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.
595 -- The principle here is that
596 -- let x = a +# b in c *# x
597 -- should behave equivalently to
599 -- Since lets with cheap RHSs are accepted,
600 -- so should paps with cheap arguments
603 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
604 -- In principle we should worry about primops
605 -- that return a type variable, since the result
606 -- might be applied to something, but I'm not going
607 -- to bother to check the number of args
610 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
611 go_sel _ = False -- look cheap, so we will substitute it inside a
612 -- lambda. Particularly for dictionary field selection.
613 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
614 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
616 isCheapApp :: CheapAppFun
617 isCheapApp fn n_val_args
619 || n_val_args < idArity fn
621 isExpandableApp :: CheapAppFun
622 isExpandableApp fn n_val_args
624 || n_val_args < idArity fn
625 || go n_val_args (idType fn)
627 -- See if all the arguments are PredTys (implicit params or classes)
628 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
631 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
632 | Just (arg, ty) <- splitFunTy_maybe ty
633 , isPredTy arg = go (n_val_args-1) ty
637 Note [Expandable overloadings]
638 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
639 Suppose the user wrote this
640 {-# RULE forall x. foo (negate x) = h x #-}
641 f x = ....(foo (negate x))....
642 He'd expect the rule to fire. But since negate is overloaded, we might
644 f = \d -> let n = negate d in \x -> ...foo (n x)...
645 So we treat the application of a function (negate in this case) to a
646 *dictionary* as expandable. In effect, every function is CONLIKE when
647 it's applied only to dictionaries.
650 %************************************************************************
654 %************************************************************************
657 -- | 'exprOkForSpeculation' returns True of an expression that is:
659 -- * Safe to evaluate even if normal order eval might not
660 -- evaluate the expression at all, or
662 -- * Safe /not/ to evaluate even if normal order would do so
664 -- It is usually called on arguments of unlifted type, but not always
665 -- In particular, Simplify.rebuildCase calls it on lifted types
666 -- when a 'case' is a plain 'seq'. See the example in
667 -- Note [exprOkForSpeculation: case expressions] below
669 -- Precisely, it returns @True@ iff:
671 -- * The expression guarantees to terminate,
673 -- * without raising an exception,
674 -- * without causing a side effect (e.g. writing a mutable variable)
676 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
677 -- As an example of the considerations in this test, consider:
679 -- > let x = case y# +# 1# of { r# -> I# r# }
682 -- being translated to:
684 -- > case y# +# 1# of { r# ->
689 -- We can only do this if the @y + 1@ is ok for speculation: it has no
690 -- side effects, and can't diverge or raise an exception.
691 exprOkForSpeculation :: CoreExpr -> Bool
692 exprOkForSpeculation (Lit _) = True
693 exprOkForSpeculation (Type _) = True
694 exprOkForSpeculation (Coercion _) = True
696 exprOkForSpeculation (Var v)
697 | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
698 | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
699 || isDataConWorkId v -- Nullary constructors
700 || idArity v > 0 -- Functions
701 || isEvaldUnfolding (idUnfolding v) -- Let-bound values
703 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
704 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
706 exprOkForSpeculation (Case e _ _ alts)
707 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
708 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
710 exprOkForSpeculation other_expr
711 = case collectArgs other_expr of
712 (Var f, args) -> spec_ok (idDetails f) args
716 spec_ok (DataConWorkId _) _
717 = True -- The strictness of the constructor has already
718 -- been expressed by its "wrapper", so we don't need
719 -- to take the arguments into account
721 spec_ok (PrimOpId op) args
722 | isDivOp op, -- Special case for dividing operations that fail
723 [arg1, Lit lit] <- args -- only if the divisor is zero
724 = not (isZeroLit lit) && exprOkForSpeculation arg1
725 -- Often there is a literal divisor, and this
726 -- can get rid of a thunk in an inner looop
728 | DataToTagOp <- op -- See Note [dataToTag speculation]
732 = primOpOkForSpeculation op &&
733 all exprOkForSpeculation args
734 -- A bit conservative: we don't really need
735 -- to care about lazy arguments, but this is easy
737 spec_ok (DFunId _ new_type) _ = not new_type
738 -- DFuns terminate, unless the dict is implemented with a newtype
739 -- in which case they may not
743 -- | True of dyadic operators that can fail only if the second arg is zero!
744 isDivOp :: PrimOp -> Bool
745 -- This function probably belongs in PrimOp, or even in
746 -- an automagically generated file.. but it's such a
747 -- special case I thought I'd leave it here for now.
748 isDivOp IntQuotOp = True
749 isDivOp IntRemOp = True
750 isDivOp WordQuotOp = True
751 isDivOp WordRemOp = True
752 isDivOp FloatDivOp = True
753 isDivOp DoubleDivOp = True
757 Note [exprOkForSpeculation: case expressions]
758 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
759 It's always sound for exprOkForSpeculation to return False, and we
760 don't want it to take too long, so it bales out on complicated-looking
761 terms. Notably lets, which can be stacked very deeply; and in any
762 case the argument of exprOkForSpeculation is usually in a strict context,
763 so any lets will have been floated away.
765 However, we keep going on case-expressions. An example like this one
766 showed up in DPH code (Trac #3717):
769 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
771 If exprOkForSpeculation doesn't look through case expressions, you get this:
773 \ (ww :: GHC.Prim.Int#) ->
775 __DEFAULT -> case (case <# ds 5 of _ {
776 GHC.Types.False -> lvl1;
777 GHC.Types.True -> lvl})
779 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
783 The inner case is redundant, and should be nuked.
785 Note [dataToTag speculation]
786 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
788 f x = let v::Int# = dataToTag# x
790 We say "yes", even though 'x' may not be evaluated. Reasons
792 * dataToTag#'s strictness means that its argument often will be
793 evaluated, but FloatOut makes that temporarily untrue
794 case x of y -> let v = dataToTag# y in ...
796 case x of y -> let v = dataToTag# x in ...
797 Note that we look at 'x' instead of 'y' (this is to improve
798 floating in FloatOut). So Lint complains.
800 Moreover, it really *might* improve floating to let the
803 * CorePrep makes sure dataToTag#'s argument is evaluated, just
804 before code gen. Until then, it's not guaranteed
807 %************************************************************************
809 exprIsHNF, exprIsConLike
811 %************************************************************************
814 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
816 -- | exprIsHNF returns true for expressions that are certainly /already/
817 -- evaluated to /head/ normal form. This is used to decide whether it's ok
820 -- > case x of _ -> e
826 -- and to decide whether it's safe to discard a 'seq'.
828 -- So, it does /not/ treat variables as evaluated, unless they say they are.
829 -- However, it /does/ treat partial applications and constructor applications
830 -- as values, even if their arguments are non-trivial, provided the argument
831 -- type is lifted. For example, both of these are values:
833 -- > (:) (f x) (map f xs)
834 -- > map (...redex...)
836 -- because 'seq' on such things completes immediately.
838 -- For unlifted argument types, we have to be careful:
842 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
843 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
844 -- unboxed type must be ok-for-speculation (or trivial).
845 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
846 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
850 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
851 -- data constructors. Conlike arguments are considered interesting by the
853 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
854 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
856 -- | Returns true for values or value-like expressions. These are lambdas,
857 -- constructors / CONLIKE functions (as determined by the function argument)
860 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
861 exprIsHNFlike is_con is_con_unf = is_hnf_like
863 is_hnf_like (Var v) -- NB: There are no value args at this point
864 = is_con v -- Catches nullary constructors,
865 -- so that [] and () are values, for example
866 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
867 || is_con_unf (idUnfolding v)
868 -- Check the thing's unfolding; it might be bound to a value
869 -- We don't look through loop breakers here, which is a bit conservative
870 -- but otherwise I worry that if an Id's unfolding is just itself,
871 -- we could get an infinite loop
873 is_hnf_like (Lit _) = True
874 is_hnf_like (Type _) = True -- Types are honorary Values;
875 -- we don't mind copying them
876 is_hnf_like (Coercion _) = True -- Same for coercions
877 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
878 is_hnf_like (Note _ e) = is_hnf_like e
879 is_hnf_like (Cast e _) = is_hnf_like e
880 is_hnf_like (App e (Type _)) = is_hnf_like e
881 is_hnf_like (App e (Coercion _)) = is_hnf_like e
882 is_hnf_like (App e a) = app_is_value e [a]
883 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
884 is_hnf_like _ = False
886 -- There is at least one value argument
887 app_is_value :: CoreExpr -> [CoreArg] -> Bool
888 app_is_value (Var fun) args
889 = idArity fun > valArgCount args -- Under-applied function
890 || is_con fun -- or constructor-like
891 app_is_value (Note _ f) as = app_is_value f as
892 app_is_value (Cast f _) as = app_is_value f as
893 app_is_value (App f a) as = app_is_value f (a:as)
894 app_is_value _ _ = False
898 %************************************************************************
900 Instantiating data constructors
902 %************************************************************************
904 These InstPat functions go here to avoid circularity between DataCon and Id
907 dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
908 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
910 dataConRepInstPat = dataConInstPat (repeat ((fsLit "ipv")))
911 dataConRepFSInstPat = dataConInstPat
913 dataConInstPat :: [FastString] -- A long enough list of FSs to use for names
914 -> [Unique] -- An equally long list of uniques, at least one for each binder
916 -> [Type] -- Types to instantiate the universally quantified tyvars
917 -> ([TyVar], [Id]) -- Return instantiated variables
918 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
919 -- (ex_tvs, arg_ids),
921 -- ex_tvs are intended to be used as binders for existential type args
923 -- arg_ids are indended to be used as binders for value arguments,
924 -- and their types have been instantiated with inst_tys and ex_tys
925 -- The arg_ids include both evidence and
926 -- programmer-specified arguments (both after rep-ing)
929 -- The following constructor T1
932 -- T1 :: forall b. Int -> b -> T(a,b)
935 -- has representation type
936 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
939 -- dataConInstPat fss us T1 (a1',b') will return
941 -- ([a1'', b''], [c :: (a1', b')~(a1'', b''), x :: Int, y :: b''])
943 -- where the double-primed variables are created with the FastStrings and
944 -- Uniques given as fss and us
945 dataConInstPat fss uniqs con inst_tys
946 = (ex_bndrs, arg_ids)
948 univ_tvs = dataConUnivTyVars con
949 ex_tvs = dataConExTyVars con
950 arg_tys = dataConRepArgTys con
954 -- split the Uniques and FastStrings
955 (ex_uniqs, id_uniqs) = splitAt n_ex uniqs
956 (ex_fss, id_fss) = splitAt n_ex fss
958 -- Make existential type variables
959 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
960 mk_ex_var uniq fs var = mkTyVar new_name kind
962 new_name = mkSysTvName uniq fs
965 -- Make the instantiating substitution
966 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
968 -- Make value vars, instantiating types
969 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (Type.substTy subst ty) noSrcSpan
970 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
973 %************************************************************************
977 %************************************************************************
980 -- | A cheap equality test which bales out fast!
981 -- If it returns @True@ the arguments are definitely equal,
982 -- otherwise, they may or may not be equal.
984 -- See also 'exprIsBig'
985 cheapEqExpr :: Expr b -> Expr b -> Bool
987 cheapEqExpr (Var v1) (Var v2) = v1==v2
988 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
989 cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
990 cheapEqExpr (Coercion c1) (Coercion c2) = c1 `coreEqCoercion` c2
992 cheapEqExpr (App f1 a1) (App f2 a2)
993 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
995 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
996 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
998 cheapEqExpr _ _ = False
1002 exprIsBig :: Expr b -> Bool
1003 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1004 exprIsBig (Lit _) = False
1005 exprIsBig (Var _) = False
1006 exprIsBig (Type _) = False
1007 exprIsBig (Coercion _) = False
1008 exprIsBig (Lam _ e) = exprIsBig e
1009 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1010 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1015 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
1016 -- Compares for equality, modulo alpha
1017 eqExpr in_scope e1 e2
1018 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
1020 id_unf _ = noUnfolding -- Don't expand
1024 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1025 -- ^ Compares expressions for equality, modulo alpha.
1026 -- Does /not/ look through newtypes or predicate types
1027 -- Used in rule matching, and also CSE
1029 eqExprX id_unfolding_fun env e1 e2
1032 go env (Var v1) (Var v2)
1033 | rnOccL env v1 == rnOccR env v2
1036 -- The next two rules expand non-local variables
1037 -- C.f. Note [Expanding variables] in Rules.lhs
1038 -- and Note [Do not expand locally-bound variables] in Rules.lhs
1040 | not (locallyBoundL env v1)
1041 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
1042 = go (nukeRnEnvL env) e1' e2
1045 | not (locallyBoundR env v2)
1046 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1047 = go (nukeRnEnvR env) e1 e2'
1049 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1050 go env (Type t1) (Type t2) = eqTypeX env t1 t2
1051 go env (Coercion co1) (Coercion co2) = coreEqCoercion2 env co1 co2
1052 go env (Cast e1 co1) (Cast e2 co2) = coreEqCoercion2 env co1 co2 && go env e1 e2
1053 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1054 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1056 go env (Lam b1 e1) (Lam b2 e2)
1057 = eqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1058 && go (rnBndr2 env b1 b2) e1 e2
1060 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1061 = go env r1 r2 -- No need to check binder types, since RHSs match
1062 && go (rnBndr2 env v1 v2) e1 e2
1064 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1065 = all2 (go env') rs1 rs2 && go env' e1 e2
1067 (bs1,rs1) = unzip ps1
1068 (bs2,rs2) = unzip ps2
1069 env' = rnBndrs2 env bs1 bs2
1071 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1073 && eqTypeX env (idType b1) (idType b2)
1074 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1079 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1080 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1083 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1084 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1091 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1092 locallyBoundL rn_env v = inRnEnvL rn_env v
1093 locallyBoundR rn_env v = inRnEnvR rn_env v
1097 %************************************************************************
1099 \subsection{The size of an expression}
1101 %************************************************************************
1104 coreBindsSize :: [CoreBind] -> Int
1105 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1107 exprSize :: CoreExpr -> Int
1108 -- ^ A measure of the size of the expressions, strictly greater than 0
1109 -- It also forces the expression pretty drastically as a side effect
1110 -- Counts *leaves*, not internal nodes. Types and coercions are not counted.
1111 exprSize (Var v) = v `seq` 1
1112 exprSize (Lit lit) = lit `seq` 1
1113 exprSize (App f a) = exprSize f + exprSize a
1114 exprSize (Lam b e) = varSize b + exprSize e
1115 exprSize (Let b e) = bindSize b + exprSize e
1116 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1117 exprSize (Cast e co) = (seqCo co `seq` 1) + exprSize e
1118 exprSize (Note n e) = noteSize n + exprSize e
1119 exprSize (Type t) = seqType t `seq` 1
1120 exprSize (Coercion co) = seqCo co `seq` 1
1122 noteSize :: Note -> Int
1123 noteSize (SCC cc) = cc `seq` 1
1124 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1126 varSize :: Var -> Int
1127 varSize b | isTyVar b = 1
1128 | otherwise = seqType (idType b) `seq`
1129 megaSeqIdInfo (idInfo b) `seq`
1132 varsSize :: [Var] -> Int
1133 varsSize = sum . map varSize
1135 bindSize :: CoreBind -> Int
1136 bindSize (NonRec b e) = varSize b + exprSize e
1137 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1139 pairSize :: (Var, CoreExpr) -> Int
1140 pairSize (b,e) = varSize b + exprSize e
1142 altSize :: CoreAlt -> Int
1143 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1147 data CoreStats = CS { cs_tm, cs_ty, cs_co :: Int }
1149 plusCS :: CoreStats -> CoreStats -> CoreStats
1150 plusCS (CS { cs_tm = p1, cs_ty = q1, cs_co = r1 })
1151 (CS { cs_tm = p2, cs_ty = q2, cs_co = r2 })
1152 = CS { cs_tm = p1+p2, cs_ty = q1+q2, cs_co = r1+r2 }
1154 zeroCS, oneTM :: CoreStats
1155 zeroCS = CS { cs_tm = 0, cs_ty = 0, cs_co = 0 }
1156 oneTM = zeroCS { cs_tm = 1 }
1158 sumCS :: (a -> CoreStats) -> [a] -> CoreStats
1159 sumCS f = foldr (plusCS . f) zeroCS
1161 coreBindsStats :: [CoreBind] -> CoreStats
1162 coreBindsStats = sumCS bindStats
1164 bindStats :: CoreBind -> CoreStats
1165 bindStats (NonRec v r) = bindingStats v r
1166 bindStats (Rec prs) = sumCS (\(v,r) -> bindingStats v r) prs
1168 bindingStats :: Var -> CoreExpr -> CoreStats
1169 bindingStats v r = bndrStats v `plusCS` exprStats r
1171 bndrStats :: Var -> CoreStats
1172 bndrStats v = oneTM `plusCS` tyStats (varType v)
1174 exprStats :: CoreExpr -> CoreStats
1175 exprStats (Var {}) = oneTM
1176 exprStats (Lit {}) = oneTM
1177 exprStats (Type t) = tyStats t
1178 exprStats (Coercion c) = coStats c
1179 exprStats (App f a) = exprStats f `plusCS` exprStats a
1180 exprStats (Lam b e) = bndrStats b `plusCS` exprStats e
1181 exprStats (Let b e) = bindStats b `plusCS` exprStats e
1182 exprStats (Case e b _ as) = exprStats e `plusCS` bndrStats b `plusCS` sumCS altStats as
1183 exprStats (Cast e co) = coStats co `plusCS` exprStats e
1184 exprStats (Note _ e) = exprStats e
1186 altStats :: CoreAlt -> CoreStats
1187 altStats (_, bs, r) = sumCS bndrStats bs `plusCS` exprStats r
1189 tyStats :: Type -> CoreStats
1190 tyStats ty = zeroCS { cs_ty = typeSize ty }
1192 coStats :: Coercion -> CoreStats
1193 coStats co = zeroCS { cs_co = coercionSize co }
1196 %************************************************************************
1198 \subsection{Hashing}
1200 %************************************************************************
1203 hashExpr :: CoreExpr -> Int
1204 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1205 -- Two expressions that hash to the different Ints are definitely unequal.
1207 -- The emphasis is on a crude, fast hash, rather than on high precision.
1209 -- But unequal here means \"not identical\"; two alpha-equivalent
1210 -- expressions may hash to the different Ints.
1212 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1213 -- (at least if we want the above invariant to be true).
1215 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1216 -- UniqFM doesn't like negative Ints
1218 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1220 hash_expr :: HashEnv -> CoreExpr -> Word32
1221 -- Word32, because we're expecting overflows here, and overflowing
1222 -- signed types just isn't cool. In C it's even undefined.
1223 hash_expr env (Note _ e) = hash_expr env e
1224 hash_expr env (Cast e _) = hash_expr env e
1225 hash_expr env (Var v) = hashVar env v
1226 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1227 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1228 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1229 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1230 hash_expr env (Case e _ _ _) = hash_expr env e
1231 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1232 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1233 -- Shouldn't happen. Better to use WARN than trace, because trace
1234 -- prevents the CPR optimisation kicking in for hash_expr.
1235 hash_expr _ (Coercion _) = WARN(True, text "hash_expr: coercion") 1
1237 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1238 fast_hash_expr env (Var v) = hashVar env v
1239 fast_hash_expr env (Type t) = fast_hash_type env t
1240 fast_hash_expr env (Coercion co) = fast_hash_co env co
1241 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1242 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1243 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1244 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1245 fast_hash_expr _ _ = 1
1247 fast_hash_type :: HashEnv -> Type -> Word32
1248 fast_hash_type env ty
1249 | Just tv <- getTyVar_maybe ty = hashVar env tv
1250 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1251 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1254 fast_hash_co :: HashEnv -> Coercion -> Word32
1256 | Just cv <- getCoVar_maybe co = hashVar env cv
1257 | Just (tc,cos) <- splitTyConAppCo_maybe co = let hash_tc = fromIntegral (hashName (tyConName tc))
1258 in foldr (\c n -> fast_hash_co env c + n) hash_tc cos
1261 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1262 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1264 hashVar :: HashEnv -> Var -> Word32
1266 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1270 %************************************************************************
1274 %************************************************************************
1276 Note [Eta reduction conditions]
1277 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1278 We try for eta reduction here, but *only* if we get all the way to an
1279 trivial expression. We don't want to remove extra lambdas unless we
1280 are going to avoid allocating this thing altogether.
1282 There are some particularly delicate points here:
1284 * Eta reduction is not valid in general:
1286 This matters, partly for old-fashioned correctness reasons but,
1287 worse, getting it wrong can yield a seg fault. Consider
1289 h y = case (case y of { True -> f `seq` True; False -> False }) of
1290 True -> ...; False -> ...
1292 If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
1293 says f=bottom, and replaces the (f `seq` True) with just
1294 (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
1295 *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
1296 the definition again, so that it does not termninate after all.
1297 Result: seg-fault because the boolean case actually gets a function value.
1300 So it's important to to the right thing.
1302 * Note [Arity care]: we need to be careful if we just look at f's
1303 arity. Currently (Dec07), f's arity is visible in its own RHS (see
1304 Note [Arity robustness] in SimplEnv) so we must *not* trust the
1305 arity when checking that 'f' is a value. Otherwise we will
1310 Which might change a terminiating program (think (f `seq` e)) to a
1311 non-terminating one. So we check for being a loop breaker first.
1313 However for GlobalIds we can look at the arity; and for primops we
1314 must, since they have no unfolding.
1316 * Regardless of whether 'f' is a value, we always want to
1317 reduce (/\a -> f a) to f
1318 This came up in a RULE: foldr (build (/\a -> g a))
1319 did not match foldr (build (/\b -> ...something complex...))
1320 The type checker can insert these eta-expanded versions,
1321 with both type and dictionary lambdas; hence the slightly
1324 * Never *reduce* arity. For example
1326 Then if h has arity 1 we don't want to eta-reduce because then
1327 f's arity would decrease, and that is bad
1329 These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
1332 Note [Eta reduction with casted arguments]
1333 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1335 (\(x:t3). f (x |> g)) :: t3 -> t2
1339 This should be eta-reduced to
1343 So we need to accumulate a coercion, pushing it inward (past
1344 variable arguments only) thus:
1345 f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
1346 f (x:t) |> co --> (f |> (t -> co)) x
1347 f @ a |> co --> (f |> (forall a.co)) @ a
1348 f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
1349 These are the equations for ok_arg.
1351 It's true that we could also hope to eta reduce these:
1354 But the simplifier pushes those casts outwards, so we don't
1355 need to address that here.
1358 tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
1359 tryEtaReduce bndrs body
1360 = go (reverse bndrs) body (mkReflCo (exprType body))
1362 incoming_arity = count isId bndrs
1364 go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
1365 -> CoreExpr -- Of type tr
1366 -> Coercion -- Of type tr ~ ts
1367 -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
1368 -- See Note [Eta reduction with casted arguments]
1369 -- for why we have an accumulating coercion
1371 | ok_fun fun = Just (mkCoerce co fun)
1373 go (b : bs) (App fun arg) co
1374 | Just co' <- ok_arg b arg co
1377 go _ _ _ = Nothing -- Failure!
1380 -- Note [Eta reduction conditions]
1381 ok_fun (App fun (Type ty))
1382 | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
1385 = not (fun_id `elem` bndrs)
1386 && (ok_fun_id fun_id || all ok_lam bndrs)
1390 ok_fun_id fun = fun_arity fun >= incoming_arity
1393 fun_arity fun -- See Note [Arity care]
1394 | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
1395 | otherwise = idArity fun
1398 ok_lam v = isTyVar v || isEvVar v
1401 ok_arg :: Var -- Of type bndr_t
1402 -> CoreExpr -- Of type arg_t
1403 -> Coercion -- Of kind (t1~t2)
1404 -> Maybe Coercion -- Of type (arg_t -> t1 ~ bndr_t -> t2)
1405 -- (and similarly for tyvars, coercion args)
1406 -- See Note [Eta reduction with casted arguments]
1407 ok_arg bndr (Type ty) co
1408 | Just tv <- getTyVar_maybe ty
1409 , bndr == tv = Just (mkForAllCo tv co)
1410 ok_arg bndr (Var v) co
1411 | bndr == v = Just (mkFunCo (mkReflCo (idType bndr)) co)
1412 ok_arg bndr (Cast (Var v) co_arg) co
1413 | bndr == v = Just (mkFunCo (mkSymCo co_arg) co)
1414 -- The simplifier combines multiple casts into one,
1415 -- so we can have a simple-minded pattern match here
1416 ok_arg _ _ _ = Nothing
1420 %************************************************************************
1422 \subsection{Determining non-updatable right-hand-sides}
1424 %************************************************************************
1426 Top-level constructor applications can usually be allocated
1427 statically, but they can't if the constructor, or any of the
1428 arguments, come from another DLL (because we can't refer to static
1429 labels in other DLLs).
1431 If this happens we simply make the RHS into an updatable thunk,
1432 and 'execute' it rather than allocating it statically.
1435 -- | This function is called only on *top-level* right-hand sides.
1436 -- Returns @True@ if the RHS can be allocated statically in the output,
1437 -- with no thunks involved at all.
1438 rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
1439 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1440 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1441 -- update flag on it and (iii) in DsExpr to decide how to expand
1444 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1445 -- (a) a value lambda
1446 -- (b) a saturated constructor application with static args
1448 -- BUT watch out for
1449 -- (i) Any cross-DLL references kill static-ness completely
1450 -- because they must be 'executed' not statically allocated
1451 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1452 -- this is not necessary)
1454 -- (ii) We treat partial applications as redexes, because in fact we
1455 -- make a thunk for them that runs and builds a PAP
1456 -- at run-time. The only appliations that are treated as
1457 -- static are *saturated* applications of constructors.
1459 -- We used to try to be clever with nested structures like this:
1460 -- ys = (:) w ((:) w [])
1461 -- on the grounds that CorePrep will flatten ANF-ise it later.
1462 -- But supporting this special case made the function much more
1463 -- complicated, because the special case only applies if there are no
1464 -- enclosing type lambdas:
1465 -- ys = /\ a -> Foo (Baz ([] a))
1466 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1468 -- But in fact, even without -O, nested structures at top level are
1469 -- flattened by the simplifier, so we don't need to be super-clever here.
1473 -- f = \x::Int. x+7 TRUE
1474 -- p = (True,False) TRUE
1476 -- d = (fst p, False) FALSE because there's a redex inside
1477 -- (this particular one doesn't happen but...)
1479 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1480 -- n = /\a. Nil a TRUE
1482 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1485 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1486 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1488 -- b) (C x xs), where C is a contructor is updatable if the application is
1491 -- c) don't look through unfolding of f in (f x).
1493 rhsIsStatic _is_dynamic_name rhs = is_static False rhs
1495 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1498 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1499 is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
1500 is_static in_arg (Cast e _) = is_static in_arg e
1502 is_static _ (Lit lit)
1504 MachLabel _ _ _ -> False
1506 -- A MachLabel (foreign import "&foo") in an argument
1507 -- prevents a constructor application from being static. The
1508 -- reason is that it might give rise to unresolvable symbols
1509 -- in the object file: under Linux, references to "weak"
1510 -- symbols from the data segment give rise to "unresolvable
1511 -- relocation" errors at link time This might be due to a bug
1512 -- in the linker, but we'll work around it here anyway.
1515 is_static in_arg other_expr = go other_expr 0
1517 go (Var f) n_val_args
1518 #if mingw32_TARGET_OS
1519 | not (_is_dynamic_name (idName f))
1521 = saturated_data_con f n_val_args
1522 || (in_arg && n_val_args == 0)
1523 -- A naked un-applied variable is *not* deemed a static RHS
1525 -- Reason: better to update so that the indirection gets shorted
1526 -- out, and the true value will be seen
1527 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1528 -- are always updatable. If you do so, make sure that non-updatable
1529 -- ones have enough space for their static link field!
1531 go (App f a) n_val_args
1532 | isTypeArg a = go f n_val_args
1533 | not in_arg && is_static True a = go f (n_val_args + 1)
1534 -- The (not in_arg) checks that we aren't in a constructor argument;
1535 -- if we are, we don't allow (value) applications of any sort
1537 -- NB. In case you wonder, args are sometimes not atomic. eg.
1538 -- x = D# (1.0## /## 2.0##)
1539 -- can't float because /## can fail.
1541 go (Note n f) n_val_args = notSccNote n && go f n_val_args
1542 go (Cast e _) n_val_args = go e n_val_args
1545 saturated_data_con f n_val_args
1546 = case isDataConWorkId_maybe f of
1547 Just dc -> n_val_args == dataConRepArity dc