[clang] [llvm] [RISCV] Add Qualcomm uC Xqcisim (Simulation Hint) extension (PR #128833)

[Sam Elliott via llvm-commits]

lenary wrote:

> Is there any documentation thats say what instructions these hint encodings belong to?

Not explicitly, but these overlap with `SLTI` and `C.SLLI` if I'm reading our docs correctly. We do intend to move these to use aliases, but we'd like to land them like this first.

https://github.com/llvm/llvm-project/pull/128833