From 9526ada5b1e4a3463833bd74a15473d2ff7b53c1 Mon Sep 17 00:00:00 2001
From: "simonpj@microsoft.com" <unknown>
Date: Tue, 22 Apr 2008 12:01:43 +0000
Subject: [PATCH] Comments only

---
 compiler/basicTypes/BasicTypes.lhs |   18 +++++++++++++++---
 compiler/basicTypes/Id.lhs         |   12 ++++++++++++
 compiler/simplCore/OccurAnal.lhs   |   11 +++++++++--
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/compiler/basicTypes/BasicTypes.lhs b/compiler/basicTypes/BasicTypes.lhs
index d60321a..cdfc28c 100644
--- a/compiler/basicTypes/BasicTypes.lhs
+++ b/compiler/basicTypes/BasicTypes.lhs
@@ -378,14 +378,26 @@ data OccInfo
  	!OneBranch
 	!InterestingCxt
 
-  | IAmALoopBreaker	-- Used by the occurrence analyser to mark loop-breakers
-			-- in a group of recursive definitions
+  | IAmALoopBreaker	-- Note [LoopBreaker OccInfo]
 	!RulesOnly	-- True <=> This is a weak or rules-only loop breaker
-			--  See OccurAnal Note [Weak loop breakers]
+			--  	    See OccurAnal Note [Weak loop breakers]
 
 type RulesOnly = Bool
 \end{code}
 
+Note [LoopBreaker OccInfo]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+An OccInfo of (IAmLoopBreaker False) is used by the occurrence 
+analyser in two ways:
+  (a) to mark loop-breakers in a group of recursive 
+      definitions (hence the name)
+  (b) to mark binders that must not be inlined in this phase
+      (perhaps it has a NOINLINE pragma)
+Things with (IAmLoopBreaker False) do not get an unfolding 
+pinned on to them, so they are completely opaque.
+
+See OccurAnal Note [Weak loop breakers] for (IAmLoopBreaker True).
+
 
 \begin{code}
 isNoOcc :: OccInfo -> Bool
diff --git a/compiler/basicTypes/Id.lhs b/compiler/basicTypes/Id.lhs
index 9145bad..acd4d5e 100644
--- a/compiler/basicTypes/Id.lhs
+++ b/compiler/basicTypes/Id.lhs
@@ -136,12 +136,24 @@ Absolutely all Ids are made by mkId.  It is just like Var.mkId,
 but in addition it pins free-tyvar-info onto the Id's type, 
 where it can easily be found.
 
+Note [Free type variables]
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+At one time we cached the free type variables of the type of an Id
+at the root of the type in a TyNote.  The idea was to avoid repeating
+the free-type-variable calculation.  But it turned out to slow down
+the compiler overall. I don't quite know why; perhaps finding free
+type variables of an Id isn't all that common whereas applying a 
+substitution (which changes the free type variables) is more common.
+Anyway, we removed it in March 2008.
+
 \begin{code}
 mkLocalIdWithInfo :: Name -> Type -> IdInfo -> Id
 mkLocalIdWithInfo name ty info = Var.mkLocalId name ty info
+	-- Note [Free type variables]
 
 mkExportedLocalId :: Name -> Type -> Id
 mkExportedLocalId name ty = Var.mkExportedLocalId name ty vanillaIdInfo
+	-- Note [Free type variables]
 
 mkGlobalId :: GlobalIdDetails -> Name -> Type -> IdInfo -> Id
 mkGlobalId details name ty info = Var.mkGlobalId details name ty info
diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs
index 794217f..fb72577 100644
--- a/compiler/simplCore/OccurAnal.lhs
+++ b/compiler/simplCore/OccurAnal.lhs
@@ -346,8 +346,9 @@ occAnalRec (CyclicSCC nodes) (body_usage, binds)
 
     tag_node :: UsageDetails -> Node Details -> (UsageDetails, Node Details)
 	-- (a) Tag the binders in the details with occ info
-	-- (b) Mark the binder with OccInfo saying "no preInlineUnconditionally" if
-	-- 	it is used in any rule (lhs or rhs) of the recursive group
+	-- (b) Mark the binder with "weak loop-breaker" OccInfo 
+	--	saying "no preInlineUnconditionally" if it is used
+	-- 	in any rule (lhs or rhs) of the recursive group
 	--      See Note [Weak loop breakers]
     tag_node usage (ND bndr rhs rhs_usage rhs_fvs, k, ks)
       = (usage `delVarEnv` bndr, (ND bndr2 rhs rhs_usage rhs_fvs, k, ks))
@@ -506,6 +507,12 @@ reOrderCycle (bind : binds)
         | is_con_app rhs = 2    -- Data types help with cases
                 -- Note [conapp]
 
+-- If an Id is marked "never inline" then it makes a great loop breaker
+-- The only reason for not checking that here is that it is rare
+-- and I've never seen a situation where it makes a difference,
+-- so it probably isn't worth the time to test on every binder
+--	| isNeverActive (idInlinePragma bndr) = -10
+
         | inlineCandidate bndr rhs = 1  -- Likely to be inlined
                 -- Note [Inline candidates]
 
-- 
1.7.10.4