> If it's so cheap and good, why is it an extension and not part of the base then?
I think what you mean is why it is not in the G extension which encompasses IMAFD but not C. I agree that is a bit odd.
I think it would have been very wrong if it was part of the I base instruction set. That should be as minimal as possible.
But I guess a question like this easily becomes very philosophical. For me it makes sense that C is not in G, because C is really an optimization and not about capability. A software developer, tool maker etc would care more about the instructions available I think than particular optimizations.
> E.g. the A9 has to carry around all the 32-bit legacy baggage
But surely that counts in RISC-V favor as ARM has no alternative modern minimal 32-bit instruction set. With RISC-V you can use 64-bit and 32-bit instructions with minimal code change.
And I don't see how ARM-64 would have made any of this any better, as it has over 1000 instructions. I am highly skeptical that you can make tiny cores out of that. But I am not a CPU guy so I am okay with being told I am wrong ;-) As long as you can give me a proper reason.
> Doesn't mean that it's a particularly relevant argument for evaluating ISA's for production usage.
True, but I think there is a value in the whole package. You see people evaluating RISC-V and finding that sure there are commercial offerings performing slightly better, or they could make custom ISA that does better. But the conclusion for many is that RISC-V is good enough and with the growing eco-system, that still makes it a better choice in sum. If you are to make a custom ISA today, it better be a lot better than RISC-V to be worth it, I would think.
I would also think there is a value for hardware makers to be on the same platform which Universities and research institutions are going to be using. As well as the same platform students are going to come out of University knowing.
Anyway thanks for the discussion. While I am pushing back on everything (seemingly) I do find this kind of discussion very valuable in learning better pros and cons. It spurs me to look up and learn more things.
I think what you mean is why it is not in the G extension which encompasses IMAFD but not C. I agree that is a bit odd.
I think it would have been very wrong if it was part of the I base instruction set. That should be as minimal as possible.
But I guess a question like this easily becomes very philosophical. For me it makes sense that C is not in G, because C is really an optimization and not about capability. A software developer, tool maker etc would care more about the instructions available I think than particular optimizations.
> E.g. the A9 has to carry around all the 32-bit legacy baggage
But surely that counts in RISC-V favor as ARM has no alternative modern minimal 32-bit instruction set. With RISC-V you can use 64-bit and 32-bit instructions with minimal code change.
And I don't see how ARM-64 would have made any of this any better, as it has over 1000 instructions. I am highly skeptical that you can make tiny cores out of that. But I am not a CPU guy so I am okay with being told I am wrong ;-) As long as you can give me a proper reason.
> Doesn't mean that it's a particularly relevant argument for evaluating ISA's for production usage.
True, but I think there is a value in the whole package. You see people evaluating RISC-V and finding that sure there are commercial offerings performing slightly better, or they could make custom ISA that does better. But the conclusion for many is that RISC-V is good enough and with the growing eco-system, that still makes it a better choice in sum. If you are to make a custom ISA today, it better be a lot better than RISC-V to be worth it, I would think.
I would also think there is a value for hardware makers to be on the same platform which Universities and research institutions are going to be using. As well as the same platform students are going to come out of University knowing.
Anyway thanks for the discussion. While I am pushing back on everything (seemingly) I do find this kind of discussion very valuable in learning better pros and cons. It spurs me to look up and learn more things.