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, exprIsBottom,
29 exprIsCheap, exprIsExpandable, exprIsCheap', CheapAppFun,
30 exprIsHNF, exprOkForSpeculation, exprIsBig, exprIsConLike,
31 rhsIsStatic, isCheapApp, isExpandableApp,
33 -- * Expression and bindings size
34 coreBindsSize, exprSize,
40 cheapEqExpr, eqExpr, eqExprX,
45 -- * Manipulating data constructors and types
46 applyTypeToArgs, applyTypeToArg,
47 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
50 #include "HsVersions.h"
64 import TcType ( isPredTy )
72 import PrelNames( absentErrorIdKey )
81 %************************************************************************
83 \subsection{Find the type of a Core atom/expression}
85 %************************************************************************
88 exprType :: CoreExpr -> Type
89 -- ^ Recover the type of a well-typed Core expression. Fails when
90 -- applied to the actual 'CoreSyn.Type' expression as it cannot
91 -- really be said to have a type
92 exprType (Var var) = idType var
93 exprType (Lit lit) = literalType lit
94 exprType (Let _ body) = exprType body
95 exprType (Case _ _ ty _) = ty
96 exprType (Cast _ co) = snd (coercionKind co)
97 exprType (Note _ e) = exprType e
98 exprType (Lam binder expr) = mkPiType binder (exprType expr)
100 = case collectArgs e of
101 (fun, args) -> applyTypeToArgs e (exprType fun) args
103 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
105 coreAltType :: CoreAlt -> Type
106 -- ^ Returns the type of the alternatives right hand side
107 coreAltType (_,bs,rhs)
108 | any bad_binder bs = expandTypeSynonyms ty
109 | otherwise = ty -- Note [Existential variables and silly type synonyms]
112 free_tvs = tyVarsOfType ty
113 bad_binder b = isTyCoVar b && b `elemVarSet` free_tvs
115 coreAltsType :: [CoreAlt] -> Type
116 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
117 coreAltsType (alt:_) = coreAltType alt
118 coreAltsType [] = panic "corAltsType"
121 Note [Existential variables and silly type synonyms]
122 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
124 data T = forall a. T (Funny a)
129 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
130 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
131 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
134 Various possibilities suggest themselves:
136 - Ignore the problem, and make Lint not complain about such variables
138 - Expand all type synonyms (or at least all those that discard arguments)
139 This is tricky, because at least for top-level things we want to
140 retain the type the user originally specified.
142 - Expand synonyms on the fly, when the problem arises. That is what
143 we are doing here. It's not too expensive, I think.
146 mkPiType :: EvVar -> Type -> Type
147 -- ^ Makes a @(->)@ type or a forall type, depending
148 -- on whether it is given a type variable or a term variable.
149 mkPiTypes :: [EvVar] -> Type -> Type
150 -- ^ 'mkPiType' for multiple type or value arguments
153 | isId v = mkFunTy (idType v) ty
154 | otherwise = mkForAllTy v ty
156 mkPiTypes vs ty = foldr mkPiType ty vs
160 applyTypeToArg :: Type -> CoreExpr -> Type
161 -- ^ Determines the type resulting from applying an expression to a function with the given type
162 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
163 applyTypeToArg fun_ty _ = funResultTy fun_ty
165 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
166 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
167 -- The first argument is just for debugging, and gives some context
168 applyTypeToArgs _ op_ty [] = op_ty
170 applyTypeToArgs e op_ty (Type ty : args)
171 = -- Accumulate type arguments so we can instantiate all at once
174 go rev_tys (Type ty : args) = go (ty:rev_tys) args
175 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
177 op_ty' = applyTysD msg op_ty (reverse rev_tys)
178 msg = ptext (sLit "applyTypeToArgs") <+>
181 applyTypeToArgs e op_ty (_ : args)
182 = case (splitFunTy_maybe op_ty) of
183 Just (_, res_ty) -> applyTypeToArgs e res_ty args
184 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
186 panic_msg :: CoreExpr -> Type -> SDoc
187 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
190 %************************************************************************
192 \subsection{Attaching notes}
194 %************************************************************************
197 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
198 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
199 mkCoerceI (IdCo _) e = e
200 mkCoerceI (ACo co) e = mkCoerce co e
202 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
203 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
204 mkCoerce co (Cast expr co2)
205 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
206 (_from_ty2, to_ty2) = coercionKind co2} in
207 from_ty `coreEqType` to_ty2 )
208 mkCoerce (mkTransCoercion co2 co) expr
211 = let (from_ty, _to_ty) = coercionKind co in
212 -- if to_ty `coreEqType` from_ty
215 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
220 -- | Wraps the given expression in the cost centre unless
221 -- in a way that maximises their utility to the user
222 mkSCC :: CostCentre -> Expr b -> Expr b
223 -- Note: Nested SCC's *are* preserved for the benefit of
224 -- cost centre stack profiling
225 mkSCC _ (Lit lit) = Lit lit
226 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
227 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
228 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
229 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
230 mkSCC cc expr = Note (SCC cc) expr
234 %************************************************************************
236 \subsection{Other expression construction}
238 %************************************************************************
241 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
242 -- ^ @bindNonRec x r b@ produces either:
248 -- > case r of x { _DEFAULT_ -> b }
250 -- depending on whether we have to use a @case@ or @let@
251 -- binding for the expression (see 'needsCaseBinding').
252 -- It's used by the desugarer to avoid building bindings
253 -- that give Core Lint a heart attack, although actually
254 -- the simplifier deals with them perfectly well. See
255 -- also 'MkCore.mkCoreLet'
256 bindNonRec bndr rhs body
257 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
258 | otherwise = Let (NonRec bndr rhs) body
260 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
261 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
262 needsCaseBinding :: Type -> CoreExpr -> Bool
263 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
264 -- Make a case expression instead of a let
265 -- These can arise either from the desugarer,
266 -- or from beta reductions: (\x.e) (x +# y)
270 mkAltExpr :: AltCon -- ^ Case alternative constructor
271 -> [CoreBndr] -- ^ Things bound by the pattern match
272 -> [Type] -- ^ The type arguments to the case alternative
274 -- ^ This guy constructs the value that the scrutinee must have
275 -- given that you are in one particular branch of a case
276 mkAltExpr (DataAlt con) args inst_tys
277 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
278 mkAltExpr (LitAlt lit) [] []
280 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
281 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
285 %************************************************************************
287 \subsection{Taking expressions apart}
289 %************************************************************************
291 The default alternative must be first, if it exists at all.
292 This makes it easy to find, though it makes matching marginally harder.
295 -- | Extract the default case alternative
296 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
297 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
298 findDefault alts = (alts, Nothing)
300 isDefaultAlt :: CoreAlt -> Bool
301 isDefaultAlt (DEFAULT, _, _) = True
302 isDefaultAlt _ = False
305 -- | Find the case alternative corresponding to a particular
306 -- constructor: panics if no such constructor exists
307 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
308 -- A "Nothing" result *is* legitmiate
309 -- See Note [Unreachable code]
312 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
316 go (alt@(con1,_,_) : alts) deflt
317 = case con `cmpAltCon` con1 of
318 LT -> deflt -- Missed it already; the alts are in increasing order
320 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
322 ---------------------------------
323 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
324 -- ^ Merge alternatives preserving order; alternatives in
325 -- the first argument shadow ones in the second
326 mergeAlts [] as2 = as2
327 mergeAlts as1 [] = as1
328 mergeAlts (a1:as1) (a2:as2)
329 = case a1 `cmpAlt` a2 of
330 LT -> a1 : mergeAlts as1 (a2:as2)
331 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
332 GT -> a2 : mergeAlts (a1:as1) as2
335 ---------------------------------
336 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
339 -- > case (C a b x y) of
342 -- We want to drop the leading type argument of the scrutinee
343 -- leaving the arguments to match agains the pattern
345 trimConArgs DEFAULT args = ASSERT( null args ) []
346 trimConArgs (LitAlt _) args = ASSERT( null args ) []
347 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
350 Note [Unreachable code]
351 ~~~~~~~~~~~~~~~~~~~~~~~
352 It is possible (although unusual) for GHC to find a case expression
353 that cannot match. For example:
355 data Col = Red | Green | Blue
359 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
361 Suppose that for some silly reason, x isn't substituted in the case
362 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
363 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
367 lvl = case x of { Green -> e1; Blue -> e2 })
372 Now if x gets inlined, we won't be able to find a matching alternative
373 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
374 we generate (error "Inaccessible alternative").
376 Similar things can happen (augmented by GADTs) when the Simplifier
377 filters down the matching alternatives in Simplify.rebuildCase.
380 %************************************************************************
384 %************************************************************************
388 @exprIsTrivial@ is true of expressions we are unconditionally happy to
389 duplicate; simple variables and constants, and type
390 applications. Note that primop Ids aren't considered
393 Note [Variable are trivial]
394 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
395 There used to be a gruesome test for (hasNoBinding v) in the
397 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
398 The idea here is that a constructor worker, like \$wJust, is
399 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
400 So it should be treated like a lambda. Ditto unsaturated primops.
401 But now constructor workers are not "have-no-binding" Ids. And
402 completely un-applied primops and foreign-call Ids are sufficiently
403 rare that I plan to allow them to be duplicated and put up with
406 Note [SCCs are trivial]
407 ~~~~~~~~~~~~~~~~~~~~~~~
408 We used not to treat (_scc_ "foo" x) as trivial, because it really
409 generates code, (and a heap object when it's a function arg) to
410 capture the cost centre. However, the profiling system discounts the
411 allocation costs for such "boxing thunks" whereas the extra costs of
412 *not* inlining otherwise-trivial bindings can be high, and are hard to
416 exprIsTrivial :: CoreExpr -> Bool
417 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
418 exprIsTrivial (Type _) = True
419 exprIsTrivial (Lit lit) = litIsTrivial lit
420 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
421 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
422 exprIsTrivial (Cast e _) = exprIsTrivial e
423 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
424 exprIsTrivial _ = False
427 exprIsBottom is a very cheap and cheerful function; it may return
428 False for bottoming expressions, but it never costs much to ask.
429 See also CoreArity.exprBotStrictness_maybe, but that's a bit more
433 exprIsBottom :: CoreExpr -> Bool
437 go n (Var v) = isBottomingId v && n >= idArity v
438 go n (App e a) | isTypeArg a = go n e
439 | otherwise = go (n+1) e
440 go n (Note _ e) = go n e
441 go n (Cast e _) = go n e
442 go n (Let _ e) = go n e
447 %************************************************************************
451 %************************************************************************
455 @exprIsDupable@ is true of expressions that can be duplicated at a modest
456 cost in code size. This will only happen in different case
457 branches, so there's no issue about duplicating work.
459 That is, exprIsDupable returns True of (f x) even if
460 f is very very expensive to call.
462 Its only purpose is to avoid fruitless let-binding
463 and then inlining of case join points
467 exprIsDupable :: CoreExpr -> Bool
468 exprIsDupable (Type _) = True
469 exprIsDupable (Var _) = True
470 exprIsDupable (Lit lit) = litIsDupable lit
471 exprIsDupable (Note _ e) = exprIsDupable e
472 exprIsDupable (Cast e _) = exprIsDupable e
477 go (App f a) n_args = n_args < dupAppSize
483 dupAppSize = 4 -- Size of application we are prepared to duplicate
486 %************************************************************************
488 exprIsCheap, exprIsExpandable
490 %************************************************************************
492 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
493 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
494 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
495 it is obviously in weak head normal form, or is cheap to get to WHNF.
496 [Note that that's not the same as exprIsDupable; an expression might be
497 big, and hence not dupable, but still cheap.]
499 By ``cheap'' we mean a computation we're willing to:
500 push inside a lambda, or
501 inline at more than one place
502 That might mean it gets evaluated more than once, instead of being
503 shared. The main examples of things which aren't WHNF but are
508 (where e, and all the ei are cheap)
511 (where e and b are cheap)
514 (where op is a cheap primitive operator)
517 (because we are happy to substitute it inside a lambda)
519 Notice that a variable is considered 'cheap': we can push it inside a lambda,
520 because sharing will make sure it is only evaluated once.
522 Note [exprIsCheap and exprIsHNF]
523 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
524 Note that exprIsHNF does not imply exprIsCheap. Eg
525 let x = fac 20 in Just x
526 This responds True to exprIsHNF (you can discard a seq), but
527 False to exprIsCheap.
530 exprIsCheap :: CoreExpr -> Bool
531 exprIsCheap = exprIsCheap' isCheapApp
533 exprIsExpandable :: CoreExpr -> Bool
534 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
536 type CheapAppFun = Id -> Int -> Bool
537 exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
538 exprIsCheap' _ (Lit _) = True
539 exprIsCheap' _ (Type _) = True
540 exprIsCheap' _ (Var _) = True
541 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
542 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
543 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
544 || exprIsCheap' good_app e
546 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
547 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
548 -- Experimentally, treat (case x of ...) as cheap
549 -- (and case __coerce x etc.)
550 -- This improves arities of overloaded functions where
551 -- there is only dictionary selection (no construction) involved
553 exprIsCheap' good_app (Let (NonRec x _) e)
554 | isUnLiftedType (idType x) = exprIsCheap' good_app e
556 -- Strict lets always have cheap right hand sides,
557 -- and do no allocation, so just look at the body
558 -- Non-strict lets do allocation so we don't treat them as cheap
561 exprIsCheap' good_app other_expr -- Applications and variables
564 -- Accumulate value arguments, then decide
565 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
566 | otherwise = go f val_args
568 go (Var _) [] = True -- Just a type application of a variable
569 -- (f t1 t2 t3) counts as WHNF
571 = case idDetails f of
572 RecSelId {} -> go_sel args
573 ClassOpId {} -> go_sel args
574 PrimOpId op -> go_primop op args
575 _ | good_app f (length args) -> go_pap args
576 | isBottomingId f -> True
578 -- Application of a function which
579 -- always gives bottom; we treat this as cheap
580 -- because it certainly doesn't need to be shared!
585 go_pap args = all exprIsTrivial args
586 -- For constructor applications and primops, check that all
587 -- the args are trivial. We don't want to treat as cheap, say,
589 -- We'll put up with one constructor application, but not dozens
592 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
593 -- In principle we should worry about primops
594 -- that return a type variable, since the result
595 -- might be applied to something, but I'm not going
596 -- to bother to check the number of args
599 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
600 go_sel _ = False -- look cheap, so we will substitute it inside a
601 -- lambda. Particularly for dictionary field selection.
602 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
603 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
605 isCheapApp :: CheapAppFun
606 isCheapApp fn n_val_args
608 || n_val_args < idArity fn
610 isExpandableApp :: CheapAppFun
611 isExpandableApp fn n_val_args
613 || n_val_args < idArity fn
614 || go n_val_args (idType fn)
616 -- See if all the arguments are PredTys (implicit params or classes)
617 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
620 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
621 | Just (arg, ty) <- splitFunTy_maybe ty
622 , isPredTy arg = go (n_val_args-1) ty
626 Note [Expandable overloadings]
627 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
628 Suppose the user wrote this
629 {-# RULE forall x. foo (negate x) = h x #-}
630 f x = ....(foo (negate x))....
631 He'd expect the rule to fire. But since negate is overloaded, we might
633 f = \d -> let n = negate d in \x -> ...foo (n x)...
634 So we treat the application of a function (negate in this case) to a
635 *dictionary* as expandable. In effect, every function is CONLIKE when
636 it's applied only to dictionaries.
639 %************************************************************************
643 %************************************************************************
646 -- | 'exprOkForSpeculation' returns True of an expression that is:
648 -- * Safe to evaluate even if normal order eval might not
649 -- evaluate the expression at all, or
651 -- * Safe /not/ to evaluate even if normal order would do so
653 -- It is usually called on arguments of unlifted type, but not always
654 -- In particular, Simplify.rebuildCase calls it on lifted types
655 -- when a 'case' is a plain 'seq'. See the example in
656 -- Note [exprOkForSpeculation: case expressions] below
658 -- Precisely, it returns @True@ iff:
660 -- * The expression guarantees to terminate,
662 -- * without raising an exception,
663 -- * without causing a side effect (e.g. writing a mutable variable)
665 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
666 -- As an example of the considerations in this test, consider:
668 -- > let x = case y# +# 1# of { r# -> I# r# }
671 -- being translated to:
673 -- > case y# +# 1# of { r# ->
678 -- We can only do this if the @y + 1@ is ok for speculation: it has no
679 -- side effects, and can't diverge or raise an exception.
680 exprOkForSpeculation :: CoreExpr -> Bool
681 exprOkForSpeculation (Lit _) = True
682 exprOkForSpeculation (Type _) = True
684 exprOkForSpeculation (Var v)
685 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
686 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
687 || isDataConWorkId v -- Nullary constructors
688 || idArity v > 0 -- Functions
689 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
691 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
692 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
694 exprOkForSpeculation (Case e _ _ alts)
695 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
696 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
698 exprOkForSpeculation other_expr
699 = case collectArgs other_expr of
700 (Var f, args) | f `hasKey` absentErrorIdKey -- Note [Absent error Id]
701 -> all exprOkForSpeculation args -- in WwLib
703 -> spec_ok (idDetails f) args
707 spec_ok (DataConWorkId _) _
708 = True -- The strictness of the constructor has already
709 -- been expressed by its "wrapper", so we don't need
710 -- to take the arguments into account
712 spec_ok (PrimOpId op) args
713 | isDivOp op, -- Special case for dividing operations that fail
714 [arg1, Lit lit] <- args -- only if the divisor is zero
715 = not (isZeroLit lit) && exprOkForSpeculation arg1
716 -- Often there is a literal divisor, and this
717 -- can get rid of a thunk in an inner looop
719 | DataToTagOp <- op -- See Note [dataToTag speculation]
723 = primOpOkForSpeculation op &&
724 all exprOkForSpeculation args
725 -- A bit conservative: we don't really need
726 -- to care about lazy arguments, but this is easy
728 spec_ok (DFunId _ new_type) _ = not new_type
729 -- DFuns terminate, unless the dict is implemented with a newtype
730 -- in which case they may not
734 -- | True of dyadic operators that can fail only if the second arg is zero!
735 isDivOp :: PrimOp -> Bool
736 -- This function probably belongs in PrimOp, or even in
737 -- an automagically generated file.. but it's such a
738 -- special case I thought I'd leave it here for now.
739 isDivOp IntQuotOp = True
740 isDivOp IntRemOp = True
741 isDivOp WordQuotOp = True
742 isDivOp WordRemOp = True
743 isDivOp FloatDivOp = True
744 isDivOp DoubleDivOp = True
748 Note [exprOkForSpeculation: case expressions]
749 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
750 It's always sound for exprOkForSpeculation to return False, and we
751 don't want it to take too long, so it bales out on complicated-looking
752 terms. Notably lets, which can be stacked very deeply; and in any
753 case the argument of exprOkForSpeculation is usually in a strict context,
754 so any lets will have been floated away.
756 However, we keep going on case-expressions. An example like this one
757 showed up in DPH code (Trac #3717):
760 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
762 If exprOkForSpeculation doesn't look through case expressions, you get this:
764 \ (ww :: GHC.Prim.Int#) ->
766 __DEFAULT -> case (case <# ds 5 of _ {
767 GHC.Types.False -> lvl1;
768 GHC.Types.True -> lvl})
770 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
774 The inner case is redundant, and should be nuked.
776 Note [dataToTag speculation]
777 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
779 f x = let v::Int# = dataToTag# x
781 We say "yes", even though 'x' may not be evaluated. Reasons
783 * dataToTag#'s strictness means that its argument often will be
784 evaluated, but FloatOut makes that temporarily untrue
785 case x of y -> let v = dataToTag# y in ...
787 case x of y -> let v = dataToTag# x in ...
788 Note that we look at 'x' instead of 'y' (this is to improve
789 floating in FloatOut). So Lint complains.
791 Moreover, it really *might* improve floating to let the
794 * CorePrep makes sure dataToTag#'s argument is evaluated, just
795 before code gen. Until then, it's not guaranteed
798 %************************************************************************
800 exprIsHNF, exprIsConLike
802 %************************************************************************
805 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
807 -- | exprIsHNF returns true for expressions that are certainly /already/
808 -- evaluated to /head/ normal form. This is used to decide whether it's ok
811 -- > case x of _ -> e
817 -- and to decide whether it's safe to discard a 'seq'.
819 -- So, it does /not/ treat variables as evaluated, unless they say they are.
820 -- However, it /does/ treat partial applications and constructor applications
821 -- as values, even if their arguments are non-trivial, provided the argument
822 -- type is lifted. For example, both of these are values:
824 -- > (:) (f x) (map f xs)
825 -- > map (...redex...)
827 -- because 'seq' on such things completes immediately.
829 -- For unlifted argument types, we have to be careful:
833 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
834 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
835 -- unboxed type must be ok-for-speculation (or trivial).
836 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
837 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
841 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
842 -- data constructors. Conlike arguments are considered interesting by the
844 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
845 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
847 -- | Returns true for values or value-like expressions. These are lambdas,
848 -- constructors / CONLIKE functions (as determined by the function argument)
851 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
852 exprIsHNFlike is_con is_con_unf = is_hnf_like
854 is_hnf_like (Var v) -- NB: There are no value args at this point
855 = is_con v -- Catches nullary constructors,
856 -- so that [] and () are values, for example
857 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
858 || is_con_unf (idUnfolding v)
859 -- Check the thing's unfolding; it might be bound to a value
860 -- We don't look through loop breakers here, which is a bit conservative
861 -- but otherwise I worry that if an Id's unfolding is just itself,
862 -- we could get an infinite loop
864 is_hnf_like (Lit _) = True
865 is_hnf_like (Type _) = True -- Types are honorary Values;
866 -- we don't mind copying them
867 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
868 is_hnf_like (Note _ e) = is_hnf_like e
869 is_hnf_like (Cast e _) = is_hnf_like e
870 is_hnf_like (App e (Type _)) = is_hnf_like e
871 is_hnf_like (App e a) = app_is_value e [a]
872 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
873 is_hnf_like _ = False
875 -- There is at least one value argument
876 app_is_value :: CoreExpr -> [CoreArg] -> Bool
877 app_is_value (Var fun) args
878 = idArity fun > valArgCount args -- Under-applied function
879 || is_con fun -- or constructor-like
880 app_is_value (Note _ f) as = app_is_value f as
881 app_is_value (Cast f _) as = app_is_value f as
882 app_is_value (App f a) as = app_is_value f (a:as)
883 app_is_value _ _ = False
887 %************************************************************************
889 Instantiating data constructors
891 %************************************************************************
893 These InstPat functions go here to avoid circularity between DataCon and Id
896 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
897 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
899 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
900 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
901 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
903 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
904 -- Remember to include the existential dictionaries
906 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
907 -> [FastString] -- A long enough list of FSs to use for names
908 -> [Unique] -- An equally long list of uniques, at least one for each binder
910 -> [Type] -- Types to instantiate the universally quantified tyvars
911 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
912 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
913 -- (ex_tvs, co_tvs, arg_ids),
915 -- ex_tvs are intended to be used as binders for existential type args
917 -- co_tvs are intended to be used as binders for coercion args and the kinds
918 -- of these vars have been instantiated by the inst_tys and the ex_tys
919 -- The co_tvs include both GADT equalities (dcEqSpec) and
920 -- programmer-specified equalities (dcEqTheta)
922 -- arg_ids are indended to be used as binders for value arguments,
923 -- and their types have been instantiated with inst_tys and ex_tys
924 -- The arg_ids include both dicts (dcDictTheta) and
925 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
928 -- The following constructor T1
931 -- T1 :: forall b. Int -> b -> T(a,b)
934 -- has representation type
935 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
938 -- dataConInstPat fss us T1 (a1',b') will return
940 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
942 -- where the double-primed variables are created with the FastStrings and
943 -- Uniques given as fss and us
944 dataConInstPat arg_fun fss uniqs con inst_tys
945 = (ex_bndrs, co_bndrs, arg_ids)
947 univ_tvs = dataConUnivTyVars con
948 ex_tvs = dataConExTyVars con
949 arg_tys = arg_fun con
950 eq_spec = dataConEqSpec con
951 eq_theta = dataConEqTheta con
952 eq_preds = eqSpecPreds eq_spec ++ eq_theta
955 n_co = length eq_preds
957 -- split the Uniques and FastStrings
958 (ex_uniqs, uniqs') = splitAt n_ex uniqs
959 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
961 (ex_fss, fss') = splitAt n_ex fss
962 (co_fss, id_fss) = splitAt n_co fss'
964 -- Make existential type variables
965 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
966 mk_ex_var uniq fs var = mkTyVar new_name kind
968 new_name = mkSysTvName uniq fs
971 -- Make the instantiating substitution
972 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
974 -- Make new coercion vars, instantiating kind
975 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
976 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
978 new_name = mkSysTvName uniq fs
979 co_kind = substTy subst (mkPredTy eq_pred)
981 -- make value vars, instantiating types
982 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
983 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
987 %************************************************************************
991 %************************************************************************
994 -- | A cheap equality test which bales out fast!
995 -- If it returns @True@ the arguments are definitely equal,
996 -- otherwise, they may or may not be equal.
998 -- See also 'exprIsBig'
999 cheapEqExpr :: Expr b -> Expr b -> Bool
1001 cheapEqExpr (Var v1) (Var v2) = v1==v2
1002 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1003 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1005 cheapEqExpr (App f1 a1) (App f2 a2)
1006 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1008 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1009 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1011 cheapEqExpr _ _ = False
1015 exprIsBig :: Expr b -> Bool
1016 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1017 exprIsBig (Lit _) = False
1018 exprIsBig (Var _) = False
1019 exprIsBig (Type _) = False
1020 exprIsBig (Lam _ e) = exprIsBig e
1021 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1022 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1027 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1028 -- Compares for equality, modulo alpha
1029 eqExpr in_scope e1 e2
1030 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1032 id_unf _ = noUnfolding -- Don't expand
1036 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1037 -- ^ Compares expressions for equality, modulo alpha.
1038 -- Does /not/ look through newtypes or predicate types
1039 -- Used in rule matching, and also CSE
1041 eqExprX id_unfolding_fun env e1 e2
1044 go env (Var v1) (Var v2)
1045 | rnOccL env v1 == rnOccR env v2
1048 -- The next two rules expand non-local variables
1049 -- C.f. Note [Expanding variables] in Rules.lhs
1050 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1052 | not (locallyBoundL env v1)
1053 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1054 = go (nukeRnEnvL env) e1' e2
1057 | not (locallyBoundR env v2)
1058 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1059 = go (nukeRnEnvR env) e1 e2'
1061 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1062 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1063 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1064 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1065 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1067 go env (Lam b1 e1) (Lam b2 e2)
1068 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1069 && go (rnBndr2 env b1 b2) e1 e2
1071 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1072 = go env r1 r2 -- No need to check binder types, since RHSs match
1073 && go (rnBndr2 env v1 v2) e1 e2
1075 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1076 = all2 (go env') rs1 rs2 && go env' e1 e2
1078 (bs1,rs1) = unzip ps1
1079 (bs2,rs2) = unzip ps2
1080 env' = rnBndrs2 env bs1 bs2
1082 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1084 && tcEqTypeX env (idType b1) (idType b2)
1085 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1090 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1091 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1094 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1095 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1102 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1103 locallyBoundL rn_env v = inRnEnvL rn_env v
1104 locallyBoundR rn_env v = inRnEnvR rn_env v
1108 %************************************************************************
1110 \subsection{The size of an expression}
1112 %************************************************************************
1115 coreBindsSize :: [CoreBind] -> Int
1116 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1118 exprSize :: CoreExpr -> Int
1119 -- ^ A measure of the size of the expressions, strictly greater than 0
1120 -- It also forces the expression pretty drastically as a side effect
1121 exprSize (Var v) = v `seq` 1
1122 exprSize (Lit lit) = lit `seq` 1
1123 exprSize (App f a) = exprSize f + exprSize a
1124 exprSize (Lam b e) = varSize b + exprSize e
1125 exprSize (Let b e) = bindSize b + exprSize e
1126 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1127 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1128 exprSize (Note n e) = noteSize n + exprSize e
1129 exprSize (Type t) = seqType t `seq` 1
1131 noteSize :: Note -> Int
1132 noteSize (SCC cc) = cc `seq` 1
1133 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1135 varSize :: Var -> Int
1136 varSize b | isTyCoVar b = 1
1137 | otherwise = seqType (idType b) `seq`
1138 megaSeqIdInfo (idInfo b) `seq`
1141 varsSize :: [Var] -> Int
1142 varsSize = sum . map varSize
1144 bindSize :: CoreBind -> Int
1145 bindSize (NonRec b e) = varSize b + exprSize e
1146 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1148 pairSize :: (Var, CoreExpr) -> Int
1149 pairSize (b,e) = varSize b + exprSize e
1151 altSize :: CoreAlt -> Int
1152 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1156 %************************************************************************
1158 \subsection{Hashing}
1160 %************************************************************************
1163 hashExpr :: CoreExpr -> Int
1164 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1165 -- Two expressions that hash to the different Ints are definitely unequal.
1167 -- The emphasis is on a crude, fast hash, rather than on high precision.
1169 -- But unequal here means \"not identical\"; two alpha-equivalent
1170 -- expressions may hash to the different Ints.
1172 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1173 -- (at least if we want the above invariant to be true).
1175 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1176 -- UniqFM doesn't like negative Ints
1178 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1180 hash_expr :: HashEnv -> CoreExpr -> Word32
1181 -- Word32, because we're expecting overflows here, and overflowing
1182 -- signed types just isn't cool. In C it's even undefined.
1183 hash_expr env (Note _ e) = hash_expr env e
1184 hash_expr env (Cast e _) = hash_expr env e
1185 hash_expr env (Var v) = hashVar env v
1186 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1187 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1188 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1189 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1190 hash_expr env (Case e _ _ _) = hash_expr env e
1191 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1192 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1193 -- Shouldn't happen. Better to use WARN than trace, because trace
1194 -- prevents the CPR optimisation kicking in for hash_expr.
1196 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1197 fast_hash_expr env (Var v) = hashVar env v
1198 fast_hash_expr env (Type t) = fast_hash_type env t
1199 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1200 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1201 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1202 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1203 fast_hash_expr _ _ = 1
1205 fast_hash_type :: HashEnv -> Type -> Word32
1206 fast_hash_type env ty
1207 | Just tv <- getTyVar_maybe ty = hashVar env tv
1208 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1209 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1212 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1213 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1215 hashVar :: HashEnv -> Var -> Word32
1217 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1221 %************************************************************************
1225 %************************************************************************
1227 Note [Eta reduction conditions]
1228 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1229 We try for eta reduction here, but *only* if we get all the way to an
1230 trivial expression. We don't want to remove extra lambdas unless we
1231 are going to avoid allocating this thing altogether.
1233 There are some particularly delicate points here:
1235 * Eta reduction is not valid in general:
1237 This matters, partly for old-fashioned correctness reasons but,
1238 worse, getting it wrong can yield a seg fault. Consider
1240 h y = case (case y of { True -> f `seq` True; False -> False }) of
1241 True -> ...; False -> ...
1243 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1244 says f=bottom, and replaces the (f `seq` True) with just
1245 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1246 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1247 the definition again, so that it does not termninate after all.
1248 Result: seg-fault because the boolean case actually gets a function value.
1251 So it's important to to the right thing.
1253 * Note [Arity care]: we need to be careful if we just look at f's
1254 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1255 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1256 arity when checking that 'f' is a value. Otherwise we will
1261 Which might change a terminiating program (think (f `seq` e)) to a
1262 non-terminating one. So we check for being a loop breaker first.
1264 However for GlobalIds we can look at the arity; and for primops we
1265 must, since they have no unfolding.
1267 * Regardless of whether 'f' is a value, we always want to
1268 reduce (/\a -> f a) to f
1269 This came up in a RULE: foldr (build (/\a -> g a))
1270 did not match foldr (build (/\b -> ...something complex...))
1271 The type checker can insert these eta-expanded versions,
1272 with both type and dictionary lambdas; hence the slightly
1275 * Never *reduce* arity. For example
1277 Then if h has arity 1 we don't want to eta-reduce because then
1278 f's arity would decrease, and that is bad
1280 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1283 Note [Eta reduction with casted arguments]
1284 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1286 (\(x:t3). f (x |> g)) :: t3 -> t2
1290 This should be eta-reduced to
1294 So we need to accumulate a coercion, pushing it inward (past
1295 variable arguments only) thus:
1296 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1297 f (x:t) |> co --> (f |> (t -> co)) x
1298 f @ a |> co --> (f |> (forall a.co)) @ a
1299 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1300 These are the equations for ok_arg.
1302 It's true that we could also hope to eta reduce these:
1305 But the simplifier pushes those casts outwards, so we don't
1306 need to address that here.
1309 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1310 tryEtaReduce bndrs body
1311 = go (reverse bndrs) body (IdCo (exprType body))
1313 incoming_arity = count isId bndrs
1315 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1316 -> CoreExpr -- Of type tr
1317 -> CoercionI -- Of type tr ~ ts
1318 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1319 -- See Note [Eta reduction with casted arguments]
1320 -- for why we have an accumulating coercion
1322 | ok_fun fun = Just (mkCoerceI co fun)
1324 go (b : bs) (App fun arg) co
1325 | Just co' <- ok_arg b arg co
1328 go _ _ _ = Nothing -- Failure!
1331 -- Note [Eta reduction conditions]
1332 ok_fun (App fun (Type ty))
1333 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1336 = not (fun_id `elem` bndrs)
1337 && (ok_fun_id fun_id || all ok_lam bndrs)
1341 ok_fun_id fun = fun_arity fun >= incoming_arity
1344 fun_arity fun -- See Note [Arity care]
1345 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1346 | otherwise = idArity fun
1349 ok_lam v = isTyCoVar v || isDictId v
1352 ok_arg :: Var -- Of type bndr_t
1353 -> CoreExpr -- Of type arg_t
1354 -> CoercionI -- Of kind (t1~t2)
1355 -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1356 -- (and similarly for tyvars, coercion args)
1357 -- See Note [Eta reduction with casted arguments]
1358 ok_arg bndr (Type ty) co
1359 | Just tv <- getTyVar_maybe ty
1360 , bndr == tv = Just (mkForAllTyCoI tv co)
1361 ok_arg bndr (Var v) co
1362 | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co)
1363 ok_arg bndr (Cast (Var v) co_arg) co
1364 | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co)
1365 -- The simplifier combines multiple casts into one,
1366 -- so we can have a simple-minded pattern match here
1367 ok_arg _ _ _ = Nothing
1371 %************************************************************************
1373 \subsection{Determining non-updatable right-hand-sides}
1375 %************************************************************************
1377 Top-level constructor applications can usually be allocated
1378 statically, but they can't if the constructor, or any of the
1379 arguments, come from another DLL (because we can't refer to static
1380 labels in other DLLs).
1382 If this happens we simply make the RHS into an updatable thunk,
1383 and 'execute' it rather than allocating it statically.
1386 -- | This function is called only on *top-level* right-hand sides.
1387 -- Returns @True@ if the RHS can be allocated statically in the output,
1388 -- with no thunks involved at all.
1389 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1390 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1391 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1392 -- update flag on it and (iii) in DsExpr to decide how to expand
1395 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1396 -- (a) a value lambda
1397 -- (b) a saturated constructor application with static args
1399 -- BUT watch out for
1400 -- (i) Any cross-DLL references kill static-ness completely
1401 -- because they must be 'executed' not statically allocated
1402 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1403 -- this is not necessary)
1405 -- (ii) We treat partial applications as redexes, because in fact we
1406 -- make a thunk for them that runs and builds a PAP
1407 -- at run-time. The only appliations that are treated as
1408 -- static are *saturated* applications of constructors.
1410 -- We used to try to be clever with nested structures like this:
1411 -- ys = (:) w ((:) w [])
1412 -- on the grounds that CorePrep will flatten ANF-ise it later.
1413 -- But supporting this special case made the function much more
1414 -- complicated, because the special case only applies if there are no
1415 -- enclosing type lambdas:
1416 -- ys = /\ a -> Foo (Baz ([] a))
1417 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1419 -- But in fact, even without -O, nested structures at top level are
1420 -- flattened by the simplifier, so we don't need to be super-clever here.
1424 -- f = \x::Int. x+7 TRUE
1425 -- p = (True,False) TRUE
1427 -- d = (fst p, False) FALSE because there's a redex inside
1428 -- (this particular one doesn't happen but...)
1430 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1431 -- n = /\a. Nil a TRUE
1433 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1436 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1437 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1439 -- b) (C x xs), where C is a contructor is updatable if the application is
1442 -- c) don't look through unfolding of f in (f x).
1444 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1446 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1449 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1450 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1451 is_static in_arg (Cast e _) = is_static in_arg e
1453 is_static _ (Lit lit)
1455 MachLabel _ _ _ -> False
1457 -- A MachLabel (foreign import "&foo") in an argument
1458 -- prevents a constructor application from being static. The
1459 -- reason is that it might give rise to unresolvable symbols
1460 -- in the object file: under Linux, references to "weak"
1461 -- symbols from the data segment give rise to "unresolvable
1462 -- relocation" errors at link time This might be due to a bug
1463 -- in the linker, but we'll work around it here anyway.
1466 is_static in_arg other_expr = go other_expr 0
1468 go (Var f) n_val_args
1469 #if mingw32_TARGET_OS
1470 | not (_is_dynamic_name (idName f))
1472 = saturated_data_con f n_val_args
1473 || (in_arg && n_val_args == 0)
1474 -- A naked un-applied variable is *not* deemed a static RHS
1476 -- Reason: better to update so that the indirection gets shorted
1477 -- out, and the true value will be seen
1478 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1479 -- are always updatable. If you do so, make sure that non-updatable
1480 -- ones have enough space for their static link field!
1482 go (App f a) n_val_args
1483 | isTypeArg a = go f n_val_args
1484 | not in_arg && is_static True a = go f (n_val_args + 1)
1485 -- The (not in_arg) checks that we aren't in a constructor argument;
1486 -- if we are, we don't allow (value) applications of any sort
1488 -- NB. In case you wonder, args are sometimes not atomic. eg.
1489 -- x = D# (1.0## /## 2.0##)
1490 -- can't float because /## can fail.
1492 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1493 go (Cast e _) n_val_args = go e n_val_args
1496 saturated_data_con f n_val_args
1497 = case isDataConWorkId_maybe f of
1498 Just dc -> n_val_args == dataConRepArity dc