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 (Var v) = Var v
204 mkInlineMe e = Note InlineMe e
208 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
209 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
211 mkCoerceI (ACo co) e = mkCoerce co e
213 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
214 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
215 mkCoerce co (Cast expr co2)
216 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
217 (_from_ty2, to_ty2) = coercionKind co2} in
218 from_ty `coreEqType` to_ty2 )
219 mkCoerce (mkTransCoercion co2 co) expr
222 = let (from_ty, _to_ty) = coercionKind co in
223 -- if to_ty `coreEqType` from_ty
226 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
231 -- | Wraps the given expression in the cost centre unless
232 -- in a way that maximises their utility to the user
233 mkSCC :: CostCentre -> Expr b -> Expr b
234 -- Note: Nested SCC's *are* preserved for the benefit of
235 -- cost centre stack profiling
236 mkSCC _ (Lit lit) = Lit lit
237 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
238 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
239 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
240 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
241 mkSCC cc expr = Note (SCC cc) expr
245 %************************************************************************
247 \subsection{Other expression construction}
249 %************************************************************************
252 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
253 -- ^ @bindNonRec x r b@ produces either:
259 -- > case r of x { _DEFAULT_ -> b }
261 -- depending on whether we have to use a @case@ or @let@
262 -- binding for the expression (see 'needsCaseBinding').
263 -- It's used by the desugarer to avoid building bindings
264 -- that give Core Lint a heart attack, although actually
265 -- the simplifier deals with them perfectly well. See
266 -- also 'MkCore.mkCoreLet'
267 bindNonRec bndr rhs body
268 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
269 | otherwise = Let (NonRec bndr rhs) body
271 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
272 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
273 needsCaseBinding :: Type -> CoreExpr -> Bool
274 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
275 -- Make a case expression instead of a let
276 -- These can arise either from the desugarer,
277 -- or from beta reductions: (\x.e) (x +# y)
281 mkAltExpr :: AltCon -- ^ Case alternative constructor
282 -> [CoreBndr] -- ^ Things bound by the pattern match
283 -> [Type] -- ^ The type arguments to the case alternative
285 -- ^ This guy constructs the value that the scrutinee must have
286 -- given that you are in one particular branch of a case
287 mkAltExpr (DataAlt con) args inst_tys
288 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
289 mkAltExpr (LitAlt lit) [] []
291 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
292 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
296 %************************************************************************
298 \subsection{Taking expressions apart}
300 %************************************************************************
302 The default alternative must be first, if it exists at all.
303 This makes it easy to find, though it makes matching marginally harder.
306 -- | Extract the default case alternative
307 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
308 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
309 findDefault alts = (alts, Nothing)
311 isDefaultAlt :: CoreAlt -> Bool
312 isDefaultAlt (DEFAULT, _, _) = True
313 isDefaultAlt _ = False
316 -- | Find the case alternative corresponding to a particular
317 -- constructor: panics if no such constructor exists
318 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
319 -- A "Nothing" result *is* legitmiate
320 -- See Note [Unreachable code]
323 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
327 go (alt@(con1,_,_) : alts) deflt
328 = case con `cmpAltCon` con1 of
329 LT -> deflt -- Missed it already; the alts are in increasing order
331 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
333 ---------------------------------
334 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
335 -- ^ Merge alternatives preserving order; alternatives in
336 -- the first argument shadow ones in the second
337 mergeAlts [] as2 = as2
338 mergeAlts as1 [] = as1
339 mergeAlts (a1:as1) (a2:as2)
340 = case a1 `cmpAlt` a2 of
341 LT -> a1 : mergeAlts as1 (a2:as2)
342 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
343 GT -> a2 : mergeAlts (a1:as1) as2
346 ---------------------------------
347 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
350 -- > case (C a b x y) of
353 -- We want to drop the leading type argument of the scrutinee
354 -- leaving the arguments to match agains the pattern
356 trimConArgs DEFAULT args = ASSERT( null args ) []
357 trimConArgs (LitAlt _) args = ASSERT( null args ) []
358 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
361 Note [Unreachable code]
362 ~~~~~~~~~~~~~~~~~~~~~~~
363 It is possible (although unusual) for GHC to find a case expression
364 that cannot match. For example:
366 data Col = Red | Green | Blue
370 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
372 Suppose that for some silly reason, x isn't substituted in the case
373 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
374 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
378 lvl = case x of { Green -> e1; Blue -> e2 })
383 Now if x gets inlined, we won't be able to find a matching alternative
384 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
385 we generate (error "Inaccessible alternative").
387 Similar things can happen (augmented by GADTs) when the Simplifier
388 filters down the matching alternatives in Simplify.rebuildCase.
392 %************************************************************************
394 \subsection{Figuring out things about expressions}
396 %************************************************************************
398 @exprIsTrivial@ is true of expressions we are unconditionally happy to
399 duplicate; simple variables and constants, and type
400 applications. Note that primop Ids aren't considered
403 There used to be a gruesome test for (hasNoBinding v) in the
405 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
406 The idea here is that a constructor worker, like \$wJust, is
407 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
408 So it should be treated like a lambda. Ditto unsaturated primops.
409 But now constructor workers are not "have-no-binding" Ids. And
410 completely un-applied primops and foreign-call Ids are sufficiently
411 rare that I plan to allow them to be duplicated and put up with
414 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
415 a) it really generates code, (and a heap object when it's
416 a function arg) to capture the cost centre
417 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
420 exprIsTrivial :: CoreExpr -> Bool
421 exprIsTrivial (Var _) = True -- See notes above
422 exprIsTrivial (Type _) = True
423 exprIsTrivial (Lit lit) = litIsTrivial lit
424 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
425 exprIsTrivial (Note (SCC _) _) = False -- See notes above
426 exprIsTrivial (Note _ e) = exprIsTrivial e
427 exprIsTrivial (Cast e _) = exprIsTrivial e
428 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
429 exprIsTrivial _ = False
433 @exprIsDupable@ is true of expressions that can be duplicated at a modest
434 cost in code size. This will only happen in different case
435 branches, so there's no issue about duplicating work.
437 That is, exprIsDupable returns True of (f x) even if
438 f is very very expensive to call.
440 Its only purpose is to avoid fruitless let-binding
441 and then inlining of case join points
445 exprIsDupable :: CoreExpr -> Bool
446 exprIsDupable (Type _) = True
447 exprIsDupable (Var _) = True
448 exprIsDupable (Lit lit) = litIsDupable lit
449 exprIsDupable (Note InlineMe _) = True
450 exprIsDupable (Note _ e) = exprIsDupable e
451 exprIsDupable (Cast e _) = exprIsDupable e
456 go (App f a) n_args = n_args < dupAppSize
462 dupAppSize = 4 -- Size of application we are prepared to duplicate
465 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
466 it is obviously in weak head normal form, or is cheap to get to WHNF.
467 [Note that that's not the same as exprIsDupable; an expression might be
468 big, and hence not dupable, but still cheap.]
470 By ``cheap'' we mean a computation we're willing to:
471 push inside a lambda, or
472 inline at more than one place
473 That might mean it gets evaluated more than once, instead of being
474 shared. The main examples of things which aren't WHNF but are
479 (where e, and all the ei are cheap)
482 (where e and b are cheap)
485 (where op is a cheap primitive operator)
488 (because we are happy to substitute it inside a lambda)
490 Notice that a variable is considered 'cheap': we can push it inside a lambda,
491 because sharing will make sure it is only evaluated once.
494 exprIsCheap' :: (Id -> Bool) -> CoreExpr -> Bool
495 exprIsCheap' _ (Lit _) = True
496 exprIsCheap' _ (Type _) = True
497 exprIsCheap' _ (Var _) = True
498 exprIsCheap' _ (Note InlineMe _) = True
499 exprIsCheap' is_conlike (Note _ e) = exprIsCheap' is_conlike e
500 exprIsCheap' is_conlike (Cast e _) = exprIsCheap' is_conlike e
501 exprIsCheap' is_conlike (Lam x e) = isRuntimeVar x
502 || exprIsCheap' is_conlike e
503 exprIsCheap' is_conlike (Case e _ _ alts) = exprIsCheap' is_conlike e &&
504 and [exprIsCheap' is_conlike rhs | (_,_,rhs) <- alts]
505 -- Experimentally, treat (case x of ...) as cheap
506 -- (and case __coerce x etc.)
507 -- This improves arities of overloaded functions where
508 -- there is only dictionary selection (no construction) involved
509 exprIsCheap' is_conlike (Let (NonRec x _) e)
510 | isUnLiftedType (idType x) = exprIsCheap' is_conlike e
512 -- strict lets always have cheap right hand sides,
513 -- and do no allocation.
515 exprIsCheap' is_conlike other_expr -- Applications and variables
518 -- Accumulate value arguments, then decide
519 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
520 | otherwise = go f val_args
522 go (Var _) [] = True -- Just a type application of a variable
523 -- (f t1 t2 t3) counts as WHNF
525 = case idDetails f of
526 RecSelId {} -> go_sel args
527 ClassOpId _ -> go_sel args
528 PrimOpId op -> go_primop op args
530 _ | is_conlike f -> go_pap args
531 | length args < idArity f -> go_pap args
534 -- Application of a function which
535 -- always gives bottom; we treat this as cheap
536 -- because it certainly doesn't need to be shared!
541 go_pap args = all exprIsTrivial args
542 -- For constructor applications and primops, check that all
543 -- the args are trivial. We don't want to treat as cheap, say,
545 -- We'll put up with one constructor application, but not dozens
548 go_primop op args = primOpIsCheap op && all (exprIsCheap' is_conlike) args
549 -- In principle we should worry about primops
550 -- that return a type variable, since the result
551 -- might be applied to something, but I'm not going
552 -- to bother to check the number of args
555 go_sel [arg] = exprIsCheap' is_conlike arg -- I'm experimenting with making record selection
556 go_sel _ = False -- look cheap, so we will substitute it inside a
557 -- lambda. Particularly for dictionary field selection.
558 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
559 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
561 exprIsCheap :: CoreExpr -> Bool
562 exprIsCheap = exprIsCheap' isDataConWorkId
564 exprIsExpandable :: CoreExpr -> Bool
565 exprIsExpandable = exprIsCheap' isConLikeId
569 -- | 'exprOkForSpeculation' returns True of an expression that is:
571 -- * Safe to evaluate even if normal order eval might not
572 -- evaluate the expression at all, or
574 -- * Safe /not/ to evaluate even if normal order would do so
576 -- Precisely, it returns @True@ iff:
578 -- * The expression guarantees to terminate,
582 -- * without raising an exception,
584 -- * without causing a side effect (e.g. writing a mutable variable)
586 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
587 -- As an example of the considerations in this test, consider:
589 -- > let x = case y# +# 1# of { r# -> I# r# }
592 -- being translated to:
594 -- > case y# +# 1# of { r# ->
599 -- We can only do this if the @y + 1@ is ok for speculation: it has no
600 -- side effects, and can't diverge or raise an exception.
601 exprOkForSpeculation :: CoreExpr -> Bool
602 exprOkForSpeculation (Lit _) = True
603 exprOkForSpeculation (Type _) = True
604 -- Tick boxes are *not* suitable for speculation
605 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
606 && not (isTickBoxOp v)
607 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
608 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
609 exprOkForSpeculation other_expr
610 = case collectArgs other_expr of
611 (Var f, args) -> spec_ok (idDetails f) args
615 spec_ok (DataConWorkId _) _
616 = True -- The strictness of the constructor has already
617 -- been expressed by its "wrapper", so we don't need
618 -- to take the arguments into account
620 spec_ok (PrimOpId op) args
621 | isDivOp op, -- Special case for dividing operations that fail
622 [arg1, Lit lit] <- args -- only if the divisor is zero
623 = not (isZeroLit lit) && exprOkForSpeculation arg1
624 -- Often there is a literal divisor, and this
625 -- can get rid of a thunk in an inner looop
628 = primOpOkForSpeculation op &&
629 all exprOkForSpeculation args
630 -- A bit conservative: we don't really need
631 -- to care about lazy arguments, but this is easy
635 -- | True of dyadic operators that can fail only if the second arg is zero!
636 isDivOp :: PrimOp -> Bool
637 -- This function probably belongs in PrimOp, or even in
638 -- an automagically generated file.. but it's such a
639 -- special case I thought I'd leave it here for now.
640 isDivOp IntQuotOp = True
641 isDivOp IntRemOp = True
642 isDivOp WordQuotOp = True
643 isDivOp WordRemOp = True
644 isDivOp IntegerQuotRemOp = True
645 isDivOp IntegerDivModOp = True
646 isDivOp FloatDivOp = True
647 isDivOp DoubleDivOp = True
652 -- | True of expressions that are guaranteed to diverge upon execution
653 exprIsBottom :: CoreExpr -> Bool
654 exprIsBottom e = go 0 e
656 -- n is the number of args
657 go n (Note _ e) = go n e
658 go n (Cast e _) = go n e
659 go n (Let _ e) = go n e
660 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
661 go n (App e _) = go (n+1) e
662 go n (Var v) = idAppIsBottom v n
664 go _ (Lam _ _) = False
665 go _ (Type _) = False
667 idAppIsBottom :: Id -> Int -> Bool
668 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
673 -- | This returns true for expressions that are certainly /already/
674 -- evaluated to /head/ normal form. This is used to decide whether it's ok
677 -- > case x of _ -> e
683 -- and to decide whether it's safe to discard a 'seq'.
684 -- So, it does /not/ treat variables as evaluated, unless they say they are.
685 -- However, it /does/ treat partial applications and constructor applications
686 -- as values, even if their arguments are non-trivial, provided the argument
687 -- type is lifted. For example, both of these are values:
689 -- > (:) (f x) (map f xs)
690 -- > map (...redex...)
692 -- Because 'seq' on such things completes immediately.
694 -- For unlifted argument types, we have to be careful:
698 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
699 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
700 -- unboxed type must be ok-for-speculation (or trivial).
701 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
702 exprIsHNF (Var v) -- NB: There are no value args at this point
703 = isDataConWorkId v -- Catches nullary constructors,
704 -- so that [] and () are values, for example
705 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
706 || isEvaldUnfolding (idUnfolding v)
707 -- Check the thing's unfolding; it might be bound to a value
708 -- A worry: what if an Id's unfolding is just itself:
709 -- then we could get an infinite loop...
711 exprIsHNF (Lit _) = True
712 exprIsHNF (Type _) = True -- Types are honorary Values;
713 -- we don't mind copying them
714 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
715 exprIsHNF (Note _ e) = exprIsHNF e
716 exprIsHNF (Cast e _) = exprIsHNF e
717 exprIsHNF (App e (Type _)) = exprIsHNF e
718 exprIsHNF (App e a) = app_is_value e [a]
721 -- There is at least one value argument
722 app_is_value :: CoreExpr -> [CoreArg] -> Bool
723 app_is_value (Var fun) args
724 = idArity fun > valArgCount args -- Under-applied function
725 || isDataConWorkId fun -- or data constructor
726 app_is_value (Note _ f) as = app_is_value f as
727 app_is_value (Cast f _) as = app_is_value f as
728 app_is_value (App f a) as = app_is_value f (a:as)
729 app_is_value _ _ = False
732 These InstPat functions go here to avoid circularity between DataCon and Id
735 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
736 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
738 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
739 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
740 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
742 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
743 -- Remember to include the existential dictionaries
745 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
746 -> [FastString] -- A long enough list of FSs to use for names
747 -> [Unique] -- An equally long list of uniques, at least one for each binder
749 -> [Type] -- Types to instantiate the universally quantified tyvars
750 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
751 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
752 -- (ex_tvs, co_tvs, arg_ids),
754 -- ex_tvs are intended to be used as binders for existential type args
756 -- co_tvs are intended to be used as binders for coercion args and the kinds
757 -- of these vars have been instantiated by the inst_tys and the ex_tys
758 -- The co_tvs include both GADT equalities (dcEqSpec) and
759 -- programmer-specified equalities (dcEqTheta)
761 -- arg_ids are indended to be used as binders for value arguments,
762 -- and their types have been instantiated with inst_tys and ex_tys
763 -- The arg_ids include both dicts (dcDictTheta) and
764 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
767 -- The following constructor T1
770 -- T1 :: forall b. Int -> b -> T(a,b)
773 -- has representation type
774 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
777 -- dataConInstPat fss us T1 (a1',b') will return
779 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
781 -- where the double-primed variables are created with the FastStrings and
782 -- Uniques given as fss and us
783 dataConInstPat arg_fun fss uniqs con inst_tys
784 = (ex_bndrs, co_bndrs, arg_ids)
786 univ_tvs = dataConUnivTyVars con
787 ex_tvs = dataConExTyVars con
788 arg_tys = arg_fun con
789 eq_spec = dataConEqSpec con
790 eq_theta = dataConEqTheta con
791 eq_preds = eqSpecPreds eq_spec ++ eq_theta
794 n_co = length eq_preds
796 -- split the Uniques and FastStrings
797 (ex_uniqs, uniqs') = splitAt n_ex uniqs
798 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
800 (ex_fss, fss') = splitAt n_ex fss
801 (co_fss, id_fss) = splitAt n_co fss'
803 -- Make existential type variables
804 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
805 mk_ex_var uniq fs var = mkTyVar new_name kind
807 new_name = mkSysTvName uniq fs
810 -- Make the instantiating substitution
811 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
813 -- Make new coercion vars, instantiating kind
814 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
815 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
817 new_name = mkSysTvName uniq fs
818 co_kind = substTy subst (mkPredTy eq_pred)
820 -- make value vars, instantiating types
821 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
822 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
824 -- | Returns @Just (dc, [x1..xn])@ if the argument expression is
825 -- a constructor application of the form @dc x1 .. xn@
826 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
827 exprIsConApp_maybe (Cast expr co)
828 = -- Here we do the KPush reduction rule as described in the FC paper
829 case exprIsConApp_maybe expr of {
831 Just (dc, dc_args) ->
833 -- The transformation applies iff we have
834 -- (C e1 ... en) `cast` co
835 -- where co :: (T t1 .. tn) ~ (T s1 ..sn)
836 -- That is, with a T at the top of both sides
837 -- The left-hand one must be a T, because exprIsConApp returned True
838 -- but the right-hand one might not be. (Though it usually will.)
840 let (from_ty, to_ty) = coercionKind co
841 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
842 -- The inner one must be a TyConApp
844 case splitTyConApp_maybe to_ty of {
846 Just (to_tc, to_tc_arg_tys)
847 | from_tc /= to_tc -> Nothing
848 -- These two Nothing cases are possible; we might see
849 -- (C x y) `cast` (g :: T a ~ S [a]),
850 -- where S is a type function. In fact, exprIsConApp
851 -- will probably not be called in such circumstances,
852 -- but there't nothing wrong with it
856 tc_arity = tyConArity from_tc
858 (univ_args, rest1) = splitAt tc_arity dc_args
859 (ex_args, rest2) = splitAt n_ex_tvs rest1
860 (co_args_spec, rest3) = splitAt n_cos_spec rest2
861 (co_args_theta, val_args) = splitAt n_cos_theta rest3
863 arg_tys = dataConRepArgTys dc
864 dc_univ_tyvars = dataConUnivTyVars dc
865 dc_ex_tyvars = dataConExTyVars dc
866 dc_eq_spec = dataConEqSpec dc
867 dc_eq_theta = dataConEqTheta dc
868 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
869 n_ex_tvs = length dc_ex_tyvars
870 n_cos_spec = length dc_eq_spec
871 n_cos_theta = length dc_eq_theta
873 -- Make the "theta" from Fig 3 of the paper
874 gammas = decomposeCo tc_arity co
875 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
876 theta = zipOpenTvSubst dc_tyvars new_tys
878 -- First we cast the existential coercion arguments
879 cast_co_spec (tv, ty) co
880 = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
881 cast_co_theta eqPred (Type co)
882 | (ty1, ty2) <- getEqPredTys eqPred
883 = Type $ mkSymCoercion (substTy theta ty1)
885 `mkTransCoercion` (substTy theta ty2)
886 new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
887 zipWith cast_co_theta dc_eq_theta co_args_theta
889 -- ...and now value arguments
890 new_val_args = zipWith cast_arg arg_tys val_args
891 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
894 ASSERT( length univ_args == tc_arity )
895 ASSERT( from_tc == dataConTyCon dc )
896 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
897 ASSERT( all isTypeArg (univ_args ++ ex_args) )
898 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 )
900 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
904 -- We do not want to tell the world that we have a
905 -- Cons, to *stop* Case of Known Cons, which removes
907 exprIsConApp_maybe (Note (TickBox {}) expr)
909 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
913 exprIsConApp_maybe (Note _ expr)
914 = exprIsConApp_maybe expr
915 -- We ignore InlineMe notes in case we have
916 -- x = __inline_me__ (a,b)
917 -- All part of making sure that INLINE pragmas never hurt
918 -- Marcin tripped on this one when making dictionaries more inlinable
920 -- In fact, we ignore all notes. For example,
921 -- case _scc_ "foo" (C a b) of
923 -- should be optimised away, but it will be only if we look
924 -- through the SCC note.
926 exprIsConApp_maybe expr = analyse (collectArgs expr)
928 analyse (Var fun, args)
929 | Just con <- isDataConWorkId_maybe fun,
930 args `lengthAtLeast` dataConRepArity con
931 -- Might be > because the arity excludes type args
934 -- Look through unfoldings, but only cheap ones, because
935 -- we are effectively duplicating the unfolding
936 analyse (Var fun, [])
937 | let unf = idUnfolding fun,
938 isExpandableUnfolding unf
939 = exprIsConApp_maybe (unfoldingTemplate unf)
946 %************************************************************************
948 \subsection{Equality}
950 %************************************************************************
953 -- | A cheap equality test which bales out fast!
954 -- If it returns @True@ the arguments are definitely equal,
955 -- otherwise, they may or may not be equal.
957 -- See also 'exprIsBig'
958 cheapEqExpr :: Expr b -> Expr b -> Bool
960 cheapEqExpr (Var v1) (Var v2) = v1==v2
961 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
962 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
964 cheapEqExpr (App f1 a1) (App f2 a2)
965 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
967 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
968 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
970 cheapEqExpr _ _ = False
972 exprIsBig :: Expr b -> Bool
973 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
974 exprIsBig (Lit _) = False
975 exprIsBig (Var _) = False
976 exprIsBig (Type _) = False
977 exprIsBig (App f a) = exprIsBig f || exprIsBig a
978 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
984 %************************************************************************
986 \subsection{The size of an expression}
988 %************************************************************************
991 coreBindsSize :: [CoreBind] -> Int
992 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
994 exprSize :: CoreExpr -> Int
995 -- ^ A measure of the size of the expressions, strictly greater than 0
996 -- It also forces the expression pretty drastically as a side effect
997 exprSize (Var v) = v `seq` 1
998 exprSize (Lit lit) = lit `seq` 1
999 exprSize (App f a) = exprSize f + exprSize a
1000 exprSize (Lam b e) = varSize b + exprSize e
1001 exprSize (Let b e) = bindSize b + exprSize e
1002 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1003 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1004 exprSize (Note n e) = noteSize n + exprSize e
1005 exprSize (Type t) = seqType t `seq` 1
1007 noteSize :: Note -> Int
1008 noteSize (SCC cc) = cc `seq` 1
1009 noteSize InlineMe = 1
1010 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1012 varSize :: Var -> Int
1013 varSize b | isTyVar b = 1
1014 | otherwise = seqType (idType b) `seq`
1015 megaSeqIdInfo (idInfo b) `seq`
1018 varsSize :: [Var] -> Int
1019 varsSize = sum . map varSize
1021 bindSize :: CoreBind -> Int
1022 bindSize (NonRec b e) = varSize b + exprSize e
1023 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1025 pairSize :: (Var, CoreExpr) -> Int
1026 pairSize (b,e) = varSize b + exprSize e
1028 altSize :: CoreAlt -> Int
1029 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1033 %************************************************************************
1035 \subsection{Hashing}
1037 %************************************************************************
1040 hashExpr :: CoreExpr -> Int
1041 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1042 -- Two expressions that hash to the different Ints are definitely unequal.
1044 -- The emphasis is on a crude, fast hash, rather than on high precision.
1046 -- But unequal here means \"not identical\"; two alpha-equivalent
1047 -- expressions may hash to the different Ints.
1049 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1050 -- (at least if we want the above invariant to be true).
1052 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1053 -- UniqFM doesn't like negative Ints
1055 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1057 hash_expr :: HashEnv -> CoreExpr -> Word32
1058 -- Word32, because we're expecting overflows here, and overflowing
1059 -- signed types just isn't cool. In C it's even undefined.
1060 hash_expr env (Note _ e) = hash_expr env e
1061 hash_expr env (Cast e _) = hash_expr env e
1062 hash_expr env (Var v) = hashVar env v
1063 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1064 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1065 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1066 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1067 hash_expr env (Case e _ _ _) = hash_expr env e
1068 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1069 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1070 -- Shouldn't happen. Better to use WARN than trace, because trace
1071 -- prevents the CPR optimisation kicking in for hash_expr.
1073 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1074 fast_hash_expr env (Var v) = hashVar env v
1075 fast_hash_expr env (Type t) = fast_hash_type env t
1076 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1077 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1078 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1079 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1080 fast_hash_expr _ _ = 1
1082 fast_hash_type :: HashEnv -> Type -> Word32
1083 fast_hash_type env ty
1084 | Just tv <- getTyVar_maybe ty = hashVar env tv
1085 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1086 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1089 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1090 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1092 hashVar :: HashEnv -> Var -> Word32
1094 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1097 %************************************************************************
1099 \subsection{Determining non-updatable right-hand-sides}
1101 %************************************************************************
1103 Top-level constructor applications can usually be allocated
1104 statically, but they can't if the constructor, or any of the
1105 arguments, come from another DLL (because we can't refer to static
1106 labels in other DLLs).
1108 If this happens we simply make the RHS into an updatable thunk,
1109 and 'execute' it rather than allocating it statically.
1112 -- | This function is called only on *top-level* right-hand sides.
1113 -- Returns @True@ if the RHS can be allocated statically in the output,
1114 -- with no thunks involved at all.
1115 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1116 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1117 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1118 -- update flag on it and (iii) in DsExpr to decide how to expand
1121 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1122 -- (a) a value lambda
1123 -- (b) a saturated constructor application with static args
1125 -- BUT watch out for
1126 -- (i) Any cross-DLL references kill static-ness completely
1127 -- because they must be 'executed' not statically allocated
1128 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1129 -- this is not necessary)
1131 -- (ii) We treat partial applications as redexes, because in fact we
1132 -- make a thunk for them that runs and builds a PAP
1133 -- at run-time. The only appliations that are treated as
1134 -- static are *saturated* applications of constructors.
1136 -- We used to try to be clever with nested structures like this:
1137 -- ys = (:) w ((:) w [])
1138 -- on the grounds that CorePrep will flatten ANF-ise it later.
1139 -- But supporting this special case made the function much more
1140 -- complicated, because the special case only applies if there are no
1141 -- enclosing type lambdas:
1142 -- ys = /\ a -> Foo (Baz ([] a))
1143 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1145 -- But in fact, even without -O, nested structures at top level are
1146 -- flattened by the simplifier, so we don't need to be super-clever here.
1150 -- f = \x::Int. x+7 TRUE
1151 -- p = (True,False) TRUE
1153 -- d = (fst p, False) FALSE because there's a redex inside
1154 -- (this particular one doesn't happen but...)
1156 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1157 -- n = /\a. Nil a TRUE
1159 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1162 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1163 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1165 -- b) (C x xs), where C is a contructors is updatable if the application is
1168 -- c) don't look through unfolding of f in (f x).
1170 rhsIsStatic _this_pkg rhs = is_static False rhs
1172 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1175 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1177 is_static _ (Note (SCC _) _) = False
1178 is_static in_arg (Note _ e) = is_static in_arg e
1179 is_static in_arg (Cast e _) = is_static in_arg e
1181 is_static _ (Lit lit)
1183 MachLabel _ _ _ -> False
1185 -- A MachLabel (foreign import "&foo") in an argument
1186 -- prevents a constructor application from being static. The
1187 -- reason is that it might give rise to unresolvable symbols
1188 -- in the object file: under Linux, references to "weak"
1189 -- symbols from the data segment give rise to "unresolvable
1190 -- relocation" errors at link time This might be due to a bug
1191 -- in the linker, but we'll work around it here anyway.
1194 is_static in_arg other_expr = go other_expr 0
1196 go (Var f) n_val_args
1197 #if mingw32_TARGET_OS
1198 | not (isDllName _this_pkg (idName f))
1200 = saturated_data_con f n_val_args
1201 || (in_arg && n_val_args == 0)
1202 -- A naked un-applied variable is *not* deemed a static RHS
1204 -- Reason: better to update so that the indirection gets shorted
1205 -- out, and the true value will be seen
1206 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1207 -- are always updatable. If you do so, make sure that non-updatable
1208 -- ones have enough space for their static link field!
1210 go (App f a) n_val_args
1211 | isTypeArg a = go f n_val_args
1212 | not in_arg && is_static True a = go f (n_val_args + 1)
1213 -- The (not in_arg) checks that we aren't in a constructor argument;
1214 -- if we are, we don't allow (value) applications of any sort
1216 -- NB. In case you wonder, args are sometimes not atomic. eg.
1217 -- x = D# (1.0## /## 2.0##)
1218 -- can't float because /## can fail.
1220 go (Note (SCC _) _) _ = False
1221 go (Note _ f) n_val_args = go f n_val_args
1222 go (Cast e _) n_val_args = go e n_val_args
1226 saturated_data_con f n_val_args
1227 = case isDataConWorkId_maybe f of
1228 Just dc -> n_val_args == dataConRepArity dc