[MLIR] [TableGen] Avoid generating an assert which is always true.

[jurahul]

Summary

• Avoid generating "assert(resultTypes.size() >= 0u)" which is always true

mlir/tools/mlir-tblgen/OpDefinitionsGen.cpp

auto emit = [&](AttrParamKind attrType, TypeParamKind paramKind,
     case TypeParamKind::Separate:
       for (int i = 0, e = op.getNumResults(); i < e; ++i) {
         if (op.getResult(i).isOptional())
           body << "  if (" << resultNames[i] << ")\n  ";
         body << "  " << builderOpState << ".addTypes(" << resultNames[i]
              << ");\n";
       }
       return;
-    case TypeParamKind::Collective:
+    case TypeParamKind::Collective: {
+      int numResults = op.getNumResults();
+      int numVariadicResults = op.getNumVariableLengthResults();
+      int numNonVariadicResults = numResults - numVariadicResults;
+      bool hasVariadicResult = numVariadicResults != 0;
+
+      // Avoid emitting "resultTypes.size() >= 0u" which is always true.
+      if (!(hasVariadicResult && numNonVariadicResults == 0))
         body << "  "
              << "assert(resultTypes.size() "
-           << (op.getNumVariableLengthResults() == 0 ? "==" : ">=") << " "
-           << (op.getNumResults() - op.getNumVariableLengthResults())
+             << (hasVariadicResult ? ">=" : "==") << " "
+             << numNonVariadicResults
              << "u && \"mismatched number of results\");\n";
       body << "  " << builderOpState << ".addTypes(resultTypes);\n";
+    }
       return;
     }
     llvm_unreachable("unhandled TypeParamKind");
   };
 
   // A separate arg param builder method will have a signature which is
   // ambiguous with the collective params build method (generated in
   // `genCollectiveParamBuilder` function below) if it has a single