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
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,
35 CoreStats(..), coreBindsStats,
41 cheapEqExpr, eqExpr, eqExprX,
46 -- * Manipulating data constructors and types
47 applyTypeToArgs, applyTypeToArg,
48 dataConRepInstPat, dataConRepFSInstPat
51 #include "HsVersions.h"
81 %************************************************************************
83 \subsection{Find the type of a Core atom/expression}
85 %************************************************************************
88 exprType :: CoreExpr -> Type
89 -- ^ Recover the type of a well-typed Core expression. Fails when
90 -- applied to the actual 'CoreSyn.Type' expression as it cannot
91 -- really be said to have a type
92 exprType (Var var) = idType var
93 exprType (Lit lit) = literalType lit
94 exprType (Coercion co) = coercionType co
95 exprType (Let _ body) = exprType body
96 exprType (Case _ _ ty _) = ty
97 exprType (Cast _ co) = pSnd (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 (_,bs,rhs)
109 | any bad_binder bs = expandTypeSynonyms ty
110 | otherwise = ty -- Note [Existential variables and silly type synonyms]
113 free_tvs = tyVarsOfType ty
114 bad_binder b = isTyVar b && b `elemVarSet` free_tvs
116 coreAltsType :: [CoreAlt] -> Type
117 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
118 coreAltsType (alt:_) = coreAltType alt
119 coreAltsType [] = panic "corAltsType"
122 Note [Existential variables and silly type synonyms]
123 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
125 data T = forall a. T (Funny a)
130 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
131 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
132 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
135 Various possibilities suggest themselves:
137 - Ignore the problem, and make Lint not complain about such variables
139 - Expand all type synonyms (or at least all those that discard arguments)
140 This is tricky, because at least for top-level things we want to
141 retain the type the user originally specified.
143 - Expand synonyms on the fly, when the problem arises. That is what
144 we are doing here. It's not too expensive, I think.
147 mkPiType :: Var -> Type -> Type
148 -- ^ Makes a @(->)@ type or a forall type, depending
149 -- on whether it is given a type variable or a term variable.
150 mkPiTypes :: [Var] -> Type -> Type
151 -- ^ 'mkPiType' for multiple type or value arguments
154 | isId v = mkFunTy (idType v) ty
155 | otherwise = mkForAllTy v ty
157 mkPiTypes vs ty = foldr mkPiType ty vs
161 applyTypeToArg :: Type -> CoreExpr -> Type
162 -- ^ Determines the type resulting from applying an expression to a function with the given type
163 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
164 applyTypeToArg fun_ty _ = funResultTy fun_ty
166 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
167 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
168 -- The first argument is just for debugging, and gives some context
169 applyTypeToArgs _ op_ty [] = op_ty
171 applyTypeToArgs e op_ty (Type ty : args)
172 = -- Accumulate type arguments so we can instantiate all at once
175 go rev_tys (Type ty : args) = go (ty:rev_tys) args
176 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
178 op_ty' = applyTysD msg op_ty (reverse rev_tys)
179 msg = ptext (sLit "applyTypeToArgs") <+>
182 applyTypeToArgs e op_ty (_ : args)
183 = case (splitFunTy_maybe op_ty) of
184 Just (_, res_ty) -> applyTypeToArgs e res_ty args
185 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
187 panic_msg :: CoreExpr -> Type -> SDoc
188 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
191 %************************************************************************
193 \subsection{Attaching notes}
195 %************************************************************************
198 -- | Wrap the given expression in the coercion safely, dropping
199 -- identity coercions and coalescing nested coercions
200 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
201 mkCoerce co e | isReflCo co = e
202 mkCoerce co (Cast expr co2)
203 = ASSERT(let { Pair from_ty _to_ty = coercionKind co;
204 Pair _from_ty2 to_ty2 = coercionKind co2} in
205 from_ty `eqType` to_ty2 )
206 mkCoerce (mkTransCo co2 co) expr
209 = let Pair from_ty _to_ty = coercionKind co in
210 -- if to_ty `eqType` from_ty
213 WARN(not (from_ty `eqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
218 -- | Wraps the given expression in the cost centre unless
219 -- in a way that maximises their utility to the user
220 mkSCC :: CostCentre -> Expr b -> Expr b
221 -- Note: Nested SCC's *are* preserved for the benefit of
222 -- cost centre stack profiling
223 mkSCC _ (Lit lit) = Lit lit
224 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
225 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
226 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
227 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
228 mkSCC cc expr = Note (SCC cc) expr
232 %************************************************************************
234 \subsection{Other expression construction}
236 %************************************************************************
239 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
240 -- ^ @bindNonRec x r b@ produces either:
246 -- > case r of x { _DEFAULT_ -> b }
248 -- depending on whether we have to use a @case@ or @let@
249 -- binding for the expression (see 'needsCaseBinding').
250 -- It's used by the desugarer to avoid building bindings
251 -- that give Core Lint a heart attack, although actually
252 -- the simplifier deals with them perfectly well. See
253 -- also 'MkCore.mkCoreLet'
254 bindNonRec bndr rhs body
255 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
256 | otherwise = Let (NonRec bndr rhs) body
258 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
259 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
260 needsCaseBinding :: Type -> CoreExpr -> Bool
261 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
262 -- Make a case expression instead of a let
263 -- These can arise either from the desugarer,
264 -- or from beta reductions: (\x.e) (x +# y)
268 mkAltExpr :: AltCon -- ^ Case alternative constructor
269 -> [CoreBndr] -- ^ Things bound by the pattern match
270 -> [Type] -- ^ The type arguments to the case alternative
272 -- ^ This guy constructs the value that the scrutinee must have
273 -- given that you are in one particular branch of a case
274 mkAltExpr (DataAlt con) args inst_tys
275 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
276 mkAltExpr (LitAlt lit) [] []
278 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
279 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
283 %************************************************************************
285 \subsection{Taking expressions apart}
287 %************************************************************************
289 The default alternative must be first, if it exists at all.
290 This makes it easy to find, though it makes matching marginally harder.
293 -- | Extract the default case alternative
294 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
295 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
296 findDefault alts = (alts, Nothing)
298 isDefaultAlt :: CoreAlt -> Bool
299 isDefaultAlt (DEFAULT, _, _) = True
300 isDefaultAlt _ = False
303 -- | Find the case alternative corresponding to a particular
304 -- constructor: panics if no such constructor exists
305 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
306 -- A "Nothing" result *is* legitmiate
307 -- See Note [Unreachable code]
310 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
314 go (alt@(con1,_,_) : alts) deflt
315 = case con `cmpAltCon` con1 of
316 LT -> deflt -- Missed it already; the alts are in increasing order
318 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
320 ---------------------------------
321 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
322 -- ^ Merge alternatives preserving order; alternatives in
323 -- the first argument shadow ones in the second
324 mergeAlts [] as2 = as2
325 mergeAlts as1 [] = as1
326 mergeAlts (a1:as1) (a2:as2)
327 = case a1 `cmpAlt` a2 of
328 LT -> a1 : mergeAlts as1 (a2:as2)
329 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
330 GT -> a2 : mergeAlts (a1:as1) as2
333 ---------------------------------
334 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
337 -- > case (C a b x y) of
340 -- We want to drop the leading type argument of the scrutinee
341 -- leaving the arguments to match agains the pattern
343 trimConArgs DEFAULT args = ASSERT( null args ) []
344 trimConArgs (LitAlt _) args = ASSERT( null args ) []
345 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
348 Note [Unreachable code]
349 ~~~~~~~~~~~~~~~~~~~~~~~
350 It is possible (although unusual) for GHC to find a case expression
351 that cannot match. For example:
353 data Col = Red | Green | Blue
357 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
359 Suppose that for some silly reason, x isn't substituted in the case
360 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
361 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
365 lvl = case x of { Green -> e1; Blue -> e2 })
370 Now if x gets inlined, we won't be able to find a matching alternative
371 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
372 we generate (error "Inaccessible alternative").
374 Similar things can happen (augmented by GADTs) when the Simplifier
375 filters down the matching alternatives in Simplify.rebuildCase.
378 %************************************************************************
382 %************************************************************************
386 @exprIsTrivial@ is true of expressions we are unconditionally happy to
387 duplicate; simple variables and constants, and type
388 applications. Note that primop Ids aren't considered
391 Note [Variable are trivial]
392 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
393 There used to be a gruesome test for (hasNoBinding v) in the
395 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
396 The idea here is that a constructor worker, like \$wJust, is
397 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
398 So it should be treated like a lambda. Ditto unsaturated primops.
399 But now constructor workers are not "have-no-binding" Ids. And
400 completely un-applied primops and foreign-call Ids are sufficiently
401 rare that I plan to allow them to be duplicated and put up with
404 Note [SCCs are trivial]
405 ~~~~~~~~~~~~~~~~~~~~~~~
406 We used not to treat (_scc_ "foo" x) as trivial, because it really
407 generates code, (and a heap object when it's a function arg) to
408 capture the cost centre. However, the profiling system discounts the
409 allocation costs for such "boxing thunks" whereas the extra costs of
410 *not* inlining otherwise-trivial bindings can be high, and are hard to
414 exprIsTrivial :: CoreExpr -> Bool
415 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
416 exprIsTrivial (Type _) = True
417 exprIsTrivial (Coercion _) = 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 (Coercion {}) = Just n
473 go n (Var {}) = decrement n
474 go n (Note _ e) = go n e
475 go n (Cast e _) = go n e
476 go n (App f a) | Just n' <- go n a = go n' f
477 go n (Lit lit) | litIsDupable lit = decrement n
480 decrement :: Int -> Maybe Int
481 decrement 0 = Nothing
482 decrement n = Just (n-1)
485 dupAppSize = 8 -- Size of term we are prepared to duplicate
486 -- This is *just* big enough to make test MethSharing
487 -- inline enough join points. Really it should be
488 -- smaller, and could be if we fixed Trac #4960.
491 %************************************************************************
493 exprIsCheap, exprIsExpandable
495 %************************************************************************
497 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
498 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
499 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
500 it is obviously in weak head normal form, or is cheap to get to WHNF.
501 [Note that that's not the same as exprIsDupable; an expression might be
502 big, and hence not dupable, but still cheap.]
504 By ``cheap'' we mean a computation we're willing to:
505 push inside a lambda, or
506 inline at more than one place
507 That might mean it gets evaluated more than once, instead of being
508 shared. The main examples of things which aren't WHNF but are
513 (where e, and all the ei are cheap)
516 (where e and b are cheap)
519 (where op is a cheap primitive operator)
522 (because we are happy to substitute it inside a lambda)
524 Notice that a variable is considered 'cheap': we can push it inside a lambda,
525 because sharing will make sure it is only evaluated once.
527 Note [exprIsCheap and exprIsHNF]
528 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
529 Note that exprIsHNF does not imply exprIsCheap. Eg
530 let x = fac 20 in Just x
531 This responds True to exprIsHNF (you can discard a seq), but
532 False to exprIsCheap.
535 exprIsCheap :: CoreExpr -> Bool
536 exprIsCheap = exprIsCheap' isCheapApp
538 exprIsExpandable :: CoreExpr -> Bool
539 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
541 type CheapAppFun = Id -> Int -> Bool
542 exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
543 exprIsCheap' _ (Lit _) = True
544 exprIsCheap' _ (Type _) = True
545 exprIsCheap' _ (Coercion _) = True
546 exprIsCheap' _ (Var _) = True
547 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
548 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
549 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
550 || exprIsCheap' good_app e
552 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
553 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
554 -- Experimentally, treat (case x of ...) as cheap
555 -- (and case __coerce x etc.)
556 -- This improves arities of overloaded functions where
557 -- there is only dictionary selection (no construction) involved
559 exprIsCheap' good_app (Let (NonRec x _) e)
560 | isUnLiftedType (idType x) = exprIsCheap' good_app e
562 -- Strict lets always have cheap right hand sides,
563 -- and do no allocation, so just look at the body
564 -- Non-strict lets do allocation so we don't treat them as cheap
567 exprIsCheap' good_app other_expr -- Applications and variables
570 -- Accumulate value arguments, then decide
571 go (Cast e _) val_args = go e val_args
572 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
573 | otherwise = go f val_args
575 go (Var _) [] = True -- Just a type application of a variable
576 -- (f t1 t2 t3) counts as WHNF
578 = case idDetails f of
579 RecSelId {} -> go_sel args
580 ClassOpId {} -> go_sel args
581 PrimOpId op -> go_primop op args
582 _ | good_app f (length args) -> go_pap args
583 | isBottomingId f -> True
585 -- Application of a function which
586 -- always gives bottom; we treat this as cheap
587 -- because it certainly doesn't need to be shared!
592 go_pap args = all (exprIsCheap' good_app) args
593 -- Used to be "all exprIsTrivial args" due to concerns about
594 -- duplicating nested constructor applications, but see #4978.
597 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
598 -- In principle we should worry about primops
599 -- that return a type variable, since the result
600 -- might be applied to something, but I'm not going
601 -- to bother to check the number of args
604 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
605 go_sel _ = False -- look cheap, so we will substitute it inside a
606 -- lambda. Particularly for dictionary field selection.
607 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
608 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
610 isCheapApp :: CheapAppFun
611 isCheapApp fn n_val_args
613 || n_val_args < idArity fn
615 isExpandableApp :: CheapAppFun
616 isExpandableApp fn n_val_args
618 || n_val_args < idArity fn
619 || go n_val_args (idType fn)
621 -- See if all the arguments are PredTys (implicit params or classes)
622 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
625 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
626 | Just (arg, ty) <- splitFunTy_maybe ty
627 , isPredTy arg = go (n_val_args-1) ty
631 Note [Expandable overloadings]
632 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
633 Suppose the user wrote this
634 {-# RULE forall x. foo (negate x) = h x #-}
635 f x = ....(foo (negate x))....
636 He'd expect the rule to fire. But since negate is overloaded, we might
638 f = \d -> let n = negate d in \x -> ...foo (n x)...
639 So we treat the application of a function (negate in this case) to a
640 *dictionary* as expandable. In effect, every function is CONLIKE when
641 it's applied only to dictionaries.
644 %************************************************************************
648 %************************************************************************
651 -- | 'exprOkForSpeculation' returns True of an expression that is:
653 -- * Safe to evaluate even if normal order eval might not
654 -- evaluate the expression at all, or
656 -- * Safe /not/ to evaluate even if normal order would do so
658 -- It is usually called on arguments of unlifted type, but not always
659 -- In particular, Simplify.rebuildCase calls it on lifted types
660 -- when a 'case' is a plain 'seq'. See the example in
661 -- Note [exprOkForSpeculation: case expressions] below
663 -- Precisely, it returns @True@ iff:
665 -- * The expression guarantees to terminate,
667 -- * without raising an exception,
668 -- * without causing a side effect (e.g. writing a mutable variable)
670 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
671 -- As an example of the considerations in this test, consider:
673 -- > let x = case y# +# 1# of { r# -> I# r# }
676 -- being translated to:
678 -- > case y# +# 1# of { r# ->
683 -- We can only do this if the @y + 1@ is ok for speculation: it has no
684 -- side effects, and can't diverge or raise an exception.
685 exprOkForSpeculation :: CoreExpr -> Bool
686 exprOkForSpeculation (Lit _) = True
687 exprOkForSpeculation (Type _) = True
688 exprOkForSpeculation (Coercion _) = True
690 exprOkForSpeculation (Var v)
691 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
692 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
693 || isDataConWorkId v -- Nullary constructors
694 || idArity v > 0 -- Functions
695 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
697 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
698 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
700 exprOkForSpeculation (Case e _ _ alts)
701 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
702 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
704 exprOkForSpeculation other_expr
705 = case collectArgs other_expr of
706 (Var f, args) -> spec_ok (idDetails f) args
710 spec_ok (DataConWorkId _) _
711 = True -- The strictness of the constructor has already
712 -- been expressed by its "wrapper", so we don't need
713 -- to take the arguments into account
715 spec_ok (PrimOpId op) args
716 | isDivOp op, -- Special case for dividing operations that fail
717 [arg1, Lit lit] <- args -- only if the divisor is zero
718 = not (isZeroLit lit) && exprOkForSpeculation arg1
719 -- Often there is a literal divisor, and this
720 -- can get rid of a thunk in an inner looop
722 | DataToTagOp <- op -- See Note [dataToTag speculation]
726 = primOpOkForSpeculation op &&
727 all exprOkForSpeculation args
728 -- A bit conservative: we don't really need
729 -- to care about lazy arguments, but this is easy
731 spec_ok (DFunId _ new_type) _ = not new_type
732 -- DFuns terminate, unless the dict is implemented with a newtype
733 -- in which case they may not
737 -- | True of dyadic operators that can fail only if the second arg is zero!
738 isDivOp :: PrimOp -> Bool
739 -- This function probably belongs in PrimOp, or even in
740 -- an automagically generated file.. but it's such a
741 -- special case I thought I'd leave it here for now.
742 isDivOp IntQuotOp = True
743 isDivOp IntRemOp = True
744 isDivOp WordQuotOp = True
745 isDivOp WordRemOp = True
746 isDivOp FloatDivOp = True
747 isDivOp DoubleDivOp = True
751 Note [exprOkForSpeculation: case expressions]
752 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
753 It's always sound for exprOkForSpeculation to return False, and we
754 don't want it to take too long, so it bales out on complicated-looking
755 terms. Notably lets, which can be stacked very deeply; and in any
756 case the argument of exprOkForSpeculation is usually in a strict context,
757 so any lets will have been floated away.
759 However, we keep going on case-expressions. An example like this one
760 showed up in DPH code (Trac #3717):
763 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
765 If exprOkForSpeculation doesn't look through case expressions, you get this:
767 \ (ww :: GHC.Prim.Int#) ->
769 __DEFAULT -> case (case <# ds 5 of _ {
770 GHC.Types.False -> lvl1;
771 GHC.Types.True -> lvl})
773 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
777 The inner case is redundant, and should be nuked.
779 Note [dataToTag speculation]
780 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
782 f x = let v::Int# = dataToTag# x
784 We say "yes", even though 'x' may not be evaluated. Reasons
786 * dataToTag#'s strictness means that its argument often will be
787 evaluated, but FloatOut makes that temporarily untrue
788 case x of y -> let v = dataToTag# y in ...
790 case x of y -> let v = dataToTag# x in ...
791 Note that we look at 'x' instead of 'y' (this is to improve
792 floating in FloatOut). So Lint complains.
794 Moreover, it really *might* improve floating to let the
797 * CorePrep makes sure dataToTag#'s argument is evaluated, just
798 before code gen. Until then, it's not guaranteed
801 %************************************************************************
803 exprIsHNF, exprIsConLike
805 %************************************************************************
808 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
810 -- | exprIsHNF returns true for expressions that are certainly /already/
811 -- evaluated to /head/ normal form. This is used to decide whether it's ok
814 -- > case x of _ -> e
820 -- and to decide whether it's safe to discard a 'seq'.
822 -- So, it does /not/ treat variables as evaluated, unless they say they are.
823 -- However, it /does/ treat partial applications and constructor applications
824 -- as values, even if their arguments are non-trivial, provided the argument
825 -- type is lifted. For example, both of these are values:
827 -- > (:) (f x) (map f xs)
828 -- > map (...redex...)
830 -- because 'seq' on such things completes immediately.
832 -- For unlifted argument types, we have to be careful:
836 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
837 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
838 -- unboxed type must be ok-for-speculation (or trivial).
839 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
840 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
844 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
845 -- data constructors. Conlike arguments are considered interesting by the
847 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
848 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
850 -- | Returns true for values or value-like expressions. These are lambdas,
851 -- constructors / CONLIKE functions (as determined by the function argument)
854 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
855 exprIsHNFlike is_con is_con_unf = is_hnf_like
857 is_hnf_like (Var v) -- NB: There are no value args at this point
858 = is_con v -- Catches nullary constructors,
859 -- so that [] and () are values, for example
860 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
861 || is_con_unf (idUnfolding v)
862 -- Check the thing's unfolding; it might be bound to a value
863 -- We don't look through loop breakers here, which is a bit conservative
864 -- but otherwise I worry that if an Id's unfolding is just itself,
865 -- we could get an infinite loop
867 is_hnf_like (Lit _) = True
868 is_hnf_like (Type _) = True -- Types are honorary Values;
869 -- we don't mind copying them
870 is_hnf_like (Coercion _) = True -- Same for coercions
871 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
872 is_hnf_like (Note _ e) = is_hnf_like e
873 is_hnf_like (Cast e _) = is_hnf_like e
874 is_hnf_like (App e (Type _)) = is_hnf_like e
875 is_hnf_like (App e (Coercion _)) = is_hnf_like e
876 is_hnf_like (App e a) = app_is_value e [a]
877 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
878 is_hnf_like _ = False
880 -- There is at least one value argument
881 app_is_value :: CoreExpr -> [CoreArg] -> Bool
882 app_is_value (Var fun) args
883 = idArity fun > valArgCount args -- Under-applied function
884 || is_con fun -- or constructor-like
885 app_is_value (Note _ f) as = app_is_value f as
886 app_is_value (Cast f _) as = app_is_value f as
887 app_is_value (App f a) as = app_is_value f (a:as)
888 app_is_value _ _ = False
892 %************************************************************************
894 Instantiating data constructors
896 %************************************************************************
898 These InstPat functions go here to avoid circularity between DataCon and Id
901 dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
902 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
904 dataConRepInstPat = dataConInstPat (repeat ((fsLit "ipv")))
905 dataConRepFSInstPat = dataConInstPat
907 dataConInstPat :: [FastString] -- A long enough list of FSs to use for names
908 -> [Unique] -- An equally long list of uniques, at least one for each binder
910 -> [Type] -- Types to instantiate the universally quantified tyvars
911 -> ([TyVar], [Id]) -- Return instantiated variables
912 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
913 -- (ex_tvs, arg_ids),
915 -- ex_tvs are intended to be used as binders for existential type args
917 -- arg_ids are indended to be used as binders for value arguments,
918 -- and their types have been instantiated with inst_tys and ex_tys
919 -- The arg_ids include both evidence and
920 -- programmer-specified arguments (both after rep-ing)
923 -- The following constructor T1
926 -- T1 :: forall b. Int -> b -> T(a,b)
929 -- has representation type
930 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
933 -- dataConInstPat fss us T1 (a1',b') will return
935 -- ([a1'', b''], [c :: (a1', b')~(a1'', b''), x :: Int, y :: b''])
937 -- where the double-primed variables are created with the FastStrings and
938 -- Uniques given as fss and us
939 dataConInstPat fss uniqs con inst_tys
940 = (ex_bndrs, arg_ids)
942 univ_tvs = dataConUnivTyVars con
943 ex_tvs = dataConExTyVars con
944 arg_tys = dataConRepArgTys con
948 -- split the Uniques and FastStrings
949 (ex_uniqs, id_uniqs) = splitAt n_ex uniqs
950 (ex_fss, id_fss) = splitAt n_ex fss
952 -- Make existential type variables
953 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
954 mk_ex_var uniq fs var = mkTyVar new_name kind
956 new_name = mkSysTvName uniq fs
959 -- Make the instantiating substitution
960 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
962 -- Make value vars, instantiating types
963 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (Type.substTy subst ty) noSrcSpan
964 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
967 %************************************************************************
971 %************************************************************************
974 -- | A cheap equality test which bales out fast!
975 -- If it returns @True@ the arguments are definitely equal,
976 -- otherwise, they may or may not be equal.
978 -- See also 'exprIsBig'
979 cheapEqExpr :: Expr b -> Expr b -> Bool
981 cheapEqExpr (Var v1) (Var v2) = v1==v2
982 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
983 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
984 cheapEqExpr (Coercion c1) (Coercion c2) = c1 `coreEqCoercion` c2
986 cheapEqExpr (App f1 a1) (App f2 a2)
987 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
989 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
990 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
992 cheapEqExpr _ _ = False
996 exprIsBig :: Expr b -> Bool
997 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
998 exprIsBig (Lit _) = False
999 exprIsBig (Var _) = False
1000 exprIsBig (Type _) = False
1001 exprIsBig (Coercion _) = False
1002 exprIsBig (Lam _ e) = exprIsBig e
1003 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1004 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1009 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1010 -- Compares for equality, modulo alpha
1011 eqExpr in_scope e1 e2
1012 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1014 id_unf _ = noUnfolding -- Don't expand
1018 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1019 -- ^ Compares expressions for equality, modulo alpha.
1020 -- Does /not/ look through newtypes or predicate types
1021 -- Used in rule matching, and also CSE
1023 eqExprX id_unfolding_fun env e1 e2
1026 go env (Var v1) (Var v2)
1027 | rnOccL env v1 == rnOccR env v2
1030 -- The next two rules expand non-local variables
1031 -- C.f. Note [Expanding variables] in Rules.lhs
1032 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1034 | not (locallyBoundL env v1)
1035 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1036 = go (nukeRnEnvL env) e1' e2
1039 | not (locallyBoundR env v2)
1040 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1041 = go (nukeRnEnvR env) e1 e2'
1043 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1044 go env (Type t1) (Type t2) = eqTypeX env t1 t2
1045 go env (Coercion co1) (Coercion co2) = coreEqCoercion2 env co1 co2
1046 go env (Cast e1 co1) (Cast e2 co2) = coreEqCoercion2 env co1 co2 && go env e1 e2
1047 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1048 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1050 go env (Lam b1 e1) (Lam b2 e2)
1051 = eqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1052 && go (rnBndr2 env b1 b2) e1 e2
1054 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1055 = go env r1 r2 -- No need to check binder types, since RHSs match
1056 && go (rnBndr2 env v1 v2) e1 e2
1058 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1059 = all2 (go env') rs1 rs2 && go env' e1 e2
1061 (bs1,rs1) = unzip ps1
1062 (bs2,rs2) = unzip ps2
1063 env' = rnBndrs2 env bs1 bs2
1065 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1067 && eqTypeX env (idType b1) (idType b2)
1068 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1073 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1074 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1077 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1078 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1085 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1086 locallyBoundL rn_env v = inRnEnvL rn_env v
1087 locallyBoundR rn_env v = inRnEnvR rn_env v
1091 %************************************************************************
1093 \subsection{The size of an expression}
1095 %************************************************************************
1098 coreBindsSize :: [CoreBind] -> Int
1099 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1101 exprSize :: CoreExpr -> Int
1102 -- ^ A measure of the size of the expressions, strictly greater than 0
1103 -- It also forces the expression pretty drastically as a side effect
1104 -- Counts *leaves*, not internal nodes. Types and coercions are not counted.
1105 exprSize (Var v) = v `seq` 1
1106 exprSize (Lit lit) = lit `seq` 1
1107 exprSize (App f a) = exprSize f + exprSize a
1108 exprSize (Lam b e) = varSize b + exprSize e
1109 exprSize (Let b e) = bindSize b + exprSize e
1110 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1111 exprSize (Cast e co) = (seqCo co `seq` 1) + exprSize e
1112 exprSize (Note n e) = noteSize n + exprSize e
1113 exprSize (Type t) = seqType t `seq` 1
1114 exprSize (Coercion co) = seqCo co `seq` 1
1116 noteSize :: Note -> Int
1117 noteSize (SCC cc) = cc `seq` 1
1118 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1120 varSize :: Var -> Int
1121 varSize b | isTyVar b = 1
1122 | otherwise = seqType (idType b) `seq`
1123 megaSeqIdInfo (idInfo b) `seq`
1126 varsSize :: [Var] -> Int
1127 varsSize = sum . map varSize
1129 bindSize :: CoreBind -> Int
1130 bindSize (NonRec b e) = varSize b + exprSize e
1131 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1133 pairSize :: (Var, CoreExpr) -> Int
1134 pairSize (b,e) = varSize b + exprSize e
1136 altSize :: CoreAlt -> Int
1137 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1141 data CoreStats = CS { cs_tm, cs_ty, cs_co :: Int }
1143 plusCS :: CoreStats -> CoreStats -> CoreStats
1144 plusCS (CS { cs_tm = p1, cs_ty = q1, cs_co = r1 })
1145 (CS { cs_tm = p2, cs_ty = q2, cs_co = r2 })
1146 = CS { cs_tm = p1+p2, cs_ty = q1+q2, cs_co = r1+r2 }
1148 zeroCS, oneTM :: CoreStats
1149 zeroCS = CS { cs_tm = 0, cs_ty = 0, cs_co = 0 }
1150 oneTM = zeroCS { cs_tm = 1 }
1152 sumCS :: (a -> CoreStats) -> [a] -> CoreStats
1153 sumCS f = foldr (plusCS . f) zeroCS
1155 coreBindsStats :: [CoreBind] -> CoreStats
1156 coreBindsStats = sumCS bindStats
1158 bindStats :: CoreBind -> CoreStats
1159 bindStats (NonRec v r) = bindingStats v r
1160 bindStats (Rec prs) = sumCS (\(v,r) -> bindingStats v r) prs
1162 bindingStats :: Var -> CoreExpr -> CoreStats
1163 bindingStats v r = bndrStats v `plusCS` exprStats r
1165 bndrStats :: Var -> CoreStats
1166 bndrStats v = oneTM `plusCS` tyStats (varType v)
1168 exprStats :: CoreExpr -> CoreStats
1169 exprStats (Var {}) = oneTM
1170 exprStats (Lit {}) = oneTM
1171 exprStats (Type t) = tyStats t
1172 exprStats (Coercion c) = coStats c
1173 exprStats (App f a) = exprStats f `plusCS` exprStats a
1174 exprStats (Lam b e) = bndrStats b `plusCS` exprStats e
1175 exprStats (Let b e) = bindStats b `plusCS` exprStats e
1176 exprStats (Case e b _ as) = exprStats e `plusCS` bndrStats b `plusCS` sumCS altStats as
1177 exprStats (Cast e co) = coStats co `plusCS` exprStats e
1178 exprStats (Note _ e) = exprStats e
1180 altStats :: CoreAlt -> CoreStats
1181 altStats (_, bs, r) = sumCS bndrStats bs `plusCS` exprStats r
1183 tyStats :: Type -> CoreStats
1184 tyStats ty = zeroCS { cs_ty = typeSize ty }
1186 coStats :: Coercion -> CoreStats
1187 coStats co = zeroCS { cs_co = coercionSize co }
1190 %************************************************************************
1192 \subsection{Hashing}
1194 %************************************************************************
1197 hashExpr :: CoreExpr -> Int
1198 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1199 -- Two expressions that hash to the different Ints are definitely unequal.
1201 -- The emphasis is on a crude, fast hash, rather than on high precision.
1203 -- But unequal here means \"not identical\"; two alpha-equivalent
1204 -- expressions may hash to the different Ints.
1206 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1207 -- (at least if we want the above invariant to be true).
1209 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1210 -- UniqFM doesn't like negative Ints
1212 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1214 hash_expr :: HashEnv -> CoreExpr -> Word32
1215 -- Word32, because we're expecting overflows here, and overflowing
1216 -- signed types just isn't cool. In C it's even undefined.
1217 hash_expr env (Note _ e) = hash_expr env e
1218 hash_expr env (Cast e _) = hash_expr env e
1219 hash_expr env (Var v) = hashVar env v
1220 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1221 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1222 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1223 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1224 hash_expr env (Case e _ _ _) = hash_expr env e
1225 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1226 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1227 -- Shouldn't happen. Better to use WARN than trace, because trace
1228 -- prevents the CPR optimisation kicking in for hash_expr.
1229 hash_expr _ (Coercion _) = WARN(True, text "hash_expr: coercion") 1
1231 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1232 fast_hash_expr env (Var v) = hashVar env v
1233 fast_hash_expr env (Type t) = fast_hash_type env t
1234 fast_hash_expr env (Coercion co) = fast_hash_co env co
1235 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1236 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1237 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1238 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1239 fast_hash_expr _ _ = 1
1241 fast_hash_type :: HashEnv -> Type -> Word32
1242 fast_hash_type env ty
1243 | Just tv <- getTyVar_maybe ty = hashVar env tv
1244 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1245 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1248 fast_hash_co :: HashEnv -> Coercion -> Word32
1250 | Just cv <- getCoVar_maybe co = hashVar env cv
1251 | Just (tc,cos) <- splitTyConAppCo_maybe co = let hash_tc = fromIntegral (hashName (tyConName tc))
1252 in foldr (\c n -> fast_hash_co env c + n) hash_tc cos
1255 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1256 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1258 hashVar :: HashEnv -> Var -> Word32
1260 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1264 %************************************************************************
1268 %************************************************************************
1270 Note [Eta reduction conditions]
1271 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1272 We try for eta reduction here, but *only* if we get all the way to an
1273 trivial expression. We don't want to remove extra lambdas unless we
1274 are going to avoid allocating this thing altogether.
1276 There are some particularly delicate points here:
1278 * Eta reduction is not valid in general:
1280 This matters, partly for old-fashioned correctness reasons but,
1281 worse, getting it wrong can yield a seg fault. Consider
1283 h y = case (case y of { True -> f `seq` True; False -> False }) of
1284 True -> ...; False -> ...
1286 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1287 says f=bottom, and replaces the (f `seq` True) with just
1288 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1289 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1290 the definition again, so that it does not termninate after all.
1291 Result: seg-fault because the boolean case actually gets a function value.
1294 So it's important to to the right thing.
1296 * Note [Arity care]: we need to be careful if we just look at f's
1297 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1298 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1299 arity when checking that 'f' is a value. Otherwise we will
1304 Which might change a terminiating program (think (f `seq` e)) to a
1305 non-terminating one. So we check for being a loop breaker first.
1307 However for GlobalIds we can look at the arity; and for primops we
1308 must, since they have no unfolding.
1310 * Regardless of whether 'f' is a value, we always want to
1311 reduce (/\a -> f a) to f
1312 This came up in a RULE: foldr (build (/\a -> g a))
1313 did not match foldr (build (/\b -> ...something complex...))
1314 The type checker can insert these eta-expanded versions,
1315 with both type and dictionary lambdas; hence the slightly
1318 * Never *reduce* arity. For example
1320 Then if h has arity 1 we don't want to eta-reduce because then
1321 f's arity would decrease, and that is bad
1323 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1326 Note [Eta reduction with casted arguments]
1327 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1329 (\(x:t3). f (x |> g)) :: t3 -> t2
1333 This should be eta-reduced to
1337 So we need to accumulate a coercion, pushing it inward (past
1338 variable arguments only) thus:
1339 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1340 f (x:t) |> co --> (f |> (t -> co)) x
1341 f @ a |> co --> (f |> (forall a.co)) @ a
1342 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1343 These are the equations for ok_arg.
1345 It's true that we could also hope to eta reduce these:
1348 But the simplifier pushes those casts outwards, so we don't
1349 need to address that here.
1352 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1353 tryEtaReduce bndrs body
1354 = go (reverse bndrs) body (mkReflCo (exprType body))
1356 incoming_arity = count isId bndrs
1358 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1359 -> CoreExpr -- Of type tr
1360 -> Coercion -- Of type tr ~ ts
1361 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1362 -- See Note [Eta reduction with casted arguments]
1363 -- for why we have an accumulating coercion
1365 | ok_fun fun = Just (mkCoerce co fun)
1367 go (b : bs) (App fun arg) co
1368 | Just co' <- ok_arg b arg co
1371 go _ _ _ = Nothing -- Failure!
1374 -- Note [Eta reduction conditions]
1375 ok_fun (App fun (Type ty))
1376 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1379 = not (fun_id `elem` bndrs)
1380 && (ok_fun_id fun_id || all ok_lam bndrs)
1384 ok_fun_id fun = fun_arity fun >= incoming_arity
1387 fun_arity fun -- See Note [Arity care]
1388 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1389 | otherwise = idArity fun
1392 ok_lam v = isTyVar v || isEvVar v
1395 ok_arg :: Var -- Of type bndr_t
1396 -> CoreExpr -- Of type arg_t
1397 -> Coercion -- Of kind (t1~t2)
1398 -> Maybe Coercion -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1399 -- (and similarly for tyvars, coercion args)
1400 -- See Note [Eta reduction with casted arguments]
1401 ok_arg bndr (Type ty) co
1402 | Just tv <- getTyVar_maybe ty
1403 , bndr == tv = Just (mkForAllCo tv co)
1404 ok_arg bndr (Var v) co
1405 | bndr == v = Just (mkFunCo (mkReflCo (idType bndr)) co)
1406 ok_arg bndr (Cast (Var v) co_arg) co
1407 | bndr == v = Just (mkFunCo (mkSymCo co_arg) co)
1408 -- The simplifier combines multiple casts into one,
1409 -- so we can have a simple-minded pattern match here
1410 ok_arg _ _ _ = Nothing
1414 %************************************************************************
1416 \subsection{Determining non-updatable right-hand-sides}
1418 %************************************************************************
1420 Top-level constructor applications can usually be allocated
1421 statically, but they can't if the constructor, or any of the
1422 arguments, come from another DLL (because we can't refer to static
1423 labels in other DLLs).
1425 If this happens we simply make the RHS into an updatable thunk,
1426 and 'execute' it rather than allocating it statically.
1429 -- | This function is called only on *top-level* right-hand sides.
1430 -- Returns @True@ if the RHS can be allocated statically in the output,
1431 -- with no thunks involved at all.
1432 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1433 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1434 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1435 -- update flag on it and (iii) in DsExpr to decide how to expand
1438 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1439 -- (a) a value lambda
1440 -- (b) a saturated constructor application with static args
1442 -- BUT watch out for
1443 -- (i) Any cross-DLL references kill static-ness completely
1444 -- because they must be 'executed' not statically allocated
1445 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1446 -- this is not necessary)
1448 -- (ii) We treat partial applications as redexes, because in fact we
1449 -- make a thunk for them that runs and builds a PAP
1450 -- at run-time. The only appliations that are treated as
1451 -- static are *saturated* applications of constructors.
1453 -- We used to try to be clever with nested structures like this:
1454 -- ys = (:) w ((:) w [])
1455 -- on the grounds that CorePrep will flatten ANF-ise it later.
1456 -- But supporting this special case made the function much more
1457 -- complicated, because the special case only applies if there are no
1458 -- enclosing type lambdas:
1459 -- ys = /\ a -> Foo (Baz ([] a))
1460 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1462 -- But in fact, even without -O, nested structures at top level are
1463 -- flattened by the simplifier, so we don't need to be super-clever here.
1467 -- f = \x::Int. x+7 TRUE
1468 -- p = (True,False) TRUE
1470 -- d = (fst p, False) FALSE because there's a redex inside
1471 -- (this particular one doesn't happen but...)
1473 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1474 -- n = /\a. Nil a TRUE
1476 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1479 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1480 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1482 -- b) (C x xs), where C is a contructor is updatable if the application is
1485 -- c) don't look through unfolding of f in (f x).
1487 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1489 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1492 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1493 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1494 is_static in_arg (Cast e _) = is_static in_arg e
1496 is_static _ (Lit lit)
1498 MachLabel _ _ _ -> False
1500 -- A MachLabel (foreign import "&foo") in an argument
1501 -- prevents a constructor application from being static. The
1502 -- reason is that it might give rise to unresolvable symbols
1503 -- in the object file: under Linux, references to "weak"
1504 -- symbols from the data segment give rise to "unresolvable
1505 -- relocation" errors at link time This might be due to a bug
1506 -- in the linker, but we'll work around it here anyway.
1509 is_static in_arg other_expr = go other_expr 0
1511 go (Var f) n_val_args
1512 #if mingw32_TARGET_OS
1513 | not (_is_dynamic_name (idName f))
1515 = saturated_data_con f n_val_args
1516 || (in_arg && n_val_args == 0)
1517 -- A naked un-applied variable is *not* deemed a static RHS
1519 -- Reason: better to update so that the indirection gets shorted
1520 -- out, and the true value will be seen
1521 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1522 -- are always updatable. If you do so, make sure that non-updatable
1523 -- ones have enough space for their static link field!
1525 go (App f a) n_val_args
1526 | isTypeArg a = go f n_val_args
1527 | not in_arg && is_static True a = go f (n_val_args + 1)
1528 -- The (not in_arg) checks that we aren't in a constructor argument;
1529 -- if we are, we don't allow (value) applications of any sort
1531 -- NB. In case you wonder, args are sometimes not atomic. eg.
1532 -- x = D# (1.0## /## 2.0##)
1533 -- can't float because /## can fail.
1535 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1536 go (Cast e _) n_val_args = go e n_val_args
1539 saturated_data_con f n_val_args
1540 = case isDataConWorkId_maybe f of
1541 Just dc -> n_val_args == dataConRepArity dc