%
-% (c) The GRASP/AQUA Project, Glasgow University, 1993-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1993-1998
%
\section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser}
\begin{code}
-#include "HsVersions.h"
-
-module WwLib (
- WwBinding(..),
-
- worthSplitting, setUnpackStrategy,
- mkWwBodies, mkWrapper
- ) where
+module WwLib ( mkWwBodies, mkWWstr, mkWorkerArgs ) where
-IMP_Ubiq(){-uitous-}
+#include "HsVersions.h"
import CoreSyn
-import Id ( idType, mkSysLocal, dataConArgTys )
-import IdInfo ( mkStrictnessInfo, nonAbsentArgs, Demand(..) )
-import PrelVals ( aBSENT_ERROR_ID, voidId )
-import TysPrim ( voidTy )
-import SrcLoc ( noSrcLoc )
-import Type ( isPrimType, mkTyVarTys, mkForAllTys, mkFunTys,
- splitForAllTy, splitFunTyExpandingDicts,
- maybeAppDataTyConExpandingDicts
+import CoreUtils ( exprType )
+import Id ( Id, idType, mkSysLocal, idNewDemandInfo, setIdNewDemandInfo,
+ isOneShotLambda, setOneShotLambda, setIdUnfolding,
+ setIdInfo
)
-import UniqSupply ( returnUs, thenUs, thenMaybeUs,
- getUniques, getUnique, SYN_IE(UniqSM)
+import IdInfo ( vanillaIdInfo )
+import DataCon ( splitProductType_maybe, splitProductType )
+import NewDemand ( Demand(..), DmdResult(..), Demands(..) )
+import MkId ( realWorldPrimId, voidArgId, mkRuntimeErrorApp, rUNTIME_ERROR_ID )
+import TysWiredIn ( tupleCon )
+import Type ( Type, isUnLiftedType, mkFunTys,
+ splitForAllTys, splitFunTys, splitRecNewType_maybe, isAlgType
)
-import Util ( zipWithEqual, zipEqual, assertPanic, panic )
+import BasicTypes ( Boxity(..) )
+import Var ( Var, isId )
+import UniqSupply ( returnUs, thenUs, getUniquesUs, UniqSM )
+import Util ( zipWithEqual, notNull )
+import Outputable
+import List ( zipWith4 )
\end{code}
-%************************************************************************
-%* *
-\subsection[datatype-WwLib]{@WwBinding@: a datatype for worker/wrapper-ing}
-%* *
-%************************************************************************
-
-In the worker/wrapper stuff, we want to carry around @CoreBindings@ in
-an ``intermediate form'' that can later be turned into a \tr{let} or
-\tr{case} (depending on strictness info).
-
-\begin{code}
-data WwBinding
- = WwLet [CoreBinding]
- | WwCase (CoreExpr -> CoreExpr)
- -- the "case" will be a "strict let" of the form:
- --
- -- case rhs of
- -- <blah> -> body
- --
- -- (instead of "let <blah> = rhs in body")
- --
- -- The expr you pass to the function is "body" (the
- -- expression that goes "in the corner").
-\end{code}
%************************************************************************
%* *
%* *
%************************************************************************
- ************ 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}
+\subsection{The worker wrapper core}
%* *
%************************************************************************
-\begin{code}
-mAX_WORKER_ARGS :: Int -- ToDo: set via flag
-mAX_WORKER_ARGS = 6
+@mkWwBodies@ is called when doing the worker/wrapper split inside a module.
-setUnpackStrategy :: [Demand] -> [Demand]
-setUnpackStrategy ds
- = snd (go (mAX_WORKER_ARGS - nonAbsentArgs ds) ds)
+\begin{code}
+mkWwBodies :: Type -- Type of original function
+ -> [Demand] -- Strictness of original function
+ -> DmdResult -- Info about function result
+ -> [Bool] -- One-shot-ness of the function
+ -> 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
+
+-- wrap_fn_args E = \x y -> E
+-- work_fn_args E = E x y
+
+-- wrap_fn_str E = case x of { (a,b) ->
+-- case a of { (a1,a2) ->
+-- E a1 a2 b y }}
+-- work_fn_str E = \a2 a2 b y ->
+-- let a = (a1,a2) in
+-- let x = (a,b) in
+-- E
+
+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) ->
+ mkWWstr wrap_args `thenUs` \ (work_args, wrap_fn_str, work_fn_str) ->
+ let
+ (work_lam_args, work_call_args) = mkWorkerArgs work_args res_ty
+ in
+ -- Don't do CPR if the worker doesn't have any value arguments
+ -- Then the worker is just a constant, so we don't want to unbox it.
+ (if any isId work_args then
+ mkWWcpr res_ty res_info
+ else
+ returnUs (id, id, res_ty)
+ ) `thenUs` \ (wrap_fn_cpr, work_fn_cpr, cpr_res_ty) ->
+
+ returnUs ([idNewDemandInfo v | v <- work_args, isId v],
+ Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_call_args . Var,
+ mkLams work_lam_args. work_fn_str . work_fn_cpr . work_fn_args)
+ -- We use an INLINE unconditionally, even if the wrapper turns out to be
+ -- something trivial like
+ -- fw = ...
+ -- f = __inline__ (coerce T fw)
+ -- The point is to propagate the coerce to f's call sites, so even though
+ -- f's RHS is now trivial (size 1) we still want the __inline__ to prevent
+ -- fw from being inlined into f's RHS
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 -- True <=> the wrapper would not be an identity function
-worthSplitting [] = False
-worthSplitting (WwLazy True : ds) = True -- Absent arg
-worthSplitting (WwUnpack True _ : ds) = True -- Arg to unpack
-worthSplitting (d : ds) = worthSplitting ds
-
-allAbsent :: [Demand] -> Bool
-allAbsent (WwLazy True : ds) = allAbsent ds
-allAbsent (WwUnpack True cs : ds) = allAbsent cs && allAbsent ds
-allAbsent (d : ds) = False
-allAbsent [] = True
+ one_shots' = one_shots ++ repeat False
\end{code}
%************************************************************************
%* *
-\subsection{The worker wrapper core}
+\subsection{Making wrapper args}
%* *
%************************************************************************
-@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).
+During worker-wrapper stuff we may end up with an unlifted thing
+which we want to let-bind without losing laziness. So we
+add a void argument. E.g.
-\begin{code}
-mkWrapper :: Type -- Wrapper type
- -> [Demand] -- Wrapper strictness info
- -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
+ f = /\a -> \x y z -> E::Int# -- E does not mention x,y,z
+==>
+ fw = /\ a -> \void -> E
+ f = /\ a -> \x y z -> fw realworld
-mkWrapper fun_ty demands
- = let
- n_wrap_args = length demands
- in
- getUniques n_wrap_args `thenUs` \ wrap_uniqs ->
- let
- (tyvars, tau_ty) = splitForAllTy fun_ty
- (arg_tys, body_ty) = splitFunTyExpandingDicts tau_ty
- wrap_args = zipWith mk_ww_local wrap_uniqs arg_tys
- leftover_arg_tys = drop n_wrap_args arg_tys
- final_body_ty = mkFunTys leftover_arg_tys body_ty
- in
- mkWwBodies tyvars wrap_args final_body_ty demands `thenUs` \ (wrap_fn, _, _) ->
- returnUs wrap_fn
+We use the state-token type which generates no code.
+
+\begin{code}
+mkWorkerArgs :: [Var]
+ -> Type -- Type of body
+ -> ([Var], -- Lambda bound args
+ [Var]) -- Args at call site
+mkWorkerArgs args res_ty
+ | any isId args || not (isUnLiftedType res_ty)
+ = (args, args)
+ | otherwise
+ = (args ++ [voidArgId], args ++ [realWorldPrimId])
\end{code}
-@mkWwBodies@ is called when doing the worker/wrapper split inside a module.
+
+%************************************************************************
+%* *
+\subsection{Coercion stuff}
+%* *
+%************************************************************************
+
+
+We really want to "look through" coerces.
+Reason: I've seen this situation:
+
+ let f = coerce T (\s -> E)
+ in \x -> case x of
+ p -> coerce T' f
+ q -> \s -> E2
+ r -> coerce T' f
+
+If only we w/w'd f, we'd get
+ let f = coerce T (\s -> fw s)
+ fw = \s -> E
+ in ...
+
+Now we'll inline f to get
+
+ let fw = \s -> E
+ in \x -> case x of
+ p -> fw
+ q -> \s -> E2
+ r -> fw
+
+Now we'll see that fw has arity 1, and will arity expand
+the \x to get what we want.
\begin{code}
-mkWwBodies :: [TyVar] -> [Id] -> Type -- Original fn args and body type
- -> [Demand] -- Strictness info for original fn; corresp 1-1 with args
- -> UniqSM (Id -> CoreExpr, -- Wrapper body, lacking only the worker Id
- CoreExpr -> CoreExpr, -- Worker body, lacking the original function body
- [Demand]) -- Strictness info for worker
-
-mkWwBodies tyvars args body_ty demands
- | allAbsent demands &&
- isPrimType body_ty
- = -- Horrid special case. If the worker would have no arguments, and the
- -- function returns a primitive type value, that would make the worker into
- -- an unboxed value. We box it by passing a dummy void argument, thus:
- --
- -- f = /\abc. \xyz. fw abc void
- -- fw = /\abc. \v. body
+-- mkWWargs is driven off the function type and arity.
+-- It chomps bites off foralls, arrows, newtypes
+-- and keeps repeating that until it's satisfied the supplied arity
+
+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 demands one_shots
+ | Just rep_ty <- splitRecNewType_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
+ -- of a function whose type is, in effect, infinite
+ -- [Arity is driven by looking at the term, not just the type.]
--
- getUnique `thenUs` \ void_arg_uniq ->
+ -- It's also important when we have a function returning (say) a pair
+ -- 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 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)
+
+ | notNull demands
+ = getUniquesUs `thenUs` \ wrap_uniqs ->
let
- void_arg = mk_ww_local void_arg_uniq voidTy
+ (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
- returnUs (\ work_id -> mkLam tyvars args (App (mkTyApp (Var work_id) (mkTyVarTys tyvars)) (VarArg voidId)),
- \ body -> mkLam tyvars [void_arg] body,
- [WwLazy True])
+{- ASSERT( notNull tyvars || notNull 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)
-mkWwBodies tyvars args body_ty demands
| otherwise
- = let
- args_w_demands = zipEqual "mkWwBodies" args demands
- in
- mkWW args_w_demands `thenUs` \ (wrap_fn, work_args_w_demands, work_fn) ->
- let
- (work_args, work_demands) = unzip work_args_w_demands
- in
- returnUs (\ work_id -> mkLam tyvars args (wrap_fn (mkTyApp (Var work_id) (mkTyVarTys tyvars))),
- \ body -> mkLam tyvars work_args (work_fn body),
- work_demands)
-\end{code}
+ = returnUs ([], id, id, fun_ty)
+
+applyToVars :: [Var] -> CoreExpr -> CoreExpr
+applyToVars vars fn = mkVarApps fn vars
+
+mk_wrap_arg uniq ty dmd one_shot
+ = set_one_shot one_shot (setIdNewDemandInfo (mkSysLocal FSLIT("w") uniq ty) dmd)
+ where
+ set_one_shot True id = setOneShotLambda id
+ set_one_shot False id = id
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Strictness stuff}
+%* *
+%************************************************************************
\begin{code}
-mkWW :: [(Id,Demand)]
- -> UniqSM (CoreExpr -> CoreExpr, -- Wrapper body, lacking the inner call to the worker
- -- and without its lambdas
- [(Id,Demand)], -- Worker args and their demand infos
- CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function
+mkWWstr :: [Var] -- Wrapper args; have their demand info on them
+ -- *Includes type variables*
+ -> UniqSM ([Var], -- Worker args
+ CoreExpr -> CoreExpr, -- Wrapper body, lacking the worker call
+ -- and without its lambdas
+ -- This fn adds the unboxing
+
+ CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function,
+ -- and lacking its lambdas.
+ -- This fn does the reboxing
+
+----------------------
+nop_fn body = body
+----------------------
+mkWWstr []
+ = returnUs ([], nop_fn, nop_fn)
- -- Empty case
-mkWW []
- = returnUs (\ wrapper_body -> wrapper_body,
- [],
- \ worker_body -> worker_body)
+mkWWstr (arg : args)
+ = mkWWstr_one arg `thenUs` \ (args1, wrap_fn1, work_fn1) ->
+ mkWWstr args `thenUs` \ (args2, wrap_fn2, work_fn2) ->
+ returnUs (args1 ++ args2, wrap_fn1 . wrap_fn2, work_fn1 . work_fn2)
- -- Absent case
-mkWW ((arg,WwLazy True) : ds)
- = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
- returnUs (\ wrapper_body -> wrap_fn wrapper_body,
- worker_args,
- \ worker_body -> mk_absent_let arg (work_fn worker_body))
+----------------------
+-- mkWWstr_one wrap_arg = (work_args, wrap_fn, work_fn)
+-- * wrap_fn assumes wrap_arg is in scope,
+-- brings into scope work_args (via cases)
+-- * work_fn assumes work_args are in scope, a
+-- brings into scope wrap_arg (via lets)
+mkWWstr_one arg
+ | isTyVar arg
+ = returnUs ([arg], nop_fn, nop_fn)
+
+ | otherwise
+ = case idNewDemandInfo arg of
+
+ -- 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)) ->
+ returnUs ([], nop_fn, mk_absent_let arg)
-- Unpack case
-mkWW ((arg,WwUnpack True cs) : ds)
- = getUniques (length inst_con_arg_tys) `thenUs` \ uniqs ->
- let
- unpk_args = zipWith mk_ww_local uniqs inst_con_arg_tys
- unpk_args_w_ds = zipEqual "mkWW" unpk_args cs
- in
- mkWW (unpk_args_w_ds ++ ds) `thenUs` \ (wrap_fn, worker_args, work_fn) ->
- returnUs (\ wrapper_body -> mk_unpk_case arg unpk_args data_con arg_tycon (wrap_fn wrapper_body),
- worker_args,
- \ worker_body -> work_fn (mk_pk_let arg data_con tycon_arg_tys unpk_args worker_body))
+ Eval (Prod 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 "mkWWstr" set_worker_arg_info unpk_args cs
+ unbox_fn = mk_unpk_case arg unpk_args data_con arg_tycon
+ rebox_fn = Let (NonRec arg con_app)
+ con_app = mkConApp data_con (map Type tycon_arg_tys ++ map Var unpk_args)
+ in
+ mkWWstr unpk_args_w_ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ returnUs (worker_args, unbox_fn . wrap_fn, work_fn . rebox_fn)
+ -- Don't pass the arg, rebox instead
+
+ -- `seq` demand; evaluate in wrapper in the hope
+ -- of dropping seqs in the worker
+ Eval (Poly Abs)
+ -> let
+ arg_w_unf = arg `setIdUnfolding` evaldUnfolding
+ -- Tell the worker arg that it's sure to be evaluated
+ -- so that internal seqs can be dropped
+ in
+ returnUs ([arg_w_unf], mk_seq_case arg, nop_fn)
+ -- Pass the arg, anyway, even if it is in theory discarded
+ -- Consider
+ -- f x y = x `seq` y
+ -- x gets a (Eval (Poly Abs)) demand, but if we fail to pass it to the worker
+ -- we ABSOLUTELY MUST record that x is evaluated in the wrapper.
+ -- Something like:
+ -- f x y = x `seq` fw y
+ -- fw y = let x{Evald} = error "oops" in (x `seq` y)
+ -- If we don't pin on the "Evald" flag, the seq doesn't disappear, and
+ -- we end up evaluating the absent thunk.
+ -- But the Evald flag is pretty weird, and I worry that it might disappear
+ -- during simplification, so for now I've just nuked this whole case
+
+ -- Other cases
+ other_demand -> returnUs ([arg], nop_fn, nop_fn)
+
where
- inst_con_arg_tys = dataConArgTys data_con tycon_arg_tys
- (arg_tycon, tycon_arg_tys, data_con)
- = case (maybeAppDataTyConExpandingDicts (idType arg)) of
+ -- 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 (setIdNewDemandInfo worker_arg demand)
+
+ set_one_shot | isOneShotLambda arg = setOneShotLambda
+ | otherwise = \x -> x
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{CPR stuff}
+%* *
+%************************************************************************
- Just (arg_tycon, tycon_arg_tys, [data_con]) ->
- -- The main event: a single-constructor data type
- (arg_tycon, tycon_arg_tys, data_con)
- Just (_, _, data_cons) -> panic "mk_ww_arg_processing: not one constr (interface files not consistent/up to date ?)"
- Nothing -> panic "mk_ww_arg_processing: not datatype"
+@mkWWcpr@ takes the worker/wrapper pair produced from the strictness
+info and adds in the CPR transformation. The worker returns an
+unboxed tuple containing non-CPR components. The wrapper takes this
+tuple and re-produces the correct structured output.
+The non-CPR results appear ordered in the unboxed tuple as if by a
+left-to-right traversal of the result structure.
- -- Other cases
-mkWW ((arg,other_demand) : ds)
- = mkWW ds `thenUs` \ (wrap_fn, worker_args, work_fn) ->
- returnUs (\ wrapper_body -> wrap_fn (App wrapper_body (VarArg arg)),
- (arg,other_demand) : worker_args,
- work_fn)
+
+\begin{code}
+mkWWcpr :: Type -- function body type
+ -> DmdResult -- CPR analysis results
+ -> UniqSM (CoreExpr -> CoreExpr, -- New wrapper
+ CoreExpr -> CoreExpr, -- New worker
+ Type) -- Type of worker's body
+
+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 == 1 && isUnLiftedType con_arg_ty1
+ -- Special case when there is a single result of unlifted type
+ --
+ -- Wrapper: case (..call worker..) of x -> C x
+ -- Worker: case ( ..body.. ) of C x -> x
+ = getUniquesUs `thenUs` \ (work_uniq : arg_uniq : _) ->
+ let
+ work_wild = mk_ww_local work_uniq body_ty
+ arg = mk_ww_local arg_uniq con_arg_ty1
+ con_app = mkConApp data_con (map Type tycon_arg_tys ++ [Var arg])
+ in
+ returnUs (\ wkr_call -> Case wkr_call arg (exprType con_app) [(DEFAULT, [], con_app)],
+ \ body -> workerCase body work_wild con_arg_ty1 [(DataAlt data_con, [arg], Var arg)],
+ con_arg_ty1)
+
+ | otherwise -- The general case
+ -- Wrapper: case (..call worker..) of (# a, b #) -> C a b
+ -- Worker: case ( ...body... ) of C a b -> (# a, b #)
+ = getUniquesUs `thenUs` \ uniqs ->
+ let
+ (wrap_wild : work_wild : args) = zipWith mk_ww_local uniqs (ubx_tup_ty : body_ty : con_arg_tys)
+ arg_vars = map Var args
+ ubx_tup_con = tupleCon Unboxed n_con_args
+ ubx_tup_ty = exprType ubx_tup_app
+ ubx_tup_app = mkConApp ubx_tup_con (map Type con_arg_tys ++ arg_vars)
+ con_app = mkConApp data_con (map Type tycon_arg_tys ++ arg_vars)
+ in
+ returnUs (\ wkr_call -> Case wkr_call wrap_wild (exprType con_app) [(DataAlt ubx_tup_con, args, con_app)],
+ \ body -> workerCase body work_wild ubx_tup_ty [(DataAlt data_con, args, ubx_tup_app)],
+ ubx_tup_ty)
+ where
+ (_, tycon_arg_tys, data_con, con_arg_tys) = splitProductType "mkWWcpr" 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
+--
+-- then we want the CPR'd worker to look like
+-- \ x -> _scc_ "foo" (case E of I# x -> x)
+-- and definitely not
+-- \ x -> case (_scc_ "foo" E) of I# x -> x)
+--
+-- This transform doesn't move work or allocation
+-- from one cost centre to another
+
+workerCase (Note (SCC cc) e) arg ty alts = Note (SCC cc) (Case e arg ty alts)
+workerCase e arg ty alts = Case e arg ty alts
\end{code}
\begin{code}
mk_absent_let arg body
- | not (isPrimType arg_ty)
- = Let (NonRec arg (mkTyApp (Var aBSENT_ERROR_ID) [arg_ty])) body
+ | not (isUnLiftedType arg_ty)
+ = 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 = mkRuntimeErrorApp rUNTIME_ERROR_ID arg_ty msg
+ msg = "Oops! Entered absent arg " ++ showSDocDebug (ppr arg <+> ppr (idType arg))
mk_unpk_case arg unpk_args boxing_con boxing_tycon body
- = Case (Var arg)
- (AlgAlts [(boxing_con, unpk_args, body)]
- NoDefault
- )
-
-mk_pk_let arg boxing_con con_tys unpk_args body
- = Let (NonRec arg (Con boxing_con con_args)) body
- where
- con_args = map TyArg con_tys ++ map VarArg unpk_args
-
-mk_ww_local uniq ty
- = mkSysLocal SLIT("ww") uniq ty noSrcLoc
+ -- A data type
+ = Case (Var arg)
+ (sanitiseCaseBndr arg)
+ (exprType body)
+ [(DataAlt boxing_con, unpk_args, body)]
+
+mk_seq_case arg body = Case (Var arg) (sanitiseCaseBndr arg) (exprType body) [(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.
+-- But we *must* throw away all its IdInfo. In particular, the argument
+-- will have demand info on it, and that demand info may be incorrect for
+-- the case binder. e.g. case ww_arg of ww_arg { I# x -> ... }
+-- Quite likely ww_arg isn't used in '...'. The case may get discarded
+-- if the case binder says "I'm demanded". This happened in a situation
+-- like (x+y) `seq` ....
+sanitiseCaseBndr id = id `setIdInfo` vanillaIdInfo
+
+mk_ww_local uniq ty = mkSysLocal FSLIT("ww") uniq ty
\end{code}