[llvm] [Mips][nanoMIPS] Add initial nanoMIPS target support (PR #223032)

[Jiaxun Yang via llvm-commits]

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@@ -153,6 +153,41 @@ let Namespace = "Mips" in {
   def FP_64   : Mips64GPRReg< 30, "fp",  [FP]>, DwarfRegNum<[30]>;
   def RA_64   : Mips64GPRReg< 31, "ra",  [RA]>, DwarfRegNum<[31]>;
 
+  // General Purpose nanoMIPS Registers
+  let isConstant = true in
+  def ZERO_NM : MipsGPRReg< 0, "zero">, DwarfRegNum<[0]>;
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FlyGoat wrote:

Hmm, it seems to be a little bit overkilling to define whole new Reg for nanoMIPS?
See RISC-V's `ABIRegAltName`.

https://github.com/llvm/llvm-project/pull/223032