From dbcff8ab57f64bcc6abff68448fc33691410266e Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Mon, 11 Dec 2006 16:51:41 +0000
Subject: [PATCH] Add comments, plus fix zapFragileInfo to zap worker info

This is a minor fix up to the patch
 * retain arity for let-bound vars in simplifier
---
 compiler/basicTypes/IdInfo.lhs  |    2 ++
 compiler/simplCore/SimplEnv.lhs |    9 +++++++--
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/compiler/basicTypes/IdInfo.lhs b/compiler/basicTypes/IdInfo.lhs
index 9b39ccb..3261adf 100644
--- a/compiler/basicTypes/IdInfo.lhs
+++ b/compiler/basicTypes/IdInfo.lhs
@@ -702,7 +702,9 @@ zapDemandInfo info@(IdInfo {newDemandInfo = dmd})
 
 \begin{code}
 zapFragileInfo :: IdInfo -> Maybe IdInfo
+-- Zap info that depends on free variables
 zapFragileInfo info = Just (info `setSpecInfo` emptySpecInfo
+				 `setWorkerInfo` NoWorker
                                  `setUnfoldingInfo` NoUnfolding)
 \end{code}
 
diff --git a/compiler/simplCore/SimplEnv.lhs b/compiler/simplCore/SimplEnv.lhs
index 040240c..245f313 100644
--- a/compiler/simplCore/SimplEnv.lhs
+++ b/compiler/simplCore/SimplEnv.lhs
@@ -608,8 +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
@@ -620,7 +624,8 @@ substLetIdBndr env@(SimplEnv { seInScope = in_scope, seIdSubst = id_subst }) old
   where
     id1	   = uniqAway in_scope old_id
     id2    = substIdType env id1
-    -- we want to get rid of any info that's dependent on free variables,
+
+    -- 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
 
-- 
1.7.10.4