2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreRules]{Transformation rules}
7 -- | Functions for collecting together and applying rewrite rules to a module.
8 -- The 'CoreRule' datatype itself is declared elsewhere.
14 emptyRuleBase, mkRuleBase, extendRuleBaseList,
15 unionRuleBase, pprRuleBase,
17 -- ** Checking rule applications
20 -- ** Manipulating 'SpecInfo' rules
21 mkSpecInfo, extendSpecInfo, addSpecInfo,
24 -- * Misc. CoreRule helpers
25 rulesOfBinds, getRules, pprRulesForUser,
27 lookupRule, mkLocalRule, roughTopNames
30 #include "HsVersions.h"
32 import CoreSyn -- All of it
33 import OccurAnal ( occurAnalyseExpr )
34 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
35 import CoreUtils ( tcEqExprX, exprType )
36 import PprCore ( pprRules )
37 import Type ( Type, TvSubstEnv )
38 import TcType ( tcSplitTyConApp_maybe )
39 import CoreTidy ( tidyRules )
41 import IdInfo ( SpecInfo( SpecInfo ) )
45 import Name ( Name, NamedThing(..) )
47 import Unify ( ruleMatchTyX, MatchEnv(..) )
48 import BasicTypes ( Activation )
49 import StaticFlags ( opt_PprStyle_Debug )
60 %************************************************************************
62 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
64 %************************************************************************
66 A @CoreRule@ holds details of one rule for an @Id@, which
67 includes its specialisations.
69 For example, if a rule for @f@ contains the mapping:
71 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
73 then when we find an application of f to matching types, we simply replace
74 it by the matching RHS:
76 f (List Int) Bool dict ===> f' Int Bool
78 All the stuff about how many dictionaries to discard, and what types
79 to apply the specialised function to, are handled by the fact that the
80 Rule contains a template for the result of the specialisation.
82 There is one more exciting case, which is dealt with in exactly the same
83 way. If the specialised value is unboxed then it is lifted at its
84 definition site and unlifted at its uses. For example:
86 pi :: forall a. Num a => a
88 might have a specialisation
90 [Int#] ===> (case pi' of Lift pi# -> pi#)
92 where pi' :: Lift Int# is the specialised version of pi.
95 mkLocalRule :: RuleName -> Activation
96 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
97 -- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
98 -- compiled. See also 'CoreSyn.CoreRule'
99 mkLocalRule name act fn bndrs args rhs
100 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
101 ru_bndrs = bndrs, ru_args = args,
102 ru_rhs = rhs, ru_rough = roughTopNames args,
106 roughTopNames :: [CoreExpr] -> [Maybe Name]
107 -- ^ Find the \"top\" free names of several expressions.
108 -- Such names are either:
110 -- 1. The function finally being applied to in an application chain
111 -- (if that name is a GlobalId: see "Var#globalvslocal"), or
113 -- 2. The 'TyCon' if the expression is a 'Type'
115 -- This is used for the fast-match-check for rules;
116 -- if the top names don't match, the rest can't
117 roughTopNames args = map roughTopName args
119 roughTopName :: CoreExpr -> Maybe Name
120 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
121 Just (tc,_) -> Just (getName tc)
123 roughTopName (App f _) = roughTopName f
124 roughTopName (Var f) | isGlobalId f = Just (idName f)
125 | otherwise = Nothing
126 roughTopName _ = Nothing
128 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
129 -- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
130 -- definitely can't match @tpl@ by instantiating @tpl@.
131 -- It's only a one-way match; unlike instance matching we
132 -- don't consider unification.
135 -- @ruleCantMatch [Nothing] [Just n2] = False@
136 -- Reason: a template variable can be instantiated by a constant
138 -- @ruleCantMatch [Just n1] [Nothing] = False@
139 -- Reason: a local variable @v@ in the actuals might [_$_]
141 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
142 ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as
143 ruleCantMatch _ _ = False
147 pprRulesForUser :: [CoreRule] -> SDoc
148 -- (a) tidy the rules
149 -- (b) sort them into order based on the rule name
150 -- (c) suppress uniques (unless -dppr-debug is on)
151 -- This combination makes the output stable so we can use in testing
152 -- It's here rather than in PprCore because it calls tidyRules
153 pprRulesForUser rules
154 = withPprStyle defaultUserStyle $
157 tidyRules emptyTidyEnv rules
159 le_rule r1 r2 = ru_name r1 <= ru_name r2
163 %************************************************************************
165 SpecInfo: the rules in an IdInfo
167 %************************************************************************
170 -- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
171 -- for putting into an 'IdInfo'
172 mkSpecInfo :: [CoreRule] -> SpecInfo
173 mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
175 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
176 extendSpecInfo (SpecInfo rs1 fvs1) rs2
177 = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
179 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
180 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
181 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
183 addIdSpecialisations :: Id -> [CoreRule] -> Id
184 addIdSpecialisations id []
186 addIdSpecialisations id rules
187 = setIdSpecialisation id $
188 extendSpecInfo (idSpecialisation id) rules
190 -- | Gather all the rules for locally bound identifiers from the supplied bindings
191 rulesOfBinds :: [CoreBind] -> [CoreRule]
192 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
194 getRules :: RuleBase -> Id -> [CoreRule]
195 -- The rules for an Id come from two places:
196 -- (a) the ones it is born with (idCoreRules fn)
197 -- (b) rules added in subsequent modules (extra_rules)
198 -- PrimOps, for example, are born with a bunch of rules under (a)
199 getRules rule_base fn
200 | isLocalId fn = idCoreRules fn
201 | otherwise = WARN( not (isPrimOpId fn) && notNull (idCoreRules fn),
202 ppr fn <+> ppr (idCoreRules fn) )
203 idCoreRules fn ++ (lookupNameEnv rule_base (idName fn) `orElse` [])
204 -- Only PrimOpIds have rules inside themselves, and perhaps more besides
208 %************************************************************************
212 %************************************************************************
215 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
216 type RuleBase = NameEnv [CoreRule]
217 -- The rules are are unordered;
218 -- we sort out any overlaps on lookup
220 emptyRuleBase :: RuleBase
221 emptyRuleBase = emptyNameEnv
223 mkRuleBase :: [CoreRule] -> RuleBase
224 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
226 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
227 extendRuleBaseList rule_base new_guys
228 = foldl extendRuleBase rule_base new_guys
230 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
231 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
233 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
234 extendRuleBase rule_base rule
235 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
237 pprRuleBase :: RuleBase -> SDoc
238 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
239 | rs <- nameEnvElts rules ]
243 %************************************************************************
245 \subsection{Matching}
247 %************************************************************************
249 Note [Extra args in rule matching]
250 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
251 If we find a matching rule, we return (Just (rule, rhs)),
252 but the rule firing has only consumed as many of the input args
253 as the ruleArity says. It's up to the caller to keep track
254 of any left-over args. E.g. if you call
255 lookupRule ... f [e1, e2, e3]
256 and it returns Just (r, rhs), where r has ruleArity 2
257 then the real rewrite is
258 f e1 e2 e3 ==> rhs e3
260 You might think it'd be cleaner for lookupRule to deal with the
261 leftover arguments, by applying 'rhs' to them, but the main call
262 in the Simplifier works better as it is. Reason: the 'args' passed
263 to lookupRule are the result of a lazy substitution
266 -- | The main rule matching function. Attempts to apply all (active)
267 -- supplied rules to this instance of an application in a given
268 -- context, returning the rule applied and the resulting expression if
270 lookupRule :: (Activation -> Bool) -> InScopeSet
272 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
274 -- See Note [Extra args in rule matching]
275 -- See comments on matchRule
276 lookupRule is_active in_scope fn args rules
277 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
280 (m:ms) -> Just (findBest (fn,args) m ms)
282 rough_args = map roughTopName args
284 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
286 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
287 Just e -> go ((r,e):ms) rs
288 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
289 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
292 findBest :: (Id, [CoreExpr])
293 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
294 -- All these pairs matched the expression
295 -- Return the pair the the most specific rule
296 -- The (fn,args) is just for overlap reporting
298 findBest _ (rule,ans) [] = (rule,ans)
299 findBest target (rule1,ans1) ((rule2,ans2):prs)
300 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
301 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
302 | debugIsOn = let pp_rule rule
303 | opt_PprStyle_Debug = ppr rule
304 | otherwise = doubleQuotes (ftext (ru_name rule))
305 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
306 (vcat [if opt_PprStyle_Debug then
307 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
309 ptext (sLit "Rule 1:") <+> pp_rule rule1,
310 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
311 findBest target (rule1,ans1) prs
312 | otherwise = findBest target (rule1,ans1) prs
316 isMoreSpecific :: CoreRule -> CoreRule -> Bool
317 isMoreSpecific (BuiltinRule {}) _ = True
318 isMoreSpecific _ (BuiltinRule {}) = False
319 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
320 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
321 = isJust (matchN in_scope bndrs2 args2 args1)
323 in_scope = mkInScopeSet (mkVarSet bndrs1)
324 -- Actually we should probably include the free vars
325 -- of rule1's args, but I can't be bothered
327 noBlackList :: Activation -> Bool
328 noBlackList _ = False -- Nothing is black listed
330 matchRule :: (Activation -> Bool) -> InScopeSet
331 -> [CoreExpr] -> [Maybe Name]
332 -> CoreRule -> Maybe CoreExpr
334 -- If (matchRule rule args) returns Just (name,rhs)
335 -- then (f args) matches the rule, and the corresponding
336 -- rewritten RHS is rhs
338 -- The bndrs and rhs is occurrence-analysed
343 -- forall f g x. map f (map g x) ==> map (f . g) x
345 -- CoreRule "map/map"
346 -- [f,g,x] -- tpl_vars
347 -- [f,map g x] -- tpl_args
348 -- map (f.g) x) -- rhs
350 -- Then the call: matchRule the_rule [e1,map e2 e3]
351 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
353 -- Any 'surplus' arguments in the input are simply put on the end
356 matchRule _is_active _in_scope args _rough_args
357 (BuiltinRule { ru_try = match_fn })
358 = case match_fn args of
359 Just expr -> Just expr
362 matchRule is_active in_scope args rough_args
363 (Rule { ru_act = act, ru_rough = tpl_tops,
364 ru_bndrs = tpl_vars, ru_args = tpl_args,
366 | not (is_active act) = Nothing
367 | ruleCantMatch tpl_tops rough_args = Nothing
369 = case matchN in_scope tpl_vars tpl_args args of
371 Just (binds, tpl_vals) -> Just (mkLets binds $
372 rule_fn `mkApps` tpl_vals)
374 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
375 -- We could do this when putting things into the rulebase, I guess
379 -- For a given match template and context, find bindings to wrap around
380 -- the entire result and what should be substituted for each template variable.
381 -- Fail if there are two few actual arguments from the target to match the template
382 matchN :: InScopeSet -- ^ In-scope variables
383 -> [Var] -- ^ Match template type variables
384 -> [CoreExpr] -- ^ Match template
385 -> [CoreExpr] -- ^ Target; can have more elements than the template
386 -> Maybe ([CoreBind],
389 matchN in_scope tmpl_vars tmpl_es target_es
390 = do { (tv_subst, id_subst, binds)
391 <- go init_menv emptySubstEnv tmpl_es target_es
392 ; return (fromOL binds,
393 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
395 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
396 -- See Note [Template binders]
398 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
400 go _ subst [] _ = Just subst
401 go _ _ _ [] = Nothing -- Fail if too few actual args
402 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
403 ; go menv subst1 ts es }
405 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
406 lookup_tmpl tv_subst id_subst tmpl_var'
407 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
409 Nothing -> unbound tmpl_var'
410 | otherwise = case lookupVarEnv id_subst tmpl_var' of
412 _ -> unbound tmpl_var'
414 unbound var = pprPanic "Template variable unbound in rewrite rule"
415 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
418 Note [Template binders]
419 ~~~~~~~~~~~~~~~~~~~~~~~
420 Consider the following match:
421 Template: forall x. f x
423 This should succeed, because the template variable 'x' has
424 nothing to do with the 'x' in the target.
426 On reflection, this case probably does just work, but this might not
427 Template: forall x. f (\x.x)
429 Here we want to clone when we find the \x, but to know that x must be in scope
431 To achive this, we use rnBndrL to rename the template variables if
432 necessary; the renamed ones are the tmpl_vars'
435 ---------------------------------------------
436 The inner workings of matching
437 ---------------------------------------------
440 -- These two definitions are not the same as in Subst,
441 -- but they simple and direct, and purely local to this module
443 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
444 -- variables passed into the match.
446 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
447 -- from nested matches; see the Let case of match, below
449 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
450 type IdSubstEnv = IdEnv CoreExpr
452 emptySubstEnv :: SubstEnv
453 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
456 -- At one stage I tried to match even if there are more
457 -- template args than real args.
459 -- I now think this is probably a bad idea.
460 -- Should the template (map f xs) match (map g)? I think not.
461 -- For a start, in general eta expansion wastes work.
467 -> CoreExpr -- Template
468 -> CoreExpr -- Target
471 -- See the notes with Unify.match, which matches types
472 -- Everything is very similar for terms
474 -- Interesting examples:
476 -- \x->f against \f->f
477 -- When we meet the lambdas we must remember to rename f to f' in the
478 -- second expresion. The RnEnv2 does that.
481 -- forall a. \b->b against \a->3
482 -- We must rename the \a. Otherwise when we meet the lambdas we
483 -- might substitute [a/b] in the template, and then erroneously
484 -- succeed in matching what looks like the template variable 'a' against 3.
486 -- The Var case follows closely what happens in Unify.match
487 match menv subst (Var v1) e2
488 | Just subst <- match_var menv subst v1 e2
491 match menv subst e1 (Note _ e2)
492 = match menv subst e1 e2
493 -- Note [Notes in RULE matching]
494 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
495 -- Look through Notes. In particular, we don't want to
496 -- be confused by InlineMe notes. Maybe we should be more
497 -- careful about profiling notes, but for now I'm just
498 -- riding roughshod over them.
499 --- See Note [Notes in call patterns] in SpecConstr
501 -- Here is another important rule: if the term being matched is a
502 -- variable, we expand it so long as its unfolding is a WHNF
503 -- (Its occurrence information is not necessarily up to date,
504 -- so we don't use it.)
505 match menv subst e1 (Var v2)
506 | isCheapUnfolding unfolding
507 = match menv subst e1 (unfoldingTemplate unfolding)
510 unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
511 -- Notice that we look up v2 in the in-scope set
512 -- See Note [Lookup in-scope]
513 -- Remember to apply any renaming first (hence rnOccR)
515 -- Note [Matching lets]
516 -- ~~~~~~~~~~~~~~~~~~~~
517 -- Matching a let-expression. Consider
518 -- RULE forall x. f (g x) = <rhs>
519 -- and target expression
520 -- f (let { w=R } in g E))
521 -- Then we'd like the rule to match, to generate
522 -- let { w=R } in (\x. <rhs>) E
523 -- In effect, we want to float the let-binding outward, to enable
524 -- the match to happen. This is the WHOLE REASON for accumulating
525 -- bindings in the SubstEnv
527 -- We can only do this if
528 -- (a) Widening the scope of w does not capture any variables
529 -- We use a conservative test: w is not already in scope
530 -- If not, we clone the binders, and substitute
531 -- (b) The free variables of R are not bound by the part of the
532 -- target expression outside the let binding; e.g.
533 -- f (\v. let w = v+1 in g E)
534 -- Here we obviously cannot float the let-binding for w.
536 -- You may think rule (a) would never apply, because rule matching is
537 -- mostly invoked from the simplifier, when we have just run substExpr
538 -- over the argument, so there will be no shadowing anyway.
539 -- The fly in the ointment is that the forall'd variables of the
540 -- RULE itself are considered in scope.
542 -- I though of various cheapo ways to solve this tiresome problem,
543 -- but ended up doing the straightforward thing, which is to
544 -- clone the binders if they are in scope. It's tiresome, and
545 -- potentially inefficient, because of the calls to substExpr,
546 -- but I don't think it'll happen much in pracice.
548 {- Cases to think about
549 (let x=y+1 in \x. (x,x))
550 --> let x=y+1 in (\x1. (x1,x1))
551 (\x. let x = y+1 in (x,x))
552 --> let x1 = y+1 in (\x. (x1,x1)
553 (let x=y+1 in (x,x), let x=y-1 in (x,x))
554 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
557 (let x=y+1 in let z=x+1 in (z,z)
558 --> matches (p,p) but watch out that the use of
560 I'm removing the cloning because that makes the above case
561 fail, because the inner let looks as if it has locally-bound vars -}
563 match menv (tv_subst, id_subst, binds) e1 (Let bind e2)
564 | all freshly_bound bndrs,
565 not (any locally_bound bind_fvs)
566 = match (menv { me_env = rn_env' })
567 (tv_subst, id_subst, binds `snocOL` bind')
571 bndrs = bindersOf bind
572 bind_fvs = varSetElems (bindFreeVars bind)
573 locally_bound x = inRnEnvR rn_env x
574 freshly_bound x = not (x `rnInScope` rn_env)
577 rn_env' = extendRnInScopeList rn_env bndrs
579 (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
580 s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
581 subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
582 (bind', e2') | null s_prs = (bind, e2)
583 | otherwise = (s_bind, substExpr subst e2)
584 s_bind = case bind of
585 NonRec {} -> NonRec (head bndrs') (head rhss)
586 Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
589 match _ subst (Lit lit1) (Lit lit2)
593 match menv subst (App f1 a1) (App f2 a2)
594 = do { subst' <- match menv subst f1 f2
595 ; match menv subst' a1 a2 }
597 match menv subst (Lam x1 e1) (Lam x2 e2)
598 = match menv' subst e1 e2
600 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
602 -- This rule does eta expansion
603 -- (\x.M) ~ N iff M ~ N x
604 -- It's important that this is *after* the let rule,
605 -- so that (\x.M) ~ (let y = e in \y.N)
606 -- does the let thing, and then gets the lam/lam rule above
607 match menv subst (Lam x1 e1) e2
608 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
610 (rn_env', new_x) = rnBndrL (me_env menv) x1
611 menv' = menv { me_env = rn_env' }
613 -- Eta expansion the other way
614 -- M ~ (\y.N) iff M y ~ N
615 match menv subst e1 (Lam x2 e2)
616 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
618 (rn_env', new_x) = rnBndrR (me_env menv) x2
619 menv' = menv { me_env = rn_env' }
621 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
622 = do { subst1 <- match_ty menv subst ty1 ty2
623 ; subst2 <- match menv subst1 e1 e2
624 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
625 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
628 match menv subst (Type ty1) (Type ty2)
629 = match_ty menv subst ty1 ty2
631 match menv subst (Cast e1 co1) (Cast e2 co2)
632 = do { subst1 <- match_ty menv subst co1 co2
633 ; match menv subst1 e1 e2 }
635 {- REMOVING OLD CODE: I think that the above handling for let is
636 better than the stuff here, which looks
637 pretty suspicious to me. SLPJ Sept 06
638 -- This is an interesting rule: we simply ignore lets in the
639 -- term being matched against! The unfolding inside it is (by assumption)
640 -- already inside any occurrences of the bound variables, so we'll expand
641 -- them when we encounter them. This gives a chance of matching
642 -- forall x,y. f (g (x,y))
644 -- f (let v = (a,b) in g v)
646 match menv subst e1 (Let bind e2)
647 = match (menv { me_env = rn_env' }) subst e1 e2
649 (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
650 -- It's important to do this renaming, so that the bndrs
651 -- are brought into the local scope. For example:
653 -- forall f,x,xs. f (x:xs)
655 -- f (let y = e in (y:[]))
656 -- We must not get success with x->y! So we record that y is
657 -- locally bound (with rnBndrR), and proceed. The Var case
658 -- will fail when trying to bind x->y
661 -- Everything else fails
662 match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
665 ------------------------------------------
666 match_var :: MatchEnv
669 -> CoreExpr -- Target
671 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
672 | v1' `elemVarSet` me_tmpls menv
673 = case lookupVarEnv id_subst v1' of
674 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
675 -> Nothing -- Occurs check failure
676 -- e.g. match forall a. (\x-> a x) against (\y. y y)
678 | otherwise -- No renaming to do on e2, because no free var
679 -- of e2 is in the rnEnvR of the envt
680 -- Note [Matching variable types]
681 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
682 -- However, we must match the *types*; e.g.
683 -- forall (c::Char->Int) (x::Char).
684 -- f (c x) = "RULE FIRED"
685 -- We must only match on args that have the right type
686 -- It's actually quite difficult to come up with an example that shows
687 -- you need type matching, esp since matching is left-to-right, so type
688 -- args get matched first. But it's possible (e.g. simplrun008) and
689 -- this is the Right Thing to do
690 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
691 -- c.f. match_ty below
692 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
694 Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
700 | otherwise -- v1 is not a template variable; check for an exact match with e2
702 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
707 v1' = rnOccL rn_env v1
708 -- If the template is
709 -- forall x. f x (\x -> x) = ...
710 -- Then the x inside the lambda isn't the
711 -- template x, so we must rename first!
714 ------------------------------------------
715 match_alts :: MatchEnv
717 -> [CoreAlt] -- Template
718 -> [CoreAlt] -- Target
720 match_alts _ subst [] []
722 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
724 = do { subst1 <- match menv' subst r1 r2
725 ; match_alts menv subst1 alts1 alts2 }
728 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
734 Matching Core types: use the matcher in TcType.
735 Notice that we treat newtypes as opaque. For example, suppose
736 we have a specialised version of a function at a newtype, say
738 We only want to replace (f T) with f', not (f Int).
741 ------------------------------------------
747 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
748 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
749 ; return (tv_subst', id_subst, binds) }
753 Note [Lookup in-scope]
754 ~~~~~~~~~~~~~~~~~~~~~~
755 Consider this example
756 foo :: Int -> Maybe Int -> Int
758 foo m (Just n) = foo (m-n) (Just n)
760 SpecConstr sees this fragment:
762 case w_smT of wild_Xf [Just A] {
763 Data.Maybe.Nothing -> lvl_smf;
764 Data.Maybe.Just n_acT [Just S(L)] ->
765 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
766 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
769 and correctly generates the rule
771 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
772 sc_snn :: GHC.Prim.Int#}
773 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
774 = \$s\$wfoo_sno y_amr sc_snn ;]
776 BUT we must ensure that this rule matches in the original function!
777 Note that the call to \$wfoo is
778 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
780 During matching we expand wild_Xf to (Just n_acT). But then we must also
781 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
782 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
785 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
789 %************************************************************************
791 \subsection{Checking a program for failing rule applications}
793 %************************************************************************
795 -----------------------------------------------------
797 -----------------------------------------------------
799 We want to know what sites have rules that could have fired but didn't.
800 This pass runs over the tree (without changing it) and reports such.
803 -- | Report partial matches for rules beginning with the specified
804 -- string for the purposes of error reporting
805 ruleCheckProgram :: (Activation -> Bool) -- ^ Rule activation test
806 -> String -- ^ Rule pattern
807 -> RuleBase -- ^ Database of rules
808 -> [CoreBind] -- ^ Bindings to check in
809 -> SDoc -- ^ Resulting check message
810 ruleCheckProgram is_active rule_pat rule_base binds
812 = text "Rule check results: no rule application sites"
814 = vcat [text "Rule check results:",
816 vcat [ p $$ line | p <- bagToList results ]
819 results = unionManyBags (map (ruleCheckBind (RuleCheckEnv is_active rule_pat rule_base)) binds)
820 line = text (replicate 20 '-')
822 data RuleCheckEnv = RuleCheckEnv {
823 rc_is_active :: Activation -> Bool,
824 rc_pattern :: String,
825 rc_rule_base :: RuleBase
828 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
829 -- The Bag returned has one SDoc for each call site found
830 ruleCheckBind env (NonRec _ r) = ruleCheck env r
831 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (_,r) <- prs]
833 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
834 ruleCheck _ (Var _) = emptyBag
835 ruleCheck _ (Lit _) = emptyBag
836 ruleCheck _ (Type _) = emptyBag
837 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
838 ruleCheck env (Note _ e) = ruleCheck env e
839 ruleCheck env (Cast e _) = ruleCheck env e
840 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
841 ruleCheck env (Lam _ e) = ruleCheck env e
842 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
843 unionManyBags [ruleCheck env r | (_,_,r) <- as]
845 ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
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 _ = 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 env fn args
857 | null name_match_rules = emptyBag
858 | otherwise = unitBag (ruleAppCheck_help (rc_is_active env) fn args name_match_rules)
860 name_match_rules = filter match (getRules (rc_rule_base env) fn)
861 match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
863 ruleAppCheck_help :: (Activation -> Bool) -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
864 ruleAppCheck_help is_active 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_act = act,
887 ru_bndrs = rule_bndrs, ru_args = rule_args})
888 | not (is_active 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 }