The unsolvability of the halting problems means that it is impossible to have a general algorithm that makes non-trivial statements about the behavior of a given program.
In the context of IA-64, that means that generally, the compiler will not be able to determine when it's save to use parallelism. We can only program it to use parallelism in a bunch of special cases for which we think it will be safe.
Given that simias originally asked for a simpler platform that we can trust in more, this seems to be a pretty strong argument that IA-64 is not that architecture.
Can you elaborate on how the halting problem relates to the IA-64 architecture?