[TableGen] Avoid repeated hash lookups (NFC) (#127373)

Author: kazutakahirata

llvm/utils/TableGen/AsmMatcherEmitter.cpp

@@ -2333,9 +2333,9 @@ emitConvertFuncs(CodeGenTarget &Target, StringRef ClassName,
     OS << "  // " << InstructionConversionKinds[Row] << "\n";
     OS << "  { ";
     for (unsigned i = 0, e = ConversionTable[Row].size(); i != e; i += 2) {
-      OS << OperandConversionKinds[ConversionTable[Row][i]] << ", ";
-      if (OperandConversionKinds[ConversionTable[Row][i]] !=
-          CachedHashString("CVT_Tied")) {
+      const auto &OCK = OperandConversionKinds[ConversionTable[Row][i]];
+      OS << OCK << ", ";
+      if (OCK != CachedHashString("CVT_Tied")) {
         OS << (unsigned)(ConversionTable[Row][i + 1]) << ", ";
         continue;
       }