The location about VTA JIT runtime system

I’m currently researching TVM build flow for VTA especially the JIT runtime system mentioned in the paper https://arxiv.org/abs/1807.04188.
If I understand correctly, it needs to build the module with the target ext_dev -device vta ... in deploy_vision_on_vta.py example. Now, I just began to look for the JIT codegen part from relay.build because I guessed it would be like I want.

However, I haven’t find it, It’s still a bit complex for me, so I need more time.
Is there any hint where I should read to know the JIT runtime system (or the actual codegen)?? Thanks,