I may be missing something, but I don't think that is the interesting issue here.
I agree.
I think the issue is whether we want to have a way to see all currently valid SSA_NAMEs. Right now we can have SSA_NAMEs in the list which are no longer used, and we have no way to tell whether they are used or not. Thus the only way to see all valid SSA_NAMEs is to walk the code. If that is acceptable, then there is no issue here. If that is not acceptable, then we need to fix the code to correctly mark SSA_NAMEs which are no longer used. Whether we recycle the memory in the unused SSA_NAMEs is a separate (and less interesting) discussion.
IMHO, it's not acceptable, because it leaves no way to do DFS walks that don't involve kludges and hacks.
Ian
