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, mkIfThenElse, mkAltExpr,
13 -- Taking expressions apart
16 -- Properties of expressions
17 exprType, coreAltsType,
18 exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
19 exprIsValue,exprOkForSpeculation, exprIsBig,
20 exprIsConApp_maybe, exprIsAtom,
21 idAppIsBottom, idAppIsCheap,
22 exprArity, isRuntimeVar, isRuntimeArg,
24 -- Expr transformation
26 exprArity, exprEtaExpandArity,
35 cheapEqExpr, eqExpr, applyTypeToArgs
38 #include "HsVersions.h"
41 import GlaExts -- For `xori`
44 import CoreFVs ( exprFreeVars )
45 import PprCore ( pprCoreExpr )
46 import Var ( Var, isId, isTyVar )
49 import Name ( hashName )
50 import Literal ( hashLiteral, literalType, litIsDupable )
51 import DataCon ( DataCon, dataConRepArity )
52 import PrimOp ( primOpOkForSpeculation, primOpIsCheap )
53 import Id ( Id, idType, globalIdDetails, idStrictness, idLBVarInfo,
54 mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda,
55 isDataConId_maybe, mkSysLocal, hasNoBinding
57 import IdInfo ( LBVarInfo(..),
60 import Demand ( appIsBottom )
61 import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
62 applyTys, isUnLiftedType, seqType, mkUTy, mkTyVarTy,
63 splitForAllTy_maybe, splitNewType_maybe, isForAllTy
65 import TysWiredIn ( boolTy, trueDataCon, falseDataCon )
66 import CostCentre ( CostCentre )
67 import UniqSupply ( UniqSupply, splitUniqSupply, uniqFromSupply )
69 import TysPrim ( alphaTy ) -- Debugging only
70 import CmdLineOpts ( opt_KeepStgTypes )
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 == to_ty2 )
190 mkCoerce to_ty from_ty2 expr
192 mkCoerce to_ty from_ty expr
193 | to_ty == from_ty = expr
194 | otherwise = ASSERT( from_ty == 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 | isUnLiftedType (idType bndr) = Case rhs bndr [(DEFAULT,[],body)]
229 | otherwise = Let (NonRec bndr rhs) body
233 mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
234 -- This guy constructs the value that the scrutinee must have
235 -- when you are in one particular branch of a case
236 mkAltExpr (DataAlt con) args inst_tys
237 = mkConApp con (map Type inst_tys ++ map varToCoreExpr args)
238 mkAltExpr (LitAlt lit) [] []
241 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
242 mkIfThenElse guard then_expr else_expr
243 = Case guard (mkWildId boolTy)
244 [ (DataAlt trueDataCon, [], then_expr),
245 (DataAlt falseDataCon, [], else_expr) ]
249 %************************************************************************
251 \subsection{Taking expressions apart}
253 %************************************************************************
257 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
258 findDefault [] = ([], Nothing)
259 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null alts && null args )
261 findDefault (alt : alts) = case findDefault alts of
262 (alts', deflt) -> (alt : alts', deflt)
264 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
268 go [] = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
269 go (alt : alts) | matches alt = alt
270 | otherwise = go alts
272 matches (DEFAULT, _, _) = True
273 matches (con1, _, _) = con == con1
277 %************************************************************************
279 \subsection{Figuring out things about expressions}
281 %************************************************************************
283 @exprIsTrivial@ is true of expressions we are unconditionally happy to
284 duplicate; simple variables and constants, and type
285 applications. Note that primop Ids aren't considered
288 @exprIsBottom@ is true of expressions that are guaranteed to diverge
292 exprIsTrivial (Var v)
293 | hasNoBinding v = idArity v == 0
294 -- WAS: | Just op <- isPrimOpId_maybe v = primOpIsDupable op
295 -- The idea here is that a constructor worker, like $wJust, is
296 -- really short for (\x -> $wJust x), becuase $wJust has no binding.
297 -- So it should be treated like a lambda.
298 -- Ditto unsaturated primops.
299 -- This came up when dealing with eta expansion/reduction for
301 -- Here we want to eta-expand. This looks like an optimisation,
302 -- but it's important (albeit tiresome) that CoreSat doesn't increase
305 exprIsTrivial (Type _) = True
306 exprIsTrivial (Lit lit) = True
307 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
308 exprIsTrivial (Note _ e) = exprIsTrivial e
309 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
310 exprIsTrivial other = False
312 exprIsAtom :: CoreExpr -> Bool
313 -- Used to decide whether to let-binding an STG argument
314 -- when compiling to ILX => type applications are not allowed
315 exprIsAtom (Var v) = True -- primOpIsDupable?
316 exprIsAtom (Lit lit) = True
317 exprIsAtom (Type ty) = True
318 exprIsAtom (Note (SCC _) e) = False
319 exprIsAtom (Note _ e) = exprIsAtom e
320 exprIsAtom other = False
324 @exprIsDupable@ is true of expressions that can be duplicated at a modest
325 cost in code size. This will only happen in different case
326 branches, so there's no issue about duplicating work.
328 That is, exprIsDupable returns True of (f x) even if
329 f is very very expensive to call.
331 Its only purpose is to avoid fruitless let-binding
332 and then inlining of case join points
336 exprIsDupable (Type _) = True
337 exprIsDupable (Var v) = True
338 exprIsDupable (Lit lit) = litIsDupable lit
339 exprIsDupable (Note InlineMe e) = True
340 exprIsDupable (Note _ e) = exprIsDupable e
344 go (Var v) n_args = True
345 go (App f a) n_args = n_args < dupAppSize
348 go other n_args = False
351 dupAppSize = 4 -- Size of application we are prepared to duplicate
354 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
355 it is obviously in weak head normal form, or is cheap to get to WHNF.
356 [Note that that's not the same as exprIsDupable; an expression might be
357 big, and hence not dupable, but still cheap.]
359 By ``cheap'' we mean a computation we're willing to:
360 push inside a lambda, or
361 inline at more than one place
362 That might mean it gets evaluated more than once, instead of being
363 shared. The main examples of things which aren't WHNF but are
368 (where e, and all the ei are cheap)
371 (where e and b are cheap)
374 (where op is a cheap primitive operator)
377 (because we are happy to substitute it inside a lambda)
379 Notice that a variable is considered 'cheap': we can push it inside a lambda,
380 because sharing will make sure it is only evaluated once.
383 exprIsCheap :: CoreExpr -> Bool
384 exprIsCheap (Lit lit) = True
385 exprIsCheap (Type _) = True
386 exprIsCheap (Var _) = True
387 exprIsCheap (Note InlineMe e) = True
388 exprIsCheap (Note _ e) = exprIsCheap e
389 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
390 exprIsCheap (Case e _ alts) = exprIsCheap e &&
391 and [exprIsCheap rhs | (_,_,rhs) <- alts]
392 -- Experimentally, treat (case x of ...) as cheap
393 -- (and case __coerce x etc.)
394 -- This improves arities of overloaded functions where
395 -- there is only dictionary selection (no construction) involved
396 exprIsCheap (Let (NonRec x _) e)
397 | isUnLiftedType (idType x) = exprIsCheap e
399 -- strict lets always have cheap right hand sides, and
402 exprIsCheap other_expr
403 = go other_expr 0 True
405 go (Var f) n_args args_cheap
406 = (idAppIsCheap f n_args && args_cheap)
407 -- A constructor, cheap primop, or partial application
409 || idAppIsBottom f n_args
410 -- Application of a function which
411 -- always gives bottom; we treat this as cheap
412 -- because it certainly doesn't need to be shared!
414 go (App f a) n_args args_cheap
415 | not (isRuntimeArg a) = go f n_args args_cheap
416 | otherwise = go f (n_args + 1) (exprIsCheap a && args_cheap)
418 go other n_args args_cheap = False
420 idAppIsCheap :: Id -> Int -> Bool
421 idAppIsCheap id n_val_args
422 | n_val_args == 0 = True -- Just a type application of
423 -- a variable (f t1 t2 t3)
425 | otherwise = case globalIdDetails id of
427 RecordSelId _ -> True -- I'm experimenting with making record selection
428 -- look cheap, so we will substitute it inside a
429 -- lambda. Particularly for dictionary field selection
431 PrimOpId op -> primOpIsCheap op -- In principle we should worry about primops
432 -- that return a type variable, since the result
433 -- might be applied to something, but I'm not going
434 -- to bother to check the number of args
435 other -> n_val_args < idArity id
438 exprOkForSpeculation returns True of an expression that it is
440 * safe to evaluate even if normal order eval might not
441 evaluate the expression at all, or
443 * safe *not* to evaluate even if normal order would do so
447 the expression guarantees to terminate,
449 without raising an exception,
450 without causing a side effect (e.g. writing a mutable variable)
453 let x = case y# +# 1# of { r# -> I# r# }
456 case y# +# 1# of { r# ->
461 We can only do this if the (y+1) is ok for speculation: it has no
462 side effects, and can't diverge or raise an exception.
465 exprOkForSpeculation :: CoreExpr -> Bool
466 exprOkForSpeculation (Lit _) = True
467 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
468 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
469 exprOkForSpeculation other_expr
470 = go other_expr 0 True
472 go (Var f) n_args args_ok
473 = case globalIdDetails f of
474 DataConId _ -> True -- The strictness of the constructor has already
475 -- been expressed by its "wrapper", so we don't need
476 -- to take the arguments into account
478 PrimOpId op -> primOpOkForSpeculation op && args_ok
479 -- A bit conservative: we don't really need
480 -- to care about lazy arguments, but this is easy
484 go (App f a) n_args args_ok
485 | not (isRuntimeArg a) = go f n_args args_ok
486 | otherwise = go f (n_args + 1) (exprOkForSpeculation a && args_ok)
488 go other n_args args_ok = False
493 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
494 exprIsBottom e = go 0 e
496 -- n is the number of args
497 go n (Note _ e) = go n e
498 go n (Let _ e) = go n e
499 go n (Case e _ _) = go 0 e -- Just check the scrut
500 go n (App e _) = go (n+1) e
501 go n (Var v) = idAppIsBottom v n
503 go n (Lam _ _) = False
505 idAppIsBottom :: Id -> Int -> Bool
506 idAppIsBottom id n_val_args = appIsBottom (idStrictness id) n_val_args
509 @exprIsValue@ returns true for expressions that are certainly *already*
510 evaluated to WHNF. This is used to decide wether it's ok to change
511 case x of _ -> e ===> e
513 and to decide whether it's safe to discard a `seq`
515 So, it does *not* treat variables as evaluated, unless they say they are.
517 But it *does* treat partial applications and constructor applications
518 as values, even if their arguments are non-trivial;
519 e.g. (:) (f x) (map f xs) is a value
520 map (...redex...) is a value
521 Because `seq` on such things completes immediately
523 A possible worry: constructors with unboxed args:
525 Suppose (f x) diverges; then C (f x) is not a value. True, but
526 this form is illegal (see the invariants in CoreSyn). Args of unboxed
527 type must be ok-for-speculation (or trivial).
530 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
531 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
533 exprIsValue (Lit l) = True
534 exprIsValue (Lam b e) = isRuntimeVar b || exprIsValue e
535 exprIsValue (Note _ e) = exprIsValue e
536 exprIsValue other_expr
539 go (Var f) n_args = idAppIsValue f n_args
542 | not (isRuntimeArg a) = go f n_args
543 | otherwise = go f (n_args + 1)
545 go (Note _ f) n_args = go f n_args
547 go other n_args = False
549 idAppIsValue :: Id -> Int -> Bool
550 idAppIsValue id n_val_args
551 = case globalIdDetails id of
553 PrimOpId _ -> n_val_args < idArity id
554 other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id)
555 | otherwise -> n_val_args < idArity id
556 -- A worry: what if an Id's unfolding is just itself:
557 -- then we could get an infinite loop...
560 @isRuntimeVar v@ returns if (Lam v _) really becomes a lambda at runtime,
561 i.e. if type applications are actual lambdas because types are kept around
565 isRuntimeVar :: Var -> Bool
566 isRuntimeVar v = opt_KeepStgTypes || isId v
567 isRuntimeArg :: CoreExpr -> Bool
568 isRuntimeArg v = opt_KeepStgTypes || isTypeArg v
574 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
575 exprIsConApp_maybe (Note InlineMe expr) = exprIsConApp_maybe expr
576 -- We ignore InlineMe notes in case we have
577 -- x = __inline_me__ (a,b)
578 -- All part of making sure that INLINE pragmas never hurt
579 -- Marcin tripped on this one when making dictionaries more inlinable
581 exprIsConApp_maybe expr = analyse (collectArgs expr)
583 analyse (Var fun, args)
584 | Just con <- isDataConId_maybe fun,
585 length args >= dataConRepArity con
586 -- Might be > because the arity excludes type args
589 -- Look through unfoldings, but only cheap ones, because
590 -- we are effectively duplicating the unfolding
591 analyse (Var fun, [])
592 | let unf = idUnfolding fun,
594 = exprIsConApp_maybe (unfoldingTemplate unf)
596 analyse other = Nothing
601 %************************************************************************
603 \subsection{Eta reduction and expansion}
605 %************************************************************************
607 @etaReduce@ trys an eta reduction at the top level of a Core Expr.
609 e.g. \ x y -> f x y ===> f
611 But we only do this if it gets rid of a whole lambda, not part.
612 The idea is that lambdas are often quite helpful: they indicate
613 head normal forms, so we don't want to chuck them away lightly.
616 etaReduce :: CoreExpr -> CoreExpr
617 -- ToDo: we should really check that we don't turn a non-bottom
618 -- lambda into a bottom variable. Sigh
620 etaReduce expr@(Lam bndr body)
621 = check (reverse binders) body
623 (binders, body) = collectBinders expr
626 | not (any (`elemVarSet` body_fvs) binders)
629 body_fvs = exprFreeVars body
631 check (b : bs) (App fun arg)
632 | (varToCoreExpr b `cheapEqExpr` arg)
635 check _ _ = expr -- Bale out
637 etaReduce expr = expr -- The common case
642 exprEtaExpandArity :: CoreExpr -> (Int, Bool)
643 -- The Int is number of value args the thing can be
644 -- applied to without doing much work
645 -- The Bool is True iff there are enough explicit value lambdas
646 -- at the top to make this arity apparent
647 -- (but ignore it when arity==0)
649 -- This is used when eta expanding
650 -- e ==> \xy -> e x y
652 -- It returns 1 (or more) to:
653 -- case x of p -> \s -> ...
654 -- because for I/O ish things we really want to get that \s to the top.
655 -- We are prepared to evaluate x each time round the loop in order to get that
657 -- Consider let x = expensive in \y z -> E
658 -- We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
660 -- Hence the list of Bools returned by go1
661 -- NB: this is particularly important/useful for IO state
662 -- transformers, where we often get
663 -- let x = E in \ s -> ...
664 -- and the \s is a real-world state token abstraction. Such
665 -- abstractions are almost invariably 1-shot, so we want to
666 -- pull the \s out, past the let x=E.
667 -- The hack is in Id.isOneShotLambda
672 go :: Int -> CoreExpr -> (Int,Bool)
673 go ar (Lam x e) | isId x = go (ar+1) e
674 | otherwise = go ar e
675 go ar (Note n e) | ok_note n = go ar e
676 go ar other = (ar + ar', ar' == 0)
678 ar' = length (go1 other)
680 go1 :: CoreExpr -> [Bool]
681 -- (go1 e) = [b1,..,bn]
682 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
683 -- where bi is True <=> the lambda is one-shot
685 go1 (Note n e) | ok_note n = go1 e
686 go1 (Var v) = replicate (idArity v) False -- When the type of the Id
687 -- encodes one-shot-ness, use
690 -- Lambdas; increase arity
691 go1 (Lam x e) | isId x = isOneShotLambda x : go1 e
694 -- Applications; decrease arity
695 go1 (App f (Type _)) = go1 f
696 go1 (App f a) = case go1 f of
697 (one_shot : xs) | one_shot || exprIsCheap a -> xs
700 -- Case/Let; keep arity if either the expression is cheap
701 -- or it's a 1-shot lambda
702 go1 (Case scrut _ alts) = case foldr1 (zipWith (&&)) [go1 rhs | (_,_,rhs) <- alts] of
703 xs@(one_shot : _) | one_shot || exprIsCheap scrut -> xs
705 go1 (Let b e) = case go1 e of
706 xs@(one_shot : _) | one_shot || all exprIsCheap (rhssOfBind b) -> xs
711 ok_note (Coerce _ _) = True
712 ok_note InlineCall = True
713 ok_note other = False
714 -- Notice that we do not look through __inline_me__
715 -- This may seem surprising, but consider
716 -- f = _inline_me (\x -> e)
717 -- We DO NOT want to eta expand this to
718 -- f = \x -> (_inline_me (\x -> e)) x
719 -- because the _inline_me gets dropped now it is applied,
724 min_zero :: [Int] -> Int -- Find the minimum, but zero is the smallest
725 min_zero (x:xs) = go x xs
727 go 0 xs = 0 -- Nothing beats zero
729 go min (x:xs) | x < min = go x xs
730 | otherwise = go min xs
736 etaExpand :: Int -- Add this number of value args
738 -> CoreExpr -> Type -- Expression and its type
740 -- (etaExpand n us e ty) returns an expression with
741 -- the same meaning as 'e', but with arity 'n'.
743 -- Given e' = etaExpand n us e ty
745 -- ty = exprType e = exprType e'
747 -- etaExpand deals with for-alls and coerces. For example:
749 -- where E :: forall a. T
750 -- newtype T = MkT (A -> B)
753 -- (/\b. coerce T (\y::A -> (coerce (A->B) (E b) y)
755 etaExpand n us expr ty
757 -- The ILX code generator requires eta expansion for type arguments
758 -- too, but alas the 'n' doesn't tell us how many of them there
759 -- may be. So we eagerly eta expand any big lambdas, and just
760 -- cross our fingers about possible loss of sharing in the
762 -- The Right Thing is probably to make 'arity' include
763 -- type variables throughout the compiler. (ToDo.)
765 -- Saturated, so nothing to do
768 | otherwise -- An unsaturated constructor or primop; eta expand it
769 = case splitForAllTy_maybe ty of {
770 Just (tv,ty') -> Lam tv (etaExpand n us (App expr (Type (mkTyVarTy tv))) ty')
774 case splitFunTy_maybe ty of {
775 Just (arg_ty, res_ty) -> Lam arg1 (etaExpand (n-1) us2 (App expr (Var arg1)) res_ty)
777 arg1 = mkSysLocal SLIT("eta") uniq arg_ty
778 (us1, us2) = splitUniqSupply us
779 uniq = uniqFromSupply us1
783 case splitNewType_maybe ty of {
784 Just ty' -> mkCoerce ty ty' (etaExpand n us (mkCoerce ty' ty expr) ty') ;
786 Nothing -> pprTrace "Bad eta expand" (ppr expr $$ ppr ty) expr
791 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
792 It tells how many things the expression can be applied to before doing
793 any work. It doesn't look inside cases, lets, etc. The idea is that
794 exprEtaExpandArity will do the hard work, leaving something that's easy
795 for exprArity to grapple with. In particular, Simplify uses exprArity to
796 compute the ArityInfo for the Id.
798 Originally I thought that it was enough just to look for top-level lambdas, but
799 it isn't. I've seen this
801 foo = PrelBase.timesInt
803 We want foo to get arity 2 even though the eta-expander will leave it
804 unchanged, in the expectation that it'll be inlined. But occasionally it
805 isn't, because foo is blacklisted (used in a rule).
807 Similarly, see the ok_note check in exprEtaExpandArity. So
808 f = __inline_me (\x -> e)
809 won't be eta-expanded.
811 And in any case it seems more robust to have exprArity be a bit more intelligent.
814 exprArity :: CoreExpr -> Int
815 exprArity e = go e `max` 0
817 go (Lam x e) | isId x = go e + 1
820 go (App e (Type t)) = go e
821 go (App f a) = go f - 1
822 go (Var v) = idArity v
827 %************************************************************************
829 \subsection{Equality}
831 %************************************************************************
833 @cheapEqExpr@ is a cheap equality test which bales out fast!
834 True => definitely equal
835 False => may or may not be equal
838 cheapEqExpr :: Expr b -> Expr b -> Bool
840 cheapEqExpr (Var v1) (Var v2) = v1==v2
841 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
842 cheapEqExpr (Type t1) (Type t2) = t1 == t2
844 cheapEqExpr (App f1 a1) (App f2 a2)
845 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
847 cheapEqExpr _ _ = False
849 exprIsBig :: Expr b -> Bool
850 -- Returns True of expressions that are too big to be compared by cheapEqExpr
851 exprIsBig (Lit _) = False
852 exprIsBig (Var v) = False
853 exprIsBig (Type t) = False
854 exprIsBig (App f a) = exprIsBig f || exprIsBig a
855 exprIsBig other = True
860 eqExpr :: CoreExpr -> CoreExpr -> Bool
861 -- Works ok at more general type, but only needed at CoreExpr
863 = eq emptyVarEnv e1 e2
865 -- The "env" maps variables in e1 to variables in ty2
866 -- So when comparing lambdas etc,
867 -- we in effect substitute v2 for v1 in e1 before continuing
868 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
869 Just v1' -> v1' == v2
872 eq env (Lit lit1) (Lit lit2) = lit1 == lit2
873 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
874 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
875 eq env (Let (NonRec v1 r1) e1)
876 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
877 eq env (Let (Rec ps1) e1)
878 (Let (Rec ps2) e2) = length ps1 == length ps2 &&
879 and (zipWith eq_rhs ps1 ps2) &&
882 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
883 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
884 eq env (Case e1 v1 a1)
885 (Case e2 v2 a2) = eq env e1 e2 &&
886 length a1 == length a2 &&
887 and (zipWith (eq_alt env') a1 a2)
889 env' = extendVarEnv env v1 v2
891 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
892 eq env (Type t1) (Type t2) = t1 == t2
895 eq_list env [] [] = True
896 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
897 eq_list env es1 es2 = False
899 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
900 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
902 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
903 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2
904 eq_note env InlineCall InlineCall = True
905 eq_note env other1 other2 = False
909 %************************************************************************
911 \subsection{The size of an expression}
913 %************************************************************************
916 coreBindsSize :: [CoreBind] -> Int
917 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
919 exprSize :: CoreExpr -> Int
920 -- A measure of the size of the expressions
921 -- It also forces the expression pretty drastically as a side effect
922 exprSize (Var v) = varSize v
923 exprSize (Lit lit) = lit `seq` 1
924 exprSize (App f a) = exprSize f + exprSize a
925 exprSize (Lam b e) = varSize b + exprSize e
926 exprSize (Let b e) = bindSize b + exprSize e
927 exprSize (Case e b as) = exprSize e + varSize b + foldr ((+) . altSize) 0 as
928 exprSize (Note n e) = noteSize n + exprSize e
929 exprSize (Type t) = seqType t `seq` 1
931 noteSize (SCC cc) = cc `seq` 1
932 noteSize (Coerce t1 t2) = seqType t1 `seq` seqType t2 `seq` 1
933 noteSize InlineCall = 1
934 noteSize InlineMe = 1
936 varSize :: Var -> Int
937 varSize b | isTyVar b = 1
938 | otherwise = seqType (idType b) `seq`
939 megaSeqIdInfo (idInfo b) `seq`
942 varsSize = foldr ((+) . varSize) 0
944 bindSize (NonRec b e) = varSize b + exprSize e
945 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
947 pairSize (b,e) = varSize b + exprSize e
949 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
953 %************************************************************************
957 %************************************************************************
960 hashExpr :: CoreExpr -> Int
961 hashExpr e | hash < 0 = 77 -- Just in case we hit -maxInt
964 hash = abs (hash_expr e) -- Negative numbers kill UniqFM
966 hash_expr (Note _ e) = hash_expr e
967 hash_expr (Let (NonRec b r) e) = hashId b
968 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
969 hash_expr (Case _ b _) = hashId b
970 hash_expr (App f e) = hash_expr f * fast_hash_expr e
971 hash_expr (Var v) = hashId v
972 hash_expr (Lit lit) = hashLiteral lit
973 hash_expr (Lam b _) = hashId b
974 hash_expr (Type t) = trace "hash_expr: type" 1 -- Shouldn't happen
976 fast_hash_expr (Var v) = hashId v
977 fast_hash_expr (Lit lit) = hashLiteral lit
978 fast_hash_expr (App f (Type _)) = fast_hash_expr f
979 fast_hash_expr (App f a) = fast_hash_expr a
980 fast_hash_expr (Lam b _) = hashId b
981 fast_hash_expr other = 1
984 hashId id = hashName (idName id)