My point is that the spec does not give the behaviour-to-machine-instruction mapping, only the other way round, and reversing the mapping is non-trivial. Table

My point is that the spec does not give the behaviour-to-machine-instruction mapping, only the other way round, and reversing the mapping is non-trivial. Table driven assemblers and disassemblers would be straightforward to produce from this spec, yes, because those just need to care about the instruction patterns and the mnemonics. A compiler backend needs to care about the semantics of the instructions, which are in the pseudocode, and thus harder to automatically reason about. (For instance lots of the instructions include an add somewhere, but how do you find the one that is just a plain add rather than saturating or simd or also setting the condition flags?) Writing something smart enough would I think be vastly more work than just doing a compiler backend by hand, and likely produce worse code anyway. (A sibling comment suggests it would be phd-thesis level work and I think I'd agree with that.)