\section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
\begin{code}
-{-# OPTIONS_GHC -w #-}
+{-# OPTIONS -w #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and fix
-- any warnings in the module. See
--- http://hackage.haskell.org/trac/ghc/wiki/WorkingConventions#Warnings
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
-- for details
module WorkWrap ( wwTopBinds, mkWrapper ) where
import NewDemand ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..),
Demands(..), mkTopDmdType, isBotRes, returnsCPR, topSig, isAbsent
)
-import UniqSupply ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
+import UniqSupply
import Unique ( hasKey )
import BasicTypes ( RecFlag(..), isNonRec, isNeverActive )
import VarEnv ( isEmptyVarEnv )
import Maybes ( orElse )
-import DynFlags
import WwLib
import Util ( lengthIs, notNull )
import Outputable
+import MonadUtils
\end{code}
We take Core bindings whose binders have:
\end{enumerate}
\begin{code}
+wwTopBinds :: UniqSupply -> [CoreBind] -> [CoreBind]
-wwTopBinds :: DynFlags
- -> UniqSupply
- -> [CoreBind]
- -> IO [CoreBind]
-
-wwTopBinds dflags us binds
- = do {
- showPass dflags "Worker Wrapper binds";
-
- -- Create worker/wrappers, and mark binders with their
- -- "strictness info" [which encodes their worker/wrapper-ness]
- let { binds' = workersAndWrappers us binds };
-
- endPass dflags "Worker Wrapper binds"
- Opt_D_dump_worker_wrapper binds'
- }
-\end{code}
-
-
-\begin{code}
-workersAndWrappers :: UniqSupply -> [CoreBind] -> [CoreBind]
-
-workersAndWrappers us top_binds
- = initUs_ us $
- mapUs wwBind top_binds `thenUs` \ top_binds' ->
- returnUs (concat top_binds')
+wwTopBinds us top_binds
+ = initUs_ us $ do
+ top_binds' <- mapM wwBind top_binds
+ return (concat top_binds')
\end{code}
%************************************************************************
-- the caller will convert to Expr/Binding,
-- as appropriate.
-wwBind (NonRec binder rhs)
- = wwExpr rhs `thenUs` \ new_rhs ->
- tryWW NonRecursive binder new_rhs `thenUs` \ new_pairs ->
- returnUs [NonRec b e | (b,e) <- new_pairs]
+wwBind (NonRec binder rhs) = do
+ new_rhs <- wwExpr rhs
+ new_pairs <- tryWW NonRecursive binder new_rhs
+ return [NonRec b e | (b,e) <- new_pairs]
-- Generated bindings must be non-recursive
-- because the original binding was.
wwBind (Rec pairs)
- = mapUs do_one pairs `thenUs` \ new_pairs ->
- returnUs [Rec (concat new_pairs)]
+ = return . Rec <$> concatMapM do_one pairs
where
- do_one (binder, rhs) = wwExpr rhs `thenUs` \ new_rhs ->
- tryWW Recursive binder new_rhs
+ do_one (binder, rhs) = do new_rhs <- wwExpr rhs
+ tryWW Recursive binder new_rhs
\end{code}
@wwExpr@ basically just walks the tree, looking for appropriate
\begin{code}
wwExpr :: CoreExpr -> UniqSM CoreExpr
-wwExpr e@(Type _) = returnUs e
-wwExpr e@(Lit _) = returnUs e
-wwExpr e@(Note InlineMe expr) = returnUs e
+wwExpr e@(Type _) = return e
+wwExpr e@(Lit _) = return e
+wwExpr e@(Note InlineMe expr) = return e
-- Don't w/w inside InlineMe's
wwExpr e@(Var v)
- | v `hasKey` lazyIdKey = returnUs lazyIdUnfolding
- | otherwise = returnUs e
+ | v `hasKey` lazyIdKey = return lazyIdUnfolding
+ | otherwise = return e
-- HACK alert: Inline 'lazy' after strictness analysis
-- (but not inside InlineMe's)
wwExpr (Lam binder expr)
- = wwExpr expr `thenUs` \ new_expr ->
- returnUs (Lam binder new_expr)
+ = Lam binder <$> wwExpr expr
wwExpr (App f a)
- = wwExpr f `thenUs` \ new_f ->
- wwExpr a `thenUs` \ new_a ->
- returnUs (App new_f new_a)
+ = App <$> wwExpr f <*> wwExpr a
wwExpr (Note note expr)
- = wwExpr expr `thenUs` \ new_expr ->
- returnUs (Note note new_expr)
+ = Note note <$> wwExpr expr
-wwExpr (Cast expr co)
- = wwExpr expr `thenUs` \ new_expr ->
- returnUs (Cast new_expr co)
+wwExpr (Cast expr co) = do
+ new_expr <- wwExpr expr
+ return (Cast new_expr co)
wwExpr (Let bind expr)
- = wwBind bind `thenUs` \ intermediate_bind ->
- wwExpr expr `thenUs` \ new_expr ->
- returnUs (mkLets intermediate_bind new_expr)
-
-wwExpr (Case expr binder ty alts)
- = wwExpr expr `thenUs` \ new_expr ->
- mapUs ww_alt alts `thenUs` \ new_alts ->
- returnUs (Case new_expr binder ty new_alts)
+ = mkLets <$> wwBind bind <*> wwExpr expr
+
+wwExpr (Case expr binder ty alts) = do
+ new_expr <- wwExpr expr
+ new_alts <- mapM ww_alt alts
+ return (Case new_expr binder ty new_alts)
where
- ww_alt (con, binders, rhs)
- = wwExpr rhs `thenUs` \ new_rhs ->
- returnUs (con, binders, new_rhs)
+ ww_alt (con, binders, rhs) = do
+ new_rhs <- wwExpr rhs
+ return (con, binders, new_rhs)
\end{code}
%************************************************************************
The only reason this is monadised is for the unique supply.
+Note [Don't w/w inline things]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's very important to refrain from w/w-ing an INLINE function
+If we do so by mistake we transform
+ f = __inline (\x -> E)
+into
+ f = __inline (\x -> case x of (a,b) -> fw E)
+ fw = \ab -> (__inline (\x -> E)) (a,b)
+and the original __inline now vanishes, so E is no longer
+inside its __inline wrapper. Death! Disaster!
+
+Furthermore, if the programmer has marked something as INLINE,
+we may lose by w/w'ing it.
+
+If the strictness analyser is run twice, this test also prevents
+wrappers (which are INLINEd) from being re-done.
+
+Notice that we refrain from w/w'ing an INLINE function even if it is
+in a recursive group. It might not be the loop breaker. (We could
+test for loop-breaker-hood, but I'm not sure that ever matters.)
+
\begin{code}
tryWW :: RecFlag
-> Id -- The fn binder
-- if two, then a worker and a
-- wrapper.
tryWW is_rec fn_id rhs
- | isNonRec is_rec && certainlyWillInline unfolding
- -- No point in worker/wrappering a function that is going to be
- -- INLINEd wholesale anyway. If the strictness analyser is run
- -- twice, this test also prevents wrappers (which are INLINEd)
- -- from being re-done.
- --
- -- It's very important to refrain from w/w-ing an INLINE function
- -- If we do so by mistake we transform
- -- f = __inline (\x -> E)
- -- into
- -- f = __inline (\x -> case x of (a,b) -> fw E)
- -- fw = \ab -> (__inline (\x -> E)) (a,b)
- -- and the original __inline now vanishes, so E is no longer
- -- inside its __inline wrapper. Death! Disaster!
+ | -- isNonRec is_rec && -- Now omitted: see Note [Don't w/w inline things]
+ certainlyWillInline unfolding
|| isNeverActive inline_prag
-- No point in worker/wrappering if the thing is never inlined!
-- Because the no-inline prag will prevent the wrapper ever
-- being inlined at a call site.
- = returnUs [ (new_fn_id, rhs) ]
+ = return [ (new_fn_id, rhs) ]
| is_thunk && worthSplittingThunk maybe_fn_dmd res_info
= ASSERT2( isNonRec is_rec, ppr new_fn_id ) -- The thunk must be non-recursive
= splitFun new_fn_id fn_info wrap_dmds res_info inline_prag rhs
| otherwise
- = returnUs [ (new_fn_id, rhs) ]
+ = return [ (new_fn_id, rhs) ]
where
fn_info = idInfo fn_id
---------------------
splitFun fn_id fn_info wrap_dmds res_info inline_prag rhs
- = WARN( not (wrap_dmds `lengthIs` arity), ppr fn_id <+> (ppr arity $$ ppr wrap_dmds $$ ppr res_info) )
+ = WARN( not (wrap_dmds `lengthIs` arity), ppr fn_id <+> (ppr arity $$ ppr wrap_dmds $$ ppr res_info) )
+ (do {
-- The arity should match the signature
- mkWwBodies fun_ty wrap_dmds res_info one_shots `thenUs` \ (work_demands, wrap_fn, work_fn) ->
- getUniqueUs `thenUs` \ work_uniq ->
- let
+ (work_demands, wrap_fn, work_fn) <- mkWwBodies fun_ty wrap_dmds res_info one_shots
+ ; work_uniq <- getUniqueM
+ ; let
work_rhs = work_fn rhs
work_id = mkWorkerId work_uniq fn_id (exprType work_rhs)
`setInlinePragma` inline_prag
wrap_rhs = wrap_fn work_id
wrap_id = fn_id `setIdWorkerInfo` HasWorker work_id arity
- in
- returnUs ([(work_id, work_rhs), (wrap_id, wrap_rhs)])
+ ; return ([(work_id, work_rhs), (wrap_id, wrap_rhs)]) })
-- Worker first, because wrapper mentions it
-- mkWwBodies has already built a wrap_rhs with an INLINE pragma wrapped around it
where
-- Otherwise we spuriously float stuff out of case-expression join points,
-- which is very annoying.
get_one_shots (Lam b e)
- | isId b = isOneShotLambda b : get_one_shots e
+ | isIdVar b = isOneShotLambda b : get_one_shots e
| otherwise = get_one_shots e
get_one_shots (Note _ e) = get_one_shots e
get_one_shots other = noOneShotInfo
-- I# y -> let x = I# y in x }
-- See comments above. Is it not beautifully short?
-splitThunk fn_id rhs
- = mkWWstr [fn_id] `thenUs` \ (_, wrap_fn, work_fn) ->
- returnUs [ (fn_id, Let (NonRec fn_id rhs) (wrap_fn (work_fn (Var fn_id)))) ]
+splitThunk fn_id rhs = do
+ (_, wrap_fn, work_fn) <- mkWWstr [fn_id]
+ return [ (fn_id, Let (NonRec fn_id rhs) (wrap_fn (work_fn (Var fn_id)))) ]
\end{code}
= any worth_it ds || returnsCPR res
-- worthSplitting returns False for an empty list of demands,
-- and hence do_strict_ww is False if arity is zero and there is no CPR
-
- -- We used not to split if the result is bottom.
- -- [Justification: there's no efficiency to be gained.]
- -- But it's sometimes bad not to make a wrapper. Consider
- -- fw = \x# -> let x = I# x# in case e of
- -- p1 -> error_fn x
- -- p2 -> error_fn x
- -- p3 -> the real stuff
- -- The re-boxing code won't go away unless error_fn gets a wrapper too.
- -- [We don't do reboxing now, but in general it's better to pass
- -- an unboxed thing to f, and have it reboxed in the error cases....]
+ -- See Note [Worker-wrapper for bottoming functions]
where
worth_it Abs = True -- Absent arg
worth_it (Eval (Prod ds)) = True -- Product arg to evaluate
worth_it other = False
\end{code}
+Note [Worker-wrapper for bottoming functions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We used not to split if the result is bottom.
+[Justification: there's no efficiency to be gained.]
+
+But it's sometimes bad not to make a wrapper. Consider
+ fw = \x# -> let x = I# x# in case e of
+ p1 -> error_fn x
+ p2 -> error_fn x
+ p3 -> the real stuff
+The re-boxing code won't go away unless error_fn gets a wrapper too.
+[We don't do reboxing now, but in general it's better to pass an
+unboxed thing to f, and have it reboxed in the error cases....]
%************************************************************************
-> StrictSig -- Wrapper strictness info
-> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
-mkWrapper fun_ty (StrictSig (DmdType _ demands res_info))
- = mkWwBodies fun_ty demands res_info noOneShotInfo `thenUs` \ (_, wrap_fn, _) ->
- returnUs wrap_fn
+mkWrapper fun_ty (StrictSig (DmdType _ demands res_info)) = do
+ (_, wrap_fn, _) <- mkWwBodies fun_ty demands res_info noOneShotInfo
+ return wrap_fn
noOneShotInfo = repeat False
\end{code}
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