Add comments, plus fix zapFragileInfo to zap worker info

[ghc-hetmet.git] / compiler / simplCore / SimplEnv.lhs

diff --git a/compiler/simplCore/SimplEnv.lhs b/compiler/simplCore/SimplEnv.lhs
index 765fd00..245f313 100644 (file)
--- a/compiler/simplCore/SimplEnv.lhs
+++ b/compiler/simplCore/SimplEnv.lhs
@@ -21,7 +21,7 @@ module SimplEnv (
        setEnclosingCC, getEnclosingCC,
 
        -- Environments
-       SimplEnv(..),   -- Temp not abstract
+       SimplEnv(..), pprSimplEnv,      -- Temp not abstract
        mkSimplEnv, extendIdSubst, SimplEnv.extendTvSubst, 
        zapSubstEnv, setSubstEnv, 
        getInScope, setInScope, setInScopeSet, modifyInScope, addNewInScopeIds,
@@ -129,6 +129,12 @@ data SimplEnv
 
     }
 
+pprSimplEnv :: SimplEnv -> SDoc
+-- Used for debugging; selective
+pprSimplEnv env
+  = vcat [ptext SLIT("TvSubst:") <+> ppr (seTvSubst env),
+         ptext SLIT("IdSubst:") <+> ppr (seIdSubst env) ]
+
 type SimplIdSubst = IdEnv SimplSR      -- IdId |--> OutExpr
        -- See Note [Extending the Subst] in CoreSubst
 
@@ -144,10 +150,10 @@ instance Outputable SimplSR where
   ppr (DoneId v) = ptext SLIT("DoneId") <+> ppr v
   ppr (ContEx tv id e) = vcat [ptext SLIT("ContEx") <+> ppr e {-,
                                ppr (filter_env tv), ppr (filter_env id) -}]
-       where
-         fvs = exprFreeVars e
-         filter_env env = filterVarEnv_Directly keep env
-         keep uniq _ = uniq `elemUFM_Directly` fvs
+       -- where
+       -- fvs = exprFreeVars e
+       -- filter_env env = filterVarEnv_Directly keep env
+       -- keep uniq _ = uniq `elemUFM_Directly` fvs
 \end{code}
 
 
@@ -602,8 +608,12 @@ substLetIdBndr :: SimplEnv -> InBndr       -- Env and binder to transform
               -> (SimplEnv, OutBndr)
 -- C.f. substIdBndr above
 -- Clone Id if necessary, substitute its type
--- Return an Id with completely zapped IdInfo
+-- Return an Id with its fragile info zapped
+--     namely, any info that depends on free variables
 --     [addLetIdInfo, below, will restore its IdInfo]
+--     We want to retain robust info, especially arity and demand info,
+--     so that they are available to occurrences that occur in an
+--     earlier binding of a letrec
 -- Augment the subtitution 
 --     if the unique changed, *or* 
 --     if there's interesting occurrence info
@@ -614,7 +624,10 @@ substLetIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) old
   where
     id1           = uniqAway in_scope old_id
     id2    = substIdType env id1
-    new_id = setIdInfo id2 vanillaIdInfo
+
+    -- We want to get rid of any info that's dependent on free variables,
+    -- but keep other info (like the arity).
+    new_id = zapFragileIdInfo id2
 
        -- Extend the substitution if the unique has changed,
        -- or there's some useful occurrence information