On Tue, Nov 24, 2020 at 9:49 AM Walter Dnes <[email protected]> wrote: > > On Tue, Nov 24, 2020 at 07:56:07PM +1100, Adam Carter wrote > > > 3) AMD code runs only on same or newer AMD, because it has the 3DNow! > > > instruction set the others lack. > > > > > > > FYI 3dnow and 3dnowext went away some time ago. It's not in any of the > > Bulldozer or Zen CPUs. > > So you're saying that newer AMDs may not run code optimized for older > AMDs ???
It depends on what you mean by "optimized." If you mean using -march, then yes, newer AMD OR Intel CPUs may not run software built for older ones. They get rid of instructions as well as adding them, and some lines have instructions not present in others. If you use -mtune then the code will work on any amd64 processor - AMD or Intel. If you use -march then you generally need to rebuild everything without it (or at least @system) before you go switching CPUs. -- Rich
