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 exprIsTrivial args
593 -- For constructor applications and primops, check that all
594 -- the args are trivial. We don't want to treat as cheap, say,
596 -- We'll put up with one constructor application, but not dozens
599 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
600 -- In principle we should worry about primops
601 -- that return a type variable, since the result
602 -- might be applied to something, but I'm not going
603 -- to bother to check the number of args
606 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
607 go_sel _ = False -- look cheap, so we will substitute it inside a
608 -- lambda. Particularly for dictionary field selection.
609 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
610 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
612 isCheapApp :: CheapAppFun
613 isCheapApp fn n_val_args
615 || n_val_args < idArity fn
617 isExpandableApp :: CheapAppFun
618 isExpandableApp fn n_val_args
620 || n_val_args < idArity fn
621 || go n_val_args (idType fn)
623 -- See if all the arguments are PredTys (implicit params or classes)
624 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
627 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
628 | Just (arg, ty) <- splitFunTy_maybe ty
629 , isPredTy arg = go (n_val_args-1) ty
633 Note [Expandable overloadings]
634 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
635 Suppose the user wrote this
636 {-# RULE forall x. foo (negate x) = h x #-}
637 f x = ....(foo (negate x))....
638 He'd expect the rule to fire. But since negate is overloaded, we might
640 f = \d -> let n = negate d in \x -> ...foo (n x)...
641 So we treat the application of a function (negate in this case) to a
642 *dictionary* as expandable. In effect, every function is CONLIKE when
643 it's applied only to dictionaries.
646 %************************************************************************
650 %************************************************************************
653 -- | 'exprOkForSpeculation' returns True of an expression that is:
655 -- * Safe to evaluate even if normal order eval might not
656 -- evaluate the expression at all, or
658 -- * Safe /not/ to evaluate even if normal order would do so
660 -- It is usually called on arguments of unlifted type, but not always
661 -- In particular, Simplify.rebuildCase calls it on lifted types
662 -- when a 'case' is a plain 'seq'. See the example in
663 -- Note [exprOkForSpeculation: case expressions] below
665 -- Precisely, it returns @True@ iff:
667 -- * The expression guarantees to terminate,
669 -- * without raising an exception,
670 -- * without causing a side effect (e.g. writing a mutable variable)
672 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
673 -- As an example of the considerations in this test, consider:
675 -- > let x = case y# +# 1# of { r# -> I# r# }
678 -- being translated to:
680 -- > case y# +# 1# of { r# ->
685 -- We can only do this if the @y + 1@ is ok for speculation: it has no
686 -- side effects, and can't diverge or raise an exception.
687 exprOkForSpeculation :: CoreExpr -> Bool
688 exprOkForSpeculation (Lit _) = True
689 exprOkForSpeculation (Type _) = True
690 exprOkForSpeculation (Coercion _) = True
692 exprOkForSpeculation (Var v)
693 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
694 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
695 || isDataConWorkId v -- Nullary constructors
696 || idArity v > 0 -- Functions
697 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
699 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
700 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
702 exprOkForSpeculation (Case e _ _ alts)
703 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
704 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
706 exprOkForSpeculation other_expr
707 = case collectArgs other_expr of
708 (Var f, args) -> spec_ok (idDetails f) args
712 spec_ok (DataConWorkId _) _
713 = True -- The strictness of the constructor has already
714 -- been expressed by its "wrapper", so we don't need
715 -- to take the arguments into account
717 spec_ok (PrimOpId op) args
718 | isDivOp op, -- Special case for dividing operations that fail
719 [arg1, Lit lit] <- args -- only if the divisor is zero
720 = not (isZeroLit lit) && exprOkForSpeculation arg1
721 -- Often there is a literal divisor, and this
722 -- can get rid of a thunk in an inner looop
724 | DataToTagOp <- op -- See Note [dataToTag speculation]
728 = primOpOkForSpeculation op &&
729 all exprOkForSpeculation args
730 -- A bit conservative: we don't really need
731 -- to care about lazy arguments, but this is easy
733 spec_ok (DFunId _ new_type) _ = not new_type
734 -- DFuns terminate, unless the dict is implemented with a newtype
735 -- in which case they may not
739 -- | True of dyadic operators that can fail only if the second arg is zero!
740 isDivOp :: PrimOp -> Bool
741 -- This function probably belongs in PrimOp, or even in
742 -- an automagically generated file.. but it's such a
743 -- special case I thought I'd leave it here for now.
744 isDivOp IntQuotOp = True
745 isDivOp IntRemOp = True
746 isDivOp WordQuotOp = True
747 isDivOp WordRemOp = True
748 isDivOp FloatDivOp = True
749 isDivOp DoubleDivOp = True
753 Note [exprOkForSpeculation: case expressions]
754 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
755 It's always sound for exprOkForSpeculation to return False, and we
756 don't want it to take too long, so it bales out on complicated-looking
757 terms. Notably lets, which can be stacked very deeply; and in any
758 case the argument of exprOkForSpeculation is usually in a strict context,
759 so any lets will have been floated away.
761 However, we keep going on case-expressions. An example like this one
762 showed up in DPH code (Trac #3717):
765 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
767 If exprOkForSpeculation doesn't look through case expressions, you get this:
769 \ (ww :: GHC.Prim.Int#) ->
771 __DEFAULT -> case (case <# ds 5 of _ {
772 GHC.Types.False -> lvl1;
773 GHC.Types.True -> lvl})
775 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
779 The inner case is redundant, and should be nuked.
781 Note [dataToTag speculation]
782 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
784 f x = let v::Int# = dataToTag# x
786 We say "yes", even though 'x' may not be evaluated. Reasons
788 * dataToTag#'s strictness means that its argument often will be
789 evaluated, but FloatOut makes that temporarily untrue
790 case x of y -> let v = dataToTag# y in ...
792 case x of y -> let v = dataToTag# x in ...
793 Note that we look at 'x' instead of 'y' (this is to improve
794 floating in FloatOut). So Lint complains.
796 Moreover, it really *might* improve floating to let the
799 * CorePrep makes sure dataToTag#'s argument is evaluated, just
800 before code gen. Until then, it's not guaranteed
803 %************************************************************************
805 exprIsHNF, exprIsConLike
807 %************************************************************************
810 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
812 -- | exprIsHNF returns true for expressions that are certainly /already/
813 -- evaluated to /head/ normal form. This is used to decide whether it's ok
816 -- > case x of _ -> e
822 -- and to decide whether it's safe to discard a 'seq'.
824 -- So, it does /not/ treat variables as evaluated, unless they say they are.
825 -- However, it /does/ treat partial applications and constructor applications
826 -- as values, even if their arguments are non-trivial, provided the argument
827 -- type is lifted. For example, both of these are values:
829 -- > (:) (f x) (map f xs)
830 -- > map (...redex...)
832 -- because 'seq' on such things completes immediately.
834 -- For unlifted argument types, we have to be careful:
838 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
839 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
840 -- unboxed type must be ok-for-speculation (or trivial).
841 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
842 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
846 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
847 -- data constructors. Conlike arguments are considered interesting by the
849 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
850 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
852 -- | Returns true for values or value-like expressions. These are lambdas,
853 -- constructors / CONLIKE functions (as determined by the function argument)
856 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
857 exprIsHNFlike is_con is_con_unf = is_hnf_like
859 is_hnf_like (Var v) -- NB: There are no value args at this point
860 = is_con v -- Catches nullary constructors,
861 -- so that [] and () are values, for example
862 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
863 || is_con_unf (idUnfolding v)
864 -- Check the thing's unfolding; it might be bound to a value
865 -- We don't look through loop breakers here, which is a bit conservative
866 -- but otherwise I worry that if an Id's unfolding is just itself,
867 -- we could get an infinite loop
869 is_hnf_like (Lit _) = True
870 is_hnf_like (Type _) = True -- Types are honorary Values;
871 -- we don't mind copying them
872 is_hnf_like (Coercion _) = True -- Same for coercions
873 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
874 is_hnf_like (Note _ e) = is_hnf_like e
875 is_hnf_like (Cast e _) = is_hnf_like e
876 is_hnf_like (App e (Type _)) = is_hnf_like e
877 is_hnf_like (App e (Coercion _)) = is_hnf_like e
878 is_hnf_like (App e a) = app_is_value e [a]
879 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
880 is_hnf_like _ = False
882 -- There is at least one value argument
883 app_is_value :: CoreExpr -> [CoreArg] -> Bool
884 app_is_value (Var fun) args
885 = idArity fun > valArgCount args -- Under-applied function
886 || is_con fun -- or constructor-like
887 app_is_value (Note _ f) as = app_is_value f as
888 app_is_value (Cast f _) as = app_is_value f as
889 app_is_value (App f a) as = app_is_value f (a:as)
890 app_is_value _ _ = False
894 %************************************************************************
896 Instantiating data constructors
898 %************************************************************************
900 These InstPat functions go here to avoid circularity between DataCon and Id
903 dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
904 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
906 dataConRepInstPat = dataConInstPat (repeat ((fsLit "ipv")))
907 dataConRepFSInstPat = dataConInstPat
909 dataConInstPat :: [FastString] -- A long enough list of FSs to use for names
910 -> [Unique] -- An equally long list of uniques, at least one for each binder
912 -> [Type] -- Types to instantiate the universally quantified tyvars
913 -> ([TyVar], [Id]) -- Return instantiated variables
914 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
915 -- (ex_tvs, arg_ids),
917 -- ex_tvs are intended to be used as binders for existential type args
919 -- arg_ids are indended to be used as binders for value arguments,
920 -- and their types have been instantiated with inst_tys and ex_tys
921 -- The arg_ids include both evidence and
922 -- programmer-specified arguments (both after rep-ing)
925 -- The following constructor T1
928 -- T1 :: forall b. Int -> b -> T(a,b)
931 -- has representation type
932 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
935 -- dataConInstPat fss us T1 (a1',b') will return
937 -- ([a1'', b''], [c :: (a1', b')~(a1'', b''), x :: Int, y :: b''])
939 -- where the double-primed variables are created with the FastStrings and
940 -- Uniques given as fss and us
941 dataConInstPat fss uniqs con inst_tys
942 = (ex_bndrs, arg_ids)
944 univ_tvs = dataConUnivTyVars con
945 ex_tvs = dataConExTyVars con
946 arg_tys = dataConRepArgTys con
950 -- split the Uniques and FastStrings
951 (ex_uniqs, id_uniqs) = splitAt n_ex uniqs
952 (ex_fss, id_fss) = splitAt n_ex fss
954 -- Make existential type variables
955 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
956 mk_ex_var uniq fs var = mkTyVar new_name kind
958 new_name = mkSysTvName uniq fs
961 -- Make the instantiating substitution
962 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
964 -- Make value vars, instantiating types
965 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (Type.substTy subst ty) noSrcSpan
966 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
969 %************************************************************************
973 %************************************************************************
976 -- | A cheap equality test which bales out fast!
977 -- If it returns @True@ the arguments are definitely equal,
978 -- otherwise, they may or may not be equal.
980 -- See also 'exprIsBig'
981 cheapEqExpr :: Expr b -> Expr b -> Bool
983 cheapEqExpr (Var v1) (Var v2) = v1==v2
984 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
985 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
986 cheapEqExpr (Coercion c1) (Coercion c2) = c1 `coreEqCoercion` c2
988 cheapEqExpr (App f1 a1) (App f2 a2)
989 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
991 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
992 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
994 cheapEqExpr _ _ = False
998 exprIsBig :: Expr b -> Bool
999 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1000 exprIsBig (Lit _) = False
1001 exprIsBig (Var _) = False
1002 exprIsBig (Type _) = False
1003 exprIsBig (Coercion _) = False
1004 exprIsBig (Lam _ e) = exprIsBig e
1005 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1006 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1011 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1012 -- Compares for equality, modulo alpha
1013 eqExpr in_scope e1 e2
1014 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1016 id_unf _ = noUnfolding -- Don't expand
1020 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1021 -- ^ Compares expressions for equality, modulo alpha.
1022 -- Does /not/ look through newtypes or predicate types
1023 -- Used in rule matching, and also CSE
1025 eqExprX id_unfolding_fun env e1 e2
1028 go env (Var v1) (Var v2)
1029 | rnOccL env v1 == rnOccR env v2
1032 -- The next two rules expand non-local variables
1033 -- C.f. Note [Expanding variables] in Rules.lhs
1034 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1036 | not (locallyBoundL env v1)
1037 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1038 = go (nukeRnEnvL env) e1' e2
1041 | not (locallyBoundR env v2)
1042 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1043 = go (nukeRnEnvR env) e1 e2'
1045 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1046 go env (Type t1) (Type t2) = eqTypeX env t1 t2
1047 go env (Coercion co1) (Coercion co2) = coreEqCoercion2 env co1 co2
1048 go env (Cast e1 co1) (Cast e2 co2) = coreEqCoercion2 env co1 co2 && go env e1 e2
1049 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1050 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1052 go env (Lam b1 e1) (Lam b2 e2)
1053 = eqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1054 && go (rnBndr2 env b1 b2) e1 e2
1056 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1057 = go env r1 r2 -- No need to check binder types, since RHSs match
1058 && go (rnBndr2 env v1 v2) e1 e2
1060 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1061 = all2 (go env') rs1 rs2 && go env' e1 e2
1063 (bs1,rs1) = unzip ps1
1064 (bs2,rs2) = unzip ps2
1065 env' = rnBndrs2 env bs1 bs2
1067 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1069 && eqTypeX env (idType b1) (idType b2)
1070 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1075 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1076 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1079 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1080 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1087 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1088 locallyBoundL rn_env v = inRnEnvL rn_env v
1089 locallyBoundR rn_env v = inRnEnvR rn_env v
1093 %************************************************************************
1095 \subsection{The size of an expression}
1097 %************************************************************************
1100 coreBindsSize :: [CoreBind] -> Int
1101 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1103 exprSize :: CoreExpr -> Int
1104 -- ^ A measure of the size of the expressions, strictly greater than 0
1105 -- It also forces the expression pretty drastically as a side effect
1106 -- Counts *leaves*, not internal nodes. Types and coercions are not counted.
1107 exprSize (Var v) = v `seq` 1
1108 exprSize (Lit lit) = lit `seq` 1
1109 exprSize (App f a) = exprSize f + exprSize a
1110 exprSize (Lam b e) = varSize b + exprSize e
1111 exprSize (Let b e) = bindSize b + exprSize e
1112 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1113 exprSize (Cast e co) = (seqCo co `seq` 1) + exprSize e
1114 exprSize (Note n e) = noteSize n + exprSize e
1115 exprSize (Type t) = seqType t `seq` 1
1116 exprSize (Coercion co) = seqCo co `seq` 1
1118 noteSize :: Note -> Int
1119 noteSize (SCC cc) = cc `seq` 1
1120 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1122 varSize :: Var -> Int
1123 varSize b | isTyVar b = 1
1124 | otherwise = seqType (idType b) `seq`
1125 megaSeqIdInfo (idInfo b) `seq`
1128 varsSize :: [Var] -> Int
1129 varsSize = sum . map varSize
1131 bindSize :: CoreBind -> Int
1132 bindSize (NonRec b e) = varSize b + exprSize e
1133 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1135 pairSize :: (Var, CoreExpr) -> Int
1136 pairSize (b,e) = varSize b + exprSize e
1138 altSize :: CoreAlt -> Int
1139 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1143 data CoreStats = CS { cs_tm, cs_ty, cs_co :: Int }
1145 plusCS :: CoreStats -> CoreStats -> CoreStats
1146 plusCS (CS { cs_tm = p1, cs_ty = q1, cs_co = r1 })
1147 (CS { cs_tm = p2, cs_ty = q2, cs_co = r2 })
1148 = CS { cs_tm = p1+p2, cs_ty = q1+q2, cs_co = r1+r2 }
1150 zeroCS, oneTM :: CoreStats
1151 zeroCS = CS { cs_tm = 0, cs_ty = 0, cs_co = 0 }
1152 oneTM = zeroCS { cs_tm = 1 }
1154 sumCS :: (a -> CoreStats) -> [a] -> CoreStats
1155 sumCS f = foldr (plusCS . f) zeroCS
1157 coreBindsStats :: [CoreBind] -> CoreStats
1158 coreBindsStats = sumCS bindStats
1160 bindStats :: CoreBind -> CoreStats
1161 bindStats (NonRec v r) = bindingStats v r
1162 bindStats (Rec prs) = sumCS (\(v,r) -> bindingStats v r) prs
1164 bindingStats :: Var -> CoreExpr -> CoreStats
1165 bindingStats v r = bndrStats v `plusCS` exprStats r
1167 bndrStats :: Var -> CoreStats
1168 bndrStats v = oneTM `plusCS` tyStats (varType v)
1170 exprStats :: CoreExpr -> CoreStats
1171 exprStats (Var {}) = oneTM
1172 exprStats (Lit {}) = oneTM
1173 exprStats (Type t) = tyStats t
1174 exprStats (Coercion c) = coStats c
1175 exprStats (App f a) = exprStats f `plusCS` exprStats a
1176 exprStats (Lam b e) = bndrStats b `plusCS` exprStats e
1177 exprStats (Let b e) = bindStats b `plusCS` exprStats e
1178 exprStats (Case e b _ as) = exprStats e `plusCS` bndrStats b `plusCS` sumCS altStats as
1179 exprStats (Cast e co) = coStats co `plusCS` exprStats e
1180 exprStats (Note _ e) = exprStats e
1182 altStats :: CoreAlt -> CoreStats
1183 altStats (_, bs, r) = sumCS bndrStats bs `plusCS` exprStats r
1185 tyStats :: Type -> CoreStats
1186 tyStats ty = zeroCS { cs_ty = typeSize ty }
1188 coStats :: Coercion -> CoreStats
1189 coStats co = zeroCS { cs_co = coercionSize co }
1192 %************************************************************************
1194 \subsection{Hashing}
1196 %************************************************************************
1199 hashExpr :: CoreExpr -> Int
1200 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1201 -- Two expressions that hash to the different Ints are definitely unequal.
1203 -- The emphasis is on a crude, fast hash, rather than on high precision.
1205 -- But unequal here means \"not identical\"; two alpha-equivalent
1206 -- expressions may hash to the different Ints.
1208 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1209 -- (at least if we want the above invariant to be true).
1211 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1212 -- UniqFM doesn't like negative Ints
1214 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1216 hash_expr :: HashEnv -> CoreExpr -> Word32
1217 -- Word32, because we're expecting overflows here, and overflowing
1218 -- signed types just isn't cool. In C it's even undefined.
1219 hash_expr env (Note _ e) = hash_expr env e
1220 hash_expr env (Cast e _) = hash_expr env e
1221 hash_expr env (Var v) = hashVar env v
1222 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1223 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1224 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1225 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1226 hash_expr env (Case e _ _ _) = hash_expr env e
1227 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1228 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1229 -- Shouldn't happen. Better to use WARN than trace, because trace
1230 -- prevents the CPR optimisation kicking in for hash_expr.
1231 hash_expr _ (Coercion _) = WARN(True, text "hash_expr: coercion") 1
1233 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1234 fast_hash_expr env (Var v) = hashVar env v
1235 fast_hash_expr env (Type t) = fast_hash_type env t
1236 fast_hash_expr env (Coercion co) = fast_hash_co env co
1237 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1238 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1239 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1240 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1241 fast_hash_expr _ _ = 1
1243 fast_hash_type :: HashEnv -> Type -> Word32
1244 fast_hash_type env ty
1245 | Just tv <- getTyVar_maybe ty = hashVar env tv
1246 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1247 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1250 fast_hash_co :: HashEnv -> Coercion -> Word32
1252 | Just cv <- getCoVar_maybe co = hashVar env cv
1253 | Just (tc,cos) <- splitTyConAppCo_maybe co = let hash_tc = fromIntegral (hashName (tyConName tc))
1254 in foldr (\c n -> fast_hash_co env c + n) hash_tc cos
1257 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1258 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1260 hashVar :: HashEnv -> Var -> Word32
1262 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1266 %************************************************************************
1270 %************************************************************************
1272 Note [Eta reduction conditions]
1273 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1274 We try for eta reduction here, but *only* if we get all the way to an
1275 trivial expression. We don't want to remove extra lambdas unless we
1276 are going to avoid allocating this thing altogether.
1278 There are some particularly delicate points here:
1280 * Eta reduction is not valid in general:
1282 This matters, partly for old-fashioned correctness reasons but,
1283 worse, getting it wrong can yield a seg fault. Consider
1285 h y = case (case y of { True -> f `seq` True; False -> False }) of
1286 True -> ...; False -> ...
1288 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1289 says f=bottom, and replaces the (f `seq` True) with just
1290 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1291 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1292 the definition again, so that it does not termninate after all.
1293 Result: seg-fault because the boolean case actually gets a function value.
1296 So it's important to to the right thing.
1298 * Note [Arity care]: we need to be careful if we just look at f's
1299 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1300 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1301 arity when checking that 'f' is a value. Otherwise we will
1306 Which might change a terminiating program (think (f `seq` e)) to a
1307 non-terminating one. So we check for being a loop breaker first.
1309 However for GlobalIds we can look at the arity; and for primops we
1310 must, since they have no unfolding.
1312 * Regardless of whether 'f' is a value, we always want to
1313 reduce (/\a -> f a) to f
1314 This came up in a RULE: foldr (build (/\a -> g a))
1315 did not match foldr (build (/\b -> ...something complex...))
1316 The type checker can insert these eta-expanded versions,
1317 with both type and dictionary lambdas; hence the slightly
1320 * Never *reduce* arity. For example
1322 Then if h has arity 1 we don't want to eta-reduce because then
1323 f's arity would decrease, and that is bad
1325 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1328 Note [Eta reduction with casted arguments]
1329 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1331 (\(x:t3). f (x |> g)) :: t3 -> t2
1335 This should be eta-reduced to
1339 So we need to accumulate a coercion, pushing it inward (past
1340 variable arguments only) thus:
1341 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1342 f (x:t) |> co --> (f |> (t -> co)) x
1343 f @ a |> co --> (f |> (forall a.co)) @ a
1344 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1345 These are the equations for ok_arg.
1347 It's true that we could also hope to eta reduce these:
1350 But the simplifier pushes those casts outwards, so we don't
1351 need to address that here.
1354 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1355 tryEtaReduce bndrs body
1356 = go (reverse bndrs) body (mkReflCo (exprType body))
1358 incoming_arity = count isId bndrs
1360 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1361 -> CoreExpr -- Of type tr
1362 -> Coercion -- Of type tr ~ ts
1363 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1364 -- See Note [Eta reduction with casted arguments]
1365 -- for why we have an accumulating coercion
1367 | ok_fun fun = Just (mkCoerce co fun)
1369 go (b : bs) (App fun arg) co
1370 | Just co' <- ok_arg b arg co
1373 go _ _ _ = Nothing -- Failure!
1376 -- Note [Eta reduction conditions]
1377 ok_fun (App fun (Type ty))
1378 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1381 = not (fun_id `elem` bndrs)
1382 && (ok_fun_id fun_id || all ok_lam bndrs)
1386 ok_fun_id fun = fun_arity fun >= incoming_arity
1389 fun_arity fun -- See Note [Arity care]
1390 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1391 | otherwise = idArity fun
1394 ok_lam v = isTyVar v || isEvVar v
1397 ok_arg :: Var -- Of type bndr_t
1398 -> CoreExpr -- Of type arg_t
1399 -> Coercion -- Of kind (t1~t2)
1400 -> Maybe Coercion -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1401 -- (and similarly for tyvars, coercion args)
1402 -- See Note [Eta reduction with casted arguments]
1403 ok_arg bndr (Type ty) co
1404 | Just tv <- getTyVar_maybe ty
1405 , bndr == tv = Just (mkForAllCo tv co)
1406 ok_arg bndr (Var v) co
1407 | bndr == v = Just (mkFunCo (mkReflCo (idType bndr)) co)
1408 ok_arg bndr (Cast (Var v) co_arg) co
1409 | bndr == v = Just (mkFunCo (mkSymCo co_arg) co)
1410 -- The simplifier combines multiple casts into one,
1411 -- so we can have a simple-minded pattern match here
1412 ok_arg _ _ _ = Nothing
1416 %************************************************************************
1418 \subsection{Determining non-updatable right-hand-sides}
1420 %************************************************************************
1422 Top-level constructor applications can usually be allocated
1423 statically, but they can't if the constructor, or any of the
1424 arguments, come from another DLL (because we can't refer to static
1425 labels in other DLLs).
1427 If this happens we simply make the RHS into an updatable thunk,
1428 and 'execute' it rather than allocating it statically.
1431 -- | This function is called only on *top-level* right-hand sides.
1432 -- Returns @True@ if the RHS can be allocated statically in the output,
1433 -- with no thunks involved at all.
1434 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1435 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1436 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1437 -- update flag on it and (iii) in DsExpr to decide how to expand
1440 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1441 -- (a) a value lambda
1442 -- (b) a saturated constructor application with static args
1444 -- BUT watch out for
1445 -- (i) Any cross-DLL references kill static-ness completely
1446 -- because they must be 'executed' not statically allocated
1447 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1448 -- this is not necessary)
1450 -- (ii) We treat partial applications as redexes, because in fact we
1451 -- make a thunk for them that runs and builds a PAP
1452 -- at run-time. The only appliations that are treated as
1453 -- static are *saturated* applications of constructors.
1455 -- We used to try to be clever with nested structures like this:
1456 -- ys = (:) w ((:) w [])
1457 -- on the grounds that CorePrep will flatten ANF-ise it later.
1458 -- But supporting this special case made the function much more
1459 -- complicated, because the special case only applies if there are no
1460 -- enclosing type lambdas:
1461 -- ys = /\ a -> Foo (Baz ([] a))
1462 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1464 -- But in fact, even without -O, nested structures at top level are
1465 -- flattened by the simplifier, so we don't need to be super-clever here.
1469 -- f = \x::Int. x+7 TRUE
1470 -- p = (True,False) TRUE
1472 -- d = (fst p, False) FALSE because there's a redex inside
1473 -- (this particular one doesn't happen but...)
1475 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1476 -- n = /\a. Nil a TRUE
1478 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1481 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1482 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1484 -- b) (C x xs), where C is a contructor is updatable if the application is
1487 -- c) don't look through unfolding of f in (f x).
1489 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1491 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1494 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1495 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1496 is_static in_arg (Cast e _) = is_static in_arg e
1498 is_static _ (Lit lit)
1500 MachLabel _ _ _ -> False
1502 -- A MachLabel (foreign import "&foo") in an argument
1503 -- prevents a constructor application from being static. The
1504 -- reason is that it might give rise to unresolvable symbols
1505 -- in the object file: under Linux, references to "weak"
1506 -- symbols from the data segment give rise to "unresolvable
1507 -- relocation" errors at link time This might be due to a bug
1508 -- in the linker, but we'll work around it here anyway.
1511 is_static in_arg other_expr = go other_expr 0
1513 go (Var f) n_val_args
1514 #if mingw32_TARGET_OS
1515 | not (_is_dynamic_name (idName f))
1517 = saturated_data_con f n_val_args
1518 || (in_arg && n_val_args == 0)
1519 -- A naked un-applied variable is *not* deemed a static RHS
1521 -- Reason: better to update so that the indirection gets shorted
1522 -- out, and the true value will be seen
1523 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1524 -- are always updatable. If you do so, make sure that non-updatable
1525 -- ones have enough space for their static link field!
1527 go (App f a) n_val_args
1528 | isTypeArg a = go f n_val_args
1529 | not in_arg && is_static True a = go f (n_val_args + 1)
1530 -- The (not in_arg) checks that we aren't in a constructor argument;
1531 -- if we are, we don't allow (value) applications of any sort
1533 -- NB. In case you wonder, args are sometimes not atomic. eg.
1534 -- x = D# (1.0## /## 2.0##)
1535 -- can't float because /## can fail.
1537 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1538 go (Cast e _) n_val_args = go e n_val_args
1541 saturated_data_con f n_val_args
1542 = case isDataConWorkId_maybe f of
1543 Just dc -> n_val_args == dataConRepArity dc