+@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