Interesting! I just read [1] this morning, which describes an optimizing BF compiler (written in Rust) that compiles to LLVM IR. The article also gives a good overview of optimization techniques used.
[1]: http://www.wilfred.me.uk/blog/2015/08/29/an-optimising-bf-co...
Edit: Just saw this was also discussed on HN: https://news.ycombinator.com/item?id=10141604