// gradients.
//
// `ZerosLike` is not expected to be called and returns a nullptr. The creation
// of default zeros grads is handled by the `DefaultGradientFunction` registered
// for each op.
// TODO(srbs): We need to define `ZerosLike` here to keep the compiler happy.
// Figure out a way to avoid this.
// TODO(srbs): Should ZerosLike check-fail instead of returning nullptr?
class TapeTensor {

int64_t ToId(const AbstractTensorHandle* t) {
  return static_cast<int64_t>(reinterpret_cast<uintptr_t>(t));
}

Status ZerosLike(AbstractContext* ctx, AbstractTensorHandle* t,
                 AbstractTensorHandle** result) {
  AbstractOperationPtr op(ctx->CreateOperation());
  TF_RETURN_IF_ERROR(op->Reset("ZerosLike", /*raw_device_name=*/nullptr));
  if (isa<tracing::TracingOperation>(op.get())) {

    DCHECK(build_default_zeros_grads || zero_indices.empty());
    if (any_gradient_nonzero) {
      for (const auto i : zero_indices) {
        out_gradients[i] = trace.output_tensor_info[i].ZerosLike();
      }
      Status s;
      s = vspace.CallBackwardFunction(trace.op_type, trace.backward_function,
                                      unneeded_gradients, out_gradients,

*   Added support for Type III DCT, and `tf.spectral.idct(type=2|3)`.
*   Correctly handle CuDNN RNN weight loaded when nest in `TimeDistributed`.
*   Adding per-element weight support for `WALSComputePartialLhsAndRhsOp`.
*   ZerosLike and OnesLike ops treated as constants by Graph Transform Tool.
*   Gamma distribution and the derived distributions (Beta, Dirichlet, Student's
    t, inverse Gamma) now fully reparameterized.