Ph.D Transfer from other country to US
In general, it is difficult to transfer between universities in different countries unless one is moving with the thesis advisor. This is in part because of funding rules: usually, money in one country cannot be used to fund graduate students working or studying in another country. (In the US, for instance, graduate fellowships are normally valid only at US universities.)

If you were to attempt to transfer on your own, the most likely scenario is that you would be expected to start the PhD over; depending on the department, they may not recognize coursework completed at your old school, or at best may choose to give you placement out of the equivalent courses, but still expect you to complete additional electives. It would be even more challenging to move your project over, if funding isn't available to work on the same project.

Since you are just starting, perhaps it would be possible to complete a master's degree in Singapore, and then try to transfer to another university for the doctoral studies. (I'm not sure how doctoral programs in CS handle an international master's. In my department, though, students with master's from abroad were still expected to complete the "core" coursework requirements.)