diff --git a/llvm/test/TableGen/trydecode-emission.td b/llvm/test/TableGen/trydecode-emission.td
index 47d47c9c96183..c3178dd71cf4b 100644
--- a/llvm/test/TableGen/trydecode-emission.td
+++ b/llvm/test/TableGen/trydecode-emission.td
@@ -37,8 +37,8 @@ def InstB : TestInstruction {
 // CHECK:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-NEXT: /* 3 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 6, 0, // Skip to: 17
-// CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, Skip to: 17
-// CHECK-NEXT: /* 17 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 17
+// CHECK-NEXT: /* 17 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
 // CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
 
 // CHECK: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
@@ -50,8 +50,8 @@ def InstB : TestInstruction {
 // CHECK-LARGE:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-LARGE-NEXT: /* 3 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-LARGE-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 7, 0, 0, // Skip to: 19
-// CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, Skip to: 19
-// CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
+// CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
 // CHECK-LARGE-NEXT: /* 23 */      MCD::OPC_Fail,
 
 // CHECK-LARGE: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
diff --git a/llvm/test/TableGen/trydecode-emission2.td b/llvm/test/TableGen/trydecode-emission2.td
index 593da63cd7616..4c8a95eff5dd1 100644
--- a/llvm/test/TableGen/trydecode-emission2.td
+++ b/llvm/test/TableGen/trydecode-emission2.td
@@ -36,7 +36,7 @@ def InstB : TestInstruction {
 // CHECK-NEXT: /* 5 */       MCD::OPC_ExtractField, 5, 3,  // Inst{7-5} ...
 // CHECK-NEXT: /* 8 */       MCD::OPC_FilterValueOrFail, 0
 // CHECK-NEXT: /* 10 */      MCD::OPC_CheckField, 0, 2, 3, 6, 0, // Skip to: 22
-// CHECK-NEXT: /* 16 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, Skip to: 22
+// CHECK-NEXT: /* 16 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 22
 // CHECK-NEXT: /* 22 */      MCD::OPC_CheckFieldOrFail, 3, 2, 0,
 // CHECK-NEXT: /* 26 */      MCD::OPC_TryDecodeOrFail, {{[0-9]+}}, {{[0-9]+}}, 1,
 // CHECK-NEXT: /* 30 */      MCD::OPC_Fail,
@@ -49,7 +49,7 @@ def InstB : TestInstruction {
 // CHECK-LARGE-NEXT: /* 5 */       MCD::OPC_ExtractField, 5, 3,  // Inst{7-5} ...
 // CHECK-LARGE-NEXT: /* 8 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-LARGE-NEXT: /* 10 */      MCD::OPC_CheckField, 0, 2, 3, 7, 0, 0, // Skip to: 24
-// CHECK-LARGE-NEXT: /* 17 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, Skip to: 24
+// CHECK-LARGE-NEXT: /* 17 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 24
 // CHECK-LARGE-NEXT: /* 24 */      MCD::OPC_CheckFieldOrFail, 3, 2, 0,
 // CHECK-LARGE-NEXT: /* 28 */      MCD::OPC_TryDecodeOrFail, {{[0-9]+}}, {{[0-9]+}}, 1,
 // CHECK-LARGE-NEXT: /* 32 */      MCD::OPC_Fail,
diff --git a/llvm/test/TableGen/trydecode-emission3.td b/llvm/test/TableGen/trydecode-emission3.td
index e2b739d8338de..f262bfab77c3b 100644
--- a/llvm/test/TableGen/trydecode-emission3.td
+++ b/llvm/test/TableGen/trydecode-emission3.td
@@ -38,7 +38,7 @@ def InstB : TestInstruction {
 // CHECK:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-NEXT: /* 3 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 6, 0, // Skip to: 17
-// CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, Skip to: 17
+// CHECK-NEXT: /* 11 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 17
 // CHECK-NEXT: /* 17 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
 // CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
 
@@ -47,8 +47,8 @@ def InstB : TestInstruction {
 // CHECK-LARGE:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-LARGE-NEXT: /* 3 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-LARGE-NEXT: /* 5 */       MCD::OPC_CheckField, 2, 2, 0, 7, 0, 0, // Skip to: 19
-// CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, Skip to: 19
-// CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-LARGE-NEXT: /* 12 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
+// CHECK-LARGE-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
 // CHECK-LARGE-NEXT: /* 23 */      MCD::OPC_Fail,
 
 // CHECK-LARGE: if (!Check(S, DecodeInstBOp(MI, tmp, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
diff --git a/llvm/test/TableGen/trydecode-emission4.td b/llvm/test/TableGen/trydecode-emission4.td
index 39a3187c38bda..2c63229c053a5 100644
--- a/llvm/test/TableGen/trydecode-emission4.td
+++ b/llvm/test/TableGen/trydecode-emission4.td
@@ -36,8 +36,8 @@ def InstB : TestInstruction {
 // CHECK:      /* 0 */       MCD::OPC_ExtractField, 250, 3, 4,  // Inst{509-506} ...
 // CHECK-NEXT: /* 4 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-NEXT: /* 6 */       MCD::OPC_CheckField, 248, 3, 2, 0, 6, 0, // Skip to: 19
-// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, Skip to: 19
-// CHECK-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 19
+// CHECK-NEXT: /* 19 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
 // CHECK-NEXT: /* 23 */      MCD::OPC_Fail,
 
 // CHECK: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
@@ -46,8 +46,8 @@ def InstB : TestInstruction {
 // CHECK-LARGE:      /* 0 */       MCD::OPC_ExtractField, 250, 3, 4,  // Inst{509-506} ...
 // CHECK-LARGE-NEXT: /* 4 */       MCD::OPC_FilterValueOrFail, 0,
 // CHECK-LARGE-NEXT: /* 6 */       MCD::OPC_CheckField, 248, 3, 2, 0, 7, 0, 0, // Skip to: 21
-// CHECK-LARGE-NEXT: /* 14 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, Skip to: 21
-// CHECK-LARGE-NEXT: /* 21 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA
+// CHECK-LARGE-NEXT: /* 14 */      MCD::OPC_TryDecode, {{[0-9]+}}, {{[0-9]+}}, 0, 0, 0, 0, // Opcode: InstB, DecodeIdx: {{[0-9]+}}, Skip to: 21
+// CHECK-LARGE-NEXT: /* 21 */      MCD::OPC_Decode, {{[0-9]+}}, {{[0-9]+}}, 1, // Opcode: InstA, DecodeIdx: {{[0-9]+}}
 // CHECK-LARGE-NEXT: /* 25 */      MCD::OPC_Fail,
 
 // CHECK-LARGE: if (!Check(S, DecodeInstB(MI, insn, Address, Decoder))) { DecodeComplete = false; return MCDisassembler::Fail; }
diff --git a/llvm/utils/TableGen/DecoderEmitter.cpp b/llvm/utils/TableGen/DecoderEmitter.cpp
index 3990836e9077f..56c3644c134f1 100644
--- a/llvm/utils/TableGen/DecoderEmitter.cpp
+++ b/llvm/utils/TableGen/DecoderEmitter.cpp
@@ -975,6 +975,8 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       emitULEB128(I, OS);
 
       // Decoder index.
+      unsigned DecodeIdx = decodeULEB128(&*I, nullptr, EndPtr, &ErrMsg);
+      assert(ErrMsg == nullptr && "ULEB128 value too large!");
       emitULEB128(I, OS);
 
       auto EncI = OpcodeToEncodingID.find(Opc);
@@ -982,18 +984,17 @@ void DecoderEmitter::emitTable(formatted_raw_ostream &OS, DecoderTable &Table,
       auto EncodingID = EncI->second;
 
       if (!IsTry) {
-        OS << "// Opcode: " << NumberedEncodings[EncodingID] << "\n";
+        OS << "// Opcode: " << NumberedEncodings[EncodingID]
+           << ", DecodeIdx: " << DecodeIdx << '\n';
         break;
       }
 
       // Fallthrough for OPC_TryDecode.
-
       if (!IsFail) {
         uint32_t NumToSkip = emitNumToSkip(I, OS);
-        OS << "// Opcode: " << NumberedEncodings[EncodingID];
+        OS << "// Opcode: " << NumberedEncodings[EncodingID]
+           << ", DecodeIdx: " << DecodeIdx;
         emitNumToSkipComment(NumToSkip, /*InComment=*/true);
-      } else {
-        OS << "// Opcode: " << NumberedEncodings[EncodingID];
       }
       OS << '\n';
       break;
@@ -2249,7 +2250,8 @@ static DecodeStatus decodeInstruction(const uint8_t DecodeTable[], MCInst &MI,
     const uint8_t DecoderOp = *Ptr++;
     switch (DecoderOp) {
     default:
-      errs() << Loc << ": Unexpected decode table opcode!\n";
+      errs() << Loc << ": Unexpected decode table opcode: "
+             << (int)DecoderOp << '\n';
       return MCDisassembler::Fail;
     case MCD::OPC_ExtractField: {
       // Decode the start value.