[clang] [llvm] [RISC-V] Add CSR read/write builtins (PR #85091)

[Craig Topper via cfe-commits]

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@@ -20,6 +20,12 @@ class RISCVBuiltin<string prototype, string features = ""> : TargetBuiltin {
 
 let Attributes = [NoThrow, Const] in {
 //===----------------------------------------------------------------------===//
+// Zicsr extension.
+//===----------------------------------------------------------------------===//
+def csrr : RISCVBuiltin<"unsigned long int(unsigned long int)", "zicsr">;
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topperc wrote:

I don't think these are `Const` since they operate on state that is not part of their arguments/return.

https://github.com/llvm/llvm-project/pull/85091