[RISCV] Add the CSR names from Smrnmi. (#83370)

Specification is here
https://github.com/riscv/riscv-isa-manual/blob/main/src/rnmi.adoc

CSRs numbers defined here
https://github.com/riscv/riscv-isa-manual/blob/main/src/priv-csrs.adoc

Author: topperc

llvm/docs/ReleaseNotes.rst

@@ -108,6 +108,7 @@ Changes to the RISC-V Backend
 * The experimental Ssnpm, Smnpm, Smmpm, Sspm, and Supm 0.8.1 Pointer Masking extensions are supported.
 * The experimental Ssqosid extension is supported.
 * Zacas is no longer experimental.
+* Added the CSR names from the Resumable Non-Maskable Interrupts (Smrnmi) extension.
 
 Changes to the WebAssembly Backend
 ----------------------------------

llvm/lib/Target/RISCV/RISCVSystemOperands.td

@@ -418,7 +418,16 @@ def : SysReg<"vsieh", 0x214>;
 def : SysReg<"vsiph", 0x254>;
 } // isRV32Only
 
+//===-----------------------------------------------
 // Jump Vector Table CSR
 //===-----------------------------------------------
 
 def : SysReg<"jvt", 0x017>;
+
+//===-----------------------------------------------
+// Resumable Non-Maskable Interrupts(Smrnmi) CSRs
+//===-----------------------------------------------
+def : SysReg<"mnscratch", 0x740>;
+def : SysReg<"mnepc", 0x741>;
+def : SysReg<"mncause", 0x742>;
+def : SysReg<"mnstatus", 0x744>;

llvm/test/MC/RISCV/rv32-machine-csr-names.s

@@ -1149,3 +1149,59 @@ csrrs t2, 0x319, zero
 csrrs t1, miph, zero
 # uimm12
 csrrs t2, 0x354, zero
+
+################################################
+# Resumable Non-Maskable Interrupts(Smrnmi) CSRs
+################################################
+
+# mnscratch
+# name
+# CHECK-INST: csrrs t1, mnscratch, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x00,0x74]
+# CHECK-INST-ALIAS: csrr t1, mnscratch
+# uimm12
+# CHECK-INST: csrrs t2, mnscratch, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x00,0x74]
+# CHECK-INST-ALIAS: csrr t2, mnscratch
+csrrs t1, mnscratch, zero
+# uimm12
+csrrs t2, 0x740, zero
+
+# mnepc
+# name
+# CHECK-INST: csrrs t1, mnepc, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x10,0x74]
+# CHECK-INST-ALIAS: csrr t1, mnepc
+# uimm12
+# CHECK-INST: csrrs t2, mnepc, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x10,0x74]
+# CHECK-INST-ALIAS: csrr t2, mnepc
+csrrs t1, mnepc, zero
+# uimm12
+csrrs t2, 0x741, zero
+
+# mncause
+# name
+# CHECK-INST: csrrs t1, mncause, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x20,0x74]
+# CHECK-INST-ALIAS: csrr t1, mncause
+# uimm12
+# CHECK-INST: csrrs t2, mncause, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x20,0x74]
+# CHECK-INST-ALIAS: csrr t2, mncause
+csrrs t1, mncause, zero
+# uimm12
+csrrs t2, 0x742, zero
+
+# mnstatus
+# name
+# CHECK-INST: csrrs t1, mnstatus, zero
+# CHECK-ENC: encoding: [0x73,0x23,0x40,0x74]
+# CHECK-INST-ALIAS: csrr t1, mnstatus
+# uimm12
+# CHECK-INST: csrrs t2, mnstatus, zero
+# CHECK-ENC: encoding: [0xf3,0x23,0x40,0x74]
+# CHECK-INST-ALIAS: csrr t2, mnstatus
+csrrs t1, mnstatus, zero
+# uimm12
+csrrs t2, 0x744, zero