import Outputable
import FastString
import Maybes
-import OrdList
import Bag
import Util
import Data.List
%************************************************************************
%* *
-\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
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)
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]
| 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
-- * 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.
-- 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
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
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
(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
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