+++ /dev/null
-%
-% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
-%
-\section[WorkWrap]{Worker/wrapper-generating back-end of strictness analyser}
-
-\begin{code}
-module WorkWrap ( wwTopBinds, mkWrapper ) where
-
-#include "HsVersions.h"
-
-import CoreSyn
-import CoreUnfold ( certainlyWillInline )
-import CoreLint ( showPass, endPass )
-import CoreUtils ( exprType, exprIsHNF )
-import Id ( Id, idType, isOneShotLambda,
- setIdNewStrictness, mkWorkerId,
- setIdWorkerInfo, setInlinePragma,
- idInfo )
-import MkId ( lazyIdKey, lazyIdUnfolding )
-import Type ( Type )
-import IdInfo ( WorkerInfo(..), arityInfo,
- newDemandInfo, newStrictnessInfo, unfoldingInfo, inlinePragInfo
- )
-import NewDemand ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..),
- Demands(..), mkTopDmdType, isBotRes, returnsCPR, topSig, isAbsent
- )
-import UniqSupply ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
-import Unique ( hasKey )
-import BasicTypes ( RecFlag(..), isNonRec, Activation(..) )
-import VarEnv ( isEmptyVarEnv )
-import Maybes ( orElse )
-import DynFlags
-import WwLib
-import Util ( lengthIs, notNull )
-import Outputable
-\end{code}
-
-We take Core bindings whose binders have:
-
-\begin{enumerate}
-
-\item Strictness attached (by the front-end of the strictness
-analyser), and / or
-
-\item Constructed Product Result information attached by the CPR
-analysis pass.
-
-\end{enumerate}
-
-and we return some ``plain'' bindings which have been
-worker/wrapper-ified, meaning:
-
-\begin{enumerate}
-
-\item Functions have been split into workers and wrappers where
-appropriate. If a function has both strictness and CPR properties
-then only one worker/wrapper doing both transformations is produced;
-
-\item Binders' @IdInfos@ have been updated to reflect the existence of
-these workers/wrappers (this is where we get STRICTNESS and CPR pragma
-info for exported values).
-\end{enumerate}
-
-\begin{code}
-
-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')
-\end{code}
-
-%************************************************************************
-%* *
-\subsection[wwBind-wwExpr]{@wwBind@ and @wwExpr@}
-%* *
-%************************************************************************
-
-@wwBind@ works on a binding, trying each \tr{(binder, expr)} pair in
-turn. Non-recursive case first, then recursive...
-
-\begin{code}
-wwBind :: CoreBind
- -> UniqSM [CoreBind] -- returns a WwBinding intermediate form;
- -- 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]
- -- 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)]
- where
- do_one (binder, rhs) = wwExpr rhs `thenUs` \ new_rhs ->
- tryWW Recursive binder new_rhs
-\end{code}
-
-@wwExpr@ basically just walks the tree, looking for appropriate
-annotations that can be used. Remember it is @wwBind@ that does the
-matching by looking for strict arguments of the correct type.
-@wwExpr@ is a version that just returns the ``Plain'' Tree.
-
-\begin{code}
-wwExpr :: CoreExpr -> UniqSM CoreExpr
-
-wwExpr e@(Type _) = returnUs e
-wwExpr e@(Lit _) = returnUs e
-wwExpr e@(Note InlineMe expr) = returnUs e
- -- Don't w/w inside InlineMe's
-
-wwExpr e@(Var v)
- | v `hasKey` lazyIdKey = returnUs lazyIdUnfolding
- | otherwise = returnUs e
- -- Inline 'lazy' after strictness analysis
- -- (but not inside InlineMe's)
-
-wwExpr (Lam binder expr)
- = wwExpr expr `thenUs` \ new_expr ->
- returnUs (Lam binder new_expr)
-
-wwExpr (App f a)
- = wwExpr f `thenUs` \ new_f ->
- wwExpr a `thenUs` \ new_a ->
- returnUs (App new_f new_a)
-
-wwExpr (Note note expr)
- = wwExpr expr `thenUs` \ new_expr ->
- returnUs (Note note new_expr)
-
-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)
- where
- ww_alt (con, binders, rhs)
- = wwExpr rhs `thenUs` \ new_rhs ->
- returnUs (con, binders, new_rhs)
-\end{code}
-
-%************************************************************************
-%* *
-\subsection[tryWW]{@tryWW@: attempt a worker/wrapper pair}
-%* *
-%************************************************************************
-
-@tryWW@ just accumulates arguments, converts strictness info from the
-front-end into the proper form, then calls @mkWwBodies@ to do
-the business.
-
-We have to BE CAREFUL that we don't worker-wrapperize an Id that has
-already been w-w'd! (You can end up with several liked-named Ids
-bouncing around at the same time---absolute mischief.) So the
-criterion we use is: if an Id already has an unfolding (for whatever
-reason), then we don't w-w it.
-
-The only reason this is monadised is for the unique supply.
-
-\begin{code}
-tryWW :: RecFlag
- -> Id -- The fn binder
- -> CoreExpr -- The bound rhs; its innards
- -- are already ww'd
- -> UniqSM [(Id, CoreExpr)] -- either *one* or *two* pairs;
- -- if one, then no worker (only
- -- the orig "wrapper" lives on);
- -- 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!
- = returnUs [ (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
- splitThunk new_fn_id rhs
-
- | is_fun && worthSplittingFun wrap_dmds res_info
- = splitFun new_fn_id fn_info wrap_dmds res_info inline_prag rhs
-
- | otherwise
- = returnUs [ (new_fn_id, rhs) ]
-
- where
- fn_info = idInfo fn_id
- maybe_fn_dmd = newDemandInfo fn_info
- unfolding = unfoldingInfo fn_info
- inline_prag = inlinePragInfo fn_info
-
- -- In practice it always will have a strictness
- -- signature, even if it's a uninformative one
- strict_sig = newStrictnessInfo fn_info `orElse` topSig
- StrictSig (DmdType env wrap_dmds res_info) = strict_sig
-
- -- new_fn_id has the DmdEnv zapped.
- -- (a) it is never used again
- -- (b) it wastes space
- -- (c) it becomes incorrect as things are cloned, because
- -- we don't push the substitution into it
- new_fn_id | isEmptyVarEnv env = fn_id
- | otherwise = fn_id `setIdNewStrictness`
- StrictSig (mkTopDmdType wrap_dmds res_info)
-
- is_fun = notNull wrap_dmds
- is_thunk = not is_fun && not (exprIsHNF rhs)
-
----------------------
-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) )
- -- 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_rhs = work_fn rhs
- work_id = mkWorkerId work_uniq fn_id (exprType work_rhs)
- `setInlinePragma` inline_prag
- `setIdNewStrictness` StrictSig (mkTopDmdType work_demands work_res_info)
- -- Even though we may not be at top level,
- -- it's ok to give it an empty DmdEnv
-
- wrap_rhs = wrap_fn work_id
- wrap_id = fn_id `setIdWorkerInfo` HasWorker work_id arity
- `setInlinePragma` AlwaysActive -- Zap any inline pragma;
- -- Put it on the worker instead
- in
- returnUs ([(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
- fun_ty = idType fn_id
-
- arity = arityInfo fn_info -- The arity is set by the simplifier using exprEtaExpandArity
- -- So it may be more than the number of top-level-visible lambdas
-
- work_res_info | isBotRes res_info = BotRes -- Cpr stuff done by wrapper
- | otherwise = TopRes
-
- one_shots = get_one_shots rhs
-
--- If the original function has one-shot arguments, it is important to
--- make the wrapper and worker have corresponding one-shot arguments too.
--- 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
- | otherwise = get_one_shots e
-get_one_shots (Note _ e) = get_one_shots e
-get_one_shots other = noOneShotInfo
-\end{code}
-
-Thunk splitting
-~~~~~~~~~~~~~~~
-Suppose x is used strictly (never mind whether it has the CPR
-property).
-
- let
- x* = x-rhs
- in body
-
-splitThunk transforms like this:
-
- let
- x* = case x-rhs of { I# a -> I# a }
- in body
-
-Now simplifier will transform to
-
- case x-rhs of
- I# a -> let x* = I# b
- in body
-
-which is what we want. Now suppose x-rhs is itself a case:
-
- x-rhs = case e of { T -> I# a; F -> I# b }
-
-The join point will abstract over a, rather than over (which is
-what would have happened before) which is fine.
-
-Notice that x certainly has the CPR property now!
-
-In fact, splitThunk uses the function argument w/w splitting
-function, so that if x's demand is deeper (say U(U(L,L),L))
-then the splitting will go deeper too.
-
-\begin{code}
--- splitThunk converts the *non-recursive* binding
--- x = e
--- into
--- x = let x = e
--- in case x of
--- 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)))) ]
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Functions over Demands}
-%* *
-%************************************************************************
-
-\begin{code}
-worthSplittingFun :: [Demand] -> DmdResult -> Bool
- -- True <=> the wrapper would not be an identity function
-worthSplittingFun ds res
- = 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....]
- where
- worth_it Abs = True -- Absent arg
- worth_it (Eval (Prod ds)) = True -- Product arg to evaluate
- worth_it other = False
-
-worthSplittingThunk :: Maybe Demand -- Demand on the thunk
- -> DmdResult -- CPR info for the thunk
- -> Bool
-worthSplittingThunk maybe_dmd res
- = worth_it maybe_dmd || returnsCPR res
- where
- -- Split if the thing is unpacked
- worth_it (Just (Eval (Prod ds))) = not (all isAbsent ds)
- worth_it other = False
-\end{code}
-
-
-
-%************************************************************************
-%* *
-\subsection{The worker wrapper core}
-%* *
-%************************************************************************
-
-@mkWrapper@ is called when importing a function. We have the type of
-the function and the name of its worker, and we want to make its body (the wrapper).
-
-\begin{code}
-mkWrapper :: Type -- Wrapper type
- -> 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
-
-noOneShotInfo = repeat False
-\end{code}
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