[TableGen][CodeEmitterGen] Avoid empty OpNum switches in getOperandBitOffset()

[iii]

Summary

getOperandBitOffset() causes the following warning on MSVC:

E:\llvm\ninja\lib\Target\SystemZ\SystemZGenMCCodeEmitter.inc(15414): warning C4060: switch statement contains no 'case' or 'default' labels

Do not emit empty OpNum switches.

[uweigand]

LGTM. As this is fixing a build failure on some platforms, please go ahead and commit.

[RKSimon]

Sorry, this just replaces the warning with:

warning C4065: switch statement contains 'default' but no 'case' labels

You're going to have to avoid emitting empty cases entirely.

[iii]

• Avoid emitting empty cases entirely.

[RKSimon]

LGTM - cheers

llvm/utils/TableGen/CodeEmitterGen.cpp

for (const RecordVal &RV : EncodingDef->getValues()) {
     // Ignore fixed fields in the record, we're looking for values like:
     //    bits<5> RST = { ?, ?, ?, ?, ? };
     if (RV.isNonconcreteOK() || RV.getValue()->isComplete())
       continue;
 
     Success &= addCodeToMergeInOperand(R, BI, std::string(RV.getName()), Case,
                                        BitOffsetCase, Target);
   }
+  BitOffsetCase += "      default:\n";
+  BitOffsetCase += "        break;\n";
   BitOffsetCase += "      }\n";
 
   if (!Success) {
     // Dump the record, so we can see what's going on...
     std::string E;
     raw_string_ostream S(E);
     S << "Dumping record for previous error:\n";
     S << *R;