Check invalid types not invalid ops per review comments from JK and AA

Author: ai-mannamalai

lib/Transforms/ConvertToCiphertextSemantics/ConvertToCiphertextSemantics.cpp

@@ -1064,7 +1064,20 @@ struct ConvertToCiphertextSemantics
 
     RewritePatternSet patterns(context);
     ConversionTarget target(*context);
-    target.markUnknownOpDynamicallyLegal([&](Operation* op) {
+
+    // check for invalid types and bail out of the pass
+    SmallVector<Type, 2> _invalid_types = {mlir::IndexType::get(context)};
+    mlir::TypeRange invalid_types(_invalid_types);
+    auto _helper_valid_type =
+        [invalid_types](const Type &type) -> LogicalResult {
+      return (llvm::is_contained(invalid_types, type) ? failure() : success());
+    };
+    if (!walkAndValidateTypes<secret::GenericOp>(module, _helper_valid_type)
+             .succeeded()) {
+      return signalPassFailure();
+    }
+
+    target.markUnknownOpDynamicallyLegal([&](Operation *op) {
       return isa<ModuleOp>(op) || hasMaterializedAttr(op);
     });