maximum size needs to be a constant and 2) a push op can be found with a
    known shape, and all push ops need to have the same shape.

    A stack creation op "tf.StackV2" will be turned in to two zero-initialized
    variables, for the buffer and current size. Each push will be turned into
    ```mlir
      %old_val = "tf.ReadVariableOp"(%buffer)
      %old_size = "tf.ReadVariableOp"(%size)