but microcoding has existed for ever and while uops is probably a very specialized form of microcoding, it still not a new thing.
Also I do not think uops are fixed size as IIRC they can take a variable number of slots in the uop cache, and fix size instructions is pretty much one of the only two remaining differentiating RISC features. The internal x86 microarchitecture is also not load-store, the other one RISC feature, at least in the fused domain, and as far as I understand, in the uop cache.
So, even if we want to abuse the RISC term to describe the microarchitecture, I do not think it cleanly apply to the usual x86 implementations.
edit: this is a pet peeve of mine. It seems I have this discussion every 6 months on HN :)
Everything I've read about Intel uOps says that they're fixed size[1]. Now, the size isn't a power of 2 multiple of a byte like you'd see in a RISC design. I seem to recall some Intel architecture with 83 bit uOps? But it is fixed. And the uOp caches for both Intel and AMD are fixed size. Haswell stores 1.5k uOps[2] and Zen 2k[3] for instance.
But the important thing is that uOps are much higher level than microcode instructions. Except for the odd encoding size they would make a lot of sense as an early RISC ISA. Now, they expose a lot of the odd corner cases of the underlying architecture in a way that no modern ISA would but the original Berkeley RISC had branch delay slots and followed the philosophy that you'd just recompile the code when the ISA changes.
I'm at the edge of my knowledge here but I understand that microcoded instructions would tend to be much lower level, being things like read from memory to such and such an internal buffer. By contrast uOps do specify registers or constants, though they do so (post-rename) in terms of physical rather than architectural registers. But the decision on whether to get that arguments from the physical register or the bypass network is still made further down the pipe as with a RISC processor.
Is the analogy perfect? No, of course not. No analogy ever is. But I do think it illuminates more than it misleads for people learning about the evolution of processors - just as long as people can keep architecture and micro-architecture straight.
FWIW, Agner says that if a uop has multiple constants (for example an address and an immediate), it will borrow up to 32 bits from the next uop cache slot.
Encoding constants in the instructions themselves is a very non-RISC thing BTW.
Also I do not think uops are fixed size as IIRC they can take a variable number of slots in the uop cache, and fix size instructions is pretty much one of the only two remaining differentiating RISC features. The internal x86 microarchitecture is also not load-store, the other one RISC feature, at least in the fused domain, and as far as I understand, in the uop cache.
So, even if we want to abuse the RISC term to describe the microarchitecture, I do not think it cleanly apply to the usual x86 implementations.
edit: this is a pet peeve of mine. It seems I have this discussion every 6 months on HN :)