data SimplSR
= DoneEx OutExpr -- Completed term
- | DoneId OutId OccInfo -- Completed term variable, with occurrence info
+ | DoneId OutId -- Completed term variable
| ContEx TvSubstEnv -- A suspended substitution
SimplIdSubst
InExpr
a77 -> a77
from the substitution, when we decide not to clone a77, but it's quite
legitimate to put the mapping in the substitution anyway.
-
- Indeed, we do so when we want to pass fragile OccInfo to the
- occurrences of the variable; we add a substitution
- x77 -> DoneId x77 occ
- to record x's occurrence information.]
Furthermore, consider
let x = case k of I# x77 -> ... in
Of course, the substitution *must* applied! Things in its domain
simply aren't necessarily bound in the result.
-* substId adds a binding (DoneId new_id occ) to the substitution if
- EITHER the Id's unique has changed
- OR the Id has interesting occurrence information
- So in effect you can only get to interesting occurrence information
- by looking up the *old* Id; it's not really attached to the new id
- at all.
+* substId adds a binding (DoneId new_id) to the substitution if
+ the Id's unique has changed
+
Note, though that the substitution isn't necessarily extended
if the type changes. Why not? Because of the next point:
substId :: SimplEnv -> Id -> SimplSR
substId (SimplEnv { seInScope = in_scope, seIdSubst = ids }) v
| not (isLocalId v)
- = DoneId v NoOccInfo
+ = DoneId v
| otherwise -- A local Id
= case lookupVarEnv ids v of
- Just (DoneId v occ) -> DoneId (refine v) occ
- Just res -> res
- Nothing -> let v' = refine v
- in DoneId v' (idOccInfo v')
- -- We don't put LoopBreakers in the substitution (unless then need
- -- to be cloned for name-clash rasons), so the idOccInfo is
- -- very important! If isFragileOcc returned True for
- -- loop breakers we could avoid this call, but at the expense
- -- of adding more to the substitution, and building new Ids
- -- a bit more often than really necessary
+ Just (DoneId v) -> DoneId (refine v)
+ Just res -> res
+ Nothing -> DoneId (refine v)
where
-- Get the most up-to-date thing from the in-scope set
-- Even though it isn't in the substitution, it may be in
-- Extend the substitution if the unique has changed
-- See the notes with substTyVarBndr for the delSubstEnv
new_subst | new_id /= old_id
- = extendVarEnv id_subst old_id (DoneId new_id (idOccInfo old_id))
+ = extendVarEnv id_subst old_id (DoneId new_id)
| otherwise
= delVarEnv id_subst old_id
\end{code}
-- or there's some useful occurrence information
-- See the notes with substTyVarBndr for the delSubstEnv
occ_info = occInfo (idInfo old_id)
- new_subst | new_id /= old_id || isFragileOcc occ_info
- = extendVarEnv id_subst old_id (DoneId new_id occ_info)
+ new_subst | new_id /= old_id
+ = extendVarEnv id_subst old_id (DoneId new_id)
| otherwise
= delVarEnv id_subst old_id
\end{code}
mk_subst tv_env id_env = CoreSubst.mkSubst in_scope tv_env (mapVarEnv fiddle id_env)
fiddle (DoneEx e) = e
- fiddle (DoneId v occ) = Var v
+ fiddle (DoneId v) = Var v
fiddle (ContEx tv id e) = CoreSubst.substExpr (mk_subst tv id) e
substExpr :: SimplEnv -> CoreExpr -> CoreExpr