[mlir] fix a crash in linalg.generic parser

[ftynse]

Summary

Report an error when the iterator_types attribute is missing.

mlir/lib/Dialect/Linalg/IR/LinalgOps.cpp

 }
 
 ParseResult GenericOp::parse(OpAsmParser &parser, OperationState &result) {
   DictionaryAttr dictAttr;
   // Parse the core linalg traits that must check into a dictAttr.
   // The name is unimportant as we will overwrite result.attributes.
   // The core linalg traits must contain the information necessary to pass the
   // verifier.
+  llvm::SMLoc attributeLocation = parser.getCurrentLocation();
   if (parser.parseAttribute(dictAttr, "_", result.attributes))
     return failure();
   result.attributes.assign(dictAttr.getValue().begin(),
                            dictAttr.getValue().end());
 
-  // Convert array of string into an array of IteratyType enums. This is needed,
-  // because tests still use the old format when 'iterator_types' attribute is
-  // represented as an array of strings.
+  // Convert array of string into an array of IteratorType enums. This is
+  // needed, because tests still use the old format when 'iterator_types'
+  // attribute is represented as an array of strings.
   // TODO: Remove this conversion once tests are fixed.
-  ArrayAttr iteratorTypes =
-      result.attributes.get(getIteratorTypesAttrName(result.name))
-          .cast<ArrayAttr>();
+  auto iteratorTypes = dyn_cast_or_null<ArrayAttr>(
+      result.attributes.get(getIteratorTypesAttrName(result.name)));
+  if (!iteratorTypes) {
+    return parser.emitError(attributeLocation)
+           << "expected " << getIteratorTypesAttrName(result.name)
+           << " array attribute";
+  }
 
   SmallVector<Attribute> iteratorTypeAttrs;
 
   for (StringRef s : iteratorTypes.getAsValueRange<StringAttr>()) {
     auto maybeIteratorType = utils::symbolizeIteratorType(s);
     if (!maybeIteratorType.has_value())
       return parser.emitError(parser.getCurrentLocation())
              << "unexpected iterator_type (" << s << ")";

mlir/test/Dialect/Linalg/invalid.mlir

func.func @broadcast_size_1_extension_not_supported(
     -> tensor<4x?x16xf32> {
   // expected-error @+1 {{'linalg.broadcast' op input dim 0 should match init dim 0. input: 1, init: 4}}
   %bcast = linalg.broadcast
       ins(%input:tensor<1x16xf32>)
       outs(%init:tensor<4x?x16xf32>)
       dimensions = [1]
   func.return %bcast : tensor<4x?x16xf32>
 }
+
+// -----
+
+func.func @missing_iterator_types() {
+  // expected-error @below {{expected "iterator_types" array attribute}}
+  linalg.generic {} ins() outs()
+  return
+}