Index: llvm/trunk/include/llvm/Target/Target.td
===================================================================
--- llvm/trunk/include/llvm/Target/Target.td
+++ llvm/trunk/include/llvm/Target/Target.td
@@ -913,6 +913,17 @@
   let usesCustomInserter = 1;
   let mayLoad = 1;
 }
+
+// Generic opcode used by the IRTranslator.
+// After ISel, this opcode should not appear.
+def G_ADD : Instruction {
+  let OutOperandList = (outs unknown:$dst);
+  let InOperandList = (ins unknown:$src1, unknown:$src2);
+  let AsmString = "";
+  let hasSideEffects = 0;
+  let isCommutable = 1;
+}
+// TODO: Add the other generic opcodes.
 }
 
 //===----------------------------------------------------------------------===//
Index: llvm/trunk/include/llvm/Target/TargetOpcodes.h
===================================================================
--- llvm/trunk/include/llvm/Target/TargetOpcodes.h
+++ llvm/trunk/include/llvm/Target/TargetOpcodes.h
@@ -129,9 +129,27 @@
   /// comparisons into existing memory operations.
   FAULTING_LOAD_OP = 22,
 
+  /// The following generic opcodes are not supposed to appear after ISel.
+  /// This is something we might want to relax, but for now, this is convenient
+  /// to produce diagnostic.
+  PRE_ISEL_GENERIC_OPCODE_START,
+  // Generic opcodes used before ISel are here.
+
+  /// Generic ADD instruction. This is an integer add.
+  G_ADD = PRE_ISEL_GENERIC_OPCODE_START,
+  // TODO: Add more generic opcodes as we move along.
+  // FIXME: Right now, we have to manually add any new opcode in
+  // CodeGenTarget.cpp for TableGen to pick them up.
+  // Moreover the order must match.
+
+  /// Marker for the end of the generic opcode.
+  /// This is used to check if an opcode is in the range of the
+  /// generic opcodes.
+  PRE_ISEL_GENERIC_OPCODE_END,
+
   /// BUILTIN_OP_END - This must be the last enum value in this list.
   /// The target-specific post-isel opcode values start here.
-  GENERIC_OP_END = FAULTING_LOAD_OP,
+  GENERIC_OP_END = PRE_ISEL_GENERIC_OPCODE_END,
 };
 } // end namespace TargetOpcode
 } // end namespace llvm
Index: llvm/trunk/test/TableGen/trydecode-emission.td
===================================================================
--- llvm/trunk/test/TableGen/trydecode-emission.td
+++ llvm/trunk/test/TableGen/trydecode-emission.td
@@ -36,8 +36,8 @@
 // CHECK:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-NEXT: /* 3 */       MCD::OPC_FilterValue, 0, 14, 0, // Skip to: 21
 // CHECK-NEXT: /* 7 */       MCD::OPC_CheckField, 2, 2, 0, 5, 0, // Skip to: 18
-// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, 24, 0, 0, 0, // Opcode: InstB, skip to: 18
-// CHECK-NEXT: /* 18 */      MCD::OPC_Decode, 23, 1, // Opcode: InstA
+// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, 25, 0, 0, 0, // Opcode: InstB, skip to: 18
+// CHECK-NEXT: /* 18 */      MCD::OPC_Decode, 24, 1, // Opcode: InstA
 // CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
 
 // CHECK: if (DecodeInstB(MI, insn, Address, Decoder) == MCDisassembler::Fail) { DecodeComplete = false; return MCDisassembler::Fail; }
Index: llvm/trunk/test/TableGen/trydecode-emission2.td
===================================================================
--- llvm/trunk/test/TableGen/trydecode-emission2.td
+++ llvm/trunk/test/TableGen/trydecode-emission2.td
@@ -35,9 +35,9 @@
 // CHECK-NEXT: /* 7 */       MCD::OPC_ExtractField, 5, 3,  // Inst{7-5} ...
 // CHECK-NEXT: /* 10 */      MCD::OPC_FilterValue, 0, 22, 0, // Skip to: 36
 // CHECK-NEXT: /* 14 */      MCD::OPC_CheckField, 0, 2, 3, 5, 0, // Skip to: 25
-// CHECK-NEXT: /* 20 */      MCD::OPC_TryDecode, 24, 0, 0, 0, // Opcode: InstB, skip to: 25
+// CHECK-NEXT: /* 20 */      MCD::OPC_TryDecode, 25, 0, 0, 0, // Opcode: InstB, skip to: 25
 // CHECK-NEXT: /* 25 */      MCD::OPC_CheckField, 3, 2, 0, 5, 0, // Skip to: 36
-// CHECK-NEXT: /* 31 */      MCD::OPC_TryDecode, 23, 1, 0, 0, // Opcode: InstA, skip to: 36
+// CHECK-NEXT: /* 31 */      MCD::OPC_TryDecode, 24, 1, 0, 0, // Opcode: InstA, skip to: 36
 // CHECK-NEXT: /* 36 */      MCD::OPC_Fail,
 
 // CHECK: if (DecodeInstB(MI, insn, Address, Decoder) == MCDisassembler::Fail) { DecodeComplete = false; return MCDisassembler::Fail; }
Index: llvm/trunk/test/TableGen/trydecode-emission3.td
===================================================================
--- llvm/trunk/test/TableGen/trydecode-emission3.td
+++ llvm/trunk/test/TableGen/trydecode-emission3.td
@@ -37,8 +37,8 @@
 // CHECK:      /* 0 */       MCD::OPC_ExtractField, 4, 4,  // Inst{7-4} ...
 // CHECK-NEXT: /* 3 */       MCD::OPC_FilterValue, 0, 14, 0, // Skip to: 21
 // CHECK-NEXT: /* 7 */       MCD::OPC_CheckField, 2, 2, 0, 5, 0, // Skip to: 18
-// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, 24, 0, 0, 0, // Opcode: InstB, skip to: 18
-// CHECK-NEXT: /* 18 */      MCD::OPC_Decode, 23, 1, // Opcode: InstA
+// CHECK-NEXT: /* 13 */      MCD::OPC_TryDecode, 25, 0, 0, 0, // Opcode: InstB, skip to: 18
+// CHECK-NEXT: /* 18 */      MCD::OPC_Decode, 24, 1, // Opcode: InstA
 // CHECK-NEXT: /* 21 */      MCD::OPC_Fail,
 
 // CHECK: if (DecodeInstBOp(MI, tmp, Address, Decoder) == MCDisassembler::Fail) { DecodeComplete = false; return MCDisassembler::Fail; }
Index: llvm/trunk/utils/TableGen/CodeGenTarget.cpp
===================================================================
--- llvm/trunk/utils/TableGen/CodeGenTarget.cpp
+++ llvm/trunk/utils/TableGen/CodeGenTarget.cpp
@@ -301,6 +301,9 @@
 /// their enum value.
 void CodeGenTarget::ComputeInstrsByEnum() const {
   // The ordering here must match the ordering in TargetOpcodes.h.
+  // FIXME: It would be nice to have the opcode directly extracted
+  // to avoid potential errors. At the very, least a compile time
+  // error would be appreciated if the order does not match.
   static const char *const FixedInstrs[] = {
       "PHI",          "INLINEASM",     "CFI_INSTRUCTION",  "EH_LABEL",
       "GC_LABEL",     "KILL",          "EXTRACT_SUBREG",   "INSERT_SUBREG",
@@ -308,6 +311,8 @@
       "REG_SEQUENCE", "COPY",          "BUNDLE",           "LIFETIME_START",
       "LIFETIME_END", "STACKMAP",      "PATCHPOINT",       "LOAD_STACK_GUARD",
       "STATEPOINT",   "LOCAL_ESCAPE",   "FAULTING_LOAD_OP",
+      // Generic opcodes for GlobalISel start here.
+      "G_ADD",
       nullptr};
   const auto &Insts = getInstructions();
   for (const char *const *p = FixedInstrs; *p; ++p) {