When a function is streaming-compatible and calls a function with a normal or streaming
interface, it may need to enable/disable stremaing mode before the call, and
needs to restore PSTATE.SM after the call.
This patch implements this with a Pseudo node that gets expanded to a
conditional branch and smstart/smstop node.
More details about the SME attributes and design can be found
in D131562.
Not a big deal, but this seems like an odd optimization to do. One would think that this would be infrequent enough that we wouldn't need to add special handling for it, and if it's not infrequent, why?