[project @ 2002-11-19 15:51:16 by simonpj]

Comments

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index 063a288..e02bf5e 100644 (file)
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -487,11 +487,10 @@ We can't start with 'not-demanded' because then consider
 
 In the first iteration we'd have no demand info for x, so assume
 not-demanded; then we'd get TopRes for f's CPR info.  Next iteration
-we'd see that t was demanded, and so give it the CPR property, but
-by now f has TopRes, so it will stay TopRes.  
-ever_in
-Instead, with the Nothing setting the first time round, we say
-'yes t is demanded' the first time.  
+we'd see that t was demanded, and so give it the CPR property, but by
+now f has TopRes, so it will stay TopRes.  Instead, with the Nothing
+setting the first time round, we say 'yes t is demanded' the first
+time.
 
 However, this does mean that for non-recursive bindings we must
 iterate twice to be sure of not getting over-optimistic CPR info,
@@ -729,10 +728,15 @@ extendSigEnvList = extendVarEnvList
 
 extendSigsWithLam :: SigEnv -> Id -> SigEnv
 -- Extend the SigEnv when we meet a lambda binder
---  If the binder is marked demanded with a product demand, then give it a CPR 
+-- If the binder is marked demanded with a product demand, then give it a CPR 
 -- signature, because in the likely event that this is a lambda on a fn defn 
 -- [we only use this when the lambda is being consumed with a call demand],
--- it'll be w/w'd and so it will be CPR-ish.
+-- it'll be w/w'd and so it will be CPR-ish.  E.g.
+--     f = \x::(Int,Int).  if ...strict in x... then
+--                             x
+--                         else
+--                             (a,b)
+-- We want f to have the CPR property because x does, by the time f has been w/w'd
 --
 --     NOTE: see notes [CPR-AND-STRICTNESS]
 --

diff --git a/ghc/compiler/stranal/WwLib.lhs b/ghc/compiler/stranal/WwLib.lhs
index 58060b0..49571f3 100644 (file)
--- a/ghc/compiler/stranal/WwLib.lhs
+++ b/ghc/compiler/stranal/WwLib.lhs
@@ -420,6 +420,9 @@ mkWWcpr body_ty RetCPR
 
     | 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
@@ -431,6 +434,8 @@ mkWWcpr body_ty RetCPR
                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)
@@ -440,7 +445,7 @@ mkWWcpr body_ty RetCPR
        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 [(DataAlt ubx_tup_con, args, con_app)],
+      returnUs (\ wkr_call -> Case wkr_call wrap_wild   [(DataAlt ubx_tup_con, args, con_app)],
                \ body     -> workerCase body work_wild [(DataAlt data_con,    args, ubx_tup_app)],
                ubx_tup_ty)
     where