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 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, exprIsExpandable,
29 exprIsHNF,exprOkForSpeculation, exprIsBig,
32 -- * Expression and bindings size
33 coreBindsSize, exprSize,
41 -- * Manipulating data constructors and types
42 applyTypeToArgs, applyTypeToArg,
43 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
46 #include "HsVersions.h"
79 %************************************************************************
81 \subsection{Find the type of a Core atom/expression}
83 %************************************************************************
86 exprType :: CoreExpr -> Type
87 -- ^ Recover the type of a well-typed Core expression. Fails when
88 -- applied to the actual 'CoreSyn.Type' expression as it cannot
89 -- really be said to have a type
90 exprType (Var var) = idType var
91 exprType (Lit lit) = literalType lit
92 exprType (Let _ body) = exprType body
93 exprType (Case _ _ ty _) = ty
94 exprType (Cast _ co) = snd (coercionKind co)
95 exprType (Note _ e) = exprType e
96 exprType (Lam binder expr) = mkPiType binder (exprType expr)
98 = case collectArgs e of
99 (fun, args) -> applyTypeToArgs e (exprType fun) args
101 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
103 coreAltType :: CoreAlt -> Type
104 -- ^ Returns the type of the alternatives right hand side
105 coreAltType (_,bs,rhs)
106 | any bad_binder bs = expandTypeSynonyms ty
107 | otherwise = ty -- Note [Existential variables and silly type synonyms]
110 free_tvs = tyVarsOfType ty
111 bad_binder b = isTyVar b && b `elemVarSet` free_tvs
113 coreAltsType :: [CoreAlt] -> Type
114 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
115 coreAltsType (alt:_) = coreAltType alt
116 coreAltsType [] = panic "corAltsType"
119 Note [Existential variables and silly type synonyms]
120 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
122 data T = forall a. T (Funny a)
127 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
128 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
129 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
132 Various possibilities suggest themselves:
134 - Ignore the problem, and make Lint not complain about such variables
136 - Expand all type synonyms (or at least all those that discard arguments)
137 This is tricky, because at least for top-level things we want to
138 retain the type the user originally specified.
140 - Expand synonyms on the fly, when the problem arises. That is what
141 we are doing here. It's not too expensive, I think.
144 mkPiType :: Var -> Type -> Type
145 -- ^ Makes a @(->)@ type or a forall type, depending
146 -- on whether it is given a type variable or a term variable.
147 mkPiTypes :: [Var] -> Type -> Type
148 -- ^ 'mkPiType' for multiple type or value arguments
151 | isId v = mkFunTy (idType v) ty
152 | otherwise = mkForAllTy v ty
154 mkPiTypes vs ty = foldr mkPiType ty vs
158 applyTypeToArg :: Type -> CoreExpr -> Type
159 -- ^ Determines the type resulting from applying an expression to a function with the given type
160 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
161 applyTypeToArg fun_ty _ = funResultTy fun_ty
163 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
164 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
165 -- The first argument is just for debugging, and gives some context
166 applyTypeToArgs _ op_ty [] = op_ty
168 applyTypeToArgs e op_ty (Type ty : args)
169 = -- Accumulate type arguments so we can instantiate all at once
172 go rev_tys (Type ty : args) = go (ty:rev_tys) args
173 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
175 op_ty' = applyTysD msg op_ty (reverse rev_tys)
176 msg = ptext (sLit "applyTypeToArgs") <+>
179 applyTypeToArgs e op_ty (_ : args)
180 = case (splitFunTy_maybe op_ty) of
181 Just (_, res_ty) -> applyTypeToArgs e res_ty args
182 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
184 panic_msg :: CoreExpr -> Type -> SDoc
185 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
188 %************************************************************************
190 \subsection{Attaching notes}
192 %************************************************************************
195 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
196 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
198 mkCoerceI (ACo co) e = mkCoerce co e
200 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
201 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
202 mkCoerce co (Cast expr co2)
203 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
204 (_from_ty2, to_ty2) = coercionKind co2} in
205 from_ty `coreEqType` to_ty2 )
206 mkCoerce (mkTransCoercion co2 co) expr
209 = let (from_ty, _to_ty) = coercionKind co in
210 -- if to_ty `coreEqType` from_ty
213 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
218 -- | Wraps the given expression in the cost centre unless
219 -- in a way that maximises their utility to the user
220 mkSCC :: CostCentre -> Expr b -> Expr b
221 -- Note: Nested SCC's *are* preserved for the benefit of
222 -- cost centre stack profiling
223 mkSCC _ (Lit lit) = Lit lit
224 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
225 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
226 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
227 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
228 mkSCC cc expr = Note (SCC cc) expr
232 %************************************************************************
234 \subsection{Other expression construction}
236 %************************************************************************
239 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
240 -- ^ @bindNonRec x r b@ produces either:
246 -- > case r of x { _DEFAULT_ -> b }
248 -- depending on whether we have to use a @case@ or @let@
249 -- binding for the expression (see 'needsCaseBinding').
250 -- It's used by the desugarer to avoid building bindings
251 -- that give Core Lint a heart attack, although actually
252 -- the simplifier deals with them perfectly well. See
253 -- also 'MkCore.mkCoreLet'
254 bindNonRec bndr rhs body
255 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
256 | otherwise = Let (NonRec bndr rhs) body
258 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
259 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
260 needsCaseBinding :: Type -> CoreExpr -> Bool
261 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
262 -- Make a case expression instead of a let
263 -- These can arise either from the desugarer,
264 -- or from beta reductions: (\x.e) (x +# y)
268 mkAltExpr :: AltCon -- ^ Case alternative constructor
269 -> [CoreBndr] -- ^ Things bound by the pattern match
270 -> [Type] -- ^ The type arguments to the case alternative
272 -- ^ This guy constructs the value that the scrutinee must have
273 -- given that you are in one particular branch of a case
274 mkAltExpr (DataAlt con) args inst_tys
275 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
276 mkAltExpr (LitAlt lit) [] []
278 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
279 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
283 %************************************************************************
285 \subsection{Taking expressions apart}
287 %************************************************************************
289 The default alternative must be first, if it exists at all.
290 This makes it easy to find, though it makes matching marginally harder.
293 -- | Extract the default case alternative
294 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
295 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
296 findDefault alts = (alts, Nothing)
298 isDefaultAlt :: CoreAlt -> Bool
299 isDefaultAlt (DEFAULT, _, _) = True
300 isDefaultAlt _ = False
303 -- | Find the case alternative corresponding to a particular
304 -- constructor: panics if no such constructor exists
305 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
306 -- A "Nothing" result *is* legitmiate
307 -- See Note [Unreachable code]
310 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
314 go (alt@(con1,_,_) : alts) deflt
315 = case con `cmpAltCon` con1 of
316 LT -> deflt -- Missed it already; the alts are in increasing order
318 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
320 ---------------------------------
321 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
322 -- ^ Merge alternatives preserving order; alternatives in
323 -- the first argument shadow ones in the second
324 mergeAlts [] as2 = as2
325 mergeAlts as1 [] = as1
326 mergeAlts (a1:as1) (a2:as2)
327 = case a1 `cmpAlt` a2 of
328 LT -> a1 : mergeAlts as1 (a2:as2)
329 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
330 GT -> a2 : mergeAlts (a1:as1) as2
333 ---------------------------------
334 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
337 -- > case (C a b x y) of
340 -- We want to drop the leading type argument of the scrutinee
341 -- leaving the arguments to match agains the pattern
343 trimConArgs DEFAULT args = ASSERT( null args ) []
344 trimConArgs (LitAlt _) args = ASSERT( null args ) []
345 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
348 Note [Unreachable code]
349 ~~~~~~~~~~~~~~~~~~~~~~~
350 It is possible (although unusual) for GHC to find a case expression
351 that cannot match. For example:
353 data Col = Red | Green | Blue
357 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
359 Suppose that for some silly reason, x isn't substituted in the case
360 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
361 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
365 lvl = case x of { Green -> e1; Blue -> e2 })
370 Now if x gets inlined, we won't be able to find a matching alternative
371 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
372 we generate (error "Inaccessible alternative").
374 Similar things can happen (augmented by GADTs) when the Simplifier
375 filters down the matching alternatives in Simplify.rebuildCase.
378 %************************************************************************
380 Figuring out things about expressions
382 %************************************************************************
384 @exprIsTrivial@ is true of expressions we are unconditionally happy to
385 duplicate; simple variables and constants, and type
386 applications. Note that primop Ids aren't considered
389 Note [Variable are trivial]
390 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
391 There used to be a gruesome test for (hasNoBinding v) in the
393 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
394 The idea here is that a constructor worker, like \$wJust, is
395 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
396 So it should be treated like a lambda. Ditto unsaturated primops.
397 But now constructor workers are not "have-no-binding" Ids. And
398 completely un-applied primops and foreign-call Ids are sufficiently
399 rare that I plan to allow them to be duplicated and put up with
402 Note [SCCs are trivial]
403 ~~~~~~~~~~~~~~~~~~~~~~~
404 We used not to treat (_scc_ "foo" x) as trivial, because it really
405 generates code, (and a heap object when it's a function arg) to
406 capture the cost centre. However, the profiling system discounts the
407 allocation costs for such "boxing thunks" whereas the extra costs of
408 *not* inlining otherwise-trivial bindings can be high, and are hard to
412 exprIsTrivial :: CoreExpr -> Bool
413 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
414 exprIsTrivial (Type _) = True
415 exprIsTrivial (Lit lit) = litIsTrivial lit
416 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
417 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
418 exprIsTrivial (Cast e _) = exprIsTrivial e
419 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
420 exprIsTrivial _ = False
424 @exprIsDupable@ is true of expressions that can be duplicated at a modest
425 cost in code size. This will only happen in different case
426 branches, so there's no issue about duplicating work.
428 That is, exprIsDupable returns True of (f x) even if
429 f is very very expensive to call.
431 Its only purpose is to avoid fruitless let-binding
432 and then inlining of case join points
436 exprIsDupable :: CoreExpr -> Bool
437 exprIsDupable (Type _) = True
438 exprIsDupable (Var _) = True
439 exprIsDupable (Lit lit) = litIsDupable lit
440 exprIsDupable (Note _ e) = exprIsDupable e
441 exprIsDupable (Cast e _) = exprIsDupable e
446 go (App f a) n_args = n_args < dupAppSize
452 dupAppSize = 4 -- Size of application we are prepared to duplicate
455 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
456 it is obviously in weak head normal form, or is cheap to get to WHNF.
457 [Note that that's not the same as exprIsDupable; an expression might be
458 big, and hence not dupable, but still cheap.]
460 By ``cheap'' we mean a computation we're willing to:
461 push inside a lambda, or
462 inline at more than one place
463 That might mean it gets evaluated more than once, instead of being
464 shared. The main examples of things which aren't WHNF but are
469 (where e, and all the ei are cheap)
472 (where e and b are cheap)
475 (where op is a cheap primitive operator)
478 (because we are happy to substitute it inside a lambda)
480 Notice that a variable is considered 'cheap': we can push it inside a lambda,
481 because sharing will make sure it is only evaluated once.
484 exprIsCheap' :: (Id -> Bool) -> CoreExpr -> Bool
485 exprIsCheap' _ (Lit _) = True
486 exprIsCheap' _ (Type _) = True
487 exprIsCheap' _ (Var _) = True
488 exprIsCheap' is_conlike (Note _ e) = exprIsCheap' is_conlike e
489 exprIsCheap' is_conlike (Cast e _) = exprIsCheap' is_conlike e
490 exprIsCheap' is_conlike (Lam x e) = isRuntimeVar x
491 || exprIsCheap' is_conlike e
492 exprIsCheap' is_conlike (Case e _ _ alts) = exprIsCheap' is_conlike e &&
493 and [exprIsCheap' is_conlike rhs | (_,_,rhs) <- alts]
494 -- Experimentally, treat (case x of ...) as cheap
495 -- (and case __coerce x etc.)
496 -- This improves arities of overloaded functions where
497 -- there is only dictionary selection (no construction) involved
498 exprIsCheap' is_conlike (Let (NonRec x _) e)
499 | isUnLiftedType (idType x) = exprIsCheap' is_conlike e
501 -- strict lets always have cheap right hand sides,
502 -- and do no allocation.
504 exprIsCheap' is_conlike other_expr -- Applications and variables
507 -- Accumulate value arguments, then decide
508 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
509 | otherwise = go f val_args
511 go (Var _) [] = True -- Just a type application of a variable
512 -- (f t1 t2 t3) counts as WHNF
514 = case idDetails f of
515 RecSelId {} -> go_sel args
516 ClassOpId {} -> go_sel args
517 PrimOpId op -> go_primop op args
519 _ | is_conlike f -> go_pap args
520 | length args < idArity f -> go_pap args
523 -- Application of a function which
524 -- always gives bottom; we treat this as cheap
525 -- because it certainly doesn't need to be shared!
530 go_pap args = all exprIsTrivial args
531 -- For constructor applications and primops, check that all
532 -- the args are trivial. We don't want to treat as cheap, say,
534 -- We'll put up with one constructor application, but not dozens
537 go_primop op args = primOpIsCheap op && all (exprIsCheap' is_conlike) args
538 -- In principle we should worry about primops
539 -- that return a type variable, since the result
540 -- might be applied to something, but I'm not going
541 -- to bother to check the number of args
544 go_sel [arg] = exprIsCheap' is_conlike arg -- I'm experimenting with making record selection
545 go_sel _ = False -- look cheap, so we will substitute it inside a
546 -- lambda. Particularly for dictionary field selection.
547 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
548 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
550 exprIsCheap :: CoreExpr -> Bool
551 exprIsCheap = exprIsCheap' isDataConWorkId
553 exprIsExpandable :: CoreExpr -> Bool
554 exprIsExpandable = exprIsCheap' isConLikeId -- See Note [CONLIKE pragma] in BasicTypes
558 -- | 'exprOkForSpeculation' returns True of an expression that is:
560 -- * Safe to evaluate even if normal order eval might not
561 -- evaluate the expression at all, or
563 -- * Safe /not/ to evaluate even if normal order would do so
565 -- Precisely, it returns @True@ iff:
567 -- * The expression guarantees to terminate,
571 -- * without raising an exception,
573 -- * without causing a side effect (e.g. writing a mutable variable)
575 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
576 -- As an example of the considerations in this test, consider:
578 -- > let x = case y# +# 1# of { r# -> I# r# }
581 -- being translated to:
583 -- > case y# +# 1# of { r# ->
588 -- We can only do this if the @y + 1@ is ok for speculation: it has no
589 -- side effects, and can't diverge or raise an exception.
590 exprOkForSpeculation :: CoreExpr -> Bool
591 exprOkForSpeculation (Lit _) = True
592 exprOkForSpeculation (Type _) = True
593 -- Tick boxes are *not* suitable for speculation
594 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
595 && not (isTickBoxOp v)
596 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
597 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
598 exprOkForSpeculation other_expr
599 = case collectArgs other_expr of
600 (Var f, args) -> spec_ok (idDetails f) args
604 spec_ok (DataConWorkId _) _
605 = True -- The strictness of the constructor has already
606 -- been expressed by its "wrapper", so we don't need
607 -- to take the arguments into account
609 spec_ok (PrimOpId op) args
610 | isDivOp op, -- Special case for dividing operations that fail
611 [arg1, Lit lit] <- args -- only if the divisor is zero
612 = not (isZeroLit lit) && exprOkForSpeculation arg1
613 -- Often there is a literal divisor, and this
614 -- can get rid of a thunk in an inner looop
617 = primOpOkForSpeculation op &&
618 all exprOkForSpeculation args
619 -- A bit conservative: we don't really need
620 -- to care about lazy arguments, but this is easy
622 spec_ok (DFunId new_type) _ = not new_type
623 -- DFuns terminate, unless the dict is implemented with a newtype
624 -- in which case they may not
628 -- | True of dyadic operators that can fail only if the second arg is zero!
629 isDivOp :: PrimOp -> Bool
630 -- This function probably belongs in PrimOp, or even in
631 -- an automagically generated file.. but it's such a
632 -- special case I thought I'd leave it here for now.
633 isDivOp IntQuotOp = True
634 isDivOp IntRemOp = True
635 isDivOp WordQuotOp = True
636 isDivOp WordRemOp = True
637 isDivOp FloatDivOp = True
638 isDivOp DoubleDivOp = True
643 {- Never used -- omitting
644 -- | True of expressions that are guaranteed to diverge upon execution
645 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
646 exprIsBottom e = go 0 e
648 -- n is the number of args
649 go n (Note _ e) = go n e
650 go n (Cast e _) = go n e
651 go n (Let _ e) = go n e
652 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
653 go n (App e _) = go (n+1) e
654 go n (Var v) = idAppIsBottom v n
656 go _ (Lam _ _) = False
657 go _ (Type _) = False
659 idAppIsBottom :: Id -> Int -> Bool
660 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
666 -- | This returns true for expressions that are certainly /already/
667 -- evaluated to /head/ normal form. This is used to decide whether it's ok
670 -- > case x of _ -> e
676 -- and to decide whether it's safe to discard a 'seq'.
677 -- So, it does /not/ treat variables as evaluated, unless they say they are.
678 -- However, it /does/ treat partial applications and constructor applications
679 -- as values, even if their arguments are non-trivial, provided the argument
680 -- type is lifted. For example, both of these are values:
682 -- > (:) (f x) (map f xs)
683 -- > map (...redex...)
685 -- Because 'seq' on such things completes immediately.
687 -- For unlifted argument types, we have to be careful:
691 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
692 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
693 -- unboxed type must be ok-for-speculation (or trivial).
694 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
695 exprIsHNF (Var v) -- NB: There are no value args at this point
696 = isDataConWorkId v -- Catches nullary constructors,
697 -- so that [] and () are values, for example
698 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
699 || isEvaldUnfolding (idUnfolding v)
700 -- Check the thing's unfolding; it might be bound to a value
701 -- A worry: what if an Id's unfolding is just itself:
702 -- then we could get an infinite loop...
704 exprIsHNF (Lit _) = True
705 exprIsHNF (Type _) = True -- Types are honorary Values;
706 -- we don't mind copying them
707 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
708 exprIsHNF (Note _ e) = exprIsHNF e
709 exprIsHNF (Cast e _) = exprIsHNF e
710 exprIsHNF (App e (Type _)) = exprIsHNF e
711 exprIsHNF (App e a) = app_is_value e [a]
714 -- There is at least one value argument
715 app_is_value :: CoreExpr -> [CoreArg] -> Bool
716 app_is_value (Var fun) args
717 = idArity fun > valArgCount args -- Under-applied function
718 || isDataConWorkId fun -- or data constructor
719 app_is_value (Note _ f) as = app_is_value f as
720 app_is_value (Cast f _) as = app_is_value f as
721 app_is_value (App f a) as = app_is_value f (a:as)
722 app_is_value _ _ = False
725 These InstPat functions go here to avoid circularity between DataCon and Id
728 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
729 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
731 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
732 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
733 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
735 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
736 -- Remember to include the existential dictionaries
738 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
739 -> [FastString] -- A long enough list of FSs to use for names
740 -> [Unique] -- An equally long list of uniques, at least one for each binder
742 -> [Type] -- Types to instantiate the universally quantified tyvars
743 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
744 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
745 -- (ex_tvs, co_tvs, arg_ids),
747 -- ex_tvs are intended to be used as binders for existential type args
749 -- co_tvs are intended to be used as binders for coercion args and the kinds
750 -- of these vars have been instantiated by the inst_tys and the ex_tys
751 -- The co_tvs include both GADT equalities (dcEqSpec) and
752 -- programmer-specified equalities (dcEqTheta)
754 -- arg_ids are indended to be used as binders for value arguments,
755 -- and their types have been instantiated with inst_tys and ex_tys
756 -- The arg_ids include both dicts (dcDictTheta) and
757 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
760 -- The following constructor T1
763 -- T1 :: forall b. Int -> b -> T(a,b)
766 -- has representation type
767 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
770 -- dataConInstPat fss us T1 (a1',b') will return
772 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
774 -- where the double-primed variables are created with the FastStrings and
775 -- Uniques given as fss and us
776 dataConInstPat arg_fun fss uniqs con inst_tys
777 = (ex_bndrs, co_bndrs, arg_ids)
779 univ_tvs = dataConUnivTyVars con
780 ex_tvs = dataConExTyVars con
781 arg_tys = arg_fun con
782 eq_spec = dataConEqSpec con
783 eq_theta = dataConEqTheta con
784 eq_preds = eqSpecPreds eq_spec ++ eq_theta
787 n_co = length eq_preds
789 -- split the Uniques and FastStrings
790 (ex_uniqs, uniqs') = splitAt n_ex uniqs
791 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
793 (ex_fss, fss') = splitAt n_ex fss
794 (co_fss, id_fss) = splitAt n_co fss'
796 -- Make existential type variables
797 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
798 mk_ex_var uniq fs var = mkTyVar new_name kind
800 new_name = mkSysTvName uniq fs
803 -- Make the instantiating substitution
804 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
806 -- Make new coercion vars, instantiating kind
807 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
808 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
810 new_name = mkSysTvName uniq fs
811 co_kind = substTy subst (mkPredTy eq_pred)
813 -- make value vars, instantiating types
814 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
815 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
819 %************************************************************************
823 %************************************************************************
826 -- | A cheap equality test which bales out fast!
827 -- If it returns @True@ the arguments are definitely equal,
828 -- otherwise, they may or may not be equal.
830 -- See also 'exprIsBig'
831 cheapEqExpr :: Expr b -> Expr b -> Bool
833 cheapEqExpr (Var v1) (Var v2) = v1==v2
834 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
835 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
837 cheapEqExpr (App f1 a1) (App f2 a2)
838 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
840 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
841 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
843 cheapEqExpr _ _ = False
845 exprIsBig :: Expr b -> Bool
846 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
847 exprIsBig (Lit _) = False
848 exprIsBig (Var _) = False
849 exprIsBig (Type _) = False
850 exprIsBig (Lam _ e) = exprIsBig e
851 exprIsBig (App f a) = exprIsBig f || exprIsBig a
852 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
858 %************************************************************************
860 \subsection{The size of an expression}
862 %************************************************************************
865 coreBindsSize :: [CoreBind] -> Int
866 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
868 exprSize :: CoreExpr -> Int
869 -- ^ A measure of the size of the expressions, strictly greater than 0
870 -- It also forces the expression pretty drastically as a side effect
871 exprSize (Var v) = v `seq` 1
872 exprSize (Lit lit) = lit `seq` 1
873 exprSize (App f a) = exprSize f + exprSize a
874 exprSize (Lam b e) = varSize b + exprSize e
875 exprSize (Let b e) = bindSize b + exprSize e
876 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
877 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
878 exprSize (Note n e) = noteSize n + exprSize e
879 exprSize (Type t) = seqType t `seq` 1
881 noteSize :: Note -> Int
882 noteSize (SCC cc) = cc `seq` 1
883 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
885 varSize :: Var -> Int
886 varSize b | isTyVar b = 1
887 | otherwise = seqType (idType b) `seq`
888 megaSeqIdInfo (idInfo b) `seq`
891 varsSize :: [Var] -> Int
892 varsSize = sum . map varSize
894 bindSize :: CoreBind -> Int
895 bindSize (NonRec b e) = varSize b + exprSize e
896 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
898 pairSize :: (Var, CoreExpr) -> Int
899 pairSize (b,e) = varSize b + exprSize e
901 altSize :: CoreAlt -> Int
902 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
906 %************************************************************************
910 %************************************************************************
913 hashExpr :: CoreExpr -> Int
914 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
915 -- Two expressions that hash to the different Ints are definitely unequal.
917 -- The emphasis is on a crude, fast hash, rather than on high precision.
919 -- But unequal here means \"not identical\"; two alpha-equivalent
920 -- expressions may hash to the different Ints.
922 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
923 -- (at least if we want the above invariant to be true).
925 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
926 -- UniqFM doesn't like negative Ints
928 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
930 hash_expr :: HashEnv -> CoreExpr -> Word32
931 -- Word32, because we're expecting overflows here, and overflowing
932 -- signed types just isn't cool. In C it's even undefined.
933 hash_expr env (Note _ e) = hash_expr env e
934 hash_expr env (Cast e _) = hash_expr env e
935 hash_expr env (Var v) = hashVar env v
936 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
937 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
938 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
939 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
940 hash_expr env (Case e _ _ _) = hash_expr env e
941 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
942 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
943 -- Shouldn't happen. Better to use WARN than trace, because trace
944 -- prevents the CPR optimisation kicking in for hash_expr.
946 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
947 fast_hash_expr env (Var v) = hashVar env v
948 fast_hash_expr env (Type t) = fast_hash_type env t
949 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
950 fast_hash_expr env (Cast e _) = fast_hash_expr env e
951 fast_hash_expr env (Note _ e) = fast_hash_expr env e
952 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
953 fast_hash_expr _ _ = 1
955 fast_hash_type :: HashEnv -> Type -> Word32
956 fast_hash_type env ty
957 | Just tv <- getTyVar_maybe ty = hashVar env tv
958 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
959 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
962 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
963 extend_env (n,env) b = (n+1, extendVarEnv env b n)
965 hashVar :: HashEnv -> Var -> Word32
967 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
970 %************************************************************************
972 \subsection{Determining non-updatable right-hand-sides}
974 %************************************************************************
976 Top-level constructor applications can usually be allocated
977 statically, but they can't if the constructor, or any of the
978 arguments, come from another DLL (because we can't refer to static
979 labels in other DLLs).
981 If this happens we simply make the RHS into an updatable thunk,
982 and 'execute' it rather than allocating it statically.
985 -- | This function is called only on *top-level* right-hand sides.
986 -- Returns @True@ if the RHS can be allocated statically in the output,
987 -- with no thunks involved at all.
988 rhsIsStatic :: PackageId -> CoreExpr -> Bool
989 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
990 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
991 -- update flag on it and (iii) in DsExpr to decide how to expand
994 -- The basic idea is that rhsIsStatic returns True only if the RHS is
995 -- (a) a value lambda
996 -- (b) a saturated constructor application with static args
999 -- (i) Any cross-DLL references kill static-ness completely
1000 -- because they must be 'executed' not statically allocated
1001 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1002 -- this is not necessary)
1004 -- (ii) We treat partial applications as redexes, because in fact we
1005 -- make a thunk for them that runs and builds a PAP
1006 -- at run-time. The only appliations that are treated as
1007 -- static are *saturated* applications of constructors.
1009 -- We used to try to be clever with nested structures like this:
1010 -- ys = (:) w ((:) w [])
1011 -- on the grounds that CorePrep will flatten ANF-ise it later.
1012 -- But supporting this special case made the function much more
1013 -- complicated, because the special case only applies if there are no
1014 -- enclosing type lambdas:
1015 -- ys = /\ a -> Foo (Baz ([] a))
1016 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1018 -- But in fact, even without -O, nested structures at top level are
1019 -- flattened by the simplifier, so we don't need to be super-clever here.
1023 -- f = \x::Int. x+7 TRUE
1024 -- p = (True,False) TRUE
1026 -- d = (fst p, False) FALSE because there's a redex inside
1027 -- (this particular one doesn't happen but...)
1029 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1030 -- n = /\a. Nil a TRUE
1032 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1035 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1036 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1038 -- b) (C x xs), where C is a contructor is updatable if the application is
1041 -- c) don't look through unfolding of f in (f x).
1043 rhsIsStatic _this_pkg rhs = is_static False rhs
1045 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1048 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1050 is_static _ (Note (SCC _) _) = False
1051 is_static in_arg (Note _ e) = is_static in_arg e
1052 is_static in_arg (Cast e _) = is_static in_arg e
1054 is_static _ (Lit lit)
1056 MachLabel _ _ _ -> False
1058 -- A MachLabel (foreign import "&foo") in an argument
1059 -- prevents a constructor application from being static. The
1060 -- reason is that it might give rise to unresolvable symbols
1061 -- in the object file: under Linux, references to "weak"
1062 -- symbols from the data segment give rise to "unresolvable
1063 -- relocation" errors at link time This might be due to a bug
1064 -- in the linker, but we'll work around it here anyway.
1067 is_static in_arg other_expr = go other_expr 0
1069 go (Var f) n_val_args
1070 #if mingw32_TARGET_OS
1071 | not (isDllName _this_pkg (idName f))
1073 = saturated_data_con f n_val_args
1074 || (in_arg && n_val_args == 0)
1075 -- A naked un-applied variable is *not* deemed a static RHS
1077 -- Reason: better to update so that the indirection gets shorted
1078 -- out, and the true value will be seen
1079 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1080 -- are always updatable. If you do so, make sure that non-updatable
1081 -- ones have enough space for their static link field!
1083 go (App f a) n_val_args
1084 | isTypeArg a = go f n_val_args
1085 | not in_arg && is_static True a = go f (n_val_args + 1)
1086 -- The (not in_arg) checks that we aren't in a constructor argument;
1087 -- if we are, we don't allow (value) applications of any sort
1089 -- NB. In case you wonder, args are sometimes not atomic. eg.
1090 -- x = D# (1.0## /## 2.0##)
1091 -- can't float because /## can fail.
1093 go (Note (SCC _) _) _ = False
1094 go (Note _ f) n_val_args = go f n_val_args
1095 go (Cast e _) n_val_args = go e n_val_args
1099 saturated_data_con f n_val_args
1100 = case isDataConWorkId_maybe f of
1101 Just dc -> n_val_args == dataConRepArity dc