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 mkInlineMe, 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,
30 exprIsConApp_maybe, exprIsBottom,
33 -- * Expression and bindings size
34 coreBindsSize, exprSize,
42 -- * Manipulating data constructors and types
43 applyTypeToArgs, applyTypeToArg,
44 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
47 #include "HsVersions.h"
78 import GHC.Exts -- For `xori`
82 %************************************************************************
84 \subsection{Find the type of a Core atom/expression}
86 %************************************************************************
89 exprType :: CoreExpr -> Type
90 -- ^ Recover the type of a well-typed Core expression. Fails when
91 -- applied to the actual 'CoreSyn.Type' expression as it cannot
92 -- really be said to have a type
93 exprType (Var var) = idType var
94 exprType (Lit lit) = literalType lit
95 exprType (Let _ body) = exprType body
96 exprType (Case _ _ ty _) = ty
97 exprType (Cast _ co) = snd (coercionKind co)
98 exprType (Note _ e) = exprType e
99 exprType (Lam binder expr) = mkPiType binder (exprType expr)
101 = case collectArgs e of
102 (fun, args) -> applyTypeToArgs e (exprType fun) args
104 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
106 coreAltType :: CoreAlt -> Type
107 -- ^ Returns the type of the alternatives right hand side
108 coreAltType (_,_,rhs) = exprType rhs
110 coreAltsType :: [CoreAlt] -> Type
111 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
112 coreAltsType (alt:_) = coreAltType alt
113 coreAltsType [] = panic "corAltsType"
117 mkPiType :: Var -> Type -> Type
118 -- ^ Makes a @(->)@ type or a forall type, depending
119 -- on whether it is given a type variable or a term variable.
120 mkPiTypes :: [Var] -> Type -> Type
121 -- ^ 'mkPiType' for multiple type or value arguments
124 | isId v = mkFunTy (idType v) ty
125 | otherwise = mkForAllTy v ty
127 mkPiTypes vs ty = foldr mkPiType ty vs
131 applyTypeToArg :: Type -> CoreExpr -> Type
132 -- ^ Determines the type resulting from applying an expression to a function with the given type
133 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
134 applyTypeToArg fun_ty _ = funResultTy fun_ty
136 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
137 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
138 -- The first argument is just for debugging, and gives some context
139 applyTypeToArgs _ op_ty [] = op_ty
141 applyTypeToArgs e op_ty (Type ty : args)
142 = -- Accumulate type arguments so we can instantiate all at once
145 go rev_tys (Type ty : args) = go (ty:rev_tys) args
146 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
148 op_ty' = applyTysD msg op_ty (reverse rev_tys)
149 msg = ptext (sLit "applyTypeToArgs") <+>
152 applyTypeToArgs e op_ty (_ : args)
153 = case (splitFunTy_maybe op_ty) of
154 Just (_, res_ty) -> applyTypeToArgs e res_ty args
155 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
157 panic_msg :: CoreExpr -> Type -> SDoc
158 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
161 %************************************************************************
163 \subsection{Attaching notes}
165 %************************************************************************
167 mkNote removes redundant coercions, and SCCs where possible
171 mkNote :: Note -> CoreExpr -> CoreExpr
172 mkNote (SCC cc) expr = mkSCC cc expr
173 mkNote InlineMe expr = mkInlineMe expr
174 mkNote note expr = Note note expr
178 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
179 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
180 not be *applied* to anything.
182 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
185 f = inline_me (coerce t fw)
186 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
187 We want the split, so that the coerces can cancel at the call site.
189 However, we can get left with tiresome type applications. Notably, consider
190 f = /\ a -> let t = e in (t, w)
191 Then lifting the let out of the big lambda gives
193 f = /\ a -> let t = inline_me (t' a) in (t, w)
194 The inline_me is to stop the simplifier inlining t' right back
195 into t's RHS. In the next phase we'll substitute for t (since
196 its rhs is trivial) and *then* we could get rid of the inline_me.
197 But it hardly seems worth it, so I don't bother.
200 -- | Wraps the given expression in an inlining hint unless the expression
201 -- is trivial in some sense, so that doing so would usually hurt us
202 mkInlineMe :: CoreExpr -> CoreExpr
203 mkInlineMe e@(Var _) = e
204 mkInlineMe e@(Note InlineMe _) = e
205 mkInlineMe e = Note InlineMe e
209 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
210 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
212 mkCoerceI (ACo co) e = mkCoerce co e
214 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
215 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
216 mkCoerce co (Cast expr co2)
217 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
218 (_from_ty2, to_ty2) = coercionKind co2} in
219 from_ty `coreEqType` to_ty2 )
220 mkCoerce (mkTransCoercion co2 co) expr
223 = let (from_ty, _to_ty) = coercionKind co in
224 -- if to_ty `coreEqType` from_ty
227 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
232 -- | Wraps the given expression in the cost centre unless
233 -- in a way that maximises their utility to the user
234 mkSCC :: CostCentre -> Expr b -> Expr b
235 -- Note: Nested SCC's *are* preserved for the benefit of
236 -- cost centre stack profiling
237 mkSCC _ (Lit lit) = Lit lit
238 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
239 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
240 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
241 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
242 mkSCC cc expr = Note (SCC cc) expr
246 %************************************************************************
248 \subsection{Other expression construction}
250 %************************************************************************
253 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
254 -- ^ @bindNonRec x r b@ produces either:
260 -- > case r of x { _DEFAULT_ -> b }
262 -- depending on whether we have to use a @case@ or @let@
263 -- binding for the expression (see 'needsCaseBinding').
264 -- It's used by the desugarer to avoid building bindings
265 -- that give Core Lint a heart attack, although actually
266 -- the simplifier deals with them perfectly well. See
267 -- also 'MkCore.mkCoreLet'
268 bindNonRec bndr rhs body
269 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
270 | otherwise = Let (NonRec bndr rhs) body
272 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
273 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
274 needsCaseBinding :: Type -> CoreExpr -> Bool
275 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
276 -- Make a case expression instead of a let
277 -- These can arise either from the desugarer,
278 -- or from beta reductions: (\x.e) (x +# y)
282 mkAltExpr :: AltCon -- ^ Case alternative constructor
283 -> [CoreBndr] -- ^ Things bound by the pattern match
284 -> [Type] -- ^ The type arguments to the case alternative
286 -- ^ This guy constructs the value that the scrutinee must have
287 -- given that you are in one particular branch of a case
288 mkAltExpr (DataAlt con) args inst_tys
289 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
290 mkAltExpr (LitAlt lit) [] []
292 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
293 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
297 %************************************************************************
299 \subsection{Taking expressions apart}
301 %************************************************************************
303 The default alternative must be first, if it exists at all.
304 This makes it easy to find, though it makes matching marginally harder.
307 -- | Extract the default case alternative
308 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
309 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
310 findDefault alts = (alts, Nothing)
312 isDefaultAlt :: CoreAlt -> Bool
313 isDefaultAlt (DEFAULT, _, _) = True
314 isDefaultAlt _ = False
317 -- | Find the case alternative corresponding to a particular
318 -- constructor: panics if no such constructor exists
319 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
320 -- A "Nothing" result *is* legitmiate
321 -- See Note [Unreachable code]
324 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
328 go (alt@(con1,_,_) : alts) deflt
329 = case con `cmpAltCon` con1 of
330 LT -> deflt -- Missed it already; the alts are in increasing order
332 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
334 ---------------------------------
335 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
336 -- ^ Merge alternatives preserving order; alternatives in
337 -- the first argument shadow ones in the second
338 mergeAlts [] as2 = as2
339 mergeAlts as1 [] = as1
340 mergeAlts (a1:as1) (a2:as2)
341 = case a1 `cmpAlt` a2 of
342 LT -> a1 : mergeAlts as1 (a2:as2)
343 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
344 GT -> a2 : mergeAlts (a1:as1) as2
347 ---------------------------------
348 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
351 -- > case (C a b x y) of
354 -- We want to drop the leading type argument of the scrutinee
355 -- leaving the arguments to match agains the pattern
357 trimConArgs DEFAULT args = ASSERT( null args ) []
358 trimConArgs (LitAlt _) args = ASSERT( null args ) []
359 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
362 Note [Unreachable code]
363 ~~~~~~~~~~~~~~~~~~~~~~~
364 It is possible (although unusual) for GHC to find a case expression
365 that cannot match. For example:
367 data Col = Red | Green | Blue
371 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
373 Suppose that for some silly reason, x isn't substituted in the case
374 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
375 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
379 lvl = case x of { Green -> e1; Blue -> e2 })
384 Now if x gets inlined, we won't be able to find a matching alternative
385 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
386 we generate (error "Inaccessible alternative").
388 Similar things can happen (augmented by GADTs) when the Simplifier
389 filters down the matching alternatives in Simplify.rebuildCase.
393 %************************************************************************
395 \subsection{Figuring out things about expressions}
397 %************************************************************************
399 @exprIsTrivial@ is true of expressions we are unconditionally happy to
400 duplicate; simple variables and constants, and type
401 applications. Note that primop Ids aren't considered
404 There used to be a gruesome test for (hasNoBinding v) in the
406 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
407 The idea here is that a constructor worker, like \$wJust, is
408 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
409 So it should be treated like a lambda. Ditto unsaturated primops.
410 But now constructor workers are not "have-no-binding" Ids. And
411 completely un-applied primops and foreign-call Ids are sufficiently
412 rare that I plan to allow them to be duplicated and put up with
415 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
416 a) it really generates code, (and a heap object when it's
417 a function arg) to capture the cost centre
418 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
421 exprIsTrivial :: CoreExpr -> Bool
422 exprIsTrivial (Var _) = True -- See notes above
423 exprIsTrivial (Type _) = True
424 exprIsTrivial (Lit lit) = litIsTrivial lit
425 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
426 exprIsTrivial (Note (SCC _) _) = False -- See notes above
427 exprIsTrivial (Note _ e) = exprIsTrivial e
428 exprIsTrivial (Cast e _) = exprIsTrivial e
429 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
430 exprIsTrivial _ = False
434 @exprIsDupable@ is true of expressions that can be duplicated at a modest
435 cost in code size. This will only happen in different case
436 branches, so there's no issue about duplicating work.
438 That is, exprIsDupable returns True of (f x) even if
439 f is very very expensive to call.
441 Its only purpose is to avoid fruitless let-binding
442 and then inlining of case join points
446 exprIsDupable :: CoreExpr -> Bool
447 exprIsDupable (Type _) = True
448 exprIsDupable (Var _) = True
449 exprIsDupable (Lit lit) = litIsDupable lit
450 exprIsDupable (Note InlineMe _) = True
451 exprIsDupable (Note _ e) = exprIsDupable e
452 exprIsDupable (Cast e _) = exprIsDupable e
457 go (App f a) n_args = n_args < dupAppSize
463 dupAppSize = 4 -- Size of application we are prepared to duplicate
466 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
467 it is obviously in weak head normal form, or is cheap to get to WHNF.
468 [Note that that's not the same as exprIsDupable; an expression might be
469 big, and hence not dupable, but still cheap.]
471 By ``cheap'' we mean a computation we're willing to:
472 push inside a lambda, or
473 inline at more than one place
474 That might mean it gets evaluated more than once, instead of being
475 shared. The main examples of things which aren't WHNF but are
480 (where e, and all the ei are cheap)
483 (where e and b are cheap)
486 (where op is a cheap primitive operator)
489 (because we are happy to substitute it inside a lambda)
491 Notice that a variable is considered 'cheap': we can push it inside a lambda,
492 because sharing will make sure it is only evaluated once.
495 exprIsCheap' :: (Id -> Bool) -> CoreExpr -> Bool
496 exprIsCheap' _ (Lit _) = True
497 exprIsCheap' _ (Type _) = True
498 exprIsCheap' _ (Var _) = True
499 exprIsCheap' _ (Note InlineMe _) = True
500 exprIsCheap' is_conlike (Note _ e) = exprIsCheap' is_conlike e
501 exprIsCheap' is_conlike (Cast e _) = exprIsCheap' is_conlike e
502 exprIsCheap' is_conlike (Lam x e) = isRuntimeVar x
503 || exprIsCheap' is_conlike e
504 exprIsCheap' is_conlike (Case e _ _ alts) = exprIsCheap' is_conlike e &&
505 and [exprIsCheap' is_conlike rhs | (_,_,rhs) <- alts]
506 -- Experimentally, treat (case x of ...) as cheap
507 -- (and case __coerce x etc.)
508 -- This improves arities of overloaded functions where
509 -- there is only dictionary selection (no construction) involved
510 exprIsCheap' is_conlike (Let (NonRec x _) e)
511 | isUnLiftedType (idType x) = exprIsCheap' is_conlike e
513 -- strict lets always have cheap right hand sides,
514 -- and do no allocation.
516 exprIsCheap' is_conlike other_expr -- Applications and variables
519 -- Accumulate value arguments, then decide
520 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
521 | otherwise = go f val_args
523 go (Var _) [] = True -- Just a type application of a variable
524 -- (f t1 t2 t3) counts as WHNF
526 = case idDetails f of
527 RecSelId {} -> go_sel args
528 ClassOpId _ -> go_sel args
529 PrimOpId op -> go_primop op args
531 _ | is_conlike f -> go_pap args
532 | length args < idArity f -> go_pap args
535 -- Application of a function which
536 -- always gives bottom; we treat this as cheap
537 -- because it certainly doesn't need to be shared!
542 go_pap args = all exprIsTrivial args
543 -- For constructor applications and primops, check that all
544 -- the args are trivial. We don't want to treat as cheap, say,
546 -- We'll put up with one constructor application, but not dozens
549 go_primop op args = primOpIsCheap op && all (exprIsCheap' is_conlike) args
550 -- In principle we should worry about primops
551 -- that return a type variable, since the result
552 -- might be applied to something, but I'm not going
553 -- to bother to check the number of args
556 go_sel [arg] = exprIsCheap' is_conlike arg -- I'm experimenting with making record selection
557 go_sel _ = False -- look cheap, so we will substitute it inside a
558 -- lambda. Particularly for dictionary field selection.
559 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
560 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
562 exprIsCheap :: CoreExpr -> Bool
563 exprIsCheap = exprIsCheap' isDataConWorkId
565 exprIsExpandable :: CoreExpr -> Bool
566 exprIsExpandable = exprIsCheap' isConLikeId
570 -- | 'exprOkForSpeculation' returns True of an expression that is:
572 -- * Safe to evaluate even if normal order eval might not
573 -- evaluate the expression at all, or
575 -- * Safe /not/ to evaluate even if normal order would do so
577 -- Precisely, it returns @True@ iff:
579 -- * The expression guarantees to terminate,
583 -- * without raising an exception,
585 -- * without causing a side effect (e.g. writing a mutable variable)
587 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
588 -- As an example of the considerations in this test, consider:
590 -- > let x = case y# +# 1# of { r# -> I# r# }
593 -- being translated to:
595 -- > case y# +# 1# of { r# ->
600 -- We can only do this if the @y + 1@ is ok for speculation: it has no
601 -- side effects, and can't diverge or raise an exception.
602 exprOkForSpeculation :: CoreExpr -> Bool
603 exprOkForSpeculation (Lit _) = True
604 exprOkForSpeculation (Type _) = True
605 -- Tick boxes are *not* suitable for speculation
606 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
607 && not (isTickBoxOp v)
608 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
609 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
610 exprOkForSpeculation other_expr
611 = case collectArgs other_expr of
612 (Var f, args) -> spec_ok (idDetails f) args
616 spec_ok (DataConWorkId _) _
617 = True -- The strictness of the constructor has already
618 -- been expressed by its "wrapper", so we don't need
619 -- to take the arguments into account
621 spec_ok (PrimOpId op) args
622 | isDivOp op, -- Special case for dividing operations that fail
623 [arg1, Lit lit] <- args -- only if the divisor is zero
624 = not (isZeroLit lit) && exprOkForSpeculation arg1
625 -- Often there is a literal divisor, and this
626 -- can get rid of a thunk in an inner looop
629 = primOpOkForSpeculation op &&
630 all exprOkForSpeculation args
631 -- A bit conservative: we don't really need
632 -- to care about lazy arguments, but this is easy
636 -- | True of dyadic operators that can fail only if the second arg is zero!
637 isDivOp :: PrimOp -> Bool
638 -- This function probably belongs in PrimOp, or even in
639 -- an automagically generated file.. but it's such a
640 -- special case I thought I'd leave it here for now.
641 isDivOp IntQuotOp = True
642 isDivOp IntRemOp = True
643 isDivOp WordQuotOp = True
644 isDivOp WordRemOp = True
645 isDivOp FloatDivOp = True
646 isDivOp DoubleDivOp = True
651 -- | True of expressions that are guaranteed to diverge upon execution
652 exprIsBottom :: CoreExpr -> Bool
653 exprIsBottom e = go 0 e
655 -- n is the number of args
656 go n (Note _ e) = go n e
657 go n (Cast e _) = go n e
658 go n (Let _ e) = go n e
659 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
660 go n (App e _) = go (n+1) e
661 go n (Var v) = idAppIsBottom v n
663 go _ (Lam _ _) = False
664 go _ (Type _) = False
666 idAppIsBottom :: Id -> Int -> Bool
667 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
672 -- | This returns true for expressions that are certainly /already/
673 -- evaluated to /head/ normal form. This is used to decide whether it's ok
676 -- > case x of _ -> e
682 -- and to decide whether it's safe to discard a 'seq'.
683 -- So, it does /not/ treat variables as evaluated, unless they say they are.
684 -- However, it /does/ treat partial applications and constructor applications
685 -- as values, even if their arguments are non-trivial, provided the argument
686 -- type is lifted. For example, both of these are values:
688 -- > (:) (f x) (map f xs)
689 -- > map (...redex...)
691 -- Because 'seq' on such things completes immediately.
693 -- For unlifted argument types, we have to be careful:
697 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
698 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
699 -- unboxed type must be ok-for-speculation (or trivial).
700 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
701 exprIsHNF (Var v) -- NB: There are no value args at this point
702 = isDataConWorkId v -- Catches nullary constructors,
703 -- so that [] and () are values, for example
704 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
705 || isEvaldUnfolding (idUnfolding v)
706 -- Check the thing's unfolding; it might be bound to a value
707 -- A worry: what if an Id's unfolding is just itself:
708 -- then we could get an infinite loop...
710 exprIsHNF (Lit _) = True
711 exprIsHNF (Type _) = True -- Types are honorary Values;
712 -- we don't mind copying them
713 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
714 exprIsHNF (Note _ e) = exprIsHNF e
715 exprIsHNF (Cast e _) = exprIsHNF e
716 exprIsHNF (App e (Type _)) = exprIsHNF e
717 exprIsHNF (App e a) = app_is_value e [a]
720 -- There is at least one value argument
721 app_is_value :: CoreExpr -> [CoreArg] -> Bool
722 app_is_value (Var fun) args
723 = idArity fun > valArgCount args -- Under-applied function
724 || isDataConWorkId fun -- or data constructor
725 app_is_value (Note _ f) as = app_is_value f as
726 app_is_value (Cast f _) as = app_is_value f as
727 app_is_value (App f a) as = app_is_value f (a:as)
728 app_is_value _ _ = False
731 These InstPat functions go here to avoid circularity between DataCon and Id
734 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
735 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
737 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
738 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
739 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
741 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
742 -- Remember to include the existential dictionaries
744 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
745 -> [FastString] -- A long enough list of FSs to use for names
746 -> [Unique] -- An equally long list of uniques, at least one for each binder
748 -> [Type] -- Types to instantiate the universally quantified tyvars
749 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
750 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
751 -- (ex_tvs, co_tvs, arg_ids),
753 -- ex_tvs are intended to be used as binders for existential type args
755 -- co_tvs are intended to be used as binders for coercion args and the kinds
756 -- of these vars have been instantiated by the inst_tys and the ex_tys
757 -- The co_tvs include both GADT equalities (dcEqSpec) and
758 -- programmer-specified equalities (dcEqTheta)
760 -- arg_ids are indended to be used as binders for value arguments,
761 -- and their types have been instantiated with inst_tys and ex_tys
762 -- The arg_ids include both dicts (dcDictTheta) and
763 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
766 -- The following constructor T1
769 -- T1 :: forall b. Int -> b -> T(a,b)
772 -- has representation type
773 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
776 -- dataConInstPat fss us T1 (a1',b') will return
778 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
780 -- where the double-primed variables are created with the FastStrings and
781 -- Uniques given as fss and us
782 dataConInstPat arg_fun fss uniqs con inst_tys
783 = (ex_bndrs, co_bndrs, arg_ids)
785 univ_tvs = dataConUnivTyVars con
786 ex_tvs = dataConExTyVars con
787 arg_tys = arg_fun con
788 eq_spec = dataConEqSpec con
789 eq_theta = dataConEqTheta con
790 eq_preds = eqSpecPreds eq_spec ++ eq_theta
793 n_co = length eq_preds
795 -- split the Uniques and FastStrings
796 (ex_uniqs, uniqs') = splitAt n_ex uniqs
797 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
799 (ex_fss, fss') = splitAt n_ex fss
800 (co_fss, id_fss) = splitAt n_co fss'
802 -- Make existential type variables
803 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
804 mk_ex_var uniq fs var = mkTyVar new_name kind
806 new_name = mkSysTvName uniq fs
809 -- Make the instantiating substitution
810 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
812 -- Make new coercion vars, instantiating kind
813 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
814 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
816 new_name = mkSysTvName uniq fs
817 co_kind = substTy subst (mkPredTy eq_pred)
819 -- make value vars, instantiating types
820 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
821 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
823 -- | Returns @Just (dc, [x1..xn])@ if the argument expression is
824 -- a constructor application of the form @dc x1 .. xn@
825 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
826 exprIsConApp_maybe (Cast expr co)
827 = -- Here we do the KPush reduction rule as described in the FC paper
828 case exprIsConApp_maybe expr of {
830 Just (dc, dc_args) ->
832 -- The transformation applies iff we have
833 -- (C e1 ... en) `cast` co
834 -- where co :: (T t1 .. tn) ~ (T s1 ..sn)
835 -- That is, with a T at the top of both sides
836 -- The left-hand one must be a T, because exprIsConApp returned True
837 -- but the right-hand one might not be. (Though it usually will.)
839 let (from_ty, to_ty) = coercionKind co
840 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
841 -- The inner one must be a TyConApp
843 case splitTyConApp_maybe to_ty of {
845 Just (to_tc, to_tc_arg_tys)
846 | from_tc /= to_tc -> Nothing
847 -- These two Nothing cases are possible; we might see
848 -- (C x y) `cast` (g :: T a ~ S [a]),
849 -- where S is a type function. In fact, exprIsConApp
850 -- will probably not be called in such circumstances,
851 -- but there't nothing wrong with it
855 tc_arity = tyConArity from_tc
857 (univ_args, rest1) = splitAt tc_arity dc_args
858 (ex_args, rest2) = splitAt n_ex_tvs rest1
859 (co_args_spec, rest3) = splitAt n_cos_spec rest2
860 (co_args_theta, val_args) = splitAt n_cos_theta rest3
862 arg_tys = dataConRepArgTys dc
863 dc_univ_tyvars = dataConUnivTyVars dc
864 dc_ex_tyvars = dataConExTyVars dc
865 dc_eq_spec = dataConEqSpec dc
866 dc_eq_theta = dataConEqTheta dc
867 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
868 n_ex_tvs = length dc_ex_tyvars
869 n_cos_spec = length dc_eq_spec
870 n_cos_theta = length dc_eq_theta
872 -- Make the "theta" from Fig 3 of the paper
873 gammas = decomposeCo tc_arity co
874 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
875 theta = zipOpenTvSubst dc_tyvars new_tys
877 -- First we cast the existential coercion arguments
878 cast_co_spec (tv, ty) co
879 = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
880 cast_co_theta eqPred (Type co)
881 | (ty1, ty2) <- getEqPredTys eqPred
882 = Type $ mkSymCoercion (substTy theta ty1)
884 `mkTransCoercion` (substTy theta ty2)
885 new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
886 zipWith cast_co_theta dc_eq_theta co_args_theta
888 -- ...and now value arguments
889 new_val_args = zipWith cast_arg arg_tys val_args
890 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
893 ASSERT( length univ_args == tc_arity )
894 ASSERT( from_tc == dataConTyCon dc )
895 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
896 ASSERT( all isTypeArg (univ_args ++ ex_args) )
897 ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
899 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
903 -- We do not want to tell the world that we have a
904 -- Cons, to *stop* Case of Known Cons, which removes
906 exprIsConApp_maybe (Note (TickBox {}) expr)
908 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
912 exprIsConApp_maybe (Note _ expr)
913 = exprIsConApp_maybe expr
914 -- We ignore InlineMe notes in case we have
915 -- x = __inline_me__ (a,b)
916 -- All part of making sure that INLINE pragmas never hurt
917 -- Marcin tripped on this one when making dictionaries more inlinable
919 -- In fact, we ignore all notes. For example,
920 -- case _scc_ "foo" (C a b) of
922 -- should be optimised away, but it will be only if we look
923 -- through the SCC note.
925 exprIsConApp_maybe expr = analyse (collectArgs expr)
927 analyse (Var fun, args)
928 | Just con <- isDataConWorkId_maybe fun,
929 args `lengthAtLeast` dataConRepArity con
930 -- Might be > because the arity excludes type args
933 -- Look through unfoldings, but only cheap ones, because
934 -- we are effectively duplicating the unfolding
935 analyse (Var fun, [])
936 | let unf = idUnfolding fun,
937 isExpandableUnfolding unf
938 = exprIsConApp_maybe (unfoldingTemplate unf)
945 %************************************************************************
947 \subsection{Equality}
949 %************************************************************************
952 -- | A cheap equality test which bales out fast!
953 -- If it returns @True@ the arguments are definitely equal,
954 -- otherwise, they may or may not be equal.
956 -- See also 'exprIsBig'
957 cheapEqExpr :: Expr b -> Expr b -> Bool
959 cheapEqExpr (Var v1) (Var v2) = v1==v2
960 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
961 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
963 cheapEqExpr (App f1 a1) (App f2 a2)
964 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
966 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
967 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
969 cheapEqExpr _ _ = False
971 exprIsBig :: Expr b -> Bool
972 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
973 exprIsBig (Lit _) = False
974 exprIsBig (Var _) = False
975 exprIsBig (Type _) = False
976 exprIsBig (App f a) = exprIsBig f || exprIsBig a
977 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
983 %************************************************************************
985 \subsection{The size of an expression}
987 %************************************************************************
990 coreBindsSize :: [CoreBind] -> Int
991 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
993 exprSize :: CoreExpr -> Int
994 -- ^ A measure of the size of the expressions, strictly greater than 0
995 -- It also forces the expression pretty drastically as a side effect
996 exprSize (Var v) = v `seq` 1
997 exprSize (Lit lit) = lit `seq` 1
998 exprSize (App f a) = exprSize f + exprSize a
999 exprSize (Lam b e) = varSize b + exprSize e
1000 exprSize (Let b e) = bindSize b + exprSize e
1001 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1002 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1003 exprSize (Note n e) = noteSize n + exprSize e
1004 exprSize (Type t) = seqType t `seq` 1
1006 noteSize :: Note -> Int
1007 noteSize (SCC cc) = cc `seq` 1
1008 noteSize InlineMe = 1
1009 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1011 varSize :: Var -> Int
1012 varSize b | isTyVar b = 1
1013 | otherwise = seqType (idType b) `seq`
1014 megaSeqIdInfo (idInfo b) `seq`
1017 varsSize :: [Var] -> Int
1018 varsSize = sum . map varSize
1020 bindSize :: CoreBind -> Int
1021 bindSize (NonRec b e) = varSize b + exprSize e
1022 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1024 pairSize :: (Var, CoreExpr) -> Int
1025 pairSize (b,e) = varSize b + exprSize e
1027 altSize :: CoreAlt -> Int
1028 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1032 %************************************************************************
1034 \subsection{Hashing}
1036 %************************************************************************
1039 hashExpr :: CoreExpr -> Int
1040 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1041 -- Two expressions that hash to the different Ints are definitely unequal.
1043 -- The emphasis is on a crude, fast hash, rather than on high precision.
1045 -- But unequal here means \"not identical\"; two alpha-equivalent
1046 -- expressions may hash to the different Ints.
1048 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1049 -- (at least if we want the above invariant to be true).
1051 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1052 -- UniqFM doesn't like negative Ints
1054 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1056 hash_expr :: HashEnv -> CoreExpr -> Word32
1057 -- Word32, because we're expecting overflows here, and overflowing
1058 -- signed types just isn't cool. In C it's even undefined.
1059 hash_expr env (Note _ e) = hash_expr env e
1060 hash_expr env (Cast e _) = hash_expr env e
1061 hash_expr env (Var v) = hashVar env v
1062 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1063 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1064 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1065 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1066 hash_expr env (Case e _ _ _) = hash_expr env e
1067 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1068 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1069 -- Shouldn't happen. Better to use WARN than trace, because trace
1070 -- prevents the CPR optimisation kicking in for hash_expr.
1072 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1073 fast_hash_expr env (Var v) = hashVar env v
1074 fast_hash_expr env (Type t) = fast_hash_type env t
1075 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1076 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1077 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1078 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1079 fast_hash_expr _ _ = 1
1081 fast_hash_type :: HashEnv -> Type -> Word32
1082 fast_hash_type env ty
1083 | Just tv <- getTyVar_maybe ty = hashVar env tv
1084 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1085 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1088 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1089 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1091 hashVar :: HashEnv -> Var -> Word32
1093 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1096 %************************************************************************
1098 \subsection{Determining non-updatable right-hand-sides}
1100 %************************************************************************
1102 Top-level constructor applications can usually be allocated
1103 statically, but they can't if the constructor, or any of the
1104 arguments, come from another DLL (because we can't refer to static
1105 labels in other DLLs).
1107 If this happens we simply make the RHS into an updatable thunk,
1108 and 'execute' it rather than allocating it statically.
1111 -- | This function is called only on *top-level* right-hand sides.
1112 -- Returns @True@ if the RHS can be allocated statically in the output,
1113 -- with no thunks involved at all.
1114 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1115 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1116 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1117 -- update flag on it and (iii) in DsExpr to decide how to expand
1120 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1121 -- (a) a value lambda
1122 -- (b) a saturated constructor application with static args
1124 -- BUT watch out for
1125 -- (i) Any cross-DLL references kill static-ness completely
1126 -- because they must be 'executed' not statically allocated
1127 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1128 -- this is not necessary)
1130 -- (ii) We treat partial applications as redexes, because in fact we
1131 -- make a thunk for them that runs and builds a PAP
1132 -- at run-time. The only appliations that are treated as
1133 -- static are *saturated* applications of constructors.
1135 -- We used to try to be clever with nested structures like this:
1136 -- ys = (:) w ((:) w [])
1137 -- on the grounds that CorePrep will flatten ANF-ise it later.
1138 -- But supporting this special case made the function much more
1139 -- complicated, because the special case only applies if there are no
1140 -- enclosing type lambdas:
1141 -- ys = /\ a -> Foo (Baz ([] a))
1142 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1144 -- But in fact, even without -O, nested structures at top level are
1145 -- flattened by the simplifier, so we don't need to be super-clever here.
1149 -- f = \x::Int. x+7 TRUE
1150 -- p = (True,False) TRUE
1152 -- d = (fst p, False) FALSE because there's a redex inside
1153 -- (this particular one doesn't happen but...)
1155 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1156 -- n = /\a. Nil a TRUE
1158 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1161 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1162 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1164 -- b) (C x xs), where C is a contructors is updatable if the application is
1167 -- c) don't look through unfolding of f in (f x).
1169 rhsIsStatic _this_pkg rhs = is_static False rhs
1171 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1174 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1176 is_static _ (Note (SCC _) _) = False
1177 is_static in_arg (Note _ e) = is_static in_arg e
1178 is_static in_arg (Cast e _) = is_static in_arg e
1180 is_static _ (Lit lit)
1182 MachLabel _ _ _ -> False
1184 -- A MachLabel (foreign import "&foo") in an argument
1185 -- prevents a constructor application from being static. The
1186 -- reason is that it might give rise to unresolvable symbols
1187 -- in the object file: under Linux, references to "weak"
1188 -- symbols from the data segment give rise to "unresolvable
1189 -- relocation" errors at link time This might be due to a bug
1190 -- in the linker, but we'll work around it here anyway.
1193 is_static in_arg other_expr = go other_expr 0
1195 go (Var f) n_val_args
1196 #if mingw32_TARGET_OS
1197 | not (isDllName _this_pkg (idName f))
1199 = saturated_data_con f n_val_args
1200 || (in_arg && n_val_args == 0)
1201 -- A naked un-applied variable is *not* deemed a static RHS
1203 -- Reason: better to update so that the indirection gets shorted
1204 -- out, and the true value will be seen
1205 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1206 -- are always updatable. If you do so, make sure that non-updatable
1207 -- ones have enough space for their static link field!
1209 go (App f a) n_val_args
1210 | isTypeArg a = go f n_val_args
1211 | not in_arg && is_static True a = go f (n_val_args + 1)
1212 -- The (not in_arg) checks that we aren't in a constructor argument;
1213 -- if we are, we don't allow (value) applications of any sort
1215 -- NB. In case you wonder, args are sometimes not atomic. eg.
1216 -- x = D# (1.0## /## 2.0##)
1217 -- can't float because /## can fail.
1219 go (Note (SCC _) _) _ = False
1220 go (Note _ f) n_val_args = go f n_val_args
1221 go (Cast e _) n_val_args = go e n_val_args
1225 saturated_data_con f n_val_args
1226 = case isDataConWorkId_maybe f of
1227 Just dc -> n_val_args == dataConRepArity dc