import CoreSyn
import CoreUnfold ( certainlyWillInline )
import CoreLint ( showPass, endPass )
-import CoreUtils ( exprType )
-import Id ( Id, idType, idNewStrictness, idArity, isOneShotLambda,
- setIdNewStrictness, zapIdNewStrictness, idInlinePragma, mkWorkerId,
- setIdWorkerInfo, setInlinePragma )
+import CoreUtils ( exprType, exprIsValue )
+import Id ( Id, idType, isOneShotLambda,
+ setIdNewStrictness, mkWorkerId,
+ setIdWorkerInfo, setInlinePragma,
+ idInfo )
import Type ( Type )
-import IdInfo ( WorkerInfo(..) )
-import NewDemand ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..),
- mkTopDmdType, isBotRes, returnsCPR
+import IdInfo ( WorkerInfo(..), arityInfo,
+ newDemandInfo, newStrictnessInfo, unfoldingInfo, inlinePragInfo
+ )
+import NewDemand ( Demand(..), StrictSig(..), DmdType(..), DmdResult(..), Keepity(..),
+ mkTopDmdType, isBotRes, returnsCPR, topSig
)
import UniqSupply ( UniqSupply, initUs_, returnUs, thenUs, mapUs, getUniqueUs, UniqSM )
-import BasicTypes ( RecFlag(..), isNonRec, Activation(..), isNeverActive )
+import BasicTypes ( RecFlag(..), isNonRec, Activation(..) )
+import Maybes ( orElse )
import CmdLineOpts
import WwLib
import Outputable
-- if two, then a worker and a
-- wrapper.
tryWW is_rec fn_id rhs
- | isNeverActive inline_prag
- -- Don't split NOINLINE things, because they will never be inlined
- -- Furthermore, zap the strictess info in the Id. Why? Because
- -- the NOINLINE says "don't expose any of the inner workings at the call
- -- site" and the strictness is certainly an inner working.
- --
- -- More concretely, the demand analyser discovers the following strictness
- -- for unsafePerformIO: C(U(AV))
- -- But then consider
- -- unsafePerformIO (\s -> let r = f x in
- -- case writeIORef v r s of (# s1, _ #) ->
- -- (# s1, r #)
- -- The strictness analyser will find that the binding for r is strict,
- -- (becuase of uPIO's strictness sig), and so it'll evaluate it before
- -- doing the writeIORef. This actually makes tests/lib/should_run/memo002
- -- get a deadlock!
- --
- -- Solution: don't expose the strictness of unsafePerformIO.
- = returnUs [ (zapIdNewStrictness fn_id, rhs) ]
-
- | arity == 0
- -- Don't worker-wrapper thunks
- || isNonRec is_rec && certainlyWillInline fn_id
+ | 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)
-- fw = \ab -> (__inline (\x -> E)) (a,b)
-- and the original __inline now vanishes, so E is no longer
-- inside its __inline wrapper. Death! Disaster!
- || not (worthSplitting strict_sig)
- -- Strictness info suggests not to w/w
= returnUs [ (fn_id, rhs) ]
- | otherwise -- Do w/w split!
- = WARN( arity /= length wrap_dmds, ppr fn_id <+> (ppr arity $$ ppr strict_sig) )
+ | is_thunk && worthSplittingThunk fn_dmd res_info
+ = ASSERT( isNonRec is_rec ) -- The thunk must be non-recursive
+ splitThunk fn_id rhs
+
+ | is_fun && worthSplittingFun wrap_dmds res_info
+ = splitFun fn_id fn_info wrap_dmds res_info inline_prag rhs
+
+ | otherwise
+ = returnUs [ (fn_id, rhs) ]
+
+ where
+ fn_info = idInfo fn_id
+ fn_dmd = newDemandInfo fn_info
+ unfolding = unfoldingInfo fn_info
+ inline_prag = inlinePragInfo fn_info
+ strict_sig = newStrictnessInfo fn_info `orElse` topSig
+
+ StrictSig (DmdType _ wrap_dmds res_info) = strict_sig
+
+ is_fun = not (null wrap_dmds)
+ is_thunk = not is_fun && not (exprIsValue rhs)
+
+---------------------
+splitFun fn_id fn_info wrap_dmds res_info inline_prag rhs
+ = WARN( arity /= length wrap_dmds, ppr fn_id <+> (ppr arity $$ 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 ->
-- 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
+ 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 = idArity fn_id -- The arity is set by the simplifier using exprEtaExpandArity
- -- So it may be more than the number of top-level-visible lambdas
- inline_prag = idInlinePragma fn_id
- strict_sig = idNewStrictness 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
- StrictSig (DmdType _ wrap_dmds res_info) = strict_sig
work_res_info | isBotRes res_info = BotRes -- Cpr stuff done by wrapper
| otherwise = TopRes
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}
+
%************************************************************************
%* *
%************************************************************************
\begin{code}
-worthSplitting :: StrictSig -> Bool
+worthSplittingFun :: [Demand] -> DmdResult -> Bool
-- True <=> the wrapper would not be an identity function
-worthSplitting (StrictSig (DmdType _ ds res))
+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 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.]
worth_it Abs = True -- Absent arg
worth_it (Seq _ ds) = True -- Arg to evaluate
worth_it other = False
+
+worthSplittingThunk :: Demand -- Demand on the thunk
+ -> DmdResult -- CPR info for the thunk
+ -> Bool
+worthSplittingThunk dmd res
+ = worth_it dmd || returnsCPR res
+ where
+ -- Split if the thing is unpacked
+ worth_it (Seq Defer ds) = False
+ worth_it (Seq _ ds) = any not_abs ds
+ worth_it other = False
+
+ not_abs Abs = False
+ not_abs other = True
\end{code}
\section[WwLib]{A library for the ``worker/wrapper'' back-end to the strictness analyser}
\begin{code}
-module WwLib ( mkWwBodies ) where
+module WwLib ( mkWwBodies, mkWWstr ) where
#include "HsVersions.h"
import DataCon ( splitProductType_maybe, splitProductType )
import NewDemand ( Demand(..), Keepity(..), DmdResult(..) )
import DmdAnal ( both )
-import PrelInfo ( realWorldPrimId, aBSENT_ERROR_ID, eRROR_CSTRING_ID )
+import PrelInfo ( eRROR_CSTRING_ID )
import TysPrim ( realWorldStatePrimTy )
import TysWiredIn ( tupleCon )
import Type ( Type, isUnLiftedType, mkFunTys,
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) ->
+ mkWWstr wrap_args `thenUs` \ (work_args, wrap_fn_str, work_fn_str) ->
+ hackWorkArgs work_args cpr_res_ty `thenUs` \ work_args' ->
- returnUs (work_dmds,
- Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . Var,
- work_fn_str . work_fn_cpr . work_fn_args)
+ returnUs ([idNewDemandInfo v | v <- work_args, isId v],
+ Note InlineMe . wrap_fn_args . wrap_fn_cpr . wrap_fn_str . applyToVars work_args' . Var,
+ mkLams work_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 = ...
-- fw from being inlined into f's RHS
where
one_shots' = one_shots ++ repeat False
+
+ -- 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
+ --
+ -- We use the state-token type which generates no code
+hackWorkArgs work_args res_ty
+ | any isId work_args || not (isUnLiftedType res_ty)
+ = returnUs work_args
+ | otherwise
+ = getUniqueUs `thenUs` \ void_arg_uniq ->
+ let
+ void_arg = mk_ww_local void_arg_uniq realWorldStatePrimTy
+ in
+ returnUs (work_args ++ [void_arg])
\end{code}
%************************************************************************
\begin{code}
-mkWWstr :: Type -- Result type
- -> [Var] -- Wrapper args; have their demand info on them
+mkWWstr :: [Var] -- Wrapper args; have their demand info on them
-- *Includes type variables*
- -> UniqSM ([Demand], -- Demand on worker (value) args
+ -> UniqSM ([Var], -- Worker args
CoreExpr -> CoreExpr, -- Wrapper body, lacking the worker call
-- and without its lambdas
- -- This fn adds the unboxing, and makes the
- -- call passing the unboxed things
+ -- This fn adds the unboxing
CoreExpr -> CoreExpr) -- Worker body, lacking the original body of the function,
- -- but *with* lambdas
-
-mkWWstr res_ty wrap_args
- = mk_ww_str_s wrap_args `thenUs` \ (work_args, take_apart, put_together) ->
- let
- 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 . applyToVars work_args,
- mkLams work_args . put_together)
- else
- -- 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
- --
- -- We use the state-token type which generates no code
- getUniqueUs `thenUs` \ void_arg_uniq ->
- let
- void_arg = mk_ww_local void_arg_uniq realWorldStatePrimTy
- in
- returnUs ([Lazy],
- take_apart . applyToVars [realWorldPrimId] . apply_to work_args,
- mkLams work_args . Lam void_arg . put_together)
+ -- and lacking its lambdas.
+ -- This fn does the reboxing
----------------------
nop_fn body = body
----------------------
-mk_ww_str_s []
+mkWWstr []
= returnUs ([], nop_fn, nop_fn)
-mk_ww_str_s (arg : args)
- = mk_ww_str arg `thenUs` \ (args1, wrap_fn1, work_fn1) ->
- mk_ww_str_s args `thenUs` \ (args2, wrap_fn2, work_fn2) ->
+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)
----------------------
-mk_ww_str arg
+mkWWstr_one arg
| isTyVar arg
= returnUs ([arg], nop_fn, nop_fn)
-> 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'
+ 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)
-- S(LA) --> U(LL)
Drop -> cs
in
- mk_ww_str_s unpk_args_w_ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
+ mkWWstr unpk_args_w_ds `thenUs` \ (worker_args, wrap_fn, work_fn) ->
-- case keep of
-- Keep -> returnUs (arg : worker_args, unbox_fn . wrap_fn, work_fn)
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