> If a program crashes on an older CPU, it damn sure will crash on a modern CPU just as well.
Not necessarily; if the crash is caused by an instruction that's absent on older CPUs (for instance, trying to use an AVX2 instruction when the most the CPU has is SSE2), it will work on a modern CPU but crash on an older CPU.
Not necessarily; if the crash is caused by an instruction that's absent on older CPUs (for instance, trying to use an AVX2 instruction when the most the CPU has is SSE2), it will work on a modern CPU but crash on an older CPU.