2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreRules]{Transformation rules}
8 RuleBase, emptyRuleBase,
10 ruleBaseIds, pprRuleBase, ruleCheckProgram,
12 lookupRule, addRule, addIdSpecialisations
15 #include "HsVersions.h"
17 import CoreSyn -- All of it
18 import OccurAnal ( occurAnalyseRule )
19 import CoreFVs ( exprFreeVars, ruleRhsFreeVars )
20 import CoreUnfold ( isCheapUnfolding, unfoldingTemplate )
21 import CoreUtils ( eqExpr )
22 import CoreTidy ( pprTidyIdRules )
23 import Subst ( Subst, SubstResult(..), extendIdSubst,
24 getTvSubstEnv, setTvSubstEnv,
25 emptySubst, isInScope, lookupIdSubst, lookupTvSubst,
26 bindSubstList, unBindSubstList, substInScope
28 import Id ( Id, idUnfolding, idSpecialisation, setIdSpecialisation )
29 import Var ( Var, isId )
32 import TcType ( mkTyVarTy )
33 import qualified Unify ( matchTyX )
34 import BasicTypes ( Activation, CompilerPhase, isActive )
38 import Maybe ( isJust, isNothing, fromMaybe )
39 import Util ( sortLe )
41 import List ( isPrefixOf )
45 %************************************************************************
47 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
49 %************************************************************************
51 A @CoreRule@ holds details of one rule for an @Id@, which
52 includes its specialisations.
54 For example, if a rule for @f@ contains the mapping:
56 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
58 then when we find an application of f to matching types, we simply replace
59 it by the matching RHS:
61 f (List Int) Bool dict ===> f' Int Bool
63 All the stuff about how many dictionaries to discard, and what types
64 to apply the specialised function to, are handled by the fact that the
65 Rule contains a template for the result of the specialisation.
67 There is one more exciting case, which is dealt with in exactly the same
68 way. If the specialised value is unboxed then it is lifted at its
69 definition site and unlifted at its uses. For example:
71 pi :: forall a. Num a => a
73 might have a specialisation
75 [Int#] ===> (case pi' of Lift pi# -> pi#)
77 where pi' :: Lift Int# is the specialised version of pi.
80 %************************************************************************
84 %************************************************************************
87 matchRules :: (Activation -> Bool) -> InScopeSet
88 -> [CoreRule] -> [CoreExpr] -> Maybe (RuleName, CoreExpr)
89 -- See comments on matchRule
90 matchRules is_active in_scope [] args = Nothing
91 matchRules is_active in_scope (rule:rules) args
92 = case matchRule is_active in_scope rule args of
93 Just result -> Just result
94 Nothing -> matchRules is_active in_scope rules args
96 noBlackList :: Activation -> Bool
97 noBlackList act = False -- Nothing is black listed
99 matchRule :: (Activation -> Bool) -> InScopeSet
100 -> CoreRule -> [CoreExpr] -> Maybe (RuleName, CoreExpr)
102 -- If (matchRule rule args) returns Just (name,rhs)
103 -- then (f args) matches the rule, and the corresponding
104 -- rewritten RHS is rhs
106 -- The bndrs and rhs is occurrence-analysed
111 -- forall f g x. map f (map g x) ==> map (f . g) x
113 -- CoreRule "map/map"
114 -- [f,g,x] -- tpl_vars
115 -- [f,map g x] -- tpl_args
116 -- map (f.g) x) -- rhs
118 -- Then the call: matchRule the_rule [e1,map e2 e3]
119 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
121 -- Any 'surplus' arguments in the input are simply put on the end
125 -- A1. No top-level variable is bound in the target
126 -- A2. No template variable is bound in the target
127 -- A3. No lambda bound template variable is free in any subexpression of the target
129 -- To see why A1 is necessary, consider matching
130 -- \x->f against \f->f
131 -- When we meet the lambdas we substitute [f/x] in the template (a no-op),
132 -- and then erroneously succeed in matching f against f.
134 -- To see why A2 is needed consider matching
135 -- forall a. \b->b against \a->3
136 -- When we meet the lambdas we substitute [a/b] in the template, and then
137 -- erroneously succeed in matching what looks like the template variable 'a' against 3.
139 -- A3 is needed to validate the rule that says
142 -- (\x->E) matches (\x->F x)
145 matchRule is_active in_scope rule@(BuiltinRule name match_fn) args
146 = case match_fn args of
147 Just expr -> Just (name,expr)
150 matchRule is_active in_scope rule@(Rule rn act tpl_vars tpl_args rhs) args
151 | not (is_active act)
154 = go tpl_args args emptySubst
155 -- We used to use the in_scope set, but I don't think that's necessary
156 -- After all, the result is going to be simplified again with that in_scope set
158 tpl_var_set = mkVarSet tpl_vars
160 -----------------------
162 go (tpl_arg:tpl_args) (arg:args) subst = match tpl_arg arg tpl_var_set (go tpl_args args) subst
164 -- Two easy ways to terminate
165 go [] [] subst = Just (rn, app_match subst (mkLams tpl_vars rhs) tpl_vars)
166 go [] args subst = Just (rn, app_match subst (mkLams tpl_vars rhs) tpl_vars `mkApps` args)
168 -- One tiresome way to terminate: check for excess unmatched
169 -- template arguments
170 go tpl_args [] subst = Nothing -- Failure
173 -----------------------
174 app_match subst fn vs = foldl go fn vs
176 go fn v = case lookupVar subst v of
178 Nothing -> pprPanic "app_match: unbound tpl" (ppr v)
180 lookupVar :: Subst -> Var -> Maybe CoreExpr
182 | isId v = case lookupIdSubst subst v of
183 Just (DoneEx ex) -> Just ex
185 | otherwise = case lookupTvSubst subst v of
186 Just ty -> Just (Type ty)
189 -----------------------
190 {- The code below tries to match even if there are more
191 template args than real args.
193 I now think this is probably a bad idea.
194 Should the template (map f xs) match (map g)? I think not.
195 For a start, in general eta expansion wastes work.
198 = case eta_complete tpl_args (mkVarSet leftovers) of
199 Just leftovers' -> Just (rn, mkLams done (mkLams leftovers' rhs),
200 mk_result_args subst done)
201 Nothing -> Nothing -- Failure
203 (done, leftovers) = partition (\v -> isJust (lookupSubstEnv subst_env v))
204 (map zapOccInfo tpl_vars)
206 subst_env = substEnv subst
208 -----------------------
209 eta_complete [] vars = ASSERT( isEmptyVarSet vars )
211 eta_complete (Type ty:tpl_args) vars
212 = case getTyVar_maybe ty of
213 Just tv | tv `elemVarSet` vars
214 -> case eta_complete tpl_args (vars `delVarSet` tv) of
215 Just vars' -> Just (tv:vars')
219 eta_complete (Var v:tpl_args) vars
220 | v `elemVarSet` vars
221 = case eta_complete tpl_args (vars `delVarSet` v) of
222 Just vars' -> Just (v:vars')
225 eta_complete other vars = Nothing
228 zapOccInfo bndr | isTyVar bndr = bndr
229 | otherwise = zapLamIdInfo bndr
234 type Matcher result = VarSet -- Template variables
235 -> (Subst -> Maybe result) -- Continuation if success
236 -> Subst -> Maybe result -- Substitution so far -> result
237 -- The *SubstEnv* in these Substs apply to the TEMPLATE only
239 -- The *InScopeSet* in these Substs is HIJACKED,
240 -- to give the set of variables bound so far in the
241 -- target term. So when matching forall a. (\x. a x) against (\y. y y)
242 -- while processing the body of the lambdas, the in-scope set will be {y}.
243 -- That lets us do the occurs-check when matching 'a' against 'y'
245 -- It starts off empty
247 match :: CoreExpr -- Template
248 -> CoreExpr -- Target
253 -- ToDo: remove this debugging junk
254 -- match e1 e2 tpls kont subst = pprTrace "match" (ppr e1 <+> ppr e2 <+> ppr subst) $ match_ e1 e2 tpls kont subst
257 match_ (Var v1) e2 tpl_vars kont subst
258 = case lookupIdSubst subst v1 of
259 Nothing | v1 `elemVarSet` tpl_vars -- v1 is a template variable
260 -> if (any (`isInScope` subst) (varSetElems (exprFreeVars e2))) then
261 match_fail -- Occurs check failure
262 -- e.g. match forall a. (\x-> a x) against (\y. y y)
264 kont (extendIdSubst subst v1 (DoneEx e2))
267 | eqExpr (Var v1) e2 -> kont subst
268 -- v1 is not a template variable, so it must be a global constant
270 Just (DoneEx e2') | eqExpr e2' e2 -> kont subst
274 match_ (Lit lit1) (Lit lit2) tpl_vars kont subst
278 match_ (App f1 a1) (App f2 a2) tpl_vars kont subst
279 = match f1 f2 tpl_vars (match a1 a2 tpl_vars kont) subst
281 match_ (Lam x1 e1) (Lam x2 e2) tpl_vars kont subst
282 = bind [x1] [x2] (match e1 e2) tpl_vars kont subst
284 -- This rule does eta expansion
285 -- (\x.M) ~ N iff M ~ N x
287 match_ (Lam x1 e1) e2 tpl_vars kont subst
288 = bind [x1] [x1] (match e1 (App e2 (mkVarArg x1))) tpl_vars kont subst
290 -- Eta expansion the other way
291 -- M ~ (\y.N) iff \y.M y ~ \y.N
293 -- Remembering that by (A), y can't be free in M, we get this
294 match_ e1 (Lam x2 e2) tpl_vars kont subst
295 | new_id == x2 -- If the two are equal, don't bind, else we get
296 -- a substitution looking like x->x, and that sends
297 -- Unify.matchTy into a loop
298 = match (App e1 (mkVarArg new_id)) e2 tpl_vars kont subst
300 = bind [new_id] [x2] (match (App e1 (mkVarArg new_id)) e2) tpl_vars kont subst
302 new_id = uniqAway (substInScope subst) x2
303 -- This uniqAway is actually needed. Here's the example:
304 -- rule: foldr (mapFB (:) f) [] = mapList
305 -- target: foldr (\x. mapFB k f x) []
307 -- k = \x. mapFB ... x
308 -- The first \x is ok, but when we inline k, hoping it might
309 -- match (:) we find a second \x.
312 match_ (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2) tpl_vars kont subst
313 = (match_ty ty1 ty2 tpl_vars $
314 match e1 e2 tpl_vars case_kont) subst
316 case_kont subst = bind [x1] [x2] (match_alts alts1 (sortLe le_alt alts2))
319 match_ (Type ty1) (Type ty2) tpl_vars kont subst
320 = match_ty ty1 ty2 tpl_vars kont subst
322 match_ (Note (Coerce to1 from1) e1) (Note (Coerce to2 from2) e2)
324 = (match_ty to1 to2 tpl_vars $
325 match_ty from1 from2 tpl_vars $
326 match e1 e2 tpl_vars kont) subst
329 {- I don't buy this let-rule any more
330 The let rule fails on matching
331 forall f,x,xs. f (x:xs)
333 f (let y = e in (y:[]))
334 because we just get x->y, which is bogus.
336 -- This is an interesting rule: we simply ignore lets in the
337 -- term being matched against! The unfolding inside it is (by assumption)
338 -- already inside any occurrences of the bound variables, so we'll expand
339 -- them when we encounter them. Meanwhile, we can't get false matches because
340 -- (also by assumption) the term being matched has no shadowing.
341 match e1 (Let bind e2) tpl_vars kont subst
342 = match e1 e2 tpl_vars kont subst
345 -- Here is another important rule: if the term being matched is a
346 -- variable, we expand it so long as its unfolding is a WHNF
347 -- (Its occurrence information is not necessarily up to date,
348 -- so we don't use it.)
349 match_ e1 (Var v2) tpl_vars kont subst
350 | isCheapUnfolding unfolding
351 = match e1 (unfoldingTemplate unfolding) tpl_vars kont subst
353 unfolding = idUnfolding v2
356 -- We can't cope with lets in the template
358 match_ e1 e2 tpl_vars kont subst = match_fail
361 ------------------------------------------
362 match_alts [] [] tpl_vars kont subst
364 match_alts ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2) tpl_vars kont subst
366 = bind vs1 vs2 (match r1 r2) tpl_vars
367 (match_alts alts1 alts2 tpl_vars kont)
369 match_alts alts1 alts2 tpl_vars kont subst = match_fail
371 le_alt (con1, _, _) (con2, _, _) = con1 <= con2
373 ----------------------------------------
374 bind :: [CoreBndr] -- Template binders
375 -> [CoreBndr] -- Target binders
378 -- This makes uses of assumption (A) above. For example,
380 -- Template: (\x.y) (y is free)
381 -- Target : (\y.y) (y is bound)
382 -- We rename x to y in the template... but then erroneously
383 -- match y against y. But this can't happen because of (A)
384 bind vs1 vs2 matcher tpl_vars kont subst
385 = WARN( not (all not_in_subst vs1), bug_msg )
386 matcher tpl_vars kont' subst'
388 kont' subst'' = kont (unBindSubstList subst'' vs1 vs2)
389 subst' = bindSubstList subst vs1 vs2
391 -- The unBindSubst relies on no shadowing in the template
392 not_in_subst v = isNothing (lookupVar subst v)
393 bug_msg = sep [ppr vs1, ppr vs2]
395 ----------------------------------------
396 mkVarArg :: CoreBndr -> CoreArg
397 mkVarArg v | isId v = Var v
398 | otherwise = Type (mkTyVarTy v)
401 Matching Core types: use the matcher in TcType.
402 Notice that we treat newtypes as opaque. For example, suppose
403 we have a specialised version of a function at a newtype, say
405 We only want to replace (f T) with f', not (f Int).
408 ----------------------------------------
409 match_ty ty1 ty2 tpl_vars kont subst
410 = case Unify.matchTyX tpl_vars (getTvSubstEnv subst) ty1 ty2 of
411 Just tv_env' -> kont (setTvSubstEnv subst tv_env')
412 Nothing -> match_fail
417 %************************************************************************
419 \subsection{Adding a new rule}
421 %************************************************************************
424 addRule :: Id -> CoreRules -> CoreRule -> CoreRules
426 -- Add a new rule to an existing bunch of rules.
427 -- The rules are for the given Id; the Id argument is needed only
428 -- so that we can exclude the Id from its own RHS free-var set
430 -- Insert the new rule just before a rule that is *less specific*
431 -- than the new one; or at the end if there isn't such a one.
432 -- In this way we make sure that when looking up, the first match
433 -- is the most specific.
435 -- We make no check for rules that unify without one dominating
436 -- the other. Arguably this would be a bug.
438 addRule id (Rules rules rhs_fvs) rule@(BuiltinRule _ _)
439 = Rules (rule:rules) rhs_fvs
440 -- Put it at the start for lack of anything better
442 addRule id (Rules rules rhs_fvs) rule
443 = Rules (insertRule rules new_rule) (rhs_fvs `unionVarSet` new_rhs_fvs)
445 new_rule = occurAnalyseRule rule
446 new_rhs_fvs = ruleRhsFreeVars new_rule `delVarSet` id
448 -- Don't include the Id in its own rhs free-var set.
449 -- Otherwise the occurrence analyser makes bindings recursive
450 -- that shoudn't be. E.g.
451 -- RULE: f (f x y) z ==> f x (f y z)
453 insertRule rules new_rule@(Rule _ _ tpl_vars tpl_args _)
456 tpl_var_set = mkInScopeSet (mkVarSet tpl_vars)
457 -- Actually we should probably include the free vars of tpl_args,
458 -- but I can't be bothered
461 go (rule:rules) | new_is_more_specific rule = (new_rule:rule:rules)
462 | otherwise = rule : go rules
464 new_is_more_specific rule = isJust (matchRule noBlackList tpl_var_set rule tpl_args)
466 addIdSpecialisations :: Id -> [CoreRule] -> Id
467 addIdSpecialisations id rules
468 = setIdSpecialisation id new_specs
470 new_specs = foldl (addRule id) (idSpecialisation id) rules
474 %************************************************************************
476 \subsection{Looking up a rule}
478 %************************************************************************
481 lookupRule :: (Activation -> Bool) -> InScopeSet
482 -> Id -> [CoreExpr] -> Maybe (RuleName, CoreExpr)
483 lookupRule is_active in_scope fn args
484 = case idSpecialisation fn of
485 Rules rules _ -> matchRules is_active in_scope rules args
489 %************************************************************************
491 \subsection{Checking a program for failing rule applications}
493 %************************************************************************
495 -----------------------------------------------------
497 -----------------------------------------------------
499 We want to know what sites have rules that could have fired but didn't.
500 This pass runs over the tree (without changing it) and reports such.
502 NB: we assume that this follows a run of the simplifier, so every Id
503 occurrence (including occurrences of imported Ids) is decorated with
504 all its (active) rules. No need to construct a rule base or anything
508 ruleCheckProgram :: CompilerPhase -> String -> [CoreBind] -> SDoc
509 -- Report partial matches for rules beginning
510 -- with the specified string
511 ruleCheckProgram phase rule_pat binds
513 = text "Rule check results: no rule application sites"
515 = vcat [text "Rule check results:",
517 vcat [ p $$ line | p <- bagToList results ]
520 results = unionManyBags (map (ruleCheckBind (phase, rule_pat)) binds)
521 line = text (replicate 20 '-')
523 type RuleCheckEnv = (CompilerPhase, String) -- Phase and Pattern
525 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
526 -- The Bag returned has one SDoc for each call site found
527 ruleCheckBind env (NonRec b r) = ruleCheck env r
528 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (b,r) <- prs]
530 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
531 ruleCheck env (Var v) = emptyBag
532 ruleCheck env (Lit l) = emptyBag
533 ruleCheck env (Type ty) = emptyBag
534 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
535 ruleCheck env (Note n e) = ruleCheck env e
536 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
537 ruleCheck env (Lam b e) = ruleCheck env e
539 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
540 unionManyBags [ruleCheck env r | (_,_,r) <- as]
542 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
543 ruleCheckApp env (Var f) as = ruleCheckFun env f as
544 ruleCheckApp env other as = ruleCheck env other
548 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
549 -- Produce a report for all rules matching the predicate
550 -- saying why it doesn't match the specified application
552 ruleCheckFun (phase, pat) fn args
553 | null name_match_rules = emptyBag
554 | otherwise = unitBag (ruleAppCheck_help phase fn args name_match_rules)
556 name_match_rules = case idSpecialisation fn of
557 Rules rules _ -> filter match rules
558 match rule = pat `isPrefixOf` unpackFS (ruleName rule)
560 ruleAppCheck_help :: CompilerPhase -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
561 ruleAppCheck_help phase fn args rules
562 = -- The rules match the pattern, so we want to print something
563 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
564 vcat (map check_rule rules)]
567 i_args = args `zip` [1::Int ..]
569 check_rule rule = rule_herald rule <> colon <+> rule_info rule
571 rule_herald (BuiltinRule name _) =
572 ptext SLIT("Builtin rule") <+> doubleQuotes (ftext name)
573 rule_herald (Rule name _ _ _ _) =
574 ptext SLIT("Rule") <+> doubleQuotes (ftext name)
577 | Just (name,_) <- matchRule noBlackList emptyInScopeSet rule args
578 = text "matches (which is very peculiar!)"
580 rule_info (BuiltinRule name fn) = text "does not match"
582 rule_info (Rule name act rule_bndrs rule_args _)
583 | not (isActive phase act) = text "active only in later phase"
584 | n_args < n_rule_args = text "too few arguments"
585 | n_mismatches == n_rule_args = text "no arguments match"
586 | n_mismatches == 0 = text "all arguments match (considered individually), but the rule as a whole does not"
587 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
589 n_rule_args = length rule_args
590 n_mismatches = length mismatches
591 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
592 not (isJust (match_fn rule_arg arg))]
594 bndr_set = mkVarSet rule_bndrs
595 match_fn rule_arg arg = match rule_arg arg bndr_set (\s -> Just ()) emptySubst
599 %************************************************************************
601 \subsection{Getting the rules ready}
603 %************************************************************************
606 data RuleBase = RuleBase
607 IdSet -- Ids with their rules in their specialisations
608 -- Held as a set, so that it can simply be the initial
609 -- in-scope set in the simplifier
610 -- This representation is a bit cute, and I wonder if we should
611 -- change it to use (IdEnv CoreRule) which seems a bit more natural
613 ruleBaseIds (RuleBase ids) = ids
614 emptyRuleBase = RuleBase emptyVarSet
616 extendRuleBaseList :: RuleBase -> [IdCoreRule] -> RuleBase
617 extendRuleBaseList rule_base new_guys
618 = foldl extendRuleBase rule_base new_guys
620 extendRuleBase :: RuleBase -> IdCoreRule -> RuleBase
621 extendRuleBase (RuleBase rule_ids) (IdCoreRule id _ rule)
622 = RuleBase (extendVarSet rule_ids new_id)
624 new_id = setIdSpecialisation id (addRule id old_rules rule)
625 old_rules = idSpecialisation (fromMaybe id (lookupVarSet rule_ids id))
626 -- Get the old rules from rule_ids if the Id is already there, but
627 -- if not, use the Id from the incoming rule. If may be a PrimOpId,
628 -- in which case it may have rules in its belly already. Seems
629 -- dreadfully hackoid.
631 pprRuleBase :: RuleBase -> SDoc
632 pprRuleBase (RuleBase rules) = vcat [ pprTidyIdRules id | id <- varSetElems rules ]