//
// tf_executor.island wraps "tf.OpA"
// tf_executor.island {
//  "tf_device.replicate" {n = 2} {
//    "tf.OpB"
//    "tf_device.parallel_execute"() ({
//      "tf.OpC"
//    }, {
//      "tf.OpD"
//    })
//  }
//
// The above IR will be flattened after `ReplicateToIslandPass` and
// `ParallelExecuteToIslandsPass` as follows:
//
// tf_executor.island wraps "tf.OpA"

    For example, the following:

    ```mlir
    func @single_op_launch() {
      %a = "tf.opA"() {device = "CPU:0"} : () -> tensor<i1>
      return %a
    }
    ```

    will be transformed into:

    ```mlir
    func @single_op_launch() {
      %1 = tf_device.launch() ( {
        %a = "tf.opA"() : () -> tensor<i1>
        tf_device.return %a
      }) {device = "CPU:0"} : () -> tensor<i1>

  //
  // Two ops with the same groups and different branches are considered
  // parallel so are not made dependent. For example if `OpA` has parallel_ids
  //   `{group0:branch0, group1:branch0}`
  // and `OpB` has parallel_ids
  //   `{group0:branch1, graph1:branch0}`
  // then `OpA` and `OpB` are executed in parallel because `group0` is common
  // with a different branch.
  //

  %1 = "tf.ReadVariableOp"(%0) : (tensor<!tf_type.resource<tensor<i32>>>) -> tensor<i32>
  // CHECK:      [[COMPUTATION:%.+]] = "tf_device.parallel_execute"()
  // CHECK:      "tf.OpA"([[READ0]])
  %2 = "tf_device.parallel_execute"() ({
    "tf_device.launch"() ({
      "tf.OpA"(%1) : (tensor<i32>) -> ()
      tf_device.return
    }) {device = "TPU_REPLICATED_HOST_0"} : () -> ()
    tf_device.return
  }, {

	case config.PolicyOPASubSys:
		// In case legacy OPA config is being set, we treat it as if the
		// AuthZPlugin is being set.
		subSys = config.PolicyPluginSubSys
		fallthrough
	case config.PolicyPluginSubSys:
		if ppargs, err := polplugin.LookupConfig(s, GetDefaultConnSettings(), xhttp.DrainBody); err != nil {
			return err
		} else if ppargs.URL == nil {
			// Check if legacy opa is configured.

      "tf.OpA"(%0) : (tensor<f32>) -> ()
    }
    ```

    will be transformed into:

    ``mlir
    %0 = "tf.ReadVariableOp"(%arg0) : (tensor<*x!tf_type.resource<tensor<f32>>>) -> tensor<f32>
    tf_device.replicate {n = 2 : i32} {
      "tf.OpA"(%0) : (tensor<f32>) -> ()
    }
    ```

func.func @simple_independent_chains(%arg0: !tf_res, %arg1: !tf_res, %arg2: tensor<f32>) {
  // CHECK: tf_executor.graph {
  tf_executor.graph {
    // CHECK: %[[A_CONTROL:.*]] = tf_executor.island wraps "tf.OpA"() : () -> ()
    %control_A = tf_executor.island wraps "tf.OpA"() : () -> ()
    // CHECK: %[[CHAIN_CONSTANT:.*]], %{{.*}} = tf_executor.island wraps "tf.Const"() <{value = dense<1> : tensor<i32>}> : () -> tensor<i32>

          %0 = "tf.opA"(%arg0) : (tensor<f32>) -> tensor<f32>
          return %0 : tensor<f32>
        }
      }
    }
    ```

    will be transformed into:

    ```mlir
    module  {
      func @foo(%arg0: tensor<f32>) -> tensor<f32> {
        %0 = tf_executor.graph {
          %outputs, %control = tf_executor.island {
            %1 = "tf.opA"(%arg0) : (tensor<f32>) -> tensor<f32>

    %handle0, %handle0_control = tf_executor.island wraps "tf.SomeOp"() : () -> !tf_res
    %handle1, %handle1_control = tf_executor.island wraps "tf.SomeOp"() : () -> !tf_res
    %control_A = tf_executor.island wraps "tf.OpA"() : () -> ()
    %while_out:2, %while_control = tf_executor.island(%control_A) wraps "tf.While"(
            %handle0, %handle1) {
        body = @body, cond = @cond, is_stateless = false

	}

	if authZPluginCfg.URL == nil {
		opaCfg, err := opa.LookupConfig(s[config.PolicyOPASubSys][config.Default],
			NewHTTPTransport(), xhttp.DrainBody)
		if err != nil {
			iamLogIf(ctx, fmt.Errorf("Unable to initialize AuthZPlugin from legacy OPA config: %w", err))
		} else {
			authZPluginCfg.URL = opaCfg.URL
			authZPluginCfg.AuthToken = opaCfg.AuthToken