2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Commonly useful utilites for manipulating the Core language
18 -- * Constructing expressions
19 mkSCC, mkCoerce, mkCoerceI,
20 bindNonRec, needsCaseBinding,
21 mkAltExpr, mkPiType, mkPiTypes,
23 -- * Taking expressions apart
24 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
26 -- * Properties of expressions
27 exprType, coreAltType, coreAltsType,
28 exprIsDupable, exprIsTrivial, exprIsCheap, exprIsExpandable,
29 exprIsHNF, exprOkForSpeculation, exprIsBig, exprIsConLike,
30 rhsIsStatic, isCheapApp, isExpandableApp,
32 -- * Expression and bindings size
33 coreBindsSize, exprSize,
39 cheapEqExpr, eqExpr, eqExprX,
44 -- * Manipulating data constructors and types
45 applyTypeToArgs, applyTypeToArg,
46 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
49 #include "HsVersions.h"
66 import TcType ( isPredTy )
74 import PrelNames( absentErrorIdKey )
83 %************************************************************************
85 \subsection{Find the type of a Core atom/expression}
87 %************************************************************************
90 exprType :: CoreExpr -> Type
91 -- ^ Recover the type of a well-typed Core expression. Fails when
92 -- applied to the actual 'CoreSyn.Type' expression as it cannot
93 -- really be said to have a type
94 exprType (Var var) = idType var
95 exprType (Lit lit) = literalType lit
96 exprType (Let _ body) = exprType body
97 exprType (Case _ _ ty _) = ty
98 exprType (Cast _ co) = snd (coercionKind co)
99 exprType (Note _ e) = exprType e
100 exprType (Lam binder expr) = mkPiType binder (exprType expr)
102 = case collectArgs e of
103 (fun, args) -> applyTypeToArgs e (exprType fun) args
105 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
107 coreAltType :: CoreAlt -> Type
108 -- ^ Returns the type of the alternatives right hand side
109 coreAltType (_,bs,rhs)
110 | any bad_binder bs = expandTypeSynonyms ty
111 | otherwise = ty -- Note [Existential variables and silly type synonyms]
114 free_tvs = tyVarsOfType ty
115 bad_binder b = isTyCoVar b && b `elemVarSet` free_tvs
117 coreAltsType :: [CoreAlt] -> Type
118 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
119 coreAltsType (alt:_) = coreAltType alt
120 coreAltsType [] = panic "corAltsType"
123 Note [Existential variables and silly type synonyms]
124 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
126 data T = forall a. T (Funny a)
131 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
132 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
133 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
136 Various possibilities suggest themselves:
138 - Ignore the problem, and make Lint not complain about such variables
140 - Expand all type synonyms (or at least all those that discard arguments)
141 This is tricky, because at least for top-level things we want to
142 retain the type the user originally specified.
144 - Expand synonyms on the fly, when the problem arises. That is what
145 we are doing here. It's not too expensive, I think.
148 mkPiType :: EvVar -> Type -> Type
149 -- ^ Makes a @(->)@ type or a forall type, depending
150 -- on whether it is given a type variable or a term variable.
151 mkPiTypes :: [EvVar] -> Type -> Type
152 -- ^ 'mkPiType' for multiple type or value arguments
155 | isId v = mkFunTy (idType v) ty
156 | otherwise = mkForAllTy v ty
158 mkPiTypes vs ty = foldr mkPiType ty vs
162 applyTypeToArg :: Type -> CoreExpr -> Type
163 -- ^ Determines the type resulting from applying an expression to a function with the given type
164 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
165 applyTypeToArg fun_ty _ = funResultTy fun_ty
167 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
168 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
169 -- The first argument is just for debugging, and gives some context
170 applyTypeToArgs _ op_ty [] = op_ty
172 applyTypeToArgs e op_ty (Type ty : args)
173 = -- Accumulate type arguments so we can instantiate all at once
176 go rev_tys (Type ty : args) = go (ty:rev_tys) args
177 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
179 op_ty' = applyTysD msg op_ty (reverse rev_tys)
180 msg = ptext (sLit "applyTypeToArgs") <+>
183 applyTypeToArgs e op_ty (_ : args)
184 = case (splitFunTy_maybe op_ty) of
185 Just (_, res_ty) -> applyTypeToArgs e res_ty args
186 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
188 panic_msg :: CoreExpr -> Type -> SDoc
189 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
192 %************************************************************************
194 \subsection{Attaching notes}
196 %************************************************************************
199 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
200 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
201 mkCoerceI (IdCo _) e = e
202 mkCoerceI (ACo co) e = mkCoerce co e
204 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
205 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
206 mkCoerce co (Cast expr co2)
207 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
208 (_from_ty2, to_ty2) = coercionKind co2} in
209 from_ty `coreEqType` to_ty2 )
210 mkCoerce (mkTransCoercion co2 co) expr
213 = let (from_ty, _to_ty) = coercionKind co in
214 -- if to_ty `coreEqType` from_ty
217 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
222 -- | Wraps the given expression in the cost centre unless
223 -- in a way that maximises their utility to the user
224 mkSCC :: CostCentre -> Expr b -> Expr b
225 -- Note: Nested SCC's *are* preserved for the benefit of
226 -- cost centre stack profiling
227 mkSCC _ (Lit lit) = Lit lit
228 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
229 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
230 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
231 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
232 mkSCC cc expr = Note (SCC cc) expr
236 %************************************************************************
238 \subsection{Other expression construction}
240 %************************************************************************
243 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
244 -- ^ @bindNonRec x r b@ produces either:
250 -- > case r of x { _DEFAULT_ -> b }
252 -- depending on whether we have to use a @case@ or @let@
253 -- binding for the expression (see 'needsCaseBinding').
254 -- It's used by the desugarer to avoid building bindings
255 -- that give Core Lint a heart attack, although actually
256 -- the simplifier deals with them perfectly well. See
257 -- also 'MkCore.mkCoreLet'
258 bindNonRec bndr rhs body
259 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
260 | otherwise = Let (NonRec bndr rhs) body
262 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
263 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
264 needsCaseBinding :: Type -> CoreExpr -> Bool
265 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
266 -- Make a case expression instead of a let
267 -- These can arise either from the desugarer,
268 -- or from beta reductions: (\x.e) (x +# y)
272 mkAltExpr :: AltCon -- ^ Case alternative constructor
273 -> [CoreBndr] -- ^ Things bound by the pattern match
274 -> [Type] -- ^ The type arguments to the case alternative
276 -- ^ This guy constructs the value that the scrutinee must have
277 -- given that you are in one particular branch of a case
278 mkAltExpr (DataAlt con) args inst_tys
279 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
280 mkAltExpr (LitAlt lit) [] []
282 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
283 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
287 %************************************************************************
289 \subsection{Taking expressions apart}
291 %************************************************************************
293 The default alternative must be first, if it exists at all.
294 This makes it easy to find, though it makes matching marginally harder.
297 -- | Extract the default case alternative
298 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
299 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
300 findDefault alts = (alts, Nothing)
302 isDefaultAlt :: CoreAlt -> Bool
303 isDefaultAlt (DEFAULT, _, _) = True
304 isDefaultAlt _ = False
307 -- | Find the case alternative corresponding to a particular
308 -- constructor: panics if no such constructor exists
309 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
310 -- A "Nothing" result *is* legitmiate
311 -- See Note [Unreachable code]
314 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
318 go (alt@(con1,_,_) : alts) deflt
319 = case con `cmpAltCon` con1 of
320 LT -> deflt -- Missed it already; the alts are in increasing order
322 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
324 ---------------------------------
325 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
326 -- ^ Merge alternatives preserving order; alternatives in
327 -- the first argument shadow ones in the second
328 mergeAlts [] as2 = as2
329 mergeAlts as1 [] = as1
330 mergeAlts (a1:as1) (a2:as2)
331 = case a1 `cmpAlt` a2 of
332 LT -> a1 : mergeAlts as1 (a2:as2)
333 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
334 GT -> a2 : mergeAlts (a1:as1) as2
337 ---------------------------------
338 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
341 -- > case (C a b x y) of
344 -- We want to drop the leading type argument of the scrutinee
345 -- leaving the arguments to match agains the pattern
347 trimConArgs DEFAULT args = ASSERT( null args ) []
348 trimConArgs (LitAlt _) args = ASSERT( null args ) []
349 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
352 Note [Unreachable code]
353 ~~~~~~~~~~~~~~~~~~~~~~~
354 It is possible (although unusual) for GHC to find a case expression
355 that cannot match. For example:
357 data Col = Red | Green | Blue
361 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
363 Suppose that for some silly reason, x isn't substituted in the case
364 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
365 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
369 lvl = case x of { Green -> e1; Blue -> e2 })
374 Now if x gets inlined, we won't be able to find a matching alternative
375 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
376 we generate (error "Inaccessible alternative").
378 Similar things can happen (augmented by GADTs) when the Simplifier
379 filters down the matching alternatives in Simplify.rebuildCase.
382 %************************************************************************
386 %************************************************************************
390 @exprIsTrivial@ is true of expressions we are unconditionally happy to
391 duplicate; simple variables and constants, and type
392 applications. Note that primop Ids aren't considered
395 Note [Variable are trivial]
396 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
397 There used to be a gruesome test for (hasNoBinding v) in the
399 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
400 The idea here is that a constructor worker, like \$wJust, is
401 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
402 So it should be treated like a lambda. Ditto unsaturated primops.
403 But now constructor workers are not "have-no-binding" Ids. And
404 completely un-applied primops and foreign-call Ids are sufficiently
405 rare that I plan to allow them to be duplicated and put up with
408 Note [SCCs are trivial]
409 ~~~~~~~~~~~~~~~~~~~~~~~
410 We used not to treat (_scc_ "foo" x) as trivial, because it really
411 generates code, (and a heap object when it's a function arg) to
412 capture the cost centre. However, the profiling system discounts the
413 allocation costs for such "boxing thunks" whereas the extra costs of
414 *not* inlining otherwise-trivial bindings can be high, and are hard to
418 exprIsTrivial :: CoreExpr -> Bool
419 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
420 exprIsTrivial (Type _) = True
421 exprIsTrivial (Lit lit) = litIsTrivial lit
422 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
423 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
424 exprIsTrivial (Cast e _) = exprIsTrivial e
425 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
426 exprIsTrivial _ = False
430 %************************************************************************
434 %************************************************************************
438 @exprIsDupable@ is true of expressions that can be duplicated at a modest
439 cost in code size. This will only happen in different case
440 branches, so there's no issue about duplicating work.
442 That is, exprIsDupable returns True of (f x) even if
443 f is very very expensive to call.
445 Its only purpose is to avoid fruitless let-binding
446 and then inlining of case join points
450 exprIsDupable :: CoreExpr -> Bool
451 exprIsDupable (Type _) = True
452 exprIsDupable (Var _) = True
453 exprIsDupable (Lit lit) = litIsDupable lit
454 exprIsDupable (Note _ e) = exprIsDupable e
455 exprIsDupable (Cast e _) = exprIsDupable e
460 go (App f a) n_args = n_args < dupAppSize
466 dupAppSize = 4 -- Size of application we are prepared to duplicate
469 %************************************************************************
471 exprIsCheap, exprIsExpandable
473 %************************************************************************
475 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
476 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
477 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
478 it is obviously in weak head normal form, or is cheap to get to WHNF.
479 [Note that that's not the same as exprIsDupable; an expression might be
480 big, and hence not dupable, but still cheap.]
482 By ``cheap'' we mean a computation we're willing to:
483 push inside a lambda, or
484 inline at more than one place
485 That might mean it gets evaluated more than once, instead of being
486 shared. The main examples of things which aren't WHNF but are
491 (where e, and all the ei are cheap)
494 (where e and b are cheap)
497 (where op is a cheap primitive operator)
500 (because we are happy to substitute it inside a lambda)
502 Notice that a variable is considered 'cheap': we can push it inside a lambda,
503 because sharing will make sure it is only evaluated once.
505 Note [exprIsCheap and exprIsHNF]
506 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
507 Note that exprIsHNF does not imply exprIsCheap. Eg
508 let x = fac 20 in Just x
509 This responds True to exprIsHNF (you can discard a seq), but
510 False to exprIsCheap.
513 exprIsCheap :: CoreExpr -> Bool
514 exprIsCheap = exprIsCheap' isCheapApp
516 exprIsExpandable :: CoreExpr -> Bool
517 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
520 exprIsCheap' :: (Id -> Int -> Bool) -> CoreExpr -> Bool
521 exprIsCheap' _ (Lit _) = True
522 exprIsCheap' _ (Type _) = True
523 exprIsCheap' _ (Var _) = True
524 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
525 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
526 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
527 || exprIsCheap' good_app e
529 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
530 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
531 -- Experimentally, treat (case x of ...) as cheap
532 -- (and case __coerce x etc.)
533 -- This improves arities of overloaded functions where
534 -- there is only dictionary selection (no construction) involved
536 exprIsCheap' good_app (Let (NonRec x _) e)
537 | isUnLiftedType (idType x) = exprIsCheap' good_app e
539 -- Strict lets always have cheap right hand sides,
540 -- and do no allocation, so just look at the body
541 -- Non-strict lets do allocation so we don't treat them as cheap
544 exprIsCheap' good_app other_expr -- Applications and variables
547 -- Accumulate value arguments, then decide
548 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
549 | otherwise = go f val_args
551 go (Var _) [] = True -- Just a type application of a variable
552 -- (f t1 t2 t3) counts as WHNF
554 = case idDetails f of
555 RecSelId {} -> go_sel args
556 ClassOpId {} -> go_sel args
557 PrimOpId op -> go_primop op args
558 _ | good_app f (length args) -> go_pap args
559 | isBottomingId f -> True
561 -- Application of a function which
562 -- always gives bottom; we treat this as cheap
563 -- because it certainly doesn't need to be shared!
568 go_pap args = all exprIsTrivial args
569 -- For constructor applications and primops, check that all
570 -- the args are trivial. We don't want to treat as cheap, say,
572 -- We'll put up with one constructor application, but not dozens
575 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
576 -- In principle we should worry about primops
577 -- that return a type variable, since the result
578 -- might be applied to something, but I'm not going
579 -- to bother to check the number of args
582 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
583 go_sel _ = False -- look cheap, so we will substitute it inside a
584 -- lambda. Particularly for dictionary field selection.
585 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
586 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
588 isCheapApp :: Id -> Int -> Bool
589 isCheapApp fn n_val_args
591 || n_val_args < idArity fn
593 isExpandableApp :: Id -> Int -> Bool
594 isExpandableApp fn n_val_args
596 || n_val_args < idArity fn
597 || go n_val_args (idType fn)
599 -- See if all the arguments are PredTys (implicit params or classes)
600 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
603 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
604 | Just (arg, ty) <- splitFunTy_maybe ty
605 , isPredTy arg = go (n_val_args-1) ty
609 Note [Expandable overloadings]
610 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
611 Suppose the user wrote this
612 {-# RULE forall x. foo (negate x) = h x #-}
613 f x = ....(foo (negate x))....
614 He'd expect the rule to fire. But since negate is overloaded, we might
616 f = \d -> let n = negate d in \x -> ...foo (n x)...
617 So we treat the application of a function (negate in this case) to a
618 *dictionary* as expandable. In effect, every function is CONLIKE when
619 it's applied only to dictionaries.
622 %************************************************************************
626 %************************************************************************
629 -- | 'exprOkForSpeculation' returns True of an expression that is:
631 -- * Safe to evaluate even if normal order eval might not
632 -- evaluate the expression at all, or
634 -- * Safe /not/ to evaluate even if normal order would do so
636 -- Precisely, it returns @True@ iff:
638 -- * The expression guarantees to terminate,
640 -- * without raising an exception,
641 -- * without causing a side effect (e.g. writing a mutable variable)
643 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
644 -- As an example of the considerations in this test, consider:
646 -- > let x = case y# +# 1# of { r# -> I# r# }
649 -- being translated to:
651 -- > case y# +# 1# of { r# ->
656 -- We can only do this if the @y + 1@ is ok for speculation: it has no
657 -- side effects, and can't diverge or raise an exception.
658 exprOkForSpeculation :: CoreExpr -> Bool
659 exprOkForSpeculation (Lit _) = True
660 exprOkForSpeculation (Type _) = True
661 -- Tick boxes are *not* suitable for speculation
662 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
663 && not (isTickBoxOp v)
664 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
665 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
667 exprOkForSpeculation (Case e _ _ alts)
668 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
669 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
671 exprOkForSpeculation other_expr
672 = case collectArgs other_expr of
673 (Var f, args) | f `hasKey` absentErrorIdKey -- Note [Absent error Id]
674 -> all exprOkForSpeculation args -- in WwLib
676 -> spec_ok (idDetails f) args
680 spec_ok (DataConWorkId _) _
681 = True -- The strictness of the constructor has already
682 -- been expressed by its "wrapper", so we don't need
683 -- to take the arguments into account
685 spec_ok (PrimOpId op) args
686 | isDivOp op, -- Special case for dividing operations that fail
687 [arg1, Lit lit] <- args -- only if the divisor is zero
688 = not (isZeroLit lit) && exprOkForSpeculation arg1
689 -- Often there is a literal divisor, and this
690 -- can get rid of a thunk in an inner looop
693 = primOpOkForSpeculation op &&
694 all exprOkForSpeculation args
695 -- A bit conservative: we don't really need
696 -- to care about lazy arguments, but this is easy
698 spec_ok (DFunId new_type) _ = not new_type
699 -- DFuns terminate, unless the dict is implemented with a newtype
700 -- in which case they may not
704 -- | True of dyadic operators that can fail only if the second arg is zero!
705 isDivOp :: PrimOp -> Bool
706 -- This function probably belongs in PrimOp, or even in
707 -- an automagically generated file.. but it's such a
708 -- special case I thought I'd leave it here for now.
709 isDivOp IntQuotOp = True
710 isDivOp IntRemOp = True
711 isDivOp WordQuotOp = True
712 isDivOp WordRemOp = True
713 isDivOp FloatDivOp = True
714 isDivOp DoubleDivOp = True
718 Note [exprOkForSpeculation: case expressions]
719 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
721 It's always sound for exprOkForSpeculation to return False, and we
722 don't want it to take too long, so it bales out on complicated-looking
723 terms. Notably lets, which can be stacked very deeply; and in any
724 case the argument of exprOkForSpeculation is usually in a strict context,
725 so any lets will have been floated away.
727 However, we keep going on case-expressions. An example like this one
728 showed up in DPH code:
731 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
733 If exprOkForSpeculation doesn't look through case expressions, you get this:
735 \ (ww :: GHC.Prim.Int#) ->
737 __DEFAULT -> case (case <# ds 5 of _ {
738 GHC.Bool.False -> lvl1;
739 GHC.Bool.True -> lvl})
741 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
745 The inner case is redundant, and should be nuked.
748 %************************************************************************
750 exprIsHNF, exprIsConLike
752 %************************************************************************
755 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
757 -- | exprIsHNF returns true for expressions that are certainly /already/
758 -- evaluated to /head/ normal form. This is used to decide whether it's ok
761 -- > case x of _ -> e
767 -- and to decide whether it's safe to discard a 'seq'.
769 -- So, it does /not/ treat variables as evaluated, unless they say they are.
770 -- However, it /does/ treat partial applications and constructor applications
771 -- as values, even if their arguments are non-trivial, provided the argument
772 -- type is lifted. For example, both of these are values:
774 -- > (:) (f x) (map f xs)
775 -- > map (...redex...)
777 -- because 'seq' on such things completes immediately.
779 -- For unlifted argument types, we have to be careful:
783 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
784 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
785 -- unboxed type must be ok-for-speculation (or trivial).
786 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
787 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
791 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
792 -- data constructors. Conlike arguments are considered interesting by the
794 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
795 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
797 -- | Returns true for values or value-like expressions. These are lambdas,
798 -- constructors / CONLIKE functions (as determined by the function argument)
801 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
802 exprIsHNFlike is_con is_con_unf = is_hnf_like
804 is_hnf_like (Var v) -- NB: There are no value args at this point
805 = is_con v -- Catches nullary constructors,
806 -- so that [] and () are values, for example
807 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
808 || is_con_unf (idUnfolding v)
809 -- Check the thing's unfolding; it might be bound to a value
810 -- We don't look through loop breakers here, which is a bit conservative
811 -- but otherwise I worry that if an Id's unfolding is just itself,
812 -- we could get an infinite loop
814 is_hnf_like (Lit _) = True
815 is_hnf_like (Type _) = True -- Types are honorary Values;
816 -- we don't mind copying them
817 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
818 is_hnf_like (Note _ e) = is_hnf_like e
819 is_hnf_like (Cast e _) = is_hnf_like e
820 is_hnf_like (App e (Type _)) = is_hnf_like e
821 is_hnf_like (App e a) = app_is_value e [a]
822 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
823 is_hnf_like _ = False
825 -- There is at least one value argument
826 app_is_value :: CoreExpr -> [CoreArg] -> Bool
827 app_is_value (Var fun) args
828 = idArity fun > valArgCount args -- Under-applied function
829 || is_con fun -- or constructor-like
830 app_is_value (Note _ f) as = app_is_value f as
831 app_is_value (Cast f _) as = app_is_value f as
832 app_is_value (App f a) as = app_is_value f (a:as)
833 app_is_value _ _ = False
837 %************************************************************************
839 Instantiating data constructors
841 %************************************************************************
843 These InstPat functions go here to avoid circularity between DataCon and Id
846 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
847 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
849 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
850 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
851 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
853 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
854 -- Remember to include the existential dictionaries
856 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
857 -> [FastString] -- A long enough list of FSs to use for names
858 -> [Unique] -- An equally long list of uniques, at least one for each binder
860 -> [Type] -- Types to instantiate the universally quantified tyvars
861 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
862 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
863 -- (ex_tvs, co_tvs, arg_ids),
865 -- ex_tvs are intended to be used as binders for existential type args
867 -- co_tvs are intended to be used as binders for coercion args and the kinds
868 -- of these vars have been instantiated by the inst_tys and the ex_tys
869 -- The co_tvs include both GADT equalities (dcEqSpec) and
870 -- programmer-specified equalities (dcEqTheta)
872 -- arg_ids are indended to be used as binders for value arguments,
873 -- and their types have been instantiated with inst_tys and ex_tys
874 -- The arg_ids include both dicts (dcDictTheta) and
875 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
878 -- The following constructor T1
881 -- T1 :: forall b. Int -> b -> T(a,b)
884 -- has representation type
885 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
888 -- dataConInstPat fss us T1 (a1',b') will return
890 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
892 -- where the double-primed variables are created with the FastStrings and
893 -- Uniques given as fss and us
894 dataConInstPat arg_fun fss uniqs con inst_tys
895 = (ex_bndrs, co_bndrs, arg_ids)
897 univ_tvs = dataConUnivTyVars con
898 ex_tvs = dataConExTyVars con
899 arg_tys = arg_fun con
900 eq_spec = dataConEqSpec con
901 eq_theta = dataConEqTheta con
902 eq_preds = eqSpecPreds eq_spec ++ eq_theta
905 n_co = length eq_preds
907 -- split the Uniques and FastStrings
908 (ex_uniqs, uniqs') = splitAt n_ex uniqs
909 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
911 (ex_fss, fss') = splitAt n_ex fss
912 (co_fss, id_fss) = splitAt n_co fss'
914 -- Make existential type variables
915 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
916 mk_ex_var uniq fs var = mkTyVar new_name kind
918 new_name = mkSysTvName uniq fs
921 -- Make the instantiating substitution
922 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
924 -- Make new coercion vars, instantiating kind
925 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
926 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
928 new_name = mkSysTvName uniq fs
929 co_kind = substTy subst (mkPredTy eq_pred)
931 -- make value vars, instantiating types
932 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
933 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
937 %************************************************************************
941 %************************************************************************
944 -- | A cheap equality test which bales out fast!
945 -- If it returns @True@ the arguments are definitely equal,
946 -- otherwise, they may or may not be equal.
948 -- See also 'exprIsBig'
949 cheapEqExpr :: Expr b -> Expr b -> Bool
951 cheapEqExpr (Var v1) (Var v2) = v1==v2
952 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
953 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
955 cheapEqExpr (App f1 a1) (App f2 a2)
956 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
958 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
959 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
961 cheapEqExpr _ _ = False
965 exprIsBig :: Expr b -> Bool
966 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
967 exprIsBig (Lit _) = False
968 exprIsBig (Var _) = False
969 exprIsBig (Type _) = False
970 exprIsBig (Lam _ e) = exprIsBig e
971 exprIsBig (App f a) = exprIsBig f || exprIsBig a
972 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
977 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
978 -- Compares for equality, modulo alpha
979 eqExpr in_scope e1 e2
980 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
982 id_unf _ = noUnfolding -- Don't expand
986 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
987 -- ^ Compares expressions for equality, modulo alpha.
988 -- Does /not/ look through newtypes or predicate types
989 -- Used in rule matching, and also CSE
991 eqExprX id_unfolding_fun env e1 e2
994 go env (Var v1) (Var v2)
995 | rnOccL env v1 == rnOccR env v2
998 -- The next two rules expand non-local variables
999 -- C.f. Note [Expanding variables] in Rules.lhs
1000 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1002 | not (locallyBoundL env v1)
1003 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1004 = go (nukeRnEnvL env) e1' e2
1007 | not (locallyBoundR env v2)
1008 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1009 = go (nukeRnEnvR env) e1 e2'
1011 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1012 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1013 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1014 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1015 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1017 go env (Lam b1 e1) (Lam b2 e2)
1018 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1019 && go (rnBndr2 env b1 b2) e1 e2
1021 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1022 = go env r1 r2 -- No need to check binder types, since RHSs match
1023 && go (rnBndr2 env v1 v2) e1 e2
1025 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1026 = all2 (go env') rs1 rs2 && go env' e1 e2
1028 (bs1,rs1) = unzip ps1
1029 (bs2,rs2) = unzip ps2
1030 env' = rnBndrs2 env bs1 bs2
1032 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1034 && tcEqTypeX env (idType b1) (idType b2)
1035 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1040 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1041 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1044 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1045 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1052 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1053 locallyBoundL rn_env v = inRnEnvL rn_env v
1054 locallyBoundR rn_env v = inRnEnvR rn_env v
1058 %************************************************************************
1060 \subsection{The size of an expression}
1062 %************************************************************************
1065 coreBindsSize :: [CoreBind] -> Int
1066 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1068 exprSize :: CoreExpr -> Int
1069 -- ^ A measure of the size of the expressions, strictly greater than 0
1070 -- It also forces the expression pretty drastically as a side effect
1071 exprSize (Var v) = v `seq` 1
1072 exprSize (Lit lit) = lit `seq` 1
1073 exprSize (App f a) = exprSize f + exprSize a
1074 exprSize (Lam b e) = varSize b + exprSize e
1075 exprSize (Let b e) = bindSize b + exprSize e
1076 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1077 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1078 exprSize (Note n e) = noteSize n + exprSize e
1079 exprSize (Type t) = seqType t `seq` 1
1081 noteSize :: Note -> Int
1082 noteSize (SCC cc) = cc `seq` 1
1083 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1085 varSize :: Var -> Int
1086 varSize b | isTyCoVar b = 1
1087 | otherwise = seqType (idType b) `seq`
1088 megaSeqIdInfo (idInfo b) `seq`
1091 varsSize :: [Var] -> Int
1092 varsSize = sum . map varSize
1094 bindSize :: CoreBind -> Int
1095 bindSize (NonRec b e) = varSize b + exprSize e
1096 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1098 pairSize :: (Var, CoreExpr) -> Int
1099 pairSize (b,e) = varSize b + exprSize e
1101 altSize :: CoreAlt -> Int
1102 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1106 %************************************************************************
1108 \subsection{Hashing}
1110 %************************************************************************
1113 hashExpr :: CoreExpr -> Int
1114 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1115 -- Two expressions that hash to the different Ints are definitely unequal.
1117 -- The emphasis is on a crude, fast hash, rather than on high precision.
1119 -- But unequal here means \"not identical\"; two alpha-equivalent
1120 -- expressions may hash to the different Ints.
1122 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1123 -- (at least if we want the above invariant to be true).
1125 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1126 -- UniqFM doesn't like negative Ints
1128 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1130 hash_expr :: HashEnv -> CoreExpr -> Word32
1131 -- Word32, because we're expecting overflows here, and overflowing
1132 -- signed types just isn't cool. In C it's even undefined.
1133 hash_expr env (Note _ e) = hash_expr env e
1134 hash_expr env (Cast e _) = hash_expr env e
1135 hash_expr env (Var v) = hashVar env v
1136 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1137 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1138 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1139 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1140 hash_expr env (Case e _ _ _) = hash_expr env e
1141 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1142 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1143 -- Shouldn't happen. Better to use WARN than trace, because trace
1144 -- prevents the CPR optimisation kicking in for hash_expr.
1146 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1147 fast_hash_expr env (Var v) = hashVar env v
1148 fast_hash_expr env (Type t) = fast_hash_type env t
1149 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1150 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1151 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1152 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1153 fast_hash_expr _ _ = 1
1155 fast_hash_type :: HashEnv -> Type -> Word32
1156 fast_hash_type env ty
1157 | Just tv <- getTyVar_maybe ty = hashVar env tv
1158 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1159 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1162 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1163 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1165 hashVar :: HashEnv -> Var -> Word32
1167 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1171 %************************************************************************
1175 %************************************************************************
1177 Note [Eta reduction conditions]
1178 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1179 We try for eta reduction here, but *only* if we get all the way to an
1180 trivial expression. We don't want to remove extra lambdas unless we
1181 are going to avoid allocating this thing altogether.
1183 There are some particularly delicate points here:
1185 * Eta reduction is not valid in general:
1187 This matters, partly for old-fashioned correctness reasons but,
1188 worse, getting it wrong can yield a seg fault. Consider
1190 h y = case (case y of { True -> f `seq` True; False -> False }) of
1191 True -> ...; False -> ...
1193 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1194 says f=bottom, and replaces the (f `seq` True) with just
1195 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1196 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1197 the definition again, so that it does not termninate after all.
1198 Result: seg-fault because the boolean case actually gets a function value.
1201 So it's important to to the right thing.
1203 * Note [Arity care]: we need to be careful if we just look at f's
1204 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1205 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1206 arity when checking that 'f' is a value. Otherwise we will
1211 Which might change a terminiating program (think (f `seq` e)) to a
1212 non-terminating one. So we check for being a loop breaker first.
1214 However for GlobalIds we can look at the arity; and for primops we
1215 must, since they have no unfolding.
1217 * Regardless of whether 'f' is a value, we always want to
1218 reduce (/\a -> f a) to f
1219 This came up in a RULE: foldr (build (/\a -> g a))
1220 did not match foldr (build (/\b -> ...something complex...))
1221 The type checker can insert these eta-expanded versions,
1222 with both type and dictionary lambdas; hence the slightly
1225 * Never *reduce* arity. For example
1227 Then if h has arity 1 we don't want to eta-reduce because then
1228 f's arity would decrease, and that is bad
1230 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1233 Note [Eta reduction with casted arguments]
1234 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1236 (\(x:t3). f (x |> g)) :: t3 -> t2
1240 This should be eta-reduced to
1244 So we need to accumulate a coercion, pushing it inward (past
1245 variable arguments only) thus:
1246 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1247 f (x:t) |> co --> (f |> (t -> co)) x
1248 f @ a |> co --> (f |> (forall a.co)) @ a
1249 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1250 These are the equations for ok_arg.
1252 It's true that we could also hope to eta reduce these:
1255 But the simplifier pushes those casts outwards, so we don't
1256 need to address that here.
1259 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1260 tryEtaReduce bndrs body
1261 = go (reverse bndrs) body (IdCo (exprType body))
1263 incoming_arity = count isId bndrs
1265 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1266 -> CoreExpr -- Of type tr
1267 -> CoercionI -- Of type tr ~ ts
1268 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1269 -- See Note [Eta reduction with casted arguments]
1270 -- for why we have an accumulating coercion
1272 | ok_fun fun = Just (mkCoerceI co fun)
1274 go (b : bs) (App fun arg) co
1275 | Just co' <- ok_arg b arg co
1278 go _ _ _ = Nothing -- Failure!
1281 -- Note [Eta reduction conditions]
1282 ok_fun (App fun (Type ty))
1283 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1286 = not (fun_id `elem` bndrs)
1287 && (ok_fun_id fun_id || all ok_lam bndrs)
1291 ok_fun_id fun = fun_arity fun >= incoming_arity
1294 fun_arity fun -- See Note [Arity care]
1295 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1296 | otherwise = idArity fun
1299 ok_lam v = isTyCoVar v || isDictId v
1302 ok_arg :: Var -- Of type bndr_t
1303 -> CoreExpr -- Of type arg_t
1304 -> CoercionI -- Of kind (t1~t2)
1305 -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1306 -- (and similarly for tyvars, coercion args)
1307 -- See Note [Eta reduction with casted arguments]
1308 ok_arg bndr (Type ty) co
1309 | Just tv <- getTyVar_maybe ty
1310 , bndr == tv = Just (mkForAllTyCoI tv co)
1311 ok_arg bndr (Var v) co
1312 | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co)
1313 ok_arg bndr (Cast (Var v) co_arg) co
1314 | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co)
1315 -- The simplifier combines multiple casts into one,
1316 -- so we can have a simple-minded pattern match here
1317 ok_arg _ _ _ = Nothing
1321 %************************************************************************
1323 \subsection{Determining non-updatable right-hand-sides}
1325 %************************************************************************
1327 Top-level constructor applications can usually be allocated
1328 statically, but they can't if the constructor, or any of the
1329 arguments, come from another DLL (because we can't refer to static
1330 labels in other DLLs).
1332 If this happens we simply make the RHS into an updatable thunk,
1333 and 'execute' it rather than allocating it statically.
1336 -- | This function is called only on *top-level* right-hand sides.
1337 -- Returns @True@ if the RHS can be allocated statically in the output,
1338 -- with no thunks involved at all.
1339 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1340 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1341 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1342 -- update flag on it and (iii) in DsExpr to decide how to expand
1345 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1346 -- (a) a value lambda
1347 -- (b) a saturated constructor application with static args
1349 -- BUT watch out for
1350 -- (i) Any cross-DLL references kill static-ness completely
1351 -- because they must be 'executed' not statically allocated
1352 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1353 -- this is not necessary)
1355 -- (ii) We treat partial applications as redexes, because in fact we
1356 -- make a thunk for them that runs and builds a PAP
1357 -- at run-time. The only appliations that are treated as
1358 -- static are *saturated* applications of constructors.
1360 -- We used to try to be clever with nested structures like this:
1361 -- ys = (:) w ((:) w [])
1362 -- on the grounds that CorePrep will flatten ANF-ise it later.
1363 -- But supporting this special case made the function much more
1364 -- complicated, because the special case only applies if there are no
1365 -- enclosing type lambdas:
1366 -- ys = /\ a -> Foo (Baz ([] a))
1367 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1369 -- But in fact, even without -O, nested structures at top level are
1370 -- flattened by the simplifier, so we don't need to be super-clever here.
1374 -- f = \x::Int. x+7 TRUE
1375 -- p = (True,False) TRUE
1377 -- d = (fst p, False) FALSE because there's a redex inside
1378 -- (this particular one doesn't happen but...)
1380 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1381 -- n = /\a. Nil a TRUE
1383 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1386 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1387 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1389 -- b) (C x xs), where C is a contructor is updatable if the application is
1392 -- c) don't look through unfolding of f in (f x).
1394 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1396 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1399 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1401 is_static _ (Note (SCC _) _) = False
1402 is_static in_arg (Note _ e) = is_static in_arg e
1403 is_static in_arg (Cast e _) = is_static in_arg e
1405 is_static _ (Lit lit)
1407 MachLabel _ _ _ -> False
1409 -- A MachLabel (foreign import "&foo") in an argument
1410 -- prevents a constructor application from being static. The
1411 -- reason is that it might give rise to unresolvable symbols
1412 -- in the object file: under Linux, references to "weak"
1413 -- symbols from the data segment give rise to "unresolvable
1414 -- relocation" errors at link time This might be due to a bug
1415 -- in the linker, but we'll work around it here anyway.
1418 is_static in_arg other_expr = go other_expr 0
1420 go (Var f) n_val_args
1421 #if mingw32_TARGET_OS
1422 | not (_is_dynamic_name (idName f))
1424 = saturated_data_con f n_val_args
1425 || (in_arg && n_val_args == 0)
1426 -- A naked un-applied variable is *not* deemed a static RHS
1428 -- Reason: better to update so that the indirection gets shorted
1429 -- out, and the true value will be seen
1430 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1431 -- are always updatable. If you do so, make sure that non-updatable
1432 -- ones have enough space for their static link field!
1434 go (App f a) n_val_args
1435 | isTypeArg a = go f n_val_args
1436 | not in_arg && is_static True a = go f (n_val_args + 1)
1437 -- The (not in_arg) checks that we aren't in a constructor argument;
1438 -- if we are, we don't allow (value) applications of any sort
1440 -- NB. In case you wonder, args are sometimes not atomic. eg.
1441 -- x = D# (1.0## /## 2.0##)
1442 -- can't float because /## can fail.
1444 go (Note (SCC _) _) _ = False
1445 go (Note _ f) n_val_args = go f n_val_args
1446 go (Cast e _) n_val_args = go e n_val_args
1450 saturated_data_con f n_val_args
1451 = case isDataConWorkId_maybe f of
1452 Just dc -> n_val_args == dataConRepArity dc