[RISCV] Add DecoderNamespace to Zcmt instructions.

[craig.topper]

Summary

The Zcmt instructions overlap encoding space with some C extension
instructions. Isolate to a separate namespace.

[jrtc27]

llvm/lib/Target/RISCV/RISCVInstrInfoZc.td

152

Update, maybe?

[craig.topper]

Update comment

[VincentWu]

LGTM

llvm/lib/Target/RISCV/Disassembler/RISCVDisassembler.cpp

if (!STI.hasFeature(RISCV::Feature64Bit)) {
     LLVM_DEBUG(
         dbgs() << "Trying RISCV32Only_16 table (16-bit Instruction):\n");
     // Calling the auto-generated decoder function.
     Result = decodeInstruction(DecoderTableRISCV32Only_16, MI, Insn, Address,
                                this, STI);
     if (Result != MCDisassembler::Fail)
       return Result;
   }
+  if (STI.hasFeature(RISCV::FeatureStdExtZcmt)) {
+    LLVM_DEBUG(
+        dbgs() << "Trying Zcmt table (16-bit Table Jump Instructions):\n");
+    Result = decodeInstruction(DecoderTableRVZcmt16, MI, Insn, Address,
+                               this, STI);
+    if (Result != MCDisassembler::Fail)
+      return Result;
+  }
 
   LLVM_DEBUG(dbgs() << "Trying RISCV_C table (16-bit Instruction):\n");
   // Calling the auto-generated decoder function.
   return decodeInstruction(DecoderTable16, MI, Insn, Address, this, STI);
 }

llvm/lib/Target/RISCV/RISCVInstrInfoZc.td

def C_LH  : CLoadH_ri<0b100001, 0b1, "c.lh">,
             Sched<[WriteLDH, ReadMemBase]>;
 
 def C_SB : CStoreB_rri<0b100010, "c.sb">,
            Sched<[WriteSTB, ReadStoreData, ReadMemBase]>;
 def C_SH : CStoreH_rri<0b100011, 0b1, "c.sh">,
            Sched<[WriteSTH, ReadStoreData, ReadMemBase]>;
 }
 
-let Predicates = [HasStdExtZcmt],
+let DecoderNamespace = "RVZcmt", Predicates = [HasStdExtZcmt],
     hasSideEffects = 0, mayLoad = 0, mayStore = 0 in {
 def CM_JT : RVInst16CJ<0b101, 0b10, (outs), (ins uimm5:$index),
                        "cm.jt", "$index">{
   bits<5> index;
 
   let Inst{12-7} = 0b000000;
   let Inst{6-2} = index;
 }
 
 def CM_JALT : RVInst16CJ<0b101, 0b10, (outs), (ins uimm8ge32:$index),
                          "cm.jalt", "$index">{
   bits<8> index;
 
   let Inst{12-10} = 0b000;
   let Inst{9-2} = index;
 }
-} // Predicates = [HasStdExtZcmt]
+} // DecoderNamespace = "RVZcmt", Predicates = [HasStdExtZcmt]...
 
 
 let Predicates = [HasStdExtZcb, HasStdExtMOrZmmul] in{
 def : CompressPat<(MUL GPRC:$rs1, GPRC:$rs1, GPRC:$rs2),
                   (C_MUL GPRC:$rs1, GPRC:$rs2)>;
 let isCompressOnly = true in
 def : CompressPat<(MUL GPRC:$rs1, GPRC:$rs2, GPRC:$rs1),
                   (C_MUL GPRC:$rs1, GPRC:$rs2)>;