[llvm] [RISCV] Add scheduler definitions for SpacemiT-X60 (PR #137343)

[Alex Bradbury via llvm-commits]

asb wrote:

I've discussed earlier versions of this patch with Mikhail a fair bit so I'd appreciate a review from outside our org, but I will just share my thoughts on criteria for whether this makes sense to merge at this point:

For me the key thing is that per Mikhail's benchmarking it's at the point where there's pretty much across the board improvements and importantly, there's no evidence of regressions due to introducing scalar but not having vector scheduling. As for the fine details of the model, we're not going to get the very high fidelity of the 7-series model without much more microarchitectural information or a lot more reverse engineering. What is here seems a reasonable starting point.

I'd appreciate comments on anything that seems anomalous vs other scheduling models - we should aim to basically match the pattern of others unless there's data or documented information to differ. With that in mind, the store latency of 3 is a slight oddity vs other similar models. But the A55 had latency=4 up to f73334c46d59ffdbf12353932d5985049335a6c7 and the commit comment indicates it has very limited impact on scheduling anyway. So unless people feel strongly it's worth more investigation right now, I propose sticking with what Mikhail suggests.

(Incidentally, should any of our models be setting RetireOOO like the A55 does?)

https://github.com/llvm/llvm-project/pull/137343