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 ( occurAnalyseExpr )
21 import CoreFVs ( exprFreeVars, exprsFreeVars, rulesRhsFreeVars )
22 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
23 import CoreUtils ( tcEqExprX )
24 import PprCore ( pprRules )
25 import Type ( TvSubstEnv )
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, 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 ( ruleMatchTyX, MatchEnv(..) )
41 import BasicTypes ( Activation, CompilerPhase, isActive )
44 import Maybes ( isJust, orElse )
46 import Util ( singleton )
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
119 -- Notice that there is no case
120 -- ruleCantMatch (Just n1 : ts) (Nothing : as) = True
121 -- Reason: a local variable 'v' in the actuals might
122 -- have an unfolding which is a global.
123 -- This quite often happens with case scrutinees.
124 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
125 ruleCantMatch (t : ts) (a : as) = ruleCantMatch ts as
126 ruleCantMatch ts as = False
130 %************************************************************************
132 SpecInfo: the rules in an IdInfo
134 %************************************************************************
137 mkSpecInfo :: [CoreRule] -> SpecInfo
138 mkSpecInfo rules = SpecInfo rules (rulesRhsFreeVars rules)
140 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
141 extendSpecInfo (SpecInfo rs1 fvs1) rs2
142 = SpecInfo (rs2 ++ rs1) (rulesRhsFreeVars rs2 `unionVarSet` fvs1)
144 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
145 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
146 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
148 addIdSpecialisations :: Id -> [CoreRule] -> Id
149 addIdSpecialisations id rules
150 = setIdSpecialisation id $
151 extendSpecInfo (idSpecialisation id) rules
153 rulesOfBinds :: [CoreBind] -> [CoreRule]
154 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
158 %************************************************************************
162 %************************************************************************
165 type RuleBase = NameEnv [CoreRule]
166 -- Maps (the name of) an Id to its rules
167 -- The rules are are unordered;
168 -- we sort out any overlaps on lookup
170 emptyRuleBase = emptyNameEnv
172 mkRuleBase :: [CoreRule] -> RuleBase
173 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
175 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
176 extendRuleBaseList rule_base new_guys
177 = foldl extendRuleBase rule_base new_guys
179 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
180 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
182 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
183 extendRuleBase rule_base rule
184 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
186 pprRuleBase :: RuleBase -> SDoc
187 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
188 | rs <- nameEnvElts rules ]
192 %************************************************************************
194 \subsection{Matching}
196 %************************************************************************
199 lookupRule :: (Activation -> Bool) -> InScopeSet
200 -> RuleBase -- Imported rules
201 -> Id -> [CoreExpr] -> Maybe (RuleName, CoreExpr)
202 lookupRule is_active in_scope rule_base fn args
203 = matchRules is_active in_scope fn args rules
205 -- The rules for an Id come from two places:
206 -- (a) the ones it is born with (idCoreRules fn)
207 -- (b) rules added in subsequent modules (extra_rules)
208 -- PrimOps, for example, are born with a bunch of rules under (a)
209 rules = extra_rules ++ idCoreRules fn
210 extra_rules | isLocalId fn = []
211 | otherwise = lookupNameEnv rule_base (idName fn) `orElse` []
213 matchRules :: (Activation -> Bool) -> InScopeSet
215 -> [CoreRule] -> Maybe (RuleName, CoreExpr)
216 -- See comments on matchRule
217 matchRules is_active in_scope fn args rules
218 = case go [] rules of
220 (m:ms) -> Just (case findBest (fn,args) m ms of
221 (rule, ans) -> (ru_name rule, ans))
223 rough_args = map roughTopName args
225 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
227 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
228 Just e -> go ((r,e):ms) rs
231 findBest :: (Id, [CoreExpr])
232 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
233 -- All these pairs matched the expression
234 -- Return the pair the the most specific rule
235 -- The (fn,args) is just for overlap reporting
237 findBest target (rule,ans) [] = (rule,ans)
238 findBest target (rule1,ans1) ((rule2,ans2):prs)
239 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
240 | rule2 `isMoreSpecific` rule1 = findBest target (rule1,ans1) prs
242 | otherwise = pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
243 (vcat [ptext SLIT("Expression to match:") <+> ppr fn <+> sep (map ppr args),
244 ptext SLIT("Rule 1:") <+> ppr rule1,
245 ptext SLIT("Rule 2:") <+> ppr rule2]) $
246 findBest target (rule1,ans1) prs
248 | otherwise = findBest target (rule1,ans1) prs
253 isMoreSpecific :: CoreRule -> CoreRule -> Bool
254 isMoreSpecific (BuiltinRule {}) r2 = True
255 isMoreSpecific r1 (BuiltinRule {}) = False
256 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
257 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
258 = isJust (matchN in_scope bndrs2 args2 args1)
260 in_scope = mkInScopeSet (mkVarSet bndrs1)
261 -- Actually we should probably include the free vars
262 -- of rule1's args, but I can't be bothered
264 noBlackList :: Activation -> Bool
265 noBlackList act = False -- Nothing is black listed
267 matchRule :: (Activation -> Bool) -> InScopeSet
268 -> [CoreExpr] -> [Maybe Name]
269 -> CoreRule -> Maybe CoreExpr
271 -- If (matchRule rule args) returns Just (name,rhs)
272 -- then (f args) matches the rule, and the corresponding
273 -- rewritten RHS is rhs
275 -- The bndrs and rhs is occurrence-analysed
280 -- forall f g x. map f (map g x) ==> map (f . g) x
282 -- CoreRule "map/map"
283 -- [f,g,x] -- tpl_vars
284 -- [f,map g x] -- tpl_args
285 -- map (f.g) x) -- rhs
287 -- Then the call: matchRule the_rule [e1,map e2 e3]
288 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
290 -- Any 'surplus' arguments in the input are simply put on the end
293 matchRule is_active in_scope args rough_args
294 (BuiltinRule { ru_name = name, ru_try = match_fn })
295 = case match_fn args of
296 Just expr -> Just expr
299 matchRule is_active in_scope args rough_args
300 (Rule { ru_name = rn, ru_act = act, ru_rough = tpl_tops,
301 ru_bndrs = tpl_vars, ru_args = tpl_args,
303 | not (is_active act) = Nothing
304 | ruleCantMatch tpl_tops rough_args = Nothing
306 = case matchN in_scope tpl_vars tpl_args args of
308 Just (tpl_vals, leftovers) -> Just (rule_fn
312 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
313 -- We could do this when putting things into the rulebase, I guess
318 -> [Var] -- Template tyvars
319 -> [CoreExpr] -- Template
320 -> [CoreExpr] -- Target; can have more elts than template
321 -> Maybe ([CoreExpr], -- What is substituted for each template var
322 [CoreExpr]) -- Leftover target exprs
324 matchN in_scope tmpl_vars tmpl_es target_es
325 = do { (subst, leftover_es) <- go init_menv emptySubstEnv tmpl_es target_es
326 ; return (map (lookup_tmpl subst) tmpl_vars, leftover_es) }
328 init_menv = ME { me_tmpls = mkVarSet tmpl_vars, me_env = init_rn_env }
329 init_rn_env = mkRnEnv2 (extendInScopeSetList in_scope tmpl_vars)
331 go menv subst [] es = Just (subst, es)
332 go menv subst ts [] = Nothing -- Fail if too few actual args
333 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
334 ; go menv subst1 ts es }
336 lookup_tmpl :: (TvSubstEnv, IdSubstEnv) -> Var -> CoreExpr
337 lookup_tmpl (tv_subst, id_subst) tmpl_var
338 | isTyVar tmpl_var = case lookupVarEnv tv_subst tmpl_var of
340 Nothing -> unbound tmpl_var
341 | otherwise = case lookupVarEnv id_subst tmpl_var of
343 other -> unbound tmpl_var
345 unbound var = pprPanic "Template variable unbound in rewrite rule" (ppr var)
349 ---------------------------------------------
350 The inner workings of matching
351 ---------------------------------------------
354 -- These two definitions are not the same as in Subst,
355 -- but they simple and direct, and purely local to this module
356 -- The third, for TvSubstEnv, is the same as in VarEnv, but repeated here
357 -- for uniformity with IdSubstEnv
358 type SubstEnv = (TvSubstEnv, IdSubstEnv)
359 type IdSubstEnv = IdEnv CoreExpr
361 emptySubstEnv :: SubstEnv
362 emptySubstEnv = (emptyVarEnv, emptyVarEnv)
365 -- At one stage I tried to match even if there are more
366 -- template args than real args.
368 -- I now think this is probably a bad idea.
369 -- Should the template (map f xs) match (map g)? I think not.
370 -- For a start, in general eta expansion wastes work.
376 -> CoreExpr -- Template
377 -> CoreExpr -- Target
380 -- See the notes with Unify.match, which matches types
381 -- Everything is very similar for terms
383 -- Interesting examples:
385 -- \x->f against \f->f
386 -- When we meet the lambdas we must remember to rename f to f' in the
387 -- second expresion. The RnEnv2 does that.
390 -- forall a. \b->b against \a->3
391 -- We must rename the \a. Otherwise when we meet the lambdas we
392 -- might substitute [a/b] in the template, and then erroneously
393 -- succeed in matching what looks like the template variable 'a' against 3.
395 -- The Var case follows closely what happens in Unify.match
396 match menv subst@(tv_subst, id_subst) (Var v1) e2
397 | v1 `elemVarSet` me_tmpls menv
398 = case lookupVarEnv id_subst v1' of
399 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
400 -> Nothing -- Occurs check failure
401 -- e.g. match forall a. (\x-> a x) against (\y. y y)
404 -> Just (tv_subst, extendVarEnv id_subst v1 e2)
406 Just e2' | tcEqExprX (nukeRnEnvL rn_env) e2' e2
411 | -- v1 is not a template variable; check for an exact match with e2
412 Var v2 <- e2, v1' == rnOccR rn_env v2
417 v1' = rnOccL rn_env v1
419 -- Here is another important rule: if the term being matched is a
420 -- variable, we expand it so long as its unfolding is a WHNF
421 -- (Its occurrence information is not necessarily up to date,
422 -- so we don't use it.)
423 match menv subst e1 (Var v2)
424 | isCheapUnfolding unfolding
425 = match menv subst e1 (unfoldingTemplate unfolding)
427 unfolding = idUnfolding v2
429 match menv subst (Lit lit1) (Lit lit2)
433 match menv subst (App f1 a1) (App f2 a2)
434 = do { subst' <- match menv subst f1 f2
435 ; match menv subst' a1 a2 }
437 match menv subst (Lam x1 e1) (Lam x2 e2)
438 = match menv' subst e1 e2
440 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
442 -- This rule does eta expansion
443 -- (\x.M) ~ N iff M ~ N x
444 match menv subst (Lam x1 e1) e2
445 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
447 (rn_env', new_x) = rnBndrL (me_env menv) x1
448 menv' = menv { me_env = rn_env' }
450 -- Eta expansion the other way
451 -- M ~ (\y.N) iff M y ~ N
452 match menv subst e1 (Lam x2 e2)
453 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
455 (rn_env', new_x) = rnBndrR (me_env menv) x2
456 menv' = menv { me_env = rn_env' }
458 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
459 = do { subst1 <- match_ty menv subst ty1 ty2
460 ; subst2 <- match menv subst1 e1 e2
461 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x2 x2 }
462 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
465 match menv subst (Type ty1) (Type ty2)
466 = match_ty menv subst ty1 ty2
468 match menv subst (Note (Coerce to1 from1) e1) (Note (Coerce to2 from2) e2)
469 = do { subst1 <- match_ty menv subst to1 to2
470 ; subst2 <- match_ty menv subst1 from1 from2
471 ; match menv subst2 e1 e2 }
473 -- This is an interesting rule: we simply ignore lets in the
474 -- term being matched against! The unfolding inside it is (by assumption)
475 -- already inside any occurrences of the bound variables, so we'll expand
476 -- them when we encounter them.
477 match menv subst e1 (Let (NonRec x2 r2) e2)
478 = match menv' subst e1 e2
480 menv' = menv { me_env = fst (rnBndrR (me_env menv) x2) }
481 -- It's important to do this renaming. For example:
483 -- forall f,x,xs. f (x:xs)
485 -- f (let y = e in (y:[]))
486 -- We must not get success with x->y! Instead, we
487 -- need an occurs check.
489 -- Everything else fails
490 match menv subst e1 e2 = Nothing
492 ------------------------------------------
493 match_alts :: MatchEnv
495 -> [CoreAlt] -- Template
496 -> [CoreAlt] -- Target
498 match_alts menv subst [] []
500 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
502 = do { subst1 <- match menv' subst r1 r2
503 ; match_alts menv subst1 alts1 alts2 }
506 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
508 match_alts menv subst alts1 alts2
512 Matching Core types: use the matcher in TcType.
513 Notice that we treat newtypes as opaque. For example, suppose
514 we have a specialised version of a function at a newtype, say
516 We only want to replace (f T) with f', not (f Int).
519 ------------------------------------------
520 match_ty menv (tv_subst, id_subst) ty1 ty2
521 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
522 ; return (tv_subst', id_subst) }
526 %************************************************************************
528 \subsection{Checking a program for failing rule applications}
530 %************************************************************************
532 -----------------------------------------------------
534 -----------------------------------------------------
536 We want to know what sites have rules that could have fired but didn't.
537 This pass runs over the tree (without changing it) and reports such.
539 NB: we assume that this follows a run of the simplifier, so every Id
540 occurrence (including occurrences of imported Ids) is decorated with
541 all its (active) rules. No need to construct a rule base or anything
545 ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
546 -- Report partial matches for rules beginning
547 -- with the specified string
548 ruleCheckProgram phase rule_pat binds
550 = text "Rule check results: no rule application sites"
552 = vcat [text "Rule check results:",
554 vcat [ p $$ line | p <- bagToList results ]
557 results = unionManyBags (map (ruleCheckBind (phase, rule_pat)) binds)
558 line = text (replicate 20 '-')
560 type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
562 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
563 -- The Bag returned has one SDoc for each call site found
564 ruleCheckBind env (NonRec b r) = ruleCheck env r
565 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
567 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
568 ruleCheck env (Var v) = emptyBag
569 ruleCheck env (Lit l) = emptyBag
570 ruleCheck env (Type ty) = emptyBag
571 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
572 ruleCheck env (Note n e) = ruleCheck env e
573 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
574 ruleCheck env (Lam b e) = ruleCheck env e
575 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
576 unionManyBags [ruleCheck env r | (_,_,r) <- as]
578 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
579 ruleCheckApp env (Var f) as = ruleCheckFun env f as
580 ruleCheckApp env other as = ruleCheck env other
584 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
585 -- Produce a report for all rules matching the predicate
586 -- saying why it doesn't match the specified application
588 ruleCheckFun (phase, pat) fn args
589 | null name_match_rules = emptyBag
590 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
592 name_match_rules = filter match (idCoreRules fn)
593 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
595 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
596 ruleAppCheck_help phase fn args rules
597 = -- The rules match the pattern, so we want to print something
598 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
599 vcat (map check_rule rules)]
602 i_args = args `zip` [1::Int ..]
603 rough_args = map roughTopName args
605 check_rule rule = rule_herald rule <> colon <+> rule_info rule
607 rule_herald (BuiltinRule { ru_name = name })
608 = ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
609 rule_herald (Rule { ru_name = name })
610 = ptext SLIT("Rule") <+> doubleQuotes (ftext name)
613 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
614 = text "matches (which is very peculiar!)"
616 rule_info (BuiltinRule {}) = text "does not match"
618 rule_info (Rule { ru_name = name, ru_act = act,
619 ru_bndrs = rule_bndrs, ru_args = rule_args})
620 | not (isActive phase act) = text "active only in later phase"
621 | n_args < n_rule_args = text "too few arguments"
622 | n_mismatches == n_rule_args = text "no arguments match"
623 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
624 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
626 n_rule_args = length rule_args
627 n_mismatches = length mismatches
628 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
629 not (isJust (match_fn rule_arg arg))]
631 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
632 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
634 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
635 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
636 , me_tmpls = mkVarSet rule_bndrs }