> Sony [...] as they were developing the toolchain for the PS4 [...] couldn't add their contributions into the LLVM toolchain

Why is that? Do you have something I can read about this?

This is the only thing I can find on the topic, and it mentions upstreaming by default after some time ("living on trunk"): http://llvm.org/devmtg/2013-11/slides/Robinson-PS4Toolchain....