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,
41 -- * Manipulating data constructors and types
42 applyTypeToArgs, applyTypeToArg,
43 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
46 #include "HsVersions.h"
64 import TcType ( isPredTy )
80 %************************************************************************
82 \subsection{Find the type of a Core atom/expression}
84 %************************************************************************
87 exprType :: CoreExpr -> Type
88 -- ^ Recover the type of a well-typed Core expression. Fails when
89 -- applied to the actual 'CoreSyn.Type' expression as it cannot
90 -- really be said to have a type
91 exprType (Var var) = idType var
92 exprType (Lit lit) = literalType lit
93 exprType (Let _ body) = exprType body
94 exprType (Case _ _ ty _) = ty
95 exprType (Cast _ co) = snd (coercionKind co)
96 exprType (Note _ e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 -- ^ Returns the type of the alternatives right hand side
106 coreAltType (_,bs,rhs)
107 | any bad_binder bs = expandTypeSynonyms ty
108 | otherwise = ty -- Note [Existential variables and silly type synonyms]
111 free_tvs = tyVarsOfType ty
112 bad_binder b = isTyVar b && b `elemVarSet` free_tvs
114 coreAltsType :: [CoreAlt] -> Type
115 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
116 coreAltsType (alt:_) = coreAltType alt
117 coreAltsType [] = panic "corAltsType"
120 Note [Existential variables and silly type synonyms]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
123 data T = forall a. T (Funny a)
128 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
129 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
130 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
133 Various possibilities suggest themselves:
135 - Ignore the problem, and make Lint not complain about such variables
137 - Expand all type synonyms (or at least all those that discard arguments)
138 This is tricky, because at least for top-level things we want to
139 retain the type the user originally specified.
141 - Expand synonyms on the fly, when the problem arises. That is what
142 we are doing here. It's not too expensive, I think.
145 mkPiType :: Var -> Type -> Type
146 -- ^ Makes a @(->)@ type or a forall type, depending
147 -- on whether it is given a type variable or a term variable.
148 mkPiTypes :: [Var] -> Type -> Type
149 -- ^ 'mkPiType' for multiple type or value arguments
152 | isId v = mkFunTy (idType v) ty
153 | otherwise = mkForAllTy v ty
155 mkPiTypes vs ty = foldr mkPiType ty vs
159 applyTypeToArg :: Type -> CoreExpr -> Type
160 -- ^ Determines the type resulting from applying an expression to a function with the given type
161 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
162 applyTypeToArg fun_ty _ = funResultTy fun_ty
164 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
165 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
166 -- The first argument is just for debugging, and gives some context
167 applyTypeToArgs _ op_ty [] = op_ty
169 applyTypeToArgs e op_ty (Type ty : args)
170 = -- Accumulate type arguments so we can instantiate all at once
173 go rev_tys (Type ty : args) = go (ty:rev_tys) args
174 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
176 op_ty' = applyTysD msg op_ty (reverse rev_tys)
177 msg = ptext (sLit "applyTypeToArgs") <+>
180 applyTypeToArgs e op_ty (_ : args)
181 = case (splitFunTy_maybe op_ty) of
182 Just (_, res_ty) -> applyTypeToArgs e res_ty args
183 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
185 panic_msg :: CoreExpr -> Type -> SDoc
186 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
189 %************************************************************************
191 \subsection{Attaching notes}
193 %************************************************************************
196 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
197 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
199 mkCoerceI (ACo co) e = mkCoerce co e
201 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
202 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
203 mkCoerce co (Cast expr co2)
204 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
205 (_from_ty2, to_ty2) = coercionKind co2} in
206 from_ty `coreEqType` to_ty2 )
207 mkCoerce (mkTransCoercion co2 co) expr
210 = let (from_ty, _to_ty) = coercionKind co in
211 -- if to_ty `coreEqType` from_ty
214 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
219 -- | Wraps the given expression in the cost centre unless
220 -- in a way that maximises their utility to the user
221 mkSCC :: CostCentre -> Expr b -> Expr b
222 -- Note: Nested SCC's *are* preserved for the benefit of
223 -- cost centre stack profiling
224 mkSCC _ (Lit lit) = Lit lit
225 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
226 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
227 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
228 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
229 mkSCC cc expr = Note (SCC cc) expr
233 %************************************************************************
235 \subsection{Other expression construction}
237 %************************************************************************
240 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
241 -- ^ @bindNonRec x r b@ produces either:
247 -- > case r of x { _DEFAULT_ -> b }
249 -- depending on whether we have to use a @case@ or @let@
250 -- binding for the expression (see 'needsCaseBinding').
251 -- It's used by the desugarer to avoid building bindings
252 -- that give Core Lint a heart attack, although actually
253 -- the simplifier deals with them perfectly well. See
254 -- also 'MkCore.mkCoreLet'
255 bindNonRec bndr rhs body
256 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
257 | otherwise = Let (NonRec bndr rhs) body
259 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
260 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
261 needsCaseBinding :: Type -> CoreExpr -> Bool
262 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
263 -- Make a case expression instead of a let
264 -- These can arise either from the desugarer,
265 -- or from beta reductions: (\x.e) (x +# y)
269 mkAltExpr :: AltCon -- ^ Case alternative constructor
270 -> [CoreBndr] -- ^ Things bound by the pattern match
271 -> [Type] -- ^ The type arguments to the case alternative
273 -- ^ This guy constructs the value that the scrutinee must have
274 -- given that you are in one particular branch of a case
275 mkAltExpr (DataAlt con) args inst_tys
276 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
277 mkAltExpr (LitAlt lit) [] []
279 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
280 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
284 %************************************************************************
286 \subsection{Taking expressions apart}
288 %************************************************************************
290 The default alternative must be first, if it exists at all.
291 This makes it easy to find, though it makes matching marginally harder.
294 -- | Extract the default case alternative
295 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
296 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
297 findDefault alts = (alts, Nothing)
299 isDefaultAlt :: CoreAlt -> Bool
300 isDefaultAlt (DEFAULT, _, _) = True
301 isDefaultAlt _ = False
304 -- | Find the case alternative corresponding to a particular
305 -- constructor: panics if no such constructor exists
306 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
307 -- A "Nothing" result *is* legitmiate
308 -- See Note [Unreachable code]
311 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
315 go (alt@(con1,_,_) : alts) deflt
316 = case con `cmpAltCon` con1 of
317 LT -> deflt -- Missed it already; the alts are in increasing order
319 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
321 ---------------------------------
322 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
323 -- ^ Merge alternatives preserving order; alternatives in
324 -- the first argument shadow ones in the second
325 mergeAlts [] as2 = as2
326 mergeAlts as1 [] = as1
327 mergeAlts (a1:as1) (a2:as2)
328 = case a1 `cmpAlt` a2 of
329 LT -> a1 : mergeAlts as1 (a2:as2)
330 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
331 GT -> a2 : mergeAlts (a1:as1) as2
334 ---------------------------------
335 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
338 -- > case (C a b x y) of
341 -- We want to drop the leading type argument of the scrutinee
342 -- leaving the arguments to match agains the pattern
344 trimConArgs DEFAULT args = ASSERT( null args ) []
345 trimConArgs (LitAlt _) args = ASSERT( null args ) []
346 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
349 Note [Unreachable code]
350 ~~~~~~~~~~~~~~~~~~~~~~~
351 It is possible (although unusual) for GHC to find a case expression
352 that cannot match. For example:
354 data Col = Red | Green | Blue
358 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
360 Suppose that for some silly reason, x isn't substituted in the case
361 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
362 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
366 lvl = case x of { Green -> e1; Blue -> e2 })
371 Now if x gets inlined, we won't be able to find a matching alternative
372 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
373 we generate (error "Inaccessible alternative").
375 Similar things can happen (augmented by GADTs) when the Simplifier
376 filters down the matching alternatives in Simplify.rebuildCase.
379 %************************************************************************
383 %************************************************************************
387 @exprIsTrivial@ is true of expressions we are unconditionally happy to
388 duplicate; simple variables and constants, and type
389 applications. Note that primop Ids aren't considered
392 Note [Variable are trivial]
393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
394 There used to be a gruesome test for (hasNoBinding v) in the
396 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
397 The idea here is that a constructor worker, like \$wJust, is
398 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
399 So it should be treated like a lambda. Ditto unsaturated primops.
400 But now constructor workers are not "have-no-binding" Ids. And
401 completely un-applied primops and foreign-call Ids are sufficiently
402 rare that I plan to allow them to be duplicated and put up with
405 Note [SCCs are trivial]
406 ~~~~~~~~~~~~~~~~~~~~~~~
407 We used not to treat (_scc_ "foo" x) as trivial, because it really
408 generates code, (and a heap object when it's a function arg) to
409 capture the cost centre. However, the profiling system discounts the
410 allocation costs for such "boxing thunks" whereas the extra costs of
411 *not* inlining otherwise-trivial bindings can be high, and are hard to
415 exprIsTrivial :: CoreExpr -> Bool
416 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
417 exprIsTrivial (Type _) = True
418 exprIsTrivial (Lit lit) = litIsTrivial lit
419 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
420 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
421 exprIsTrivial (Cast e _) = exprIsTrivial e
422 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
423 exprIsTrivial _ = False
427 %************************************************************************
431 %************************************************************************
435 @exprIsDupable@ is true of expressions that can be duplicated at a modest
436 cost in code size. This will only happen in different case
437 branches, so there's no issue about duplicating work.
439 That is, exprIsDupable returns True of (f x) even if
440 f is very very expensive to call.
442 Its only purpose is to avoid fruitless let-binding
443 and then inlining of case join points
447 exprIsDupable :: CoreExpr -> Bool
448 exprIsDupable (Type _) = True
449 exprIsDupable (Var _) = True
450 exprIsDupable (Lit lit) = litIsDupable lit
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 %************************************************************************
468 exprIsCheap, exprIsExpandable
470 %************************************************************************
474 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
475 it is obviously in weak head normal form, or is cheap to get to WHNF.
476 [Note that that's not the same as exprIsDupable; an expression might be
477 big, and hence not dupable, but still cheap.]
479 By ``cheap'' we mean a computation we're willing to:
480 push inside a lambda, or
481 inline at more than one place
482 That might mean it gets evaluated more than once, instead of being
483 shared. The main examples of things which aren't WHNF but are
488 (where e, and all the ei are cheap)
491 (where e and b are cheap)
494 (where op is a cheap primitive operator)
497 (because we are happy to substitute it inside a lambda)
499 Notice that a variable is considered 'cheap': we can push it inside a lambda,
500 because sharing will make sure it is only evaluated once.
503 exprIsCheap :: CoreExpr -> Bool
504 exprIsCheap = exprIsCheap' isCheapApp
506 exprIsExpandable :: CoreExpr -> Bool
507 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
510 exprIsCheap' :: (Id -> Int -> Bool) -> CoreExpr -> Bool
511 exprIsCheap' _ (Lit _) = True
512 exprIsCheap' _ (Type _) = True
513 exprIsCheap' _ (Var _) = True
514 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
515 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
516 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
517 || exprIsCheap' good_app e
519 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
520 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
521 -- Experimentally, treat (case x of ...) as cheap
522 -- (and case __coerce x etc.)
523 -- This improves arities of overloaded functions where
524 -- there is only dictionary selection (no construction) involved
526 exprIsCheap' good_app (Let (NonRec x _) e)
527 | isUnLiftedType (idType x) = exprIsCheap' good_app e
529 -- Strict lets always have cheap right hand sides,
530 -- and do no allocation, so just look at the body
531 -- Non-strict lets do allocation so we don't treat them as cheap
533 exprIsCheap' good_app other_expr -- Applications and variables
536 -- Accumulate value arguments, then decide
537 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
538 | otherwise = go f val_args
540 go (Var _) [] = True -- Just a type application of a variable
541 -- (f t1 t2 t3) counts as WHNF
543 = case idDetails f of
544 RecSelId {} -> go_sel args
545 ClassOpId {} -> go_sel args
546 PrimOpId op -> go_primop op args
547 _ | good_app f (length args) -> go_pap args
548 | isBottomingId f -> True
550 -- Application of a function which
551 -- always gives bottom; we treat this as cheap
552 -- because it certainly doesn't need to be shared!
557 go_pap args = all exprIsTrivial args
558 -- For constructor applications and primops, check that all
559 -- the args are trivial. We don't want to treat as cheap, say,
561 -- We'll put up with one constructor application, but not dozens
564 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
565 -- In principle we should worry about primops
566 -- that return a type variable, since the result
567 -- might be applied to something, but I'm not going
568 -- to bother to check the number of args
571 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
572 go_sel _ = False -- look cheap, so we will substitute it inside a
573 -- lambda. Particularly for dictionary field selection.
574 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
575 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
577 isCheapApp :: Id -> Int -> Bool
578 isCheapApp fn n_val_args
580 || n_val_args < idArity fn
582 isExpandableApp :: Id -> Int -> Bool
583 isExpandableApp fn n_val_args
585 || n_val_args < idArity fn
586 || go n_val_args (idType fn)
588 -- See if all the arguments are PredTys (implicit params or classes)
589 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
592 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
593 | Just (arg, ty) <- splitFunTy_maybe ty
594 , isPredTy arg = go (n_val_args-1) ty
598 Note [Expandable overloadings]
599 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
600 Suppose the user wrote this
601 {-# RULE forall x. foo (negate x) = h x #-}
602 f x = ....(foo (negate x))....
603 He'd expect the rule to fire. But since negate is overloaded, we might
605 f = \d -> let n = negate d in \x -> ...foo (n x)...
606 So we treat the application of a function (negate in this case) to a
607 *dictionary* as expandable. In effect, every function is CONLIKE when
608 it's applied only to dictionaries.
611 %************************************************************************
615 %************************************************************************
618 -- | 'exprOkForSpeculation' returns True of an expression that is:
620 -- * Safe to evaluate even if normal order eval might not
621 -- evaluate the expression at all, or
623 -- * Safe /not/ to evaluate even if normal order would do so
625 -- Precisely, it returns @True@ iff:
627 -- * The expression guarantees to terminate,
631 -- * without raising an exception,
633 -- * without causing a side effect (e.g. writing a mutable variable)
635 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
636 -- As an example of the considerations in this test, consider:
638 -- > let x = case y# +# 1# of { r# -> I# r# }
641 -- being translated to:
643 -- > case y# +# 1# of { r# ->
648 -- We can only do this if the @y + 1@ is ok for speculation: it has no
649 -- side effects, and can't diverge or raise an exception.
650 exprOkForSpeculation :: CoreExpr -> Bool
651 exprOkForSpeculation (Lit _) = True
652 exprOkForSpeculation (Type _) = True
653 -- Tick boxes are *not* suitable for speculation
654 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
655 && not (isTickBoxOp v)
656 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
657 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
658 exprOkForSpeculation other_expr
659 = case collectArgs other_expr of
660 (Var f, args) -> spec_ok (idDetails f) args
664 spec_ok (DataConWorkId _) _
665 = True -- The strictness of the constructor has already
666 -- been expressed by its "wrapper", so we don't need
667 -- to take the arguments into account
669 spec_ok (PrimOpId op) args
670 | isDivOp op, -- Special case for dividing operations that fail
671 [arg1, Lit lit] <- args -- only if the divisor is zero
672 = not (isZeroLit lit) && exprOkForSpeculation arg1
673 -- Often there is a literal divisor, and this
674 -- can get rid of a thunk in an inner looop
677 = primOpOkForSpeculation op &&
678 all exprOkForSpeculation args
679 -- A bit conservative: we don't really need
680 -- to care about lazy arguments, but this is easy
682 spec_ok (DFunId new_type) _ = not new_type
683 -- DFuns terminate, unless the dict is implemented with a newtype
684 -- in which case they may not
688 -- | True of dyadic operators that can fail only if the second arg is zero!
689 isDivOp :: PrimOp -> Bool
690 -- This function probably belongs in PrimOp, or even in
691 -- an automagically generated file.. but it's such a
692 -- special case I thought I'd leave it here for now.
693 isDivOp IntQuotOp = True
694 isDivOp IntRemOp = True
695 isDivOp WordQuotOp = True
696 isDivOp WordRemOp = True
697 isDivOp FloatDivOp = True
698 isDivOp DoubleDivOp = True
702 %************************************************************************
704 exprIsHNF, exprIsConLike
706 %************************************************************************
711 -- | exprIsHNF returns true for expressions that are certainly /already/
712 -- evaluated to /head/ normal form. This is used to decide whether it's ok
715 -- > case x of _ -> e
721 -- and to decide whether it's safe to discard a 'seq'.
723 -- So, it does /not/ treat variables as evaluated, unless they say they are.
724 -- However, it /does/ treat partial applications and constructor applications
725 -- as values, even if their arguments are non-trivial, provided the argument
726 -- type is lifted. For example, both of these are values:
728 -- > (:) (f x) (map f xs)
729 -- > map (...redex...)
731 -- because 'seq' on such things completes immediately.
733 -- For unlifted argument types, we have to be careful:
737 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
738 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
739 -- unboxed type must be ok-for-speculation (or trivial).
740 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
741 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
745 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
746 -- data constructors. Conlike arguments are considered interesting by the
748 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
749 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
751 -- | Returns true for values or value-like expressions. These are lambdas,
752 -- constructors / CONLIKE functions (as determined by the function argument)
755 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
756 exprIsHNFlike is_con is_con_unf = is_hnf_like
758 is_hnf_like (Var v) -- NB: There are no value args at this point
759 = is_con v -- Catches nullary constructors,
760 -- so that [] and () are values, for example
761 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
762 || is_con_unf (idUnfolding v)
763 -- Check the thing's unfolding; it might be bound to a value
764 -- We don't look through loop breakers here, which is a bit conservative
765 -- but otherwise I worry that if an Id's unfolding is just itself,
766 -- we could get an infinite loop
768 is_hnf_like (Lit _) = True
769 is_hnf_like (Type _) = True -- Types are honorary Values;
770 -- we don't mind copying them
771 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
772 is_hnf_like (Note _ e) = is_hnf_like e
773 is_hnf_like (Cast e _) = is_hnf_like e
774 is_hnf_like (App e (Type _)) = is_hnf_like e
775 is_hnf_like (App e a) = app_is_value e [a]
776 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
777 is_hnf_like _ = False
779 -- There is at least one value argument
780 app_is_value :: CoreExpr -> [CoreArg] -> Bool
781 app_is_value (Var fun) args
782 = idArity fun > valArgCount args -- Under-applied function
783 || is_con fun -- or constructor-like
784 app_is_value (Note _ f) as = app_is_value f as
785 app_is_value (Cast f _) as = app_is_value f as
786 app_is_value (App f a) as = app_is_value f (a:as)
787 app_is_value _ _ = False
791 %************************************************************************
793 Instantiating data constructors
795 %************************************************************************
797 These InstPat functions go here to avoid circularity between DataCon and Id
800 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
801 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
803 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
804 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
805 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
807 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
808 -- Remember to include the existential dictionaries
810 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
811 -> [FastString] -- A long enough list of FSs to use for names
812 -> [Unique] -- An equally long list of uniques, at least one for each binder
814 -> [Type] -- Types to instantiate the universally quantified tyvars
815 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
816 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
817 -- (ex_tvs, co_tvs, arg_ids),
819 -- ex_tvs are intended to be used as binders for existential type args
821 -- co_tvs are intended to be used as binders for coercion args and the kinds
822 -- of these vars have been instantiated by the inst_tys and the ex_tys
823 -- The co_tvs include both GADT equalities (dcEqSpec) and
824 -- programmer-specified equalities (dcEqTheta)
826 -- arg_ids are indended to be used as binders for value arguments,
827 -- and their types have been instantiated with inst_tys and ex_tys
828 -- The arg_ids include both dicts (dcDictTheta) and
829 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
832 -- The following constructor T1
835 -- T1 :: forall b. Int -> b -> T(a,b)
838 -- has representation type
839 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
842 -- dataConInstPat fss us T1 (a1',b') will return
844 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
846 -- where the double-primed variables are created with the FastStrings and
847 -- Uniques given as fss and us
848 dataConInstPat arg_fun fss uniqs con inst_tys
849 = (ex_bndrs, co_bndrs, arg_ids)
851 univ_tvs = dataConUnivTyVars con
852 ex_tvs = dataConExTyVars con
853 arg_tys = arg_fun con
854 eq_spec = dataConEqSpec con
855 eq_theta = dataConEqTheta con
856 eq_preds = eqSpecPreds eq_spec ++ eq_theta
859 n_co = length eq_preds
861 -- split the Uniques and FastStrings
862 (ex_uniqs, uniqs') = splitAt n_ex uniqs
863 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
865 (ex_fss, fss') = splitAt n_ex fss
866 (co_fss, id_fss) = splitAt n_co fss'
868 -- Make existential type variables
869 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
870 mk_ex_var uniq fs var = mkTyVar new_name kind
872 new_name = mkSysTvName uniq fs
875 -- Make the instantiating substitution
876 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
878 -- Make new coercion vars, instantiating kind
879 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
880 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
882 new_name = mkSysTvName uniq fs
883 co_kind = substTy subst (mkPredTy eq_pred)
885 -- make value vars, instantiating types
886 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
887 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
891 %************************************************************************
895 %************************************************************************
898 -- | A cheap equality test which bales out fast!
899 -- If it returns @True@ the arguments are definitely equal,
900 -- otherwise, they may or may not be equal.
902 -- See also 'exprIsBig'
903 cheapEqExpr :: Expr b -> Expr b -> Bool
905 cheapEqExpr (Var v1) (Var v2) = v1==v2
906 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
907 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
909 cheapEqExpr (App f1 a1) (App f2 a2)
910 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
912 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
913 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
915 cheapEqExpr _ _ = False
917 exprIsBig :: Expr b -> Bool
918 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
919 exprIsBig (Lit _) = False
920 exprIsBig (Var _) = False
921 exprIsBig (Type _) = False
922 exprIsBig (Lam _ e) = exprIsBig e
923 exprIsBig (App f a) = exprIsBig f || exprIsBig a
924 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
930 %************************************************************************
932 \subsection{The size of an expression}
934 %************************************************************************
937 coreBindsSize :: [CoreBind] -> Int
938 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
940 exprSize :: CoreExpr -> Int
941 -- ^ A measure of the size of the expressions, strictly greater than 0
942 -- It also forces the expression pretty drastically as a side effect
943 exprSize (Var v) = v `seq` 1
944 exprSize (Lit lit) = lit `seq` 1
945 exprSize (App f a) = exprSize f + exprSize a
946 exprSize (Lam b e) = varSize b + exprSize e
947 exprSize (Let b e) = bindSize b + exprSize e
948 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
949 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
950 exprSize (Note n e) = noteSize n + exprSize e
951 exprSize (Type t) = seqType t `seq` 1
953 noteSize :: Note -> Int
954 noteSize (SCC cc) = cc `seq` 1
955 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
957 varSize :: Var -> Int
958 varSize b | isTyVar b = 1
959 | otherwise = seqType (idType b) `seq`
960 megaSeqIdInfo (idInfo b) `seq`
963 varsSize :: [Var] -> Int
964 varsSize = sum . map varSize
966 bindSize :: CoreBind -> Int
967 bindSize (NonRec b e) = varSize b + exprSize e
968 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
970 pairSize :: (Var, CoreExpr) -> Int
971 pairSize (b,e) = varSize b + exprSize e
973 altSize :: CoreAlt -> Int
974 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
978 %************************************************************************
982 %************************************************************************
985 hashExpr :: CoreExpr -> Int
986 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
987 -- Two expressions that hash to the different Ints are definitely unequal.
989 -- The emphasis is on a crude, fast hash, rather than on high precision.
991 -- But unequal here means \"not identical\"; two alpha-equivalent
992 -- expressions may hash to the different Ints.
994 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
995 -- (at least if we want the above invariant to be true).
997 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
998 -- UniqFM doesn't like negative Ints
1000 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1002 hash_expr :: HashEnv -> CoreExpr -> Word32
1003 -- Word32, because we're expecting overflows here, and overflowing
1004 -- signed types just isn't cool. In C it's even undefined.
1005 hash_expr env (Note _ e) = hash_expr env e
1006 hash_expr env (Cast e _) = hash_expr env e
1007 hash_expr env (Var v) = hashVar env v
1008 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1009 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1010 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1011 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1012 hash_expr env (Case e _ _ _) = hash_expr env e
1013 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1014 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1015 -- Shouldn't happen. Better to use WARN than trace, because trace
1016 -- prevents the CPR optimisation kicking in for hash_expr.
1018 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1019 fast_hash_expr env (Var v) = hashVar env v
1020 fast_hash_expr env (Type t) = fast_hash_type env t
1021 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1022 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1023 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1024 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1025 fast_hash_expr _ _ = 1
1027 fast_hash_type :: HashEnv -> Type -> Word32
1028 fast_hash_type env ty
1029 | Just tv <- getTyVar_maybe ty = hashVar env tv
1030 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1031 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1034 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1035 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1037 hashVar :: HashEnv -> Var -> Word32
1039 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1042 %************************************************************************
1044 \subsection{Determining non-updatable right-hand-sides}
1046 %************************************************************************
1048 Top-level constructor applications can usually be allocated
1049 statically, but they can't if the constructor, or any of the
1050 arguments, come from another DLL (because we can't refer to static
1051 labels in other DLLs).
1053 If this happens we simply make the RHS into an updatable thunk,
1054 and 'execute' it rather than allocating it statically.
1057 -- | This function is called only on *top-level* right-hand sides.
1058 -- Returns @True@ if the RHS can be allocated statically in the output,
1059 -- with no thunks involved at all.
1060 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1061 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1062 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1063 -- update flag on it and (iii) in DsExpr to decide how to expand
1066 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1067 -- (a) a value lambda
1068 -- (b) a saturated constructor application with static args
1070 -- BUT watch out for
1071 -- (i) Any cross-DLL references kill static-ness completely
1072 -- because they must be 'executed' not statically allocated
1073 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1074 -- this is not necessary)
1076 -- (ii) We treat partial applications as redexes, because in fact we
1077 -- make a thunk for them that runs and builds a PAP
1078 -- at run-time. The only appliations that are treated as
1079 -- static are *saturated* applications of constructors.
1081 -- We used to try to be clever with nested structures like this:
1082 -- ys = (:) w ((:) w [])
1083 -- on the grounds that CorePrep will flatten ANF-ise it later.
1084 -- But supporting this special case made the function much more
1085 -- complicated, because the special case only applies if there are no
1086 -- enclosing type lambdas:
1087 -- ys = /\ a -> Foo (Baz ([] a))
1088 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1090 -- But in fact, even without -O, nested structures at top level are
1091 -- flattened by the simplifier, so we don't need to be super-clever here.
1095 -- f = \x::Int. x+7 TRUE
1096 -- p = (True,False) TRUE
1098 -- d = (fst p, False) FALSE because there's a redex inside
1099 -- (this particular one doesn't happen but...)
1101 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1102 -- n = /\a. Nil a TRUE
1104 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1107 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1108 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1110 -- b) (C x xs), where C is a contructor is updatable if the application is
1113 -- c) don't look through unfolding of f in (f x).
1115 rhsIsStatic _this_pkg rhs = is_static False rhs
1117 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1120 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1122 is_static _ (Note (SCC _) _) = False
1123 is_static in_arg (Note _ e) = is_static in_arg e
1124 is_static in_arg (Cast e _) = is_static in_arg e
1126 is_static _ (Lit lit)
1128 MachLabel _ _ _ -> False
1130 -- A MachLabel (foreign import "&foo") in an argument
1131 -- prevents a constructor application from being static. The
1132 -- reason is that it might give rise to unresolvable symbols
1133 -- in the object file: under Linux, references to "weak"
1134 -- symbols from the data segment give rise to "unresolvable
1135 -- relocation" errors at link time This might be due to a bug
1136 -- in the linker, but we'll work around it here anyway.
1139 is_static in_arg other_expr = go other_expr 0
1141 go (Var f) n_val_args
1142 #if mingw32_TARGET_OS
1143 | not (isDllName _this_pkg (idName f))
1145 = saturated_data_con f n_val_args
1146 || (in_arg && n_val_args == 0)
1147 -- A naked un-applied variable is *not* deemed a static RHS
1149 -- Reason: better to update so that the indirection gets shorted
1150 -- out, and the true value will be seen
1151 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1152 -- are always updatable. If you do so, make sure that non-updatable
1153 -- ones have enough space for their static link field!
1155 go (App f a) n_val_args
1156 | isTypeArg a = go f n_val_args
1157 | not in_arg && is_static True a = go f (n_val_args + 1)
1158 -- The (not in_arg) checks that we aren't in a constructor argument;
1159 -- if we are, we don't allow (value) applications of any sort
1161 -- NB. In case you wonder, args are sometimes not atomic. eg.
1162 -- x = D# (1.0## /## 2.0##)
1163 -- can't float because /## can fail.
1165 go (Note (SCC _) _) _ = False
1166 go (Note _ f) n_val_args = go f n_val_args
1167 go (Cast e _) n_val_args = go e n_val_args
1171 saturated_data_con f n_val_args
1172 = case isDataConWorkId_maybe f of
1173 Just dc -> n_val_args == dataConRepArity dc