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 = 8 -- Size of term we are prepared to duplicate
485 -- This is *just* big enough to make test MethSharing
486 -- inline enough join points. Really it should be
487 -- smaller, and could be if we fixed Trac #4960.
490 %************************************************************************
492 exprIsCheap, exprIsExpandable
494 %************************************************************************
496 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
497 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
498 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
499 it is obviously in weak head normal form, or is cheap to get to WHNF.
500 [Note that that's not the same as exprIsDupable; an expression might be
501 big, and hence not dupable, but still cheap.]
503 By ``cheap'' we mean a computation we're willing to:
504 push inside a lambda, or
505 inline at more than one place
506 That might mean it gets evaluated more than once, instead of being
507 shared. The main examples of things which aren't WHNF but are
512 (where e, and all the ei are cheap)
515 (where e and b are cheap)
518 (where op is a cheap primitive operator)
521 (because we are happy to substitute it inside a lambda)
523 Notice that a variable is considered 'cheap': we can push it inside a lambda,
524 because sharing will make sure it is only evaluated once.
526 Note [exprIsCheap and exprIsHNF]
527 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
528 Note that exprIsHNF does not imply exprIsCheap. Eg
529 let x = fac 20 in Just x
530 This responds True to exprIsHNF (you can discard a seq), but
531 False to exprIsCheap.
534 exprIsCheap :: CoreExpr -> Bool
535 exprIsCheap = exprIsCheap' isCheapApp
537 exprIsExpandable :: CoreExpr -> Bool
538 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
540 type CheapAppFun = Id -> Int -> Bool
541 exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
542 exprIsCheap' _ (Lit _) = True
543 exprIsCheap' _ (Type _) = True
544 exprIsCheap' _ (Var _) = True
545 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
546 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
547 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
548 || exprIsCheap' good_app e
550 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
551 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
552 -- Experimentally, treat (case x of ...) as cheap
553 -- (and case __coerce x etc.)
554 -- This improves arities of overloaded functions where
555 -- there is only dictionary selection (no construction) involved
557 exprIsCheap' good_app (Let (NonRec x _) e)
558 | isUnLiftedType (idType x) = exprIsCheap' good_app e
560 -- Strict lets always have cheap right hand sides,
561 -- and do no allocation, so just look at the body
562 -- Non-strict lets do allocation so we don't treat them as cheap
565 exprIsCheap' good_app other_expr -- Applications and variables
568 -- Accumulate value arguments, then decide
569 go (Cast e _) val_args = go e val_args
570 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
571 | otherwise = go f val_args
573 go (Var _) [] = True -- Just a type application of a variable
574 -- (f t1 t2 t3) counts as WHNF
576 = case idDetails f of
577 RecSelId {} -> go_sel args
578 ClassOpId {} -> go_sel args
579 PrimOpId op -> go_primop op args
580 _ | good_app f (length args) -> go_pap args
581 | isBottomingId f -> True
583 -- Application of a function which
584 -- always gives bottom; we treat this as cheap
585 -- because it certainly doesn't need to be shared!
590 go_pap args = all exprIsTrivial args
591 -- For constructor applications and primops, check that all
592 -- the args are trivial. We don't want to treat as cheap, say,
594 -- We'll put up with one constructor application, but not dozens
597 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
598 -- In principle we should worry about primops
599 -- that return a type variable, since the result
600 -- might be applied to something, but I'm not going
601 -- to bother to check the number of args
604 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
605 go_sel _ = False -- look cheap, so we will substitute it inside a
606 -- lambda. Particularly for dictionary field selection.
607 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
608 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
610 isCheapApp :: CheapAppFun
611 isCheapApp fn n_val_args
613 || n_val_args < idArity fn
615 isExpandableApp :: CheapAppFun
616 isExpandableApp fn n_val_args
618 || n_val_args < idArity fn
619 || go n_val_args (idType fn)
621 -- See if all the arguments are PredTys (implicit params or classes)
622 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
625 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
626 | Just (arg, ty) <- splitFunTy_maybe ty
627 , isPredTy arg = go (n_val_args-1) ty
631 Note [Expandable overloadings]
632 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
633 Suppose the user wrote this
634 {-# RULE forall x. foo (negate x) = h x #-}
635 f x = ....(foo (negate x))....
636 He'd expect the rule to fire. But since negate is overloaded, we might
638 f = \d -> let n = negate d in \x -> ...foo (n x)...
639 So we treat the application of a function (negate in this case) to a
640 *dictionary* as expandable. In effect, every function is CONLIKE when
641 it's applied only to dictionaries.
644 %************************************************************************
648 %************************************************************************
651 -- | 'exprOkForSpeculation' returns True of an expression that is:
653 -- * Safe to evaluate even if normal order eval might not
654 -- evaluate the expression at all, or
656 -- * Safe /not/ to evaluate even if normal order would do so
658 -- It is usually called on arguments of unlifted type, but not always
659 -- In particular, Simplify.rebuildCase calls it on lifted types
660 -- when a 'case' is a plain 'seq'. See the example in
661 -- Note [exprOkForSpeculation: case expressions] below
663 -- Precisely, it returns @True@ iff:
665 -- * The expression guarantees to terminate,
667 -- * without raising an exception,
668 -- * without causing a side effect (e.g. writing a mutable variable)
670 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
671 -- As an example of the considerations in this test, consider:
673 -- > let x = case y# +# 1# of { r# -> I# r# }
676 -- being translated to:
678 -- > case y# +# 1# of { r# ->
683 -- We can only do this if the @y + 1@ is ok for speculation: it has no
684 -- side effects, and can't diverge or raise an exception.
685 exprOkForSpeculation :: CoreExpr -> Bool
686 exprOkForSpeculation (Lit _) = True
687 exprOkForSpeculation (Type _) = True
689 exprOkForSpeculation (Var v)
690 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
691 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
692 || isDataConWorkId v -- Nullary constructors
693 || idArity v > 0 -- Functions
694 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
696 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
697 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
699 exprOkForSpeculation (Case e _ _ alts)
700 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
701 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
703 exprOkForSpeculation other_expr
704 = case collectArgs other_expr of
705 (Var f, args) -> spec_ok (idDetails f) args
709 spec_ok (DataConWorkId _) _
710 = True -- The strictness of the constructor has already
711 -- been expressed by its "wrapper", so we don't need
712 -- to take the arguments into account
714 spec_ok (PrimOpId op) args
715 | isDivOp op, -- Special case for dividing operations that fail
716 [arg1, Lit lit] <- args -- only if the divisor is zero
717 = not (isZeroLit lit) && exprOkForSpeculation arg1
718 -- Often there is a literal divisor, and this
719 -- can get rid of a thunk in an inner looop
721 | DataToTagOp <- op -- See Note [dataToTag speculation]
725 = primOpOkForSpeculation op &&
726 all exprOkForSpeculation args
727 -- A bit conservative: we don't really need
728 -- to care about lazy arguments, but this is easy
730 spec_ok (DFunId _ new_type) _ = not new_type
731 -- DFuns terminate, unless the dict is implemented with a newtype
732 -- in which case they may not
736 -- | True of dyadic operators that can fail only if the second arg is zero!
737 isDivOp :: PrimOp -> Bool
738 -- This function probably belongs in PrimOp, or even in
739 -- an automagically generated file.. but it's such a
740 -- special case I thought I'd leave it here for now.
741 isDivOp IntQuotOp = True
742 isDivOp IntRemOp = True
743 isDivOp WordQuotOp = True
744 isDivOp WordRemOp = True
745 isDivOp FloatDivOp = True
746 isDivOp DoubleDivOp = True
750 Note [exprOkForSpeculation: case expressions]
751 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
752 It's always sound for exprOkForSpeculation to return False, and we
753 don't want it to take too long, so it bales out on complicated-looking
754 terms. Notably lets, which can be stacked very deeply; and in any
755 case the argument of exprOkForSpeculation is usually in a strict context,
756 so any lets will have been floated away.
758 However, we keep going on case-expressions. An example like this one
759 showed up in DPH code (Trac #3717):
762 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
764 If exprOkForSpeculation doesn't look through case expressions, you get this:
766 \ (ww :: GHC.Prim.Int#) ->
768 __DEFAULT -> case (case <# ds 5 of _ {
769 GHC.Types.False -> lvl1;
770 GHC.Types.True -> lvl})
772 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
776 The inner case is redundant, and should be nuked.
778 Note [dataToTag speculation]
779 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
781 f x = let v::Int# = dataToTag# x
783 We say "yes", even though 'x' may not be evaluated. Reasons
785 * dataToTag#'s strictness means that its argument often will be
786 evaluated, but FloatOut makes that temporarily untrue
787 case x of y -> let v = dataToTag# y in ...
789 case x of y -> let v = dataToTag# x in ...
790 Note that we look at 'x' instead of 'y' (this is to improve
791 floating in FloatOut). So Lint complains.
793 Moreover, it really *might* improve floating to let the
796 * CorePrep makes sure dataToTag#'s argument is evaluated, just
797 before code gen. Until then, it's not guaranteed
800 %************************************************************************
802 exprIsHNF, exprIsConLike
804 %************************************************************************
807 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
809 -- | exprIsHNF returns true for expressions that are certainly /already/
810 -- evaluated to /head/ normal form. This is used to decide whether it's ok
813 -- > case x of _ -> e
819 -- and to decide whether it's safe to discard a 'seq'.
821 -- So, it does /not/ treat variables as evaluated, unless they say they are.
822 -- However, it /does/ treat partial applications and constructor applications
823 -- as values, even if their arguments are non-trivial, provided the argument
824 -- type is lifted. For example, both of these are values:
826 -- > (:) (f x) (map f xs)
827 -- > map (...redex...)
829 -- because 'seq' on such things completes immediately.
831 -- For unlifted argument types, we have to be careful:
835 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
836 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
837 -- unboxed type must be ok-for-speculation (or trivial).
838 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
839 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
843 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
844 -- data constructors. Conlike arguments are considered interesting by the
846 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
847 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
849 -- | Returns true for values or value-like expressions. These are lambdas,
850 -- constructors / CONLIKE functions (as determined by the function argument)
853 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
854 exprIsHNFlike is_con is_con_unf = is_hnf_like
856 is_hnf_like (Var v) -- NB: There are no value args at this point
857 = is_con v -- Catches nullary constructors,
858 -- so that [] and () are values, for example
859 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
860 || is_con_unf (idUnfolding v)
861 -- Check the thing's unfolding; it might be bound to a value
862 -- We don't look through loop breakers here, which is a bit conservative
863 -- but otherwise I worry that if an Id's unfolding is just itself,
864 -- we could get an infinite loop
866 is_hnf_like (Lit _) = True
867 is_hnf_like (Type _) = True -- Types are honorary Values;
868 -- we don't mind copying them
869 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
870 is_hnf_like (Note _ e) = is_hnf_like e
871 is_hnf_like (Cast e _) = is_hnf_like e
872 is_hnf_like (App e (Type _)) = is_hnf_like e
873 is_hnf_like (App e a) = app_is_value e [a]
874 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
875 is_hnf_like _ = False
877 -- There is at least one value argument
878 app_is_value :: CoreExpr -> [CoreArg] -> Bool
879 app_is_value (Var fun) args
880 = idArity fun > valArgCount args -- Under-applied function
881 || is_con fun -- or constructor-like
882 app_is_value (Note _ f) as = app_is_value f as
883 app_is_value (Cast f _) as = app_is_value f as
884 app_is_value (App f a) as = app_is_value f (a:as)
885 app_is_value _ _ = False
889 %************************************************************************
891 Instantiating data constructors
893 %************************************************************************
895 These InstPat functions go here to avoid circularity between DataCon and Id
898 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
899 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
901 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
902 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
903 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
905 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
906 -- Remember to include the existential dictionaries
908 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
909 -> [FastString] -- A long enough list of FSs to use for names
910 -> [Unique] -- An equally long list of uniques, at least one for each binder
912 -> [Type] -- Types to instantiate the universally quantified tyvars
913 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
914 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
915 -- (ex_tvs, co_tvs, arg_ids),
917 -- ex_tvs are intended to be used as binders for existential type args
919 -- co_tvs are intended to be used as binders for coercion args and the kinds
920 -- of these vars have been instantiated by the inst_tys and the ex_tys
921 -- The co_tvs include both GADT equalities (dcEqSpec) and
922 -- programmer-specified equalities (dcEqTheta)
924 -- arg_ids are indended to be used as binders for value arguments,
925 -- and their types have been instantiated with inst_tys and ex_tys
926 -- The arg_ids include both dicts (dcDictTheta) and
927 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
930 -- The following constructor T1
933 -- T1 :: forall b. Int -> b -> T(a,b)
936 -- has representation type
937 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
940 -- dataConInstPat fss us T1 (a1',b') will return
942 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
944 -- where the double-primed variables are created with the FastStrings and
945 -- Uniques given as fss and us
946 dataConInstPat arg_fun fss uniqs con inst_tys
947 = (ex_bndrs, co_bndrs, arg_ids)
949 univ_tvs = dataConUnivTyVars con
950 ex_tvs = dataConExTyVars con
951 arg_tys = arg_fun con
952 eq_spec = dataConEqSpec con
953 eq_theta = dataConEqTheta con
954 eq_preds = eqSpecPreds eq_spec ++ eq_theta
957 n_co = length eq_preds
959 -- split the Uniques and FastStrings
960 (ex_uniqs, uniqs') = splitAt n_ex uniqs
961 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
963 (ex_fss, fss') = splitAt n_ex fss
964 (co_fss, id_fss) = splitAt n_co fss'
966 -- Make existential type variables
967 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
968 mk_ex_var uniq fs var = mkTyVar new_name kind
970 new_name = mkSysTvName uniq fs
973 -- Make the instantiating substitution
974 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
976 -- Make new coercion vars, instantiating kind
977 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
978 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
980 new_name = mkSysTvName uniq fs
981 co_kind = substTy subst (mkPredTy eq_pred)
983 -- make value vars, instantiating types
984 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
985 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
989 %************************************************************************
993 %************************************************************************
996 -- | A cheap equality test which bales out fast!
997 -- If it returns @True@ the arguments are definitely equal,
998 -- otherwise, they may or may not be equal.
1000 -- See also 'exprIsBig'
1001 cheapEqExpr :: Expr b -> Expr b -> Bool
1003 cheapEqExpr (Var v1) (Var v2) = v1==v2
1004 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1005 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1007 cheapEqExpr (App f1 a1) (App f2 a2)
1008 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1010 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1011 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1013 cheapEqExpr _ _ = False
1017 exprIsBig :: Expr b -> Bool
1018 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1019 exprIsBig (Lit _) = False
1020 exprIsBig (Var _) = False
1021 exprIsBig (Type _) = False
1022 exprIsBig (Lam _ e) = exprIsBig e
1023 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1024 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1029 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1030 -- Compares for equality, modulo alpha
1031 eqExpr in_scope e1 e2
1032 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1034 id_unf _ = noUnfolding -- Don't expand
1038 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1039 -- ^ Compares expressions for equality, modulo alpha.
1040 -- Does /not/ look through newtypes or predicate types
1041 -- Used in rule matching, and also CSE
1043 eqExprX id_unfolding_fun env e1 e2
1046 go env (Var v1) (Var v2)
1047 | rnOccL env v1 == rnOccR env v2
1050 -- The next two rules expand non-local variables
1051 -- C.f. Note [Expanding variables] in Rules.lhs
1052 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1054 | not (locallyBoundL env v1)
1055 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1056 = go (nukeRnEnvL env) e1' e2
1059 | not (locallyBoundR env v2)
1060 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1061 = go (nukeRnEnvR env) e1 e2'
1063 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1064 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1065 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1066 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1067 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1069 go env (Lam b1 e1) (Lam b2 e2)
1070 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1071 && go (rnBndr2 env b1 b2) e1 e2
1073 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1074 = go env r1 r2 -- No need to check binder types, since RHSs match
1075 && go (rnBndr2 env v1 v2) e1 e2
1077 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1078 = all2 (go env') rs1 rs2 && go env' e1 e2
1080 (bs1,rs1) = unzip ps1
1081 (bs2,rs2) = unzip ps2
1082 env' = rnBndrs2 env bs1 bs2
1084 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1086 && tcEqTypeX env (idType b1) (idType b2)
1087 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1092 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1093 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1096 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1097 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1104 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1105 locallyBoundL rn_env v = inRnEnvL rn_env v
1106 locallyBoundR rn_env v = inRnEnvR rn_env v
1110 %************************************************************************
1112 \subsection{The size of an expression}
1114 %************************************************************************
1117 coreBindsSize :: [CoreBind] -> Int
1118 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1120 exprSize :: CoreExpr -> Int
1121 -- ^ A measure of the size of the expressions, strictly greater than 0
1122 -- It also forces the expression pretty drastically as a side effect
1123 exprSize (Var v) = v `seq` 1
1124 exprSize (Lit lit) = lit `seq` 1
1125 exprSize (App f a) = exprSize f + exprSize a
1126 exprSize (Lam b e) = varSize b + exprSize e
1127 exprSize (Let b e) = bindSize b + exprSize e
1128 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1129 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1130 exprSize (Note n e) = noteSize n + exprSize e
1131 exprSize (Type t) = seqType t `seq` 1
1133 noteSize :: Note -> Int
1134 noteSize (SCC cc) = cc `seq` 1
1135 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1137 varSize :: Var -> Int
1138 varSize b | isTyCoVar b = 1
1139 | otherwise = seqType (idType b) `seq`
1140 megaSeqIdInfo (idInfo b) `seq`
1143 varsSize :: [Var] -> Int
1144 varsSize = sum . map varSize
1146 bindSize :: CoreBind -> Int
1147 bindSize (NonRec b e) = varSize b + exprSize e
1148 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1150 pairSize :: (Var, CoreExpr) -> Int
1151 pairSize (b,e) = varSize b + exprSize e
1153 altSize :: CoreAlt -> Int
1154 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1158 %************************************************************************
1160 \subsection{Hashing}
1162 %************************************************************************
1165 hashExpr :: CoreExpr -> Int
1166 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1167 -- Two expressions that hash to the different Ints are definitely unequal.
1169 -- The emphasis is on a crude, fast hash, rather than on high precision.
1171 -- But unequal here means \"not identical\"; two alpha-equivalent
1172 -- expressions may hash to the different Ints.
1174 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1175 -- (at least if we want the above invariant to be true).
1177 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1178 -- UniqFM doesn't like negative Ints
1180 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1182 hash_expr :: HashEnv -> CoreExpr -> Word32
1183 -- Word32, because we're expecting overflows here, and overflowing
1184 -- signed types just isn't cool. In C it's even undefined.
1185 hash_expr env (Note _ e) = hash_expr env e
1186 hash_expr env (Cast e _) = hash_expr env e
1187 hash_expr env (Var v) = hashVar env v
1188 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1189 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1190 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1191 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1192 hash_expr env (Case e _ _ _) = hash_expr env e
1193 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1194 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1195 -- Shouldn't happen. Better to use WARN than trace, because trace
1196 -- prevents the CPR optimisation kicking in for hash_expr.
1198 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1199 fast_hash_expr env (Var v) = hashVar env v
1200 fast_hash_expr env (Type t) = fast_hash_type env t
1201 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1202 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1203 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1204 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1205 fast_hash_expr _ _ = 1
1207 fast_hash_type :: HashEnv -> Type -> Word32
1208 fast_hash_type env ty
1209 | Just tv <- getTyVar_maybe ty = hashVar env tv
1210 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1211 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1214 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1215 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1217 hashVar :: HashEnv -> Var -> Word32
1219 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1223 %************************************************************************
1227 %************************************************************************
1229 Note [Eta reduction conditions]
1230 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1231 We try for eta reduction here, but *only* if we get all the way to an
1232 trivial expression. We don't want to remove extra lambdas unless we
1233 are going to avoid allocating this thing altogether.
1235 There are some particularly delicate points here:
1237 * Eta reduction is not valid in general:
1239 This matters, partly for old-fashioned correctness reasons but,
1240 worse, getting it wrong can yield a seg fault. Consider
1242 h y = case (case y of { True -> f `seq` True; False -> False }) of
1243 True -> ...; False -> ...
1245 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1246 says f=bottom, and replaces the (f `seq` True) with just
1247 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1248 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1249 the definition again, so that it does not termninate after all.
1250 Result: seg-fault because the boolean case actually gets a function value.
1253 So it's important to to the right thing.
1255 * Note [Arity care]: we need to be careful if we just look at f's
1256 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1257 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1258 arity when checking that 'f' is a value. Otherwise we will
1263 Which might change a terminiating program (think (f `seq` e)) to a
1264 non-terminating one. So we check for being a loop breaker first.
1266 However for GlobalIds we can look at the arity; and for primops we
1267 must, since they have no unfolding.
1269 * Regardless of whether 'f' is a value, we always want to
1270 reduce (/\a -> f a) to f
1271 This came up in a RULE: foldr (build (/\a -> g a))
1272 did not match foldr (build (/\b -> ...something complex...))
1273 The type checker can insert these eta-expanded versions,
1274 with both type and dictionary lambdas; hence the slightly
1277 * Never *reduce* arity. For example
1279 Then if h has arity 1 we don't want to eta-reduce because then
1280 f's arity would decrease, and that is bad
1282 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1285 Note [Eta reduction with casted arguments]
1286 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1288 (\(x:t3). f (x |> g)) :: t3 -> t2
1292 This should be eta-reduced to
1296 So we need to accumulate a coercion, pushing it inward (past
1297 variable arguments only) thus:
1298 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1299 f (x:t) |> co --> (f |> (t -> co)) x
1300 f @ a |> co --> (f |> (forall a.co)) @ a
1301 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1302 These are the equations for ok_arg.
1304 It's true that we could also hope to eta reduce these:
1307 But the simplifier pushes those casts outwards, so we don't
1308 need to address that here.
1311 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1312 tryEtaReduce bndrs body
1313 = go (reverse bndrs) body (IdCo (exprType body))
1315 incoming_arity = count isId bndrs
1317 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1318 -> CoreExpr -- Of type tr
1319 -> CoercionI -- Of type tr ~ ts
1320 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1321 -- See Note [Eta reduction with casted arguments]
1322 -- for why we have an accumulating coercion
1324 | ok_fun fun = Just (mkCoerceI co fun)
1326 go (b : bs) (App fun arg) co
1327 | Just co' <- ok_arg b arg co
1330 go _ _ _ = Nothing -- Failure!
1333 -- Note [Eta reduction conditions]
1334 ok_fun (App fun (Type ty))
1335 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1338 = not (fun_id `elem` bndrs)
1339 && (ok_fun_id fun_id || all ok_lam bndrs)
1343 ok_fun_id fun = fun_arity fun >= incoming_arity
1346 fun_arity fun -- See Note [Arity care]
1347 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1348 | otherwise = idArity fun
1351 ok_lam v = isTyCoVar v || isDictId v
1354 ok_arg :: Var -- Of type bndr_t
1355 -> CoreExpr -- Of type arg_t
1356 -> CoercionI -- Of kind (t1~t2)
1357 -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1358 -- (and similarly for tyvars, coercion args)
1359 -- See Note [Eta reduction with casted arguments]
1360 ok_arg bndr (Type ty) co
1361 | Just tv <- getTyVar_maybe ty
1362 , bndr == tv = Just (mkForAllTyCoI tv co)
1363 ok_arg bndr (Var v) co
1364 | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co)
1365 ok_arg bndr (Cast (Var v) co_arg) co
1366 | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co)
1367 -- The simplifier combines multiple casts into one,
1368 -- so we can have a simple-minded pattern match here
1369 ok_arg _ _ _ = Nothing
1373 %************************************************************************
1375 \subsection{Determining non-updatable right-hand-sides}
1377 %************************************************************************
1379 Top-level constructor applications can usually be allocated
1380 statically, but they can't if the constructor, or any of the
1381 arguments, come from another DLL (because we can't refer to static
1382 labels in other DLLs).
1384 If this happens we simply make the RHS into an updatable thunk,
1385 and 'execute' it rather than allocating it statically.
1388 -- | This function is called only on *top-level* right-hand sides.
1389 -- Returns @True@ if the RHS can be allocated statically in the output,
1390 -- with no thunks involved at all.
1391 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1392 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1393 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1394 -- update flag on it and (iii) in DsExpr to decide how to expand
1397 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1398 -- (a) a value lambda
1399 -- (b) a saturated constructor application with static args
1401 -- BUT watch out for
1402 -- (i) Any cross-DLL references kill static-ness completely
1403 -- because they must be 'executed' not statically allocated
1404 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1405 -- this is not necessary)
1407 -- (ii) We treat partial applications as redexes, because in fact we
1408 -- make a thunk for them that runs and builds a PAP
1409 -- at run-time. The only appliations that are treated as
1410 -- static are *saturated* applications of constructors.
1412 -- We used to try to be clever with nested structures like this:
1413 -- ys = (:) w ((:) w [])
1414 -- on the grounds that CorePrep will flatten ANF-ise it later.
1415 -- But supporting this special case made the function much more
1416 -- complicated, because the special case only applies if there are no
1417 -- enclosing type lambdas:
1418 -- ys = /\ a -> Foo (Baz ([] a))
1419 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1421 -- But in fact, even without -O, nested structures at top level are
1422 -- flattened by the simplifier, so we don't need to be super-clever here.
1426 -- f = \x::Int. x+7 TRUE
1427 -- p = (True,False) TRUE
1429 -- d = (fst p, False) FALSE because there's a redex inside
1430 -- (this particular one doesn't happen but...)
1432 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1433 -- n = /\a. Nil a TRUE
1435 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1438 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1439 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1441 -- b) (C x xs), where C is a contructor is updatable if the application is
1444 -- c) don't look through unfolding of f in (f x).
1446 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1448 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1451 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1452 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1453 is_static in_arg (Cast e _) = is_static in_arg e
1455 is_static _ (Lit lit)
1457 MachLabel _ _ _ -> False
1459 -- A MachLabel (foreign import "&foo") in an argument
1460 -- prevents a constructor application from being static. The
1461 -- reason is that it might give rise to unresolvable symbols
1462 -- in the object file: under Linux, references to "weak"
1463 -- symbols from the data segment give rise to "unresolvable
1464 -- relocation" errors at link time This might be due to a bug
1465 -- in the linker, but we'll work around it here anyway.
1468 is_static in_arg other_expr = go other_expr 0
1470 go (Var f) n_val_args
1471 #if mingw32_TARGET_OS
1472 | not (_is_dynamic_name (idName f))
1474 = saturated_data_con f n_val_args
1475 || (in_arg && n_val_args == 0)
1476 -- A naked un-applied variable is *not* deemed a static RHS
1478 -- Reason: better to update so that the indirection gets shorted
1479 -- out, and the true value will be seen
1480 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1481 -- are always updatable. If you do so, make sure that non-updatable
1482 -- ones have enough space for their static link field!
1484 go (App f a) n_val_args
1485 | isTypeArg a = go f n_val_args
1486 | not in_arg && is_static True a = go f (n_val_args + 1)
1487 -- The (not in_arg) checks that we aren't in a constructor argument;
1488 -- if we are, we don't allow (value) applications of any sort
1490 -- NB. In case you wonder, args are sometimes not atomic. eg.
1491 -- x = D# (1.0## /## 2.0##)
1492 -- can't float because /## can fail.
1494 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1495 go (Cast e _) n_val_args = go e n_val_args
1498 saturated_data_con f n_val_args
1499 = case isDataConWorkId_maybe f of
1500 Just dc -> n_val_args == dataConRepArity dc