import IdInfo ( IdInfo, vanillaIdInfo,
occInfo, isFragileOcc, setOccInfo,
specInfo, setSpecInfo,
- setArityInfo, unknownArity,
+ setArityInfo, unknownArity, arityInfo,
unfoldingInfo, setUnfoldingInfo,
WorkerInfo(..), workerExists, workerInfo, setWorkerInfo, WorkerInfo,
lbvarInfo, LBVarInfo(..), setLBVarInfo, hasNoLBVarInfo
go (Let (Rec pairs) body) = Let (Rec pairs') (substExpr subst' body)
where
- (subst', bndrs') = substRecIds subst (map fst pairs)
+ (subst', bndrs') = substRecBndrs subst (map fst pairs)
pairs' = bndrs' `zip` rhss'
rhss' = map (substExpr subst' . snd) pairs
-- we *don't* need to use it to track occurrence info.
simplBndr subst bndr
| isTyVar bndr = substTyVar subst bndr
- | otherwise = subst_id isFragileOcc subst subst bndr
+ | otherwise = subst_id False subst subst bndr
simplBndrs :: Subst -> [Var] -> (Subst, [Var])
simplBndrs subst bndrs = mapAccumL simplBndr subst bndrs
= (subst', bndr' `setIdUnfolding` substUnfolding subst old_unf)
where
old_unf = idUnfolding bndr
- (subst', bndr') = subst_id isFragileOcc subst subst bndr
+ (subst', bndr') = subst_id False subst subst bndr
simplLetId :: Subst -> Id -> (Subst, Id)
-- Used by the simplifier to compute new IdInfo for a let(rec) binder,
-- subsequent to simplLetId having zapped its IdInfo
simplIdInfo subst old_info
- = case substIdInfo subst isFragileOcc zapped_old_info of
+ = case substIdInfo False subst old_info of
Just new_info -> new_info
Nothing -> old_info
- where
- zapped_old_info = old_info `setArityInfo` unknownArity
- -- Like unfolding, arity gets set later
- -- Maybe we should do this in substIdInfo?
\end{code}
\begin{code}
substBndr :: Subst -> Var -> (Subst, Var)
substBndr subst bndr
| isTyVar bndr = substTyVar subst bndr
- | otherwise = subst_id keepOccInfo subst subst bndr
+ | otherwise = subst_id True {- keep fragile info -} subst subst bndr
substBndrs :: Subst -> [Var] -> (Subst, [Var])
substBndrs subst bndrs = mapAccumL substBndr subst bndrs
-substRecIds :: Subst -> [Id] -> (Subst, [Id])
+substRecBndrs :: Subst -> [Id] -> (Subst, [Id])
-- Substitute a mutually recursive group
-substRecIds subst bndrs
+substRecBndrs subst bndrs
= (new_subst, new_bndrs)
where
-- Here's the reason we need to pass rec_subst to subst_id
- (new_subst, new_bndrs) = mapAccumL (subst_id keepOccInfo new_subst) subst bndrs
+ (new_subst, new_bndrs) = mapAccumL (subst_id True {- keep fragile info -} new_subst)
+ subst bndrs
keepOccInfo occ = False -- Never fragile
\end{code}
\begin{code}
-subst_id :: (OccInfo -> Bool) -- True <=> the OccInfo is fragile
+subst_id :: Bool -- True <=> keep fragile info
-> Subst -- Substitution to use for the IdInfo
-> Subst -> Id -- Substitition and Id to transform
-> (Subst, Id) -- Transformed pair
-- In this case, the var in the DoneId is the same as the
-- var returned
-subst_id is_fragile_occ rec_subst subst@(Subst in_scope env) old_id
+subst_id keep_fragile rec_subst subst@(Subst in_scope env) old_id
= (Subst (in_scope `extendInScopeSet` new_id) new_env, new_id)
where
-- id1 is cloned if necessary
-- new_id has the right IdInfo
-- The lazy-set is because we're in a loop here, with
-- rec_subst, when dealing with a mutually-recursive group
- new_id = maybeModifyIdInfo (substIdInfo rec_subst is_fragile_occ) id2
+ new_id = maybeModifyIdInfo (substIdInfo keep_fragile rec_subst) id2
-- Extend the substitution if the unique has changed
-- See the notes with substTyVar for the delSubstEnv
id1 = setVarUnique old_id uniq
id2 = substIdType subst id1
- new_id = maybeModifyIdInfo (substIdInfo rec_subst isFragileOcc) id2
+ new_id = maybeModifyIdInfo (substIdInfo False rec_subst) id2
new_env = extendSubstEnv env old_id (DoneId new_id NoOccInfo)
substAndCloneIds :: Subst -> UniqSupply -> [Id] -> (Subst, [Id])
%************************************************************************
\begin{code}
-substIdInfo :: Subst
- -> (OccInfo -> Bool) -- True <=> zap the occurrence info
+substIdInfo :: Bool -- True <=> keep even fragile info
+ -> Subst
-> IdInfo
-> Maybe IdInfo
+-- The keep_fragile flag is True when we are running a simple expression
+-- substitution that preserves all structure, so that arity and occurrence
+-- info are unaffected. The False state is used more often.
+--
-- Substitute the
-- rules
-- worker info
-- LBVar info
-- Zap the unfolding
--- Zap the occ info if instructed to do so
+-- If keep_fragile then
+-- keep OccInfo
+-- keep Arity
+-- else
+-- keep only 'robust' OccInfo
+-- zap Arity
--
-- Seq'ing on the returned IdInfo is enough to cause all the
-- substitutions to happen completely
-substIdInfo subst is_fragile_occ info
+substIdInfo keep_fragile subst info
| nothing_to_do = Nothing
- | otherwise = Just (info `setOccInfo` (if zap_occ then NoOccInfo else old_occ)
+ | otherwise = Just (info `setOccInfo` (if keep_occ then old_occ else NoOccInfo)
+ `setArityInfo` (if keep_arity then old_arity else unknownArity)
`setSpecInfo` substRules subst old_rules
`setWorkerInfo` substWorker subst old_wrkr
`setUnfoldingInfo` noUnfolding)
-- setSpecInfo does a seq
-- setWorkerInfo does a seq
where
- nothing_to_do = not zap_occ &&
+ nothing_to_do = keep_occ && keep_arity &&
isEmptyCoreRules old_rules &&
not (workerExists old_wrkr) &&
not (hasUnfolding (unfoldingInfo info))
- zap_occ = is_fragile_occ old_occ
+ keep_occ = keep_fragile || not (isFragileOcc old_occ)
+ keep_arity = keep_fragile || old_arity == unknownArity
+ old_arity = arityInfo info
old_occ = occInfo info
old_rules = specInfo info
old_wrkr = workerInfo info
-> SimplM (FloatsWith SimplEnv)
simplLazyBind env top_lvl is_rec bndr bndr1 rhs rhs_se
- = -- Substitute the rules for this binder in the light
- -- of earlier substitutions in this very letrec group,
- -- add the substituted rules to the IdInfo, and
- -- extend the in-scope env, so that the IdInfo for this
- -- binder extends over the RHS for the binder itself.
+ = let -- Transfer the IdInfo of the original binder to the new binder
+ -- This is crucial: we must preserve
+ -- strictness
+ -- rules
+ -- worker info
+ -- etc. To do this we must apply the current substitution,
+ -- which incorporates earlier substitutions in this very letrec group.
--
+ -- NB 1. We do this *before* processing the RHS of the binder, so that
+ -- its substituted rules are visible in its own RHS.
-- This is important. Manuel found cases where he really, really
-- wanted a RULE for a recursive function to apply in that function's
-- own right-hand side.
--
- -- NB: does no harm for non-recursive bindings
- --
- -- NB2: just rules! In particular, the arity of an Id is not visible
+ -- NB 2: We do not transfer the arity (see Subst.substIdInfo)
+ -- The arity of an Id should not be visible
-- in its own RHS, else we eta-reduce
-- f = \x -> f x
-- to
-- f = f
-- which isn't sound. And it makes the arity in f's IdInfo greater than
-- the manifest arity, which isn't good.
- let
+ -- The arity will get added later.
+ --
+ -- NB 3: It's important that we *do* transer the loop-breaker OccInfo,
+ -- because that's what stops the Id getting inlined infinitely, in the body
+ -- of the letrec.
+
+ -- NB 4: does no harm for non-recursive bindings
+
bndr2 = bndr1 `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
env1 = modifyInScope env bndr2 bndr2
rhs_env = setInScope rhs_se env1
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