X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2Fspecialise%2FRules.lhs;h=f9d02e5ab727f8b8a77612eb15cea4a547873898;hp=87999a4dfd29779206122fff41eef4c856c095dc;hb=86add45dbfb6f962b65e371143dd467ae783f9e7;hpb=d2ce0f52d42edf32bb9f13796e6ba6edba8bd516 diff --git a/compiler/specialise/Rules.lhs b/compiler/specialise/Rules.lhs index 87999a4..f9d02e5 100644 --- a/compiler/specialise/Rules.lhs +++ b/compiler/specialise/Rules.lhs @@ -24,22 +24,23 @@ module Rules ( -- * Misc. CoreRule helpers rulesOfBinds, getRules, pprRulesForUser, - lookupRule, mkRule, mkLocalRule, roughTopNames + lookupRule, mkRule, roughTopNames ) where #include "HsVersions.h" import CoreSyn -- All of it -import OccurAnal ( occurAnalyseExpr ) +import CoreSubst +import OccurAnal ( occurAnalyseExpr ) import CoreFVs ( exprFreeVars, exprsFreeVars, bindFreeVars, rulesFreeVars ) -import CoreUtils ( exprType, eqExprX ) +import CoreUtils ( exprType, eqExpr ) import PprCore ( pprRules ) -import Type ( Type, TvSubstEnv ) +import Type ( Type ) import TcType ( tcSplitTyConApp_maybe ) +import Coercion import CoreTidy ( tidyRules ) import Id import IdInfo ( SpecInfo( SpecInfo ) ) -import Var ( Var ) import VarEnv import VarSet import Name ( Name, NamedThing(..) ) @@ -55,7 +56,6 @@ import Util import Data.List \end{code} - Note [Overall plumbing for rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * After the desugarer: @@ -105,7 +105,7 @@ Note [Overall plumbing for rules] The HomePackageTable doesn't have a single RuleBase because technically we should only be able to "see" rules "below" this module; so we generate a RuleBase for (c) by combing rules from all the modules - "below" us. That's whye we can't just select the home-package RuleBase + "below" us. That's why we can't just select the home-package RuleBase from HscEnv. [NB: we are inconsistent here. We should do the same for external @@ -156,22 +156,16 @@ might have a specialisation where pi' :: Lift Int# is the specialised version of pi. \begin{code} -mkLocalRule :: RuleName -> Activation - -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule --- ^ Used to make 'CoreRule' for an 'Id' defined in the module being --- compiled. See also 'CoreSyn.CoreRule' -mkLocalRule = mkRule True - -mkRule :: Bool -> RuleName -> Activation +mkRule :: Bool -> Bool -> RuleName -> Activation -> Name -> [CoreBndr] -> [CoreExpr] -> CoreExpr -> CoreRule -- ^ Used to make 'CoreRule' for an 'Id' defined in the module being -- compiled. See also 'CoreSyn.CoreRule' -mkRule is_local name act fn bndrs args rhs +mkRule is_auto is_local name act fn bndrs args rhs = Rule { ru_name = name, ru_fn = fn, ru_act = act, ru_bndrs = bndrs, ru_args = args, ru_rhs = occurAnalyseExpr rhs, ru_rough = roughTopNames args, - ru_local = is_local } + ru_auto = is_auto, ru_local = is_local } -------------- roughTopNames :: [CoreExpr] -> [Maybe Name] @@ -189,11 +183,13 @@ roughTopNames args = map roughTopName args roughTopName :: CoreExpr -> Maybe Name roughTopName (Type ty) = case tcSplitTyConApp_maybe ty of - Just (tc,_) -> Just (getName tc) - Nothing -> Nothing + Just (tc,_) -> Just (getName tc) + Nothing -> Nothing +roughTopName (Coercion _) = Nothing roughTopName (App f _) = roughTopName f -roughTopName (Var f) | isGlobalId f = Just (idName f) - | otherwise = Nothing +roughTopName (Var f) | isGlobalId f -- Note [Care with roughTopName] + , isDataConWorkId f || idArity f > 0 + = Just (idName f) roughTopName _ = Nothing ruleCantMatch :: [Maybe Name] -> [Maybe Name] -> Bool @@ -214,6 +210,25 @@ ruleCantMatch (_ : ts) (_ : as) = ruleCantMatch ts as ruleCantMatch _ _ = False \end{code} +Note [Care with roughTopName] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Consider this + module M where { x = a:b } + module N where { ...f x... + RULE f (p:q) = ... } +You'd expect the rule to match, because the matcher can +look through the unfolding of 'x'. So we must avoid roughTopName +returning 'M.x' for the call (f x), or else it'll say "can't match" +and we won't even try!! + +However, suppose we have + RULE g (M.h x) = ... + foo = ...(g (M.k v)).... +where k is a *function* exported by M. We never really match +functions (lambdas) except by name, so in this case it seems like +a good idea to treat 'M.k' as a roughTopName of the call. + + \begin{code} pprRulesForUser :: [CoreRule] -> SDoc -- (a) tidy the rules @@ -345,7 +360,7 @@ lookupRule :: (Activation -> Bool) -- When rule is active -- See Note [Extra args in rule matching] -- See comments on matchRule lookupRule is_active id_unf in_scope fn args rules - = -- pprTrace "matchRules" (ppr fn <+> ppr rules) $ + = -- pprTrace "matchRules" (ppr fn <+> ppr args $$ ppr rules ) $ case go [] rules of [] -> Nothing (m:ms) -> Just (findBest (fn,args) m ms) @@ -388,8 +403,18 @@ findBest target (rule1,ans1) ((rule2,ans2):prs) (fn,args) = target isMoreSpecific :: CoreRule -> CoreRule -> Bool -isMoreSpecific (BuiltinRule {}) _ = True -isMoreSpecific _ (BuiltinRule {}) = False +-- This tests if one rule is more specific than another +-- We take the view that a BuiltinRule is less specific than +-- anything else, because we want user-define rules to "win" +-- In particular, class ops have a built-in rule, but we +-- any user-specific rules to win +-- eg (Trac #4397) +-- truncate :: (RealFrac a, Integral b) => a -> b +-- {-# RULES "truncate/Double->Int" truncate = double2Int #-} +-- double2Int :: Double -> Int +-- We want the specific RULE to beat the built-in class-op rule +isMoreSpecific (BuiltinRule {}) _ = False +isMoreSpecific (Rule {}) (BuiltinRule {}) = True isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 }) (Rule { ru_bndrs = bndrs2, ru_args = args2 }) = isJust (matchN id_unfolding_fun in_scope bndrs2 args2 args1) @@ -483,30 +508,31 @@ matchN :: IdUnfoldingFun -- Fail if there are two few actual arguments from the target to match the template matchN id_unf in_scope tmpl_vars tmpl_es target_es - = do { (tv_subst, id_subst, binds) - <- go init_menv emptySubstEnv tmpl_es target_es - ; return (binds, - map (lookup_tmpl tv_subst id_subst) tmpl_vars') } + = do { subst <- go init_menv emptyRuleSubst tmpl_es target_es + ; return (rs_binds subst, + map (lookup_tmpl subst) tmpl_vars') } where (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars - -- See Note [Template binders] + -- See Note [Template binders] - init_menv = ME { me_tmpls = mkVarSet tmpl_vars', me_env = init_rn_env } + init_menv = RV { rv_tmpls = mkVarSet tmpl_vars', rv_lcl = init_rn_env + , rv_fltR = mkEmptySubst (rnInScopeSet init_rn_env) + , rv_unf = id_unf } go _ subst [] _ = Just subst go _ _ _ [] = Nothing -- Fail if too few actual args - go menv subst (t:ts) (e:es) = do { subst1 <- match id_unf menv subst t e + go menv subst (t:ts) (e:es) = do { subst1 <- match menv subst t e ; go menv subst1 ts es } - lookup_tmpl :: TvSubstEnv -> IdSubstEnv -> Var -> CoreExpr - lookup_tmpl tv_subst id_subst tmpl_var' - | isTyCoVar tmpl_var' = case lookupVarEnv tv_subst tmpl_var' of - Just ty -> Type ty - Nothing -> unbound tmpl_var' - | otherwise = case lookupVarEnv id_subst tmpl_var' of - Just e -> e - _ -> unbound tmpl_var' - + lookup_tmpl :: RuleSubst -> Var -> CoreExpr + lookup_tmpl (RS { rs_tv_subst = tv_subst, rs_id_subst = id_subst }) tmpl_var' + | isId tmpl_var' = case lookupVarEnv id_subst tmpl_var' of + Just e -> e + _ -> unbound tmpl_var' + | otherwise = case lookupVarEnv tv_subst tmpl_var' of + Just ty -> Type ty + Nothing -> unbound tmpl_var' + unbound var = pprPanic "Template variable unbound in rewrite rule" (ppr var $$ ppr tmpl_vars $$ ppr tmpl_vars' $$ ppr tmpl_es $$ ppr target_es) \end{code} @@ -528,30 +554,45 @@ To achive this, we use rnBndrL to rename the template variables if necessary; the renamed ones are the tmpl_vars' - --------------------------------------------- +%************************************************************************ +%* * + The main matcher +%* * +%************************************************************************ + + --------------------------------------------- The inner workings of matching --------------------------------------------- \begin{code} --- These two definitions are not the same as in Subst, --- but they simple and direct, and purely local to this module --- -- * The domain of the TvSubstEnv and IdSubstEnv are the template -- variables passed into the match. -- --- * The BindWrapper in a SubstEnv are the bindings floated out +-- * The BindWrapper in a RuleSubst are the bindings floated out -- from nested matches; see the Let case of match, below -- -type SubstEnv = (TvSubstEnv, IdSubstEnv, BindWrapper) - +data RuleEnv = RV { rv_tmpls :: VarSet -- Template variables + , rv_lcl :: RnEnv2 -- Renamings for *local bindings* + -- (lambda/case) + , rv_fltR :: Subst -- Renamings for floated let-bindings + -- domain disjoint from envR of rv_lcl + -- See Note [Matching lets] + , rv_unf :: IdUnfoldingFun + } + +data RuleSubst = RS { rs_tv_subst :: TvSubstEnv -- Range is the + , rs_id_subst :: IdSubstEnv -- template variables + , rs_binds :: BindWrapper -- Floated bindings + , rs_bndrs :: VarSet -- Variables bound by floated lets + } + type BindWrapper = CoreExpr -> CoreExpr -- See Notes [Matching lets] and [Matching cases] -- we represent the floated bindings as a core-to-core function -type IdSubstEnv = IdEnv CoreExpr - -emptySubstEnv :: SubstEnv -emptySubstEnv = (emptyVarEnv, emptyVarEnv, \e -> e) +emptyRuleSubst :: RuleSubst +emptyRuleSubst = RS { rs_tv_subst = emptyVarEnv, rs_id_subst = emptyVarEnv + , rs_binds = \e -> e, rs_bndrs = emptyVarSet } -- At one stage I tried to match even if there are more -- template args than real args. @@ -562,12 +603,11 @@ emptySubstEnv = (emptyVarEnv, emptyVarEnv, \e -> e) -- SLPJ July 99 -match :: IdUnfoldingFun - -> MatchEnv - -> SubstEnv +match :: RuleEnv + -> RuleSubst -> CoreExpr -- Template -> CoreExpr -- Target - -> Maybe SubstEnv + -> Maybe RuleSubst -- See the notes with Unify.match, which matches types -- Everything is very similar for terms @@ -585,198 +625,238 @@ match :: IdUnfoldingFun -- succeed in matching what looks like the template variable 'a' against 3. -- The Var case follows closely what happens in Unify.match -match idu menv subst (Var v1) e2 - | Just subst <- match_var idu menv subst v1 e2 - = Just subst - -match idu menv subst (Note _ e1) e2 = match idu menv subst e1 e2 -match idu menv subst e1 (Note _ e2) = match idu menv subst e1 e2 +match renv subst (Var v1) e2 = match_var renv subst v1 e2 +match renv subst (Note _ e1) e2 = match renv subst e1 e2 +match renv subst e1 (Note _ e2) = match renv subst e1 e2 -- Ignore notes in both template and thing to be matched -- See Note [Notes in RULE matching] -match id_unfolding_fun menv subst e1 (Var v2) -- Note [Expanding variables] +match renv subst e1 (Var v2) -- Note [Expanding variables] | not (inRnEnvR rn_env v2) -- Note [Do not expand locally-bound variables] - , Just e2' <- expandUnfolding_maybe (id_unfolding_fun v2') - = match id_unfolding_fun (menv { me_env = nukeRnEnvR rn_env }) subst e1 e2' + , Just e2' <- expandUnfolding_maybe (rv_unf renv v2') + = match (renv { rv_lcl = nukeRnEnvR rn_env }) subst e1 e2' where v2' = lookupRnInScope rn_env v2 - rn_env = me_env menv + rn_env = rv_lcl renv -- Notice that we look up v2 in the in-scope set -- See Note [Lookup in-scope] -- No need to apply any renaming first (hence no rnOccR) -- because of the not-inRnEnvR -match idu menv (tv_subst, id_subst, binds) e1 (Let bind e2) - | okToFloat rn_env bndrs (bindFreeVars bind) -- See Note [Matching lets] - = match idu (menv { me_env = rn_env' }) - (tv_subst, id_subst, binds . Let bind) +match renv subst e1 (Let bind e2) + | okToFloat (rv_lcl renv) (bindFreeVars bind) -- See Note [Matching lets] + = match (renv { rv_fltR = flt_subst' }) + (subst { rs_binds = rs_binds subst . Let bind' + , rs_bndrs = extendVarSetList (rs_bndrs subst) new_bndrs }) e1 e2 where - rn_env = me_env menv - rn_env' = extendRnInScopeList rn_env bndrs - bndrs = bindersOf bind + flt_subst = addInScopeSet (rv_fltR renv) (rs_bndrs subst) + (flt_subst', bind') = substBind flt_subst bind + new_bndrs = bindersOf bind' {- Disabled: see Note [Matching cases] below -match idu menv (tv_subst, id_subst, binds) e1 +match renv (tv_subst, id_subst, binds) e1 (Case scrut case_bndr ty [(con, alt_bndrs, rhs)]) | exprOkForSpeculation scrut -- See Note [Matching cases] , okToFloat rn_env bndrs (exprFreeVars scrut) - = match idu (menv { me_env = rn_env' }) + = match (renv { me_env = rn_env' }) (tv_subst, id_subst, binds . case_wrap) e1 rhs where - rn_env = me_env menv + rn_env = me_env renv rn_env' = extendRnInScopeList rn_env bndrs bndrs = case_bndr : alt_bndrs case_wrap rhs' = Case scrut case_bndr ty [(con, alt_bndrs, rhs')] -} -match _ _ subst (Lit lit1) (Lit lit2) +match _ subst (Lit lit1) (Lit lit2) | lit1 == lit2 = Just subst -match idu menv subst (App f1 a1) (App f2 a2) - = do { subst' <- match idu menv subst f1 f2 - ; match idu menv subst' a1 a2 } +match renv subst (App f1 a1) (App f2 a2) + = do { subst' <- match renv subst f1 f2 + ; match renv subst' a1 a2 } -match idu menv subst (Lam x1 e1) (Lam x2 e2) - = match idu menv' subst e1 e2 +match renv subst (Lam x1 e1) (Lam x2 e2) + = match renv' subst e1 e2 where - menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 } + renv' = renv { rv_lcl = rnBndr2 (rv_lcl renv) x1 x2 + , rv_fltR = delBndr (rv_fltR renv) x2 } -- This rule does eta expansion -- (\x.M) ~ N iff M ~ N x -- It's important that this is *after* the let rule, -- so that (\x.M) ~ (let y = e in \y.N) -- does the let thing, and then gets the lam/lam rule above -match idu menv subst (Lam x1 e1) e2 - = match idu menv' subst e1 (App e2 (varToCoreExpr new_x)) +match renv subst (Lam x1 e1) e2 + = match renv' subst e1 (App e2 (varToCoreExpr new_x)) where - (rn_env', new_x) = rnBndrL (me_env menv) x1 - menv' = menv { me_env = rn_env' } + (rn_env', new_x) = rnEtaL (rv_lcl renv) x1 + renv' = renv { rv_lcl = rn_env' } -- Eta expansion the other way -- M ~ (\y.N) iff M y ~ N -match idu menv subst e1 (Lam x2 e2) - = match idu menv' subst (App e1 (varToCoreExpr new_x)) e2 +match renv subst e1 (Lam x2 e2) + = match renv' subst (App e1 (varToCoreExpr new_x)) e2 where - (rn_env', new_x) = rnBndrR (me_env menv) x2 - menv' = menv { me_env = rn_env' } - -match idu menv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2) - = do { subst1 <- match_ty menv subst ty1 ty2 - ; subst2 <- match idu menv subst1 e1 e2 - ; let menv' = menv { me_env = rnBndr2 (me_env menv) x1 x2 } - ; match_alts idu menv' subst2 alts1 alts2 -- Alts are both sorted + (rn_env', new_x) = rnEtaR (rv_lcl renv) x2 + renv' = renv { rv_lcl = rn_env' } + +match renv subst (Case e1 x1 ty1 alts1) (Case e2 x2 ty2 alts2) + = do { subst1 <- match_ty renv subst ty1 ty2 + ; subst2 <- match renv subst1 e1 e2 + ; let renv' = rnMatchBndr2 renv subst x1 x2 + ; match_alts renv' subst2 alts1 alts2 -- Alts are both sorted } -match _ menv subst (Type ty1) (Type ty2) - = match_ty menv subst ty1 ty2 +match renv subst (Type ty1) (Type ty2) + = match_ty renv subst ty1 ty2 +match renv subst (Coercion co1) (Coercion co2) + = match_co renv subst co1 co2 -match idu menv subst (Cast e1 co1) (Cast e2 co2) - = do { subst1 <- match_ty menv subst co1 co2 - ; match idu menv subst1 e1 e2 } +match renv subst (Cast e1 co1) (Cast e2 co2) + = do { subst1 <- match_co renv subst co1 co2 + ; match renv subst1 e1 e2 } -- Everything else fails -match _ _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $ - Nothing +match _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (text "e2:" <+> ppr _e2)) $ + Nothing + +------------- +match_co :: RuleEnv + -> RuleSubst + -> Coercion + -> Coercion + -> Maybe RuleSubst +match_co renv subst (CoVarCo cv) co + = match_var renv subst cv (Coercion co) +match_co _ _ co1 _ + = pprTrace "match_co baling out" (ppr co1) Nothing + +------------- +rnMatchBndr2 :: RuleEnv -> RuleSubst -> Var -> Var -> RuleEnv +rnMatchBndr2 renv subst x1 x2 + = renv { rv_lcl = rnBndr2 rn_env x1 x2 + , rv_fltR = delBndr (rv_fltR renv) x2 } + where + rn_env = addRnInScopeSet (rv_lcl renv) (rs_bndrs subst) + -- Typically this is a no-op, but it may matter if + -- there are some floated let-bindings ------------------------------------------ -okToFloat :: RnEnv2 -> [Var] -> VarSet -> Bool -okToFloat rn_env bndrs bind_fvs - = all freshly_bound bndrs - && foldVarSet ((&&) . not_captured) True bind_fvs +match_alts :: RuleEnv + -> RuleSubst + -> [CoreAlt] -- Template + -> [CoreAlt] -- Target + -> Maybe RuleSubst +match_alts _ subst [] [] + = return subst +match_alts renv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2) + | c1 == c2 + = do { subst1 <- match renv' subst r1 r2 + ; match_alts renv subst1 alts1 alts2 } + where + renv' = foldl mb renv (vs1 `zip` vs2) + mb renv (v1,v2) = rnMatchBndr2 renv subst v1 v2 + +match_alts _ _ _ _ + = Nothing + +------------------------------------------ +okToFloat :: RnEnv2 -> VarSet -> Bool +okToFloat rn_env bind_fvs + = foldVarSet ((&&) . not_captured) True bind_fvs where - freshly_bound x = not (x `rnInScope` rn_env) not_captured fv = not (inRnEnvR rn_env fv) ------------------------------------------ -match_var :: IdUnfoldingFun - -> MatchEnv - -> SubstEnv - -> Var -- Template - -> CoreExpr -- Target - -> Maybe SubstEnv -match_var idu menv subst@(tv_subst, id_subst, binds) v1 e2 - | v1' `elemVarSet` me_tmpls menv - = case lookupVarEnv id_subst v1' of - Nothing | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2)) - -> Nothing -- Occurs check failure +match_var :: RuleEnv + -> RuleSubst + -> Var -- Template + -> CoreExpr -- Target + -> Maybe RuleSubst +match_var renv@(RV { rv_tmpls = tmpls, rv_lcl = rn_env, rv_fltR = flt_env }) + subst v1 e2 + | v1' `elemVarSet` tmpls + = match_tmpl_var renv subst v1' e2 + + | otherwise -- v1' is not a template variable; check for an exact match with e2 + = case e2 of -- Remember, envR of rn_env is disjoint from rv_fltR + Var v2 | v1' == rnOccR rn_env v2 + -> Just subst + + | Var v2' <- lookupIdSubst (text "match_var") flt_env v2 + , v1' == v2' + -> Just subst + + _ -> Nothing + + where + v1' = rnOccL rn_env v1 + -- If the template is + -- forall x. f x (\x -> x) = ... + -- Then the x inside the lambda isn't the + -- template x, so we must rename first! + +------------------------------------------ +match_tmpl_var :: RuleEnv + -> RuleSubst + -> Var -- Template + -> CoreExpr -- Target + -> Maybe RuleSubst + +match_tmpl_var renv@(RV { rv_lcl = rn_env, rv_fltR = flt_env }) + subst@(RS { rs_id_subst = id_subst, rs_bndrs = let_bndrs }) + v1' e2 + | any (inRnEnvR rn_env) (varSetElems (exprFreeVars e2)) + = Nothing -- Occurs check failure -- e.g. match forall a. (\x-> a x) against (\y. y y) - | otherwise -- No renaming to do on e2, because no free var - -- of e2 is in the rnEnvR of the envt - -- Note [Matching variable types] + | Just e1' <- lookupVarEnv id_subst v1' + = if eqExpr (rnInScopeSet rn_env) e1' e2' + then Just subst + else Nothing + + | otherwise + = -- Note [Matching variable types] -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- However, we must match the *types*; e.g. -- forall (c::Char->Int) (x::Char). - -- f (c x) = "RULE FIRED" + -- f (c x) = "RULE FIRED" -- We must only match on args that have the right type -- It's actually quite difficult to come up with an example that shows -- you need type matching, esp since matching is left-to-right, so type -- args get matched first. But it's possible (e.g. simplrun008) and -- this is the Right Thing to do - -> do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst (idType v1') (exprType e2) - -- c.f. match_ty below - ; return (tv_subst', extendVarEnv id_subst v1' e2, binds) } - - Just e1' | eqExprX idu (nukeRnEnvL rn_env) e1' e2 - -> Just subst - - | otherwise - -> Nothing - - | otherwise -- v1 is not a template variable; check for an exact match with e2 - = case e2 of - Var v2 | v1' == rnOccR rn_env v2 -> Just subst - _ -> Nothing - - where - rn_env = me_env menv - v1' = rnOccL rn_env v1 - -- If the template is - -- forall x. f x (\x -> x) = ... - -- Then the x inside the lambda isn't the - -- template x, so we must rename first! - - ------------------------------------------- -match_alts :: IdUnfoldingFun - -> MatchEnv - -> SubstEnv - -> [CoreAlt] -- Template - -> [CoreAlt] -- Target - -> Maybe SubstEnv -match_alts _ _ subst [] [] - = return subst -match_alts idu menv subst ((c1,vs1,r1):alts1) ((c2,vs2,r2):alts2) - | c1 == c2 - = do { subst1 <- match idu menv' subst r1 r2 - ; match_alts idu menv subst1 alts1 alts2 } + do { subst' <- match_ty renv subst (idType v1') (exprType e2) + ; return (subst' { rs_id_subst = id_subst' }) } where - menv' :: MatchEnv - menv' = menv { me_env = rnBndrs2 (me_env menv) vs1 vs2 } + -- e2' is the result of applying flt_env to e2 + e2' | isEmptyVarSet let_bndrs = e2 + | otherwise = substExpr (text "match_tmpl_var") flt_env e2 -match_alts _ _ _ _ _ - = Nothing -\end{code} + id_subst' = extendVarEnv (rs_id_subst subst) v1' e2' + -- No further renaming to do on e2', + -- because no free var of e2' is in the rnEnvR of the envt -Matching Core types: use the matcher in TcType. -Notice that we treat newtypes as opaque. For example, suppose -we have a specialised version of a function at a newtype, say - newtype T = MkT Int -We only want to replace (f T) with f', not (f Int). - -\begin{code} ------------------------------------------ -match_ty :: MatchEnv - -> SubstEnv +match_ty :: RuleEnv + -> RuleSubst -> Type -- Template -> Type -- Target - -> Maybe SubstEnv -match_ty menv (tv_subst, id_subst, binds) ty1 ty2 - = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2 - ; return (tv_subst', id_subst, binds) } + -> Maybe RuleSubst +-- Matching Core types: use the matcher in TcType. +-- Notice that we treat newtypes as opaque. For example, suppose +-- we have a specialised version of a function at a newtype, say +-- newtype T = MkT Int +-- We only want to replace (f T) with f', not (f Int). + +match_ty renv subst ty1 ty2 + = do { tv_subst' <- Unify.ruleMatchTyX menv tv_subst ty1 ty2 + ; return (subst { rs_tv_subst = tv_subst' }) } + where + tv_subst = rs_tv_subst subst + menv = ME { me_tmpls = rv_tmpls renv, me_env = rv_lcl renv } \end{code} Note [Expanding variables] @@ -823,40 +903,47 @@ Then we'd like the rule to match, to generate let { w=R } in (\x. ) E In effect, we want to float the let-binding outward, to enable the match to happen. This is the WHOLE REASON for accumulating -bindings in the SubstEnv - -We can only do this if - (a) Widening the scope of w does not capture any variables - We use a conservative test: w is not already in scope - If not, we clone the binders, and substitute - (b) The free variables of R are not bound by the part of the - target expression outside the let binding; e.g. - f (\v. let w = v+1 in g E) - Here we obviously cannot float the let-binding for w. - -You may think rule (a) would never apply, because rule matching is -mostly invoked from the simplifier, when we have just run substExpr -over the argument, so there will be no shadowing anyway. -The fly in the ointment is that the forall'd variables of the -RULE itself are considered in scope. - -I though of various ways to solve (a). One plan was to -clone the binders if they are in scope. But watch out! - (let x=y+1 in let z=x+1 in (z,z) - --> should match (p,p) but watch out that - the use of x on z's rhs is OK! -If we clone x, then the let-binding for 'z' is then caught by (b), -at least unless we elaborate the RnEnv stuff a bit. - -So for we simply fail to match unless both (a) and (b) hold. - -Other cases to think about - (let x=y+1 in \x. (x,x)) - --> let x=y+1 in (\x1. (x1,x1)) - (\x. let x = y+1 in (x,x)) - --> let x1 = y+1 in (\x. (x1,x1) - (let x=y+1 in (x,x), let x=y-1 in (x,x)) - --> let x=y+1 in let x1=y-1 in ((x,x),(x1,x1)) +bindings in the RuleSubst + +We can only do this if the free variables of R are not bound by the +part of the target expression outside the let binding; e.g. + f (\v. let w = v+1 in g E) +Here we obviously cannot float the let-binding for w. Hence the +use of okToFloat. + +There are a couple of tricky points. + (a) What if floating the binding captures a variable? + f (let v = x+1 in v) v + --> NOT! + let v = x+1 in f (x+1) v + + (b) What if two non-nested let bindings bind the same variable? + f (let v = e1 in b1) (let v = e2 in b2) + --> NOT! + let v = e1 in let v = e2 in (f b2 b2) + See testsuite test "RuleFloatLet". + +Our cunning plan is this: + * Along with the growing substitution for template variables + we maintain a growing set of floated let-bindings (rs_binds) + plus the set of variables thus bound. + + * The RnEnv2 in the MatchEnv binds only the local binders + in the term (lambdas, case) + + * When we encounter a let in the term to be matched, we + check that does not mention any locally bound (lambda, case) + variables. If so we fail + + * We use CoreSubst.substBind to freshen the binding, using an + in-scope set that is the original in-scope variables plus the + rs_bndrs (currently floated let-bindings). So in (a) above + we'll freshen the 'v' binding; in (b) above we'll freshen + the *second* 'v' binding. + + * We apply that freshening substitution, in a lexically-scoped + way to the term, although lazily; this is the rv_fltR field. + Note [Matching cases] ~~~~~~~~~~~~~~~~~~~~~ @@ -962,6 +1049,7 @@ ruleCheck :: RuleCheckEnv -> CoreExpr -> Bag SDoc ruleCheck _ (Var _) = emptyBag ruleCheck _ (Lit _) = emptyBag ruleCheck _ (Type _) = emptyBag +ruleCheck _ (Coercion _) = emptyBag ruleCheck env (App f a) = ruleCheckApp env (App f a) [] ruleCheck env (Note _ e) = ruleCheck env e ruleCheck env (Cast e _) = ruleCheck env e @@ -1025,10 +1113,12 @@ ruleAppCheck_help env fn args rules not (isJust (match_fn rule_arg arg))] lhs_fvs = exprsFreeVars rule_args -- Includes template tyvars - match_fn rule_arg arg = match (rc_id_unf env) menv emptySubstEnv rule_arg arg + match_fn rule_arg arg = match renv emptyRuleSubst rule_arg arg where - in_scope = lhs_fvs `unionVarSet` exprFreeVars arg - menv = ME { me_env = mkRnEnv2 (mkInScopeSet in_scope) - , me_tmpls = mkVarSet rule_bndrs } + in_scope = mkInScopeSet (lhs_fvs `unionVarSet` exprFreeVars arg) + renv = RV { rv_lcl = mkRnEnv2 in_scope + , rv_tmpls = mkVarSet rule_bndrs + , rv_fltR = mkEmptySubst in_scope + , rv_unf = rc_id_unf env } \end{code}