Having consistent instruction set with CPU doesn't help much. Learning new instruction doesn't takes that long as more recent instructions set all shares same i

Having consistent instruction set with CPU doesn't help much. Learning new instruction doesn't takes that long as more recent instructions set all shares same ideas and don't really have quirks like in the old days. When you go hand-optimizing, you want to squeeze the last bit of performance. And that (currently) is very CPU-specific. Because all CPUs have different cache/memory system, instruction latency, and pipeline structure. When I was doing low-level work (for video processing), a lot of time I has to strike a balance across various microarchicture. Some more extreme people (including the code by Intel ICC) target each CPU model specifically. Because the MIC has vastly different architecture, the resulting hand-optimized code will be vastly different. You still need to learn both of them anyway.