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 )
80 %************************************************************************
82 \subsection{Find the type of a Core atom/expression}
84 %************************************************************************
87 exprType :: CoreExpr -> Type
88 -- ^ Recover the type of a well-typed Core expression. Fails when
89 -- applied to the actual 'CoreSyn.Type' expression as it cannot
90 -- really be said to have a type
91 exprType (Var var) = idType var
92 exprType (Lit lit) = literalType lit
93 exprType (Let _ body) = exprType body
94 exprType (Case _ _ ty _) = ty
95 exprType (Cast _ co) = snd (coercionKind co)
96 exprType (Note _ e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 -- ^ Returns the type of the alternatives right hand side
106 coreAltType (_,bs,rhs)
107 | any bad_binder bs = expandTypeSynonyms ty
108 | otherwise = ty -- Note [Existential variables and silly type synonyms]
111 free_tvs = tyVarsOfType ty
112 bad_binder b = isTyCoVar b && b `elemVarSet` free_tvs
114 coreAltsType :: [CoreAlt] -> Type
115 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
116 coreAltsType (alt:_) = coreAltType alt
117 coreAltsType [] = panic "corAltsType"
120 Note [Existential variables and silly type synonyms]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
123 data T = forall a. T (Funny a)
128 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
129 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
130 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
133 Various possibilities suggest themselves:
135 - Ignore the problem, and make Lint not complain about such variables
137 - Expand all type synonyms (or at least all those that discard arguments)
138 This is tricky, because at least for top-level things we want to
139 retain the type the user originally specified.
141 - Expand synonyms on the fly, when the problem arises. That is what
142 we are doing here. It's not too expensive, I think.
145 mkPiType :: EvVar -> Type -> Type
146 -- ^ Makes a @(->)@ type or a forall type, depending
147 -- on whether it is given a type variable or a term variable.
148 mkPiTypes :: [EvVar] -> Type -> Type
149 -- ^ 'mkPiType' for multiple type or value arguments
152 | isId v = mkFunTy (idType v) ty
153 | otherwise = mkForAllTy v ty
155 mkPiTypes vs ty = foldr mkPiType ty vs
159 applyTypeToArg :: Type -> CoreExpr -> Type
160 -- ^ Determines the type resulting from applying an expression to a function with the given type
161 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
162 applyTypeToArg fun_ty _ = funResultTy fun_ty
164 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
165 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
166 -- The first argument is just for debugging, and gives some context
167 applyTypeToArgs _ op_ty [] = op_ty
169 applyTypeToArgs e op_ty (Type ty : args)
170 = -- Accumulate type arguments so we can instantiate all at once
173 go rev_tys (Type ty : args) = go (ty:rev_tys) args
174 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
176 op_ty' = applyTysD msg op_ty (reverse rev_tys)
177 msg = ptext (sLit "applyTypeToArgs") <+>
180 applyTypeToArgs e op_ty (_ : args)
181 = case (splitFunTy_maybe op_ty) of
182 Just (_, res_ty) -> applyTypeToArgs e res_ty args
183 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
185 panic_msg :: CoreExpr -> Type -> SDoc
186 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
189 %************************************************************************
191 \subsection{Attaching notes}
193 %************************************************************************
196 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
197 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
198 mkCoerceI (IdCo _) e = e
199 mkCoerceI (ACo co) e = mkCoerce co e
201 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
202 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
203 mkCoerce co (Cast expr co2)
204 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
205 (_from_ty2, to_ty2) = coercionKind co2} in
206 from_ty `coreEqType` to_ty2 )
207 mkCoerce (mkTransCoercion co2 co) expr
210 = let (from_ty, _to_ty) = coercionKind co in
211 -- if to_ty `coreEqType` from_ty
214 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
219 -- | Wraps the given expression in the cost centre unless
220 -- in a way that maximises their utility to the user
221 mkSCC :: CostCentre -> Expr b -> Expr b
222 -- Note: Nested SCC's *are* preserved for the benefit of
223 -- cost centre stack profiling
224 mkSCC _ (Lit lit) = Lit lit
225 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
226 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
227 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
228 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
229 mkSCC cc expr = Note (SCC cc) expr
233 %************************************************************************
235 \subsection{Other expression construction}
237 %************************************************************************
240 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
241 -- ^ @bindNonRec x r b@ produces either:
247 -- > case r of x { _DEFAULT_ -> b }
249 -- depending on whether we have to use a @case@ or @let@
250 -- binding for the expression (see 'needsCaseBinding').
251 -- It's used by the desugarer to avoid building bindings
252 -- that give Core Lint a heart attack, although actually
253 -- the simplifier deals with them perfectly well. See
254 -- also 'MkCore.mkCoreLet'
255 bindNonRec bndr rhs body
256 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
257 | otherwise = Let (NonRec bndr rhs) body
259 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
260 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
261 needsCaseBinding :: Type -> CoreExpr -> Bool
262 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
263 -- Make a case expression instead of a let
264 -- These can arise either from the desugarer,
265 -- or from beta reductions: (\x.e) (x +# y)
269 mkAltExpr :: AltCon -- ^ Case alternative constructor
270 -> [CoreBndr] -- ^ Things bound by the pattern match
271 -> [Type] -- ^ The type arguments to the case alternative
273 -- ^ This guy constructs the value that the scrutinee must have
274 -- given that you are in one particular branch of a case
275 mkAltExpr (DataAlt con) args inst_tys
276 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
277 mkAltExpr (LitAlt lit) [] []
279 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
280 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
284 %************************************************************************
286 \subsection{Taking expressions apart}
288 %************************************************************************
290 The default alternative must be first, if it exists at all.
291 This makes it easy to find, though it makes matching marginally harder.
294 -- | Extract the default case alternative
295 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
296 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
297 findDefault alts = (alts, Nothing)
299 isDefaultAlt :: CoreAlt -> Bool
300 isDefaultAlt (DEFAULT, _, _) = True
301 isDefaultAlt _ = False
304 -- | Find the case alternative corresponding to a particular
305 -- constructor: panics if no such constructor exists
306 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
307 -- A "Nothing" result *is* legitmiate
308 -- See Note [Unreachable code]
311 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
315 go (alt@(con1,_,_) : alts) deflt
316 = case con `cmpAltCon` con1 of
317 LT -> deflt -- Missed it already; the alts are in increasing order
319 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
321 ---------------------------------
322 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
323 -- ^ Merge alternatives preserving order; alternatives in
324 -- the first argument shadow ones in the second
325 mergeAlts [] as2 = as2
326 mergeAlts as1 [] = as1
327 mergeAlts (a1:as1) (a2:as2)
328 = case a1 `cmpAlt` a2 of
329 LT -> a1 : mergeAlts as1 (a2:as2)
330 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
331 GT -> a2 : mergeAlts (a1:as1) as2
334 ---------------------------------
335 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
338 -- > case (C a b x y) of
341 -- We want to drop the leading type argument of the scrutinee
342 -- leaving the arguments to match agains the pattern
344 trimConArgs DEFAULT args = ASSERT( null args ) []
345 trimConArgs (LitAlt _) args = ASSERT( null args ) []
346 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
349 Note [Unreachable code]
350 ~~~~~~~~~~~~~~~~~~~~~~~
351 It is possible (although unusual) for GHC to find a case expression
352 that cannot match. For example:
354 data Col = Red | Green | Blue
358 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
360 Suppose that for some silly reason, x isn't substituted in the case
361 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
362 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
366 lvl = case x of { Green -> e1; Blue -> e2 })
371 Now if x gets inlined, we won't be able to find a matching alternative
372 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
373 we generate (error "Inaccessible alternative").
375 Similar things can happen (augmented by GADTs) when the Simplifier
376 filters down the matching alternatives in Simplify.rebuildCase.
379 %************************************************************************
383 %************************************************************************
387 @exprIsTrivial@ is true of expressions we are unconditionally happy to
388 duplicate; simple variables and constants, and type
389 applications. Note that primop Ids aren't considered
392 Note [Variable are trivial]
393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
394 There used to be a gruesome test for (hasNoBinding v) in the
396 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
397 The idea here is that a constructor worker, like \$wJust, is
398 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
399 So it should be treated like a lambda. Ditto unsaturated primops.
400 But now constructor workers are not "have-no-binding" Ids. And
401 completely un-applied primops and foreign-call Ids are sufficiently
402 rare that I plan to allow them to be duplicated and put up with
405 Note [SCCs are trivial]
406 ~~~~~~~~~~~~~~~~~~~~~~~
407 We used not to treat (_scc_ "foo" x) as trivial, because it really
408 generates code, (and a heap object when it's a function arg) to
409 capture the cost centre. However, the profiling system discounts the
410 allocation costs for such "boxing thunks" whereas the extra costs of
411 *not* inlining otherwise-trivial bindings can be high, and are hard to
415 exprIsTrivial :: CoreExpr -> Bool
416 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
417 exprIsTrivial (Type _) = True
418 exprIsTrivial (Lit lit) = litIsTrivial lit
419 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
420 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
421 exprIsTrivial (Cast e _) = exprIsTrivial e
422 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
423 exprIsTrivial _ = False
426 exprIsBottom is a very cheap and cheerful function; it may return
427 False for bottoming expressions, but it never costs much to ask.
428 See also CoreArity.exprBotStrictness_maybe, but that's a bit more
432 exprIsBottom :: CoreExpr -> Bool
436 go n (Var v) = isBottomingId v && n >= idArity v
437 go n (App e a) | isTypeArg a = go n e
438 | otherwise = go (n+1) e
439 go n (Note _ e) = go n e
440 go n (Cast e _) = go n e
441 go n (Let _ e) = go n e
446 %************************************************************************
450 %************************************************************************
454 @exprIsDupable@ is true of expressions that can be duplicated at a modest
455 cost in code size. This will only happen in different case
456 branches, so there's no issue about duplicating work.
458 That is, exprIsDupable returns True of (f x) even if
459 f is very very expensive to call.
461 Its only purpose is to avoid fruitless let-binding
462 and then inlining of case join points
466 exprIsDupable :: CoreExpr -> Bool
468 = isJust (go dupAppSize e)
470 go :: Int -> CoreExpr -> Maybe Int
471 go n (Type {}) = Just n
472 go n (Var {}) = decrement n
473 go n (Note _ e) = go n e
474 go n (Cast e _) = go n e
475 go n (App f a) | Just n' <- go n a = go n' f
476 go n (Lit lit) | litIsDupable lit = decrement n
479 decrement :: Int -> Maybe Int
480 decrement 0 = Nothing
481 decrement n = Just (n-1)
484 dupAppSize = 6 -- Size of term we are prepared to duplicate
487 %************************************************************************
489 exprIsCheap, exprIsExpandable
491 %************************************************************************
493 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
494 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
495 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
496 it is obviously in weak head normal form, or is cheap to get to WHNF.
497 [Note that that's not the same as exprIsDupable; an expression might be
498 big, and hence not dupable, but still cheap.]
500 By ``cheap'' we mean a computation we're willing to:
501 push inside a lambda, or
502 inline at more than one place
503 That might mean it gets evaluated more than once, instead of being
504 shared. The main examples of things which aren't WHNF but are
509 (where e, and all the ei are cheap)
512 (where e and b are cheap)
515 (where op is a cheap primitive operator)
518 (because we are happy to substitute it inside a lambda)
520 Notice that a variable is considered 'cheap': we can push it inside a lambda,
521 because sharing will make sure it is only evaluated once.
523 Note [exprIsCheap and exprIsHNF]
524 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
525 Note that exprIsHNF does not imply exprIsCheap. Eg
526 let x = fac 20 in Just x
527 This responds True to exprIsHNF (you can discard a seq), but
528 False to exprIsCheap.
531 exprIsCheap :: CoreExpr -> Bool
532 exprIsCheap = exprIsCheap' isCheapApp
534 exprIsExpandable :: CoreExpr -> Bool
535 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
537 type CheapAppFun = Id -> Int -> Bool
538 exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
539 exprIsCheap' _ (Lit _) = True
540 exprIsCheap' _ (Type _) = True
541 exprIsCheap' _ (Var _) = True
542 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
543 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
544 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
545 || exprIsCheap' good_app e
547 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
548 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
549 -- Experimentally, treat (case x of ...) as cheap
550 -- (and case __coerce x etc.)
551 -- This improves arities of overloaded functions where
552 -- there is only dictionary selection (no construction) involved
554 exprIsCheap' good_app (Let (NonRec x _) e)
555 | isUnLiftedType (idType x) = exprIsCheap' good_app e
557 -- Strict lets always have cheap right hand sides,
558 -- and do no allocation, so just look at the body
559 -- Non-strict lets do allocation so we don't treat them as cheap
562 exprIsCheap' good_app other_expr -- Applications and variables
565 -- Accumulate value arguments, then decide
566 go (Cast e _) val_args = go e val_args
567 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
568 | otherwise = go f val_args
570 go (Var _) [] = True -- Just a type application of a variable
571 -- (f t1 t2 t3) counts as WHNF
573 = case idDetails f of
574 RecSelId {} -> go_sel args
575 ClassOpId {} -> go_sel args
576 PrimOpId op -> go_primop op args
577 _ | good_app f (length args) -> go_pap args
578 | isBottomingId f -> True
580 -- Application of a function which
581 -- always gives bottom; we treat this as cheap
582 -- because it certainly doesn't need to be shared!
587 go_pap args = all exprIsTrivial args
588 -- For constructor applications and primops, check that all
589 -- the args are trivial. We don't want to treat as cheap, say,
591 -- We'll put up with one constructor application, but not dozens
594 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
595 -- In principle we should worry about primops
596 -- that return a type variable, since the result
597 -- might be applied to something, but I'm not going
598 -- to bother to check the number of args
601 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
602 go_sel _ = False -- look cheap, so we will substitute it inside a
603 -- lambda. Particularly for dictionary field selection.
604 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
605 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
607 isCheapApp :: CheapAppFun
608 isCheapApp fn n_val_args
610 || n_val_args < idArity fn
612 isExpandableApp :: CheapAppFun
613 isExpandableApp fn n_val_args
615 || n_val_args < idArity fn
616 || go n_val_args (idType fn)
618 -- See if all the arguments are PredTys (implicit params or classes)
619 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
622 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
623 | Just (arg, ty) <- splitFunTy_maybe ty
624 , isPredTy arg = go (n_val_args-1) ty
628 Note [Expandable overloadings]
629 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
630 Suppose the user wrote this
631 {-# RULE forall x. foo (negate x) = h x #-}
632 f x = ....(foo (negate x))....
633 He'd expect the rule to fire. But since negate is overloaded, we might
635 f = \d -> let n = negate d in \x -> ...foo (n x)...
636 So we treat the application of a function (negate in this case) to a
637 *dictionary* as expandable. In effect, every function is CONLIKE when
638 it's applied only to dictionaries.
641 %************************************************************************
645 %************************************************************************
648 -- | 'exprOkForSpeculation' returns True of an expression that is:
650 -- * Safe to evaluate even if normal order eval might not
651 -- evaluate the expression at all, or
653 -- * Safe /not/ to evaluate even if normal order would do so
655 -- It is usually called on arguments of unlifted type, but not always
656 -- In particular, Simplify.rebuildCase calls it on lifted types
657 -- when a 'case' is a plain 'seq'. See the example in
658 -- Note [exprOkForSpeculation: case expressions] below
660 -- Precisely, it returns @True@ iff:
662 -- * The expression guarantees to terminate,
664 -- * without raising an exception,
665 -- * without causing a side effect (e.g. writing a mutable variable)
667 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
668 -- As an example of the considerations in this test, consider:
670 -- > let x = case y# +# 1# of { r# -> I# r# }
673 -- being translated to:
675 -- > case y# +# 1# of { r# ->
680 -- We can only do this if the @y + 1@ is ok for speculation: it has no
681 -- side effects, and can't diverge or raise an exception.
682 exprOkForSpeculation :: CoreExpr -> Bool
683 exprOkForSpeculation (Lit _) = True
684 exprOkForSpeculation (Type _) = True
686 exprOkForSpeculation (Var v)
687 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
688 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
689 || isDataConWorkId v -- Nullary constructors
690 || idArity v > 0 -- Functions
691 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
693 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
694 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
696 exprOkForSpeculation (Case e _ _ alts)
697 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
698 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
700 exprOkForSpeculation other_expr
701 = case collectArgs other_expr of
702 (Var f, args) -> spec_ok (idDetails f) args
706 spec_ok (DataConWorkId _) _
707 = True -- The strictness of the constructor has already
708 -- been expressed by its "wrapper", so we don't need
709 -- to take the arguments into account
711 spec_ok (PrimOpId op) args
712 | isDivOp op, -- Special case for dividing operations that fail
713 [arg1, Lit lit] <- args -- only if the divisor is zero
714 = not (isZeroLit lit) && exprOkForSpeculation arg1
715 -- Often there is a literal divisor, and this
716 -- can get rid of a thunk in an inner looop
718 | DataToTagOp <- op -- See Note [dataToTag speculation]
722 = primOpOkForSpeculation op &&
723 all exprOkForSpeculation args
724 -- A bit conservative: we don't really need
725 -- to care about lazy arguments, but this is easy
727 spec_ok (DFunId _ new_type) _ = not new_type
728 -- DFuns terminate, unless the dict is implemented with a newtype
729 -- in which case they may not
733 -- | True of dyadic operators that can fail only if the second arg is zero!
734 isDivOp :: PrimOp -> Bool
735 -- This function probably belongs in PrimOp, or even in
736 -- an automagically generated file.. but it's such a
737 -- special case I thought I'd leave it here for now.
738 isDivOp IntQuotOp = True
739 isDivOp IntRemOp = True
740 isDivOp WordQuotOp = True
741 isDivOp WordRemOp = True
742 isDivOp FloatDivOp = True
743 isDivOp DoubleDivOp = True
747 Note [exprOkForSpeculation: case expressions]
748 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
749 It's always sound for exprOkForSpeculation to return False, and we
750 don't want it to take too long, so it bales out on complicated-looking
751 terms. Notably lets, which can be stacked very deeply; and in any
752 case the argument of exprOkForSpeculation is usually in a strict context,
753 so any lets will have been floated away.
755 However, we keep going on case-expressions. An example like this one
756 showed up in DPH code (Trac #3717):
759 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
761 If exprOkForSpeculation doesn't look through case expressions, you get this:
763 \ (ww :: GHC.Prim.Int#) ->
765 __DEFAULT -> case (case <# ds 5 of _ {
766 GHC.Types.False -> lvl1;
767 GHC.Types.True -> lvl})
769 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
773 The inner case is redundant, and should be nuked.
775 Note [dataToTag speculation]
776 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
778 f x = let v::Int# = dataToTag# x
780 We say "yes", even though 'x' may not be evaluated. Reasons
782 * dataToTag#'s strictness means that its argument often will be
783 evaluated, but FloatOut makes that temporarily untrue
784 case x of y -> let v = dataToTag# y in ...
786 case x of y -> let v = dataToTag# x in ...
787 Note that we look at 'x' instead of 'y' (this is to improve
788 floating in FloatOut). So Lint complains.
790 Moreover, it really *might* improve floating to let the
793 * CorePrep makes sure dataToTag#'s argument is evaluated, just
794 before code gen. Until then, it's not guaranteed
797 %************************************************************************
799 exprIsHNF, exprIsConLike
801 %************************************************************************
804 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
806 -- | exprIsHNF returns true for expressions that are certainly /already/
807 -- evaluated to /head/ normal form. This is used to decide whether it's ok
810 -- > case x of _ -> e
816 -- and to decide whether it's safe to discard a 'seq'.
818 -- So, it does /not/ treat variables as evaluated, unless they say they are.
819 -- However, it /does/ treat partial applications and constructor applications
820 -- as values, even if their arguments are non-trivial, provided the argument
821 -- type is lifted. For example, both of these are values:
823 -- > (:) (f x) (map f xs)
824 -- > map (...redex...)
826 -- because 'seq' on such things completes immediately.
828 -- For unlifted argument types, we have to be careful:
832 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
833 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
834 -- unboxed type must be ok-for-speculation (or trivial).
835 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
836 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
840 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
841 -- data constructors. Conlike arguments are considered interesting by the
843 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
844 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
846 -- | Returns true for values or value-like expressions. These are lambdas,
847 -- constructors / CONLIKE functions (as determined by the function argument)
850 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
851 exprIsHNFlike is_con is_con_unf = is_hnf_like
853 is_hnf_like (Var v) -- NB: There are no value args at this point
854 = is_con v -- Catches nullary constructors,
855 -- so that [] and () are values, for example
856 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
857 || is_con_unf (idUnfolding v)
858 -- Check the thing's unfolding; it might be bound to a value
859 -- We don't look through loop breakers here, which is a bit conservative
860 -- but otherwise I worry that if an Id's unfolding is just itself,
861 -- we could get an infinite loop
863 is_hnf_like (Lit _) = True
864 is_hnf_like (Type _) = True -- Types are honorary Values;
865 -- we don't mind copying them
866 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
867 is_hnf_like (Note _ e) = is_hnf_like e
868 is_hnf_like (Cast e _) = is_hnf_like e
869 is_hnf_like (App e (Type _)) = is_hnf_like e
870 is_hnf_like (App e a) = app_is_value e [a]
871 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
872 is_hnf_like _ = False
874 -- There is at least one value argument
875 app_is_value :: CoreExpr -> [CoreArg] -> Bool
876 app_is_value (Var fun) args
877 = idArity fun > valArgCount args -- Under-applied function
878 || is_con fun -- or constructor-like
879 app_is_value (Note _ f) as = app_is_value f as
880 app_is_value (Cast f _) as = app_is_value f as
881 app_is_value (App f a) as = app_is_value f (a:as)
882 app_is_value _ _ = False
886 %************************************************************************
888 Instantiating data constructors
890 %************************************************************************
892 These InstPat functions go here to avoid circularity between DataCon and Id
895 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
896 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
898 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
899 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
900 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
902 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
903 -- Remember to include the existential dictionaries
905 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
906 -> [FastString] -- A long enough list of FSs to use for names
907 -> [Unique] -- An equally long list of uniques, at least one for each binder
909 -> [Type] -- Types to instantiate the universally quantified tyvars
910 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
911 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
912 -- (ex_tvs, co_tvs, arg_ids),
914 -- ex_tvs are intended to be used as binders for existential type args
916 -- co_tvs are intended to be used as binders for coercion args and the kinds
917 -- of these vars have been instantiated by the inst_tys and the ex_tys
918 -- The co_tvs include both GADT equalities (dcEqSpec) and
919 -- programmer-specified equalities (dcEqTheta)
921 -- arg_ids are indended to be used as binders for value arguments,
922 -- and their types have been instantiated with inst_tys and ex_tys
923 -- The arg_ids include both dicts (dcDictTheta) and
924 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
927 -- The following constructor T1
930 -- T1 :: forall b. Int -> b -> T(a,b)
933 -- has representation type
934 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
937 -- dataConInstPat fss us T1 (a1',b') will return
939 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
941 -- where the double-primed variables are created with the FastStrings and
942 -- Uniques given as fss and us
943 dataConInstPat arg_fun fss uniqs con inst_tys
944 = (ex_bndrs, co_bndrs, arg_ids)
946 univ_tvs = dataConUnivTyVars con
947 ex_tvs = dataConExTyVars con
948 arg_tys = arg_fun con
949 eq_spec = dataConEqSpec con
950 eq_theta = dataConEqTheta con
951 eq_preds = eqSpecPreds eq_spec ++ eq_theta
954 n_co = length eq_preds
956 -- split the Uniques and FastStrings
957 (ex_uniqs, uniqs') = splitAt n_ex uniqs
958 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
960 (ex_fss, fss') = splitAt n_ex fss
961 (co_fss, id_fss) = splitAt n_co fss'
963 -- Make existential type variables
964 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
965 mk_ex_var uniq fs var = mkTyVar new_name kind
967 new_name = mkSysTvName uniq fs
970 -- Make the instantiating substitution
971 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
973 -- Make new coercion vars, instantiating kind
974 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
975 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
977 new_name = mkSysTvName uniq fs
978 co_kind = substTy subst (mkPredTy eq_pred)
980 -- make value vars, instantiating types
981 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
982 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
986 %************************************************************************
990 %************************************************************************
993 -- | A cheap equality test which bales out fast!
994 -- If it returns @True@ the arguments are definitely equal,
995 -- otherwise, they may or may not be equal.
997 -- See also 'exprIsBig'
998 cheapEqExpr :: Expr b -> Expr b -> Bool
1000 cheapEqExpr (Var v1) (Var v2) = v1==v2
1001 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1002 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1004 cheapEqExpr (App f1 a1) (App f2 a2)
1005 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1007 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1008 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1010 cheapEqExpr _ _ = False
1014 exprIsBig :: Expr b -> Bool
1015 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1016 exprIsBig (Lit _) = False
1017 exprIsBig (Var _) = False
1018 exprIsBig (Type _) = False
1019 exprIsBig (Lam _ e) = exprIsBig e
1020 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1021 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1026 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1027 -- Compares for equality, modulo alpha
1028 eqExpr in_scope e1 e2
1029 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1031 id_unf _ = noUnfolding -- Don't expand
1035 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1036 -- ^ Compares expressions for equality, modulo alpha.
1037 -- Does /not/ look through newtypes or predicate types
1038 -- Used in rule matching, and also CSE
1040 eqExprX id_unfolding_fun env e1 e2
1043 go env (Var v1) (Var v2)
1044 | rnOccL env v1 == rnOccR env v2
1047 -- The next two rules expand non-local variables
1048 -- C.f. Note [Expanding variables] in Rules.lhs
1049 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1051 | not (locallyBoundL env v1)
1052 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1053 = go (nukeRnEnvL env) e1' e2
1056 | not (locallyBoundR env v2)
1057 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1058 = go (nukeRnEnvR env) e1 e2'
1060 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1061 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1062 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1063 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1064 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1066 go env (Lam b1 e1) (Lam b2 e2)
1067 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1068 && go (rnBndr2 env b1 b2) e1 e2
1070 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1071 = go env r1 r2 -- No need to check binder types, since RHSs match
1072 && go (rnBndr2 env v1 v2) e1 e2
1074 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1075 = all2 (go env') rs1 rs2 && go env' e1 e2
1077 (bs1,rs1) = unzip ps1
1078 (bs2,rs2) = unzip ps2
1079 env' = rnBndrs2 env bs1 bs2
1081 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1083 && tcEqTypeX env (idType b1) (idType b2)
1084 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1089 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1090 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1093 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1094 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1101 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1102 locallyBoundL rn_env v = inRnEnvL rn_env v
1103 locallyBoundR rn_env v = inRnEnvR rn_env v
1107 %************************************************************************
1109 \subsection{The size of an expression}
1111 %************************************************************************
1114 coreBindsSize :: [CoreBind] -> Int
1115 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1117 exprSize :: CoreExpr -> Int
1118 -- ^ A measure of the size of the expressions, strictly greater than 0
1119 -- It also forces the expression pretty drastically as a side effect
1120 exprSize (Var v) = v `seq` 1
1121 exprSize (Lit lit) = lit `seq` 1
1122 exprSize (App f a) = exprSize f + exprSize a
1123 exprSize (Lam b e) = varSize b + exprSize e
1124 exprSize (Let b e) = bindSize b + exprSize e
1125 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1126 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1127 exprSize (Note n e) = noteSize n + exprSize e
1128 exprSize (Type t) = seqType t `seq` 1
1130 noteSize :: Note -> Int
1131 noteSize (SCC cc) = cc `seq` 1
1132 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1134 varSize :: Var -> Int
1135 varSize b | isTyCoVar b = 1
1136 | otherwise = seqType (idType b) `seq`
1137 megaSeqIdInfo (idInfo b) `seq`
1140 varsSize :: [Var] -> Int
1141 varsSize = sum . map varSize
1143 bindSize :: CoreBind -> Int
1144 bindSize (NonRec b e) = varSize b + exprSize e
1145 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1147 pairSize :: (Var, CoreExpr) -> Int
1148 pairSize (b,e) = varSize b + exprSize e
1150 altSize :: CoreAlt -> Int
1151 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1155 %************************************************************************
1157 \subsection{Hashing}
1159 %************************************************************************
1162 hashExpr :: CoreExpr -> Int
1163 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1164 -- Two expressions that hash to the different Ints are definitely unequal.
1166 -- The emphasis is on a crude, fast hash, rather than on high precision.
1168 -- But unequal here means \"not identical\"; two alpha-equivalent
1169 -- expressions may hash to the different Ints.
1171 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1172 -- (at least if we want the above invariant to be true).
1174 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1175 -- UniqFM doesn't like negative Ints
1177 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1179 hash_expr :: HashEnv -> CoreExpr -> Word32
1180 -- Word32, because we're expecting overflows here, and overflowing
1181 -- signed types just isn't cool. In C it's even undefined.
1182 hash_expr env (Note _ e) = hash_expr env e
1183 hash_expr env (Cast e _) = hash_expr env e
1184 hash_expr env (Var v) = hashVar env v
1185 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1186 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1187 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1188 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1189 hash_expr env (Case e _ _ _) = hash_expr env e
1190 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1191 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1192 -- Shouldn't happen. Better to use WARN than trace, because trace
1193 -- prevents the CPR optimisation kicking in for hash_expr.
1195 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1196 fast_hash_expr env (Var v) = hashVar env v
1197 fast_hash_expr env (Type t) = fast_hash_type env t
1198 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1199 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1200 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1201 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1202 fast_hash_expr _ _ = 1
1204 fast_hash_type :: HashEnv -> Type -> Word32
1205 fast_hash_type env ty
1206 | Just tv <- getTyVar_maybe ty = hashVar env tv
1207 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1208 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1211 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1212 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1214 hashVar :: HashEnv -> Var -> Word32
1216 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1220 %************************************************************************
1224 %************************************************************************
1226 Note [Eta reduction conditions]
1227 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1228 We try for eta reduction here, but *only* if we get all the way to an
1229 trivial expression. We don't want to remove extra lambdas unless we
1230 are going to avoid allocating this thing altogether.
1232 There are some particularly delicate points here:
1234 * Eta reduction is not valid in general:
1236 This matters, partly for old-fashioned correctness reasons but,
1237 worse, getting it wrong can yield a seg fault. Consider
1239 h y = case (case y of { True -> f `seq` True; False -> False }) of
1240 True -> ...; False -> ...
1242 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1243 says f=bottom, and replaces the (f `seq` True) with just
1244 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1245 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1246 the definition again, so that it does not termninate after all.
1247 Result: seg-fault because the boolean case actually gets a function value.
1250 So it's important to to the right thing.
1252 * Note [Arity care]: we need to be careful if we just look at f's
1253 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1254 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1255 arity when checking that 'f' is a value. Otherwise we will
1260 Which might change a terminiating program (think (f `seq` e)) to a
1261 non-terminating one. So we check for being a loop breaker first.
1263 However for GlobalIds we can look at the arity; and for primops we
1264 must, since they have no unfolding.
1266 * Regardless of whether 'f' is a value, we always want to
1267 reduce (/\a -> f a) to f
1268 This came up in a RULE: foldr (build (/\a -> g a))
1269 did not match foldr (build (/\b -> ...something complex...))
1270 The type checker can insert these eta-expanded versions,
1271 with both type and dictionary lambdas; hence the slightly
1274 * Never *reduce* arity. For example
1276 Then if h has arity 1 we don't want to eta-reduce because then
1277 f's arity would decrease, and that is bad
1279 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1282 Note [Eta reduction with casted arguments]
1283 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1285 (\(x:t3). f (x |> g)) :: t3 -> t2
1289 This should be eta-reduced to
1293 So we need to accumulate a coercion, pushing it inward (past
1294 variable arguments only) thus:
1295 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1296 f (x:t) |> co --> (f |> (t -> co)) x
1297 f @ a |> co --> (f |> (forall a.co)) @ a
1298 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1299 These are the equations for ok_arg.
1301 It's true that we could also hope to eta reduce these:
1304 But the simplifier pushes those casts outwards, so we don't
1305 need to address that here.
1308 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1309 tryEtaReduce bndrs body
1310 = go (reverse bndrs) body (IdCo (exprType body))
1312 incoming_arity = count isId bndrs
1314 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1315 -> CoreExpr -- Of type tr
1316 -> CoercionI -- Of type tr ~ ts
1317 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1318 -- See Note [Eta reduction with casted arguments]
1319 -- for why we have an accumulating coercion
1321 | ok_fun fun = Just (mkCoerceI co fun)
1323 go (b : bs) (App fun arg) co
1324 | Just co' <- ok_arg b arg co
1327 go _ _ _ = Nothing -- Failure!
1330 -- Note [Eta reduction conditions]
1331 ok_fun (App fun (Type ty))
1332 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1335 = not (fun_id `elem` bndrs)
1336 && (ok_fun_id fun_id || all ok_lam bndrs)
1340 ok_fun_id fun = fun_arity fun >= incoming_arity
1343 fun_arity fun -- See Note [Arity care]
1344 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1345 | otherwise = idArity fun
1348 ok_lam v = isTyCoVar v || isDictId v
1351 ok_arg :: Var -- Of type bndr_t
1352 -> CoreExpr -- Of type arg_t
1353 -> CoercionI -- Of kind (t1~t2)
1354 -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1355 -- (and similarly for tyvars, coercion args)
1356 -- See Note [Eta reduction with casted arguments]
1357 ok_arg bndr (Type ty) co
1358 | Just tv <- getTyVar_maybe ty
1359 , bndr == tv = Just (mkForAllTyCoI tv co)
1360 ok_arg bndr (Var v) co
1361 | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co)
1362 ok_arg bndr (Cast (Var v) co_arg) co
1363 | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co)
1364 -- The simplifier combines multiple casts into one,
1365 -- so we can have a simple-minded pattern match here
1366 ok_arg _ _ _ = Nothing
1370 %************************************************************************
1372 \subsection{Determining non-updatable right-hand-sides}
1374 %************************************************************************
1376 Top-level constructor applications can usually be allocated
1377 statically, but they can't if the constructor, or any of the
1378 arguments, come from another DLL (because we can't refer to static
1379 labels in other DLLs).
1381 If this happens we simply make the RHS into an updatable thunk,
1382 and 'execute' it rather than allocating it statically.
1385 -- | This function is called only on *top-level* right-hand sides.
1386 -- Returns @True@ if the RHS can be allocated statically in the output,
1387 -- with no thunks involved at all.
1388 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1389 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1390 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1391 -- update flag on it and (iii) in DsExpr to decide how to expand
1394 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1395 -- (a) a value lambda
1396 -- (b) a saturated constructor application with static args
1398 -- BUT watch out for
1399 -- (i) Any cross-DLL references kill static-ness completely
1400 -- because they must be 'executed' not statically allocated
1401 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1402 -- this is not necessary)
1404 -- (ii) We treat partial applications as redexes, because in fact we
1405 -- make a thunk for them that runs and builds a PAP
1406 -- at run-time. The only appliations that are treated as
1407 -- static are *saturated* applications of constructors.
1409 -- We used to try to be clever with nested structures like this:
1410 -- ys = (:) w ((:) w [])
1411 -- on the grounds that CorePrep will flatten ANF-ise it later.
1412 -- But supporting this special case made the function much more
1413 -- complicated, because the special case only applies if there are no
1414 -- enclosing type lambdas:
1415 -- ys = /\ a -> Foo (Baz ([] a))
1416 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1418 -- But in fact, even without -O, nested structures at top level are
1419 -- flattened by the simplifier, so we don't need to be super-clever here.
1423 -- f = \x::Int. x+7 TRUE
1424 -- p = (True,False) TRUE
1426 -- d = (fst p, False) FALSE because there's a redex inside
1427 -- (this particular one doesn't happen but...)
1429 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1430 -- n = /\a. Nil a TRUE
1432 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1435 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1436 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1438 -- b) (C x xs), where C is a contructor is updatable if the application is
1441 -- c) don't look through unfolding of f in (f x).
1443 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1445 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1448 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1449 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1450 is_static in_arg (Cast e _) = is_static in_arg e
1452 is_static _ (Lit lit)
1454 MachLabel _ _ _ -> False
1456 -- A MachLabel (foreign import "&foo") in an argument
1457 -- prevents a constructor application from being static. The
1458 -- reason is that it might give rise to unresolvable symbols
1459 -- in the object file: under Linux, references to "weak"
1460 -- symbols from the data segment give rise to "unresolvable
1461 -- relocation" errors at link time This might be due to a bug
1462 -- in the linker, but we'll work around it here anyway.
1465 is_static in_arg other_expr = go other_expr 0
1467 go (Var f) n_val_args
1468 #if mingw32_TARGET_OS
1469 | not (_is_dynamic_name (idName f))
1471 = saturated_data_con f n_val_args
1472 || (in_arg && n_val_args == 0)
1473 -- A naked un-applied variable is *not* deemed a static RHS
1475 -- Reason: better to update so that the indirection gets shorted
1476 -- out, and the true value will be seen
1477 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1478 -- are always updatable. If you do so, make sure that non-updatable
1479 -- ones have enough space for their static link field!
1481 go (App f a) n_val_args
1482 | isTypeArg a = go f n_val_args
1483 | not in_arg && is_static True a = go f (n_val_args + 1)
1484 -- The (not in_arg) checks that we aren't in a constructor argument;
1485 -- if we are, we don't allow (value) applications of any sort
1487 -- NB. In case you wonder, args are sometimes not atomic. eg.
1488 -- x = D# (1.0## /## 2.0##)
1489 -- can't float because /## can fail.
1491 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1492 go (Cast e _) n_val_args = go e n_val_args
1495 saturated_data_con f n_val_args
1496 = case isDataConWorkId_maybe f of
1497 Just dc -> n_val_args == dataConRepArity dc