2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Commonly useful utilites for manipulating the Core language
18 -- * Constructing expressions
19 mkInlineMe, mkSCC, mkCoerce, mkCoerceI,
20 bindNonRec, needsCaseBinding,
21 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
23 -- * Taking expressions apart
24 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
26 -- * Properties of expressions
27 exprType, coreAltType, coreAltsType,
28 exprIsDupable, exprIsTrivial, exprIsCheap,
29 exprIsHNF,exprOkForSpeculation, exprIsBig,
30 exprIsConApp_maybe, exprIsBottom,
33 -- * Arity and eta expansion
34 manifestArity, exprArity,
35 exprEtaExpandArity, etaExpand,
37 -- * Expression and bindings size
38 coreBindsSize, exprSize,
44 cheapEqExpr, tcEqExpr, tcEqExprX,
46 -- * Manipulating data constructors and types
47 applyTypeToArgs, applyTypeToArg,
48 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
51 #include "HsVersions.h"
87 import GHC.Exts -- For `xori`
91 %************************************************************************
93 \subsection{Find the type of a Core atom/expression}
95 %************************************************************************
98 exprType :: CoreExpr -> Type
99 -- ^ Recover the type of a well-typed Core expression. Fails when
100 -- applied to the actual 'CoreSyn.Type' expression as it cannot
101 -- really be said to have a type
102 exprType (Var var) = idType var
103 exprType (Lit lit) = literalType lit
104 exprType (Let _ body) = exprType body
105 exprType (Case _ _ ty _) = ty
106 exprType (Cast _ co) = snd (coercionKind co)
107 exprType (Note _ e) = exprType e
108 exprType (Lam binder expr) = mkPiType binder (exprType expr)
110 = case collectArgs e of
111 (fun, args) -> applyTypeToArgs e (exprType fun) args
113 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
115 coreAltType :: CoreAlt -> Type
116 -- ^ Returns the type of the alternatives right hand side
117 coreAltType (_,_,rhs) = exprType rhs
119 coreAltsType :: [CoreAlt] -> Type
120 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
121 coreAltsType (alt:_) = coreAltType alt
122 coreAltsType [] = panic "corAltsType"
126 mkPiType :: Var -> Type -> Type
127 -- ^ Makes a @(->)@ type or a forall type, depending
128 -- on whether it is given a type variable or a term variable.
129 mkPiTypes :: [Var] -> Type -> Type
130 -- ^ 'mkPiType' for multiple type or value arguments
133 | isId v = mkFunTy (idType v) ty
134 | otherwise = mkForAllTy v ty
136 mkPiTypes vs ty = foldr mkPiType ty vs
140 applyTypeToArg :: Type -> CoreExpr -> Type
141 -- ^ Determines the type resulting from applying an expression to a function with the given type
142 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
143 applyTypeToArg fun_ty _ = funResultTy fun_ty
145 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
146 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
147 -- The first argument is just for debugging, and gives some context
148 applyTypeToArgs _ op_ty [] = op_ty
150 applyTypeToArgs e op_ty (Type ty : args)
151 = -- Accumulate type arguments so we can instantiate all at once
154 go rev_tys (Type ty : args) = go (ty:rev_tys) args
155 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
157 op_ty' = applyTys op_ty (reverse rev_tys)
159 applyTypeToArgs e op_ty (_ : args)
160 = case (splitFunTy_maybe op_ty) of
161 Just (_, res_ty) -> applyTypeToArgs e res_ty args
162 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
165 %************************************************************************
167 \subsection{Attaching notes}
169 %************************************************************************
171 mkNote removes redundant coercions, and SCCs where possible
175 mkNote :: Note -> CoreExpr -> CoreExpr
176 mkNote (SCC cc) expr = mkSCC cc expr
177 mkNote InlineMe expr = mkInlineMe expr
178 mkNote note expr = Note note expr
182 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
183 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
184 not be *applied* to anything.
186 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
189 f = inline_me (coerce t fw)
190 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
191 We want the split, so that the coerces can cancel at the call site.
193 However, we can get left with tiresome type applications. Notably, consider
194 f = /\ a -> let t = e in (t, w)
195 Then lifting the let out of the big lambda gives
197 f = /\ a -> let t = inline_me (t' a) in (t, w)
198 The inline_me is to stop the simplifier inlining t' right back
199 into t's RHS. In the next phase we'll substitute for t (since
200 its rhs is trivial) and *then* we could get rid of the inline_me.
201 But it hardly seems worth it, so I don't bother.
204 -- | Wraps the given expression in an inlining hint unless the expression
205 -- is trivial in some sense, so that doing so would usually hurt us
206 mkInlineMe :: CoreExpr -> CoreExpr
207 mkInlineMe (Var v) = Var v
208 mkInlineMe e = Note InlineMe e
212 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
213 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
215 mkCoerceI (ACo co) e = mkCoerce co e
217 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
218 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
219 mkCoerce co (Cast expr co2)
220 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
221 (_from_ty2, to_ty2) = coercionKind co2} in
222 from_ty `coreEqType` to_ty2 )
223 mkCoerce (mkTransCoercion co2 co) expr
226 = let (from_ty, _to_ty) = coercionKind co in
227 -- if to_ty `coreEqType` from_ty
230 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
235 -- | Wraps the given expression in the cost centre unless
236 -- in a way that maximises their utility to the user
237 mkSCC :: CostCentre -> Expr b -> Expr b
238 -- Note: Nested SCC's *are* preserved for the benefit of
239 -- cost centre stack profiling
240 mkSCC _ (Lit lit) = Lit lit
241 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
242 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
243 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
244 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
245 mkSCC cc expr = Note (SCC cc) expr
249 %************************************************************************
251 \subsection{Other expression construction}
253 %************************************************************************
256 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
257 -- ^ @bindNonRec x r b@ produces either:
263 -- > case r of x { _DEFAULT_ -> b }
265 -- depending on whether we have to use a @case@ or @let@
266 -- binding for the expression (see 'needsCaseBinding').
267 -- It's used by the desugarer to avoid building bindings
268 -- that give Core Lint a heart attack, although actually
269 -- the simplifier deals with them perfectly well. See
270 -- also 'MkCore.mkCoreLet'
271 bindNonRec bndr rhs body
272 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
273 | otherwise = Let (NonRec bndr rhs) body
275 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
276 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
277 needsCaseBinding :: Type -> CoreExpr -> Bool
278 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
279 -- Make a case expression instead of a let
280 -- These can arise either from the desugarer,
281 -- or from beta reductions: (\x.e) (x +# y)
285 mkAltExpr :: AltCon -- ^ Case alternative constructor
286 -> [CoreBndr] -- ^ Things bound by the pattern match
287 -> [Type] -- ^ The type arguments to the case alternative
289 -- ^ This guy constructs the value that the scrutinee must have
290 -- given that you are in one particular branch of a case
291 mkAltExpr (DataAlt con) args inst_tys
292 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
293 mkAltExpr (LitAlt lit) [] []
295 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
296 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
298 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
299 mkIfThenElse guard then_expr else_expr
300 -- Not going to be refining, so okay to take the type of the "then" clause
301 = Case guard (mkWildId boolTy) (exprType then_expr)
302 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
303 (DataAlt trueDataCon, [], then_expr) ]
307 %************************************************************************
309 \subsection{Taking expressions apart}
311 %************************************************************************
313 The default alternative must be first, if it exists at all.
314 This makes it easy to find, though it makes matching marginally harder.
317 -- | Extract the default case alternative
318 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
319 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
320 findDefault alts = (alts, Nothing)
322 -- | Find the case alternative corresponding to a particular
323 -- constructor: panics if no such constructor exists
324 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
327 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
328 _ -> go alts panic_deflt
330 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
333 go (alt@(con1,_,_) : alts) deflt
334 = case con `cmpAltCon` con1 of
335 LT -> deflt -- Missed it already; the alts are in increasing order
337 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
339 isDefaultAlt :: CoreAlt -> Bool
340 isDefaultAlt (DEFAULT, _, _) = True
341 isDefaultAlt _ = False
343 ---------------------------------
344 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
345 -- ^ Merge alternatives preserving order; alternatives in
346 -- the first argument shadow ones in the second
347 mergeAlts [] as2 = as2
348 mergeAlts as1 [] = as1
349 mergeAlts (a1:as1) (a2:as2)
350 = case a1 `cmpAlt` a2 of
351 LT -> a1 : mergeAlts as1 (a2:as2)
352 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
353 GT -> a2 : mergeAlts (a1:as1) as2
356 ---------------------------------
357 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
360 -- > case (C a b x y) of
363 -- We want to drop the leading type argument of the scrutinee
364 -- leaving the arguments to match agains the pattern
366 trimConArgs DEFAULT args = ASSERT( null args ) []
367 trimConArgs (LitAlt _) args = ASSERT( null args ) []
368 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
372 %************************************************************************
374 \subsection{Figuring out things about expressions}
376 %************************************************************************
378 @exprIsTrivial@ is true of expressions we are unconditionally happy to
379 duplicate; simple variables and constants, and type
380 applications. Note that primop Ids aren't considered
383 There used to be a gruesome test for (hasNoBinding v) in the
385 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
386 The idea here is that a constructor worker, like \$wJust, is
387 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
388 So it should be treated like a lambda. Ditto unsaturated primops.
389 But now constructor workers are not "have-no-binding" Ids. And
390 completely un-applied primops and foreign-call Ids are sufficiently
391 rare that I plan to allow them to be duplicated and put up with
394 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
395 a) it really generates code, (and a heap object when it's
396 a function arg) to capture the cost centre
397 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
400 exprIsTrivial :: CoreExpr -> Bool
401 exprIsTrivial (Var _) = True -- See notes above
402 exprIsTrivial (Type _) = True
403 exprIsTrivial (Lit lit) = litIsTrivial lit
404 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
405 exprIsTrivial (Note (SCC _) _) = False -- See notes above
406 exprIsTrivial (Note _ e) = exprIsTrivial e
407 exprIsTrivial (Cast e _) = exprIsTrivial e
408 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
409 exprIsTrivial _ = False
413 @exprIsDupable@ is true of expressions that can be duplicated at a modest
414 cost in code size. This will only happen in different case
415 branches, so there's no issue about duplicating work.
417 That is, exprIsDupable returns True of (f x) even if
418 f is very very expensive to call.
420 Its only purpose is to avoid fruitless let-binding
421 and then inlining of case join points
425 exprIsDupable :: CoreExpr -> Bool
426 exprIsDupable (Type _) = True
427 exprIsDupable (Var _) = True
428 exprIsDupable (Lit lit) = litIsDupable lit
429 exprIsDupable (Note InlineMe _) = True
430 exprIsDupable (Note _ e) = exprIsDupable e
431 exprIsDupable (Cast e _) = exprIsDupable e
436 go (App f a) n_args = n_args < dupAppSize
442 dupAppSize = 4 -- Size of application we are prepared to duplicate
445 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
446 it is obviously in weak head normal form, or is cheap to get to WHNF.
447 [Note that that's not the same as exprIsDupable; an expression might be
448 big, and hence not dupable, but still cheap.]
450 By ``cheap'' we mean a computation we're willing to:
451 push inside a lambda, or
452 inline at more than one place
453 That might mean it gets evaluated more than once, instead of being
454 shared. The main examples of things which aren't WHNF but are
459 (where e, and all the ei are cheap)
462 (where e and b are cheap)
465 (where op is a cheap primitive operator)
468 (because we are happy to substitute it inside a lambda)
470 Notice that a variable is considered 'cheap': we can push it inside a lambda,
471 because sharing will make sure it is only evaluated once.
474 exprIsCheap :: CoreExpr -> Bool
475 exprIsCheap (Lit _) = True
476 exprIsCheap (Type _) = True
477 exprIsCheap (Var _) = True
478 exprIsCheap (Note InlineMe _) = True
479 exprIsCheap (Note _ e) = exprIsCheap e
480 exprIsCheap (Cast e _) = exprIsCheap e
481 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
482 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
483 and [exprIsCheap rhs | (_,_,rhs) <- alts]
484 -- Experimentally, treat (case x of ...) as cheap
485 -- (and case __coerce x etc.)
486 -- This improves arities of overloaded functions where
487 -- there is only dictionary selection (no construction) involved
488 exprIsCheap (Let (NonRec x _) e)
489 | isUnLiftedType (idType x) = exprIsCheap e
491 -- strict lets always have cheap right hand sides,
492 -- and do no allocation.
494 exprIsCheap other_expr -- Applications and variables
497 -- Accumulate value arguments, then decide
498 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
499 | otherwise = go f val_args
501 go (Var _) [] = True -- Just a type application of a variable
502 -- (f t1 t2 t3) counts as WHNF
504 = case globalIdDetails f of
505 RecordSelId {} -> go_sel args
506 ClassOpId _ -> go_sel args
507 PrimOpId op -> go_primop op args
509 DataConWorkId _ -> go_pap args
510 _ | length args < idArity f -> go_pap args
513 -- Application of a function which
514 -- always gives bottom; we treat this as cheap
515 -- because it certainly doesn't need to be shared!
520 go_pap args = all exprIsTrivial args
521 -- For constructor applications and primops, check that all
522 -- the args are trivial. We don't want to treat as cheap, say,
524 -- We'll put up with one constructor application, but not dozens
527 go_primop op args = primOpIsCheap op && all exprIsCheap args
528 -- In principle we should worry about primops
529 -- that return a type variable, since the result
530 -- might be applied to something, but I'm not going
531 -- to bother to check the number of args
534 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
535 go_sel _ = False -- look cheap, so we will substitute it inside a
536 -- lambda. Particularly for dictionary field selection.
537 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
538 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
542 -- | 'exprOkForSpeculation' returns True of an expression that is:
544 -- * Safe to evaluate even if normal order eval might not
545 -- evaluate the expression at all, or
547 -- * Safe /not/ to evaluate even if normal order would do so
549 -- Precisely, it returns @True@ iff:
551 -- * The expression guarantees to terminate,
555 -- * without raising an exception,
557 -- * without causing a side effect (e.g. writing a mutable variable)
559 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
560 -- As an example of the considerations in this test, consider:
562 -- > let x = case y# +# 1# of { r# -> I# r# }
565 -- being translated to:
567 -- > case y# +# 1# of { r# ->
572 -- We can only do this if the @y + 1@ is ok for speculation: it has no
573 -- side effects, and can't diverge or raise an exception.
574 exprOkForSpeculation :: CoreExpr -> Bool
575 exprOkForSpeculation (Lit _) = True
576 exprOkForSpeculation (Type _) = True
577 -- Tick boxes are *not* suitable for speculation
578 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
579 && not (isTickBoxOp v)
580 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
581 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
582 exprOkForSpeculation other_expr
583 = case collectArgs other_expr of
584 (Var f, args) -> spec_ok (globalIdDetails f) args
588 spec_ok (DataConWorkId _) _
589 = True -- The strictness of the constructor has already
590 -- been expressed by its "wrapper", so we don't need
591 -- to take the arguments into account
593 spec_ok (PrimOpId op) args
594 | isDivOp op, -- Special case for dividing operations that fail
595 [arg1, Lit lit] <- args -- only if the divisor is zero
596 = not (isZeroLit lit) && exprOkForSpeculation arg1
597 -- Often there is a literal divisor, and this
598 -- can get rid of a thunk in an inner looop
601 = primOpOkForSpeculation op &&
602 all exprOkForSpeculation args
603 -- A bit conservative: we don't really need
604 -- to care about lazy arguments, but this is easy
608 -- | True of dyadic operators that can fail only if the second arg is zero!
609 isDivOp :: PrimOp -> Bool
610 -- This function probably belongs in PrimOp, or even in
611 -- an automagically generated file.. but it's such a
612 -- special case I thought I'd leave it here for now.
613 isDivOp IntQuotOp = True
614 isDivOp IntRemOp = True
615 isDivOp WordQuotOp = True
616 isDivOp WordRemOp = True
617 isDivOp IntegerQuotRemOp = True
618 isDivOp IntegerDivModOp = True
619 isDivOp FloatDivOp = True
620 isDivOp DoubleDivOp = True
625 -- | True of expressions that are guaranteed to diverge upon execution
626 exprIsBottom :: CoreExpr -> Bool
627 exprIsBottom e = go 0 e
629 -- n is the number of args
630 go n (Note _ e) = go n e
631 go n (Cast e _) = go n e
632 go n (Let _ e) = go n e
633 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
634 go n (App e _) = go (n+1) e
635 go n (Var v) = idAppIsBottom v n
637 go _ (Lam _ _) = False
638 go _ (Type _) = False
640 idAppIsBottom :: Id -> Int -> Bool
641 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
646 -- | This returns true for expressions that are certainly /already/
647 -- evaluated to /head/ normal form. This is used to decide whether it's ok
650 -- > case x of _ -> e
656 -- and to decide whether it's safe to discard a 'seq'.
657 -- So, it does /not/ treat variables as evaluated, unless they say they are.
658 -- However, it /does/ treat partial applications and constructor applications
659 -- as values, even if their arguments are non-trivial, provided the argument
660 -- type is lifted. For example, both of these are values:
662 -- > (:) (f x) (map f xs)
663 -- > map (...redex...)
665 -- Because 'seq' on such things completes immediately.
667 -- For unlifted argument types, we have to be careful:
671 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
672 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
673 -- unboxed type must be ok-for-speculation (or trivial).
674 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
675 exprIsHNF (Var v) -- NB: There are no value args at this point
676 = isDataConWorkId v -- Catches nullary constructors,
677 -- so that [] and () are values, for example
678 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
679 || isEvaldUnfolding (idUnfolding v)
680 -- Check the thing's unfolding; it might be bound to a value
681 -- A worry: what if an Id's unfolding is just itself:
682 -- then we could get an infinite loop...
684 exprIsHNF (Lit _) = True
685 exprIsHNF (Type _) = True -- Types are honorary Values;
686 -- we don't mind copying them
687 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
688 exprIsHNF (Note _ e) = exprIsHNF e
689 exprIsHNF (Cast e _) = exprIsHNF e
690 exprIsHNF (App e (Type _)) = exprIsHNF e
691 exprIsHNF (App e a) = app_is_value e [a]
694 -- There is at least one value argument
695 app_is_value :: CoreExpr -> [CoreArg] -> Bool
696 app_is_value (Var fun) args
697 = idArity fun > valArgCount args -- Under-applied function
698 || isDataConWorkId fun -- or data constructor
699 app_is_value (Note _ f) as = app_is_value f as
700 app_is_value (Cast f _) as = app_is_value f as
701 app_is_value (App f a) as = app_is_value f (a:as)
702 app_is_value _ _ = False
705 These InstPat functions go here to avoid circularity between DataCon and Id
708 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
709 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
711 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
712 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
713 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
715 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
716 -- Remember to include the existential dictionaries
718 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
719 -> [FastString] -- A long enough list of FSs to use for names
720 -> [Unique] -- An equally long list of uniques, at least one for each binder
722 -> [Type] -- Types to instantiate the universally quantified tyvars
723 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
724 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
725 -- (ex_tvs, co_tvs, arg_ids),
727 -- ex_tvs are intended to be used as binders for existential type args
729 -- co_tvs are intended to be used as binders for coercion args and the kinds
730 -- of these vars have been instantiated by the inst_tys and the ex_tys
731 -- The co_tvs include both GADT equalities (dcEqSpec) and
732 -- programmer-specified equalities (dcEqTheta)
734 -- arg_ids are indended to be used as binders for value arguments,
735 -- and their types have been instantiated with inst_tys and ex_tys
736 -- The arg_ids include both dicts (dcDictTheta) and
737 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
740 -- The following constructor T1
743 -- T1 :: forall b. Int -> b -> T(a,b)
746 -- has representation type
747 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
750 -- dataConInstPat fss us T1 (a1',b') will return
752 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
754 -- where the double-primed variables are created with the FastStrings and
755 -- Uniques given as fss and us
756 dataConInstPat arg_fun fss uniqs con inst_tys
757 = (ex_bndrs, co_bndrs, arg_ids)
759 univ_tvs = dataConUnivTyVars con
760 ex_tvs = dataConExTyVars con
761 arg_tys = arg_fun con
762 eq_spec = dataConEqSpec con
763 eq_theta = dataConEqTheta con
764 eq_preds = eqSpecPreds eq_spec ++ eq_theta
767 n_co = length eq_preds
769 -- split the Uniques and FastStrings
770 (ex_uniqs, uniqs') = splitAt n_ex uniqs
771 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
773 (ex_fss, fss') = splitAt n_ex fss
774 (co_fss, id_fss) = splitAt n_co fss'
776 -- Make existential type variables
777 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
778 mk_ex_var uniq fs var = mkTyVar new_name kind
780 new_name = mkSysTvName uniq fs
783 -- Make the instantiating substitution
784 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
786 -- Make new coercion vars, instantiating kind
787 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
788 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
790 new_name = mkSysTvName uniq fs
791 co_kind = substTy subst (mkPredTy eq_pred)
793 -- make value vars, instantiating types
794 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
795 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
797 -- | Returns @Just (dc, [x1..xn])@ if the argument expression is
798 -- a constructor application of the form @dc x1 .. xn@
799 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
800 exprIsConApp_maybe (Cast expr co)
801 = -- Here we do the KPush reduction rule as described in the FC paper
802 case exprIsConApp_maybe expr of {
804 Just (dc, dc_args) ->
806 -- The transformation applies iff we have
807 -- (C e1 ... en) `cast` co
808 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
809 -- That is, with a T at the top of both sides
810 -- The left-hand one must be a T, because exprIsConApp returned True
811 -- but the right-hand one might not be. (Though it usually will.)
813 let (from_ty, to_ty) = coercionKind co
814 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
815 -- The inner one must be a TyConApp
817 case splitTyConApp_maybe to_ty of {
819 Just (to_tc, to_tc_arg_tys)
820 | from_tc /= to_tc -> Nothing
821 -- These two Nothing cases are possible; we might see
822 -- (C x y) `cast` (g :: T a ~ S [a]),
823 -- where S is a type function. In fact, exprIsConApp
824 -- will probably not be called in such circumstances,
825 -- but there't nothing wrong with it
829 tc_arity = tyConArity from_tc
831 (univ_args, rest1) = splitAt tc_arity dc_args
832 (ex_args, rest2) = splitAt n_ex_tvs rest1
833 (co_args_spec, rest3) = splitAt n_cos_spec rest2
834 (co_args_theta, val_args) = splitAt n_cos_theta rest3
836 arg_tys = dataConRepArgTys dc
837 dc_univ_tyvars = dataConUnivTyVars dc
838 dc_ex_tyvars = dataConExTyVars dc
839 dc_eq_spec = dataConEqSpec dc
840 dc_eq_theta = dataConEqTheta dc
841 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
842 n_ex_tvs = length dc_ex_tyvars
843 n_cos_spec = length dc_eq_spec
844 n_cos_theta = length dc_eq_theta
846 -- Make the "theta" from Fig 3 of the paper
847 gammas = decomposeCo tc_arity co
848 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
849 theta = zipOpenTvSubst dc_tyvars new_tys
851 -- First we cast the existential coercion arguments
852 cast_co_spec (tv, ty) co
853 = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
854 cast_co_theta eqPred (Type co)
855 | (ty1, ty2) <- getEqPredTys eqPred
856 = Type $ mkSymCoercion (substTy theta ty1)
858 `mkTransCoercion` (substTy theta ty2)
859 new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
860 zipWith cast_co_theta dc_eq_theta co_args_theta
862 -- ...and now value arguments
863 new_val_args = zipWith cast_arg arg_tys val_args
864 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
867 ASSERT( length univ_args == tc_arity )
868 ASSERT( from_tc == dataConTyCon dc )
869 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
870 ASSERT( all isTypeArg (univ_args ++ ex_args) )
871 ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
873 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
877 -- We do not want to tell the world that we have a
878 -- Cons, to *stop* Case of Known Cons, which removes
880 exprIsConApp_maybe (Note (TickBox {}) expr)
882 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
886 exprIsConApp_maybe (Note _ expr)
887 = exprIsConApp_maybe expr
888 -- We ignore InlineMe notes in case we have
889 -- x = __inline_me__ (a,b)
890 -- All part of making sure that INLINE pragmas never hurt
891 -- Marcin tripped on this one when making dictionaries more inlinable
893 -- In fact, we ignore all notes. For example,
894 -- case _scc_ "foo" (C a b) of
896 -- should be optimised away, but it will be only if we look
897 -- through the SCC note.
899 exprIsConApp_maybe expr = analyse (collectArgs expr)
901 analyse (Var fun, args)
902 | Just con <- isDataConWorkId_maybe fun,
903 args `lengthAtLeast` dataConRepArity con
904 -- Might be > because the arity excludes type args
907 -- Look through unfoldings, but only cheap ones, because
908 -- we are effectively duplicating the unfolding
909 analyse (Var fun, [])
910 | let unf = idUnfolding fun,
912 = exprIsConApp_maybe (unfoldingTemplate unf)
919 %************************************************************************
921 \subsection{Eta reduction and expansion}
923 %************************************************************************
926 -- ^ The Arity returned is the number of value args the
927 -- expression can be applied to without doing much work
928 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
930 exprEtaExpandArity is used when eta expanding
933 It returns 1 (or more) to:
934 case x of p -> \s -> ...
935 because for I/O ish things we really want to get that \s to the top.
936 We are prepared to evaluate x each time round the loop in order to get that
938 It's all a bit more subtle than it looks:
942 Consider one-shot lambdas
943 let x = expensive in \y z -> E
944 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
945 Hence the ArityType returned by arityType
947 2. The state-transformer hack
949 The one-shot lambda special cause is particularly important/useful for
950 IO state transformers, where we often get
951 let x = E in \ s -> ...
953 and the \s is a real-world state token abstraction. Such abstractions
954 are almost invariably 1-shot, so we want to pull the \s out, past the
955 let x=E, even if E is expensive. So we treat state-token lambdas as
956 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
958 3. Dealing with bottom
961 f = \x -> error "foo"
962 Here, arity 1 is fine. But if it is
966 then we want to get arity 2. Tecnically, this isn't quite right, because
968 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
969 do so; it improves some programs significantly, and increasing convergence
970 isn't a bad thing. Hence the ABot/ATop in ArityType.
972 Actually, the situation is worse. Consider
976 Can we eta-expand here? At first the answer looks like "yes of course", but
979 This should diverge! But if we eta-expand, it won't. Again, we ignore this
980 "problem", because being scrupulous would lose an important transformation for
986 Non-recursive newtypes are transparent, and should not get in the way.
987 We do (currently) eta-expand recursive newtypes too. So if we have, say
989 newtype T = MkT ([T] -> Int)
993 where f has arity 1. Then: etaExpandArity e = 1;
994 that is, etaExpandArity looks through the coerce.
996 When we eta-expand e to arity 1: eta_expand 1 e T
997 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
999 HOWEVER, note that if you use coerce bogusly you can ge
1001 And since negate has arity 2, you might try to eta expand. But you can't
1002 decopose Int to a function type. Hence the final case in eta_expand.
1006 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
1008 -- A limited sort of function type
1009 data ArityType = AFun Bool ArityType -- True <=> one-shot
1010 | ATop -- Know nothing
1013 arityDepth :: ArityType -> Arity
1014 arityDepth (AFun _ ty) = 1 + arityDepth ty
1017 andArityType :: ArityType -> ArityType -> ArityType
1018 andArityType ABot at2 = at2
1019 andArityType ATop _ = ATop
1020 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
1021 andArityType at1 at2 = andArityType at2 at1
1023 arityType :: DynFlags -> CoreExpr -> ArityType
1024 -- (go1 e) = [b1,..,bn]
1025 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
1026 -- where bi is True <=> the lambda is one-shot
1028 arityType dflags (Note _ e) = arityType dflags e
1029 -- Not needed any more: etaExpand is cleverer
1030 -- removed: | ok_note n = arityType dflags e
1031 -- removed: | otherwise = ATop
1033 arityType dflags (Cast e _) = arityType dflags e
1036 = mk (idArity v) (arg_tys (idType v))
1038 mk :: Arity -> [Type] -> ArityType
1039 -- The argument types are only to steer the "state hack"
1040 -- Consider case x of
1042 -- False -> \(s:RealWorld) -> e
1043 -- where foo has arity 1. Then we want the state hack to
1044 -- apply to foo too, so we can eta expand the case.
1045 mk 0 tys | isBottomingId v = ABot
1046 | (ty:_) <- tys, isStateHackType ty = AFun True ATop
1048 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
1049 mk n [] = AFun False (mk (n-1) [])
1051 arg_tys :: Type -> [Type] -- Ignore for-alls
1053 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1054 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1057 -- Lambdas; increase arity
1058 arityType dflags (Lam x e)
1059 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1060 | otherwise = arityType dflags e
1062 -- Applications; decrease arity
1063 arityType dflags (App f (Type _)) = arityType dflags f
1064 arityType dflags (App f a)
1065 = case arityType dflags f of
1066 ABot -> ABot -- If function diverges, ignore argument
1067 ATop -> ATop -- No no info about function
1069 | exprIsCheap a -> xs
1072 -- Case/Let; keep arity if either the expression is cheap
1073 -- or it's a 1-shot lambda
1074 -- The former is not really right for Haskell
1075 -- f x = case x of { (a,b) -> \y. e }
1077 -- f x y = case x of { (a,b) -> e }
1078 -- The difference is observable using 'seq'
1079 arityType dflags (Case scrut _ _ alts)
1080 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1081 xs | exprIsCheap scrut -> xs
1082 AFun one_shot _ | one_shot -> AFun True ATop
1085 arityType dflags (Let b e)
1086 = case arityType dflags e of
1087 xs | cheap_bind b -> xs
1088 AFun one_shot _ | one_shot -> AFun True ATop
1091 cheap_bind (NonRec b e) = is_cheap (b,e)
1092 cheap_bind (Rec prs) = all is_cheap prs
1093 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1095 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1096 -- dictionary bindings. This improves arities. Thereby, it also
1097 -- means that full laziness is less prone to floating out the
1098 -- application of a function to its dictionary arguments, which
1099 -- can thereby lose opportunities for fusion. Example:
1100 -- foo :: Ord a => a -> ...
1101 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1102 -- -- So foo has arity 1
1104 -- f = \x. foo dInt $ bar x
1106 -- The (foo DInt) is floated out, and makes ineffective a RULE
1107 -- foo (bar x) = ...
1109 -- One could go further and make exprIsCheap reply True to any
1110 -- dictionary-typed expression, but that's more work.
1112 arityType _ _ = ATop
1114 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1115 ok_note InlineMe = False
1116 ok_note other = True
1117 -- Notice that we do not look through __inline_me__
1118 -- This may seem surprising, but consider
1119 -- f = _inline_me (\x -> e)
1120 -- We DO NOT want to eta expand this to
1121 -- f = \x -> (_inline_me (\x -> e)) x
1122 -- because the _inline_me gets dropped now it is applied,
1131 -- | @etaExpand n us e ty@ returns an expression with
1132 -- the same meaning as @e@, but with arity @n@.
1136 -- > e' = etaExpand n us e ty
1138 -- We should have that:
1140 -- > ty = exprType e = exprType e'
1141 etaExpand :: Arity -- ^ Result should have this number of value args
1142 -> [Unique] -- ^ Uniques to assign to the new binders
1143 -> CoreExpr -- ^ Expression to expand
1144 -> Type -- ^ Type of expression to expand
1146 -- Note that SCCs are not treated specially. If we have
1147 -- etaExpand 2 (\x -> scc "foo" e)
1148 -- = (\xy -> (scc "foo" e) y)
1149 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1151 etaExpand n us expr ty
1152 | manifestArity expr >= n = expr -- The no-op case
1154 = eta_expand n us expr ty
1156 -- manifestArity sees how many leading value lambdas there are
1157 manifestArity :: CoreExpr -> Arity
1158 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1159 | otherwise = manifestArity e
1160 manifestArity (Note _ e) = manifestArity e
1161 manifestArity (Cast e _) = manifestArity e
1164 -- etaExpand deals with for-alls. For example:
1166 -- where E :: forall a. a -> a
1168 -- (/\b. \y::a -> E b y)
1170 -- It deals with coerces too, though they are now rare
1171 -- so perhaps the extra code isn't worth it
1172 eta_expand :: Int -> [Unique] -> CoreExpr -> Type -> CoreExpr
1174 eta_expand n _ expr ty
1176 -- The ILX code generator requires eta expansion for type arguments
1177 -- too, but alas the 'n' doesn't tell us how many of them there
1178 -- may be. So we eagerly eta expand any big lambdas, and just
1179 -- cross our fingers about possible loss of sharing in the ILX case.
1180 -- The Right Thing is probably to make 'arity' include
1181 -- type variables throughout the compiler. (ToDo.)
1183 -- Saturated, so nothing to do
1186 -- Short cut for the case where there already
1187 -- is a lambda; no point in gratuitously adding more
1188 eta_expand n us (Lam v body) ty
1190 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1193 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1195 -- We used to have a special case that stepped inside Coerces here,
1196 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1197 -- = Note note (eta_expand n us e ty)
1198 -- BUT this led to an infinite loop
1199 -- Example: newtype T = MkT (Int -> Int)
1200 -- eta_expand 1 (coerce (Int->Int) e)
1201 -- --> coerce (Int->Int) (eta_expand 1 T e)
1203 -- --> coerce (Int->Int) (coerce T
1204 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1205 -- by the splitNewType_maybe case below
1208 eta_expand n us expr ty
1209 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1210 case splitForAllTy_maybe ty of {
1213 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1215 lam_tv = setVarName tv (mkSysTvName uniq (fsLit "etaT"))
1216 -- Using tv as a base retains its tyvar/covar-ness
1220 case splitFunTy_maybe ty of {
1221 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1223 arg1 = mkSysLocal (fsLit "eta") uniq arg_ty
1229 -- newtype T = MkT ([T] -> Int)
1230 -- Consider eta-expanding this
1233 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1235 case splitNewTypeRepCo_maybe ty of {
1236 Just(ty1,co) -> mkCoerce (mkSymCoercion co)
1237 (eta_expand n us (mkCoerce co expr) ty1) ;
1240 -- We have an expression of arity > 0, but its type isn't a function
1241 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1242 -- Essentially the programmer is playing fast and loose with types
1243 -- (Happy does this a lot). So we simply decline to eta-expand.
1244 -- Otherwise we'd end up with an explicit lambda having a non-function type
1249 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1250 It tells how many things the expression can be applied to before doing
1251 any work. It doesn't look inside cases, lets, etc. The idea is that
1252 exprEtaExpandArity will do the hard work, leaving something that's easy
1253 for exprArity to grapple with. In particular, Simplify uses exprArity to
1254 compute the ArityInfo for the Id.
1256 Originally I thought that it was enough just to look for top-level lambdas, but
1257 it isn't. I've seen this
1259 foo = PrelBase.timesInt
1261 We want foo to get arity 2 even though the eta-expander will leave it
1262 unchanged, in the expectation that it'll be inlined. But occasionally it
1263 isn't, because foo is blacklisted (used in a rule).
1265 Similarly, see the ok_note check in exprEtaExpandArity. So
1266 f = __inline_me (\x -> e)
1267 won't be eta-expanded.
1269 And in any case it seems more robust to have exprArity be a bit more intelligent.
1270 But note that (\x y z -> f x y z)
1271 should have arity 3, regardless of f's arity.
1273 Note [exprArity invariant]
1274 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1275 exprArity has the following invariant:
1276 (exprArity e) = n, then manifestArity (etaExpand e n) = n
1278 That is, if exprArity says "the arity is n" then etaExpand really can get
1279 "n" manifest lambdas to the top.
1281 Why is this important? Because
1282 - In TidyPgm we use exprArity to fix the *final arity* of
1283 each top-level Id, and in
1284 - In CorePrep we use etaExpand on each rhs, so that the visible lambdas
1285 actually match that arity, which in turn means
1286 that the StgRhs has the right number of lambdas
1288 An alternative would be to do the eta-expansion in TidyPgm, at least
1289 for top-level bindings, in which case we would not need the trim_arity
1290 in exprArity. That is a less local change, so I'm going to leave it for today!
1294 -- | An approximate, fast, version of 'exprEtaExpandArity'
1295 exprArity :: CoreExpr -> Arity
1298 go (Var v) = idArity v
1299 go (Lam x e) | isId x = go e + 1
1301 go (Note _ e) = go e
1302 go (Cast e co) = trim_arity (go e) 0 (snd (coercionKind co))
1303 go (App e (Type _)) = go e
1304 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1305 -- NB: exprIsCheap a!
1306 -- f (fac x) does not have arity 2,
1307 -- even if f has arity 3!
1308 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1309 -- unknown, hence arity 0
1312 -- Note [exprArity invariant]
1315 | Just (_, ty') <- splitForAllTy_maybe ty = trim_arity n a ty'
1316 | Just (_, ty') <- splitFunTy_maybe ty = trim_arity n (a+1) ty'
1317 | Just (ty',_) <- splitNewTypeRepCo_maybe ty = trim_arity n a ty'
1321 %************************************************************************
1323 \subsection{Equality}
1325 %************************************************************************
1328 -- | A cheap equality test which bales out fast!
1329 -- If it returns @True@ the arguments are definitely equal,
1330 -- otherwise, they may or may not be equal.
1332 -- See also 'exprIsBig'
1333 cheapEqExpr :: Expr b -> Expr b -> Bool
1335 cheapEqExpr (Var v1) (Var v2) = v1==v2
1336 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1337 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1339 cheapEqExpr (App f1 a1) (App f2 a2)
1340 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1342 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1343 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1345 cheapEqExpr _ _ = False
1347 exprIsBig :: Expr b -> Bool
1348 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1349 exprIsBig (Lit _) = False
1350 exprIsBig (Var _) = False
1351 exprIsBig (Type _) = False
1352 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1353 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1359 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1360 -- ^ A kind of shallow equality used in rule matching, so does
1361 -- /not/ look through newtypes or predicate types
1363 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1365 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1367 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1368 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1369 tcEqExprX _ (Lit lit1) (Lit lit2) = lit1 == lit2
1370 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1371 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1372 tcEqExprX env (Let (NonRec v1 r1) e1)
1373 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1374 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1375 tcEqExprX env (Let (Rec ps1) e1)
1376 (Let (Rec ps2) e2) = equalLength ps1 ps2
1377 && and (zipWith eq_rhs ps1 ps2)
1378 && tcEqExprX env' e1 e2
1380 env' = foldl2 rn_bndr2 env ps2 ps2
1381 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1382 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1383 tcEqExprX env (Case e1 v1 t1 a1)
1384 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1385 && tcEqTypeX env t1 t2
1386 && equalLength a1 a2
1387 && and (zipWith (eq_alt env') a1 a2)
1389 env' = rnBndr2 env v1 v2
1391 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1392 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1393 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1394 tcEqExprX _ _ _ = False
1396 eq_alt :: RnEnv2 -> CoreAlt -> CoreAlt -> Bool
1397 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1399 eq_note :: RnEnv2 -> Note -> Note -> Bool
1400 eq_note _ (SCC cc1) (SCC cc2) = cc1 == cc2
1401 eq_note _ (CoreNote s1) (CoreNote s2) = s1 == s2
1402 eq_note _ _ _ = False
1406 %************************************************************************
1408 \subsection{The size of an expression}
1410 %************************************************************************
1413 coreBindsSize :: [CoreBind] -> Int
1414 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1416 exprSize :: CoreExpr -> Int
1417 -- ^ A measure of the size of the expressions, strictly greater than 0
1418 -- It also forces the expression pretty drastically as a side effect
1419 exprSize (Var v) = v `seq` 1
1420 exprSize (Lit lit) = lit `seq` 1
1421 exprSize (App f a) = exprSize f + exprSize a
1422 exprSize (Lam b e) = varSize b + exprSize e
1423 exprSize (Let b e) = bindSize b + exprSize e
1424 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1425 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1426 exprSize (Note n e) = noteSize n + exprSize e
1427 exprSize (Type t) = seqType t `seq` 1
1429 noteSize :: Note -> Int
1430 noteSize (SCC cc) = cc `seq` 1
1431 noteSize InlineMe = 1
1432 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1434 varSize :: Var -> Int
1435 varSize b | isTyVar b = 1
1436 | otherwise = seqType (idType b) `seq`
1437 megaSeqIdInfo (idInfo b) `seq`
1440 varsSize :: [Var] -> Int
1441 varsSize = sum . map varSize
1443 bindSize :: CoreBind -> Int
1444 bindSize (NonRec b e) = varSize b + exprSize e
1445 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1447 pairSize :: (Var, CoreExpr) -> Int
1448 pairSize (b,e) = varSize b + exprSize e
1450 altSize :: CoreAlt -> Int
1451 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1455 %************************************************************************
1457 \subsection{Hashing}
1459 %************************************************************************
1462 hashExpr :: CoreExpr -> Int
1463 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1464 -- Two expressions that hash to the different Ints are definitely unequal.
1466 -- The emphasis is on a crude, fast hash, rather than on high precision.
1468 -- But unequal here means \"not identical\"; two alpha-equivalent
1469 -- expressions may hash to the different Ints.
1471 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1472 -- (at least if we want the above invariant to be true).
1474 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1475 -- UniqFM doesn't like negative Ints
1477 type HashEnv = (Int, VarEnv Int) -- ^ Hash code for bound variables
1479 hash_expr :: HashEnv -> CoreExpr -> Word32
1480 -- Word32, because we're expecting overflows here, and overflowing
1481 -- signed types just isn't cool. In C it's even undefined.
1482 hash_expr env (Note _ e) = hash_expr env e
1483 hash_expr env (Cast e _) = hash_expr env e
1484 hash_expr env (Var v) = hashVar env v
1485 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1486 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1487 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1488 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1489 hash_expr env (Case e _ _ _) = hash_expr env e
1490 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1491 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1492 -- Shouldn't happen. Better to use WARN than trace, because trace
1493 -- prevents the CPR optimisation kicking in for hash_expr.
1495 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1496 fast_hash_expr env (Var v) = hashVar env v
1497 fast_hash_expr env (Type t) = fast_hash_type env t
1498 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1499 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1500 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1501 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1502 fast_hash_expr _ _ = 1
1504 fast_hash_type :: HashEnv -> Type -> Word32
1505 fast_hash_type env ty
1506 | Just tv <- getTyVar_maybe ty = hashVar env tv
1507 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1508 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1511 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1512 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1514 hashVar :: HashEnv -> Var -> Word32
1516 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1519 %************************************************************************
1521 \subsection{Determining non-updatable right-hand-sides}
1523 %************************************************************************
1525 Top-level constructor applications can usually be allocated
1526 statically, but they can't if the constructor, or any of the
1527 arguments, come from another DLL (because we can't refer to static
1528 labels in other DLLs).
1530 If this happens we simply make the RHS into an updatable thunk,
1531 and 'execute' it rather than allocating it statically.
1534 -- | This function is called only on *top-level* right-hand sides.
1535 -- Returns @True@ if the RHS can be allocated statically in the output,
1536 -- with no thunks involved at all.
1537 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1538 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1539 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1540 -- update flag on it and (iii) in DsExpr to decide how to expand
1543 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1544 -- (a) a value lambda
1545 -- (b) a saturated constructor application with static args
1547 -- BUT watch out for
1548 -- (i) Any cross-DLL references kill static-ness completely
1549 -- because they must be 'executed' not statically allocated
1550 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1551 -- this is not necessary)
1553 -- (ii) We treat partial applications as redexes, because in fact we
1554 -- make a thunk for them that runs and builds a PAP
1555 -- at run-time. The only appliations that are treated as
1556 -- static are *saturated* applications of constructors.
1558 -- We used to try to be clever with nested structures like this:
1559 -- ys = (:) w ((:) w [])
1560 -- on the grounds that CorePrep will flatten ANF-ise it later.
1561 -- But supporting this special case made the function much more
1562 -- complicated, because the special case only applies if there are no
1563 -- enclosing type lambdas:
1564 -- ys = /\ a -> Foo (Baz ([] a))
1565 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1567 -- But in fact, even without -O, nested structures at top level are
1568 -- flattened by the simplifier, so we don't need to be super-clever here.
1572 -- f = \x::Int. x+7 TRUE
1573 -- p = (True,False) TRUE
1575 -- d = (fst p, False) FALSE because there's a redex inside
1576 -- (this particular one doesn't happen but...)
1578 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1579 -- n = /\a. Nil a TRUE
1581 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1584 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1585 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1587 -- b) (C x xs), where C is a contructors is updatable if the application is
1590 -- c) don't look through unfolding of f in (f x).
1592 rhsIsStatic _this_pkg rhs = is_static False rhs
1594 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1597 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1599 is_static _ (Note (SCC _) _) = False
1600 is_static in_arg (Note _ e) = is_static in_arg e
1601 is_static in_arg (Cast e _) = is_static in_arg e
1603 is_static _ (Lit lit)
1605 MachLabel _ _ -> False
1607 -- A MachLabel (foreign import "&foo") in an argument
1608 -- prevents a constructor application from being static. The
1609 -- reason is that it might give rise to unresolvable symbols
1610 -- in the object file: under Linux, references to "weak"
1611 -- symbols from the data segment give rise to "unresolvable
1612 -- relocation" errors at link time This might be due to a bug
1613 -- in the linker, but we'll work around it here anyway.
1616 is_static in_arg other_expr = go other_expr 0
1618 go (Var f) n_val_args
1619 #if mingw32_TARGET_OS
1620 | not (isDllName _this_pkg (idName f))
1622 = saturated_data_con f n_val_args
1623 || (in_arg && n_val_args == 0)
1624 -- A naked un-applied variable is *not* deemed a static RHS
1626 -- Reason: better to update so that the indirection gets shorted
1627 -- out, and the true value will be seen
1628 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1629 -- are always updatable. If you do so, make sure that non-updatable
1630 -- ones have enough space for their static link field!
1632 go (App f a) n_val_args
1633 | isTypeArg a = go f n_val_args
1634 | not in_arg && is_static True a = go f (n_val_args + 1)
1635 -- The (not in_arg) checks that we aren't in a constructor argument;
1636 -- if we are, we don't allow (value) applications of any sort
1638 -- NB. In case you wonder, args are sometimes not atomic. eg.
1639 -- x = D# (1.0## /## 2.0##)
1640 -- can't float because /## can fail.
1642 go (Note (SCC _) _) _ = False
1643 go (Note _ f) n_val_args = go f n_val_args
1644 go (Cast e _) n_val_args = go e n_val_args
1648 saturated_data_con f n_val_args
1649 = case isDataConWorkId_maybe f of
1650 Just dc -> n_val_args == dataConRepArity dc