Export tf.func attributes as AttrValue.NameAttrList.

Add support for exporting #tf.func<@name, {}> attributes as AttrValue.NameAttrList when converting TF MLIR to GraphDef. On import #tf.func may be introduced, modeling AttrValue.NameAttrList (func) attributes in TensorFlow. This updates the export path so round-tripping from Graph -> TF MLIR -> Graph will preserve such attributes properly.

PiperOrigin-RevId: 321382977
Change-Id: Ica0aa2eede960e76b69074e0a8fc7f9306dc6a0c

tensorflow/compiler/mlir/tensorflow/tests/mlir2graphdef/func_attr.mlir

@@ -0,0 +1,40 @@
+// RUN: tf-mlir-translate -mlir-to-graphdef %s | tf-mlir-translate -graphdef-to-mlir | tf-mlir-translate -mlir-to-graphdef | FileCheck %s
+
+// Tests #tf.func attributes are exported as AttrValue.NameAttrList attributes
+// with its attr field populated with nested attributes.
+
+module attributes {tf.versions = {bad_consumers = [], min_consumer = 12 : i32, producer = 458 : i32}} {
+  func @main() {
+    tf_executor.graph {
+      %control = tf_executor.island wraps "tf.NoOp"() {_f = #tf.func<@callee, {attr2 = true, attr3 = 8.0 : f32}>} : () -> ()
+      tf_executor.fetch
+    }
+    return
+  }
+  func @callee() {
+    tf_executor.graph {
+      tf_executor.fetch
+    }
+    return
+  }
+}
+
+// CHECK:        op: "NoOp"
+// CHECK-NEXT:   attr
+// CHECK-NEXT:     key: "_f"
+// CHECK-NEXT:     value
+// CHECK-NEXT:       func
+// CHECK-NEXT:         name: [[FUNC_NAME:".*"]]
+// CHECK-NEXT:         attr
+// CHECK-NEXT:           key: "attr2"
+// CHECK-NEXT:           value
+// CHECK-NEXT:             b: true
+// CHECK:              attr
+// CHECK-NEXT:           key: "attr3"
+// CHECK-NEXT:           value
+// CHECK-NEXT:             f: 8
+
+// CHECK:      library
+// CHECK-NEXT:   function
+// CHECK-NEXT:     signature
+// CHECK-NEXT:       name: [[FUNC_NAME]]

tensorflow/compiler/mlir/tensorflow/utils/export_utils.cc

@@ -121,6 +121,20 @@ Status ConvertAttribute(const mlir::TF::ShapeAttr& attr, AttrValue* value) {
   return Status::OK();
 }
 
+Status ConvertAttribute(const mlir::FlatSymbolRefAttr& attr, AttrValue* value) {
+  value->mutable_func()->set_name(attr.getValue().str());
+  return Status::OK();
+}
+
+Status ConvertAttribute(const mlir::TF::FuncAttr& attr, AttrValue* value) {
+  TF_RETURN_IF_ERROR(
+      ConvertAttribute(attr.GetName().cast<mlir::FlatSymbolRefAttr>(), value));
+  TF_RETURN_IF_ERROR(ConvertAttributes(attr.GetAttrs().getValue(),
+                                       /*attrs_to_ignore=*/{},
+                                       value->mutable_func()->mutable_attr()));
+  return Status::OK();
+}
+
 Status ConvertAttribute(const mlir::StringAttr& attr, AttrValue* value) {
   absl::string_view attr_value(attr.getValue().data(), attr.getValue().size());
   switch (mangling_util::GetMangledKind(attr_value)) {
@@ -160,11 +174,6 @@ Status ConvertAttribute(const mlir::UnitAttr& attr, AttrValue* value) {
   return Status::OK();
 }
 
-Status ConvertAttribute(const mlir::FlatSymbolRefAttr& attr, AttrValue* value) {
-  value->mutable_func()->set_name(std::string(attr.getValue()));
-  return Status::OK();
-}
-
 Status ConvertAttribute(const mlir::ArrayAttr& attr, AttrValue* value) {
   auto* list = value->mutable_list();
   for (mlir::Attribute a : attr.getValue()) {
@@ -372,8 +381,8 @@ Status ConvertAttributes(
     AttrValue value;
     switch (attr.getKind()) {
       case mlir::StandardAttributes::SymbolRef: {
-        auto func_attr = attr.cast<mlir::FlatSymbolRefAttr>();
+        TF_RETURN_IF_ERROR(
-        value.mutable_func()->set_name(std::string(func_attr.getValue()));
+            ConvertAttribute(attr.cast<mlir::FlatSymbolRefAttr>(), &value));
         func_call_attrs[string(name)] = value;
         continue;
       }
@@ -415,6 +424,12 @@ Status ConvertAttributes(
         TF_RETURN_IF_ERROR(
             ConvertAttribute(attr.cast<mlir::TF::ShapeAttr>(), &value));
         break;
+      case static_cast<unsigned>(mlir::TF::AttrKind::FUNC): {
+        TF_RETURN_IF_ERROR(
+            ConvertAttribute(attr.cast<mlir::TF::FuncAttr>(), &value));
+        func_call_attrs[string(name)] = value;
+        continue;
+      }
       // AffineMap kind is not implemented.
       case mlir::StandardAttributes::AffineMap:
         return errors::Unimplemented("AffineMap attribute (needed for '",