> "Alias" means nothing to a CPU, nor is it an ABI.

But the language isn't defined in terms of a CPU. It's defined in terms of abstract semantic rules. You shouldn't think about implementation, especially at the CPU level, when talking about semantics.

The idea is that the alias is implicit in pass-by-reference. It isn't implicit in pass-by-value. How you implement that alias is irrelevant for discussion at this level.