I am a firm believer that if AMD wasn't in the position to be able to come up with AMD64 architecture, eventually those Itanium issues would have been sorted out, Windows XP was already there and there was no other way for 64 bit going forward.

It has never happened that a compiler was able to do static scheduling of general purpose instructions over the long term.

Every CPU changes the cycles it takes for many instructions, adds new instructions etc.

Out of order execution is a huge dividing line in performance for a reason. The CPU itself needs to figure these things out to minimize memory latency, cache latency, pipelining, prefetching and all that stuff.

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I don't know anything about Itanium in particular, but AMD's NPU uses a VLIW architecture and they had to break backwards compatibility in the ISA for the second generation NPU (XDNA2) to get better performance.