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 OccurAnal ( occurAnalyseExpr )
23 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
24 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
25 import CoreUtils ( tcEqExprX, exprType )
26 import PprCore ( pprRules )
27 import Type ( Type, TvSubstEnv )
28 import Coercion ( coercionKind )
29 import TcType ( tcSplitTyConApp_maybe )
30 import CoreTidy ( tidyRules )
31 import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName, idType,
32 idSpecialisation, idCoreRules, setIdSpecialisation )
33 import IdInfo ( SpecInfo( SpecInfo ) )
37 import Name ( Name, NamedThing(..) )
39 import Unify ( ruleMatchTyX, MatchEnv(..) )
40 import BasicTypes ( Activation, CompilerPhase, isActive )
41 import StaticFlags ( opt_PprStyle_Debug )
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,
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 (rulesFreeVars rules)
141 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
142 extendSpecInfo (SpecInfo rs1 fvs1) rs2
143 = SpecInfo (rs2 ++ rs1) (rulesFreeVars 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 %************************************************************************
199 Note [Extra args in rule matching]
200 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
201 If we find a matching rule, we return (Just (rule, rhs)),
202 but the rule firing has only consumed as many of the input args
203 as the ruleArity says. It's up to the caller to keep track
204 of any left-over args. E.g. if you call
205 lookupRule ... f [e1, e2, e3]
206 and it returns Just (r, rhs), where r has ruleArity 2
207 then the real rewrite is
208 f e1 e2 e3 ==> rhs e3
210 You might think it'd be cleaner for lookupRule to deal with the
211 leftover arguments, by applying 'rhs' to them, but the main call
212 in the Simplifier works better as it is. Reason: the 'args' passed
213 to lookupRule are the result of a lazy substitution
216 lookupRule :: (Activation -> Bool) -> InScopeSet
217 -> RuleBase -- Imported rules
218 -> Id -> [CoreExpr] -> Maybe (CoreRule, CoreExpr)
219 -- See Note [Extra argsin rule matching]
220 lookupRule is_active in_scope rule_base fn args
221 = matchRules is_active in_scope fn args rules
223 -- The rules for an Id come from two places:
224 -- (a) the ones it is born with (idCoreRules fn)
225 -- (b) rules added in subsequent modules (extra_rules)
226 -- PrimOps, for example, are born with a bunch of rules under (a)
227 rules = extra_rules ++ idCoreRules fn
228 extra_rules | isLocalId fn = []
229 | otherwise = lookupNameEnv rule_base (idName fn) `orElse` []
231 matchRules :: (Activation -> Bool) -> InScopeSet
233 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
234 -- See comments on matchRule
235 matchRules is_active in_scope fn args rules
236 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
239 (m:ms) -> Just (findBest (fn,args) m ms)
241 rough_args = map roughTopName args
243 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
245 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
246 Just e -> go ((r,e):ms) rs
247 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
248 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
251 findBest :: (Id, [CoreExpr])
252 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
253 -- All these pairs matched the expression
254 -- Return the pair the the most specific rule
255 -- The (fn,args) is just for overlap reporting
257 findBest target (rule,ans) [] = (rule,ans)
258 findBest target (rule1,ans1) ((rule2,ans2):prs)
259 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
260 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
262 | otherwise = let pp_rule rule
263 | opt_PprStyle_Debug = ppr rule
264 | otherwise = doubleQuotes (ftext (ru_name rule))
265 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
266 (vcat [if opt_PprStyle_Debug then
267 ptext SLIT("Expression to match:") <+> ppr fn <+> sep (map ppr args)
269 ptext SLIT("Rule 1:") <+> pp_rule rule1,
270 ptext SLIT("Rule 2:") <+> pp_rule rule2]) $
271 findBest target (rule1,ans1) prs
273 | otherwise = findBest target (rule1,ans1) prs
278 isMoreSpecific :: CoreRule -> CoreRule -> Bool
279 isMoreSpecific (BuiltinRule {}) r2 = True
280 isMoreSpecific r1 (BuiltinRule {}) = False
281 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
282 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
283 = isJust (matchN in_scope bndrs2 args2 args1)
285 in_scope = mkInScopeSet (mkVarSet bndrs1)
286 -- Actually we should probably include the free vars
287 -- of rule1's args, but I can't be bothered
289 noBlackList :: Activation -> Bool
290 noBlackList act = False -- Nothing is black listed
292 matchRule :: (Activation -> Bool) -> InScopeSet
293 -> [CoreExpr] -> [Maybe Name]
294 -> CoreRule -> Maybe CoreExpr
296 -- If (matchRule rule args) returns Just (name,rhs)
297 -- then (f args) matches the rule, and the corresponding
298 -- rewritten RHS is rhs
300 -- The bndrs and rhs is occurrence-analysed
305 -- forall f g x. map f (map g x) ==> map (f . g) x
307 -- CoreRule "map/map"
308 -- [f,g,x] -- tpl_vars
309 -- [f,map g x] -- tpl_args
310 -- map (f.g) x) -- rhs
312 -- Then the call: matchRule the_rule [e1,map e2 e3]
313 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
315 -- Any 'surplus' arguments in the input are simply put on the end
318 matchRule is_active in_scope args rough_args
319 (BuiltinRule { ru_name = name, ru_try = match_fn })
320 = case match_fn args of
321 Just expr -> Just expr
324 matchRule is_active in_scope args rough_args
325 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
326 ru_bndrs = tpl_vars, ru_args = tpl_args,
328 | not (is_active act) = Nothing
329 | ruleCantMatch tpl_tops rough_args = Nothing
331 = case matchN in_scope tpl_vars tpl_args args of
333 Just (binds, tpl_vals) -> Just (mkLets binds $
334 rule_fn `mkApps` tpl_vals)
336 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
337 -- We could do this when putting things into the rulebase, I guess
342 -> [Var] -- Template tyvars
343 -> [CoreExpr] -- Template
344 -> [CoreExpr] -- Target; can have more elts than template
345 -> Maybe ([CoreBind], -- Bindings to wrap around the entire result
346 [CoreExpr]) -- What is substituted for each template var
348 matchN in_scope tmpl_vars tmpl_es target_es
349 = do { (tv_subst, id_subst, binds)
350 <- go init_menv emptySubstEnv tmpl_es target_es
351 ; return (fromOL binds,
352 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
354 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
355 -- See Note [Template binders]
357 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
359 go menv subst [] es = Just subst
360 go menv subst ts [] = Nothing -- Fail if too few actual args
361 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
362 ; go menv subst1 ts es }
364 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
365 lookup_tmpl tv_subst id_subst tmpl_var'
366 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
368 Nothing -> unbound tmpl_var'
369 | otherwise = case lookupVarEnv id_subst tmpl_var' of
371 other -> unbound tmpl_var'
373 unbound var = pprPanic "Template variable unbound in rewrite rule"
374 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
377 Note [Template binders]
378 ~~~~~~~~~~~~~~~~~~~~~~~
379 Consider the following match:
380 Template: forall x. f x
382 This should succeed, because the template variable 'x' has
383 nothing to do with the 'x' in the target.
385 On reflection, this case probably does just work, but this might not
386 Template: forall x. f (\x.x)
388 Here we want to clone when we find the \x, but to know that x must be in scope
390 To achive this, we use rnBndrL to rename the template variables if
391 necessary; the renamed ones are the tmpl_vars'
394 ---------------------------------------------
395 The inner workings of matching
396 ---------------------------------------------
399 -- These two definitions are not the same as in Subst,
400 -- but they simple and direct, and purely local to this module
402 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
403 -- variables passed into the match.
405 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
406 -- from nested matches; see the Let case of match, below
408 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
409 type IdSubstEnv = IdEnv CoreExpr
411 emptySubstEnv :: SubstEnv
412 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
415 -- At one stage I tried to match even if there are more
416 -- template args than real args.
418 -- I now think this is probably a bad idea.
419 -- Should the template (map f xs) match (map g)? I think not.
420 -- For a start, in general eta expansion wastes work.
426 -> CoreExpr -- Template
427 -> CoreExpr -- Target
430 -- See the notes with Unify.match, which matches types
431 -- Everything is very similar for terms
433 -- Interesting examples:
435 -- \x->f against \f->f
436 -- When we meet the lambdas we must remember to rename f to f' in the
437 -- second expresion. The RnEnv2 does that.
440 -- forall a. \b->b against \a->3
441 -- We must rename the \a. Otherwise when we meet the lambdas we
442 -- might substitute [a/b] in the template, and then erroneously
443 -- succeed in matching what looks like the template variable 'a' against 3.
445 -- The Var case follows closely what happens in Unify.match
446 match menv subst (Var v1) e2
447 | Just subst <- match_var menv subst v1 e2
450 match menv subst e1 (Note n e2)
451 = match menv subst e1 e2
452 -- Note [Notes in RULE matching]
453 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
454 -- Look through Notes. In particular, we don't want to
455 -- be confused by InlineMe notes. Maybe we should be more
456 -- careful about profiling notes, but for now I'm just
457 -- riding roughshod over them.
458 --- See Note [Notes in call patterns] in SpecConstr
460 -- Here is another important rule: if the term being matched is a
461 -- variable, we expand it so long as its unfolding is a WHNF
462 -- (Its occurrence information is not necessarily up to date,
463 -- so we don't use it.)
464 match menv subst e1 (Var v2)
465 | isCheapUnfolding unfolding
466 = match menv subst e1 (unfoldingTemplate unfolding)
469 unfolding = idUnfolding (lookupRnInScope rn_env (rnOccR rn_env v2))
470 -- Notice that we look up v2 in the in-scope set
471 -- See Note [Lookup in-scope]
472 -- Remember to apply any renaming first (hence rnOccR)
474 -- Note [Matching lets]
475 -- ~~~~~~~~~~~~~~~~~~~~
476 -- Matching a let-expression. Consider
477 -- RULE forall x. f (g x) = <rhs>
478 -- and target expression
479 -- f (let { w=R } in g E))
480 -- Then we'd like the rule to match, to generate
481 -- let { w=R } in (\x. <rhs>) E
482 -- In effect, we want to float the let-binding outward, to enable
483 -- the match to happen. This is the WHOLE REASON for accumulating
484 -- bindings in the SubstEnv
486 -- We can only do this if
487 -- (a) Widening the scope of w does not capture any variables
488 -- We use a conservative test: w is not already in scope
489 -- If not, we clone the binders, and substitute
490 -- (b) The free variables of R are not bound by the part of the
491 -- target expression outside the let binding; e.g.
492 -- f (\v. let w = v+1 in g E)
493 -- Here we obviously cannot float the let-binding for w.
495 -- You may think rule (a) would never apply, because rule matching is
496 -- mostly invoked from the simplifier, when we have just run substExpr
497 -- over the argument, so there will be no shadowing anyway.
498 -- The fly in the ointment is that the forall'd variables of the
499 -- RULE itself are considered in scope.
501 -- I though of various cheapo ways to solve this tiresome problem,
502 -- but ended up doing the straightforward thing, which is to
503 -- clone the binders if they are in scope. It's tiresome, and
504 -- potentially inefficient, because of the calls to substExpr,
505 -- but I don't think it'll happen much in pracice.
507 {- Cases to think about
508 (let x=y+1 in \x. (x,x))
509 --> let x=y+1 in (\x1. (x1,x1))
510 (\x. let x = y+1 in (x,x))
511 --> let x1 = y+1 in (\x. (x1,x1)
512 (let x=y+1 in (x,x), let x=y-1 in (x,x))
513 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
516 (let x=y+1 in let z=x+1 in (z,z)
517 --> matches (p,p) but watch out that the use of
519 I'm removing the cloning because that makes the above case
520 fail, because the inner let looks as if it has locally-bound vars -}
522 match menv subst@(tv_subst, id_subst, binds) e1 (Let bind e2)
523 | all freshly_bound bndrs,
524 not (any locally_bound bind_fvs)
525 = match (menv { me_env = rn_env' })
526 (tv_subst, id_subst, binds `snocOL` bind')
530 bndrs = bindersOf bind
531 bind_fvs = varSetElems (bindFreeVars bind)
532 locally_bound x = inRnEnvR rn_env x
533 freshly_bound x = not (x `rnInScope` rn_env)
536 rn_env' = extendRnInScopeList rn_env bndrs
538 (rn_env', bndrs') = mapAccumL rnBndrR rn_env bndrs
539 s_prs = [(bndr, Var bndr') | (bndr,bndr') <- zip bndrs bndrs', bndr /= bndr']
540 subst = mkSubst (rnInScopeSet rn_env) emptyVarEnv (mkVarEnv s_prs)
541 (bind', e2') | null s_prs = (bind, e2)
542 | otherwise = (s_bind, substExpr subst e2)
543 s_bind = case bind of
544 NonRec {} -> NonRec (head bndrs') (head rhss)
545 Rec {} -> Rec (bndrs' `zip` map (substExpr subst) rhss)
548 match menv subst (Lit lit1) (Lit lit2)
552 match menv subst (App f1 a1) (App f2 a2)
553 = do { subst' <- match menv subst f1 f2
554 ; match menv subst' a1 a2 }
556 match menv subst (Lam x1 e1) (Lam x2 e2)
557 = match menv' subst e1 e2
559 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
561 -- This rule does eta expansion
562 -- (\x.M) ~ N iff M ~ N x
563 -- It's important that this is *after* the let rule,
564 -- so that (\x.M) ~ (let y = e in \y.N)
565 -- does the let thing, and then gets the lam/lam rule above
566 match menv subst (Lam x1 e1) e2
567 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
569 (rn_env', new_x) = rnBndrL (me_env menv) x1
570 menv' = menv { me_env = rn_env' }
572 -- Eta expansion the other way
573 -- M ~ (\y.N) iff M y ~ N
574 match menv subst e1 (Lam x2 e2)
575 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
577 (rn_env', new_x) = rnBndrR (me_env menv) x2
578 menv' = menv { me_env = rn_env' }
580 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
581 = do { subst1 <- match_ty menv subst ty1 ty2
582 ; subst2 <- match menv subst1 e1 e2
583 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
584 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
587 match menv subst (Type ty1) (Type ty2)
588 = match_ty menv subst ty1 ty2
590 match menv subst (Cast e1 co1) (Cast e2 co2)
591 | (from1, to1) <- coercionKind co1
592 , (from2, to2) <- coercionKind co2
593 = do { subst1 <- match_ty menv subst to1 to2
594 ; subst2 <- match_ty menv subst1 from1 from2
595 ; match menv subst2 e1 e2 }
597 {- REMOVING OLD CODE: I think that the above handling for let is
598 better than the stuff here, which looks
599 pretty suspicious to me. SLPJ Sept 06
600 -- This is an interesting rule: we simply ignore lets in the
601 -- term being matched against! The unfolding inside it is (by assumption)
602 -- already inside any occurrences of the bound variables, so we'll expand
603 -- them when we encounter them. This gives a chance of matching
604 -- forall x,y. f (g (x,y))
606 -- f (let v = (a,b) in g v)
608 match menv subst e1 (Let bind e2)
609 = match (menv { me_env = rn_env' }) subst e1 e2
611 (rn_env', _bndrs') = mapAccumL rnBndrR (me_env menv) (bindersOf bind)
612 -- It's important to do this renaming, so that the bndrs
613 -- are brought into the local scope. For example:
615 -- forall f,x,xs. f (x:xs)
617 -- f (let y = e in (y:[]))
618 -- We must not get success with x->y! So we record that y is
619 -- locally bound (with rnBndrR), and proceed. The Var case
620 -- will fail when trying to bind x->y
623 -- Everything else fails
624 match menv subst e1 e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr e1) $$ (text "e2:" <+> ppr e2)) $
627 ------------------------------------------
628 match_var :: MatchEnv
631 -> CoreExpr -- Target
633 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
634 | v1' `elemVarSet` me_tmpls menv
635 = case lookupVarEnv id_subst v1' of
636 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
637 -> Nothing -- Occurs check failure
638 -- e.g. match forall a. (\x-> a x) against (\y. y y)
640 | otherwise -- No renaming to do on e2, because no free var
641 -- of e2 is in the rnEnvR of the envt
642 -- However, we must match the *types*; e.g.
643 -- forall (c::Char->Int) (x::Char).
644 -- f (c x) = "RULE FIRED"
645 -- We must only match on args that have the right type
646 -- It's actually quite difficult to come up with an example that shows
647 -- you need type matching, esp since matching is left-to-right, so type
648 -- args get matched first. But it's possible (e.g. simplrun008) and
649 -- this is the Right Thing to do
650 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
651 -- c.f. match_ty below
652 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
654 Just e1' | tcEqExprX (nukeRnEnvL rn_env) e1' e2
660 | otherwise -- v1 is not a template variable; check for an exact match with e2
662 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
667 v1' = rnOccL rn_env v1
668 -- If the template is
669 -- forall x. f x (\x -> x) = ...
670 -- Then the x inside the lambda isn't the
671 -- template x, so we must rename first!
674 ------------------------------------------
675 match_alts :: MatchEnv
677 -> [CoreAlt] -- Template
678 -> [CoreAlt] -- Target
680 match_alts menv subst [] []
682 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
684 = do { subst1 <- match menv' subst r1 r2
685 ; match_alts menv subst1 alts1 alts2 }
688 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
690 match_alts menv subst alts1 alts2
694 Matching Core types: use the matcher in TcType.
695 Notice that we treat newtypes as opaque. For example, suppose
696 we have a specialised version of a function at a newtype, say
698 We only want to replace (f T) with f', not (f Int).
701 ------------------------------------------
707 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
708 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
709 ; return (tv_subst', id_subst, binds) }
713 Note [Lookup in-scope]
714 ~~~~~~~~~~~~~~~~~~~~~~
715 Consider this example
716 foo :: Int -> Maybe Int -> Int
718 foo m (Just n) = foo (m-n) (Just n)
720 SpecConstr sees this fragment:
722 case w_smT of wild_Xf [Just A] {
723 Data.Maybe.Nothing -> lvl_smf;
724 Data.Maybe.Just n_acT [Just S(L)] ->
725 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
726 $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
729 and correctly generates the rule
731 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
732 sc_snn :: GHC.Prim.Int#}
733 $wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
734 = $s$wfoo_sno y_amr sc_snn ;]
736 BUT we must ensure that this rule matches in the original function!
737 Note that the call to $wfoo is
738 $wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
740 During matching we expand wild_Xf to (Just n_acT). But then we must also
741 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
742 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
745 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
749 %************************************************************************
751 \subsection{Checking a program for failing rule applications}
753 %************************************************************************
755 -----------------------------------------------------
757 -----------------------------------------------------
759 We want to know what sites have rules that could have fired but didn't.
760 This pass runs over the tree (without changing it) and reports such.
762 NB: we assume that this follows a run of the simplifier, so every Id
763 occurrence (including occurrences of imported Ids) is decorated with
764 all its (active) rules. No need to construct a rule base or anything
768 ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
769 -- Report partial matches for rules beginning
770 -- with the specified string
771 ruleCheckProgram phase rule_pat binds
773 = text "Rule check results: no rule application sites"
775 = vcat [text "Rule check results:",
777 vcat [ p $$ line | p <- bagToList results ]
780 results = unionManyBags (map (ruleCheckBind (phase, rule_pat)) binds)
781 line = text (replicate 20 '-')
783 type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
785 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
786 -- The Bag returned has one SDoc for each call site found
787 ruleCheckBind env (NonRec b r) = ruleCheck env r
788 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
790 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
791 ruleCheck env (Var v) = emptyBag
792 ruleCheck env (Lit l) = emptyBag
793 ruleCheck env (Type ty) = emptyBag
794 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
795 ruleCheck env (Note n e) = ruleCheck env e
796 ruleCheck env (Cast e co) = ruleCheck env e
797 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
798 ruleCheck env (Lam b e) = ruleCheck env e
799 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
800 unionManyBags [ruleCheck env r | (_,_,r) <- as]
802 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
803 ruleCheckApp env (Var f) as = ruleCheckFun env f as
804 ruleCheckApp env other as = ruleCheck env other
808 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
809 -- Produce a report for all rules matching the predicate
810 -- saying why it doesn't match the specified application
812 ruleCheckFun (phase, pat) fn args
813 | null name_match_rules = emptyBag
814 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
816 name_match_rules = filter match (idCoreRules fn)
817 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
819 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
820 ruleAppCheck_help phase fn args rules
821 = -- The rules match the pattern, so we want to print something
822 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
823 vcat (map check_rule rules)]
826 i_args = args `zip` [1::Int ..]
827 rough_args = map roughTopName args
829 check_rule rule = rule_herald rule <> colon <+> rule_info rule
831 rule_herald (BuiltinRule { ru_name = name })
832 = ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
833 rule_herald (Rule { ru_name = name })
834 = ptext SLIT("Rule") <+> doubleQuotes (ftext name)
837 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
838 = text "matches (which is very peculiar!)"
840 rule_info (BuiltinRule {}) = text "does not match"
842 rule_info (Rule { ru_name = name, ru_act = act,
843 ru_bndrs = rule_bndrs, ru_args = rule_args})
844 | not (isActive phase act) = text "active only in later phase"
845 | n_args < n_rule_args = text "too few arguments"
846 | n_mismatches == n_rule_args = text "no arguments match"
847 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
848 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
850 n_rule_args = length rule_args
851 n_mismatches = length mismatches
852 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
853 not (isJust (match_fn rule_arg arg))]
855 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
856 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
858 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
859 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
860 , me_tmpls = mkVarSet rule_bndrs }