2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Commonly useful utilites for manipulating the Core language
18 -- * Constructing expressions
19 mkInlineMe, mkSCC, mkCoerce, mkCoerceI,
20 bindNonRec, needsCaseBinding,
21 mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
23 -- * Taking expressions apart
24 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
26 -- * Properties of expressions
27 exprType, coreAltType, coreAltsType,
28 exprIsDupable, exprIsTrivial, exprIsCheap,
29 exprIsHNF,exprOkForSpeculation, exprIsBig,
30 exprIsConApp_maybe, exprIsBottom,
33 -- * Arity and eta expansion
34 manifestArity, exprArity,
35 exprEtaExpandArity, etaExpand,
37 -- * Expression and bindings size
38 coreBindsSize, exprSize,
44 cheapEqExpr, tcEqExpr, tcEqExprX,
46 -- * Manipulating data constructors and types
47 applyTypeToArgs, applyTypeToArg,
48 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
51 #include "HsVersions.h"
87 import GHC.Exts -- For `xori`
91 %************************************************************************
93 \subsection{Find the type of a Core atom/expression}
95 %************************************************************************
98 exprType :: CoreExpr -> Type
99 -- ^ Recover the type of a well-typed Core expression. Fails when
100 -- applied to the actual 'CoreSyn.Type' expression as it cannot
101 -- really be said to have a type
102 exprType (Var var) = idType var
103 exprType (Lit lit) = literalType lit
104 exprType (Let _ body) = exprType body
105 exprType (Case _ _ ty _) = ty
106 exprType (Cast _ co) = snd (coercionKind co)
107 exprType (Note _ e) = exprType e
108 exprType (Lam binder expr) = mkPiType binder (exprType expr)
110 = case collectArgs e of
111 (fun, args) -> applyTypeToArgs e (exprType fun) args
113 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
115 coreAltType :: CoreAlt -> Type
116 -- ^ Returns the type of the alternatives right hand side
117 coreAltType (_,_,rhs) = exprType rhs
119 coreAltsType :: [CoreAlt] -> Type
120 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
121 coreAltsType (alt:_) = coreAltType alt
122 coreAltsType [] = panic "corAltsType"
126 mkPiType :: Var -> Type -> Type
127 -- ^ Makes a @(->)@ type or a forall type, depending
128 -- on whether it is given a type variable or a term variable.
129 mkPiTypes :: [Var] -> Type -> Type
130 -- ^ 'mkPiType' for multiple type or value arguments
133 | isId v = mkFunTy (idType v) ty
134 | otherwise = mkForAllTy v ty
136 mkPiTypes vs ty = foldr mkPiType ty vs
140 applyTypeToArg :: Type -> CoreExpr -> Type
141 -- ^ Determines the type resulting from applying an expression to a function with the given type
142 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
143 applyTypeToArg fun_ty _ = funResultTy fun_ty
145 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
146 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
147 -- The first argument is just for debugging, and gives some context
148 applyTypeToArgs _ op_ty [] = op_ty
150 applyTypeToArgs e op_ty (Type ty : args)
151 = -- Accumulate type arguments so we can instantiate all at once
154 go rev_tys (Type ty : args) = go (ty:rev_tys) args
155 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
157 op_ty' = applyTysD msg op_ty (reverse rev_tys)
158 msg = panic_msg e op_ty
160 applyTypeToArgs e op_ty (_ : args)
161 = case (splitFunTy_maybe op_ty) of
162 Just (_, res_ty) -> applyTypeToArgs e res_ty args
163 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
165 panic_msg :: CoreExpr -> Type -> SDoc
166 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
169 %************************************************************************
171 \subsection{Attaching notes}
173 %************************************************************************
175 mkNote removes redundant coercions, and SCCs where possible
179 mkNote :: Note -> CoreExpr -> CoreExpr
180 mkNote (SCC cc) expr = mkSCC cc expr
181 mkNote InlineMe expr = mkInlineMe expr
182 mkNote note expr = Note note expr
186 Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
187 that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
188 not be *applied* to anything.
190 We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
193 f = inline_me (coerce t fw)
194 As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
195 We want the split, so that the coerces can cancel at the call site.
197 However, we can get left with tiresome type applications. Notably, consider
198 f = /\ a -> let t = e in (t, w)
199 Then lifting the let out of the big lambda gives
201 f = /\ a -> let t = inline_me (t' a) in (t, w)
202 The inline_me is to stop the simplifier inlining t' right back
203 into t's RHS. In the next phase we'll substitute for t (since
204 its rhs is trivial) and *then* we could get rid of the inline_me.
205 But it hardly seems worth it, so I don't bother.
208 -- | Wraps the given expression in an inlining hint unless the expression
209 -- is trivial in some sense, so that doing so would usually hurt us
210 mkInlineMe :: CoreExpr -> CoreExpr
211 mkInlineMe (Var v) = Var v
212 mkInlineMe e = Note InlineMe e
216 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
217 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
219 mkCoerceI (ACo co) e = mkCoerce co e
221 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
222 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
223 mkCoerce co (Cast expr co2)
224 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
225 (_from_ty2, to_ty2) = coercionKind co2} in
226 from_ty `coreEqType` to_ty2 )
227 mkCoerce (mkTransCoercion co2 co) expr
230 = let (from_ty, _to_ty) = coercionKind co in
231 -- if to_ty `coreEqType` from_ty
234 ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
239 -- | Wraps the given expression in the cost centre unless
240 -- in a way that maximises their utility to the user
241 mkSCC :: CostCentre -> Expr b -> Expr b
242 -- Note: Nested SCC's *are* preserved for the benefit of
243 -- cost centre stack profiling
244 mkSCC _ (Lit lit) = Lit lit
245 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
246 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
247 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
248 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
249 mkSCC cc expr = Note (SCC cc) expr
253 %************************************************************************
255 \subsection{Other expression construction}
257 %************************************************************************
260 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
261 -- ^ @bindNonRec x r b@ produces either:
267 -- > case r of x { _DEFAULT_ -> b }
269 -- depending on whether we have to use a @case@ or @let@
270 -- binding for the expression (see 'needsCaseBinding').
271 -- It's used by the desugarer to avoid building bindings
272 -- that give Core Lint a heart attack, although actually
273 -- the simplifier deals with them perfectly well. See
274 -- also 'MkCore.mkCoreLet'
275 bindNonRec bndr rhs body
276 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
277 | otherwise = Let (NonRec bndr rhs) body
279 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
280 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
281 needsCaseBinding :: Type -> CoreExpr -> Bool
282 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
283 -- Make a case expression instead of a let
284 -- These can arise either from the desugarer,
285 -- or from beta reductions: (\x.e) (x +# y)
289 mkAltExpr :: AltCon -- ^ Case alternative constructor
290 -> [CoreBndr] -- ^ Things bound by the pattern match
291 -> [Type] -- ^ The type arguments to the case alternative
293 -- ^ This guy constructs the value that the scrutinee must have
294 -- given that you are in one particular branch of a case
295 mkAltExpr (DataAlt con) args inst_tys
296 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
297 mkAltExpr (LitAlt lit) [] []
299 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
300 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
302 mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
303 mkIfThenElse guard then_expr else_expr
304 -- Not going to be refining, so okay to take the type of the "then" clause
305 = Case guard (mkWildId boolTy) (exprType then_expr)
306 [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
307 (DataAlt trueDataCon, [], then_expr) ]
311 %************************************************************************
313 \subsection{Taking expressions apart}
315 %************************************************************************
317 The default alternative must be first, if it exists at all.
318 This makes it easy to find, though it makes matching marginally harder.
321 -- | Extract the default case alternative
322 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
323 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
324 findDefault alts = (alts, Nothing)
326 -- | Find the case alternative corresponding to a particular
327 -- constructor: panics if no such constructor exists
328 findAlt :: AltCon -> [CoreAlt] -> CoreAlt
331 (deflt@(DEFAULT,_,_):alts) -> go alts deflt
332 _ -> go alts panic_deflt
334 panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
337 go (alt@(con1,_,_) : alts) deflt
338 = case con `cmpAltCon` con1 of
339 LT -> deflt -- Missed it already; the alts are in increasing order
341 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
343 isDefaultAlt :: CoreAlt -> Bool
344 isDefaultAlt (DEFAULT, _, _) = True
345 isDefaultAlt _ = False
347 ---------------------------------
348 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
349 -- ^ Merge alternatives preserving order; alternatives in
350 -- the first argument shadow ones in the second
351 mergeAlts [] as2 = as2
352 mergeAlts as1 [] = as1
353 mergeAlts (a1:as1) (a2:as2)
354 = case a1 `cmpAlt` a2 of
355 LT -> a1 : mergeAlts as1 (a2:as2)
356 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
357 GT -> a2 : mergeAlts (a1:as1) as2
360 ---------------------------------
361 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
364 -- > case (C a b x y) of
367 -- We want to drop the leading type argument of the scrutinee
368 -- leaving the arguments to match agains the pattern
370 trimConArgs DEFAULT args = ASSERT( null args ) []
371 trimConArgs (LitAlt _) args = ASSERT( null args ) []
372 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
376 %************************************************************************
378 \subsection{Figuring out things about expressions}
380 %************************************************************************
382 @exprIsTrivial@ is true of expressions we are unconditionally happy to
383 duplicate; simple variables and constants, and type
384 applications. Note that primop Ids aren't considered
387 There used to be a gruesome test for (hasNoBinding v) in the
389 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
390 The idea here is that a constructor worker, like \$wJust, is
391 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
392 So it should be treated like a lambda. Ditto unsaturated primops.
393 But now constructor workers are not "have-no-binding" Ids. And
394 completely un-applied primops and foreign-call Ids are sufficiently
395 rare that I plan to allow them to be duplicated and put up with
398 SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
399 a) it really generates code, (and a heap object when it's
400 a function arg) to capture the cost centre
401 b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
404 exprIsTrivial :: CoreExpr -> Bool
405 exprIsTrivial (Var _) = True -- See notes above
406 exprIsTrivial (Type _) = True
407 exprIsTrivial (Lit lit) = litIsTrivial lit
408 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
409 exprIsTrivial (Note (SCC _) _) = False -- See notes above
410 exprIsTrivial (Note _ e) = exprIsTrivial e
411 exprIsTrivial (Cast e _) = exprIsTrivial e
412 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
413 exprIsTrivial _ = False
417 @exprIsDupable@ is true of expressions that can be duplicated at a modest
418 cost in code size. This will only happen in different case
419 branches, so there's no issue about duplicating work.
421 That is, exprIsDupable returns True of (f x) even if
422 f is very very expensive to call.
424 Its only purpose is to avoid fruitless let-binding
425 and then inlining of case join points
429 exprIsDupable :: CoreExpr -> Bool
430 exprIsDupable (Type _) = True
431 exprIsDupable (Var _) = True
432 exprIsDupable (Lit lit) = litIsDupable lit
433 exprIsDupable (Note InlineMe _) = True
434 exprIsDupable (Note _ e) = exprIsDupable e
435 exprIsDupable (Cast e _) = exprIsDupable e
440 go (App f a) n_args = n_args < dupAppSize
446 dupAppSize = 4 -- Size of application we are prepared to duplicate
449 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
450 it is obviously in weak head normal form, or is cheap to get to WHNF.
451 [Note that that's not the same as exprIsDupable; an expression might be
452 big, and hence not dupable, but still cheap.]
454 By ``cheap'' we mean a computation we're willing to:
455 push inside a lambda, or
456 inline at more than one place
457 That might mean it gets evaluated more than once, instead of being
458 shared. The main examples of things which aren't WHNF but are
463 (where e, and all the ei are cheap)
466 (where e and b are cheap)
469 (where op is a cheap primitive operator)
472 (because we are happy to substitute it inside a lambda)
474 Notice that a variable is considered 'cheap': we can push it inside a lambda,
475 because sharing will make sure it is only evaluated once.
478 exprIsCheap :: CoreExpr -> Bool
479 exprIsCheap (Lit _) = True
480 exprIsCheap (Type _) = True
481 exprIsCheap (Var _) = True
482 exprIsCheap (Note InlineMe _) = True
483 exprIsCheap (Note _ e) = exprIsCheap e
484 exprIsCheap (Cast e _) = exprIsCheap e
485 exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
486 exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
487 and [exprIsCheap rhs | (_,_,rhs) <- alts]
488 -- Experimentally, treat (case x of ...) as cheap
489 -- (and case __coerce x etc.)
490 -- This improves arities of overloaded functions where
491 -- there is only dictionary selection (no construction) involved
492 exprIsCheap (Let (NonRec x _) e)
493 | isUnLiftedType (idType x) = exprIsCheap e
495 -- strict lets always have cheap right hand sides,
496 -- and do no allocation.
498 exprIsCheap other_expr -- Applications and variables
501 -- Accumulate value arguments, then decide
502 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
503 | otherwise = go f val_args
505 go (Var _) [] = True -- Just a type application of a variable
506 -- (f t1 t2 t3) counts as WHNF
508 = case globalIdDetails f of
509 RecordSelId {} -> go_sel args
510 ClassOpId _ -> go_sel args
511 PrimOpId op -> go_primop op args
513 DataConWorkId _ -> go_pap args
514 _ | length args < idArity f -> go_pap args
517 -- Application of a function which
518 -- always gives bottom; we treat this as cheap
519 -- because it certainly doesn't need to be shared!
524 go_pap args = all exprIsTrivial args
525 -- For constructor applications and primops, check that all
526 -- the args are trivial. We don't want to treat as cheap, say,
528 -- We'll put up with one constructor application, but not dozens
531 go_primop op args = primOpIsCheap op && all exprIsCheap args
532 -- In principle we should worry about primops
533 -- that return a type variable, since the result
534 -- might be applied to something, but I'm not going
535 -- to bother to check the number of args
538 go_sel [arg] = exprIsCheap arg -- I'm experimenting with making record selection
539 go_sel _ = False -- look cheap, so we will substitute it inside a
540 -- lambda. Particularly for dictionary field selection.
541 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
542 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
546 -- | 'exprOkForSpeculation' returns True of an expression that is:
548 -- * Safe to evaluate even if normal order eval might not
549 -- evaluate the expression at all, or
551 -- * Safe /not/ to evaluate even if normal order would do so
553 -- Precisely, it returns @True@ iff:
555 -- * The expression guarantees to terminate,
559 -- * without raising an exception,
561 -- * without causing a side effect (e.g. writing a mutable variable)
563 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
564 -- As an example of the considerations in this test, consider:
566 -- > let x = case y# +# 1# of { r# -> I# r# }
569 -- being translated to:
571 -- > case y# +# 1# of { r# ->
576 -- We can only do this if the @y + 1@ is ok for speculation: it has no
577 -- side effects, and can't diverge or raise an exception.
578 exprOkForSpeculation :: CoreExpr -> Bool
579 exprOkForSpeculation (Lit _) = True
580 exprOkForSpeculation (Type _) = True
581 -- Tick boxes are *not* suitable for speculation
582 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
583 && not (isTickBoxOp v)
584 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
585 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
586 exprOkForSpeculation other_expr
587 = case collectArgs other_expr of
588 (Var f, args) -> spec_ok (globalIdDetails f) args
592 spec_ok (DataConWorkId _) _
593 = True -- The strictness of the constructor has already
594 -- been expressed by its "wrapper", so we don't need
595 -- to take the arguments into account
597 spec_ok (PrimOpId op) args
598 | isDivOp op, -- Special case for dividing operations that fail
599 [arg1, Lit lit] <- args -- only if the divisor is zero
600 = not (isZeroLit lit) && exprOkForSpeculation arg1
601 -- Often there is a literal divisor, and this
602 -- can get rid of a thunk in an inner looop
605 = primOpOkForSpeculation op &&
606 all exprOkForSpeculation args
607 -- A bit conservative: we don't really need
608 -- to care about lazy arguments, but this is easy
612 -- | True of dyadic operators that can fail only if the second arg is zero!
613 isDivOp :: PrimOp -> Bool
614 -- This function probably belongs in PrimOp, or even in
615 -- an automagically generated file.. but it's such a
616 -- special case I thought I'd leave it here for now.
617 isDivOp IntQuotOp = True
618 isDivOp IntRemOp = True
619 isDivOp WordQuotOp = True
620 isDivOp WordRemOp = True
621 isDivOp IntegerQuotRemOp = True
622 isDivOp IntegerDivModOp = True
623 isDivOp FloatDivOp = True
624 isDivOp DoubleDivOp = True
629 -- | True of expressions that are guaranteed to diverge upon execution
630 exprIsBottom :: CoreExpr -> Bool
631 exprIsBottom e = go 0 e
633 -- n is the number of args
634 go n (Note _ e) = go n e
635 go n (Cast e _) = go n e
636 go n (Let _ e) = go n e
637 go _ (Case e _ _ _) = go 0 e -- Just check the scrut
638 go n (App e _) = go (n+1) e
639 go n (Var v) = idAppIsBottom v n
641 go _ (Lam _ _) = False
642 go _ (Type _) = False
644 idAppIsBottom :: Id -> Int -> Bool
645 idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
650 -- | This returns true for expressions that are certainly /already/
651 -- evaluated to /head/ normal form. This is used to decide whether it's ok
654 -- > case x of _ -> e
660 -- and to decide whether it's safe to discard a 'seq'.
661 -- So, it does /not/ treat variables as evaluated, unless they say they are.
662 -- However, it /does/ treat partial applications and constructor applications
663 -- as values, even if their arguments are non-trivial, provided the argument
664 -- type is lifted. For example, both of these are values:
666 -- > (:) (f x) (map f xs)
667 -- > map (...redex...)
669 -- Because 'seq' on such things completes immediately.
671 -- For unlifted argument types, we have to be careful:
675 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
676 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
677 -- unboxed type must be ok-for-speculation (or trivial).
678 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
679 exprIsHNF (Var v) -- NB: There are no value args at this point
680 = isDataConWorkId v -- Catches nullary constructors,
681 -- so that [] and () are values, for example
682 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
683 || isEvaldUnfolding (idUnfolding v)
684 -- Check the thing's unfolding; it might be bound to a value
685 -- A worry: what if an Id's unfolding is just itself:
686 -- then we could get an infinite loop...
688 exprIsHNF (Lit _) = True
689 exprIsHNF (Type _) = True -- Types are honorary Values;
690 -- we don't mind copying them
691 exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
692 exprIsHNF (Note _ e) = exprIsHNF e
693 exprIsHNF (Cast e _) = exprIsHNF e
694 exprIsHNF (App e (Type _)) = exprIsHNF e
695 exprIsHNF (App e a) = app_is_value e [a]
698 -- There is at least one value argument
699 app_is_value :: CoreExpr -> [CoreArg] -> Bool
700 app_is_value (Var fun) args
701 = idArity fun > valArgCount args -- Under-applied function
702 || isDataConWorkId fun -- or data constructor
703 app_is_value (Note _ f) as = app_is_value f as
704 app_is_value (Cast f _) as = app_is_value f as
705 app_is_value (App f a) as = app_is_value f (a:as)
706 app_is_value _ _ = False
709 These InstPat functions go here to avoid circularity between DataCon and Id
712 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
713 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
715 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
716 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
717 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
719 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
720 -- Remember to include the existential dictionaries
722 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
723 -> [FastString] -- A long enough list of FSs to use for names
724 -> [Unique] -- An equally long list of uniques, at least one for each binder
726 -> [Type] -- Types to instantiate the universally quantified tyvars
727 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
728 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
729 -- (ex_tvs, co_tvs, arg_ids),
731 -- ex_tvs are intended to be used as binders for existential type args
733 -- co_tvs are intended to be used as binders for coercion args and the kinds
734 -- of these vars have been instantiated by the inst_tys and the ex_tys
735 -- The co_tvs include both GADT equalities (dcEqSpec) and
736 -- programmer-specified equalities (dcEqTheta)
738 -- arg_ids are indended to be used as binders for value arguments,
739 -- and their types have been instantiated with inst_tys and ex_tys
740 -- The arg_ids include both dicts (dcDictTheta) and
741 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
744 -- The following constructor T1
747 -- T1 :: forall b. Int -> b -> T(a,b)
750 -- has representation type
751 -- forall a. forall a1. forall b. (a :=: (a1,b)) =>
754 -- dataConInstPat fss us T1 (a1',b') will return
756 -- ([a1'', b''], [c :: (a1', b'):=:(a1'', b'')], [x :: Int, y :: b''])
758 -- where the double-primed variables are created with the FastStrings and
759 -- Uniques given as fss and us
760 dataConInstPat arg_fun fss uniqs con inst_tys
761 = (ex_bndrs, co_bndrs, arg_ids)
763 univ_tvs = dataConUnivTyVars con
764 ex_tvs = dataConExTyVars con
765 arg_tys = arg_fun con
766 eq_spec = dataConEqSpec con
767 eq_theta = dataConEqTheta con
768 eq_preds = eqSpecPreds eq_spec ++ eq_theta
771 n_co = length eq_preds
773 -- split the Uniques and FastStrings
774 (ex_uniqs, uniqs') = splitAt n_ex uniqs
775 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
777 (ex_fss, fss') = splitAt n_ex fss
778 (co_fss, id_fss) = splitAt n_co fss'
780 -- Make existential type variables
781 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
782 mk_ex_var uniq fs var = mkTyVar new_name kind
784 new_name = mkSysTvName uniq fs
787 -- Make the instantiating substitution
788 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
790 -- Make new coercion vars, instantiating kind
791 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
792 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
794 new_name = mkSysTvName uniq fs
795 co_kind = substTy subst (mkPredTy eq_pred)
797 -- make value vars, instantiating types
798 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
799 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
801 -- | Returns @Just (dc, [x1..xn])@ if the argument expression is
802 -- a constructor application of the form @dc x1 .. xn@
803 exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
804 exprIsConApp_maybe (Cast expr co)
805 = -- Here we do the KPush reduction rule as described in the FC paper
806 case exprIsConApp_maybe expr of {
808 Just (dc, dc_args) ->
810 -- The transformation applies iff we have
811 -- (C e1 ... en) `cast` co
812 -- where co :: (T t1 .. tn) :=: (T s1 ..sn)
813 -- That is, with a T at the top of both sides
814 -- The left-hand one must be a T, because exprIsConApp returned True
815 -- but the right-hand one might not be. (Though it usually will.)
817 let (from_ty, to_ty) = coercionKind co
818 (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
819 -- The inner one must be a TyConApp
821 case splitTyConApp_maybe to_ty of {
823 Just (to_tc, to_tc_arg_tys)
824 | from_tc /= to_tc -> Nothing
825 -- These two Nothing cases are possible; we might see
826 -- (C x y) `cast` (g :: T a ~ S [a]),
827 -- where S is a type function. In fact, exprIsConApp
828 -- will probably not be called in such circumstances,
829 -- but there't nothing wrong with it
833 tc_arity = tyConArity from_tc
835 (univ_args, rest1) = splitAt tc_arity dc_args
836 (ex_args, rest2) = splitAt n_ex_tvs rest1
837 (co_args_spec, rest3) = splitAt n_cos_spec rest2
838 (co_args_theta, val_args) = splitAt n_cos_theta rest3
840 arg_tys = dataConRepArgTys dc
841 dc_univ_tyvars = dataConUnivTyVars dc
842 dc_ex_tyvars = dataConExTyVars dc
843 dc_eq_spec = dataConEqSpec dc
844 dc_eq_theta = dataConEqTheta dc
845 dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
846 n_ex_tvs = length dc_ex_tyvars
847 n_cos_spec = length dc_eq_spec
848 n_cos_theta = length dc_eq_theta
850 -- Make the "theta" from Fig 3 of the paper
851 gammas = decomposeCo tc_arity co
852 new_tys = gammas ++ map (\ (Type t) -> t) ex_args
853 theta = zipOpenTvSubst dc_tyvars new_tys
855 -- First we cast the existential coercion arguments
856 cast_co_spec (tv, ty) co
857 = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
858 cast_co_theta eqPred (Type co)
859 | (ty1, ty2) <- getEqPredTys eqPred
860 = Type $ mkSymCoercion (substTy theta ty1)
862 `mkTransCoercion` (substTy theta ty2)
863 new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
864 zipWith cast_co_theta dc_eq_theta co_args_theta
866 -- ...and now value arguments
867 new_val_args = zipWith cast_arg arg_tys val_args
868 cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
871 ASSERT( length univ_args == tc_arity )
872 ASSERT( from_tc == dataConTyCon dc )
873 ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
874 ASSERT( all isTypeArg (univ_args ++ ex_args) )
875 ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
877 Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
881 -- We do not want to tell the world that we have a
882 -- Cons, to *stop* Case of Known Cons, which removes
884 exprIsConApp_maybe (Note (TickBox {}) expr)
886 exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
890 exprIsConApp_maybe (Note _ expr)
891 = exprIsConApp_maybe expr
892 -- We ignore InlineMe notes in case we have
893 -- x = __inline_me__ (a,b)
894 -- All part of making sure that INLINE pragmas never hurt
895 -- Marcin tripped on this one when making dictionaries more inlinable
897 -- In fact, we ignore all notes. For example,
898 -- case _scc_ "foo" (C a b) of
900 -- should be optimised away, but it will be only if we look
901 -- through the SCC note.
903 exprIsConApp_maybe expr = analyse (collectArgs expr)
905 analyse (Var fun, args)
906 | Just con <- isDataConWorkId_maybe fun,
907 args `lengthAtLeast` dataConRepArity con
908 -- Might be > because the arity excludes type args
911 -- Look through unfoldings, but only cheap ones, because
912 -- we are effectively duplicating the unfolding
913 analyse (Var fun, [])
914 | let unf = idUnfolding fun,
916 = exprIsConApp_maybe (unfoldingTemplate unf)
923 %************************************************************************
925 \subsection{Eta reduction and expansion}
927 %************************************************************************
930 -- ^ The Arity returned is the number of value args the
931 -- expression can be applied to without doing much work
932 exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
934 exprEtaExpandArity is used when eta expanding
937 It returns 1 (or more) to:
938 case x of p -> \s -> ...
939 because for I/O ish things we really want to get that \s to the top.
940 We are prepared to evaluate x each time round the loop in order to get that
942 It's all a bit more subtle than it looks:
946 Consider one-shot lambdas
947 let x = expensive in \y z -> E
948 We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
949 Hence the ArityType returned by arityType
951 2. The state-transformer hack
953 The one-shot lambda special cause is particularly important/useful for
954 IO state transformers, where we often get
955 let x = E in \ s -> ...
957 and the \s is a real-world state token abstraction. Such abstractions
958 are almost invariably 1-shot, so we want to pull the \s out, past the
959 let x=E, even if E is expensive. So we treat state-token lambdas as
960 one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
962 3. Dealing with bottom
965 f = \x -> error "foo"
966 Here, arity 1 is fine. But if it is
970 then we want to get arity 2. Tecnically, this isn't quite right, because
972 should diverge, but it'll converge if we eta-expand f. Nevertheless, we
973 do so; it improves some programs significantly, and increasing convergence
974 isn't a bad thing. Hence the ABot/ATop in ArityType.
976 Actually, the situation is worse. Consider
980 Can we eta-expand here? At first the answer looks like "yes of course", but
983 This should diverge! But if we eta-expand, it won't. Again, we ignore this
984 "problem", because being scrupulous would lose an important transformation for
990 Non-recursive newtypes are transparent, and should not get in the way.
991 We do (currently) eta-expand recursive newtypes too. So if we have, say
993 newtype T = MkT ([T] -> Int)
997 where f has arity 1. Then: etaExpandArity e = 1;
998 that is, etaExpandArity looks through the coerce.
1000 When we eta-expand e to arity 1: eta_expand 1 e T
1001 we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1003 HOWEVER, note that if you use coerce bogusly you can ge
1005 And since negate has arity 2, you might try to eta expand. But you can't
1006 decopose Int to a function type. Hence the final case in eta_expand.
1010 exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
1012 -- A limited sort of function type
1013 data ArityType = AFun Bool ArityType -- True <=> one-shot
1014 | ATop -- Know nothing
1017 arityDepth :: ArityType -> Arity
1018 arityDepth (AFun _ ty) = 1 + arityDepth ty
1021 andArityType :: ArityType -> ArityType -> ArityType
1022 andArityType ABot at2 = at2
1023 andArityType ATop _ = ATop
1024 andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
1025 andArityType at1 at2 = andArityType at2 at1
1027 arityType :: DynFlags -> CoreExpr -> ArityType
1028 -- (go1 e) = [b1,..,bn]
1029 -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
1030 -- where bi is True <=> the lambda is one-shot
1032 arityType dflags (Note _ e) = arityType dflags e
1033 -- Not needed any more: etaExpand is cleverer
1034 -- removed: | ok_note n = arityType dflags e
1035 -- removed: | otherwise = ATop
1037 arityType dflags (Cast e _) = arityType dflags e
1040 = mk (idArity v) (arg_tys (idType v))
1042 mk :: Arity -> [Type] -> ArityType
1043 -- The argument types are only to steer the "state hack"
1044 -- Consider case x of
1046 -- False -> \(s:RealWorld) -> e
1047 -- where foo has arity 1. Then we want the state hack to
1048 -- apply to foo too, so we can eta expand the case.
1049 mk 0 tys | isBottomingId v = ABot
1050 | (ty:_) <- tys, isStateHackType ty = AFun True ATop
1052 mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
1053 mk n [] = AFun False (mk (n-1) [])
1055 arg_tys :: Type -> [Type] -- Ignore for-alls
1057 | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
1058 | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
1061 -- Lambdas; increase arity
1062 arityType dflags (Lam x e)
1063 | isId x = AFun (isOneShotBndr x) (arityType dflags e)
1064 | otherwise = arityType dflags e
1066 -- Applications; decrease arity
1067 arityType dflags (App f (Type _)) = arityType dflags f
1068 arityType dflags (App f a)
1069 = case arityType dflags f of
1070 ABot -> ABot -- If function diverges, ignore argument
1071 ATop -> ATop -- No no info about function
1073 | exprIsCheap a -> xs
1076 -- Case/Let; keep arity if either the expression is cheap
1077 -- or it's a 1-shot lambda
1078 -- The former is not really right for Haskell
1079 -- f x = case x of { (a,b) -> \y. e }
1081 -- f x y = case x of { (a,b) -> e }
1082 -- The difference is observable using 'seq'
1083 arityType dflags (Case scrut _ _ alts)
1084 = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
1085 xs | exprIsCheap scrut -> xs
1086 AFun one_shot _ | one_shot -> AFun True ATop
1089 arityType dflags (Let b e)
1090 = case arityType dflags e of
1091 xs | cheap_bind b -> xs
1092 AFun one_shot _ | one_shot -> AFun True ATop
1095 cheap_bind (NonRec b e) = is_cheap (b,e)
1096 cheap_bind (Rec prs) = all is_cheap prs
1097 is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
1099 -- If the experimental -fdicts-cheap flag is on, we eta-expand through
1100 -- dictionary bindings. This improves arities. Thereby, it also
1101 -- means that full laziness is less prone to floating out the
1102 -- application of a function to its dictionary arguments, which
1103 -- can thereby lose opportunities for fusion. Example:
1104 -- foo :: Ord a => a -> ...
1105 -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
1106 -- -- So foo has arity 1
1108 -- f = \x. foo dInt $ bar x
1110 -- The (foo DInt) is floated out, and makes ineffective a RULE
1111 -- foo (bar x) = ...
1113 -- One could go further and make exprIsCheap reply True to any
1114 -- dictionary-typed expression, but that's more work.
1116 arityType _ _ = ATop
1118 {- NOT NEEDED ANY MORE: etaExpand is cleverer
1119 ok_note InlineMe = False
1120 ok_note other = True
1121 -- Notice that we do not look through __inline_me__
1122 -- This may seem surprising, but consider
1123 -- f = _inline_me (\x -> e)
1124 -- We DO NOT want to eta expand this to
1125 -- f = \x -> (_inline_me (\x -> e)) x
1126 -- because the _inline_me gets dropped now it is applied,
1135 -- | @etaExpand n us e ty@ returns an expression with
1136 -- the same meaning as @e@, but with arity @n@.
1140 -- > e' = etaExpand n us e ty
1142 -- We should have that:
1144 -- > ty = exprType e = exprType e'
1145 etaExpand :: Arity -- ^ Result should have this number of value args
1146 -> [Unique] -- ^ Uniques to assign to the new binders
1147 -> CoreExpr -- ^ Expression to expand
1148 -> Type -- ^ Type of expression to expand
1150 -- Note that SCCs are not treated specially. If we have
1151 -- etaExpand 2 (\x -> scc "foo" e)
1152 -- = (\xy -> (scc "foo" e) y)
1153 -- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
1155 etaExpand n us expr ty
1156 | manifestArity expr >= n = expr -- The no-op case
1158 = eta_expand n us expr ty
1160 -- manifestArity sees how many leading value lambdas there are
1161 manifestArity :: CoreExpr -> Arity
1162 manifestArity (Lam v e) | isId v = 1 + manifestArity e
1163 | otherwise = manifestArity e
1164 manifestArity (Note _ e) = manifestArity e
1165 manifestArity (Cast e _) = manifestArity e
1168 -- etaExpand deals with for-alls. For example:
1170 -- where E :: forall a. a -> a
1172 -- (/\b. \y::a -> E b y)
1174 -- It deals with coerces too, though they are now rare
1175 -- so perhaps the extra code isn't worth it
1176 eta_expand :: Int -> [Unique] -> CoreExpr -> Type -> CoreExpr
1178 eta_expand n _ expr ty
1180 -- The ILX code generator requires eta expansion for type arguments
1181 -- too, but alas the 'n' doesn't tell us how many of them there
1182 -- may be. So we eagerly eta expand any big lambdas, and just
1183 -- cross our fingers about possible loss of sharing in the ILX case.
1184 -- The Right Thing is probably to make 'arity' include
1185 -- type variables throughout the compiler. (ToDo.)
1187 -- Saturated, so nothing to do
1190 -- Short cut for the case where there already
1191 -- is a lambda; no point in gratuitously adding more
1192 eta_expand n us (Lam v body) ty
1194 = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
1197 = Lam v (eta_expand (n-1) us body (funResultTy ty))
1199 -- We used to have a special case that stepped inside Coerces here,
1200 -- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
1201 -- = Note note (eta_expand n us e ty)
1202 -- BUT this led to an infinite loop
1203 -- Example: newtype T = MkT (Int -> Int)
1204 -- eta_expand 1 (coerce (Int->Int) e)
1205 -- --> coerce (Int->Int) (eta_expand 1 T e)
1207 -- --> coerce (Int->Int) (coerce T
1208 -- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
1209 -- by the splitNewType_maybe case below
1212 eta_expand n us expr ty
1213 = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
1214 case splitForAllTy_maybe ty of {
1217 Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
1219 lam_tv = setVarName tv (mkSysTvName uniq (fsLit "etaT"))
1220 -- Using tv as a base retains its tyvar/covar-ness
1224 case splitFunTy_maybe ty of {
1225 Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
1227 arg1 = mkSysLocal (fsLit "eta") uniq arg_ty
1233 -- newtype T = MkT ([T] -> Int)
1234 -- Consider eta-expanding this
1237 -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
1239 case splitNewTypeRepCo_maybe ty of {
1240 Just(ty1,co) -> mkCoerce (mkSymCoercion co)
1241 (eta_expand n us (mkCoerce co expr) ty1) ;
1244 -- We have an expression of arity > 0, but its type isn't a function
1245 -- This *can* legitmately happen: e.g. coerce Int (\x. x)
1246 -- Essentially the programmer is playing fast and loose with types
1247 -- (Happy does this a lot). So we simply decline to eta-expand.
1248 -- Otherwise we'd end up with an explicit lambda having a non-function type
1253 exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
1254 It tells how many things the expression can be applied to before doing
1255 any work. It doesn't look inside cases, lets, etc. The idea is that
1256 exprEtaExpandArity will do the hard work, leaving something that's easy
1257 for exprArity to grapple with. In particular, Simplify uses exprArity to
1258 compute the ArityInfo for the Id.
1260 Originally I thought that it was enough just to look for top-level lambdas, but
1261 it isn't. I've seen this
1263 foo = PrelBase.timesInt
1265 We want foo to get arity 2 even though the eta-expander will leave it
1266 unchanged, in the expectation that it'll be inlined. But occasionally it
1267 isn't, because foo is blacklisted (used in a rule).
1269 Similarly, see the ok_note check in exprEtaExpandArity. So
1270 f = __inline_me (\x -> e)
1271 won't be eta-expanded.
1273 And in any case it seems more robust to have exprArity be a bit more intelligent.
1274 But note that (\x y z -> f x y z)
1275 should have arity 3, regardless of f's arity.
1277 Note [exprArity invariant]
1278 ~~~~~~~~~~~~~~~~~~~~~~~~~~
1279 exprArity has the following invariant:
1280 (exprArity e) = n, then manifestArity (etaExpand e n) = n
1282 That is, if exprArity says "the arity is n" then etaExpand really can get
1283 "n" manifest lambdas to the top.
1285 Why is this important? Because
1286 - In TidyPgm we use exprArity to fix the *final arity* of
1287 each top-level Id, and in
1288 - In CorePrep we use etaExpand on each rhs, so that the visible lambdas
1289 actually match that arity, which in turn means
1290 that the StgRhs has the right number of lambdas
1292 An alternative would be to do the eta-expansion in TidyPgm, at least
1293 for top-level bindings, in which case we would not need the trim_arity
1294 in exprArity. That is a less local change, so I'm going to leave it for today!
1298 -- | An approximate, fast, version of 'exprEtaExpandArity'
1299 exprArity :: CoreExpr -> Arity
1302 go (Var v) = idArity v
1303 go (Lam x e) | isId x = go e + 1
1305 go (Note _ e) = go e
1306 go (Cast e co) = trim_arity (go e) 0 (snd (coercionKind co))
1307 go (App e (Type _)) = go e
1308 go (App f a) | exprIsCheap a = (go f - 1) `max` 0
1309 -- NB: exprIsCheap a!
1310 -- f (fac x) does not have arity 2,
1311 -- even if f has arity 3!
1312 -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
1313 -- unknown, hence arity 0
1316 -- Note [exprArity invariant]
1319 | Just (_, ty') <- splitForAllTy_maybe ty = trim_arity n a ty'
1320 | Just (_, ty') <- splitFunTy_maybe ty = trim_arity n (a+1) ty'
1321 | Just (ty',_) <- splitNewTypeRepCo_maybe ty = trim_arity n a ty'
1325 %************************************************************************
1327 \subsection{Equality}
1329 %************************************************************************
1332 -- | A cheap equality test which bales out fast!
1333 -- If it returns @True@ the arguments are definitely equal,
1334 -- otherwise, they may or may not be equal.
1336 -- See also 'exprIsBig'
1337 cheapEqExpr :: Expr b -> Expr b -> Bool
1339 cheapEqExpr (Var v1) (Var v2) = v1==v2
1340 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
1341 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
1343 cheapEqExpr (App f1 a1) (App f2 a2)
1344 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
1346 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
1347 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
1349 cheapEqExpr _ _ = False
1351 exprIsBig :: Expr b -> Bool
1352 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
1353 exprIsBig (Lit _) = False
1354 exprIsBig (Var _) = False
1355 exprIsBig (Type _) = False
1356 exprIsBig (App f a) = exprIsBig f || exprIsBig a
1357 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
1363 tcEqExpr :: CoreExpr -> CoreExpr -> Bool
1364 -- ^ A kind of shallow equality used in rule matching, so does
1365 -- /not/ look through newtypes or predicate types
1367 tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
1369 rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
1371 tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
1372 tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
1373 tcEqExprX _ (Lit lit1) (Lit lit2) = lit1 == lit2
1374 tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
1375 tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
1376 tcEqExprX env (Let (NonRec v1 r1) e1)
1377 (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
1378 && tcEqExprX (rnBndr2 env v1 v2) e1 e2
1379 tcEqExprX env (Let (Rec ps1) e1)
1380 (Let (Rec ps2) e2) = equalLength ps1 ps2
1381 && and (zipWith eq_rhs ps1 ps2)
1382 && tcEqExprX env' e1 e2
1384 env' = foldl2 rn_bndr2 env ps2 ps2
1385 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
1386 eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
1387 tcEqExprX env (Case e1 v1 t1 a1)
1388 (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
1389 && tcEqTypeX env t1 t2
1390 && equalLength a1 a2
1391 && and (zipWith (eq_alt env') a1 a2)
1393 env' = rnBndr2 env v1 v2
1395 tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
1396 tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
1397 tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1398 tcEqExprX _ _ _ = False
1400 eq_alt :: RnEnv2 -> CoreAlt -> CoreAlt -> Bool
1401 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
1403 eq_note :: RnEnv2 -> Note -> Note -> Bool
1404 eq_note _ (SCC cc1) (SCC cc2) = cc1 == cc2
1405 eq_note _ (CoreNote s1) (CoreNote s2) = s1 == s2
1406 eq_note _ _ _ = False
1410 %************************************************************************
1412 \subsection{The size of an expression}
1414 %************************************************************************
1417 coreBindsSize :: [CoreBind] -> Int
1418 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1420 exprSize :: CoreExpr -> Int
1421 -- ^ A measure of the size of the expressions, strictly greater than 0
1422 -- It also forces the expression pretty drastically as a side effect
1423 exprSize (Var v) = v `seq` 1
1424 exprSize (Lit lit) = lit `seq` 1
1425 exprSize (App f a) = exprSize f + exprSize a
1426 exprSize (Lam b e) = varSize b + exprSize e
1427 exprSize (Let b e) = bindSize b + exprSize e
1428 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1429 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1430 exprSize (Note n e) = noteSize n + exprSize e
1431 exprSize (Type t) = seqType t `seq` 1
1433 noteSize :: Note -> Int
1434 noteSize (SCC cc) = cc `seq` 1
1435 noteSize InlineMe = 1
1436 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1438 varSize :: Var -> Int
1439 varSize b | isTyVar b = 1
1440 | otherwise = seqType (idType b) `seq`
1441 megaSeqIdInfo (idInfo b) `seq`
1444 varsSize :: [Var] -> Int
1445 varsSize = sum . map varSize
1447 bindSize :: CoreBind -> Int
1448 bindSize (NonRec b e) = varSize b + exprSize e
1449 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1451 pairSize :: (Var, CoreExpr) -> Int
1452 pairSize (b,e) = varSize b + exprSize e
1454 altSize :: CoreAlt -> Int
1455 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1459 %************************************************************************
1461 \subsection{Hashing}
1463 %************************************************************************
1466 hashExpr :: CoreExpr -> Int
1467 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1468 -- Two expressions that hash to the different Ints are definitely unequal.
1470 -- The emphasis is on a crude, fast hash, rather than on high precision.
1472 -- But unequal here means \"not identical\"; two alpha-equivalent
1473 -- expressions may hash to the different Ints.
1475 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1476 -- (at least if we want the above invariant to be true).
1478 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1479 -- UniqFM doesn't like negative Ints
1481 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1483 hash_expr :: HashEnv -> CoreExpr -> Word32
1484 -- Word32, because we're expecting overflows here, and overflowing
1485 -- signed types just isn't cool. In C it's even undefined.
1486 hash_expr env (Note _ e) = hash_expr env e
1487 hash_expr env (Cast e _) = hash_expr env e
1488 hash_expr env (Var v) = hashVar env v
1489 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1490 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1491 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1492 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1493 hash_expr env (Case e _ _ _) = hash_expr env e
1494 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1495 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1496 -- Shouldn't happen. Better to use WARN than trace, because trace
1497 -- prevents the CPR optimisation kicking in for hash_expr.
1499 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1500 fast_hash_expr env (Var v) = hashVar env v
1501 fast_hash_expr env (Type t) = fast_hash_type env t
1502 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1503 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1504 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1505 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1506 fast_hash_expr _ _ = 1
1508 fast_hash_type :: HashEnv -> Type -> Word32
1509 fast_hash_type env ty
1510 | Just tv <- getTyVar_maybe ty = hashVar env tv
1511 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1512 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1515 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1516 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1518 hashVar :: HashEnv -> Var -> Word32
1520 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1523 %************************************************************************
1525 \subsection{Determining non-updatable right-hand-sides}
1527 %************************************************************************
1529 Top-level constructor applications can usually be allocated
1530 statically, but they can't if the constructor, or any of the
1531 arguments, come from another DLL (because we can't refer to static
1532 labels in other DLLs).
1534 If this happens we simply make the RHS into an updatable thunk,
1535 and 'execute' it rather than allocating it statically.
1538 -- | This function is called only on *top-level* right-hand sides.
1539 -- Returns @True@ if the RHS can be allocated statically in the output,
1540 -- with no thunks involved at all.
1541 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1542 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1543 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1544 -- update flag on it and (iii) in DsExpr to decide how to expand
1547 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1548 -- (a) a value lambda
1549 -- (b) a saturated constructor application with static args
1551 -- BUT watch out for
1552 -- (i) Any cross-DLL references kill static-ness completely
1553 -- because they must be 'executed' not statically allocated
1554 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1555 -- this is not necessary)
1557 -- (ii) We treat partial applications as redexes, because in fact we
1558 -- make a thunk for them that runs and builds a PAP
1559 -- at run-time. The only appliations that are treated as
1560 -- static are *saturated* applications of constructors.
1562 -- We used to try to be clever with nested structures like this:
1563 -- ys = (:) w ((:) w [])
1564 -- on the grounds that CorePrep will flatten ANF-ise it later.
1565 -- But supporting this special case made the function much more
1566 -- complicated, because the special case only applies if there are no
1567 -- enclosing type lambdas:
1568 -- ys = /\ a -> Foo (Baz ([] a))
1569 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1571 -- But in fact, even without -O, nested structures at top level are
1572 -- flattened by the simplifier, so we don't need to be super-clever here.
1576 -- f = \x::Int. x+7 TRUE
1577 -- p = (True,False) TRUE
1579 -- d = (fst p, False) FALSE because there's a redex inside
1580 -- (this particular one doesn't happen but...)
1582 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1583 -- n = /\a. Nil a TRUE
1585 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1588 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1589 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1591 -- b) (C x xs), where C is a contructors is updatable if the application is
1594 -- c) don't look through unfolding of f in (f x).
1596 rhsIsStatic _this_pkg rhs = is_static False rhs
1598 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1601 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1603 is_static _ (Note (SCC _) _) = False
1604 is_static in_arg (Note _ e) = is_static in_arg e
1605 is_static in_arg (Cast e _) = is_static in_arg e
1607 is_static _ (Lit lit)
1609 MachLabel _ _ -> False
1611 -- A MachLabel (foreign import "&foo") in an argument
1612 -- prevents a constructor application from being static. The
1613 -- reason is that it might give rise to unresolvable symbols
1614 -- in the object file: under Linux, references to "weak"
1615 -- symbols from the data segment give rise to "unresolvable
1616 -- relocation" errors at link time This might be due to a bug
1617 -- in the linker, but we'll work around it here anyway.
1620 is_static in_arg other_expr = go other_expr 0
1622 go (Var f) n_val_args
1623 #if mingw32_TARGET_OS
1624 | not (isDllName _this_pkg (idName f))
1626 = saturated_data_con f n_val_args
1627 || (in_arg && n_val_args == 0)
1628 -- A naked un-applied variable is *not* deemed a static RHS
1630 -- Reason: better to update so that the indirection gets shorted
1631 -- out, and the true value will be seen
1632 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1633 -- are always updatable. If you do so, make sure that non-updatable
1634 -- ones have enough space for their static link field!
1636 go (App f a) n_val_args
1637 | isTypeArg a = go f n_val_args
1638 | not in_arg && is_static True a = go f (n_val_args + 1)
1639 -- The (not in_arg) checks that we aren't in a constructor argument;
1640 -- if we are, we don't allow (value) applications of any sort
1642 -- NB. In case you wonder, args are sometimes not atomic. eg.
1643 -- x = D# (1.0## /## 2.0##)
1644 -- can't float because /## can fail.
1646 go (Note (SCC _) _) _ = False
1647 go (Note _ f) n_val_args = go f n_val_args
1648 go (Cast e _) n_val_args = go e n_val_args
1652 saturated_data_con f n_val_args
1653 = case isDataConWorkId_maybe f of
1654 Just dc -> n_val_args == dataConRepArity dc