[TableGen] Add error messages

[Flakebi]

Summary

Print an error instead of crashing in two places.

If someone has a better error message for the first case, I would be glad to use it.

[dsanders]

llvm/utils/TableGen/SearchableTableEmitter.cpp

122–128

This one makes sense to me. The return statement ought to be updated to use Entry though:
return std::string(Entry->first)

603–605

I'm not sure this one should really be an error as having an empty table doesn't seem wrong as such. It probably wasn't intentional though so maybe a warning makes sense.

What breaks if the table is empty?

[Flakebi]

Thank you for the fast review!

What breaks if the table is empty?

In the case where I encountered it, the types cannot be determined because the for loop is never executed and it crashed below, trying to access null types.
I guess you are right that empty tables can work if all types are specified, so I changed it to a warning as you suggested and throw a fatal error only if a type does not exist.

[Flakebi]

ping for review

[Flakebi]

friendly ping

[dsanders]

LGTM

llvm/utils/TableGen/SearchableTableEmitter.cpp

std::string primaryRepresentation(const GenericField &Field, Init *I) {
     else if (BitInit *BI = dyn_cast<BitInit>(I))
       return BI->getValue() ? "true" : "false";
     else if (CodeInit *CI = dyn_cast<CodeInit>(I))
       return std::string(CI->getValue());
     else if (Field.IsIntrinsic)
       return "Intrinsic::" + getIntrinsic(I).EnumName;
     else if (Field.IsInstruction)
       return I->getAsString();
-    else if (Field.Enum)
+    else if (Field.Enum) {
+      auto *Entry = Field.Enum->EntryMap[cast<DefInit>(I)->getDef()];
+      if (!Entry)
+        PrintFatalError(Twine("entry for field '") + Field.Name + "' is null");
       return std::string(
           Field.Enum->EntryMap[cast<DefInit>(I)->getDef()]->first);
+    }
     PrintFatalError(Twine("invalid field type for field '") + Field.Name +
                     "', expected: string, bits, bit or code");
   }
 
   bool isIntrinsic(Init *I) {
     if (DefInit *DI = dyn_cast<DefInit>(I))
       return DI->getDef()->isSubClassOf("Intrinsic");
     return false;
if (ValueField.empty()) {
 
     for (size_t i = 0; i < Enum.Entries.size(); ++i)
       Enum.Entries[i]->second = i;
   }
 }
 
 void SearchableTableEmitter::collectTableEntries(
     GenericTable &Table, const std::vector<Record *> &Items) {
+  if (Items.empty())
+    PrintFatalError(Twine("Table '") + Table.Name + "' has no items");
+
   for (auto EntryRec : Items) {
     for (auto &Field : Table.Fields) {
       auto TI = dyn_cast<TypedInit>(EntryRec->getValueInit(Field.Name));
       if (!TI || !TI->isComplete()) {
         PrintFatalError(EntryRec->getLoc(),
                         Twine("Record '") + EntryRec->getName() +
                             "' in table '" + Table.Name +
                             "' is missing field '" + Field.Name + "'");