2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreRules]{Transformation rules}
8 RuleBase, emptyRuleBase, mkRuleBase, extendRuleBaseList,
9 unionRuleBase, pprRuleBase, ruleCheckProgram,
11 mkSpecInfo, extendSpecInfo, addSpecInfo,
12 rulesOfBinds, addIdSpecialisations,
16 lookupRule, mkLocalRule, roughTopNames
19 #include "HsVersions.h"
21 import CoreSyn -- All of it
22 import CoreSubst ( substExpr, mkSubst )
23 import OccurAnal ( occurAnalyseExpr )
24 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesRhsFreeVars )
25 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
26 import CoreUtils ( tcEqExprX )
27 import PprCore ( pprRules )
28 import Type ( TvSubstEnv )
29 import Coercion ( coercionKind )
30 import TcType ( tcSplitTyConApp_maybe )
31 import CoreTidy ( tidyRules )
32 import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName,
33 idSpecialisation, idCoreRules, setIdSpecialisation )
34 import IdInfo ( SpecInfo( SpecInfo ) )
38 import Name ( Name, NamedThing(..), nameOccName )
40 import Unify ( ruleMatchTyX, MatchEnv(..) )
41 import BasicTypes ( Activation, CompilerPhase, isActive )
48 import List hiding( mapAccumL ) -- Also defined in Util
52 %************************************************************************
54 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
56 %************************************************************************
58 A @CoreRule@ holds details of one rule for an @Id@, which
59 includes its specialisations.
61 For example, if a rule for @f@ contains the mapping:
63 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
65 then when we find an application of f to matching types, we simply replace
66 it by the matching RHS:
68 f (List Int) Bool dict ===> f' Int Bool
70 All the stuff about how many dictionaries to discard, and what types
71 to apply the specialised function to, are handled by the fact that the
72 Rule contains a template for the result of the specialisation.
74 There is one more exciting case, which is dealt with in exactly the same
75 way. If the specialised value is unboxed then it is lifted at its
76 definition site and unlifted at its uses. For example:
78 pi :: forall a. Num a => a
80 might have a specialisation
82 [Int#] ===> (case pi' of Lift pi# -> pi#)
84 where pi' :: Lift Int# is the specialised version of pi.
87 mkLocalRule :: RuleName -> Activation
88 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
89 -- Used to make CoreRule for an Id defined in this module
90 mkLocalRule name act fn bndrs args rhs
91 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
92 ru_bndrs = bndrs, ru_args = args,
93 ru_rhs = rhs, ru_rough = roughTopNames args,
94 ru_orph = Just (nameOccName fn), ru_local = True }
97 roughTopNames :: [CoreExpr] -> [Maybe Name]
98 roughTopNames args = map roughTopName args
100 roughTopName :: CoreExpr -> Maybe Name
101 -- Find the "top" free name of an expression
102 -- a) the function in an App chain (if a GlobalId)
103 -- b) the TyCon in a type
104 -- This is used for the fast-match-check for rules;
105 -- if the top names don't match, the rest can't
106 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
107 Just (tc,_) -> Just (getName tc)
109 roughTopName (App f a) = roughTopName f
110 roughTopName (Var f) | isGlobalId f = Just (idName f)
111 | otherwise = Nothing
112 roughTopName other = Nothing
114 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
115 -- (ruleCantMatch tpl actual) returns True only if 'actual'
116 -- definitely can't match 'tpl' by instantiating 'tpl'.
117 -- It's only a one-way match; unlike instance matching we
118 -- don't consider unification
120 -- Notice that there is no case
121 -- ruleCantMatch (Just n1 : ts) (Nothing : as) = True
122 -- Reason: a local variable 'v' in the actuals might
123 -- have an unfolding which is a global.
124 -- This quite often happens with case scrutinees.
125 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
126 ruleCantMatch (t : ts) (a : as) = ruleCantMatch ts as
127 ruleCantMatch ts as = False
131 %************************************************************************
133 SpecInfo: the rules in an IdInfo
135 %************************************************************************
138 mkSpecInfo :: [CoreRule] -> SpecInfo
139 mkSpecInfo rules = SpecInfo rules (rulesRhsFreeVars rules)
141 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
142 extendSpecInfo (SpecInfo rs1 fvs1) rs2
143 = SpecInfo (rs2 ++ rs1) (rulesRhsFreeVars rs2 `unionVarSet` fvs1)
145 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
146 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
147 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
149 addIdSpecialisations :: Id -> [CoreRule] -> Id
150 addIdSpecialisations id rules
151 = setIdSpecialisation id $
152 extendSpecInfo (idSpecialisation id) rules
154 rulesOfBinds :: [CoreBind] -> [CoreRule]
155 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
159 %************************************************************************
163 %************************************************************************
166 type RuleBase = NameEnv [CoreRule]
167 -- Maps (the name of) an Id to its rules
168 -- The rules are are unordered;
169 -- we sort out any overlaps on lookup
171 emptyRuleBase = emptyNameEnv
173 mkRuleBase :: [CoreRule] -> RuleBase
174 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
176 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
177 extendRuleBaseList rule_base new_guys
178 = foldl extendRuleBase rule_base new_guys
180 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
181 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
183 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
184 extendRuleBase rule_base rule
185 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
187 pprRuleBase :: RuleBase -> SDoc
188 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
189 | rs <- nameEnvElts rules ]
193 %************************************************************************
195 \subsection{Matching}
197 %************************************************************************
200 lookupRule :: (Activation -> Bool) -> InScopeSet
201 -> RuleBase -- Imported rules
202 -> Id -> [CoreExpr] -> Maybe (CoreRule, CoreExpr)
203 lookupRule is_active in_scope rule_base fn args
204 = matchRules is_active in_scope fn args rules
206 -- The rules for an Id come from two places:
207 -- (a) the ones it is born with (idCoreRules fn)
208 -- (b) rules added in subsequent modules (extra_rules)
209 -- PrimOps, for example, are born with a bunch of rules under (a)
210 rules = extra_rules ++ idCoreRules fn
211 extra_rules | isLocalId fn = []
212 | otherwise = lookupNameEnv rule_base (idName fn) `orElse` []
214 matchRules :: (Activation -> Bool) -> InScopeSet
216 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
217 -- See comments on matchRule
218 matchRules is_active in_scope fn args rules
219 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
222 (m:ms) -> Just (findBest (fn,args) m ms)
224 rough_args = map roughTopName args
226 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
228 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
229 Just e -> go ((r,e):ms) rs
230 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
231 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
234 findBest :: (Id, [CoreExpr])
235 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
236 -- All these pairs matched the expression
237 -- Return the pair the the most specific rule
238 -- The (fn,args) is just for overlap reporting
240 findBest target (rule,ans) [] = (rule,ans)
241 findBest target (rule1,ans1) ((rule2,ans2):prs)
242 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
243 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
245 | otherwise = pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
246 (vcat [ptext SLIT("Expression to match:") <+> ppr fn <+> sep (map ppr args),
247 ptext SLIT("Rule 1:") <+> ppr rule1,
248 ptext SLIT("Rule 2:") <+> ppr rule2]) $
249 findBest target (rule1,ans1) prs
251 | otherwise = findBest target (rule1,ans1) prs
256 isMoreSpecific :: CoreRule -> CoreRule -> Bool
257 isMoreSpecific (BuiltinRule {}) r2 = True
258 isMoreSpecific r1 (BuiltinRule {}) = False
259 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
260 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
261 = isJust (matchN in_scope bndrs2 args2 args1)
263 in_scope = mkInScopeSet (mkVarSet bndrs1)
264 -- Actually we should probably include the free vars
265 -- of rule1's args, but I can't be bothered
267 noBlackList :: Activation -> Bool
268 noBlackList act = False -- Nothing is black listed
270 matchRule :: (Activation -> Bool) -> InScopeSet
271 -> [CoreExpr] -> [Maybe Name]
272 -> CoreRule -> Maybe CoreExpr
274 -- If (matchRule rule args) returns Just (name,rhs)
275 -- then (f args) matches the rule, and the corresponding
276 -- rewritten RHS is rhs
278 -- The bndrs and rhs is occurrence-analysed
283 -- forall f g x. map f (map g x) ==> map (f . g) x
285 -- CoreRule "map/map"
286 -- [f,g,x] -- tpl_vars
287 -- [f,map g x] -- tpl_args
288 -- map (f.g) x) -- rhs
290 -- Then the call: matchRule the_rule [e1,map e2 e3]
291 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
293 -- Any 'surplus' arguments in the input are simply put on the end
296 matchRule is_active in_scope args rough_args
297 (BuiltinRule { ru_name = name, ru_try = match_fn })
298 = case match_fn args of
299 Just expr -> Just expr
302 matchRule is_active in_scope args rough_args
303 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
304 ru_bndrs = tpl_vars, ru_args = tpl_args,
306 | not (is_active act) = Nothing
307 | ruleCantMatch tpl_tops rough_args = Nothing
309 = case matchN in_scope tpl_vars tpl_args args of
311 Just (binds, tpl_vals) -> Just (mkLets binds $
312 rule_fn `mkApps` tpl_vals)
314 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
315 -- We could do this when putting things into the rulebase, I guess
320 -> [Var] -- Template tyvars
321 -> [CoreExpr] -- Template
322 -> [CoreExpr] -- Target; can have more elts than template
323 -> Maybe ([CoreBind], -- Bindings to wrap around the entire result
324 [CoreExpr]) -- What is substituted for each template var
326 matchN in_scope tmpl_vars tmpl_es target_es
327 = do { (tv_subst, id_subst, binds)
328 <- go init_menv emptySubstEnv tmpl_es target_es
329 ; return (fromOL binds,
330 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
332 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
333 -- See Note [Template binders]
335 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
337 go menv subst [] es = Just subst
338 go menv subst ts [] = Nothing -- Fail if too few actual args
339 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
340 ; go menv subst1 ts es }
342 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
343 lookup_tmpl tv_subst id_subst tmpl_var'
344 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
346 Nothing -> unbound tmpl_var'
347 | otherwise = case lookupVarEnv id_subst tmpl_var' of
349 other -> unbound tmpl_var'
351 unbound var = pprPanic "Template variable unbound in rewrite rule"
352 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
355 Note [Template binders]
356 ~~~~~~~~~~~~~~~~~~~~~~~
357 Consider the following match:
358 Template: forall x. f x
360 This should succeed, because the template variable 'x' has
361 nothing to do with the 'x' in the target.
363 On reflection, this case probably does just work, but this might not
364 Template: forall x. f (\x.x)
366 Here we want to clone when we find the \x, but to know that x must be in scope
368 To achive this, we use rnBndrL to rename the template variables if
369 necessary; the renamed ones are the tmpl_vars'
372 ---------------------------------------------
373 The inner workings of matching
374 ---------------------------------------------
377 -- These two definitions are not the same as in Subst,
378 -- but they simple and direct, and purely local to this module
380 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
381 -- variables passed into the match.
383 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
384 -- from nested matches; see the Let case of match, below
386 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
387 type IdSubstEnv = IdEnv CoreExpr
389 emptySubstEnv :: SubstEnv
390 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
393 -- At one stage I tried to match even if there are more
394 -- template args than real args.
396 -- I now think this is probably a bad idea.
397 -- Should the template (map f xs) match (map g)? I think not.
398 -- For a start, in general eta expansion wastes work.
404 -> CoreExpr -- Template
405 -> CoreExpr -- Target
408 -- See the notes with Unify.match, which matches types
409 -- Everything is very similar for terms
411 -- Interesting examples:
413 -- \x->f against \f->f
414 -- When we meet the lambdas we must remember to rename f to f' in the
415 -- second expresion. The RnEnv2 does that.
418 -- forall a. \b->b against \a->3
419 -- We must rename the \a. Otherwise when we meet the lambdas we
420 -- might substitute [a/b] in the template, and then erroneously
421 -- succeed in matching what looks like the template variable 'a' against 3.
423 -- The Var case follows closely what happens in Unify.match
424 match menv subst (Var v1) e2
425 | Just subst <- match_var menv subst v1 e2
428 match menv subst e1 (Note n e2)
429 = match menv subst e1 e2
430 -- Note [Notes in RULE matching]
431 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
432 -- Look through Notes. In particular, we don't want to
433 -- be confused by InlineMe notes. Maybe we should be more
434 -- careful about profiling notes, but for now I'm just
435 -- riding roughshod over them.
436 --- See Note [Notes in call patterns] in SpecConstr
438 -- Here is another important rule: if the term being matched is a
439 -- variable, we expand it so long as its unfolding is a WHNF
440 -- (Its occurrence information is not necessarily up to date,
441 -- so we don't use it.)
442 match menv subst e1 (Var v2)
443 | isCheapUnfolding unfolding
444 = match menv subst e1 (unfoldingTemplate unfolding)
447 unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
448 -- Notice that we look up v2 in the in-scope set
449 -- See Note [Lookup in-scope]
450 -- Remember to apply any renaming first (hence rnOccR)
452 -- Note [Matching lets]
453 -- ~~~~~~~~~~~~~~~~~~~~
454 -- Matching a let-expression. Consider
455 -- RULE forall x. f (g x) = <rhs>
456 -- and target expression
457 -- f (let { w=R } in g E))
458 -- Then we'd like the rule to match, to generate
459 -- let { w=R } in (\x. <rhs>) E
460 -- In effect, we want to float the let-binding outward, to enable
461 -- the match to happen. This is the WHOLE REASON for accumulating
462 -- bindings in the SubstEnv
464 -- We can only do this if
465 -- (a) Widening the scope of w does not capture any variables
466 -- We use a conservative test: w is not already in scope
467 -- If not, we clone the binders, and substitute
468 -- (b) The free variables of R are not bound by the part of the
469 -- target expression outside the let binding; e.g.
470 -- f (\v. let w = v+1 in g E)
471 -- Here we obviously cannot float the let-binding for w.
473 -- You may think rule (a) would never apply, because rule matching is
474 -- mostly invoked from the simplifier, when we have just run substExpr
475 -- over the argument, so there will be no shadowing anyway.
476 -- The fly in the ointment is that the forall'd variables of the
477 -- RULE itself are considered in scope.
479 -- I though of various cheapo ways to solve this tiresome problem,
480 -- but ended up doing the straightforward thing, which is to
481 -- clone the binders if they are in scope. It's tiresome, and
482 -- potentially inefficient, because of the calls to substExpr,
483 -- but I don't think it'll happen much in pracice.
485 match menv subst@(tv_subst, id_subst, binds) e1 (Let bind e2)
486 | not (any locally_bound bind_fvs)
487 = match (menv { me_env = rn_env' })
488 (tv_subst, id_subst, binds `snocOL` bind')
492 bndrs = bindersOf bind
493 rhss = rhssOfBind bind
494 bind_fvs = varSetElems (bindFreeVars bind)
495 locally_bound x = inRnEnvR rn_env x
496 (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
497 s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
498 subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
499 (bind', e2') | null s_prs = (bind, e2)
500 | otherwise = (s_bind, substExpr subst e2)
501 s_bind = case bind of
502 NonRec {} -> NonRec (head bndrs') (head rhss)
503 Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
505 match menv subst (Lit lit1) (Lit lit2)
509 match menv subst (App f1 a1) (App f2 a2)
510 = do { subst' <- match menv subst f1 f2
511 ; match menv subst' a1 a2 }
513 match menv subst (Lam x1 e1) (Lam x2 e2)
514 = match menv' subst e1 e2
516 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
518 -- This rule does eta expansion
519 -- (\x.M) ~ N iff M ~ N x
520 -- It's important that this is *after* the let rule,
521 -- so that (\x.M) ~ (let y = e in \y.N)
522 -- does the let thing, and then gets the lam/lam rule above
523 match menv subst (Lam x1 e1) e2
524 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
526 (rn_env', new_x) = rnBndrL (me_env menv) x1
527 menv' = menv { me_env = rn_env' }
529 -- Eta expansion the other way
530 -- M ~ (\y.N) iff M y ~ N
531 match menv subst e1 (Lam x2 e2)
532 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
534 (rn_env', new_x) = rnBndrR (me_env menv) x2
535 menv' = menv { me_env = rn_env' }
537 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
538 = do { subst1 <- match_ty menv subst ty1 ty2
539 ; subst2 <- match menv subst1 e1 e2
540 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
541 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
544 match menv subst (Type ty1) (Type ty2)
545 = match_ty menv subst ty1 ty2
547 match menv subst (Cast e1 co1) (Cast e2 co2)
548 | (from1, to1) <- coercionKind co1
549 , (from2, to2) <- coercionKind co2
550 = do { subst1 <- match_ty menv subst to1 to2
551 ; subst2 <- match_ty menv subst1 from1 from2
552 ; match menv subst2 e1 e2 }
554 {- REMOVING OLD CODE: I think that the above handling for let is
555 better than the stuff here, which looks
556 pretty suspicious to me. SLPJ Sept 06
557 -- This is an interesting rule: we simply ignore lets in the
558 -- term being matched against! The unfolding inside it is (by assumption)
559 -- already inside any occurrences of the bound variables, so we'll expand
560 -- them when we encounter them. This gives a chance of matching
561 -- forall x,y. f (g (x,y))
563 -- f (let v = (a,b) in g v)
565 match menv subst e1 (Let bind e2)
566 = match (menv { me_env = rn_env' }) subst e1 e2
568 (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
569 -- It's important to do this renaming, so that the bndrs
570 -- are brought into the local scope. For example:
572 -- forall f,x,xs. f (x:xs)
574 -- f (let y = e in (y:[]))
575 -- We must not get success with x->y! So we record that y is
576 -- locally bound (with rnBndrR), and proceed. The Var case
577 -- will fail when trying to bind x->y
580 -- Everything else fails
581 match menv subst e1 e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
584 ------------------------------------------
585 match_var :: MatchEnv
588 -> CoreExpr -- Target
590 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
591 | v1' `elemVarSet` me_tmpls menv
592 = case lookupVarEnv id_subst v1' of
593 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
594 -> Nothing -- Occurs check failure
595 -- e.g. match forall a. (\x-> a x) against (\y. y y)
597 | otherwise -- No renaming to do on e2
598 -> Just (tv_subst, extendVarEnv id_subst v1' e2, binds)
600 Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
606 | otherwise -- v1 is not a template variable; check for an exact match with e2
608 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
613 v1' = rnOccL rn_env v1
614 -- If the template is
615 -- forall x. f x (\x -> x) = ...
616 -- Then the x inside the lambda isn't the
617 -- template x, so we must rename first!
620 ------------------------------------------
621 match_alts :: MatchEnv
623 -> [CoreAlt] -- Template
624 -> [CoreAlt] -- Target
626 match_alts menv subst [] []
628 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
630 = do { subst1 <- match menv' subst r1 r2
631 ; match_alts menv subst1 alts1 alts2 }
634 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
636 match_alts menv subst alts1 alts2
640 Matching Core types: use the matcher in TcType.
641 Notice that we treat newtypes as opaque. For example, suppose
642 we have a specialised version of a function at a newtype, say
644 We only want to replace (f T) with f', not (f Int).
647 ------------------------------------------
648 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
649 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
650 ; return (tv_subst', id_subst, binds) }
654 Note [Lookup in-scope]
655 ~~~~~~~~~~~~~~~~~~~~~~
656 Consider this example
657 foo :: Int -> Maybe Int -> Int
659 foo m (Just n) = foo (m-n) (Just n)
661 SpecConstr sees this fragment:
663 case w_smT of wild_Xf [Just A] {
664 Data.Maybe.Nothing -> lvl_smf;
665 Data.Maybe.Just n_acT [Just S(L)] ->
666 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
667 $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
670 and correctly generates the rule
672 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
673 sc_snn :: GHC.Prim.Int#}
674 $wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
675 = $s$wfoo_sno y_amr sc_snn ;]
677 BUT we must ensure that this rule matches in the original function!
678 Note that the call to $wfoo is
679 $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
681 During matching we expand wild_Xf to (Just n_acT). But then we must also
682 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
683 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
686 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
690 %************************************************************************
692 \subsection{Checking a program for failing rule applications}
694 %************************************************************************
696 -----------------------------------------------------
698 -----------------------------------------------------
700 We want to know what sites have rules that could have fired but didn't.
701 This pass runs over the tree (without changing it) and reports such.
703 NB: we assume that this follows a run of the simplifier, so every Id
704 occurrence (including occurrences of imported Ids) is decorated with
705 all its (active) rules. No need to construct a rule base or anything
709 ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
710 -- Report partial matches for rules beginning
711 -- with the specified string
712 ruleCheckProgram phase rule_pat binds
714 = text "Rule check results: no rule application sites"
716 = vcat [text "Rule check results:",
718 vcat [ p $$ line | p <- bagToList results ]
721 results = unionManyBags (map (ruleCheckBind (phase, rule_pat)) binds)
722 line = text (replicate 20 '-')
724 type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
726 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
727 -- The Bag returned has one SDoc for each call site found
728 ruleCheckBind env (NonRec b r) = ruleCheck env r
729 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
731 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
732 ruleCheck env (Var v) = emptyBag
733 ruleCheck env (Lit l) = emptyBag
734 ruleCheck env (Type ty) = emptyBag
735 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
736 ruleCheck env (Note n e) = ruleCheck env e
737 ruleCheck env (Cast e co) = ruleCheck env e
738 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
739 ruleCheck env (Lam b e) = ruleCheck env e
740 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
741 unionManyBags [ruleCheck env r | (_,_,r) <- as]
743 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
744 ruleCheckApp env (Var f) as = ruleCheckFun env f as
745 ruleCheckApp env other as = ruleCheck env other
749 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
750 -- Produce a report for all rules matching the predicate
751 -- saying why it doesn't match the specified application
753 ruleCheckFun (phase, pat) fn args
754 | null name_match_rules = emptyBag
755 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
757 name_match_rules = filter match (idCoreRules fn)
758 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
760 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
761 ruleAppCheck_help phase fn args rules
762 = -- The rules match the pattern, so we want to print something
763 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
764 vcat (map check_rule rules)]
767 i_args = args `zip` [1::Int ..]
768 rough_args = map roughTopName args
770 check_rule rule = rule_herald rule <> colon <+> rule_info rule
772 rule_herald (BuiltinRule { ru_name = name })
773 = ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
774 rule_herald (Rule { ru_name = name })
775 = ptext SLIT("Rule") <+> doubleQuotes (ftext name)
778 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
779 = text "matches (which is very peculiar!)"
781 rule_info (BuiltinRule {}) = text "does not match"
783 rule_info (Rule { ru_name = name, ru_act = act,
784 ru_bndrs = rule_bndrs, ru_args = rule_args})
785 | not (isActive phase act) = text "active only in later phase"
786 | n_args < n_rule_args = text "too few arguments"
787 | n_mismatches == n_rule_args = text "no arguments match"
788 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
789 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
791 n_rule_args = length rule_args
792 n_mismatches = length mismatches
793 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
794 not (isJust (match_fn rule_arg arg))]
796 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
797 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
799 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
800 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
801 , me_tmpls = mkVarSet rule_bndrs }