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
34 import OccurAnal ( occurAnalyseExpr )
35 import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars )
36 import CoreUtils ( exprType, eqExpr )
37 import PprCore ( pprRules )
39 import TcType ( tcSplitTyConApp_maybe )
41 import CoreTidy ( tidyRules )
43 import IdInfo ( SpecInfo( SpecInfo ) )
46 import Name ( Name, NamedThing(..) )
48 import Unify ( ruleMatchTyX, MatchEnv(..) )
49 import BasicTypes ( Activation, CompilerPhase, isActive )
50 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 (Coercion _) = Nothing
189 roughTopName (App f _) = roughTopName f
190 roughTopName (Var f) | isGlobalId f -- Note [Care with roughTopName]
191 , isDataConWorkId f || idArity f > 0
193 roughTopName _ = Nothing
195 ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool
196 -- ^ @ruleCantMatch tpl actual@ returns True only if @actual@
197 -- definitely can't match @tpl@ by instantiating @tpl@.
198 -- It's only a one-way match; unlike instance matching we
199 -- don't consider unification.
202 -- @ruleCantMatch [Nothing] [Just n2] = False@
203 -- Reason: a template variable can be instantiated by a constant
205 -- @ruleCantMatch [Just n1] [Nothing] = False@
206 -- Reason: a local variable @v@ in the actuals might [_$_]
208 ruleCantMatch (Just n1 : ts) (Just n2 : as) = n1 /= n2 || ruleCantMatch ts as
209 ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as
210 ruleCantMatch _ _ = False
213 Note [Care with roughTopName]
214 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
216 module M where { x = a:b }
217 module N where { ...f x...
219 You'd expect the rule to match, because the matcher can
220 look through the unfolding of 'x'. So we must avoid roughTopName
221 returning 'M.x' for the call (f x), or else it'll say "can't match"
222 and we won't even try!!
224 However, suppose we have
226 foo = ...(g (M.k v))....
227 where k is a *function* exported by M. We never really match
228 functions (lambdas) except by name, so in this case it seems like
229 a good idea to treat 'M.k' as a roughTopName of the call.
233 pprRulesForUser :: [CoreRule] -> SDoc
234 -- (a) tidy the rules
235 -- (b) sort them into order based on the rule name
236 -- (c) suppress uniques (unless -dppr-debug is on)
237 -- This combination makes the output stable so we can use in testing
238 -- It's here rather than in PprCore because it calls tidyRules
239 pprRulesForUser rules
240 = withPprStyle defaultUserStyle $
243 tidyRules emptyTidyEnv rules
245 le_rule r1 r2 = ru_name r1 <= ru_name r2
249 %************************************************************************
251 SpecInfo: the rules in an IdInfo
253 %************************************************************************
256 -- | Make a 'SpecInfo' containing a number of 'CoreRule's, suitable
257 -- for putting into an 'IdInfo'
258 mkSpecInfo :: [CoreRule] -> SpecInfo
259 mkSpecInfo rules = SpecInfo rules (rulesFreeVars rules)
261 extendSpecInfo :: SpecInfo -> [CoreRule] -> SpecInfo
262 extendSpecInfo (SpecInfo rs1 fvs1) rs2
263 = SpecInfo (rs2 ++ rs1) (rulesFreeVars rs2 `unionVarSet` fvs1)
265 addSpecInfo :: SpecInfo -> SpecInfo -> SpecInfo
266 addSpecInfo (SpecInfo rs1 fvs1) (SpecInfo rs2 fvs2)
267 = SpecInfo (rs1 ++ rs2) (fvs1 `unionVarSet` fvs2)
269 addIdSpecialisations :: Id -> [CoreRule] -> Id
270 addIdSpecialisations id []
272 addIdSpecialisations id rules
273 = setIdSpecialisation id $
274 extendSpecInfo (idSpecialisation id) rules
276 -- | Gather all the rules for locally bound identifiers from the supplied bindings
277 rulesOfBinds :: [CoreBind] -> [CoreRule]
278 rulesOfBinds binds = concatMap (concatMap idCoreRules . bindersOf) binds
280 getRules :: RuleBase -> Id -> [CoreRule]
281 -- See Note [Where rules are found]
282 getRules rule_base fn
283 = idCoreRules fn ++ imp_rules
285 imp_rules = lookupNameEnv rule_base (idName fn) `orElse` []
288 Note [Where rules are found]
289 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
290 The rules for an Id come from two places:
291 (a) the ones it is born with, stored inside the Id iself (idCoreRules fn),
292 (b) rules added in other modules, stored in the global RuleBase (imp_rules)
294 It's tempting to think that
295 - LocalIds have only (a)
296 - non-LocalIds have only (b)
298 but that isn't quite right:
300 - PrimOps and ClassOps are born with a bunch of rules inside the Id,
301 even when they are imported
303 - The rules in PrelRules.builtinRules should be active even
304 in the module defining the Id (when it's a LocalId), but
305 the rules are kept in the global RuleBase
308 %************************************************************************
312 %************************************************************************
315 -- | Gathers a collection of 'CoreRule's. Maps (the name of) an 'Id' to its rules
316 type RuleBase = NameEnv [CoreRule]
317 -- The rules are are unordered;
318 -- we sort out any overlaps on lookup
320 emptyRuleBase :: RuleBase
321 emptyRuleBase = emptyNameEnv
323 mkRuleBase :: [CoreRule] -> RuleBase
324 mkRuleBase rules = extendRuleBaseList emptyRuleBase rules
326 extendRuleBaseList :: RuleBase -> [CoreRule] -> RuleBase
327 extendRuleBaseList rule_base new_guys
328 = foldl extendRuleBase rule_base new_guys
330 unionRuleBase :: RuleBase -> RuleBase -> RuleBase
331 unionRuleBase rb1 rb2 = plusNameEnv_C (++) rb1 rb2
333 extendRuleBase :: RuleBase -> CoreRule -> RuleBase
334 extendRuleBase rule_base rule
335 = extendNameEnv_Acc (:) singleton rule_base (ruleIdName rule) rule
337 pprRuleBase :: RuleBase -> SDoc
338 pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs)
339 | rs <- nameEnvElts rules ]
343 %************************************************************************
347 %************************************************************************
350 -- | The main rule matching function. Attempts to apply all (active)
351 -- supplied rules to this instance of an application in a given
352 -- context, returning the rule applied and the resulting expression if
354 lookupRule :: (Activation -> Bool) -- When rule is active
355 -> IdUnfoldingFun -- When Id can be unfolded
358 -> [CoreRule] -> Maybe (CoreRule, CoreExpr)
360 -- See Note [Extra args in rule matching]
361 -- See comments on matchRule
362 lookupRule is_active id_unf in_scope fn args rules
363 = -- pprTrace "matchRules" (ppr fn <+> ppr args $$ ppr rules ) $
366 (m:ms) -> Just (findBest (fn,args) m ms)
368 rough_args = map roughTopName args
370 go :: [(CoreRule,CoreExpr)] -> [CoreRule] -> [(CoreRule,CoreExpr)]
372 go ms (r:rs) = case (matchRule is_active id_unf in_scope args rough_args r) of
373 Just e -> go ((r,e):ms) rs
374 Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$
375 -- ppr [ (arg_id, unfoldingTemplate unf)
376 -- | Var arg_id <- args
377 -- , let unf = idUnfolding arg_id
378 -- , isCheapUnfolding unf] )
381 findBest :: (Id, [CoreExpr])
382 -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr)
383 -- All these pairs matched the expression
384 -- Return the pair the the most specific rule
385 -- The (fn,args) is just for overlap reporting
387 findBest _ (rule,ans) [] = (rule,ans)
388 findBest target (rule1,ans1) ((rule2,ans2):prs)
389 | rule1 `isMoreSpecific` rule2 = findBest target (rule1,ans1) prs
390 | rule2 `isMoreSpecific` rule1 = findBest target (rule2,ans2) prs
391 | debugIsOn = let pp_rule rule
392 | opt_PprStyle_Debug = ppr rule
393 | otherwise = doubleQuotes (ftext (ru_name rule))
394 in pprTrace "Rules.findBest: rule overlap (Rule 1 wins)"
395 (vcat [if opt_PprStyle_Debug then
396 ptext (sLit "Expression to match:") <+> ppr fn <+> sep (map ppr args)
398 ptext (sLit "Rule 1:") <+> pp_rule rule1,
399 ptext (sLit "Rule 2:") <+> pp_rule rule2]) $
400 findBest target (rule1,ans1) prs
401 | otherwise = findBest target (rule1,ans1) prs
405 isMoreSpecific :: CoreRule -> CoreRule -> Bool
406 -- This tests if one rule is more specific than another
407 -- We take the view that a BuiltinRule is less specific than
408 -- anything else, because we want user-define rules to "win"
409 -- In particular, class ops have a built-in rule, but we
410 -- any user-specific rules to win
412 -- truncate :: (RealFrac a, Integral b) => a -> b
413 -- {-# RULES "truncate/Double->Int" truncate = double2Int #-}
414 -- double2Int :: Double -> Int
415 -- We want the specific RULE to beat the built-in class-op rule
416 isMoreSpecific (BuiltinRule {}) _ = False
417 isMoreSpecific (Rule {}) (BuiltinRule {}) = True
418 isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 })
419 (Rule { ru_bndrs = bndrs2, ru_args = args2 })
420 = isJust (matchN id_unfolding_fun in_scope bndrs2 args2 args1)
422 id_unfolding_fun _ = NoUnfolding -- Don't expand in templates
423 in_scope = mkInScopeSet (mkVarSet bndrs1)
424 -- Actually we should probably include the free vars
425 -- of rule1's args, but I can't be bothered
427 noBlackList :: Activation -> Bool
428 noBlackList _ = False -- Nothing is black listed
431 Note [Extra args in rule matching]
432 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
433 If we find a matching rule, we return (Just (rule, rhs)),
434 but the rule firing has only consumed as many of the input args
435 as the ruleArity says. It's up to the caller to keep track
436 of any left-over args. E.g. if you call
437 lookupRule ... f [e1, e2, e3]
438 and it returns Just (r, rhs), where r has ruleArity 2
439 then the real rewrite is
440 f e1 e2 e3 ==> rhs e3
442 You might think it'd be cleaner for lookupRule to deal with the
443 leftover arguments, by applying 'rhs' to them, but the main call
444 in the Simplifier works better as it is. Reason: the 'args' passed
445 to lookupRule are the result of a lazy substitution
448 ------------------------------------
449 matchRule :: (Activation -> Bool) -> IdUnfoldingFun
451 -> [CoreExpr] -> [Maybe Name]
452 -> CoreRule -> Maybe CoreExpr
454 -- If (matchRule rule args) returns Just (name,rhs)
455 -- then (f args) matches the rule, and the corresponding
456 -- rewritten RHS is rhs
458 -- The bndrs and rhs is occurrence-analysed
463 -- forall f g x. map f (map g x) ==> map (f . g) x
465 -- CoreRule "map/map"
466 -- [f,g,x] -- tpl_vars
467 -- [f,map g x] -- tpl_args
468 -- map (f.g) x) -- rhs
470 -- Then the call: matchRule the_rule [e1,map e2 e3]
471 -- = Just ("map/map", (\f,g,x -> rhs) e1 e2 e3)
473 -- Any 'surplus' arguments in the input are simply put on the end
476 matchRule _is_active id_unf _in_scope args _rough_args
477 (BuiltinRule { ru_try = match_fn })
478 -- Built-in rules can't be switched off, it seems
479 = case match_fn id_unf args of
480 Just expr -> Just expr
483 matchRule is_active id_unf in_scope args rough_args
484 (Rule { ru_act = act, ru_rough = tpl_tops,
485 ru_bndrs = tpl_vars, ru_args = tpl_args,
487 | not (is_active act) = Nothing
488 | ruleCantMatch tpl_tops rough_args = Nothing
490 = case matchN id_unf in_scope tpl_vars tpl_args args of
492 Just (bind_wrapper, tpl_vals) -> Just (bind_wrapper $
493 rule_fn `mkApps` tpl_vals)
495 rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs)
496 -- We could do this when putting things into the rulebase, I guess
498 ---------------------------------------
499 matchN :: IdUnfoldingFun
500 -> InScopeSet -- ^ In-scope variables
501 -> [Var] -- ^ Match template type variables
502 -> [CoreExpr] -- ^ Match template
503 -> [CoreExpr] -- ^ Target; can have more elements than the template
504 -> Maybe (BindWrapper, -- Floated bindings; see Note [Matching lets]
506 -- For a given match template and context, find bindings to wrap around
507 -- the entire result and what should be substituted for each template variable.
508 -- Fail if there are two few actual arguments from the target to match the template
510 matchN id_unf in_scope tmpl_vars tmpl_es target_es
511 = do { subst <- go init_menv emptyRuleSubst tmpl_es target_es
512 ; return (rs_binds subst,
513 map (lookup_tmpl subst) tmpl_vars') }
515 (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars
516 -- See Note [Template binders]
518 init_menv = RV { rv_tmpls = mkVarSet tmpl_vars', rv_lcl = init_rn_env
519 , rv_fltR = mkEmptySubst (rnInScopeSet init_rn_env)
522 go _ subst [] _ = Just subst
523 go _ _ _ [] = Nothing -- Fail if too few actual args
524 go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e
525 ; go menv subst1 ts es }
527 lookup_tmpl :: RuleSubst -> Var -> CoreExpr
528 lookup_tmpl (RS { rs_tv_subst = tv_subst, rs_id_subst = id_subst }) tmpl_var'
529 | isId tmpl_var' = case lookupVarEnv id_subst tmpl_var' of
531 _ -> unbound tmpl_var'
532 | otherwise = case lookupVarEnv tv_subst tmpl_var' of
534 Nothing -> unbound tmpl_var'
536 unbound var = pprPanic "Template variable unbound in rewrite rule"
537 (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es)
540 Note [Template binders]
541 ~~~~~~~~~~~~~~~~~~~~~~~
542 Consider the following match:
543 Template: forall x. f x
545 This should succeed, because the template variable 'x' has
546 nothing to do with the 'x' in the target.
548 On reflection, this case probably does just work, but this might not
549 Template: forall x. f (\x.x)
551 Here we want to clone when we find the \x, but to know that x must be in scope
553 To achive this, we use rnBndrL to rename the template variables if
554 necessary; the renamed ones are the tmpl_vars'
557 %************************************************************************
561 %************************************************************************
563 ---------------------------------------------
564 The inner workings of matching
565 ---------------------------------------------
568 -- * The domain of the TvSubstEnv and IdSubstEnv are the template
569 -- variables passed into the match.
571 -- * The BindWrapper in a RuleSubst are the bindings floated out
572 -- from nested matches; see the Let case of match, below
574 data RuleEnv = RV { rv_tmpls :: VarSet -- Template variables
575 , rv_lcl :: RnEnv2 -- Renamings for *local bindings*
577 , rv_fltR :: Subst -- Renamings for floated let-bindings
578 -- domain disjoint from envR of rv_lcl
579 -- See Note [Matching lets]
580 , rv_unf :: IdUnfoldingFun
583 data RuleSubst = RS { rs_tv_subst :: TvSubstEnv -- Range is the
584 , rs_id_subst :: IdSubstEnv -- template variables
585 , rs_binds :: BindWrapper -- Floated bindings
586 , rs_bndrs :: VarSet -- Variables bound by floated lets
589 type BindWrapper = CoreExpr -> CoreExpr
590 -- See Notes [Matching lets] and [Matching cases]
591 -- we represent the floated bindings as a core-to-core function
593 emptyRuleSubst :: RuleSubst
594 emptyRuleSubst = RS { rs_tv_subst = emptyVarEnv, rs_id_subst = emptyVarEnv
595 , rs_binds = \e -> e, rs_bndrs = emptyVarSet }
597 -- At one stage I tried to match even if there are more
598 -- template args than real args.
600 -- I now think this is probably a bad idea.
601 -- Should the template (map f xs) match (map g)? I think not.
602 -- For a start, in general eta expansion wastes work.
608 -> CoreExpr -- Template
609 -> CoreExpr -- Target
612 -- See the notes with Unify.match, which matches types
613 -- Everything is very similar for terms
615 -- Interesting examples:
617 -- \x->f against \f->f
618 -- When we meet the lambdas we must remember to rename f to f' in the
619 -- second expresion. The RnEnv2 does that.
622 -- forall a. \b->b against \a->3
623 -- We must rename the \a. Otherwise when we meet the lambdas we
624 -- might substitute [a/b] in the template, and then erroneously
625 -- succeed in matching what looks like the template variable 'a' against 3.
627 -- The Var case follows closely what happens in Unify.match
628 match renv subst (Var v1) e2 = match_var renv subst v1 e2
629 match renv subst (Note _ e1) e2 = match renv subst e1 e2
630 match renv subst e1 (Note _ e2) = match renv subst e1 e2
631 -- Ignore notes in both template and thing to be matched
632 -- See Note [Notes in RULE matching]
634 match renv subst e1 (Var v2) -- Note [Expanding variables]
635 | not (inRnEnvR rn_env v2) -- Note [Do not expand locally-bound variables]
636 , Just e2' <- expandUnfolding_maybe (rv_unf renv v2')
637 = match (renv { rv_lcl = nukeRnEnvR rn_env }) subst e1 e2'
639 v2' = lookupRnInScope rn_env v2
641 -- Notice that we look up v2 in the in-scope set
642 -- See Note [Lookup in-scope]
643 -- No need to apply any renaming first (hence no rnOccR)
644 -- because of the not-inRnEnvR
646 match renv subst e1 (Let bind e2)
647 | okToFloat (rv_lcl renv) (bindFreeVars bind) -- See Note [Matching lets]
648 = match (renv { rv_fltR = flt_subst' })
649 (subst { rs_binds = rs_binds subst . Let bind'
650 , rs_bndrs = extendVarSetList (rs_bndrs subst) new_bndrs })
653 flt_subst = addInScopeSet (rv_fltR renv) (rs_bndrs subst)
654 (flt_subst', bind') = substBind flt_subst bind
655 new_bndrs = bindersOf bind'
657 {- Disabled: see Note [Matching cases] below
658 match renv (tv_subst, id_subst, binds) e1
659 (Case scrut case_bndr ty [(con, alt_bndrs, rhs)])
660 | exprOkForSpeculation scrut -- See Note [Matching cases]
661 , okToFloat rn_env bndrs (exprFreeVars scrut)
662 = match (renv { me_env = rn_env' })
663 (tv_subst, id_subst, binds . case_wrap)
667 rn_env' = extendRnInScopeList rn_env bndrs
668 bndrs = case_bndr : alt_bndrs
669 case_wrap rhs' = Case scrut case_bndr ty [(con, alt_bndrs, rhs')]
672 match _ subst (Lit lit1) (Lit lit2)
676 match renv subst (App f1 a1) (App f2 a2)
677 = do { subst' <- match renv subst f1 f2
678 ; match renv subst' a1 a2 }
680 match renv subst (Lam x1 e1) (Lam x2 e2)
681 = match renv' subst e1 e2
683 renv' = renv { rv_lcl = rnBndr2 (rv_lcl renv) x1 x2
684 , rv_fltR = delBndr (rv_fltR renv) x2 }
686 -- This rule does eta expansion
687 -- (\x.M) ~ N iff M ~ N x
688 -- It's important that this is *after* the let rule,
689 -- so that (\x.M) ~ (let y = e in \y.N)
690 -- does the let thing, and then gets the lam/lam rule above
691 match renv subst (Lam x1 e1) e2
692 = match renv' subst e1 (App e2 (varToCoreExpr new_x))
694 (rn_env', new_x) = rnEtaL (rv_lcl renv) x1
695 renv' = renv { rv_lcl = rn_env' }
697 -- Eta expansion the other way
698 -- M ~ (\y.N) iff M y ~ N
699 match renv subst e1 (Lam x2 e2)
700 = match renv' subst (App e1 (varToCoreExpr new_x)) e2
702 (rn_env', new_x) = rnEtaR (rv_lcl renv) x2
703 renv' = renv { rv_lcl = rn_env' }
705 match renv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2)
706 = do { subst1 <- match_ty renv subst ty1 ty2
707 ; subst2 <- match renv subst1 e1 e2
708 ; let renv' = rnMatchBndr2 renv subst x1 x2
709 ; match_alts renv' subst2 alts1 alts2 -- Alts are both sorted
712 match renv subst (Type ty1) (Type ty2)
713 = match_ty renv subst ty1 ty2
714 match renv subst (Coercion co1) (Coercion co2)
715 = match_co renv subst co1 co2
717 match renv subst (Cast e1 co1) (Cast e2 co2)
718 = do { subst1 <- match_co renv subst co1 co2
719 ; match renv subst1 e1 e2 }
721 -- Everything else fails
722 match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $
731 match_co renv subst (CoVarCo cv) co
732 = match_var renv subst cv (Coercion co)
734 = pprTrace "match_co baling out" (ppr co1) Nothing
737 rnMatchBndr2 :: RuleEnv -> RuleSubst -> Var -> Var -> RuleEnv
738 rnMatchBndr2 renv subst x1 x2
739 = renv { rv_lcl = rnBndr2 rn_env x1 x2
740 , rv_fltR = delBndr (rv_fltR renv) x2 }
742 rn_env = addRnInScopeSet (rv_lcl renv) (rs_bndrs subst)
743 -- Typically this is a no-op, but it may matter if
744 -- there are some floated let-bindings
746 ------------------------------------------
747 match_alts :: RuleEnv
749 -> [CoreAlt] -- Template
750 -> [CoreAlt] -- Target
752 match_alts _ subst [] []
754 match_alts renv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2)
756 = do { subst1 <- match renv' subst r1 r2
757 ; match_alts renv subst1 alts1 alts2 }
759 renv' = foldl mb renv (vs1 `zip` vs2)
760 mb renv (v1,v2) = rnMatchBndr2 renv subst v1 v2
765 ------------------------------------------
766 okToFloat :: RnEnv2 -> VarSet -> Bool
767 okToFloat rn_env bind_fvs
768 = foldVarSet ((&&) . not_captured) True bind_fvs
770 not_captured fv = not (inRnEnvR rn_env fv)
772 ------------------------------------------
776 -> CoreExpr -- Target
778 match_var renv@(RV { rv_tmpls = tmpls, rv_lcl = rn_env, rv_fltR = flt_env })
780 | v1' `elemVarSet` tmpls
781 = match_tmpl_var renv subst v1' e2
783 | otherwise -- v1' is not a template variable; check for an exact match with e2
784 = case e2 of -- Remember, envR of rn_env is disjoint from rv_fltR
785 Var v2 | v1' == rnOccR rn_env v2
788 | Var v2' <- lookupIdSubst (text "match_var") flt_env v2
795 v1' = rnOccL rn_env v1
796 -- If the template is
797 -- forall x. f x (\x -> x) = ...
798 -- Then the x inside the lambda isn't the
799 -- template x, so we must rename first!
801 ------------------------------------------
802 match_tmpl_var :: RuleEnv
805 -> CoreExpr -- Target
808 match_tmpl_var renv@(RV { rv_lcl = rn_env, rv_fltR = flt_env })
809 subst@(RS { rs_id_subst = id_subst, rs_bndrs = let_bndrs })
811 | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2))
812 = Nothing -- Occurs check failure
813 -- e.g. match forall a. (\x-> a x) against (\y. y y)
815 | Just e1' <- lookupVarEnv id_subst v1'
816 = if eqExpr (rnInScopeSet rn_env) e1' e2'
821 = -- Note [Matching variable types]
822 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
823 -- However, we must match the *types*; e.g.
824 -- forall (c::Char->Int) (x::Char).
825 -- f (c x) = "RULE FIRED"
826 -- We must only match on args that have the right type
827 -- It's actually quite difficult to come up with an example that shows
828 -- you need type matching, esp since matching is left-to-right, so type
829 -- args get matched first. But it's possible (e.g. simplrun008) and
830 -- this is the Right Thing to do
831 do { subst' <- match_ty renv subst (idType v1') (exprType e2)
832 ; return (subst' { rs_id_subst = id_subst' }) }
834 -- e2' is the result of applying flt_env to e2
835 e2' | isEmptyVarSet let_bndrs = e2
836 | otherwise = substExpr (text "match_tmpl_var") flt_env e2
838 id_subst' = extendVarEnv (rs_id_subst subst) v1' e2'
839 -- No further renaming to do on e2',
840 -- because no free var of e2' is in the rnEnvR of the envt
842 ------------------------------------------
848 -- Matching Core types: use the matcher in TcType.
849 -- Notice that we treat newtypes as opaque. For example, suppose
850 -- we have a specialised version of a function at a newtype, say
851 -- newtype T = MkT Int
852 -- We only want to replace (f T) with f', not (f Int).
854 match_ty renv subst ty1 ty2
855 = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2
856 ; return (subst { rs_tv_subst = tv_subst' }) }
858 tv_subst = rs_tv_subst subst
859 menv = ME { me_tmpls = rv_tmpls renv, me_env = rv_lcl renv }
862 Note [Expanding variables]
863 ~~~~~~~~~~~~~~~~~~~~~~~~~~
864 Here is another Very Important rule: if the term being matched is a
865 variable, we expand it so long as its unfolding is "expandable". (Its
866 occurrence information is not necessarily up to date, so we don't use
867 it.) By "expandable" we mean a WHNF or a "constructor-like" application.
868 This is the key reason for "constructor-like" Ids. If we have
869 {-# NOINLINE [1] CONLIKE g #-}
870 {-# RULE f (g x) = h x #-}
872 let v = g 3 in ....(f v)....
873 we want to make the rule fire, to replace (f v) with (h 3).
875 Note [Do not expand locally-bound variables]
876 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
877 Do *not* expand locally-bound variables, else there's a worry that the
878 unfolding might mention variables that are themselves renamed.
880 case x of y { (p,q) -> ...y... }
881 Don't expand 'y' to (p,q) because p,q might themselves have been
882 renamed. Essentially we only expand unfoldings that are "outside"
885 Hence, (a) the guard (not (isLocallyBoundR v2))
886 (b) when we expand we nuke the renaming envt (nukeRnEnvR).
888 Note [Notes in RULE matching]
889 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
890 Look through Notes in both template and expression being matched. In
891 particular, we don't want to be confused by InlineMe notes. Maybe we
892 should be more careful about profiling notes, but for now I'm just
893 riding roughshod over them. cf Note [Notes in call patterns] in
898 Matching a let-expression. Consider
899 RULE forall x. f (g x) = <rhs>
900 and target expression
901 f (let { w=R } in g E))
902 Then we'd like the rule to match, to generate
903 let { w=R } in (\x. <rhs>) E
904 In effect, we want to float the let-binding outward, to enable
905 the match to happen. This is the WHOLE REASON for accumulating
906 bindings in the RuleSubst
908 We can only do this if the free variables of R are not bound by the
909 part of the target expression outside the let binding; e.g.
910 f (\v. let w = v+1 in g E)
911 Here we obviously cannot float the let-binding for w. Hence the
914 There are a couple of tricky points.
915 (a) What if floating the binding captures a variable?
916 f (let v = x+1 in v) v
918 let v = x+1 in f (x+1) v
920 (b) What if two non-nested let bindings bind the same variable?
921 f (let v = e1 in b1) (let v = e2 in b2)
923 let v = e1 in let v = e2 in (f b2 b2)
924 See testsuite test "RuleFloatLet".
926 Our cunning plan is this:
927 * Along with the growing substitution for template variables
928 we maintain a growing set of floated let-bindings (rs_binds)
929 plus the set of variables thus bound.
931 * The RnEnv2 in the MatchEnv binds only the local binders
932 in the term (lambdas, case)
934 * When we encounter a let in the term to be matched, we
935 check that does not mention any locally bound (lambda, case)
936 variables. If so we fail
938 * We use CoreSubst.substBind to freshen the binding, using an
939 in-scope set that is the original in-scope variables plus the
940 rs_bndrs (currently floated let-bindings). So in (a) above
941 we'll freshen the 'v' binding; in (b) above we'll freshen
942 the *second* 'v' binding.
944 * We apply that freshening substitution, in a lexically-scoped
945 way to the term, although lazily; this is the rv_fltR field.
948 Note [Matching cases]
949 ~~~~~~~~~~~~~~~~~~~~~
950 {- NOTE: This idea is currently disabled. It really only works if
951 the primops involved are OkForSpeculation, and, since
952 they have side effects readIntOfAddr and touch are not.
953 Maybe we'll get back to this later . -}
956 f (case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
957 case touch# fp s# of { _ ->
959 This happened in a tight loop generated by stream fusion that
960 Roman encountered. We'd like to treat this just like the let
961 case, because the primops concerned are ok-for-speculation.
962 That is, we'd like to behave as if it had been
963 case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) ->
964 case touch# fp s# of { _ ->
967 Note [Lookup in-scope]
968 ~~~~~~~~~~~~~~~~~~~~~~
969 Consider this example
970 foo :: Int -> Maybe Int -> Int
972 foo m (Just n) = foo (m-n) (Just n)
974 SpecConstr sees this fragment:
976 case w_smT of wild_Xf [Just A] {
977 Data.Maybe.Nothing -> lvl_smf;
978 Data.Maybe.Just n_acT [Just S(L)] ->
979 case n_acT of wild1_ams [Just A] { GHC.Base.I# y_amr [Just L] ->
980 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
983 and correctly generates the rule
985 RULES: "SC:$wfoo1" [0] __forall {y_amr [Just L] :: GHC.Prim.Int#
986 sc_snn :: GHC.Prim.Int#}
987 \$wfoo_smW sc_snn (Data.Maybe.Just @ GHC.Base.Int (GHC.Base.I# y_amr))
988 = \$s\$wfoo_sno y_amr sc_snn ;]
990 BUT we must ensure that this rule matches in the original function!
991 Note that the call to \$wfoo is
992 \$wfoo_smW (GHC.Prim.-# ds_Xmb y_amr) wild_Xf
994 During matching we expand wild_Xf to (Just n_acT). But then we must also
995 expand n_acT to (I# y_amr). And we can only do that if we look up n_acT
996 in the in-scope set, because in wild_Xf's unfolding it won't have an unfolding
999 That is why the 'lookupRnInScope' call in the (Var v2) case of 'match'
1002 %************************************************************************
1004 Rule-check the program
1006 %************************************************************************
1008 We want to know what sites have rules that could have fired but didn't.
1009 This pass runs over the tree (without changing it) and reports such.
1012 -- | Report partial matches for rules beginning with the specified
1013 -- string for the purposes of error reporting
1014 ruleCheckProgram :: CompilerPhase -- ^ Rule activation test
1015 -> String -- ^ Rule pattern
1016 -> RuleBase -- ^ Database of rules
1017 -> [CoreBind] -- ^ Bindings to check in
1018 -> SDoc -- ^ Resulting check message
1019 ruleCheckProgram phase rule_pat rule_base binds
1020 | isEmptyBag results
1021 = text "Rule check results: no rule application sites"
1023 = vcat [text "Rule check results:",
1025 vcat [ p $$ line | p <- bagToList results ]
1028 env = RuleCheckEnv { rc_is_active = isActive phase
1029 , rc_id_unf = idUnfolding -- Not quite right
1030 -- Should use activeUnfolding
1031 , rc_pattern = rule_pat
1032 , rc_rule_base = rule_base }
1033 results = unionManyBags (map (ruleCheckBind env) binds)
1034 line = text (replicate 20 '-')
1036 data RuleCheckEnv = RuleCheckEnv {
1037 rc_is_active :: Activation -> Bool,
1038 rc_id_unf :: IdUnfoldingFun,
1039 rc_pattern :: String,
1040 rc_rule_base :: RuleBase
1043 ruleCheckBind :: RuleCheckEnv -> CoreBind -> Bag SDoc
1044 -- The Bag returned has one SDoc for each call site found
1045 ruleCheckBind env (NonRec _ r) = ruleCheck env r
1046 ruleCheckBind env (Rec prs) = unionManyBags [ruleCheck env r | (_,r) <- prs]
1048 ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc
1049 ruleCheck _ (Var _) = emptyBag
1050 ruleCheck _ (Lit _) = emptyBag
1051 ruleCheck _ (Type _) = emptyBag
1052 ruleCheck _ (Coercion _) = emptyBag
1053 ruleCheck env (App f a) = ruleCheckApp env (App f a) []
1054 ruleCheck env (Note _ e) = ruleCheck env e
1055 ruleCheck env (Cast e _) = ruleCheck env e
1056 ruleCheck env (Let bd e) = ruleCheckBind env bd `unionBags` ruleCheck env e
1057 ruleCheck env (Lam _ e) = ruleCheck env e
1058 ruleCheck env (Case e _ _ as) = ruleCheck env e `unionBags`
1059 unionManyBags [ruleCheck env r | (_,_,r) <- as]
1061 ruleCheckApp :: RuleCheckEnv -> Expr CoreBndr -> [Arg CoreBndr] -> Bag SDoc
1062 ruleCheckApp env (App f a) as = ruleCheck env a `unionBags` ruleCheckApp env f (a:as)
1063 ruleCheckApp env (Var f) as = ruleCheckFun env f as
1064 ruleCheckApp env other _ = ruleCheck env other
1068 ruleCheckFun :: RuleCheckEnv -> Id -> [CoreExpr] -> Bag SDoc
1069 -- Produce a report for all rules matching the predicate
1070 -- saying why it doesn't match the specified application
1072 ruleCheckFun env fn args
1073 | null name_match_rules = emptyBag
1074 | otherwise = unitBag (ruleAppCheck_help env fn args name_match_rules)
1076 name_match_rules = filter match (getRules (rc_rule_base env) fn)
1077 match rule = (rc_pattern env) `isPrefixOf` unpackFS (ruleName rule)
1079 ruleAppCheck_help :: RuleCheckEnv -> Id -> [CoreExpr] -> [CoreRule] -> SDoc
1080 ruleAppCheck_help env fn args rules
1081 = -- The rules match the pattern, so we want to print something
1082 vcat [text "Expression:" <+> ppr (mkApps (Var fn) args),
1083 vcat (map check_rule rules)]
1085 n_args = length args
1086 i_args = args `zip` [1::Int ..]
1087 rough_args = map roughTopName args
1089 check_rule rule = rule_herald rule <> colon <+> rule_info rule
1091 rule_herald (BuiltinRule { ru_name = name })
1092 = ptext (sLit "Builtin rule") <+> doubleQuotes (ftext name)
1093 rule_herald (Rule { ru_name = name })
1094 = ptext (sLit "Rule") <+> doubleQuotes (ftext name)
1097 | Just _ <- matchRule noBlackList (rc_id_unf env) emptyInScopeSet args rough_args rule
1098 = text "matches (which is very peculiar!)"
1100 rule_info (BuiltinRule {}) = text "does not match"
1102 rule_info (Rule { ru_act = act,
1103 ru_bndrs = rule_bndrs, ru_args = rule_args})
1104 | not (rc_is_active env act) = text "active only in later phase"
1105 | n_args < n_rule_args = text "too few arguments"
1106 | n_mismatches == n_rule_args = text "no arguments match"
1107 | n_mismatches == 0 = text "all arguments match (considered individually), but rule as a whole does not"
1108 | otherwise = text "arguments" <+> ppr mismatches <+> text "do not match (1-indexing)"
1110 n_rule_args = length rule_args
1111 n_mismatches = length mismatches
1112 mismatches = [i | (rule_arg, (arg,i)) <- rule_args `zip` i_args,
1113 not (isJust (match_fn rule_arg arg))]
1115 lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars
1116 match_fn rule_arg arg = match renv emptyRuleSubst rule_arg arg
1118 in_scope = mkInScopeSet (lhs_fvs `unionVarSet` exprFreeVars arg)
1119 renv = RV { rv_lcl = mkRnEnv2 in_scope
1120 , rv_tmpls = mkVarSet rule_bndrs
1121 , rv_fltR = mkEmptySubst in_scope
1122 , rv_unf = rc_id_unf env }