On 18/10/21 20:15, Linus Torvalds wrote:
* Use a bitwise-OR instead of a logical-OR to aggregate the reserved * bits and EPT's invalid memtype/XWR checks to avoid an extra Jcc * (this is extremely unlikely to be short-circuited as true).That makes very little sense. It seems to be avoiding a 'jcc' and replace it with a 'setcc' and an 'or'. Which is likely both bigger and slower.
The compiler knows that the setcc is unnecessary, because a!=0|b!=0 is the same as (a|b)!=0.
If the jcc were unpredictable, maybe that would be one thing. But at least from a quick look, that doesn't even seem likely The other use of that function has a "WARN_ONCE()" on it, so presumably it normally doesn't ever trigger either of the boolean conditions.
Yes, and that was why it used a "|". Anyway, not worth arguing for or against; I'll just change it to logical OR. Paolo
