3 ms·

Apparently modern Intel CPUs will fuse JO instructions to preceding adds, producing the effect of dedicated "checked add" instructions: https://gist.github.com

• chrisseaton 10y ago
  In the examples the article this shows this will not help, as the overflow is in indirect addressing, not add instructions. I'm not a microcode expert but I guess arithmetic instructions, even without a jo, are not as efficient as indirect addressing, so we can't switch to arithmetic instructions with jo.
  • dbaupp 10y ago
    The efficiency of the add/jo combo does help (i.e. checking overflow isn't a total drag), it just doesn't completely solve the performance problem.
    • chrisseaton 10y ago
      Perhaps we could have a new addressing mode that is the same as normal indirect but falls through and sets o if some part of it overflows. Then you'd do mov, jo which could then be fused. But I don't really know what I'm talking about.