The Glasgow Haskell Compiler and LLVM
blog.llvm.org
blog.llvm.org
http://news.ycombinator.com/item?id=1158300
A sample from that article: "Which LLVM passes to use, and which order to run them, with what analysis in between, is a huge search problem, though. There are roughly 200 optimization and analysis flags, and these, mostly, can be run in any order, any number of times. If we want to run say, twenty of the passes (about what -O3 does), that’s what, about 10^46 arrangements!"
Not that any significant number of people use it yet...
I'd give this kind of a post 2 thumbs up if I could.