Make SpecConstr work better for nested functions

In SpecConstr.scBind, we should pass the optimised body (body') to
specialise, not the un-optimised one. In this way we'll benefit from
specialising any nested functions inside body.

Discovered by Roman.

diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs
index 9570c24..9d1ba01 100644 (file)
--- a/compiler/specialise/SpecConstr.lhs
+++ b/compiler/specialise/SpecConstr.lhs
@@ -98,6 +98,8 @@ of n is needed (else we'd avoid the eval but pay more for re-boxing n).
 So in this case we want that the *only* uses of n are in case statements.
 
 
+Note [Good arguments]
+~~~~~~~~~~~~~~~~~~~~~
 So we look for
 
 * A self-recursive function.  Ignore mutual recursion for now, 
@@ -441,7 +443,10 @@ scBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, ScUsage, CoreBind)
 scBind env (Rec [(fn,rhs)])
   | notNull val_bndrs
   = scExpr env_fn_body body            `thenUs` \ (usg, body') ->
-    specialise env fn bndrs body usg   `thenUs` \ (rules, spec_prs) ->
+    specialise env fn bndrs body' usg  `thenUs` \ (rules, spec_prs) ->
+       -- Note body': the specialised copies should be based on the 
+       --             optimised version of the body, in case there were
+       --             nested functions inside.
     let
        SCU { calls = calls, occs = occs } = usg
     in
@@ -510,6 +515,7 @@ specialise env fn bndrs body (SCU {calls=calls, occs=occs})
 
 ---------------------
 good_arg :: ConstrEnv -> IdEnv ArgOcc -> (CoreBndr, CoreArg) -> Bool
+-- See Note [Good arguments] above
 good_arg con_env arg_occs (bndr, arg)
   = case is_con_app_maybe con_env arg of       
        Just _ ->  bndr_usg_ok arg_occs bndr arg