import StaticFlags ( opt_SpecInlineJoinPoints )
import BasicTypes ( Activation(..) )
import Maybes ( orElse, catMaybes, isJust, isNothing )
+import NewDemand
+import DmdAnal ( both )
import Util
-import List ( nubBy, partition )
import UniqSupply
import Outputable
import FastString
import UniqFM
import MonadUtils
import Control.Monad ( zipWithM )
+import Data.List
\end{code}
-----------------------------------------------------
spec_occ = mkSpecOcc (nameOccName fn_name)
rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
spec_rhs = mkLams spec_lam_args spec_body
+ spec_str = calcSpecStrictness fn spec_lam_args pats
spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
+ `setIdNewStrictness` spec_str -- See Note [Transfer strictness]
+ `setIdArity` count isId spec_lam_args
body_ty = exprType spec_body
rule_rhs = mkVarApps (Var spec_id) spec_call_args
rule = mkLocalRule rule_name specConstrActivation fn_name qvars pats rule_rhs
; return (spec_usg, OS call_pat rule spec_id spec_rhs) }
+calcSpecStrictness :: Id -- The original function
+ -> [Var] -> [CoreExpr] -- Call pattern
+ -> StrictSig -- Strictness of specialised thing
+-- See Note [Transfer strictness]
+calcSpecStrictness fn qvars pats
+ = StrictSig (mkTopDmdType spec_dmds TopRes)
+ where
+ spec_dmds = [ lookupVarEnv dmd_env qv `orElse` lazyDmd | qv <- qvars, isId qv ]
+ StrictSig (DmdType _ dmds _) = idNewStrictness fn
+
+ dmd_env = go emptyVarEnv dmds pats
+
+ go env ds (Type {} : pats) = go env ds pats
+ go env (d:ds) (pat : pats) = go (go_one env d pat) ds pats
+ go env _ _ = env
+
+ go_one env d (Var v) = extendVarEnv_C both env v d
+ go_one env (Box d) e = go_one env d e
+ go_one env (Eval (Prod ds)) e
+ | (Var _, args) <- collectArgs e = go env ds args
+ go_one env _ _ = env
+
-- In which phase should the specialise-constructor rules be active?
-- Originally I made them always-active, but Manuel found that
-- this defeated some clever user-written rules. So Plan B
specConstrActivation = ActiveAfter 0 -- Baked in; see comments above
\end{code}
+Note [Transfer strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+We must transfer strictness information from the original function to
+the specialised one. Suppose, for example
+
+ f has strictness SS
+ and a RULE f (a:as) b = f_spec a as b
+
+Now we want f_spec to have strictess LLS, otherwise we'll use call-by-need
+when calling f_spec instead of call-by-value. And that can result in
+unbounded worsening in space (cf the classic foldl vs foldl')
+
+See Trac #3437 for a good example.
+
+The function calcSpecStrictness performs the calculation.
+
+
%************************************************************************
%* *
\subsection{Argument analysis}