Who do you think does most of the work in LLVM for example?
It is full of PhD paper contributions.
For example, research students doing internships at Embecosm (https://embecosm.com), as many others, plenty of material from LLVM Developers Meeting sessions.
I guess this is due to the tag line of the company. I am not familiar with the compiler/LLVM space so unsure how the different branches (compiler maintenance and AI tool infrastructure for example) are covered by the PHD internships, etc.
A lot of modern compilers don't seem to be directly done by academics though. If you know of such modern examples I'd be happy to be proven wrong.