2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreRules]{Transformation rules}
7 -- | Functions for collecting together and applying rewrite rules to a module.
8 -- The 'CoreRule' datatype itself is declared elsewhere.
14 emptyRuleBase, mkRuleBase, extendRuleBaseList,
15 unionRuleBase, pprRuleBase,
17 -- ** Checking rule applications
20 -- ** Manipulating 'SpecInfo' rules
21 mkSpecInfo, extendSpecInfo, addSpecInfo,
24 -- * Misc. CoreRule helpers
25 rulesOfBinds, getRules, pprRulesForUser,
27 lookupRule, mkLocalRule, roughTopNames
30 #include "HsVersions.h"
32 import CoreSyn -- All of it
33 import OccurAnal ( occurAnalyseExpr )
34 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
35 import CoreUtils ( exprType )
36 import PprCore ( pprRules )
37 import Type ( Type, TvSubstEnv, tcEqTypeX )
38 import TcType ( tcSplitTyConApp_maybe )
39 import CoreTidy ( tidyRules )
41 import IdInfo ( SpecInfo( SpecInfo ) )
45 import Name ( Name, NamedThing(..) )
47 import Unify ( ruleMatchTyX, MatchEnv(..) )
48 import BasicTypes ( Activation )
49 import StaticFlags ( opt_PprStyle_Debug )
60 %************************************************************************
62 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
64 %************************************************************************
66 A @CoreRule@ holds details of one rule for an @Id@, which
67 includes its specialisations.
69 For example, if a rule for @f@ contains the mapping:
71 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
73 then when we find an application of f to matching types, we simply replace
74 it by the matching RHS:
76 f (List Int) Bool dict ===> f' Int Bool
78 All the stuff about how many dictionaries to discard, and what types
79 to apply the specialised function to, are handled by the fact that the
80 Rule contains a template for the result of the specialisation.
82 There is one more exciting case, which is dealt with in exactly the same
83 way. If the specialised value is unboxed then it is lifted at its
84 definition site and unlifted at its uses. For example:
86 pi :: forall a. Num a => a
88 might have a specialisation
90 [Int#] ===> (case pi' of Lift pi# -> pi#)
92 where pi' :: Lift Int# is the specialised version of pi.
95 mkLocalRule :: RuleName -> Activation
96 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
97 -- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
98 -- compiled. See also 'CoreSyn.CoreRule'
99 mkLocalRule name act fn bndrs args rhs
100 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
101 ru_bndrs = bndrs, ru_args = args,
102 ru_rhs = rhs, ru_rough = roughTopNames args,
106 roughTopNames :: [CoreExpr] -> [Maybe Name]
107 -- ^ Find the \"top\" free names of several expressions.
108 -- Such names are either:
110 -- 1. The function finally being applied to in an application chain
111 -- (if that name is a GlobalId: see "Var#globalvslocal"), or
113 -- 2. The 'TyCon' if the expression is a 'Type'
115 -- This is used for the fast-match-check for rules;
116 -- if the top names don't match, the rest can't
117 roughTopNames args = map roughTopName args
119 roughTopName :: CoreExpr -> Maybe Name
120 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
121 Just (tc,_) -> Just (getName tc)
123 roughTopName (App f _) = roughTopName f
124 roughTopName (Var f) | isGlobalId f = Just (idName f)
125 | otherwise = Nothing
126 roughTopName _ = Nothing
128 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
129 -- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
130 -- definitely can't match @tpl@ by instantiating @tpl@.
131 -- It's only a one-way match; unlike instance matching we
132 -- don't consider unification.
135 -- @ruleCantMatch [Nothing] [Just n2] = False@
136 -- Reason: a template variable can be instantiated by a constant
138 -- @ruleCantMatch [Just n1] [Nothing] = False@
139 -- Reason: a local variable @v@ in the actuals might [_$_]
141 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
142 ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as
143 ruleCantMatch _ _ = False
147 pprRulesForUser :: [CoreRule] -> SDoc
148 -- (a) tidy the rules
149 -- (b) sort them into order based on the rule name
150 -- (c) suppress uniques (unless -dppr-debug is on)
151 -- This combination makes the output stable so we can use in testing
152 -- It's here rather than in PprCore because it calls tidyRules
153 pprRulesForUser rules
154 = withPprStyle defaultUserStyle $
157 tidyRules emptyTidyEnv rules
159 le_rule r1 r2 = ru_name r1 <= ru_name r2
163 %************************************************************************
165 SpecInfo: the rules in an IdInfo
167 %************************************************************************
170 -- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
171 -- for putting into an 'IdInfo'
172 mkSpecInfo :: [CoreRule] -> SpecInfo
173 mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
175 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
176 extendSpecInfo (SpecInfo rs1 fvs1) rs2
177 = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
179 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
180 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
181 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
183 addIdSpecialisations :: Id -> [CoreRule] -> Id
184 addIdSpecialisations id []
186 addIdSpecialisations id rules
187 = setIdSpecialisation id $
188 extendSpecInfo (idSpecialisation id) rules
190 -- | Gather all the rules for locally bound identifiers from the supplied bindings
191 rulesOfBinds :: [CoreBind] -> [CoreRule]
192 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
194 getRules :: RuleBase -> Id -> [CoreRule]
195 -- The rules for an Id come from two places:
196 -- (a) the ones it is born with (idCoreRules fn)
197 -- (b) rules added in subsequent modules (extra_rules)
198 -- PrimOps, for example, are born with a bunch of rules under (a)
199 getRules rule_base fn
200 | isLocalId fn = idCoreRules fn
201 | otherwise = WARN( not (isPrimOpId fn) && notNull (idCoreRules fn),
202 ppr fn <+> ppr (idCoreRules fn) )
203 idCoreRules fn ++ (lookupNameEnv rule_base (idName fn) `orElse` [])
204 -- Only PrimOpIds have rules inside themselves, and perhaps more besides
208 %************************************************************************
212 %************************************************************************
215 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
216 type RuleBase = NameEnv [CoreRule]
217 -- The rules are are unordered;
218 -- we sort out any overlaps on lookup
220 emptyRuleBase :: RuleBase
221 emptyRuleBase = emptyNameEnv
223 mkRuleBase :: [CoreRule] -> RuleBase
224 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
226 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
227 extendRuleBaseList rule_base new_guys
228 = foldl extendRuleBase rule_base new_guys
230 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
231 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
233 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
234 extendRuleBase rule_base rule
235 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
237 pprRuleBase :: RuleBase -> SDoc
238 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
239 | rs <- nameEnvElts rules ]
243 %************************************************************************
245 \subsection{Matching}
247 %************************************************************************
249 Note [Extra args in rule matching]
250 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
251 If we find a matching rule, we return (Just (rule, rhs)),
252 but the rule firing has only consumed as many of the input args
253 as the ruleArity says. It's up to the caller to keep track
254 of any left-over args. E.g. if you call
255 lookupRule ... f [e1, e2, e3]
256 and it returns Just (r, rhs), where r has ruleArity 2
257 then the real rewrite is
258 f e1 e2 e3 ==> rhs e3
260 You might think it'd be cleaner for lookupRule to deal with the
261 leftover arguments, by applying 'rhs' to them, but the main call
262 in the Simplifier works better as it is. Reason: the 'args' passed
263 to lookupRule are the result of a lazy substitution
266 -- | The main rule matching function. Attempts to apply all (active)
267 -- supplied rules to this instance of an application in a given
268 -- context, returning the rule applied and the resulting expression if
270 lookupRule :: (Activation -> Bool) -> InScopeSet
272 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
274 -- See Note [Extra args in rule matching]
275 -- See comments on matchRule
276 lookupRule is_active in_scope fn args rules
277 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
280 (m:ms) -> Just (findBest (fn,args) m ms)
282 rough_args = map roughTopName args
284 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
286 go ms (r:rs) = case (matchRule is_active in_scope args rough_args r) of
287 Just e -> go ((r,e):ms) rs
288 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
289 -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] )
292 findBest :: (Id, [CoreExpr])
293 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
294 -- All these pairs matched the expression
295 -- Return the pair the the most specific rule
296 -- The (fn,args) is just for overlap reporting
298 findBest _ (rule,ans) [] = (rule,ans)
299 findBest target (rule1,ans1) ((rule2,ans2):prs)
300 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
301 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
302 | debugIsOn = let pp_rule rule
303 | opt_PprStyle_Debug = ppr rule
304 | otherwise = doubleQuotes (ftext (ru_name rule))
305 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
306 (vcat [if opt_PprStyle_Debug then
307 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
309 ptext (sLit "Rule 1:") <+> pp_rule rule1,
310 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
311 findBest target (rule1,ans1) prs
312 | otherwise = findBest target (rule1,ans1) prs
316 isMoreSpecific :: CoreRule -> CoreRule -> Bool
317 isMoreSpecific (BuiltinRule {}) _ = True
318 isMoreSpecific _ (BuiltinRule {}) = False
319 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
320 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
321 = isJust (matchN in_scope bndrs2 args2 args1)
323 in_scope = mkInScopeSet (mkVarSet bndrs1)
324 -- Actually we should probably include the free vars
325 -- of rule1's args, but I can't be bothered
327 noBlackList :: Activation -> Bool
328 noBlackList _ = False -- Nothing is black listed
330 matchRule :: (Activation -> Bool) -> InScopeSet
331 -> [CoreExpr] -> [Maybe Name]
332 -> CoreRule -> Maybe CoreExpr
334 -- If (matchRule rule args) returns Just (name,rhs)
335 -- then (f args) matches the rule, and the corresponding
336 -- rewritten RHS is rhs
338 -- The bndrs and rhs is occurrence-analysed
343 -- forall f g x. map f (map g x) ==> map (f . g) x
345 -- CoreRule "map/map"
346 -- [f,g,x] -- tpl_vars
347 -- [f,map g x] -- tpl_args
348 -- map (f.g) x) -- rhs
350 -- Then the call: matchRule the_rule [e1,map e2 e3]
351 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
353 -- Any 'surplus' arguments in the input are simply put on the end
356 matchRule _is_active _in_scope args _rough_args
357 (BuiltinRule { ru_try = match_fn })
358 = case match_fn args of
359 Just expr -> Just expr
362 matchRule is_active in_scope args rough_args
363 (Rule { ru_act = act, ru_rough = tpl_tops,
364 ru_bndrs = tpl_vars, ru_args = tpl_args,
366 | not (is_active act) = Nothing
367 | ruleCantMatch tpl_tops rough_args = Nothing
369 = case matchN in_scope tpl_vars tpl_args args of
371 Just (binds, tpl_vals) -> Just (mkLets binds $
372 rule_fn `mkApps` tpl_vals)
374 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
375 -- We could do this when putting things into the rulebase, I guess
379 -- For a given match template and context, find bindings to wrap around
380 -- the entire result and what should be substituted for each template variable.
381 -- Fail if there are two few actual arguments from the target to match the template
382 matchN :: InScopeSet -- ^ In-scope variables
383 -> [Var] -- ^ Match template type variables
384 -> [CoreExpr] -- ^ Match template
385 -> [CoreExpr] -- ^ Target; can have more elements than the template
386 -> Maybe ([CoreBind],
389 matchN in_scope tmpl_vars tmpl_es target_es
390 = do { (tv_subst, id_subst, binds)
391 <- go init_menv emptySubstEnv tmpl_es target_es
392 ; return (fromOL binds,
393 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
395 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
396 -- See Note [Template binders]
398 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
400 go _ subst [] _ = Just subst
401 go _ _ _ [] = Nothing -- Fail if too few actual args
402 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
403 ; go menv subst1 ts es }
405 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
406 lookup_tmpl tv_subst id_subst tmpl_var'
407 | isTyVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
409 Nothing -> unbound tmpl_var'
410 | otherwise = case lookupVarEnv id_subst tmpl_var' of
412 _ -> unbound tmpl_var'
414 unbound var = pprPanic "Template variable unbound in rewrite rule"
415 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
418 Note [Template binders]
419 ~~~~~~~~~~~~~~~~~~~~~~~
420 Consider the following match:
421 Template: forall x. f x
423 This should succeed, because the template variable 'x' has
424 nothing to do with the 'x' in the target.
426 On reflection, this case probably does just work, but this might not
427 Template: forall x. f (\x.x)
429 Here we want to clone when we find the \x, but to know that x must be in scope
431 To achive this, we use rnBndrL to rename the template variables if
432 necessary; the renamed ones are the tmpl_vars'
435 ---------------------------------------------
436 The inner workings of matching
437 ---------------------------------------------
440 -- These two definitions are not the same as in Subst,
441 -- but they simple and direct, and purely local to this module
443 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
444 -- variables passed into the match.
446 -- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out
447 -- from nested matches; see the Let case of match, below
449 type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind)
450 type IdSubstEnv = IdEnv CoreExpr
452 emptySubstEnv :: SubstEnv
453 emptySubstEnv = (emptyVarEnv, emptyVarEnv, nilOL)
456 -- At one stage I tried to match even if there are more
457 -- template args than real args.
459 -- I now think this is probably a bad idea.
460 -- Should the template (map f xs) match (map g)? I think not.
461 -- For a start, in general eta expansion wastes work.
467 -> CoreExpr -- Template
468 -> CoreExpr -- Target
471 -- See the notes with Unify.match, which matches types
472 -- Everything is very similar for terms
474 -- Interesting examples:
476 -- \x->f against \f->f
477 -- When we meet the lambdas we must remember to rename f to f' in the
478 -- second expresion. The RnEnv2 does that.
481 -- forall a. \b->b against \a->3
482 -- We must rename the \a. Otherwise when we meet the lambdas we
483 -- might substitute [a/b] in the template, and then erroneously
484 -- succeed in matching what looks like the template variable 'a' against 3.
486 -- The Var case follows closely what happens in Unify.match
487 match menv subst (Var v1) e2
488 | Just subst <- match_var menv subst v1 e2
491 match menv subst (Note _ e1) e2 = match menv subst e1 e2
492 match menv subst e1 (Note _ e2) = match menv subst e1 e2
493 -- Ignore notes in both template and thing to be matched
494 -- See Note [Notes in RULE matching]
496 match menv subst e1 (Var v2) -- Note [Expanding variables]
497 | not (locallyBoundR rn_env v2) -- Note [Do not expand locally-bound variables]
498 , Just e2' <- expandId v2'
499 = match (menv { me_env = nukeRnEnvR rn_env }) subst e1 e2'
501 v2' = lookupRnInScope rn_env v2
503 -- Notice that we look up v2 in the in-scope set
504 -- See Note [Lookup in-scope]
505 -- No need to apply any renaming first (hence no rnOccR)
506 -- becuase of the not-locallyBoundR
508 match menv (tv_subst, id_subst, binds) e1 (Let bind e2)
509 | all freshly_bound bndrs -- See Note [Matching lets]
510 , not (any (locallyBoundR rn_env) bind_fvs)
511 = match (menv { me_env = rn_env' })
512 (tv_subst, id_subst, binds `snocOL` bind')
516 bndrs = bindersOf bind
517 bind_fvs = varSetElems (bindFreeVars bind)
518 freshly_bound x = not (x `rnInScope` rn_env)
521 rn_env' = extendRnInScopeList rn_env bndrs
523 match _ subst (Lit lit1) (Lit lit2)
527 match menv subst (App f1 a1) (App f2 a2)
528 = do { subst' <- match menv subst f1 f2
529 ; match menv subst' a1 a2 }
531 match menv subst (Lam x1 e1) (Lam x2 e2)
532 = match menv' subst e1 e2
534 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
536 -- This rule does eta expansion
537 -- (\x.M) ~ N iff M ~ N x
538 -- It's important that this is *after* the let rule,
539 -- so that (\x.M) ~ (let y = e in \y.N)
540 -- does the let thing, and then gets the lam/lam rule above
541 match menv subst (Lam x1 e1) e2
542 = match menv' subst e1 (App e2 (varToCoreExpr new_x))
544 (rn_env', new_x) = rnBndrL (me_env menv) x1
545 menv' = menv { me_env = rn_env' }
547 -- Eta expansion the other way
548 -- M ~ (\y.N) iff M y ~ N
549 match menv subst e1 (Lam x2 e2)
550 = match menv' subst (App e1 (varToCoreExpr new_x)) e2
552 (rn_env', new_x) = rnBndrR (me_env menv) x2
553 menv' = menv { me_env = rn_env' }
555 match menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
556 = do { subst1 <- match_ty menv subst ty1 ty2
557 ; subst2 <- match menv subst1 e1 e2
558 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
559 ; match_alts menv' subst2 alts1 alts2 -- Alts are both sorted
562 match menv subst (Type ty1) (Type ty2)
563 = match_ty menv subst ty1 ty2
565 match menv subst (Cast e1 co1) (Cast e2 co2)
566 = do { subst1 <- match_ty menv subst co1 co2
567 ; match menv subst1 e1 e2 }
569 -- Everything else fails
570 match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
573 ------------------------------------------
574 match_var :: MatchEnv
577 -> CoreExpr -- Target
579 match_var menv subst@(tv_subst, id_subst, binds) v1 e2
580 | v1' `elemVarSet` me_tmpls menv
581 = case lookupVarEnv id_subst v1' of
582 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
583 -> Nothing -- Occurs check failure
584 -- e.g. match forall a. (\x-> a x) against (\y. y y)
586 | otherwise -- No renaming to do on e2, because no free var
587 -- of e2 is in the rnEnvR of the envt
588 -- Note [Matching variable types]
589 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
590 -- However, we must match the *types*; e.g.
591 -- forall (c::Char->Int) (x::Char).
592 -- f (c x) = "RULE FIRED"
593 -- We must only match on args that have the right type
594 -- It's actually quite difficult to come up with an example that shows
595 -- you need type matching, esp since matching is left-to-right, so type
596 -- args get matched first. But it's possible (e.g. simplrun008) and
597 -- this is the Right Thing to do
598 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
599 -- c.f. match_ty below
600 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
602 Just e1' | eqExpr (nukeRnEnvL rn_env) e1' e2
608 | otherwise -- v1 is not a template variable; check for an exact match with e2
610 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
615 v1' = rnOccL rn_env v1
616 -- If the template is
617 -- forall x. f x (\x -> x) = ...
618 -- Then the x inside the lambda isn't the
619 -- template x, so we must rename first!
622 ------------------------------------------
623 match_alts :: MatchEnv
625 -> [CoreAlt] -- Template
626 -> [CoreAlt] -- Target
628 match_alts _ subst [] []
630 match_alts menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
632 = do { subst1 <- match menv' subst r1 r2
633 ; match_alts menv subst1 alts1 alts2 }
636 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
642 Matching Core types: use the matcher in TcType.
643 Notice that we treat newtypes as opaque. For example, suppose
644 we have a specialised version of a function at a newtype, say
646 We only want to replace (f T) with f', not (f Int).
649 ------------------------------------------
655 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
656 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
657 ; return (tv_subst', id_subst, binds) }
660 Note [Expanding variables]
661 ~~~~~~~~~~~~~~~~~~~~~~~~~~
662 Here is another Very Important rule: if the term being matched is a
663 variable, we expand it so long as its unfolding is "expandable". (Its
664 occurrence information is not necessarily up to date, so we don't use
665 it.) By "expandable" we mean a WHNF or a "constructor-like" application.
666 This is the key reason for "constructor-like" Ids. If we have
667 {-# NOINLINE [1] CONLIKE g #-}
668 {-# RULE f (g x) = h x #-}
670 let v = g 3 in ....(f v)....
671 we want to make the rule fire, to replace (f v) with (h 3).
673 Note [Do not expand locally-bound variables]
674 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
675 Do *not* expand locally-bound variables, else there's a worry that the
676 unfolding might mention variables that are themselves renamed.
678 case x of y { (p,q) -> ...y... }
679 Don't expand 'y' to (p,q) because p,q might themselves have been
680 renamed. Essentially we only expand unfoldings that are "outside"
683 Hence, (a) the guard (not (isLocallyBoundR v2))
684 (b) when we expand we nuke the renaming envt (nukeRnEnvR).
686 Note [Notes in RULE matching]
687 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
688 Look through Notes in both template and expression being matched. In
689 particular, we don't want to be confused by InlineMe notes. Maybe we
690 should be more careful about profiling notes, but for now I'm just
691 riding roughshod over them. cf Note [Notes in call patterns] in
696 Matching a let-expression. Consider
697 RULE forall x. f (g x) = <rhs>
698 and target expression
699 f (let { w=R } in g E))
700 Then we'd like the rule to match, to generate
701 let { w=R } in (\x. <rhs>) E
702 In effect, we want to float the let-binding outward, to enable
703 the match to happen. This is the WHOLE REASON for accumulating
704 bindings in the SubstEnv
706 We can only do this if
707 (a) Widening the scope of w does not capture any variables
708 We use a conservative test: w is not already in scope
709 If not, we clone the binders, and substitute
710 (b) The free variables of R are not bound by the part of the
711 target expression outside the let binding; e.g.
712 f (\v. let w = v+1 in g E)
713 Here we obviously cannot float the let-binding for w.
715 You may think rule (a) would never apply, because rule matching is
716 mostly invoked from the simplifier, when we have just run substExpr
717 over the argument, so there will be no shadowing anyway.
718 The fly in the ointment is that the forall'd variables of the
719 RULE itself are considered in scope.
721 I though of various ways to solve (a). One plan was to
722 clone the binders if they are in scope. But watch out!
723 (let x=y+1 in let z=x+1 in (z,z)
724 --> should match (p,p) but watch out that
725 the use of x on z's rhs is OK!
726 If we clone x, then the let-binding for 'z' is then caught by (b),
727 at least unless we elaborate the RnEnv stuff a bit.
729 So for we simply fail to match unless both (a) and (b) hold.
731 Other cases to think about
732 (let x=y+1 in \x. (x,x))
733 --> let x=y+1 in (\x1. (x1,x1))
734 (\x. let x = y+1 in (x,x))
735 --> let x1 = y+1 in (\x. (x1,x1)
736 (let x=y+1 in (x,x), let x=y-1 in (x,x))
737 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
740 Note [Lookup in-scope]
741 ~~~~~~~~~~~~~~~~~~~~~~
742 Consider this example
743 foo :: Int -> Maybe Int -> Int
745 foo m (Just n) = foo (m-n) (Just n)
747 SpecConstr sees this fragment:
749 case w_smT of wild_Xf [Just A] {
750 Data.Maybe.Nothing -> lvl_smf;
751 Data.Maybe.Just n_acT [Just S(L)] ->
752 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
753 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
756 and correctly generates the rule
758 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
759 sc_snn :: GHC.Prim.Int#}
760 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
761 = \$s\$wfoo_sno y_amr sc_snn ;]
763 BUT we must ensure that this rule matches in the original function!
764 Note that the call to \$wfoo is
765 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
767 During matching we expand wild_Xf to (Just n_acT). But then we must also
768 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
769 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
772 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
776 eqExpr :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
777 -- ^ A kind of shallow equality used in rule matching, so does
778 -- /not/ look through newtypes or predicate types
780 eqExpr env (Var v1) (Var v2)
781 | rnOccL env v1 == rnOccR env v2
784 -- The next two rules expand non-local variables
785 -- C.f. Note [Expanding variables]
786 -- and Note [Do not expand locally-bound variables]
787 eqExpr env (Var v1) e2
788 | not (locallyBoundL env v1)
789 , Just e1' <- expandId (lookupRnInScope env v1)
790 = eqExpr (nukeRnEnvL env) e1' e2
792 eqExpr env e1 (Var v2)
793 | not (locallyBoundR env v2)
794 , Just e2' <- expandId (lookupRnInScope env v2)
795 = eqExpr (nukeRnEnvR env) e1 e2'
797 eqExpr _ (Lit lit1) (Lit lit2) = lit1 == lit2
798 eqExpr env (App f1 a1) (App f2 a2) = eqExpr env f1 f2 && eqExpr env a1 a2
799 eqExpr env (Lam v1 e1) (Lam v2 e2) = eqExpr (rnBndr2 env v1 v2) e1 e2
800 eqExpr env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eqExpr env e1 e2
801 eqExpr env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && eqExpr env e1 e2
802 eqExpr env (Type t1) (Type t2) = tcEqTypeX env t1 t2
804 eqExpr env (Let (NonRec v1 r1) e1)
805 (Let (NonRec v2 r2) e2) = eqExpr env r1 r2
806 && eqExpr (rnBndr2 env v1 v2) e1 e2
807 eqExpr env (Let (Rec ps1) e1)
808 (Let (Rec ps2) e2) = equalLength ps1 ps2
809 && and (zipWith eq_rhs ps1 ps2)
812 env' = foldl2 rn_bndr2 env ps2 ps2
813 rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
814 eq_rhs (_,r1) (_,r2) = eqExpr env' r1 r2
815 eqExpr env (Case e1 v1 t1 a1)
816 (Case e2 v2 t2 a2) = eqExpr env e1 e2
817 && tcEqTypeX env t1 t2
819 && and (zipWith (eq_alt env') a1 a2)
821 env' = rnBndr2 env v1 v2
825 eq_alt :: RnEnv2 -> CoreAlt -> CoreAlt -> Bool
826 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && eqExpr (rnBndrs2 env vs1 vs2) r1 r2
828 eq_note :: RnEnv2 -> Note -> Note -> Bool
829 eq_note _ (SCC cc1) (SCC cc2) = cc1 == cc2
830 eq_note _ (CoreNote s1) (CoreNote s2) = s1 == s2
831 eq_note _ (InlineMe) (InlineMe) = True
832 eq_note _ _ _ = False
838 locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
839 locallyBoundL rn_env v = inRnEnvL rn_env v
840 locallyBoundR rn_env v = inRnEnvR rn_env v
843 expandId :: Id -> Maybe CoreExpr
845 | isExpandableUnfolding unfolding = Just (unfoldingTemplate unfolding)
846 | otherwise = Nothing
848 unfolding = idUnfolding id
851 %************************************************************************
853 Rule-check the program
855 %************************************************************************
857 We want to know what sites have rules that could have fired but didn't.
858 This pass runs over the tree (without changing it) and reports such.
861 -- | Report partial matches for rules beginning with the specified
862 -- string for the purposes of error reporting
863 ruleCheckProgram :: (Activation -> Bool) -- ^ Rule activation test
864 -> String -- ^ Rule pattern
865 -> RuleBase -- ^ Database of rules
866 -> [CoreBind] -- ^ Bindings to check in
867 -> SDoc -- ^ Resulting check message
868 ruleCheckProgram is_active rule_pat rule_base binds
870 = text "Rule check results: no rule application sites"
872 = vcat [text "Rule check results:",
874 vcat [ p $$ line | p <- bagToList results ]
877 results = unionManyBags (map (ruleCheckBind (RuleCheckEnv is_active rule_pat rule_base)) binds)
878 line = text (replicate 20 '-')
880 data RuleCheckEnv = RuleCheckEnv {
881 rc_is_active :: Activation -> Bool,
882 rc_pattern :: String,
883 rc_rule_base :: RuleBase
886 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
887 -- The Bag returned has one SDoc for each call site found
888 ruleCheckBind env (NonRec _ r) = ruleCheck env r
889 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (_,r) <- prs]
891 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
892 ruleCheck _ (Var _) = emptyBag
893 ruleCheck _ (Lit _) = emptyBag
894 ruleCheck _ (Type _) = emptyBag
895 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
896 ruleCheck env (Note _ e) = ruleCheck env e
897 ruleCheck env (Cast e _) = ruleCheck env e
898 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
899 ruleCheck env (Lam _ e) = ruleCheck env e
900 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
901 unionManyBags [ruleCheck env r | (_,_,r) <- as]
903 ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
904 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
905 ruleCheckApp env (Var f) as = ruleCheckFun env f as
906 ruleCheckApp env other _ = ruleCheck env other
910 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
911 -- Produce a report for all rules matching the predicate
912 -- saying why it doesn't match the specified application
914 ruleCheckFun env fn args
915 | null name_match_rules = emptyBag
916 | otherwise = unitBag (ruleAppCheck_help (rc_is_active env) fn args name_match_rules)
918 name_match_rules = filter match (getRules (rc_rule_base env) fn)
919 match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
921 ruleAppCheck_help :: (Activation -> Bool) -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
922 ruleAppCheck_help is_active fn args rules
923 = -- The rules match the pattern, so we want to print something
924 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
925 vcat (map check_rule rules)]
928 i_args = args `zip` [1::Int ..]
929 rough_args = map roughTopName args
931 check_rule rule = rule_herald rule <> colon <+> rule_info rule
933 rule_herald (BuiltinRule { ru_name = name })
934 = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
935 rule_herald (Rule { ru_name = name })
936 = ptext (sLit "Rule") <+> doubleQuotes (ftext name)
939 | Just _ <- matchRule noBlackList emptyInScopeSet args rough_args rule
940 = text "matches (which is very peculiar!)"
942 rule_info (BuiltinRule {}) = text "does not match"
944 rule_info (Rule { ru_act = act,
945 ru_bndrs = rule_bndrs, ru_args = rule_args})
946 | not (is_active act) = text "active only in later phase"
947 | n_args < n_rule_args = text "too few arguments"
948 | n_mismatches == n_rule_args = text "no arguments match"
949 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
950 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
952 n_rule_args = length rule_args
953 n_mismatches = length mismatches
954 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
955 not (isJust (match_fn rule_arg arg))]
957 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
958 match_fn rule_arg arg = match menv emptySubstEnv rule_arg arg
960 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
961 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
962 , me_tmpls = mkVarSet rule_bndrs }