\section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser}
\begin{code}
-module WwLib (
- mkWwBodies,
- worthSplitting, setUnpackStrategy
- ) where
+module WwLib ( mkWwBodies ) where
#include "HsVersions.h"
import CoreSyn
import CoreUtils ( exprType )
-import Id ( Id, idType, mkSysLocal, idDemandInfo, setIdDemandInfo,
+import Id ( Id, idType, mkSysLocal, idNewDemandInfo, setIdNewDemandInfo,
isOneShotLambda, setOneShotLambda,
setIdInfo
)
-import IdInfo ( CprInfo(..), vanillaIdInfo )
-import DataCon ( splitProductType )
-import Demand ( Demand(..), wwLazy, wwPrim )
-import PrelInfo ( realWorldPrimId, aBSENT_ERROR_ID )
+import IdInfo ( vanillaIdInfo )
+import DataCon ( splitProductType_maybe, splitProductType )
+import NewDemand ( Demand(..), Keepity(..), DmdResult(..) )
+import PrelInfo ( realWorldPrimId, aBSENT_ERROR_ID, eRROR_CSTRING_ID )
import TysPrim ( realWorldStatePrimTy )
import TysWiredIn ( tupleCon )
import Type ( Type, isUnLiftedType, mkFunTys,
splitForAllTys, splitFunTys, splitNewType_maybe, isAlgType
)
+import Literal ( Literal(MachStr) )
import BasicTypes ( Arity, Boxity(..) )
import Var ( Var, isId )
import UniqSupply ( returnUs, thenUs, getUniqueUs, getUniquesUs, UniqSM )
%* *
%************************************************************************
- ************ WARNING ******************
- these comments are rather out of date
- *****************************************
-
-@mkWrapperAndWorker@ is given:
-\begin{enumerate}
-\item
-The {\em original function} \tr{f}, of the form:
-\begin{verbatim}
-f = /\ tyvars -> \ args -> body
-\end{verbatim}
-The original-binder \tr{f}, the \tr{tyvars}, \tr{args}, and \tr{body}
-are given separately.
-
-We use the Id \tr{f} mostly to get its type.
-
-\item
-Strictness information about \tr{f}, in the form of a list of
-@Demands@.
-
-\item
-A @UniqueSupply@.
-\end{enumerate}
-
-@mkWrapperAndWorker@ produces (A BIT OUT-OF-DATE...):
-\begin{enumerate}
-\item
-Maybe @Nothing@: no worker/wrappering going on in this case. This can
-happen (a)~if the strictness info says that there is nothing
-interesting to do or (b)~if *any* of the argument types corresponding
-to ``active'' arg postitions is abstract or will be to the outside
-world (i.e., {\em this} module can see the constructors, but nobody
-else will be able to). An ``active'' arg position is one which the
-wrapper has to unpack. An importing module can't do this unpacking,
-so it simply has to give up and call the wrapper only.
-
-\item
-Maybe \tr{Just (wrapper_Id, wrapper_body, worker_Id, worker_body)}.
-
-The @wrapper_Id@ is just the one that was passed in, with its
-strictness IdInfo updated.
-\end{enumerate}
-
-The \tr{body} of the original function may not be given (i.e., it's
-BOTTOM), in which case you'd jolly well better not tug on the
-worker-body output!
-
Here's an example. The original function is:
+
\begin{verbatim}
g :: forall a . Int -> [a] -> a
g = /\ a -> \ x ys ->
case x of
- I# x# -> g.wrk a x# ys
+ I# x# -> $wg a x# ys
-- call the worker; don't forget the type args!
-- worker
-g.wrk :: forall a . Int# -> [a] -> a
+$wg :: forall a . Int# -> [a] -> a
-g.wrk = /\ a -> \ x# ys ->
+$wg = /\ a -> \ x# ys ->
let
x = I# x#
in
\end{verbatim}
Something we have to be careful about: Here's an example:
+
\begin{verbatim}
-- "f" strictness: U(P)U(P)
f (I# a) (I# b) = a +# b
g = f -- "g" strictness same as "f"
\end{verbatim}
+
\tr{f} will get a worker all nice and friendly-like; that's good.
{\em But we don't want a worker for \tr{g}}, even though it has the
same strictness as \tr{f}. Doing so could break laziness, at best.
%************************************************************************
%* *
-\subsection{Functions over Demands}
-%* *
-%************************************************************************
-
-\begin{code}
-mAX_WORKER_ARGS :: Int -- ToDo: set via flag
-mAX_WORKER_ARGS = 6
-
-setUnpackStrategy :: [Demand] -> [Demand]
-setUnpackStrategy ds
- = snd (go (mAX_WORKER_ARGS - nonAbsentArgs ds) ds)
- where
- go :: Int -- Max number of args available for sub-components of [Demand]
- -> [Demand]
- -> (Int, [Demand]) -- Args remaining after subcomponents of [Demand] are unpacked
-
- go n (WwUnpack _ cs : ds) | n' >= 0
- = WwUnpack True cs' `cons` go n'' ds
- | otherwise
- = WwUnpack False cs `cons` go n ds
- where
- n' = n + 1 - nonAbsentArgs cs
- -- Add one because we don't pass the top-level arg any more
- -- Delete # of non-absent args to which we'll now be committed
- (n'',cs') = go n' cs
-
- go n (d:ds) = d `cons` go n ds
- go n [] = (n,[])
-
- cons d (n,ds) = (n, d:ds)
-
-nonAbsentArgs :: [Demand] -> Int
-nonAbsentArgs [] = 0
-nonAbsentArgs (WwLazy True : ds) = nonAbsentArgs ds
-nonAbsentArgs (d : ds) = 1 + nonAbsentArgs ds
-
-worthSplitting :: [Demand]
- -> Bool -- Result is bottom
- -> Bool -- True <=> the wrapper would not be an identity function
-worthSplitting ds result_bot = any worth_it ds
- -- 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.
-
- where
- worth_it (WwLazy True) = True -- Absent arg
- worth_it (WwUnpack True _) = True -- Arg to unpack
- worth_it WwStrict = False -- Don't w/w just because of strictness
- worth_it other = False
-
-allAbsent :: [Demand] -> Bool
-allAbsent ds = all absent ds
- where
- absent (WwLazy is_absent) = is_absent
- absent (WwUnpack True cs) = allAbsent cs
- absent other = False
-\end{code}
-
-
-%************************************************************************
-%* *
\subsection{The worker wrapper core}
%* *
%************************************************************************
\begin{code}
mkWwBodies :: Type -- Type of original function
- -> Arity -- Arity of original function
-> [Demand] -- Strictness of original function
- -> Bool -- True <=> function returns bottom
+ -> DmdResult -- Info about function result
-> [Bool] -- One-shot-ness of the function
- -> CprInfo -- Result of CPR analysis
-> UniqSM ([Demand], -- Demands for worker (value) args
Id -> CoreExpr, -- Wrapper body, lacking only the worker Id
CoreExpr -> CoreExpr) -- Worker body, lacking the original function rhs
-- let x = (a,b) in
-- E
-mkWwBodies fun_ty arity demands res_bot one_shots cpr_info
- = mkWWargs fun_ty arity demands' res_bot one_shots' `thenUs` \ (wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
- mkWWcpr res_ty cpr_info `thenUs` \ (wrap_fn_cpr, work_fn_cpr, cpr_res_ty) ->
- mkWWstr cpr_res_ty wrap_args `thenUs` \ (work_dmds, wrap_fn_str, work_fn_str) ->
+mkWwBodies fun_ty demands res_info one_shots
+ = mkWWargs fun_ty demands one_shots' `thenUs` \ (wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
+ mkWWcpr res_ty res_info `thenUs` \ (wrap_fn_cpr, work_fn_cpr, cpr_res_ty) ->
+ mkWWstr cpr_res_ty wrap_args `thenUs` \ (work_dmds, wrap_fn_str, work_fn_str) ->
returnUs (work_dmds,
Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . Var,
-- f's RHS is now trivial (size 1) we still want the __inline__ to prevent
-- fw from being inlined into f's RHS
where
- demands' = demands ++ repeat wwLazy
one_shots' = one_shots ++ repeat False
\end{code}
-- It chomps bites off foralls, arrows, newtypes
-- and keeps repeating that until it's satisfied the supplied arity
-mkWWargs :: Type -> Arity
- -> [Demand] -> Bool -> [Bool] -- Both these will in due course be derived
- -- from the type. The [Bool] is True for a one-shot arg.
- -- ** Both are infinite, extended with neutral values if necy **
+mkWWargs :: Type
+ -> [Demand]
+ -> [Bool] -- True for a one-shot arg; ** may be infinite **
-> UniqSM ([Var], -- Wrapper args
CoreExpr -> CoreExpr, -- Wrapper fn
CoreExpr -> CoreExpr, -- Worker fn
Type) -- Type of wrapper body
-mkWWargs fun_ty arity demands res_bot one_shots
- | (res_bot || arity > 0) && (not (null tyvars) || n_arg_tys > 0)
- -- If the function returns bottom, we feel free to
- -- build lots of wrapper args:
- -- \x. let v=E in \y. bottom
- -- = \xy. let v=E in bottom
- = getUniquesUs `thenUs` \ wrap_uniqs ->
- let
- val_args = zipWith4 mk_wrap_arg wrap_uniqs arg_tys demands one_shots
- wrap_args = tyvars ++ val_args
- n_args | res_bot = n_arg_tys
- | otherwise = arity `min` n_arg_tys
- new_fun_ty | n_args == n_arg_tys = body_ty
- | otherwise = mkFunTys (drop n_args arg_tys) body_ty
- in
- mkWWargs new_fun_ty
- (arity - n_args)
- (drop n_args demands)
- res_bot
- (drop n_args one_shots) `thenUs` \ (more_wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
-
- returnUs (wrap_args ++ more_wrap_args,
- mkLams wrap_args . wrap_fn_args,
- work_fn_args . applyToVars wrap_args,
- res_ty)
-
- | Just rep_ty <- splitNewType_maybe fun_ty,
- arity >= 0
+mkWWargs fun_ty demands one_shots
+ | Just rep_ty <- splitNewType_maybe fun_ty
-- The newtype case is for when the function has
-- a recursive newtype after the arrow (rare)
-- We check for arity >= 0 to avoid looping in the case
-- wrapped in a recursive newtype, at least if CPR analysis can look
-- through such newtypes, which it probably can since they are
-- simply coerces.
- = mkWWargs rep_ty arity demands res_bot one_shots `thenUs` \ (wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
+ = mkWWargs rep_ty demands one_shots `thenUs` \ (wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
returnUs (wrap_args,
Note (Coerce fun_ty rep_ty) . wrap_fn_args,
work_fn_args . Note (Coerce rep_ty fun_ty),
res_ty)
+ | not (null demands)
+ = getUniquesUs `thenUs` \ wrap_uniqs ->
+ let
+ (tyvars, tau) = splitForAllTys fun_ty
+ (arg_tys, body_ty) = splitFunTys tau
+
+ n_demands = length demands
+ n_arg_tys = length arg_tys
+ n_args = n_demands `min` n_arg_tys
+
+ new_fun_ty = mkFunTys (drop n_demands arg_tys) body_ty
+ new_demands = drop n_arg_tys demands
+ new_one_shots = drop n_args one_shots
+
+ val_args = zipWith4 mk_wrap_arg wrap_uniqs arg_tys demands one_shots
+ wrap_args = tyvars ++ val_args
+ in
+{- ASSERT( not (null tyvars) || not (null arg_tys) ) -}
+ if (null tyvars) && (null arg_tys) then
+ pprTrace "mkWWargs" (ppr fun_ty $$ ppr demands)
+ returnUs ([], id, id, fun_ty)
+ else
+
+ mkWWargs new_fun_ty
+ new_demands
+ new_one_shots `thenUs` \ (more_wrap_args, wrap_fn_args, work_fn_args, res_ty) ->
+
+ returnUs (wrap_args ++ more_wrap_args,
+ mkLams wrap_args . wrap_fn_args,
+ work_fn_args . applyToVars wrap_args,
+ res_ty)
+
| otherwise
= returnUs ([], id, id, fun_ty)
- where
- (tyvars, tau) = splitForAllTys fun_ty
- (arg_tys, body_ty) = splitFunTys tau
- n_arg_tys = length arg_tys
-
applyToVars :: [Var] -> CoreExpr -> CoreExpr
applyToVars vars fn = mkVarApps fn vars
mk_wrap_arg uniq ty dmd one_shot
- = set_one_shot one_shot (setIdDemandInfo (mkSysLocal SLIT("w") uniq ty) dmd)
+ = set_one_shot one_shot (setIdNewDemandInfo (mkSysLocal SLIT("w") uniq ty) dmd)
where
set_one_shot True id = setOneShotLambda id
set_one_shot False id = id
mkWWstr res_ty wrap_args
= mk_ww_str wrap_args `thenUs` \ (work_args, take_apart, put_together) ->
let
- work_dmds = [idDemandInfo v | v <- work_args, isId v]
+ work_dmds = [idNewDemandInfo v | v <- work_args, isId v]
apply_to args fn = mkVarApps fn args
in
if not (null work_dmds && isUnLiftedType res_ty) then
returnUs ( work_dmds,
- take_apart . apply_to work_args,
+ take_apart . applyToVars work_args,
mkLams work_args . put_together)
else
-- Horrid special case. If the worker would have no arguments, and the
let
void_arg = mk_ww_local void_arg_uniq realWorldStatePrimTy
in
- returnUs ([wwPrim],
- take_apart . apply_to [realWorldPrimId] . apply_to work_args,
+ returnUs ([Lazy],
+ take_apart . applyToVars [realWorldPrimId] . apply_to work_args,
mkLams work_args . Lam void_arg . put_together)
-- Empty case
returnUs (arg : worker_args, wrap_fn, work_fn)
| otherwise
- = case idDemandInfo arg of
+ = case idNewDemandInfo arg of
- -- Absent case
- WwLazy True ->
+ -- Absent case. We don't deal with absence for unlifted types,
+ -- though, because it's not so easy to manufacture a placeholder
+ -- We'll see if this turns out to be a problem
+ Abs | not (isUnLiftedType (idType arg)) ->
mk_ww_str ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
returnUs (worker_args, wrap_fn, mk_absent_let arg . work_fn)
+ -- Seq and keep
+ Seq Keep _ [] -> mk_ww_str ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ returnUs (arg : worker_args, mk_seq_case arg . wrap_fn, work_fn)
+ -- Pass the arg, no need to rebox
+
+ -- Seq and discard
+ Seq Drop _ [] -> mk_ww_str ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ returnUs (worker_args, mk_seq_case arg . wrap_fn, mk_absent_let arg . work_fn)
+ -- Don't pass the arg, build absent arg
+
-- Unpack case
- WwUnpack True cs ->
- getUniquesUs `thenUs` \ uniqs ->
- let
- unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
- unpk_args_w_ds = zipWithEqual "mk_ww_str" set_worker_arg_info unpk_args cs
- in
- mk_ww_str (unpk_args_w_ds ++ ds) `thenUs` \ (worker_args, wrap_fn, work_fn) ->
- returnUs (worker_args,
- mk_unpk_case arg unpk_args data_con arg_tycon . wrap_fn,
- work_fn . mk_pk_let arg data_con tycon_arg_tys unpk_args)
- where
- (arg_tycon, tycon_arg_tys, data_con, inst_con_arg_tys) = splitProductType "mk_ww_str" (idType arg)
+ Seq keep _ cs
+ | Just (arg_tycon, tycon_arg_tys, data_con, inst_con_arg_tys)
+ <- splitProductType_maybe (idType arg)
+ -> getUniquesUs `thenUs` \ uniqs ->
+ let
+ unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
+ unpk_args_w_ds = zipWithEqual "mk_ww_str" set_worker_arg_info unpk_args cs
+ unbox_fn = mk_unpk_case arg unpk_args data_con arg_tycon
+ rebox_fn = mk_pk_let arg data_con tycon_arg_tys unpk_args
+ in
+ mk_ww_str (unpk_args_w_ds ++ ds) `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ case keep of
+ Keep -> returnUs (arg : worker_args, unbox_fn . wrap_fn, work_fn)
+ -- Pass the arg, no need to rebox
+ Drop -> returnUs (worker_args, unbox_fn . wrap_fn, work_fn . rebox_fn)
+ -- Don't pass the arg, rebox instead
+
+ | otherwise ->
+ WARN( True, ppr arg )
+ mk_ww_str ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ returnUs (arg : worker_args, wrap_fn, work_fn)
-- Other cases
other_demand ->
-- If the wrapper argument is a one-shot lambda, then
-- so should (all) the corresponding worker arguments be
-- This bites when we do w/w on a case join point
- set_worker_arg_info worker_arg demand = set_one_shot (setIdDemandInfo worker_arg demand)
+ set_worker_arg_info worker_arg demand = set_one_shot (setIdNewDemandInfo worker_arg demand)
set_one_shot | isOneShotLambda arg = setOneShotLambda
| otherwise = \x -> x
\begin{code}
mkWWcpr :: Type -- function body type
- -> CprInfo -- CPR analysis results
+ -> DmdResult -- CPR analysis results
-> UniqSM (CoreExpr -> CoreExpr, -- New wrapper
CoreExpr -> CoreExpr, -- New worker
Type) -- Type of worker's body
-mkWWcpr body_ty NoCPRInfo
- = returnUs (id, id, body_ty) -- Must be just the strictness transf.
-
-mkWWcpr body_ty ReturnsCPR
+mkWWcpr body_ty RetCPR
| not (isAlgType body_ty)
= WARN( True, text "mkWWcpr: non-algebraic body type" <+> ppr body_ty )
returnUs (id, id, body_ty)
n_con_args = length con_arg_tys
con_arg_ty1 = head con_arg_tys
+mkWWcpr body_ty other -- No CPR info
+ = returnUs (id, id, body_ty)
+
-- If the original function looked like
-- f = \ x -> _scc_ "foo" E
--
\begin{code}
mk_absent_let arg body
| not (isUnLiftedType arg_ty)
- = Let (NonRec arg (mkTyApps (Var aBSENT_ERROR_ID) [arg_ty])) body
+ = Let (NonRec arg abs_rhs) body
| otherwise
= panic "WwLib: haven't done mk_absent_let for primitives yet"
where
arg_ty = idType arg
+-- abs_rhs = mkTyApps (Var aBSENT_ERROR_ID) [arg_ty]
+ abs_rhs = mkApps (Var eRROR_CSTRING_ID) [Type arg_ty, Lit (MachStr (_PK_ msg))]
+ msg = "Oops! Entered absent arg " ++ showSDocDebug (ppr arg <+> ppr (idType arg))
mk_unpk_case arg unpk_args boxing_con boxing_tycon body
-- A data type
(sanitiseCaseBndr arg)
[(DataAlt boxing_con, unpk_args, body)]
+mk_seq_case arg body = Case (Var arg) (sanitiseCaseBndr arg) [(DEFAULT, [], body)]
+
sanitiseCaseBndr :: Id -> Id
-- The argument we are scrutinising has the right type to be
-- a case binder, so it's convenient to re-use it for that purpose.
where
con_args = map Type con_tys ++ map Var unpk_args
-
mk_ww_local uniq ty = mkSysLocal SLIT("ww") uniq ty
-
\end{code}
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