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, exprIsConLike,
30 rhsIsStatic, isCheapApp, isExpandableApp,
32 -- * Expression and bindings size
33 coreBindsSize, exprSize,
39 cheapEqExpr, eqExpr, eqExprX,
44 -- * Manipulating data constructors and types
45 applyTypeToArgs, applyTypeToArg,
46 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
49 #include "HsVersions.h"
67 import TcType ( isPredTy )
75 import PrelNames( absentErrorIdKey )
84 %************************************************************************
86 \subsection{Find the type of a Core atom/expression}
88 %************************************************************************
91 exprType :: CoreExpr -> Type
92 -- ^ Recover the type of a well-typed Core expression. Fails when
93 -- applied to the actual 'CoreSyn.Type' expression as it cannot
94 -- really be said to have a type
95 exprType (Var var) = idType var
96 exprType (Lit lit) = literalType lit
97 exprType (Let _ body) = exprType body
98 exprType (Case _ _ ty _) = ty
99 exprType (Cast _ co) = snd (coercionKind co)
100 exprType (Note _ e) = exprType e
101 exprType (Lam binder expr) = mkPiType binder (exprType expr)
103 = case collectArgs e of
104 (fun, args) -> applyTypeToArgs e (exprType fun) args
106 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
108 coreAltType :: CoreAlt -> Type
109 -- ^ Returns the type of the alternatives right hand side
110 coreAltType (_,bs,rhs)
111 | any bad_binder bs = expandTypeSynonyms ty
112 | otherwise = ty -- Note [Existential variables and silly type synonyms]
115 free_tvs = tyVarsOfType ty
116 bad_binder b = isTyCoVar b && b `elemVarSet` free_tvs
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"
124 Note [Existential variables and silly type synonyms]
125 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
127 data T = forall a. T (Funny a)
132 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
133 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
134 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
137 Various possibilities suggest themselves:
139 - Ignore the problem, and make Lint not complain about such variables
141 - Expand all type synonyms (or at least all those that discard arguments)
142 This is tricky, because at least for top-level things we want to
143 retain the type the user originally specified.
145 - Expand synonyms on the fly, when the problem arises. That is what
146 we are doing here. It's not too expensive, I think.
149 mkPiType :: EvVar -> Type -> Type
150 -- ^ Makes a @(->)@ type or a forall type, depending
151 -- on whether it is given a type variable or a term variable.
152 mkPiTypes :: [EvVar] -> Type -> Type
153 -- ^ 'mkPiType' for multiple type or value arguments
156 | isId v = mkFunTy (idType v) ty
157 | otherwise = mkForAllTy v ty
159 mkPiTypes vs ty = foldr mkPiType ty vs
163 applyTypeToArg :: Type -> CoreExpr -> Type
164 -- ^ Determines the type resulting from applying an expression to a function with the given type
165 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
166 applyTypeToArg fun_ty _ = funResultTy fun_ty
168 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
169 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
170 -- The first argument is just for debugging, and gives some context
171 applyTypeToArgs _ op_ty [] = op_ty
173 applyTypeToArgs e op_ty (Type ty : args)
174 = -- Accumulate type arguments so we can instantiate all at once
177 go rev_tys (Type ty : args) = go (ty:rev_tys) args
178 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
180 op_ty' = applyTysD msg op_ty (reverse rev_tys)
181 msg = ptext (sLit "applyTypeToArgs") <+>
184 applyTypeToArgs e op_ty (_ : args)
185 = case (splitFunTy_maybe op_ty) of
186 Just (_, res_ty) -> applyTypeToArgs e res_ty args
187 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
189 panic_msg :: CoreExpr -> Type -> SDoc
190 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
193 %************************************************************************
195 \subsection{Attaching notes}
197 %************************************************************************
200 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
201 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
202 mkCoerceI (IdCo _) e = e
203 mkCoerceI (ACo co) e = mkCoerce co e
205 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
206 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
207 mkCoerce co (Cast expr co2)
208 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
209 (_from_ty2, to_ty2) = coercionKind co2} in
210 from_ty `coreEqType` to_ty2 )
211 mkCoerce (mkTransCoercion co2 co) expr
214 = let (from_ty, _to_ty) = coercionKind co in
215 -- if to_ty `coreEqType` from_ty
218 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
223 -- | Wraps the given expression in the cost centre unless
224 -- in a way that maximises their utility to the user
225 mkSCC :: CostCentre -> Expr b -> Expr b
226 -- Note: Nested SCC's *are* preserved for the benefit of
227 -- cost centre stack profiling
228 mkSCC _ (Lit lit) = Lit lit
229 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
230 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
231 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
232 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
233 mkSCC cc expr = Note (SCC cc) expr
237 %************************************************************************
239 \subsection{Other expression construction}
241 %************************************************************************
244 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
245 -- ^ @bindNonRec x r b@ produces either:
251 -- > case r of x { _DEFAULT_ -> b }
253 -- depending on whether we have to use a @case@ or @let@
254 -- binding for the expression (see 'needsCaseBinding').
255 -- It's used by the desugarer to avoid building bindings
256 -- that give Core Lint a heart attack, although actually
257 -- the simplifier deals with them perfectly well. See
258 -- also 'MkCore.mkCoreLet'
259 bindNonRec bndr rhs body
260 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
261 | otherwise = Let (NonRec bndr rhs) body
263 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
264 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
265 needsCaseBinding :: Type -> CoreExpr -> Bool
266 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
267 -- Make a case expression instead of a let
268 -- These can arise either from the desugarer,
269 -- or from beta reductions: (\x.e) (x +# y)
273 mkAltExpr :: AltCon -- ^ Case alternative constructor
274 -> [CoreBndr] -- ^ Things bound by the pattern match
275 -> [Type] -- ^ The type arguments to the case alternative
277 -- ^ This guy constructs the value that the scrutinee must have
278 -- given that you are in one particular branch of a case
279 mkAltExpr (DataAlt con) args inst_tys
280 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
281 mkAltExpr (LitAlt lit) [] []
283 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
284 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
288 %************************************************************************
290 \subsection{Taking expressions apart}
292 %************************************************************************
294 The default alternative must be first, if it exists at all.
295 This makes it easy to find, though it makes matching marginally harder.
298 -- | Extract the default case alternative
299 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
300 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
301 findDefault alts = (alts, Nothing)
303 isDefaultAlt :: CoreAlt -> Bool
304 isDefaultAlt (DEFAULT, _, _) = True
305 isDefaultAlt _ = False
308 -- | Find the case alternative corresponding to a particular
309 -- constructor: panics if no such constructor exists
310 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
311 -- A "Nothing" result *is* legitmiate
312 -- See Note [Unreachable code]
315 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
319 go (alt@(con1,_,_) : alts) deflt
320 = case con `cmpAltCon` con1 of
321 LT -> deflt -- Missed it already; the alts are in increasing order
323 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
325 ---------------------------------
326 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
327 -- ^ Merge alternatives preserving order; alternatives in
328 -- the first argument shadow ones in the second
329 mergeAlts [] as2 = as2
330 mergeAlts as1 [] = as1
331 mergeAlts (a1:as1) (a2:as2)
332 = case a1 `cmpAlt` a2 of
333 LT -> a1 : mergeAlts as1 (a2:as2)
334 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
335 GT -> a2 : mergeAlts (a1:as1) as2
338 ---------------------------------
339 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
342 -- > case (C a b x y) of
345 -- We want to drop the leading type argument of the scrutinee
346 -- leaving the arguments to match agains the pattern
348 trimConArgs DEFAULT args = ASSERT( null args ) []
349 trimConArgs (LitAlt _) args = ASSERT( null args ) []
350 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
353 Note [Unreachable code]
354 ~~~~~~~~~~~~~~~~~~~~~~~
355 It is possible (although unusual) for GHC to find a case expression
356 that cannot match. For example:
358 data Col = Red | Green | Blue
362 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
364 Suppose that for some silly reason, x isn't substituted in the case
365 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
366 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
370 lvl = case x of { Green -> e1; Blue -> e2 })
375 Now if x gets inlined, we won't be able to find a matching alternative
376 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
377 we generate (error "Inaccessible alternative").
379 Similar things can happen (augmented by GADTs) when the Simplifier
380 filters down the matching alternatives in Simplify.rebuildCase.
383 %************************************************************************
387 %************************************************************************
391 @exprIsTrivial@ is true of expressions we are unconditionally happy to
392 duplicate; simple variables and constants, and type
393 applications. Note that primop Ids aren't considered
396 Note [Variable are trivial]
397 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
398 There used to be a gruesome test for (hasNoBinding v) in the
400 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
401 The idea here is that a constructor worker, like \$wJust, is
402 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
403 So it should be treated like a lambda. Ditto unsaturated primops.
404 But now constructor workers are not "have-no-binding" Ids. And
405 completely un-applied primops and foreign-call Ids are sufficiently
406 rare that I plan to allow them to be duplicated and put up with
409 Note [SCCs are trivial]
410 ~~~~~~~~~~~~~~~~~~~~~~~
411 We used not to treat (_scc_ "foo" x) as trivial, because it really
412 generates code, (and a heap object when it's a function arg) to
413 capture the cost centre. However, the profiling system discounts the
414 allocation costs for such "boxing thunks" whereas the extra costs of
415 *not* inlining otherwise-trivial bindings can be high, and are hard to
419 exprIsTrivial :: CoreExpr -> Bool
420 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
421 exprIsTrivial (Type _) = True
422 exprIsTrivial (Lit lit) = litIsTrivial lit
423 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
424 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
425 exprIsTrivial (Cast e _) = exprIsTrivial e
426 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
427 exprIsTrivial _ = False
431 %************************************************************************
435 %************************************************************************
439 @exprIsDupable@ is true of expressions that can be duplicated at a modest
440 cost in code size. This will only happen in different case
441 branches, so there's no issue about duplicating work.
443 That is, exprIsDupable returns True of (f x) even if
444 f is very very expensive to call.
446 Its only purpose is to avoid fruitless let-binding
447 and then inlining of case join points
451 exprIsDupable :: CoreExpr -> Bool
452 exprIsDupable (Type _) = True
453 exprIsDupable (Var _) = True
454 exprIsDupable (Lit lit) = litIsDupable lit
455 exprIsDupable (Note _ e) = exprIsDupable e
456 exprIsDupable (Cast e _) = exprIsDupable e
461 go (App f a) n_args = n_args < dupAppSize
467 dupAppSize = 4 -- Size of application we are prepared to duplicate
470 %************************************************************************
472 exprIsCheap, exprIsExpandable
474 %************************************************************************
476 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
477 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
478 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
479 it is obviously in weak head normal form, or is cheap to get to WHNF.
480 [Note that that's not the same as exprIsDupable; an expression might be
481 big, and hence not dupable, but still cheap.]
483 By ``cheap'' we mean a computation we're willing to:
484 push inside a lambda, or
485 inline at more than one place
486 That might mean it gets evaluated more than once, instead of being
487 shared. The main examples of things which aren't WHNF but are
492 (where e, and all the ei are cheap)
495 (where e and b are cheap)
498 (where op is a cheap primitive operator)
501 (because we are happy to substitute it inside a lambda)
503 Notice that a variable is considered 'cheap': we can push it inside a lambda,
504 because sharing will make sure it is only evaluated once.
506 Note [exprIsCheap and exprIsHNF]
507 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
508 Note that exprIsHNF does not imply exprIsCheap. Eg
509 let x = fac 20 in Just x
510 This responds True to exprIsHNF (you can discard a seq), but
511 False to exprIsCheap.
514 exprIsCheap :: CoreExpr -> Bool
515 exprIsCheap = exprIsCheap' isCheapApp
517 exprIsExpandable :: CoreExpr -> Bool
518 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
521 exprIsCheap' :: (Id -> Int -> Bool) -> CoreExpr -> Bool
522 exprIsCheap' _ (Lit _) = True
523 exprIsCheap' _ (Type _) = True
524 exprIsCheap' _ (Var _) = True
525 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
526 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
527 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
528 || exprIsCheap' good_app e
530 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
531 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
532 -- Experimentally, treat (case x of ...) as cheap
533 -- (and case __coerce x etc.)
534 -- This improves arities of overloaded functions where
535 -- there is only dictionary selection (no construction) involved
537 exprIsCheap' good_app (Let (NonRec x _) e)
538 | isUnLiftedType (idType x) = exprIsCheap' good_app e
540 -- Strict lets always have cheap right hand sides,
541 -- and do no allocation, so just look at the body
542 -- Non-strict lets do allocation so we don't treat them as cheap
545 exprIsCheap' good_app other_expr -- Applications and variables
548 -- Accumulate value arguments, then decide
549 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
550 | otherwise = go f val_args
552 go (Var _) [] = True -- Just a type application of a variable
553 -- (f t1 t2 t3) counts as WHNF
555 = case idDetails f of
556 RecSelId {} -> go_sel args
557 ClassOpId {} -> go_sel args
558 PrimOpId op -> go_primop op args
559 _ | good_app f (length args) -> go_pap args
560 | isBottomingId f -> True
562 -- Application of a function which
563 -- always gives bottom; we treat this as cheap
564 -- because it certainly doesn't need to be shared!
569 go_pap args = all exprIsTrivial args
570 -- For constructor applications and primops, check that all
571 -- the args are trivial. We don't want to treat as cheap, say,
573 -- We'll put up with one constructor application, but not dozens
576 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
577 -- In principle we should worry about primops
578 -- that return a type variable, since the result
579 -- might be applied to something, but I'm not going
580 -- to bother to check the number of args
583 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
584 go_sel _ = False -- look cheap, so we will substitute it inside a
585 -- lambda. Particularly for dictionary field selection.
586 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
587 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
589 isCheapApp :: Id -> Int -> Bool
590 isCheapApp fn n_val_args
592 || n_val_args < idArity fn
594 isExpandableApp :: Id -> Int -> Bool
595 isExpandableApp fn n_val_args
597 || n_val_args < idArity fn
598 || go n_val_args (idType fn)
600 -- See if all the arguments are PredTys (implicit params or classes)
601 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
604 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
605 | Just (arg, ty) <- splitFunTy_maybe ty
606 , isPredTy arg = go (n_val_args-1) ty
610 Note [Expandable overloadings]
611 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
612 Suppose the user wrote this
613 {-# RULE forall x. foo (negate x) = h x #-}
614 f x = ....(foo (negate x))....
615 He'd expect the rule to fire. But since negate is overloaded, we might
617 f = \d -> let n = negate d in \x -> ...foo (n x)...
618 So we treat the application of a function (negate in this case) to a
619 *dictionary* as expandable. In effect, every function is CONLIKE when
620 it's applied only to dictionaries.
623 %************************************************************************
627 %************************************************************************
630 -- | 'exprOkForSpeculation' returns True of an expression that is:
632 -- * Safe to evaluate even if normal order eval might not
633 -- evaluate the expression at all, or
635 -- * Safe /not/ to evaluate even if normal order would do so
637 -- Precisely, it returns @True@ iff:
639 -- * The expression guarantees to terminate,
641 -- * without raising an exception,
642 -- * without causing a side effect (e.g. writing a mutable variable)
644 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
645 -- As an example of the considerations in this test, consider:
647 -- > let x = case y# +# 1# of { r# -> I# r# }
650 -- being translated to:
652 -- > case y# +# 1# of { r# ->
657 -- We can only do this if the @y + 1@ is ok for speculation: it has no
658 -- side effects, and can't diverge or raise an exception.
659 exprOkForSpeculation :: CoreExpr -> Bool
660 exprOkForSpeculation (Lit _) = True
661 exprOkForSpeculation (Type _) = True
662 -- Tick boxes are *not* suitable for speculation
663 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
664 && not (isTickBoxOp v)
665 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
666 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
668 exprOkForSpeculation (Case e _ _ alts)
669 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
670 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
672 exprOkForSpeculation other_expr
673 = case collectArgs other_expr of
674 (Var f, args) | f `hasKey` absentErrorIdKey -- Note [Absent error Id]
675 -> all exprOkForSpeculation args -- in WwLib
677 -> spec_ok (idDetails f) args
681 spec_ok (DataConWorkId _) _
682 = True -- The strictness of the constructor has already
683 -- been expressed by its "wrapper", so we don't need
684 -- to take the arguments into account
686 spec_ok (PrimOpId op) args
687 | isDivOp op, -- Special case for dividing operations that fail
688 [arg1, Lit lit] <- args -- only if the divisor is zero
689 = not (isZeroLit lit) && exprOkForSpeculation arg1
690 -- Often there is a literal divisor, and this
691 -- can get rid of a thunk in an inner looop
694 = primOpOkForSpeculation op &&
695 all exprOkForSpeculation args
696 -- A bit conservative: we don't really need
697 -- to care about lazy arguments, but this is easy
699 spec_ok (DFunId new_type) _ = not new_type
700 -- DFuns terminate, unless the dict is implemented with a newtype
701 -- in which case they may not
705 -- | True of dyadic operators that can fail only if the second arg is zero!
706 isDivOp :: PrimOp -> Bool
707 -- This function probably belongs in PrimOp, or even in
708 -- an automagically generated file.. but it's such a
709 -- special case I thought I'd leave it here for now.
710 isDivOp IntQuotOp = True
711 isDivOp IntRemOp = True
712 isDivOp WordQuotOp = True
713 isDivOp WordRemOp = True
714 isDivOp FloatDivOp = True
715 isDivOp DoubleDivOp = True
719 Note [exprOkForSpeculation: case expressions]
720 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
722 It's always sound for exprOkForSpeculation to return False, and we
723 don't want it to take too long, so it bales out on complicated-looking
724 terms. Notably lets, which can be stacked very deeply; and in any
725 case the argument of exprOkForSpeculation is usually in a strict context,
726 so any lets will have been floated away.
728 However, we keep going on case-expressions. An example like this one
729 showed up in DPH code:
732 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
734 If exprOkForSpeculation doesn't look through case expressions, you get this:
736 \ (ww :: GHC.Prim.Int#) ->
738 __DEFAULT -> case (case <# ds 5 of _ {
739 GHC.Bool.False -> lvl1;
740 GHC.Bool.True -> lvl})
742 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
746 The inner case is redundant, and should be nuked.
749 %************************************************************************
751 exprIsHNF, exprIsConLike
753 %************************************************************************
756 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
758 -- | exprIsHNF returns true for expressions that are certainly /already/
759 -- evaluated to /head/ normal form. This is used to decide whether it's ok
762 -- > case x of _ -> e
768 -- and to decide whether it's safe to discard a 'seq'.
770 -- So, it does /not/ treat variables as evaluated, unless they say they are.
771 -- However, it /does/ treat partial applications and constructor applications
772 -- as values, even if their arguments are non-trivial, provided the argument
773 -- type is lifted. For example, both of these are values:
775 -- > (:) (f x) (map f xs)
776 -- > map (...redex...)
778 -- because 'seq' on such things completes immediately.
780 -- For unlifted argument types, we have to be careful:
784 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
785 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
786 -- unboxed type must be ok-for-speculation (or trivial).
787 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
788 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
792 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
793 -- data constructors. Conlike arguments are considered interesting by the
795 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
796 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
798 -- | Returns true for values or value-like expressions. These are lambdas,
799 -- constructors / CONLIKE functions (as determined by the function argument)
802 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
803 exprIsHNFlike is_con is_con_unf = is_hnf_like
805 is_hnf_like (Var v) -- NB: There are no value args at this point
806 = is_con v -- Catches nullary constructors,
807 -- so that [] and () are values, for example
808 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
809 || is_con_unf (idUnfolding v)
810 -- Check the thing's unfolding; it might be bound to a value
811 -- We don't look through loop breakers here, which is a bit conservative
812 -- but otherwise I worry that if an Id's unfolding is just itself,
813 -- we could get an infinite loop
815 is_hnf_like (Lit _) = True
816 is_hnf_like (Type _) = True -- Types are honorary Values;
817 -- we don't mind copying them
818 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
819 is_hnf_like (Note _ e) = is_hnf_like e
820 is_hnf_like (Cast e _) = is_hnf_like e
821 is_hnf_like (App e (Type _)) = is_hnf_like e
822 is_hnf_like (App e a) = app_is_value e [a]
823 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
824 is_hnf_like _ = False
826 -- There is at least one value argument
827 app_is_value :: CoreExpr -> [CoreArg] -> Bool
828 app_is_value (Var fun) args
829 = idArity fun > valArgCount args -- Under-applied function
830 || is_con fun -- or constructor-like
831 app_is_value (Note _ f) as = app_is_value f as
832 app_is_value (Cast f _) as = app_is_value f as
833 app_is_value (App f a) as = app_is_value f (a:as)
834 app_is_value _ _ = False
838 %************************************************************************
840 Instantiating data constructors
842 %************************************************************************
844 These InstPat functions go here to avoid circularity between DataCon and Id
847 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
848 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
850 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
851 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
852 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
854 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
855 -- Remember to include the existential dictionaries
857 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
858 -> [FastString] -- A long enough list of FSs to use for names
859 -> [Unique] -- An equally long list of uniques, at least one for each binder
861 -> [Type] -- Types to instantiate the universally quantified tyvars
862 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
863 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
864 -- (ex_tvs, co_tvs, arg_ids),
866 -- ex_tvs are intended to be used as binders for existential type args
868 -- co_tvs are intended to be used as binders for coercion args and the kinds
869 -- of these vars have been instantiated by the inst_tys and the ex_tys
870 -- The co_tvs include both GADT equalities (dcEqSpec) and
871 -- programmer-specified equalities (dcEqTheta)
873 -- arg_ids are indended to be used as binders for value arguments,
874 -- and their types have been instantiated with inst_tys and ex_tys
875 -- The arg_ids include both dicts (dcDictTheta) and
876 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
879 -- The following constructor T1
882 -- T1 :: forall b. Int -> b -> T(a,b)
885 -- has representation type
886 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
889 -- dataConInstPat fss us T1 (a1',b') will return
891 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
893 -- where the double-primed variables are created with the FastStrings and
894 -- Uniques given as fss and us
895 dataConInstPat arg_fun fss uniqs con inst_tys
896 = (ex_bndrs, co_bndrs, arg_ids)
898 univ_tvs = dataConUnivTyVars con
899 ex_tvs = dataConExTyVars con
900 arg_tys = arg_fun con
901 eq_spec = dataConEqSpec con
902 eq_theta = dataConEqTheta con
903 eq_preds = eqSpecPreds eq_spec ++ eq_theta
906 n_co = length eq_preds
908 -- split the Uniques and FastStrings
909 (ex_uniqs, uniqs') = splitAt n_ex uniqs
910 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
912 (ex_fss, fss') = splitAt n_ex fss
913 (co_fss, id_fss) = splitAt n_co fss'
915 -- Make existential type variables
916 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
917 mk_ex_var uniq fs var = mkTyVar new_name kind
919 new_name = mkSysTvName uniq fs
922 -- Make the instantiating substitution
923 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
925 -- Make new coercion vars, instantiating kind
926 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
927 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
929 new_name = mkSysTvName uniq fs
930 co_kind = substTy subst (mkPredTy eq_pred)
932 -- make value vars, instantiating types
933 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
934 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
938 %************************************************************************
942 %************************************************************************
945 -- | A cheap equality test which bales out fast!
946 -- If it returns @True@ the arguments are definitely equal,
947 -- otherwise, they may or may not be equal.
949 -- See also 'exprIsBig'
950 cheapEqExpr :: Expr b -> Expr b -> Bool
952 cheapEqExpr (Var v1) (Var v2) = v1==v2
953 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
954 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
956 cheapEqExpr (App f1 a1) (App f2 a2)
957 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
959 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
960 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
962 cheapEqExpr _ _ = False
966 exprIsBig :: Expr b -> Bool
967 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
968 exprIsBig (Lit _) = False
969 exprIsBig (Var _) = False
970 exprIsBig (Type _) = False
971 exprIsBig (Lam _ e) = exprIsBig e
972 exprIsBig (App f a) = exprIsBig f || exprIsBig a
973 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
978 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
979 -- Compares for equality, modulo alpha
980 eqExpr in_scope e1 e2
981 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
983 id_unf _ = noUnfolding -- Don't expand
987 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
988 -- ^ Compares expressions for equality, modulo alpha.
989 -- Does /not/ look through newtypes or predicate types
990 -- Used in rule matching, and also CSE
992 eqExprX id_unfolding_fun env e1 e2
995 go env (Var v1) (Var v2)
996 | rnOccL env v1 == rnOccR env v2
999 -- The next two rules expand non-local variables
1000 -- C.f. Note [Expanding variables] in Rules.lhs
1001 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1003 | not (locallyBoundL env v1)
1004 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1005 = go (nukeRnEnvL env) e1' e2
1008 | not (locallyBoundR env v2)
1009 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1010 = go (nukeRnEnvR env) e1 e2'
1012 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1013 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1014 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1015 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1016 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1018 go env (Lam b1 e1) (Lam b2 e2)
1019 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1020 && go (rnBndr2 env b1 b2) e1 e2
1022 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1023 = go env r1 r2 -- No need to check binder types, since RHSs match
1024 && go (rnBndr2 env v1 v2) e1 e2
1026 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1027 = all2 (go env') rs1 rs2 && go env' e1 e2
1029 (bs1,rs1) = unzip ps1
1030 (bs2,rs2) = unzip ps2
1031 env' = rnBndrs2 env bs1 bs2
1033 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1035 && tcEqTypeX env (idType b1) (idType b2)
1036 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1041 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1042 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1045 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1046 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1053 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1054 locallyBoundL rn_env v = inRnEnvL rn_env v
1055 locallyBoundR rn_env v = inRnEnvR rn_env v
1059 %************************************************************************
1061 \subsection{The size of an expression}
1063 %************************************************************************
1066 coreBindsSize :: [CoreBind] -> Int
1067 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1069 exprSize :: CoreExpr -> Int
1070 -- ^ A measure of the size of the expressions, strictly greater than 0
1071 -- It also forces the expression pretty drastically as a side effect
1072 exprSize (Var v) = v `seq` 1
1073 exprSize (Lit lit) = lit `seq` 1
1074 exprSize (App f a) = exprSize f + exprSize a
1075 exprSize (Lam b e) = varSize b + exprSize e
1076 exprSize (Let b e) = bindSize b + exprSize e
1077 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1078 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1079 exprSize (Note n e) = noteSize n + exprSize e
1080 exprSize (Type t) = seqType t `seq` 1
1082 noteSize :: Note -> Int
1083 noteSize (SCC cc) = cc `seq` 1
1084 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1086 varSize :: Var -> Int
1087 varSize b | isTyCoVar b = 1
1088 | otherwise = seqType (idType b) `seq`
1089 megaSeqIdInfo (idInfo b) `seq`
1092 varsSize :: [Var] -> Int
1093 varsSize = sum . map varSize
1095 bindSize :: CoreBind -> Int
1096 bindSize (NonRec b e) = varSize b + exprSize e
1097 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1099 pairSize :: (Var, CoreExpr) -> Int
1100 pairSize (b,e) = varSize b + exprSize e
1102 altSize :: CoreAlt -> Int
1103 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1107 %************************************************************************
1109 \subsection{Hashing}
1111 %************************************************************************
1114 hashExpr :: CoreExpr -> Int
1115 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1116 -- Two expressions that hash to the different Ints are definitely unequal.
1118 -- The emphasis is on a crude, fast hash, rather than on high precision.
1120 -- But unequal here means \"not identical\"; two alpha-equivalent
1121 -- expressions may hash to the different Ints.
1123 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1124 -- (at least if we want the above invariant to be true).
1126 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1127 -- UniqFM doesn't like negative Ints
1129 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1131 hash_expr :: HashEnv -> CoreExpr -> Word32
1132 -- Word32, because we're expecting overflows here, and overflowing
1133 -- signed types just isn't cool. In C it's even undefined.
1134 hash_expr env (Note _ e) = hash_expr env e
1135 hash_expr env (Cast e _) = hash_expr env e
1136 hash_expr env (Var v) = hashVar env v
1137 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1138 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1139 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1140 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1141 hash_expr env (Case e _ _ _) = hash_expr env e
1142 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1143 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1144 -- Shouldn't happen. Better to use WARN than trace, because trace
1145 -- prevents the CPR optimisation kicking in for hash_expr.
1147 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1148 fast_hash_expr env (Var v) = hashVar env v
1149 fast_hash_expr env (Type t) = fast_hash_type env t
1150 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1151 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1152 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1153 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1154 fast_hash_expr _ _ = 1
1156 fast_hash_type :: HashEnv -> Type -> Word32
1157 fast_hash_type env ty
1158 | Just tv <- getTyVar_maybe ty = hashVar env tv
1159 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1160 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1163 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1164 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1166 hashVar :: HashEnv -> Var -> Word32
1168 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1172 %************************************************************************
1176 %************************************************************************
1178 Note [Eta reduction conditions]
1179 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1180 We try for eta reduction here, but *only* if we get all the way to an
1181 trivial expression. We don't want to remove extra lambdas unless we
1182 are going to avoid allocating this thing altogether.
1184 There are some particularly delicate points here:
1186 * Eta reduction is not valid in general:
1188 This matters, partly for old-fashioned correctness reasons but,
1189 worse, getting it wrong can yield a seg fault. Consider
1191 h y = case (case y of { True -> f `seq` True; False -> False }) of
1192 True -> ...; False -> ...
1194 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1195 says f=bottom, and replaces the (f `seq` True) with just
1196 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1197 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1198 the definition again, so that it does not termninate after all.
1199 Result: seg-fault because the boolean case actually gets a function value.
1202 So it's important to to the right thing.
1204 * Note [Arity care]: we need to be careful if we just look at f's
1205 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1206 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1207 arity when checking that 'f' is a value. Otherwise we will
1212 Which might change a terminiating program (think (f `seq` e)) to a
1213 non-terminating one. So we check for being a loop breaker first.
1215 However for GlobalIds we can look at the arity; and for primops we
1216 must, since they have no unfolding.
1218 * Regardless of whether 'f' is a value, we always want to
1219 reduce (/\a -> f a) to f
1220 This came up in a RULE: foldr (build (/\a -> g a))
1221 did not match foldr (build (/\b -> ...something complex...))
1222 The type checker can insert these eta-expanded versions,
1223 with both type and dictionary lambdas; hence the slightly
1226 * Never *reduce* arity. For example
1228 Then if h has arity 1 we don't want to eta-reduce because then
1229 f's arity would decrease, and that is bad
1231 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1235 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1236 tryEtaReduce bndrs body
1237 = go (reverse bndrs) body
1239 incoming_arity = count isId bndrs
1241 go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round
1242 go [] fun | ok_fun fun = Just fun -- Success!
1243 go _ _ = Nothing -- Failure!
1245 -- Note [Eta reduction conditions]
1246 ok_fun (App fun (Type ty))
1247 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1250 = not (fun_id `elem` bndrs)
1251 && (ok_fun_id fun_id || all ok_lam bndrs)
1254 ok_fun_id fun = fun_arity fun >= incoming_arity
1256 fun_arity fun -- See Note [Arity care]
1257 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1258 | otherwise = idArity fun
1260 ok_lam v = isTyCoVar v || isDictId v
1262 ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg
1265 %************************************************************************
1267 \subsection{Determining non-updatable right-hand-sides}
1269 %************************************************************************
1271 Top-level constructor applications can usually be allocated
1272 statically, but they can't if the constructor, or any of the
1273 arguments, come from another DLL (because we can't refer to static
1274 labels in other DLLs).
1276 If this happens we simply make the RHS into an updatable thunk,
1277 and 'execute' it rather than allocating it statically.
1280 -- | This function is called only on *top-level* right-hand sides.
1281 -- Returns @True@ if the RHS can be allocated statically in the output,
1282 -- with no thunks involved at all.
1283 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1284 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1285 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1286 -- update flag on it and (iii) in DsExpr to decide how to expand
1289 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1290 -- (a) a value lambda
1291 -- (b) a saturated constructor application with static args
1293 -- BUT watch out for
1294 -- (i) Any cross-DLL references kill static-ness completely
1295 -- because they must be 'executed' not statically allocated
1296 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1297 -- this is not necessary)
1299 -- (ii) We treat partial applications as redexes, because in fact we
1300 -- make a thunk for them that runs and builds a PAP
1301 -- at run-time. The only appliations that are treated as
1302 -- static are *saturated* applications of constructors.
1304 -- We used to try to be clever with nested structures like this:
1305 -- ys = (:) w ((:) w [])
1306 -- on the grounds that CorePrep will flatten ANF-ise it later.
1307 -- But supporting this special case made the function much more
1308 -- complicated, because the special case only applies if there are no
1309 -- enclosing type lambdas:
1310 -- ys = /\ a -> Foo (Baz ([] a))
1311 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1313 -- But in fact, even without -O, nested structures at top level are
1314 -- flattened by the simplifier, so we don't need to be super-clever here.
1318 -- f = \x::Int. x+7 TRUE
1319 -- p = (True,False) TRUE
1321 -- d = (fst p, False) FALSE because there's a redex inside
1322 -- (this particular one doesn't happen but...)
1324 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1325 -- n = /\a. Nil a TRUE
1327 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1330 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1331 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1333 -- b) (C x xs), where C is a contructor is updatable if the application is
1336 -- c) don't look through unfolding of f in (f x).
1338 rhsIsStatic _this_pkg rhs = is_static False rhs
1340 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1343 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1345 is_static _ (Note (SCC _) _) = False
1346 is_static in_arg (Note _ e) = is_static in_arg e
1347 is_static in_arg (Cast e _) = is_static in_arg e
1349 is_static _ (Lit lit)
1351 MachLabel _ _ _ -> False
1353 -- A MachLabel (foreign import "&foo") in an argument
1354 -- prevents a constructor application from being static. The
1355 -- reason is that it might give rise to unresolvable symbols
1356 -- in the object file: under Linux, references to "weak"
1357 -- symbols from the data segment give rise to "unresolvable
1358 -- relocation" errors at link time This might be due to a bug
1359 -- in the linker, but we'll work around it here anyway.
1362 is_static in_arg other_expr = go other_expr 0
1364 go (Var f) n_val_args
1365 #if mingw32_TARGET_OS
1366 | not (isDllName _this_pkg (idName f))
1368 = saturated_data_con f n_val_args
1369 || (in_arg && n_val_args == 0)
1370 -- A naked un-applied variable is *not* deemed a static RHS
1372 -- Reason: better to update so that the indirection gets shorted
1373 -- out, and the true value will be seen
1374 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1375 -- are always updatable. If you do so, make sure that non-updatable
1376 -- ones have enough space for their static link field!
1378 go (App f a) n_val_args
1379 | isTypeArg a = go f n_val_args
1380 | not in_arg && is_static True a = go f (n_val_args + 1)
1381 -- The (not in_arg) checks that we aren't in a constructor argument;
1382 -- if we are, we don't allow (value) applications of any sort
1384 -- NB. In case you wonder, args are sometimes not atomic. eg.
1385 -- x = D# (1.0## /## 2.0##)
1386 -- can't float because /## can fail.
1388 go (Note (SCC _) _) _ = False
1389 go (Note _ f) n_val_args = go f n_val_args
1390 go (Cast e _) n_val_args = go e n_val_args
1394 saturated_data_con f n_val_args
1395 = case isDataConWorkId_maybe f of
1396 Just dc -> n_val_args == dataConRepArity dc