While looping through all args or all return values, we may mark a use
of a later iteration as live. Previously when we got to that later value
it would ignore that and continue adding to Uses instead of marking it
live. For example, when looping through arg#0 and arg#1,
MarkValue(arg#0, Live) may cause some use of arg#1 to be live, but
MarkValue(arg#1, MaybeLive) will not notice that and continue adding
Now MarkValue(RA, MaybeLive) will MarkLive(RA) if any use is live.