+-- simplBndr and simplLetId are used by the simplifier
+
+simplBndr :: Subst -> Var -> (Subst, Var)
+-- Used for lambda and case-bound variables
+-- Clone Id if necessary, substitute type
+-- Return with IdInfo already substituted, but (fragile) occurrence info zapped
+-- The substitution is extended only if the variable is cloned, because
+-- we *don't* need to use it to track occurrence info.
+simplBndr subst bndr
+ | isTyVar bndr = substTyVar subst bndr
+ | otherwise = subst_id False subst subst bndr
+
+simplBndrs :: Subst -> [Var] -> (Subst, [Var])
+simplBndrs subst bndrs = mapAccumL simplBndr subst bndrs
+
+simplLamBndr :: Subst -> Var -> (Subst, Var)
+-- Used for lambda binders. These sometimes have unfoldings added by
+-- the worker/wrapper pass that must be preserved, becuase they can't
+-- be reconstructed from context. For example:
+-- f x = case x of (a,b) -> fw a b x
+-- fw a b x{=(a,b)} = ...
+-- The "{=(a,b)}" is an unfolding we can't reconstruct otherwise.
+simplLamBndr subst bndr
+ | not (isId bndr && hasSomeUnfolding old_unf)
+ = simplBndr subst bndr -- Normal case
+ | otherwise
+ = (subst', bndr' `setIdUnfolding` substUnfolding subst old_unf)
+ where
+ old_unf = idUnfolding bndr
+ (subst', bndr') = subst_id False subst subst bndr
+
+
+simplLetId :: Subst -> Id -> (Subst, Id)
+-- Clone Id if necessary
+-- Substitute its type
+-- Return an Id with completely zapped IdInfo
+-- [A subsequent substIdInfo will restore its IdInfo]
+-- Augment the subtitution
+-- if the unique changed, *or*
+-- if there's interesting occurrence info
+
+simplLetId subst@(Subst in_scope env) old_id
+ = (Subst (in_scope `extendInScopeSet` new_id) new_env, new_id)
+ where
+ old_info = idInfo old_id
+ id1 = uniqAway in_scope old_id
+ id2 = substIdType subst id1
+ new_id = setIdInfo id2 vanillaIdInfo
+
+ -- Extend the substitution if the unique has changed,
+ -- or there's some useful occurrence information
+ -- See the notes with substTyVar for the delSubstEnv
+ occ_info = occInfo old_info
+ new_env | new_id /= old_id || isFragileOcc occ_info
+ = extendSubstEnv env old_id (DoneId new_id occ_info)
+ | otherwise
+ = delSubstEnv env old_id
+
+simplIdInfo :: Subst -> IdInfo -> IdInfo
+ -- 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 False subst old_info of
+ Just new_info -> new_info
+ Nothing -> old_info
+\end{code}
+
+\begin{code}
+-- substBndr and friends are used when doing expression substitution only
+-- In this case we can *preserve* occurrence information, and indeed we *want*
+-- to do so else lose useful occ info in rules. Hence the calls to
+-- simpl_id with keepOccInfo
+
+substBndr :: Subst -> Var -> (Subst, Var)
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