I think two are almost the same presentation:
https://www.youtube.com/watch?v=PQDwvatwjD8 (July 2010) 10S6P4 Christian Schafmeister 2010 UNTT 3rd Annual Conference Session 6 Presentation 4
https://www.youtube.com/watch?v=8X69_42Mj-g (July 2015) Clasp: Common Lisp using LLVM and C++ for Molecular Metaprogramming
https://www.youtube.com/watch?v=0rSMt1pAlbE (Aug 2015) Clasp: Common Lisp using LLVM and C++ for Designing Molecules
https://www.youtube.com/watch?v=9HXfvT85EFE (Oct 2018) Modular Polymer Catalysts - Chris Schafmeister
https://www.youtube.com/watch?v=mbdXeRBbgDM (Nov 2018) LLVM Developers Meeting: C. Schafmeister lessons Learned Implementing Common Lisp with LLVM