[llvm] [TableGen] Implement getOperandIdxName (PR #154944)

[Robert Imschweiler via llvm-commits]

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@@ -223,17 +223,104 @@ void InstrInfoEmitter::EmitOperandInfo(raw_ostream &OS,
   }
 }
 
+static void emitGetInstructionIndexForOpLookup(
+    raw_ostream &OS, const MapVector<SmallVector<int>, unsigned> &OperandMap,
+    ArrayRef<unsigned> InstructionIndex) {
+  StringRef Type = OperandMap.size() <= UINT8_MAX + 1 ? "uint8_t" : "uint16_t";
+  OS << "LLVM_READONLY\n";
+  OS << "static " << Type
+     << " getInstructionIndexForOpLookup(uint16_t Opcode) {\n";
+  OS << "  static constexpr " << Type << " InstructionIndex[] = {";
+  for (auto [TableIndex, Entry] : enumerate(InstructionIndex))
+    OS << (TableIndex % 16 == 0 ? "\n    " : " ") << Entry << ',';
+  OS << "\n  };\n";
+  OS << "  return InstructionIndex[Opcode];\n";
+  OS << "}\n";
+}
+
+static void
+emitGetNamedOperandIdx(raw_ostream &OS, StringRef Namespace,
+                       const MapVector<StringRef, unsigned> &OperandNameToID,
+                       const MapVector<SmallVector<int>, unsigned> &OperandMap,
+                       unsigned MaxOperandNo, unsigned NumOperandNames) {
+  OS << "LLVM_READONLY\n";
+  OS << "int16_t getNamedOperandIdx(uint16_t Opcode, OpName Name) {\n";
+  OS << "  assert(Name != OpName::NUM_OPERAND_NAMES);\n";
+  if (!NumOperandNames) {
+    // There are no operands, so no need to emit anything
+    OS << "  return -1;\n}\n";
+    return;
+  }
+  assert(MaxOperandNo <= INT16_MAX &&
+         "Too many operands for the operand name -> index table");
+  StringRef Type = MaxOperandNo <= INT8_MAX ? "int8_t" : "int16_t";
+  OS << "  static constexpr " << Type << " OperandMap[][" << NumOperandNames
+     << "] = {\n";
+  for (const auto &[OpList, _] : OperandMap) {
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ro-i wrote:

The current behavior does seem a little inconsistent: https://godbolt.org/z/eM1xj54P7
Interestingly, a standalone variable with the name `_` is not flagged as unused

https://github.com/llvm/llvm-project/pull/154944