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Diffstat (limited to 'compiler/stranal/WwLib.lhs')
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diff --git a/compiler/stranal/WwLib.lhs b/compiler/stranal/WwLib.lhs new file mode 100644 index 0000000000..e44e521c83 --- /dev/null +++ b/compiler/stranal/WwLib.lhs @@ -0,0 +1,514 @@ +% +% (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} |