It turns out that Ivan has answered (in the metadata thread) regarding the result from a NaR and a None in a normal (read two-input, exu-side) operation: The None wins; see his response #558:
IMHO, this still leaves unclear what happens when either a None or a NaR are inputs to an address calculation (e.g., as base, offset or index inputs the the address calc.), either as a separate calc or as part of a load or store operation. The rules for address calculations (on the flow side) might be different than for exu-side ops.
We know that Nones as data values silently act as no-ops when stored, and that inaccessible addresses return Nones when loaded from. However, I’m still puzzled re what load/store ops do when their effective address is None. My best guess is that a NaR effective address will make both loads and stores fault, but the desired behavior may well be different for an effective address of None.
- This reply was modified 8 years, 11 months ago by LarryP.