If you have code that makes use of custom instructions, even if only sprinkled in a few places, the emulator must support them.
If you have a cpu with those extra instructions that is otherwise backwards compatible, you can run code that doesn't make use of such instructions just fine (of course, you won't benefit from the functionality/performance offered by those new instructions)
If you have code that makes use of custom instructions, even if only sprinkled in a few places, the emulator must support them.
If you have a cpu with those extra instructions that is otherwise backwards compatible, you can run code that doesn't make use of such instructions just fine (of course, you won't benefit from the functionality/performance offered by those new instructions)