-- ** Substituting into expressions and related types
deShadowBinds, substSpec, substRulesForImportedIds,
- substTy, substExpr, substBind, substUnfolding,
- substInlineRuleGuidance, lookupIdSubst, lookupTvSubst, substIdOcc,
+ substTy, substExpr, substExprSC, substBind, substBindSC,
+ substUnfolding, substUnfoldingSC,
+ substUnfoldingSource, lookupIdSubst, lookupTvSubst, substIdOcc,
-- ** Operations on substitutions
emptySubst, mkEmptySubst, mkSubst, mkOpenSubst, substInScope, isEmptySubst,
cloneIdBndr, cloneIdBndrs, cloneRecIdBndrs,
-- ** Simple expression optimiser
- simpleOptExpr
+ simpleOptPgm, simpleOptExpr
) where
#include "HsVersions.h"
import CoreSyn
import CoreFVs
import CoreUtils
-import OccurAnal( occurAnalyseExpr )
+import PprCore
+import OccurAnal( occurAnalyseExpr, occurAnalysePgm )
import qualified Type
import Type ( Type, TvSubst(..), TvSubstEnv )
+import Coercion ( isIdentityCoercion )
+import OptCoercion ( optCoercion )
import VarSet
import VarEnv
import Id
import Unique
import UniqSupply
import Maybes
+import ErrUtils
+import DynFlags ( DynFlags, DynFlag(..) )
+import BasicTypes ( isAlwaysActive )
import Outputable
import PprCore () -- Instances
import FastString
-- 'extendIdSubst' and 'extendTvSubst'
extendSubst :: Subst -> Var -> CoreArg -> Subst
extendSubst (Subst in_scope ids tvs) tv (Type ty)
- = ASSERT( isTyVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty)
+ = ASSERT( isTyCoVar tv ) Subst in_scope ids (extendVarEnv tvs tv ty)
extendSubst (Subst in_scope ids tvs) id expr
= ASSERT( isId id ) Subst in_scope (extendVarEnv ids id expr) tvs
extendSubstList subst ((var,rhs):prs) = extendSubstList (extendSubst subst var rhs) prs
-- | Find the substitution for an 'Id' in the 'Subst'
-lookupIdSubst :: Subst -> Id -> CoreExpr
-lookupIdSubst (Subst in_scope ids _) v
+lookupIdSubst :: SDoc -> Subst -> Id -> CoreExpr
+lookupIdSubst doc (Subst in_scope ids _) v
| not (isLocalId v) = Var v
| Just e <- lookupVarEnv ids v = e
| Just v' <- lookupInScope in_scope v = Var v'
-- Vital! See Note [Extending the Subst]
- | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope )
+ | otherwise = WARN( True, ptext (sLit "CoreSubst.lookupIdSubst") <+> ppr v $$ ppr in_scope $$ doc)
Var v
-- | Find the substitution for a 'TyVar' in the 'Subst'
-- No left-right shadowing
-- ie the substitution for (\x \y. e) a1 a2
-- so neither x nor y scope over a1 a2
-mkOpenSubst :: [(Var,CoreArg)] -> Subst
-mkOpenSubst pairs = Subst (mkInScopeSet (exprsFreeVars (map snd pairs)))
- (mkVarEnv [(id,e) | (id, e) <- pairs, isId id])
- (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
+mkOpenSubst :: InScopeSet -> [(Var,CoreArg)] -> Subst
+mkOpenSubst in_scope pairs = Subst in_scope
+ (mkVarEnv [(id,e) | (id, e) <- pairs, isId id])
+ (mkVarEnv [(tv,ty) | (tv, Type ty) <- pairs])
------------------------------
isInScope :: Var -> Subst -> Bool
--
-- Do *not* attempt to short-cut in the case of an empty substitution!
-- See Note [Extending the Subst]
-substExpr :: Subst -> CoreExpr -> CoreExpr
-substExpr subst expr
+substExprSC :: SDoc -> Subst -> CoreExpr -> CoreExpr
+substExprSC _doc subst orig_expr
+ | isEmptySubst subst = orig_expr
+ | otherwise = -- pprTrace "enter subst-expr" (doc $$ ppr orig_expr) $
+ subst_expr subst orig_expr
+
+substExpr :: SDoc -> Subst -> CoreExpr -> CoreExpr
+substExpr _doc subst orig_expr = subst_expr subst orig_expr
+
+subst_expr :: Subst -> CoreExpr -> CoreExpr
+subst_expr subst expr
= go expr
where
- go (Var v) = lookupIdSubst subst v
+ go (Var v) = lookupIdSubst (text "subst_expr") subst v
go (Type ty) = Type (substTy subst ty)
go (Lit lit) = Lit lit
go (App fun arg) = App (go fun) (go arg)
go (Note note e) = Note (go_note note) (go e)
- go (Cast e co) = Cast (go e) (substTy subst co)
- go (Lam bndr body) = Lam bndr' (substExpr subst' body)
+ go (Cast e co)
+ | isIdentityCoercion co' = go e
+ | otherwise = Cast (go e) co'
+ where
+ co' = optCoercion (getTvSubst subst) co
+ -- Optimise coercions as we go; this is good, for example
+ -- in the RHS of rules, which are only substituted in
+
+ go (Lam bndr body) = Lam bndr' (subst_expr subst' body)
where
(subst', bndr') = substBndr subst bndr
- go (Let bind body) = Let bind' (substExpr subst' body)
+ go (Let bind body) = Let bind' (subst_expr subst' body)
where
(subst', bind') = substBind subst bind
where
(subst', bndr') = substBndr subst bndr
- go_alt subst (con, bndrs, rhs) = (con, bndrs', substExpr subst' rhs)
+ go_alt subst (con, bndrs, rhs) = (con, bndrs', subst_expr subst' rhs)
where
(subst', bndrs') = substBndrs subst bndrs
-- | Apply a substititon to an entire 'CoreBind', additionally returning an updated 'Subst'
-- that should be used by subsequent substitutons.
-substBind :: Subst -> CoreBind -> (Subst, CoreBind)
-substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (substExpr subst rhs))
+substBind, substBindSC :: Subst -> CoreBind -> (Subst, CoreBind)
+
+substBindSC subst bind -- Short-cut if the substitution is empty
+ | not (isEmptySubst subst)
+ = substBind subst bind
+ | otherwise
+ = case bind of
+ NonRec bndr rhs -> (subst', NonRec bndr' rhs)
+ where
+ (subst', bndr') = substBndr subst bndr
+ Rec pairs -> (subst', Rec (bndrs' `zip` rhss'))
+ where
+ (bndrs, rhss) = unzip pairs
+ (subst', bndrs') = substRecBndrs subst bndrs
+ rhss' | isEmptySubst subst' = rhss
+ | otherwise = map (subst_expr subst') rhss
+
+substBind subst (NonRec bndr rhs) = (subst', NonRec bndr' (subst_expr subst rhs))
where
(subst', bndr') = substBndr subst bndr
-substBind subst (Rec pairs) = (subst', Rec pairs')
+substBind subst (Rec pairs) = (subst', Rec (bndrs' `zip` rhss'))
where
- (subst', bndrs') = substRecBndrs subst (map fst pairs)
- pairs' = bndrs' `zip` rhss'
- rhss' = map (substExpr subst' . snd) pairs
+ (bndrs, rhss) = unzip pairs
+ (subst', bndrs') = substRecBndrs subst bndrs
+ rhss' = map (subst_expr subst') rhss
\end{code}
\begin{code}
-- 'IdInfo' is preserved by this process, although it is substituted into appropriately.
substBndr :: Subst -> Var -> (Subst, Var)
substBndr subst bndr
- | isTyVar bndr = substTyVarBndr subst bndr
- | otherwise = substIdBndr subst subst bndr
+ | isTyCoVar bndr = substTyVarBndr subst bndr
+ | otherwise = substIdBndr (text "var-bndr") subst subst bndr
-- | Applies 'substBndr' to a number of 'Var's, accumulating a new 'Subst' left-to-right
substBndrs :: Subst -> [Var] -> (Subst, [Var])
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 (substIdBndr new_subst) subst bndrs
+ (new_subst, new_bndrs) = mapAccumL (substIdBndr (text "rec-bndr") new_subst) subst bndrs
\end{code}
\begin{code}
-substIdBndr :: Subst -- ^ Substitution to use for the IdInfo
+substIdBndr :: SDoc
+ -> Subst -- ^ Substitution to use for the IdInfo
-> Subst -> Id -- ^ Substitition and Id to transform
-> (Subst, Id) -- ^ Transformed pair
-- NB: unfolding may be zapped
-substIdBndr rec_subst subst@(Subst in_scope env tvs) old_id
- = (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
+substIdBndr _doc rec_subst subst@(Subst in_scope env tvs) old_id
+ = -- pprTrace "substIdBndr" (doc $$ ppr old_id $$ ppr in_scope) $
+ (Subst (in_scope `extendInScopeSet` new_id) new_env tvs, new_id)
where
id1 = uniqAway in_scope old_id -- id1 is cloned if necessary
id2 | no_type_change = id1
\begin{code}
-- | Very similar to 'substBndr', but it always allocates a new 'Unique' for
--- each variable in its output and removes all 'IdInfo'
+-- each variable in its output. It substitutes the IdInfo though.
cloneIdBndr :: Subst -> UniqSupply -> Id -> (Subst, Id)
cloneIdBndr subst us old_id
= clone_id subst subst (old_id, uniqFromSupply us)
-- | See 'Type.substTy'
substTy :: Subst -> Type -> Type
-substTy (Subst in_scope _id_env tv_env) ty
- = Type.substTy (TvSubst in_scope tv_env) ty
+substTy subst ty = Type.substTy (getTvSubst subst) ty
+
+getTvSubst :: Subst -> TvSubst
+getTvSubst (Subst in_scope _id_env tv_env) = TvSubst in_scope tv_env
\end{code}
------------------
-- | Substitute into some 'IdInfo' with regard to the supplied new 'Id'.
--- Always zaps the unfolding, to save substitution work
substIdInfo :: Subst -> Id -> IdInfo -> Maybe IdInfo
substIdInfo subst new_id info
| nothing_to_do = Nothing
------------------
-- | Substitutes for the 'Id's within an unfolding
-substUnfolding :: Subst -> Unfolding -> Unfolding
+substUnfolding, substUnfoldingSC :: Subst -> Unfolding -> Unfolding
-- Seq'ing on the returned Unfolding is enough to cause
-- all the substitutions to happen completely
-substUnfolding subst (DFunUnfolding con args)
- = DFunUnfolding con (map (substExpr subst) args)
-substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_guidance = guide@(InlineRule {}) })
+substUnfoldingSC subst unf -- Short-cut version
+ | isEmptySubst subst = unf
+ | otherwise = substUnfolding subst unf
+
+substUnfolding subst (DFunUnfolding ar con args)
+ = DFunUnfolding ar con (map (substExpr (text "dfun-unf") subst) args)
+
+substUnfolding subst unf@(CoreUnfolding { uf_tmpl = tmpl, uf_src = src })
-- Retain an InlineRule!
+ | not (isStableSource src) -- Zap an unstable unfolding, to save substitution work
+ = NoUnfolding
+ | otherwise -- But keep a stable one!
= seqExpr new_tmpl `seq`
- new_mb_wkr `seq`
- unf { uf_tmpl = new_tmpl, uf_guidance = guide { ug_ir_info = new_mb_wkr } }
+ new_src `seq`
+ unf { uf_tmpl = new_tmpl, uf_src = new_src }
where
- new_tmpl = substExpr subst tmpl
- new_mb_wkr = substInlineRuleGuidance subst (ug_ir_info guide)
+ new_tmpl = substExpr (text "subst-unf") subst tmpl
+ new_src = substUnfoldingSource subst src
-substUnfolding _ (CoreUnfolding {}) = NoUnfolding -- Discard
- -- Always zap a CoreUnfolding, to save substitution work
-
-substUnfolding _ unf = unf -- Otherwise no substitution to do
+substUnfolding _ unf = unf -- NoUnfolding, OtherCon
-------------------
-substInlineRuleGuidance :: Subst -> InlineRuleInfo -> InlineRuleInfo
-substInlineRuleGuidance subst (InlWrapper wkr)
- = case lookupIdSubst subst wkr of
- Var w1 -> InlWrapper w1
- other -> WARN( not (exprIsTrivial other), text "CoreSubst.substWorker:" <+> ppr wkr )
- InlUnSat -- Worker has got substituted away altogether
- -- (This can happen if it's trivial, via
- -- postInlineUnconditionally, hence only warning)
-substInlineRuleGuidance _ info = info
+substUnfoldingSource :: Subst -> UnfoldingSource -> UnfoldingSource
+substUnfoldingSource (Subst in_scope ids _) (InlineWrapper wkr)
+ | Just wkr_expr <- lookupVarEnv ids wkr
+ = case wkr_expr of
+ Var w1 -> InlineWrapper w1
+ _other -> -- WARN( True, text "Interesting! CoreSubst.substWorker1:" <+> ppr wkr
+ -- <+> ifPprDebug (equals <+> ppr wkr_expr) )
+ -- Note [Worker inlining]
+ InlineStable -- It's not a wrapper any more, but still inline it!
+
+ | Just w1 <- lookupInScope in_scope wkr = InlineWrapper w1
+ | otherwise = -- WARN( True, text "Interesting! CoreSubst.substWorker2:" <+> ppr wkr )
+ -- This can legitimately happen. The worker has been inlined and
+ -- dropped as dead code, because we don't treat the UnfoldingSource
+ -- as an "occurrence".
+ -- Note [Worker inlining]
+ InlineStable
+
+substUnfoldingSource _ src = src
------------------
substIdOcc :: Subst -> Id -> Id
-- These Ids should not be substituted to non-Ids
-substIdOcc subst v = case lookupIdSubst subst v of
+substIdOcc subst v = case lookupIdSubst (text "substIdOcc") subst v of
Var v' -> v'
other -> pprPanic "substIdOcc" (vcat [ppr v <+> ppr other, ppr subst])
------------------
substRulesForImportedIds :: Subst -> [CoreRule] -> [CoreRule]
substRulesForImportedIds subst rules
- = map (substRule subst (\name -> name)) rules
+ = map (substRule subst not_needed) rules
+ where
+ not_needed name = pprPanic "substRulesForImportedIds" (ppr name)
------------------
substRule :: Subst -> (Name -> Name) -> CoreRule -> CoreRule
substRule _ _ rule@(BuiltinRule {}) = rule
substRule subst subst_ru_fn rule@(Rule { ru_bndrs = bndrs, ru_args = args
- , ru_fn = fn_name, ru_rhs = rhs })
+ , ru_fn = fn_name, ru_rhs = rhs
+ , ru_local = is_local })
= rule { ru_bndrs = bndrs',
- ru_fn = subst_ru_fn fn_name,
- ru_args = map (substExpr subst') args,
- ru_rhs = substExpr subst' rhs }
+ ru_fn = if is_local
+ then subst_ru_fn fn_name
+ else fn_name,
+ ru_args = map (substExpr (text "subst-rule" <+> ppr fn_name) subst') args,
+ ru_rhs = substExpr (text "subst-rule" <+> ppr fn_name) subst' rhs }
where
(subst', bndrs') = substBndrs subst bndrs
= foldVarSet (unionVarSet . subst_fv subst) emptyVarSet fvs
where
subst_fv subst fv
- | isId fv = exprFreeVars (lookupIdSubst subst fv)
+ | isId fv = exprFreeVars (lookupIdSubst (text "substVarSet") subst fv)
| otherwise = Type.tyVarsOfType (lookupTvSubst subst fv)
\end{code}
+Note [Worker inlining]
+~~~~~~~~~~~~~~~~~~~~~~
+A worker can get sustituted away entirely.
+ - it might be trivial
+ - it might simply be very small
+We do not treat an InlWrapper as an 'occurrence' in the occurence
+analyser, so it's possible that the worker is not even in scope any more.
+
+In all all these cases we simply drop the special case, returning to
+InlVanilla. The WARN is just so I can see if it happens a lot.
+
+
%************************************************************************
%* *
The Very Simple Optimiser
-- may change radically
simpleOptExpr expr
- = go init_subst (occurAnalyseExpr expr)
+ = -- pprTrace "simpleOptExpr" (ppr init_subst $$ ppr expr)
+ simple_opt_expr init_subst (occurAnalyseExpr expr)
where
init_subst = mkEmptySubst (mkInScopeSet (exprFreeVars expr))
-- It's potentially important to make a proper in-scope set
-- It's a bit painful to call exprFreeVars, because it makes
-- three passes instead of two (occ-anal, and go)
- go subst (Var v) = lookupIdSubst subst v
- go subst (App e1 e2) = App (go subst e1) (go subst e2)
- go subst (Type ty) = Type (substTy subst ty)
- go _ (Lit lit) = Lit lit
- go subst (Note note e) = Note note (go subst e)
- go subst (Cast e co) = Cast (go subst e) (substTy subst co)
- go subst (Let bind body) = go_let subst bind body
- go subst (Lam bndr body) = Lam bndr' (go subst' body)
- where
- (subst', bndr') = substBndr subst bndr
-
- go subst (Case e b ty as) = Case (go subst e) b'
- (substTy subst ty)
- (map (go_alt subst') as)
- where
- (subst', b') = substBndr subst b
-
+----------------------
+simpleOptPgm :: DynFlags -> [CoreBind] -> [CoreRule] -> IO ([CoreBind], [CoreRule])
+simpleOptPgm dflags binds rules
+ = do { dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
+ (pprCoreBindings occ_anald_binds);
- ----------------------
- go_alt subst (con, bndrs, rhs) = (con, bndrs', go subst' rhs)
- where
- (subst', bndrs') = substBndrs subst bndrs
+ ; return (reverse binds', substRulesForImportedIds subst' rules) }
+ where
+ occ_anald_binds = occurAnalysePgm binds rules
+ (subst', binds') = foldl do_one (emptySubst, []) occ_anald_binds
+
+ do_one (subst, binds') bind
+ = case simple_opt_bind subst bind of
+ (subst', Nothing) -> (subst', binds')
+ (subst', Just bind') -> (subst', bind':binds')
+
+----------------------
+type InVar = Var
+type OutVar = Var
+type InId = Id
+type OutId = Id
+type InExpr = CoreExpr
+type OutExpr = CoreExpr
+
+-- In these functions the substitution maps InVar -> OutExpr
+
+----------------------
+simple_opt_expr :: Subst -> InExpr -> OutExpr
+simple_opt_expr subst expr
+ = go expr
+ where
+ go (Var v) = lookupIdSubst (text "simpleOptExpr") subst v
+ go (App e1 e2) = App (go e1) (go e2)
+ go (Type ty) = Type (substTy subst ty)
+ go (Lit lit) = Lit lit
+ go (Note note e) = Note note (go e)
+ go (Cast e co) | isIdentityCoercion co' = go e
+ | otherwise = Cast (go e) co'
+ where
+ co' = substTy subst co
+
+ go (Let bind body) = maybeLet mb_bind (simple_opt_expr subst' body)
+ where
+ (subst', mb_bind) = simple_opt_bind subst bind
+ go lam@(Lam {}) = go_lam [] subst lam
+ go (Case e b ty as) = Case (go e) b' (substTy subst ty)
+ (map (go_alt subst') as)
+ where
+ (subst', b') = subst_opt_bndr subst b
----------------------
- go_let subst (Rec prs) body
- = Let (Rec (reverse rev_prs')) (go subst'' body)
+ go_alt subst (con, bndrs, rhs)
+ = (con, bndrs', simple_opt_expr subst' rhs)
where
- (subst', bndrs') = substRecBndrs subst (map fst prs)
- (subst'', rev_prs') = foldl do_pr (subst', []) (prs `zip` bndrs')
- do_pr (subst, prs) ((b,r), b') = case go_bind subst b r of
- Left subst' -> (subst', prs)
- Right r' -> (subst, (b',r'):prs)
-
- go_let subst (NonRec b r) body
- = case go_bind subst b r of
- Left subst' -> go subst' body
- Right r' -> Let (NonRec b' r') (go subst' body)
- where
- (subst', b') = substBndr subst b
-
+ (subst', bndrs') = subst_opt_bndrs subst bndrs
----------------------
- go_bind :: Subst -> Var -> CoreExpr -> Either Subst CoreExpr
- -- (go_bind subst old_var old_rhs)
- -- either extends subst with (old_var -> new_rhs)
- -- or return new_rhs for a binding new_var = new_rhs
- go_bind subst b r
- | Type ty <- r
- , isTyVar b -- let a::* = TYPE ty in <body>
- = Left (extendTvSubst subst b (substTy subst ty))
-
- | isId b -- let x = e in <body>
- , safe_to_inline (idOccInfo b) || exprIsTrivial r'
- = Left (extendIdSubst subst b r')
-
- | otherwise
- = Right r'
- where
- r' = go subst r
+ -- go_lam tries eta reduction
+ go_lam bs' subst (Lam b e)
+ = go_lam (b':bs') subst' e
+ where
+ (subst', b') = subst_opt_bndr subst b
+ go_lam bs' subst e
+ | Just etad_e <- tryEtaReduce bs e' = etad_e
+ | otherwise = mkLams bs e'
+ where
+ bs = reverse bs'
+ e' = simple_opt_expr subst e
+
+----------------------
+simple_opt_bind :: Subst -> CoreBind -> (Subst, Maybe CoreBind)
+simple_opt_bind subst (Rec prs)
+ = (subst'', Just (Rec (reverse rev_prs')))
+ where
+ (subst', bndrs') = subst_opt_bndrs subst (map fst prs)
+ (subst'', rev_prs') = foldl do_pr (subst', []) (prs `zip` bndrs')
+ do_pr (subst, prs) ((b,r), b') = case simple_opt_pair subst b r of
+ Left subst' -> (subst', prs)
+ Right r' -> (subst, (b2,r'):prs)
+ where
+ b2 = add_info subst b b'
+
+simple_opt_bind subst (NonRec b r)
+ = case simple_opt_pair subst b r of
+ Left ext_subst -> (ext_subst, Nothing)
+ Right r' -> (subst', Just (NonRec b2 r'))
+ where
+ (subst', b') = subst_opt_bndr subst b
+ b2 = add_info subst' b b'
+
+----------------------
+simple_opt_pair :: Subst -> InVar -> InExpr -> Either Subst OutExpr
+ -- (simple_opt_pair subst in_var in_rhs)
+ -- either extends subst with (in_var -> out_rhs)
+ -- or return out_rhs for a binding out_var = out_rhs
+simple_opt_pair subst b r
+ | Type ty <- r -- let a::* = TYPE ty in <body>
+ = ASSERT( isTyCoVar b )
+ Left (extendTvSubst subst b (substTy subst ty))
+
+ | isId b -- let x = e in <body>
+ , safe_to_inline (idOccInfo b)
+ , isAlwaysActive (idInlineActivation b) -- Note [Inline prag in simplOpt]
+ , not (isStableUnfolding (idUnfolding b))
+ , not (isExportedId b)
+ = Left (extendIdSubst subst b r')
+
+ | otherwise
+ = Right r'
+ where
+ r' = simple_opt_expr subst r
- ----------------------
-- Unconditionally safe to inline
safe_to_inline :: OccInfo -> Bool
- safe_to_inline IAmDead = True
- safe_to_inline (OneOcc in_lam one_br _) = not in_lam && one_br
safe_to_inline (IAmALoopBreaker {}) = False
- safe_to_inline NoOccInfo = False
+ safe_to_inline IAmDead = True
+ safe_to_inline (OneOcc in_lam one_br _) = (not in_lam && one_br) || exprIsTrivial r'
+ safe_to_inline NoOccInfo = exprIsTrivial r'
+
+----------------------
+subst_opt_bndr :: Subst -> InVar -> (Subst, OutVar)
+subst_opt_bndr subst bndr
+ | isTyCoVar bndr = substTyVarBndr subst bndr
+ | otherwise = subst_opt_id_bndr subst bndr
+
+subst_opt_id_bndr :: Subst -> InId -> (Subst, OutId)
+-- Nuke all fragile IdInfo, unfolding, and RULES;
+-- it gets added back later by add_info
+-- Rather like SimplEnv.substIdBndr
+--
+-- It's important to zap fragile OccInfo (which CoreSubst.SubstIdBndr
+-- carefully does not do) because simplOptExpr invalidates it
+
+subst_opt_id_bndr subst@(Subst in_scope id_subst tv_subst) old_id
+ = (Subst new_in_scope new_id_subst tv_subst, new_id)
+ where
+ id1 = uniqAway in_scope old_id
+ id2 = setIdType id1 (substTy subst (idType old_id))
+ new_id = zapFragileIdInfo id2 -- Zaps rules, worker-info, unfolding
+ -- and fragile OccInfo
+ new_in_scope = in_scope `extendInScopeSet` new_id
+
+ -- Extend the substitution if the unique has changed,
+ -- or there's some useful occurrence information
+ -- See the notes with substTyVarBndr for the delSubstEnv
+ new_id_subst | new_id /= old_id
+ = extendVarEnv id_subst old_id (Var new_id)
+ | otherwise
+ = delVarEnv id_subst old_id
+
+----------------------
+subst_opt_bndrs :: Subst -> [InVar] -> (Subst, [OutVar])
+subst_opt_bndrs subst bndrs
+ = mapAccumL subst_opt_bndr subst bndrs
+
+----------------------
+add_info :: Subst -> InVar -> OutVar -> OutVar
+add_info subst old_bndr new_bndr
+ | isTyCoVar old_bndr = new_bndr
+ | otherwise = maybeModifyIdInfo mb_new_info new_bndr
+ where
+ mb_new_info = substIdInfo subst new_bndr (idInfo old_bndr)
+
+----------------------
+maybeLet :: Maybe CoreBind -> CoreExpr -> CoreExpr
+maybeLet Nothing e = e
+maybeLet (Just b) e = Let b e
\end{code}
+
+Note [Inline prag in simplOpt]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+If there's an INLINE/NOINLINE pragma that restricts the phase in
+which the binder can be inlined, we don't inline here; after all,
+we don't know what phase we're in. Here's an example
+
+ foo :: Int -> Int -> Int
+ {-# INLINE foo #-}
+ foo m n = inner m
+ where
+ {-# INLINE [1] inner #-}
+ inner m = m+n
+
+ bar :: Int -> Int
+ bar n = foo n 1
+
+When inlining 'foo' in 'bar' we want the let-binding for 'inner'
+to remain visible until Phase 1
+
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