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 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"
86 import GHC.Exts -- For `xori`
90 %************************************************************************
92 \subsection{Find the type of a Core atom/expression}
94 %************************************************************************
97 exprType :: CoreExpr -> Type
98 -- ^ Recover the type of a well-typed Core expression. Fails when
99 -- applied to the actual 'CoreSyn.Type' expression as it cannot
100 -- really be said to have a type
101 exprType (Var var) = idType var
102 exprType (Lit lit) = literalType lit
103 exprType (Let _ body) = exprType body
104 exprType (Case _ _ ty _) = ty
105 exprType (Cast _ co) = snd (coercionKind co)
106 exprType (Note _ e) = exprType e
107 exprType (Lam binder expr) = mkPiType binder (exprType expr)
109 = case collectArgs e of
110 (fun, args) -> applyTypeToArgs e (exprType fun) args
112 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
114 coreAltType :: CoreAlt -> Type
115 -- ^ Returns the type of the alternatives right hand side
116 coreAltType (_,_,rhs) = exprType rhs
118 coreAltsType :: [CoreAlt] -> Type
119 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
120 coreAltsType (alt:_) = coreAltType alt
121 coreAltsType [] = panic "corAltsType"
125 mkPiType :: Var -> Type -> Type
126 -- ^ Makes a @(->)@ type or a forall type, depending
127 -- on whether it is given a type variable or a term variable.
128 mkPiTypes :: [Var] -> Type -> Type
129 -- ^ 'mkPiType' for multiple type or value arguments
132 | isId v = mkFunTy (idType v) ty
133 | otherwise = mkForAllTy v ty
135 mkPiTypes vs ty = foldr mkPiType ty vs
139 applyTypeToArg :: Type -> CoreExpr -> Type
140 -- ^ Determines the type resulting from applying an expression to a function with the given type
141 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
142 applyTypeToArg fun_ty _ = funResultTy fun_ty
144 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
145 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
146 -- The first argument is just for debugging, and gives some context
147 applyTypeToArgs _ op_ty [] = op_ty
149 applyTypeToArgs e op_ty (Type ty : args)
150 = -- Accumulate type arguments so we can instantiate all at once
153 go rev_tys (Type ty : args) = go (ty:rev_tys) args
154 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
156 op_ty' = applyTysD msg op_ty (reverse rev_tys)
157 msg = ptext (sLit "applyTypeToArgs") <+>
160 applyTypeToArgs e op_ty (_ : args)
161 = case (splitFunTy_maybe op_ty) of
162 Just (_, res_ty) -> applyTypeToArgs e res_ty args
163 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
165 panic_msg :: CoreExpr -> Type -> SDoc
166 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
169 %************************************************************************
171 \subsection{Attaching notes}
173 %************************************************************************
175 mkNote removes redundant coercions, and SCCs where possible
179 mkNote :: Note -> CoreExpr -> CoreExpr
180 mkNote (SCC cc) expr = mkSCC cc expr
181 mkNote InlineMe expr = mkInlineMe expr
182 mkNote note expr = Note note expr
186 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
187 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
188 not be *applied* to anything.
190 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
193 f = inline_me (coerce t fw)
194 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
195 We want the split, so that the coerces can cancel at the call site.
197 However, we can get left with tiresome type applications. Notably, consider
198 f = /\ a -> let t = e in (t, w)
199 Then lifting the let out of the big lambda gives
201 f = /\ a -> let t = inline_me (t' a) in (t, w)
202 The inline_me is to stop the simplifier inlining t' right back
203 into t's RHS. In the next phase we'll substitute for t (since
204 its rhs is trivial) and *then* we could get rid of the inline_me.
205 But it hardly seems worth it, so I don't bother.
208 -- | Wraps the given expression in an inlining hint unless the expression
209 -- is trivial in some sense, so that doing so would usually hurt us
210 mkInlineMe :: CoreExpr -> CoreExpr
211 mkInlineMe (Var v) = Var v
212 mkInlineMe e = Note InlineMe e
216 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
217 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
219 mkCoerceI (ACo co) e = mkCoerce co e
221 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
222 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
223 mkCoerce co (Cast expr co2)
224 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
225 (_from_ty2, to_ty2) = coercionKind co2} in
226 from_ty `coreEqType` to_ty2 )
227 mkCoerce (mkTransCoercion co2 co) expr
230 = let (from_ty, _to_ty) = coercionKind co in
231 -- if to_ty `coreEqType` from_ty
234 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
239 -- | Wraps the given expression in the cost centre unless
240 -- in a way that maximises their utility to the user
241 mkSCC :: CostCentre -> Expr b -> Expr b
242 -- Note: Nested SCC's *are* preserved for the benefit of
243 -- cost centre stack profiling
244 mkSCC _ (Lit lit) = Lit lit
245 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
246 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
247 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
248 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
249 mkSCC cc expr = Note (SCC cc) expr
253 %************************************************************************
255 \subsection{Other expression construction}
257 %************************************************************************
260 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
261 -- ^ @bindNonRec x r b@ produces either:
267 -- > case r of x { _DEFAULT_ -> b }
269 -- depending on whether we have to use a @case@ or @let@
270 -- binding for the expression (see 'needsCaseBinding').
271 -- It's used by the desugarer to avoid building bindings
272 -- that give Core Lint a heart attack, although actually
273 -- the simplifier deals with them perfectly well. See
274 -- also 'MkCore.mkCoreLet'
275 bindNonRec bndr rhs body
276 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
277 | otherwise = Let (NonRec bndr rhs) body
279 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
280 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
281 needsCaseBinding :: Type -> CoreExpr -> Bool
282 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
283 -- Make a case expression instead of a let
284 -- These can arise either from the desugarer,
285 -- or from beta reductions: (\x.e) (x +# y)
289 mkAltExpr :: AltCon -- ^ Case alternative constructor
290 -> [CoreBndr] -- ^ Things bound by the pattern match
291 -> [Type] -- ^ The type arguments to the case alternative
293 -- ^ This guy constructs the value that the scrutinee must have
294 -- given that you are in one particular branch of a case
295 mkAltExpr (DataAlt con) args inst_tys
296 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
297 mkAltExpr (LitAlt lit) [] []
299 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
300 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
304 %************************************************************************
306 \subsection{Taking expressions apart}
308 %************************************************************************
310 The default alternative must be first, if it exists at all.
311 This makes it easy to find, though it makes matching marginally harder.
314 -- | Extract the default case alternative
315 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
316 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
317 findDefault alts = (alts, Nothing)
319 -- | Find the case alternative corresponding to a particular
320 -- constructor: panics if no such constructor exists
321 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
324 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
325 _ -> go alts panic_deflt
327 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
330 go (alt@(con1,_,_) : alts) deflt
331 = case con `cmpAltCon` con1 of
332 LT -> deflt -- Missed it already; the alts are in increasing order
334 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
336 isDefaultAlt :: CoreAlt -> Bool
337 isDefaultAlt (DEFAULT, _, _) = True
338 isDefaultAlt _ = False
340 ---------------------------------
341 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
342 -- ^ Merge alternatives preserving order; alternatives in
343 -- the first argument shadow ones in the second
344 mergeAlts [] as2 = as2
345 mergeAlts as1 [] = as1
346 mergeAlts (a1:as1) (a2:as2)
347 = case a1 `cmpAlt` a2 of
348 LT -> a1 : mergeAlts as1 (a2:as2)
349 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
350 GT -> a2 : mergeAlts (a1:as1) as2
353 ---------------------------------
354 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
357 -- > case (C a b x y) of
360 -- We want to drop the leading type argument of the scrutinee
361 -- leaving the arguments to match agains the pattern
363 trimConArgs DEFAULT args = ASSERT( null args ) []
364 trimConArgs (LitAlt _) args = ASSERT( null args ) []
365 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
369 %************************************************************************
371 \subsection{Figuring out things about expressions}
373 %************************************************************************
375 @exprIsTrivial@ is true of expressions we are unconditionally happy to
376 duplicate; simple variables and constants, and type
377 applications. Note that primop Ids aren't considered
380 There used to be a gruesome test for (hasNoBinding v) in the
382 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
383 The idea here is that a constructor worker, like \$wJust, is
384 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
385 So it should be treated like a lambda. Ditto unsaturated primops.
386 But now constructor workers are not "have-no-binding" Ids. And
387 completely un-applied primops and foreign-call Ids are sufficiently
388 rare that I plan to allow them to be duplicated and put up with
391 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
392 a) it really generates code, (and a heap object when it's
393 a function arg) to capture the cost centre
394 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
397 exprIsTrivial :: CoreExpr -> Bool
398 exprIsTrivial (Var _) = True -- See notes above
399 exprIsTrivial (Type _) = True
400 exprIsTrivial (Lit lit) = litIsTrivial lit
401 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
402 exprIsTrivial (Note (SCC _) _) = False -- See notes above
403 exprIsTrivial (Note _ e) = exprIsTrivial e
404 exprIsTrivial (Cast e _) = exprIsTrivial e
405 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
406 exprIsTrivial _ = False
410 @exprIsDupable@ is true of expressions that can be duplicated at a modest
411 cost in code size. This will only happen in different case
412 branches, so there's no issue about duplicating work.
414 That is, exprIsDupable returns True of (f x) even if
415 f is very very expensive to call.
417 Its only purpose is to avoid fruitless let-binding
418 and then inlining of case join points
422 exprIsDupable :: CoreExpr -> Bool
423 exprIsDupable (Type _) = True
424 exprIsDupable (Var _) = True
425 exprIsDupable (Lit lit) = litIsDupable lit
426 exprIsDupable (Note InlineMe _) = True
427 exprIsDupable (Note _ e) = exprIsDupable e
428 exprIsDupable (Cast e _) = exprIsDupable e
433 go (App f a) n_args = n_args < dupAppSize
439 dupAppSize = 4 -- Size of application we are prepared to duplicate
442 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
443 it is obviously in weak head normal form, or is cheap to get to WHNF.
444 [Note that that's not the same as exprIsDupable; an expression might be
445 big, and hence not dupable, but still cheap.]
447 By ``cheap'' we mean a computation we're willing to:
448 push inside a lambda, or
449 inline at more than one place
450 That might mean it gets evaluated more than once, instead of being
451 shared. The main examples of things which aren't WHNF but are
456 (where e, and all the ei are cheap)
459 (where e and b are cheap)
462 (where op is a cheap primitive operator)
465 (because we are happy to substitute it inside a lambda)
467 Notice that a variable is considered 'cheap': we can push it inside a lambda,
468 because sharing will make sure it is only evaluated once.
471 exprIsCheap :: CoreExpr -> Bool
472 exprIsCheap (Lit _) = True
473 exprIsCheap (Type _) = True
474 exprIsCheap (Var _) = True
475 exprIsCheap (Note InlineMe _) = True
476 exprIsCheap (Note _ e) = exprIsCheap e
477 exprIsCheap (Cast e _) = exprIsCheap e
478 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
479 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
480 and [exprIsCheap rhs | (_,_,rhs) <- alts]
481 -- Experimentally, treat (case x of ...) as cheap
482 -- (and case __coerce x etc.)
483 -- This improves arities of overloaded functions where
484 -- there is only dictionary selection (no construction) involved
485 exprIsCheap (Let (NonRec x _) e)
486 | isUnLiftedType (idType x) = exprIsCheap e
488 -- strict lets always have cheap right hand sides,
489 -- and do no allocation.
491 exprIsCheap other_expr -- Applications and variables
494 -- Accumulate value arguments, then decide
495 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
496 | otherwise = go f val_args
498 go (Var _) [] = True -- Just a type application of a variable
499 -- (f t1 t2 t3) counts as WHNF
501 = case globalIdDetails f of
502 RecordSelId {} -> go_sel args
503 ClassOpId _ -> go_sel args
504 PrimOpId op -> go_primop op args
506 DataConWorkId _ -> go_pap args
507 _ | length args < idArity f -> go_pap args
510 -- Application of a function which
511 -- always gives bottom; we treat this as cheap
512 -- because it certainly doesn't need to be shared!
517 go_pap args = all exprIsTrivial args
518 -- For constructor applications and primops, check that all
519 -- the args are trivial. We don't want to treat as cheap, say,
521 -- We'll put up with one constructor application, but not dozens
524 go_primop op args = primOpIsCheap op && all exprIsCheap args
525 -- In principle we should worry about primops
526 -- that return a type variable, since the result
527 -- might be applied to something, but I'm not going
528 -- to bother to check the number of args
531 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
532 go_sel _ = False -- look cheap, so we will substitute it inside a
533 -- lambda. Particularly for dictionary field selection.
534 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
535 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
539 -- | 'exprOkForSpeculation' returns True of an expression that is:
541 -- * Safe to evaluate even if normal order eval might not
542 -- evaluate the expression at all, or
544 -- * Safe /not/ to evaluate even if normal order would do so
546 -- Precisely, it returns @True@ iff:
548 -- * The expression guarantees to terminate,
552 -- * without raising an exception,
554 -- * without causing a side effect (e.g. writing a mutable variable)
556 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
557 -- As an example of the considerations in this test, consider:
559 -- > let x = case y# +# 1# of { r# -> I# r# }
562 -- being translated to:
564 -- > case y# +# 1# of { r# ->
569 -- We can only do this if the @y + 1@ is ok for speculation: it has no
570 -- side effects, and can't diverge or raise an exception.
571 exprOkForSpeculation :: CoreExpr -> Bool
572 exprOkForSpeculation (Lit _) = True
573 exprOkForSpeculation (Type _) = True
574 -- Tick boxes are *not* suitable for speculation
575 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
576 && not (isTickBoxOp v)
577 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
578 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
579 exprOkForSpeculation other_expr
580 = case collectArgs other_expr of
581 (Var f, args) -> spec_ok (globalIdDetails f) args
585 spec_ok (DataConWorkId _) _
586 = True -- The strictness of the constructor has already
587 -- been expressed by its "wrapper", so we don't need
588 -- to take the arguments into account
590 spec_ok (PrimOpId op) args
591 | isDivOp op, -- Special case for dividing operations that fail
592 [arg1, Lit lit] <- args -- only if the divisor is zero
593 = not (isZeroLit lit) && exprOkForSpeculation arg1
594 -- Often there is a literal divisor, and this
595 -- can get rid of a thunk in an inner looop
598 = primOpOkForSpeculation op &&
599 all exprOkForSpeculation args
600 -- A bit conservative: we don't really need
601 -- to care about lazy arguments, but this is easy
605 -- | True of dyadic operators that can fail only if the second arg is zero!
606 isDivOp :: PrimOp -> Bool
607 -- This function probably belongs in PrimOp, or even in
608 -- an automagically generated file.. but it's such a
609 -- special case I thought I'd leave it here for now.
610 isDivOp IntQuotOp = True
611 isDivOp IntRemOp = True
612 isDivOp WordQuotOp = True
613 isDivOp WordRemOp = True
614 isDivOp IntegerQuotRemOp = True
615 isDivOp IntegerDivModOp = True
616 isDivOp FloatDivOp = True
617 isDivOp DoubleDivOp = True
622 -- | True of expressions that are guaranteed to diverge upon execution
623 exprIsBottom :: CoreExpr -> Bool
624 exprIsBottom e = go 0 e
626 -- n is the number of args
627 go n (Note _ e) = go n e
628 go n (Cast e _) = go n e
629 go n (Let _ e) = go n e
630 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
631 go n (App e _) = go (n+1) e
632 go n (Var v) = idAppIsBottom v n
634 go _ (Lam _ _) = False
635 go _ (Type _) = False
637 idAppIsBottom :: Id -> Int -> Bool
638 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
643 -- | This returns true for expressions that are certainly /already/
644 -- evaluated to /head/ normal form. This is used to decide whether it's ok
647 -- > case x of _ -> e
653 -- and to decide whether it's safe to discard a 'seq'.
654 -- So, it does /not/ treat variables as evaluated, unless they say they are.
655 -- However, it /does/ treat partial applications and constructor applications
656 -- as values, even if their arguments are non-trivial, provided the argument
657 -- type is lifted. For example, both of these are values:
659 -- > (:) (f x) (map f xs)
660 -- > map (...redex...)
662 -- Because 'seq' on such things completes immediately.
664 -- For unlifted argument types, we have to be careful:
668 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
669 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
670 -- unboxed type must be ok-for-speculation (or trivial).
671 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
672 exprIsHNF (Var v) -- NB: There are no value args at this point
673 = isDataConWorkId v -- Catches nullary constructors,
674 -- so that [] and () are values, for example
675 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
676 || isEvaldUnfolding (idUnfolding v)
677 -- Check the thing's unfolding; it might be bound to a value
678 -- A worry: what if an Id's unfolding is just itself:
679 -- then we could get an infinite loop...
681 exprIsHNF (Lit _) = True
682 exprIsHNF (Type _) = True -- Types are honorary Values;
683 -- we don't mind copying them
684 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
685 exprIsHNF (Note _ e) = exprIsHNF e
686 exprIsHNF (Cast e _) = exprIsHNF e
687 exprIsHNF (App e (Type _)) = exprIsHNF e
688 exprIsHNF (App e a) = app_is_value e [a]
691 -- There is at least one value argument
692 app_is_value :: CoreExpr -> [CoreArg] -> Bool
693 app_is_value (Var fun) args
694 = idArity fun > valArgCount args -- Under-applied function
695 || isDataConWorkId fun -- or data constructor
696 app_is_value (Note _ f) as = app_is_value f as
697 app_is_value (Cast f _) as = app_is_value f as
698 app_is_value (App f a) as = app_is_value f (a:as)
699 app_is_value _ _ = False
702 These InstPat functions go here to avoid circularity between DataCon and Id
705 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
706 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
708 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
709 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
710 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
712 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
713 -- Remember to include the existential dictionaries
715 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
716 -> [FastString] -- A long enough list of FSs to use for names
717 -> [Unique] -- An equally long list of uniques, at least one for each binder
719 -> [Type] -- Types to instantiate the universally quantified tyvars
720 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
721 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
722 -- (ex_tvs, co_tvs, arg_ids),
724 -- ex_tvs are intended to be used as binders for existential type args
726 -- co_tvs are intended to be used as binders for coercion args and the kinds
727 -- of these vars have been instantiated by the inst_tys and the ex_tys
728 -- The co_tvs include both GADT equalities (dcEqSpec) and
729 -- programmer-specified equalities (dcEqTheta)
731 -- arg_ids are indended to be used as binders for value arguments,
732 -- and their types have been instantiated with inst_tys and ex_tys
733 -- The arg_ids include both dicts (dcDictTheta) and
734 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
737 -- The following constructor T1
740 -- T1 :: forall b. Int -> b -> T(a,b)
743 -- has representation type
744 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
747 -- dataConInstPat fss us T1 (a1',b') will return
749 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
751 -- where the double-primed variables are created with the FastStrings and
752 -- Uniques given as fss and us
753 dataConInstPat arg_fun fss uniqs con inst_tys
754 = (ex_bndrs, co_bndrs, arg_ids)
756 univ_tvs = dataConUnivTyVars con
757 ex_tvs = dataConExTyVars con
758 arg_tys = arg_fun con
759 eq_spec = dataConEqSpec con
760 eq_theta = dataConEqTheta con
761 eq_preds = eqSpecPreds eq_spec ++ eq_theta
764 n_co = length eq_preds
766 -- split the Uniques and FastStrings
767 (ex_uniqs, uniqs') = splitAt n_ex uniqs
768 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
770 (ex_fss, fss') = splitAt n_ex fss
771 (co_fss, id_fss) = splitAt n_co fss'
773 -- Make existential type variables
774 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
775 mk_ex_var uniq fs var = mkTyVar new_name kind
777 new_name = mkSysTvName uniq fs
780 -- Make the instantiating substitution
781 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
783 -- Make new coercion vars, instantiating kind
784 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
785 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
787 new_name = mkSysTvName uniq fs
788 co_kind = substTy subst (mkPredTy eq_pred)
790 -- make value vars, instantiating types
791 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
792 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
794 -- | Returns @Just (dc, [x1..xn])@ if the argument expression is
795 -- a constructor application of the form @dc x1 .. xn@
796 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
797 exprIsConApp_maybe (Cast expr co)
798 = -- Here we do the KPush reduction rule as described in the FC paper
799 case exprIsConApp_maybe expr of {
801 Just (dc, dc_args) ->
803 -- The transformation applies iff we have
804 -- (C e1 ... en) `cast` co
805 -- where co :: (T t1 .. tn) ~ (T s1 ..sn)
806 -- That is, with a T at the top of both sides
807 -- The left-hand one must be a T, because exprIsConApp returned True
808 -- but the right-hand one might not be. (Though it usually will.)
810 let (from_ty, to_ty) = coercionKind co
811 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
812 -- The inner one must be a TyConApp
814 case splitTyConApp_maybe to_ty of {
816 Just (to_tc, to_tc_arg_tys)
817 | from_tc /= to_tc -> Nothing
818 -- These two Nothing cases are possible; we might see
819 -- (C x y) `cast` (g :: T a ~ S [a]),
820 -- where S is a type function. In fact, exprIsConApp
821 -- will probably not be called in such circumstances,
822 -- but there't nothing wrong with it
826 tc_arity = tyConArity from_tc
828 (univ_args, rest1) = splitAt tc_arity dc_args
829 (ex_args, rest2) = splitAt n_ex_tvs rest1
830 (co_args_spec, rest3) = splitAt n_cos_spec rest2
831 (co_args_theta, val_args) = splitAt n_cos_theta rest3
833 arg_tys = dataConRepArgTys dc
834 dc_univ_tyvars = dataConUnivTyVars dc
835 dc_ex_tyvars = dataConExTyVars dc
836 dc_eq_spec = dataConEqSpec dc
837 dc_eq_theta = dataConEqTheta dc
838 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
839 n_ex_tvs = length dc_ex_tyvars
840 n_cos_spec = length dc_eq_spec
841 n_cos_theta = length dc_eq_theta
843 -- Make the "theta" from Fig 3 of the paper
844 gammas = decomposeCo tc_arity co
845 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
846 theta = zipOpenTvSubst dc_tyvars new_tys
848 -- First we cast the existential coercion arguments
849 cast_co_spec (tv, ty) co
850 = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
851 cast_co_theta eqPred (Type co)
852 | (ty1, ty2) <- getEqPredTys eqPred
853 = Type $ mkSymCoercion (substTy theta ty1)
855 `mkTransCoercion` (substTy theta ty2)
856 new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
857 zipWith cast_co_theta dc_eq_theta co_args_theta
859 -- ...and now value arguments
860 new_val_args = zipWith cast_arg arg_tys val_args
861 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
864 ASSERT( length univ_args == tc_arity )
865 ASSERT( from_tc == dataConTyCon dc )
866 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
867 ASSERT( all isTypeArg (univ_args ++ ex_args) )
868 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 )
870 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
874 -- We do not want to tell the world that we have a
875 -- Cons, to *stop* Case of Known Cons, which removes
877 exprIsConApp_maybe (Note (TickBox {}) expr)
879 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
883 exprIsConApp_maybe (Note _ expr)
884 = exprIsConApp_maybe expr
885 -- We ignore InlineMe notes in case we have
886 -- x = __inline_me__ (a,b)
887 -- All part of making sure that INLINE pragmas never hurt
888 -- Marcin tripped on this one when making dictionaries more inlinable
890 -- In fact, we ignore all notes. For example,
891 -- case _scc_ "foo" (C a b) of
893 -- should be optimised away, but it will be only if we look
894 -- through the SCC note.
896 exprIsConApp_maybe expr = analyse (collectArgs expr)
898 analyse (Var fun, args)
899 | Just con <- isDataConWorkId_maybe fun,
900 args `lengthAtLeast` dataConRepArity con
901 -- Might be > because the arity excludes type args
904 -- Look through unfoldings, but only cheap ones, because
905 -- we are effectively duplicating the unfolding
906 analyse (Var fun, [])
907 | let unf = idUnfolding fun,
909 = exprIsConApp_maybe (unfoldingTemplate unf)
916 %************************************************************************
918 \subsection{Eta reduction and expansion}
920 %************************************************************************
923 -- ^ The Arity returned is the number of value args the
924 -- expression can be applied to without doing much work
925 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
927 exprEtaExpandArity is used when eta expanding
930 It returns 1 (or more) to:
931 case x of p -> \s -> ...
932 because for I/O ish things we really want to get that \s to the top.
933 We are prepared to evaluate x each time round the loop in order to get that
935 It's all a bit more subtle than it looks:
939 Consider one-shot lambdas
940 let x = expensive in \y z -> E
941 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
942 Hence the ArityType returned by arityType
944 2. The state-transformer hack
946 The one-shot lambda special cause is particularly important/useful for
947 IO state transformers, where we often get
948 let x = E in \ s -> ...
950 and the \s is a real-world state token abstraction. Such abstractions
951 are almost invariably 1-shot, so we want to pull the \s out, past the
952 let x=E, even if E is expensive. So we treat state-token lambdas as
953 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
955 3. Dealing with bottom
958 f = \x -> error "foo"
959 Here, arity 1 is fine. But if it is
963 then we want to get arity 2. Tecnically, this isn't quite right, because
965 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
966 do so; it improves some programs significantly, and increasing convergence
967 isn't a bad thing. Hence the ABot/ATop in ArityType.
969 Actually, the situation is worse. Consider
973 Can we eta-expand here? At first the answer looks like "yes of course", but
976 This should diverge! But if we eta-expand, it won't. Again, we ignore this
977 "problem", because being scrupulous would lose an important transformation for
983 Non-recursive newtypes are transparent, and should not get in the way.
984 We do (currently) eta-expand recursive newtypes too. So if we have, say
986 newtype T = MkT ([T] -> Int)
990 where f has arity 1. Then: etaExpandArity e = 1;
991 that is, etaExpandArity looks through the coerce.
993 When we eta-expand e to arity 1: eta_expand 1 e T
994 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
996 HOWEVER, note that if you use coerce bogusly you can ge
998 And since negate has arity 2, you might try to eta expand. But you can't
999 decopose Int to a function type. Hence the final case in eta_expand.
1003 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
1005 -- A limited sort of function type
1006 data ArityType = AFun Bool ArityType -- True <=> one-shot
1007 | ATop -- Know nothing
1010 arityDepth :: ArityType -> Arity
1011 arityDepth (AFun _ ty) = 1 + arityDepth ty
1014 andArityType :: ArityType -> ArityType -> ArityType
1015 andArityType ABot at2 = at2
1016 andArityType ATop _ = ATop
1017 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
1018 andArityType at1 at2 = andArityType at2 at1
1020 arityType :: DynFlags -> CoreExpr -> ArityType
1021 -- (go1 e) = [b1,..,bn]
1022 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
1023 -- where bi is True <=> the lambda is one-shot
1025 arityType dflags (Note _ e) = arityType dflags e
1026 -- Not needed any more: etaExpand is cleverer
1027 -- removed: | ok_note n = arityType dflags e
1028 -- removed: | otherwise = ATop
1030 arityType dflags (Cast e _) = arityType dflags e
1033 = mk (idArity v) (arg_tys (idType v))
1035 mk :: Arity -> [Type] -> ArityType
1036 -- The argument types are only to steer the "state hack"
1037 -- Consider case x of
1039 -- False -> \(s:RealWorld) -> e
1040 -- where foo has arity 1. Then we want the state hack to
1041 -- apply to foo too, so we can eta expand the case.
1042 mk 0 tys | isBottomingId v = ABot
1043 | (ty:_) <- tys, isStateHackType ty = AFun True ATop
1045 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
1046 mk n [] = AFun False (mk (n-1) [])
1048 arg_tys :: Type -> [Type] -- Ignore for-alls
1050 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1051 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1054 -- Lambdas; increase arity
1055 arityType dflags (Lam x e)
1056 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1057 | otherwise = arityType dflags e
1059 -- Applications; decrease arity
1060 arityType dflags (App f (Type _)) = arityType dflags f
1061 arityType dflags (App f a)
1062 = case arityType dflags f of
1063 ABot -> ABot -- If function diverges, ignore argument
1064 ATop -> ATop -- No no info about function
1066 | exprIsCheap a -> xs
1069 -- Case/Let; keep arity if either the expression is cheap
1070 -- or it's a 1-shot lambda
1071 -- The former is not really right for Haskell
1072 -- f x = case x of { (a,b) -> \y. e }
1074 -- f x y = case x of { (a,b) -> e }
1075 -- The difference is observable using 'seq'
1076 arityType dflags (Case scrut _ _ alts)
1077 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1078 xs | exprIsCheap scrut -> xs
1079 AFun one_shot _ | one_shot -> AFun True ATop
1082 arityType dflags (Let b e)
1083 = case arityType dflags e of
1084 xs | cheap_bind b -> xs
1085 AFun one_shot _ | one_shot -> AFun True ATop
1088 cheap_bind (NonRec b e) = is_cheap (b,e)
1089 cheap_bind (Rec prs) = all is_cheap prs
1090 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1092 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1093 -- dictionary bindings. This improves arities. Thereby, it also
1094 -- means that full laziness is less prone to floating out the
1095 -- application of a function to its dictionary arguments, which
1096 -- can thereby lose opportunities for fusion. Example:
1097 -- foo :: Ord a => a -> ...
1098 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1099 -- -- So foo has arity 1
1101 -- f = \x. foo dInt $ bar x
1103 -- The (foo DInt) is floated out, and makes ineffective a RULE
1104 -- foo (bar x) = ...
1106 -- One could go further and make exprIsCheap reply True to any
1107 -- dictionary-typed expression, but that's more work.
1109 arityType _ _ = ATop
1111 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1112 ok_note InlineMe = False
1113 ok_note other = True
1114 -- Notice that we do not look through __inline_me__
1115 -- This may seem surprising, but consider
1116 -- f = _inline_me (\x -> e)
1117 -- We DO NOT want to eta expand this to
1118 -- f = \x -> (_inline_me (\x -> e)) x
1119 -- because the _inline_me gets dropped now it is applied,
1128 -- | @etaExpand n us e ty@ returns an expression with
1129 -- the same meaning as @e@, but with arity @n@.
1133 -- > e' = etaExpand n us e ty
1135 -- We should have that:
1137 -- > ty = exprType e = exprType e'
1138 etaExpand :: Arity -- ^ Result should have this number of value args
1139 -> [Unique] -- ^ Uniques to assign to the new binders
1140 -> CoreExpr -- ^ Expression to expand
1141 -> Type -- ^ Type of expression to expand
1143 -- Note that SCCs are not treated specially. If we have
1144 -- etaExpand 2 (\x -> scc "foo" e)
1145 -- = (\xy -> (scc "foo" e) y)
1146 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1148 etaExpand n us expr ty
1149 | manifestArity expr >= n = expr -- The no-op case
1151 = eta_expand n us expr ty
1153 -- manifestArity sees how many leading value lambdas there are
1154 manifestArity :: CoreExpr -> Arity
1155 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1156 | otherwise = manifestArity e
1157 manifestArity (Note _ e) = manifestArity e
1158 manifestArity (Cast e _) = manifestArity e
1161 -- etaExpand deals with for-alls. For example:
1163 -- where E :: forall a. a -> a
1165 -- (/\b. \y::a -> E b y)
1167 -- It deals with coerces too, though they are now rare
1168 -- so perhaps the extra code isn't worth it
1169 eta_expand :: Int -> [Unique] -> CoreExpr -> Type -> CoreExpr
1171 eta_expand n _ expr ty
1173 -- The ILX code generator requires eta expansion for type arguments
1174 -- too, but alas the 'n' doesn't tell us how many of them there
1175 -- may be. So we eagerly eta expand any big lambdas, and just
1176 -- cross our fingers about possible loss of sharing in the ILX case.
1177 -- The Right Thing is probably to make 'arity' include
1178 -- type variables throughout the compiler. (ToDo.)
1180 -- Saturated, so nothing to do
1183 -- Short cut for the case where there already
1184 -- is a lambda; no point in gratuitously adding more
1185 eta_expand n us (Lam v body) ty
1187 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1190 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1192 -- We used to have a special case that stepped inside Coerces here,
1193 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1194 -- = Note note (eta_expand n us e ty)
1195 -- BUT this led to an infinite loop
1196 -- Example: newtype T = MkT (Int -> Int)
1197 -- eta_expand 1 (coerce (Int->Int) e)
1198 -- --> coerce (Int->Int) (eta_expand 1 T e)
1200 -- --> coerce (Int->Int) (coerce T
1201 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1202 -- by the splitNewType_maybe case below
1205 eta_expand n us expr ty
1206 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1207 case splitForAllTy_maybe ty of {
1210 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1212 lam_tv = setVarName tv (mkSysTvName uniq (fsLit "etaT"))
1213 -- Using tv as a base retains its tyvar/covar-ness
1217 case splitFunTy_maybe ty of {
1218 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1220 arg1 = mkSysLocal (fsLit "eta") uniq arg_ty
1226 -- newtype T = MkT ([T] -> Int)
1227 -- Consider eta-expanding this
1230 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1232 case splitNewTypeRepCo_maybe ty of {
1233 Just(ty1,co) -> mkCoerce (mkSymCoercion co)
1234 (eta_expand n us (mkCoerce co expr) ty1) ;
1237 -- We have an expression of arity > 0, but its type isn't a function
1238 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1239 -- Essentially the programmer is playing fast and loose with types
1240 -- (Happy does this a lot). So we simply decline to eta-expand.
1241 -- Otherwise we'd end up with an explicit lambda having a non-function type
1246 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1247 It tells how many things the expression can be applied to before doing
1248 any work. It doesn't look inside cases, lets, etc. The idea is that
1249 exprEtaExpandArity will do the hard work, leaving something that's easy
1250 for exprArity to grapple with. In particular, Simplify uses exprArity to
1251 compute the ArityInfo for the Id.
1253 Originally I thought that it was enough just to look for top-level lambdas, but
1254 it isn't. I've seen this
1256 foo = PrelBase.timesInt
1258 We want foo to get arity 2 even though the eta-expander will leave it
1259 unchanged, in the expectation that it'll be inlined. But occasionally it
1260 isn't, because foo is blacklisted (used in a rule).
1262 Similarly, see the ok_note check in exprEtaExpandArity. So
1263 f = __inline_me (\x -> e)
1264 won't be eta-expanded.
1266 And in any case it seems more robust to have exprArity be a bit more intelligent.
1267 But note that (\x y z -> f x y z)
1268 should have arity 3, regardless of f's arity.
1270 Note [exprArity invariant]
1271 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1272 exprArity has the following invariant:
1273 (exprArity e) = n, then manifestArity (etaExpand e n) = n
1275 That is, if exprArity says "the arity is n" then etaExpand really can get
1276 "n" manifest lambdas to the top.
1278 Why is this important? Because
1279 - In TidyPgm we use exprArity to fix the *final arity* of
1280 each top-level Id, and in
1281 - In CorePrep we use etaExpand on each rhs, so that the visible lambdas
1282 actually match that arity, which in turn means
1283 that the StgRhs has the right number of lambdas
1285 An alternative would be to do the eta-expansion in TidyPgm, at least
1286 for top-level bindings, in which case we would not need the trim_arity
1287 in exprArity. That is a less local change, so I'm going to leave it for today!
1291 -- | An approximate, fast, version of 'exprEtaExpandArity'
1292 exprArity :: CoreExpr -> Arity
1295 go (Var v) = idArity v
1296 go (Lam x e) | isId x = go e + 1
1298 go (Note _ e) = go e
1299 go (Cast e co) = trim_arity (go e) 0 (snd (coercionKind co))
1300 go (App e (Type _)) = go e
1301 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1302 -- NB: exprIsCheap a!
1303 -- f (fac x) does not have arity 2,
1304 -- even if f has arity 3!
1305 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1306 -- unknown, hence arity 0
1309 -- Note [exprArity invariant]
1312 | Just (_, ty') <- splitForAllTy_maybe ty = trim_arity n a ty'
1313 | Just (_, ty') <- splitFunTy_maybe ty = trim_arity n (a+1) ty'
1314 | Just (ty',_) <- splitNewTypeRepCo_maybe ty = trim_arity n a ty'
1318 %************************************************************************
1320 \subsection{Equality}
1322 %************************************************************************
1325 -- | A cheap equality test which bales out fast!
1326 -- If it returns @True@ the arguments are definitely equal,
1327 -- otherwise, they may or may not be equal.
1329 -- See also 'exprIsBig'
1330 cheapEqExpr :: Expr b -> Expr b -> Bool
1332 cheapEqExpr (Var v1) (Var v2) = v1==v2
1333 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1334 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1336 cheapEqExpr (App f1 a1) (App f2 a2)
1337 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1339 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1340 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1342 cheapEqExpr _ _ = False
1344 exprIsBig :: Expr b -> Bool
1345 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1346 exprIsBig (Lit _) = False
1347 exprIsBig (Var _) = False
1348 exprIsBig (Type _) = False
1349 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1350 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1356 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1357 -- ^ A kind of shallow equality used in rule matching, so does
1358 -- /not/ look through newtypes or predicate types
1360 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1362 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1364 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1365 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1366 tcEqExprX _ (Lit lit1) (Lit lit2) = lit1 == lit2
1367 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1368 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1369 tcEqExprX env (Let (NonRec v1 r1) e1)
1370 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1371 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1372 tcEqExprX env (Let (Rec ps1) e1)
1373 (Let (Rec ps2) e2) = equalLength ps1 ps2
1374 && and (zipWith eq_rhs ps1 ps2)
1375 && tcEqExprX env' e1 e2
1377 env' = foldl2 rn_bndr2 env ps2 ps2
1378 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1379 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1380 tcEqExprX env (Case e1 v1 t1 a1)
1381 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1382 && tcEqTypeX env t1 t2
1383 && equalLength a1 a2
1384 && and (zipWith (eq_alt env') a1 a2)
1386 env' = rnBndr2 env v1 v2
1388 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1389 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1390 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1391 tcEqExprX _ _ _ = False
1393 eq_alt :: RnEnv2 -> CoreAlt -> CoreAlt -> Bool
1394 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1396 eq_note :: RnEnv2 -> Note -> Note -> Bool
1397 eq_note _ (SCC cc1) (SCC cc2) = cc1 == cc2
1398 eq_note _ (CoreNote s1) (CoreNote s2) = s1 == s2
1399 eq_note _ _ _ = False
1403 %************************************************************************
1405 \subsection{The size of an expression}
1407 %************************************************************************
1410 coreBindsSize :: [CoreBind] -> Int
1411 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1413 exprSize :: CoreExpr -> Int
1414 -- ^ A measure of the size of the expressions, strictly greater than 0
1415 -- It also forces the expression pretty drastically as a side effect
1416 exprSize (Var v) = v `seq` 1
1417 exprSize (Lit lit) = lit `seq` 1
1418 exprSize (App f a) = exprSize f + exprSize a
1419 exprSize (Lam b e) = varSize b + exprSize e
1420 exprSize (Let b e) = bindSize b + exprSize e
1421 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1422 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1423 exprSize (Note n e) = noteSize n + exprSize e
1424 exprSize (Type t) = seqType t `seq` 1
1426 noteSize :: Note -> Int
1427 noteSize (SCC cc) = cc `seq` 1
1428 noteSize InlineMe = 1
1429 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1431 varSize :: Var -> Int
1432 varSize b | isTyVar b = 1
1433 | otherwise = seqType (idType b) `seq`
1434 megaSeqIdInfo (idInfo b) `seq`
1437 varsSize :: [Var] -> Int
1438 varsSize = sum . map varSize
1440 bindSize :: CoreBind -> Int
1441 bindSize (NonRec b e) = varSize b + exprSize e
1442 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1444 pairSize :: (Var, CoreExpr) -> Int
1445 pairSize (b,e) = varSize b + exprSize e
1447 altSize :: CoreAlt -> Int
1448 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1452 %************************************************************************
1454 \subsection{Hashing}
1456 %************************************************************************
1459 hashExpr :: CoreExpr -> Int
1460 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1461 -- Two expressions that hash to the different Ints are definitely unequal.
1463 -- The emphasis is on a crude, fast hash, rather than on high precision.
1465 -- But unequal here means \"not identical\"; two alpha-equivalent
1466 -- expressions may hash to the different Ints.
1468 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1469 -- (at least if we want the above invariant to be true).
1471 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1472 -- UniqFM doesn't like negative Ints
1474 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1476 hash_expr :: HashEnv -> CoreExpr -> Word32
1477 -- Word32, because we're expecting overflows here, and overflowing
1478 -- signed types just isn't cool. In C it's even undefined.
1479 hash_expr env (Note _ e) = hash_expr env e
1480 hash_expr env (Cast e _) = hash_expr env e
1481 hash_expr env (Var v) = hashVar env v
1482 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1483 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1484 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1485 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1486 hash_expr env (Case e _ _ _) = hash_expr env e
1487 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1488 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1489 -- Shouldn't happen. Better to use WARN than trace, because trace
1490 -- prevents the CPR optimisation kicking in for hash_expr.
1492 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1493 fast_hash_expr env (Var v) = hashVar env v
1494 fast_hash_expr env (Type t) = fast_hash_type env t
1495 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1496 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1497 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1498 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1499 fast_hash_expr _ _ = 1
1501 fast_hash_type :: HashEnv -> Type -> Word32
1502 fast_hash_type env ty
1503 | Just tv <- getTyVar_maybe ty = hashVar env tv
1504 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1505 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1508 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1509 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1511 hashVar :: HashEnv -> Var -> Word32
1513 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1516 %************************************************************************
1518 \subsection{Determining non-updatable right-hand-sides}
1520 %************************************************************************
1522 Top-level constructor applications can usually be allocated
1523 statically, but they can't if the constructor, or any of the
1524 arguments, come from another DLL (because we can't refer to static
1525 labels in other DLLs).
1527 If this happens we simply make the RHS into an updatable thunk,
1528 and 'execute' it rather than allocating it statically.
1531 -- | This function is called only on *top-level* right-hand sides.
1532 -- Returns @True@ if the RHS can be allocated statically in the output,
1533 -- with no thunks involved at all.
1534 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1535 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1536 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1537 -- update flag on it and (iii) in DsExpr to decide how to expand
1540 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1541 -- (a) a value lambda
1542 -- (b) a saturated constructor application with static args
1544 -- BUT watch out for
1545 -- (i) Any cross-DLL references kill static-ness completely
1546 -- because they must be 'executed' not statically allocated
1547 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1548 -- this is not necessary)
1550 -- (ii) We treat partial applications as redexes, because in fact we
1551 -- make a thunk for them that runs and builds a PAP
1552 -- at run-time. The only appliations that are treated as
1553 -- static are *saturated* applications of constructors.
1555 -- We used to try to be clever with nested structures like this:
1556 -- ys = (:) w ((:) w [])
1557 -- on the grounds that CorePrep will flatten ANF-ise it later.
1558 -- But supporting this special case made the function much more
1559 -- complicated, because the special case only applies if there are no
1560 -- enclosing type lambdas:
1561 -- ys = /\ a -> Foo (Baz ([] a))
1562 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1564 -- But in fact, even without -O, nested structures at top level are
1565 -- flattened by the simplifier, so we don't need to be super-clever here.
1569 -- f = \x::Int. x+7 TRUE
1570 -- p = (True,False) TRUE
1572 -- d = (fst p, False) FALSE because there's a redex inside
1573 -- (this particular one doesn't happen but...)
1575 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1576 -- n = /\a. Nil a TRUE
1578 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1581 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1582 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1584 -- b) (C x xs), where C is a contructors is updatable if the application is
1587 -- c) don't look through unfolding of f in (f x).
1589 rhsIsStatic _this_pkg rhs = is_static False rhs
1591 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1594 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1596 is_static _ (Note (SCC _) _) = False
1597 is_static in_arg (Note _ e) = is_static in_arg e
1598 is_static in_arg (Cast e _) = is_static in_arg e
1600 is_static _ (Lit lit)
1602 MachLabel _ _ -> False
1604 -- A MachLabel (foreign import "&foo") in an argument
1605 -- prevents a constructor application from being static. The
1606 -- reason is that it might give rise to unresolvable symbols
1607 -- in the object file: under Linux, references to "weak"
1608 -- symbols from the data segment give rise to "unresolvable
1609 -- relocation" errors at link time This might be due to a bug
1610 -- in the linker, but we'll work around it here anyway.
1613 is_static in_arg other_expr = go other_expr 0
1615 go (Var f) n_val_args
1616 #if mingw32_TARGET_OS
1617 | not (isDllName _this_pkg (idName f))
1619 = saturated_data_con f n_val_args
1620 || (in_arg && n_val_args == 0)
1621 -- A naked un-applied variable is *not* deemed a static RHS
1623 -- Reason: better to update so that the indirection gets shorted
1624 -- out, and the true value will be seen
1625 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1626 -- are always updatable. If you do so, make sure that non-updatable
1627 -- ones have enough space for their static link field!
1629 go (App f a) n_val_args
1630 | isTypeArg a = go f n_val_args
1631 | not in_arg && is_static True a = go f (n_val_args + 1)
1632 -- The (not in_arg) checks that we aren't in a constructor argument;
1633 -- if we are, we don't allow (value) applications of any sort
1635 -- NB. In case you wonder, args are sometimes not atomic. eg.
1636 -- x = D# (1.0## /## 2.0##)
1637 -- can't float because /## can fail.
1639 go (Note (SCC _) _) _ = False
1640 go (Note _ f) n_val_args = go f n_val_args
1641 go (Cast e _) n_val_args = go e n_val_args
1645 saturated_data_con f n_val_args
1646 = case isDataConWorkId_maybe f of
1647 Just dc -> n_val_args == dataConRepArity dc