2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Commonly useful utilites for manipulating the Core language
18 -- * Constructing expressions
19 mkSCC, mkCoerce, mkCoerceI,
20 bindNonRec, needsCaseBinding,
21 mkAltExpr, mkPiType, mkPiTypes,
23 -- * Taking expressions apart
24 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
26 -- * Properties of expressions
27 exprType, coreAltType, coreAltsType,
28 exprIsDupable, exprIsTrivial, exprIsBottom,
29 exprIsCheap, exprIsExpandable, exprIsCheap', CheapAppFun,
30 exprIsHNF, exprOkForSpeculation, exprIsBig, exprIsConLike,
31 rhsIsStatic, isCheapApp, isExpandableApp,
33 -- * Expression and bindings size
34 coreBindsSize, exprSize,
40 cheapEqExpr, eqExpr, eqExprX,
45 -- * Manipulating data constructors and types
46 applyTypeToArgs, applyTypeToArg,
47 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
50 #include "HsVersions.h"
64 import TcType ( isPredTy )
80 %************************************************************************
82 \subsection{Find the type of a Core atom/expression}
84 %************************************************************************
87 exprType :: CoreExpr -> Type
88 -- ^ Recover the type of a well-typed Core expression. Fails when
89 -- applied to the actual 'CoreSyn.Type' expression as it cannot
90 -- really be said to have a type
91 exprType (Var var) = idType var
92 exprType (Lit lit) = literalType lit
93 exprType (Let _ body) = exprType body
94 exprType (Case _ _ ty _) = ty
95 exprType (Cast _ co) = snd (coercionKind co)
96 exprType (Note _ e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 -- ^ Returns the type of the alternatives right hand side
106 coreAltType (_,bs,rhs)
107 | any bad_binder bs = expandTypeSynonyms ty
108 | otherwise = ty -- Note [Existential variables and silly type synonyms]
111 free_tvs = tyVarsOfType ty
112 bad_binder b = isTyCoVar b && b `elemVarSet` free_tvs
114 coreAltsType :: [CoreAlt] -> Type
115 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
116 coreAltsType (alt:_) = coreAltType alt
117 coreAltsType [] = panic "corAltsType"
120 Note [Existential variables and silly type synonyms]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
123 data T = forall a. T (Funny a)
128 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
129 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
130 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
133 Various possibilities suggest themselves:
135 - Ignore the problem, and make Lint not complain about such variables
137 - Expand all type synonyms (or at least all those that discard arguments)
138 This is tricky, because at least for top-level things we want to
139 retain the type the user originally specified.
141 - Expand synonyms on the fly, when the problem arises. That is what
142 we are doing here. It's not too expensive, I think.
145 mkPiType :: EvVar -> Type -> Type
146 -- ^ Makes a @(->)@ type or a forall type, depending
147 -- on whether it is given a type variable or a term variable.
148 mkPiTypes :: [EvVar] -> Type -> Type
149 -- ^ 'mkPiType' for multiple type or value arguments
152 | isId v = mkFunTy (idType v) ty
153 | otherwise = mkForAllTy v ty
155 mkPiTypes vs ty = foldr mkPiType ty vs
159 applyTypeToArg :: Type -> CoreExpr -> Type
160 -- ^ Determines the type resulting from applying an expression to a function with the given type
161 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
162 applyTypeToArg fun_ty _ = funResultTy fun_ty
164 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
165 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
166 -- The first argument is just for debugging, and gives some context
167 applyTypeToArgs _ op_ty [] = op_ty
169 applyTypeToArgs e op_ty (Type ty : args)
170 = -- Accumulate type arguments so we can instantiate all at once
173 go rev_tys (Type ty : args) = go (ty:rev_tys) args
174 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
176 op_ty' = applyTysD msg op_ty (reverse rev_tys)
177 msg = ptext (sLit "applyTypeToArgs") <+>
180 applyTypeToArgs e op_ty (_ : args)
181 = case (splitFunTy_maybe op_ty) of
182 Just (_, res_ty) -> applyTypeToArgs e res_ty args
183 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
185 panic_msg :: CoreExpr -> Type -> SDoc
186 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
189 %************************************************************************
191 \subsection{Attaching notes}
193 %************************************************************************
196 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
197 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
198 mkCoerceI (IdCo _) e = e
199 mkCoerceI (ACo co) e = mkCoerce co e
201 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
202 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
203 mkCoerce co (Cast expr co2)
204 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
205 (_from_ty2, to_ty2) = coercionKind co2} in
206 from_ty `coreEqType` to_ty2 )
207 mkCoerce (mkTransCoercion co2 co) expr
210 = let (from_ty, _to_ty) = coercionKind co in
211 -- if to_ty `coreEqType` from_ty
214 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
219 -- | Wraps the given expression in the cost centre unless
220 -- in a way that maximises their utility to the user
221 mkSCC :: CostCentre -> Expr b -> Expr b
222 -- Note: Nested SCC's *are* preserved for the benefit of
223 -- cost centre stack profiling
224 mkSCC _ (Lit lit) = Lit lit
225 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
226 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
227 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
228 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
229 mkSCC cc expr = Note (SCC cc) expr
233 %************************************************************************
235 \subsection{Other expression construction}
237 %************************************************************************
240 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
241 -- ^ @bindNonRec x r b@ produces either:
247 -- > case r of x { _DEFAULT_ -> b }
249 -- depending on whether we have to use a @case@ or @let@
250 -- binding for the expression (see 'needsCaseBinding').
251 -- It's used by the desugarer to avoid building bindings
252 -- that give Core Lint a heart attack, although actually
253 -- the simplifier deals with them perfectly well. See
254 -- also 'MkCore.mkCoreLet'
255 bindNonRec bndr rhs body
256 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
257 | otherwise = Let (NonRec bndr rhs) body
259 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
260 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
261 needsCaseBinding :: Type -> CoreExpr -> Bool
262 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
263 -- Make a case expression instead of a let
264 -- These can arise either from the desugarer,
265 -- or from beta reductions: (\x.e) (x +# y)
269 mkAltExpr :: AltCon -- ^ Case alternative constructor
270 -> [CoreBndr] -- ^ Things bound by the pattern match
271 -> [Type] -- ^ The type arguments to the case alternative
273 -- ^ This guy constructs the value that the scrutinee must have
274 -- given that you are in one particular branch of a case
275 mkAltExpr (DataAlt con) args inst_tys
276 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
277 mkAltExpr (LitAlt lit) [] []
279 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
280 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
284 %************************************************************************
286 \subsection{Taking expressions apart}
288 %************************************************************************
290 The default alternative must be first, if it exists at all.
291 This makes it easy to find, though it makes matching marginally harder.
294 -- | Extract the default case alternative
295 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
296 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
297 findDefault alts = (alts, Nothing)
299 isDefaultAlt :: CoreAlt -> Bool
300 isDefaultAlt (DEFAULT, _, _) = True
301 isDefaultAlt _ = False
304 -- | Find the case alternative corresponding to a particular
305 -- constructor: panics if no such constructor exists
306 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
307 -- A "Nothing" result *is* legitmiate
308 -- See Note [Unreachable code]
311 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
315 go (alt@(con1,_,_) : alts) deflt
316 = case con `cmpAltCon` con1 of
317 LT -> deflt -- Missed it already; the alts are in increasing order
319 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
321 ---------------------------------
322 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
323 -- ^ Merge alternatives preserving order; alternatives in
324 -- the first argument shadow ones in the second
325 mergeAlts [] as2 = as2
326 mergeAlts as1 [] = as1
327 mergeAlts (a1:as1) (a2:as2)
328 = case a1 `cmpAlt` a2 of
329 LT -> a1 : mergeAlts as1 (a2:as2)
330 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
331 GT -> a2 : mergeAlts (a1:as1) as2
334 ---------------------------------
335 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
338 -- > case (C a b x y) of
341 -- We want to drop the leading type argument of the scrutinee
342 -- leaving the arguments to match agains the pattern
344 trimConArgs DEFAULT args = ASSERT( null args ) []
345 trimConArgs (LitAlt _) args = ASSERT( null args ) []
346 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
349 Note [Unreachable code]
350 ~~~~~~~~~~~~~~~~~~~~~~~
351 It is possible (although unusual) for GHC to find a case expression
352 that cannot match. For example:
354 data Col = Red | Green | Blue
358 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
360 Suppose that for some silly reason, x isn't substituted in the case
361 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
362 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
366 lvl = case x of { Green -> e1; Blue -> e2 })
371 Now if x gets inlined, we won't be able to find a matching alternative
372 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
373 we generate (error "Inaccessible alternative").
375 Similar things can happen (augmented by GADTs) when the Simplifier
376 filters down the matching alternatives in Simplify.rebuildCase.
379 %************************************************************************
383 %************************************************************************
387 @exprIsTrivial@ is true of expressions we are unconditionally happy to
388 duplicate; simple variables and constants, and type
389 applications. Note that primop Ids aren't considered
392 Note [Variable are trivial]
393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
394 There used to be a gruesome test for (hasNoBinding v) in the
396 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
397 The idea here is that a constructor worker, like \$wJust, is
398 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
399 So it should be treated like a lambda. Ditto unsaturated primops.
400 But now constructor workers are not "have-no-binding" Ids. And
401 completely un-applied primops and foreign-call Ids are sufficiently
402 rare that I plan to allow them to be duplicated and put up with
405 Note [SCCs are trivial]
406 ~~~~~~~~~~~~~~~~~~~~~~~
407 We used not to treat (_scc_ "foo" x) as trivial, because it really
408 generates code, (and a heap object when it's a function arg) to
409 capture the cost centre. However, the profiling system discounts the
410 allocation costs for such "boxing thunks" whereas the extra costs of
411 *not* inlining otherwise-trivial bindings can be high, and are hard to
415 exprIsTrivial :: CoreExpr -> Bool
416 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
417 exprIsTrivial (Type _) = True
418 exprIsTrivial (Lit lit) = litIsTrivial lit
419 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
420 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
421 exprIsTrivial (Cast e _) = exprIsTrivial e
422 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
423 exprIsTrivial _ = False
426 exprIsBottom is a very cheap and cheerful function; it may return
427 False for bottoming expressions, but it never costs much to ask.
428 See also CoreArity.exprBotStrictness_maybe, but that's a bit more
432 exprIsBottom :: CoreExpr -> Bool
436 go n (Var v) = isBottomingId v && n >= idArity v
437 go n (App e a) | isTypeArg a = go n e
438 | otherwise = go (n+1) e
439 go n (Note _ e) = go n e
440 go n (Cast e _) = go n e
441 go n (Let _ e) = go n e
446 %************************************************************************
450 %************************************************************************
454 @exprIsDupable@ is true of expressions that can be duplicated at a modest
455 cost in code size. This will only happen in different case
456 branches, so there's no issue about duplicating work.
458 That is, exprIsDupable returns True of (f x) even if
459 f is very very expensive to call.
461 Its only purpose is to avoid fruitless let-binding
462 and then inlining of case join points
466 exprIsDupable :: CoreExpr -> Bool
468 = isJust (go dupAppSize e)
470 go :: Int -> CoreExpr -> Maybe Int
471 go n (Type {}) = Just n
472 go n (Var {}) = decrement n
473 go n (Note _ e) = go n e
474 go n (Cast e _) = go n e
475 go n (App f a) | Just n' <- go n a = go n' f
476 go n (Lit lit) | litIsDupable lit = decrement n
479 decrement :: Int -> Maybe Int
480 decrement 0 = Nothing
481 decrement n = Just (n-1)
484 dupAppSize = 6 -- Size of term we are prepared to duplicate
487 %************************************************************************
489 exprIsCheap, exprIsExpandable
491 %************************************************************************
493 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
494 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
495 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
496 it is obviously in weak head normal form, or is cheap to get to WHNF.
497 [Note that that's not the same as exprIsDupable; an expression might be
498 big, and hence not dupable, but still cheap.]
500 By ``cheap'' we mean a computation we're willing to:
501 push inside a lambda, or
502 inline at more than one place
503 That might mean it gets evaluated more than once, instead of being
504 shared. The main examples of things which aren't WHNF but are
509 (where e, and all the ei are cheap)
512 (where e and b are cheap)
515 (where op is a cheap primitive operator)
518 (because we are happy to substitute it inside a lambda)
520 Notice that a variable is considered 'cheap': we can push it inside a lambda,
521 because sharing will make sure it is only evaluated once.
523 Note [exprIsCheap and exprIsHNF]
524 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
525 Note that exprIsHNF does not imply exprIsCheap. Eg
526 let x = fac 20 in Just x
527 This responds True to exprIsHNF (you can discard a seq), but
528 False to exprIsCheap.
531 exprIsCheap :: CoreExpr -> Bool
532 exprIsCheap = exprIsCheap' isCheapApp
534 exprIsExpandable :: CoreExpr -> Bool
535 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
537 type CheapAppFun = Id -> Int -> Bool
538 exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
539 exprIsCheap' _ (Lit _) = True
540 exprIsCheap' _ (Type _) = True
541 exprIsCheap' _ (Var _) = True
542 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
543 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
544 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
545 || exprIsCheap' good_app e
547 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
548 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
549 -- Experimentally, treat (case x of ...) as cheap
550 -- (and case __coerce x etc.)
551 -- This improves arities of overloaded functions where
552 -- there is only dictionary selection (no construction) involved
554 exprIsCheap' good_app (Let (NonRec x _) e)
555 | isUnLiftedType (idType x) = exprIsCheap' good_app e
557 -- Strict lets always have cheap right hand sides,
558 -- and do no allocation, so just look at the body
559 -- Non-strict lets do allocation so we don't treat them as cheap
562 exprIsCheap' good_app other_expr -- Applications and variables
565 -- Accumulate value arguments, then decide
566 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
567 | otherwise = go f val_args
569 go (Var _) [] = True -- Just a type application of a variable
570 -- (f t1 t2 t3) counts as WHNF
572 = case idDetails f of
573 RecSelId {} -> go_sel args
574 ClassOpId {} -> go_sel args
575 PrimOpId op -> go_primop op args
576 _ | good_app f (length args) -> go_pap args
577 | isBottomingId f -> True
579 -- Application of a function which
580 -- always gives bottom; we treat this as cheap
581 -- because it certainly doesn't need to be shared!
586 go_pap args = all exprIsTrivial args
587 -- For constructor applications and primops, check that all
588 -- the args are trivial. We don't want to treat as cheap, say,
590 -- We'll put up with one constructor application, but not dozens
593 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
594 -- In principle we should worry about primops
595 -- that return a type variable, since the result
596 -- might be applied to something, but I'm not going
597 -- to bother to check the number of args
600 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
601 go_sel _ = False -- look cheap, so we will substitute it inside a
602 -- lambda. Particularly for dictionary field selection.
603 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
604 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
606 isCheapApp :: CheapAppFun
607 isCheapApp fn n_val_args
609 || n_val_args < idArity fn
611 isExpandableApp :: CheapAppFun
612 isExpandableApp fn n_val_args
614 || n_val_args < idArity fn
615 || go n_val_args (idType fn)
617 -- See if all the arguments are PredTys (implicit params or classes)
618 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
621 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
622 | Just (arg, ty) <- splitFunTy_maybe ty
623 , isPredTy arg = go (n_val_args-1) ty
627 Note [Expandable overloadings]
628 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
629 Suppose the user wrote this
630 {-# RULE forall x. foo (negate x) = h x #-}
631 f x = ....(foo (negate x))....
632 He'd expect the rule to fire. But since negate is overloaded, we might
634 f = \d -> let n = negate d in \x -> ...foo (n x)...
635 So we treat the application of a function (negate in this case) to a
636 *dictionary* as expandable. In effect, every function is CONLIKE when
637 it's applied only to dictionaries.
640 %************************************************************************
644 %************************************************************************
647 -- | 'exprOkForSpeculation' returns True of an expression that is:
649 -- * Safe to evaluate even if normal order eval might not
650 -- evaluate the expression at all, or
652 -- * Safe /not/ to evaluate even if normal order would do so
654 -- It is usually called on arguments of unlifted type, but not always
655 -- In particular, Simplify.rebuildCase calls it on lifted types
656 -- when a 'case' is a plain 'seq'. See the example in
657 -- Note [exprOkForSpeculation: case expressions] below
659 -- Precisely, it returns @True@ iff:
661 -- * The expression guarantees to terminate,
663 -- * without raising an exception,
664 -- * without causing a side effect (e.g. writing a mutable variable)
666 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
667 -- As an example of the considerations in this test, consider:
669 -- > let x = case y# +# 1# of { r# -> I# r# }
672 -- being translated to:
674 -- > case y# +# 1# of { r# ->
679 -- We can only do this if the @y + 1@ is ok for speculation: it has no
680 -- side effects, and can't diverge or raise an exception.
681 exprOkForSpeculation :: CoreExpr -> Bool
682 exprOkForSpeculation (Lit _) = True
683 exprOkForSpeculation (Type _) = True
685 exprOkForSpeculation (Var v)
686 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
687 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
688 || isDataConWorkId v -- Nullary constructors
689 || idArity v > 0 -- Functions
690 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
692 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
693 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
695 exprOkForSpeculation (Case e _ _ alts)
696 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
697 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
699 exprOkForSpeculation other_expr
700 = case collectArgs other_expr of
701 (Var f, args) -> spec_ok (idDetails f) args
705 spec_ok (DataConWorkId _) _
706 = True -- The strictness of the constructor has already
707 -- been expressed by its "wrapper", so we don't need
708 -- to take the arguments into account
710 spec_ok (PrimOpId op) args
711 | isDivOp op, -- Special case for dividing operations that fail
712 [arg1, Lit lit] <- args -- only if the divisor is zero
713 = not (isZeroLit lit) && exprOkForSpeculation arg1
714 -- Often there is a literal divisor, and this
715 -- can get rid of a thunk in an inner looop
717 | DataToTagOp <- op -- See Note [dataToTag speculation]
721 = primOpOkForSpeculation op &&
722 all exprOkForSpeculation args
723 -- A bit conservative: we don't really need
724 -- to care about lazy arguments, but this is easy
726 spec_ok (DFunId _ new_type) _ = not new_type
727 -- DFuns terminate, unless the dict is implemented with a newtype
728 -- in which case they may not
732 -- | True of dyadic operators that can fail only if the second arg is zero!
733 isDivOp :: PrimOp -> Bool
734 -- This function probably belongs in PrimOp, or even in
735 -- an automagically generated file.. but it's such a
736 -- special case I thought I'd leave it here for now.
737 isDivOp IntQuotOp = True
738 isDivOp IntRemOp = True
739 isDivOp WordQuotOp = True
740 isDivOp WordRemOp = True
741 isDivOp FloatDivOp = True
742 isDivOp DoubleDivOp = True
746 Note [exprOkForSpeculation: case expressions]
747 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
748 It's always sound for exprOkForSpeculation to return False, and we
749 don't want it to take too long, so it bales out on complicated-looking
750 terms. Notably lets, which can be stacked very deeply; and in any
751 case the argument of exprOkForSpeculation is usually in a strict context,
752 so any lets will have been floated away.
754 However, we keep going on case-expressions. An example like this one
755 showed up in DPH code (Trac #3717):
758 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
760 If exprOkForSpeculation doesn't look through case expressions, you get this:
762 \ (ww :: GHC.Prim.Int#) ->
764 __DEFAULT -> case (case <# ds 5 of _ {
765 GHC.Types.False -> lvl1;
766 GHC.Types.True -> lvl})
768 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
772 The inner case is redundant, and should be nuked.
774 Note [dataToTag speculation]
775 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
777 f x = let v::Int# = dataToTag# x
779 We say "yes", even though 'x' may not be evaluated. Reasons
781 * dataToTag#'s strictness means that its argument often will be
782 evaluated, but FloatOut makes that temporarily untrue
783 case x of y -> let v = dataToTag# y in ...
785 case x of y -> let v = dataToTag# x in ...
786 Note that we look at 'x' instead of 'y' (this is to improve
787 floating in FloatOut). So Lint complains.
789 Moreover, it really *might* improve floating to let the
792 * CorePrep makes sure dataToTag#'s argument is evaluated, just
793 before code gen. Until then, it's not guaranteed
796 %************************************************************************
798 exprIsHNF, exprIsConLike
800 %************************************************************************
803 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
805 -- | exprIsHNF returns true for expressions that are certainly /already/
806 -- evaluated to /head/ normal form. This is used to decide whether it's ok
809 -- > case x of _ -> e
815 -- and to decide whether it's safe to discard a 'seq'.
817 -- So, it does /not/ treat variables as evaluated, unless they say they are.
818 -- However, it /does/ treat partial applications and constructor applications
819 -- as values, even if their arguments are non-trivial, provided the argument
820 -- type is lifted. For example, both of these are values:
822 -- > (:) (f x) (map f xs)
823 -- > map (...redex...)
825 -- because 'seq' on such things completes immediately.
827 -- For unlifted argument types, we have to be careful:
831 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
832 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
833 -- unboxed type must be ok-for-speculation (or trivial).
834 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
835 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
839 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
840 -- data constructors. Conlike arguments are considered interesting by the
842 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
843 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
845 -- | Returns true for values or value-like expressions. These are lambdas,
846 -- constructors / CONLIKE functions (as determined by the function argument)
849 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
850 exprIsHNFlike is_con is_con_unf = is_hnf_like
852 is_hnf_like (Var v) -- NB: There are no value args at this point
853 = is_con v -- Catches nullary constructors,
854 -- so that [] and () are values, for example
855 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
856 || is_con_unf (idUnfolding v)
857 -- Check the thing's unfolding; it might be bound to a value
858 -- We don't look through loop breakers here, which is a bit conservative
859 -- but otherwise I worry that if an Id's unfolding is just itself,
860 -- we could get an infinite loop
862 is_hnf_like (Lit _) = True
863 is_hnf_like (Type _) = True -- Types are honorary Values;
864 -- we don't mind copying them
865 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
866 is_hnf_like (Note _ e) = is_hnf_like e
867 is_hnf_like (Cast e _) = is_hnf_like e
868 is_hnf_like (App e (Type _)) = is_hnf_like e
869 is_hnf_like (App e a) = app_is_value e [a]
870 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
871 is_hnf_like _ = False
873 -- There is at least one value argument
874 app_is_value :: CoreExpr -> [CoreArg] -> Bool
875 app_is_value (Var fun) args
876 = idArity fun > valArgCount args -- Under-applied function
877 || is_con fun -- or constructor-like
878 app_is_value (Note _ f) as = app_is_value f as
879 app_is_value (Cast f _) as = app_is_value f as
880 app_is_value (App f a) as = app_is_value f (a:as)
881 app_is_value _ _ = False
885 %************************************************************************
887 Instantiating data constructors
889 %************************************************************************
891 These InstPat functions go here to avoid circularity between DataCon and Id
894 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
895 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
897 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
898 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
899 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
901 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
902 -- Remember to include the existential dictionaries
904 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
905 -> [FastString] -- A long enough list of FSs to use for names
906 -> [Unique] -- An equally long list of uniques, at least one for each binder
908 -> [Type] -- Types to instantiate the universally quantified tyvars
909 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
910 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
911 -- (ex_tvs, co_tvs, arg_ids),
913 -- ex_tvs are intended to be used as binders for existential type args
915 -- co_tvs are intended to be used as binders for coercion args and the kinds
916 -- of these vars have been instantiated by the inst_tys and the ex_tys
917 -- The co_tvs include both GADT equalities (dcEqSpec) and
918 -- programmer-specified equalities (dcEqTheta)
920 -- arg_ids are indended to be used as binders for value arguments,
921 -- and their types have been instantiated with inst_tys and ex_tys
922 -- The arg_ids include both dicts (dcDictTheta) and
923 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
926 -- The following constructor T1
929 -- T1 :: forall b. Int -> b -> T(a,b)
932 -- has representation type
933 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
936 -- dataConInstPat fss us T1 (a1',b') will return
938 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
940 -- where the double-primed variables are created with the FastStrings and
941 -- Uniques given as fss and us
942 dataConInstPat arg_fun fss uniqs con inst_tys
943 = (ex_bndrs, co_bndrs, arg_ids)
945 univ_tvs = dataConUnivTyVars con
946 ex_tvs = dataConExTyVars con
947 arg_tys = arg_fun con
948 eq_spec = dataConEqSpec con
949 eq_theta = dataConEqTheta con
950 eq_preds = eqSpecPreds eq_spec ++ eq_theta
953 n_co = length eq_preds
955 -- split the Uniques and FastStrings
956 (ex_uniqs, uniqs') = splitAt n_ex uniqs
957 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
959 (ex_fss, fss') = splitAt n_ex fss
960 (co_fss, id_fss) = splitAt n_co fss'
962 -- Make existential type variables
963 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
964 mk_ex_var uniq fs var = mkTyVar new_name kind
966 new_name = mkSysTvName uniq fs
969 -- Make the instantiating substitution
970 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
972 -- Make new coercion vars, instantiating kind
973 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
974 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
976 new_name = mkSysTvName uniq fs
977 co_kind = substTy subst (mkPredTy eq_pred)
979 -- make value vars, instantiating types
980 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
981 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
985 %************************************************************************
989 %************************************************************************
992 -- | A cheap equality test which bales out fast!
993 -- If it returns @True@ the arguments are definitely equal,
994 -- otherwise, they may or may not be equal.
996 -- See also 'exprIsBig'
997 cheapEqExpr :: Expr b -> Expr b -> Bool
999 cheapEqExpr (Var v1) (Var v2) = v1==v2
1000 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1001 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1003 cheapEqExpr (App f1 a1) (App f2 a2)
1004 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1006 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1007 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1009 cheapEqExpr _ _ = False
1013 exprIsBig :: Expr b -> Bool
1014 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1015 exprIsBig (Lit _) = False
1016 exprIsBig (Var _) = False
1017 exprIsBig (Type _) = False
1018 exprIsBig (Lam _ e) = exprIsBig e
1019 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1020 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1025 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1026 -- Compares for equality, modulo alpha
1027 eqExpr in_scope e1 e2
1028 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1030 id_unf _ = noUnfolding -- Don't expand
1034 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1035 -- ^ Compares expressions for equality, modulo alpha.
1036 -- Does /not/ look through newtypes or predicate types
1037 -- Used in rule matching, and also CSE
1039 eqExprX id_unfolding_fun env e1 e2
1042 go env (Var v1) (Var v2)
1043 | rnOccL env v1 == rnOccR env v2
1046 -- The next two rules expand non-local variables
1047 -- C.f. Note [Expanding variables] in Rules.lhs
1048 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1050 | not (locallyBoundL env v1)
1051 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1052 = go (nukeRnEnvL env) e1' e2
1055 | not (locallyBoundR env v2)
1056 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1057 = go (nukeRnEnvR env) e1 e2'
1059 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1060 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1061 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1062 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1063 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1065 go env (Lam b1 e1) (Lam b2 e2)
1066 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1067 && go (rnBndr2 env b1 b2) e1 e2
1069 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1070 = go env r1 r2 -- No need to check binder types, since RHSs match
1071 && go (rnBndr2 env v1 v2) e1 e2
1073 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1074 = all2 (go env') rs1 rs2 && go env' e1 e2
1076 (bs1,rs1) = unzip ps1
1077 (bs2,rs2) = unzip ps2
1078 env' = rnBndrs2 env bs1 bs2
1080 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1082 && tcEqTypeX env (idType b1) (idType b2)
1083 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1088 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1089 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1092 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1093 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1100 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1101 locallyBoundL rn_env v = inRnEnvL rn_env v
1102 locallyBoundR rn_env v = inRnEnvR rn_env v
1106 %************************************************************************
1108 \subsection{The size of an expression}
1110 %************************************************************************
1113 coreBindsSize :: [CoreBind] -> Int
1114 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1116 exprSize :: CoreExpr -> Int
1117 -- ^ A measure of the size of the expressions, strictly greater than 0
1118 -- It also forces the expression pretty drastically as a side effect
1119 exprSize (Var v) = v `seq` 1
1120 exprSize (Lit lit) = lit `seq` 1
1121 exprSize (App f a) = exprSize f + exprSize a
1122 exprSize (Lam b e) = varSize b + exprSize e
1123 exprSize (Let b e) = bindSize b + exprSize e
1124 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1125 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1126 exprSize (Note n e) = noteSize n + exprSize e
1127 exprSize (Type t) = seqType t `seq` 1
1129 noteSize :: Note -> Int
1130 noteSize (SCC cc) = cc `seq` 1
1131 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1133 varSize :: Var -> Int
1134 varSize b | isTyCoVar b = 1
1135 | otherwise = seqType (idType b) `seq`
1136 megaSeqIdInfo (idInfo b) `seq`
1139 varsSize :: [Var] -> Int
1140 varsSize = sum . map varSize
1142 bindSize :: CoreBind -> Int
1143 bindSize (NonRec b e) = varSize b + exprSize e
1144 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1146 pairSize :: (Var, CoreExpr) -> Int
1147 pairSize (b,e) = varSize b + exprSize e
1149 altSize :: CoreAlt -> Int
1150 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1154 %************************************************************************
1156 \subsection{Hashing}
1158 %************************************************************************
1161 hashExpr :: CoreExpr -> Int
1162 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1163 -- Two expressions that hash to the different Ints are definitely unequal.
1165 -- The emphasis is on a crude, fast hash, rather than on high precision.
1167 -- But unequal here means \"not identical\"; two alpha-equivalent
1168 -- expressions may hash to the different Ints.
1170 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1171 -- (at least if we want the above invariant to be true).
1173 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1174 -- UniqFM doesn't like negative Ints
1176 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1178 hash_expr :: HashEnv -> CoreExpr -> Word32
1179 -- Word32, because we're expecting overflows here, and overflowing
1180 -- signed types just isn't cool. In C it's even undefined.
1181 hash_expr env (Note _ e) = hash_expr env e
1182 hash_expr env (Cast e _) = hash_expr env e
1183 hash_expr env (Var v) = hashVar env v
1184 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1185 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1186 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1187 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1188 hash_expr env (Case e _ _ _) = hash_expr env e
1189 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1190 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1191 -- Shouldn't happen. Better to use WARN than trace, because trace
1192 -- prevents the CPR optimisation kicking in for hash_expr.
1194 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1195 fast_hash_expr env (Var v) = hashVar env v
1196 fast_hash_expr env (Type t) = fast_hash_type env t
1197 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1198 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1199 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1200 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1201 fast_hash_expr _ _ = 1
1203 fast_hash_type :: HashEnv -> Type -> Word32
1204 fast_hash_type env ty
1205 | Just tv <- getTyVar_maybe ty = hashVar env tv
1206 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1207 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1210 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1211 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1213 hashVar :: HashEnv -> Var -> Word32
1215 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1219 %************************************************************************
1223 %************************************************************************
1225 Note [Eta reduction conditions]
1226 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1227 We try for eta reduction here, but *only* if we get all the way to an
1228 trivial expression. We don't want to remove extra lambdas unless we
1229 are going to avoid allocating this thing altogether.
1231 There are some particularly delicate points here:
1233 * Eta reduction is not valid in general:
1235 This matters, partly for old-fashioned correctness reasons but,
1236 worse, getting it wrong can yield a seg fault. Consider
1238 h y = case (case y of { True -> f `seq` True; False -> False }) of
1239 True -> ...; False -> ...
1241 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1242 says f=bottom, and replaces the (f `seq` True) with just
1243 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1244 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1245 the definition again, so that it does not termninate after all.
1246 Result: seg-fault because the boolean case actually gets a function value.
1249 So it's important to to the right thing.
1251 * Note [Arity care]: we need to be careful if we just look at f's
1252 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1253 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1254 arity when checking that 'f' is a value. Otherwise we will
1259 Which might change a terminiating program (think (f `seq` e)) to a
1260 non-terminating one. So we check for being a loop breaker first.
1262 However for GlobalIds we can look at the arity; and for primops we
1263 must, since they have no unfolding.
1265 * Regardless of whether 'f' is a value, we always want to
1266 reduce (/\a -> f a) to f
1267 This came up in a RULE: foldr (build (/\a -> g a))
1268 did not match foldr (build (/\b -> ...something complex...))
1269 The type checker can insert these eta-expanded versions,
1270 with both type and dictionary lambdas; hence the slightly
1273 * Never *reduce* arity. For example
1275 Then if h has arity 1 we don't want to eta-reduce because then
1276 f's arity would decrease, and that is bad
1278 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1281 Note [Eta reduction with casted arguments]
1282 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1284 (\(x:t3). f (x |> g)) :: t3 -> t2
1288 This should be eta-reduced to
1292 So we need to accumulate a coercion, pushing it inward (past
1293 variable arguments only) thus:
1294 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1295 f (x:t) |> co --> (f |> (t -> co)) x
1296 f @ a |> co --> (f |> (forall a.co)) @ a
1297 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1298 These are the equations for ok_arg.
1300 It's true that we could also hope to eta reduce these:
1303 But the simplifier pushes those casts outwards, so we don't
1304 need to address that here.
1307 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1308 tryEtaReduce bndrs body
1309 = go (reverse bndrs) body (IdCo (exprType body))
1311 incoming_arity = count isId bndrs
1313 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1314 -> CoreExpr -- Of type tr
1315 -> CoercionI -- Of type tr ~ ts
1316 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1317 -- See Note [Eta reduction with casted arguments]
1318 -- for why we have an accumulating coercion
1320 | ok_fun fun = Just (mkCoerceI co fun)
1322 go (b : bs) (App fun arg) co
1323 | Just co' <- ok_arg b arg co
1326 go _ _ _ = Nothing -- Failure!
1329 -- Note [Eta reduction conditions]
1330 ok_fun (App fun (Type ty))
1331 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1334 = not (fun_id `elem` bndrs)
1335 && (ok_fun_id fun_id || all ok_lam bndrs)
1339 ok_fun_id fun = fun_arity fun >= incoming_arity
1342 fun_arity fun -- See Note [Arity care]
1343 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1344 | otherwise = idArity fun
1347 ok_lam v = isTyCoVar v || isDictId v
1350 ok_arg :: Var -- Of type bndr_t
1351 -> CoreExpr -- Of type arg_t
1352 -> CoercionI -- Of kind (t1~t2)
1353 -> Maybe CoercionI -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1354 -- (and similarly for tyvars, coercion args)
1355 -- See Note [Eta reduction with casted arguments]
1356 ok_arg bndr (Type ty) co
1357 | Just tv <- getTyVar_maybe ty
1358 , bndr == tv = Just (mkForAllTyCoI tv co)
1359 ok_arg bndr (Var v) co
1360 | bndr == v = Just (mkFunTyCoI (IdCo (idType bndr)) co)
1361 ok_arg bndr (Cast (Var v) co_arg) co
1362 | bndr == v = Just (mkFunTyCoI (ACo (mkSymCoercion co_arg)) co)
1363 -- The simplifier combines multiple casts into one,
1364 -- so we can have a simple-minded pattern match here
1365 ok_arg _ _ _ = Nothing
1369 %************************************************************************
1371 \subsection{Determining non-updatable right-hand-sides}
1373 %************************************************************************
1375 Top-level constructor applications can usually be allocated
1376 statically, but they can't if the constructor, or any of the
1377 arguments, come from another DLL (because we can't refer to static
1378 labels in other DLLs).
1380 If this happens we simply make the RHS into an updatable thunk,
1381 and 'execute' it rather than allocating it statically.
1384 -- | This function is called only on *top-level* right-hand sides.
1385 -- Returns @True@ if the RHS can be allocated statically in the output,
1386 -- with no thunks involved at all.
1387 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1388 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1389 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1390 -- update flag on it and (iii) in DsExpr to decide how to expand
1393 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1394 -- (a) a value lambda
1395 -- (b) a saturated constructor application with static args
1397 -- BUT watch out for
1398 -- (i) Any cross-DLL references kill static-ness completely
1399 -- because they must be 'executed' not statically allocated
1400 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1401 -- this is not necessary)
1403 -- (ii) We treat partial applications as redexes, because in fact we
1404 -- make a thunk for them that runs and builds a PAP
1405 -- at run-time. The only appliations that are treated as
1406 -- static are *saturated* applications of constructors.
1408 -- We used to try to be clever with nested structures like this:
1409 -- ys = (:) w ((:) w [])
1410 -- on the grounds that CorePrep will flatten ANF-ise it later.
1411 -- But supporting this special case made the function much more
1412 -- complicated, because the special case only applies if there are no
1413 -- enclosing type lambdas:
1414 -- ys = /\ a -> Foo (Baz ([] a))
1415 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1417 -- But in fact, even without -O, nested structures at top level are
1418 -- flattened by the simplifier, so we don't need to be super-clever here.
1422 -- f = \x::Int. x+7 TRUE
1423 -- p = (True,False) TRUE
1425 -- d = (fst p, False) FALSE because there's a redex inside
1426 -- (this particular one doesn't happen but...)
1428 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1429 -- n = /\a. Nil a TRUE
1431 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1434 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1435 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1437 -- b) (C x xs), where C is a contructor is updatable if the application is
1440 -- c) don't look through unfolding of f in (f x).
1442 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1444 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1447 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1448 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1449 is_static in_arg (Cast e _) = is_static in_arg e
1451 is_static _ (Lit lit)
1453 MachLabel _ _ _ -> False
1455 -- A MachLabel (foreign import "&foo") in an argument
1456 -- prevents a constructor application from being static. The
1457 -- reason is that it might give rise to unresolvable symbols
1458 -- in the object file: under Linux, references to "weak"
1459 -- symbols from the data segment give rise to "unresolvable
1460 -- relocation" errors at link time This might be due to a bug
1461 -- in the linker, but we'll work around it here anyway.
1464 is_static in_arg other_expr = go other_expr 0
1466 go (Var f) n_val_args
1467 #if mingw32_TARGET_OS
1468 | not (_is_dynamic_name (idName f))
1470 = saturated_data_con f n_val_args
1471 || (in_arg && n_val_args == 0)
1472 -- A naked un-applied variable is *not* deemed a static RHS
1474 -- Reason: better to update so that the indirection gets shorted
1475 -- out, and the true value will be seen
1476 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1477 -- are always updatable. If you do so, make sure that non-updatable
1478 -- ones have enough space for their static link field!
1480 go (App f a) n_val_args
1481 | isTypeArg a = go f n_val_args
1482 | not in_arg && is_static True a = go f (n_val_args + 1)
1483 -- The (not in_arg) checks that we aren't in a constructor argument;
1484 -- if we are, we don't allow (value) applications of any sort
1486 -- NB. In case you wonder, args are sometimes not atomic. eg.
1487 -- x = D# (1.0## /## 2.0##)
1488 -- can't float because /## can fail.
1490 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1491 go (Cast e _) n_val_args = go e n_val_args
1494 saturated_data_con f n_val_args
1495 = case isDataConWorkId_maybe f of
1496 Just dc -> n_val_args == dataConRepArity dc