X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fspecialise%2FRules.lhs;h=cfba1a19823befe1baadfe7a00fd47e697f5157e;hb=9abe297285fe213ccd804f47d253055797cf667a;hp=e1dc9276765fc4c03f8ebd7821c65d2f912a1537;hpb=0e04bfecd870305bdf5945ba3ab80f314c708265;p=ghc-hetmet.git diff --git a/compiler/specialise/Rules.lhs b/compiler/specialise/Rules.lhs index e1dc927..cfba1a1 100644 --- a/compiler/specialise/Rules.lhs +++ b/compiler/specialise/Rules.lhs @@ -50,7 +50,6 @@ import StaticFlags ( opt_PprStyle_Debug ) import Outputable import FastString import Maybes -import OrdList import Bag import Util import Data.List @@ -328,26 +327,10 @@ pprRuleBase rules = vcat [ pprRules (tidyRules emptyTidyEnv rs) %************************************************************************ %* * -\subsection{Matching} + Matching %* * %************************************************************************ -Note [Extra args in rule matching] -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -If we find a matching rule, we return (Just (rule, rhs)), -but the rule firing has only consumed as many of the input args -as the ruleArity says. It's up to the caller to keep track -of any left-over args. E.g. if you call - lookupRule ... f [e1, e2, e3] -and it returns Just (r, rhs), where r has ruleArity 2 -then the real rewrite is - f e1 e2 e3 ==> rhs e3 - -You might think it'd be cleaner for lookupRule to deal with the -leftover arguments, by applying 'rhs' to them, but the main call -in the Simplifier works better as it is. Reason: the 'args' passed -to lookupRule are the result of a lazy substitution - \begin{code} -- | The main rule matching function. Attempts to apply all (active) -- supplied rules to this instance of an application in a given @@ -374,8 +357,11 @@ lookupRule is_active id_unf in_scope fn args rules go ms (r:rs) = case (matchRule is_active id_unf in_scope args rough_args r) of Just e -> go ((r,e):ms) rs Nothing -> -- pprTrace "match failed" (ppr r $$ ppr args $$ - -- ppr [(arg_id, unfoldingTemplate unf) | Var arg_id <- args, let unf = idUnfolding arg_id, isCheapUnfolding unf] ) - go ms rs + -- ppr [ (arg_id, unfoldingTemplate unf) + -- | Var arg_id <- args + -- , let unf = idUnfolding arg_id + -- , isCheapUnfolding unf] ) + go ms rs findBest :: (Id, [CoreExpr]) -> (CoreRule,CoreExpr) -> [(CoreRule,CoreExpr)] -> (CoreRule,CoreExpr) @@ -415,7 +401,26 @@ isMoreSpecific (Rule { ru_bndrs = bndrs1, ru_args = args1 }) noBlackList :: Activation -> Bool noBlackList _ = False -- Nothing is black listed +\end{code} + +Note [Extra args in rule matching] +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +If we find a matching rule, we return (Just (rule, rhs)), +but the rule firing has only consumed as many of the input args +as the ruleArity says. It's up to the caller to keep track +of any left-over args. E.g. if you call + lookupRule ... f [e1, e2, e3] +and it returns Just (r, rhs), where r has ruleArity 2 +then the real rewrite is + f e1 e2 e3 ==> rhs e3 + +You might think it'd be cleaner for lookupRule to deal with the +leftover arguments, by applying 'rhs' to them, but the main call +in the Simplifier works better as it is. Reason: the 'args' passed +to lookupRule are the result of a lazy substitution +\begin{code} +------------------------------------ matchRule :: (Activation -> Bool) -> IdUnfoldingFun -> InScopeSet -> [CoreExpr] -> [Maybe Name] @@ -458,30 +463,29 @@ matchRule is_active id_unf in_scope args rough_args | ruleCantMatch tpl_tops rough_args = Nothing | otherwise = case matchN id_unf in_scope tpl_vars tpl_args args of - Nothing -> Nothing - Just (binds, tpl_vals) -> Just (mkLets binds $ - rule_fn `mkApps` tpl_vals) + Nothing -> Nothing + Just (bind_wrapper, tpl_vals) -> Just (bind_wrapper $ + rule_fn `mkApps` tpl_vals) where rule_fn = occurAnalyseExpr (mkLams tpl_vars rhs) -- We could do this when putting things into the rulebase, I guess -\end{code} -\begin{code} --- For a given match template and context, find bindings to wrap around --- the entire result and what should be substituted for each template variable. --- Fail if there are two few actual arguments from the target to match the template +--------------------------------------- matchN :: IdUnfoldingFun -> InScopeSet -- ^ In-scope variables -> [Var] -- ^ Match template type variables -> [CoreExpr] -- ^ Match template -> [CoreExpr] -- ^ Target; can have more elements than the template - -> Maybe ([CoreBind], + -> Maybe (BindWrapper, -- ^ Floated bindings; see Note [Matching lets] [CoreExpr]) +-- For a given match template and context, find bindings to wrap around +-- the entire result and what should be substituted for each template variable. +-- 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 (fromOL binds, + ; return (binds, map (lookup_tmpl tv_subst id_subst) tmpl_vars') } where (init_rn_env, tmpl_vars') = mapAccumL rnBndrL (mkRnEnv2 in_scope) tmpl_vars @@ -535,15 +539,19 @@ necessary; the renamed ones are the tmpl_vars' -- * The domain of the TvSubstEnv and IdSubstEnv are the template -- variables passed into the match. -- --- * The (OrdList CoreBind) in a SubstEnv are the bindings floated out +-- * The BindWrapper in a SubstEnv are the bindings floated out -- from nested matches; see the Let case of match, below -- -type SubstEnv = (TvSubstEnv, IdSubstEnv, OrdList CoreBind) +type SubstEnv = (TvSubstEnv, IdSubstEnv, BindWrapper) + +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, nilOL) - +emptySubstEnv = (emptyVarEnv, emptyVarEnv, \e -> e) -- At one stage I tried to match even if there are more -- template args than real args. @@ -599,19 +607,29 @@ match id_unfolding_fun menv subst e1 (Var v2) -- Note [Expanding variables] -- because of the not-inRnEnvR match idu menv (tv_subst, id_subst, binds) e1 (Let bind e2) - | all freshly_bound bndrs -- See Note [Matching lets] - , not (any (inRnEnvR rn_env) bind_fvs) + | okToFloat rn_env bndrs (bindFreeVars bind) -- See Note [Matching lets] = match idu (menv { me_env = rn_env' }) - (tv_subst, id_subst, binds `snocOL` bind') - e1 e2' + (tv_subst, id_subst, binds . Let bind) + e1 e2 where rn_env = me_env menv - bndrs = bindersOf bind - bind_fvs = varSetElems (bindFreeVars bind) - freshly_bound x = not (x `rnInScope` rn_env) - bind' = bind - e2' = e2 - rn_env' = extendRnInScopeList rn_env bndrs + rn_env' = extendRnInScopeList rn_env bndrs + bndrs = bindersOf bind + +{- Disabled: see Note [Matching cases] below +match idu menv (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' }) + (tv_subst, id_subst, binds . case_wrap) + e1 rhs + where + rn_env = me_env menv + 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) | lit1 == lit2 @@ -664,6 +682,15 @@ match _ _ _ _e1 _e2 = -- pprTrace "Failing at" ((text "e1:" <+> ppr _e1) $$ (tex Nothing ------------------------------------------ +okToFloat :: RnEnv2 -> [Var] -> VarSet -> Bool +okToFloat rn_env bndrs bind_fvs + = all freshly_bound bndrs + && 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 @@ -799,13 +826,13 @@ 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. + (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 @@ -831,7 +858,25 @@ Other cases to think about (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)) - +Note [Matching cases] +~~~~~~~~~~~~~~~~~~~~~ +{- NOTE: This idea is currently disabled. It really only works if + the primops involved are OkForSpeculation, and, since + they have side effects readIntOfAddr and touch are not. + Maybe we'll get back to this later . -} + +Consider + f (case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) -> + case touch# fp s# of { _ -> + I# n# } } ) +This happened in a tight loop generated by stream fusion that +Roman encountered. We'd like to treat this just like the let +case, because the primops concerned are ok-for-speculation. +That is, we'd like to behave as if it had been + case readIntOffAddr# p# i# realWorld# of { (# s#, n# #) -> + case touch# fp s# of { _ -> + f (I# n# } } ) + Note [Lookup in-scope] ~~~~~~~~~~~~~~~~~~~~~~ Consider this example