[clang] [llvm] [RISCV][MC] Add experimental Smidctrl, Ssidctrl, Smnip, and Ssnip support (PR #218108)

[Zeyi Xu via llvm-commits]

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@@ -1130,6 +1139,15 @@ def HasStdExtSsip : Predicate<"Subtarget->hasStdExtSsip()">,
                         "'Ssip' (Support for Interrupt Handler Push/Pop at "
                         "Supervisor Level)">;
 
+def FeatureStdExtSmnip
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zeyi2 wrote:

The extension names and descriptions are derived from [here](https://github.com/riscv/riscv-fast-interrupt/blob/b623d1262ed40a255fd290333d8e0c6d0c44b2e8/src/aclic.adoc?plain=1#L190-L203).

https://github.com/llvm/llvm-project/pull/218108