2 % (c) The University of Glasgow 2006
3 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
6 Utility functions on @Core@ syntax
9 {-# OPTIONS -fno-warn-incomplete-patterns #-}
10 -- The above warning supression flag is a temporary kludge.
11 -- While working on this module you are encouraged to remove it and fix
12 -- any warnings in the module. See
13 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
16 -- | Commonly useful utilites for manipulating the Core language
18 -- * Constructing expressions
19 mkSCC, mkCoerce, mkCoerceI,
20 bindNonRec, needsCaseBinding,
21 mkAltExpr, mkPiType, mkPiTypes,
23 -- * Taking expressions apart
24 findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
26 -- * Properties of expressions
27 exprType, coreAltType, coreAltsType,
28 exprIsDupable, exprIsTrivial, exprIsCheap, exprIsExpandable,
29 exprIsHNF, exprOkForSpeculation, exprIsBig, exprIsConLike,
30 rhsIsStatic, isCheapApp, isExpandableApp,
32 -- * Expression and bindings size
33 coreBindsSize, exprSize,
39 cheapEqExpr, eqExpr, eqExprX,
41 -- * Manipulating data constructors and types
42 applyTypeToArgs, applyTypeToArg,
43 dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
46 #include "HsVersions.h"
64 import TcType ( isPredTy )
80 %************************************************************************
82 \subsection{Find the type of a Core atom/expression}
84 %************************************************************************
87 exprType :: CoreExpr -> Type
88 -- ^ Recover the type of a well-typed Core expression. Fails when
89 -- applied to the actual 'CoreSyn.Type' expression as it cannot
90 -- really be said to have a type
91 exprType (Var var) = idType var
92 exprType (Lit lit) = literalType lit
93 exprType (Let _ body) = exprType body
94 exprType (Case _ _ ty _) = ty
95 exprType (Cast _ co) = snd (coercionKind co)
96 exprType (Note _ e) = exprType e
97 exprType (Lam binder expr) = mkPiType binder (exprType expr)
99 = case collectArgs e of
100 (fun, args) -> applyTypeToArgs e (exprType fun) args
102 exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
104 coreAltType :: CoreAlt -> Type
105 -- ^ Returns the type of the alternatives right hand side
106 coreAltType (_,bs,rhs)
107 | any bad_binder bs = expandTypeSynonyms ty
108 | otherwise = ty -- Note [Existential variables and silly type synonyms]
111 free_tvs = tyVarsOfType ty
112 bad_binder b = isTyVar b && b `elemVarSet` free_tvs
114 coreAltsType :: [CoreAlt] -> Type
115 -- ^ Returns the type of the first alternative, which should be the same as for all alternatives
116 coreAltsType (alt:_) = coreAltType alt
117 coreAltsType [] = panic "corAltsType"
120 Note [Existential variables and silly type synonyms]
121 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
123 data T = forall a. T (Funny a)
128 Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
129 That means that 'exprType' and 'coreAltsType' may give a result that *appears*
130 to mention an out-of-scope type variable. See Trac #3409 for a more real-world
133 Various possibilities suggest themselves:
135 - Ignore the problem, and make Lint not complain about such variables
137 - Expand all type synonyms (or at least all those that discard arguments)
138 This is tricky, because at least for top-level things we want to
139 retain the type the user originally specified.
141 - Expand synonyms on the fly, when the problem arises. That is what
142 we are doing here. It's not too expensive, I think.
145 mkPiType :: Var -> Type -> Type
146 -- ^ Makes a @(->)@ type or a forall type, depending
147 -- on whether it is given a type variable or a term variable.
148 mkPiTypes :: [Var] -> Type -> Type
149 -- ^ 'mkPiType' for multiple type or value arguments
152 | isId v = mkFunTy (idType v) ty
153 | otherwise = mkForAllTy v ty
155 mkPiTypes vs ty = foldr mkPiType ty vs
159 applyTypeToArg :: Type -> CoreExpr -> Type
160 -- ^ Determines the type resulting from applying an expression to a function with the given type
161 applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
162 applyTypeToArg fun_ty _ = funResultTy fun_ty
164 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
165 -- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
166 -- The first argument is just for debugging, and gives some context
167 applyTypeToArgs _ op_ty [] = op_ty
169 applyTypeToArgs e op_ty (Type ty : args)
170 = -- Accumulate type arguments so we can instantiate all at once
173 go rev_tys (Type ty : args) = go (ty:rev_tys) args
174 go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
176 op_ty' = applyTysD msg op_ty (reverse rev_tys)
177 msg = ptext (sLit "applyTypeToArgs") <+>
180 applyTypeToArgs e op_ty (_ : args)
181 = case (splitFunTy_maybe op_ty) of
182 Just (_, res_ty) -> applyTypeToArgs e res_ty args
183 Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
185 panic_msg :: CoreExpr -> Type -> SDoc
186 panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
189 %************************************************************************
191 \subsection{Attaching notes}
193 %************************************************************************
196 -- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
197 mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
199 mkCoerceI (ACo co) e = mkCoerce co e
201 -- | Wrap the given expression in the coercion safely, coalescing nested coercions
202 mkCoerce :: Coercion -> CoreExpr -> CoreExpr
203 mkCoerce co (Cast expr co2)
204 = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
205 (_from_ty2, to_ty2) = coercionKind co2} in
206 from_ty `coreEqType` to_ty2 )
207 mkCoerce (mkTransCoercion co2 co) expr
210 = let (from_ty, _to_ty) = coercionKind co in
211 -- if to_ty `coreEqType` from_ty
214 WARN(not (from_ty `coreEqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
219 -- | Wraps the given expression in the cost centre unless
220 -- in a way that maximises their utility to the user
221 mkSCC :: CostCentre -> Expr b -> Expr b
222 -- Note: Nested SCC's *are* preserved for the benefit of
223 -- cost centre stack profiling
224 mkSCC _ (Lit lit) = Lit lit
225 mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
226 mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
227 mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
228 mkSCC cc (Cast e co) = Cast (mkSCC cc e) co -- Move _scc_ inside cast
229 mkSCC cc expr = Note (SCC cc) expr
233 %************************************************************************
235 \subsection{Other expression construction}
237 %************************************************************************
240 bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
241 -- ^ @bindNonRec x r b@ produces either:
247 -- > case r of x { _DEFAULT_ -> b }
249 -- depending on whether we have to use a @case@ or @let@
250 -- binding for the expression (see 'needsCaseBinding').
251 -- It's used by the desugarer to avoid building bindings
252 -- that give Core Lint a heart attack, although actually
253 -- the simplifier deals with them perfectly well. See
254 -- also 'MkCore.mkCoreLet'
255 bindNonRec bndr rhs body
256 | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
257 | otherwise = Let (NonRec bndr rhs) body
259 -- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
260 -- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
261 needsCaseBinding :: Type -> CoreExpr -> Bool
262 needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
263 -- Make a case expression instead of a let
264 -- These can arise either from the desugarer,
265 -- or from beta reductions: (\x.e) (x +# y)
269 mkAltExpr :: AltCon -- ^ Case alternative constructor
270 -> [CoreBndr] -- ^ Things bound by the pattern match
271 -> [Type] -- ^ The type arguments to the case alternative
273 -- ^ This guy constructs the value that the scrutinee must have
274 -- given that you are in one particular branch of a case
275 mkAltExpr (DataAlt con) args inst_tys
276 = mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
277 mkAltExpr (LitAlt lit) [] []
279 mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
280 mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
284 %************************************************************************
286 \subsection{Taking expressions apart}
288 %************************************************************************
290 The default alternative must be first, if it exists at all.
291 This makes it easy to find, though it makes matching marginally harder.
294 -- | Extract the default case alternative
295 findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
296 findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
297 findDefault alts = (alts, Nothing)
299 isDefaultAlt :: CoreAlt -> Bool
300 isDefaultAlt (DEFAULT, _, _) = True
301 isDefaultAlt _ = False
304 -- | Find the case alternative corresponding to a particular
305 -- constructor: panics if no such constructor exists
306 findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
307 -- A "Nothing" result *is* legitmiate
308 -- See Note [Unreachable code]
311 (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
315 go (alt@(con1,_,_) : alts) deflt
316 = case con `cmpAltCon` con1 of
317 LT -> deflt -- Missed it already; the alts are in increasing order
319 GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
321 ---------------------------------
322 mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
323 -- ^ Merge alternatives preserving order; alternatives in
324 -- the first argument shadow ones in the second
325 mergeAlts [] as2 = as2
326 mergeAlts as1 [] = as1
327 mergeAlts (a1:as1) (a2:as2)
328 = case a1 `cmpAlt` a2 of
329 LT -> a1 : mergeAlts as1 (a2:as2)
330 EQ -> a1 : mergeAlts as1 as2 -- Discard a2
331 GT -> a2 : mergeAlts (a1:as1) as2
334 ---------------------------------
335 trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
338 -- > case (C a b x y) of
341 -- We want to drop the leading type argument of the scrutinee
342 -- leaving the arguments to match agains the pattern
344 trimConArgs DEFAULT args = ASSERT( null args ) []
345 trimConArgs (LitAlt _) args = ASSERT( null args ) []
346 trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
349 Note [Unreachable code]
350 ~~~~~~~~~~~~~~~~~~~~~~~
351 It is possible (although unusual) for GHC to find a case expression
352 that cannot match. For example:
354 data Col = Red | Green | Blue
358 _ -> ...(case x of { Green -> e1; Blue -> e2 })...
360 Suppose that for some silly reason, x isn't substituted in the case
361 expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
362 gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
366 lvl = case x of { Green -> e1; Blue -> e2 })
371 Now if x gets inlined, we won't be able to find a matching alternative
372 for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
373 we generate (error "Inaccessible alternative").
375 Similar things can happen (augmented by GADTs) when the Simplifier
376 filters down the matching alternatives in Simplify.rebuildCase.
379 %************************************************************************
383 %************************************************************************
387 @exprIsTrivial@ is true of expressions we are unconditionally happy to
388 duplicate; simple variables and constants, and type
389 applications. Note that primop Ids aren't considered
392 Note [Variable are trivial]
393 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
394 There used to be a gruesome test for (hasNoBinding v) in the
396 exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
397 The idea here is that a constructor worker, like \$wJust, is
398 really short for (\x -> \$wJust x), becuase \$wJust has no binding.
399 So it should be treated like a lambda. Ditto unsaturated primops.
400 But now constructor workers are not "have-no-binding" Ids. And
401 completely un-applied primops and foreign-call Ids are sufficiently
402 rare that I plan to allow them to be duplicated and put up with
405 Note [SCCs are trivial]
406 ~~~~~~~~~~~~~~~~~~~~~~~
407 We used not to treat (_scc_ "foo" x) as trivial, because it really
408 generates code, (and a heap object when it's a function arg) to
409 capture the cost centre. However, the profiling system discounts the
410 allocation costs for such "boxing thunks" whereas the extra costs of
411 *not* inlining otherwise-trivial bindings can be high, and are hard to
415 exprIsTrivial :: CoreExpr -> Bool
416 exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
417 exprIsTrivial (Type _) = True
418 exprIsTrivial (Lit lit) = litIsTrivial lit
419 exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
420 exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
421 exprIsTrivial (Cast e _) = exprIsTrivial e
422 exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
423 exprIsTrivial _ = False
427 %************************************************************************
431 %************************************************************************
435 @exprIsDupable@ is true of expressions that can be duplicated at a modest
436 cost in code size. This will only happen in different case
437 branches, so there's no issue about duplicating work.
439 That is, exprIsDupable returns True of (f x) even if
440 f is very very expensive to call.
442 Its only purpose is to avoid fruitless let-binding
443 and then inlining of case join points
447 exprIsDupable :: CoreExpr -> Bool
448 exprIsDupable (Type _) = True
449 exprIsDupable (Var _) = True
450 exprIsDupable (Lit lit) = litIsDupable lit
451 exprIsDupable (Note _ e) = exprIsDupable e
452 exprIsDupable (Cast e _) = exprIsDupable e
457 go (App f a) n_args = n_args < dupAppSize
463 dupAppSize = 4 -- Size of application we are prepared to duplicate
466 %************************************************************************
468 exprIsCheap, exprIsExpandable
470 %************************************************************************
472 Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
473 ~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
474 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
475 it is obviously in weak head normal form, or is cheap to get to WHNF.
476 [Note that that's not the same as exprIsDupable; an expression might be
477 big, and hence not dupable, but still cheap.]
479 By ``cheap'' we mean a computation we're willing to:
480 push inside a lambda, or
481 inline at more than one place
482 That might mean it gets evaluated more than once, instead of being
483 shared. The main examples of things which aren't WHNF but are
488 (where e, and all the ei are cheap)
491 (where e and b are cheap)
494 (where op is a cheap primitive operator)
497 (because we are happy to substitute it inside a lambda)
499 Notice that a variable is considered 'cheap': we can push it inside a lambda,
500 because sharing will make sure it is only evaluated once.
502 Note [exprIsCheap and exprIsHNF]
503 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
504 Note that exprIsHNF does not imply exprIsCheap. Eg
505 let x = fac 20 in Just x
506 This responds True to exprIsHNF (you can discard a seq), but
507 False to exprIsCheap.
510 exprIsCheap :: CoreExpr -> Bool
511 exprIsCheap = exprIsCheap' isCheapApp
513 exprIsExpandable :: CoreExpr -> Bool
514 exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
517 exprIsCheap' :: (Id -> Int -> Bool) -> CoreExpr -> Bool
518 exprIsCheap' _ (Lit _) = True
519 exprIsCheap' _ (Type _) = True
520 exprIsCheap' _ (Var _) = True
521 exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
522 exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
523 exprIsCheap' good_app (Lam x e) = isRuntimeVar x
524 || exprIsCheap' good_app e
526 exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
527 and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
528 -- Experimentally, treat (case x of ...) as cheap
529 -- (and case __coerce x etc.)
530 -- This improves arities of overloaded functions where
531 -- there is only dictionary selection (no construction) involved
533 exprIsCheap' good_app (Let (NonRec x _) e)
534 | isUnLiftedType (idType x) = exprIsCheap' good_app e
536 -- Strict lets always have cheap right hand sides,
537 -- and do no allocation, so just look at the body
538 -- Non-strict lets do allocation so we don't treat them as cheap
541 exprIsCheap' good_app other_expr -- Applications and variables
544 -- Accumulate value arguments, then decide
545 go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
546 | otherwise = go f val_args
548 go (Var _) [] = True -- Just a type application of a variable
549 -- (f t1 t2 t3) counts as WHNF
551 = case idDetails f of
552 RecSelId {} -> go_sel args
553 ClassOpId {} -> go_sel args
554 PrimOpId op -> go_primop op args
555 _ | good_app f (length args) -> go_pap args
556 | isBottomingId f -> True
558 -- Application of a function which
559 -- always gives bottom; we treat this as cheap
560 -- because it certainly doesn't need to be shared!
565 go_pap args = all exprIsTrivial args
566 -- For constructor applications and primops, check that all
567 -- the args are trivial. We don't want to treat as cheap, say,
569 -- We'll put up with one constructor application, but not dozens
572 go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
573 -- In principle we should worry about primops
574 -- that return a type variable, since the result
575 -- might be applied to something, but I'm not going
576 -- to bother to check the number of args
579 go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
580 go_sel _ = False -- look cheap, so we will substitute it inside a
581 -- lambda. Particularly for dictionary field selection.
582 -- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
583 -- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
585 isCheapApp :: Id -> Int -> Bool
586 isCheapApp fn n_val_args
588 || n_val_args < idArity fn
590 isExpandableApp :: Id -> Int -> Bool
591 isExpandableApp fn n_val_args
593 || n_val_args < idArity fn
594 || go n_val_args (idType fn)
596 -- See if all the arguments are PredTys (implicit params or classes)
597 -- If so we'll regard it as expandable; see Note [Expandable overloadings]
600 | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
601 | Just (arg, ty) <- splitFunTy_maybe ty
602 , isPredTy arg = go (n_val_args-1) ty
606 Note [Expandable overloadings]
607 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
608 Suppose the user wrote this
609 {-# RULE forall x. foo (negate x) = h x #-}
610 f x = ....(foo (negate x))....
611 He'd expect the rule to fire. But since negate is overloaded, we might
613 f = \d -> let n = negate d in \x -> ...foo (n x)...
614 So we treat the application of a function (negate in this case) to a
615 *dictionary* as expandable. In effect, every function is CONLIKE when
616 it's applied only to dictionaries.
619 %************************************************************************
623 %************************************************************************
626 -- | 'exprOkForSpeculation' returns True of an expression that is:
628 -- * Safe to evaluate even if normal order eval might not
629 -- evaluate the expression at all, or
631 -- * Safe /not/ to evaluate even if normal order would do so
633 -- Precisely, it returns @True@ iff:
635 -- * The expression guarantees to terminate,
637 -- * without raising an exception,
638 -- * without causing a side effect (e.g. writing a mutable variable)
640 -- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
641 -- As an example of the considerations in this test, consider:
643 -- > let x = case y# +# 1# of { r# -> I# r# }
646 -- being translated to:
648 -- > case y# +# 1# of { r# ->
653 -- We can only do this if the @y + 1@ is ok for speculation: it has no
654 -- side effects, and can't diverge or raise an exception.
655 exprOkForSpeculation :: CoreExpr -> Bool
656 exprOkForSpeculation (Lit _) = True
657 exprOkForSpeculation (Type _) = True
658 -- Tick boxes are *not* suitable for speculation
659 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
660 && not (isTickBoxOp v)
661 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
662 exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
664 exprOkForSpeculation (Case e _ _ alts)
665 = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
666 && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
668 exprOkForSpeculation other_expr
669 = case collectArgs other_expr of
670 (Var f, args) -> spec_ok (idDetails f) args
674 spec_ok (DataConWorkId _) _
675 = True -- The strictness of the constructor has already
676 -- been expressed by its "wrapper", so we don't need
677 -- to take the arguments into account
679 spec_ok (PrimOpId op) args
680 | isDivOp op, -- Special case for dividing operations that fail
681 [arg1, Lit lit] <- args -- only if the divisor is zero
682 = not (isZeroLit lit) && exprOkForSpeculation arg1
683 -- Often there is a literal divisor, and this
684 -- can get rid of a thunk in an inner looop
687 = primOpOkForSpeculation op &&
688 all exprOkForSpeculation args
689 -- A bit conservative: we don't really need
690 -- to care about lazy arguments, but this is easy
692 spec_ok (DFunId new_type) _ = not new_type
693 -- DFuns terminate, unless the dict is implemented with a newtype
694 -- in which case they may not
698 -- | True of dyadic operators that can fail only if the second arg is zero!
699 isDivOp :: PrimOp -> Bool
700 -- This function probably belongs in PrimOp, or even in
701 -- an automagically generated file.. but it's such a
702 -- special case I thought I'd leave it here for now.
703 isDivOp IntQuotOp = True
704 isDivOp IntRemOp = True
705 isDivOp WordQuotOp = True
706 isDivOp WordRemOp = True
707 isDivOp FloatDivOp = True
708 isDivOp DoubleDivOp = True
712 Note [exprOkForSpeculation: case expressions]
713 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
715 It's always sound for exprOkForSpeculation to return False, and we
716 don't want it to take too long, so it bales out on complicated-looking
717 terms. Notably lets, which can be stacked very deeply; and in any
718 case the argument of exprOkForSpeculation is usually in a strict context,
719 so any lets will have been floated away.
721 However, we keep going on case-expressions. An example like this one
722 showed up in DPH code:
725 foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
727 If exprOkForSpeculation doesn't look through case expressions, you get this:
729 \ (ww :: GHC.Prim.Int#) ->
731 __DEFAULT -> case (case <# ds 5 of _ {
732 GHC.Bool.False -> lvl1;
733 GHC.Bool.True -> lvl})
735 T.$wfoo (GHC.Prim.-# ds_XkE 1) };
739 The inner case is redundant, and should be nuked.
742 %************************************************************************
744 exprIsHNF, exprIsConLike
746 %************************************************************************
749 -- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
751 -- | exprIsHNF returns true for expressions that are certainly /already/
752 -- evaluated to /head/ normal form. This is used to decide whether it's ok
755 -- > case x of _ -> e
761 -- and to decide whether it's safe to discard a 'seq'.
763 -- So, it does /not/ treat variables as evaluated, unless they say they are.
764 -- However, it /does/ treat partial applications and constructor applications
765 -- as values, even if their arguments are non-trivial, provided the argument
766 -- type is lifted. For example, both of these are values:
768 -- > (:) (f x) (map f xs)
769 -- > map (...redex...)
771 -- because 'seq' on such things completes immediately.
773 -- For unlifted argument types, we have to be careful:
777 -- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
778 -- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
779 -- unboxed type must be ok-for-speculation (or trivial).
780 exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
781 exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
785 -- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
786 -- data constructors. Conlike arguments are considered interesting by the
788 exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
789 exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
791 -- | Returns true for values or value-like expressions. These are lambdas,
792 -- constructors / CONLIKE functions (as determined by the function argument)
795 exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
796 exprIsHNFlike is_con is_con_unf = is_hnf_like
798 is_hnf_like (Var v) -- NB: There are no value args at this point
799 = is_con v -- Catches nullary constructors,
800 -- so that [] and () are values, for example
801 || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
802 || is_con_unf (idUnfolding v)
803 -- Check the thing's unfolding; it might be bound to a value
804 -- We don't look through loop breakers here, which is a bit conservative
805 -- but otherwise I worry that if an Id's unfolding is just itself,
806 -- we could get an infinite loop
808 is_hnf_like (Lit _) = True
809 is_hnf_like (Type _) = True -- Types are honorary Values;
810 -- we don't mind copying them
811 is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
812 is_hnf_like (Note _ e) = is_hnf_like e
813 is_hnf_like (Cast e _) = is_hnf_like e
814 is_hnf_like (App e (Type _)) = is_hnf_like e
815 is_hnf_like (App e a) = app_is_value e [a]
816 is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
817 is_hnf_like _ = False
819 -- There is at least one value argument
820 app_is_value :: CoreExpr -> [CoreArg] -> Bool
821 app_is_value (Var fun) args
822 = idArity fun > valArgCount args -- Under-applied function
823 || is_con fun -- or constructor-like
824 app_is_value (Note _ f) as = app_is_value f as
825 app_is_value (Cast f _) as = app_is_value f as
826 app_is_value (App f a) as = app_is_value f (a:as)
827 app_is_value _ _ = False
831 %************************************************************************
833 Instantiating data constructors
835 %************************************************************************
837 These InstPat functions go here to avoid circularity between DataCon and Id
840 dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
841 dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
843 dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
844 dataConRepFSInstPat = dataConInstPat dataConRepArgTys
845 dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
847 dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
848 -- Remember to include the existential dictionaries
850 dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
851 -> [FastString] -- A long enough list of FSs to use for names
852 -> [Unique] -- An equally long list of uniques, at least one for each binder
854 -> [Type] -- Types to instantiate the universally quantified tyvars
855 -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
856 -- dataConInstPat arg_fun fss us con inst_tys returns a triple
857 -- (ex_tvs, co_tvs, arg_ids),
859 -- ex_tvs are intended to be used as binders for existential type args
861 -- co_tvs are intended to be used as binders for coercion args and the kinds
862 -- of these vars have been instantiated by the inst_tys and the ex_tys
863 -- The co_tvs include both GADT equalities (dcEqSpec) and
864 -- programmer-specified equalities (dcEqTheta)
866 -- arg_ids are indended to be used as binders for value arguments,
867 -- and their types have been instantiated with inst_tys and ex_tys
868 -- The arg_ids include both dicts (dcDictTheta) and
869 -- programmer-specified arguments (after rep-ing) (deRepArgTys)
872 -- The following constructor T1
875 -- T1 :: forall b. Int -> b -> T(a,b)
878 -- has representation type
879 -- forall a. forall a1. forall b. (a ~ (a1,b)) =>
882 -- dataConInstPat fss us T1 (a1',b') will return
884 -- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
886 -- where the double-primed variables are created with the FastStrings and
887 -- Uniques given as fss and us
888 dataConInstPat arg_fun fss uniqs con inst_tys
889 = (ex_bndrs, co_bndrs, arg_ids)
891 univ_tvs = dataConUnivTyVars con
892 ex_tvs = dataConExTyVars con
893 arg_tys = arg_fun con
894 eq_spec = dataConEqSpec con
895 eq_theta = dataConEqTheta con
896 eq_preds = eqSpecPreds eq_spec ++ eq_theta
899 n_co = length eq_preds
901 -- split the Uniques and FastStrings
902 (ex_uniqs, uniqs') = splitAt n_ex uniqs
903 (co_uniqs, id_uniqs) = splitAt n_co uniqs'
905 (ex_fss, fss') = splitAt n_ex fss
906 (co_fss, id_fss) = splitAt n_co fss'
908 -- Make existential type variables
909 ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
910 mk_ex_var uniq fs var = mkTyVar new_name kind
912 new_name = mkSysTvName uniq fs
915 -- Make the instantiating substitution
916 subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
918 -- Make new coercion vars, instantiating kind
919 co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
920 mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
922 new_name = mkSysTvName uniq fs
923 co_kind = substTy subst (mkPredTy eq_pred)
925 -- make value vars, instantiating types
926 mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
927 arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
931 %************************************************************************
935 %************************************************************************
938 -- | A cheap equality test which bales out fast!
939 -- If it returns @True@ the arguments are definitely equal,
940 -- otherwise, they may or may not be equal.
942 -- See also 'exprIsBig'
943 cheapEqExpr :: Expr b -> Expr b -> Bool
945 cheapEqExpr (Var v1) (Var v2) = v1==v2
946 cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
947 cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
949 cheapEqExpr (App f1 a1) (App f2 a2)
950 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
952 cheapEqExpr (Cast e1 t1) (Cast e2 t2)
953 = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
955 cheapEqExpr _ _ = False
959 exprIsBig :: Expr b -> Bool
960 -- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
961 exprIsBig (Lit _) = False
962 exprIsBig (Var _) = False
963 exprIsBig (Type _) = False
964 exprIsBig (Lam _ e) = exprIsBig e
965 exprIsBig (App f a) = exprIsBig f || exprIsBig a
966 exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
971 eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
972 -- Compares for equality, modulo alpha
973 eqExpr in_scope e1 e2
974 = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
976 id_unf _ = noUnfolding -- Don't expand
980 eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
981 -- ^ Compares expressions for equality, modulo alpha.
982 -- Does /not/ look through newtypes or predicate types
983 -- Used in rule matching, and also CSE
985 eqExprX id_unfolding_fun env e1 e2
988 go env (Var v1) (Var v2)
989 | rnOccL env v1 == rnOccR env v2
992 -- The next two rules expand non-local variables
993 -- C.f. Note [Expanding variables] in Rules.lhs
994 -- and Note [Do not expand locally-bound variables] in Rules.lhs
996 | not (locallyBoundL env v1)
997 , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
998 = go (nukeRnEnvL env) e1' e2
1001 | not (locallyBoundR env v2)
1002 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
1003 = go (nukeRnEnvR env) e1 e2'
1005 go _ (Lit lit1) (Lit lit2) = lit1 == lit2
1006 go env (Type t1) (Type t2) = tcEqTypeX env t1 t2
1007 go env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && go env e1 e2
1008 go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
1009 go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
1011 go env (Lam b1 e1) (Lam b2 e2)
1012 = tcEqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
1013 && go (rnBndr2 env b1 b2) e1 e2
1015 go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
1016 = go env r1 r2 -- No need to check binder types, since RHSs match
1017 && go (rnBndr2 env v1 v2) e1 e2
1019 go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
1020 = all2 (go env') rs1 rs2 && go env' e1 e2
1022 (bs1,rs1) = unzip ps1
1023 (bs2,rs2) = unzip ps2
1024 env' = rnBndrs2 env bs1 bs2
1026 go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
1028 && tcEqTypeX env (idType b1) (idType b2)
1029 && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
1034 go_alt env (c1, bs1, e1) (c2, bs2, e2)
1035 = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
1038 go_note (SCC cc1) (SCC cc2) = cc1 == cc2
1039 go_note (CoreNote s1) (CoreNote s2) = s1 == s2
1046 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
1047 locallyBoundL rn_env v = inRnEnvL rn_env v
1048 locallyBoundR rn_env v = inRnEnvR rn_env v
1052 %************************************************************************
1054 \subsection{The size of an expression}
1056 %************************************************************************
1059 coreBindsSize :: [CoreBind] -> Int
1060 coreBindsSize bs = foldr ((+) . bindSize) 0 bs
1062 exprSize :: CoreExpr -> Int
1063 -- ^ A measure of the size of the expressions, strictly greater than 0
1064 -- It also forces the expression pretty drastically as a side effect
1065 exprSize (Var v) = v `seq` 1
1066 exprSize (Lit lit) = lit `seq` 1
1067 exprSize (App f a) = exprSize f + exprSize a
1068 exprSize (Lam b e) = varSize b + exprSize e
1069 exprSize (Let b e) = bindSize b + exprSize e
1070 exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
1071 exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
1072 exprSize (Note n e) = noteSize n + exprSize e
1073 exprSize (Type t) = seqType t `seq` 1
1075 noteSize :: Note -> Int
1076 noteSize (SCC cc) = cc `seq` 1
1077 noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
1079 varSize :: Var -> Int
1080 varSize b | isTyVar b = 1
1081 | otherwise = seqType (idType b) `seq`
1082 megaSeqIdInfo (idInfo b) `seq`
1085 varsSize :: [Var] -> Int
1086 varsSize = sum . map varSize
1088 bindSize :: CoreBind -> Int
1089 bindSize (NonRec b e) = varSize b + exprSize e
1090 bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
1092 pairSize :: (Var, CoreExpr) -> Int
1093 pairSize (b,e) = varSize b + exprSize e
1095 altSize :: CoreAlt -> Int
1096 altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
1100 %************************************************************************
1102 \subsection{Hashing}
1104 %************************************************************************
1107 hashExpr :: CoreExpr -> Int
1108 -- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
1109 -- Two expressions that hash to the different Ints are definitely unequal.
1111 -- The emphasis is on a crude, fast hash, rather than on high precision.
1113 -- But unequal here means \"not identical\"; two alpha-equivalent
1114 -- expressions may hash to the different Ints.
1116 -- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
1117 -- (at least if we want the above invariant to be true).
1119 hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
1120 -- UniqFM doesn't like negative Ints
1122 type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
1124 hash_expr :: HashEnv -> CoreExpr -> Word32
1125 -- Word32, because we're expecting overflows here, and overflowing
1126 -- signed types just isn't cool. In C it's even undefined.
1127 hash_expr env (Note _ e) = hash_expr env e
1128 hash_expr env (Cast e _) = hash_expr env e
1129 hash_expr env (Var v) = hashVar env v
1130 hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1131 hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
1132 hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
1133 hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
1134 hash_expr env (Case e _ _ _) = hash_expr env e
1135 hash_expr env (Lam b e) = hash_expr (extend_env env b) e
1136 hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
1137 -- Shouldn't happen. Better to use WARN than trace, because trace
1138 -- prevents the CPR optimisation kicking in for hash_expr.
1140 fast_hash_expr :: HashEnv -> CoreExpr -> Word32
1141 fast_hash_expr env (Var v) = hashVar env v
1142 fast_hash_expr env (Type t) = fast_hash_type env t
1143 fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
1144 fast_hash_expr env (Cast e _) = fast_hash_expr env e
1145 fast_hash_expr env (Note _ e) = fast_hash_expr env e
1146 fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
1147 fast_hash_expr _ _ = 1
1149 fast_hash_type :: HashEnv -> Type -> Word32
1150 fast_hash_type env ty
1151 | Just tv <- getTyVar_maybe ty = hashVar env tv
1152 | Just (tc,tys) <- splitTyConApp_maybe ty = let hash_tc = fromIntegral (hashName (tyConName tc))
1153 in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
1156 extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
1157 extend_env (n,env) b = (n+1, extendVarEnv env b n)
1159 hashVar :: HashEnv -> Var -> Word32
1161 = fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
1164 %************************************************************************
1166 \subsection{Determining non-updatable right-hand-sides}
1168 %************************************************************************
1170 Top-level constructor applications can usually be allocated
1171 statically, but they can't if the constructor, or any of the
1172 arguments, come from another DLL (because we can't refer to static
1173 labels in other DLLs).
1175 If this happens we simply make the RHS into an updatable thunk,
1176 and 'execute' it rather than allocating it statically.
1179 -- | This function is called only on *top-level* right-hand sides.
1180 -- Returns @True@ if the RHS can be allocated statically in the output,
1181 -- with no thunks involved at all.
1182 rhsIsStatic :: PackageId -> CoreExpr -> Bool
1183 -- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
1184 -- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
1185 -- update flag on it and (iii) in DsExpr to decide how to expand
1188 -- The basic idea is that rhsIsStatic returns True only if the RHS is
1189 -- (a) a value lambda
1190 -- (b) a saturated constructor application with static args
1192 -- BUT watch out for
1193 -- (i) Any cross-DLL references kill static-ness completely
1194 -- because they must be 'executed' not statically allocated
1195 -- ("DLL" here really only refers to Windows DLLs, on other platforms,
1196 -- this is not necessary)
1198 -- (ii) We treat partial applications as redexes, because in fact we
1199 -- make a thunk for them that runs and builds a PAP
1200 -- at run-time. The only appliations that are treated as
1201 -- static are *saturated* applications of constructors.
1203 -- We used to try to be clever with nested structures like this:
1204 -- ys = (:) w ((:) w [])
1205 -- on the grounds that CorePrep will flatten ANF-ise it later.
1206 -- But supporting this special case made the function much more
1207 -- complicated, because the special case only applies if there are no
1208 -- enclosing type lambdas:
1209 -- ys = /\ a -> Foo (Baz ([] a))
1210 -- Here the nested (Baz []) won't float out to top level in CorePrep.
1212 -- But in fact, even without -O, nested structures at top level are
1213 -- flattened by the simplifier, so we don't need to be super-clever here.
1217 -- f = \x::Int. x+7 TRUE
1218 -- p = (True,False) TRUE
1220 -- d = (fst p, False) FALSE because there's a redex inside
1221 -- (this particular one doesn't happen but...)
1223 -- h = D# (1.0## /## 2.0##) FALSE (redex again)
1224 -- n = /\a. Nil a TRUE
1226 -- t = /\a. (:) (case w a of ...) (Nil a) FALSE (redex)
1229 -- This is a bit like CoreUtils.exprIsHNF, with the following differences:
1230 -- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
1232 -- b) (C x xs), where C is a contructor is updatable if the application is
1235 -- c) don't look through unfolding of f in (f x).
1237 rhsIsStatic _this_pkg rhs = is_static False rhs
1239 is_static :: Bool -- True <=> in a constructor argument; must be atomic
1242 is_static False (Lam b e) = isRuntimeVar b || is_static False e
1244 is_static _ (Note (SCC _) _) = False
1245 is_static in_arg (Note _ e) = is_static in_arg e
1246 is_static in_arg (Cast e _) = is_static in_arg e
1248 is_static _ (Lit lit)
1250 MachLabel _ _ _ -> False
1252 -- A MachLabel (foreign import "&foo") in an argument
1253 -- prevents a constructor application from being static. The
1254 -- reason is that it might give rise to unresolvable symbols
1255 -- in the object file: under Linux, references to "weak"
1256 -- symbols from the data segment give rise to "unresolvable
1257 -- relocation" errors at link time This might be due to a bug
1258 -- in the linker, but we'll work around it here anyway.
1261 is_static in_arg other_expr = go other_expr 0
1263 go (Var f) n_val_args
1264 #if mingw32_TARGET_OS
1265 | not (isDllName _this_pkg (idName f))
1267 = saturated_data_con f n_val_args
1268 || (in_arg && n_val_args == 0)
1269 -- A naked un-applied variable is *not* deemed a static RHS
1271 -- Reason: better to update so that the indirection gets shorted
1272 -- out, and the true value will be seen
1273 -- NB: if you change this, you'll break the invariant that THUNK_STATICs
1274 -- are always updatable. If you do so, make sure that non-updatable
1275 -- ones have enough space for their static link field!
1277 go (App f a) n_val_args
1278 | isTypeArg a = go f n_val_args
1279 | not in_arg && is_static True a = go f (n_val_args + 1)
1280 -- The (not in_arg) checks that we aren't in a constructor argument;
1281 -- if we are, we don't allow (value) applications of any sort
1283 -- NB. In case you wonder, args are sometimes not atomic. eg.
1284 -- x = D# (1.0## /## 2.0##)
1285 -- can't float because /## can fail.
1287 go (Note (SCC _) _) _ = False
1288 go (Note _ f) n_val_args = go f n_val_args
1289 go (Cast e _) n_val_args = go e n_val_args
1293 saturated_data_con f n_val_args
1294 = case isDataConWorkId_maybe f of
1295 Just dc -> n_val_args == dataConRepArity dc