[clang] [llvm] [RISCV] Add MIPS extensions (PR #121394)

[Craig Topper via llvm-commits]

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@@ -514,6 +514,78 @@ class RVInstJ<RISCVOpcode opcode, dag outs, dag ins, string opcodestr,
   let Inst{6-0} = opcode.Value;
 }
 
+//===----------------------------------------------------------------------===//
+// MIPS custom instruction formats
+//===----------------------------------------------------------------------===//
+
+// Load double pair format.
+class LDPFormat<dag outs, dag ins, string opcodestr, string argstr>
+    : RVInst<outs, ins, opcodestr, argstr, [], InstFormatI> {
+  bits<7> imm7;
+  bits<5> rs1;
+  bits<5> rd1;
+  bits<5> rd2;
+
+  let Inst{31-27} = rd2;
+  let Inst{26-23} = imm7{6-3};
+  let Inst{22-20} = 0b000;
+  let Inst{19-15} = rs1;
+  let Inst{14-12} = 0b100;
+  let Inst{11-7} = rd1;
+  let Inst{6-0} = 0b0001011;
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topperc wrote:

This use the `OPC_CUSTOM_0.Value` for readability

https://github.com/llvm/llvm-project/pull/121394