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,
14 lookupRule, mkLocalRule, roughTopNames
17 #include "HsVersions.h"
19 import CoreSyn -- All of it
20 import OccurAnal ( occurAnalyseGlobalExpr )
21 import CoreFVs ( exprFreeVars, exprsFreeVars, rulesRhsFreeVars )
22 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
23 import CoreUtils ( tcEqExprX )
24 import PprCore ( pprRules )
26 import TcType ( tcSplitTyConApp_maybe )
27 import CoreTidy ( tidyRules )
28 import Id ( Id, idUnfolding, isLocalId, isGlobalId, idName,
29 idSpecialisation, idCoreRules, setIdSpecialisation )
30 import IdInfo ( SpecInfo( SpecInfo ) )
32 import VarEnv ( IdEnv, TyVarEnv, InScopeSet, emptyTidyEnv,
33 emptyInScopeSet, mkInScopeSet, extendInScopeSetList,
34 emptyVarEnv, lookupVarEnv, extendVarEnv,
35 nukeRnEnvL, mkRnEnv2, rnOccR, rnOccL, inRnEnvR,
36 rnBndrR, rnBndr2, rnBndrL, rnBndrs2 )
38 import Name ( Name, NamedThing(..), nameOccName )
40 import Unify ( tcMatchTyX, MatchEnv(..) )
41 import BasicTypes ( Activation, CompilerPhase, isActive )
45 import Maybe ( isJust )
47 import List ( isPrefixOf )
51 %************************************************************************
53 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
55 %************************************************************************
57 A @CoreRule@ holds details of one rule for an @Id@, which
58 includes its specialisations.
60 For example, if a rule for @f@ contains the mapping:
62 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
64 then when we find an application of f to matching types, we simply replace
65 it by the matching RHS:
67 f (List Int) Bool dict ===> f' Int Bool
69 All the stuff about how many dictionaries to discard, and what types
70 to apply the specialised function to, are handled by the fact that the
71 Rule contains a template for the result of the specialisation.
73 There is one more exciting case, which is dealt with in exactly the same
74 way. If the specialised value is unboxed then it is lifted at its
75 definition site and unlifted at its uses. For example:
77 pi :: forall a. Num a => a
79 might have a specialisation
81 [Int#] ===> (case pi' of Lift pi# -> pi#)
83 where pi' :: Lift Int# is the specialised version of pi.
86 mkLocalRule :: RuleName -> Activation
87 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
88 -- Used to make CoreRule for an Id defined in this module
89 mkLocalRule name act fn bndrs args rhs
90 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
91 ru_bndrs = bndrs, ru_args = args,
92 ru_rhs = rhs, ru_rough = roughTopNames args,
93 ru_orph = Just (nameOccName fn), ru_local = True }
96 roughTopNames :: [CoreExpr] -> [Maybe Name]
97 roughTopNames args = map roughTopName args
99 roughTopName :: CoreExpr -> Maybe Name
100 -- Find the "top" free name of an expression
101 -- a) the function in an App chain (if a GlobalId)
102 -- b) the TyCon in a type
103 -- This is used for the fast-match-check for rules;
104 -- if the top names don't match, the rest can't
105 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
106 Just (tc,_) -> Just (getName tc)
108 roughTopName (App f a) = roughTopName f
109 roughTopName (Var f) | isGlobalId f = Just (idName f)
110 | otherwise = Nothing
111 roughTopName other = Nothing
113 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
114 -- (ruleCantMatch tpl actual) returns True only if 'actual'
115 -- definitely can't match 'tpl' by instantiating 'tpl'.
116 -- It's only a one-way match; unlike instance matching we
117 -- don't consider unification
118 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
119 ruleCantMatch (Just n1 : ts) (Nothing : as) = True
120 ruleCantMatch (t : ts) (a : as) = ruleCantMatch ts as
121 ruleCantMatch ts as = False
125 %************************************************************************
127 SpecInfo: the rules in an IdInfo
129 %************************************************************************
132 mkSpecInfo :: [CoreRule] -> SpecInfo
133 mkSpecInfo rules = SpecInfo rules (rulesRhsFreeVars rules)
135 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
136 extendSpecInfo (SpecInfo rs1 fvs1) rs2
137 = SpecInfo (rs2 ++ rs1) (rulesRhsFreeVars rs2 `unionVarSet` fvs1)
139 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
140 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
141 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
143 addIdSpecialisations :: Id -> [CoreRule] -> Id
144 addIdSpecialisations id rules
145 = setIdSpecialisation id $
146 extendSpecInfo (idSpecialisation id) rules
148 rulesOfBinds :: [CoreBind] -> [CoreRule]
149 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
153 %************************************************************************
157 %************************************************************************
160 type RuleBase = NameEnv [CoreRule]
161 -- Maps (the name of) an Id to its rules
162 -- The rules are are unordered;
163 -- we sort out any overlaps on lookup
165 emptyRuleBase = emptyNameEnv
167 mkRuleBase :: [CoreRule] -> RuleBase
168 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
170 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
171 extendRuleBaseList rule_base new_guys
172 = foldl extendRuleBase rule_base new_guys
174 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
175 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
177 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
178 extendRuleBase rule_base rule
179 = extendNameEnv_C add rule_base (ruleIdName rule) [rule]
181 add rules _ = rule : rules
183 pprRuleBase :: RuleBase -> SDoc
184 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
185 | rs <- nameEnvElts rules ]
189 %************************************************************************
191 \subsection{Matching}
193 %************************************************************************
196 lookupRule :: (Activation -> Bool) -> InScopeSet
197 -> RuleBase -- Imported rules
198 -> Id -> [CoreExpr] -> Maybe (RuleName, CoreExpr)
199 lookupRule is_active in_scope rule_base fn args
200 = matchRules is_active in_scope fn args rules
202 rules | isLocalId fn = idCoreRules fn
203 | otherwise = case lookupNameEnv rule_base (idName fn) of
207 matchRules :: (Activation -> Bool) -> InScopeSet
209 -> [CoreRule] -> Maybe (RuleName, CoreExpr)
210 -- See comments on matchRule
211 matchRules is_active in_scope fn args rules
212 = case go [] rules of
214 (m:ms) -> Just (case findBest (fn,args) m ms of
215 (rule, ans) -> (ru_name rule, ans))
217 rough_args = map roughTopName args
219 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
221 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
222 Just e -> go ((r,e):ms) rs
225 findBest :: (Id, [CoreExpr])
226 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
227 -- All these pairs matched the expression
228 -- Return the pair the the most specific rule
229 -- The (fn,args) is just for overlap reporting
231 findBest target (rule,ans) [] = (rule,ans)
232 findBest target (rule1,ans1) ((rule2,ans2):prs)
233 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
234 | rule2 `isMoreSpecific` rule1 = findBest target (rule1,ans1) prs
235 | otherwise = pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
236 (vcat [ptext SLIT("Expression to match:") <+> ppr fn <+> sep (map ppr args),
237 ptext SLIT("Rule 1:") <+> ppr rule1,
238 ptext SLIT("Rule 2:") <+> ppr rule2]) $
239 findBest target (rule1,ans1) prs
243 isMoreSpecific :: CoreRule -> CoreRule -> Bool
244 isMoreSpecific (BuiltinRule {}) r2 = True
245 isMoreSpecific r1 (BuiltinRule {}) = False
246 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
247 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
248 = isJust (matchN in_scope bndrs2 args2 args1)
250 in_scope = mkInScopeSet (mkVarSet bndrs1)
251 -- Actually we should probably include the free vars
252 -- of rule1's args, but I can't be bothered
254 noBlackList :: Activation -> Bool
255 noBlackList act = False -- Nothing is black listed
257 matchRule :: (Activation -> Bool) -> InScopeSet
258 -> [CoreExpr] -> [Maybe Name]
259 -> CoreRule -> Maybe CoreExpr
261 -- If (matchRule rule args) returns Just (name,rhs)
262 -- then (f args) matches the rule, and the corresponding
263 -- rewritten RHS is rhs
265 -- The bndrs and rhs is occurrence-analysed
270 -- forall f g x. map f (map g x) ==> map (f . g) x
272 -- CoreRule "map/map"
273 -- [f,g,x] -- tpl_vars
274 -- [f,map g x] -- tpl_args
275 -- map (f.g) x) -- rhs
277 -- Then the call: matchRule the_rule [e1,map e2 e3]
278 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
280 -- Any 'surplus' arguments in the input are simply put on the end
283 matchRule is_active in_scope args rough_args
284 (BuiltinRule { ru_name = name, ru_try = match_fn })
285 = case match_fn args of
286 Just expr -> Just expr
289 matchRule is_active in_scope args rough_args
290 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
291 ru_bndrs = tpl_vars, ru_args = tpl_args,
293 | not (is_active act) = Nothing
294 | ruleCantMatch tpl_tops rough_args = Nothing
296 = case matchN in_scope tpl_vars tpl_args args of
298 Just (tpl_vals, leftovers) -> Just (rule_fn
302 rule_fn = occurAnalyseGlobalExpr (mkLams tpl_vars rhs)
303 -- We could do this when putting things into the rulebase, I guess
308 -> [Var] -- Template tyvars
309 -> [CoreExpr] -- Template
310 -> [CoreExpr] -- Target; can have more elts than template
311 -> Maybe ([CoreExpr], -- What is substituted for each template var
312 [CoreExpr]) -- Leftover target exprs
314 matchN in_scope tmpl_vars tmpl_es target_es
315 = do { (subst, leftover_es) <- go init_menv emptySubstEnv tmpl_es target_es
316 ; return (map (lookup_tmpl subst) tmpl_vars, leftover_es) }
318 init_menv = ME { me_tmpls = mkVarSet tmpl_vars, me_env = init_rn_env }
319 init_rn_env = mkRnEnv2 (extendInScopeSetList in_scope tmpl_vars)
321 go menv subst [] es = Just (subst, es)
322 go menv subst ts [] = Nothing -- Fail if too few actual args
323 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
324 ; go menv subst1 ts es }
326 lookup_tmpl :: (TvSubstEnv, IdSubstEnv) -> Var -> CoreExpr
327 lookup_tmpl (tv_subst, id_subst) tmpl_var
328 | isTyVar tmpl_var = case lookupVarEnv tv_subst tmpl_var of
330 Nothing -> unbound tmpl_var
331 | otherwise = case lookupVarEnv id_subst tmpl_var of
333 other -> unbound tmpl_var
335 unbound var = pprPanic "Template variable unbound in rewrite rule" (ppr var)
339 ---------------------------------------------
340 The inner workings of matching
341 ---------------------------------------------
344 -- These two definitions are not the same as in Subst,
345 -- but they simple and direct, and purely local to this module
346 -- The third, for TvSubstEnv, is the same as in VarEnv, but repeated here
347 -- for uniformity with IdSubstEnv
348 type SubstEnv = (TvSubstEnv, IdSubstEnv)
349 type IdSubstEnv = IdEnv CoreExpr
350 type TvSubstEnv = TyVarEnv Type
352 emptySubstEnv :: SubstEnv
353 emptySubstEnv = (emptyVarEnv, emptyVarEnv)
356 -- At one stage I tried to match even if there are more
357 -- template args than real args.
359 -- I now think this is probably a bad idea.
360 -- Should the template (map f xs) match (map g)? I think not.
361 -- For a start, in general eta expansion wastes work.
367 -> CoreExpr -- Template
368 -> CoreExpr -- Target
371 -- See the notes with Unify.match, which matches types
372 -- Everything is very similar for terms
374 -- Interesting examples:
376 -- \x->f against \f->f
377 -- When we meet the lambdas we must remember to rename f to f' in the
378 -- second expresion. The RnEnv2 does that.
381 -- forall a. \b->b against \a->3
382 -- We must rename the \a. Otherwise when we meet the lambdas we
383 -- might substitute [a/b] in the template, and then erroneously
384 -- succeed in matching what looks like the template variable 'a' against 3.
386 -- The Var case follows closely what happens in Unify.match
387 match menv subst@(tv_subst, id_subst) (Var v1) e2
388 | v1 `elemVarSet` me_tmpls menv
389 = case lookupVarEnv id_subst v1' of
390 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
391 -> Nothing -- Occurs check failure
392 -- e.g. match forall a. (\x-> a x) against (\y. y y)
395 -> Just (tv_subst, extendVarEnv id_subst v1 e2)
397 Just e2' | tcEqExprX (nukeRnEnvL rn_env) e2' e2
402 | otherwise -- v1 is not a template variable
404 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
408 v1' = rnOccL rn_env v1
410 -- Here is another important rule: if the term being matched is a
411 -- variable, we expand it so long as its unfolding is a WHNF
412 -- (Its occurrence information is not necessarily up to date,
413 -- so we don't use it.)
414 match menv subst e1 (Var v2)
415 | isCheapUnfolding unfolding
416 = match menv subst e1 (unfoldingTemplate unfolding)
418 unfolding = idUnfolding v2
420 match menv subst (Lit lit1) (Lit lit2)
424 match menv subst (App f1 a1) (App f2 a2)
425 = do { subst' <- match menv subst f1 f2
426 ; match menv subst' a1 a2 }
428 match menv subst (Lam x1 e1) (Lam x2 e2)
429 = match menv' subst e1 e2
431 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
433 -- This rule does eta expansion
434 -- (\x.M) ~ N iff M ~ N x
435 match menv subst (Lam x1 e1) e2
436 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
438 (rn_env', new_x) = rnBndrL (me_env menv) x1
439 menv' = menv { me_env = rn_env' }
441 -- Eta expansion the other way
442 -- M ~ (\y.N) iff M y ~ N
443 match menv subst e1 (Lam x2 e2)
444 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
446 (rn_env', new_x) = rnBndrR (me_env menv) x2
447 menv' = menv { me_env = rn_env' }
449 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
450 = do { subst1 <- match_ty menv subst ty1 ty2
451 ; subst2 <- match menv subst1 e1 e2
452 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x2 x2 }
453 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
456 match menv subst (Type ty1) (Type ty2)
457 = match_ty menv subst ty1 ty2
459 match menv subst (Note (Coerce to1 from1) e1) (Note (Coerce to2 from2) e2)
460 = do { subst1 <- match_ty menv subst to1 to2
461 ; subst2 <- match_ty menv subst1 from1 from2
462 ; match menv subst2 e1 e2 }
464 -- This is an interesting rule: we simply ignore lets in the
465 -- term being matched against! The unfolding inside it is (by assumption)
466 -- already inside any occurrences of the bound variables, so we'll expand
467 -- them when we encounter them.
468 match menv subst e1 (Let (NonRec x2 r2) e2)
469 = match menv' subst e1 e2
471 menv' = menv { me_env = fst (rnBndrR (me_env menv) x2) }
472 -- It's important to do this renaming. For example:
474 -- forall f,x,xs. f (x:xs)
476 -- f (let y = e in (y:[]))
477 -- We must not get success with x->y! Instead, we
478 -- need an occurs check.
480 -- Everything else fails
481 match menv subst e1 e2 = Nothing
483 ------------------------------------------
484 match_alts :: MatchEnv
486 -> [CoreAlt] -- Template
487 -> [CoreAlt] -- Target
489 match_alts menv subst [] []
491 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
493 = do { subst1 <- match menv' subst r1 r2
494 ; match_alts menv subst1 alts1 alts2 }
497 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
499 match_alts menv subst alts1 alts2
503 Matching Core types: use the matcher in TcType.
504 Notice that we treat newtypes as opaque. For example, suppose
505 we have a specialised version of a function at a newtype, say
507 We only want to replace (f T) with f', not (f Int).
510 ------------------------------------------
511 match_ty menv (tv_subst, id_subst) ty1 ty2
512 = do { tv_subst' <- Unify.tcMatchTyX menv tv_subst ty1 ty2
513 ; return (tv_subst', id_subst) }
517 %************************************************************************
519 \subsection{Checking a program for failing rule applications}
521 %************************************************************************
523 -----------------------------------------------------
525 -----------------------------------------------------
527 We want to know what sites have rules that could have fired but didn't.
528 This pass runs over the tree (without changing it) and reports such.
530 NB: we assume that this follows a run of the simplifier, so every Id
531 occurrence (including occurrences of imported Ids) is decorated with
532 all its (active) rules. No need to construct a rule base or anything
536 ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
537 -- Report partial matches for rules beginning
538 -- with the specified string
539 ruleCheckProgram phase rule_pat binds
541 = text "Rule check results: no rule application sites"
543 = vcat [text "Rule check results:",
545 vcat [ p $$ line | p <- bagToList results ]
548 results = unionManyBags (map (ruleCheckBind (phase, rule_pat)) binds)
549 line = text (replicate 20 '-')
551 type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
553 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
554 -- The Bag returned has one SDoc for each call site found
555 ruleCheckBind env (NonRec b r) = ruleCheck env r
556 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
558 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
559 ruleCheck env (Var v) = emptyBag
560 ruleCheck env (Lit l) = emptyBag
561 ruleCheck env (Type ty) = emptyBag
562 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
563 ruleCheck env (Note n e) = ruleCheck env e
564 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
565 ruleCheck env (Lam b e) = ruleCheck env e
566 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
567 unionManyBags [ruleCheck env r | (_,_,r) <- as]
569 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
570 ruleCheckApp env (Var f) as = ruleCheckFun env f as
571 ruleCheckApp env other as = ruleCheck env other
575 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
576 -- Produce a report for all rules matching the predicate
577 -- saying why it doesn't match the specified application
579 ruleCheckFun (phase, pat) fn args
580 | null name_match_rules = emptyBag
581 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
583 name_match_rules = filter match (idCoreRules fn)
584 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
586 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
587 ruleAppCheck_help phase fn args rules
588 = -- The rules match the pattern, so we want to print something
589 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
590 vcat (map check_rule rules)]
593 i_args = args `zip` [1::Int ..]
594 rough_args = map roughTopName args
596 check_rule rule = rule_herald rule <> colon <+> rule_info rule
598 rule_herald (BuiltinRule { ru_name = name })
599 = ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
600 rule_herald (Rule { ru_name = name })
601 = ptext SLIT("Rule") <+> doubleQuotes (ftext name)
604 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
605 = text "matches (which is very peculiar!)"
607 rule_info (BuiltinRule {}) = text "does not match"
609 rule_info (Rule { ru_name = name, ru_act = act,
610 ru_bndrs = rule_bndrs, ru_args = rule_args})
611 | not (isActive phase act) = text "active only in later phase"
612 | n_args < n_rule_args = text "too few arguments"
613 | n_mismatches == n_rule_args = text "no arguments match"
614 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
615 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
617 n_rule_args = length rule_args
618 n_mismatches = length mismatches
619 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
620 not (isJust (match_fn rule_arg arg))]
622 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
623 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
625 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
626 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
627 , me_tmpls = mkVarSet rule_bndrs }