2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreRules]{Transformation rules}
8 -- The above warning supression flag is a temporary kludge.
9 -- While working on this module you are encouraged to remove it and fix
10 -- any warnings in the module. See
11 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
14 -- | Functions for collecting together and applying rewrite rules to a module.
15 -- The 'CoreRule' datatype itself is declared elsewhere.
21 emptyRuleBase, mkRuleBase, extendRuleBaseList,
22 unionRuleBase, pprRuleBase,
24 -- ** Checking rule applications
27 -- ** Manipulating 'SpecInfo' rules
28 mkSpecInfo, extendSpecInfo, addSpecInfo,
31 -- * Misc. CoreRule helpers
32 rulesOfBinds, getRules, pprRulesForUser,
34 lookupRule, mkLocalRule, roughTopNames
37 #include "HsVersions.h"
39 import CoreSyn -- All of it
40 import OccurAnal ( occurAnalyseExpr )
41 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
42 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
43 import CoreUtils ( tcEqExprX, exprType )
44 import PprCore ( pprRules )
45 import Type ( Type, TvSubstEnv )
46 import Coercion ( coercionKind )
47 import TcType ( tcSplitTyConApp_maybe )
48 import CoreTidy ( tidyRules )
50 import IdInfo ( SpecInfo( SpecInfo ) )
54 import Name ( Name, NamedThing(..) )
56 import Unify ( ruleMatchTyX, MatchEnv(..) )
57 import BasicTypes ( Activation, CompilerPhase, isActive )
58 import StaticFlags ( opt_PprStyle_Debug )
69 %************************************************************************
71 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
73 %************************************************************************
75 A @CoreRule@ holds details of one rule for an @Id@, which
76 includes its specialisations.
78 For example, if a rule for @f@ contains the mapping:
80 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
82 then when we find an application of f to matching types, we simply replace
83 it by the matching RHS:
85 f (List Int) Bool dict ===> f' Int Bool
87 All the stuff about how many dictionaries to discard, and what types
88 to apply the specialised function to, are handled by the fact that the
89 Rule contains a template for the result of the specialisation.
91 There is one more exciting case, which is dealt with in exactly the same
92 way. If the specialised value is unboxed then it is lifted at its
93 definition site and unlifted at its uses. For example:
95 pi :: forall a. Num a => a
97 might have a specialisation
99 [Int#] ===> (case pi' of Lift pi# -> pi#)
101 where pi' :: Lift Int# is the specialised version of pi.
104 mkLocalRule :: RuleName -> Activation
105 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
106 -- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
107 -- compiled. See also 'CoreSyn.CoreRule'
108 mkLocalRule name act fn bndrs args rhs
109 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
110 ru_bndrs = bndrs, ru_args = args,
111 ru_rhs = rhs, ru_rough = roughTopNames args,
115 roughTopNames :: [CoreExpr] -> [Maybe Name]
116 -- ^ Find the \"top\" free names of several expressions.
117 -- Such names are either:
119 -- 1. The function finally being applied to in an application chain
120 -- (if that name is a GlobalId: see "Var#globalvslocal"), or
122 -- 2. The 'TyCon' if the expression is a 'Type'
124 -- This is used for the fast-match-check for rules;
125 -- if the top names don't match, the rest can't
126 roughTopNames args = map roughTopName args
128 roughTopName :: CoreExpr -> Maybe Name
129 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
130 Just (tc,_) -> Just (getName tc)
132 roughTopName (App f a) = roughTopName f
133 roughTopName (Var f) | isGlobalId f = Just (idName f)
134 | otherwise = Nothing
135 roughTopName other = Nothing
137 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
138 -- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
139 -- definitely can't match @tpl@ by instantiating @tpl@.
140 -- It's only a one-way match; unlike instance matching we
141 -- don't consider unification.
144 -- @ruleCantMatch [Nothing] [Just n2] = False@
145 -- Reason: a template variable can be instantiated by a constant
147 -- @ruleCantMatch [Just n1] [Nothing] = False@
148 -- Reason: a local variable @v@ in the actuals might [_$_]
150 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
151 ruleCantMatch (t : ts) (a : as) = ruleCantMatch ts as
152 ruleCantMatch ts as = False
156 pprRulesForUser :: [CoreRule] -> SDoc
157 -- (a) tidy the rules
158 -- (b) sort them into order based on the rule name
159 -- (c) suppress uniques (unless -dppr-debug is on)
160 -- This combination makes the output stable so we can use in testing
161 -- It's here rather than in PprCore because it calls tidyRules
162 pprRulesForUser rules
163 = withPprStyle defaultUserStyle $
166 tidyRules emptyTidyEnv rules
168 le_rule r1 r2 = ru_name r1 <= ru_name r2
172 %************************************************************************
174 SpecInfo: the rules in an IdInfo
176 %************************************************************************
179 -- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
180 -- for putting into an 'IdInfo'
181 mkSpecInfo :: [CoreRule] -> SpecInfo
182 mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
184 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
185 extendSpecInfo (SpecInfo rs1 fvs1) rs2
186 = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
187 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
188 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
189 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
191 addIdSpecialisations :: Id -> [CoreRule] -> Id
192 addIdSpecialisations id rules
193 = setIdSpecialisation id $
194 extendSpecInfo (idSpecialisation id) rules
196 -- | Gather all the rules for locally bound identifiers from the supplied bindings
197 rulesOfBinds :: [CoreBind] -> [CoreRule]
198 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
200 getRules :: RuleBase -> Id -> [CoreRule]
201 -- The rules for an Id come from two places:
202 -- (a) the ones it is born with (idCoreRules fn)
203 -- (b) rules added in subsequent modules (extra_rules)
204 -- PrimOps, for example, are born with a bunch of rules under (a)
205 getRules rule_base fn
206 | isLocalId fn = idCoreRules fn
207 | otherwise = WARN( not (isPrimOpId fn) && notNull (idCoreRules fn),
208 ppr fn <+> ppr (idCoreRules fn) )
209 idCoreRules fn ++ (lookupNameEnv rule_base (idName fn) `orElse` [])
210 -- Only PrimOpIds have rules inside themselves, and perhaps more besides
214 %************************************************************************
218 %************************************************************************
221 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
222 type RuleBase = NameEnv [CoreRule]
223 -- The rules are are unordered;
224 -- we sort out any overlaps on lookup
226 emptyRuleBase = emptyNameEnv
228 mkRuleBase :: [CoreRule] -> RuleBase
229 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
231 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
232 extendRuleBaseList rule_base new_guys
233 = foldl extendRuleBase rule_base new_guys
235 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
236 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
238 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
239 extendRuleBase rule_base rule
240 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
242 pprRuleBase :: RuleBase -> SDoc
243 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
244 | rs <- nameEnvElts rules ]
248 %************************************************************************
250 \subsection{Matching}
252 %************************************************************************
254 Note [Extra args in rule matching]
255 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
256 If we find a matching rule, we return (Just (rule, rhs)),
257 but the rule firing has only consumed as many of the input args
258 as the ruleArity says. It's up to the caller to keep track
259 of any left-over args. E.g. if you call
260 lookupRule ... f [e1, e2, e3]
261 and it returns Just (r, rhs), where r has ruleArity 2
262 then the real rewrite is
263 f e1 e2 e3 ==> rhs e3
265 You might think it'd be cleaner for lookupRule to deal with the
266 leftover arguments, by applying 'rhs' to them, but the main call
267 in the Simplifier works better as it is. Reason: the 'args' passed
268 to lookupRule are the result of a lazy substitution
271 -- | The main rule matching function. Attempts to apply all (active)
272 -- supplied rules to this instance of an application in a given
273 -- context, returning the rule applied and the resulting expression if
275 lookupRule :: (Activation -> Bool) -> InScopeSet
277 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
279 -- See Note [Extra args in rule matching]
280 -- See comments on matchRule
281 lookupRule is_active in_scope fn args rules
282 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
285 (m:ms) -> Just (findBest (fn,args) m ms)
287 rough_args = map roughTopName args
289 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
291 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
292 Just e -> go ((r,e):ms) rs
293 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
294 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
297 findBest :: (Id, [CoreExpr])
298 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
299 -- All these pairs matched the expression
300 -- Return the pair the the most specific rule
301 -- The (fn,args) is just for overlap reporting
303 findBest target (rule,ans) [] = (rule,ans)
304 findBest target (rule1,ans1) ((rule2,ans2):prs)
305 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
306 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
307 | debugIsOn = let pp_rule rule
308 | opt_PprStyle_Debug = ppr rule
309 | otherwise = doubleQuotes (ftext (ru_name rule))
310 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
311 (vcat [if opt_PprStyle_Debug then
312 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
314 ptext (sLit "Rule 1:") <+> pp_rule rule1,
315 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
316 findBest target (rule1,ans1) prs
317 | otherwise = findBest target (rule1,ans1) prs
321 isMoreSpecific :: CoreRule -> CoreRule -> Bool
322 isMoreSpecific (BuiltinRule {}) r2 = True
323 isMoreSpecific r1 (BuiltinRule {}) = False
324 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
325 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
326 = isJust (matchN in_scope bndrs2 args2 args1)
328 in_scope = mkInScopeSet (mkVarSet bndrs1)
329 -- Actually we should probably include the free vars
330 -- of rule1's args, but I can't be bothered
332 noBlackList :: Activation -> Bool
333 noBlackList act = False -- Nothing is black listed
335 matchRule :: (Activation -> Bool) -> InScopeSet
336 -> [CoreExpr] -> [Maybe Name]
337 -> CoreRule -> Maybe CoreExpr
339 -- If (matchRule rule args) returns Just (name,rhs)
340 -- then (f args) matches the rule, and the corresponding
341 -- rewritten RHS is rhs
343 -- The bndrs and rhs is occurrence-analysed
348 -- forall f g x. map f (map g x) ==> map (f . g) x
350 -- CoreRule "map/map"
351 -- [f,g,x] -- tpl_vars
352 -- [f,map g x] -- tpl_args
353 -- map (f.g) x) -- rhs
355 -- Then the call: matchRule the_rule [e1,map e2 e3]
356 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
358 -- Any 'surplus' arguments in the input are simply put on the end
361 matchRule is_active in_scope args rough_args
362 (BuiltinRule { ru_name = name, ru_try = match_fn })
363 = case match_fn args of
364 Just expr -> Just expr
367 matchRule is_active in_scope args rough_args
368 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
369 ru_bndrs = tpl_vars, ru_args = tpl_args,
371 | not (is_active act) = Nothing
372 | ruleCantMatch tpl_tops rough_args = Nothing
374 = case matchN in_scope tpl_vars tpl_args args of
376 Just (binds, tpl_vals) -> Just (mkLets binds $
377 rule_fn `mkApps` tpl_vals)
379 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
380 -- We could do this when putting things into the rulebase, I guess
384 -- For a given match template and context, find bindings to wrap around
385 -- the entire result and what should be substituted for each template variable.
386 -- Fail if there are two few actual arguments from the target to match the template
387 matchN :: InScopeSet -- ^ In-scope variables
388 -> [Var] -- ^ Match template type variables
389 -> [CoreExpr] -- ^ Match template
390 -> [CoreExpr] -- ^ Target; can have more elements than the template
391 -> Maybe ([CoreBind],
394 matchN in_scope tmpl_vars tmpl_es target_es
395 = do { (tv_subst, id_subst, binds)
396 <- go init_menv emptySubstEnv tmpl_es target_es
397 ; return (fromOL binds,
398 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
400 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
401 -- See Note [Template binders]
403 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
405 go menv subst [] es = Just subst
406 go menv subst ts [] = Nothing -- Fail if too few actual args
407 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
408 ; go menv subst1 ts es }
410 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
411 lookup_tmpl tv_subst id_subst tmpl_var'
412 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
414 Nothing -> unbound tmpl_var'
415 | otherwise = case lookupVarEnv id_subst tmpl_var' of
417 other -> unbound tmpl_var'
419 unbound var = pprPanic "Template variable unbound in rewrite rule"
420 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
423 Note [Template binders]
424 ~~~~~~~~~~~~~~~~~~~~~~~
425 Consider the following match:
426 Template: forall x. f x
428 This should succeed, because the template variable 'x' has
429 nothing to do with the 'x' in the target.
431 On reflection, this case probably does just work, but this might not
432 Template: forall x. f (\x.x)
434 Here we want to clone when we find the \x, but to know that x must be in scope
436 To achive this, we use rnBndrL to rename the template variables if
437 necessary; the renamed ones are the tmpl_vars'
440 ---------------------------------------------
441 The inner workings of matching
442 ---------------------------------------------
445 -- These two definitions are not the same as in Subst,
446 -- but they simple and direct, and purely local to this module
448 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
449 -- variables passed into the match.
451 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
452 -- from nested matches; see the Let case of match, below
454 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
455 type IdSubstEnv = IdEnv CoreExpr
457 emptySubstEnv :: SubstEnv
458 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
461 -- At one stage I tried to match even if there are more
462 -- template args than real args.
464 -- I now think this is probably a bad idea.
465 -- Should the template (map f xs) match (map g)? I think not.
466 -- For a start, in general eta expansion wastes work.
472 -> CoreExpr -- Template
473 -> CoreExpr -- Target
476 -- See the notes with Unify.match, which matches types
477 -- Everything is very similar for terms
479 -- Interesting examples:
481 -- \x->f against \f->f
482 -- When we meet the lambdas we must remember to rename f to f' in the
483 -- second expresion. The RnEnv2 does that.
486 -- forall a. \b->b against \a->3
487 -- We must rename the \a. Otherwise when we meet the lambdas we
488 -- might substitute [a/b] in the template, and then erroneously
489 -- succeed in matching what looks like the template variable 'a' against 3.
491 -- The Var case follows closely what happens in Unify.match
492 match menv subst (Var v1) e2
493 | Just subst <- match_var menv subst v1 e2
496 match menv subst e1 (Note n e2)
497 = match menv subst e1 e2
498 -- Note [Notes in RULE matching]
499 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
500 -- Look through Notes. In particular, we don't want to
501 -- be confused by InlineMe notes. Maybe we should be more
502 -- careful about profiling notes, but for now I'm just
503 -- riding roughshod over them.
504 --- See Note [Notes in call patterns] in SpecConstr
506 -- Here is another important rule: if the term being matched is a
507 -- variable, we expand it so long as its unfolding is a WHNF
508 -- (Its occurrence information is not necessarily up to date,
509 -- so we don't use it.)
510 match menv subst e1 (Var v2)
511 | isCheapUnfolding unfolding
512 = match menv subst e1 (unfoldingTemplate unfolding)
515 unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
516 -- Notice that we look up v2 in the in-scope set
517 -- See Note [Lookup in-scope]
518 -- Remember to apply any renaming first (hence rnOccR)
520 -- Note [Matching lets]
521 -- ~~~~~~~~~~~~~~~~~~~~
522 -- Matching a let-expression. Consider
523 -- RULE forall x. f (g x) = <rhs>
524 -- and target expression
525 -- f (let { w=R } in g E))
526 -- Then we'd like the rule to match, to generate
527 -- let { w=R } in (\x. <rhs>) E
528 -- In effect, we want to float the let-binding outward, to enable
529 -- the match to happen. This is the WHOLE REASON for accumulating
530 -- bindings in the SubstEnv
532 -- We can only do this if
533 -- (a) Widening the scope of w does not capture any variables
534 -- We use a conservative test: w is not already in scope
535 -- If not, we clone the binders, and substitute
536 -- (b) The free variables of R are not bound by the part of the
537 -- target expression outside the let binding; e.g.
538 -- f (\v. let w = v+1 in g E)
539 -- Here we obviously cannot float the let-binding for w.
541 -- You may think rule (a) would never apply, because rule matching is
542 -- mostly invoked from the simplifier, when we have just run substExpr
543 -- over the argument, so there will be no shadowing anyway.
544 -- The fly in the ointment is that the forall'd variables of the
545 -- RULE itself are considered in scope.
547 -- I though of various cheapo ways to solve this tiresome problem,
548 -- but ended up doing the straightforward thing, which is to
549 -- clone the binders if they are in scope. It's tiresome, and
550 -- potentially inefficient, because of the calls to substExpr,
551 -- but I don't think it'll happen much in pracice.
553 {- Cases to think about
554 (let x=y+1 in \x. (x,x))
555 --> let x=y+1 in (\x1. (x1,x1))
556 (\x. let x = y+1 in (x,x))
557 --> let x1 = y+1 in (\x. (x1,x1)
558 (let x=y+1 in (x,x), let x=y-1 in (x,x))
559 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
562 (let x=y+1 in let z=x+1 in (z,z)
563 --> matches (p,p) but watch out that the use of
565 I'm removing the cloning because that makes the above case
566 fail, because the inner let looks as if it has locally-bound vars -}
568 match menv subst@(tv_subst, id_subst, binds) e1 (Let bind e2)
569 | all freshly_bound bndrs,
570 not (any locally_bound bind_fvs)
571 = match (menv { me_env = rn_env' })
572 (tv_subst, id_subst, binds `snocOL` bind')
576 bndrs = bindersOf bind
577 bind_fvs = varSetElems (bindFreeVars bind)
578 locally_bound x = inRnEnvR rn_env x
579 freshly_bound x = not (x `rnInScope` rn_env)
582 rn_env' = extendRnInScopeList rn_env bndrs
584 (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
585 s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
586 subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
587 (bind', e2') | null s_prs = (bind, e2)
588 | otherwise = (s_bind, substExpr subst e2)
589 s_bind = case bind of
590 NonRec {} -> NonRec (head bndrs') (head rhss)
591 Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
594 match menv subst (Lit lit1) (Lit lit2)
598 match menv subst (App f1 a1) (App f2 a2)
599 = do { subst' <- match menv subst f1 f2
600 ; match menv subst' a1 a2 }
602 match menv subst (Lam x1 e1) (Lam x2 e2)
603 = match menv' subst e1 e2
605 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
607 -- This rule does eta expansion
608 -- (\x.M) ~ N iff M ~ N x
609 -- It's important that this is *after* the let rule,
610 -- so that (\x.M) ~ (let y = e in \y.N)
611 -- does the let thing, and then gets the lam/lam rule above
612 match menv subst (Lam x1 e1) e2
613 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
615 (rn_env', new_x) = rnBndrL (me_env menv) x1
616 menv' = menv { me_env = rn_env' }
618 -- Eta expansion the other way
619 -- M ~ (\y.N) iff M y ~ N
620 match menv subst e1 (Lam x2 e2)
621 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
623 (rn_env', new_x) = rnBndrR (me_env menv) x2
624 menv' = menv { me_env = rn_env' }
626 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
627 = do { subst1 <- match_ty menv subst ty1 ty2
628 ; subst2 <- match menv subst1 e1 e2
629 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
630 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
633 match menv subst (Type ty1) (Type ty2)
634 = match_ty menv subst ty1 ty2
636 match menv subst (Cast e1 co1) (Cast e2 co2)
637 = do { subst1 <- match_ty menv subst co1 co2
638 ; match menv subst1 e1 e2 }
640 {- REMOVING OLD CODE: I think that the above handling for let is
641 better than the stuff here, which looks
642 pretty suspicious to me. SLPJ Sept 06
643 -- This is an interesting rule: we simply ignore lets in the
644 -- term being matched against! The unfolding inside it is (by assumption)
645 -- already inside any occurrences of the bound variables, so we'll expand
646 -- them when we encounter them. This gives a chance of matching
647 -- forall x,y. f (g (x,y))
649 -- f (let v = (a,b) in g v)
651 match menv subst e1 (Let bind e2)
652 = match (menv { me_env = rn_env' }) subst e1 e2
654 (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
655 -- It's important to do this renaming, so that the bndrs
656 -- are brought into the local scope. For example:
658 -- forall f,x,xs. f (x:xs)
660 -- f (let y = e in (y:[]))
661 -- We must not get success with x->y! So we record that y is
662 -- locally bound (with rnBndrR), and proceed. The Var case
663 -- will fail when trying to bind x->y
666 -- Everything else fails
667 match menv subst e1 e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
670 ------------------------------------------
671 match_var :: MatchEnv
674 -> CoreExpr -- Target
676 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
677 | v1' `elemVarSet` me_tmpls menv
678 = case lookupVarEnv id_subst v1' of
679 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
680 -> Nothing -- Occurs check failure
681 -- e.g. match forall a. (\x-> a x) against (\y. y y)
683 | otherwise -- No renaming to do on e2, because no free var
684 -- of e2 is in the rnEnvR of the envt
685 -- Note [Matching variable types]
686 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
687 -- However, we must match the *types*; e.g.
688 -- forall (c::Char->Int) (x::Char).
689 -- f (c x) = "RULE FIRED"
690 -- We must only match on args that have the right type
691 -- It's actually quite difficult to come up with an example that shows
692 -- you need type matching, esp since matching is left-to-right, so type
693 -- args get matched first. But it's possible (e.g. simplrun008) and
694 -- this is the Right Thing to do
695 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
696 -- c.f. match_ty below
697 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
699 Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
705 | otherwise -- v1 is not a template variable; check for an exact match with e2
707 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
712 v1' = rnOccL rn_env v1
713 -- If the template is
714 -- forall x. f x (\x -> x) = ...
715 -- Then the x inside the lambda isn't the
716 -- template x, so we must rename first!
719 ------------------------------------------
720 match_alts :: MatchEnv
722 -> [CoreAlt] -- Template
723 -> [CoreAlt] -- Target
725 match_alts menv subst [] []
727 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
729 = do { subst1 <- match menv' subst r1 r2
730 ; match_alts menv subst1 alts1 alts2 }
733 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
735 match_alts menv subst alts1 alts2
739 Matching Core types: use the matcher in TcType.
740 Notice that we treat newtypes as opaque. For example, suppose
741 we have a specialised version of a function at a newtype, say
743 We only want to replace (f T) with f', not (f Int).
746 ------------------------------------------
752 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
753 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
754 ; return (tv_subst', id_subst, binds) }
758 Note [Lookup in-scope]
759 ~~~~~~~~~~~~~~~~~~~~~~
760 Consider this example
761 foo :: Int -> Maybe Int -> Int
763 foo m (Just n) = foo (m-n) (Just n)
765 SpecConstr sees this fragment:
767 case w_smT of wild_Xf [Just A] {
768 Data.Maybe.Nothing -> lvl_smf;
769 Data.Maybe.Just n_acT [Just S(L)] ->
770 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
771 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
774 and correctly generates the rule
776 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
777 sc_snn :: GHC.Prim.Int#}
778 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
779 = \$s\$wfoo_sno y_amr sc_snn ;]
781 BUT we must ensure that this rule matches in the original function!
782 Note that the call to \$wfoo is
783 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
785 During matching we expand wild_Xf to (Just n_acT). But then we must also
786 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
787 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
790 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
794 %************************************************************************
796 \subsection{Checking a program for failing rule applications}
798 %************************************************************************
800 -----------------------------------------------------
802 -----------------------------------------------------
804 We want to know what sites have rules that could have fired but didn't.
805 This pass runs over the tree (without changing it) and reports such.
808 -- | Report partial matches for rules beginning with the specified
809 -- string for the purposes of error reporting
810 ruleCheckProgram :: CompilerPhase -- ^ Phase to check in
811 -> String -- ^ Rule pattern
812 -> RuleBase -- ^ Database of rules
813 -> [CoreBind] -- ^ Bindings to check in
814 -> SDoc -- ^ Resulting check message
815 ruleCheckProgram phase rule_pat rule_base binds
817 = text "Rule check results: no rule application sites"
819 = vcat [text "Rule check results:",
821 vcat [ p $$ line | p <- bagToList results ]
824 results = unionManyBags (map (ruleCheckBind (phase, rule_pat, rule_base)) binds)
825 line = text (replicate 20 '-')
827 type RuleCheckEnv = (CompilerPhase, String, RuleBase) -- Phase and Pattern
829 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
830 -- The Bag returned has one SDoc for each call site found
831 ruleCheckBind env (NonRec b r) = ruleCheck env r
832 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
834 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
835 ruleCheck env (Var v) = emptyBag
836 ruleCheck env (Lit l) = emptyBag
837 ruleCheck env (Type ty) = emptyBag
838 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
839 ruleCheck env (Note n e) = ruleCheck env e
840 ruleCheck env (Cast e co) = ruleCheck env e
841 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
842 ruleCheck env (Lam b e) = ruleCheck env e
843 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
844 unionManyBags [ruleCheck env r | (_,_,r) <- as]
846 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
847 ruleCheckApp env (Var f) as = ruleCheckFun env f as
848 ruleCheckApp env other as = ruleCheck env other
852 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
853 -- Produce a report for all rules matching the predicate
854 -- saying why it doesn't match the specified application
856 ruleCheckFun (phase, pat, rule_base) fn args
857 | null name_match_rules = emptyBag
858 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
860 name_match_rules = filter match (getRules rule_base fn)
861 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
863 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
864 ruleAppCheck_help phase fn args rules
865 = -- The rules match the pattern, so we want to print something
866 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
867 vcat (map check_rule rules)]
870 i_args = args `zip` [1::Int ..]
871 rough_args = map roughTopName args
873 check_rule rule = rule_herald rule <> colon <+> rule_info rule
875 rule_herald (BuiltinRule { ru_name = name })
876 = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
877 rule_herald (Rule { ru_name = name })
878 = ptext (sLit "Rule") <+> doubleQuotes (ftext name)
881 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
882 = text "matches (which is very peculiar!)"
884 rule_info (BuiltinRule {}) = text "does not match"
886 rule_info (Rule { ru_name = name, ru_act = act,
887 ru_bndrs = rule_bndrs, ru_args = rule_args})
888 | not (isActive phase act) = text "active only in later phase"
889 | n_args < n_rule_args = text "too few arguments"
890 | n_mismatches == n_rule_args = text "no arguments match"
891 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
892 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
894 n_rule_args = length rule_args
895 n_mismatches = length mismatches
896 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
897 not (isJust (match_fn rule_arg arg))]
899 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
900 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
902 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
903 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
904 , me_tmpls = mkVarSet rule_bndrs }