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 )
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)
188 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
189 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
190 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
192 addIdSpecialisations :: Id -> [CoreRule] -> Id
193 addIdSpecialisations id rules
194 = setIdSpecialisation id $
195 extendSpecInfo (idSpecialisation id) rules
197 -- | Gather all the rules for locally bound identifiers from the supplied bindings
198 rulesOfBinds :: [CoreBind] -> [CoreRule]
199 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
201 getRules :: RuleBase -> Id -> [CoreRule]
202 -- The rules for an Id come from two places:
203 -- (a) the ones it is born with (idCoreRules fn)
204 -- (b) rules added in subsequent modules (extra_rules)
205 -- PrimOps, for example, are born with a bunch of rules under (a)
206 getRules rule_base fn
207 | isLocalId fn = idCoreRules fn
208 | otherwise = WARN( not (isPrimOpId fn) && notNull (idCoreRules fn),
209 ppr fn <+> ppr (idCoreRules fn) )
210 idCoreRules fn ++ (lookupNameEnv rule_base (idName fn) `orElse` [])
211 -- Only PrimOpIds have rules inside themselves, and perhaps more besides
215 %************************************************************************
219 %************************************************************************
222 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
223 type RuleBase = NameEnv [CoreRule]
224 -- The rules are are unordered;
225 -- we sort out any overlaps on lookup
227 emptyRuleBase = emptyNameEnv
229 mkRuleBase :: [CoreRule] -> RuleBase
230 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
232 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
233 extendRuleBaseList rule_base new_guys
234 = foldl extendRuleBase rule_base new_guys
236 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
237 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
239 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
240 extendRuleBase rule_base rule
241 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
243 pprRuleBase :: RuleBase -> SDoc
244 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
245 | rs <- nameEnvElts rules ]
249 %************************************************************************
251 \subsection{Matching}
253 %************************************************************************
255 Note [Extra args in rule matching]
256 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
257 If we find a matching rule, we return (Just (rule, rhs)),
258 but the rule firing has only consumed as many of the input args
259 as the ruleArity says. It's up to the caller to keep track
260 of any left-over args. E.g. if you call
261 lookupRule ... f [e1, e2, e3]
262 and it returns Just (r, rhs), where r has ruleArity 2
263 then the real rewrite is
264 f e1 e2 e3 ==> rhs e3
266 You might think it'd be cleaner for lookupRule to deal with the
267 leftover arguments, by applying 'rhs' to them, but the main call
268 in the Simplifier works better as it is. Reason: the 'args' passed
269 to lookupRule are the result of a lazy substitution
272 -- | The main rule matching function. Attempts to apply all (active)
273 -- supplied rules to this instance of an application in a given
274 -- context, returning the rule applied and the resulting expression if
276 lookupRule :: (Activation -> Bool) -> InScopeSet
278 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
280 -- See Note [Extra args in rule matching]
281 -- See comments on matchRule
282 lookupRule is_active in_scope fn args rules
283 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
286 (m:ms) -> Just (findBest (fn,args) m ms)
288 rough_args = map roughTopName args
290 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
292 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
293 Just e -> go ((r,e):ms) rs
294 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
295 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
298 findBest :: (Id, [CoreExpr])
299 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
300 -- All these pairs matched the expression
301 -- Return the pair the the most specific rule
302 -- The (fn,args) is just for overlap reporting
304 findBest target (rule,ans) [] = (rule,ans)
305 findBest target (rule1,ans1) ((rule2,ans2):prs)
306 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
307 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
308 | debugIsOn = let pp_rule rule
309 | opt_PprStyle_Debug = ppr rule
310 | otherwise = doubleQuotes (ftext (ru_name rule))
311 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
312 (vcat [if opt_PprStyle_Debug then
313 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
315 ptext (sLit "Rule 1:") <+> pp_rule rule1,
316 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
317 findBest target (rule1,ans1) prs
318 | otherwise = findBest target (rule1,ans1) prs
322 isMoreSpecific :: CoreRule -> CoreRule -> Bool
323 isMoreSpecific (BuiltinRule {}) r2 = True
324 isMoreSpecific r1 (BuiltinRule {}) = False
325 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
326 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
327 = isJust (matchN in_scope bndrs2 args2 args1)
329 in_scope = mkInScopeSet (mkVarSet bndrs1)
330 -- Actually we should probably include the free vars
331 -- of rule1's args, but I can't be bothered
333 noBlackList :: Activation -> Bool
334 noBlackList act = False -- Nothing is black listed
336 matchRule :: (Activation -> Bool) -> InScopeSet
337 -> [CoreExpr] -> [Maybe Name]
338 -> CoreRule -> Maybe CoreExpr
340 -- If (matchRule rule args) returns Just (name,rhs)
341 -- then (f args) matches the rule, and the corresponding
342 -- rewritten RHS is rhs
344 -- The bndrs and rhs is occurrence-analysed
349 -- forall f g x. map f (map g x) ==> map (f . g) x
351 -- CoreRule "map/map"
352 -- [f,g,x] -- tpl_vars
353 -- [f,map g x] -- tpl_args
354 -- map (f.g) x) -- rhs
356 -- Then the call: matchRule the_rule [e1,map e2 e3]
357 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
359 -- Any 'surplus' arguments in the input are simply put on the end
362 matchRule is_active in_scope args rough_args
363 (BuiltinRule { ru_name = name, ru_try = match_fn })
364 = case match_fn args of
365 Just expr -> Just expr
368 matchRule is_active in_scope args rough_args
369 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
370 ru_bndrs = tpl_vars, ru_args = tpl_args,
372 | not (is_active act) = Nothing
373 | ruleCantMatch tpl_tops rough_args = Nothing
375 = case matchN in_scope tpl_vars tpl_args args of
377 Just (binds, tpl_vals) -> Just (mkLets binds $
378 rule_fn `mkApps` tpl_vals)
380 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
381 -- We could do this when putting things into the rulebase, I guess
385 -- For a given match template and context, find bindings to wrap around
386 -- the entire result and what should be substituted for each template variable.
387 -- Fail if there are two few actual arguments from the target to match the template
388 matchN :: InScopeSet -- ^ In-scope variables
389 -> [Var] -- ^ Match template type variables
390 -> [CoreExpr] -- ^ Match template
391 -> [CoreExpr] -- ^ Target; can have more elements than the template
392 -> Maybe ([CoreBind],
395 matchN in_scope tmpl_vars tmpl_es target_es
396 = do { (tv_subst, id_subst, binds)
397 <- go init_menv emptySubstEnv tmpl_es target_es
398 ; return (fromOL binds,
399 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
401 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
402 -- See Note [Template binders]
404 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
406 go menv subst [] es = Just subst
407 go menv subst ts [] = Nothing -- Fail if too few actual args
408 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
409 ; go menv subst1 ts es }
411 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
412 lookup_tmpl tv_subst id_subst tmpl_var'
413 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
415 Nothing -> unbound tmpl_var'
416 | otherwise = case lookupVarEnv id_subst tmpl_var' of
418 other -> unbound tmpl_var'
420 unbound var = pprPanic "Template variable unbound in rewrite rule"
421 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
424 Note [Template binders]
425 ~~~~~~~~~~~~~~~~~~~~~~~
426 Consider the following match:
427 Template: forall x. f x
429 This should succeed, because the template variable 'x' has
430 nothing to do with the 'x' in the target.
432 On reflection, this case probably does just work, but this might not
433 Template: forall x. f (\x.x)
435 Here we want to clone when we find the \x, but to know that x must be in scope
437 To achive this, we use rnBndrL to rename the template variables if
438 necessary; the renamed ones are the tmpl_vars'
441 ---------------------------------------------
442 The inner workings of matching
443 ---------------------------------------------
446 -- These two definitions are not the same as in Subst,
447 -- but they simple and direct, and purely local to this module
449 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
450 -- variables passed into the match.
452 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
453 -- from nested matches; see the Let case of match, below
455 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
456 type IdSubstEnv = IdEnv CoreExpr
458 emptySubstEnv :: SubstEnv
459 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
462 -- At one stage I tried to match even if there are more
463 -- template args than real args.
465 -- I now think this is probably a bad idea.
466 -- Should the template (map f xs) match (map g)? I think not.
467 -- For a start, in general eta expansion wastes work.
473 -> CoreExpr -- Template
474 -> CoreExpr -- Target
477 -- See the notes with Unify.match, which matches types
478 -- Everything is very similar for terms
480 -- Interesting examples:
482 -- \x->f against \f->f
483 -- When we meet the lambdas we must remember to rename f to f' in the
484 -- second expresion. The RnEnv2 does that.
487 -- forall a. \b->b against \a->3
488 -- We must rename the \a. Otherwise when we meet the lambdas we
489 -- might substitute [a/b] in the template, and then erroneously
490 -- succeed in matching what looks like the template variable 'a' against 3.
492 -- The Var case follows closely what happens in Unify.match
493 match menv subst (Var v1) e2
494 | Just subst <- match_var menv subst v1 e2
497 match menv subst e1 (Note n e2)
498 = match menv subst e1 e2
499 -- Note [Notes in RULE matching]
500 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
501 -- Look through Notes. In particular, we don't want to
502 -- be confused by InlineMe notes. Maybe we should be more
503 -- careful about profiling notes, but for now I'm just
504 -- riding roughshod over them.
505 --- See Note [Notes in call patterns] in SpecConstr
507 -- Here is another important rule: if the term being matched is a
508 -- variable, we expand it so long as its unfolding is a WHNF
509 -- (Its occurrence information is not necessarily up to date,
510 -- so we don't use it.)
511 match menv subst e1 (Var v2)
512 | isCheapUnfolding unfolding
513 = match menv subst e1 (unfoldingTemplate unfolding)
516 unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
517 -- Notice that we look up v2 in the in-scope set
518 -- See Note [Lookup in-scope]
519 -- Remember to apply any renaming first (hence rnOccR)
521 -- Note [Matching lets]
522 -- ~~~~~~~~~~~~~~~~~~~~
523 -- Matching a let-expression. Consider
524 -- RULE forall x. f (g x) = <rhs>
525 -- and target expression
526 -- f (let { w=R } in g E))
527 -- Then we'd like the rule to match, to generate
528 -- let { w=R } in (\x. <rhs>) E
529 -- In effect, we want to float the let-binding outward, to enable
530 -- the match to happen. This is the WHOLE REASON for accumulating
531 -- bindings in the SubstEnv
533 -- We can only do this if
534 -- (a) Widening the scope of w does not capture any variables
535 -- We use a conservative test: w is not already in scope
536 -- If not, we clone the binders, and substitute
537 -- (b) The free variables of R are not bound by the part of the
538 -- target expression outside the let binding; e.g.
539 -- f (\v. let w = v+1 in g E)
540 -- Here we obviously cannot float the let-binding for w.
542 -- You may think rule (a) would never apply, because rule matching is
543 -- mostly invoked from the simplifier, when we have just run substExpr
544 -- over the argument, so there will be no shadowing anyway.
545 -- The fly in the ointment is that the forall'd variables of the
546 -- RULE itself are considered in scope.
548 -- I though of various cheapo ways to solve this tiresome problem,
549 -- but ended up doing the straightforward thing, which is to
550 -- clone the binders if they are in scope. It's tiresome, and
551 -- potentially inefficient, because of the calls to substExpr,
552 -- but I don't think it'll happen much in pracice.
554 {- Cases to think about
555 (let x=y+1 in \x. (x,x))
556 --> let x=y+1 in (\x1. (x1,x1))
557 (\x. let x = y+1 in (x,x))
558 --> let x1 = y+1 in (\x. (x1,x1)
559 (let x=y+1 in (x,x), let x=y-1 in (x,x))
560 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
563 (let x=y+1 in let z=x+1 in (z,z)
564 --> matches (p,p) but watch out that the use of
566 I'm removing the cloning because that makes the above case
567 fail, because the inner let looks as if it has locally-bound vars -}
569 match menv subst@(tv_subst, id_subst, binds) e1 (Let bind e2)
570 | all freshly_bound bndrs,
571 not (any locally_bound bind_fvs)
572 = match (menv { me_env = rn_env' })
573 (tv_subst, id_subst, binds `snocOL` bind')
577 bndrs = bindersOf bind
578 bind_fvs = varSetElems (bindFreeVars bind)
579 locally_bound x = inRnEnvR rn_env x
580 freshly_bound x = not (x `rnInScope` rn_env)
583 rn_env' = extendRnInScopeList rn_env bndrs
585 (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
586 s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
587 subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
588 (bind', e2') | null s_prs = (bind, e2)
589 | otherwise = (s_bind, substExpr subst e2)
590 s_bind = case bind of
591 NonRec {} -> NonRec (head bndrs') (head rhss)
592 Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
595 match menv subst (Lit lit1) (Lit lit2)
599 match menv subst (App f1 a1) (App f2 a2)
600 = do { subst' <- match menv subst f1 f2
601 ; match menv subst' a1 a2 }
603 match menv subst (Lam x1 e1) (Lam x2 e2)
604 = match menv' subst e1 e2
606 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
608 -- This rule does eta expansion
609 -- (\x.M) ~ N iff M ~ N x
610 -- It's important that this is *after* the let rule,
611 -- so that (\x.M) ~ (let y = e in \y.N)
612 -- does the let thing, and then gets the lam/lam rule above
613 match menv subst (Lam x1 e1) e2
614 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
616 (rn_env', new_x) = rnBndrL (me_env menv) x1
617 menv' = menv { me_env = rn_env' }
619 -- Eta expansion the other way
620 -- M ~ (\y.N) iff M y ~ N
621 match menv subst e1 (Lam x2 e2)
622 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
624 (rn_env', new_x) = rnBndrR (me_env menv) x2
625 menv' = menv { me_env = rn_env' }
627 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
628 = do { subst1 <- match_ty menv subst ty1 ty2
629 ; subst2 <- match menv subst1 e1 e2
630 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
631 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
634 match menv subst (Type ty1) (Type ty2)
635 = match_ty menv subst ty1 ty2
637 match menv subst (Cast e1 co1) (Cast e2 co2)
638 = do { subst1 <- match_ty menv subst co1 co2
639 ; match menv subst1 e1 e2 }
641 {- REMOVING OLD CODE: I think that the above handling for let is
642 better than the stuff here, which looks
643 pretty suspicious to me. SLPJ Sept 06
644 -- This is an interesting rule: we simply ignore lets in the
645 -- term being matched against! The unfolding inside it is (by assumption)
646 -- already inside any occurrences of the bound variables, so we'll expand
647 -- them when we encounter them. This gives a chance of matching
648 -- forall x,y. f (g (x,y))
650 -- f (let v = (a,b) in g v)
652 match menv subst e1 (Let bind e2)
653 = match (menv { me_env = rn_env' }) subst e1 e2
655 (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
656 -- It's important to do this renaming, so that the bndrs
657 -- are brought into the local scope. For example:
659 -- forall f,x,xs. f (x:xs)
661 -- f (let y = e in (y:[]))
662 -- We must not get success with x->y! So we record that y is
663 -- locally bound (with rnBndrR), and proceed. The Var case
664 -- will fail when trying to bind x->y
667 -- Everything else fails
668 match menv subst e1 e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
671 ------------------------------------------
672 match_var :: MatchEnv
675 -> CoreExpr -- Target
677 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
678 | v1' `elemVarSet` me_tmpls menv
679 = case lookupVarEnv id_subst v1' of
680 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
681 -> Nothing -- Occurs check failure
682 -- e.g. match forall a. (\x-> a x) against (\y. y y)
684 | otherwise -- No renaming to do on e2, because no free var
685 -- of e2 is in the rnEnvR of the envt
686 -- Note [Matching variable types]
687 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
688 -- However, we must match the *types*; e.g.
689 -- forall (c::Char->Int) (x::Char).
690 -- f (c x) = "RULE FIRED"
691 -- We must only match on args that have the right type
692 -- It's actually quite difficult to come up with an example that shows
693 -- you need type matching, esp since matching is left-to-right, so type
694 -- args get matched first. But it's possible (e.g. simplrun008) and
695 -- this is the Right Thing to do
696 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
697 -- c.f. match_ty below
698 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
700 Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
706 | otherwise -- v1 is not a template variable; check for an exact match with e2
708 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
713 v1' = rnOccL rn_env v1
714 -- If the template is
715 -- forall x. f x (\x -> x) = ...
716 -- Then the x inside the lambda isn't the
717 -- template x, so we must rename first!
720 ------------------------------------------
721 match_alts :: MatchEnv
723 -> [CoreAlt] -- Template
724 -> [CoreAlt] -- Target
726 match_alts menv subst [] []
728 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
730 = do { subst1 <- match menv' subst r1 r2
731 ; match_alts menv subst1 alts1 alts2 }
734 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
736 match_alts menv subst alts1 alts2
740 Matching Core types: use the matcher in TcType.
741 Notice that we treat newtypes as opaque. For example, suppose
742 we have a specialised version of a function at a newtype, say
744 We only want to replace (f T) with f', not (f Int).
747 ------------------------------------------
753 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
754 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
755 ; return (tv_subst', id_subst, binds) }
759 Note [Lookup in-scope]
760 ~~~~~~~~~~~~~~~~~~~~~~
761 Consider this example
762 foo :: Int -> Maybe Int -> Int
764 foo m (Just n) = foo (m-n) (Just n)
766 SpecConstr sees this fragment:
768 case w_smT of wild_Xf [Just A] {
769 Data.Maybe.Nothing -> lvl_smf;
770 Data.Maybe.Just n_acT [Just S(L)] ->
771 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
772 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
775 and correctly generates the rule
777 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
778 sc_snn :: GHC.Prim.Int#}
779 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
780 = \$s\$wfoo_sno y_amr sc_snn ;]
782 BUT we must ensure that this rule matches in the original function!
783 Note that the call to \$wfoo is
784 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
786 During matching we expand wild_Xf to (Just n_acT). But then we must also
787 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
788 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
791 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
795 %************************************************************************
797 \subsection{Checking a program for failing rule applications}
799 %************************************************************************
801 -----------------------------------------------------
803 -----------------------------------------------------
805 We want to know what sites have rules that could have fired but didn't.
806 This pass runs over the tree (without changing it) and reports such.
809 -- | Report partial matches for rules beginning with the specified
810 -- string for the purposes of error reporting
811 ruleCheckProgram :: (Activation -> Bool) -- ^ Rule activation test
812 -> String -- ^ Rule pattern
813 -> RuleBase -- ^ Database of rules
814 -> [CoreBind] -- ^ Bindings to check in
815 -> SDoc -- ^ Resulting check message
816 ruleCheckProgram is_active rule_pat rule_base binds
818 = text "Rule check results: no rule application sites"
820 = vcat [text "Rule check results:",
822 vcat [ p $$ line | p <- bagToList results ]
825 results = unionManyBags (map (ruleCheckBind (RuleCheckEnv is_active rule_pat rule_base)) binds)
826 line = text (replicate 20 '-')
828 data RuleCheckEnv = RuleCheckEnv {
829 rc_is_active :: Activation -> Bool,
830 rc_pattern :: String,
831 rc_rule_base :: RuleBase
834 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
835 -- The Bag returned has one SDoc for each call site found
836 ruleCheckBind env (NonRec b r) = ruleCheck env r
837 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
839 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
840 ruleCheck env (Var v) = emptyBag
841 ruleCheck env (Lit l) = emptyBag
842 ruleCheck env (Type ty) = emptyBag
843 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
844 ruleCheck env (Note n e) = ruleCheck env e
845 ruleCheck env (Cast e co) = ruleCheck env e
846 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
847 ruleCheck env (Lam b e) = ruleCheck env e
848 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
849 unionManyBags [ruleCheck env r | (_,_,r) <- as]
851 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
852 ruleCheckApp env (Var f) as = ruleCheckFun env f as
853 ruleCheckApp env other as = ruleCheck env other
857 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
858 -- Produce a report for all rules matching the predicate
859 -- saying why it doesn't match the specified application
861 ruleCheckFun env fn args
862 | null name_match_rules = emptyBag
863 | otherwise = unitBag (ruleAppCheck_help (rc_is_active env) fn args name_match_rules)
865 name_match_rules = filter match (getRules (rc_rule_base env) fn)
866 match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
868 ruleAppCheck_help :: (Activation -> Bool) -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
869 ruleAppCheck_help is_active fn args rules
870 = -- The rules match the pattern, so we want to print something
871 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
872 vcat (map check_rule rules)]
875 i_args = args `zip` [1::Int ..]
876 rough_args = map roughTopName args
878 check_rule rule = rule_herald rule <> colon <+> rule_info rule
880 rule_herald (BuiltinRule { ru_name = name })
881 = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
882 rule_herald (Rule { ru_name = name })
883 = ptext (sLit "Rule") <+> doubleQuotes (ftext name)
886 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
887 = text "matches (which is very peculiar!)"
889 rule_info (BuiltinRule {}) = text "does not match"
891 rule_info (Rule { ru_name = name, ru_act = act,
892 ru_bndrs = rule_bndrs, ru_args = rule_args})
893 | not (is_active act) = text "active only in later phase"
894 | n_args < n_rule_args = text "too few arguments"
895 | n_mismatches == n_rule_args = text "no arguments match"
896 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
897 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
899 n_rule_args = length rule_args
900 n_mismatches = length mismatches
901 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
902 not (isJust (match_fn rule_arg arg))]
904 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
905 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
907 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
908 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
909 , me_tmpls = mkVarSet rule_bndrs }