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, mkRule, 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, eqExprX )
36 import PprCore ( pprRules )
37 import Type ( Type, TvSubstEnv )
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, CompilerPhase, isActive )
49 import StaticFlags ( opt_PprStyle_Debug )
59 Note [Overall plumbing for rules]
60 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
61 * After the desugarer:
62 - The ModGuts initially contains mg_rules :: [CoreRule] of
63 locally-declared rules for imported Ids.
64 - Locally-declared rules for locally-declared Ids are attached to
65 the IdInfo for that Id. See Note [Attach rules to local ids] in
68 * TidyPgm strips off all the rules from local Ids and adds them to
69 mg_rules, so that the ModGuts has *all* the locally-declared rules.
71 * The HomePackageTable contains a ModDetails for each home package
72 module. Each contains md_rules :: [CoreRule] of rules declared in
73 that module. The HomePackageTable grows as ghc --make does its
74 up-sweep. In batch mode (ghc -c), the HPT is empty; all imported modules
75 are treated by the "external" route, discussed next, regardless of
76 which package they come from.
78 * The ExternalPackageState has a single eps_rule_base :: RuleBase for
79 Ids in other packages. This RuleBase simply grow monotonically, as
80 ghc --make compiles one module after another.
82 During simplification, interface files may get demand-loaded,
83 as the simplifier explores the unfoldings for Ids it has in
84 its hand. (Via an unsafePerformIO; the EPS is really a cache.)
85 That in turn may make the EPS rule-base grow. In contrast, the
86 HPT never grows in this way.
88 * The result of all this is that during Core-to-Core optimisation
89 there are four sources of rules:
91 (a) Rules in the IdInfo of the Id they are a rule for. These are
92 easy: fast to look up, and if you apply a substitution then
93 it'll be applied to the IdInfo as a matter of course.
95 (b) Rules declared in this module for imported Ids, kept in the
96 ModGuts. If you do a substitution, you'd better apply the
97 substitution to these. There are seldom many of these.
99 (c) Rules declared in the HomePackageTable. These never change.
101 (d) Rules in the ExternalPackageTable. These can grow in response
102 to lazy demand-loading of interfaces.
104 * At the moment (c) is carried in a reader-monad way by the CoreMonad.
105 The HomePackageTable doesn't have a single RuleBase because technically
106 we should only be able to "see" rules "below" this module; so we
107 generate a RuleBase for (c) by combing rules from all the modules
108 "below" us. That's why we can't just select the home-package RuleBase
111 [NB: we are inconsistent here. We should do the same for external
112 pacakges, but we don't. Same for type-class instances.]
114 * So in the outer simplifier loop, we combine (b-d) into a single
116 (b) from the ModGuts,
117 (c) from the CoreMonad, and
118 (d) from its mutable variable
119 [Of coures this means that we won't see new EPS rules that come in
120 during a single simplifier iteration, but that probably does not
124 %************************************************************************
126 \subsection[specialisation-IdInfo]{Specialisation info about an @Id@}
128 %************************************************************************
130 A @CoreRule@ holds details of one rule for an @Id@, which
131 includes its specialisations.
133 For example, if a rule for @f@ contains the mapping:
135 forall a b d. [Type (List a), Type b, Var d] ===> f' a b
137 then when we find an application of f to matching types, we simply replace
138 it by the matching RHS:
140 f (List Int) Bool dict ===> f' Int Bool
142 All the stuff about how many dictionaries to discard, and what types
143 to apply the specialised function to, are handled by the fact that the
144 Rule contains a template for the result of the specialisation.
146 There is one more exciting case, which is dealt with in exactly the same
147 way. If the specialised value is unboxed then it is lifted at its
148 definition site and unlifted at its uses. For example:
150 pi :: forall a. Num a => a
152 might have a specialisation
154 [Int#] ===> (case pi' of Lift pi# -> pi#)
156 where pi' :: Lift Int# is the specialised version of pi.
159 mkRule :: Bool -> Bool -> RuleName -> Activation
160 -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule
161 -- ^ Used to make 'CoreRule' for an 'Id' defined in the module being
162 -- compiled. See also 'CoreSyn.CoreRule'
163 mkRule is_auto is_local name act fn bndrs args rhs
164 = Rule { ru_name = name, ru_fn = fn, ru_act = act,
165 ru_bndrs = bndrs, ru_args = args,
166 ru_rhs = occurAnalyseExpr rhs,
167 ru_rough = roughTopNames args,
168 ru_auto = is_auto, ru_local = is_local }
171 roughTopNames :: [CoreExpr] -> [Maybe Name]
172 -- ^ Find the \"top\" free names of several expressions.
173 -- Such names are either:
175 -- 1. The function finally being applied to in an application chain
176 -- (if that name is a GlobalId: see "Var#globalvslocal"), or
178 -- 2. The 'TyCon' if the expression is a 'Type'
180 -- This is used for the fast-match-check for rules;
181 -- if the top names don't match, the rest can't
182 roughTopNames args = map roughTopName args
184 roughTopName :: CoreExpr -> Maybe Name
185 roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of
186 Just (tc,_) -> Just (getName tc)
188 roughTopName (App f _) = roughTopName f
189 roughTopName (Var f) | isGlobalId f = Just (idName f)
190 | otherwise = Nothing
191 roughTopName _ = Nothing
193 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
194 -- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
195 -- definitely can't match @tpl@ by instantiating @tpl@.
196 -- It's only a one-way match; unlike instance matching we
197 -- don't consider unification.
200 -- @ruleCantMatch [Nothing] [Just n2] = False@
201 -- Reason: a template variable can be instantiated by a constant
203 -- @ruleCantMatch [Just n1] [Nothing] = False@
204 -- Reason: a local variable @v@ in the actuals might [_$_]
206 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
207 ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as
208 ruleCantMatch _ _ = False
212 pprRulesForUser :: [CoreRule] -> SDoc
213 -- (a) tidy the rules
214 -- (b) sort them into order based on the rule name
215 -- (c) suppress uniques (unless -dppr-debug is on)
216 -- This combination makes the output stable so we can use in testing
217 -- It's here rather than in PprCore because it calls tidyRules
218 pprRulesForUser rules
219 = withPprStyle defaultUserStyle $
222 tidyRules emptyTidyEnv rules
224 le_rule r1 r2 = ru_name r1 <= ru_name r2
228 %************************************************************************
230 SpecInfo: the rules in an IdInfo
232 %************************************************************************
235 -- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
236 -- for putting into an 'IdInfo'
237 mkSpecInfo :: [CoreRule] -> SpecInfo
238 mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
240 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
241 extendSpecInfo (SpecInfo rs1 fvs1) rs2
242 = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
244 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
245 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
246 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
248 addIdSpecialisations :: Id -> [CoreRule] -> Id
249 addIdSpecialisations id []
251 addIdSpecialisations id rules
252 = setIdSpecialisation id $
253 extendSpecInfo (idSpecialisation id) rules
255 -- | Gather all the rules for locally bound identifiers from the supplied bindings
256 rulesOfBinds :: [CoreBind] -> [CoreRule]
257 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
259 getRules :: RuleBase -> Id -> [CoreRule]
260 -- See Note [Where rules are found]
261 getRules rule_base fn
262 = idCoreRules fn ++ imp_rules
264 imp_rules = lookupNameEnv rule_base (idName fn) `orElse` []
267 Note [Where rules are found]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 The rules for an Id come from two places:
270 (a) the ones it is born with, stored inside the Id iself (idCoreRules fn),
271 (b) rules added in other modules, stored in the global RuleBase (imp_rules)
273 It's tempting to think that
274 - LocalIds have only (a)
275 - non-LocalIds have only (b)
277 but that isn't quite right:
279 - PrimOps and ClassOps are born with a bunch of rules inside the Id,
280 even when they are imported
282 - The rules in PrelRules.builtinRules should be active even
283 in the module defining the Id (when it's a LocalId), but
284 the rules are kept in the global RuleBase
287 %************************************************************************
291 %************************************************************************
294 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
295 type RuleBase = NameEnv [CoreRule]
296 -- The rules are are unordered;
297 -- we sort out any overlaps on lookup
299 emptyRuleBase :: RuleBase
300 emptyRuleBase = emptyNameEnv
302 mkRuleBase :: [CoreRule] -> RuleBase
303 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
305 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
306 extendRuleBaseList rule_base new_guys
307 = foldl extendRuleBase rule_base new_guys
309 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
310 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
312 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
313 extendRuleBase rule_base rule
314 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
316 pprRuleBase :: RuleBase -> SDoc
317 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
318 | rs <- nameEnvElts rules ]
322 %************************************************************************
326 %************************************************************************
329 -- | The main rule matching function. Attempts to apply all (active)
330 -- supplied rules to this instance of an application in a given
331 -- context, returning the rule applied and the resulting expression if
333 lookupRule :: (Activation -> Bool) -- When rule is active
334 -> IdUnfoldingFun -- When Id can be unfolded
337 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
339 -- See Note [Extra args in rule matching]
340 -- See comments on matchRule
341 lookupRule is_active id_unf in_scope fn args rules
342 = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $
345 (m:ms) -> Just (findBest (fn,args) m ms)
347 rough_args = map roughTopName args
349 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
351 go ms (r:rs) = case (matchRule is_active id_unf in_scope args rough_args r) of
352 Just e -> go ((r,e):ms) rs
353 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
354 -- ppr [ (arg_id, unfoldingTemplate unf)
355 -- | Var arg_id <- args
356 -- , let unf = idUnfolding arg_id
357 -- , isCheapUnfolding unf] )
360 findBest :: (Id, [CoreExpr])
361 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
362 -- All these pairs matched the expression
363 -- Return the pair the the most specific rule
364 -- The (fn,args) is just for overlap reporting
366 findBest _ (rule,ans) [] = (rule,ans)
367 findBest target (rule1,ans1) ((rule2,ans2):prs)
368 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
369 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
370 | debugIsOn = let pp_rule rule
371 | opt_PprStyle_Debug = ppr rule
372 | otherwise = doubleQuotes (ftext (ru_name rule))
373 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
374 (vcat [if opt_PprStyle_Debug then
375 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
377 ptext (sLit "Rule 1:") <+> pp_rule rule1,
378 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
379 findBest target (rule1,ans1) prs
380 | otherwise = findBest target (rule1,ans1) prs
384 isMoreSpecific :: CoreRule -> CoreRule -> Bool
385 isMoreSpecific (BuiltinRule {}) _ = True
386 isMoreSpecific _ (BuiltinRule {}) = False
387 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
388 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
389 = isJust (matchN id_unfolding_fun in_scope bndrs2 args2 args1)
391 id_unfolding_fun _ = NoUnfolding -- Don't expand in templates
392 in_scope = mkInScopeSet (mkVarSet bndrs1)
393 -- Actually we should probably include the free vars
394 -- of rule1's args, but I can't be bothered
396 noBlackList :: Activation -> Bool
397 noBlackList _ = False -- Nothing is black listed
400 Note [Extra args in rule matching]
401 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
402 If we find a matching rule, we return (Just (rule, rhs)),
403 but the rule firing has only consumed as many of the input args
404 as the ruleArity says. It's up to the caller to keep track
405 of any left-over args. E.g. if you call
406 lookupRule ... f [e1, e2, e3]
407 and it returns Just (r, rhs), where r has ruleArity 2
408 then the real rewrite is
409 f e1 e2 e3 ==> rhs e3
411 You might think it'd be cleaner for lookupRule to deal with the
412 leftover arguments, by applying 'rhs' to them, but the main call
413 in the Simplifier works better as it is. Reason: the 'args' passed
414 to lookupRule are the result of a lazy substitution
417 ------------------------------------
418 matchRule :: (Activation -> Bool) -> IdUnfoldingFun
420 -> [CoreExpr] -> [Maybe Name]
421 -> CoreRule -> Maybe CoreExpr
423 -- If (matchRule rule args) returns Just (name,rhs)
424 -- then (f args) matches the rule, and the corresponding
425 -- rewritten RHS is rhs
427 -- The bndrs and rhs is occurrence-analysed
432 -- forall f g x. map f (map g x) ==> map (f . g) x
434 -- CoreRule "map/map"
435 -- [f,g,x] -- tpl_vars
436 -- [f,map g x] -- tpl_args
437 -- map (f.g) x) -- rhs
439 -- Then the call: matchRule the_rule [e1,map e2 e3]
440 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
442 -- Any 'surplus' arguments in the input are simply put on the end
445 matchRule _is_active id_unf _in_scope args _rough_args
446 (BuiltinRule { ru_try = match_fn })
447 -- Built-in rules can't be switched off, it seems
448 = case match_fn id_unf args of
449 Just expr -> Just expr
452 matchRule is_active id_unf in_scope args rough_args
453 (Rule { ru_act = act, ru_rough = tpl_tops,
454 ru_bndrs = tpl_vars, ru_args = tpl_args,
456 | not (is_active act) = Nothing
457 | ruleCantMatch tpl_tops rough_args = Nothing
459 = case matchN id_unf in_scope tpl_vars tpl_args args of
461 Just (bind_wrapper, tpl_vals) -> Just (bind_wrapper $
462 rule_fn `mkApps` tpl_vals)
464 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
465 -- We could do this when putting things into the rulebase, I guess
467 ---------------------------------------
468 matchN :: IdUnfoldingFun
469 -> InScopeSet -- ^ In-scope variables
470 -> [Var] -- ^ Match template type variables
471 -> [CoreExpr] -- ^ Match template
472 -> [CoreExpr] -- ^ Target; can have more elements than the template
473 -> Maybe (BindWrapper, -- Floated bindings; see Note [Matching lets]
475 -- For a given match template and context, find bindings to wrap around
476 -- the entire result and what should be substituted for each template variable.
477 -- Fail if there are two few actual arguments from the target to match the template
479 matchN id_unf in_scope tmpl_vars tmpl_es target_es
480 = do { (tv_subst, id_subst, binds)
481 <- go init_menv emptySubstEnv tmpl_es target_es
483 map (lookup_tmpl tv_subst id_subst) tmpl_vars') }
485 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
486 -- See Note [Template binders]
488 init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env }
490 go _ subst [] _ = Just subst
491 go _ _ _ [] = Nothing -- Fail if too few actual args
492 go menv subst (t:ts) (e:es) = do { subst1 <- match id_unf menv subst t e
493 ; go menv subst1 ts es }
495 lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr
496 lookup_tmpl tv_subst id_subst tmpl_var'
497 | isTyCoVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of
499 Nothing -> unbound tmpl_var'
500 | otherwise = case lookupVarEnv id_subst tmpl_var' of
502 _ -> unbound tmpl_var'
504 unbound var = pprPanic "Template variable unbound in rewrite rule"
505 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
508 Note [Template binders]
509 ~~~~~~~~~~~~~~~~~~~~~~~
510 Consider the following match:
511 Template: forall x. f x
513 This should succeed, because the template variable 'x' has
514 nothing to do with the 'x' in the target.
516 On reflection, this case probably does just work, but this might not
517 Template: forall x. f (\x.x)
519 Here we want to clone when we find the \x, but to know that x must be in scope
521 To achive this, we use rnBndrL to rename the template variables if
522 necessary; the renamed ones are the tmpl_vars'
525 ---------------------------------------------
526 The inner workings of matching
527 ---------------------------------------------
530 -- These two definitions are not the same as in Subst,
531 -- but they simple and direct, and purely local to this module
533 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
534 -- variables passed into the match.
536 -- * The BindWrapper in a SubstEnv are the bindings floated out
537 -- from nested matches; see the Let case of match, below
539 type SubstEnv = (TvSubstEnv, IdSubstEnv, BindWrapper)
541 type BindWrapper = CoreExpr -> CoreExpr
542 -- See Notes [Matching lets] and [Matching cases]
543 -- we represent the floated bindings as a core-to-core function
545 type IdSubstEnv = IdEnv CoreExpr
547 emptySubstEnv :: SubstEnv
548 emptySubstEnv = (emptyVarEnv, emptyVarEnv, \e -> e)
550 -- At one stage I tried to match even if there are more
551 -- template args than real args.
553 -- I now think this is probably a bad idea.
554 -- Should the template (map f xs) match (map g)? I think not.
555 -- For a start, in general eta expansion wastes work.
559 match :: IdUnfoldingFun
562 -> CoreExpr -- Template
563 -> CoreExpr -- Target
566 -- See the notes with Unify.match, which matches types
567 -- Everything is very similar for terms
569 -- Interesting examples:
571 -- \x->f against \f->f
572 -- When we meet the lambdas we must remember to rename f to f' in the
573 -- second expresion. The RnEnv2 does that.
576 -- forall a. \b->b against \a->3
577 -- We must rename the \a. Otherwise when we meet the lambdas we
578 -- might substitute [a/b] in the template, and then erroneously
579 -- succeed in matching what looks like the template variable 'a' against 3.
581 -- The Var case follows closely what happens in Unify.match
582 match idu menv subst (Var v1) e2
583 | Just subst <- match_var idu menv subst v1 e2
586 match idu menv subst (Note _ e1) e2 = match idu menv subst e1 e2
587 match idu menv subst e1 (Note _ e2) = match idu menv subst e1 e2
588 -- Ignore notes in both template and thing to be matched
589 -- See Note [Notes in RULE matching]
591 match id_unfolding_fun menv subst e1 (Var v2) -- Note [Expanding variables]
592 | not (inRnEnvR rn_env v2) -- Note [Do not expand locally-bound variables]
593 , Just e2' <- expandUnfolding_maybe (id_unfolding_fun v2')
594 = match id_unfolding_fun (menv { me_env = nukeRnEnvR rn_env }) subst e1 e2'
596 v2' = lookupRnInScope rn_env v2
598 -- Notice that we look up v2 in the in-scope set
599 -- See Note [Lookup in-scope]
600 -- No need to apply any renaming first (hence no rnOccR)
601 -- because of the not-inRnEnvR
603 match idu menv (tv_subst, id_subst, binds) e1 (Let bind e2)
604 | okToFloat rn_env bndrs (bindFreeVars bind) -- See Note [Matching lets]
605 = match idu (menv { me_env = rn_env' })
606 (tv_subst, id_subst, binds . Let bind)
610 rn_env' = extendRnInScopeList rn_env bndrs
611 bndrs = bindersOf bind
613 {- Disabled: see Note [Matching cases] below
614 match idu menv (tv_subst, id_subst, binds) e1
615 (Case scrut case_bndr ty [(con, alt_bndrs, rhs)])
616 | exprOkForSpeculation scrut -- See Note [Matching cases]
617 , okToFloat rn_env bndrs (exprFreeVars scrut)
618 = match idu (menv { me_env = rn_env' })
619 (tv_subst, id_subst, binds . case_wrap)
623 rn_env' = extendRnInScopeList rn_env bndrs
624 bndrs = case_bndr : alt_bndrs
625 case_wrap rhs' = Case scrut case_bndr ty [(con, alt_bndrs, rhs')]
628 match _ _ subst (Lit lit1) (Lit lit2)
632 match idu menv subst (App f1 a1) (App f2 a2)
633 = do { subst' <- match idu menv subst f1 f2
634 ; match idu menv subst' a1 a2 }
636 match idu menv subst (Lam x1 e1) (Lam x2 e2)
637 = match idu menv' subst e1 e2
639 menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
641 -- This rule does eta expansion
642 -- (\x.M) ~ N iff M ~ N x
643 -- It's important that this is *after* the let rule,
644 -- so that (\x.M) ~ (let y = e in \y.N)
645 -- does the let thing, and then gets the lam/lam rule above
646 match idu menv subst (Lam x1 e1) e2
647 = match idu menv' subst e1 (App e2 (varToCoreExpr new_x))
649 (rn_env', new_x) = rnEtaL (me_env menv) x1
650 menv' = menv { me_env = rn_env' }
652 -- Eta expansion the other way
653 -- M ~ (\y.N) iff M y ~ N
654 match idu menv subst e1 (Lam x2 e2)
655 = match idu menv' subst (App e1 (varToCoreExpr new_x)) e2
657 (rn_env', new_x) = rnEtaR (me_env menv) x2
658 menv' = menv { me_env = rn_env' }
660 match idu menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
661 = do { subst1 <- match_ty menv subst ty1 ty2
662 ; subst2 <- match idu menv subst1 e1 e2
663 ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 }
664 ; match_alts idu menv' subst2 alts1 alts2 -- Alts are both sorted
667 match _ menv subst (Type ty1) (Type ty2)
668 = match_ty menv subst ty1 ty2
670 match idu menv subst (Cast e1 co1) (Cast e2 co2)
671 = do { subst1 <- match_ty menv subst co1 co2
672 ; match idu menv subst1 e1 e2 }
674 -- Everything else fails
675 match _ _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
678 ------------------------------------------
679 okToFloat :: RnEnv2 -> [Var] -> VarSet -> Bool
680 okToFloat rn_env bndrs bind_fvs
681 = all freshly_bound bndrs
682 && foldVarSet ((&&) . not_captured) True bind_fvs
684 freshly_bound x = not (x `rnInScope` rn_env)
685 not_captured fv = not (inRnEnvR rn_env fv)
687 ------------------------------------------
688 match_var :: IdUnfoldingFun
692 -> CoreExpr -- Target
694 match_var idu menv subst@(tv_subst, id_subst, binds) v1 e2
695 | v1' `elemVarSet` me_tmpls menv
696 = case lookupVarEnv id_subst v1' of
697 Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
698 -> Nothing -- Occurs check failure
699 -- e.g. match forall a. (\x-> a x) against (\y. y y)
701 | otherwise -- No renaming to do on e2, because no free var
702 -- of e2 is in the rnEnvR of the envt
703 -- Note [Matching variable types]
704 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
705 -- However, we must match the *types*; e.g.
706 -- forall (c::Char->Int) (x::Char).
707 -- f (c x) = "RULE FIRED"
708 -- We must only match on args that have the right type
709 -- It's actually quite difficult to come up with an example that shows
710 -- you need type matching, esp since matching is left-to-right, so type
711 -- args get matched first. But it's possible (e.g. simplrun008) and
712 -- this is the Right Thing to do
713 -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2)
714 -- c.f. match_ty below
715 ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) }
717 Just e1' | eqExprX idu (nukeRnEnvL rn_env) e1' e2
723 | otherwise -- v1 is not a template variable; check for an exact match with e2
725 Var v2 | v1' == rnOccR rn_env v2 -> Just subst
730 v1' = rnOccL rn_env v1
731 -- If the template is
732 -- forall x. f x (\x -> x) = ...
733 -- Then the x inside the lambda isn't the
734 -- template x, so we must rename first!
737 ------------------------------------------
738 match_alts :: IdUnfoldingFun
741 -> [CoreAlt] -- Template
742 -> [CoreAlt] -- Target
744 match_alts _ _ subst [] []
746 match_alts idu menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
748 = do { subst1 <- match idu menv' subst r1 r2
749 ; match_alts idu menv subst1 alts1 alts2 }
752 menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 }
757 ------------------------------------------
763 -- Matching Core types: use the matcher in TcType.
764 -- Notice that we treat newtypes as opaque. For example, suppose
765 -- we have a specialised version of a function at a newtype, say
766 -- newtype T = MkT Int
767 -- We only want to replace (f T) with f', not (f Int).
769 match_ty menv (tv_subst, id_subst, binds) ty1 ty2
770 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
771 ; return (tv_subst', id_subst, binds) }
774 Note [Expanding variables]
775 ~~~~~~~~~~~~~~~~~~~~~~~~~~
776 Here is another Very Important rule: if the term being matched is a
777 variable, we expand it so long as its unfolding is "expandable". (Its
778 occurrence information is not necessarily up to date, so we don't use
779 it.) By "expandable" we mean a WHNF or a "constructor-like" application.
780 This is the key reason for "constructor-like" Ids. If we have
781 {-# NOINLINE [1] CONLIKE g #-}
782 {-# RULE f (g x) = h x #-}
784 let v = g 3 in ....(f v)....
785 we want to make the rule fire, to replace (f v) with (h 3).
787 Note [Do not expand locally-bound variables]
788 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
789 Do *not* expand locally-bound variables, else there's a worry that the
790 unfolding might mention variables that are themselves renamed.
792 case x of y { (p,q) -> ...y... }
793 Don't expand 'y' to (p,q) because p,q might themselves have been
794 renamed. Essentially we only expand unfoldings that are "outside"
797 Hence, (a) the guard (not (isLocallyBoundR v2))
798 (b) when we expand we nuke the renaming envt (nukeRnEnvR).
800 Note [Notes in RULE matching]
801 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
802 Look through Notes in both template and expression being matched. In
803 particular, we don't want to be confused by InlineMe notes. Maybe we
804 should be more careful about profiling notes, but for now I'm just
805 riding roughshod over them. cf Note [Notes in call patterns] in
810 Matching a let-expression. Consider
811 RULE forall x. f (g x) = <rhs>
812 and target expression
813 f (let { w=R } in g E))
814 Then we'd like the rule to match, to generate
815 let { w=R } in (\x. <rhs>) E
816 In effect, we want to float the let-binding outward, to enable
817 the match to happen. This is the WHOLE REASON for accumulating
818 bindings in the SubstEnv
820 We can only do this if
821 (a) Widening the scope of w does not capture any variables
822 We use a conservative test: w is not already in scope
823 If not, we clone the binders, and substitute
824 (b) The free variables of R are not bound by the part of the
825 target expression outside the let binding; e.g.
826 f (\v. let w = v+1 in g E)
827 Here we obviously cannot float the let-binding for w.
829 You may think rule (a) would never apply, because rule matching is
830 mostly invoked from the simplifier, when we have just run substExpr
831 over the argument, so there will be no shadowing anyway.
832 The fly in the ointment is that the forall'd variables of the
833 RULE itself are considered in scope.
835 I though of various ways to solve (a). One plan was to
836 clone the binders if they are in scope. But watch out!
837 (let x=y+1 in let z=x+1 in (z,z)
838 --> should match (p,p) but watch out that
839 the use of x on z's rhs is OK!
840 If we clone x, then the let-binding for 'z' is then caught by (b),
841 at least unless we elaborate the RnEnv stuff a bit.
843 So for we simply fail to match unless both (a) and (b) hold.
845 Other cases to think about
846 (let x=y+1 in \x. (x,x))
847 --> let x=y+1 in (\x1. (x1,x1))
848 (\x. let x = y+1 in (x,x))
849 --> let x1 = y+1 in (\x. (x1,x1)
850 (let x=y+1 in (x,x), let x=y-1 in (x,x))
851 --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1))
853 Note [Matching cases]
854 ~~~~~~~~~~~~~~~~~~~~~
855 {- NOTE: This idea is currently disabled. It really only works if
856 the primops involved are OkForSpeculation, and, since
857 they have side effects readIntOfAddr and touch are not.
858 Maybe we'll get back to this later . -}
861 f (case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
862 case touch# fp s# of { _ ->
864 This happened in a tight loop generated by stream fusion that
865 Roman encountered. We'd like to treat this just like the let
866 case, because the primops concerned are ok-for-speculation.
867 That is, we'd like to behave as if it had been
868 case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
869 case touch# fp s# of { _ ->
872 Note [Lookup in-scope]
873 ~~~~~~~~~~~~~~~~~~~~~~
874 Consider this example
875 foo :: Int -> Maybe Int -> Int
877 foo m (Just n) = foo (m-n) (Just n)
879 SpecConstr sees this fragment:
881 case w_smT of wild_Xf [Just A] {
882 Data.Maybe.Nothing -> lvl_smf;
883 Data.Maybe.Just n_acT [Just S(L)] ->
884 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
885 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
888 and correctly generates the rule
890 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
891 sc_snn :: GHC.Prim.Int#}
892 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
893 = \$s\$wfoo_sno y_amr sc_snn ;]
895 BUT we must ensure that this rule matches in the original function!
896 Note that the call to \$wfoo is
897 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
899 During matching we expand wild_Xf to (Just n_acT). But then we must also
900 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
901 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
904 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
907 %************************************************************************
909 Rule-check the program
911 %************************************************************************
913 We want to know what sites have rules that could have fired but didn't.
914 This pass runs over the tree (without changing it) and reports such.
917 -- | Report partial matches for rules beginning with the specified
918 -- string for the purposes of error reporting
919 ruleCheckProgram :: CompilerPhase -- ^ Rule activation test
920 -> String -- ^ Rule pattern
921 -> RuleBase -- ^ Database of rules
922 -> [CoreBind] -- ^ Bindings to check in
923 -> SDoc -- ^ Resulting check message
924 ruleCheckProgram phase rule_pat rule_base binds
926 = text "Rule check results: no rule application sites"
928 = vcat [text "Rule check results:",
930 vcat [ p $$ line | p <- bagToList results ]
933 env = RuleCheckEnv { rc_is_active = isActive phase
934 , rc_id_unf = idUnfolding -- Not quite right
935 -- Should use activeUnfolding
936 , rc_pattern = rule_pat
937 , rc_rule_base = rule_base }
938 results = unionManyBags (map (ruleCheckBind env) binds)
939 line = text (replicate 20 '-')
941 data RuleCheckEnv = RuleCheckEnv {
942 rc_is_active :: Activation -> Bool,
943 rc_id_unf :: IdUnfoldingFun,
944 rc_pattern :: String,
945 rc_rule_base :: RuleBase
948 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
949 -- The Bag returned has one SDoc for each call site found
950 ruleCheckBind env (NonRec _ r) = ruleCheck env r
951 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (_,r) <- prs]
953 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
954 ruleCheck _ (Var _) = emptyBag
955 ruleCheck _ (Lit _) = emptyBag
956 ruleCheck _ (Type _) = emptyBag
957 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
958 ruleCheck env (Note _ e) = ruleCheck env e
959 ruleCheck env (Cast e _) = ruleCheck env e
960 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
961 ruleCheck env (Lam _ e) = ruleCheck env e
962 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
963 unionManyBags [ruleCheck env r | (_,_,r) <- as]
965 ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
966 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
967 ruleCheckApp env (Var f) as = ruleCheckFun env f as
968 ruleCheckApp env other _ = ruleCheck env other
972 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
973 -- Produce a report for all rules matching the predicate
974 -- saying why it doesn't match the specified application
976 ruleCheckFun env fn args
977 | null name_match_rules = emptyBag
978 | otherwise = unitBag (ruleAppCheck_help env fn args name_match_rules)
980 name_match_rules = filter match (getRules (rc_rule_base env) fn)
981 match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
983 ruleAppCheck_help :: RuleCheckEnv -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
984 ruleAppCheck_help env fn args rules
985 = -- The rules match the pattern, so we want to print something
986 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
987 vcat (map check_rule rules)]
990 i_args = args `zip` [1::Int ..]
991 rough_args = map roughTopName args
993 check_rule rule = rule_herald rule <> colon <+> rule_info rule
995 rule_herald (BuiltinRule { ru_name = name })
996 = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
997 rule_herald (Rule { ru_name = name })
998 = ptext (sLit "Rule") <+> doubleQuotes (ftext name)
1001 | Just _ <- matchRule noBlackList (rc_id_unf env) emptyInScopeSet args rough_args rule
1002 = text "matches (which is very peculiar!)"
1004 rule_info (BuiltinRule {}) = text "does not match"
1006 rule_info (Rule { ru_act = act,
1007 ru_bndrs = rule_bndrs, ru_args = rule_args})
1008 | not (rc_is_active env act) = text "active only in later phase"
1009 | n_args < n_rule_args = text "too few arguments"
1010 | n_mismatches == n_rule_args = text "no arguments match"
1011 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
1012 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
1014 n_rule_args = length rule_args
1015 n_mismatches = length mismatches
1016 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
1017 not (isJust (match_fn rule_arg arg))]
1019 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
1020 match_fn rule_arg arg = match (rc_id_unf env) menv emptySubstEnv rule_arg arg
1022 in_scope = lhs_fvs `unionVarSet` exprFreeVars arg
1023 menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope)
1024 , me_tmpls = mkVarSet rule_bndrs }