Improve arity propagation in the specialiser

[ghc-hetmet.git] / compiler / specialise / Specialise.lhs

diff --git a/compiler/specialise/Specialise.lhs b/compiler/specialise/Specialise.lhs
index 015332f..037db7a 100644 (file)
--- a/compiler/specialise/Specialise.lhs
+++ b/compiler/specialise/Specialise.lhs
@@ -16,7 +16,7 @@ module Specialise ( specProgram ) where
 
 import Id              ( Id, idName, idType, mkUserLocal, idCoreRules,
                          idInlineActivation, setInlineActivation, setIdUnfolding,
-                          isLocalId ) 
+                          isLocalId, idArity, setIdArity ) 
 import TcType          ( Type, mkTyVarTy, tcSplitSigmaTy, 
                          tyVarsOfTypes, tyVarsOfTheta, isClassPred,
                          tcCmpType, isUnLiftedType
@@ -826,6 +826,7 @@ specDefn subst calls fn rhs
   
   where
     fn_type           = idType fn
+    fn_arity          = idArity fn
     (tyvars, theta, _) = tcSplitSigmaTy fn_type
     n_tyvars          = length tyvars
     n_dicts           = length theta
@@ -906,6 +907,10 @@ specDefn subst calls fn rhs
                 spec_id_ty = mkPiTypes lam_args body_ty
        
            ; spec_f <- newSpecIdSM fn spec_id_ty
+          ; let spec_f_w_arity = setIdArity spec_f (max 0 (fn_arity - n_dicts))
+               -- Adding arity information just propagates it a bit faster
+               -- See Note [Arity decrease] in Simplify
+
            ; (spec_rhs, rhs_uds) <- specExpr rhs_subst2 (mkLams lam_args body)
           ; let
                -- The rule to put in the function's specialisation is:
@@ -917,13 +922,13 @@ specDefn subst calls fn rhs
                                  (idName fn)
                                  (poly_tyvars ++ inst_dict_ids)
                                  inst_args 
-                                 (mkVarApps (Var spec_f) app_args)
+                                 (mkVarApps (Var spec_f_w_arity) app_args)
 
                -- Add the { d1' = dx1; d2' = dx2 } usage stuff
                final_uds = foldr addDictBind rhs_uds dx_binds
 
-               spec_pr | inline_rhs = (spec_f `setInlineActivation` inline_act, Note InlineMe spec_rhs)
-                       | otherwise  = (spec_f,                               spec_rhs)
+               spec_pr | inline_rhs = (spec_f_w_arity `setInlineActivation` inline_act, Note InlineMe spec_rhs)
+                       | otherwise  = (spec_f_w_arity,                                  spec_rhs)
 
           ; return (Just (spec_pr, final_uds, spec_env_rule)) } }
       where