashLiteral lit
1064 fast_hash_expr (App f (Type _)) = fast_hash_expr f
1065 fast_hash_expr (App f a) = fast_hash_expr a
1066 fast_hash_expr (Lam b _) = hashId b
1067 fast_hash_expr other = 1
1070 hashId id = hashName (idName id)