+++ /dev/null
-%
-% (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}
-module WwLib ( mkWwBodies, mkWWstr, mkWorkerArgs ) where
-
-#include "HsVersions.h"
-
-import CoreSyn
-import CoreUtils ( exprType )
-import Id ( Id, idType, mkSysLocal, idNewDemandInfo, setIdNewDemandInfo,
- isOneShotLambda, setOneShotLambda, setIdUnfolding,
- setIdInfo
- )
-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 BasicTypes ( Boxity(..) )
-import Var ( Var, isId )
-import UniqSupply ( returnUs, thenUs, getUniquesUs, UniqSM )
-import Util ( zipWithEqual, notNull )
-import Outputable
-import List ( zipWith4 )
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection[mkWrapperAndWorker]{@mkWrapperAndWorker@}
-%* *
-%************************************************************************
-
-Here's an example. The original function is:
-
-\begin{verbatim}
-g :: forall a . Int -> [a] -> a
-
-g = /\ a -> \ x ys ->
- case x of
- 0 -> head ys
- _ -> head (tail ys)
-\end{verbatim}
-
-From this, we want to produce:
-\begin{verbatim}
--- wrapper (an unfolding)
-g :: forall a . Int -> [a] -> a
-
-g = /\ a -> \ x ys ->
- case x of
- I# x# -> $wg a x# ys
- -- call the worker; don't forget the type args!
-
--- worker
-$wg :: forall a . Int# -> [a] -> a
-
-$wg = /\ a -> \ x# ys ->
- let
- x = I# x#
- in
- case x of -- note: body of g moved intact
- 0 -> head ys
- _ -> head (tail ys)
-\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.
-
-Consequently, we insist that the number of strictness-info items is
-exactly the same as the number of lambda-bound arguments. (This is
-probably slightly paranoid, but OK in practice.) If it isn't the
-same, we ``revise'' the strictness info, so that we won't propagate
-the unusable strictness-info into the interfaces.
-
-
-%************************************************************************
-%* *
-\subsection{The worker wrapper core}
-%* *
-%************************************************************************
-
-@mkWwBodies@ is called when doing the worker/wrapper split inside a module.
-
-\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
- one_shots' = one_shots ++ repeat False
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection{Making wrapper args}
-%* *
-%************************************************************************
-
-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.
-
- 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
-
-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}
-
-
-%************************************************************************
-%* *
-\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}
--- 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.]
- --
- -- 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
- (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( 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)
-
- | otherwise
- = 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}
-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)
-
-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)
-
-
-----------------------
--- 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
- 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
- -- 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}
-%* *
-%************************************************************************
-
-
-@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.
-
-
-\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}
-
-
-%************************************************************************
-%* *
-\subsection{Utilities}
-%* *
-%************************************************************************
-
-
-\begin{code}
-mk_absent_let arg 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
- -- 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}
projects / ghc-hetmet.git / blobdiff