+ fn_info = idInfo fn_id
+ maybe_fn_dmd = newDemandInfo fn_info
+ unfolding = unfoldingInfo fn_info
+ inline_prag = inlinePragInfo fn_info
+
+ -- In practice it always will have a strictness
+ -- signature, even if it's a uninformative one
+ strict_sig = newStrictnessInfo fn_info `orElse` topSig
+ StrictSig (DmdType env wrap_dmds res_info) = strict_sig
+
+ -- new_fn_id has the DmdEnv zapped.
+ -- (a) it is never used again
+ -- (b) it wastes space
+ -- (c) it becomes incorrect as things are cloned, because
+ -- we don't push the substitution into it
+ new_fn_id | isEmptyVarEnv env = fn_id
+ | otherwise = fn_id `setIdNewStrictness`
+ StrictSig (mkTopDmdType wrap_dmds res_info)
+
+ is_fun = notNull wrap_dmds
+ is_thunk = not is_fun && not (exprIsValue rhs)
+
+---------------------
+splitFun fn_id fn_info wrap_dmds res_info inline_prag rhs
+ = WARN( not (wrap_dmds `lengthIs` arity), 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 ->
+ let
+ work_rhs = work_fn rhs
+ work_id = mkWorkerId work_uniq fn_id (exprType work_rhs)
+ `setInlinePragma` inline_prag
+ `setIdNewStrictness` StrictSig (mkTopDmdType work_demands work_res_info)
+ -- Even though we may not be at top level,
+ -- 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
+ 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 = 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
+
+ work_res_info | isBotRes res_info = BotRes -- Cpr stuff done by wrapper
+ | otherwise = TopRes
+
+ one_shots = get_one_shots rhs
+
+-- If the original function has one-shot arguments, it is important to
+-- make the wrapper and worker have corresponding one-shot arguments too.
+-- Otherwise we spuriously float stuff out of case-expression join points,
+-- which is very annoying.
+get_one_shots (Lam b e)
+ | isId b = isOneShotLambda b : get_one_shots e
+ | otherwise = get_one_shots e
+get_one_shots (Note _ e) = get_one_shots e
+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}
+
+
+%************************************************************************
+%* *
+\subsection{Functions over Demands}
+%* *
+%************************************************************************
+
+\begin{code}
+worthSplittingFun :: [Demand] -> DmdResult -> Bool
+ -- True <=> the wrapper would not be an identity function
+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 there is no CPR
+
+ -- 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.
+ -- [We don't do reboxing now, but in general it's better to pass
+ -- an unboxed thing to f, and have it reboxed in the error cases....]
+ where
+ worth_it Abs = True -- Absent arg
+ worth_it (Eval (Prod ds)) = True -- Product arg to evaluate
+ worth_it other = False
+
+worthSplittingThunk :: Maybe Demand -- Demand on the thunk
+ -> DmdResult -- CPR info for the thunk
+ -> Bool
+worthSplittingThunk maybe_dmd res
+ = worth_it maybe_dmd || returnsCPR res
+ where
+ -- Split if the thing is unpacked
+ worth_it (Just (Eval (Prod ds))) = not (all isAbsent ds)
+ worth_it other = False
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\subsection{The worker wrapper core}
+%* *
+%************************************************************************
+
+@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).
+
+\begin{code}
+mkWrapper :: Type -- Wrapper type
+ -> StrictSig -- Wrapper strictness info
+ -> UniqSM (Id -> CoreExpr) -- Wrapper body, missing worker Id
+
+mkWrapper fun_ty (StrictSig (DmdType _ demands res_info))
+ = mkWwBodies fun_ty demands res_info noOneShotInfo `thenUs` \ (_, wrap_fn, _) ->
+ returnUs wrap_fn
+
+noOneShotInfo = repeat False