Currently Trans.trans_call takes an argument indicating whether it's an
initializing call, but it always behaves as though it's initializing, even if
the argument is false. This is because there's a bit of a subtlety involved in
refcounted values: the same referent may be used as both dst of the call and as
an arg, and we want to avoid having it drop before being pinned as an arg,
because the dst was dropped.
The existing code may have been born in the CoW era and may no longer represent
a real hazard if rearranged to just pin args first then drop dst; will need a
few careful tests to be sure the arrangement actually works.
(Alternatively: worst case, make a static pass that prohibits x = f(x) the same
way f(x,x) is to be prohibited if both slots are alias-mode.)
Currently Trans.trans_call takes an argument indicating whether it's an
initializing call, but it always behaves as though it's initializing, even if
the argument is false. This is because there's a bit of a subtlety involved in
refcounted values: the same referent may be used as both dst of the call and as
an arg, and we want to avoid having it drop before being pinned as an arg,
because the dst was dropped.
The existing code may have been born in the CoW era and may no longer represent
a real hazard if rearranged to just pin args first then drop dst; will need a
few careful tests to be sure the arrangement actually works.
(Alternatively: worst case, make a static pass that prohibits x = f(x) the same
way f(x,x) is to be prohibited if both slots are alias-mode.)