"The LLVM project started in 2000 at the University of Illinois at Urbana–Champaign, under the direction of Vikram Adve and Chris Lattner. LLVM was originally developed as a research infrastructure to investigate dynamic compilation techniques for static and dynamic programming languages. LLVM was released under the University of Illinois/NCSA Open Source License,[3] a permissive free software licence. In 2005, Apple Inc. hired Lattner and formed a team to work on the LLVM system for various uses within Apple's development systems."
Apple hired Chris Lattner straight out of college. LLVM was the subject of his Masters Thesis.
It existed, but certainly wasn't yet ready for prime time. You can watch Chris give a Tech Talk at Google introducing Clang and LLVM and going over the features added in LLVM 2.0 while he was at Apple.
He joined Apple in 2005. and this talk was in 2007.
"The LLVM project started in 2000 at the University of Illinois at Urbana–Champaign, under the direction of Vikram Adve and Chris Lattner. LLVM was originally developed as a research infrastructure to investigate dynamic compilation techniques for static and dynamic programming languages. LLVM was released under the University of Illinois/NCSA Open Source License,[3] a permissive free software licence. In 2005, Apple Inc. hired Lattner and formed a team to work on the LLVM system for various uses within Apple's development systems."
https://en.wikipedia.org/wiki/LLVM